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Home My WebLink AboutSW5200602_Responce to Comments_2020082091st� �:srvi,cs Ilune. ® Sta nt@C 227ArysIeyTown Blvd. Suite 300, Charlotte, NC 28273 August 14, 2020 File: 178440214 Attention: Mr. Jim Farkas North Carolina Department of Environmental Quality Division of Energy, Mineral, & Land Resources - Stormwater Program 512 N. Salisbury Street 1612 Mail Service Center Raleigh, NC 27699 Dear Mr. Farkas, Reference: Comment Response Letter This is our response to comments received from your office on July 15, 2020. We have reviewed these comments and respond in the following manner: 1. Since this project is not claiming vested rights, Section IV, 2b should not be checked off. Revised 2. The River Basin shown in Section IV, 3 should just be "Tar -Pamlico". Revised 3. The drainage area information shown in Section IV, 10 should only be an accounting of the areas that drain directly to the proposed SCMs, not the study points. This is also true for the drainage areas in the Supplement-EZ Form. Updated. 4. Please provide additional calculations (Section VI, 7). Additional calculations should include the following: a. Since this project drains to a Nutrient Sensitive Watershed (NSW), please provide calculations showing that the requirements outlined in 15A NCAC 02B .0731 have been fully addressed. Used Snap to model Nitrogen and phosphorus annual loading and by utilizing SCMS such as proposed sandfilters and level spreader filter strips, 15A NCAC 02B .0731 rule has been met. b. Calculations showing that the inlets and outlets of the proposed SCMs are stable (General MDC 4). August 14, 2020 Mr. Jim Farkas Page 2 of 5 Reference: Comment Response Letter ST added to the stormwater calculation report. Summary shown on sheet C-603. c. Design volume calculations. The design volume should be calculated using either the Simple Method (For the entire drainage area to the proposed SCM) or the Discrete NRCS Curve Number Method (Using both the pervious and impervious portions of the entire drainage area to the proposed SCM). More information can be found in Part B of the Manual. Recalculated using the simple method. d. It was noted during the review that the sum of the areas (square feet) in the post - construction drainage area 1 a curve number calculation table did not add up properly. Please ensure that all provided calculations are correct and consistent. Revised. 5. Please provide plans folded to approximately 8.5" x 14" (Section VI, 8). This is required so that we may mail an approved plan set to the Applicant with the approved Permit. Plans that do not contain information pertinent to the review (such as utility sheets, detail sheets, E&SC sheets, etc...) do not need to be included and the plan sheets can be reduced to 24" x 36" or a comparable size. Provided. 6. Please dimension the property boundary with bearings and distances (Section VI, 8i). Property boundary dimensions have been included. 7. Please dimension and/or label all existing, removed, and proposed BUA (Section VI, 8j). The information shown in the calculations and Application should be verifiable on the plans. You may wish to provide a table, similar to the one in the Application, breaking down the on -site BUA on each of these plan sheets. You may also wish to add callouts/labels, similar to the square footage labels on the buildings on sheet C200, for all BUA areas. Pre and Post BUA summary sheets and tables added. 8. Please delineate the wetlands on the plans or provide a note stating that no wetlands exist. Provide documentation of the qualifications and identity of the individual who made this determination (Section VI, 8m). Note added to plan. See sheet C001. 9. Please delineate the drainage areas to the proposed SCMs in the main set of plans (Section Added as sheet C307 in the plan set. 10. Please show the maintenance accesses and easements to the proposed SCMs on the plans (General MDCs 8&9). August 14, 2020 Mr. Jim Farkas Page 3 of 5 Reference: Comment Response Letter A maintenance access easement area has been identified on the plans. See sheet C300. 