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Home My WebLink AboutNC0036269_Correspondence_20231116309 East Morehead Street, Suite 220 Charlotte, NC 28202 T: 704.358.7204 November 9, 2023 Brown ANo . Caldwell ' Ori Tuvia NC DEQ/ Division of Water Resources/ Permitting 610 East Center Avenue Mooresville, NC 28115 158720 Subject: NPDES NCO03629 - ATC 036269AO6 - Additional Information Request and Responses Dear Mr. Tuvia, Brown and Caldwell received NCDEQ's request for additional pertaining to the ATC 036269AO6 application package for the expansion of the Rocky River Regional Wastewater Treatment Plant (RRRWWTP) in an email dated November 3, 2023. This let- ter includes NCDEQ's original comments in bold and our responses immediately after. ATC Application Review: 1. Page 5- Residual Management plan - How will the additional sludge be disposed. The application includes parts regarding addition of DAFT'S units, dewatering and in- cineration won't that require change in the residual management process? Also need a confirmation that the hauler can handle the increased hauling and the land appli- cation/landfill will accept the additional sludge. The sludge produced will continue to be disposed of in accordance with Permit No. WQ0032332 Class A Biosolid Ash Residuals Program. In the foreseeable future, the ap- proved Site 03 located within the RRRWWTP property will be used as application site. Applier and hauler is WSACC. Dewatering capacity is discussed in paragraph 9.1 of the PER (Attachment C). A single operating centrifuge (throughput capacity 3,755 dry Ib/h) can handle the anticipated sludge production at 34 MGD (83,291 dry Ib/d), if operated continuously for 337 days within a calendar year. A second standby centrifuge is installed, and a full rotating as- sembly is also available onsite. The incinerator (throughput capacity of 2.08 DT/h) can handle the anticipated sludge production at 34 MGD (83,291 dry Ib/d), if operated con- tinuously for 304 days per year. Both dewatering and incineration are continuous 24/7 processes. The only downtime is for preventative maintenance that usually lasts no more than a two -week period. NC003629-ATC036269A06 Additional Information Request and Response Letter Rpt 2023-11-9 Ori Tuvia NC DEQ/ Division of Water Resources/ Permitting November 9, 2023 Page 2 2. Page 7 part 2, table has higher average influent concentrations than the design, please review. We had a couple of errors in the table as noted below, but your observation is correct. The concentrations from the past 12 months appear to be higher than the basis of de- sign concentrations. As explained in the next few paragraphs, our basis of design con- tains enough conservatism already not to require any further changes. Project Basis of Design Design Influent Design Influent Influent Concentration Load Concentration - (Must be (Must be Current Annual supported by supported by Design Effluent Average (past Engineering Engineering Concentration and/or NPDES Permit Limits 12 months) if Calculations Calculations (monthly average) Parameter Available Section 3.H Section 3.H])Load Ammonia Nitrogen 33.5 mg/L 31.6 8.960 1.6 mg/L Summer 1.6 mg/L Summer (NH3-N) (Pri. Clar. Infl.)3.7 —3�mg/L 7,920 1b/day mg/L Winter 3.7 mg/L Winter Biochemical 86.200 10.0 mg/L Summer 10.0 mg/L Summer Oxygen Demand 338 mg/L 304 mg/L 76,080lb/day (GODS) 20.0 mg/L Winter 20.0 mg/L Winter Fecal Coliform 200 per 100 mL 200 per 100 ml. Nitrate + Nitrite Nitrogen (NO3-N + N/A mg/L N/A mg/L NO2-N) Total Kjeldahl N/A mg/L Nitrogen N/A mg/L N/A mg/L Total Nitrogen N/A lb/year N/A lb/year N/A mg/L N/A mg/L Total Phosphorus N/A mg/L 8.0 mg/L 2,280lb/day N/Alb/year N/Alb/year Total Suspended 383 mg/L 336 mg/L 95,300lb/day 30.0 mg/L 30.0 mg/L Solids (TSS) First, when developing the basis of design, we do not rely on just one year of data. The last 12 months for example have been a "dry" year and the lower flows have skewed the concentrations to higher than typical values. Figure 1 below demonstrates the inverse correlation between ammonia and flow and how dry months drive up the concentration even though the load is about the same. NC003629-ATC036269A06 Additional Information Request and Response Letter Rpt 2023-11-9 Ori Tuvia NC DEQ/ Division of Water Resources/ Permitting November 9, 2023 Page 3 40 38 Jc L 36 z 34 M Z 32 30 A 28 Q 26 s c 24 2 22 20 • R= = 0.5794 15 17 19 21 23 25 27 29 Monthly Average Flow (MGD) Figure 1. Correlation between ammonia concentration and WWTP flow Secondly, our design is based on loads. Here is