Energy and Earth Science Vol. 7, No. 2, 2024 www.scholink.org/ojs/index.php/ees ISSN 2578-1359 (Print) ISSN 2578-1367 (Online) 1 Original Paper Flare Pollution Loads and Carbon-Dioxide Effect on Rainwater Acidity in Niger-Delta: A Review, Investigation and Model for Safe Living Quarter Ugwunna D. Amadi 1* & Godpower C. Enyi 1 1 Department of Petroleum and Gas, University of Salford, M4 5WT, United Kingdom * Ugwunna D. Amadi, Department of Petroleum and Gas, University of Salford, M4 5WT, United Kingdom Received: July 7, 2024 Accepted: July 18, 2024 Online Published: August 12, 2024 doi:10.22158/ees.v7n2p1 URL: http://dx.doi.org/10.22158/ees.v7n2p1 Abstract Carbon-dioxide does not only affect climate change, but also contribute tremendously in acidification of rain water. Hazard identification and risk assessment are fundamental components of effective risk management, specifically in sensitive areas where adverse effects can have significant consequences. This study provides novel methodology for environmental and safety assessment of flared gases in sensitive areas such as residential homes. Distancing Sampling Technique (DST) was used to investigate the sensitivity of rain water pH at distances away from flare site in order to develop a Risk Management Model for sensitive regions. First, a review on rain water acidity was made around flaring and non-flaring areas in Niger-Delta states, which revealed Moderate-High acidity effect around flaring zones and no effect on non-flaring zone. Secondly, Flared Gas Quantification, pH Experimental Evaluation (PEE) and Risk Assessment Matrix (RAM) were the three systematic approaches used respectively to quantify, measure and evaluate the effects of CO2 and other flare pollutants around the area of study. An average of 809,300,000 Mscf of associated petroleum gases were flared around the oil and gas producing areas in Delta State, causing a release of around 43x10 6 tons of CO2 from 2012-2022. Experimental results showed the range of pH from 4.56 ± 0.06 to 5.10 ± 0.06 for the 33 samples of harvested rainwater in Kwale community, Delta state causing a deviation of 16.38 to 30.05% from standard. The developed and validated model suggests 4.81KM radius as the safe distance for human habitation from flare sites. Based on these findings, carbon-capture and sequestration projects must be activated in Niger-Delta to curb the menace. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 2 Published by SCHOLINK INC. Keywords Acid rain, Distance sampling, Standard Deviation, Risk Matrix, CO2 sequestration 1. Introduction The need to address risk issues in a continuously evolving environment, coupled with improved information and communication technologies has led to the development of several techniques, hazard identification and risk assessment methods (Villa & Cozzani, 2015). Risk analysis by dynamic approach have been an evolving method for identifying, assessing, and quantifying increasing risk in a system with uncertainty, real-time changing environment, and system complexity (Bucelli, et al., 2018; Villa & Cozzani, 2015). A systematic approach for defining safe residential quarters due to pollution by flared gases around flare regions are still lacking. Nduka, J. et al. (2008), collected rainwater samples from Portharcourt and Warri, which are two major oil and gas industrial areas in Niger-Delta, to determine the water pH, while control samples were collected from Awka in Anambra state, which was non-oil and gas hub. The samples were collected up to 115m from a reference point in a triangular equilibrium using clean plastic basins. The pH readings are as follows: Portharcourt (4.71,4.94,4.93); (5.04,5.73,4.91): Warri (4.81,4.70,6.15);(4.79,4.80,4.72): Awka (6.04,5.88,5.75); (6.00,5.10,5.96). The pH of rainwater in Portharcourt and Warri, were highly acidic due to industrial activities (gas flaring) while the pH of Awka acting as control is within acceptable range. Odjugo, P. & Osemwenkhae, E. (2009), determined the effects of gas flaring on crops grown in Niger-Delta. The results of their work reveals that the flare affects extends beyond 110 meters from the flare location and therefore advised on further studies to validate the claim. Atuma, M. I., & Ojeh, V. (2013), examined the effect of flared gases on soil and casava productivity from five sites in Ebedei, Ukwani LGA of Delta State in Niger-Delta. The soil samples were harvested at varying depths and distances ranging from 0 - 20cm and 50m - 250m respectively from the bund wall of the flares. Critical analysis using multiple regression and paired t-test methods shows wide acidity variation in the results obtained in flaring area to those from the controlled site (non-flaring area). However, the researchers did not attempt to model a safe threshold for human habitation in those areas due to adverse effects of rain acidity. In this research, Environmental assessment