Ground Water Resources of British Columbia
Chapter 10 — Ground Water Resources of the Plateaus and Highlands Ground Water Regions
10.1 INTERIOR PLATEAUS AND HIGHLANDS
10.1.1 THOMPSON PLATEAU
by
M. Zubel
GENERAL SETTING
Figure 10.1 outlines the general extent of the Thompson Plateau, bounded on the east by the Okanagan and Shuswap Highlands and on the west and south by the Cascade Mountains. The main population centres include Kamloops, Kelowna, Penticton, Princeton, Merritt and Cache Creek.
PHYSIOGRAPHY
Holland (1964) described this plateau as a gently rolling upland of low relief, generally between 1,200 m (4,000 ft.) and 1,500m (5,000 ft.), covering an area of approximately 28,500 sq. km. (11,000 sq. miles), and representing the late Tertiary erosion surface that has been dissected by three major rivers, i.e. Thompson, Similkameen and Okanagan and their tributaries. Other major hydrologic features include Kamloops Lake and Okanagan Lake.
GEOLOGY
According to Nasmith (1962), this area was occupied by Pleistocene ice. A thick mantle of glacial drift covers bedrock over a large proportion of the plateau. According to Holland (1976), the plateau is comprised of a diversity of rocks; stocks of granitic rock intrude sedimentary and volcanic formations of Palaeozoic age; flat-lying or gently dipping early Tertiary (Eocene) lavas obscure large areas of older rocks.
Figure 10.1 Thompson Plateau and watershed areas
GROUND WATER RESOURCE
The ground water resources within the Thompson Plateau are described as follows for each of the watershed areas within this plateau. For each of these areas, the corresponding figures (i.e. 10.2, 10.3, 10.4, 10.5) outline the general extent of known and potential major aquifers or ground water reservoirs within unconsolidated sediments. The delineation of these aquifers is based primarily on surficial geology ( i.e. locations of sand and/or gravel deposits), and water well drillers' lithological descriptions as reported on water well records.
Thompson River Watershed
The principal aquifers within this watershed are located in the main river valleys. About 73% of the approximately 1100 reported wells in the area have been constructed in water-bearing sand and/or gravel deposits (i.e. unconsolidated aquifers). About 90% of these wells have reported yields of less than 1 L/s (i.e. sufficient for domestic needs), while the remainder (approximately 70 wells) have reported higher yields between 6 L/s and 95 L/s.
These higher yield wells, used for irrigation, municipal and agricultural purposes are located primarily in the Cache Creek area (i.e. Semlin valley, Bonaparte River floodplain), the Cherry Creek area, and the Salmon River area (particularly Westwold), as shown in Figure 10.2. Based on available well record data and extent of aquifers, there is a significant potential for further ground water development.
There are approximately 300 wells constructed in bedrock, mostly located in the Kamloops area. Reported yields vary up to 5 L/s (Barriere area), with a large proportion at about 0.1 L/s.
An analysis of limited ground water quality data indicates that ground water from wells constructed in bedrock are principally bicarbonate and/or sulphate type, while ground water from wells constructed in unconsolidated materials are predominantly a bicarbonate type. Most of the water samples analyzed showed high levels of Total Dissolved Solids, i.e. greater than 500 mg/L, and some samples showed high levels of Sulphate, exceeding the Canadian Drinking Water Quality Standards' maximum acceptable concentration of 500 mg/L. A probable source of the Sulphate may be from sulphate-rich rocks located around the east end of Kamloops Lake.
Figure 10.2 Thompson River watershed
Chemical analyses of ground water samples from wells in the Deadman River area indicate that the water is very hard, highly mineralized and contains mercury levels at concentrations of up to 0.005 mg/L. The Canadian Drinking Water Quality Standards' maximum acceptable concentration is 0.001 mg/L. Mercury levels in excess of 0.0002 mg/L are considered toxic to fish culture. The probable source of mercury may be from mercury bearing rock occurring in the Deadman River watershed and the west end of Kamloops Lake.
Other ground water concerns within the Thompson River watershed include:
- potential ground water - surface water interference in the Cherry Creek valley west of Kamloops, where there is evidence suggesting that major ground water withdrawals affect creek flows indirectly, by lowering the head in the aquifer and inducing recharge from the creek. Other areas where ground water use may affect creek flows include Peterson Creek just south of Kamloops, Campbell Creek east of Kamloops, and the Salmon River valley area.
- ground water mining conditions east of Cache Creek, where it is reported by Livingston (1983) that extensive ground water withdrawals from large capacity irrigation wells are depleting the artesian aquifer underlying the Semlin valley and threatening to significantly diminish production from this aquifer.
- impacts of proposed municipal sewerage disposal schemes on ground water in high population areas.
Nicola River Watershed
There has been only a limited amount of ground water development within this watershed area. A review of the 242 well records on file with the Ministry of Environment indicates that 110 wells were constructed in bedrock (providing sufficient water for domestic needs), while the remaining 132 wells, constructed in unconsolidated deposits, 31 wells have reported yields between 6 L/s and 128 L/s. Most of these higher yielding wells, being utilized for municipal water supply needs and industrial (mining) needs, are located in the Douglas Lake area, Lower Moore Creek area and the Monck Park campsite area on the north side of Nicola Lake.
There are three known aquifers in the Merritt area; two confined aquifers located about 60 m and 100 m below ground. and a third, shallow, but discontinuous aquifer about 16 m below ground in the Nicola and Canford areas and as much as 50 m deep in the Merritt area, where yields from wells constructed in this shallower aquifer have been reported up to 120 L/s.
