There is currently no required horizontal separation distance from a properly abandoned drilled well to a potential source of contamination.  The well casing may be pulled or it may remain in place.

If a closed-loop geothermal well is installed there is no required horizontal separation distance to a source of contamination provided that the well is NOT cased and it is grouted from bottom to top.  However, if the geothermal well is cased, it must meet the horizontal separation distances in Table 3.1.

Please take notice that's there are no construction differences between the abandoned drilled well and the cased geothermal well.  However, they are treated drastically different with respect to separation distances.  This is not logical.