of risk of CO2 and other flare pollutants was investigated by evaluating the pH of rainwater around Delta state, a region in Niger-Delta, which was conducted 2KM from flare sites for two consecutive years. The study was aimed at providing simple methodology for safety and environmental assessment of flared gases in sensitive areas at defined distances from flare sites followed by measuring the pH of the water and modelling safe human quarters. pH is an incredible parameter that plays a key role in assessing water quality. In environmental sampling and monitoring, the pH value indicates the pollution index of the water, which has potential adverse effect www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 3 Published by SCHOLINK INC. on the environment, people and ecosystem. On the light of the above, the present work on impact assessment focuses more on the influence of flared gases on rainwater acidity at specific intervals up to 2KM. Niger-Delta region of Nigeria has proven natural gas reserves of 203.16 Trillion Cubic Feet (TCF) and crude oil reserves of 36.89 billion barrels (bb) and between 400 TCF-600 TCF of undiscoverable natural gas reserves. This is estimated to be within 7.7% -15.5% of global quantity of undiscoverable natural gas resources. Judging by the trend, some considerable amount of the associated gases when produced would be flared leading to huge economic loss and consistently endangering human health, ecosystem and general environment. Acid rain and most environmental pollutant have been widely attributed to impact of gas flaring especially in the Niger Delta region of Nigeria (Elijah 2022; Ebong, et al., 2022; Nwankwo & Ogagarue, 2011). Gas flaring does not only affect climate change but also pollutes the environment, with utmost effect to inhabitant in close proximity to flare sites. Hazard identification, risk assessment and mitigation plan are keys for prevention of chances of diseases, calamities and mishaps in sensitive areas. 2. Review of Literature Rainwater is water fallen as rain that has not collected soluble matter from the soil and is therefore soft. It is also a surface water obtained from rain fall, which is an excellent source of domestic water for rural areas and dispersed population (Anyata, 2008; Odume, 2022). Water is essential for the environment, human health, food security and sustainable development, whose quality is an indispensable requirement for healthy living (Schiller, 1982; Adeyeye, et al., 2019). It becomes a problem to humanity, ecosystem and the environment when the physical and chemical balances of the water chemistry are altered due to natural or anthropogenic activities. Acid rain is a normal rain acidified by certain air pollutants. Rain water acidification is a serious environmental problem of trans-boundary nature caused by the oxides of sulfur and nitrogen and worsened by increasing amount of carbon-dioxide in the atmosphere (Singh & Agrawal, 2007). Whereas the normal rain cleanses, supports, enriches life and the environment, acid rain dirties and damages life, ecosystem and the environment (Abbasi, et al., 2013). Acid rain is considered by many as one of the grave environmental threat of our time caused by air pollution that have led to fish extinction and forest dieback (Grennfelt et al., 2020). Acidic rain poisons our water bodies and lowers the soil pH. Lowered soil pH leaches away nutrients cations and increases the exposure of heavy toxic metals, which reduces soil chemical properties that enhances soil fertility. When the soil chemistry is compromised, it impacts negatively on growth and productivity of plants and forest trees. Basically, the degree of acidity of water and soil is measured by pH, which is a shorthand version of potential hydrogen. Figure 1 displays the origin of pollutants that www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 4 Published by SCHOLINK INC. acidifies rain water, cause climate change and other environmental threats. Figure 1. Cause and Effect Diagram for Environmental Pollutants Which Acidifies Rain Water 2.1 Gas Flaring Proximity to Residential Areas In Niger-Delta, there are widespread perceptions that due to human habitation in close proximity to flare locations, it has adversely affected the region in terms of human health status, environmental degradation, and social-economic issues (Nriagu et al., 2016; Otache et al., 2021). This is due to daily released amount of the dangerous toxins into the atmosphere, resulting to the pollution of air, water, soil and the ecosystem (Oghenejoboh et al., 2007). The impact of gas flaring spreads across extensive radius from the point of generation. In Niger-Delta at least Two Million (2,000,000) people lives within Four Kilometres (4KM) (2.5 miles) in flaring locations (NOAA Virtual Night Flare, 2018). Figure 2. Yellow Spots Showing Population of Residential Homes at less than 2KM from Flare Sites