M
TABLE OF CONTENTS
Page
Title Page
Table of Contents
Executive Summary
Acknowledgement
Study Team
List of abbreviations and Acronyms
List of Figures
List of Tables
i
iii
ix
ix
x
xi
xii
CHAPTER 1
INTRODUCTION
Objectives And Scope Of Study
General Features Of The Study Areas
1
1
3
CHAPTER 2
MATERIALS AND METHODS OF STUDY
Meteorology
Wind speed and direction
Air Quality Measurements
Suspended Particulate Matter
Determination of CO2, NOX, SO2, and Total Hydrocarbons in Air
Flare Radiation
Temperature/Relative Humidity
Soil Studies
Vegetation Studies
Aquatic Studies
7
7
7
7
7
7
8
8
11
14
15
CHAPTER 3
BACKGROUND INFORMATION RELEVANT TO GAS FLARE STUDIES
Gas Flares
Air Pollution, Atmospheric Dispersion Of Pollutants, And The Quality Of Life
Atmospheric Models
Air Pollution And The Quality Of Life
Energy Transfer In The Atmosphere
18
18,
23
24
26
29
CHAPTER4
RESULTS AND DISCUSSION
Meteorology .
Wind speed and direction
Air Quality Measurements
,
Radiation, Temperature And Relative Humidity
Soil
49
Vegetation
■
31
31
31
37
43
'
.
•
.-■
' 52
Aquatic Studies
.
Rain Water
Rivers, Creek And Burrow Pit Water Samples
Aquatic Macrophytes
54
54
60
61
CHAPTER 5
SUMMARY AND CONCLUSIONS
Meteorology
Air Quality
Radiation Temperature and Relative Humidity
Soils
Vegetation
Aquatic Studies
66
66
67
67
68
69
69
71
Conclusion
72
REFERENCES
74
APPENDICES
EXECUTIVE SUMMARY
INTRODUCTION
The Nigerian Agip Oil Company (NAOC), desirous of knowing the effects of gas flares on
the environment, wanted a characterisation of the various environments in which some of
their gas flares are situated, particularly the gas flares at Akri, Ebocha, Obiafu/Obrikom, and
Oshi Flowstation areas.
The objective of the study was thus a characterisation, in each gas flare area, of the natural
environment by way of comprehensive baseline data on the existing state of all identifiable
ecosystems in the areas involved, against which the effect of the gas flares, if any, can be
assessed. Efforts were thus made to determine the prevailing dominant winds and the extent
to which pollutants introduced into the environment would disperse.
The study evaluated the various pollutants in the ambient environment of the gas flare,
damage to vegetation and crops, resulting from heat radiated by the gas flares, as well as a
determination of the maximum distance from the gas flares to which heat radiated from the
gas flares would impact the environment, particularly, vegetation. Rain water samples were
collected during the early rainy season of April 1997, when the rains had attained some
degree of frequency or regularity in May 1997, at the peak of the rains in October 1997 and at
the end of the rainy season in November/December, to determine the possible occurrence of
acid rains.
WIND SPEED AND DIRECTION
The wind speed varied more between light breeze ( 4 - 6 knots equivalent to 1.6 -3.3m/Sec)
and gentle breeze ( 7 - 1 0 knots equivalent to 3.4 - 5.4m/Sec). Winds considered as strong
breeze 22 - 27 knots (10.8 - 13.8m/Sec) were rare. Strong winds could only be obtained
during the rainy season and during the occurrence of squall lines and local thunderstorms.
There are however, periods of calm (i.e. periods of no wind movement) especially at night
between the hours of 11 pm to 6 am.
.
Most times of the year in Nigeria, the wind blows from the south westerly (SW) direction.
This is followed by the southerly (SE). These winds blow from the coast into the hinterlands.
Nevertheless, occasionally, during the dry season in December/January, the north easterly
winds (NE) considered as the Harmattan wind is also felt. The wind direction during the dry
season (January) have the prevalence of the northerly winds. Nevertheless, the influence of
the southerly is also felt during this period. In July, during the wet season, the southerly
winds prevail.
Generally in the flare site areas studied, the southerly winds were dominant with occasional
winds from the west and less so from the east. The wind was mostly south westerly with a
speed in the range of about 2 - 4 m/s i.e. light to gentle breeze dominant in all the flare sites.
Intermittently winds of 7 - 8 m/s classified as moderate breeze were obtained. There were
occasional gusts of 9 - 13 m/s wind i.e. fresh to strong breeze. Winds in the flare site areas
were not only more frequent but were stronger than previously observed for non gas flare site
areas. This is attributed to the correctional current effect resulting from the gas flares which
emit considerable heat and force the hot gasses and particulate matter released far into the air.
IV
AIR QUALITY
'
The concentrations of carbon monoxide (CO) were generally low and were less than 2.0 ppm
in all the determinations made at the various flare sites. Nitrogen dioxide (NO 2) was either
not detected or detected in very low concentrations (< 2.0 ppm) in all the sample stations
while sulphur dioxide (SO 2) was not detected in all the stations sampled indicating no
significant sulphur emission from the flares.
■
Total Hydrocarbon (THC) and Total Suspended Particulates (TSP) were detected in all the
stations sampled but the values obtained for the TSP was generally low especially as the
determinations were made at the peak of the dry season, when rains have not been active in
precipitating particulate matter suspended in the atmosphere. Total hydrocarbon contents
were quite significant and in a few cases particularly downwind in the Ebocha area,went up to
about 190 u,g/m3. The Ebocha area is particularly unique in that both rthe upwind and
downwind values were high and could be attributed to the Obiafu/Obrikom flares which are
located approximately 5 km upwind from Ebocha along the predominantly southerly (mostly
SW) winds. The ambient air pollutant concentrations however, fall within FEPA's ambient
air quality standards limits.
