Surface Disposal

A surface disposal site is an area of land on which wastewater solids are placed for disposal. Examples of surface disposal practices include the following:

• Sludge-only landfills (monofills)

• Sludge piles or mounts

• Sludge lagoon used for final disposal

• Surface application sites where wastewater solids are applied at rates in excess of the agronomic rate

Surface disposal of wastewater solids differs from land application in that it principally uses the land for final disposal instead of using the solids to enhance the productivity of the land. However, some surface disposal practices, where the solids are applied on the surface of the land, may be very similar to land application practices. For example, a surface disposal site, where solids are applied at rates in excess of the agronomic rate needed by vegetation grown on the site and a food, feed, or fiber crop is grown or animals are grazed, may appear to be a land application site, but the site is a surface disposal site if it is for the final disposal of solids. In this situation, management practices must be implemented to control activities such as the growing of crops or animal grazing.

The storage or treatment of sludge, other than treatment to reduce pathogen levels and vector attraction characteristics, is not regulated by Part 503. Lagoons, in particular, are frequently used to dewater or stabilize wastewater sludge as well as for storage. The most obvious indicator that the land-based activity is treatment or storage is whether the wastewater treatment plant has designated a subsequent sludge use or disposal plan. Unless a final use or disposal plan has been identified for the sludge, the land-based activity is considered as final disposal.

Storage is placement of biosolids on land on which it remains for two years or less. Therefore, a factor used to distinguish between storage and final disposal is the length of time that the biosolids remain on the land. Biosolids remaining on the land for longer than two years is considered final disposal unless the person who prepares the biosolids establishes a basis for leaving the biosolids on the land for longer than two years prior to final disposal. Wastewater treatment plants that generate small quantities of biosolids may stockpile biosolids for a reasonable period of time that is longer than two years before use or disposal. Even some large treatment plants may stockpile biosolids for a lengthy period when they unexpectedly lose access to their disposal practice.

Some provisions of the surface disposal subpart apply to biosolids, some to the location or siting of the surface disposal site, and others to operation of the surface disposal site. Not all of the management practices, frequency of monitoring, and record-keeping requirements apply to every surface disposal site. For example, some apply only to sites with a liner and leachate collection system; others apply only to sites on which a cover is placed over the biosolids.

General Requirements The four general requirements for placing waste-water solids on an active site (surface unit is the phrase used in Part 503) are the following:

• Wastewater solids cannot be placed on an active sludge disposal unit unless the requirements of Subpart C of Part 503 are met.

• An active unit cannot be located within 60 m of a fault with displacement in Holocene time, in an unstable area, or in a wetland.

• The owner or operator of an active unit must submit a written closure and postclosure plan 180 days before the unit is due to close.

• The owner of a surface disposal unit must provide written notification to the subsequent owner of the site that wastewater solids were placed on the land.

The first general requirement places the responsibility on the person who places wastewater solids on an active sewage sludge unit to ensure that the requirements related to the surface disposal are met when the solids are actually placed on the unit. The person who places the solids on the land could be either the preparer or the owner/operator of the surface disposal site. If the person who places the solids is not the preparer, that person should request the information from the preparer that indicates that the treatment-related Part 503 surface disposal requirements have been met. These include pollutant concentrations in the sludge and whether pathogen reduction and vector attraction reduction have been achieved through treatment.

If an active sewage sludge disposal unit falls into one of the three categories of the second general requirement listed above, the owner or operator must develop a compliance schedule that addresses closure activities and time frames. The closure plan, at a minimum, must address the following three specific items:

• Operation and maintenance of the leachate collection system if the unit has a liner and leachate collection system

• Methane gas monitoring if a final cover is placed on the unit

• Public access restriction to the site

Leachate Collection System Leachate can contaminate groundwater, surface water, and soil if it is not controlled. If the active land disposal unit has a liner and a leachate collection system, the closure and postclosure plan must describe how the leachate collection system will be operated and maintained for three years after closure. The owner or operator must comply with all local, state, and federal requirements for leachate collection and disposal.

Methane Gas Monitoring System Since methane gas, a by-product of anaerobic decomposition of organic matter, is explosive within a certain concentration range in air, Part 503 requires continuous monitoring of air for methane gas at sites where the sewage sludge is covered. Additionally, air must be monitored for methane for a period of three years after closure if a final cover is placed on an active sewage sludge unit at closure.

