The Bore Hole
The Greensand aquifer forms a narrow ribbon up to ten miles in width running approximately North East from Henley to Kings Lynn mainly shadowing the chalk hills of the Chilterns and on along the East Anglian heights from the Gog Magog Hills to Newmarket Heath skirting the Breckland up to the Wash, along much the same pathway as the ancient Peddars Way. In our area it is about eight miles wide, running from Sandy through the catchment of the western tributaries of the river Cam. It is a relatively under exploited aquifer containing ancient often pre-industrial water, devoid of modern agricultural, industrial and biological contaminants. It is of exceptional purity in biological terms, but having virtually no entrained air tastes “flat” unless energetically aerated.
Before extensive extraction occurred in the last century many local farms drew their water supplies from greensand boreholes which were artesian, that is to say the subterranean water pressure was powerful enough for the open bores to run continuously above ground level. In our case the artesian pressure supports a head of about 2ft above ground level. There was a Victorian borehole in front of the house, which still runs to this day. Originally it ran along a brick conduit to the three seat privy which still stands in the garden, flushing the privy into the ditch, now widened and dredged to form the garden pond, before draining to the boundary ditch to the south. The old bore now feeds a modern drain running into the pond.
In 1999 Philip commissioned the long established firm of George Lack, water supply engineers from Cottenham, to sink a new modern pumped borehole to supply the property. They struck into the greensand at a depth of 45 meters below ground level (BLG) and extended down another 7 meters to ensure a plentiful supply. The bore comprises a steel pipe housing a three phase Grundfos submersible pump, delivering 700 gallons per hour at a variable pressure currently set at 80 PSI, about 4 atmospheres.
Activation of the pump is controlled by two pressurised 75 litre air cylinders, which also maintain working pressure in the pipelines distributing the water throughout the property. As pressure drops to a critical level, about 65 PSI, the pump is activated until pressure reaches a maximum setting of 85 PSI, at which point the pump switches off. Whilst this system delivers variable pressure it avoids the pump hunting in and out constantly and to date it has never been replaced, despite pumping probably millions of gallons of water.
We retain the town water supply for the kitchens, to avoid compliance requirements for health and hygiene, but all our other water requirements are met from the borehole, saving us a fortune and enabling us to maintain the gardens even in times of drought. As detailed in the reed bed section, all the water supplied by the borehole is returned to the water table on site.