An engineered cover - (Diagram) was designed for the UC-4 Mud Pit C. The cover on Mud Pit C used a Geosynthetic Clay Liner as opposed to the vegetated monolayer cover used on the UC-1 Central Mud Pit (CMP). Cover construction activities included: Mud relocation trench constructed at the east end of Mud Pit C Excavation and relocation of drilling mud from UC-4 Area S, CAS 58-10-03 to the relocation trench Installation of geogrid over mud pit and relocation trench Addition of a 2-foot stabilization layer of clean and petroleum hydrocarbon-impacted material (from UC-1 Area S, UC-3 Area Z, and UC-4 Area W) on the geogrid Addition of a 2-foot shaping layer of clean fill over the stabilization layer Addition of a 6-inch bedding layer of clean fill over the shaping layer Installation of a geosynthetic clay liner on the bedding layer Addition of a 6-inch buffer layer over the geosynthetic clay liner Addition of a 1-foot erosion control layer over the buffer layer Installation of a cover fence, warning signs, and subsidence monuments Two permanent subsidence monuments were installed on the mud pit cover to provide an elevation control reference that allows monitoring of the settlement of the engineered cover. Based on geotechnical data from the UC-4 site, ninety percent (90%) of the settlement is expected to occur within the first year after installation of the cover. The Closure Plan - (Large document! 28.5 Meg pdf file) for the CNTA surface requires biannual subsidence surveys. At the time of the first post-closure monitoring report, all settlement values were within the expected calculated values.