MNA and in situ reactive barrier approaches for groundwater contaminated by petroleum hydrocarbons

Monitored natural attenuation (MNA) is fast becoming the preferred remedial option for groundwater contaminated by petroleum hydrocarbons. Contaminant plumes (mainly BTEX) are anticipated to extend typically 300 m long. Other BTEX plumes show signs of surging ahead after apparent stabilization. It is important to understand the controls on plume length and long-term behaviour if MNA is to be reliably applied. Factors such as source strength, aquifer geology (especially as it influences transverse dispersion), and electron acceptor type and availability are significant. Where MNA is not appropriate and rapid clean up of plume and source is not possible or too expensive, in situ plume control might be entertained. Five pilot and full scale in situ permeable reactive barrier systems are discussed. Design rationale, cost, performance, and potential applications are presented.