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HomeMy WebLinkAboutWPO201600006 Plan - Revision 2014-11-19on C Mr. Max Greene County of Albemarle Department of Planning and Community Development 401 McIntire Road Charlottesville, VA 22902-4596 Dear Mr. Greene: November 19, 2014 Re: Revised Erosion and Sediment Control Plan and Stormwater Management Plan North and South Rivanna WTPs W PO201400069, W PO201400073 The Rivanna Water and Sewer Authority is proposing upgrades to the North Rivanna and the South Rivanna Water Treatment Plants (WTP). In response to review comments by the County of Albemarle, we hereby offer revised erosion and sediment control and stormwater management plans for both the North Rivanna WTP and South Rivanna WTP additions. Previous submittals to the County entered total parcel area in the "Site Data" tab of the Virginia Runoff Reduction Method (VA RRM) worksheet used to determine pollutant reduction required. Comments received from the County in a letter dated November 12, 2014 informed us, however, the area disturbed by construction activities is to be entered in this place on the worksheet. As the disturbed area is less than the parcel area for both sites, the required pollutant removal has been reduced at both the North Rivanna WTP and the South Rivanna WTP by 0.17 Ib/yr and 1.07 Iblyr, respectively (Table 1, below). As such, the stormwater requirements at each site have decreased, and a change in stormwater management has resulted. Because of the relatively small change in pollutant reduction required at North Rivanna, no changes to the proposed stormwater management BMP is proposed. As a result, North Rivanna has an excess 0.19 Iblyr nutrient removal credit, as calculated by the VA RRM worksheet. Communication with the County, as well as reference to the Code of Virginia (§ 62.1-44.19:18) have determined the excess credit is transferable between projects located within the same tributary, as the North and South Rivanna WTPs are. The excess pollutant removal credit thereby resulting from the North Rivanna WTP bioretention area, along with the decreased removal requirements at both sites, has allowed for the removal of one of the original two bioretention cells and the sand filter originally proposed for the South Rivanna WTP. The decrease in site area at the South Rivanna site means the removal Im LOWN requirement drops from 2.02 Ib/yr of pollutant to 0.95 Ib/yr of pollutant. As shown in Table 1, 0.08 Ib/yr of the excess credit generated at North Rivanna WTP will be transferred to South Rivanna WTP to offset the remaining pollutant removal and obtain compliance for the site. Table 1: Pollutant Removal Reauirements North Rivanna WTP South Rivanna WTP Previous Pollutant Removal 0.55 2.02 Resubmittal Required Ib/ (10/02/2014) Pollutant Removal 0.57 2.06 Achieved lb/ Pollutant Removal Current Required Ib/ r 0.38 0.95 Resubmittal Pollutant Removal (11119/2014) Achieved Ib/ r 0.57 0.87 Excess Credit +0.19 -0.08 Please find attached two (2) copies of drawings illustrating the additional work to the North Rivanna WTP, two (2) copies of drawings illustrating the additional work to the South Rivanna WTP, two (2) copies of a descriptive Erosion and Sedimentation Control and Stormwater Management Plan for each site, two (2) copies of the Stormwater Pollution Prevention Plan for each site, and a Virginia Stormwater Management Program (VSMP) application for each site. Please do not hesitate to contact me should you require any additional information or have any questions. Attachments Sincerely, HAZEN AND SAWYER, P.C. Corinne E. Wilson, EIT Assistant Engineer IM CM WP0201400069 County of Albemarle Department of Community Development 401 McIntire Road Charlottesville, VA 22902-4596 Attn: Max Greene Dear Mr. Greene: November 19, 2014 Re: North Rivanna WTP Improvements — W P0201400069 Response to comments Please find below response to comments made for the North Rivanna Water Treatment Plant. Also attached in this submittal are updated drawings, updated stormwater and E&S calculations, and figures. In response to comments made by the Albemarle County Department of Community Development in a letter dated November 12, 2014, Hazen and Sawyer offers the following on behalf of the Rivanna Water and Sewer Authority. A. Stormwater Pollution Prevention Plan (SWPPP) Max Greene Please have the owner fill out the required forms for the SWPPP for plan approval. The owner is the Operator until the plan is approved, the "Operator" can be transferred to additional personnel at any time during the duration of the project, see transfer forms in SWPPP. The link to the Albemarle County preferred SWPPP form is: hftp://www.albemade.org/upload/images/f`orms — center/departments/Community_Developm ent/forms/ Engineering_and_WPO_Forms/Stormwater_Pollution_Prevention_Plan_SWPPP template.doc Response: The owner has filled out the required forms for the SWPPP and the forms have been included within the SWPPP included in this submittal. B. Pollution Prevention Plan (PPP) Max Greene 1. Appears adequately addressed at this time. Response: Comment noted. C. Stormwater Management Plan (SWMP) Max Greene 1. VRRM updated spread sheet appears to be for 5.2 acres of disturbance. The VRRM spreadsheet should be for the proposed new construction/ disturbed area. The drainage area to the water quality structure appears to be @ 3/ of an acre. Please Correct the VRRM Spreadsheet and show the drainage areas on the plan for conformation. 0"M cm Response: The VRRM spreadsheet has been adiusted to the area of disturbance rather than the parcel area. As a result, the stormwater results have been adiusted as detailed in the narrative. D. Erosion and Sediment Control Plan (ESCP) Max Greene 1. The Variance for the Modified Mud Traps is approved for this project due to the confined space on site and proximity to the flood plain. Response: Comment noted. 2. Narrative/introduction is incorrect. a. It is impossible for the North Fork Rivanna Treatment plant to source water from the South Fork Rivanna River Reservoir. b. Adjacent areas are incorrect. This parcel does not have boundaries with the South Fork Rivanna Reservoir. c. The property does not slope towards the South Fork Rivanna Reservoir. d. Off -site stormwater issues are to protect the North Fork Rivanna River from sediment laden runoff. e. The permanent measures proposed will need to include the bio-retention basin. Response: The narrative has been updated to reflect the correct conditions of the North Rivanna Water Treatment Plant. Two (2) copies of the revised plans, calculations, narrative, and SWPPP have been provided, illustrating the responses above. We trust this information will allow you to complete your review for this application. Please do not hesitate to contact me with any questions or concerns. Sincerely, HAZEN AND SAWYER, P.C. G"�� . V/-�- Corinne E. Wilson, EIT Assistant Engineer