Aquifers in BC

The original is a great PDF. But complex. This is only here in case they take down the original.

WHICH IS HERE: http://www.forrex.org/sites/default/files/publications/articles/Streamline_Vol13_No1_Art3.pdf

10 Streamline

Watershed Management Bulletin Vol. 13/No. 1 Fall 2009

Understanding the

Types of Aquifers in

the Canadian Cordillera

Hydrogeologic Region to

Better Manage and Protect

Groundwater

Mike Wei, Diana Allen, Alan Kohut, Steve Grasby, Kevin Ronneseth,

and Bob Turner

Peer-reviewed Synthesis Article

Introduction

G

roundwater is often viewed as

a mysterious and challenging

resource to manage as it is hidden

underground. Generally, the only

obvious sign of groundwater to the

public is water flowing from a spring

or from a well. Where and how the

groundwater got to the spring or

well and how much is available are

questions of interest when trying

to protect the resource. Extending

knowledge of groundwater and

aquifers

—permeable, water-bearing

geological formations or deposits that

transmit and store groundwater—to

communities and land and water

resource decision makers has been a

challenge in British Columbia because

of the general lack of comprehensive

studies in many areas. If similar types

of aquifers have similar characteristics,

it may be reasonable to extrapolate

knowledge from well-studied areas to

predict properties of a specific aquifer

where little is known. Although this

inferred knowledge does not replace

actual testing and assessment of the

local aquifer, it can be useful, as a first

step, to develop a working hypothesis

about the local aquifer, especially in

sparsely studied areas. This article

describes a system of categorizing

aquifers in the Canadian Cordillera

Hydrogeologic Region (first described

by Halstead [1967] and here referred

to as the “Region” or “Cordillera”)

based on general hydrogeological

characteristics (Figure 1). Categorizing

aquifers promotes increased general

knowledge and understanding of

the characteristics of local aquifers in

this Region, and thus supports the

management and protection of local

groundwater resources.

The Canadian Cordillera Hydrogeologic

Region occupies the

mountainous region that covers

much of British Columbia (except

the Peace River country), as well

as the Rocky Mountain foothills of

southwestern Alberta, the southern

part of the Yukon Territory, and

part of the Northwest Territories;

it is the westernmost of Canada’s

hydrogeologic regions (Figure 1;

Sharpe et al., in press). Aquifers in the

Region supply water to an estimated

1 million persons for drinking water,

as well as for irrigation, aquaculture,

and industrial processing needs. The

Region is physiographically diverse,

comprising massive mountain ranges,

highlands, foothills, plateaus, basins,

and lowlands, with a total relief of

over 4000 m (the greatest in Canada)

and covering over 1 million km

2. The

Region’s climate varies widely from

Mediterranean conditions along the

southwest coast to polar conditions

Figure 1. Hydrogeologic regions of Canada (Source: Rivera, in press; reproduced with

permission of the Geological Survey of Canada).

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Watershed Management Bulletin Vol. 13/No. 1 Fall 2009 11

Continued on page 12

at high mountain elevations and in

the north. Mean annual precipitation

generally decreases from west to

east across the Region (following the

general movement of the weather

fronts), ranging, for example, from

3306 mm at Tofino on the west coast

of Vancouver Island to 293 mm at

Kamloops and 472 mm at Banff,

Alberta. Annual precipitation also

generally increases with elevation due

to orographic effects.

Seasonal climatic variations control

the annual quantity and form of

precipitation, thereby affecting the

timing and amount of runoff to

streams and recharge to aquifers

in the Cordillera. Coastal areas

experience highest precipitation

during the winter months, with much

of it falling as rain, except at higher

elevations where it may fall as snow.

In these coastal areas, groundwater

recharge mostly occurs during the

winter months when the rate of

evaporation and transpiration are at

their seasonal lowest. Consequently,

the natural groundwater levels in

coastal areas show a seasonal high

during winter or early spring, and

decline from spring to late fall (see

Figure 2a). In contrast, interior areas

have their highest precipitation

during the summer months, but

much of this is evaporated or

transpired and does not normally

contribute to groundwater recharge.