RADIATION, TEMPERATURE, AND RELATIVE HUMIDITY
Gas flare radiation, temperature and relative humidity measurements at the various flare sites
were affected by a number of variables. Flare radiation figures were higher, the higher the
solar radiation. Solar radiation figures at about mid day to 2 pm. was always much higher
than flare radiation values. At night, radiation effects from flares were not felt at distances
more than 100 m from the flares.
The variables like cloud cover, vegetation cover and relative position of the sun however did
not affect the temperature and relative humidity readings. Temperatures recorded for both the
peak of the rainy season and the peak of the dry season on account of the tropical nature of
. the environment were quite high for both seasons and were highest near the flares, with slight
differences between season. Relative humidity figures, however, for the rainy season were
higher than those obtained for similar periods of the day in the dry season.
The minimum distance beyond which the flare radiation effects were similar to background
radiation, varied between the various flare sites studied and with season. For the various
upright flare sites, the following spheres of influence beyond which the flares had little or no
radiation was delineated for the wet and dry season respectively as follows:
The radiation and heat effect of horizontal flares located at Obiafu/Obrikom go far beyond
those of upright flares. The radiation and heat effects of these flares go well beyond 250 m
and pollutants emitted from them are not well dispersed and diluted like in the case of upright
flares.
SOILS
Most of the soils in the various flare site areas were in the slightly acid (pH 6.0 - 7.0) to
moderately acid (pH 5.0 - 6.0) range with a few particularly in the Oshi, area falling within
the strongly acid (< 5.0) range. The electrical conductivity values were low as would bje
expected of the fresh water soils areas in which the gas flares are sighted.
The percentage organic carbon (% C) and percentage total nitrogen (% N) were, with the
exception of a few soils in the Oshi area, low. The heat generated from the flares did not
result in any significant reduction in organic carbon and total nitrogen contents of the soils.
These were generally low and showed no significant difference in content in soils collected
at a distance of 75 m from flares where heat radiation was strongly felt and with distance up
to 450m from flares.
Exchangeable cations (Na, K, Ca, Mg) were quite high in the Akri soils and about adequate in
the Ebocha, Obiafu/Obrikom and Oshi areas. Exchangeable magnesium values were
however, low for the Ebocha and Obiafu/Obrikom areas which were subjected to heavy
farming. Available phosphorus levels were low in all the soils but mineral-nitrogen values
were moderate to high. On the whole, but for the low organic carbon, total nitrogen and
available phosphorus levels, the soils could be said to be of moderate fertility. However, the
low organic carbon, nitrogen and available phosphorus levels at distances beyond 50 m from
the flares can not traced to flare effects but to the natural degradation of organic materials in
heavily farmed soils with very short fallow periods.
VEGETATION
The ground around the flares in the various flare sites were completely devoid of vegetation
on account of the heat radiated from the flares which drastically affected plant growth. Such
bare areas were a radius of about 50 - 75 m from the flares. At Ebocha near the facility area, a
lot of spear grass apparently tolerant of the intense heat radiated to them thrive. In flare sites
where vegetation was within 50 - 100 m from the flares, scorching of the vegetation was
noticed. Scorching of the vegetation was not however, more than 5-10 m deep into the
vegetation. After this area of scorching, the appearance and health of the vegetation was not
visibly seen to have been affected. The distances beyond which vegetation and crops were
not affected by the gas flares roughly corresponded with the distance beyond which the heat
radiation,effect "was not significant i.e. about 100 m at Oshi and 175 m at Akri, Ebocha,
Obiafu/Obrikom.
AQUATIC STUDIES
Rain Water
The four flare site environments where rain water was collected had different characteristics
in the physico-chemical qualities of the water samples particularly pH. In the Akri area, the
pH values of the rain water did not differ significantly over the four rainfall pattern periods.
Rainwater pH values of pH 5.7 (equilibrium pH level of carbon dioxide dissolution in water)
and below were obtained in rain water collected from the Akri area. The pH values were
generally low throughout the rain water collection period. This was accompanied by the
presence of significant quantities of nitrates in the rain water samples which suggests the low
pH values in the rain water must have resulted from the dissolution of NOX emitted from the
VI
gas flares. Other than the low pH values and significant nitrate contents, the conductivity and
total dissolved solids were low in all the Akri rain water samples.
In the Ebocha area pH values were as low as pH 5.5 - 5.7 only during the early rains of April
and May 1997, Thereafter pH values were of the order of pH 6.0 and above. Nitrate levels
were also generally low throughout this period. The conductivity, total dissolved solids, and
ammonium-nitrogen (NH4-N) values were also very low.
In the Obiafu/Obrikom area pH values were low during the April/May period and towards the
end of the rains in late October/November when pH values below pH 5.7 were obtained.
Conductivity and total dissolved solids values were low and like in the Akri rain water
samples, significant quantities of nitrate-nitrogen (NO3-N) and ammonium-nitrogen (NH4-N)
were obtained. Low pH values tended to be related to the elapsed period between the
previous rain and when low pH values were obtained - the pH being lower, the longer the
time interval but this was not clearly demonstrated in all the samples.
In the Oshi area, low pH values beiow pH 5.7 in rain water and correspondingly higher nitrate
levels were obtained during the April/May period. The pH values of all the rain water
samples after the April/May period were about pH 6.0 or slightly more and correspondingly
the nitrate levels were less than in the April/May period.
