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The Apache facility is located in Cochise County seven miles southeast of the town of Benson, and 2.5 miles southwest of the town of St. David. PowerPoint PPT Presentation


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Apache Nitrogen Products Inc. (ANPI) has manufactured industrial chemicals and explosives for the copper mining industry, including nitroglycerin, nitric acid, ammonium nitrate, and blasting agents in Benson, Arizona since 1922.

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The Apache facility is located in Cochise County seven miles southeast of the town of Benson, and 2.5 miles southwest of the town of St. David.

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Apache Nitrogen Products Inc. (ANPI) has manufactured industrial chemicals and explosives for the copper mining industry, including nitroglycerin, nitric acid, ammonium nitrate, and blasting agents in Benson, Arizona since 1922.

Currently, ANP manufactures nitric acid, ammonium nitrate, and nitrogeneous fertilizer solutions.


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The Apache facility is located in Cochise County seven miles southeast of the town of Benson, and 2.5 miles southwest of the town of St. David.

The San Pedro River runs along the eastern side of the site, running from the southeast corner of the property towards the northwest.


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The Apache facility is located in Cochise County seven miles southeast of the town of Benson, and 2.5 miles southwest of the town of St. David.

The San Pedro River runs along the eastern side of the site, running from the southeast corner of the property towards the northwest.


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  • Wastewaters contain high levels of nitrates

  • Prior to 1971, wastewaters were discharged on site into dry washes

  • Flowed directly into the San Pedro River

  • After 1971, wastewaters were contained in unlined evaporation ponds.


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The evaporation ponds allowed seepage of high nitrate waters into the ground.

This water seeped downward until it encountered the underlying St. David clay.

The clay trapped the water beneath the ponds.

At one location, the trapped water began to flow eastward toward the shallow aquifer.


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The seepage of high nitrate waters from the ponds over several years of ANP’s operating history eventually formed a plume within the shallow aquifer nearly 3 miles long along the west side of the San Pedro River.


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To eliminate the problem, Apache undertook two major projects.

The first project identified methods to eliminate the discharges to unlined ponds.

In 1994 Apache constructed a Brine Concentrator which is a distillation process.


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With this distillation process, Apache can

  • Reclaimed water is returned to the production process

  • Concentrated impurities become a fertilizer ingredient

  • Achieved zero-discharge

  • Reduced groundwater consumption


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By eliminating the practice of discharging wastewater to the ponds, and allowing them to dry out, the impact on the shallow aquifer has significantly decreased.

As a result, the area of nitrate contamination in the shallow aquifer is shrinking.


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By eliminating the practice of discharging wastewater to the ponds, and allowing them to dry out, the impact on the shallow aquifer has significantly decreased.

As a result, the area of nitrate contamination in the shallow aquifer is shrinking.


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The second major project dealt with groundwater remediation at the site.

Apache decided to implement a pump-and-treat remediation technology which utilizes biological treatment methods to deal with the northern area of groundwater contamination.


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In November 1997 Apache completed construction of a treatment wetland designed to reduce the nitrates in the groundwater extracted from the shallow aquifer.

  • Treat up to 250 gallons per minute of incoming water

  • Containing up to 300 ppm dissolved nitrate

  • Uses “biological denitrification“

  • Residence time of 5 days

  • Reduces the nitrate concentration to less than 10 ppm


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  • Groundwater is pumped from a 93-foot deep shallow aquifer well

  • Transported via a 5,100 ft long 4-inch pipe-line to the wetland

  • Wetland is comprised of 5 ponds covering approximately 4.3 acres


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The groundwater enters the first of a series of three ponds planted with cattails and flows from pond to pond via gravity. The ponds planted with cattails are called the "denitrification ponds".


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The purpose of the cattails is to provide a source of organic carbon in the pond bottom sediments.

The cattails provide this carbon by dying and depositing dead plant materials on the bottom of the pond.

Water depths in these ponds are relatively shallow, approximately 1 to 2 feet, just sufficient to provide moisture to the plants and bottom sediments.


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In previous years, cattail caterpillars (Simyra Henrici) have decimated the cattails and delayed the startup of discharge from the wetland project.

Apache has sprayed an agent that works on the alkaline core of the caterpillars. Due to its makeup this agent is safe for other insects, reptiles and mammals.

The search continues for predatory insects as a more natural means of pest control. Some of the possible insects are praying mantis, lacewings, and ladybugs.


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Bacteria which feed upon the carbon from the dead cattails, require oxygen. Since the incoming water contains 300 ppm nitrates (NO3), which is a combination of both nitrogen (N2)and oxygen (O2), the  bacteria steal the required oxygen from the nitrates. The result is the liberation of free nitrogen back into the atmosphere, hence, the removal of nitrate from the water.  


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In the process of removing nitrates from the water in the denitrification ponds ammonia is created.  Ammonia is also generated through decomposition of cattails.

Water, with greatly reduced nitrate concentrations but elevated ammonia (NH3) concentrations, exits the third pond and enters a deeper (4 to 6 feet) pond which is planted with underwater plants. The function of this pond is to convert any ammonia that was generated in the denitrification ponds back into nitrate (NO3) via oxidation.


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The purpose of the underwater plants, Potamogeton, is to create high levels of oxygen (O2) in pond 4, to facilitate oxidation. 

The underwater plants accomplish this task by liberating oxygen via photosynthesis. 


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Upon exiting the fourth pond, the water is routed through a final denitrification pond, a polishing cell, to remove residual dissolved nitrate (NO3)created by oxidation in Pond 4.NO3is reduced to a concentration less than 10 ppm.


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At this point the water is fit to be returned to the environment.

The treated water is routed through a 2,900 foot pipeline back to a dry wash, where it is discharged onto a limestone riprap.

The limestone helps reduce phosphorous levels in the effluent stream.

The water then may either infiltrate into the wash channel or flow into the San Pedro River.


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In the southern area the perched zone has continued to decrease in size.

Isolated pockets of concentrated nitrates remain.

The perched zone remains a potential source of contaminants to shallow aquifer.


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In the southern area the perched zone has continued to decrease in size.

Isolated pockets of concentrated nitrates remain.

The perched zone remains a potential source of contaminants to shallow aquifer.


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Additionally, perchlorates have been identified in perched zone and the southern area of the shallow aquifer.

Concentrations of both contaminants in the shallow aquifer have decreased.

Apache has proposed Monitored Natural Attenuation with some further action in the perched zone.

In-situ treatment using molasses injection is an option.


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Flooding creates new


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