Late Pleistocene and Holocene groundwater recharge from the chloride mass balance method and chlorine‐36 data

Abstract

[1] The chloride mass balance (CMB) method for estimating groundwater recharge is economic and effective, provided that the hydrological conditions for its applications are met and the modeling parameters are known. However, modeling parameters such as precipitation and Cl À deposition rates vary temporally, most notably as a result of the climatic changes from late Pleistocene to Holocene. The temporal variability of atmospheric Cl À input and annual precipitation were considered in this study by using a discrete steady state CMB model with different parameters for late Pleistocene and Holocene. Cl À deposition rates, estimated from 36 Cl data, were lower in late Pleistocene than Holocene at Yucca Mountain, Nevada, but higher in late Pleistocene than Holocene at Black Mesa, Arizona. Paleoclimate proxies at both Yucca Mountain and Black Mesa point to higher precipitation rates in late Pleistocene than Holocene. The resulting average recharge estimates for Black Mesa are 9 ± 5 mm/yr for Holocene and 35 ± 22 mm/yr for late Pleistocene. Local recharge rates at Yucca Mountain were estimated from the 36 Cl/Cl ratios and Cl À concentrations in perched waters. The estimated recharge for Yucca Mountain is 5 ± 1 mm/yr for Holocene and 15 ± 5 mm/yr for late Pleistocene. These recharge rates are comparable to results of independent numerical groundwater flow models and watershed-scale infiltration models at Black Mesa and Yucca Mountain, respectively.INDEX TERMS: 1040 Geochemistry: Isotopic composition/chemistry; 1829 Hydrology: Groundwater hydrology; 1045 Geochemistry: Low-temperature geochemistry; 1836 Hydrology: Hydrologic budget (1655); KEYWORDS: recharge, Yucca mountain, chloride mass balance, chlorine-36, paleohydrology Citation: Zhu, C., J. R. Winterle, and E. I. Love, Late Pleistocene and Holocene groundwater recharge from the chloride mass balance method and chlorine-36 data, Water Resour.

In situ feldspar dissolution rates in an aquifer

“…The decrease of Cl Ϫ concentration along the flow path is likely a result of paleoclimate changes (Zhu et al, 2003). Nevertheless, halite dissolution and precipitation was included in the model as a computer code artifact because charge balance is always calculated regardless in PHREEQC (Parkhurst, 1997).…”

Simple solutions for steady–state diffuse recharge evaluation in sloping homogeneous unconfined aquifers by means of atmospheric tracers

“…The steady state condition is acceptable as a first approach in many common situations, but may be a serious limitation in low recharge areas and especially when the unsaturated zone is thick, as may be the case in arid areas. In these areas the tracer concentration along the unsaturated zone is variable and reflect past environmental changes (Zhu et al 1987) or important land use changes; so tracer concentration in water leaving the upper zone (in-transit recharge) may be quite different from that in water entering the water table. In this case, recharge calculations are erroneous.…”

Origen de las aguas de pequeños manantiales de la costa del norte de Chile, en las cercanías de Antofagasta.

“…In principle it is expected that recharged water moves vertically downward in diffuse form, preferably through the rock matrix, except after very heavy rainfall events, when flow through fractures could dominate up to certain depth. There is also the possibility that water penetrating through fractures temporarily accumulate above some very low permeability, tilted and sealed laterally level, which can favor concentrated recharge along fault planes, as in the ignimbrites of Yucca Mountain in Nevada (Zhu et al, 2003). In such situations, if shallow, occasional storm water may move fast to the water table.…”