35 MASS LOADING FOR INHALATION

35.1 DEFINITION

The mass loading parameter is the concentration of soil particles in the air and is obtained directly from empirical data for locations and conditions similar to those applicable for the scenario used. This parameter is measured in grams per cubic meter (g/m³).

Three models are commonly used for the process by which dust becomes airborne. One is a resuspension factor model in which the airborne dust concentration (C_dust) is given as a function of the resuspension factor (R_f), the effective depth of the layer of dust from which resuspension occurs (d_r), and the bulk soil density (_b). The formula relating these variables is

The second is a resuspension rate model in which the airborne dust concentration is given as a function of the resuspension rate (R_r), surface dust concentration (_s = _b d_r), and the average deposition velocity (V_d). The formula is

The third model used by the RESRAD code is a mass loading model in which an average value of the airborne dust concentration is specified on the basis of empirical data.

Use of a mass loading factor from empirical data eliminates consideration of details of the resuspension mechanisms; in particular, the effective depth of the disturbed layer can be ignored.

Average, ambient concentrations of transportable particles range from 3.3 × 10^-5 to 2.54 × 10^-4 g/m³ in urban locations and from 9 × 10^-6 to 7.9 × 10^-5 g/m³ in nonurban locations (Gilbert et al. 1983). Anspaugh et al. (1974) and Healy and Rodgers (1979) used 1 × 10^-4 g/m³ for predictive purposes and found that the predicted results and the real cases are comparable. The EPA (EPA 1977) has used the same value to screen calculations.

The mass loading value will fluctuate above its ambient level depending on human activities such as plowing and cultivating dry soil or driving on an unpaved road. The estimated mass loading for construction activities is about 6.0 × 10^-4 g/m³; for exposure to construction traffic on unpaved roads it is 4.0 × 10^-4 g/m³; and for agriculture-generated dust, it is about 3.0 × 10^-4 g/m³ (Oztunali et al. 1981). The maximum respirable dust loading inside the cab of heavy construction equipment during a surface coal mining operation was found to be 1.8 × 10^-3 g/m³ (Oztunali et al. 1981). Estimates of mass loadings have been as high as 1.3 g/m³ for instantaneous mass loadings during tilling.

35.2 RESRAD DATA INPUT REQUIREMENTS

Gilbert et al. (1983) suggest a mass loading factor of 2.0 × 10^-4 g/m³ for transportable particles at an on-site loading to take into account short periods of high mass loading and sustained periods of normal farmyard activities for which the dust level may be somewhat higher than ambient. This value (2.0 × 10^-4 g/m³) is the default value used in RESRAD. Sehmel (1980) has conducted an excellent review of particle resuspension. Users are referred to this paper for a detailed review of particle resuspension and mass loading.

36 SHIELDING FACTOR FOR INHALATION PATHWAY

36.1 DEFINITION

This factor is the ratio of airborne dust concentration indoors on-site to the concentration outdoors on-site. It is based on the fact that a building provides shielding against entry of wind-blown dust particles. Therefore, calculation of the effective dose from the dust inhalation pathway should take into account this shielding effect. The occupancy factor, FO₂, for the inhalation pathway can then be calculated by RESRAD according to the following equation:

where TF₁ is the fraction of time spent outdoors on-site (an input parameter, Section 29), TF₂ is the fraction of time spent indoors on-site (an input parameter, Section 28), and TF₃ is the fraction of time spent off-site (not an input parameter, Sections 28 and 29).

36.2 RESRAD DATA INPUT REQUIREMENTS

This parameter should be input as a fraction ranging from 0 to 1. The default shielding factor for dust inhalation in RESRAD is 0.4, which assumes that the dust level indoors is 40% of the outdoor level (Alzona et al. 1979).

37 DEPTH OF ROOTS

37.1 DEFINITION

This parameter is the average root depth of various plants grown in the contaminated zone. The root depth varies for different plants. For some plants, such as beets, carrots, lettuce, and so forth, it does not extend below about 0.3 m. For others, such as fruit trees, the roots may extend 2 or 3 m below the surface; tap roots for some crops (e.g., alfalfa) can extend to 5 m. Most of the plant roots from which nutrients are obtained, however, usually extend to less than 1 m below the surface.

