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Home My WebLink AboutWPO201600068 Calculations 2017-01-25 Erosion Control Plan & Stormwater Management Plan Crozet Water Treatment Plant - Finished Water Pump Station Minor Amendment to Approved Site Development Plan #201400014 Albemarle, County SEH No. RIVAN 137749 4.00 January 11 , 2017 APPROVED by the Albemarle County Community evelopir�ent Department Date f/g--//'7 File W Pd2olb oc_bg i SEH Building a Better World for All of Us" Engineers I Architects I Planners I Scientists RECEIVED JAN102017 COMMUNITY DEVELOPMENT January 11, 2017 RE: Crozet Water Treatment Plant- Finished Water Pump Station Minor Amendment to Approved Site Development Plan WPO-2014-0008 Albemarle, County SEH No. RIVAN 137749 Engineering Albemarle County Community Development 401 McIntire Road, North Wing Charlottesville, VA 22902 Dear: On February 8, 2016, representatives of Rivanna Water and Sewer Authority (RWSA) and Short Elliott Hendrickson, Inc. (SEH ®) met with representatives of the County, referred as the County hence forth, to discuss the Crozet Water Treatment Plant— Finished Water Pump Station. A result of this meeting was for the County, RWSA and SEH to complete a Minor Site Plan Amendment to the approved Site Development Plan 201400014. Notes provided by the county from this meeting are included in Appendix A. On July 26, 2016, representatives of RWSA and SEH met with representatives of the County's Engineering Department to discuss WPO requirements for the project mention above. At this meeting items decided that RWSA and SEH could modify the existing approved WPO permit WPO-2014-00008. Enclosed with this letter is an outline of the modifications to the approved Erosion Control Plan and Stormwater Management Plan for permit WPO201400008. The original Erosion Control Plan and Stormwater Management Plan is included in the Appendix E. Please contact me with any questions at 651-247-4306, or email cshetterholm@sehinc.com. Sincerely, Miles B. Jensen, P.E. Regional Practice Center Leader MNT \\sp3020-1\projects\pt\r\rivan\137749\3-env-stdy-regs\36-reg\stormwater\fwps\proposal\resubmittal\2017 1 6\smp&ecp\1 ecp and smp admendment report docx SEH is a registered trademark of Short Elliott Hendrickson Inc. Erosion Control Plan &Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority Page 1 Crozet Water Treatment Plant - Finished Water Pump Station Minor Amendment to Approved Site Development Plan #201400014 Erosion Control Plan & Stormwater Management Plan Albemarle, County SEH No. RIVAN 137749 January 11, 2017 I hereby certify that this report was prepared by me or under my direct supervision, and that I am a duly Licensed Professional Engineer under the laws of the State of Virginia. Miles B. Jensen, P.E Regional Practice Center Leader Date: 1/12/17 Lic. No.: 0402051131 Short Elliott Hendrickson Inc. 3535 Vadnais Center Dr. St Paul, MN 55110 Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority 3 Table of Contents Letter of Transmittal Certification Page Title Page Table of Contents Page 1.0 Introduction 1 2.0 Project Description 2 2.1 Drainage 2 2.2 Disturbance 2 2.3 Soils 2 2.4 Adjacent Areas 3 2.5 Critical Slopes 3 3.0 Erosion Control Plan 3 3.1 Temporary Measures 3 3.1.1 Construction Entrance (CE) 3 3.1.2 Temporary Diversion Dike (DD) 3 3.1.3 Silt Fence (SF) 4 3.1.4 Storm Drain Inlet Protection (IP) 4 3.1.5 Tree Preservation & Protection (TP) 4 3.1.6 Temporary Slope Drain (TSD) 4 3.1.7 Stabilization 4 3.1.7.1 Temporary Stabilization 4 3.1.7.2 Permanent Stabilization 4 3.1.7.3 Seeding 5 3.2 Erosion Control Sequence 5 3.3 Maintenance and Sediment Disposal 6 4.0 Stormwater Management Plan 7 4.1 Introduction 7 4.2 Water Quality Requirements (9VAC25-870-63. Water quality design criteria requirements.) 8 4.3 Water Quantity Requirements (9VAC25-870-66. Water quality.) 8 4.3.1 Channel Protection 8 4.3.1.1 Bioretention Design 9 4.3.2 Flood Protection 9 4.3.2.1 Peak Runoff from Site 9 4.3.2.2 Adequate Channel Analysis 9 4.4 Conclusion 10 Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority E-i Table of Contents (Continued) List of Tables Table 1. Project Composition 7 Table 2. Watershed Composition 8 Table 3. Channel Protection Requirement 8 Table 4. Peak Runoff 9 List of Appendices Appendix A. February 08, 2016 Pre-Application Conference Notes Appendix B. Temporary Diversion Dike Calculations Appendix C. Water Quality Calculations Appendix D. Water Quantity Calculations Appendix E. Original ECP and SMP RIVAN 137749 Erosion Control Plan&Stormwater Management Plan ii Rivanna Water&Sewer Authority January 2017 Erosion Control Plan & Stormwater Management Plan Crozet Water Treatment Plant - Finished Water Pump Station Minor Amendment to Approved Site Development Plan #201400014 Prepared for Rivanna Water & Sewer Authority 1.0 Introduction The Rivanna Water and Sewer Authority (RWSA) is proposing to replace their existing finish water pump station (FWPS) at the Crozet water treatment location (WTP). The existing FWPS and 0.5 MG ground storage tank (GST)were constructed in 1966. The pump station houses three finished water vertical turbine booster pumps, motors and associated piping and valves. A diesel generator next to the pump station powers both the pump station and the WTP. The existing FWPS is not air conditioned and is poorly ventilated, which causes the pumping station to experience temperatures in excess of what the motors and electrical equipment are normally rated for. An electric unit heater heats the pump station. The door to the pump station faces up a hill; large rain events cause flooding to occur near, and sometimes within the pumping station. Large storm events can make the steep downhill access to the facility and generator challenging and unsafe. The electrical, pumps, motors, piping and structure with the exception of the roof are original and are nearing the end of their useful life. The gate and butterfly valves have been recently replaced with new. The original truss roof was removed to allow for removal/repair of pumps/motors within the pump station. The roof was replaced in kind with a truss roof and asphalt shingles. Given the age and condition of the pump station and its equipment, the pump station will be replaced. The pump station cannot be reconstructed in its existing location because: • The existing pumping facility needs to remain in operation until a new facility can be built and put into service. • The existing facility is located in current County zoning/buffer requirements. • The footprint of the existing facility is too small to house the necessary pump, piping, electrical and mechanical equipment needed for a modern pumping station. • Finally, the site grades leading to the existing facility are much too steep for safe, convenient vehicle access for normal operations and maintenance. On the same parcel as the proposed Crozet WTP FWPS, a granular activated carbon (GAC) building upgrades is under construction. This project was permitted by the county as a Major Erosion Control Plan &Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority E-1 Amendment to Approved Site Development Plan#199900043, and designated Site Development Plan #201400014. As previously discussed with the County, the Crozet FWPS project will be submitted as a Minor Site Plan Amendment to SDP#201400014. After discussion with county staff, the requirements of the Water Protection Ordinance (WPO)will be addressed as amendments to the Erosion Control Plan (ECP) and Stormwater Management Plan (SMP) for the GAC project(WPO-2014-00008). This report outlines the changes and additions to WPO201400008. The original GAC ECP and SMP are attached in Appendix E. For this document, WPO20140008 will be referenced as GAC facility or project. The Crozet WTP FWPS project will be referenced as FWPS. 2.0 Project Description The FWPS site is located at 4685 Three Notched Rd, Crozet, VA. The parcel the FWPS site is located within is 4 acres and owned by Rivanna Sewer and Water Authority. The east half of the parcel is fairly flat and the Crozet WTP, Crozet GAC facility (currently under construction), and two maintenance building used by Albemarle County Service Authority (ACSA) are located here. The 0.5 MG GST and existing FWPS is located on the west half of the parcel. These buildings are approximately 40 feet lower in elevation than the east half of the parcel. A grove of trees and brush separate the two halves. 2.1 Drainage Most of the parcel drains westward to a drainage swale west of the 0.5 MG GST. The south east corner of the site drains to the south. The entire FWPS site drains to the drainage swale. No additional drainage from the North or East or West enters the parcel. Approximately 0.8 acres drains onto the parcel from the south. A drainage area map for the parcel can be found in the GAC ECP and SMP attached to this report. Approximately 0.38 acres are disturbed by the FWPS project. The disturbance extents are the trees and brush to the north, the GST to the south, the trees and brush to the east, and the 30' buffer to the west. There will be a little disturbance within the 30' buffer due to the removal of the existing FWPS and the construction. Managed Steep slopes exist within the trees and brush to the east of the site and north of the existing FWPS. 2.2 Disturbance As mentioned above the disturbed area for the site is approximately 0.38 acres. The GAC project disturbs approximately 1.12 acres. There exists some overlap in disturbance areas between the GAC project and the FWPS project. This is approximately 0.11 acres. Therefore, when looking at the total disturbance area for both the GAC project and the FWPS project, the total disturbance is 1.39 acres. This is used to calculate the total phosphorus removal required for both projects combined. 2.3 Soils Two soil types exist on site. These soils have been identified and classed by the Natural Resources Conservation Services (NRCS), and are detailed below. Both soil types are classified as a hydraulic soil group of B. 36B-Hayesville Loam RIVAN 137749 Erosion Control Plan&Stormwater Management Plan 2 Rivanna Water&Sewer Authority The Hayesville series soils, a well-draining series, exist predominantly on hillsides and typically have depth to the water table of over 80 inches. Hayesville series soils originate form residuum weathered from granite and gneiss. Slopes range from 2 to 7 percent. 37C3—Hayesville Clay Loam This soil portrays the same characteristics as the Hayesville soil listed above, yet contains predominantly clay loam soils, rather than loam soils, within the first 7 inches. Slopes range from 7 to 15 percent and are severely eroded. 2.4 Adjacent Areas Land use immediately surrounding the property consists of residential development and rural areas. The property is bounded to the west by residential lots, and on all other borders by rural areas. The parcel shares its northern boundary with a VDOT public right-of-way, occupied by Three Notched Road. All minimum yard requirements are met for this parcel along its boundaries. 2.5 Critical Slopes Critical slopes exist between the existing FWPS and generator. These slopes are considered managed slopes and can be disturbed. 3.0 Erosion Control Plan The erosion and sediment control devices and measures have been designed and placed in accordance with the Virginia Erosion and Sediment Control Handbook (VESCH), Third Edition, 1992. Temporary measures are used to divert clean water away, limit erosion and contain sediment from cleared areas prior to the establishment of vegetation. 3.1 Temporary Measures 3.1.1 Construction Entrance (CE) A temporary stone construction entrance shall be used to prevent tracking of material from construction vehicles off of the site. The construction entrance shall be constructed in accordance with plate 3.02-1 of the VESCH and meet construction specifications of Std. & Spec. 3.02 of the VESCH. Maintenance of the construction entrance shall be in accordance with Std. and Spec. 3.02 of the VESCH. See E&S plan sheet of the SWPPP for placement location. 3.1.2 Temporary Diversion Dike (DD) A temporary diversion dike shall be constructed to divert clean water around the disturbed area. The temporary diversion dike shall be constructed in accordance with plate 3.09-1 of the VESCH, and meet construction specifications of Std. & Spec. 3.09 of the VESCH. The channel shall be stabilized with rip-rap (RR) with a Dso of 0.3'. The gradation, thickness, quality, and placement shall be in accordance with Std. & Spec. 3.19 of the VESCH. The rip rap shall extend 3' from the toe of the dike. Filter fabric meeting specifications in Std. & Spec. 3.19 of the VESCH shall be placed under the rip rap. At the outlet of the temporary diversion ditch, temporary rip rap (RR) shall be placed. The length and width of the temporary rip rap shall be 8 and 9 feet respectively with a D50 of 6 inches. Rip rap gradation, quality and placement shall meet Std. & Spec. 3.19 of the VESCH. Design calculations for the temporary diversion dike are located in Appendix B. Erosion Control Plan &Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority 3 3.1.3 Silt Fence (SF) Silt fence shall be use to prevent sediment from leaving the site. Silt fence shall be constructed in accordance with plate 3.05-2 of the VESCH. Installation, construction specification, and maintenance of the silt fence shall meet Std. & Spec. 3.05 of the VESCH. See E&S plan sheet of the SWPPP for placement location. At the low point of the silt fence a modified mud trap (MM) shall be used to provide detention and filtration of runoff. The modified mud trap shall be constructed and maintained in accordance with the Modified Mud Trap standard detail on the E&S Detail plan sheet. See E&S plan sheet of the SWPPP for placement location. 3.1.4 Storm Drain Inlet Protection (IP) Storm drain inlet protection shall be used to prevent sediment from entering the stormsewer system. Inlet protection shall be installed according to plates 3.07-3 and 3.07-8 of the VESCH. All construction and maintenance requirements of Std. & Spec. 3.07 shall be met. See E&S plan for placement location. 3.1.5 Tree Preservation & Protection (TP) Tree protection fence shall be used to protect existing groves of trees. The tree protection fence shall be constructed and maintained in accordance with the Tree Protection Fence standard detail on the E&S Detail plan sheet of the SWPPP. See the E&S plan sheet of the SWPPP for placement location. 3.1.6 Temporary Slope Drain (TSD) A temporary slope Drain shall be used to convey water from the outlet of the stormwater system to the modified mud trap before the bioretention basin is installed. The temporary slope drain shall attach to the outlet pipe such there are no leaks. The outlet of the temporary slope drain shall meet standard plates 3.15-2 and 3.15-3 of the VESCH. Maintenance and construction of the slope drain shall be in accordance with Std. & Spec. 3.15. 3.1.7 Stabilization 3.1.7.1 Temporary Stabilization Temporary stabilization shall be obtained by temporary seeding (TS) and mulching (MU). Temporary seeding shall performed in accordance with Std. & Spec. 3.31 of the VESCH, and temporary mulching shall be performed in accordance with Std. & Spec. 3.35. Temporary seeding and mulching shall be used on any disturbed area that shall not be worked for more than 14 days. 3.1.7.2 Permanent Stabilization Permanent stabilization shall be obtained by permanent seeding (PS) and soil stabilization blanket& matting (B/M). Permanent seeding shall be in accordance with Std. & Spec 3.32. Treatment 1 soil stabilization blanket meeting Std. & Spec 3.36 shall be used over the permanent seeding. Placement of the soil stabilization blanket shall be in accordance with standard plates 3.36-1 and 3.36-2. RIVAN 137749 Erosion Control Plan&Stormwater Management Plan 4 Rivanna Water&Sewer Authority 3.1.7.3 Seeding Seeding shall conform to the following: Minimum Minimum Maximum Seed Purity Germination Weed Seed Type (%) (%) (%) Kentucky 31 Tall Fescue 97 85 0.50 Perennial Ryegrass 98 90 0.50 Kentucky Bluegrass 97 85 0.50 Annual Ryegrass 97 90 0.50 Weeping Lovegrass 98 87 0.50 German Millet 98 85 0.50 Cereal (Winter) Rye 98 85 0.50 Redtop 94 80 0.50 Seeding mixtures to be used on the projected as follows: Permanent Seeding 180 Kentucky 31 5 Perennial 5 Kentucky #/acre Tall Fescue #/acre Ryegrass #/acre Bluegrass Temporary Winter 575 Annual 75 Cereal Seeding #/acre Ryegrass #/acre (Winter) Rye — -------- - ----------------------------------------------------------- Temporary Spring 75 Annual Seeding #/acre Ryegrass ------- ------------------- Temporary Summer 75 German Seeding #/acre Millet 3.2 Erosion Control Sequence 1. No demolition, construction or land disturbance activities may begin until all perimeter erosion control measures have been installed as per Contract Drawings. Perimeter control devices includes the diversion dike with temporary rip rap at the outlets of the diversion dike, silt fence with the modified mud trap at the low point in the silt fence, temporary stone construction entrance and tree protection fence. If clearing is required for installation of a particular measure, all other measures shown shall be installed first; clearing of the land necessary may then proceed. 