TUCSON, Ariz. -- At the National Ground Water Association 's (NGWA) Annual Convention in Las Vegas, Nevada, Hargis + Associates, Inc., (H+A) a local hydrogeology and engineering consulting firm, was selected by NGWA to receive the inaugural "Outstanding Ground Water Remediation Award." The award was presented to Hargis + Associates for their design of an "environmentally- friendly" solution to a groundwater remediation project, the Apache Wetland in Cochise County, Arizona. Dr. Dennis Goldman, Science Counsel for NGWA stated, "...the committee was particularly impressed with the quality and innovation shown for the Apache project."
Dr. Leo, S. Leonhart, Senior Technical Manager of H+A's Tucson Office said, "Hargis + Associates designed the Apache Treatment Wetland project as an attempt to focus nature on a specific environmental problem." The remedial action undertaken by Apache Nitrogen Products, Inc. (ANP) is designed ta remove nitrate contamination in groundwater along a portion of the San Pedro River. In contrast to many remedial actions that employ "machinery" based treatment plants, the wetland, although man-made and operated, appears and functions as an extension of the natural setting. "As the wetland treats contaminated water, it also provides a friendly oasis for wildlife, an aesthetically pleasing natural feature, and an opportunity to study a different technological approach to an environmental problem" stated Leonhart.
The wetland project, approved by the U.S. Environmental Protection Agency under the Superfund Laws to address historical contamination from the ANP manufacturing facility, is believed to be the only one of its kind currently being used for Superfund remedial action. The entire cost of the project was approximately $360,000. Wetland construction was completed by the Ashton Company and Barnatt & Shore, both Tucson based contractors, under Hargis + Associates supervision.
The Apache Wetland project is capable of reducing nitrate concentrations exceeding 300 parts per million (ppm) to less than 10 ppm, which, is the standard for drinking water. Contaminated groundwater is pumped from a shallow aquifer well at a rate of approximately 250 gallons per minute (gpm). The water is transported from the well via pipeline nearly 1 mile and lifted 140 feet to the 5-acre, 5-pond wetland.
Through a process referred to as "biological denitrification," the wetland cultivates the growth of cattails allowing them to grow, mature, and die. As a result, a base of organic carbon is established in the pond sediments. The carbon base provides a food source for existing microorganisms, which need a source of oxygen for their biological processes. In the absence of oxygen from the atmosphere, these microorganisms can use the oxygen on the nitrate molecule. This process changes the nitrate to nitrogen gas and releases it into the atmosphere which already consists of 78 percent nitrogen. Once treated, the water is transported from the wetland via another pipeline and discharged to a nearby wash. Upon discharge, the water either seeps back into the aquifer or flows into the San Pedro River.
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