Falls City Mill Site
Karnes County, Texas
Years of Operation |
Status of Mill or Plant Site |
Uranium Ore Processed (Million Short Tons) |
Production (Million Pounds U3O8) |
1961-1973, 1978-1982 |
Decommissioned |
2.72 |
8.66 |
Mill/Plant Area (Acres) |
Disposal Cell Area (Acres) |
Disposal Cell Radioactive Waste Volume (Million Cubic Yards) |
Disposal Cell Total Radioactivity (Ci, 226Ra) |
Disposal Cell Average Tailings Radioactivity (pCi/g, 226Ra) |
UMTRA Project Final Cost (Million Dollars) |
232 |
127 |
5.80 |
1,277 |
189 |
56.25 |
Location: The mill site is located about 8 miles southwest of Falls City in Karnes County, Texas.
Background: Uranium discoveries were made in southwestern Karnes County, Texas, in 1954-55. The early finds, shallow small deposits behind sandstone outcrops, were too small to support the long haulage distance to the nearest mill in northwestern New Mexico. From January 1960 to May 1961, the U.S. Atomic Energy Commission (AEC) operated a uranium-ore buying station in western Karnes County near the uranium deposits and it stockpiled some 111,000 tons of ore that assayed 0.19 percent U3O8. In July 1960, Susquehanna-Western, Inc., (SWI) entered into a contract to produce uranium for sale to the AEC, and these sales continued over the period 1960-1968 under two such contracts. SWI began construction in 1960 of a sulfuric acid leach mill on a site that originally covered about 1,600 acres. The mill was placed in operation in April 1961 with an initial capacity of 220 tons of ore per day (TPD) throughput, and it was expanded by 1969 to 1,000 TPD. Mill feed came largely from company-owned mines developed in ore deposits located relatively near the mill site in the central coastal plain area in south Texas. Over the period 1961-1964, all the ore that had been purchased at the AEC’s ore-buying station was sold to SWI for processing at the Falls City mill. A total of about 1.2 million tons of ore that averaged 0.19 percent U3O8 was processed during the period of AEC contracts (1961-1968). About 95 percent of the uranium was recovered from the ore. Of the uranium concentrate produced in those years, 31 percent was sold to the AEC and 61 percent was sold commercially. After expiration of the AEC contracts, the mill continued to produce uranium for commercial sales until it was closed in 1973. In the late 1970s, Solution Engineering, Inc., acquired about 200 acres of the Falls City mill site, including the mill and four of the nearby tailings piles. Between 1978-1982, Solution Engineering, under a license from the State of Texas, used a solution mining process to produce a relatively small quantity of uranium concentrate from the in-place tailings piles.
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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.
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