Contamination near the Little Colondo RlTer near Cameron. Arizona.

The Cameron Uranium Mining Belt is in the western part of the Navajo Indian Reservation. Host mining occurred within a curved belt approximately 2 miles wide extending 6 miles north of Cameron along U.S. Highways 89 and 164, and 5 miles wide extending 18 miles southeast along the Little Colorado River (fig. 1). Hlning started around 1950, reached a production peak In 1957, and ceased In 1962. A total of 289,300 tons of spoil and over 600 tons of uranium ore was extracted from 98 mining sites. Host of the ore was processed at Rare Hetals near Hoenkopi Wash (fig. 1) (Don Payne, Navajo Nation, written comnun., 1986).

No regulations for stabilization of abandoned mines existed in 1962. As a consequence, many pits in the Cameron Uranium Hlning Belt are open and have filled with water. Gross alpha activities in water samples collected from 48 locations (pits, springs, wells, Impoundments, and the Little Colorado River) ranged from 24 to 9,400 pCl/L. Host gross alpha activity was attributed to radium-226 and uranium. Radium-226 activity ranged from less than 0.4 to 760 pCl/L. Uranium activity In samples collected from mining pits ranged from 24 to over 4,000 pCl/L. Additionally, elevated concentrations of chromium and lead were detected in some of the water samples (Don Payne, written conmun. , 1986). The temporal relation of gross alpha and gross beta activities at the Little Colorado River at Cameron are shown in figure 5.

Related to Cameron-area uranium mining is an ore-processing plant located at Rare Hetals, Arizona. A mound of ground water beneath a tailings pile at the plant Is contaminated with radionuclides and other trace elements. A plume of contamination may be emanating from the area of

Figure 5.--Gross alpha and gross beta activities in the Little Colorado River at Cameron, Arizona. Arizona maximum allowable limits are 15 picocuries per liter of gross alpha minus uranium and 30 picocuries per liter of gross alpha plus gross beta. The gross alpha activities are not corrected for uranium activity.

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.

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Mining has also resulted In contamination of surface water and ground water near Cameron, Arizona. Uranium was 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 common. , 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 Che 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:

o 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.