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HomeMy WebLinkAboutSW3240801_Response to Comments_20241118 •ESP North Carolina Department of Environmental Quality— Stormwater Adelina Phase 1 1st Submittal Review Comments dated 10/15/2024 Date: October 29, 2024 1st Submittal Review Comments: 1. Comment: As designed, SCM 3 is considered to be just a sand filter and not a dry detention basin & sand filter(the sand filter SCM includes the sand layer in addition to the storage provided above the sand layer in the sand chamber and sediment chamber). Please revise the submittal materials as needed to reflect this. Later comments will be made in the context of considering SCM 3 as only a sand filter. If peak flow attenuation is desired(or required for local ordinances) this is acceptable,but the SCM, as designed,must meet the Sand Filter MDC. Please also revise the project documentation to address the following MDC's that were not met: a. Sand Filter MDC 1 —A SHWT evaluation within the footprint of the SCM as not provided, so compliance with this MDC could not be verified. For open-bottom sand filters, a minimum separation of two feet must be maintained from the SHWT. b. Sand Filter MDC 2—Storage volume in each chamber(sand and sediment)must be equal. If peak flow mitigation is desired,only the sediment chamber may be the larger of the two,but both most contain at least half of the design volume. Response: SCM 3 has be revised to exclude the Dry Pond on the respective documents. Geotechnical Report have been provided with submittal for the determination of the SHWT and footprint within the proposed Sand Filter. 2. Comment: Per Wet Pond MDC 5,the entrance of a wet pond's forebay shall be deeper than the exit. All proposed Wet Pods are not in compliance with this MDC. Please revise the project package as necessary for compliance with the MDC as well as consistency with the required revisions. Response: All Wet Pond's forebays entrances have been revised to meet Wet Pond MDC 5. Please refer to all supporting documents submitted. Consistency 3. Comment: Please revise the following for consistency: a. The BUA fpr Drainage Area 5 on the Application states 277,042 sf and the Drainage Area Page of the Supplement-EZ form states 276,813 sf.Please revise for consistency. Response: All proposed drainage area's have been revised to be consistent with calculations provided with this submittal.Please refer to all supporting documentation. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com •ESP Application 4. Comment: Section IV,4—Please revise this line to indicate the desired project area associated with this phase of development. This project area should also be delineated by bearings and distances on the main set of plans. Response: An exhibit as been added to the plan set to show the following bearings and distances of the property area and project area.Please refer to sheet C1.1. 5. Comment: Section IV, 6—Please ensure that all surface water within the delineated project area is accounted for in this section of the Application. Response: Surface Water has now been accounted for in this section of the application,as well as accounting for stream offset buffers proposed within the construction plan. Please refer to supporting documentation for details. 6. Comment: Section IV, 7—Please revise this section to account for the surface waters on-site by subtraction the surface area associated with the surface waters from the property area listed in Section IV,4. Response: Section has been updated per accounting of surface waters within projects scope. 7. Comment: Section IV, 8—Please revise the total project's Percent BUA to reflect the changes in the above comments. Response: Section has been updated to reflect the changes to surface water.Please refer to all supporting documents. Supplement-EZ Form 8. Comment: On the Cover page please revise the following Line 2 and 4 per comments above on the Application. Response: Lines 2 & 4 have been revised to reflect changes to surface water area. 9. Comment: On line 22,Please remove this, as a Dry Pond is not being permitted at this time. Response: Line 22 has been updated to reflect no Dry Pond. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com •ESP 10. Comment: Drainage Area Page a. Please complete this page(lines 9,10, and 12). The BUA accounting present on this page should reflect what is shown in Section IV, 10 of the Application. The Entire Site column may not necessarily be a sum of the other columns on all lines but should reflect the site as a whole. b. Line 18—Please complete this line. c. Line 21 —This line refers to the calculation method used to find the minimum required treatment volume.Please revise as necessary. Response: Lines 9,10,and 12 have been completed, and been shown to reflect Section IV, 10.Line 18 has been completed.Line 21 is correct, and the minimum treatment volume on Line 2 has been updated to reflect the method used. 11. Comment: Wet Pond Page Line 2—Please revise the entries on this line to correspond to the Minimum required Treatment Volume calculated using the mrthod outlined on Line 21 of the Drainage Areas Page. Response: Line 2 has been updated to reflect the method used to calculate the minimum required treatment volume.Please refer to the Supplement-EZ form. 12. Comment: Wet Pond Page Line 8—Please revise to indicate compliance with General MDC 5. Response: A concrete emergency spillway has been added to comply with Line 8 of the Wet Pond General MDC 5. 13. Comment: Line 35-Please revise this line to indicate the actual design volume of each Wet Pond. Please note that the design volume of a wet pond is the volume stored between the elevations of the permanent pool and the invert of the lowest bypass device. Response: The design volume of all proposed Wet Ponds have been updated on line 35 to reflect the stated specifications above.Please refer to line 35 and calculation package provided with this submittal. 14. Comment: Line 43 and 44—See earlier comment with regard to Wet Pond MDC 5. Response: Lines 43 and 44 have been updated per Wet Pond MDC 5. 15. Comment: Wet Pond Page Line 53—Wetland seed mixes may not be used as vegetation for Wet Ponds. Please revise the grass to be used sop that compliance with Wet Pond MDC 11 may be verified. Response: Line 53 has been updated to reflect a Tall Fescue grass type instead of a wetland seed mix. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com •ESP 16. Comment: Sand Filter Page Line 8—Please revise to indicate that there will be an overflow or bypass for inflow volumes in excess of the design volume,as required by General MDC 5. There appears to be a riser structure provided that will act as a bypass device. Response: Line 8 has been updated to reflect the use of the riser structure as the bypass device. 17. Comment: Sand Filter Page Line 9—A drawdown orifice to dewater the SCM for maintenance could not be found on the provided set of plans. Please include and indicate this orifice or revise the type of drawdown device to be used for maintenance on this line of the Supplement-EZ form. Response: Drawdown orifice to be attached to the riser structure to dewater the Sand Filer for maintenance. 18. Comment: Sand Filter Page Line 18—Per Sand Filter MDC 1,the minimum separation between the lowest point of the Sand Filter System and the SHWT shall be two feet for open-bottom designs.A SHWT evaluation inside the footprint of the SCM was not provided with this submission, so compliance with the MDC could not be verified. Please provide a SHWT boring within the footprint of the SCM and revise this line to indicate the elevation of the SHWT so that compliance with the MDC can be verified. Response: A Survey/Geotechnical boring location and SHWT table report have been submitted with this submittal. 19. Comment: Sand Filter Page Line 23-29—Please complete this section of the Supplement-EZ form. Please note that, as designed,the forebay of the"dry pond"is considered the sediment chamber of the Sand Filter SCM, and the information entered here should reflect its design and dimensions. Response: Lines 23-29 have been updated. 20. Comment: Sand Filter Page Line 30—For a Sand Filter,the volume retained in the sand chamber is considered to be the only inclusive of the volume stored directly above the and surface between the top of the sand layer and the invert of the lowest bypass device. Please revise this line to indicate that volume. Response: The volume of the sand filter has been recalculated and updated per the information above. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com •ESP 21. Comment: Sand Filter Page Line 33—The physical depth of the sand chamber is the depth from the lowest bypass invert(Line 35)to the lowest excavated point of the sand chamber(below the underdrains). Response: Line 33 has been updated based off the information provided above. 22. Comment: Sand Filter Page Line 34—The ponding depth of the sand chamber is the depth from the lowest bypass invert(Line 35)to the top of the sand layer(Line 31). Response: Line 34 has been updated based off the information provided above. 23. Comment: Dry Pond Page.Please remove this page. Response: Dry Pond page has been removed. 24. Comment: On the Plan set,Please revise the provided Wet Pond details to indicate all relevant elevations(bottom, sediment storage,forebay entrance and exit, etc.)as required by 15A NCAC 02H.1042(2)(h)(i). Response: All wet pond details have been updated to provide the information requested above. 25. Comment: On the Plan set,please indicate the type of grass that will be planted for each Wet Pond on the planting plans, so that compliance with Wet Pond MDC 11 may be verified. Wetland Mixes may not be used. Response: The type of grass to be used will be Tall Fescue on all proposed Wet Ponds. Please refer to the Wet Pond Details on the plan set. 26. Comment: On the Plan set,The maintenance accesses and easements required by General MDC's 8 and 9 could not be found on the main set of plans. Please revise the provided plan sheets to indicate these accesses and easements or direct the reviewer to this information. Please note that maintenance accesses and easements shall be at least 10 feet in width, contain no slopes steeper than 3:1, and contain all portions of the SCM,including outlet structures. Response: The maintenance access and easements have been called out as "Prop. 12' Access Drive Easement,as well the SCM easement has now been highlighted on the plan set to easily identify the proposed accesses and easements. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com •ESP 27. Comment: On the Plan set,Please revise the orifice diameters provided to be consistent with what is shown in the calculations and on the Supplement-EZ Form. Response: All orifices calculations have been updated and now remain consistent with the calculation package and Supplement-EZ form. 28. Comment: Please delineate the project area associated with this phase of development on the main set of plans with bearings and distances, as required by Section VI, 8i of the Application. Response: A Property and Phase boundary Exhibit has been provided with this submittal, Please refer to Sheet C1.1 for all boundary information bearings and distances. 29. Comment: O&M Agreement Form—Please provide a revised O&M Agreement with the Dry Pond information removed, as it is not being permitted at this time. Response: Dry Pond Page has been removed front the O&M Agreement form. 30. Comment: O&M Agreement Form—The elevations given with the O&M Agreement are not currently shown on the provided set of plans, as indicated in earlier comments. When this is revised,please ensure these elevations are consistent with what is shown in the O&M Agreement. If the elevations on the O&M Agreement are inaccurate,the will need to be revised. Response: The O&M Agreement Form has been updated with the correct elevations according to the calculation method used in the Supplement-EZ form. 31. Comment: Calculations—For wet pond calculations,the Equation 3 average depth when the shelf is partially or fully submerged and the shelf is being excluded from the average depth calculation, the value of Vpp should be the main pool volume at the permanent pool elevation. The provided calculations use the total volume of the permanent pool. Please revise these calculations.At this time,the draw down calculations are unverifiable due to the average depth discrepancy. Response: The average depth calculation has been updated to the information provided above. ESP Associates,Inc. P.O.Box 7030 • Charlotte,NC 28241 1.800.960.7317 • NC:704.583.4949,fax 704.583.4950 • SC:803.802.2440,fax 803.802.2515 www.espassociates.com