Lower Welland River Characterization Report - Niagara Peninsula ...
Lower Welland River Study Area Characterization Report The delineation of vulnerable areas produced through the Source Water Protection program is comparable to the mapping produced through the 2005 Groundwater Study for the Lower Welland River watershed, aside from the addition of shallow bedrock vulnerability and transport pathways. Transport pathways that were considered to increase groundwater vulnerability include private water wells (including unused wells needing decommissioning), „unknown‟ status oil and gas wells, aggregate operations, and construction activities along the Welland Canal (outside of study area) (NPCA 2010c). Potential Groundwater Discharge and Significant Groundwater Recharge areas are illustrated on Figure 11 as identified through the Niagara Peninsula Source Protection Area Assessment Report (NPCA 2010c). Discharge areas are locations where groundwater leaves the aquifer and flows to the surface. Groundwater discharge occurs where the water table (or potentiometric surface) intersects the land surface. Potential discharge areas in the Lower Welland River include portions of the Welland River floodplain, lower Thompsons Creek, and the Chippawa Power Canal. The potential height of the water table ranges between 0 and 4 meters below the ground surface at these sites. Groundwater recharge areas are locations where water is transmitted downward to an aquifer. The amount of water that infiltrates to the water table depends on, for example, vegetation cover, slope, soil composition, surficial geology, and depth to the water table. SGRA‟s are identified where the groundwater is recharged by a factor of 1.15 or more than the average recharge rate for the whole NPCA watershed. The average recharge rate for NPCA is 46 mm/year and the criterion 53 mm/year. The estimates of recharge were determined through HEC-HMS continuous surface water modelling. HEC-HMS catchment recharge results were distributed using infiltration factors that are a function of topography, land cover and soil texture (Campbell 2011). The Clean Water Act (MOE 2006) requires the delineation and protection of vulnerable groundwater areas for quantity protection (i.e. SGRAs) as well as for quality protection (i.e. HVAs) as mentioned above. Under The Clean Water Act-Ontario Regulation 187/07 a SGRA is defined as “an area within which it is desirable to regulate or monitor drinking water threats that may affect the recharge of an aquifer”. As described earlier, recharge areas are classified as „significant‟ when they supply more water to an aquifer used as a drinking water source that the surrounding area. There are no SGRA‟s in the Lower Welland River study area; however an area south of the study area in the Grassy Brook subwatershed has been identified as an SGRA. Figure 12 illustrates areas with high, medium and low groundwater vulnerability. The Lower Welland River watershed has been delineated as having predominately low groundwater vulnerability due to the thick deposits of clay and silt of the Haldimand Clay Plain. This material restricts the downward movement of infiltrating surface water, making the underlying groundwater much less susceptible to associated contamination (WHI 2005). Areas of medium groundwater vulnerability are found in the eastern portion of the study area. These areas typically coincide with areas where the overburden is less than 20 meters in thickness. These areas are illustrated in orange on Figure 12. 44
Lower Welland River Study Area Characterization Report Figure 12: Groundwater Vulnerability 45
Lower Welland River Study Area Char