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HomeMy WebLinkAboutSDP200600131 Review Comments Major Amendment, Final Site Plan 2008-04-28ALg�,�� �'IRGINZ� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: SDP - 2006 - 00131, City of Charlottesville CTS Operations Center WPO- 2007 - 00091, City of Charlottesville CTS Operations Center Plan preparer: Steve Davis, VMDO [email: davis @vmdo.com] Owner or rep.: Scott Hendrix, Charlottesville [email: hendrix@charlottesville.org] Date received: 24 October 2007 (plan rev. date 22 October 2007) 20 Mar 2008 (Revl) Date of Comment: 12 December 2007 28 Apr 2008 (Revl) Engineer: Phil Custer Jonathan Sharp (Revl) [phone: 566 -2578] Engineering cannot recommend approval to the final major amendment for the City of Charlottesville CTS Operations Center until the following comments have been addressed. A. General review comments: 1. The site plan submission must include a signed and dated professional seal. [DM] Rev]: comments addressed. 2. Please note that there is no existing WPO buffer along the tributary to Moore's creek on TMP 71E1 -01. If the applicant wishes to propose a buffer, please indicate clearly on the plan. Rev]: comments addressed. 3. A temporary construction easement is required on TMP 77E1 -1D for the grading necessary to construct the improvements on Avon Street Extended. Rev]: comments not addressed. At a minimum, temporary construction easements can be handled by a letter of intent by the owner of the parcel. If a formal easement is pursed, it must be recorded prior to site plan approval. 4. The variation from Section 18 -4 -12.16 has not been granted. Justification must be given to convince the Zoning Administrator that "the public health, safety or welfare would be equally or better served by the modification or waiver and that the modification or waiver would not otherwise be contrary to the purpose and intent of [Chapter 18 -4]." Revl: comments addressed. 5. Site plan approval cannot be granted until all of VDOT's concerns and comments have been addressed. VDOT comments will be forwarded once we receive them. Rev]: VDOT approval is required. A copy of the plans has been submitted to VDOT for review. 6. For all review sections below, additional comments may be forthcoming on the next submittal. Rev]: See additional comments throughout the comment response letter. B. Site Plan comments: 7. Please label the floodplain with the FEMA map number and date. [DM] Rev]: comments addressed. 8. The 100 -year floodplain shown on the existing conditions page does not appear to match the latest FEMA map. Please correct. [DM] Revl: comments addressed. 9. Not all critical slopes are hatched on the existing conditions sheet. Please show all slopes that are greater than 25 %. [32.5.6d] Rev]: comments addressed. 10. The travelway in the parking lot must have a width of 24ft if parking spaces of less than loft width are provided. [4.12.16c.1] Rev]: comments addressed. 11. Please provide more labels on the site plan indicating the types of curbing used. [DM] Rev]: comments addressed. 12. In locations where curbing is proposed, please show two lines to demonstrate its width. Sidewalks widths do not include the width of the curb. The applicant may have to adjust the dimensioning in some areas if bumper blocks are to be avoided. [DM] Rev]: The following in regards to parking areas must be revised: a. In the parking area adjacent to the CTS operations building, the space directly opposite the last fuel efficient vehicle space is only 14.47 feet in length because part of the space extends into the adjacent travelway (travelway measuring 22.73 ft in width). Please reconfigure this part of the parking area so that spaces are a minimum of 16 feet in length. b. Curbing is required for the parking spaces directly adjacent to the CTS maintenance building. The width required for the curbing cannot be included in the 6 feet width needed for the sidewalk. c. Parking spaces directly adjacent to the CTS maintenance building must be 18 feet in length. d. The travelway adjacent to the CTS maintenance building is labeled as 26 feet in width and the adjacent parking spaces opposite the building are labeled 16 feet in length, when they should be labeled 24 feet and 18 feet, respectively. Please correct this. 13. The width of all parallel parking spaces must be 9ft. [4.12.16c.2] Rev1: The travelway adjacent to the parallel parking should be 2 way in circulation and a minimum of 20 feet wide. 14. Please show sight distance triangles onto VDOT ROW. [DM] Rev]: comments addressed. 15. The minimum length of a loading space is 25ft. [4.12.18a] Rev]: comments addressed. 16. The maximum grade for parking spaces, loading spaces, and access aisles abutting parking or loading spaces shall not exceed five percent in any direction. [4.12.15c] Rev]: The employee parking area adjacent to the CTS maintenance building between elevations 435 and 441 is at a slope of 5.2 %. Please revise to a maximum of 5% in slope. 17. There appears to be proposed slopes steeper than 2:1 on site. Please correct. [DM] Rev]: comments addressed. 