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FIELD REPORT PHASE II - WELL INSTALLATION AND DEVELOPMENT SAN JOAQUIN COUNTY HUMAN SERVICES AGENCY BUILDING, STOCKTON, CALIFORNIA ' Introduction On May 13-25, 1991, ROY F WESTON, INC (WESTON) installed five groundwater monitoring wells in the vicinity of the new Human Services Building in downtown Stockton, California Previous soil and groundwater investigation indicated the presence of hydrocarbon ' compounds in soil and groundwater at the site The primary goal of the new well installation was to establish a means of monitoring groundwater to determine the extent of the hydrocarbons ' in groundwater All work followed guidelines established in the WESTON Work Pian dated September 26, 1989 ' Well Installation The five wells were designated MW-4, MW-5, MW-6, MW-7 and MW-8 and were drilled using a CME550 hollow stem auger drilling rig Saturated conditions were encountered in the wells t depths ranging from 49-51 feet below ground surface (BGS) Total borehole depths matched total well depths with the exception of the first well, MW-6, which was advanced to a depth of 79 feet This well was advanced to a greater depth to gain additional geologic and hydrologic data for the area Table A-1 presents the monitoring well specifications ' Split spoon soil samples were collected while: drilling each of the wells to establish a lithologic profile Samples were collected at 5 foot intervals in the first well, MW-6 Once a regional depth to water of approximately 50 feet BGS had been established in the first well, samples were ' collected every 10 feet to a depth of 40 feet, then every 5 feet below 40 feet Samples were collected strictly for the purpose of determining lithology and for identifying indications of contamination, no laboratory chemical analysis was performed on any of the samples All soil ' samples and cuttings were screened with an Organic Vapor Monitor (OVM) for indications of contamination No elevated organic vapors were detected during the drilling of any of the five wells All drill cuttings were placed in labeled 55 gallon drums and stored in the vacant lot used ' for construction staging, pending a decision on the disposition of the cuttings ' During the initial drilling, the borehole was advanced using an 8 inch diameter hollow stem auger Once a saturated split spoon sample was encountered, indicating groundwater, the water in the borehole was given time to equilibrate Based on the measured depth to water, ' preliminary well specifications were calculated so that 13 feet of the 20 feet of screen was beneath the top of the water table In order to build a well with an adequate sand pack surrounding the screen, it was necessary to drill the borehole a second time with a 12 114 inch nominal auger This provided a well with approximately 4 118 inches of sand pack from the outside of the well screen to the edge of the borehole The well was installed inside of the augers, and sand was emplaced as the augers were being removed to ensure that no bridging occurred After the sand pack was installed, it was surged using a decontaminated 10 foot long and 3 inch diameter bailer The bailer was moved up and down through the screened interval ' P RPA - 1 05131,92 I'S1SlC 1�4