In the Highland Valley, there is a significant artesian aquifer extending throughout most of the valley, approximately 30 m in thickness and located at a depth of about 75 m. Wells constructed in this aquifer have been reported to yield in excess of 38 L/s, with some wells flowing as much as 6.3 L/s.
According to Brown et al (1980), the quality of ground water in the Highland Valley area can be classified as a moderately hard, calcium bicarbonate type water, low in Total Dissolved Solids (250 mg/L to 400 mg/L) and suitable for domestic and industrial use. Elsewhere in this watershed, the results of very limited chemical analyses of ground water indicates that the water quality is generally good; within recommended drinking water quality standards.
The amount of ground water use within this watershed is not definitely known due to a lack to metered data. However, based on the extent of known and potential aquifers and the limited amount of ground water wells, it appears that there is a significant potential for further ground water development particularly in the Highland Valley, Logan Lake area, Douglas Lake area, Pennask Lake area, Lower Moore area and the area at the confluence of the Lower Coldwater River and Nicola River.
Similkameen River Watershed
The Ground Water Section of the Ministry of Environment has on file the records of approximately 800 water wells constructed within this watershed area, for domestic, livestock, irrigation and municipal use. About 550 of these wells (drilled to depths of up to 126 m) have been constructed within the unconsolidated deposits of the valley bottoms, on the terraces of the Similkameen River and its tributaries, and on fans at the mouths of tributary creeks. These unconsolidated deposits comprise the major aquifers as shown in Figure 10.4. Depths to the tops of the shallow unconfined sand and gravel aquifers range from 1 m to 66 m and averages 8 m. In most cases, drilling did not penetrate to the bottoms of the aquifers, estimated to be at least 10 m thick. Deeper aquifers also exist, as evidenced by one well in the Cawston area reported to have penetrated 67 m of water bearing sands and gravels.
Figure 10.3 Nicola River watershed
Figure 10.4 Similkameen River watershed
About 440 wells are located in the Keremeos/Cawston area. More than 100 of these wells have reported yields in excess of 6.3 L/s, and up to 150 L/s (i.e. Fairview Heights Irrigation District). Observation well data indicates the depth to the water table ranges between 1 m to 8 m. The estimated potential withdrawal from these wells is about 3000 L/s. Transmissivity values obtained from 24 hr. pumping tests at rates between 30 L/s and 100 L/s were calculated at between 0.14 m2/sec to 0.29 m2/sec. Production well pumping test drawdown measurements taken in observation wells located at distances of about 23 m to 70 m showed less than 0.3m of drawdown from pumping at rates up to 100 L/s for more than 24 hrs. Based on analyses of pumping test data and observation well data it appears that interference effects among large production wells and with Similkameen River flows is not significant.
Between Princeton and Hedley there are more than 200 wells constructed in unconsolidated deposits in the vicinity of the Similkameen River. Ground water from these wells is used primarily for domestic, irrigation and municipal use, and wells are reported to have yields as high as 60 L/s (e.g. Hedley Waterworks District).
Analysis of ground water level data from observation wells in the Keremeos area (for the period between 1967 - 1982) and the Princeton area (for the period 1977 - 1980) indicates that the ground water levels are stable (i.e. showing no overall declining or rising trends), notwithstanding the increased amount of well construction and ground water use during this period. It appears that there is good potential for further ground water development in both these areas.
Ground water within the bedrock can be found in joints and/or fractures, along bedding plane partings and in the interflow zones of lava. An analysis of well record data for wells within this watershed indicates that the majority of wells (approximately 200) constructed in sedimentary or volcanic bedrock have yields generally less than 1 L/s, (i.e. sufficient for domestic purposes). Some of the bedrock wells are reported to be dry. The potential for further ground water development from bedrock is limited.
Okanagan Watershed
As a result of intense glaciation in the Okanagan valley during the Pleistocene period, a thick sequence of unconsolidated sediments filled the valley. Test wells drilled in the Okanagan valley north of Armstrong encountered more than 570 m of unconsolidated sediments. However, it is within the top 100 m of these sediments that the greatest amount of ground water development has occurred.
Of the approximately 3,600 reported wells within this watershed, about 50% are shallow dug wells of limited capacity and yield; 10% are reported to be constructed in bedrock and have limited yields (i.e. less than 0.6 L/s). Of the remaining 40% of reported wells (i.e. about 1,500), approximately 250 wells have yields in excess of 6 L/s. These higher yield wells, used primarily for irrigation, municipal, water works districts and agricultural purposes are located as shown in Figure 10.5, mainly in the Osoyoos to Okanagan Falls area, Kelowna and Vernon areas.
The actual amount of ground water utilization within this watershed is not fully known. Ground water level trends in the Westwold and Summerland areas appear to be declining, suggesting that the potential for further ground water development may be limited, while ground water levels in other parts of the valley, such as Osoyoos, do not show any long term declining trends, suggesting that there is good potential for further ground water development in these areas.
Based on limited ground water chemical analysis data, the quality of ground waters throughout the watershed is generally good, and may be classified as calcium and magnesium bicarbonate type, with moderate hardness and low total dissolved solids (generally less than 500 mg/L).
Ground water concerns include:
- anomolously high levels of fluoride (3.5 mg/L to 4.0 mg/L) in ground waters in wells located south-east of Naramata and on the slopes of Silver Star Mountain.
- high nitrate levels (>10 mg/L) in ground water in wells in the Rutland, Okanagan Landing and Osoyoos areas; the possible sources may be from septic tank effluent discharge, treatment plant disposal fields (Rutland area), and leaching of nitrates from fertilized soils (Osoyoos area).
- high (total) phosphorous concentrations of 0.337 mg/L to 0.675 mg/L in ground water in flowing artesian wells in the Okanagan Landing area.
Figure 10.5 Okanagan Watershed
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