Preliminary Assessment and Site Investigation  Canyon City mill  

  Remediation Alternatives

  • Alternative 1.0:                       No Action 
  •                                       A no action alternative would be feasible for the Canyon City Mill site due to the low risk associated with the contamination. While there is elevated carcinogenic risk for adolescent recreational receptors, the risk remains low as it is unknown how frequently the site is actually used for recreational purposes. There is no cost associated with this alternative.
  • Altenative  2.0:                                      Phytoremediation  
  •                               Phytoremediation is a bioremediation process that uses plants to extract the pollutants on site and restore the native vegetation. Additionally, plants would decrease erosion and contaminant migration from wind and water. This would benefit the surrounding ecology and has potential to restore the site to background levels. To analyze the cost of phytoremediation, the site was classified as a small moderate site. The moderate rating refers to the ability to navigate the site’s terrain. To remediate a small moderate site with phytoremediation, it would cost approximately $5.00 per square foot of land. DU1 has a land area of 52,000 square feet (not including concrete foundations), which would cost the BLM approximately $260,000 to remediate with native plants.  
  • Alternative 3.0:                            Institutional Controls
  •                                       Institutional controls would consist of fencing and signage around DU1 where site contamination is predominately located. Access to site structures located on DU1 (concrete holding pond and concrete slabs) would be restricted. Direct exposure to humans and large mammals would be prevented through institutional controls. The approximate cost for fencing materials is $13.00 per linear foot, and the approximate cost for labor is $30.00 per hour. The estimated completion time for this project is 130 hours. This alternative is estimated to cost $21,000.  
  • Alternative 4.0:                                                Excavation
  •                         Excavation of the site would consist of removing the top layer of soil then treating or disposing of the soil ex-situ. This would effectively remove the contamination from the site, making this option highly effective in reducing human and ecological risk. Considering the difficult access to the site and the uneven terrain of DU1, this option would likely be a challenge to implement. Another challenge concerning excavation is the high cost. Assuming that the cost of soil removal and disposal is $2,500 per ton, and the size of DU1 is 52,000 square feet (not including concrete foundations) and the depth of soil to be removed is half a foot, the total estimation of excavation cost would be approximately $2,900,000.
  • Alternative 5.0:                                                                                          Phytoremediation and Institutional Controls
  •                                 Alternative five combines both phytoremediation and institutional controls. The phytoremediation process will use plants to remove pollutants at the site. These plants will be native to Arizona to ensure no habitat destruction. Again, the site will be classified as a small moderate site. The expected cost will be approximately $260,000 to remediate with native plants. Institutional controls will require fencing and signage where the site is contaminated the most. This will restrict recreational use to the public and limit access to the local fauna in the area. The institutional controls are expected to cost $21,000. Both the phytoremediation and institutional controls will be in DU1. The fencing will surround the area while the flora will be planted inside the fence, covering all of DU1. Overall alternative 5 is estimated to cost $281,000.  

 

 

Remediation Alternative Analysis    

A decision matrix was constructed to determine what alternative was best for the site. Four different criteria were selected and used to analyze each alternative. The decision matrix constructed can be found in the table below: 

 Table 1: Decision Matrix  

 Alternative 5, a combination of phytoremediation and institutional controls, scored the highest. For phytoremediation, short grass species and sunflowers are recommended for the vegetation to be plated. According to the EPA, small plants like ferns and grasses are used in areas where soil contamination is shallow . Since contamination is predominantly at the surface, grass would be recommended. Deer grass is highly recommended for use because it requires low to moderate water, can endure large exposure to the sun, can live above 2,000 ft in elevation, and is native to Arizona. Yellow Pygmy Sunflowers are suggested due to their ability to withstand high amounts of arsenic. Josue A. Juarez, an alumnus of NAU conducted a research study that showed that not only were Yellow Pygmy Sunflowers able to absorb arsenic from the soil, but they were also found to be taller and healthier than sunflowers not exposed to arsenic . Sunflowers are also native to Arizona, can withstand high exposure to sunlight, need low to moderate water, and can survive in elevations above 2,000 ft. Fencing and signage will also be put around DU1. Signage will warn recreational visitors and inform the public of potential hazards on the site. Signage will also include information regarding the process of phytoremediation and the plants being used. Fencing will cover the perimeter of DU1 to prevent human and animal access.