This parameter is used to calculate the cover and depth factor for the plant, meat, and milk pathways because edible plants become contaminated through root uptake of radionuclides. Uptake of radionuclides from plant roots is assumed possible only when the roots extend to the contaminated zone and is limited to the fraction of roots that have direct contact with contaminated soil.

37.2 RESRAD DATA INPUT REQUIREMENTS

The average root depth should be entered in units of meters (m). The default value in the RESRAD code is 0.9 m.

38 SOIL INGESTION RATE

38.1 DEFINITION

This parameter is the accidental ingestion rate of soil material or soil dust. Children, especially those under 18 months, tend to mouth or ingest substances that are not considered to be food. When this behavior extends beyond the age of 18 months, the child is said to practice pica (Barltrop 1966; Robischon 1971; Ziai 1983). Many factors such as nutrition, quality of care, and parental relationship (Bicknell 1974; Glickman 1981; Danford et al. 1982; Behrman and Vaughan 1983; Forfar and Arneil 1984; Bellinger et al. 1986) influence the extent of this behavior. However, it is believed that a child who practices pica is no different from one who does not because pica cannot be consistently predicted (Feldman 1986), even though severe pica usually occurs among grossly disturbed or mentally retarded children.

According to the literature, a wide variety of substances are ingested: soil, clay, sand, dust, grass, leaves, plaster, hair, starch, paint chips, string, soap, wood, powders, chalk, and paper. No quantitative ingestion rates have been suggested because children with known pica behavior have not been studied. "Abnormal" soil ingestion (pica) is believed to be uncommon and may need to be addressed separately.

On the basis of observational data, children are most likely to ingest soil from the age of 1 to 6 (Cooper 1957; Sayre et al. 1974; Charney et al. 1980; Walter et al. 1980). Beyond age 6 or 7, ingestion of nonfood substances is usually caused by inadvertent ingestion or developmental problems. Paustenbach et al. (1986) summarized the normal amount of soil ingested by children on the basis of the age of the child. Vermeer and Frate (1979) pointed out that the environmental setting is also an important factor for children in rural areas who tend to ingest a higher amount of soil. Hawley (1985) used data from the literature to develop scenarios to estimate ingestion amounts for young and older children and adults. He divided each year into two activity periods: May through October when individuals spend more time outdoors and November through April when most of the time, weather conditions eliminate outdoor activities. Hawley's study indicated that the amount ingested by young children (2.5 years old, weighing 13.2 kg), during outdoor activity between May and October (5 d/week) is 250 mg/d. During November through April, the ingestion during indoor activity is 100 mg/d. For children six-years old, weighing approximately 20.8 kg, the ingestion amount is 50 mg/d during outdoor activity from May through October and 3 mg/d year-round for indoor activity. Working in attics or other uncleaned areas of a house can cause adults (weighing 70 kg) to ingest 110 mg/d of soil for an assumed duration of 12 d/yr. For living space activities, the ingestion amount is 0.56 mg/d. For outdoor activities from May through October, the ingestion amount is 480 mg/active d, assuming 8 hours is spent outdoors per day, 2 d/week.

According to Binder et al. (1986), the average quantity of soil ingested by children is about 108 mg/d (within a range of 4-708 mg/d). Clausing et al. (1987) estimated that the ingestion rate of children is 105 mg/d, with a range of 23-362 mg/d. Binder et al. (1986) and Clausing et al. (1987) have also provided some limited information on the upper limit of the soil ingestion rate on the basis of evidence that the upper range of the ingestion rate for children is around 800 mg/d or more.

An amount has not been estimated for abnormal soil ingestion behavior among children. However, some evidence suggests that a rate of 5 to 10 g/d may not be unreasonable. The EPA used 5 g/d in its risk assessment for tetrachlorodibenzo-p-dioxin (TCDD) (EPA 1984a). The USDA used a value of 10 g/d in conducting exposure assessments related to the use of sludge in gardens and soils.