an example that shows that our design includes enough conservatism for this expansion. The annual average ammonia load from past 12 months can be calculated as 22.4 MGD x 33.5 mg1L x 8.34 = 6,258 Ib/d. If you normalize load to flow (6,258 Ib/d / 22.4 MGD = 279 lb-N/MG) and scale it up to our design annual average flow of 29.3 MGD (34 MGD MMF) you get 8,175 Ib/d (29.3 MGD x 279 lb-N/MG), which is 10% below our design influent load of 8,960 lb/day. Our design influent load is based on maximum month, so performing the same calculation using the maximum month (flow and load) from the past year (April 2023) we get NH3-N 32.2 mg/L, flow 27.3 MGD, load 7,331 Ib/d and normalized load of 269 lb/MG. The scaled -up load using 34 MGD equals 9,146 Ib/d, which is only 186 Ib/d or 2% higher than our basis of design load of 8,960 Ib/d. Even if the ammonia concentrations end up being higher than we projected, the second- ary treatment design includes several safety factors including 1.5 times the minimum SRT for nitrification and designing for complete nitrification year-round, which is well be- low the permit limits. We also included some additional conservatism when selecting the blowers. Note also that the basis of design loads were already increased from TM No.4 Influent Flows, Loads, and Projections dated October 2, 2020 to those appearing in the PER for the Expansion to 34 MGD dated July 21, 2023. The basis of design loads from these two documents are shown in Tables 2 and 1-2, respectively. As also stated in the PER, the design loads were increased to provide additional conservatism in the design due to the low frequency of influent data. NC003629-ATC036269A06 Additional Information Request and Response Letter Rpt 2023-11-9 Dri Tuvia NC DEQ/ Division of Water Resources/ Permitting November 9, 2023 Page 4 pollutant Annual Average Load (lb/d) Annual Ave Conc. (mglp Month Load pb/d) Max Month Cone. (mgl* GOD BOD5 149,700 61,400 660 271 192,300 74.800 678 264 TSS TAN 06,600 293 34A 93,400 9,200 329 32.4 7,g00 34 MGV Ann. 34 MGD Ann. Annual Ake i @ sign 30 MGD Max 34 MGD Max Max Month Pollutant Month Load Month Load Ave. Load pb/d) Ave. Load (Ib/d) Cone_ ft/L) Conic. (M93) (Ib/d) (lb/d) COD 135,90U 154,000 619 190,200 215.600 760 01130106 54,300 61,500 211 76,000 S6.20t] 304 TSS 60,100 68,100 200 94,100 95,301] 336 TKN 10,300 11,700 52 14,400 ifi,300 57 TP 1r440 11630 7.0 2ra10 2,280 8.0 Attachments: 1. How was the 73.3 MGD PHF chosen? Table 1.1 in attachment C lists PHF of 115.8 MGD? Please explain the assumption made for EQ capacity of 41.8 MGD PHF. Attachment E, Calculations Cover Letter and Attachment E.1 provide the background on the sizing of the equalization tanks. In brief, 73.3 MGD is the needed firm capacity of the Main Pump Station (PS) to deliver the peak of 115.8 MGD at the RRRWWTP head - works. The other 42.5 MGD will come from Lower Rocky River PS (ATC#036269A03). TM No.3 Equipment List and Capacity Assessment dated Jan. 27, 2021 and provided as part of the previous ATC application for Phase 3 (ATC#036269A05) explained how the two influent pump stations contribute to the overall RRRWWTP headworks flows (refer to Table 2 and associated discussion in that TM No.3). Through the EQ sizing analysis of Attachment E.1, we determined that a 17-MG EQ tank volume is more than sufficient to reduce the peak flow through the main RRRWWTP (downstream of headworks and Box 10) from 115.8 down to 74 MGD. 2. Will the Secondary clarifier improvements result in the clarifiers being able to handle increased capacity? No, the clarifier improvements are in -kind, maintenance type improvements and will not alter their capacity. As shown in Section 6-2 and Table 6-2, the secondary clarifiers could handle flows as high as 106.4 MGD. With the 17-MG equalization volume pro- vided, the peak flow through the main WWTP will not exceed 74 MGD, which is well be- low the peak process capacity of the secondary clarification process. Brown and Caldwell appreciates NCDEQ's thorough and timely review of the ATC applica- tion package. Should you have any additional questions, please do not hesitate to email me again at.9-anipsitakis@brwncald.com . NC003629-ATC036269A06 Additional Information Request and Response Letter Rpt 2023-11-9 Ori Tuvia NC DEQ/ Division of Water Resources/ Permitting November 9, 2023 Page 5 Very truly yours, Brown and Ca George Anipsitakis, Ph.D., PE Managing Principal Charlotte, NC cc: Chad VonCannon, PE, WSACC NC003629-ATC036269A06 Additional Information Request and Response Letter Rpt 2023-11-9