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11.0 METHODS <br /> . 1.1 Soil Sampling and Contamination Reduction <br /> Soil borings and soil sampling are performed under the direction of a Delta engineer or geologist The <br /> soil borings are advanced using a truck-mounted hollow-stem auger drill rig <br /> 1 To reduce the chances of cross-contamination between boreholes, all downhole drilling equipment is <br /> steamed-cleaned between each boring To reduce cross-contamination between samples, the split-barrel <br />' sampler is washed in a soap solution and a double-rinsed between each sampling event <br />' Soil sampling is done in accordance with ASTM 1586-84 Using this procedure, a 2-inch <br /> outside-diameter split-barrel sampler or a 2-inch inside-diameter California-type sampler is driven into <br /> the soil by a 140-pound weight failing 30 inches After an initial set of 6 inches, the number of blows <br /> required to drive the sampler an additional 12 inches is known as penetration resistance, or the "N" value <br /> The N value is used as an empirical measure of the relative density of cohesionless soils and the <br /> consistency of cohesive soils <br /> Upon recovery, a portion of the soil sample is placed into a plastic bag and sealed for later screening with <br /> Ma photoionization detector Another portion of the soil sample 1s used for classification and description <br /> That part of the soil sample collected in brass tubes within the Calxforma-type sampler is stored at <br /> approximately 4°C for transport to the laboratory <br /> 1.2 Soil Classification <br /> As the samples are obtained in the field, they are classified by the crew chief/geologist in accordance with <br />' the United Soil Classification System (USCS) Representative portions of the samples are then retained <br /> for further examination and for verification of the field classification Logs of the borings indicating the <br />' depth and identification of the various strata, the N value, and pertinent information regarding the method <br /> of maintaining and advancing the borehole will be made <br />' 1.3 Soil-Sample ScreeninglhNu Photoionization Detector Method <br /> After soil in the plastic bag are brought to ambient temperature, the headspace vapors of the soil sample <br /> 1 bags are screened with a portable photoionization detector equipped with a 10 2 eV lamp calibrated to <br /> benzene The sample bag is opened and the detector probe immediately placed within the headspace of <br /> ' the plastic bag The highest observed reading is recorded <br />