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URS Mr. Jarel Starling 10 October 2001 Page 2 length of time, URS will consult with the drilling contractor that performs this work to assure appropriate pressure times based on the grout composition; however, in our estimation, w anticipate pumping grout in three stages, with each stage to approximately 10 feet above screen interval and maintaining pressure for at least 15 to 30 minutes at each stage.] • RWQCB Comment#4: The Work Plan states that "additional grout will be added to the casing if any settlement occurs". This is absolutely essential to providing a good seal, so how will you determine if the grout has stopped settling? I am concerned that the drillers will demob fro the site before the grout has settled completely. [The level of the top of the grout will be check d following the initial grout placement and "topped off", if needed by either the drilling contractor, or if already demobilized from the site, by URS technicians (up to 2 to 3 days following the initial grout placement).] • RWQCB Comment#5: The Work Plan does not specify where the tremie pipe will be placed during pressure grouting. Will you start at the bottom of the well and withdraw it as the w 1 fills with grout? Will you place the tremie pipe adjacent to the perforated intervals to try to force grout through the perforations? Be specific. [The tremie pipe will initially be set at the bottom of the well and will be lifted upward as grout placement occurs; therefore, during the proced]ire of emplacing grout and lifting tremie, the bottom of the tremie pipe will be located adjacent t screen intervals but won't be held there. We anticipate the grout weight and pressure will orce grout through screen intervals.] Comments received from Harlin Knoll [followed by responses] are as follows: • SJCEHD Comment#1: Calculate grout volume (in gallons) needed to fill the casing to 29 feet bgs. [The calculated volume is approximately 2,475 gallons (30 feet of 18-inch diameter ce sing [396 gallons] + 260 feet of 14-inch diameter casing[2,079 gallons] = a total of 2,475 gal ns).] • SJCEHD Comment#2: Calculate PSI of the pressure grouting at the screen intervals and z t total depth. [Using a 16 pounds per gallon grout slurry,pounds per square inch (PSI)pressure s estimated to be approximately 0.83 PSI per foot of depth, therefore, PSI at the screen inter als and at total depth would be approximately 103 PSI(at 124 feet), 149 PSI(at 179 feet), 165 PSI (at 199 feet), and 241 PSI(at 290 feet) (plus the pressure applied at the surface, which will be determined by the drilling contractor).] • SJCEHD Comment#3: The casing diameter/depth information documented on the SHAD Well 2 data sheet is misleading; please clarify. [Casing diameter and depth is 18-inch casing fro ground surface to 30 feet bgs, and 14-inch casing from 30 to 290 feet bgs.] • SJCEHD Comment#4: After casing is cut off 2 feet below grade, make sure grout is placed in a "mushroom-shaped" area about 2 feet surrounding the well. [Comment will be followed du)-ing abandonment.] Questions or comments may be communicated by phone (916-679-2267) or e-mail (dick_vandyke @urscorp.com).