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Water Quality in Maardu Phosphate Rock Mining Area in Estonia
Margit Kolats, Ingo Valgma, Karin Robam Tallinn University of Technology (Estonia)
Abstract - In Maardu region water moves through layers of limestone, clay, pyrite, phosphate rock, sandstone and argillite. In limestone mining areas the main rocks influencing water quality are limestone, clay and quaternary sediments plus oil shale in oil shale areas. Waste rock and unbroken rock have similar influence on the water quality.
I. INTRODUCTION
Phosphate rock in Estonia has been mined and processed only in Maardu region. Mining ended in 1991. Phosphate rock deposit in Maardu lies on an area of ~ 18 km2. In Maardu area there are two phosphate rock mines (Ülgase and Maardu) and one phosphate rock open cast, which is divided into the Northern and Southern open casts. In addition, there are limestone quarries.
Maardu mine is filled with water, in addition there is accumulated water in Ülgase dewatering workings and Northern and Southern open cast trenches. Water flows from the trenches to Maardu lake and then through Kroodi stream to the sea. As water moves through the mined out area, the decomposition of rocks appears, which affects the quality of water in the region. Water quality is also affected by human activities such as garbage pollution, wastewater from houses, agriculture, etc. Similar processes appear in the areas of Ubja region [25][23][4][3] and in Jõhvi region related to the oil shale mining [7][29][20]. Oil shale areas is Eastern Estonia have been exploited with similar technology [15][1][24]. The mining conditions are similar and similarity water movement can be taken into account in current study [6][28][14]. For evaluating environmental effect of low bedded phosphate rock mining, the movement and properties of water should be analysed. [11][10][9]
II. METHODS
In order to find out what and how water is affected in Maardu area a study was conducted which mapped water movement, volume and quality. Fieldworks were done during two years, in all of the observation points and generally in the area (Fig. 1). [5]
The total water volume in the region, which is under observation, was estimated to be 12.5 million m3. Most of the water is in the lake of Maardu (2.37 million m3) and the least is in Ülgase mine (200 m3). Water volume was calculated using the depth and areas of objects. [22]
Northern and Southern open cast tranches have been calculated in accordance with the depth of phosphate rock bottom and the value by area of the water surface. Maardu and Ülgase mine water capacity is calculated based on the
mined out area of the mine and height of the workings [13]. Water volume in Kroodi stream and Maardu Lake is calculated with water surface area and average depths. In the bottom of the Maardu lake is 6 m thick impermeable layer of sediments. [2][26]
Ground altitude in the Northern open cast is 40 m, which decreases towards the north-west and the north, and it is 33 m at the lake of Maardu. The altitude of the bottom of the phosphate rock is 29 m in the Northern open cast, which also decreases towards the south and in the Southern open cast it is 21 m. [8][19]
In Maardu region the water is divided into still and flowing water. Water quality indicators are outlined in the legal act of the Minister of Environment Regulation No. 44 "Surface water composition and surface water bodies in their list which class status should be determined by the state of surface water bodies classes and classes corresponding to the state of the values of quality indicators and the procedure for determining the status of classes" Annexes 2, 4 and 5. Based on the regulation, Lake of Maardu is listed as type II: shallow lake, medium hard water. Kroodi stream is not on the list, but basically corresponds to the type IB, clear water and low organic matter content (chemical oxygen demand (CODMn = KHTMn) is 90% below the value of 25 mgO/l), rivers with catchment area of 10-100 km2. Water in open cast tranches can be compared to Kroodi stream and Maardu lake conditions and status indicators.
The ecological status of still water is determined by the following physical-chemical indicators: unit of pH, total phosphorus (Total P) and total nitrogen (Total N).
The ecological status of flowing water is determined by the following physical-chemical indicators: dissolved oxygen, biochemical oxygen demand (BOD7 = in Estonian it is BHT7), total phosphorus (Total P), total nitrogen (Total N), ammonium (NH4+), and pH unit.
In the study we also measured the electrical conductivity, sulphate (SO4
2-) concentration, chemical oxygen demand (CODMn = in Estonian it is KHTMn) and solid suspension. On each fieldwork the water flow and velocity was determined in cross section of the water bed.
During the fieldworks situation of the area was mapped and possible locations of thresholds were determined. Characteristic places where selected to monitor the water movement, level, flows and quality. In each survey point the water level was observed. [27]
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Fig. 1. Water survey points in Maardu area: 1 - Maardu lake outflow; 2 - inflow to Maardu lake from south phosphate rock open cast; 3 - inflow to Maardu lake; 4 - outflow from Maardu phosphate rock mine; 5 - outflow from Maardu phosphate rock mine after the culvert; 6 - outflow to the sea; 7 - outflow from Ülgase phosphate rock mine; 8 - north phosphate rock open cast; 9 - north phosphate rock open cast; 10 - south phosphate rock open cast; 20 - north phosphate rock open cast; 21 - Sedimentation pond of south phosphate rock open cast; 22 – Ülgase clay pit (Fig. 9).
Fig. 2. Southern phosphate rock open cast (survey point 10).
Fig. 3. Northern phosphate rock open cast (survey point 9).
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Fig. 4. Maardu lake outflow (survey point 1).
Fig. 5. Inflow to Maardu Lake (survey point 3).
Fig. 6. Outflow from the adit of Maardu phosphate rock mine (survey point 4).
Fig. 7. Outflow to sea (survey point 6).
