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A <br /> September 4, 1997 <br /> Page 2 <br /> The former USTs consisted of three gasoline fuel (5,000-gallon supreme, 2,000-gallon <br /> mid-grade, and 5,000-gallon regular) tanks of single wall steel construction located on <br /> the western portion of the site and one 550-gallon used oil tank of single wall steel <br /> construction located northeast of the former station building <br /> PREVIOUS INVESTIGATIONS <br /> In February 1995, The MARK Group, Inc (MARK) conducted a Phase I Environmental <br /> Site Assessment (ESA) The ESA included a field reconnaissance of the site and <br /> adjacent properties, literature reviews regarding historical land-use and hydrogeology, <br /> interviews, and review of governmental environmental databases Based on the results <br /> of the ESA, further environmental investigation was recommended (MARK, February <br /> 1995) <br /> In April 1995, MARK conducted a preliminary subsurface investigation which included <br /> the drilling of six exploratory borings The six borings included one adjacent to the <br /> former waste oil tank, one at the location of the former hydraulic hoist, one at the <br /> location of the former pump island, one adjacent to the location of the former product <br /> lies and two at the location of the former gasoline USTs Total petroleum <br /> hydrocarbons calculated as gasoline (TPH-g), and benzene, toluene, ethylbenzene, and <br /> . xylenes (131 EX compounds) were detected at 3 feet below ground surface (bgs) within <br /> the fotmer UST excavation backfill TPH-g and benzene were detected at <br /> concentrations of 170 parts pei million (ppm) and 0 051 ppm, respectively No TPI [-g <br /> or BTEX compounds wc,rc_ daecteu in any of the other samples collected (MARK April <br /> 1995) <br /> Subsuiface materials repotted during drilling included near-surface clayey fill and <br /> clayey fill with concrete debris within the former UST excavation backfill, and native. <br /> soil consisting of clay (noundwatei was not encountered and based on regional <br /> information groundwatLr flow was estimated to be to the southwest at a depth in excess <br /> of 50 feet (MARK, April 1995) <br /> On lune 18, 1996, a gcophysic,il sur,,ey of the site was conducted by NorCal <br /> Geophysical Consultants Inc. which included the use of ground penetrating radar and <br /> magnetometer technologies The survey identified five "anomalies" The anomalies <br /> were the waste oil tank and associated sump drain line, two corners of the former <br /> building where utilities formerly entered the building, one location adjacent to the <br /> foi mcr product island and most likely associated with the former product lines, and one <br /> location southwest of the building located approximately where the former product lines <br /> and iitthty lines crossed Subsequent ctp[oratory excavations revealed miscellaneous <br /> debris within two feet of the ground surface including asphalt both clay and metal <br /> utiles, piptng and woes <br /> On September 23, and Octobei 23 1996 PAC11-IC observed the etcavation and <br /> =c.nio\,Il activities at tht- 1,L1hJLct ,its ALLIX arcs tricludcd the it-wo\al of the waste MI <br /> �`uu,u i tt,s ��itE'it i <br />