Socio-hydrologic approaches for managing groundwater contamination problems: Strategies for the arsenic problem in Bangladesh

This thesis takes a combined socio-hydrologic approach to managing problems of groundwater contamination. Groundwater flow and transport modeling and the economics of remediation are considered here. This thesis presents two illustrative examples.; The first example considers the use of pump-and-treat systems at Superfund sites in the United States. The effects of mass-transfer processes and the use of representative treatment cost functions on the selection of a pumping rate are examined. The main conclusion is that the optimal pumping rate is always an end-member rate. That is, the minimum present value cost strategy is to pump at either the minimum rate sufficient to prevent contamination from migrating off-site or at the maximum rate before the aquifer is stressed. Intermediate rates can be more expensive. Results can be generalized over a wide range of aquifer and economic parameters.; The second example considers the arsenic problem in Bangladesh. The health effects of the problem are estimated using a combination of geostatistics and dose-response modeling. These calculations show that if policy interventions are not adopted and current exposures continue 1,800,000 arsenicosis cases, 125,000 skin cancers, and several thousand deaths each year from various internal cancers may result. The use of deep wells in select regions can potentially reduce health effects by 70%.; Geochemical evidence from Sreenagar, Munshiganj demonstrate that arsenic mobilization is in part driven by the recent inflow of young carbon. A numerical groundwater model is developed and is based on aquifer pump tests, water level data, irrigation information, and local hydrologic data. This numerical model demonstrates that irrigated agriculture plays an important indirect role in mobilizing arsenic. This work does not, however, conclude that irrigation pumping is the cause of high arsenic concentrations everywhere in Bangladesh.; Lastly, the costs for various policy options are compared. The deep well option is cost-effective and is socially acceptable. Issues of sustainability concern the extent to which the shallow and deep aquifers are hydraulically connected. Particle-tracking simulations demonstrate that if the marine clay separating the shallow and deep aquifer is absent, the deep aquifer will remain safe for 700 years provided it is properly sealed.