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API REPORT 80-24 Document Information:
Title
Agronomic Impacts Resulting from Land Disposal of Used Drilling Fluids and Cuttings
American Petroleum Institute
Publication Date:
Dec 31, 1982
Scope:
ABSTRACT
Drilling fluids and cuttings remaining upon completion of an oil or gas well are normally incorporated into soil near the well site by backfilling the mud storage pit or by disking after spreading the waste fluids on the surface. Drilling fluids contain a variety of potentially toxic elements (Cr, Cd, Cu, Pb, Zn, Hg, and As) that my pose hazards to soils and plants in the disposal site. A field study was conducted to assess the agronomic impacts of land disposal of waste drilling fluids and cuttings.
Soil samples (surface to 90 cm) and plant samples were collected from 10 sites in the western United States where drilling fluids were applied to soils. Six of the sites had received wastes associated with drilling nearby gas wells, 3 sites were research plots treated with varying types and amounts of drilling muds, and 1 site was a commercial wheat field that had been partially treated with drilling fluids. Soil and plant samples were analyzed for total amounts of toxic elements and the levels of DTPA-extractable metals in soils were also determined. A number of physical and chemical characteristics of soil were also measured and the plant dry matter yield was determined. Comparisons were made between the composition of plants and soils in drilling fluid-amended and unamended areas.
The addition of drilling fluids increased the total concentrations of Zn, Cu, Pb, Cr, and Ba in soils at most sites. However, the addition of drilling fluids had variable effects upon the levels of DTPA-extractable (presumably plant available) Zn, Cu, Cd, Cr, Pb, and Ba in soils. The concentrations of DTPA-extractable metals increased at some sites, decreased at some sites, and were unaffected at other sites by drilling fluid addition. In general, the trace elements in mud-amended soils were not present in forms that can be taken up by plants (i.e., were not extractable by the DTPA reagent). The low solubility of metals in the samples studied likely resulted from the high natural and drilling fluid-induced soil pH values and from strong sorption to soil components. The application of drilling fluids did not greatly affect the levels of most trace elements in plants growing at the disposal site although both increases and decreases in plant metal levels were observed as a result of mud addition. Drilling fluid addition resulted in slightly increased concentrations of Cu, Cd, Pb. Hg and As in plants at 30-50% of sites examined. The application of drilling fluids increased pH, electrical conductivity, and extractable hydrocarbon levels of soils at several sites, but most soil properties were unaffected by mud addition.
Dry matter yields of plants did not appear to be affected by drilling mud application although some changes in plant species growing at sites were noted. The levels of DTPA-extractable Cu, Zn, Cd, Cr, Pb, and Ba in soils were positively correlated with the total metal levels in soil and negatively correlated with soil pH at some sites. The concentrations of total Pb, Cr, Zn, Hg, and As in soil were positively correlated with the levels of these elements in plant tissue from at least 2 sites. Likewise, the concentrations of DTPA-extractable Cu, Pb, Zn, Cr, and Ba in soil were positively related to the levels of these elements in plants from at least 5 sites. The inherent spatial variability in natural soil properties tends to mask the relatively small effects resulting from drilling fluid addition to soil. The application of drilling fluids to soil does not appear to present unacceptable risks to the integrity or usefulness of the soil-plant system for producing food.
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