The extent and variability of radionuclides and other trace elements In the region is unknown. More importantly, no reliable means for assessing future changes in potable water supplies is available. Information is needed on the occurrence and movement of contaminants in surface and ground water to enable reliable estimates of potential contamination and to provide a basis for comprehensive water-resource planning and development in these basins.

Naturally occurring contamination is compounded by releases from mining activities. Uranium mining in two regions of the southern Colorado Plateau--the Grants Mineral Belt of New Mexico and the Cameron Uranium Mining Belt of Arizona--has resulted in increased releases of radionuclides and other hazardous trace elements in the Puerco River and lower Little Colorado River basins (fig. 1). The single largest spill of uranium tailings liquid in United States history occurred in 1979 at the United Nuclear Corporation mill in the headwaters of the Puerco River near Church Rock, New Mexico (fig. 2) (Shuey, 1982). Additionally, mine dewatering discharges containing radionuclides and other trace elements created perennial flow in the otherwise ephemeral Puerco River to Chambers, Arizona, in the late 1950's and between 1969 and 1986. Contamination of surface water and ground water in the alluvial aquifer has been verified in several studies (Gallaher and Cary, 1986; Shuey, 1982, 1986; Arizona Department of Health Services, 1986a; Webb and others, 1987a and b). Weimer and others (1981) documented contamination in sediments.

Figure 2.--The Church Rock mill was the site of the largest accidental

release of uranium tailings liquid in United States history. In July 1979, approximately 94 million gallons of liquid and more than 1,100 tons of tailings were released into the Puerco River. The total activity of gross alpha inthe Puerco River on the day of the spill was as much as 130,000 picocuries per liter. Recommended limits of gross alpha in surface water in Arizona is 30 picocuries per liter.

Mining has also resulted In contamination of surface water and ground water near Cameron, Arizona. Uranium vas mined from 98 sites between 1950 and 1962. No measures for stabilization of abandoned mines were implemented. Pits are open and some are filled with water. Samples of water from springs, wells, impoundments, abandoned pits and Little Colorado River contained high concentrations of uranium, radium-226, lead, and chromium (Don Payne, Navajo Nation, written commun. , 1986).

OBJECTIVES The U.S. Geological Survey proposes to study the occurrence of radionuclides and other trace elements and their mechansims of movement in the Puerco River and lower Little Colorado River basins. The study has three objectives:

1. To determine types, concentrations, spatial variability, and

recent origins of radionuclides and other trace elements in surface water, fluvial sediments, and ground water in and near the Puerco and lower Little Colorado Rivers.

2. To quantify transport rates of selected radionuclides and other

trace elements in surface water from Gallup, New Mexico, to the Colorado River near Grand Canyon, Arizona.

3. To estimate the amount and extent of contaminant movement between

surface and ground waters.

BENEFITS

Both resource-evaluation and scientific benefits will result

from a process-oriented study of contaminant transport.

This study will evaluate the presence and potential for contamination In the Puerco River and lower Little Colorado River basins. As a resource evaluation, the following benefits will be realized:

O Quality of surface and ground water In the alluvial aquifer will be intensely monitored over a five-year period. Emphasis will be on new areas of contamination, areas where contamination is greatest, and areas where impacts of contamination would be the greatest.

o Identification of sources, extent, and movement of contaminants is the first step in development of technically sound remedial measures or the development of alternate sources of water.

o Evaluation of contaminant movement in surface water will aid in reliable estimates of future trends in contamination.

O Evaluation of baseline data will aid in determination of

environmental threats to endangered species, such as the
humpback chub near the mouth of the Little Colorado River.

O Measurement of contaminant volumes in the Little Colorado River will provide accurate data on the amount of sediment and contaminants entering the Colorado River in Grand Canyon National Park. Results from this endeavor will also have scientific benefits, including a better understanding of:

G Transport mechanisms of radionuclides and other trace elements in ephemeral streams.

O Movement of contaminants between surface water and ground water.

O Sediment-transport rates in ephemeral streams.