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Addendum to the Well Installation and Hydraulic Testing Report and Additional ARCADIS Well Installation Work Plan Former Occidental Chemical Corporation Lathrop, California was then increased in 5-gpm increments until the extraction rate was approximately 65 gpm. Groundwater extraction continued at 65 gpm for approximately 12 hours; however, groundwater elevations did not stabilize and continued to decline.The extraction rate was then reduced to 30 gpm. Groundwater elevations quickly stabilized in the observation wells at the 30 gpm extraction rate.After maintaining an extraction rate of 30 gpm for approximately three hours,the extraction pump was turned off and the aquifer was allowed to recharge. Calculation of Transmissivity. Storativity, Hydraulic Conductivity, and Radius of Influence The drawdown characteristics measured during the pumping test were used to estimate several hydrogeologic parameters of the water table zone, including transmissivity, storativity, and hydraulic conductivity. In addition, a radius of influence was estimated for extraction well EW-09. Several methods are available to calculate these parameters.A variation of the Jacob method, known as the Distance-Drawdown Method,was chosen based on the field data (e.g., Sutch and Dirth, 2003). Drawdown at the three observation wells(PW27-40, PW28-40, and PW29-40)was measured simultaneously while extracting from EW-09 at a constant pumping rate of 65 gpm.The observed drawdown in PW27-40 located 15 ft north of the pumping well was 6.89 ft.The drawdown in PW28-40 located 20 ft south of the pumping well was 6.70 ft and drawdown in PW29-40 located 30 ft north of the pumping well was 5.71 ft.Transmissivity was calculated using the following equation (Sutch and Dirth, 2003): T=70`Q/ds (Equation 1) where Q = Groundwater extraction rate in gpm, equal to 65 gpm ds= Drawdown per log-cycle of distance, i.e., measured as 7.7-3.7=4 ft, using Figure 4. T = Transmissivity, in ft2/day The hydraulic conductivity was calculated using the following equation: K=T/b (Equation 2) where T = Transmissivity, in ft2/day, calculated to be 1137.5 ft2/day using Equation 1 2012-0913 addendum well Install work plan_hy test rpt.docx 3