Public Access Restriction Part 503 restricts public access to a closed surface disposal unit to prevent:

• Possible exposure to methane

• Direct contact with, or ingestion of, the sewage sludge or sewage sludge-soil mixture

• Traffic that could damage the final cover

Final Cover If a final cover is placed on an active sewage sludge disposal unit that is to be closed, the cover should be designed to:

• Control volatilization of pollutants

• Account for settling or subsidence in the unit

• Resist erosion

• Control runoff and prevent other damage to the cover

Notification to Subsequent Owner The owner of a surface disposal site must provide a subsequent owner of the site with written notification stating that the land has been used for surface disposal of wastewater solids. The notice must describe the wastewater solids disposal activities as well as provide details about the design and operation of the site.

Pollutant Limits If a sewage sludge disposal unit is equipped with a liner and a leachate collection system, there are no pollutant limits because the liner retards the movement of pollutants in sewage sludge into the groundwater. A liner is clay or synthetic material that has a hydraulic conductivity of 1 x 10-7 cm/s or less. If the liner does not meet this specification, the unit is considered unlined for the purpose of assigning pollutant limits to the sewage sludge placed in the unit.

Sludge placed in an active unit without a liner, and a leachate collection system must meet pollutant limits for arsenic, chromium, and nickel. The specific pollutant limits to apply depend on the distance from the active sewage sludge disposal unit boundary to the surface disposal site property line. The limits allowed are listed in Table 1.4.

The permitting authority may determine that the conditions of the active sewage sludge disposal unit warrant the development of site-specific limits, in which case the authority may use site-specific data and develop sewage sludge pollutant limits different from the limits in Table 1.4. In addition, if a surface disposal site has several different types of active sewage sludge units, the sewage sludge placed on various units will be subject to different pollutant limits, depending on the active sludge unit in which it is placed.

TABLE 1.4 Pollutant Concentration Limits in Active Sewage Sludge Disposal Unit Without a Liner and Leachate Collection System

Distance from Boundary to Property Line (m)

Pollutant Concentrationa


0 to <25




25 to <50




50 to <75




75 to <100




100 to <125




125 to <150




150 or greater




Management Practices Management practices dealing with the location, design, and operation of wastewater sludge surface disposal facilities include the following:

• Sludge shall not be placed in an active sewage sludge disposal unit if threatened or endangered species of plant, fish, or wildlife are identified within or near the unit during any stage of their life cycles. However, if the unit is located within the migratory path of an endangered species, the permitting authority may prohibit the disposal of sludge only during the migration period.

• An active sewage sludge disposal unit shall not restrict the flow of a base flood (100-year flood). If the owner or operator of the unit can demonstrate that the unit will not pose unacceptable threats of higher flood levels and flood velocity, the requirements of this provision are met.

• When an active sewage sludge disposal unit is located in a seismic impact zone, the unit shall withstand the maximum recorded horizontal ground-level acceleration. A seismic impact zone is an area that has a 10% or greater probability that the horizontal ground-level acceleration of the rock in the area exceeds 0.10 gravity once in 250 years.

• An active sewage sludge disposal unit shall not be located within 60 m of a fault that has a displacement in Holocene time, which is approximately the last 11,000 years.

• An active sewage sludge disposal unit shall not be located in an unstable area, such as landslide-prone areas, karst terrains, and surface areas weakened by underground mining or oil, water, or water withdrawals.

• An active sewage sludge disposal unit shall not be located in a wetland unless the owner or operator applies and receives a Section 404 permit from the U.S Army Corps of Engineers.

• The runoff collection system for an active sewage sludge disposal unit shall have the capacity to handle runoff from a 24-hour 25-year event, and the runoff shall be disposed in accordance with a National Pollutant Discharge Elimination System (NPDES) permit.

• The leachate collection system for an active sewage sludge disposal unit that has a liner and leachate collection system shall be operated and maintained, and the leachate shall be disposed of in accordance with the applicable requirements during the period the unit is active and for three years after the unit closes.

• If sewage sludge is covered with soil or other material, proper equipment shall be installed to monitor methane continuously in air in structures and at the site property line. Methane levels cannot exceed 25% of the lower explosive limit (LEL) in on-site structures, and cannot exceed the LEL at the site property line. The monitoring shall continue and the LEL limit requirements shall be met for three years after the sewage sludge unit closes.

