Air monitoring at Minnesota silica sand facilities

The MPCA received air quality monitoring data from Shakopee, Tiller, and Jordan silica sand facilities between 2012 and 2017. In addition, due to citizen concerns along a silica sand transport route, the MPCA conducted its own monitoring in Winona and a reference site (Figure 1. Monitoring Dates and Pollutants).

The measured concentrations are available within the site-specific tabs on this webpage including:

  • Measured pollutant concentrations
  • Wind direction and speed
  • Comparisons to ambient air quality standards (fine particles (PM2.5), total suspended particles (TSP), particulate matter under 10 microns (PM10) and the inhalation health benchmark (respirable crystalline silica (PM4).

The Minnesota Department of Health’s inhalation health benchmark for respirable crystalline silica represents an air concentration level below which silicosis is unlikely to occur in sensitive populations, even if exposure occurs over an entire lifetime.

If you would like to receive raw data tables for any of these data sets, please contact Jeff Hedman (651-757-2416 or jeffrey.hedman@state.mn.us) or Kristie Ellickson (651-757-2336 or Kristie.Ellickson@state.mn.us). 

graphic of Silica sand monitoring dates and pollutants

 

Lessons learned from ambient air monitoring related to silica sand mining, processing and transport

  1. Ambient monitoring for respirable crystalline silica on the fenceline of mines and processing facilities did not find air concentrations above the inhalation health benchmark for respirable crystalline silica.
  2. Silica sand mines and processing facilities have the potential to be a source of total suspended particulate and PM10, but this was not a consistent finding across all sites.

Why was this monitoring conducted?

There was an increase in oil and natural gas extraction by hydraulic fracturing methodologies in the United States in recent times (Figure 2 - www.rockproducts.com). Minnesota and Wisconsin have extensive deposits of hard round silica sand that meets specifications to be used as proppants in hydraulic fracturing. To date, the highest level of extraction of silica sand for use in hydraulic fracturing has been from approximately 2009 to around 2014.

Figure 2 Increase in silica sand production and hydraulic fracturing

Figure 2 Increase in silica sand production and hydraulic fracturing (www.rockproducts.com)

Silica sand processing- and mining-related air monitoring in Minnesota

During this time, the MPCA received many citizen concerns about the potential for increased ambient air pollutants surrounding silica sand mines and processing facilities. The MPCA began to request and conduct its own air monitoring in response to these concerns, and in light of the quick increase in production and the lack of related of ambient air monitoring.

Map of silica sand sites

Pollutants of interest for silica sand-related ambient monitoring

Silica sand mining and processing facilities are potential sources for two categories of air pollutants: particulate matter and diesel vehicle emissions. Respirable crystalline silica has been of notable concern due to its association with silicosis at elevated levels and for extended lengths of exposure.

Upwind vs. downwind analysis

One way to test if an air pollution source impacts resulting air concentration measurements is to investigate the data based on its position with respect to the air pollution source. Upwind means that the monitor collects air prior to arriving at a facility. Downwind reflects air after it travels over a facility. The following charts compare the mean concentrations for all monitors at each facility when the wind direction is downwind or upwind.

mean concentrations for all monitors at each facility when the wind direction is downwind or upwind

Site comparisons

One way to test whether or not a source of air pollution influences the area surrounding it is to compare air concentrations measured at that location with air concentrations measured at reference sites. The following tables compare the mean concentrations measured at each monitor at each facility to selected ambient air monitoring sites in Minnesota and Wisconsin. Note that “higher” means the facility monitoring site has a higher mean concentration than the comparison site, and lower means the facility monitoring site has a lower mean concentration than the comparison site.

