NEW revision to risk level for water quantity at Region of Halton’s Wells serving Georgetown in the
Credit Valley Source Protection Area (CVSPA)
The risk level for the vulnerable groundwater quantity area around wells serving Georgetown has been reduced
to moderate based on new technical direction from the Ministry of the Environment. The following is a brief
description of the process and summary of results from the recently updated assessment. This work was done to
evaluate where there are or may be water quantity threats around the Region of Halton’s municipal wells
serving Acton and Georgetown. This information is being used to update the Approved Assessment Report for
the CVSPA. The updated assessment report will be submitted to the Ministry of the Environment in 2014 for
approval and will be available (here).
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:
 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:



The cone of influence of the municipal supply wells (Well Head Protection Area for Quantity-1 (WHPAQ1)); and
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 (i.e.
part of the watershed of Beeney Creek up gradient of some wells in Georgetown).
 The Local Area Risk Assessment -is the evaluation of a series of risk scenarios within the Local Area. Once the
Tier 3 Water Budget Model has been calibrated and validated, and the Local Areas delineated, the Local
Area Risk Assessment is undertaken for each Area.
The Local Area Risk Assessment involves evaluation of a series of risk scenarios which consider existing,
allocated and planned 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 in the Local Areas for the Region of Halton’s wells in the CVSPA
are shown in Table: 1.
Table: 1 – Risk Assessment Model Scenario
Model Scenario Details
Scenario
Time Period
C
Period for which climate
and stream flow data are
available for the Local Area
(2008)
Existing
Existing
Steady-state, Average Annual Recharge
D
10 year drought period
Existing
Existing
Transient (1960-2006); Monthly recharge rates
Planned or existing plus
committed (Official Plan)
Allocated
Groundwater Recharge Reduction and
Increase in Demand
Existing
Allocated
Groundwater Discharge Reduction from
Increase in Demand
G(3)
Planned or existing plus
committed (Official Plan)
Existing
Groundwater Recharge Reduction from Land
Cover
G(4)
Existing
Allocated
Per G(2); Impacts on other users
G(5)
Existing
Planned
Per G(2); Impacts on other users
Planned or existing plus
committed (Official Plan)
Existing plus
Committed
Groundwater Recharge Reduction and
Increase in Demand
G(1)
G(2)
H(1)
Period for which climate
and stream flow data are
available for the Local Area
10 year drought period
Land Cover
Municipal
Pumping
Model Simulation
H(2)
10 year drought period
Existing
Allocated
Groundwater Discharge Reduction from
Increase in Demand
H(3)
10 year drought period
Planned or existing plus
committed (Official Plan)
Existing
Groundwater Discharge Reduction from
Increase in Demand
Steady-state,
Average
Annual
Recharge
Transient
(1960-2006);
Monthly
recharge rates
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 existing and future
consumptive water uses and activities which reduce recharge are classified as significant water quantity
threats. In a Local Area assigned a moderate risk level, only future consumptive water uses and activities
which reduce recharge are classified as significant water quantity 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 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), and the Local Area – 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 Halton’s Wells
serving Acton and Georgetown in the CVSPA
The Region of Halton’s municipal drinking water wells supplying the communities of Acton and Georgetown in
the Town of Halton Hills are located within sub watersheds 10 and 11 of the Credit River watershed. These two
sub watersheds were previously identified in the Tier 2 Water Budget Study as having moderate groundwater
quantity stress. A Tier 3 Water Budget study has been completed for municipal drinking water wells located in
these sub watersheds under the direction of a Steering Committee with membership from the CTC, the Ministry
of the Environment (MOE), the Ministry of Natural Resources (MNR) and the Region of Halton. Funding for the
study was provided by the province as part of its commitment to the development of source water protection
plans. The Region of Halton was responsible for hiring and managing the consultants, providing information on
the municipal wells, the current and future municipal water demands and the proposed development per the
current municipal Official Plans. CTC provided technical review and managed the external peer review. MOE and
MNR staff provided technical direction on work required to meet the Technical Rules.
The Tier 3 Water Budget Study for Acton and Georgetown began in 2010, with an initial objective of addressing
data gaps identified through previous studies. These gaps were reduced through an extensive field program
which entailed drilling new boreholes and seismic surveying. This program yielded new high quality data that
allowed for a vast improvement to the previous understanding of the geology within the localized area,
particularly with respect to the hydrogeological conditions influencing the municipal well fields. This work has
prompted several key revisions to the conceptual and numerical groundwater models that were used in 2009 to
delineate Well Head Protection Areas (WHPAs) around these wells. In October 2012, revised WHPAs were
delineated based on this new work and submitted to the MOE for approval as part of the Proposed Updated
Assessment Report: CVSPA.
Three Local Areas were delineated within the study area based on assessing the potential interactions amongst
clusters of wells. The drinking water quantity threats were assessed for each Area. An IPZ-Q was delineated to
include Beeney Creek, a surface water system with proven hydrological connection to the municipal aquifer
west of Georgetown.
The Local Areas are shown on Figure: 1
Figure: 1 – Local Area A, B and C
The Local Area A (shown in buff on Figure: 1) was assigned a “Significant” Risk Level based on the following:

