Humber River State of the Watershed Report -

Geology and Groundwater Resources

2008

Humber River State of the Watershed Report – Geology and Groundwater Resources

EXECUTIVE SUMMARY

This report summarizes the quantity and quality of the groundwater resources within the Humber River watershed. Links between the groundwater system and other aspects of the natural heritage system are noted. At the end of this document, the groundwater related management objectives from the Humber Watershed Strategy, Legacy: A Strategy For A Healthy Humber (MTRCA, 1997), are outlined and updated watershed report card ratings are assigned. Lastly, potential future management actions to address key groundwater management issues and to help achieve the groundwater related objectives are presented.

Geology

• In most of the Humber River watershed, the bedrock consists of Georgian Bay Formation Shale. Limestone bedrock is also present, but only in the extreme upper reaches of the Main Humber subwatershed. • Prior to 135,000 years ago, extensive erosion took place over the span of a million years or more, resulting in the formation of a deeply cut bedrock valley system (Laurentian Valley). This valley system extends from Georgian Bay to Lake Ontario near Toronto. Water well records indicate that the bedrock valley was filled with permeable sediments, and accordingly, forms an interconnected aquifer system. • The Quaternary sediments deposited in the watershed 135,000 to 10,000 years before present are of significant importance in the groundwater flow regime across the watershed. The main stratigraphic units, in order from oldest to youngest, are: o Scarborough Formation; o Sunnybrook Drift; o Thorncliffe Formation; o Newmarket Till; o Regional Unconformities (or Tunnel Channels); o Oak Ridges Moraine and Mackinaw Interstadial Deposits; o Halton Till; and o Surficial Lacustrine Deposits.

Hydrogeology

• Hydrostratigraphy differs from the geologic stratigraphy in the sense that hydrostratigraphic layers represent a classification of the geologic units into aquifers or aquitards, and also combines different geologic units with similar hydraulic properties into single hydrostratigraphic units. • The hydrostratigraphic units considered to influence groundwater flow within the watershed are as follows: o Recent Deposits (Aquifer) o Halton Aquitard o Oak Ridges Aquifer Complex (ORAC) including ORAC Silts o Newmarket Aquitard o Thorncliffe Aquifer Complex (TAC), including Tunnel Channel Aquifer o Sunnybrook Aquitard o Scarborough Aquifer Complex (SAC) o Weathered Bedrock (Aquifer).

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Humber River State of the Watershed Report – Geology and Groundwater Resources

• Characteristics of the hydrostratigraphic units that influence the flow of groundwater in the watershed include: o Configuration of the bedrock valleys and their inter-connectivity; o Thickness and lateral extent of the Newmarket Aquitard and the Sunnybrook Aquitard; o The location of tunnel channels in the watershed area; and, o Thickness, lateral extension and nature of the sediments in the aquifer complexes. • Municipal wells located in the Humber Watershed portions of York Region and Peel Region tap into the ORAC, TAC and SAC aquifer systems for potable drinking water supplies.

Water Budget

• The Oak Ridges Moraine Conservation Plan, 2002, requires that watershed-based water budgets be prepared for all streams originating on the Oak Ridges Moraine (ORM). • The Humber River watershed receives precipitation, including rainfall, dew, snowfall and condenstation, ranging from an average of 798 millimetres per year in the South Slope/Peel Plain zone to an average of 933 millimetres per year in the Oak Ridges Moraine/Horseshoe Moraine zone. • Evapotranspiration (evaporation + plant transpiration) is not directly measurable but can be estimated. The mean annual actual evapotranspiration for the region has been estimated to be between 530 to 560 millimetres per year, reflecting seasonal periods of soil moisture limitations. • Any precipitation that doesn’t evaporate or get transpired by plants will either infiltrate or form run- off. To estimate rates and spatial distribution of infiltration (or recharge) and run-off over the watershed, water budget models have been developed for this watershed. • The major recharge areas within the watershed occur in the northern portion, on the hummocky terrain of the Oak Ridges Moraine, where infiltration to surficial sand and gravel deposits exceeds 200 mm per year. • The portions of the Humber watershed containing urban settlements have the highest run-off rates due to the influence of impervious surfaces (roads, parking areas, rooftops, etc.). • Groundwater flow direction within all aquifers in the watershed is generally from the ORM in the north to Lake Ontario in the south. Significant flow occurs in all aquifers eastward off of the Niagara Escarpment. The headwaters area of the watershed generally functions as a groundwater divide for all three aquifer systems in the Humber Watershed. However, this divide is less pronounced in the vicinity of Nobleton, perhaps due to the influence of tunnel channels within the subsurface that may be allowing some inter-basin flow of groundwater from the Lake Simcoe watershed into the Humber watershed. • Inter-basin flow is believed to occur from the Credit River watershed into the Humber River watershed and from the Humber River watershed (East Humber subwatershed) to the Rouge and Don River watersheds. • The major zone of groundwater discharge to streams within the Humber River watershed occurs along the southern flank of the Oak Ridges Moraine. Another zone occurs south of the Lake Iroquois shoreline where the deeper aquifer complexes discharge directly to the river or as seeps along the riverbanks. • Uncertainty remains as to whether observed baseflows along highly urbanized reaches in Vaughan and Toronto are a result of groundwater discharge or a combination of groundwater discharge, storm sewer discharges and leakage from water infrastructure. • Groundwater takings occur from the major aquifer systems within the watershed for potable water supply, agricultural irrigation, industrial processing, commercial and recreational purposes (e.g., golf course turf irrigation).

