Cost of treat­ing drink­ing water rises to $11m


The cost of treat­ing Lower Hutt’s con­tam­i­nated water sup­ply has es­ca­lated to $11 mil­lion, with a 1.5-kilo­me­tre pipe­line needed to di­vert water away from the Water­loo treat­ment plant.

E-coli had been found in water drawn from the Wai­whetu Aquifer, which goes to the plant, on three oc­ca­sions since late last year, and an in­crease in co­l­iform bac­te­ria was also de­tected.

With an in­ves­ti­ga­tion un­able to de­ter­mine the cause of the prob­lem, Greater Welling­ton Re­gional Coun­cil agreed to con­tinue per­ma­nent chlo­ri­na­tion and ul­tra-vi­o­let (UV) treat­ment of the water, at an up-front cost of $4.6m.

How­ever, fur­ther in­ves­ti­ga­tion has re­vealed the amount of ‘‘misty’’ water not suit­able for UV treat­ment is higher than first thought, and that water will have to be shifted else­where via a pipe­line.

Misty water, which is gen­er­ated by bore pumps when they first start up, ap­pears the same as clear water, but con­tains par­ti­cles which can mask po­ten­tially harm­ful or­gan­isms dur­ing treat­ment.

Welling­ton Water, which car­ried out the in­ves­ti­ga­tions, had hoped the water could be diverted to the nearby Opahu stream or stored at the treat­ment plant un­til it ran clear, but it un­der­es­ti­mated the vol­ume of water it had to shift.

‘‘The costs as­so­ci­ated with the di­ver­sion of the ‘pump start-up water’ es­ca­lated quickly.’’

‘‘As the pro­gramme of work has pro­gressed, the costs as­so­ci­ated with the di­ver­sion of the ‘pump start-up water’ es­ca­lated quickly,’’ the re­port said.

‘‘Mul­ti­ple ap­proaches to man­ag­ing the sig­nif­i­cant vol­ume of water were con­sid­ered dur­ing the de­sign phase.

‘‘How­ever, the only vi­able op­tion in­volves the con­struc­tion of a 1.5km pipe­line from the bore field to Te Awa Kairangi/Hutt River.’’

The Water­loo plant sup­plies water to up to 240,000 peo­ple across Welling­ton and Lower Hutt, Welling­ton Water group man­ager for net­work, strat­egy and plan­ning Mark Kin­vig said.

Four bore pumps in the Water­loo well­field, along Knights Rd, are still out of ac­tion due to the water they pump be­ing con­tam­i­nated, and it is hoped they will be op­er­at­ing again in time to meet sum­mer de­mand.

The first of two UV units needed to re­turn to full op­er­a­tion was in­stalled ear­lier this month, with the sec­ond to be­gin op­er­at­ing once the pipe­line is con­structed, hope­fully by Jan­uary.

Of the ad­di­tional $6.4m re­quired for the pipe­line, $4.2m will be taken from the coun­cil’s planned 2017-18 spend­ing, in­clud­ing $2.7m from a re­silience project aimed at en­sur­ing the Welling­ton re­gion has dual water sup­plies in an emer­gency. The $60m project in­volves off­shore bores ex­plor­ing po­ten­tial aquifers off the Mi­ra­mar penin­sula.

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