Oxidation pond plan criticised at hearing

Press, 2 May 1984, Page 3

Oxidation pond plan criticised at hearing

The proposed single primary oxidation pond planned by Ellesmere County Council for the new Lincoln sewerage scheme would produce an effluent of poorer quality than the present unsatisfactory treatment plant, a planning tribunal hearing was told yesterday. The hearing concerns an appeal by Ellesmere County Council against a North Canterbury Catchment and Regional Water Board decision on the discharge of treated sewage effluent into the L2 River and thence to Lake Ellesmere. The Regional Water Board agreed to give the council a water right to discharge into the lake up to 1700 cu m of treated sewage effluent a day, from a primary oxidation pond it plans to build, into the L2 River, with a provision that a treatment plant also be built. The Regional Water

Board believes the proposed pond alone would not sufficiently reduce the nutrientcontaining algae which could destroy the delicate balance of Lake Ellesmere’s water. The present sewerage system is overloaded and subject to malfunction and high maintenance costs. A scientist from the North Canterbury Catchment Board and Regional Water Board, Dr I. W. Lineham, said that with a single oxidation pond no attempt is made to reduce nutrient content, especially phosphorus. The treatment plant requested by the board would remove about 70 per cent of the effluent algae. The improvement in the effluent quality due to algae removal is estimated to be 5 per cent for nitrogen and between 9 per cent and 13 per cent for phosphorus. “Although the over-all improvement in the total lake

loading is expected to be small, the contribution of Lincoln sewage to the controllable nutrient load is significant,” he said. Dr Lineham said a single oxidation pond by itself would produce an effluent of poorer quality than the present unsatisfactory treatment plant. Ellesmere County Council objects to the condition being included in the water right as it considers the filtration plant would have little effect on the nutrient levels in Lake Ellesmere and would be an unnecessary financial burden on ratepayers. Adding a filtration plant would increase the proposed cost of the new scheme by 100 per cent with a capital cost of $615,000 and an annual expense of $117,000. The manager of the resource investigations division of North Canterbury Catchment Board and Re-

gional Water Board, Mr M. J. Bowden, said that the control of the inflow of nutrients to the lake from groundwater and non-point surface run-off are not readily controllable. “Therefore, to exercise any control over the inflow of nutrients into this grossly overloaded lake the board must deal with point discharges,” he said. The major point discharges of effluent in the Ellesmere catchment include dairy shed wastes and sewage discharges. The tribunal comprised Judge Skelton, Mr R. N. McLennan and Mrs N. J. Johnson. Mr G. H. Nation appeared for Ellesmere County Council; Mr C. B. Atkinson, Q.C., for North Canterbury Catchment and Regional Water Board, and Mr M. D. de Goldi for the North Canterbury Acclimatisation Society. The hearing will conclude today.