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January 30, 1987 Project 116-1.5 <br />resistant than PVC, there is no waste in the trenches that will have an <br />adverse impact on PVC, and the Class II -1 trenches will never again accept <br />waste. Therefore, the substantially greater expense of stainless steel is <br />not justified. Centralizers will be used to keep the casing centered in <br />the borehole. A centralizer will be placed at the top and at the bottom of <br />the well screen, and every 40 feet along the blank well casing. <br />Well Screen and Filter Pack <br />The size of the screen openings will be small enough to retain between 80 <br />and 90 percent of the filter pack. The filter pack will be engineered, <br />based on sieve analyses performed on aquifer material collected during the <br />soil sampling of phase 1. The method outlined in the California Site <br />Mitigation Desision Tree2 will be followed. The filter pack will be <br />tremied, using formation water or none at all, into the annular space <br />surrounding the screen with a 2 inch diameter pipe. The filter pack will <br />extend from the bottom of the screen to 1.5 to 2 feet above the screen. <br />Well Seals <br />A 3 foot bentonite seal will be placed above the gravel pack. Sodium <br />bentonite pellets (1/4 inch) will be tremied into the annular space with a <br />2 inch diameter pipe. Potable water will be added for hydration of the <br />bentonite. <br />The remaining annular space will be sealed with a cement -bentonite grout. <br />The grout will be blended by the dry batch method, using potable water and <br />5.6 pounds of bentonite per 94 pound sack of cement. The grout will be <br />pumped through a tremie pipe. <br />Well Protection <br />A top cap will cover the top of the casing, and a locking vault will be set <br />in concrete to protect the well from unauthorized access. A Christy box <br />with a metal lid will be set in concrete over the vault, a few inches above <br />the ground surface to prevent ponding of water above the well. <br />Well Develo-pement <br />The ground water monitoring wells will be developed by mechanical surging <br />using a vented surge block. The wells will be developed until they produce <br />sand free, nonturbid water samples. No water will be introduced during <br />developement, and the equipment will be thoroughly steam cleaned between <br />wells. <br />Well Sampling and Analysis <br />Once the new monitoring wells are constructed, the Forward, Inc. Landfill <br />- 3 <br />