Storage and disposal
All farm wastewater generated from: dairies and adjacent entry/exit races, stock holding/sale yards, feed/stand-off/loafing pads, wintering barns, piggeries, poultry farms, stock underpasses, and transit races (if used for standoff and the like) must be contained and/or reticulated to a storage/treatment system.
- Weeping walls for solids separation.
- Large volume contingency storage.
- Land application as the primary means of disposal.
- Resource consent to discharge when soils are saturated.
Sludge bed/weeping walls are designed to remove solids from farm wastewater prior to land application/storage.
Advantages of adequate contingency storage include:
- Ease of management.
- Less demand on labour when farm systems are under the most pressure, that is, during calving and wet conditions.
- Land application can be timed to optimise nutrient recovery.
- Irrigators can be run for long periods in a steady state of operation when conditions are suitable.
Wastewater can be stored until conditions are suitable, reducing the risk of:
- Unnecessary contamination of water;
- Non-compliance with regional rules;
- Surface or ground water contamination; and
- Loss of valuable nutrients.
Contingency storage ponds
Northland soils are often saturated from May through to October. It is therefore a requirement that enough storage is provided to hold all wastewater generated over that period.
For consented farms
For farms holding a discharge resource consent there is a condition (depending on age of consent) requiring;
- All ponds to be at/near empty by 1 May each year or,
- The treatment system must be adequately maintained (includes desludging/emptying of ponds).
All consented farms have been ‘sized’ to allow adequate storage of farm wastewater during the wetter months and ensure wastewater is adequately treated prior to any discharge. This is based on all ponds being emptied prior to winter.
For Permitted Activity farms
For farms operating under the permitted activity criteria (no discharge to water) the regional rule requires that;
- Ponds must have at least 75 percent working volume available between 1 March and 1 May each year.
For permitted activity farms, the key measures to ensure there is adequate storage available for the predominantly wet period thru May – October are:
- Having the pond/s at or near empty by May.
- Continuing to apply wastewater to land when conditions are suitable throughout if possible i.e. with no overland flow or excessive ponding over 3 hours.
- Having a contingency pump (or access to one) in case of break-down to enable irrigation of wastewater whenever ground conditions are suitable (as above).
- Store wastewater when soil conditions are not suitable for land application.
- Divert as much stormwater as is practical – particularly when rain is forecast.
Research has proven that if wastewater is applied to saturated soils it can result in up to 80% of the wastewater running off to surface or ground water. Therefore, to comply with regional rules, wastewater must not be applied to pasture when soils are at or near saturation.
|Wastewater should only be irrigated to land when soils are in moisture deficit (that is, dry) and pasture is actively growing.|
Additional storage is often required when:
- There is an increase in cow numbers;
- The dairy is used for winter milking;
- The yard is used for stand-off;
- There is an open stand-off or feed pad; or
- Stormwater is not routinely diverted.
Recommended storage volumes
Your local Fonterra Sustainable Dairying Advisor can also help with pond sizing calculations for farms operating both under the Permitted Activity criteria (no discharge), and farms operating with a consent to discharge treated effluent.
These volumes are based on:
- herd size and milking regime
- calving regime
- effluent volumes generated at the dairy (largely impacted by water use)
- stand-off/feed pad use
- stormwater diversion (and its use)
- roof water from the dairy and surrounding buildings (if pond is sized to accommodate this, otherwise it should be diverted)
- average local rainfall
- soil types.