Hydrological Science & Engineering Program, Department of Geology & Geological Engineering, Colorado School of Mines, 1500 Illinois St, Golden, Colorado 80401, United States.
Environ Sci Technol. 2013 Jun 4;47(11):5954-62. doi: 10.1021/es400316c. Epub 2013 May 16.
Increased human health risk associated with groundwater contamination from potential carbon dioxide (CO2) leakage into a potable aquifer is predicted by conducting a joint uncertainty and variability (JUV) risk assessment. The approach presented here explicitly incorporates heterogeneous flow and geochemical reactive transport in an efficient manner and is used to evaluate how differences in representation of subsurface physical heterogeneity and geochemical reactions change the calculated risk for the same hypothetical aquifer scenario where a CO2 leak induces increased lead (Pb(2+)) concentrations through dissolution of galena (PbS). A nested Monte Carlo approach was used to take Pb(2+) concentrations at a well from an ensemble of numerical reactive transport simulations (uncertainty) and sample within a population of potentially exposed individuals (variability) to calculate risk as a function of both uncertainty and variability. Pb(2+) concentrations at the well were determined with numerical reactive transport simulation ensembles using a streamline technique in a heterogeneous 3D aquifer. Three ensembles with variances of log hydraulic conductivity (σ(2)lnK) of 1, 3.61, and 16 were simulated. Under the conditions simulated, calculated risk is shown to be a function of the strength of subsurface heterogeneity, σ(2)lnK and the choice between calculating Pb(2+) concentrations in groundwater using equilibrium with galena and kinetic mineral reaction rates. Calculated risk increased with an increase in σ(2)lnK of 1 to 3.61, but decreased when σ(2)lnK was increased from 3.61 to 16 for all but the highest percentiles of uncertainty. Using a Pb(2+) concentration in equilibrium with galena under CO2 leakage conditions (PCO2 = 30 bar) resulted in lower estimated risk than the simulations where Pb(2+) concentrations were calculated using kinetic mass transfer reaction rates for galena dissolution and precipitation. This study highlights the importance of understanding both hydrologic and geochemical conditions when numerical simulations are used to perform quantitative risk calculations.
通过进行联合不确定性和变异性（JUV）风险评估，可以预测由于潜在二氧化碳（CO2）泄漏到饮用水含水层而导致的人类健康风险增加。本文提出的方法以有效的方式明确纳入了非均匀流和地球化学反应输运，用于评估在相同的假设含水层情景下，由于方铅矿（PbS）溶解导致 CO2 泄漏引起 Pb（2+）浓度增加，地下物理非均质性和地球化学反应的代表性差异如何改变计算出的风险。使用嵌套蒙特卡罗方法，从数值反应传输模拟的集合（不确定性）中获取井中的 Pb（2+）浓度，并在潜在暴露个体的种群中进行采样（变异性），以计算风险作为不确定性和变异性的函数。使用非均匀 3D 含水层中的流线技术，通过数值反应传输模拟集合确定井中的 Pb（2+）浓度。模拟了具有水力传导率对数方差（σ（2）lnK）分别为 1、3.61 和 16 的三个集合。在所模拟的条件下，计算出的风险显示为地下非均质性强度、σ（2）lnK 的函数，以及在使用与方铅矿平衡和动力学矿物反应速率计算地下水 Pb（2+）浓度之间的选择。随着σ（2）lnK 从 1 增加到 3.61，计算出的风险增加，但当σ（2）lnK 从 3.61 增加到 16 时，除了不确定性的最高百分位数外，风险都会降低。在 CO2 泄漏条件下（PCO2 = 30 巴），使用与方铅矿平衡的 Pb（2+）浓度导致的风险估计低于使用动力学质量转移反应速率计算方铅矿溶解和沉淀时的模拟。本研究强调了在使用数值模拟进行定量风险计算时，了解水文地质和地球化学条件的重要性。
