Air monitoring and human health
The Minnesota Department of Health (MDH) develops guidance to evaluate potential health risks from exposures to chemicals in air. For Water Gremlin, MDH provided a long-term air guidance level of 70 micrograms per cubic meter (µg/m3) of trans-1,2-Dichloroethene (tDCE), as an amount that poses little to no risk to health if breathed over many years. The MPCA uses this guidance to create emission limits that are protective of human health and the environment.
The MPCA has not seen any levels of ambient air pollution around the Water Gremlin site that would require immediate action since the company resumed coating operations. The agency will continue to review monitoring data to determine whether levels of VOCs at the Water Gremlin facility differ from the values recorded at other air monitors in the Twin Cities. The MPCA typically collects at least one year of data to make valid comparisons to other monitoring sites or comparisons with long-term health benchmarks.
The March 2019 settlement agreement between Water Gremlin and MPCA prohibits the company from emitting more than 90 tons of volatile organic compounds (VOCs), per year (based on a rolling 12-month sum). If the company exceeds this limit, it must shut down operations until the rolling sum drops below the limit. This graph shows the cumulative Total VOC emissions (blue line) from the entire Water Gremlin facility, including tDCE emissions from FluoSolv, and compares this value to the annual limit of Total VOCs allowed from the entire Water Gremlin facility (green line).
Stack monitoring of emissions
Stack monitors are one method of measuring emissions from a facility. Because they are measured directly in the emissions stack, there is very little influence from external factors, such as weather, wind direction, emissions from neighboring facilities, etc. At the same time, one limitation of stack monitoring is that it does not account for these temporary factors that create variations in the quality of air people breathe. This is why MPCA looks at a variety of factors to evaluate a regulated facility’s performance.
The graph below shows daily tDCE emission levels measured at Water Gremlin’s in-stack monitor since May 1, 2019, when the monitor was installed. The red bars represent a period of time when the company’s pollution control equipment was not yet installed, and the company was required to limit their production. The yellow bars reflect tDCE emissions after pollution control equipment was installed, but was still being tested and adjusted to reach full efficiency. The green bars represent the time period after the pollution control equipment was fully operational. Note that this measurement is recorded in pounds per hour. It is not directly comparable with the facility’s annual TCE emission limit of 90 tons per year (because production levels may vary), nor does it correspond to health benchmarks, which are calculated and measured in a different way.
Ambient air quality sampling
As another requirement of the stipulation agreement, Water Gremlin must submit to air sampling at five locations around the edge of its property. These five monitors sample for a number of VOCs, including tDCE and TCE. Air samples are collected for one 24-hour period every three days. This work is being performed by Pace Analytical, an independent environmental consultant. Results are reported directly to MPCA.
The graph below reports the results of the air sampling for tDCE from the five ambient air monitors surrounding the Water Gremlin site. The ambient monitors, located near the perimeter of the facility, sample a mixture of surrounding outdoor air that includes some emissions from Water Gremlin. Data collected at these monitors, therefore, is influenced both by the effectiveness of pollution control equipment and by other external factors.
Ambient air monitoring results can vary considerably with wind direction (if stack emissions are blowing directly toward a monitor), and when weather conditions temporarily trap air near the surface or disperse it quickly. Ambient monitors can also detect VOCs that come from other nearby sources. Despite this variability, ambient air monitors are an important data point because they reflect VOC concentrations in the air people are actually breathing.
MPCA is closely tracking ambient air quality around Water Gremlin, and cross-checking this information with other data points. As Water Gremlin’s pollution control equipment continues to be fine-tuned, MPCA expects that the level of VOCs detected at ambient air monitors will decrease.
Results marked with circles are below the lab's reporting limit. Some results are missing due to technical problems, which occasionally occur when conducting air monitoring. Hover over a bar or point to view the site location and hourly wind speeds and directions (measured at Minneapolis-Crystal Airport).
In spring 2019, when Water Gremlin’s new pollution control equipment was not yet operational, the MPCA implemented stringent limits on the amount of tDCE the company could use. During that time, Water Gremlin was required to reduce its tDCE usage whenever ambient air concentrations of tDCE exceeded an action level established in the settlement agreement. The intent of this restriction was to prevent the company from using excessive amounts of tDCE. Now that pollution control equipment and robust monitoring is in place, this particular restriction does not apply.
MPCA continues to track daily use of FluoSolv at the facility. This additional data point can help with interpreting and validating other monitoring results. The graph below reports daily use of FluoSolv at the Water Gremlin facility.