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Home My WebLink AboutSW5220801_Response To Comments_20221220Bowman Project: Dollar General Location: NC Hwy 54, Orange County, NC Jurisdiction: NCDEQ Date: 11/21/22 Subject: NCDEQ SW Comments 4006 Barrett Drive, Suite 104 Raleigh, North Carolina, 27609 TEL (919) 553-6570 Comment Response Per the information provided in the stage -storage table, the cross -sectional ✓ The revised sum is 4825sf. Not all areas below the permanent area of the stormwater wetland at the permanent pool elevation (354.0') is pool elevation are factored into the forebay (at the lowest shown to be 4,450 sf. Adding up the provided surface areas of the parts of the point), non -deep forebay (at the lowest point) and shallow stormwater wetland that are below the permanent pool (forebay, non-forebay water zone (not below 353.25). deep pools, & shallow water zone) results in an area of 2,691.4 sf (633.4 sf + 398.0 sf + 1,660.0 sf). Please revise as needed (Stormwater Wetland MDCs 3 & 6-9). The provided drawdown calculations do not appear to be correct (Stormwater ✓ A third of the driving head has been used to calculate the Wetland MDC 10), they appear to assume a constant drawdown rate (0.012 orifice drawdown rate. The orifice is now 0.9in. cfs) that was calculated for a pending elevation of 354.7'. As the temporary pool drains, the rate of discharge decreases and this does not appear to be accounted for in the calculations resulting in an undersized orifice (We recommend using a third of the driving head to calculate the orifice drawdown rate to account for this decreasing rate of discharge). Please revise as needed. The design volume of a stormwater wetland is the volume that can be stored ✓ The bypass invert has been lowered to the 354.7 elevation. above the permanent pool (354.0') and below the invert of the lowest bypass This elevation is 0.1 ft higher than what is required and is (355.0'). Per the provided stage -storage table, this SCM provides a design accounted for in the design. The surface area at 354.7 volume of 5,154 cf. This design volume should be used for the sizing -based (5580st) is used for the MDC 6-10 percentages. MDCs (Stormwater Wetland MDC 3, & 6- 10). Please revise as needed. NOTE: You may wish to lower the bypass invert if you would like to keep the temporary pool elevation/volume as shown in the calculations/Supplement- EZ Form. The provided profile view of the stormwater wetland shows the 1.0" storm ✓ The bypass invert has been lowered to the 354.7 elevation. elevation at 354.3'. Per the provided stage -storage table, the pending This elevation is 0.1 ft higher than what is required and is Bowman 4006 Barrett Drive, Suite 104 Raleigh, North Carolina, 27609 TEL (919) 553-6570 elevation for the 1.0" design storm (2,950 cf) would be closer to 354.6'. accounted for in the design. The 1.0" storm elevation is Please revise as needed. determined via hydraflow calculations. Supplement EZ Form ✓ Setback width is provided. Cover Page: i. Line 7 — Please provide the vegetated setback width (per 15A NCAC 02H .1003(4) & .1017(10)). It is noted that there are no surface waters located on - site, however the setback width should still be included. Supplement EZ Form ✓ Impervious summary table has been revised. There is less Drainage Area Page: BUA shown draining to the SCM. There is 481 sf impervious area bypassing the pond. i. Line 8 — There is more BUA shown draining to the SCM (36,327 sf) than is shown for the entire site area (35,923 sf), but there is no off -site component to the drainage area. Please revise as needed. Supplement EZ Form ✓ The bypass invert has been lowered to the 354.7 elevation. Stormwater Wetland Page: This elevation is 0.1 ft higher than what is required and is accounted for in the design. The volume at 354.7 is 3554 cf. i. Line 18 — See earlier comment. This item refers to the design volume of the SCM (the volume that can be stored between the permanent pool and bypass invert). Supplement EZ Form ✓ Peak attenuation has been revised. Stormwater Wetland Page: ii, Line 24 — This item appears to refer to the 2-year design storm pending elevation or 15" above the permanent pool elevation. If the SCM is designed to attenuate peak flows (typically required to meet local quantity management requirements or provide for non -erosive 10-year design storm discharge rates) please indicate the peak attenuation elevation. If peak attenuation is not required, this