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SECTION 4.0 SITE INVESTIGATION ACTIVITIES Site Investigation activities conducted by URSGWC for this additional groundwater study included (1) a local well survey, (2) discrete vertical sampling of groundwater in three monitoring wells, and (3) estimation of hydraulic conductivity through the performance of three slug tests 4.1 LOCAL WELL SURVEY A review of public well records maintained by the CDWR and the USGS was conducted for the Shop 10 site The Califorrua Water Service Company, the primary provider of water to residents in Stockton, was also contacted regarding the water supply wells in the area According to the California Water Service Company, a public water well is located approximately 1,000 feet south of the site The District Manager of the California Water Service Company, Mr Enc Mar, indicated that he is not aware of any hydraulic communication between the shallow aquifer and the deeper aquifer(Mar, 1998) Approximately 37 percent of the water supply for the California Water Service Company is currently derived from groundwater Subsequent conversations with Mr Mar and a field reconnaissance place the well, identified as pump station 46-01, on 4`h Street approximately 900 feet southeast of the southern property boundary of Shop 10 The reported depth of the well is 450 feet, and is screened from 209 to 426 feet (Mar, 2000) Additional information is provided in Appendix D A local well driller, Clark Well and Equipment Co (Clark Well), located at the corner of South B Street and Charter Way, was contacted on August 24, 1999 regarding local private water wells Mr Mike Clark indicated that they have two wells on their property one well is screened from 50 to 180 feet bgs and is used to supply water to support their drilling operations, and the second well is screened from 250 to 300 feet bgs and is used to supply drinking water for their property These wells are located approximately 550 feet northeast of northern property boundary of the Shop 10 site The grout seals for the two wells extend from the surface to the top of the respective screen intervals Mr Clark indicated that he and his father have drilled the majority of residential, agricultural, and industrial wells in the area, and that they are aware of a number of ' residential wells more than 500 feet from the Caltrans site Mr Clark further indicated that the majority of residential wells in the vicinity were installed before 1972 and that these wells did ' not have grout seals or had 20-foot grout seals After 1972, when well permits became a requirement, a 50-foot grout seal was required Ten years ago, a 100-foot grout seal became the requirement (Clark, 1999) ' Based on conversations with Mr Clark in February 2000, the shallow well was used occasionally until 1999, and has since been shut off The deeper well is reportedly used occasionally and when used, is pumped at approximately 60 gallons per minute Mr Clark also indicated that there have been private wells located on the Charter Mobile Home Park property, located adjacent to the south of Clark Well and adjacent to the north of Stockton Yard, and on the San Joaquin County S%PROJ%4104010ao4isHOPIO�SHoaiasaoac 4-1 URS Greiner Woodward Clyde