The allocated quantity of water for the Fourth Line Well A is not met in Scenarios H(1) and H(2) (See
Table: 1-Drought Scenarios). Drawdown is impacted primarily due to increased pumping rates.
The Local Area B (shown in the insert on Figure: 1) was assigned a ‘Low’ Risk Level as the well systems are
simulated to be able to meet their allocated quantity of water without impacting other uses or being impacted
by reduction in recharge from current approved growth plans or from drought simulations.
The Local Area C (shown in turquoise on Figure: 1) was assigned a “Moderate” Risk Level based on the following:

Groundwater discharge to Hospital Tributary, a designated coldwater stream, is reduced by more than
20% in Scenario G(2) (Average Climate, Allocated Pumping); and

Groundwater discharge to Lower Beeney Creek, a designated coldwater stream, is reduced by more
than 20% in Scenario G (2) (Average Climate, Allocated Pumping), and

Groundwater levels are lowered by a measurable and unacceptable amount beneath provincially
significant wetlands on Hospital Tributary (Average Climate, Allocated Pumping).
Results of the scenario analyses suggest the tolerance of the Halton Region wells located in the CTC SPR is high,
as the drinking water systems are able to meet their existing water demands.
Water Quantity Threats
Water Demand
Since Local Area A was assigned a Significant Risk Level, all existing and future consumptive demands lying
within this Local Area are classified as Significant Water Quantity Threats. Local Area C was assigned a Moderate
Risk Level, thus all future consumptive demands lying within this Local Area are classified as Significant Water
Quantity Threats while the existing demands are classified as Moderate Water Quantity Threats. These threat
activities are shown in
. The Risk Level in the Local Area B was assigned as Low, meaning there are no existing or future moderate or
significant water quantity threats in this area. 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 – Existing Consumptive Water Uses
Area
Risk Level
Local Area A
Significant
Local Area B
Low
Local Area C
Moderate
Permitted Consumptive Demand
(Threat)
Fourth Line Well A
Davidson Well
Prospect Park Well
Lindsay Court Well 9
Princess Anne Well5
Princess Anne Well 6
Cedarvale Well 1A
Cedarvale Well 3A
Cedarvale Well 4
Cedarvale Well 4A
Threat Classification
Significant
Significant
Moderate
Moderate
Moderate
Moderate
Moderate
Moderate
Moderate
Recharge Reduction
The Technical Rules (2009) also specify reduction in groundwater recharge as a potential water quantity threat
within the Local Area. 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 Local Area A (existing and future activities) and Local Area C (future activities
only) are classified as significant water quantity threats. Currently the majority of planned development 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.
Based on the findings of significant drinking water quantity threats, the CTC Source Protection Committee must
develop policies that when implemented are intended to reduce or eliminate the significant water quantity
threats in Local Areas A (existing and future) and C (future). Note that some parts of the Local Areas A and C
extend outside the boundary of the CVSPA into the Lake Erie and Halton-Hamilton Source Protection Regions
(SPR) respectively. Groundwater often flows across watershed boundaries which are based on surface water
flow patterns. The Source Protection Committees in the adjacent SPR have the responsibility for developing
policies to apply within the parts of these Local Areas which extend into their jurisdictions.