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N Addendum to Interim Corrective Action Plan Frontier Transportation, Inc. i`. April 14, 2006 Page 3 identified maximum TPH-g, BTEX, and MTBE concentrations of 700 mg/kg, I � 115 ,000 ug/kg, and 25,000 ug/kg in soil collected from MW- 13 at 10 ' bgs . Soil concentrations attenuate by 99% at 15 ' bgs. No detectable TPH-g, BTEX, and MTBE were identified in MW- 12 . Also, monitoring well MW-3 was abandoned prior to excavation and removal of 325 tons of impacted soil and replaced by MW- 3R. In June 2003 , BEII installed an additional groundwater monitoring well (MW- 14) screened from 30 ' bg to 40 ' bg. Soil sample results identified a maximum MTBE concentration of 1 , 020 ug/kg at 10 ' bg using EPA Method 8260B . No -I detectable concentrations of TPH-g or BTEX were identified in the soil collected l from MW- 14 . See Figure 2 for well locations. J In January 2004, BEII installed four additional groundwater monitoring wells . Deep monitoring wells MW- 15 , MW= 16 and MW- 18 were advanced to 40 ' j bgs and screened from 30' bgs to 40 ' bgs . Shallow monitoring well MW47 was J advanced to 20 ' bgs and screened from 5 ' bgs to 20 ' bgs. Soil sample results identified a maximum MTBE concentration of 1 ,310 ug/kg at 10 ' bgs in MW- 15 using EPA Method 8260B . No other oxygenates or lead scavengers were detected, f- l 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 I through MW- 18 . See Figure 2 for well locations. In August 2005 , BEA installed three additional shallow groundwater �. ( 1 monitoring wells, screened from 5' bgs to 20 ' bgs . Analytical results from the soil y urn -VA1 ' 1 samples identified MTBE in each of the new wells, MW- 19, MW-20 and MW-21 . co"�ky C TPH-gas was identified in MW- 19 and MW-21 . BTEX was identified in MW-21 at Y1V) d16v, 10 ' bgs and 20 ' bgs. MW49 contained ethylbenzene and xylene at 10 ' bgs. AW� t t 3.0) SITE GEOLOGY/HYDROGEOLOGY The site is located on the boundary of the Sacramento Valley and the San j l 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) . -I L- 3 �a .