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REGIONAL GROUNDWATER POTENTIAL FOR SUPPLYING IRRIGATION WATER: 1986

NORTH SAANICH, B.C.

K.D. Ronneseth Ministry of Agriculture and Food

March 1986

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TABLE OF CONTENTS

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TABLE OF CONTENTS ................................................ L I S T OF FIGURES .................................................. ACKNOWLEDGEMENTS .................................................

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1.

2.

3.

4 .

5.

INTRODUCTION ..................................................... 1

PHYSIOGRAPHY ..................................................... 3

‘ 3 BEDROCK GEOLOGY ..................................................

UNCONSOLIDATED DEPOSITS .............................................. 3

GROUNDWATER POTENTIAL ............................................ 5.1 Bedrock ..................................................... 5.2 Unconsolidated ................................................ EXTENT OF DEVELOPED AND POTENTIAL AQUIFERS ....................... 6 . 11

7.

8.

13

CONCLUSIONS ...................................................... 20

9. REFERENCES ....................................................... 21

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Figure 1

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F igu re 3

F igu re 4

F igu re 5

F i g u r e 6

F igu re 7

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LIST OF FIGURES

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Index Map o f Study Area ................................... 2

Regional Groundwater P o t e n t i a l f o r Supply ing Ins ide o f

C 1 imat ic-Geologic Uni ts , S t ra t i g raphy and Late

Fence Diagram ( S i dney Aqui fer South o f Sidney 1 ............ 10

S a l i n i t y Hazard Level s I nd i ca ted by Groundwater Analyses . 15

Water We1 1s Where Ch lo r ide ' Level s Greater than 330 mg/L was Reported .......................................;...... 17

Sodium Hazard Levels Ind i ca ted by Groundwater Analyses .................................................. 19

I r r i g a t i o n Water 928.063 ........................... Back Cover

Pleistocene-Environments of the Study Area ................ 5

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ACKNOWLEDGEMENTS

The author wishes to acknowledge the support, the use of groundwater data and the technical ass is tance provided by the s t a f f of the Groundwater Section of the Water Management Branch, Ministry of Environment. Special thanks to Mr. Barry McCliggott, who was covtracted to a s s i s t i n the compilation and analysis of the extensive amounts of data and information.

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1. INTRODUCTION

The Ministry of Agriculture and Food i n conjunction w i t h the Agricultural Land Commission are involved i n a detailed assessment of the agricul tural capabi l i ty of the eas t coast of Vancouver Island. An analysis of the hydrological data was ident i f ied as an important requirement i n the above assessment w i t h groundwater being a major component.

This report and accompanying maps provides a discussion and analysis o f developed and potential aquifers, for the North Saanich area (Figure 11, based on presently available groundwater and geologic data. The map sheet which covers the study area is 92B.063 (1:20,000 sca l e ) and i s ident i f ied as F i g u r e 2.

The hydrogeological information, thenatical l y presented on the maps and fence diagram, are based on the tabulated da ta from approximately 1,500 water well records, water well location maps (both on f i l e w i t h the Groundwater Section, Ministry of Environment) , pub1 i shed surf i c i a1 geology maps and reports (Halstead, 1967; Learning, 1968; Muller, 19771, t e r r a in maps (Ministry of Environment, British Columbia) and soi l maps and reports (Ministry of Agriculture and Food and Ministry o f Environment, British Col umbi a 1.

Tabulated data from water well records (e.g., aquifer charac te r i s t ics , depth to bedrock, e t c . ) were t ransferred to water well location maps ( s ca l e 1:5,000) which were used as a working base. Surf ic ia l geology/terrain units and glacial features (e.g., g lacial outwash) which were considered hydro- geologically s ign i f icant i n terms of groundwater potential were transferred t o these same maps. A synthesis of this data was then transferred t o the f ina l 1:20,000 scale base map.

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Q

SCALE 1 : 250,000

FIGURE 1: Index Map of Study Area

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2. PHYSIOGRAPHY

The major geomorphic features o f the study area are the r e s u l t o f s t r u c t u r a l , eros ional and deposi t ional processes. Fo ld ing and f a u l t i n g o f

t h e bedrock; e ros ion and repeated g l a c i a t i o n , i s o s t a t i c and e u s t a t i c changes o f sea l e v e l have a l l c o n t r i b u t e d t o the physiographic features o f the

Saanich Peninsula. The topography o f the study area cons is ts o f a saddle

shaped lowland o f r o l l i n g farmland, marsh and t i d a l f l a t s bounded by uplands

t o the n o r t h (Cloake and Hor th H i l l s ) and south (Mount Newton), and s a l t

water t o the eas t (Haro S t r a i t ) and west (Saanich I n l e t ) .