item does not need to be answered. Bowman 4006 Barrett Drive, Suite 104 Raleigh, North Carolina, 27609 TEL (919) 553-6570 Supplement EZ Form ✓ Temporary pool elevation shown at 354.7 Stormwater Wetland Page: iii. Line 25 — See earlier comment Supplement EZ Form ✓ Line 28 has been revised. Stormwater Wetland Page: iv. Line 28 — Per the plans, the elevation of the bottom of the forebay at the deepest point is at elevation 351.0 ft. Supplement EZ Form ✓ Line 29 has been revised. Stormwater Wetland Page: v. Line 29 — Per the plans, the elevation of the bottom of the forebay at the shallowest point is at elevation 352.0 ft. Supplement EZ Form ✓ The bypass invert has been lowered to the 354.7 elevation. Stormwater Wetland Page: This elevation is 0.1 ft higher than what is required and is accounted for in the design. The temporary pool surface area vi. Line 31 — See earlier comment. The provided value (4,461.0 sf) does not at 354.7 (5580sf) is used for the MDC 6-10 percentages. The correspond to the sum of Lines 32-35 (4,081 sf) or the value shown in the revised sum is 4825sf. Not all areas below the permanent stage -storage table (5,440 sf � 354.7'). pool elevation are factored into the forebay (at the lowest point), non -deep forebay (at the lowest point) and shallow water zone not below 353.25 . Supplement EZ Form ✓ The revised sum is 4825sf. Not all areas below the permanent Stormwater Wetland Page: pool elevation are factored into the forebay (at the lowest point), non -deep forebay (at the lowest point) and shallow vii. Lines 32-35 — The sum of these items is equal to 4,081 sf (4,461 sf is water zone (not below 353.25). shown on Line 31). Supplement EZ Form ✓ Forebay has a total of 625 sf at the lowest point. The surface Stormwater Wetland Page: area for the temporary pool elevation is 5580 sf. This is a percentage of 11.2%. Other percentages have been accounted viii. Line 38 — The forebay deep pool area is shown as 633.4 sf and the total for the temporary pool elevation surface area of 5580 sf. area (sum of Lines 32-35) is 4,081 sf. This results in the percent area provided Bowman 4006 Barrett Drive, Suite 104 Raleigh, North Carolina, 27609 TEL (919) 553-6570 for the forebay of 15.5% which is larger than allowable. NOTE: Lines 36-39 may need to be revise in accordance with previous comments. Supplement EZ Form ✓ Depth has been revised. Stormwater Wetland Page: ix. Line 40 — See earlier comment. Supplement EZ Form ✓ Temporary pool elevation shown at 354.7 (0.7'x12"=8.4"). Stormwater Wetland Page: x. Line 41— See earlier comments. Supplement EZ Form ✓ Orifice diameter has been revised. Stormwater Wetland Page: xi. Line 46 — See earlier comment. Supplement EZ Form ✓ Lines have been deleted. Stormwater Wetland Page: xii. Lines 47 & 48 — Lines 46-48 refer to the drawdown method of the temporary pool and typically either a weir or orifice are used, but rarely are both used. In this case, the temporary pool drawdown is handled by an orifice so Lines 47-48 are not needed. Supplement EZ Form ✓ Drawdown time has been revised. Stormwater Wetland Page: xiii. Line 49 — See earlier comment. This project drains to Nutrient Sensitive Waters (NSW). Please ensure that the ✓ SNAP tool calculations have been provided. design complies with 15A NCAC 02H .1017(9)(c). While not required, it is recommended to provide a drainage area of at least 2 ✓ Noted for future projects. acres for a stormwater wetland so that adequate ear -round hydration can be Bowman 4006 Barrett Drive, Suite 104 Raleigh, North Carolina, 27609 TEL (919) 553-6570 provided to the wetland plants. You may wish to consider using a different SCM for this project. Please upload the electronic files for this project to our online repository (link ✓ Files have been uploaded. below) as indicated in the 8/25/2022 email from our office. Electronic copies of files are required per 15A NCAC 02H .1042(2). Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy ✓ Hard copies have been provided. of other documents, and a response to comments letter briefly describing how the comments have been addressed. a. PDFs must be uploaded using the form at: https://edocs.deq.nc.gov/Fonns/SW-Soplemental-Upload b. Hard copies must be mailed or delivered to the following address: i. For FedEx/UPS: Jim Farkas 512 N. Salisbury Street, Office 640E Raleigh, NC 27604 ii. For USPS: Jim Farkas 1612 Mail Service Center Raleigh, NC 27699-1612 iii. 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.