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Helping a retired couple save considerable dollars by providing them with cost-effective solutions to safely build their dream home

The Project

A retired couple in Whanganui sought the help of 4Sight consulting to assist them with cost effective solutions to remediate a former market garden / community allotment in Whanganui where they were looking to build their dream home.

The Approach

The client purchased a small (800 m2) plot of land in Whanganui that was vacant and undeveloped. Through the client's due diligence process and building consent application notice, it was apparent (as mentioned) that the site was formerly part of a small market garden / community orchard.

Market gardens are an activity listed on the Ministry for the Environment (MfE) Hazardous Activities and Industries List (HAIL) as something which has the potential to contaminate soil, and therefore potentially pose a risk to human health, due to the potential use of pesticides.

4Sight were approached by the client to complete a Preliminary Site Investigation (PSI) and Detailed Site Investigation (DSI) to support the resource consent application process.

Soil sampling indicated widespread impact by arsenic to shallow soils across much of the property, which was likely to be from the application and use of spray fertilisers, plus the use of CCA treated timbers, associated with the former use of the site.

To combat this, 4Sight developed a cost effective remediation strategy involving the removal of soils from highly impacted areas, and vertical soil/mixing and blending of shallower soils with cleaner deeper soils in less impacted areas. We then worked with the client to help them better understand and refine development plans, which subsequently resulted in 4Sight undertaking a Tier 2 site-specific risk assessment to determine the risk (if any) posed to human health by residual concentrations of arsenic in the soil.

The Outcome

The outcomes of the assessment revealed that all soils remaining on-site did not exceed the derived site-specific assessment criteria, and by working with the client to adjust the proposed building footprint we were able to encapsulate residual impact beneath the building footprint so that residual concentrations of arsenic in shallow soils at the site would be highly unlikely to pose a risk to human health.

By conducting limited soil remediation via a multi-staged approach, and subsequently conducting a Tier 2 risk assessment, we were able to save the client over an estimated $100,000 in soil disposal costs alone, in addition to avoiding costly project delays.

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