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HomeMy WebLinkAboutWPO201100071 Review Comments Erosion Control Plan 2012-03-02ALg�,�� �'IRGINZ� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: WPO- 2011 - 00071, RE- Store'n Station ESC Plan Plan preparer: Mr. Nat Perkins, PE; NP Engineering Owner: Jefferies IL LLC Owner's Rep.: Mrs. Jo Higgins; Project Development Limited Date received: 31 August 2011 (Rev. 1) 14 February 2012 Date of Comment: 15 October 2011 (Rev. 1) 2 March 2012 Engineer: Phil Custer The first revision to the ESC plan for the RE- Store'n Station (WPO- 2011 - 00071), received on 14 February 2012, has been reviewed. The plan can be approved after the following comments have been addressed: 1. It appears that the ESC Plans were all printed at 30scale, not 40. If this is correct, please replace all references to 40 scale with 30 scale. (Rev. 1) Comment has been addressed. 2. On all three phases, please clearly show and label the limits of disturbance boundary. (Rev. 1) In phases I and 2, extend the limits of disturbance around the outlet protection below the sediment basin. In phase 2, show the limits into the VDOT ROW. In phase 3, show limits of disturbance. 3. Please show all proposed grading on Phase 2 and Phase 3. It is difficult to evaluate the adequacy of these phases without proposed contours. Additional comments may be necessary because the plan was not able to be fully evaluated. (Rev. 1) In phase 3, please show the proposed grade lines for the fill required to provide the proper cover over the detention facility and the final proposed grading in the area of the sediment basin after it is removed. An adequate channel will need to be provided in the area previous disturbed by the sediment basin. 4. Related to the previous comment, the sediment basin and sediment trap should be sized for the largest watershed each facility will likely experience as the site is filled in. For instance, the site will likely be tipped towards the sediment basin, since the stormwater facility is located in the vicinity, so its drainage area will increase as the earthwork progresses. (Rev. 1) The sediment trap drainage area is larger than the watershed shown in the plan. Free Town Lane does not divert water away from this trap as the map implies. Since the last submittal, structure 7B was added which indicates a larger watershed to the sediment basin than designed. Please account for this acreage in the calculations. Also, when the design of the sediment basin was modified, an error was made with regard to the embankment. According to the calculations, the top of embankment must be 691, but the plan is graded to show an embankment top of 690. Please correct. An embankment width of at least 6ft is required. Silt fence is frequently proposed perpendicular to contour lines in this plan which is not allowed per state guidelines. In these instances, water will not travel through the fence but will be redirected downhill, like a diversion. Please replace the silt fence on the east side of the property line with a diversion from the northeast corner to the sediment trap. On the west end of the property, please simply remove the silt fence. If a visual boundary is desired by the applicant, I recommend a type of safety fence. (Rev. 1) Comment has been addressed, though the first step in the construction sequence was not modified accordingly. It seems step 3 can refer to silt fence. Similarly, the construction sequence still refers to raintanks, which have been eliminated with this application. The contech structures should be installed after the site has been stabilized, in phase 3. 6. Please remove the silt fence from directly below the outlet of both settling facilities. Silt fence cannot receive concentrated flow. (Rev. 1) Comment has been addressed. During the review of the preliminary site plan, the Chief of Current Development, Bill Fritz, approved the disturbance of a 20ft wide section of the undisturbed buffer to the south. Please show the area of the buffer that was approved for disturbance. It appears that the area shown on this submittal does match the area approved by Bill. If the area proposed for disturbance is, in fact, different, another waiver of this disturbance may need to be processed. (Rev. 1) In this ESC application, the center of the 20ft of allowable disturbed buffer is 99ft from the property corner. In the approved preliminary plan, the center of the 20ft buffer is 74.5ft from the property corner. The disturbed area of this buffer was moved. However, Bill Fritz has determined that this change does not negatively affect the previous approval and the revised location is acceptable. The embankment of the sediment basin ties into existing grade within the undisturbed buffer (see where the 676 contour line would be). Please modify the plan to make sure no disturbance to the undisturbed buffer occurs, other than the area previously authorized. (Rev. 1) Comment has been addressed. 9. In plan view, please draw the sediment basin bottom as 671. (Rev. 1) Comment has not been addressed. Please draw the 671 contour line in the sediment basin and modify the bottom dimensions to meet this contour line. Update the sediment basin bottom dimension reference in the embankment detail accordingly. 10. Please show Permanent Seeding (PS) symbols throughout the plan where necessary. (Rev. 1) Comment has been addressed. 11. Please include the county's paved wash rack detail in this sheet set. This detail can be found in the county's design manual on page 28 of 35. (Rev. 1) Comment has been addressed. 12. The county has updated its standard ESC Note set. Please use the latest version found in the county's design manual. (Rev. 1) Comment has been addressed. 13. An analysis of the downstream channel per Minimum Standard 19 was not provided with the ESC plan. Please refer to page 7 (of 35) of the County's Design Manual and the Virginia Erosion and Sediment Control Handbook for what the county expects for an analysis of downstream channels. Per state law, this analysis must be performed using the 24 -hour storm. (Rev. 1) Comment has not been addressed. A downstream channel analysis is required in any situation where the velocity, peak rate, or volume of runoff is increased in a development. Normal detention does not eliminate the requirement for the applicant to check downstream channels because volume is increased unless a significant amount of infiltration is provided. If an analysis cannot be performed, the applicant must proceed as if an inadequate channel is present and provide over - detention meeting State Code Section 10.1 -561. 14. Please provide the cross - sections and calculations (2 -year velocity and 10 -year capacity) for the new VDOT ditch. Please specify any liner, if necessary. (Rev. 1) Comment has not been addressed. The response to this comment in the applicant's letter refers to the placement of north arrows on the plan. 15. To receive a bond estimate, please provide a completed Bond Estimate Request Form to the County Engineer after all comments have been addressed. All owners of properties disturbed with this application must sign this document and be party to the bond unless all offsite easements are recorded. The easements must be written in a manner that allows the county and its assigns to the construction site. (Rev. 1) WPO bond amounts will be calculated after plan approval.