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	Status: Active	Database Name: River Terrace RV Park
	Location: Soldotna, Alaska	Latitude/Longitude: See database entry
DEC Contaminated Sites contact: Rich Sundet, Project Manager, 907-269-7578

Workers inject Hydrogen Release Compound (HRC) around monitoring well No. 47 during the HRC treatment phase VI in August 2009 (see photos, above). HRC has been used at the River Terrace RV Park site to enhance the natural attenuation (primarily bioremediation) of PCE and its degradation products to treat the groundwater before it migrates off the River Terrace property. In the top photo, the worker on the right pours the HRC, which has the consistency of honey at room temperature, into the hopper while the worker on the left uses a hose attached to the drill to inject the HRC � heated, so it�s more fluid � underground. An instrument connected to the drill head has already pinpointed where the contamination is. The workers inject the HRC about every vertical foot in the groundwater area that�s contaminated. Most of the injection holes are installed on a permanent basis with a perforated steel pipe underground and capped, so more HRC can be injected later if necessary. The view is facing north; the Sterling Highway is in the background, along with the building that�s the former dry cleaner. The bottom photo shows the site looking southeast with the Kenai River in the background. The HRC is in the white buckets. (DEC photos, August 2009)

The major source of soil contamination that was practical to excavate � 2,700 cubic yards � was successfully treated. Some soil contamination in deep pockets (39 feet below ground surface) remains in the lower plume area.

The groundwater at this site in both plume areas was contaminated with PCE. A treatment technology using Hydrogen Release Compound (HRC) was initiated in 2000 to treat the contamination in the groundwater. The technology was immediately effective in breaking down the PCE, but the degradation process stalled at the cis-1,2-dichloroethylene (cis-DCE) degradation product stage and further degradation into non-toxic substances was not occurring. The persistence of this contamination resulted in a study to indicate if there was an absence of the bacteria necessary to break it down to its non-toxic compounds. In November 2002, DEC initiated a pilot study using bioaugmentation (injection of bacteria) to assist in the degradation of contamination. The bacteria were injected into several lower plume groundwater monitoring points and the initial results were positive. The levels of degradation compounds (trichloroethylene, DCE and vinyl chloride) increased above previous concentrations, which is normal during the remediation process.

In 2002, additional work in the lower plume area showed that the contamination remaining after the 1997 excavation was more extensive than previously thought. Elevated levels of contamination were found in the area of the deepest excavation (around monitoring well No. 44). Between 2000 and 2004, DEC focused on treating groundwater prior to it migrating off the River Terrace property, and HRC was injected in the upper and lower contaminant plumes to enhance natural attenuation (HRC treatment phases I-III). Between 2005 and 2009, the treatment of groundwater prior to migration off the River Terrace property has been augmented by hot-spot treatment of the remaining source area in the deeper lower plume (HRC treatment phases IV-VI). Monitoring data between 2005 and 2010 show that while bioaugmentation sped up natural attenuation in the pilot study area of the lower plume, HRC has worked to significantly decrease the total contaminant mass in both the lower and upper plume areas.

Public Health and Environmental Concerns

Groundwater and some soil contaminated with PCE and its breakdown products are the main threat to public health and the environment. PCE is listed by the U.S. Environmental Protection Agency as highly toxic and is a suspected human carcinogen. Avenues of human exposure have been blocked, so the area of concern is now to protect the Kenai River � specifically its sediments � from contamination.

Current Status

In 2009, work was done to clarify the size of the remaining deep source of PCE in the lower plume (around monitoring wells Nos. 44 and 47). HRC was also injected into this area for a third time, but the 2009 injection included using a less-viscous (more free flowing) type of HRC to obtain greater penetration into the tight soils in this area. Monitoring data will be used to determine the progress of the enhanced natural attenuation process and whether additional HRC injections will be necessary.

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