See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/349988433

A proposed framework for hydrogeological conceptual modelling.

Article in Water and Environment Journal · March 2021

CITATIONS READS

6 584

2 authors, including:

Rick Brassington
Newcastle University
58 PUBLICATIONS 66 CITATIONS

SEE PROFILE

All content following this page was uploaded by Rick Brassington on 30 March 2021.

The user has requested enhancement of the downloaded file.

 Water and Environment Journal. Print ISSN 1747-6585

A proposed framework for hydrogeological conceptual modelling

F. C. Brassington, FCIWEM1 & P. L. Younger, FREng, FCIWIEM2
1
School of Civil Engineering & Geosciences, Newcastle University, Newcastle upon Tyne, UK and 2Sir Joseph Swan Institute, Newcastle University,
Newcastle upon Tyne, UK

Keywords Abstract
conceptual model; environmental assessment;
The process whereby hydrogeologists interpret the available information to
groundwater; hydrogeology; impact
assessment; risk. produce a justifiable set of simplifying assumptions to describe a groundwater
system is called conceptual modelling. Although this process is inherent in all
Correspondence hydrogeological assessments and can therefore be regarded as synonymous
F. C. Brassington, Rick Brassington Consultant with hydrogeological practice there are no standard specifications for it. A
Hydrogeologist, 12 Culcheth Hall Drive, framework for conceptual modelling has been designed to both assist in the
Culcheth, Warrington WA3 4PS, UK. Email: planning and process of the work and to provide an audit trail to facilitate
rick@brassingtonhydrogeology.co.uk
independent scrutiny. The application of this framework is illustrated by two
case histories, one of a small-scale investigation for a proposed cemetery and
doi:10.1111/j.1747-6593.2009.00173.x
the other of an investigation of the migration of a large-scale sulphate plume in
a public supply aquifer. This framework is applicable across the full range of
scales of hydrogeological systems, and indeed is readily extendable to other
analogous areas of endeavour in the management of natural resources.

related environmental sciences. Whereas any practice of

Introduction hydrogeological judgements being made by those without
The requirement by UK environmental regulators for adequate training is not condoned, this common practice
auditable risk assessments has continued to increase cannot be ignored and emphasizes the need for a standard
across a wide range of activities that have potential and auditable method to make these assessments as
environmental impacts (Anon 2000). Examples where suggested here. The framework will also provide guidance
hydrogeological assessments are needed include applica- for those with limited practical experience in this field and
tions to the Environment Agency for new abstraction may also act as an aide-mémoire for more experienced
licences, waste management licences to operate landfills hydrogeologists. An essential element is an audit trail that
or discharge consents for an effluent to go to a soakaway. allows a third party to undertake an independent review.
The natural mineral water regulations specifically require Such audits may be part of the appraisal undertaken by a
a hydrogeological assessment to be completed to identify regulator of an application and are also part of the
the catchment for the source. Planning applications for scrutiny carried out at a public inquiry or even a court
quarrying and mining need to be supported by hydro- case.
geological assessments to define the potential impacts.
Hydrogeological evaluations are also often required to
demonstrate the sustainability of any private water supply
before planning consent is given for new properties in
Conceptual modelling
areas where mains water supplies are not available. Such Models are of fundamental importance in most scientific
evaluations are also used by developers, industry and investigations and have become one of the principal tools
many others to help located new water supply boreholes, of modern applied science (Silvert 2001). Models range
for example, or to assess the feasibility of a geothermal from physical or imaginary objects to three-dimensional
energy scheme for a new building. structures, descriptions, equations or combinations of
The present national shortage of qualified hydrogeolo- several of these groups. In order to develop any of these
gists (Brassington 2004) means that many of the straight- models it is necessary to create a theory-based description
forward hydrogeological assessments are undertaken by that represents the phenomena being studied founded
scientists from other branches of geology or even from on a set of variables with logical and quantitative

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 261
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

