20E016 - Practical Considerations on Resolving Groundwater and Surface Water Interaction at Contaminated Sites
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Background/Objectives: Practically resolving groundwater and surface water interaction is becoming an increasingly critical challenge at contaminated sites adjoining surface water bodies.

This is particularly the case in Australia as substantial industrial development has occurred in close proximity to coastlines and rivers. However, most conventional approaches to evaluate groundwater – surface water interaction are not suited to the relatively small scale at which contaminated groundwater typically occurs as they have been developed for broader water resource studies at the catchment scale. Hence, there is merit in outlining a specific set of tools and approaches to improve the resolution of this challenge in a more practical manner, at a scale that is relevant to the typical exposure scenarios evaluated in risk assessments at contaminated sites.

Approach/Activities: There is a growing range of tools and approaches available. Drive-point piezometers are typically deployed in soft sediments where the groundwater table is shallow. Seepage meters are well suited to near-shore environments, also favoring sites with soft sediments, and can provide direct measurements of discharge rates and composition. Depending on the temperature contrast between groundwater and surface water, portable or distributed temperature sensors can assist in locating and characterizing discharge zone(s). Passive flux meters can be deployed in monitoring wells provided the rate of groundwater discharge remains relatively constant during the deployment period. Applied and environmental tracers are very useful to assess the degree of groundwater – surface water mixing within aquifers prior to discharge, the surface water residence time in the hyporheic zone or the discharge rate when it is variable (e.g. tidal environments). Compound specific isotope analysis has proven to be valuable in demonstrating the role played by the hyporheic zone in acting as a natural bioreactor.

Results/Lessons Learned: The paper presents examples of the use of these methods in contaminated site settings within Australia, including the results obtained and how they were used to further our understanding of environmental risk. The successful selection and implementation of these tools and techniques should consider the following at the investigation design stage:

- A plausible and robust hypothesis on the extent and nature of the groundwater – surface water interaction, as a component of a sound risk assessment. There is a higher chance of success if the tool selection and data collection is guided by the verification of this hypothesis with empirical data.

- The investigation design should aim to differentiate the contaminant loading attributable to groundwater – surface water interaction from other potential contamination sources affecting the receiving environment (e.g. off-site contribution, effluent discharge, sediment, air-borne deposition).

- The collection of high-resolution spatial and temporal data is critical to appropriately assessing what are often highly dynamic environments (for example, in tidally influenced zones where changes occur on an hourly basis).

- The best results are achieved through integration of multiple lines of evidence to resolve the dominant processes affecting contaminant fate and transport at the groundwater – surface water interface (physical, chemical and biological).

Publication Summary

  • Geosyntec Authors: Frederic Cosme, Lange Jorstad
  • All Authors: Frederic Cosme, Lange Jorstad, Geosyntec Consultants; Matt Edwards, Greg Luke, BlueSphere
  • Title: EcoForum 2020 eConference
  • Event or Publication: Event
  • Practice Areas: Groundwater Assessment and Remediation
  • Citation: Geosyntec will deliver five presentations and one keynote at EcoForum 2020 eConference on September 14-18, 2020.
  • Date: September 14-18, 2020
  • Location: eConference
  • Publication Type: Platform Presentation