2. Once all measures have been installed, the site shall be cleared and grubbed as necessary within the limits of disturbance as per the Contract Drawings. Efforts shall be made to minimize the amount of cleared area exposed at any given time. Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority 5 3. Once clearing and grubbing is complete, any necessary topsoil stripping may begin. Topsoil shall be stockpiled on site in the stockpile areas per the Contract Drawings. The stockpile shall receive such temporary seeding measures as may be required. Any soil take offsite shall be stockpiled at locations with all required permits. If offsite location does not have all required permits, the contractor is responsible for obtaining all required permits. 4. Demolition, earthwork and construction operations may begin once topsoil has been removed and stockpiled. 5. Once perimeter erosion control measures are in place, construction activities for the new FWPS may begin. 6. All pipes shall be installed in accordance with standard construction techniques. Only the length of trench in which pipe can be installed in one day's time shall be open at any time, with spoil material placed on the uphill side of the trench. Piping shall be capped at the end of each day's work to prevent sediment from entering. The trench shall be backfilled at the end of each day's work and the disturbed area seeded and mulched within seven (7)days of backfill. 7. All inlets shall have inlet protection installed immediately after installation. The outlet of the stormsewer system must be extended to 10 feet from the modified mud trap with a temporary slope drain until the bioretention basin is approved to receive flow. No discharge from the stormwater system can discharge to the slope permanent BMP's are installed. 8. Temporary soil stabilization shall be applied within seven (7) days to denude areas that may not be at final grade but will remain dormant for longer than fourteen (14) days, except for that portion of the site on which work will be continuous beyond fourteen (14) days. 9. Once construction activities are complete, final grading may begin. At this time the diversion dike and temporary rip rap can be removed. 10. After grading is complete, deeply till the bioretention basin floor with rotary tillers to provide a well-aerated, highly porous surface texture. Install the bioretention gravel, sand, and fill media as noted in the Contract Drawings. Install vegetation and ground cover for the bioretention area. Finally, install silt fence around the basin until final stabilization is reached 11. Upon completion of final grading, permanent seeding, mulching and fertilization measures shall be employed on all disturbed areas. Permanent soil stabilization shall be applied within seven (7) days after final grade is reached on any portion of the site. All remaining erosion control measures shall remain in place until the entire site has been stabilized. 12. Once permanent stabilization has occurred, temporary sediment control measures shall be removed. Any areas disturbed by the removal of these measures shall be returned as closely as possible to original condition and seeded, mulched and fertilized. 3.3 Maintenance and Sediment Disposal All sediment and erosion control measures shall be inspected upon installation, at least once every fourteen (14) days and within 48 hours following any runoff-producing rainfall event. Repairs to, or replacement of, measures shall occur immediately if necessary and accumulated sediment removed as needed. RIVAN 137749 Erosion Control Plan&Stormwater Management Plan 6 Rivanna Water& Sewer Authority Sediment shall be removed from all erosion control measures when the sediment storage volume of the measure has become 50% full. All removed sediment shall be disposed of in an approved manner at the stockpile location or a location to be designated by the Engineer or Owner. Steps shall be taken at the disposal site to insure that further sediment transport does not occur. All disturbed areas shall be permanently seeded as soon as possible, but in no case later than seven (7)calendar days after construction activities are complete. Areas shall be seeded, fertilized and mulched in accordance with the seeing schedule above. 4.0 Stormwater Management Plan 4.1 Introduction This stormwater management plan (SMP) has been prepared in accordance with the Albemarle County Water Protection Ordnance. The SMP addresses water quality and water quantity requirements for the construction improvements to the Crozet WTP Finished Water Pump Station (FWPS). Albemarle county code Sec. 17-501.B. directs any land disturbing activity to obtain initial general permit coverage on or after July 1, 2014 shall be conducted in accordance with the technical criteria in 9VAC25-870-93 through 9VAC25-870-99. As mentioned above this report outlines the modification to the existing project Crozet WTP GAC Facility Improvements (GAC) due to the FWPS project. Compliance was determined by evaluating the two projects as one site. The table below summarizes the two sites. Note that the combined disturbance is not the GAC Project and FWPS Project added together. This is because there is 0.11 acres overlap in the projects disturbance areas. Table 1. Project Composition FWPS GAC Combined GAC Project and Project Project FWPS Project Disturbed Disturbed Pre Post Area Area Development Development Impervious (acres) 0.07 0.38 0.39 0.46 Grassed, good condition (acres) 0.31 0.74 1.00 0.93 Wooded, good condition (acres) 0.00 0.00 0.00 0.00 Total 0.38 1.12 1.39 1.39 The two projects make up approximately 1.39 acres of a 3.37 acre watershed. This is shown Appendix V of the GAC SMP. The watershed is composed of brushy groves, mowed grass, buildings, tanks, roadways, sidewalks and gravel. The collection point of this watershed is at the southwest corner of the property, and ultimately collects in the Licking Hole Basin, located southwest of the property. Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority 7 Table 2. Watershed Composition Pre Development Post Development Impervious (acres) 1.20 1.22 Grassed, good condition (acres) 1.45 1.43 Wooded, good condition (acres) 1.02 1.02 Total 3.67 3.67 4.2 Water Quality Requirements (9VAC25.870-63. Water quality design criteria requirements.) Virginia Runoff Reduction Method Spreadsheet(VRRMS) version 3 was utilized to meet water quality requirements outlined in section 9VAC25-870-63 of Virginia Code. The pre and post development land cover entered is shown above in Table 1, under Combined GAC Project and FWPS Project. This this resulted in a total reduction requirement of 0.38 lb/yr of phosphorous. The three bioretention basins proposed with the GAC building were entered into tabs D.A. A, D.A. B, and D.A. C for Basin 1, 2, and 3 respectively The bioretention basin proposed for the FWPS was entered into tab D.A. D. The total reduction obtained is 0.75 lb/yr of phosphorous. A figure showing the drainage areas for the GAC project bioretention basin is included in the GAC SMP. A figure showing the drainage area of the FWPS project bioretention basin is included in Appendix D of this report. The Site Summary Page from the VRRMS is attached in the Appendix C of this report. 4.3 Water Quantity Requirements (9VAC25-870-66. Water quality.) 4.3.1 Channel Protection The methodology outlined in 9VAC25-870-66.3.a was used to meet channel protection requirements. The full calculations are provided in the Appendix D of this report. A summary of the results are provided in the table below. QDeveloped < /'F.* (QPredeveloped * RVPredeveloped)/RVDeveloped Table 3. Channel Protection Requirement I.F. (site > 1 acre): 0.8 QDeveloped: cfs 3.64 RVDeveloped: et 9,600 QPre-Developed: cfs 4.09 RVPre-Developed: cf 10,700 I.F. (Qpre-Developed RVPre-Developed) RVDeveloped 3.65 For all calculations the watershed area was used, 3.67 acres. The Runoff Volume for pre and post development were calculated using the SCS TR-55 method. The Peak Runoff was calculated using the graphical peak discharge method. To account for the runoff reduction due to the three bioretention basins proposed with GAC project and the one bioretention basin proposed with the FWPS project, the VRRMS was used to determine an adjusted curve number. This new curve number, 69.8, was then used to calculate an adjusted QDeveloped and RVDeveloped, 3.64 cfs and 9600 cf respectively. As shown in the table the QDeveloped is less than RIVAN 137749 Erosion Control Plan&Stormwater Management Plan 8 Rivanna Water&Sewer Authority the maximum allowable runoff from the site. The peak flow for post development, 3.64 cfs, is also less than pre development's peak flow, 4.09 cfs. 4.3.1.1 Bioretention Design The bioretention basin was designed to meet requirements for a Micro-Biortention Design Level 2, Design Specification No. 9. The calculations provided in the Appendix D of this report, shows the minimum surface area required to meet channel protection requirements is 154 sf. The bioretention basin surface area provided is 267 sf. The Drainage Area Land Use Characteristics Table shown on the Bioretention design page describes the area draining to the basin, 0.35 acres. The Treatment Area Required describes the area need to be treated, 0.16 acres, to meet requirements. To prevent the basin from receiving too much flow, the basin is designed to be off line. 4.3.2 Flood Protection 4.3.2.1 Peak Runoff from Site The pre and post peek runoff for the drainage area for the FWPS project was calculated using the Rational Formula. The table below summarizes the results and the calculation can be found in the Appendix D of this report. Table 4. Peak Runoff Units Predevelopment Post development Composite C 0.45 0.45 2-yr Peak Flow(Q) cfs 7.84 7.84 10-yr Peak Flow (Q) cfs 10.40 10.40 Change in Q 0.00% This table shows that there is not a perceivable increase in the runoff from the site, even though the impervious area increases. This is because the composite C, and the time of concentration is the same for pre and post development. When calculating the composite C value all known C values used in the calculation have a significant figure of 2. Therefore the composite C value should be rounded to a significant figure of 2. Due to rounding the composite C value come out to be 0.45 in the post development same as in the predevelopment. The time of concentration between the pre and post development also stays the same. As shown in the Appendix V in the GAC SMP, the time of concentration starts at the WTP and travels behind the ACSA Maintenance Building. It then slopes to the GST and finally runs along the south edge of the GST and outlets on the west side of the GST. This path does not cross through the FWPS project site, and the FWPS project does not create a more hydraulically distant point. For those reasons the time of concentration stays the same in pre and post development, causing no change in the runoff. 4.3.2.2 Adequate Channel Analysis For the GAC project, analysis on the downstream channel was performed. It was determined that the channel had capacity for the current flow from the site. A field visit indicated erosion was occurring downstream of the parcel, where additional flow from a development enter the channel. Both the field visit and the model demonstrated that the erosion was due to the additional flow and not the flow from the GAC parcel. The full analysis can be found in the GAC SMP. Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority 9 As noted above the FWPS project causes an insignificant change in the flow from the site. Since the existing channel is adequate for the flow from the current site and the proposed project does not increase the flow, the existing channel should be adequate for this project. Further analysis of the channel would not then be needed. 4.4 Conclusion As shown in this report, the stormwater management plan address all requirements of the WPO. Bioretention basins are used to meet phosphorous removal and runoff reduction requirements. There is no increase in runoff from the site, making the receiving channel analysis applicable for the addition of the FWPS project. MNT RIVAN 137749 Erosion Control Plan& Stormwater Management Plan 10 Rivanna Water&Sewer Authority Appendix A February 08, 2016 Pre-Application Conference Notes Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water& Sewer Authority A-1 County of Albemarle PRE-APPLICATION CONFERENCE NOTES for By-Right Applications Tax Map and Parcel(s): 05700000002960 Date: 02-08-20I6 This checklist is intended to facilitate and document the meeting discussion. Visitors: Doug March, Miles Jensen Staff: Current Development: x Planning: Ellie Ray Zoning: x Engineering/County Engineer: John Anderson VDOT: Service Authority: Building Official: Housing Office: Description of Location: Crozet on Route 240 Existing Zoning: LI Zoning/Planning History: Several SDPs (SDP20 1 4000 1 4 is most recent), WPOs, SPs and ZMAs. See CountyView Comp. Plan location and land use designation Crozet; Light Industrial AGENDA [Typically, the Planning Division planner will lead the meeting.] I. Introductions and Disclaimer: "This pre-application conference is advisory and based on information provided prior to the meeting. Since details are rarely provided at a pre-application conference, staffs comments will be general in nature. If staff doesn't have answers to an applicant's questions, we will get back to you over the next week. Similarly, if staff needs additional information to assist you in making a future application, we will get back to you over the course of the week to obtain that information." 2. Applicant explains proposal and asks questions. Summary of proposal/Questions: The applicant is proposing construction of a new pump station (unmanned). The existing smaller pump station will also be removed. Concept plan provided prior to meeting; see other documents. 3. Staff answers questions and identifies issues. (A list of some potential issues is provided below.) Question/answer: What type of application is necessary? The proposal is for a small pump station,which requires no additional parking and does not necessitate any entrance changes, so a Minor Site Plan amendment should be submitted. This application will amend SDP201400014. A WPO application and possibly an ARB application will also be required. Question/answer: The applicant was advised that there is a required 30' buffer between the subject parcel and the adjacent property near the proposed pump station. The concept provided prior to the meeting shows disturbance in this buffer area, but the applicant said they believed that the disturbance could be avoided. If it can't, a special exception as outlined in Section 26.5(d) will be required.Special Exceptions must be approved by the Board of Supervisors. Question/answer: The existing pump station is located within the required buffer, and is proposed to be removed;will the removal be considered buffer disturbance? I consulted with Ron Higgins and he said as long as the removal doesn't result in any tree removal or grading, it would not be considered disturbance. If any trees need to be removed or any grading is necessary, the applicant will need to apply for a special exception as outlined in Section 26.5(d). Question/answer What type of ARB application is required? Margaret was not able to make it to this pre-app meeting due to being double-booked in this time slot. The applicant was advised to speak with her directly regarding ARB issues. I also followed up with Margaret to ask that she contact the applicant if she doesn't hear from them. Issue: John spoke with the applicant concerning WPO and VSMP requirements. John said he'd send links to worksheets and directions for easy access to CountyView documents. Both of these items were provided via email after the meeting. See below for additional Engineering comments. Issue: Previous ZMAs;are there any issues with the proposal as it relates to the previous ZMAs? I consulted with Ron Higgins and he said it appears the ZMAs were unrelated to the existing use of the site, so there shouldn't be any issues. Issue: *One item not discussed during the meeting is the required setback between adjacent residential or rural areas districts and any proposed structure. A 50' side setback is required (see Section 4.20). The concept provided isn't dimensioned, but it looks like this setback is probably met, but the application will want to make sure a 50' side setback is maintained. Issue: Topics Discussed (Check those that apply; add notes as necessary) Comp. Plan recommendations including Master Plans and RA Plan recommendations Following Special Use Permit: meeting conditions, application plan conformance Following ZMA: application plan conformance, proffer conformance NMD Conformance with Code of Development Variation(s) required x Waivers/exceptions/variations from Site Plan or Sub ordinance x Setbacks Transportation Need for transportation study Interconnections to adjacent property/development (street/ped/bike) -- DA Public road access internal circulation (in conjunction with Engineer or Current Planner) Private Street request Natural Features/Open Space Plan / Greenway System Urban Design / Public Spaces / Parks or RA- rural character issues Other community facility issues x Entrance Corridor/ARB Historic Preservation Rural clustering RPD option and conservation easement options Easements Deeds required New and Existing Utility (ACSA, RWSA, Private)/Building Code Issues Fire/Rescue Groundwater assessment, including LUST sites x W PO Jurisdictional area issues 4. PROCESS DISCUSSION: Staff summarizes the review process. (Depending on application type, respective department representative explains application process, including:timing, submittal requirements, application details, scheduling hearing.) Discussion/Issues A Minor Amendment shall be submitted according to the submittal schedule: (http://www.albemarle.org/upload/images/forms_center/departments/Community_Development/forms/Site_Plan_Applicati ons/Review_Schedule_for_Site_Plan_&_Tier_I I_Wireless_Applications.pdf) The plan will be distributed the Tuesday following the associated submittal date and comments should be provided within 21 days. The applicant should consult with Engineering and ARB for the process for those applications. 