The Stream Power Index (SPI) is a measure of the erosive power of flowing water and can help identify areas on the landscape where concentrated flow and gully erosion are more likely to occur. The SPI is a function of both slope and contributing area. High SPI values indicate areas with large drainage areas and steeper slopes.
Why should farmers and landowners care about the SPI?
Think of high SPI values like conveyer belts that can transport sediment, nutrients/manure and pesticides off fields during snowmelt or heavy rainfall events. Installing grassed waterways, edge of field prairie strips or other conservation practices in areas with high SPI values can help reduce this risk. It may not be practical to address all SPI areas on your farm, so prioritize based on color (darker orange areas) and proximity to streams.
Details about these Data
The SPI for the Root River Watershed was created using a non-hydro conditioned 3-meter resolution digital elevation model from a 2008 LiDAR flight. Data were filtered to only show the 85th percentile and above values. These data are currently only available for the Root River Watershed with plans to expand to other areas when they become available.
Note: High SPI values in flatter landscapes found in Mower and Dodge County may not always appear. SPI values do not factor in existing conservation practices.
The SPI for the Root River Watershed was done in connection with the Root River Field to Stream Partnership
Two remaining Responsible Parties for the Site, CMC Heartland Partners and U.S. Borax, investigated the Site's soil and groundwater from 1995 through 2006. The investigations defined the levels of arsenic present in the soil at the Site and provided a better understanding of the contaminated groundwater plume below and beyond the Site. Surface soil contamination ranged from background concentrations to 5,200 milligrams per kilogram. The subsurface soil in some locations was contaminated to a depth of 25 feet, which is also the depth to the water table at the Site.
The Site is underlain by several feet of sand and silty sand fill, which is underlain by Middle Terrace Deposits consisting of fine to coarse grained sand (Minnesota Geological Survey, 1989; Exponent, 2004). The fill and terrace deposits are generally 30-50 feet thick and are underlain by glacial till composed of sandy clay to silty sand. The till is approximately 25-30 feet thick across most of the Site.
A buried bedrock valley, oriented north-south, intersects the southwestern corner of the Site. The Platteville Formation (Platteville; primarily limestone), Glenwood Shale and the upper St. Peter Formation (St. Peter; primarily sandstone) are absent within the valley and have been replaced largely by till. The uppermost bedrock under most of the Site is the Platteville. The St. Peter is the uppermost bedrock in the bedrock valley, found at depths of approximately 95 feet.
Two remaining Responsible Parties for the Site, CMC Heartland Partners and U.S. Borax, investigated the Site's soil and groundwater from 1995 through 2006. The investigations defined the levels of arsenic present in the soil at the Site and provided a better understanding of the contaminated groundwater plume below and beyond the Site. Surface soil contamination ranged from background concentrations to 5,200 milligrams per kilogram. The subsurface soil in some locations was contaminated to a depth of 25 feet, which is also the depth to the water table at the Site.
The Site is underlain by several feet of sand and silty sand fill, which is underlain by Middle Terrace Deposits consisting of fine to coarse grained sand (Minnesota Geological Survey, 1989; Exponent, 2004). The fill and terrace deposits are generally 30-50 feet thick and are underlain by glacial till composed of sandy clay to silty sand. The till is approximately 25-30 feet thick across most of the Site.
A buried bedrock valley, oriented north-south, intersects the southwestern corner of the Site. The Platteville Formation (Platteville; primarily limestone), Glenwood Shale and the upper St. Peter Formation (St. Peter; primarily sandstone) are absent within the valley and have been replaced largely by till. The uppermost bedrock under most of the Site is the Platteville. The St. Peter is the uppermost bedrock in the bedrock valley, found at depths of approximately 95 feet.
Cleanup began in the fall of 2004 and was completed in 2005. Approximately 62,000 cubic yards of contaminated soil and debris were excavated from the Site. For comparison, a typical dump truck can hold between 10 to 14 cubic yards of soil. Soil was removed in a central hot spot on the Site where the underlying soil was contaminated to a depth of about 25 feet. The primary purpose of removing the central hot spot soil was to aid in the reduction of arsenic loading to the groundwater.
Additional arsenic contaminated soil was removed from shallower depths to ensure that no contaminated soil was shallower than four feet from the final surface of the Site after it had been redeveloped. The most contaminated soil was treated with EnviroBlend chemicals to ensure the arsenic would not leach from the soil when it was removed from the Site. The soil and debris removed from the Site were disposed of at an industrial landfill in Minnesota. An additional 300 cubic yards of soil contaminated with mercury were disposed of at a landfill in Wisconsin.
Cleanup began in the fall of 2004 and was completed in 2005. Approximately 62,000 cubic yards of contaminated soil and debris were excavated from the Site. For comparison, a typical dump truck can hold between 10 to 14 cubic yards of soil. Soil was removed in a central hot spot on the Site where the underlying soil was contaminated to a depth of about 25 feet. The primary purpose of removing the central hot spot soil was to aid in the reduction of arsenic loading to the groundwater.
Additional arsenic contaminated soil was removed from shallower depths to ensure that no contaminated soil was shallower than four feet from the final surface of the Site after it had been redeveloped. The most contaminated soil was treated with EnviroBlend chemicals to ensure the arsenic would not leach from the soil when it was removed from the Site. The soil and debris removed from the Site were disposed of at an industrial landfill in Minnesota. An additional 300 cubic yards of soil contaminated with mercury were disposed of at a landfill in Wisconsin.
The monitoring well network includes both on-site and off-site wells. The water table is present at depths of approximately 24-28 feet below ground surface at the Site. The depth to ground water increases to the west and southwest of the Site. The shallow groundwater below the Site flows towards the west-southwest. The flow direction of the deeper groundwater in the St. Peter formation is towards the northeast.
The monitoring well network has been sampled regularly for arsenic. Elevated concentrations of arsenic have been found in the groundwater below and downgradient of the Site. The groundwater contaminant plume extends approximately 2,000 feet southwest of the Site in the terrace and glacial till deposits. The bedrock deposits do not appear to have been contaminated with arsenic from the Site.
The MDA and the Minnesota Department of Health (MDH) reviewed available well records and conducted site visits to determine the status and use of any private wells near the Site. Based on this survey, there does not appear to be any users of groundwater within the arsenic groundwater plume emanating from the Site.
