groundwater aquifers

GROUNDWATER AQUIFERS
INTRODUCTION TO GROUNDWATER AQUIFERS
GROUNDWATER AQUIFERS
Melvyn E. Best, Bemex Consulting International
Hydrogeology
Introduction
Figure 1 is a schematic illustration of a
ground water aquifer system depicting recharge and
discharge areas, confined, unconfined and perched
aquifers, water table, potentiometric surface,
confining layers and ground water flow directions.
These hydrogeological terms are defined below.
A detailed water well data base was constructed for
Central Saanich using the digital water well data
provided by the Groundwater Section of the British
Columbia Ministry of Environment, Lands and Parks.
The location and elevation of approximately 800
wells from this data base were digitized from the 1:5
000 scale well location maps provided by the
Ministry. Only wells on these maps were entered into
the Central Saanich water well data base, even though
therewere several hundred more in theMinistry's data
base. The locations for these additional wells were
either not known or not yet entered onto themaps.
The Central Saanich water well data base
containswelllocations and elevations, flow rate data,
lithological/geological information and a host of
factors related to drilling and completing the wells.
This data base provided information used to generate
maps and geological sections for the atlas.
Information on the structure of the data base and a
complete data listing is found in the “Well Log
Database”, which is available from the Municipality
of Central Saanich.
Three east-west and two north-south
geological cross sections, at a scale of approximately
1:30,000, illustrate the general behavior of the
surficial and bedrock geology within Central
Saanich. A 1:40,000 map (MAP GA2) showing the
location of surficial aquifers within Central Saanich,
and a qualitative estimate of their productivity, is also
included in the atlas. Contour maps of overburden
(surficial sediment) thickness (MAP GA4) and
elevation of the bedrock surface above sea level
(MAP GA5) are also included. A map showing the
location of all the wells (MAP GA1) in the data base
and the location of the 5 cross sections is provided at
the same scale as the contourmaps. A locationmapof
all the bedrock wells (MAP GA3) and the deeper
sediment wells (used to generate the two contour
maps mentioned earlier) is included.
We have
included thebedrock geology map (MAP B1) with an
overlay showing flow rate ranges of all bedrock wells
that have flow rates listed inthe data base. Finally we
have included the overburden thickness map with an
overlay showing the location of the surficial aquifers
and flow rate ranges of surficial wells that have flow
rates listed inthe data base (MAPGA7).
either in an area where the aquifer outcrops or by slow
leakage (seepage) upward through the bottom
confining layer and/or downward through the upper
confining layer.
Unconfined or water table aquifer - An aquifer that
extends from the surface to the top of a confining layer
at the base of the aquifer. Recharge can be from
downward seepage through the unsaturated zone ,
through lateral ground water flow or upward seepage
through the underlying leaky confining layer.
Hydrogeological definitions
Aquifer - a geological unit that can store and transmit
ground water at rates fast enough to supply reasonable
amounts to wells.
Confining layer - A geological unit that acts as a
barrier to flow or as a seal to an aquifer.
Water table - The depth below the ground surface in
an unconfined aquifer where the aquifer becomes 100
% saturated with water. Above this depth the aquifer
is only partially saturated with water and below this
depth theaquifer is completed saturatedwithwater.
Aquitard or leaky confining layer - A geological unit
that can store ground water and also transmit it slowly
from oneaquifer to another.
Confined aquifer - An aquifer that is overlain and
underlain by confining layers. Recharge can occur
Perched aquifer - The saturated zone (100 % water)
above a lens-shaped confining layer that is embedded
in an unconfined aquifer. For example a clay lens
(leaky confining layer) in an unconfined sand or
gravel aquifer.
non-flowing
well
potentiometric surface
flowing
well
P
ground
surface
D spring
D
stream
recharge to
unconfined aquifer
U
recharge to
confined aquifer
confining layer
D
discharge
C
confined aquifer
U
unconfined aquifer
P
perched aquifer
Hydraulic head or head - The height to which water
rises in a well drilled into a confined aquifer. The
head is composed of two parts; (1) the elevation of the
aquifer at the well and (2) the water pressure at the
well converted to an equivalent height ofwater.
Potentiometric surface - An imaginary surface that
represents the head at any position in a confined
aquifer.
Artesian flow - If a well is drilled into a confined
aquifer and the head is above the ground surface, the
well will flow without pumping, i.e. an artesian or
flowingwell.
Recharge - This is the volume of external water per
unit time that is added to an aquifer. The water can be
added (1) through infiltration (seepage) from the
surface for an unconfined aquifer and through
seepage from the surface that lies above outcropping
areas of a confined aquifer as shown at the left edge of
Figure 1, (2) by upward or downward seepage
through leaky confining layers and (3) through lateral
groundwaterflow.
Discharge - This is the volume of ground water per
unit time that is removed from an aquifer. The
water can be removed (1) through discharge
(seepage) into lakes and rivers (2) through seepage
from springs (3) through upward or downward
seepage in leaky confining layers and (4) through
evapotranspiration.
Evapotranspiration - the removal (discharge) of
water from an aquifer by (1) evaporation of soil
moisture and (2) plant transpiration ( ground water
carried to the surface through the roots of plants and
then discharged through their leaves and trunk by
evaporation).
