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→Planning Considerations:
Common concerns about permeable paving include the following:
Common concerns about permeable paving include the following:
* Risk of Groundwater Contamination: Most pollutants in urban runoff are well retained by infiltration practices and soils and therefore, have a low to moderate potential for groundwater contamination (Pitt et al., 1999). Chloride and sodium from de-icing salts applied to roads and parking areas during winter are not well attenuated in soil and can easily travel to shallow groundwater. Infiltration of deicing salt constituents is also known to increase the mobility of certain heavy metals in soil (e.g., lead, copper and cadmium), thereby raising the potential for elevated concentrations in underlying groundwater (Amrhein et al., 1992; Bauske and Goetz, 1993). However, very few studies that have sampled groundwater below infiltration facilities or roadside ditches receiving de-icing salt laden runoff have found concentrations of heavy metals that exceed drinking water standards (e.g., Howard and Beck, 1993; Granato et al., 1995). To minimize risk of groundwater contamination the following management approaches are recommended (Pitt et al., 1999; TRCA, 2009b):
* Risk of Groundwater Contamination: Most pollutants in urban runoff are well retained by infiltration practices and soils and therefore, have a low to moderate potential for groundwater contamination (Pitt et al., 1999). Chloride and sodium from de-icing salts applied to roads and parking areas during winter are not well attenuated in soil and can easily travel to shallow groundwater. Infiltration of deicing salt constituents is also known to increase the mobility of certain heavy metals in soil (e.g., lead, copper and cadmium), thereby raising the potential for elevated concentrations in underlying groundwater (Amrhein et al., 1992; Bauske and Goetz, 1993). However, very few studies that have sampled groundwater below infiltration facilities or roadside ditches receiving de-icing salt laden runoff have found concentrations of heavy metals that exceed drinking water standards (e.g., Howard and Beck, 1993; Granato et al., 1995). To minimize risk of groundwater contamination the following management approaches are recommended (Pitt et al., 1999; TRCA, 2009b):
- stormwater infiltration practices should not receive runoff from high traffic areas where large amounts of de-icing salts are applied (e.g., busy highways), nor from pollution hot spots (e.g., source areas where land uses or activities have the potential to generate highly contaminated runoff such as vehicle fuelling, servicing or demolition areas, outdoor storage or handling areas for hazardous materials and some heavy industry sites);
- prioritize infiltration of runoff from source areas that are comparatively less contaminated such as roofs, low traffic roads and parking areas; and,
- apply sedimentation pretreatment practices (e.g., oil and grit separators) before infiltration of road or parking area runoff.