Course:EOSC311/2022/The Prince Edward Island Aquifer

Introduction

In Canada, one-third of the national population, including 80 percent of the rural population, gets their drinking water from groundwater. According to Environment Canada, Ontario has the most people who rely on groundwater resources, with 1.3 million. Furthermore, the entire population of Prince Edward Island (PEI.) is dependent on groundwater sources. According to Statistics Canada, PEI. has 24.7 people per square kilometre and approximately 308 wells, making this region heavily reliant on aquifer water. These aquifers will dry up faster than they can be recharged as a result of climate change. As a result, learning how to correctly use these vulnerable sources that support people's daily lives is critical. This project provides general concepts of groundwater/aquifers and focuses primarily on aquifers in Prince Edward Island due to the province's complete reliance on groundwater for potable water supply and residents' needs, which are met by a single bedrock aquifer underlying the Province.

Relationship with My Major

The Global Resource Systems programme allows students to investigate and comprehend the development and issues of natural and agricultural resources from a global perspective. A study of freshwater preservation and protection is essential for those with a resource specialization in food and environmental sustainability. The majority of the water on Earth is salt water, with only 3% being freshwater suitable for human consumption. And the majority of the freshwater that people can easily access is stored underground (aquifer). As a result, it is critical to comprehend this vital resource and learn how to use it wisely.The study focusing on the aquifer in Prince Edward Island is a valuable case study for the reader to understand how to fully utilize and protect freshwater from the aquifer.

Groundwater / Aquifer

Figure 1: Groundwater flow movement and residence time in different types of aquifer.

What is Aquifer?

In general, groundwater is the water that is infiltrated into the ground and stored in aquifers. According to Environment Canada, freshwater accounts for approximately 2.53 percent of total global water, with freshwater that is stored underground accounting for only 30.06 percent. As illustrated in Figure 1, groundwater extraction necessitates drilling a well at least as deep as the water table, which is the surface of groundwater. Furthermore, the groundwater reservoir must have high porosity and a large number of pore spaces, as well as a connection between the pore spaces so that water in other pore spaces can quickly replace the water pumped out.

An aquifer is the body of rock or unconsolidated sediment that is permeable enough to allow groundwater to flow through it. Unconsolidated materials such as gravel, sand, and even silt, as well as rocks such as sandstone, are considered as good aquifers. Other rocks that are well fractured can also be good aquifers. In addition to aquifer, an aquitard is a non-permeable body of water such as clay, till, or poorly fractured igneous or metamorphic rocks. There are two general types of aquifers: unconfined and confined. Aquifers that are unconfined are those that are visible at the ground surface. Confined aquifers have lower permeability materials between the aquifer and the surface, whereas confining layers are aquitards that cover the aquifer. In this case, the entire province of Prince Edward Island is underlain by a single bedrock aquifer known as the 'Redbed Aquifer'.

Figure 2: The water cycle with detailed processes.

Figure 3: Hydraulic conductivity of solid rocks and unconsolidated materials.

Process of Groundwater Stored in Aquifer

Groundwater does not remain static, but rather flows from higher elevations to lower elevations, where it empties into streams or the ocean. The area where water moved into and out of an aquifer is called a recharge area and a discharge area. The head difference between recharge and discharge areas is the driving force for groundwater flow. Water from rain, melting snows and streams of rivers recharges the aquifer every year. The process involved in this water movement is called the water cycle. Among all the processes in the water cycle shown in Figure 2, infiltration is the most important process that lead to the formation of aquifer. When rainwater fall and soak into the ground, it flows down through the sentiments and rocks with high permeability. These natural filters of aquifer can trap particles such as bacteria and purifying the groundwater. The groundwater is stopped by the upper layers of the unconsolidated materials with high porosity and low hydraulic conductivity such as clay (in Figure 3) and is stored into an aquifer.

The large capacity of a "highly productive aquifer" can be attributed to a few basic factors: aquifer size, storage capacity, permeability, recharge amount, and the relationship of recharge to groundwater discharge for the stream system.

Porosity and Permeability of PEI. Aquifer

Porosity measures the proportion of pore space within an unconsolidated sediment or a rock, while permeability measures how well those pores are shaped and interconnected which allows water to flow through them.

Groundwater flow velocity is determined by the hydraulic gradient and the aquifer's porosity / permeability. The flow of groundwater is via aquifer's pore spaces, and/or fractures in aquifer.

The relatively high proportion of porous sandstones in the geological section hosting PEI's groundwater resources is an important feature of the geological formation hosting PEI's groundwater resources in comparison to many other sedimentary environments. This large "storage capacity" is complemented by the formation's high permeability, which is caused by a combination of inter-granular porosity and the presence of water-bearing fractures. The total volume of available groundwater is determined by the aquifer's porosity (% void spaces). The aquifer on PEI. has a porosity of 15%. As a result, each cubic metre of aquifer contains approximately 150 litres of groundwater.

