A performance test of the Horseshoe Bend plant was completed in November 2007, as mandated by the Record of Decision. Based on the performance review, water discharged from the plant meets all discharge standards for contaminants of concern set by the EPA. Additional adjustments still need to be made to address pH. In general, plant operations are going as expected.
The following is EPA’s assessment of the performance test, excerpted from the 2011 Five Year Review Report on the site, pages 43-45:
The influent water for the 2007 Performance Test consisted only of HSB (Horseshoe Bend) water, as water from the Berkeley Pit is not yet required to be pumped and treated in the plant. The results of this test indicated that all final discharge limits could be met except for effluent pH. In order to meet the cadmium limit, the pH in the final treatment stage needed to be raised to 11.2.
Consequently, the effluent pH did not drop to below the discharge standard of 9.5 through natural aeration. Methods for lowering the pH of the effluent to below the discharge standard of 9.5 have been evaluated on a conceptual level, but will require a more formal analysis before final discharge to Silver Bow Creek is necessary.
The results of the performance test also determined a need to revisit the applicability of the final performance standard for beta/photon emitters, which is expressed as a dose of 4 millirem per year (mrem/yr). There are approximately 179 radionuclides that need to be analyzed in order to calculate the actual beta/photon emitter dose, bringing into question the practicality of the laboratory procedures needed to meet the beta/photon standard.
Opportunities for Optimization
Based on the results of the most recent performance test and plant operations and maintenance activities, there are several areas where optimization is needed. They include:
- effluent pH adjustment (when discharge to Silver Bow Creek is necessary),
- equipment and pipeline scaling from gypsum and
- equipment corrosion issues.
Each of these issues is undergoing various levels of engineering evaluation and testing to determine the best long term course of action.
Early Indicators of Potential Issues
There are no indications of potential equipment problems or operational problems that would put the protectiveness of the HSB WTP at risk. However, it is unknown whether discharge of treated water saturated with gypsum will adversely affect aquatic life in Silver Bow Creek.
It is also possible that delayed precipitation of gypsum could cause exceedances of the TSS discharge standard. This issue will require further evaluation before discharge occurs.
Implementation of Institutional Controls and Other Measures
Based on the information obtained from a review of the site documentation in the administrative record and from interviews with the site RPM and other stakeholders, the ICs implemented for the BMFOU continue to effectively protect the remedy and the public. Publications such as the PITWATCH, inform the public as to progress on the BMFOU. The current DNRC order prohibits use of the BMFOU aquifer for domestic use. Enforcement and monitoring of this prohibition is important.