Loading...
HomeMy WebLinkAboutSUB201100138 Review Comments Road Plan and Comps. 2012-01-02� OF AL ,. vIRGI1`IZP COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: Clifton Lake Subdivision ESC, SWM, mitigation, and Road Plans (WPO- 2011 -00094 and SUB - 2011 - 00138) Plan preparer: Mr. Mike Myers, PE; Dominion Engineering Owner: Virginia Land Trust Owner's Rep.: Mr. Andrew Baldwin Plan received date: 18 November 2011 Date of comments: 2 January 2012 Reviewer: Phil Custer The first submittal of the ESC, SWM, mitigation, and Road plans for Clifton Lake, also known as Keswick Lake (SUB- 2011 -00138 and WPO- 2011 - 00094), received 18 November 2011, has been reviewed. Engineering can approve the plans after the following comments have been addressed. A. General Review 1. The private road east of the lake does not match the master plan approved by the Board of Supervisors when this property was rezoned. A variation from the Planning Department will be needed prior to approval of this plan. The Director of Planning should specify any new design standards or conditions that will be required by the applicant after this variation. 2. A parking lot has been provided off of Road C. After reviewing Section 32.2.a.5 of the Zoning Ordinance, the Chief of Current Development has determined that this new parking lot will require a site plan to be reviewed and approved by the county. Because of the existing zoning map, there is some confusion as to which Zoning Ordinance this parking lot should be reviewed under. This issue should be resolved with the variation process. I have noted, however, that the parking lot does not appear to meet a few of the design standards of the 1980 Zoning Ordinance. The following changes are required in order for the parking lot to meet the standards set forth in the 1980 Zoning Ordinance: a. A VDOT Standard entrance is needed from the private street. Please callout a VDOT commercial entrance and draw a profile to confirm that the standard is met. [4.12.6.1] b. The minimum width of a two way travelway is 20ft. [4.12.6.2] c. Parking spaces must be delineated per 4.12.6.3. d. The parking lot "shall be constructed and maintained with a dust free surface ". I do not think only gravel meets this standard. [4.12.6.2] e. Section 32.5.5 of the 1980 Zoning Ordinance states that "the county engineer shall approve the construction standards of all other paved areas." Section 32.5.10 states that "Parking areas design and construction shall be approved by the county engineer in accordance with sound engineering practices." Unfortunately, I could find no maximum slope allowed in the parking regulations of the zoning ordinance. However, Section 4 -5 of the Subdivision Ordinance is clear in requiring a maximum slope of 8% with a possible waiver of the Planning Commission to no more than 10 %. In light of this information and the design standard of the 2011 county ordinance, county engineering sets the maximum grade of the entrance to this parking lot at 10 %. 3. Please provide to the county a certification from a certified engineer that the existing dam has been Albemarle County Community Development Engineering Review Comments Page 2 of 6 tested and it is safe. [Condition #7] 4. Please provide an approval letter from the Army Corps of Engineers for all of the stream and wetland disturbances. 5. Does this dam fall under the jurisdiction of the Virginia Dam Safety Act? If so, construction will not be allowed by the county until the applicant provides a copy of their construction permit from the Virginia Soil and Water Conservation Board. 6. Stream buffers are needed 100ft from the edge of all streams and lakes or the limits of the floodplain, whichever is greater. Please amend both the Road and WPO plans to show these changes. B. Erosion and Sediment Control Plan Review (WPO- 2011 - 00094) 1. Please remove all fill from the floodplain that is not being considered in SP- 2010 -00040 or amend the submittal of SP- 2010 -00040 to match the current plan. 2. Please identify a typical detail and construction standard for the trail system around the development. Depending on the type of trail, this work may require ESC measures. 3. Please update the ESC note set so that it matches the set in the current edition of the County's Design Manual. 4. Please move the construction entrance on existing Shadwell Road south of the high point and provide a diversion east of the access road to Sediment Basin 1. Provide a note in the area stating that the construction entrance is to drain to Sediment Basin 1. The upgrade work to Shadwell road will likely be performed in the last weeks of construction and should only be part of the construction zone on the days that the work is occurring. 5. Please add a construction entrance off of North Milton Road and direct it to a sediment trap or basin. Most of the work on this site will take place at the dam and this access point will likely be preferable to the contractor. 