3. BEDROCK GEOLOGY

According t o M u l l e r (19771, Vancouver I s l a n d i s the main component o f

t h e I n s u l a r B e l t , the westernmost major t e c t o n i c subd iv is ion o f the Canadian C o r d i l l e r a . The study area contains Lower Mesozoic rocks (Bonanza Volcanics

from the Vancouver Group) which are i n t r u d e d by Middle Mesozoic rocks (s tocks o f g r a n o d i o r i t e o f the I s l a n d I n t r u s i o n s ) . These granod ior i tes are

unconformab ly o v e r l a i n by Lower Mesozoic r o c k s ( a s u c c e s s i o n o f conglomerate, sandstone, shale, s i1 ts tone, mudsto'ne and coal s t r a t a o f the

Late Cretaceous Nanaimo Group).

4. UNCONSOLIDATED DEPOSITS

Most of the unconsol idated m a t e r i a l s found i n the study area may be a t t r i b u t e d t o the regimen and wast ing o f g l a c i a l i c e dur ing the L a t e

Pleistocene. Though some o f the unconsol idated deposi ts are the r e s u l t o f i n t e r g l a c i a l (Cowichan Head Sediments) a c t i v i t y , the m a j o r i t y o f the

deposi ted sediments are from the Fraser G lac ia t ion . The Fraser G l a c i a t i o n probably represents the same geologic-c l i m a t i c t ime per iod as the c l a s s i c a l

La te Wisconsin G l a c i a t i o n o f the mid-cont inent reg ion (A1 l e y and Chatwin, 1979). Clapp, (19131, the M i n i s t r y o f Environment (19611, Halstead (1967),

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and Fyl es ( 1963) have mapped the surf ici a1 unconsol i dated sediments w i t h i n the study area a t a scale of 1:62,500, 1:50,000 and 1:25,000 respectively.

A s t ra t igraphic framework of unconsolidated sediments and a chronology of Late Pleistocene environments i n the study area, i s shown i n Figure 3.

5. GROUNDWATER POTENTIAL

5.1 Bedrock

Groundwater w i t h i n bedrock can be found i n f rac tures , along bedding plane par t ings , i n the inter-flow zones of lava, i n the inter- granular openings i n the rock, and i n the case of limestone; i n the channels formed by the dissolution of the rock by water. Water wells d r i l l e d on Vancouver Island, indicate f ractures , bedding plane partings and solution channels a re probably the m a i n sources of groundwater from the bedrock. Of the 1,286 known bedrock wells i n the study area, 239 were reported to be completed i n sedimentary rocks ( sha les and/or sandstones) and 969 i n g ran i t ic rocks (Saanich granodiorite of the Island Intrusions) . The bedrock type i n 78 wells was not reported. .

The rapid accumulation of sediments which make up the sedimentary rocks, accounts for t h e i r being poorly sorted, massive and, i n general, lacking i n pore <paces and conduits fo r the t r anmiss ion of water (Halstead and Treichel, 1966). Water wells dr i l led i n these rocks ind ica te f ractures and bedding plane partings are the main sources of groundwater.

The major bedrock groundwater supplies i n the study area come from the grani t ic rocks. Clapp (1913) reported t h a t a l l intrusive rocks on the Saanich Peninsula are highly fractured and tha t the Saanich Granodiorite has regular and large j o i n t s and fractur ing. These large, open f rac tures

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CLIMATIC-GEOLOGIC UNITS, STRATIGRAPHY AND LATE PLEISTOCENE ENVIRONMENTS OF THE STUDY AREA

!EARS BEFORE PRE Sf N1

(#ot t o Sca le) CLIMATIC UNITS

Presen t

5 , on0

10.0w

15.or1o

20,000

25,OW

30,000

60.000

?

GEOLOGIC UNITS

SAL I S H

SEDIMENTS

.-- __.---- _..- *_-- -. CAPILANO

SEDI1lENTS

YASIION DRIFT

QUADRA SAND ,'

COWICHAN HEAD FORMAT I ON

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OASHWOOO DRIFT ?

MAPLECUARO SEDIMENTS ?

ENVlRONMENT

LUVlAL

...- ..---- MARINE AND

__-* __/-

GLAC IO- MAR1 NE

LACIO-LACUSTRINE

ILACIO-FLUV I A L

#LAC I AL

8LAtlO-FLUV I A L

I

LUVIAL STURINE

lARINE

,LAC IO-MAR I N E ;LAC IM

'LUVIAL .ACUSTRINE

STRAT 1 GRAPHY

Gravel. sand. s l l t . clay. pea t ; a l l uv ia l fan deposits; blocks and rubble; pea t and nuck

___.--

__.__----- S i l t , c lay . stony c lay ,

____----- ____-_- ----- randy gravel generally underlain ._----

)y c lay ; stony gravel. stony l o r n Sand and gravel. IbaIfnbted s i l t y and clay

;ravel, sand and r l l t y fomlng Ice-contacl le1 t a s k e y t i l l . rand to clayey tex ture

Sand, gravel and s l l t

S i l t , gravel. sand, peat. peaty s o i l , nnd d r l f twood

Clay. stony c lay , s l l t containlng a s r lne she l l s . local basal laminated clay and r l l t

Grey t i l l . s i l t y t o sandy t e r t u r c Contaln s i l t y and gravel lenses

