A 1000 ha (2471 ac) area around the community of Bodo in Rivers State, Nigeria, was affected by two large pipeline spills in 2008 and numerous smaller discharges between 2009 and present, primarily related to oil theft, transport and indigenous refining. This paper describes the remediation of affected environments which represents the largest cleanup and restoration of a mangrove ecosystem due to oil-related damage ever undertaken and serves as a potential model for other areas of the Niger Delta similarly affected.
Cleanup activities include: (1) raking / mixing of surface sediments to break up a thick algal mat and removal of heavily polluted dead mangrove debris while lesser-oiled (most common) debris is broken up and left in place to aid re-establishment of mangrove plants and animal life used as a food source by the Bodo Community; (2) pressure flushing using ambient water from adjacent channels; (3) compressed air with water from a barge-mounted system, (4) use of hard boom and sorbents around the work area to capture off-floating oil, and (5) manual collection of floating oil using sorbents and hand bailers, followed by transfer to a central collection point and disposal at a government approved facility. High-volume low-pressure flushing system proved effective in releasing much of the deeply penetrated oil without damaging the sedimentary structure of the mangrove platform. Innovative methods are continually being sought. After confirmation of cleanup requirements, former mangrove areas (~860 ha, 2125 ac) will be planted with mangrove seedlings to phytoremediate remaining oil. Close-out criteria are based upon visual assessment followed by chemical sampling to meet government approved risk-based site-specific target levels. Potential major impediments to the successful completion of this Project are community unrest, security issues and reoiling from illegal activities and pipeline operations.
The objectives of this paper are to provide an update on the ongoing cleanup and restoration of a former mangrove-dominated area in the Niger River delta that was affected by oil spills in 2008 and other spills continuing on a daily basis to present. Success is not guaranteed. Hopefully, lessons learned in this case may assist the remediation of similar areas found throughout the Niger River delta.
Geographic Setting and Context
The cleanup area is located in the eastern Niger Delta. The nearest settlement is the community of Bodo with approximately 75,000 inhabitants located along the northeastern shoreline of the impacted area. Bodo is located in Gokana Local Government Area in Rivers State, Nigeria, and is part of Ogoniland (Figure 1).
Ogoniland has unfortunately been an area of civil strife and hostility towards petroleum producing companies (e.g. Boele et al., 2001). A major study of oil operation sites in Ogoniland by the United Nations Environment Programme (UNEP, 2013) found numerous areas of high oil contamination, including some sites in the Bodo area. The UNEP report focused primarily on land-based sites, whereas this Project concerns contaminated intertidal areas and adjacent shorelines. The recommendations of the UNEP report are currently in process of implementation by HYPREP (https://hyprep.gov.ng/), a government agency created specifically for this purpose.
Two oil spills, attributed to pipeline defects, occurred south of Bodo town in 2008 and affected an area of ~1000 ha (2471 ac) of intertidal habitats extending a linear distance of 10 × 5.2 km (6.3 × 3.2 mi). The affected area is dominated (98%) by mangrove habitat and numerous mud-lined channels. The remaining 2% consists of tidal flats, muddy sand shorelines and fish ponds. The two spills led to the rapid loss of many of the mangroves within the affected area. Additionally, there are a minimum of 43 shoreside indigenous illegal refineries (18 ha; 44 ac) not related to the 2008 oil spills but are included as part of the cleanup.
Bodo residents historically use these waters and mangrove areas for food gathering (fish, shrimp, crabs and snails) as well as for wood cutting. These activities were either stopped or greatly reduced by the two oil spills in 2008. Tides are diurnal (twice daily) with a range from 1.4–2.2 m (4.6–7.3 ft). Currents are strong in the main channels (up to 1.6 kn (3 km/h) and salinities roughly range from 18 to 24 ppt (Gundlach, 2018).
