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Stantec Well Destruction Summary Report 76 (Former BP) Service Station No. 11193 September 28, 2012 t Between December 5, 2011 and February 2, 2012, Stantec supervised WDC Exploration and Wells of Zamora, California (WDC) destroy a total of 23 wells; twelve groundwater monitoring wells (MW-1 R, MW-2R, MW-3 through MW-11, and MWA3), one vapor extraction well (VW-1), and ten remediation wells (OS-1 through OS-10). WDC destroyed MW-1 R, MW-2R, MW-5, MW-6, MW=10, MW-11, VW-1, OS-5, OS-8, and OS-9 via pressure grout. Each well was press u re-g routed.to total depth with 'neat cement-grout. Rigid tremie-pipe was inserted to within one foot of the well bottom and used to pump neat cement- rout t p pumping into each well. Upon um in a sufficient volume of neat cement-grout to fill the well 9 g casing and filter-pack annulus, each well was sealed with-a pressure-tight cap designed for compressed air service. A maximum pressure of approximately 25 pounds per square-inch was applied for 10 to 20 minutes to ensure sufficient permeation of neat cement-grout into'the filter- pack annulus. This process was repeated at each location untilthe level.of the neat cement- grout remained constant during, and subsequent to the application of pressure, which effectively closed the conduit to the surface. Onee.the neat cement-grout fully cured,.WDC removed all well construction materials from the bore-holes to depths ranging from.one'foot below ground surface (ft-bgs) to three ft-bgs. The total depth of well material removal was determined by proximity of underground utilities and regulatory approval. WDC set a neat cement-grout "mushroom cap" seal;above the casing in each bore-hole. The void space was backfilled with unconsolidated dry sack concrete from the top of the "mushroom cap" seal to approximately 6 inches-bgs. The abandoned wells were completed at the surface with concrete to match existing surface conditions. WDC destroyed wellsiMW-3, MW-4, MW-7 through MW-9, MW-13, OS-1 through OS-4, OS-6, OS-7, and OS-10 via over drill. Prior to auger advancement, each well location was cleared of utilities by airknife to approximately 6.5 ft-bgs, at a diameter equal to 120% of the proposed auger diameter. Subsequently, hollow-stem augers equipped with a well-destruction bit were advanced to well total'depth, destroying and evacuating all well construction materials. Augers were used as tremie-pipe to pump neat cement-grout into each well from total depth to approximately one ft-bgs. The abandoned wells were completed at the surface with concrete to match existing surface conditions. Field notes are included as Attachment B and well completion reports provided by WDC are included as Attachment C. During over-drilling activities at MW-13 a guide-rod system was employed to ensure augers remained on the well.to total depth. During the advancement of 8=inch augers, approximately 120 ft of 'guide-rodI became detached at approximately 30 ft-bgs. Guide-rod recovery was attempted by over-drilling with 15-inch augers. During recovery activities a "twisted ball of metal" with a diameter larger than 15 inches was encountered at approximately 30 ft-bgs that l'lI prevented any further auger advancement. After numerous attempts to move past the 1 obstruction Stantec requested a SJCEHD variance to destroy the well via pressure grout. Onsite SJCEHD inspector -Michael Infurna approved the, destruction of MW-13 by pressure grout. Augers were used as tremie-pipe to pump neat cement-grout into the well to approximately one ft-bgs. MW-13 was completed at the surface with concrete to match existing surface conditions. All waste generated during the well destruction activities was temporarily stored on-site in Department of Transportation-approved 55 gallon. drums. Upon characterization, waste was i transported by a disposal contractor to an appropriate disposal or treatment facility. Copies of the waste manifests'are included as Attachment.D. f €� 11193 Well Destruction Report.doc 2 t