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
Brine-impacted soil is the most common environmental problem associated with the onshore production of oil and gas. Salt causes the outright death of plants, and the consequent erosion of topsoil. 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),. This treatment entails the application of gypsum, hay, etc. to the soil to restore its permeability and fertility. Since such treatments are designed to encourage the downward movement of salt through the soil profile, they will fail if there is an impediment (such as a low-permeability subsoil) to this downward movement. Such conditions are not uncommon in the oil-producing counties of northeastern Oklahoma, for example.
Subsurface drainage may be used to accelerate the remediation of brine-impacted soil by enhancing the lateral movement of salt through the contaminated topsoil. This project, which concerns the further development of this technology, has three objectives. The first is to evaluate innovative uses of limestone gravel in the drainage for the purpose of reducing the cost of installing the drainage. This material 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. In addition to the treatment of a contemporary brine spill, this strategy will be considered for the treatment a historical "brine scar", where topsoil applied to the site must be protected from the upward migration of salt during periods of dryness. The third objective is to demonstrate the use of a solar evaporation pond for collecting the salty leachate from a subsurface drainage system, and reducing its volume through evaporation in order to reduce the cost of disposal.
The Keefer lease, 1 mile east of Bartlesville, Oklahoma on Highway 60, has been chosen as the site for this demonstration. This lease was the site of a large waterflooding operation in the 1960's. It is currently operated by Marjo Oil Co. One area within this site (Area I) is contaminated with salt but has retained much of its topsoil. Another more extensive area (Area II) is deeply scarred by erosion, with absolutely no topsoil remaining.
During initial site visits surveying was performed to help develop the design and layout of the remediation systems. The data from this surveying was put into topographic maps of the test area. During this survey an area of hydrocarbon contaminated soil was identified within the study area. This area will be avoided in construction of the remediation systems because the soil is unsuitable for a subsurface drainage system.
Soil geotechnical property tests and soil type identification were performed on samples from the site. The samples were collected with a stainless steel continuous tube sampler. Intact profiles were tested for permeability in a constant head permeameter using ASTM method D-2434. The permeabililty of the soil varied from 1.4 x 10-5 to 1 x 10-7 cm/sec with the vast majority of the samples in the 10-6 range. Known depth sections of the tube samples were used for measuring moisture content by ASTM method D-2216, density by ASTM method D-2937 and salt content using a saturated paste extract. The moisture content of the soil in the contemporary spill area (Area I) ranged from 15-18%, whereas the moisture content in the historic spill area (Area II) ranged from 19-44%. The soil pH was close to neutral and varied from 6.9 to 7.6 in Area 1 and 6.9 to 7.2 in Area II. Based on this information the soil was classified as a silty clay soil.
The soil microbial biomass was estimated using soil samples collected with a pre-sterilized tube sampler. Only material isolated, using sterile techniques, from the inner core of the sample collected in the tube sampler was utilized in this type of analysis. The average heterogeneous microbial population in the soil around the site was 8.3 x 10-4 CFU/gm.