Milton Tier 3 Water Budget and Water Quantity Risk Assessment, Milton, Ontario:

Milton Tier 3 Water Budget and Water Quantity Risk Assessment, Milton, Ontario:

Client: Halton-Hamilton Source Protection Region, 4052 Milburough Line, RR#2, Campbellville, Ontario. Diane L. Bloomfield, M.Sc., P.Geo. (905.854.9229 ext. 223)
Key Personnel: E.J. Wexler, D. Kassenaar

The Region of Halton operates 3 municipal wellfields for the Town of Milton- the fastest growing community in Canada. The wells lie within a re-entrant (valley) cut into the Niagara Escarpment. High recharge occurs over the exposed Paleozoic bedrock in the upland and over the glacial outwash sediments in the valley. Kelso wellfield is located 400 m from Kelso Lake, part of the flood control system for Milton. The degree of interaction between the reservoir and the deep wells was unknown at the outset of this study. Nearby limestone quarry operations also indirectly affect the wellfields.

An integrated groundwater/surface water model was developed using the USGS GSFLOW code and applied to a 270 km2 area straddling the Escarpment. The model represents eight hydrostratigraphic layers and uses cells as small as 5×5 m in the wellfield. Soil water processes and cascading overland flow were simulated using the PRMS submodel. All mapped streams, wetlands, quarry lakes, and ponds were represented along with reservoir outlets and upstream diversions. Other key inputs included NEXRAD precipitation data and detailed land use information. The groundwater submodel uses MODFLOW-NWT, a much more stable version that allowed simulation of groundwater flow and spring discharge all along the edge of the Niagara Escarpment.

Simulations matched seasonal response including the spring freshet. Wetlands in the upland area fill during the spring months and release flow throughout the summer. The model was calibrated to reservoir discharges and the stream gage on 16-Mile Creek. The filling of the reservoir systems was very sensitive to correctly representing runoff, wetland attenuation, seasonal discharge from quarries, and the operation of diversion structures. Simulated groundwater levels matched the seasonal response and showed that the Kelso Lake was connected to the wellfield through a glacial meltwater channel that breached the confining unit. Seasonal temperature and water quality changes support these conclusions. Drawdowns near the well were sensitive to reservoir operation as well as antecedent conditions in the upstream area.

Project deliverables included an updated database containing all geologic logs, groundwater levels, climate and flow data, a report library, and an updated hydrostratigraphic model.