40 CFR 503: EPA Sewage Sludge (Biosolids) Standards

Regulatory citation: 40 CFR Part 503, Standards for the Use or Disposal of Sewage Sludge

What Are the Sewage Sludge Standards?

40 CFR Part 503 sets standards for sewage sludge that is applied to land, placed on a surface disposal site or fired in an incinerator. Sewage sludge is the solid, semi-solid or liquid residue from treating domestic sewage. EPA uses the term biosolids for sewage sludge treated to meet Part 503 and intended for land application.

The rule applies to anyone who prepares sewage sludge, applies it to land or owns or operates a surface disposal site or incinerator. Hazardous sludge, sludge with PCBs at or above 50 mg/kg, industrial sludge, grit and screenings and incinerator ash are excluded.

Why Biosolids Standards Matter

Biosolids recycle nutrients onto farmland, but untreated sludge can carry metals, pathogens and odors that attract vectors such as flies and rodents. Part 503 controls each of these risks.

Core Requirements

1. Meet Pollutant Ceiling Limits (503.13, Table 1)

Sludge applied to land must not exceed ceiling concentrations, on a dry weight basis, of 75 mg/kg arsenic, 85 cadmium, 4,300 copper, 840 lead, 57 mercury, 75 molybdenum, 420 nickel, 100 selenium and 7,500 zinc. Sludge must also meet cumulative loading rates (Table 2), monthly average pollutant concentrations (Table 3) or annual loading rates for bagged sludge (Table 4).

2. Reduce Pathogens to Class A or Class B (503.32)

Class A sludge must have fecal coliform below 1,000 Most Probable Number (MPN) per gram of total solids, or Salmonella below 3 MPN per 4 grams, and meet one of six treatment alternatives. Class B sludge can be shown by a geometric mean of seven samples below 2,000,000 MPN or colony forming units per gram, or by treatment in a Process to Significantly Reduce Pathogens.

3. Observe Class B Site Restrictions (503.32(b)(5))

Where Class B sludge is applied, food crops with harvested parts touching the soil mix cannot be harvested for 14 months. Food crops with harvested parts below the soil surface wait 20 months if the sludge stays on the surface for 4 months or more before incorporation, or 38 months if it stays less than 4 months. Animals cannot graze for 30 days. Public access is restricted for 1 year on land with high potential for exposure and 30 days on land with low potential.

4. Meet a Vector Attraction Reduction Option (503.33)

Options include reducing volatile solids by at least 38 percent, raising pH to 12 or higher for 2 hours and then 11.5 for 22 more hours, drying to at least 75 or 90 percent solids, injecting below the surface, or incorporating into soil within 6 hours. The options allowed depend on where the sludge goes.

5. Follow Management Practices (503.14)

Bulk sludge must not be applied where it is likely to harm threatened or endangered species, or to flooded, frozen or snow-covered land where it could reach wetlands or other waters. It must not be applied 10 meters or less from waters of the United States unless the permitting authority allows it, and must be applied at or below the agronomic rate. Bagged sludge needs a label or information sheet.

6. Monitor at the Required Frequency (503.16)

Monitoring frequency depends on the amount applied per 365-day period, in dry metric tons. It is once per year for under 290, quarterly for 290 to under 1,500, once every 60 days for 1,500 to under 15,000 and monthly for 15,000 or more.

7. Keep Records and Report Annually (503.17 and 503.18)

Most records must be kept for 5 years, and some cumulative loading records indefinitely. Class I sludge management facilities, POTWs with a design flow of 1 million gallons per day or more and POTWs serving 10,000 people or more must report each year by February 19. Reports are filed electronically.

Common Compliance Approaches

Sample on a Fixed Schedule

Set the sampling calendar from last year's tonnage and adjust it if output crosses a threshold.

Give Appliers Written Information

Preparers send land appliers the nitrogen content, pathogen class and site restriction details with each delivery.

Example: Biosolids Management in Practice

A regional wastewater plant serving 60,000 people produces about 2,000 dry metric tons of anaerobically digested Class B biosolids a year. It samples metals and pathogens every 60 days and shows 38 percent volatile solids reduction for vector attraction. A contract hauler injects the biosolids on farm fields and posts the site restrictions. The plant files its annual report electronically by February 19 and keeps its records for five years.

Related regulations: EPA General Pretreatment Regulations, EPA Industrial Stormwater, EPA Hazardous Waste Generators.

Note: EPA is the permitting authority for biosolids in most states. A few states are authorized to run the program, and many states add their own biosolids rules. Always check current Part 503 text and state requirements.

Frequently Asked Questions

What is the difference between Class A and Class B biosolids?

Class A biosolids meet strict pathogen density limits and one of six treatment alternatives. Class B biosolids meet a less strict standard, so the land where they are applied is subject to restrictions on harvesting, grazing and public access.

Who must file an annual biosolids report?

Class I sludge management facilities, POTWs with a design flow of 1 million gallons per day or more and POTWs serving 10,000 people or more.

Does Part 503 apply to industrial sludge?

No. Sludge from industrial processes, hazardous sludge and drinking water treatment sludge are excluded.