In the interior, snow accumulations

during the winter months, and at

higher elevations, are important for

recharge during the spring and early

summer when snowmelt occurs.

Thus, groundwater levels in the

interior generally are at a seasonal

high in late spring or early summer

and then decline over the summer

and early fall. The groundwater level

generally reaches a seasonal low

during the winter months, when

precipitation at the land surface is

frozen (see Figure 2b).

Glacial history, surficial and bedrock

geology, and tectonic history

greatly influence the occurrence,

distribution, and characteristics of

aquifers in the Region. Most surficial

or unconsolidated aquifers are formed

by deposition of sand and gravel in

moving water under a fluvial or, if by

moving water during glacial times, a

glaciofluvial environment related to

the last period of glaciation. Glaciofluvial

sand and gravel aquifers formed

during ice advance tend to be overlain

by till or glaciolacustrine clay and

silt, and are lithologically confined.

Glaciofluvial sand and gravel aquifers

formed during the melting of the

Figure 2a. Average monthly precipitation at Nanaimo (coastal setting: the blue bars represent

rainfall and the grey bars represent snowfall). The mean annual precipitation at Nanaimo

is 1163 mm. Also plotted (dark blue line) is the average monthly groundwater level from

Observation Well No. 228. Groundwater level in the aquifer is recharged by rain falling during

the fall and winter months (November to February).

Figure 2b. Average monthly precipitation at Cranbrook (interior setting: the blue bars

represent rainfall and the grey bars represent snowfall). The mean annual precipitation at

Cranbrook is 411 mm. Also plotted (dark blue line) is the average monthly groundwater level

from Observation Well No. 291. Groundwater level in the aquifer is recharged, not from the

relatively high precipitation in May–June, but rather from snowmelt from the preceding winter

months (November to March).

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Precipitation (mm)

Groundwater level (m)

OW 228

0

40

80

120

160

200 3

4

5

6

7

8

9

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Precipitation (mm)

Groundwater level (m)

0

10

20

30

40

50

60

10

11

12

13

14

9

OW 291

12 Streamline

Watershed Management Bulletin Vol. 13/No. 1 Fall 2009

Continued from page 11

ice are commonly unconfined. The

bedrock geology of the Cordillera is

extremely varied and complex due

to the Region’s geologic, tectonic,

and volcanic history. Holland (1976)

generalized the bedrock geology of

the Region into six main bedrock

types:

1. intrusive igneous rocks;

2. flat-lying lava, and some

sedimentary rocks;

3. flat or gently dipping sedimentary

rocks;

4. folded sedimentary rocks;

5. folded and faulted volcanic and

sedimentary rocks; and

6. foliated metamorphic rocks of

various ages.

Despite the presence of different

types of bedrock in the Cordillera,

bedrock permeability exists mostly

as a result of development of

fractures or faults from tectonic

forces or, in limestone, from

development of dissolution cavities

(karst). In the Cordillera, fractures

and faults developed in igneous

intrusive, foliated metamorphic,

and folded and faulted volcanic

and sedimentary rocks, give these

types of rocks sufficient secondary

permeability to form aquifers. The

permeability, however, is often

anisotropic

1 because the fractures or

faults are discrete and have specific

orientations in the bedrock. The

porosity and

storativity 2 of fractured

or faulted bedrock are also very low

(e.g., porosity of less than a few

percent). Extensive areas of central

British Columbia are underlain by

relatively unaltered, flat-lying lava

of Tertiary age (e.g., the Cariboo-

Chilcotin area). These are mostly

basalts and individual flows that

can be hundreds of metres thick.

This lava forms an important aquifer

because groundwater typically

occurs in joints, and in fractured and

weathered contact zones between

the lava flows.

