Ground Water Resources of British Columbia
Chapter 9 — Ground Water Resources of the Basins, Lowlands and Plains
9.1 COASTAL BASINS, LOWLANDS AND PLAINS
9.1.1 FRASER LOWLAND
by
Allan Dakin
Acknowledgement: Much of this section has been adapted from Halstead, 1986.
GENERAL SETTING
Topography
The southwest corner of the Pacific coast mainland of Canada and the adjoining northwest corner of the continental United States are commonly referred to as the Fraser Lowland (see inset on Figure 8.3). This triangular area extends from Hope westward to the Strait of Georgia, a distance of about 105 km. It has relatively low relief and is bounded on the north by the Coast Mountains, on the southeast by the Cascade and Chuckanut Mountains and on the west by the Strait of Georgia. The lowland covers an area of about 2600 km2.
The Fraser River flows over Fraser Lowland sediments, which were deposited into a bedrock valley averaging 5 km wide and up to 300 m deep during the late glacial and post-glacial period. This river ends in a growing delta, 31 km long and 24 km wide. North and south of the Fraser River, the Fraser Lowland consists mainly of gently rolling and flat-topped uplands, with elevation less than 175 m and separated by wide flat-bottomed valleys. The area of these uplands range from small (3 km2) up to quite extensive (400 km2).
In addition to the valley occupied by the present Fraser River, there are two other major flat-bottomed valleys which dissect the upland areas of the Fraser Lowland. They are the Nicomekl and Sumas River valleys, with bottom elevations ranging from up to 100 m, both of which were once arms of the sea during the period 13,000 to 11,000 years B.P. (before present) (Armstrong, 1981). The Nicomekl Valley is more than 30 km long and 5 km wide and stretches from Boundary Bay northeast to the Fraser River. The Sumas Valley also averages 5 km in width and, in Canada, extends northeast 25 km from the United States border towards the Fraser River.
Surface Drainage
Most of the lowland is drained from east to west by the Fraser River into the Strait of Georgia. Estimated mean annual flow at the mouth of the Fraser River is 3,700 m3/s with about 80% of the annual runoff occurring between May 1 and July 16 each, the annual freshet period. Mean monthly flow ranges from about 483 m3/s (17,000 cfs) in March to 10,800 m3/s (380,000 cfs) in June. The flow at Hope is about 75% of that at the mouth. Hydraulic gradients range from about 1m/km (metres per kilometre) at Hope to about 0.1 m/km near the mouth. A tidal influence extends up to about Sumas, some 72 kilometres inland.
A number of tributary rivers and creeks originate in the adjacent Coast and Cascade Ranges. The larger rivers include the Coquitlam, Alouette, Pitt, Stave, Harrison and Chilliwack Rivers, all of which drain through large lakes (see Figure 9.1). Smaller drainages into the Fraser River on its north side is through Silverdale, Whonock, Norrish and Kanaka Creeks and on the south side through Sumas and Salmon Rivers and Nathan Creek.
There are, however, some creeks that do not drain into the Fraser River. The Nicomekl-Serpentine system and tributaries, as well as the Campbell River, discharge into the Strait of Georgia at Semiahmoo Bay. Fishtrap and Bertrand Creeks drain south across the International Border and into the Nooksack drainage system in Washington State. The lower reaches of all of these smaller creeks are effluent streams, receiving ground water discharge which maintains up to 100% of the flow during the drier summer months.
Climate and Ground Water Recharge
The Fraser Lowland can generally be characterized as having warm, wet winters and relatively cool dry summers. During winter, a fairly steady succession of low pressure systems moving eastward from the Pacific Ocean produces cloudy, rainy conditions, whereas the summers have frequent long periods of sunny weather as high pressure cells extend over the coast. Temperatures are warm and rainfall is low. Soil moisture deficiencies frequently develop, and irrigation is required on some soils to maintain good agricultural production.
