2020 – 2024: ADEQ conducted annual inspections of the caps, per the Record of Decision (ROD).

2019: ADEQ conducted annual inspections of the caps per the ROD and made drainage repairs on and around the cap on parcel 110-47-006.

2018: The ROD for the site was issued in April 2018.  The ROD documented the description of the final remedy, engineered tailings caps, for the site. The ROD prescribed remedy was constructed.

2017: ADEQ issued the Feasibility Study Report and Proposed Remedial Action Plan for the site.

2016: In March, April and November, impacted soils around five residences and the lower tailings pile were remediated. In October and November, impacted media in Klondyke Road was remediated and replaced with clean material.

2015: In March, mining tailings were removed from areas around the lower tailings pile. In December, soil samples from Klondyke Road were collected to evaluate contamination in the materials used to construct the road.

2014: The Environmental Protection Agency (EPA), with the assistance of ADEQ, completed soil removal actions near the residences on three properties near the site. Soil removed from these properties was consolidated in the downstream tailings piles.

The Remedial Investigation Report (RI) was released in October.

2013: The EPA, with the assistance of ADEQ, finalized the soil removal actions on three properties near the site. 

2011 – 2012: The EPA, with the assistance of ADEQ, evaluated soil removal options on four residential properties near the site. 

2010: The EPA, with the assistance of ADEQ, evaluated soil removal options on the residential properties near the site. The EPA provided the results of additional soil samples collected from five properties near the site in August. Average concentration of lead detected on each property ranged from 190 to 3,500 milligrams per kilogram (mg/kg). Arsenic concentrations above the residential soil remediation level of 10 mg/kg were also detected with the average arsenic concentrations on the properties ranging from 5 to 76 mg/kg. Elevated lead and arsenic concentrations were detected from the same sample locations. 

2008: Results of soil samples collected in late 2007 and provided to ADEQ in 2008 indicated, with the exception of the contribution of contamination from the Laurel Creek watershed, that the extent of soil contamination above the residential soil remediation level of 400 mg/kg for lead has been defined on all properties that allowed ADEQ access to collect samples.

In June, ADEQ and their contractors completed the consolidation, capping with a two-foot clean soil cover and installation of erosion protection on the upstream pile. 

2007: For the RI, ADEQ continued collecting soil samples from properties adjacent to the tailings piles to determine the extent of contamination in the area. Approximately 500 additional soil samples were collected.

Groundwater sampling continued at the site and analyses of groundwater samples from on-site wells indicated no impacts to the groundwater beneath the site above Aquifer Water Quality Standards. Private wells in the area continued to be sampled at the property owner’s request.

ADEQ continued evaluating the proposed ERA alternatives. The August 2006 flooding altered the channels of Aravaipa and Laurel Creeks. Based on the flooding, ADEQ was concerned that consolidating the tailings or constructing berms in the floodplain may have adversely impacted adjoining properties. The proposed ERA remedies were re-evaluated considering the new conditions. The floodplain analysis was updated and also evaluated the impacts of the most recent flood assuming the proposed ERA remedy and possible alternative options were in place at the time of the flood. After reviewing the updated floodplain analysis, it was determined that moving the tailings out of the 100-year floodplain was not possible. It was also determined that threats exist to the upper tailings pile from flooding and lateral migration of Aravaipa Creek. ADEQ moved forward with a plan to protect upper tailings piles in its current location. ADEQ also decided to move a small portion of the lower tailings pile, closest to Aravaipa Creek, to be consolidated with the upper tailings pile.

In August, United Research Services Corporation (URS) provided ADEQ with an Erosion Protection Alternatives Analysis. The Erosion Protection Alternatives Analysis evaluated estimated construction costs and operation and maintenance costs for several methods of erosion protection of the upper pile. In October, ADEQ authorized URS to begin designing the erosion protection for the upper tailings pile using gabion mattresses. In December, URS and ADEQ met with the U.S. Army Corps of Engineers (USACE) and determined no permit from USACE would be required.

2005 – 2006: ADEQ completed one early response action (ERA) at the site. During the ERA, ADEQ excavated 11 geophysical targets previously identified during the geophysical survey. No buried tanks, drums or pipelines requiring removal were found. During the ERA, a small amount of laboratory reagents still present at the site were also removed, and ADEQ conducted minor earth moving repairs, such as repairing berms around the tailings piles and correcting drainage problems to contain storm water runoff on the tailings piles.

ADEQ continued with the RI activities including soil sampling of the entire site to determine the extent of soil contamination. Sampling results indicated that adjacent properties also needed to be evaluated. Over 1,700 soil samples were collected and analyzed using X-ray fluorescence. Samples were collected from the surface, a depth of six inches, a depth of one foot and a depth of two feet. The RI also included sediment sampling in Aravaipa and Laurel Creeks both upstream and downstream of the site.

In addition, four groundwater monitor wells were installed at the site and quarterly monitoring and analyses of groundwater samples from these wells indicated no impacts to the groundwater beneath the site from metals above AWQS.

A significant flood event occurred in Aravaipa and Laurel Creeks during late July and early August. ADEQ continued to evaluate ERA activities at the site. Two ERA alternatives were proposed in a 2004 report to begin to consolidate the tailings at the site.

2002 – 2003: Aerial photography and topographic mapping were conducted to provide the technical background necessary to conduct a geomorphic and floodplain analysis of the site. The 100-year and the 500-year flood plains were delineated. Soil sampling was conducted for bioavailability testing. The results of that testing indicated a wide range of bioavailability for lead-contaminated soils and tailings and a low level of bioavailability for arsenic in soils and tailings. Biological, archeological and cultural resource surveys were also completed. 

2001 – 2002: Magnetic and electromagnetic geophysical surveys were conducted to identify the possible presence of buried drums, tanks, and piping that may contain contaminants.

2001: In July, fifteen private wells in the Klondyke area were sampled. No drinking water standards were exceeded in any of the wells tested. Results indicated very good water quality. In December, samples of tailings were collected and analyzed to assess the long-term potential for generating and releasing acidity and metals from the tailings as a result of storm water runoff. The results of the Phase I investigation indicated high levels of stored acidity in the two tailings piles.

1999: ADEQ contracted with URS to conduct the RI for the site.

1998: In September, the site was placed on WQARF Registry with an Eligibility and Evaluation score of 69 out of a possible 120.

1997: In October, ADEQ received an Arizona Water Protection Fund Grant to conduct a preliminary investigation, compile existing data, and evaluate possible remedial alternatives at the site. The U.S. Fish and Wildlife Service conducted fish tissue sampling and analysis of fish in Aravaipa Creek at two sites within Nature Conservancy property. The results of that investigation revealed elevated levels of arsenic, cadmium and lead in fish tissue, though not at levels that threatened native fish species.

1993: In March, a complaint concerning erosion and runoff from the tailings pile was filed with ADEQ, and an investigation began. The results of that investigation revealed high levels of lead and arsenic in the tailings piles and surrounding soils and acidic runoff emanating from the site. 

1870 – 1950: From the 1870s through the 1950s, lead, zinc, copper, silver, and gold mining was conducted in the Klondyke area of the Aravaipa Mining District. In 1948, the Athletic Mining Company constructed a flotation mill next to Aravaipa Creek that operated until about 1958 and generated, in part, the tailings at the site. Other possible sources are being investigated.