A tale of two developments Stephen Gardner Environment Canterbury

Overview 1.Background to developments 2.Receiving environment 3.Compliance approach 4.Prestons North and South - different methodologies for achieving compliance 5.Outcomes

2010/2011 Quakes

Residential red - zone

Prestons

Background to Prestons development Earmarked for development prior to quakes 2010/2011 earthquakes led to shortage of houses and land Huge demand from red-zoned residents 3500 sections Race to have new sections for sale first!

CBD Prestons Styx River Snellings Drain

Post quake land issues Much of the “good” Christchurch land already built on Located in Marshlands – name says it all Extensive engineering required – bringing TC3 land up to TC1 quality Thousands of tonnes of material removed and replaced with gravel Shallow groundwater and springs in area Two “100 year floods” within two months in 2014 Stormwater runoff to “high value” waterways

The Styx Spring-fed high value waterway Modified urban catchment Still in relatively good health compared to Avon and Heathcote Rivers Greater incentive to protect water quality

Consents Initially covered under one consent Split into two due to different ownership Identical conditions – different approaches to compliance Visual clarity limit of 40% into Styx River and 20% into Snellings Drain

Compliance approach Attend every site meeting Site walkovers pre-meeting Discussions regarding ESCP on site, ideas tested and tried Constant formalised revisions of ESCP Trust established between ECan, consultants and contractors Encouraged to advise Environment Canterbury of issues Big change from “usual” approach

Prestons North Original plan –Divide development into stages and treat water separately in each area. –Groundwater to be discharged directly off site Eventual plan –All stormwater retained on site and then discharged –Groundwater required treatment due to fine silts –Water pumped to a central pond(s), then treated with flocculant dosing system before being discharged. –Approx $50,000 a month spent on ESC –Visual clarity and pH monitored at discharge point

Good use of a swimming pool

Prestons South Sandy, peaty soils Original treatment based around floccing of stormwater before discharge –Issues with organic material covering floc socks and manifolds Dewatering later used as sediment control

Initial sediment treatment

March 2014 floods

Dewatering as sediment control Very good infiltration of stormwater at site. All stormwater drained through sand which acted as a natural filter and was discharged through the dewatering system as clean water. Wellpointing occurring at around 12m depth below site. 50 – 100 spears in ground across a traverse All dewatering water clean and low in sediment Untested approach but it worked! Confirmed through written change to ESCP.

Outcomes Prestons NorthPrestons South Full time floc systemDewatering All stormwater retained on site and treated before discharge Stormwater retained and infiltrated on site $50,000 month$15,000 – $45,000 month Fully compliant with consent

Outcomes Early involvement key Developing trust between contractors, consultants, consent holders and compliance officer Collaborative approach led to good outcomes for both subdivisions

Questions?