Groundwater is contaminated with chlorinated volatile organic compounds (CVOCs) including trichloroethene (TCE), tetrachloroethene (PCE), and their degradation products at a 230-acre formerly used defense site in Pennsylvania. Unconsolidated overburden materials ranging in thicknesses from 15 to 60 feet overlie two types of bedrock: quartzitic sandstone and phyllite on the eastern sloping hills and limestone and dolomite on the western flat-lying terrane. Karst is well developed in the carbonate rocks and is characterized by a pinnacle-and-cutter bedrock surface, solution-enlarged fractures/conduits at depths up to 450 feet below ground surface (bgs), caverns in tens of feet, and frequent occurrence of sinkholes. The PCE and TCE concentrations in groundwater samples suggest that dense non-aqueous phase liquid penetration extended to depths on the order of 400–450 feet bgs in the carbonate bedrock. A dye trace study was conducted to help refine the conceptual site model. The study consisted of five fluorescent dyes that were injected in five wells that encountered karst conduits/caverns at various depths from 32 to 216 feet bgs. The dyes were monitored at 40 monitoring wells and 16 points along a stream to the west of the site. The dye tracing results established positive dye detections at seven monitoring points in the stream. Field observations, infrared thermography imaging, and water quality survey confirmed that three of them, i.e., Spring-15, Spring-17, and Spring-26, are groundwater discharge points in the stream, i.e., submerged springs. Discovery of the submerged springs significantly contributed to the refinement of the conceptual site model and provided an opportunity to effectively remediate and manage the contaminated groundwater. These springs confirmed the exposure pathways that connect the site-impacted groundwater to surface water receptors, and the final remedy included measures to address potentially unacceptable risks to human beings and the environment in the stream and ensure that the state-regulated ambient water quality criteria are met for the site CVOCs at established compliance monitoring stations. These springs also helped optimize an existing pump and treat system that has been active since 1994. Shutdown and restart-up tests were conducted to evaluate the effectiveness of different extraction scenarios in the removal of the CVOCs at the springs under wet and dry seasons. The results led to a new configuration of the extraction wells by including a previously inactive extraction well CW-20.

在宾夕法尼亚州一个 230 英亩的以前使用的防御地点，地下水被氯化挥发性有机化合物 (CVOC) 污染，包括三氯乙烯 (TCE)、四氯乙烯 (PCE) 及其降解产物。厚度从 15 英尺到 60 英尺不等的松散覆盖层材料覆盖着两种类型的基岩：东部倾斜山丘上的石英质砂岩和千枚岩以及西部平坦地体上的石灰岩和白云岩。喀斯特在碳酸盐岩中发育良好，其特点是基岩表面呈尖峰状，在地表以下 450 英尺（bgs）深度处溶解扩大的裂缝/导管，数十英尺的洞穴，并且频繁发生天坑。地下水样品中的 PCE 和 TCE 浓度表明，密集的非水相液体渗透延伸到碳酸盐基岩中 400-450 英尺 bgs 的深度。进行了染料痕量研究，以帮助完善概念性场地模型。该研究由五种荧光染料组成，这些染料注入五口井中，这些井在 32 至 216 英尺 bgs 的不同深度遇到岩溶管道/洞穴。染料在 40 个监测井和 16 个点沿场地以西的一条溪流进行监测。染料追踪结果在河流中的七个监测点建立了阳性染料检测。野外观测、红外热成像、水质调查证实，其中15泉、17泉、26泉3处为溪流地下水排放点，即潜泉。潜泉的发现极大地促进了概念场地模型的完善，并为有效修复和管理受污染的地下水提供了机会。这些泉水证实了将受场地影响的地下水与地表水受体连接起来的暴露途径，最终的补救措施包括解决河流中人类和环境可能面临的不可接受风险的措施，并确保国家规定的环境水质标准符合要求。在已建立的合规监测站满足现场 CVOC 的要求。这些弹簧还有助于优化自 1994 年以来一直运行的现有泵和处理系统。进行了关闭和重启测试，以评估不同提取方案在雨季和旱季去除泉水中 CVOC 的有效性。结果通过包括以前不活动的提取井 CW-20 导致了提取井的新配置。