Post-Calibration Uncertainty Analysis for Travel Times at a Naval Weapons Industrial Reserve Plant

The Naval Weapons Industrial Reserve Plant (NWIRP) in McGregor, Texas began manufacturing explosives in 1980 and several hazardous chemicals were discovered in lakes and streams surrounding the site in 1998. Contaminants traveled to local lakes and streams much faster than initially predicted. This research estimated contaminant travel times and identified locations where monitoring wells should be installed to yield the greatest reductions in uncertainties in travel-time predictions. To this end, groundwater and particle-tracking models for NWIRP site were built to predict hydraulic heads and contaminant travel times. Next, parameter (hydraulic conductivities) uncertainties, parameter identifiabilities, observation (hydraulic heads) worth, and predictive (contaminant travel times) uncertainties were quantified. Parameter uncertainties were reduced by up to 92%; a total of 19 of 158 parameters were at least moderately identifiable; travel-time uncertainties were reduced up to 92%. Additionally, travel-time predictions and post-calibration parameter distributions were generated using the null-space Monte Carlo (NSMC) technique. NSMC predicted that conservative tracers exited the flow system within a year, which matches with field data. Finally, an observations-worth analysis found that additional 11 more measurements would reduce travel-time uncertainties by factors from 1.04 to 4.3 over existing data if monitoring wells were installed at the suggested locations

Temperature: an easy, inexpensive, but useful tool for mapping karst spring habitats.

Karst aquifer spring habitats around the world support a diversity of specially-adapted, unusual, or rare aquatic flora and fauna. Temperature is one of the most appealing attributes of spring habitats because the consistent groundwater flow associated with springs maintains more constant temperatures than surface flows susceptible to seasonal and diurnal fluxes. Karst aquifers commonly have specific point-source discharge resulting from fractures causing more abrupt changes in local water conditions compared to discharge from granular sand aquifers. Mapping the temperature distribution associated with karst spring discharge can help delineate the most important habitat areas associated with spring-dependent organisms. The downtown spring complex in the Northern Segment of the Edwards Balcones Fault Zone aquifer in central Texas is home to several spring-dependent organisms including an endemic salamander, Eurycea chisolmensis, that is federally listed as “threatened”. Temperatures were measured with a Solinst TLC meter and with a hand-held infrared camera. The Solinst TLC meter was able to measure temperature rapidly and the FLIR infrared camera provided dramatic visual images while documenting dynamics associated with spring discharge temperatures. The temperature data were comparable to specific conductance data indicating that temperature could be used to map areas of basic water chemistry changes in local systems. Aquatic plant assemblages correlated well with the areas delineated by temperature gradients. Overall, temperatures in Salado Creek and the associated spring orifices of the downtown spring complex showed a relationship between temperature and preferred habitat for spring organisms. The results indicated that temperature was an effective parameter to use in spring habitat studies due to its high importance to spring dependent organisms, low cost, and ease of collection

Post-Calibration Uncertainty Analysis for Travel Times at a Naval Weapons Industrial Reserve Plant

The Naval Weapons Industrial Reserve Plant (NWIRP) in McGregor, Texas began manufacturing explosives in 1980 and several hazardous chemicals were discovered in lakes and streams surrounding the site in 1998. Contaminants traveled to local lakes and streams much faster than initially predicted. This research estimated contaminant travel times and identified locations where monitoring wells should be installed to yield the greatest reductions in uncertainties in travel-time predictions. To this end, groundwater and particle-tracking models for NWIRP site were built to predict hydraulic heads and contaminant travel times. Next, parameter (hydraulic conductivities) uncertainties, parameter identifiabilities, observation (hydraulic heads) worth, and predictive (contaminant travel times) uncertainties were quantified. Parameter uncertainties were reduced by up to 92%; a total of 19 of 158 parameters were at least moderately identifiable; travel-time uncertainties were reduced up to 92%. Additionally, travel-time predictions and post-calibration parameter distributions were generated using the null-space Monte Carlo (NSMC) technique. NSMC predicted that conservative tracers exited the flow system within a year, which matches with field data. Finally, an observations-worth analysis found that additional 11 more measurements would reduce travel-time uncertainties by factors from 1.04 to 4.3 over existing data if monitoring wells were installed at the suggested locations

Teaching Hydrogeology in the 21st Century: Resources Demonstrating the Interface Between Hydrogeology and Other Scientific and Social Disciplines

Presented at Geological Society of America National Meeting The field of hydrogeology has a rich and ongoing history of contributions to the solution of problems in many scientific and social disciplines. For example, hydrogeology has brought greater understanding to the many processes in the Earth\u27s crust that involve ground and surface waters, such as sedimentary diagenesis, the formation of hydrothermal mineral deposits, the shaping of landforms, the deformation of rock, metamorphism, magma generation, and the transport of hydrocarbons. Hydrogeology has a prominent role in many societal issues, such as the development of water resources, protection of the environment, and the shaping of laws and public policy. Students can gain a deeper appreciation of the broad relevance of hydrogeology and can become better equipped to apply it if problems from other disciplines that can be solved using hydrogeologic principles can be integrated into hydrogeology courses. To help accomplish this, a working group consisting of the authors of the present communication was organized at the On the Cutting Edge: Teaching Hydrogeology in the 21st Century workshop held July 23-28, 2005 to develop and collect effective teaching resources that could be shared with other hydrogeology instructors. The resources are accessible for download from the Teaching Hydrogeology website at http://serc.carleton.edu/NAGTWorkshops/hydrogeo/index.html. The resources being collected consist of (1) calculations that can be performed by hand, using a spreadsheet, or a simple computer program, (2) laboratory and field exercises, (3) lecture presentations, (4) data sets, and (5) case studies. Contributions from people outside of the working group are also welcomed and can be uploaded at the website above or by contacting one of the working group members