Rehabilitation of an old bore can become necessary for a variety of reasons, poor construction technique, aggressive water quality, geological conditions or changing hydro geological factors.
A poorly constructed bore may yield successfully for a few months or even years, however eventually the bore will fail. Often bores are constructed “cut price” by unscrupulous drillers. They do this many ways, not installing enough casing in the bore and not adequately developing the bore. A bore should always have suitable casing , generally not less than class 9 PVC Bore casing, installed the full depth of the bore. The bore should always be adequately developed to ensure clean water from first pumping and throughout the lifetime of the bore.
Aggressive water can cause problems in some instances, with decomposition of steel bore casing and even stainless steel. Generally the best option is to remove the steel casing and replace with a PVC bore casing. High mineral contents may cause problems, especially Iron bacteria, which is easily remedied, generally with a chlorine treatment.
A bore constructed in clay and sand formations will occasionally need to be re-developed to remove inward moving fine particles which will not only reduce the yield of the bore, but also shorten the life of the pump.
Generally speaking a bore constructed to the minimum construction standard and properly developed and completed will be a reliable ongoing water supply for years to come. With the advent of PVC Bore casing and stainless steel pump products, less bore and pump failure is being caused by rust and decomposition. As I say to many new clients, “If a jobs worth doing, do it properly and you’ll only need to do it once”.