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HomeMy WebLinkAboutWPO200900017 Review Comments Stormwater Management Plan 2009-06-15� 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: Plan preparer: Owner or rep.: Plan received date: Date of comments: Reviewer: Wal -Mart Major Amendment Dewberry & Davis, Inc. Wal -Mart Real Estate Business (Rev. 1) 18 May 2009 14 April 2009 (Rev. 1) 15 June 2009 5 May 2009 Phil Custer [SDP- 2008 - 00028, WPO- 2008 - 000171 The site plan amendment, ESC, and SWM plans for the Wal -Mart Expansion Project, received on 18 May 2009, have been reviewed. Comments for all three plans are provided in this letter. A. Final Site Plan [SDP- 2009 - 00028] 1. On sheet C2, please note the date and source of the topography. (Rev. 1) Comment has been addressed. 2. On sheet C2, please shade all critical slopes. A waiver is needed for critical slope disturbance. Engineering review of the critical slope waiver request is provided in a separate document. (Rev. 1) Comment has been addressed. 3. The steepest slope allowed in the County is 2:1. All slopes steeper than 3:1 must have a low maintenance, non -grass groundcover. Though there are no slopes shown with proposed contours that fall into these categories, it is safe to assume that the steep slopes uphill of new walls will be disturbed. When the slopes are restored, show the proposed grading and make sure all slopes steeper than 3:1 have a low maintenance, non -grass groundcover. (Rev. 1) Comment has not been addressed. The extent of the slope disturbance has not been shown on either the grading plan or the wall detail sheet. The impacts to this slope must be determined before many of these comments can be addressed. When the slope uphill of the wall is restored it cannot be restored to existing grade because some slopes are steeper than 2:1. Please show restoration grading and propose low - maintenance groundcover on any slope steeper than 3:1. 4. Please show topography (existing and proposed, if necessary) and top of wall spot elevations on the wall detail on sheet C4.1. All segments of the wall taller than 4ft will require a safety railing. Please show this on the wall section detail and plan view. (Rev. I) Comment has been addressed. 5. On sheet C4.1, please show a dashed line on the plan where the back base of all walls will approximately be located. (Rev. 1) Comment has not been addressed. The extent of the slope disturbance has not been shown on either the grading plan or the wall detail sheet. The impacts to this slope must be determined before many of these comments can be addressed. 6. VDOT approval is required. At this time, VDOT approval has not yet been received. (Rev. 1) VDOT approval has not yet been received. 7. Engineering has reviewed the traffic study prepared by Ramsey Kemp and has some concerns with the calculations and findings. The appendix showed several movements within the study area with Albemarle County Community Development Engineering Review Comments Page 2 of 6 a level of service of E. The applicant should investigate possible improvements to bring those movements up to a level of service of at least D. The County's review of the study also questions whether a bypass reduction should be used for traffic on Hilton Heights Rd. In addition, the county believes the increase in peak hour traffic is underestimated because the TTE estimate for PM peak hour generation (370, considering bypass reduction) is well below the existing traffic counts for peak hour trips into and out of the site (607 4PM -5PM and 597 5PM -6PM). (Rev. 1) The applicant's traffic study acknowledges that after the Walmart building expansion, three turning movements affected by development (Left and Thru from EB Hilton Heights and Left from NB 29) will be operating at an E Level of Service, which is considered by engineering review to not meet Section 18- 32.7.2 (Safe and Convenient Access). Engineering review recommends that the site plan not be approved unless the applicant addresses the delay experienced for the affected movements at the surrounding intersections. Is this plan proposing to close the garden entrance? After visiting the site and watching traffic enter from Hilton Heights Road for a few cycles, I am concerned that pedestrians utilizing this northern entrance results in longer queues at the traffic light. Cars turning left into the parking lot may be forced to wait in the intersection as pedestrians enter and exit the building. Can this entrance be closed or can foot - traffic in this area be controlled? (Rev. 1) On sheets 3 and 4, please provide a note at the east corner of the building that the garden entrance will be permanently closed and that no public entrance to the building will be provided 125ft of this building corner. 