Effective Air Delivery from a Horizontal Sparging Well

Horizontal air sparging (HASP) wells offer several potential advantages compared to linear arrays of vertical air sparging wells. For some of these advantages to be realized, however, HASP wells must be able to deliver air uniformly along the length of the well. HASP wells can fail to deliver air uniformly for either engineering or geological reasons.
A 58 m (190-foot) long HASP well, with a 15 m (50-foot) long screen interval, was designed, installed, and tested in eolian dune sand. The relative uniformity of the geologic medium allowed specific evaluation of the impact of the well design on air delivery. A variety of monitoring approaches were used during a six-day pilot test. Pressure drop within the sparge well was found to be negligible through the screen interval of the well. Soil gas pressure and ground water mounding responses were very similar at both ends of the well screen, suggesting relatively uniform air delivery throughout. Electrical resistance tomography results confirmed that airflow in the formation was similar at both ends of the screen interval and that the principal region of airflow was within 1.5 m (5 feet) of the axis of the well. Increased dissolved oxygen was primarily limited to a region within 2.3 m (7.5 feet) of the well and occurred throughout the length of the screen interval. These monitoring results show that HASP wells, properly constructed and installed, can supply air in a generally uniform manner along their length.