The natural contribution of lightning during thunderstorms to the nitrate contents of the
rainwater samples however is not known. The low pH values (< 5.7) of rainwater samples
obtained are however complicated by the fact that there are other flares close to and within air
pollutants transport distance of the flares studied. These flares are the Shell Akri Flowstation
flare close to the NAOC Akri flare, the Elf Obagi Flowstation flare close to the NAOC
Ebocha and Obiafu/Obrikom flares and the Shell Oshi Flowstation flare close to the NAOC
Oshi Flowstation flare. Whatever effect the NAOC flares would have on neighbouring
communities is complicated by the presence of these flares.
The volume of rain water that brings down the NOX formed during gas flaring is important.
The acidity of the rain water obtained will be expected to be lower, the smaller the volume of
rain water in which the NOX is dissolved. Thus a situation where NOX is brought down by
moisture in the form of dew is likely to result in the lowest possible pH.
Wind speed in each of the flare sites and its ability to rapidly disperse pollutants must have
contributed to the different results obtained at the various flare sites. The Ebocha and
Obiafu/Obrikom area which is an intensively farmed area with few secondary bushes or
forests have more frequent and higher wind speeds than the Akri and Oshi areas where the
seasonal swamp_ forest environment does not allow rapid movement of wind as in the Ebocha
and Obiafu/Obrikom areas. Thus wind speed is more likely to explain the pH values of most
of the rain water samples remaining at about pH 6.0 in the Ebocha/Obiafu/Obrikom area
where the pollutants are rapidly transported to considerable distances as against the Akri and
Oshi areas where such rapid transport does not take place.
Their is no doubt that the flares produce oxides of nitrogen which lead to acid rains but their
contribution to rusting either directly or indirectly by accelerating the process can not be
definitely ascertained without carrying out corrosion test on corrugated iron sheets.
VII
Rivers, Creek And Burrow Pit Water Samples
Water temperatures in the rainy season ranged from 25.0 °C - 26.0 °C and in the dry season
temperatures were higher and ranged from 26.5 °C to 29.0 °C. Aquatic weeds were more
extensive in the wet season than in the dry season. Hydrogen ion concentration (pH) of the
surface waters was higher during the wet season than in the dry season when the waters in the
various flare sites water sample areas was acidic. Turbidity in terms of total dissolved solids
was more in the dry season than in the rainy season especially in the burrow pits. Electrical
conductivity (EC) values showed no seasonal pattern and were generally low in both seasons
ranging from 21 u.S/cm at Ebocha in the wet season to 180 jiS/cm at Oshi in the dry season.
Dissolved Oxygen (DO) values of the water bodies varied greatly. Akri-2 had the lowest DO
value of 1.9 mg/1 in the wet season. This low value for DO shows that this sample location is
poorly oxygenated and would not support aerobic organisms. The highest DO value was
recorded at Obiafu/Obrikom-2 in the dry season. This observation is not surprising since the
Obiafu/Obrikom-2 sample location is the Orashi River with a lot of turbulent water
movement observed during the study. The Biochemical Oxygen Demand (BOD) values
ranged from 0.9 mg/1 to above 7.0 mg/1 in the rainy season at Akri-2 and Ebocha-2
respectively. No dissolved oxygen was present in the BOD water samples from Oshi-1 and
Ebocha-2 stations indicating that BOD was greater than the DO.
Ten classes and 38 species of phytoplankton were recorded. The diatoms Bacillariophyecae
and green algae (Chlorophyecae) were well represented accounting for 62% and 17%
respectively of the plankton. In all stations, phytoplankton density was higher in the dry
season than in the rainy season. Ziooplankton density was generally low in the water bodies
studied. Only five (5) classes were encountered. They are Holotricha, Peritriacha,
Spirotricha, Rotitera and Crustacean. The density of zooplankton was however, high in the
wet season than in the dry season. This is attributed to the abundant phytoplankton which
they feed on during the wet season. The class Peritricha occurred only in the wet season
while the Holotricha and Rotifera occurred in both seasons.
Aquatic Macrophytes
Aquatic plants were observed extensively during the wet season. These include the water lily
(Nymphea lotus) water lettuce {Pistia stratioles), cat tail {Typha Spp.), water hyacinth
(Eichornia crasispes) pond weed (Potanogeton spp.), eel grass (vallisneria spiralis), swamp
weed (Alisma aqualica) and creeping water primrose {Jussiaea repens). The density and
number of each was however greatly reduced in the dry season. By and large, the study area
is the home for many economically important aquatic macrophytes.
CONCLUSION
The results of the flare studies show quite clearly that the gaseous emission of pollutants from
, the flares high into the atmosphere, does not result in any significant effect on the air quality
of the surrounding environment for distances up to 5 km and beyond. Radiation from the gas
flares do not affect vegetation as well as soil properties and human comfort at distances
beyond 175 m. Drastic effects of gas flares on vegetation, depending on flare size and
number, is expected only within a distance of 50 - 100 m from the flares. Other than the
effects on vegetation, the other possible effect on the gas flare environment is acid rain
formation which was demonstrated by some rain water samples containing significant
contents of nitrate-nitrogen. It is postulated that condensation of much stronger acid moisture
VIII
would be expected if the oxides of nitrogen (NOX) formed during gas combustion is dissolved
and brought down by dew. This needs further investigation.
Their is no doubt that the flares produce oxides of nitrogen which lead to acid rains but their
contribution to rusting either directly or indirectly by accelerating the process can not be
definitely ascertained without carrying out corrosion test on corrugated iron sheets.
IX
ACKNOWLEDGEMENTS
We wish to thank the Management of the Nigerian Agip Oil Company (NAOC) for giving us
the opportunity to carry out this study. We particularly appreciate NAOC's concern for the
environment, a concern which has led to a very sound health, safety and environment policy
without which this work would not have been possible.
We also like to thank in particular the General Manager District, and the staff of the
Environmental and Quality Control (EQC) Department in Port Harcourt for arranging
excellent logistics support and for generously making available to us, all necessary facilities
to enable us carry out our field studies smoothly.