9. All parking rows must be protected by a curb island of a 311 minimum width. Exceptions can be made in the area of the handicap spaces as long as bollards are located at the corners of the pavement hatching. Other than the handicap parking area, there are two instances where a curb island is required. (Rev. I) Comment has been addressed. 10. Because of the bollards at the end of the spaces in the parking area north of the building, the 18ft minimum depth is not provided. It appears as though the spaces are only 16ft long. Please provide 18ft long parking spaces in this area or request a waiver from the Zoning Administrator. Engineering review will not recommend approval of this waiver. (Rev. 1) All bollards have been removed. Please provide a bumper block for the parking space east of the 6ft wide MS -1. 11. Please provide a sidewalk on the southern side of the parking lot from the bus stop to the sidewalk along Route 29. [18- 32.7.2.8] The sidewalk must be a minimum of 5ft. If bumper blocks are not used when sidewalk is adjacent to perpendicular parking, the width must be 6ft. (Rev. 1) Comment has not been addressed. The sidewalk from the bus stop must be a full 5ft in width until the sidewalk along Route 29 is reached. If bumper blocks are not provided for the parking spaces adjacent to the sidewalk, then the width must be 6ft. The sidewalk should be aligned through the existing hole in the vegetation at the front of the site. Please provide a note on the plan that all trees in the area are to remain undamaged and no more than one juniper will be removed if necessary. Please also show the sidewalk on the landscape plan. The existing shrub bed shown on sheet 7.0 should remain. 12. With the current grading, the truck entrance will intercept most of the drainage area to the VDOT inlet and direct it into the site. Please provide a new curb inlet uphill of the entrance or modify the grading so a 4in/hr storm will continue draining to the existing DI -3 inlet. (Rev.]) On sheet 4 please provide the CG -9D callout note. The grading for the travelway also does not match the necessary vertical geometry of a CG -9D. Please provide a vertical profile detail for this entrance to verify that the all CG -9D standards are met. 13. Please reduce the truck exit travelway grade to 10% or flatter. (Rev. 1) Comment has been addressed. Albemarle County Community Development Engineering Review Comments Page 3 of 6 14. Please provide at least four spot elevations on the compactor pad showing that water does not run across it. (Rev. 1) Comment has been addressed. 15. Please provide pavement sections for all new or replaced pavement. (Rev. 1) Comment has been addressed. 16. Please provide typical sections for sidewalks and the compactor pad. These sections must be at least as strong as the sections described in the checklist of the County's Design Manual. (Rev. 1) Please specify the concrete for the sidewalk as 3000psi at 28 days or stronger. Please callout on the compactor pad detail that the heavy duty concrete section must be utilized. 17. Please provide the Albemarle County General Construction notes in the plan set. (Rev. 1) Comment has been addressed. 18. The modified inlet between the northern entrance and the truck exit must be a VDOT standard inlet. It appears that a DI -1 is best suited for this retrofit. (Rev. 1) Comment has not been addressed. 19. Please show the proposed grade in the drainage profiles. (Rev. 1) Comment has been addressed. 20. Please show the depth of MH -1 in the drainage profile. (Rev. 1) Comment has not been addressed. 21. There is a discrepancy in the label of MH -2 between the profile and sheet C4. (Rev. 1) Comment has been addressed. 22. In a parking lot drainage system, all changes in direction or slope require a VDOT standard manhole or inlet. (Rev.]) Please show the manifold risers in the drainage profile. These structures must be a VDOT Standard MH -1. 23. Please label the material and strength class for each pipe in the drainage system. (Rev. 1) Comment has been addressed. 24. The minimum diameter of a private drainage system is 12 ". Engineering review recommends a minimum pipe diameter of 15 ". (Rev. 1) Comment has been addressed. 25. All flow drops of 4ft or greater (surface to Inv Out or Inv In to Inv Out) require inlet shaping (VDOT Standard IS -1). Please specify IS -1 on all necessary structures in the drainage profiles. (Rev. 1) Comment has been addressed. 