2D inversion of electrical resistivity investigation of contaminant plume around a dumpsite near Onitsha expressway in southeastern Nigeria

The study tries to utilize vertical electrical sounding (VES) and 2D resistivity tomography to evaluate the region of influence of the leachate plume on the groundwater around a dumpsite at Onitsha expressway, southeastern Nigeria. The borehole log data were acquired and their respective geoposition logged with Garmin GPS device. In addition, four 1D (VES) soundings and 2D electrical profile data were acquired in the field utilizing the Schlumberger and Wenner profiles respectively. Petrozenith PZ-03 Resistivity meter was used to acquire the electrical data, while RES2DINV and WinResist software were used to interpret the 2D and 1D data respectively. The resulting geoelectic layers were correlated with the borehole logs and were interpreted according to their resistivity distribution. Results of the 2D inversion at profiles 1 and 3 showed low resistivity zones indicating influence from the leachate plume. Profiles 2 and 4 gave low resistivity zone within 14.6 and 44.3 Ωm from surface to between 0.375 and 3.60 m depths indicating influence from leachate plume. Likewise, profiles 1 and 3, which penetrated groundwater, also showed very low resistivity with resistivity ranging from 3.12 to 8.7 Ωm, from surface to few meters depths. This indicates that it has been polluted by the leachate. In contrast, Profiles 2 and 4, from the 2D inversion, has no leachate influence on the groundwater. The VES result showed that the depth to the water table at location 1, 2, 3 and 4 are 21.7 m, 17.9 m, 15.9 m and 12.2 m respectively, with the leachate plume flowing in the southeast direction in line with the groundwater flow direction.

Determination of Leachate Plume Migrations from Selected Cemeteries in Benin-City Metropolis using Integrated Physicochemical and Geophysical Methods

Environmental geo-forensics which involves an integrated suite of geochemical and geophysical techniques was used to detect and evaluate contaminant plume migrations from three cemeteries (names of the cemeteries are; First, second and third cemeteries, all in Benin City) within Benin-City metropolis, South-South Nigeria. The study aimed at determining the risks to groundwater and soil by assessing the rate of leachate plume migrations on the study area. The Very Low Frequency-Electromagnetic (VLF-EM) surveys revealed locations of conductive bodies. The Electrical Resistivity Imaging (ERI) surveys showed patterns and resistivity values indicating the presence of leachate plumes around second and third cemeteries, and no presence of leachate around first cemetery. Soil samples from shallow depths within the vicinities of the cemeteries revealed pollution which had probably migrated from the study area. The surface and subsurface soil investigations showed pure laterites which is impervious to fluid flow. Generally, many depressions were identified within the study area, although migration rate is low because it is controlled mainly by the subsurface geology. A time lapse study showed contaminant migration rates of 41.6 cm/month and 51.7 cm/month in the horizontal directions in the second and third cemeteries respectively and 19.2 cm/month in the vertical directions for both (second and third) cemeteries. Also, the arrival time of migrating plumes in laterite layer under was estimated to be 4 years. This investigation demonstrates the suitability of environmental and criminal geo-forensics for identification and evaluation of electrically conductive contaminant plumes, and also to monitor the plume as it travels within the subsurface.

The Application of Geophysical Techniques in Tracking Leachate Plumes Migration in a Typical Cemetery within the Sandy formation in Benin City, Nigeria.

The survey aim is to track leachate plumes within the sandy formation which is below the surface laterite layer. It investigates the presence and migration of leachate plumes in the sandy region in a typical cemetery (Third Cemetery), in Benin City, Nigeria. The research engaged Vertical Electrical Sounding (VES), 2-Dimensional computation of time- lapse to detect the time rate of migration in both the vertical and horizontal directions.The field work covered a time – lapse of six months (June 2017 to December 2017). The electrical resistivity data collected in parallel equidistant lines was processed to obtain geoelectric models using Res2dinv. The leachate plumes in the cemetery migrate vertically and horizontally at different rates. The maximum and minimum rates of vertical migration are 4.1 cm/day and 0.2 cm/day respectively, while the maximum and minimum rates of horizontal migration are 32.8 cm/day and 1.7 cm/day respectively. The volumetric analysis of the plume zones indicates that of the 75,231m3 of the subsurface imaged, 6,322 m3 is the zone contaminated by leachate plume, that is, 8.4 % of the earth volume investigated contained leachate plume. The research also showed that repeated ERT surveys can track movement of leachate plume emanating from decomposed dead bodies over time in active cemetery. The average travel time for a leachate plume to transverse a vertical distance of 6.6 m in coarse sand is 366.7 days at constant migration speed of 1.8 cm/day.

Volumetric Analysis 0f 3-D Resistivity Distribution of Leachate Plume in Third Cemetery, Benin, South-South, Nigeria

This paper aims to carry out the volumetric analysis of 3-D resistivity distribution of leachate plume in Third Cemetery, Benin City, South-South, Nigeria. If not appropriately located or not sufficiently protected, cemeteries pose a significant health problem for the people (Fisher and Croupkamp,1993). Health concern about the possible impact of the cemeteries in Nigeria on the water supply has prompted this research. The research engaged 2-Dimensional and 3-Dimensional imaging (tomography) to investigate the presence and migration of leachate plumes in the cemetery and computation of time-lapse to detect the time rate of migration in both the vertical and horizontal directions. The geoelectric models obtained for the surveys displayed leachate plumes starting from the laterite (the burial environment) down to the sandy formation (the regional water supply source). The leachate plumes presence in the sand bed is modeled and described as shown in the 2-D and 3-D displays. This study showed that parts of the cemetery had been contaminated. This contamination was also observed to have infiltrated into the aquifer in the cemetery. 3-D block model, using Voxler 4.0 software was employed to carry out the volumetric analysis of the 3-D resistivity distribution of leachate plume in the Third Cemetery.

2D Resistivity Tomography Survey for Leachate Plume from Isundunrin Poultry Disposal Pits

Management of dead birds in poultry farms has been a major problem in Nigeria. This study aimed at using 2D resistivity tomography to outline leachate plume from disposal pits in a poultry farm. 2D electrical resistivity tomography were conducted along three profiles, two of which were 3.0 m and 25.0 m respectively to the two available mortality pits (Pit1 and Pit 2) while the third was 300.0 m away from the mortality Pit 1. Profile length of 100.0 m each and interspaced 5.0 m oriented in the North-East (Profile 1), South-East (Profile 2) and North-East (Profile 3) directions respectively was covered. 2D resistivity data inversions were performed on the obtained converted apparent resistivity using DIPROWIN software. Five water samples collected from five different hand dug wells available within the poultry farm were analysed for hydro chemical parameters. 2D results showed conductive paths occurrence in transverse one at the depth of 5.0 m, a horizontal distance of 45.0 m to 55.0 m, and had migrated down to the depth of 10.0 m. The second traverse showed varying resistivity values ranged 7.0 Ω m to 31.0 Ω m up to a depth of 15.0 m, an indication of the presence of clay soil. Low resistivity values ranged 14.0 Ω m to 49.0 Ω m were recorded in traverse 3. The extent of the contaminant is prominent at the topmost part of the soil and to almost 10.0 m depth. This was attributable to the contaminant from the deposit site of faeces of the poultry. Hydro chemical analysis indicated high values of Conductivity and Total Dissolved Solids (TDS). This confirms the migration of leachate from the disposal pits to the surrounding soils and groundwater and the 2D results obtained from disposal Pit 1. Other alternative methods of disposing dead birds are hereby recommended.