The Province of British Columbia

and the Canadian Government

(through the Geological Survey of

Canada and Environment Canada)

have conducted groundwater studies

in the Region since the 1950s. The

Province of British Columbia has

also been mapping and classifying

developed aquifers in the Region

since 1994 (for background on the

BC Aquifer Classification System, see

adjacent sidebar and Berardinucci

and Ronneseth 2002). This work, and

the resulting inventory, has enabled

the identification of aquifer types

within the Region and improved

our understanding of their general

hydrogeologic characteristics.

Major Aquifer Types in

the Canadian Cordillera

Hydrogeologic Region

In the Cordillera Hydrogeologic

Region, aquifers generally fall into the

following six categories (refer also to

Figures 3a and 3b).

Unconsolidated Sand and

Gravel Aquifers

1.

Unconfined 3 fluvial or glaciofluvial

aquifers along river or stream

valleys

a. Aquifers along major higherorder

rivers, where the potential

of hydraulic connection with

the river exists,

b. Aquifers along moderate-order

rivers, where the potential of

hydraulic connection with the

river exists, or

c. Aquifers along lower-order

(< 3–4) streams in confined

valleys, where aquifer thickness

and lateral extent are more

limited

2. Unconfined deltaic aquifers

3. Unconfined alluvial fan or colluvial

aquifers

4. Aquifers of glacial or pre-glacial

origin

a. Unconfined glaciofluvial

outwash or ice contact aquifers,

b.

Confined 4 aquifers of glacial or

pre-glacial origin, or

Continued on page 14

c. Confined aquifers associated

with glaciomarine environments

Bedrock Aquifers

5. Sedimentary rock aquifers

a. Fractured sedimentary bedrock

aquifers, or

b. Karstic limestone aquifers

6. Crystalline rock aquifers

a. Flat-lying or gently-dipping

volcanic flow rock aquifers, or

b. Crystalline granitic,

metamorphic, metasedimentary,

meta-volcanic,

and volcanic rock aquifers

The categories of aquifer types are

based on geologic and hydrologic

properties, as well as on practical

considerations, such as data

availability. The main geologic

factors are the origin and type of the

geologic deposit that comprise an

aquifer (e.g., sand and gravel aquifer

forming a delta at the mouth of a

river or a plutonic granitic fractured

bedrock aquifer). The origin and type

of geologic deposit often governs an

aquifer’s hydraulic properties, such

as the nature of the porous medium

(porous sand and gravel, or fractured

bedrock) and ability to transmit and

store water. Another consideration is

the hydraulic connection between an

aquifer and a river, stream, or lake.

A direct hydraulic connection can

be advantageous for potential well

yields because pumping could induce

infiltration of surface water into those

aquifers. A practical consideration,

particularly for unconsolidated

aquifers buried at depth, is that it is

often difficult to identify the origin

of these buried unconsolidated sand

and gravel aquifers based on very

limited well record data. Buried

unconsolidated sand and gravel

aquifers are grouped into confined,

unconsolidated sand and gravel

aquifers of glacial or pre-glacial

origin (Type 4b). Descriptions of the

aquifer types are presented directly

below; many of the aquifer types are

illustrated in Figures 3a and 3b, which

represent aquifers in a coastal and

interior setting, respectively.

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Watershed Management Bulletin Vol. 13/No. 1 Fall 2009 13

T

he British Columbia Aquifer Classification System was developed in 1994

(Kreye and Wei 1994). Its objective was to interpret raw data (primarily well

records and geologic mapping) to identify and classify aquifers, and thus:

provide a framework to direct detailed aquifer mapping and characterization;

provide a method of screening and prioritizing management, protection,

and remedial efforts on a provincial, regional, and local level;

identify the level of management and protection an aquifer requires;

build an inventory of the aquifers in the province; and

increase public knowledge and understanding of their local aquifer.

The aquifer classification system has two main components (Figure A-1):

a. classification component

b. ranking value component

The

classification component classifies an aquifer on the basis its level

of development and its vulnerability to contamination. The classification

component categorizes an aquifer based on its current level of groundwater

development and vulnerability to contamination (categories A, B, and C for

high, moderate, and low vulnerability, respectively). The level of development

(categories I, II, and III for high, moderate, and light development, respectively)

compares the amount of groundwater withdrawn from an aquifer (demand)

to the aquifer’s inferred ability to supply groundwater for use (productivity).

