2024: EPA requested Participating Companies (PCs) to collect groundwater samples for per-and polyfluoroalkyl Substances (PFAS) analysis.

2023: EPA conducted vapor intrusion study in buildings located in Area 7.

2021: In September, the third five year review (FYR) was approved. The FYR summarized the remedies at the IBW site. The FYR concluded that the remedy was currently protective of human health and the environment. However, indoor air near areas where soil was contaminated needed to be re-evaluated and the extent of groundwater flow at the Western Margin needed to be thoroughly defined. 

2019: In March, the EPA completed a Vapor Intrusion Assessment regarding soil contamination in Area 7. In December, the PCs completed a human health risk assessment for soil contamination in Area 7 for vapor intrusion.

2018: The PCs installed a vapor mitigation system to an apartment complex located in proximity to soil contamination at Area 7.

2017: In April, the EPA released a fact sheet explaining what vapor intrusion is, how it is determined if vapor intrusion is a concern, and the areas to be re-evaluated at the IBW. 

2016: In September, the second FYR was approved. The FYR summarized the remedies at the IBW site and concluded that while remedies are still protective of groundwater, indoor air near areas where soil was contaminated would need to be re-evaluated.

2015: In April, EPA issued a letter of Determination for Closure of the Area 7 SVE System. In May the PCs submitted a soil vapor extraction (SVE) system Decommissioning Plan.

2014: In April, the PCs submitted an Operation and Maintenance Plan for the Central Groundwater Treatment Facility (CGTF), Area 7 and Area 12 Groundwater Extraction and Treatment Systems.  

2013: The NIBW Granular Activated Carbon Treatment Facility (NGTF) was completed. A pipeline connects the NGTF to the Chapparal Water Treatment Plant, allowing the City of Scottsdale beneficial use of the treated water. 30 upper alluvial unit (UAU) monitoring wells were abandoned.

2012: A final long term remedy for PCX-1 was approved.  PCX-1 is treated at the Miller Road Treatment Facility (MRTF) and under the Long-Term Operating Plan conditionally approved to discharge to the adjacent Salt River Project (SRP) canal. A treatment facility was constructed and completed in 2013. The NIBW PCs conducted site monitoring and sampling and submitted a request to reduce the monitoring well network in the UAU due to the reduction in contamination and comprehensive monitoring of data.

2011: FYR report was approved in the fall. The FYR summarized the remedies at the IBW site are currently protective of human health and the environment, and exposure pathways that could result in unacceptable risks are being controlled. The agencies and NIBW PCs negotiated a final long-term remedy for the MRTF.

2010: Rehabilitation of the MRTF was completed by the NIBW PCs. The FYR process began, which included interviews with stakeholders and community members as well as site inspections to aid in the assessment of the remedy effectiveness.

2009: On April 20, the NIBW PCs, working with EPCOR (formerly Arizona American Water Company [AAWQ]), EPA and ADEQ, began a rehabilitation of the MRTF.

2008: On January 16, an operator returning to the MRTF found that the blower operating in the treatment tower was not operating. The operator re-started the blower but the plant was shut down at approximately 9 a.m. It was found that the plant had been running without the blower operating since approximately 2:30 p.m. on January 15. Between the times that the blower turned off and the time the plant was shut down, approximately 3,639,000 gallons of water was delivered from the MRTF to the AAWC. Water with up to 22 parts per billion (ppb) of trichloroethene (TCE) was delivered to the Paradise Valley customers of AAWC. In agreement with the EPA, ADEQ, and Maricopa County, the MRTF was shut down pending an investigation and modifications to the plant. The plant was examined by a third-party consultant who re-evaluated both the plant infrastructure and its operating methods. The plant was restarted on April 25 with the following important modifications to the plant and its operations:

• The PCX-1 Well and its treatment train were totally isolated from the drinking water system using physical separations. Water from Well PCX-1 was treated and placed in the Arizona Canal and was sampled on a daily basis during the initial startup phases.
• The MRTF would be manned on a 24-hour per day, 7-day per week basis when operating.
• Malfunctioning electrical equipment, including instrumentation and alarms, would be repaired or replaced.
• Sampling frequency was expanded.
• A complete third-party engineering evaluation of the MRTF was conducted.
• The Arizona Department of Health Services stated that there was no public health hazard because of the low rate of exposure to the tap water.

In July, a study was conducted at the Hohokam Elementary School to determine if past irrigation had resulted in contamination to the school grounds. Two separate sampling events occurred; one on July 3, and the other on October 10. Sampling was conducted by the NIBW PCs through a contractor with oversight by ADEQ and consultants for the EPA. Sampling was done of both soil and soil gas at the site. No threat to public health was found in a review completed by the Agency for Toxic Substances and Disease Registry (ATSDR). Also in July, the NIBW PCs presented a draft Long-Term Operations Work Plan. A revised work plan was submitted in November.

A complete third-party engineering review and rehabilitation of the CGTF was completed. No significant concerns were found and modifications to the plant operating system were completed to bring the technology up to current levels.

2007: The City of Scottsdale began demolition of buildings at the former Rolamech facility at Area 7 and completed work by the end of 2007. EPA and ADEQ worked with Maricopa County Air Quality Department (MCAQD) to determine if air emission controls for the air stripping groundwater treatment systems could be removed and still be protective for human health and the environment. ADEQ and MCAQD issued letters stating that the air emission controls cannot be removed.

