Practically impractical - the limits of LNAPL recovery and relationship to risk

Light non-aqueous phase liquids (LNAPL) are commonly a source of detectable hydrocarbon concentrations in water and vapor phases that may present potential health and environmental risks. As a result, many regulatory agencies have adopted a policy of requiring LNAPL recovery to the {open_quotes}maximum extent practicable{close_quotes}. However, the technical, economic, and social definition of {open_quotes}practicable{close_quotes} is not generally described. This can be a significant hurdle to effective policy implementation, especially with respect to risk-based corrective actions. This paper addresses the technical implications of LNAPL recovery limits to assist policy makers and businesses in achieving cleanup goals. Field, lab, and theoretical evidence of the limits to LNAPL recovery are summarized for a range of conditions and then linked to the impact on the magnitude and longevity of potential risk. Core tests and an extensive history of primary, secondary, and tertiary recovery efforts in petroleum reservoirs demonstrate that porous media have a substantial capacity for retaining mobile and immobile oil. For example, primary oil production commonly recovers only about 40% of the mobile oil present in the reservoir. Similarly, the efficiency of LNAPL recovery is generally low, especially where low permeability soil and/or high viscosity LNAPL is concerned. Measured residual LNAPL saturations inmore » water-wet soil may range from about 2% to 60% of the pore volume, depending on soil and LNAPL properties. These figures represent the minimum LNAPL saturations left behind following recovery pumping.« less