Total Suspended Particulate Comparisons

Facility Monitor Anoka Airport - Blaine (27-003-1002) Apple Valley, MN (27-037-0470) Near Road - Minneapolis, MN (27-053-0962) Didion Milling - Columbia County, WI (55-021-0019) Midwest Energy - Douglas County, WI (55-031-0011)
Great Plains Sands Higher Higher Lower Higher Higher
Jordan Sands North Higher Higher Lower No measurement comparison possible No measurement comparison possible
Jordfan Sands South Higher Higher Same No measurement comparison possible No measurement comparison possible

 

PM10 Comparisons

Facility Monitor Anoka Airport - Blaine (27-003-1002) Ramsey Health Center - St. Paul (27-123-0868) Horicon - Dodge County, WI (55-027-0001)
Great Plains Sands 1 Higher Lower Higher
Great Plains Sands 2 Higher Higher Higher
Jordan Sands North Higher Lower Higher
Jordan Sands South Higher Same Higher
Titan Lansing North Same Lower Higher
Titan Lansing South Same Lower Higher

 

PM2.5 Comparisons

Facility Monitor Anoka Airport - Blaine (27-003-1002) Apple Valley, MN (27-037-0470) Near Road - Minneapolis, MN (27-053-0962) Ramsey Health Center - St. Paul (27-123-0868) Winona
27-169-5220
Horicon - Dodge County, WI (55-027-0001)
Jordan Sands North Same Same Lower Lower Same Lower
Jordan Sands South Same Same Lower Lower Same Same
Titan Lansing North Same Same Lower Lower Same Same
Titan Lansing South Same Same Lower Lower Same Same

 

Respirable crystalline silica was collected and measured over a 24-hour period every 6 days. This schedule guarantees measurements will fall on each day of the week, and results in approximately 60 measurements per year. The straight mean of these values is not used for comparison with the inhalation health benchmark because this could result in underestimating potential health effects. The upper 95% confidence limit of the mean was calculated if at least 45 of the measurements are completed and five or more include detections of respirable crystalline silica. This upper bound of the mean can then be compared to the inhalation health benchmark to assess the risk of human health effects.

National ambient air quality standards are developed by the U.S. Environmental Protection Agency from an analysis of many scientific studies. They set protective limits that include:

  • An air concentration level that is not to be exceeded
  • An averaging time over which concentrations are summarized (e.g., 1 year, 24 hours, 8 hours).
  • The form of the standard (e.g., annual mean, 98th percentile, not to be exceeded more than once).

The form of a standard includes the length of time that measurements must take place and the type of statistical summary to use. The form of a standard and the averaging time are applied to monitoring data to make an averaging statistic called a design value. The design value can then be compared to a standard’s concentration level to assess whether a site exceeds or violates the standard. Preliminary design values from each site are included in the individual site reports. To calculate true design values requires at least three years of continuous monitoring. A single measurement cannot be used to determine whether a site exceeds a standard.

HTML icon National Ambient Air Quality Standards (U.S. EPA)

Ambient air monitors were placed near the fence line of two sites at the Shakopee Sands facility (Jordan, Minn.) in the third quarter of 2012, and have been collecting:

  • total suspended particle (TSP)
  • particulate matter (PM10)
  • respirable crystalline silica (as PM10)*

The period of collection is not yet sufficient for a true comparison to the ambient air quality standards, so these data are considered preliminary at the current time. As of the date of the publication of the report linked below, these results were below the respirable silica health based value and did not suggest any exceedances of ambient air quality standards. We will continue to review and analyze these types of data as they are submitted.

