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GEOMATRIX 4.2 Additional Soil Assessment The additional soil assessment was performed on 6 through 9 November 1995. Additional soil charac- terization consisted of advancing eight soil borings (SB7 through SB 14) using a Cone Penetrometer Test (CPT) rig equipped with a piston-type soil sampler. CPT services were provided by Gregg In Situ, Inc. ' of Martinez, California. Soil samples were collected every 5 feet for lithologic logging, field screening, and possible chemical analysis as described in Section 4.1. ' 4.3 Well Installation The groundwater monitoring well (MW4) was installed on 13 November 1995. Drilling services were ' provided by Spectrum Exploration, Inc. of Stockton, California. The monitoring well was installed using hollow-stem auger methods. Soil samples were collected every 5 feet for lithologic logging, field screening, and possible chemical analysis as described in Section 4.1. Field screening results indicated ' that petroleum hydrocarbons were not present in the soil samples and no samples were submitted to a laboratory for chemical analysis. The monitoring well was installed inside the hollow-stem augers after the boring had been advanced to 75 feet bgs and sampling was complete. The well was constructed of 4-inch diameter, schedule 40 polyvinylchloride casing and screen. The well screen slot size was 0.010 inches. The top of the screened interval was placed 5 feet above the groundwater surface (55 feet bgs) and extended from 50 to 75 feet bgs. The augers were removed simultaneously as the filter material, transition seal, and grout seal were emplaced. The filter material was Lonestar Lapis Lustre #2116. The filter material was placed in the annulus from the bottom of the boring to a depth about 2 feet above the top of the well screen. A transition seal consisting of bentonite pellets was placed in ' the annulus to a depth of about 2 feet above the top of the filter material. The remainder of the annulus was sealed with a cement/bentonite slurry. The well was finished flush with the ground surface with a locking cover and a water-tight, traffic-rated vault. Well construction details are summarized on the ' well construction summary included in Appendix B. ' The well was developed on 14 November 1995 by bailing, surging, and pumping. Field water quality parameters (temperature, pH, and specific electrical conductance) were monitored and the clarity of the water was observed during development. Well development was continued until the field water quality ' parameters were relatively stable. ' 4.4 Groundwater Monitoring Groundwater monitoring was performed on 17 November 1995 and 15 March 1996 and consisted of measuring groundwater levels, observing the groundwater in the wells for the presence of separate- - �- - -"`pliase petroleum hydrocarbon;arid-collectirig graundwater sainples.---Prior—to-collecting-groundwater" samples,the water level in the well was measured using an electric water level sounder, and at least four casing volumes of groundwater were removed from each well. Purging and groundwater monitoring were performed using an electric submersible pump. Prior to collecting groundwater samples, the pump flow rate was reduced to 100 milliliters per minute until the discharge line was purged. During purging, 4