Cr(VI) flushing from the vadose zone to the groundwater (with subsequent Cr(VI) removal in groundwater by pump-and-treat system) is a promising remedial technique that has recently been used at field scale. This laboratory study was conducted to provide the technical basis to design a field soil flushing strategy. The objectives were to (1) quantify the relationship between sediment Cr(VI) and Cr(III) mass and release rates and subsequent Cr(VI) leaching; (2) investigate different methodologies to maximize Cr(VI) leaching, and (3) investigate methods to minimize leaching of remaining residual Cr. Characterization of Cr-contaminated sediments (Hanford Site, WA) exhibited Cr(VI) showed that leach rates that were correlated to different Cr surface phases. Sediments with low leachable Cr(VI) (<2 μg/g) leached Cr rapidly, so slow infiltration of water in a single pulse was sufficient to leach most Cr. In contrast, sediments with high Cr (2 to 200 μg/g) released some Cr(VI) quickly but 10 to 50% Cr(VI) slowly (tens to hundreds of hours). Efficient unsaturated leaching of these sediments required a different infiltration strategy that includes: multiple slow leach pulses with time between flushing cycles; the use of a surfactant to increase Cr leaching from low-permeability zones, and the use of a reductant (Na-dithionite or Ca-polysulfide) in the final leach water was highly effective at decreasing residual Cr leaching. This study clearly demonstrated that the methodology of basing laboratory Cr flushing on parameters such as Cr release mass and rates could be used to improve the efficiency of soil flushing at field scale.

中文翻译：

---

用于铬修复的包气带土壤冲洗：支持现场规模应用的实验室调查

Cr(VI) 从渗流带冲洗到地下水（随后通过抽水处理系统去除地下水中的 Cr(VI)）是一种很有前途的补救技术，最近已在野外规模使用。本实验室研究旨在为设计田间土壤冲洗策略提供技术基础。目标是 (1) 量化沉积物 Cr(VI) 和 Cr(III) 质量和释放率与随后的 Cr(VI) 浸出之间的关系；(2) 研究使 Cr(VI) 浸出最大化的不同方法，以及 (3) 研究使剩余残余 Cr 浸出最小化的方法。对含有 Cr(VI) 的 Cr 污染沉积物（Hanford Site，WA）的表征表明，浸出率与不同的 Cr 表面相相关。具有低可浸出 Cr(VI) (<2 μg/g) 的沉积物迅速浸出 Cr，如此缓慢的水在单个脉冲中的渗透足以浸出大部分 Cr。相比之下，高 Cr（2 至 200 μg/g）的沉积物会快速释放一些 Cr(VI)，但会缓慢释放 10% 至 50% 的 Cr(VI)（数十至数百小时）。这些沉积物的有效不饱和浸出需要不同的渗透策略，包括：多次缓慢浸出脉冲，冲洗周期之间有时间；使用表面活性剂增加 Cr 从低渗透区的浸出，以及在最终浸出水中使用还原剂（连二亚硫酸钠或多硫化钙）在减少残余 Cr 浸出方面非常有效。这项研究清楚地表明，基于 Cr 释放质量和速率等参数的实验室 Cr 冲洗方法可用于提高田间土壤冲洗的效率。