Bringing Water Gremlin into compliance
The March 2019 settlement agreement between Water Gremlin and the MPCA prohibits the company from emitting more than 90 tons of volatile organic compounds (VOCs) — including tDCE — 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.
The MPCA used the MDH health protective guidance for tDCE inhalation that was available at the time to create the 90-ton VOC limit. Subsequently, MDH reevaluated their health guidance and the updated guidance will be reflected in Water Gremlin’s upcoming permit. MPCA has not seen ambient air pollution levels around the Water Gremlin site that would require immediate action since the company resumed coating operations.
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).
Figure note: The coating lines did not operate between August 24, 2019 and January 22, 2020, by MPCA administrative order.
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, stack monitoring results do not reflect the temporary factors that cause variation and do not represent the air quality where people breathe it in. 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. 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.
Ambient air monitoring results can vary considerably with wind direction (e.g., if stack emissions blow directly toward a monitor), and when weather conditions temporarily trap air near the surface or disperse it quickly. Ambient monitors can also detect VOCs or lead that come from other nearby sources. Despite this variability, ambient air monitors are an important data point because they provide actual air concentrations measured in each sample. Concentrations in the air that nearby residents actually breathe are lower than what the monitors measure at locations on Water Gremlin property.
The graph below shows the highest 365-day rolling average ambient air concentration of tDCE monitored around the facility. This average is compared to the MDH long-term air guidance of 20 µg/m3 for tDCE. Note that the long-term air guidance is protective of human health if air with tDCE levels at or below the long-term air guidance level is breathed over many years. Ambient air tDCE concentrations near the facility in 2019 were below the air guidance level of 70 µg/m3 at the time, but were above the May 2020 revised guidance level of 20 µg/m3. tDCE concentrations fell below the revised air guidance level in 2020 after the facility began using a water-based solvent.
In September 2019, the MPCA added two monitors for lead closer to the facility. The lead monitors will continue sampling until a new air quality permit is issued.
The graphs below report the results of the air sampling from the air monitors surrounding the Water Gremlin site. Data collected at these monitors is influenced both by the effectiveness of Water Gremlin's pollution control equipment and 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 or lead that come from other nearby sources. Despite this variability, ambient air monitors are an important data point because they estimate concentrations in the air people are breathing in the nearby neighborhoods, which vary from the levels measured by air monitors located on Water Gremlin property. MPCA is closely tracking ambient air quality around Water Gremlin, and comparing this information with Water Gremlin's tDCE usage and stack emissions.
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).
Figure note: Lead monitoring began 9/18/19. Sampling occurs every six days, with results updated here after MPCA and the lab verify the data. Sampling and data reporting are ongoing.
Tracking FluoSolv usage
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 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.