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Humber River State of the Watershed Report – Geology and Groundwater Resources

• Twelve (12) municipal water supply wells operate within the Humber River watershed to provide drinking water to approximately 21,000 individuals. • Annual groundwater withdrawals from the Humber River watershed total approximately 7,340,000 m3/yr. Withdrawals for municipal drinking water supplies accounts for about 47% of the total while the remainder is split amongst other users (i.e., agricultural, domestic, recreational and livestock). • Based on preliminary estimates, total annual groundwater withdrawals represent approximately 6% of total annual recharge over the watershed. This is considered low stress, but given that the withdrawals are concentrated, local rates may be higher. Therefore, further study is warranted to confirm that none of the subwatersheds are under stress.

Groundwater Levels (Quantity)

• Measured groundwater level fluctuations in PGMN wells are less than 1.5 m. These fluctuations are not considered significant and suggest that aquifer water levels are stable. • A watershed report card rating of “good” was assigned for the extent to which the watershed strategy objective “Protect groundwater sources” is being achieved. The rating reflects the stable groundwater condition within the watershed as indicated by available PGMN well monitoring data and results of a preliminary analysis of groundwater withdrawals as a percentage of total annual recharge. This is further supported by the fact that no significant negative trends in mean monthly baseflow rates have been observed at Humber River stream gauges over the period of record. • Groundwater monitoring of the three major aquifer systems within the watershed at five different locations is recommended. This would mean a monitoring well network comprising fifteen different locales. This will require the installation of an additional five wells.

Groundwater Chemistry (Quality)

• The concept of aquifer vulnerability assumes that the physical characteristics of the subsurface formations provide some degree of protection to aquifers from the migration of potential contaminants. In general, areas of relatively higher aquifer vulnerability occur along the Oak Ridges Moraine and south of the Lake Iroquois Shoreline. The areas associated with the Lake Iroquois Shoreline contain more permeable near surface sediments and a shallow water table. Areas of lower vulnerability correspond to the South Slope till plain where thick till and glaciolacustrine deposits require longer travel times. • Groundwater quality sampling is undertaken quarterly at Humber River watershed monitoring wells. For the sampling events that have been completed and analysed to date, all parameter concentrations have been reported below the more stringent applicable criteria (Ontario Drinking Water Standards or Provincial Water Quality Guidelines). High concentrations of iron and manganese reported in samples from the Bolton and Nobleton monitoring wells are likely due to natural reasons associated with the mineral composition of the soil. These limited monitoring results suggest that there are generally no serious concerns regarding groundwater quality within the Humber River watershed. • A watershed report card rating of “good” was assigned for the extent to which the watershed strategy objective “Prevent groundwater contamination” is being achieved. The rating reflects the fact that groundwater chemistry parameter concentrations in samples taken from PGMN wells meet provincial standards or objectives.