• Growing of food, feed, or fiber crops or the grazing of animals on an active sewage sludge disposal unit is prohibited unless the owner or operator of the site demonstrates to the permitting authority through management practices that public health and the environment are protected from adverse effects when crops are grown or when animals are grazed.

• Public access to a surface disposal site is restricted when the unit is active and for three years after the site closes.

• The owner or operator of a sewage sludge disposal unit shall demonstrate to the permitting authority that the unit does not contaminate an aquifer (1) by providing a certification by a qualified groundwater scientist that the unit will not contaminate the aquifer, or (2) by performing ground-water monitoring.

Pathogen and Vector Attraction Reduction Requirements Sewage sludge to be placed in an active sewage sludge disposal unit must meet one of the class A or B pathogen reduction alternatives by the preparer unless the sludge is covered with soil or other material by the owner or operator at the end of each operating day. One of the first eight vector attraction reduction alternatives, or an equivalent alternative as determined by the permitting authority, is required to be met by the preparer of the sludge. Also, one of three vector attraction reduction alternatives (discussed further later in the chapter) is required to be met by the owner or operator of the sewage sludge unit.

Monitoring Sewage sludge placed on unlined units must be monitored for the three regulated pollutants (arsenic, chromium, and nickel), pathogen reduction (fecal coliform or Salmonella, enteric viruses, and helminth ova), and vector attraction reduction (volatile solids reduction, specific oxygen uptake rate, pH, and percent solids). Sludge placed on units equipped with liners and leachate collection systems is subject only to pathogen and vector attraction reduction requirements.

The frequency of monitoring is typically established through permits on a case-by-case basis. However, to enhance the self-implementation of regulation, monitoring frequencies have been established in Part 503. The frequencies established are shown in Table 1.5, but the permitting authority has the discretion to require more frequent monitoring.

Record Keeping Records must be kept to demonstrate that permit conditions that implement all applicable regulatory requirements of Part 503 are being met. Specific information must be kept to show compliance with pollutant concentrations, pathogen reduction, vector attraction reduction, and management practices. These records must be retained for at least five years.

Reporting Only the following types of facilities are required to report to the permitting authority under the Part 503 regulation:

TABLE 1.5 Frequency of Monitoring: Surface Disposal

Amount of Sludge"

(metric tons/365-day



0 to <290


290 to <1500

Once/quarter (4 times/year)

1500 to <15,000

Once/60 days (6 times/year)

15,000 or grater

Once/month (12 times/year)

a Dry weight basis.

a Dry weight basis.

• Class I sludge management facilities

• Publicly owned treatment works with a flow rate equal to or greater than 3800 m3/day (1 mgd)

• Publicly owned treatment works serving a population of 10,000 or greater

Surface D isposal of Domestic Septage The regulatory requirements for the surface disposal of domestic septage are not as extensive as sewage sludge. The requirements include meeting the same management practices that are required for the surface disposal of sewage sludge. There are no specific pathogen reduction requirements for domestic septage applied on surface disposal sites. However, to meet the vector attraction reduction requirements, it must be (1) injected into the subsurface of the land, (2) applied to the surface and incorporated into the soil, (3) covered with soil or other material at the end of each operating day, or (4) treated with an alkaline material to raise the pH to 12 or higher for at least 30 minutes.

Placement of Sludge in a Municipal Solid Waste Landfill There are no specific requirements for disposal of sewage sludge in a municipal solids waste landfill (MSWLF) in Part 503. Instead, Part 503 requires compliance with 40 CFR Part 258. Thus, the design standards and operating standards for MSWLFs established in Part 258 serve as alternative standards for protection of public health and the environment. To meet the Part 258 requirements, the preparer of the sewage sludge must ensure that (1) the sewage sludge is non-hazardous, and (2) it does not contain free liquids as defined by the paint filter test. The owner or operator of a MSWLF unit must ensure that the material used to cover the unit is capable of controlling disease vectors, fires, odors, blowing litter, and scavenging without a threat to human health and the environment. Therefore, if sewage sludge is used as an alternative cover material, it may have to be treated for vector attraction reduction prior to its use. Use of sewage sludge as a cover material must also be approved by the state agency regulating MSWLFs.

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