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SPEEDY FOOD MART <br /> 8200 HWY 99, Stockton <br /> Page 2 <br /> Due to the high level of MTBE concentrations in ground water and potential <br /> threat to local receptors, this site is considered a high priority site for MTBE <br /> cleanup. You must make all efforts to meet these dates set by EHD. EHD <br /> requests you begin applying for pre-approval from the Clean Up Fund <br /> immediately. Failure to submit application for pre-approval to the Clean Up <br /> Fund is not a legitimate reason for delay -n the installation of an interim <br /> groundwater remediation system. <br /> • Procedures for installation of the two proposed down gradient wells to the north of <br /> the groundwater plume. <br /> Based on the map (Figure 5) in the work plan, the proposed locations of the <br /> two monitoring wells were about 100 feet northwest and 110 feet northeast <br /> of MW-6, and over 110 feet from each other. Assuming the central axis of <br /> the MTBE contamination plume lies on a line running between MW-1 where <br /> the former underground storage tank system was located and the down <br /> gradient wells MW-3, MW-4,and MW-6 which have been consistently <br /> impacted with MTBE (see Figure 1 below), the two proposed wells appear to <br /> be too far from the central axis of the plume. <br /> EHD recommends installing the proposed new wells closer to the central <br /> axis of the plume and MW-6 by changing the locations to a distance of about <br /> 200 feet from MW-1. Additional monitoring wells may be needed to define <br /> the longitudinal and transverse dimensions of the contamination and to serve <br /> as sentinel wells between the plume and the down gradient private drinking <br /> wells based on the results of these two wells in the future. <br /> Fi re 1 MTBE concentrations in groundwater sarn les <br /> 08/01 11/01 03/02 06/02 09/02 12/02 <br /> MW3 2,000 4,900 740 4,100 15,000 12,000 <br /> MW4 32,000 12,000 14,000 42,000 18,000 21,000 <br /> MW6 780 3,700 2,100 46 2,800 940 <br /> MW5 <2.0 26 24 4.5 68 <2.0 <br /> MW7 <2.0 <2.0 <2.0 <2.0 <2.0 <2.0 <br /> MW8 <2.0 <2.0 <2.0 <2.0 <2.0 <2.0 <br /> Results are all in micrograms per liter (µg/1) <br /> • Installation of a deep-zone well in the area of the release source (MW1) in addition <br /> to the proposed deep-zone (200 to 220 feet bsg) monitoring well near MW7. <br /> The area proposed for the deep-zone monitoring well near MW7 is located <br /> about 110 feet from MWl (the source area). Groundwater flow direction has <br /> occasionally fluctuated to the east toward MW7,but MW7 samples have <br />