6.2.2 Hazardous waste quantity. Assign a hazardous waste quantity factor value for the air migration pathway as specified in section 2.4.2. Enter this value in table 6-1.

6.2.3 Calculation of waste characteristics factor category value. Multiply the toxicity/ mobility factor value and the hazardous waste quantity factor value, subject to a maximum product of 1x108. Based on this product, assign a value from table 2-7 (section 2.4.3.1) to the waste characteristics factor category. Enter this value in table 6-1. 6.3 Targets.

Evaluate the targets factor category based on four factors: nearest individual, population, resources, and sensitive environments. Include only those targets (for example, individuals, sensitive environments) located within the 4-mile target distance limit, except: if an observed release is established beyond the 4-mile target distance limit, include those additional targets that are specified below in this section and in section 6.3.4.

Evaluate the nearest individual and population factors based on whether the target populations are subject to Level I concentrations, Level II concentrations, or potential

contamination. Determine which applies to a target population as follows.

If no samples meet the criteria for an observed release to air and if there is no observed release by direct observation, consider the entire population within the 4-mile target distance limit to be subject to potential contamination.

If one or more samples meet the criteria for an observed release to air or if there is an observed release by direct observation, evaluate the population as follows:

• Determine the most distant sample location that meets the criteria for Level I concentrations as specified in sections 2.5.1 and 2.5.2 and the most distant location (that is, sample location or direct observation location) that meets the criteria for Level II concentrations. Use the health-based benchmarks from table 6-14 in determining the level of contamination for sample locations. If the most distant Level II location is closer to a source than the most distant Level I sample location, do not consider the Level II location.

• Determine the single most distant location (sample location or direct observation location) that meets the criteria for Level I or Level II concentrations.

• If this single most distant location is within the 4-mile target distance limit, identify the distance categories from table 6-15 in which the selected Level I concentrations sample and Level II concentrations sample (or direct observation location) are located: -Consider the target population anywhere within this furthest Level I distance category, or anywhere within a distance category closer to a source at the site, as subject to Level I concentrations.

-Consider the target population located beyond any Level I distance categories, up to and including the population anywhere within the furthest Level II distance category, as subject to Level II concentrations.

-Consider the remainder of the target population within the 4-mile target distance limit as subject to potential contamination.

• If the single most distant location is beyond the 4-mile target distance limit, identify the distance at which the selected Level I concentrations sample and Level II concentrations sample (or direct observation location) are located:

-If the Level I sample location is within the 4-mile target distance limit, identify the target population subject to Level I concentrations as specified above.

-If the Level I sample location is beyond the 4-mile target distance limit, consider the target population located anywhere within a distance from the sources at the site equal to the distance to this sample location to be subject to Level I concentrations and include them in the evaluation. -Consider the target population located beyond the Level I target population, but located anywhere within a distance from the sources at the site equal to the distance to the selected Level II location, to be subject to Level II concentrations and include them in the evaluation.

-Do not include any target population as subject to potential contamination.

TABLE 6-14-HEALTH-BASED BENCHMARKS FOR HAZARDOUS SUBSTANCES IN AIR

• Concentration corresponding to National Ambient Air Quality Standard (NAAQS).

• Concentration corresponding to National Emission Standards for Hazardous Air Pollutants

(NESHAPS).

• Screening concentration for cancer corresponding to that concentration that corresponds to the 10-6 individual cancer risk for inhalation exposures.

• Screening concentration for noncancer toxicological responses corresponding to the Reference Dose (RfD) for inhalation exposures.

6.3.1 Nearest individual. Assign the nearest individual factor a value as follows:

• If one or more residences or regularly occupied buildings or areas is subject to Level I concentrations as specified in section 6.3, assign a value of 50.

• If not, but if one or more a residences or regularly occupied buildings or areas is subject to Level II concentrations, assign a value of 45.

• If none of the residences and regularly occupied buildings and areas is subject to Level I or Level II concentrations, assign a value to this factor based on the shortest distance to any residence or regularly occupied building or area, as measured from any source at the site with an air migration containment factor value greater than 0. Based on this shortest distance, assign a value from table 6-16 to the nearest individual factor.

Enter the value assigned in table 6-1. TABLE 6-16-NEAREST INDIVIDUAL FACTOR

6.3.2 Population. In evaluating the population factor, count residents, students, and workers regularly present within the target distance limit. Do not count transient populations such as customers and travelers passing through the area.

In estimating residential population, when the estimate is based on the number of residences, multiply each residence by the average number of persons per residence for the county in which the residence is located.

