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Surfacewater samples are analyzed eve ryfive (5) Years for the following COCs: Total Organic Carbon Semi-Volatile Organic Compounds Inorganics (dissolved) Chlorophenoxy Herbicides Volatile Organic Compounds(extended list) Organophosphorus Compounds Surface water COC samples were last collected on April 15, 2010. The next COC surface water monitoring event is scheduled for the first quarter of 2015. Saturated (Vadose) Zone Soil Pore Gas In accordance with the Waste Discharge Requirements and the Monitoring and Reporting program for the site, soil gas wells GW-1 through GW-7 are monitored for methane, oxygen, carbon dioxide, and VOCs (EPA Method TO-15) quarterly. In August 2013 two additional soil gas wells (GW-8 and GW-9) were installed. Starting in June of 2006, samples for VOC analysis have been collected from one probe at each well. At wells in which methane was detected, the VOC sample was collected from the probe with the highest methane content. Where no gas is detected, the VOC sample is collected from the deepest probe unless the sampling technician determined that there might be an obstruction to the probe, in which case a sample is collected from the next higher probe. Sampling has continued from those probes that were originally selected in 2006. Statistical Analysis of Groundwater Samples At the CHSL, the County has been approved to use the intrawell tolerance limit method (each well i provides its own background data) for groundwater analysis, and to use the interwell tolerance limit method for surface water analysis. Concentration limits are updated quarterly, and were most recently updated this quarter. When a statistically significant trend exists for the current data, or when greater than 50 percent of the data consists of non-detects, or when there are insufficient data, then the latest calculated concentration limit is presented (Table 1). Analytical results from the current quarter monitoring event were compared to the concentration limits shown. The Sanitas®program is used for statistical analysis. Calculation of tolerance limits for intrawell analysis requires less than 50 background observations. In cases where the total number of observations is more than 50 and there is no increasing trend,the 50 most current observations are used for intrawell tolerance limit analysis. i Corral Hollow Sanitary Landfill Department of Public Works/Soiid Waste I�'Quarter 2014 Groundwater Monitoring County of San Joaquin—March 15,2014