C
unconfined well
water table
flow direction in unconfined aquifer
confined well
flow direction in confined aquifer
Figure GA.1. Schematic illustration of ground water flow
GA-1
Municipality of Central Saanich Resource Atlas
GROUNDWATER AQUIFERS
Properties of rocks and sediments
Darcy's Law
Porosity (φ) - The ratio of the volume of void or
empty space in a material to its total bulk volume.
For example, a sediment with a porosity of 30 %
means 0.3 of the bulk volume of the material
consists of void space. This is the space in an
aquifer that can be filled with water.
Water saturation (S) - The ratio of the volume of the
void space in a material filled with water to the
total volume of the void space in a material. For
example a water saturation of 50 % in a material
means that 0.5 of the total void space is filled with
water. If the water saturation is 100%, then all the
void space is filled with water. This is the normal
situation for a confined aquifer and for an
unconfined aquifer below the water table. The
portion of the pore space not filled with water is
usually filled with air. However, it could be filled
with other fluids that do not mix with water such as
gasoline, liquid hydrocarbons (benzine for example)
or solvents.
Permeability (k) - A property of a rock or sediment
that determines the ability of the material to
transmit water. This parameter is required to
determine the rate at which water can flow through
an aquifer. Permeability k has units of square
meters.
Hydraulic conductivity (K) - A parameter that
depends on the permeability as well as the density
and viscosity (friction) of the water. It also is a
measure of the ability of a material to transmit
water. Hydraulic conductivity has units of meters
per second.
HYDROGEOLOGY OF GROUNDWATER AQUIFERS
The primary permeability of these rocks is usually
very small (usually less than 10-18 m2). However,
fractures can increase the bulk or average
permeability by several orders of magnitude and
within a fracture zone the permeability can be quite
high (sometimes even larger than 10-15 m2).
Darcy's Law determines the rate and direction of water flow within an aquifer.
The basic formula for Darcy's Law is
Flow = Area x (hydraulic conductivity) x (change in hydraulic head per unit distance)
where
flow is in cubic meters per second
area is the cross sectional area of the aquifer perpendicular to the direction of flow (square meters)
The ability of a well toproduce from bedrock depends
on the amount or density of fracturing encountered in
the well. Unfortunately the location and density of
fractures are very difficult to predict before drilling.
Note: The change in hydraulic head per unit distance is also called the hydraulic gradient
The direction of flow is always from higher to lower head.
CentralSaanich Aquifers
some unconsolidated sediments.
Typical physical values for unconsolidated
sediments and bedrock
The porosity and permeability (hydraulic conductivity)
of crystalline bedrock (volcanic rocks, granites,
granodiorite) and limestone bedrock depend to a large
extent on the amount of fracturing in the rock.
We have seen how porosity and saturation determine
the amount of water stored in an aquifer and have also
seen how permeability (hydraulic conductivity)
determines the flow rate of water in an aquifer
(permeability also turns out to determine the
productivity of a well, i.e. how easy is it to produce
water from a well).
The primary, solid rock or matrix, porosity of these rocks
is usually small (typically 2 - 5 %, perhaps higher for
limestone). Fractures tends to increase the bulk or
average porosity of these rocks by a few percent at most.
However, within the fracture zones porosity can locally
be enhanced. Surface weathering can increase bedrock
porosity but it is localized near the surface.
Table 1 lists typical ranges of these parameters for
Table GA1. Approximate parameter ranges for unconsolidated sediments
Material
Porosity
Permeability
Clay
33 - 60 %
10 - 10 m
Silt, sandy silt,
clayey silt
35 - 50 %
10 - 10 m
Hydraulic
conductivity
-18
-15
2
10 - 10 m/s
-15
-13
2
10 - 10 m/s
-15
-13
2
10 - 10 m/s
-14
-12
2
10 - 10 m/s
-12
-10
2
10 - 10 m/s
-11
-9
Till
10 - 20 %
10 - 10 m
Fine sand,
silty sand
15 - 40 %
10 - 10 m
Well sorted sand
25 -50 %
10 - 10 m
Gravel
25 - 50 %
10 - 10 m
2
-11
-8
Aquifer
quality
confining layer
-8
-6
-8
-6
poor to adequate aquifer
-7
-5
moderate to good aquifer
-5
-3
good aquifer
-4
-2
good aquifer
10 - 10 m/s
poor aquifer
Five cross sections depicting the surficial and
bedrock subsurface geology within Central Saanich
were generated from the water well data base. The
lithological information in the data base was quite
sketchy and there were problemswiththeconsistency
of geological units and terms used by different
drillers. However three east-west and two northsouth cross sections were created to illustrate the
internal character of the surficial aquifers and the
bedrock variations within Central Saanich. The
surficial lithology is consistent with the Quaternary
database and map (MAP G1) produced by Huntley et
al.(1998) in this atlas.
