Evaluation of Potential for Monitored Natural Attenuation of Perchlorate in Groundwater

Solutions-IES conducted an evaluation of the potential for Monitored Natural Attenuation (MNA) of perchlorate as a groundwater remedy at a rocket propellant manufacturing facility in Maryland. The work was funded by the Environmental Security and Technology Certification Program (ESTCP Project ER-0428). The project used a tiered approach described in a Perchlorate MNA Protocol Report (ESTCP, 2008) developed by Solutions-IES for the same project to systematically evaluate the commingled perchlorate and trichloroethene (TCE) plume located at a Solid Waste Management Unit (SWMU) on the east side of the facility. Demonstration Tier 1 -- Perchlorate Plume Stability and Geometry Most of the perchlorate contamination within the TCE/Perchlorate SWMU was previously defined using a network of monitoring wells screened in the shallow, intermediate zones of the surficial aquifer and the deep aquifer underlying the site. In the source area, both the shallow and intermediate zones are impacted with perchlorate with reported concentrations as high as 1,240 microg/L. The contaminant plume follows groundwater flow moving from west to east beyond the property boundaries, approximately 2,750 ft from the presumed source. The distal extent appears to be limited at Little Elk Creek as data indicated that perchlorate is below analytical detection beyond (east) of Little Elk Creek. By contrast, limited data suggest that TCE may possibly have migrated beyond the creek. These results suggest that mechanisms that could control perchlorate fate and transport are active prior to groundwater discharging into the creek. Little Elk Creek is a shallow stream that traverses a zone of undeveloped land covered with shrubs, vines and trees. The width of the naturally occurring buffer on the west side of the creek is approximately 25 feet including the stream bank which is an alluvium deposit composed of sand and gravel.