Abstract

An innovative remedial system featuring intersecting horizontal and vertical wells allowed the development of a prominent Brownfields site in Houston. A dual-phase extraction system targeting a gasoline plume was installed to operate beneath the new Federal Reserve Bank of Houston at the site of a former hospital, without interfering with bank operations. Distillation of a complex hydrogeologic setting into a groundwater flow model reflecting key parameter trends was crucial to meeting a compressed design-build schedule. Severe space restrictions were overcome with an innovative horizontal well design. Through the combined effects of two complex-curved horizontal wells and complementary vertical dual-phase extraction wells, the system achieved its remediation goals and regulatory site closure on schedule. The horizontal well system was designed using a three-dimensional groundwater flow model. The model was constructed and calibrated on the basis of a three-dimensional geologic model of the subsurface, pumping tests, slug tests, laboratory permeability tests, and grain-size analyses of soil cores. The geologic model exhibited strong vertical and horizontal heterogeneity. Aquifer tests and grain size analyses indicated a wide range of hydraulic properties. To meet the time constraints of the design schedule, the model construction reflected a conceptual model of the subsurface that captured the essential spatial trends in hydrogeologic properties. The model conservatively predicted the flow rate of the system and the degree of dewatering in the area impacted by the gasoline plume. The system removed 150 thousand pounds of hydrocarbons during 16 months of operation, at a cost of approximately six dollars per pound.