Sand. r l l t . minor clay and gravel

I ~ ~~~

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i i n the granodiorite extend t o depths beyond 200 metres (Al-Mooji, 1982). I t i s through t h i s network of j o i n t s and f ractures t h a t groundwater i s stored and transmitted. Based on water well log information, the y ie lds from wells constructed i n the bedrock are generally low ( l e s s than 1 L / s ) and large capacity wells are the exception (Zubel, 1980). In places, however, the f ractur ing can be so great , the rock i s un f i t fo r building purposes ( C l a p p , 19131, i n f a c t , some wells must be screened ( the way sand i s screened i n wells constructed i n unconsolidated deposits) (Brown e t a l , 1976). According to Al-Mooji (19821, there i s a general increase of well y i e lds w i t h depth, w i t h the grea tes t y ie lds observed between 40 and 80 metres, the second highest yields reported between 80 and 140 metres and the lowest y ie lds found between 0 and 40 metres. The h igher producing wells are current ly located i n the lowland areas adjacent t o Mt. Newton.

\

Some bedrock aquifers w i t h i n the study area are capable of yielding s u f f i c i e n t supplies of groundwater for i r r iga t ion purposes. One well i s reported t o y ie ld over 15 L/s and able to meet i r r iga t ion demands. E i g h t o ther wells report y ie lds greater t h a n 3 L/s ( 3 L/s i s s igni f icant when considering i r r iga t ion requirements). One out of every 10 wells report y i e lds between 1 and 3 L/s. By conducting more detai led studies (e.g. , on f r ac tu re and y ie ld pat terns) some of these wells could be targeted fo r deepening in to the 40 t o 80 metre zone discussed previously and possibly increasing t h e i r productivity. If greater y ie lds were obtained longer d u r a t i o n pumping t e s t s would be required t o verify i f these bedrock aquifers are capable of a sustained h i g h withdrawal ra te .

5.2 Unconsol idated DePosi t s

Most of the groundwater used on Vancouver Island comes from unconsolidated deposits which receive water from i n f i l t r a t i o n of e i t h e r prec ip i ta t ion or surface water sources. The amount of water obtainable from these mater ia ls , depends on the permeability of the aquifer material ,

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the thickness and extent of the aquifer , the r a t e of aqui fe r recharge and on well construction. Though the majority of the wells i n the study area a r e constructed i n bedrock, there a r e regions where unconsolidated deposi ts a r e hydrogeological l y s ign i f i can t i n terms of groundwater potent ia l f o r i r r i g a t i o n purposes.

The unconsolidated deposi ts w h i c h a re s ign i f i can t a r e primarily comprised of sand and/or gravel. Thickness o f any saturated sand and/or gravel deposit 0.3 metres o r grea te r a r e considered s ign i f i can t i n terms of groundwater potent ia l . The m a i n deposi ts which f a l l i n t o this category a r e 1 i sted and discussed bel ow:

1) The glaciof luvial deposits of the Quadra Sediments known as the Quadra Sand (Clague, 1977). The groundwater potential of this geologic u n i t merits an expanded understanding of i t s d i s t r ibu t ion and or igin. Over1 a i n by sediments of the Olympia Intergl aci a1 interval the current theory on the or ig in of Quadra Sand i s summarized by Clague (1977) bel ow:

"The sand was deposited, i n par t , a s d i s t a l outwash aprons a t successive posit ion i n f ron t of and perhaps along the margins of g lac ie rs moving from the Coast Mountains i n t o the Georgia Depression and Puget Lowland during Late Wisconsin time. After deposition a t a s i te , b u t before burial by ice, the sand was dissected by meltwater and the eroded d e t r i t u s was transported f a r t h e r down the basin t o si tes where aggradation continued."

The Quadra Sediments a re the o ldes t exposed su r f i c i a l deposi ts i n the study area. Consisting mainly of horizontal ly and c ross - s t r a t i f i ed , well sorted, f ine t o coarse grained sands w i t h minor gravels and s i l t (Por te r , 19801, the nearest radio-carbon date t o the study area shows

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these sediments were deposited appoximately 22,600 + 300 years before -

p'resen t . 2) The Cowichan Head Formation which under l ies the Quadra Sediments.

T h i s u n i t cons is ts o f s t r a t i f i e d f l u v i a l , estuar ine, and marine sedi- ments deposited d u r i ng an i n t e r g l a c i a1 i n t e r v a l [chronologica l l y

p laced i n the Olympia non-glacial i n t e r v a l (F igure 311. Clague (1977)

has descr ibed t h i s u n i t as "hor izon ta l beds o f s i l t , sand and gravel ,

commonly ox id ized t o reddish hues and conta in ing abundant organic

mat ter . There are occasional known occurrences o f t h i s u n i t i n the

study area (Por te r , 1980).

U n i t s one and b o would be hydrogeologica l ly s i g n i f i c a n t i n terms o f groundwater p o t e n t i a l f o r i r r i g a t i o n purposes. Two major unconsol i -

dated aqu i fe rs e x i s t w i t h i n the study area. For purposes o f t h i s r e p o r t they are r e f e r r e d t o as the Nor th Saanich Aqu i fe r and the Sidney Aqui fer .

