This site consists of co-mingled plumes of groundwater contaminated with VOCs, primarily TCE, and hexavalent chromium that initially extended approximately 4,000 feet downgradient of the source areas. Remedial activities performed by EA at the site include operation and maintenance of a groundwater pump and treat system, in-well stripping system, soil vapor extraction system, in situ injections, and soil removal. EA inherited operation of the groundwater extraction and treatment system, which was originally designed by the Washington Department of Ecology. EA initially evaluated the system, identified inefficiencies, and made design upgrades to improve system performance that simplified the system treatment train and proper pump sizing to reduce power consumptions by 30%, redesigned inefficient pipe runs (multiple tees, elbows, and parallel pipe runs), and properly sized resin canisters. In addition, EA saved client over $300,000 per year by installing an infiltration gallery to bypass city treatment system and began using passive diffusion bags for VOC sampling that resulted in a 50% reduction in labor cost compared to low flow methods. The TCE and chromium mass removal efficiency was enhanced by a combination of optimized groundwater extraction to achieve high pore volume flushing in source areas, and design modification to air stripper and ion exchange canisters. Further mass destruction was achieved in recalcitrant areas through chemical and biological reduction of TCE and chromium using zero valent iron, HRC, MRC, and emulsified oil.
Groundwater extraction and treatment and source area removal, the plume footprint has been reduced by 90% of its initial size. Recent computer model (MODFLOW2000 coupled with MT3DMS), data trend analysis, and matrix diffusion assessments indicate that the project is on or ahead of schedule for cessation or significant reduction of active groundwater extraction by 2020 with an increased focus on natural attenuation.
