Age Dating of Shallow Groundwater with Chlorofluorocarbons, Tritium/Helium: 3, and Flow Path Analysis, Southern New Jersey Coastal Plain

Water Resources Research - Tập 32 Số 4 - Trang 1023-1038 - 1996
Zoltán Szabó1, Dudley D. Rice1, L. Niel Plummer1, Eurybiades Busenberg1, S. Drenkard2, Peter Schlösser2
1United States Geological Survey
2Columbia University

Tóm tắt

Groundwater age dating through the combination of transient tracer methods (chlorofluorocarbons (CFCs) and tritium/helium 3 (3H/3He)) and groundwater flow path analysis is useful for investigating groundwater travel times, flow patterns, and recharge rates, as demonstrated by this study of the homogeneous shallow, unconfined Kirkwood‐Cohansey aquifer system in the southern New Jersey coastal plain. Water samples for age dating were collected from three sets of nested observation wells (10 wells) with 1.5‐m‐long screens located near groundwater divides. Three steady state finite difference groundwater flow models were calibrated by adjusting horizontal and vertical hydraulic conductivities to match measured heads and head differences (range, 0.002–0.23 m) among the nested wells, with a uniform recharge rate of 0.46 m per year and porosities of 0.35 (sand) and 0.45 (silt) that were assumed constant for all model simulations and travel time calculations. The simulated groundwater travel times increase with depth in the aquifer, ranging from about 1.5 to 6.5 years for the shallow wells (screen bottoms 3–4 m below the water table), from about 10 to 25 years for the medium‐depth wells (screen bottoms 8–19 m below the water table), and from about 30 to more than 40 years for the deep wells (screen bottoms 24–26 m below the water table). Apparent groundwater ages based on CFC‐ and 3H/3He‐dating techniques and model‐based travel times could not be statistically differentiated, and all were strongly correlated with depth. Confinement of 3He was high because of the rapid vertical flow velocity (of the order of 1 m/yr), resulting in clear delineation of groundwater travel times based on the 3H/3He‐dating technique. The correspondence between the 3H/3He and CFC ages indicates that dispersion has had a minimal effect on the tracer‐based ages of water in this aquifer. Differences between the tracer‐based apparent ages for seven of the 10 samples were smaller than the error values. A slight bias toward older apparent ages, found not to be statistically significant, was noted for the 3H/3He‐dating technique relative to the CFC‐dating technique. This result may be caused by enrichment of local air in CFC‐Il and CFC‐12 from urban and industrial sources in the northeastern United States and minor contamination from sampling equipment. The demonstrated validity of the combined tracer‐dating techniques to determine the age of water in the Kirkwood‐Cohansey aquifer system indicates that groundwater flow models can be refined when apparent ages based on 3H/3He‐ and CFC‐ dating are used as calibration targets.

Từ khóa


Tài liệu tham khảo

10.1007/BF00646402

10.1029/95WR01584

10.1016/0967-0637(95)00052-8

10.1029/92WR01263

Busenberg E., 1993, Use of trichlorofluorocarbon‐113 (CFC‐113) as a hydrologic tracer and age‐dating tool of young groundwater (abstract, Geol. Soc. Am. Abstr. Programs, 25, A‐365

Busenberg E. E. P.Weeks L. N.Plummer R. C.Bartholemay Age dating groundwater by use of chlorofluorocarbons (CCl3F and CCl2F2) and distribution of chlorofluorocarbons in the unsaturated zone Snake River Plain aquiferU.S. Geol. Surv. Water Resour. Invest. Rep. 93‐4054Idaho National Engineering Laboratory Idaho 1993.

Carlston C. W. L. L.Thatcher E. C.Rhodehamel Tritium as a hydrologic tool: The Wharton Tract study IASH Publ. 52 503–512 1960.

Chemical Manufacturers Association1, 1992, Alternative fluorocarbons environmental acceptability study, Production and atmospheric release data for CFC‐11 and CFC‐12 (through 1991)

10.1016/0020-708X(76)90082-X

10.1029/94WR02232

10.1029/94WR02528

10.1029/93WR02073

10.1029/94WR00156

10.1038/364780a0

10.1016/0960-1686(93)90357-5

10.1029/1998WR900047

10.1029/95WR00221

Lacombe P. J. R.Rosman Hydrology of the unconfined aquifer system upper Maurice River Basin and adjacent areas in Gloucester County New Jersey 1986–87U.S. Geol. Surv. Water Resour. Invest. Rep. 92‐4128 1995.

10.1038/230379a0

10.1021/es00029a009

Martin M. Groundwater flow in the New Jersey Coastal Plain U.S. Geol. Surv. Prof. Pap. 1404‐H 1996.

10.1016/0004-6981(77)90065-8

McDonald M. G. A. W.Harbaugh A modular three‐dimensional finite‐difference groundwater flow model U.S. Geol. Surv. Tech. Water Resour. Invest. Rep. book 6chap. Al 1988.

Nemickas B., 1976, Stratigraphic and hydrologic relation of the Piney Point aquifer and the Alloway Clay member of the Kirkwood Formation in New Jersey, U.S. Geol. Surv. J. Res., 4, 1

Owens J. P., 1969, Geology of Selected Areas in New Jersey and Eastern Pennsylvania, and Guidebook of Excursions, 235

Plummer L. N., 1993, Regional Groundwater Quality, 255

Pollock D. W. Documentation of computer programs to compute and display pathlines using results from the U.S. Geological Survey modular three‐dimensional finite‐difference groundwater flow modelU.S. Geol. Surv. Open File Rep. 89‐381 1989.

10.1016/0022-1694(88)90002-9

10.1029/JD092iD06p06579

10.1029/93WR02655

Rhodehamel E. C. Geology and water resources of the Wharton Tract and the Mullica River Basin in southern New JerseyN. J. Div. Water Resour. Spec. Rep. 36 1973.

10.1029/WR019i001p00057

10.1016/0012-821X(88)90122-7

10.1016/0012-821X(89)90144-1

10.1029/91WR01446

10.1029/93WR00968

Thatcher L. L. V. J.Janzer K. W.Edwards Methods for determination of radioactive substances in water and fluvial sediments U.S. Geol. Surv. Tech. Water Resour. Invest. book 5chap. A5 79–81 1977.

10.1029/WR015i003p00546

10.1351/pac199264040529

10.1016/0198-0149(85)90099-8

10.1029/WR018i005p01365

10.1029/GL015i002p00188

Zapecza O. S. Hydrogeologic framework of the New Jersey Coastal Plain U.S. Geol. Surv. Prof. Pap. 1404‐B 1989.