The bedrock geology
descriptions in the water well data base were not very
useful as most bedrock is described as "granite or
bedrock". Consequently the bedrock on the cross
sections is a combination of the bedrock described in
the water well data base and the bedrock information
contained in the bedrock map (MAP B1 and MAP
GA6) in this atlas (Riddell, 1998). There is some
information on the depth and number of fractures
within bedrock given in the water well data base but
this study was too limited in time to investigate the
relation of the fracturing to themeasured flow rates.
In addition to these cross sections, maps of minimum
overburden (surficial sediment) thickness in meters
(MAP GA4) and maximum elevation of the bedrock
surface in meters (MAP GA5) above sea level were
generated from the water well data base using all the
wells that penetrated bedrock plus thedeeper surficial
wells.
Photo Ga1. A rea below Saanichton. Seepage on base of
slope above Municipal wells. A likely area of
groundwater discharge.
Municipality of Central Saanich Resource Atlas
GA-2
GROUNDWATER AQUIFERS
CROSS SECTIONS OF GROUNDWATER AQUIFERS
Cross Section of Aquifers in Central Saanich
They have been simplified from those given in the
data base in order to illustrate the general
hydrogeological setting within Central Saanich.
In general the cross sections appear to be self
consistent as well as consistent with the known
surficial aquifers.
Introduction to Cross Sections
The cross sections are based on the lithological
information provided in the Central Saanich water
well data base. The lithological information is quite
sketchy in places and can be described differently
from driller to driller, i.e. well to well, (the driller's
logs are the main source of information for the water
well data base).
100
North-south sections
The flow rate of wells with a non-zero flow value in
the data base have been posted at the top of the
cross section above the well identification number.
There are three east-west and two north-south cross
sections. The locations of the cross sections are
given in Map 1.
SOUTH
West Saanich Cross Section
Except for the southern portion of the section that
crosses the western edge of the Keating Aquifer, this
section clearly shows the thin veneer of till that
overlies bedrock on the west side of Central Saanich.
The underlying bedrock along this section is Island
Intrusive granodiorite (JIg). This section also
illustrates the rapid changes in bedrock topography
in the vicinity of Hagen Creek and Mount Newton
Valley.
NORTH
22
(D)
10
(D)
80
WEST SAANICH CROSS SECTION - SOUTH TO NORTH
5
(D) 13
(1)
4
East Saanich Cross Section
1
(4)
JIg
27
(5)
37
30 (D) 31
(D) (D)
60
18
(D) 20
17
(D)
(D)
1
(5)
10
8
3
(5)
6
4
(3)
14
(20)
13
(7)
46
(4)
15
(12)
18
(8)
JIg
JIg
16
(3)
JIg
15
18 (5)
(20)
JIg
40
JIg
21
(3)
grey
shale?
3
(2)
(D)
till
coarse sand-gravel
sand
clay
clay with sand or silt
JIg
17
(2)
or
20
well number
flow (gpm)
dug well
well
bedrock depth
known contact
inferred contact
outcrop
West
Saanich
Road
0
Keating
X Road
Wallace
Drive
Stelly’s
X Road
Hagan
Creek
-9 m
This section follows the East Saanich Aquifer from
near the southern end of the Aquifer to the northern
end just south of Saanichton. It then continues
northward following the Hagen Creek Aquifer from
its southern end in Saanichton. Note the distinct
break between the Hagen Creek and East Saanich
Aquifers just south of Mt. Newton X Road. The
underlying bedrock along this sections is Island
Intrusive granodiorite (JIg).
-62 m
5378000
5379000
5380000
Northing
5381000
5382000
5383000
West Saanich Road
100
SOUTH
43
NORTH
32
(D)
39
38
(6)
EAST SAANICH CROSS SECTION - SOUTH TO NORTH
37
(4)
7
(D)
40
80
16
(50)
26
(D) 24
(D)
42
(60)
9
(4)
39
60
18
14
(2)
41
(7)
44
(3)
40
2
(5)
17
(5)
40
(15)
JIg
3
(2)
14 13
(10) (3)
3
(4)
5
(5)
8
(2)
JIg
3
(2)
(D)
11
(15)
23
(2)
JIg
JIg
20
JIg
JIg
JIg
Tanner
Road
Keating
X Road
Central
Saanich
Road
East
Saanich
Road
Stelly’s
X Road
0
5377000
or
JIg
Mt. Newton
X Road
Haldon Road
-164 m
Hovey Road
5378000
5379000
5380000
Northing
5381000
till
coarse sand-gravel
sand
clay
clay with sand or silt
well number
flow (gpm)
dug well
well
bedrock depth
known contact
inferred contact
5382000
5383000
5384000
Central Saanich/East Saanich Roads
Municipality of Central Saanich Resource Atlas
GA-3
GROUNDWATER AQUIFERS
CROSS SECTIONS GROUNDWATER AQUIFERS
100
WEST
EAST
East-west sections
80
47
9 (7)
7 (5)
(4)
MOUNT NEWTON CROSS SECTION - WEST TO EAST
11
(20)
18 3
(4)(2)
60
JIg
41
(3)
30
JIg
15
(2)
39
37 (60)
(30)
3 16
(4)(2.5)
JIg
2
(4)
4
(13)
2
53 (3)
(3)
20
11
9 (1)
(0.1)
6
17 (1)
(3)
These three sections illustrate the thin veneer
of till over bedrock along the west side of
Central Saanich and show the general thickening of
surficial sediments (overburden) to the east. The
sands and gravels of the surficial aquifers are clearly
outlined on these sections. The sections illustrate
the complexity of the surficial geology as well.
