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Aug 21, 2017 - depth of the aquifer was obtained as 12.7 m while the aquifer resistivity ranged from 161 to 1728 om. The mean value of transmissivity obtained ...
hydrology Article

Lithological Identification and Underground Water Conditions in Jeddo Using Geophysical and Geochemical Methods Ruth Iserhien-Emekeme 1, *, Merrious Oviri Ofomola 1 Ochuko Anomohanran 1 1 2

*

ID

, Musa Bawallah 2 and

Department of Physics, Delta State University, 330106 Abraka, Nigeria; [email protected] (M.O.O.); [email protected] (O.A.) Department of Applied Geophysics, Federal University of Technology, 340252 Akure, Nigeria; [email protected] Correspondence: [email protected]

Received: 18 July 2017; Accepted: 16 August 2017; Published: 21 August 2017

Abstract: Resistivity soundings and hydrogeochemical methods were carried out in order to establish the characteristics of the aquifer in Jeddo, Southern Nigeria. Results of the resistivity sounding revealed that the formation is made up of clay, clayey sand, and fine- to coarse-grained sand. The mean depth of the aquifer was obtained as 12.7 m while the aquifer resistivity ranged from 161 to 1728 Ωm. The mean value of transmissivity obtained for the aquifer is 169 m2 day−1 while analysis of the transmissivity revealed that about 6% of the study area has greatest potential for a productive aquifer. The study also revealed that the underground water flows in the northeast–southwest direction. The hydro geochemical analysis of water samples showed that some parameters such as lead, color and pH exceeded the permissible limits, which were established by Federal Environmental Protection Agency and the World Health Organization. It is concluded from the water quality index (WQI) that the groundwater is of poor quality and requires some remediation before it can be used for domestic and industrial purposes. Keywords: electrical resistivity; aquifer transmissivity; aquifer protective capacity; groundwater flow; water quality index

1. Introduction Jeddo, the study area, is in the western part of the Niger Delta region of Delta State, Nigeria. It has altitude of about 23 m, an elevation of about 3–12 m above sea level and it is about 437 km south-west of the country’s capital city, Abuja. It lies between latitude 5.583◦ N and 5.600◦ N and longitude 5.710◦ E and 5.716◦ E (Figure 1). The area is characterized by tropical equatorial climate with a mean annual temperature of 32.8 ◦ C and an annual rainfall of 2673.8 mm [1]. It is an established fact that the annual temperature and amount of rainfall is highly variable from year to year [2]. The region has witness an influx of people in recent times due to its proximity to the Warri Refinery and Petrochemical Company (WRPC), resulting in an ever-rising demand for water. Municipal water supply is not available in the community, thus several water wells have been drilled by individuals without preliminary geophysical, geological, and hydrogeological investigation, in search of potable drinking water. The lithological identification of the subsurface and underground water characteristics of an area can be effectively determined by drilling of several boreholes and interpretation of the soil and water samples collected. This is both cost- and labor-intensive. Today however, great emphasis is placed on planned exploration and utilization of water resources which is a non-invasive, relatively cheap and quantitative technique. This exploration requires the use of various geophysical, hydrogeological and

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on planned exploration and utilization of water resources which is a non-invasive, relatively cheap and quantitative technique. exploration requires the use of various geophysical, hydrogeological geochemical methods such as This seismic, electromagnetic, magnetic, ground probing radar, and electrical and geochemical methods such as seismic, electromagnetic, magnetic, ground probing radar, and resistivity methods among others. electrical resistivity methods among others. The surface electrical resistivity method uses various techniques and instruments in its The surface electrical resistivity method uses various techniques and instruments in its investigation and is useful in determining the thickness and resistivity distribution of the subsurface [3]. investigation and is useful in determining the thickness and resistivity distribution of the subsurface The technique measures the properties of an earth material, which are related to hydraulic parameters. [3]. The technique measures the properties of an earth material, which are related to hydraulic The success of the method is due to the variation of conductivity within the earth’s subsurface layers, parameters. The success of the method is due to the variation of conductivity within the earth’s which in turn affects the distribution of electric potential. The degree of this effect depends on the subsurface layers, which in turn affects the distribution of electric potential. The degree of this effect shape, size, location and bulk resistivity of the subsurface The bulk electrical resistivity depends on the shape, size,electrical location and bulk electrical resistivity layers. of the subsurface layers. The bulk depends on the mineralogy of the rocks and its contained fluids [4]. electrical resistivity depends on the mineralogy of the rocks and its contained fluids [4]. TheThe useuse of of electrical methods studiesisiswell welldocumented documented many electrical methodsapplied appliedto to environmental environmental studies byby many geophysicists [5–16]. This paper (resistivity)method methodfor forparameter parameter estimation geophysicists [5–16].This paperprovides providesaa geoelectrical geoelectrical (resistivity) estimation as complimentary/alternative direct methods methodsand andisisaimed aimedatatestimating estimating lithology, as complimentary/alternativeapproach approach to direct thethe lithology, resistivity, longitudinal conductance and transverse hydraulic conductivity, resistivity, longitudinal conductance and transverse resistance,resistance, hydraulic conductivity, transmissivity, transmissivity, directionwater of underground flow, capacity and protective aquifer in Jeddo, direction of underground flow, and water protective of thecapacity aquifer of in the Jeddo, located within within the Niger Delta basin.results It also of includes ofcarried water analysis carried out ascertain the located Niger Delta basin. It also includes water results analysis out to ascertain thetogeochemical the geochemical ofwater. the underground water. composition of the composition underground