18. Please provide an adequate landing all new entrances on the site. "As a guideline, the approach grade should not exceed four percent for a distance of not less than forty feet measured from the edge of the street being intersected." Please also include the VDOT entrance designation on the grading sheet. [4.12.17b] Rev]: The entrance to Avon Street adjacent to building D is shown at 5.4% in slope. Please revise to a maximum of 4% slope for a distance of 40 feet. 19. On sheets, S -I and S -2 Type C pavement in the VDOT ROW was labeled as "Turf block ". Rev]: comments addressed. 20. Parallel parking spaces will not be permitted on Avon Street Extended. Rev]: comments addressed. 21. There seems to be no overland flow relief if structures 8 -2 and 8 -1 become clogged. Please correct. [DM] Rev]: comments addressed. 22. Site runoff must not drain into streets. Please correct grading and drainage structures around the southern entrance to fix this problem. [DM] Rev1: comments addressed. 23. All slopes steeper than 3:1 must have low maintenance groundcover specified. [DM] Rev]: Low maintenance ground cover cannot be any type of grass. 24. Please show inlet shaping (IS -1) on all inlets and in all manholes that do not already have scour protection. [DM] Rev]: comments addressed. 25. Contour lines that are perpendicular to the centerline of the travelway will not be permitted. Please either crown or slope to one gutter. [DM] Rev]: comments addressed. 26. Show and dimension riprap outlet protection on the plan per calculations. [DM] Rev]: comments addressed. 27. Is existing stormwater structure #7 to be demolished? If so, please remove from development plans. Rev1: comments addressed. 28. The inverts of structure 1 -5 do not match between the profiles and calculation. [DM] Rev]: comments addressed. 29. Please draw inlets so that they represent the correct dimensions. [DM] Rev1: comments addressed. 30. In table 7, some of the throat lengths do not match between columns 3 and 25. [DM] Rev]: comments addressed. Additional Comments: a) All sidewalks must be concrete, not gravel. [per DM] b) I cannot find drainage area maps that correspond to the inlets. There should be drainage area maps separate from the SWM drainage area maps, showing the drainage going to each inlet. The SWM drainage area maps are confusing. Some of the drainage areas do not correspond the actual areas draining to inlet. The drainage areas shown for drainage structures along Avon Street do not include ROW drainage, and do not match the drainage calculations. Several drainage areas along Avon Street are missing. Please provide separate drainage area maps for the drainage plan, with drainage areas corresponding to each inlet. The destination structure of the drainage areas should be labeled for each drainage area. Also, showing drainage pipes and structures on the drainage area map is helpful. c) There appears to be an existing structure with endwall very close to line S -5 to 5 -13. The plans do not indicate if this structure will be removed. Please clarify. d) Portions of proposed improvements are missing on the grading plans (5 -3,4) near the northern entrance. Please include all proposed improvements on the grading plans. e) The drainage concept for the proposed cistern system is confusing. It appears that roof runoff will drain to a large cistern in the CTS maintenance building. Will the system be able to collect the first 1 inch of runoff for water quality volume requirements? Please show that this volume will make it into the cistern, and will not spill over the roof or gutters. Only this volume needs to be conveyed to the cistern for water quality purposes Overflows can be provided at each building for larger storm events so the large storm events do not pass through the cistern system. If larger storms are not conveyed through the cistern (such as the 2 and 10 year storm), identify which drainage structures convey the runoff and size the structures /facilities appropriately to handle the additional runoff. f) Please provide pipe profiles and calculations for the bus canopy drainage system. g) There is a concern with the outfall of the proposed SWM facility #5. The outfall appears to flow through a waste area, and there is a concern with sedimentation and erosion in this area. Please provide a plan which will ensure the runoff from outfall of the facility will not flow through the waste area. h) Please analyze the existing drainage systems that the site ties into (structures 6 -7, S- 13, and the DI below 4 -8) to ensure that adequate downstream pipes /channels are provided all the way to Moore's Creek. [MS -19] C. Stormwater Management review comments: 31. Engineering review will consider the roofdrain collection and resupply systems private and not subject to the normal requirements of our design manual. However, the downstream drainage system should be designed assuming that the cistern overflows for all design storm and provides no detention at all. Rev1: Additional information is needed for the cistern system. See comments about drainage in the additional comment d) under the site plan comments and comment 32 below. It appears that the cistern is still being used for detention. 