The Nor th Saanich Aqu i fe r i s loca ted immediately n o r t h o f the V i c t o r i a

I n t e r n a t i o n a l A i r p o r t . Consis t ing mainly o f Quadra Sediments (Por ter ,

19801, d r i 11 holes have ' encountered gravel l y mater i a1 under ly ing the Quadra Sand which may belong t o the Cowichan Head Formation. Wells

d r i l l e d i n t h i s area encountered 20 metres o f saturated sand and/or gravel . Though most w e l l s d r i l l e d i n the study area repor ted low t o

moderate y i e l d s , g rea ter y i e l ds w i t h improved w e l l development are

poss ib le . P o r t e r (1980) est imates t h i s a q u i f e r receives approximately

170,000,000 U.S. ga l lons o f recharge year ly . Th is a q u i f e r i s not

be ing ex tens ive ly u t i l i z e d and may have good p o t e n t i a l f o r f u r t h e r

development.

The Sidney Aqu i fe r i s loca ted southeast o f Sidney and west o f Bazan

Bay. Marine eros ion has removed the stony clay, till and probably

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much of the sand in certain areas, and produced a number of distinct terraces in the area. The t o t a l thicknesses of the sand and/or gravel deposits exceed 22 metres and the water saturated sands and/or gravels exceeding 6 metres. Refer t o the fence diagram i n Figure 4 t o observe the stratigraphic nature of the deposits and the thickness o f the sands and/or gravels found here. Recharge i s mainly from precipitation from the northeast slope of M t . Newton. The experimental farm and local residents w h i c h use water from outside the region may contribute a small amount t o the recharge of this aquifer through irrigation and septic fields. The main users of this aquifer was the Town of Sidney ( w h i c h pumped an estimated 30 m i l l i o n gallons per year), a number of farmers and local residents. Sidney and probably a number of the other users are currently supplied w i t h water from the Greater Victoria Water District. W i t h 7 wells reporting yields between 1 and 3 l i t r e s per second from this aquifer and many of the former users not u t i l i z i n g this aquifer there i s potential for future development for irrigation purposes. I t should be noted t h a t a number of unused wells are already constructed in the aquifer or into the underlying bedrock and may be available for use.

Inset map "A" and "B" of Figure 2 and the fence diagram of Figure 4 reveal some of the complexity of the Sidney Aquifer Area. Please note t h a t b l ank spaces exist around some water wells i n Figure 4 when the l i t ho logy was not recorded on the well log. As previously stated 7 wells reported yields between 1 and 3 L/s from the sands and/or gravels and are probably capable of higher yields. In the same area, 25 wells completed i n the bedrock aquifer reported yields greater than 1 L/s w i t h 18 wells reporting between 1 and 3 L/s and 7 wells greater t h a n 3 L/s. There may be some interest i n investigating the possibility of combining these already developed sources of groundwater (estimated 50 t o 100 L/s) f o r irrigation purposes.

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a

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LEGEND

SAND and/or GRAVEL

SILT, CLAY and/or TILL

BEDROCK

FENCE- DIAGRAM SIDNEY AQUIFER REGION

SEA LEVEL

A water wel l found on rnapsheet No. W W 928.063.2 .4 ,

on f i le w i th the Groundwate r Section, Water Management

Branch, Min is t ry of Environment.

79

HORIZONTAL SCALE: 1 cm. = 50 m.

VERTICAL SCALE: 1 cm. = 5 m.

RONNESETH, K.D. 1986

d INDEX PLAN

SCALE: 1 cm. = 280 m.

60

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FIGURE 4: Fence Diagram

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++++++++++++++++ ++++++++++++++++: +++++++++++++++++ +++++++++++++++++ +++++++++++++++++ +++++++++++++++++ ++++++++++++++++$ ++++++++++++++++: ++++++++++++++++ ++++++++++++++++'

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6. EXTENT OF D E V E L O P E D AND POTENTIAL AQUIFERS

out1 i n e where s a n d and/or gravel a q u i f e r s (g rea t e r t h a n 0.3 metres i n thickness) have been ident i f ied a t depth based on water well l i thology records. These aquifers may be e i t h e r confined or unconfined. The boundaries of these areas

The fo l lowing i s a description of each component shown on the 1:20,000 scale base map (Figure 2 ) .

POTENTIAL UNCONSOLIDATED UNCONFINED AQUIFERS: These area; ou t l ine . the su r f i c i a l extent of unconsolidated deposits primarily conpri sed of sand and/or gravels. They outine areas where there i s a h i g h probabili ty of locating water- bear ing sand and/or gravel aquifers b u t does

imply the existence o f water-bearing sand and/or gravel aquifers. I n some areas for exanple the sand and gravel deposits may be very t h i n and dry throughout t he i r en t i r e thickness.

