Klondyke Tailings Project | Site History

2020: 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, and in the future, the downstream pile will receive the same erosion protection and clean soil-cap installation as the upstream pile.

ADEQ and their contractor have finalized the RI report and the report was mailed to interested parties in September 2014.

2013: The EPA, with the assistance of ADEQ, is finalizing the soil removal actions on three properties near the site. Soil removed from these properties will be consolidated in the downstream tailings piles, and in the future, the downstream pile will receive the same erosion protection and clean soil-cap installation as the upstream pile.

ADEQ and their contractor solicited comments on the draft RI, as well as input on the proposed remedial objectives for the site.

2011 – 2012: The U.S. EPA, with the assistance of ADEQ, is currently evaluating soil removal options on four residential properties near the site. Once the scope of a removal is determined, soil removed from these properties will be consolidated in both the upstream and downstream tailings piles, and the downstream pile will receive the same erosion protection and clean soil cap installation as the upstream pile.

ADEQ and their contractor are working to finalize the draft RI report.

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 mg/kg. The residential soil remediation level for lead is 400 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. Once the scope of a removal is determined, soil removed from these properties will be consolidated with the downstream tailings pile, and the downstream pile will receive the same erosion protection and clean soil cap installation as the upstream pile.

ADEQ continues working to finalize the draft RI report.

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. Construction of the erosion protection and cap for the upstream tailings pile took place. ADEQ received a draft of the RI report from the contractor.

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 indicate no impacts to the groundwater beneath the site above AWQS. Private wells in the area continue 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, 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 and determined no permit from the U.S. Corps of Engineers would be required.