Ahtna performed a remedial investigation and remedial action at the former Tank Farm located at Gustavus, Alaska. The primary known release mechanism for petroleum contamination is the application of oil beneath the aboveground storage tanks (ASTs) to an underground header system to minimize corrosion. Fuels known to have been present at the former Tank Farm are diesel, gasoline, and aviation fuel. Our project objectives included: 1) investigate soils in the footprint and adjacent to the former Tank Farm; 2) install seven additional groundwater monitoring wells to delineate the extent of groundwater contamination; 3) conduct free product removal from existing Monitoring Well-4 (MW-4); and 4) collect groundwater samples from 11 monitoring wells (4 existing and 7 new monitoring wells). To execute the work, we developed a Conceptual Site Model using previous investigations and the Alaska Department of Environmental Conservation (ADEC) Guidance on Developing Conceptual Site Models.
Ahtna advanced seven borings for the placement of seven new monitoring wells. All analytical soil samples collected from the borings were analyzed for DRO, RRO, GRO, BTEX, and PAH. From the three existing and the seven new monitoring wells, we collected groundwater samples using a peristaltic pump, which were also submitted for analysis of DRO, RRO, GRO, BTEX, and PAH. We advanced five test pits beneath five former ASTs. We collected waste characterization soil samples to characterize the contamination in the soil. We also collected discrete grab samples from each test pit at depths of 2 feet and 4 feet below ground surface (bgs). Slight hydrocarbon odor was noted in two test pits. We advanced the test pits and collected additional soil samples at depths of 7 feet bgs and 12–13 feet bgs. Contaminants were detected at concentrations less than the ADEC Method Two, Over 40-Inch Zone, Direct Contact, Outdoor Inhalation, and Ingestion pathway cleanup levels.
Initially, the test-pitting performed was intended as a waste characterization tool only. However, Ahtna successfully negotiated with the Federal Aviation Administration (FAA) and ADEC to use the test pits to investigate the horizontal/vertical extent of contamination and determine maximum concentrations on site. Based on this approach, we discovered that contaminant concentrations were less than the applicable cleanup levels, eliminating the need to perform soil excavation. In addition, because it was agreed that the groundwater would not be used as a drinking water source due to industrial activity in the area and poor water quality as a result of the proximity to the Icy Strait, the FAA and ADEC agreed and approved alternative cleanup levels that were more representative of the site, resulting in project cost savings of $161,000.
To manage risks associated with contaminated groundwater, we recommended an institutional control restricting the use of groundwater as a drinking water source. From MW-4, we used a product bailer to remove approximately 0.5 gallon of free product/groundwater. To complete the project, Ahtna returned all disturbed areas to a surface condition resembling their original state. Borings were backfilled with the original soil cuttings.
Federal Aviation Administration
Federal Aviation Administration
DTFAAL-10-D-00002 / TO#0038