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Canepa's Car Wash %aw Page 2 of 2 <br /> 248 E. Park Street April 1, 2010 <br /> Stockton, CA <br /> description of the hydrogeological framework and the contaminant type and distribution <br /> with cross-sections and maps as appropriate. <br /> The WP includes groundwater data for the existing monitoring well network and newly <br /> installed monitoring wells MW-8 though MW-17 that were sampled during the third <br /> quarter monitoring event of 2009 which revealed that the groundwater is significantly <br /> impacted. Intermediate monitoring wells MW-5, MW-9, MW-11, and MW-14 were the <br /> most impacted with TPH-g concentrations ranging from 95,000 to 110,000 Pg/l. The <br /> deep monitoring wells MW-10 and MW-12 were also significantly impacted with TPH-g <br /> concentrations ranging from 39,000 ,ug/I to 85,000 Ng/I. Farthest downgradient deep well <br /> MW-17 was less impacted with 1,100 ,ug/I TPH-g which indicate the minimum distance <br /> that plume appears to have migrated off site in the deeper zone. Shallow monitoring <br /> wells MW-8, MW-13, and MW-15, screened from 25 to 45, feet bsg are the only shallow <br /> monitoring wells constructed so far in this depth interval. These wells are variably <br /> impacted with COC concentrations ranging from below detection limits to as high as <br /> 3,000,ug/I TPH-g and 20 ,ug/I benzene. This data indicates that most of the groundwater <br /> contamination exists in the intermediate and deeper zones in which the vertical and <br /> lateral extent is still not defined. The EHD directs that a site conceptual model (SCM) be <br /> prepared and submitted to the EHD for review by June 7, 2010. Please include in the <br /> SCM a mass estimate of the sorbed and dissolved contamination plumes and locations <br /> where future assessment is needed to complete the delineation of the extent of <br /> contamination. <br /> Historical groundwater sample analytical results from MW-5 show a significant increase <br /> of TPH-g concentrations from 44,000 ,ug/I during the first quarter monitoring event of <br /> 2008 to 160,000 ug/I during the second quarter monitoring event of 2008. More ground <br /> water monitoring data, particularly from the newly installed wells, is needed to further <br /> evaluate the groundwater plume. The EHD directs that the newly installed monitoring <br /> wells MW-8 through MW-17 be monitored on a quarterly basis for one year and then be <br /> reduced to a semi-annual frequency. MW-1 though MW-7 shall be monitored in <br /> accordance with the schedule noted in the EHD letter dated July 15, 2009. <br /> The reports for the third and fourth quarter 2009 groundwater monitoring events have <br /> not been submitted to Geotracker (State Water Resources Control Board internet <br /> database system). Please submit the reports for the third and fourth quarter 2009 <br /> monitoring events to EHD and Geotracker by June 7, 2010. <br /> If you have any questions, please contact Frank Girardi at (209) 953-7868. <br /> A� <br /> Frank Girardi, Senior REHS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> C: James Barton, RWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 <br /> C: Art Deicke, Advanced GeoEnvironmental Inc., 837 Shaw Rd., Stockton, CA 95215 <br />