These areas out l ine potential unconfined aquifers a t surface, i t does not show dis t r ibu t ion a t depth. This i s especially relevant t o the Quadra Sand and possibly t o some pre-Fraser Glaciation unconsolidated sediments (e .g . , Cowichan Head sediments) which my under1 i e younger deposits (marine clays fo r example) i n - the region.

were a r b i t r a r i l y s e t a t a 100 metre r ad ius from a d a t a p o i n t (water well) which ident i f ied a sand and/or gravel aquifer greater t h a n 0.5 metres i n

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thickness. Where two we l ls , l oca ted w i t h i n 400 metres o f each other, show

s i m i l a r l i t h o l o g i e s and the geomorphology o f the area was homogeneous, the

boundaries were extended t o i nc lude the area between the two we l l s .

e x i s t a t depth as evidenced throughout these areas where s i t e s p e c i f i c data

a r e ava i l ab le - , Where ground moraine depos i ts have been mapped i n these

areas, l o c a l l y there may be sand and/or gravel deposi ts found a t surface o r i n lenses a t depth. Also, o l d e r geologic u n i t s (e.g., Quadra Sand) t h a t a re s i g n i f i c a n t aqu i fe rs may be o v e r l a i n by the marine and moraine deposits.

Produc t ive aqu i fe rs may be found i n these o lde r geologic u n i t s .

BEDROCK AQUIFERS: These areas i d e n t i f y where bedrock i s l oca ted a t o r near ground surface

and/or where w e l l logs i n d i c a t e bedrock aqu i fe rs .

The b o u n d a r i e s f o r t h e s e a r e a s were a l s o

a r b i t r a r i l y s e t a t 100 metre rad ius from a data

p o i n t (e.g., bedrock we1 1 o r rock outcrop). Th is

d is tance was extended t o 400 metres between data p o i n t s i f water we l l

1 i tho1 ogy and the surface morpho1 ogy so warranted.

Water w e l l s where y i e l d s g rea ter than 3 L/s have

When found i n known developed

unconsol idated a q u i f e r regions, these areas show

the h ighes t p o t e n t i a l f o r ob ta in ing groundwater

supp l ies t o meet i r r i g a t i o n requirements.

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Water wells where y ie lds between 1 and 3 L/s are reported. These areas a lso show h i g h potential f o r obtaining i r r iga t ion supplies of ground- water.

7. WATER QUALITY

The concentration and composition of dissolved const i tuents i n a water determine i t s quali ty for i r r iga t ion use. Three of the charac te r i s t ics of an i r r iga t ion water appear to be the most important i n determining i t s qual i ty are the total concentrations of soluble s a l t s , the r e l a t ive proportion o f sodium t o other cations and the concentrations of boron and other elements t ha t may be toxic.

The t o t a l concentration of soluble s a l t s can be expressed i n terms of i t s e l ec t r i ca l conductivity and i s often expressed as micromhos/cm a t 2 5 O C . The higher the concentration o f soluble s a l t s and minerals the h igher the conductivity. The e l ec t r i ca l conductivity of the three laboratory analyses of groundwaters from unconsolidated aquifers were 176, 200 and 200 micromhos/cm. All three of these waters are i n the low sa l in i ty hazard c l a s s (Richards, 1969).

According t o Richards (1969) :

"Low sa l in i ty water can be used for i r r iga t ion w i t h most crops w i t h l i t t l e l ikelihood tha t soi l s a l in i ty will develop. Some leaching i s required, b u t this occurs under normal i r r iga t ion pract ices except i n s o i l s of extremely low permeabi 1 i ty. I'

The e l ec t r i ca l conductivity of the 103 laboratory analyses of ground- waters from bedrock aquifers ranged from 167 t o 4 780 micromhos/cm. Six of

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these waters a re i n the low sa l in i ty hazard c lass , 65 a r e i n the medium s a l i n i t y hazard c l a s s , 28 a r e i n the h i g h s a l i n i t y hazard c l a s s and 6 a r e i n the very h i g h s a l i n i t y hazard c l a s s (Richards, 1969). Figure 5 shows 1 oca1 l y the sal i n i ty hazard based on groundwater analyses.

According t o Richards:

"Medium s a l i n i t y water can be used i f a moderate amount of leaching occurs. Plants w i t h moderate s a l t tolerance can be grown i n most cases without special pract ices for s a l i n i t y control . High s a l i n i t y water cannot be used on s o i l s w i t h r e s t r i c t e d drainage. Even w i t h adequate drainage, special management of s a l i n i t y control may be required and plants w i t h good s a l t tolerance should be selected. Very h i g h

s a l i n i t y water i s not sui t a b l e for i r r i g a t i o n under ordinary conditions, b u t may be used occasional ly under very speci a1 circumstances. The s o i l s must be permeable, drainage m u s t be adequate, i r r i ga t ion water must be applied i n excess to provide considerable leaching, and very s a l t t o l e ran t crops should be selected.

The concentration of chl or i des i s another impor tan t el ernent i n determining the quali ty of i r r iga t ion waters. The chloride levels of f ive 1 aboratory analyses of the groundwaters from unconsolidated materials ranged from 14 t o 32 mg/L. These concentrations would be considered very sui table f o r agr icul tural purposes (Anderson, 1973). The chloride leve ls o f the 134 1 aboratory analyses of groundwaters . from bedrock aquifers ranged from 2.35 t o 1 500 mg/L. One hundred and eleven of the 134 analyses reported chloride leve ls l e s s t h a n 150 mg/L, 2 1 analyses reported leve ls between 150 and 500 mg/L and 7 reported greater than 500 mg/L. According to Anderson (1973) waters w i t h chloride readings l e s s t h a n 150 mg/L a r e safe for most crop p lan ts , chloride leve ls between 150 and 500 wi l l require special pract ices

LEGEND

1 (LOW): Water considered safe for most crops. Extremely low permeable soils may require special irrigation practices.

