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Paper N0: IV.09

Protecting a Water Course from Gneiss-Quarry Caused Pollution

Mladen Zelenika, Jerko Nuić, Božo Soldo

Abstract: Very fine gneiss debris released from a wet beneficiation plant of two gneiss quarries Mikleuska enters the stream Kamenjaca at a rate of 70 tons/day, together with 700 m3/day of water. The stream flowers from northern, mostly forest covered, catchment area of approximately 15 km2 and passes between the two quarries. The Croatian regulation prescribe the classification of waters into five groups according to their quality. Water in this permanent stream was categorized in the State registry of waters as a first-class water. Water quality variables used in the classification includes pH value, oxygen, nitrogen, phosphorus, hygienic indicator bacteria, radioactivity and toxic substance, bat without the water colour, and turbidity. Criteria generated were based on the needs set by relevant kinds of water used and its general environmental condition. In this paper exploration of possibilities for technically, environmentally and economically sustainable exploitation of quarries that would ensure protection of water quality in the stream Kamenjaca is described. Keywords: gneiss, quarry, suspended solids, sedimentation sump, beneficiation plant.

1. Introduction Gneiss in adequate sizes of fraction is an important stone-ware for construction of many foundations of major engineering structures or as engineering material. Mikleuska gneiss-quarry is the most important source of this kind stone in the northern Croatia. It is located on southern slopes of Moslavacka gora, 19 km away from Kutina, in the village Mikleuska on the Podgaric-Kutina road. The stream Kamenjaca which passes in its immediate vicinity belongs to the drainage basin of the Lonjsko polje. It is essential to prevent its degradation due to the influx of contaminants from the quarry.

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Excavation of gneiss in the quarry does not present a threat to the quality of water in the water course. Since gneiss has a similar mineralogical composition as granite (quartz, feldspar and mica) and its components are mostly insoluble in water, dissolved pollutants have not been detected in the water even after its usage in the wet beneficiation plant nor in the Kamenjaca stream that passes largely through gneiss rocks. However, unacceptably high concentrations of suspended load, close to 133 g/l were measured in the water that leaves wet beneficiation plant (see Figure 1). The suspended load in water from the beneficiation plant used to be discharged into the stream for 8 to 10 hours every working day.

Kop - QuarriMikleuška II

Kop - QuarriMikleuška I

Mokra separacijaWet separation

Pumping station Pumpna stanica PS

Kamenjača potokKamenjaca stream

Kamenjača potokKamenjaca stream

Voda iz potokaWater stream Mutna voda

Murky water

1 23

- Točke opažanja na potoku- Monitoring points on stream

- Smjer optoka vode kroz mokru suspenziju- Direction of water through wet separation

1,2,3

Figure 1 Present solution of water circulation

Due to high production cost and low market prices of the classified gneiss, a more complex and expensive method for purification can not be used. Therefore here is presented an environmentally as well as economically acceptable way for prevention of Kamenjaca water course. The construction of two rectangular sedimentation sumps and a lagoon using gravitational forces is proposed (see Figure 3).

Kamenjaca is a relatively small permanent surface stream with a flow rate between 24 and 47 l/s. Beside on the water quality it was categorized in the State registry as a ˝first class water˝. Extensive hydrogeological investigation have been performed in the downstream Gracenica and in Lonjsko polje that receives water from the stream Kamenjaca. Kamenjaca is a mountain watercourse being turbid during periods of intense precipitation and snow melting.

2. General data about the quarry • Intrusion of Moslavina granites in the older metamorphic complex has caused its

metasomatical alteration. In this manner few hundred meters to one kilometre wide

Protecting a Watercourse from Gneiss-Quarry caused Pollution 335

belt of heterogeneous and homogenous migmatites was formed. Gneiss that has a similar mineralogical composition as granite consists of approximately 45 % guartz, 40 to 45 % feldspars and 10 to 15 % mica. Some other silicates are also present in amounts lower than 1 percent. These compounds are mostly insoluble and do not present a threat to the quality of the water in stream (Braun, 1988).

