EPA-340/1-79-002
  CONTROL OF AIR EMISSIONS
FROM PROCESS OPERATIONS IN
THE ROCK CRUSHING  INDUSTRY
                      by

                    JACA Corp.
                  550 Pinetown Road
                Fort Washington, PA 19034
             EPA Project Officer: Norman Edminsten
                    Region X
                 Enforcement Division
                Contract No. 68-01 -4135
                    Task No. 19
                    Prepared for

           U.S. ENVIRONMENTAL PROTECTION AGENCY
            Division of Stationary Source Enforcement
                 Washington, DC 20460

                   February 1979

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                          ABSTRACT








         Three basic methods of controlling emission from process



operations in crushed stone plants are described - dry captive



systems using fabric filters,  wet suppression systems and com-



binations of these.   Operational problems with these systems



associated with plant portability and product size are discussed.



Examples of good design practices and maintenance procedures for



these control options are covered.  An electrostatic charged fog



technique for control of small dust particles is described and



operational problems listed.  A second part analyzes the down-



wind effects of reducing emissions for worker safety.

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       This report was furnished to the U.S. Environmental Protection




Agency by JACA Corp., Fort Washington, Pennsylvania, in partial fulfillment




of Contract No. 68-01-4135, Task No. 19.  The contents of this report



are reproduced herein as received from the contractor.  The opinions,




findings, and conclusions expressed are those of the author and not




necessarily those of the Environmental Protection Agency.
                                  -i-

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                            ACKNOWLEDGEMENT








       The technical discussions, data, and photographs supplied to




JACA from many sources are gratefully appreciated.  We especially would




like to note the assistance of the Pennsylvania Department of Environmental




Resources, The Oregon Department of Transportation, The Oregon Water




Resources Board, Professor Stuart Hoenig of the University of Arizona,




Mike Natale of Johnson March, William Ward of Ward Engineering, James Fee




of L.B. Smith, and William Rundquist formerly of Portec Corporation, now




a technical editor for Pit § Quarry.
                                  -11-

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                                SUMMARY









       The basic operationally proved methods of controlling dust emissions




are:  (1) suppression of the dust by the application of wet sprays preferably




with a surface active ingredient to reduce water surface tension and




(2) the use of hoods,ductwork and fabric filters in a dry capture system.




It is not unusual to find a combination suppression and capture system




with emissions from the early parts of the process  (larger size stone)




controlled by suppression and later process points  (smaller size stone)




controlled by captive means.




       Performance of either of these systems degrades appreciably when




appropriate maintenance procedures are not followed.  Operation and




maintenance practices are simple and inexpensive to follow.




       Portable plants that are moved frequently encounter take-down




and set-up delays and added costs due to configuration induced difficulties




of  connecting ductwork to the appropriate emission  sources.  These




difficulties are not insurmountable.




       Water costs for wet suppression systems or combination dry  (captive)




and wet  suppression systems in arid regions  add to  production costs.




These incremental costs viewed in the industry economic context should




not preclude use of wet techniques however.




       A new potential method of controlling fine particles less than




10  microns by an electrostatically charged fog is now emerging from the




experimental stage.  Important operational and economic factors must be




resolved before the system will find widespread usage in stone crushing




operations.






                                -iii-

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       Efforts to control emissions from stone crushing plants benefit




both the worker who is in proximity to the equipment and the residents




of the surrounding area.   Efforts of a company (except for receptor




control) to meet either the MSHA or EPA standards are mutually helpful,
                                  -3V-

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                           Table of Contents
SUMMARY                                                            in

TASK PURPOSE                                                        ix

INTRODUCTION                                                         1

        Industry Background                                          1
        Sources of Air Pollution                                     6

SECTION I  AIR POLLUTION CONTROL OF PROCESS OPERATIONS              11

        Wet Suppression System                                      15
        Baghouse System                                             35
        Combination Wet Suppression § Baghouse System               52
        Electrostatic Spray Systems                                 53

SECTION II  EFFECTS OF MESA CONTROL STRATEGIES ON
            DOWNWIND AMBIENT CONDITIONS                             63

        Introduction                                                63
        Occupational Health Regulations                             64
        Relationship of Control for Workers to SIP Control          70

APPENDIX A:  Effect of Mesa on NAAQS                                73

REFERENCES                                                          83
                                   -v-

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                      List of Tables and Figures









Table No.                                                         Page




   1        CRUSHED STONE PLANT SITES BY STATES                     2




   2        DISTRIBUTION OF ROCK CRUSHING PLANT SITES BY SIZE       5




   3        MODEL WET SUPPRESSION COSTS FOR PROCESS PORTIONS OF




            CRUSHED STONE PLANTS                                   33




   4        MODEL FABRIC FILTER SYSTEM COSTS FOR PROCESS PORTIONS




            OF CRUSHED STONE PLANTS                                45




   5        MODEL WET SUPPRESSION - FABRIC FILTER SYSTEM COSTS




            FOR PROCESS PORTIONS OF CRUSHED STONE PLANTS           54









   1-A      EFFECT  OF CHOICE OF STABILITY CLASS                    81




 Figure No.




    1       TYPICAL HARD  ROCK  STONE CRUSHING  PLANT  OPERATING AT




            300  TONS PER  HOUR                                        9




    2       TYPICAL HARD  ROCK  STONE CRUSHING  PLANT  OPERATING AT




             600  TONS PER  HOUR                                      10



    3        PERMANENT CRUSHED  STONE PLANT WITH COVERED SCREEN




             HOUSES                                                 12




    4        DISTANT VIEW OF PLANT PRODUCING CRUSHED STONE          12




    5        CLOSE UP OF PLANT SHOWN IN FIGURE 4                    13




    6        A STONE CRUSHING PLANT CONSISTING OF UNITIZED




             PORTABLE EQUIPMENT                                     14




    7        TYPICAL SPRAY BAR APPLICATION                          16




    8        TYPICAL APPLICATION POINTS FOR A WET SUPPRESSION




             SYSTEM IN A CRUSHED STONE PLANT                        18
                                  -vi-

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                       List of Figures Continued









Figure No.




    9       BEFORE AND AFTER APPLICATIONS OF WET SUPPRESSION




            ON A PORTABLE PLANT                                     20




   10       BEFORE AND AFTER WET SUPPRESSION ON A SCREENING




            OPERATION                                               21




   11       BEFORE AND AFTER WET SUPPRESSION ON A PORTABLE




            CRUSHER-SCREENING OPERATION                             22




   12       PROPORTIONER, MAIN PUMP AND SURFACTANT DRUM             26




   13       CRUSHED AGRICULTURAL LIME OPERATION                     37




   14       GOOD PICKUP DESIGN ON A PORTABLE PLANT                  37




   15       GOOD HOOD DESIGN ON SCREENING OPERATIONS                38




   16       HOOD WITH RUBBER SKIRT AT SECONDARY CRUSHER OUTPUT      38



   17       DUCTING SUPPORTS                                        47




   18       FLEXIBLE SECTION BETWEEN HOOD AND DUCT TAKEOFF ON




            SECONDARY OF A PORTABLE PLANT                           49




   19       DUCTWORK CONNECTIONS TO A TERTIARY TRIPLE SCREEN UNIT




            OF A PORTABLE PLANT                                     49




   20       CRIBBING ON PRIMARY IMPELLER TYPE CRUSHER IN A




            PORTABLE PLANT                                          50




   21       EXTENSIVE CRIBBING ON TERTIARY CONE CRUSHER WITH




            TRIPLE DECK SCREENS                                     50




   22       TALL NARROW BAGHOUSE IN BACKGROUND ON A PORTABLE PLANT  51




   23       TALL NARROW BAGHOUSE USED WITH A PORTABLE PLANT         51
                                 -vii-

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                       List of Figures Continued





Figure No.                                                         Page


  24        CHARGE ON TRAP ROCK (3 RUNS)                           56


  25        CHARGE ON SILICA SAND  (5 RUNS)                         57


  26        TEST SET UP CEMENT PLANT "A"                           59


  27        PLAN VIEW OF SURGE BUILDING CEMENT PLANT  "A"           60


  28        CONCENTRATION VS PARTICLE SIZE BEFORE AND AFTER


            SPRAY IN SURGE BUILDING CEMENT PLANT "A"               61
 1-A        SKETCH OF THE GEOMETRIC RELATION BETWEEN THE


            VIRTUAL SOURCE POINT, THE SOURCE AREA AND AVERAGE


            POLLUTION CONCENTRATION at  LI and  L2                   75


 2-A        THE PRODUCT OF a a  AS A FUNCTION  OF DOWNWIND DISTANCE
                            y z

            FROM THE SOURCE                                        78
                                  -Vlll-

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                             TASK PURPOSE








       Under Task 19 of Contract 68-01-4135 the Contractor was to describe




control systems commonly used on stone crushing plants to control process




fugitive dust.  Typical annualized costs and maintenance procedures were to




be noted.  Special problems in the control of portable plants in arid regions




were to be addressed.




       In addition, the Contractor was to examine the possible amelioration




of downwind ambient particulate contributions from plant operations resulting




from process control designed to meet MESA (now Mine Safety and Health




Administration) requirements.




       This report is divided into two sections:  Section I, Air Pollution




Control of Process Operations, and Section II, Effects of MESA Control



Strategies on Downwind Ambient Conditions.
                               -ix-

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                             INTRODUCTION








Industry Background








       In evaluating information on control of air pollution resulting from




crushed stone operations it is desirable to have a general concept of the




industry.  This includes plant distribution, size, concentration, raw




materials, customers, and market economics.




       The crushed stone industry is one of the largest mining industries




in the United States with production in 1975 totaling 902 million tons,



valued at $2 billion,  Crushed stone sites are found in every state except




Delaware.  There were, according to the Bureau of Mines, 5,523 operating




plant sites in the United States in 1975.  The plant site count by state




is shown in Table 1.  The production and market for this crushed stone




is all within the United States.  Export trade and foreign imports are




negligible.




       The raw materials used in the crushed stone industry are derived




from all three geological classes of rock:  igneous, sedimentary and




metamorphic.  The specific stone used is basically a function of its



availability, quality and ability to meet the specifications and standards




for a specific product.  Some stone types are not well suited to the crushed




stone market requirements.  Shale, shaley limestone and slate are examples




of stone whose chemical and physical properties are undesirable.  On the




other hand, the properties of limestone allow it to be used for a variety of




end products.  Because of its versatility and availability, about 70% of all




stone crushed in the U.S. is limestone.  Other stone types used extensively
                                   -1-

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                      Table  1



        CRUSHED STONE PLANT  SITES BY STATES*

   State                         Crushed Stone
Alabama                                 54
Alaska                                  116
Arizona                                 43
Arkansas                                93
California                              517
Colorado                                81
Connecticut                             18
Delaware
Florida                                 122
Georgia                                 74
Hawaii                                  34
Idaho                                   69
Illinois                                325
Indiana                                 130
Iowa                                    337
Kansas                                  196
Kentucky                                111
Louisiana                               20
Maine                                   17
Maryland                                31
Massachusetts                           34
Michigan                                49
Minnesota                               102
Mississippi                              8
Missouri                                274
Montana                                 74
Nebraska                                27
Nevada                                  96
New Hampshire                           38
New Jersey                              32
New Mexico                              41
New York                                92
North Carolina                          92
North Dakota                             5
Ohio                                    159
Oklahoma                                76
Oregon                                  420
Pennsylvania                            216
Rhode Island                             4
South Carolina                          34
South Dakota                            21
Tennessee                               135
Texas                                   206
Utah                                    26
Vermont                                 46
Virginia                                1?T
Washington                              254
West Virginia                           52
Wisconsin                               369
Wyoming                                 25
                           Total     5,523
*Source, Reference 1.
                         -2-

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for crushing are:  granite, traprock, argillite, diabase, sandstone, marble,


quartzite, quartz and gneiss.


       The largest market for crushed stone is the construction industry.


