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The South Island network of stock-truck effluent disposal sites will take a major step closer to completion when Transit New Zealand commissions a facility near Kaikoura. BY HUGH DE LACY At $400,000, Kaikoura’s addition to the growing stock-truck effluent disposal network has come at a greater price than most because of the need to upgrade the township’s sewerage system to accommodate the additional volume.Works Infrastructure has the contract for the job which was 75 percent complete by early this month. It includes the construction of a new anaerobic digester lagoon at the local wastewater treatment plant north of the town, which will have the added benefit of being able to pre-treat the Kaikoura District’s septic tank waste. The roadside disposal site itself is to the south of the town, at the junction of State Highway 1 and State Highway 73 (the inland route past Mount Lyford). The roll-out of a national system of stock effluent disposal sites was driven by a Road Controlling Authorities forum that in 1997 established a National Stock Effluent Working Group (NSEWG). This had, in turn, been prompted by road safety issues and the increasing public disquiet over the amount of effluent spilling from stock-trucks onto the roads – or, more disturbingly, onto the windscreens of following vehicles. By 1999 an industry code of practice for the minimisation of the problem had been formulated by a range of stakeholders comprising the Road Transport Forum, Federated Farmers, the Ministry of Transport, the New Zealand Police, the Road Transport Association, the Meat Industry Association, stock and station agents, territorial authorities and Lincoln University. In August the following year Lincoln University’s environmental management and design division published its guiding document, Pathway to the Elimination of Stock Effluent Spillage on New Zealand Roads, and the roll-out began. In Canterbury the regional council, ECan, contributes to the construction and maintenance of Transit’s facilities on behalf of all local authorities. As important as the installation of the disposal sites themselves was the buy-in by road transport operators who had to fit holding tanks ranging in size between 180 and 500 litres each on the national fleet of stock crates. As Transit’s consultant in the Canterbury-West Coast regions, Beca Infrastructure has been involved in the design and construction of eight disposal facilities, of which Kaikoura is the sixth. The remaining two will be the Reefton/Springs Junction area west of the Lewis Pass, and the other on State Highway 73 west of Arthurs Pass. Those already in place are at Hokitika, Glasnevin (near Waipara), Springfield, Tinwald in central Canterbury and Pareora south of Timaru. The Kaikoura process has been more involved than most because of the need to build the digester lagoon at the town’s wastewater treatment plant. In March of 2005 the district council let a 12-week $315,000 contract for the upgrade of the Kaikoura oxidation ponds. Once that work was complete, Transit was able to let the contract for the disposal facility and digester lagoon. Before the lagoon was built, septic tank effluent had to be emptied directly into the settling ponds. The progressive rollout of stock-truck effluent disposal sites has seen a steady refinement of the standard design, with Kaikoura’s being pretty much state-of-the-art. The site is on a former roadside rest area that is approached by a six-metre-wide sealed access leading onto a 5.6 metre by 10.8 metre concrete apron, which slopes in towards the centre. Two four-metre by two-metre galvanised steel grates straddle the effluent receptors, which drain into two 8000 litre buried concrete tanks each 2.3 metres in diameter and 2.4 metres deep. Only one of these tanks fills at a time, with the overflow going into the second. Effluent level sensors in the first tank send a message to the council’s septag contractor depot when it is full, who uploads the effluent and transports it the 10 kilometres across town to the new digester lagoon. The lagoon itself is 40 metres by 17 metres and is 3.5 metres deep, with an effluent depth of up to three metres. Natural bacteria in the digester pre-treat the effluent which is then pumped into the council oxidation ponds for final treatment. The lagoon is unique to the Kaikoura facility. Effluent from other disposal sites, like those at Hokitika and Tinwald, is emptied directly into existing wastewater treatment facilities. Though it varies seasonally, as many as 40 trucks may discharge up to 8000 litres a week into the Kaikoura facility. Given the increasing two-way traffic of livestock across Cook Strait, some of that effluent comes all the way from the North Island. And by the time the roll-out of all the effluent disposal sites has been completed, the incidence of innocent motorists being splattered with sheep and cattle excrement when they come up behind a stock-truck will be, thankfully, rare. Contractor Vol.31 No.4 May 2007 |