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:
Ø 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 (WHPA-Q1)); 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).
Ø 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
Scenario / Time Period / Model Scenario Details /Land Cover / Municipal Pumping / Model Simulation /
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
G(1) / Period for which climate and stream flow data are available for the Local Area / Planned or existing plus committed (Official Plan) / Allocated / Groundwater Recharge Reduction and Increase in Demand / Steady-state, Average Annual Recharge
G(2) / 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
H(1) / 10 year drought period / Planned or existing plus committed (Official Plan) / Existing plus Committed / Groundwater Recharge Reduction and Increase in Demand / Transient (1960-2006); Monthly recharge rates
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
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:
- 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.
- Characterization of Municipal Wells and Intakes - detailed characterization of wells and intakes, specifically identifying the low water operating constraints of those wells and intakes.
- Estimation of Allocated Quantity of Water – assessment of existing, committed, plus planned demand (pumping rates) for municipal wells.
- 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.
- Characterization of Future Land Use - comparison of Official Plans with current land use and incorporates assumptions relating to additional imperviousness from future developments.
- Characterization of Drinking Water Quantity Threats – consumptive demand, land use change.
- 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.
- 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.
- 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.
- 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 Table: 2. 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