Loading...
HomeMy WebLinkAboutWPO201200008 Review Comments Stormwater Management Plan 2012-03-30ALg�,�� �'IRGINZ� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: Old Trail Creekside Phase II of Phase III; Road and SWM Plans SUB - 2012 -00010 and WPO- 2012 -00008 Plan preparer: Mr. Scott Collins, PE; Collins Engineering Owner or rep.: Mr. Jackie Shifflett Date received: 17 January 2012 (Rev. 1) 9 March 2012 Date of Comment: 15 February 2012 (Rev. 1) 30 March 2012 Lead Engineer: Phil Custer The first revision to the road and SWM plans for Phase II of Old Trail Creekside Phase III, received on 9 March 2012, has been reviewed. These plans can be approved after the following comments have been addressed: A. General Review Comments 1. Bonus density was granted to this development for the dedication of open space on the assumption that a trail system was installed by the developer. While the trail standard did not seem to be specifically identified, it is clear from the review of Board of Supervisor meeting minutes that the trail must at least meet the standards of a Class B type 2 path which includes a 10% maximum longitudinal slope and a 2% maximum cross slope. These standards also require a drainage system be designed as if it were a public road. For this path, this requirement will cause a channel to be created on the uphill side of the path with culverts directing the concentrated water to the stream at adequate points. Calculations for the channels and culverts as well as a grading plan meeting the Class B Type 2 standards must be provided on the next submittal. The ESC plan must include the construction of the path within the Limits of Disturbance and protect the construction per the State Handbook. (Rev. 1) Please show a ditch on the cut side of the trail in the typical detail. Please also connect the proposed trail to the existing trail system of the previous phases of the Creekside development. 2. Details of all footbridges proposed with this plan must be provided in this set. Bridge profiles with computations showing the deck has freeboard on the 10 -year storm must also be provided. (Please note that future development plans will need to analyze the stream channel for adequacy so it is recommended that the applicant be conservative when designing the footbridge.) (Rev. 1) Some information has been provided regarding the two bridges along the trail, but it is insufficient. I could not find any hydrologic calculations, only notes stating the 2 and 10 year discharges, for bridge 1. A profile of the bridges or, in other words, cross - sections of the channels the bridges are crossing was not provided. These profiles must show spot elevations at the top of the each end of the bridges as well as the important water elevations in the channels (10 year for bridge 1, 100 year for bridge 2) with supporting channel calculations. Because bridge I is at an acute angle, please provide a 20scale detail of this crossing with all necessary spot elevations. A structural engineer must seal the bridge details with a statement describing what the design vehicles for each bridge are. For simplicity of design and maintenance, it seems that bridge 2 can be replaced with a series of higher class RCP pipes, as long as the routing calculations show an adequate 100 year freeboard. The current design of bridge 2 seems to block the emergency spillway entirely. Does bridge 1 need to be designed for a vehicle? Is this requirement coming from the County's Park and Recreation Department? 3. Please move the sanitary sewer line as far as practical away from the stream on lots 14 -16. If allowed by ACSA and VDOT, the sewer line should be able to cross the stream above the culvert when the next phase is constructed. [17- 319.B.1] (Rev. 1) Comment has been addressed. Though, the limits of disturbance in the ESC plan must be limited to not disturb more of the buffer than necessary to construct the sewer line. 4. All references to Mount Vista Lane must be replaced with Windmere Lane. (Rev. 1) Comment has been addressed. 5. Please supply a mitigation plan for the disturbance to the stream buffer proposed with this plan. [17 -321] (Rev. 1) Comment has been addressed. Please see comment section E for a review of the mitigation plan. B. Road Plan Review Comments (SUB- 2012 - 00010) 1. VDOT approval is required. At the time of this letter, VDOT approval has not been received. VDOT will need to make a determination what subdivision street standards apply to this phase, since new standards were approved in 2009. Please copy me on all correspondence with VDOT so I can be kept in the loop regarding the required road standards. (Rev. 1) Comment remains unchanged. 2. Please provide all horizontal design information (PC, PT, Radius, etc.) on S -1, or provide a new sheet with this information, so a complete road plan review can be performed. (Rev. 1) Please identify the station information in the road design tables on Sheet S -1. 3. Please show sight distance triangles on S -1. (Rev. 1) Comment has been addressed. 4. Please label the stop and street name signs at the end of Wellbourne. (Rev. 1) Comment has been addressed. 5. Please provide speed limit signs on all roads. (Rev. 1) Please provide two speed limit signs on Birchwood. 6. Please provide a note on each drainage profile sheet that IS -1 is required on all structures where there is a drop of 411, including from the surface to the bottom of the structure. (Rev. 1) Comment has been addressed. 