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Humber River State of the Watershed Report – Geology and Groundwater Resources

TABLE OF CONTENTS

EXECUTIVE SUMMARY...... I 1.0 INTRODUCTION...... 1 1.1 Organization of the Report ...... 3 1.2 Understanding Groundwater...... 3 1.3 Groundwater Quantity ...... 4 1.4 Groundwater Quality...... 4 1.5 Groundwater in the Rural and Urban Landscape...... 5 1.6 Groundwater Monitoring...... 5 1.7 Groundwater Modeling...... 6 2.0 PHYSICAL SETTING ...... 7 2.1 Physiography...... 7 2.2 Climate ...... 9 3.0 GEOLOGIC SETTING...... 13 3.1 Methodology...... 13 3.2 Surficial Geology...... 13 3.3 Stratigraphic Framework ...... 13 3.4 Bedrock...... 16 3.5 Overburden Sediments ...... 18 3.5.1 Scarborough Formation ...... 19 3.5.2 Sunnybrook Drift...... 21 3.5.3 Thorncliffe Formation...... 21 3.5.4 Newmarket Till ...... 24 3.5.5 Tunnel Channels...... 24 3.5.6 Oak Ridges Moraine and Mackinaw Interstadial Deposits ...... 27 3.5.7 Halton Till ...... 30 3.5.8 Surficial Lacustrine Deposits ...... 30 4.0 HYDROGEOLOGY...... 32 4.1 Hydrostratigraphy ...... 32 4.2 Water Budget ...... 38 4.2.1 Precipitation ...... 40 4.2.2 Evapotranspiration...... 40 4.2.3 Run-off...... 40 4.2.4 Recharge...... 41 4.2.5 Storage...... 43 4.2.6 Groundwater Flow ...... 43 4.2.7 Groundwater Discharge ...... 50 4.2.8 Groundwater Use...... 52 4.2.9 Other water Takings...... 55 4.2.10 Overall Water Budget...... 55

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Humber River State of the Watershed Report – Geology and Groundwater Resources

4.2.11 Trends in Groundwater Levels ...... 58 4.2.12 Groundwater Chemistry...... 60 5.0 WATERSHED REPORT CARD RATINGS...... 65 5.1 Groundwater Quantity ...... 65 5.2 Groundwater Quality...... 65 6.0 GROUNDWATER MANAGEMENT CONSIDERATIONS ...... 67 6.1 Groundwater Recharge ...... 67 6.2 Groundwater Levels...... 67 6.3 Groundwater Takings ...... 68 6.4 Groundwater Quality...... 69 6.5 Policies And Procedures ...... 69 7.0 GLOSSARY...... 71 8.0 LIST OF ACRONYMS...... 73 9.0 REFERENCES ...... 74

LIST OF FIGURES

Figure 1-1: Humber River Watershed ...... 2 Figure 2-1: Physiographic Regions...... 8 Figure 2-2 : Climate Stations in the Humber Watershed...... 11 Figure 2-3: Long-term Precipitation (Toronto – Queen’s Park)...... 12 Figure 3-1: Surficial Geology...... 14 Figure 3-2: Hummocky Topography Areas (Leney and Kenny, 2003) ...... 15 Figure 3-3: Bedrock Surface Topography (Kassenaar and Wexler, 2006)...... 17 Figure 3-4: Quaternary Deposits and Paleozoic Bedrock Found Within the Study Area...... 18 Figure 3-5: Thickness of Scarborough Aquifer...... 20 Figure 4-1: Geologic Model Cross Section Locations...... 34 Figure 4-2: Main Humber River Profile...... 35 Figure 4-3: East Humber River Profile...... 36 Figure 4-4: West Humber River Profile...... 37 Figure 4-5: Hydrologic Cycle ...... 38 Figure 4-6: Estimated Groundwater Recharge Rates; mm/year (Earthfx, 2008) ...... 42 Figure 4-7: Water Table Elevation (in metres above sea level)...... 44 Figure 4-8: Depth to Water Table (in metres) ...... 45 Figure 4-9: Modeled Oak Ridges Aquifer Water Levels (in metres above sea level)...... 47 Figure 4-10: Modeled Thorncliffe Aquifer Water Levels (in metres above sea level)...... 48 Figure 4-11: Modeled Scarborough Aquifer Complex Water Levels (in metres above sea level) .... 49 Figure 4-12: Modeled Groundwater Discharge to Streams ...... 51 Figure 4-13: Contribution to Total Baseflow by Humber River Secondary Subwatersheds ...... 52 Figure 4-14: Locations of Municipal and PGMN Wells...... 54 Figure 4-15: Humber River Watershed Water Budget…….……………………………………….…….56

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Humber River State of the Watershed Report – Geology and Groundwater Resources

