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Home My WebLink AboutSW1221002_Response To Comments_20231208 Gresham ` Smith December 7, 2023 Mr. Jim Farkas NCDEQ 512 North Salisbury Street Raleigh, NC 27699-1612 Subject: Asheville Regional Airport Terminal Modernization and Expansion Asheville, NC Gresham Smith Project Number: 43483.02 Dear Mr. Farkas: The following are Gresham Smith responses to your comments from your email dated November 21, 2023 regarding Asheville Regional Airport Terminal Modernization and Expansion. 1. Comment: Please provide the SHWT Elevation. Please use the borings provided as part of the 7/11/2022 geotechnical report as these borings were taken within the footprint of the proposed SCM and report the depth to the SHWT (not just the depth to encountered water as this fluctuates over time whereas SHWT is more constant and what the MDC requires). The two borings from the 7/11/2022 geotechnical report indicate the depth from the existing ground surface to the SHWT so in order to determine the elevation of the SHWT,the elevation of the existing ground surface for these two borings needs to be provided. Please provide these two existing ground surface elevations and update the Supplement-EZ Form (and any other submittal items) needed to reflect this SHWT elevation. 222 Second Avenue South GreshamSmith.com Suite 1400 Genuine Ingenuity Nashville,TN 37201 615.770.8100 Jim Farkas State Stormwater Engineer DEMLR Post-Construction Stormwater Program December 7,2023 Response: The 7/11/2022 geotechnical report indicates minimum depths for the SHWT at borings Ksat-1 and Ksat-2. At the time of the borings, the existing surface elevation at Ksat-1 was 2119.00 and 2119.38 at Ksat-2. From the geotechnical report, the SHWT is noted as a minimum of 36" from the surface elevation at Ksat-1, which correlates to a maximum SHWT elevation of 2116.00. Additionally, the SHWT is noted as a minimum of 34" from the surface elevation at Ksat-2,which correlates to a maximum SHWT elevation of 2116.58. The existing ground elevation at the boring locations, prior to the South Apron Expansion Project in May 2020, was 2103.87 at Ksat-1 and 2112.61 at Ksat-2. These are based on the existing survey file used for the design of project SW1190702 by Parrish and Partners. Therefore, due to fill being placed during the May 2020 project SW1190702, it is assumed to be extremely unlikely the SHWT reaches above the existing ground elevation prior to fill being placed.As a conservative assumption,the SHWT has been listed as 2112.61. Please see the boring elevations exhibit included with this resubmittal for boring locations and elevations for the two topographical surveys, dated September 2019 and September 2020. 2. Comment: Please provide a sealed hard copy of the calculations (This item is required per 15A NCAC 02H .1042(2)(f)).The provided hard copy of the calculations were signed, but not sealed. You can just provide a signed &sealed hard copy of the cover page and we can slipsheet it into the full hard copy of the calculations that we currently have. Response: A signed and sealed cover page of the drainage report has been included with this resubmittal. 3. Comment: The percent BUA for the dry pond does not appear to be calculated correctly. Unlike with the project area,the drainage area of an SCM cannot exclude existing BUA from the density calculation (per 15A NCAC 02H .1003(3)(b)). Please make the following changes: o Application, Section IV, 10, Drainage Area Column 1: ■ Proposed Impervious Area - Change the provided value (33,842 sf) to 215,541 sf to account for the existing BUA within the DA. ■ Percent Impervious Area - Change the provided value (54.50%) to 88.41% to account for the existing BUA within the DA. ■ Existing BUA - Change the provided value ("-" sf) to 181,699 sf to account for the existing BUA within the DA. ■ Total - Change the provided value (33,842 sf) to 215,541 sf to account for the existing BUA within the DA. Page 12 Jim Farkas State Stormwater Engineer DEMLR Post-Construction Stormwater Program December 7,2023 o Supplement-EZ Form, Drainage Area Page, Dry Detention Pond Column: ■ Line 18 - Change the provided value (55%) to 88% to account for the existing BUA within the DA. Response: Application, Section IV, 10, Drainage Area Column 1 has been updated to list 215,541 sf for proposed impervious area, 88.41% for percent impervious area, 181,699 sf for existing BUA, and 215,541 sf for total impervious area. Supplement-EZ Form, Drainage Area Page, Dry Detention Pond Column has been updated to list 88% for percent impervious area. 4. Comment: Supplement-EZ Form, Dry Pond Page, Line 29 - This cell automatically rounds to the nearest whole inch (2") whereas the proposed orifice diameter is 1.9". Please either manually correct this cell of the spreadsheet (to show 1.9") or specify in the Additional Information (Line 37) that the actual drawdown orifice diameter is 1.9". Response: Supplement-EZ Form, Dry Pond Page, Line 29 has been updated to show the accurate orifice diameter of 1.9". 5. Comment: Please provide the following: - 1x hard copy & ix electronic copy of the existing ground surface elevation for the two borings from the 7/11/2022 geotechnical report (to determine the SHWT elevation). - 1x hard copy & ix electronic copy of the revised pages of the Supplement-EZ Form. - 1x hard copy & 1x electronic copy of the revised pages of the Application. - 1x hard copy & 1x electronic copy of the revised pages of the calculations (signed &sealed). - 1x hard copy (2x hard copies for plans) & ix electronic copy of anything else needed to address these comments. Response: The above information has been included with this resubmittal. 6. Comment: Hard copies should be mailed to me at the following address: For FedEx/UPS: Jim Farkas 512 N. Salisbury Street, Office 640M Raleigh, NC 27604 For USPS: Jim Farkas 1612 Mail Service Center Page 13 Jim Farkas State Stormwater Engineer DEMLR Post-Construction Stormwater Program December 7,2023 Raleigh, NC 27699-1612 Hand Delivery: Please reach out to me prior to hand delivering a submission to make sure that I (or someone else in my group) will be able to receive the submission. Do not leave the package in the foyer with the security guard. NOTE: Hard copies should not be sent to a Regional Office. Doing so will delay the review process and the submission package may be lost while being sent from the Regional Office to me in the Central Office. Electronic copies should be uploaded at the following location: https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload Response: Acknowledged. If you have any questions, please do not hesitate to call me at 615-770-8155. Sincerely, Nathan Hudgens, P.E. Gresham Smith Page 14