2017 APWA NC Stormwater Management Division Conference Greenville, NC Evaluation of Pollutants in Wastewater Produced from Air Conditioning Cleaning Operations City of Durham Public Works Department - Stormwater & GIS Services Jonathan Baker and Patrick Hogan PUBLIC WORKS DEPARTMENT STORMWATER & GIS SERVICES DIVISION 101 City Hall Plaza Durham N.C. 27701 P 919.560.4326 F 919.560.4316 Jonathan.Baker@durhamnc.gov Durham Where Great Things Happen
Background Information
Why do companies clean air conditioning units? Prevent coil and fin corrosion and prolong the life of the unit Improve or maintain the unit s energy efficiency (Carrier, 2009) Contamination on condenser fins of air conditioner unit at a commercial property in Durham, NC (Carrier, 2009)
How do companies typically clean air conditioning units?
Why did we conduct this kind of study? In 2014, City of Durham staff identified two illicit discharges from coil cleaning operations Private Property City Owned Property
Regulatory Drivers for Durham Phase I Stormwater Program required under the City s NPDES permit City Stormwater Management & Pollution Control Ordinance Streams on the State s 303(d) List for Impaired Waters: Copper Zinc Dissolved Oxygen Turbidity Biological Impairment TMDLs Jordan Lake (chlorophyll-a) Northeast Creek (fecal coliform) Third Fork Creek (turbidity) Nutrient Management Strategies Jordan Lake Falls Lake Neuse River Basin
Study Design
Purpose and Scope of the Study Identify and quantify pollutants from AC coil cleaning operations Quantify annual pollutant loads Validate the requirements of the City s Stormwater Ordinance
Monitoring Plan www.durhampolice.com City of Durham Stormwater & GIS Services Local HVAC Maintenance Company Site 1 Site 2 Site 3 Sampled in May 2015 Located on ground level Estimated as medium level of dirtiness Cleaned with tap water and product with ph of 9 Sampled in May 2015 Located on ground level Estimated as high level of dirtiness Cleaned with tap water and product with ph of 14 Sampled in July 2015 Located on rooftop Estimated as low level of dirtiness Cleaned with tap water only
Field Measurements www.durhampolice.com Temperature and Dissolved Oxygen Turbidity ph and Conductivity Water Volume
Analytical Measurements Metals Nutrients Other Parameter Aluminum, Dissolved Aluminum, Total Cadmium, Dissolved Cadmium, Total Copper, Dissolved Copper, Total Zinc, Dissolved Zinc, Total Ammonia as N Nitrate+Nitrite as N Total Kjeldahl Nitrogen Total Phosphorus Biochemical Oxygen Demand Methylene Blue Active Substances Total Suspended Solids Units of Measurement ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l
Sample Collection
Field & Equipment Blank Sample Collection
Let the cleaning begin! www.durhampolice.com
Site ID 1 2 3 Duration of Sampling Event 43 min 33 min 27 min Volume of Wastewater 447 L 380 L 254 L Volume of Grab Samples 750 ml 900 ml 900 ml Interval Between Samples 5 min 3 min 3 min Total Number of Samples 9 10 10 Total Composite Volume 6,750 ml 9,000 ml 9,000 ml www.durhampolice.com Sample Collection
ph and Conductivity Measurements
Composite Sample Collection www.durhampolice.com Equipment: ISCO Avalanche automated sampler with 9.5 L carboy 15 L churn split sampler 0.45 µm filter and Geotech peristaltic pump
Site 1 Sanitary sewer vent on rooftop www.durhampolice.com Site 2 Hauled off site and disposed in sanitary sewer Site 3 Sanitary sewer vent on rooftop Wastewater Disposal
Study Results
Study Results Quality Control Field Blanks At site 3 there were hits for metals and TSS in the blanks MDL = Method Detection Limit PQL = Practical Quantitation Limit Field Blank = Combined Field Blank and Equipment Blank
Study Results Duplicate Sample All duplicate concentrations were within 10% of the associated wastewater composite concentrations 1.63% 3.13% 1.08% 0.85% 1.14% 7.17% 1.71% 2.17% 3.92% 0.00% 3.89% 1.73% 0.00% 0.00% 4.65% Metals Nutrients Other
Total & Dissolved Metals Concentrations EPA Recommended Water Quality Criteria 1 Aluminum: 87 ug/l 1 Water quality criteria for aluminum at a ph of 6.5 9.0
Total & Dissolved Metals Concentrations NC Surface Water Standards 1 Zinc: 36 ug/l Copper: 3.6 ug/l Cadmium: 0.82 ug/l 1 Acute toxicity standards for hardness-dependent metals, assuming hardness value of 25 mg/l
Nutrient Concentrations www.durhampolice.com
BOD, MBAS & TSS Concentrations www.durhampolice.com