2 (NEDIUM): Water considered safe for plants with moderate salt tolerance. Plants can be grown in most cases without special practices for salinity control.

3 (HIGH): Water cannot be used on soils with restricted drainage. With adequate drainage, special management for salinity control and the selection of salt tolerant crops are required.

4 (VERY HIGH): Water not suitable for irrigation under most conditions. Require very permeable soils, excess irrigation water to provide considerable leaching and very salt tolerant crops should be selected.

Ratings based on Richards (1969). I I

- 15 -

2

2

222 2

2

2

2 2

2 2

2

3 323% 43 4 2 2 2 3 2

3 2

2: 1

2

3

3

112 2

2

2

1000 0

Scalein Metres

FIGURE 5 : Salinity Hazard Based on Groundwater Analyses.

- 16 -

I I I I I

I I I I I

f o r s a l in i ty control, chloride levels greater than 500 mg/L a r e generally unsafe for i r r iga t ion purposes. Figure 6 shows the location of groundwaters where chloride levels greater than 300 mg/L were measured. The majority of these brackish groundwaters occur along a major s t ructural lineament i n the fractured grani t ic bedrock. The areal d i s t r ibu t ion of the chloride and other const i tuents i n the groundwaters and potentiometric head d is t r ibu t ion ind ica te the zone i s w i t h i n a regional groundwater discharge area, the flow system o f which or iginates on the upland north of the zone (Kohut and Petrie, 1978). This study indicates tha t seawater intrusion i s - not the source of these brackish waters.

The re la t ive proportion of sodium to other cations (usual ly calcium and magnesium) i n groundwaters may make some waters undesirable for some crops. T h i s re la t ionship i s usually expressed as the sodium absorption r a t i o (SARI

where SAR = Na+/ 2/ ( C A + + + M g + + ) / Z and can be used for i d e n t i - fying the s u i t a b i l i t y of groundwaters for i r r iga t ion purposes. The formula appl ies where a l l concentrations are expressed i n epm. Applying the SAR formula to three laboratory analyses of groundwaters from unconsolidated aquifers revealed the sodium hazard level as being low. Applying the SAR formula to 103 1 aboratory analyses of groundwaters from bedrock aquifers revealed the sodium hazard level as being low i n 96 water samples, medium i n 8 samples, high i n 1 sample and very high i n 1 sample. Figure 7 shows loca l ly the sodium hazard based on groundwater analyses. Please note tha t some o f the h i g h sodium values may be due to the use of water sof teners .

According t o Richards (1969):

"Low sodium water can be used for i r r iga t ion on almost a l l soils w i t h l i t t l e danger of the development of harmful levels of exchangeable sodium. However, sodium sens i t ive crops such a s s tone-frui t trees and avacados may accumulate injur ious concentrations of sodium. Medium sodium water will present

- 17 -

a

0 1000

a

SCALE IN METRES

FIGURE 6: Water Wells Where Chloride Levels ,Greater Than 300.mg/L Were Reported.

I I I I I II I I II I ~I I I I II I ~I I I

- 18 -

an appreciable sodium hazard i n f ine textured soils having h i g h cation exchange capaci ty , especially under low leaching conditions, unless gypsum i s present i n the so i l . T h i s water may be used on coarse textured or organic s o i l s w i t h good permeability. High sodium water may produce harmful levels of exchangeable sodium i n most s o i l s and will require special soil management - good drainage, h i g h leaching and organic matter additions. Gypsiferous soils may not develop harmful 1 eve1 s of exchangeable sodium from such waters. Chemical amendments may be required for replacement of exchangeable sodium, except t ha t amendments may not be feas ib le w i t h waters of very h i g h s a l in i ty . Very h i g h sodium water i s general l y unsatisfactory for i r r iga t ion purposes except a t low and perhaps medium sa l in i ty , where the solution of calcium from the soils or the use of gypsum o r other amend- ments may make the use of these waters feasible . Sometimes the i r r iga t ion water may dissolve su f f i c i en t calcium from cal careous soi 1 s to decrease the sodium hazard appreciably, and this should be taken into account i n the use of low sal ini ty-high sodium and low salinity-very high sodium waters. For calcareous s o i l s w i t h h i g h pH values or for non-calcareous so i l s , the sodium s t a tus of waters i n c lasses low salinity-high sodium, low salinity-very h i g h sodium and medium salinity-very h i g h sodium may be improved by the addition of gypsum t o the water. Similarly, i t may be beneficial t o add gypsum to the soi l periodically when medium salinity-high sodium and h i g h salinity-medium sodium waters are used."

