Hydrocarbon Remediation By Natural Attenuation at Baruwa, Lagos

Hydrocarbon Remediation by Natural
Attenuation at Baruwa, Lagos Nigeria
Uduebor, Micheal A.
Department of Civil and Environmental Engineering, The Federal University of
Technology, Akure, Ondo State, Nigeria.
e-mail: [email protected]
Ola Samuel A.
Department of Civil and Environmental Engineering, The Federal University of
Technology, Akure, Ondo State, Nigeria.
e-mail: [email protected]
ABSTRACT
This research is concerned with characterization and assessment of Natural Attenuation of hydrocarbon
contaminated site. The specific study site is Baruwa community in Alimosho Local government area of
Lagos state, Nigeria, with a population of over 100,000 people. There are over 150 wells within the
community which have been affected by the oil pollution which dates back to 1994, when there was a burst
in an N.N.P.C (Nigerian National Petroleum Corporation) Valve pit located at the Federal Housing Estate
(Jakande Estate) opposite the study site. Earlier studies carried out by Adekunte (2008) and Balogun (2009)
have established a case of the pollution of the groundwater via hydro-chemical analysis and
geoenvironmental assessment coupled with stratigraphic characterisation of the contaminated site using
wells within the area respectively. This study employed the collection of field data in 2014 from the
contaminated site to sufficiently characterize the hydrocarbon contamination within the area.
Characterization of the study area was conducted utilizing the methodology prescribed by United States
Environmental Protection Agency (USEPA, 2001). 25 Hand dug wells to a depth of 26.5 metres within the
area were utilized for the study. Water levels and Free Hydrocarbon Thicknesses were measured with the
aid of an oil/water interface meter, Total Petroleum Hydrocarbon (TPH) was also measured both in
groundwater and soil vapour using a portable Hydrocarbon Analyser. Comparisons were made with data
obtained in 2006 of previous studies and Natural Attenuation occurrence established based on Tiers 1 and 2
criteria (USEPA, 1999). LNAPL thickness decreases of 86.4% to 99.7% were recorded in comparison with
that from previous studies (2006 - 2014). TPH surveys carried out in the groundwater are in agreement with
LNAPL flow direction. Decreases in TPH concentrations varying from 33.13% to 57.61% were observed in
comparison with earlier studies (2006 - 2014). All the wells investigated within the study area indicated
that significant Natural Attenuation has occurred over the period (2006 - 2014).
KEYWORDS:
Petroleum hydrocarbon, Volumetric characterization, Remediation, Natural
Attenuation
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INTRODUCTION
Hydrocarbon contamination originating from the activities of man have entered the
subsurface environment through spillage, land application and waste disposal practices, either on
purpose or by accident. The presence and transport of these contaminants constitute a potential
threat to human health and ecosystems. Protection of public health and ecosystems rely on the
ability to predict the transport and distribution of contaminants in the vadose and saturated zones
(Van de Weerd, 2000).
Light non-aqueous phase liquids affect ground-water quality at many sites across the country.
The most common LNAPL related ground-water contamination problems result from the release
of petroleum products. These products are typically multicomponent organic mixtures composed
of chemicals with varying degrees of water solubility. Some additives (e.g., methyl tertiary-butyl
ether and alcohols) are highly soluble. Other components (e.g., benzene, toluene, ethyl benzene,
and xylenes) are slightly soluble. Many components (e.g., n-dodecane and n-heptane) have
relatively low water solubility under ideal conditions. In general, LNAPLs represent potential
long-term sources for continued ground-water contamination at many sites (Newell et al, 1995).
The Baruwa area in Lagos, Nigeria is one of such sites where large volume of refined
petroleum hydrocarbon has been released into the subsurface of the soil and has so far been
transported from the source to the whole area, rendering groundwater practically unusable, with
residents having to go through untold hardships and cost to carry out their daily domestic
activities because of the contaminated groundwater.