5. NEXT STEPS Additional information to be provided by staff: Additional information to be provided by applicant: Summary/Other Issues: From Engineering: I. Applicant may examine possibility that a recently-approved SWM plan (WPO201400008) might include excess SWM design capacity that may help meet water quality or water quantity requirements under the current proposal. WPO201400008 file information does not make clear whether this is a real possibility, or not. Former staff email may include details relating to design computations, but these are inaccessible and not shown on plan sheets. Engineering encourages Applicant to discuss computational details of Approved 2014 SWM plans with Hazen and Sawyer(Mark Bishop/David Briley; Final Design Plan; I2/19/14)to explore whether 2014 design may help partially offset SWM requirements that otherwise apply to this proposal. 3 small bioretention cells were approved under WPO201400008. 2. This proposal should be evaluated against Part IIB Technical Criteria listed at 9VAC25-870-65 (Quality)/9VAC25-870-66 (Quantity)—link: https://lis.virginia.gov/cgi-bin/Iegp604.exe?000+reg+9VAC25-870-66 3. 9VAC25-870-65.A. requires use of the Virginia Runoff Reduction Method (spreadsheet). The re-development spreadsheet should be used. 4. Review of ordinance indicates proposal is subject to VESCP and VSMP, Article III, Ch. 17—that is, erosion and sediment control, and stormwater management regulations apply, even though area of proposed land disturbance is less than 10,000 square feet. 5.John asked if there may be future WTP additions/modifications. It appears a possibility. RWSA Crozet WTP is a Common Plan of Development or Sale [17-205]—Def: The term "common plan of development or sale" means a contiguous area where separate and distinct construction activities may be taking place at different times on different schedules. Appendix B Temporary Diversion Dike Calculations Erosion Control Plan & Stormwater Management Plan RIVAN 137749 Rivanna Water& Sewer Authority B-1 LEGEND• • -T� ERGENBRIGHT, RICHARD JR D i v e rs� n Dike a:i 6 a g A as ),, ', ,i _,.\\-I \\ 19-1 OR BEVERLY& IRENE SPROUSE `- DB 698-215 11I / EXISTING GRAVEL SURFACE ^R n F - ZONING: RURAL AREA \\ \ /: z=$.. _ USE: SINGLE FAMILY s - V 1 V`\V�y,vv '�, , / / a0! e i \ \ ' \' N Channel was modeled as a v-s le utter. With a flow of 2.02 cfs the 1 , 4'ivo i'i4 STRUCTURE REMOVAL ' ngi ' \\ \ \\\\ width of spread is 5.6 feet and the depth of spread is 0.16 feet. The I/ ; / • ` \ \ \ velocitywithin the dike is 4.5 ft/s. Based on Table 3.17-A this is too great / / --- EXISTING MAJOR CONTOUR \ \ \ \ 0 / - --- EXISTING MINOR CONTOUR \ ?� \ \ of a velocity for slopes greater than 10/o. Therefore, along the edge of / / / - \ "�'- \ \ + _ / / EXISTING PIPE �� Lkul TAX MAP 57A-2C-35 �� , r + I \ the dike extending outwards 3 feet, filter fabric and rip rap shall be ,/ _ , OREM, PHWP J III ..\ , • \ / _ / / PIPE TO BE REMOVED N Ir, ZONINDB G: R40RESIDENTTAL �\ ��, ` i ` . placed. Using Plate 3.19-3, the D50 of the rip rap needed was �� __� , USE: SINGLE FAMILY RES 1 \ \N --\\'�\ �' �� EXISTING CHAIN LINK FENCE \ _ determined to be 0.30. /___/ ; \ ♦ \ _ �, + / AREA OF PROPOSED IMPROVEMENTS \ \ _ U TAX MAP 57-10A ._-_ _ - _ TEMP BENCHMARK \ ;/ EXISTING tREE CANOPY ye\ '� + _-..,_„ RNANNA WATER do -- '\ \\ _.-- ' --' ,/ / O \ AREA 1 = 9290 SF \ \ -, SEWER AUTHORITY = - / 1 I \10fri. : \ "'_"t- - _ -' DB 622-411ti:^ /_ Y ��,---� / 7 \\ \ \ 1 + �_ '_. ZONING: RURAL AREA -- �- \ \ - --_ __ ' / Zce / •x \ •\ l ti^ SE: LOCAL GOVERNMENT__-- \ \ \ \ _ -�!r--..._i t~n 1 I- Drainage area 3. ` REE OTCHED f�D SR 240 _ ______J� / 0.30 acres / 1 (30' PRESCRIPTIVE ROW — IX z TAX MAP 57A-2C-37 \ 7.1 Drams to the modified mud tra �~ "' _, ►- - �� GERGERS, CASSIA \ ` Runoff Coef. 0.25 p ` �- 1 T7J / ` ` `'�- �� _ �' N DB 3130-698 � ce ZONING: R4 RESIDENTIAL + �- �' ~ ~ Flow .34 cfs4110440 I '"' �rwae O o \ / USE: SINGLE FAMILY RES \ - \fir �' \ // :4 \ / �. " / TAX - 57-11�,�� r Q T Q \ / // � / / AC ��_ ---� SPROUS• IRENE :: / 11 t \\ \ \ .t / / imam a �� DB 2419-259 " w h> g a \ !J-- , \ - / ) & e": /:.� NFAM��- \ �" i \ TREES AND BRUSH TO -E "'-1 \, - �y - ,, (1�a�ul� �,: _„'1 , �:" F ^..� / .. liir�. ��...' �_`i.�,►��I '` .n--- '--.._ -. o' xk } 4 t \`\ A _L =_ \ \ \ r \ I d_ '-RWSA MAINTE?� - PROGRAM �' '� f 'F�k>•►' /1\I,1```ice ,' ' `I �, Ce 1-()w 0-_ 40 \ l ,,,,,,,,,..,,,....:......,...,,_,..\--- \ ,x-ate _ ', • // 1,,,,,,,, � ��:.I��\��' ` i! _ 3 Q \ Viejo 1. / •� © r�- - �"' z g G �.�.,r_4 l" c� \\i \MANAGED \\ ` \ ✓ t ' \,1 C-iN,x w Q a Q :��♦e,.,-. .. STEEP SLOPE __ e' ;,� Drainage area 1. m z ,l , •r ��-4.EXISTING *W/\ . \ \ 1/ \ ' _. _ a ...-- I , p 1, g ly Q r ENERATOR ,-A"7 I\1\ ` \ \ ' 1 \ \ \ \ I �� - _ ' , 04 acres J U O �� \ \ \ ` III 'gib ' '}-- _.-> 1 Drains to the north west temporary diversion dike a ,, :. \\+� \I \ \ \ \ \ \ I 1 I , / S�$ DUSTING - cANOP11 p ry , \\ 4 1 \ \ \ I I t ,: �•.,,`. 8.1 , .EA 3 = 7610 SF --,----^! /. c i i \`\\\\ \ \ \: — ___; /-ALr3EVAR 1 _ . _.. -4ge / Runoff Coef. 0.42 "�lM �' t �� \ \ \I \ '•"� ``._'�_...- /{ Flow 1.98 cfs b% ay __ ' r Aft \\\\ \, \ I 1 Drainage area 2. \ '`� \\\,\ \ ' I I 1 \ 0.55 acres ,��1 , _ o� �� 1 ' /// III\III\ '' \\ \\ Drains to the east temporary diversion dike � ," " -- �`. �' l2, ! r/ t /� 11 \ 1 - 1, i \ \ Runoff Coef. 0.81 \ ..:.r� /11 -r \ 11 n \\\\ ' TEMP BM CONc Flow 2.02 cfs 1 I i / / / �• opoireek �� V 1 1/r1 oa FOUNDla\ EX, - 'PPP \\\\`• \ j k� CANOPY//L .: .i I I ay Q r., t \\\` `ill'•'+• 1t l J�l .-. TAX MAP 57A-2C-38 ,,„,"/,,- I , V I \ \1' , / t 1/1 - 1 a _ �r III , --��" / I 1/ WEBER, RENATE I / }!\ \ ,! - ! I :h. l i ' 1 114 '`'ice ;1►7�iIr_i / ' it'l I DB 3095-618 i f 1 / 1111 ++ 1 / 1 dR I ! 1 \ 4..� ZONING: R4 RESIDENTIAL - 1 / ( I 1 / /1/1/1 S// !1!, \ \ , \ 1 ! , \ /! f '/// USE: SINGLE FAMILY RES ,- it x t1 // i/'///Oil//l `, \ _`„ti x`^-�"'.`,;-x "�� P Lcios-=� \ \ \ 1 ttf/1t� - -_ 1 / / /// ,/I/JII/ \ \ "`. - _ -� �s`�'r \ \\ 1 I III / f I 1/ .4 - z; _ -- - - 111, 1 \ �� + + - - _��_ \ I I \ II III f 1! / 3 X l/ I,1/l t v • '- / '° • �r '_ A I I l 1 t t r w u _ 1 / 1/tt/l1/ vvv - - - `\ v •v vv • �0.rl� v\ ___,�� w-- v / r i I r 111 It \ / t t ° r /////// �` _ __ --,` \�-\\ \ \\ \ \ \ \\ \\ \ \ ss `�+,...a/ \ \_ I 1 1 I 1111t 11 r,/ m I I ''�, /1 N `�, �\ \ \ \ \ \ \kS \ '\III I �► '1' • \ This area drains south of the diversion dikes \ I ( 1 r 11 t /, 1, o '--� \` \\ \ \\ \ ` \\ Therefore flow was not calculated for this ` \ \i I i 1,1t _z w > _ -1 I\\ \ \ \ \\ \\ \ \ \ \ olodm 1 1 I \ \ \ \ •\ \\ \ \ \\ \ 'III\1\ I I No ii \ \ \ ` \ \ \ \ \ \ \ , '� - t n II I \\\ \\\ \\\ \\\ \\\ \\\ \\ \\ \\\ \\\ \\ \\ \\ \\ \\\ \\\ \ \\\ \ \\\ \\ \\ \ +1`` 11 ,� / a a a o • This area drains off the site. Therefore flow cn W W\ i \\ \\ \\ \`\ \\ \\ \\ `\ \ \ \` '\\\ \\ \\\ N', was not calculated for this area. o z \ ,..> \\ .\ ♦ \ N `, \\ \\ \ \ \ `\ \ TAX MAP 57-29B \ I _ -Z a 4 0 \ / \ \ \ \ \ \ \ \ \ \ \ \ \ RNANNA WATER & SEWER n rn \ ,� \ \ \ \ \ \ \ AUTHORITY Z a a \ ' \ \ \ `\ `\ \ `\ \ \ `\ \ \ DB 4669 PG 198-210 \ Z w TAX MAP 57A-2B-21 2 J \/ \ \ \ \ \ \ \ \ \ ZONING: LIGHT INDUSTRY \ rc CRAIG ENTERPRISE INC J m " "� \ \ ` ` \ \ \ \ \ \ \ USE: GOVERNMENT BUILDING \ ZONINDB G: R4IRESIDENTIAL _-_,........ \\ \\ \\ \\ \\ \\ \\ \ \\ \\ \\ �\ -. \\ -.• ``r '.,�. I �� ZJ USE: SINGLE FAMILY RES ~+'X \ \\ `\ \ \ \ \ \ `\ \ \ \ \ \ I Ili , . " \ c ;.._- �. \ \ \ ,. \\ ♦ \ \ ►\\ \ L-'L� .i a SHEET ▪ m TAX MAP 57-29EA .._.,�-"'x � _ ��♦�1./"1N \\ \\ '' 2 2 i VAUGHN, ANGELICA �\-""_` X'�^-.�„��. , \ ` \ �N ,-f s t of 11 rl /� Appendix C Water Quality Calculations Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority E-1 Virginia Runoff Reduction Method Worksheet Quality Calculations DEQ Virginia Runoff Reduction Method Re-Development Compliance Spreadsheet -Version 3.0 BMP Design Specifications List: 2013 Draft Stds&Specs Site Summary Total Rainfall(in): 43 Total Disturbed Acreage: 1.38 Site Land Cover Summary Pre-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.99 0.00 0.00 0.99 72 Impervious Cover(acres) 0.00 0.39 0.00 0.00 0.39 28 1.38 100 Post-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.92 0.00 0.00 0.92 67 Impervious Cover(acres) 0.00 0.46 0.00 0.00 0.46 33 1.38 100 Site Tv and Land Cover Nutrient Loads Final Post-Development Post- Pre- Final Post-Development Post-ReDevelopment TP Post- Development Adjusted Pre- ReDevelopment TP Load per acre Load per acre (Post-ReDevelopment &New Impervious) ReDevelopment (New Impervious) ReDevelopment TP Load per acre P ) (Ib/acre/yr) (lb/acre/yr) (Ib/acre/yr) Site Rv 0.45 0.42 0.95 0.42 0.97 1.03 0.97 Treatment Volume(ft3) 2,254 2,013 241 2,013 TP Load(Ib/yr) 1.42 1.26 0.15 1.26 Total TP Load Reduction Required(Ib/yr) 0.38 0.25 0.12 Final Post-Development Load Pre- (Post-ReDevelopment&New Impervious) ReDevelopment TN Load(lb/yr) 10.13 9.28 _______________________ Site Compliance Summary Maximum%Reduction Required Below Pre-ReDevelopment Load 20% Summary Print Virginia Runoff Reduction Method Worksheet Total Runoff Volume Reduction(ft3) 1,066 Total TP Load Reduction Achieved(Ib/yr) 0.75 Total TN Load Reduction Achieved(Ib/yr) 5.50 Remaining Post Development TP Load (Ib/yr) 0.66 Remaining TP Load Reduction(Ib/yr) 0.00 **TARGET TP REDUCTION EXCEEDED BY 0.38 LB/YEAR** Required ----------------------------------------------------------------------------- Drainage Area Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Managed Turf(acres) 0.10 0.05 0.17 0.28 0.00 0.60 Impervious Cover(acres) 0.15 0.05 0.03 0.07 0.00 0.30 Total Area(acres) 0.25 0.10 0.20 0.35 0.00 0.90 Drainage Area Compliance Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total TP Load Reduced(Ib/yr) 0.33 0.12 0.13 0.17 0.00 0.75 TN Load Reduced(lb/yr) 2.44 0.86 0.94 1.27 0.00 5.50 Drainage Area A Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.10 0.00 0.00 0.10 40 Impervious Cover(acres) 0.00 0.15 0.00 0.00 0.15 60 0.25 BMP Selections Managed Turf Impervious TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit Upstream (acres) Area(acres) Volume(ft3) Practices(Ibs) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed Total Impervious Cover Treated(acres) 0.15 Total Turf Area Treated(acres) 0.10 Summary Print Virginia Runoff Reduction Method Worksheet Total TP Load Reduction Achieved in D.A. (lb/yr) 0.33 Total TN Load Reduction Achieved in D.A. (I b/yr) 2.44 Drainage Area B Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.05 0.00 0.00 0.05 50 Impervious Cover(acres) 0.00 0.05 0.00 0.00 0.05 50 0.10 BMP Selections Managed Turf Impervious TP Load from BMP Treatment Practice Credit Area Cover Credit Upstream Untreated TP Load TP Removed TP Remaining Downstream Treatment (acres) Area(acres) Volume(ft,) Practices(Ibs) to Practice(Ibs) (Ib/yr) (lb/yr) to be Employed 'Total Impervious Cover Treated(acres) 0.05 Total Turf Area Treated(acres) 0.05 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.12 Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.86 Drainage Area C Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.17 0.00 0.00 0.17 85 Impervious Cover(acres) 0.00 0.03 0.00 0.00 0.03 15 0.20 BMP Selections Managed Turf Impervious TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit Upstream (acres) Area(acres) Volume(fta) Practices(Ibs) to Practice(Ibs) (lb/yr) (lb/yr) to be Employed Total Impervious Cover Treated(acres) 0.03 Total Turf Area Treated(acres) 0.17 Summary Print Virginia Runoff Reduction Method Worksheet Total TP Load Reduction Achieved in D.A. (Ib/yr) 0.13 Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.94 Drainage Area D Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.28 0.00 0.00 0.28 80 Impervious Cover(acres) 0.00 0.07 0.00 0.00 0.07 20 0.35 BMP Selections Managed Turf Impervious TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit Upstream (acres) Area(acres) Volume(ftn) Practices(Ibs) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed Total Impervious Cover Treated(acres) 0.07 Total Turf Area Treated(acres) 0.09 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.17 Total TN Load Reduction Achieved in D.A. (lb/yr) 1.27 Drainage Area E Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Cover Credit Upstream (acres) Area(acres) Volume(fta) Practices(Ibs) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Summary Print Virginia Runoff Reduction Method Worksheet Total TP Load Reduction Achieved in D.A. (lb/yr) 0.00 Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.00 Runoff Volume and CN Calculations 1-year storm 2-year storm 10-year storm Target Rainfall Event(in) 3.04 3.35 5.15 Drainage Areas RV&CN Drainage Area A Drainage Area B Drainage Area C Drainage Area D Drainage Area E V CN 83 80 67 68 0 RR(f63) 472 167 182 245 0 - RV wo RR(ws-In) 1.48 1.28 0.60 0.65 0.00 1-year return period RV w RR(ws-in) 0.96 0.82 0.35 0.45 0.00 CN adjusted 74 72 60 63 0 RV wo RR(ws-in) 1.73 1.52 0.77 0 82 0.00 2-year return period RV w RR(ws-In) 1.21 1.06 0.52 0.62 0 00 CN adjusted 75 73 61 64 0 RV wo RR(ws-in) 3.31 3.02 1.91 1.99 0.00 10-year return period RV w RR(ws-In) 2.79 2.56 1.66 1.79 0.00 CN adjusted 77 75 64 66 0 Summary Print Appendix D Water Quantity Calculations Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority E-1 J Prepared By Maria Tiegs SEH Date of Calculations 8/18/2016 Building a Better World Client RSWA for All of Us° Project Name Crozet FWPS Description 2 yr& 10 yr Runoff Calculations Reviewer Date Reviewed Table 1: Drainage Area Calculations Predevelopment Postdevelopment [ac] [ac] Impervious 0.95 1.20 1.22 Grassed 0.25 1.45 1.43 Wooded 0.15 1.02 1.02 Total 3.67 3.67 Table 2: Rational Method Calculations Tc [min]: 7.2 Units Predevelopment Postdevelopment Composite C 0.45 0.45 2-yr Intensity(I) in/hr 4.75 4.75 10-yr Intensity (I) in/hr 6.30 6.30 2-yr Peak Flow (Q) cfs 7.84 7.84 10-yr Peak Flow (Q) cfs 10.40 10.40 Change in Q 0.00% CIA Where: Q =discharge (cfs) C =runoff coefficient representing a ratio of runoff to rainfall I =rainfall intensity (in/hr) A =drainage area(acres) 2 yr 10 yr Runoff Calculations 1 of 7 if Prepared By Maria Tiegs SEH Date of Calculations 8/18/2016 Building a Better Woric Client RSWA for All of Us' Project Name Crozet FWPS Description Runoff Calculations Reviewer Date Reviewed Table 1: Drainage Area Calculations CN Predevelopment Postdevelopment [ac] [ac] Impervious 98 1.20 1.22 Grassed 61 1.45 1.43 Wooded 55 1.02 1.02 Total 3.67 3.67 Table 2: Pre and Post Volume units Predeveloped Developed Developed (with Treatment) 1-yr(24hr) precipitation (P) in 3.04 3.04 3.04 Composite CNa 71.4 71.6 69.8 Storage Capacity (S) in 4.01 3.97 4.33 Initial abstraction (la) in 0.80 0.79 0.87 Runoff Depth (Q) in 0.80 0.81 0.72 Drainage Area sf 160,000 160,000 160,000 RV (Runoff Volume) cf 10,700 10,800 9,600 a Composite CN value for "postdevelopment with treatment" obtained from Virginia RRM Spreadsheet, Runoff Volume and CN tab Table 3: Peak Flow(1yr-24hr) units Predeveloped Developed Developed (with Treatment) 1-yr(24hr) Peak Flow (Qp)b cfs 4.09 4.14 3.64 b Peak Flow values obtained from SCS Graphical Peak Discharge Spreadsheet Runoff Calculations 2 of 7 Table 4: Qdeveloped< I.F.