The Mendip Hills are full of holes that some think are suitable for waste disposal and infilling, as karst solution processes result in features, such as caves, closed depressions and swallets. Quarrying and mining has occurred since at least Roman times.
Infilling with inert, farm, household or other waste, whether licensed or not, must be treated with extreme caution, for not only can the results be unsightly, but they have the potential to seriously affect the intrinsic character of the Mendip Hills.
Perhaps the filling of swallets causes the most insidious effects. These are open features caused by the collapse of the surface after solution of the limestone, and lead directly to cave systems underground. In some cases streams may sink directly into swallets, in other cases the swallet may be dry in normal circumstances, but take surface flow underground after heavy rain. Groups of swallets often occur within closed depressions, large areas of lower-lying land on the plateau with no valley out.
Filling these features not only means that diversity in the landscape is lost, making Mendip less interesting, but that access to cave systems may be blocked and that caves and risings (the major springs around the scarp bottoms) may be polluted. Mendip is a major water source, famous for providing Bristol as well as local towns and villages with pure water. Dumping rubbish in swallets and old quarries is tantamount to directly interfering with the public water supply.
Dumping in old mine working and quarries also results in a lost of interest, particularly as some of the surface workings are Roman or medieval in age. Rakes are long channels cut in the plateau surface where lead ore bodies have been removed, and gruffy ground describes areas of humps and bumps where mine workings, minor shafts, buddles (ore separation floors), leats (mine watercourses) and old mine dumps coalesce.
Whilst it is generally unlikely that planning permission will now be given for such infilling, a permission was given for in 1999 to fill a rake against archaeological advice. Moreover fly tipping, disposal of building waste and attempts to level fields to improve agriculture continue, particularly away from public roads and tracks. Enforcement against the lack of planning consent is difficult to achieve, although there have been notable successes by the planning authorities. Actual removal of material, once tipped, is rarely achieved.