32. Engineering review will give quality credit for the use of the cistern if it is sized to capture the water quality volume for the all the buildings. Please provide this calculation and a simple detail of the cistern showing its dimensions. Rev]: Please provide a detail of the cistern in the SWM plans. Our water quality requirements are based on volume. The first I inch of runoff must be able to be collected within the cistern. Please show that the first I inch of runoff will make it into the cistern (not overflow over the gutter system on the roofs of buildings) and that the cistern can hold the volume of the first I inch of runoff in addition to an average storage volume of water in the tank for between storms. Will the water in the tank be used up very quickly? Please calculate an average volume of water that will be stored in the cistern based on water usage so that if a storm event occurs the entire I inch of runoff will be treated and will not overflow from the cistern. 33. Drainage area lines appear to be incorrect in some places. Please correct. Drainage area lines should not stop at property lines in analysis. To perform an accurate analysis, the applicant may need to use a different scale to provide a fuller view of the development and the surrounding points of analysis for the drainage area maps. Rev]: comments not addressed. Drainage area maps for stormwater detention should include all areas draining to analysis points, facilities, or structures. Please show the area draining to each facility. Sub -areas draining to inlets should not be shown, only areas drainage to each facility. In the case of facilities in series, it is usually easier to provide 2 sets of drainage area maps: I set showing the drainage areas draining to BMPs, and another showing drainage areas to detention facilities. 34. It appears that the removal rate provided in SWM facilities #2 and #4 are inadequate for the drainage area. Please correct. [VSMH, DM] Rev]: Water quality drainage areas should not include offsite drainage areas when calculating removal rates. SWM facility #2 includes offsite area. When done correctly, the removal rates for facility #2 becomes 65 %. Also, in the water quality compliance table, the removal rate for SWM #4 is listed as 100 0/c, when it should be listed as 65% (removal rate of an infiltration trench). 35. It appears that no stormwater treatment will occur in the underground facility. Please provide treatment in this area. If infiltration credit is sought, the applicant must supply soil tests verifying that the soil is adequate to use an infiltration measure. Generally, the soils found in this region do not allow for infiltration to be used with any degree of confidence. [DM] Rev]: The underground facility should be designed as an Infiltration Trench (VSMH 3.10). Our water quality requirements are based on volume. In order to achieve a 65% removal rate, the facility must be sized to infiltrate the first I inch of runoff. The volume used for infiltration should not be included in the storage volume for detention. For example, if 220 cu yd are needed for water quality volume and this volume is located at elevation 438, then storage for detention routing should begin at elevation 438. 36. Detention calculations appear to be missing. Please route all detention structures to show that all detention requirements are met. [DM] Rev]: The detention calculations are very confusing. The narrative states that only the underground facility will be utilized for detention, when it appears on the detention compliance table all the facilities are being used for detention. The compliance table shows that the 10 year storm is not met for the rational method. The rational method should be used for drainage areas of the small size found on site. The detention compliance table is very confusing. Areas not draining to the underground facility are being treated as if they are being routed through the facility. Please show the total drainage draining to each facility (as the facilities are in series and downstream facilities capture drainage from upstream facilities). There is not enough information provided to verify whether or not detention is met. Calculations should include all outlet structure information. Typically the downstream most facilities are designed and sized to handle stormwater detention, and upstream facilities serve only as water quality facilities. There are too many questions and concerns to discuss in a comment letter. Please contact Engineering to discuss how stormwater detention is handled and consult the County Design Manual. Engineering is available for meetings every Thursday from 2:30 to 4:06pm. Please call to schedule a meeting. 37. It is unclear how any detention is provided on site. Please provide greater details on the outlet control structures for all detention facilities. See above comment. Rev]: Stormwater facility outlet structure information should be located on the SWM plan sheet included with the cross sections for each facility. See comment #44. 38. Sediment forebays are required on all water quality facilities that receive concentrated flow. Please design each forebay to the standard in the Virginia Stormwater Management Handbook. [VSMH] Rev]: Forebays are needed for SWM facilities #1 and #2. 39. It appears that development of this site will demolish the existing stormwater management facility and replace it with a new one. If this is the case, the pre - development analysis should assume an undeveloped site because the site is currently detaining water to meet the initial pre - development rate. Rev]: comments addressed. 