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       Equation 13 can be used to estimate the cancer risk at a specified distance downwind
of the excavation area.  Cancer risk is a measure of the increased probability of developing
cancer in a lifetime as a result of the exposure in question.  Equation 13 assumes continuous
exposure (24 hours/day, 365 days/year for 70 years) to the estimated annual average
concentration in air.
                                    R - (CJ(IUR)                             (Eq.  13)

       R is the cancer risk from long-term exposure to a specific compound in air, (unitless);
C. is the annual average ambient concentration estimated from Equation 12,  Og/m3); IUR  is
the inhalation unit risk factor, (/xg/m3)'1 obtained from Tables 5, 6, or 7.

       If the source operates for less than 70 years, multiply C. by x/70, where x is the
expected operating time of the source in years before using Equation 13. If more than one
contaminant is present,  the cancer risks for each contaminant can be  summed to derive the
total cancer risk at a specified distance downwind of the source.

Non-Cancer Effects Due to Long-Term Exposure

       Non-cancer effects can be evaluated by using chronic inhalation reference
concentrations  (RfCs).  An inhalation RfC is an estimate (with uncertainty spanning perhaps
an order of magnitude) of continuous exposure of the human population to contaminants in
the air that is likely  to be without appreciable risk of deleterious effects during a lifetime.
During the past three years, the EPA has become increasingly active in the development of
chemical specific RfCs.

       If inhalation RfCs were not available from either IRIS or HEAST, then chronic oral
reference dose (RfD) data (in mg/kg/day) were multiplied by 70 kg (average body weight of
an adult), then divided by 20 nrVday (average adult inhalation rate), and finally multiplied  by
1000 ttg/rng to derive a value in /xg/m3. This methodology was selected as the best available
approach for this screening document. The EPA, however, does not condone derivation of
RfCs from data for other routes of exposure on a chemical specific basis.
                                         29
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       The EPA considers the minimum basis for the derivation of an RfC to be a properly
conducted inhalation study that examines portal of entry effects.  Portal of entry effects are
particularly important with respect to inhalation. There are many known cases where
respiratory effects due to inhalation exposure are much more severe than effects resulting
from equivalent oral doses.  Therefore, ambient air action levels based on extrapolated oral
data should be used cautiously since there may be significant differences between the oral
and inhalation exposure pathways.

       For compounds lacking RfC or RfD values, action levels were based on occupational
exposure levels recommended by the Occupational Safety and Health Administration
(OSHA)19 and the American Conference of Governmental Industrial Hygienists  (ACGIH).20
The  action levels  were estimated by  using the lower of the OSHA Permissible Exposure
Limit-Time Weighted Average (PEL-TWA) level (or ceiling value)  or the ACGIH Threshold
Limit Value-Time Weighted Average (TLV-TWA)  level (or ceiling  value). The lower value
was  divided by 1000 to compensate for differences between occupational and residential
exposures. It should be noted that occupational exposure levels are not intended for
evaluation or control of community air pollution or in estimating the toxic potential of
continuous, uninterrupted exposures.  Therefore, ambient air action levels based on
occupational exposure limits are not precise distinctions between safe  and dangerous ambient
air concentrations, nor are they necessarily indices of toxicity.

       Long-term ambient air action level concentrations for non-carcinogens based on RfCs,
extrapolated RfDs and occupational exposure levels are also listed in Tables 5, 6, and 7.
The action levels are in units of ftg/m3 to facilitate comparison to the ambient air
concentrations estimated from Equation 12.

Short-Term Exposure

       The short-term (one hour) action levels, in uglrn1,  are presented  in the last coiumn of
Tables 5, 6,  and 7.  The listed values were obtained by dividing the lowest of (1) the OSHA
PEL-TWA or (2)  the ACGIH  TLV-TWA (or ceiling limits if 8-hour averages are not
available) by 100. Division by 100 accounts  for variations in human sensitivity (occupational
                                         30
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levels are designed to protect healthy adult workers) and for uncertainties in using
occupational exposure levels to derive ambient air action levels.


       The occupational exposure levels on which the short-term action levels are based are
subject to change.  To check the values in Tables 5, 6, and 7 (or to derive values for
compounds not listed in the tables), determine the current OSHA PEL-TWA values by con-
sulting 29 CFR Section 1910 and the most recent edition of the ACGIH publication entitled
Threshold Limit Values and Biological Exposure Indices.


