Water Stewardship

Ground Water Resources of British Columbia

Chapter 9 — Ground Water Resources of the Basins, Lowlands and Plains

9.2 2 ROCKY MOUNTAIN TRENCH

by

B.I. Ingimundson

INTRODUCTION

The Rocky Mountain Trench is a remarkable structurally controlled valley, extending from south of the Canada/US border northwest almost to the Yukon border. The total distance is over 1,000 km, with a definite physiographic division about midway at the McGregor River. The trench is breached by the McGregor Plateau east of Prince George. Therefore, the trench has been divided into north and south sections. South of the McGregor River the trench forms a defined valley between the Rocky Mountains to the east and the Columbia Mountains to the west. The valley varies from 3 to 12 km wide and is occupied by Kinbasket Lake and the north flowing Columbia River. North of the McGregor Plateau, the Rocky Mountain Trench is a straight northwest trending valley containing the Williston Lake reservoir, the south flowing Finlay and Fox Rivers and the north flowing Kechika River.

North Rocky Mountain Trench Section

GENERAL SETTING

The physiographic division separating the north section from the south section of the Rocky Mountain Trench occurs approximately at the drainage divide between the headwaters of the Parsnip and McGregor Rivers. The nearest community is the tiny settlement of Summit Lake, north of Prince George on Highway 97. The trench becomes a well defined north-west (North 33° West) trending valley, for approximately 500 km., as shown on Figure 8.5. This trench section is bounded by the Omineca and Cassiar Mountains to the west and the Rocky Mountains to the east, which rise up to 4,800 m above the valley floor. The trench floor is 6 km wide, narrows to approximately 3 km along the Fox and Kechika Rivers and then broadens again near the Yukon boundary. The north section of the trench is drained into the Peace River system by the Parsnip River system from the south, and by the Finlay and Fox River systems from the north. At the head waters of the Fox River, at the Sifton Pass, the drainage divides again and the trench is then drained north by the Kechika River which drains into the Liard River drainage system.

Since 1968 much of the southern half of the north trench section has been inundated by the Williston Lake reservoir, created by the damming of the trench rivers by the W. A. C. Bennett Dam.

GEOLOGY

Bedrock Geology

The north section of the Rocky Mountain Trench forms the physiographic and structural boundary between the Rocky Mountains and the Dominica/Cassiar Mountains. Sedimentary rocks, primarily Palaeozoic, form the Rocky Mountains to the east, while the mountains west of the trench, the Omineca/ Cassiar mountains, consist primarily of folded volcanic and some sedimentary Mesozoic rock. Throughout the length of northern section of the trench, the underlying rocks consist of Precambrian and Lower Palaeozoic age. Generally the trench bottom is overlain by thick glacial lake and stream deposits, with relatively few bedrock outcroppings.

Surficial Geology

The floor of the northern section of the trench is overlain with several hundred metres of glaciofluvial, glaciolacustrine and glacial till deposits. Multiple glaciation has been a major factor in the distribution of the surficial deposits present in the trench today.

The oldest unconsolidated materials are sands and gravels overlain by the oldest major till unit. With the Early glacial advance, outwash sediments were deposited in the major river valleys. The advance of glaciers originating west of the Trench was extensive. During deglaciation, glaciolacustrine and glaciofluvial sediments were deposited. The following glacial advance, the Early Portage Mountain, extended from west to east across the Trench and the Rocky Mountains into the plateau area to the east. During the following deglaciation a massive glacial lake formed, dammed by Laurentide ice, east of the Trench. Again, more glaciofluvial and glaciolacustrine sediments were deposited within the trench. The Late Portage Mountain advance which followed, was less extensive and more topographically controlled. The ice flowed down the Finlay and Peace valleys and up the Parsnip valley. During deglaciation, more glaciofluvial and glaciolacustrine sediments were deposited. Some time after this, a minor event known as the Deserters Canyon advance occurred. Radiocarbon dating indicate the Early and Late Portage Mountain advances and the Deserters Canyon advance are of late Wisconsin age. The early advance tills and underlying inter-glacial deposits are probably early Wisconsin or older.

