What’s This HWA Design Thing All About??? Design Capacity HWA Info from one POTW CITY OF GREENSBORO North Buffalo POTW

NORTH BUFFALO POTW  Design Flow: 16 MGD Current Flow = ~10.0 MGD  Primary Treatment  Secondary Treatment Trickling Filters Activated Sludge with Nitrification  Tertiary Treatment Phosphorus removal  Chemical Addition/Precipitation Effluent Sand Filters

NB CURRENT MAHL CALCULATION CBOD [Actual Removal/Actual Flow] NPDES Permit Limit: 8.0 mg/l (summer) Removal Rate: 98.8% (270 data points/MRE) Actual Flow: 14.2 MGD** 8.0 mg/l = 8.0 = 666 mg/l max. allowable influent conc. 666 * 8.34 * 14.2 MGD = 78,952 pounds **DWQ required use of actual flow..flow has dropped since then. These are the approved headworks calculations from December 2003

“DESIGN CRITERIA” NORTH BUFFALO POTW  From Hazen and Sawyer Engineers Original Design (~1980 Upgrade)  BOD = 196 mg/l  TSS = 245 mg/l  Total Phosphorus = 6.0 mg/l  NH 3 -N = 18.5 mg/l

NB “DESIGN CRITERIA” per DWQ MAHL CALCULATION: CBOD  Engineering Design BOD = 196 mg/l Used BOD as CBOD  Engineering Design Flow = 16 MGD 196 * 8.34 * 16.0 = 26,154 pounds MAHL  Current Domestic BOD Loading: 27,615 lbs  20 of last 24 monthly average influent concentrations exceeded 196 mg/l while resulting in average effluent CBOD of <2 mg/l  CAN YOU SPELL OVERALLOCATED?????

NB CURRENT HWA CALCULATION TSS [Actual Removal/Actual Flow] NPDES Permit Limit: 30.0 mg/l Removal Rate: 97.8% (271 data points/MRE) Actual Flow: 14.2 MGD 30.0 mg/l = 30.0 = 1363 mg/l max. allow influent conc * 8.34 * 14.2 MGD = 161,492 pounds **DWQ required use of actual flow..flow has dropped since then. These are the approved headworks calculations from December 2003

NB “DESIGN CRITERIA” CALCULATIONS: TSS  Engineering Design TSS = 245 mg/l  Engineering Design Flow = 16 MGD 245 * 8.34 * 16.0 = 32,693 pounds [Current Domestic TSS Loading: 22,289]  Not overallocated now, but flow is only ~10.0 MGD  Domestic alone will use up the rest of the allocation

IMPLICATIONS  Underestimating POTW Conventional Pollutant Capacities and Capabilities Potential Over-Allocation With Just Domestic Loading! Loss of Potential New Industrial Users Potential Moratorium  “Domestic concentration” is rising due to newer plumbing fixtures  BOD Limits for All SIUs North Carolina Local Limits Policy

North Buffalo Current Loading Situation: DISMAL  Actual Influent CBOD Loading = 19,718 lbs 213 mg/l * 8.34 * 11.1 MGD [24 mo. avg]  DWQ Design Loading = 26,154 lbs 6436 lbs CBOD left…[“domestic” on paper is >MAHL] BOD Limits for Everyone!!!! [75.4% “loaded”]  Actual Influent TSS Loading = 32,401 lbs 350 * 8.34 * 11.1 MGD [24 mo. avg]  DWQ Design Loading = 32,693 lbs Only 292 Pounds of TSS Left…but over 4 MGD of hydraulic capacity left… TSS Limits for Everyone!!!! [~100% “loaded”]

North Buffalo SUMMARY CALCULATION METHOD Influent mg/l MAHL pounds BOD Pass-Thru Cal/Actual Flow66678,952 O&M “Design” (Proposed DWQ)19626,154 TSS Pass-Thru Cal/Actual Flow ,493 O&M “Design” (Proposed DWQ)24532,693