After reviewing the limited data available, the EPA (1990a) decided that the studies of Binder et al. (1986) and Clausing et al. (1987) appear to be the most reliable and suggested that an estimate of 0.2 g/d be used as an average value for young children (under the age of 7). An upper range of soil ingestion is 0.8 g/d. For other age groups (children older than 7 years), 0.1 g/d should be used for the soil ingestion amount. These factors account for ingestion of both outdoor soil and indoor dust. Site conditions, for example, snow cover, will affect the soil ingestion rate because the cold weather will limit outdoor activities in the winter, and because snow also provides an additional cover for the contaminated soil. However, presently there is no recommended approach to correct these influences, and any correction should be conservatively applied.

According to EPA guidance (EPA 1990b), soil ingestion should be considered separately for adults and children for a residential scenario. For the first stage (for children), 0.2 g/d is the recommended ingestion rate with an exposure duration of 6 years, and for the second stage, with an exposure duration of 24 years, the recommended ingestion rate is 0.1 g/d. In RESRAD, only one soil ingestion rate is required, which is the yearly intake rate (g/yr) without the differentiation between contaminated soil and uncontaminated soil. RESRAD will automatically adjust this soil ingestion rate with an area factor, an occupancy factor, and a cover-and-depth factor, so that only the contaminated source is accounted. The input value for the soil ingestion rate depends strongly on the assumed scenario. For a residential scenario with an exposure duration of 30 years, 43.8 g/yr [(36.5 g/yr × 24 yr + 73 g/yr × 6 yr)/30 yr] is an applicable input value to RESRAD according to EPA guidance.

The EPA (1991) has chosen 50 mg/d as the standard default value for adult soil ingestion in the workplace based on a pilot study by Calabrese et al. (1990). This 50 mg/d value is to be used in conjunction with an exposure frequency of 250 d/yr and an exposure duration of 25 yr. For outdoor activities in the commercial/industrial setting (e.g., construction on landscaping) a soil ingestion rate of 480 mg/d is recommended by the EPA; however, this type of work is usually short-term and is often dictated by weather.

38.2 MEASUREMENT METHODOLOGY

Several methods have been used to characterize soil ingestion by children. Lepow et al. (1975) measured hand dust by applying preweighed adhesive labels to the hands and weighing the amount of dirt that was removed. They also observed "mouthing" behavior and reported that a child would put his or her fingers into the mouth about 10 times a day. Day et al. (1975) and Duggan and Williams (1977) also measured the amount of dust on children's hands. Binder et al. (1986) studied the ingestion of soil among children 1 to 3 years of age who wear diapers. Both excreta and soil from the play yards were analyzed for materials that were thought to be poorly absorbed in the gut. Clausing et al. (1987) conducted a soil ingestion study by using a tracer element method similar to that of Binder et al. (1986). They also collected fecal samples for six hospitalized, bedridden children to represent a control group.

Presently there is no widely accepted method for determining the relative contribution of each medium (i.e., soil versus dust) to the daily ingestion amounts and the effect of climatic variations (e.g., snow cover).

38.3 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the soil ingestion rate should be entered in units of grams per year (g/yr). The default value of 36.5 g/yr is used, which accounts for an average soil intake rate of 0.1 g/d for 365 d/yr. The 0.1 g/d ingestion rate is a value recommended by the EPA for adults in a residential scenario.

39 THICKNESS OF CONTAMINATED ZONE

39.1 DEFINITION

This parameter is the distance between the uppermost and lowermost soil samples that have radionuclide concentrations clearly above background. In determining whether the measured soil concentration is above the background level, a DOE-approved method based on a statistical analysis of site measurements in comparison to background measurements should be used (DOE 1991a, Section 7). In case such an approach is not available, then as a default approach, a soil sample should be treated as clearly contaminated if the radionuclide concentration is greater than the average background radionuclide concentration plus twice the standard deviation of the background measurements.