in Niger-Delta Source: Global Gas Flaring Tracker Report, July, 2020; https://gasflaretracker.ng/ www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 5 Published by SCHOLINK INC. These emissions have caused series of litigation from the host communities to the oil and gas company, government agencies, resulting to claims and counter claims (Nduka et al., 2008). Flaring as a major source of greenhouse gases generates noise and heat leading to health issues and environmental degradation (Emam, 2015; CAPP 2012; Abiodun, 2014; Oseji, 2007; Ejiogu et al., 2019). Scientific studies have identified over 250 toxins released from flaring. They include carcinogens such as benzopyrene, benzene, carbon-disulphide (CS2), carbonyl-sulphide (COS) and toluene. Others are metals such as mercury, arsenic and chromium, sour gas with H2S and SO2, nitrogen oxides (NOx), carbon-dioxide (CO2), methane (CH4) etc which contributes to greenhouse gases (EPA 2014; Christiansen et al., 2016; Mobolaji Sunmoni, 2018). 2.2 Specific Effects of Acid Rain Specifically, acid rain affects human health, damages the soil, plants, trees as wells as buildings and structures (Singh & Agrawal, 2007; Abbasi et al., 2013). Acid rain not only damages the chemistry of soil but also changes the quality of soil (Fiza Fatima et al., 2021). It distorts the enzymes of microbes in the soil, kills them, leaches the soil essential nutrients, decreases soil fertility and causes stunted growth of plants (Singh & Agrawal, 2007; Atuma & Ojeh, 2013). Acid rain washes heavy metal toxins like Magnesium (Mn), Aluminium (Al), Lead (Pb), Iron (fe), Mercury (Hg) and gets them dissolved in the soil, which permeates down to the ground drinking water and poisons it. While some of these toxins are washed off and flows to the rivers, lakes and streams (Nwankwo & Ogagarue, 2011; Ejiogu et al., 2019; Ebong et al., 2022). The accumulated heavy metals in human bodies through ingestion of the poisoned water, causes headache, irritation of throat and nose, coughs etc. Excess ingestion of these toxins contributes to kidney and heart issues, lung diseases such as Asthma, bronchial problems, etc. Direct exposure of human body to acidified liquids affects the immune system, which drastically reduces human antibodies (Nagae et al., 2011). The direct droplet of acidic rain water lowers the pH of the water bodies therefore adversely affects the living things in the water. Accumulation of heavy metals in the water bodies affects the breaths of fishes leading to premature deaths. The above phenomenon equally affects the food chain at different levels. When humans eat these poisoned fishes, the heavy metals will be deposited into the human body, also when animals or birds eat the dead fishes; they also become a secondary receiver of the poisoned food. 2.3 Chemistry of CO2 Release from Combustion Process Flared gases are composed of various forms of gases (methane, ethane, propane, butane, pentane, hexane, etc.), water vapour, hydrogen sulphide, nitrogen, volatile organic matters, etc. (Peterson, 2007; Putriastuti, et al., 2021). During gas flaring, the combusted gases generate mainly Carbon-dioxide (CO2), water vapor and heat (Gzar & Kseer, 2009). This is evident in equations (2.1-2.5). www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 6 Published by SCHOLINK INC. The presence of CO2 in the atmosphere causes acidity of rain water according to the chemical reactions blow. In equation (2.6), carbon dioxide (CO2) reacts with rainwater (H2O) to form carbonic acid. The presence of hydrogen ion molecules “H +” in the water renders it acidic by lowering the pH as shown in equation (2.7). Accumulation of H + due to higher concentration of CO2 from combustion process further acidifies the rain water. 3. Materials and Methods In this research, a field work around a flare location in a community in Kwale area of Delta state was carried out. The sole purpose was to measure the pH of rain water harvested in the format describe in Figure 3 and in three stages as described in Figures 4, 5 & 6. A measurement tape, machete, labeled white plastic bowls, labeled retrieval bottles, Beaker and a digital pH meter were the key apparatus used for the field sampling and experimental evaluation. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 7 Published by SCHOLINK INC. Figure 3. Model for Rain Water Sampling Points: F=Farm Area; R=Residential Area; X1,X2,X3=Sampling Axis with Sampling Points. 3.1 Research Method The sampling stages and experimental scenarios follow the sequence defined in Figures 4, 5 & 6 of this report. 