Contruction use accounts for about 85% of crushed stone production which


includes:  dense-graded road base, concrete aggregate, bituminous aggregate,


cement, and riprap.  Other major crushed stone products are:  lime, agricul-


tural lime, mineral fillers, filter stone, glass, refractory stone and chemi-


cal stone.


       Portable plants are often used by producers to solve a number of


production and market problems.  In situations where the demand for stone


from a particular quarry does not justify the capital expenditure required


for a permanent plant, a portable unit can be used to serve a cluster of


quarries.  This is often the case in the midwest and western areas where


portable plants are used to build up stockpiles of crushed products, after


which the plant is moved to the next quarry owned by the producer.  It is


difficult to pin down the number of portable plants.  The Bureau of Mines


reports activities at plant sites, a number of which could be served by a


single portable plant.  About 28% of the reported plant sites are worked by

                                                              2
portable plant equipment, according to Bureau of Mines figures .  Portable


plant sites by leading states in descending order of number of sites are:


 Iowa, Wisconsin,  Illinois,  and Oregon.


        The wide distribution of crushed stone operations is due in part


 to the high costs of transportation relative to the cost of the product.


 The cost of transportation of crushed stone by water is significantly less


 than that for rail or truck, and where producer and user are close to water


 transport, the market sphere is enlarged.
                                   -3-

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       Plant operations can range from a production capability of about




100 tons/hr. to over 1,000 tons per hour with annual production ranging




from less than 100,000 tons to over 2 million tons.  Bureau of Mines data




for 1973 (see Table 2) show that about 40% of the production is from plant




sites of 900,000 tons and over annually, which account for only 10% of the




total number of plant sites.  Those with an annual production of less than




100,000 tons accounted for 23% of the total number, yet only 4%  of the




total production.  This seemingly high concentration ratio is exaggerated




by the fact that several plant sites are serviced by one portable plant.




The crushed stone industry, nevertheless, illustrates a high concentration




ratio with plant sites producing 1 million tons or greater, exerting a pro-




nounced effect on total production.




       The crushed stone industry competitive posture can be characterized




by the following:








       1)   Production is concentrated close to urban areas




       2)   Within a marketing region, yard prices are competitive



       3)   On public bids delivered price is competitive



       4)   Transportation costs are the dominant cost feature in




            competition




       5)   Product demand is essentially inelastic




       6)   Competition is basically intra industry; some inter industry




            competition exists where crushed stone may be substituted for




            sand and gravel.
                                  -4-

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                               Table 2
DISTRIBUTION OF
Plant Size
thousand tons per year
50-99
100-199
200-299
300-399
400-499
500-599
600-699
700-799
800-899
over 900
ROCK CRUSHING PLANT
No. of Plants
in size range !
989
1,075
516
387
301
215
172
129
86
430
SITES BY
fc of Total
23
25
12
9
7
5
4
3
1
4.
10
100
SIZE*
Contribution to National
Production, % of Total
4
9
7
8
8
7
6
6
4
41
100
*Source of Data,  U.S.  Bureau of Mines 1973 Statistics.
                                  —5—

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       The inelasticity of overall industry demand, the concentration of




quarries and plant sites near urban areas, and the high cost of product




transportation results in a localized competitive picture, although com-




petitive spheres of operation can be large in instances where the quarry




(or pit) and customer are located near a rail or barge loading facility and/




or if the quarry (or pit) produces unusual sizes or quality of material.









Sources of Air Pollution









       Rock crushing activities can be broadly classified as quarrying




and beneficiation.  Quarrying consists of removal of overburden, the earth




over the desired stone deposit; drilling blast holes; blasting; transport




to beneficiation facilities.  Beneficiation or process facilities include




crushing, screening for size, conveying and storage.  The information on




controls for rock crushing plants and the effect of MESA compliance on down-




wind ambient in this report cover the beneficiation portion of the activities




only.




      The beneficiation may take place using either wet or dry techniques




at the  various  crushing or screening processes points.  Some plants use




dry processing  in all product sizes except the "fines" production, where




wet processing  is often used.  Where wet techniques are involved the'




air emissions are significantly reduced over those in dry process operations.




In those instances where wet process points are involved, processing of




the water effluent is needed to correct for total suspended solids (TSS)




in the  wash water.  Stone quarries  are under a zero discharge system require-




ment which  requires recirculation of the water with appropriate settling






                                -6-

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  ponds  and  in  some  instances  treatment by  flocculating agents to increase




  sedimentation rate.




        The  plants considered  in  this report are dry processing plants




  although the  raw stone may be in  an initial wet  condition.




        Once the rock is broken into  pieces which can be accommodated by the




primary crusher, either directly from a well-controlled blast or by  a com-




bination of  blast and drop ball,  the fractured rock is trucked to the first




or primary  crusher, where it  is  dumped onto a scalping screen and feeder




which scalps  (or removes) the smaller pieces and  overburden which do not




require primary crushing, therefore reducing the  load on the crusher and




removing unusable material, freeing the crusher for its purpose of crushing




only the larger rocks.  The scalped material is conveyed to a separate spoils




pile for disposal,  while the  crushed material is  generally conveyed  to a



surge pile  (temporary storage pile) for distribution to subsequent processing




points.



        Crushers utilize compression and impact to mechanically stress the




rock beyond its breaking point.  Some crushers rely almost solely on impact,




whereas  at  the  other end of the  range compression is used.  The more impact




involved for a  given stone, the  more mechanical propulsion of particles and




air turbulence  tends to increase emissions.



        Screens  are  located before  each crusher.   Screens agitate the




particles as they proceed across the surface so that each particle has an




opportunity to  align its two  smallest dimensions  with the screen holes.




This process of agitation frequently developed by an eccentric action pro-




duces airborne  dust by mechanical  and air  turbulence forces.





                                   -7-

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       Whenever a material is transferred into a bin or hopper, or from




one conveyor to the other, or into a screen deck or crusher, air is induced




and displaced.  This action is largely responsible for the smaller particles



becoming airborne.




       Thus the process areas that must be controlled for fugitive dust




in stone crushing beneficiation steps are:








       •    Crushing Operations




       •    Screening Operations




       •    Storage



       •    Transfer Points








       The number, location, type, and size of crusher and screens vary




from plant to paint depending on many factors.  These factors include type




of stone, production rate, range of products, and process space available.




Figures 1 and 2 taken from Reference 4  show typical plant operations




at 300 and 600 tons per hour.  These are the model plants costed for




air pollution controls later in this section.
                                  -8-

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                                  Figure  1
   TYPICAL HARD ROCK STONE CRUSHING  PLANT OPERATING AT  300  TONS  PER HOUR
-9-

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                                                             Figure 2
                             TYPICAL HARD ROCK  STONE CRUSHING PLANT OPERATING AT 600 TONS PER HOUR
CleyOOO_
                                       -10-

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                               Section I








              AIR POLLUTION CONTROL OF PROCESS OPERATIONS








       Dust in the process operations of crushing, conveying, and sizing




in crushed stone operations is generally controlled either by suppressing




the tendency of the dust to become airborne by applying water that has been




mixed with a suitable chemical to reduce its surface tension directly to




the material, or by capturing dust that might otherwise become airborne in




a closed dry collection system.  The first will be referred to as wet sup-




pression and the latter as a baghouse system.  A recently introduced system




using charged water sprays is emerging from the experimental phase but remains




to be proven in field  operations for crushed stone plants.  All three of




these systems will be described with emphasis on the first two since they




have been successfully used in the field while the third is not fully demon-




strated.




       Crushed stone plants can be permanently placed with individual




parts of the process nearly completely covered like those shown in Figures




3, 4, or 5; or they can be highly portable, mounted on truck beds, with a




typical eight-day cycle from start of preparation for a move to completed




erection of the plant at a new site  (see Figure 6).




       Unique application problems with portable plants are discussed at the




end of each section on the two main control strategies covered in this




report.
                                  -11-

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                             Figure  3
   Permanent  crushed  stone  plant  with  covered  screen  houses  to  the  left.
      Plant  is  controlled by  two  baghouses,  one  left  foreground,  the
                      second  right background.
(Photo courtesy Pennsylvania  Department  of Environmental  Resources, PennDER)
                               Figure  4
    Distant view  of  plant  producing  crushed  stone.   All  process  units
       enclosed.   Plant  controlled by  cyclone  primary and  baghouse.
                     (Photo  courtesy of  PennDER)

                                  -12-

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                               Figure 5

Close up of plant shown in Figure 4, emphasizing the covered, permanent
                       type of plant operation.
                     (Photo courtesy of PennDER)
                                 13-

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                           Figure 6

A Stone Crushing Plant Consisting of Unitized Portable Equipment
   (Photo courtesy of Cedarapids, Iowa Manufacturing Company)
                            -14-

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                         Wet  Suppression  System








       The use of water as  a means of dust suppression has been practiced




for more than thirty years  in both coal and non-coal mining operations.   Water




sprays, either directed by  nozzles at transfer points, crusher exits and




screening operations or applied manually by spray hose at muck piles (piles of




rock from blasting) significantly reduce emissions.



        System design is not guided by equations based on the physics of the




 situation,  but rather on rules-of-thumb learned from many years of applica-




 tion experience.   A wet suppression system as the name implies prevents or




 suppresses  the tendency of the particles  to become airborne.  From the  modest




 amount of water added (about 1/2 of 1% of weight of stone feed),  it is  ob-




 vious that an increase in  density of a particle by means of retention of the




 water is not the sole mechanism for preventing emissions.  The agglomeration




 of the small particles and the "sticking" of small particles to large pieces




 of stone is also involved.  The precise mechanism of suppression is not as




 important as the fact that dust is suppressed when water is applied. As dis-




 cussed later, water alone  has poor wetting properties and a solution includ-




 ing a surfactant or surface active ingredient is usually applied.   This



 substantially reduces (about 4:1) the amount of water that is required.



        Application is made by spray heads mounted on a spray bar as in




 Figure 7.  There are hundreds of different spray head designs when the  com-




 binations of flow, droplet size, coverage angle, spray crossections, etc.  are




 considered.  Droplets are  generally formed by the water pressure on specially




 designed channels and exit orifices in the spray heads.   Very small droplet




 sizes that  rely on air atomization are practically never used,  Different




 size and types of sprays are often used on different parts of the  plant -  the
                                   -15-

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            Figure  7



  Typical  Spray Bar Application



(Photo  courtesy of  Johnson March)
             -16-

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larger droplet types early in the production and the finer droplet size with




the smaller size materials.  Choice of spray heads are affected by production




rate, stone size, and location ability.  The spray bars on which the spray




heads are mounted are located with sufficient clearance from the belt, screen,




etc. to make sure that moving stone does not impact, trucks or other vehicles




are not likely to hit it (as for instance in the loading area of the primary



crusher) and so the unit can be observed and maintained with reasonable ease.




Sprays are usually located about 3 to 6 feet from the contact point - splash-




ing occurs if too close to the surface and the advantage of a fine spray will




be lost, while if spray bars are too far from the surface, crosswinds will




have more of a chance to deflect the spray away from its target.  The design-




er usually examines the access problem, stone size and production rate in




determining the number, type, and location of the spray positions in a proc-




ess.




      A good figure  '   for the amount  of solution sprayed on the stone is



1.5 gallons per ton of plant production.  If chemicals that reduce the sur-




face tension of water are not used, this figure could be three or four times




greater.  The 1.5 gallons of solution per ton of production is not applied



at one point, rather it is the sum of the solution distributed at various




points throughout the plant.  Figure 8 shows typical application points for




such a system.




       Plain water with a surface tension of 73 dynes per cm at 20 C does




not exhibit good qualities of wetting, spreading and penetrating.  Use of




water as the sole spray materials therefore would require more gallons per




ton of production than a solution containing a surfactant.  When surfactant
                                 -17-

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      TRUCK DUMP
                                    INCOMING WATER LINE
                                                          Surfactant
                               PROPORTIONER
                                 Figure 8

Typical Application Points  for a Wet Suppression System  in  a  Crushed
                               Stone Plant
                                   -18-

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are added, the surface tension of water is reduced to 20 to 30 dynes per




cm which greatly enhances the dust suppression since the water is able to




penetrate the dust particle creating a cementing action between dust particles




so that the agglomerates thus formed are too heavy to become airborne.




