mech10.txt

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     Office of Air Quality, Permitting & Enforcement Division

               Mechanical Section Policy Memorandum

                 

Date:  February 17, 1994                            No.: 10

From:  Skip Clark, P.e. 

Approved by:  Gary I. Wallin, P.E. 

Subject:  Standard Exemption Nos. 77 and 114

                  

Policy:   

Both exemptions cover sand and gravel production facilities. 
Standard Exemption No. 77 is to be used when the sand and
gravel is mined from subterranean and subaqueous beds, or in
other words, the material is mined wet naturally.  Standard
Exemption No. 114 is to be used when the sand and gravel is
mined dry.  In both cases, no crushing is allowed, but
classification can be done.

In both cases, in-plant roads can be either sprinkled with
water and/or chemicals or paved and cleaned.  

Background:   

These exemptions were developed for mining naturally occurring
deposits of sand and gravel.  Since the subterranean and
subaqueous beds are wet to begin with, the allowed production
rate is 500 tons per hour.  Additional watering of the process
and/or stockpiles is permitted, along with the required
sprinkling of the in-plant roads (unless paved).  For the
deposits that are dry, usually this means surface mining, the
production rate is limited to fifty tons per hour.  Water
sprays are required on screens, transfer points, stockpiles,
in-plant roads (unless paved) and where necessary.  Again, no
crushing is allowed in either exemption.

Necessary Action:  

The exemptions need to have the wording concerning the
in-plant roads clarified to reflect the intent that they can
be either paved and cleaned or sprinkled with water and/or
chemicals as necessary to achieve maximum control of dust
emissions.

cc:  All Mechanical Section