well number
flow (gpm)
dug well
well
bedrock depth
known contact
inferred contact
or
20 21
(D) (D)
JIg
JIg
23 22
(33)
JIg
JIg
8
(6)
JIg
1
(1)
0
9
(D)
12
(15)
JIg
40
3
(2)
(D)
till
coarse sand-gravel
sand
clay
clay with sand or silt
2
West Saanich
Road
9
(8)
4
7
(3) (0.4)
East Saanich
Road
-43m -14m -44m
Mount Newton Cross Section
-15m
-108m -150m 465000 -38m
466000
467000
468000
469000
Easting
470000
471000
JIg
This section crosses the southern portion of the
Hagen Creek Aquifer east of 46800 easting.
The underlying bedrock consists of Island Intrusive
granodiorite (JIg). All wells within the western half
of the section produce water from bedrock.
Mount Newton Cross Road
100
STELLY’S CROSS SECTION - NORTH PORTION
WEST
EAST
20
(D)
80
14 1
(20) (3)
2
(7)
11
12
10 (?)
(CaCO3) 6
(0.6) (20)
12
(10)
15
(D)
12
(8)
40
22
JIg
JIg
JIg
JIg
15
(D)
11
(10)
JIg
0
JIg
-12 m -20 m
465000
Wallace
Drive
468000
WEST
469000
Easting
14
(2)
470000
JIg
471000
-80 m
17
(5)
18
(D)
(2)
4
(4)
60
31 15 37
(D) (D) 40
36 38
(3)
21 13 (2)(1)
(3) (D)
JIg
TrK
33
13 14
(3) (1)
TrK
43
(D)
9
(D) 6
15
42 (10)
(60)
11
29
10
28
(D)
35
(D) 32
(8) 27
(2)
or
17
(3) 4
well number
flow (gpm)
dug well
well
bedrock depth
known contact
inferred contact
This section, going from west to east, crosses the
Keating, East Saanich and Cowichan Head Aquifers.
The underlying bedrock consists of Karmutsen
Volcanics (TrK), Quatsino Limestone (TrQ) and
Island Intrusive granodiorite (JIg). The cross
section shows the Keating and East Saanich Aquifers
may be connected at depth. Note the
inter-bedded clays within the Keating Aquifer that
can act as no-flow or low flow boundaries (seals or
leaky seals). Almost all the wells in the western
portion of the section produce water from within the
bedrock.
11
JIg
JIg
TrK JIg
34
(100)
20
(180)
9 10
(D)(75)
(4)
Keating Cross Section
3
(2)
(D)
JIg
11
(100)
40
20
472000
till
coarse sand-gravel
sand
clay
clay with sand or silt
Fe
staining
39
(25)
16
This section, going from west to east, crosses the
East Saanich and Cowichan Head Aquifers. Again,
wells within the western portion of the section
produce water from within the bedrock. The
underlying bedrock along this section consists of
Island Intrusive granodioirite (JIg).
8
(2)
EAST
KEATING CROSS SECTION - WEST TO EAST
80
2
(20)
5
8
(D) (D)
-65 m
JIg
467000
Stelly's Cross Section
JIg
Veyaness
Road
-38 m
466000
Stelly’s Cross Road
100
19
(50)
JIg
8
(7)
West Saanich
Road
bedrock depth
known contact
inferred contact
COWICHAN HEAD AQUIFER
JIg
5
(7)
well number
flow (gpm)
dug well
well
or
JIg
10
9 (9)
(3)
20
3
(2)
(D)
till
coarse sand-gravel
sand
clay
clay with sand or silt
18
(?)
13
JIg
60
13
(1)
25
(D)
JIg
TrQ
26
(D)
sulfurous
TrK
TrK
West Saanich
Road
0
-54 m
465000
-85 m
-39 m
466000
-69 m
Oldfield
Road
Central
Saanich
Road
Veyaness
Road
Pat
Bay
Hwy
JIg
-34 m
467000
JIg
468000
Keating Cross Road
Easting
469000
470000
471000
472000
473000
Municipality of Central Saanich Resource Atlas
GA-4
GROUNDWATER AQUIFERS
CROSS SECTIONS AND LOCATION MAP OF ALL GROUNDWATER WELLS
464000
469000
474000
464000
469000
474000
Two maps, one showing the locations of all wells
(more than 800) and the five cross sections (MAP
GA1) and one showing the locations of all the
bedrock wells (MAP GA3) plus the deeper surficial
wells (about 500 wells), were generated from the
water well data base to provide the reader with an
overall impression of well coverage used to generate
the maps and cross sections. Map GA3 provides the
reader with a qualitative estimate of the reliability of
the contour maps at any location. For example, there
are very few wells between Mount Newton and
Stellys Cross Roads to the west of East Saanich Road,
in other words in Hagen Creek Valley.
