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Ms. Julie Raining • -3- <br /> Cost Analysis <br /> GP has only estimated costs for natural attenuation and AS/SVE since the other alternatives were not <br /> believed to be effective. As noted above, I do not agree that ground water pump and treat is not <br /> effective. GP should include a cost estimate for ground water extraction from selected wells in the <br /> source area. <br /> GP estimates the cost for development and implementation of the natural attenuation option to be <br /> approximately $170,000 over the next 15 years. These costs would include development and <br /> implementation of a work plan to monitor natural attenuation. <br /> GP estimates the cost for testing, design, construction, operation, and maintenance of an AS/SVE <br /> system is expected to cost a minimum of$425,000 over the next seven years. These costs would <br /> include $30,000 per year of operation and maintenance cost for five years and seven years of <br /> semi-annual monitoring during system testing, design, operation, and post-operation at approximately <br /> $17,000 per year. <br /> GP should give more details on what is included in the costs for the AS/SVE system. GP should also <br /> consider possible ways to reduce these costs, such as reducing monitoring to annually after three years <br /> for a savings of$34,000 or operating the system for only 2.5 years for a savings of $75,000. SVE has <br /> been shown in some cases to be very effective at removing VOCs from ground water. It is possible <br /> that the remediation time may not be as long as five years. This could save $120,000 plus savings in <br /> monitoring if remediation was only necessary for one year. <br /> GP has selected natural attenuation as the appropriate remedial alternative since it is more economical. <br /> GP states that although natural remediation is predicted to be nine years longer than for an AS/SVE <br /> system, natural remediation is appropriate for the following reasons: <br /> 1) Chloroform has stopped expanding and appears to be receding due to natural processes. <br /> This may be true, but there are still significant concentrations of chloroform in the source areas <br /> which, if left in place, will prolong the time for concentrations to reach remedial goals. <br /> 2) The remediation times presented for both options are estimates and there is no guarantee that the <br /> remedial goals will be met through the use of an AS/SVE system within the time predicted. <br /> There is also no guarantee that remedial goals will be met within the time period predicted for <br /> natural attenuation. Considering that chloroform has a half-life of approximately 5.5 years in the <br /> source area as opposed to the three years used to estimate the time for natural attenuation to <br /> remediate chloroform to the remedial goal, it will likely take longer than the predicted 15 years for <br /> natural attenuation to achieve the remedial goal in this area. <br /> 3) There is no risk to the local population from the chloroform-affected shallow groundwater since <br /> the shallow water-bearing zone is administratively controlled by the City of Tracy. <br /> Chloroform has already impacted ground water which has been designated by the Basin Plan as a <br /> source of drinking water. The chloroform-affected shallow groundwater may also impact the <br /> lower water-bearing zones due to vertical migration downward. <br /> Our mission is to preserve and enhance the quality of California's water resources,and <br /> Recycled Paper ensure their proper allocation and efficient use for the benefit of present andfuture generations. <br />