CORRESPONDENCE_2007 (1/07 - 6/07)

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h � ]l encountered. However, if the thickness of the water above the Corcoran Clay Aquitard is less than 15 feet, then screen length would be shortened to avoid drilling through the . This decision will be made in the field by the field geologist. At this time, it is estimated that MW -8 will be drilled to a depth of approximately 85 feet. The depth of MW -9 may be much less (Figures 2 and 4). After the boring is complete, the screen (up to 15 feet long) and well casing (fitted with end cap) will be suspended in the center of the hollow stem auger so that the screen interval occurs at the well design depth. The hollow stem augers (HSAs) will slowly be removed from the borehole as the sand pack is placed around the screen with the HSA serving as a tremie pipe. During placement of the sand pack, frequent measurement of the top of the sand pack will be made to ensure that the bottom of the HSA is not above the top of the sand pack. Before placing the bentonite seal, the sand pack will be carefully surged and then re -measured to ensure correct sand pack position. All well installation procedures will follow CHSL drilling specification Section 02670 (Appendix A). The geologist will record all well completion details on the geologic boring log. After the wells are installed, a State -Licensed surveyor will perform a vertical and horizontal survey of the top of casing. The surveyor will utilize the nearest benchmark(s) for vertical control relative to mean sea level and the appropriate monuments for horizontal control for the survey. 2.2.3 Well Development The permanent wells will be developed using a combination of bailing, surging, and pumping techniques. Equipment used during the well development procedure will be cleaned using a steam cleaner or an Alconox , or equivalent, detergent solution rinse prior to use at each well location. During development, field parameters (pH, temperature, conductivity, turbidity, and suspended sediment) will be monitored and recorded. The well will be developed until field parameters are stable and the discharged water is relatively clear of suspended sediment. Measurements of turbidity, temperature, conductivity, pH, and volume of purged water and observations of purge water clarity and sediment content will be recorded on a well development data form and will be included in the report. Corral Hollow EMP WPlan Rev2Mar 22-07.DOC 2.4 March 20, 2007