13.3 Biosolids Quality, Land Application Rules & OAR 340-050 / 40 CFR 503

5.3 Biosolids Quality, Land Application Rules & OAR 340-050 / 40 CFR 503

The transformation of municipal sewage sludge into beneficial, nutrient-rich biosolids is subject to some of the most rigorous public health and environmental protection standards in environmental engineering. In the State of Oregon, biosolids handling and land application are governed under a dual regulatory framework: the federal Clean Water Act Section 405(d) standards codified at 40 CFR Part 503, and the state regulations administered by the Oregon Department of Environmental Quality (DEQ) under Oregon Administrative Rules (OAR) Chapter 340, Division 050.

Certified operators must understand that while federal 503 rules establish baseline national criteria, Oregon DEQ adds state requirements on top of the federal criteria: written site authorizations, DEQ-approved biosolids management plans, annual reporting, and best management practices for site selection and application.

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The Dual Regulatory Framework: Federal vs. Oregon DEQ

 ┌────────────────────────────────────────────────────────────────────────┐
 │                     BIOSOLIDS REGULATORY HIERARCHY                     │
 │                                                                        │
 │                 U.S. EPA REGION 10 (40 CFR PART 503)                   │
 │                 - Promulgated under Clean Water Act § 405              │
 │                 - National Baseline Standards                          │
 │                 - Class A / Class B Pathogen Criteria                  │
 │                 - Vector Attraction Reduction (10 Options)             │
 │                 - Trace Metal Pollutant Limits (Tables 1-4)            │
 │                                  │                                     │
 │                                  ▼                                     │
 │                OREGON DEQ (OAR CHAPTER 340, DIVISION 050)              │
 │                - State rules; EPA keeps Part 503 authority             │
 │                - Mandatory Biosolids Management Plans (BMP)            │
 │                - Individual Written Site Authorizations                │
 │                - Agronomic Nitrogen Rate Enforcement (PAN)             │
 │                - Site BMPs: buffers, groundwater depth          │
 │                - Annual report to DEQ by February 19         │
 └────────────────────────────────────────────────────────────────────────┘

Sewage Sludge vs. Biosolids: The Legal Distinction

Under both federal and state definitions, raw or un-stabilized solids removed from municipal wastewater treatment processes are legally defined as sewage sludge. The term biosolids is legally reserved only for sewage sludge that has undergone proven physical, chemical, or biological stabilization processes that satisfy three non-negotiable regulatory gates:

1. Pathogen Reduction: Class A or Class B pathogen standards.
2. Vector Attraction Reduction (VAR): Destroying putrescible organics or establishing physical barriers so that disease vectors (flies, mosquitoes, rodents, birds) are not attracted to the material.
3. Trace Metal Pollutant Limits: Complying with ceiling concentrations and cumulative pollutant loading thresholds.

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Pathogen Reduction: Class A vs. Class B Biosolids

Pathogens include enteric viruses, pathogenic bacteria (Salmonella, Shigella, E. coli), and viable helminth ova (Ascaris lumbricoides). Federal and Oregon rules divide treated residuals into two pathogen classes based on treatment intensity and allowable public exposure:

+----------------------------------------------------------------------------------------------------+
|                                CLASS A VS. CLASS B BIOSOLIDS CRITERIA                              |
|                                                                                                    |
|  CLASS A BIOSOLIDS                                    CLASS B BIOSOLIDS                            |
|  - Standard: Pathogens reduced to below               - Standard: Pathogens significantly reduced; |
|    detectable limits                                    viable indicator bacteria remain           |
|  - Microbial Criteria:                                - Microbial Criteria:                        |
|    • Fecal Coliform: < 1,000 MPN / g dry solids, OR     • Fecal Coliform: Geometric mean of        |
|    • Salmonella: < 3 MPN / 4 g dry solids               7 discrete samples < 2,000,000 MPN/g TS    |
|  - Treatment Technique:                               - Treatment Technique:                       |
|    • Processes to Further Reduce Pathogens (PFRP)       • Processes to Significantly Reduce        |
|  - Public Distribution:                                 Pathogens (PSRP)                           |
|    • Unrestricted public distribution if EQ           - Public Distribution:                       |
|    • Sold in bags/bulk for gardens, lawns, turf         • Strictly controlled bulk agricultural use|
|  - Site Restrictions: None required                     • Mandatory site and public access bans    |
+----------------------------------------------------------------------------------------------------+