7. Please specify a sump on structure Y -2 in the plan and profile. Please specify the grate type on the yard inlet as well. (Rev.]) Please specify the grate type of the 24" inlet. Two of the four 24" grate types offered by ADS will not work for the proposed discharge to this structure. 8. Please update the County's General Notes for Street plans. The first note refers to county inspections. The county no longer inspects streets that are to be accepted by VDOT. (Rev. 1) Comment has been addressed. 9. In plan view, the side slopes from the roadways are graded at 2:1 but are marked as 3:1 in the road sections. Please correct this discrepancy. Except at the stream crossing, I recommend the use of 3:1 slopes since these slopes are going to be in front lawns. (Rev. 1) Comment has been addressed. 10. Please show CD -1's and CD -2's in the road profiles where required. (Rev. 1) Comment has been addressed. 11. Please specify an end section and outlet protection at the end of pipe 83. Comment has been a(' 12. (Rev. 1) Please provide sidewalk on both sides of the street as required by 14 -410 and 14 -422 unless a waiver had been granted by the Planning Commission at some point. 13. (Rev. 1) A faint outline of a temporary turnaround is shown in Sheet S -1. If a possible temporary turnaround is proposed, please show in a separate detail what the grading of the roadway would be around the turnaround. C. Stormwater Management Review Comments (WPO- 2012 - 00008) The Lickinghole fee for all of Old Trail Creekside Phase III was paid with WPO -2006- 00019. The fee was processed for 48 acres of development. 2. A detention waiver for this project was granted with preliminary plat, SUB - 2005- 00259, with the condition that downstream channel calculations were provided confirming adequacy and the first 1 /2" of runoff was treated in addition to the Lickinghole fee. (Rev. 1) Please see the comments below and the adequate channel comment in Section D. 3. Please modify the biofilter bed cross - section detail so there is not a slope to the media mix. In other words, make sure the boundary between the biofilter media mix and the existing soil is a vertical line. In most facilities, a small slope is negligible to the effectiveness of the facility. But, considering the small width, a sloped biofilter bed in this facility would not operate properly. (Rev. 1) Comment has been addressed. 4. Please remove all references in the plans to "Luckstone" biofilter mix and replace with "State- Approved Mix." (Rev. 1) Comment has been addressed. 5. The two biofilter sections in the plan do not match. It seems the one in the upper left corner of SWM -1 should be removed. (Rev. 1) Comment has been addressed. 6. Nearly all volume -based stormwater quality features in the Virginia Stormwater Management Handbook require sediment forebays. Biofilters are no exception. Please provide a sediment forebay equal to 10 -20% of the bed area in this facility. A simple stone ring, similar to the outlet of the sediment trap, would suffice in separating the biofilter forebay from the main cell without any other changes to the plan being needed. (Rev. 1) Comment has been addressed. 7. Please move the spillway so that it is in cut and not over fill until the toe of the embankment is reached. (Rev. 1) Comment has been addressed. 8. There are two bridges shown in the biofilter detail. Please delete the incorrect one. The bridge will need to be relocated to address the previous comment. (Rev. 1) Comment has been addressed. 9. The Pre - Development condition must be based on what the site looked like before the approval of the previous biofilter plan. In other words, no development should be shown. (Rev. 1) Comment has been addressed. 10. Please make the length and width dimensions in the plan view detail of the biofilter detail easier to read. Please also label the proposed contours in the plan view biofilter detail. Please do not provide contour lines for any elevation below the bed elevation of 703.5. Please dash the contour line for 703.5 so the dimensions stop at a line. (Rev. 1) This comment has been addressed. The biofilter has been dimensioned as requested and the proposed bed area is acceptable, though the calculations are incorrect. 11. In the biofilter section detail, please specify an impervious core, cutoff trench, and the elevation of the 100 -year storm showing at least I ft of freeboard. (Rev. 1) A routing is necessary to confirm that the 100 year storm elevation meets standards. Specifying the type of 18" grate, and therefore the stage discharge relationship, is critical to verifying this standard through a routing. 12. The Post - Development drainage area map is not correct in the upper reaches of the watershed around Three Board Lane. (Rev. 1) The modified drainage area map is acceptable. It is understood that this map assumes the future buildout of Birchwood Drive which, at that time, it will intercept area currently draining to YD -2 and direct it to a new stormwater facility located just off of the intermittent stream. However, when determining the 100 year elevation in the facility for the previous comment, please route the worst hydrologic condition: full buildout or with the additional 2 -3 acres of meadow as shown on DP -l. 13. Before a grading permit can be issued, the WPO bond must be posted. To receive a WPO bond estimate, please provide a completed Bond Estimate Request Form to the County Engineer. Both property owners will need to sign the request document and be party to the bond and grading permit. (Rev. 1) This comment has been acknowledged by the applicant.