Since the 2008 spills, there have been repeated spills in the area primarily caused by illegal activities involving the tapping of transiting 24- and 28-inch crude oil transport pipelines, extraction of crude oil using illegally installed valves and hoses to small and large vessels, transport to shore-based artisanal refineries, refining in steel drums heated by crude-oil fire pits, and then transport of the refined product to Bodo and other drop off locations on the mainland (Gundlach, 2018). As background, Maclean and Wordu (2019) provide the following definition: “Artisanal refining is a concept used to refer to the use of primitive and illegal process in which crude oil is boiled and the resultant fumes are collected, cooled and condensed in tanks to be used locally for lighting, energy or transport”.
During all phases of the illegal refining process, spillage is likely. Ground surveys, satellite imagery, and aerial overflights indicate that oil is continuously present in the waters around Bodo and neighboring communities. A total of 52 spill events were recorded in this same area between 2008 and May 2019 by NOSDRA (National Oil Spill Detection & Response Agency), the Nigerian federal agency tasked with compilation of spill-related data and incident assessment. Non-pipeline events such as discharges from oil-filled boats and illegal refining are not recorded.
In 2015, The Shell Petroleum Development Company of Nigeria Ltd. (SPDC) agreed to remunerate affected Bodo citizens and to remediate 1000 ha of damaged habitat. A negotiated process, organized by the Bodo Mediation Initiative (BMI) sponsored by the Dutch Embassy in Nigeria, cleared the way for cleanup acceptance by the community.
In preparation for field activities, SCAT (Shoreline Cleanup and Assessment Technique) surveys were undertaken in July and August 2015. Cleanup was scheduled to begin in September 2015 but local hostile actions postponed startup until September 2017.
This paper summarizes cleanup activities undertaken in 2017 and 2018 (designated as Phase 1) and Phase 2 operations beginning in October 2019 and scheduled to continue for two years. Because these operations are specific to mangrove habitats, we include background information related to site characteristics.
Mangrove Remediation Background
Mangroves are among the most sensitive habitats to oiling (e.g Gundlach and Hayes, 1978) because of resident living plants and associated biota, mud-dominated conditions (making oil clean up and work conditions difficult) and are commonly depositional conditions enabling oil to settle and accumulate.
Guidelines for oil spills in mangroves focus on preventing oil from reaching these sensitive plant areas. When oil does enter, natural recovery is the preferred method to prevent further damage. Manual oil removal / cleaning, sediment reworking / tilling are considered ‘not applicable’ response methods in mangroves, whereas deluge flooding at low pressure is considered applicable but with some adverse impacts (NOAA, 2014).
Unfortunately, vast areas of the Niger Delta of former mangroves are completely or nearly completely dead and retain highly contaminated base sediments. In the 11-year period between 2008 and 2019, natural mangrove recovery in the Bodo area has been very limited, attributable to high levels of oil contamination from the initial and continuing spills and the lack of adjacent seed stock/propagules.
Without intervention, we estimate that natural recovery could take 60 years (after stoppage of the continual oil spills) based on an estimated 40 years for mangrove propagules (seed pods) to take root and cover damaged areas and then around 20 years to grow to maturity. Therefore, this remediation program is focused on reducing the level of oil contamination sufficient to protect human health, sustain living mangrove plants and then to replant the damaged area. Via active planting, the time required for habitat recovery can be substantially shortened and the plants will serve to phytoremediate remaining hydrocarbons (e.g. Moreira et al., 2011).
Area to be Remediated
The area designated for remediation was determined from satellite imagery and detailed aerial mosaics in natural color and false-color red (IR) from 2013, supported by ground surveys in 2013, 2015 and 2017. The analysis of imagery indicated areas of mangrove loss by comparing 2006/2007 imagery to images from 2009 and later (Gundlach, 2018). Ground surveys confirmed impacted mangroves with little evidence of recovery and delineated heavily contaminated shorelines within the area of spill influence. Within the area, 1000 ha damaged by the 2008 spills and utilized by the Bodo community were identified to be remediated.
