I.3.0 METEOROLOGY AND AIR QUALITY
The following subsections discuss Hanford Site climatology and air quality. The meteorological section summarizes measurements of wind, temperature and humidity, precipitation, fog and visibility, severe weather, and atmospheric dispersion. The air quality section includes information on air quality standards, emissions sources, and air quality monitoring.
I.3.1 METEOROLOGY
The Cascade Mountains greatly influence the climate of the Hanford Site by their rain shadow effect. This range also serves as a source of cold air drainage, which has a considerable effect on the wind regime over the Site.
Climatological data has been collected at Hanford Meteorological Monitoring Network sites. The Hanford Meteorological Station (HMS), located between the 200 East and 200 West Areas, is the most completely instrumented station. The HMS data are considered representative for assessing proposed TWRS activities. The following meteorological discussion is largely based on the Hanford Climatological Summaries (Stone et al. 1972), as well as information compiled by Cushing (Cushing 1994).
I.3.1.1 Wind
Figure I.3.1.1 shows winds measured at the Meteorological Monitoring Network sites. Prevailing winds at the HMS are from the west-northwest and northwest in all months of the year. Monthly average wind speeds are lowest during December, averaging 10 km/hr (6 mi/hr), and highest during June, averaging approximately 15 km/hr (9 mi/hr). The most prevalent wind speed class,
6 to 11 km/hr (4 to 7 mi/hr), occurs 36 percent of the time. Wind speeds are less than 21 km/hr (13 mi/hr) 84 percent of the time, and greater than 29 km/hr (18 mi/hr) less than 5 percent of the time. Peak gusts occur from the south-southwest, southwest, and west-southwest during all months.
I.3.1.2 Temperature and Humidity
From 1961 through 1990, the average monthly temperatures varied from -1 centigrade (C) (30.3 Fahrenheit [F]) in January to 24.6 C (76.2 F) in July with a yearly average of 11.8 C (53.2 F). On the average, 51 days during the year (April through September) had maximum temperatures greater than or equal to 32 C (90 F), and 12 days (May through September) had a maximum temperature greater than or equal to 37.8 C (100 F). Also, an average of 25 days during the year (October through February) experienced maximum temperatures less than 0 C (32 F). An average of 106 days per year (October through April) experienced minimum temperatures less than 0 C (32 F). An average of 4 days per winter season (November through February) experienced daily minimum temperatures less than -18 C (0 F) but approximately half of all winters were free of such days. The record maximum and minimum temperatures recorded during the period 1945 to 1991 were 45 C (113 F) in 1961 and -45 C (-23 F) in 1950.
The annual average relative humidity, based on data from the years 1950 through 1993, was 54.5 percent. Relative humidity was highest during the winter months, averaging 80.2 percent in December, and lowest during the summer, averaging 33.3 percent in July.
I.3.1.3 Precipitation
The average annual precipitation measured at the HMS is 17 cm (6.6 in.). The bulk of the precipitation (54 percent) occurs during November through February. As the wettest month, December receives an average of 2.5 cm (1 in.) of precipitation while July averages 0.5 cm (0.2 in.) and is the driest month. On the average, only 1 day per year experiences precipitation greater than 1.3 cm (0.5 in.), and 68 days per year have precipitation greater than 0.02 cm (0.01 in.) per year. An average of 125 days per year receive a trace amount or more of precipitation. The monthly total time during which precipitation occurs ranges from 12.4 percent in December to 1.5 percent in July. Winter monthly average snowfall ranges from 0.8 cm (0.3 in.) in March to 13.5 cm (5.3 in.) in January. Yearly snowfall has ranged from 0.8 cm (0.3 in.) to 140 cm (56 in.). Annual average snowfall is 38 cm (15 in.).
I.3.1.4 Fog and Visibility
Although fog (visibility less than or equal to 10 km [6 mi]), has been recorded during every month of the year at the HMS, nearly 90 percent of the occurrences are during the late fall and winter months. The months of April through September account for only about 1 percent of the occurrences. On average, 46 days per year experience fog and 24 days per year experience dense fog (visibility less than or equal to 0.4 km [0.25 mi]).
Other phenomena restricting visibility to 10 km (6 mi) or less include dust, blowing dust, and smoke (typically from wildfires, orchard smudging, and agricultural field burning). An average of 5 days per year have dust or blowing dust and only about 2 days per year have reduced visibility resulting from smoke. On an annual basis, 3.8 percent of the hourly observations recorded for the years 1960 through 1980 indicate restricted visibility because of all phenomena.
