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MEMORANDUM CALIFORNIA REGIONAL WATE QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 255-3000 Sacramento, CA 95827-3098 CALNET: 8-494-3000 TO: Gordon L. Boggs FROM: Elizabeth A. Thayer Underground T ogram Manager Associate Engineer DATE: 10 March 1995 SIGNATURE: - �— SUBJECT: AMW7O #4 REVIEW OF IlV SHU BIOREMM1477ON PROPOSAL, EAST BAY MUD, 1804 WEST MA11V STREET, STOCKWN, SAN JOAQUIN COUNTY In Addendum No. I to the Additional Site Assessment and Remedial Options Report; Remedial Action Plan (RAP), Black and Veatch consultants (BV) propose to conduct in-situ bioremediation of ground water contamination at the EBMUD site. A Report of Waste Discharge was included in the RAP because BV has proposed to reinject treated ground water and a permit, Waste Discharge Requirements, may be necessary. Pat Leary, also of this office, will review the adequacy of the Report of Waste Discharge and prepare a permit, if necessary. This memo, regarding the slug tests and the bioremediation proposal, contains questions and requests for clarification which must be answered by EBMUD. An attached memo contains a summary of the site history, file contents, and a list of reports missing from our file. GENERAL STTE CONDITIONS A. Soil consists of clayey material from the surface to approximately 10 to 12 feet bgs. Below the clayey layer is a sandy layer that extends to an approximate depth of 20 feet bgs. B. Depth to ground water has varied between 7 and 14 feet since 1989. C. Direction of ground water flow over most of the site has most often been to the southwest. However, the gradient has been to the northeast and east and on occasion an apparent depression has been measured near MW4, resulting in gradients to the northeast, west, and southwest throughout the site on the same date. D. Regional gradient is to the northwest. E. There is no indication of large volumes of soil contamination, other than that associated with contaminated ground water. F. Ground water contamination has been as high as 19,000 ppb TPHg and 1600 ppb benzene in MW8, 5000 ppb TPHg and 1200 ppb benzene in MW1, and 62 ppb TPHg and 1.7 ppb benzene in MW9. Contamination in the other six wells has been low to nonexistent. SLUG TEST A. The data from the rising and falling head slug tests performed on MWl, MW8, and MW9 were plotted and, from the graphs, lag time was estimated. 1. Hydraulic conductivities (K) were calculated using the commonly used Hvorslev method. - What porosity wto used for tyre sand pwJc, to caktdaw Ia 2. The average K was calculated using all Ks from the three wells. 3. Multiplying the average K and the hydraulic gradient (fairly constant based on several quarters of ground water elevation data), an average aquifer velocity was calculated. 4. According to reference literature, slug test data may underestimate K, and, therefore, velocity, by one to two orders of magnitude. Using average values for K and velocity may compound the error.