Flow rate ranges for those bedrock wells that have
flow rates listed in the data basewere overlayed on the
bedrock map generated by J. Riddell (1998). They
provide an overall impression of the pattern of flow
rates for bedrock wells within Central Saanich.
Finally, the flow rate ranges for those surficial wells
that have flow rate listed in the data base were
overlayed on the surficial thickness map, with the
outlines of the boundaries of the surficial aquifers
fromMAPGA7..
Map GA1.
This map shows the locations of all the wells in the
Central Saanich derived from the “Well Log
database”. There are more than 800 wells in the data
base. Approximately 200 additional wells in the
original water well data base obtained from the
Groundwater Section of the B.C. Ministry of
Environment, Lands and Parks are not included in the
Central Saanich water well data base. The missing
wells are a mixture of wells with unknown or poorly
determined locations and new wells that have not yet
been located on the Ministrywater wellmaps.
The locations of the wellsweredigitizedfrom 1:5 000
maps provided by the Ministry. The accuracy of the
location of the well on the surface is approximately
+
_ 15 m, although the uncertainty in the location of
these wells on the maps may be much larger since
they were located from descriptions provided by the
drilling companies.
The elevation contour interval on these maps (1978) is
10 ft (approximately 3 m), thus giving an elevation
_ 1.5 m.
accuracy of approximately +
(Keating,
Stellys andMountNewton) and 2 north-south sections
(East Saanich andWestSaanich).
Map GA1. All well locations in the Central Saanich Municipality with locations of geological aquifer cross sections.1998.
1000 m
0m
1000 m
Scale 1:40 000
2000 m
Municipality of Central Saanich Resource Atlas
GA-5
GROUNDWATER AQUIFERS
PRODUCTIVITY OF SURFICIAL AQUIFERS
469000
464000
474000
SurficialAquifers
The surficial aquifers in Central Saanich are the
Cowichan Head Aquifer, the Keating Aquifer, the
East Saanich Aquifer and the Hagen Creek Aquifer.
The boundaries of the aquifers are shown on the 1:40
000map(Map2). The boundaries are similar to those
determined previously (Callan, 1968, Halstead, 1968,
Livingston, 1961) but have been modified to include
the updated information in the water well data base.
In particular, the overburden (surficial sediment)
thickness map indicates the boundaries of the East
SaanichAquifer and the Hagen Creek Aquifer can be
extended (indicated on the map by dashed lines). An
area south of the Keating Aquifer (Old West)
containing several isolated regions of thicker
sediments has been identified from the overburden
thickness map as a potential surficial aquifer.
However further investigations are required before
this area canbedesignated as a surficial aquifer.
HAGAN
CREEK
Flow rate ranges from the surficial wells are
plotted on the overburden thickness map (Map 7) and
the combination of sediment thickness, lithology
(Table 1) and flow rate were used to estimate the
quality of the aquifers.
Three categories were used to define the productivity
of the aquifer: good, moderate
and adequate.
Good aquifer - a good aquifer is one that has a
reasonable thickness (10 to 30 meters) of high
permeabilitysediments, for example coarse sands and
gravels, and has a high probability that wells drilled
into it will have a rate of 50 gallons per minute or
better.
Moderate aquifer- a moderate aquifer is one that has
a reasonable thickness (10 to 30 meters) of high to
moderate permeability sediments, for example coarse
to fine sands, and has a high probability that wells
drilled into it will have a rate of 25 to 50 gallons per
minute.
Adequate aquifer - an adequate aquifer is one that
has a reasonable thickness (10 to 30 meters) of
moderate to poor permeability sediments, for
example fine sands, or a thin layer of good
permeability sands and gravels and has a high
probability that wells drilled into it will have a rate of
5 to 25 gallons perminute.
Map GA2.
This map shows the outlines of the surficial aquifers in Central
Saanich based on information contained in the Central Saanich
waterwell data base, the surficialmapinthisresourceatlasand
earlier reports provided by the Groundwater Section of the
British Columbia Ministry of Environment, Lands and Parks.
It incorporates all the existing data plus new information
(lithological, overburden thickness, bedrock surface elevation
KEATING
EAST
SAANICH
COWICHAN
HEAD
OLD
WEST
464000
474000
469000
MAP GA2. Surficial Aquifers in Central Saanich. 1998.
and flow rate information) provided by the water well data base.
Estimates of aquifer deliverability (the ability of an aquifer to
produce water at a sustained flow rate) are qualitatively provided
and are based on flow rate information, aquifer lithology and
anticipatedrecharge of the aquifer.
Potential regions where surficial aquifers may be exposed to
1000 m
0m
1000 m
2000 m
Scale 1:40 000
industrial contamination are also outlined on the map. Potential
agricultural contamination (pesticides, nitrates, etc.) is possible
within these surficial aquifers wherever extensive farming exists
Good
Aquifer boundary
Moderate
Newly mapped aquifer
or extension of boundary
of previously mapped
aquifer.
