MHYDRO-SERRCHinC A Tetra Tech Company Suitability of B romide as a Ground-W ater Tracer Sunnyside Mine San Juan County, Colorado August 29, 1 994 Prepared for: Sunnyside Gold Corporation Prepared by: Hydro-Search, Inc. 5 0 W e s t Liberty Street, Suite 5 0 0 Reno, Nevada 89501 (702) 324-5900 (800) 347-4937 Senior Hydrogeologist Hydro-Search, Inc. l:\ADMIN\WP\DIANE\BROMIDE.RPT 50 West Liberty Street, Suite 500, Reno, Nevada 89501 Telephone (702) 324-5900 (800) 347-4937 Facsimile (702) 324-5924 i t SU N NYSIOE COLD CORPORATION AN ECHO BAY COMPANY P.O. Box 177 .Silverton, CO 81433 Phone (303) 387-5533 .Telecopy (303) 387-5310 August 3 0, 1994 Bill Robb Dufford & Brown 1700 Broadway, Suite 1700 Denver, CO 80290-1701 Dear Bill: Enclosed please find the additional information on the bromide suitability study. If you have any questions please call either Larry or myself. Sincerely, Bill Goodhard TABLE OF CONTENTS Section Page 1.0 E X E C U T I V E S U M M A R Y .................................................... 1 2.0 INTRODUCTION ............................................................. 2 3.0 BROMIDE IS SUITABLE AS A TRACER ................................... 3 ^ 4.0 U S E O F B R O M I D E IS A C C E P T E D P R A C T I C E ............................. 3 5.0 L A C K O F D E N S I T Y S E T T L I N G ............................................. 4 6.0 B R O M I D E W I L L D I S S O L V E IN M I N E W A T E R S ............................. 4 7.0 BROMIDE WILL REMAIN IN SOLUTION ................................... 5 8.0 LACK OF ADSORPTION OR ION EXCHANGE ............................. 6 9.0 TRACER TEST NOT EXPECTED TO IMPACT STREAM ENVIRONMENT . 8 10.0 R E F E R E N C E S C I T E D ......................................................... 9 APPENDIX A SELECTED REFERENCES PERTAINING TO BROMIDE USED AS A GROUND­ WATER TRACER 1.0 EXECUTIVE SUMMARY In September 1993 a work plan was submitted for applying a proven ground-water tracing methodology to a proposed underground water impoundment at the Sunnyside Mine located in San Juan County, Colorado (Simon Hydro-Search, Inc. and Tracer Research Corporation, 1993). The work plan specified the use of bromide as ^ ground-water tracer. This report provides details of the suitability of the use of bromide as a tracer which include: ♦ The use of bromide is accepted practice for ground-water tracing, ♦ bromide is stable, (it does not break down or change into something else), ♦ bromide is not removed by absorption or adsorption by clays or other geologic materials, ♦ bromide will not be attenuated nor slowed down by ion exchange, ♦ bromide will not be affected by biological activity, « bromide will not be precipitated, and ♦ bromide, if introduced as recommended in the work plan, will not be affected b y density settling. In consideration of the above characteristics the use of bromide as a ground-water tracer is considered a reliable m e a n s of establishing whether water which reaches the surface has passed through the underground workings of the Sunnyside Mine. I:\ADMIN\WP\DIANE\BR0MIDE.RPT 1 A s part of the mine closure plan for the Sunnyside Mine, Sunnyside Gold Corporation (SGC) proposes to install underground bulkheads in the American Tunnel, Terry Tunnel, and Brenneman Vein. The bulkheads are designed to contain mine drainage, fill the lower mine workings with water, and allow ground water to return to an approximation of pre-mining hydrologic conditions. Detailed analyses of the hydrologic and hydrogeochemical impacts of the proposed bulkheads are discussed in Evaluation of Hydraulic and Hydrochemical Aspects of Proposed Bulkheads, Sunnyside Mine, San Juan County, Colorado dated March 12, 1993 by Simon Hydro-Search, Inc. To differentiate natural water chemistry from the chemistry of waters which have passed through the Sunnyside Mine it has been proposed that a tracer be placed in the m i n e w o r k i n g s so that waters w h i c h h a v e p a s s e d through the m i n e c a n b e identified as such. Bromide w a s selected as the best choice for a ground-water tracer (Simon Hydro-Search, Inc. and Tracer Research Corporation, 1993). The Colorado Department of Health has expressed concern over the use of bromide as a tracer. This report addresses those concerns. 