       "Wetting Agents" is a broad category which covers such items as emul-




sifiers, solubilizers, detergents, foams, penetrants, thickeners, etc.  Dust




control compounds, on the other hand, are carefully formulated blends in



which one or more special surface active agents ("surfactants") have been




incorporated.  The molecules of these compounds are composed of two groups




exhibiting differing solubility characteristics.  One part, usually a long




chain hydrophilic or water loving group is usually a sulfate, sulfonate,




hydroxide, ethylene oxide, etc.  The other group is a long chain hydrophobic




or water hating group.  When properly proportioned, these compounds effect-




ively reduce the water surface  tension.



       Wet suppressent systems with surfactant solutions appear effective




in dust control although there is no quantitative data to specify the degree




of control attained.  Figures 9 through 11 indicate the effectiveness of well




designed wet suppression systems.  Such systems, however, cannot be univer-



sally used for dust control.  A spokesman  for one of the largest companies




that makes and installs wet suppression systems stated that in their experi-




ence about 75% to 85% of crushed stone operations could use wet suppression




systems.  Some stone type and product size operations could not use the systems.




In these cases, dry collection equipment is used or a combination wet suppres-




sion and dry collection.
                                 -19-

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                              Figure 9
Before and After Applications of Wet Suppression on a Portable Plant
                  (Photo courtesy of Johnson March)
                                 -20-

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                        Figure 10
Before and After Wet Suppression on a Screening Operation
              (Photo courtesy Johnson March)
                         -21-

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                               Figure 11

Before and After Wet Suppression on a Portable Crusher-Screening Operation
                    (Photo courtesy of Johnson March)
                                -22-

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       In the initial process stages of production, i.e. primary crushing




and screening and secondary crushing and screening, problems associated with




wet suppression are minimal.  However, when used to control dust at tertiary




crushing and screening where small product sizes and screen openings are en-




countered, problems may arise.  The wetted dust tends to blind the openings




in fine screens.  In agricultural limestone where very fine material  is re-




quired in a dry state, the addition of water is not practical.  Many states




also have what is known as a wash out test specification on certain grades




of stone.  This test is designed to measure and thereby control the amount




of -200 mesh (74 microns) particles in the product.  A given amount of




product is washed in a prescribed fashion and the amount of particles




passing a 200 mesh screen weighed.  If the weight of these particles exceeds




a certain amount of the product weight (usually 1% to 2%), the lot from




which the sample was taken is rejected.  If the stone is to be used for cer-




tain types of concrete products, both the fines and any surfactant remains




may have to be washed out of the stone before it is acceptable.  This requires




an additional plant operation with the need for more water, on the order of




several hundred gallons per ton of product processed.  The water residue




would then have to be treated for solids removal before discharge to surface




waters.  If discharge is to municipal facilities, a charge based quantity




discharge and a surcharge based on solids content may be levied.   If the




plant discharges into a municipal system that was constructed or upgraded




with a government grant under the Federal Water Pollution Control Act, the




plant would be assessed both a User Charge and an Industrial Cost Recovery



Charge.
                                -23-

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              A potential problem is occasionally noted relative to a tendency

       of the surfactant material to cause air voids in concrete and bituminous

       mixes.  No data could be found to identify this as a practical problem

       on a national basis.  Several producers in the Pennsylvania-New York

       border refrain from using surfactants in their wet suppression systems,

       but no national pattern or test evidence was uncovered.
        System Configuration



               The method of suppression described above requires a series of spray

        bars and nozzles, a supply of surfactant which is proportioned and mixed with

        the water, a set of connecting pipes, pumps to force the water to the spray

        heads, and appropriate filters.  A method of automatically turning on the

        system only when material is being produced is required, as is winterizing

        equipment when  the system is to be employed in beldw-freezing weather.

                The  system  is  shown below  in  schematic with  only two spray bars

         to demonstrate  the equipment  involved.
           Incoming Water
Drum of Surfactant
Proportioner
                                                    Spray  Bar #1
                                          -24-
                                           Spray Bar #2

                                                 A
                                                                Spray
                                                              Controller
                                                                 'M.
                                                                      Control
                                                                    Actuator (s)
                                                         Spray
                                                       Controller

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       The function of the proportioner shown in Figure 12 is to filter




the input water if necessary, add surfactant from a drum at the rate of




one part to 1000 parts water or more, and develop a pump head of about




150 psi.  This pressure is typically used at the truck dump at the front




end of the crusher and reduced to about 60 psi at the other spray bars by




means of pressure regulators.




        The control actuators automatically detect presence of stone on the




conveyor  and  transmit  the signal to  the spray controllers.  The actuators




operate on a  variety of principles including mechanical displacement of




the  conveyor  belt, weight, electrical  interlock with the  conveyor drive




motors, by measuring the  current load  to drive motors, and for fine or




light weight  materials that  cause little conveyor deflection or motor




drag, by  a device mounted on top of  the conveyor that  is  deflected by




material  on the conveyor.




        A  spray  jet controller  is mounted before each spray jet header and




consists  of a filter and  a method of governing the flow of the mixed




solution  supplied by the  proportioner.








Maintenance








        According to a  report prepared  for the U.S. Bureau of Mines by MSA




Research  Corporation in April,  1974  ,  adequate maintenance of dust control




systems in non-coal mining and ore processing operations  seems to be the




exception, rather than the rule.  The  report contained results of visits




to 50 mines and 51 mills  (processing plants) of which  seven were crushed




stone.
                                 -25-

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                 Figure 12

Proportioner, Main Pump and Surfactant Drum
     (Photo courtesy of Johnson March)
                  -26-

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       Where wet suppression systems were employed spray bars were found




where the nozzles were either completely clogged or clogged to the point




where they were ineffective.  In most cases, this problem was due to




inadequately maintained water line filters.  The report was generally




critical of the state of maintenance of control equipment which was reported




in a poor state of repair in relation to general plant.




       As with any dust control device,  a  wet suppression system must be




adequately maintained to keep its efficiency at peak levels.  The principal




source of trouble is in foreign material blocking the liquid flow.  If the




system operates on city water the filters can go for months without serious




effects whereas if the water is from wells, rivers, or ponds more maintenance




will be involved.  Although the system  details vary from manufacturer to




manufacturer there are generally three filters, one at the proportioner, one




at each spray controller, and one in each spray.  The main filter in the




proportioner demands the most attention because it is first to "see" the




conditions of the supply water.   One manufacturer  suggests the following




maintenance procedures.   After some experience is gained with the system the




maintenance schedule can be adjusted.  For  instance if the strainer baskets



remain clean after several weekly checks this procedure could be extended.




On the other hand,  the strainer basket in the proportioner might need more




frequent attention if the input water has a high amount of solids.
                                  -27-

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DAILY MAINTENANCE








1.    At time of start-up of Proportioner




      a.   Check pump discharge pressure.




      b.   Check operation of level control valve.




      c.   Check operation of surfactant pump.




      d.   Check level of surfactant compact in drum.




      e.   Check operation of Inlet Water Filter,




2.    Visually check spray pattern and direction of all spray jets.




      Clean and adjust as necessary.








WEEKLY MAINTENANCE








1.    Clean strainer basket in each Flow Controller.




2.    Clean strainer basket in the Proportioner.




3.    Check operation of all Automatic Spray Controls.








GENERAL








1.    Lubricate all equipment requiring lubrication, including




      wheels on Automatic Spray Controls, when other plant equipment




      is lubricated.




2.    Before first freezing weather, check all heating equipment.




       (Winterizing is accomplished by wrapping electrical heating




      tape around pipes much the  same as in winterizing residential.)
                           -28-

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       More detailed information is usually contained in the System and




Equipment Operation and Maintenance Instructions generally furnished by




the vendors with the equipment.








Portable Plant Applications








       Spray systems are readily installed in portable plants, and by the




use of flexible connections from the proportioner to the spray headers,




can accomodate changes in plant layout.   In cold weather there is a problem



in winterizing such installations by using heating tape because of the




flexible nature of the hose and its heat transfer characteristics compared




to metal piping.



       In areas where arid conditions are encountered, there are special




problems on water needs for the system which must be considered in setting




up the plant.  As noted previously, if a surfactant is used, the total water




needs for a plant would be about 1.5 gallons per ton of product.  If a




surfactant is not used, water requirements would be 4 to 5 gallons of water




per ton of production.




       There are several regions of the country which have arid conditions




and where portable plants are extensively used.  Eastern Oregon, for example,




is one such region of low precipitation and with high reliance on portable



plants.




       Stone crushing operations in this region might obtain water from three




sources;  ground water (wells or old quarries that have intercepted the water




table), surface water (rivers,  streams,  lakes,  ponds, etc.), or tank truck.




Water wells may be constructed when a plant is  to remain in one location for
                                  -29-

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a period of time or if the plant returns periodically to the location.   This,




of course, means that sufficient ground water supplies must be available to




meet the plant's needs, and because ground water occurs sporadically in




Oregon, well drilling is relatively uncommon.  The cost of drilling a well




is about $20 to $25 per foot plus $15 per foot for casing (steel).  Water




when available via wells occurs within 100 to 300 feet of the surface which




would cost between $3400 (drilled to 100' and cased to 75') and $10,000




(drilled to 300' and cased to 225'.).



       Surface water supplies can be used when they are available,  A plant




could purchase water from the owner of a farm pond.  In other instances, a



stream may be temporarily dammed to serve as a source of water for the




crushing operation.  The cost of water is about $10 per 1000 gallons or




about $0.01/gallon.  This is the prevailing  cost of water in both Eastern




and Western Oregon according to Oregon  sources.



       When neither ground water nor surface water supplies are available




to a stone crushing operation, water can be  supplied by tank truck.  These



tank trucks can be purchased or rented  by the crushing plant.  Crushed  stone




plants with their own  water trucks, are frequently of the  "home-made" variety.




 That is,  a  tank will  be mounted  on the  bed of an  old  truck and used  for




 hauling  water.  The  cost  is  less than half of a new truck.  The cost of




 purchasing  a  new tank  truck  can  be from about $22,000  for  a 4,000 gallon




 truck  to $43,000 for  a 10,000  gallon truck  (either diesel  or  gasoline  engine




 powered).   The  operating  cost  of one of these trucks  is about  $0.02/ton of




 product  (this includes labor,  rent,  fuel and servicing).




       Another  way of approaching  the cost is to  use  rental figures  set




 forth  in a  state's method of adjusting  highway  construction contract




 figures  for unanticipated additional work.   In  Oregon,  for example,




                                 -30-

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                                     g
according to Oregon highway personnel  when the state requires supplemental

work done and desires to use a contractor's equipment, there is a set pay-

ment schedule on what is known as a "force account".  This schedule shows

that on a weekly basis the contractor would be paid an amount of $399.65 +

15% for overhead and profit for the use of a diesel powered gravity type

sprinkling truck (the closest to a water truck on the schedule).  Assuming


profit at 1/2 of the 15% figure, the weekly cost would be $430 or $10.75

per hour prorated over a 40-hour week.  This figure includes all expenses,

including fuel  and oil, but excludes labor.  Labor at $12.35 per hour

including markup is, according to contacts with Oregon highway personnel,

a realistic  labor rate to drive the water haul truck to and from a pick-up

point.  Since   only  about 2 hours per day would be spent in driving the

truck, the hourly prorated amount would be 2/8 of $12.35 or $3.09.  The

total hourly cost would be $10.75 + $3.09, or $13.84.  For a 300 ton

per hour plant  (one  that could be supplied by one 4,000 gallon truck on

one trip per day) the cost per ton  capacity would be $13.84 T 300 tons

or 4.61$ per ton.  To this must be  added the cost of the water.

