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N-, <br /> CONCLUSIONS <br /> Conclusions based on the result of this groundwater monitoring and sampling event, are as <br /> follows. <br /> :7 <br /> Analysis of groundwater samples using EPA Method 8260 have (1) confirmed the presence <br /> of MTBE in groundwater samples collected from monitoring wells, and (2) detected-lower <br /> concentrations of TAME than MTBE in samples collected from Wells MW-2 and MW-3 on <br /> May 7, 1998 . <br /> Concentrations of MTBE in groundwater samples collected in March 1997 were two orders <br /> • of magnitude higher that the results of the previous monitoring event. . <br /> • Increased MTBE and TPH-G concentrations are not correlated to changing groundwater <br /> _ elevations. <br /> • The increasing MTBE and TPH-G concentrations in groundwater samples are most likely a <br /> cs result of the absence of release protection devices necessary to comply with the December <br /> 1998 Federal and State release detection and protection requirements. <br /> RECOMMENDATIONS <br /> From the results of this monitoring event and evaluation of data,we recommend the following: <br /> • Perform additional assessment to include installation of additional groundwater <br /> monitoring wells and destruction of Monitoring Well MW-7 to further assess the extent of <br /> >�. dissolved-phase petroleum hydrocarbons and fuel oxygenates in the groundwater. These <br /> activities were proposed in the Work Plan for Supplemental Site Investigation dated May <br /> 18, 199 8 and submitted to the San Joaquin County Public Health Services. <br /> • Continue analysis of groundwater samples for fuel oxygenates (MTBE,DIPE,ETBE, <br /> �.;.; TAME, and TBA) for one additional sampling event to include the proposed additional <br /> i sj groundwater monitoring wells, after which the need for further analysis should be <br /> evaluated. <br /> ':111 <br /> N/460 I <br /> .I <br />