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Mr. Donald Rodgers - 2 - 1 April 2008 515 West Charter Way, Stocer, San Joaquin County VW-2S, and VW-3S, to determine whether off-gassing of volatile components of petroleum hydrocarbons is occurring from the aquifer to the vadose zone, and whether soil vapor extraction will be needed during the proposed groundwater remediation. The assessment phase of the biosparging pilot test will include collecting baseline data prior to air injection, and then test data to determine changes in oxygen and carbon dioxide gas levels in the headspace of select observation wells during and after the air injection phase. A portable air compressor will be used to conduct the pressure step tests. An initial air pressure of 10 pounds per square inch (psi), which is near the expected hydrostatic pressure for the sparge well screen interval, will be increased to 15 psi and then to 20 psi for each 2-hour maximum pressure test. If, during pressure testing, the pressure gauge shows an increase over the baseline reading and stabilizes after reading the pressure gauge three times in a row in the nearest (10 feet away) observation well, that pressure test will be ended (minimum 45 minutes of testing per the above listed sampling frequency). The DO levels in water will continue to be monitored post pressure testing in two select wells at the following rates: every 15 minute for the first hour, every 30 minutes for the next three hours, once hourly for the next four hours, and once per day for the next 4 days. The Workplan concludes that the results of the biosparging pilot study will be incorporated into the design of the Final Remediation Plan (FRP) for full-scale remediation. The FRP will include an implementation schedule for construction of the treatment system, the plans and specifications for the system construction, startup protocols, routine operations and maintenance manual, performance monitoring criteria and evaluation reporting, and eventual systems decommissioning. The Workplan states the FRP will be prepared in accordance with Appendix A-Reports, Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites, 16 April 2004. Report Comment: Please work with the drapery shop on your property to ensure that upgradient well MW-2R is accessible for sampling during future quarterly groundwater monitoring events. Workplan Comments: At this time I cannot approve the Workplan. The following comments will require a written response from your consultant. Upon review of the responses and with the stipulation that the responses adequately address our concerns, I will provide approval to the Workplan. 1) The Workplan provides two differing sparge well diameters (1 inch in Section 4 and Figure 6, 2 inch in Section 5) to be constructed in a 3 '/z inch diameter boring. A) Please advise which casing diameter is correct in your response to comments. B) Also note that California Department of Water Resources Water Well Standards, which the San Joaquin County Environmental Health Department (SJCEHD) has adopted as the SJCEHD well regulations for permitting purposes, do not allow installation of a well casing with less than 2 inches of annular spacing measured around all sides of the well casing. In other words, a 1-inch outside diameter well casing requires a minimum 5-inch boring diameter (a 2 inch well casing requires a minimum 6 inch boring, etc.). In recent communication with the SJCEHD, I was informed that there are no know instances of SJCEHD variances given for this well