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RESPONSE TO SAN JOAQUIN COUNTY PUBLIC HEALTH SERVICES, ENVIRONMENTAL HEALTH DIVISION, LETTER DATED APRIL 17, 1992 This response addresses the San Joaquin County Public Health Services, Environmental Health Division (SJCPHS), letter of April 17, 1992, regarding the Alton Geoscience quarterly ground water monitoring and sampling report dated March 26, 1992. The issues raised in this letter are addressed as follows: First Issue: SJCPHS was not notified of the February 21, 1992 sampling event. For future events, notify Mary Meays. Response: Alton Geoscience will provide a minimum 48-hour notification for all future site activity. Second Issue: Water Sampling Field Survey Data Sheets (February 21) did not have information on temperature, pH, or electroconductivity. For future events these parameters should be measured and recorded. Response: It is standard practice of Alton Geoscience personnel to measure and record temperature, pH, and electroconductivity during purging of ground water prior to sampling. On February 21, 1992, a tri-meter was brought to the field to measure these parameters, however, the meter malfunctioned and was not repairable. Conditions on that day were inclement, as indicated on the held technician's Daily Field Work Report. It is possible that rain damaged the internal workings of the meter, thereby rendering it inoperable. Stabilization of temperature,pH, and electroconductivity following purging is considered to be an indication that formational ground water has entered the monitoring well. On February 21, three casing volumes were purged from each well prior to sampling. A review of past Water Sampling Field Survey Data Sheets indicates that on eight out of eight occasions these ground water parameters had stabilized with the evacuation of three casing volumes of ground water. Hence, it may be concluded that they had stabilized prior to sample collection. Moreover, field survey forms for the April 7 and 24, 1992 sampling events confirm this conclusion (Appendix F). Third Issue: SJCPHS was notified and present during the pump out of AW-3 on March 26, 1992. Obvious petroleum odors were observed, as approximately 200 gallons of ground water was removed during the pump out. Response: Alton Geoscience does not contend that ground water in the vicinity of AW-3 has not been impacted by hydrocarbons, however, sample procurement and handling was in accordance with Alton Geoscience