The level of vulnerability (categories I, II, and III for high, moderate, and low

vulnerability, respectively) of an aquifer is based on whether or not an aquifer is

confined.

The combination of the three development and three vulnerability categories

results in nine aquifer classes. The nine aquifer classes have an implied priority

from a general management and protection standpoint, from IIIC, which is the

lowest priority, to IA, which is the highest (Figure A-2).

The

ranking value component assigns a number value to indicate the relative

importance of an aquifer. Assigned values are derived from the following

criteria:

1. aquifer productivity;

2. aquifer vulnerability to surface contamination;

3. aquifer area or size;

4. demand on the resource;

5. type of groundwater use; and known documented

groundwater concerns related to:

6. quality; and

7. quantity.

The ranking value is determined by summing the points for each criterion

(Figure A-3): the lowest ranking value possible is 5, and the highest ranking

value possible is 21. Generally, the aquifer with the greater ranking value has

the greater priority. Figure A-3 shows the ranking values applied for each

criterion.

The classification and ranking value components are determined for the aquifer

as a whole, and not for parts of aquifers.

To promote the appropriate use of the aquifer classification system, a guidance

document was produced to assist users in interpreting and using the aquifer

maps. This document can be found at:

http://www.env.gov.bc.ca/wsd/plan_protect_

sustain/groundwater/aquifers/reports/aquifer_maps.pdf

The aquifer maps and other hydrological information are also available online

at:

http://www.env.gov.bc.ca/wsd/data_searches/wrbc/index.html

The BC Aquifer Classification System

Figure A-1. The British Columbia Aquifer

Classification System (Source: Rivera, in press;

reproduced with permission of the Geological

Survey of Canada).

Figure A-2. Aquifer classes (Source: Rivera,

in press; reproduced with permission of the

Geological Survey of Canada).

Figure A-3. Criteria and points for aquifer

ranking value (Source: Rivera, in press;

reproduced with permission of the Geological

Survey of Canada).

14 Streamline

Watershed Management Bulletin Vol. 13/No. 1 Fall 2009

Type 1 –

This category covers sand

and gravel aquifers that are generally

shallow, unconfined, and occur

along river or stream valleys. Often

both fluvial and glaciofluvial sand

and gravel deposits form an aquifer

along the river or stream valley

bottom. Therefore, shallow sand and

gravel aquifers underlying river or

stream valleys—whether of fluvial or

glaciofluvial origin—are categorized

as the same general aquifer type. This

category is further subdivided into

the following three sub-categories.

Type 1a – Aquifers found along

major higher-order rivers with

potential hydraulic connection to

the river. These rivers are generally

of low gradient and the depositional

energy is relatively low to

cause deposition of mostly sand,

silt, some clay, and some gravel

(e.g., the Chilliwack-Rosedale

aquifer along the Fraser River near

the City of Chilliwack).

Type 1b – Unconfined sand and

gravel aquifers found along

moderate-order rivers with

potential hydraulic connection to

the river. These rivers have higher

gradients compared to rivers of

higher stream orders and the

depositional energy is relatively

high to cause deposition of mostly

sand and gravel (e.g., the fluvial

sand and gravel deposit along

the Cowichan River on the east

coast of Vancouver Island near the

community of Duncan; the fluvial

and terraced glaciofluvial sand and

gravel deposits along the Kettle

River at the Southern Interior

community of Grand Forks).

Type 1c – Sand and gravel aquifers

found along lower-order (< 3–4)

streams in confined valleys with

floodplains of limited lateral

extent, where aquifer thickness

and size are more limited (e.g.,

fluvial or glaciofluvial deposits

along a mountain stream).

Type 2 –

This category covers sand

and gravel aquifers that are shallow,

unconfined, and which form deltas

Figure 3b. Schematic diagram showing some of the different types of aquifers in the Region

in an interior setting (Source: Rivera, in press; reproduced with permission of the Geological

Survey of Canada).

