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SIPC emery pond closure design
Project Summary
Hanson has provided the Southern Illinois Power Cooperative (SIPC) with engineering services for multiple projects, including a subsurface investigation and closure design for SIPC’s Emery Pond.
The project involved the clean-closed coal combustion residual (CCR) unit (Emery Pond) and the adjacent flue gas desulfurization (FGD) loadout area. Hanson evaluated the groundwater monitoring system, drilled and pressure tested a 150-foot bedrock boring to evaluate hydraulic conductivity, slug tested monitoring wells and collected soil samples for geotechnical testing. The pond’s closure required a groundwater flow and contaminant transport models (using the U.S. Geological Survey’s MODFLOW and MT3D) to evaluate the length of time groundwater cleanup would take.
Hanson retrofitted the closed pond with a CCR rule-compliant composite liner system (recompacted soil with a geomembrane). A perimeter toe drain was installed adjacent to the liner to prevent potential liner uplift and aid cleanup by removing groundwater. The latter required updating the facility’s National Pollutant Discharge Elimination System (NPDES) permit. Hanson collected various pond and stream water samples for analysis and used that data to perform an antidegradation analysis to support the permit modification.
Hanson has also assisted the SIPC with:
NPDES permit modification: Hanson provided services to update the NPDES permit for the SIPC’s Marion Station in Marion County, Illinois. Hanson conducted an antidegradation study to consider the potential impacts of short-term discharges from Emery Pond to the South Fly Ash Pond. Hanson also prepared Illinois Environmental Protection Agency documentation for the modification of the SIPC permit for the short-term discharge of untreated liquids from Emery Pond.
Unit 4 closing water management plan: Hanson evaluated the ponds that support the closing of the Marion Power Plant, Unit 4 shutdown and pond decommissioning.
Pond assessment for CCR material: Hanson was asked to evaluate the presence of CCR at the SIPC’s NPDES pond system. Borings were advanced adjacent to each pond or in berms separating ponds. Hanson inspected and photographed samples, which were analyzed for the presence of CCR indicator parameters.
Pond bathymetric surveys: Hanson subcontracted for a dual-channel bathymetric survey of SIPC’s NPDES pond system, then analyzed the data and created low- and high-frequency surfaces from the bathymetry data. One surface was subtracted from the other to create a map of the sediment thickness in each pond. These thickness maps were used to devise a sampling plan. Samples were collected from a small boat using a clamshell sampler at each pond and analyzed for the presence of CCR. A portion of the sediment samples were also sent to a subcontractor for visual evaluation for the presence of CCR.