40. Please include the planting plan for each biofilter in the stormwater section of the plan set. Each biofilter detail should have its own planting schedule. [DM] Rev]: comments addressed. 41. Please provide sizing calculation for each biofilter. [DM] Rev]: Biofilter sizing calculations are based on surface area, not volume. Biofilter floors should be sized for 2.5% of the impervious area draining to the facility for a 50% removal rate requirement, and 4% of the impervious area draining to the facility for a 65% removal rate requirement. 42. Please label minimum bed dimensions in each biofilter. [DM] Rev]: comments addressed. 43. Each biofilter shall specify 3 species of tree and 3 species of shrub. [VSMH, DM] Rev]: comments addressed. 44. Please provide a typical section for each biofilter. [DM] Rev]: Cross - sections are needed for each biofilter including the following information and meeting the following criteria (directly from Design Manual): Embankments (between 3 and 25 ft in height) a) top width 8ft min., 10' for heights 15' to 20',12' for dams over 20', heights measured from the outside toe b) upstream face slope 2:1 or flatter, labeled c) downstream slope 3:1 or flatter, labeled d) 10yr and 100yr high water elevations labeled with 1 ft freeboard for 100yr storm with emergency spillway or 2 ft freeboard without emergency spillway e) an impervious core f) a cutoff trench of minimum 4' wide, 4' deep and 1:1 sloped sides Principle spillway a) riser crest 1' below emergency spillway if present b) riser crest stays within weir flow control during the 10yr storm c) trash racks over all inlets and controls to prevent clogging d) trash rack over riser crest is not flat (no DI -7's) e) riser size and materials labeled f) barrel size, strength, material, inverts and slope labeled g) all orifices, weirs or other control devices labeled with dimensions and inverts h) control orifices not more than 25% of riser perimeter at any point (does not affect riser structural integrity, 25% is a target) i) riser base size and dimensions labeled j) access to riser is provided (riser should be in dam, not free - standing) Emergency spillway a) dimensioned and labeled b) invert labeled c) dimensions in control section d) dimensions in channel section provided if different than control section e) linings labeled and shown where applicable f) spillway over native soils, and/or sufficient armoring provided Sediment forebays a) provided for all retention basins, constructed wetlands, and basin biofilters at all inlets b) sized to 0.25" of runoff per impervious acre (can be included in WQV) c) direct vehicle access provided Biofilters a) minimum floor dimensions labeled b) does not receive any stream base flows c) areas of sheet flow into facilities are protected from erosion by appropriate scour d) protection stone or energy dissipation measure e) plants are shown and labeled with height or caliper f) 3 plant species are specified (3 trees if present, 3 shrubs) with sizes g) biofilter floor is 2.5% of impervious cover for type I, or 4% of impervious cover for type II h) 2.5' depth of sand/soil media i) 1.5' stone drain in geotech fabric under media, with 6" perforated PVC pipe to daylight j) 0.5' -1.0' ponding depth provided in facility k) overflow provided 1) biofilter area is flat m) cleanouts are provided at the end of the underdrain pipe, and every 50' 45. Please submit a stormwater facility maintenance agreement and fee to the county. [DM] Rev]: comments addressed. 46. Please encompass all SWM facilities in an easement (including the cistern). [DM] Rev]: comments addressed. 47. Please remove the fire hydrant from within SWM facility #1. Rev]: Please remove the fire hydrant outside of SWM facility #4. 48. Engineering review does not recommend the use of CMP detention structures. Rev]: comments addressed. Additional Comments: a) Please remove all water lines, gas lines, sanitary sewer lines, data conduits, electric lines, stormwater overflow piping, etc. from the biofilter areas. b) The underground infiltration system should be designed according to an Infiltration Trench: MOB of the VSMH. Please provide adequate depth and surface area calculations. Pretreatment facilities are recommended at each inlet to prevent clogging of the facility. The VSMH suggests that the facility is wrapped in filter fabric, and that the insides of the detention pipes are also wrapped in fabric. c) The underground facility does not appear to have enough storage. The maximum elevation for the 2 and 10 year storms are above the top of the facility. d) It does not appear that an overflow structure has been provided for SWM #2. e) The outlet of the SWM detention facility will always hold water because of the 2 riser structures in series. The 15" pipe will always remain in pressure flow. Please combine the riser structures to one structure, or increase the 15" pipe to a 36" pipe and provide a 3" drain down orifice on the second riser to keep standing water out of structures. f) It appears that the outlet structures for the detention facility are 15" risers connecting to 