There was very little activity at the site in 2012 until the fourth quarter, when construction, mining, blasting and stockpiling began:Quarter 3 2012 (July 2012 – September 2012): start-up of monitors prior to permit issuance

  • Quarter 4 2012 (October 2012 – December 2012): Permit issued October 19, 2013 for construction, mining, blasting, stockpiling
  • Quarter 1 2013 (January 2013 – March 2013): Construction, mining, blasting, stockpiling
  • Quarter 2 2013 (April, 2013 – June 2013): Construction, mining, blasting, stockpiling
  • Quarter 3 2013 (July, 2013 – September, 2013): Construction, mining, blasting, stockpiling
  • Quarter 4 2013 (October, 2013 – December, 2013): Construction, mining, blasting, stockpiling
  • Quarter 1 2014 (January, 2014 – March, 2014): Construction, mining, blasting, stockpiling
  • Quarter 2 2014 (April, 2014 – June, 2014): Construction, mining, blasting, stockpiling
  • Quarter 3 2014 (July, 2014 – September, 2014): Construction, mining, blasting, stockpiling
  • Quarter 4 2014 (October, 2014 – December, 2014): Construction, mining, blasting, stockpiling
  • Quarter 1 2015 (January, 2015 – March, 2015): Construction, mining, blasting, stockpiling
  • Quarter 2 2015 (April, 2015 – June, 2015): Construction, mining, blasting, stockpiling

Please click on the link below to open a more detailed report including air measurements, wind direction and speed, and comparisons to ambient air particulate measurements from other sites. This report is in the process of being updated, however, the charts below have the most current data.

Respirable Crystalline Silica Air Data

Shakopee Sands — Respirable Crystalline Silica Air Data

*Respirable crystalline silica is being collected as PM10, and compared to a health based value relevant to PM4. This is a conservative measurement to represent PM4, since PM4 particles are included in the PM10 mass.

Air Concentrations of PM10 Air Data

Shakopee Sands — Air Concentrations of PM10 Air Data

Measured Concentrations of Total Suspended Particulates Air Data

Shakopee Sands — Measured Concentrations of Total Suspended Particulates Air Data

Ambient air monitors were placed near the fence line of two sites at the Titan Lansing Transload facility (formerly known as the Tiller facility in North Branch, Minn.) in the second quarter of 2013, and have been collecting:

  • particulate matter (PM2.5)
  • particulate matter (PM10)
  • respirable crystalline silica (as PM4)

The period of collection is not yet sufficient for a true comparison to the ambient air quality standards, so these data are considered preliminary at the current time. As of the date of the publication of the report linked below, the high estimate of an annual mean was below the respirable silica health based value and the PM10 and PM2.5 data did not suggest any exceedances of ambient air quality standards. We will continue to review and analyze these types of data as they are submitted.

  • Quarter 2, 2013 (April 2013 – June 2013): Operation of silica sand processing facility
  • Quarter 3, 2013 (July 2013 – September 2013): Operation of silica sand processing facility
  • Quarter 4,, 2013 (October 2013 – December 2013): Operation of silica sand processing facility
  • Quarter 1, 2014 (January 2014 – March 2014): Operation of silica sand processing facility
  • Quarter 2, 2014 (April 2014 – June 2014): Operation of silica sand processing facility
  • Quarter 3, 2014 (July 2014 – September 2014): Operation of silica sand processing facility
  • Quarter 4, 2014 (October 2014 – December 2014): Operation of silica sand processing facility
  • Quarter 1, 2015 (January 2015 – March 2015): Operation of silica sand processing facility
  • Quarter 2, 2015 (April 2015 – June 2015): Operation of silica sand processing facility

Open the file below for a more detailed report including air measurements, wind direction and speed, and comparisons to ambient air particulate measurements from other sites. This report is in the process of being updated, however, the charts below have the most up to date data.

Measured PM2.5 Concentrations

Measured PM2.5 concentrations at Tiller

Measured PM10 Concentrations

Tiller — measured PM10 concentrations

 

Respirable Crystalline Silica (PM4) at the North Monitor

Respirable Crystalline Silica (PM4) at the North Monitor

Respirable Crystalline Silica (PM4) at the South Monitor

Respirable Crystalline Silica (PM4) at the South Monitor

Important Dates

  • Quarter 3, 2014 (July, 2014 – September, 2014): Air Quality permit acquired, finalizing Water Quality permit
  • Quarter 4, 2014 (October, 2014 – November, 2014): Construction
  • Quarter 4, 2014 (December 2014) - present: Construction, mining, blasting, stockpiling, operation of silica sand processing facility
  • Jordan Sands started their sand dryer and the final leg of processing on December 5, 2014.
  • Jordan Sands placed a sample saver on the air samplers to reduce passive loading on August 1, 2015
  • Jordan Sands agreed to six additional months of ambient air sampling on their fenceline commencing on March 1, 2017 and was completed on August 29, 2017.