STUDY TEAM
CONSULTANTS
Prof. C. T. I. Odu Dr.
J. F. Alfred-Ockiya
Mr. F. O. C. Harry Mr.
A. Olaposi
(Soils/Vegetation) Project Leader
(Hydrobiology)
(Chemistry)
(Meteorology)
TECHNICAL ASSISTANTS
Mr. W. Ngeri-Bunu Mr.
Lah Oreuyie Zukwue Mr.
Prince Obah Mr. R. Amah
LIST OF ABBREVIATIONS AND ACRONYMS
BOD
CEC
Cells/L
cfu
cm
cm2
DO
g
Ha
HET "
Kg/ha
km
j^m2
L
m
meq
mg
ml
mS ■
>S
N
N/d
No./litre
ppm
Spp.
mg
mg/L
mS
vvt
I
=
=
=
=
=
=
=
=
=
=
=
=
.
■ . ..
=
■
.
=
=
=
■.■■.■=
.
.
=
=
=
=
=
=
=•
=
Biochemical Oxygen Demand
Cation exchange capacity
Cells per litre
Colony forming units
Centimetre
Centimetre squared
Dissolved Oxygen
Gramme
Hectare
Heterotrophic bacteria
Kilogram per hectare '■'
Kilometre
= , Square Kilometre
= Litre
Metre
=* . Milli-equivalent
Milligram
Millitres
MilliSiamens
MicroSiamens
3= Normal
Not detected
Number per Hire
Parts per million
Species
Microgram
Micrograms per litre
Microsiemens
Weight
XI
LIST OF FIGURES
Xil
LIST OF TABLES
X1H
GAS FLARE STUDY OF OBIAFU/OBRIKOM GAS RECYCLING PLANT, EBOCHA
OIL CENTRE, OSHIE FLOWSTATIQN AND AKRI FLOWSTATION
BY
18 Ohacto Street, D Line, Port Harcourt
CHAPTER -1
1.1. INTRODUCTION
The Nigerian Agip Oil Company (NAOC) desirous of knowing the effects of gas flares on the
environment, wanted a characterization of the various environments in which some of their
gas flares are situated, particularly the gas flares at Akri, Ebocha, Obiafu/Obrikom, and Oshi
Flowstation areas.
Efforts were made particularly to determine the prevailing dominant winds and the extent to
which pollutants introduced into the environment would disperse. The study aim was to
evaluate the various pollutants in the ambient environment of the gas flare and among others
evaluate economic damage if any, attributable to air pollution by way of soiling effects of
particulates, damage to vegetation and crops, resulting from excessive concentration of
gasses.
Heat radiated by the gas flares were determined with a view to determining the extent of
adverse impact "of each flare site. Rain water samples were collected at the end of the rainy
season, early rainy season, and when the rains attained some degree frequency or regularity
with a view of determining the possibility of acid rains.
Consequently, this study was commissioned to assess the existing environmental conditions
around NAOC's Flowstation locations with a view to evaluating the effect of gas flaring on
the ecosystem.
.
1.2. OBJECTIVES AND SCOPE OF STUDY
The objective of the study was thus a characterisation, in each gas flare area, of the natural
environment by way of comprehensive baseline data on the existing state of all identifiable
ecosystems in the areas involved, against which the effect of the gas flares, if any, can be
assessed. More detailed studies were to involve the following:
(1) Meteorology
The objective of the meteorological study was:
(i)
to obtain the prevailing dominant winds and to what extent a pollutant will
, travel.
(ii) to provide the meteorological and climatic conditions that govern when and
where pollutants dispersed from the flare will have its greatest impact.
(iii) to identify the atmospheric circulation pattern for the area.
For description and inference purposes of the physical conditions, the wind speed/direction
were to be, determined, to provide information on dominant wind directions prevailing in the
area and the extent to which pollutants introduced into the environment are dispersed.
(2) Air Quality Measurement
The gas flare study was to involve:
•
... .
a study of the air quality in the immediate environment of the gas flare and at
various distances away from the flare up to some kilometers away.
the identification of the major pollutants contained in the ambient environment
of the gas flare.
a description, measure and quantity of the existing levels of general air pollution
parameters and any other pollutant likely to be associated with the flare.
a determination of the air pollutant transport and the areas likely to be affected.
evaluation and assessment of the general impacts on air resources (flora, fauna,
health, etc.) likely to arise from the gas flare.
determine the buffer zone in each flare site.
The parameters to be measured included the general air pollution parameters (sulphur dioxide
SO2, nitrogen oxide NO X, Total Hydrocarbons (THC), as well as Total Suspended
Particulates (TSP). All data generated during the air quality study were to be collated,
analysed and interpreted. Statistical analyse's were to be applied where necessary. Impacts of
gaseous emission from the gas flares were to be assessed and quantified.
(3) Radiation, Temperature, and Relative Humidity Measurements
Heat radiation from the flare were to be determined and compared with radiation from the sun
as well as background radiation in the study area. Temperature and relative humidity
measurements were also to be determined.
1.3. GENERAL FEATURES OF THE STUDY AREAS
1.3.1. Akri
The Akri flare site is on the Sombreiro-Warri Deltaic Plain formation. These soils occur in
the eastern part of the delta, outside the Niger Delta zone. They are much older than the
present delta and have been mostly eroded away. The soils are very sandy with moderate
clay contents of 25 - 35%. The colour of the soils is brown to strong brown and are acid in
reaction, pH around 5.
The Akri area is a swamp forest/ dryland vegetation area. The ground in the swamp forest is
very irregular with frequent patches of open water even in the dry season; it is flooded in the
rainy season. The forest too is very irregular and superficially resembles broken or
secondary forest caused by man's disturbance; in fact, however, these areas of swamp forest
are more or less virgin as the land is quite unsuitable for farming and habitation.
