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Nitrate in groundwater isotopic source assessment

Nitrate in groundwater isotopic source assessment

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CLIENT

Water Corporation

SECTOR

Water

SOLUTIONS

Groundwater and water resources

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Carolyn Brumley

Senior Principal Risk Assessor

Overview

Senversa was engaged by the Water Corporation of WA to conduct a detailed assessment of a nitrate in groundwater plume associated with one of their wastewater treatment plants (WWTP) in regional WA.

The nitrate plume was thought to be approximately 2 km in length, and previous modelling by another consultant suggested it may reach the coastal environment in 20 to 30 years. There was limited data to support this however, and Senversa accordingly scoped and completed a detailed hydrochemical, microbiological and isotopic assessment of groundwater to gain a better understanding of other potential nitrate sources.

Stable nitrogen and oxygen isotopes in particular (refer below) were assessed, to provide better insights into nitrate plume origin and behaviour.

Nitrate in groundwater, intermediate aquifer

Outcome

The detailed hydrochemical, microbiological and isotopic assessment indicated that the nitrate plume was unlikely to be 2 km in length, and instead was interpreted to consist of two smaller plumes, an ‘older’ denitrified plume and a ‘newer’ expanding plume, both approximately 500 m in length.

The source of nitrate impacts in a key monitoring well located 2 km from the WWTP site were found to be associated instead with a former septic tank located in close proximity to the impacted well.

The Senversa investigations provided a basis for a new, improved conceptual site model (CSM) and lowered the WWTP risk profile.