radioactivity in sewer sludge

[scott dennerlein <sdennerlein@radsci.com>]

People are correct in assuming the majority of the radioactivity input
to Publicly Owned Treatment Works (POTW's) is from drinking
water/irrigation, however this material is by nature soluble, i.e. it
entered the system as water and it leaves as water. The POTW's job is to
remove biosolids, kill pathogens, and let as much water as possible pass
through the system. The problem is insoluble material being "screened
out" in settling ponds and clarifiers,  reconcentrated, and removed as
dewatered sludge. Hence, the NRC'c prohibition on insoluble,
non-dispersible discharges. The sludge is either ashed and landfilled,
or applied to land as fertilizer.

    The NRC's "Site Decommissioning Management Plan" (NUREG-1444) has a
good summary of the contamination at the NE Ohio Sewer District. Levels
of Co-60 in soil ranged up to 9,000 pCi/g. Nothing to sneeze at for
those of us working to attain levels of 5 pCi/g at many environmental
sites! There has been ten to fifteen incidents of contamination at
POTW's over the last few decades, most of which were readily traced back
to the "offending" company. This may or may not be alot depending on
your point of view. However, all of these sites were discovered by
"accident" setting of alarms at the landfill, or during remediation of
nearby licensed sites. That is why a nationwide screening program is a
good proactive approach to determine the extent of the problem.

As far as regulatory control is concerned, regards the Ohio incident,
the contaminee? was a manufacturor of Co-60 therapy units. The
requirements for their decommissioning fund may have been too low.
Rather than lower discharge limits, perhaps requiring greater amounts of
money to be set aside for decommissiong, to include cleanup of the local
POTW, may be appropriate.

Scott Dennerlein
Radiation Science Inc.
sdennerlein@radsci.com

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