       The short-term action levels listed in Tables  5, 6, and 7 can be compared directly
with the estimated maximum hourly ambient air concentrations obtained by using
Equation 11 and Figure 2. Use of the short term action levels should consider that no EPA
accepted  method exists to determine the short-term concentrations of airborne  chemicals
acceptable for community exposure.


EXAMPLE


       The following steps illustrate the use of the estimation procedures presented in this
document.  The goal is to estimate the maximum hourly and annual average ambient air
concentrations at the nearest receptor to area sources of PM emissions and compare these
values to the action level concentrations listed  in Tables 5, 6, and 7.


Step 1        First, collect all necessary information.  For  this example, assume that a
              Superfund site exists in Durham, NC and soil is excavated from a pit and
              transported to a storage pile  500 m away. The backhoe moves  4 m3 of soil at
              a time, and dumps the  excavated soil directly into trucks.  Ten truckloads a
              day are moved with each truck containing 20 m3 of soil.  In addition, a
              bulldozer works over the storage pile for an hour each day.  The soil moisture
              content is 10% and the average  wind speed at the site is 2 m/sec.  The lead
              content of the soil is 100 jig/g.  The removal is expected to be in continual
              operation for 20 days (1.728 x 106  seconds).   The nearest off-site downwind
              receptor is 400 merers  away. The site also contains a one acre  dry surface
              impoundment. The soil has  a silt content of  8%. A subset of the
              contaminated soil is excavated every other day, placed in an (active) storage
              pile, and then fed into  a stabilization  process. The  storage pile  has a surface
              area of 2000 m2.  One thousand kilograms per day-of the stabilized material is
              placed in a lined portion of the dry surface impoundment.
                                          31
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Step 2       Estimate the PM10 emission rate from each activity.  To find the total PM10
             emissions from this site, first convert the 20 m3 of soil for ten trucks to a
             mass, using the default soil density of 1.5 g/cm3:

         (20 m3)(1.5 g/cm3)(0.001 kg/g)(106 cm3/m3)(10 trucks) = 300,000 kg soil.

             The particle size multiplier for < 10 /tm is 0.35. Use Equation 1 for the
             backhoe emissions:

            ER = 0.35 * (0.0016) * 300,000 * (2/2.2)1-3 / (10/2)14  =  15.6 g.

             This number should be multiplied by 2, because the soil will be dumped once
             into the trucks and dumped a second  time onto the storage pile.  Thus the total
             emissions from dumping are 31 g and the average emission rate is 31 g/day
             '(3.6 x 104 g/sec).

             To find the lead emissions from the backhoe operations, first calculate the
             fraction of lead in the windblown dust using Equation 7 with the lead content
             of the soil (100 /*g/g) and the enrichment factor for lead from Table 2 (7.34):

              Xj - (100)(7.34)(1(TS) = 7.34x10*  (g lead/g windblown dust)

             This value is then used with the average emission rate calculated above (31
             g/day) and Equation 6:

                EF^ = (7.34x10^(31) = 0.023  g/day (2.6 x 10"7 g/sec).

             To find the PM,0 emissions from transport, the silt content of the unpaved
             surface is needed, as well as the number of wheels per truck, the vehicle
             weight,  and the vehicle speed. Assume that these all equal the default values
             from Table 1.  The number of days with precipitation > 0.01" for North
             Carolina is found from Figure 1. From Equation 5, the transport emissions
             are:

           EF = 610 (8/12)(20/48)(30/2.7f 7(10/4)03(365-120)/365 = 970 g/km.

             A total of 10 truckloads are driven over a 1 km roundtrip,  so the total
             emissions  (ignoring the weight difference between the empty  and full truck)
             are 9,700  g or 9.7 kg.  The average emission rate is 9.7 kg/day.

             Finally, to find the emission  rate due  to the bulldozing, use Equation 3:


                           ER - SSLSJH .  0.085 g/sec
                                    (10)"
                                         32
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      Since the activity is underway for one hour, the total emissions are about 300
      g per day.