39.2 MEASUREMENT METHODOLOGY

A DOE-approved statistical approach (DOE 1991a, Section 7) should always be considered first when estimating average, handling distribution analyses and estimating central tendency soil concentrations. The default approach provided below is a conservative method that may sometimes significantly overestimate the dose. To determine the thickness of a contaminated zone with an area greater than 100 m², the average contamination thickness of boreholes drilled to take soil samples is calculated over any integral subarea of 100 m². If one or more boreholes in the subarea have a contamination thickness exceeding the average thickness by a factor larger than three, then the average value is replaced by one-third the maximum contamination thickness. The thickness of the contaminated zone is then taken as the maximum average thickness calculated over a 100-m² subarea. For a contaminated zone with an area less than 100 m², the average contamination thickness over the contaminated zone or one-third of the maximum contamination thickness in a borehole (if the thickness is greater than three times the average value) is taken as the representative value of the contaminated zone thickness.

39.3 RESRAD DATA INPUT REQUIREMENTS

In RESRAD, the thickness of this ideal contaminated zone is entered in units of meters (m). The default value is 2 m.

40 RADIATION DOSE LIMIT

The radiation dose used in the RESRAD code is the effective dose equivalent from external radiation plus the committed effective dose equivalent from internal radiation (International Commission on Radiological Protection [ICRP] 1984). The radiation dose limit is used in RESRAD to derive soil guidelines (i.e., cleanup criteria). The calculated guidelines are linearly proportional to the dose limit. If the RESRAD code is used to calculate doses (rather than soil guidelines), the input value of the radiation dose limit will not affect the calculated doses.

In the RESRAD code, 30 mrem/yr (0.3 mSv/yr) is used as the default value. This value is less than the 100 mrem/yr basic radiation dose limit specified in DOE Order 5400.5. The 100 mrem/yr dose limit has been used to calculate the derived concentration guides (DCGs) listed in Chapter 3 of DOE Order 5400.5. It is unacceptable, however, to derive authorized limits for soil by using the 100 mrem/yr primary dose limit as a dose standard, when actual or likely use of the sites is considered. As with DCGs, 100 mrem/yr represents a reasonable upper bound on concentration. Authorized limits for release must comply with the as low as reasonably achievable (ALARA) process (DOE 1991b) and should be a small fraction of the dose limit. Therefore, when using realistic parameters and considering likely use scenarios, a default dose limit of 30 mrem/yr (0.3 mSv/yr) is used in RESRAD.

41 SEAFOOD CONSUMPTION RATE

41.1 DEFINITION

National recreational catch data for coastal areas were obtained by the National Marine Fisheries Service (NMFS) in 1985. The NMFS conducted a direct survey of fishermen in the field and an independent telephone survey of households (NMFS 1986). Total fish consumption data were obtained from a one-year survey conducted by NPD Research, Inc., during 1973 and 1974 and funded by the Tuna Research Institute. Questionnaires were answered by 6,980 families representing the U.S. population.

Javitz (1980) used the data obtained by NPD Research, Inc., to calculate the mean and 95th percentile of seafood consumption for seafood consumers in the United States as 14.3 g/d (5.2 kg/yr) and 41.7 g/d (15.2 kg/yr), respectively. The mean average of 14.3 g/d (5.2 kg/yr) for seafood consumption includes 2.1 g/d (0.8 kg/yr) for nonfish seafood consumption, that is, lobsters, oysters, scallops, shrimps, squids, and so forth. Unfortunately, NPD Research, Inc.'s original survey data for seafood consumption did not distinguish between recreationally caught and purchased fish; therefore, this difference is not reflected in the calculated mean and 95th percentile values.

Puffer et al. (1982) conducted 1,059 interviews with sport fishermen in the Los Angeles Harbor area. The interviews revealed that sport fishermen keep 67 to 89% of the finfish and 97% of the shellfish that they catch. The median and 90th percentile seafood (fish plus shellfish) consumption rates of sport fishermen are 37 and 225 g/d, respectively.

