In the modified in-situ retorting process the region of retorting will at as a large subsurface sink and lead to a massive dowatering of the surrounding hydrogeologic system. The present study has been aimed at studying the possible alteration of the groundwater regime in and around the C-a and the C-b tracts due to the proposed MIS strategies. Our approach has been one of scenario analysis and parametric studies, using a numerical model.