A 24-acre land at Aboso serves as the site where municipal solid waste from Tarkwa and its environs are openly dumped. Evaluation of the suitability of this existing landfill site for the construction of an engineered landfill was determined. Reconnaissance survey, structural mapping, determination of depth to groundwater, geotechnical site investigation as well as socio-economic indicators showed that the existing landfill site is not suitable for an engineered landfill construction. A multi-criteria GIS model was used to select an alternative suitable area for the construction of an engineered landfill. The multicriteria GIS modelling identified fourteen (14) suitable areas for the siting of landfill in the Tarkwa area. A site located in Domeabra was chosen due to its proximity to the neighbouring communities of Tarkwa, Nsuta and Aboso. The suitability of the proposed site in Domeabra was assessed using geotechnical and geophysical methods. The geotechnical methods included the testing of soil properties such as moisture content, particle size distribution, Atterberg limit, bulk density, specific gravity, and compactibility. The soils at Domeabra site are predominantly gravel and sand, well graded with gradual increase in clay content with depth and good moisture content (less than 30%). The gravel and sandy soils have good to excellent shear strength and work ability. The soils in Domeabra have suitable dry density (1.3 - 2.1 Mg/m 3), bulk density (1.7 - 2.5 Mg/m 3) and specific gravity (2.2 - 2.9) for landfill construction. The geophysical method involved the use of seismic refraction tomography. The geophysical survey showed that the site is made up of four layers namely the top soil (0.5 - 2 m), weathered material (5 - 15 m), saturated material (10 - 15 m) and fresh rock. The water table occurs at a depth of 12 to 15 m. The proposed area in Domeabra based on the geophysical and geotechnical investigations is suitable for the construction of engineered landfill.
Waste generation is on the ascendancy in both developing and developed countries. With increase in the global population and the rising demand for food and other essentials, there has been a rise in the amount of waste being generated daily by each household [
In Ghana, waste disposal and location of landfills are a major problem. Typically, most urban landscapes are characterised by mountains of uncollected garbage, gutters choked with waste, open reservoirs that appear to be a little more than toxic pools of liquid waste and beaches strewn with plastic garbage [
The Ghana landfill guidelines published by the EPA is an attempt to promote and help upgrade landfills, initially by improving site selection, waste compaction and drainage resulting in high density aerobic landfills and culminating in achieving operation of sanitary landfills by 2020. However, slow this process might be, there is evidence to show that progress is being made to achieve these targets [
Currently, there is no engineered landfill site for the waste generated in Tarkwa, Nsuta, Aboso and Domeabra; however, there is an existing open landfill serving Tarkwa and its environs at Aboso (
The EPA [
Identifying suitable landfill sites is very difficult since one must consider the future effect of the waste on the environment, meeting regulatory standards as
Criteria | Buffer Zone | Reason for Buffer Distance |
---|---|---|
Wetlands | 500 m | To help prevent the creation of breeding grounds for insects like mosquitoes which transmits the malaria parasite |
Roads | 300 m | To prevent expensive cost of constructing connecting roads to the landfill site |
Railway | 300 m | To prevent the habitants from being involved in any accident which can be caused by the train as they go out to dump their waste |
Built-up areas | 300 m | To help minimise the health hazards caused by landfills on inhabitants |
Surface water | 300 m | To prevent leachate seeping in the surface water |
Modified after EPA [
well as geophysical, geotechnical and other parameters. This study seeks to determine a suitable landfill site for Tarkwa and its environs using multi-criteria GIS, Geophysical and Geotechnical evaluation approach.
