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HomeMy WebLinkAboutWPO201200047 Review Comments Stormwater Management Plan 2012-06-18ALg�,�� �'IRGINZ� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road, Room 227 Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: SUB - 2012 - 00057, Foothill Crossing Road Plan WPO- 2012 - 00047, Foothill Crossing ESC and SWM Plans Plan preparer: Mr. Scott Collins, PE; Collins Engineering Owner or rep.: Foothills Crossing Inc. Date received: 10 May 2012 Date of Comment: 18 June 2012 Engineer: Phil Custer The E &SC, SWM, and Road Plans for Foothill Crossing, received on 10 May 2012, have been reviewed. The plans cannot be approved as submitted and will require the following changes /corrections prior to final approval. A. General Review Comments 1. The topography does not show the 20ft tall stockpile and other things that have been disturbed since the original survey. 2. A grading permit cannot be issued for sections of the site where a road plan has not been approved. Please either reduce the scope of the ESC plan so that only a grading permit for Phases I1 and III is sought or provide road plans for all other phases. Considering the county's 9 month deadline for permanent seeding, it seems breaking up the development into constructible chunks is prudent. 3. The Phase I of Park Ridge Drive has not been completed. Several sheets in this application assume that the road has been constructed. This application will need to include the construction of this section of road in its scope. Please update all ESC and road sheets accordingly. 4. Please replace all county notes sets within the plan with the note sets in the latest edition of the design manual, available online. 5. This plan cannot be approved until ACSA approval has been provided. 6. This plan cannot be approved until Planning Department approval has been provided. 7. The Tree Preservation Areas H and J are optimistic. Even if a contractor was able to preserve a 25ft by 25ft piece of forest, there may not be any tree within it. If there were one or two trees in this small patch of land, they would be subject to much higher forces from the wind and likely would not survive. No changes to the plan are required by this comment; I'm raising this now to make the applicant aware that there may be issues in the future if the amount of tree preservation assumed in this plan are not carried out and the property is subject to a Zoning Violation. B. Road and Drainage Plan Review Comments (SUB- 2012 - 00057) 1. Please refer to Comment A.2. The applicant has only submitted road plans for Phases II and III. The road plan review focuses only on those elements contained in Phases II and III. Any comment on an aspect of the plan that deals with other phases has only been provided as a courtesy to the applicant. Please remove all information and detail from this set that is not necessary for the review and approval of Phases II and III. 2. The ADT for the eastern connector is 10,000, not 4,100. 3. The assumed ADTs and proposed pavement sections for Elk Ridge Lane and Brookstone Court are incorrect. 4. Crossings of perennial streams require box culverts or arch culverts. 5. In the plan and profile, please identify the station for start of construction (please refer to comment A.3). At this location, please also write the Roudabush and Gale Station since stationing no longer matches. 6. An ADT of 2000 for Park Ridge Drive underestimates the full buildout traffic for this road. The existing VDOT count for Park Ridge Drive between Route 240 and Western Ridge is 4000. A value closer to 3000 seems more appropriate for this segment of Park Ridge Road once the Eastern Connector is operational. This would increase the design standard for the road to the 30mph category. The cross - section, horizontal geometry, and vertical geometry are already acceptable to the 30mph Design Speed Standard. The following must be changed: the listed design speed (from 25mph to 30mph), the pavement strength, and the required sight distance onto Park Ridge Drive. 7. Please provide a stop sign and a street name sign at the intersection of Park Ridge Drive and Cardinal Crest Court. 8. Please provide at least two speed limit signs on Park Ridge Drive. 9. The designs of the stormwater structures at Sta 33 +50 and Sta. 34 +00 must be included in this plan set. 10. Inlet efficiency seems to be incorrectly calculated in one of the curb inlet tables. 11. Please increase the width of the sidewalks (and therefore the necessary ROW) along Cardinal Crest Court to 5ft. 12. Please provide overland flow relief in the event of failure of inlet 38. 13. VDOT approval is required. 14. It is recommended that a face -of -curb to face -of -curb width of 32ft is proposed for Cardinal Crest Court to comply with Fire and Rescue's latest road standard request. C. Stormwater Management Plan Review Comments (WPO- 2012 - 00047) 1. The applicant might not be fully mindful of how the county will review this property with regard to Stormwater Treatment. For all properties that drain directly to the Lickinghole Regional Stormwater Management Facility, stormwater quality is taken care of by the payment of pro -rata fee. This fee, for the entire property, was already paid in August of 2009. Therefore, the county considers stormwater quality treatment for this property already addressed. The applicant may simply convert these facilities to dry detention basins. However, if this application continues to propose water quality facilities, they must be designed according to the standards of the VSMH. The following comments have to do with review of the water quality facilities currently proposed by the applicant (the remaining comments have to do with just detention): a. This parcel is within a water supply protection area and the removal rate computation must refer to this row, not the development area row. This puts the target removal rates for facilities 1 and 2 as 70% and 57%, respectively. This causes Facilities 1 and 2 to undertreating their watersheds. b. To receive a 35% removal rate, the orifice on the extended detention facility must be sized to drain the 2xWQV in 30 hours using the equation in Chapter 5 of the Virginia Stormwater Management Handbook. The current proposal is not satisfactory. c. The forebay in the extended detention facility is not effective. Most discharges will flow through the forebay with very little settling or other treatment. 