15" pipes. How will this configuration work? g) It appears that the detention facility may need to be lowered. It appears to be partly located in fill. Infiltration facilities cannot be placed in fill. Also, it appears that there in some areas, there is no space between the top of the gravel for the facility and the base gravel for the concrete pavement. Lastly, there is a retaining wall within 5 feet from the facility, with a bottom of wall elevation below the top elevation for the facility. If the wall configuration is to remain, the wall should be designed with the facility in mind. h) Please label the elevations of the detention facility on sheet SWM -8. i) A SWM bond will be computed by the County once the plans have been approved. D. Erosion and sediment control comments: 49. Please include a detailed construction sequence in the erosion and sediment control narrative. [VESCH] Revl: comments addressed. 50. The underground detention structure can not come online until the site has been deemed stabilized by the county erosion and sediment control inspector. Please include this note on the plan and demonstrate how the facility is to be constructed without being clogged. [DM] Rev]: The construction sequence refers to plugging inlets and providing diversions. Please show how this will work on the plans, and address how to ensure drainage will make it to downstream traps or basins. Another possible solution may be to provide temporary slope drains through the facility from each inlet into the facility to keep sediment from entering the facility, and to install the weir outlet structures after final stabilization has occurred and the temporary slope drains are removed. 51. The drainage area to sediment trap 2 is greater than 3 acres. A sediment basin is needed at this location. [VESCH] Rev1: comments not addressed. During the second phase of ESC, the drainage area to sediment trap #2 will exceed 3 acres, as the drainage system will be conveyed to the trap. Please size the trap for the entire southern drainage area, and provide adequate perimeter protection with diversion dikes and temporary slopes drains to convey all drainage to a basin. Realistically, this is what will happen in the field as sediment trap #4 is located in the way of grading /construction. There appears to be plenty of space to provide perimeter protection for the site draining to an adequate sediment basin at the lowest portion of the site. This will allow the contractor to install ESC measures at the beginning of construction and then he can focus on grading and construction of buildings and improvements. 52. Please show tree protection fencing on the plan per standard 3.08 in the VESCH or remove from plan if not needed for other agency requirements. For example, the fencing must be placed 5ft outside of the dripline of the tree. Also, it appears that in some locations, drainage structures, silt fence placement, and grading will interfere with tree protection fencing and may compromise the health of the tree. Rev]: Tree protection must be shown at the drip line of trees per the VESCH to ensure the protection of the trees. No construction or grading should occur within the limits of the tree protection. 53. Please provide a staging area on site. [DM] Rev]: comments addressed. 54. Please show the demolition to the curb island in the adjacent parcel within the limits of construction. Rev]: comments addressed. 55. It appears the drive aisle down to the soil stockpile is not protected with any ESC measures. Please address. [VESCH] Rev]: Silt fence on the downhill side of the haul road is adequate. Provide diversions on the uphill side of the haul road to divert runoff to sediment trap #2 and to keep runoff from spilling onto the haul road. 56. ESC measures appear to be in the way of site grading between phases 1 and 2. Rev]: comments not addressed. Please remove ESC measures in the way of grading and replace with adequate perimeter controls. 57. Construction traffic shall only enter and exit the limits of disturbance through the approved construction entrance. Please show a barricade in the locations where construction traffic may be likely to leave the site without using the approved construction entrance. [VESCH] Rev1: comments addressed. 58. Existing structure 11 needs some form of protection. It appears that for both structures in this vicinity, a culvert inlet sediment trap is the most reasonable measure to be used. [VESCH] Rev]: comments addressed. 59. The northern property line is not adequately protected. Please address. [VESCH] Rev]: comments addressed. 60. The ESC protection at the northern site entrance will need to be amended. The silt fence through pavement in this area will be an inadequate ESC measure. [VESCH] Rev1: comments addressed. Additional Comments: a) Portions of disturbance are not shown on the ESC plans (as the limits of disturbance run off the page. All limits of disturbance must be clearly shown on all phases of the ESC plans. b) If existing swales are to be used to diversions, please provide calculations to show that the swale will be adequate. c) Temporary slope drains should be sized according to drainage area per the VESCH. d) An ESC bond will be computed by the County once the plans have been approved.