LIST OF TABLES

Table 4-1: Municipal Water Supply Wells, Humber River Watershed...... 53 Table 4-2: Total Annual Groundwater Withdrawals, Humber Watershed (TRCA, 2006a)...... 57 Table 4-3: Water Level Trends...... 59 Table 4-4: Water Quality Sampling Events, PGMN Wells…………………………………………….61 Table 4-5: Groundwater Quality Comparisons, PGMN Wells………………………………………..62 Table 5-1 Groundwater Quantity Indicators…………………………………………………………..65 Table 5-2: Groundwater Quality Indicators…………………………………………………………….66

LIST OF APPENDICES

Appendix A Monitoring Well Hydrographs………………………………………………………………79

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Humber River State of the Watershed Report – Geology and Groundwater Resources

1.0 INTRODUCTION

In 1997, the Humber Watershed Task Force released the Humber River Watershed Strategy, Legacy: A Strategy For A Healthy Humber (MTRCA, 1997), which provided thirty objectives for a healthy, sustainable watershed, and a set of actions necessary to achieve them. It also provided an overview of the state of the Humber River watershed at that time. Since the release of the watershed strategy, a significant amount of new information has become available through monitoring, special studies and the experiences of watershed partners.

In 2004, the Toronto and Region Conservation Authority (TRCA), in partnership with watershed municipalities and the Humber Watershed Alliance initiated a study to develop an integrated watershed management plan for the Humber River. This study was initiated to fulfill the watershed planning requirements of the Oak Ridges Moraine Conservation Plan , 2002, and to update the strategies and recommendations of Legacy, in light of new information, a stronger scientific foundation and better understanding of the effects of human actions on natural ecosystems. The watershed plan is intended to inform and guide municipalities, provincial and federal governments, TRCA, non-governmental organizations and private landowners regarding management actions needed to maintain and improve watershed health.

This State of the Watershed Report provides updated information on current conditions, emerging trends and identifies key watershed management issues and opportunities in the Humber pertaining to geology and groundwater resources. Links between the groundwater system and other aspects of the natural heritage system which include surface water, fish and plants are noted. At the end of this document, the groundwater related management objectives from Legacy are outlined and updated watershed report card ratings are assigned based on indicators of watershed health and associated targets. Ratings for a full suite of indicators of watershed health are summarized in, Listen to Your River: A Report Card on the Health of the Humber River Watershed (TRCA, 2007). Lastly, potential future management actions to address key groundwater management issues and to help achieve the groundwater related objectives of the watershed management strategy are presented.

The Humber River watershed drains approximately 903 km 2 of urban, suburban and rural lands within the Greater Toronto Area (GTA) as shown on Figure 1-1. Groundwater is an important resource of this watershed and knowledge of the hydrogeologic setting is required to understand the flow and function of groundwater within the watershed ecosystem. A number of hydrogeological studies have been completed in the watershed. These watershed studies were part of an overall strategy to understand the groundwater regime in the GTA in general and Oak Ridges Moraine in particular. The Geological Survey of Canada (GSC), Ontario Geological Survey (OGS) and Conservation Authorities Moraine Coalition (CAMC) have made considerable contributions to these studies. Since 2001, through a partnership between the Regions of York, Peel, and Durham, City of Toronto and the Conservation Authorities Moraine Coalition (YPDT-CAMC) hydrogeological investigations have been conducted, existing information has been consolidated and many data gaps have been filled. Many of the geological and hydrogeological concepts presented herein are based on findings contained in the YPDT-CAMC report (Kassenaar and Wexler, 2006).

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Figure 1-1: Humber River Watershed

Humber River State of the Watershed Report – Geology and Groundwater Resources

1.1 ORGANIZATION OF THE REPORT

Section 1 of the report provides general information about groundwater in the context of watershed management. It describes groundwater occurrence and methods of measuring groundwater quality and quantity, how groundwater is influenced by human activities and urbanization and issues that might arise from unsustainable use of groundwater.

Section 2 of the report describes the physical setting of the watershed including physiography and climate. Sections 3 and 4 describe the geology and hydrostratigraphy. The hydrostratigraphy section also discusses recharge and discharge areas, infiltration capacity of the different hydrostratigraphic layers and describes the concept of a water budget. Water level information is provided for the different hydrostratigraphic layers and available water level data from monitoring wells in the Humber Watershed is presented. Groundwater quality conditions currently prevailing within the watershed are also briefly described.

Section 4 further summarizes and identifies key groundwater management issues with linkages between other components and indicators. Section 5 discusses groundwater management issues and potential management recommendations to address these issues that will be considered for inclusion in the updated watershed management plan.

