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JV GC - WISUTEC
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p.a. GEOCONSULT ZT GmbH
CONSULTING ENGINEERS
DHMP-PIU
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Bishkek 720055
Kyrgyz Republic
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The Kyrgyz Republic:
Disaster Hazard Mitigation Project (DHMP), Component A
Relocation of TP3 and TP18 to TP6
Conception of the Cover Design for the
New Landfill on Tailings Pond 6
Chemnitz, April 2008
Authors:
U. Barnekow (WISUTEC GmbH / WISMUT GmbH)
M. Roscher (WISUTEC GmbH / WISMUT GmbH)
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Table of Contents
1 INTRODUCTION .......................................................................................................... 3
2 INPUT DATA FOR THE WATER BALANCE CALCULATIONS ................................................. 4
2.1 Geometry data .................................................................................................. 4
2.2 Climate data...................................................................................................... 4
2.3 Data of soil properties of the cover .................................................................... 5
2.4 Data for calculation of runoff ............................................................................. 5
2.5 Vegetation period data ...................................................................................... 5
3 PROPOSED COVER SYSTEM TO BE EVALUATED ............................................................ 6
4 HYDROLOGIC CALCULATIONS ..................................................................................... 7
5 RESULTS OF THE WATER BALANCE CALCULATIONS ....................................................... 8
5.1 Results for long-term state (Scenarios 30 and 40) ............................................ 8
5.2 Results for the dry period (scenario 31, 32 and 41, 42) ..................................... 8
5.3 Results for the wet period (scenario 33, 34 and 43, 44) .................................... 9
6 CONCLUSIONS REGARDING THE CONCEPTION OF THE COVER DESIGN ..........................10
7 REFERENCES ...........................................................................................................11
List of Annexes
Annex 1:
Table 1: Results of HELP-modelling of the cover designed for the new landfill on
TP 6
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1 Introduction
The Disaster Hazard Mitigation Project – Component A encloses, among other remedial
activities, the relocation of up to approximately 130,000 m3 tailings, radioactively
contaminated soils and mine wastes from tailings pond no. 3 (TP 3) and in addition
approximately 5,000 m3 of tailings, subsoil and mine wastes from tailings pond no. 18 (TP
18) to tailings pond no. 6 (TP 6). The relocated materials shall be disposed into a new landfill
planned to be constructed on TP 6.
The tailings, radioactively contaminated soils and mine wastes disposed in the new landfill
must be covered by a proper surface cover system. The preferable cover system was
evaluated in [1]. Resulting from this evaluation no specific functional requirement was
derived with respect to the acceptable maximum percolation rate through the surface cover
of the new landfill on TP 6. The surface cover must avoid any contact or direct access to the
wastes for people and animals. In addition the cover system is to reduce radon exhalation
rate to an acceptable value. Therefore it was proposed in [1] to evaluate the functionality of a
cost-effective store-and-release-cover (SRC). The use of such a store-and-release cover is
supported by the fact, that with respect to the environmental impact of the new landfill on TP
6 the water pathway was identified in [1] to be of minor concern.
The functionality of a store-and-release cover depends on the geometry of the landfill, the
soil properties of the cover layer and of the underlying layers and on the climate of the
location. The day-to-day water balance of different cover designs were modelled and
evaluated in [2].
This report presents the conception of the cover design for the new landfill on TP 6. As part
of the conception this report presents the results of the water balance calculations applying
the HELP modelling tool (German version 3.80). The model results are used to derive the
design conception for the cover system as a basis for the cover design of the new landfill on
TP 6 presented with [3].
The water balance of a cover system was calculated for the plateau area of the new landfill
inclined ca. 11% and for dam slope area of the new landfill inclined at least 40%.
