Ellen Z. Harrison, Director

Cornell Waste Management Institute

March 22, 2000
House Committee on Science Hearing on EPA and Sludge Rules

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Research Needs Pertaining to Land Application of Sewage Sludges

These are some areas in which additional research is needed. It is important to recognize that different soils, crops, sludges and sludge products will respond differently so that research results will vary depending on these and other variables. Research should be supported through an entity that is independent of the sludge stakeholders.

Sludge Quality and Variability

• Survey US sludges for additional contaminants (such as surfactants) and using improved analytic methods (as recommended by National Research Council)
• Analyze the temporal variability of quality and nutrient content of sludges from individual WWTPs. Quality varies significantly from sample to sample. Farmers and their advisors apply based on monitoring results not obtained from the particular sludge load being delivered and may thus over or under apply nutrients.

Nutrients

• At what rate does the N in selected sludges and sludge products become available as a plant nutrient?
• How variable over time is the N and P content and availability of N in sludge from particular treatment plants?
• What are the relationships between P availability and sewage treatment processes?

Groundwater Quality

• How much of trace metals applied in sludges and sludge products leaches through soils?
• What is the role in the movement of contaminants to groundwater of preferential flow through macropores?
• What is the role in the movement of contaminants to groundwater of facilitated transport by complexation of contaminants with organic matter?
• How much nitrogen applied in sludges, fertilizers and manures leaches through soils?
• Do pathogens applied in sludges leach through soils? Particularly viruses leaching from Class B sludges.
• What groundwater flow model will predict mobility of contaminants?

Crop Yield and Quality

• What are the yield responses of sensitive crops (like alfalfa) to sludge applied metals in long-term applications to acidic agricultural soils?
• What is the concentration of molybdenum and the Cu:Mo ratio in forage crops and pasture grown on agricultural soils in to which sludges have been added (both short and long term)? And what are the implications for dairy farms?

Surfactants

• At what levels are surfactants and their metabolites present in sludges and in soils to which sludges have been applied?
• What is their fate when land applied?
• Are they volatilized during sludge composting and other treatment processes?

Aerosols and Health

• To what chemicals and pathogens are people exposed from aerosols and volatile emissions from land applications and sludge processing sites and what are the health risks associated with those exposures?

Pollution Prevention/Sludge Quality

• What are the sources that are responsible for concentrations of particular contaminants of concern in sludges?
• What can be done to reduce or eliminate the discharge of those pollutants into WWTP?

Testing and Monitoring

• What analytic methods will detect and quantify (if necessary) infective viruses and other pathogens?
• What analytic methods are appropriate for monitoring movement to groundwater?
• What analytic methods are appropriate for monitoring soils contaminants and their bioavailability?

Risk Assessment

• What is the impact on soil microbial system of long term sludge additions?
• What is the impact on wildlife exposed to sludge-treated systems?
• What are the likely exposures and impact of those exposures to the dairy farm family.
• Need to address multiple exposure pathways being experienced simultaneously (drinking water, breathing air, eating dairy, meat and vegetables, ingesting soil).
• Need to reassess direct ingestion risk since dioxin risk assessment uses 400mg/day ingestion rate and TSD used 200mg/day and since direct ingestion was the most limiting pathway for a number of the contaminants. Also need to evaluate the potential for acute toxicity from one-time high ingestion days.
• Need to apply probabilistic vs. deterministic methods of risk assessment

Alternative Uses

• What other uses might be made of sludges that would pose fewer risks?