Lee Jimi, Rao P S C, Poyer Irene C, Toole Robyn M, Annable M D, Hatfield K
School of Civil Engineering, Purdue University, West Lafayette, IN 47907-2051, USA.
J Contam Hydrol. 2007 Jul 17;92(3-4):208-29. doi: 10.1016/j.jconhyd.2006.12.002. Epub 2007 Jan 11.
We report here on the extension of Passive Flux Meter (PFM) applications for measuring fluxes of oxyanions in groundwater, and present results for laboratory and field studies. Granular activated carbon, with and without impregnated silver (GAC and SI-GAC, respectively), was modified with a cationic surfactant, hexadecyltrimethylammonium (HDTMA), to enhance the anion exchange capacity (AEC). Langmuir isotherm sorption maxima for oxyanions measured in batch experiments were in the following order: perchlorate>>chromate>selenate, consistent with their selectivity. Linear sorption isotherms for several alcohols suggest that surfactant modification of GAC and SI-GAC reduced (approximately 30-45%) sorption of alcohols by GAC. Water and oxyanion fluxes (perchlorate and chromate) measured by deploying PFMs packed with surfactant-modified GAC (SM-GAC) or surfactant-modified, silver-impregnated GAC (SM-SI-GAC) in laboratory flow chambers were in close agreement with the imposed fluxes. The use of SM-SI-GAC as a PFM sorbent was evaluated at a field site with perchlorate contamination of a shallow unconfined aquifer. PFMs packed with SM-SI-GAC were deployed in three existing monitoring wells with a perchlorate concentration range of approximately 2.5 to 190 mg/L. PFM-measured, depth-averaged, groundwater fluxes ranged from 1.8 to 7.6 cm/day, while depth-averaged perchlorate fluxes varied from 0.22 to 1.7 g/m2/day. Groundwater and perchlorate flux distributions measured in two PFM deployments closely matched each other. Depth-averaged Darcy fluxes measured with PFMs were in line with an estimate from a borehole dilution test, but much smaller than those based on hydraulic conductivity and head gradients; this is likely due to flow divergence caused by well-screen clogging. Flux-averaged perchlorate concentrations measured with PFM deployments matched concentrations in groundwater samples taken from one well, but not in two other wells, pointing to the need for additional field testing. Use of the surfactant-modified GACs for measuring fluxes of other anions of environmental interest is discussed.
我们在此报告被动通量计（PFM）在测量地下水中含氧阴离子通量方面应用的扩展情况，并展示实验室和现场研究的结果。分别用阳离子表面活性剂十六烷基三甲基铵（HDTMA）对载银和未载银的颗粒活性炭（分别为GAC和SI - GAC）进行改性，以提高其阴离子交换容量（AEC）。在批量实验中测得的含氧阴离子的朗缪尔等温吸附最大值顺序如下：高氯酸盐>>铬酸盐>硒酸盐，与其选择性一致。几种醇类的线性吸附等温线表明，GAC和SI - GAC经表面活性剂改性后，GAC对醇类的吸附减少（约30 - 45%）。在实验室流动室中，通过部署填充有表面活性剂改性GAC（SM - GAC）或表面活性剂改性、载银GAC（SM - SI - GAC）的PFM测量的水和含氧阴离子通量（高氯酸盐和铬酸盐）与施加的通量密切一致。在一个浅层无压含水层受高氯酸盐污染的现场对使用SM - SI - GAC作为PFM吸附剂进行了评估。将填充有SM - SI - GAC的PFM部署在三口现有的监测井中，高氯酸盐浓度范围约为2.5至190 mg/L。PFM测量的深度平均地下水流速范围为1.8至7.6厘米/天，而深度平均高氯酸盐通量在0.22至1.7克/平方米/天之间变化。在两次PFM部署中测量的地下水和高氯酸盐通量分布彼此紧密匹配。用PFM测量的深度平均达西流速与钻孔稀释试验的估计值一致，但远小于基于水力传导率和水头梯度的流速；这可能是由于井筛堵塞导致的水流分散所致。PFM部署测量的通量平均高氯酸盐浓度与从一口井采集的地下水样本中的浓度匹配，但与另外两口井不匹配，这表明需要进行更多的现场测试。还讨论了使用表面活性剂改性GAC测量其他具有环境意义的阴离子通量的情况。