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2 Input data for the water balance calculations
The HELP-model needs consistent and complete data sets to model the day-to-day water
balance of the soil layers. The required datasets are listed below:
1. Geometry/design data of the landfill site (area of the landfill site, slope
inclination of plateau and dam slope surfaces, slope length, design of the
cover system, "curve number value" (CN-value) for calculation of the runoff
applying the SCS-method
2. Climate data (precipitation, air temperature, wind speed, humidity, solar
radiation)
3. Soil physical properties (porosity, field capacity, plant-available field
capacity, hydraulic conductivity)
4. Vegetation data (growing season start and end day, maximum leaf area
index, evaporative zone depth)
2.1
Geometry data
The geometry of the new landfill surface area was implemented from [3]. The transverse
slope inclination of the plateau surface is 5%. The longitudinal slope inclination of the plateau
surface is ca. 13%. Consequently the resulting slope is approx. 11%. The average slope
length of the plateau surface was estimated to be 115 m. The plateau area covers 2.0
hectare. The slope inclination of the dam slope area is 40%. The average slope length of the
dam was estimated to be 50 m. The dam slope area covers nearly 0.85 hectare. The entire
cover surface of the new landfill on TP 6 encloses nearly 2,85 hectare.
2.2
Climate data
Climate data for the region of Mailuu Suu were not available. Therefore the data of the
nearest weather station located in Jalal-Abad were used. This weather station is located on a
similar altitude like Mailuu-Suu. Like Mailuu-Suu Jalal-Abad is located at the northeastern
border of the Fergana valley. Therefore the climate data of both locations can be estimated
to be comparable.
The following climate data of this weather station have been available for the period 20012005 as listed below:
-
daily sums of precipitation
-
daily average values of the air temperature
-
daily average values of the wind speed
-
monthly average values of the humidity.
No data have been available regarding the solar radiation. Therefore the solar radiation data
were estimated based on climate data of a comparable climate station at a similar latitude
like the latitude of Mailuu Suu. Finally the solar radiation data used for the HELP-modelling
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were generated based on the measured daily sums of precipitation for Jalal-Abad and on the
climate data of the meteorological station in Northplatte, USA.
In addition the measured period of available climate data for Jalal-Abad is very short.
Therefore the applicability of the results of the water balance modelling applying HELP must
be seen to be limited. Usually the series of climate data used for such water balance
calculations shall enclose a period of at least 20 years.
Therefore the available short climate data series available from the meteorological station at
Jalal-Abad for the period of 2001 till 2005 were added to series of 20 years. The
implementation of such added data rows allowed to get results of the HELP-modelling
applicable for cover designing.
2.3
Data of soil properties of the cover
Soil data of the cover material were taken directly from the available data or derived based
on the available soil property data. In addition soil samples were taken from different
locations in the area of Mailuu Suu to get data from the potential cover material for the new
landfill on TP 6. The soil samples were analyzed to estimate the soil type and soil properties
of the available cover material.
Potential cover material is located near TP 6 and can be classified in average as a clayey silt
soil. The soil parameters of this potential cover material depends on the bulk density of the
soil after placement of the respective surface cover. The bulk density immediately after the
construction change with time to the long term. Therefore both scenarios were modelled the
short term state immediately after construction and the long term state of the cover. The
physical soil properties used for both scenarios are shown in table 1 (Annex 1).
2.4
Data for calculation of runoff
The HELP-model needs a curve number value for the calculation of the runoff. The cover soil
curve number values ("CN-values") for the calculations were estimated based on experience
from HELP-modelling on other sites. The CN-values of the cover from TP 6 depends on the
type of use and the surface slope. For the calculations on the plateau surface we used a CNvalue of 80,9. On the dam surface we implemented a CN-value of 82,3.
2.5
Vegetation period data
The growing season's start and end day could be determined with respect to the air
temperature. As a boundary condition the first day of a year with an air temperature above
0°C was the first day of the growing season (here: February, 24th). The last day of the year
with an air temperature below 0°C was the end of the growing season (November, 27th).
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3 Proposed cover system to be evaluated
Resulting from the evaluation of different cover systems we proposed a preliminary cover
design for the plateau area and for the dam slope area with [2].
