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Chevron <br /> Chevron Corporation <br /> 576 Standard Avenue, Richmond, CA 94802-0627 <br /> 1 J �Qr <br /> July 13 , 1988 <br /> ENFERPAIT/SERVICE JtTFI <br /> Addition to Tracy <br /> Bioventing Work Plan <br /> Mr . David L. Brent <br /> Environmental Affairs <br /> California Regional Water <br /> Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road <br /> Sacramento, California 95827-3098 <br /> Dear Mr . Brent: <br /> Chevron is currently running a bioventing field test in the Alden <br /> Park area o Tracv, California, as described in the work plan <br /> dated December 18, 1987. We now plan to test the system at a <br /> vacuum that requires removing water from the well. The purpose <br /> of this letter is to inform you of this addition to the work plan <br /> and describe why it is required. <br /> We have been operating the test continuously at well vacuums <br /> between 4 and 30 in. of water . (The vacuum was increased in <br /> steps for the first month of the test. The attached time line <br /> shows the general sequence of events. ) These vacuums result in <br /> air flow rates that are too low to completely assess venting ' s <br /> feasibility at the site. <br /> We have run short tests of a few minutes duration at a higher <br /> vacuum. These tests have been of short duration because the <br /> water level in a well rises when the well is under vacuum. Under <br /> high vacuum the rise of the water eventually blocks off the well <br /> screen, stopping the test. <br /> The flow rates generated under the higher vacuum were sufficient <br /> to measure hydrocarbon removal rates, but the tests were too <br /> short to see if those levels can be sustained. They were also <br /> too short to allow us to measure the radial influence of the well <br /> ( "reach" ) . Both removal rate and reach are crucial parameters in <br /> assessing venting' s feasibility. <br /> We are now planning to run a series of tests at higher vacuum, <br /> each test for eight hours duration. To do this, we will <br /> continually remove water from the well at the same time we are <br /> venting, thus keeping the water level in the well from rising. <br /> The eight-hour tests are needed to determine if longer term, con- <br /> tinuous testing at higher vacuums would be feasible and useful . <br />