The majority of these salinity-sodium combinations are found i n the study area. I t should be restated tha t most sources of groundwater on the e a s t coast of Vancouver Island capable of yielding quant i t ies sui table for

1 (LOW):

2 (MEDIUM) :

3 (HIGH):

4 (VERY HIGH):

LEGEND

Water considered safe for most crops. Sodium sensitive plants may require soil management.

Water will present an appreciable sodium hazard in some soils. These soils will require extra management.

Water may produce harmful levels of exchangeable sodium in most soils and will require special soil management.

Water is generally unsatisfactory for irrigation purposes. The few exceptions would require special soil management.

Ratings based on Richards (1969)

- 19. -

1

1 I L FIGURE 7: Sodium Hazard Based On Groundwater Analyses.

2 2

1 1

1

3

1 1

1 11 1 2 2 5 2

1 1

1: 1

l1

1

1000

Scale in Metres

0

‘I 1 I I 1 I I I I I I I I I I 11 I I I

- 20 -

i r r i g a t i o n purposes w i 11 come from unconsol i dated aquifers. The sal i n i ty and sodium hazard were generally reported to be low.

Another important cha rac t e r i s t i c of i r r iga t ion waters a re concentra- t ions of boron and other elements t ha t may be toxic. The boron concentra- t ions from 21 1 aboratory analyses of groundwater from bedrock aquifers ranged from .021 t o .6 mg/L. Eighteen of these water samples would be regarded as safe (Anderson, 1973) while three samples may be safe fo r ce r t a in conditions or crops yet may be unsafe under other conditions or crops (Anderson, 1973). These waters would bear greater scrutiny pr ior t o any development.

a. CONCLUSION

Locally, there i s potential fo r locating groundwater supplies capable of meeting i r r iga t ion requirements i n the study area. The unconsolidated deposits w i t h the grea tes t hydrogeologic significance include the sands and/or gravels from the Quadra Sediments and the Cowichan Head Formation. The major unconsolidated aquifers are the North Saanich and the Sidney Aquifers. Well y ie lds up to 3 L/s have been reported from these deposits. The major groundwater supplies i n the study area cane from the highly f ractured grani t ic rocks. Well y ie lds up to 15 L/s have been reported from these bedrock aquifers.

Natural water qua l i ty is expected to be acceptable from the ground- waters o f unconsolidated deposits. Analyses of these waters indicate a low s a l i n i t y hazard, low chloride leve ls and a low proportion of sodium to other cat ions. Special i r r i g a t i o n pract ices are usually not necessary from these water types. The analyses of groundwaters from bedrock aquifers report the s a l i n i t y and sodium hazards r ang ing from low to very h i g h . Chloride levels have been reported to range up to 1 500 mg/L. Boron concentrations i n three analyses indicate unacceptable leve ls fo r devel opi ng these groundwaters for

- 21 - -

i r r i ga t ion purposes. T h i s va r i ab i l i t y i n quali ty from bedrock aquifers stresses the need for adequate qual i ty analyses t o determine s u i t a b i l i t y fo r use. However, the majority of the analyses of groundwater from bedrock aquifers indicate waters sui tab le i n qual i ty for i r r iga t ion purposes.

T h i s report i s regional i n scope and identifies areas which have the potent ia l t o supply i r r iga t ion water. I t does not provide a quant i ta t ive assessment of water ava i l ab i l i t y for a si te spec i f ic location. To provide such an assessment, more accurate delineation of aquifer boundaries and estimation of groundwater recharge, movement, aquifer parameters and w i t h - drawal would be required on a s i te specif ic basis. The extensive amounts of hydrogeologic information avai lable f o r this study area would great ly f a c i l i t a t e future assessments.

9. REFERENCES

Alley, N.F. and C h a t w i n , S.C. 1979. Late Pleistocene History and Geomorphol ogy . Southwestern Vancouver Island, British Columbia. Canadian Journal of Earth Sciences, Vol. 16, No. 9, pp. 1645-1657.

k' Al-Mooji, Y. 1982. Saline Groundwaters i n the Bedrocks of the North\

Saanich Peninsula, Vancouver Is land, British Columbia. Master Thesis, University of Waterloo. 195 p. (Unpublished) .

Anderson, K.E. 1973. Water Well Handbook, Missouri Water Well 8 Pump Contractors Association, Inc. Scholin Bros. Pr int ing Co., St. Louis, Montana, U.S.A., 281 p.

Armstrong, J.E., Crandell, D.R. , Easterbrook, D.J. and Noble, J.B. 1965. Late Pleistocene Stratigraphy and Chronology i n Southwestern British Columbia and Northwestern Washington. Geological Society of America, Bulletin, Vol. 76, pp. 321-330.

I I I I I I I I I I I I I I I I I I I

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Brown, W.L., McDougall, A., and Dakin, R.A. 1976. B u l k Water Supply - North Saanich Peninsula. A report prepared fo r the British Columbia Ministry o f Environment, 5 1 pp. (Unpublished).

Clague, J . J . 1976. Quadra Sands and i t s Relation t o the Late Wisconsin Glaciation of Southwestern British Columbia. Geological Survey of Canada, Canadian Journal of Earth Sciences, Vol. 13, pp. 803-815.

