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Earlier this year, the U.S. Supreme Court decided the case Atlantic Richfield Co. v. Christian which involved the Anaconda Smelting Site in Montana, one of the largest National Priorities List (NPL) sites ever listed under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). At over 300 square miles, a massive clean-up project[1] was underway when a group of landowners who were unhappy with the overall clean-up plan sued to gain the right to implement an alternative plan under State rather than Federal law. The Court held that the landowners could propose a new plan but would need to go through the CERCLA process and gain EPA’s approval prior to implementing the plan. Here our experts provide a review of several innovative remedial technologies that would help further reduce the residual risk while being acceptable to all parties.

 

The landowners propose a restoration plan that calls for a maximum soil contamina­tion concentration for arsenic of 15 ppm (rather than 250 ppm as set by EPA); excavation of contaminated soil within residential yards to a depth of two feet (instead of one foot as proposed by EPA); and capture and treatment of shallow groundwater through an 8,000-foot long, 15-foot deep, and 3-foot wide underground permeable barrier, a plan the agency rejected as costly and unnecessary to secure safe drinking water.[2] The landowners estimate that their  clean-up would cost Atlantic Richfield an additional $50 to $58 million.

 

The property owners, like other community groups, expect zero or near zero risk after a clean-up plan is implemented; any measurable level of risk is often not acceptable to the public. This situation was compounded by EPA’s plan to clean up highly contaminated areas via hot spot removals which reduce the risk at the hot spots but not at areas that pose less risk. Another problematic element of EPA’s clean-up and restoration plan is that it was developed 35 years ago and was based on records of decision (RODs) ranging in approval dates from 1987 to 1998 (with two amendments dated 2011 and 2013). It would certainly make sense to revisit and update the remedies to account for improvements in clean-up technologies that have occurred over the years since the last ROD was issued.

Innovative Remedial Technologies

While EPA established soil clean-up criteria for arsenic of 250 mg/kg, the landowners requested 15 mg/kg.  This criteria represents orders of magnitude increases in both excavated soil volume and remediation costs. I resolving this issue, the parties should focus on how to reduce the arsenic risk from the soil by a means other than a blanket lowering of the clean-up criteria or by implementing more institutional controls, which would have the unwanted effect of lowering property values and increasing stigma.

 

Following are several approaches to soil remediation our experts recommend that reduce risk without the adverse impacts associated with overly intrusive and pervasive remedies.

Bioavailability Reduction

One solution is to reduce the bioavailability of the arsenic in the soil. The major human health risk factor for the arsenic in soil is from ingestion and inhalation. Metals bioavailability and toxicity in humans is controlled by the dissolution of the metals in the GI tract and its absorption into the blood. The form of the arsenic and its associations with soil minerals dictates human bioavailability. Arsenic salts such as arsenic sulfates are highly bioavailable, however when arsenic is bound within a mineral matrix (e.g., arsenopyrite, arseno-apatites, arseno-carbonates, or arseno-silicates), bioavailability and absorption is reduced. Furthermore, some arsenic minerals are less bioavailable than others. The “biomineralization” process is a remedial technology that incorporates and immobilizes toxic metals (including arsenic) into geologically stable biominerals using specialty bacteria and nutrient solutions. The resulting arsenic-biominerals are stable and minimize the absorption of toxic metals in the human digestive system. Furthermore, the process can be used to bio-engineer specific mineral types by manipulating the nutrient solutions resulting in the formation of specific bioavailable resistant metal-mineral complexes. The technology can be easily applied to the halo soils to reduce arsenic bioavailability and associated risks with ingestion.

Phytoremediation

A second approach to reduce soil toxicity of the halo soils would be to use phytoremediation. In phytoremediation, plants and trees are used to intercept and either destroy or capture contaminants. For metals, herbaceous plants known as “hyperaccumulators” naturally remove metals from the soil and concentrate them in the above-ground plant organs. The plants are periodically harvested and the metal-laden biomass is disposed of. This is considered a volume reduction technology since the soil contaminants are transferred to a much smaller volume (as compared to the soil). After several cycles of plantings and harvesting, the soil concentrations gradually and steadily decrease. An added benefit is that phytoremediation stabilizes the surficial soil horizon, rendering it less prone to erosion and transport of ingestible contaminated dust. The specific hyperaccumulators are selected based on regional climatic and soil characteristics.

In Situ Biomineralization

A cost-effective alternative to the permeable reactive barrier proposed by the landowners would be to use the in situ biomineralization process for groundwater. There are two modes of implementation: (1) As a source control (in lieu of costly excavation), the microbes can immobilize the metals in-place, so they are not mobile and do not leach into the groundwater; (2) Microbes and nutrients, developed by the biomineralization process, can be injected into the aquifer and transform the mobile-phase arsenic into a stable non-leachable biomineral.

 

Lowering the inherent bioavailability of arsenic in soils, naturally removing metals from the soil and concentrating them in hyperaccumulating plants, and naturally immobilizing the contamination are just a few of the innovative remedial technologies that may prove acceptable to both the landowners and EPA for this site. Scientists and engineers at First Environment have experience in providing innovative solutions such as these to complex remedial problems and can bridge the gap between divergent parties, whether in litigation or as part of the remedial investigation, selection, and design process. Please contact us if you have questions about a particular remedial technology or site.

 

[1] The clean-up involves 800 residential and commer­cial properties; the removal of 10 million cubic yards of tailings, mine waste, and contaminated soil; capping in place 500 million cubic yards of waste over 5,000 acres; and reclaim 12,500 acres of land at a cost of $450 million. (EPA, Superfund Priority “Anaconda” 9 (Apr. 2018)).

[2] In addition, an amendment (2011) to one of the original Records of Decision (ROD) (1998) waives the 10 ug/L Federal MCL requirement for arsenic in surface and ground water and maintains the 18 ug/L standard set forth in the 1998 ROD. EPA’s rationale for the waiver is that there is no feasible technology to address the lower groundwater treatment concentration.

 

Authors:

Scott Beckman, PhD, is a Senior Consulting Scientist at First Environment who has provided innovative solutions to complex remedial problems at CERCLA sites for over 30 years.

 

Arthur Clarke, JD, is the Market Area Director for Litigation and Regulatory Services at First Environment who routinely provides technical solutions on litigation matters at CERCLA and state-led clean-up sites throughout the United States.