2018 – 2023: ADEQ conducted regular groundwater monitoring, as prescribed by the Record of Decision (ROD).

2017: The ROD for the site was issued in March 2017.  The ROD documented the description of the final remedy, monitored natural attenuation, for the site. As described in the ROD, regular groundwater monitoring events were implemented to monitor remedial progress and evaluate remedy acceleration. The first event was conducted in September 2017.

2016: ADEQ sampled 16 groundwater monitoring wells in March. Trichloroethene (TCE) was detected in groundwater in three wells with concentrations ranging from 0.51 to 1.0 micrograms per liter (µg/L). All TCE concentrations detected were below the Aquifer Water Quality Standard (AWQS) of 5.0 µg/L. Cis-1,2-dichloroethene (cis-1,2-DCE) was detected in groundwater at concentrations ranging from 0.64 to 210 µg/L. Concentrations of cis-1,2-DCE were detected above the AWQS of 70 µg/L in three wells. Vinyl chloride (VC) was detected in groundwater at concentrations ranging from 2.9 to 48 µg/L. Concentrations of VC were detected above the AWQS of 2.0 µg/L in nine wells. No other contaminants were detected at concentrations exceeding their respective regulatory standards.

2011 – 2016: Groundwater monitoring activities were conducted biannually. Only contaminants of concern (COCs) VC and cis-1,2-DCE were detected at concentrations above their respective AWQSs. The revised Proposed Remedial Action Plan (PRAP) was issued in February 2015, followed by a 30-day period of public comment.

2009: ADEQ personnel met with the City of Phoenix (COP) on August 24th to discuss the Responsiveness Summary and ROD.

2008: In January, landfill vapor samples were collected. 

2004 – 2008: Groundwater monitoring was performed once or twice per year to evaluate groundwater flow patterns and chemical migration patterns. A site visit was conducted in November 2007 to evaluate the status of the site. Landfill vapor samples were collected in January 2008 and analyzed for volatile organic compounds (VOCs) and methane.

2001 – 2003: The Land and Water Use Study was issued in July 2001 as a supplement to the July 1999 Remedial Investigation (RI) report.  With the issuance of the Remedial Objectives (RO) report in January 2002, the RI report for the site was final. The Feasibility Study (FS) report was completed in July 2002. The PRAP was issued for public comment on June 30, 2002.

1998 – 1999: The site was placed on the Water Quality Assurance Revolving Fund (WQARF) Registry in April 1998 with an eligibility and evaluation score of 45 out of a possible 120. Until 1999, ADEQ provided regulatory oversight and technical review of site investigations and activities performed by the COP. In March 1999, ADEQ took over responsibility of completing the RI, FS and other site activities. ADEQ completed the RI report in July 1999. The report defined the extent of soil and groundwater contamination emanating from the landfill.

1997: The COP submitted a draft RI report for ADEQ’s review in September.

1988 – 2001: Quarterly groundwater monitoring activities were conducted at the site in support of site characterization, RI and an FS. In addition to groundwater monitoring, other technical activities completed include installation of monitoring wells and piezometers; collection of soil, groundwater and soil gas samples; geophysical surveys; and several aquifer tests. Compounds existing at detectable levels in site groundwater as a result of onsite and offsite activities included VC, trans-1,2-dichloroethene, cis-1,2-DCE, TCE, 1,2-dichlorobenzene, chlorobenzene, 1,1-dichloroethene, 1,4-dichlorobenzene, tetrachloroethene, benzene, 1,2-dichloroethane, chloroform, bis (2-ethylhexyl) phthalate, arsenic, barium, chromium, cadmium, lead, manganese and nitrate.

1987: The COP initiated a Phase I Groundwater Quality Investigation in response to the observed groundwater contamination.

1982: In response to flooding along the Salt River in 1978, 1979 and 1980, the COP acquired the Estes Landfill through eminent domain. COP, in conjunction with local, state and federal flood control and transportation agencies initiated a program of river channelization and bank stabilization. As part of this program, the Estes Landfill was excavated and moved onto the southern portion of the site, out of the riverbed. Hazardous wastes were segregated and shipped offsite for disposal.

1980 – 1982: Groundwater contamination was discovered in two industrial supply wells located down gradient of the landfill. One of these wells was located on the Bradley Landfill and one on the former Tanner property west of 40th Street. The primary contaminants detected in the supply well were cis-1,2-DCE and vinyl chloride, which are degradation products of TCE. Groundwater sampling of eight wells, four on the Estes Landfill and four on the Bradley Landfill through the mid-1980s, confirmed the presence of groundwater contamination in the area. The greatest contaminant concentrations were in the vicinity of a former liquid waste disposal pit on Estes Landfill.

1953 – 1973: The Estes Landfill was privately owned and operated from 1953 until 1973 when it was permanently closed. The unregulated landfill was reported to have accepted industrial, commercial, residential and liquid wastes. Liquid wastes, which would now be considered hazardous, were discharged into ponds excavated in the refuse pits.