Figure 9.1 Map of Fraser Lowland showing significant
hydrogeological features
Since precipitation is the principle source of ground water, its range and patterns are significant factors to be considered when assessing aquifer yields. There are over 30 climate stations in the Fraser Valley, some of which have been in operation for more than 50 years. There is a significant increase (over double) in total annual precipitation, as one moves from south to north and from west to east, which are attributed to orographic effects of the nearby Coast and Cascade Mountains. Histograms in Figure 9.2 show the average monthly and the average annual precipitation for the 30 year period 1950 to 1981 at a few selected stations in the valley.
About 75% of the annual precipitation occurs between October and March, when evaporation and evapotranspiration are minimal; hence it is only during this period that there is potential for rain water to percolate into the soils, and eventually to recharge or replenish the aquifers. The effect of the recharge is illustrated in Figure 9.3, which shows a plot of ground water levels in a observation well (unpumped) in the north Langley area during the period 1971 to mid-1988. When the monthly water levels, as shown in Graph 4 of Figure 9.3, are compared with monthly total Langley precipitation data (Graph 1 of Figure 9.3), it can be seen that the water levels are affected by the amount of winter precipitation.
Variation in total annual precipitation is also significant, especially when there are many successive years of less than normal precipitation. This effect is seen when comparing the two graphs for 1976 to 1980, i.e., a downward slope on the cumulative deviation graph (Graph C of Figure 9.3), and for ground water levels. The reverse is seen when successively wet years occur, such as 1981 to 1982.
During dry years, it is not uncommon for recharge to the ground water table to be insufficient to sustain yields in the shallower dug wells, and hence deepening of wells is required to intercept the declining water table.
Figure 9.2 Precipitation and temperature trends in the Fraser Valley
Figure 9.3 Hydrograph of water levels in Salmon River Aquifer,
showing dependence upon precipitation bedrock geology
GEOLOGY
The geologic setting of the Fraser Lowland is that of a major structural trough which has subsided repeatedly since late Cretaceous time (Mathews, 1972). This trough has been gradually filled, during the Quaternary period, the glacioclimatic episode of the last 1.8 million years. First it was filled with sediment brought by rivers from denudation of the adjacent mountains, and more recently with sediments of marine, fluvial and glacial origin. The shallower (i.e., less than 100 m deep) surficial deposits are the common source of ground water in the valley, but in some locations bedrock may also serve as an aquifer for providing a dependable water supply.
Bedrock Geology
The Coast and Cascade Mountains that form the boundaries of the Fraser Lowland are major mountain systems that have existed since Upper Cretaceous time, about 65 to 80 million years ago. The geological record for this area indicates that about 300 million years ago, prior to the mountain-building episode, volcanic and sedimentary strata were subjected to the intrusion of magmatic material which on cooling resulted in formation of coarse-textured crystalline igneous rocks, referred to as granitic rocks. They make up 70% to 90% of the Coast Mountains and 30% to 40% of the Cascade Mountains (Roddick, 1965) and provide many local aquifers with limited supplies.
Following the mountain building episode, the uplifted land masses were subjected to weathering. Streams and rivers carried the weathered materials, namely clay, silt, sand, gravel organic material to the adjacent seas. These materials are now exposed as shales, siltstones, sandstones and conglomerates along the flanks of the mountain and are found in drillholes that reach depths of more than 300 m in the Fraser Lowland. They generally do not constitute favourable water bearing units.
Surficial Geology
The Fraser Lowland is underlain by Quaternary deposits up to 300 m thick, with bedrock hills projecting through the Quaternary covering at a few localities, such as Sumas Mountain (Armstrong, 1977). These sediments provide the physical framework which controls the configuration and character of the ground water flow system sin the Fraser Lowland.
Surface distribution of the Quarternary deposits in the Fraser Lowland is shown in Figure 9.1 and the stratigraphic record indicates that the lowland was repeatedly invaded by glaciers from the adjacent high mountains during the last ice age (Pleistocene Epoch). A complex sequence of low permeability tills were deposited by overriding ice followed by more permeable sediments being laid down and by fluvial, marine and mass-wasting processes during nonglacial intervals, each successive advance and retreat of the ice causing significant to partial erosion of the older sediments. As a result of these processes, the Quaternary deposits in the Fraser Lowland and consist of several drift advances separated by unconformities and by nonglacial deposits (Clague and Luternauer, 1982).