After identifying the spill-affected area described above, the level of contamination within that area was determined by SCAT surveys. The SCAT team is comprised of representatives of the Bodo Community, Nigerian state and federal agencies, SPDC, BMI and non-governmental organizations. As site conditions are dominated by water-saturated, soft mud and mangrove rooted sediments (Chikoko mud), the SCAT standard visual pit (or trench) and oil layer analysis could not be used. Instead, oil level was determined by digging a pit 25–40 cm (10–16 in) deep, allowing water to seep into the pit over an approximate 5-minute time span, and then estimating the percent cover of oil (2 categories: sheen or black / brown oil) on the surface water in the pit. Additional field measurements were taken of surface oiling, sediment type by depth, percent cover by living mangroves and nipa palm (an invasive species), and the presence of crabs, periwinkles (snails) and shrimp. Over 1000 SCAT survey sites were completed during the period of 2015 and 2017/2018. All data are stored in a relational database and are able to be queried and plotted using QGIS software. See also Iroakasi et al (2020, this Conference).
An extensive chemical sampling program was undertaken in 2015 and 2017 to determine levels of contamination and potentially to evaluate cleanup effectiveness. Composite samples were taken from the surface (0–5 cm) and subsurface (15–25 cm) (0–2 in, 6–10 in) from five pits located at each SCAT site. Samples were shipped to the United Kingdom for analysis. Results reported here are of total petroleum hydrocarbons (TPH), a sum of total aliphatics (C5-44) and aromatics (C5-44). Over 600 samples were analyzed (Bonte et al., 2019).
Depth of Oiling
SCAT surveys visually reviewed the top 25–40 cm (10–16 in) of the designated area of remediation. To obtain deeper samples, a vibracoring program obtained 30 cores along six transects extending to a maximum depth of 3.6 m (12 ft). Chemical samples were taken for analysis at cm depths of 0–5, 20–25, 50, 100, 150, 200, etc., and at the end of core.
Mangrove Test Planting
In order to gauge the potential for mangrove survival and sustainable growth in the area to be remediated, a total of 347 red mangrove seedlings were planted at seven sites and monitored again 6, 12 and 24 months after planting. Chemical samples were taken at the time of planting and after two years. Monitoring included measurements of plant mortality, height, stem diameter, leaf number and condition, prop root development and other factors at ten plants within each site.
Risk-Based Health Assessment and NEBA Review
The Nigerian regulatory structure regarding cleanup endpoints in the oil and gas industry supports the application of a risk-based tiered approach for the protection of human health and the environment or acceptance of a single value of 5000 mg/kg TPH (referred to as the Tier 1 intervention value; EGASPIN, 2018). BMI and SPDC, with the participation of the BMI technical working group, completed a combined detailed human health risk assessment (including both cancer and non-cancer health impacts) resulting in development of Site-Specific Target Levels (SSTLs) and includes the application of a Net Environmental Benefit Analysis (NEBA) related to environmental factors including aquatic organisms, mangrove plants, and human health (Gundlach et al, 2019). The proposed Tier 2 levels were approved by Nigerian regulatory authorities and serve as the basis for close-out criteria discussed under results.
This report covers two phases of remediation in the area. Phase 1 activities focused on the recovery of ‘free-floating oil’ defined as surface oil and including oil released from sediments when agitated. These actions occurred between September 2017 and August 2018. Phase 2 began on 1 October 2019 and will continue for two years. Mangrove planting and monitoring will extend further. Phase 2 additionally includes cleanup of indigenous refineries, asphalt and tar removal, and potentially on-site sediment treatment / washing.
Treat and properly dispose of all oil and oil-contaminated material in conformance with Nigerian regulatory requirements and good international practice.
Employ extensive local participation to provide employment to ensure a boost to the local economy and increase community support and satisfaction in the work being performed. Altogether, approximately 1000 people are participating in Phase 2 activities in 2020 including 800 local workers, supervisors, management personnel, boat drivers, food caterers, military escorts, gun-boat personnel, site security agents, waste haulers, mangrove planters and site monitors. A new staff of 800 Bodo workers will be trained to IMO certification levels and placed in service every six months.
Use local v-shaped boats (length: 6–8 m, 20 to 25 ft). Although not specifically suited to conducting oil spill operations in shallow creeks, local boats are utilized to provide an economic lift to the community and increase community participation. The advantage is that the boat operators are familiar with the operating conditions and narrow creeks of the area.