• There are two quarries producing in the last 30 years approximately 100000 m3/year of gneiss stone classed in six marketable stone aggregate sizes. One quarry, Mikleuska I is on the left side and the other quarry, Mikleuska II is on the right of the watercourse. Excavation is oriented towards the gneiss massive and planned production level is between 90000 and 120000 m3 of the stone per year during the next 15 years.

• Owners of the quarry have constructed a 2 meter high concrete dam in stream channel at elevation of 155 m near the plateau of the Mikleuska I quarry. Wet beneficiation plant and other quarry structures were constructed near the dam to ensure continuous supply of technical water. Small natural spring at the elevation of 154 m has been captured to ensure availability of drinking water for employees of the quarry.

3. General information regarding pollution

Dissolved harmful compounds have not been detected in samples of rainfall water (that falls flows) and/or accumulates on the open excavation surfaces, nor in the water from the stream that was used in the wet beneficiation plant (Braun, 1988). To confirm this statement water samples were taken during the year 1998 and in January of 1999 from 3 various places in the watercourse, upstream and downstream from the quarry (see observation points 1, 2 and 3 in Figure 1).

• No increase in amount of suspended particles in water of the stream of Kamenjaca was noted when it was compared to the amount of suspended particles in the rainfall waters flowing over plowed land and forest roads. However, precipitated water that flows over surfaces in the quarry should be systematically collected in properly designed retention basins and its quality should be controlled before discharge into the stream.

• Large amounts of suspended stone particles are present in water that occasionally used for washing of the equipment and regularly for washing of finer stone fractions the process of wet beneficiation. Wet beneficiation plant uses 700 m3 of water from the dammed water course every working day continuously for 8 to 10 hours. Approximately same volume contaminated with small gneiss particles is returned to the stream a few meters downstream from the weir (see Figure 1).

• Environmental impact study for the quarry Mikleuska (Nuic, Zelenika et al., 1999) recommended excavation of useful substance at horizons with elevations between

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162 and 155 m in the Mikleuska I quarry and between 175 to 160 m in Mikleuska II quarry to endure efficient reclamation and more efficient use the present and final horizons of activity in the quarry. Excavation of gneiss at elevations lower than present working plateau in Mikleuska I would create an area for the sedimentation sumps and on lowest part of the quarry at elevations between 151.2 to 153.5 m as a lagoon for extended sedimentation of the smallest particles would be created. Sedimentation sumps would be transformed into recreational swimming pools and lagoon into the pond for fish farm.

4. Results of additional investigation

The unit for laboratory examination of Petrokemija d.d. in Kutina performed analysis of more than 30 physical, chemical and biological variables (Dzajo, 1999) in water samples taken from each observation point. Samples of the water that were taken were turbid and did not comply with the present state regulations for quality of a first class water due to the suspended load.

Data that were collected through the examinations of turbid water samples related to sedimentation of suspended solid particles at the laboratory of Geotechnical faculty in Varazdin (Levacic, Stuhec, 1999) are presented in the table 1. These data demonstrate that clearing of water with suspended gneiss particles can be achieved if the sample is immobile or in the conditions of laminar flow.

It was noted that clearing was fastest in a sample taken from the outlet of the wet beneficiation plant was transported in a shorter distance. Clearing was somewhat slower in the fresh sample taken 50 m downstream from the outlet and the slowest in the sample taken from the outlet that was transported for the longest time. Noted differences are probably caused by additional breakdown of bigger gneiss grains during transport in the container and stream. Large amount of serictised feldspars in the rock facilitates this crushing process. For this reason future location of sedimentation sumps should be as close to the wet beneficiation plant as possible. Table 1 Speed of settling of solid particles suspended in 1000 ml of water used in the wet beneficiation process

Volume of turbid and clear water ml Date of the sampling Components in the decanter 1 hour 3 hour 24 hour 48 hour

Coarse residue 100 120 120 120 Total residue 915 640 500 440

Outle Dec. 1998

Clear water 85 360 500 510 Coarse residue 80 80 80 80 Total residue 870 680 430 380

Outle Jan. 1998

Clear water 130 390 570 620 Coarse residue 15 15 15 15 Total residue 15 150 85 64,5

50 m down-stream Jan.

