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A trend line with a negative slope illustrates that natural attenuation is taking place. <br /> MW-3R and MW-813 have achieved water quality goals. <br /> 175 <br /> The wells were natural attenuation is illustrated are MW-1, MW-IR, MW-2, MW-2R, MW-3, <br /> MW-5, MW-6, MW-7S and MW-8S. <br /> The post-pumping trend line for MW-I has a positive slope for MTBE with a post-pumping high <br /> 180 of 7.5ug/L versus a pre-pumping high of 1,400ug/L. The post-pumping trend line for MW-3 has <br /> a positive slope for 1,2-DCA with a post-pumping high of 1.1 ug/L versus a pre-pumping high of <br /> 6.2ug/L. The trend line for MW-6 has a positive slope for 1,2-DCA, but concentrations have <br /> stabilized at a low concentration of only 9ug/L. The trend line for MW-9 has a positive slope for <br /> 1,2-DCA, but has stabilized at a low concentration of only 2ug/L. <br /> 185 <br /> MW-10 is showing an increasing trend for Benzene and TPHg with a current high of 470ug/L <br /> and-2,900ug/L respectively. MW-1 I is showing an increasing trend for MTBE with a current <br /> concentration of only 3.2ug/L. <br /> 190 The post-pumping trend lines for EW-1 have a positive slope for TPHg, MTBE and 1,2-DCA <br /> which appears to have stabilized at a concentrations of around 120,000ug/L, 15ug/L and 7lug/L, <br /> respectively. Note that the 3/23/12 concentrations for MTBE and 1,2-DCA are significantly <br /> lower than the previous sampling. <br /> 195 6. CONCLUSIONS <br /> The 40'-80' sand layer holds 98% of the mass remaining and is represented by wells MW-1, <br /> MW-2, MW-3, MW-7S, MW-8S, MW-10, MW-11 and EW-1. The wells that represent a <br /> majority of the mass remaining illustrate natural attenuation is taking place. <br /> 200 7. RECOMMENDATIONS <br /> Prior to issuing approval of the proposed bio-reactor, Foothill Engineering recommends that the <br /> EHD review the submitted trend lines and consider if this site is a potential candidate for closure <br /> under the current criteria for No Further Action status. <br /> 205 Foothill Engineering considers this site to be a strong candidate for closure because the wells that <br /> represent a majority of the mass remaining illustrate natural attenuation is taking place. The <br /> current development laws and the permanent record keeping of Geo-Tracker will provide <br /> sufficient safeguards against the water being used for human consumption. <br /> 5 of 82 <br />