Aquifers and Groundwater
Living as we do in the Earth’s biosphere, our view of the world is almost entirely horizontal. Who can witness a spectacular sunset with the last golden-red rays touching the mountain tops and not be thrilled at the horizontal nature and majesty of our environment although we can also see it is being polluted.
From time to time, we may look up appreciatively at the sky, a gossamer-thin life-enabling blanket of nitrogen, oxygen, and 1% other stuff that contributes to climate change. At night, we may gaze into the infinity of outer space and realize how small we really are.
We rarely look down because we can’t. Only a few of us, miners, construction workers and the like who work underground, are first-hand witnesses of the complex layers of earth, gravel, sand, minerals and rock, much of which is permeated by precious groundwater.
About the Science of Aquifers and Groundwater
Groundwater is the term we use to describe water, usually rainfall, that has been absorbed into the soil and then drawn downward by gravity. It collects, mainly in porous underground geological formations or units that we call aquifers.
This dark underground territory and it’s aquifers involve many secrets about the whereabouts and movement of groundwater on Earth, and are studied by the sciences of geology, geoscience, Earth science, hydrology and hydrogeology.
While hydrology is the study of water on Earth's surface, which includes its distribution and movement across the land, hydrogeology is the study of groundwater and it's occurrence, distribution and movement through the Earth's crust.
So when we ask questions about aquifers, many answers will come from the study of hydrogeology, a revealing portal that helps us to understand the complex variabilities in the geologic formations below our feet where precious groundwater resources may reside.
Fresh Water
All life on Earth requires fresh clean water but 97.5% of the Earth’s water is salt water. Only 2.5% of the water on Earth is fresh water and over half of that is frozen in glaciers and polar caps. The lakes and rivers of the world cradle but a fraction of one percent of the fresh water available. This means that the groundwater, moving and stored underground is, realistically, our primary source of fresh water. In BC 28.5% of the population depend on ground water
Although the fraction of fresh water on Earth seems impossibly small, the spontaneous regeneration of fresh water in our atmosphere is simply awesome. Fresh water production begins when water evaporates from oceans, lakes and river and through plant transpiration, and during that process, salts and contaminants are left behind. The resulting pure H2O molecules rise as water vapour, eventually condensing and forming clouds. After about 10 days aloft the water falls back into the ocean or land as rain or snow. The dramatic weather and storm events we often see are all part of the hydrologic cycle, more commonly known as the water cycle. This is the process which serves to continuously replenish us with clean fresh water.
Evaporation
One cannot leave the water cycle without a quick look at evaporation. 90 percent of the moisture in the atmosphere evaporates from oceans, lakes and rivers and about 10 percent from plant transpiration. A very small amount of water changes from solid snow or ice, directly into water vapour (skipping the liquid state entirely). This process is called sublimation and occurs during Chinook wind conditions, (warm air blowing over snow or ice).
For evaporation to occur energy is required to break the bonds that hold water molecules together. Thus the process of evaporation removes heat from the local environment explaining why you feel coolness when water evaporates from your skin.
The rate of evaporation on a lake is driven by atmospheric humidity, temperature, and wind speed. The three primary conditions that increase evaporation on a lake are:
Warm lake water temperatures with overlying cold air temperatures,
low relative humidity in the overlying air, and
high wind speed across the lake.
The Fall and Winter months can introduce such conditions so evaporation rates will be high unless ice covers the surface. Hotel Lake rarely freezes over so evaporation generally continues all Winter and, in ideal conditions, can reach up to 0.6 inches a day. That loss is generally offset by the considerable rate of precipitation into the lake and its catchment area during winters.
Moving Underground
As mentioned earlier, groundwater is the term we use to describe water, usually rainfall, that has been absorbed into the soil and is then drawn downward by gravity and is then collected in porous underground geological formations that we call aquifers. The replenishment of aquifers with ground water is a process called recharging.
As you might imagine any effort to explain the hydrogeology of aquifers beneath our feet is an almost impossible task. Impossible because we really know so very little about what’s down there and there is very little for us to see from the surface. So we have approached this subject with a bit of drama and hope you enjoy the journey.
