Ken Kirk, Executive Director
Association of Metropolitan Sewage Agencies
Albert Gray, Deputy Executive Director
Water Environment Federation
601 Wythe Street
Alexandria, Virginia 22314

Dear Messrs. Kirk and Gray:

Thank you for your letter of October 31, 2000, in which you expressed some concerns about the National Institute for Occupational Safety and Health (NIOSH) Hazard ID Number 10: Workers Exposed to Class B Biosolids During and After Field Application. I have consulted with our scientists and their comments are incorporated into this letter to address the issues that you raised. In particular, you had concerns about the NIOSH recommendations to minimize storage time for dewatered Class B biosolids, recommendations for incorporation of biosolids into the soil and recommendations to avoid mechanical disturbance of field-applied biosolids. In addition, you raised several points related to risk assessment, risk management, and the perceived regulatory impact of NIOSH recommendations for worker protection. You also suggested that the Hazard ID does not adequately address risk assessment issues and that it creates additional regulatory burdens without having gone through formal rulemaking procedures.

The Hazard ID was never intended to be a comprehensive review or risk assessment of all issues associated with biosolids use and was limited by format to four pages in length. Its purpose was to identify worker exposure issues and to recommend prudent public health measures that could be applied to reduce workers' risk. Hazard IDs are intended to be brief user-friendly documents that summarize results of NIOSH studies at a specific worksite, that identify new or current health and safety hazards, and offer the best recommendations for control or prevention.

NIOSH does not have statutory authority to promulgate occupational safety and health regulations. The responsibility for promulgating such rules is vested in the Occupational Safety and Health Administration by the OSHA Act of 1970, and in the Mine Safety and Health Administration by the Mine Safety and Health Act of 1977. It is the Institute's responsibility to make recommendations to those agencies, and to disseminate guidance for worker protection. In our opinion, we feel that Hazard ID #10 does this for workers exposed to Class B biosolids. We do not feel a revision to the Hazard ID is warranted.

Our-response to your specific concerns follow:

1. Storage Time for Dewatered Class B Biosolids.

One concern is the NIOSH recommendation to minimize storage time for dewatered filter cake at the treatment facility and in the field to prevent the regrowth of pathogens. In your letter, you state that storage is part of the biosolids treatment process and that sludge drying and lagooning are acceptable treatment practices that reduce pathogen concentration. The NIOSH recommendation which is intended to protect workers at Class B biosolids land application sites, pertains to storage of dewatered filter cake. The NIOSH recommendation is not intended to address storage of liquids in tanks, lagoons, or storage of properly stabilized biosolids. The recommendation is made because there are few safeguards in place to alert workers when handling biosolids during periods of peak microbial activity such as in the case of "blooms." Minimizing storage time at both the sewage treatment facility and in the field will serve to reduce the probability of regrowth of pathogenic organisms and other opportunistic environmental organisms that could also present a hazard to the workers.

We did locate the quote you provided from the USEPA/USDA "Biosolids Field Storage Guide" on page 33 of the document. It is interesting to note that the quote actually addresses the potential for growth of organisms during storage of Class A biosolids. The discussion makes it clear that bacterial regrowth can occur during storage under certain conditions, and this is also assumed for Class B biosolids. We agree that this guide contains more detailed information on conditions conducive to pathogen growth and the need for various management practices when biosolids are stored. The guide does recognize the need to increase management oversight as storage time increases. We will reference the guide, where applicable, in future reports.

2. Soil Incorporation of Class B Biosolids

Another concern is the use of the term "where feasible" in regard to soil incorporation of biosolids. In your letter you recommended substitution with the term "where availability of equipment, soil conditions, and types of crops allow." We agree that there are instances, such as the application of biosolids on no-till pasture land, where soil incorporation may not be feasible. Also, upon initial distribution of the material on the land, there will be a period of time when the biosolids are not yet incorporated. For these situations, Hazard ID #10 recommends the use of personal protective equipment by workers exposed to such land-applied biosolids. Additionally, in the "Recommendations for Prevention" section, the use of the term "should" in the current document is sufficient to maintain emphasis on the best practice of soil incorporation while allowing for other alternatives. Recognizing the plain English definition of feasible as "capable of being done or accomplished," combined with the fact that the NIOSH Hazard ID has no regulatory authority, should alleviate the concern over legal interpretations.

For vector control an acceptable alternative to soil incorporation is outlined in the EPA regulations, i.e. injection below the surface of the land [40 CFR 503.33(a)(5) and 503.33(b)(9) and (10)]. Although acceptable to NIOSH as a control that would be protective of workers, the omission of this option does not warrant modification of the Hazard 1D.

3. Avoidance of Mechanical Disturbances

Another concern you raised is that the public might interpret the NIOSH recommendation for workers to avoid mechanical disturbance of applied Class B Biosolids during the restricted period as a suggestion to the general public for the need for signs, fencing, and other restrictions. The EPA has 1-year site restrictions for the general public for handling soil from fields and walking in fields where biosolids have been applied. We feel that the

NIOSH Hazard ID recommendation is clearly directed to workers who have access during the restricted period and that it is based on prudent public health practice; avoiding mechanical disturbance of applied biosolids will minimize exposures.

4. Key Points and Description of the Hazard

You question whether the NIOSH recommendation to "implement engineering controls and work practices that minimize employee exposure to biosolids aerosols" is justified based on NIOSH findings of the presence of enteric bacteria in LeSourdesville samples. You also state that "No conclusive evidence or objective data are cited that indicate wastewater treatment plant workers, including those that handle processed or unprocessed sewage sludge/biosolids, are at any greater risk than workers in other industries."

There are no occupational exposure standards for bioaerosols in the U.S. The NIOSH approach to assess bioaerosol exposure includes assessing symptoms, monitoring potential sources, and applying professional judgement. Even when investigators work from testable hypotheses and well-formulated sampling plans, results from bioaerosols monitoring are often inconclusive.

5. General Comment

You requested that we modify the hazard ID to differentiate between perceived risk, risk assessment, and managing risk and that we clarify the misconception that the NIOSH report is a risk assessment. The basis for the request is that "properly treated sludge (biosolids) is safe for the public and the environment when managed according to federal standards." NIOSH states in the Hazard ID: "Whereas EPA rules restrict public access to treated lands in order to protect public health, these rules do not apply to workers involved with applying biosolids to land. The recommendations in this document are intended to provide guidance to employers and workers to minimize occupational risks from Class B biosolids through the use of engineering controls, personal protective equipment, and worker training. These recommendations are not intended to address non-occupational exposure." The above statement adequately reflects the basis for recommendations made in the document and we feel that further clarification is unnecessary.

6. NIOSH's Hazard ID #10 Extends Beyond Guidance

You question whether the NIOSH Hazard ID puts forth additional burdens on publicly owned treatment works (POTW) in terms of minimizing storage time, incorporation into soil, and avoidance of mechanical disturbances, that exceed current regulatory requirements for biosolids reuse. NIOSH is not a regulatory agency and our recommendations do not have the force of law. The recommendations contained in the Hazard ID do reflect what we believe to be best work practices to protect the health of workers.

In closing, let me again thank you for your letter. We will be continuing our research into the storage and application of Class B Biosolids. If future findings persuade us that more detailed reports are warranted, we may further address the mentioned topics in your letter.