The study area consisted of Tarkwa, Nsuta, Aboso and Domeabra as shown in
There are mainly two types of soil in the Tarkwa-Prestea area, the forest oxysols in the south and the forest ochrosol-oxysol integrates in the north [
The study area (
The Birimian rocks fall within Paleoproterozoic terrane which is characterised by narrow sedimentary basins and a dominantly linear arcuate bimodal volcanic and volcano-sedimentary with mostly felsic to intermediate protolith [
The term “Birimian” was introduced by Kitson [
The Birimian and Tarkwaian rocks that underlie the area are largely crystalline and inherently impermeable, unless fractured or weathered. Groundwater occurrence is therefore attributed with the development of secondary permeability and porosity. According to Kortatsi [
The weathered zone aquifer is generally phreatic, and the principal groundwater flow occurs where relic’ s quartz veins are more abundant. The regolith is generally dominated by clay and silt, rendering the aquifer highly porous, with high storage, but low permeability. Thus, the aquifers here are either un-confined or semi-confined, depending on the clay and silt proportion. Aquifers are recharged by direct infiltration of precipitation through brecciated zones and the weathered outcrop [
A site visit was undertaken to ascertain the current state of the existing open landfill at Aboso. During the visit, the factors such as the topography of the study area, closeness of the landfill to surface waters, settlement and general accessibility of the site were studied.
Geographic Information Systems (GIS) has proven to be a useful tool in site selection, thus, over the years many researchers have employed GIS in landfill site selection [
Multi-Criteria Evaluation (MCE) is used to deal with the difficulties that decision makers encounter in handling large amounts of complex information [
The flow chart in
Secondary data from Ghana Geological Survey was used for this research. They included boundary, road, surface water, wetlands, railway and built-up areas shapefiles of Tarkwa and its environs. The data was processed using ArcGIS platform. The buffer zones were created based on the concept of proximity using EPA guideline for landfill in
from the buffer generation were vector-based data. The vector-based data were converted to raster-based data before they were reclassified. The binary model approach was used to reclassify all raster-based maps. The Boolean approach was used to the overlay the individual criterion binary maps to generate a final suitability map. The Boolean expression contains two operands and one logical operator. In the expression (Wetlands) = 1, wetlands and 1 are the operands and “=” is the logic operator. Five expressions ((Wetlands) = 1 (Roads) = 1 (Railway) = 1 (Built-up areas) = 1 (Surface water) = 1) have been developed from the five criteria considered. In merging the expressions, the Boolean AND connector was used to separate the cells that satisfies suitability.
Seismic-refraction methods measure the time taken for compressional sound wave generated by a sound source to travel down through the subsurface and back up to detectors (geophones) placed on the land surface. The field data acquired consist of measured geophone distances and seismic travel times. From the time-distance information, depths and velocity variations to individual layers can be calculated and modelled [
In the study area, geophysical data was gathered using Geometric ES-3000 Seismodule Controller with a 12-channel seismograph. Four (4) seismic refraction profiles were randomly acquired across the study area. Nine (9) offsets were carried out over each profile line, to have maximum coverage of the subsurface for the tomographic analysis. Stack of three (3) shots were used at various shot locations on a profile to minimize background noise effect and to increase signal to noise ratio. A sampling rate of 62.50 µs with recording length of 0.25s was used. Additionally, a low-cut filter of 15 Hz was used to filter noise frequency from traffic and a notch filter of 60 Hz was used to filter frequency noise from power lines.
Data processing started with the picking of the first arrivals using Pickwinsoftware. The next step was to use Plotrefasoftware to assign layers to the various traveltimes. After the layer assignment, an initial velocity model was estimated using Time-term inversion. In this case, two types of inversions, namely time-term inversion and, tomographic inversion, must be performed. The time-term inversion was used to generate the initial velocity model. The depths to the top of the underlying layers are calculated under each point on the traveltime versus offset distance plot. 2D subsurface Seismic Refraction Tomography (SRT) model for the various profiles were generated using tomographic inversion method.
After the initial velocity model, a tomographic inversion was generated after some number of iterations were completed. After each iteration, ray tracing was initiated. The ray tracing produced a calculated travel time curve. The difference between the calculated and the observed travel times is referred to as the Root Mean Square (RMS) error; the smaller the RMS error, the higher the accuracy of the data. The iterations for the tomographic inversions were stopped when the RMS error reduced to a minimum value, i.e. where further iterations results in no change in the RMS error.