       Despite  the fact that  there  is a considerable difference in precipi-

tation between  eastern and western  Oregon, adequate water supplies are

available if trucking is done and the prevailing rate of about  $10 per

 1000  gallons of water holds in both regions   .  The water cost, assuming

 1.5 gallons  per ton  of product would  add  1.5$ to the  trucking cost for  a


 total of 6.11$  (4.61$ +  1.5$) per ton of  stone  crushed for  a 300  ton per

hour  plant.  For  a 600 ton per hour plant  the cost  is 4.45$  (see  Table  3)

per ton  added.


                                  -31-

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       Therefore, the trucking cost alone more than doubles per ton


control costs by wet suppression of a plant required to haul water over


a plant which is not required to haul water.   This cost of control, however,


viewed in relation to product cost and market posture of the industry is


not unreasonable.  While operations using wet suppressent methods in


arid regions will experience higher operating costs, the inelastic nature


of the market and the strong effect transportation exerts on price indicates


that such costs can be passed through with negligible change in product


demand.


       A portable 300 ton per hour plant using a wet suppression system


would experience control costs of 9.84£ (see Table 3) per ton if water


had  to be hauled.  The price of crushed stone FOB quarry is on the order


of $2.50 per ton.  It varies according to location of the quarry and size


stone produced.  The average price of 1975 stone received by one state


depot in Pennsylvania in response to competitive bids was $2.41 for 2A

                                         q
stone, and 2.73
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                                 Table 3

                         MODEL WET SUPPRESSION COSTS

               FOR PROCESS PORTIONS OF CRUSHED STONE PLANTS
                   Capital Costs for Installed System

                                      Small Plant           Large Plant
                                      500 Tons/Hr.          600 Tons/Hr.

Wet Suppression Equipment          $58,643               $69,108


Annualized Capital Costs                      $ 7,330                $ 8,639
  (12.50% of Capital)
                                                 2
                          Operating § Maintenance

Electricity §  .04/KWH               $    115               $    288

Maintenance Operation  £  Supplies    $14,048               $22,398

Total Annualized  O&M                          $14,163                $22,686

Total Annualized  Cost                         $21,493                $31,325
  (Capital  + O&M)

     Cost/Ton (excluding water hauling           3.73^                 2.72$
               £ water costs in arid
               regions)

      Added Cost/Ton for water $ hauling
        in  arid regions                          6. Hi                 4.45
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       At that time the average price of a cubic yard of concrete in place




was $125.  The average price of the stone at the quarry was $1.73 per ton;




FOB delivered it cost approximately $3.00.  This was less than 1.4% and




2.5%, respectively, of the price of the concrete.  Thus a 10% increase in




the price of the stone at the quarry would have a negligible effect on the




per yard cost of concrete in place, increasing the price by $.17.  The




effect of a 10% increase in the price of stone would have about a $7 increase




in the price of a $30,000 home; a $500,000 building would be increased by




$180, a $400,000 per mile highway by $640 per mile and a $360,000 school




building by $140.




       Transportation costs make the industry one of local competition




with the notable exceptions of some stone sources with access to cheap




water transportation.  Stone transportation costs range roughly from 12




to 19
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                            Baghouse Systems







        Dust in process operations of crushed stone plants is often




 controlled by dry collection techniques using appropriate methods to capture




 the dust and transport it to one or more baghouses.  Whether a central




 baghouse is used or two separate baghouses depends principally on the



 layout of the plant and is decided on the basis of installation and operational




 economics.  Baghouses must be used in those operations where stone type and/




 or small product size preclude the use of wet suppression techniques.
 Principal System Components








        A baghouse system in crushed stone process operations can be examined




 in the light of the four functions which make up the total system design:








        •     Pick up design




        •     Ducting design



        •     Filtering design




        •     Filter catch handling






Pick Up Design:








        This is  a key factor in a dry collection system.   If the dust that




would otherwise  become fugitive is not properly "picked up", the system will




fail in its job.  A pick up system consists of a hood or enclosure and an




indraft sufficiently high to entrain the dust that may otherwise become




fugitive.   The indraft velocity in feet per minute multiplied by the area




of the hood opening in square feet yields the volume flow in cfm required




to adequately vent a particular dust emission point to the connecting duct




                                 -35-

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and thence to the baghouse.   There is general agreement on indraft design.
A minimum draft flow of 200 fpm at pick up points is frequently used.
Some general rules applied at various operational points are:
        1.     Volume flow rate at conveyor transfer points of 350 cfm per
              foot of belt width for belt speeds of less than 200 feet per
              minute and 500 cfm per foot of belt for speeds over 200 feet
              per minute.
        2.     Volume flow rates of 100 cfm per square foot of casing cross
              section for bucket elevators.
        3.     Volume flow rates of 50 cfm per square foot of screen area
              on vibrating screens either single or multiple deck.

        Not  only must the necessary  indraft  flow be provided,  but the
 emission point  should be covered as completely as  possible  to avoid the
 effects of  wind interference  which  would otherwise blow the particle away.
 For example if  a 200 feet per minute (fpm)  indraft velocity is used,  a
 cross  wind  of 10 miles per hour would exert a cross draft of  880 feet per
 minute on the particle.   Its  resulting trajectory  rather than being up and
 into' the hood and to the transfer duct would then  be at 87° to the intended
 direction,  and  would likely not be  captured.   Good enclosure  and hood
 design are  indicated in Figures 13,  14 and  15.
        It is common practice  to use abrasion resistant  rubber liners around
 hoods  venting crushers or transfer  points (see Figure 16).   These  liners are
 often constructed with slits  in the lower edges so that they  can be slightly
 larger than the openings, but not impede material  flow  on conveyor access
 points and  crusher openings.   It is good practice  to cover  conveyor belts to
 prevent dust being carried away by  the wind.   Screen houses are frequently
 enclosed and vented from the  top.
                                -36-

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                                    Figure 13
Crushed Agricultural Line Operation Showing Good Enclosure Design at Transfer Points
                           (Photo courtesy of PennDER)
                                                            Figure  14
                                              Good  pickup  design  on a  portable plant
                                                          (JACA Photo)
                                     -37-

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                                   Figure 15
Good Hood Design on Screening Operations of an Agricultural Crushed Stone Plant
                            (Photo courtesy PennDER)
                                                          Figure 16
                                             Hood With Rubber Skirt at Secondary
                                                       Crusher Output
                                                        (JACA Photo)
                                     -38-

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Ducting:







       Air velocities  in the ducts leading from the hoods to the baghouse are




typically 3500 to 4500 fpm.  This velocity is needed to keep the particles




entrained in the air stream rather than settling out at bends, turns and




connecting points in the ductwork system.  Tight bends should be avoided




both because particles may be knocked out there and because of abrasion of the




metal walls.  In addition bends and abrupt connecting of ductwork introduces



frictional air losses which must be compensated for by larger fans and motors.




Vibration is also a problem at crusher and screen pick ups which is frequent-




ly solved by using a flexible section at the inlet to minimize damage.








Fabric Filters:








       The actual filtering operation in crushed stone operations is a reason-




ably simple one.  Problems such as high gas temperatures and corrosive atmos-




pheres that constitute design problems in many baghouse installations are not




present.  Nomex and fiberglass bags need not be used, insulation is not




generally required, and temperature adjustment and temperature safety devices



are not called for.  Sizing, as in any baghouse, remains a critical design




factor.  The ratio of the amount of air by volume to the lateral area of the



bags, the so called air-to-cloth ratio, can vary from 2 or 3 to 1 for mechan-




ically shaken bags to 6 or 7 to one for pulse air type units.  In the mechan-




ically shaken bag  method the baghouse is larger because of the lower air to




cloth ratio and  the fact that one compnrimiMii must !><• tiiKon of) ••( ro.'un fur




shaking, while in the positive air blowdown the full system is essentially




always on stream.  While mechanical shake baghouses are larger for a given




gas handling capacity, they require less in the way of bag cleaning equip-




ment.  Air blowdown requires sets of solenoids and air headers on each row




of bags, air Venturis for each bag, and an air compressor to supply the nec-




essary blow down air.



                                 -39-

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        The fan is usually located on the side of the baghouse opposite the


baghouse inlet - the "clean side" of the system.   The air is pulled through



the baghouse giving rise to the term negative pressure baghouse.   Thus, the


fan blades do not experience the wear they might  otherwise if the fan was


located on the dirty side of the system.  The negative pressure aspects, how-


ever, means that the baghouse should be well sealed, and leaks in ducting


promptly repaired.






Dust Disposal:






        What  is done with the captured fines varies from plant to plant


depending on  the product being manufactured and "outside11 markets for the


fines in that particular area.


        Dust  hoppers usually have an air lock valve emptying the bin either


into a truck  or via a screw conveyor or a pneumatic conveyor to some other


direct use or storage for  future use.   For  instance,  the  baghouse  controlling


the primary crusher of  report  75-STN-3   periodically discharged the catch


during the cleaning cycle  through an air lock onto  the covered conveyor lead-


ing to the secondary crusher.   Its discharge of  about 10  tons daily is fed


directly back into the  process.   The second baghouse which collects material


from secondary and tertiary crushing and screening  operations discharges


directly into an agricultural  stone bin and is used as final product.

                                            13
         The baghouse reported in 75-STN-78    discharges a total of about four


 tons per day into a truck.   The material was then used as choke material in


 road based stone.


         Whether the material is reintroduced into the product, sold separately


 as fines or discarded  in a suitable dump site depends on the markets open


 to a particular plant.
                                   -40-

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Maintenance








        Failure of a conveyor, a crusher, or screening operations would




constitute immediate plant problems, production might stop, and if the nature




of screen failure involved holes in the screen out of size rejects would




mount.  Therefore these portions  of the plant receive preventative mainten-




ance to reduce potential downtime.  If failure occurred prompt attention




would be taken to restore production and assure quality control.  The dry




pollution collection system  is not  integral to the plant  - the plant can




produce quality stone  even if the pollution control  equipment is not function-




ing properly.  Therefore there is a temptation to devote  more maintenance




attention to the productive  processes rather than the control process.




This  was noted by Reference  7, a  study on  control efficiency in non coal




mines,  both  surface  and deep, that  stated, "It is obvious that production




maintenance  has priority over dust  control maintenance."




        Maintenance  starts with enclosures and enclosure  skirts.  As mentioned




earlier in this section proper enclosures  plus an adequate indraft  is  essen-




tial  for capture of  what might otherwise be  fugitive dust.  Enclosures  can be




quickly examined - once a week should be sufficient  - to  detect  frayed  skirts



or loose or  ill fitting enclosures.




        Ducting should have  suitable clean out holes which should be examined




for dust build-up first on a weekly basis  and then adjusted to more or  less




frequent cleaning depending  on the  amount  of build-up.  Ducting  should  also




be inspected weekly  for holes and separations.   If the  enclosures and  skirts




have  a  reasonable fit  and the ductwork is  clear  and  without holes the  remain-




ing points to  inspect  are the baghouse and operating mechanisms  and the air



moving  apparatus.






                                  -41-

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       The amount of air moving through the system is important because




the amount of air for a given ductwork and hood design determines indraft




and duct conveying velocities.  If there is reduced airflow the system




may be working ineffectively.  Airflow and systems operation can be checked




very easily by the aid of two inexpensive instruments, costing less than




$100 each - a simple pressure gauge (either u-type water gauge, or magne-




helic) and a hand tachometer.




        The pressure gauge is used to measure system pressure drop and




pressure  drop across the baghouse.  The tachometer is used to measure the




fan  speed.



        As  air moves along ductwork, especially at restrictions,  joints,




bends etc. it encounters a resistance to flow reflected in a static pressure




drop   There is also a drop  in moving through the  baghouse, and around any




dampers that might be in the system.  System resistance can increase if




dampers are incorrectly set, bags in the baghouse  blind, and ducts become




obstructed.  If the system pressure drop increases the capacity of the system




to handle the air flow has decreased and it will not have sufficient



indraft.



