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0 • WORK PLAN FOR LYSIMETER INSTALLATION FORWARD LANDFILL, STOCKTON, CALIFORNIA The Waste Discharge Requirements for the Forward Landfill adopted by the Regional Water Quality Control Board, call for the installation of four lysimeters to be placed under the trenches in Waste Management Unit A. The following work plan dictates the methods to be used in placing these lysimeters and potential problems involved. Trench 1 in Waste Management Unit A was initially constructed in 1978 and has been designed with the bottom clay liner sloped at approximately .5%southward. A sump and riser were installed in the trench prior to any waste being dumped into the trench, however, a leachate collection layer is not present. The riser, buried since 1978 and recently excavated, plunges at an angle of 29 degrees to the north and extends 105.5 feet to the sump. The ideal location of the lysimeter is within 10 feet from the bottom of the LCRS sump, as dictated in the WDR's. The drilling and placement of the lysimeter in this location is not possible because municipal wastes have been buried immediately to the south of the riser and drilling through the buried waste may be hazardous. Additionally, because the measured angle of the riser does not remain constant with depth, the exact location of the sump is not known and, thus, the angle and depth to drill is undeterminable. Because of these difficulties EBA feels that attempting to drill an angled borehole in this area is excessively risky and poses a substantial threat to the integrity of the existing bottom liner. The best practical position for the placement of the lysimeters; is under the eastern bottom corner of the Trench 1, at the point where the 3/4:1 side slopes of the trench meet the bottom 3%® slopes. This is not the lowest point in the trench, however, it is a position which allows for installation of the lysimeters with fairly little risk of damaging the existing liner. The drilling will begin at approximately 550 south of the main east-west access road and 198 feet west of the property boundary fence line. The hole will be drilled at an angle of 30 degrees from vertical to the west and will be 60 feet in length. This will result in the placement of the lysimeter at 10 feet below the bottom liner east of the sump. The WDR's also require lysimeters to be installed at a position within 10 feet of the sumps in Trenches 2,3 and 4. The placement of these lysimeters; is a much more formidable and risky task than that of Trench 1. The only way the lysimeters can be placed in these trenches is drilling to the south under the sumps, using the riser as a guideline to the positioning of the lysimeters. However, the riser in trench 2 is known to become steeper, as much as 3%with depth, and, as in the case with Trench 1, it is unknown exactly where the sump is in relation to the surface opening of the riser. The surface angle of the riser in Trench 4 is 17 degrees, substantially less than that of the other trenches and certainly not accurate for the riser as a whole presuming Trench 4 was built basically the same way as the previous trenches.