Kang Mary, Jackson Robert B
Department of Earth System Science, Stanford University, Stanford, CA 94305;
Department of Earth System Science, Stanford University, Stanford, CA 94305; Woods Institute for the Environment, Stanford University, Stanford, CA 94305; Precourt Institute for Energy, Stanford University, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2016 Jul 12;113(28):7768-73. doi: 10.1073/pnas.1600400113. Epub 2016 Jun 27.
Deep groundwater aquifers are poorly characterized but could yield important sources of water in California and elsewhere. Deep aquifers have been developed for oil and gas extraction, and this activity has created both valuable data and risks to groundwater quality. Assessing groundwater quantity and quality requires baseline data and a monitoring framework for evaluating impacts. We analyze 938 chemical, geological, and depth data points from 360 oil/gas fields across eight counties in California and depth data from 34,392 oil and gas wells. By expanding previous groundwater volume estimates from depths of 305 m to 3,000 m in California's Central Valley, an important agricultural region with growing groundwater demands, fresh [<3,000 ppm total dissolved solids (TDS)] groundwater volume is almost tripled to 2,700 km(3), most of it found shallower than 1,000 m. The 3,000-m depth zone also provides 3,900 km(3) of fresh and saline water, not previously estimated, that can be categorized as underground sources of drinking water (USDWs; <10,000 ppm TDS). Up to 19% and 35% of oil/gas activities have occurred directly in freshwater zones and USDWs, respectively, in the eight counties. Deeper activities, such as wastewater injection, may also pose a potential threat to groundwater, especially USDWs. Our findings indicate that California's Central Valley alone has close to three times the volume of fresh groundwater and four times the volume of USDWs than previous estimates suggest. Therefore, efforts to monitor and protect deeper, saline groundwater resources are needed in California and beyond.
深层地下含水层的特征鲜为人知，但在加利福尼亚州及其他地区可能是重要的水源。深层含水层已被开发用于石油和天然气开采，这一活动既产生了有价值的数据，也给地下水质量带来了风险。评估地下水量和水质需要基线数据以及用于评估影响的监测框架。我们分析了加利福尼亚州八个县360个油气田的938个化学、地质和深度数据点，以及34392口油气井的深度数据。通过将加利福尼亚州中央谷地（一个地下水需求不断增长的重要农业地区）先前对305米深度的地下水量估计扩展到3000米，淡水（总溶解固体含量<3000 ppm）地下水量几乎增加了两倍，达到2700立方千米，其中大部分位于1000米以下。3000米深度带还提供了3900立方千米此前未估算的淡水和咸水，可归类为地下饮用水源（总溶解固体含量<10000 ppm）。在这八个县，分别有高达19%和35%的油气活动直接发生在淡水区和地下饮用水源区。诸如废水注入等更深层的活动也可能对地下水，尤其是地下饮用水源构成潜在威胁。我们的研究结果表明，仅加利福尼亚州的中央谷地，其淡水地下水量就几乎是先前估计的三倍，地下饮用水源量是先前估计的四倍。因此，在加利福尼亚州及其他地区，需要努力监测和保护更深层的咸水地下水资源。
