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L .1 R&B Trucking Preliminary Site Assessment Page: 5 _. 4.2 Ground Water Monitoring 4.2.1 Monitoring Well Installation Geological Technics proposes one monitoring well(MW-1)to be installed midway in the tank cluster adjacent to tank#5(Figure 3)near where most of the soil contamination was located. The well will be drilled by Osterberg and Stewart using a 7.25 inch hollow stem continuous flight auger. The depth of the well will depend on the geology of the site. It will either extend 10 to 15 feet into the aquifer or will terminate in a lower bounding clay unit that is thicker then 3 feet. If the geology at this site is similar to other places in Tracy,a thick clay layer is expected to be encountered at a depth of about 25 to 30 feet. The bottom of the well would then be seated in this clay. During the drilling, soil samples will be collected every 3 feet and screened to determine which samples should be sent to ChromaLab in San Ramon for analysis. By applying a field screening process(section 5.4),Geological Technics can determine which samples need to be analyzed,reduce the cost of the study,and still maintain a high quality of work. The well will be constructed of 2 inch threaded joint PVC pipe that is factory perforated with 0.04 inch slots. Perforations will extend no higher than 5 feet above water table. A filter pack composed of #3 sand will be installed from the bottom of the well to about 2 feet above the perforated zone. An annular seal composed of bentonite grout(Benseal and Quick Gel)will be installed above the filter pack by the tremie method. This seal will be at least 5 feet thick. Above the seal, the annular space will be filled with neat cement. The well will be secured with a locking cap and a water tight well cover. Figure 4 illustrates _ the general construction plan of this monitoring well. 4.2.2 Monitoring Schedule The well will be developed by pumping until a clear stream of water is obtained. A jet pump will be used to develop the well. After a clear stream of water is obtained,an additional 5 well volumes will be removed. One well volume is equivalent to the water contained in the well casing and in the annular space. The extracted water will be containerized until the lab results are reviewed. After development of MW-1,a water sample will be collected and analyzed for aromatic hydrocarbons (BTX&E),and TPH as diesel. Detection limits for these compounds are given in section 5.12. After this information has been gathered,Geological Technics will propose a monitoring schedule and alternatives for the future course of action at this site.