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Drilling-Waste Disposal Methods

Drilling waste is composed of the mud, cuttings and chemical byproducts that result from extracting oil and gas. Oil-well drilling and gas-well drilling bring up mud and other material with high hydrocarbon levels requiring special disposal practices. Synthetic chemicals sometimes are used in the drilling process that further contaminate waste. For these reasons, the Environmental Protection Agency (EPA) regulates on-shore drilling-waste disposal. Offshore drilling-waste disposal is regulated jointly by the EPA, the Minerals Management Service (MMS) and the Department of Energy (DOE).

  1. Landfill Disposal

    • Wastes that are non-toxic can be disposed into man-made or naturally excavated pits. These landfills are low-cost and low-technology. Waste does not have to be transported off-site, but the waste cannot exceed certain levels for oil, salt, metals or industrial chemicals, because of the threat of release to groundwater supplies. Even with low-concentration levels, pits must be structurally sound and isolated from groundwater sources. The disposal process begins by placing waste into the pit. Any valuable hydrocarbons are recovered by skimming floating material, and liquid is removed from the waste through natural evaporation of other mechanisms. The pit is covered with native soils, and the surface is re-graded so water drains away from the site. Vegetation with native species is added to reduce erosion. Waste with slightly higher concentrations can be blended with clean soil to meet acceptable levels. Pits can be located within plant rooting zones, but cannot intersect with ground water tables. If waste exhibits toxic concentrations, disposal can only occur in specially engineered and legally permitted landfills (on-site or off-site).

    Landfill Designs

    • Drilling wastes can be transported off-site for disposal in municipal, industrial or hazardous waste landfills, if needed. This method is more costly and is suitable for wastes that could pose harm to the public or wildlife if released into the environment. These types of landfills need government permits to operate and are specially designed to prevent releases. Landfills are not placed within highly permeable soils nor in areas with shallow groundwater tables. There are strict engineering and monitoring requirements designed to prevent groundwater contamination and reduce liability concerns. Texas permits salt caverns for drilling-waste disposal because the waste, pumped deep into an impermeable and self-sealing matrix of salt, cannot be released into the environment.

    Off-Shore Drilling-Waste Disposal

    • Off-shore drilling waste must be treated before disposal.

      The EPA in conjunction with the MMS and DOE have developed Effluent Limitation Guidelines (ELGs) for synthetic-based mud disposal off-shore. Off-shore drilling often requires the addition of synthetic-based chemicals into the well resulting in contaminated mud byproducts that need to be treated before discharging them into the ocean. The prescribed method entails placing drilling waste onto a vibrating screen, called a shale shaker, and progressing through finer mesh screens. When screened waste meets contaminant requirements, such as 1 milligram per kilogram for mercury or 3 milligrams per kilogram of cadmium, waste can be discharged. If screened dry powder or liquid waste does not meet requirements, it must be transported back to shore for disposal in a regulated landfill.

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