United States Environmental Protection Agency Biosolids Technology Fact Sheet Use of Landfilling for Biosolids Management DESCRIPTION common methods of monofilling wastewater biosolids are the trench, area, and ramp methods. Current options for managing wastewater biosolids in the United States include both beneficial reuse Trench monofilling (Figure 1) involves excavating technologies (such as land application, landfilling a trench, placing the biosolids in the trench, and with biogas recovery, and energy recovery through then backfilling the trench to return the soil to its incineration) and non-reuse options, including original contours. Monofill trenches can be narrow landfilling. While implementing some type of or wide, depending on the solids concentrations of beneficial reuse is the preferred method for the biosolids to be filled. Narrow trenches managing wastewater biosolids, this is not always (typically less than 3 m [approximately 10 ft] wide) practical. For example, land acquisition constraints are generally used for disposal of biosolids with a or poor material quality may limit beneficial reuse low solids content. Wide trenches (typically greater options. In these situations, landfilling of biosolids than 3 m [approximately 10 ft] wide) are used for may be a viable alternative. disposal of biosolids with a solids content of 20 percent or more. If the biosolids contain less than Biosolids landfilling options include disposal in a 20 percent solids, they will not support the monofill (a landfill that accepts only wastewater machinery used to place the cover material over the treatment plant biosolids), or in a co-disposal trench. landfill (a landfill that combines biosolids with municipal solid waste). Although co-disposal Application rates for trenches less than 3 m in landfilling is more common than monofilling, width are approximately 2,270-10,580 m3/ha biosolids typically represent only a small percentage (1,200- 5,600 yd3/acre). Typical application rates of the total waste in a co-disposal landfill (WEF, for wider trenches range from 6,000-27,000 m3/ha 1998). (3,200-14,500 yd3/acre) (U.S. EPA, 1978). Landfill disposal of biosolids should not be The trench method provides efficient use of confused with use of biosolids to amend final cover available land space. However, this method is material at landfills. This practice is a form of land application in which biosolids are added to soil to enhance conditions for growing cover vegetation. The EPA fact sheet Land Application of Biosolids addresses the use of biosolids in rehabilitating disturbed lands. Biosolids Monofilling Biosolids monofilling consists of preparing the site, transferring the biosolids to the site, and covering the biosolids with a layer of cover material. Depending on the concentration of pollutants in the biosolids, site preparation may include installing a FIGURE 1 EXCAVATED CROSS-SECTION liner to prevent contaminants from migrating OF BIOSOLIDS TRENCH downward into the site soil. The three most generally not used at sites that require a liner TABLE 1 MAXIMUM POLLUTANT because of the potential to damage the liner during CONCENTRATION FOR SURFACE trench excavation. DISPOSAL OF BIOSOLIDS In the area method, biosolids are placed in a natural Pollutant Concentration or excavated depression, or they are mixed with soil (Dry Weight Basis) and placed on top of the existing soil layer. Distance from Biosolids to be landfilled in this manner are Boundary of Arsenic Chromium Nickel Active Biosolids generally stabilized prior to landfilling because mg/kg mg/kg mg/kg these sites do not always apply daily cover. The Unit to Property Line, m area method is particularly well suited to areas where bedrock or ground water are shallow, and 0 to less than 25 30 200 210 excavation (as is required for the trench method) is 25 to less than 50 34 220 240 difficult. However, this method requires substantial 50 to less than 75 39 260 270 amounts of soil for fill and results in changes to the local topography. 75 to less than 100 46 300 320 100 to less than 53 360 390 The ramp method involves spreading and 125 compacting the biosolids along a slope. The soil 125 to less than 62 450 420 higher on the slope is pushed over the top of the 150 biosolids as a cover material. Equal to or greater 73 600 420 than 150 Applicable Regulations Source: Part 503 Regulations Landfilling of biosolids in monofills is regulated by the Environmental Protection Agency under Subpart C of 40 CFR, Part 503, Standards for the Co-Disposal Landfilling Use and Disposal of Sewage Sludge as surface disposal. The Part 503 Regulations establish Co-disposal landfilling involves combining maximum concentrations of arsenic, chromium, and wastewater solids with municipal solid waste and