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IRM Rehabilitation • -2- • 29 March 1993 <br /> DDRW, Tracy <br /> ► Work Plan development and Regional Board approval of chemical <br /> benchtest and chemical treatment processes prior to implementation of <br /> treatment. <br /> Other proposed activities related to the rehabilitation program include: <br /> ► Increasing the distance for swale repair to correct extraction well <br /> vault flooding problem. <br /> ► Increasing pipeline length installation from 480 to 780 feet to <br /> provide direct conveyance of treated water from the IRM system to the <br /> waste water treatment plant percolation-evaporation ponds 1 and 2. <br /> ► Discharge treated water from the IRM system into the stormwater pond <br /> and waste water treatment plant percolation-evaporation ponds. <br /> The Board supports DDRW, Tracy's efforts to optimize the IRM system. However, <br /> there are some concerns and issues that need clarification. The first concern <br /> involves the use of chemicals in the rehabilitation program. The Board <br /> prefers mechanical rehabilitation methods over chemical treatment methods. <br /> Common biocides contain chlorine. When ambient water containing natural <br /> organic matter is chlorinated, trihalomethanes (THMs) are produced (Marshack, <br /> 1986) . Chloroform, a potential carcinogen, is one of four chemicals that are <br /> THMs. The appropriate water quality goal for application to the protection of <br /> an ambient source of domestic supply from chloroform is the 10.6 cancer risk <br /> level of 0. 19 parts per billion (ppb) . <br /> We understand that chemical treatment may be necessary in this case to <br /> adequately disinfect the IRM system. As agreed upon in the conference call , <br /> the Board will allow DDRW, Tracy to use chemicals on a one time basis to <br /> disinfect the stripping tower and injection wells provided that steps are <br /> taken to collect the rinsates and purge water after treatment. All cleanout <br /> wastes are to be discharged into the lined waste ponds at the waste water <br /> treatment plant. The Board will not support use of a post stripping tower <br /> continuous feed chlorine injection program, unless DDRW, Tracy can <br /> conclusively show that degradation of the groundwater will not occur. <br /> The second issue requiring clarification, involves the IRM stripping tower <br /> rehabilitation. In our conversations we stated that the current tower packing <br /> may not be adequately cleaned out due to the severity of the growth. In that <br /> case, replacement of the packing material should be considered. Work Plans <br /> were proposed for the chemical benchtest and chemical treatment processes <br /> prior to implementation of treatment. A Work Plan for the stripping tower <br /> rehabilitation should also be prepared for Board concurrence. This Work Plan <br /> may be in the form of a letter outlining the stripping tower rehabilitation, <br /> but should contain sufficient detail such as: What chemicals, and how much <br /> will be used? How much water will be used in this process? How will success <br />