        Since the air handling system is open to atmosphere at both ends,




the  system pressure drop is  numerically equal to the static pressure



across the  fan.   It is much  easier to measure the  static pressure drop across




the  fan than to measure all  the  individual pressure drops that make up the




system pressure drop.  A 3/8' pipe metal static tube can be inserted and




welded  into the outlet and inlet side of the fan positioned opposite to the




direction of flow to measure only the static pressure.  The inlet side is




first connected via a  suitable flexible tube to the  low pressure  end of the




gauge,  and a reading taken.   The flexible  tube  is  then attached  to  the out-
                                -42-

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let side of the fan and the high pressure end, and a second reading is taken.




The difference is the pressure drop in the system.  If these readings are




taken when the system is known to be in good operative condition, a diff-




erence of - 20% or more at a later date from the initial condiction at




satisfactory operation indicates some system problem.  Lower pressures




point to leaks between the dirty and clean side of the baghouse and/or




large holes in the ductwork, or reduced fan speed.  Higher pressures indicate




such problems as obstructions in the ducts, blinding of filter bags in the




baghouse and dents in the ductwork.




         Test points for static pressure should also be provided across the




dirty and clean sides of the baghouse,   A pressure gauge can be permanently




placed there, and is frequently included with the equipment.  This narrows




the diagnosis to the baghouse.   If pressure is lower than normal this can mean




that a hole or tear has developed in one or more of the bags, a clamp has




become loose at the plenum spearators,  a separation has occurred in the seal




or weld of the plenum separator.  If the pressure is higher than normal




it can mean that the bags are blinding either because of damp material or



incomplete cleaning.




         The tachometer can be used to measure the fan RPM by pressing the



tachometer tip firmly against the center of the fan shaft while the plant




is in operation.  Since most fans encountered in stone crushing operations




are positive displacement devices the amount of air handled is directly pro-




portional to the speed of the fan.   A decrease in fan speed which might be




due to operational wear or stretch of the belts used in the drive will re-




sult in a decrease in air handling capacity of the system including the



critical indraft portion.
                                 -43-

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       Bag cleaning mechanisms should be checked about once a week.   Mechani-



cal shakers should be checked for lubrication and wear.  Positive pressure



air cleaning devices should be checked for solenoid operation, and com-



pressor performance about once per week.  Manufacturers of compressors and



bags provide maintenance instruction with their equipment.  These are usually



broken down into daily (mostly visual), weekly, and monthly maintenance pro-



cedures.  Special sections are frequently included on preparations for lengthy



shutdown periods (viz. over winter months in northern states) and turn on.






Control Costs
       Control costs for a model plant fabric filter system installed is set



forth in Table 4.  The plant installation estimated was shown in Figures 1



and 2.






Portable Plant Applications






       Portable plant operations with  fabric filter systems are  faced with



certain problems  if  frequent plant movement is required.



       Five  portable stone crushing plant manufacturers were  contacted



regarding  baghouse systems for portable plants.  None offered  baghouses



as a  standard part of their portable rock processing plant  line.   Three



of the manufacturers who make portable asphalt plants  offer such units  in-


                                                                         1 2
tegral to  their portable plant line.   We were also told by  two  companies '



which serve  only  the after market  in control systems and  who  offer both wet



suppression  and baghouse  systems that  they  have  never  applied baghouses to
                                  -44-

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                                 Table 4

                     MODEL FABRIC FILTER SYSTEM COSTS

               FOR PROCESS PORTIONS OF CRUSHED STONE PLANTS
                    Capital Costs for Installed System

                                 Small Plant               Large Plant
                                 500 Tons/Hr.	        600 Tons/Hr.
Fabric Filter System
Equipment Costs  Installed     $125,922                 $200,802


Annualized Capital Costs                   $15,740                  $25,100
 (12.5% of Capital)
                                                 2
                          Operating § Maintenance

Electricity @ .04/KWH          $ 8,083                  $15,110

Operations § Supplies          $19,589                  $50,153

Total Annual 0§M                           $27,672

Total Annualized Cost                      $43,412

     Cost/Ton                                 7.54
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portable plants although both had supplied wet suppression systems to many




portable plants.  The difficulty of applying a baghouse system to portable



plants does not stem from making the baghouse proper portable since that is




frequently done for asphalt concrete plants whose configuration is constant




and where only one (in the case of drum mix plants) or at least no more than




three or four duct connections (in hot mix asphalt batch plants) to the




plant are involved.  In portable stone processing, difficulty arises from




the multiplicity of ductwork connections and supports, different plant lay-




outs at new sites, and resulting changes in dust loads.    This can be



demonstrated by examining one plant in Pennsylvania, and one located in




Maryland.





       Both of these plants consist of three portable units.  The plant




located in Pennsylvania produced about 2000 tons per day comprised of five




different product sizes.  The operation consists of a primary impeller




crusher, secondary crusher and double screen deck and tertiary cone crusher




and triple screens.  There are seven pick-up points, four in the secondary




section and three on the tertiary.




       The Maryland unit produces about 1600 tons per day comprised of two



products.  It includes a primary jaw, a single shaker screen, and a




secondary cone crusher with double-deck screens.  There are eight pick-up




points, one on the primary, two on the shaker screen and five on the double-




deck and secondary crusher.




       The ducting from both operations is quite extensive and is supported




by outriggers welded to various pieces of operating equipment  (see Figure  17)




or ground mounted A frames. The pick up hoods are also attached to operating




equipment and often have a flexible section to help dissipate equipment




vibration.  (See Figure 18).  Some connections are welded directly to pieces
                                 -46-

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                             Figure 17

Outrigger Support on Far Left of Duct and Ground Mounted Support on
Right.  Center Input Duct Shows Poor Design with Three Short Radius
Bends, and a Perpendicular Duct Intersection.  Wear is Evidenced by
                   White Sections That are Taped.

                            (JACA Photo)
                              -47-

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of equipment as shown in Figure 19.




       The baghouses at both locations were tall units having 132 bags each




arranged in 11 rows of 12 bags.  (See Figures 22 § 23).  In shipment they




were designed to be laid on their side on a flat bed.  The tall narrow




configuration simplifies dust load out and reduces the number of air headers




and air solenoid valves used in the air pulse cleaning system.  In the




Pennsylvania plant the baghouse was mounted with tie brackets on a concrete




base  while the Maryland plant was placed on rail-road ties and secured




with four guy wires from the top of the baghouse to a power pole and parts




of the stone operating equipment.




       Difficulty is encountered in breaking down this equipment and rein-




stalling it at another location.  The A frames must be dismantled and the




ducts must be cut into pieces that can be stored for highway travel.  The




outriggers and ducts must be cut free.  It is estimated that this dismantling




and reinstallation plus the same for the baghouse essentially doubles the




time normally required to move the plant when configuration at the new site




is identical to the old.  The most difficult problem in such reinstallation




is lining up the ductwork with the holes cut in the operating units and




the various hoods.  In the Pennsylvania plant, duct connections are made




to two operating units which are on  long flat beds which are positioned




by truck, the dollys removed, and the units cribbed as shown  in Figures 20




and 21.  The Maryland system requires interconnections to  three units.  It




is difficult to maneuver the equipment beds to the position where seven




or eight ductwork connections  can match up.  Field cutting and fitting then




must be undertaken  to perfect  the fit.
                                  -48-

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                                                         Figure 18
                                             Flexible Section Between Hood and
                                              Duct Takeoff on Secondary of a
                                                      Portable Plant
                                                       (JACA Photo)
                                Figure 19
Ductwork Connections to a Tertiary Triple Screen Unit of a Portable Plant.
Holes Were Cut in Unit and Duct Welded in.    Duct Radius and Intersection
                         Points Show Good Design
                               (JACA Photo)
                                 -49-

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-50-

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            Figure 22
Tall Narrow Baghouse in Background
        on a Portable Plant

Baghouse attached to frame mounted
on concrete slab. Caged ladder and
handrails in accordance with OSHA.
Bin empties into truck.   Note un-
usual design of exit stack which
exits from clean plenum of the bag-
house  (top of filter house)  and
then runs horizontally (view ob-
scured  by foreground equipment)
           (JACA Photo)
                                                           Figure 25
                                                Tall  Narrow Baghouse Used With a
                                                        Portable Plant

                                               Baghouse has been placed on ground
                                               and  steadied by guy wires.  Baghouse
                                               empties  from screw at the bottom of
                                               the  house going to the left.  Filter
                                               catch  is merely piled there and pro-
                                               tected by a  tarpaulin.   Damp condi-
                                               tion of  this site required use  of
                                               system less  than 10% of the time.
                                               In dry areas this arrangement would
                                               not  be adequate.
                                                          (JACA Photo)
                                    -51-

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       This situation is greatly aggravated if the stone processing operation




changes configuration.  Local terrain limitations and or product requirements




might dictate that the process units comprising the operation be grouped in




other than a straight line.  This is not infrequent and might involve a




semicircle, T, or L configuration.  In this case the ductwork would require




redesign and considerable installation modifications.



       Another difficulty, not as dramatic as the reconfiguration problem




lies in the necessity to keep the ductwork compact for shipment but pro-




viding low air movement friction  loss and wear.  A rule of thumb in duct




design is to have radius turns equal to at least two diameters, and to



keep intersections of ducts at 30  or less.  These practices reduce wear




on the ductwork and fans and motors and conserve energy but make the system




more difficult to transport.



       While  astute design can affect a reasonable engineering  compromise




between system life and energy needs on the one  hand and  compactness on the




other, the problem of ducting for multiple connections  in a reconfigured




deployment of process equipment  is  of more serious proportions.    It would



appear to be  a principal  reason  for the fact  that  such  systems  are not




generally  offered as  a  part  of  the  overall original process equipment.








 Combination Wet  Suppression  and  Baghouse  Systems








       When water availability  is not a problem and  where fine  size products




 that really  agglomerate are  being made  (crushing and screening  operations  on




-1/4" particles)  a  combination system is often employed.   Wet  suppression is




 generally used  at  the initial portions  of the process,  i.e.,  the primary




 crushing  and screening  operations,  reclaim feeders and conveyor transfer
                                  -52-

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points.  Emission points following these process activities such as




secondary and tertiary crusher and screen and recirculating conveyors would




be controlled by a baghouse collector.  Combination systems have higher




annualized costs than full wet suppression systems, but less than fully dry




systems when water is readily available.  When water must be trucked in the




added  costs of the hauling must be included in the analysis.  Since water  is




applied to only a portion of the system, the water use will be  about 40%




that of the total wet suppression system or about  2
-------
                                Table 5

           MODEL WET SUPPRESSION  - FABRIC FILTER SYSTEM  COSTS

              FOR PROCESS PORTIONS OF CRUSHED STONE  PLANTS1
                   Capital Costs for  Installed System
                                      Small  Plant
                                      300 Tons/Hr.
Fabric Filter and Wet
Suppression Equipment Installed
$107,852
                           Large Plant
                           600 Tons/Hr.
                                                              $132,840
Annualized Capital Cost                           $13,482
 (12.5% of Capital)
                                                 2
                          Operating § Maintenance

Electricity § .04/KWH                 $  2,909

Maintenance, Operation £ Supplies     $ 18,396

Total Annual 0$M                                  $21,305

Total Annualized Cost                             $34,787
 (Capital + 0§M)

