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Beacon Station No 419 August 13, 1997 Stockton, California Aquifer Testing Report J ®r-, Groundwater data collected previously had shown a groundwater flow generally towards the southwest beneath the site, with an average gradient of 0 002 Aquifer Pumping Tests Field work was conducted in accordance with the Honzon Site Safety Plan dated March 5, 1997 Between May 28 and 30, 1997, Horizon conducted aquifer pumping tests at the site to evaluate aquifer characteristics of the shallow water-bearing zone beneath the site The tests were performed by using a 4-inch diameter submersible pump to pump groundwater from monitoring well MW-3, and measuring drawdown in observation wells MWA, MW-2, and MW-6 Automated data loggers were used to continuously record water level data in observation wells MW-1 and MW-6 Additionally, electronic water level indicators were used to measure water levels to the nearest 0 01 foot in observation wells MW-1, MW-2 and MW-6, as well as pumping well MW-3 Monitoring well MW-3 was selected as the pumping well because historically this well has had the highest concentrations of benzene detected during sampling and monitoring episodes On May 28, 1997 pumping tests were initiated at the site Initial groundwater levels were found to be present at depths between 51 0 to 51 5 feet bgs Water-level data collected on May 28, 1997 was used to construct a Groundwater Contour Map (Figure 2) During a preliminary test, groundwater was initially pumped from well MW-3 at a rate of 4 0 gallons • per minute (gpm) for 30 minutes, then well MW-3 was allowed to recover for 64 minutes back to the initial water level At that time, a the pumping test was started Groundwater was pumped from well MW-3 at a rate of 4 0 gpm for 210 minutes until an electrical problem shut the pump down Later in the afternoon, the pumping test was restarted, and ran at a rate of 4 0 gpm for 47 hours and 20 minutes After completion of the pump test, pumping of MW-3 continued at the site until June 16, 1997, to evaluate the long-term pumping effects on well MW-3 Horizon's Field Methods and Procedures are included in Attachment A Graphs of the groundwater drawdown measurements are presented in Attachment B Water-level data collected on June 9, 1997 was used to construct the Groundwater Pumping Contour Map (Figure 3) Approximately 12,200 gallons of groundwater was produced during the three days of pumping for the aquifer testing After completion of the pump test, the pump continued to operate at flow rates between 2 0 gpm and 4 0 gpm at the site until June 16, 1997 At that time, approximately 66,600 gallons of groundwater had been pumped from well MW-3 The pumped groundwater was routed from the pumping well to a flowmeter, and then into a 200-pound carbon canister prior to discharge Groundwater was discharged to the City of Stockton sanitary sewer system under a Municipal Utilities Department Special Permit for Wastewater Discharge dated September 1, 1995, and effective until August 30, 2000 1419 11-rpt HORIZON ENVIRONMENTAL INC