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WASTE DISCHARGE REQUIREMENTS ORDER R5-2015-0058-01 -13- <br />SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS <br />FOOTHILL SANITARY LANDFILL, INC. <br />FOOTHILL LANDFILL <br />SAN JOAQUIN COUNTY <br /> <br />Soil Gas Probe Monitoring Results <br />Constituent Average Concentration, ppbv1 <br /> Shallow Deep <br /> SG-6 SG-112 SG-1 <br />Freon 11 382 4.5 <0.5 <br />Freon 12 1,054 600 115 <br />Freon 113 23.1 0.6 <0.5 <br />Freon 114 42.6 153 <0.5 <br />Toluene 67.9 80.8 53 <br />Vinyl Chloride <0.5 36.6 418 <br /> <br />1. Based on semiannual monitoring conducted from October 2003 through March 2014. <br />2. This probe also had the highest concentration of methane (17% by volume). <br />The monitoring and reporting program in these WDRs requires that the Discharger <br />continue semiannual monitoring of all the unit perimeter soil gas probes for field <br />gases and sample a probe for VOCs any time the field gas concentration in that <br />probe exceeds a specified threshold criteria based on field measurement of methane <br />and total organic vapor concentrations. See MRP, Section A.2.b.ii.7 <br />57. The soil gas monitoring system also includes 25 triple probe methane migration <br />monitoring wells (SG-12 and SG-102 through SG-125) installed along the facility <br />perimeter to per Local Enforcement Agency (LEA) requirements (Title 27, section <br />20919 et seq.). Soil gas well SG-12 was installed in 2004 and soil gas wells SG-102 <br />through SG-125 were installed in 2009. All wells were completed to a maximum <br />depth of 160 feet MSL with upper, intermediate, and lower zone nested probes <br />relative to landfill waste. The locations of these wells are shown in Attachment E: <br />Gas Controls & Monitoring. <br />58. Semiannual monitoring of the methane migration monitoring wells at the site <br />conducted under the facility’s Solid Waste Facilities Permit has not indicated any <br />methane exceedances along the site perimeter since installation of the wells. Also, <br />the wells were not historically monitored under previous WDRs, which were adopted <br />in 2003 before installation of the wells. Given the detection of methane and VOCs in <br />the soil gas probes along the perimeter of the landfill unit, these WDRs require that <br />the Discharger conduct VOC sampling at any methane migration monitoring well or <br />probe in which the above threshold criteria is exceeded.7 Copies of the monitoring <br />results submitted to the LEA are also required. See MRP, Section A.2.b.ii. <br />Soil Pore Water <br />59. LF-1 does not have a soil pore water monitoring system given that it is unlined and <br />predates Chapter 15 regulations. LF-2, Module 1 was constructed with <br /> <br />7. VOC sampling required in all soil pore gas probes in which methane is detected above 1% by volume <br />and/or total organic vapors are detected above 50 ppbv during a monitoring event.