The Crossroads Elementary School is located on an approximately 8-acre parcel of land at the northeast corner of the intersection of Front Avenue and Kent Street, in a predominantly residential area of St. Paul, Minn. The property has a history of industrial use dating back to the late 1800s including manufacturing, ammunitions manufacturing, galvanizing and machining.
Eight buildings were originally located on the site, including three structures that were built in the late 1800s for manufacturing purposes, a milling plant, and some warehouses that were constructed by 1903. A second row of warehouses were built in 1927.
Some of these buildings were demolished in the late 1980s with the rest coming down in 1995. Crossroads Elementary School opened its doors in 1999.
What's the problem?
When the site was being prepared for redevelopment in 1996, 10 soil borings and 5 temporary groundwater monitoring wells were installed. Test results found trichloroethene (TCE) in soil and groundwater at the site. TCE is a commonly used industrial solvent.
The maximum concentration of TCE detected in soil samples was 340 μg/kg in the southeast corner of the site. Because of this contamination, approximately 36,000 cubic yards of soil were removed from the site as it was being redeveloped.
Additional groundwater testing conducted in 1999 found TCE as well as tetrachloroethene (PCE), cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride. At that time, no additional efforts were made to address the groundwater pollutants because drinking water supplies were not affected. In addition, soil vapor contamination was not evaluated to the same degree we evaluate it today because the sampling and analytical technology was not as advanced.
But we now know that groundwater contaminated with PCE and TCE can release vapors back into the soil which can migrate through the soil into nearby homes and buildings where it can pose health risks to the people living and working in them. This is commonly referred to as vapor intrusion. The MPCA wants to identify vapor intrusion and take steps to reduce or eliminate it where possible.
In mid-August, vapor samples collected from underneath the foundation of the school were analyzed. Test results indicated that there are elevated levels of TCE and PCE underneath the building.
On August 30th, the MPCA collected air samples from inside the school to assess the potential for elevated levels of TCE and PCE in the building. Testing did not detect any levels of these chemicals.
Usually, when chemical vapors enter buildings through the foundation, the amount in indoor air is not high enough to affect most people’s health. Exposure to these contaminants may increase the risk of cancer based on studies in workers or animals breathing very high levels of TCE or PCE (thousands of times greater than what may be found at the school). TCE is also known to cause immune system impacts in animals when they are exposed to high TCE levels.
There are also short-term exposure concerns for women who are pregnant or may become pregnant. Breathing in TCE during the first trimester of pregnancy may increase the risk of heart defects to the baby. If you have health concerns please contact the Minnesota Department of Health's Site Assessment and Consultation Unit:
- Call — 651-201-4897
- Email — email@example.com
What's being done
To prevent any future problems, a vapor mitigation system is being installed at the Crossroads Elementary School and will be operational the week of Sept. 4. Systems such as these are designed and operate like a home radon mitigation system. The vapor mitigation system creates a slight depressurization beneath the building floor slab using a low-wattage fan installed in PVC piping. Vapors collected from beneath the building are then exhausted above the roof line.
Measurements collected before and after installation of the mitigation system are used to verify that the system is functioning properly.
Minnesota Department of Health