Category I Landfill – Cell 4 and Interim Channel Construction
As described in the previous email blast, excavation for the Category I landfill facility (Cell 4) began the first week of November, 2011. The final extent of excavation activities had been reached, and verified with survey data. In all, approximately 150,000 cubic yards of slag, and 140,000 cubic yards of native material was removed from the landfill footprint and Parker Brothers Arroyo, and placed in stockpiles on the plant site. Construction crews have completed placing clean engineered fill to build the bottom of the landfill. The landfill is now ready for the 6-inch thick prepared subgrade. An engineered 60-mil thick high density polyethylene (HDPE) liner over a geosynthetic clay liner will be installed over the prepared subgrade. A protective layer of selected impacted material will be carefully placed over the liner. Impacted soils and debris from the former smelter will then be placed into the cell and compacted. A soil cover will be placed over the filled cell to encapsulate the impacted material. Drainage improvements and erosion prevention measures will be installed as filling of the cell is completed. The final cover will be contoured to blend into the surrounding topography.
Basement Backfill Design and Placement
Starting after Thanksgiving 2012, the Trust’s contractors began using Category II material from the excavation of the Cell 4 and Interim Channel Construction area in the Parker Brother’s Arroyo to backfill building basements at the site. The material is an engineered soil backfill that will facilitate future development on the plant site. The volume of Category II material used to date as backfill is approximately 55,000 cubic yards with an estimated 20,000 cubic yards more to be placed. The basements backfilled to date using Category II material are the ore unloading building basement and the north area of the ConTop. Additional basements to be filled include the engineering building, pipe trench, and the south end of the ConTop. Additional Category II material is planned to be used as sub-base before a clean cover is placed on top, as part of the remedy. 6500 CY of clean soil was also used as backfill in five very small basements due to limited access and difficult placement conditions. These basements including: the cooling tower house pits, the warehouse basement, the east scale pit, the antimony pits, and the train scale house pits.
Schedule
A revised design package for the landfill liner system was submitted to TCEQ on July 9, 2012 with additional modeling submitted on January 15, 2013 in response to comments by TCEQ. Excavation and placement of engineered backfill in Cell 4 to create the bottom shape of the cell is complete. Excavation of the Interim Channel began at the end of January 2012 and was completed in July 2012.
Installation of the Cell 4 liner will begin once the prepared subgrade is complete and we receive concurrence from TCEQ and EPA to proceed with the installation; this is anticipated in February 2013. It is anticipated that filling of the landfill will take 12-18 months.
We will continue to monitor the field demonstration of the two PRBs, detailed monitoring of the treatment results will occur for at least a year and long-term monitoring of the PRBs will continue as part of the site operations and maintenance.
Basement backfill is anticipated to be complete by April 2013. Click here to view relevant documents.