                                                    6.04
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       As is not infrequently the situation in scientific work, the develop-


ment of this technique to control dust was ancillary to the main thrust


of a study conducted at the University of Arizona under the aegis of the


National Aeronautics and Space Administration,  Beginning in 1973 a number


of studies were performed to determine if electrostatic charging was a factor


in the levitation of dust on Mars.  Since no Mars dust samples were avail-


able, tests of necessity were run on a variety of industrial and naturally


occurring particulate materials.  Results of this work are described in a

      14
report   dated August, 1977.  The report contains a large amount of experimen-


tal data on dust charges and dust reduction results after applying various


amounts of charged spray.  In broad terms particles below 8 microns tend


to be charged negatively while larger particles tend to have positive charges


or to be uncharged.  However, there is considerable variation among dusts


and the same dust with various impurities.  The physics underlying the


charge phenomena and the settling mechanism is not fully developed but a


government funded study is currently under way to provide a better under-


standing of the phenomena


       The variety of charge type and strength is illustrated by two bar


charts taken from the report  .   The first, Figure 24, shows that trap


rock, a hard ingenous rock often found in crushed stone quarries, exhibits


negative charge for all discrete particle size ranges tested up to 11


microns.  Silica sand (also frequently found in stone quarries) in contrast


exhibits positive as well as negative charges at some particle sizes (See


Figure 25).
                                 -55-

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II
    PARTICLE  SIZE
    MICROMETERS
   Figure 24

CHARGE ON TRAP ROCK
   3 RUNS
      INDICATES  SPREAD
          OF THE DATA
                      W/////////////M/M
                                                   I	1
                                    3            2
                             CHARGE ( ARBITRARY   UNITS )
                                          0
                                   Ci

-------
        PARTICLE  SIZE

        MICROMETERS
    6 -
cn
•~j
i
    0
                I-
                                                 WI///tlJ/llffh ABOVE  II
       -1
              INDICATES  SPREAD

                 OF THE DATA
Figure 25
CHARGE ON SILICA SAND
5 RUNS
I
• » »
d
:AD ///.
'IL
\ -. .,
'• r • • 	 ' "• 	
7///////////////////////////^^
\
i I I 	

1
1
— n_ I
1 1 t_.
               12
10      8      6       4       2

   CHARGE  (ARBITRARY  UNITS)
0

-------
       The method employed uses small charged water particle fog.  The




oppositely charged fog droplets enhance contact between the particulates




and the fog droplets.  After contact is made, the wetted particulates agglom-




erate and fall rapidly.  The device consists of a modified commercial




electrostatic paint spray gun that uses compressed air to atomize the




water droplets.  The droplets can be formed uncharged, or with positive or



negative charges as desired.




       Dust tunnel studies were conducted on a variety of dust samples




using various quantities of water and different charge polarities.  Water




flow rates were nominally 30 ml/min per gun  (0.475 gallon/hour) and air flow




100 standard cubic feet per hour.  All of these studies indicated reductions




in dust concentration  for particles smaller than 9 microns in the test dust




tunne1.




       Field data most closely related to crushed stone operations were




gathered at a cement plant in Arizona.  Samples of dust were first taken




from the belt conveyor in the quarry surge building and tested in the dust




tunnel for sign  which indicated a preponderence of negatively charged dust.




The in-plant test utilized two modified REA guns made by the Ransburg




Corporation of Indiana.  These two guns were mounted as shown in Figure 26,




       A sampling head was then located at belt level (5', 152 cms.) and




about two feet from the edge of the belt.  Floor to ceiling curtains were




arranged as shown in Figure 27 to prevent dust blowing in or out of the




test area.  Results of this in-plant test are shown in Figure 28 for




particles up to nine microns.  The data indicate reduction of dust level,




with the most improvement coming after 30 minutes of dust loading,
                                  -58-

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         Figure 26




TEST SET UP CEMENT PLANT "A"
                                           o
                          FOG    GUNS
/////// -1 '///'"'
                   / * '////////'/
          -59-

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                    Figure  27

   PLAN VIEW OF SURGE BUILDING  CEMENT PLANT "A"
       WALL
                                 FOG     GUNS
                                                              $
       -EDGE    OF    BELT    PLATFORM
j SAMPLING
| STATION
{ 5' ( 152 cm )
| ABOVE FLOOR
1
I
^^^^ FLOOR T
1 ^ 	 CEILING
CURTAIN
x, 	 	 	 	 — 	 • — • 	 • 	
8* / ?£. £.

\ \
2' { 50.7 cm)
51 (i
0 .^^^
I
I

c m i • • - •»

52 cm }


                      -60-
JACA CORP. •  ENVIRONMENTAL CONSULTANTS & ENGINEERS

-------
!2
10
 e
    to

     bO


     H
     H-l
     C/5
                                   Figure 28

                          CONCENTRATION VS. PARTICLE SIZE

                             BEFORE AND AFTER SPRAY IN

                          SURGE BUILDING CEMENT PLANT "A"
                                      WATER    F'LOW    RATE
                                      60  ml /  min

                                      AIR   FLOW    RATE
                                      200   S  C F H
                       INITIAL    DUST    LEVEL
              DATA
              UNCERTAIN
                       DUST     LEVEL    AFTER     5   MINUTES
                       OF    POSITIVE     FOG
                                      DUST    LEVEL    AFTER    30
                                     'MINUTES   OF    POSITIVE    FOG
          b	
                    2       3
                     PARTICLE
                                     4567
                                       SIZE  (MICROMETERS)
                                    -61-

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       It is not possible to report on annualized costs for different

crushed stone installations as was done in the case of baghouse and wet

suppression systems because the system has not been deployed in the field.

Individual guns consisting of a water and air atomizing head and a self-

contained device to charge the particles for either polarity sell for

$2,000 each from the Ransburg Corporation.  One or more device must be

located at each process source of dust, the area shielded from wind action,

and the necessary water and air connections made.  The air use of 100 SCFPH

per gun is low so that even if 20 units were required (two at each of 10

emission points) plant air could readily meet the need.  Water consumption

for twenty units would be 9.5 gallons per hour, a small fraction of the

450 gallons per hour of water needed for a production rate of 300 tons per

hour of crushed stone in a wet surpression system.

       In summary, the electrostatic spray system has been applied experi-

mentally to the control of fine dusts  (less than 10 microns) with varying

degrees of efficiency.  There has not been operational application to

crushed stone operations at this time to the author's knowledge.

       Because it operates most efficiently on small particles and is

essentially not helpful on particles larger than 10 microns, it cannot be

characterized as a direct practical, alternative to the baghouse or wet

suppression techniques extensively used in control of dust from crushed

stone process operations.  It should be considered for further experimentation

on the smaller size dust generated by tertiary crushing which sometimes

cannot be controlled by wet suppression systems because of the desire to

keep the product dry.  It might also be applied to dust before entering a

device whose efficiency is dependent on particle mass diameter such as a

cyclone or wet scrubber.  Removal of the fine particles before the existing

control device tends to improve its efficiency and reduce the energy

necessary to effect separation by particle dynamics.
                                  -62-

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                              Section II



                  EFFECTS OF MESA CONTROL STRATEGIES

                    ON DOWNWIND AMBIENT CONDITIONS



 Introduction



       The Mining and Enforcement Safety Administration  (MESA)* and state

 agencies have promulgated and enforced worker health standards which have

 the potential for interaction with the enforcement of regulations promul-

 gated pursuant  to the Clean Air Act.  The purpose of the work reported in

 this section of the report was to briefly examine the effects of control

 strategies for  MESA on downwind ambient conditions.

       Emission controls installed for worker protection under MESA or

 state occupational health requirements were found to ameliorate downwind

 ambient particulate contributions from plant operations.  With certain

 simplifying assumptions the salutary effect on National Ambient Air Quality

 Standards can be calculated.  However the effect of MESA and other occupa-

 tional health regulations on current SIP regulations often cannot be

 quantitatively  evaluated because SIP regulations use a different measurement

 criteria or are often semi-quantifiable.

      It is important to note that control  of process emissions for air

 pollution reasons, which is favored by MSHA over  controlling the receptor

 (worker) by using  protective respiration  devices  or  a work enclosure,

 etc., is significantly aided by use of air  pollution  control devices

 noted in the main section of this  report.
*MESA has  recently been moved  from the Bureau of Mines,  Department  of
 the Interior to the Department  of Labor.   The changeover  has  been  recc
 and the name has been  changed to  the  Mine  Safety 6  Health Administration
                                 -63-

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Occupational Health Regulations








       Stone quarries,  also referred to as surface mining operations or




simply mining in this discussion,  can be regulated by more than one agency.




Occupational health and safety regulations which may have an impact on air




pollution control by the rock crushing industry exist at the Federal level.




In addition some states also have occupational health regulations that




pertain to this industry.  Since there is  considerable variation in state




activity we will generally use Oregon and Pennsylvania as illustrative




examples.



       MESA.  The federal Mining Enforcement and Safety Administration (MESA),




an agency of the U.S. Department of Interior, was created in 1973 to take




over from the Bureau of Mines the authority to develop and enforce health




and safety standards under the Federal Coal Mine Health and Safety Act




and the Federal Metallic and Nonmetallic Mine Safety Act  (FM§NMSA),




30 U.S.C. §721 et seq.



       The FM^NMSA, which applies essentially to all mining operations,




both deep and surface, grants MESA authority to enter and inspect all




subject mines.  The Act  empowers MESA  to promulgate two types of health




and safety  standards:  voluntary and mandatory.  Voluntary standards may




be set to protect life,  promote health and safety, and prevent accidents.




Voluntary standards  are  similar to guidelines:  operators may not be




penalized for violating  them.  MESA may  also set mandatory standards to




regulate practices reasonably  expected to  cause death or  serious physical




harm.  Violations of mandatory standards may  lead  to imposition  of  the




penalties specified  in the Act.




       The  states may be delegated  inspection  and  enforcement  authority





                                 -64-

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under the FMSNMSA if they submit a plan that is approved by the Department




of  Interior.  If the state plan is approved,MESA essentially turns over




the enforcement of the standards to the state.   To  date six states have




been delegated inspection and enforcement authority.  Oregon and Pennsylvania




are among those that have not been delegated such authority.  State mine




regulatory laws that are not in conflict with FMSNMSA, or that regulate




mines more strictly than the Act, are not superseded by it, so Pennsylvania's




law and the FM&NMSA are both enforced in Pennsylvania.  This is also true




in  Oregon, except that an accomodation has been reached between the two




enforcement agencies so that little overlap occurs in field enforcement.




       OSHA.  The Occupational Safety and Health Act of 1970, 29 U.S.C. §65




et  seq., created the federal Occupational Safety and Health Administration




and gave it authority to enter and inspect all business establishments in




the United States and its territories.  OSHA has authority to set and




enforce standards,  issue citations, assess fines, and petition federal




courts to close down establishments where employees are threatened by




imminent hazards.




       OSHA currently exercises no jurisdiction over mining enterprises,




except for practices occurring in buildings outside the mine or pit (crushing,




screening, and conveying are deemed not "outside the pit").  While neither




the OSHA Act nor the FMfiNMSA preclude OSHA from setting and enforcing regula-




tions pertaining to mines,  any such action would be a mere duplication of




MESA's efforts.   OSHA has issued no safety or health standards for mines to




date, nor does it presently enter and inspect mines, despite its legal




authority to do both.




       EPA - SIP.  The federal Environmental Protection Agency is charged




with enforcing the  federal  Clean Air Act (CAA),  42 U.S.C.  §1857 et seq.





                                 -65-

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The CAA is based on a regulatory concept involving ambient air quality and




emissions limitations; it does not give EPA authority to set exposure levels




of air pollutants for workers.  EPA,  in any case,  only retains primary




enforcement authority over hazardous  emissions (including asbestos) and




emissions from certain new sources (not yet including any quarrying opera-




tions).  Enforcement of emission limitations for non-hazardous pollutants




from existing sources can be delegated to the states after approval of




their state implementation plans.  EPA can enforce state SIP's if state




enforcement is inadequate.




       State Health Agencies.  Some states also have state industrial health




organizations that regulate and inspect mining operations.  For example,




when the Pennsylvania Department of Environmental Resources (DER) was




created in 1970, among the powers it  was delegated was the power to set and




enforce health and safety regulations for mines, previously invested in




the Department of Labor and Industry.  DER's authority over mines is




derived from the Pennsylvania Surface Mining Conservation and Reclamation




Act, 52 P.S. §1396.1 et seq.  The inspection and enforcement is handled




by the Bureau of Occupational Health.




