Ground-Water Age and Atmospheric Tracers: Simulation Studies and Analysis of Field Data from the Mirror Lake Site, New Hampshire
Goode, Daniel J., 1998, Ground-water age and atmospheric tracers: Simulation studies and analysis of field data from the Mirror Lake site, New Hampshire: Ph.D. thesis, Princeton University, Department of Civil Engineering and Operations Research, 194 p.
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- Complete thesis (5.5 M)
- Front & Back (137K): Cover, Abstract, Table of Contents
List of Figures, List of Tables, Acknowledgments
Chapter 1: Introduction
Chapter 6: Summary and Conclusions
- Chapter 2 (2.4M): Direct Simulation of Ground-Water Age
- Chapter 3 (357K): Effects of Temperature Fluctuations on CFC-11 Transport from the Atmosphere to the Water Table
- Chapter 4 (1.5M): Field Study of CFC Concentrations at the Water Table at the Mirror Lake Site, New Hampshire
- Chapter 5 (2.1M): Regional-Scale Simulation of Ground-Water Age and CFC-11 Transport at the Mirror Lake Site, New Hampshire
The use of environmental tracers in characterization of ground-water systems is investigated through mathematical modeling of ground-water age and atmospheric tracer transport, and by a field study at the Mirror Lake site, New Hampshire. Theory is presented for modeling ground-water age using the advective-dispersive transport equation. The transport equation includes a zero-order source of unit strength, corresponding to the rate of aging, and can accommodate matrix diffusion and other exchange processes. The effect of temperature fluctuations and layered soils on transport of atmospheric gases to the water table is investigated using a one-dimensional numerical model of chlorofluorocarbon (CFC-11) transport. The nonlinear relation between temperature and Henry's Law coefficient (reflecting air/water phase partitioning) can cause the apparent recharge temperature to be elevated above the annual mean temperature where the water table is shallow. In addition, fine-grained soils can isolate the air phase in the unsaturated zone from the atmosphere. At the USGS' Mirror Lake, New Hampshire fractured-rock research site CFC concentrations near the water table are depleted where dissolved oxygen is low. CFC-11 and CFC-113 are completely absent under anaerobic conditions, while CFC-12 is as low as one-third of modern concentrations. Anaerobic biodegradation apparently consumes CFC's near the water table at this site. One area of active degradation appears to be associated with streamflow loss to ground water. Soil gas concentrations are generally close to atmospheric levels, although some spatial correlation is observed between depleted concentrations of CFC-11 and CFC-113 in soil gas and water-table samples. Results of unsaturated-zone monitoring indicate that recharge occurs throughout the year in the watershed, even during summer evapotranspiration periods, and that seasonal temperature fluctuations occur as much as 5 meters below land surface. Application of ground-water age and CFC-11 transport models to the large-scale ground-water system at Mirror Lake illustrates the similarities between age and chemical transport. Generally, bedrock porosities required to match observed apparent ages from CFC concentrations are high relative to porosities measured on cores. Although matrix diffusion has no effect on steady-state age, it can significantly reduce CFC concentrations in fractured rock in which the effective porosity is low.
- Goode, D.J., Busenberg, E., Plummer, L.N., Shapiro, A.M., and Vroblesky, D.A., 1999, CFC's in the unsaturated zone and in shallow ground water at Mirror Lake, New Hampshire: in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program-- Proceedings of the Technical Meeting , Charleston, South Carolina, March 8-12, 1999--Volume 3 of 3--Subsurface Contamination from Point Sources: U.S. Geological Survey Water-Resources Investigations Report 99-4018C, p. 809-820.
- Goode, D.J., 1997, CFC transport to and degradation near a shallow water table, Mirror Lake area, Grafton County, New Hampshire : (abs.), p. S176 in 1997 Spring Meeting, supplement to Eos, 29 April 1997, American Geophysical Union, Washington DC.
- Goode, D.J., Busenberg, Eurybiades, Plummer, L.N., Shapiro, A.M., and Vroblesky, D.A., 1997, CFC degradation under anaerobic water table conditions in glacial drift at Mirror Lake New Hampshire: (abs.), GSA Abstracts with Programs, vol. 29, no. 6, p. 77.
- Goode, D.J., 1996, Direct simulation of groundwater age: Water Resources Research, v. 32, no. 2, p. 289-296.