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Addendum to Interim Corrective Action Plan �„t rJ UI "V -6 6 " _ Frontier Transportation, Inc. S � April 14, 2006 Page 2 l Six (6) underground fuel storage tanks (USTs), three diesel tanks located I northeast of the terminal and three gasoline tanks located southeast of the terminal, were removed from the site on July 21 , 1995 . Soil sample analysis identified total petroleum hydrocarbons as gasoline (TPH-g) and total petroleum hydrocarbons as diesel (TPH-d) in the gasoline tank excavation at maximum concentrations of 9, 800 i mg/kg and 120 mg/kg, respectively. Groundwater sample analysis identified dissolved phase TPH-d in the diesel excavation pit at a maximum concentration of 1 ,200 ug/L . In August of 1996, Twinning Laboratories, Inc. (Twinning) advanced six vertical soil borings (B- 1 , B -2, 13-3 , M 1RA3MW4RB, and MW-2RA) and one angle boring (134) to depths between 1 �3 ' and 115 ' below grade (bgs) to assess subsurface conditions near the northeastern excavation. In addition, two hand augers (S- 1 and S-2) were advanced to 3 ' bgs to assess subsurface conditions beneath the dispenser and product lines and three groundwater monitoring wells, MW- 1 through MW-3 , were drilled to approximately 25 ' bgs to assess the subsurface water beneath the site. Initial subsurface water was encountered at 10 . 5 ' bgs. Boring B-4 located northwest of the former USTs identified maximum TPH-g, a BTEX (Benzene, Toluene, Ethylbenzene, and Xylene) , and MTBE (MethyWert Butyl Ether) as 1 ,300 mg/kg, 180 . 7 mg/kg, and 110 mg/kg, respectively at 10 .2' bgs. lGroundwater samples were collected from monitoring wells MW- 1 , MW-2 , J' and MW-3 on August 30, 1996 and April 21 , 1997 by Twinning. In January of 1998 , Blakely Environmental Investigations, Inc . (BEII) advanced four (4) groundwater monitoring wells (MW-4 through MW-7) to assess 1 the extent of subsurface contamination beneath the site . Soil samples were collected every five feet. Laboratory analysis of soil samples identified no detectable concentrations of TPH-g, BTEX, or MTBE . In January 2000, BEII advanced two borings (13-5 and B-6), installed four additional groundwater monitoring wells (MW4 through MW- 11 ) , and collected - nine soil vapor samples for a soil vapor survey as part of an additional site - - assessment. Soil sample analysis identified no detectable concentrations of petroleum hydrocarbons with the exception of boring 13-6. Maximum contaminant levels in B -6 were identified 100 mg/kg as TPH-g, 2, 343 ug/kg as BTEX, and -4 10 ,600 ug/kg as MTBE at 10' bgs . Maximum soil vapor concentrations were identified at sample point V5 at 4' bgs . Groundwater samples were subsequently i � collected from all monitoring wells . - In May 2002, BEII installed two additional groundwater monitoring wells (MW42 and MW43) screened from 30' bgs to 40' bgs. Soil sample results !� I 2