Another source for the seafood consumption rate of sport fishermen is a survey conducted in Commencement Bay at Tacoma, Washington, by Pierce et al. (1981) in 1981. The sample size (304 fishermen) was smaller than that of Puffer et al. (1982) and the sampling frequency was lower. It was found that over half of the fishermen caught and consumed fish weekly. Pierce et al. (1981) concluded that the mean average seafood consumption rate for the surveyed fishermen was 23 g/d (within a range of 12-54 g/d); the 90th percentile was 54 g/d.

Although the surveys conducted by Puffer et al. (1982) and Pierce et al. (1981) are limited to the West Coast, the EPA (1990a) considers these studies to be representative of actual annual consumption rates for recreational fishermen. By averaging the results of these two surveys, the EPA (1990a) has suggested that the 50th and 90th percentile seafood consumption rates of fishermen are 30 g/d (11 kg/yr) and 140 g/d (51 kg/yr), respectively.

Because sport fishermen and their families consume much more seafood than other people, the EPA recommends that consumption rates of fishermen based on Puffer et al.'s (1982) and Pierce et al.'s (1981) surveys be used as comparative references for any area where there is a large body of water and widespread contamination is possible.

The NRC (1977) used values of 2.2, 5.2, and 6.9 kg/yr for average individual fish consumption for children, teenagers, and adults, respectively. Average individual consumption rates of other seafood were 0.33, 0.75, and 1.0 kg/yr for the three different groups. For a worst-case scenario, the fish consumption rates were 6.9, 16, and 21 kg/yr for children, teenagers, and adults, respectively. For other seafood consumption rates, values of 1.7, 3.8, and 5 kg/yr were used.

The input seafood consumption rate in RESRAD is the yearly total consumption rate, which does not take into account the difference between the contaminated and uncontaminated portion. It is assumed that if a surface water body (a pond) is located on a site, it will provide 50% of the consumed seafood. If a RESRAD user would like to use a different fraction, then the fraction of aquatic food from the site (an input parameter) needs to be modified so that the calculated dose accounts for the correct contaminated amount of the consumption rate.

41.2 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the seafood consumption rate should be entered in units of kilograms per year (kg/yr). The default value for the consumption rate is 5.4 kg/yr for fish and 0.9 kg/yr for other seafood.

42 FRUIT, VEGETABLE, AND GRAIN CONSUMPTION RATE

42.1 DEFINITION

According to the latest survey by the National Gardening Association (1987), 38% or a total of 34 million U.S. households participated in vegetable gardening in 1986. The size of the home vegetable garden, however, has decreased from 600 ft² in 1982 to 325 ft² in 1986 (National Gardening Association 1987). The distribution of home gardens varies geographically, with a large percentage located in the Midwest and South, and more in rural areas than in cities and suburbs. Therefore, homegrown fruits and vegetables make up a larger portion of the average consumption rate in rural areas than in cities or suburbs.

The EPA has made recommendations on the consumption rates of homegrown fruits and vegetables on the basis of two sources: Foods Commonly Eaten by Individuals: Amount Per Day and Per Eating Occasion (Pao et al. 1982) and Food Consumption: Households in the United States, Seasons and Year 1977-1978 (USDA 1983). The first source used data collected by the USDA in 1977-1978 from home interviews of 37,874 respondents who were asked to recall food consumed one day before the interview, the day of the interview, and the day after the interview, to calculate percentiles of total fruit and vegetable consumption of the U.S. population. The consumption rate of homegrown fruits and vegetables can be calculated by subtracting the data of the "bought" category for all foods from the data of the "all" category in the USDA food consumption survey. Homegrown dark green vegetables make up approximately one-third of the dark green vegetables consumed. This category includes mustard greens, kale, kohlrabi, and broccoli. Consumption of homegrown corn, cucumbers, green beans, and tomatoes makes a significant contribution to total consumption. The proportion of homegrown fruits consumed is highest for strawberries, peaches, and pears, and lowest for citrus fruits.