1. Class A Pathogen Standards & PFRP Technologies

To qualify as Class A, biosolids must reduce pathogens to levels below standard analytical detection limits. Pathogen densities at the time of discharge must satisfy:

• Fecal Coliform Density: Less than $1,000 \text{ MPN}$ (Most Probable Number) per gram of total dry solids, OR
• Salmonella sp. Bacteria Density: Less than $3 \text{ MPN}$ per $4 \text{ grams}$ of total dry solids.

Class A status is achieved by meeting one of the Part 503 Class A alternatives along with the density limits. The alternatives include the Processes to Further Reduce Pathogens (PFRP) in Appendix B and the time-temperature and high-pH options:

1. Thermophilic Composting: Utilizing within-vessel composting or aerated static pile systems where temperatures are maintained at $\ge 55^\circ\text{C}$ ($131^\circ\text{F}$) for at least 3 consecutive days. For open windrow composting, the temperature must be kept at $\ge 55^\circ\text{C}$ for at least 15 consecutive days, during which the windrow must be turned a minimum of 5 complete times.
2. Thermal Heat Drying: Subjecting cake to direct or indirect heat drying to reduce moisture to $<10\%$ ($>90\%$ total solids) where the internal particle temperature exceeds $80^\circ\text{C}$ ($176^\circ\text{F}$).
3. High pH-High Temperature Treatment (Class A Alternative 2): Alkaline material raises the pH above $12$ for at least 72 hours, with the temperature above $52^\circ\text{C}$ for at least 12 hours of that time, followed by air drying to over 50 percent solids. This is a Class A alternative, not one of the Appendix B PFRPs.
4. Thermophilic Aerobic Digestion (TAD): Slurry is agitated and aerated at $55^\circ\text{C} \text{ to } 60^\circ\text{C}$ with a minimum mean residence time of $10 \text{ days}$.

2. Exceptional Quality (EQ) Biosolids

Biosolids that achieve Exceptional Quality (EQ) status represent the gold standard of solids management. To earn an EQ rating, biosolids must satisfy three criteria:

1. Class A Pathogen Reduction (PFRP verified).
2. Pollutant Concentration Limits (Table 3 trace heavy metals).
3. Vector Attraction Reduction (satisfying one of the processing VAR Options 1 through 8).

3. Class B Pathogen Standards & PSRP Technologies

Class B criteria ensure that pathogens are significantly reduced, though substantial bacterial populations remain. Fecal coliform density must achieve a geometric mean of less than $2,000,000 \text{ MPN}$ (or CFU) per gram of total dry solids based on 7 discrete grab samples collected at the time of beneficial use.

Class B status is achieved via Processes to Significantly Reduce Pathogens (PSRP):

1. Anaerobic Digestion: Maintained at $35^\circ\text{C} \text{ to } 55^\circ\text{C}$ ($95^\circ\text{F}$) for an SRT of at least $15 \text{ days}$, or at least $60 \text{ days}$ at $20^\circ\text{C}$.
2. Aerobic Digestion: Mean cell residence time times temperature between $40 \text{ days}$ at $20^\circ\text{C}$ and $60 \text{ days}$ at $15^\circ\text{C}$.
3. Lime Stabilization: Sufficient lime added to raise pH to $>12$ after 2 hours of contact.
4. Air Drying: Liquid sludge dried on sand beds for a minimum of $3 \text{ months}$, during which ambient daily temperatures exceed $0^\circ\text{C}$ for at least 2 of those months.

