This technology status report provides a snapshot of the status of the in situ flushing remediation technology. The information provided herein is a reflection of the content of the Ground-Water Remediation Technologies Analysis Center’s (GWRTAC’s) case study database for innovative technologies. GWRTAC’s case study database is not represented as being comprehensive, nor are the case studies included screened to verify their validity, quality, or “success” in remediation. Rather the case study database and resultant summaries are intended to provide members of the ground-water remediation community with basic information on activity in laboratory research, field demonstration, or fullscale application of innovative technologies in both the public and private sectors. The summaries are provided as a “snapshot” of the contents of GWRTAC’s “living” case study database. Analysis of information present in GWRTAC’s case study database and presented herein, is by GWRTAC.
In situ flushing is defined as the injection or infiltration of an aqueous solution into a zone of contaminated soil/groundwater, followed by downgradient extraction of groundwater and elutriate (flushing solution mixed with the contaminants) and aboveground treatment and discharge or reinjection. The majority of pilotscale demonstrations of in situ flushing to date have involved the use of surfactants and cosolvents, while in the U.S., where fullscale site remedies have utilized in situ flushing, plain water is typically used as the flushing solution. GWRTAC is including plain water flushing solutions as in situ flusing cases, following the convention previously established by U.S. EPA. Halogenated VOCs are the most frequently targeted contaminant based on projects of all scales.
Some sources of information to GWRTAC have indicated a reluctance of regulatory personnel to the use of injectants for site remediation due to toxicity concerns. Research efforts underway at some institutions are focusing on the development of low toxicity, biodegradable, or U.S. Food and Drug Administration (FDA) approved food additive flushing reagents to address this concern. In addition to toxicity concerns relative to injectants, persons responsible for implementing or regulating in situ flushing projects are concerned with containment, since the alteration of hydraulic and chemical properties, if uncontrolled, could exacerbate the contamination problem they are attempting to remediate. These two reasons are the most likely technical reasons for the small number of fullscale projects using surfactants, and why many of the enforcement sites flush within physically contained subsurface zones, such as sites first bound by slurry walls. Economically, recycling and reuse of surfactants or other flushing additives is also of concern, especially to site owners or potentially responsible parties (PRPs). Some research projects are specifically addressing recycling and reuse, as well as modeling of the flushing process.