On Groundwater, from AECOM 2014:
As noted, municipal drinking water is provided to many residents along Hammonds Plains and Lucasville Roads. However, groundwater is a source of domestic water for many residents living within the watershed, particularly those along Gatehouse Run and the connecting streets in the central portion of the watershed (Figure 4). Groundwater is found in both bedrock and surficial aquifers, but most potable groundwater wells are completed in bedrock. Records of 100 wells installed within the watershed indicate the yield of bedrock wells is typically less than 20 L/min. This is generally sufficient for individual residential consumption and is consistent with observed average yields of HRM bedrock wells (FracFlow 2004).
Groundwater quality data are limited in the Sandy Lake watershed, but results from three samples reported by NSDNR (2013) indicate the groundwater quality is generally good and is consistent with groundwater quality elsewhere in the region (AECOM 2013). One of the three samples was taken from an aquifer in the surficial deposits while the other two were taken from bedrock aquifers. The surficial aquifer sample exhibited elevated concentrations of iron, manganese, sodium and chloride. All three samples exhibited elevated concentrations of dissolved minerals indicating moderately hard water.
Groundwater recharge rates were estimated for the Sandy Lake watershed using a GIS based groundwater recharge model (Appendix D). Groundwater recharge occurs throughout the study area, but is greatest in areas where the slope is moderate, vegetative cover allows for infiltration and the soils are coarse grained and permeable. Areas with higher recharge are shown on Figure 6. These areas are in the drumlin-rich areas north and east of Sandy and Marsh Lakes extending toward the Sackville River. Areas with high groundwater recharge rates are ecologically valuable since they produce cool, clean baseflow to streams, lakes and wetlands during low-flow periods. They also represent areas of potential groundwater vulnerability since pollutants released at surface can access deeper potable water aquifers though the recharge path. The protection of these areas is a priority identified in Regional Plan Policy E-17.
p15 under 3.2 Potential Sources of Contamination: Septic Systems
Aging septic systems may not be effective at reducing phosphorus from water dispersed in the septic field. The systems may not function as designed because the system components are broken or corroded. The soils in the septic field exhaust their retention capacity and become saturated with phosphorus as the system ages. This saturation results in the discharge of phosphorus to groundwater and surface water that can increase the phosphorus load to lakes. In the Sandy Lake watershed there are no residences on Marsh Lake and there are approximately 20 residences situated within 300 m of Sandy Lake and approximately 200 residences within 300 m of watercourses. These residences rely on private septic systems to treat residential wastewater. In addition, trailhead peat toilets were installed at the Lion s Beach Park in 2002. Given their proximity to the lake, all of these systems are potential sources of nutrients to Sandy Lake depending on their age and maintenance history.
From 3.3 Development Constraints:
The potential impacts of development on water quality in Sandy Lake can be mitigated, to a degree, by the implementation of effective planning strategies. To this effect, a constraints map is developed for the Sandy Lake watershed identifying areas that are not suitable for development and areas that are suitable for development, but may require environmental controls to mitigate potential impacts on surface water quality. Consequently, a constraints map (Figure 7) has been developed. Two categories of constraints are identified; Type 1 and Type 2. Type 1 constraints are for areas where development is not recommended to occur to protect water quality. Watercourses, wetlands and watercourse buffers are considered Type 1 constraints. Type 2 constraints are for areas where methods to protect the environment may be required if development occurs in these areas. Areas with high groundwater recharge, areas underlain by acid generating bedrock and slopes greater than 20% are areas recommended for Type 2 constraints.
The Type 1 constraints include watercourses and associated buffers surrounding the watercourses. A review and analysis of setbacks and vegetated buffers in Nova Scotia was undertaken…
Type 2 constraints are reserved for areas suitable for development but may require additional environmental controls. Areas with steep slopes (>20%) are more likely to erode and contribute sediment to watercourses. The areas in Sandy Lake watershed with slope greater than 20% are identified in Figure 7 and are recognized as development constraints in the watershed. Prior to development, these areas should be assessed to evaluate if Areas with high groundwater recharge potential are important to groundwater users and the lakes and streams in the Sandy Lake watershed. The groundwater recharge model completed for the Sandy Lake watershed used surficial geology, slope and vegetative cover to predict how precipitation is partitioned into groundwater recharge and surface runoff. Areas with high groundwater recharge (>150 mm/yr) provide pathways for water to enter the groundwater system. Protecting these areas with high recharge is important to the groundwater quantity of the watershed which is utilized by water source wells and contributes to the hydraulic budget of the lakes in the watershed. Protecting these areas also protects groundwater quality in the watershed because they are potential pathways for contaminants to enter the groundwater system. Therefore, areas with recharge >150 mm/yr identified in Figure 6 are included in the development constraints as a Type 2 constraints. It is recommended that areas identified to have high groundwater recharge potential are suitable for development with conditions that allow for recharge rates to be maintained, such as:
- Restricting the types of development to developments with low risk for groundwater contamination; and
- Implementation of groundwater quality protection measures to avoid groundwater contamination.
From 10. Policy E-17 Objectives (p44)
a) Recommend measures to protect and manage quantity and quality of groundwater resources. As summarized in Section 2.6 (Groundwater) and Appendix A (Environmental Conditions), groundwater is a source of domestic water for many residents living within watershed and contributes 11 % of the flow from the watershed (Appendix D). The constraints mapping (Section 3.3) identifies areas with high recharge rates (>150 mm/yr) as Tier 2 constraints that can allow for development, but with controls in place to allow for recharge to continue to contribute to groundwater quantity and with controls that protect water quality. These areas provide pathways for water to enter the groundwater system at higher rates than other areas in the watershed. Protection measures during future development are recommended to preserve the hydraulic properties of these areas. Recommendations to protect these areas include maintaining a high proportion of permeable surfaces, maintaining native plants, avoiding compaction of soils and use of rain gardens. Protecting the areas with high recharge rates to encourage sustainable groundwater use will need to be coupled with measures to protect the quality of water entering the groundwater system. Recommendations to protect the quality of recharge water include prohibition of bulk fuel storage, prohibition of hazardous material facilities, prohibition of aggregate extraction, spill prevention for home heating fuel tanks, limited lawn fertilizer use and reduced use of road salts in these areas of high recharge potential.