According to Sukiman [
Both field and laboratory tests were undertaken to obtain data for the research. The field work involved visit to the site and sampling. This was followed by laboratory tests to establish the engineering properties of the soil. Laboratory equipment and materials at the soil and rock laboratory of the University of Mines and Technology Tarkwa were used for the laboratory works. These included the Cassagrande apparatus, sieves, wax, mould, hammer, and moisture cans.
The field work involved visits to the study area to take samples for the laboratory work. Other relevant information that was obtained during the field work was the topography and drainage of the area, nature and condition of the soil present. The samples were taken from eight different points (
K = C H ∗ ( D 10 ) 2 (1)
where:
CH = Empirical constant (0.01157)
D10 = the particle size for which 10% of the material is finer (mm)
Buffer maps (
The final suitability map (
The results of the seismic tomographic sections are shown in
area coupled with the velocity gradient from the tomographic inversion as stated by Raghava et al. [
The moisture content test was conducted for the in-situ soil samples. A known mass of each sample for each hole was oven dried and the dried mass of the samples were determined. The moisture content was determined as follows:
Moisture content ( % ) = ( In-situMass-DriedMass ) / DriedMass (2)
The average moisture content (
The specific gravity (
The bulk density (
The Plastic Index (PI) ranges from 3.49% to 27.9%, Liquid Limit (LL) from 37.4% to 59.62% and PL from 31.6% to 36.2% as shown in
The Maximum Dry Density (MDD) ranges from 1.81 g/m3 to 2.12 g/m3 for all the samples at depth 2 m to 3 m as in
The hydraulic conductivity (
The multicriteria GIS modelling generated suitable and unsuitable areas for the construction of an engineered landfill. The suitable areas are those which are beyond 500 m buffer distance and the unsuitable areas below the 500 m buffer distance. The suitability map (
From the Seismic Refraction Tomography (SRT) analysis, it can be inferred that the subsurface is made up of four layers. The first layer is the top soil with thickness ranging from 0.5 m to 2 m. The second layer is the weathered or loose material with thickness ranging from 5 m to 15 m. The third layer is the saturated material with a thickness ranging from 10 m to 15 m. The fourth layer is the fresh bedrock which is vertically extensive.
The moisture content values indicate that the area has good moisture content depicting well drained soils. Das [
Profile | Velocity (m/s) | Average thickness (m) | Layer Description |
---|---|---|---|
SD 1 | 300 - 500 | 0.5 | Dry Sand |