Continued from page 12

Figure 3a. Schematic diagram showing some of the different types of aquifers in the Region

in a coastal setting (Source: Rivera, in press; reproduced with permission of the Geological

Survey of Canada).

at the mouth of rivers and streams

(e.g., the Scotch Creek aquifer at

Shuswap Lake). Older deltas buried at

depth below till, glaciolacustrine, or

glaciomarine deposits have not been

included here because it is generally

difficult to identify buried sand and

gravel as deltas based on limited

data. These buried aquifers would be

categorized under sand and gravel

aquifers of glacial or pre-glacial origin

(i.e., aquifer Type 4b).

Type 3 –

This category covers sand

and gravel aquifers that form alluvial

fans or are of colluvial origin near the

land surface. As with Type 2 aquifers,

this category excludes older alluvial or

colluvial aquifers buried at depth. The

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Watershed Management Bulletin Vol. 13/No. 1 Fall 2009 15

Vedder River Fan aquifer at the City

of Chilliwack is an example of this

type of aquifer.

Type 4 –

This category covers known

glaciofluvial sand and gravel aquifers,

as well as other sand and gravel

aquifers identified in well records

as occurring at depth, underneath

till or glaciolacustrine deposits, and

glaciomarine sand, sand and gravel

aquifers. This category is further

subdivided into the following three

sub-categories.

Type 4a – Unconfined glaciofluvial

outwash or ice contact sand

and gravel aquifers, generally

formed near or at the end of

the last period of glaciation. The

Abbotsford-Sumas Aquifer is

perhaps the most well-known and

studied aquifer of this type in the

Cordillera Region.

Type 4b – Confined sand and

gravel aquifers underneath till,

in between till layers, or

underlying glaciolacustrine

deposits. The Quadra Sand,

which occurs in the Georgia

Depression on the east coast of

Vancouver Island and along the

southern mainland coast, is an

excellent example of a confined

glaciofluvial sand and gravel

aquifer consisting of sand and

gravel deposited as the glacier

advanced south along the Georgia

Depression. Other confined

glaciofluvial sand and gravel

aquifers occur between till layers,

which is indicative of deposition

during glaciation. Still other

confined sand and gravel aquifers

may be fluvial, alluvial, or colluvial

deposits from a time prior to

glaciation (and therefore lie

underneath till or glaciolacustrine

deposits). Unless a confined sand

and gravel aquifer has been well

studied, it is often difficult to

determine its geologic origin and

geomorphology based on limited

data. Therefore, any waterbearing

sand and gravel occurring

underneath till, in between till

layers, or under glaciolacustrine

deposits is included in this

sub-category.

Type 4c – Sand and gravel aquifers

that occur underneath known

sand, silt, and clay deposited

under a marine environment near

the coast. Most of the few known

aquifers in this category occur

in the deep marine sediments at

depth in low-lying areas in the

Fraser Lowland, in Surrey and

Langley, east of Vancouver.

Type 5 –

This category is further

subdivided into two sub-categories:

(a) fractured sedimentary rocks

and (b) karstic limestone rocks.

The Nanaimo Group of fractured

and faulted sedimentary rocks in

the Gulf Islands and east coast of

Vancouver Island is a classic example

of the former sub-category. The

limestone formations in the Rocky

Mountains are an example of the

latter sub-category. For fractured

sedimentary rocks, groundwater

flow occurs mostly along joints and

in fractures and faults. Although

this classification may also apply

to karstic limestone, the major

difference is that groundwater may

flow in open dissolution channels

and large cavities in karstic limestone

aquifers.

Type 6 –

This category is subdivided

into two sub-categories: (a) flatlying

to gently dipping volcanic flow

aquifers and (b) fractured crystalline

rocks. Groundwater flow in flat-lying

to gently dipping volcanic rocks can

be through joints and fractures, but

also in broken, weathered zones

between flows. The large volcanic

flow bedrock aquifer in the Central

Interior of British Columbia near

70-Mile House is an example of this

type of aquifer.

