Sunday, April 21, 2024

Better off compliant

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A warning from the regional council to sort out his effluent system led a Raglan farmer to expedite the work required to become compliant.
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A warning from the regional council to sort out his effluent system led a Raglan farmer to expedite the work required to become compliant.

Raglan dairy farmer Gavin Hayes is breathing a sigh of relief now that his effluent system is not only 100% compliant, but more efficient as well.

Milking 345 cows once-a-day on 104ha effective Kauroa Farms, Hayes and wife Teresa were in the early stages of on-farm system upgrades when a visit from Waikato Regional Council in 2020 pushed them to expedite the process.

“We received a warning to upgrade our effluent system,” Hayes says.

“We had been exploring our options for about three to four years already, but the warning pushed us along.

“We also changed banks and that made it more favourable to undertake the work we needed to.”

Hayes had already built a covered feedpad in 2018 as the very first stage of a system upgrade and water meters were installed around the property in 2019 to gather data which would help make decisions around the future of the effluent and irrigation systems.

In September 2020, after the visit from WRC, the data was analysed and planning began for the effluent and irrigation system overhaul.

Data from the rainfall catchment area, in-shed water use monitors and existing infrastructure was used to determine the pond storage requirements and available irrigation days.

“Part of the process was accurately calculating the area on which it was practical to irrigate, taking into consideration soil type, nutrient loading, water tables and waterway setback areas,” he says.

“The farm can get wet in winter and we discovered that only around one-third of the property is suitable for winter irrigation.”

The original effluent pond’s location was not ideal – close to a waterway and on land with a high water table – so the team dug test holes around the property to determine a more appropriate position.

They established that the extra power cables needed to build the pond on a hill away from the dairy shed would be less costly than the earthworks and management required to build the pond close to the shed.

The end result is a 40m x 40m x 3m pond, with a total usable volume of 2.6 million litres.

The volume is around 300,000 litres above the legal requirements which, given Hayes’s low water use, is a considerable surplus – about 20 days storage above requirements.

Viking Containment installed the liner system for the pond and standoff pad.

It consisted of a 1.5mm High Density Polyethylene (HDPE) liner, with a protective geotextile and a geocomposite gas venting system. 

The HDPE liner rolls weigh 1.8 tonnes and were deployed using a purpose-built spreader bar and spindles suspended from an excavator. The 8m wide panels allow efficient deployment and installation, which was completed in one day.

The seam welding process is also unique, incorporating an air channel within the seam, which can be pressure tested to ensure its integrity.

Experienced technicians carry out all the welding and testing, which was documented in a comprehensive Quality Assurance Report and for peace of mind and assurance, Viking’s HDPE liner also has a 20-year product warranty.

For safety, Viking Geoladders® were incorporated to provide safe access for emergency evacuation of the pond and could be utilised for maintenance when servicing pumps or control equipment.

A German-built Wangen pump was installed, a piece of machinery that has huge benefits, including low power usage, low wear-and-tear and high performance.

The Wangen pump uses just 7.5kw to run, producing flow rates of up to 20,000l/hour and head pressure of up to 90m; by comparison, traditional pumps use 22kw to achieve an equal performance.

The pump is also low speed at 155rpm, compared to traditional pumps at 2800rpm.

A custom designed pond stirring system was also installed.

But perhaps the biggest impact on the pond storage specification was the decision to upgrade from a traditional boom irrigator, with a 20-25mm application depth and 20m spread, to a new Weta irrigator, with an application depth of 4-9mm and a 60m spread.

The Weta irrigator runs more slowly, applies effluent at a lower intensity and requires less labour because it is moved less often. The lower the intensity at which effluent is applied, the more days a year you can irrigate.

Choosing this irrigator meant Hayes’ new pond is 60% smaller than what he would have needed with a traditional irrigator.

Construction of the pond started in late April and by mid-May it was ready to be filled.

The full system install was planned for the week New Zealand went into covid-19 Alert Level 4 in August, so the install was pushed out by a couple of weeks; it was commissioned in the first week of September.

Having milked empty cows and late calvers through, Hayes says the pond is holding at least three months’ storage; the irrigators have only been going since early September.

When the weather improves, phase 2 of the project is to build a 300,000l overflow pond for the existing 90,000l concrete sump at the cowshed. 

The overflow pond will provide another 15-20 days backup storage, which will overflow using gravity should the system experience any power or pump issues.

“We have a few jobs to finish off, but we have got done what needed to be done for it to be operational,” he says.

“The system has been designed and constructed to the industry Design Standards and Code of Practice, which achieves a level above the WRC’s permitted activity rules.

“We have more storage than we really needed, to be safe – it’s good peace of mind. “The council’s off my back now; being compliant has been the biggest positive result from this system upgrade.”

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