6. Silt fence does not appear to be used appropriately in several instances in this plan. Silt fence cannot be placed in any manner other than parallel to contour lines. Otherwise, silt fence acts as a diversion and blowouts occur at low points. Also, silt fence must not be used in any place where the depth of the sheet flow is greater than 100ft. Road C and Shadwell Road Extended from Road B to Culvert C are the places where the 100ft depth standard appears to be violated. On Road C, Shadwell Court, and from the end Shadwell Road Extended to Culvert D the silt fence across contour line standard is violated. Please replace silt fence in these cases with more traps, basins, and diversions. Specifically for Road C, at least one basin (at the outlet of culvert G) and one trap (west of the parking lot) must be dug into the ground. No fill will be allowed unless it is approved by the Board of Supervisors via the SP process. Disturbance of the standing water will likely need Army Corps Approval. Please contact their representative, Vinny Pero. Check dams are not a sediment filter device. They are only to be specified to limit the velocity in channels. A different strategy on road C northwest of the dam is needed. (Please see previous comment.) No ESC measures have been provided for the construction of the dam. This construction feature is the most critical area of the entire plan because of the amount of earthwork and the large stream. A detailed ESC plan and construction sequence will be needed for the dam work. Please identify where the soil material for dam construction will come from (onsite -east side, onsite -west side, or offsite), how the stream will be bypassed around the construction area, the size of the bypass channel and what storm it is sized for, how the embankment will be filled, where the access roads will be, and the location and size of a sediment trapping measure at the toe of the dam. If temporary stream crossings are to be used, they must be sized for the 10 -year storm if the crossing Albemarle County Community Development Engineering Review Comments Page 3 of 6 will remain more than 14 days. 9. Please extend the ROW diversion so that it goes all the way to the embankment of Sediment Trap 2. Also, please make sure ST -2 shows up on Sheet C4. 10. Silt fence appears to be indiscriminately placed on the west side of the water line along Shadwell Road. In some cases, however, it looks as though the contours will require that the silt fence be placed on the east side of the line. Please label more contours on Sheet C5 so the ESC measures for the line construction can more easily be design and checked. 11. How is the water line in the Shadwell Road ROW to be constructed? In most cases, the water line is proposed to be constructed a few feet from the centerline of the ditch. In these cases, the ESC methods will be extremely difficult because the ditches will likely be disturbed and, when a rain event occurs, will result in concentrated sediment -laden water that can only be treated with a sediment trapping measure. For instance, the silt fence at Station 10 will likely be a blowout point for the construction area. Please address these concerns. 12. Calculations for Sediment Basins 2 and 3 are included in the ESC narrative, but I do not see them in the plan at all. Please clearly identify them. 13. For Sediment Basin 1, the provided dry storage volume should be calculated to the suppressed weir, not the crest of the riser, since it is the lowest outlet point after the dewatering orifice. This weir may need to be blocked to provide the necessary dry storage volume. 14. Sediment Basin 1 does not appear to be adequately designed. With a drainage area of 7.43 acres, the required total volume of the facility must be 995.62cy. To the crest of the riser (see previous comment), there is only about 500cy provided. The facility will need to double in size. 15. The downstream channel analysis (MS -19) provided by the applicant is not satisfactory and will require the following changes: a. Please refer to the latest edition of the design manual for expectations for each MS -19 analysis. For each segment in each crosssection, please provide a separate velocity. Velocities are higher in the deeper portions of the channel. Erosive velocities may be hidden due to the wider sections of the channel bringing up the average velocities. Each segment should also have identified a permissible velocity from Table 5 -22. b. It appears that for the majority of the cross - sections, the software shows velocities higher than the permissible velocities listed in Table 5 -22 for the channel linings on site. Therefore, it seems many of these segments are inadequate. Considerable reductions to outlet discharges or channel upgrades appear to be necessary. c. Concentrated water is released from this project in many more locations than analyzed by the calculations. Please provide analyses downstream from the following storm conveyance systems: Culvert D, Culvert G, SCC A and B, SCC I, SCC4, SCC C1, SCC C2, and any other point of concentrated water necessary after the SWM plan is modified to address the water quality requirement. d. All text on AQ3 is blacked out. e. The USDA soil survey identifies most of these soils