Superfund Research Program
Hydrogeology Core
Project Leader: Alexander F. van Geen
Grant Number: P42ES010349
Funding Period: 2000-2021
Project-Specific Links
Final Progress Reports
PublicationsFinal Progress Reports
The Hydrogeology Support Core provides information on the groundwater and surface water flow and transport regime at field sites in the US and Bangladesh.
The Core’s continued focus in 2005 has been on hydraulic and tracer studies, as well as groundwater flow and transport modeling. The analysts continued to collect hydraulic head time series data from our well nests and a series of private wells in Bangladesh. They also collected monthly precipitation amounts and samples for stable isotope measurements at our monitoring station in Dhaka and conducted several sample collection campaigns.
A study by postdoctoral researcher Saugata Datta compared the stable isotope (18O, 2H) composition of precipitation and surface waters with that of groundwater in Araihazar and showed that whether the source of groundwater is directly recharged from precipitation or from surface waters, some of which may be ponds or fields created by irrigation, does not seem to be an important factor in Arsenic mobilization in this area. This finding does not support the hypothesis that recharge from organic-rich surface water bodies created by irrigation is responsible for elevated dissolved As concentrations in our area.
Allan Horneman, a graduate student in the Department of Earth & Environmental Engineering defended his PhD thesis in December 2005. He explored tracer and modeling techniques in Bangladesh to better understand the dynamics of the groundwater flow system. In order to address the utility of SF6 as an inexpensive age tracer in Bangladesh, he determined SF6, noble gas, and 3H concentrations of groundwater from two well nests in Bangladesh. He found that SF6 ages were often too high relative to the 3H/3He ages. By using SF6 solubility data generated by undergraduate student Jennifer Ivanowski, he excluded the possibility that peat was responsible for the retardation of SF6. However, a simple model that incorporated a continuous gas exchange with pre-1965 trapped air with an air-to-water ratio of 0.02-0.1 is consistent with the observed SF6 deficiencies. This study indicates that further studies are needed to better understand the behavior of SF6 in Bangladesh ground waters before a widespread use can be recommended.
Allan also created a 3-D model for groundwater flow in the shallow aquifer for a 7 km2 area in the Araihazar study area. The model incorporates properties of the surface cover, hydraulic conductivities, thickness of shallow aquifer, daily precipitation, evapotranspiration, and bi-weekly measurements of river levels. It uses observed well hydraulic heads and groundwater tracer ages as calibration targets. The results indicate a net recharge of the shallow aquifer of 27 cm yr-1, which is strongly affected by irrigation. The horizontal distance a parcel of water has traveled from the surface to pumped shallow wells range from less than 40 m in the upper-most part to more than 350 m below a depth of 20 m. A comparison of modeled groundwater age with As distributions shows a correlation roughly consistent with the dissolved As versus 3H/3He age relationship found in drinking water and observation wells in Araihazar.