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Corral Hollow Sanitary Landfill Closure Plan SCH # 93052006 Page 2 is 0 Storm water runoff from the site will be directed to two drainage basins on opposite sides of the site. The drainage basins will act as sedimentation ponds to reduce the amount of sediment entering Corral Hollow Creek. Acquisition of property adjacent to the existing site is required to establish drainage and fire control measures and a landfill gas monitoring network. The landfill gas monitoring system will consist of gas monitoring wells placed around the perimeter of the site at a spacing not to exceed 1,000 feet. Each well will contain three monitoring probes. Existing onsite control measures include a groundwater monitoring network which is monitored in accordance with RWQCB Discharge Requirement 86-406. California Integrated Waste Management Board (Board) staff have reviewed the Negative Declaration ) and offer the following comments: GENERAL COMMENTS The Environmental Evaluation Checklist attached to the ND indicated through a series of "yes" answers that potential impacts could occur as a result of the project. In addition, project specific mitigation monitoring include a drainage control system, a fire control measures, and possible installation of a landfill gas collection system. Since the ND discussed potential project -related impacts, and mitigation measures necessary for these impacts, Board staff recommend that the document be recognized as a Mitigated Negative Declaration (MND) rather than a ND. 1. EARTH The ND states that a four foot thick layer of soils will be placed over the existing sanitary landfill surface. One of the soil layers will consist of a 12" layer of very low permeability clay soil. If available, Board staff request that the following information be identified in the final MND: * Additional soil(s) to be used for final cover; * Permeability in cm/sec for the final cover. 3. WATER - SURFACE WATER DRAINAGE CONTROL SYSTEM The,MND states that a storm water drainage control system would be constructed as a portion of the Closure Plan. During this activity, the site will apparently continue to operate in accordance with water protection measures under RWQCB Discharge Requirement Order Number 86-046. If any modification of Discharge Requirement (DR) 86-046 is required, Board staff request that the lead agency notify the Local Enforcement Agency (LEA) and the Board prior to any modification in DR 86-046 as a result of drainage control system activities. It would be helpful if this request were addressed in the final MND.