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». 27 June 1996 <br /> AGE-NC Project No. 95-0118 <br /> Page 2 of 23 <br /> -` 2.3. MONITORING WELL INSTALLATION AND ASSESSMENT <br /> On 20 June 1994, one soil boring(B-1)was drilled at the site. The boring was drilled near the center <br /> of the former UST and advanced to a depth of 38 feet bsg. TPH-g and BTE&X were detected in all <br /> four soil samples collected from'B-1. The highest concentration of gasoline was detected in B-1 at <br /> a depth of 30 feet bsg at 3,200 ppm. During drilling, ground water was encountered at 36 feet bsg. <br /> On 30 August 1994,three additional borings were drilled at the site to depths of 49 feet bsg and were <br /> completed as 2-inch ground water monitoring wells MW-1, MW-2 and MW-3. A total of 13.soil <br /> samples were analyzed for TPH as gasoline and BTE&X. Laboratory analyses detected TPH-g in <br /> 6 of the 13 samples analyzed. TPH-g and BTE&X were detected in two samples from MW-3; <br /> cs� <br /> toluene was detected in one sample from MW-2; and xylenes were detected in three samples from <br /> =' MW-2. Petroleum hydrocarbons were not detected in'samples from MW-1. <br /> On 31 August, 1995, three borings were drilled at the site to depths of 49 feet bsg and completed as <br /> 2-111ch diameter ground water monitoring wells MW-4, MW-5 and MW-6. Two soil samples from <br /> each boring were submitted for analysis. Petroleum hydrocarbon contamination was not detected in <br /> any of the soil samples analyzed. The locations of the wells are shown on Figure 2. <br /> ... 2.4. GROUND WATER MONITORING <br /> The ground water monitoring wells were initially monitored and sampled in September 1994. The <br /> hydraulic gradient was calculated to be 0.0029 ft/ft(0.17°) flowing toward the southeast. <br /> Analysis of the ground water samples detected TPH-g in MW-1,MW72 and MW-3 at concentrations <br /> -'� of 280 parts per billion (ppb, reported as micrograms per liter), 9,500 ppb and 1,200ppb, <br /> respectively.BTE&X were detected in samples from MW-2 and MW-3 at concentrations up to 1,600 <br /> -..� ppb (toluene, MW-2). No BTE&X were detected in MW-l.. Petroleum hydrocarbons were not <br /> I detected in the first sampling of MW-4, MW-5 and MW-6. The analytical results of all ground water <br /> samples are summarized in Table 3. <br /> t' <br /> 3.0. SOIL VAPOR EXTRACTION/IN-SITU AIR SPARGING WELL INSTALLATION <br /> 3.1. DRILLING AND SAMPLING <br /> On 26 January 1996, two soil borings were drilled at the site. Each boring was drilled using a truck- <br /> LA <br /> mounted HT-55 drill rig equipped with hollow-stem augers. The drill rig and a three-man crew were <br /> supplied by Mitchell Drilling Environmental, Inc. (MDE) of Rancho Cordova, California. Borings <br />