The flowstation itself is built on a raised area from soil collected from a borrow pit that
almost surrounds the flowstation. Human impact around the flowstation area has resulted in
the drylarjd areas having a savanna type vegetation. There were two flares at the Akri
flowstation - one nearer the facility area is large and smoky while the other' farther away is
relatively clean.
1.3.2. Ebocha
The Ebocha flare site area is also located on the Sombreiro-Warri Deltaic Plain. These soils
have been described earlier under Akri. The Ebocha flowstation area which was once a
dry/swamp forest area is now a mosaic of oil palm/swamp. The area is heavily farmed and
the fallow vegetation of the area shows a preponderance of Eupatorium odorata with other
plants like Aspilia latifolia and Asystasia gigantica. Other commonly occurring species were
the Gramineae, Urena lobata, Convulvulus sp., Napoleona imperialis, Vosia sp.,
Pauridiantha hirtella, Baphia nitida and the oil palm (Elaeis guineensis) which is the
emergent plant in the farm fallow areas and hence the term mosaic of oil palm/swamp being
used to describe the predominant vegetation of the Ebocha area.
The smaller flare closest to the facility area burns smokeless but the other two giant flares
bum with a lot of soot. Many birds were seen flying around the flares. The ground near the
flares is completely devoid of vegetation, no doubt as a result of the heat from the flares.
Closer to the flare and father away from the facility area, the vegetation is scorched.
Scorching of the vegetation was not however, more than 5-10 m deep. Near the facility area,
a lot of spear grass thrives. They appear to be tolerant of the heat radiated from the flares.
1.3.3. Obiafu/Obrikom
The Obiafu/Obrikom flare site area is also located on the Sombreiro-Warri Deltaic Plain
formation and is very similar to the Ebocha area except for the influence of the Orashi fiver
and its riparian vegetation near the Gas Plant. The soils are also similar and have been
described earlier under Akri.
Except in the swampy riparian vegetation areas,
the
Obiafu/Obrikom sector is dominated by bush with scattered oil palm (Elaeis guineensis)
stands and farmlands better described as a mosaic of farmland/oil palm forest.
'..
1.3.4. Oshi
Soils of the Oshi area belong to the upper Deltaic Plain. This area is characterised by the
presence of high lying meander belts and levees of lower lying basins which arc less
frequently inundated by the Orashi river. Generally the soils of the levees consist of loamy
sand, sandy loam and loam or silt loam. The pH of these soils vary from strongly to medium
acid with pH values in the range of 5.1 to 6. The organic carbon content of the soils are low
(<1%) and depending on soil texture, the cation exchange capacity is low to medium.
The Oshi flowstation is located in a seasonal forest swamp area. The flowstation itself is
surrounded by a disturbed vegetation with unkempt farms and bush fallows. The vegetation
of the area however is the least disturbed of the four flowstation areas stu died. The
flowstation is surrounded by a disturbed high forest and this no doubt is a result of the
seasonal swamp nature of the area. The disturbed vegetation contains some bamboo trees.
Figures 1 and 2 shows the location of the various flare sites and their
surrounding communities.
Figure 1:
Locations of the various Flowstation flares studied in NAOC's operational
areas.
SCALE: 1/250,000
N
Flare/Rainwater
collection sites
Figure 2:
Map of the various flare sites studied and their neighbouring
communities
CHAPTER - 2
2. MATERIALS AND METHODS OF STUDY
2.1 METEOROLOGY
2.1.1 Wind Speed And Direction
Wind speed in the flare site areas was determined at about 200 m from each flare site area,
using a battery operated Munro Digital Hand Held Anemometer. When the equipment is
switched on, the equipment indicates the actual fluctuating wind speed for a period of up to
12 - 15 seconds and then indicates the highest gust during the last 10 seconds of the display.
After the maximum speed has been displayed, the average speed over a 12 to 15 second
period can then be displayed by the pressing of a button. There are four possible displays
(knots, miles/hour, metres/second, kilometres/hour). Readings were displayed in
meters/second. Wind frequency and speed of the winds from different directions were
measured on hourly basis over a period of four hours over the period March 8 to 15, 1998
which is the peak of the dry season. The duration of the wind was measured with a stop
watch and the minimum and maximum times the wind was blowing were obtained.
For the wind direction, an improvised low mass material (a piece of linen) was used to
observe thp direction of drift and relating this to the compass points of a portable compass.
2.2. AIR QUALITY MEASUREMENTS
2.2.1. Suspended Particulate Matter
Many pollutants are composed of minute particles in the air. Large particles fall to the
ground quickly but respirable sized particles can stay airborne for long periods. Suspended
particulate matter which is accepted as total suspended particulate (TSP) matter was
measured using an ELE Digital aerosol monitor - an instrument for surveying airborne
particulate levels.
The instrument quantifies the weight of respirable particulates in the air using an
opto-etectrical detection system. It has been found useful in industrial surveys, dust
monitoring, pollution investigations and environmental impact assessments. It has a large
digital display, and a quick response time (1 or 10 seconds selectable).
2.2.2. Determination ol'CO2, NO,, SO2, and Total Hydrocarbons in Air
Drager-Tubc-Measurement-Sysleni
The Drager-Tube measurement system was used for the determination of carbon monoxide
(CO) nitrogen dioxide (NO2), sulphur dioxide (SO2) and total hydrocarbons in the air. It
consists'of a Drager-Tube and a Drager gas detector pump. Each Drager-Tube contains a
very sensitive reagent system that produces accurate readings when the
technical
•characteristic of the gas detector pump precisely match the reaction kinetics of the reagent
system in the tube. Therefore, a gas detector pump delivering the correct volume must also
pull the sample through the Drager-Tube at the proper rate. In effect, the pump and tube form
a sampling unit. To interchange the pumps and tubes of various manufacturers can lead to
erroneous results. These requirements are referenced in international as well as national lube
standards or norms which require or recommend that detector tubes be used with a matching
gas detector pump from the same manufacturer.
