Quality Control De

*D geologic framework models for regional hydrogeology

and land-use management: a case study from a Quaternary basin

of southwestern Quebec, Canada

Martin Ross Michel Parent Ren Lefebvre

Abstract During a regional hydrogeologic survey in the Resumen Se construy un Modelo del Marco Geol gico

St. Lawrence Lowlands, Canada, a computer-based 3D (GFM) 3D basado en computadora durante un levanta-

Geologic Framework Model (GFM) was constructed to miento hidrogeol gico regional en las Tierras Bajas de St.

obtain a consistent representation of this typical Quater- Lawrence, Canada para obtener una representaci n con-

nary glaciated basin over a 1,400 km2 area. Such a de- sistente de esta cuenca glaciar Cuaternaria t pica en un

rea de 1,400 km2. Se necesit tal grado de reconstrucci n

tailed stratigraphic reconstruction was needed because the

Quaternary sediments control the recharge to the under- estratigr fica debido a que los sedimentos Cuaternarios

lying regional fractured rock aquifer and also because controlan la recarga del acu fero rocoso fracturado re-

buried granular aquifers are partly connected to the re- gional subyacente y tambi n porque los acu feros granu-

gional system. The objectives of this geomodeling effort lares enterrados est n parcialmente conectados con el

are 1) to improve understanding of subsurface conditions sistema regional. Los objetivos de este esfuerzo de mo-

above the regional aquifer and; 2) to provide a common delizado geol gico son: 1) mejorar el entendimiento de

stratigraphic framework for hydrogeologic applications. las condiciones subsuperficiales por encima del acu fero

The method draws on knowledge-driven discrete model- regional y; 2) aportar un marco estratigr fico com n para

ing using gOcad, as well as standardization and quality aplicaciones hidrogeol gicas. El m todo se basa en el

control procedures to maximize the use of a multisource conocimiento de modelizado discreto utilizando gOcad,

database. The resulting model represents the bedrock to- as como tambi n en estandarizaci n y procedimientos de

pography and the complex stratigraphic architecture of control de calidad para maximizar el uso de bancos de

overlying sediments. The regional till aquitard, the marine datos de fuentes m ltiples. El modelo obtenido representa

clay aquiclude and the buried granular aquifers have been la topograf a del macizo rocoso y la arquitectura de la

modeled with unprecedented details thus providing a compleja estratigraf a de los sedimentos sobreyacentes. El

well-constrained 3D hydrostratigraphic framework. The acuitardo regional de tillita, el acuicludo arcilloso marino

recharge zones of the rock aquifer represent about 35% y los acu feros granulares enterrados se han modelizado

of the study area. Buried granular aquifers are directly con detalles sin precedentes aportando de este modo un

connected to the regional aquifer system over about 10% marco hidroestratigr fico 3D bien definido. Las zonas de

of the area. The model allows several applications such as recarga del acu fero rocoso representan casi el 35% del

assessing aquifer vulnerability and areal groundwater re- rea de estudio. Los acu feros granulares enterrados est n

charge rates; improving the GFM inter-operability with conectados directamente al sistema acu fero regional so-

groundwater modeling systems would be the next logical bre aproximadamente el 10% del rea. El modelo permite

step. varias aplicaciones tal como evaluar la vulnerabilidad de

acu feros y ritmos de recarga areales de agua subterr nea;

el paso l gico siguiente ser a mejorar la inter-operabilidad

Received: 25 July 2003 / Accepted: 31 May 2004 del GFM con los sistemas de modelizado de agua sub-

Published online: 3 August 2004

terr nea.

