Design engineers currently lack means to easily incorporate the influence of underground water flow into the design of vertical-bore heat exchangers (VBHE_x). This paper presents the development of a pseudo or “effective” thermal conductivity correlation for analysis of single-bore VBHEx with groundwater flow. Using the solution to the moving line heat source, a dimensionless correlation, containing parameters for Peclet number and porosity, is provided. The resulting adjusted (i.e., effective) thermal conductivity can be used for analysis and is a good first step toward accounting for groundwater flow in a VBHE_x.