3.0 BROMIDE IS SUITABLE AS A TRACER Bromide is an excellent ground-water tracer for almost all applications. Bromide is an anionic tracer. Davis et al. (1985, p. 1) list the properties of a n ideal tracer as o n e which travels at the sa m e velocity and direction as water, does not interact with solid material, is non-toxic, is relatively inexpensive, is easily detected, and do e s not modify the hydraulic medium. Davis et al.(1985, p.86) then go on to state that dilute concentrations of certain anions, in particular, ap p r o a c h the characteristics of an ideal tracer. Davis et al. (1985, p. 166) specifically state that b r o m i d e is stable a n d that there is no sorption. Schmotzer et al. (1973) found that bromide (Br) is not adsorbed, absorbed, precipitated, or affected by biological activity. Davis et al. (1980, p. 16) reports that *' Br" offers one of the best possibilities as a general tracer for ground­ water studies" because of bromide's favorable properties as a tracer, including low sorption. The theoretical reasons behind the chemical and physical characteristics of bromide are detailed in the following sections. 4 .0 USE OF BROMIDE IS ACCEPTED PRACTICE Bromide's excellent attributes as a ground-water tracer, combined with its reasonable cost, have led to its use in a wide range of applications. Davis et al. (1985, p.94) state that "Br is perhaps the most commonly used ion tracer." Appendix A lists 60 publications which discuss the use of bromide as a ground-water tracer, and the list is b y no means exhaustive. The wide use of bromide as a ground-water tracer demonstrates that its use is accepted practice. 5.0 LACK OF DENSITY SETTLING Density settling will not be a p r o b l e m if br o m i d e is introduced into the m i n e wo r k i n g s as proposed (Simon Hydro-Search, Inc. and Tracer Research Corporation, 1993). The a v e rage p r o p o s e d concentration of br o m i d e in the mi n e wo r k i n g s is 1 part per million (ppm). Davis et al. (1980) state that density settling will not be a problem with chloride if it is introduced in concentrations of less than 3 0 0 0 p p m of Cl'. D u e to the heavier atomic weight of bromide, the corresponding value of bromide would be 1300 ppm of Br* (which is 1700 ppm of NaBr). The proposed method of bromide innoculation will not result in concentrations approaching this value. 6.0 BROMIDE WILL DISSOLVE IN MINE WATERS Based upon well established solubilities, the introduced bromide tracer will rapidly dissolve as water levels rise behind the bulkheads in the Sunnyside Mine. The bromide tracer will be introduced into the mine in a manner which distributes the bromide throughout the mine workings and will not result in an anomalously high concentration in any one area (Simon Hydro-Search, Inc. and Tracer Research Corporation, 1993). The average concentration of dissolved bromide will be approximately one milligram per liter. I:\ADMIN\WP\DIANE\BR0M1DE.RPT 4 T h e b r o m i d e will b e introduced into the m i n e w o r k i n g s as either s o d i u m b r o m i d e or potassium bromide solution sprayed on mine walls. The solubility of sodium bromide in w a t e r is 1 1 6 0 gr a m s per liter (at 50° C) a n d the solubility of po t a s s i u m br o m i d e at 0° C is 534.8 grams per liter (Weast and Astle, 1979 pp. B-109 and.B-124). The solubility is s o m e w h a t greater for w a r m water. T h e solubility of either c o m p o u n d is three orders of magnitude greater than anticipated concentrations and the bromide will certainly dissolve in rising mine waters in the event that the water evaporates from the initially applied solution. 7.0 BROMIDE WILL REMAIN IN SOLUTION B r o m i d e is a halide. Other c o m m o n halides include chloride, fluoride, a n d iodide. Most halide co m p o u n d s are saltlike compounds, and, like table salt (sodium chloride), are very soluble in water. Very fe w halides are insoluble, and bromide especially tends to b e soluble. In ground water there is a natural evolution, as water ages, from bicarbonate as the dominant anion, to sulfate as the dominant anion, to chloride as the dominant anion (Freeze and Cherry, 1979, p. 242). The sequence is caused by the combination of mineral availability and mineral solubility.