Resulting from the evaluation of the climate data (heavy precipitation rates) and of the soil
data of the available cover materials we concluded in [2] that it is necessary to additionally
plan for erosion protection measures on top of the proposed surface cover system of the new
landfill on TP 6. We recommend herewith to build an erosion protection layer on the top of
the store-and-release cover on both the plateau area and the dam slope area. This layer
shall be 50 cm thick. It shall consist of a mixture of coarse-grained gravel-pebble material
and fine-grained material. The sizing of proper coarse- and fine-grained materials depend on
the slope inclination.
The erosion protection layer is underlain by the store-and-release cover proposed with [2].
The required minimum thicknesses of this store-and-release cover were evaluated in [2]. The
results of the calculations presented with [2] were used to optimize the design for the cover
system on the plateau surface and the dam slope. Resulting from [2] and implementing the
required erosion protection layer presented above the day-to-day water balance of the
following cover designs were calculated in this report:
Plateau surface:
On the plateau surface we calculated the day-to-day water balance of a cover with a total
thickness of 2.0 m.
The upper 50 cm will be built as an erosion protection layer consisting of 50% of coarsegrained material (gravel-pebble mixture 80/150) and 50% of sandy-loamy soil.
Under the erosion protection layer we propose to place a 150 cm thick store-and-release
layer.
In order to avoid any relevant upward pore water flow during long dry periods of intensive
evapotranspiration we recommend to compact the lower 50 cm thick part of this layer.
Dam slopes:
On the dam slopes we calculated the day-to-day water balance of a cover of in total 1.5 m
thickness.
The upper 50 cm layer of the cover shall be an erosion protection layer. The amount of
coarse-grained material (gravel-pebble mixture) of this layer should be 50%, the amount of
sandy loamy soil shall be about 50%.
The erosion protection layer shall be underlain by a single 1.0 m thick storage layer. This
layer shall not be compacted.
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4 Hydrologic calculations
The day-to-day water balance was calculated applying the HELP-model for the two cover
designs presented with chpt. 3. Only the climate data (dry period, wet period, 20 years
period) and the soil properties (short term state immediately after construction and long term
state) were modified for the different scenarios.
At first we calculated the day-to-day water balance for the two types of the cover design for a
period of 20 years. Because of the available short data series the values of Jalal-Abad for the
period of 2001 till 2005 were added to series of 20 years (chapter 2.2). The soil properties of
the different layers are depending on the bulk density in situ. Therefore we implemented the
bulk density immediately after construction phase for the first five years of the calculation.
The soil properties for a the bulk density in the estimated long-term state were used starting
from the 6th year of calculation till the end.
Scenario 30 and 40 represent the water balance calculation of the cover on the plateau
surface and the dam slope area for a period of 20 years.
Secondly we calculated the day-to-day water balance for a dry period. This dry period is an
estimation with respect to the driest year of the period 2001 to 2005. The driest year 2001
was added to five years period. The day-to-day water balance of the cover was calculated for
such a dry period implementing the soil properties for both scenarios the state immediately
after the construction and the long-term state. Scenario 31, 32 and 41, 42 represent the
water balance calculations of the cover on the plateau surface and the dam slope for the dry
period.
At last we calculated the day-to-day water balance for a wet period. This wet period is an
estimation with respect to the wettest year of the period 2001 to 2005. The wettest year 2003
was added to five years period. The day-to-day water balance of the cover was calculated for
such a wet period implementing the soil properties for both scenarios the state immediately
after the construction and the long-term state. Scenario 33, 34 and 43, 44 represent the
water balance calculations of the cover on the plateau surface and the dam slope for the wet
period.
The detailed input data used for the hydrologic calculations are shown in table 1 (Annex 1).
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5 Results of the water balance calculations
The modelling results for all scenarios are listed in detail in table 1 (Annex 1).
