Out of all sources found in our review, GETEM provides the best evidence of an accurate cost relationship. First, the GETEM cost model is derived from ASPEN simulations of wellfield surface piping, including typical features such as expansion loops, check valves, and insulation. While the details of these simulations are not available or reproducible, this level of detail in-and-of itself provides certainty beyond the rule-of-thumb approximations given by EPA (2008; 2010), Esposito et al. (2019), and GEOPHIRES. Second, a linear relationship cost model with pipe diameter does not reflect the complexity of purchasing and handling large-diameter piping. Thus, a second-order relationship based on GETEM simulations is a better way to estimate surface piping costs. As a result, the genGEO cost relationship is a regression of the surface pipe cost data provided by GETEM. The genGEO relationship differs from GETEM by removing the first-order pipe diameter term, which was not statistically significant. All four of these relations considered in this analysis and the genGEO relationship are given in Table and plotted in Figure . Figure shows that all cost models align near a pipe diameter of 0.20 m (8 inches), where the variation is the smallest at +/-11%. Thus, it is possible that most pipe cost models were derived by assuming a linear relationship with pipe diameter and calculated the cost from this single data point.