2. Overall, the setup of the detention calculations is not correct. The following comments are provided for Sheets SWM -1, SWM -2, and the overall outline presented in the detention calculations. a. On SWM -2, the northeast corner of DA -lA is not accurate; Park Ridge Road north of Cardinal Crest Court is captured in the pipe system to Stormwater Facility 1. b. On SWM -2, the applicant assumes that 50ft south of the ROW for Brookstone Court is redirected to Stormwater Facility 1 which is impractical and not even exhibited by the current grading plan. c. Stormwater Facility 2 must compensate for the free release of the increased discharge from Phase I, half of lots 9 -17, and the uncaptured portion of Park Ridge Road. This must be clearly demonstrated in the Detention Compliance Tables. d. Stormwater Facility 1 must compensate for the free release of the increased discharge from most of lots 76 -84, 39 -53, 27 -32, and the rest of the Eastern Connector that has not currently been accounted for in this stormwater management detention analysis (south of post -dev 1B). Except for a Drainage Area 1B, these free release areas seem to be ignored. Because water quality requirements are covered by the Lickinghole basin, many lots and roadways can be released freely but this increase in post - development discharge must be accounted for and mitigated by overdetention of the areas that are directed to a detention facility. This calculation must be clearly exhibited in the Detention Compliance Tables. e. In the pre - development condition, rain falling on the lagoons does not runoff. 3. The following modifications to the routings are required: a. The routing of Stormwater Facility 2 does not match the design of the lowest orifice. b. The antivortex devices should be routed "in riser" not "through dam". c. The invert used for outlet barrel in the routing should be the invert out of the riser, not invert out of the pipe. d. Please update the routings as each facility is modified. Additional comments may be required if new errors are introduced to the routing calculations. 4. All dry facilities need low flow channels from the pipe outlet directly to the riser that is sized to be non - erosive during the 2 year storm and have a minimum slope of 0.5 %. 5. Please provide more detail on what needs to be done to the riser in stormwater facility 1. There are also no orifice or elevations specified. Without the routing, which is hard to read without a familiarity with program, it would be difficult to determine all characteristics of the riser. 6. The details for both facilities show a impervious core and cut off trench, but facility 1 is already constructed. Does the contractor need to reconstruct this facility to provide the impervious core on the plan? 7. Emergency spillways must be proposed in cut. For Stormwater Facility 1, it seems a deeper spillway will likely be necessary because a 75ft spillway in cut would be impractical. The spillway to Stormwater Facility 2 simply needs to be rotated slightly. 8. Please replace all references to Trashrack Technical Bulletin #7 with a reference to the exact trashrack parameters within Chapter 2 of the Virginia Stormwater Management Handbook. 9. The perforated pipe in the extended detention facility is not an acceptable trashrack. 10. What kinds of seepage control have been constructed or proposed for Stormwater Facility 1? 11. Access to Stormwater Facility 1 must also be provided from Phase H since it will be the sole route to this facility for an indeterminate amount of time. 12. Direct vehicular access to the forebay and pipe system outlet into Stormwater Facility 1 is needed. 13. The 90 degree turn just after the 10% slope on the grass access path is dangerous and unnecessary. Please put more of a horizontal curve on this road with a consistent grade from the pipe (from Brookstone) crossing. 14. Stormwater Facility Maintenance Agreements are needed for all parcels with a stormwater facility proposed on it. Please submit these completed documents to Ana Kilmer after reviewing the information online. 15. It is recommended that the embankment of Stormwater Facility 2 is designed for a full buildout scenario of its watershed for the 100 -year storm to avoid any increase in liability for the HOA when the adjacent property is developed. 16. Once the plans are approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive a SWM bond computation. D. Erosion and Sediment Control Plan Review Comments (WPO- 2012 - 00047) 1. Please refer to Comment A.2. The ESC plan cannot be approved without all road plans approved. Considering the county's 9month deadline for permanent seeding, it seems breaking up the development into constructible chunks is prudent. 2. Please provide all state and federal permits for disturbances to streams and wetlands. 3. ESC -3 is essentially a blank sheet. ESC -2 contains the entire ESC plan crammed into one sheet at a scale that is very difficult to read and review. Please disperse the ESC information in two phases: one with existing grades and perimeter measures and the second one with final proposed contours and road infrastructure in place. Show the drainage area to each sediment trap and sediment basin for each phase and make sure each facility is sized for the phase when its drainage area is the largest. A smaller scale, no greater than 50, must also be used for each of the phases. Once the plan is clearer, additional comments may be provided. 