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DRILLING TECHNIQUES AND SOIL SAMPLING PROCEDURES DRILLING Under the supervision of a California Registered Geologist, the soil borings are advanced using a truck-mounted hollow-stem auger drill rig. Each auger flight is 5 feet in length with an inner diameter of 3.5 inches and an outer diameter of 8 inches. A pilot assembly, consisting of a drill bit and center plug, is lowered through the auger stem and prevents soil from plugging the hollow-stem portion of the auger. The hollow auger also acts as a "temporary casing" preventing collapse of the bore hole wall. During drilling, soil cuttings are lifted up to the surface via the auger flights. When the desired sample depth is reached, the drill bit and plug are removed from the center rod and replaced with a split-spoon sampling tool. Usually, sampling is done at the end of each 5-foot auger flight This sampler consists of an outer "split barrel" sampler in which a thin-walled • set of rings is inserted. These rings are brass or stainless steel cylinders, and are 3 to 6 inches long, totaling 16 to 18 inches in length. ' A 140-pound hammer is used to drive the sampler into the formation below the bottom of the auger flight, thereby filling all of the sampling rings with soil. This method allows for collection of undisturbed soil samples and minimizes the introduction of overburden soil by the drilling process. The number of hammer blows (blows per foot, BPF) to advance the sampler a given distance is recorded on the boring log This gives an indication of the density and consistency of the soil. After retrieving and dismantling the sampler, all the thin tube rings are removed The bottom ring is immediately sealed for laboratory analysis by covering both ends with Teflon sheeting, plastic caps, and securing the caps with tape. If some of the soil in the bottom ring has fallen out or appears to have been disturbed during the recovery operation, the second to last ring is used. This ring is labeled and placed in an ice chest for cold storage pending transportation to the laboratory. This packaging protocol is designed to prevent loss of volatiles from the soil sample, and to minimize any cross-contamination. Standard chain-of-custody procedures are . followed for all samples collected for laboratory analysis.