The CMC Heartland Lite Yard site (Site) is located in Minneapolis, Minnesota at the northwest intersection of Hiawatha Avenue and 28th Street South. Records show that Reade Manufacturing Company, an arsenical pesticide manufacturer, had leased and operated on the Site for nearly 25 years, from early 1938 to 1963. The five-acre Site was used for processing technical arsenic, a white powder, into sodium arsenate, a liquid that was used as a general biocide along railroad lines. Lead arsenate may also have been produced at the Site. US Borax sub-leased the land from 1963 to 1968, and manufactured, stored and shipped arsenic based pesticides for a portion of that period. Soil contamination was discovered in 1994 during reconstruction of the Hiawatha Avenue corridor.
By 1996, the Site was covered with one to two feet of crushed asphalt and clean fill. The covering, which kept dust from blowing off the Site, remained intact until cleanup was initiated in 2004.
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.
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 Minnesota Department of Agriculture (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.
Special Well Construction Area
In 2005, the MDH established a Special Well Construction Area (SWCA) for the Site and surrounding area. The SWCA requires MDH review of all wells proposed to be installed within the SWCA. Water supply wells will not be approved for completion in the unconsolidated deposits or the Platteville or St. Peter formations. Special construction and/or monitoring requirements may be imposed by the MDH for wells, in addition to other restrictions. The SWCA includes the area bounded by East 26th Street on the north, 26th Avenue on the east, Lake Street on the south, and Bloomington Avenue South on the west, within the City of Minneapolis
Site Redevelopment and Additional Cleanup
An office/warehouse was constructed on the Site in 2005-2006 by 2800 Hiawatha LLC. Approximately 2,450 cubic yards of contaminated soil was excavated during construction of the office/warehouse and disposed of off-site.
The responsible party is currently monitoring arsenic contamination in the groundwater in the terrace, glacial till and bedrock formations beneath and adjacent to the Site.
Site Use Restrictions
In July 2008 an environmental covenant was placed on the Site by 2800 Hiawatha LLC (Hennepin County Document No. 9159456). The environmental covenant documents the extent of cleanup and the remaining contamination present at the Site. The environmental covenant also restricts the usage of the Site to industrial activities and requires approval from the MDA staff for certain activities.
Exponent, 2004, Response Action Plan: CMC Heartland Partners, Lite Yard Site, Minneapolis, Minnesota.
Minnesota Geological Survey, 1989, Geologic Atlas for Hennepin County, Minnesota.
Minnesota Department of Health