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GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon, California 95320 �Q Telephone: (209)838-9888 Facsimile: (209)838-9883 ICES 'f June 24,2005 Mr.Jeffrey Wong San Joaquin County Public Health Services Environmental Health division 304 East Weber Avenue,Third Floor Stockton,CA 95202 Subject: Work Plan to Evaluate Potential Effect of Water Supply I Well on Dissolved Contaminant Plume Speedy Mart,8200 N.Highway 99,Stockton,CA Dear.Mr.Wong: Enclosed is a work plan to present a proposed scope of work to evaluate the potential effect of pumping from the private domestic well(PDW)on the dissolved contaminant plume at the subject site. The work plan is submitted in response to your letter dated May 18,2005. Copies of the work plan have been submitted to Jim Barton of the Regional Board, Mr_ David trey of the San Joaquin County District Attorney's office,and to the responsible parties. Pursuant to your letter,the work plan is designed to evaluate the potential effect on the dissolved contaminant plume• from pumping groundwater from the PDW at a level substantially greater than current water usage. The rate and duration of pumping from the PDW was selected based in part on discussions with Mr. Barton of the Regional Board. Ground Zero would like to clarify other issues expressed in your letter. Our responses follow the italicized excerpts from your letter: In a meeting at San Joaquin District Attorney's office on November 30, 2004, EHD stated that the pump test as proposed in the November 12, 2004 work plan, which calls for pumping from .MW--13C screened from 202 to 222 feet below surface grade (bsg), at a rate of 3 gallons per minute (gpm)for 8 to 10 hours to test for hydraulic communication with the deeper PDW which draws from approximately 330 feet bsg, is not likely to work since there is a vertical distance of more than a hundred feet between the bottom of the MW-13C screen and the top of the screen on the private drinking water well. As proposed, water would have to move against gravity rather than with gravity as would be the case when the PDW is pumping. As you know,the purpose of pumping from a well is to induce the flow of groundwater against gravity to bring the water to the surface; many wells in the area pull water from depths far greater than 100 feet. Even so, a pumping i test does not measure the vertical or lateral movement of water in a well or an aquifer; a pump test measures the head of water(force)that causes water to flow through an aquifer toward the pumping well. If wells MW13C and the PDW are screened within the same homogeneous aquifer, then the induced head would theoretically be observable in either well,regardless of the depth of the pump setting. EHD suggested at the meeting that level loggers should be placed in nearby wells in all 3 zones to begin collecting , data T or 2 days before the pump test to characterize natural water level fluctuations, then pumping from the PD W at a moderate rate, and continue the DTW monitoring for 1 day after the pump test. I All of the above elements were included in the December 6,2004 work plan. j w I WPp1cstcvr_rev2.doc a ,f