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I <br /> Historical Summary Langston's Market <br /> Page 2 of 3 <br /> I <br /> April 1999 Advanced Geo Environmental Inc (AGE) advanced 4 Geoprobe soil borings at the <br /> I site to collect soil and grab ground water samples, then perform a mass balance <br /> calculation of remaining petroleum hydrocarbons in the subsurface and prepare a <br /> Closure Summary Report B-1 was advanced to 50 feet, the remainder were <br />' advanced to 25 feet <br /> May 1999 SEMCO did not pay AGE for work done, so AGE stopped all work on Langston's <br /> Market <br /> Aug 1999 EHD directed installation of additional monitoring wells on-site <br /> April 2000 AGE submitted an Additional Site Assessment Report indicating that ground water <br /> contamination was detected in four soil borings (B-1 to B-4) from April 1999 and <br /> that further investigation was warranted, TPH-g, BTEX, and MTBE were detected <br /> in grab water samples from on- and off-site push points <br /> I May 2000 EHD issued a letter informing the Langstons that additional work needed to be done <br /> to define vertical and lateral extent of the MTBE plume A sensitive receptor survey <br /> was also required AGE resumed active monitoring of the site <br />' • June 2000 EHD approved AGE's Monitoring Well Installation Work Plan,dated 23 June 2000 <br />' Sept 2000 AGE installed four additional monitoring wells MW-5 completed to 35 feet bsg and <br /> MW-6 through MW-8 to 30 feet bsg Since AGE began quarterly ground water <br /> monitoring at the site in March 1999, the inferred ground water gradient has <br />' consistently been toward the northwest <br />' Dec 2000 First monitoring event to include the new wells, results of the monitoring event <br /> detected high concentrations of TPH-g and MTBE in sample MW-5 (from the <br /> original UST area) and above-California's MCL for benzene Ground water flow <br />' direction was towards the northwest, There are no ground water monitoring wells <br /> down-gradient of MW-5 <br />' May 2001 EHD approved AGE's Work Plan Addendum dated 16 May 2001 for additional soil <br /> borings northwest and east and vertical at UST area to define vertical and lateral <br /> extent of contaminated ground water <br />' Nov 2001 AGE advanced three soil borings (B5, B6 and 139) for collection of soil and ground <br /> water samples No analytes of concern were detected in the analyzed soil samples <br />' collected from the three borings However, high concentrations of petroleum <br /> hydrocarbons were detected in the ground water sample collected from boring B9, <br /> • located east of the former UST location, target analytes were not detected in ground <br /> Advanced GeoEnvironmental,Inc <br />