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1.� N4 <br /> Assumptions and System Operations <br /> In designing the remediation system, several assumptions were <br /> made which will have varying degrees of impact on the system and <br /> its cost. One major assumption is that the proposed development <br /> has not changed from the plans received at EA dated 10/29/87 . <br /> Should the plans change significantly, the system layout may have <br /> to be reconsidered. <br /> Another major assumption is that the proposed location of the <br /> treatment system with an above-ground oil/water separator is <br /> acceptable to the Fire Department ( Figure 1 , Figure 2 ) . Since <br /> there is a high probability of recovering free product at this <br /> site, the Fire Department may require that the oil/water <br /> separator be located a certain minimum distance from nearby <br /> buildings . Relocation of the system should have little or no <br /> impact on the cost. Should the Fire Department disapprove the <br /> proposed location and if there is no other location that will be <br /> not hinder the development of this site, however , then the <br /> oil/water separator must be relocated to an underground location. <br /> This would involve re-specification of the oil/water separator, <br /> additional permitting for an underground tank with hazardous <br /> wastes, and additional monitoring for potential leak detection. <br /> The additional work and materials involved would have a <br /> significant impact on the total cost of the treatment system. If <br /> no free product is encountered after the system is in place, the <br /> oil/water separator may easily be disconnected and removed for <br /> use at another site. <br /> Due to the pending development of the site and possible long term <br /> existence of the system, the assumption that power to the site <br /> will be accessed underground has been made, with a maximum power <br /> supply run of 220 feet ( Figure 1 ) . This is a conservative <br /> assumption. Should power via an above-ground source become <br /> available and acceptable, the system will then access this <br /> source. Doing so will reduce the overall cost of the system. <br /> The remediation system layout is designed to create a hydraulic <br /> barrier such that contaminated ground water from a potential <br /> upgradient source will be diverted from the subject site ( Figure <br /> 1 ) . Due to the low hydraulic conductivity of the soils beneath <br /> the site, a injection trench will be used to create a more <br /> effective hydraulic barrier, instead of using existing wells MW4 <br /> and MW7 as injection wells. Any excess water will be discharged <br /> through the storm sewer system. The cost estimate assumes that <br /> one National Pollutant Discharge Elimination System (NPDES ) <br /> permit will apply for both reinjection into the trench and <br /> discharge into the storm sewer of the treated groundwater . The <br /> Regional Water Quality Control Board ( RWQCB ) which issues the <br /> NPDES permits, however, may require separate permits. <br /> Four groundwater depression pumps will be located downgradient of <br /> the former locations of both the tank field and pump islands in <br /> existing wells. These pumps are located both on- and off-site in <br /> 3 <br />