SITE INFORMATION AND CORRESPONDENCE

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N%60� Page 2 of 3 Morita Brothers \%W111 06 February 2009 r 814 E.Charter Way Stockton, California into groundwater has dropped below the rate necessary to maintain the higher concentration; MTBE in soil in the saturated zone is no longer significantly impacting groundwater and is unlikely to do so in the future. Based on the predominant groundwater gradient direction and the analytical results from the grab groundwater samples collected from SB-2 and SB-3, GTI concluded that the total petroleum hydrocarbons quantified as gasoline (TPH-g) impacting monitoring wells MW-108 and MW-208 originated from the site at 749 E. Charter Way, and in view of the results reported in RRE and historical groundwater monitoring results, GTI recommended case closure consideration for the site. The EHD concurs with GTI's conclusions that the elevated TPH-g concentrations in MW-208 are likely to be related to the fuel release from the UST system on the site at 749 E. Charter Way. In addition to the professional opinions put forth by GTI, the following observations lead the EHD to agree with GTI regarding source of the TPH-g in MW-108 and MW-208: • The screen intervals of monitoring wells MW-5, MW-2 and MW-202 partially or wholly overlap those of MW-108 and MW-208 and the former wells lie between the latter wells and the suspected on-site source of hydrocarbon contamination, yet the contaminant monitoring history of the former wells do not demonstrate migration of the plume of impacted groundwater to the latter wells. Groundwater in MW-5 and MW-202 has essentially not been impacted, although MW-2 has been impacted, primarily by TPH-g and BTEX. • TPH-g was recently detected in a grab groundwater sample collected from a temporary well (SB-3) with the same screen interval as MW-208; the TPH-g concentrations in SB-3 were comparable to those in MW-208, although TPH-g was not detected in the closer SB-2 grab groundwater sample. Both borings were located between the suspected off-site source at 749 E. Charter Way and the impacted on-site wells MW-108 and MW-208. • Based on totality of observations — the monitoring system design, the direction of the predominant maximum groundwater gradient, the magnitude of the releases on each site, the location and monitoring history of the various data collection points, the EHD agrees that the source of the dissolved TPH-g in MW-108 and MW-208 is not likely to be the former on-site UST system, but may be the off-site UST system at 749 E. Charter Way. While reviewing the site data last summer to consider the case closure request, the EHD noted that MTBE concentrations in monitoring well MW-109 were displaying a slow, steady rise similar to that observed in MW-106, which appears to have maximized at a concentration of 25.6 pg/L (in MW-106) in May 2006 and has been gradually declining since. The EHD interprets the data to show a migrating plume with a low mass of MTBE encountering MW-109; if correct, the plume would not fit the definition of a stable and declining plume, which is required for closure. The EHD discussed this data with GTI and it was decided to collect a few more quarterly samples before considering the site for closure to test the EHD interpretation. The MTBE concentrations appear to Closure Request Response and Monitoring Frequency Letter 0209