Fig. 8. Ülgase dewatering workings (survey point 7).
Fig. 9. Ülgase clay pit (survey point 22).
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Fig. 10. pH values in observation points.
III. RESULTS
Following result can be concluded for Maardu mined out area:
Still water is in survey points 1, 2, 8, 9, and 10 (Fig. 2, Fig. 3, Fig. 4).
The average pH in this survey points is 8,1 what corresponds to ecological status indicator table as result of good (Fig. 10).
The average PÜld in this survey points is 40,9 µg/l what corresponds in ecological status indicator table to result of good.
The average NÜld in this survey points is 840,0 µg/l what corresponds in ecological status indicator table to result of good. (TABLE I, TABLE II)
Flowing water is in survey points 3, 4, 5, 6, and 7 (Fig. 5, Fig. 6, Fig. 7, Fig. 8).
The average pH in this survey points is 7,5 what
corresponds in ecological status indicator table to result of very good (Fig. 10).
The average PÜld in this survey points is 0,05 mg/l what corresponds in ecological status indicator table to result of good.
The average NÜld in this survey points is 2,2 mg/l what corresponds in ecological status indicator table to result of good.
The average NH4 in this survey points is 0,2 mg/l what corresponds in ecological status indicator table to result of good.
The average BHT7 in this survey points is 2,3 mgO2/l what corresponds in ecological status indicator table to result of good. (TABLE I, TABLE II) [27]
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TABLE I
MAARDU LAKE AND MINED OUT AREA, TECHNOLOGICAL RESERVOIRS (TRENCHES), STILL WATER, ECOLOGICAL STATUS, PHYSICAL-CHEMICAL INDICATORS
(ARITHMETICAL MEAN IN ALL SURVEY POINTS DURING THE PERIOD OF 2011-2013) [16][17][18]
Survey point no
pH unit Total P, µg/lTotal N,
µg/l
Electric conduction, µS/cm
SO42–
, mg/l
8,59 > 8,3 8,8 30,4 30 60 1299 > 1000 1500 617 192
Medium Good Medium ― ―
8,00 > 8 8,3 52 30 60 483 1317 427
Good Good Very good ― ―
7,7 7 8 34 30 60 638 500 1000 2165 988
Very good Good Good ― ―
7,7 7 8 61 > 60 80 972 500 1000 3718 2050
Very good Medium Good ― ―
8,31 > 8,3 8,8 27 809 500 1000 1364 452
Medium Very good Good ― ―
1
2
8
9
10
Very good
Very good
Medium Good
Good
Good
Good
Quality indicator limits
Quality indicator limits
Quality indicator limits
Medium
Very good
< 500
Good
Good
Medium
Very good
< 30
Medium
Good
TABLE II
MAARDU LAKE AND MINED OUT AREA, TECHNOLOGICAL RESERVOIRS (TRENCHES), FLOWING WATER, ECOLOGICAL STATUS, PHYSICAL-CHEMICAL
INDICATORS, (ARITHMETICAL MEAN IN ALL SURVEY POINTS DURING THE PERIOD OF 2011-2013) [16][17][18]
Survey point no
pH unitTotal P,
mg/lTotal N,
mg/lNH4+, mg N/l
BHT₇, mgO₂/l
Electric conduction, µS/cm
SO42–,
mg/l
8,06 6 9 0,101 > 0,1 0,12 4,648 > 3 6 0,343 0,45 0,6 2,57 1,8 3 723 90Very good
Bad Medium Bad Good ― ―
7,09 6 9 0,030 0,723 0,060 2,02 1,8 3 3090 1433Very good
Very good
Very good
Very good
Good ― ―
7,09 6 9 0,027 1,02 0,07 1,67 2184 1514Very good
Very good
Very good
Very good
Very good
― ―
7,97 6 9 0,071 0,05 0,08 2,60 1,5 3 0,361 0,45 0,6 3,57 > 3 4 2184 805Very good
Good Good Bad Medium ― ―
7,7 6 9 0,019 2,049 1,5 3 0,16 0,1 0,3 1,82 1,8 3 1446 540Very good
Very good
Good Good Good ― ―7
4
5
6
3Very good
Quality indicator
limits
Quality indicator
limits
Quality indicator
limits
Very good
Very good
Very good
Very good Good
Medium
< 1,8
Very good
< 1,5
Very good
Good
Good
Bad
Quality indicator
limits
Quality indicator
limits
Bad
< 0,05
Very good
Medium
< 1,5
Very good
Good
Good
Bad
Good
Very good
Very good
< 0,1
< 0,1< 0,05
Very good
< 0,05
Very good
Good
IV. DISCUSSION
The overall assessment for still and flowing water based on ecological status indicator table is good. But if you look at the survey points separately then some ecological status indicators are bad. Electric conduction and sulphate concentration are not listed in the legal act of the Minister of Environment Regulation No. 44. But if they are high then some degradation processes are taking place, like pyrite decay and it is not good for water quality. [21][27]
ACKNOWLEDGEMENTS
The paper is part of the study Sustainable and environmentally acceptable Oil shale mining No. 3.2.0501.11-0025 mi.ttu.ee/etp and the project B36 Extraction and processing of rock with selective methods - mi.ttu.ee/separation. KIK11067 - Study of the quality of technogenic groundwater in Maardu phosphate rock deposit- mi.ttu.ee/maardu. Publication of this paper has been supported by European Social Fund (project “Doctoral School of Energy and Geotechnology II”).
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