Air quality around the gas flares was determined using an ELE gas detector. This is a simple
but accurate device which consists of 2 parts, a hand pump and a Drager detector tube. The
pump has a bellows action which can be operated by one hand to draw in exactly 100 ml of
gas per stroke. The glass detector tube is fused at both ends and contains an indicator
substance. For measurement, botii ends of the tube are broken off and one end inserted into
the pump. The prescribed number of stroke for a given parameter is made and the colour
change in the tube is measured against a graduated scale on the side of the tube. The
numerical value determined is a measure of the gas concentration.
Air quality measurements were made at distances ranging from 100m to 5 km depending on
accessibility and convenience, SW and NE of the flare site areas. Measurements were limited
to a maximum of 5 km because a gust of wind at a maximum of about 13 km/sec note'd
during the wind measurement studies is expected to transport pollutants to a distance of 4 km
by which time the concentration of pollutants would have been considerably reduced.
Determinations were made on three different occasions within a period of one hour and the
highest reading obtained was recorded.
2.3. FLARE RADIATION
Radiation'from the gas flares at various distances from the flare was measured with an ELE
Quantum Radiation Measuring Unit. Photosynthesis in plants occurs only within the
wavelength range of 400 - 700 nm - the photosynthetically active waveband. Within this
waveband, the photosynthetic efficiency per quantum increases with wavelength, red photons
being about 30 % more efficient than blue photons. This variation in response is^taken into
account by the photosynthetically active radiation (PAR) sensor system, but the measurement
taken with the quantum radiation sensing system has a sensitivity to photons, independent of
wavelength, between 400 - 700 nm, and so gives an objective measure of quanta available for
photosynthesis. The sensor has a cosine corrected head, and an ultra high input impedance of
the measuring and display unit, preserves linearity. Radiation from the gas flares was
determined along transects originating from the gas flares starting from a distance of 75 - 125
m from the flares. Measurements were taken as follows:
(i)
(ii)
(iii)
(iv)
with the sensor facing the ground,
■ with the sensor directed at the flares,
with the sensor directed at the opposite direction to the flares while backing the flares,
with the sensor facing the sun in the sky.
Determinations were made along the transects at intervals of 25 m away from the flares as
shown in Figures 3 - 6 and readings recorded in (amol/m2/sec.
Figure 4: Sketch of Ebocha Flowstation area showing radiation and soil studies transects.
Figure 6: Sketch of Oshi Flowstation area showing radiation and soil studies transects.
2.4. TEMPERATURE/RELATIVE HUMIDITY
Temperature and humidity were measured with an electronic temperature/humidity meter.
This simple to use instrument shows both temperature and relative humidity on a clear LCD
display. The internal memory stores the maximum and minimum temperature since the last
reset.
2.5. SOILS STUDIES
-2.5.1. FIELD METHODS
Soil samples were collected along transects used for radiation measurements. Soil samples
were collected starting from an area 75 m from the flares at Obiafu/Obrikom and Oshi, 100 m
from the flare at Akri and 175m at Ebocha. Thereafter, soil samples were collected at
intervals of 25 m followed by 100 m intervals, At each sample location, soil samples were
collected from at least five random spots with a 9 cm diameter Dutch auger and bulked
together to give one composite sample. Soil samples were collected to depths of 0 -15 only
with a view to assessing the effect of radiation from the flares on soil characteristics.
The soil samples were collected at the peak of the dry season over the period 23/1/98 to
1/2/98,
Very careful attention was given to the collection of soil samples for analyses. This is
because the success or failure of soil analyses as an aid to the acquisition of factual data on
the environment depends on securing a representative soil sample, plus subsequent handling
operations.
Soil samples are taken for analyses to obtain information on that particular soil. Since the
sample is seldom the entire soil mass, the information obtained would only be of interest if it
yields information representative of the whole soil mass. Since with soils, heterogeneity
seems to be the rule rather than the exception, accurate sampling to estimate parameters
which characterise it with an accuracy which meets the needs at the lowest possible cost
becomes necessary.
Several steps are needed to obtain the final sample and these are:
(1) the taking and mixing of a series of cores from the area to be sampled;
(2) sub-sampling this original sample; and
(3) air drying, grinding, sieving, mixing and storing.
The greatest possibility of error, assuming proper sub-sampling, drying, grinding, and sieving
techniques, lies in securing a representative sample at the beginning and this is why great
pains were taken in securing the original sample. In our sampling we have therefore, used
augers capable of obtaining uniform cores of equal volume to the desired depth at all spots
-the quantity of composite sample being such that the whole sample (total cores collected) was
processed for analyses in the laboratory without sub-sampling in the field. This allowed for
more accurate sub-samples that better represented the area sampled and cuts
down
12
considerably on errors due to sample splitting and sub-sampling in the field -a rarely
satisfactory procedure when core samples are so large that sub-samples from cores obtained
have to be taken for laboratory analyses.
2.5.2. LABOKATORY METHOI)S
Soil samples collected from the various transacts were subjected to complete soil analyses for
pH, EC, organic carbon, total nitrogen, mineral nitrogen (NII4, NO2, NO3), exchangeable
actions (Ma, K, Ca, Mg) and available phosphorus.
Soil samples collected from the different study areas were air-dried and made to pass through
a 2 mm sieve. The fine earth was then used for the above analyses. The following is a
description of the methods used for the different analyses carried out on the soil samples.
