2010-01-13_GENERAL DOCUMENTS - M1983083

Home Browse Search

Construction Work Description: Please refer to maps and figures in the permit file for locations of features described below. Task 1 Mobilization/Demobilization: Colorado Cleanup Corporation (CCC) mobilized to the site on August 30, 2009. Equipment mobilized included a 330 and 450 Excavator, (2)980C CAT Loaders, 1 CAT Backhoe, several large haul trucks, 1 Skid Bobcat, and numerous pickup trucks and concrete trucks. Task 2 Project Safety Plan: A project site safety plan was submitted by CCC prior to construction at the site. Task 3 Construction Sediment and Dust Control: The Division obtained a Storm Water Permit(SWMP)from the Colorado Department of Public Health and the Environment. The Best Management Practices from the SWMP were incorporated into the bid document. Sediment control measures included use of the existing tailings pond and installation of silt fence in Gilson Gulch. The reclaimed surface was scarified to act as an additional sediment control measure. Silt fence remains in Gilson Gulch to contain any sediment that may adversely flow into the gulch until revegetation is established. A dust control plan was submitted by CCC prior to construction at the site. Task 4 Facility Demolition and Equipment/Debris Removal: Structures demolished on site include the mill building, oil shed, storage shed, pump house, two (2)trailers, underground storage tanks, and miscellaneous debris on site. All structures were tested for asbestos prior to demolition, and were found to be asbestos free. Structures were demolished using excavators and loaded into dump trucks to be disposed at an off-site landfill. Remaining water in Pond 4 was pumped and used to control dust during demolition of the mill building. The concrete block walls and foundations were pulverized using a hydraulic shear attached to the excavator. The pulverized concrete was buried in the backfill and covered with 4 feet of existing fill material. All other trash and debris were hauled to an off- site landfill. The substation located adjacent to the mill was removed by Xcel Energy prior to construction at no cost to the Division. Task 5 Grading of Facility Area, Ponds and Waste Material: Once the structures were demolished and removed, the site was backfilled and graded to blend in with the surrounding area. Backfilled slopes on the former mill area range from 2.5H:1V(near the historic Franklin tailings pile)to 4H:1V on the north end. Pond 4 water was pumped and used for dust suppression for demolition of the mill. The pond liner was cut and folded in pieces and buried with the concrete rubble. During the grading of Pond 4, unexpected soft, wet clayey saturated tailings material was encountered to a depth of seven (7)to nine (9)feet below the surface. The tailings material was mixed with native fill soil at a ratio of 1 part tailings to 2 part clean fill and pushed down slope to dry. A grain size distribution analysis was performed on the 1 part tailings to 3 part clean fill to determine if the material was suitable for backfill (this was a mix ratio that would represent the anticipated backfill). The Division was also concerned with the consistency of material in Tailings Pond 5, so a test trench was dug to determine the depth and nature of the tailings material. The tailings in Pond 5 were similar to that of Pond 4 and were approximately 13 feet deep. The tailings consisted of fine-grained particles of sand and silt with a high percentage of pyrite. The tailings were saturated and had no structural integrity as backfill. Due to the abundance of tailings material in Ponds 4 and 5, the Division revised the reclamation plan to keep the Pond 5 embankment in place and route Gilson Gulch 60 feet further towards the west. The one-part tailings and two-part overburden mix removed from Pond 4 was amended with 120 tons of dry Portland cement and placed in the 0.6 acre footprint of Pond 5. This was done to provide a less-permeable cover over the tailings material and minimize surface water infiltration into the tailings material. Once the cement was mixed in with the cover material, over two (2)feet of overburden material was graded across Pond 5 to create 4H:1V to 5H:1 V slopes. A core sample of the Pond 5 embankment was obtained to test the in-place shear strength. DRMS Mineral's Staff engineer analyzed the stability of the embankment and determined that in general the embankment was stable, but recommended slope reduction to allow vegetation to establish. Pond 5 slopes were buttressed and reduced to 2H:1V. A spillway was constructed to allow storm water that enters the backfilled area of the pond to safely discharge across the embankment. Task 6- New Access Road Construction: With the changes in the backfilling and grading plan, the planned new access road to adjacent property could be eliminated from the project. The existing access road where it crosses over Pond 5 embankment will remain in place for access to the lower portion of Gilson Gulch. Task 7-Gilson Gulch Reconstruction: The Franklin Mine is a valley fill situated in Gilson Gulch, which flows from northwest to southeast through the site. There is an existing drainage system for the mine that was designed to route the 10-year, 24- hour storm event. The main focus of reclamation of the site is to reconstruct the drainage channels to accommodate higher flow rates and provide a more stable long term configuration. The Gilson Gulch Reconstruction Channel was designed by Deere and Ault, Inc. to accommodate storms greater than the 25-year, 24-hour storm event. The drainage plan utilized the existing drainage location to convey storm flows around the mine into Culvert Cl. The drainage channel was excavated and lined with rock lined channels and fifteen (15) boulder drop structures. At Culvert Cl flows split into two different channels.