11. An SCM cannot be both a sand filter and a dry detention basin at the same time. We do allow sand filters to be designed with an open bottom and attenuate peak flows so this review was completed under the assumption that Pond 1 is a sand filter. If this assumption is incorrect, please let me know. a. Please correct the Supplement-EZ Form and O&M Agreement Form so that Pond 1 is listed as a sand filter only. Both of these forms will need to be re -signed. Revised. b. Please provide a SHWT boring in the area of the proposed sand filter so that separation from the SHWT can be assessed (Sand Filter MDC 1). Per Geotech report by Terracon Consultants dated on 0211212020, ground water was not observed in project test borings. c. The volume of the sediment chamber and the sand chamber should be equal or close to it (Sand Filter MDC 2). The sediment chamber can be oversized since the facility is being designed for peak attenuation (Per the guidance in the Manual), but the sediment chamber should not be smaller than the sand chamber. Revised. See plan d. Please ensure that the treatment volume is calculated correctly (Sand Filter MDC 3, See earlier comment). Re -designed and re -calculated. (The provided treatment volume is greater than added impervious area required) 12. Generally, the State does not require quantity management for stormwater runoff. If Pond 2 is not needed to meet the requirements of 15A NCAC 02B .0731, then it does not need to be included in the submission. Since NSW calculations were not provided showing the need for Pond 2, it was not reviewed for compliance with the MDC. If Pond 2 is needed to meet the NSW requirements, it will be reviewed for compliance in the next review. Sandfilter 2 is needed to meet the requirements of 15A NCAC 02B .0731, see SNAP output. 13. Please separate the provided stage -storage table for Pond 1 into sediment chamber and sand chamber parts so that the storage volume information in the Supplement-EZ Form can be verified. Stage -storage table for sandfilter 1 and 2 have been separated into sediment chamber and sand chamber parts. 14. Please correct the following issues with the Supplement-EZ Form: a. Cover Page: i. Line 4 — This item should match Section IV, 6 of the Application. Revised August 14, 2020 Mr. Jim Farkas Page 4 of 5 Reference: Comment Response Letter ii. Lines 7-10 — Vegetated setbacks are only required from surface waters. Since no surface waters are located on or around the project site, these items are not needed. Revised iii. Line 22 — See earlier comment. Revised Drainage Areas Page: i. Click on the "Click to Load Forms" button to fully load this form. ii. Line 4 — See earlier comment. Revised iii. Entire Site Column: 1. There should not be any off -site components to the entire site column since they are by definition not part of the site. 2. Lines 4 & 17 — 19 are not required. Revised iv. Drainage Area 1 (Pond 1): 1. Lines 4 & 18 — See earlier comments. Revised c. Sand Filter Page i. Line 2 — See prior comment. Revised ii. Line 3 — This is a general MDC and must be met. Revised iii. Line 18 — See prior comment. No groundwater observed per Geotech report iv. Line 31 — The bottom of the sand chamber is the lowest excavated part of the sand chamber. Based on the provided detail, it appears that this value should be 439.5 ft. Revised v. Line 33 — This value should be the distance between Line 31 & Line 35 (Temporary pool elevation). Revised vi. Lines 35 — 37 — These items are required. Added vii. Line 38 — This value is the depth of the sand layer above the underdrain pipe. Based on the provided detail, it appears that this value should be 18 in. Revised d. General: i. Make any other corrections to the Supplement-EZ Form as needed due to addressing any of the earlier comments. Revised 15. It is recommended to check with Franklin County to see if they should be reviewing this project since projects in Nutrient Sensitive Watersheds tend to be reviewed by local jurisdictions. The stormwater permitting interactive map on our website may not be 100% accurate and/or up to date. Coordination has been made and verified that only NCDEQ review and approval are needed. 16. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of other documents. Pdfs must be uploaded using the form at: htti)s:Hedocs.deg.nc.gov/Forms/SW Project Submittal Provided. August 14, 2020 Mr. Jim Farkas Page 5 of 5 Reference: Comment Response Letter Regards, Stain ec SoutcLIlHJ11 g Servuces Ili c -10 f e 4 00 Jleff II"'Cte Il1:3IIIIIIIIII Senior Principal Phone: 678 764 6624 Jeff. Rice@stantec.com Attachment: Af`f'arhireigl'. c. C:s C:s fa document17