*(()Pre-Developed*RVPre-Developed)/RVDeveloped) I.F. (site > 1 acre): 0.8 ()Developed• 3.64 RN/Developed: 9,600 QPre-Developed• 4.09 RVPre-Developed• 10,700 I.F.*(Qpre-Developed*RVPre-Developed)/RVDeveloped 3.65 (P — Ia)2 Q = runoff(in) _ Q (P—Ia)+S P = rainfall (in) S = potential maximum retention after runoff Ia = 0.25 begins (in) and Ia = initial abstraction (in) 1000 S = _10 CN Runoff Calculations 3 of 7 /Am Prepared By Maria Tiegs SEH Date of Calculations 8/18/2016 Building a Better Worlc for All of Use Client RSWA Project Name Crozet FWPS Description SCS Graphical Peak Discharge Reviewer Date Reviewed Table 1: Drainage Area Calculations Predevelopment Postdevelopment CN [ac] [ac] Impervious 98 1.20 1.22 Grassed 61 1.45 1.43 Wooded 55 1.02 1.02 Total 3.67 3.67 Table 2: Runoff Depth T, [hr]: 0.12 units Predeveloped Developed Developed (with Treatment) 1-yr(24hr) precipitation (P) in 3.04 3.04 3.04 Composite CNa 71.4 71.6 69.8 Storage Capacity (S) in 4.01 3.97 4.33 Initial Abstraction (la) in 0.80 0.79 0.87 Runoff Depth (Q) in 0.80 0.81 0.72 a Composite CN value for"postdevelopment with treatment" obtained from Virginia RRM Spreadsheet, Runoff Volume and CN tab Table 3: Unit Peak Discharge Developed (with units Predeveloped Developed Treatment) Initial Abstraction (la)b in 0.801 0.794 0.865 la/P 0.26 0.26 0.28 Unit Peak Discharge (q„)` csm/in 896 896 888 bValues interpolated from Table 4-1 `Values obtained from Exibit 4-1l. Unit Peak Discharge for NRCS (SCS) type II raingall distribution SCS Graphical Peak Discharge 4 of 7 • Table 4: Peak Discharge units Predeveloped Developed Developed (with Treatment) Drainage area (Am) mi2 0.0057 0.0057 0.0057 Pond and Swamp adjustment factor(Fr) 1 1 1 Peak Discharge (qp) cfs 4.09 4.14 3.64 qp = quAmQi'p qp = peak discharge (cfs) qu = unit peak discharge (csmlin) Am = drainage area (mil) Q = runoff (in) Fp= pond and swamp adjustment factor Exhibit 4-II Unit peal discharge(q„)for NRCS(SCS)type II rainfall distribution 1 uuu 800 - 600 - 500 - * 400- Or0 c Q J0 S u 300_ 0°40 ,9s P 0 mrn 'SO .c 200- M a 4 a a c 100- 80- 60- 50 i iI I .1 .2 .4 .6 .6 1 2 4 6 8 10 Time of concentration(T.),(hours) SCS Graphical Peak Discharge 5 of 7 f Table 4-1 Ia values for runoff curve numbers Curve Ia Curve La number (in) number (in) 40 3.000 70 0.857 41 2.878 71 0.817 42 2.762 72 0.778 43 2.651 73 0.740 44 2.545 74 0.703 45 2.444 75 0.667 46 2.348 76 0.632 47 2.255 77 0.597 48 2.167 78 0.564 49 2.082 79 0.532 50 2.000 80 0.500 51 1.922 81 0.469 52 1.846 82 0.439 53 1.774 83 0.410 54 1.704 84 0.381 55 1.636 85 0.353 56 1.571 86 0.326 57 1.509 87 0.299 58 1.448 88 0.273 59 1.390 89 0.247 60 1.333 90 0.222 61 1.279 91 0.198 62 1.226 92 0.174 63 1.175 93 0.151 64 1.125 94 0.128 65 1.077 95 0.105 66 1.030 96 0.083 67 0.985 97 0.062 68 0.941 98 0.041 69 0.899 SCS Graphical Peak Discharge 6 of 7 Prepared By Maria Tiegs SEH Date of Calculations 8/18/2016 Building a Better Worlc for All of Us' Client RSWA Project Name Crozet FWPS Description Micro-Bioretention Design Level 2 Reviewer Date Reviewed Table 1: Drainage Area Land Use Caracteristics Area (ac) CN Rv Pervious 0.28 61 0.20 Impervious 0.07 98 0.95 Total 0.35 68 0.35 Table 2: Treatment Volume Calculation Precipitation depth, P in 1 1" water quality event Treatment Area Required ac 0.16 Rvpost - 0.35 Treatment Volume,Tv cf 203 (P)(Rv)(Area)/12 Table 3: Design Depth Calcuation Layer Depth (ft) Void Ratio (Vr) Storage (ft) Gravel 1.0 0.40 0.40 Media 3.0 0.25 0.75 Ponding 0.5 1.00 0.50 Total (Design Depth) 1.65 Table 4: Surface Area Calculation Surface Area, SA sf 154 (1.25*Tv)/(design depth) Length ft Width ft Bioretention Sizing 7 of 7 Virginia Runoff Reduction Method Worksheet Adjusted CN DEQ Virginia Runoff Reduction Method Re-Development Compliance Spreadsheet -Version 3.0 BMP Design Specifications List: 2013 Draft Stds&Specs Site Summary Total Rainfall(in): _ 43 Total Disturbed Acreage: 3.67 Site Land Cover Summary Pre-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals %of Total Forest/Open(acres) 0.00 1.02 0.00 0.00 1.02 28 Managed Turf(acres) 0.00 _ 1.45 0.00 0.00 1.45 40 Impervious Cover(acres) 0.00 1.20 0.00 0.00 1.20 33 3.67 100 Post-ReDevelopment Land Cover (acres) A soils B Soils C Soils D Soils Totals %of Total Forest/Open(acres) 0.00 1.02 0.00 0.00 1.02 28 * Managed Turf(acres) 0.00 1.43 0.00 0.00 1.43 39 Impervious Cover(acres) 0.00 1.22 0.00 0.00 1.22 33 *Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 3.67 100 Site Tv and Land Cover Nutrient Loads Final Post-Development Post- Pre- Final Post-Development Post-ReDevelopment TP (Post-ReDevelopment Post- Development Adjusted Pre- ReDevelopment TP Load per acre Load per acre &New Impervious) ReDevelopment (New Impervious) ReDevelopment TP Load per acre p ) (Ib/acre/yr) (Ib/acre/yr) (Ib/acre/yr) Site Rv 0.40 0.40 0.95 0.40 0.91 0.92 0.91 Treatment Volume(ft3) 5,348 5,290 59 5,290 TP Load(Ib/yr) 3.36 3.32 0.04 3.32 Total TP Load Reduction Required(Ib/yr) 0.69 0.66 0.03 Final Post-Development Load Pre- (Post-ReDevelopment&New Impervious) ReDevelopment TN Load(Ib/yr) 24.04 23.83 Site Compliance Summary Maximum%Reduction Required Below 20ff Pre-ReDevelopment Load Total Runoff Volume Reduction(ft3) 1,348 Summary Print Virginia Runoff Reduction Method Worksheet Total TP Load Reduction Achieved(Ib/yr) 0.94 Total TN Load Reduction Achieved(Ib/yr) 6.88 Remaining Post Development TP Load (Ib/yr) 2.42 Remaining TP Load Reduction(Ib/yr) 0.00 **TARGET TP REDUCTION EXCEEDED BY 0.25 LB/YEAR** Required Drainage Area Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total Forest/Open(acres) 1.02 0.00 0.00 0.00 0.00 1.02 Managed Turf(acres) 1.43 0 00 0.00 0.00 0.00 1.43 • Impervious Cover(acres) 1.22 0.00 0.00 0.00 0.00 1.22 Total Area(acres) 3.67 0.00 0.00 0.00 0.00 3.67 Drainage Area Compliance Summary D.A.A D.A.B D.A.C D.A.D D.A.E Total TP Load Reduced(Ib/yr) 0.94 0.00 0.00 0.00 0.00 0.94 TN Load Reduced(Ib/yr) 6.88 0.00 0.00 0.00 0.00 6.88 Drainage Area A Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 1.02 0.00 0.00 1.02 28 Managed Turf(acres) 0.00 1.43 0.00 0.00 1.43 39 Impervious Cover(acres) 0.00 1.22 0.00 0.00 1.22 33 3.67 BMP Selections Managed Turf Impervious Cover TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Credit Area Upstream Volume(ft3) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) (acres) Practices(Ibs) Total Impervious Cover Treated(acres) 0.40 Total Turf Area Treated(acres) 0.38 Total TP Load Reduction Achieved in D.A. , (Ib/yr) 0.94 Total TN Load Reduction Achieved in D.A. 6.88 (Ib/yr) • Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area B Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious Cover BMP Treatment TP Load from Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Credit Area Upstream Volume(ft3) to Practice(Ibs) (lb/yr) (lb/yr) to be Employed (acres) (acres) Practices(Ibs) Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A. (Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.00 Drainage Area C Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious Cover TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Credit Area Upstream Volume(ft3) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) (acres) Practices(Ibs) Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A. (lb/yr) 0.00 Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.00 Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area D Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious Cover TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Credit Area Upstream Volume(ft3) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) (acres) Practices(Ibs) Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A. 0.00 (Ib/yr) Total TN Load Reduction Achieved in D.A. (Ib/yr) 0.00 Drainage Area E Summary Land Cover Summary A Soils B Soils C Soils D Soils Total %of Total Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0 Managed Turf(acres) 0.00 0.00 0.00 0.00 0.00 0 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0 0.00 BMP Selections Managed Turf Impervious Cover TP Load from BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment Practice Credit Area Credit Area 3 Upstream Volume(ft) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed (acres) (acres) Practices(Ibs) Total Impervious Cover Treated(acres) 0.00 Total Turf Area Treated(acres) 0.00 Total TP Load Reduction Achieved in D.A. (Ib/yr) 0.00 Total TN Load Reduction Achieved in D.A. 0.00 (Ib/yr) Runoff Volume and CN Calculations . Summary Pnnt Virginia Runoff Reduction Method Worksheet 1-year storm 2-year storm 10-year storm Target Rainfall Event(in) 3.04 3.35 5.15 Drainage Areas RV&CN Drainage Area A Drainage Area B Drainage Area C Drainage Area D Drainage Area E CN 72 0 0 0 0 RR(ft3) 1,348 0 0 0 0 RV wo RR(ws-in) 0.83 0.00 0 00 0.00 0 00 1-year return period RV w RR(ws-in) 0.73 0.00 0.00 0.00 0.00 CN adjusted 70 0 0 0 0 RV wo RR(ws-in) 1.02 0.00 0.00 0 00 0.00 2-year return period RV w RR(ws-in) 0 92 0.00 0.00 0.00 0 00 CN adjusted 70 0 0 0 0 RV wo RR(ws-in) 2.31 0.00 0.00 0.00 0.00 10-year return period RV w RR(ws-In) 2.21 0.00 0.00 0.00 0 00 CN adjusted 71 0 0 0 0 Value is 69.8, but shown rounded to 70 here Summary Print NEW CONCRETE PAD LEGEND: / / FOR TRANSFORMER °$ N PROPOSED �� _ ' EXISTING GRAVEL SURFACE U°'R^'8 COATED BLACK �' OF WALL 637 00 -R POLY CHAIN .,� ``IIOW33.00 -_ � .. _ PROPOSED CONCRETE e LINK FENCE i r - '� VIM W TOP'., 639.00 �'- r.rs,,\. i I -_ 1 if :Eh. '��_ - PROPOSED BITUMINOUS SURFACE \ �', ,1 I SOT OF ,i L 639400 _. N1144 5 3 �-` '411 OV O-<Nir _�� - 00000� PROPOSED PRETREATMENT CELL —� 30 0, U�y / R20.0' ` -, - .�-�-�-�-.- PROPOSED GRASS FILTER STRIP a�oisrUR �� ` �' „, Bf0 MH / PROPOSED RETENTION BASIN ��// Z VI / RI REo NIOGK . . . . .. . ii O MH 3 I_. SEE i Q O 1 r k OTE PROPOSED CONC SURGE BASIN tit) •IM. _ _ _ •POSED ///!///i I-� illio _ , ' •TE EXISTING MA.IOR CONTOURme�•J ` �� . EXISTINGMINORCONTOUR `__ Z\��' PROPOSED MAJORCONTOURp�� a / ` � 4 PROPOSED MINOR CONTOURW I- CONNECT TO ' ` 4 ,.. �yEXISTING FENCE , / p � IL I , A ' ® � � 8.0 EXISTING PIPE ii Z �' ` OF •LL• 6$7All PROPOSED PIPE -+ -� ` ` �� R O 0 ALL 636.25 `� J I lr III. 233 �' NfLBH /^" Ho �` w ® 1� ' • PROPOSED RETAINING WALL w l M 4 ME. P S �� TOP OF -•LL• 637.• — EXISTING CHAIN LINK FENCE ; y RI ••.4.39 ` B TAT 'OT OF ALL. 633.00 H / F ` UI�rNC Al `� 6 SEE NO'f. - �— PROPOSED CHAIN UNK FENCE F- .- ' £rCHT 637 /oo; efr*1p. O.®swt4 ; &4 4111 ••\\\ 4♦/� BH/3/r•71 i /fr TOP OF 'ALL 633� Plii. •GT � -111.12ib-!.1:411411/0/Plii 4‘ir1177,-'\ / ---,Naar ®,{J// I/ q ` � ,*\4 "-INSTALL NEW 90• ;*11 .�, :, _. �/! BEND AND / - `_' ,/�� DEFLECT JOINTS `, ' / ' ,11P.1,,_,,... - ''' 411%,01.„,#.. / G� Div \ 1 / ` ` 111 , '1 ' 1 DRAINA ARE '' I ,• A." :`'"'+•.,,,,, - , m..,.,m�,. .,_.....,.._ .. .� -_ / 1 1 j j Ii � 11 1 I ) II 1 I ' 1 I jrPN, /EET tBH/4/BORE HOLE 1 ; 1 ; rn m w \ i . i ,J. / // u /// J( .71 \. I s ¢ o F,E1It 1 I I r a I Xc 1- / tx I I�t� , zzW , x ,. CONNECI TO / ' — �i w W om EXISTING FENCE • fry c_ / =o N N Y - <�/ ,' 11 I V I. 1 , ' 1 1 1 i 1 ' rw v1 FWPS BORETENTION BASIN 1 , , / / , 4 g w t / „L._ , -- f DRAINAGE AREA .2. z _ La Et a m F < � / r © P n - \ �' " - - SITE LAN SHEET 0 10 o �� _ 3 of 11 1 Appendix E Original ECP and SMP Erosion Control Plan&Stormwater Management Plan RIVAN 137749 Rivanna Water&Sewer Authority E-1 R1VANN YNNA diree.---"%>6"4"....1.%4Sc""N ir WATER & SEWER AUTHORITY .--1) Granular Activated Carbon Contactor Facilities at the Crozet Water Treatment Plant Major Amendment to Approved Site Development Plan # 199900043 Erosion Control Plan and Stormwater Management Plan Including Erosion Control Narrative and Calculations, Stormwater Analysis, and Related Specifications Submitted to: County of Albemarle May 2014 ,,,,1/111111,.,�r r M a:- 1' ,rit I 1 1 \,f it AS:-0 S 4c\ 4 ryrli��1111111111�.�r~w HAZEN AND SAWYER Environmental Enalneers & Scientist: 4011 WestChase Boulevard, Suite 500 Raleigh, NC 27607 NARRATIVE REPORT INTRODUCTION The Rivanna Water and Sewer Authority (RWSA) is proposing upgrades to one of their existing water treatment plant (WTP)facilities to meet recent US EPA regulations addressing disinfectants and disinfection byproducts (DBPs) and microbial pathogens. The WTP is located west of the City of Charlottesville in the town of Crozet. The Crozet Water Treatment Plant sources water from the Beaver Creek Reservoir. To meet DBP regulations, new carbon contactors containing granular activated carbon (GAC) will be added to the plant between the processes of filtration and primary disinfection. The Crozet WTP resides within the jurisdiction of Albemarle County, and all necessary permits will be coordinated with the County. All proposed construction will take place within the Crozet WTP property; no construction will occur outside of the property boundaries. The site is located within the Albemarle County Entrance Corridor and as a result is subject to the County's Architectural Review Board requirements. The disturbed area for these improvements is approximately 1.12 acres. Any excess and unsuitable soil will be stockpiled onsite by the contractor with the option of unsuitable material to be disposed of in an approved location with all required permits to be acquired by the contractor. Erosion and sediment control measures will be used to limit erosion and contain sediment from the construction and cleared areas prior to the establishment of vegetation. SOILS Two soil types exist on site. These soils have been identified and classed by the Natural Resources Conservation Service (NRCS), and are detailed below. 36B — Hayesville Loam The Hayesville series soils, a well-draining series, exist predominantly on hillsides and typically have a depth to the water table of over 80 inches. Hayesville series soils originate from residuum weathered from granite and gneiss. Slopes range from 2 to 7 percent. 37C3 — Hayesville Clay Loam This soil portrays the same characteristics as the Hayesville soil listed above, yet contains predominantly clay loam soils, rather than loam soils, within the first 7 inches. Slopes range from 7 to 15 percent and are severely eroded. ADJACENT AREAS Land use immediately surrounding the property consists of residential development and rural areas. The property is bounded to the west by residential lots, and on all other borders by rural areas. The parcel shares its northern boundary with a VDOT public right-of-way, occupied by Three Notch'd Road. All minimum yard requirements are met for this parcel along its boundaries. EROSION AND SEDIMENT CONTROL MEASURES A majority of the erosion and sediment control devices and measures have been designed and placed in accordance with the Virginia Erosion and Sediment Control Handbook (VESCH), Third Edition, 1992. Temporary measures will be used to limit erosion and contain sediment from cleared areas prior to the establishment of vegetation. Once construction, including all structural measures, is complete and permanent vegetative cover has been established, these measures may be removed with approval from the engineer. Vegetative cover for disturbed areas will consist of grasses as recommended by the Virginia Erosion and Sediment Control Handbook. See the Plans and Specification Section 02910 — Final Grading and Landscaping for the proposed Seeding schedule, attached. The temporary measures proposed for this improvement include silt fence, construction entrances, and temporary seeding measures as required. The above devices will filter sediment from runoff to prevent sediment from being deposited off-site, while the temporary seeding will limit erosion during construction activities. Permanent measures proposed include permanent seeding. See Specification Section 02276 — Erosion and Sedimentation Control and Section 02910 — Final Grading and Landscaping for further details on these temporary and permanent measures. Temporary Stabilization A majority of the temporary sediment and erosion control measures were designed and chosen based on criteria from the Virginia Erosion and Sediment Control Handbook (VESCH). Stabilization construction entrances/exits and silt fence are designed in accordance with the guidelines established in VESCH Sections 3.02 and 3.05. Temporary seeding measures were chosen as per the recommendations of VESCH Section 3.31. Temporary rolled erosion control mat was designed in accordance with the procedures outlined in Section 3.36. Permanent Stabilization Upon completion of the project, permanent vegetative plantings will be used to achieve stabilization of the site. All temporary erosion and sediment control measures will be removed once the site has been stabilized. All permanent vegetative plantings conform to those specified in the VESCH Section 3.32. See Specification Section 02910 — Final Grading and Landscaping, attached, for the proposed seeding schedule. Erosion Control Sequence 1) No demolition, construction or land disturbance activities may begin until all perimeter erosion control measures have been installed as per Contract Drawings. If clearing is required for installation of a particular measure, all other measures shown shall be installed first; clearing of the land necessary may then proceed. 