1.2 UNDERSTANDING GROUNDWATER

Groundwater is water that occurs below the earth’s surface in spaces between soil particles as well as small voids, fractures, fissures and joints in bedrock. Groundwater originates as precipitation as part of the hydrologic water cycle. Infiltration is the key process that determines groundwater quantity and distribution. For water to infiltrate into soil, the surface area must be porous and permeable. Climate has a significant influence on infiltration because it governs precipitation and evapotranspiration, which control the volume of water that is available for infiltration and run-off. Aquifers store and transmit the infiltrated water. Groundwater flow within an aquifer system can take hundreds or thousands of years before discharging as springs or seepage to streams and rivers.

Contribution of groundwater flow to surface water bodies cannot be underestimated. In some cases, the river or stream flow depends solely on groundwater discharge. Groundwater discharge plays an important role in the proper functioning of a watershed as it is a source of clean, cold water for streams and lakes. Groundwater discharge also moderates stream temperatures both in winter and summer which provides critical habitat for temperature sensitive fish and other aquatic organisms.

Water is an essential part for human existence and nearly all human needs depend on it in one way or another. Nearly 98% of fresh water resources exist as groundwater. Groundwater usage includes potable drinking supplies in addition to agricultural, recreational and industrial demands. During drought conditions, where surface water flows are minimal, groundwater resources become important. Groundwater can also be protection from bacterial contamination through natural filtration processes. In addition many plants and aquatic organisms depend on groundwater or groundwater discharge for survival.

3 Humber River State of the Watershed Report – Geology and Groundwater Resources

1.3 GROUNDWATER QUANTITY

Geology significantly affects the soil’s capacity to infiltrate water. The type and structure of the subsurface materials control how much water can be stored, how deep it penetrates and how fast it can migrate. The slope of ground surfaces strongly influences infiltration rates. Areas with steep slopes are not conducive for higher infiltration rates. Conversely, areas with gentle slopes and local depressions provide maximum opportunities for infiltration.

Vegetative cover and local depressions also affect infiltration. Vegetation influences infiltration because plants intercept precipitation and surface run-off and reduce the surface sheet flow velocity, thus allowing water more time to infiltrate. The amount of water retention varies with vegetation type. Root structures increase the permeability of the surface soils by creating secondary porosity. This porosity also provides short-term groundwater storage.

Surface water that infiltrates into the ground moves vertically downward to the water table (the zone where the pore spaces are fully saturated). It flows by gravity following the path of least resistance, similar to surface flow. A sufficiently permeable zone in soil or rock is referred to as an “aquifer". Conversely, a zone of low permeability materials is referred to as an “aquitard”. Groundwater moves very slowly in aquitards. This slow movement retards the vertical migration of groundwater and potential contaminants to underlying aquifers. Depending on the local geology, two or more aquifer zones may occur separated by an aquitard. Groundwater may take hundreds or thousands of years to migrate through the subsurface formations to the deep aquifers that eventually discharge to a surface water body. Shallow groundwater travels along shorter flow paths through shallow soils.

Groundwater in saturated sediments beneath and beside stream or river beds discharges to surface water in areas known as hyporheic zones. These critical zones determine the health of river systems in relation to water quantity, quality and habitat environment. Small streams and wetlands, not directly linked by surface water, also play important roles in maintaining the health of river systems as they function as subsurface groundwater connections. Acting as important storage areas, they absorb water during periods of excess moisture and release it during drought, providing both recharge and discharge functions.

1.4 GROUNDWATER QUALITY

As mentioned in Section 1.2 groundwater quality is often better than surface water quality because of groundwater’s slower movement and the natural filtration and reaction processes that occur as it moves through the subsurface. However, remediation of contaminated groundwater remains very difficult, expensive and time consuming because of the slower, unconstrained movement of water in the subsurface. Total aquifer clean-up may not be even achievable.

Contaminants such as road de-icing salts move readily through the groundwater system with little or no attenuation. Short groundwater flow paths between contaminant sources (e.g., a landfill) and local discharge areas may provide insufficient natural attenuation. Also, some aquifers exhibit naturally elevated chloride and iron concentrations due to the mineral composition of the soil or rock.

4 Humber River State of the Watershed Report – Geology and Groundwater Resources

Relatively stable groundwater temperatures occur throughout the year in southern Ontario between 8 and 10 degrees Celsius. Streams with significant groundwater discharge often provide coldwater aquatic habitats where temperatures remain below 20 °C year round.

