Home > Chemical > Understanding Oil Spill And Groundwater Impact

Understanding Oil Spill And Groundwater Impact

It is common knowledge that the adverse effects of pollution can be felt in places far from the source. Water pollution transfers contaminants from the source of origin to distant communities, leading to a loss of economic uses of scarce water resources. All forms of pollution leave devastating effects, including cases where the causes are natural (such as wildfires, volcanoes, and sometimes dust from dry soils in the deserts), but avoidable man-made cases are even more worrisome.

There has been a recent and worrying trend in Nigeria, where its Niger Delta region is now associated with spills which have led to enormous economic and environmental losses. The Oil Spill Monitor – the official reporting database of the National Oil Spill Detection and Regulatory Agency-reports that in 2021 alone, there were 412 publicly available oil spill records. This is only marginally less than the 442 spills reported in 2020. The spills in 2021 released 3,730,629 litres of crude oil; the equivalent of 118 oil tankers.

From the report, there were two major spills with over 250 barrels of oil, and six spills between 25 and 250 barrels considered medium spills. Although, some of the spilled crude was reported as recovered, but a vast amount is left in situ to either volatilise (leading to air pollution), smother soil plants and animals, or percolate to groundwater, leading to groundwater contamination.

The oil spill monitor does not provide a risk assessment that shows whether these spills are high-risk spills or less but what is certain is that a spill above 250 barrels is a high risk simply because of the volume. When I consider our environmental context and well-documented water shortage, a question bothering me is, “What is higher risk than fouling groundwater”?

Let us consider the hypothetical case of Chief Chukwu and his family in Rural Rivers State. If not that nature kindly mitigates some spills in the Niger Delta by slowing their downward travel to contaminate usable groundwater, he would long have no water to consume. Because in some cases, the shallow water table just under the soil surface (primary aquifer) holds oil afloat. But Chief Chukwu has not been lucky recently. In his community, there are two lengths of 16 inches pipelines running parallel to his house. As a child, his parents lost some portions of their land to oil companies now designated as Right-of-Way.

The hypothetical Chief Chukwu is inundated daily with disturbances from heavy-duty trucks plying the Right-of-Way. A large number of workers access their work site using the road in front of his house, or security and surveillance personnel on patrol duties. If these were his only problems, he would not have bothered much. Recently, he noticed that he could perceive fumes of hydrocarbon in his living room. What started as a casual occurrence soon turned into something more serious as the smell became stronger by the day.

He soon noticed that the smell was not present in his bedroom. It took no formal education to realise that because his living room was not cemented, he could perceive vapour, but not in his bedroom with a layer of cement over it. This is soil vapour intrusion! For those in the contaminated land industry like myself, this is worrisome as volatile hydrocarbons are usually deadly. This is because they are the hydrocarbon bands associated with cancer, but this isn’t the worst.

Upon receiving the news of the soil contamination, his hand-dug borehole began to show a fine cover of pure crude oil. A well in existence for over 10 years had suddenly started producing pure crude. He originally thought he had struck pure gold because he did not know of any recent crude oil spill within his street or line of sight. He only accidentally stumbled into a spill location some seven kilometres away when he visited friends. Now, his first attempt at the inquiry was rebuffed by oil workers. “Come on, how can you say you can find oil in your well? You live far away, the spill happened over a month ago.

Oil spill here, groundwater impact there! It took months or more for the spill head to lead to Chief Chukwu’s house, contaminate his well, and leave him without clean water. This is very possible scientifically.

When spill occurs, depending on the soil profile, it begins to break down, volatilise, penetrate the ground, and travel overland or with water depending on the environment. Subsurface movement can be lateral, vertical, or a combination of both. Where there are man-made holes in the ground, this could become preferential travel routes. For Chief Chukwu, it was a combination of all these. A spill of close to 200 barrels had happened. 80 barrels had been recovered and the other 120 barrels found their way to the ground and flowed towards his residence. He sand-filled his premises considerably before erecting his house which could have explained the ease of vapour intrusion to his living room. Because his water well was present and not deep, it was a preferential receptor for groundwater contamination from crude oil.

To add to Chief Chukwu’s woes, the cause of the spill was officially pronounced as sabotage, meaning he had no claim to compensation from the company except on purely humanitarian grounds.

What will I do to remedy the situation? Upon receiving a report of a spill, the approach is to first test the spilled crude for a hydrocarbon fingerprint, this will be compared with the original source of spill to determine the similarity of profiles. Once similarity is confirmed, a series of monitoring and recovery wells can be dug along the contaminant pathway to the chief’s house to delineate the oil impact vertically along to soil column. Chief’s entire compound should receive a new concrete pavement and an active air monitoring programme should commence.

Furthermore, if the exposure to fumes exceeds the allowable limits for contaminants in the air, then he is to be relocated immediately. The existing well should serve as a monitoring and recovery well. A monitoring and recovery well helps to monitor the crude, recover free-flowing crude for testing; collect and calculate the rate of recharge which helps to determine or estimate the travel time, estimated quantity in the subsurface and the extent of work required.

Although it is difficult to determine a groundwater remediation approach to adopt, there are often very expensive methods commercially available. One is to pump and treat, which entails pumping as much free phase as possible and treating water outside the reservoir before disposing the treated water. But imagine the logistic requirements for this. Another is air sparging and biosparging which introduces oxygen into subsurface to promote a quick microbial degradation of the hydrocarbon. Again, imagine the huge requirements required for pumping air into soil columns, the pumps, and the probes required.

One approach that has received widespread acceptance is the monitoring of natural attenuation that will be designed after much free-flowing oil has been recovered. This method is a nature-based solution that relies on naturally occurring microorganisms and their biochemical processes. Here, the experts watch out for biomarkers and indicators of hydrocarbon degradation to determine if the contamination is breaking down. This takes a painfully long time and is only advised if there is no immediate risk for the residents or users of the contaminated land area.

In his case, Chief Chukwu is already at significant risk; implying the need for immediate action. Unfortunately, someone somewhere is facing a similar problem and only a long-term nature-based solution is scientifically recommended. Whereas the above case is hypothetical, it is the reality of many within the Niger Delta region, who, despite having nothing to do with sabotage or operational spills, suffer dire consequences despite living several kilometres away and not knowing that a spill has occurred.

From an economic perspective, the loss is first from the volume lost to the environment and the enormous environmental response requirement. Usually, the cost of cleaning a contaminated land is several times more than the revenue from the oil if it were to be sold. The social services required, the man-hour loss for negotiating peaceful working areas, the restitution works, and others contribute to a sad reality. It is best imagined and avoided than experienced. All these are avoidable if oil is left in the pipelines.

Source: Punch


Leave a Reply

Your email address will not be published. Required fields are marked *