EPA Grant Number: R827015-01-0
Title: Demonstration of a Subsurface Drainage System for the Remediation of Brine-Impacted Soil
Investigators: Thomas M. Harris, John Veenstra
Institutions: University of Tulsa, Oklahoma State University
EPA Project Officer: Bala Krishnan
Project Period: February 1, 2000 to December 21, 2000 (N/C Ext. to April 22, 2001)
Project Amount: $99,769
Research Category: Brine spill remediation
Abstract
Oilfield brine-impacted soil is the most common environmental problem associated with oil production in Oklahoma. Salt causes the outright death of plants, and the consequent erosion of topsoil. Also, brine-impacted soil serves to contaminate surface waters and shallow aquifers. In addition to these issues, the remediation of brine-impacted soil may be motivated by lease agreements, federal and state regulations, landowner claims, and the fear of long-term liability.
At the present time, the most common remediation strategy applied to brine-impacted soil is in-situ chemical amendment (ISCA), in which gypsum, manure and/or other materials are added to the soil to restore its permeability and fertility. Of course, this strategy is inappropriate when groundwater must be protected from contamination. At the same time, the ISCA approach will fail if the salt is unable to migrate downward through the soil profile. Such conditions exist, for example, in the Tallgrass Prairie Preserve in Oklahoma; the subsoil is naturally impermeable in this region. A field demonstration of a subsurface drainage system that has been operating in the Preserve since December, 1997, features disposal of the salty leachate in an existing injection well.
The project proposed below, which concerns the further development of subsurface drainage systems for brine-impacted soil remediation, has two objectives. The first is to evaluate innovative uses of limestone gravel in the drainage, for the purpose of reducing installation costs, and extending this technology to "historical" spill sites (i.e. where much of the topsoil has been eroded). The second objective is to demonstrate the use of a solar evaporation pond for crystallizing the salt from the leachate, so that it may be disposed of at minimal cost. Such ponds should allow subsurface drainage to be applied at sites where an injection well is not available.
Gravel is commonly employed in subsurface drainage systems to limit the accumulation of sediment in the drainage pipes. If limestone gravel is employed, it may also serve to enhance the permeability of the surrounding soil, by providing the calcium ions required to counteract the sodicity of the brine-impacted soil. Combining sulfur with the limestone should allow the calcium carbonate to be converted (through the action of soil microbes) to the more soluble calcium sulfate. In addition to the treatment of contemporary spills, these strategies will be considered for the treatment historical spills, where "clean" topsoil applied to the site must be protected from the upward migration of salt during periods of dryness.
Thomas M. Harris John Veenstra Department of Chemistry/Biochemistry School of Civil and Department of Chemical Engineering Environmental Engineering University of Tulsa Oklahoma State University Tulsa, OK 74104 Stillwater, OK 74078