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i PROBLEM ASSESSMENTJRT 14800 West Frontage Road Manteca California 5 2.1 No Action This alternative to groundwater remediation involves a negotiated plan to monitor groundwater quality without an active remediation system Generally speaking, for this option to be considered, free-phase product must not be present on the groundwater table For example, it is a matter of policy with the California Regional Water Quality Control Board regarding leaking underground fuel tanks sites that free-phase petroleum product must be removed from the groundwater table in all cases In any event, contaminants in groundwater must be demonstrated not to pose an immediate and/or long-term threat to the public health This option requires definition of the horizontal and vertical extent of hydrocarbons in groundwater via regular sampling of monitoring wells It must include a complete evaluation of the beneficial uses of the impacted water-bearing zone, as well as the background (regional) quality of the groundwater After a complete assessment of the extent of groundwater contamination, the beneficial uses of the water-bearing zone, and background water quality, an in-depth assessment of the potential threat to the public health must be undertaken In some cases this must be presented in the form of a formal health risk assessment prepared by a certified industrial hygienist In addition to the issues outlined above, the potential for migration of the groundwater plume must be evaluated When all of these parameters have been defined, and no significant threat to the public health has been demonstrated, a long-term groundwater monitoring program may be negotiated with the concerned regulatory agencies 5.2.2 In-Situ Groundwater Remediation Alternatives As mentioned in Section 5 2 this broad category of groundwater remediation alternatives does not include extraction, treatment, and discharge of treated groundwater Generally speaking, the technical approach is either to cause or enhance biodegradation and may include injection of various media including, but not limited to, air, nutrients, bio-cultures, and/or a combination of these elements 5.2.2.1 In-Situ Vapor Extraction As with in-situ soil vapor extraction, a groundwater remediation alternative utilizes a series of vapor extraction wells to remove volatile hydrocarbons from the subsurface A vacuum is applied to the extraction wells, typically by means of a blower, and volatile constituents on and dissolved in groundwater may be effectively removed In-situ vapor extraction can be a time- and cost-effective remedial technology in permeable soil, and if contaminants are volatile at ambient temperatures Vapor extraction systems have been shown to efficiently remove lighter-chain petroleum hydrocarbons from groundwater 90-097A PAR 12