A state-of-the-art landfill closure cell for containment of refinery solid and sludge hazardous wastes has been completed at a Wyoming refinery site.
The cell, which was designed and constructed by ENSR Consulting & Engineering, Fort Collins, Colo., is at Frontier Oil & Refining Co.'s 36,000 b/d Cheyenne refinery.
The cell is designed to contain certain stabilized hazardous wastes, and includes a leachate collection and monitoring system in order to enhance groundwater protection.
The closure cell, measuring approximately 450 ft x 350 ft x 20 ft, contains about 16,000 cu yd of wastes, says ENSR.
The following EPA-listed hazardous wastes, which may contain elevated concentrations of chromium or lead, are stored in the cell:
- K049-Slop oil emulsion solids
- K050-Heat exchanger bundle cleaning sludge
- K051 -API separator sludge.
Wastewater treatment sludge, which exceeded extraction procedure toxicity levels for chromium and selenium, was also included in the cell.
The wastes were stabilized and solidified with a mixture of fly ash and kiln dust. This is a proven technology for achieving the chemical and physical properties needed for landfilling. Stabilization/solidification improves the handling and physical characteristics of the sludges and, through chemical changes, reduces the solubility of the pollutants in the treated waste.
Fig. 1 shows a typical cross section of the landfill closure cell. The leachate collection system consists of a high density polyethylene (HDPE) drainage net, a 60-mil HDPE flexible membrane liner (FML), 6-in. HDPE perforated drainage pipes, and a sump.
The drainage net overlies the 60-mil FML and has a transmissivity of approximately 3 gpm per ft of width. The drainage surfaces are sloped to the drainage pipes, which carry approximately 300 gpm at a slope of 7%.
The sump, which collects any leachate from the pipes, is located in a corner of the cell. Leachate from the waste material can be monitored and collected through a riser pipe which extends from the bottom of the sump to 3 ft above the cell cap.
The minimum life of the cell is estimated to be 30 years. The value of the contract was approximately $1.5 million.
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