Hydraulic conductivity of rio claro formation using grain size analysis

Abstract

The hydraulic conductivity (K) is a key hydraulic parameter of aquifers, conditioning the fluid transmission and governing groundwater velocity in distinct geological layers. Thus, a fundamental parameter for understanding groundwater and contaminant fluxes. In the present study grain size analysis was used to determine the hydraulic conductivity distribution of the Rio Claro Aquifer, based solely on the sediment physical properties. The K values were obtained by three methods – Hazen, Shepherd and Krumbein & Monk – and the results were compared with slug tests (Hvorslev) carried out in existing wells. Rio Claro Formation presents a large range in sand/clay ratio, ranging from clean sands to silt and clay rich lenses. A large grain size distribution is observed near the contact with the Corumbataí Formation, ranging from clay, silt, fine sands to conglomerates. This lithological variability affects the K values distribution, with values ranging from 8 x 10-3 to 2 x 10-3 cm/s for sandstones and those for clay lenses of about two-three orders of magnitude lower. The Rio Claro Formation sandstones presents high hydraulic conductivity values, but the occurrence of thick clay lenses may act as hydraulic barriers. This aquifer unit is of limited thickness and presents high lithological heterogeneity, thus its productivity is highly dependent on the occurrence and spatial continuity of clean sandstone layers.