relationships. Such a theory-based description is termed a the process itself being shown in Fig. 1. The assumptions
conceptual model. made about each predominant characteristic of a ground-
The procedure whereby hydrogeologists interpret the water system are repeatedly re-evaluated to further de-
available information to produce an adequate description velop understanding as new evidence is acquired and
of a groundwater system is called conceptual modelling (e.g. tested against the evolving conceptual model, frequently
Rushton 2003) and applies to all scales of hydrogeological taking a number of iterations to accomplish. Figure 2
work. A conceptual model will comprise an assemblage of represents this process as an upward flowing spiral.
justifiable, simplifying assumptions which summarize the This iterative process of development by testing each
principal characteristics of the real system so that its aspect forms the structure for all hydrogeological projects,
behaviour may be more clearly understood. The model even those that are limited to a desk study using only
should be developed so that it represents the current published information. It can identify the need for new
consensus on system behaviour, whether this is informed fundamental information as is illustrated by a study of the
by direct interpretation of published information with or Sherwood Sandstone aquifer in the Lancashire Fylde by
without field and laboratory data, or whether further the Environment Agency (Seymour et al. 2006). When
understanding has been extracted from these data by numerical methods were used to simulate groundwater
mathematical modelling. In most cases, the purpose of fluctuations predicted groundwater levels in the Preston
developing a conceptual model is to arrive at a sufficient area did not match the historical records unless the
understanding of the relationships between the principal aquifer thickness was significantly reduced. A borehole
characteristics of a system so that deductive and/or math- was drilled that showed significant thinning of the aquifer
ematical methods can be used to evaluate possible out- beneath the centre of Preston possibly resulting from a
comes of changes within the system for a range of feasible previously unknown horst structure.
situations. An example of such changes is variations in
abstraction patterns within a wellfield and the possible
outcomes may be the potential impacts on surface water
Available guidelines
flows and wetlands resulting from the associated changes Some form of structured approach to system interpreta-
in groundwater levels. tion based on scientific reasoning and an understanding
Conceptual modelling should always precede any at- of geology has been used since the earliest days of applied
tempt to mathematically model a groundwater system hydrogeology (Mather 2004). However, formal ‘concep-
(Environment Agency 2001, 2002; Rushton 2003; Younger tual modelling’ as such has only begun to be discussed in
2007). However, conceptual modelling does not necessarily hydrogeological textbooks relatively recently, with many
have to be followed by mathematical modelling at all standard works including little or no mention of concep-
(Brassington 2006; Younger 2007). Rather, the development tual modelling as illustrated by Table 1.
of conceptual models of groundwater systems is frequently A number of textbooks provide some guidance (e.g.
an end in itself, as it forms the basis for the majority of Bear & Verruijt 1987; Rushton 2003; Younger 2007)
hydrogeological projects where the understanding of the although none is in sufficient detail to act as an instruc-
system provided by the conceptual model allows decisions tion manual. Several guidance manuals have been pro-
to be made and the risks associated with new developments duced although they generally focus on large-scale and
to be evaluated to a satisfactory level of accuracy. often, specialized investigations. Guidance on conceptual
The scale of hydrogeological assessments and investiga- modelling as a precursor to a large-scale mathematical
tions is very variable. At one extreme, a desktop study model-based study is provided in Environment Agency
using published data to locate a new borehole site may publications (2001, 2002), written primarily as a guide for
take an experienced hydrogeologist less than half a day. regional-scale investigations and would be difficult to
This contrasts with the effort required in a major investi- apply to smaller-scale projects. More recent Environment
gation such as that by UK-Nirex (Chaplow 1996) for the Agency publications (2003a, b) include advice and gui-
proposed deep repository for radioactive waste at Sella- dance on undertaking hydrogeological assessments speci-
field that took a large multidisciplinary team of geologists, fically in relation to landfills with similar advice relating
hydrogeologists and many other specialists most of a to new groundwater abstractions in a more recent Envir-
decade to complete. Most groundwater studies fall be- onment Agency document (2007). These three later pub-
tween these extremes involving some fieldwork in addi- lications refer to the importance of creating an audit trail
tion to the collection and interpretation of the available in this process. The Institute of Geologists of Ireland
information. (Anon 2002) provides useful information for the geologi-
Data acquisition is key to the conceptual modelling cal and hydrogeological aspects of environmental impact
process with the relationship between obtaining data and assessments. The same organization has also published a

262 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

Definition of purpose &

project brief
Define purpose

Field Data Scoping study

Report
scoping study

Collation of data &

formulation of
Develop conceptual conceptual model
Field Data
model

Phase 1
Report
conceptual model

Project review

Development of
historical model
Construct historical
numerical model
Field Data

Phase 2
Compare results with field
data & refine model

Report
historical numerical
model

Predictions & options

appraisal
Predictions & option
Field Data
appraisal
Phase 3

Report
prediction simulations

Final report

Further operational
use
Update numerical
Field Data
model

Report
Maintain model as an Fig. 1. Flow chart for developing a conceptual
model evaluation &
operational tool
update model in large-scale investigations (after Environ-
ment Agency 2002.r Environment Agency copy-
right. All rights reserved).

checklist of data types required for the assessment of new (2000) advocate the development of a conceptual model
quarries (Anon 2007) that has a wider application. Most to aid planning a groundwater contamination study.
of the documents mentioned here are available on-line in El-Ghonemy et al. (2004) describe a conceptual modelling
electronic format. methodology for assessing radioactive contaminated land
Cashman & Preene (2001) discuss the development of for BNFL using the low-level radioactive waste disposal
conceptual models as the first step in designing dewater- site at Drigg in Cumbria as an example. The method lends
ing schemes in civil engineering construction. They list itself to detailed investigations of complex contaminated
geological parameters that must be considered as well as sites rather than a more general application. Examples of
the features of the potential dewatering system and conceptual models are given in some text books (e.g.
provide an example set out as a proforma that could be Rushton 2003; Younger 2007). Other examples are in-
used as a template for similar assessments. Bedient et al. cluded in papers on specific hydrogeological topics, and

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 263
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

occasionally are found as the main subject, such as Black Proposed framework
& Brightman (1996), Burgess et al. (2002) and Brassing-
Although inexorably linked, the activities necessary to
ton (2007).
complete a hydrogeological investigation and the metho-
Although these various publications provide advice on
dology of developing a conceptual model are not exactly
the overall process of conceptual modelling, as well as the
the same. The actions at each stage of a hydrogeological
individual considerations that are necessary to achieve it,
investigation are generally focused on collecting informa-
no overall framework has been provided for this activity
tion whereas the emphasis in developing a conceptual
that is generally accepted as a standard approach. The
model is the interpretation of data as they are collected
auditable framework for completing hydrogeological as-
and identifying additional information needed to com-
sessments that is described below is put forward as such a
plete the conceptual understanding. A typical hydrogeo-
standard procedure that can be used in investigations on
logical investigation can be divided into a number of
all scales.
separate parts, each building on the previous one so that
eventually an adequate understanding of the system
being studied may be achieved. It will always be necessary
to tailor the details of the investigation to the needs of
each particular study; however, the essential elements or
phases that would be expected to be included in the
lop
Deve majority of investigations are as set out below (adapted
Best conceptual model
Test
from Brassington 2006):
Process

lop  Desk study

Better conceptual model Deve
Test  Walkover survey
 Exploration
lop
First conceptual model Deve  Monitoring programme
Test
 Data management
elo p  Water balance
Initial ideas Dev
 Completion of the conceptual model.
The various steps in the proposed framework for devel-
Fig. 2. Diagram of the conceptual modelling process (after Environment oping a conceptual model as proposed here, are set out in
Agency 2002.r Environment Agency copyright. All rights reserved). Fig. 3. The order follows the logical sequence taken to

Table 1 Summary of comments on conceptual modelling in selected hydrogeology publications

