Abstract
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.
Highlights
The Naval Weapons Industrial Reserve Plant (NWIRP) occupies about 40 km2 in southwestMcGregor, Texas on a topographic divide underlain by a shallow groundwater system within fractured limestone bedrock (Figure 1)
Even though some dissolved perchlorate is transported off site, the source persists as residual perchlorate in the lower fractured zone awaiting remobilization during the storm
Observation worth is quantified based on the reduction in uncertainty in a parameter or prediction that is accrued through the acquisition of that data point [24]
Summary
The Naval Weapons Industrial Reserve Plant (NWIRP) occupies about 40 km in southwest. Authorities failed on two fronts: (1) they significantly underestimated travel times for contaminants to reach nearby streams and (2) they failed to appropriately monitor the system after discovery of wastes exiting the site. To address these issues, a heterogeneous MODFLOW-NWT [6] model was developed to simulate flow and transport at the NWIRP site. We suggested locations for additional monitoring wells and a future data collection plan to better characterize and monitor the site to support improved waste-containment operations These additional data were selected to ensure the greatest reductions in model-prediction uncertainty
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
