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Kristi Shelton Page 2 June 2,2008 • 2-inch d:amc ,:r PVC well casing is grouted inside the conductor casing with neat cement(with 5% bentonite) grout. The borehole below the conductor casing is 8-inches in diameter to total well depth,which ranges from between 49 to 63 feet bgs for the three wells. A 10-foot-long screen(0.020-inch slots)with filter pack(#3 sand)is placed at the bottom of each borehole. A.bentonite seal occurs between the filter pack and the bottom of the 8-5/8 inch conductor casing. The annular space between the 2-inch PVC and 8- 5/8 inch conductor casing is then grouted with neat cement jwith5% bentonite grout)to ground surface. (w The current constriction i ing annular seal) of these wells is r2pustand protective of groundwater condition . There is a competent cement(with 5% bentonite) grout seal throughout the conductor casing and then a bentonite seal between the conductor casing and top of screen. The screen is only 10-foot long. Any attempt to over drill and remove all conductor casing/well casing materials would damage this competent seal. An infeasibly large and complex drilling effort would be required to abandon these wells,which could cause cross contamination from the shallow-to-deep hydrogeologic units. Modified Scope of Work to Destroy the 3 Deeper Wells The three deeper wells will be destroyed by pressure grouting methods instead of over drilling. The wells will be abandoned as follows,in accordance with Section 6.3.6 of the San Joaquin County Well Standards(February 2005,sogov.org/ehd/docs/pdf/Well%20Standards.pdf): • For the protection of the seal,and to facilitate the future use of the land site,a hole at least one foot larger in diameter than the originally drilled hole will be excavated around the outside of the well casing to a depth not less than three feet below the ground surface.The well casing will then be cut off six inches above the bottom of this excavation and removed. • During the sealing(pressure grouting)operation,the grout used to fill the well will be allowed to spill over into the excavation and fill it for a thickness of one foot and form a cap which has a diameter of at least on foot greater than the diameter of the originally drilled hole. This procedure should result in the exposed edge of the casing being covered with six inches of grout. • After the sealing operation and the sealing material have set,the excavation will be back filled with clean native soil. A well destruction permit application will be prepared and submitted to the San Joaquin County Environmental Health Department(EHD). Well destruction will not commence until a permit is received and arrangements have been made for an EHD inspector to be present during the well destruction work. ES102007015SCO/HOLT_WORK_PLAN_ADDENDUM.DOC/073050005 COPYRIGHT 2008 BY CH2M HILL,INC.•COMPANY CONFIDENTIAL