I.3.1.5 Severe Weather
Severe high winds are associated with thunderstorms. On average the Hanford Site may experience 10 thunderstorms per year, most frequently (80 percent) occurring May through August. However, thunderstorms have been observed to occur in every month of the year. Estimates of the extreme wind velocities, based on peak gusts observed from 1945 through 1980, are shown in Table I.3.1.1 (Stone et al. 1983).
Tornadoes are smaller and less frequent in the northwest portion of the United States than elsewhere in the country. There were no reports of violent tornadoes for the region surrounding the Hanford Site. The HMS climatological summary (Stone et al. 1983) and the National Severe Storms Forecast Center database list 22 separate tornado occurrences within 160 km (100 mi) of the Hanford Site from 1916 through August 1982. Two additional tornadoes have been reported since August 1982. The probability of a tornado striking at the Hanford Site has been estimated to be approximately one in 10,000 (NRC 1977).
Table I.3.1.1 Estimates of Extreme Winds at the Hanford Site
I.3.1.6 Atmospheric Dispersion
Atmospheric dispersion is a function of wind speed, duration and direction of wind, atmospheric stability, and mixing depth. Dispersion conditions are generally good if winds are moderate to strong, the atmosphere is of neutral or unstable stratification, and there is a deep mixing layer. Good dispersion conditions associated with neutral and unstable stratification exist about 57 percent of the time during the summer at the Hanford Site. Less favorable dispersion conditions may occur when the wind speed is light and the mixing layer is shallow. These conditions are most common during the winter when moderately to extremely stable stratification exists about 66 percent of the time. Less favorable conditions also occur periodically for surface and low-level releases in all seasons from sunset to 1 hour after sunrise as a result of ground-based temperature inversions and shallow mixing layers. Mixing layer thicknesses have been estimated at the HMS using remote sensors. The variations in the mixing layer are summarized in Table I.3.1.2.
The Hanford Site may experience occasional extended periods of poor dispersion conditions associated with stagnant air in stationary high-pressure systems that occur primarily during the winter months.
Table I.3.1.2 Percent Frequency of Mixing-Layer Thickness by Season and Time of Day
The probability of an inversion period (e.g., poor dispersion conditions) extending more than 12 hours varies from a low of about 10 percent in May and June to a high of about 64 percent in September and October (Stone et al. 1972).
I.3.2 AIR QUALITY
Federal and State ambient air quality standards have been set for a limited number of pollutants. Monitoring is conducted to measure levels of selected pollutants that can then be compared to the standards.
I.3.2.1 Air Quality Standards
National Ambient Air Quality Standards (NAAQS) have been established by EPA, as mandated in the 1970 Clean Air Act. Ambient air is the portion of the atmosphere, external to buildings, that is accessible to the general public. The NAAQS define levels of air quality that, with an adequate margin of safety, are protective of public health (primary standards) and welfare (secondary standards). NAAQS exist for the following six criteria pollutants; sulfur oxides (measured as sulfur dioxide), nitrogen dioxide, carbon monoxide, particulate matter (PM-10, measured as particles less than 10 micrometers [µm] aerodynamic diameter), lead, and ozone. The standards specify the maximum pollutant concentrations and frequencies of occurrence that are allowed for various averaging periods ranging from 1 hour to 1 year depending on the pollutant.
Washington State has largely adopted the current NAAQS. However, Washington State has established more stringent standards for sulfur dioxide and ozone and maintains an air quality standard for total suspended particulates and gaseous fluorides. Table I.3.2.1 summarizes the NAAQS and supplemental Washington State standards.
The Hanford Site also evaluates concentrations of selected pollutants for which national and State ambient air quality standards do not exist. For toxic organic compounds (e.g., toluene, benzene), comparisons are made to the Occupational Safety and Health Administration's maximum allowable concentrations (29 Code of Federal Regulations [CFR] 1910). Concentrations of polychlorinated biphyenyls are compared against the National Institute of Occupational Safety and Health limit of 1,000 micrograms per m3 (µg/m3) as a 10-hour time-weighted average.
Table I.3.2.1 Federal and Washington State Ambient Air Quality Standards
I.3.2.2 Emission Sources
Sources of airborne emissions at the Hanford Site include combustion equipment (e.g., steam boilers, electric generation plants), coal handling operations, chemical separation processes, storage tanks, waste handling, and waste disposal. These activities result in routine emissions of air pollutants, including radionuclides.
