From Technologically Enhanced Naturally Occurring Radioactive Materials in the Southwestern Copper Belt of Arizona
U.S. Environmental Protection Agency,
Office of Radiation and Indoor Air,
Radiation Protection Division
401 M St. SW,
Washington, D.C. 20460

 

 

2. Cyprus Sierrita Corporation, Sierrita Mine

The Sierrita mine is located 62 miles due south of Tucson, Arizona on Highway I-19 near the town of Green Valley. The mine encompasses approximately 20000 acres, and lies on the eastern flank of the Sierrita Mountains and the western margin of the upper Santa Cruz basin. Operations consist of three open pit copper/molybdenum mines, a 115000 ton-per-day concentrator, two molybdenum roasting plants, a ferromolybdenum plant, a rehenium plant, a dump leaching operation, and an SX-EW plant. In 1996, Cyprus Sierrita started mining a 70-million-ton oxide deposit. Construction has begun on a new in-pit crusher and conveyor system to reduce haulage costs. The heap leach operations and the waste rock dumps and collection ponds overlie fractured bedrock. A thick sequence of deposits fills the basin and comprises the principal aquifer. Tailings from the mill are discharged to the tailings impoundment which overlies the basin-fill deposits aquifer. Cyprus Sierrita presently operates an interceptor wellfield to capture tailings impoundment seepage water containing increased concentrations of sulfate and total dissolved solids. Cyprus Sierrita began preparing its APPA in 1986 The APPA was submitted to ADEQ in September of 1994. At the time this report was prepared, negotiations with ADEQ were proceeding (Cyprus 1997b).

 

In 1997, Cyprus Sierrita sampled six monitoring wells and nine piezometers for TENORM at the Sierrita and Esperanza mine, mill, and concentrator facilities (Figure K). The results of these sampling events were submitted to ADEQ on November 13, 1997 as part of its APPA. The samples were analyzed for radiochemicals and the results are summarized in Table 23. Monitoring wells MW 21, 22, 23 and piezometers 3, 4, 5, 6 are located near the mills and concentrators.

Some of these wells show elevated levels of gross alpha and beta activity, in addition to elevated Ra-226 and Ra-228. Monitoring wells MW 18, 19 and piezometers 1, 2, 13, 14, are located to the south of the leach dumps and are downgradient of them. Monitoring well MW-17 is located near Tinaja Wash and it appears to be upgradient of the leach dumps. It shows elevated Ra-226 at 9.3 to 130 pCi/L and Ra-228 at 15 to 19 pCi/L in groundwater.

Table 23
Radiochemical Analyses
of Monitoring Well Samples Cyprus Sierrita Mine,

November 1997 (pCi/L)

Monitoring Wells

and Piezometers

Gross Alpha

Gross Beta

Total U1

Ra-226

Ra-228

MW-17 6/26/97

85

56

0.82

9.3

15

8/15/97

85

57

0.07

130

19

MW-18 6/19/97

14

13

0.13

0.9

0.0

8/14/97

12

4.7

0.12

0.0

0.9

MW-19 7/31/97

23

0.2

0.14

0.1

0.6

8/25/97

23

21

0.16

1.5

1.2

MW-21 7/16/97

557

334

7.55

7.3

9.1

8/15/97

406

299

5.01

15

6.2

MW-22 6/24/97

262

122

3.43

0.0

1.7

8/19/97

117

132

2.61

0.4

1.1

MW-23 7/02/97

70

71

0.37

0.4

5.6

8/21/97

17

8.0

0.51

0.5

1.0

PZ-1

6/18/97

7.5

8.2

0.03

0.0

0.1

              8/12/97

   9.7

9.5

0.02

0.0

0.0

PZ-2

6/27/97

48

40

0.12

1.2

10

              8/13/97

 14

  59

0.14

2.2

10

PZ-3

6/26/97

61

49

0.51

2.0

1.7

              8/13/97

   32

  50

0.49

4.5

13

PZ-4

6/23/97

63

49

0.82

0.6

0.8

              8/20/97

   56

  70

0.82

0.5

1.6

PZ-5     6/26/97

232

150

3.84

1.4

5.8

    8/19/97

245

129

2.40

3.1

7.1

PZ-6    7/02/97

26

27

0.12

2.7

30

    8/20/97

19

44

0.14

3.2

8.3

PZ-9*   7/11/97

137

50

1.44

0.0

1.5

     8/26/97

186

37

1.17

0.2

0.0

PZ-13   8/06/97

15

47

0.21

0.0

2.1

    8/25/97

29

1.0

0.23

0.0

0.9

PZ-14  8/01/97

53

14

0.14

0.1

0.0

    8/22/97

14

4.0

0.16

0.1

1.1

 
MCL Levels:                    15 pCi/L        50 pCi/L         30 ug/L            5 pCi/L combined
MCL = Maximum Contaminant Level
Levels of radioactivity in excess of federal MCLs or Arizona guidelines are shown in red

Reference: Cyprus, 11/1997b

* = Not shown on Figure K1 Converted from mg/L to pCi assumes equilibrium condition for Tot-U = (mg/L)(701.000pCi/L)(10-6 g/ug) = pCi/L

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