Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Apache Powder Company
EPA #: AZD008399263
City: St. David
Congressional District: 05
Other Names: Apache Nitrogen Products, Inc.
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 06/10/86
Final Date: 08/30/90
The Apache Powder Superfund Site (Site) is located in Cochise County, Arizona, approximately seven miles southeast of the incorporated town of Benson and 2.5 miles southwest of the unincorporated town of St. David. The site study area covers approximately nine square miles and includes 1,100 acres of land owned by Apache Nitrogen Products, Inc. (ANPI), formerly known as the Apache Powder Company. The San Pedro River bounds the eastern side of the Site, running from the southeast corner of the property north towards the northwest. The San Pedro River National Conservation Area (SPRNCA), owned by the Bureau of Land Management, is located approximately two miles south of the Site along the San Pedro River.
In 1922, ANPI began manufacturing industrial chemicals and explosives, including nitroglycerin, nitric acid, ammonium nitrates, and blasting agents. Presently, ANPI manufactures solid and liquid ammonium nitrate, ammonium nitrate-based fertilizers, nitric acid and aqua ammonia primarily for agricultural and mining customers. . Historically, these operations produced both liquid and solid wastes that were disposed of on ANPI property. These past use and disposal practices resulted in contamination of soils on the facility and groundwater contamination in a perched system underneath the plant’s operations area, in the nearby shallow aquifer and the San Pedro River. The groundwater contaminants in this Southern Area of the Site are nitrate and perchlorate. In the Northern Area of the Site the shallow aquifer groundwater is contaminated only with nitrate. In the early 1990s, ANPI undertook a program to replace eight privately-owned domestic supply wells by constructing new wells tapping the uncontaminated deeper aquifer after these households were provided bottled water in 1989.
The Site was placed on the National Priorities List (NPL) or Superfund list in 1990. In September 1994, EPA signed a Record of Decision (ROD) which selected various remedial alternatives for cleanup of the soils and groundwater contamination at the Site. Since then, many cleanup actions as well as additional investigative studies have been completed to either remove or reduce the amount of contamination in both soils and groundwater at the Site.
Contaminants and Risks
- Surface Water
- Soil and Sludges
- Environmentally Sensitive Area
A Baseline Public Health Evaluation and Ecological Assessment was completed by the EPA for the Site on September 22, 1992. The health evaluation process included: (1) the identification of contaminants from historical operations that were then present in groundwater, surface water, soils and sediments; (2) characterizing the population potentially exposed to these contaminants; and (3) evaluating the potential health effects resulting from exposure to contaminated groundwater, surface water, soil and sediments. EPA evaluated how individuals might be exposed to these contaminants under both current and future conditions as well as potential contaminant risks to natural resources.
The initial list of groundwater Contaminants of Concern (COCs) identified at the Site in 1992 included: arsenic, fluoride and nitrate in the perched groundwater; and nitrate in the shallow groundwater aquifer in both the Southern Area and Northern Area of the Site. Later in 1998, perchlorate was also identified in the perched and shallow aquifer groundwater in the Southern Area only.
The COCs identified in soils included; arsenic, antimony, barium, beryllium, chromium, lead, manganese and nitrate in the Inactive Pond soils and sediments; as well as 2,4-DNT, 2,6-DNT and lead in Wash Area 3. Vanadium pentoxide and paraffins were also found on Site. In 1998, TNT was discovered in soils.
The primary human health risk posed by the Site was the potential for accidental ingestion of contaminated shallow aquifer groundwater or accidental direct contact with contaminated soils. A Declaration of Environmental Use Restriction (DEUR) was placed on the property by the Arizona Department of Environmental Quality (ADEQ) in August 2008. The DEUR does not allow the construction of any wells for drinking water purposes into the contaminated shallow aquifer on ANPI’s property and restricts access and requires the maintenance of a cap over inactive ponds on ANPI’s property where contaminated soils remain in place. The construction of any new wells within the vicinity of the contaminated shallow aquifer requires a permit from the Arizona Department of Water Resources (ADWR). These permits are coordinated with ADEQ to ensure that drinking water wells are not installed where groundwater is known to be contaminated. New drinking water wells are installed in the uncontaminated deep regional aquifer rather than the shallow aquifer. And, as previously discussed, deep aquifer replacement wells were installed for the eight households in the immediate vicinity of the ANPI property that were placed on bottled water in the late 1980s. At this time, there is no known exposure pathway to contaminated groundwater or soils at the Site. EPA's selected remedy for the Site is protective, meets Applicable and/or Relevant and Appropriate Requirements (ARARs), is effective for the long-term and is permanent.
Who is Involved
This Site is being addressed through federal, state and potentially responsible parties' actions.
Investigation and Cleanup Activities
Various response activities have been undertaken by both EPA and the State of Arizona since 1980. ANPI completed, with EPA and ADEQ oversight, the construction of all remedial actions required at the Site in September 2008. The Site is currently in the operations and maintenance (O&M) phase of the remedy. The agencies continue to coordinate oversight of O&M activities and conduct technical meetings on a periodic basis.
