Developing Risk-Based Cleanup Standards for Soils in Nigeria

Abstract

Regulators outside of the United States either have not set cleanup goals for Total Petroleum Hydrocarbons (TPH) and other chemicals in soil, or they have proposed very low concentrations based on reviews of European and North American regulations. Soil TPH or oil and grease cleanup levels range from 50 to 10,000 ppm (mg/kg) in North America and Europe. This reflects that not all jurisdictions acknowledge differences between types of hydrocarbon mixtures (e.g., gasoline and crude oil), not all jurisdictions recognize that soil organic matter can report as TPH, and that not all jurisdictions utilize a risk analysis approach for evaluating human health and environmental impacts. In addition to these issues, there has been until recently no standardized, scientifically defensible procedure for interpreting risk associated with complex mixtures of hydrocarbons like TPH. However, recent efforts by the TPH Criteria Working Group (TPHCWG) and the Petroleum Environmental Research Forum (PERF) have established procedures to derive human-health Risk-Based Screening Levels (RBSLs) for refined petroleum products and crude oils. In 1999, the Nigeria Department of Petroleum Resources proposed using Intervention and Target Values established by the Dutch Ministry of Housing, Spatial Planning, and the Environment for soil remediation at oil impacted sites in Nigeria. They proposed using the Dutch Target Value for mineral oil of 50 mg/kg; however, since that time the Dutch have adopted an approach similar to that of the TPHCWG. This paper discusses the new approach being used by the Dutch, as well as the Risk-Based Corrective Action approach for TPH and other chemicals being used by many state regulators in the United States. A modified approach for developing Nigeria specific RBSLs for oil impacted soil is proposed. Introduction A review of upstream TPH regulations in North America and Europe indicates that acceptable soil concentrations set for complex petroleum hydrocarbon mixtures characterized as TPH or oil and grease (O&G) are highly variable, ranging from 50 to 10,000 mg/kg soil. TPH regulations for some of the major U.S. oil producing states and one Canadian province are shown in Table 1. Overall, these values do not recognize that soil organic matter itself can report as TPH and the range reflects the facts that not all jurisdictions acknowledge differences between particular types of hydrocarbon mixtures (e.g., gasoline and crude oil), or utilize a risk analysis approach for setting acceptable levels. In reality, most of these regulations are not based upon an evaluation of the risk that TPH may pose to human health or the environment. Recently, several U.S. states (e.g., Texas, New Mexico, and Louisiana) have begun reevaluating existing programs and are considering adopting or have adopted a risk-based approach for hydrocarbon impacted sites. Evaluating the potential risk of TPH in the environment based on the actual composition of the petroleum mixture is a fairly new technology that has not been incorporated into regulatory guidelines until quite recently. Considering the composition of the TPH mixture is very important when developing cleanup levels. For example, it is expected that gasoline spilled in soil will behave differently and pose different health risks than a crude oil spilled in the same soil. While gasoline and crude are both TPH mixtures, the cleanup levels developed for them should reflect their different compositions.