Site B400 is situated south of the cantonment “triangle” in the area between the flightline and the northern apron at the Galena airport. Building 400 was a wooden structure that included a 750-gallon AST, baseboard heat, a 4-inch-diameter water well (Water Well #5), a septic system, and underground lines that provided electricity to the facility. The facility had an oil-fired boiler heating system (189,000 British thermal units). The AST was used to store heating oil for the facility. The wastewater system at Building 400 has been described as an underground septic tank with a leach field and a wood crib cesspool. Building 400 was demolished sometime between 1992 and 1998. The source of fuel-related contamination at Site B400 appears to be releases from the former AST at its southern location. The AST was used to store heating oil. A release of TCE from an unknown source appears to have occurred at the southern AST location which may be due to historic spills. The nature and extent of contamination at Site B400 in soil has been delineated laterally and vertically except for TCE. However, the extent of contamination in groundwater has not been delineated to the south of Site B400 and is a data gap. Additional investigation of downgradient groundwater contamination is needed. In addition, a baseline human health risk assessment under CERCLA will need to be conducted to complete the DQOs of the RI. The Method Two evaluation indicates a potential for unacceptable risks or hazards to future occupational workers, future excavation/construction workers, and hypothetical future residents. The concentration of benzo(a)pyrene in surface soil at one location exceeds the human health Method Two CUL; however, this location is adjacent to the runway and apron runoff may have contributed to contamination at this location. Low-level PAHs were detected in surface soil throughout the site. Concentrations of other COIs in soil from 0 and 15 feet bgs do not exceed the human health Method Two CULs. Soil in the vadose zone has TCE contamination at concentrations greater than migration to groundwater Method Two CULs. Soil in the variably saturated zone has DRO, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and TCE contamination at concentrations greater than migration to groundwater Method Two CULs. Only TCE in groundwater exceeds the ADEC groundwater CULs at one sample location. TCE appears to have impacted groundwater in the variably saturated zone at the location of the former UST, but groundwater impacts from upgradient and from the deeper part of the variably saturated zone is currently unknown and represents a data gap. A potentially-complete vapor intrusion pathway (under future conditions) cannot be ruled out at this time and further evaluation may be needed to assess the vapor intrusion pathway under an unrestricted land use scenario. There is no vegetation at the site; therefore, the site provides no viable ecological habitat or risk to ecological receptors. Similarly, exposure pathways for aquatic receptors are incomplete because the site is more than 1,000 feet from the Yukon River (that is, groundwater discharge to surface water in the Yukon River is considered incomplete) and there is no surface water onsite. Water Well #5 was abandoned when Building 400 was demolished (Radian, March 1996). Because the SI/SC/RI investigation site reconnaissance did not identify the presence of a well, and GPR results confirmed demolition debris from the former building foundation, no additional measures are necessary to locate the former water well. The exact location of the septic drain field is uncertain and is a potential data gap, and confirmation of the septic drain field location is needed. Recommend additional file review to confirm the location of the septic system and, if ,unconfirmed, collect additional samples under a supplemental RI to verify the absence of contamination. Although the cesspool at B400 has been found to not be a Class V UIC well under the EPA UIC definition, it may still require further closure under the Alaska Waste Water program. The uniform plumbing code, Appendix K 11.0 (B) requires that abandoned cesspools shall have the sewage removed therefrom and be completely filled with earth, sand, gravel, or other approved material. The B400 site information is being made available to the Division of Water, Wastewater program. Based on the results for the SI portions of the site, Trichlorethene (TCE) contamination in soil and groundwater above DEC cleanup levels was confirmed. The Site B400 moved to a Remedial Investigation (RI) phase and will be invetigated under CERCLA. No remediation has oocured at the site