Each major glaciation was accompanied by a depression of the land surface and relative changes in sea level of up to 200 m. As a consequence, low lying land areas were repeatedly inundated by the sea, with consequent deposition of marine, glaciomarine and deltaic sediments.
The early Quaternary history of the Fraser Lowland is little known, except for records of deep drillholes which indicate thick marine sequences underlying large parts of the lowland. The late Quaternary stratigraphic units, revealed in surface exposures, have been divided into the nine mappable units shown in Table 9.1.
HYDROSTRATIGRAPHIC UNITS
Halstead (1986) has grouped these sediments into six units of significance to ground water, either acting as barriers to flow or as units that readily transmit ground water. These hydrostratigraphic units are described on Table 9.1 and are indicated on the hydrogeologic profile shown on Figure 9.4. A brief description of each unit, starting with the youngest follows:
Hydrostratigraphic Unit A
Hydrostratigraphic Unit A includes clay, stoney clay and silty clays, with varying stone content, as well as silty lenses, sandy silts and in some places marine shells. In outcrop, this unit has a characteristic buff colour and a weathered stony clay with blocky structure. This material was mainly derived from ice sheets ending in the sea during the overall retreat of the last major Fraser Lowland ice. Thin layers of low permeability, post-glacial materials, such as peat and floodplain deposits, which typically overlie the stony clays are included in this unit.
Unit A is present at or near ground surface, throughout the central part of the Lower Fraser Valley, with the exception of areas where it is overlain by Unit C, which consist of permeable, glaciofluvial ice-contact deposits, glaciofluvial deltas and occasional thin patches of till; all of which was left upon retreat of a final resurgence of glacier ice in the Fraser Lowland. Unit A is commonly less than 30 m thick and includes the Capilano sediments and Fort Langley formations, listed on Table 9.1. Typically, at or near its base, there is a sand layer with thin lenses of till, which often is sufficiently permeable to yield water sufficient only for domestic use. Water analyses indicate that total dissolved solids are generally less than 120 mg/L, and pH ranges from 6 to 8.
Hydrostratigraphic Unit B
This unit is of glaciomarine origin and consists of stony clay with shells. Based on a review of driller's logs, the stone content as well as the clay content appears to be greater than in Unit A. It is a unit of low permeability generally forming an aquiclude and is found in the Langley Upland east of Abbotsford, as well as in the valley of the Nicomekl and Serpentine Rivers. In a deep test hole near Aldergrove (see hole No. 10 on Figure 9.4), about 56 m of Unit B was penetrated (Halstead, 1964), while deep test holes in the Milner and Fort Langley areas penetrated as much as 90 m of this material. Well yields from Unit B are generally less than 0.2 L/s and water quality is poor.
Hydrostratigraphic Unit C
Hydrostratigraphic Unit C consists mainly of glaciofluvial sand and gravel, deposited by meltwater streams. Where the streams emptied into the sea, deltas were built up. With isostatic rebound of the land during and following deglaciation, these deltas are now elevated above sea level and cover large parts of Townships 7, 10 and 11 (see Figure 9.2). This unit generally overlies Unit B, and occasionally Unit A.
As is discussed in the following sections, all major aquifers are located in this unit. For example, a large raised delta, located south of Langley forms the Langley Aquifer, and former meltwater streams that issued from stagnant melting ice masses in the vicinity of Sumas Mountain have built up a plain of very permeable sand and gravel south of Abbotsford (the Abbotsford Aquifer). Discharge of ground water by springs is commonly observed along the edges of the deltas and is responsible for maintaining perennial flows in many streams, such as Anderson, Fishtrap and Chilliwack Creeks (see Figures 9.5, 9.6 and 9.7, respectively).
Yields from wells developed in these aquifers range up to 153 L/s. This unit is the ground water source for all of the municipal fish hatchery and irrigation wells listed on Tables 9.3 and 9.4.
Water quality in Unit C is excellent; with total dissolved solids typically less than 200 mg/L and pH ranging from 6.5 to 7.5.