(I) pH
The pH values of the soils and sediment samples were determined in the laboratory using an
EIL Model 720 pH meter. The pH was determined by dipping the electrode into a 1: 2.5 soil:
water suspension that had been stirred and allowed to equilibrate for about 1 hour.
(ii) Electrical conductivity (EC)
m
The EC of soil and sediment samples were determined on the filtrate obtained after filtering
the suspension used for the pH determination. The Conductivity bridge used for the
measurement was the Griffin Conductance bridge. Conductivity was expressed as jj-S/cm.
(iii) Exchangeable actions
Two and halfportions of a finely ground representative sample were shaken in a conical flask
with 25 ml of IN ammonium acetate for about 1 hour and filtered into plastic cups. The
filtrate was used for the determination of sodium (Na+), potassium (K+) by flame photometry
while calcium (Ca++) and iron (Fe+++), were determined with a Perking Elmer Atomic
Absorption Spectrophotometer. The concentrations of the cations were calculated after
taking due note of the dilution factors and expressed either in parts per million (ppm) or
milligram equivalent per 100 g soil (meq/100 g soil).
(iv) Total nitrogen
Two and half grammes of a representative air dry soil was accurately weighed into Teeator
digestion flasks and a catalyst mixture containing selenium, CUSO4 and Na2SO4 was added
followed by 10 ml of concentrated analytical grade sulphuric acid. The contents of the flask
were mixed by gentle swirling and then digested on a Teeator block until the digest cleared
(light green or grey colour). Heating was continued for another one hour before the digest
was allowed to cool. The digest was then transferred quantitatively with distilled water to a
150 ml conical flask and made up to mark with distilled water. Aliquots of this was then
taken and used for the determination of ammonium-nitrogen using an auto-analyser. The
percentage nitrogen contents of the soil was then calculated after taking into account the
different dilution factors.
,
13
(v) NH4+, NO2" and NO3■ Ammonium, nitrite and nitrate-nitrogen were determined in soil extracts obtained by
shaking 5 g of a representative soil sample with 50 ml of \N K2SO4. Aliquots of this
extract were used for ammonium - nitrogen determination by nesslerization.
Nitrite-nitrogen was determined by the Greiss-Uosvay method using alphanapthylamine and
sulphanilic acid and nitrate-nitrogen was determined by the phenoldisulphonic acid method.
Nitrite concentrations were generally low and so did not require removal by decomposition
with sulphamic acid before nitrate determination.
(vi) Organic carbon
Carbon was determined by the wet combustion method of Walkley and Black (1934). One
gramme of finely ground representative sample was weighed in duplicates into beakers. Ten
milli-litre of potassium dichromate solution was accurately pipetted into each beaker and
rotated gently to wet the soil sample completely. This was followed by the addition of 20 ml
of cone. H2SO4 using a graduated cylinder, taking a few seconds only in the operation. The
beaker was rotated again to effect more complete oxidation and allowed to stand for 10
minutes before dilution with distilled water to about 200-250 ml. Twenty five ml of 0.5 N
ferrous ammonium sulphate was then added and titrated with 0.4 N potassium permanganate
'under a strong light.
(vii) Available phosphorus (Bray P-l)
Available phosphorus in the soil samples was determined by weighing 1 g of a representative
sample into an extraction flask. This was followed by the addition of 10 ml of Bray P-l
extracting solution (0.25 N HCI & 0.3 N NH4F) and shaking immediately for 1 minute and
filtered. Five millilitre of the filtrate was then pipetted into 25 ml volumetric flask and
diluted to about 20 ml with distilled water followed by 4 ml of ascorbic acid solution (0.056 g
ascorbic acid in 250 ml molybdate-tartarate solution) and diluted to volume. This was
allowed to wait for at least 30 minutes for full colour development before reading from a
Spectronic 70 at 730 mu. Phosphorus (PC^") concentrations were then calculated after
reference to a standard curve.
(viii) Estimation of soil micro-organisms (bacteria and Fungi)
Soil micro-organisms were estimated by the soil dilution plate method in which serial
dilutions of a soil sample in sterile distilled water were plated on a suitable agar medium.
One gramme of the air-dried soil was added to and shaken with 10 ml sterile distilled water In
a McCartney bottle, to give a soil suspension at a dilution of 10"1. A clean sterile pipette was
used to transfer 1 ml of the soil suspension to another McCartney bottle containing 9 ml
sterile distilled water. The contents of the bottle were gently shaken together to give a soil
suspension dilution of 102. A further series of dilutions were carried out to give dilutions of
10-vtol0-(>.
For the fungal counts, 1 ml of soil dilutions of the 10"3 dilution was transferred with sterile
pipettes into McCartney bottles containing 9 ml of molten Potato Dextrose Agar (PDA)
maintained at a temperature of 42 - 45 °C in a water bath. The ultimate dilution used
was
14
thus 10~4. With another sterile pipette, 0.1 ml of streptomycin solution of an appropriate
strength was added to suppress bacterial growth. The contents in each bottle were mixed by
gently rocking the bottle, poured into sterile petri-dishes, and incubated in triplicates at 25 °C
- 28 °C for two to three days, before counting and identifying the fungal colonies that
developed.
For microbial counts, 1 ml of the 10-6 dilution was plated in triplicates on. manitol-extract
agar and incubated aerobically for 3 days at 25 °C - 28 °C before counting.
2.6. VEGETATION STUDIES
2.6.1. FIELD METHODS
Characterization of the vegetation of the flare site areas was carried out initially by a general
and casual inspection to estimate the natural stratification of the plant community.
A rapid assessment of the vegetation of the area was also undertaken. This involved rapid
assessment of the nature and health of the vegetation of the areas close to the flare sites as
well as observing the vegetation as one moves farther away from the flare and comparing it
with vegetation close to the flares.
