SLOVENIA
Zirovski Vrh Uranium Mine,
Slovenia
Case History
Prepared by
Zmago Logar
Pribram, Czech Republic, October 12 -14, 2004
ABSTRACT
1. INTRODUCTION
The facilities of the Zirovski Vrh Uranium Mine
are situated 45 km west from Ljubljana. Uranium mineralization in Groeden
sandstone was discovered in 1960, the ore production started in 1982, yellow
cake production started in 1984. Only 610,000 ton of ore with 0.7 kg of U per
ton of ore was processed and 452 ton of yellow cake was produced during six
years of the mill life. The production ceased in 1990 due to decision of the
Slovenian Government, with no notice given to the operator.
The mine and its
facilities lie on the north-eastern slopes of the Zirovski Vrh ridge (960 m).
The region belongs to the Julian Alps foothills. The underground mine elevation
is from 430 m (bottom of the river valley) to 580 m (P-1 adit). The mill
was located in the valley of the Brebovscica river (415 m) and the mill tailings are located on the
southern slope (530 – 560 m) of Crna Gora hill (611 m). A total of
3 307 000 tons of crude ore was won (633 000 tons of high graded
ore, 206 000 tons of low graded ore and 2 468 000 tons of mine
waste).
The mine is located in well-populated farming
area. Radioactive impact is small, the yearly dose contribution swings from 0.3
to 0.4 mSv/a (Benedik 2002). Uranium and radium concentrations in nearby
surface water flows are elevated.
Rudnik Zirovski Vrh, d.o.o. - public company
for the close-out of uranium mine is a company owned by the state. Its basic
purpose is the performance of permanent closeout of exploitation of Uranium
Mine Zirovski vrh. After the submission of the last closing program that the
Government of Slovenia adopted in the year 2001 on the basis of changes and
amendments of the fundamental act of the year 2000, it is necessary to
implement the project of the mine close-out in a five year period. The total
costs of the project implementation will be 37.3 million EUR. The company will
prepare a revision of the closing program due to delays in financing and
implementation of existing closing program and new cognitions.
For the
emission of contaminants via the water and air pathways the limits were set by
the decision of the Ministry of Health of the Republic of Slovenia and are
shown in the Table I (ZIRS 1996).
Non-radiological
requirements for the discharge of contaminants in the water are defined by the
environmental legislation concerning the conservation of water resources.
Additionally, location permits define basic conditions for the operation of the
mining and milling sites and also for their closeout. In the case of the waste
piles P 1 and P 9 the location permit allows only a temporary storage of the
mine waste. The requirements of the location permits are taken into
consideration in the remediation plans of RZV.
Table I: Authorized limits issued for the
closeout of the liabilities of the Zirovski Vrh Mine
|
Contaminant |
Concentration |
Annual
load |
Water
discharges |
|
|
|
Mine
water (P-10) |
Uranium |
250 mg/m3 |
170 kg |
|
Ra-226 |
60 Bq/m3 |
50 MBq |
Mine
waste pile Jazbec |
Uranium |
510 mg/m3 |
85 kg |
|
Ra-226 |
40 Bq/m3 |
25 MBq |
|
Th-230,
Pb-210, Po-210 (total) |
100 Bq/m3 |
|
Mill
tailings Borst |
Ra-226
(annual average) |
60 Bq/m3 |
50 MBq |
Airborne |
|
|
|
Mine
waste pile Jazbec |
Rn-222 |
0.1 Bq/m2
s |
|
Mill
tailings Borst |
Rn-222 |
0.74 Bq/m2
s |
|
External
radiation |
Average
over the first 1.25 m above the ground |
200 nGy/h
|
|
RZV
(total contribution) |
Annual
effective dose |
0.3 mSv/a |
|
2.1 Description
The underground uranium mine extends 2000 m in
North-South direction, 150 m East-West and in height up to 180 m. About 60 km
of underground mine openings were built mostly having a cross section to allow
transport and production. The mine is divided into 4 horizons, the horisonts
into 14 blocks of 200 m width. Uranium ore was mined by room-and-pillar method.
10 % of the total ore was won by top to bottom winning technology leaving extensive
open mine space with height up to 15 m. 90 % of uranium were won from bottom up
with cut-and-fill mining leaving a minimal open space.