600 - 1250 | 15 | Fractured/Loose Material | |
1500 - 2400 | 10 | Saturated Material | |
2700 - 3000 | - | Fresh | |
SD 2 | 300 - 500 | 0.5 | Dry Sand |
600 - 1250 | 7 | Loose/Fractured Material | |
1500 - 2400 | 12 | Saturated Material | |
2700 - 3000 | - | Fresh | |
SD 3 | 300 - 500 | 1 | Dry Sand |
600 - 1250 | 8 | Loose/Fractured Material | |
1450 - 1850 | 10 | Saturated Material | |
2000 - 3000 | - | Fresh | |
SD 4 | 300 - 500 | 2 | Dry Sand |
600 - 1250 | 5 | Loose/fractured Material | |
1450 - 2400 | 10 | Saturated Material | |
2700 - 3000 | Fresh |
Sample ID | Depth (m) | Moisture Content |
---|---|---|
SP01 | 0.0 - 1.0 | 14.36 |
1.0 - 2.0 | 16.75 | |
2.0 - 3.0 | 20.44 | |
SP02 | 0.0 - 1.0 | 11.98 |
1.0 - 2.0 | 14.36 | |
2.0 - 3.0 | 17.44 | |
SP03 | 0.0 - 1.0 | 13.96 |
SP04 | 0.0 - 1.0 | 12.61 |
1.0 - 2.0 | 21.46 | |
2.0 - 3.0 | 25.57 | |
SP05 | 0.0 - 1.0 | 17.15 |
1.0 - 2.0 | 22.7 | |
SP06 | 0.0 - 1.0 | 21.46 |
1.0 - 2.0 | 25.57 | |
2.0 - 3.0 | 27.82 | |
SP07 | 0.0 - 1.0 | 18.34 |
1.0 - 2.0 | 21.5 | |
2.0 - 3.0 | 24.31 | |
SP08 | 0.0 - 1.0 | 30.72 |
1.0 - 2.0 | 37.15 |
Sample ID | Depth | Cu | Grading | % Gravel | % Sand | % Silt | % Clay |
---|---|---|---|---|---|---|---|
SP01 | 0.0 - 1.0 | 6 | Well graded | 30.89 | 64.82 | 3.89 | 0.4 |
1.0 - 2.0 | 5 | Uniformly graded | 42.3 | 54.31 | 2.96 | 0.43 | |
2.0 - 3.0 | 6 | Well graded | 42.33 | 51.13 | 5.94 | 0.6 | |
SP02 | 1.0 - 2.0 | 5 | Uniformly graded | 44.1 | 52.13 | 3.6 | 0.17 |
2.0 - 3.0 | 6 | Well graded | 38.84 | 54.49 | 2.4 | 4.27 | |
SP04 | 1.0 - 2.0 | 6 | Well graded | 36.11 | 61.67 | 2 | 0.22 |
2.0 - 3.0 | 6 | Well graded | 45.36 | 42.87 | 1.9 | 9.87 | |
SP05 | 1.0 - 2.0 | 6 | Well graded | 37.64 | 59.02 | 3 | 0.34 |
SP06 | 1.0 - 2.0 | 6 | Well graded | 37.64 | 52.4 | 1.66 | 8.3 |
2.0 - 3.0 | 6 | Well graded | 47.73 | 37.29 | 4.72 | 10.26 | |
SP07 | 1.0 - 2.0 | 6 | Well graded | 36.01 | 53.52 | 0.4 | 10.07 |
2.0 - 3.0 | 6 | Well graded | 44.72 | 41.29 | 2.26 | 11.73 | |
SP08 | 1.0 - 2.0 | 6 | Well graded | 42.6 | 54.46 | 1.44 | 1.5 |
2.0 - 3.0 | 6 | Well graded | 30.5 | 35.13 | 21.8 | 12.57 |
Cu is coefficient of uniformity.
Sample ID | Depth (m) | Average Specific Gravity |
---|---|---|
SP01 | 0.0 - 1.0 | 2.51 |
1.0 - 2.0 | 2.41 | |
2.0 - 3.0 | 2.6 | |
SP02 | 0.0 - 1.0 | 2.41 |
1.0 - 2.0 | 2.29 | |
2.0 - 3.0 | 2.67 | |
SP03 | 0.0 - 1.0 | 2.4 |
SP04 | 0.0 - 1.0 | 2.41 |
1.0 - 2.0 | 2.61 | |
2.0 - 3.0 | 2.85 | |
SP05 | 0.0 - 1.0 | 2.38 |
1.0 - 2.0 | 2.5 | |
SP06 | 0.0 - 1.0 | 2.85 |
1.0 - 2.0 | 2.52 | |
2.0 - 3.0 | 2.34 | |
SP07 | 0.0 - 1.0 | 2.73 |
1.0 - 2.0 | 2.44 | |
2.0 - 3.0 | 2.43 | |
SP08 | 0.0 - 1.0 | 2.53 |
1.0 - 2.0 | 2.4 | |
2.0 - 3.0 | 2.38 |