4. Many of the diversion dikes at the perimeter of the construction site are too flat to be constructed properly, shown going uphill, or proposed perpendicular to existing gullies which will result in a blow out. Please add more sediment trapping measures, where necessary, and adjust problematic diversions so that they can be constructed with a reasonable downhill slope. The diversions west of sediment basin 5 to the western corner of the site and north of sediment trap 2 are the biggest concerns. Sediment traps or basins will likely be needed around MH 32 and MH 24. 5. Please remove the internal diversion from the site. 6. The edge of the existing pavement is a few feet after Raven Stone Road and this is where the limits of construction must begin. However, providing a construction entrance here with the existing houses on either side of the road would be difficult to achieve. Therefore, the CE(paved wash rack) must be moved farther south into the watershed of Sediment Trap 1 with a ROW diversion directing runoff across the travelway. Construction road stabilization from the edge of existing pavement to this ROW diversion will be needed for the entire width of the stream crossing. This area must remain clean from mud. 7. The construction of the stream crossing for the Eastern Connector must comply with County Engineer Commentary #5. Sediment Basin 4 can be used as one of these flanking sediment trapping measures if it is lowered considerably. 8. Please detail and provide typical VESCH references for how the construction of the stream crossing will occur. For example, will a temporary stream crossing be necessary? If so, where and what size is the crossing? 9. Sediment Basin 4 becomes isolated from half its drainage area when the construction of the Eastern Connector occurs because it will act as a diversion keeping dirty water on the eastern side of the road. Please provide another measure adjacent to the stream on the eastern side of this road. 10. There are critical issues with the design of Sediment Basin 1. First of all, the construction of the northern end of the Eastern Connector cannot be treated by the sediment basin until the storm pipe has been placed, which is unacceptable. Secondly, structure 106 becomes the low point in the facility once pipe 105 is constructed. The riser and structure 106 will be about the same elevation and water will escape out the barrel and downstream of structure 106, which is a problem. Lastly, the outlet of pipe 105 will be placed below the water elevation in the sediment basin and will be a risk of clogging. Please move the invert out of pipe 105 to at least the wet storage elevation so flushing out of the pipe can occur. As a result of these comments, Sediment Basin 1 will likely need to be moved closer to the stream. 11. In the construction sequence, there is a mention of construction of a greenway through the wooded area. Please clarify. If a greenway trail is to be constructed, please identify what standard it must meet, show all improvements for it, and include all necessary ESC measures in the ESC plan. If a greenway trail is not to be constructed by the applicant, please remove any reference to it from the plan set. 12. Please provide Inlet Protection (IP) on all inlets proposed in Phase II of the ESC plan. 13. Inlet protection for curb inlets on grade will simply cause the runoff to pass on to the next structure until a sump or basin is encountered. This would cause the drainage area to Sediment Trap 1 to increase dramatically in Phase I1. Please convert this facility to a basin sized for its drainage area from Park Ridge Road and the area to the north or design an alternative method that addresses this concern. 14. Sediment traps have a maximum height of 5ft. Please adjust the design of sediment trap to meet this requirement. 15. A diversion is needed west of Sediment Trap 1 at the edge of the limits of disturbance since the topography shows some of the disturbed area sheet flowing directly to the stream. 16. The soil boundaries are not clear on the ESC plan. It may be best to show the soil information on sheet E -1 instead. 17. The disturbance southwest of Sediment Basin 2 is not protected and seems unnecessary. Please clarify. 18. Please provide more information on Sediment Basin 3. It does not appear there is a pipe or riser in the current proposal. 19. Please remove the 15" pipe from Sediment Basin 2, if it is no longer needed, rather than plugging it in place and it being a potential maintenance issue. Replace with a metal drain valve if one is desired by the applicant. 20. Please remove details from the previous design if the details contain conflicting information as the current proposal. 21. Please provide dewatering orifice calculations. Each seems to be oversized. The calculations should use required dry volume and the height of required dry volume rather than provided. 22. Please move the note regarding the regrading of Stormwater Facility 1 from the SWM sheets to Phase 1 of the ESC plan 23. Please show Permanent Seeding (PS) symbols throughout the plan. 24. Please show staging, stockpile, and parking areas on the plan. 25. An analysis of all downstream channels per MS -19 must be provided. The applicant has shown a few cross - sections downstream of detention facilities in the plan but has not provided any analysis. Also, the cross - sections are not provided to the point that the 1% rule is reached. 26. Once the plans are approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive a ESC bond computation. All parcels disturbed with this plan must sign this bond request form and be party to the bond unless easements are recorded. E. Mitigation Plan Review Comments As was required with the previous construction plan, a mitigation plan for all non - exempt disturbances to the buffer is required. Please provide a sheet showing all proposed stream buffer disturbances (include those disturbed by Phase I as well as possible exempted disturbance), proposed mitigation planting, and a table comparing the disturbed area, minus the exempted areas (to be reviewed by the Engineering Department), and the newly planted areas. Because of changes to staffing levels, the county has not setup a program to accept dedication of stream buffers for perpetual agreements as expected shortly after 2007. That option is no longer available to the applicant.