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San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD), <br /> subsequently required further assessment of the lateral extent of groundwater <br /> contamination Comfort Air appealed this request to the San Joaquin County Board of <br /> Supervisors, and was granted permission to install a single well northeast of MW-3 to <br /> delineate the down-gradient extent of the dissolved-phase contamination plume <br /> 3.0 PROCEDURES <br /> 3.1 Drilling and Sampling <br /> Groundwater depths measured by RESNA on March 3, March 17, October 20, and <br /> Novembei 20, 1992 indicated that groundwater flows to the northeast or east at this site <br /> Measurements taken October 11, 1993 confirmed this flow direction Therefore, Monitoring <br /> Well MW-4 was placed to the north of the office building (Figure 2) <br /> On October 12, 1993, one soil boring was drilled at the site The boring was advanced to <br /> a depth of 50 feet and completed as groundwater monitoring well MW-4 Auger returns <br /> were placed in 55-gallon DOT drums and stored on-site <br /> was drilled using a truck-mounted B-61 HDX drill ri The drill n and two-man <br /> The boring g g g <br /> crew were supplied by V & W Drilling During drilling, auger returns were monitored for <br /> the presence of organic vapors using a photo-ionization detector (PID. Thermo <br /> Environmental 580A, 10 0 eV, calibrated to isobutylene) <br /> Discrete soil samples were collected ahead of the drill bit using a split-tube sampler loaded <br /> with three pre-cleaned 2-mcli by 6-inch brass sleeves The samples were collected at five- <br /> foot intervals, using a 140 pound hammer to advance the sampler 18 inches The number <br /> of blows required to advance the sampler in 6-mch increments was recorded on the boring <br /> logs To avoid cross contamination, the sampling equipment was washed in a tri-sodium <br /> phosphate (TSP) solution and rinsed twice with water prior to each sampling run <br /> For each sample, both ends of the lead tube were covered yoth aluminum sheets, capped <br /> and sealed with tape The samples were then stored on ice and transported under chain of <br /> custody to Geochem Environmental Laboratories Mobile Unit <br /> 3.2 Logging <br /> Soil was extruded from the second brass tube and screened for the presence of organic <br /> vapors, using a PID, and the readings were recorded on the bonng logs The soil was then <br /> described in accordance with the Unified Soil Classification System (see Boring Logs, <br /> Appendix Al <br /> 4 <br />