Completion of Tier 3 Water Budget for Region of York and Region of Durham Wells in the
Toronto and Region Source Protection Area (TRSPA)
The following is a brief description of the process and summary of results from the recently completed
science work. This work was done to evaluate where there are or may be water quantity threats around
the Region of York municipal wells serving Kleinburg, Nobleton, King City, and Whitchurch-Stouffville
and Region of Durham municipal wells serving the Uxville Industrial Park. The study also included Region
of York wells located in the South Georgian Bay Lake Simcoe (SGBLS) Source Protection Region. Further
information about the work undertaken and findings in SGBLS is available on their website (here).
This new information will be used to update the Approved Assessment Report for the TRSPA. The
updated assessment report will be submitted to the Ministry of the Environment for approval in 2014.
Tier 3 Water Budget Assessments - Overview
The overall objective of the Tier 3 Water Budget Assessment is to determine whether a municipality is
able to meet its planned water quantity requirements, considering increased municipal water demand,
future land development, drought conditions, and other water uses.
The Tier 3 Water Budget Assessment is required to:

Estimate the likelihood that a municipal drinking water source is able to sustain its allocated
(existing plus committed or planned) pumping rates, while maintaining the requirements of
other water uses (e.g. ecological requirements and other water takings), and

Identify water quantity threats that may influence a municipality’s ability to meet their allocated
and planned pumping rates
The two prescribed activities which are drinking water quantity threat are defined in the Ontario
Regulation 287/07 under the Clean Water Act, 2006. These activities are:


Any consumptive use of water (demand for water); or
Any activity that reduces recharge to an aquifer.
The information used to assess these water quantity threats include detailed characterization of current
and future municipal and non-municipal consumptive uses (demand), the amount of water available for
use in the aquifer or surface water body, as well as potential reduction in recharge from future changes
in land use based on the current Official Plan and zoning.
The two major components of the Tier 3 Water Budget Assessment are:
1.
The Model – is the result from combining both numerical groundwater and surface water models,
which are used to evaluate local surface and or groundwater conditions at each water supply well
or surface water intake.
The Tier 3 Water Budget represents improvements to the Tier 2 Water Budget, in terms of the
model simulation and more accurate estimates of groundwater movement between and across sub
watershed boundaries. This is made possible by refinements in the geological conceptualization
and subsurface characterization of the Study Area, particularly in the vicinity of municipal
wellheads and surface water intakes. The model is used to map the area around each well or group
of wells where the water comes from to supply that well(s) – called the Local Area. Local Areas are
the vulnerable areas that are considered as most important to protect the quantity of water
required by a municipality to meet their current or future water needs. The Local Area is
determined by combining the following areas:



2.
The cone of influence of the municipal supply wells (Well Head Protection Area for Quantity-1
(WHPA-Q1));
The areas where a reduction in recharge would have a measurable impact on the cone of
influence of the well(s) (WHPA-Q2); and
Any additional part of the WHPA-Q2 that is a drainage area that contributes surface water to
the groundwater system and directly influences the quantity of recharge available to a
municipal well (there is no such area for the wells in this study).
The Local Area Risk Assessment -is the evaluation of a series of risk scenarios within the
combined WHPA-Q1/Q2 areas collectively called the Local Area. Once the Tier 3 Water Budget
Model has been calibrated and validated, and the Local Area delineated, the Local Area Risk
Assessment is undertaken.
The Local Area Risk Assessment involves evaluation of a series of risk scenarios which consider
existing and allocated pumping rates, and current and planned land uses. The scenarios are used
to simulate the response of groundwater and surface water movement and levels, to variations in
pump rates (demand) and in land use; and in so doing, allow for an assessment of the future
sustainability of a municipal water source. The evaluation of risk scenarios also considers the
water demands of other uses, particularly those that must be maintained by provincial or federal
law such as wastewater assimilation flows and the ecological flow requirements of cold water fish
habitats and wetlands. The risk scenarios use the calibrated surface water and groundwater flow
models to estimate changes in water levels in a municipal supply aquifer, and to estimate the
impacts to groundwater discharge to maintain flows in streams under average and drought
climate conditions based on review of historical climate data.
The risk assessment scenarios undertaken and results in the Local Area are shown in Table 1 below.
