**5. Discussion and conclusion**

Groundwater flow in a well‐developed karst aquifer is mainly dominated within the fractures, conduits and caves formed and/or enlarged by carbonate dissolution. In general, most groundwater‐modeling methods, such as MODFLOW‐2000, apply Darcy equation to simulate groundwater flow, in which groundwater flow is laminar in the primary porosity (i.e., matrix porosity) of the aquifer. However, Darcian principle is not applicable in a well‐developed karst aquifer due to the dual permeability properties present in the aquifer. Therefore, advanced methodologies, such as the discrete‐continuum model, should be used to model groundwater flow in karst aquifers.

The physically based discrete‐continuum numerical models are widely applied to simulate groundwater flow and solute transport in a karst aquifer with conduit networks. The CFPM1 is able to accurately simulate groundwater flow in karst aquifers. The major hypothesis of this study was that CFPM1 would more accurately simulate flow in karst aquifers than MOD‐ FLOW‐2000 because CFPM1 accounts for turbulent flow, as well as pipe parameters such as pipe diameter, tortuosity, etc. In Gallegos et al. [22], a CFPM1 model of the Woodville Karst Plain was developed based on a previous MODFLOW‐2000 model by Davis et al. [35]. Both the CFPM1 and MODFLOW‐2000 models are created to run a transient simulation of an actual storm event. The simulated monitoring wells match well with the observations.

The coupled CFPv2 and UMT3D models are able to simulate solute transport in a karst aquifer. Chloride concentration plumes are originated from the sprayfields and extended southward to Wakulla Springs. Sprayfields in the south of Tallahassee and septic tanks in the rural area are the major source of chloride contamination in the WKP. From the monitoring wells observation, chloride concentration started to increased, especially after the SEF sprayfield went into service in 1980s and remained a high value in future prediction. Chloride contami‐ nation transported through the conduit network and formed extended plumes far away from the sprayfield. The transport method modified the flow and solute transport within conduits and considered the exchange between conduits and matrix, generated more accurate simula‐ tion results due to more precise description of conduits in the model.