3.1.1 Stage 1: Chart for Rain Water Harvesting and pH Experimentation along Axis X1 Total of thirty three (33) rain water samples were harvest from axis X1, X2, X3 for the three (3) stages of field work as describe below. Figure 4 is the first stage done which involves sampling points clearing, positioning of bowl for rainwater collection and pH experimentation. Four points cleared in Day 1, seven points in Day 2 while the bowls were positioned on the eleven cleared points in Day 3, followed by pH evaluation in Day 4. Figure 4. Sampling and pH Evaluation Timeline along X1 Axis www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 8 Published by SCHOLINK INC. Stage 2: Chart for Rain water harvesting and pH experimentation along Axis X2 Figures 5 & 6 is the second stage of the sampling and experimentation process along axis X2 and X3.The process includes sampling points clearing, bowls positioning and pH evaluation in the laboratory for the harvested water samples. Figure 5. Sampling and pH Evaluation Timeline along X2 Axis Stage 3: Chart for Rain water harvesting and pH experimentation along Axis X3 Figures 3 & 4, is the last stage of the sampling and experimentation process along axis X3 done in the third year of this research. The process is in similar fashion with stages X1 and X2. Figure 6. Sampling and pH Evaluation Timeline along X2 axis Where; X1, X2, X3=Axis of measurement P1, P2, P3 … P11=Sampling points; B1, B2, B3 … B11=Sampling Bowls pH.S1, pH.S2, pH.S3…….pH.S11=Evaluated pH of each retrieved water samples www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 9 Published by SCHOLINK INC. 3.1.2 Assessment of Flared Gases and CO2 in Niger-Delta Using Quantification Approach The amount of flared gases and emitted CO2 over 11 years (2012-2022) as monitored by Nigeria Gas Flare Tracker, an online software was use to quantify the volume of flared gases (MSCF) released on daily basis in Niger-Delta states and its environ. Earth Observation Group (EOG) at the Colorado School of mines in 2011 developed this satellite software that tracts and records flaring data with locations, temperature, source, sizes and radiant heats from infrared emitters worldwide. In Nigeria, this software is monitored via (https://gasflaretracker.ng) and managed by National Oil Spill Detection and Response Agency (NOSDRA). Table 1 displays volume of flared gas vis-a-vis the amount of CO2 respectively emitted in Edo, Delta, Rivers, Bayelsa, Akwa-Ibom, Imo and Abia state. These are the states that comprise Niger-Delta. Table 1. 11 Years Profile of Emitted Carbon-dioxide (x10 3 Tonnes) from Flared Gases (x10 3 MSCF) in Niger-Delta States Yr. EDO DELTA RIVERS BAYELSA AKWAI-IBO M IMO ABIA F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 F.Gas x103 E.CO2 x103 2012 12200 648.9 49000 2600 55400 2900 30400 1600 3700 197.3 15100 800.1 45.9 2.4 2013 19100 1000 67600 3600 57500 3100 34500 1800 6800 359.9 16400 869.5 1300 71.3 2014 21200 1100 62200 3300 68100 3600 36200 1900 5500 294.1 9400 500 1000 54.1 2015 21600 1100 65900 3500 56800 3000 26500 1400 6100 322.2 7500 397.9 458.8 24.4 2016 9900 527.6 52400 2800 68000 3600 37000 2000 5700 304.8 8400 444.5 132.9 7.1 2017 14100 746.9 69600 3700 70000 3700 36200 1900 6000 316.8 7600 404.9 451 24 2018 24800 1300 113200 6000 65700 3500 45500 2400 5900 312.7 6600 353.8 1200 64.5 2019 24800 1300 105200 5600 68900 3700 47000 2500 4600 246.5 8200 435.2 1100 56.8 2020 17800 947.8 99700 5300 57900 3100 42400 2300 3100 164.8 10300 545 603.1 32 2021 16900 897.8 66300 3500 38600 2100 23500 1200 2500 130.3 6900 366.3 385.5 20.5 2022 12900 684.1 58200 3100 31800 1700 18100 1000 2500 130.9 4600 241.8 0 0 Note. Where: F.Gas=Flared Gas; E.CO2=Emitted CO2. 3.1.3 Experimental Procedure Thirty three (33) samples were collected at intervals of 200 meters (0.2KM) from the bunk wall of a typical flare site to a distance of 2KM along axis X1, X2 and X3. The task includes clearing of sampling points, positioning of water collection bowl and laboratory investigation. Upon retrieval of the harvested rain water in labeled receptacles, standard quantity of 100ml of the sample was measured and poured into a calibrated beaker, and the digital pH meter was switched ON www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 10 Published by SCHOLINK INC. for 30 minutes to warm up, next was calibration of the unit in a buffer solution. The sample was stirred for 2 minutes, the electrode rinsed, the meter set in pH mode and the electrode inserted into the beaker followed by activating the pH measurement button. A stable pH reading was achieved within 60 seconds. After each reading the electrode was rinsed with distilled water and second and third reading done on same sample for result comparison. By implication, all harvested rain waters were tested thrice for data validation using same procedure. 