Hydrostratigraphic Unit D
Hydrostratigraphic Unit D includes a range of coarse to fine sediments, commonly referred to as till or diamictons, the components of which are brought together by a wide variety of glacial processes. The advancing glaciers moved southward down valleys within the Coast Mountains and overrode a landscape that had previously been fashioned by subaerial processes, especially river and stream action. Plenty of loose material was available for pickup and transport beneath and within the ice masses. Upon disappearance of the ice, tills consisting of heterogeneous mixtures of clay, silt, sand, gravel and boulders of varied shape and size were left.
Although the tills represent repeated invasions by glaciers in the lowland, all are included in Hydrostratigraphic Unit D.
Till has been found as deep as 90 m below sea level in the Nicomekl and Serpentine Valleys, and is representative of a penultimate glaciation. The rest of the (shallower) tills shown on Figure 9.4 are related to the last or Fraser glaciation, 11,000 to 26,000 year B.P. (Armstrong, 1981).
These tills are not continuous across the valleys in the Fraser Lowland, but do underly the uplands at an elevation of between plus and minus 15 m relative to present sea level. A multi-till sequence of till-outwash-till underlies the front of the Langley Upland, and is interpreted as the deposits of a single glacier rather than an evidence of multiple glaciation. Tills were encountered in a deep test hole near Aldergrove, with a base elevation of 12 m and a thickness of 13 m (Hole No. 10 and Figure 9.4).
Tills and till complexes of this Hydrostratigraphic Unit constitute significant confined aquifer systems with water quality characteristically of the sodium-bicarbonate type, with total dissolved solids less than 500 mg/L. Because ample supplies of good quality ground water (for households) are available in the upper Units A and C, within the top 90 m of drilling, test holes have rarely been continued to depths where these deeper and older tills are found.
Hydrostratigraphic Unit E
All the materials included in Units A to D were deposited by processes related to retreating ice masses and sea level changes brought about by glacioclimatic events accompanying the Fraser Glaciation. Unit E comprises older materials, mostly marine sediments interbedded with estuarine and fluvial deposits consisting of fine sand, silt and clayey silts. All drillholes that penetrate to depths of more than 90 m have encountered these materials. Typically, ground water flow in this Unit has a long residence time and hence water quality is poor.
Hydrostratigraphic Unit F
Unit F consists of bedrock. Within the Fraser Lowland bedrock is usually found at depth greater than 300 m, but evidence of bedrock "highs" have been detected in some areas of townships 10, 14 and 16 (see Figure 9.1). Fractured bedrock is the source of ground water for areas north of the Fraser River sediments in Townships 12 and 15 as well as in upland areas such as Chilliwack, Sumas and Vedder Mountains. Individual well yields rarely exceed 1 L/s.
Figure 9.4 West to East hydrogeologic profile through Fraser Valley
Figure 9.5 Plan, section, water balance and water level trends
in Langley aquifer (No. 11)
Figure 9.6 Plan, section and hydrographs of wells
in Abbotsford aquifer
Figure 9.7 Plan, section and hydrographs of a well
in Vedder aquifer
GROUND WATER SOURCES
Availability of Data on Ground Water
The Ground Water Section of B.C. Environment estimates that there are records of over 10,000 wells having been drilled in the Lower Fraser Valley.
The National Hydrology Research Institute (NHRI) recently published a paper on the ground water supply in the Fraser Lowland (Halstead, 1986). This paper deals with the area extending from Agassiz and westwards up to the Strait of Georgia. A series of maps and diagrams illustrate the locations and stratigraphy of selected wells for townships 1, 7, 8, 9 (part only), 13, 14 and 16. In addition, there are many unpublished reports prepared by consulting hydrogeologists, engineers and government hydrogeologists (a partial list is included in the references).
In 1987, water levels were being monitored, using either chart recorders or by manual measurements, in about 18 unpumped wells in the Fraser Valley. Locations of some of these are shown on Figure 9.1.
Plots of these water level data (called hydrographs) are vital for assessing precipitation/rainfall recharge relationships and the effects of ground water usage in a particular aquifer (see examples in Figures 9.3 and 9.5 to 9.7).
