Turning Tides: Effective Water Treatment on a Challenging Coastal Construction Site

When your construction site is just metres from the sea, and subject to a resource consent, with specific conditions attached with trigger values of contamination, the stakes are high. This was the challenge faced on a recent project where Prime Fluid Management stepped in to deliver a compliant, efficient water treatment solution for drainage contractor McLatchie and Sharp for CentrePort in Wellington

Here’s how we overcame tidal influences, hydrocarbons, and sludge to achieve clean, safe water discharge.

A Complex Coastal Challenge

The site, situated on a disused landfill from the 1930s, had significant groundwater contamination. Hydrocarbons, oil, and sludge added complexity to an already difficult situation. The site’s proximity to the sea (approximately 15 metres) meant the water table fluctuated with the tides, with a recorded maximum flow of 250m³/h during high tide. Dewatering and treating the water efficiently were non-negotiable.

The Solution: Expertise and Innovation

Prime Fluid Management brought a tailored combination of products and expertise to the table. Key to our approach were:

• Two Envirohub HL50 Lamella Settling Tanks: Essential for removing hydrocarbons and solids from the contaminated water. Compact with a footprint of under 7m², yet capable of settling 50m³/ hr.
  

• BBA BA150 Pump with Rose Bud: Deployed in a sump to maintain water levels effectively.
• Wellpointing System: Including two highly efficient BBA PT150 well pointing pumps. Cleverly, the dewatering method used the ground itself as a natural filter.

Overcoming the Obstacles

The water table’s sensitivity to tidal changes, combined with the high levels of hydrocarbon contamination, was a significant challenge. The site demanded both innovative thinking and specialised equipment to meet environmental discharge consents.

Achieving Clean, Compliant Water Discharge

The customer needed a solution that ensured efficient dewatering and compliance with environmental standards. Prime Fluid Management delivered, exceeding expectations by producing water quality that surpassed consent requirements. Gerhard Rudolph, Prime Fluid Hire Operations Wellington, reflected on the challenge: “The oil skimmers on our Envirohub were a turning point, allowing safe discharge of heavily contaminated water.”

A Tailored Approach

Our methodology combined effective dewatering with precise water treatment, removing hydrocarbons and solids. The wellpointing system worked in tandem with the Lamella Clarifier to filter and treat the water, while the BBA BA150 pump maintained stable water levels.

Critical Facts and Figures:

• Excavation Depth: 6m
• Distance from Sea Wall: ~15m
• Maximum Flow During High Tide: 250m³/h
• Timeframe: The core works were completed in just two weeks.

Results That Exceeded Expectations

Prime Fluid Management delivered a solution that not only met but exceeded the customer’s objectives. We achieved water quality far superior to the consented standards, ensuring the project progressed smoothly. Our success stemmed from the combination of industry knowledge, experience, and the right equipment—with the oil skimmers on the Envirohub playing a crucial role.

Images: Images show dewatering and water treatment in progress at CentrePort. Thank you to main contractor, McLatchie & Sharp and CentrePort for their input into this case study.