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.
Area I was divided into a grid with 12 subsections, each approximately 35' x 35'. Each subsection was delineated with a berm of topsoil approximately 12 ' high. One subsection was not utilized because of the presence of a concrete pad and a protruding production pipe. Three of the subsections (assigned randomly) were designated as controls. The remaining subsections (assigned randomly) were bisected with 8" wide ditches, dug with a backhoe. In two subsections the ditch was filled with gravel only, and then covered with soil. In another two subsections the ditch was filled with gravel and elemental sulfur, and was then covered with soil. In another two subsections the ditch contained 4" diameter polyethylene corrugated slotted drainpipe in addition to gravel (covered with topsoil). The last two subsections contained drainpipe covered with a "sock", and backfilled with soil (no gravel in this case).
All of the drainage pipes were connected to a collection system consisting of unslotted polyethylene pipe. At the point of each connection a sampling sump was installed, which allow for the collection of leachate samples from the individual test subsections. The collection system drains into a 500 gallon fiberglass tank. This tank will be pumped out by a level-contolled sump pump into the produced water disposal system for the lease.
Area II was divided into a grid with 4 subsections, each approximately 50' x 50'. The entire area was first graded with a bulldozer. Each subsection was delineated with a berm of topsoil approximately 18 ' high. One subsection was designated as the control. Approximately 8" of topsoil (sandy loam) was applied to another subsection, on top of one line of drainage pipe (covered with a sock) bisecting the subsection. In another subsection the sandy loam layer was underlain with a 2" layer of gravel, and one line of drainage pipe (covered with a sock). The last subsection was identical to the third, with the exception that sulfur was applied to the gravel before the sandy loam was placed on top of it. The three subsections with drain pipe were outfitted with sample sumps as described above. The lines were then connected to a collection line that ran directly to the evaporation pond.
The evaporation pond lies immediately downhill from the Area II subsections. It is approximately 4' deep, 90' on a side, and is lined with a 60-mil thick polyethylene liner (with heat-sealed seams). The pond itself was was constructed with a bulldozer.
The construction activities described above were performed by Whaling Construction Co. of Bartlesville, OK. The pond liner was installed by Manhattan Environmental Co. of Tulsa, OK. This work was performed during late August and early September.
A series of preliminary surface composite soil samples were collected within the test subsections at the conclusion of the construction activities. These samples have been analyzed in our laboratory for the salt content. These data represent the time "0" values in the monitoring of the progress of the remediation.