Services:

Alaska Department of Environmental Conservation (ADEC) River Terrace RV Park Site Investigation and Remedial Action

Issue:

The River Terrace site was a former dry cleaning facility adjacent to the Kenai River in Soldotna, Alaska. The contaminant of concern was tetrachloroethene (PCE) in groundwater, and two separate PCE plumes were present: one was migrating into the Kenai River; the other was impacting a storm sewer. Approximately 3,300 cubic yards of contaminated soil were removed from the site under an EPA CERCLA order. However, only a portion of the contaminated soil was removed, and PCE solvent contamination continued to affect site groundwater and sediments in the Kenai River.

Solution:

OASIS performed the RI/FS at the site including a treatability study; selection of a remedial alternative; development of a proposed plan and record of decision (ROD); and design of an HRC™ in-situ remediation system for solvent-contaminated groundwater and an air stripping system for solvent-contaminated storm water. Six remedial alternatives were considered in the final analysis: intrinsic remediation, permeable reactive barrier, in-situ air sparging curtain, funnel and gate system, water extraction with air stripping, and in-situ biological treatment. In-situ biological treatment was selected, mainly because the technology promised to shorten the treatment time frame by remediating the source area, not just intercepting and treating groundwater prior to sub-surface discharge into the river. A bench scale treatabilty study was performed using samples of site groundwater, then a field pilot study and performance evaluation were performed - data regarding contamination concentration, reduction-oxidation potential, volatile acid residue, and other factors useful in assessing performance of the system were collected. All work was performed in accordance with the State of Alaska Contaminated Site Regulations and RCRA.

Results:

The RI report included pieziometric surface maps, groundwater contaminant fate and transport modeling, aquitard maps, cross sections of the site, estimation of groundwater discharge rates, estimates of contaminant volume, groundwater production characteristics and analysis of natural attenuation. Data logger output and temporal groundwater data were evaluated using databases and spreadsheets to identify contaminant trends and to clearly document the relationship between the site and the Kenai River. The USEPA used the results of the SESOIL modeling to issue a “contained in” determination for the soil and to allow the site owner to dispose of the treated soil on-site. ADEC decided to scale up the pilot-scale system to a full-scale system to commence treatment sooner. In-situ bioremediation at the site is ongoing. Monitoring is performed quarterly to assess the remediation progress and to assess potential impact to the Kenai River.

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