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Wastewater Treatment Plant Monitoring

MCES is responsible for collecting and treating wastewater in the seven-county Twin Cities Metropolitan Area (TCMA). MCES owns and operates eight wastewater treatment plants that treat and discharge 300 million gallons of wastewater daily to the Mississippi, Minnesota, St. Croix, and Vermillion Rivers.

Performance monitoring of all 8 MCES wastewater treatment plant discharges is conducted regularly to meet National Pollutant Discharge Elimination System (NPDES) Permit requirements and to assess the quality of treated wastewater discharged to the large rivers in the TCMA. Both biological and chemical monitoring are conducted on the wastewater treatment plant discharges. In addition, the chemical characteristics of groundwater in the vicinity of some MCES wastewater treatment plants are measured through a network of monitoring wells.

Effluent Toxicity Testing

MCES staff conduct toxicity tests on the treated wastewater (effluent) discharged from all 8 MCES wastewater treatment plants, according to U.S. Environmental Protection Agency (EPA) methods. It is valuable to conduct effluent toxicity tests to help determine the potential toxicity of numerous chemicals contained in treated wastewater, and to determine the effects of effluent discharges on aquatic life in TCMA rivers. Effluent toxicity testing, which exposes aquatic test organisms to treated wastewater under controlled laboratory conditions, is also conducted to determine compliance with federal and state regulations prohibiting the "discharge of toxic materials in toxic amounts." Effluent toxicity testing measures the short-term (acute) and long-term (chronic) effects of treated wastewater on the survival, growth and reproduction of aquatic test organisms. In addition to measuring the biological effects, physical and chemical analyses are conducted on the effluent to further characterize its quality. MCES began its toxicity testing program in 1979 as a self monitoring tool; however NPDES permits have required toxicity testing since 1988. Results of all NPDES permit required effluent toxicity tests are reported to the Minnesota Pollution Control Agency (MPCA).

For complete details of test methods, check the U.S. Environmental Protection Agency web site locations listed below.

• Methods for Measuring the Acute Toxicity of Effluents and Receiving Water to Freshwater Organisms
• Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Water to Freshwater Organisms

Effluent Suspended Sediment Toxics Monitoring

Monitoring of toxics associated with the suspended sediment in the Metro Plant effluent has been conducted since 1990, as required by the Metro Plant NPDES Permit. Suspended sediments are solids that are held in suspension by the force of flowing water. A variety of potentially toxic materials have a tendency to adsorb to the surface of these very small particles. Ninety-day composite samples of suspended sediment are collected quarterly in the Metro Plant effluent channel and at an upstream control site in the Mississippi River (UM 836.8, approximately 1.5 miles upstream from the Metro Plant outfall). Suspended sediment is collected using a sampler, which consists of a 10 foot stainless steel pole with three sets of four glass bottles attached at top, mid and bottom locations in the water column. After a collection period of 90 days, the samples are processed and analyzed for 36 contaminants of interest, including total and volatile solids, total organic carbon, phosphorus, seven metals (cadmium, chromium copper, lead, mercury, nickel, and zinc), and 25 pesticides, including 7 PCB aroclors. As required by the Metro Plant NPDES Permit, monitoring results are reported to the Minnesota Pollution Control Agency (MPCA) on a quarterly basis.

Groundwater Monitoring

MCES and its predecessor agencies have been monitoring groundwater at various wastewater treatment plant locations since 1975, to determine the impacts of past biosolids disposal practices on local groundwater quality. Groundwater monitoring has been conducted for planning purposes, and to meet NPDES and State Disposal Permit requirements of the MPCA and local governments. MCES maintains a database containing all existing MCES groundwater monitoring data. Routine groundwater monitoring is conducted quarterly at the Metro and Seneca Plant ash disposal facilities, and data are reported to the MPCA as required by solid waste permits. Quarterly groundwater monitoring is also conducted at the Metro Plant ash lagoons.

Since some groundwater de-watering is necessary at the Seneca Plant to maintain the structural integrity of the treatment tanks, the Seneca NPDES Permit also requires measurement of surface water flows and groundwater elevation monitoring in the nearby Nichols Fen. This monitoring is conducted in cooperation with the Minnesota Department of Natural Resources and the City of Eagan.

Glossary

Helpful definitions for words located through the Rivers, Streams and Lakes web page.

For further information on wastewater treatment plant monitoring, please contact Garry Durland.

gary.durland@metc.state.mn.us