We are solving inverse problems in groundwater modeling. Given values of hydraulic head at discrete locations, we seek to approximate values of hydraulic conductivity for the entire field. Our finite element code, ADH, was developed by the USACE in Vicksburg, MS. When using ADH, extreme run-times prohibit the frequent function calls needed for parameter estimation for large, complex problems. Proper Orthogonal Decomposition (POD) is a method to reduce the size of the problem to calibrate ADH, reducing the number of full function calls needed. We will introduce the problem, discuss POD and how it is used, and demonstrate the accuracy of the POD solution compared to the full ADH solution. This is work done in conjunction with Tim Kelley, NCSU.