TROUBLE AT HUTT

Evening Post, Volume CXXIII, Issue 20, 25 January 1937, Page 10

TROUBLE AT HUTT

SUPPLIES AFFECTED

RIVER EXCAVATION

Concern is felt, at the fall, varying according to locality, in the level of water obtained from artesian wells in the lower part of the Hutt Valley, and it, is considered probable that this is the result of the dredging operations which have been carried out'by the Public Works Department to obtain spoil for the Scabey Island reclamation scheme, to recover an Eg-ea of about ninety acres. Two drag-line excavators have been in operation. The drags are pulled to and fro across the river bed by steam-driven winches, and have cut deeper and deeper into the gravel into the hard-packed impervious silt layer above the waterbearing gravels. If this is so, a considerable volume of the water which normally lias been impounded under pressure finds its way directly upwards, and this release of the pressure has resulted in a fall in the levels, to which the water will rise in the various wells driven in the vicinity. The northern drag line has not been in operation since Wednesday last. 'In the c. • • of the twenty city wells, the "head" is as a rule about 11 feet, but this has fallen to 9ft 6in. There is thus still- a substantial margin, and in any the Gear Island wells, which are called upon to augment city supplies only when the surface supplies from Wain'ui and Orongorongo are running low in dry periods, have not been in operation for some months. •There are a good many other wells in the vicinity, arid these are more or less affected; In certain cases, where the piping was installed to make the fullest possible use of the artesian head—'that is, where the lead is taken from near ' the ■ maximum level to which the water rose—the fall has resulted ■•in''.serious The Petone-and Lower Hutt Borough wells are also affected, but as they are located at some distance from the mouth of the river the effect is not so marked. . Lower Hutt has a second set of wells off Seaview Road, nearer the river mouth, and .here the effect is evident. DEPTH OF WELLS. .The wells vary a good deal in depth. The City Council's wells at Gear Island are probably as deep as any, and they go down from 80 to 100 feet, or iflore; higher ,in the valley water is obtained at smaller depths. The sealing layer, however, lies at a much smaller depth than .this,, probably, at about 50 to 60 feet, and the water-bearing strata are probably, interconnected, so that if the artesian' rOof ,was broken through at this depth .deeper wells would be adversely affected. Some time ago, when the Point Howard Wharf was being constructed and dredging operations were in progress,' the impervious layer was apparently broken, and for a time wells were slightly affected, but this fault remedied itself over a period of time. When the City Council proposed to drive its wells 'at Gear Island there was some outcry from other well owrnfrs in the Valley that the draw-off required by the city for auxiliary supplies—about four or five million gallons ■ daily—would adversely affect other'nearby wells. Tests made when the city wells were running at much greater, flow than this showed that other wells were only slightly affected, and the fall in levels now noted suggests that there is a loss much greater than the normal draw-off from the Gear Island wells.