Ravensdown Civil Construction Works – Stormwater and Intake Project

Purpose

The Ravensdown Stormwater and Intake project is part of the Ravensdown Fertiliser Cooperative’s Hornby Works. The fertiliser manufacturing facility is located in Hornby, Christchurch.

Overview

The project was comprised of four separable portions which formed a stormwater retention and discharge system, a new fertiliser intake system (which required reconstruction following an extensive sulphur fire in October 2018) and disposal of a considerable amount of contaminated soils resulting from construction.

Separable portions (SP) 1 and 2 comprised the stormwater retention basins and drainage network. They formed part of Ravensdown’s resource consent requirements for the ongoing operation of the Hornby site. As background, during the fertiliser intake and dispatch process from the site, fertiliser dust can settle on the hard surfaces at the site. During rainfall events the fertiliser compounds can become soluble and are dissolved into solution and high nutrient stormwater can result. This stormwater was entering the Christchurch City Council stormwater network which fed into tributaries of the Heathcote River. The design split the receiving waters into roof-sourced water and hard stand runoff. The system was designed so that the roof water could continue to pass into the municipal stormwater network, whilst the hard stand runoff was collected in the retention basin ponds and discharged at a rate of 4 litres per second into the City Council sewerage network as trade waste.

SP3 and 4 involved the removal of contaminated ground, so that the new intake building footings and large earth ramps could be constructed. The large intake building had to be correctly sequenced. This included removing contaminated ground, excavating the building foundation and backfilling with engineered fill. During the placement of the concrete building panels, site won material was placed in the lower story of the building. So as not to load the panels during construction, the panel fill had to be placed evenly on both sides.

The contract included the following works:

SP1 & 2 – Stormwater Basins

• Liaison with Ravensdown operations staff, customers, and suppliers including heavy vehicle operators servicing the site to mitigate the impact of the works as far as practicable
• Management of health and safety of the worksite, including temporary traffic management
• Construction of three stormwater retention basins, bulk excavation and cut to stockpile
• Construction of geosynthetic membrane liners for the retention basins
• Construction of drainage network infeed to the basins and trade waste connections into the municipal sewer
• Construction of associated stormwater infrastructure
• Installation of a “downstream deflector” water separator
• Liaison with utility companies and construction of service trenches to enable relocation of existing services as required
• Construction of road surfaces and making good along the drainage network
• Mechanical and electrical automation installation for drainage basins automation
• Pavement construction and surfacing
• Line marking and signage
• Street furniture and roadside barriers
• Landscaping, fencing and planting
• Related safety improvements

SP3 – Intake Building Ramps and Site Works

• Liaison with Ravensdown operations staff, customers, and suppliers including heavy vehicle operators servicing the site to mitigate the impact of the works as far as practicable
• Management of health and safety of the worksite, including temporary traffic management
• Bulk excavation and cut to stockpile
• Cut from stockpile and base up foundations and heavy vehicle ramps
• Remove contaminated waste from stockpile to encapsulation area and form batters
• Completely seam weld encapsulation plastic liner
• Construction of drainage network from hard surfaces and encapsulation
• Extensive coordination with other mechanical and vertical building contractors working in close proximity
• Construction of road surfaces and associated kerb and channel and making good along the existing hard surfaces
• Pavement construction and surfacing
• Line marking and signage
• Street furniture and roadside barriers
• Landscaping, fencing and planting
• Related safety improvements

SP4 – Contaminated Waste Removal Offsite

• Liaison with Ravensdown operations staff, customers, and suppliers including heavy vehicle operators servicing the site to mitigate the impact of the works as far as practicable
• Management of health and safety of the worksite, including temporary traffic management
• Extensive asbestos monitoring and supervision protocols
• Management of specialist asbestos subcontractors
• Management of multiple bin truck operators to maximise efficiency of loader operations and offsite disposal timeframe

Challenges

This was a technically difficult project with a number of challenges due to the site, the design requirements, and the need to minimise disruption to business-as-usual for Ravensdown.

Site Conditions

• Brownfields contaminated site - fertiliser operations date back to 1930 with historical unmapped onsite disposal locations
• High heavy traffic volume movements – both fertiliser intake and sulphuric acid and fertiliser dispatch
• Additional unforeseen contamination significantly more than predicted scheduled volumes
• Dry dust conditions
• Covid shutdown and remobilising works
• Narrow time frame for construction of SP1 &2 to meet Environment Canterbury’s deadline
• Narrow, confined site
• Stockpile management - due to the extensive contaminated ground that was encountered, the stockpile area was fully utilised to ensure truck and trailers were carting full both ways
• Weather – very hot dry days in the extended summer make excavation and dust control challenging especially given the contaminated nature of some of the ground, and this made construction difficult as the ground conditions were poor.

