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located further to the east at the WRP treatment plant are about 30 feet deep. Well depths significantly greater than about 30 feet below land surface are most likely not necessary to monitor shallow groundwater conditions beneath Lathrop's WRP. Decontamination Procedures At this time, no hazardous constituents are expected at the proposed drilling locations. Should conditions change, or new information suggest that proposed well sites are located in potential problem areas, it may be necessary to ' determine soil quality and water quality characteristics prior to well construction. If problems are confirmed, the following suggested decontamination procedures shall be modified on a site- and contaminant-specific basis. iBecause no hazardous constituents are expected, drilling equipment shall be rinsed between well construction sites with potable water. The rinseate and drill ' cuttings will be spread on the ground near each site. If the well is located in a developed area, the rinseate and cuttings will be transported to a nearby application field for spreading and disposal. To the extent possible, drilling ' activities shall proceed in order from up gradient to down gradient wells. Soil Sampling and Borehole Looping During drilling, a split-spoon sampler will provide a continuous geologic core for analysis. The texture and moisture content of the drill cuttings will be recorded ' and reported on a well boring and construction form (an example boring and construction form is provided in Appendix A). At the discretion of the field hydrogeologist, core samples can be photographed to document changes in ' sediment texture, color and structure, and selected cutting intervals may be sampled and a vacuum pump and filter employed to extract the associated pore- water. The electrical conductivity of extracted water can be utilized to assess the ' pre-project depth distribution of groundwater salinity at the monitoring well locations. C. Monitoring Well Design Our proposed monitoring well design is shown in Figure 4. The design is consistent with SJCEHD Well Standards and State of California Well Standards. ' The 4-inch diameter, Schedule 40 PVC well casings shall be placed in 10-inch diameter, 24-feet deep boreholes. All casing joints shall be flush-threaded and watertight. In circumstances where it is desirable to increase monitoring well depths (i.e., wells about 30-feet deep), the additional depth will be accommodated by increasing either the cement seal length, or screened interval length, or both depending on local hydrogeologic conditions. - 6 -