on site as C/D soils. When calculating curve numbers, please use the average between C/D CN values in the Greenbook. f. Channels A, B, and C become undefined once the floodplain is reached and the water deltas to the perennial stream. Defined channels will need to be constructed from the existing channels to the perennial stream. Crossings of these channels by the trail will need to be accounted for in the plan. 16. Since this is the construction plan for the dam and the SP is primarily focused on the use, please include all hydraulic calculations for the dam in this set so they can be reviewed for adequacy. All sheets (Gloeckner and Dominion) refer to an archculvert and spillway designed "by others ". This design information must be reviewed and approved. Albemarle County Community Development Engineering Review Comments Page 4 of 6 17. The wooded area that will be temporarily inundated with water for SB -1 will need to be cleared. As part of a conversion to a Stormwater management facility, silt will need to be removed from it with existing grades established. Please include it in the limits of construction. 18. After the plans have been approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive an ESC Bond. The bond estimate request form must be signed by all property owners disturbed with this plan. Both property owners must also be party to the WPO bond that must be posted prior to a grading permit. C. Stormwater Management Plan Review (WPO- 2011 - 00094) 1. The stormwater plan shows a biofilter within the public ROW. State Law was amended to allow VDOT to approve such facilities in the ROW but only after each locality signs an agreement with VDOT and each individual situation is approved by the locality. At this time, the Board of Supervisors has not authorized the County Executive to sign this agreement. In fact, this request has not been presented to the Board. Please remove all stormwater facilities from the public ROW until such an agreement has been provided. For this reason, Biofilter 1 has not been reviewed. 2. This development does not meet Section 315.A of the Water Protection Ordinance. A very small portion of the development is being treated at all. Please revise the plan so all impervious areas that can be practicably treated are directed to a stormwater facility. As a guideline, if water is concentrated in the permanent or ESC stage, usually it can practicably be treated. 3. The required removal rate for the drainage area to SWM -1 is at least 65 %. Much of this facility's watershed goes through a biofilter before reaching this facility. However, the house site for Lot 29, more than a quarter of Shadwell Drive Extended, and half of Road A solely rely on this facility for water quality treatment. Please provide calculations for SWM -1 showing 1) that it was designed properly and 2) that the required removal rate for this watershed has been achieved with the current layout. 4. There has not been an attempt to design much of the development (approximately 60 %) to comply with 17 -314. If the applicant wishes not to provide detention for the remainder of the development, please provide a detention waiver request to the Engineering Department outlining the factors listed in 17- 314.G. 5. A sediment forebay is needed at each inflow point for each stormwater facility. 6. Stormwater facility maintenance paths must be no steeper than 20 %. For sections of the path that are steeper than 10 %, the travelway must be graveled or equivalent. The paths to SWM -1 and Biofilter 3 do not comply with these standards. The maintenance paths must also reach the sediment forebay for each facility as well. 7. SWM -1 is proposed on an intermittent stream. What is the estimated base flow? Will this disrupt the operation of the low flow orifice? 8. The hydrologic calculations assume a small of amount of impervious area for the construction of each lot. I anticipate that the development of each lot will result in more than impervious area than 4,000sf. Please provide more realistic assumptions for impervious area or place a note on each plat sheet stating that only 4,000sf of impervious area will be permitted on each lot. 9. Please add the County's General Stormwater Management Notes to the set. 10. Please provide a signed Stormwater Management/BMP Facilities Maintenance Agreement and fee to the county after reading all instructions online. 11. After the plans have been approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive a SWM Bond. D. Road Plan Review (SUB- 2011 - 00138) 1. VDOT approval is required. VDOT approval should include a statement that the state had looked at the intersection of Route 250 East and Route 709 to determine whether signs or warning lights Albemarle County Community Development Engineering Review Comments Page 5 of 6 are necessary. If such improvements are necessary, the applicant is compelled to construct them at his expense. [Condition 13] 2. Maximum street grades shall not exceed 8 %, except that, in the case of special circumstance, the Commission may, in its discretion, provide for grades not in excess of 10 %. [4 -6] Please amend the road profiles and grading plans so an 8% grade is not exceeded. 