RE: radioactivity in sewer sludge

["Weiner, Ruth" <rfweine@sandia.gov>]

Scott, all material carried in water, especially runoff water, is not
dissolved.  Suspended material can be carried by water (and is -- most soil
carried to river deltas is suspended material rather than dissolved
material),  Moreover, there is not a clear differentiation between "soluble"
and "insoluble."  Everything is "soluble" to some extent -- one looks at the
solubility product: the solubility equilibrium constant Ksp.  Many salts
(e.g. NaCl) are very soluble, but even they can saturate a solution.  The
saturation concentration for NaCl is around 330,000 ppm. Nitrates are very
soluble, phosphates less so, but one generally should speak in terms of
greater or less solubility, not in terms of solubility or lack thereof.
This is straight from one of my freshman chemistry lectures.

Ruth F. Weiner, Ph. D.
Sandia National Laboratories 
MS 0718, POB 5800
Albuquerque, NM 87185-0718
505-844-4791; fax 505-844-0244
rfweine@sandia.gov
 

-----Original Message-----
From: scott dennerlein [mailto:sdennerlein@radsci.com]
Sent: Thursday, July 29, 1999 7:17 AM
To: Multiple recipients of list
Subject: radioactivity in sewer sludge


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

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html