Risk Assessment Model Scenarios
Quantity of
Water
Scenario
Time Period
C
Period for which climate and
stream flow data are available for
the Local Area
Existing
Existing Demand
Existing Demand
Low
10 year drought period
Existing
Existing Demand
Existing Demand
Low
Projected Demand and
Reduction in Recharge
Allocated
Anticipated Demand
Low
Existing
Allocated
Existing Demand
Low
Reduction in Recharge
Existing Demand
Anticipated Demand
Low
Existing
Allocated
Existing Demand
Moderate
Existing
Planned
Existing Demand
-
Projected Demand and
Reduction in Recharge
Allocated
Anticipated Demand
Low
Existing
Allocated
Existing Demand
Low
Reduction in Recharge
Existing Demand
Anticipated Demand
Low
(base)
D
(base with drought)
G(1)
(Impact on municipal
wells)
Land Cover
Results – Risk Level
Other Permitted Water Demand
Local Area
G(2)
(Impact on municipal
wells)
G(3)
(Impact on municipal
wells)
Period for which climate and
stream flow data are available for
the Local Area
G(4)
(Impact on other uses)
G(5)
(Impact on other uses)
H(1)
(Impact on municipal
wells)
H(2)
(Impact on municipal
wells)
10 year drought period
H(3)
(Impact on municipal
wells)
Table 1 - Results of Risk Assessment Scenarios in the Local Area in the York-Durham Tier 3 Water Budget
Where the risk scenarios identify the potential that a well will not be able to supply its allocated or
planned supply, the Local Area is assigned a ‘moderate’ or ‘significant’ water quantity risk level. Once
the risk level is assigned to the Local Area, any activity within the Local Area, that reduces recharge to
the aquifer, or that removes water from an aquifer without returning it to the same aquifer (demand) is
identified as being a drinking water quantity threat.
The drinking water threats within the Local Area are classified as low, moderate or significant depending
on the risk level assigned to the Local Area. If the risk level is significant, then all consumptive water uses
and activities which reduce recharge are classified as significant drinking water threats. Part IX.1 to Part
IX.4 of the Technical Rules (2009) and Ministries of the Environment and of Natural Resources Bulletin
(MOE and MNR, 2010) set the requirements and deliverables for the Local Area Assessment and
assignment of the Risk Level.
Tier 3 Water Budget Assessments - Information Products
The major information products resulting from the Tier 3 Water Budget and Local Area Risk Assessments
are:
1. Development and calibration of a Tier 3 Water Budget Model – Numerical surface water and
groundwater models created to simulate the movement of surface water and groundwater in
the Study Area.
2. Characterization of Municipal Wells and Intakes - detailed characterization of wells and intakes,
specifically identifying the low water operating constraints of those wells and intakes.
3. Estimation of Allocated Quantity of Water – assessment of existing, committed, plus planned
demand (pumping rates) for municipal wells.
4. Characterization of Other Water Uses – identification of other uses that might be influenced by
municipal pumping and identify water quantity constraints according to those other uses.
5. Characterization of Future Land Use - comparison of Official Plans with current land use and
incorporates assumptions relating to additional imperviousness from future developments.
6. Characterization of Drinking Water Quantity Threats – consumptive demand, land use change.
7. Delineation of Water Quantity Vulnerable Areas (WHPA-Q1 and WHPA-Q2) which together are
called the Local Area – all of these areas are delineated using the Tier 3 Water Budget Model.
8. Evaluation of the Risk Scenarios within the Local Area- assessed in terms of the municipalities’
ability to pump water at each well along with the impact to other water uses.
9. Assignment of Risk Level - a risk ranking (low, moderate, or significant) is assigned to each of the
vulnerable areas based on the results of the scenarios.
10. Identification of Drinking Water Quantity Threats and the associated risk level for the threat
activity (based on the risk level assigned to the Local Area).
SUMMARY OF TECHNICAL WORK AND FINDINGS –Tier 3 Water Budget for Region of York and Region
of Durham Wells in the Toronto and Region Source Protection Area (TRSPA)
Municipal drinking water supplies for Whitchurch-Stouffville are, in part, drawn from within the Little
Rouge River, Stouffville, and Reesor Creek subwatersheds of the Toronto Region Source Protection Area
(TRSPA), and are located in the vicinity of Whitchurch-Stouffville. In addition, the drinking water supplies
for the communities of Kleinburg, Nobleton, and King City are, in part, drawn from wells within the
Humber River watershed, within the York/Durham Tier 3 Local Area (WHPA-Q1 and WHPA-Q2).
