Hinsdale/Sexton Landfill in foreground. Hickory Lane Buffer and Wolf Road Prairie outlined in orange. Drainage flows from the landfill into the Middle Fork and then eastward into Salt Creek, shown in blue. Chicago skyline in the distance. Click image for larger version and photo data       Background 3: Urbanization Urbanization has increased runoff from an upstream subdivision known as Ashley Woods and the 275 acre Hinsdale/Sexton landfill. This results in nonpoint source (NPS) pollutants such as oil, road salts, soil fertilizers and pesticides entering the stream. The landfill is capped with seven feet of clay, which acts as an impervious surface and, thereby, causes higher runoff volumes to the Middle Fork. The landfill is being monitored by the Illinois Environmental Protection Agency for groundwater and surface water contaminants. Upstream runoff impacts the MIddle Fork and its watershed prior to discharge into the Wolf Road Prairie wetland known as Harrier Marsh. Siltation buildup in Harrier Marsh chokes out native species and results in loss of riparian vegetation which adversely effects water quality and habitat. Advance to Background 4: Water Quality Impairments