Aquifers and Karst Landscapes
Trying to understand what an aquifer is and how water behaves underground requires an open mind; after all, this is a relatively new frontier! From the hundreds of diagrams, illustrations, animations and videos online it is easy to get the impression that aquifers are underground caverns or lakes or underground rivers. However these can only be found in areas called “karst landscapes” (two examples shown above are on Vancouver Island). Karst landscapes host soluble carbonate bedrock formations such as limestone, marble, dolomite and gypsum, which dissolve over centuries thus creating sink holes, sinking streams, caves, etc.
The process that creates karst formations begins when rain drops fall through the atmosphere and while doing so pick-up CO2. After rain lands it percolates through the soil and picks up more CO2 from the carbonate bedrock thus forming a weak solution of carbonic acid: H2O + CO2 = H2CO3. Underground, the infiltrating water naturally exploits any existing joints or fractures in the bedrock and the acid causes the carbonate bedrock to slowly dissolve, creating larger openings which, over many thousands of years, eventually leads to the development of underground drainage systems and caves.
Although still largely uncharted, about 16% of BC is considered to be world-class karst areas. These are located in the Rocky Mountains, on Vancouver Island, on Haida Gwaii, along the coastal mainland, in the interior mountain ranges, the Cariboo Mountains, and in Northwest B.C. These underground caves, caverns, sink holes and the like are of greater interest as tourist attractions than as a source of drinking water.
Nevertheless, we have included this brief look at karst landscapes because they are a significant component of the hydrogeology of BC. One of the best animated videos that we could find on this subject is provided below. Produced by the Minnesota Department of Agriculture, it depicts aquifers located in the south-east Minnesota Karst landscape and while that geology is obviously very different to the geology under Hotel Lake and north Pender Harbour, the animated depictions of ground water and its movement are enlightening, perhaps even entertaining.
How Groundwater Moves in the Karst Landscape (A Short Animation)
Setting karst landscapes aside we move on to the aquifers in BC that provide groundwater for our domestic and industrial use and more. Completely different from karst landscapes are the broad fluvial deposits of highly porous sand and gravel. etc., deposited by glaciers and BC’s rivers over thousands of years. The Fraser Valley is a major glacial and fluvial outwash of sand and gravel. Its aquifers are extensively used for municipal, domestic, and industrial water supplies. The valley is densely populated and thus accommodates many wells. The large number of wells (blue dots) have contribute to a data base that supports and identifies many overlapping aquifers that can be seen in the second map of aquifers in the Langley-Abbotsford area.
Groundwater in aquifers is almost always in motion; the rate at which groundwater moves within an aquifer is determined by the permeability of the rock or sediment such as gravel, sandstone, conglomerates, and fractured limestone and granite that the water is passing through. This mobility means that groundwater is, to some extent, being naturally filtered as it passes through cracks or small gaps in the aquifer sediment. The complex aquifer mapping of the Fraser Valley shown above is a result of thousands of years during which many layers of glacier and river sediment were deposited.
Aquifers can exist at various depths and they may be interconnected hydraulically or not. An aquifer lying under a permeable layer of soil near Earth’s surface is an “unconfined aquifer” meaning that water from above can flow down into it and this means that unconfined aquifers can be vulnerable to contamination.
A deeper aquifer that lies below an impermeable or confining layer (typically clay, silt or till, called an aquitard) may be called a “confined aquifer” because water cannot easily enter or escape the aquifer due to the impermeable nature of the layer above. Because of this confined aquifers tend to be less vulnerable to contamination than unconfined aquifers.
Water Table
In the two diagrams above you will note that the “water table" is illustrated. The term water table refers to the boundary between ground above the water table which is unsaturated with water and the ground that lies below it which is saturated with water and called an aquifer. Because of this, water table elevation data is a very important tool when measuring and evaluating aquifers. Water tables may not be entirely horizontal but may follow topographical undulations or geological fractures. In some cases a water table may intersect with down-sloping terrain causing a spring to appear. Groundwater can resurface naturally as springs or as the top of a water table in wetlands or by seepage into streams or lakes or be mechanically drawn-up in artificially drilled wells. Surface water in swamps or wetland areas can be considered to be roughly level with the water table and as such may actually be the top of an underlying aquifer. In a process called “recharging” heavy rain or snow can replenish an aquifer and this can cause water tables to rise.
