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The inglorious legacy of COGEMA in Gabon - Decommissioning of the Mounana uranium mine and mill site

(last updated 8 Sep 2004)

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The Mounana uranium mine and mill operation

From 1961 to 1999, COGEMA's subsidiary COMUF produced nearly 28,000 tonnes of uranium at its uranium mill in Mounana, Gabon.
Extraction of the ore began at the Mounana open pit mine (1960 - 1975), followed by the mine at Oklo (1970 - 1985). Ore was also extracted from underground mines, first at Mounana, then at Oklo (1977 - 1997), and at Boyindzi (1980 - 1991). During the last two years, the open pit at Mikouloungou was mined (1997 - 1999), located at a distance of 60 km. The total amount of uranium ore extracted from the Mounana district was 7.5 million metric tonnes at an average grade of 0.37% U.

The Compagnie des Mines d'Uranium de Franceville (COMUF) was formed in 1958. COMUF is owned by COGEMA (68.4%), the Govt. of Gabon (25.8%) and some unknown "domestic private" (5.8%).

The uranium from all mines was extracted from the ore in the Mounana uranium mill (a first smaller mill was replaced by a larger one in 1982).
During the first 15 years of operation, from 1961 to 1975, COMUF simply released the uranium mill tailings into the next creek, totalling over 2 million tonnes. Later, another 4 million tonnes of tailings were dumped in the former Mounana open pit mine. Only in 1990, COMUF built a dam to hold the tailings produced during the last years of operation. It has received, however, only the small remainder of the total of 7.5 million tonnes of tailings.

During the operation of the uranium mill, effluents were released to the Ngamaboungou creek at a rate of 100 cubic meters per hour. The acidic effluent released to the creek was not neutralized, though a neutralization plant had been constructed; but, it was never operated, since the cost of importing the necessary lime would have been prohibitive.
The Ngamaboungou flows into the Mitembe River, a tributary to Lekedi River, which itself flows into Ogooué River.

The embankment for the tailings dam built in 1990 was made from waste rock and laterite soil and was erected across the valley of the Ngamaboungou creek, with a maximum height of 11 meters. The tailings stored behind the embankment are covering an area of 6 hectares. The tailings are covered with nothing but a water layer of 1 meter minimum.
To maintain the water cover, the Ngamaboungou creek is led through the tailings dam and then leaves it through an overflow spillway - without any treatment.

 

Environmental Impacts

The practice of releasing the untreated acidic mill effluent into the Ngamaboungou resulted in pH levels in the creek in the range of pH 1.5 - 2.
The mine and mill effluents, moreover, led to high contaminant concentrations even in the Mitembe river, and dead fish were often observed in the river. In 1996/1997, still, levels of up to 3.2 Bq/l of soluble radium-226 and 1.7 mg/l of soluble uranium-238 were found in the river water. After shutdown of the mine in 1999, these values are reported to have decreased to below 0.7 Bq/l for radium, and below 0.1 mg/l for uranium (for comparison: WHO recommends 0.015 mg/l for uranium in drinking water).

The tailings released to the Ngamaboungou during the first 15 years were carried over kilometers to the Mitembe river. In the creek valley, they partly settled on the river bed, forming a reservoir for long-term re-mobilization of contaminants. The tailings moreover formed large deposits on the bank of the creek and on the valley floor, presenting a hazard from external radiation and from resuspension of radioactive dust. COMUF calculated that residents crossing the valley to reach their plantations have been receiving radiation doses between 2.3 and 2.9 mSv per year.
The initial practice of intentionally releasing the tailings into the environment (for 15 years!) presents a rather unique violation of any minimal environmental standards in the uranium mining industry. The only other known such intentional release of uranium mill tailings has taken place from 1947 to 1958 in Bukhovo, Bulgaria. There, the tailings were released into a glen, from where they later were washed away and eventually covered 120 hectares of agricultural land.

The tailings dumped in the open pit were left without a cover for long years; children used to play on the dusty surface without being told about the hazards.