Adequate
Potential
contamination
(industrial)
Not certain
Municipality of Central Saanich Resource Atlas
GA-6
GROUNDWATER AQUIFERS
LOCATION MAP OF BEDROCK WELLS
464000
469000
474000
464000
469000
474000
The aquifer productivity classification shown on page
GA-6 is qualitative but provides the reader with a
rough idea of aquifer productivity. For example, the
central portion of the East Saanich Aquifer is
considered a good aquifer while the southern portion
of the Cowichan Head Aquifer is considered an
adequate aquifer. The flow rate ranges plotted on the
overburden thickness map are consistent with these
ranges (MAPGA7)..
In addition to the productivity of the aquifers themap
also shows the areas of potential industrial
contamination. The two areas highlighted on themap
are the Keating Industrial Park on the east side of the
Keating Aquifer and the town of Saanichton at the
southern end of the Hagen Creek Aquifer.
Agricultural contamination (pesticides and nitrates
from fertilizers) could occur within the surficial
aquifers directly below and down gradient (along the
flow direction) of areaswhere extensive agriculture is
practiced.
At the present time industrial and
agricultural contamination of the surficial aquifers
does not appear to be a problem.
Keating Aquifer
This aquifer underlies Keating Cross Road roughly
between Oldfield Road and West Saanich Road. The
aquifer thins to the north and west as observed on the
Keating Cross Section and the overburden thickness
map. It is limited in the south (about 500 m south of
Keating cross Road) by bedrock. To the east the
control (well data) is poor, although there are some
indications that the Keating and East Saanich
Aquifers may joinat depth. If they do the thickness of
the adjoining aquifer is likely nomorethan20m. The
Keating Cross Road Section shows that the sands and
gravels making up the aquifer are inter-bedded with
clay layers (confining layers), at least in the western
half of the aquifer. The productivity of the aquifer is
moderate because of the complexity of the layering
and the moderate flow rate ranges recorded in the data
base and plotted on the overburden thickness map.
The Keating Industrial Park is potentially an area
where industrial contamination ( eg. Forms of
hydrocarbons, solvents, and cleaning chemicals )
could enter the KeatingAquifer, although there are no
serious problems at the present time. Up to 30 m thick
layers of sands and gravels of the KeatingAquifer can
be seen in Butler's gravel pit (see overview map at
beginning of this atlas). There is a sandy till overlying
most of the aquifer and a thin veneer of clay lies on top
of the till at elevations less than about 80 m (Callan,
1968).
MAP GA3. Bedrock wells in Central Saanich.1998.
1000 m
Map GA3.
This figure shows the location of all the bedrock wells
plus deeper surficial sediment wells (depth greater than
20 m on average) in the Central Saanich water well data base.
These wells were used to generate overburden thickness
and bedrock elevation maps (Maps GA4 and GA5).
0m
1000 m
2000 m
Scale 1:40 000
Those wells that penetrate bedrock and have a recorded flow
rate were used to generate the bedrock flow map (Map GA6).
Approximately 325 bedrock wells plus 125 deeper surficial
sediment wells are shown on this map.
bedrock well
deep surficial well
Municipality of Central Saanich Resource Atlas
GA-7
GROUNDWATER AQUIFERS
OVERBURDEN THICKNESS
464000
469000
464000
469000
474000
East SaanichAquifer
The East Saanich Aquifer is a roughly north-south
ridge that follows Central Saanich Road at the
southern end of the aquifer to the junction with East
Saanich Road. The aquifer then approximately
parallels East Saanich Road to just south of Mount
Newton Cross Road where it terminates. This aquifer
consists of thick (up to 50 m) layers of sands and
gravels. Its southern boundary is just south of the
southern boundary of Central Saanich. The northern
boundary occurs where the sands and gravels pinch
out against a bedrock high. This feature can be seen
just south of Mount Newton Cross Road on the East
Saanich Cross Section. The bedrock high appears to
separate the East Saanich Aquifer from the Hagen
Creek Aquifer to the north. More data is needed to
verify this since the bedrock elevation map does not
have enough wells in the area to show the details of
this feature.
The East Saanich Cross Section is slightly to the east
of the aquifer between the junction of Central and East
Saanich Roads and Stellys Cross Road.
The
remainder of the eastern boundary of the aquifer is
inferred from the topography. The southern end of the
East Saanich Cross section is west of the aquifer and
crosses a small sand and gravel deposit associated
with an abandoned pit in the area. The western
boundary of the aquifer is more problematic. There
are some indications from the Keating Cross Section
that the East Saanich and KeatingAquifersmayjoinat
depth, at least along Keating Cross Road. The
overburden thickness (MAP GA4) also indicates the
western limit of the aquifer south of Stellys Cross
Road and northeast of the Keating Aquifer may
extend quite a bit further to the west than indicated on
theolder maps.
