Anders Robert, Mendez Gregory O, Futa Kiyoto, Danskin Wesley R
USGS California Water Science Center, 4165 Spruance Rd., Ste. 200, San Diego, CA 92101.
Ground Water. 2014 Sep-Oct;52(5):756-68. doi: 10.1111/gwat.12108. Epub 2013 Aug 28.
Geochemical evaluation of the sources and movement of saline groundwater in coastal aquifers can aid in the initial mapping of the subsurface when geological information is unavailable. Chloride concentrations of groundwater in a coastal aquifer near San Diego, California, range from about 57 to 39,400 mg/L. On the basis of relative proportions of major-ions, the chemical composition is classified as Na-Ca-Cl-SO4, Na-Cl, or Na-Ca-Cl type water. δ(2)H and δ(18)O values range from -47.7‰ to -12.8‰ and from -7.0‰ to -1.2‰, respectively. The isotopically depleted groundwater occurs in the deeper part of the coastal aquifer, and the isotopically enriched groundwater occurs in zones of sea water intrusion. (87)Sr/(86)Sr ratios range from about 0.7050 to 0.7090, and differ between shallower and deeper flow paths in the coastal aquifer. (3)H and (14)C analyses indicate that most of the groundwater was recharged many thousands of years ago. The analysis of multiple chemical and isotopic tracers indicates that the sources and movement of saline groundwater in the San Diego coastal aquifer are dominated by: (1) recharge of local precipitation in relatively shallow parts of the flow system; (2) regional flow of recharge of higher-elevation precipitation along deep flow paths that freshen a previously saline aquifer; and (3) intrusion of sea water that entered the aquifer primarily during premodern times. Two northwest-to-southeast trending sections show the spatial distribution of the different geochemical groups and suggest the subsurface in the coastal aquifer can be separated into two predominant hydrostratigraphic layers.
在缺乏地质信息的情况下，对沿海含水层中咸水地下水的来源和运移进行地球化学评估有助于初步绘制地下结构图。加利福尼亚州圣地亚哥附近沿海含水层中地下水的氯化物浓度范围约为57至39400mg/L。根据主要离子的相对比例，其化学成分被归类为Na-Ca-Cl-SO4型、Na-Cl型或Na-Ca-Cl型水。δ(2)H值范围为-47.7‰至-12.8‰，δ(18)O值范围为-7.0‰至-1.2‰。同位素贫化的地下水出现在沿海含水层的较深部分，同位素富集的地下水出现在海水入侵区域。(87)Sr/(86)Sr比值范围约为0.7050至0.7090，在沿海含水层较浅和较深的流动路径之间存在差异。(3)H和(14)C分析表明，大部分地下水是在数千年前补给的。多种化学和同位素示踪剂的分析表明，圣地亚哥沿海含水层中咸水地下水的来源和运移主要受以下因素控制：(1)在流动系统相对较浅的部分补给当地降水；(2)沿深层流动路径补给高海拔降水的区域水流，使先前的咸水含水层变淡；(3)海水入侵，海水主要在近代以前进入含水层。两条西北向东南走向的剖面显示了不同地球化学组的空间分布，并表明沿海含水层的地下可分为两个主要的水文地层层。
