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URS Ms Vickie McCartney, REHS Page 3 . San Joaquin County Environmental Health Department ARCO 2186 Drilling and Monitoring Well Installation On April 13 through April 16 and April 19 and 20, 2004, Gregg Drilling, of Martinez, California, drilled four soil borings (BH-1 through BH-4) and installed one 2-inch diameter groundwater monitoring well (MW-8), one 4-inch SVE well (VW-4), and one 2-inch AS well (AW-1) at the site Prior to drilling, utility clearance was obtained from Underground Service Alert (USA) Cruz Brothers Locators, a private utility location contractor, cleared proposed boring locations to ensure that private utilities would not be damaged during drilling Boring locations were cleared to a depth of 5 feet below ground surface (bgs) with an air knife device prior to drilling Boring/well locations are shown on Figure 2 The borings were drilled using a drill rig equipped with 8- and 10-inch-outside-diameter (OD) hollow- stem augers (HSAs) to accommodate the installation of 2- and 4-inch diameter groundwater monitoring and remediation wells The total depth of the borings ranged from approximately 40 to 135 feet bgs First groundwater was encountered at approximately 48 feet bgs in the borings During the drilling of the boring for MW-8 (BH-3), the driller's sample hammer cable broke off at approximately 112 feet bgs In an attempt to recover his sample hammer, the driller had to over drill to 116 feet bgs Based on driller observations, the lithology in the depth interval from 112 to 116 feet bgs was thought to be saturated sand However, because the interval was not sampled, the lithology could not be confirmed Since the lithology could not be confirmed to the depth interval from 112 to 116 feet bgs in boring 1314-3 (Itthology data were needed for well-screen placement), the boring was backfilled with neat cement grout from the bottom to the ground surface Boring BH-4 was drilled approximately 5 feet to the east- northeast of BH-3 to install well MW-8 Boring BH-4 was cored continuously from 108 feet bgs to 135 feet bgs for lithologic characterization ' Soil samples were collected at 5-foot intervals using a modified California split-spoon sampler from 5 feet bgs to the total depth in the borings drilled for wells VW-4 and AW-1 Soil samples were collected at 5-foot intervals using a modified California split-spoon sampler from 5 feet bgs to 75 feet bgs in the boring for well MW-8, most of the depth interval from 75 feet bgs to 135 feet bgs was cored -- continuously Soils were logged by a URS geologist according to the Unified Soil Classification System No hydrocarbon staining or odor were noted for any of the soil samples A maximum photoionization detector (PID) reading of 22 6 parts per million (ppm) was noted near the capillary fringe during the drilling of well AW-1 During the drilling of well MW-8, a maximum PID reading of 8 9 ppm was noted at a depth of 54 5 feet bgs During the drilling of well VW-4, all PID readings were noted as 0 0 ppm Soil samples were submitted for laboratory analysts from each soil boring Soil samples pgre analyzed V-11- for depths of approximately 50 and 97 feet bgs for MW-8,40 feet bgs for VW-4,and, 'feet bgs for /I Sas AW-1 Soil samples were sealed in 2-inch-diameter brass sleeves with Teflon® squares and plastic end caps Samples were then labeled and placed on ice in a cooler, pending delivery to Sequoia Analytical Laboratories in Petaluma, California Soil samples were analyzed for gasoline range organics (GRO), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and for fuel oxygenates/additives (including MtBE) by U S EPA Method 8260B K IWproeessU5 BP ARC010218612004 Assessmentleeport 04 doe