Inorganic water chemistry data has been collected on an intermittent basis by NHRI, B.C. Environment and Ministry of Health personnel and by many private citizens and their consultants, and some of this has been entered into a computer data base operated by B.C. Environment. Liebscher (1979) prepared preliminary generalized hydrogeochemical maps of the western portion of the Lower Fraser Valley.
Significant Aquifers
The probable areal extent of thirteen significant aquifers with good water quality, in the Lower Fraser Valley are shown in Figure 9.1. There are a number of aquifers that could sustain high yield wells but, because of poor water quality, usually associated with high dissolved iron, manganese or chloride, they have not been developed. All thirteen aquifers are capable of sustaining yields of at least 80 L/s to wells in one or more zones, within the aquifer. They are mostly located in Hydrostratigraphic Unit C, with the rest in recent river deposits included in Unit A. Approximate data on these aquifers is summarized in Table 9.2 and the following is a brief description of salient features of each aquifer.
White Rock Sunnyside Aquifer (Aquifer I in TP 1)
This is a thin (10 m thick) areally extensive aquifer that consists of sand and gravel with lenses of till. White Rock Utilities Ltd. have five wells in this confined aquifer, producing yields of between 28 and 63 L/s (see Table 9.3). These wells are located on the Sunnyside Upland and all but one is deeper than 100 m, and have static water levels a few metres above sea level. Northeast of the upland, the aquifer is confined with a high hydrostatic pressure and a number of wells reported to have free flows up to 30 L/s. Halstead (1986) estimated that prior to 1972, the average annual aquifer yield was four million cubic metes (M m3/yr). However, the ultimate yield and areal extent of the aquifer unknown.
Langley Aquifer (Aquifer II in TP 7)
This aquifer occupies a raised delta, located in the northwest corner of the Township No. 7 and consists of semi confined and unconfined sands and gravels (Unit C). It extends over an area of about 25 km2, and has an average thickness of about 30 m. A plan and section through this aquifer is illustrated in Figure 9.6. Recharge comes from direct precipitation and exfiltration from Anderson and Campbell Creeks. It has been estimated that the potential average annual recharge to this aquifer is 430 L/s (14M m3 yr) (Piteau Associates, 1983a).
The Corporation of the Township of Langley has nine production wells in the aquifer (see Table 9.2). Average yield in 1987, from the wells, was about 40 L/s or 1.3M m3/yr. Irrigation for a large forest nursery, many small trailer parks and about 2,000 domestic wells increases the total aquifer withdrawal by about 1.7M m3/yr for a total of 3M m3/yr. This represents about 14% of the average annual recharge (see Table on Fig. 9.5).
Salmon River Aquifer (Aquifer III)
There are a number of aquifers in Townships 10 and 11 and in the northwest and southwest corners of Townships 13 and 14, respectively. Ground water flow directions in these aquifers are quite varied and it is possible that many of these confined and unconfined aquifers are likely interconnected. However, for sake of simplicity, they have been somewhat arbitrarily designated as the Fort Langley, Salmon River, and Aldergrove Aquifers.
The Salmon River Aquifer covers an area of about 40 km2 and generally occupies the ridges extending between small creeks. Ground water flow in the aquifer is towards discharge areas in the upper Nicomekl River Valley, many tributaries of the Salmon and Beaver Rivers and Natham Creek. Well yields are very variable and depend on many factors, such as boundaries, sources of recharge etc. Local perched water table aquifers are present in many areas, about the Salmon River Aquifer.
Soon after a number of high capacity irrigation wells (up to 125 L/s) started pumping the Sperling area of North Central Langley, the water level in the aquifer started to drop quite significantly and piezometric levels have continued to decline ever since. This effect is illustrated by B.C. Environment monitoring well No. 10 (shown on Figure 9.3), which is located in the aquifer.
Fort Langley (Aquifer IV)
The Township of Langley operates a 20 m deep well, which penetrate sediments of a backfilled former channel of the Fraser River. This unconfined aquifer is located south of Fort Langley and has an arcuate shape. The well yields about 126 L/s, and is in a zone that is well flushed by exfiltration from the Salmon River, and hence has good quality water. In contrast to this, a well in a less flushed portion of the same aquifer had the same potential yield but, because of a high dissolved iron concentration, the water was undrinkable (Dakin and Holmes, 1987).