According to the EPA (1990), the average consumption rate of vegetables per person is 200 g/d (73 kg/yr); homegrown products account for 25% of the total consumption rate, which is 50 g/d (18 kg/yr). Total average daily fruit intake is 140 g/d (51 kg/yr) per individual. The total homegrown fruit consumption rate is 28 g/d (10 kg/yr), which is 20% of the total intake rate. For a reasonable worst case, it is suggested that 40% of the total intake be used for homegrown vegetable consumption and 30% of the total intake be used for homegrown fruit consumption. Table 42.1 summarizes the EPA's recommendations.

The EPA data provided above do not include information about grain product consumption. In NRC Regulatory Guide 1.109 (NRC 1977), different total consumption amounts of fruits, vegetables, and grains are suggested for different age groups. The average individual consumption for a child is 200 kg/yr, for a teenager it is 240 kg/yr, and for an adult it is 190 kg/yr. Suggested values for the maximally exposed individual in a worst-case scenario are 520, 630, and 520 kg/yr, for a child, teenager, and adult, respectively. The total consumption for the maximum exposure case consists of 22% for fruit consumption, 54% for vegetable consumption, and 24% for grain consumption.

To run the RESRAD code, a yearly consumption rate for fruit, vegetables, and grain is needed that does not differentiate the contaminated fraction from the uncontaminated fraction. An area factor will automatically be calculated and used to adjust the consumption rate. It is assumed that if an area is greater than 1,000 m², then 50% of the consumption is obtained from the site; if the area is smaller than 1,000 m², then the fraction of the contaminated product is the ratio of the contaminated area to an area of 2,000 m². The upper bound in the RESRAD default adjustment for the fraction of contaminated products is 50%. If this value differs from that obtained from site-specific data, the user should adjust the yearly consumption rate so that an accurate consumption rate of the contaminated product is used to derive the total dose.

42.2 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the consumption rate should be entered in units of kilograms per year (kg/yr). The default value for the consumption rate is 160 kg/yr for fruit, vegetables, and grains.

43 INHALATION RATE

43.1 DEFINITION

The inhalation rate varies with activity level, age, weight, sex, and general physical condition. Anthropometric data (EPA 1985) have been used to propose several formulas for calculating the inhalation rate for a human at rest. However, in general, the formulas are based on measurements from relatively small sample sizes and are limited to calculating the inhalation rate at rest only.

The EPA (1985) has compiled the available data, most of which is from early studies, and has derived an inhalation rate expressed in cubic meters per hour (m³/h). Inhalation rates were compiled for each age/sex group at rest and at light, moderate, and heavy activity levels. The activity levels were categorized according to criteria developed by the Environmental Criteria and Assessment Office of the EPA for the air quality document for ozone. A male adult with a body weight of 70 kg was used as a reference, and activity level categories for the other age/sex groups were extrapolated from the criteria for male adults on the basis of body weight (American Industrial Hygiene Association 1971). Table 43.1 gives a summary of human inhalation rates at different age/sex/activity levels (EPA 1985). Resting is characterized by such activities as watching television, reading, or sleeping. Light activity includes level walking, meal cleanup, care of laundry and clothes, domestic work and other miscellaneous household chores, attending to personal needs, photography, hobbies, and conducting minor indoor repairs and home improvements. Moderate activity includes climbing stairs, heavy indoor cleanup, and performing major indoor repairs and alterations (e.g., remodeling). Heavy activity consists of vigorous physical exercise such as weight lifting, dancing, or riding an exercise bike.

Assuming 16 hours of light activity and 8 hours of resting, the ICRP (1981) has reported a 23-m³/d inhalation rate for adult males and a 21-m³/d rate for adult females, yielding an average value of 22 m³/d (8,030 m³/yr) for adults.

Data presented by the EPA (1985) suggest lower inhalation rates for light and resting activity levels. Using the same assumption as the ICRP (1981), the daily inhalation rate would be about 14 m³/d (5,110 m³/yr). In addition to assuming lower rates for light and resting activity levels, the EPA also estimated the daily inhalation rate for moderate and heavy activity levels; therefore, it is possible to estimate the total inhalation rate for any combination of activity levels. The EPA's data suggest that the maximum inhalation rate is roughly twice the reported mean rates for all activity levels.

