Revised On: Feb. 16, 2024 - 4:00 p.m.

2021: Two new triple-nested monitoring wells were installed in the downgradient portion of the plume. The ISCO groundwater treatment pilot study continued throughout the year.

2020: An in-situ chemical oxidation (ISCO) groundwater treatment pilot study was initiated in February 2020. The Proposed Remedial Action Plan (PRAP) was released in April 2020.

2019: The triple-nested monitoring well 24MW-21 was installed to delineate the downgradient portion of the plume. The Draft Remedial Investigation (RI) Report was released in March. The Proposed Remedial Objectives (RO) Report was released in May. The Final RI Report and Feasibility Study (FS) Work Plan were released in June. The Final FS Report was completed in September.

2018: In February, three deep soil borings were advanced to assess contaminants in the deep vadose zone. Tetrachloroethene (PCE) was not detected in samples collected from the borings. In June, two additional groundwater monitoring wells were installed to better define the downgradient extent of the plume. In October, Geosyntec performed a Human Health Risk Assessment for the site. The assessment indicated remaining contaminant concentrations in soil vapor do not pose an unacceptable risk to site receptors.

2017: The Soil Vapor Extraction (SVE) system was shut down in August due to low contaminant mass yield and to perform a soil vapor rebound evaluation. No significant soil vapor rebound was observed and the system remained shut down.

2016: Design and implementation of an SVE remediation system was initiated as part of an early response action (ERA) at the corner of 24th Street and Thomas Road.

2015: A total of five groundwater and four soil vapor monitor wells were installed throughout the site. A total of 124 groundwater samples and 32 soil vapor samples were collected. A planned Draft RI report was not completed due to the need for additional groundwater monitoring.

2014: Five groundwater monitor wells were installed and a total of 68 groundwater samples were retrieved.

2008: As part of a prospective purchase agreement (PPA), CVS Pharmacy conducted a limited site assessment at the former location of a dry cleaner on the northeast corner of 24th Street and Thomas Road. As a condition of the PPA, CVS Pharmacy installed an onsite groundwater monitor well located northeast of the intersection of North 24th Street and East Thomas Road. The initial groundwater sample collected from the well had a PCE concentration of 170 micrograms per Liter (µg/L). CVS Pharmacy also conducted a soil and soil vapor survey to 85 feet below ground surface (bgs). PCE concentrations in soil ranged from less than the laboratory reporting limit to 0.20 milligrams per kilogram (mg/kg). The highest concentration of PCE detected in soil vapor was 2,000 parts per billion by volume from a sample collected at 50 feet bgs.

During a routine groundwater monitoring event, PCE was detected in Salt River Project (SRP) well 16.0E-6.8N at a concentration of 12 µg/L. The groundwater monitor well located on the CVS Pharmacy property was sampled at multiple depths. The PCE concentrations ranged from 230 to 260 µg/L.

2007: In June, ADEQ sent out notices per A.R.S. §49-287.03 initiating the remedial investigation for the site. During a routine groundwater monitoring event, PCE was detected in the SRP well at a concentration of 12 µg/L.

2002 – 2006: Routine groundwater monitoring activities were conducted at the site by ADEQ. The PCE concentration in the SRP well ranged from 7.9 µg/L to 11 µg/L.

2000: In May, the site was placed on the WQARF Registry with a score of 29 out of a possible 120. Groundwater sample collection from the SRP well has generally been conducted by ADEQ on a yearly basis with levels of PCE above the Arizona Water Quality Standard (AWQS) of 5.0 µg/L.

1985 – 1988: Groundwater samples were collected by SRP from their well, 16.0E-6.8N, located east of the intersection of 24th Street and the Grand Canal. A sampling event conducted in January 1995 yielded the highest detection of PCE yet observed in the SRP well, a concentration of 8.8 µg/L.