Aldergrove (Aquifer V)
This is a thin, mostly confined aquifer, positioned between the Salmon River and Abbotsford Aquifers, in the west central area of Township 13 (see Figure 9.1). The degree of hydraulic connection between all three aquifers is not well known, but is likely well connected to the Abbotsford Aquifer. The Township of Langley have four production wells in the aquifer that pump an average of about 4 M m3/yr.
Abbotsford (Aquifer VI)
The Abbotsford Upland, encompassing a broad area of 48 km2, is situated southwest of Abbotsford (TP's 13 and 16) and is underlain by a succession of glaciofluvial sand and gravel deposits which constitute a major aquifer (Kohut, 1987). This aquifer extends from Sumas Mountains southwestwards and into the State of Washington (Figure 9.6) and ground water outflow from this portion of the aquifer feeds into the Nooksack River system (State of Washington, 1960).
The outwash sediments are highly stratified and often interspersed with minor till and silty lenses. The base of the aquifer has not been fully explored, but is known to be at least 70 m thick. Profiles through the aquifer are shown on Figures 9.4 and 9.6. Ground water flows in all directions with significant discharge to the west and east. The easterly discharge was formerly via a series of large springs that flowed into Lonzo Creek. Prior to development of high yield wells in this aquifer, the total spring discharge was estimated at 263 L/s or 8.3M m3/yr (Halstead, 1986). Kohut (1987) estimated that the average annual ground water recharge to the aquifer was equivalent to at least 37% of the average annual precipitation and that the recharge was about 26.8M m3 (or 850 L/s). Ground water extraction has been centred in the southeast corner of the upland where the four wells of the Fraser Valley Trout Hatchery abstract about 4M m3 per year (see Table 9.4) and the District of Abbotsford wells used to pump about 3.7M m3/yr and accounted for more than 60% of the total aquifer withdrawals.
The total quantity of water in 1985 from all wells tapping the aquifer was estimated at 12M m3/yr (Kohut, 1987). An approximate breakdown is industrial (41%), municipal (34%), irrigation (21%) and domestic (4%).
Ground water level monitoring at a number of places in the Aquifer has not detected any persistent ground water level decline (see hydrographs on Figure 9.6).
Vedder (Aquifer VII)
Chilliwack River enters the Fraser Valley beneath the community of Vedder Crossing on TP 26. At this location, the aquifer consists of a very permeable sandy, gravel fan deposit which is thickest at an apex near the bridge and thins out towards the north and west of the village (Figure 9.7). As with the Langley Aquifer, recharge comes both from infiltration of precipitation and leakage from the perched bed of the Vedder River (see Sections on Figure 9.7). The estimated total recharge is about 15M m3/yr and total abstraction is about 8M m3/yr.
Two of the 30 m deep wells in the area, owned by the District of Chilliwack, have proven safe yields that each exceed 200 L/s. Water quality is very good and water temperatures vary significantly throughout the year, confirming the relatively fast rate of movement through the aquifer.
Rosedale (Aquifer VIII)
The areally extensive river channel deposits and possibly some of the underlying glaciofluvial sediments form good aquifers in the areas east and north of Rosedale. A rapid flattening of the hydraulic gradient in the former Fraser River channels has resulted in deposition of coarse sand and gravel alluvium. In areas where subsequent ground water flushing has prevented a buildup of dissolved iron the sediments, high yielding wells (> 50 L/s) can be developed to produce potable water. However, south and west of Rosedale, where organic content in the aquifer is higher and where flushing rates are low, the ground water is typically has a high dissolved iron content, and is generally not potable. To date, this aquifer has not been extensively developed.
Chawuthen and Flood (Aquifers VIX)
Good well yields (> 25 L/s) can be expected in these two gravelly sand aquifers which have not yet been extensively developed.
Upper Chilliwack Artesian (Aquifer X)
This is a deep (150 m) confined sandy, gravel aquifer that probably extends for many kilometres up the Chilliwack River valley, from its confluence with Slesse Creek. The Chilliwack Salmon Hatchery well field has three artesian wells; free flow is about 30 L/s and pumped yields from two of the wells are greater than 120 L/s (PAEL, 1985). The full extent of this aquifer has never been explored.