Recently, York Region has provided supplementary drinking water to all of these communities via
pipelines from the Region of Peel's and City of Toronto’s water systems. Both Peel and Toronto obtain
these supplies from Lake Ontario. The Uxville groundwater supply system operated by Durham Region
is located in the Stouffville and Reesor Creeks subwatershed, and serves an industrial subdivision.
Although not a municipal residential supply, this system was included in the TRSPA Terms of Reference
based upon a resolution passed by Durham Region.
The Tier 3 Water Budget Study for York Region and Uxville began in 2010 under the direction of a
Steering Committee with membership from the CTC and South Georgian Bay Lake Simcoe (SGBLS)
Source Protection Regions (SPRs), the Ministry of Natural Resources (MNR) and the Regional
Municipalities of York and Durham. Collaboration between the CTC and South Georgian Bay SPRs was
required because the local area for the Stouffville and Uxville wells overlapped the Local Area for the
northern York Region water supplies within stressed Lake Simcoe subwatersheds.
One Local Area was delineated within the study area, as shown on Error! Reference source not found..
Figure 1 Local Area (WHPA-Q1/Q2) York/Durham Tier 3 Water Budget– Toronto and Region Source Protection Area
The Local Area for the York/Durham Tier 3 Water budget, referred to as the York /Durham Tier 3 Local Area
(WHPA-Q1/Q2), was assigned a ‘moderate’ risk level based on the following circumstances:
1. Increases in pumping to meet allocated demand are predicted to have a greater than 20% reduction in
base flow in select stream reaches in the Yonge Street Aquifer area; and
2. Increases in pumping to meet allocated demand are predicted to create a greater than 1 metre
incremental drawdown in other permitted wells and under provincially significant wetlands.
Water Quantity Threats
Water Demand
Since the York/Durham Tier 3 Local Area (WHPA-Q1/Q2) was assigned a Risk Level of Moderate, all existing
consumptive demands lying within this Local Area are classified moderate and all future consumptive demands
as Significant Water Quantity Threats. The existing consumptive threats (moderate) are enumerated in Table 2.
The consumptive water users include the permitted water demands (e.g., municipal pumping, golf courses) and
non-permitted water demands (e.g., domestic water wells, livestock watering).
Table 2 - Summary of Existing Moderate Drinking Water Quantity Threats (Consumptive Use)
York/Durham Tier 3 Local Area
(Total)
TRSPA Portion of Local Area
Municipal
53
15
Non-Municipal Permitted
146
62
Non-Municipal Non-Permitted
14,550
5,493
Total
14,749
5,570
Type
Recharge Reduction
The Technical Rules (2009) also specify reduction in groundwater recharge as a potential water quantity threat
within the Local Area (WHPA-Q1/Q2). The Tier 3 Scenarios considered the impact of existing and future land
development on groundwater recharge and the resulting impact on water levels in the municipal aquifer at the
wells. Reductions in groundwater recharge within the York Tier 3 Local Area have the potential to be classified
as significant water quantity threats. However, the analyses conclude that the vast majority of planned
development which was assessed is slated to occur outside of the areas of significant recharge, and as such
should not create an unacceptable impact on the municipal aquifers. Any proposed future development that
was not part of the approved Official Plans which were in place when the risk scenarios were modelled would
need to be evaluated as to its potential impact.
Therefore new water takings or reductions in recharge which were not included in this risk analysis could be
significant drinking water threats in the future. Therefore, policies are required to ensure that such activities do
not become a significant drinking water threat in the future.
The CTC Source Protection Committee may also develop policies that when implemented are intended to
prevent the moderate drinking water threats in the Local Area from becoming significant and must develop
policies that when implemented are intended to prevent future significant threats. Note that the Local Area
extends well outside the boundary of the TRSPA into the South Georgian Bay-Lake Simcoe Source Protection
Region (SPR) as well as a small portion of the Local Area (WHPA-Q1/Q2) in the Region Durham that extends into
the Trent Conservation Coalition Source Protection Region. Groundwater often flows across watershed
boundaries which are based on surface water flow patterns. The Source Protection Committees in the adjacent
SPRs have the responsibility for developing policies to apply within the parts of the Local Area that extend into
their jurisdictions.