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Pipeline work sees earthmoving firm look further afield Richard Loader
‘massive upgrade’ Kelly Deeks Milburn Lime has developed a New Zealand-wide reputation for its high-quality agricultural lime which, according Roger Mahan, gives top results for both plant and animal health. In July 1993, his Hilton Lime Co opened a plant in the Milburn quarry in the Milton in South Otago; he secured limestone from the former Dominion lime and phosphate quarry. In 1995 the company’s name was changed to Milburn Lime. The new firm began with six employees, and now employs up to 14 people during the peak summer season. Roger says the company has experienced a massive upgrading of machinery. The 20-tonne excavator has been replaced by a 110-tonne model, and motor scrapers with 25-tonne capacity have been replaced with three dump trucks, each of which can carry 100 tonnes. Milburn Lime can now produce more than 2000 tonnes of lime a day, and its annual tonnage is now well over 100,000 tonnes. The processing plant produces agricultural lime for South Otago, West Otago, Central Otago and Southland farmers. “Processing the lime involves shifting the overburden on top, then drilling and blasting the 32-metre-high lime-wall face,” Roger says. Each blast contains several tonnes of
explosives, and each blast design yields 60,000 to 70,000 tonnes of well broken limestone. The lime is then carted from the quarry to the crushing and processing plant. A 15,000-tonne storage shed holds processed dry, very white lime which is available all year round. As well as agricultural lime, Milburn produces knaprock for dairy lanes. Roger Mahan says Milburn lime is combined with calcium, magnesium, potassium, sodium, sulphur, zinc, copper, boron, and phosphate to make the final product.. “The phosphate present in Milburn lime is a plus, especially for clovers, which are so important for nitrogen in the soil,” he says. “Some limes contain iron, which tends to lock up the other minerals. Limes that are not pure white are generally contaminated with seabed clays, which hold moisture and generally clog, and require kiln-drying. Because Milburn lime is very dry when taken from the quarry, it does not require drying.” The Milburn quarry is thought to hold fossils that are 30 million years old. A shed which Milburn Lime has built at a look-out past the lime works holds a large whale-jaw fossil and other fossils. There are also historic photos of the limeworks, showing the various eras of operation and equipment. The look-out, which is maintained by the Waihola Looking Forward Group, is well worth a visit, says Roger
Laying high-density polythene pipe (HDPE) pipe within a strict height tolerance is all in a day’s work for Harmer Earthmoving’s specialists working on the 130-kilometre pipeline project for the Amuri irrigation scheme. Due for completion this September, the project will replace the open water races in the Amuri Basin with a tentacle-like network of underground pipes carrying water from the Waiau and Hurunui rivers to support farm irrigation. Methven-based Harmer Earthmoving, along with two other earthmoving contractors, has been engaged by the lead contractor, Monadelphous, to do the the excavation and pipe-laying work. Harmer Earthmoving specialises in dairy-track development and maintenance, land conversions, forestry work, landfill, effluent ponds and systems, subdivisions and irrigation systems. It employs a staff of 40 and has a fleet of diggers, logging trucks, general loaders and bulldozers, graders and other specialist machinery. Managing director Jon Harmer says that in the last five years the company has made a push into the installation of irrigation pipelines. “In the last four years we have installed well over 200km of pipe,” he says. “We started off laying 1.6-metre pipe with Valetta Irrigation, then worked with Monadelphous on the Barrhill Chertsey irrigation (BCI) scheme in Mid Canterbury.” Harmer Earthmoving’s decision to take on more specialised jobs, such as the installation of piping under rivers, led to an approach from Monadelphous to venture outside Mid Canterbury
region by tendering for further infrastructure works. This experience led to the firm being awarded the Amuri contract. Ranging from 1600-millimetre diameter pipe down to 75mm, the Amuri project involves a glassreinforced plastic (GRP) for the large bore and high-pressure applications with HDPE making up the majority of the smaller branch pipes to property offtakes. Harmer Earthmoving has the responsibility for laying all 50km of the HDPE product. “Everything we do up there is dug to grade, so we get issued with GPS files electronically. This is uploaded into the digger and grader computers,” says Jon Harmer. “The digger operator still puts the digger bucket down to the required depth in the ground, but he’s watching the screen in front of him all the time.” To avoid airlocks in the pipe, a strict tolerance is adhered to when it is being laid. Anything higher or lower than design has to be adjusted. While any operator can drive the diggers, a lot of skill is required when using the specialist technology and getting the trench depth exactly right, says Jon. There have not been any issues so far, he says. On average, the firm ia laying about 300 metres a day of HDPE pipe. On a good day, however. this can be as much as 500 metres. It just depends on whether or not all the ducks are in a row on any given day, he says. He says he and and his staff have been very impressed with the way the farmers have treated them. “They have been very good to deal with, giving us access to their land. At the end of the day, we are really working for them.”
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