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{ File No.2070-2 19 Dccember 1991 Pagc 11 5.1 In-situ Groundwater Treatment -- In-situ groundwater treatment is accomplished by injecting petroleum hydrocarbon consuming bacteria] microbes along with required nutrients into the contaminated aquifer. The bacterial microbes biologically detoxify the organic contaminants by converting them to harmless byproducts such as carbon dioxide and water. In-situ treatment systems can be relatively low cost remediation alternatives. A relatively small capital expenditure is required and disposal of the treated groundwater is usually not necessary. However, limited success is usually achieved via this treatment method due to subsurface formational restrictions which limit the movement of the bacterial microbes. Further complicating this treatment method is the difficulty involved in maintaining optimum conditions (ample oxygen and nutrients, for example). For these reasons, this treatment method usually needs to be supplemented by a chemical or physical treatment method (Proceedings of Petroleum Hydrocarbon and Organic Chemicals in Ground Water: Prevention, Detection and Restoration, 1988). Since the majority of the subsurface soil conditions at the P,ainbo Bakery site consist of silt and clay, this treatment method would be expected to achieve only limited success (as a result of formational restrictions). We therefore do rot recommend this treatment alternative for the ltainbn Bakery site. 5.2 Groundwater Extraction Systems G: water extraction systems involve the removal of the contaminated groundwater from the aquifer via extraction wells. The contaminated groundwater is then processed via a treatment system and the treated groundwater discarded. Four commonly used alternatives exist for the treatment of extracted groundwater contaminated with petroleum hydrocarbons. The treatment alternatives can be classified as biolog.al, chemical and physical treatment systems. Following are brief explanations of these treatment alternatives and their applications to the Rainbo Bakery site. 5.2.1 Groundwater Extraction and Biological Treatment This groundwater treatment alternative first requires the extraction of the contaminated groundwater from the aquifer via a groundwater extraction system. The contaminated groundwater is then transferred to a specially constructed containment basin. While in the containment basin, the contaminated groundwater is treated in the same manner as the in-situ biological treatment method previously discussed. However, since the contaminated groundwater is extracted priorto the introduction of microbes and nutrients, a more accurate monitoring of pertinent variables such as nutrients, temperature, flow rate, etc., is possible. This allows for a more efficient treatment of the contaminated groundwater to be performed. Upon completion of the biological treatment, tht treated water is discarded. ANDERSON C CONSULTING GROUP i WOMEN Vit.