January 7, 1991         


MEMORANDUM

SUBJECT:  Pit Retention from Stone Quarries

FROM:     Jawad S. Touma
          Techniques Evaluation Section, SRAB (MD-14)

TO:       Rebecca H. Calby
          Technical Analysis Section, Region V (5AR26)


     In response to your request, the Model Clearinghouse has
reviewed the approach for quantifying the effects of pit
retention, prepared by Illinois EPA that was attached to your
memorandum.  The pit retention report you referenced contains
five analytical techniques for predicting the escape fraction of
particles from surface coal mine pits.  The report suggests that
while the simplest of these predictive techniques appears to
perform best, none of the techniques predict escape fraction
reliably over the range of meteorological conditions measured at
the surface coal mines.  An independent data collection and
analysis program is needed to determine which, if any, of these
predictive techniques performs the best.  TRC, the Contractor who
did the study, actually contacted a trade association to solicit
funding for such a program but was unsuccessful in raising the
money.

     The Illinois EPA selected the simplest predictive technique
and used certain assumptions to arrive at an escape fraction. 
Another analyst could justify another technique or use different
assumptions to arrive at a different conclusion.  The state of
knowledge does not allow us to recommend a reliable predictive
technique at this time.  Thus, we conclude that the use of any
technique to account for the pit retention of particles is not
warranted unless accompanied by a performance evaluation based on
site-specific data.

cc:  J. Tikvart
     T. Pace