The Geoenvironmental Engineering research group in Federal University of Technology,
Akure (FUTA), started Geoenvironmental site assessment, geotechnical, background and natural
attenuation studies for the site in 2006. Earlier studies carried out by Adekunte (2008) and
Balogun (2009) have tried to establish a case of the pollution of the groundwater via hydrochemical analysis and geoenvironemtal assessment coupled with stratigraphic characterisation of
the contaminated site using wells within the area respectively.
After an extensive site investigation it is important to reliably evaluate the potential efficiency
of Monitored Natural Attenuation as a remediation alternative (USEPA, 1999). This step includes
the gathering of site specific data to quantify the rate of the attenuation processes and to estimate
the period of time required to achieve the defined remediation objectives.
The data collected was processed based on three independent but converging lines of
evidence, which include (e.g., Wiedemeier at al., 1995, 1997; USDOE, 1998; USEPA, 1999;
Pennington et al., 1999; USAirForce, 1999):
1. Historical groundwater and/or soil chemistry data that demonstrate a clear and
meaningful trend of decreasing contaminant mass and/or concentration over time at appropriate
monitoring points.
2. Hydrogeological and geochemical data that illustrate that geochemical conditions are
suitable for biodegradation and to indirectly demonstrate the type(s) and rates of the Natural
Attenuation processes active at the site. This often includes;
a. depletion of electron donors and acceptors;
b. increase in metabolic by-product concentrations;
c. decreasing parent compound concentrations; and
d. increase in daughter compound concentrations.
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3. Data from field or microcosm studies, which directly demonstrate the occurrence of a
particular Natural Attenuation process at the site and to verify the ability of insitu contaminant
degradation.
For achieving regulatory approval for Monitored Natural Attenuation application, it is
generally necessary to provide both historical data (type 1 above) and data characterizing the
nature and rates of Natural Attenuation processes active at the site (type 2 above). Where the
latter is inadequate or inconclusive, data from microcosm studies (type 3 above) may also be
required. In addition to these lines of evidence, analytical or numerical solute transport models
can be used to examine the processes influencing the fate and transport of organic contaminants
in groundwater (Wiedemeier et al., 1999).
METHODOLOGY
Description of the Study Area
Baruwa area (Latitude 06˚ 35' 12'' N, Longitude 03˚ 16' 21'' E) is located in Ipaja, between the
popular Iyana-Ipaja Bus-stop and the Ikotun Area of Alimosho Local Government Council of
Lagos State, South West Nigeria. It is about 2.5km from Iyana-Ipaja Bus Terminal and is
bounded by Gowon Estate and Abesan Estate to the right and left respectively while coming from
Iyana-Ipaja Bus Terminal. It is accessible by a network of roads through Ipaja and Ayobo and is a
densely populated residential area with a population of over 100,000 people living in the area. Its
existence dates back to the early 20th Century but it became prominent in the 1970s due to
population explosion witnessed in Lagos, which led to the development of satellite communities
(Adekunte, 2008). Figure 1 shows the map of Baruwa-Lagos indicating the position of the study
area (Baruwa).The area has a few cottage industries and small scale enterprises and has fair to
good supply of electricity, with a network of earth roads without a proper drainage system leading
to impassability of some roads during the rainy season.
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Figure 1a: Map of Nigeria Indicating the Location of Baruwa-Lagos.
Figure 1b: Field Schematic showing Locations of Wells Monitored and Direction of
Groundwater Flow (2014)
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505
There are over 150 wells within the community which have been affected by the oil
pollution which dates back to 1994, when there was a burst in an N.N.P.C Valve pit located at the
Federal Housing Estate (Jakande Estate) opposite the study site.
Experimental Programme
The study employed the collection of field data from the contaminated site in Baruwa,
Lagos employing equipment and methods to sufficiently characterize the hydrocarbon
contamination within the area. Characterization of the study area was conducted utilizing the
methodology prescribed by United States Environmental Protection Agency (USEPA) (2001).
