Project Specifics

Geosyntec designed a low-maintenance groundwater treatment system to prevent arsenic discharge from a coal ash landfill  into the Great Lakes.

Previous investigations at a coal ash landfill in Michigan associated with a nearby coal-fired power plant indicated that there was the potential for a discharge of arsenic to the Great Lakes at concentrations above the State’s Groundwater Surface Water Interface (GSI) Mixing Zone Criteria for arsenic. A previous groundwater flux study had evaluated arsenic concentrations into the lake. Geosyntec was retained to provide design-build services for the installation of a groundwater extraction and treatment system to prevent further arsenic discharge into the lake.

Geosyntec Scope of Services

Geosyntec revised an existing Modflow groundwater model to reflect an updated conceptual site model and to simulate pumping scenarios which were presented to the state for approval. Based upon that approval, we performed a bench scale test to select a treatment system that would reduce arsenic concentrations and provide a low-cost, low-maintenance corrective measure to mitigate the potential for an arsenic GSI exceedance. Our studies confirmed aeration, ferric chloride treatment, flocculation, and filtration as the most cost-effective solution to treat extracted groundwater.

We designed a force main system and extraction wells to capture groundwater along a 2,900-foot-long exposure of the landfill and pump it over 3,550 feet to the treatment building. The treatment system is composed of an aeration tank, a chemical feed system for the addition of ferric chloride, a settling tank, and bag filtration prior to discharge into the power plant water discharge channel. This treatment process oxidizes the reduced arsenic to a stable form in the first tank which floculates in the second tank. Water is then pumped from the second tank through four bag filters to the NPDES outfall, from which we collected influent and effluent samples to document that the treatment system is meeting the NPDES permit requirements.

Notable Accomplishments

Geosyntec designed a low-cost, low-maintenance groundwater extraction and treatment system that meets the NPDES discharge limit requirements for the facility. The system reduced discharge of arsenic-impacted groundwater, reduced future reporting requirements, and most importantly for our client, allowed the continued operation of the power plant.

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