Sample ID | Depth (m) | Bulk Density (Mg/m3) | Dry Density (Mg/m3) |
---|---|---|---|
SP01 | 0.0 - 1.0 | 2.015 | 2.004 |
1.0 - 2.0 | 2.286 | 2.036 | |
2.0 - 3.0 | 1.868 | 1.633 | |
SP02 | 0.0 - 1.0 | 2 | 1.986 |
1.0 - 2.0 | 2.15 | 2.138 | |
2.0 - 3.0 | 2.452 | 2.072 | |
SP03 | 0.0 - 1.0 | 1.862 | 1.654 |
SP04 | 0.0 - 1.0 | 2.219 | 1.872 |
1.0 - 2.0 | 2.232 | 2.001 | |
2.0 - 3.0 | 2.44 | 2.112 | |
SP05 | 0.0 - 1.0 | 2.085 | 2.075 |
1.0 - 2.0 | 2.404 | 2.102 | |
SP06 | 0.0 - 1.0 | 2.327 | 1.826 |
1.0 - 2.0 | 2.219 | 1.826 | |
2.0 - 3.0 | 1.708 | 1.398 | |
SP07 | 0.0 - 1.0 | 2.204 | 1.883 |
1.0 - 2.0 | 2 | 1.986 | |
2.0 - 3.0 | 2.016 | 2 | |
SP08 | 0.0 - 1.0 | 1.956 | 1.594 |
1.0 - 2.0 | 2.05 | 1.495 | |
2.0 - 3.0 | 2.052 | 1.416 |
Sample ID | Depth (m) | Liquid Limit % | Plastic Limit % | Plastic Index % |
---|---|---|---|---|
SP01 | 1.0 - 2.0 | 38.94 | 34.9 | 4.04 |
2.0 - 3.0 | 49.7 | 35.1 | 14.6 | |
SP02 | 1.0 - 2.0 | 37.4 | 33.91 | 3.49 |
2.0 - 3.0 | 46.21 | 33.97 | 12.24 | |
SP04 | 1.0 - 2.0 | 35.95 | 31.6 | 4.35 |
2.0 - 3.0 | 46.27 | 36.9 | 9.37 | |
SP05 | 1.0 - 2.0 | 39.2 | 33.6 | 5.6 |
SP06 | 1.0 - 2.0 | 42.92 | 31.9 | 11.02 |
2.0 - 3.0 | 48.39 | 30.6 | 17.79 | |
SP07 | 1.0 - 2.0 | 51.92 | 36.2 | 15.72 |
2.0 - 3.0 | 59.62 | 32.5 | 27.12 | |
SP08 | 1.0 - 2.0 | 42 | 33.54 | 8.46 |
2.0 - 3.0 | 62.8 | 34.9 | 27.9 |
Sample ID | Depth (m) | Maximum Dry Density (MDD) (g/m3) | Optimum Moisture Content (OMC) (%) |
---|---|---|---|
SP01 | 1.0 - 2.0 | 1.98 | 21.7 |
2.0 - 3.0 | 2.11 | 15.5 | |
SP02 | 1.0 - 2.0 | 1.99 | 22.16 |
2.0 - 3.0 | 2.12 | 16.6 | |
SP05 | 1.0 - 2.0 | 2.15 | 17 |
SP06 | 1.0 - 2.0 | 2.01 | 15.62 |
2.0 - 3.0 | 1.95 | 21.34 | |
SP07 | 1.0 - 2.0 | 1.96 | 19.73 |
2.0 - 3.0 | 1.86 | 22.99 | |
SP08 | 1.0 - 2.0 | 1.91 | 23.6 |
Sample ID | Depth (m) | D60 | D10 | CU | Hydraulic Conductivity (m/s) |
---|---|---|---|---|---|
SP01 | 0.0 - 1.0 | 1.5 | 0.25 | 6 | 0.026 |
1.0 - 2.0 | 1.25 | 0.25 | 5 | 0.018 | |
2.0 - 3.0 | 1.6 | 0.29 | 6 | 0.030 | |
SP02 | 1.0 - 2.0 | 1.55 | 0.29 | 5 | 0.028 |
2.0 - 3.0 | 1.6 | 0.25 | 6 | 0.030 | |
SP04 | 1.0 - 2.0 | 1.65 | 0.29 | 6 | 0.031 |
2.0 - 3.0 | 1.7 | 0.3 | 6 | 0.033 | |
SP05 | 1.0 - 2.0 | 1.85 | 0.29 | 6 | 0.040 |
SP06 | 1.0 - 2.0 | 1.55 | 0.25 | 6 | 0.028 |
2.0 - 3.0 | 1.75 | 0.3 | 6 | 0.035 | |
SP07 | 1.0 - 2.0 | 1.6 | 0.25 | 6 | 0.030 |
2.0 - 3.0 | 1.4 | 0.25 | 6 | 0.023 | |
SP08 | 1.0 - 2.0 | 1.6 | 0.29 | 6 | 0.030 |
2.0 - 3.0 | 1.45 | 0.25 | 6 | 0.024 |
soils may also have moisture content up to about 50% to 80%. The soils in the proposed area have varying proportion of gravel and sand with low proportion of fine grains at 0 - 1 m depth. Higher values of moisture content are obtained at 1 - 2 m depth as that of fine-grained soils.