The underground mine is connected to the
surface by shafts and adits, which were used for ventilation, material supply
and transport. Adits P-1 and P-36 are used mainly for ventilation purposes. The
ventilation station P-1 is located in the southeastern part of the underground
mine; the ventilation station P-36 is located in the Northwest. The ventilation
of the underground mine is realized by depression induced by the ventilation
stations at these adits, removal of the mine air while fresh air flows in via
the ventilation shafts, and adits situated over the whole mine area. The
deepest adit P-10 is used for mine water discharge. The main mine access is
through adit P-11.
The Zirovski Vrh deposit is one of numerous
uranium occurrences in the Groeden Sandstone of Permian age found in a zone
extending from the Southern Alps in northern Italy, through southern Austria
and central Slovenia, into Hungary. The ore-hosting rocks are grey Sandstone
and conglomerates (grey series) of the lower part of the Groeden Sandstone of
Middle Permian age. The Groeden Sandstone rests unconformable on black shale of
Permo carboniferous age and is overlain by upper Permian Bellerophon dolomite.
During the Alpine Orogeny the entire sequence was folded, heavily sheared, cut
by north-south and northwest-southeast faults. The complex geology leads to
geomechanical stability problems with the mine workings. The rock is relatively
friable making extensive rock bolting and support necessary.
In the northwestern part the uranium bearing
structures of Zirovski Vrh are overthrust by the Jazbec scale (Groeden rocks).
It is estimated that this thrust represents an impermeable barrier with a
hydraulic conductivity of 10-9 m/s. The overlying layers of
sandstone and conglomerates have a high hydraulic conductivity RZV 9/00.
Water inflow into the mine mainly occurs on the
fractures and cracks in sandstone and conglomerates along discontinuities and
fault zones. Particularly the conglomerates present an important aquifer (3rd
horizon). The Northwest part of the mine is more permeable because of the
cracks. The layers with ore deposit are less permeable.
Ground water entering the mine becomes
contaminated due to passing trough ore-enriched zones. Another source of mine
water contamination are exploration boreholes in the ore horizons. Some mine
workings (blind tunnels) cannot drain and get flooded. The water in these
tunnels have uranium concentrations exceeding 6 mg/l.
During the ore production the inflow of
groundwater in the upper parts of the mine decreased. The highest inflow of
water is presently found on the deepest mine levels. According to (IBE 2000n)
the connection between water inflow and precipitation is evident in the higher
parts of the mine, while in deeper parts a long delay can be observed. The
total discharge from the mine ranges between 15 and 30 l/s.
The yearly average of the uranium concentration
in the mine water discharged through the adit P-10 was between 250 and 350
μgU/l in the time period 1992 to 2000. The radium concentration (Ra-226)
was between 30 and 100 Bq/m3 during the same time. A decrease of
uranium and radium concentration in the mine water was observed after uranium
production ceased. Iron concentration in the discharged mine water is below the
detection limit. The sulphate concentration is very low compared to the discharge
observed in other mines.
2.2 Objectives of the Mine Remediation
UNI 4/99 defines the objectives regarding the
remediation of the mine as follows:
Reduction of radon emission from the underground
openings,
Long term stability of underground mine
facilities to prevent the inflow of surface waters to the mine resulting from
the collapse of mine openings,
Permanent discharge of mine water through adit
P-10 meeting the regulated limits for uranium,
Permanent discharge of uncontaminated
groundwater through P-11 and P-9,
Protection of underground and surface water
(within the regulated limits),
Reclamation of the surface area in the
surrounding of shafts, raises and adits,
Prevention of unauthorised access to underground
openings.
2.3. Work done in the mine
For a better collection of the
inflowing groundwater and to avoid the contact of groundwater with the ore
deposit, drainage boreholes of a length between 150 and 170 m were drilled in
the deepest part of the mine in 1993, the uranium concentration in the
inflowing groundwater decreased at the same time. There are measurements of
uranium concentration in the drift H-7 for the time before and after drilling
of the drainage boreholes. In the concentration of uranium which is affected by
drainage boreholes is compared to uranium concentration of H-8 where no
drainage boreholes exist.
The adit P-10 was completely
remediated over a length of 520 metres (out of its total length of 1200 metres)
between 1996 and 1997. Further mine facilities on the surface, e.g. the
crushing plant, the chemical plant and transport bridges, were torn down or
handed over after decontamination to users outside RZV.
