Septage ManagementRegulations for the land application of domestic septage are similar to those for municipal biosolids. However, there are important differences between septage and municipal biosolids regulations. These include:
Types of SeptageThere are three classes of domestic septage depending on its source and degree of stabilization.
Pathogen and Vector Attraction Reduction RequirementsClass I and III Septage
Class I and III septage are considered to be adequately stabilized for land application, when certain management and access restrictions are observed. Vector attraction reduction requirements are met either by alkaline treatment or by injecting or tilling into the soil.
Alkaline treatment reduces the numbers of pathogenic and odor-producing microbes in the septage by raising the pH. Enough lime must be added to maintain the pH at 12 for at least 30 minutes, and the septage must be tested to check that this pH has been maintained. If the septage is being managed as municipal biosolids, follow biosolids treatment rules in Chapter 173-308 WAC, Biosolids Management. Because alkaline treatment destroys only microbes - not organic matter - odors may return after several weeks. Therefore, alkaline treatment may not control odors when septage is stored for more than a short time before land application. Sites receiving alkaline-treated septage must meet all biosolids requirements for waiting periods for food crops as defined by WAC 173-308-210.
If Class I or III septage is not lime-treated, it must be injected into the soil or tilled into the soil within six hours of application, to provide a barrier to vector attraction. These sites must meet all biosolids requirements for waiting periods for crop production and public contact.
Class II Septage
Class II septage is mostly unstabilized material, and is not considered suitable for direct application to the land. Before land application, Class II septage must be treated to meet at least Class B pathogen reduction standards, or be analyzed to demonstrate that it meets Class B standards for fecal coliform density as defined by Chapter 173-308-170 (Pathogen Reduction). Vector attraction reduction is accomplished through alkaline treatment, soil injection, or soil incorporation. When batches of Class I septage contain less than 25% Class II material, treat the entire batch as Class I. The more stringent requirements for Class II apply when a load or batch contains more than 25% Class II material.
Monitoring RequirementsIf septage is lime-treated, monitor every batch to make sure that alkaline treatment requirements are met. Septage managers don't have to measure septage nutrients and metals, as long as they base land application rates on the standard calculation described below. If septage is managed as biosolids derived from municipal sewage sludge, then all applicable requirements for monitoring biosolids derived from municipal sewage sludge (including nutrients and trace elements) must be met. This approach will generally not be practical except for relatively sophisticated septage operations.
If you need to estimate septage production in an area, use the U.S. EPA formula based on septage production data:
Estimated volume=(populaton using septic systems) x (60 gal/person/year)
This formula provides a starting estimate for septage volume. More accurate estimates can be made by analyzing actual septage pumpouts. By keeping central records on pumpouts, you can determine local annual septage volume, seasonal trends, and daily peak volumes. By knowing this information, it will be easier to plan septage treatment and handling facilities, and estimate the needed acreage for land application.
RecordsThe person who is responsible for applying domestic septage to land is also responsible for maintaining application records. Required records include:
Domestic septage can become contaminated if it is mixed with commercial or industrial wastes. Septage from commercial or industrial sources can be applied to land only if it is known to come from septic tanks that receive only domestic quality sewage (Class III septage). If you have any doubt about the quality of the septage, do not pump the source or accept a load of septage until the quality can be verified.
Application RateSeptage applications are more suitable for sites where peak productivity is not a major concern because the equation for calculating application rates is conservative and probably will not provide the full nitrogen requirement of the crop. This is especially the case when pH adjustment is used, resulting in a loss of ammonia. When the septage equation was developed for the federal biosolids rule, both the agronomic rate, and the underlying risk assessment were considered. The rate calculation for septage applications can be used without measuring the nutrient content of the septage.
Use the following equation to calculate the maximum application rate:
AAR = N/0.0026
AAR is the annual application in gallons per acre per 365-days, and N is the amount of nitrogen needed by the crop in pounds per acre per 365 days.
The table below shows the highest annual septage rates calculated from the equation. If you use this table, you do not need to analyze the septage for nutrients or trace elements. Remember that the rates in this table may not supply the full nitrogen requirement of the crop.
You can also calculate a site-specific agronomic application rate using this application rate worksheet. If you choose this method, you will need to analyze the septage for both nitrogen and trace elements, and meet all other requirements for land application of biosolids. This approach typically works best for relatively sophisticated septage operations. If you store, or further process septage before land application (such as alkaline treatment or lagoons), consider managing the septage to meet all requirements for land application of biosolids as this will often allow you to apply more material per acre than when using the standard septage equation.
Waiting Periods and Restrictions on Public AccessRequirements for posting sites to restrict public access are the same as for Class B biosolids.
The following restrictions apply for all septage application:
BuffersAll land application sites must have large enough buffers to protect receiving waters. 100 feet is the minimum buffer distance to surface water for septage applications. All other minimum buffers are the same as for Class B biosolids. For special situations, buffers may need to be larger.
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