Chehalis, Alouette and Norrish Creek (Aquifers XI, XII, XIII)
These are all relatively thin, very permeable sand and gravel water table aquifers, that are almost directly connected to a nearby creek or river source. Hatchery well fields have been developed in all three aquifers. See locations on Figure 9.1 and summary of data on Chehalis, Alouette and Inches Creeks (in Norrish Aquifer) hatcheries on Table 9.4.
GROUND WATER QUALITY
Ground water in water table aquifers of the Fraser Lowland are commonly of calcium bicarbonate type, with a total dissolved solids content less than 200 mg/L. The pH of ground water is commonly low, resulting in corrosive properties. Ground water in the confined intermediate flow systems, has a total dissolved solids concentration ranging from 150 to 500 mg/L, and is mainly of a sodium and bicarbonate type water. Sodium chloride type water, with total dissolved solids greater than 1000 mg/L, are found in the discharge areas of deeper regional ground water flow systems, where residence times may be several hundred years and ground water movement is slow. For example, many deep wells in the Nicomekl Valley have chloride concentrations exceeding 800 mg/L (Halstead, 1978).
Iron and manganese are the most troublesome water quality parameters in the Fraser Lowland and are prevalent in many of the water table aquifer. This is particularly common in areas where organic matter is deposited in the aquifer sediments or recharge areas, and where ground water movement is slow.
It is not uncommon to find good quality water in the middle or below less well flushed zones containing high concentrations of chloride or dissolved iron. Aquifer contamination has occurred in the Fraser Lowland, but in most cases a point source, such as a manure stockpile, a nearby landfill or seepage from buried fuel tanks, can be identified. A build up of nitrate concentrations has been identified in the Abbotsford Aquifer (Kwong, 1986) and the Langley Aquifer (PAEL, 1983). Nitrogen sources appear to be a combination of agricultural waste spreading and septic tanks.
GROUND WATER TEMPERATURE
Ground water temperatures are generally very close to the average annual air temperature in the recharge areas. Anomalous zones have been identified in only two areas: a deep sluggish aquifer, located northeast of Langely (Area A1 on Figure 1) and an elongated Bedrock Zone (A2) extending from the Harrison River mouth, northwards to Harrison Hotsprings (Nevin, et al 1985).
GROUND WATER USAGE
The estimated total volume of ground water abstracted in 1987 from aquifers in the Fraser Valley is 4M m3, which is an increase of about 26% over the 32 million m3 volume estimated for 1981 (Halstead, 1986). Most of the increased usage was for fish hatcheries. Usage is conveniently discussed under the following categories:
Municipal
There are four organizations supplying large quantities of ground water through municipal water distribution systems. These are District of Chilliwack, Town of Hope, Corporation of the Township of Langley, and White Rock Utilities Ltd. The Dewdney/Alouette Regional District and District of Matsqui have a number of capacity wells, but use them only as a backup source for a surface water supply coming from Norrish Creek.
Estimated annual municipal consumption in 1987 was 15.2M m3. This compares with an estimated 16.6M m3 consumed in 1981 (Halstead, 1986). This small decrease is mainly due to the Districts of Abbotsford and Mission switching to a surface water source.
Domestic Wells
There are an estimated 10,000 domestic wells in the valley and, assuming an average per well consumption of 1.4 m3/day throughout the year, the total annual domestic usage is estimated at about 5.1M m3.
Industrial
Industrial usage includes forest nurseries, dairies, gravel pit operations and industries located in isolated areas away from municipal water sources. The estimated annual consumption is 1.6M m3.
Hatcheries
There are five major fish hatcheries located in the valley using an estimated 14.3M m3 of ground water. In addition, there are a dozen or more small private hatcheries and small trout rearing operations that use warm ground water during the late winter for fish rearing. A summary of data on larger hatcheries is given on Table 9.4.
Irrigation
A number of berry farmers use high capacity wells for irrigation during the summer months. There are no accurate records for this water usage, but it is not expected to exceed 5M m3/yr (Halstead, 1981).
Back to Table of Contents
| 