3.1 Description of the Mine
Waste Rock Piles
The waste rock piles P-1 (70 000
ton) and P-9 (143 000 ton) are situated close to the adits P-1 and P-9
respectively. There are no water sources in the area of waste pile P-1. From
the adit P-9 about 0,5 l/s uncontaminated mine water is discharged and passes
the waste pile P-9. The uranium concentration of this water is about 400 mg/l.
Jazbec is the main waste rock pile
of RZV (1,5 million ton) situated in the Jazbec valley right below the entrance
to adit P-11. The slope of the waste pile is 1:2 with 3 m wide berms placed at
each 12 m of height. At the present the highest point of the waste pile is 493
m a.s.l. On the supporting dam formed by mine waste on the eastern pile face a
road leads to the former crusher site. Judged by the measured water levels in
the mine pile, this dam is less permeable than the stored material. There is no
seepage water observed on the pile face.
In addition to waste rock Red Mud from
the uranium ore processing was disposed off on the waste pile. The red mud is a
precipitate of the uranium leaching solution generated by neutralisation with
lime. The main components are calcium, gypsum, iron hydroxide, uranium (0,5 Bq
/g), Ra-226 (0,2 Bq/g) and Th-230 (62 Bq/g). Th-230 has a 8 times higher
enrichment than the Ra-226 concentration in the tailings. The material was
stored alternately in layers: on 80 cm of mine waste 20 cm of red mud follows.
A 5 m thick zone on the aerial side of the pile consists only of coarse mine
waste. Demolition debris from the remediation of the milling site was deposited
on the waste pile as well.
The concentrations of the
radionuclides Ra-226 and uranium in the waste rock are about 0,5 Bq/g. The
sulphate and iron concentration of the waste rock is low. Acid mine drainage in
the pile is unlikely to develop. The mine waste material is a very
water-permeable material, that consists of a quartz conglomerate, sandstone and
aleurit. The red mud is a less-permeable material consisting of an aleurite
clay fraction. The uranium content of the waste rock is the main source of
contamination of the mine waste pile seepage.
The Hotavlje fault, with some wet
moor areas on the surface cut the Jazbec valley. At the bottom of the Jazbec
valley are dark grey limestone outcrops IBE 2000n showing characteristic
karstic properties. Along the Brebovščica river numerous springs exist which
are fed by karstic groundwater. There is a 329 m long concrete channel at the
bottom of the waste pile. In the upstream section (152 m) the channel has a
diameter of 1 m and in the downstream section (177 m) of 3 m. This channel
collects the water from three creeks in the upstream valleys as well as the
drainage water from the pile. This water is discharged into the Brebovščica
river. Before construction of the waste pile a drainage system was build at the
bottom of the valley. Pipes connected to the concrete channel dewatered small
springs. At present the drainage channel is in good condition, however, the
drainage pipes are mostly in a poor condition. Currently additional horizontal
drainage boreholes are drilled from a large diameter well in the upper part of
the waste pile (near P-11) to reduce groundwater inflow to the pile from the
hinterland.
The groundwater is polluted because
of the infiltration of meteoric water percolating through the uncovered waste
pile and leaching the red mud. Various sampling points on and around the waste
pile allow the evaluation of the groundwater. The water at the bottom of the
waste pile contains up to 5000 μg/l uranium. Downstream the pile in the
alluvial terrace of the Brebovščica river no groundwater is found (borehole
BS-20) while concentrations of about 150 μg/l uranium were measured in the
deeper karst aquifer. Downstream, the Brebovščica river springs are probably
fed by water from the karstic limestone layer (RZV 9-2000).
The water discharged from the
drainage channel at the bottom of the waste pile has annual average uranium
concentrations of 250 to 550 μUg/l (1991 to 1999). In the same period the
sulphate concentrations were between 200 and 300 mgU/l, which is about 10 times
higher than in the mine water discharge.
