THE FINAL COVERING

The final securing intervention was based upon a good cover of the whole surface of the waste plant, with particular attention to the part in correspondence of the waste of basin n 3, then adding to it an erosion control net

Fig. 4 is just the schematic standard cross section, direction N-S, of basin n°3.

Loam soil d 2 50 cm

Drainage ditch

Clay sealing (K < 10' 8cm/s)

Loam soil reinforced with a cell-like synthetic sheet

Fine gravel lor drainage o . o

^-Clay sealing (K < 10" 8cm/s ) d > 40 cm

Undisturbed base

the over-sheet tank

To the under sheet lank

Fig. 4 - Cross section of the cover

The intervention was based on a multilayers cap of natural materials, laid on the waste plant surface. The heart of the intervention was of course the clay layer, that was made with minerals of very good quality. In that way it was drastically decreased any percolating water inside the waste, and sealed the contaminated material with a very effective geochemical barrier, due to the absorption characteristics of clay toward caesium.

Very important were some erosion control nets, that is to say a surficial rain-water collecting network, able of conveying all the surficial rain water outside the waste facility, in order to prevent any consistent erosion of the protective layers.

Fig. 5 represents the starting point for the final intervention and the first clay layer (20 cm) deposited during the interim action is visible: it had been carried out in order to make the

Fig. 5 - The situation after the interim intervention

surface of the site safe from the radiological point of view, and in order to let people and vehicles go freely all around to take measurements and samples.

The new layers were deposited after a scarification of the whole previous surface, in order to link them to the mentioned first clay layer. Then, three more clay layers, 20 cm each, were deposited in correspondence of the basin n° 3, and one clay layer, same depth, in correspondence of the other basins (fig. 6).

The works were carried out according to a proper planning: the whole area involved was divided in twenty-four portions, and for each of them the duration, the beginning and the type of works planned.

Great care was placed in the sequence of actions, in order to expose every clay layer to air only for a short time.

Moreover, some precautions against risks of swelling that could rise for gas production inside the mass of waste were taken by interposing a thin sand-gravel layer between the clay and loam layers on the top, and between the waste and clay layer in the middle, both connected with some proper ventilation openings.

The upper layer consisted in a continuous deposition of 5CN-80 cm loam soil layer, on which some grass was planted.

Fig. 6 - Scarification of the first protective clay layer on the top surface

CONCLUSIONS

So far, the contaminated material is well confined inside the mentioned waste disposal, well protected by suitable physical and geochemical barriers, capable of avoiding any contamination in the environment for a very long time.

The methodology used reached the aim of both localizing which part of the waste was contaminated and measuring Csl37: everything inside a great quantity of material.

Moreover, all the actions were carried out in safe conditions and without any (or almost any) contact of the contaminated material with the environment

The project of the final covers was realized utilizing natural material and conventional and cheap technologies.

The physical multilayers cover has been very well and successfully tested during the last two years by very bad weather conditions.

BIBLIOGRAPHY

- Antonioli F., W. Bocola (1983): Esperienze sulla migrazione di Cs, Sr e I in argille prelevate in alcuni bacirti italiani - ENEA/RT/PROT(83)4.

Antonioli F. et al.(1985): Element diffusion and oxidation phenomena along permeable fractures in clay formations at Monterotondo, Italy - Proceedings of the International Clay Conference, Denver, 1985 - The Clay Minerals Society, Bloomington, Indiana, 415-421(1987).

Beone G., Carbone A. I., Zagaroli M.: La bonifica di aree contaminate -ENEA/RT/PAS/88/31.

Carlsson S. (1978): A model for the movement and loss ofCs!37 in a small watershed -Health Phys. Vol 34, pp 33+37.

Coleman N.T. et al.(1965): Ion exchange displacement of caesium from soil vermiculite - Soil Sci. - Vol. 99, pp. 243-250.

Cochi C. et al. (1989): Programma di intervento per la messa in sicurezza della discarica di Capriano del Colle (BS) - Messa in sicurezza meteorica - Specifica tecnica - ENEA-AMB-RIF-CRIA

Cpchi C. et al. (1990): Programma di intervento per la messa in sicurezza della discarica di Capriano del Colle (BS) - Piano di prelevamento di campioni nel corpo della discarica - Prescrizioni tecniche - ENEA- AMB-RIF-CRIA.

Cochi C. et al. (1990): Programma di intervento per la messa in sicurezza della discarica di Capriano del Colle (BS) - Faselll - Copertura finale - Prescrizioni Tecniche - ENEA-AMB-RIF-CRIA.

Daniel D. et al. (1986): Field permeability test for earthen liners - Proceedings of a Specialty Conference on Use of in Situ Tests in Geotechnical Enginneering -Geotechnical Special Publication - Samuel P. Clemence Editor - pp. 146-160.

Jones et al. (1986): Development of waste containment structure for Niagara Falls storage site - Canadian Nuclear Society: Conference Proceedings of 2nd International Conference on Radioactive Waste Management - Sept. 7,11,1986.

Paris P. (1989): Una valutazione di limiti di concentrazione non pericolose per lo smaltimento del rifiuti radioattivi in una discarica superficiale - ENEA DISP/SER/NOR-RT(89)6.