Engage international cleanup specialists. Nigerian contractors have the participation of an international remediation company and individuals placed on-site to provide guidance to operations.
Ensure all additives to aid remediation are on the Nigerian government list of approved agents for oil spills and undergo a demonstration, review and approval by the Bodo Community and the BMI Directorate overseeing the cleanup.
Avoid causing more harm than good. The extensive disruption of sediments within former mangrove areas may cause the area to be unsuitable for sustaining mangrove seedlings. The primary concern is that excessive flushing may liquify base sediments, thereby destroying the present root structure and inhibiting the repopulation of the area by mangroves. Similarly, an excessive use of heavy equipment may result in sediment compaction, also restricting future mangrove growth. During all phases, direct flushing around the base of living mangroves is avoided.
Keep broken mangrove plant remains (sticks) in place as they provide habitat for snails and crabs and inhibit sediment loss. Heavily caked prop-roots remains may be broken and / or removed if they inhibit cleanup of underlying sediments or pose a continued threat of oiling.
Avoid large-scale sediment removal and trenching.
Collect and appropriately store liquid wastes, asphalt, tar, plastics and other cleanup materials in a central facility for subsequent removal to a government approved treatment facility. Heavily contaminated sediments not able to be flushed sufficient to meet cleanup requirements are applicable for onsite treatment options.
Allow natural recovery as a viable option where plant regrowth and low oiling conditions are present.
Plant mangrove seedlings as part of the remediation process of hydrocarbon degradation and habitat restoration.
Remove nipa palm. The nipa palm (Nypa fructicans) is native to the Indo-Pacific and has been taking over mangrove habitats, particularly where natural mangroves are killed off or degraded. In the Bodo remediation area, nipa will be pulled out or cut to assist restoration of the indigenous mangrove habitat.
Distribution of Oil
SCAT observations and chemical sampling found that oil contamination was patchy, varying greatly even when measured in close proximity. Observations of oil coverage on the surface water of 1062 pits 25–40 cm (10–16 in) deep are shown in Figure 2. The coring program found little to no oil substantial oil at depths below 50 cm (20 in) in the 30 cores taken (Iroakasi et al., 2020).
Results of chemical sampling undertaken 2015 and 2017 are shown in Table 1 referring to site treatment undertaken during Phase 1 operations. (Note: Little et al (2018) describe results from 2015.) The median TPH value of surface samples is higher (38,000 – 55,000 mg/kg) than subsurface levels (690–12,250 mg/kg), likely due to the continuing influx of new oiling and the limited downward migration of surface oil due to the relatively cohesive clay substrate having a high level of water saturation.
The relation between the visual estimate of pit oiling and values derived from chemical analysis was not strong using methods applied in Phase 1. At that time, a visual estimate from a single center-point pit was compared to a composite sample of five pits taken around the center point (Bonte et al., 2019). Sampling in Phase 2 uses an average of visual observations from the same three pits from which a composited sample is derived. To date (March 2020), Phase 2 chemical results from all sites (20 in total) having ≤ 25% pit oiling show TPH values < 25,000 mg/kg. The importance of SCAT pit oiling observations referenced to values obtained by chemical sampling is discussed under Close-Out Criteria later in this paper.
Cleanup actions include the following based on location of the oil:
Muddy Creeks, Former Mangrove Areas, Tidal Flats and Shorelines
Breakup of surface algae and algal mat on the mangrove platform and tidal flats. An algal mat, sometimes mixed with tar (Figure 3), has become prevalent in many areas as natural grazers (e.g. snails) were killed off by oiling. The presence of the mat inhibits aeration and oil degradation of the underlying sediments. Breakup and mixing of the surface aids recovery. Where tar is present, it is removed. Figure 4 shows raking actions releasing oil from surface sediments. Hand tilling resulting in the turn-over of surface sediments is also used.