26. All new structures taller than 12ft require VDOT Standard SL -1. (Rev. 1) Comment has not been addressed. 27. A drainage area map has been excluded from this submittal. Please submit an inlet drainage area map which includes: drainage area lines to proposed structures and channels, acreages for each drainage area, hydrologic coefficients matching calculations, time of concentration for each drainage area, and the structure label. (Rev. 1) Comment has been addressed. 28. Please specify the dimensions of the concrete ditch and provide capacity calculations. (Rev. 1) Comment has been addressed. 29. Please provide headwater analyses for all new grate inlets. Please show spot elevations around DI- 5 showing that sufficient headwater is provided without backing water up into the walkway. (Rev. 1) Comment has been addressed. B. Stormwater Management Plan [WPO- 2009 - 00017] 1. Before the plan can be approved, the applicant must submit a completed, signed Stormwater Facility Maintenance agreement and fee. This document is available online document and procedures). For any questions regarding this process, please contact Pam Shifflett at 434 -296- Albemarle County Community Development Engineering Review Comments Page 4 of 6 5832 x3246. (Rev. 1) Comment has not been addressed. 2. Please submit an approval letter from Filterra. (Rev. 1) Comment has not been addressed. 3. Please provide drainage area maps of the existing and proposed condition to confirm detention compliance. Each map should include: the drainage area from the point of analysis, acreage of the drainage area, average hydrologic coefficient, and time of concentration used. Without these maps, it is difficult to verify that the calculations are accurate. (Rev. 1) A drainage area map with the required information has been received but it will likely need to be revised based on comments to follow. 4. It appears as though the new impervious area is not being treated. Instead, the applicant is proposing to treat existing impervious areas within the parking lot. Please provide a separate exhibit showing that the drainage areas treated by the Filterras are equal to or greater than the new impervious area. (Rev. 1) Please remove water quality structures 2 and 8. It is unlikely that their proposed locations will intercept much water with the current grading. Water quality requirements will be met by keeping the remaining 6 structures on the plan. 5. Please provide the County's General Construction Notes for Stormwater Management Plans in the set. (Rev. 1) Comment has been addressed. 6. The detention pipes must be accessible at each end of the facility. The control orifice should be easily accessible. (Rev. 1) The minimum diameter outlet pipe is 15in. Also, the detention system should be arraigned in a way so that if the control orifice is clogged with debris it is easily accessible for maintenance. Right now, a clogged orifice would require someone diving into the manhole. 7. Trash racks are required on all orifices. (Rev. 1) Comment has been addressed. 8. The detention calculations are unclear and will require modifications. a. There are a few pages that analyze runoff from the entire site. The analysis should be restricted to the watershed of the detention facility. (Rev. 1) Comment has been addressed. b. It does not appear the 2 -year storm was routed. (Rev. 1) Comment has been addressed. c. The input data for on sheet 1 of 16 does not appear to match the characteristics of the proposed detention facility. (Rev. 1) The drainage area to the detention facility as shown is 1.47 acres, not 0.88 acres. The inputs will change based on other requrements. d. Included in the calculation packet is a stage- storage table that appears to compute the volume of a singular 5ft diameter pipe that has no slope when the proposed system is two 411 pipes at a 0.5% slope. I recommend using a routing program that can route pipe detention systems more easily. If requested, I can also provide you with a stage- storage table computed by the program the County uses. (Rev. 1) Comment has been addressed. e. The program states that the storm being routed is the 24 hour storm, which usually has a peak of around 12 hours, but the routing results looks as if the Modified Rational Method was used. If the Modified Ration Method is used, the applicant must show that the critical storm was routed. (Rev. 1) Routing results are unsatisfactory. The applicant must route the facility using the modified rational method (using the critical storm) or the SCS method. Albemarle County Community Development Engineering Review Comments Page 5 of 6 f. The precipitation depth (P) for the 2 and 10 year storms in Albemarle County are 3.7in. and 5.6in. (Rev. 1) Comment has been noted by the applicant. 