http://www.epa.gov/owm/mtb/biosolids/fsguide/
Guide to Field Storage of Biosolids and Other Organic By-Products Used in Agriculture and for Soil
Resource Management
[Pathogen Regrowth]
"In general, storage of Class A biosolids present few pathogen concerns due to the level of pathogen reduction
achieved by the treatment processes. The potential for exposure to viruses or parasites (helminth ova) in Class A
product in insignificant as a result of treatment, and because these organisms cannot grow outside a suitable host
organism. This potential does not increase during storage. Treatment also reduces bacterial pathogens to safe
levels."
"However, bacteria grow without a host organism; they depend on readily available sources of nutrients, adequate
water, and favorable environmental conditions. In specific and very limited situations, the necessary combinations of
these facts have been found to occur in stored Class A biosolids. Two examples of these circumstances are:
"1. If Class A biosolids compost that is no longer self-heating is blended with green or unstabilized organic materials,
such as fresh yard trimmings, fresh hay, or green woodchips, the bacterial population can grow rapidly.
"This is because these fresh materials contain readily available carbon that bacteria need and the compost lacks."
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...."If a Class A product is inadequately composted, or its nutrients are not well stabilized, bacterial pathogen growth will
not occur as long as the material is kept very dry, i.e., total solids content of 80 percent or greater. However, if such
dry materials take on moisture during storage, and nutrients, pH, temperature, and other environmental conditions are
favorable, pathogen and microbial regrowth could occur.
"Preparers should be aware that if they conduct various types of blending operations with Class A product the potential
for temporary increases in bacterial growth exists. If pathogen regrowth occurs, the material should be held in storage
until populations decline to acceptable levels or it should be retreated to meet standard pathogen limits."
"The potential for pathogen growth should be considered in establishing appropriate storage conditions and in blending
or augmenting Class A biosolids with other organic materials."
"2. If the pH of Class A alkaline stabilized material drops significantly during extended storage and the color,
consistency, or odor of the product has deteriorated, then re-testing for pathogens may be advisable. Significant
decreases in pH have, on occasion, been associated with increases in the level of fecal coliforms above the 1000 MPN
(most probable number) per gram regulatory limit."
Pasge 31 - TESTING - "When is Retesting Required?
"Class A and EQ - For EQ ("exceptional quality" biosolids the Part 503 requirements to test stored materials prior to use
depends on WHO has control of the stored material. If the material remains in the control of the original preparer
(directly or indirectly through a contracted proceswsor or applier), the material MUST BE RETESTED PRIOR TO FINAL
USE. If a preparer gives or sells EQ biosolids to a second party, for instance a landscaper, who then stores the material
before land application, testing for pathogens is not required under Part 503."
"The two examples above are often referred to as the "quirk" of the EQ concept. One one case, the EQ biosolids is still
subject to the Part 503 requirements when something happens to it because it is still under the control of the preparer.
In the other case, the same EQ biosolids is not subject to the Part 503 requirements when something happens to it
because it is NO LONGER UNDER THE CONTROL OF THE PREPARER.
Loss of control by the preparer is the critical difference conceptually. However, even second party receivers of EQ
materials shoud be aware that pathogen testing is recommended when bulk blending operations of biosolids with
materials that contain available nutrients occur."