       The Surface Mining Act gives DER exclusive authority to enter and




inspect any surface mine in the state.  The Act also empowers DER to issue




and enforce such regulations as are necessary to protect mine workers and




public health and safety.  This Act does not distinguish between voluntary




and mandatory standards; all standards issued by DER are mandatory and




enforceable.  The state regulations and those of MESA are essentially




identical insofar as worker exposure is concerned,




       Oregon's situation in respect to state involvement with occupational




health at surface mining installations is similar in theory, but not in
                                 -66-

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practice.   There  is regulatory overlap between MESA and the Accident

Prevention  Division  (APD) of the Worker's Compensation Department

 (formerly Workman's Compensation Board).  The APD and MESA, however,

have an  arrangement under which MESA has primary inspection responsibility.

APD only inspects if they happen to be on the site for another purpose, and

have determined that there has not been a recent inspection.  Copies of

inspection  reports are exchanged between APD and MESA.


       Comparing Pennsylvania,  the leading stone producing state,  and Oregon,

approximately the thirteenth in terms of production,  insofar as  regulatory

bodies concerned with air pollution at stone crushing operations we see the

following:
                Enforcement Agencies for Fugitive Dust

                    From Stone Crushing Operations

      Pennsylvania                                      Oregon
Pennsylvania Department of
  Environmental Resources
  (Bureau of Air Quality and
  Noise Control) enforces
  EPA approved SIP.

Pennsylvania Department of
  Environmental Resources
  (Bureau of Occupational
  Health) inspects surface
  mines and enforces worker
  standards.

MESA inspects and enforces
  worker standards in surface
  mines.
Oregon Department of
  Environmental Quality
  enforces EPA approved
  SIP.
Oregon APD of the Worker's
  Compensation Department
  inspects and enforces worker
  standards in a variety of
  industries including surface
  mines.

Same.
                                 -67-

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       Thus there is an overlap in both Pennsylvania and Oregon between




state and MESA inspections and enforcement authority.




       Worker Exposure Regulations.  The MESA standards that apply to




worker related air contaminants are mandatory in nature.  They are based




on the threshold limit values (TLV's) for nuisance dusts and dusts con-




taining quartz and asbestos recommended by the American Conference of




Governmental Industrial Hygienists (ACGIH).   The following common TLV's




are therefore applicable to the rock crushing industry:
   Substance                                      TLV






Nuisance Dust                      10mg/m3




Quartz                             (10mg/m3) T (% Respirable Quartz + 2)




Asbestos                           5 fibers/ml, (fibers greater than 5y in length








       Under these regulations, no employee in a rock crushing plant is to be




exposed to an averaged 8 hour working day dust concentration greater than




the TLV.  For 5% Quartz content, the above TLV formula reduces to:









       10 mg/m3 T (5% + 2) = 1.43 mg/m3 or 1430 yg/m3








       SIP Regulations on  Fugitive Dust.  The  SIP requirements for non




 stack  emitted  dust  (fugitive dust) in states vary to the extreme.  Several




 examples will  illustrate  this point.  The reader is cautioned that the




 following examples note highlights of the regulations, and  are not to be




 considered as  exhaustive  or definitive  legal treatments.
                                 -68-

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       Pennsylvania permits no fugitive dust unless the operation falls in




either of eight categories (construction, agriculture, etc.)  or is classified




by PennDER as an "insignificant" source.   Stone crushing is not inlcuded in




the eight categories and each operation is judged on its own  as to whether




or not it is an insignificant source.   If significant no fugitive emissions




are permitted, while if insignificant, measurements are made  downwind at the




property line using a Konimeter, a device which is intended to provide particle




count and size information.  The DER regulations specify no more than 150



particles per cubic centimeter downwind air above background  at the property




line.  These instruments have been found to be unacceptable for this purpose




by this contractor and the state, and their use has been abandoned.




       Oregon does not have a performance regulation on fugitive emission,




but requires the "installation of hoods,  fans, and fabric filters to enclose




and vent the handling of dusty materials" (OAR 21-060, 20).  These regulations




apply however only if a nuisance condition exists or if any other regulation




is violated.  The existence of a nuisance condition is determined by such




factors as population density, duration of the activity and others (OAR 21-050




(2)).  This regulatory arrangement leads to the not uncommon problem posed




by having objective criteria which cannot be quantitatively applied.




        In addition,  existing sources  outside Special Control  areas are




 subject to a 40% opacity limitation (Ringelmann 2).   All new  sources and




 existing sources outside the Special  Control areas are subject to a 20%




 opacity limitation (Ringelmann 1)  (OAR 21-015).
                                  -69-

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       Arizona fugitive dust regulations require the use of "reasonable




precautions" to prevent particulates from becoming airborne from certain




activities.  For crushing, screening, handling, or conveying of materials,




such reasonable precautions are defined to include (but are not limited to)




spray bars, wetting agents, and hoods (Arizona Rules and Regulations R9-3-302




CD)).




        In Texas,  in the Standard Metropolitan Statistical  Areas (SMSAs)  in




 which federal ambient air quality standards for particulates  are exceeded, fine




 material may not  be handled,  transported,  or stored  unless stockpiles  and




 other surfaces from which airborn dust  may arise are coated with water,




 chemicals,  or other suitable  materials;  hoods,  fans, and filters are used




 to collect dusty  materials;  and open vehicles are covered  and materials




 wetted (Texas Regulation I,  Rule 104).   Portable rock crushers on site less




 than six months and engaged  in public works projects are exempt from




 visible emissions and process rate standards (Rules  103 and 105) as long as




 they are located  at least one mile outside the nearest town limits, occupied




 facility, or recreational area; equipped with cyclones, wet scrubbers, or




 water sprays (or  equivalent)  at transfer pointc; do  not create a nuisance;




 and not in Dallas or Harris  counties (Regulation I,  Rule  106).




        In Utah, all sources  emitting over 100 tons of particulates annually




 (uncontrolled) must achieve  85% control.  No methods are specified (Utah State




 Division of Health Code of Air Conservation Regulations §2.3.1).









           Relationship of Control for Workers to SIP Control









        An interesting topic concerns the extent to which control of fugitive




 dust emissions from stone crushing operations to satisfy MESA type requirements







                                   -70-

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aids in the attainment of SIP standards.  This is a very difficult subject.




MESA requirements are based on a dosage concept that involves a pollution field




and a receptor (the worker).  The TLV's are based on an eight hour working day




exposure.   The method of test for worker dust exposure is to attach on the upper




torso clothing of a worker the input section of a calibrated vacuum pump so that




it provides an inspired volume flow rate similar to a normal adult worker.   The





worker shuts the device off during work breaks so that the air inspired by the




device is similar to that inhaled by a worker acting on the job over an eight




hour period.  Dust is separated into respirable and non respirable fractions




by a small cyclone in the device and the respirable portion caught on a filter.




Gravimetric determination of the filter catch is made and the weight




of dust divided by the volume of air passed through the device over an eight




hour period.  The result is an eight hour average exposure which is then




compared to the pertinent TLV.  Anything that will reduce the worker's exposure




such as work rotation, dust free booths, personal protection (respirators) can




be used.  Note that the pollution field has not been reduced, only the workers




exposure to that field has been lessened.  MESA prefers engineering controls




at the source (emission controls) or at the receptor (by enclosing the employee




in a dust-free booth).  Source emission controls are therefore the only ones




that could possibly be analyzed as to the degree to which MESA standards attain-




ment helps SIP attainment.  Because,  as  was  shown  earlier, the  SIP standards  for




fugitive dust vary significantly among the states and are usually not given in



concentration terms it is extremely difficult to make such analysis.




       A statement of the question in different terms helps the analysis:




To what extent does the attainment of MESA standards by emission control
                                 -71-

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strategies on otherwise non MESA compliance operations improve the National


Air Quality STandards (NAAQS) in the vicinity of the operation?  NAAQS for


particulates are:





       Annual daily geometric mean:     Primary      75pg/m3


                                       Secondary    60yg/m



       Maximum 24 hour average:        Primary     260ug/m

                                                          3
                                       Secondary   ISOpg/m





       The restated question may be addressed more effectively than the


former question, and if certain simplifying assumptions are made, a mathe-


matical expression relating such variables as distance to the property line,


wind speed, etc. can be formulated.  Appendix A of this report includes an


example of how such an analysis can be made, given with underlying


assumptions.


       The plant with the particular geometry described in Appendix A has


reduced its contribution to  the 24 hour average ambient at the property


line by nearly 53%  (from 286.1ygm-3 to 135. lygnr3) by meeting MESA


standards for the working environment.* Differing backgrounds, geometries,


work shifts, and before-control worker ambient  levels would yield differing


results in accordance with equations 1, 2  and 3 of the Appendix, and  the


correction from  8 hour TLV   to a 24 hour ambient.  Thus the enforcement of


applicable emission regulations and worker exposure provisions are


considered mutually supportive and  complementary  to the other program


objectives.
 *For  a  given  r  and  stability class.  See the Appendix for the ranpe of

 possibilities.
                                 -72-

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                APPENDIX A
Example Analysis of Effect of MESA on NMQS
                  -73-

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       The question addressed is,  what extent will pollution controls



intended to meet one standard (i.e.  MESA standards) contribute toward



meeting another standard (i.e. National Ambient Air Quality Standards)?



The answer depends upon the extent to which the pollutant being regulated



contributes to the pollutant governed by the second standard.  In this



discussion we will assume that the second pollutant is identical to the



first.  Also, we will assume inert pollutants (e.g. 5% quartz stone dust) with

                                                                        f-r

no fall out, an ambient particulate background concentration of 100 yg/m^, and



atmospheric conditions such that the dilution downstream from the source is



governed by the Gaussian plume relationship.



        It is reasonable to use the Gaussian model in this situation since we



are not concerned with particle fallout, rather only those particles that do



not fall out within the plant property  line.  In terms of MESA Standards we



are concerned with respirable size particles, i.e. 0.1 ym to 10 ym diameter,



and their control.  These particles remain airborne for sufficient time periods



to consider  their dispersion  according  to the Gaussian plume model.




        As  a starting point,  we  define the  following pollution concentrations



 in micrograms per cubic meter:







        XR - pollutant regulated by the first standard;



        X?  - pollutant governed  by the second standard;



        X , , x?h - concentrations  of XR and x2 before  controls are instituted;



        XD   Xo  - concentrations  of XD and X9 after controls are instituted.
         Ra   ^.a                      K      /






 These relations follow by definition also:
        AXR " XRb " XRa ;
        AX2 = X2b - X2a .
                                 -74-

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These represent the controlled pollutant concentrations.




        Let  us  now  examine how AXD  and  AX~ are related  as  a  function  of
                                 K        £


 distance  d  downwind of the  pollution source  area.   To  do  so we  can envision



 a Gaussian plume dispersion  model extending downwind of the  plant  site area



 A  as sketched in  Figure 1-A. The pollution concentration  at ground level




 averaged over about one hour  is  sketched at LI  and L? showing the pollution



 spread out  and decreased in concentration.  In a later example, L_ will be



 taken to be the boundary of the plant property at which NAAQS must be met



 and  LI is the critical point with regard to MESA standards.



        The  ground  level  concentration  is a Maximum  at  the plume centerline



 and decreases  from L,  to L_  according  to the relation
            irayazy



 where
        X(ygm~  )  is  the  pollutant  concentration,



        Q(ygs   )  is  the  source strength,


              2

        0yoz(m )  is  the  product of Gaussian plume  dispersion parameters and,



        y(ms   ) is wind  speed.
 The above expression is  for a continuous  point  source with ground level



 release.



        From the above relationship  we  see that  the  ratio of concentraion at



 !.,„ to that at  L,  is  r where;
   Turner, D.B., 1969:   Workbook of Atmospheric Dispersion Estimates.  Public

   Health Service,  HEW.



