1.3 Hydrogeological Assessment

1.3 Hydrogeological Assessment

A hydrogeological assessment (HA) is a broad evaluation that often incorporates the findings from multiple field investigations, along with other available data and information. As a minimum, the following background information should be obtained through a desktop study:

  • Site history
    • What has the site been used for in the past? (Practices and incident history)
    • What contaminants are likely to be present?
  • Hydrogeological setting
    • Type of aquifer, e.g. confined, unconfined, etc.
    • Aquifer configuration
    • Direction of groundwater flow
    • Hydraulic conductivity
    • How vulnerable the aquifer system is to contamination
  • Previous field investigation data
    • Bore logs
    • Bore depth and construction details
    • Location and length of the screened interval
    • Previous water level measurements

Groundwater Bore Networks

A groundwater bore network is a collection of strategically located monitoring wells or boreholes across a specific area. It aims to comprehensively monitor and understand groundwater conditions, including levels, quality, and flow patterns.

Considerations include:

  • Groundwater flow direction and gradient
  • Recharge and discharge areas
  • Contaminant sources and plumes
  • Spatial distribution and variability
  • Depth of bores
  • Project budget
  • Compliance with regulatory (EPA) requirements

Typically, the majority of hydrogeological site investigations will need to include:

  • One bore placed up-gradient on the site (and potentially off-site) to provide insight into the quality of the groundwater inflow into the site
  • Two to three bores per aquifer, situated nearby but down-gradient and laterally from each major contaminant source, for the purpose of monitoring

The requirements of the bore network may change over time, with the possibility of adding or removing bores based on evolving needs. Regular maintenance is crucial to maintain reliable data within the bore network.

See p25-27, section 3.4.4 of EPA’s document 668.1

 

Hydrogeological Field Investigation

A hydrogeological field investigation is a systematic process of collecting data and conducting studies in the field to understand the distribution, movement, and characteristics of groundwater within a specific geological setting. It is required if the initial Conceptual Hydrogeological Model or Conceptual Site Model does not meet the objective of the desktop study.

  • Is a specialised type of CSM focusing on groundwater flow, geological formations, and hydrogeological properties
  • Explains groundwater movement, interactions with surface water, and contamination pathways
  • Is crucial for designing effective groundwater-related remediation strategies
  • Evolves with additional data and contributes to informed decision-making

Conceptual Site Model (CSM)

  • Visual and descriptive representation of site conditions, contamination sources, pathways, and impacts
  • Helps stakeholders understand site complexities and make decisions for management and remediation
  • Evolves with new data and aids communication among parties

Page 22, section 3.4 of EPA’s document 668.1

 

Contamination Assessment

A contamination assessment specifically focuses on evaluating the presence, nature, extent, and potential risks associated with contaminants in groundwater resources. The goal is to determine whether contaminants have entered the groundwater system, to understand their movement and distribution, and to assess the potential impacts on both human health and the environment.

p23, section 3.4.2 of EPAs document 668.1

 

NAPL Assessment

NAPL stands for Non-Aqueous Phase Liquid and describes a liquid substance that does not readily dissolve in water and exists as a separate phase within an aquifer or substance environment.

In cases where NAPL might be present, or there’s a potential for contamination between aquifer zones and water samples, careful selection of drilling methods and bore locations is imperative to minimise these risks. It’s essential that personnel with relevant expertise carry out this work.

During field assessments, the following aspects should be considered:

  • Employing methods to evaluate the extent and distribution of NAPL within both the unsaturated and saturated zones, while considering variations over time.
  • Conducting sampling of light NAPL (LNAPL) or dense NAPL (DNAPL), analysing physical parameters (including transmissivity), assessing chemical composition, and establishing monitoring protocols.

The below figures present a visualization of the introduction of light NAPL (LNAPL) and dense NAPL (DNAPL) into the environment.

See p23, section 3.4.3 of EPA’s document 668.1