About BC Aquifers and Groundwater
Largely ignored in the BC Water Act of 1909, groundwater in BC has been out of sight and out of mind. Today use-of-groundwater issues have attracted political action as can seen in the Water Sustainability Act 2016, where wording about groundwater and its management appear for the first time. Under the act, using water from your private well for “household purposes” is considered “domestic groundwater use”. Household purposes include drinking water, food preparation, cleaning, fire prevention, water for animals or poultry kept as pets, for household use, and water for small gardens.
In recent decades, concerns about the quality and supply of groundwater have grown. Today the need for government oversight to protect against contamination is acute. As well, the need to address interference between well users has led to increased interest in the study of aquifer connectivity. BC’s new priorities are: the identification and study of aquifers to guide future groundwater development, the identification of streams susceptible to reduced base flows as a result of heavy groundwater use, identifying what measures could be adopted to maintain a sustainable supply of groundwater and, in areas of surface water conflicts, what groundwater supply alternatives are available.
The BC Aquifer Classification System which was developed in 1994 serves as a foundation for aquifer identification, mapping, assessment, screening and prioritizing. Data from existing well-drilling-records are entered into this system (blue dots on the map below represent registered wells). This data can then be used to identify and map aquifers. In doing so the system provides a publicly-accessible inventory of aquifers and groundwater sources in the province. It must be emphasized that in most cases, a more detailed scientific assessment will generally be required in order to properly manage any particular aquifer.
Below is a fact sheet about AQUIFER #559 located between north Pender Harbour and Sakinaw Lake. This standardized fact sheet is reproduced from the BC Aquifer Classification System. This document was updated in 2012 using data from existing wells to determine the aquifer's boundary, productive water levels and flows. By clicking here you will be able to access the entire fact sheet on line with with active links to a companion documents which explain how to interpret the information presented on the fact sheet.
Aquifer #559
Taking a closer look at Aquifer #559, the solid red line (following coastlines and a high ridge watershed divide) is the aquifer boundary and it implies one simplistic bedrock aquifer under the north Pender Harbour to Sakinaw area.
Actual groundwater well-drilling-records were used as the primary source of data for defining this aquifer. Data, such as depth information of the types of material or rock being drilled as well as damp spots or water-flow-rates as well as other comments. Such data collected from the 57 registered and documented wells in this area as well as data from another 22 unregistered wells (from unreported sources) contributed to the creation of Aquifer #559 in the BC Aquifer Classification system.
In defining and delineating bedrock aquifer boundaries the degree of accuracy is dependent on the quality and amount of information available. If limited well drilling report information is available, only the immediate area of water-well-development are delineated as a bedrock aquifer. When more drilling information becomes available, the aquifer boundary may be adjusted.
In the case of Aquifer #559, its current boundary is extended to the ocean and Sakinaw Lake shoreline. Both shorelines are considered to be the general boundary between Aquifer #559 and the salt water/aquifer beneath the ocean or Sakinaw Lake's deep body of fresh water with underlying salt water. Inland, the aquifer boundary is depicted as following a high ridged watershed divide. This does not necessarily mean there is only one aquifer beneath us but rather that insufficient information exists to differentiate and identify two or more aquifers or their depth or if hydraulic connectivity exists between them.
In addition to the fact sheet another document is available, the Aquifer Mapping Report, sometimes called a Classification Worksheet. This document provide a detailed explanation of how drilling data and other information from various sources contribute to a particular aquifer boundaries and classification. Click Here for this report/worksheet.
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Just outside the mouth of Pender Harbour lies Pearson Island. a quick looks reveals that 8 wells have been drilled and that drilling data from those wells have contributed to the identification of Aquifer #953. The wells were drilled in 1988 and 1989 down to various depths, the deepest being 447 ft below ground. Only two of these wells produced any fresh water and that was around the 230’ - 375” level. This is a tiny but good example of how the system uses drilling information.
Near our Aquifer #559 are 6 other aquifers:
#953 (Pearson Island)
#954 (Sakinaw, near Steep Spring),
#561(Kleindale, east of Pender H.),
#565 (Francis Peninsular),
#956 ( Lily Lake) and
#955 (Gunboat Bay - south shore)
In every one of the above aquifers the underlying geological formation is described as follows:
“fractured crystalline (igneous intrusive or meta-morphic, meta-sedimentary,
meta-volcanic, vol-canic) rock aquifer (subtype = 6b)”.