Potential groundwater contamination problems were first identified by the Arizona Department of Health Services (ADHS) in 1979 during the course of a surface impoundment assessment. Both ADHS, as well as, the Southeast Arizona Governments Organization (SEAGO) conducted groundwater and surface water sampling during the early 1980s to assess the level of nitrate contamination associated with ANPI. In 1980, EPA found high levels of heavy metals (such as lead, chromium, zinc and strontium) in some of the on-site ponds. Ten shallow wells down-gradient from the facility were found to contain nitrate. Most notably, the sampling detected 470 mg/l nitrate in a domestic drinking well located north-west of the Site. Additional site inspections were conducted by the ADHS in early 1986 to confirm these findings, whereupon ADHS instructed ANPI to obtain a state groundwater protection permit to address source discharges. ANPI however, continued to operate in violation of applicable state water quality regulations during the period of 1988 through 1993.
In response to contamination concerns raised by the State, EPA proposed listing the Site on the National Priorities List (NPL) in 1986. EPA then conducted a Preliminary Investigation (PI) of the Site which was completed in June 1988. The PI confirmed the State’s earlier findings of nitrate contamination. Additionally, the PI detected elevated levels of heavy metals in the sediments of on-site evaporation ponds and detected other soils contamination in the drum disposal areas. While investigations proceeded and alternatives were reviewed for cleanup of the Site, interim actions (including bottled water and eventually deep aquifer replacement wells) were taken to address potential threats to public health. The investigations identified a shallow and a deep aquifer which are separated by a substantially thick clay aquitard underlying the entire study area, thus protecting the deeper drinking water aquifer from contamination. A Remedial Investigation (RI) Report and a Feasibility Study (FS) for the Site were completed in June 1994.
At the time of the RI, nitrate above drinking water standards was detected in several drinking water wells near the Site. Residents living near the Site historically used the shallow aquifer groundwater as a source for drinking water. After this discovery in 1993, ANPI installed eight deep aquifer replacement wells to be used by these households. The deep aquifer, located 600 feet below the surface and protected by a 300 - 400 foot clay unit, is not contaminated. Today, all new wells installed in the vicinity of the Site near the contaminated shallow aquifer plume are completed in the deep aquifer.
In June 1994, EPA released a Proposed Plan under Superfund (CERCLA) requiring ANPI clean up five areas with groundwater and soils contamination due to historical practices: (1) Perched Groundwater, (2) Shallow Aquifer Groundwater, (3) Inactive Pond Soils and Sediments, (4) White Waste Materials and Drum Storage Area, and (5) the Wash 3 area (excluding the Ash and Burn Area). Concurrently, ADEQ addressed the company’s on-going manufacturing processes under the authority of a State Consent Decree to reduce or eliminate the threat of future contamination.
In September 1994, EPA signed the Record of Decision (ROD) for the Site. The selected groundwater remedy components were: (1) Pumping and extracting the perched groundwater and treating it by forced evaporation (through a brine concentrator); and (2) Pumping and treating the shallow aquifer by use of constructed wetlands and recharging the treated water back into the shallow aquifer. The soils remedies included on-site containment and capping of soils in the inactive ponds and excavation and off-site disposal of contaminated soils from the White Waste Material and Drum Storage Area and the Wash 3 Area.
In April 1997, EPA signed an Explanation of Significant Differences (ESD) #1 to modify the groundwater component of the remedy to: (1) Allow the perched groundwater to be extracted and treated by constructed wetlands (rather than the brine concentrator) in conjunction with the shallow aquifer groundwater in the Southern Area of the Site; (2) Allow for two locations (a Northern and Southern Area) for siting the constructed wetlands; (3) Allow for the recharge of treated groundwater by pipe discharge and additional extraction wells; and (4) Allow for characterization, treatment and removal of newly discovered areas of contaminated soils.
In November 1997, ANPI completed construction of a 4.5 acre constructed wetlands (Northern Area Remediation System or NARS) to treat the nitrate-contaminated groundwater in the Northern Area of the Site. The establishment phase (planting wetland vegetation and pilot testing the treatment efficiency) was completed in 2004, with full-scale pumping, treatment and discharge beginning in 2005. The wetlands currently are treating the nitrate-contaminated groundwater to below Federal and State maximum contaminant levels (MCLs) for dinking water year-round. Currently, one extraction well pumps an estimated 220 gallons per minute (115 million gallons per year) of contaminated water into the wetlands. Nitrate levels are declining in most monitoring wells within the Northern Area plume. This innovative technology has been well received both by the State and ANPI for several reasons including: the realization of a cost savings of $15 million dollars over the use of other engineering technologies; lower long-term operations costs, maintenance costs and energy demands; and the enhancement of habitat for species in the vicinity of the San Pedro River, a valued state resource.
However, in 1998, when perchlorate was discovered in the perched and shallow aquifer groundwater in the Southern Area, ANPI began another round of investigation of the Southern Area shallow aquifer groundwater and the San Pedro River for a period of several years to determine the extent of perchlorate contamination. Construction of a wetlands system in the Southern Area was not begun. Extensive groundwater investigations were conducted, including additional exploratory borings, well construction, and seismic geophysical surveying to determine the extent of contaminant migration.