Springer-Verlag 2004

R sum Dans le cadre d une tude d hydrog ologie r -

gionale dans les basses terres du Saint-Laurent (Canada),

M. Ross R. Lefebvre un Mod le surfacique g ologique en 3D (MSG) a t

Institut National de la Recherche Scientifique (INRS-ETE),

d velopp pour obtenir une repr sentation coh rente par

880 chemin Sainte-Foy, bur. 840, C.P. 7500, Qu bec (Qc.),

ordinateur de ce bassin quaternaire sur une superficie

G1V 4C7, Canada

de plus de 1,400 km2. Une telle reconstitution stratigra-

e-mail: abo8v5@r.postjobfree.com

phique tait n cessaire en raison du contr le qu exercent

Tel.: +418-***-****

les s diments quaternaires sur la recharge de l aquif re

Fax: +418-***-****

r gional fractur sous-jacent et aussi parce que les aqui-

M. Parent

f res granulaires enfouis sont partiellement connect s au

Geological Survey of Canada,

syst me r gional. Les objectifs de cet effort de g omo-

880 chemin Sainte-Foy, Suite 840, Qu bec (Qc.), G1S 2L2, Canada

Hydrogeology Journal (2005) 13:690 707 DOI 10.1007/s10040-004-0365-x

691

d lisation sont: 1) d am liorer la compr hension des benefit is that it does away with the necessity of redoing

conditions de sous-surface au-dessus de l aquif re r gio- much of the interpretation and stratigraphic modeling to

nal et; 2) de fournir un cadre stratigraphique commun adjust to the specific requirements of various applications;

des fins de caract risation hydrog ologique. La m thode in the end, time savings can be huge.

repose sur l int gration de l interpr tation g ologique In recent years it has become technologically feasible

dans la mod lisation discr te effectu e l aide du logiciel to build in a reasonable time frame complex 3D geologic

gOcad, ainsi que sur des proc dures d uniformisation et or hydrostratigraphic models, to incorporate and analyze

de contr le de la qualit des donn es afin d optimiser their properties and to export the information to other

l utilisation d une base de donn es multisources. Le MSG software systems to meet the specific requirements of an

repr sente la topographie du roc et l architecture strati- application. This has opened a new perspective in hy-

graphique des s diments sus-jacents. L aquitard r gional drogeology where a number of applications require that

(till), l aquiclude d argile marine et les aquif res granu- all the available hydrogeological information be incor-

laires ont t mod lis s un niveau de d tail sans pr - porated into a full three-dimensional conceptual model

c dent, fournissant ainsi un cadre hydrostratigraphique (e.g., Frind et al. 2002). Consequently, producing such

solidement tabli. Les zones de recharge de l aquif re computer-based geologic models is becoming an impor-

rocheux repr sentent environ 35% de la zone d tude. Les tant objective in many hydrogeologic surveys. For in-

aquif res granulaires enfouis sont connect s directement stance, the Geological Survey of Canada (GSC) has in-

au syst me aquif re r gional sur au moins 10% du terri- tegrated some aspects of 3D modeling in its hydrogeo-

toire. Le MSG permet de multiples usages tels l valua- logic investigations since the mid 90s (Sharpe et al. 1996;

tion de la vuln rabilit des aquif res et l estimation de la Parent et al. 1998; Ricketts 2000; Girard 2001; Logan

distribution de la recharge; la prochaine tape logique et al. 2001; Thorleifson et al. 2001; Ross et al. 2002).

serait l am lioration de l interop rabilit avec les sys- Also, US federal and state agencies have developed 3D

t mes de mod lisation num rique de l coulement. mapping programs for regional hydrogeologic studies

(Belcher et al. 2002; Herzog et al. 2003), hydrogeologic

Keywords 3D geological models Spatial database characterization of underground nuclear test areas (US

Hydrogeology Quaternary St. Lawrence Lowlands Department of Energy 1997) and radioactive waste re-

pository (Clayton 2000), and for land-use planning and

management (Soller et al. 1999; Berg et al. 2000). Efforts

Introduction are also carried out elsewhere such as in Finland (Artimo

et al. 2003). However, regional 3D models and associated

In recent years, Quaternary deposits of northern US and multiple usages are still uncommon due to organizational