Figure thestudy studyarea. area. Figure1.1.Map MapofofDelta DeltaState State showing showing the

2. Geology Study Area 2. Geology of of Study Area subsurface geology theNiger NigerDelta DeltaBasin Basin to to which established, [17–20]. TheThe subsurface geology ofofthe whichJeddo Jeddobelongs belongsisiswell well established [17–20]. The basin fill is made up of three formations, namely the Benin, Agbada and Akata Formations, from The basin fill is made up of three formations, namely the Benin, Agbada and Akata Formations, the youngest to oldest. The continental Miocene–Recent Benin Formation conformably overlies the from the youngest to oldest. The continental Miocene–Recent Benin Formation conformably overlies Agbada Formation. Its lithologic composition is 90% sand and about 10% clay and lignite bed [17]. the Agbada Formation. Its lithologic composition is 90% sand and about 10% clay and lignite bed [17]. The sands range in size from gravelly, coarse- to fine-grained. They are also poorly-sorted, subThe sands range in size from gravelly, coarse- to fine-grained. They are also poorly-sorted, sub-angular angular to well-rounded, and bear lignite streaks and wood fragments. Its porosity, which decreases to well-rounded, and bear lignite streaks and wood fragments. Its porosity, which decreases with depth, with depth, ranges from 15 to 31% in the basin [21]. It has numerous prolific aquifers. The Agbada

ranges from 15 to 31% in the basin [21]. It has numerous prolific aquifers. The Agbada Formation conformably overlies the Akata Formation in the subsurface. It is a parallic sequence of alternating shale and sandstone with a variable age ranging from Eocene to Pliocene/Pleistocene and Recent in the

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Formation conformably overlies the Akata Formation in the subsurface. It is a parallic sequence of

Delta surface. shale The Akata Formation, also known age as marine Paleocene to Holocene alternating and sandstone with a variable rangingshale fromranges Eocenefrom to Pliocene/Pleistocene and in ageRecent and isin composed of shale, silts, clay and turbidity sand at the base of the Delta sequence. The shale the Delta surface. The Akata Formation, also known as marine shale ranges from Paleocene is believed to beinover and highly compacted to Holocene age pressured and is composed of shale, silts, clay[18]. and turbidity sand at the base of the Delta sequence. The shale is believed to be over pressured and highly compacted [18].

3. Methodology

3. Many Methodology investigative techniques are commonly employed in estimating the spatial distribution of

aquifer Many parameters [5–16].techniques In this research work, the Allied Ohmega Terrameter was used to obtain investigative are commonly employed in estimating the spatial distribution of aquifer parameters [5–16]. In this research work, the Allied Ohmegathe Terrameter was used to obtain seventeen vertical electrical soundings (VES) in order to establish characteristics of the aquifers seventeen electrical soundingsare (VES) in orderin to Figure establish the characteristics of theresults aquifers in the study vertical area. The VES locations as shown 2.Interpretation of VES was in the study area. The VES locations are as shown in Figure 2.Interpretation of VES results was done done using the RESIST software, which is an iterative inversion-modeling program. Analysis of the using the RESISTresistivity software,versus which the is an iterative inversion-modeling program. Analysis of thethe resulting apparent half-current electrode separations were used to obtain resulting apparent resistivity versus the half-current electrode separations were used to obtain earth models composed of individual layers of specified thickness (h) and apparent resistivity (ρ)the from earth composed of individual of specified thickness resistance (h) and apparent which themodels longitudinal conductance (SL =layers h/ρ unit Ω−1 ), transverse (R = hρresistivity unit Ωm2(ρ) ) and from which the longitudinal 2conductance (SL = h/ρ unit Ω−1), transverse resistance (R = hρ unit Ωm2) transmissivity (T = Kh, unit m /s) were calculated. and transmissivity (T = Kh, unit m2/s) were calculated. Several groundwater surface maps contoured using Surfer 8 software were used for analysis. Several groundwater surface maps contoured using Surfer 8 software were used for analysis. Hydrogeochemical analysis was also carried out on water samples collected from existing hand dug Hydrogeochemical analysis was also carried out on water samples collected from existing hand dug wells and boreholes in the study area to predict the quality of the underground water. The water wells and boreholes in the study area to predict the quality of the underground water. The water samples areare Grab samples dugwells wellsand andboreholes boreholes using new one-liter samples Grab samplescollected collectedfrom fromvarious various hand hand dug using new one-liter bottle and analyzed in the Analytical Laboratory of the Department of Chemistry, Delta State University, bottle and analyzed in the Analytical Laboratory of the Department of Chemistry, Delta State Abraka, Nigeria. University, Abraka, Nigeria. 5 36 N