      Example calculations for paniculate matter emissions of less than 10 microns
      from the other sources are given below. Emissions from the surface impound-
      ment are estimated using Equation 8.  The surface area of the impoundment is
      one acre or 4050 m2.  The particle size multiplier for < 10 pm is 0.5, the time
      between disturbances is two days, and the default erosion potential is  33 g/m2.
      The emission rate from the surface impoundment is:


                m (0.5)(4050)(33) =
                    (2X86,400)         *            *   "
      Paniculate matter from wind erosion of continuously active piles can be
      estimated using Equation 9.  The number of rainy days from Figure 1 is 120:
      Assuming 50% of the TSP is PM10, the emissions of PM10 from the storage
      pile are:

               ER = (1.41)(50/100)(2000) =  1400 g/day.

      The emissions of PM10 emissions from the transfer of the stabilized waste can
      be estimated using Equation  10 (assuming that all the PM is PM10):
—
                          (f
                                 (1,000)
                                        = 0.49 g per day
      The emissions can be summed from ail activities.  Emissions of paniculate
      matter are equal to the sum of emissions from the backhoe operation,
      transport, bulldozer operation, dry surface impoundment, storage piles, and
      waste transfer:

31 -I- 9,700 + 300 + 33,000 -I- 1400 + 0.49 =* 44,000 g/day = 0.51 g/sec
                                  33
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             Emissions from the dry surface impoundment and transfer operations represent
             the vast majority of the PM10 emissions.  Assuming all of the soil is
             contaminated with lead, then the emission rate for lead is (7.34 x
             = 3.7x10"* g/sec.  The fraction of lead in the windblown dust, 7.34 x 1C*4,
             was calculated in Step 2.

Step 3       Estimate the downwind ambient air concentrations. Several activities are
             performed at this site, so separate calculations could be performed for the
             backhoe emissions, transport emissions, surface impoundment emissions, and
             so forth. For simplicity, all emission sources are assumed to be located
             together and only the most conservative dispersion  factor is used.  From
             Figure 2, the maximum dispersion factor at a distance of 400 meters for any
             of the activities is approximately 3000 ug/m3 per g/sec emission rate.  This
             corresponds to an annual average dispersion factor  of 240 ug/m3 per g/s (3000
             x 0.08 = 240). The ambient air concentrations estimated from Equations 11
             and 12 are presented  in Table 8. Using Equation 11, the hourly average
             ambient air concentration for lead would be:
         •

                          Cm = (0.00037)(3000)  =1.1 ug/m3

             Using Equation 12, the annual average air ambient concentration for lead
             would be:

                          C. = (0.00037)(240) = 0.089 ug/m3

Step 4       Compare the downwind concentrations to the action level ambient air
             concentrations.  The short-term and long-term action levels from Table 7 for
             lead are presented in Table 9. The estimated  maximum hourly ambient
             concentration for lead is slightly below the applicable action level.  The  annual
             average ambient concentration also is  somewhat below the long-term action
             level.

Step 5       Document the results of the air pathway analysis and define a future course of
             action. Based on these screening level results, a more rigorous analysis  of the
             air impacts  is not warranted.  The air impacts should be re-examined,
             however, when site-specific input data are available, if the inputs differ from
             the default values.  Also, it would still be adviseable to perform an ambient air
             monitoring program during the remediation  to document actual worker and
             community exposures.
                                         34
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                      Table 8.
Estimated Emission Rates and Ambient Air Concentrations
"•"."::>' '•:
Lead
Soil Concentration
For Example Problem Qtg/g)
100
Emission Rate
(g/s)
3.7 x 10-1
Ambient Concentrations (/tg/m3)
Maximum Hourly
1.1
Annual Average
0.089
                      Table 9.
             Action Level Concentrations

Lead
Table 7 Action Levels /ig/m3
Short-Term
1.50
Long-Term
0.15
                         35
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CONCLUSIONS


       The procedures presented here are not intended to negate the need for rigorous

analyses that consider site specific meteorological conditions and the health effects of the

specific compounds involved. Although the procedures are based on what is typical and

reasonable for cleaning up Superfund sites, the underlying assumptions need to be kept in

mind.  For example, emission models assume typical operating conditions, dispersion models

assume Gaussian distribution of the plume, and many of the health levels are not endorsed by

the Environmental Protection  Agency.  EPA's Regional lexicologist should be contacted for

general lexicological information and technical guidance on evaluation of chemicals without

established  toxicity values.