Mandatory Class B Site Restrictions

Because Class B biosolids contain viable pathogens, land application is restricted exclusively to authorized agricultural fields, rangelands, or forest plantations subject to strict post-application waiting periods:

• Public Access Restrictions:
  • Land with low potential for public exposure (private farmland, timberland): public access prohibited for at least $30 \text{ days}$.
  • Land with high potential for public exposure (public parks, golf courses, turf farms, athletic fields): public access prohibited for at least $1 \text{ full year}$ ($12 \text{ months}$).
• Animal Grazing Restrictions: Grazing of livestock animals (dairy cows, beef cattle, sheep) whose meat or milk is consumed by humans is prohibited for at least $30 \text{ days}$ following application.
• Food Crop Harvesting Restrictions:
  • Crops with harvested parts below ground (root crops: potatoes, carrots, radishes, onions) where biosolids remain on the ground surface $\ge 4 \text{ months}$ prior to incorporation: harvesting prohibited for $20 \text{ months}$.
  • Root crops where biosolids are incorporated into the soil $< 4 \text{ months}$ after application: harvesting prohibited for $38 \text{ months}$.
  • Crops with harvested parts touching the ground surface (strawberries, melons, cucumbers, squash): harvesting prohibited for $14 \text{ months}$.
  • Feed, fiber, and food crops whose harvested parts do not touch the ground (field corn, wheat, barley, tree apples, hazelnuts): harvesting prohibited for $30 \text{ days}$.

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Vector Attraction Reduction (VAR) Standards

Vectors—including houseflies, blowflies, mosquitoes, rodents, and seagulls—can transfer pathogens from applied sludge directly to humans or livestock. Vector Attraction Reduction (VAR) requires either biologically reducing volatile organics or creating a physical barrier between the biosolids and potential vectors. 40 CFR 503.33 specifies 10 compliance options:

Calculating Volatile Solids Reduction: The Van Kleeck Formula

Under VAR Option 1, digested biosolids must achieve at least $38\%$ Volatile Solids Reduction (VSR). Because fixed (mineral ash) solids pass through the digester completely unchanged while volatile organic solids are destroyed and converted into biogas, calculating VSR by simply subtracting raw and digested volatile percentages is mathematically invalid.

Operators must calculate VSR using the Van Kleeck Formula, which accounts for the conservation of fixed mineral solids:

$\% \text{ VSR} = \left[ \frac{\text{VS}_{\text{in}} - \text{VS}_{\text{out}}}{\text{VS}_{\text{in}} - (\text{VS}_{\text{in}} \times \text{VS}_{\text{out}})} \right] \times 100$

Where:

• $\text{VS}_{\text{in}}$ = Volatile solids of raw sludge feed, expressed as a decimal fraction of total solids.
• $\text{VS}_{\text{out}}$ = Volatile solids of digested sludge, expressed as a decimal fraction of total solids.

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Trace Metal Pollutant Limits

40 CFR Part 503.13 and OAR 340-050 regulate nine toxic heavy metals. Municipal sludges that exceed these limits present chronic risks of phytotoxicity to crops and bioaccumulation in human and animal food chains:

The Three Metal Limit Categories

1. Ceiling Concentration Limits (Table 1): Absolute statutory ceilings. If a batch of biosolids exceeds the ceiling concentration for even one metal, that material CANNOT be land-applied anywhere under any regulatory program; it must be disposed of in a municipal solid waste landfill or incinerated.
2. Pollutant Concentration Limits (Table 3): Conservative monthly average limits required for Exceptional Quality (EQ) certification. Biosolids with metal concentrations below Table 3 are exempt from cumulative site tracking.
3. Cumulative Pollutant Loading Rates (CPLR - Table 2): The maximum lifetime mass of heavy metals that can ever be applied to a specific acre of agricultural land. For non-EQ bulk biosolids, the utility must maintain detailed GIS records tracking cumulative metal additions. Once a farm field reaches the CPLR limit for any single metal (most frequently copper or zinc), no further non-EQ biosolids may ever be applied to that site.

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Oregon DEQ Biosolids Management Rules (OAR Chapter 340, Division 050)

OAR 340-050 adopts the Part 503 land-application standards (pollutant limits, a pathogen class, a vector attraction option and management practices) and adds Oregon procedures.

1. Biosolids management plans (OAR 340-050-0031)

Anyone who will land-apply biosolids or domestic septage submits a solids management plan for DEQ approval, normally at least 60 days before land application begins. The plan becomes an enforceable condition of the NPDES, WPCF or solid waste permit. It must describe:

• the treatment processes, solids removal, thickening, digestion and dewatering, with annual solids quantities;
• how pathogen reduction and stability are achieved, with supporting data;
• storage, transport and application methods;
• a monitoring program covering nitrogen forms, phosphorus, potassium, solids, metals and pH;
• site selection criteria, crops and agronomic rates;
• authorized sites, monitoring and recordkeeping; and
• remedial procedures for process failures and spills.