Aquatic macrophytes were assessed and characterised by the rapid assessment method. This
included recording the prevalent species, and their distribution based on the present or absent
method. All the plant species were as far as possible identified and listed. Those that could
not be immediately identified with certainty were collected, labelled, subsequently pressed,
and taken for identification in a herbarium.
■
15
2.7. AQUATIC STUDIES
2.7.1. COLLECTION AND ANALYSIS OF RAINWATER SAMPLES
Rain water samples were collected over the period April 1997 to January 1998 to cover four
different periods of the rainy season i.e. the early rains in April, the period May to June when
the rains become more regular, 'followed by the peak of the rains at about July to September,
and the November to January period when the rains become less frequent and irregular.
Rain water samples were collected with clean 42 cm. diameter plastic basins placed on stands
one meter high" located about 1 km upwind (SW) and downwind (NE) of the flare sites at
Akri, Ebocha, Obiafu/Obrikom and Oshi indicated in Fig. 2. After each rain, the rainwater in
the plastic basins were transferred into 250 ml plastic cans which were filled to the brim to
exclude air, stoppered and taken to the laboratory for analysis.
The pH, electrical conductivity (EC), Total Dissolved Solids (TDS), ammonium (NH4) and
nitrate (NO3) were determined as described under soil studies and below using aliquots of the
rain water samples.
2.7.2. FIELD INVESTIGATIONS
On the basis of a reconnaissance visit to the study area comprising Akri, Obrikom, Ebocha
and Oshi, a sampling protocol was designed using a purposeful sampling technique i.e.,
sampling sites were based an available water bodies around gas flaring sites. Consequently,
eight (8) sampling sites were chosen; two water bodies per each gas flaring site. Sampling
was carried out in both the rainy season (October 17th - 22nd 1997) and the dry season
(January 27th - 22nd February 1998).
At each selected water body (Burrow pit/creek/River/Swamp) surface water was collected
based on the Standard Methods for the Examination of Water and Waste water (APHA, 1990)
for the determination of chemical properties later.
(i) Water quality parameters
In each station surface water temperature, dissolved oxygen concentration (DO) and
hydrogen ion concentration (pli) and electrical conductivity were measured. Water samples
were collected and kept in an ice chest for the determination of other quality parameters in the
laboratory.
(ii) Plankton samples
In each sampling point phytoplankter were obtained by fixing 1-litre surface water sample
with 4% neutral formalin solution and 2.5 ml. of Lugol's solution.. The JugolVsolution is
used to stain organisms that are present in the water sample. ■
16
Zooplankters were obtained from each station by vertical towing with a plankton net of mesh
size 55u.m. Ten hauls were made in each station and the solution was preserved in 4%
neutral formalin for subsequent examination in the laboratory.
(iii) Surface water temperature
The surface water temperature was determined from the water collected in a large bucket
using a glass in mercury thermometer.
(iv) Hydrogen ion concentration (pH)
The pH of each water sample was determined using a Griffin and George field pH meter.
(v) Electrical Conductivity
The conductivity of each water was determined using a Metrohm - Herisan conductivity
jneter. .Conductivity was expressed as micro Siemens cm"' ((.iS/cm"').
(vi) Dissolved oxygen concentration (DO)
The dissolved oxygen concentration of the water sample from each station was determined
using a Griffin field dissolved oxygen meter model 40. Water samples were collected for the
determination of chemical properties as well as other parameters in the laboratory.
(vii) Aquatic macrophytcs
The survey was conducted by recording the presence or absence of macrophytes within the
selected sampling stations and environs. Subjective estimates were made also of the relative
abundance of each macrophyte within the stations. Separate records were made for possible
effects of the gas flares on the macrophytes especially whether there was any significant
floristic gradient with respect to species distribution amongst the stations and also to
determine the underlying environmental factors that may determine such gradient if any.
2.7.2. LABORATORY STUDIES
'
.
'
,
Water samples collected in the field were used for the determination of their chemical
properties following the procedures already described for the soil extracts. Other
physico-chemical properties were determined as follows:
(i) Total dissolved solids
Water samples (100 ml) previously filtered through What ■san's filter paper No. 4 was
evaporated to dry ness-at 103 °C in an evaporating basin of )wn weight. The increase in
weight of the evaporating basin was used in computing dissoi ved solids in mg/1.
(ii) Biochemical oxygen demand (BOD)
17
The Biochemical Oxygen Demand of water sample from each station was determined using a
pair of light and dark bottles which were each filled with water sample from each station.
Each pair was incubated at 20 °C for 5 days. The oxygen of the sample was determined prior
to and after incubation. The BOD was computed as the difference between the initial oxygen
content and final oxygen and expressed as mg 02/1.5days.
(iii) Plankton analysis
To assess the composition and abundance of the phytoplankters, the preserved water sample
was concentrated to a uniform volume of 500 ml. Then subsamplcs of 1 ml were pipetted
onto a Sedgewick-Rafter counting chamber. Microscopic observation of species
identification based on keys by Nccdham and Nccdham (1962), and enumeration were
undertaken. From each sample, three sub-samples were analyzed and the values obtained
were expressed as individuals per litre.
Water samples for the zooplankters was allowed to stand for 24 hours and the supernatant
was carefully pipetted off until a 10 ml concentrated sample volume was obtained.
Zooplankton identification and enumeration was done by pipetting 1 ml of the concentrated
sample onto a Sedgewick-Rafter counting chamber using a Stampel pipette. Identification of
zooplankton was with relevant keys, description and drawings in Newell and Newell (1963),
Needham andNeedham (1962) and Nwadiaro (1990). The number of individual zooplankton
'on each taxa was counted for each sample, and repeated three times and recorded as
individuals per litre.