1999. Clear water 985 850 915 865

Protecting a Watercourse from Gneiss-Quarry caused Pollution 337

Data in table 1 indicate that a design of the sedimentation sump with appropriate dimensions for removal of suspended solids in justified. In the adequately designed, constructed and maintained sedimentation sumps it is possible to reduce amount of the suspended solids to the required concentration, as measured in samples of water that were taken upstream from the quarry.

Diagrams of granulometric composition of solids suspended in water samples that were taken on observation points 1 and 2 (see Figure 1) are shown in the Figure 2.

Figure 2 Diagrams of the granulometric composition of suspended solids 1 – Sample of water taken in December 1998. at observation point 1; 2 – Sample of mud water taken in Janury 1999. at obervation point 1;

3 – Sample of water taken at obervation point 2, (see Figure 1)

• As shown in the diagram 1 of Figure 2 granulometric composition of particles in the sample was sand 33,26 %, silt 55,80 % and clay 10,95 %. These values give a total of 133 grams (133 kg/m3) of dry matter per litre of suspension or 85 litre of residue per cubic meter of suspension.

• The effect of natural dissolution of the turbid water used in wet beneficiation plant can not prevent water quality in the small water stream. Turbid water used in wet beneficiation plant and for washing of the equipment should be treated in properly designed sedimentation sumps and gradually discharged in the water course. If finest particles of colloidal dimensions san not be removed, a special lagoon (pond) for deposition of the effluent that are discharged from sedimentation sumps should be designed. At the times when high concentration of colloidal particles are detected in the water is released from the lagoon the stream it should be diverted back into the wet beneficiation plant (see Figure 3). Such of lagoon water is especially convenient during periods of the low water discharge in the stream.

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338

5. Sedimentation sumps Release of contaminated water from the wet beneficiation plant to the stream Kamenjaca is the main threat to the water quality. The owner of the quarry is obliged to remove suspended solids from water used in production process. Market prices of quarry products are relatively low, and investments in the equipment for removal of solids are very high (desander, desilter, centrifuges, devices that use flocullators for acceleration of settling etc). Since there is available enough space for construction of an adequate sedimentation sump within the quarry, it has to considered as a possible solution for the pollution problem.

The level of the contaminated water in the wet beneficiation plant is higher than 155 m, and lowest horizon of the exploitation area downstream along the banks of the Kamenjaca has an elevation between 150.2 m and 152.6 m. The planned sedimentation sump should be situated between the elevation point 155.5 m near the wet beneficiation plant and the lowest part of the terrain with the elevations from 151,2 m to 152,5 m. The difference in height of 3.5 m (155.5 m – 152.0 m = 3,5 m) leaves enough space for a settlement zone and ensures gravitational flow of the water through the settlement zone to the lake (lagoon).

Besides size of suspended particles, sedimentation speed is also strongly influenced by the difference in the density between the fluid and suspended particles versus viscosity of the fluid (Linsley et al. 1992), as indicated in the Stokes formula for laminar flow of the fluid with suspended particles.

( )

µρρ

18dg

v2cc

t⋅−⋅

= (1)

where: = sedimentation speed of the given particle, m/s; tv g = gravity acceleration, m/s2;

cρ = density of the suspended particles, kg/m3; ρ =density of the fluid, kg/m3; = particle diameter, m; cd µ = dynamic viscosity of the suspension, Pas.

For a given inflow of water from the wet beneficiation plant smQ 320.0= , sedimentation sump height , and given time of retention in the sedimentation sump , it is possible to calculate area of the sump A, volume of the sump V, and flow velocity of particles passing through the sump in accordance with following equations:

oh sto 80.10=

ov

ooo thv = (2), QVto = (3), ohVA = (4), AQvo = (5)

Based on the above given parameters, and size of the rectangular horizontal sedimentation sump, values of other parameters can be calculated from equation given above.