5.1
Results for long-term state (Scenarios 30 and 40)
Scenario 30 and 40 include the hydrologic calculations of the cover for the period of 20
years.
Table 1 (Annex 1) shows that on the plateau surface (scenario 30) the percolation through
the cover has been calculated to be around 31 percent of the annual precipitation rate. Most
of the remaining 65 percent of the annual precipitation rate will evaporate. Only a little part of
the precipitation will run off on the surface (ca. 4%). The change in water storage of the cover
layer is nearly constant for this scenario.
Sceanrio 40 represents the designed cover on the dam slope. According to the steeper slope
the runoff rate on the dam slope is calculated to be 10% of the precipitation rate. Only 57
percent of the annual precipitation rate evaporate. The percolation rate slightly increases on
the dam surface by 2 percent. The reason for this increment is the lacking lowest compacted
layer and the permeable dam body underlying the cover.
The calculation results of these scenarios can be seen as representative for the two different
cover designs. With regrad to the climate data we determined a percolation rate of about
30% of the annual precipitation rate. This percolation rate is acceptable because no specific
requirements regarding the maximum percolation rate are needed acc. to [1].
5.2
Results for the dry period (scenario 31, 32 and 41, 42)
Scenario 31 and 41 include the hydrologic calculations of the cover for the dry period for
both the plateau surface and the dam slope area with respect to the short term state
immediately after construction.
Scenario 32 and 42 include the hydrologic calculations of the cover for the dry period for
both the plateau surface and the dam slope area with respect to the long term state.
Both the calculation for plateau surface and the calculation for the dam slope area show
comparable results. During the period after construction the annual runoff will be larger than
for the long-term state for both areas. On the plateau surface the runoff was calculated to be
13% and on the dam slope area 33% of the annual precipitation rate for the state after
construction. For the long-term state the runoff will decrease to 1%…2% for both the cover
on the plateau area and on the dam slope area.
The time-dependent development of the evapotranspiration rate also depends on the bulk
density of the cover material. Immediately after construction phase the evaporation rate was
calculated to be 60% of the annual precipitation rate on the plateau area and 48% of the
annual precipitation rate on the dam slope area. In the long-term state the evapotranspiration
rate will increase to 66 or 56 percent respectively.
The percolation rate will increase from the short-term to the long-term state on both areas.
Especially on the dam slope area the percolation rate will increase significantly in the long-
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term state (46% of the annual precipitation rate). The reason is the estimated increase of the
hydraulic conductivity of the cover material to the long term.
The HELP-modeling shows that the during the summer months of the dry period the water
content of the evaporative zone of the cover system will be near the welting point. This could
result in temporary stress for the vegetation on the cover system. Therefore the cover is to
be vegetated by seeding sorts of grass adopted to the regional climate conditions.
5.3
Results for the wet period (scenario 33, 34 and 43, 44)
Scenario 33 and 43 include the hydrologic calculations of the cover for the wet period for
both the plateau surface and the dam slope area with respect to the short term state
immediately after construction.
Scenario 34 and 44 include the hydrologic calculations of the cover for the wet period for
both the plateau surface and the dam slope area with respect to the long term state.
The results for scenario 33 and 34 presented with table 1 (Annex 1) show evapotranspiration
rates of 57% and 59% of the annual precipitation rate. The time dependent development of
the runoff on the plateau surface for the wet period is comparable with scenario 31 and 32.
On the plateau surface the annual runoff reduces from 11% immediately after construction to
2% of the annual precipitation rate in the long term state. According to the decreasing runoff
the percolation rate is increased from the construction state till the long-term state on the
plateau surface by 6%.
The results for scenario 43 and 44 presented with table 1 (Annex 1) show an
evapotranspiration rate of 51% and 55% of the annual precipitation rate. The runoff and the
percolation rate are the only two parameters that will change time dependently to the long
term. The runoff decreases from the construction state to the long-term state from 40 to 1
percent of the annual precipitation rate. The percolation rate will increase at comparable
values because of increas of the hydraulic conductivity for the cover material to the long
term.