6.3.2.1 Level of contamination. Evaluate the population factor based on three factors: Level I concentrations, Level II concentrations, and potential contamination.

Evaluate the population subject to Level I concentrations (see section 6.3) as specified in section 6.3.2.2, the population subject to Level II concentrations as specified in section 6.3.2.3, and the population subject to potential contamination as specified in section 6.3.2.4.

For the potential contamination factor, use population ranges in evaluating the factor as specified in section 6.3.2.4. For the Level I and Level II concentrations factors, use the population estimate, not population ranges, in evaluating both factors.

6.3.2.2 Level I concentrations. Sum the number of people subject to Level I concentrations. Multiply this sum by 10. Assign the product as the value for this factor. Enter this value in table 6-1.

6.3.2.3 Level II concentrations. Sum the number of people subject to Level II concentrations. Do not include those people already counted under the Level I concentrations factor. Assign this sum as the value for this factor. Enter this value in table 6-1.

6.3.2.4 Potential contamination. Determine the number of people within each distance category of the target distance limit (see table 6-15) who are subject to potential contamination. Do not include those people already counted under the Level I and Level II concentrations factors.

W1-Distance-weighted population from table 6-17 for distance category i.

n=Number of distance categories.

If PI is less than 1, do not round it to the nearest integer; if PI is 1 or more, round to the nearest integer. Enter this value in table 6-1.

6.3.2.5 Calculation of population factor value. Sum the factor values for Level I concentrations, Level II concentrations, and potential contamination. Do not round this sum to the nearest integer. Assign this sum as the population factor value. Enter this value in table 6-1.

TABLE 6-17-DISTANCE-WEIGHTED POPULATION VALUES FOR POTENTIAL CONTAMINATION FACTOR FOR AIR PATHWAY a

a Round the number of people present within a distance category to nearest integer. Do not round the assigned distance-weighted population value to nearest integer.

6.3.3

Resources. Evaluate the resources factor as follows:

• Assign a value of 5 if one or more of the following resources are present within onehalf mile of a source at the site having an air migration containment factor value greater than 0:

-Commercial agriculture.
-Commercial silviculture.

-Major or designated recreation area.

• Assign a value of 0 if none of these resources is present.

Enter the value assigned in table 6-1. 6.3.4

Sensitive environments. Evaluate sensitive environments based on two factors: actual contamination and potential contamination. Determine which factor applies as follows.

If no samples meet the criteria for an observed release to air and if there is no observed release by direct observation, consider all sensitive environments located, partially or wholly, within the target distance limit to be subject to potential contamination.

If one or more samples meet the criteria for an observed release to air or if there is an observed release by direct observation, determine the most distant location (that is, sample location or direct observation location) that meets the criteria for an observed release:

• If the most distant location meeting the criteria for an observed release is within the 4-mile target distance limit, identify the distance category from table 6-15 in which it is located:

-Consider sensitive environments located, partially or wholly, anywhere within this distance category or anywhere within a distance category closer to a source at the site as subject to actual contamination. -Consider all other sensitive environments located, partially or wholly, within the target distance limit as subject to potential contamination.

• If the most distant location meeting the criteria for an observed release is beyond the 4-mile target distance limit, identify the distance at which it is located:

-Consider sensitive environments located, partially or wholly, anywhere within a distance from the sources at the site equal to the distance to this location to be subject to actual contamination and include all such sensitive environments in the evaluation.

-Do not include any sensitive environments as subject to potential contamination.

each sensitive environment subject to actual contamination.

For those sensitive environments that are wetlands, assign an additional value from table 6-18. In assigning a value from table 618, include only those portions of wetlands located within distance categories subject to actual contamination. If a wetland is located partially in a distance category subject to actual contamination and partially in one subject to potential contamination, then solely for purposes of table 6-18, count the portion in the distance category subject to potential contamination under the potential contamination factor in section 6.3.4.2. Determine the total acreage of wetlands within those distance categories subject to actual contamination and assign a value from table 6-18 based on this total acreage.

Calculate the actual contamination factor value (EA) as follows:

6.3.4.2 Potential contamination. Determine those sensitive environments located, partially or wholly, within the target distance limit that are subject to potential contamination. Assign value(s) from table 4-23 to each sensitive environment subject to potential contamination. Do not include those sensitive environments already counted for table 4-23 under the actual contamination factor.

For each distance category subject to potential contamination, sum the value(s) assigned from table 4-23 to the sensitive environments in that distance category. If a sensitive environment is located in more than one distance category, assign the sensitive