Publication Comments
Text books
Bear & Verruijt (1987) Provides definition and list of contents for a conceptual model
Bedient et al. (2000) Discusses conceptual modelling in planning groundwater contamination studies
Brassington (2006) Discusses the use of a conceptual model in planning field work and suggests outline procedure
Cashman & Preene (2001) Provide proforma method for use in design of dewatering schemes
Domenico & Schwartz (1997) Not mentioned
Fetter (2001) Conceptual modelling seen as part of mathematical modelling
Rushton (2003) Strongly advocates conceptual modelling as basis of more detailed analysis and gives examples
Todd & Hayes (2005) Not mentioned
Younger (2007) Includes guidance and an example of a conceptual model
Reports and papers
Anon (2002) General information in relation to environmental impact assess
Anon (2007) Useful check-list for planning data collection
El-Ghonemy et al. (2004) Provide method for large-scale nuclear waste related investigations
Environment Agency (2001) Guidance provided – only applies to large-scale investigations
Environment Agency (2002) Guidance provided – only applies to large-scale investigations
Environment Agency (2003a) Guidance provided – concentrates on monitoring around landfills
Environment Agency (2003b) Guidance provided – concentrates on landfill
Environment Agency (2004) No mention of conceptual modelling, outline advice on hydrogeological assessment
Environment Agency (2007) Guidance provided – concentrates on proposed new abstractions
Neuman & Wierenga (2003) Guidance provided in the context of investigations of nuclear installations

264 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

Step Primary sources of Activity Other sources of Review process Audit trail (examples)
information information
1 Define Client’s needs. Define elements of Regulator’s policy Review with Minutes of meetings; letters/emails
objectives Regulator’s requirements study needed to documents, laws and regulator and/or client with client/regulator; agreed
Research objectives provide the required regulations before starting statement with client
information project
2 Topography Published topographical Identify water Walk over survey Compare field List of maps used. Copy of field
and surface maps features, estimate observations with notes
water catchment boundary map information
3 Geology Published topographical Interpret data. Additional mapping Start to develop List of maps and reports; boreholes
maps, geological maps, Identify gaps in and new boreholes conceptual model records; logs for boreholes drilled
reports and borehole information and geophysical during the study; geophysical
records surveys surveys
4 Aquifer The results from Steps 2 Determine need for Site specific Continue developing List of aquifers; records of pumping
framework and 3, reports of pumping field tests and/or information from conceptual model tests and other field tests; copies of
tests and other published laboratory pumping tests or using new data lab test certificates; copies of data
data measurements falling head tests analysis and interpretation reports
5 Groundwater The results from Steps 2, Identify need for Measurements Review conceptual List of observation boreholes;
flow 3 and 4 using published more data points and taken in new model using new copies of groundwater level
topography maps, levelling in to piezometers and/or data. Use computer measurements
borehole records common datum boreholes model to test ideas
6 Aquifer Information from Steps 2, Assess relationships Data from new Review conceptual Copies of data collected/used in this
relationships 3, 4 and 5. Preliminary between pumping tests, model using new step; copies of calculations, flow
results of computer model groundwater levels, water chemistry and data. Use nets etc; records of outputs of each
if used other aquifers and spring/stream flow developing numerical model run in summary
surface water measurements computer model to form; list of assumptions tested in
bodies test ideas each model run
7 Water Long-term records of Assess available Use rainfall, Review conceptual Copies of data used for water
balance hydrogeologically groundwater evaporation and model using new balance calculation
effective precipitation resources using stream flow data to data. Use computer
water balance refine estimates model to test ideas
8 Description Apply conceptual model to assess environmental impacts or further refine computer model to Written description of the
of model make predictions of potential impacts. Any new data and the results of the computer modelling conceptual model illustrated by
should be reviewed against the conceptual model and the assumptions on which it is based diagrams and supplemented by the
records from Steps 1 – 8

Fig. 3. Outline of the proposed framework for conceptual modelling.

develop a conceptual model and defines the information using topographical maps that also have contour informa-
sources, activities, review process and audit trail at each tion that will allow the elevation of each feature to be
step. The repeated reviews are an essential element of the determined. The contours are also used to define the
process and may require earlier stages to be developed surface water catchment areas for comparison with the
further. geological information in the next step and for subse-
quent interpretation. Flow data for springs, streams and
rivers may already be available otherwise it will be
Step 1 – defining the objectives necessary to take field measurements.
The objectives for the investigation must be defined
before the commencement of data acquisition and should Step 3 – defining the geology
be set out in writing and agreed with the client, regulator
The geology of an area controls its hydrogeology; hence, it
or other persons or organizations with interests in the
is essential to understand the types of rocks present in the
outcomes of the project. It is important to ensure the
area of interest, their lithologies and their structural inter-
objectives focus attention on all the key questions that
relationships. This is key to defining the three-dimen-
need answering to ensure that the field investigations will
sional variations in permeability and storage properties
provide all necessary data.
(Younger 1993) and how these influence groundwater
flow directions and rates, and recharge processes. The
information can be derived from existing geological maps
Step 2 – defining the topography and
and reports that are interpreted within the framework of
surface water drainage elevations provided by the topographical maps and may
Groundwater systems are usually closely linked to surface also include records from boreholes drilled for the study
water catchments and in order to understand the hydro- or for other purposes and geophysical surveys. The geol-
geology of an area it is essential that this is undertaken in ogy also enables the relationship between the ground-
the context of both the surface and groundwater catch- water and surface water systems to be understood.
ment areas. Key surface water features such as water- The review of the available geological information may
courses, springs and ponds should be identified, initially show that more data are needed, possibly involving