Groundwater flow in fractured

crystalline rocks is mostly along

joints, fractures, and faults. This

sub-category includes igneous

intrusive or metamorphic rocks

(such as the fractured granodiorite

aquifer underlying the Saanich

Peninsula, north of Victoria). The

meta-sedimentary, older volcanic,

and meta-volcanic rocks are most

similar in hydrogeological properties

to granitic and metamorphic rocks

and, therefore, have been included

in this sub-category.

General Aquifer

Characteristics

A summary of some of the

characteristics for each category or

sub-category of aquifer is presented

in Table 1, including size, reported

well depths and yields, representative

transmissivity

5 values, and potential

hydraulic connection to surface

water. The summary information in

Table 1 was compiled from available

well records, attribute data associated

with the classified aquifers, and

available groundwater reports.

Generally, sand and gravel aquifers

(Types 1–4) are of limited size (<

1 km

2 to over 100 km2, with average

sizes of a few to 10s of square

kilometres). Their limited size reflects

the variable topography and relief

of the Canadian Cordillera Hydrogeologic

Region. Bedrock aquifers can

be larger, but even so, aquifers in the

Cordillera are not typically considered

“regional” aquifers.

Table 1 also shows that unconfined

sand and gravel aquifers (Types 1,

2, 3, and 4a) are generally shallower

(inferred from the well depth) than

confined sand and gravel aquifers

(Types 4b and 4c) and bedrock

aquifers (Types 5 and 6). The

shallower, unconfined sand and

gravel aquifers (Types 1, 2, 3, and

4a) are considered highly vulnerable

to contamination whereas the

generally deeper, confined sand and

gravel aquifers (Type 4b and 4c)

are considered to have a moderate

to low vulnerability. In the Region,

widespread nitrate contamination

from human activities is found in

unconsolidated, unconfined aquifers

(Types 1b, 2, 4a) where intense

agricultural activity occurs or a high

density of on-site sewerage systems

and shallow water tables are present;

these are the most vulnerable aquifers.

Continued on page 17

16 Streamline

Watershed Management Bulletin Vol. 13/No. 1 Fall 2009

Table 1. Summary of hydrogeologic characteristics of the major aquifer system types in the Cordillera

Hydrogeologic Region (Source: Rivera in press; reproduced with permission of the Geological Survey of Canada).

Aquifer type

Range;

average

size (km

2)

Average

range;

average

median

well depths

(m)

Average

range;

average

median

well yields

(L/s)

Range;

geometric

mean

transmissivity

(m

2/d)

Hydraulic

connections

with surface

water?

Examples of aquifer types

1. Unconfined aquifers of fluvial or glaciofluvial origin along river valley bottoms

a. Aquifers along

higher-order rivers

< 1–140;

27

12–83;

23

2–17;

3

350–22 000;

4500

Common

Agassiz, Chilliwack-

Rosedale

b. Aquifers along

moderate-order rivers

< 1–120;

15

11–53;

22

2–41;

6

1–36 000;

1300

Common

Grand Forks, Duncan,

Chemainus, Nechako,

Merritt

c. Aquifers along

lower-order streams

< 1–23;

7

9–43;

19

1–22;

4

160–240;

200 (based on

two values)

Cache Creek, Little Fort

2. Unconfined deltaic

aquifers

< 1–19;

4

5–27;

12

2–15;

6

960–2390;

1500

Common Scotch Creek near Chase

3. Unconfined

alluvial, colluvial fan

aquifers

< 1–54;

5

13–47;

24

2–23;

4

25–5600;

710

Common

in aquifers

adjacent to

surface water

Vedder River Fan at

Chilliwack

4. Aquifers of glacial or pre-glacial origin

a. Unconfined glaciofluvial

aquifers

< 1–90;

8

12–59;

24

1–22;

3

2–89 000;

690

Common

in aquifers

adjacent to

surface water

Abbotsford, Langley,

Hopington

b. Confined glacial or

pre-glacial aquifers

< 1–330;

13

20–83;

39

0.8–12;

2

1–120 000;