To Ughoton

VES16

VES17

HDW4 Cranefield Schools BH8 ch tS igh He

VES15

BH6

To

VES14 VES13

Road utieyin Winners Church Oman

LATITUDE

HDW3

BH5

Jeddo Sec Sch

r ate Gre

VES12

ad Ro VES11 re be BH7 Og

VES6

VES10

VES9

treet ude S Idum

w Ne

VES8

ut yo La

VES5

Ogiendo Pri Sch

HDW2

ad BH4 Ro sy as b Em

t ri s Ch VES4

VES7

CG

BH2

KEY

BH3 VES2

Eyu

be

nt sce Cre HDW1

VES3

From Effurun

300 m SPDC Farm

5 35 N 5 42 E

eet StrVES1 ield ut 1 layo ma U du ad g Ro BH1 usin A Ho DDP

nef Cra

ad o R

150

gi A go

et St re

o d d Je

Roads Built up Area Sounding Stations Boreholes(BH) Hand Dug wells (HDW) 0

oad MR

LONGITUDE

5 43 E

Figure 2. Map ofof the study of boreholes boreholesand andvertical verticalelectrical electrical soundings. Figure 2. Map the studyarea areashowing showingthe the positions positions of soundings.

4. Results and Data Analysis 4. Results and Data Analysis

4.1.4.1. Geoelectric Model Geoelectric Model reveal geologic sections various parts the studyarea, area,geoelectric geoelectricsections sectionsbased basedon onthe To To reveal thethe geologic sections in in various parts ofof the study the interpretation of results VES results (Table 1) were generated shownin in Figures Figures 3–5. to to water interpretation of VES (Table 1) were generated asasshown 3–5.The Thedepth depth water table was determined (rangingfrom from1.5 1.5m mto to 35 35 m m with with an ofof 12.7 m)m) and twotwo table was determined (ranging an average averageaquifer aquiferdepth depth 12.7 and sediments (unsaturated and saturated) identified. The unsaturated sediments consist of topsoil with sediments (unsaturated and saturated) identified. The unsaturated sediments consist of topsoil with resistivity values varying from 21 to 226 Ωm. The location studied shows a sequence of saturated sediment consisting of clay layers (16 ≤ ρ ≤ 92 Ωm) for VES 2, 3, 4, 5, 10 and 12, while clayey sand

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resistivity varying from identified 21 to 226 Ωm. The location of saturated layers (95 ≤ values ρ ≤ 113 Ωm) were for VES 5, 9, 10 studied and 16. shows Fine- atosequence medium-grained sand sediment consisting of clay layers (16 ≤ ρ ≤ 92 Ωm) for VES 2,3,4,5,10 and 12, while clayey layers in (113 ≤ ρ ≤ 1728 Ωm), indicating the presence of productive aquifers in the area, was alsosand identified (95 ≤ ρ ≤ 113 Ωm) were identified for VES 5, 9, 10 and 16. Fine- to medium-grained sand (113 ≤ ρ ≤ all VES. Coarse sand encountered in VES 6 has a resistivity of 4205 Ωm. 1728 Ωm), indicating the presence of productive aquifers in the area, was also identified in all VES. CoarseS sand encountered in VES 6 has a resistivity of 4205 Ωm. N VES 2

0

S

VES 4

VES 2

VES 5

VES 4

VES 5

0

Borehole Log

VES 15

N

VES 15

loamy topsoil Borehole Log clayey sand loamy topsoil finesand sand clayey

10

fine sand

fine - medium grained sand

fine - medium grained sand medium - coarse grained sand

20

medium - coarse grained sand

20

Depth (m)

Depth (m)

10

30 30

40

40

50

50

60 60 Legend Legend topsoil (24-78 topsoil (24-78 m) m)

70 70

clay (29-68 clay (29-68

m) m)

clayey sand (124 clayey sand (124

m) m)

fine - grainedsand sand(169-705 (169-705 fine - grained

m) m)

medium - grainedsand sand(1112-1379 (1112-1379 medium - grained

m) m)