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 265
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

additional field mapping, drilling exploratory boreholes or that are not at any risk or may not be relevant to the
geophysical surveys. Such additional field work should be assessment.
planned using the results of the desk study with each
element of the new work testing specific aspects of the
developing conceptual model. Step 5 – defining groundwater flow
directions
Groundwater flow directions are best defined using rest
Step 4 – defining the aquifer framework groundwater levels measured in nonpumping boreholes
and boundaries interpreted using the geological information and informa-
tion on the aquifers taken from Step 4. Information taken
The aquifer or aquifers being studied exist as three-
from topographical maps on the location and elevation of
dimensional bodies and consequently the aquifer bound-
springs and surface watercourses is also used.
aries need to be defined on the top, bottom and all sides.
Groundwater flow is driven by a three-dimensional
This information is often most easily understood as a
field of hydraulic heads from which it follows that the
series of maps and cross sections.
vertical component of head is likely to drive flow along
The geological information derived from Step 3 should
boreholes, even where these penetrate an apparently
be used to identify the aquifers and to estimate the
single aquifer unit (Fetter 2001). Measurements of both
possible values for the aquifer properties. Two major
groundwater levels and water chemistry are likely to be
reports (Allen et al. 1997; Jones et al. 2000) of the
altered by such intraborehole flow, and the interpretation
hydraulic properties of aquifers in England and Wales
of field data must take this possibility into account
provide a good starting point in these countries. Robins
(Brassington 1992).
(1990, 1996) provides information on the major aquifers
It is likely that the desk study phase of the investigation
in Scotland and Northern Ireland. More detailed local
will comprise the initial appraisal of the data used in Steps
information may be available in published reports such as
1–4 of the conceptual modelling process. A walkover
Plant et al. (1999) and from data held by regulators such as
survey will then help further develop understanding and
the Environment Agency and Scottish Environment Pro-
should be planned in advance from the information
tection Agency (SEPA).
collated during the desk study bearing in mind that for
Pumping tests may be required to provide data from
large study areas several such surveys may be needed.
which the hydraulic properties can be calculated and
Such first-hand observations are important as they allow
should be conducted carefully to provide reliable data
the hydrogeologist to picture the geology and envisage
following the procedures described by Brassington (2006)
how groundwater is flowing through the rocks, using the
and the British Standards Institute (2003). The data
information assembled in the desk study. Groundwater
should be analysed following appropriate methods (e.g.
flow is usually controlled by lithology and secondary
Kruseman & de Ridder 1990) and details of these calcula-
structural features, such as joints, cracks and fissures.
tions kept as part of the audit trail.
Flow generally converges on natural discharge zones,
Groundwater is part of the hydrological cycle and the
which typically correspond to the lines of streams and
potential links between surface and groundwater systems
rivers running along valley bottoms. Bearing these gen-
in the study area must be identified. A comparison of
eralizations in mind it is possible to envisage the overall
information from the geological maps and watercourses
groundwater flow system.
shown on topographical maps will allow an initial assess-
ment of these relationships and provides a first approx-
imation of the most appropriate aquifer catchment area
Step 6 – defining the aquifer
to be studied. As more detailed information is accumu-
lated these boundaries may well be refined. This exercise
relationships
is important to the next step by providing clues to This step follows naturally from Steps 4 and 5 and
where aquifer recharge occurs, the discharge areas and involves considering the flow rates and volumes of
groundwater flow paths. Defining the groundwater groundwater flowing through the system from one part
catchment boundaries based on an interpretation of the of an aquifer to another, between aquifers and between
available data is far better practice than the common use the aquifers and the surface water system. Such flow
of a fixed radius from the point of interest (e.g. proposed should be quantified and will usually involve calculations
new borehole). Such an oversimplified approach may based on the Darcy equation or the Dupuit assumption.
miss identifying key water features at risk from the This is the point to decide on the need for a numerical
proposal or equally, can imply threats to water features model to assist in the development of the conceptual

266 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

understanding and/or to make predictions on aspects of applications of the conceptual modelling process ranging
the system when part of it is stressed (e.g. by new or from simple desk studies to complex regional studies. The
increased abstraction). purpose of the audit trail is to record the sources of data
New data are likely to be gathered during this step and that have been used and the reasons for the way that the
should be compared with existing data sets by repeating data have been interpreted. An audit trail simply com-
earlier steps of the framework. The new data may confirm prises copies of the correspondence relating to the project
existing ideas, expand on developing concepts or even and a list of all the information sources (possibly including
challenge them. This is also the point in the process where actual records of field measurements) that have been used
the current understanding of the system should be criti- and will enable a third party to follow the logic steps used
cally evaluated to identify any gaps in the available throughout the conceptual modelling process. A record of
evidence which could be addressed by field investigations. the changing and evolving understanding should be
As financial budgets are always critical, the cost-benefits included with brief notes on what changes were made
need to be taken into account before any decisions are and why. Figure 3 includes examples of the documents
made on this additional work. and records that will constitute the audit trail in most
groundwater investigations.
The report for a small-scale study should contain this
Step 7 – water balance information as a list of reports and maps used and the
A water balance involves the calculation of the volume of explanation of the logic behind the hydrogeological inter-
water both entering and leaving the aquifer system being pretation. The key assumptions made and their justifica-
studied and incorporates the elements shown in Table 2. tions should be summarized in a table. Larger studies may
This is an important factor in all groundwater assessments involve meetings to discuss progress at which aspects of
as it defines the resources available to support wetlands the hydrogeological interpretation may be discussed and
and provide dilution factors in contamination studies. agreed with notes kept as part of the audit trail. Large
Where numerical models are being developed, a water projects may require small associated studies to reviews
balance may be used to gauge the accuracy of the model aspects of the hydrogeological system with the reports on
in replicating the hydrogeological processes involved. such studies forming part of the audit trail. Where a
numerical model is developed it is standard practice to
keep a record of all model runs including the aspects of
Step 8 – describing the conceptual model the system being tested by that run and the conclusions
The continual review of the available information and drawn from the exercise. These records should form part
collection of necessary data will eventually result in the of the project reports although they are often kept as
development of a conceptual model that is adequate for reference documents and not part of the main report or its
the purposes set out in the objectives (Step 1). When that appendices.
point is reached the conceptual model should be set out in
a written description that is illustrated by maps and
diagrams as necessary. It is then used to answer the
Example application of the conceptual
questions posed in the objectives. In small-scale studies modelling framework
the description of the conceptual model is likely to be brief The application of this proposed framework to real cases is
and may be simply presented as the conclusions of the illustrated using two examples: the first is an assessment
report. In larger projects it is likely to be a separate section of the potential impact on groundwater sources from a
of the report. proposed new cemetery; and the second is a more com-
plex investigation of the migration of a contaminant
plume through a major aquifer.
Audit trail The potential for water contamination has to be identi-
An essential feature of the conceptual modelling process fied before a new cemetery can receive the necessary
is that it should be auditable and is a requirement in all permissions. Brassington (2006) provides an example of