HYDROLOGY

Relatively little information pertaining to the hydrogeology is available in the north Rocky Mountain Trench section, mainly due to the lack of settlement. The largest community within the northern trench is Mackenzie, population 5,000. North of Mackenzie are the native settlements of Fort Ware and Ingenika. In all of the drilling information studied, most of the wells were completed in overburden sediments. In only two cases did any of the wells reach or penetrate bedrock. In both cases the wells were located on the outer edges of the trench in the adjacent mountain foothills and the wells were abandoned or completed above the bedrock. Therefore, we have directed our assessment to overburden aquifers only.

Well drilling information indicates random depths for water wells within the trench zone from 15 m to 120 m. Therefore it is safe to conclude that the full stratigraphic section of the trench sediments has not been penetrated to date. In all cases except two, the required amount of ground water has been achieved by depth drilled, therefore it was not necessary to drill deeper. In the exception, the wells were reported to have been abandoned at 120 and 140 m in till, presumably without having encountered a suitable ground water supply.

The most extensive drilling and hydrogeologic exploration within the northern trench as been done at Mackenzie, in unconsolidated glacial deposits, for municipal supply and industrial process water. Where water bearing glaciofluvial outwash sandy gravels have been penetrated and properly developed wells have been constructed, the well yields are high.

The examination of the drill logs generally indicates an extensive complex stratigraphic sequence of discontinuous sediments. In most drill holes till was encountered and often glaciolacustrine clay. Figure 9.20 shows the lithology as noted at the Finlay Forest Industries (FFI) mill at Mackenzie, adjacent to the Williston Lake reservoir. In many of the well logs examined, the water bearing glaciofluvial sands and gravels were overlain by a confining layer of glacial till or glaciolacustrine silt or clay, thus resulting in an artesian condition. Table 9.7 gives a range of well information from wells drilled within the trench sediments.

Figure 9.20 Stratigraphic section at the Finlay Forest Industries
Process Well at Mackenzie, B.C.

Table 9.7: Typical Well Characteristics

Only the industrial and municipal wells at Mackenzie and Fort Ware have been fully tested and analyzed. Table 9.8 shows the aquifer characteristics represented by the testing of these wells and should be taken as being only representing the aquifers penetrated at that location. However these characteristics are expected to exist elsewhere within the trench.

Table 9.8 Aquifer Characteristics

Aquifer characteristics are as variable as the trench sediment stratigraphy. The potential for water supply from within the north Rocky Mountain Trench sediments is extremely variable, depending upon location. Close to the centerline of the well-defined trench lineament north of McLeod Lake, one would expect potentially high yields in the glaciofluvial coarse granular sediments. As noted, the known drilling to date has probably not penetrated the entire depth of the trench sediments, and further aquifers may exist at depths greater than the approximately 100 m drilling depth.

Observed recharge to the trench aquifers during studies at Mackenzie is seasonal precipitation. Hydrographs plotted from recording wells at Mackenzie show a 14 metre variation in non-pumping water levels over an annual cycle. The low water levels occur during the month of May. Once the ground frost is gone the water levels rise rapidly to a peak height during September - October before declining. The studies also indicate the artesian aquifer does not appear to have a direct hydraulic connection to the Williston Lake reservoir. However it is expected that a body of water of that size will have some impact upon the aquifer characteristics. To date no information is available on this impact.

GROUND WATER QUALITY

Water quality information is limited to the few locations where wells have been developed for human consumption and industrial use. Both the artesian and water table aquifers, developed within the trench, indicate water of moderate mineralization. Most parameters tested fall within the Canadian drinking water standards; however, the samples often tested high in concentrations of iron and manganese. This has resulted in treatment for process water use to eliminate incrustation.

South Rocky Mountain Trench Section

by

J.C. Foweraker

GENERAL SETTING

The south section of the Rocky Mountain Trench, see Figure 9.21, extends from south of the McGregor River for 725 km to the International Border. Holland (1964) describes this feature as a somewhat sinuous valley lying between the Columbia Mountains on the west and the Rocky Mountains on the east. The valley varies from 3 km to 16 km in width and it is occupied by the northward flowing section of the Fraser River, Kinbasket Lake, the north flowing section of the Columbia and between Canal Flats and the International Border, by the south flowing Kootenay River. At Canal Flats the Rocky Mountain Trench is intersected by two smaller `u' shaped valleys, a west trending hanging valley containing Findlay Creek and a north east trending valley containing the Kootenay River (Haughton, 1978).