Pegoyev A. and Fridman D (1978).: Vertical profiles of caesium 137 in soils - Soviet Soil Sci., Vol. 10, pp. 468+472

Polyakov Y.A., Kader G.M. and Krintskii V.V. (1973): Behaviour ofSr 90 and Csl37 in soils - Radioecology, pp. 78+102. Wiley, New York.

Rogowski A.S., Tamura T.(1970): Environmental mobility ofCs!37 - Radiat. Bot., Vol 10, pp. 35+45.

Saltelli A., Antonioli F. (1985): Radioactive -waste disposal in clay formations: a systematic approach to the problem of fractures and faults permeability - Radioactive Waste Management and Nuclear Fuel Cycle - Volume 6(2), June 1985, pp. 101-120.

Sawhney B.L. (1966): Kinetics of caesium sorption by clay minerals - Soil Sci Soc.

Am. Proc., Vol 30, pp. 565+569.

Tamura T. (1964): Selective sorption reactions of caesium with soil minerals - Nucl.

Saf., Vol 5, pp. 262+268.

U.O. Fisica e Tutela Ambiente - P.M.I.P. di Milano - U.S.S.L. 75/111 - Sezione di Radioprotezione - Relazione Tecnica: Risultati delle analisi di radiocontamina-zione sui campioni di residuo prelevati presso la discarica Montenetto di Capriano del Colle (BS) - Milano, 8 Novembre 1991

TECHNOLOGY FOR RESTORATION OF CONTAMINATED SITES; REVIEW OF AVAILABLE EXPERIENCE IN THE FIELD OF ENVIRONMENTAL RESTORATION IN ROMANIA

P. SANDRU

Institute of Atomic Physics, Bucharest, Romania

Abstract

In Romania as a result of human activities there are several contaminated sites with low specific activity widely dispersed. Among these uranium mining and milling, fertilizer industry and coal-fired power plants are the most significant. Particularly, for heaps resulting from uranium mining and milling activities the environmental restoration is justified but no comprehensive optimization process (multi-attribute cost benefit analysis) was implemented so far. The lack of specific technology and necessary financial resources are major problems in the implementing of environmental restoration work. Regarding contaminated sites from the fertilizer industry and coal-fired plants the justification for restoration is not complete. The same difficulty is foreseen with respect to available

technology and necessary funds. However, a number of research projects are under development and could be considered in the light of international co-operation programmes. Limited remedial actions were performed in order to do something with respect to smaller areas of contamination with higher specific activity.

1. PRELIMINARY

In Romania there are a number of important issues related to environmental restoration:

(i) regulatory and scientific aspects; the most important problems are:

a. a clear definition of contaminated sites in terms of specific activity and/or effective dose;

b. the definition of action levels in terms of specific activity, effective dose or risk values. A definition of action levels in terms of risks appears to be more appropriate because other associated non-radioactive risks are

involved. Moreover the heaps from uranium mining and milling activities present potential exposure, which is defined in terms of risk limits and risk constraints, rather than occupational exposure which is associated with dose limits and dose constraints [1]. In the same way actual regulations [2] offer only general principles on closing of the extraction activities for raw materials;

c. guidelines for remedial action plan.

(ii) organizational problems associated with a diversity of structures involving human activities which could lead to environmental restoration. Due to the lack of

national and international regulations it is hard to have a consensus on this subject.

(iii) available technology and funding of environmental restoration work. Mainly, as a result of uranium mining and milling, the fertilizer industry and coal-fired power plants we have widely dispersed contamination with low specific activity. This

situation led to large areas and volumes of low activity contaminated soil which requires specific technology and large financial resources.

Presently, there is a lack of funding for the remediation of contaminated sites.

Concerning higher specific activity in smaller areas of contamination, limited remedial actions were performed in order to clean-up an old facility used for temporary storage of radioactive waste. Its use was due to the lack of a repository.

2. ENVIRONMENTAL RESTORATION RELATED TO URANIUM MINING AND MILLING ACTIVITIES IN ROMANIA

2.1. Review of actual situation

Presently, there are about 173 contaminated sites as a result of uranium mining and milling, containing about 5,350,000 waste rocks (annually predicted quantity is

300,000 tonnes), and 30,400 tonnes low grade uranium ore (ore heaps) [3].

The distribution of the waste rocks and the ore heaps is summarized in

table I, [3,4,5,6]. The radiological characterization and the restoration criteria laid down for each side is offered in table II, [4,5,6].

TABLE I

The distribution of waste rocks and ore heaps in Romania Area

TABLE

Radiological characterization of contaminated sites following mining and milling activities in Romania

(*) No recent measurements (**) No available information

2.2. Related technology for environmental restoration

The contaminated sites following uranium mining and milling activities are characterized by widely dispersed low specific activity. Thus very large areas and volumes should be considered in the environmental restoration plans. So far technology used for environmental restoration of the heaps is an extension of classical equipment adopted to radiological conditions. In the past the low specific activity of these heaps was considered an argument for simple remedial plants and classical technology usage. The lack of national regulations with respect to action levels at which remedial actions should be implemented was a reason for doing something. In the same

connection it is worth mentioning the lack of international guidelines in this respect. For instance at Barzava for a low activity uranium ore heap, classical technology was adopted for covering it with a 5 cm thick concrete layer to prevent wind and rain corrosion.

After a while the concrete cracked hi some places and following these the gamma dose rate of 9 mSv/h was measured (as compared to 1-2 mSv/h over the concrete shield and 0.17mSv/h in the background in the nearest village).