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drilling will be paused for approximately 15 to 30 minutes and the water level will be monitored. Records of water level measurements will be noted on the log. 5.2 Previous Site Assessments Previous work was described in the Revised Work Plan. 5.3 Details of Field Investigation 5.3.1 General • No monitoring wells are proposed in the Revised Work Plan. • Survey details are as indicated on Figure A2. • Equipment Decontamination. All drilling equipment will be decontaminated on site using steam cleaning. Chloroform has a high vapor pressure and will readily volatilize with the application of steam or heat. • A site specific health and safety plan is provided in Appendix A of this addendum. 5.3.2 Drilling Details Triple E is now in negotiations with drillers to provide services using either mud rotary, air hammer, or hollow stem auger drilling techniques. All these methods have been used successfully in the past at this site. The descriptive log will be prepared by a geologist under the direct supervision of a California Certified Hydrogeologist. 5.3.3 Extraction Well Design • The well will be constructed within the drilling rod (either auger or drill steel) and no surface casing will be necessary, unless mud rotary methods are used. With mud rotary, a surface casing my be employed to 10 feet or more, depending on conditions. • The outer diameter of the boring will be 8-12 inches depending on the method used. • The surface seal will be fifty feet deep and composed of three to five feet of dry granular and hydrated bentonite, and a slurry of cement with 5%bentonite mix. • Well construction materials will be 6-inch diameter, flush threaded PVC screen and blank casing, and granular filter pack. • A diagram of the well completion is provided in Figure A3. • The well cap will be of locking expansion type, or the well will be plumbed directly to an outflow pipe for groundwater extraction. Security will be provided with a monument type completion. • The perforations will be slotted, of 0.020" width and with approximately 24 square inches of open area per linear foot of screen. • A filter pack of#3 sand will be installed by tremie or other means to minimize free fall of filter pack through water, thus maintaining the designed gradation of the sand. • The bentonite seal will be emplaced on clean sands approximately 10 feet above the water table. The bentonite seal will be composed of approximately five feet of _ hydrated bentonite. • The sand pack will extend a minimum of ten feet above the current water table. n 3 'VLW �� CONDOR