HYDROGEOLOGICAL SERVICES

Groundwater Monitoring & Analysis

Groundwater level and hydrochemical/contaminant monitoring are critical for developing understanding of groundwater flow and quality so as to achieve optimal resource management and protection. The scale and duration of monitoring projects may be highly variable, from individual wells, to catchments, to regional aquifer studies, and from days to years depending on the objectives of the monitoring program.

We offer bespoke groundwater, spring and surface water monitoring design and execution tailored to client requirements. We are strong advocates of rigorous QA/QC procedures and hold that fewer reliable data are better than more poor quality information. Sampling and data handling QA/QC are often either lacking or not correctly implemented, and it is important for those conducting sampling to have a vested interest in data quality, as well as for those interpreting data to understand problems that may have occurred in the field.

The natural and contaminant hydrochemistry of aquifers provides abundant information about the provenance, history and quality of groundwater. We are able to offer expert advice on the design and conduct of hydrochemical sampling campaigns, in both water supply and contaminated land situations. We offer sampling services according to the relevant British Standards and always use UKAS and MCERTS accredited laboratories for analysis.

With nearly two decades of experience in groundwater monitoring and analysis, including ultra-low concentration and forensic contamination studies, we take pride in our focus on delivering high quality groundwater science to best inform management decisions.

Karst

We have extensive experience of working with karst aquifers (please see Publications and Projects pages) and offer consultancy services relating to:

Groundwater/Surface water interactions in karst

– Karstic aquifers (e.g. the Carboniferous limestone, the Chalk and various other Permian and Jurassic limestones) are typified by sinking streams, large springs and subsurface channel flow.

Flow interaction between the surface and subsurface is not generally amenable to standard methods of hydrogeologic analysis and great care must be taken to ensure that appropriate methodologies and techniques of analysis are employed in karst aquifers.

Contaminant transport in karst

– Karst aquifers are particularly vulnerable to contamination due to high groundwater velocities (up to km/d) and limited dilution and attenuation.

– Sinking rivers, preferential flow, turbulent flow and other karstic features result in particular groundwater management requirements for karst.

– We offer Source Protection Zone (SPZ) delineation and testing, especially where Equivalent Porous Medium (EPM) models, such as MODFLOW, have been used to determine well or spring catchments and 50 and 400 day travel times in karst aquifers.

– Planning, conduct and interpretation of tracer tests. This information is useful for SPZ definition/testing as well as for characterising karstic response to pollution events, e.g. for how long may a particular well/borehole remain out of service following a pollution event.

– Management strategies for wells/wellfields in the event of pollution.

Karst water supply

– Optimisation of water resources from karst.

– Karst water quality analysis and optimisation.

Tracer tests

Within the UK, injected (or artificial) tracers are particularly useful for testing Source Protection Zones around wells, which are typically defined using MODFLOW models to determine 50 day and 400 day travel time boundaries, in addition to the well catchment. Tracer tests may be used post-modelling, to test model findings, or pre-modelling to constrain the modelling effort.

A comprehensive tracer test may entirely obviate the need for modelling, which is frequently unable to characterise potential contaminant transport with any great accuracy, especially in bedrock aquifers.

Other industry-relevant uses include the determination of potential contaminant sources and as contaminant analogues for the prediction of aquifer recovery following pollution. Tracer-derived information is generally useful for understanding the origin, quality and vulnerability of groundwater supplies.

We have considerable expertise in the conduct and analysis of artificial tracer tests (please see our Publications page) and can offer a comprehensive tracer testing service which may include the following elements:

– Cost-Benefit analysis of tracer testing

– Appraisal of possible outcomes prior to testing

– Regulator liaison

– Source Protection Zone delineation

– Source Protection Zone testing

– Aquifer response and recovery from pollution events

– Determination of principal contaminant transport and storage mechanisms in your aquifer/well field

– Determination of contaminant sources and analysis of likely future behaviour in your aquifer/well field

– Inputs into/testing of groundwater modelling efforts

We have good regulatory connections and are able to produce tracer testing programs that will be acceptable to the regulator in Public Water Supply and Private Licensed Abstractions situations. Please CONTACT us for further details.