2) Once all measures have been installed, the site shall be cleared and grubbed as necessary within the limits of disturbance as per the Contract Drawings. Efforts shall be made to minimize the amount of cleared area exposed at any given time. 3) Once clearing and grubbing is complete, any necessary topsoil stripping may begin. Topsoil shall be stockpiled on site in the stockpiling areas per the Contract Drawings. The stockpile shall receive such temporary seeding measures as may be required. Any soil taken offsite shall be stockpiled at locations with all required permits. If offsite location does not have all required permits, the contractor is responsible for obtaining any required permits. 4) Demolition, earthwork and construction operations may begin once topsoil has been removed and stockpiled. 5) Once perimeter erosion control measures are in place, construction activities for the new GAC facility and proposed roadway may begin. 6) All pipes shall be installed in accordance with standard construction techniques. Only the length of trench in which pipe can be installed in one day's time shall be open at any time, with spoil material placed on the uphill side of the trench. Piping shall be capped at the end of each day's work to prevent sediment from entering. The trench shall be backfilled at the end of each day's work and the disturbed area seeded and mulched within seven (7) days of backfill. 7) Temporary soil stabilization shall be applied within seven (7) days to denuded areas that may not be at final grade but will remain dormant for longer than fourteen (14)days, except for that portion of the site on which work will be continuous beyond fourteen (14) days. 8) Once construction activities are complete, final grading may begin. 9) Upon completion of final grading, permanent seeding, mulching and fertilizing measures shall be employed on all disturbed areas as per Section 02910 — Final Grading and Landscaping. Permanent soil stabilization shall be applied within seven (7) days after final grade is reached on any portion of the site. All erosion control measures shall remain in place until the entire site has been stabilized. 10) Upon completion of stabilization of the watershed, remove all accumulated sediment and excavate bioretention area to proposed depth. Use relatively light, tracked equipment to avoid compaction of the basin floor. After grading is complete, deeply till the basin floor with rotary tillers to provide a well-aerated, highly porous surface texture. Install the bioretention gravel, sand, and fill media as noted in the Contract Drawings. Install vegetation and ground cover for the bioretention area. 11)Once permanent stabilization has occurred, temporary sediment control measures shall be removed. Any areas disturbed by the removal of these measures shall be returned as closely as possible to original condition and seeded, mulched and fertilized as per Specification Section 02910. Maintenance and Sediment Disposal All sediment and erosion control measures shall be inspected upon installation, at least once every fourteen (14) days and within 48 hours following any runoff-producing rainfall event. Repairs to, or replacement of, measures shall occur immediately if necessary and accumulated sediment removed as needed. Sediment shall be removed from all erosion control measures when the sediment storage volume of the measure has become 50% full. All removed sediment shall be disposed of in an approved manner at the stockpile location or a location to be designated by the Engineer or Owner. Steps shall be taken at the disposal site to insure that further sediment transport does not occur. All disturbed areas shall be permanently seeded as soon as possible, but in no case later than seven (7) calendar days after construction activities are complete. Areas shall be seeded, fertilized and mulched in accordance with the Seeding schedule in Section 02910— Final Grading and Landscaping, of the Specifications. STORMWATER ANALYSIS Introduction This stormwater analysis has been prepared in response to the Crozet WTP improvements. The material provided in this analysis evaluates how the proposed project will affect stormwater runoff and nutrient export from the site. All material provided in this analysis has been prepared and is presented in general accordance with the guidelines outlined in the Albemarle County Water Protection Ordinance. This analysis focuses on both stormwater quantity and quality. The area of the study currently consists of approximately 2.63 acres, a combination of grassed areas, buildings, tanks, and other impervious cover such as roadway, sidewalk, and gravel. The entirety of this area drains to the southwest corner of the property, and is ultimately collected in the Licking Hole Basin, located southwest of the property. A majority of the proposed Crozet improvements will be constructed in an area of the site which is currently gravel pavement. The improvement plan includes decreasing the amount of existing gravel and restoring the area to maintained grass. As a result, the overall impervious area for the site will decrease and an overall decrease in runoff is anticipated. Our project is located within the Drinking Water Watershed and is categorized as a redevelopment based on the Albemarle County Simple Method spreadsheet. As a result a stormwater BMP appropriately sized to treat 0.16 lbs of stormwater pollutant is needed to offset the proposed improvement. Methodologies and Procedures The primary task of this stormwater analysis is to determine the degree of stormwater treatment required for the proposed project for quantity, quality and adequacy. The extent of this analysis accounted for the following factors: the location of the project site, the size of the site respective to the total watershed, and the degree of proposed development. Water Quantity Concerns Channel Protection (VA Minimum Standard 19, Albemarle County Code 17-314) On 4-10-14, Hazen and Sawyer conducted a site visit to access the existing channel receiving runoff from the Crozet Water Treatment Plant(WTP) property. Per the County's recommendation, we estimated cross sections and took photos every 50' —or for each change of condition - along the channel as it drains to the existing detention pond (Appendix V). Based on our measurements in the field we were able to record the approximate side slopes and depths at each cross section, shown in the captions in the field notes. After reviewing the pictures and available contour data we developed estimated depths and widths for each cross section to be used in the channel flow calculations necessary as per MS-19 regulations. As stormwater leaves the WTP site at a point on the western boundary of the property, it flows along a barely defined existing channel within the adjacent residential neighborhood. The existing channel becomes more clearly defined at approximately STA 0+50 downstream of the WTP property's discharge point. No visual signs of erosion or flooding were noted until STA 1+59, where minor channel bed erosion is evident. At this point, flow from approximately 0.5 acres of the residential property of the existing channel enters the channel as sheet flow. We observed increased erosion at STA 2+50 where a stormwater channel beginning at a culvert draining from the northern residential development joins the subject channel. In the channel's current state, it appears the channel is adequate to handle flow from the WTP site as erosion does not occur until additional flow from the surrounding residential development also enters the channel. As we have discussed previously, the stormwater BMPs proposed as part of the WTP site upgrade, combined with a reduction of the overall impervious surface on site, will result in a decrease of the peak flow to the existing channel. When modeled, this reduction in flow is approximately 0.17 cfs for the 2- yr storm and 0.22 cfs for the 10-year storm.This lesser flow will reduce the erosion potential within the existing channel. Our calculations (Appendix V) show the channel to be adequate for capacity and velocity for the 2- and 10-year storm events for a distance of 159' feet downstream of the RWSA property. After reviewing the available data on the County's GIS website and discussing this matter with RWSA, it has been determined that the downstream residential development was constructed sometime around 2003, well after the development of the Water Treatment Plant. Without disregarding the requirements of MS-19, it must be noted the WTP predates the residential development. The evidence from our field visit presented here indicates it is the addition of runoff from the surrounding residential development which causes erosion in the existing channel. Also, it appears that RWSA is in compliance with one of the Virginia DCR Technical Bulletin's (4VAC50- 30-40.19.c) listed of suggestions for channels deemed in inadequate. Item number three from this list suggest that applicants shall: "(3)Develop a site design that will not cause the pre-development peak runoff rate from a two-year storm to increase when runoff out falls into a natural channel or will not cause the pre-development peak runoff rate from a ten- year storm to increase when runoff falls into a man-made channel" Given the result of our calculations presented above, combined with our observations of no erosion in the channel immediately downstream of RWSA property and noting the proposed project improvement will result in a net reduction in the total runoff and peak flow rate from the WTP site for the 2- and 10-year storm, it is our conclusion that the existing downstream channel is adequate to handle stormwater flow form the WTP property. As noted above, project construction will result in a slight decrease in the total impervious area at the site. With this proposed decrease in impervious area, 2-year and 10-year peak discharges from the site will also decrease. No quantity controls are proposed, as the site meets criteria as outlined in Section 17-314 (A)and (B) of the Albemarle County Code of Ordinances. Calculations are found in Appendix V. Channel Protection (9VAC25-870-66) According to Paragraph B (3) of Section 66, Chapter 870, Agency 25, Title 9 of the Virginia Administrative Code (9VCS25-870-66), natural stormwater conveyance systems must be checked for the 1-year, 24-hour storm for compliance under the following methodology: QDeveloped< I•F•*(QPredeveloped* RVPredeveloped)/RVDeveloped,where QDeveloped = Allowable peak flow rate of runoff from the developed site I.F. (Improvement Factor) = 0.8 for sites > 1 acre or 0.9 for sites <_ 1 acre QPredeveloped = Peak flow rate of runoff from the site in the pre-developed condition RVPredeveloped = Volume of runoff from the site in pre-developed condition RVDeveloped = Volume of runoff from the site in the developed condition An overall curve number (CN) was calculated for both the predeveloped and developed conditions. From these curve numbers RVPredeveloped and RVDeveloped (without treatment) were calculated using the formula below: Q (Runoff Volume) = RA Where: A= Drainage Area R(Runoff Depth) = (P — Ia)2 (P + Ia — S) • P (Precipitation) = Precipitation depth of 1-year, 24-hour storm event(3.04" *) 1000 S (Storage) = 10 CN la(Initial Abstraction) = 0.2S * NOAA's Nation Weather Service precipitation estimates. To account for the runoff reduction credit given to the proposed bioretention cells, treated drainage areas for the three bioretention cells were entered into the Virginia Runoff Reduction Method (RRM) Spreadsheet. The spreadsheet calculates an adjusted RVdeveloped and curve number(CN) based on the developed conditions. The SCS Graphical Peak Discharge Method was used to determine QPredeveloped and QDeveloped. A composite curve number based on the predeveloped conditions was used to calculate QPredeveioped; the adjusted curve number was used to calculate QDeveioped. As the site is greater than one acre, an improvement factor (I.F.) of 0.08 was used in the above equation. The above equation determined that the QDeveloped must be less than or equal to 3.74 cfs. At QDeveloped = 3.73 cfs, the site meets requirements of 9VAC25-870-66. Calculations can be found in Appendix VI. Water Quality Concerns The point of analysis for the pre- and post-construction drainage areas is a depression in the southwest corner of the property, adjacent to the existing water storage tank. Based on the calculation of the Albemarle County Simple Method BMP Spreadsheet, the pre-construction drainage area to the point of analysis is 36% impervious; therefore, the project is considered a redevelopment because it is over the 20% impervious threshold. As shown in the Albemarle County BMP worksheet, the post-construction impervious area draining to the point of analysis is 35%, lower than the pre-construction impervious percentage. The Crozet WTP is located within the Drinking Water Watersheds of Albemarle County. According to the Albemarle County BMP Worksheet, this project which is located in the drinking water watershed and categorized as a redevelopment is required to treat 0.16 lbs of stormwater pollutant, which computes to a required 13% removal of phosphorus. Therefore, stormwater quality treatment is required. Proposed Bioretention Cells Three bioretention cells (BRCs) were proposed to treat the needed pollutant removal rate associated with the proposed development. The bioretention cells were sited in an effort to treat a majority of the project development. Due to site constraints including existing plant piping, steep slopes, and existing tree growth onsite, the bioretention cells will capture a total of 0.56 acres of runoff. As such, the bioretention cells have been evaluated to determine whether they will receiving and treating enough stormwater pollutant to reach the target removal of 0.16 lbs. The Albemarle County BMP worksheet was used to evaluate the drainage areas of all three bioretention cells. It was determined that BRC 1 receives 0.42 lbs of stormwater pollutant, BRC 2 receives 0.15 lbs of stormwater pollutant, and BRC 3 receives 0.16 lbs of stormwater pollutant, totaling 0.73 lbs of stormwater pollutant received by the bioretention cells. According to the Virginia Stormwater Management Handbook, First Edition, section 3.11 Bioretention, a bioretention cell sized to handle the 1"water quality volume will have a removal efficiency of 65%. The proposed bioretention cells at a pollutant efficiency of 65% will treat 0.47 lbs of the pollutant export received, exceeding the required removal of 0.16 lbs. Stormwater design analysis can be found in Appendix IV. Conclusion Project improvements as well as the proposed bioretention cells will reduce the overall peak flow and volume of stormwater draining from the property. A stormwater analysis of the project's receiving channels was evaluated to ensure adequacy based on the compliance of Minimum Standards 19 and 9VAC25-870-66. Calculations can be found in Appendices V and VI. Using the Albemarle County Simple Method Spreadsheet, it was determined that the site is required to reduce post-construction storm pollutant export by 0.16 lbs to meet the pre- construction loading rate. Three bioretention cells with 65% removal efficiencies are proposed, and will treat 0.47 lbs of stormwater pollutant. Calculations can be found in Appendix VI. Under these proposed conditions for the management/treatment of stormwater runoff, the Crozet WTP improvement is under compliance of all applicable performance standards and requirements CRITICAL SLOPES Critical slopes, as defined by the County of Albemarle, are areas of topographic inclines that exceed a 25% slope. By definition, if these slopes exist naturally, no disturbance or impact are to be made to these slopes without approval by the County. Critical slopes do exist on this site, however, the new development will not disturb or impact these slopes. Appendices Appendix I — Maps (FIRM, Vicinity, Soils) Appendix II — Contract Drawings (Under Separate Cover) Appendix III — Erosion Control Calculations Appendix IV— Stormwater Analysis Calculations Appendix V— MS-19 Calculations Appendix VI — Conveyance Calculations Appendix VII —Specifications Section 02050— Demolition Section 02100 — Clearing, Grubbing, and Site Preparation Section 02200 — Earthwork Section 02202 — Excavation by Blasting Section 02207—Aggregate Materials Section 02276 — Erosion and Sedimentation Control Section 02500 —Surface Restoration Section 02510 — Paving and Surfacing Section 02604— Utility Structures Section 02831 — Steel Fencing Section 02910— Final Grading and Landscaping Appendix I Maps (FIRM, Vicinity, Soils) BEAVER CREEK \ N RESERVOIR rA 1I_��_1t '''',:.