                                   -75-

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Virtual
Source
of
Pollution
                      Source Area
                      A.
Sketch of
Pollution
Concentration
at Edge of Site
                                                                                 Plume
                                                                                 Transport
                                                                                 Directior
Sketch of
Pollution
Concentration
Further Downwind
               Figure 1-A: Sketch of the Geometric Relation Between

                  the Virtual Source Point 0', the Source Area As

                 and Average Pollution Concentration at L^ and L,2
                                       -76-

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        « 2f£2l .  hH^       (Equation 1)
         X(Ljj    [ayaz](L2)        M
 The  ratio  of  Gaussian parameter products can be estimated for various values



 of L,  and  L~  from  the following table derived from the graph of Figure  2-A for



 various  stability  classes.  This table presents the values of the Gaussian



 parameter  products a a  for various stability categories at the correspond-
                    y z


 ing  downwind  distance.
                                         2
     Gaussian  Parameter  Products, 00   (m )  for Various Stability  Classes
Downwind Distance,
Class B
Class C
Class D
Class E
And Downwind
L(km) .1
120 4
96 1
40
25
Distance
.5
,500
,800
660
360
L(km)
1
16,000
6,400
2,100
1,103
5
400,000
115,000
26,500
12,000
10
off graph
400,000
74,000
32,000
       Applying the distance reduction to AX- which would be at L7 and
AXR at L, shows that
       o    X2bCL2^ = rXRb^Ll^       (Equation 2)




       °    X2a(V = rXRa(V       (Equation 3)








These relations show how pollution concentrations due to control measures




initiated at point LI relative to pertinent regulations translate to pollu-




tant concentration at point L2 relative to another standard.  Thus under the




simplifying assumptions made, any reduction in source strength from the




various fugitive sources will have the effect of a corresponding decrease in
                                 -77-

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   0.1
1                    10
 Distance Downwind,  km
                                                                      100
Figure 2-A:The Product of ayaz as a Function of Downwind Distance From
the Source.  (A Represents Unstable Conditions and F very stable.)
Source:  Turner, D.B., Workbook of Atmospheric Dispersion Estimates, U.S. EPA.
                                 -78-

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their contributions to the downwind ambient.  How this would work in the case




of a stone crushing operation can be seen in the following example of a stone




crushing operation processing 5% quartz stone with a plant area ambient con-


                              _3

centration of dust at 7150 ygm  .   The TLV criteria for 5% quartz dust es-




tablished by MESA is 1430ygm   as noted earlier in this section of the report.




To meet this standard an 80% reduction of quartz bearing dust is accomplished




at the plant site by employing emission controls.  For this operating site




with L,=lkm, what is the impact of these operating site controls at the plant




boundary 4 km beyond the operating area, i.e. L =5 km?




       Notice that the particulate concentration measured in the plant area



                                               -3
includes the background concentration of lOOygm  .  To determine only the




plant's contribution to the ambient concentration at the plant boundary, the




background concentration should be subtracted from the plant area concentra-




tions before applying equations2 and 3.  Thus the plant area concentration




attributed to plant operations prior to control, xRh  is 7050 ygm"  and after




control, xRa, is-1330 yg/m .




       The following calculations exemplify the use of equations 2 and 3




in determining the effect of controls initiated within the plant area on




the ambient concentration at the property line.  Calculations are based on




atmospheric stability class D.




     From Figure 2-A and equation 1 we find that:



       r= °y°z (Ll) =  2100m2 = 0.0792

          °y°z (L )   26500m2






       During an eight hour work day




       X2b (L2)  = r (xRb) = 0.0792 (7050) = 558.4 yg/m3




       X7a (L9)  = r (XD ) = 0.0792 (1330) = 105.3 yg/m3
        ^ d   £        Kcl

                            3

       AX9 (L9)  - 453.1 yg/m
                                -79-

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       The contribution of the plant to the ambient  particulate  concentration
                                                                _5
at the plant boundary before and after control is thus 558.4  ygm   and 105.3

ygnf , respectively.   There is approximately an 80%  reduction in the plant's

contribution to the ambient.  Since we assumed a background concentration

of 100 ygm  , the actual ambient concentration of particulates 5  km downwind
                  _•?                             _3
would be 658.4 ygm   before control and 205.3 ygm   after controls were initi-

ated at the plant.  These values must then be converted to 24 hour average

concentrations to be compared to the NAAQS for particulates of 260 pgm
                                                                    _3
       During non-working hours the ambient concentration is 100 ygm  .  There-

fore, the 24 hour average concentration is

        24 hr                                         ,
       X2b  (L2) - 1/3  (658.4) + 2/3  (100) - 286.1 y g/in

       and

        24 hr                                         .
       X2a  (L2) = 1/3  (205.3) + 2/3  (100)  = 135.1 yg/m
        Thus  the plant with this particular  geometry  (the assumed  LI  and L^)

 for  atmospheric stability class D has  reduced  its  contribution  to the  24 hour

 average ambient at  the  property line by nearly 53% by meeting MESA standards

 for  the working environment.   In doing so,  the ambient  concentration was re-

 duced below the NAAQS  for particulates of 260  ygm" .  Differing backgrounds,

 atmospheric stability  classes, geometries,  shifts, and  before  control  worker

 ambient levels would yield  differing  results in accordance with equations 1, 2,

 and 3 and the correction from 8 hour  TLV to a 24 hour ambient.

      Table 1-A shows the effect of the choice of stability class  on the 24

 hour average ambient concentration.  The values were developed in the same
                                  -80-

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manner as the preceding calculations, only the value of r was changed in

accordance with the Gaussian parameter products from Figure 2-A.
                             Table  1-A
B
. 0425
199.9
118.8
40.57
C
.0557
230.9
124.7
45.99
D
.0792
286.1
135.1
52.78
E
.0917
315.8
140.7
55.45
Stability Class
       _24 hr

       *2b (V
       _24 hr
       X2a (L2)
  % reduction of ambient
  24 hr. avg. concentra-
  tion
       This table shows that the 24 hours average concentration at the prop-

erty line decreases going from Class E to B as the atmosphere becomes more

unstable.  Obviously, this is because the diffusion capability of the atmos-

phere increases in proportion to the atmospheric turbulence.  Granted, the

background concentration would also vary with atmospheric stability, but

this effect is beyond the scope of our analysis.  Additionally, the percent

reduction of the ambient 24 hour average concentration decreases as the

atmosphere becomes more unstable.  This is because the contribution to the

ambient  from the plant during the 8 hour working day decreased with the ratio

of the Gaussian parameter products while the background concentration was

assumed  constant for the 24 hour period.  Thus the effect of the controls

initiated at the plant is reduced in terms of the 24 hour average concentra-

tion.

       Notice that for stability classes B and C the 24 hour average concen-

tration  at the property line is already within the limit of the NAAQS before
                                -81-

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controls were initiated at the plant.  Thus, pollutant control is not necessary




to meet these standards if the property line is 5km from the source.  Stabil-




ity Class D, neutral stability, is more or less the worst case situation in




terms of downwind centerline concentration during an 8 hour work day.  By




definition stability class E does not occur during the day.  This shows that




by controlling particulate concentrations at the plant by 80% in order to




meet MESA standards a corresponding 53% reduction in the ambient concentra-




tion at the property line will result which also meets the NAAQS.  As pre-




viously stated, different background concentrations, plant geometries, shifts




and before control worker ambient levels will yield different numerical re-



sults.




      Controls installed for air pollution control  reasons  also  have  the




salutary effect of reducing worker ambient levels.   Thus  MESA (now MSHA)




and EPA regulations have mutually desirable effects.
                               -82-

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                               REFERENCES
 1.   Bureau of Mines,  Department of the Interior, Minerals Yearbook, 1975.

 2.   Private communication with the U.S.  Bureau of Mines, Non Metallic
     Minerals Division (based on 1972 figures).

 3.   JACA Corp.,  Differential Impact of Pollution Control Requirements on
     Small vs. Large Businesses in Grain and Stone Industries, for Small
     Business Administration under Contract No. SBA-1757-PRA-74, May 1975.

 4.   Evans, Robert J., Methods and Costs of Dust Control in Stone Crushing
     Operations,  U.S.  Bureau of Mines, Circular 8669,  1974.

 5.   Discussion with William Ward of Ward Engineering, Swarthmore, PA re
     Aquadyne System.

 6.   Discussion with Mike Natale of Johnson March Co., Philadelphia, PA re
     Chem-Jet System.

 7.   MSA Research Corp.,  Survey of Past and Present Methods Used to Control
     Respirable Dust in Noncoal Mines and Ore Processing Mills, for U.S.
     Bureau of Mines,  April 30, 1974.NTIS No. PB 240662.

 8.   Johnson March Company recommendations for Chem-Jet System maintenance.

 9.   Communications with M.D. Glenn, Oregon Department of Transportation,
     Highway Division, Construction Section - Materials and George Sanford -
     Cost Analysis.

10.   Telephone conversation with William McCall - Oregon Water Resources
     Board.

11.   Engineering Science, Inc., Air Pollution Emission Test for EPA under
     Contract No. 68-02-1406, Task 7, Report No. 75-STN-3.

12.   Discussions with James Fee of L.B. Smith Company, Camp Hill, PA.

13.   Clayton Environmental Consultants, Inc., Air Pollution Emission Test,
     for EPA under Contract No. 68-02-1406, Task 6, EPA Report No. 75-STN-7.

14.   Hoenig, Stuart, The Use of Electrostatically Charged Fog for Control
     of Dust From Open Sources, EPA Grant No. R 805228010, August 1977.

15.   Visit with Dr. Stuart Hoenig of the University of Arizona, Tuscon, AZ.

16.   Hoenig, Stuart, Use of Electrostatically Charged Fog for Control of
     Fugitive Emissions.  iiPA-600/7-77-131 . Nnypmh^-r 1077	'	—
                                -83-

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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
13.
iient's .icce jsioa No.
4. Title and Subtitle
 Control of Air Emissions From Process Operations in
 the Rock Crushing Industry
                                          5. Report Date
                                            February  1978
                                          6.
7. Author(s)
  JACA Corp.
                                          8. Performing Organization Kept.
                                            No.
9. Performing Organization Name and Address
  JACA Corporation
  550 Pinetown  Road
  Fort Washington, PA  19034
                                          10. Provct/Task/tt'oik Unit No.
                                          11. Contract/Grant No.

                                           68-01-4135-Task-19
12. Sponsoring Organization Name and Address
  Division of  Stationary Source Enforcement
  U.S.  Environmental  Protection Agency
  Washington,  DC  20460
                                          13. Type of Report & Period
                                             Covered
                                           Applied  Research
                                          14.
15. Supplementary Notes
16. Abstracts
   Three basic methods  of controlling emissions from process  operations
   in crushed  stone plants are described -  dry captive systems  using
   fabric filters, wet  suppression systems  and combinations of  these.
   Operational problems with these systems  associated with plant por-
   tability  and product size are  discussed.   Examples of good design
   practices and maintenance procedures for these control options are
   covered.  An electrostatic charged fog technique  for control of small
   dust particles is described and operational problems listed.   A second
   part analyzes the downwind effects of reducing emissions for worker
   safety.
17. Key Words and Docuraer: Analysis.  17a. Descriptors

   Rock Crushing Industry
   Crushed Stone Plants
   Controlling Emissions from Process Operations
   Dry Captive Systems Using Fabric Filters/crushed  stone plants
   Wet Suppression Systems/Crushed stone  plants
   Operations  problems-controlling emissions-crushed stone plants
I7b. Ideiitifiers/Open-Ended Terms
                                                              ~\
I7c. COSATI Field/Group
18. Availability Statement
                                 19. Security Class (This
                                   Report)   ....  ,
                                  unclassified
                                                   20. Security Class (This
                                                         unclassifie
          21. No. of Pages
                                                    22. Hiice
FORM NTis-35 iHEv. 10-73)  ENDORSED BY ANSI AND UNESCO.
                                             THIS FORM MAY BE REPRODUCED
                                                                      USCOMM-DC B2B5-f»7<

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