Table 2 Water-balance equation

Inflows Outflows
Rainfall+recharge from surface water+seawater intrusion+inflow = Abstraction+spring flow+base flow in rivers+discharge to the  Change in
from other Aquifers+leakage+artificial discharge sea+flows to other aquifers+evapotranspiration aquifer storage

Adapted from Brassington (2006) with permission from John Wiley & Sons.

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 267
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

Step Primary sources of Activity Other sources of Review process Audit trail
information information
1 Define Environment Agency’s To define hydrogeology, Environment Agency’s Discussions with Records of
objectives policy. Need to avoid groundwater flow policies and guidelines Environment Agency and correspondence
water contamination directions and identify risk client (including emails) with
using source, flow path, the Environment
receptor model Agency and client
2 Topography Published 1: 25 000 Identify water features. Walk over survey Compare field and Name of map used
and surface scale Ordnance Define topography of confirmed water map data and copy of field
water Survey map area features on map notes/photographs
3 Geology Published OS maps and Define drift and solid Geological information Compare field data List of BGS maps and
BGS maps, reports geology of area from piezometer with map and report report; piezometer
(Rees & Wilson 1998) construction details
4 Aquifer The geological Aquifer boundaries Information on aquifer The conceptual model List of data sources
framework information was used derived from geology. properties in Jones et now defined the three- used.
to delineate the extent Need for flow line al. (2000) dimensional aquifer.
of the aquifer information identified No additional
information needed.
5 Groundwater Piezometer data Interpret groundwater Water level data from Compare all water Piezometer records;
flow interpreted using contours, flow pumping station level data and review copies of maps
results from Steps 2, 3 directions. Flow lines boreholes. against developing
and 4. used as boundaries conceptual model
6 Aquifer Information from Steps Re-examine geological No requirements for Review conceptual Copies of data used in
relationships 2, 3 and 4. information to consider additional information model using new data. this Step
inter-aquifer flow were identified.
7 Water Long-term average Calculate inputs and Licensed quantities for Compare flux with Copies of data used.
balance monthly MORECS outputs of water pumping station. abstraction figures Consultancy report
data used to quantify balance
groundwater flux
8 Description The conceptual model was described in consultancy report.
of model

Fig. 4. Development of the conceptual model for a cemetery study.

such an investigation that led to a successful application (Fig. 5). These show that the groundwater flow is towards
for permission to construct the cemetery. Figure 4 shows the north-west and not towards the spring as was initially
the steps taken in developing the conceptual model and assumed from the topographical information. Flow lines
lists sources of information used in completing each step were used to define lateral boundaries for the study area.
in this process. Records show that groundwater levels at a major
The site lies on the north-west side of the Potteries groundwater source in the sandstone aquifer some 2 km
where a sheet of glacial sand overlies Upper Carbonifer- from the proposed cemetery have fallen by about 30 m
ous mudstones directly beneath the site and extends since the wells were constructed some 70 years earlier.
westwards over part of the Sherwood Sandstone aquifer This implies that groundwater levels have declined across
located on the eastern edge of the Cheshire Basin with a the sandstone aquifer thereby encouraging groundwater
faulted boundary separating the solid formations. The in the sands to drain into the sandstone and changing its
geology of the area is shown on published British Geolo- flow direction away from the spring.
gical Survey maps and is described by Rees & Wilson The resulting conceptual model was used to assess the
(1998). In Fig. 5 the proposed cemetery is the field potential impact from the anticipated number of burials
immediately to the east of the cricket ground. It is located using data published by the Environment Agency (2004).
on a watershed between two minor watercourses. The It was concluded that the available dilution in the
closest surface water feature lies about 100 m to the south groundwater flow means that the source would not be
and comprises a small spring forming the head of a minor impacted by the additional loading. The relatively simple
watercourse. A preliminary conceptual model supposed hydrogeological system and limited groundwater abstrac-
that the groundwater flow from the site would be to the tions meant that it was not necessary to develop a
south in the direction of this spring. numerical model to assess the potential impacts.
Groundwater levels were monitored using a series of The second example is an investigation of the migra-
six purpose drilled standpipe piezometers installed round tion of a plume of contaminated groundwater originating
the periphery of the site that also provided information on from abandoned coal workings below the Magnesian
the sand thickness. Measurements were taken over a Limestone aquifer in North-east England. This project led
12-month period to identify the seasonal variation in to the successful application of a numerical model based
groundwater levels with the highest recorded levels on a conceptual model derived in accordance with the
(March 2004) used to construct groundwater contours proposed framework. Although a summary of the project

268 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

113.2 m Pear tree farm

SPZ 3
113.4 m
113.6 m
114. 273
113.408
113.243 Chasele
113.7 m
Cricket Pol
ground Off
113.3 m 113.428
114.193

113.658
113.5 m

Key
Wall farm
113.428
Spring Piezometer with elevation Fig. 5. The proposed cemetery is the field to the
in metres OD
east of the cricket ground. Groundwater contours
113.2 m have been constructed from measurements
made on the six piezometers shown (after Bras-
Groundwater contour
sington 2006 with permission of John Wiley &
0 Scale 100 m Sons. Map r Crown Copyright. All rights re-
served).

