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°"° Y SANJOAQUIN <br />COUNTY-- <br />�cr Gsreotnessrows here. <br />Department of Public works <br />Kris Balaji, Director of Public Works <br />Fritz Buchman, Deputy Director/Development <br />Kt Michael Selling, Deputy DirectorJEngineering <br />Wodit for YOU Jim Stone, Deputy Director/Operations <br />Najee Zarif, Interim Business Administrator <br />July 27, 2017 <br />Mr. Todd Del Frate, PG <br />Engineering Geologist <br />Central Valley California Regional Water Quality Control Board <br />11020 Sun Center Drive, #200 <br />Rancho Cordova, California 95670-6114 <br />SUBJECT: FIRST SEMIANNUAL 2017 GROUNDWATER AND SURFACE WATER <br />MONITORING REPORT, FOOTHILL SANITARY LANDFILL <br />Dear Mr. Del Frate: <br />Enclosed is the First Semiannual 2017 Groundwater and Surface Water Monitoring Report for <br />the Foothill Sanitary Landfill, submitted in accordance with WDR No. R5-2015-0058. <br />The water at all groundwater wells was at drinking water standards, and monitoring constituents <br />were generally consistent with previous monitoring periods. Below is a summary of the findings <br />for this monitoring period: <br />• MW -1A — calcium and magnesium were slightly exceeded in the 1St Quarter 2017 <br />sampling event. <br />• MW -2R — there were no exceedances during the first semester of 2017. <br />• MW -3 — the concentration limits for sodium and calcium were slightly exceeded <br />during the 1St Quarter 2017 sampling event. Magnesium and bicarbonate alkalinity <br />were slightly exceeded in both the 1 st and 2nd Quarter 2017 sampling events. <br />• MW -4 was dry during the 1St and 2nd Quarter 2017 sampling events <br />• MW -5 — calcium and magnesium were slightly exceeded in the 1 st Quarter 2017 <br />sampling event. <br />• MW -6 — magnesium and sodium were slightly exceeded in the 1 St Quarter 2017 <br />sampling event. <br />Although some concentrations slightly exceeded the tolerance limits, they are still within the <br />range of historical data. <br />Two VOCs (1,1-Dichloroethene and Trichloroethene) were detected in MW -3 during the 1St <br />Quarter 2017 sampling event. Three VOCs (1,1-Dichloroethane, 1,1-Dichloroethene, and <br />Trichloroethene) were detected in MW -3 during the 2nd Quarter 2017 sampling event. <br />Methane was detected in one interior soil gas well (SG -1), but below the regulatory limit for off- <br />site migration. The unusual amount of rainfall that was experienced at the site during this <br />monitoring period has caused an increase in the amount methane generation from the refuse in <br />the landfill. This increased amount of methane generation has also been noticed at many other <br />landfills throughout the State. This over -abundance of methane within the landfill will require <br />additional time to extract with the current landfill gas extraction system in place. To accentuate <br />1810 East Hazelton Avenue I Stockton, California 95205 1 T 209 468 3000 I F 209 468 2999 <br />