3.1.4 Rain Water pH Analytical Procedure The evaluated pH data was analyzed by Risk Matrix Approach using percentage standard deviation method. Risk is a function of probability of occurrence of an undesired event in addition with a measure of its adverse consequence. The procedure involves identification of the hazards, quantification of likelihood and consequence of those hazards on health and environment. Standard deviation is a measure of amount of dispersion or variation from the data set. It specifically gives a clue on how far each value lies from the average or mean. A high standard deviation indicates that the values are far from the mean and vise verse. This approach was used in this research to analyze the rain water pH along X1, X2 and X3 axis and compared with the standard mean (ẍ) value of 5.6. The Standard Percentage Deviation (SPD) for the harvested rain water pH data was computed in Excel spreadsheet using equation (3.1). Presented in Table 2 and 3 are the Flared Gas Risk Assessment Matrix and Risk Factor respectively employed as tools for the Risk Evaluator based on the magnitude of the flare pollutants effects on the people, community or environment. The Risk Factor (R.F) is a product of probability of occurrence (Likelihood) and severity. Mathematically, Where; ; www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 11 Published by SCHOLINK INC. Table 2. Risk Assessment Matrix www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 12 Published by SCHOLINK INC. Table 3. Risk Factor 3.1.5 Impact Rating and Description Negligible-Low Risk Zone (NLRZ): It is characterized with negligible effects from flaring activities but mitigation measures may be desirable. The flare impact may not result to significant effects on the people, community or environment even if ignored. Low-Medium Risk Zone (LMRZ): It is characterized with significant impact, requiring mitigation to curb the effects. The flare impacts may results to negative Short-to-Medium Term effects on the people, community or environment. Medium-High Risk Zone (MHRZ): It is characterized with serious impact requiring immediate mitigation plan to drastically curb the menace. The flare impacts may result to a Medium-to-Long Term effects on the people, community or environment. High-Critical Risk Zone (HCRZ): It is characterized with severe impact on the people, community and the environment if adequate steps are not employed to stem it. The flare impact may have already resulted to a Long Term adverse effect on the people, community or environment around that zone. Critical-Intolerable Risk Zone (CIRZ): It is characterized with very severe impact on the people, community and environment. These effects are usually immitigable if the practice continues. The only panacea is to stop the practice generating the effects. 3.2 Model for Determining Safe Habitation Quarter in Sensitive Areas In order to predict the safe human habitation zone from flare locations, R-Squared was used to study the variance of the independent variable (Distance) to the dependent variable (pH), using the mean regression equation. R-Squared is a coefficient of determination in statistical regression model for evaluating the proportion of variance of the variables (dependent from independent) which defines the goodness of fit from their relationship. Based on the generated R-Squared value, which is more than 80% for the mean pH as shown in figure (12), a regression model was developed. The regression equation along the path of investigation is defined by: www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 13 Published by SCHOLINK INC. = = By Gaussian elimination Method = 3.3 Risk Evaluation Model Generic Risk Model at varied distance, xi 4. Results and Discussion This research was done by quantifying the amount of released carbon-dioxide vis-à-vis emitted flared gases for 11 years in seven states of Niger-Delta. This is followed by determination and analyzation of the pH value of 33 samples collected at 200 meters interval and finally evaluating the safe zone for human habitation from flare locations. All data were calculated via Excel worksheet, graphical figures developed analyzed using Origin 2023(10.0) software. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 14 Published by SCHOLINK INC. Figure 7. Emitted Flared Gas Profile for 11 Years in Niger-Delta State 4.1 Volume of Emitted Gases Vis-a-vis of CO2 Released for 10 Years in Niger-Delta States Figure 8. Area Profile of Emitted CO2 per State in Niger-Delta The basic function of the satellite flaring data software is to detect the amount of gas flared on daily basis. Which includes the amount of carbon-dioxide (CO2) emitted from the flared gases, economic value of the flared gases as well as the potential power generation from the flared gases. Table 1 shows the amount of CO2 respectively emitted in Edo, Delta, Rivers, Bayelsa, Akwa-Ibom, Imo and Abia state. Within these periods under study (2012 - 2022), Niger-Delta region has cumulatively flared 2,180,677,000 MSCF of natural gas with the release of 115,749,500 Tonnes of CO2 in the air space within the study period. The trend revealed Delta state taking the lead on the amount of emitted CO2 from flared gases within the period of 2018 till 2022. This is closely followed by Rivers