INDIAN BEND WASH AREA
On this page:
- What Has Been Done to Clean Up the Site?
- What Is the Current Site Status?
- Activity and Use Limitations
- Sampling and Monitoring
- Enforcement Information
On related pages:
The entire area of the Indian Bend Wash site (IBW site) covers about 13 square miles in Scottsdale and Tempe, Arizona. There are numerous industrial facilities located near the IBW site. Up until the 1970s, before current environmental regulations existed, industrial solvents containing volatile organic compounds (VOCs) were typically disposed of directly onto the ground or in dry wells. These disposal practices, along with other releases, resulted in the present soil and groundwater contamination at the site. EPA divided the site into two areas, known as North Indian Bend Wash (NIBW) and South Indian Bend Wash (SIBW). NIBW and SIBW are on separate cleanup tracks, as discussed below. Final Remedies are in place and cleanup activities have been completed or are currently underway.
What Has Been Done to Clean Up the Site?
EPA is addressing NIBW as a separate area of study from SIBW because the contaminants come from different sources and the groundwater plumes are not contiguous.
Groundwater: The long-term remedy for NIBW groundwater, selected in 1988, included extraction and treatment. Currently, groundwater extraction and treatment is ongoing at five facilities. The oldest, The Central Groundwater Treatment Facility (CGTF) began operating in 1994. The CGTF treats the contaminated groundwater using a technology known as air stripping and provides treated water to the City of Scottsdale for use as part of their municipal water supply. The newest facility, the Northern Groundwater Treatment Facility (NGTF), adjacent to the Miller Road Treatment Facility (MRTF) began operating in 2013 and provides plume containment for the northern extent of the groundwater plume. Granular Activated Carbon (GAC) is used to remove contaminants and the treated water is blended into the potable supply. Two other groundwater extraction and treatment facilities are located within Source Areas 7 and 12 to contain and treat the most contaminated groundwater. At Area 7 extracted water is treated by UV Oxidation before being re-injected into the upper aquifer as part of the plume containment. At Area 12 extracted water is treated by Air Stripping before being discharged to the irrigation canal. Groundwater treatment is anticipated to be necessary for about 70 years.
Groundwater at the NIBW site is present in three separated levels or layers. These layers are referred to as the Upper, Middle and Lower Aquifers. Cleanup objectives in the Upper Aquifer have been met in most of the NIBW monitoring wells. Depth to groundwater contamination in the area of the plume averages about 200 feet or more below ground surface; thus vapor intrusion is generally not a concern for properties overlying the groundwater plume. Land uses near the IBW site include residential and industrial/commercial areas, agricultural uses, recreation areas, undeveloped open space and waterways.
Soils: The long-term remedy for NIBW soils, selected in 1991, included the use of soil vapor extraction (SVE) to clean up contaminated soil (in three specific areas) and continued monitoring of the upper aquifer. SVE was required at Area 7, Area 8 and Area 12 because it was determined that these areas could continue to contaminate the groundwater. A voluntary SVE cleanup was also undertaken at Area 6. The cleanup standards specified in the 1991 Record of Decision that were based upon groundwater protection criteria have been met at all sites.
Final Remedy: The first Record of Decision for groundwater extraction and treatment was signed in 1988. Following construction and initial operation of this remedy it became apparent that the groundwater contamination in the middle and lower parts of the aquifer had not been contained or captured and that the CGTF was not adequately controlling and treating the groundwater plume. As a result, additional actions known as the “Remedy Enhancements” were needed, which included new monitoring and extraction wells, a second groundwater treatment facility and other improvements. EPA signed a final Record of Decision (ROD) Amendment in September 2001, which was further modified by an Explanation of Significant Differences in 2012. The final remedy included, in addition to the actions required by the 1988 remedy:
- construction of the Northern Groundwater Treatment Facility (NGTF);
- the Remedy Enhancements described above;
- one new extraction well and one new recharge well
- continued evaluation of groundwater conditions using the groundwater model; and
- contingency actions for Area 7 and Area 12 groundwater plumes.
Construction of the NIBW final remedy was completed in 2013.
Soils: The 1993 Record of Decision selected Soil Vapor Extraction to address soils contaminated with volatile organic compounds (VOCs). Within the SIBW study area there are many facilities at separate locations known as “subsites.” Cleanups to date have been completed at the DCE Circuits subsite as well as voluntary cleanup at two other subsites . EPA also determined that soil cleanup was not required at seven subsites: Circuit Express, Allstate Mine Supply, Desert Sportswear, Cerprobe, Service and Sales, and the City of Tempe Right-of-Way. EPA is currently evaluating the adequacy of cleanup at all former source areas with respect to the vapor intrusion pathway, in response to the recommendations of the 2016 Five Year Review.
Groundwater: The long-term remedy for SIBW groundwater, selected in the 1998 Record of Decision, addressed all three groundwater plumes at the SIBW Site: the western plume, the central plume and the eastern plume. The remedy selected for the central and eastern plumes was monitored natural attenuation (MNA), while a contingency remedy of extraction and treatment was specified for the western plume. The ROD was amended in 2004 when it became apparent that the western plume was also rapidly achieving drinking water standards under MNA and extraction and treatment would not be required. A pilot test of In-Situ ChemicalOxidation using permanganate injection was applied to hasten the cleanup of the eastern plume in 2013. At the time it was estimated that it would take 10 to 30 years for the eastern plume to achieve cleanup levels. During the 2016 annual sampling event drinking water standards were attained for the first time in all monitoring wells sampled in all 3 groundwater plumes.
What Is the Current Site Status?
Significant progress has been made to date towards acheivement of cleanup objectives. In Scottsdale, over 120 billion gallons of water have been treated, removing over 91,000 lbs of trichloroethylene. Groundwater in the area of Tempe is already attaining drinking water standards.
Activity and Use Limitations
At this site, activity and use limitations that EPA calls institutional controls are in place. Institutional controls play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use. They also guide human behavior. For instance, zoning restrictions prevent land uses – such as residential uses – that are not consistent with the level of cleanup.
For more background, see Institutional Controls.
Wells cannot be drilled in the state of Arizona without a permit from the Arizona Department of Water Resources (ADWR). EPA works with ADWR to coordinate the cleanup efforts at the IBW site. If someone applied for a well permit, ADWR would inform them of the risks of using the groundwater.Wells cannot be drilled in the state of Arizona without a permit from the Arizona Department of Water Resources (ADWR). EPA works with ADWR to coordinate the cleanup efforts at the IBW site. If someone applied for a well permit, ADWR would inform them of the risks of using the groundwater.
Sampling and Monitoring
EPA is currently re-evaluating former industrial source areas to determine if residual soil contamination could present a potential vapor intrusion risk into nearby residential or commercial buildings, as well as air emissions from groundwater extraction and treatment facilities to ensure continued remedy protectiveness.
EPA and the State of Arizona have been involved in investigations and cleanup activities at the IBW site since the initial discovery of VOCs in the groundwater in 1981. In Scottsdale, the NIBW Participating Companies are working under a Consent Decree to complete the cleanup under EPA oversight. In Tempe, EPA is implementing the cleanup following cash-out settlements with potentially responsible parties.