Environment, Federal Government, North America, United States, Water
Cashing in on Sustainability at Two Superfund Sites
Green approach helps EPA reduce PCE contamination in water supplies at two communities
Superfund sites in Vienna and Ravenswood, West Virginia, shared the common issues of groundwater contamination with tetrachloroethene (PCE) threatening public water supplies. In Vienna, two PCE plumes from two former dry cleaners had led to the shutdown of six city drinking water wells, with two more downgradient city wells at risk. At the nearby, smaller Ravenswood site, PCE from undefined sources was detected in five municipal drinking wells.
Using the knowledge gained through our remedial investigation, feasibility study, remedial design, remedial action and treatment system operation at the Vienna site, CDM Smith helped the U.S. Environmental Protection Agency (EPA) to significantly reduce the Vienna PCE contamination, while also benefitting the Ravenswood site, yielding cost savings for EPA through a green approach that reused one of Vienna’s treatment units.
Collection of vapor samples in a Vienna treatment unit.
At the Vienna site, CDM Smith designed an air sparge (AS) and soil vapor extraction (SVE) system for EPA to remove PCE from the subsurface, coupled with an extraction hydraulic control well strategically placed to maintain the hydraulic gradient of the larger plume away from the city’s wells. The design was based on thorough groundwater sampling to accurately characterize contaminant trends over time and the extent of the two PCE plumes. CDM Smith’s groundwater flow model predicted the capture zone of the hydraulic control well to guide accurate selection of the optimum location and pumping rate to hydraulically control the larger PCE plume.
Four separate treatment buildings were designed and constructed with AS and SVE treatment systems. The individual solenoid valves on each AS and SVE well, combined with a programmable logic controller (PLC), allowed CDM Smith to create multiple pulsing networks, which are modified periodically to optimize PCE removal. Design and installation of four smaller treatment systems rather than a single, large treatment system and operation of the systems in pulsing rather than continuous modes allowed the use of smaller capacity compressors and blowers for capital and energy savings and increased system effectiveness. Optimization of flow balances between the AS and SVE pulsing networks has further reduced electrical usage by 30 percent.
Subsequently, at the Ravenswood site, CDM Smith evaluated existing data from the state of West Virginia’s extensive investigations and developed a groundwater flow model, plume maps, trend analyses and mass balance calculations to define treatment options. Ravenswood’s existing municipal Venturi strippers had been providing limited treatment capacity, with high maintenance needs.
Leveraging the experience gained at the Vienna site and the Ravenswood groundwater model, CDM Smith helped EPA develop a strategy to reuse Vienna’s decommissioned TU4 AS/SVE treatment system at Ravenswood for a pilot study, enabling rapid installation with limited costs.
At the Vienna site, within the first 4 years of treatment system operation, 1,529 pounds of PCE mass were removed, with a >98 percent decrease at the larger source area. By the end of 2013, 1,778 pounds of PCE had been removed.
CDM Smith’s installation and operation of the pilot system at the Ravenswood site has limited the PCE entering the municipal water supply, as EPA designs a larger, permanent treatment system for Ravenswood.
Both sites have realized energy savings from the pulsing networks employed to increase system effectiveness. Excavated materials from both the Vienna and Ravenswood systems were recycled and reused as additional green measures.