The productivity of the East Saanich Aquifer is quite
variable. The eastern central portion (see Map GA2)
is considered to be a good aquifer while the southern
portion is considered moderate. The northern portion
of the aquifer has been rated as adequate. These are
based on the type of material in the aquifer (from the
cross sections) , the thickness of the aquifer sediments
(from the overburden thickness MAPGA4) and the
flow rates of wells within the aquifer (from the flow
rate data overlaid on the overburden thickness (MAP
GA7). The aquifer is overlain by up to 10 m of sandy
till with a thin veneer of clay over the tills at elevations
less than about 80 m (Callan, 1968)
474000
MAP GA4. Overburden thickness in Central Saanich. 1998
Map GA4. This figure is a map of overburden thickness obtained from the
Central Saanich water well data base. It includes all bedrock wells (true
overburden thickness) and all deeper surficial sediment wells (minimum
thickness of overburden) so this map actually provides an estimate of the
minimum thickness of overburden throughout Central Saanich. The thick
sediments north of Island View Road and east of the Cowichan Head.
Aquifer may be on artifact of gridding since there are few wells in this area.
overburden thickness
1000 m
0m
1000 m
Scale 1:40 000
2000 m
> 50
40 - 50
30 - 40
20 - 30
10 - 20
< 10
Municipality of Central Saanich Resource Atlas
GA-8
GROUNDWATER AQUIFERS
ELEVATION OF BEDROCK
464000
469000
464000
469000
474000
Hagen Creek Aquifer
The Hagen CreekAquifer is north of the East Saanich
Aquifer. It consists of layers of sand and gravel up to
25 m thick covered by a sandy till with a maximum
thickness of 10 m. Again there is a thin veneer of clay
overlying the till at elevations less than about 80 m.
The southern boundary has been described earlier in
the section on the East Saanich Aquifer. The western
boundary is controlled by topography (Mount
Newton) and the eastern boundary is controlled
mainly by a bedrock ridge that is exposed on the east
side of East Saanich Road about 1.5 kilometers north
of Mount Newton Cross Road. The overburden map
indicates the northern boundary of the Aquifer
extends further north than previously mapped.
However, there are a limited number of wells in the
area so this should be approached cautiously. The
productivity of the aquifer has been rated asmoderate
based on flow rates, overburden thickness and type of
surficial material in the aquifer. The potential
northern extension of the aquifer has been rated as
adequate since there is only a limited amount of
information in thisportion of the aquifer. The town of
Saanichton could be a potential source of industrial
contamination for the Hagen Creek Aquifer.
However there arenoindications of any problems
at this time.
Cowichan HeadAquifer
The Cowichan Head Aquifer roughly parallels the
coast along the eastern side of Central Saanich from
near the southern boundary of theMunicipality to just
south of Mount Newton Cross Roads near Highway
17. The aquifer consists of sand and gravel layers up
to50 m ormore in thicknesswithamarineclay layer at
the base of the aquifer and a sandy till layer up to 10 m
thick overlying the aquifer (see the Keating and
Stellys Cross RoadCross Sections). The eastern edge
of the aquifer is eroded and significant groundwater is
lost due to seepage from the exposed cliff face. The
northern portion of the aquifer (north of Island View
Road) has been rated as moderate while the southern
portion has been rated as adequate based on flow
rates, aquifer material and total surficial thickness.
The western boundary of the aquifer is based on
topography and the overburden thickness map.
However there are only a few wells in the western
portion of the aquifer so the boundary is mostly
defined by topography.
474000
MAP GA5. Bedrock Elevation in Central Saanich. 1998.
1000 m
Map GA5.
This figure shows the elevation of the top of the bedrock (meters above sea level)
obtained from the Central Saanich water well data base. It includes all bedrock wells
(true elevation) plus deeper surficial sediment wells (maximum elevation of top of bedrock)
so this map actually provides an estimate of the maximum elevation of the top of bedrock
throughout Central Saanich.
0m
1000 m
Scale 1:40 000
2000 m
>180
160 - 180
140 - 160
120 - 140
100 - 120
80 - 100
60 - 80
40 - 60
20 - 40
0 - 20
_ 20 - 0
< _ 20
Municipality of Central Saanich Resource Atlas
GA-9
GROUNDWATER AQUIFERS
FLOW RATES OF BEDROCK WELLS AND BEDROCK GEOLOGY
469000
464000
474000
Jlg
BedrockAquifers
Jlg
exposed
exposed
Wells deriving their water from bedrock range from
good to poor, depending on whether or not a particular
well encountered fractures. Bedrock flow rates are
plotted on the bedrock geology map provided by
Riddell (1998) to illustrate the pattern of flow rates
within Central Saanich (Map GA6). Some bedrock
wells have reported flow rates of 100 gallons per
minute or better while many are between 3 and 5
gallons per minute (suitable for domestic use only).
The range and distribution of flow rates reflects the
nature of fractured bedrock. There does not appear to
be a direct relationship between bedrock type and
quality of the bedrock wells, except perhaps for the
Karmutsen volcanic rocks in the vicinity of
Butchart Gardens where the flow rates are higher.
There is no doubt that bedrock aquifers in Central
Saanich provideamajor source of groundwater.
Tomake more effective use of bedrock aquifers in the
Central Saanich more work is required to map and
locate the distribution and density of fractures.