The western front of the Rocky Mountains forms the eastern wall of the Trench and the eastern front of the Columbia Mountains forms the western wall of the Trench. At the north end, near the McGregor River, the Trench mergers into the Fraser Basin at an elevation of 610 m (Holland 1964).

Figure 9.21 South section of the Rocky Mountain Trench Subregion

SURFICIAL GEOLOGY

The south section of the Trench was probably drained during Tertiary times according to Holland (1964), by a south flowing Columbia River and the Kootenay River. Holland believed the Trench developed as an erosional form during the Tertiary period by streams whose courses were antecedent to the building of the Rocky Mountains. Further, the erosion of the Trench was essentially completed by the end of the Pliocene. One major effect of subsequent glaciation was to derange the previously established drainage systems in the Trench.

During deglaciation, the present day river courses became established and since then the river have become incised to varying degrees into the deep drift deposits of the Trench valley floor. The south section of the Trench valley floor has been filled to varying depths with fluvial, glaciofluvial, glacial lacustrine and till deposits.

GROUND WATER RESOURCES

Within the heterogeneous valley fill deposits of the South Rocky Mountain Trench Section there exist productive aquifers of sand and gravel which have been developed for domestic, community and industrial water supplies. One of the most accessible sources of ground water in the southern section of the Trench is outwash gravel underlying major meltwater channels in the Trench floor. This gravel according to Clague (1973), is permeable, and underlain by silt and clay. The City of Cranbrook for example, constructed high capacity wells in the gravels of a large meltwater channel.

The distribution of wells within the south section of the Trench shows a higher density associated with such communities as Golden, Edgewater, Invermere, Athalmer, Windermere, Canal Flats, Wasa, Fort Steele, Cranbrook, Wardner, Jaffray and Baynes Lake.

Well records indicate the unconsolidated deposits in some areas of the Trench are deep. A well record for a site north of Athalmer reportedly reached a depth of over 180 m in unconsolidated materials, and a well depth of 143 m is recorded at Fort Steele, while at Elko, Wardner and Canal Flats, wells completed in unconsolidated deposits have reached depths of over 91 m.

There are over 1,700 known well records on file in the Ground Water Section for the South Rocky Mountain Trench Section. This well record information is supplied gratuitously to the Province by well drilling contractors and others. The following sections are based in part on these records, and the information presented below should be used with caution as the records may be incomplete and their accuracy and reliability have not been independently confirmed.

The majority of the available well records, namely 79% or 1,360, are for low capacity wells producing less than 1L/s. Approximately 90% or 1,540 of the recorded wells are completed in unconsolidated deposits and 78% or 1,205 of these have either no reported well yield or the reported yields are estimated as under 1 L/s. The remaining 22% or 335 wells completed in unconsolidated deposits, are reported to have higher potential yields. These remaining wells have been divided into two groups based on yield. Group 1 consists of 250 wells which range in potential yield from 1 L/s to less than 4 L/s. Group 2 consists of 85 wells with reported potential yields of over 4 L/s.

Bedrock wells account for 10% or 170 wells out of a total of over 1,700 wells located in the south section of the Trench. Approximately 88% or 150 of these bedrock wells have either no record of well yield or the yield is less than 1 L/s. Only 12% or 20 bedrock wells have reported potential yields greater than 1 L/s.

Details on some selected higher capacity wells completed in unconsolidated deposits in the South Rocky Mountain Trench Section are given below, commencing at the north end.

North end of the South Trench Section: Very little information is available on the ground water potential at the north end. Shallow wells have been completed near Dome Creek, and at Crescent Spur, three 150 mm wells ranging in depth from 20 m to 52 m have been completed in unconsolidated deposits approximately 60 to 150 m from the Fraser River. These wells were reported to have potential yields from 2.3 L/s to 3.8 L/s.

Northwest of McBride: Near the McBride Provincial Park, two wells 22 m and 14 m deep, were completed in water bearing gravels lying below clay. These wells were reported to have produced yields of 1.9 L/s and 1.5 L/s respectively.