3. On all ditches of grades steeper than 5 %, please provide a paved section. [4-6] This standard applies to all ditches from the VDOT ROW to their outlet to a natural stream. The paved section must meet a VDOT standard. 4. The minimum paved radius for all culdesacs is 40ft with a minimum ROW radius of 50ft. [4 -8] 5. Please provide no less than a 20ft wide pavement section for all public streets within this subdivision per the approved application plan. 6. Please widen all public road ROW widths to 50ft. [Condition #14, 1 -43] 7. Please provide no parking signs along all streets and in all culdesacs. If VDOT will require a 24ft wide section per the current standards for streets with no parking, it will be determined by VDOT whether No Parking signs are required. [6 -1 -5, 32.5.11] 8. Please provide "No Outlet" on all streets ending in a turnaround or culdesac. [32.5.9] 9. Please label all proposed signs. 10. In all places where a slope steeper than 3:1 is proposed, please provide a low maintenance, non - grassed groundcover. Examples of acceptable groundcovers can be found in Table 3.37.0 of the VESCH. [6 -1 -12] Additionally, the slopes of all roads but Road C appear to use cut and fill slopes of 3:1, which is the county preferred maximum slope. If this is the current proposal for Roads A and B and the public roads, please modify details 3/C 13 and 4/C 13 accordingly. 11. The note set in the plan is missing at least one note from the current street note set in the County's Design Standard Manual. 12. The outlet protection dimensions are based on a slope of 0% per detail 2/C13. According to the profiles on Sheet C3, no outlet protection apron is provided at a 0 %. 1 recommend reevaluating the design of all outlets to make sure there are no issues in the field. 13. In detail 5/C13, 4ft + 7.5ft + 7.5ft + 7.5ft does not equal 50ft. Please revise. A minimum easement width of 40ft will be required of this road per Condition 14. However, in granting a variation, the Planning Director can stipulate a larger ROW width if he so chooses. 14. Please set the low point of the roadside ditch 8ft off of the edge of pavement for all private roads as had been done for the public roads. [Condition #3] 15. At Station 32, SCC -11 will need to widen. By the time the end is reached, the channel should be twice as deep and wide as the original design. The cut slope on the east side of the Road C will need to be adjusted accordingly because of the wider ditch. 16. The profiles of culverts A, B, and C do not match the calculations. 17. Please provide separate sight distance profiles for both directions coming out of Road B. 18. The immediate curve design in Shadwell Road Extended creates a danger to someone exiting the driveway of TMP 19C -A -14. Please establish sight distance and provide a sight distance easement for this driveway. [Condition #3] 19. Slopes steeper than 2:1 are not permitted. 20. Please include all details on specifying all pertinent information on the design of the archculvert in the road plan set. Please also provide a scour analysis of the culvert for the 100 -year storm. 21. County Engineering will note at this time that much of the design of the internal public streets (pavement width, minimum horizontal curve, design speed, sight distance, etc.) do not meet the current VDOT design standards of GS -SSR Shoulder and ditch section for an ADT of less than 2000. If the applicant is requesting that VDOT consider this subdivision using the AASHTO design standards for roads with an ADT less than 400, county engineering requests to be copied in all correspondence. Albemarle County Community Development Engineering Review Comments Page 6 of 6 22. The turnaround design of the two private roads deadends is currently acceptable. [Condition #3] E. Mitigation Plan Review (WPO- 2011 - 00094) 1. Please redo the calculation after comment A6 is addressed. Please note that the applicant's CAD wetland layer indicates an intermittent stream in the valley west of Clifton Court. 2. Stormwater facilities do not need to be mitigated because they are exempt if engineering review deems them necessary. Please do not include SWM -1 and other SWM facilities, if no other alternatives exist, from the stream buffer calculation. 3. Mitigation areas A4, B1, C1, and C2 provide almost no environmental benefit. Instead of planting in these areas, the applicant should look at areas on site to perform streambank stabilization (1 linear foot of stream embankment stabilization is equal 100ft of disturbed area) or planting a bare stream buffer on a nearby property. [17- 322.D.3] 4. Mitigation must be equal to twice the disturbed area. [ 17 -320.D and Design Manual] 5. There are currently canopy trees in mitigation areas Al, A2, and B2. Success rates in this area will likely be minimal for seedlings. If any additional landscaping is needed, only larger, more mature, understory plantings will be worthwhile. Even then, only partial credit will be provided because of the already established canopy trees.