The manufacture of elemental phosphorus required the use of ponds throughout the plant’s history to manage materials generated in the furnace building, as well as the calciners that prepared the ore before it was introduced to the furnaces.
These ponds consist of the RCRA Ponds, which received precipitator slurry and “phossy water” (water that had come into contact with phosphorus), and the Calciner Ponds, which primarily received calciner air emission control scrubber water containing calcined ore dust. Ponds that closed before RCRA regulations came into effect in 1990 are referred to as CERCLA ponds and are also discussed in the Superfund/CERCLA section.
In March 1990, the FMC facility became subject to RCRA Subtitle C hazardous waste regulations when the “Bevill Exemption” was withdrawn from certain phosphorus production wastes (slag and calciner ponds materials are RCRA non-hazardous). Withdrawal of the Bevill Exemption meant that numerous ponds that were used for managing and disposing of process waste streams became RCRA-regulated. Under the terms of an FMC-EPA RCRA Consent Decree entered on July 13, 1999, FMC closed and capped these ponds and they are currently under RCRA post-closure care. EPA approved the capping and closure of the RCRA ponds in accordance with federal law, which requires that such actions be fully protective of human health and the environment. While the Shoshone-Bannock Tribes objected to the RCRA consent decree including capping of the ponds, they later agreed that capping Pond 18 Cell A was acceptable in a 2001 agreement in which FMC provided $40 million to the Tribes.
The caps covering the closed RCRA ponds are engineered structures that EPA approved as meeting RCRA requirements. The caps include multiple synthetic and geotextile liners, overlain with up to seven feet of soil that have been vegetated with native grasses. The design of the ponds also took into consideration the potential for phosphine gas to form under the cap as the pond contents settled and aged. As a result, a piping system was incorporated into the design of each of the pond structures to allow for gas capture and treatment, if the need arises. The piping system can collect the phosphine gas and direct it to an extraction system where it can be treated in carbon beds. Phosphine gas extraction and treatment systems have proven effective at reducing the phosphine gas concentrations. As of November 2010, the Pond 16S phosphine gas extraction and treatment system had successfully demonstrated meeting all performance objectives and the system was turned off.
During the post-closure monitoring and maintenance of the RCRA ponds, including gas extraction and treatment at certain ponds, there has been no risk to public health and phosphine gas has not been detected beyond the boundary of the ponds themselves. All contractors are trained to detect and respond to phosphine gas if detected.
As described in Plant History, with the installation of traveling grate calciners at the plant in 1968 to prepare the ore for introduction into the furnaces, unlined ponds (referred to as the old calciner ponds) were constructed to receive and reuse calciner air emission control scrubber water. In the late 1980s and early 1990s, FMC closed and excavated the old ponds and upgraded the facility by constructing a series of five double-lined calciner ponds. The new ponds were built in the same area as the closed old ponds.
The calciner scrubber water remains exempt from RCRA hazardous waste requirements under the “Bevill Exemption” and, thus, the calciner ponds are not subject to RCRA closure requirements. Nonetheless, the five lined calciner ponds and any residual from the old unlined ponds were remediated (“closed”) with RCRA type covers under a Voluntary Compliance Order (VCO) that FMC entered into with the State of Idaho on July 8, 2002. The calciner ponds are currently under ongoing post-remediation monitoring and maintenance pursuant to the VCO.