Tete Jeune Cache: The potential yield estimates of six wells constructed for a subdivision at Tete Jeune Cache, south of the Fraser River, ranged from 1.5 to 7.5 L/s.

South of Valemount: A well drilled for a subdivision site approximately 1.6 km south of Valemount was rated at 2.7 L/s. The well was completed in sand and gravel at a depth of 49 m below a sequence of silts and fine sand, transmissivity of the aquifer was calculated at 1.38 x 10-4 m²/s. A second well drilled to 27 m at this location yield 3.3 L/s and the transmissivity value was calculated at 2.59 x 10-4 m²/s.

Golden: South of Kinbasket Lake, are several wells with reported potential yields of over 7 L/s. Ground water has been used extensively in Golden and in the communities to the south, where a thick complex sequence of unconsolidated materials have been deposited, including till, gravel, sand, silt and clay. A 150 mm observation well has been completed in unconsolidated material to a depth of 45 m at a site 5.6 km south east of Golden at Hobart. The estimated yield in this well was 1.46 L/s and the aquifer transmissivity was calculated at 3.2x10-4 m²/s (Hodge, 1990).

Also at Golden, at well sites near the Kicking Horse River, there are reported potential well yields from 13.6 L/s up to 151 L/s being produced from industrial wells completed in water bearing gravels at depths less than 30 m. The transmissivity in one aquifer at a site on the north side of the Kicking Horse River at Golden, was calculated to be 1.87 x 10-2 m²/s. South of Golden at Brisco there is a report of a well penetrating to a depth of 140 m in unconsolidated deposits.

Radium Hot Springs: A 150 mm diameter well at this location reached a depth of 112 m in unconsolidated deposits, however the well is reported to have only yielded an estimated 1.5 L/s. Also at Radium a 16.5 m deep well was reported to yield an estimated 11.4 L/s for a subdivision supply and the specific capacity of the well was calculated at 9.6 L/s/m of drawdown. The theoretical specific capacity for a larger production well at the site could be much higher.

Athalmer-Invermere Area: Many wells have penetrated fine gravel, clay, silt and fine sand in this area. This fine gravel fraction is also often present within the water bearing zones of sand and gravel. At Athalmer, potential yields of over 7 L/s were reported in a number of early well records from the 1950s. These wells were generally shallow, less than 15 m deep and water bearing sands and gravels were encountered below the overlying silts and clays.

Fairmount Hot Springs: Six well records in this area report potential yields between 1 L/s and 4 L/s, the wells are less than 30 m deep. One well record for a 19 m deep well developed in gravel below impermeable beds, reports a yield of 25 L/s.

Canal Flats: There are 10 well records with potential yields reported being between 1 L/s and 4 L/s, and two well records with estimated yields greater than 4 L/s at Canal Flats. With one exception, all these wells are reported as being less than 30 m deep.

Skookumchuck: A 200 mm diameter industrial well completed in sand and gravel at a depth of 40 m at Skookumchuck, yielded an estimated 22 L/s based on a 24 hour pumping test. Another well at Skookumchuck is reported to have a potential yield approaching 7 L/s. This well was completed in unconsolidated deposits at a depth of 18 m at a site close to the Kootenay River.

Wasa: A 18 m deep, 152 mm diameter well completed in 1960 at the Wasa Lake picnic area, was reported to have a potential yield in excess of 7 L/s, specific capacity was calculated at 11.3 L/s/m of drawdown. This sand and gravel aquifer was overlain by impermeable clay with some gravel. A second well constructed at the site was drilled to a similar depth and was pump tested for 8 hours. The preliminary results indicated that a large production well constructed at this site may have a theoretical specific capacity as high as 105 L/s/m of drawdown. Early records of three additional wells at Wasa between 18 m and 61 m deep in unconsolidated materials, report potential yields greater than 7 L/s.

Fort Steele: A 9 m deep community water supply well at Fort Steele, completed in 1955 in unconsolidated sands and gravels, was retested in 1978. The reported yield of this well based on the pump test was estimated at over 12.6 L/s. The specific capacity was calculated at 18 L/s/m of drawdown, however available drawdown in this well was only 1.4 m.

