COMPLIANCE INFO_FILE 7 - Laserfiche WebLink

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of ground water such that a constant flowrate is provided to the liquid- phase carbon vessels. Ground water is pumped from the sump pump tank at a design flow rate of 30 gpm, and processed through two existing granular activated carbon vessels, installed in-series. This granular activated carbon treatment serves as a final ground water polish to remove any VOCs remaining in ground water, prior to reinjection at the Reinjection System. Reinjection System The ground water Reinjection System will include two ground water infiltration trenches for the subsurface reinjection of treated ground water. Drawing C-4 shows the location and layout of the infiltration trenches. Each infiltration trench will be 5 feet wide and 70 feet long. The depth of each infiltration trench will extend to the water table, located at approximately 10 feet bgs. Infiltration trenches will be backfilled from 3 feet bgs to the base of the trench with a permeable gravel backfill. This gravel backfill will allow treated ground water introduced into the trenches to percolate into the saturated zone through the floor and sidewalls of the trench. Each trench will be backfilled from ground surface to 3 feet bgs with native soil, compacted to 95 percent relative compaction. Additionally, prior to backfilling, a geotextile will be placed on the floor and sidewalls of the trench to minimize the intrusion of fine- grained soils into the gravel backfill. A geotextile will also be place between the soil backfill and the gravel backfill to prevent the intrusion of the soil backfill into the gravel backfill. A 4--inch diameter, Schedule 40 PVC pipe, with 3/8-inch-diameter perforations will be installed horizontally along the entire length of the trenches. This pipe will be installed at approximately 4 feet bgs, within the permeable gravel backfill. This pipe will provide a conduit for distribution of treated ground water along the entire length of the infiltration trench. To allow distribution of treated ground water along the length of the trench, this perforated pipe will be installed at an approximate 2 percent slope within each infiltration trench. A cross sectional schematic for each infiltration trench is shown in Drawing C-7. Each infiltration trench was designed to provide an infiltration capacity equal to the Treatment System discharge rate of 30 gpm. Additionally, each infiltration trench provides an additional 25 percent infiltration capacity, for a total infiltration capacity of 37.5 gpm per trench. 5-7