This Province also benefits from a relatively humid climate and thin, generally permeable soils that cover the aquifer, resulting in very generous aquifer recharge. These high recharge rates and good aquifer permeability support groundwater's large base-flow contributions to PEI's fresh water bodies as well as the productive capacity of wells constructed in the aquifer.

Overall, groundwater use is low in comparison to recharge, but local withdrawals have been sufficient to reduce baseflow contributions to streams to acceptable levels. On a larger, watershed scale, groundwater extraction rates are always lower than recharge rates, so there is no threat of groundwater depletion.

Groundwater Sources in PEI

Figure 4: Water table changes while using wells to retrieve groundwater

A thick, fractured formation of sandstone bedrock formed 220 to 300 million years ago lies beneath the PEI soil. While the sandstone bedrock beneath Prince Edward Island appears to be solid, it is actually filled with many tiny pore spaces and fractures. Porosity refers to the area occupied by these pore spaces. As mentioned in Figure 2, precipitation initiates the water cycle. PEI. typically receives about 1100 mm of precipitation per year. Water that falls on the ground will either evaporate and return to the atmosphere (440 mm), run directly over the land surface to streams (300 mm), or soak into the ground and become groundwater (360 mm). Groundwater slowly flows from higher elevations to lower elevations, eventually discharging into surface water bodies such as streams, ponds, and so on.Then the water cycle is completed when surface water evaporates and returns to the atmosphere.

Individual groundwater flow system boundaries on PEI are roughly equivalent to surface watershed boundaries. The precipitation that infiltrates through the unsaturated zone to the water table – a process known as "recharge" – is the source of groundwater. On Prince Edward Island, this "groundwater recharge" accounts for approximately 30-35% of annual precipitation (360 mm/yr). Groundwater that is discharged through springs and seeps to rivers or the shore is commonly referred to as "baseflow." This baseflow accounts for 55-65% of average annual stream flow. Almost all of the water we see in the PEI streams during the dry summer months is groundwater discharge. Groundwater flow directions and rates in PEI are primarily determined by fractures in the bedrock and the configuration of the water table.

Like many other regions, wells are used to access groundwater that is stored in the "saturated zone" or "aquifer". As shown in Figure 4, when a well is not being pumped, the water level in the well corresponds to the elevation of the water table. And when a well pumps, the water level in and surround the well drops, forming a "cone of depression." Water flows from the aquifer into the well as it is pumped. The size and shape of the cone of depression are determined by the pumping rate and the aquifer's characteristics. Moreover, if a well is near a stream, heavy pumping may pull water from the stream into the well. PEI.'s aquifer configuration is at least 800m thick, but permeability decreases with depth due to reduced fracture frequency and size. As a matter of fact, relative water yields to wells decrease with depth, and highly productive portions of the aquifer are generally limited to the upper 200 m of the formation.

Risks of Contaminations to the PEI Groundwater

The natural quality of groundwater in Prince Edward Island is good, but because of the chemical nature of water, it can be easily contaminated. Anything water-soluble that can be sprayed onto the ground or accidentally leaked will dissolve in rainwater and be absorbed into the ground. A small amount of contamination can have a significant impact on groundwater. One litre of leaking oil, for example, can cause pollution on a million litres of drinking water. Groundwater is generally safer than surface water, but some contaminants can be filtered out. And things can be worse if the contamination reach into aquifer. Petroleum leaks and spills, agricultural waste, fertilizers and pesticides, faulty waste water treatment systems, road salt, landfill sites with older designs, and bacterial contaminations from abandoned wells are the major sources of groundwater contamination in Prince Edward Island.

Industry

There are lots of chemicals being used and stored during the industrial operations, which is often the factor that causes the most contamination. This happened in many countries. Petroleum storage tank leaks and spills continue to cause serious damage to groundwater in Prince Edward Island. One well-known disaster occurred in 1977 in Kensington, when 31 wells were contaminated by a leaking underground storage tank that had corroded. Not only do underground storage tanks endanger groundwater quality, but so do above-ground tanks in private homes. According to a 1991 survey, the majority of outside storage tanks were not properly installed. The Environmental Emergency Response Team responded to 349 spills in 1994. The majority were from above-ground tanks used to store home heating fuel. Pipes can collapse and spill oil during the winter due to settling snow and ice.

Agriculture

There is always the possibility of elevated levels of pesticides and fertilizers being used in agriculture, which can mix into groundwater.

Pesticides

Pesticides are widely believed to have an impact on groundwater quality. However, not all pesticides behave similarly, and many products, particularly newer pesticide formulations, are unlikely to enter the water table. Large amounts of concentrated material have caused problems when they have leaked or spilled. Significant portions of groundwater in two Island communities, Kensington and Tignish, have been left unused as a result of such incidents.