Cranbrook: Well yields in the Cranbrook area, are according to LeBreton (1979), commonly less than 20 L/min and generally low permeability values for aquifers in the bedrock and in the surficial deposits can be expected. However data for a shallow aquifer in the main valley running through the west side of the city show well yields up to 63 L/s are possible. Production wells for the city of Cranbrook have been completed in these deposits and are capable of producing 31.5 L/s to 63 L/s. From an analysis of the pumping test data, transmissivity values of 2.9 x 10-2 m²/s have been reported for shallow sand and gravel aquifers in the main valley. (Le Breton, 1979). Also a deeper aquifer below the aquifer in which the City of Cranbrook wells are completed is moderately productive and according to Le Breton, wells yielding 3.2 L/s to 6.3 L/s or higher are possible.

Bull River: Near the junction of the Bull River with the Kootenay River, high capacity wells have been developed for a provincial fish hatchery. These wells have been completed in a shallow coarse sand and gravel aquifer with potential yields reported as high as 126 L/s.

Wardner: There are some earlier 1950 well records reporting good domestic yields from a shallow, 6 m to 9 m deep sand and gravel aquifer at Wardner. Domestic supplies were also located in a deeper aquifer located approximately 30 m from surface.

Galloway: Some productive water bearing sands and gravels have been developed at varying depths down to 30 m for both industrial and domestic wells at Galloway.

Jaffray: Reports of potential well yields between 1 L/s and 4 L/s have been developed from a shallow sand and gravel aquifer 6 m to 9 m deep at Jaffray.

Elko: Northeast of Elko at Morrisey on the Elk River, an artesian well was reported in 1966 to be flowing at 26.5 L/s. The well was completed in a 40 m deep sand and gravel aquifer below impermeable confining beds. At Elko the potential yield from a community water supply well was reported to be 15.2 L/s. This well was screened in a gravel aquifer located between 72 m and 78 m below surface. The specific capacity was calculated at 27.3 L/s/m of drawdown. Early 1950s domestic and industrial well records for Elko indicate that productive aquifers were encountered in unconsolidated deposits at depths ranging from 29 m to 73 m.

Baynes Lake: Ground water at Baynes Lake occurs under water table conditions at shallow depth within sand and gravel outwash deposits overlying glacial till and lacustrine clays. The outwash deposits vary up to 15 m in thickness (Kohut, 1976). The heterogeneous nature of these deposits also makes the development of domestic supplies in any specific area, uncertain.

Grasmere: In the Grasmere area, clays and tills are commonly encountered during drilling and consequently wells are generally shallow and low yielding, less than 23 L/min. Gravels and sands found in the upper 30 m at some locations may have some potential for limited ground water development (Petrie, 1976). Gravels interbedded with clays and tills were encountered in one 30 m deep well near Grasmere and the reported potential yield at the time of well construction in 1960, was estimated at over 7 L/s.

GROUND WATER QUALITY

Records of selected ground water quality analyses reviewed for the South Rocky Mountain Trench Section show that the ground water is usually very hard, averaging approximately 285 mg/L, while the total dissolved solids (TDS) concentration averaged approximately 345 mg/L.

The dissolved mineralization of ground waters located within the south section of the Trench generally falls into one of two types:

In the Type 1 ground waters, the major constituents are calcium, magnesium, sodium, bicarbonate and sulphate, while in the Type 2 ground waters, the major constituents are calcium, magnesium, bicarbonate and sulphate. In Type 2 ground waters sodium is either absent or the concentration of sodium is low compared to the other major constituents.

Concentrations of manganese in ground water at sites located at Valemount and Golden are reported to be close to or to exceed the aesthetic objectives set in the Guidelines for Canadian Drinking Water Quality (1989).

At Radium Hot Springs, arsenic was reported in a 1974 analysis at concentration of 0.012 mg/L. The maximum acceptable concentration for arsenic is 0.05 mg/L.

Table 9.9 provides a comparison of major constituents found in ground waters, as well as hardness and total dissolved solids (TDS) concentration, at a number of site locations in the South Rocky Mountain Trench Section.

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