3.2 Objectives of Mine Waste
Remediation (Jazbec)
The specific aims of the technical measures for the final arrangement of
the mine waste pile are as follows:
Limitation of the radon exhalation,
Limitation of leaching of contaminants and erosion protection of the
mine waste pile by covering,
Limitation of the effect of surface and ground water from hinterland on
the mine waste (erosion, wetting of waste),
Geo-mechanical stability of mine waste pile, erosion resistance by
reshaping of mine waste pile,
Prevention of erosion and excessive wetting of the cover by means of a
drainage system,
Relocation of the waste rock piles at P-1 and P-9 to the mine waste
disposal Jazbec,
Prevention of excessive dusting.
4. Mill Tailings Disposal
Boršt
4.1 Mill
Tailings Description
From the
beginning of the operation till the end of uranium production at RUZV 600 000
ton of hydro-metallurgical tailings had been generated and deposited on the
tailings pile Boršt. The volume of the deposited material is approximately 375
000 m3. The tailings pile has an area of 4.11 ha. The storage
site is about 2 km away from the former uranium processing plant. There is an
access road at the southern and western periphery of the pile. To allow access
to the tailings ground with heavy machinery, regularly arranged roads were
constructed on the tailings pile (at every 5 m of elevation) using 73 000
t of mine waste rock. The tailings are deposited on a natural slope.
During
deposition of the tailings the following principles were followed concerning
the environment controls, water management and geotechnical stability of the
tailings:
Diversion
of surface waters out of the tailings pile to prevent contact with tailings,
Capturing
of ground water and springs and their linking to the drainage system,
Sealing of
the bottom of the tailings pile using clay material,
Capturing
of (contaminated) surface and seepage water from the tailings and discharge
into the retention pond,
20o
embankments slopes with horizontal berms.
Covering of
the tailings surface after reaching the planned elevation with material that
was previously removed from the base of the tailings pile and vegetation with
grass. The general slope of the tailings pile at the northern part is
approximately 20°, the inclination between berms is 24°- 27°. The slope was
covered with 25 cm of top soil and vegetated with grass. The top plateau of
tailings pile is partly covered with waste rock from the construction of the
drainage tunnel below the tailings pile. The immediate covering was done to
reduce the radon exhalation.
The
tailings material is a relatively coarse ground sandy-aleuritic residue of the
uranium ore processing with grain size under 0.5 mm, but more than 50%
greater than 0.125 mm. The average contents of uranium is 0.9 Bq/g or 80 g/t U3O8
and 8.6 Bq /g of Ra-226. It mainly consists of SiO2, calcite
and sulphate salts. The tailings were deposited on site with a water content of
20 – 24 %. Presently, the tailings are in a solid state. According to the
planning documents there is no danger of liquefaction. However, during
deposition liquefaction of the material was observed.
Before the
placement of tailings started, the ground on the base of the pile was prepared
using the material removed during the site preparation works. Drains and pipes
were laid on the surface and covered with a layer of clay. Water form 2 springs
subsequently covered with tailings was captured and drained in 2 PVC pipes. The
water discharge from these springs is sampled at the sampling point SDIJ
outside of the tailings pile.
The aim of
the sealing layer at the bottom of the pile was to lead the groundwater from
upstream of the pile to the receiving Todraščica brook and separate it from the
tailings seepage. Shortly after the placement of tailings started it was found
that the ground water drained below the tailings pile was chemically and
radioactively contaminated. A gradual increase of the concentrations was
observed.
The
tailings were deposited in layers and at every 4-5 m elevation in series of
nearly horizontal drains (slightly inclined to the surface) were placed. These
drains are approx. 10 m long and drain only the face of the pile. The drained
water is collected in surface water channels on the berms. Together with the
precipitation water, the drainage water flows to the retention pond before it
is released into the Todraščica brook.
The
retention basin has a total volume of 4100 m3, which allows to
retain the centennial maximum precipitation for one hour. It is divided into
two compartments enabling its function without hindrance even in case of
cleaning or maintenance. The bottom of the reservoir is reinforced and
protected by a watertight asphalt layer. The reservoir is vegetated with reed.
Sediments from the reservoir are regularly removed and stored on the Boršt
tailings pile.
In case of
rainfall, the surface run-off water from the hinterland is diverted by ditches
outside the tailings pile area to a torrent gorge on the western site of the
pile. During dry weather these ditches are empty.