REFERENCES


1.     Eklund, B., S. Smith,  and M. Hunt.  Estimation of Air Impacts For Air Stripping of
       Contaminated Water.  EPA-450/1-91-002.  May 1991.

2.     Eklund, B., S. Smith,  P. Thompson, and A. Malik.  Estimation of Air Impacts For
       Soil Vapor Extraction (SVE) Systems.  EPA Contract No. 68-D1-0031, WA13.
       December 2,  1991.

3.     Eklund, B., S. Smith,  and A. Hendler. Estimation of Air Impacts for the Excavation
       of Contaminated Soil.  EPA-450/1-92-004. March 1992.

4.     Church, H.  Excavation Handbook.  McGraw-Hill, NY,  NY.  1981.

5.     U.S. EPA. Survey of Materials - Handling Technologies Used at Hazardous Waste
       Sites.  EPA/540/2-91/010. U.S. EPA-ORD,  Washington, D.C.  June 1991.

6.     Eklund, B., et al.  Control of Air Emissions From Superfund Sites.  EPA/625/R-92-
       012. November 1992.

7.     Cowherd, C., P. Englehart, G.  Muleski, and  J. Kinsey.  Hazardous Waste TSDF
       Fugitive Particulate Matter Air Emissions Guidance Document.  EPA 450/3-89-019.
       May 1989.

8.     U.S. EPA. AP-42:  Compilation of Air Pollutant Emission Factors, Fourth Edition.
       U.S. EPA, Office of Air Quality Planning and Standards, Research Triangle Park,
       NC. September 1985.

9.     Eklund, B., et al.  Air/Superfund National Technical  Guidance Study Series.  Volume
       IQ.  Estimation  of Air Emissions from Cleanup Activities at Superfund Sites.  EPA-
       450/1-89-003.  NTIS PB89-180061/AS. January 1989.


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 10.    Momeni, M.H., Y. Yuan, and A.J. Zielen.  The Uranium Dispersion and Dosimetry
       (UDAD) Code. U.S. NRC.  NTIS NUREG/CR-0553.  May 1979

 11.    RTI. A Method for Estimating Fugitive Particulate Emissions from Hazardous Waste
       Sites.  EPA/600/2-87/066.  NTIS PB87-232203. August 1987.

 12.    U.S. EPA>  User's Guide - Emission Control Technologies and Emission Factors for
       Unpaved Road Fugitive Emissions. EPA/625/5-87/022.  September 1987.

 13.    Cowherd, C., G. Muleski, P. Englehart, and D. Gillette.  Rapid Assessment of
       Exposure to Particulate Emissions from Surface Contamination Sites.  EPA/600-8-
       85/002.  February 1985.

 14.    U.S. EPA, A Workbook of Screening Techniques for Assessing Impacts of Toxic Air
       Pollutants.  EPA-450/4-88-009.  September 1988.

 15.    Huey, N.A. and GJ. Schewe.  Empirical Factor Emission of Air Toxic Source
       Impacts. In: Proceedings of HMC/Superfund '92. Published by Hazardous Materials
       Control Resources Institute, Greenbelt, MA.  1992.

 16.    Huey, N.A. (U.S. EPA, Region VII).  Personal communication to Bart Eklund
       (Radian Corporation).  April 1993.

 17.    Guinnup, D.E.  A Tiered Modeling Approach for Assessing the Risks Due to Sources
       of Hazardous Air Pollutants.  EPA-450/4-92-001. March 1992.

 18.    Health Effects Assessment Summary Tables (BEAST). U.S. Environmental Protection
       Agency, Washington, D.C., OERR 9200.6-303 (92-1), NTIS No.  PB91-92199,
       March 1992.

 19.    29 CFR ch. XVII. Subpart Z. Section 1910.1000. July 1, 1990.

 20.    1992 - 1993 Threshold Limit Values for Chemical Substances and Physical Agents
       and  Biological Indices. American Conference of Governmental Industrial Hygienists,
       Cincinnati, Ohio, 1992.
U S Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th rioor
Chicago, IL 60604-3590
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