Ambient air monitors were placed near the fence line of two sites (north and south) at the Jordan Sands facility (Mankato, Minn.) in the third quarter of 2014, and have been collecting:

  • Total Suspended Particulates (TSP)
  • Particulate Matter (PM2.5)
  • Particulate Matter (PM10)
  • Respirable Crystalline Silica (as PM4)

Based on data collected through August 26, 2017, respirable silica, PM10, and PM2.5 have been measured at levels below health concern. For the largest particles, TSP, monitoring has measured five exceedances of the Minnesota Ambient Air Quality Standard across the two monitoring sites. As a result of these exceedances, the south monitor at Jordan Sands violated the secondary daily TSP standard in 2014, but met the standard in 2015 and 2016. The north monitor has not violated the daily TSP standards.

Open the file below for a more detailed report including air measurements, wind direction and speed, and comparisons to ambient air particulate measurements from other sites. This report is in the process of being updated, however, the charts below have the most up to date data.

TSP Exceedences

To date, the monitors at Jordan Sands have recorded four exceedances of the secondary TSP standard at the South site (October 8, 2014, October 20, 2014, February 17, 2015, and February 17, 2015), and one measured exceedance of the secondary TSP standard at the North site (April 12, 2015). A monitoring site violates the TSP standard if two or more samples are greater than 150 µg/m3 (secondary standard) or 260 µg/m3 (primary standard) in a calendar year. As a result, in 2014, the South monitor violated the secondary daily TSP standard. Based on data currently available, in 2015-17, neither the North nor the South monitor have violated the secondary daily TSP standard. No other pollutant measurements exceeded ambient air quality standards or the respirable crystalline silica health based value.

 Measured TSP Concentrations

TSP Monitoring Results: Jordan Sands LLC — North Monitor

Jordan Sands — TSP concentration at north monitor

TSP Monitoring Results: Jordan Sands LLC — South Monitor

Jordan Sands — TSP concentration at south monitor

Measured Respirable Crystalline Silica (PM4) Concentrations

Respirable Crystalline Silica (RCS) Monitoring Results: Jordan Sands LLC — North Monitor

Jordan Sands — RCS concentration at north monitor

Respirable Crystalline Silica (RCS) Monitoring Results: Jordan Sands LLC — South Monitor

Chart showing Jordan Sands RCS south monitor results

Note: BDL indicates a sample was collected but the result was below the detection limit.

Measured PM2.5 Concentrations

Fine Particle Monitoring Results: Jordan Sands LLC — North Monitor

Jordan Sands — PM2.5 concentration at north monitor

Fine Particle Monitoring Results: Jordan Sands LLC — South Monitor

Jordan Sands — PM2.5 concentration at south monitor

Measured PM10 Concentrations

PM10 Monitoring Results: Jordan Sands LLC — North Monitor

Jordan Sands — PM10 concentration at north monitor

PM10 Monitoring Results: Jordan Sands LLC — South Monitor

Jordan Sands — PM10 concentrations at south monitor

 

The Minnesota Pollution Control Agency (MPCA) placed air monitors at the Family YMCA in downtown Winona from January 2014 to December 2014 and collected:

  • hourly fine particles (PM2.5)
  • respirable crystalline silica (as PM4)

The measured air concentrations were below the respirable silica health based value and did not suggest any exceedances of ambient air quality standards.

