NPE was approached in late 2022 by our client Brown Plumbing & Civil regarding dewatering that was required for the installation of a new sewer pipe via the Micro Tunnelling drilling method due to the existing sewer pipe had been compromised, leaving some residents without working sewage in Southern River, Perth.

The Jacking and Receival drill pits had invert depths of up to 4.5m from GL (ground level); therefore, each required a temporary aquifer drawdown of 3m from static water table level to achieve adequate cone of depression.

NPE provided complete coverage over this project, starting with the dewatering methodology proposal, followed by all the
pre-dewatering requirements managed by our environmental team, which included:

• The installation of monitoring wells via Direct Push Probing
• Soil and groundwater sampling for lab analysis
• Disposal option and treatment operation strategy for dewatering discharge effluent.
• Consulting with local city/councils for approval to discharge dewatering effluent into a large infiltration swale near Conservation Wetlands
• Discharge applications for sewer chamber use to Water Authorities (Water Corporation)

Upon NPE being granted the discharge approval for Brown Plumbing & Civil, legislative set eco system criteria were to be adhered to throughout this project dewatering duration, which was followed strictly by implementing all water treatment and environmental requirements accordingly via dosing units, clarifiers, daily field water sampling & weekly lab sampling. Also included were the approval conditions with flow rate and infiltration swale capacity not to be exceeded. This was compiled into the detailed Closure Report submitted to the City/Council’s governing bodies at project completion.

Given the sensitivity of the existing compromised sewer pipe, this project start date was pushed out 12 months from the initial RFQ.

All dewatering operations installed by our AIC went exceptionally well, providing dry ground conditions for the Micro Tunnelling equipment and civil plumbers to complete their new sewer connections. AIC established additional sound attenuation to support the silenced canopy dewatering pumps, providing an even lower dB noise reduction for the residential location of these drill pits.