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Blaketown Sewage Separation Scheme, Greymouth, Parts I and II


Client: Grey District Council

Engineering Consultant: Kurtis Perrin-Smith 

Duration: 2010

Project Overview

Excavation and backfilling of trenches, Blaketown.Blaketown Sewage Scheme Parts One and Two were part of the sewer separation scheme of the wider Greymouth area. This was prompted by a nationwide government public health and environmental initiative to separate sewage and stormwater and install up-to-date sewage treatment plants in every small town in the country. The project was required to be completed by the end of 2011.

Historically Greymouth's public sanitation comprised of a combined stormwater and sewage system. In other words one set of reticulated pipes for both stormwater and sewage with the ultimate discharge being into the Grey River. This was a very low maintenance, self flushing system, every time it rained (as it does a bit on the coast), the Grey River would "flush the toilet" out into the sea where bacteria did the work. A very low maintenance, very low cost form of sewage "treatment". But this does not comply with the accepted environmental standards of today. Hence the resource consent ultimatum from government was that Greymouth's sewage had to be separated from stormwater and treated. Thankfully central government became engaged in the project as a stakeholder and provided a generous subsidy for the completion of the works, which would otherwise have been beyond the financial reach of the Greymouth community.

So the Blaketown sewage separation scheme Part One formed part of a wider Greymouth area sewage separation scheme. TruLine Civil tendered and won both stages of the Blaketown sewage separation contract, each comprising approx;

  • almost 3 km of gravity main and 
  • over 2.3 km of sewer gravity laterals
  • all associated manholes, junctions, fittings, and pump stations. 

Much of the work in Blaketown took place alongside the Grey River so at times ground water was an issue that had to be addressed continuously as the work was being undertaken.

Stage Two comprised a similar amount of gravity main and gravity laterals and was very similar in size, complexity and scope as Stage One. Both contracts were completed on time and within budget to a high standard. All pipelines required testing, sign off and were ultimately camera inspected with a CCTV pipeline inspection camera. All pipes were laid using pipelaying lasers and approved bedding and compaction methods, followed by a final reinstatement.

Kurtis Perrin-Smith was the site engineer employed by the cliient, undertaking both the design and site compliance for both contracts. 

Waste Water Upgrade Methodology

Shored trench combined backfill and excavation.Combination open cut trench and shored trench 

Our crew dug the trench with our short swing radius, 24-ton Sumitomo SE225SR excavator which works in one lane of traffic so was well suited to confined jobsites on suburban streets resulting in minimal traffic disruption. Trench faces were cut back to a safe slope using two digger buckets, first wide, then narrow. Custom hydraulic quick-fit enables fast changing of attachments on-the-fly from safety of the cab. All our excavators are custom fit with front-end dozer blades, this increases machine versatility in job applications such as spoil levelling, backfilling trenches and site clean up.

The majority of pipelines were laid in road carriageways requiring full asphalt reinstatement on completion of the pipelaying. The laterals were extended to just inside the boundary of every property in the catchment thereby allowing homeowners to connect from their dwellings to the new sewage pipeline located just inside their boundaries at minimal cost. 


To date there has been a very good rate of dwellings connecting to the newly reticulated wastewater system. The net result is that Greymouth has among the most up-to-date sewage systems in the country. All the latest PVC pipe with very good performance ratings were used thereby achieving separation to a top standard meaning no excess water infiltration into sewage lines either from stormwater or groundwater—both of which overload treatment systems downstream in a many communities. There has also been a significant public sanitation/community health benefit because there is no longer raw sewage flowing directly into the Grey River or out to the Tasman Sea, which means that while this historical situation might have been conducive to good sized whitebait in the Grey, it was not conducive to good community health.

A good working relationship was developed and prevailed during this contract which contributed to a successful outcome for all the stakeholders.

Contact us

TruLine Civil is determined to incrementally improve the service we deliver our clients, and the quality and range of civil engineering services that we offer to owners and stakeholders who expect excellence.

Excellence in Infrastructure.

TruLine Civil.

Interested in our services? You can contact us +64 (21) 228-5090 and ask for Geoff Powell or e-mail me at 

Christchurch Address 

Greywacke Road extension,
New Zealand 


Blaketown Sewage Separation Slideshow

>> Click to view the Blaketown slideshow >>

Slideshow controls: [1] Double-click to "pause" any slide, [2] Double click to "play"/continue the show. [3] Jump to any slide in the show by clicking on the relevant thumbnail. [4] To escape at any time click "x" top right.

Credits: Photos and case study documentation by Shaun G. Waugh

Click thumbnail for larger image

Blaketown Sewage Separation Scheme, Greymouth, Parts I and II Combined trench excavation and backfill, Blaketown, Greymouth. Combined trench excavation and backfill, Blaketown, Greymouth.
Manhole with laser.

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