Jlg
Jlg
exposed
exposed
Q
inferred to
overlie JIg
Jlg
exposed
Q
inferred to
overlie JIg
Recharge
The main source of recharge for the surficial sediment
aquifers in Central Saanich is through infiltration
from the surface. The tills, being quite sandy, will
have a permeability near the higher end of their range
(10 -13 m 2). This is sufficiently permeable to allow
seepage through the till into the aquifers. In areas
where there is a veneer of clay on the surface
infiltration will be less. Callan (1968) estimated the
yearly infiltration into the Keating, East Saanich and
Hagen Creek Aquifers by multiplying (1) the
approximate area of the aquifer overlain by till
without a clay veneer and (2) the amount of yearly
precipitation that infiltrates the till and ends up in the
aquifer (he assumed 20% of the average yearly
rainfall or 0.55 feet per year). The recharge for each
of these three aquifers based on these assumptions
are:
KeatingAquifer
29,000,000 gallons -
JB
exposed
TRQ
exposed
Q
Q
inferred to
overlie TRK
inferred to
overlie JIg
JB
exposed
PW
(421,000 m 3)
East SaanichAquifer
144,000,000 gallons - (2,090,000 m 3)
Hagen CreekAquifer
55,000,000 gallons -
TRQ
exposed
(798,000 m 3)
464000
1000 m
474000
469000
MAP GA6. Bedrock Well Yields in Central Saanich. 1998.
0m
1000 m
Scale 1:40 000
2000 m
Map GA6.
This figure posts flow rates of bedrock wells in gallons per minute (gpm) on top of
J. Riddell’s bedrock map. The coloured dots represent different flow rate ranges and
are posted at the bedrock well locations. About one-third of the wells in the data
base do not have a flow rate value, hence they are not plotted. Only those wells
that penetrate bedrock and have a flow rate listed were posted on the map.
Well flow rate
0-5
5 - 10
10 - 15
15 - 25
25 - 50
50 - 75
> 75
Bedrock Legend
Q
Quaternary
TQ
R
Quatsino
Limestone
Jlg
Saanich
Granodiorite
JB
Bonanza
Volcanics
Karmutsen
Formation
PW
Permian
Wark gneiss
Geological contact
exposed
inferred
Fault
Municipality of Central Saanich Resource Atlas
GA-10
GROUNDWATER AQUIFERS
SURFICIAL AQUIFERS, WELL FLOW RATES AND OVERBURDEN THICKNESS
469000
464000
Since Callanmadetheseestimates in 1968 the portion
of the aquifers covered with impermeable man-made
material has increased significantly. This will have
the effect of reducing the amount of infiltration into
the aquifers and increasing the runoff to streams and
low lying areas. This is particularly true for the
Keating Aquifer where industrial development over
the aquifer has led to large areas being covered with
asphalt, concrete and buildings. Much of this
industry is at lower elevations where the infiltration is
limited by the veneer of clay.
Residential
development over the East Saanich Aquifer has
increased dramatically during the last 30 years.
Similarly increased residential and commercial usage
in Saanichton, overlying the Hagen Creek Aquifer,
has increased during this time. The Cowichan Head
Aquifer however still remains relatively
undeveloped.
474000
HAGAN
CREEK
Recharge into bedrock is much more difficult to
estimate. The higher regions of the Saanich Peninsula
are covered with a thin veneer of till, thus allowing
precipitation to infiltrate into cracks and fissures in
thecrystalline bedrock. The infiltratedwater can then
move downward along these fracture systems to
lower elevations within the bedrock. The amount of
recharge is difficult to estimate since it depends on the
location and density of fractures within the bedrock.
KEATING
References
EAST
SAANICH
Ciancone, S., 1998. Central Saanich ResourceAtlas, Well
Log Database; An Appendix. Municipality of Central
Saanich. Saanichton, BC.
COWICHAN
HEAD
Callan, D.M., 1968, A preliminary assessment of
ground water potential in the District of Central Saanich:
File 0239013, Water Investigation Branch.
Halstead, E.C., 1968, The Cowichan ice tongue,
Vancouver Island: Canadian Journal of Earth Sciences, 5,
1409-1415.
OLD
WEST
Huntley, D.H., Bobrowsky, P.T., and Clague, J..J., 1998,
Quaternary history of Central Saanich: in this atlas.
Livingston, E., 1961, Surficial geology and ground water
resources of part of the Saanich Peninsula: File 0239013,
Water Investigation Branch.
Riddell, J., 1998, Bedrock geology of Central Saanich:
in this atlas.
464000
474000
469000
MAP GA7. Aquifers on Overburden in Central Saanich. 1998.
1000 m
Map GA7.
This figure outlines the boundaries of the surficial aquifers on top of the
overburden thickness map (Map GA4). The symbols represent different flow
rate ranges in gallons per minute (gpm) and are posted at the surficial well locations.
Only those wells that produce water from surficial sediments and have a flow rate
listed in the data base are posted on the map (see Map GA6).
0m
1000 m
Scale 1:40 000
2000 m
Aquifer boundary
Newly mapped aquifer
or extension of boundary
of previously mapped
aquifer.
Not certain
well flow rates
0-5
5 - 10
10 - 15
15 - 25
25 - 50
50 - 75
> 75
overburden thickness
> 50
40 - 50
30 - 40
20 - 30
10 - 20
< 10
Municipality of Central Saanich Resource Atlas
GA-11