Golder Associates Ltd.
500 – 4260 Still Creek Drive
Burnaby, British Columbia, Canada V5C 6C6
Telephone (604) 296-4200
Fax (604) 298-5253
FINAL REPORT ON
COMPREHENSIVE GROUNDWATER MODELLING
TOWNSHIP OF LANGLEY
Township of Langley
Langley, British Columbia
14 Copies - Township of Langley
1 Copies - Dr. Leslie Smith
5 Copies - Golder Associates Ltd.
June 30, 2004 022-1826, Phase 5000, Task 5300
OFFICES IN AUSTRALIA, CANADA, GERMANY, HUNGARY, ITALY, SWEDEN, UNITED KINGDOM, UNITED STATES
June 2005 -i- 022-1826/5000
This report presents the results of a Comprehensive Groundwater Modelling Assignment
conducted by Golder Associates Ltd. (Golder) on behalf of the Township of Langley (the
Township). The work was initiated in the Fall of 2002 and represents a key element in
the fulfillment of the Township’s Water Resource Management Strategy (WRMS).
The WRMS was established in 1998 to provide the Township with a comprehensive and
defensible approach for managing the quantity and quality of its local groundwater and
surface water resources. The WRMS consists of a 20-Year Action Plan to address water
resource issues through initiatives that fall within three main categories: 1) public
outreach, 2) studies, and 3) management options.
One of the key groundwater studies outlined in the Action Plan, and the objective of this
assignment, was the development of a three-dimensional hydrogeologic numerical model
for the entire Township. This model will provide the foundation upon which most of the
other studies and management decisions related to groundwater will be based.
Specifically, the groundwater model was used for the assessment of aquifer water
balance, which can be used to ensure sustainable aquifer yields and the protection of fish
habitat, and for the delineation of municipal water supply well capture zones, which are
required for the protection of groundwater quality.
The comprehensive groundwater modelling assignment was carried out in four phases.
Phase 1 consisted of data compilation, during which all available information concerning
the Township’s geology, hydrology and hydrogeology was assembled and reviewed.
Phase 2 consisted of the development of a three-dimensional conceptual model of
groundwater flow within the Township. A conceptual model is a pictorial and descriptive
representation of the main features of the geology, hydrologic setting and the site-specific
relationship between geologic structure and patterns of fluid flow. Phase 3 consisted of
the construction and calibration of a three-dimensional, numerical groundwater model.
This model was used to delineate capture zones for municipal wells and to assess the
water balance for the Township. This report represents Phase 4 of the project, which is
comprised of reporting and presentation of the results.
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PHASE 1 - DATA COMPILATION
A comprehensive data gathering exercise was conducted to obtain geologic, hydrologic
and hydrogeologic information from the Township and neighbouring jurisdictions into
which key aquifers extend. The data was assembled by means of on-line searches,
telephone enquiries, visits to private and public agencies, and a search of files maintained
by the Township and Golder. Over 500 records were gathered and reviewed as part of
this effort. A searchable document control system was developed to assist with the
management of the large volume of data collected.
Key geological information assembled during this phase of the project included 6043
water well records contained within the water well database maintained by the Ministry
of Water, Land and Air Protection (MWLAP), together with 545 borehole and water well
logs derived from other information sources. Water well and borehole logs were entered
into a customized digital borehole/water well database which included location and
Information collected for the purpose of hydrology assessment included climate data
(precipitation, temperature, evapotranspiration), stream flow and stage–discharge data in
different watersheds, percent total impervious area (%TIA) representing land-use and
land-cover classes for each watershed and catchment, seasonal and annual rates of
surface water applications for various purposes, and drainage studies.
Information related to hydrogeologic parameters was obtained from water well records
contained within the MWLAP water well database, hydrogeological and geotechnical
reports, and pumping test records provided by local drillers, pumping test contractors and
the Township. Long-term water-level monitoring data was assembled and reviewed for
Township municipal pumping wells and observation wells maintained by MWLAP.
Estimates of groundwater use were made based on municipal pumping records, land use
and site-specific information.
PHASE 2 – CONCEPTUAL MODEL
Information gathered during the data compilation phase of the project was analysed and
used to develop a conceptual model of groundwater flow within the Township.
The first step in the development of the conceptual model was the establishment of a
geological framework for the Township. The lateral and vertical extent of major
stratigraphic units was defined based on the information contained within the customized
borehole/water well database, verified, and iteratively adjusted based on published
information. A total of 45 permeable units were identified as a result of the geological
interpretation. Low permeability units, or aquitards, were identified between, above or
beneath the permeable units.
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The 45 permeable units identified through the geologic interpretation were reduced to 18
“major” aquifers by combining permeable units that were hydrogeologically similar, near
to each other, and likely to be hydraulically connected. Hydrogeological parameters were
then assigned to these 18 aquifers based on data from pumping tests and grain size
analyses, together with published values for various geologic media. Groundwater flow
directions were assigned based on interpolation of hydraulic head data contained within
the customized borehole/water well database.