The EPA (1990) made the following recommendations on the basis of the above mentioned data: 20 m³/d (7,300 m³/yr) should be used as the average adult daily inhalation rate and 30 m³/d (11,000 m³/yr) as the reasonable worst-case inhalation rate, provided the activity patterns are unknown. For exposure scenarios in which the distribution of activity patterns is known, the values in Table 43.1 should be used for calculations because they are more representative rates.

For an individual performing outdoor activities, a typical activity mix can consist of 37% at a moderate activity level, 28% at both resting and light activity levels, and 7% at a heavy activity level, which results in a 1.4 m³/h (12,300 m³/yr) inhalation rate. A reasonable worst-case outdoor inhalation rate can account for 50% of the time at a heavy activity level and 50% at a moderate activity level, with an inhalation rate of 3.0 m³/h (26,300 m³/yr), according to Table 43.1.

For an individual performing indoor activities, an average assumption would include 48% of the time at both a resting and light activity level, 3% at a moderate activity level, and 1% at a heavy activity level. A reasonable worst-case includes 25% at a resting activity level, 60% at a light activity level, 10% at a moderate activity level, and 5% at a heavy activity level. The first assumption has an average inhalation rate of 0.63 m³/h (5,500 m³/yr), and the second one has a reasonable worst-case inhalation rate of 0.89 m³/h (7,800 m³/yr).

43.2 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the inhalation rate should be entered in units of cubic meters per year (m³/yr). The default value used in the code is 8,400 m³/yr.

In the RESRAD code, the yearly inhalation rate is used. This rate is an average value that accounts for different activity levels both indoors and outdoors. Therefore, a site-specific value can be obtained with the assumed exposure scenario and an activity profile. The fraction of time spent on-site and off-site should not affect this input parameter, however, because in the RESRAD calculation, an occupancy factor is automatically derived and used for adjusting the calculated dose.

44 LEAFY VEGETABLE CONSUMPTION RATE

44.1 DEFINITION

The leafy vegetable consumption rate is a dietary factor for human food consumption that includes consumption of vegetables such as spinach and lettuce. On the basis of recommended values for the maximally exposed individual in NRC Regulatory Guide 1.109 (NRC 1977), the consumption rates of leafy vegetables for children, teenagers, and adults, respectively, are 26, 42, and 64 kg/yr. Average consumption rates used by the NRC to perform environmental dose analyses for releases of radioactive effluents from nuclear power plants into the atmosphere (Strenge 1987) are 10, 20, and 30 kg/yr for children, teenagers, and adults.

The RESRAD input leafy vegetable consumption rate does not differentiate the contaminated fraction from the uncontaminated fraction. Like the fruit, vegetable, and grain consumption rate stated in Section 42, a default adjustment is automatically performed, via the contaminated area, within the RESRAD code. If this value is different than that obtained from site-specific data, then the input consumption rate needs to be modified so that RESRAD calculates the correct dose for the contaminated product.

44.2 RESRAD DATA INPUT REQUIREMENTS

The default value used in RESRAD for the leafy vegetable consumption rate is 14 kg/yr.

45 LIVESTOCK WATER INTAKE RATE FOR

BEEF CATTLE AND MILK COWS

45.1 DEFINITION

According to NRC Regulatory Guide 1.109 (NRC 1977), the water ingestion rate for beef cattle is 50 L/d. The water ingestion rate for milk cows is 14 gal/d (approximately 50 L/d) plus 1 gal for every 3 lb of milk produced (Great Lakes Basin Commission 1975). If a production rate of 10 gal/d of milk is assumed, then the water ingestion rate for milk cows would be about 160 L/d (Gilbert et al. 1983).

45.2 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the livestock water intake should be entered in units of liters per day (L/d). The default values for beef cattle and milk cows are set to 50 and 160 L/d, respectively, if the user does not specify otherwise.

