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I • 2005 2rid Quarter Groundwater Report Frontier Transportation, Inc. August 5, 2005 Page 3 ' 3.0) SITE GEOLOGY/HYDROGEOLOGY The site is located on the boundary of,the Sacramento Valley and the San Joaquin Valley ' within the west-central portion of the Great Valley Geomorphic province of California The Great Valley has been filled with a sequence of older to younger alluvium of Pliocene to ' Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age These sedimentary units, in turn, overlay a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks The shallow subsurface geology in the site vicinity is a heterogeneous mix of ' gravel, sand, silt, and clay (Reference Site Characterization Report, Twining Laboratories, October 16, 1996) BEII encountered predominantly clays with traces of interbedded sands from 0' to 25' bgs during well advancement in January of 1998 ' 5` 3 First subsurface water was encountered at depths from 4-l'to I-T bgs during tank removal and monitoring well installation at thus site in 1995 and 1996 Since then, first subsurface water ' has been encountered beneath the site between 6' and 10' bgs The groundwater flow is generally ✓hz a western direction beneath the site (See Figure 3, Groundwater Gradient Map) Historic first subsurface groundwater data identified a west or southwest flow beneath the site Groundwater I } was also encountered at approximatelyM5' bgs during installation of deep monitoring wells MW- 12 through MW-16 and MW-18 The potentiometric groundwater levels in these deep wells, however, were similar to the first subsurface water levels ' Hydrographs are presented as Figures 4 and 5 for shallow groundwater monitoring wells (up to 25-feet bgs) and deep groundwater monitoring wells (40-feet bgs) Groundwater levels ' beneath the site appear to be affected by seasonal recharge In general, the groundwater is at its yearly low in the winter and yearly high in the spring ' 4.0) QUARTERLY GROUNDWATER SAMPLE RESULTS BEA contracted Del-Tech to collect groundwater samples from 9 of the monitoring wells at the site on June 20, 2005 for laboratory analysis Monitoring wells sampled were MW-1, MW-3R, MW-9, and MW-13 through MW-18 Groundwater parameters (pH, temperature, and conductivity) were measured before, during, and after well purging (See Appendix A for Monitoring Well Field Logs) �o ' Ate' Groundwater samples were analyzed for TPH-g using EPA methods $015 and for BTEX, J � MTBE, tertiary butyl alcohol (TBA), di-isopropyl ether(DIPE), ethyl tertiary butyl ether (ETBE) and tertiary amyl methyl ether(TAME)using EPA method 8260 Laboratory analysis results for ' all monitoring episodes are presented in Table 1 Recent laboratory analytical reports are . included as Appendix B 1 I