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ALL "ARE WORKPLAN REVIEW •� •� -3- 30 October 1989 level measurements and samples taken are representative of the ground water flow and quality in the shallow zone. Additionally, All Pure should also consider the ground water flow direction and other information obtain during investigations at Defense Depot Tracy. 2. The Workplan states that the three wells will be screened from five to fifteen feet. If your information in the Assessment is correct ( a clay layer exists from 0 to 13 feet) , then your wells would only be drawing from two feet of the water bearing zone. Determination of the screened interval should be based on local stratigraphy determined from field logs and should screen the entire water bearing zone. 3. The Workplan should state the drilling method to be used for this set of monitoring wells. Furthermore, a drilling method that allows for continuous logging should be used in order to define the stratigraphy. 4. The Assessment stated that sample results from borings around the wastewater ponds indicate significant hydrocarbon contamination in the area where the monitoring wells will be located. If there is fuel product in the area, what sampling procedures will be used to prevent fuel product from getting into the water samples? 5. The Workplan states that dissolved oxygen (DO) , pH, and temperature are the field parameters to be monitored during well development and purging. The objective of well development is to set the filter pack around the screened interval and to remove filter pack material and other sediments from the well water in order to get a representative sample. The Workplan does not state how pumping the well and monitoring the stated field parameters will accomplish the above objective. Furthermore, the Workplan states that the above field parameters are to be monitored during well purging; however, electric conductivity (EC) instead of DO is usually monitored until stabilized as a standard practice. 6. The Workplan states that soil samples will be taken at five foot intervals during drilling for analysis. The Workplan needs to state the depth the first sample will be taken. Also, will the soil samples be analyzed for the same constituents as the water samples? If not, what will the soil samples be analyzed for? 7. The Workplan states that after initial sampling for trihalomethanes (EPA 601) , pesticides, and other constituents, ground water samples will only be analyzed for EPA 601 once every quarter. Chlorides, pH, EC, and TDS should be added to the sampling plan. Also, All Pure should initially take water level measurements and water samples every month for the first three months and quarterly monitoring following the third month. In conclusion, the direction of the investigation is appropriate; however, the above concerns about the Assessment and Workplan need to be addressed. Once the above concerns are resolved, we can approve installation of the ground water monitoring wells. Since the proposed work may not determine the extent of contamination, additional monitoring wells may be required as the next phase of this investigation.