nickel in biosolids to be landfilled in a monofill placing the mixture in a permitted landfill. without a liner. The limits vary with distance to Generally, a layer of municipal solid waste is spread property lines as presented in Table 1. If the near the working face of the landfill. Wastewater concentration of any of these pollutants exceeds the solids are then spread over the municipal waste and criteria, the facility must be lined. The regulations the two are thoroughly mixed using typical landfill also allow establishment of site-specific pollutant machinery. The ratio of waste to wastewater solids limits at the discretion of the permitting authority. is dependent, in part, on the solids content of the wastewater solids. Ten percent biosolids to 90 These regulations also require that biosolids placed percent solid waste (by volume) is common. The in a landfill meet either Class A or Class B mixture is then compacted and covered with a daily pathogen reduction requirements or that they be cover. covered with soil or other material at the end of each operating day. Applicable Regulations In addition, many state regulations for monofills The design and operation of co-disposal landfills is have more stringent requirements, which may regulated by EPA under Subpart I of 40 CFR, Part include installing a liner regardless of pollutant 258, Criteria for Municipal Solid Waste Landfills. concentrations. Standards set forth in the Part 258 Regulations address general requirements, pollutant limits, management practices, operational standards for pathogens and vector attraction, and monitoring, TCLP method (Method 1311) is defined in EPA record keeping, and reporting requirements. SW-846. Accepting wastewater solids at a co-disposal Finally, economics also factor into any decision to landfill generally does not add significant regulatory manage biosolids through landfilling. Landfill hurdles or permit constraints to the landfill tipping fees can be less than the full cost of land operator. In addition, co-disposal typically does not application or other reuse options. Because tipping result in additional operational requirements for the fees change in response to market conditions, a landfill other than the mixing the biosolids and periodic reassessment of solids management waste prior to placement in the permanent cell. decisions is recommended. APPLICABILITY ADVANTAGES AND DISADVANTAGES Landfilling is generally considered for wastewater Advantages biosolids management when land application or other beneficial reuse is not possible. Typical • Landfilling is suitable for biosolids with scenarios that lead to selection of landfill disposal high concentrations of metals or other rather than beneficial reuse include: toxics. • Land acquisition constraints; • Landfills may require smaller land area than land application. • High concentration of metals or other toxins in the biosolids; or • Landfilling improves packing of solid waste and increases biogas production. • Odorous material that may create a public nuisance if managed through other options. • Landfills may be the most economical biosolids management solution, especially Solids concentrations of the biosolids are also a for malodorous biosolids. factor in determining whether landfilling is a viable disposal option. For biosolids monofills, the solids Disadvantages concentration should be 15 percent or greater. Although soil may be mixed with biosolids to • Landfilling biosolids eliminates their reuse increase the solids concentration to this level, this potential and is contrary to the EPA national may not be cost effective. Biosolids are usually beneficial reuse policy. stabilized prior to monofilling. • Landfilling requires extensive planning, As a general rule, municipal solid waste landfills including selection of a proposed landfill will not accept materials with solids content less site, and operation, closure, and post closure than about 18 percent. The operator will generally care of the site. perform a paint filter test on the biosolids prior to allowing them to be deposited due to the regulatory • Operation, maintenance, and post closure prohibition of materials containing free liquids. care of landfills are labor intensive. The paint filter test is described in detail in EPA publication SW-846, Test Methods for Evaluating • Landfill sites have a potential for Solid Waste, Physical/Chemical Methods, Method groundwater contamination from leachate. 9095. In addition to the paint filter test for free liquids, a Toxicity Characterization Leaching • Decomposition of biosolids in a landfill Procedure (TCLP) must also be performed to verify produces methane gas which must be that the biosolids are non-hazardous. Passing this collected and reused or disposed of