3

o m21610800020,0tQV =⋅=⋅= (6) 3o m4325,0216hVA === (7)

Mikleuska quarry will be operating for relatively short time, and future use of sumps after ending of the stone exploitation is a very important issue. According to the Sport

Protecting a Watercourse from Gneiss-Quarry caused Pollution 339

encyclopedia (1977) typical standard sizes of swimming pool for a sport and recreational use are 25×18×2.2 m or 33.3320×2,2 or 50×25×2.2 m. Excavation of the sedimentation sump is technically and financially advantageous solution for quarry owner. It doesn´t require large investments and it can be performed in crude gneiss with the existing equipment. Sizes of sedimentation sumps are recommended similar to size of standard swimming pool to reduce future expenses associated with the change of the function.

The terrain owned by the quarry has a favourable configuration and size. It extends between the Kamenjaca stream and the wet beneficiation plant. Average content of suspended particles in water, desired frequency of residue removal and standard size of sport swimming pools had a decisive influence on size of the sedimentation sump.

Available space on the useful substance in quarry is large enough for a future sport swimming pool with standard size of 50×25×2.2 m and two smaller swimming pools with size of 25×18×2,2 m. The space on alluvial deposits will be used for a lagoon which can be later used for fish production. If two needed sedimentation sumps are placed in bigger swimming pool with an approximate volume of 2×(55×13×3.5) m can be rationally excavated. It would be divided into two parts with a 4 m wide barrier of the crude gneiss rock. Slotted pipes would be positioned on the bottom of each sump and covered with gravel of appropriate size and geotextile to ensure proper drainage, especially through the coarse deposits in the first ten meters long part of the sump. Verification of the length and width of sedimentation sump is, as follows:

(8) and length VlA o ⋅= m3,3313432wAlo === or 50 m (9)

sm00319,020,0130083,0AQv 11p =⋅== (10)

Following volume of residue can be deposited in such sedimentation sump:

(11) 3to m5,12378,11355hwlV =⋅⋅=⋅⋅=

of residue. Residue height is: mhhHh oct 10,32,02,05,3 =−−=−−= (12)

where: H = total depth of the excavation, m; = reduction of sump depth due to slotted pipes and gravel, m; = height of the weir into the sump, and could be regulated as needed, m; = width of the sump;

ch

oh

w A = surface; = length of each sump. ol

Laminar character of flow in the sedimentation sump with given size and velocity of the flow must be verified, since efficient sedimentation of suspended particles is possible only under laminar conditions. Reynolds equation of the laminar flow was used and value of Reynolds number was calculated, and compared with the value of 580, which is a critical value and indicated transition from laminar to the turbulent flow (Agroskin, 1969).

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340

criticaleReR R580344RvR =<=⋅

=ρµ

(13)

where: = average speed in the sump = 0,00319 m/s; = hydraulic radius, R=A/O=0,2 m; pv R

µ = viscosity of water with suspended particles =0,002 Pas; ρ =density of the water suspended particles =1080 kg/m3

Calculation above has confirmed laminar character of the flow since value of the Reynolds number was only 344. For this reason one sport swimming pool with standard size of 50×25×2.2 m with two sedimentation sump and two sport pools with size 25×18×2.2 m for the drying of the residua are proposed (see Figure 3).

Kop - QuarriMikleuška II

Kop - QuarriMikleuška I

Mokra separacijaWet separation

Kamenjača potokKamenjaca stream

Kamenjača potokKamenjaca stream

Mutna vodaMurky water

- Ocjedna voda iz taložnica i deponija- Drain water from sumps and sediment

gathering places

- Smjer optoka vode kroz mokru suspenziju- Direction of water through wet separation- Ventil - Valve

1

3

2

2

PS

Connection Channel

Lake

- Pumping station - Pumpna stanicaPS

- deponij za talog krupnog zrna- gathering place for coarser grains3

- deponij za talog sitnog zrna- gathering place for very fine grained sediment1 - Sedimentacijski bazen

