2023 – 2024: The US Environmental Protection Agency (EPA) sampled groundwater during a Remedial Investigation (RI) for Per-and polyfluoroalkyl substances (PFAS).

2021: EPA was in the process of planning an RI for PFAS.

2020: Eight subsites were evaluated for vapor intrusion. The assessment determined additional soil gas sampling was unneeded based on the current land uses of the subsites. 

In June, the EPA completed and approved the Remedial Action Completion Report for the entire South Indian Bend Wash (SIBW) site, which indicated remedial actions were completed and remediation goals defined in the Record of Decision (ROD) were met.

2019: EPA sampled select monitoring wells for perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). PFAS were detected in multiple samples collected exceeding the 2019 EPA preliminary remediation goal of 70 parts per trillion (nanograms per liter [ng/L]) for combined results of PFOS/PFOA. EPA determined that conducting an RI for PFOS and PFOA was needed.

2017 – 2018: Groundwater monitoring continued. Concentrations of contaminants of concern (COCs) in the upper alluvial unit (UAU) western plume and UAU central plume remained below the maximum contaminant levels (MCLs). Most eastern plume trichloroethene (TCE) concentrations are below the MCL; however, one monitoring well remained above the MCL (5 micrograms per liter [µg/L]).

2016: The second Five-Year Report (FYR) was completed in September. The FYR determined the remedies at both Indian Bend Wash (IBW) sites are currently protective of human health and the environment, and exposure pathways that could result in unacceptable risks are being controlled. Additional evaluation into vapor intrusion was recommended.

2015: In early to mid 2015, the enhanced attenuation study was submitted to ADEQ by the EPA to review the effectiveness of performance of in situ chemical oxidation (ISCO).

2014: Forty five groundwater monitoring wells were abandoned with 21 wells remaining in the study area. They will continue to be monitored through annual sampling events. The enhanced attenuation study has been completed and is currently being evaluated.

2013: EPA began an Enhanced Attenuation Study by performing ISCO at select monitoring wells, which involved introducing a chemical oxidation agent (sodium permanganate) into five monitoring wells to make contact with the contaminants and break them down into non-hazardous or less toxic compounds that are more stable, less mobile, or inert. The objective of the study was to assess the ability of this technology to restore the aquifer to the cleanup goals and to compare its cost effectiveness to monitored natural attenuation (MNA) in both time and money. Twenty five monitoring wells were abandoned. Most of the wells were either non-detect or below the MCL when initially installed and have continued to be below the past 20+ years. MNA sampling continued on a quarterly basis.

2011 – 2012: The first FYR was completed in September. The FYR determined the remedies at the IBW sites are currently protective of human health and the environment, and exposure pathways that could result in unacceptable risks were being controlled. Specifically for SIBW, identified source areas were remediated and the MNA remedy had almost met the remedial action objective to restore groundwater to beneficial use. At the DCE Circuits subsite, indoor air monitoring conducted since 2007 was ongoing to ensure concentrations remained within EPA’s acceptable levels. MNA continued and the wells were sampled on a semi-annual basis by EPA. The SIBW monitoring wells were sampled semi-annually by EPA and ADEQ. The groundwater remedy resulted in TCE contaminant concentrations that were mainly below the MCL of 5.0 parts per billion (ppb), with four wells indicating contaminant concentrations nominally above the MCL (the highest concentration of 8.9 ppb for TCE was in March 2011).

2010: An additional monitoring well was installed at the southeast boundary of the central plume during the summer. The FYR process began for this site with site inspections and interviews of community members and stakeholders.

2008 – 2009: MNA continued and the wells were sampled on a quarterly basis by EPA.

2007: In December settlements were announced with eight potentially responsible parties (PRPs): Circuit Express, Inc.; IMC Magnetics; Prestige Cleaners, Inc.; Unitog Rental Services, Inc.; Janstar Development, Inc.; K and S Interconnect, Inc.; Service and Sales, Inc.; and Sherman Leibovitz.

2006: On December 6, EPA announced that all physical construction of cleanup systems was completed. Soil cleanup was expected to be complete in the next five years and groundwater cleanup an additional 30 years.

2005: Subsequent to the removal action at DCE Circuits, soil vapor samples were collected. The samples indicated levels of soil vapor which required remediation. A mobile soil vapor extraction (SVE) system was installed and operated, and samples were collected. The analyses of these samples would indicate if further remediation was necessary. EPA conducted a “plug-in” determination for soils at the Unitog subsite in September. EPA determined the Unitog soils did not meet the plug-in determination criteria and therefore could be considered for a close out.

2004: In December, EPA conducted a removal action at DCE Circuits. A dry well which received hazardous waste in the 1980s, was removed by soil boring. Several truck roll-off bins of soils were disposed of as solid waste and several drums of waste were disposed of as hazardous waste.

2003: During February, EPA and ADEQ agreed that the former landfills along the banks of the Salt River did not pose a threat significant enough to continue to be listed as part of the site. As a result, EPA published a Notice of Intent to Delete the landfills from the National Priorities List (NPL) for public comment. The final Notice of Deletion was sent by the EPA for filing in the federal register in May.

An Amended Record of Decision (AROD) was completed that changed the remedy associated with the groundwater cleanup of the western plume on October 16. The remedy was originally prescribed as groundwater pump and treat. The AROD prescribed MNA as the remedy. This AROD made the remedy for all three groundwater plumes in the SIBW area MNA.

1999 – 2000: The EPA entered into negotiations with six PRPs in 1999 and executed an Administrative Order on Consent (AOC) with only one of the PRPs (IMC Magnetics) on September 27, 2000. This AOC required IMC Magnetics to design the MNA remedy for the central and eastern plumes. This work involved the installation of groundwater monitor wells and long-term monitoring of plume behavior and volatile organic compounds (VOC) degradation.

The western plume remedy was addressed by EPA as a fund-lead action. The DCE Circuits site and the APS Ocotillo Generating Station were thought to be contributors to the SIBW western groundwater contaminant plume. EPA and ADEQ completed technical reviews of the focused RI plug-in assessments, and determined that six sub-sites (Cerprobe Corp., former Service and Sales, Former Eldon Drapery, former Desert Sportswear, former Circuit Express and former Allstate) did not meet or exceed the plug-in criteria as described in the 1993 ROD.

1998: In September, the EPA signed a ROD for the cleanup of VOCs in the groundwater operable unit at this site. The selected remedy required MNA for the central and eastern portions of the plume, and a groundwater extraction and treatment system for the western portion of the plume.

1993: In September, the EPA issued a ROD for the cleanup of VOCs in soil at eight industrial facilities. This ROD required a "plug-in" presumptive remedy involving the use of SVE systems. Each sub-site collected soil vapor data and followed the ROD's guidelines to determine if an SVE system was necessary.

The EPA and ADEQ completed technical reviews of the focused RI plug-in assessments and determined that six sub-sites (Cerprobe Corp., former Service and Sales, former Eldon Drapery, former Desert Sportswear, former Circuit Express and former Allstate) do not meet or exceed the plug-in criteria as described in the ROD.

1987 – 1993: The EPA began an RI of the IBW site in 1983, and at the end of 1987, informally split the IBW into two study areas: the North IBW and South IBW.

1981 – 1983: SIBW was initially part of the Indian Bend Wash IBW Superfund site that was placed on the EPA NPL on September 8, 1983 after the City of Phoenix detected VOCs in municipal wells in the Scottsdale/Tempe area in 1981.