Due to the
high radium contents in tailings, both the uncovered top surface area and the
covered embankments are a considerable radon source; the exhalation was
evaluated to approximately 5 Bq/(m2.s) (in the range of 1 and
10 Bq/(m2.s)). Surface waters, water in tailings as well and
underneath the tailings are contaminated by uranium and soluble inorganic
materials (NH4+, SO42-, Cl-).
Ammonia and total inorganic materials are above the regulated discharge limits.
The
geological foundation of the Boršt tailings pile consists of karstic sediments,
yellow, red and grey clay, alternating with aleuritic layers with tuff and
tuffaceous inclusions. A large number of sub-vertical faults disrupt the
geological base.
After heavy
rainfalls in November 1990 a crack with 20 - 30 cm of vertical movement
appeared in the road on top of the tailings due to land sliding. The extent and
depth of the sliding area have been established by surveying, drilling and
borehole inclination measurements. The landslide occurred on the contact of the
karstic and tuffaceous rocks. The evaluation of the borehole survey confirmed
that the tailings pile was placed on an old landslide (paleoslide). The
landslide underlies the major part of the Boršt tailings pile and involves a
large part of geological foundation. The general movement of the slide was
towards North. The average thickness of the slide is 50 m.
Tailings
moved by landslide |
328,579 m3 |
Masses of
ground moved by landslide |
2,593,175
m3 |
Total
volume of the landslide |
2,921,754
m3 |
The main
effect on the movement of the landslide was achieved by the construction of the
drainage tunnel in 1995. The tunnel starts in the sliding face crossing the
main sliding plane at about 214 m from the entrance of the tunnel. At the
end of the tunnel two drainage wings were excavated where a drainage screen is
connected to 21 boreholes drilled from the surface. The distance between the
boreholes is about 10 m. The inflow into the drainage tunnel is in average 1.3
l/s (40 000 – 60 000 m3/a). 40 % of the inflow comes from the
drainage boreholes while 60 % enter through the tunnel face. The construction
of the tunnel has a considerable effect on the local groundwater regime. Most
of the water levels measured in the piezometers in the tailings pile and in the
close vicinity of the site decreased, however, no correlation to the distance
from the drainage tunnel was found. After construction of the tunnel the
discharge of the captured springs and measured at SDIJ, rapidly decreased (to
about 20 %).
4.2 Objectives
of Mill Tailings Remediation (Boršt)
The remedial objectives concerning the tailings storage are as follows:
Provision of permanent landslide stability by drainage channel, drainage
screen and cover construction,
Drainage curtain will be designed to facilitate tailings consolidation,
Provision of the tailings stability and enhancement of erosion
resistance by reshaping of the tailings pile,
Prevention of the radon exhalation, the leakage of hazardous
contaminants into water streams and the erosion of tailings by covering,
Protection of the tailings pile from the surface and ground water from
the hinterland (erosion, increased infiltration through the cover and the
tailings),
Prevention of the cover and the tailings from erosion by construction of
a drainage system,
Prevention of excessive dust formation.
5. Investment costs
By the submission of the last closing program estimate of closeout costs was made both per fixed and per
current prices (in EUR and SIT). In the text further we use the
presentation of investment costs and estimated fund sources of the project in
fix prices in EUR. Presentation per fixed prices includes prices as of December
2000. Presentation per fixed prices
was prepared also in EUR. The exchange rate valid on 30 June 2000 was
considered in the translation, i.e. EUR 1 = SIT 205.3542 (IBE 2000n).
Closing out of the Uranium Ore Mine Zirovski
vrh has been in progress since 1990. Costs utilized to the end of the year 2000
were estimated on the basis of the actual utilization to the time when this
novelty to the program and plan of fund utilization for the year 2000 were
drawn up an was 29.4 million EUR. Costs utilized in the year 2000 were about 2
million EUR.
According to the novelty to the program that
the Government of the Republic of Slovenia adopted in the year 2001 on the
basis of changes and amendments of the fundamental act of the year 2000, future
costs of the project implementation shall amount to 37.3 million EUR (included
VAT) in the period of five years. As the project practically started in the
beginning of the year 2002 we estimate that it will be finished by the end of
the year 2006.
Total closeout costs (incl. VAT) amount to 68,7
million EUR for the whole period between the years 1990 and 2007. The
investment costs were estimated by the following presumptions:
Costs for redundant employees and unforeseeable
costs were not planned,
After the closeout a 5-year surveillance over
the influences on the environment was planned. Costs of surveillance were
estimated annually 127 thousand EUR (total 633 thousand EUR) and were not
incorporated in the total closeout costs,
Costs of implementation of RZV liquidation
procedure have not been specially foreseen.