www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 15 Published by SCHOLINK INC. state and Bayelsa state at the second and third place. Apparently, (195,300,000 MSCF; 10,253,100 Tones), (809,300,000 MSCF; 43,000,000 Tones), (638,700,000 MSCF; 34,000,000 Tones), (377,300,000 MSCF; 20,000,000 Tones), (52,400,000 MSCF; 2,780,300 Tones), (101,000,000 MSCF; 5,359,000 Tones) and (6,677,200 MSCF;357,100 Tones) were the flared volume and emitted CO2 volume respectively emitted from Edo State, Delta State, Rivers State, Bayelsa state, Akwa-Ibom state, Imo state and Abia state. The result showed 809,300,000 MSCF of natural gas has been flared for the 11 year period with a release of 43,000,000 tonnes of CO2 in Delta state alone where the investigation was carried out. The study area is a community in Kwale area located in Delta state where flaring activity is done on daily basis and at different locations, which poses great concerns on human’s lives at close proximity to these flaring sites. 4.2 pH of 33 Harvested Rain Water Samples along X1, X2, X3 and Mean (ẍ) The lower the pH of a substance the stronger its acidity, and the higher the pH the higher the alkalinity of that substance. In this work, a pH value of 5.6 is the mean used to analyze the measured pH of the 33 water samples harvested at axis X1, X2 and X3 as shown in figure (3). Clean Rain water has a pH of 5.6 (Singh & Agrawal, 2007; Abbasi, et al., 2013; Xuan et al., 2021; Al Hameli et al., 2022). pH evaluated on the harvested rain water samples ranges between 4.56±0.06 to 5.10±0.06, which are indisputably below clean rain water pH of 5.6 and are all acidic. Figures 9, 10, 11 & 12 are four graphical representation of the measured pH along the three axis of evaluation, X1,X2,X3 and the mean pH {ẍ=(X1,X2,X3)/3}. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 16 Published by SCHOLINK INC. Figure 9. pH Measurement along X1 Axis Figure 10. pH Measurement along X2 Axis Figure 11. pH Measurement along X3 Axis Figure 12. Mean pH Estimate for X1.X2 and X3 Axis Figures 9, 10, 11 & 12 disclose stronger acidity near the flare location, which eases slowly away from it. This could be attributed to the phenomenon known as dry and wet deposition as well as pollutant plume dispersion. In dry deposition process, the pollutants settles/fall under gravitational influence usually close to the point of origin (source of generation), where it reacts and acidify water body or soil in contact. In wet deposition, the pollutant got scavenged in the cloud, travels by dispersion and falls wet at some distance from the generated location due to the influence of wind. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 17 Published by SCHOLINK INC. Figure 13. Overview pH Measurement along the Three Axis 4.3 Risk Matrix Evaluation Results The calculated standard deviation of the 33 rain water samples and the Risk Rating results using the evaluation tools (Risk Assessment Matrix, Risk Factor) are displayed as shown in Table 4. Table 4. Risk Rating and Control Measure # Deviation D:@X1 Deviation D:@X2 Deviation D:@X3 % Mean Ď: @X1,X2,X3 Severity (S) Prob. Of Impact (Pf) Risk Factor (RF) Risk Rating RIR) Remark/Panacea 1 29.8496 31.3572 28.9451 30.0506 3 E 3E High Stop Gas Flaring/ Capture & Sequester CO2 2 22.3118 28.9451 23.8194 25.0254 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 3 20.5028 22.0103 22.9149 21.8093 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 4 23.8194 20.8043 27.4375 24.0204 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 5 23.8194 22.3118 20.8043 22.3118 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 6 19.2967 20.8043 19.8998 20.0003 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 7 25.9299 19.5982 20.5028 22.0103 3 D 3D High Stop Gas Flaring/ Capture & Sequester CO2 www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 18 Published by SCHOLINK INC. 8 18.6937 21.7088 17.1862 19.1962 5 B 5B Medium Stop Gas Flaring/ Capture & Sequester CO2 9 15.3771 20.5028 17.1862 17.6887 4 B 4B Medium Stop Gas Flaring/ Capture & Sequester CO2 10 18.9952 17.4877 15.0756 17.1862 4 B 4B Medium Stop Gas Flaring/ Capture & Sequester CO2 11 15.3771 17.4877 16.2816 16.3821 3 C 3C Medium Stop Gas Flaring/ Capture & Sequester CO2 Figure 14. pH Standard Deviation along the Sampling Points The main objectives of Risk Assessment Matrix is to identify potential vulnerability to environment and health followed by defining situations management, compare alternatives, provide knowledge on patterns of events and to identify critical parts of the operations. Risk Assessment Matrix evaluated the magnitude of the deviation of the experimental results from instituted standards. It weighs the severity of potential risk against the probability or likelihood the risk might occur. In Table 2, a scale of consequences of 0, 1, 2, 3, 4 & 5 were used to designate increasing severity at the vertical axis, and