This paper describes a proposed addition to the existing SWMM5 Groundwater Module for use in calibrating long term continuous rainfall dependent inflow & infiltration (RD I/I) simulation. This addition is intended for use in cases where monthly infiltration patterns are not repetitive and the existing RTK method might not be applicable, and where the existing groundwater power function algorithm may not be applicable for modeling infiltration through defects in conduits. This proposed addition contains 2 parts. The first part includes adding an additional outlet to the existing Groundwater Aquifer to enhance the simulation of interflow infiltration into a conveyance system. The second part includes adding a second groundwater discharge algorithm to the SWMM5 Groundwater Module. Similar to the existing groundwater discharge algorithm, this new algorithm also utilizes the same 5 parameters but each having different functions than in the existing algorithm. With the same number of parameters as the existing algorithm, the new algorithm can be added into the existing SWMM code with minimal code revision. The aforementioned addition has been coded into an alpha-version of a SWMM5 engine and preliminary testing has been conducted. Testing results confirm that new algorithm works for calibrating long term continuous RD I/I simulations in cases where the RTK method and the existing groundwater power function algorithm might not be applicable.