Book Description

Previous investigations at Travis AFB concluded that groundwater in portions of the Base is contaminated with chlorinated hydrocarbons and petroleum hydrocarbons. The nature and extent of the contamination are described in Remedial Investigation (RI) reports prepared for four operable units (OUs) at Travis AFB. Each OU covers a portion of the Base and encompasses multiple sites. Natural attenuation of contaminated groundwater is a potential remedy considered for the NEWIOU. In the remedy selection process, the Natural Attenuation alternative (Alternative 2) was compared with the No Action alternative (Alternative 1) and the Extraction, Treatment, and Discharge alternative (Alternative 3). In general, sites considered favorable for natural attenuation are those for which "active" remediation (i.e., extraction, treatment, and discharge) may not be cost-effective because of the relatively low concentrations of contaminants, strong sorption of pollutants on soils, and the potential for natural processes to remediate the contaminant plume in a reasonable amount of time while being fully protective of human health and the environment. The NEWIOU Groundwater WOD selected natural attenuation as the interim remedy for one site (LF006) and identified two sites and a portion of five other sites where the selection of the interim remedy has been deferred, but where natural attenuation will be assessed further. More details regarding the relationship of these sites to the Natural Attenuation alternative are provided in the FS, Proposed Plan, and Groundwater IROD. While the nature and extent of contamination at these sites are characterized in the RI reports, data are lacking with respect to natural attenuation. The understanding of natural attenuation has only recently developed to the point where a systematic assessment of the complex processes involved is possible.