20 RADON VERTICAL DIMENSION OF MIXING
20.1 DEFINITION
The radon vertical dimension of mixing is the height of the atmospheric boundary layer near the ground surface into which the radon gas that emanates from the ground is uniformly mixed in the outdoor air. This parameter is measured in units of length (l).
20.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the radon vertical dimension of mixing that represents conditions at the site. This parameter's dimension should be given in units of meters (m).
A default value of 2 m was adopted in the RESRAD model for the
radon vertical dimension of mixing. This value of 2 m is a conservative
value, considering the height of humans. Unless other evidence indicates
use of a different value, this value should be used in the RESRAD code.
21.1 DEFINITION
The average annual wind speed is the overall average of the wind speed, measured near the ground, in a one-year period. This parameter is measured in units of length per time (lT-1).
21.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the average annual wind speed that represents conditions at the site. The dimensions of the wind speed input should be given in units of meters per second (m/s).
A default value of 2 m/s was adopted in the RESRAD model for the average annual wind speed. For more accurate use of the code, however, site-specific data should be used whenever possible. If measurements are performed to get site-specific data, these measurements should be consistent with guidance in DOE's guide for radiological effluent monitoring (DOE 1991a).
Site-specific information on the time distribution of the wind speed
and direction at the site can be obtained with the installation of a simple
meteorological station instrumented with an anemometer (for measuring the
wind speed) and wind vanes (for measuring wind direction). Although simple,
the installation, operation, and maintenance of such systems are time-consuming
and require the attention of trained personnel. A more general estimation
of the average wind speed at a site can be obtained from other meteorological
information systems in the area (such as at a commercial airport). For
most applications, in the absence of site-specific data, this approach
should suffice because of the intrinsic uncertainties associated with the
natural variability of the wind speed and direction at the site.
22 AVERAGE BUILDING AIR EXCHANGE RATE
22.1 DEFINITION
The building air exchange (or ventilation) rate is the total volume of air contained in the building that is being exchanged with outside air per unit of time. This parameter expresses the rate at which the total air contained within the building is replaced (or renewed) per unit of time and is measured in units of inverse time (T-1). For example, a building with a ventilation rate of 1 h-1 has its volume of air replaced once each hour on average.
Important factors affecting the ventilation rate include construction and operating features of the building (i.e., age, window and door weatherproofing, existence of unbalanced mechanical ventilation, the use of fireplaces, etc.), as well as environmental conditions (i.e., atmospheric pressure, temperature, and wind speed and direction). The total ventilation rate is based on three factors (Nero 1988): (1) the infiltration of air through small openings and imperfections in the building structure; (2) the exchange of air through windows, doors, or any other large openings that are kept partially or temporarily open; and (3) the mechanically supplied ventilation due to the operation of exhaust fans or other similar systems. Each of these factors varies significantly along time and, consequently, the total ventilation rate in a house is also strongly time dependent. In the United States, the average ventilation rate during the seasons when houses are kept closed lies within the range of 0.1-1.0 h-1.
22.2 MEASUREMENT METHODOLOGY
Measurement of the ventilation rate in a building can be accomplished directly by injecting a tracer gas, sulfur hexafluoride (SF6), into the house and then, after a mixing time, measuring the gas concentration as a function of time by using an infrared analyzer. The ventilation rate is equal to the rate of decay of the tracer concentration (Nero 1988).
Another available passive measurement technique consists of releasing a gaseous tracer from a small source at a constant rate inside the building. A collecting monitor, consisting of a diffusive tube and an absorber, measures the average concentration during the time the system is in operation. The measured concentration is then proportional to the inverse of the ventilation rate. Further references for these ventilation rate measurement techniques, as well as some predictive quantitative models, can be found in Nazaroff et al. (1988), Nero (1988), and Sherman (1990).
22.3 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the average building air exchange rate that represents conditions at the site. The ventilation rate should be given in units of inverse time (T-1).
For generic use of the code, a default value of 0.5 h-1 was adopted in the RESRAD model for the average building air exchange rate. For more accurate use of the code, however, site-specific data should be used whenever possible. A compilation of air exchange rate data for various types of buildings and of data on the effectiveness of mechanical air exchangers can be found in Godish (1991).
23.1 DEFINITION
The building room height expresses the average height of the house.
More specifically, it is defined as the ratio of the volume of the total
internal space of the building to the internal area of its floor surface.
This parameter is measured in units of length (l). For one-story houses
without a basement, the values for the building room height typically lie
within the range of 2.2-3.0 m.
23.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the building room
height that represents conditions at the site. The dimensions of the input
value of the room height should be given in units of meters (m).