Field Tools and Equipment
A GPS device, Garmin II plus was used to determine the position of observed wells within
the area globally. This data obtained was used in proper location and identification of the wells,
while an Oil/Water Interface meter was employed to measure the ground water levels and the
thickness of free hydrocarbon on groundwater in water supply wells.
A PHA-100 portable hydrocarbon analyser was utilized to measure levels of Total
Petroleum Hydrocarbons (TPH) in soil vapour and water in the field real time (in-situ). The
results of the PHA-100 portable hydrocarbon analyser were later confirmed using Gas
Chromatography equipped with Flame Ionisation Detector (GC FID) in the laboratory.
Study Methods
Desktop Study
A review of the site contaminant history was conducted; this included potential LNAPL
sources at the site and the affected receptors. Historical groundwater levels and quality were
obtained from previous studies within the area (Adekunte (2008), Balogun (2009)) as part of the
local geohydrological review.
Site Survey (Walkover and Visual inspection)
This was conducted to verify the validity of the information collected during the desktop
study. Emphasis was placed on fixing the exact positions of the wells (utilizing a GPS tracker),
linking previous aquifer test carried out on the existing wells within the area. Also additional
information from existing wells were collected to further enhance the study. New wells were also
identified within the area and substitutes allotted for wells that were no longer available or
accessible.
Hydrological (Water Table) and Free LNAPL Product Characterization
A water table characterization exercise was conducted as an extension of earlier studies
utilizing the number of wells that were still available for testing within the area and their
characteristic depths to liquid and to bottom. Also apparent free LNAPL thicknesses were
measured within the wells with the aid of the interface meter. The results were compared with
previous data obtained from the study site.
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506
Chemical Characterization
Chemical water analyses were conducted for the study area. Dissolved hydrocarbon
compound analysis (TPH, BTEX and Contaminant Equivalent) was carried out using the PHA100 Hydrocarbon Analyser and confirmed with Gas chromatography Equipped with Flame
Ionisation Detectior (GC FID). Contamination levels were also measured in vapour within the
wells.
RESULTS AND DISCUSSIONS
Hydrocensus
Water levels measured within the wells with the aid of the interface meter, gave a range of
the water table within the study site to be between 21.97m – 24.53m. Plotting of the contour of
water table within the area indicated a southwestern flow.
This Southwestern flow (Figure 2) is consistent with reports from previous studies.
Comparing the water table levels between the separate studies show the range between 20.28m –
25.25m (Adekunte, 2008) and 21.97m – 24.53m from the current study. A table showing the
comparison of water table levels for selected wells monitored by the two studies carried out is
given in Table 1 below.
Figure 2: Water Table Contour of Study Area (2014)
Comparison between the two separate study years have shown that there has been no
significant change in direction of groundwater flow and the water table elevations to effect a
hydro-biased movement of the contaminant plume. This is quite important as this indicates that
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507
any remediation effort by natural attenuation has not been affected due to a sudden change in the
direction of water within the subsurface in the study area.
It must also be worthy of note that as LNAPL approaches the water table, entering regions of
increasing water saturation, it may migrate laterally (EPA, 1995). Lateral migration is controlled
by the LNAPL head distribution and in general, contaminant plume migration is expected to be
greatest in the direction of ground-water flow (i.e., maximum decrease in water-table elevation).
Distribution of Free LNAPL at the Study Area
Comparing the thicknesses of hydrocarbon with those from previous studies (2006), it was
observed that the hydrocarbon thickness had reduced significantly in all the wells. The decrease
varied from 86.4% in Well No. 20 to 99.7% in Well No. 41 from 2006 to 2014 as shown in Table
2 below.
Table 1: Comparison of water table levels for two studies
Water Table Levels (m)
Owner’s Name
Well ID
Adekunte
Current
(2006*)
Study (2014*)
Alhaji Baruwa
20
24.40
24.33
Mr Ajiboye
30
23.81
24.53
Mr Oyewole
41
24.60
23.46
Alhaji Oluode
76
23.40
*The dates show the actual dates the data were taken
23.42
Table 2: Comparison of Hydrocarbon Thickness Measured Within Wells.
