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HomeMy WebLinkAboutWPO201200008 Review Comments Erosion Control Plan 2012-04-03ALg�,�� �'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; ESC and Mitigation 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) 3 April 2012 Lead Engineer: Phil Custer The first revision to the ESC plan for Phase II of Old Trail Creekside Phase III, received on 9 March 2012, has been reviewed. The first submittal of the mitigation plan has also been submitted. These plans can be approved after the following comments have been addressed: D. Erosion and Sediment Control Review Comments 1. The maximum watershed for a diversion dike (DD) is 5acres. Please replace the DD on the west side of the construction limits with a designed diversion (DV) channel. Please provide calculations supporting the size of it. Please alter the horizontal placement of it so a minimum slope of 0.5% is provided and no fill is required to construct it. (Rev. 1) Comment has been addressed. 2. Please show a Construction Entrance (CE) in phase H. (Rev. 1) Comment has been addressed. 3. In both phases, please provide a RWD across the construction entrance and provide a DD to the sediment basin. (Rev. 1) Comment has been addressed. 4. Please show the maximum drainage area to sediment trap 1. The two maximum drainage areas should overlap because of changes to the watershed from Phase 1 to Phase 2. (Rev. 1) The plan is acceptable as ST -1 is sized though it appears the drainage areas are shown incorrectly in Phase H. 5. The baffle does not increase the flow path as much as intended by the applicant. (Rev. 1) Comment has been addressed. 6. Please provide Inlet Protection (IP) on structures 38 and 3813. (Rev. 1) Comment has been addressed. 7. Please label the scale of the sediment basin detail. (Rev. 1) Comment has been addressed. 8. Please move the spillway so that it is in cut and not over fill. (Rev. 1) Comment has been addressed. 9. Please clarify the 25 -year freeboard analysis on the sediment basin. When looking at Table 3.14.0 and Plate 3.14 -8, it seems to me the freeboard on the 25 -year storm is less than lft. (Rev. 1) Comment has been addressed. 10. Please update the County's General Notes for Erosion and Sediment Control plans. (Rev. 1) Comment has been addressed. 11. Please provide outlet protection at the end of pipe 83. (Rev. 1) Please provide the label (OP) on the plans. 12. Adequate channel calculations have not been provided. Please refer to the latest edition of the County's Design Manual for expectations for the submittal of adequate channel calculations. (Rev. 1) I could not locate any adequate channel calculations. The only change to the plan that I can find with regard to concerns with adequate channels is the addition of the level spreader at the base of the biofilter. Because of the size of the Creekside development (-72 acres) compared to the drainage area to Lickinghole Creek at this site (3100 acres), an analysis of the perennial stream itself will not be needed. In the next phase of development, however, an analysis of the intermittent to Lickinghole Creek as well as a biofilter at the outlet of pipe 83 will be required. But to satisfy adequate channel concerns now, please provide a new adequate channel from pipe 83 to the intermittent stream and a new adequate channel from the outlet of the biofilter to Lickinghole Creek. A level spreader is not appropriate to use with such a steep and uneven (trunks and root mats) downstream condition. 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) Comment remains unchanged. 14. (Rev. 1) 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. E. Mitigation Review Comments (First review occurred 2 April 2012) 1. Please provide an overall graphic of the site that compares all proposed buffer disturbances with areas to be planted for mitigation. For each disturbed and planted area in the graphic, please identify the acreage. Please also provide a table summing the total acreage disturbed and planted. Please note that construction of sewer lines is exempt from stream buffer disturbance, as long as it is deemed practical by engineering review, and therefore it does not need to be included in the computation. Stormwater facilities and channels are also allowed within stream buffers without mitigation at the discretion of the engineering department. 2. Per comment A3, disturbance west of the sanitary sewer easement is not authorized. 3. In the mitigation plant list on M -1, please break up the plantings by type (shade tree, understory tree, shrub, and groundcover) so that it can be compared to the required planting detailed on page 12 of 35 of the design manual. Please make sure each proposed planting is specified at the size listed on that page. 4. Before areas outside of the stream buffer may be planted for mitigation, all non - forested areas within the buffer, but outside of sanitary sewer easements and the trail, must be planted first. For instance, the proposed plantings from the area outside of the buffer on the west side of the stream must be moved to areas in the buffer that are not forested. 5. Many trees are proposed within the sanitary sewer easement. ACSA will likely not allow anything more than shrubs within this easement. 6. A conservation seeding mix, bluestem, and switch grass are not acceptable independent forms of mitigation. These can be installed between the larger plants as a groundcover. Credit will be given for only the three landscape options listed on page 12 of 35 of the design manual.