as a whole has been presented by Neymeyer et al. (2007), sponse to annual recharge events (Parkin & Adams
the detailed explanation of the application of the con- 1998). It was therefore concluded that, for purposes of
ceptual modelling framework has not yet been published. modelling plume migration in the limestone aquifer, it
The steps taken in developing the conceptual model are could be safely assumed that flow in the coal workings
set out in Fig. 6 and details the sources of information would be accounted for adequately by representing them
used in completing each step in the conceptual modelling with a head-dependent flow boundary condition applied
process. The conceptual model described by Neymeyer across the Carboniferous–Permian unconformity. There
et al. (2007) defined the aquifer boundaries using pub- was no need on this occasion to increase model complex-
lished geological mapping supplemented by borehole logs ity and run times by explicitly simulating heads and flows
to define the top and bottom of the limestone aquifer. in the network of flooded mine voids.
Mine records were used to define the extent of the deep The lateral boundaries of the model domain (Fig. 7)
coal mining beneath the limestone and the west to east comprise:
groundwater flow direction was defined from observation (1) a fault to the north (the Butterknowle Fault), which
borehole water level measurements. Figure 7 shows the is known to be associated with a discontinuity in ground-
aquifer boundaries and groundwater flow directions as water levels in the limestone of several metres (assumed
well as the location of the study area in relation to local to be a zero-flow boundary);
towns and the coast. Figure 8 shows an east-west cross (2) the westward limit of the limestone outcrop (also
section that illustrates the geology and the major features assumed to be a zero-flow boundary);
identified in the conceptual model. (3) the River Tees in the south-east (assumed to be a
To the west of the limestone outcrop, hydraulic heads head-dependent outflow boundary);
in the worked Coal Measures is effectively maintained at a (4) a groundwater flow divide in the south-west (zero
relatively constant elevation by the decanting of ‘excess flow boundary);
recharge’ (i.e. recharge over and above that which makes (5) the coast line between the city of Hartlepool and the
its way into the limestone across the unconformity) River Tees (specified head boundary).
through several prolific surface mine water outflows to Mine water migrating into the limestone aquifer from
the River Wear to the west of Bishop Auckland. Prior the Coal Measures is joined by natural recharge. In areas
modelling of the Coal Measures in this area revealed that where glacial deposits are thin or absent, so that the
the high permeability of flow path connections to these limestone aquifer is present immediately below the soil
surface outflows results in an extremely subdued re- surface, recharge rates were estimated from MORECS

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 269
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

Step Primary sources of Activity Other sources of Review process Audit trail
information information
1 Define Environment Agency’s The main objective: to Environment Agency’s Discussions with Records of
objectives policy. Need to quantify the flow of policy; water quality Environment Agency and correspondence (and
maintain public water polluted mine water standards set by the Hartlepool Water emails) with EA and
supplies into the aquifer and Water Framework Company Hartlepool Water
predict its migration Directive Company
2 Topography Ordnance survey maps Topography of area None required Not needed at this List published maps
& surface described from map stage
water
3 Geology There are published Smith and Francis (1967) No other sources of The geological Record of published
topographical maps & contains many information were information covers the geological maps &
BGS maps, reports borehole logs and no needed full extent of the study reports, mainly Smith
(Smith & Francis 1967) insurmountable data area & Francis (1967)
& borehole records gaps were identified
4 Aquifer The geological Boundary conditions The aquifer properties The conceptual model List of data sources
framework information was used to were derived using from Cairney (1972) and now defined the three- used
delineate the extent of methods described by Younger (1995). Coal dimensional aquifer.
the aquifer Anderson and Woessner Authority records used No additional
(1997) & Rushton to identify areas where geological information
(2003) up flow from flooded was required
mines could occur
5 Groundwater Environment Agency Interpret groundwater Water level data from Once the conceptual Observation borehole
flow observation borehole contours and flow water company model development records; copies of
data interpreted using directions boreholes was relatively mature maps; copies of results
results from Steps 2 and MODFLOW was used from computer runs
3 to refine it and calculate
flow rates
6 Aquifer Information from Steps Evaluate results of No requirements Review conceptual Copies of data used in
relationships 2, 3 and 4. First results of model runs against the identified for additional model using new data this Step; copies of
computer model. conceptual model as information were Use developing results from computer
Borehole groundwater developed at this identified computer model to test runs
chemistry data used to stage ideas
define pollution plume
7 Water Abstraction data from Calculate inputs and Geological records to Identify areas with Copies of data used.
balance water companies and outputs of water identify areas covered reduced recharge. Printouts and results of
other abstractors. Used balance with thick clayey drift Modify conceptual early simulation runs
MORECS methodology model Unpublished MSc
(Hough and Jones 1997) report
8 Description The conceptual model is described in words by Neymeyer et al. (2007) & in the text. It was used as the basis of the numerical
of model simulations using MT3D (Zheng & Wang 1999) that were carried out to predict the migration of the polluted mine water

Fig. 6. Development of the conceptual model in a polluted limestone aquifer.

data (Hough & Jones 1997) to average around 0.77 mm/ concentrations in excess of the drinking water limit
day. In areas with thick ( 4 1 m) mantles of glacial (Neymeyer et al. 2007).
deposits, recharge rates were assumed to be considerably
less. Application to the local setting of reasoning sug-
gested by Brassington (2006) resulted in reductions in
Conclusions
estimated infiltration rates to an average of only 0.22 mm/
day in these areas. (1) The development of a conceptual model is the funda-
The culmination of the mathematical modelling of mental approach used in all hydrogeological assessments
flow, and then of solute transport, amounted to refine- ranging from simple desk studies to complex large-scale
ments in the understanding enshrined in the conceptual investigations. It is an iterative process involving the re-
model. As such, the entire process of numerical modelling evaluation of the interpretation as new information is
is essentially an exercise in assessing the consistency obtained until an adequate understanding of the system
between the conceptual model and the data upon which has been developed to meet the needs of the task in hand.
the derivation of the conceptual model was based (2) No widely accepted methodology that defines this
(Konikow 1981). It is only when satisfaction has been process exists, possibly because the process is necessarily
reached that such consistency exists and it becomes iterative and therefore complicated to describe. A number
justifiable to use a mathematical model to ask specific of guidelines have been published that are appropriate
questions by means of exploratory forecasting runs. In for large-scale studies and consequently are too compli-
this case the questions which were addressed related to cated to be easily adopted for more routine projects.
the likely time period before water supply boreholes Other guidelines are also available for specific types of
might be expected to be producing water with sulphate investigations.