In September 2000, EPA signed an ESD #2 to modify the previously selected remedies for the soils and related waste materials. The ESD established cleanup standards for recently detected COCs without ROD cleanup standards that had been identified in on-site soils, sediments or drums. It also modified some cleanup remedies to “no further action” for selected soils media components where hazardous substances were not detected or the levels of contamination did not exceed EPA’s soils and waste cleanup standards.
After the discovery of TNT-contaminated soils on the Site in 1998, a Removal Action was conducted in 1999-2000 to pre-treat the high concentration materials on the ANPI facility, and then excavate and remove the remaining ash and low concentration TNT-contaminated soils for off-site treatment and disposal. Also, in 2000, the contaminated soils from the White Waste and Drum Storage Area and the Wash 3 area were excavated and transported off-site for final treatment and disposal. These activities included the removal of 262 drums (55 or 110 gallons each) and the excavation of 45 cubic yards of soil from Wash 3. These materials had previously been stored on the Site in a secured storage area.
In September 2005, EPA signed a ROD Amendment to change the groundwater remedy for the Southern Area to monitored natural attenuation (MNA), with institutional controls (ICs) for the nitrate and perchlorate contaminated shallow aquifer. Southern Area investigations conducted during the late 1990s through 2004 determined that the perched system and the nearby shallow aquifer groundwater in the Southern Area were hydraulically isolated from the San Pedro River and its associated shallow aquifer. The investigations also identified nitrate and perchlorate reducing bacteria in the Southern Area soils and groundwater that could reduce the mass and concentrations of the contaminants.
In July 2008, EPA signed an ESD #3 to modify the remedy for the Northern Area Groundwater to allow the leading edge of the groundwater plume beyond the extraction well to be treated by MNA. This ESD also specified certain ICs to prevent exposure. The groundwater monitoring data indicate that the plume is shrinking and the concentrations are declining in this portion of the plume beyond the capture of the extraction well. Model simulations also supported the presence of a natural attenuation mechanism in this area.
In August 2008, the required ICs were put in place when ANPI filed a Declaration of Environmental Use Restriction (DEUR) with the State of Arizona (ADEQ) to restrict use of the groundwater underneath ANPI’s property and to restrict access to the inactive ponds where contaminated soils remained capped in place.
In September 2008, EPA signed a Preliminary Close-Out Report for the Site. This document confirms “Construction Complete” of the required remedial actions under the ROD, and the Site has entered the long-term O&M phase of the remedy. The nitrate and perchlorate concentrations in groundwater are declining and the plumes are decreasing in size. These changes are a result of the effectiveness of the NARS in the Northern Area, ongoing MNA activity, and because all sources of contamination have been eliminated.
In 2009, ANPI began the long-term operations and maintenance phase of the remedy. The groundwater cleanup in the Northern and Southern Areas is on-going. In April 2010, EPA determined that the Site is ready for reuse now that all remedial construction activities required in the ROD and other decision documents have been achieved and the institutional controls are in place.
In 2012, ANPI submitted a workplan to demolish approximately 180 buildings / structures on the facility. Work has been ongoing for this effort beginning in 2013 through 2017.
During the period of 2013 through 2015, additional characterization studies, including exploratory boring and a coastal discharge test were completed in the Molino Creek Sub-Aquifer portion of the Southern Area Groundwater.
In 2014, ANPI completed a Time Critical Removal Action for nitroglycerin and detonation cord discovered in Building 57 and another structure along the historic powder line. A controlled burn was conducted of the explosive materials in October 2014.
Cleanup Results to Date
EPA's selected remedy for the Site is protective, meets Applicable and/or Relevant and Appropriate Requirements, is effective for the long-term and is permanent. The State of Arizona has concurred with EPA’s selected remedies. All of the remedial actions required for the Site have been fully implemented. Institutional controls are in place. ANPI has implemented an Alternative Domestic Water Supply Plan and a Community Outreach Plan which are updated annually. ANPI has an on-going site wide monitoring program.
The first Five-Year Review (5YR) of the Site was completed in September 2002, prior to full-scale start up of the NARS wetlands treatment system and completion of the Ecological Risk Assessment. The second 5YR was completed in September 2007. It recommended long-term ICs be implemented in the form of a DEUR and that the portion of the nitrate plume that had migrated beyond the capture zone of the extraction well be evaluated. Both these actions were completed in 2008. The third 5YR was completed in September 2012. The review concluded that all required land use restrictions (DEUR) and other ICs are now fully in place and the remedy is protective of human health and the environment for both groundwater and soils because there is no current exposure. The fourth 5YR is scheduled to be completed in 2017.
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
Online information about the PRPs for the Site is not available.
Documents and Reports
Public Information Repositories
The public information repositories for the site are at the following locations:
Benson Public Library
302 South Huachuca
Benson, AZ 85602
EPA Site Manager
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
400 W. Congress Street, Suite 433
Tucson, AZ 85701
After Hours (Emergency Response)