250

Quadra Sand aquifers

in the Georgia Basin,

Okanagan and Coldstream

valleys

c. Confined glaciomarine

aquifers

2–190; 32

23–180;

61

0.1–14;

0.6

45–410;

150

Limited

Nicomekl-Serpentine in

Surrey and Langley

5. Sedimentary rock aquifers

a. Fractured

sedimentary rock

aquifers

< 1–700;

24

22–140;

56

0.1–3;

0.3

0.1–480;

4

Limited

Nanaimo Group aquifers

in the Gulf Islands and east

coast of Vancouver Island

b. Karstic aquifers

2–36;

11

35–130;

75

0.1–1;

0.3

N/A

Unknown,

but possible

Limestone aquifers in the

Central Canadian Rockies,

Sorrento, Fort St. James

6. Crystalline rock aquifers

a. Flat-lying volcanic

flow aquifers

< 1–6500;

420

21–130;

62

0.1–3;

0.3

11–47;

23 (based on

three values)

Limited

Aquifer classification #124

around 70 Mile House

b. Fractured

igneous intrusive,

metamorphic,

fractured volcanic, or

metavolcanic aquifers

< 1–540;

31

28–150;

71

0.1–5;

0.4

0.2–400;

9

Limited

Saanich granodiorite,

granitic aquifers along

Sunshine Coast, metabasalt

aquifer at Metchosin near

Victoria

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Watershed Management Bulletin Vol. 13/No. 1 Fall 2009 17

 

Although some nitrate is also

found in confined unconsolidated

aquifers (Type 4b), windows may

be present in the confining layers

in those aquifers; nitrate found in

Type 4b aquifers is usually isolated

or localized. The vulnerability of

bedrock aquifers (Types 5 and 6) in

the Region is variable and depends

to a large degree

on the nature

and thickness

of overlying

unconsolidated

materials.

Shallow, unconfined

sand and

gravel aquifers are

also expected to

have the greatest

potential of

hydraulic connection

to surface

water. Public water supply wells

completed into shallow Type 1, 2,

and 3 aquifers have the potential to

draw in surface water during pumping

and may require an assessment

to determine whether disinfection

of the well water is required before

distribution and use.

The productivity of aquifers, as

reflected by the reported well yield

and transmissivity, is generally

greater for sand and gravel aquifers

than bedrock aquifers. Despite their

limited size, the sand and gravel

aquifers in the Cordillera are actually

some of the most productive in

Canada (e.g., well yields of up to

several 10s of litres per second and

transmissivity values of up to 10s of

thousands of square metres per day).

The productivity of bedrock aquifers

is generally lower, but bedrock can

also be a viable source of domestic

water supply where sand and gravel

aquifers are not present.

Conclusions

Knowledge of local aquifer

characteristics is key to managing

the local groundwater resource.

Continued from page 15

To support local management and

protection of groundwater, however,

it may not be practical to conduct

detailed aquifer characterization

studies for each of the more than

900 developed aquifers known to

exist in the Canadian Cordillera

Hydrogeologic Region. Therefore, if

an aquifer’s type can be categorized

through simpler assessment

techniques such as

interpretation of

local well records

and surficial and

bedrock geologic

mapping, then it

may be possible

to ascertain

some general

characteristics of the

local aquifer (e.g.,

local extent, shallow

or deep, expected

productivity,

potential connection

to surface water, confined/

unconfined) based on similar types

of aquifers studied elsewhere.

Understanding and categorizing a

local aquifer’s general characteristics

may allow decision makers to start

developing broad management and

protection strategies. For example, it

may be important for a drinking water

officer to recognize the need to assess

the potential connection between

surface water and groundwater and

to establish disinfection requirements

for the operation of a public water

supply well that is drilled into a Type

1, 2, or 3 aquifer. Where Type 1,

2, 3, and 4a aquifers exist and are

relied upon as a water supply source,

a local government may want to

consider the use of more detailed

vulnerability mapping to identify

areas of high vulnerability or high

risk to aid in planning or zoning land

use. Finally, local governments may

want to consider establishing more

stringent pumping test requirements

under water servicing by-laws for

new subdivision developments where

the source of water supply is from

a fractured rock aquifer (Type 5b or

Type 6 aquifer).

