Approximately 2 km² of sand- and gravel-rich Pleistocene glacial-outburst megaflood sediment has accumulated in a series of five subparallel paleochannels that are an important component of a basalt-dominated aquifer system on the semiarid, ~450-km² West Plains area. Located near Spokane, Washington (USA), the West Plains paleochannel deposits have been used for artificial storage and recovery wells and for planned and passive stormwater disposal in this rapidly growing area. Recent recognition of perfluorooctanoic acid contamination and excessive drawdowns have led to the closure of multiple municipal wells on the West Plains, highlighting the challenges of developing a sustainable groundwater supply in this complex aquifer system. Geologic and hydrogeologic data, from more than 1,400 water-well reports, surface exposures, existing groundwater geochemistry reports, and modeling, reveal the interconnections between the paleochannel deposits and surrounding basalt flows in three dimensions (3D). Initially incised into the Miocene Columbia River Basalt and excavated by Pleistocene glacial-outburst megaflooding, the West Plains paleochannels are projected in unprecedented 3D. This study’s modeled interactions between the more highly hydraulically conductive (100×) paleochannel sedimentary deposits and surrounding basalt beds provide insight into ¹⁴C ages and tritium values that had been measured previously. Sediment-filled closed depressions at the bases of the paleochannels, which are features likely formed by turbulent bursts (‘kolks’) during peak megaflood flows, are potentially promising groundwater storage sites. However, because of the relatively higher permeability of the unconfined paleochannel deposits, the closed depressions also are potential conduits for infiltration of contamination to deeper parts of the aquifer system.

大约2 km ²的富含沙子和砾石的更新世冰川喷发的特大洪水沉积物已堆积在一系列五个平行的古河道中，这是半干旱地区玄武岩为主的含水层系统的重要组成部分，约450 km ²西部平原地区。位于美国华盛顿州斯波坎附近的西平原古河道沉积物已被用于人工存储和恢复井，并在这个快速增长的地区用于计划性和被动性雨水处理。最近对全氟辛酸污染的认识和过多的用水量减少导致西部平原上多个市政井的关闭，突显了在这种复杂的含水层系统中开发可持续的地下水供应所面临的挑战。来自1,400多个水井报告，地表暴露，现有地下水地球化学报告和模型的地质和水文地质数据揭示了三维通道沉积物与周围玄武岩流之间的相互联系（3D）。最初由中新世哥伦比亚河玄武岩切割而成，并由更新世的冰川喷发大洪水开挖，西部平原古河道以前所未有的3D投影方式投影。这项研究对水力传导性更高（100倍）的古河道沉积物与周围玄武岩床之间的相互作用进行了模型化研究先前已测量的¹⁴ C年龄和tri值。古河道底部的充满泥沙的封闭洼地可能是在大洪水高峰期期间湍流爆发（“卵石”）形成的特征，是潜在的地下水储存场所。但是，由于无限制古河道沉积物的渗透率较高，因此封闭的凹陷也是潜在的管道，可将污染物渗透到含水层系统的较深部分。