AIR SPARGING IN A SANDY AQUIFER (FLORENCE, OREGON, USA) - ACTUAL AND APPARENT RADIUS OF INFLUENCE

Injection of air into the saturated zone of a contaminated aquifer, ai r sparging, is a currently popular remediation alternative to the conv entional approach of groundwater extraction followed by surface treatm ent. The air flow behavior around a single air sparging well was inves tigated under natural field conditions in a relatively homogeneous aqu ifer consisting of well-sorted dune sand. The response of conventional monitoring data (including water table mounding, son gas pressure, so il gas composition and tracer gas response) was compared with the resu lts of cross-borehole electrical resistance tomography (ERT), which pr ovides a sensitive indication of the pattern of air flow in the satura ted zone. Compared with the region of air flow imaged by ERT, conventi onal monitoring data provided an ambiguous indication of the region of air flow in the saturated zone, possibly leading to an overestimation of,the radius of influence by a factor of two to eight. Critical eval uation of the conventional monitoring data indicates that the shortcom ings are a function of various factors which include the transient asp ects of pressure and water table changes, and differences in the contr ols on air flow within the saturated and unsaturated zones.