7th Street and Arizona Avenue | Site History

2021-2022: Soil vapor extraction operations continue at the northern Stone Avenue source property. Annual groundwater monitoring events continue to measure the tetrachloroethene plume across the site.

2020: An addendum to the 2014 Proposed Remedial Action Plan (PRAP) was published in February to select the remedy for the second source property. ADEQ signed the site’s Record of Decision (ROD) in June. Remedial soil vapor extraction (SVE) operations began at the Stone Avenue source property.

2017–2019: An SVE system was implemented at 847 North Stone Avenue as an early response action (ERA) for the second source. Site data gaps were addressed with the purpose of revising the Feasibility Study (FS) to include the consideration of the 847 North Stone Avenue contaminant source.

2016: One nested monitoring well, four permanent soil vapor probes and 10 temporary soil vapor probes were installed to investigate chemicals of concern  at the 847 N. Stone Ave. source in March. Sampling of the monitoring well and probes indicated concentrations of COCs exceeding applicable standards and screening levels in soil, groundwater and soil vapor at and around the source property.

Two soil borings and one monitoring well were installed to investigate the down gradient edge of the COC plume in the perched aquifer in the fourth quarter of 2016. No COCs were detected above applicable Aquifer Water Quality Standards (AWQS) in groundwater samples drawn from the borings or well.

2015: In late 2014/early 2015, a shallow soil gas survey of the former Oliver’s Cleaners was performed. Evaluation of the soil gas data indicated that there is no unacceptable health risk at the property due to its exclusive use as a parking lot, but the concentrations of tetrachloroethene (PCE) could potentially exceed Environmental Protection Agency (EPA)’s Industrial Air Regional Screening Levels at four locations in the center of the property. During the spring and summer, the final Remedial Investigation (RI), FS, and PRAP were re-evaluated for their applicability to the site. The re-evaluation indicated that revision of the FS to address data gaps and include a new contaminant source at 847 North Stone Avenue is necessary. In the winter, the ADEQ began preparation for site characterization activities and an ERA evaluation at 847 North Stone Avenue.

2014: The final RI, FS, and PRAP were completed in the spring of 2014. In the fall of 2014, ADEQ installed six (6) wells—three perched groundwater wells for plume delineation, one regional groundwater well to better define flow direction and gradient, and two nested vapor monitoring wells for soil gas delineation near the former Oliver’s Cleaners property. 

2013: A groundwater sampling event occurred in March. The highest detection of PCE was 39 µg/L. In May, eleven shallow soil gas samples were collected at the source property from depths of 5 feet. PCE was detected in all samples up to 499,000 ug/m3. The site source property is currently covered with asphalt. A Limited Site Investigation performed for the City of Tucson (COT) in 2013 indicated high concentrations of PCE in shallow subsurface soil vapor, soil and groundwater at 847 North Stone Avenue.

2012: In May, groundwater samples were collected from 28 wells and soil vapor samples were collected from 19 wells from an area including the entire site. Groundwater sampling results were consistent with previous results with only slight variations. Soil gas data were converted to soil matrix concentrations. No Arizona Soil Remediation Levels (SRLs) were exceeded. Two new wells were installed in October-November 2012, in the perched and regional aquifer respectively. One additional perched well was drilled that resulted in a dry hole.  This well was maintained as a soil vapor well.  PCE was detected in the new perched well at 4 µg/L. PCE in the new regional well was non-detect.  PCE was detected in soil gas in the new soil monitoring well at 488 µg/m3.