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The Bemidji Public School System was considering constructing an elementary school between Grant and Gould Avenues and north of First Street (Figure 1). A Georgia Pacific Hardboard plant is located approximately 2000 feet west-northwest of the school site on Nymore Beach Road. As a precaution, the Superintendent of the Bemidji Public Schools requested the Minnesota Department of Health (MDH) conduct an assessment to determine if future students and staff could be exposed to plant air emissions at levels of health concern. Based in part on MDH conclusions, the Bemidji Public Schools has determined not to build a school at the proposed site (Bemidji Public Schools 1998). This document summarizes the investigation conducted by MDH.

Initial Data Analysis

Originally MDH analyzed emissions data submitted by Georgia Pacific to the Minnesota Pollution Control Agency (MPCA) (MPCA 1994). Data were compared with health based screening guidelines developed by the MPCA (MPCA 1997a). The guidelines indicated several contaminants as potentially above health based criteria near the plant (Table 1). While acetaldehyde emissions appear, in Table 1, to be greater than the screening guidelines, exceedances by particulate matter less than 10 microns (PM10), formaldehyde, and acrolein are proportionally far larger. These three contaminants were selected for further analysis.

Table 1:

Pollutants Above MPCA Health Based Screening Guidelines 1
Contaminant MPCA Emissions Screening Guideline2 Assuming Downwash (lbs/yr) Current Emissions reported by Plant (lbs/yr) Potential Emissions Reported by the Plant (lbs/yr)
















Nitrogen dioxide


6,100 (total NOx)

31,400 (Total NOx)

1. Stack #14 Emissions are excluded since this stack is not longer in operation.

2. Maximum emissions which are conservatively modeled to result in annual concentrations no higher than the health standard

These screening values are based on health standards. The standard for PM10 is a National Ambient Air Quality Standard (NAAQS). PM10 is sometimes referred to as a criteria pollutant. The NAAQS is based on both studies of human populations exposed to high levels of the pollutant and laboratory animal studies. The standard is set at a level that is thought to protect sensitive groups of individuals from adverse health effects but not necessarily the most sensitive members of that group (USEPA 1995b).

Some health effects associated with exposures at levels above the health standard for PM10 include respiratory problems, aggravation of existing respiratory and cardiovascular disease, alterations in the body's defense systems against foreign materials, damage to lung tissue, and carcinogenesis (USEPA 1997b). The 24 hour and annual standards are in place to ensure these effects do not occur. If levels exceeded the PM10 standard near the facility, health effects may be measurable in exposed populations.

The health standards for acrolein and formaldehyde are draft Health Risks Values (HRVs) established by MDH. The HRVs are currently in a process leading to promulgation in Minnesota Rules. The draft HRV for acrolein is based on sub-chronic exposure (exposures of three month duration or less). The HRV protects sensitive populations from upper respiratory problems. Air concentrations at or below the HRV are considered by MDH to be safe.

The HRV for formaldehyde is based on carcinogenicity. At air concentration less than or equal to the draft HRV, MDH considers the cancer risk to be negligible even if an individual is exposed for a lifetime. MDH considers a lifetime risk of 1 in 100,000 to be negligible. This means that if 100,000 people were exposed to formaldehyde at a concentration equal to its chronic HRV over a lifetime, no more than 1 individual would be expected to develop cancer as a result. To keep this in perspective, approximately half of all Minnesotans are expected to develop cancer in their lifetime.

The HRVs are based on conservative assumptions and are meant to ensure that the public health is protected. Emissions from industrial facilities can be conservatively modeled to project ambient air concentrations of hazardous compounds. An initial screening compares MPCA Screening Guidelines, which have been demonstrated by conservative modeling to be protective of human health, with reported stack emissions from a facility. Since this is an initial screening, emissions as well as site-specific modeling characteristics, are typically over estimated. For the Georgia Pacific facility, the initial reported emissions were significantly above the MPCA Screening Guidelines for four of the five pollutants reviewed. Therefore, it was necessary to conduct a more thorough investigation of the actual emissions from the facility.

Screening Model

The emissions data in Table 1 were estimates provided by Georgia Pacific. Georgia Pacific submitted emission estimates for each chemical to be analyzed that were two standard deviations above the mean of 3 stack tests. MPCA staff determined these emissions estimates were unreasonably high (MDH 1998a). Therefore, Georgia Pacific submitted emissions estimates to MDH based on the means of the stack tests for three of the contaminants of greatest concern (formaldehyde, PM10 and acrolein).

After receiving the revised emissions estimates from Georgia Pacific, MDH used these and other data supplied by Georgia Pacific to estimate air contaminant concentrations near the plant. MDH used a U.S. Environmental Protection Agency (USEPA) Screening Model (USEPA 1995a). If a pollutant concentration estimated by the screening model exceeds the MDH draft HRV it does not necessarily mean that air concentrations at the proposed school site are above health based criteria. It does mean that more refined analysis and/or air monitoring may be advised.

The model was used to estimate air concentrations of pollutants from the plant at 200 meters and 700 meters using both current emission estimates from the plant and potential maximum emissions. The proposed school site is approximately 700 meters from the plant and residential housing is approximately 200 meters from the plant. The model does not include pollutants that may originate from other sources. The results of this modeling were reviewed by MPCA staff and are listed below in Tables 2 and 3.

Table 2.

Estimates of Annual and (less than annual) Average Air Concentrations Near the Georgia Pacific Plant Assuming Current Emissions from Plant (µg/m3)
Contaminant Health Standard (mg/m3) Air Concentration at 200 meters Air concentration at 700 meters


150 (24 hr)


93.3 (24 hr)


33.2 (24 hr)


0.07 (less than 3 mo.)







Table 3.

Estimated Annual and (less than annual) Average Air Concentrations Near the Georgia Pacific Plant Assuming Maximum Potential Emissions from Plant (µg/m3)
Contaminant Health Standard (mg/m3) Air Concentration at 200 meters Air concentration at 700 meters


150 (24 hr)


222.3 (24 hr)


73.5 (24 hr)


0.07 (less than 3 mo.)







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