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VV SME OF CALIFORNIA — ENVIRONMENTAL PRO ON AGENCY PETE WILSON, Govemor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARID— ��vo CENTRAL VALLEY REGION F1,111D ,, y 3443 ROUTIER ROAD, SUITE A SACRAMENTO, CA 95827-3098 PHONE: (916) 255-3000 FAX: (916) 255-3015 14 July 1993 Ms. Carrie Cummings Forward Inc. P. O. Box 6336 Stockton, CA 95206 UPPIddTAL HEALTH OVALti't 93 JUL 19 pH Z: 38 FORWARD LANDFILL, SAN JOAQUIN COUNTY (Case No. 2209) We have reviewed the report Design and Construction Documents for Waste Management Unit (WMU) D-93 submitted by CH2M Hill on 6 April 1993. The report included design drawings, engineering calculations, construction quality assurance (CQA) procedures and design certification for the 4.6 acre expansion of landfill WMU D. The landfill was designed to meet the requirements of Title 23, California Code of Regulations (23 CCR), Division 3, Chapter 15 for Class II landfills and 40 Code of Federal Regulations (40 CFR), Parts 257 and 258 (Subtitle D) for municipal solid waste landfills. The landfill design includes a composite liner and blanket leachate collection and removal system (LCRS). The composite liner includes two feet of compacted soil with a maximum permeability of 10-7 cm/s overlain by a 60 mil HDPE liner. The LCRS consists of a gravel blanket on the floor of the unit and a geocomposite drainage net (geonet bonded to geotextile) on the side slopes. The proposed design uses an admixture of imported Ione clay and native silty clay soil for the compacted clay liner. The mixing procedures and acceptance criteria for the admixture need to be specified. We understand some of this information was developed during construction of the biotreatment pads and more will be gained from the D-93 test pad program. All this information should be evaluated and'the appropriate changes made in the CQA program. Please provide us with the soil mixing procedures and CQA acceptance criteria prior to liner construction. The field permeability test method for the clay liner specified in the CQA program is ASTM Method D3385 for a double ring infiltrometer with open rings. As noted in the ASTM procedure, this method may yield unreliable results on soils with a permeability less than 10-6 cm/s. This method is subject to evaporative water loss which affects infiltration measurements. In addition, the small ring size may not provide a representative sample of the liner. For these reasons, ASTM D3385 is not acceptable. The sealed double ring infiltrometer (SDRI) ASTM Method D5093 is the method we prefer. The SDRI is overcomes the problems associated with the open ring infiltrometer and is capable of measuring very low permeabilities. The CQA plan should be revised to specify the SDRI or other acceptable method. We also prefer to see the test pad constructed outside the D-93 unit so subsequent construction activities to not disturb the infiltrometer.