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Beacon Station No 641 September 28, 1998 Stockton California _ __ Remedial Testing Report • On May 28, 1998, initial groundwater levels were found to be present at depths between 46 5 to 47.7 feet bgs Water-level data collected on May 28, 1998 was used to construct a Groundwater Contour Map (Figure 5) During a preliminary step-drawdown pumping test, groundwater was initially pumped from well MW-5 at rates of 5 gallons per minute (gpm), then 8 gpm, and then 10 gpm to evaluate a sustainable pumping rate for well MW-5 Well MW-5 was then allowed to recover for 43 minutes back to the initial water level After recovering to the initial water level, the aquifer pumping test was started at 1 00 PM Groundwater was pumped from well MW-5 at a rate of approximately 9 gpm for 22 hours Graphs of the groundwater drawdown measurements are presented in Attachment D Water- level data collected on May 29, 1998 immediately prior to the end of the pumping was used to construct the Groundwater Pumping Contour Map (Figure 6) Approximately 11,710 gallons of groundwater was produced during the pumping for the aquifer testing The extracted groundwater was cycled through two 200-pound activated carbon canisters for removal of dissolved hydrocarbons Groundwater was discharged to the City of Stockton sanitary sewer system under a Municipal Utilities Department Special Permit for Wastewater Discharge dated March 12 1998, and effective until March 12, 2003 Water samples were collected from the discharged groundwater on May 28 and 29, 1998 The collected samples were submitted under chain-of-custody (CoC) to Kiff Analytical (Kiff), a California Department of Health Services-certified analytical Iaboratory (ELAN . No 2236) located in Davis, California Groundwater samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg) according to EPA Method 8015, and the volatile aromatics benzene, toluene, ethylbenzene, and xylenes (BTEX) according to EPA Method 8020 / 602 Copies of the laboratory reports and CoC are included as Attachment B The summarized laboratory results are shown on Table 4 Water samples collected from the discharged (effluent) groundwater on May 28 and 29, 1998 indicated no detectable concentrations of TPHg (less than 50 ppb) and BTEX (less than 0 50 ppb) prior to discharge into the sanitary sewer Results of Aquifer Pumping Test Observation water-level data collected between May 28 and 29, 1998 indicated measurable drawdown in wells MW-1 (1 25 feet), MW-2 (0 42-foot), and MW-4 (0 47-foot) during the pump test Well MW-I is located approximately 14 5 feet northeast of pumping well MW- 5, well MW-2 is located approximately 58 feet west of pumping well MW-5, and well MW- 4 is located approximately 56 feet north of pumping well MW-5 Graphs of time vs drawdown, as measured with the automated data loggers are included in Attachment C The slope of the drawdown curves suggest a semi-confined aquifer response to pumping at the site Using the time-drawdown method for the datalogger data and a • pumping rate of 9 0 gpm, the calculated transmissivi ties (T) were 643 square feet per day for the MW-1 data, 1,033 square feet per day for the MW-2 data, and 1 050 square feet per day for the MW-4 data The calculated storativities (S) v,ere 0 008 for the MW-1 data, 0 017 for 1641-21 rpt 5 HORIZON ENVIRONMENTAL INC.