Aquifer Characteristics

The Equus beds are composed of a mix of clay, silt, sand and cobbles most likely deposited by a series of braided streams during the Pilocence and Pleistocene. The Equus Beds are composed of layers with highly variable sediment size, from large homogenous grains with high porosity to composed of very fine silt and clay that are much less porous (Stramel, 1966 & Stullken et al., 1985). Because the High Plains Aquifer system is characterized by the upwards-fining and upward-coarsening gradients known to be deposited by braided streams, it can be assumed that there is generally a random distribution of grain size throughout the aquifer, suggesting that it is homogenous on a regional scale regardless of its heterogeneity on a small scale (Stullken et al., 1985).

The Equus Beds are considered to be an unconfined aquifer, but in some places it does contain clay rich layers that can create areas with partial confinement (Hansen, 2011). The hydraulic conductivity of the Equus Beds Aquifer ranges from 5 to 1,200 ft/day and its specific yield ranges from 0.08 and 0.35; In the areas where the aquifer is confined it has reported specific storage values between 0.0004 and 0.16. The direction of flow within the aquifer is not consistent, groundwater flow in between the Arkansas and Little Arkansas rivers flow eastward, while groundwater north of the Little Arkansas River flows southbound (Kelly, 2013). The water table for this area can be incredibly shallow, with depths to water as close as 10 feet deep near the Arkansas river, and with a saturated thickness between 75 and 250 feet (Hansen, 2011) its no wonder this has been a water source for decades!

The chemical composure of the groundwater in the Equus Beds is predominantly of calcium bicarbonate, but as the water moves closer to the Arkansas River it becomes more influenced by sodium chloride (Stone, 2019).