In early 2007, the ATSDR agreed to conduct a public health evaluation of potential past exposures to contaminants in the municipal drinking water system at the site that may have occurred before the system’s contaminated wells were closed in 1981. ATSDR completed a public health assessment of the site in 1989 in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, as amended. ATSDR gathered additional relevant and applicable data about the site’s groundwater and municipal water to further evaluate the past exposures. ATSDR issued a report called a public health consultation which described whether the exposures had any public health implications. Please contact 800-CDC-INFO or visit the ATSDR website if you have questions or need more information regarding the report.

In October, water treated at the MRTF from Well PCX-1 was directed to Tower 2 for nine days while the normally used Tower 3 was under inspection. On October 16 a TCE exceedance occurred from the MRTF. On this date, samples were taken which contained 14 ppb of TCE exiting the treatment facility.  Due to laboratory communications and equipment failures, this was not reported to the EPA or ADEQ until November 9. Samples taken of the water leaving the MRTF on October 8 and October 22 showed no detection of TCE. Water from the treatment facility was mixed with water coming from the AAWC arsenic treatment facility, and so it was calculated that the contamination entering the drinking water system met safe drinking water standards. EPA and ADEQ directed the NIBW PCs to conduct a thorough third-party review of the plant and its operations.

2006: EPA announced that all physical construction of cleanup systems was complete. Soil cleanup was expected to be complete in the next five years and groundwater cleanup an additional 30 years. EPA and the PCs independently conducted risk assessments to determine the relative risk associated with the possibility of removing the air emission controls that were part of the current groundwater treatment systems. EPA and ADEQ determined that the air emission control systems must remain in service at that time, and agreed to look at the air emission data in March 2007. 

2004: In February, the PCs and the EPA and ADEQ entered an informal dispute relating to the requirements to maintain air emission control systems at the NIBW ground water treatment facilities.

2002: In October, negotiation and approval of the final Amended Consent Decree (ACD) were completed. All of the parties signed the ACD for the final groundwater remedy. The ACD was lodged with the district court in Phoenix, Arizona on October 31st. On November 19 and 20th, EPA and ADEQ conducted inspections of the MRTF, CGTF, Area 7 and Area 12 remediation sites. The inspections were conducted in order to certify the treatment facilities were operational and functional.

2001 – 2003: The ACD became final with the approval of the federal court on June 5, 2003. The ACD was the result of an Amended Record of Decision (AROD) which was prescribed during 2001. The AROD resulted in EPA, ADEQ and the PCs negotiating the ACD. The purpose of the ACD was to include treatment facilities which were constructed by Motorola outside of the authority of the RODs (MRTF, Area 7 & Area 12). The ACD serves as the implementation vehicle of the ROD.

2001: In April, the EPA issued a Proposed Plan. The Proposed Plan announced the required public meeting, which took place on May 9th. EPA formally selected a remedy in the amended ROD which was received by ADEQ in July. ADEQ concurred with the remedy as described in the amended ROD, and the EPA signed the ROD in September.

1995 – 2000: The OU1 Consent Decree (CD) required the PCs to conduct a feasibility study addendum (FSA) to determine the effectiveness of the OU1 remedy and to recommend a final remedy. In 1995, the PCs initiated the FSA process including the completion of a site-wide groundwater flow and transport model. The final FSA was received in November 2000.

1994: The PCs, in cooperation with the Paradise Valley Water Company, constructed the MRTF at the northern end of the groundwater plume. The MRTF pumps and treats groundwater, and supplies treated water to the SRP Arizona Canal and to the Paradise Valley distribution system. Additionally, Motorola and Siemens voluntarily installed on-site groundwater treatment systems at both areas 7 and 12 to treat middle alluvial unit (MAU) groundwater at the source areas.

1991: In September, EPA issued a ROD for operable unit (OU) 2 to address contamination in the UAU of groundwater and contaminated soils. This ROD required SVE and groundwater treatment systems at several source areas, particularly Areas 7 and 12. The OU1 remedy failed to contain the lower alluvial unit (LAU) groundwater plume. Hydrogeologic data indicated that the plume was migrating to the north and would threaten the Paradise Valley well field.

1988: In September, a ROD selected a remedy for the middle and lower alluvial units of the groundwater. The OU1, also designated the Scottsdale Operable Unit, involved operation of a groundwater treatment facility located at Pima Park (Thomas Road and 88th Street), and known as the CGTF. The facility treats groundwater from four City of Scottsdale production wells by air-stripping. The treated water is added to Scottsdale's public water distribution system.

1984 – 1991: The EPA began a remedial investigation (RI) of the site in two phases, referred to as OUs. The RI and the feasibility study (FS) for OU1 (middle and lower aquifers) began in July 1984 and were completed in April 1988. The RI/FS for OU2 (shallow aquifer and soil contamination) was completed in 1991.

1981 – 1983: The IBW site was listed on EPA's NPL on Sept. 8, 1983, after the City of Scottsdale detected volatile organic compounds in municipal wells in the Scottsdale area in 1981.