ph Concentrations During the Cleaning Process NC Surface Water Standard ph 6.0 9.0
Conductivity Concentrations During the Cleaning Process Durham s trigger level for monitoring data: > 730 µs/cm
Wastewater Comparison: Metals
Wastewater Comparison: Nutrients Wastewater Comparison (Mean Concentrations) 80.0 Concentration (ug/l) 70.0 60.0 50.0 40.0 41 68 40 70 46 Durham WRFs Durham Mobile Car Wash Study Durham AC Coil Cleaning Study Low Strength WW* Medium Strength WW* High Strength WW* 30.0 29 20.0 16 20 15 22 14 10.0 0.0 5.6 1.0 2.7 2.6 7.0 4.0 Total Nitrogen Total Kjeldahl Nitrogen Nitrate+Nitrite as N Total Phosphorus *Low, medium, and high strength wastewater concentrations from Metcalf and Eddy (2003)
Wastewater Comparison: BOD and TSS * * * *Low, medium, and high strength wastewater concentrations from Metcalf and Eddy (2003)
Annual Pollutant Loads
Calculating Annual Number of AC Units Cleaned Surveys were distributed to 17 companies that service and clean commercial air conditioning units in Durham 6 companies responded to the survey
Calculating Annual Pollutant Loads 1. Pollutant loads were calculated for each composite sample per cleaning event 2. Annual pollutant loads were calculated for each event 3. Annual pollutant loads were averaged across all sites
Annual Loads: Metals www.durhampolice.com
Annual Loads: Nutrients www.durhampolice.com
Annual Loads: TSS & BOD www.durhampolice.com
Summary www.durhampolice.com 3 commercial AC units 3 levels of contamination 3 cleaning methods Untreated domestic WW AC Coil Cleaning WW Higher concentrations of Cd, Cu, Zn, TN, BOD and TSS than in untreated domestic wastewater
Questions Jonathan Baker Water Quality Analyst City of Durham Public Works Department Stormwater & GIS Services Division P 919.560.4326, ext. 30211 Jonathan.Baker@durhamnc.gov durhamnc.gov
Additional Info
Study Results Quality Control Field Blanks Metals Nutrients Other Field Blank Site 1 Field Blank Site 2 Field Blank Site 3 Analyte Units MDL PQL Result Qualifier Result Qualifier Result Qualifier Aluminum, Dissolved ug/l 42 100 42 U 42 U 42 U Aluminum, Total ug/l 42 100 42 U 42 U 176 Cadmium, Dissolved ug/l 0.36 1 0.36 U 0.36 U 0.36 U Cadmium, Total ug/l 0.36 1 0.36 U 0.36 U 0.36 U Copper, Dissolved ug/l 1.6 10 1.6 U 1.6 U 3.89 J Copper, Total ug/l 1.6 10 1.86 J 1.6 U 24.4 Zinc, Dissolved ug/l 3.8 10 4.6 J 4 J 410 Zinc, Total ug/l 3.8 10 7.7 J 4.4 J 2290 Ammonia as N mg/l 0.045 0.1 0.045 U 0.045 U 0.045 U Nitrate+Nitrite as N mg/l 0.041 0.1 0.041 U 0.041 U 0.041 U Total Kjeldahl Nitrogen mg/l 0.26 0.48 0.26 U 0.26 U 0.26 U Total Phosphorus mg/l 0.025 0.1 0.025 U 0.025 U 0.025 U Biochemical Oxygen Demand mg/l 2 2 2 U 2 U 2 U Methylene Blue Active Substances mg/l 0.021 0.1 0.021 U 0.021 U 0.021 J Total Suspended Solids mg/l 2.5 2.5 3 U 2.5 U 9.7 Result between MDL and PQL Result exceeded PQL MDL = Method Detection Limit PQL = Practical Quantitation Limit Field Blank = Combined Field Blank and Equipment Blank
Study Results Water and Cleaner Mixture (prior to applying mixture to AC units) Metals Nutrients Other Site 1 (ph 9) Site 2 (ph 14) Site 3 (Tap Water) Analyte Units Result Qualifier Result Qualifier Result Qualifier Aluminum, Dissolved µg/l 42 U 420 U,D 42 U Aluminum, Total µg/l 42 U 420 U,D 42 U Cadmium, Dissolved µg/l 0.36 U 3.6 U,D 0.36 U Cadmium, Total µg/l 0.36 U 3.6 U,D 0.36 U Copper, Dissolved µg/l 23 74.8 J,D 104 Copper, Total µg/l 43.5 83.1 J,D 135 J7 Zinc, Dissolved µg/l 310 452 D Rejected Zinc, Total µg/l 252 486 D Rejected Ammonia Nitrogen mg/l 0.28 1.1 D 0.045 U Nitrate/Nitrite (as N) mg/l 0.32 0.39 0.47 Total Kjeldahl Nitrogen mg/l 120 D 26 U,D 2.6 U,D Total Nitrogen mg/l 120.32 Total Phosphorus mg/l 2.5 U,D 2.5 U,D 0.37 J,D Biochemical Oxygen Demand mg/l 6500 D 2600 D 2 U MBAS mg/l 0.21 U 2.2 J 0.1 U Total Suspended Solids mg/l 120 2.7 2.5 U D: Qualifier indicates the sample was analyzed at dilution. J: Qualifier indicates the estimated reported value is between the laboratory MDL and the PQL. J7: Qualifier indicates the estimated reported value is between the laboratory MDL and PQL, although the value may not be accurate because blank contamination is evident. U Qualifier: indicates the analyte was not detected at a concentration greater than the detection limit. Gray Cells: Total Nitrogen was not able to be calculated at Sites 2 and 3 because of U qualifier on the corresponding TKN results.
Calculating Annual Pollutant Loads