OPTIMIZATION OF LNAPL RECOVERY FROM A SEMI-CONFINED AQUIFER: THE IMPORTANCE OF AN ACCURATE SITE CONCEPTUAL MODEL AND UNDERSTANDING LNAPL RECOVERABILITY TECHNIQUES

Optimization of Non-Aqueous Phase Liquid (LNAPL) recovery from a semi-confined aquifer presents technical challenges due to specific stratigraphic, lithologic, and hydrogeologic factors as well as LNAPL pore-fluid saturations, LNAPL buoyancy, and recoverability of petroleum hydrocarbons. The development of an accurate Conceptual Site Model is critical to understanding the placement of recovery well locations, the effectiveness of short and long term LNAPL recoverability, and remedial system optimization. This paper presents a case study of site delineation and long term recovery of LNAPL trapped below a semi-confining unit within a Cretaceous fresh water delta in the Mid-Atlantic Area (USA). A systematic approach was developed to define stratigraphic and hydrogeologic relationships, conduct initial recoverability testing, evaluate LNAPL recoverability, and optimize LNAPL recovery by managing “recovery zone” thickness and avoiding “watering-out” a well due to over pumping.