Available hydrological information on precipitation, evapotranspiration and watershed
characteristics such as land use, land cover, topography and surficial soil was analysed to
provide reasonable estimates of watershed runoff and stormwater runoff, which in turn
provided the means of estimating base flow and recharge to groundwater.
PHASE 3 – NUMERICAL MODEL
The numerical hydrogeologic model was constructed using Visual MODFLOW (WHI,
2003). The model extends over an area of approximately 530 km2, comprising the entire
Township and portions of Surrey and Abbotsford. The model was constructed with grid
blocks set at a lateral spacing of 200 m, with refinement of the spacing to 20 m in the
vicinity of Township wells to facilitate capture zone analysis. Vertically, the model was
divided into 30 layers.
The east and west boundaries of the model correspond to groundwater divides, the north
boundary corresponds to the Fraser River, and the south boundary is coincident with the
international border. The base of the model is located approximately 30 m below the
bottom of the deepest aquifer presently used by the Township and corresponds to the
lowest elevation of potable water and/or available borehole data. The top of the model
was set to the ground elevation. A specified flux was applied to the top of the model to
simulate aerially distributed recharge from precipitation and human sources. A specified
flux boundary was also used to simulate groundwater use by minor users. Withdrawals
by major groundwater users (defined as those extracting greater than 150 m3/day) and
Township wells were simulated at grid blocks representing the locations of individual
well screens. Head-dependent boundaries were used to represent watercourses within the
area of the model domain.
The hydrogeologic model was calibrated to the average annual conditions, and to the
transition between average conditions during wet and dry seasons to provide a calibration
to both steady-state and transient conditions.
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Well Capture Zones
Once developed and calibrated, the numerical model was used to delineate captures zones
and time of travel zones for the Township water supply wells using the MODPATH
particle tracking mode. A capture zone is defined as the portion of an aquifer from which
groundwater is derived by a pumping well. For each municipal well, the total capture
zone, together with time of travel zones equivalent to 60-days, 1-year, 5-years and 20-
years, were determined for wells operating simultaneously at their maximum capacities.
The resultant capture zones vary in size and shape, depending on aquifer characteristics,
well interference effects and boundary conditions, such as the presence of nearby surface
water or aquifers. To account for potential uncertainties in the extent of the capture zones
due to the uncertainty in model input parameters, an upper bound estimate of the extent
of each capture zone was calculated by adjusting hydraulic conductivities by a factor of
±2 from the base case values.
Aquifer Water Balance
The numerical hydrogeological model was also used to conduct water balance analyses to
assess the sustainability of current and future groundwater withdrawals. Water balance
analyses were carried out for the aquifers utilized by the Township of Langley water
supply wells (Brookswood, South of Murrayville AC, West of Aldergrove, Nicomekl
Serpentine, Fort Langley, Salmon River, and Aldergrove AB Aquifers), together with the
Hopington AB Aquifer, which is used as a water supply source by numerous private
Steady-state model simulations were conducted to determine the water balance under pre-
development conditions (1961), current conditions (2003), and full OCP build-out
(2018). For full OCP build-out, two scenarios were considered. In both scenarios,
groundwater withdrawals from municipal wells were assumed to increase by a factor of
1.8 to reflect projected increases in the Township population. In Scenario 1, it was
assumed that private groundwater use would also increase by a factor of 1.8 from the
present use throughout the Township (including the area above the Hopington AB
Aquifer). In Scenario 2, private groundwater use was assumed to increase by a factor of
1.8 in all areas of the Township except the Hopington AB Aquifer, where a total increase
in private water use in this aquifer of approximately 80 m3/day above 2003 levels was
assumed, based on changes to the current zoning that would result in the addition of 79
single family lots in the Hopington area.
Results of the water balance analysis show that in unconfined aquifers, increased
pumping rates from wells (whether Township or private wells) generally result in water
level declines and water being drawn from nearby streams and creeks, which in turn
decreases the baseflow component in these water bodies. In contrast, increased pumping
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rates within confined aquifers are predominantly characterized by changes in the
contribution of flow to and from other units (adjacent aquitards and aquifers), with a
more subdued influence on baseflow expected.
