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Home My WebLink AboutSW4200501_Comment Responses_20200602CLH design, p.a. 400 Regency Forest Drive, Suite 120 Cary, North Carolina 27518 P: 919.319.6716 www.clhdesignpa.com Site Plan Comment Responses Date: June 2, 2020 Re: Lewisville Middle School- Forsyth County - State Project SW4200501 Dear Jim Farkas : Below in red are our responses to the 6t" round of review comments received for the above referenced project. Division of Energy, Mineral and Land Resources Comment 1: Please QA/QC the package prior to submission. There were a number of repeat comments found during review and this is the fifth time this project is being reviewed. This review was performed in an expedited manner as a courtesy (Given the nature of this project and the relatively minor comment from the prior review) the next review of this project will not be afforded this courtesy. Response: QA/QC was performed before this current submittal. Comment 2: Prior Comment 2 — "Please ensure that the percent impervious area for the entire site is calculated correctly (Section IV, 8)."The percent impervious area for the entire site is calculated as either the total built upon area within the project area post -construction divided by the total project area or as the difference of the total post -construction built upon area within the project area minus the existing built -upon area within the project area divided by the difference of the total project area minus the existing built -upon area within the project area (15A NCAC 2H .1003(1)). Neither of these methods yield 14.2% impervious area based on the provided information. Please provide calculations showing how the percent impervious area is being calculated and revise the submittal materials as needed to eliminate inconsistencies. Response: See sheet CO3.08 to see how calculation was calculated. Comment 3: Prior Comment 5 — "Please include Section IV, 11 of the application. It appears to be missing." Please elaborate on the information used to determine the extents of the off -site drainage area. Response: Offsite drainage areas were delineated using existing topography that was picked up during this site's survey and meshed with GIS data where survey stopped. The BUA for offsite was agreed upon to be 100% of the offsite. Comment 4: Prior Comment 10.b.i — "Entire Site Column — There appears to be a calculation error in this column:" The "Other" row appears to not be reported correctly resulting in a discrepancy between the total BUA within the project site as shown on the Supplement- EZ Form (393,224 sf) and plan sheet CO3.08 (382,098 sf = 401,700 sf-19,602 sf). Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed and numbers should match. Comment 5: Prior Comment 10.b.iii.1— "Line 16— This item does not match Section IV, 10 of the application. Revise as needed."This item, Line 16 of Drainage Area 1 (45.4%), does not match the percent impervious area total of Drainage Area 1 (45.5%). Please revise as CLH design, p.a. Site Plan Comments June 2, 2020 needed for consistency. Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed, and numbers should match. Comment 6: Prior Comments 10.c & 10.d — "Revise as needed in accordance with the other comments." Certain revisions to the design of the wet pond and stormwater wetland were not carried over to the Supplement-EZ Form. Please ensure that all of the information in the Supplement-EZ Form is consistent with the proposed design, revising as needed. Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed, and numbers should match. Comment 7: Prior Comment 11— "Please show the elevation of the top of the sediment storage area on the cross-section for the wet pond on sheet C07.04. " There appears to be some inconsistency with the proposed wet pond. a. The pond schedule shows the pond sediment storage bottom elevation (U) as 822.50. In the cross-section, this label corresponds to the thick black line (the top of the 4" of topsoil) at the bottom of the main pool. Label has been revised to be more clear. b. The note added as part of the 5/28/2020 revision states that the main pool bottom/sediment storage top elevation (Indicated by a grey dashed line) is at elevation 822.50 and the excavated sediment storage elevation (i.e. the bottom of the sediment storage) as 822.00. Numbers revised to be consistent. c. Supplement-EZ, Wet Pond Page, Line 20 indicates that the bottom of the sediment storage is at elevation 822.50 and Line 21 indicates that the main pool bottom/sediment storage top elevation is at elevation 823.00. These are correct. d. Ensure that all inconsistencies are resolved. Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed, and numbers should match. Comment 8: Prior Comment 13 - The provided stage -storage table does not match the other provided information. a. The forebay surface area and the deep pool surface area appears to be calculated incorrectly. The surface area of the forebay/deep pool should only take into consideration the portion of the forebay/deep pool that is at or below elevation 811.25 (The bottom of the shallow water zone). Any portion of the stormwater wetland that is between 0 and 9 inches below the permanent pool elevation (elevations 811.25 — 812.00) is considered to be part of the shallow water zone (Even if it is in the vicinity of the forebay/deep pool). Per the provided stagestorage table, the area of the forebay would be 276 sf, the area of the deep pool would be 267 sf, and the area of the shallow water zone would be 2,050 sf. This results in the forebay being too small (Stormwater Wetland MDC 6) and the shallow water zone being too large (Stormwater Wetland MDC 8). Wetland fine grading has been revised to have forebay and deep pools be calculated only by the area at 811.25 (9" below NP). b. The wetland schedule shows the top of the shallow land (top of temporary pool) elevation (X) as 813.00. Temporary pool revised to 812.70 on wetland detail. c. Supplement-EZ, Stormwater Wetland Page, Line 24 and the provided stage -storage table indicates that the top of the temporary pool is at elevation 812.7. Correct d. The pond schedule shows the wetland deep pool excavated bottom elevation (U) as 809.50 (NOTE: Unlike a wet pond, stormwater wetlands do not require a sediment storage area so the excavated bottom of the wetland is the bottom) See revised C07.05 for revised section view. Deep pool sediment storage removed and another label (Y) has been added to differentiate deep pool and forebay elevations. e. The provided stage -storage table indicates that the bottom elevation of the deep pool is 810.00. Correct f. Supplement-EZ, Stormwater Wetland Page, Line 44 indicates that the deep pool CLH design, p.a. Site Plan Comments June 2, 2020 is 24 inches deep (@ elevation 810.00). Correct (812 — 810 = 2'). g. Ensure that all inconsistencies are resolved. Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed, and numbers should match. Comment 9: Prior Comment 14 — "The shallow water zone encompasses all portions of the stormwater wetland between 0 and 9 inches below the permanent pool surface elevation. Therefore, the shallow water zone must be 9 inches deep (Stormwater Wetland MDC 8). Please revise accordingly. " There appears to be some inconsistency with the proposed stormwater wetland. a. The wetland schedule shows the shallow water zone bottom elevation (W) as 811.25. Correct b. Supplement-EZ, Stormwater Wetland Page, Line 26 indicates that the bottom of the shallow water zone is at elevation 811.50. Supplement-EZ has been revised. c. Supplement-EZ, Stormwater Wetland Page, Line 41 indicates that the shallow water zone is 6 inches deep. Supplement-EZ has been revised. d. Ensure that all inconsistencies are resolved. Response: The supplement-EZ form, application and sheet CO3.08 discrepancies should be removed, and numbers should match. Comment 10: Prior Comment 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: https.-Iledocs. deq. nc. gov/FormsIS ML Project Submittal" Please use the new permit number, "SW4200501" when providing additional information. Response: Hard copies and electronic upload have been completed for this submittal using this permit number. Comment 11: The drainage area delineations did not show up on revised plan sheet CO3.08. Response: Drainage areas were frozen and should show up in the new submittal. Comment 12: Supplement-EZ Form, Drainage Areas Page, Line 20 —The off -site BUA is not being added to the "Future" BUA row. Please revise. Response: Language in line 20 has been revised to read as "offsite" area. Comment 13: Ensure that the wet pond information on the 0&M Agreement is correct. Response: O&M manual has been revised and indicates the deepest part of the forebay. Comment 14: 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: https://edocs.deg.nc.gov/Forms/SW Project Submittal Response: Hard copies and electronic upload have been completed for this submittal using this permit number. Comment 15: NOTE: Per Division policy, the next review of this application will be the final review. Failure to provide the requested information will result in the project being returned as incomplete. The return of a project will necessitate resubmittal of all required items, including the application fee. Response: Noted End of Responses Thank you for all your help and please call with any questions. Sincerely, For CLH design, p.a. Renee Pfeifer, PLA Vice President CLH design, p.a.