`-it..: MAP SCALE 1 " = 1000' 500 0 1000 2000 • I l H t---+ t ( FEET Ir • ZONE A : �.. e ' hP PANEL 0235D • O 'Crozet WTP r CREEK VPARK FIRM ZONE s f �qi• FLOOD INSURANCE RATE MAP •A BEAVER J ALBEMARLE COUNTY,VIRGINIA BEAVER HILL LN AND INCORPORATED AREAS HILL LAKE DR AND THE INDEPENDENT CITY BEAVER • OF CHARLOTTESVILLE HILL DR '�? - -<7 1 i' PANEL 235 OF 575 �� I ZONE ��4 (SEE MAP INDEX FOR FIRM PANEL LAYOUT) CN,p --1 j g• OLD CONTAINS' )VER 11 S THREE NOTCH'D RD COMMUNITY P- hie ANEL SUFFIX 3E PL H �3 W! HIGHLANDS N ALBEMARLE OOUNTY 6,000E 023E D DR BROOK ►� / \. T HW1002 i �� to MECHUMS H 001 ,.- Q` HW1 /.S RIVER RD • CHURCH ' MECHUM _ op i -� ,u PLAINS DR RIVER RD -J / GI a Lj y GRASSY` AMBER e�y Q `// sZ KNL RIDGE CT Q yr • �y Nam.to Uwe The lap Imam shown berm Should no wed `� '• when placing mop order.:I the c •ppestr Nu�r = 9 •,F� Wow should M used on Insursrcr�pp/owians for:^a x yr. _� r�, ) / LICKINGHOLE \\.yo,. ZONE BROWNS community. CREEK Cy X - 4ARTy MAP NUMBER f/i ° '� °4� 51003C0135D K1 Azt�o AMBER 0� �� ; tits"�, :'° k` EFFEC11VE DATE 90 RIDGE RD ZONE Xf�v `` ttrl- " `' a'�d,�f° > o- b ��..,•.�...��. �_ _'-�"a �i�.3's�y�`_ ,tr,,;t. FEBRUARY 4,2005 k.� ` F -LING STA 705 ^" JOINS PANEL 0245 4B�M Federal Emergency Management Agency OW LN VIEW LN ZONE X ZONE AE J J This Is an official copy of a portion of the above referenced flood map It was extracted using F-MIT On-line This map does not reflect changes or amendments which may have been made subsequent to the date on the title block For the latest product Information about National Flood insurance . Program flood maps check the FEMA Flood Map Store at wow msc fema goy, General Vicinity Map Crozet WTP GAC Updates Rivanna Water and Sewer Authority !+lief _ ' . iIMTt � ,_ Jt� i ,,, CROZET WTP , (ilie] e4v'ra lever;gn � � �: v,O lvT q,.,r: ',wet t.innly Mr)I n,• •.?U; f C e.1j !� _._ • So.vy Nes1•." i(wet untied , Methodist:'hunch e em s; !� firs. It ♦ ��.. �flftj, .o • +Nh led+I 1.III CI.n t•11, % P j p Floc-Wish f+ i • �laM1 L I I r.+ •,r•• v .6'] �N+tP ieD P "No. 0 woo,- � f ;e75] ,0 i J ` '-. �� j3, f° SOURCE: GOOGLE MAPS NOT TO SCALE HAZENAND SAINYER Environmental Engineers & Scientists 3 Soil Map—Albemarle County,Virginia 3 (Crozet Water Treatment Plant) N k k ._' ,i 519' .is 70525G 3:. ! 7 0 7053 705350 705370 �',s ' y F 7�`.: 7 7 ... r�t a ti59iU 38°4'S N x � i• � i �:� i -jS•.-h7r ,,,.1�"• Ir. 4 s .$ et- -. � . � 3 �of a _ 'd� t mow. r4, A n4r� y�+ • Y .,+yam . _ L 7 R ,4" �,�r?� 210ii sN, t}i j4 r qr ' ' ' ! 144 .;..4-''ll: f.-aN, 2, :44 :4\, - '4 :'':‘,... I �..:' ; , ' ka ' } S ' s y " 31 4 1P ,-, yC � v M . ._ ti _ + 1 ,„: -" - * ;C' ,t.‘:. ,41,414 if..;-0.ite•Al Ore-4' ' ft44.1-It 11:4011 t '4 - - '-4 l' 38°3'S'N •4114164141" •l r 38 3'99'N 705150 705170 705190 705210 705230 705250 705270 70`;7`e -n5310 7;;',33 7J5350 '::'370 705390 705410 � 3 Map Scale:1:1,200 If printed on A landscape(11"x 8.5)sheet Meters N 0 15 30 60 90Fed to A 0 50 100 200 300 r�P proied3on:Web Mercator Comer coordinates:WGS84 Edge tics:UTM Zone 17N WGS84 USDA Natural Resources Web Soil Survey 2/5/2014 Conservation Service National Cooperative Soil Survey Page 1 of 3 Soil Map—Albemarle County,Virginia (Crozet Water Treatment Plant) MAP LEGEND MAP INFORMATION Area of Interest(AOI) Spoil Area The soil surveys that comprise your AOI were mapped at 1:15,800. Area of Interest(AOI) Stony Spot Warning:Soil Map may not be valid at this scale. Soils Very Stony Spot Soil Map Unit Polygons Enlargement of maps beyond the scale of mapping can cause Wet Spot misunderstanding of the detail of mapping and accuracy of soil line Soil Map Unit Lines Other placement.The maps do not show the small areas of contrasting • Soil Map Unit Points soils that could have been shown at a more detailed scale. Special Line Features Special Point Features Please rely on the bar scale on each map sheet for map Blowout Water Features V measurements. Streams and Canals El Borrow Pit Source of Map: Natural Resources Conservation Service Transportation Web Soil Survey URL: htt //websoilsurve nres.usda. ov x Clay Spot }E Rails Coordinate System: Web Mercator(EPSG:3857) g Closed Depression Interstate Highways Maps from the Web Soil Survey are based on the Web Mercator Gravel Pit US Routes projection,which preserves direction and shape but distorts distance and area.A projection that preserves area,such as the Gravelly Spot Major Roads Albers equal-area conic projection,should be used if more accurate s Landfill Local Roads calculations of distance or area are required. Lava Flow Background This product is generated from the USDA-NRCS certified data as of the version date(s)listed below. Marsh or swamp I. Aerial Photography Soil Survey Area: Albemarle County,Virginia Mine or quarry Survey Area Data: Version 10,Dec 11,2013 Miscellaneous Water Soil map units are labeled(as space allows)for map scales 1:50,000 • Perennial Water or larger. •,r Rock Outcrop Date(s)aerial images were photographed: May 10,2010—Jun 4, + Saline Spot 2011 The orthophoto or other base map on which the soil lines were Sandy Spot compiled and digitized probably differs from the background Severely Eroded Spot imagery displayed on these maps.As a result,some minor shifting of map unit boundaries may be evident. Sinkhole Slide or Slip • Sodic Spot USDA Natural Resources Web Soil Survey 2/5/2014 daill Conservation Service National Cooperative Soil Survey Page 2 of 3 • Soil Map—Albemarle County,Virginia Crozet Water Treatment Plant Map Unit Legend Albemarle County,Virginia(VA003) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 36B Hayesville loam,2 to 7 percent 2.9 70.3% slopes 37C3 Hayesville clay loam,7 to 15 1.2 29.7% percent slopes,severely eroded Totals for Area of Interest 4.1 100.0% USDA Natural Resources Web Soil Survey 2/5/2014 Conservation Service National Cooperative Soil Survey Page 3 of 3 Appendix II Contract Drawings (Under Separate Cover) H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment Appendix III Erosion Control Calculations H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment Silt Fence Calculations H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment HAZEN WTP GAC UPGRADES 5/7/2014 HAZENAND SAWYER EROSION CONTROL BY: BTE CHK. Environmental Engineers&Sclentlsle SILT FENCE CALCULATIONS JOB NO.32135-002 Objective: Determine if silt fence will contain sediment generated. References: (1) Virginia Erosion and Sediment Control Handbook, Section 3.05. Procedure: As required by Reference 1, ensure that area drained by silt fence is no greater than `/ acre per 100 feet of fencing. Fence Fence Area Number Length Drained OK? (ft) (ac) 1 90 0.13 OK 2 175 0.25 OK 3 102 0.06 OK 4 115 0.10 OK 5 51 0.04 OK Page 1 of 1 Appendix IV Stormwater Analysis H&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment Albemarle County — Engineering Simple Method Spreadsheet Pre- and Post-construction H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: GAC Upgrades for the Crozet WTP Water Resources Area: Drinking Water Watersheds Preparer: Hazen and Sawyer,P.C. Date: 14-May-14 Project Drainage Area Designation Crozet WTP upgrades L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 1.12 C pollutant concentration,mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3320 0 2291 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 271 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 Gravel areas Area Area 16602 x 0.70= 11621.4 12428 x 0.70= 8700 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 133 0 3228 Actively-grazed pasture& Area Area yards and cultivated turf 23505 x 0.08= 1880 25084 x 0.08= 2007 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 35% 34% I(pre) I(post) Rv(post) V 0.35 25.5 New Development(For Development Areas,existing impervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.36 2.49 2.44 -0.06 -2% Development Area 0.35 1.00 0% 0.36 1.25 1.22 -0.03 -2% Drinking Water Watersheds 0.40 1.00 1% 0.36 1.43 1.39 -0.03 -2% Other Rural Land *min.values Redevelopment(For Development Areas,existing impervious cover>20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.36 2.49 2.44 0.19 8% Development Area 0.35 0.85 0% 0.36 1.25 1.22 0.16 13% Drinking Water Watersheds 0.40 0.85 1% 0.36 1.43 1.39 0.18 13% Other Rural Land Albemarle County — Engineering Simple Method Spreadsheets Drainage area to BRC 1, BRC 2, BRC 3 H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: GAC Upgrades for the Crozet WTP Water Resources Area: Drinking Water Watersheds Preparer: Hazen and Sawyer,P.C. Date: 14-May-14 Project Drainage Area Designation Drainage area to BRC 1 L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 0.25 C pollutant concentration, mg/1 or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal , L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 173 0 173 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 Gravel areas Area Area 4403 x 0.70= 3082.1 4403 x 0.70= 3082.1 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2472 0 2472 Actively-grazed pasture& Area Area yards and cultivated turf 3296 x 0.08= 263.68 x 0.08= 263.68 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 55% 55% I(pre) l(post) Rv(post) V 0.55 9.2 New Development(For Development Areas,existing impervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.55 0.84 0.84 0.00 0% Development Area 0.35 1.00 0% 0.55 0.42 0.42 0.00 0% Drinking Water Watersheds 0.40 1.00 1% 0.55 0.48 0.48 0.00 0% Other Rural Land *min.values Redevelopment(For Development Areas,existing impervious cover>20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.55 0.84 0.84 0.08 10% Development Area 0.35 0.85 0% 0.55 0.42 0.42 0.06 15% Drinking Water Watersheds * 0.40 0.85 1% 0.55 0.48 0.48 0.07 15% Other Rural Land • Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: GAC Upgrades for the Crozet WTP Water Resources Area: Drinking Water Watersheds Preparer: Hazen and Sawyer,P.C. Date: 14-May-14 Project Drainage Area Designation Drainage area to BRC 2 L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(I) Pj small storm correction factor,0.9 percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 0.10 C pollutant concentration, mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(1)43560(0.5/12)/27 RR required removal , L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1941 0 1941 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 Gravel areas Area Area 0 x 0.70= 0 0 x 0.70= 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Actively-grazed pasture& Area Area yards and cultivated turf 2597 x 0.08= 207.76 2597 x 0.08= 207.76 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 49% 49% I(pre) l(post) Rv(post) V 0.49 3.3 New Development(For Development Areas,existing impervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.49 0.30 0.30 0.00 0% Development Area 0.35 1.00 0% 0.49 0.15 0.15 0.00 0% Drinking Water Watersheds 0.40 1.00 1% 0.49 0.17 0.17 0.00 0% Other Rural Land *min. values Redevelopment(For Development Areas,existing impervious cover>20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.49 0.30 0.30 0.03 10% Development Area 0.35 0.85 0% 0.49 0.15 0.15 0.02 15% Drinking Water Watersheds * 0.40 0.85 1% 0.49 0.17 0.17 0.03 15% Other Rural Land Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: GAC Upgrades for the Crozet WTP Water Resources Area: Drinking Water Watersheds Preparer: Hazen and Sawyer,P.C. Date: 14-May-14 Project Drainage Area Designation Drainage area to BRC 3 L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 1 percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 0.21 C pollutant concentration, mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1384 0 1384 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 Gravel areas Area Area 0 x 0.70= 0 0 x 0.70= 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Actively-grazed pasture& Area Area yards and cultivated turf 7529 x 0.08= 602.32 7529 x 0.08= 602.32 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 22% 22% I(pre) ((post) Rv(post) V 0.25 3.1 New Development(For Development Areas,existing impervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.25 0.32 0.32 0.00 0% Development Area 0.35 1.00 0% 0.25 0.16 0.16 0.00 0% Drinking Water Watersheds 0.40 1.00 1% 0.25 0.18 0.18 0.00 0% Other Rural Land *min.values Redevelopment(For Development Areas,existing impervious cover>20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.25 0.32 0.32 0.03 10% Development Area 0.35 0.85 0% 0.25 0.16 0.16 0.02 15% Drinking Water Watersheds * 0.40 0.85 1% 0.25 0.18 0.18 0.03 15% Other Rural Land Tc Calculation H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment U.S.Department of Agriculture FL-ENG-21 B Natural Resources Conservation Service 06/04 TR 55 Worksheet 3: Time of Concentration (Ta) or Travel Time (Tt) Project: Crozet Water Treatment Plant Designed By: Corinne Wilson, EIT Date: 4/15/14 Location: Crozet, VA Checked By: Date: Check one: Present Developed Check one: Tc Tt through subarea Bioretention Cell#1 NOTES: Space for as many as two segments per flow type can be used for each worksheet. Include a map, schematic, or description of flow segments. Sheet Flow(Applicable to Tc only) Segment ID Grass/Sheet Pavement/Sheet 1. Surface description (Table 3-1) Grass Smooth 2. Manning's roughness coeff., n(Table 3-1) 0.24 0.01 3. Flow length, L (total L < 100 ft) ft 79 88 4. Two-year 24-hour rainfall, P2 in 3.7 3.7 5. Land slope, s ft/ft 0.035 0.034 6. Tt =0.007 (nL)°e Compute Tt hr 0.15 + 0.01 = 0.16 P 205 SO4 Shallow Concetrated Flow Segment ID Grass 7. Surface description (paved or unpaved) Unpaved 8. Flow length, L ft 62 9. Watercourse slope, s fUft 0.645 10. Average velocity,V(Figure 3-1) ft/s 4.2 11. Tt = L Compute It hr 0.00 + = 0.00 3600 V Channel Flow Segment ID 12. Cross sectional flow area, a ft2 13. Wetted perimeter, Pw ft 14. Hydraulic radius, r= a Compute r ft Pw 15. Channel Slope, s ft/ft 16. Manning's Roughness Coeff., n 17.V= 1.49 r2/3 s112 Compute V ft/s n 18. Flow length, L ft 19. Tt = L Compute Tt hr + _ 3600 V 20. Watershed or subarea T,or Tt(add Tt in steps 6, 11, and 19 hr 0.16 U.S.Department of Agriculture FL-ENG-21 B Natural Resources Conservation Service 06/04 TR 55 Worksheet 3: Time of Concentration (Ta) or Travel Time (Tt) Project: Crozet Water Treatment Plant Designed By: Corinne Wilson, EIT Date: 4/15/14 Location: Crozet, VA Checked By: Date: Check one: Present I Developed Check one: 1 Tc Tt through subarea Bioretention Cell#2 NOTES: Space for as many as two segments per flow type can be used for each worksheet. Include a map, schematic, or description of flow segments. Sheet Flow(Applicable to Tc only) Segment ID Grass/Sheet 1. Surface description (Table 3-1) Grass 2. Manning's roughness coeff., n (Table 3-1) 0.24 3. Flow length, L (total L< 100 ft) ft 79 4. Two-year 24-hour rainfall, P2 in 3.7 5. Land slope, s ft/ft 0.051 6. T, =0.007 (nL)0.8 Compute T, hr 0.13 + = 0.13 P 205 SO4 Shallow Concetrated Flow Segment ID 7. Surface description (paved or unpaved) 8. Flow length, L ft 9. Watercourse slope, s ft/ft 10.Average velocity, V(Figure 3-1) ft/s 11. T, = L Compute Tt hr 0.00 + = 0.00 3600 V Channel Flow Segment ID 12. Cross sectional flow area, a ft2 13. Wetted perimeter, Pw ft 14. Hydraulic radius, r= a Compute r ft Pw 15. Channel Slope, s ft/ft 16. Manning's Roughness Coeff., n 17. V= 1.49 r213 s112 Compute V ft/s n 18. Flow length, L ft 19. T, = L Compute T, hr + _ 3600 V 20. Watershed or subarea T, or T,(add T,in steps 6, 11, and 19 hr 0.13 • U.S.Department of Agriculture FL-ENG-21 B Natural Resources Conservation Service 06/04 TR 55 Worksheet 3: Time of Concentration (Ta) or Travel Time (Tt) Project: Crozet Water Treatment Plant Designed By: Corinne Wilson, EIT Date: 4/15/14 Location: Crozet, VA Checked By: Date: Check one: Present I Developed Check one: I Tc Tt through subarea Bioretention Cell#3 NOTES: Space for as many as two segments per flow type can be used for each worksheet. Include a map, schematic, or description of flow segments. Sheet Flow(Applicable to Te only) Segment ID Grass/Sheet 1. Surface description(Table 3-1) Grass 2. Manning's roughness coeff., n(Table 3-1) 0.24 3. Flow length, L(total L< 100 ft) ft 100 4. Two-year 24-hour rainfall, P2 in 3.7 5. Land slope, s ft/ft 0.065 6. It =0.007(nL)°8 Compute Tt hr 0.14 + = 0.14 P2 05so.4 Shallow Concetrated Flow Segment ID 7. Surface description(paved or unpaved) 8. Flow length, L ft 9. Watercourse slope, s ft/ft 10.Average velocity, V(Figure 3-1) ft/s 11. Tt = L Compute Tt hr 0.00 + = 0.00 3600 V Channel Flow Segment ID Channel 12. Cross sectional flow area, a ft2 0.4 13. Wetted perimeter, PW ft 6.2 14. Hydraulic radius, r= a Compute r ft 0.1 PW 15. Channel Slope, s ft/ft 0.015 16. Manning's Roughness Coeff., n 0.03 17.V= 1.49 r213 s112 Compute V ft/s 1.0 n 18. Flow length, L ft 27 19.It = L Compute Tt hr 0.01 + = 0.01 3600 V 20. Watershed or subarea T,or It(add It in steps 6, 11, and 19 hr 0.15 Drainage Area Maps to Bioretention Cells H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment } .-`.- • { t 1 \ r --s ._.: -1:<I:.-, t{1 ._ --7 / ,-> ..- ----- - - r t —. .-. _..,. 1';:-,-/.,ri-_/--7-_- —: i:: .).•-....-i://i,:_-.-.,f ---,-/ -. i r ,,, ,,--•. .. ` -tom„ , - `.\, \```\`L. -=_.._ �_...,` , --_ •} !� ..._ _ __ _ '"" `'r" `� �','��' \\, `• -i- \ ,1:--;1,-.'t?-i )\x\\\;1'1)',''-'1,,1''\1,.-\\' ---.z,'N,--',-.,':-'i.',.......,,-...,N-.,„,,\,,..4...'s...,,'-,k:..'.'-'.'- 1\\ 1 1 P _n ij -/„'-.:.,.,// --..._1_.-_.-._.--._---.-:' t _ T:--_-:-7;-1_ -__-_ i,_,_ / / '' I I \''N N \ \ \ ' _ \-\\ i\ \ \ \ \\ vii. ''t *'.. - // `",.._..+ PROPOSED BIORETENTION CELL 3 '',� DRAINAGE AREA TO BIORETENTION o \ PROPOSED BIORETENTION CELL 2 -- CELL 3 0.21 ACRES `-. oy y:,`---,. i A / /"- ___F -, - Tc = 5 MINUTES 1 •�, \� \ DRAINAGE AREA TO BIORETENTION lir.�. `�, \ CELL 2 = 0.10 ACRES '"� ., ;� f�; Tc = 5 MINUTES - --. �"" ' �'` ,,,\ \ w. POINT OF 7. `" \ f° r .+\..... ;; ti ANALYSIS ,, ,. 1 i �,i �.�•.�46. AO ' i1." i i1ri(\j 1,i,i 11 . sII44).:I.N\I*P l4!zir*\i a'k IG1 k11A1l"i.l4lC4I I\k po11ii6i i 6I 0i iia:_iN'/*aVlg l i1..1nrp.i-fr4i;e 4a1.I4lollk4*4i1o,4,47 0.,1".640Ni.l•l,94i.*4#1‘ i..\m.a,:. : 0+ /9,, /n ii 1Im1I1t.1i%4 Np" rN.v_f I,JgI r f fF 1 i/, STORAG j TANK s ; i, (tf 0 ► lsl / PROPOSED BIORETENTION CELL 1 Ak r?' �, � � "� ,,.'' FACILI `• f --... �-- _ DRAINAGE AREA #1 TO + NUO'"' it��a - it ---/ , l •F -- -- - --___ BIORETENTION CELL 1 = 0.25 ACRES , e 1 '/N /\\\t‘, '‘) t fi Tc 5 MIN / / \\ /#1'sv. \ `;„ \ \ \ "... — iala m-----:_i*t iI f d fJffffj _ / J 1 y✓ r7:,, - ..«,"-j. if(1/ ; .„....j al.Wittftrali Jily ... ____,, .---/ V MAINTENANCE ,_ _-'` .cii DRAINAGE AREA TO / J .�.; --.... - ,�' - , .-- CELL 1 �' ' BUILDING - �_/ / -,, L\s.....„j • ` `�. 1 f __ �, A.C.S.A. ---�� i, • , `- .'"-. � '.,,. , '` �'`r''' ,/"---- --� ORAINAG Ah A Ttc: MAINTENANCE . t • CELL 2 BUILDING ' ., 50 25 0 50 N Leo. i \\ \\\ \\\'\ 1 /1/i ' *'''.N,,, '-'-----_, ,__ "—a �, DRAINAGE AREA TO - ,_- CROZET WATER TREATMENT PLANT " CELL 3 ' ' ' ,ram -- RWSA Ri \ \ \ , , ::,--, . \k 1 , 1 i - __, _ / ,„,-, ❑ - " - �" _ :. POST-CONSTRUCTION 7'T HAZEN AND SAWYER ~' -'.- � f �` .�'%' '- DRAINAGE AREA o Environmental Engineers & Scientists , -•� r_ — TO BIORETENTION CELLS o Bioretention Cell Designs H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment f HAZENAID SAWYER EnvIronmental Engineers & Scientists Prepared by Hazen and Sawyer, P.C. Corinne Wilson, EIT Date of Calculation 2/4/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Bioretention Cell#1 Design Reviewer L.Michael Santowasso, PE Date Reviewed Bioretention Cell #1 Design Table 1:Land Use Characteristics Land Use Area(ac) CN Rv Pervious 0.10 61 0.20 Impervious 0.15 98 0.95 Total 0.25 83 0.65 Table 2:Treatment Volume Calculation Precipitation depth,P in 1 1"water quality event Rvp„, - 0.65 Treatment volume,Tv cf 590 (P)(Rv)(Area)/12 Table 3:Design Depth Calculation Layer Depth(ft) Void Ratio(Vr) Storage(ft) Gravel 1 0.4 0.4 Media 3 0.25 0.75 Ponding 0.5 1 0.5 Total(Design Depth) 1.65 Table 4:Surface Area Calculation Surface area,SA sf 447 (1.25*Tv)/(design depth) Length ft 30 Width ft 15 FlizENAND SAWYER Environmental Engineers 3 Scientists Prepared by Hazen and Sawyer,P.C. Corinne Wilson, EIT Date of Calculation 2/4/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Pretreatment Design for Bioretention Cell#1 Reviewer L. Michael Santowasso, PE Date Reviewed Pretreatment Cell Design Table 5:Peak Flow Calculation Drainage Area ac 0.02 C 0.95 Impervious in/hr 6.52 10-year,5-minute storm Peak Flow,QQ cfs 0.17 SCS Tr-20(HydroCAD) Table 6:Manning's Equation b ft/s 2 y ft 0.05 z 2 Rh ft/s 0.04 s 0.09 n 0.033 gravel, riprap A sf 0.10 Qp cfs 0.17 equal to Qp,above V ft/s 1.71 maximum velocity of silt loam soil=2.3 ft/s Riprap Outlet Protection As a result of the low velocity,the minimum stone size(Class Al)is sufficient to avoid erosion of riprap HAZEN AND SAWYER Environmental Engineers & Scientists Prepared by Hazen and Sawyer, P.C. Corinne Wilson, EIT Date of Calculation 2/4/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Bioretention Cell#2 Design Reviewer L. Michael Santowasso, PE Date Reviewed Bioretention Cell #2 Design Table 1:Land Use Characteristics Land Use Area(ac) CN Rv Pervious 0.06 61 0.20 Impervious 0.04 98 0.95 Total 0.10 77 0.52 Table 2:Treatment Volume Calculation Precipitation depth, P in 1 1"water quality event flypast - 0.52 Treatment volume,Tv cf 195 (P)(Rv)(Area)/12 Table 3:Design Depth Calculation Layer Depth(ft) Void Ratio(Vr) Storage(ft) Gravel 1 0.4 0.4 Media 3 0.25 0.75 Ponding 0.5 1 0.5 Total(Design Depth) 1.65 Table 4:Surface Area Calculation Surface area,SA sf 148 (1.25*Tv)/(design depth) Length ft 15 Width ft 10 FL4ZEN AND SAWER Environmental Engineers & Scientists Prepared by Hazen and Sawyer,P.C. Corinne Wilson, EIT Date of Calculation 2/4/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Pretreatment Design for Bioretention Cell#2 Reviewer L. Michael Santowasso, PE Date Reviewed Pretreatment Cell Design Table 5:Peak Flow Calculation Drainage Area ac 0.04 C - 0.95 Impervious i in/hr 6.52 10-year,5-minute storm Peak Flow,Q. cfs 0.32 SCS Tr-20(HydroCAD) Table 6:Manning's Equation b ft/s 2 y ft 0.07 z - 2 Rh ft/s 0.06 s - 0.09 n - 0.033 gravel,riprap A sf 0.15 Qp cfs 0.32 equal to Qp,above V ft/s 2.17 maximum velocity of silt loam soil=2.3 ft/s Riprap Outlet Protection As a result of the low velocity,the minimum stone size(Class AI)is sufficient to avoid erosion of riprap HAZENA\D SAYER Environmental Engineers & Scientists Prepared by Hazen and Sawyer, P.C. Corinne Wilson, EIT Date of Calculation 5/13/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Bioretention Cell#3 Design Reviewer L. Michael Santowasso, PE Date Reviewed Bioretention Cell #3 Design Table 1: Land Use Characteristics Land Use Area (ac) CN Rv Pervious 0.17 61 0.20 Impervious 0.03 98 0.95 Total 0.21 67 0.32 Table 2:Treatment Volume Calculation Precipitation depth, P in 1 1"water quality event RvP0, - 0.32 Treatment volume,Tv cf 236 (P)(Rv)(Area)/12 Table 3: Design Depth Calculation Layer Depth(ft) Void Ratio(Vr) Storage(ft) Gravel 1 0.4 0.4 Media 3 0.25 0.75 Ponding 0.5 1 0.5 Total(Design Depth) 1.65 Table 4:Surface Area Calculation Surface area,SA sf 179 (1.25*Tv)/(design depth) HAZEN AND SAVER Environmental Engineers & Scientists Prepared by Hazen and Sawyer, P.C. Corinne Wilson, EIT Date of Calculation 5/13/2014 Client Albemarle County Project Name Crozet Water Tratment Plant Description Pretreatment Design for Bioretention Cell#3 Reviewer L. Michael Santowasso, PE Date Reviewed Pretreatment Cell Design Table 5: Peak Flow Calculation Drainage Area ac 0.03 CN - 98 Impervious Peak Flow,QP cfs 0.12 SCS Tr-20(HydroCAD) Table 6: Manning's Equation b ft/s 2 y ft 0.04 z 2 Rh ft/s 0.04 s 0.09 n 0.033 gravel, riprap A sf 0.08 Qp cfs 0.12 equal to Qp,above V ft/s 1.50 maximum velocity of silt loam soil=2.3 ft/s Riprap Outlet Protection As a result of the low velocity,the minimum stone size(Class Al)is sufficient to avoid erosion of riprap Appendix V MS-19 Calculations H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment Field Notes H&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment Oie 6- _ . . g Wodd-tkifed st-ates-VA•Alsernarl c Co ....'"*";.#. ,A , . dile' r , * ,.. ''' . •^', ' ' . . . ... , . . . -. -..''' ' lit.,. t 0..„ .. .... , * ... . . .- 40 . - . - .„. • , - - • .. - ,_,....., ---.410t. • or •• VI •... - - . - ibr... . ilk -*or. , , ..,.1...el ""-,. -146_,-,-F, i.A.- . • • - . _. _ --- . •, ....., . '-' •"*4- ' * ' z'•'•'-'--* -': STA 0+50 lk • 14.r.,,.4". "••... .. - --.t., . „. .4.;„..,- .._ `.-7 -.7- . '' ." '.'0* '''''' • . * ' TA. 1 Q 1 +00 ..•*.' .., ,.._, _ . , . ir ,.....„,- . A --- tat - .... ... . 4111 - 4... .,,, ,, • RN= -- 1,4" 5-1.4. 1-,59 (EROSION '-•...! . - , „--.„-, ,,,, ,,,... , :14t.,k--.4 - -- •,. - SIGNS BEGIN _ — z.„., ,...4...;..,': •-•. •,,,0"-----" CULVERT 0-- P4,---FURE 10) . . _ ..., STA 2+00 , ... ......_ . . -•- STA 2+50 i _ . _..._ •••- .......- f ...,. ' ... ',.... .. ., ,- -At ..... • - ...,.1.--...,,I.,- • •I..,.. - e..,,...... ',,..,,,.. .• ..,,,, .. 4.....- •- 1 .., N. , . -....0,A,....---... .....4.„)....., ,..., ....; , . . 100r Aiii&-, . .... 410 A ,,, NB 16,. . a 0= i *.:1.1 .. ",..•1,4 '' . TO DETENTION - ir ..44.4'44* BASIN ,071/4 -- , 1,. .. .. .. •-,wNc.°. lifr, ;i1 -::!...7-.II ;-.7,:. '''' 4! . .. ... . . .,.- ... ,,... .. -- '.. 71 ff.Fef..- 13 -• • att/e'r elc51/4 vl I--- 1 t.,„ Ce \ 4` LA k 3'' 0 ---_---- fAn_.. — 4 C O _0( w ,c —1,0 E i6 '!_ ; t- `T` '1 '.2N rL, fi t. 4za ew t c ; _.. ID -E- _ �\-d.-- ti� x lc,' �� ram erhw wit.el 144.../.5 .-c_iiise._. Picture 1 ts stifott .y •' * -A*N'YM ' .af '• � vy" -y' • e }, � 1 v.- it:. "__ 4 tf0k .I .�f ,,. t" j f« at t '‘-'•,,.. V, : I. 'il.,tit Sii.. .k 4,--, ;.w • '��, '. .7 1, 1 Pu ` . Ir 1 r j Q. I' m '{,'{4� n1 .},/,t'�i'tl'1, joll :s I L•s s 1 i*�w / ,.,i.,.',,.: 1 • - F. J-ti ' %Vt. i, r , .,, '. ' ' -' 7 r \ E r'. .z7 r: n ,, 1 4 i{{,,` i, ,=,,,, rat 4 s 'sue . d ' ,` .. 7 4 t,, �y,� .!' ,' > , ' i , , - „, „...„- ..., iFf' ' • • '',!'" 4 i 1 k- ' I , . , ' ',. 5 .... -, \l I.. , »°, '1* Jul,f „4 't• f 'of .z" Y ;`' :,fir / `f ^r. t l 1"-, , 'f� , .+f. t ,w . , $i' % - �; z.. , -.„,--1„b..- - 7. ,.. ',4, ..t r.p.,- ,,,40,:p , , .., . . Iv . i - , j tik tto....„---.:,..t..--4. 4,, ; .'- ...- I'.:` '!:..,..,......,,, ' . ',. : k ,,,,t - - ...„ s, 4 4 . % r •. - 0 -21' 7:t ' .,. gittip(7,'110' : iit 1_ -, ',w;",,:ciii ' i; floe 'I, --. '''r - . 7 FiaL.... ..",r . off. ► a .." • l i 1� @ 4""op z '' if i4i-i I { of •% �i y !a 4X ''I; + +, am a } l ,.,., y • . 1 et f , Beginning of"channel"at fence line between site and adjacent residential property.Water tank in background. STA 0+00 Channel approximately 4'wide x 6"deep,parabolic cross section. Picture 2 F 4 3 , 'id,s_.,...r T z 1 !�ti: ' g i,_ t 'ry w. � s w r ay • a:� ems= rtilrr '� . t '♦ r ' ° 1 jrip L 9h t C ,.c `t.* + tea+ t.r. is a', - "� _a' x ';_,.+ _t` p !pj1 t ,- A,. I `• # ? {; =\v aWit""'t, y r Il a Bend in "channel",approximately 30-degrees. STA 0+20 Channel approximately 4'wide x 3" deep, parabolic cross section. Picture 3 1,,, r' -, •y ` Agilip. : 4. • •.,:-....,.7.* ,. ti � z ;.�. -; ce. ," s E .. K'.'A. ' 4 of ,• , s,, , e w4 '� y! • ... , x ;} t . flier .,. _may„ ... .. / _. "Channel"at base of slope between properties.Off-site drainage contributing at this point. Beginning of bend. STA 0+50 Channel approximately 4'wide x,6"deep,parabolic cross section,small riprap (2"—4"stone) present in channel invert, approximately 2'wide. Picture 4 1 . • tEtE k A,:. ,, A °.n_ ... „„ _ , . ....., Jet . ,,,,,„ . ...2......, 1 I rot , . r If 9 kY. it --- .. + x F k +pia.2 144 ry d i\, rim aPit}, '[i°"".. • .. T .4' s , ff . p 1,.. - '' :-- , r „ ..„ , ., .. , . ;,*,,• - ' •,.• .---, 's — .., ..., ., ','..,,...'*17" rs V . Ir 4 { has a.�.w -7 M a` % li ' x 7 m r w L "Channel"at base of slope between properties.Additional off-site drainage contributing at this point. STA 1+00 Channel approximately 6'wide x 7"deep, parabolic cross section,small riprap(2"—4"stone) present in channel invert, approximately 2'wide. Picture 5 1 i j 0 fi itti f yy t ya-. -I. .1 ...'',', itlf. i .44 , , ... ,,t, , ,,./:, - �e • 1 k',_ + it .t . L'w+ .� " �.. ...... r - __ Sri r= . r "�} s w y ms 3 Y "' 3 ��/ '. SAG"rk e` .. fib .:•+ c [' F,.. ,.,. � ,.. .Na' ` . � +, \i Channel at base of slope between properties.Additional off site drainage contributing at this point. Cross section becomes more defined between STA 1+00 and STA 1+50. STA 1+50 Channel approximately 7'wide x 12"deep,parabolic cross section,grass. Picture 6 t`''' A. !j, 1 ! • r }} �t ; r f 1, • { j� _. .„I • <1j fy;rrs. \' 11 . �,iir•e •�, . ,1,i1 • . ;‘,i,1,1, lit ,. ....... , . :,, _ .,,„SV. • ' Fitz. 1, •_ s" '+ %. {; l !Jig }.r} :,-; ., r' T . ,t1 . � :74 r • ` ' ,.4'tom ' • - , t VE rks 'S` lt_i V 4 t �'eF P ;'Y7,,f�p> tr►4 it M `,... - , ` ji• . s9 ..111N `1 1, . r. _., ..r- • . L r �1 -.. - -- rr 'ram'.»: o'Z`,, '.-�.q i"- ' .may' a' t / r r l,r ' s ' i Picture looking form STA 1+50 looking back to STA 1+00. Grass lined channel,with riprap bottom, sending approximately at STA 1+50. Picture 7 F • ��w e a 1 y i✓F -f' / £j r e a Y Channel at base of slope between properties.Additional off-site drainage contributing at this point. Signs of bed erosion begin. STA 1+59 Channel approximately 7'wide x 12"deep,parabolic cross section,grass. ^ Picture 8 4" ALL \ � Channel at base of slope between properties.Additional off-site drainage contributing at this point. Bed erosion pronounced. STA2+QO Channel approximately 7'wide x 12"deep, parabolic cross section,grass. Eroded channel invert approximately z'wide'8^deep,rectangular insection. Picture 9 i 4. s. r /: • . -4. '. ! ti`i. r w - r+ tom'' v • i • l b 'w .• Y s aft. Y x ,,4 t v.. '.� SF'.. :`,- a ` ; Y T' '.: 1 _ , . ,.. , Itt. ". I + ,t t Channel at base of slope between properties.Additional off site drainage contributing at this point. Bed erosion head cut more pronounced @ STA 2+25. STA 2+50(near base of tree,meets larger channel.) Channel approximately 8'wide x 15"deep,parabolic cross section,grass. PPic,t_�u}re 10 r 1. ! `l- ..e. ,,� s{�� ij} ."ram ' <,;�y , .�. • '. � �i q _ _ v� ,�. 1 ,ems i A• C.• - 'ct,y .-. / . • k, .ors 1, 'i .,y 46, s 4:4 .. .. - - a." Arts* ` 4 i'' ,.'; 4. 4 ''" .�. J" '♦ , ter r .,fir & ,� . . .J, aN .,_ 11 to '• . ' r, '♦ +., �w ` ,*- } fie , •• • ' • i• f b. 1:x L.,. aI"' 1 .t • Picture downstream of larger channel, looking at end of MS-19 channel (near base of tree) and upstream to FES discharging flow for residential street/cul-de-sac. Picture 11 t. tK L ir'F' , nS r- 'f', � +, i "'' t c ,rw,T44.- y, # 1, t ' 7 E s 'I've` F+ 1 - ,t.. /^^►I �•r,.. �i.' ` ,. .. Nf_.. .y,*` t °'w t .r K a*c0 d . .per n ate* r `\ * elk:E +x aw ' a*9 *icy'41► O � - 3,. e t fir. 401;4 � 4. ..r ,� ,• + aM. .�"' .. A] M. Z.. fi r r ',C <.. . ,, " . .;, t " ` ,'mow`' .. •- ' ;fig A " `.,-: s""1.0` .iR" a .. k3 * .. ` • Picture of head cut at location where MS-19 stream joins flow from street FES.Approximately 18"deep. a Peak Flow Calculations to Point of Analysis H&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment • U.S.Department of Agriculture FL-ENG-21 B Natural Resources Conservation Service 06/04 TR 55 Worksheet 3: Time of Concentration (Ta) or Travel Time (Tt) Project: Crozet Water Treatment Plant Designed By: Corinne Wilson, EIT Date: 4/15/14 Location: Crozet, VA Checked By: Date: Check one: Present I Developed Check one: 1 T, Tt through subarea Point of Analysis NOTES: Space for as many as two segments per flow type can be used for each worksheet. Include a map, schematic, or description of flow segments. Sheet Flow(Applicable to-lc only) Segment ID Sheetflow 1. Surface description (Table 3-1) Grass 2. Manning's roughness coeff., n (Table 3-1) 0.24 3. Flow length, L (total L< 100 ft) ft 43 4. Two-year 24-hour rainfall, P2 in 3.7 5. Land slope, s ft/ft 0.035 6. Tt =0.007 (nL)°8 Compute Ti hr 0.09 + = 0.09 P2"s" Shallow Concetrated Flow Segment ID Grass Pavement 7. Surface description (paved or unpaved) Unpaved Smooth 8. Flow length, L .. ft 62 203 9. Watercourse slope, s ft/ft 0.645 0.037 10. Average velocity, V(Figure 3-1) ft/s 4.2 3.8 11. Tt = L Compute Tt hr 0.00 + 0.01 = 0.02 3600 V Channel Flow Segment ID Channel 12. Cross sectional flow area, a ft2 22.5 13. Wetted perimeter, P,„ ft 11.3 14. Hydraulic radius, r= a Compute r ft 2.0 Pw 15. Channel Slope, s ft/ft 0.078 16. Manning's Roughness Coeff., n 0.04 17. V= 1.49 r213 s1/2 Compute V ft/s 18.9 n 18. Flow length, L ft 408 19. Tt = L Compute Tt hr 0.01 + = 0.01 3600 V 20. 