Sources of high-chloride water and managed aquifer recharge in an alluvial aquifer in California, USA

O’Leary, David R.; Izbicki, John A.; Metzger, Loren F.

Sources of high-chloride water and managed aquifer recharge in an alluvial aquifer in California, USA | Origines des eaux enrichies en chlorures et gestion de la recharge des aquifères d’un aquifère alluvial de Californie, Etats-Unis d’Amérique Fuentes de agua de altamente cloruradas y manejo de la recarga de acuífero en un acuífero aluvial en California, EEUU 美国加利佛尼亚州一个冲积含水层中高氯水的来源及含水层补给管理 Origens de água rica em cloreto e recarga de aquíferos gerida num aquífero aluvial na Califórnia, EUA

2015

O’Leary, David R. | Izbicki, John A. | Metzger, Loren F.

As a result of pumping in excess of recharge, water levels in alluvial aquifers within the Eastern San Joaquin Groundwater Subbasin, 130 km east of San Francisco (California, USA), declined below sea level in the early 1950s and have remained so to the present. Chloride concentrations in some wells increased during that time and exceeded the US Environmental Protection Agency’s secondary maximum contaminant level of 250 mg/L, resulting in removal of some wells from service. Sources of high-chloride water include irrigation return in 16 % of sampled wells and water from delta sediments and deeper groundwater in 50 % of sampled wells. Chloride concentrations resulting from irrigation return commonly did not exceed 100 mg/L, although nitrate concentrations were as high as 25 mg/L as nitrogen. Chloride concentrations ranged from less than 100–2,050 mg/L in wells affected by water from delta sediments and deeper groundwater. Sequential electromagnetic logs show movement of high-chloride water from delta sediments to pumping wells through permeable interconnected aquifer layers. δD and δ¹⁸O data show most groundwater originated as recharge along the front of the Sierra Nevada, but tritium and carbon-14 data suggest recharge rates in this area are low and have decreased over recent geologic time. Managed aquifer recharge at two sites show differences in water-level responses to recharge and in the physical movement of recharged water with depth related to subsurface geology. Well-bore flow logs also show rapid movement of water from recharge sites through permeable interconnected aquifer layers to pumping wells.

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