Basically the cleanup plan entails rounding up tailings material that has escaped and corralling it in a second waste repository. An earlier repository was completed in 2007. Remaining tailings wastes, and contaminated soils scattered on adjacent residential lands, will be removed and deposited at the new repository.
Repository “gabion”(or basket) rock walls will be installed like so:
Gabion walls are designed to be high enough to sustain 100-year flooding conditions and substantial enough to withstand expected water flow velocities during those worst case flood conditions.
Additionally, the soil cap on the repository must resist erosion but since only a small amount of water shed is expected, i.e., only the area of the cap itself heavy erosion due to storm water runoff is not expected. Rather, wind erosion may be the primary erosive loss concern on the cap itself. To resist both water and wind erosion techniques must be used to ensure the proper grade, material mix and other armoring. The armoring, or rip-rap rock in most cases, should be substantial enough to resist the wind and water velocities associated with storm events. Both wind or rain storms would generate high velocity erosion, testing the mettle of the cap. Also, the material itself should be compacted and of appropriate particle size to resist erosion.
A final word on this idea. Our engineers have modeled a particle size mix that should in fact be largely resistant to erosive forces and also be amenable to plant growth which will further mitigate erosion threats. The idea here is to create a “water balance cover” where potential plant transpiration (PET) is in a nearly 1:1 ratio with precipitation (P). Significant plant growth will, with time, remove most of the water from the cap, preventing percolation of course, but also potential liquefaction and concomitant mass wasting.
The Klondyke Tailings Site is located in the unincorporated town of Klondye, Graham County, AZ (about 3 hours southeast of Phoenix). It is situated slightly upstream of the Aravaipa wilderness area along the Aravaipa Creek. The Site processed copper ore from the 1940s through the 60s. US EPA and the AZ Department of Environmental Quality will begin cleanup of the Site in May 2012.
The plan includes consolidation of tailings and contaminated soils from the bottom of the Aravaipa wash and it’s “shorelines” including an uncontrolled pile and contaminated soils on residential properties. We plan to grab this material and push it into a pile that can be contained using a gabion basket system and a cap system. The basket system and as-built height was designed to withstand a 100-year storm event. Basket wall height and rock size distribution were modeled using hydrologic data. The cap was designed for thickness first to reduce percolation rates into the contaminated material. After further study however, the team determined that the primary objective was to discourage wind erosion that would lead to cap compromise.
Environmental cleanup is my passion. Growing up amidst the pollution recognition movement, and with a Father who was active in domestic and international cleanups of contaminated sites, I developed this passion and had the opportunity to take my awareness and experience and use it as a building block for an exciting career in environmental remediation. As an On-Scene Coordinator at USEPA since 2002, I’ve had the chance to clean up numerous sites and oversee cleanups at many more. These sites have ranged from urban industrial sites like metal plating sites, to rural sites like pesticide crop duster sites and abandoned mine sites. I have had the chance to implement numerous alternative treatment technologies.
The purpose of this site is to share and gather perspectives on environmental cleanup, response, remediation and restoration of contaminated sites. I hope you’ll read and share this blog going forward. Hope you enjoy it!