Drill Cuttings - Land Treatment

Land Treatment

In land treatment (also known as land spreading), the processes are similar to those in land farming, where natural soil processes are used to biodegrade the organic constituents in the waste. However, in land treatment, a one-time application of the waste is made to a parcel of land. The objective is to dispose of the waste in a manner that preserves the subsoil's chemical, biological, and physical properties by limiting the accumulation of contaminants and protecting the quality of surface and groundwater. The land spreading area is determined on the basis of a calculated loading rate that considers the absolute salt concentration, hydrocarbon concentration, metals concentration, and pH level after mixing with the soil. The drilling waste is spread on the land and incorporated into the upper soil zone (typically upper 6-8 inches of soil) to enhance hydrocarbon volatization and biodegradation. The land is managed so that the soil system can degrade, transport, and assimilate the waste constituents. Each land treatment site is generally used only once.

Optimizing Land Treatment Operations: Addition of water, nutrients, and other amendments (e.g., manure, straw) can increase the biological activity and aeration of the soil and prevent the development of conditions that might promote leaching and mobilization of inorganic contaminants. During periods of extended dry conditions, moisture control may also be needed to minimize dust. Periodic tillage of the mixture (to increase aeration) and nutrient additions to the waste soil mixture can enhance aerobic biodegradation of hydrocarbons, although in practice not all land treatment projects include repeated tilling. After applying the wastes, hydrocarbon concentrations may be monitored to measure progress and determine the need for enhancing the biodegradation processes.

Implementation Considerations: Because land spreading sites receive only a single application of waste, the potential for accumulation of waste components in the soil is reduced (as compared with land farming, where waste is applied repeatedly). Although liners and monitoring of leachate are typically not required at land treatment sites, site topography, hydrology, and the physical and chemical composition of the waste and resultant waste-soil mixture should be assessed, with waste application rates controlled to minimize the possibility of runoff.

Experiments conducted in France showed that after spreading oil-based mud cuttings on farmland, followed by plowing, tilling, and fertilizing, approximately 10% of the initial quantity of the oil remained in the soil. Phytotoxic effects on seed germination and sprouting were not observed, but corn and wheat crop yields decreased by 10% (Smith et al. 1999). Yields of other crops were not affected. The percentage of hydrocarbon reduction and crop yield performance will vary from site to site depending on many factors (e.g., length of time after application, type of hydrocarbon, soil chemistry, temperature).

Land spreading costs are typically $2.50 to $3.00 per barrel of water-based drilling fluids not contaminated with oil, and they could be higher for oily wastes containing salts (Bansal and Sugiarto 1999). Costs also depend on sampling and analytical requirements.

Advantages of land spreading are the low treatment cost and the possibility that the approach could improve soil characteristics. Land spreading is most effectively used for drilling wastes that have low levels of hydrocarbons and salts. Potential concerns include the need for large land areas; the relatively slow degradation process (the rate of biodegradation is controlled by the inherent biodegradation properties of the waste constituents, soil temperature, soil-water content, and contact between the microorganisms and the wastes); and the need for analyses, tests, and demonstrations. Also, high concentrations of soluble salts or metals can limit the use of land spreading.

When evaluating land spreading as a drilling waste management option, several items should be considered. These include area-wide topographical and geological features; current and likely future activities around the disposal site; hydrogeologic data (location, size, and direction of flow for existing surface water bodies and fresh or usable aquifers); natural or existing drainage patterns; nearby environmentally sensitive features such as wetlands, urban areas, historical or archeological sites, and protected habitats; the presence of endangered species; and potential air quality impacts. In addition, historical rainfall distribution data should be reviewed to establish moisture requirements for land spreading and predict net evaporation rates. Devices needed to control water flow into, onto, or from facility systems should be identified. Wastes should be characterized during the evaluation; drilling wastes with high levels of hydrocarbons and salts may not be appropriate for land spreading.