Acknowledgements

This work was funded by the

Geological Survey of Canada and BC

Ministry of Environment. This article

is based on Chapter 9 (Wei et al., in

press) from the Geological Survey

of Canada’s,

Groundwater Resources

in Canada

(Rivera, in press). All

figures and tables in this article are

reproduced with permission of the

Geological Survey of Canada.

The authors would also like to

acknowledge the constructive

comments of T. Redding and two

anonymous reviewers.

Endnotes

1

Anisotropic means physical

properties of an aquifer or a

geologic formation, such as

permeability, is not the same in

all directions.

2

Storativity means the amount

of water an aquifer will release

or yield from its pores when the

groundwater level is lowered as,

for example, during pumping.

3

Unconfined means the aquifer is

not overlain by a low permeable

geological formation or deposit,

such as clay or till

4

Confined means the aquifer is

overlain by a low permeable

geological formation or deposit,

such as clay or till.

5

Transmissivity is the ability of an

aquifer to transmit groundwater

and is a product of the aquifer’s

hydraulic conductivity and

thickness.

For further information, contact:

Mike Wei

BC Ministry of Environment,

Victoria, BC

Tel: (250) 356-5062

Email: Mike.Wei@gov.bc.ca

Diana Allen

Simon Fraser University

Email: dallen@sfu.ca

Alan Kohut

Hy-Geo Consulting

Email: apkohut@telus.net

Continued on page 18

Understanding and

categorizing a local

aquifer’s general

characteristics may

allow decision makers

to start developing

broad management and

protection strategies.

18 Streamline

Watershed Management Bulletin Vol. 13/No. 1 Fall 2009

Steve Grasby

Geological Survey of Canada

Email: Steve.Grasby@nrcan-rncan.gc.ca

Kevin Ronneseth

BC Ministry of Environment

Email: Kevin.Ronneseth@gov.bc.ca

Bob Turner

Geological Survey of Canada

Email: Bob.Turner@nrcan-rncan.gc.ca

References

Berardinucci, J. and K. Ronneseth. 2002.

Guide to using the BC aquifer classification

maps for the protection

and management of groundwater.

BC Ministry of Water, Land and Air

Protection, Victoria, BC.

Halstead, E.C. 1967. Cordilleran

Hydrogeological Region.

In

Groundwater in Canada. I.C.

Brown (editor). Geological Survey

of Canada, Ottawa, ON. Economic

Geology Report No. 24, Chapter 7.

Holland, S.S. 1976. Landforms of British

Columbia: A physiographic outline.

BC Department of Mines and

Petroleum Resources, Victoria, BC.

Bulletin No. 48.

Kreye, R. and M. Wei. 1994. A proposed

aquifer classification system for

groundwater management in

British Columbia. BC Ministry of

Environment, Lands and Parks,

Water Management Division,

Hydrology Branch, Groundwater

Section, Victoria, BC.

http://www.env.gov.

bc.ca/wsd/plan_protect_sustain/

groundwater/aquifers/

Aq_Classification/

(Accessed

August 2009).

Rivera, A. (editor). [2009]. Groundwater

resources in Canada. Geological

Survey of Canada, Ottawa, ON.

In press.

Sharpe, D., D.R. Russell, H.A.J. Dyke, S.

Grasby, Y. Michaud, M.M. Savard,

M. Wei, and P. Wozniak. [2009].

In

Groundwater resources in Canada.

A. Rivera (editor). Geological

Survey of Canada, Ottawa, ON.

Chapter 8. In press.

Wei, M., D.M. Allen, S.E. Grasby, A.P.

Kohut, and K. Ronneseth. [2009].

Cordilleran Hydrogeological

Region.

In Groundwater resources

in Canada. A. Rivera (editor).

Geological Survey of Canada,

Ottawa, ON. Chapter 9. In press.

Continued from page 17

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