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I_0 METHODS LL—Soil .SamItlingand.0 nt minati n Reduction Soil borings and soil sampling will be performed under the direction of a Delta engineer or geologist. The soil borings will be advanced using a truck-mounted drill rig utilizing hollow-stem augers. To reduce the chances of cross-contamination between boreholes, all downhole drilling equipment will be cleaned between borings. To reduce cross-contamination between samples, the spit-barrel sampler will be washed in a soap solution and double-rinsed between each sampling event. Soil sampling .will be done in accordance with ASTM I586-84. Using the procedure, a two-inch outside diameter split-barrel sampler or a two-inch inside diameter California-type sampler is driven into the soil by a 140-pound weight failing 30 inches. After an initial set of 6 inches, the number of blows required to drive the sampler an additional 12 inches is known as penetration resistance, or the "N" value. The N value is used as an empirical measure of the relative density of cohesionless soils and the consistency of cohesive soils. Upon recovery, a portion of the soil sample will be placed into a glass jar and sealed for later screening with a portable photoionization detector. Another portion of the soil sample will be used for classification and description. That part of the soil sample collected in brass tubes within the California-type sampler will be stored at approximately 4°C for transport to the laboratory. 1,2 Soil Classification As the samples are obtained in the filed, they will be classified by a geologist/engineer in accordance .with ASTM: D2488-84. Representative portions of the samples will then be returned to the laboratory for further examination and for verification of the field classification. Logs of the borings indicating the depth and identification of the various strata the N value water-level information, and pertinent information regarding the method of maintaining and advancing the borehole will be made. 1.3 Soil Sample Screening/Portable Photoionization Detector Method After soil sample jars have been brought to room temperature, the headspace vapors of the soil sample jars will be screened with a portable photoionization detector equipped with a 10.2 eV lamp calibrated to benzene for direct reading in parts per million(ppm). The sample jar lid will be opened and the probe immediately placed within the headspace of the jar. The highest observed reading will be recorded. 1.4 Monitoring Well Gravel Pack and Slot Size Selection The size of the gravel pack that will be placed adjacent to the well screen will be determined by the project manager based on an estimation of the distribution of grain size in the formation which is