Saltwater Intrusion Threat

Scientist warns of dangers in Kapiti recharge plan

By Alan Tristram

A former Regional Councilor says the council has scientific advice a KCDC plan to recharge the Waikanae River by increasing draw-off from underground aquifers would result in saltwater intrusion.

Ex-councillor Chris Turver quotes Dr Douglas Mzila, a senior environmental scientist.

Dr Mzila has said ‘any increases in drawdown (during drought) will result in increases in conductivity’ in the aquifers. And Mr Turver pointed out this means saltwater intrusion.Disclosure in technical report

The disclosure has come in a technical report commissioned by the Regional Council  to assess submissions made on the KCDC plan prior to a resource consent hearing in Paraparaumu between 11-13 June

Former regional councillor Turve, who specifically warned about saltwater intrusion, says after receiving a copy of the report his worst fears have been confirmed

In a hydrogeology technical review,Dr Mzila warns that ‘the saltwater/freshwater interface is currently in a precarious equilibrium and any sustained groundwater abstraction could result in rapid and almost irreversible aquifer contamination from saline water.’

KCDC claim ‘badly wrong’

Mr Turver says one of the most alarming features of the report is that a claim by the KCDC that the saltwater/freshwater interface is located ‘several kilometres offshore’ is badly wrong.

GWRC monitors conductivity in a number of saline intrusion sentinel wells and, Dr Mzila says, ‘it is clearly evident that the saltwater wedge is located within the aquifer.’

Dr Mzila says while the KCDC says in its application that it intends to set back any new wells by one kilometre from the coastline, analysis of groundwater chemistry for the deep aquifers in the Waikanae area concluded that groundwater with ‘seawater signatures’ extends more than two (2) kilometres inland.

Dr Mzila says if the resource consent hearing agrees to the KCDC’s application, trigger levels should be set for saltwater thresholds.

And he says abstraction should be stopped if salinity levels become equal or greater than any agreed trigger levels.

Mr Turver says this point brings sharply into focus another concern in his submission:

“If during an extended drought the final trigger level is reached and abstraction has to stop, what then does the KCDC do to provide water to its ratepayers?”



Further Information:          Chris Turver                        06-3643640 or 027-2301601