An integrated approach to environment site assessment of past impacted (PI) waste pit and borrow pit in the tropics (Case Study)
In the process of oil field development which involves bush clearing, ditching and drilling, a lot of waste such as drilling muds, chemical wastes, radioactive wastes and other associated wastes including domestic wastes are generated. Wastes generated during drilling of oils are confined in excavated pits known as waste pits located very close to each well head and within its acquired location. Borrow pits are also created through the excavation soils for use in construction of roads, solidification of well head basements and construction of other operational facilities. In the long or short term some of the pits usually end up as repositories for different kinds of wastes from the production facilities. These waste pits and borrow pits are classified as Past Impacted Area (PIA). Detailed study of past impacted area were initiated as an innovative site assessment tool that can be effectively used to determine the ecological and socio-economic impacts of the sites, acquire site specific qualitative and quantitative data on the characteristics and spread of contaminants, identify sources, pathways and receptors of contaminants and recommend cost effective strategies for contaminated site rehabilitation. For a good indicators were established. High levels of heavy metals and other physico-chemical parameters were recorded in the borrow and waste pits, except dissolved oxygen which was low. Total Petroleum Hydrocarbon were also high in the soil, sediments of borrow pits and waste pit. Phytoplankton and zooplankton were distributed in both borrow and waste pits. There was however no significant difference (P>0.05) between the observed variation in abundance amongst the major divisions involved. Risk Based Corrective Action (RBCA) site classification procedure was employed. The initial response action for highly contaminated area involves restricting access to the sites by fencing. This is to protect human health impact through either inhalation of volatile organic compounds or ingestion of contaminated surficial sediments. After instituting the access restrictions, the general remedial/ corrective actions proposed for the impacted surface waters and soils/sediments can then be implemented.