Carey Grant R, Danko Anthony, Pham Anh Le-Tuan, Soderberg Keir, Hoagland Beth, Sleep Brent
Naval Facilities Engineering and Expeditionary Warfare Center, San Diego, CA.
University of Waterloo, Waterloo, ON, Canada.
Ground Water. 2025 Mar-Apr;63(2):175-191. doi: 10.1111/gwat.13456. Epub 2024 Dec 11.
The potential performance of a hypothetical colloidal-activated carbon (CAC) in situ remedy for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in groundwater in coastal zones was evaluated using estimated hydrogeologic and geochemical parameters for a coastal site in the United States. With these parameters, a reactive transport model (ISR-MT3DMS) was used to assess the effects of tidal fluctuations and near-shore geochemistry on CAC performance. The average near-shore ionic strength of 84 mM at the site was conservatively estimated to result in an increase in the adsorption of PFOA to CAC by about 50% relative to non-coastal sites with ionic strength <10 mM. The modeling also confirmed the hypothesis that tidally induced groundwater flow reversals near the shore would result in the accumulation of PFOA at the downgradient edge of the CAC zone. Slow desorption of PFOA from this downgradient CAC boundary may sustain downgradient plume concentrations above a strict cleanup criterion (e.g., USEPA MCL of 0.004 μg/L), for decades; however, there was still a large PFOA mass flux reduction (>99.9%) achieved after several decades at the shore. CAC longevity was substantially greater for PFOS with a similar source concentration; however, the higher PFOS distribution coefficient (K) in soil downgradient from the CAC zone resulted in substantially longer flushing times. It is recommended that short-term remedial action objectives for CAC remedies at coastal sites be based on mass flux reduction targets over a period of several decades, given the demonstrated challenges in trying to achieve very low cleanup criteria downgradient of a CAC zone in the short term.
利用美国一个沿海场地的估计水文地质和地球化学参数，评估了一种假设的胶体活性炭（CAC）原位修复方法对沿海地区地下水中全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS）的潜在性能。基于这些参数，使用反应性输运模型（ISR-MT3DMS）来评估潮汐波动和近岸地球化学对CAC性能的影响。保守估计该场地近岸平均离子强度为84 mM，相对于离子强度<10 mM的非沿海场地，这会导致PFOA在CAC上的吸附增加约50%。该模型还证实了这样一个假设，即潮汐引起的近岸地下水流逆转会导致PFOA在CAC区域的下游边缘积累。PFOA从该下游CAC边界的缓慢解吸可能会使下游羽流浓度在数十年内维持在严格的清理标准（例如，美国环境保护局规定的0.004 μg/L的最大污染物浓度限值）之上；然而，几十年后在岸边仍实现了大量的PFOA质量通量减少（>99.9%）。对于具有相似源浓度的PFOS，CAC的寿命要长得多；然而，PFOS在CAC区域下游土壤中的分配系数（K）较高，导致冲洗时间长得多。鉴于在短期内试图在CAC区域下游达到极低的清理标准存在明显挑战，建议沿海场地CAC修复的短期补救行动目标应基于几十年内的质量通量减少目标。