However, total costs of closeout works required
from 1 January 2002 to the final closeout amount to 37.3 million EUR they are
presented in detail in the table II (RZV 2002).
Table II: Summary of the required costs of the
project
Kind of
costs/project |
TOTAL 2002-2006 |
Year |
||||
2002 |
2003 |
2004 |
2005 |
2006 |
||
Ore exploitation |
16.438 |
3.660 |
5.883 |
3.837 |
1.451 |
1.607 |
Concentrate production |
613 |
132 |
0 |
0 |
0 |
481 |
Tailings remediation |
6.829 |
0 |
185 |
3.352 |
1.843 |
1.448 |
Other |
8.863 |
1.797 |
1.936 |
1.814 |
1.714 |
1.602 |
Total |
32.742 |
5.457 |
8.136 |
9.003 |
5.008 |
5.183 |
VAT |
4.558 |
|
|
|
|
|
Grand total |
37.300 |
|
|
|
|
|
Explanation;
Ore
exploitation = the costs for mine close-out works,
Concentrate
production = the costs for concentrate production site close out works (main
works has already been done),
Tailing remediation = the costs for remediation
of the mine waste pile Jazbec and mill tailings Boršt works.
The VAT amount is stated under the tables, but
is not included in the closeout costs. The amount of VAT is only informative,
since VAT is calculated according to the value of closeout works that are
related to the plant for ore exploitation, plant for the production of uranium
ore concentrate and disposal sites, and it is not calculated for the value of
other works referring mainly to the costs of employees in RZV (salaries, change
in employment, etc.). In accordance with the Act VAT is not added to the
investment value.
The costs of other works include:
Costs of surveillance
over influences on the environment (surveillance that should be performed at
the time of closeout and at least 5 years after the closeout),
Costs of safety at
work,
Costs of assurance of
conditions (these costs are related to the operation of the investor at the
time when the mine has not been finally closed out yet; these are cots of the
laboratory, costs of operation of technological assemblies and costs of
maintenance that are estimated in an amount),
Fixed liabilities (include costs of material and services that
are related to the operation of RZV, contribution to the land plot utilization,
hire contracts and others and costs of training),
labour costs (the calculation includes labors
costs of 36 employees),
Indemnification
(indemnification that should be paid to land owners in case of possible
intervention in their land),
Purchase of the equipment needed.
6. Conclusion
The underground mine remediation will be
finished at the end of 2005 in the scope of estimated costs. The main entrance
will be finally closed in the first half of 2006. The work at the mine waste
pile Jazbec will start in the middle of 2005 and will be finalized in 2007. The
funds foreseen in the program will satisfy the needs. The funds we foresaw for
the mill tailings remediation in the program are too small. New informative
design has required considerable more funds for the tailings site remediation.
The start of the remediation is planned for 2006 and the work will be finished
in 2008.
References
Benedik L. et al., The Report on the Environment Radioactivity Measurements of the Uranium
Mine Zirovski Vrh, Institute of Josef Stefan or Institute for Work Safety
of the RS, Ljubljana, Volumes 1990–2002
IBE (2000n) Novelty
to the Programme of Close-out of Uranium Exploitation in RUZV, IBE,
Ljubljana, November 2000
Gantar I., Zirovski
Vrh Uranium Mine – Geological Description, RZV Gorenja vas, September 2000
UNI (4-1999) Supplementary Mining Project – Permanent Close-out of Uranium
Exploitation of Uranium Ore and Prevention of the Mining Consequences in the
RUZV, University in Ljubljana, Ljubljana, April 1999
ZIRS (1999) Proceeding
approval Reg. no. 531-4/231/76-34/L14, Ministry of Health, Ljubljana, 1996
RZV (2002) Evaluation
of the Implementation of the Novelty to the Programme of Close-out of Uranium
Exploitation in RUZV, RZV, April 2002
WIS (2001) Evaluation of the Technical and
Economic Measures Planned in Relation to the Close-out of the Uranium Ore Mine
Zirovski Vrh, Slovenia, WISMUT Chemnitz, June 2001