likelihood scale of A,B,C,D & E at the horizontal axis that designated the probability of the adverse effects on the people, environment and ecosystem. The Risk Matrix Evaluator was utilized to generate the Risk Factor (RF) from the evaluated Standard Percentage Deviation (SPD) of the rain water pH along axis X1, X2 and X3 as shown in Table 3. This is considered reliable tool for analyzing and standardizing quantitative risk by categorizing all threats to safety, health, and environment based on their deviation from the acceptable limit. The Risk Factor (RF) www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 19 Published by SCHOLINK INC. was estimated from equation (3.2) by multiplying the “Severity in the vertical column to the Likelihood in the horizontal row” and consistently noting the corresponding color codes in the Risk Matrix Evaluator. For example, the ranking codes 2A, 3A and 4A are same as 2xA, 3xA and 4xA respectively. Equation (3.1) was used to calculate the Standard Percentage Deviation (SPD) with 5.6 as the mean rain water pH. The evaluated SPD along X1, X2 and X3 axis ranges from 15.3770% - 29.8496%, 17.4877% - 31.3572% and 15.0756% -30.0506% respectively. From the results, the calculated Mean Standard Deviation ranges from 16.39% - 30.05%, which falls within the BLUE and YELLOW color coded zones. The deviation at the BLUE zone is designated (10.01-20%), which covers 2C, 2D, 2E, 3B, 3C, 4B and 5B color coded background as shown in Table 2. For analytical purpose, the deviation is distributed amongst the RF which is seven in number within the BLUE zone. This is done by first calculating the deviation difference and dividing it by the total number of RF in that zone, followed by apportioning the common factor to each of the risk factors, i.e.,{(20-10.01)/7=1.43%}. The value “1.43” is added successively to each of the RF’s. The range of application of 2C, in the BLUE code zone is: 2C=(10.01%-11.44%) which means 2C lies within 10.01% to 11.44%. Others 2D, 2E, 3B, 3C, 4B and 5B are designated 2D=(11.45%-12.87%), 2E=(12.88%-14.3%), 3B=(14.44%-15.87%), 3C=(15.88%-17.31%), 4B=(17.32%-18.75) and 5B=(18.76%-20%)}. In the same vein, at the YELLOW coded zone, the deviation ranges from (20.1-50%), with the risk factors (3D, 3E, 4C, 4D & 5C) and having {(50-20.01)/5=5.98%} as the common factor. The range of application of 3D, 3E, 4C, 4D, & 5C in the YELLOW coded zone are {3D=(20.1%-26.08%), 3E=(26.09%-32.07%), 4C=(32.08%-38.06), 4D=(38.07%-44.05) and 5C=(44.06%-50%)}. The mean deviation (Ď) value “30.0506% and 25.8194%” in roll 1 and 2 of Table 4 falls within the RF “3E and 3D” respectively. Hence the Risk Factors (RF) for the calculated mean deviation in table 4 all falls within 3C, 3D, 3E, 4B and 5B. 4.4 Model Validation and Sensitivity Analysis The pH profile from the experimental evaluation was compared with those predicted by the model at same spacing, resulting to close match as shown in Figure 15. A sensitivity analysis carried out on the developed model predicted save residential area to be from 4.81 KM from the flare location (Figure 15). The model was tested at intervals of 0.1KM starting from the flare site. The predicted distance for clean rain water (where pH is 5.6) is from 4.81KM as shown in Appendix 1 of this report. The results are in tandem with the assertion by (Abassi et al., 2013; Larssen et al., 2006), “Acid rains and the pollutant that creates them are often transported far away by wind from their points of origin and the adverse effect of the pollutant reduces at some distance apart”. Again, dispersion plays a vital role in which the plume of the emitted pollutant travels far from the point of generation to points they undergoes some form of chemical reactions. The extent they travel is a function of the pollutants dispersion coefficient. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 20 Published by SCHOLINK INC. Figure15. Model Validation Figure 16. Boundary between Polluted and Unpolluted Zones for Human Habitation from Flare Areas 5. Conclusion Environmental risk of emitted CO2 from flared associated petroleum gases was investigated in this research by harvesting 33 samples of rain water within 2KM radius from the bund wall of flares. The evaluated pH was analysed by Standard Percentage Deviation (SPD) and Quantitative Risk Matrix (QRM) evaluation methods. The present work was borne out of concern for more than two million (2,000,000) people residing at close proximity to flaring locations as reported in Figure 2. Flared gases in sensitive zones such as human residential and farm areas requires improved risk management by intensified monitoring, evaluation and designed mitigation plan. First, the study shows accumulation of CO2 in the air space of the study area as disclosed by the flare tracker. This is evident in Figures 2 and Table 1 of this report. It revealed 809,300,000 MSCF of flared gases for the 