Skip directly to search Skip directly to A to Z list Skip directly to site content

DISCUSSION

The MPCA has addressed the more acute and serious concern of explosive hazards at the site by venting the landfill gas through an on-site passive venting system. Monitoring points at the perimeter of the landfill are measured to ensure a significant amount of landfill soil gas is not moving off-site. Therefore, the area where the proposed high school is planned is unlikely to be at risk from explosive gas emanating from the landfill. However, the venting of landfill gas to the ambient air has created a potential secondary health concern.

One consequence of releasing landfill gas to ambient air is that relatively small amounts of NMOCs released in the gas could represent a health concern. MDH used a USEPA screening model to estimate air concentrations of specific NMOCs at the proposed school site. The results indicate those NMOCs most likely to represent a concern (benzene, vinyl chloride, EDB and chloroform) are below levels of health concern.

However, there is uncertainty surrounding the inputs used in the model. There is a small possibility that NMOC levels of health concern occur in the area of the proposed school site. In order for this to be true, NMOC concentrations in the landfill gas would have to often be substantially higher than levels detected during the single air sampling event used for the modeling analysis. In addition, these substantially higher levels would have to be sustained over the long-term since only chronic exposures are of concern. It is unknown if these higher NMOC concentrations could be sustained over the long-term. One way to reduce this data gap is for more data collection.

Landfill gas production, site specific exposure scenarios, and site specific terrain can vary widely among Minnesota landfills. For example, the Kummer Landfill was assumed to emit 0.87 megagrams of NMOCs per year (Mg/yr) and the average landfill is estimated to 68.2 Mg/yr of non-methane organic carbon (Maier and Tam 1994). The MPCA is required to apply for a New Source Performance Standard (NSPS) permit for a landfill venting system when a landfill is estimated to emit more than 2.5 Mg/yr of NMOCs. Landfills needing a permit often have active gas extractions systems installed along with and enclosed flaring system. The enclosed flare is very efficient at destroying NMOCs.

The risk of NMOC ambient air concentrations at levels of health concern in the area of the proposed school appears to be small. However, this evaluation of the Kummer Landfill indicates that landfills with NMOCs emission rates less than 2.5 Mg/yr and passive venting systems may sometimes represent a health concern, depending on site specific variables like nearby terrain, potential exposure scenarios, and specific NMOC concentrations emitted from the landfill. For instances, if a passive venting system was located at a lower elevation than the Kummer passive venting system, estimated air pollutant concentrations would be significantly higher in the surrounding area. In addition, the USEPA screening model also predicts that NMOC concentrations would be approximately 3 times higher if the NMOC emission rate were increased from the estimated of 0.87 Mg/yr to 2.5 Mg/yr. Either one of these scenarios would increase the lifetime cancer risk.

Agency for Toxic Substances and Disease Registry (ATSDR) Child Health Initiative

ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children are of special concern in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing organ systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.

The health based criteria used in this evaluation are generally meant to protect sensitive sub-populations, including children who may live near the facility. However, it is worth noting that some laboratory animal data indicate vinyl chloride is more toxic when maturing animals are exposed than when fully mature animals are exposed (USEPA 1995b). These data underline MDH's concern about vinyl chloride.

CONCLUSIONS

  • Two health issues related to building a school near the Kummer Landfill were identified. The first is the formation of explosive gas by the landfill and its potential to migrate in the soil to the proposed school and accumulate within it. The MPCA has effectively addressed the more acute and serious concern of explosive hazards at the site by venting the landfill gas through on-site passive vents to the ambient air. The result is that the landfill gas is unlikely to migrate off-site through the soil.

  • The second is the risk associated with breathing air at the proposed site that may be contaminated with NMOCs from landfill gas vented to ambient air. Use of a USEPA air screening model indicates that NMOC air emissions from the landfill represent no apparent public health hazard to individuals located on the proposed school site. However, there is uncertainty surrounding the inputs to this model, so our confidence in this conclusion is not as high as we would like. In order to better determine air pollutant concentrations at the proposed school site more data collection and/or refined modeling would be necessary.

RECOMMENDATIONS

  • MDH recommends that annual sampling of NMOCs from the Kummer Landfill be conducted to determine if NMOCs, particularly vinyl chloride and EDB, increase substantially. The USEPA screening model indicates sustained emissions of NMOCs in Kummer landfill gas that have EDB concentrations greater than approximately 1,500 mg/m3 and vinyl chloride concentrations greater than approximately 8,000 mg/m3 may result in a cancer risk that is above what MDH considers negligible in the area of the proposed school site.

  • MDH has submitted a memorandum summarizing the results of this evaluation to the Bemidji school district, to inform their decision making process.

Document Prepared by:

Mark Staba, Health Assessor
Site Assessment and Consultation Unit
Minnesota Department of Health
Tel: 612-215-0913
Rich Soule, Hydrogeologist
Site Assessment and Consultation Unit
Minnesota Department of Health
Tel: 612-215-0917

 

Next Section     Table of Contents

  
 
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #