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Projects |
One-Pass Trenching > Citizens Landfill Aquifer Protection Project   MERSINO was hired to properly abandon existing wells at Citizen's Landfill. MERSINO worked in accordance with MDEQ standards in order to maintain the integrity of the constructed cell, thereby protecting the existing aquifer. Previously installed wells had to be re-drilled to remove the former gravel pack and to seal the aquifer from the cell. Prior to any work, MERSINO first took measures to protect the site from erosion as well as to avoid the potential for surface migration of the bentonite slurry utilized to maintain the integrity of the annular excavation. The bentonite slurry was prepared by utilizing a high-velocity/high pressure venturi jet mixer in conjunction with a high-speed/high-shear centrifugal pump as manufactured by Global Pump Company. The bentonite slurry was tested by MERSINO QC personnel as per API RP 13B-1. After the bentonite hydrated for a period not less than four hours, MERSINO proceeded to drill out the existing well utilizing a rotary bucket drill rig. The bentonite slurry was introduced to the hole immediately via a mud pump, high-pressure hoses with isolation valves, and a recirculation line to allow for the control of the flow rate to the hole, further preventing the bentonite from flooding the surface. The holes were drilled to a diameter of 42-inches and to a depth extending four vertical feet below the original well bottom, approximately 100-feet below ground surface. Upon completion of the drilling process, the hole was sounded for confirmation of the final depth. The final grout mix consisted of cement, natural soil, and additives, mixed offsite, at a ratio demonstrated to result in a low-shrink mixture with permeability no greater than 1 x 10-7 cm/sec. Tests for slump cone, density and permeability were performed by the MERSINO QC personnel prior to placement. Upon confirming the well depth, the grout was installed via a tremie pipe and a high pressure positive displacement pump. As the grout was placed, the bentonite in the excavation was pumped out, pumped through desanding equipment, and into a storage tanker. The grout backfill was tremied to the top of the natural barrier layer. At completion of the abandonment process, all site restoration included restoring the surface features to original condition. Twelve wells were successfully abandoned to the satisfaction of MERSINO QC personnel, the owner's QA consultant, and to DEQ standards. |