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Report of Findings • Frontier Transportation, Inc. ' August 31, 2005 Page 3 migration of MTBE to the west Levels of dissolved MTBE have been consistently high(above ` tMCL of 14 ug/L) in MW-1 and MW-3R Elevated levels of MTBE first appeared in MW-9 in March 2005 Shallow monitoring well MW-1q has identified dissolved MTBE during every sampling event since its installation in January 200 'v"'` -06 v 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 Re ort, Twining Laboratories, October 16, 1996) BEII encountered predominantly heterogeneous clays from 0'to 30' bgs and fine-grained sands from 30' to 40' bgs,during well advancement of MW-15 through MW-18 LeFirst subsurface water was encountered at depths from 11'to 12'bgs during tank removal and monitoring well installation at this site in 1995 and 1996 Since then, shallow subsurface water has been encountered beneath the site between 6 and 10' bgs The three newly installed r shallow wells MW-19, MW-20 and MW-21 encountered groundwater at approximately 9 5' to 14' bgs during boring advancement J ' The past groundwater gradients included in quarterly groundwater monitoring reports have identified the flow of groundwater in a generally western direction beneath the site 4.0) SITE ASSESSMENT RESULTS ' On August 1, 2005 and August 2, 2005, BEA supervised the installation of groundwater monitoring wells MW-19, MW-20 and MW-21 to help define the extent of dissolved MTBE beneath the site and determine soil column contamination (See Figure 2 for well locations) Shallow monitoring wells MW-19, MW-20 and MW-21 were advanced to 20' bgs ' An 8-inch outside and 4 25-inch inside diameter hollow stem auger was used to install the monitoring wells The new groundwater monitoring wells were constructed of schedule 40 PVC casing The screen slots were sized at 0 01-inch with a size#2/16 sand annular pack The new shallow wells were screened from 5' to 20' bgs and the sand annular pack extended from 4 5' bgs • t r