SCH Number 2025070371

Project Info

Title

Laytonville Landfill Cover Remediation and Improvements Project

Description

Mendocino County Department of Transportation (County) is proposing (i) reconstructing a portion of the final cover on the closed Laytonville Landfill; and (ii) relocation of a landfill gas (LFG) monitoring probe, relocation of a piezometer, and installation of a groundwater monitoring well. The landfill would remain closed and there would be no significant changes to current monitoring and maintenance procedures. There would be no new operations after project completion. The project would involve replacing approximately 185,000 square feet of the existing landfill cover and would include the following procedures: - Dismantling and removing the existing surface water drainage system. - Removing existing side slope final cover to the top of the foundation layer; the rock slope protection and vegetative cover soil would be stockpiled for reuse and the geosynthetic materials would be disposed of off-site. - Preparing and compacting existing foundation layer soil to meet compaction requirements in accordance with American Society for Testing and Materials (ASTM) International standard D1557; seep and LFG collectors would be placed on the foundation layer before the overlying barrier, drainage, and protective cover soil is placed. - Placing overlying low-density polyethylene, drainage materials, and protective cover soil; the drainage layer placed would discharge to toe drain collectors at the toe of slopes on the landfill site. - Reconstructing the surface water drainage system to include berm channel outlets and inlets, subsurface drains, and perimeter rock drainage swales. - Installing LFG collectors below the final cover barrier layer and LFG vents and trench collection galleries; the LFG vents would be sealed with a low-density polyethylene layer. - Relocating an existing perimeter LFG monitoring probe. - Relocating an existing sedimentary piezometer. - Hydroseeding final cover and installing fiber rolls and gravel bags for erosion control. - Installing a new groundwater monitoring well. Project construction would take place for up to 10 hours a day from 7:00 a.m. to 5:00 p.m., five days a week (Monday through Friday) for approximately 16 weeks. The project site is associated with a Land Disposal Site case for Mendocino County Laytonville Solid Waste Disposal Site (case #1B75050OMEN) with an “Open – Closed/With Monitoring” status as of 1997 and a “State Response or NPL” case for Laytonville Landfill Site (site ID 60003790) with a “Refer: Other Agency” status as of May 2024.

2 documents in project