Our Remediation/Restoration Strategy

Using the sketched site assessment map, large sites shall be subdivided into distinct Areas of Contamination (AOC) to assist in site delineation and remediation planning. An AOC is defined as a separate area of contamination within a site that is physically separate and distinct from other AOCs. These AOCs should be named logically i.e. ROW, Third-party Land, Borrow pits, etc.

AOCs shall be divided further into smaller subsections based on the degree of visual contamination observed. In order to ensure consistency, these subsections or zones shall be categorized as:

• High: Oil covering 100% of the surface soil. The colour is matt black. There is normally no vegetation in this area.
• Medium: Oil covering between 75-100% of the surface soil. The colour is dull black. Re-vegetation would have commenced in this area.
• Low: Oil covering 50-75% of the surface soil. There may be patches of re-vegetation, some of them significant.

Once the entire site has been visually delineated, a sample is taken in each area (section). This should be sent to the laboratory for analysis of nutrients (Ammonium, Nitrate, Nitrite and Phosphorus) and pollution indicators.

Each sub-section of the site shall have a vertical delineation carried out on it. This will be achieved by drilling 100cm boreholes using a graduated stainless steel hand auger. Soil samples will be collected at 0-30cm, 3060cm and 60-100cm for laboratory analysis.

To ensure accurate delineation of each AOC, the area immediately outside the perimeter of the AOC shall be delineated by both visual lateral delineation and sampling vertical delineation. Once the entire site has been delineated, a sample is taken in each area (section).

Depending on the concentration of hydrocarbon in the soil, nutrients shall be added to maintain an optimal concentration for biodegradation to take place. However, the frequency of addition shall be adjusted based on the nutrient monitoring results.

The actual remediation exercise shall involve the following steps of activities.

This is a conventional physical method of remediation aimed at accelerating the natural removal of crude oil by exposing oil-stained soils to oxygen, thus providing the essential intimate contact between oil-degrading bacteria and contaminated soils. The soil shall therefore be tilled accordingly.

To further enhance microbial growth and proliferation, a re-scarifying process of the soil will be done. This involves manual construction and scattering series of windrows or mechanically done using plough mounted tractor.

Fertilizers or other DPR approved soil nutrient types shall be added to the soil during the re-scarifying process (construction and breakage of the windrows) and soil homogenization. This will further enhance microbial growth and proliferation.

Three boreholes shall be drilled at the site, one upstream, one downstream and one control. The boreholes shall be 4’ in diameter and to the depth of the first water horizon. The wells will be screened and cased with PVC pipes, gravel packed, cemented and capped to prevent infiltration. Disturbed sediment samples will be collected by flushing the drill cuttings while water samples will be collected after flushing and equilibrating the wells for two hours.

Soil samples shall be collected from each delineated AOC using hand auger at depths of 0-30cm, 30-60cm and 60-100cm.

Composite samples shall be made from at each AOC by thoroughly mixing samples collected at the respective depths of 0-30cm, 30-60cm and 60-100cm.

Both the individual samples and the composite samples shall be analysed in line with the DPR recommended best methods stated in Appendix VIII-D1 of DPR Environmental Guidelines and Standards for the Petroleum Industry in Nigeria (EGASPIN) 2002.
The following parameters, which measure the magnitude of a hydrocarbon impact on the environment shall be analysed in all the samples,

• Total Petroleum Hydrocarbon (TPH)
• Polycyclic Aromatic Hydrocarbon (PAH)
• Aromatic Compounds (BTEX and Phenol)
• Heavy Metals: Arsenic, Barium, Cadmium, Cobalt, Mercury, Lead, Nickel, Zinc
• Total Organic Carbon
• Nutrients: Nitrate, Phosphate and Potassium

Remediation activities shall be monitored every two weeks and monthly by government regulators. Equally, regulators shall be engaged in each vital aspect of the activities viz: all sampling, borehole development, sample analyses, nutrient application and reporting.

This involves the biodegradation of the pollutants in underground water by providing the bacteria with the oxygen required for the oxidation of the hydrocarbons (BOD)by pumping air into the saturated part of the aquifer by means of injection of wells. This forces the organic vapours to the surface where they are then treated by carbon filtering

Where results from laboratory analyses show that remedial objectives have been met, DPR, MOE and other government regulators shall be invited for a close out/ certification inspection of the site.