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In the work plan dated December 6, 2004, Ground Zero proposed pumping from the PDW at a rate of 20 gpm for a period of 48 hours in addition to a 4-hour step test at rates between 10 gpm and 30 gpm. Both EHD and Central Talley Regional Water Quality Control Board(RWQCB) did not agree with the second proposal since the high rate ofpumping and total volume ofproducedwater may negatively impact the contamination plume bypulling down the contaminants to a deeper aquifer. EHD also did not agree with the need for a step test since the objective is not to evaluate the sustainability of pumping rates. The pumping rate and duration in the December 6, 2004 work plan was selected based upon a preliminary hydrogeologic evaluation of the site to estimate the theoretical drawdown in MW13C at various facility well pumping rates. Based upon the preliminary evaluation, Ground Zero estimated that a pumping rate of 20 gpm for a period of 48 hours would exert a drawdown of approximately 0.20 feet in well M W 13C,assuming communication between the C Zone and deeper aquifer. Conducting short-term step-drawdown tests prior to the long-term test is common practice in evaluating aquifer characteristics. This procedure was discussed in the meeting with EHD staff on November 30,2004 no objections or concerns were raised at that time. We agree that step-drawdown tests are not necessary if the hydraulic characteristics of the aquifer(s)will not be fully evaluated.We share your concern that an extended pumping test could draw contaminants to the deeper aquifer; thus our initial proposal to draw water from well MW13C rather than from the PDW located downgradient of the plume. EHD requests you to have your consultant Ground Zero design a test that would effectively evaluate the hydraulic condition of the two zones while minimizing the potential of pulling down the contaminants. The objective of the directive is a qualitative assessment of the effect of pumping form(sic)the PDW to evaluate the potential for the PDW to influence the plume, thereby causing vertical migration of the plume and potentially impacting the PDW itself. It is not possible to effectively evaluate the characteristics of the two zones without conducting comprehensive pump tests on both zones. However, we can get some indication of the potential effect of pumping from the PDW on the dissolved contaminant plume by conducting limiting pumping from the PDW as you request. Ground Zero maintains that the current use of the PDW, about 100 gallons per day, will have no impact on the dissolved contaminant plume. The initial work plan proposed an expected pumping rate of 3 to 4 gpm over a period of 8 to 10 hours,which would produce approximately 1,440 to 2,400 gallons total.That total exceeds the current daily usage of the PDW by approximately 14 to 24 times,which we felt was adequate to determine the potential effect of the PDW on the plume, assuming a significant increase in pumping from the PDW. This latest work plan proposes pumping from the PDW at a rate of 30 gpm for a period of 2 hours, or approximately 3,600 gallons. Please feel free to call me at(209) 838-9888 if you have any questions regarding this workplan. Sincerely, Ground Zero Analysis,Inc. John P. Lane CA Registered Geologist 6795 JPL Attachment: Work Plan to Evaluate Potential Effect of Water Supply Well on Dissolved Contaminant Plume cc: Mr. Ray Baglietto,Mr.Frank Rauzi Mr.lames L.L. Barton,RWQCB Mr.David Irey, San Joaquin County Deputy District Attorney Mr.Lee Roy Pierce,Jr.,Freeman,D'Aiuto, Pierce,Gurev,Keeling&Wolf WPpt=tcvr rev2.doc