Cold climate imposes special requirements on urban drainage systems, arising from extended storage of precipitation and pollutants in the catchment snowpack, processes occurring in the snowpack, and changes in catchment surface and transport network by snow and ice. Consequently, the resulting catchment response and runoff quantity differ from those experienced in snow- and ice-free seasons. Sources of pollutants entering urban snowpacks include airborne fallout, pavement and roadside deposits, and applications of de-icing and anti-skid agents. In the snowpack, snow, water and chemicals are subject to various processes, which affect their movement through the pack and eventual release during the melting process. Soluble constituents are flushed from the snowpack early during the melt; hydrophobic substances generally stay in the pack until the very end of melt and coarse solids with adsorbed pollutants stay on the ground after the melt is finished. The impacts of snowmelt on receiving waters have been measured mostly by the snowmelt chemical composition and inferences about its environmental significance. Recently, snowmelt has been tested by standard bioassays and often found toxic. Toxicity was attributed mostly to chloride and trace metals, and contributed to reduced diversity of benthic and plant communities. Thus, snowmelt and winter runoff discharged from urban drainage threaten aquatic ecosystems in many locations and require further studies with respect to advancing their understanding and development of best management practices.

Urban snowpacks accumulate large quantities of solids and contaminants, which originate from such sources as airborne fallout, vehicular deposition, and applied grit and salt. Both contaminants and solids may be quickly released during the periods of snowmelt and, consequently, melting contaminated snow in urban areas in cold climates has the potential to substantially impact the water quality of receiving water bodies. Although data on the water quality impacts of meltwater are relatively scarce, instances of toxicity of the highly concentrated first flush and deterioration of the receiving water quality by winter discharges of solids and chemicals have been documented. Common rainfall-runoff management techniques do not usually address snowmelt impacts because of the cold weather effects on biological systems and physical processes. Further research on adaptation of conventional Stormwater management techniques to cold climate conditions is needed.

Snowmelt runoff and rain-on-snow events present some of the highest pollutant loading and most difficult management challenges in the course of a year in regions with cold climate. Frozen conduits, thick ice layers, low biological activity, altered chemistry, and saturated or frozen ground conditions all work against effective treatment of melt runoff. Understanding the source, evolution and transition that occurs within a melt event, and defining the management objectives for specific receiving waters will help focus the search for effective management techniques. Solving the management puzzle means putting together a strategy for both soluble and solids-associated water pollutants.

The component of snowmelt pollutant washoff due to sand and salt application to roadways in Minnesota is simulated. Laboratory methods are used to extract various pollutants from sand‐salt mixtures commonly used in the Minneapolis‐St. Paul Metropolitan Area of Minnesota for keeping winter road conditions safe. Values derived in the laboratory are compared with actual snowmelt runoff values to estimate the contribution of materials application. High concentrations of solids, phosphorus, lead and zinc in snowmelt from road surfaces axe due in part to sand and salt spread to improve winter driving conditions. The source of the sand and salt appears to be influential in determining the pollutant levels. Judicious use and careful application of materials can reduce the increment of pollution due to anti‐skid sand and salt applied to road surfaces.

ABSTRACT/A newly installed combined detention/wetland stormwater treatment facility upstream from Lake McCarrons, Roseville, Minnesota, was monitored for 21 months to evaluate its effectiveness and the response of the lake to decreased phosphorus loads. The treatment facility consists of a 1.0-ha detention pond that discharges into a series of six constructed wetland "chambers." Data from snowmelt and rainfall events are presented for several pollutants. Results show good reductions for most pollutants. Discussion on the facets of the system's operation are presented. Data from the lake show very little change in its water quality from three years prior to restoration (1984)(1985)(1986) to three years following restoration (1987)(1988)(1989): the lake's phosphorus and chlorophyll has actually increased.The McCarrons wetland treatment system (MWTS) is a runoff management facility (Figure 1) consisting of a detention pond, followed in-line by six "chambered" wetlands (wet marshes) (Table 1), discharging to Lake McCarrons in Roseville, Minnesota. The system was constructed by the City of Roseville as a Clean Lakes (Section 314) project to improve the quality of surface water draining a fully developed urban watershed. Prior to construction, the area was a long, narrow wetland with a well-entrenched channel that moved surface water rapidly through with little vegetative contact and essentially no detention.The MWTS was designed to achieve a 75% reduction in the total phosphorus (TP) load from this watershed (Donohue 1983). As a result of this substantial anticipated reduction, we expected that improvements in the lake's water quality would have been observable almost immediately. The measured change in the short-term (two years) phosphorus loading regime through the MWTS and its immediate impacts on the water quality of Lake McCarrons are examined here. MethodsSurface water quality data collection focused on rainfall and snowmelt runoff events. Flow was continuously monitored from September 1986 through May 1988 and was automatically sampled during 21 rainfall and four snowmelt events at the outflow of the detention pond and at the wetland system outflow ( Figure 1). The tributary stations were all sampled manually