The Clean Air Act amendments of 1990 established a new national permitting system for major sources of air pollution, and other categories of sources, such as facilities with equipment subject to a National Emission Standard for Hazardous Air Pollutants (NESHAP). The Hanford Site is classified as a major source for one or more criteria pollutants, as well as for hazardous air pollutants. The Hanford Site is currently subject to the radionuclide NESHAP of 10 millirems (10 mrem) per year. DOE has applied for a Sitewide Air Operating Permit for the Hanford Site, which will cover all substantial emission sources for which the Site is considered a major source.
For areas in attainment of the NAAQS, the EPA has established the Prevention of Significant Deterioration (PSD) program to protect existing ambient air quality while at the same time allowing a margin for future growth. Under the PSD program, new stationary sources of air pollution may only impact air quality by set increments and they must install best available control technology emission controls. The Hanford Site obtained a PSD permit in 1980 requiring specific limits for oxides of nitrogen emitted from the PUREX Plant.
I.3.2.3 Air Quality Monitoring
Air quality data have been collected at onsite and offsite locations. The following discussion concentrates on recent monitoring activities conducted largely for the purpose of assessing air quality impacts from the Hanford Site. The information was taken from the Hanford Site Environmental Report (PNL 1995 and 1996 ) and from the Site NEPA Characterization Report (Cushing 1995 and Neitzel 1996 ).
I.3.2.3.1 Onsite Monitoring
Onsite air quality monitoring was conducted during 1990 for nitrogen oxides at three locations. The monitoring was discontinued after 1990 because the primary source ceased operation. The highest annual average concentration was less than 0.006 parts per million (ppm), well below the applicable Federal and Washington State annual ambient standard of 0.05 ppm.
Based on a review of chemicals of concern for surveillance at PCBs, the Site, three types of semi-volatile organic compounds were identified for monitoring: polycyclic aromatic hydrocarbons, and a phthalate ester plasticizer. Organochlorine pesticides also were analyzed. Four polycyclic aromatic hydrocarbons, 19 polychlorinated biphenyl congeners, and 16 organochlorine pesticides were found above detection limits. The measured concentrations of pesticides were orders of magnitude below the occupational maximum allowable concentration values. No phthalate esters were found above detection limits (PNL 1996).
Nine of a total 17 PCB samples collected during 1993 were below the detection limit of 29 µg/m3. Eight PCB samples were above the detection limit, with values ranging from 0.25 to 3.9 µg/m3, all well below the National Institute of Occupational Safety and Health occupational limit of 1,000 µg/m3. Fourteen volatile organic compound samples were obtained in 1993. All samples analyzed for benzene, alkylbenzenes, halogenated alkanes, and alkenes were within allowable limits. Volatile organic compound data from 1994 were within a similar range of values and also were within allowable limits.
I.3.2.3.2 Offsite Monitoring
The only offsite monitoring in the vicinity of the Site in 1993 was conducted by Washington State Department of Ecology. PM-10 was monitored at Columbia Center in Kennewick. The State's 24-hour PM-10 standard was exceeded twice in 1993. The maximum reading was 1,166 µ/m3, with the suspected cause being windblown dust. There was no exceedance of the annual primary standard of 50 µg/m3(Cushing 1995).
Particulate concentrations can reach relatively high levels in eastern Washington State because of exceptional natural events (i.e., dust storms, volcanic eruptions, and large brush fires) that occur in the region. State ambient air quality standards have not distinguished rural fugitive dust from exceptional natural events when estimating the maximum background concentrations of particulates in the area east of the Cascade Mountain crest. No decision has been made to designate Benton County a nonattainment area pending studies to determine the source of high local PM-10 concentrations. It is suspected that the high readings are due to natural conditions (e.g., dust storms, brush fires) rather than man-made pollution.
I.3.2.3.3 Radiological Monitoring
Data were collected in 1995 through a system of 47 radiological monitoring stations located onsite, at the Site perimeter, in nearby communities (e.g., Richland, Kennewick, and Pasco), and in distant communities (Sunnyside and Yakima). Cesium-137, Pu-239, Pu-240, Sr-90, and U were consistently detected in air samples collected in the 200 Areas. Concentrations of these radionuclides were higher than concentrations measured offsite and were in the same range as measured in recent years . The levels measured at both onsite and offsite locations were much lower than the applicable standards (PNL 1996) .
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