The document below includes a more detailed description of all of the reported results from the entire ambient air sampling effort in Winona and includes comparisons with wind direction and speed, and ambient air particulate measurements from other sites.

Respirable crystalline silica

Respirable crystalline silica (PM4 silica) samples were collected in Winona and at a reference site in Stanton, Minn. once every six days. Stanton was chosen as the reference site because it does not house silica sand related facilities or transportation, but does have other sources of airborne silica such as unpaved roads and farm fields. Airborne silica is a fairly ubiquitous pollutant and is not unique to silica sand mining and processing facilities.

The charts below summarize the final monitoring results (January 2014 – December 2014). At both monitoring sites the majority of crystalline silica results are below the detection limit, which means the amount of crystalline silica in the air was very low.

All of the detected crystalline silica samples are well below the chronic health benchmark of 3 ug/m3. The chronic health benchmark is set to protect against health effects associated with long term exposure to respirable crystalline silica. This suggests that crystalline silica levels in Winona and Stanton are not contributing to chronic health risks.

Concentration of Crystalline Silica as PM4 in Winona, Minn.

Concentration of Crystalline Silica as PM4 in Winona, Minn.

Concentration of Crystalline Silica as PM4 in Stanton, MN

Concentration of Crystalline Silica as PM4 in Stanton, Minn.

Fine particles (PM2.5)

Between January 1, 2014, and December 31, 2014, the monitor at Winona recorded one exceedance of the daily fine particle standard. (See graphic below.) This occurred on March 7, 2014, and was the result of a regional weather pattern that included a strong temperature inversion, light winds, and heavy fog. These weather conditions trap fine particle pollution near the surface, allowing concentrations to increase to unhealthy levels. A monitoring site may experience several exceedances each year without violating the air quality standard.

Winona daily fine particle results compared to the standard, January – December 2014

Daily Averages fro Winona PM2.5 Monitor

Summary of fine particle exceedance (March 7, 2014)

map of fine particle  concentrations for March 7, 2014, on an AQI scaleMap of fine particle concentrations for March 7, 2014 on an AQI scale

The map on the right depicts fine particle concentrations for March 7, 2014, on an AQI scale. The yellow and orange portions of the map are areas where fine particles were elevated. The daily fine particle concentration measured in Winona exceeded the daily fine particle standard, resulting in an air quality alert on March 7, 2014. This was the result of a weather pattern that impacted much of the central and eastern United States. On this day, the highest fine particle concentrations in the U.S. were centered over parts of Minnesota, Iowa, Wisconsin, Illinois and Indiana. Due to the regional nature of this event, the MPCA does not believe fine particle pollution associated with silica sand operations caused the exceedance in Winona. This is further illustrated in the charts at the very end of this report.

 

Fine Particle Data Comparison for Multiple Air Monitoring Sites

Daily fine particle concentrations: January 2014

Daily fine particle concentrations: January 2014

 

 

Daily fine particle concentrations: February 2014

Daily fine particle concentrations: Feb. 2014

 

 

Daily fine particle concentrations: March 2014

Daily fine particle concentrations: March 2014

 

Daily fine particle concentrations: April 2014

Daily fine particle concentrations: April 2014

 

Daily fine particle concentrations: May 2014

Daily fine particle concentrations: May 2014

 

Daily fine particle concentrations: June 2014

Daily fine particle concentrations: June 2014

 

Daily fine particle concentrations: July 2014

Daily fine particle concentrations: July 2014

 

Daily fine particle concentrations: August 2014

Daily fine particle concentrations: August 2014

 

Daily fine particle concentrations: September 2014

Daily fine particle concentrations: Sept. 2014

 

Daily fine particle concentrations: October 2014

Daily fine particle concentrations — October 2014

 

 

Daily fine particle concentrations: November 2014

Daily fine particle concentrations — November 2014

 

Daily fine particle concentrations: December 2014

Daily fine particle concentrations — December 2014