The HELP-modeling shows that the during the summer months of the wet period the water
content of the evaporative zone of the cover system will be near the welting point, particularly
from June till September. This could result in temporary stress for the vegetation on the
cover system. Therefore the cover is to be vegetated by seeding sorts of grass adopted to
the regional climate conditions.
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6 Conclusions regarding the conception of the cover design
The water balance of the evaluated cover system of the new landfill on TP 6 depends on
different factors:

The climate in the area of Maillu Suu is very variable. During winter and spring the
average monthly precipitation rate is quite high. During the summer months (June till
September) the average monthly precipitation rate is very low. In average a
precipitation sum from June till September is only 30 mm. This could result in
temporary stress for the vegetation on the cover system. Therefore the cover is to be
vegetated by seeding sorts of grass adopted to the regional climate conditions.

The time dependent development of the bulk density of the cover material from the
stage immediately after construction to the long term significantly influences the water
balance of the surface cover. Immediately after the construction of the cover system
the bulk density is quite high. With time the bulk density will decrease due to rooting,
weathering and bioturbation. The decrease of the bulk density leads to an increase of
hydraulic conductivity thus increasing the percolation rate to the long term.
Resulting from the hydrologic calculations we conclude that the evaluated cover design
conceptions presented with chpt. 3 meet the requirements of the surface cover as defined in
[1]. The conceptions of the cover designs are presented below:
Plateau surface:
On the plateau surface we propose a cover with a total thickness of 2.0 m consisting of (from
top to bottom):

a 50 cm thick erosion protection layer consisting of a mixture of 50% coarse-grained
gravel-pebble mixture (sizing 80/150 mm) material and 50% sandy-loamy soil.

a 150 cm thick store-and-release layer. During construction phase the 150 cm
storage-and-release layer shall be build by placing three layers of ca. 50 cm each. In
order to avoid any relevant upward pore water flow during long dry periods of
intensive evapotranspiration we recommend to compact the lowest 50 cm thick
sublayer.
In addition, erosion protection measures have to be planned as part of the design phase with
respect to the short term (initial phase after construction) and to the long term (after
vegetation will have developed).
Dam slopes:
On the dam slope area we propose to construct a cover with a total thickness of 1.5 m
consisting of (from top to bottom):

a 50 cm thick erosion protection layer consisting of a mixture of coarse-grained
(gravel-pebble mixture) material and fine-grained material. The coarse-grained
material (gravel-pebble mixture: 80/150 mm) should be 50% as well as the sandyloamy soil.
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
a 100 cm thick store-and-release layer. With regard to hydrological aspects a certain
compaction degree of the storage layer is not specified. We recommend to compact
the layer by at least 2 passes of the dozer everywhere to achieve sufficient ersosional
stability.
Before placing the SR-layer an at least 0.75 m thick layer consisting of coarse-grained waste
dump materials shall be placed in the upper part of the dam body. If possible the entire dam
body should be built of coarse-grained waste dump material.
As part of the design further erosion protection measures, like i.e. ditches, must be planned
for to avoid unacceptable erosion of the cover surface.
7 References
[]
[2]
[3]
JV GC – WISUTEC: The Kyrgyz Republic: Disaster Hazard Mitigation Project
(DHMP), Component A. Feasibility study - Remediation of Tailings Pond # 3
(Subcomponent A6), September 2006.
WISUTEC GmbH / WISMUT GmbH: The Kyrgyz Republic: Disaster Hazard
Mitigation Project (DHMP), Component A: Evaluation of Cover Designs for
the Landfill to be constructed on Tailings Pond 6 - Design Principles for Store
& Release Cover (SRC).- Chemnitz, January 2007
JV GC – WISUTEC: Kyrgyz Republic: Disaster Hazard Mitigation Project
(DHMP); Relocation of TP 03 and TP 18 material to TP 06, Working Design,
Explanatory Notes, November 2007