270 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

Fig. 7. The map shows the location of the study

area in relation to towns in North-east England.
The contours show the extent of the migration of
a plume of high sulphate groundwater as defined
by the observation borehole data. See Fig. 8 for
cross section that gives geological detail. [Repro-
duced from Neymeyer et al. (2007) with permis-
sion of the Geological Society.]

Fig. 8. Diagrammatic cross section summarizing

the key features of the conceptual model for
groundwater flow through the magnesian lime-
stone aquifer including mine water upflow from
the underlying flooded mine workings. [Repro-
duced from Neymeyer et al. (2007) with permis-
sion of the Geological Society.]

(3) As hydrogeological assessments are becoming in- record the purpose of the study, the logic processes
creasingly required for a wide range of environmental involved in the development of the conceptual under-
impact assessments it is important for the process to be standing sources of information and may include copies of
standardized and auditable. This will ensure that high data records. This audit trail will allow an independent
standards of assessments are maintained with the con- third part to make a comprehensive evaluation of the
sequential advantages of environmental protection. work carried out. Such assessments are important in
(4) The framework proposed in this paper is designed to reviews of applications by regulators and in the scrutiny
be used for all scales of hydrogeological investigations and carried out during a public inquiry.
includes an audit trail. The two examples used to illustrate
the process have been chosen from either end of the scale To submit a comment on this article please go to http://
in terms of extent and detail of investigation. The audit mc.manuscriptcentral.com/wej. For further information please see the
trail comprises a complete record of the documents that Author Guidelines at www.blackwellpublishing.com/wej

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 271
A proposed framework for hydrogeological conceptual modelling F. C. Brassington and P. L. Younger

References Domenico, P.A. and Schwartz, F.W. (1997) Physical and Chemical
Hydrogeology (2nd edn). John Wiley & Sons, New York.
Allen, D.J., Brewerton, L.J., Coleby, L.M., Gibbs, B.R., Lewis, El-Ghonemy, H., Watts, L. and Fowler, L. (2004) Treatment of
M.A., MacDonald, A.M., Wagstaff, S.J. and Williams, A.T. Uncertainty and Developing Conceptual Models for
(1997) The physical properties of the major aquifers in England Environmental Risk Assessments and Radioactive Waste
and Wales. British Geological Survey Technical Report WD/ Disposal Safety Cases. Environ. Int., 31, 89–97.
97/34 & Environment Agency R&D Publication 8, Key- Environment Agency. (2001) Guide to good practice for the
worth, Nottingham. development of conceptual models and the selection and application
Anderson, M.P. and Woessner, M.W. (1997) Applied Ground- of mathematical models of contaminant transport processes in the
water Modelling – Simulation of Flow and Advective Transport. subsurface. Environment Agency, National Groundwater &
Academic Press, San Diego, USA. Contaminated Land Centre Report NC/99/38/2, Bristol, July
Anon. (2000) Environmental Impact Assessment: A Guide to Proce- 2001.
dures. Thomas Telford Ltd., London for DETR and the Environment Agency. (2002) Groundwater resource modelling:
National Assembly for Wales. guidance notes and template project brief. Environment Agency
Anon. (2002) Geology in Environmental Impact Statements. Insti- R&D Guidance Notes W213, Environment Agency, Bristol.
tute of Geologists of Ireland, Dublin. Environment Agency. (2003a) Guidance on monitoring of landfill
Anon. (2007) Recommended Collection, Presentation and Interpre- leachate, groundwater and surface water. Environment Agency
tation of Geological and Hydrogeological Information for Quarry Report LFTGN02, Environment Agency, Bristol.
Developments. Institute of Geologists of Ireland, Dublin. Environment Agency. (2003b) Hydrogeological risk assessments
Bear, J. and Verruijt, A. (1987) Modeling Groundwater Flow and for landfills and the derivation of groundwater control and trigger
Pollution. D. Reidel Publishing Company, Dordrecht, levels. Environment Agency Report LFTGN01, Environment
Holland. Agency, Bristol.
Bedient, P.B., Rifia, H.S. and Newell, C.J. (2000) Ground Water Environment Agency. (2004) Assessing the Groundwater Pollution
Contamination – Transport and Remediation. Prentice-Hall, Potential of Cemetery Developments. Guidance Booklet (3rd edn).
New Jersey.
Environment Agency, Bristol.
Black, J.H. and Brightman, M.A. (1996) Conceptual Model of
Environment Agency. (2007) Hydrogeological impact appraisal for
the Hydrogeology of Sellafield. Q. J. Eng. Geol., 29, S83–S94.
groundwater abstractions. Environment Agency Science Report –
Brassington, F.C. (1992) Measurements of Head Variations
SC040020/SR2. Environment Agency, Bristol.
Within Observation Boreholes and Their Implications for
Fetter, C.W. (2001) Applied Hydrogeology (4th edn). Prentice-
Groundwater Monitoring. J. Inst. Water Environ. Manage., 6,
Hall Inc., New Jersey.
91–100.
Hough, M.N. and Jones, R.J.A. (1997) The United Kingdom
Brassington, F.C. (2004) Developments Since 1974 – Bringing
Meteorological Office rainfall and evaporation calculation system:
the Story up to Date. In: Mather, J.D. (ed). 200 Years of British
MORECS version 2.0 – an overview. Meteorological Office,
Hydrogeology, Geological Society of London Special Publication
Bracknell.
225, The Geological Society, London, pp. 363–385.
Jones, H.K., Morris, B.L., Cheney, C.S., Brewerton, L.J., Mer-
Brassington, R. (2006) Field Hydrogeology (3rd edn). John Wiley
rin, P.D., Lewis, M.A., MacDonald, A.M., Coleby, L.M.,
and Sons, Chichester.
Talbot, J.C., McKenzie, A.A., Bird, M.J., Cunningham, J.
Brassington, F.C. (2007) A Proposed Conceptual Model for the
and Robinson, V.K. (2000) The physical properties of the minor
Genesis of the Derbyshire Thermal Waters. Q. J. Eng. Geol.
Hydrogeol., 40, 35–46. aquifers in England and Wales. British Geological Survey
British Standards Institute. (2003) Hydrometric Determinations. Technical Report WD/00/4 & Environment Agency R&D
Pumping Tests for Water Wells. Considerations and Guidelines for Publication 68, Keyworth, Nottingham.
Design, Performance and Use. BS ISO 14686:2003. British Stan- Konikow, L.F. (1981) Role of Numerical Simulation in Analysis
dards Institute, London. of Ground-Water Quality Problems. Sci. Total Environ., 21,
Burgess, W.G., Burren, M., Perrin, J. and Ahmed, K.M. (2002) 299–312.
Constraints on Sustainable Development of Arsenic-Bearing Kruseman, G.P. and de Ridder, N.A. (1990) Analysis and
Aquifers in Southern Bangladesh. Part 1: A Conceptual Evaluation of Pumping Test Data – 2nd edn. ILRI Publication 47.
Model of Arsenic in the Aquifer. In Hiscock, K.M., Rivett, International Institute for Land Reclamation and Develop-
M.O. and Davison, R.M. (eds). Sustainable Groundwater ment, Wegeningen, the Netherlands.
Development, Special Publications, Vol. 193, pp. 145–163. Mather, J.D. (ed). (2004) 200 Years of British Hydrogeology,
Geological Society, London. Special Publications, Vol. 225. Geological Society, London. pp.
Cairney, T. (1972) Hydrological Investigation of the Magnesian 1–13.
Limestone of South East Durham. J. Hydrol., 16, 323–340. Neuman, S.P. and Wierenga, P.J. (2003) A comprehensive strategy
Cashman, P.M. and Preene, M. (2001) Groundwater Lowering in of hydrogeologic modeling and uncertainty analysis for nuclear
Construction: A Practical Guide. Spon Press, London. facilities and sites. Report NUREG/CR-6805, US Nuclear
Chaplow, R. (1996) The Geology and Hydrogeology of the Regulatory Commission, Office of Nuclear Regulatory Re-
Sellafield Area: An Overview. Q. J. Eng. Geol., 29, S1–S12. search, Washington, DC.

