The Site is a residential property along Fourmile Creek in the Front Range of the Rocky Mountains.  The property contains, at best estimate, 30,000-40,000 cubic yards of re-processed mill tailings that were deposited in the floodplain sometime prior to 1950.

The Site is located along Fourmile Creek immediately downstream of Salina, Colorado. It is approximately seven miles west of Boulder, Colorado, along Fourmile Canyon Drive. The latitude is 40.050869, and the longitude is -105.370810. The Site is at an elevation of roughly 6,500 feet.

The mill tailings contain elevated levels of arsenic and other heavy metals which are harmful to human health and aquatic ecosystems. Several downstream residential properties obtain water directly from the creek or from shallow fluvial wells. There is also a community water diversion downstream of the Site.

Continued erosion of the mill tailings, resulting in the release of hazardous materials into the creek, threatens residential water supplies and adversely impacts Fourmile Creek's aquatic ecosystem. Due to a severe wildfire that occurred in the area in 2010, Fourmile Creek is now especially prone to flash flooding.  This flash flooding could result in a mass failure of mill tailings into the creek. 

The tailings deposit is approximately 30,000 - 40,000 cubic yards in size and contains elevated levels of heavy metals, most notably arsenic. The average concentration of arsenic is approximately 200 mg/kg with some locations exceeding 2,000 mg/kg (EPA's screening level for arsenic is 50 mg/kg).  This contaminated material readily and regularly migrates from the deposit into Fourmile Creek.

The following criteria exist for the initiation of a removal action in accordance with 40 CFR 300.415(b)(2) of the National Contingency Plan:

• Actual or potential exposure to nearby human populations, animals or the food chain from hazardous substances or pollutants or contaminants;
• Actual or potential contamination of drinking water supplies or sensitive ecosystems;
• High levels of hazardous substances or pollutants or contaminants in soils largely at or near the surface that may migrate;
• Weather conditions that may cause hazardous substances or pollutants or contaminants to migrate or be released;
• The lack of availability of other appropriate federal or state response mechanisms to respond to the release.

Work must be performed to stabilize the mill tailings before the upcoming spring snowmelt season to prevent additional erosion of the tailings into Fourmile Creek.

1. Stabilizing the tailings in place.
2. Removing and disposing of a portion of the tailings and reconfiguring the remaining material so that it could be stabilized on Site
3. Completely removing and disposing of the the tailings to the extent practical.

• Established traffic control and public safety measures.
• Removed existing vegetation from the tailings deposit and used the vegetation to create wood chips for the Site's restoration phase.
• Diverted Fourmile Creek away from the tailings pile to the extent practical.  
• Constructed access ramps and an area to stage excavated material prior to its disposal.  
• Began excavation and disposal of contaminated material.

2.2.1.1 Planned Response Activities

If EPA is unable to complete its removal of the tailings by late winter of 2014 when the flows in Fourmile Creek begin to rise, the Site will be stabilized and work will be postponed until the fall of 2015 when flows again decrease.

Residents near the Site experienced a severe flooding event in September of 2013. The subsequent rebuilding effort has created much additional traffic and inconveniences for these residents. EPA will continue to work to minimize the impacts on residents and keep them informed.

* The above accounting of expenditures is an estimate based on figures known to the OSC at the time this report was written. The OSC does not necessarily receive specific figures on final payments made to any contractor(s). Other financial data which the OSC must rely upon may not be entirely up-to-date. The cost accounting provided in this report does not necessarily represent an exact monetary figure which the government may include in any claim for cost recovery.