1.5 GROUNDWATER IN THE RURAL AND URBAN LANDSCAPE

Human activities can significantly affect the groundwater flow system. Deforestation decreases evapotranspiration and increases run-off. Urbanization can result in decreased infiltration, relative humidity, incident radiation and wind speed while increasing run-off, cloud cover, precipitation and extreme temperatures (Phillips and McCulloch, 1972). These factors affect the volume and distribution of water reaching the water table.

Surface activities influence what happens to shallow groundwater. Land clearing reduces infiltration by reducing the impediments to overland flow. Land clearing for urban development may also increase soil compaction due to the use of heavy machinery. These activities increase surface run-off and reduce groundwater discharge. Aggregate extraction and servicing for urban development can effect groundwater flow rates and directions. Impervious surfaces (e.g., paved areas, rooftops, etc.) associated with urban environments impact natural recharge and discharge functions, without extensive mitigation measures. This can result in reduced groundwater discharge to streams. Drought, high temperatures, and increasing water consumption also threaten the maintenance of water levels in aquifers and streams.

Human activities can also affect groundwater quality. In rural areas, excessive application of fertilizers, improper storage of manure, faulty septic systems and application of road de-icing salt can lead to excessive levels of various contaminants (e.g., bacteria, phosphorus, nitrate and chloride) in groundwater. In urban areas, storage, transportation and use of hazardous materials, hydrocarbons from fuels, excessive application of fertilizers and application of road- de-icing salt are all potential sources of groundwater contamination. Contaminated groundwater affects surface water quality at discharge locations which can have negative implications on the health of both humans and aquatic organisms that utilize these resources.

1.6 GROUNDWATER MONITORING

Groundwater levels fluctuate naturally depending on seasonal patterns of precipitation. Climatic conditions strongly influence the amount of infiltrating precipitation and, accordingly, the water level response. A long term groundwater monitoring program can determine the range of groundwater fluctuation in both shallow and deep aquifers.

Groundwater level monitoring remains an important ongoing activity. Under the Provincial Groundwater Monitoring Network (PGMN) program, TRCA operates ten groundwater monitoring wells to record groundwater fluctuations in different areas of the Humber Watershed. Groundwater level measurements from municipal water supply wells and landfill monitoring wells provide additional data.

State-of- the-art data loggers and pressure transducers record hourly groundwater levels in the PGMN wells. The transducer measures the total pressure head while the data logger provides data storage. Data from each logger is either downloaded through a telemetric system or during a site visit by TRCA’s field technicians. In addition, TRCA has implemented a program

5 Humber River State of the Watershed Report – Geology and Groundwater Resources for measuring infiltration rates for various soil types within the Humber River watershed using a Guelph Permeameter. Seepage meters and mini-piezometers have been used to measure groundwater discharge rates at specific locations of interest.

The TRCA recently implemented a groundwater quality sampling program for its PGMN wells, including the ten wells within the Humber River watershed (see Section 4.2.11 for list of water quality parameters that samples are tested for). In addition, Ontario Regulation 170 requires the groundwater quality testing of municipal water supply wells. Results from this municipal testing provide another source of information on groundwater quality. Six municipal supply wells exist in the York Region portion of the Humber Watershed while another six exist in the Peel Region portion.

1.7 GROUNDWATER MODELING

Groundwater models provide a means of visualizing groundwater flow and estimating groundwater fluxes and can be used to help prepare watershed-based water budgets and predict contaminant transport. It must be recognized however, that all models are simplifications of reality, and that much uncertainty remains over the subsurface distribution of the sediments that comprise the aquifers and aquitards of the Greater Toronto Area.

The YPDT-CAMC team, in conjunction with Earthfx Inc., has developed a calibrated groundwater model for the Greater Toronto Area watersheds using the United States Geological Survey program MODFLOW (Three-dimensional MODULAR FLOW System) linked to a continuous surface water model also developed by the USGS (PRMS - Precipitation, Runoff Management System).

A key aspect of this modeling effort has been the focus on data. The model is based on a database that incorporates about 10 million data records (i.e., climate, stream flow, water level, pumping rates, and geologic parameters). The study team spent approximately four years compiling and checking the hydrogeologic data, and assembling the conceptual geologic model framework.