Flushing of mud-dominated channels and flats, extending from the channel onto the mangrove platform until heavy oiling ceases. The primary process of removing oil from the sediments is by intensive pressure flushing. Three flushing methods are described below:
Use of 3-inch hoses and an extended 1-inch nozzle (7.6 cm hose, 2.5 cm nozzle) using low-to-moderate pressure levels. The most common method uses a pump positioned on an adjacent boat connected to a hose for shoreline operations. Released oil is contained by at least two booms in 2020. Oil is collected using sorbents, by hand using a bailer and transferring captured oil to a plastic container for transport, or mechanically using disk and brush skimmers. The process is indicated in Figure 5. Liquid oil is placed into drums and transported to a holding tank on the mainland for government approved disposal.
High-pressure washer / hand wands. This method requires the transport of large holding tanks to the work area prior to operations, slowing down progress. The small volume of water injected from each system was not efficient at large scale oil removal but was good at surface agitation. Photographs of this operation are shown in Figure 6. The limited effectiveness of the process negates its widespread use in Phase 2 operations.
Development of a 4-pronged pumping platform. Both flushing systems described above result in pressure from topside downwards as the nozzle is placed into the contaminated sediments. This may force some oil deeper into the sediments and results in sediment liquification. Using a 4-pronged entry system instead of a single nozzle results in lower pressures and likely releases more oil up to the surface as the prongs are lowered to depths of 30–60 cm (1–2 ft), depending on the stability of the base sediments. This system is shown in Figure 7.
Development of air-sparging system with water influx.
Use of a barge-mounted air compressor to force air mixed with water into a multi-head system (Figure 8) is showing potentially good results in March 2020, subject to further review.
Asphalt / Tar Removal
Highly weathered oil in the form of asphalt and tar remains along shoreline banks and in illegal refining areas. Some highly viscous oil, waste products from illegal refining, is located in pits. Examples are shown in Figure 9. Material will be excavated primarily by hand and transported in bags to a centralized storage site for government-approved disposal.
Potential On-Site Treatment
There are a number of locations having oil-saturated sands for which flushing has proved ineffective at removal of oil to the required level. These sites include sandy areas near a road under construction adjacent to the SPDC pipeline corridor and pertains to artisanal refinery sites as well. For these sites, sediments may require on-site treatment. This would be advantageous as off-site transport is not required and excavated areas would be infilled using the same sediments. To date (March 2020), on-site contractors have not provided a method statement for treatment in these cases. Site characteristics are illustrated in Figure 10.
Nipa palm removal
The invasive nipa palm originated in the Indo-Pacific region and was brought to Nigeria in the early 1900s (Isichei and Akin-Fajiye, 2013). The nipa palm plant structure reduces the habitat available for fishery nursery and for mangrove associated biota. UNIDO (2007) describes it as “a negative impact on the mangrove system … leading to a loss of biodiversity and ecosystem function”. It is more difficult for food gatherers to collect in a nipa forest as compared to mangroves. From aerial and ground surveys, nipa palm is encroaching into the remediation area from the south where it is now the dominant species in many localities. Comparing nipa seedlings to mangrove seedlings in areas where both are present indicates that mangrove re-settlement is being out-competed by the numerous seed pods of the nipa (Figure 11). Cleanup operations are removing nipa seedlings and cutting larger plants to enable mangrove seedlings to successfully reach maturity. We recognize, however, that this will not stop the encroachment of nipa into this area and that nipa, like mangrove plants, provides a mechanism for the continued breakdown of residual oil in the underlying sediments.
Results of planting 346 mangrove seedlings in the area of remediation indicates that they can survive and grow in contaminated sediments. The median TPH values at the seven planted sites are 41,00 mg/kg surface and 6,100 mg/kg subsurface. However, the continued daily occurrence of newly spilled oil (both sheen and black oil) is stressing the plants and likely contributing to the observed mortality. Of the ten tagged plants at each site, there was a 67% survival rate. One site was hit by a recent spill from an illegal operation on the pipeline and 9 of 10 monitored plants were lost. As end-points of physical cleanup are completed, areas having former mangrove will be replanted, requiring approximately 2.5 million plants.
Cleanup End Points and Government Approvals
The entire work area is divided into 363 work units (‘Grids’) varying in size (15% < 1 ha, 39% < 2 ha, 63% < 3 ha, and 80% < 4 ha; where 1 ha = 2.47 ac).
