Unauthorized releases of gasoline and other petroleum products from leaking underground storage tanks (USTs) are prevalent throughout California. Soils and groundwater underlying the leaking USTs are often impacted by the released substances. This unfortunate scenario has occurred on numerous occasions at sites where USTs were used to store or distribute gasoline, diesel, or waste oil products. Depending on how much fuel was released, the site-specific geologic and hydrogeologic factors, and the land use of the site, the severity and degree of impacts can be highly variable, ranging from a low or minimal impact to the environment to a high impact (such as affect on drinking water wells or vapor migration of gasoline compounds into site structures).
The assessment and remediation of gasoline and other petroleum products released from USTs are regulated by any one of the nine Regional Water Quality Control Boards throughout California, or by local county health agencies authorized to implement corrective actions. The State Water Resources Control Board (SWRCB) administers the petroleum UST Cleanup Program. The SWRCB also administers the California UST Cleanup Fund, which was enacted to financially assist UST owners and operators the high cost of site assessment and remediation.
It has been well documented at individual UST release sites that petroleum fuels naturally attenuate in the environment through adsorption, dispersion, dilution, volatilization, and biologic degradation. This natural attenuation slows and limits the migration of dissolved petroleum plumes in groundwater. The SWRCB also recognized that the State’s technical and economic resources available for environmental restoration at UST sites are limited. Because of these natural attenuation mechanisms, and because many UST releases result in a low-impact or low-threat to the environment, on August 17, 2012, the SWRCB enacted the Low-Threat UST Case Closure Policy. The policy was enacted to expedite case closure of low-threat sites, so that available fund and regulatory agencies’ resources can be used to clean up the highest-threat cases.
To qualify for case closure under the Low-Threat UST Case Closure Policy, certain general and specific media criteria must be met. The general criteria are as follows:
Releases from USTs can impact human health and the environment through contact with groundwater, surface water, soil, and soil vapor. The media-specific criteria that must be met are divided into groundwater, vapor intrusion to indoor air, and direct contact and outdoor air exposure. Specifics pertaining to each media are based on several factors, such as distance of impact to a sensitive receptor such as a water supply well or surface water body, depth and concentration of contaminant beneath an existing or future building structure, potential of vapors intruding into indoor air, and depth and concentration of certain high-risk compounds (benzene, ethylbenzene, and naphthalene) in areas where no building exists. The specific criteria for each media, and details of the Low-Threat UST Closure Policy, are outlined in the SWRCB document found at: http://www.waterboards.ca.gov/board_decisions/adopted_orders/resolutions/2012/rs2012_0016atta.pdf
Under the Low-Threat UST Case Closure Policy, Alta Environmental has closed many UST sites by conducting site assessment activities only, without undergoing the expense of remediation. The results of the site assessments proved that the general and media-specific criteria for these sites were met.
If you are a UST owner or operator at a site where release of petroleum products have occurred, or would like more information regarding the Low-Threat UST Case Closure Policy, please contact Steve Ridenour (firstname.lastname@example.org). We can also be reached by phone at 562-495-5777.