The published hydrogeologic model consists of a seven layer, 7 million cell array based on 100 by 100 m grid cells. It simulates the groundwater system across the geographic area spanning from Mississauga eastward to Pickering, and from Lake Simcoe southward to Lake Ontario. The model predicts water levels in each of the seven layers, directions and rates of groundwater flow and groundwater discharge areas and rates (Kassenaar and Wexler, 2006). This model has recently been expanded to include 22 modeling layers and the entire Region of Peel, in part, to facilitate modeling for the Humber Watershed Plan.

Field measurements of such parameters as recharge and discharge rates, water levels in wells and boreholes, and stream flow have been used to validate the input parameters of the groundwater flow model.

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2.0 PHYSICAL SETTING

2.1 PHYSIOGRAPHY

The physiography of the watershed reflects the complex geologic history of the area. Drainage flows from the highest elevations (~490 metres above sea level) along the Niagara Escarpment and the Oak Ridges Moraine to the north shore of Lake Ontario (75 metres above sea level).

The following physiographic regions occur within the Humber River watershed ( Figure 2-1):
the Niagara Escarpment;
the Horseshoe Moraine;
the Guelph Drumlin Field;
the Oak Ridges Moraine (ORM);
the South Slope;
the Peel Plain; and,
the Lake Iroquois Sand Plain.

The Niagara Escarpment is a prominent feature that extends from Lake Michigan in the south to the Bruce Peninsula and Manitoulin Island in the north. It is defined by a crest of dolostone bedrock that is highly resistant to weathering and erosion, with little or no overburden present, and appears as sheer cliffs of bedrock along some portions of its length (Chapman and Putnam, 1984). The Niagara Escarpment traverses the north western portion of the Humber watershed. Here, the vertical cliffs of exposed rock are covered by Oak Ridges Moraine sediments, and appear in the landscape as a steep topographic rise.

The Horseshoe Moraine forms a horseshoe-shaped region above and west of the highest portions of the Niagara Escarpment. The two major landforms associated with this area are irregular stone knobs and ridges as well as pitted sand and gravel terraces and valley floors filled with swamps (Chapman and Putnam, 1984). In the Humber River watershed, the Horseshoe Moraine region is limited to the extreme northwestern portion.

The Guelph Drumlin Field physiographic region lies above and immediately to the west of the Niagara Escarpment. The area is characterized by hummocky terrain from the high concentration of drumlins, which are rounded hills formed under glacial ice. The soils are a mix of stony glacial tills and gravel terraces from former spillways (Chapman and Putnam, 1984).

The Oak Ridges Moraine (ORM) is the prominent ridge of land separating the Lake Ontario drainage basin from the Georgian Bay and Trent River drainage basins. The main ridge of sand and gravel deposits, interpreted as an interlobate moraine, formed during the recession of the Wisconsinan glaciation about 13,000 years ago (Chapman and Putnam, 1984). The moraine forms a west to east trending belt of hummocky topography characterized by rolling hills interspersed with many kettle wetlands, ponds and lakes. The majority of the moraine’s hills are comprised of sandy or gravely material. However, some of the highest points consist of till caps overlying sand. It also includes areas of hummocky Halton Till that occur along its southern flank. Due to its predominantly sandy surface material and hummocky topography, the ORM serves as the primary recharge area to underlying aquifers. Springs along the lower slopes of the moraine provide important sources of baseflow to streams that traverse the South Slope and Peel Plain regions.

7 Figure 2-1: Physiographic Regions

Humber River State of the Watershed Report – Geology and Groundwater Resources

The South Slope physiographic region is defined as the area along the southern slope of the Oak Ridges Moraine and extends along the moraine between Durham Region in the east to the Niagara Escarpment in the west. The South Slope is characterized by topography that gently slopes southward towards Lake Ontario and consists of a smooth, faintly drumlinized, clay till plain that contains deeply incised stream valleys.

The Peel Plain is characterized as a slightly undulating to flat clay till plain covered by a veneer of lacustrine deposits from former glacial Lake Peel. These glaciolacustrine deposits are up to five metres in thick in some locations.

The southern most portion of the watershed includes the former glacial Lake Iroquois Sand Plain. The 135 metre elevation topographic contour demarcates the approximate northern limit of the Lake Iroquois Sand Plain. Beach sand and lacustrine silt and clays represent the predominant deposited material. In the Humber watershed, these deposits extend approximately ten kilometres north of the current Lake Ontario shoreline.