The complete list of aquifer subtype code descriptions, can be found on the BC Government ground water website. Click Here to see: Subtype 6b is the granite bedrock that is below us and which sometimes rises sharply above us as hills or small mountains. These are the granite formations into which we drill wells looking for aquifers and ground water. The graphic below shows how bedrock is permeated by fractures. Closer to surface the bedrock is highly fractured or "weathered" which makes it more permeable for water to enter.
During the Last Glacial Period (LGP), which occurred around 115,000 – 11,700 years ago, Canada and parts of the northern United States, were blanketed by a huge ice sheet. During the later part of this period, about 25,000 years ago, glaciers emerged from British Columbia’s Coast Mountains and from Vancouver Island and flowed down, and onto coastal lowlands and advanced south into the Straights of Georgia and Juan de Fuca reaching Puget Sound around 14,000 years ago. The thickness of ice in these areas, which include today’s City of Vancouver, reached 2 kilometres.
The enormous weight of this ice caused the earths crust underneath to depress (isostatic depression) as much as 300 metres. Additionally, so much water on the planet was trapped as ice that ocean levels dropped about 122 metres lower than today.
The retreat of ice occurred “rapidly” and deglaciation to present-day ice cover was complete by about 10,000 years ago. As the world’s glacial-ice released water, ocean levels rose and inundated coastal lowlands including the depressed land of the Fraser Valley. Over time, with the weight of the ice removed, the terrain in the Fraser Valley and elsewhere slowly rose, (post-glacial rebound) and continues to do so today.
As the glaciers retreated they left behind considerable rock, sand and gravel residue called till. Ablation till was carried near the surface of the glacier and basal till was carried at the base of the glacier and subject to enormous pressures. In places where this glacial till was left behind it formed a layer of overburden on top of the granite bedrock. Basal till is very dense, strong and non-porous so it resists water flow.
Local well drilling reports often refer to the material in first few metres of drilling as “overburden”….this can be a thin veneer of geological sediments and modern organic material. In some locations glacial till will be present immediately over top of the bedrock. In 32 of the 79 well records, bedrock was encountered within one meter of the surface. In other locations the overburden was much thicker.
We can see this glacial till exposed today in many places around Hotel Lake and North Pender.
Salt Water Intrusion
About 1/3 of the boundary of Aquifer #559 is ocean shoreline along which the aquifer is in direct contact with saltwater in the ocean and any underlying saltwater aquifer unit. This contact is called the freshwater/saltwater interface which might be a relatively sharp transition or a more diffused-mixing process. Fresh water being lighter than salt water tends to remain above salt water. This creates an overlaying of fresh water over salt water at the aquifer transition referred to as a wedge.
Normally fresh groundwater follows topography and flows through an aquifer towards the ocean. However such flows can be influenced otherwise by geological faults or by storm surge conditions or from excessive well pumping of the freshwater aquifer, etc.
If over-pumping at wells located close to the coast exceed the freshwater aquifers capability to refresh, then salt water will intrude. Once this happens the intrusion of salt water may affect many wells in the aquifer causing considerable inconvenience or even the closing of businesses.
Salt water intrusion into a fresh water aquifer is a concern. A primary objective is to not drill too close to an ocean shoreline and, in north Pender Harbour with its own SCRD water system, there appears to be little likelihood that this will be necessary. Although there are many unregistered (unknown) wells on Aquifer 559, it is unlikely that many exist close to the sea.
In the future, any risk assessment methodology for source-water protection in our coast-bedrock aquifer will require a more complete study and involve additional data that can only be accessed if all wells are registered.
A Summation
The following summary about Aquifer #559 in the area involving Sakinaw Lake / Mixal Lake / Garden Bay Lake / Hotel Lake is derived from the AQUIFER CLASSIFICATION WORK SHEET which can be viewed in its entirety in our library.
The aquifer is 14.5 square kilometres; its boundaries were set in 2002 and later expanded in 2012 following a review of well elevations. The bedrock sub-type is 6b which is granite and well records indicate the granite is moderately fractured. The fractured granite is described in registered and unlocated well records as light, white, dark blue, and some green. The granite bedrock aquifer is considered to be “unconfined” meaning susceptible to pollution.