Pumping Test conduct and analysis

For the determination of:

– Sustainable yield of a groundwater abstraction

– Well or borehole performance

– Deployable output of a well/wellfield

– Site dewatering characteristics

– Estimation of aquifer parameters

– Optimal operational management systems

Tests are conducted according to BS ISO 14686:2003 and completed in agreement with the Environment Agency.

Groundwater Modelling

Typical applications of groundwater modelling include estimating the water balance of a catchment, simulation of groundwater flows, spring discharges, river-aquifer and lake-aquifer interactions,  assessing the impact of changes to the groundwater regime (through changes in abstraction, climate or other factors), setting up/optimising monitoring networks, modelling sea-water intrusion, mine/quarry dewatering, landfill siting, establishing groundwater Source Protection Zones and modelling chemical migration in the saturated zone.

Whether using analytical or numerical models, EGG Consultants Ltd. have adopted the following guidelines to ensure that modelling achieves the desired objectives:

Model Objectives

Model objectives should be closely defined as these will profoundly impact the modelling effort required.

Hydrogeological Characterization

Proper characterization of the hydrogeological conditions at a site is necessary in order to understand the  importance of relevant flow or solute transport processes. Without proper site characterization, it is not possible to select an appropriate model or develop a reliably calibrated model.

Model Conceptualization

Model conceptualization is the process in which data describing field conditions are assembled in a systematic way to describe groundwater flow and contaminant transport processes at a site. The model conceptualization aids in determining the modelling approach and which model to use.

Modelling Software Selection

After hydrogeological characterization of the site has been completed and a Conceptual Site Model (CSM) developed, a groundwater model is selected. The selected model should be capable of simulating conditions encountered at a site. For example, analytical models can be used where field data show that groundwater flow or transport processes are relatively simple. Similarly, one-dimensional/ two-dimensional/ three-dimensional groundwater flow and transport models may be selected based upon the hydrogeological characterization and model conceptualization.

Model Design (Input Parameters)

Model design includes all parameters that are used to develop a calibrated model. The input parameters for a numerical include model grid size and spacing, layer elevations, boundary conditions, hydraulic conductivity/transmissivity, recharge, any additional model input, transient or steady state modelling, dispersion coefficients, degradation rate coefficients etc.

Model Calibration

Model calibration consists of changing values of model input parameters in an attempt to match field conditions within some acceptable criteria. Model calibration requires that field conditions at a site be properly characterized. Lack of proper site characterization may result in a model calibrated to a set of conditions that are not representative of actual field conditions.

Sensitivity Analysis

A sensitivity analysis is the process of varying model input parameters over a reasonable range (range of uncertainty in value of model parameter) and observing the relative change in model response. Typically, the observed change in hydraulic head, flow rate or contaminant transport are noted. Data for which the model is relatively sensitive would require future characterization, as opposed to data for which the model is relatively insensitive.

Model Verification

A calibrated model uses selected values of hydrogeologic parameters, sources and sinks and boundary conditions to match historical field conditions. The process of model verification may result in further calibration or refinement of  the model. After the model has successfully reproduced measured changes in field conditions, it is ready for predictive simulations.

Predictive Simulations

A model may be used to predict some future groundwater flow or contaminant transport condition. The model may also be used to evaluate different remediation alternatives. However, errors and uncertainties in a groundwater flow analysis and solute transport analysis make any model prediction no better than an approximation. For this reason, all model predictions should be expressed as a range of possible outcomes that reflect the assumptions involved and uncertainty in model input data and parameter values.

Performance Monitoring Plan

Groundwater models are used to predict the migration pathway and concentrations of contaminants in groundwater. Errors in the predictive model, even though small, can result in gross errors in solutions projected forwarded in time. Performance monitoring is required to compare future field conditions with model predictions.

Please get in touch at:

enquiries@eggconsult.co.uk

Tel: 0161 818 7333