A comparison of the water balance from pre-development conditions (1961) to the
present day suggests that for the Brookswood, Fort Langley, Aldergrove AB and
Hopington AB Aquifers, reductions in baseflows within streams located within those
aquifer boundaries of 12%, 36%, 70% and 33% have occurred as a result of increased
groundwater withdrawals. If groundwater demand increases by a factor of 1.8 by full
OCP build-out (2018), the baseflow within streams located within the boundaries of the
Brookswood and Fort Langley Aquifers is predicted to be reduced by an additional 8%
and 16%, respectively. For the Aldergrove AB Aquifer, baseflow within the aquifer
boundaries is predicted to be reduced to less than zero by the year 2018, resulting in
water flowing from Bertrand Creek to the aquifer (rather than the reverse). For the
Hopington AB Aquifer, if private water use were to increase by a factor of 1.8 by full
OCP build-out, baseflow within the Salmon and Nicomekl Rivers within the aquifer
boundaries is predicted to be reduced by an additional 36% from 2003 levels. On the
other hand, if private water use for the Hopington AB Aquifer were restricted solely to
that associated with the proposed zoning changes, negligible additional reductions in
baseflow to the Salmon and Nicomekl Rivers are predicted. However, the model does
predict an overall reduction in baseflow within the aquifer boundaries of 13% due to
increased water use outside of the Hopington area by both private and municipal users.
The numerical hydrogeologic model developed for this study represents a compilation of
geological, hydrological and hydrogeological data from across the Township. The effort
related to mapping of permeable units beneath the Township and neighbouring
municipalities represents significant progress towards the understanding of the regional
hydrostratigraphy in the Township. While sufficient information was available to allow
for the characterization of the subsurface stratigraphy, more limited information was
available concerning hydrogeological parameters, and in particular, water-levels and
contemporaneous baseflow measurements. The model should be considered as a
“working tool”, which should be continually refined as additional information becomes
The Township-wide hydrogeologic model is a regional-scale model capable of assessing
average groundwater conditions over large areas (on the order of 1000 m). As such, it
can be used as an effective planning tool in assessing long-term groundwater
management strategies. The model is effective in estimating the water balance for
individual aquifers. It is capable of assessing regional impacts on the water levels due to
projected population growth and proposed land-use changes. It can assess the effects of
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large-scale stormwater infiltration and it can determine the areas where such infiltration
will provide the most benefit. It can optimize the locations of well fields in a given
The present model is not suitable for local scale applications such as well field design and
optimization. In other words, the model cannot optimize the location of an individual
well in a well field. As additional information becomes available, refinements to
individual aquifers within the model can be made to permit additional analysis.
The delineation of capture zones represents the first step required for the Township to
protect the quality of its municipal groundwater supply. Once additional information
concerning potential contaminant threats is assembled and reviewed, consideration could
be given to establishing provisions for groundwater protection within entire capture
zones, or on an incremental basis within the various time of travel zones. Some variation
in the capture zones presented in this report may occur should additional large-capacity
wells be installed in the vicinity of Township wells, or should there be significant
changes to the current pumping regime of wells operated by the Township.
The results of the water balance analysis provide the basis for the Township to address
some of its concerns related to sustainable aquifer yields and the protection of fish
habitat. At this time, it appears that future withdrawals from some of the shallow
aquifers such as the Aldergrove AB and Brookswood Aquifers cannot be sustained
without compromising baseflow in local water courses. In contrast, some of the deeper
aquifers may be capable of sustaining increased withdrawals as they appear to draw water
from a much larger area. Model predictions have indicated that if the private
groundwater withdrawals from the Hopington AB Aquifer are assumed to gradually
increase by approximately 1.8 times the estimated current rates, that this will result in an
approximately 36% reduction in the annual baseflow of the Salmon and Nicomekl Rivers
in the portions of these rivers that overlie the aquifer. However, if increases in
groundwater withdrawals are limited to a small residential development (79 additional
residential lots), the influence on both rivers would be relatively small.
Additional data were identified during the development of the numerical model that, if
obtained, could assist with the ongoing assessment of the model predictions and
refinement of the model to reduce the uncertainty in the model predictions.
Recommendations for additional data gathering include:
• The installation of monitoring wells at strategic locations to assess hydraulic heads in
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• Regular baseflow monitoring on Bertrand Creek, Anderson Creek, Salmon River and
Nicomekl River, where maximum reductions in baseflow due to groundwater
withdrawals are predicted;
• Continued maintenance of accurate pumping records by the Township, and,
• Additional long term (over 24-hours) pumping tests in several Township municipal
wells, particularly those in the Brookswood and Aldergrove AB Aquifers, to refine
the model calibration.
General recommendations related to the future management of the quantity and quality of
the Township’s groundwater resources include:
• Development of a long-term water supply strategy for the Township to identify
sources of water supply for various areas of the Township through to the Year 2018,
and possibly beyond;
• Vulnerability mapping to identify areas where surficial contamination has the
potential to compromise groundwater quality. This work, which has been recently
completed by Golder under a separate contract, will provide information required to
protect groundwater quality at private wells located outside of municipal well capture
• Detailed contaminant inventories within the capture zones to provide the information
required for the development of groundwater quality protection measures, and
• Once the work recommended above has been completed, consideration should be
given to the establishment of Groundwater Management Areas to protect groundwater
quantity and/or quality. Groundwater Management Areas may be defined on the basis
of capture zones, time of travel zones, aquifers, portions of aquifers, or a combination