What is an Underground Storage Tank System?
An underground storage tank system is a tank and any underground piping connected to the tank that has at least 10% of its combined volume underground. Underground storage tank systems have been used primarily to store petroleum, but have also been used to store other hazardous substances.
Underground storage tanks are primarily found at commercial business locations such as the obvious gasoline stations and automotive shops, but can also be found in residential areas or other areas that were once commercial. At the midpoint of the 20th century, it was not uncommon for residential homeowners to install underground tanks to store gasoline or oils used for fueling heating systems (non-gas furnaces). Knowledge of historical land use of the subject property and surrounding properties will provide valuable insight on this topic.
Why is identification/awareness of USTs important?
The biggest impact of USTs is groundwater contamination (toxic liability). UST leakage occurs from old storage tank material corrosion, faulty installation, and inadequate handling. In an area where groundwater is relatively shallow, during a leak, the petroleum or other hazardous substance immediately contaminates the surrounding groundwater molecules found in the soil particle voids. These contaminants are then carried off-site through underground streams that carry groundwater from a higher elevation to a lower elevation in most cases. In an area where the leak does not occur near the ground water table (water saturated soil), the petroleum or other hazardous substance will contaminate the soil. The contaminant in this case becomes trapped in the soil particle voids and slowly works its way deeper into the ground percolating through the voids with the help of gravity where it will eventually run into groundwater. The contaminants will also reach the groundwater as water from irrigation, rain, or a changing water table filters through the soil from the ground surface collecting the contaminants in the soil and transporting them off-site.
Apart from negatively impacting the environment, contaminated groundwater affects individuals directly. According to the US EPA, it has been reported that groundwater supplies drinking water to approximately 50 percent of the nation’s overall population and 99 percent of the population in rural areas.
The costs of regulatory mandated removal and/or cleanup, and legal fees that result from USTs can be catastrophic. USTs can be identified during the environmental due diligence process (Environmental Site Assessment Phase I). In a Phase 1 ESA, a UST can be identified as a recognized environmental condition (REC). Groundwater monitoring wells located near a property are indicators of sites with a history of contamination. To see open and closed UST sites visit the CA State Water Resources Board Geotracker.
The US Environmental Protection Agency, states and local agencies have developed programs that provide regulatory oversight for the construction, operation, repair and removal of underground storage tanks (UST). These regulating agencies aim to prevent releases of petroleum and other hazardous substances stored in USTs. Local agencies such as the San Francisco Department of Public Health have created programs that address USTs. The program conducts all routine, construction, modification, repair and closure inspections of UST systems in San Francisco.
For more information on USTs and how they can impact costs and affect your property values, consult with your environmental consultant.