1981 - 1983: SIBW was initially part of the IBW Superfund site that was placed on EPA’s NPL on September 8, 1983 after the City of Phoenix detected volatile organic compounds (VOCs) in municipal wells in the Scottsdale/Tempe area in1981.

1987 - 1993: The EPA began a remedial investigation (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 SIBW.

1993: In September, the EPA issued a Record of Decision (ROD) for the cleanup of VOCs in soil at eight industrial facilities. This ROD required a "plug-in" presumptive remedy involving the use of soil vapor extraction (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 the following 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.

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.

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 VOC degradation.

The western plume remedy is being addressed by EPA as a fund-lead action. The DCE Circuits site and the APS Ocotillo Generating Station are 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 the following 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 1993 ROD.

2003: During February, EPA and ADEQ agreed that the former landfills along the banks of the Salt River do 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 (NOID) the landfills from the NPL for public comment. The final Notice of Deletion (NOD) was sent by the EPA for filing in the federal register in May.

An Amended Record of Decision (AROD) was completed which 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 now prescribes MNA as the remedy. This AROD now makes the remedy for all three groundwater plumes in the SIBW area MNA.

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

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 SVE system was installed and operated, and samples were collected. The analyses of these samples will indicate if further remediation is necessary. EPA conducted a “plug-in” determination for soils at the Unitog sub-site in September. EPA determined the Unitog soils do not meet the plug-in determination criteria and therefore can be considered for a close out.

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.

2007: In December settlements were announced with eight 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.

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

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.

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 are being controlled. Specifically for SIBW, identified source areas have been remediated and the MNA remedy has almost met the remedial action objective to restore groundwater to beneficial use. At the DCE Circuits sub-site, indoor air monitoring conducted since 2007 is ongoing to ensure concentrations remain within EPA’s acceptable levels. MNA continued and the wells were sampled on a semi-annual basis by EPA. The SIBW monitoring wells are sampled semi-annually by EPA and ADEQ.  The groundwater remedy is resulting in contaminant concentrations which are mainly below the MCL of 5.0 ppb, with four wells indicating contaminant concentrations nominally above the MCL (highest concentration of 8.9 ppb for TCE in March 2011).

2013: EPA began an Enhanced Attenuation Study by performing ISCO at select monitoring wells which involves introducing a chemical oxidation agent (sodium permanganate) into the selected monitoring wells (5) to make contact with the contaminants and break them down into nonhazardous or less toxic compounds that are more stable, less mobile, or inert. The objective of the study is to assess the ability of this technology to restore the aquifer to the clean-up goal (2 parts per billion (ppb)) and to compare its cost effectiveness to Monitored Natural Attenuation (MNA) in both time and money. 25 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 continues on a quarterly basis.

2014: 45 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.

2015: In early to mid 2015, the enhanced attenuation study was submitted to ADEQ by the EPA to review the effectiveness of performance of ISCO.