Nitrates

Studies in Prince Edward Island and elsewhere have found a strong link between land use and nitrate levels in groundwater, with agricultural areas frequently having higher than average nitrate concentrations. A significant amount of nitrate is present at the end of the crop season and is later available to contaminate the aquifer in Prince Edward Island.

Manure

Farm manure can also contaminate groundwater. Bacterial and nitrate-laden water can rinse off fields and enter into groundwater, or it can leach from manure storage sites. In addition, hog farmers are now using storage lagoons for liquid manure. The most harmful effect are those built without an impermeable liner or directly into fractured bedrock.

Road Salt

Road salt can occasionally contaminate wells on Prince Edward Island. Each winter, approximately 23,000 tonnes of salt are spread across 500 kilometres of PEI roads. Another 1,500 tonnes has been spread on Charlottetown and Summerside streets. Because storage pile management has improved in recent years, cases of salt contamination of wells have been restricted to areas near high traffic roads and steep hills.

Waste Treatment

If specific tanks are improperly installed or faulty, wastewater treatment can be a problem, and leaking sewage pipes can allow nitrates, chemicals, bacteria, and viruses to soak into groundwater supplies.

Landfill

The capacity of nature to purify can be overwhelmed by large amounts of waste. Landfill sites, for example, contain large amounts of potentially hazardous contaminants. Rain can carry contaminants with it when it falls on the site and leaches into the soil. A few feet of soil can filter out a moderate amount of contaminant, such as bacteria, but larger or continuous amounts can contaminate significant portions of an aquifer. Some contaminants, such as petroleum products, are not as well filtered by soil particles.

Application of Groundwater in PEI

Figure 5: Groundwater usage in PEI.

How is Groundwater used in PEI?

As previously stated, groundwater is used by the entire population of Prince Edward Island in their homes, communities, and workplaces. As illustrated in Figure 5, the majority of groundwater is used in residential, industrial, heat transfer, and agricultural applications.

At Home

Groundwater is typically consumed by Island residents when drinking or bathing. It is also used to wash and cook food, as well as to circulate heat throughout the house. People do, however, flush more water down the toilet than they do for any other purpose in the house. Residents in PEI now get their water by turning a tap, which allows an average family to use 1140 to 1820 litres of water every day. Almost all wells on PEI can supply adequate water to run a household. When a well runs dry, it is usually due to the well not being deep enough to reach below the water table and tap the water in the aquifer. A pipe system distributes water from the household well to sinks, bathtubs, toilets, washing machines, and heating systems throughout the house. Most homes have these pipes hidden from view within the house's walls. After being used, household water flows down a drain and into another network of pipes that leads to the water treatment system.

In Island Communities

Despite the fact that approximately 40% of the island's population is served by private wells and nearly half of the population uses on-site wastewater treatment, many communities have a central water supply and/or a central wastewater water system. Because of groundwater seems to remain in high quality, it is rarely necessary to treat it for drinking purposes. On Prince Edward Island, the central water supply system pumps groundwater directly from "high capacity wells" and "well fields" to the distribution system. A high capacity well is one that regularly extracts a large amount of water from the aquifer. A well field is a collection of wells linked to the same distribution system. Furthermore, central water supply systems not only supply water to homes, but also to shopping malls, office buildings, hospitals, schools, and manufacturing plants. Water is pumped to fire hydrants and public swimming pools before being piped to central wastewater treatment systems.

Industrial Use

Farming, tourism, fisheries, forestry, and aquaculture account for the majority of PEI's economic productivity. Fortunately,  there is no mining or heavy industry, except for quarrying. Food processing is the second-most important industry. Water is used in all of these industries to varying degrees. The food processing industry on the island consumes a lot of water. Large food processing plants in Prince Edward Island typically use between 2 and 8 billion litres of groundwater daily to clean, mix, and cook their products. Withdrawals of this magnitude may approach the maximum safe limits in some cases. Groundwater withdrawals are restricted in these cases in order to maintain a healthy base flow in streams. Some Island industries, like municipalities and farmers, use high-capacity wells.

Conclusion

People in Prince Edward Island use the most water in Canada. Conservation has not been a high priority because water appears to be as abundant as air. Although the Prince Edward Island aquifer is unlikely to be completely depleted, there is still a risk of contamination of the source. Therefore, the Government of Prince Edward Island has enacted a number of regulations to ensure that groundwater remains of high quality. Several departments on PEI have promoted courses over the years to educate farmers and workers on proper techniques to keep the water clean. Local authorities have also put in place strict regulations to protect PEI's water supply. Before issuing construction permits, it reviews all applications for high capacity wells. After the well is drilled, it must be tested before it can be put into service. Overall, the groundwater in the Prince Edward Island aquifer is adequate for human consumption. Because of the acceleration of climate change and economic growth, more research is required; many of the references were published in previous years, and things may have changed since then.