The Impact of Urban Development on Ground Water

Within the Great Lakes basin, a significant portion of groundwater discharge occurs directly to the lakes or their tributaries. Most groundwater contaminants are closely linked to urban land use practices: excessive pesticide and fertilizer use; leaking underground storage tanks; malfunctioning private septic systems; and spills or leachate from industrial sites, uncapped wells and road salts. Groundwater also serves as a pathway for bacterial pollution of urban beaches.¹⁵ Within a watershed, the combination of extensive hardened surfaces and groundwater withdrawals for water use can limit the potential to recharge groundwater supplies, diminishing the ability to sustain historic and current stream flow rates. Reduced flows exacerbate the impact of urban pollutants, causing degradation in overall water quality. In some cases, especially under low flow conditions, base stream flow can be predominantly made up of wastewater discharge and urban runoff. Because of the variety of urban development activities that may significantly impact groundwater quality and quantity, any regional watershed plans must incorporate groundwater issues.

As noted in previous reports, progress and commitment to the implementation of Annex 16 of the Agreement, Pollution from Contaminated Ground Water, has been limited¹⁶. While the broad regional approach implied in Annex 16 would provide the best basin wide context for wise development decisions, an alternative approach could be to require developers to explicitly provide for ground water protection in their development plans. Such site hydro geological assessments would contribute to daily decision-making, and could also be compiled into a regional perspective to manage and control contaminated groundwater affecting the boundary waters of the Great Lakes system, as required under Annex 16.