USING CFP (CONDUIT FLOW PROCESS) NUMERICAL SOLUTE TRANSPORT METHOD TO SIMULATE NITRATE-N AND CHLORIDE CONTAMINATION IN WOODVILLE KARST PLAIN

The beta version of CFP (Conduit Flow Process) solute transport code and a modified version of MT3D were applied to simulate long term (1966-2018) nitrate-N and chloride contamination in Woodville Karst Plain (WKP), northern Florida where karst conduit network is well developed. Darcy’s Law was used to simulate groundwater flow in porous media, but non-laminar flow in conduits was described by Darcy-Weisbach equation using the MODFLOW-CFP flow code developed by USGS. Particularly, nitrate-N and chloride transport process in conduits and the exchange between conduits and media are considered in this study based on former studies and MT3D simulation. Some conclusions are summarized: 1) The two sprayfields as the main point sources of nitrate-N and chloride control contaminant distributions within this area, the inflow discharges from Lost Creek Sink, Wakulla Spring and Spring Creek Spring are also important nitrate-N and chloride sources that contribute to the large high concentration area. 2) Both nitrate-N and chloride contamination area are enlarged due to the slow transport in porous media and continuous contaminant inputs from inflow discharge, biosolids disposal and creeks discharging, even though the mass of nitrate-N and chloride was decline because of a reduction and eventual elimination of fertilizer usage. 3) Concentration distribution of model cells within conduits nodes is more coincidental with the reality in this study result rather than the MT3D simulation without considering conduit flow and transport. 4) Comparing with the in situ nitrate-N and chloride measurement data, the simulated concentration distribution by CFP transport code can be used to describe the contamination change in the last four decades and also to predict contaminant future evolution.