NES Earth and Space Science (307) Practice Test

Groundwater is water stored underground in pores and fractures, so it moves slowly through soil and rock. As it travels, particulates are filtered out by the surrounding material, leaving water that is mostly clear with little turbidity. Deep underground, temperatures stay fairly constant and don’t swing with the seasons, so both temperature and chemical composition tend to be steady over time. Oxygen tends to be consumed by microbes underground, so dissolved oxygen is typically very low or nearly absent. That combination—clear water, stable temperature and chemistry, and little oxygen—fits well with how groundwater behaves. The other options describe conditions more typical of surface water or recently recharged groundwater, not the long-resided groundwater described here.