- sedimentation basin2

Figure 3 Proposed solution of water circulation

The small lake (lagoon) with an area of approximately 10000 m2 positioned downstream from the sedimentation sump is proposed as an additional measure for protection of the Kamenjaca stream. The humus from the location of the future lagoon will be removed and used in the reclamation of the abandoned areas of the quarry. Absence of humus layer from the bottom of the lagoon may increase infiltration of the water into the alluvial aquifer and raise level of groundwater in wells located downstream from the quarry and in the village Mikleuška. Rise of the water table is an additional favourable effect of the proposed lagoon.

If quality of water on the outlet from the lagoon to the stream still raises some concerns among the ecologists, reuse of lagoon water into the wet beneficiation plant is recommended (see Figure 3).

Protecting a Watercourse from Gneiss-Quarry caused Pollution 341

Figure 3 shows locations of the sedimentation sump, the lagoon and the residua disposal area. Due to the expected segregation of particles in the sedimentation sump two depots for sediments are suggested. Sedimentation of the coarser grains that could be sold as a building material is expected on the first 10 to 15 meters of the sedimentation sump while accumulation of finer particles is expected in its remaining part. For this reason two disposal areas are planned for sun drying of the coarser grained and fine grained sediments. Coarse grained material will be sold as technical stone on the marker and fine grained fraction will be used to from a laminar water flow in the lagoon, filling of the holes in the quarry and for levelling of appropriate finalization planes in the quarry areas prior to their enrichment with humus and planting of plants.

Before its distribution to consumers, coarse-grained fraction will be additionally dried on a particularly designed disposal area and released water will be taken back the lagoon. Residue consisting of the smallest particles (mud) will be dried in appropriate pools. Installation of drainage devices in the pools, similar to the one in active sump is recommended.

Water in the lagoon will be directed towards the stream along an extended channel, which will be gradually formed from sediments of finest particles. Size of the channel should ensure laminar flow and efficient settling of the finest colloidal particles. After cessation of activity in the quarry, as was suggested in the study by Nuic, Zelenika, et. Al. (1999), sedimentation sump should be transformed into swimming pools of standard size and lagoon into a fish farm creating an economically favourable effect.

References Agroskin, I. I., Dmitrijev, G.T., pikalov, F. I. (1969): Hidraulika, Tehnička knjiga, prijevod na hrvatski jezik,

Građevinski fakultet, Zagreb. Baglama, I., Hanzec, A. , Zrinscak, B. (1999): Izvješće o rezultatima analize uzoraka vode iz potoka Kamenjača,

Petrokemija, Kutina. Braun, K. (1988): Eleborat o rudnim rezervama kamenoloma Mikleuška II. kraj Kutine, Geotehnički fakultet,

Varaždin. Dzajo, M. (1999): Izvješće o rezultatima analize uzoraka vode iz potoka Kamenjača, Petrokemija, Kutina. Levačić, E., Stuhec, B. (1999): Izvješće o rezultatima analize uzoraka vode iz potoka Kamenjača, Geotehnički

fakultet, Varaždin. Linsley, R. K., Francini, D.L. I dr. (1992): Water-Resources Engineering, McGraw-Hill international edition, Co-

Singapore. Nuic, J., Zelenika, M. i dr. (1999): Studija utjecaja na okoliš kamenoloma Mikleuška, Geotehnički fakultet,

Varaždin. Zelenika, M. (1998): Hidrološke prospekcije okoliša kamenoloma Mikleuška, Geotehnički fakultet, Varaždin. Sportska enciklopedija Leksikografskog zavoda ˝M Krkeža˝, Zagreb, knjiga 2, str. 82-83. Authors Mladen Zelenika: Faculty Civil Engineering Mostar, Bosnia and Herzegovina Jerko Nuić: Faculty of Mining and Petroleum Engineering, Zagreb, Croatia Božo Soldo: Geotechnical faculty, Varaždin, Croatia