272 Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM.
 F. C. Brassington and P. L. Younger A proposed framework for hydrogeological conceptual modelling

Neymeyer, A., Williams, R.T. and Younger, P.L. (2007) Migra- stones of N.W. England. In Barker, R.D. and Tellam, J.H.
tion of Polluted Mine Water in a Public Supply Aquifer. (eds). Fluid Flow and Solute Movement in Sandstones:
Q. J. Eng. Geol. Hydrogeol., 40, 75–84. The Onshore UK Permo-Triassic Red Bed Sequence, Special
Parkin, G. and Adams, R. (1998) Using Catchment Models for Publications, Vol. 263, pp. 169–185. Geological Society,
Groundwater Problems: Evaluating the Impact of Mine London.
Dewatering and Groundwater Abstraction. In Wheater, H. Silvert, W. (2001) Modelling as a Discipline. Int. J. General Syst.,
and Kirby, C. (eds). Hydrology in a Changing Environment 30, 261–282.
(Proceedings of the International Symposium Organized by the Smith, D.B. and Francis, E.A. (1967) The Geology of the Country
British Hydrological Society, 6 &10 July 1998, Exeter, UK), Vol. II Between Durham and West Hartlepool. HMSO, London.
, pp. 269–279. Wiley, Chichester. Todd, D.K. and Hayes, L.W. (2005) Ground Water Hydrology (3rd
Plant, J.A., Jones, D.G. and Haslam, H.W. (1999) The Cheshire edn). John Wiley & Sons, New York.
Basin: Basin Evolution, Fluid Movement and Mineral Resources in Younger, P.L. (1993) Simple Generalised Methods for
a Permo-Triassic Setting. British Geological Survey, Keyworth. Estimating Aquifer Storage Parameters. Q. J. Eng. Geol., 26,
Rees, J.G. and Wilson, A.A. (1998) Geology of the country around 127–135.
Stoke-on-Trent. Memoir for 1:50 000 geological sheet123 Younger, P.L. (1995) Hydrogeology. In Johnson, G.A.L. (ed).
(England and Wales). HMSO for the British Geological Robson’s Geology of North East England. (The Geology of North
Survey. East England, 2nd edn, Transactions of the Natural History Society
Robins, N.S. (1990) Hydrogeology of Scotland. British Geological of Northumbria, Vol. 56, pp. 353–359.
Survey, Wallingford. Younger, P.L. (2007) Groundwater in the Environment: An Intro-
Robins, N.S. (1996) Hydrogeology of Northern Ireland. British duction. Blackwell Publishing, Oxford.
Geological Survey, Wallingford. Zheng, C. and Wang, P. (1999) MT3DMS: a modular three-
Rushton, K.R. (2003) Groundwater Hydrology – Conceptual and dimensional multi-species transport model for simulation of
Computational Models. John Wiley and Sons, Chichester. advection, dispersion and chemical reactions of contami-
Seymour, J.K., Ingram, J.I. and Gebbett, S.J. (2006) Structural nants in groundwater systems. Documentation and Users
Controls on Groundwater Flow in the Permo-Triassic Sand- Guide [online]. http://www.us.net/envisim.

Water and Environment Journal 24 (2010) 261–273 c 2009 The Authors. Water and Environment Journal c 2009 CIWEM. 273

View publication stats