What is groundwater monitoring?

Groundwater monitoring is the process of measuring groundwater levels, groundwater quality and groundwater flow over time. It helps assess aquifer quality, determine hydrogeological characteristics, identify contamination risks and support groundwater management decisions.

Why is groundwater and surface water monitoring important?

Groundwater and surface water monitoring is important because water quality can change over short periods, particularly after pollution incidents, rainfall, drought or remediation works. Regular monitoring provides early warning of contamination, helps protect drinking water supplies and ecological receptors, and supports accurate risk assessments.

How are groundwater levels monitored?

Groundwater levels are commonly monitored using borehole standpipes / monitoring wells together with dip meters (essentially tape measures that sound when in contact with water) or data loggers. Data loggers can be set to record groundwater levels continuously at intervals ranging from 5 seconds to 24 hours, allowing changes in the water table to be assessed over time.

What does groundwater quality monitoring test for?

Groundwater quality monitoring can include physical, chemical and biological testing. Common parameters include pH, temperature, nitrates and contaminant concentrations, with results used to assess groundwater quality, identify pollution sources and compare findings against relevant standards such as Drinking Water Standards.

What equipment is used for groundwater monitoring?

Groundwater monitoring may utilise borehole standpipes/monitoring wells, with groundwater levels measured with dip meters or data loggers, samples collected using disposable bailers, inertial pumps or low-flow sampling equipment, and the retrieved samples being placed in sample containers appropriate for the intended analysis.

Groundwater Monitoring and Surface Water Monitoring

The retrieval and analysis of water samples often forms an important element of a Phase II Ground Investigation. This may comprise the sampling of groundwater from borehole standpipes, the collection of samples from surface water features such as rivers, streams, ponds and lakes, and/or the retrieval of samples from man-made features such as drainage systems and outfall pipes. Information collected via water monitoring, such as groundwater level, flow direction and the quality of both groundwater and surface water, is used to track variations in the water-table, determine hydrogeological parameters, and assess the quality of water within an aquifer or watercourse. This information feeds into the ground model (a representation of the site geology, hydrogeology, surface hydrology and contamination sources) to help describe the interactions between the different water bodies and the potential risks to specific receptors such as potable abstraction boreholes and environmentally sensitive watercourses.

Groundwater is important for water supply, agriculture and ecosystems, but can transport contaminants onto a site from off-site sources, pick up contaminants from on-site sources, and convey contaminants to neighbouring sites or receptors such as watercourses. Determining the range of contaminant concentrations within groundwater across a site area, at locations off-site and within local surface waters, are all necessary elements to form an accurate ground model from which to base risk assessments and potential mitigation strategies. Regular monitoring can provide early warnings of contamination and prevent sensitive receptors from being impacted. Good quality monitoring data is also essential should this be required for modelling purposes when undertaking a Detailed Quantitative Risk Assessment.

Due to the dynamic nature of the water environment, the chemical quality of groundwater and surface water can change over comparatively short periods of time, and can respond quickly to, for example, pollution incidents and remediation works. As such, extended periods of water monitoring are often required to determine changes to groundwater plume concentrations and dimensions, variations in surface water quality, shifts in groundwater levels from year to year and the effects of drought and rainfall.

On some heavily contaminated sites, non-aqueous phase liquids (NAPL) may be present on the surface of the groundwater or at depth. Light Non-Aqueous Phase Liquids (LNAPL), such as fuels and oils, are lighter than water and therefore float on the surface of the groundwater. Dense Non-Aqueous Phase Liquids (DNAPL), such as chlorinated solvents and coal-tar, are heavier than water and therefore continue to sink until they reach low-permeability strata. It is important that groundwater monitoring is designed to identify the presence of LNAPLs (which is generally easier for LNAPL than DNAPL) as they act as ongoing sources for dissolved contamination plumes.

Why Carry Out Groundwater Levels and Surface Water Monitoring?

The regular monitoring of water quality (i.e. the sampling and analysis of water samples at regular intervals over a period of time) is essential for detecting short- to medium-term trends, determining the significance of pollution risks and identifying the likely sources of contamination, which may be important for protecting drinking water supplies, surface watercourses and ecological receptors. Monitoring results can be compared with statutory limits, including Drinking Water Standards (DWS) and Environmental Quality Standards (EQS), to assess compliance and support decision-making.

Water monitoring programmes are often undertaken during and after remediation works to provide evidence that such works are having a positive impact, or to confirm whether natural attenuation processes are occurring (such as chemical and biological degradation, dispersion and dilution).

G&J Water Quality Monitoring Services

GG&J can design and implement appropriate water monitoring programmes with a suitable frequency to ensure reliable data is obtained in accordance with the monitoring objectives. Monitoring can be undertaken from monitoring wells/standpipes and from specific locations on surface water bodies. G&J use suitable in-situ testing and sampling techniques such as disposable bailers, inertial pumping and low-flow sampling that are appropriate to the contaminants of concern and the monitoring objectives.

We also utilise data loggers that can be installed in standpipes and set to record groundwater levels continuously over an extended period. Continuous measurements taken over the short, medium or long term can improve understanding of diurnal, tidal and seasonal variations in groundwater levels and enhance the hydrogeological model.

Geoenvironmental Consultants Ltd