Application of Sustainable Risk Based Analysis of a Fractured Aquifer Impacted by Crude Oil Spill

The site of interest is dominated by three main rock structure; namely unconsolidated alluvium, fractured cemented conglomerate and ophiolitic rock (Peridotite). The groundwater transmissivity varies from as low as 2.0 m²/day to as high as 80 m²/day. There are 21 hand dug water supply wells completed in conglomerate or peridotite on the Site and the surrounding nearby areas owned by the citizens and are used for irrigation. The contamination was not discovered immediately and was only known when the owner of one of the wells reported free floating crude oil in his well in December 1983. Since its discovery, various attempts to recover the free-floating oil in these wells using various methods were implemented. However, these actions did not help in removal of the entire light non-aqueous phase liquids (LNAPL) from the sub-surface. Recent clean-up of monitoring wells identified that the LNAPL is very minimal. A simplified conceptual site model was developed for the site to help in designing a remediation plan. The Source-pathway-receptor model was used to help in the design of the remediation plan. Investigation near the source indicated that all contamination in the unconsolidated rocks was removed. The monitoring wells and the pumping test along the pathway (i.e. groundwater) indicated that there is no recoverable hydrocarbon. This means that more effort needs to be put at the receptor side by treating the groundwater prior is used for irrigation.