Figure 3. 3. Geoelectric Geoelectricsection section showing vertical electrical soundings (VES) points along the Figure showing vertical electrical soundings (VES) points along the direction direction north–south. north–south. SW

VES 3

VES 9

VES 10

0

VES 16

NE

Borehole Log loamy topsoil clayey sand fine sand

Depth (m)

10

fine - medium grained sand medium - coarse grained sand

20 Legend

30

topsoil (21-63 clay (16-75

40

m) m)

clayey sand (95-113

m)

fine - grained sand (161-502

m)

medium - grained sand (1086-1339 coarse - grained sand (4205

m)

m)

Figure Geoelectricsection sectionshowing showing VES VES points points along Figure 4. 4. Geoelectric alongthe thedirection directionsouthwest–northeast. southwest–northeast.

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VES 7

VES 9

VES 10

0

VES 12

VES 11

E

Borehole Log loamy topsoil clayey sand fine sand

Depth (m)

10

fine - medium grained sand medium - coarse grained sand

20

30

40

Legend Topsoil (22-226 clay (16-92

m)

m)

fine - grained sand (113-819 medium - grained sand (1728

m) m)

Figure Geoelectricsection sectionshowing showing the VES west–east. Figure 5. 5. Geoelectric VES point pointalong alongthe thedirection direction west–east. Table1.1.Geoelectrical Geoelectrical model model of Table of the thestudy studyarea. area.

Nature of Sediment Nature of Sediment Unsaturated sediment Unsaturated sediment

Lithology(Inferred) Lithology (Inferred) Top soil Top soil Clay Clayey sand Clay Fine-grained sand Clayey sand Fine-grained sand Medium-grained sand Medium-grained Coarse sand sand Coarse sand

Saturated sediments Saturated sediments

Resistivity (Ωm) Resistivity (Ωm) 21 ≤ ≤ 226 226 1621≤≤ ρ≤≤92 95 16 ≤ ≤≤ρ 113 ≤ 92 11395≤≤ ρ≤≤819 113 113 ρ≤ 819 1086 ≤≤ ≤ 1728 10864205 ≤ ρ ≤ 1728 4205

4.2. Aquifer Protective Capacity

4.2. Aquifer Capacity The Protective hydrogeological characteristics of a site useful in the simulation of groundwater flow and inThe evaluating overburden protective capacity and transmissivity of an area are the Dar-Zarrouk hydrogeological characteristics of a site useful in the simulation of groundwater flow and parameters (i.e., longitudinal conductance SL, and transverse resistance R) [22]. in evaluating overburden protective capacity and transmissivity of an area are the Dar-Zarrouk The longitudinal conductance SL, which is regarded as the medium’s ability to retard and filter parameters (i.e., longitudinal conductance SL , and transverse resistance R) [22]. percolating fluid is considered as the protective capacity of the overburden and expressed as,

The longitudinal conductance SL , which is regarded as the medium’s ability to retard and filter ℎ ℎ ℎ of ℎ the overburden ℎ and expressed as, percolating fluid is considered asℎ the protective capacity =

= n

S L = /as ρ = It can also be expressed h



=



i =1

hi ρi



=

+

+

+ −−− +

(1)

h1 h h hn + 2 + 3 + −−− + ρ1 ρ2 ρ3 ρn =

It can also be expressed as



(1) (2)

Where σi is the layer conductivity analogous to S the = layer σ h transmissivity T, L

= where σi is the layer conductivity analogous to=theℎ layer transmissivity T, The total transverse resistance R is given by,

T = Kh = K

=ℎ∙

=



=ℎ

The total transverse resistance R is given by,

(2)

i

+ℎ

SL σ

+ℎ

(3)

(3) + −−−+ ℎ

(4)

n The derived longitudinal conductance values in Table 2, calculated from obtained resistivity and R = h·ρ = + −stations − − + were hn ρn used to produce a (4) 2 + h3 ρ3 VES 1 ρ1 + h i ρi ) = hlayers thicknesses using Equation (1)∑ for( hvarious at2 ρdifferent i =1 protective capacity map (Figure 6).The overburden protective capacity was evaluated based on the rating approachlongitudinal by [23], and conductance modified by [24] andinisTable given2,ascalculated >1 (excellent), (veryresistivity good), 0.1–and The derived values from0.5–1 obtained 0.49 (good), 0.06–0.09 (moderate), 0.01–0.05 (weak) and 1 (excellent), 0.5–1 (very good), 0.1–0.49 Hydrology 2017, 4, 42 6 of 15 (good), 0.06–0.09 (moderate), 0.01–0.05 (weak) and