2.2 CLIMATE

Climate varies across the watershed both spatially and temporally with local variation created by such factors as topography, prevailing winds, and proximity to the Great Lakes. Human activities can also affect local climate. For example, deforestation and urbanization may increase air temperature, stream flows and peak flood flows while decreasing evapotranspiration.

Within the Humber River watershed area, there are three main zones of relatively contiguous and uniform climate known as the Lake Ontario Shore, the South Slope/Peel Plain, and Oak Ridges Moraine/Horseshoe Moraine zones (named after the physiographic regions). The Lake Ontario Shore zone closely follows the north shore of Lake Ontario in a relatively narrow band and is under the moderating influence of the Lake. The South Slope/Peel Plain zone is topographically higher and farther from the Lake, and hence the influence of the Lake is diminished. The Oak Ridges Moraine/Horseshoe Moraine zone is the highest elevation area in the watershed and furthest from Lake Ontario. The three zones are largely distinguished by differing precipitation and temperature patterns.

Based on Environment Canada climate stations in or near the watershed with at least 30 years of records, the average annual precipitation for this watershed during the period 1971 to 2000 ranged between 798 millimetres per year (mm/yr) in Woodbridge (Station 6159575) in the South Slope/Peel Plain zone, 834 mm/yr in Toronto (Station 6158350) in the Lake Ontario Shore zone, and up to 933 mm/yr near Mono Mills (Station 6152833) in the Oak Ridges Moraine/Horseshoe Moraine zone (Environment Canada, 2007). A recent study for the York, Peel, Durham and Toronto (YPDT) Groundwater Management Project indicated that average precipitation, measured at 48 stations in the Greater Toronto Area for record periods greater than eight years during 1980 to 2002, ranged between 734 mm/yr and 946 mm/yr (Kassenaar and Wexler, 2006). The term “precipitation” includes rainfall, dew, snowfall and condensation. Figure 2-2 shows the locations of all climate stations in the watershed.

9 Humber River State of the Watershed Report – Geology and Groundwater Resources

Mean annual temperatures are useful for broad, regional comparisons. The mean annual temperature for the portion of the Lake Ontario Shore zone within the TRCA jurisdiction is approximately 8 degrees Celsius ( °C). Given its distance from Lake Ontario and higher elevation, the South Slope/Peel Plain zone has a cooler mean annual temperature of about 7°C. The Oak Ridges Moraine/Horseshoe Moraine zone has a slightly cooler mean annual temperature of about 6.5 °C (Sanderson, 2004; Environment Canada, 2007)

The mean annual actual evapotranspiration for the region including the Humber River watershed has previously been estimated to be about 530 to 560 mm/yr, reflecting seasonal periods of soil moisture limitations (Brown et al ., 1980, Phillips and McCulloch, 1972, Morton, 1983). Through recent application of water budget modelling at the watershed scale, average annual total evapotranspiration is estimated to range from 469 mm/yr in the Toronto area (Lake Ontario Shore zone) to about 589 mm/yr for the South Slope/Peel Plain zone . An average value of 517 mm/yr is estimated along the Oak Ridges Moraine/Horseshoe Moraine zone (Earthfx, 2008). A value of about 525 mm/yr is the average value for the entire watershed.

The modelled average annual water surplus (i.e., precipitation minus total evapotranspiration losses) under current conditions ranges from 277 mm/yr in the South Slope/Peel Plain zone to about 383 mm/yr in the Toronto area (Lake Ontario Shore zone). The water surplus estimate for the Oak Ridges Moraine/Horseshoe Moraine zone is about 331 mm/yr. Average water surplus for the entire watershed was estimated at 330 mm/yr. Part of the water surplus will be converted to surface runoff into area watercourses and the balance will infiltrate through the soil profile and eventually recharge the upper portion of the groundwater system.

10 Figure 2-2 : Climate Stations in the Humber Watershed

Figure 2-3: Long-term Precipitation (Toronto – Queen’s Park)

1300.0 79.0 Total Annual Precipitation (mm) - Toronto (6158350)

1200.0 Annual Average Lake Ontario Water Level (02HC048) 78.5

5 per. Mov. Avg. (Total Annual Precipitation (mm) - Toronto (6158350)) 1100.0 78.0

1000.0 77.5

900.0 77.0

800.0 76.5

700.0 76.0

600.0 75.5

500.0 75.0 Annual Total Precipitation (mm) Lake Ontario water level (m amsl)

400.0 74.5

300.0 74.0

200.0 73.5 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010