WELL
OWNER'S
HYDROCARBON THICKNESS (m)
ID No.
NAME
CURRENT
ADEKUNTE
STUDY
% DECREASE
(2006*)
(2014*)
Alhaji Baruwa
0.72
0.098
86.39
20
30
41
69
76
Mr Ajiboye
0.2
0.001
99.50
Mr Oyewole
0.35
0.001
99.71
Mr Kunle
0.12
0.001
99.17
Idowu
Alhaji Oluode
0.15
0.001
99.33
*Note: The dates show the actual dates the data were taken
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508
Figure 3a: Free Hydrocarbon Thickness for Monitored Wells within the Study Area (2014)
Figure 3b: Free Hydrocarbon Thickness for Monitored Wells Within the Study Area (2006).
(from Adekunte, 2008)
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509
The principal Natural Attenuation processes responsible for this movement of and
decrease in contaminant mass is Advection which is characterized by the transport of contaminant
due to bulk motion of the flowing groundwater and concentration gradient respectively. This
indicates that continuous flow of the groundwater would lead to lower proportions of the free
hydrocarbon within the subsurface, which after a period would eventually thin out to sheen levels
in all the wells - this is characteristic of natural attenuation studies. The resultant effect would
leave only the contamination within the soil strata and residual groundwater within the subsurface
which can then be acted upon by microbes if present, degrading the hydrocarbon (USEPA, 2001).
Dissolved Contaminants in Groundwater (TPH)
Comparing the Total hydrocarbon concentrations with those from previous studies, it is
noticed generally that the various concentrations earlier observed within the wells are now
reduced, with decreases of up to 57.61%. (See Table 3 below).
Table 3: Comparison of Total Petroleum Hydrocarbon (TPH) Measured Within Wells.
TOTAL PETORLEUM HYDROCARBON (mg/l)
OWNER'S
CURRENT
ADEKUNTE
%
NAME
STUDY
(2006**)
DECREASE
(2014**)
Alhaji Oluode
49.906
27.3
-45.3
Mr Lasun Faremi
95.0*
45.2
-52.43
Famuyiwa E.O
66.4*
35.6
-46.39
Alhaji Owolabi
68.2*
36.7
-46.19
Mr Oyewole
75.079
48.9
-34.87
Hon. Bayo
71.0*
47.5
-33.13
Alhaji Baruwa
144.86
61.4
-57.61
*Results gotten from contour **Actual dates the data were taken
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510
Figure 4a: Contours of TPH in Groundwater for the Study Area (2014).
Figure 4b: Contours of TPH in Groundwater for the Study Area (2006) (from Adekunte, 2008)
Dispersion is also responsible for the spread of the contamination across the area.
Diffusion also plays a role in spreading the contaminant concentration due to concentration
gradient after dispersion. This movement/spread would continue till the concentrations thin out
and equilibrium is achieved. The results show the importance of groundwater movement.
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CONCLUSIONS
The following conclusions were obtained based on the study;
(1) LNAPL thickness decreases of 86.4% to 99.7% were recorded in comparison with that
from previous studies (2006 - 2014).
(2) TPH surveys carried out in the groundwater are in agreement with LNAPL flow direction.
Decreases in TPH concentrations from 33.13% to 57.61% were observed in comparison with
earlier studies (2006 - 2014).
(3) All the wells investigated within the study area indicated that significant Natural
Attenuation has occurred over the period (2006 - 2014).
ACKNOWLEDGEMENTS
The authors would like to acknowledge the TETFUND National Research Fund of The Prof.
S.A. Ola Research Group, Federal University of Technology, Akure referenced
TETF/ES/NRF/013/Vol.I for the Research Project titled “Site Remediation in Nigeria: Proven
and Innovative Technologies, Recovery of Free Hydrocarbon from Soil/Groundwater.”
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