Specific gravity values from
The plasticity and plasticity index of the various samples increases with depth due to the increasing clay content with depth (
Compacting soils at the study area at water contents above 25.01% will result in a relatively dispersed soil structure that is weaker, more ductile, less pervious, softer, less susceptible to swelling and more susceptible to shrinking. Conversely, when the soil on the proposed landfill site is compacted at a water content lower than 25.01%, it will result in a flocculated soil structure with random orientation that has opposite characteristics of when it is compacted wet at the optimum water content. The samples with high clay content exhibit low MDD values with high OMC whiles samples with low clay content exhibits high MDD values with low OMC values. The hydraulic conductivity values of the in-situ soils are greater than 10−9 m/s proposed by Roehl et al. [
The following conclusions can be made:
・ The existing site at Aboso is not suitable for the construction of an engineered landfill due to high water table, leachate runoff to nearby stream, presence of structural deformation and proximity to build up areas.
・ The multicriteria GIS modelling identified fourteen (14) suitable areas for the siting of landfill in the Tarkwa area. A site located in Domeabra was chosen due to its proximity to the neighboring communities of Tarkwa, Nsuta and Aboso.
・ The geophysical survey showed that the proposed site at Domeabra is made up of four layers. The first layer is the top soil with thickness ranging from 0.5 m to 2 m. The second layer is the weathered material with thickness ranging from 5 m to 15 m. The third layer is the saturated material with thickness ranging from 10 m to 15 m. The fourth layer is the fresh rock which is vertically extensive.
・ The water table occurs at a depth of 12 to 15 m which falls within the acceptable limits for landfill construction.
・ The soil at the proposed site is predominantly gravel and sand, well graded with gradual increase in clay content with depth and has a good moisture content. The gravel and sandy soils have good to excellent shear strength and workability.
・ The proposed area has good dry density, bulk density and specific gravity soil.
・ The plasticity and plasticity index of the proposed area increases with depth due to the increasing clay content, however the soil is not a good lining material due to the high percentage of gravel.
・ The evaluated geophysical and geotechnical properties of the proposed area in Domeabrais suitable for the construction of an engineered landfill site.
・ The multicriteria GIS modelling has proven to be an accurate tool for landfill site selection.
RecommendationsThe following recommendations are being made for consideration:
・ Soil chemical test should be performed.
・ Detailed geological and structural mapping should be conducted.
・ The socio-economic impact of the proposed project should be evaluated.
The Authors would like to acknowledge Mr Osei Agyemang Jnr for his support during the ArcGIS modelling in 2014. Thanks to Mr David Amoah for his assistance during the assessment of existing open landfill at Aboso in 2017. The Authors appreciate Mr Osei Mensah Bonsu Isaac for his effort during the geotechnical site investigation at the proposed site at Domeabra in 2018.
The authors declare no conflicts of interest regarding the publication of this paper.
Asante-Annor, A., Konadu, S.A. and Ansah, E. (2018) Determination of Potential Landfill Site in Tarkwa Area Using Multi-Criteria GIS, Geophysical and Geotechnical Evaluation. Journal of Geoscience and Environment Protection, 6, 1-27. https://doi.org/10.4236/gep.2018.610001