Clague, 3.3. 1977. Quadra Sands: A Study of the Late Pleistocene Geology and Geomorphic History of Coastal Southwest British Columbia. Geological Survey of Canada, Paper 77-17, Ottawa, 24 p.

C1 ague , J . J . 1981. Late Qua ternary Geol ogy and Geochronology of Bri ti s h Columbia. Part 2 : Summary and D i scussion of Radiocarbon-Dated Quaternary History. Geological Survey of Canada, Paper 80-35, Ottawa, 41 p.

Clapp, H.C. 1913. Geology of the Victoria and Saanich Map Areas, Vancouver Island, British Columbia. Geological Survey of Canada, Memoir 36, 146

PP-

E n v i ronment, Min i s t r y of. 1961. Surf i c i a1 Geol ogy and Groundwater Resources of Saanich Peninsula. Drawing No. 4385 (Unpublished Map).

Fyles, J.G. 1963. Surf ic ia l Geology of Horne Lake and Parksville Map Areas, Vancouver Island, British Columbia, 92 F/7, 92 F/8. Geologial Survey o f Canada, Memoir 318, Ottawa, 142 p.

Halstead, E.C. 1966. Surf ic ia l Geology of Duncan and Shawnigan Map Areas, B.C. Geological Survey of Canada, Paper 65-24, 3 p.

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I I I I I I I I I I I I I I I I I I

Halstead, E.C. 1967. Hydrogeology of the Coastal Lowland, Nanaimo t o Victoria, Vancouver Island including the G u l f Islands, British Col umbi a . Geol ogi cal Survey of Canada , 44 p. ( Unpubl i shed Manuscripts).

Halstead, E.C. and Treichel , A. 1966. Groundwater Resources of the Coastal Lowland and Adjacent Islands. Nanoose Bay to Campbell River, East Coast Vancouver Island. Geological Survey of Canada, Bulletin 144.

Kohut , A.P. and Petrie, J.M. 1978. Evolution of Brackish Groundwaters, Saanich Peninsula, Vancouver Is land, British Columbia. Geological Survey of America Abstract w i t h Program 10, p. 437.

Learning, S.F. 1968. Sand and Gravel i n the S t r a i t of Georgia Area, Geological Survey of Canada, Paper 66-60, 149 p.

Muller, J.E. 1977. Geology of Vancouver Is land, Marginal Notes. 3 sheets. Geological Survey of Canada, Open F i l e Report 463.

Porter , S.A. 1980. Estimates of Recharge for a Surf ic ia l Aquifer, North Saanich Land District, Vancouver Is land, British Columbia. B.A.Sc. ,

Thesis, University of British Columbia, Vancouver, British Columbia, 95 pp. (Unpubl ished).

Richards, L.A. (Edi tor ) . 1969. Diagnosis and Improvement of Sa l ine and A1 kal i Soi 1 s. Uni ted S t a t e s Sal i n i t y Laboratory S ta f f , Agricul tural Handbook No. 60, United S t a t e s Department of Agriculture, Washington, 160 p.

Zube , M. 1980. Saanich Peninsula Water Supply - Groundwater Study. Ministry of Env i ronment, Inventory and Engineering Branch, Victoria, British Columbia, 7 pp. (Unpublished).

5 3 9 2 0 0 0

5388000

5384000

I

MINISTRY OF ENVIRONMENT Water Management Branch

Regional Groundwater Potential for Supplying Irrigation Water

Pot en ti al Unconsolidated Unconfined A quif e rs Developed Unconsolidated A qui f ers o ; o o z ; o z P o t e n t i a l unconso l ida ted unconf l ned aqui- Areas where sand and/or g rave l a q u l f e r s

w e l l l i t h o l o g y . These a q u i f e r s m y be O 0 z o o f e r s (p redominant ly sands and g rave ls ) have been i d e n t i f i e d a t depth based on + + + + +

e i t h e r con f ined or unconf lned. ~ ~ o o o ~ ~ " o ~ based on s u r f i c i a l geology maps.

Low Permeable Unconsolidated Deposits Bedrock Aquifers Areas where t h e p o s s l b l l l t y o f o b t a i n i n g Areas where t h e s u r f i c l a l unconso l lda ted

adequate supp] l e s of groundwater for d e p o s i t s (p redominant ly tl I Is, si I t s and

I r r i g a t i o n purposes a re poor. These a r e c l a y s ) a r e u n s u i t a b l e as aqu i fe rs . How- areas where bedrodc Is l oca ted a t or near ground su r face and/or where well logs a t depth.

1 nd l c a t e bedrock aqu 1 f ers.

ever, s u i t a b l e a q u i f e r m a t e r i a l s may e x i s t

Well w l t h a repo r ted es t imated y i e l d of Well w l t h a r e p o r t e d es t ima ted y i e l d o f

g r e a t e r than 3 I i t r e s pe r second. A between 1 and 3 I l t r e s pe r second- A

i toms

Ronneseth. Novl l985

9

+

2 . - -_ .

+

A' for information solidated Deposits.