Are geosynthetics affected by the constituents you would expect to find in waste disposal facilities at uranium mines? Here are some historical opinions we found on this issue.

In the Proceedings of the [first] Symposium on Uranium Mill Tailings Management (1978) W. B. Kays writes in his paper Lining Systems for Seepage Control in Uranium Mill Tailings Holding Ponds:

“Lining choice where radiation is present depends on the total integrated dosage of radiation. The inorganic linings (concrete, gunite, soils, etc.) are not affected much even at high radiation levels. Most organic materials, except fluorine-bearing compounds, degrade rapidly at high doses but speed of degradation is proportional to total integrated dosage. The organic linings generally will adsorb up to a total of around 1010 ergs pre gram of lining material before they are destroyed. This value is often given as 108 rads, since 1 rad is equal to 102 ergs. Uranium ore mine tailings are releasing relatively low amounts of radiation. Each tailings pond would of course vary but a good rule-of-thumb value to use is that the lining in such a pond would be adsorbing some 100 ergs of energy per gram of lining material per hour. Dividing the adsorbing rate in to the material’s propensity to adsorb would indicate the lining’s life of 108 hours. Since 108 hours is over 11,000 years, radioactive tailings would pose no threat to organic lining life spans due to radiation effects along. The same conclusion can be made with respects to inorganic lining systems.”

Also in 1978, the Nuclear Energy Agency ran a Seminar on Management, Stabilization and Environmental Impact of Uranium Mill Tailings in Albuquerque, New Mexico. R. E. Williams in a paper Control and Prevention of Seepage from Uranium Mill Waste Disposal Facilities, devotes six pages to a detailed survey of geosynthetics in uranium mill waste disposal facilities. He makes no mention of the effects of radioactivity. He simply concludes: “In the case of uranium mill wastes the low pH of the waste water is the most critical factor with respect to liner selection.”

In the following year, 1979, at the Second Symposium on Uranium Mill Tailings Management two papers report on the incorporation of geosynthetic liners into new uranium mill tailings impoundments. Lubina et al report that a “sheet of Hypalon 36 to 60 mil thick” was used to line the Cotter, Colorado uranium mill tailings impoundment. Welsh and Marshall report on incorporation of “1.4 million square feet of 30 mil PVC “ at the Sweetwater, Wyoming tailings impoundment. Both papers describe extensive testing of the strength and other physical properties of the geosynthetics. Neither paper mentions testing of the effect of radioactive constituents on the geosynthetics.

In the proceedings of the third symposium, 1980, is a paper by D.M. Small of Universal Linings, Inc. His nearly forty page paper discusses many aspect of the testing, selection, use, and performance of a variety of synthetic liners at uranium mills and impoundments. There is no mention of response to radioactive constituents.

The forth symposium in 1981,includes two papers that describe the use of geosynthetics at uranium mill tailings impoundments as follows: Hypalon and hydro-carbon resistant PVC at Elliot Lake in Canada; and 30 mil HDPE alloy liner at Dawn Mining, Washington. Neither mentions radioactivity as an issue in the selection and use of these materials. Also in the proceedings of the forth symposium is a paper by, Buelt and Barnes A Comparative Evaluation of Liner Materials for Inactive Uranium Mill Tailings Piles. They describe extensive testing of the physical and chemical properties and response to uranium mill tailings constituent of soils, asphalt, and geosynthetic liners. There is no mention of the effects of radioactivity etc. on the 1,000-year design life of liners. It would appear that by 1981, the issue was settled: liner materials in uranium mill tailings facilities are not susceptible to the radioactive constituents in the tailings.

In 1987 the report Canadian Uranium Mill Waste Disposal Technology was published by the Canadian National uranium Tailings Program. The only significant sentence dealing with geosynthetics in the 303-page document is this: “Most commonly used synthetic membrane materials are not likely to be affected by tailings solutions.” Both this report and G. M. Ritcey in Tailings Management (1989) quote a 1984 study by Golder Associates (that we were not able to access) who tested nine “polymeric” liners and found “with the exception of polyurethane, the base polymeric resins and asphalt indicated long-term resistance to the constituents in the uranium tailings.”

Ritcey also notes “Synthetic membranes, such as hypalon have been used extensively in uranium tailings, but because of the extremely thin material (20 to 60 mil) they are subject to rupture and therefore the integrity over time is questionable.” He provides no information about the chemical stability of the materials used “extensively.”

On the Uranium Mill Tailings Remedial Action (UMTRA) Project, we did not use liners or geosynthetics. Except that at the Durango relocated pile, we placed a GCL in the top deck cover to increase the infiltration impedance of the clays used to limit infiltration and radon emanation. Informal testing by one of my colleagues on the project showed significant radon attenuation by the GCL. The Nuclear Regulatory Agency would not allow us to include the demonstrated effectiveness of the GCL in limiting both infiltration and radon flux into our calculations, although they concurred that inclusion of the GCL was a reasonable thing to do. To my knowledge there are no data on the performance or condition of the GCL to date.

Thus today we can read and concur that radioactivity is “not a factor unless polymer is exposed to radioactive materials of sufficiently high intensity to cause chain scission, e.g., high level radioactive waste material.” Koerner et al. GRI White Paper #6, 2005.