Our experience led us to use a dedicated dust suppression system, including fixed k-line sprinklers, a water cart and where possible to compact and minimise stockpile disturbance.

Design

• Backfill of panels and panel sequencing for earthworks and ramps was vital so as not to preload the panels
• Split stormwater systems into hard surface collection and roof water
• Retention stations and associated drainage networks and pump stations for transfer of trade waste
• Design for SP3 was not fully completed at initiation and was updated and modified during construction including the incorporation of significant contaminated soils in an onsite encapsulation dump

Isaac’s flexibility and willingness to work with design changes and provide feedback and advise from an experienced contractor’s perspective, helped to overcome all of these design challenges.

Stakeholder Communication

At the pre-project award meeting, Ravensdown highlighted from the start that their site has a high number of heavy traffic movements with transport subcontractors bringing in vital fertiliser manufacturing components, and the Hornby Fertiliser Works needing to dispatch fertiliser to their farmer shareholder customers. The application of fertiliser typically has two natural peaks, autumn and spring. It was vitally important that construction did not impede the flow of fertiliser components. We had to avoid any disruption to site dispatch and Ravensdown’s farmer shareholders’ fertiliser applications which would have impacted their crop and pasture yields and in turn impacted their financial performance.

In addition, the fertiliser plant manufactures sulphuric acid which is used by industrial chemical supplier Orica. Acid dispatch needed to occur approximately twice weekly and traffic management and site construction were carefully planned, communicated, and agreed in conjunction with site operations staff.

Prior to Isaac mobilising to the site, we submitted an agreed traffic management plan with Ravensdown Hornby Operations staff. This plan was reviewed and agreed.

Our attentiveness with managing traffic flows across the site and exit and entry from designated side streets and went a long way to ensuring stakeholder requirements were being managed and met where practical over the course of the project.

Working on an active fertiliser works and around Ravensdown’s Head Office

Working on an active fertiliser production facility and also in close proximity to Ravensdown’s head office provided a number of challenges for both our crews, who were working long days and weeks due to the short programme, as well as the management team who were working from the site office. Each morning approximately 300 head office staff and 50 Hornby works staff needed to enter the roading network to access the onsite carparks. Adding to the complexity was the location of the sites within the heart of the fertiliser works, along with staff and subcontractor traffic movements and coordination as required with the other trades.

Normal biweekly fertiliser intakes increased during the prelude to the autumn season to weekly. During these intakes international freight bulk cargo ships berth at Lyttleton. As these vessels are on daily charter the urgency to remove the cargo into Ravensdown’s store was high. Trucking turn-around times were vital and construction works had to be phased to prevent disruption. Access ways and road had to be made good daily to ensure free and unimpeded traffic movements. So as not to cause delay to the program, the project crews were reassigned to other localities during the intake periods.

It is a testament to Ravensdown staff and ICL staff and subcontractors, and the cohesion and communication between them, that all stakeholders were able to be managed without delay or complaint during the construction period.

Testimonials

Peter Hay – Ravensdown

Ravensdown Christchurch Works located in Homby, Christchurch is an important manufacturing (sulphuric acid and superphosphate-based products) and distribution facility for the company. The site has been going through significant redevelopment over the last 10 years (post-earthquakes) and has recently completed a stormwater retention and discharge system and a new fertiliser intake system.

Isaac Construction were successful tenders for both the stormwater project and the civil work required for the new intake system. The was the first time we had used Isaac’s and it was important to us that we selected a contractor that we believed would become a partner in our business, not just a contractor providing a service. Developing 'preferred suppliers' and building strong long-term relationships, where parties work together for mutual benefit is important to us as it brings real value.

These were complex, high activity projects on what is already a busy site with 'business as usual'. It was critical throughout the projects that we minimised the impact on normal operations and our customers.

It is pleasing, even with the covid interruptions that both projects have been successfully executed. As client representative for Ravensdown I have worked with the Isaac's project team since the award of tender and watched them develop and deliver an ambitious and evolving project, which saw the final stage of Separable Portion 4 being completed on the 6th of August 2021.

I found the Isaac's team very proactive and responsive when dealing with issues that came up on site. They were very easy to deal with in working through many on site complexities and were consistent in offering added value solutions to any issues that arose over the course of the project.

This relatively newly developed relationship continues to prosper with Isaac's recently completing a significant roading project on site.