The Department of Environmental Quality implements a statewide program that encourages the beneficial use of biosolids in a manner to protect public health and maintain or improve environmental quality. Almost all the biosolids generated by domestic wastewater treatment facilities in Oregon are applied to the land for agriculture, silviculture, and horticulture use. All wastewater facilities operate under either a National Pollutant Discharge Elimination System or Water Pollution Control Facility permit.
What are biosolids and how are they used?
Biosolids are a nutrient-rich byproduct of sewage treatment that can be used as a natural fertilizer and a sustainable alternative to commonly used chemical fertilizers. Biosolids are also used to improve soil structure, which improves growing conditions. Before application, disease-causing organisms and potentially toxic metals present in biosolids must be removed or reduced to safe levels.
How biosolids are regulated
Oregon Administrative Rules Chapter 340, Division 50 incorporate by reference many of the federal biosolids regulations from 40 CFR Part 503, including limits for trace pollutants.
- OAR Chapter 340, Division 50 - Land Application Of Domestic Wastewater Treatment Facility Biosolids, Biosolids Derived Products, And Domestic Septage
- 40 CFR Part 503 - Standards for the Use or Disposal of Sewage Sludge
Biosolids are regulated under DEQ's water quality program, specifically through a National Pollutant Discharge Elimination System or Water Pollution Control Facility permit, a biosolids management plan, and site authorization letters. The permit, management plan, and site authorization letters are specific to a facility and include conditions that are relevant to both state and federal biosolids regulations. The conditions in the management plan and site authorization letters are considered an integral part of the permit and thus are enforceable.
DEQ requires permittees to take the following measures to safely use biosolids on farms:
The cities must process and store biosolids for a specific length of time and under certain conditions to allow disease-causing organisms to die off. They must also dry biosolids to reduce odors and moisture so as to not attract pests (rats, mosquitoes, etc.).
To ensure that biosolids are processed correctly, the cities test their biosolids annually for E. coli, nutrients and metals and report these results to DEQ annually along with information about their biosolids applications. Metals that are routinely tested for include arsenic, cadmium, copper, mercury, nickel, molybdenum, lead, selenium, and zinc. DEQ does not require the cities or farmers to take samples of the Siletz River. If cities comply with their DEQ permit requirements, runoff of biosolids to the river should not occur.
To prevent over-application of nutrients, DEQ uses Oregon State University’s fertilizer guide to set appropriate levels of nitrogen allowed on fields to grow different crops; this is known as the agronomic rate. If a DEQ permittee applies biosolids on the same area for two out of three years at the agronomic rate for nitrogen, DEQ requires the permittee to test soil conditions to ensure they are not overloading the land with nutrients. If they are applying at lower than the agronomic rate, soil sampling is not required by DEQ permit. If carryover nitrogen levels in the soil are observed above the level set by DEQ, biosolids applications must be reduced or stopped until the nitrogen soil levels are reduced by plant uptake.
DEQ also requires applications to be at least 200 feet from drinking water wells and establishes setbacks for surface waters, residences and property lines on a site-specific basis. Grazing animals must be kept off application sites for at least 30 days and milk-producing animals for 90 days, but there is no requirement to keep wild animals off of sites because it would be impractical. DEQ is also not aware of any problems that occur in elk or other wild animals exposed to biosolids.