When milling of uranium ore was ended in 1973, the mill tailings were stored in 7 impoundments: there were 6 tailings piles (four were located in unlined mined-out pits) and one pond contaminated with tailings and mill residues. These covered an area of about 146 acres on the original mill site. In 1982, the pond liquids were evaporated and all the tailings piles were stabilized by a 1.5-foot thick earthen cap that was seeded to establish an erosion-resistant vegetative cover.

UMTRA Surface Remediation:   Remedial action under UMTRA began in early 1992 and was completed in July 1994. All of the residual radioactive tailings materials, the materials from 13 vicinity properties, and waterborne and windblown contaminated soil from offsite locations were consolidating into a single stabilized disposal cell located at the mill site. The remediated area comprised two parcels containing the 7 tailings areas: Parcel “A”, 473 acres, contained 6 piles, a tailings pond, and 298 acres contaminated with windblown tailings; Parcel “B”, 134 acres, contained one pile and 80 acres contaminated with windblown tailings. Residual radioactive materials from Parcel “B,” located one mile east of the old mill site, were relocated and combined with those on Parcel “A.” A total of about 6 million cubic yards of contaminated material from both parcels was remediated and stabilized on Parcel “A.” The NRC certified the mill site reclamation in April 1977 and licensed the disposal cell in July 1997.

Disposal Area:   The final disposal cell was designed to meet EPA requirements for control of radon emissions, groundwater protection, and cell integrity. The cell cap is a multi-component covering, 6-feet thick on the top slopes and about 4-feet thick on side slopes, which are armored with crushed stone. A layer consisting of 3 feet of clayey soil was placed directly on top of the consolidated radioactive materials and serves as the radon barrier and anti-infiltration barrier. A 30-inch thick layer of soil was added above the radon/infiltration barrier. A 6-inch thick soil layer on the top slopes was seeded to establish an erosion protection layer of vegetation.

Responsibility for Remediation:   U.S. Government 90 percent; State of Texas 10 percent.

Stewardship:  The Falls City disposal cell site is being managed under the U.S. Department of Energy’s Long-Term Surveillance and Monitoring Program in accordance with the approved site specific plan.

Groundwater Program:   No groundwater remediation is planned, as supplemental standards (Title 10, CFR, Part 192.22) have been applied for this site. Contaminated occurs in three plumes in shallow aquifers near the mill site. In the uppermost aquifer, groundwater was found to contain widespread levels of contamination from several metals, chemical compounds, and radioactivity that exceed maximum accepted concentrations. This is both a naturally occurring condition and the result of human activity unrelated to uranium mining. In the mined areas, groundwater is of poor quality in the shallow sandstone aquifer beds that are hosts to naturally occurring uranium deposits. The groundwater is classified as limited use, and it cannot be effectively cleaned up for drinking water use by applying current reasonable treatments available to public water supply systems. In September 1992, NRC and the State of Texas concurred with the groundwater protection strategy for the disposal site. In September 1998, NRC approved the groundwater compliance plan. Groundwater monitoring must continue for five years, or until 2003, when the need to continue monitoring will be evaluated.