Watercare Central Interceptor Oral Submission

I took the train for the first time from Britomart to Manukau Station the other day. Very scenic I thought as we motored beside the Harbour toward Orakei. On my way to make my oral submission to commissioners....

You can see my written submission here. For my oral submission I focussed on two key points. But first I needed to talk about Combined Sewer systems and what their adverse effects are:

*  Sewage pathogens – diluted by stormwater. The dilution varies for every sewer line (in any particular rain event) because the proportion of dry weather sewage inflow to stormwater inflow is determined by the activities in the sewer line catchment

*  “Floatables”. This includes excreta, toilet paper, and other solids flushed down the toilet. This also varies for each sewer line.

*  Diluted trade wastes. Commercial and industrial trade wastes that are disposed of into sewer lines.

Then I introduced my case study example.

North Shore City's sewer network. North Shore does not have a combined sewer network (CSN). But when it rains North Shore’s wastewater collection network infiltrates stormwater up to 4 or 5 x “dry weather” flow rates, so that some trunk sewers (interceptors) quickly reach capacity… …and cause overflows affecting beaches and streams and amenity.

The point being that NSCC sewers act like Auckland's Combined Sewer network when it rains. Most North Shore sewage pump stations have “floatables” screens… but not all….

I wanted to explain to commissioners the physics of sewer overflows, in order to talk about how to manage overflows.The map on the left in this slide is the proposed Central Interceptor catchment - with the frequency of overflow points marked in red circles = bigger circle = more overflows/year. The map on the right shows roughly where North Shore's sewer overflow points were.

Frequency is just one measure. But if (as Watercare's AEE says) benefits sought are: public health, amenity values, cultural values and ecological values – other measures are important.

For example, the Volume of a discharge, the Pathogen loading of a discharge (Many distributed small volume discharges of dilute sewage have far less impact, than a single large more concentrated discharge – like a point source.)

For example – on North Shore the Wairau Pump Station was responsible for about 50% of enterococci discharged in a rainfall event. (enterococci is an indicator bacteria for faecal colliform contamination)

This next sequence of slides explains how North Shore systematically went about measuring the problems caused by its sewer network, before coming to decisions about how to manage those problems.

This slide shows indicatively how North Shore's problem might be measured if Watercare's methodology was used. Frequency of overflows....

More revealing measures convey a different picture, and lead to different technical solutions....

This map shows the relative volumes of overflow discharges from specific parts of the network in a 6 month rainstorm.... (there are 3 - the Devonport one is very small...)

...This map shows the concentrations of these overflows (based on regular measures carried out over time of overflows). Some overflows are more concentrated than others... greater health effects....

...this information is combined to give a measure of the actual amount of microbial contamination being released into the environment at each discharge point....for a given rainfall event...

... but you need to know how this is affecting water bodies and beaches and streams that people use... stream flow and tidal flushing movements move the contaminated water bodies...

...this allows different receiving environments to be assessed. These can be graded in order of  importance and significance....

In the period 2000 to 2004 approximately, North Shore City Council planned to spend about $500million making its public sewer network collection system “leak proof”.

It spent about $50 million rehabilitating Devonport sewers (see pic where resin liners inserted into trunk sewers). Some benefit so far. But other areas of city now have storage tanks underground to reduce overflows. Council spent about $150 million taking treated effluent 3km offshore, and expanding its outfall capacity. Some storage was also provided in Browns Bay using a large pipe laid in a street corridor.

These images show a couple of the storage facilities. The one bottom right shows two workmen at far end - gives an idea of scale.

These underground storage facilities receive sewer overflows while sewer interceptors and trunk sewers are at capacity (as happens to Auckland's combined sewers). Intense rain storms pass after a short time. Sewers take a couple of hours to pass their contents to wastewater treatment facility. And reduce in flow. THEN the contents of storage tanks are pumped.

This sort of approach recognises that rainfall events are not uniform. There are weather bombs. Localised extreme rainfall. Localised capacity exceedances. There is need for SCADA type network control to direct flows to parts of network with capacity. The priority is to minimise pathogen contaminant loading in environment from network discharges, for the range of anticipated weather events expected. The objective is the identification of the range of mitigation measures/fixes that will best deliver This requires a comprehensive understanding of the behaviour of the entire existing network.

The problem with Watercare's Central Interceptor is that the work hasn't been done to demonstrate that it's the best solution to the problem Auckland has.

In addition at Pg 233 of the officer's report to commissioners: "It is noted, that the benefits of the Central Interceptor project can only be realised following its completion and connection with the existing wastewater network."    (This is an important recognition of the fact that the pipe-based solution cannot be implemented incrementally - as for example North Shore's approach was - and cannot provide public benefits until it is totally finished. This is the classic problem with traditional, centralised, infrastructure. Today's thinking is much more de-centralised and less energy intensive. Watercare is Auckland’s biggest user of electrical energy.)

The Central Interceptor approach appears to be driven by the need to minimise the number of discharges (big and small), rather than the need to minimise discharge of contaminant loadings (volume x concentration) There is insufficient quantified information provided relating to combined sewer overflow effects on the receiving environment, in different rainfall events. While I accept that the Central Interceptor tunnel is likely to provide significant benefits for a part of the trunk sewer network, these need to be considered conjunctively with proposals for the whole network.

This map is drawn from watercare's AEE. It shows the whole sewer network - that leads to Mangere WWTP. The light green area is the catchment proposed to be served by Central Interceptor.

Quoting from the officer report:  “….It is the opinion of the authors of this report that the various restricted discretionary, discretionary and non-complying activity components under each plan, and as part of the overall project, are not severable from each other – i.e. the overall tunnel and associated construction sites/shafts and link sewers all form part of an interconnected project….”

In other words they note that all the bits and pieces of the Central Intercceptor project are joined up and have to be considered together.... and all consents obtained together...

What makes me really concerned is that Watercare is expecting commissioners to consider the Central Interceptor in isolation from the rest of the network. I paraphrased offer's words from above..

“….It is the opinion of the submitter that the proposed Central Interceptor project is one part of Auckland’s trunk sewer network, and as part of the overall network, is not severable from other parts of the network – i.e. the overall tunnel and link sewers all form part of an interconnected network and its function can only be assessed in conjunction with the network as a whole….”

In my submission:

I noted that at Pg 47 of the officer report, about Other Consents   “The overall Central Interceptor project involves further regional consents for the CSO Collector Sewer works … and a network discharge consent....”

And at Pg 235:   “… While the authors acknowledge that there is some risk in seeking consent for a specific infrastructure component prior to the Network Discharge package, this approach will allow the Network Discharge package to better align with the GAP project in terms of content and conditions….”

However, I understand that the RMA requires that all consents relating to an activity be applied for together – to allow integrated and coordinated consideration by consenting authority.

North Shore City Council’s network consent application provided for that, and, in my opinion, delivered an integrated set of permits, management plans, reporting requirements, and conditions. The proposed Central Interceptor tunnel is a single project whose effects and performance need to be assessed alongside other proposed and budgeted projects planned to improve the environmental performance of the whole network.

There is no timetable or requirement that I am aware of for Watercare to obtain a network discharge consent for either this part of its trunk sewer network, or for the whole network.

It is ONLY through a whole of network discharge consent process that the consent authority (Auckland Council) can consider the function and effects of the network in an integrated and coordinated way – and thereby gain some certainty regarding outcomes and applicant actions.

Therefore, EITHER the present application must be declined OR the present consents need to be interim, or conditional upon Watercare obtaining network discharge consents for interconnected and conjunctively operated networks.

I await the commissioners deliberations with interest.