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sampled at two depths, also based on lithology,but at approximately 5 and 20 feet bgs. Existing lithologs will be consulted to verify sampling depths. Continuous core borings, where lithologs are unavailable or where specific contacts are desired (e.g. the interface between the soil cover and the buried debris at the former ponds), will also be evaluated in the field to verify sampling depths. To the extent that prior samples in the vicinity indicate zones with concentrations suggestive of sources, those results will be used to modify the sample collection depths of subsequent locations from the 5 and 20 ft. default depths. Step-out sample locations, if needed, will follow the same depth selection procedure. The lithology for every soil gas location will be logged, and screen interval will be placed in the most permeable zone. A photoionization detector(PID) will be used to help determine the best soil gas sampling depth. Soil samples will be collected from the 11 soil cores retrieved during installation of the multi-depth soil gas probes in the former potential source areas. Soil samples will be collected from depths corresponding to the surface, 2.5 feet, 5 feet, 10 feet, 25 feet and approximately 40 feet bgs. The surface sample will be collected from immediately below (or from as close to immediately below as is feasible) the concrete/asphalt paving. The soil samples for analysis of dioxins and furans to be collected from the vapor borings at the former trash burning area and two downwind locations will be collected from two depths at each location: one at the surface, or immediately below pavement if presently paved, and second at approximately 2.5 feet bgs. Eight geotechnical soil samples will be collected and analyzed for geotechnical parameters. The locations and depths of the soil samples for geotechnical analysis will be determined in the field,based on soil gas results, lithology, and moisture. The cores from the installation of the soil gas points will be retained in acetate sleeves until the soil sample locations are selected. The geotechnical soil sample will be collected from the same location as the soil gas sample. The moisture content of the soil, as it can be assessed in the field, will also be considered prior to collection. The depth with the lower moisture content will be selected. The lithology for each soil point will be documented so that any other smaller layers for which a geotechnical sample is not collected can be considered in the risk analysis. Contingencies addressing potential difficulties collecting samples from the target depths are discussed in Section 5.5.11. 5.5.Field Methods 5.5.1. Utility Clearance Prior to the commencement of field activities, an underground location company will use a variety of geophysical methods which may include ground penetrating radar, Soil Gas and Soil Sampling Work Plan—Rev.4 7693-05 Former Kearney-KPF Facility Dudek Stockton,CA 13 September 2013