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August 8, 1983 Project 116-1-4 - 4 - Class 2 permeable material is described in Standard Specification of California Caltrans Manual, January 1982. The description and the gradation of the material is covered in Section 68 under subsection 1.025, Permeable Material. Based upon testing in the Terratech soil laboratory within the last week, this Caltrans Class 2 permeable material has been shown to have a permeability of 0.27 cm/sec. Hopefully this material, with a wide range in gradation, will maintain an effective drainage blanket and have sufficient density to remain where it is placed during unloading operations. E. LEACHATE RETENTION FACILITIES Based upon recent discussions with staff of various regulatory agencies, we withdraw our proposal to incorporate the use of Evaporation Pond #5 to handle leachate formed in the operation area of disposal Trench #4. As an alternative, we propose to build a temporary fluid retention pond immediately behind the waste containment area in trench A. This fluid retention area has been sized to handle 24 inches of rainfall over the entire northern half of disposal trench A. In addition, the fluid retention pond will provide sufficient capacity to handle an estimated 24 inches of rainfall into the pond itself and provide 2 feet of freeboard. This pond will be underlain by the compacted 2 foot floor liner and it will be fitted with a 10 mil black plastic liner anchored in surrounding embankments as shown on the detail in Plate 2. This temporary fluid retention area will have a capacity of 124,000 cu.ft. of fluid and will serve throughout the winter months of 1983 and 1984. Conversations conducted with Mr. Gary Reents of the California Department of Health Services on August 2, 1983 indicated that this facility would be considered part of the trench design and would not require a separate permit as a surface impoundment. We have checked with local manufacturers and they assure us that with adequate care, the 10 mil black PVC sheeting can be cemented along its seams to provide an impervious liner for the projected life of the facility. Rain water which accumulates south of the fulid retention pond will be directed to the sump on the northeast corner of this area. Following storms, it will be tested for chemical quality and, if uncontaminated, it will be pumped into the site drainage system. GBetac Associates a