The only protective measure provided for the tailings contained in the tailings dam across the Ngamaboungou creek is a water cover. While a water cover of at least 1 meter, basically is effective in limiting the radon emanation from the tailings, it provides no protection against natural forces, and it boosts the permanent seepage of contaminants from the tailings. Any long-term stability cannot be guaranteed for such water cover; nevertheless, such covers in fact have been licensed for some large uranium mill tailings deposits in Elliot Lake, Ontario, Canada.
In the case of the Ngamaboungou tailings dam, however, the situation is even worse, since the creek is not diverted around the dam, but is flowing through it, and no water treatment is carried out after passage of the dam. This approach compromises any options to control contaminant release, erosion, floods, or dam stability.

 

Reclamation and Responsibility

In 1985, COMUF started works to stabilize the course of the Ngamaboungou creek with rock, and to cover the tailings deposits formed in the valley along the Ngamaboungou with a layer of 30 - 50 cm of compacted laterite (reddish tropic soil). Up to July 1990, nearly 50 hectares had been covered with 200,000 cubic meters of that material. After completion of the covering work, the radiation doses for the residents are expected to decrease to 0.8 mSv per year. However, these figures are not calculated for a permanent stay in the freely accessible affected areas, but only assuming some estimates based on typical behavior of present residents. Shielding of the gamma radiation from the tailings to background values would require a cover thickness of 1 metre at least.
In addition, given the very high precipitation rate of approx. 2 metres per year in the area, it must be anticipated that the cover will not last longer than a few years. Another problem is that, under the direct contact with the acidic tailings, aluminium contained in the laterite may be dissolved and released into the waters. Laterite is a precursor of bauxite, and aluminium is toxic for fish, among others.

The tailings deposit in the former Mounana open pit mine was covered with a cover of broken rock and laterite soil. Contaminated areas at the processing site were covered with a layer of 0.7 metres minimum of laterite soil.

The reclamation work was completed in July 2004, at a total reclamation cost of Francs CFA (XOF) 7050 million (EUR 10.7 million).
The reclamation work was mainly paid for by the tax payers of the European Union, rather than by COGEMA: Since 1997, Gabon has been receiving a total of over EUR 50 million in aids for the development of its mining sector. Of this amount, EUR 7 million were diverted by the Gabon mining ministry for the reclamation work performed at Mounana.
While in the above mentioned case of the Bukhovo tailings release, foreign aid may be justifiable and appropriate (legacy of the Cold War era; a responsible party no longer exists), the situation in Mounana is completely different: here, a commercial enterprise (though for the most part government-owned) has intentionally breached the most basic environmental standards; the responsible party is identified, and it still exists. So, there is no reason at all, why European aid money should have been spent for this cleanup. This is solely a responsibility of COGEMA.

Another problem is that the reclamation work performed most likely will not be protective for the environment and the health of the residents in the long term. It must, therefore, be performed a thorough assessment of the remaining hazards by an independent institution, and if the outcome of the assessment is as must be suspected, then all dispersed material must be collected and disposed of in a safe way - at the cost of COGEMA.

 

Photo Gallery

 

All photos: (c) Res Gehriger 2004

Resources

[Birraux 1996] Rapport sur le contrôle de la sûreté et de la sécurité des installations nucléaires, par M. Claude Birraux, Office parlementaire d'évaluation des choix scientifiques et technologiques, 2 tomes, Assemblée Nationale No. 2651, Sénat No. 278, Paris 1996
> Download Tome I (8.3MB PDF) · Tome II (6.6MB PDF)

[Loueyit 2002] Study of the post-closure provisions for managing solid tailings from the extraction and processing of uranium ores resulting from the industrial activities of the COMUF company at Mounana, Gabon, by C.J. Loueyit, B. Keiffer, S. Fourcade, J.C. Nzengue, S. Bernhard; IAEA-SM-362/49; in: The Uranium Production Cycle and the Environment - Proceedings - International Symposium held in Vienna, 2–6 October 2000, IAEA-CSP-10/P, Vienna 2002, p. 440-448

[NEA 2004] Uranium - 2003 - Resources, Production and Demand, A joint report by the OECD Nuclear Energy Agency and the International Atomic Energy Agency, Paris 2004, 292 p.

[Gehriger 2004] Der Nachlass der Cogéma - Strahlenmüll im Dorfbach, von Res Gehriger, in: WOZ Wochenzeitung, Zürich, No.30, July 22, 2004

> See also: Current Issues - Decommissioning Mounana

 

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