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A S S O C I A T E S I N C <br />4.0 BACKGROUND <br />4.1 UST Removal <br />In February 1991, one 500 -gallon underground storage tank (UST) of unknown fuel type was <br />' removed, in August 1991, one 550 -gallon unleaded gasoline UST was removed, in October <br />1991, 47 feet of single wall piping was removed, and, in December 1991, one 7,500 -gallon <br />unleaded gasoline UST was removed Laboratory analysis of soil samples collected from <br />beneath the former USTs and piping locations indicated the presence of detectable concentrations <br />of total petroleum hydrocarbons Discoloration of soil and petroleum hydrocarbon odors was <br />noted in the field After the tanks were removed, the areas of the former tanks were backfilled <br />with the stockpiled material <br />4.2 Subsurface Investization <br />On April 23, 1998, a geologist from ATC Associates supervised the advancement of six soil <br />' borings, SB 1 through S136, to 21 feet bgs Soil samples were collected at five-foot intervals and <br />grab groundwater samples were collected from each boring Samples were analyzed for <br />petroleum hydrocarbons and elevated concentrations of petroleum hydrocarbons were detected in <br />soil and groundwater samples The April 1998 subsurface investigation results are detailed in <br />ATC's Summary Report of Subsurface Investigation, dated June 17, 1998 <br />' On September 21, 1998, an ATC geologist supervised the advancement of five soil borings, SB7 <br />through SB 11, from 5 to 31 feet bgs Soil samples were collected at five-foot intervals and grab <br />groundwater samples were collected from each boring Samples were analyzed for petroleum <br />hydrocarbons and elevated concentrations of petroleum hydrocarbons were detected in soil and <br />groundwater samples The September 1998 subsurface investigation results are detailed in <br />ATC's Summary Report of Additional Subsurface Investigation, dated November 4, 1998 <br />In January 1999, ATC supervised the advancement of three soil borings around the former <br />excavation area The borings were completed as groundwater monitoring wells Analytical data <br />indicated the soil and groundwater at the site were impacted with total petroleum hydrocarbons <br />as diesel (TPHd) and as gasoline (TPHg) The January 1999 subsurface investigation results are <br />' detailed in ATC's Summary Report ofAdditional Subsurface Investigation, dated April 7, 1999 <br />In July 1999, ATC supervised the advancement of two soil borings south and southwest of the <br />former excavation area The borings were completed as groundwater monitoring wells <br />Analytical data indicated the groundwater samples from the new wells were impacted with <br />TPHd The soil samples contained no detectable concentrations of TPHd or TPHg The July <br />1999 well installation activities are detailed in ATC's Summary Report of Well Installation <br />Activities, dated August 26, 1999 <br />w \I 30991reportslc1osure doc 4 <br />1 <br />