FIELD DOCUMENTS AND WORK PLANS 1991

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more than 5 percent passing U.S. Standard sieve No. 20 unless otherwise accepted by the Engineer. The washed silica sand shall be placed in a slow steady stream around the screen section. 2A-7.04. Lysimeters. Two lysimeters shall be installed in each lysimeter boring at depths of 25 and 50 feet below the ground surface. Each lysimeter shall consist of pressure-vacuum soil water samplers, Model 1920 Soil Moisture Equipment Corporation, or an equivalent approved by the Engineer. Each lysimeter shall include two colors of polyethylene tubing (1903L100 and 19041-100) , 3/16 inch diameter tubing with 1/8 inch wall thickness (MRT 003) , pinch clamps (Model No. 1901) and one Model 1920K1 Service Kit, consisting of pressure-vacuum hand pump with the vacuum dial gauge adapter mounted on the pump. The tubing for the lysimeters shall be run to the ground surface through 1-1/2 inch diameter, schedule 40 blank PVC riser pipe. Approximately 50 feet and 25 feet of PVC riser pipe will be required for the deep and shallow lysimeter, respectively. One casing clamp (Model 1902K1) shall be required for each lysimeter for use with the 1-1/2 inch diameter riser pipe. Silica sand with a 200 mesh gradation (silica flour) shall be placed so that 1 foot of sand is below the ceramic cup at the tip of each lysimeter, and 1 foot of sand is above the ceramic cup. The silica sand shall be placed using the tremie method. Potable water shall be used to tremie the sand into place. The deep lysimeter at each lysimeter cluster location shall be installed first. Following placement and hydration of the bentonite seal , the boring shall be backfilled with cement-bentonite grout to the bottom of the bentonite seal below the shallow lysimeter. The cement-bentonite grout shall set for a minimum of 12 hours prior to installing the shallow lysimeter. If desired, the portion of the boring between the zone monitored by the shallow and deep lysimeter may be backfilled with Volclay grout. If Volclay grout is used, the bentonite seals above the deep and below the shallow lysimeters can be eliminated. The volclay grout shall be required to set for the time period required by the manufacturer prior to installing the shallow lysimeter. Verbal authorization shall be received from the Engineer prior to installing the shallow lysimeter. 2A-8. GROUT SLURRY. The grout slurry used to backfill borings not completed as wells, monitoring tubes, and lysimeters, and around riser pipe above the bentonite seal to approximately 2 feet below ground surface shall be as required herein. Cement-bentonite grout slurry shall be used for wells and lysimeters and shall consist of 97 percent (by weight) cement and 3 percent high- swelling bentonite mixed with 7 to 8 gallons of water per 100 pounds of cement and bentonite to yield a liquid grout weighing approximately 13.5 (MARLEY SSFS ) 2A-10 (CONTRACT NO. 13) (11654.652 )