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Water wells & variations in geological formations
A minimum of 25% of water supply in Ireland is contributed from groundwater. it is estimated that there are several hundred thounsands of private wells across rural Ireland. Geologically each well is quite unique...in a sense each has its own DNA inprint. A water well is much more than a vertical shaft into the ground. The depth and nature of the overburden throughout rural & urban Ireland is very variable. It could be free standing, easily drilled, dry, boulder clay,parts of rural County Meath or it could be saturated ‘running sands’ and the layers of broken weathered bedrock containing lots of water...for example parts Dublin central. Drilling through 40 feet of dry boulder clay at 10” diameter and installing casing could take about an hour, whereas drilling and driving casing into collapsing sands and boulders could take a day. In bedrock many varied drilling problems maybe encountered to achieve proper water well construction in rocks as diverse, weathered Devonian sandstones, fractured granites, deep highly altered dolomites in Tipperary, vast open karst caves in the Galway and Roscommon lowlands , and clogged, but ultimately high yield palaeo-karst cavities in Laois, Kildare Kilkenny, Carlow and Offaly. In addition, Belfast Sherwood sandstones fissured with dolerite underlying deep superficial deposits pose challenging conditions for the driller. Water well drilling and borehole construction drilling often requires variation and adaptation.
Unfortunately, the economics of drilling measured on a per/mtr basis to determine Drilling Contractor payment does not reflect a fair rate of pay in very difficult and varied geological formation. On a recent exploration drilling programme in a rural location,our Reich rig encountered running sands and gravels containing a lot of water in a large cavity in limestones at 42 – 53 metres. The contract specification was for a 90 metre deep borehole, therefore we were obliged to make progress beyond the cavity. It took a whole ten hour day to make progress through the cavity, and 50 tonnes of sand were removed from the hole. Neither the client nor the driller expected the sand and water filled cavity. The work done to clear the cavity and get good water, was advantageous to the client, but placed a considerable strain on the drilling equipment. We were paid €450 for the days work, even though we had worked all day to meet the clients needs.
The financial & equipment risk exposure to the Drilling Contractor paid on a per/mtr basis for a water well as a result of variations in geological formations is very high. He is obliged to deal with whatever geological formation encountered irrespective of the time,wear and tear of his equipment and unforeseen operating costs including diesel,excess bit wear in order to complete the well specification.Its not surprising that a Drilling Contractor will regularly finish up working below costs.