The project A part of the Tunnel and Reservoir Plan (TARP), the north lobe of the Thornton Quarry was converted into a reservoir with capacity for nearly eight billion gallons of combined sewer overow (CSO) prior to treatment. The challenge Hayward Baker was contracted to reduce permeability of the perimeter rock formation and mitigate leakage into the groundwater. The solution Hayward Baker installed a 9,800 linear feet double-row grout curtain. Thornton Composite ReservoirOur team drilled approximately 800,000 feet of double-row grout curtain holes to depths ranging from 20-575ft. Drilling was performed at angles varying from 0-65 degrees from vertical, using a drill rig equipped with a water-actuated down-the-hole hammer. Upon completion of drilling, we grouted the rock in 20-ft stages

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