9. Please clarify how rainwater from the new roof is directed to the detention system. (Rev. 1) The county is compromising with this application by not requiring an MS -19 analysis as long as detention is provided to the maximum extent possible for the proposed building addition. Please either relocate the detention system and detain using a 3" orifice or find a way to route the building addition to the south and into the detention system at its current location. Otherwise, a full adequate channel analysis will be required. 10. The SWM portion of the WPO bond will be calculated at the time of plan approval. (Rev. 1) Comment remains unchanged. C. Erosion and Sediment Control Plan [WPO- 2009 - 00017] 1. Please provide more detail as to how the 30ft wall is to be constructed. It appears that a grading /construction easement will be needed onto the adjacent property unless pilings are used. The smaller wall between Sta. 0 +00 and 0 +90 may also require a temporary construction easement on the adjacent property. (Rev. 1) Please provide a note on both phases of the ESC plan in the area of both walls that the contractor is responsible for installing and maintaining appropriate shoring to construct the walls within the property boundaries. A temporary safety fence should also be shown at the property boundary. 2. Please include in the set the County's General Construction Notes for Erosion and Sediment Control Plans. (Rev. 1) Comment has been addressed. 3. Please reduce the limits of construction to only the area being disturbed. For instance, the western slope does not need to be included in the limits of disturbance. Also, since no earthwork is being done in the majority of the parking lot, show limits of disturbance only around the islands and curbing that will be replaced. (Rev. 1) Comment has not been addressed. 4. Please provide a construction entrance on the plan. (Rev. 1) Close and fence off the traffic aisle between the two fenced construction areas all the way to the edge of the existing building. Provide a note on the plan that the existing entrance aisle is to be used as the construction entrance. The onsite ESC and Zoning inspectors can authorize the opening of this traffic aisle if they feel vehicles can be safely managed through the construction area. 5. Please show a realistic staging and parking area on the plan. The size of this area should be coordinated with zoning /planning to make sure adequate parking is maintained during construction. This staging /contractor parking area must be fenced off from the public parking lot during construction. The temporary fencing should also be provided around the top of the cut behind all walls. (Rev. 1) A temporary safety fence around the top of cut for the wall adjacent to the building addition is required. 6. Please provide ESC symbols PS, TS, and DC on the plan where applicable. (Rev. 1) Comment has been addressed. 7. Please show all trees to be saved on the ESC plan with tree protection fencing at the drip line. (Rev. 1) Comment has been addressed. 8. Please provide a detail showing the existing soil boundaries. The plan appears to group several soil types in the same area. (Rev. 1) Comment has been addressed. Albemarle County Community Development Engineering Review Comments Page 6 of 6 9. The maximum drainage area for inlet protection is 1 acre. This comment will be confirmed once an inlet drainage map is submitted. (Rev. 1) Comment has been addressed. 10. Please provide an adequate channel analysis meeting all of the requirements specified in the County's Design Standard Manual. Alternatively, the applicant may overdetain with the facility as sited by routing the 2 and the 10 year flows through a 3inch orifice. (Rev. 1) The county is compromising with this application by not requiring an MS -19 analysis as long as detention is provided to the maximum extent possible for the proposed building addition. Please either relocate the detention system and detain using a 3" orifice or find a way to route the building addition to the south and into the detention system at its current location. Otherwise, a full adequate channel analysis will be required. 11. The ESC portion of the WPO bond will be calculated at the time of plan approval. (Rev. 1) Comment remains unchanged.