GENERAL33979 - Laserfiche WebLink

Home Browse Search

There are references to ore stockpiles at the SM-18 Mine and on other DOE sites. The April 2005 inspection report notes a stockpile of approximately 50 tons of ore on site. DRMS also notes the site was in full production. At the next inspection in October of 2006 no stockpile was noted on site. This notation bolsters the fact that stockpiles on-site are temporary by design and that no ore remains on-site longer than 180 days per DRMS policy. The 5000 tons of ore on other DOE sites are non- jurisdictional and irrelevant to this proceeding. The appellant notes the possibilities of uranium sulfate. It is duly noted that DRMS did not request or receive any data on uranium sulfate or UO2SO4. UO2SO4 is both an aqueous species and a solid, which means that if Uranium and Sulfate are both present in water, then the aqueous species UO2SO4 will be present as a dissolved aqueous species in the water. If the concentrations of Uranium and Sulfate aze high enough to reach a certain threshold the dissolved UO2SO4 can precipitate from solution as a solid. However, this scenario will only occur below pH of around 6, because UO2SO4 is only stable under conditions of acidic pH. Above pH of about 6, U will form complexes with other aqueous species, thus preventing UO2SO4 from forming as a dissolved species and from precipitating as a solid. Dissolved Uranium in water has a far greater complexation affinity for dissolved Phosphate and Carbonate than it does for Sulfate, meaning that if dissolved Phosphate is present in the water, or if the pH of the water is neutral to alkaline (usually meaning that dissolved carbonate species are present), then it will be very difficult for UO2SO4 to even form due to thermodynamic constraints, as U will tend to form complexes with Phosphate and Carbonate preferentially over Sulfate. If the pH is above 7, UO2SO4 does not form as either an aqueous species or as a precipitated solid, with or without the presence of Phosphate or Carbonate, because U will complex with Hydroxyl ion (OH-) rather than with Sulfate. Unfortunately, DRMS has no data for pH, Phosphorus, or Carbonate species in the SPLP leachates, and cannot draw any specific conclusions regarding the likely stability of UO2SO4 in the ]eachate waters. DRMS can infer a pH from the concentrations of certain ions, such as Aluminum. At neutral pH, the concentration of Al should be no greater than a few ug/L, if detectable at all, so an Al concentration of several hundred ug/L, in conjunction with other trace metal concentrations in the detectable range, suggests acidic pH, probably below 6. If an assumption of acidic pH is correct, and unless phosphate is present in the water, there is a good chance that UO2SO4 will be present as an aqueous species. There is no way to be certain without measurements of pH, P, and alkalinity (an indicator of carbonate). Additionally, the low concentrations of Sulfate in the SPLP ]eachate from the SM-18 waste (ranging from 8 to 64 mg/L) suggest that UO2SO4, if conditions are sufficiently acidic to favor its formation, will exist only at relatively low concentrations, insufficient to induce precipitation of the UO2SO4 solid. The appellant notes that DRMS did not test for Radium 226. Radium 226 is most commonly found in aqueous solutions. Since no mine waters exist at the SM-18 the inclusion of this daughter product seemed irrelevant. Other decay products noted of issue in ores exist over time. The ore stockpiles are on site for less than 180 days. Therefore, decay products are minimal on-site and represent no immediate long-term impacts. Concentrations of ore contamination within the permit boundaries are being addressed through new strategies. The removal of built up materials through shipment to a mill, or if in final reclamation the deposition of the materials within the mine workings prior to capping, will help reduce surface exposure to near background levels. This strategy is being implemented with new permits and older ones under revision.