46 MEAT AND POULTRY CONSUMPTION RATE

46.1 DEFINITION

The USDA conducted a national food consumption survey in 1977-1978 (USDA 1983). The average consumption rates for beef and dairy products, as adopted by the EPA (1984a,b), are based on the results of this survey.

According to USDA studies, 44% of annual consumption is homegrown beef. This finding is based on a survey of 900 rural farm households (USDA 1966). Because the total amount of beef consumed averages approximately 100 g/d (36.5 kg/yr), the average consumption of homegrown beef is about 44 g/d (EPA 1990), which corresponds to 16 kg/yr.

For a reasonable worst-case, the EPA (1990) has suggested that a consumption rate of 75 g/d (27 kg/yr) be used for homegrown beef in risk assessments until better data are available.

The average consumption rate of 36.5 kg/yr, as recommended by the EPA, accounts for beef only. The total consumption rate for meat and poultry should be much higher. According to NRC Regulatory Guide 1.109 (NRC 1977), the recommended average value for consumption of meat and poultry is 37 kg/yr for children, 59 kg/yr for teenagers, and 95 kg/yr for adults. Recommended values for use in a maximally exposed case are 41 kg/yr for children, 65 kg/yr for teenagers, and 110 kg/yr for adults.

Gilbert et al. (1983) used a value of 79 lb/yr (36 kg/yr) for meat, 20 lb/yr (9 kg/yr) for poultry, and 15 lb/yr (7 kg/yr) for egg consumption, with a total value of 114 lb/yr (52 kg/yr). The consumption rate used for meat is about the same as that recommended by the EPA (1990). If the same percentage of homegrown beef can be applied to consumption of poultry and eggs, then the average consumption of homegrown meat, poultry, and eggs would be 23 kg/yr; for a reasonable worst-case scenario, the value would be 39 kg/yr on the basis of data of Gilbert et al. (1983).

In the RESRAD code, it is assumed that all of the consumed meat is contaminated if the area of the contaminated zone is greater than or equal to 20,000 m². If the area is less than 20,000 m², then the fraction of the contaminated product is the ratio of the contaminated area to an area of 20,000 m². If site-specific data differ from the RESRAD default values, the input data may need to be adjusted so that the correct dose from the contaminated meat product is obtained.

46.2 RESRAD DATA INPUT REQUIREMENTS

In the RESRAD code, the consumption rate for meat and poultry should be entered in units of kilograms per year (kg/yr). The default value for the consumption rate is 63 kg/yr.

47 MILK CONSUMPTION RATE

47.1 DEFINITION

According to the EPA (1984a) and Fries (1986), the milk (fresh milk only) consumption rate can range from 254 g/d to 1,000 g/d per person, with an average rate of 305 g/d (i.e., 110 L/yr). According to a USDA (1966) survey, 40% of the dairy products consumed in a typical farm household are from the milk cows on the farm. Applying this same percentage to a typical farm scenario, 44 L/yr of the fresh milk consumed is actually from cows owned by the farmer. On the basis of EPA (1990) suggestions for a worst-case scenario, if 75% of the fresh milk consumed is assumed to be from milk cows on the farm, the average consumption rate of fresh milk would then be 83 L/yr per person for a farm scenario.

In NRC Regulatory Guide 1.109 (NRC 1977), milk consumption rates for different age groups are reported. The average rates for children, teenagers, and adults are 170, 200, and 110 L/yr, respectively. Recommended values for the maximally exposed individual are 330, 330, 400, and 310 L/yr for infants, children, teenagers, and adults.

The RESRAD code assumes that all of the consumed milk is contaminated if the area of the contaminated zone is greater than or equal to 20,000 m². If the area is less than 20,000 m², then the fraction of the contaminated product is the ratio of the contaminated area to an area of 20,000 m². Therefore, caution should be used in choosing the appropriate input data so that the correct site-specific dose level is obtained.

47.2 RESRAD DATA INPUT REQUIREMENTS

In RESRAD, the default milk consumption rate is set to 92 L/yr per person.