Cech, et al, and C. W. Kreitler reported in 1987 that ingestion or inhalation of radium (Ra) and products of its decay are considered a health risk. In the human body bones, myeloid stem cells, and lungs are particularly sensitive to radiation exposure. Epidemiologic studies have established a strong association between certain occupational and therapeutic exposures to isotopes of Ra and bone cancer. Radon (Rn)-222, an airborne progeny of decay of Ra-226, has been associated with lung cancer in miners, and recently has received national attention because of high concentrations observed in houses in some parts of the United States. Studies have also raised the issue of cancer risk associated with Ra and Rn in domestic water.
Regulatory standards for radioactivity in water have been established for Ra but not Rn. The combined activity of the two isotopes of Ra (226 and 228) should not exceed a maximum contaminant level (MCL) of 5 pCi/.l!. [13,14]. Rn in water is not yet regulated by Federal and State standards, although this is expected to change in the near future. Ra regulation under the Safe Drinking Water Act of 1974 and related amendments went into effect in 1977, but because 0£ the sheer number of public water systems in a State as large as Texas, the assessment of Ra concentrations and compliance with EPA and State regulations is a formidable task, not yet completed. In addition, approximately 4 million people in Texas use private water supplies which are not covered by current regulations and for which data on Ra are not available. No regulatory agency now routinely monitors Rn, in either public or individually-owned supplies.
Deposits of uranium, the progenitor of Ra-226 and Rn-222, occur in Texas. The major deposits occur in Eocene and younger formations and it is believed to be predominantly associated with volcanic ash in the Catahoula formation of the Miocene Age. In 1984, taking advantage of the cost-effective testing procedure available at the University of Texas at Houston, School of Public Health laboratory, a study was initiated by Cech and co-investigators, in cooperation with several ground water districts and river authorities in Texas, to assess the geographic distribution of Ra-226 and Rn-222 in domestic water in selected regions of this State. Anomalously high Ra and Rn concentrations were found in the Gulf Coast area including Harris County; Ra in excess of 20 pCi/ .t and 3000 pCi/ .t for Rn were observed in some public water supplies in this county.
Harris County, with a 1980 population of 2,684,000, has the largest number of people among Texas counties and contains 18 percent of the State population. The water supply and distribution system in Harris County is complex. The City of Houston alone operates over 200 water wells. A water well field may contain from l to 11 wells, and pump water from various depths into several collecting plants. The eastern half of the City of Houston, roughly 50 percent of the population of over one million, is supplied primarily by surface water from Lake Houston; the western half is supplied by groundwater. The boundaries of areas served by each well, well field, or by surface water cannot be defined accurately because systems are interconnected; these boundaries vary with variations in demand, pressure in water lines, season, and even time of day.
Population growth and the rapid development of new suburban subdivisions on the fringes of the City of Houston resulted in numerous smaller water utilities. Approximately 300 such municipal utility districts (MUDs) and 1700 community water systems supply ground water in Harris County besides the City of Houston. Most of the wells with Ra concentrations that exceed MCL were from these smaller utilities. Approximately 150,000 people in the rural parts of Harris County, and an estimated 10 percent of urban residents, are supplied by water from individually-owned wells. Northwest, northeast, and southwest Harris County contain undeveloped areas. All projections of urban growth indicate that these areas will be developed in the near future. Pockets of Ra-rich water found in MUD's in these parts of Harris County suggest that future subdivisions might encounter problems. However, no reliable guidance for well location is presently available to well developers in the County.
A more detailed sampling of ground and surface water was necessary in this area to assess pattern_s of distribution of Ro and Rn, so that some predictive tool could be developed to guide present and future water works. Thus, during 1985 and 1986, an intensive sampling for Ra-226 and Rn-222 was conducted in Houston-Harris County.
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