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' `. A'� '� ' CROZET WATER TREATMENT PLANT S�♦its. +♦+o♦+♦o�♦�♦�r��+�° .. . a,,, # 4No,# S....".4.4 0 , _ :-; � _ PRE-CONSTRUCTION HAZEN AND SAWYER ,� DRAINAGE AREA 4 Environmental Engineers & Scientists *,*" TO POINT OF ANALYSIS c HAZEN AND SAVWER Environmental Engineers Si Scientists Prepared by Hazen and Sawyer,P.C. Corinne Wilson, EIT Date of Calculation 4/29/2014 Client RWSA Project Name Crozet WTP GAC updates Description Rational method calculations to point of analysis Reviewer Mike Santowasso,PE Date Reviewed Table 1:Drainage Area Calculations C Predevelopment(ac) Postdevelopment(ac) Impervious 0.95 1.20 1.15 Grassed 0.25 1.45 1.50 Wooded 0.15 1.02 1.02 Total 3.67 3.67 Table 2:Rational Method Calculations Predevelopment Postdevelopment Composite C 0.45 0.44 2-yr Intensity(i) in/hr 4.75 4.75 10-yr Intensity(i) in/hr 6.30 6.30 2-yr Peak Flow(Cp) cfs 7.87 7.70 10-yr Peak Flow(QP) cfs 10.43 10.21 Change in Cp -2% HydroCAD Analysis of 2-Year Storm Velocity H&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment 1992 3.17 TABLE 3.17-A PERMISSIBLE VELOCITIES FOR GRASS-LINED CHANNELS CHANNEL LINING PERMISSIBLE SLOPE VELOCITY' Bermudagrass 6 ft./second Reed canarygrass 0 - 5% Tall fescue 5 ft./second Kentucky bluegrass Grass-legume mixture 4 ft./second Red fescue Redtop Sericea lespedeza 2.5 ft./second Annual lespedeza Small grains (temporary) Bermudagrass 5 ft./second 5 - 10% Reed canarygrass Tall fescue 4 ft./second Kentucky bluegrass Grass-legume mixture 3 ft./second Bermudagrass 4 ft./second Greater than 10% Reed canarygrass Tall fescue 3 ft./second Kentucky bluegrass For highly erodible soils, permissible velocities should be decreased by 25%. An erodibility factor (K) greater than 0.35 would indicate a highly erodible soil. Erodibility factors (K-factors) for many Virginia soils are listed in Chapter 6. Source: Soil and Water Conservation Engineering, Schwab, et.al. III - 135 HydroCAD Report: Hydrographs from the 2-Year Storm at each Cross Section. Maximum velocities tabulated below: Cross Section Maximum Velocity(ft/s) 0+00 4.78 0+20 3.71 0+50 4.79 1+00 4.42 1+50 4.57 2+00 5.75 2+50 5.50 0+00 Hydrograph 30 a3 Inflow 8 —Outflow Inflow aMa=3 bail at Avy Flow Depth=0 58' 6 RAJA vota4.78 fps r 038 Ti L=200' 3 4 S=0 0500 a CUpacityr5.93 cfs ii 3 0 5 6 7 8 9 10 11 1213141516 17 1819 20 Time (hours) 0+20 Hydr raph T 31 cfs —Inflow —Outflow utin.�w area=3 T6.i ac Avg Flcw repth=p 61 MA. .Y '.?t!ps p+ _ 5-fl 050i, Capacity:1 90 4fs 5 6 7 8 9 1011 121314 15 16 17 18 19 20 Time (hours) 0+50 Hydrograph 7 75 cfs Inflow ._Outflow Inflow Area=3 794 ac Avg Flow Cepth=0 58. Max welt-4 f9 . • n=0 035 L=5o;a 3 4 S=0 0500 i Capacity=5 93 cfs 1 a -- 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 Time (hours) 1+00 Hydrograph — -- 781 cfs —Inflow Outflow now,/Area=3 373}e Avg Flow Clepd+ O max'+el=a 12 firs n1035 5 1 50:v 4 5=0 0500'' 3 apacny=11 50 drs 2 1 0 5 6 7 8 9 10 11 12131415 16 17 18 19 20 Time (hours) 1+50 Hydrograph 7 83 cfs ...Inflow —Outflow Inflow Are.+>4 092 at. Avg Flow Depth-0 52' Max vei.4.51 R►s. r n=0 035 Ti 1*50 ' 3 _ 5=O.0500 ' 3 Capac,ty=32 89 vas 2 0 5 6 7 8 9 1011 12 13 14 1516 17 18 19 20 Time (hours) 2+00 Nydrograph 11 42 cfs —Inflow —Outflow Inflow Area=6.122 ac Avg.Flow Depth=0./5 Max Vet=5.1,5 tps 1=50.0' 5=0.0600" Capacity=23.32 cfs W 4 5 6 7 3 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 2+50 Nydrograph 14 84 cfs Endow —Outflow 14 h ffosr Area°7 99t14c 12 Avg flow Oepth=0 69 1 Max Ve4=6 5CF fps, , n=0 035 =5n a S=0 0500 it 6 Capacity=538541's 4 0 . 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 Time (hours) HEC-RAS Analysis of 10-Year Channel Capacity H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment • • Station 0+00 I -- .035 .-_. .. _..._....___._.___ ,035..__.__ _._._ .035 — Legend WS 10-Yr 814.6 814 8 WS 2-Yr Ground Bank Sta 614.4 • j 614.2 614.0 813.8 613.6 613.4 0 2 4 6 8 10 Station(ft) Station 0+20 4 .035-- -- -.035 + .035 Legend WS 10-Yr 613.6 WS 2-Yr Ground • 613.4- ( Bank Sta _ 613.2 • (fl Ul w 6130, 612.8 612.8 6124 0 2 4 6 8 10 Station(ft) Station 0+50 - .035 - 033 _ 035 Legend WS 10-Yr 812.4 WS 2-Yr Ground 612.2! • Bank Sta 612 0 x 611 8 611 6. 6114• 61121 611 0• � 0 2 4 6 8 _ 10 Station(ft) Station 1+00 035 .033 1e------ .035 Legend 810.0 WS 10-Yr WS 2-Yr 609 8 Ground Bank Sta 609.6 609 4 W 609.2 609.0 608.8 \se ? 808.6 6084 • -- 0 2 4 6 8 10 12 Station(ft) c s Station 1+50 (f--- 035 414 _ _ 035 t 035-- 608;5 WS 10-Yr WS 2-Yr 608.0 I Grau�nd • 1 Back Sta 607_5 re i t 0 8070 1 - t 806.5 / I 606.0• • 0 2 4 8 8 10 12 14 Station(ft) Station 2+00 e-- .035 + .035 .035 ). 806 0 �` Legend // WS 10-Yr / WS 2-Yr 605.5 / F Ground • Bank Sta .. 805.0 i M 804.5 604.0 I t 603.5• • I--1,- 0 2 4 6 8 10 12 14 Station(ft) • Station 2+50 035 '74 .035 .035 604.0 j Legend / WS 10-Yr 603.5- WS 2-Yr • Ground Bank Sta 603.0 ry 802.5•1 to w � 602 0 601.5 601 0• `'- 0 2 4 6 8 10 12rT'r� 14 Station(ft) Appendix VI Conveyance Calculations H-&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment Channel Adequacy Calculations H&S Project No. 32135-002 Crozet Water Treatment Plan Site Plan Amendment HAZEN AND SA%WER Environmental Engineers & Scientists Prepared by Bret Edwards, PE Date of Calculation 5/14/2014 Client RWSA Project Name Crozet WTP GAC updates Description Channel Analysis Reviewer Mike Santowasso, PE Date Reviewed Table 1: Drainage Area Calculations CN Predeveloped (ac) Developed(ac) Impervious 98 1.20 1.15 Grassed 61 1.45 1.50 Wooded 55 1.02 1.02 Total 3.67 3.67 Table 2: Pre and Post Volume units Predeveloped Developed Developed(with Treatment) 1-yr(24hr)precipitation (P) in 3.04 3.04 3.04 Composite CN a 71.4 70.9 69.50 Storage capacity(S) 4.00 4.10 4.39 Runoff Depth in 0.80 0.78 0.714 Drainage Area sf 160,011 160,011 160,011 RV(Runoff Volume) cf 10,723 10,401 9,517 a Composite CN value for"postdevelopment with treatment"obtained from Virginia RRM Spreadsheet,Channel and Flood Protection tab Table 2: Peak Flow(1 yr-24 hr) units Predeveloped Developed Developed(with Treatment) 1-yr(24hr) Peak Flow(Qp)b cfs 4.15 4.03 3.73 b Peak Flow values obtained from SCS Graphical Peak Discharge Spreadsheet Table 4:QDeveloped<I.F*(Qpre-Developed*RVPre-Developed)/RVDeveloped I.F. (site>1 acre): 0.8 QDeveloped• 3.73 RVDeveloped• 9,517 QPre-Developed 4.15 RVpre-Developed• 10,723 I•F*(QPre-Developed*RVPre-Developed)/RVDeveloped 3.74 a • Virginia Runoff Reduction Method Worksheet H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment 11 1-yearstorm 2 ear storm 10-year storm Target Rainfall Event(in) 1_ . f-,.i 7.d3 Drainage Area A • Drainage Area(acres) 3.67 Runoff Reduction Volume(cf) 849 Qrainage Area B Drainage Area(acres) 0.00 Runoff Reduction Volume(of) 0 # Drainage Area C 1 Drainage Area(acres) 0.00 Runoff Reduction Volume(cf) 0 4 Drainage Area 0 Drainage Area(acres) 0.00 Runoff Reduction Volume(cf) 0 f Drainage Area E r Drainage Area(acres) 0.00 Runoff Reduction Volume(cf) 0 -t Based on the use of Runoff Reduction practices in the various drainage areas,the spreadsheet calculates an adjusted Vdevoloped and adjusted Curve Number. Drainage Area A A soils 8 Soils C Soils D Soils - Forest/Open Space-undisturbed,protected forest/open Area jades) 0.0 1.0 0 0 0.0 - space or reforested land CN 30 55 70 77 Managed Turf-disturbed,graded for yards or other turf to be Area(acres) 0.0 1.5 0.0 0.0 mowed/managed CN 39 61 74 BO Area(acres) 0.0 1.2 0.0 0 0 Impervious Cover N 98 - 98 98 _ 98 - ..� Weighted CN S I } I 70.93 ( 4.10 1-year storm 2-year storm 10-year stone RV,,,,(In)with no Runoff Reduction 0.78 0.97 2.22 RVa„,,,„a(in)with Runoff Reduction 0.72 0.90 2.16 I _ Adjusted CN 69.5 70 70 € Drainage Area B A soils 8 Soils C Soils D Soils ForesUOpen Space--undisturbed,protected foresUopen Area(acres) 0.0 0.0 0.0 0.0 space or reforested land CN 30 55 70 77 Managed Turf disturbed,graded for yards or other turf to be Area acres) 0.0 0 0 0.0 0.0 mowed/managed CN 39 61 74 80 Impervious Cover Area(acres) 0.0 0.0 0.0 0.0 CN 98 98 98 98 _ Weighted CN S 0 ) 1000-00 1-year storm 2-year storm 10-year storm , RV0,„„,„,(in)with no Runoff Reduction 0.00 0.00 0.00 RVo,,, (in)with Runoff Reduction 0.00 0.00 0.00 . i Adjusted CN #NIA #NIA #NIA t Drainage Area C A soils B Soils C Soils D Soils _ ForestlOpen Space--undisturbed,protected foresUopen Area(acres) 0.0 0.0 0.0 0.0 space or reforested land CN 30 55 70 77 Managed Turf--disturbed,graded for yards or other turf to be Area(acres) 0.0 0.0 0 0 0.0 mowed/managed CT1 39 61 74 80 Area(acres) 0.0 0.0 0.0 0.0 Impervious Cover CN 98 98 98 98 Weighted CN S 0 I 1000 00 1-year storm 2-year storm 10-year storm RVu,w,,,„,,(in)with no Runoff Reduction 0.00 0.00 0,00 RVo,,,,,,r,,,,(in)with Runoff Reduction 0 00 0.00 0.00 Adjusted CN #NIA #N/A #NIA ......_,-_,_ Drainage Area 0 A soils 8 Soils C Soils D Soils Forest/Open Space-undisturbed,protected forest/open Area(acres) 0.0 0.0 0.0 0.0 space or reforested land CN 30 55 70 77 Managed Turf--disturbed,graded for yards or other turf to be Area(acres) 0.0 0.0 0.0 0.0 mowed/managed CN 39 61 74 80 Area(acres) 0.0 0.0 0 0 0 0 Impervious Cover CN 98 98 98 98 Weighted CN S 1 0 I 1000.00 1-year storm 2-year storm 10-year storm RVe,,,,,,p,,,(in)with no Runoff Reduction 0.00 0 00 0.00 RVw,,,,,..,(in)with Runoff Reduction 0.00 0.00 0.00 Adjusted CN #NIA #NIA #WA • Drainage Area E A soils B Soils C Soils D Soils Forest/Open Space-undisturbed,protected forest/open Area(acres) 0.0 0.0 0.0 0.0 space or reforested land CN 30 - 55 70 77 Managed Turt--disturbed,graded for yards or other turf to be Area{acres) 0.0 0 0 0 0 0.0 mowed/managed CN 39 61 74 80 Area iacresi 0.0 0.0 0 0 0 0 Impervious Cover CN 99 98 98 _ 98 Weighted CN S I 0 ( 1000 00 1-year storm 2-year storm 10-year storm RV,,,,,,,,,,,,,,(In)with no Runoff Reduction 0 00 0 00 0 00 RV,,,,,,,a,,.,(in)with Runoff Reduction 0 00 0 00 0 00 Adjusted GN qN/A NN/A I 0YN/A Using the Adjusted Curve Numbor for each drainage area,calculate peak discharges for the 1,2,and 10 year storm. Compare the peak discharges to the allowable discharge rates described in the Virginia Stormwator Management Program Permit Regulations(4VAC 50-60 86(A),conditions 1-5 and 4VAC 50—0-66(8),conditions 1-5). SCS Peak Discharge H&S Project No.32135-002 Crozet Water Treatment Plan Site Plan Amendment ► Predeveloped Page 1 • Predeveloped Site SCS METHOD 0-2000 Acres Method can be used for estimating peak flows from urban areas X 1-yr 24 hr storm Project Crozet WTP Date 5/14/14 Name BTE Check LMS 1. Runoff Curve Number Hydrologic Cover description "CN Area Product of Soil Group (table 2-2a-cl CN x area B Impervious 98 1 2 117.6 (3 Cpen Space(fair condiion,50, to 75"',1 61 15 88.45 t3 Wooded(good co:edi'i:an) 55 1.0 56.1 0 Totals 3.7 262.15 Weighted CN 71.43 2. Runoff Storm#1 Frequency yr 1 Rainfall,P(24-hr) (RD) in 3 04 Runoff,Q in 0.804 Q=(P-0.2 S)2 / (P+0.8S) S=(1000/CN)-10 4.00 SCSpeakdischarge 5/14/2014 Predeveloped Pag(.2 3.Time of Concentration(Tc)or travel time(Tt) Space for as many as two segments per flow type can be used for each worksheet Include a map,schematic,or description of flow segments .et Flow(applicable to Tc only) segment 2 1. Surface description(Table 3-1) Low Development Mod Development 2.Manning's roughness coefficient,n(Table 3-1) 0.240 3.Flow length L(not greater than 300ft) ft A3 4.One-year 24-hour rainfall P1 in 3 04 5. Land Slope,s ft/ft 0.04 6. Tt= 0.007(nL)08 computed Tt hr 0.10 0.101 P2 05 SO4 Shallow concentrated flow segment 2 7. Surface description(paved or unpaved) Low Development Mod Development 8.Flow length,L ft 62 203 9. Watercourse slope,s ft/ft 0.6450 0.037 10.Average velocity,V(Figure 3-1) ft/s 4,21 .3.8 11. Tt=L/(3600*V) computed Tt hr 0.001 0.011 0.021 Channel flow segment 1 . 12.Cross sectional flow area,a ft2 22 5 Assumption: 1ft depth(n, 13, Wetted Perimeter,p,,, ft 11 3 14. Hydraulic radius,r=a/pW ft 2 0 15. Channel slope,s ft/ft 0.078 16. Manning's roughness coefficient,n(Table 2-3) 0 04 �. 17,V=1.49(r 2/3 s1/2) /n f/s te5 Flow length, L ft ( 408 19.Tt= L/(3600*V) hr 0.007 0.007 20. Watershed or subarea Tt(add Tt in steps 6, 11, 19) 0.125 hours 4. Graphical Peak Discharge Method 1. Data Drainage area Arn 0.01 mil(acres/640) Runoff curve number CN 71.43 (from step 1) Time of concentration Tt 0.13 hr (from step 3) Rainfall distribution II (I,Ia, II, Ill) Pond and swamp areas spread 1 Assumption:min of 0%swamp area throughout watershe(table 4-2) Storm#1 2. Frequency 1 3. Rainfall, P(24-hr) 3.04 4. Initial abstraction,le (Use CN with table 4-1) 5.Compute la/P 0.26875 6.Unit peak discharge,q„ „ ` :; f)r (Use Tt and la/P with exhibit 4- II 7. Runoff,Q 0.804 (From step 2) 'ond and Swamp adjustment factor,Fp 1 r'eak discharge,qp 4.15 cfs 1863.26 gpm qp=quAmCFp SCSpeakdischarge 5/14/2014 y Developed Page 1 Developed Site SCS METHOD 0-2000 Acres Method can be used for estimating peak flows from urban areas X 1-yr 24 hr storm Project Crozet WTP Date 5/14/14 Name BTE Check LMS 1. Runoff Curve Number Hydrologic Cover description CN !Area Product of Soil Group (table 2-2a-c1 CN x area B Impervious 98 1.2 112.7 B Open Space(good condition.grass cover>75%) 61 1 5 91.5 B Wooded(good condition) 55 1.0 56.1 0 Totals 3.7 260.3 Weighted CN 70.93 2. Runoff Storm#1 Frequency yr 1 Rainfall,P(24-hr) (RD) in 3.04 Runoff,Q in 0.780 Q=(P-0.2S)2 / (P+0.8S) S=(1000/CN)-10 4.10 SCSpeakdischarge 5/14/2014 Developed Pagc 2 r 3.Time of Concentration(Tc)or travel time(Tt) Space for as many as two segments per flow type can be used for each worksheet Include a map,schematic,or description of flow segments Sheet Flow(applicable to Tc only) segment 1 2 1. Surface description(Table 3-1) Low Develo ment Mod.Development 2.Manning's roughness coefficient,n(Table 3-1) 0.240 3.Flow length L(not greater than 300ft) ft 4.One-year 24-hour rainfall P1 in 3.04-_ 5. Land Slope,s ft/ft 0.04 6. Tt= 0.007(nL)°9 computed Tt hr 0.101 I 0.10 Poa zs°4 Shallow concentrated flow segment 2 7. Surface description(paved or unpaved) Low Development Mod Development 8.Flow length,L ft 62 203 9. Watercourse slope,s ft/ft 0.6450 0.037 10.Average velocity,V(Figure 3-1) ft/s 4.2 3.8 11. Tt=L/(3600*V) computed Tt hr J 0.001 0.01 j 0.021 Channel flow segment 1 2 12.Cross sectional flow area,a ft2 22.5 Assumption: 1ft depth(normal) 13. Wetted Perimeter,p,, ft 14. Hydraulic radius,r=a/p,,, ft 15. Channel slope,s ft/ft 0.078 ,® 16. Manning's roughness coefficient,n(Table 2-3) 0-04 17,V=1.49(r 2/3 s 1/2) /n ft/s 16.5 18.Flow length,L ft L 4Q8.1. J 19.Tt= L/(3600*V) hr 0.007 0.007 20 Watershed or subarea Tt(add Tt in steps 6,11, 19) 0.125 hours 4. Graphical Peak Discharge Method 1. Data Drainage area Am 0 01 mi2(acres/640) Runoff curve number CN 70.93 (from step 1) Time of concentration Tt 0.13 hr (from step 3) Rainfall distribution I,(I,la,II,Ill) Pond and swamp areas spread Assumption:min of 5%swamp area throughout watershe(table 4-2) Storm#1 2. Frequency 1 3.Rainfall,P(24-hr) 3.04 4.Initial abstraction,I, (Use CN with table 4-1) 5.Compute la/P 0.2819079 6.Unit peak discharge,q° 7P1 (Use Tt and la/P with exhibit 4- II 7. Runoff,Q 0.780 (From step 2) 8. Pond and Swamp adjustment factor,Fp 1 9 Peak discharge,qp 4.03 cfs 1807.25 gpm qp=q,A,,QFp SCSpeakdischarge 5/14/2014 q • Developed(Treated) Page 1 Developed Site(Treated) SCS METHOD 0-2000 Acres Method can be used for estimating peak flows from urban areas X 1-yr 24 hr storm Project Crozet WTP Date 5114/14 Name STE Check LMS 1. Runoff Curve Number Weighted CN 69.70 2. Runoff Storm#1 Frequency yr Rainfall,P(24-hr) (RD) in Runoff,Q in 0.723 Q=(P-0.2S)2 / (P+O.8S) S=(1000/CN)-10 4.35 SCSpeakdischarge 5/14/2014 Developed(Treated) Pagi,' • . P 3.Time of Concentration(Tc)or travel time(Tt) Space for as many as two segments per flow type can be used for each worksheet Include a map,schematic,or description of flow segments Sheet Flow(applicable to Tc only) segment _ .. 1. Surface description(Table 3-1) Low Development Mod.Development 2.Manning's roughness coefficient,n(Table 3-1) 0,240 3.Flow length L(not greater than 300ft) ft 43 4.One-year 24-hour rainfall P1 in 3.04 5. Land Slope,s ft/ft 0.04 6. Tt= 0 007(nL)°B computed Tt hr 0.10 0.10 Foss 4 2 Shallow concentrated flow segment 2 7. Surface description(paved or unpaved) Low Development Mod.Development 8.Flow length,L ft 62 203 9. Watercourse slope,s ft/ft 0.6450 0.037 10.Average velocity,V(Figure 3-1) ft/s 4.2 3.8 11. Tt=L/(3600*V) computed Tt hr C _ 0.901 0.01 0.02 Channel flow segment 1 2 12.Cross sectional flow area,a ft2 22.5 Assumption: 1ft depth(normal) 13. Wetted Perimeter,R. ft 11.3 14. Hydraulic radius,r=a/p,w ft 2 G 15. Channel slope,s ft/ft - 0.078 16. Manning's roughness coefficient,n(Table 2-3) 0.04 17,V=1.49(r 2/3 s 1r2) /n ft/s 16 S 1 18.Flow length,L ft I 4001 19.Tt= L/(3600*V) hr [ 0.0071 I 0.0071 20. Watershed or subarea Tt(add Tt in steps 6,11, 19) 0.125 hours 4. Graphical Peak Discharge Method 1. Data Drainage area Am 0.0057344 mi2(acres/640) Runoff curve number CN 69.7 (from step 1) Time of concentration Tt 0.1251293 hr (from step 3) Rainfall distribution " ` 11(I,la,II,Ill) Pond and swamp areas spread ti Assumption.min of 5%swamp area throughout watershe(table 4-2) Storm#1 2. Frequency 1 3.Rainfall,P(24-hr) 3.04 4.Initial abstraction,I. t. scs (Use CN with table 4-1) 5.Compute Ia/P 0.2894737 6.Unit peak discharge,q u 4�a (Use Tt and la/P with exhibit 4- II 7. Runoff,Q 0.723 (From step 2) 8. Pond and Swamp adjustment factor,F5 1 9 Peak discharge,q5 3.73 cfs 1674.77 gpm gp=q,A,,QF5 SCSpeakdischarge 5/14/2014