FIELD DOCUMENTS AND WORK PLANS 1991

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Subsurface Soil Flushing System -2- 31 January 1991 Marley Cooling Tower Company enough to account for the historical dynamic regional ground water table conditions in the Stockton area. It is my understanding that there has been a dewatering of the aquifer at a rate of about ten feet per year in the last few years due to drought conditions. We are currently half way through the wet season and it appears that drought conditions may still prevail this year which indicates that the aquifer may continue to dewater. Historically, the regional ground water table has been as low as about - 55 feet mean sea level (msl), which is about 20 feet lower than the current ground water table. The regional ground water table is also known to have recovered about 55 feet in less than ten years. I have attached a table which summarizes historical ground water levels lows in the east central portion of Stockton. Because the regional ground water table is known to be a dynamic system, Marley should reevaluate the design of the monitoring tubes, injection wells and the extraction well in light of the historical ground water level information. The design of the subsurface soil flushing system should be flexible enough to account for these dynamic ground water conditions so that the system may be as fully operable as possible over the next fifteen years, regardless of the regional ground water levels. OTHER COMMENTS 1 . There are four phases of the Subsurface Soil Treatment System. These phases are: I. Construction of the Pilot Flushing System, II. Pilot Flushing System Operation, III. Construction of the Full-Scale Flushing System, IV. Full-Scale Flushing System Operation. The documents did not provide a tentative schedule for the different phases. A schedule is needed to coordinate the subsurface soil treatment system with other activities at the site. 2. The design documents state that a high strength waste treatment system will be constructed during Phase III. Black and Veatch has indicated that this system will be a pretreatment system to the new interim electrochemical reduction and pretreatment system. The operation of the high strength pretreatment system will need to be incorporated into the five year renewal of the National Pollutant Discharge Elimination System (NPDES) permit. Therefore, a Report of Waste Discharge will need to be submitted for the high strength pretreatment system four months prior to the proposed NPDES permit renewal adoption date. The RWD should include information on the monitoring program for the soil flushing system. 3. A neutron probe is to be used in the monitoring tubes to log (vertically profile) the soil moisture content. The design documents do not state whether the neutron probe will be used prior to implementation of the subsurface soil flushing system. The neutron probe should probably be run once prior to start up of the system as a baseline for the pretreatment soil moisture content. 4. The design of the monitoring tubes includes a five foot well screen section and filter pack to be installed within the lower ten feet of the tube. It is unclear why a screened interval and filter pack design is warranted, unless the monitoring