Canada have been used for an increasing number of hu- and resource constraints as well as to problems related to

man activities, such as sand mining and for waste disposal data quality, quantity and distribution. Furthermore, even

and water supply, which are known for their potential though many approaches are conceivable for the devel-

impact on groundwater. Moreover, it has become apparent opment of 3D models, they are not necessarily suitable for

that understanding relationships between Quaternary de- every field situation or survey objective. Therefore, the

posits and groundwater is also a necessity in areas where procedures developed to construct 3D geologic or hy-

most water supplies come from bedrock aquifers. Indeed, drostratigraphic models must adapt to project objectives

these deposits are frequently a major factor controlling but the resulting models should have the level of strati-

confining conditions and recharge of bedrock aquifers. graphic details required by the most demanding applica-

This situation has highlighted the urgency to improving tion.

knowledge of hydrogeologic settings of glaciated terrains The work presented in this paper is part of a regional

in rapidly developing regions. However, delineating con- hydrogeologic investigation carried out by the Geological

fining layers and sub-surface aquifers and aquitards in Survey of Canada (Savard et al. 2000). The study area is

these complex settings is by no means a trivial task and a located in the St. Lawrence Lowlands near Montreal

close integration of stratigraphic reconstructions and hy- (Fig. 1), a rapidly developing region where groundwater

drogeologic applications still represents a significant chal- conservation has become a public issue. The objectives of

lenge. this work are to: 1) improve understanding of subsurface

An important difficulty in regional hydrogeologic sur- conditions above the regional fractured rock aquifer and;

veys is to have access to sole-sourced consistent geolog- 2) to provide a common framework for different hydro-

ical information which can accommodate many specific geologic applications. To achieve these goals, a strategy

needs. A solution may be to create a computer-based has been developed to create a computer-based 3D model

repository of the stratigraphic knowledge of the study of the regional bedrock topography and overlying Qua-

area (Mallet 2003) which is common to all project team ternary stratigraphic architecture (Geologic Framework

members as opposed to a common practice in which ge- Model, GFM). This paper thus presents the strategy itself,

ologic information is stored on different media and dis- the resulting 3D model as well as a few applications. The

persed through a series of independent end-products. This GFM is used to describe the main Quaternary hydrogeo-

approach reduces redundancy and risks of inconsistencies logical settings. Also provided are brief descriptions of

and helps to streamline updating procedures. An obvious how the model was used to assess aquifer vulnerability to

Hydrogeology Journal (2005) 13:690 707 DOI 10.1007/s10040-004-0365-x

692

contamination (Ross et al. 2003) and, to some extent, to outcrops in the Laurentian Highlands as well as in two

calibrate the regional numerical model (Nastev et al. in hills (St. Andr and Oka) which also contain Cretaceous

review, a). Other potential applications are suggested. The intrusive rocks (carbonatites). Bedrock is overlain by a

main challenge for 3D modeling in such a setting stems discontinuous cover of Quaternary sediments reaching up

from the discontinuous nature of the units, their highly to 150 m in thickness and offering a great variety of hy-

variable thickness and the fact that most units are only drogeologic settings. The Quaternary geology of the study

partly exposed at the surface. The procedure applied to area has been described and interpreted by Hillaire-Marcel

construct the GFM takes advantage of the capabilities of (1974), Prichonnet (1977) and L vesque (1982), and more

modern geomodeling systems, basin analysis techniques recently by Bolduc and Ross (2000) as well as Ross et al.

(Miall 1992) and quality control as well as standardized (2001). Over 200 stratigraphic boreholes reaching bedrock

procedures to optimize the use of a multisource database. were also drilled in the early 1970s to support decision-

making for the location of the Mirabel International Air-

port (Kugler-Gagnon 1974; St-Onge 1979). The Quater-

Characteristics of the Study Area nary sequence mainly comprises Late Wisconsinan sub-

glacial (20 12 ka), proglacial (12 10 ka) and Holocene

The study area extends over about 1,500 km2 between the (

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