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Historical Summary: Langston's Market <br /> Page 2 of 3 <br /> April 1999 Advanced Geo Environmental hic. (AGE)advanced 4 Geoprobe soil borings at the <br /> 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 advancedto 50 feet;the remainderwere advanced <br /> 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 134) 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 /> May 2000 EHD issued a letter informing the Langston 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 approvedAGE'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(115,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 concentration of petroleum <br /> hydrocarbons were detected in the ground water sample collected from boring B9, <br /> Admnced Geo6nvironmentxl roc. <br />