Monday, March 31, 2008
Preliminary Hydrogeologic Assessment of Storm Water Infiltration Through Class V Injection Wells in a Coarse Grained Vadose Zone, Missoula Valley, Montana
The characteristics of sand, gravel and cobble dominated vadose zones to affect the quality of infiltrating waters is poorly understood in western alluvial valleys. Storm water in the Missoula Valley of Western Montana is managed using more than 6,000 storm sumps, classified by USEPA as Class V Injection Wells. A storm water infiltration study was developed to assess vadose zone properties to treat percolating storm water recharging a sole source, unconfined receiving aquifer. A rotary sonic drilling program was implemented to assess stratigraphy, obtain samples for laboratory analyses, and install monitoring wells. Assessment of the cores indicates that clay-rich facies are generally absent within the vadose zone, which is dominated by gravel, pebbles and cobbles with a medium-coarse sand matrix. Thin lenses of well-sorted fine-medium sands are present in addition to lenses of open-framework gravel/cobbles. These facies are consistent with an interpretation that these materials were deposited in a very high-energy environment during the catastrophic draining(s) of Glacial Lake Missoula during the most recent glacial period. Five sumps are instrumented with combinations of sandpoint wells with thermistor strings, data logging water level sensors, gypsum blocks at multiple depths, and suction lysimeters. Infiltration tests were performed to assess the efficacy of installed instruments to simulated rainfall events. A storm water sampling and analysis program has been implemented as part of this study. Planned future activities include implementation of a geophysics cross-borehole tomography program to assess geologic controls to percolation characteristics coupled with infiltration tracer tests. Additional tests include laboratory studies of the grain size distribution and geochemical characteristics of the major hydrostratigraphic units identified with the rotary sonic drilling program. Data will be utilized to support development of infiltration models to assess geologic controls to the hydraulics of storm water infiltration from point sources through coarse-grained vadose zone materials.
James Swierc, University of Montana My academic work was completed at Dartmouth College, obtaining an AB in Earth Sciences (High Honors)and Engineering as a double major (1987); an MS in Geology (1990); and a BE from the Thayer School of Engineering at Dartmough (1990). I have 8 yrs experience as an Environmental Consultant in Cincinnati, San Antonio and Montana; worked with the development and implementation of the Montana DEQ Source Water Protection Program, and taught for 5 yrs at the community college level. In 2003, an NSF Fellowship funded placement with CSIRO in Australia for work with an ASTR project.