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Home My WebLink AboutSW3201201_9314-NCDEQ COMMENT RESPONSE_20210317 Attention: Jim Farkas, NCDEQ w9ʹ tƩƚƆĻĭƷ {ƷƚƩƒǞğƷĻƩ tĻƩƒźƷ bƚʹ SW3201201 /ƚǒƓƷǤʹ Union responses to outstanding comments regarding Erosion control procedures for 1. Prior Comment 13 stating that no wetlands exist. Provide documentation of the qualifications and VI, 8 of the Application lists items that need to be included in the plans. Please place this note on a plan sheet. wĻƭƦƚƓƭĻʹ Note added to sheet G0-02 indicating no wetlands on the project site, determined by the project engineer Marc Momsen. Qualifications to sent over. 2. Prior Comment 21.b.ii. -EZ Form, Drainage Areas Page, Drainage column. This column represents the entire project site). wĻƭƦƚƓƭĻʹ The Supplement-EZ Form has been adjusted to correctly display values for the entire property and the drainage area to the proposed sand filter in the (456160 sf) includes the 181,082 sf of BUA directed to the proposed sand filter. 3. Prior Comment 21.b.ii.1. -EZ Form, Drainage Area Page, Drainage Area 1, Line 17 The design storm value should be recorde wĻƭƦƚƓƭĻʹ Design storm listed on Line 17 moved to 4. Prior Comment 21.b.ii.2. -EZ Form, Drainage Area Page, Drainage Area 1, Line 18 The design volume should be based on the design storm. Since this SCM is a sand filter you may reduce the design volume by 25% (In accordance with Sand Filter sign volume for State requirements is based on the filter. The design volume for this SCM appears in the calculations as the adjusted water quality volume, this value should be used for the design volume. wĻƭƦƚƓƭĻʹ Design volume on line 18 changed to the adjusted water quality volume of 11,120 cf. 5. Prior Comment 21.b.ii.3. -EZ Form, Drainage Area Page, Drainage Area 1, Line 19 Please use either the Simple Method or the Discrete NRCS Method to calculate the design volume. More information can be found in Part B of the Stormwater Design calculations, the design volume (adjusted water quality volume) appears to be calculated using the Simple Method. wĻƭƦƚƓƭĻʹ Calculation method moved to sand filter column and changed to Simple. 6. Prior Comment 21.c.i. -EZ Form, Sand Filter Page, Line 2 See earlier should be used for this item. Lines 23 & 30 will show the actual total treatment volume provided by the SCM. wĻƭƦƚƓƭĻʹ Design volume in line 2 of sand filter page changed to 11,120 cf. 7. Prior Comment 21.c.iii. -EZ Form, Sand Filter Page, Lines 23 & 30 These volumes should only take into consideration the provided storage below the invert of the amount of storage provided below elevation 535 ft is 12,165 cf. the bypass elevation for the sand filter is at elevation 534.9 ft, therefore, the total volume that can be retained in the sediment and sand chambers (Lines 23 + 30) must be less than 12,165 cf (The values of both Line 23 & Line 30 are larger than this value). Please revise. Also, if the storage volume provided below elevation 534.9 ft is interpolated from the provided stage storage table, an insufficient treatment volume (less than 11,120 cf) is provided. Please either adjust the sand filter design so that sufficient treatment volume is provided below the lowest bypass elevation or provide calculations showing that sufficient storage is being provided. wĻƭƦƚƓƭĻʹ The design of the orifice at 534.90 has been revised. It is now at 535.00 for the post-developed discharge in the 25-year event. Discharges and peak elevations for the 2-, 10-, and 25-year storm events have been adjusted in the calculations and plans. The orifice at 535.00 gives a treatment volume of 12,165 cf which is sufficient to the requirement. The values in lines 23 and 30 have been revised to match this revision and now add to 12,165 cf. 8. Prior Comment 21.c.iv. -EZ Form, Sand Filter Page, Lines 26 & 32 Please separate the stage-storage table for the sand filter into sediment chamber and sand chamber so that this information and shown in the Supplement-EZ Form do not match the values shown in the stage-storage table. For example, the sediment chamber area is shown as 11,605 sf in the Supplement- EZ Form, and 8,977 sf in the stage-storage table. The sand chamber area is shown as 2,550 sf in the Supplement-EZ Form & plans, and 2,558 sf in the stage-storage table. Please revise for consistency. wĻƭƦƚƓƭĻʹ The surface area shown for the sediment chamber is now 8,985 sf in the stage storage table and the EZ Form, and 2,550 sf for the sand filter area in both forms and the plans. Please note this is the surface area at the bottom of the pond at 534.00. 9. Prior Comment 22.a. for resubmitted items were not provided. Please make sure that all updated/corrected items get electronically uploaded. wĻƭƦƚƓƭĻʹ All documents will be uploaded electronically. 10. Please correct the following items on the Supplement-EZ Form: a. Drainage Areas Page, Entire Site column: i. Line 6 This line is used when there is a subdivision of the property and each lot is allocated a certain amount of BUA. Since this project does not involve the subdivision of the property, this line should not be used (Line 7 is for New BUA that is located outside of subdivided lots). NOTE: The value is correct, it is just located in the wrong spot. wĻƭƦƚƓƭĻʹ New BUA in project has been moved to Line 7. ii. Line 10 Please provide these values. This is a breakdown by type of the new BUA (Line 7, the items of Line 10 should add up to Line 7). wĻƭƦƚƓƭĻʹ BUA breakdown provided in Line 10 and matches values on sheet C3-01 and the impervious areas exhibit in the engineering calculations. Please note impervious areas for roadway and parking are combined and shown in the roadway row on the EZ Form. iii. Line 14 This item is not needed since the existing BUA predates the State post-construction rule implementation in this location. The existing BUA is not covered under a permit (since it predates the program) so it should not be reported on this line (This line is usually used for project modifications). NOTE: Lines 13 & 15 are correct and do not need to be changed. wĻƭƦƚƓƭĻʹ Values in Line 14 have been removed. Line 7 under the the proposed sand filter that will be removed and replaced but does not include the 181,082 sf of new impervious going to the 11. Please provide calculations showing that the outlet of the sand filter is stable for the 10- year storm event (General MDC 4). It is noted that riprap sizing calculations are provided from (Also, the outfall of the sand filter appears to be some sort of level-spreader type device, if that is the case, the provided riprap sizing calculation would not be appropriate to demonstrate compliance). Please also provide calculations showing that the inlet is protected from erosion from stormwater discharges (General MDC 4). wĻƭƦƚƓƭĻʹ Peak flow value revised to the 10-year storm peak discharge for sizing calcs. Rip Rap sizing for the inlet into the BMP & the BMP outfall have been revised and included in the engineering calculations, and the rip rap is displayed and dimensioned on sheet C3-05.