11 year period with a release of 43,000,000 tonnes of CO2 in Delta state alone. Secondly, www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 21 Published by SCHOLINK INC. it revealed decreasing acidification of acid rain away from the flare location as shown by the experimental data evaluations. Finally, the model predicted 4.81KM radius from flare locations for human habitation. It is worthy to note that carbon-dioxide, nitrogen oxide and sulphur oxide are the three main trans-atmospheric gases that precipitates rain water and making it acidic by increasing the concentration of hydrogen ion (H+). This work only addresses carbon-dioxide due to its deleterious and trans-boundary environmental concerns as a greenhouse gas. The research does not in any way undermine the effects of NOx and SOx as regards rain water acidification. The developed and validated risk model is a framework suitable for evaluation of safe residential zones in sensitive areas. The Physicochemical parameters should be assessed based on the criticality of the Risk Factor (RF). The response of the risk screening model may presumably differ in other Niger-Delta states due to differences in the volume of emitted flare gases as shown in Table 1. The study area was chosen because of high flaring volume on daily basis as compared to other areas. The remedy/panacea is to stop gas flaring and/or put control measures in place. One of the control measures is by initiating Carbon Capture and Sequestration (CCS) projects in Niger-Delta region of Nigeria, so as to meet the 2050 Net-Zero Goals. Hydrocarbon exploration, production and processing in Niger-Delta region of Nigeria started since 1957, which has led to reservoir depletion and abandonment. Some of the depleted reservoirs in Niger-Delta brown fields are presently termed Marginal Fields. Nigeria has not less than 251 Marginal fields (Mobolaji & Okoro, 2020), some of which are suitable for Carbon Capture and Geological Storage (CCGS), to reduce CO2 emissions and to achieve 2050 Carbon Neutrality goal. Besides Saline Aquifers, the depleted gas or oil reservoirs are proven to be suitable for implementation of CO2 geo-sequestration in Enhanced Gas Recovery or Enhanced Oil Recovery. Umar et al. (2020), Davis et al. (2022), assessed the potential for CO2 geo-sequestration in Niger-Delta Basin, using seismic and well information data from wells in Agbada formation. The results were compared to formation basin screening criteria reported by (Bachu, 2003; CO2CRC, 2008). The assessments rated Niger-Delta formation “Very Good” and “Excellent” depending on the screened criteria and parameter. Hence Niger-Delta formations are safe for geological storage of CO2. Acknowledgement The authors wish to thank Petroleum Technology Development Fund (PTDF) of Nigeria, for the studentship and the inputs of Petroleum and Gas Research Group of University of Salford, Manchester, United Kingdom. Declaration of Conflicting Interests The author(s) declared no conflicts of interest with respect to the research and publication of this article. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 22 Published by SCHOLINK INC. References Abbasi, T., Poornima, P., Kannadasan, T., & Abbasi, S. A. (2013). Acid rain: Past, present, and future. International Journal of Environmental Engineering, 5(3), 229-272. https://doi.org/10.1504/IJEE.2013.054703 Abiodun, R. (2014). Nigerian Oil Workers & Families Rage against Foreign Companies. Adeyeye, J. A., Akintan, O. B., & Adedokun, T. (2019). Physicochemical characteristics of harvested rainwater under different rooftops in Ikole Local Government Area, Ekiti State, Nigeria. 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Appendix 1 Results of sensitivity analysis on model B0 Bi DISTANCE, Xi (KM) RAIN WATER ACIDITY, p.H 0.1856 4.7018 2.0 5.0730 0.1856 4.7018 2.1 5.0916 0.1856 4.7018 2.2 5.1101 0.1856 4.7018 2.3 5.1287 0.1856 4.7018 2.4 5.1472 0.1856 4.7018 2.5 5.1658 0.1856 4.7018 2.6 5.1844 0.1856 4.7018 2.7 5.2029 0.1856 4.7018 2.8 5.2215 0.1856 4.7018 2.9 5.2400 0.1856 4.7018 3.0 5.2586 0.1856 4.7018 3.1 5.2772 0.1856 4.7018 3.2 5.2957 0.1856 4.7018 3.3 5.3143 0.1856 4.7018 3.4 5.3328 0.1856 4.7018 3.5 5.3514 0.1856 4.7018 3.6 5.3700 0.1856 4.7018 3.7 5.3885 0.1856 4.7018 3.8 5.4071 0.1856 4.7018 3.9 5.4256 0.1856 4.7018 4.0 5.4442 0.1856 4.7018 4.1 5.4628 0.1856 4.7018 4.2 5.4813 0.1856 4.7018 4.3 5.4999 0.1856 4.7018 4.4 5.5184 0.1856 4.7018 4.5 5.5370 0.1856 4.7018 4.6 5.5556 0.1856 4.7018 4.7 5.5741 0.1856 4.7018 4.8 5.5927 0.1856 4.7018 4.9 5.6112 0.1856 4.7018 5.0 5.6298 0.1856 4.7018 5.1 5.6484 www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 7, No. 2, 2024 26 Published by SCHOLINK INC. 0.1856 4.7018 5.2 5.6669 0.1856 4.7018 5.3 5.6855 0.1856 4.7018 5.4 5.7040 0.1856 4.7018 5.5 5.7226 0.1856 4.7018 5.6 5.7412 0.1856 4.7018 5.7 5.7597 0.1856 4.7018 5.8 5.7783 0.1856 4.7018 5.9 5.7968 0.1856 4.7018 6 5.8154