The granite is overlain by a thin veneer of fluvial, glaciomarine and glaciofluvial sediments (overburden). This overburden varies in thickness from 0 (bedrock at surface) to a maximum thickness of 12.19 m. Thirty-two of the 79 well records (located and unlocated) report bedrock within one meter of ground surface.
Vulnerability is described as “High". Depth to water is moderately shallow. The permeability of the aquifer material is low (fractured bedrock). The aquifer is vulnerable to salt water intrusion although most located wells are situated away from the coast.
Productivity is described as “Moderate”. Yields were reported for 73 of the 79 wells with values ranging between 0.02 and 6.31 L/s. The median well yield has been determined as 0.63 L/s while the geometric mean well yield has been determined as 0.48 L/s. It is noted that the reported well yield data are based on short-term air tests carried out by the well driller.
Direction of Groundwater Flow: No data is available to determine direction of groundwater flow. It is anticipated that flow is generally towards Sakinaw Lake and the coast. Localized flow patterns within shallow fractures may be towards Mixal Lake, Garden Bay Lake, and Hotel Lake.
Recharge: The aquifer and its water wells are likely recharged from direct infiltration of precipitation at ground surface. Surface water infiltration may be considerably high due to the absence of surface overburden overlying the fractured bedrock. Some wells may also be hydraulically connected to the lakes.
Domestic Well Density is described as “Moderate”. With approximately 5.4 domestic wells per km2, domestic well density was calculated from 62 reported domestic wells (located and unlocated) as well as 16 unknown wells with a yield of less than 1 L/s. An unknown well with a yield of less than 1 L/s is assumed to represent a domestic well, while a commercial, water supply, or irrigation well is anticipated to require a higher yield.
Reliance on Source: (Surface) Water licenses exist at Garden Lake and Hotel Lake. From a site visit on October 19, 2002, it was noted that some residents use a mix of surface water from Mixal Lake and groundwater to meet their domestic water needs.
Quality Concerns (type, source, level of concern): Isolated – The identification of high arsenic levels in wells in Powell River prompted the Coast Garibaldi Health Unit to initiate a large-scale well water survey. A total of 199 wells in Powell River and 259 wells in the Sunshine Coast area were sampled and analyzed for dissolved arsenic (Carmichael, 1995). The Mixal Lake area was included within the study area and it is apparent that two wells (DL 4282) reported arsenic levels between 0.025 and 0.050mg/L.
It is hard to sharpen the perspective on aquifer #559 any further because the water permeability and movement in the aquifer's hard fractured-granite can be difficult to assess. Limitations and vulnerabilities due to draw down as well as crystallizing concerns about pollution and hydraulic interconnections will require more and more data and much of that has to come primarily from the drilling records of existing wells.
The B.C. Water Sustainability Act of 2016 requires non-domestic wells to be registered. The offer of free registration ends on March1, 2022. The very latest blog by the government on this issue is below and contains all the info on how to register. Click here for Gov.bc blog on web registration
World-wide, a great deal of the water we use for drinking water, domestic, agricultural and industrial needs is groundwater which is accessed from wells that we drill into aquifers. But an aquifer's water is not unlimited and excessive demand will lead to “aquifer depletion”. In addition, mismanagement of agricultural pesticides and herbicides from overlaying farm land as well as irresponsible dumping of toxic materials, malfunctioning septic tanks and landfills, can all introduce toxic materials into the soil and bedrock and the aquifers below. Toxic materials in an aquifer can be hard to remove and can introduce serious health concerns and consequences concerning the use of that aquifer for domestic use.
It's as simple and as complicated as that.
DIY, Take a look! Try This For Yourself on any Aquifer in BC
If you click on this link: https://apps.nrs.gov.bc.ca/gwells/aquifers
it will take you to the general map of provincial ground wells and aquifers as shown above.
Click on the “wells” box (this will add a “wells” (blue dots) visual layer to the map). Then navigate-zoom in on an area of interest, such as Sumas for instance.
The blue dots represent wells and the orange areas are aquifers. You will find that each aquifer and registered well is an active resource. By hovering over the well or aquifer and by clicking on it a box materializes with an underlined “well or aquifer number” and if you click on the underlined number, you will access the full aquifer fact sheet or the well drilling details. At the bottom you will also find other links which open up other fact sheets or in the case of wells, the original drilling notes supplied by the company that did the drilling. This is the raw data that feeds the BC Aquifer Classification system.