Councils need to better protect our drinking water

Environment Canterbury (ECan) is proposing several variations to its regional land and water plan that will allow for increased nutrient and other pollution from irrigation and intensive agriculture on the Canterbury Plains. Commissioners are hearing submissions on Variation 1 to the proposed Land and Water Plan and I popped along to listen.

Variation 1 covers the Selwyn/Waihora zone which includes Te Waihora/ Lake Ellesmere and the much of the land between the Waimakariri and Rakaia rivers. The Canterbury Medical Officer of Health was presenting on behalf of the Canterbury District Health Board, along with the Department of Conservation and others.

Canterbury’s aquifers are the major source of drinking water for Christchurch, towns and many rural households. Medical Officer of Health, Dr Alistair Humphrey called for more conservative limits on nitrate nitrogen levels in groundwater to protect aquifers as a source of drinking water.

ECan’s proposed plan variation for the Selwyn-Waihora catchment allows for a major increase in nitrate pollution in shallow groundwater – up to 8.5 mg/l of nitrate-nitrogen. This is more than half what the World Health Organisation considers acceptable for drinking water and breaches the targets in the Canterbury Water Management Strategy (CWMS) as Dr Humphrey noted. ECan’s limit is not precautionary . It will allow nitrate levels to get too close to the unacceptable maximum for drinking water and prevent prompt remedial action such as changes in land use to reduce leaching.

Nitrate in drinking water can cause significant health effects including blue baby syndrome.

Monitoring shows increasing nitrate levels in around one third of monitored wells in Canterbury. In the Selwyn district alone, four community water supplies have already been compromised by elevated nitrate levels. This has increased the treatment costs for the Selwyn District Council and local ratepayers.

As Dr Humphrey said, “Poor water management decisions shift the costs of health from water users to the health system and the public.”

By allowing a high level of nitrate nitrogen pollution of groundwater in Variation 1, ECan is effectively implementing the National Government’s agenda of expanding dairying but it is at the cost of clean drinking water for the community. It is also ignoring the outcomes of the collaborative process which set the CWMS water quality targets.

20% of Canterbury’s dairy farms are in the Selwyn district and dairy farms and dairy support occupy around 50,000 ha in the area. Another 30,000 ha of land will be irrigated by the Central Plains Water scheme.

ECan’s weak plan limits on nitrate pollution conveniently allow for a major expansion in dairying and intensive land use in the Selwyn-Waihora zone and don’t adequately protect its aquifers as the major source of drinking water.   Once contaminated with high levels of nitrate-nitrogen, aquifers are almost impossible to clean-up.

The Medical Officer of Health also called for tighter limits on the nitrogen in discharges from septic tanks and on site water treatment systems because of their contribution to nutrient pollution of groundwater. Darfield is the largest town in New Zealand without a reticulated sewage and waste water treatment system. Dr Humphrey said the annual nitrogen losses from some septic tank systems which residents rely on, was likely to higher than the 15 kg/ha/year proposed for agricultural land use.

The Medical Officer of Health has once again flagged the need to safeguard our drinking water supplies and highlighted major problems with ECan’s current plan provisions. Will ECan listen and will Selwyn District Council provide Darfield with modern wastewater treatment ?

I’ll post more tomorrow about other water quality issues with the proposal.

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