For each Grid, a two-stage process is used for close-out.
Visual: A visual determination of pit oiling is carried out by the SCAT team at a minimum of three sites (but commonly having at least five or six sites). Grids where SCAT confirms that all measured sites (each with three pits) have an average oiling level of 25% or less, it is documented and passed to the Project Director for review.
Chemical: Once a Grid work area is confirmed by SCAT, the Project Director reviews the SCAT data and confirms in writing that it is ready for chemical sampling as required by Nigerian regulatory agencies. The values used for the chemically based closeout are described below. Sediments composited from three pits immediately beneath the top 0.5 cm (to avoid the influence of recent oiling) and at 20–25 cm (7–10 in) below the surface will analyzed.
For this Project, Nigerian regulatory agencies have approved the adoption of Tier 2 Site Specific Target Levels (SSTLs) of total petroleum hydrocarbons (TPHs), depending on exposure-based land-use (Figure 12):
Bodo shoreline visitors and adjacent residents: Area: ~2 ha (5 ac). Exposure is to Bodo residents using the shoreline and walking to fishing areas, boats and for other activities. TPH SSTL=5000 mg/kg.
Fish ponds and fishing areas: Area: ~13 ha (32 ac). Exposure is via contact with sediments during future fish pond operations and fishing. TPH SSTL=7400 mg/kg.
Visitors to oiled mangroves and refineries: Area: ~940 ha (2322 ac). Exposure occurs during passage across dead mangroves to living mangroves for wood and food collection. TPH SSTL=42,700 mg/kg.
Phase 2 will also monitor planted areas to ensure their sustainability. Areas not surviving will receive additional remediation and will be replanted.
Waste Storage and Removal
A total of 33,186 l (8765 gal) of liquid oil / mousse was collected during Phase 1 operations in addition to large quantities of plastics and other household waste. Phase 2 activities include the additional collection of asphalt / tar, nipa palm and potential effluent from onsite sediment treatments. All materials are brought to a central temporary waste storage facility with appropriate linings for subsequent transport to a government approved facility for final disposal or treatment.
There are several layers of Project monitoring and coordination. The SCAT team is responsible for field verification that Phase 2 pit oiling levels are met on a Grid-by-Grid basis, which is then verified by the BMI Project Director. The BMI Project Director issues weekly reports that include Grid cleanup status, contractor accomplishments and issues, and Key Performance Indicators. Concerns and issues with contractor performance are noted and discussed with the contractor as they arise. Bi-weekly Project management meetings are held to ensure the Project is kept on track and deficiencies are noted for correction. A stakeholder's report (available during the Project from BMICommunications2@gmail.com) is issued biweekly to inform the Bodo Community and interested parties.
Potential setbacks include:
Community unrest: The Project was stopped for two years (2015 to 2017) due to local community unrest. Factions exist within the community that believe they have been unduly excluded from contracts or not sufficiently rewarded. Work stoppages may occur.
Security: There is an increase in cult (gang) related activities as three cults vie for territory. An attempt on the life of the Paramount Ruler of Bodo was unsuccessful in December 2019 only because he was not at his residence in Bodo. Unfortunately, others were there and lost their lives. All movement of SCAT personnel to the work area is with armed escort. Ex-patriot personnel additionally are transported in an armored car with the escorted convoy.
Continued oil spillage: Illegal activities have not stopped in Bodo, resulting in continued pollution on a daily basis. In 2020, a 2-km steel pipeline was found extending from the SPDC Trans-Niger Pipeline to illegal refining sites. This pipeline and another were found to be actively leaking oil.
This is a work-in-progress. In spite of numerous obstacles, it is proceeding. Areas affected by the spills in 2008 and thereafter are actively being remediated. Visually, it looks better than it has for many years. Wildlife, particularly birds, are visibly returning. Local fishers are now seen fairly regularly in areas where none were previously observed. The procedures for success are in place. The continued active support of the Project and its objectives is required of all parties involved, including SPDC, Nigerian governmental and regulatory agencies, the Bodo Community, non-governmental organizations, international entities and others.