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1 Geo(ogxa(Technws Inc Page 4 Groundwater Monitoring Report Project No 770 2 y November 13,2001 � l 1.3 Laboratory Analyses The groundwater samples collected on September 19, 2001 were delivered to Sherwood Lab (Department of Health Services Certification No 1400), of Hilmar, California, for analysis ' Sherwood analyzed the three monitoring well groundwater samples for • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by EPA method 602 ' • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) * TEPH- Diesel and Motor Oil by EPA method 3510/8015(M) ' The detection limits for the above analyses are listed in Table 2 of Appendix A while the lab analytical results are presented in Appendix B ' 2.0 FINDINGS AND DISCUSSION ' The results of the groundwater sample analysis indicate the following • Diesel range petroleum hydrocarbons were detected in all seven monitoring wells * Minor BTEX constituents are present at levels ranging from <0 4 — 4 9 �ig/l in wells MW-4 and MW-6 • Motor oil range petroleum hydrocarbons were not present in any of the groundwater ' samples at concentrations above the laboratory reporting limits • Gasoline range petroleum hydrocarbons were present in four of the site's wells MW-1, MW-4, MW-6 and MW-105 • Deep well MW-105 contained 130 µg/l TPH-D and 69 ug/l TPH-G * Wells MW-2 & MW-3 contained diesel contamination for the second time in the current ' investigation These wells did not contain contamination during the August and December 2000 & March 2001 sampling events * The lateral extent of the diesel groundwater plume is currently undefined due to the ' continuing fluctuations in groundwater direction • The vertical extent of the plume is intermittently defined by MW-105 ' An examination of the contaminant and groundwater direction data doesn't reveal any obvious trends A consistent factor previously noted in the investigation was the increase in diesel concentrations in well MW-5, see Figure 4- MW-5 TPH-D vs Groundwater ' Elevation This event marks the first decrease in the TPH-D concentrations and Figure 4 suggests a direct relationship between groundwater elevation and contaminant ' concentrations Well MW-5 contains the highest concentrations of detected contaminants but has not been down gradient of the former UST location for the five monitoring events completed to date The reason for this anomaly is not known F