Modeling Water Quality Impacts of Petroleum Contaminated Soils in a Reservoir Catchment

Soil contamination due to spills or leaks of crude oils andrefined hydrocarbons is a common problem. Estimation of spillvolume is a crucial issue in order to determine the expectedcontaminating life span of contaminated soils. The directprocedure to determine the amount of hydrocarbon in soil is to measure the concentration of total petroleum hydrocarbon (TPH) in soil samples. The primary objective of this study was toassess the potential effects of oil contaminated soils on thewater quality of Devegecidi dam reservoir. For this purpose,limited spill data available were evaluated and soil samplingstudies were conducted in the Beykan oil field to analyze forTPH on oil contaminated soils. Available spill and measured soilTPH data were used in a subsequent modeling study to assess thereservoir water quality impacts due to dissolved mass leachingfrom hydrocarbon contaminated soils. Evaluation of availablespill data between 1989 and 1995 revealed that a total of 252recorded spills resulted in a net spill of 395 tons. The majortypes of oil spills were identified as well heads (WH), returnlines/flow lines (RL/FL), and power oil lines (POL). A total of211 soil samples was collected at selected well heads andanalyzed for TPH in the laboratory. TPH results revealed aconcentration range between 600 and 115 500 mg kg^-1 with a meanconcentration of 20 300 mg kg^-1. Modeling studies focused onbehavior assessment and involved two major components. The firstcomponent is a soil-leaching submodel for estimating theleachate concentration and contaminant mass leaching out of thecontaminated soil body. The second component is a reservoirwater quality submodel assuming complete-mix conditions forestimating the changes of hydrocarbon concentration in thereservoir water as a function of time. These two components arecoupled via a mass inflow term present in the reservoir waterquality model, accounting for contaminant mass loadingcontributed by the leaching of contaminated soil. Simulation runs performed under conservative conditions assuming an annualaverage oil spill volume of 95 tons and the minimum reservoirvolume of 7.3 × 10⁶ m³ revealed that there isno imminent threat to reservoir water quality from the dissolved phase contaminants soils. Limited amount of availablemeasurements of TPH concentrations in soil samples and benzeneconcentrations in reservoir water samples supported model results.