Horizontal In-Well Treatment, Modeling Analyses of A New Concept for Sustainable Passive In Situ Remediation

A new passive remediation concept, the horizontal in-well treatment (HIT) system, is presented that utilizes horizontal wells filled with a reactive media to passively treat contaminated groundwater in-situ.  The wells are oriented parallel to the direction of groundwater flow and passively draw impacted groundwater into the upgradient portions of the well due the transmissivity contrast which results in flow-focusing.  The groundwater is then completely treated as it flows through the reactive media in the horizontal well, and then exits the well along its down-gradient sections.  Many different types of reactive media could be used (zero valent iron, activated carbon, IX resins, zeolite, phosphate, chitin, etc.); therefore, this concept could be used to address a wide range of contaminants.  Additionally, the HIT well can also be used without reactive media but with a blank section instead, to allow for unimpacted groundwater to by-pass source areas and discharge downgradient, thus reducing contaminant mass-flux to downgradient areas. A series of quantitative three-dimensional flow and transport simulations were completed utilizing MODFLOW and MT3D to assess the general hydraulic performance, capture zones, residence times, effects of aquifer heterogeneity, and treatment effectiveness of the concept.  The results demonstrate that capture widths greater than 50 feet can be achieved, and that near-immediate reductions in down-gradient concentrations and contaminant mass flux can be achieved. General criteria for site applicability and practical implementation challenges will also be discussed.