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f ` Frontier Transportation, Inc. Well Installation Work Plan j November 14, 2006 Page 3 l 10' bgs in MW-15 using EPA Method 8260B. No other oxygenates or lead scavengers were detected. The maximum TPH-gas detected was 1 .7 mg/kg at 10' bgs in MW-15 using EPA Method 8015M. No detectable BTEX was identified in the soil column for MW-15 through (. MW- 18. See Figure 2 for well locations. In August 2005, BEA installed three shallow groundwater wells. Monitoring wells MW- 19, MW-20 and MW-21 were advanced to 20' bgs and screened from 5 ' bgs to 20' bgs. Then, in September 2006, two additional wells were installed in preparation for an aquifer pump test at MW-31Z. MW-22 and MW-23 were placed approximately 10.5 ' and 21 .5 ' north of MW-3R, I respectively. See Figure 2 for well locations. la - Quarterly groundwater monitoring has continued at the site and has identified the I. migration of MTBE to the west. Levels of dissolved MTBE have been consistently high (above MCL of 14 ug/L) in MW4 and MW-3R. Elevated levels of MTBE first appeared in MW-9 in f March 2005 and have continued to be present. 3.0) SITE GEOLOGY/HYDROGEOLOGY j 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 metamorpbic 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). BER encountered predominantly clays with some silts and sands from 0' to j 40' bgs during well advancement. First subsurface water was encountered at depths from I F to 12' bgs during tank removal j I and monitoring well installation at this site in 1995 and 1996. Since then, shallow subsurface water has been measured between 6' and 10' bgs. During well installation of MW-22 and MW- 23 groundwater was encountered at approximately 14' to 14.5' below grade surface. The flow of j ' groundwater is generally in a western direction beneath the site (See Figu3, Cir Grad' ap)• mitis 4� wa dvnS3 Ear aLi � rao� , - j 4.0) PROPOSED SCOPE OF WORK - It is clear from the recent groundwater monitoring event during September 2006 that MTBE contamination has migrated to the north and to the west. Groundwater monitoring wells _l � 1