For generic use of the code, a default value of 2.5 m was adopted in
the RESRAD model for the building room height. For more accurate use of
the code, however, site-specific data should be used whenever possible.
24 BUILDING INDOOR AREA FACTOR
24.1 DEFINITION
The building indoor area factor is the fraction of the floor area built on the contaminated area.
24.2 RESRAD DATA INPUT REQUIREMENTS
A value of 1.0 means that the entire floor area was built on the contaminated area. Values greater than 1.0 indicate a contribution from walls extending into the contaminated zone.
If 0 is entered, the code will calculate a time-dependent area factor on the basis of an assumed floor area of 100 m2 and the amount of wall area extending into the contaminated zone. For example, if the walls extend to a depth of 0.5 m into the contaminated zone, the building indoor area factor is equal to 1+0.5 × 4/100, or 1.2. The building indoor area factor is time dependent because of soil erosion of the contaminated zone. The default value used in RESRAD for the building indoor area factor is 0.
25 THICKNESS OF UNCONTAMINATED UNSATURATED ZONE
25.1 DEFINITION
The uncontaminated unsaturated zone is the portion of the uncontaminated
zone that lies below the bottom of the contaminated zone and above the
water table. The RESRAD code has provisions for up to five different horizontal
strata within this zone. Each stratum is characterized by six radionuclide-independent
parameters: (1) thickness of the layer, (2) soil density, (3) total
porosity, (4) effective porosity, (5) soil-specific b
parameter, and (6) hydraulic conductivity.
25.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for each stratum used in the calculation. Entering a nonzero thickness for a stratum activates that stratum and, similarly, changing the thickness to zero deletes the stratum. Default values are supplied by the code for all parameters of an active stratum; however, the use of site-specific data is strongly recommended.
26 BUILDING FOUNDATION THICKNESS
26.1 DEFINITION
The building foundation thickness is the average thickness of the building shell structure in the subsurface of the soil. Typical values lie around 0.15 m.
26.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the building foundation thickness that represents conditions at the site. The dimensions of the input value of the building foundation thickness should be given in units of meters (m).
A default value of 0.15 m was adopted in the RESRAD model for the building foundation thickness. For more accurate use of the code, however, site-specific data should be used whenever possible.
27 FOUNDATION DEPTH BELOW GROUND SURFACE
27.1 DEFINITION
The foundation depth below ground surface is the vertical distance in the soil from the very bottom of the basement floor slab to the ground surface. Typical values lie within the range of 0.0-3.0 m.
27.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the foundation depth below the ground surface that represents conditions at the site. The dimensions of the input value for the foundation depth should be given in units of meters (m).
A default value of 1.0 m was adopted in the RESRAD model for the foundation depth. For more accurate use of the code, however, site-specific data should be used whenever possible.
If a negative value is entered, the absolute value will be adjusted (if needed) so that the foundation depth will not extend into the contaminated zone. Thus, because of erosion of the cover and contaminated zones, the foundation depth can be time dependent and less than the (absolute) specified value.
28 FRACTION OF TIME SPENT INDOORS ON-SITE
28.1 DEFINITION
The fraction of time spent indoors on-site is the average fraction of time in a year during which an individual stays inside a house or a building on the contaminated site. A typical value lies around 0.5 (dimensionless).
28.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the fraction of time spent indoors that represents conditions at the site. This is a dimensionless parameter and should be entered as a decimal fraction rather than as a percentage. The sum of the fraction of time spent indoors on-site, the fraction of time spent outdoors on-site, and the fraction of time spent off-site (not an input data) should equal 1.
A default value of 0.5 was adopted in RESRAD for the fraction of time spent indoors on-site. For short-term realistic evaluations, site-specific data are more appropriate and should be used whenever possible. A typical local or regional value should be more representative, however, if long-term evaluations are considered.
29 FRACTION OF TIME SPENT OUTDOORS ON-SITE
29.1 DEFINITION
The fraction of time spent outdoors on-site is the average fraction of time in a year during which an individual stays outdoors on the site. This is a dimensionless parameter and the typical value lies around 0.25.
29.2 RESRAD DATA INPUT REQUIREMENTS
In RESRAD, the user is required to input a value for the fraction of time spent outdoors that represents conditions at the site. It should be entered as a decimal fraction rather than as a percentage. The sum of the fraction of time spent indoors on-site, the fraction of time spent outdoors on-site, and the fraction of time spent off-site (not an input data) should equal 1.
A default value of 0.25 was adopted in RESRAD for the fraction of time
spent outdoors on-site. For short-term realistic evaluations, site-specific
data are more appropriate and should be used whenever possible. A typical
local or regional value should be more representative, however, if long-term
evaluations are considered.