Cooperator: Wisconsin Department of Natural Resources
Project Chief: Charles P. Dunning
Location: Dane County
Project Number: 9KH32
Period of Project: July 2001–October 2005
Problem
Wisconsin State administrative code NR 151 defines performance standards for infiltration of stormwater from new developments. The stormwater infiltration standards are intended to preserve ground-water recharge and stream baseflow. However, depending on the land-use characteristics of a drainage area, stormwater may contain significant amounts of contaminants including hydrocarbons, metals, and chloride. In such cases, enforcement of infiltration performance standards has the potential to adversely affect ground-water quality.
Objective
The objective of this study is to quantify the relation between the quality of stormwater from the Stonefield neighborhood in Middleton, Wisconsin, the hydrologic character of the infiltration basin, and transport of contaminants to the ground-water system.
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Aerial photo of Stonefield neighborhood including the infiltration basin, stormwater drainage well, storm sewer outfalls, and grass spillway. |
Approach
The hydrology of the Stonefield infiltration site was characterized by defining the contributing watershed, coring and describing the sediments from the ground surface in the basin to the ground-water table, monitoring pond stage during stormwater runoff events, monitoring water-table elevation, and monitoring flow into the injection well. Water was sampled for chemical analysis from ponded stormwater, from the water table, and from the vadose zone above the water table. Water-quality sampling was done on a routine schedule as well as in response to events. The period of study was from July 2001 to June 2004, with data collection for different study aspects beginning at different times.
Progress (October 2003–October 2004)
The Stonefield basin appears to be working as an infiltration site largely because the stormwater discharge well routes ponded stormwater to porous, unsaturated sediments below. Infiltration is generally slow through the basin bottom, but could probably be improved with conditioning of the shallow soils, establishment of appropriate vegetation, and strict control of sediment and debris in the watershed. Water-quality analyses to date suggest that the concentration of many constituents is lower in the site stormwater than in vadose or ground water; this is particularly true of the concentration of solids and most metals. While much work is yet to be done in interpreting these data, it appears that for such constituents, infiltration of stormwater from this watershed may benefit rather than degrade ground-water quality. Hydrologic and water-quality data collected during stormwater events may yet reveal some interesting relations between stormwater quality and transport of contaminants at the Stonefield site. Data continue to be collected and interpretation is ongoing.
Plans (October 2004–September 2005)
No additional sampling or analyses are planned. Data reduction and interpretation will continue. The project will be summarized in a USGS Scientific Investigations Report.
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