2. Site authorization (OAR 340-050-0030)

Prior written DEQ approval is required for every land application site. For sites sensitive because of nearby homes, runoff potential or groundwater, DEQ provides public comment. If at least 10 people, or an organization representing 10 people, raise concerns, a public hearing must be offered. DEQ acts within 30 days after comment or the hearing record closes. Site authorization letters become enforceable permit conditions.

3. Agronomic rates

Application may not exceed the nitrogen needed for the crop (OAR 340-050-0025 and -0065). Crop nitrogen needs come from Oregon State University Extension guidance. Sites receiving biosolids more than two years out of three at agronomic rates need periodic soil nitrate evaluation (OAR 340-050-0080).

 ┌────────────────────────────────────────────────────────────────────────┐
 │                     PLANT AVAILABLE NITROGEN (PAN)                     │
 │                                                                        │
 │  TOTAL NITROGEN IN BIOSOLIDS                                           │
 │  ├── Inorganic Nitrate/Nitrite (NO3-N) ────► 100% Available in Year 1  │
 │  ├── Inorganic Ammonium (NH4-N)       ────► Multiplied by Kvol (0.5-1) │
 │  └── Organic Nitrogen (Org-N)         ────► Multiplied by Forg         │
 └────────────────────────────────────────────────────────────────────────┘

With nitrogen content expressed as percent of dry weight, multiply by 20 to get pounds per dry ton:

$\text{PAN (lb/dry ton)} = 20 \times \left[ \% \text{ NO}_3\text{-N} + (K_{\text{vol}} \times \% \text{ NH}_4\text{-N}) + (F_{\text{org}} \times \% \text{ Organic-N}) \right]$

• $\% \text{ Organic-N} = \% \text{ TKN} - \% \text{ NH}_4\text{-N}$
• $K_{\text{vol}}$ accounts for ammonia lost to the air. It is roughly 0.5 for surface application without incorporation and close to 1.0 for injection or prompt incorporation.
• $F_{\text{org}}$ is the fraction of organic nitrogen that mineralizes in year 1. It is typically about 0.2 to 0.3 for digested biosolids, with smaller releases in later years. Use the factors in your approved plan or OSU guidance.

$\text{Application Rate (dry tons/acre)} = \frac{\text{Crop N Requirement} - \text{Residual Soil N (lb/acre)}}{\text{PAN (lb/dry ton)}}$

Example. Biosolids contain 0.1% NO3-N, 1.0% NH4-N and 5.0% TKN, so organic N is 4.0%. Using $K_{\text{vol}} = 0.5$ and $F_{\text{org}} = 0.25$:

• PAN = 20 × (0.1 + 0.5 + 1.0) = 20 × 1.6 = 32 lb/dry ton
• For a crop needing 160 lb N/acre with 32 lb/acre residual soil N: (160 − 32) ÷ 32 = 4.0 dry tons per acre

4. Site selection best management practices (OAR 340-050-0070)

Federal management practices also apply. For example, 40 CFR 503.14 bars applying bulk biosolids to flooded, frozen or snow-covered land in a way that lets them enter wetlands or waters, and requires a 10-meter buffer from waters of the United States.

5. Access, grazing and crop BMPs (OAR 340-050-0065)

• Control public access to Class B and septage sites for at least 12 months after surface application; access control is assumed on rural private land.
• Do not plant fresh-market crops for at least 14 months after Class B application, unless the root-crop waiver in Part 503 applies.
• Keep grazing animals off, and do not harvest feed crops, for at least 30 days.
• Exceptional Quality biosolids may be used on lawns, gardens and other high public contact areas without access restrictions.

6. Monitoring and reporting (OAR 340-050-0035)

• Analyze at least as often as 40 CFR 503.16 requires for Table 1 metals, TKN, nitrate, ammonium, phosphorus, potassium, pH, total solids and volatile solids.
• Keep site application logs as permanent records.
• Track cumulative pollutant loading when annual average metals exceed the Table 3 limits.
• Submit the annual solids report by February 19 for the previous year.