The quality of produced and discharged waters is of increasing concern as the quality of potable waters within many regions of the country becomes a critical issue. The impact of discharged waters on the downstream water quality, as well as the flora and fauna within a discharge zone, is dependent on the quality of the water ultimately released into a drainage basin from a treatment system. In many regions of the country, discharge permits are being re-evaluated and sometimes recalled due to the actual and/or perceived impact upon surface and subsurface waters, particularly those providing water utilized by the human population. This is in response to the U.S. EPA's determination that the best method for dealing with produced waters was reinjection. Faced with the loss water that supports thousands of acres of wetlands across Wyoming, the State petitioned EPA to add an "Agriculture and Wildlife" exemption to allow surface discharge within lands under its jurisdiction in compliance with the NPDES program. As such, the Wyoming DEQ and Marathon Oil Company entered into a test project to ascertain the effectiveness of passive systems to treat produced waters to the NPDES toxicity requirements. The engineering design and testing of such a system was addressed in this study. The work was performed by students and faculty in the Environmental Science and Engineering and Petroleum Engineering departments at the Colorado School of Mines. The system consists of two surface flow cell units, one graded and one terraced, along with a constructed wetlands unit. These units can be independently evaluated. Untreated produced waters are presently being discharged into the drainage basin along with the diverted and treated waters. The system has been operational since July 1991. Initial results have been very promising and mechanical, chemical, and biological treatment in the surface flow and wetland units appear to significantly reduce the existing sulfide problem, as well as the released radium concentration. These are the constituents of major concern, although assays were also carried out for other parameters, including hydrocarbon content. Introduction In 1987, the U.S. Environmental Protection Agency (EPA) determined that the best practicable treatment (BPT) for produced waters was reinjection. For large operations with reinjection facilities this might not be a problem. However, for smaller producers the expense of hauling the water to a injection facility can often make the difference between profit and loss. In addition, the surface discharge of produced waters in the arid west support extensive wetlands that have become important habitat for mammals and migratory birds. After protest from producing western states, the EPA added an "Agriculture and Wildlife" subpart to allow surface discharge west of the 98th meridian in compliance with the National Pollution Discharge Elimination System (NPDES) of the Federal Water Pollution Control Act and amendments (33 U.S.C.A.).
The quality of produced water discharge is of increasing concern as the quality of potable waters in western states becomes a critical issue. The impact of discharged waters on the downstream water quality, as well as the flora and fauna within the discharge zone, is dependent on the quality of the water ultimately released into the drainage basin from the field. West of the 98th meridian, where surface discharge of produced water is permitted through the NPDES program, many permits are being re-evaluated and in some cased recalled due to actual and/or perceived impacts on the surface and ground water. In Wyoming, the quality of the water is of even further concern because of its potential use by farmers and ranchers. This paper evaluates a water treatment system that consists of four surface flow cells and a wetland unit. To develop effective design criteria and to isolate the various treatment mechanisms, the system components were independently analyzed. The system has been operational since May of 1991 with periodic sampling and testing. Initial results are very encouraging. The system appeared to handle the winter stress by a shift in active processes and locations. Mechanical, chemical, and biological treatment in the surface flow cells and wetlands unit have significantly reduced the existing sulfide problem, as well as having reduced the released radium concentration. Introduction Wyoming is currently the six largest oil and gas producing state in the country, Over the past one hundred years of production, surface discharge of what is now more than 24 billion- gallons-per-year of produced water, have created an elaborate system of voluntary wetlands. These wetlands are important habitat for mammals and migratory birds and are often the only source of water for many miles. In 1987, the U.S. Environmental Protection Agency (EPA) determined that the best practicable treatment for oilfield produced water was reinjection. For large producers with injection facilities on-site, this is not a problem, but it is an expense. However, for smaller producers, the cost of hauling the water to an off-site injection facility can make the difference between profit and loss. After protest from the producing western states, arguing that the loss of the water would have negative impacts on the quality of the range, the EPA added an "Agriculture and Wildlife" subpart to the regulation to allow discharge west of the 98th meridian under the guidelines of the NPDES program. (1)Given their mutual interest, the Wyoming Department of Environmental Quality and Marathon Oil Company entered into a cooperative project with the Colorado School of Mines, to assess the potential of a combination surface flow and wetlands system for the treatment of oilfield produced water. P. 435^
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