An analysis method for slug tests performed in a partially penetrating well within a vertical cutoff wall is presented. A steady-state shape factor for evaluating hydraulic conductivity of the material within the wall was derived by applying the method of images to the previously developed analytical solution of Zlotnik et al. (2010) for an infinite aquifer. Two distinct boundary conditions were considered: constant-head boundary for the case of direct contact between the wall and the aquifer, and no-flux boundary representing an impermeable filter cake on the sides of the wall. The constant-head and no-flux boundary conditions yield significantly higher and lower shape factors, respectively, than those for the infinite aquifer. Consequently the conventional line-fitting method for slug test analysis would yield an inaccurate estimate of the hydraulic conductivity of a vertical cutoff wall.