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PRELIMINARY ASSESSMENT Bretz Mine Section 3, T41S, R41E, W.M

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PRELIMINARY ASSESSMENT Bretz Mine Section 3, T41S, R41E, W.M PRELIMINARY ASSESSMENT Bretz Mine Section 3, T41S, R41E, W.M. Malheur County, Oregon ECSI # 2493 March 12, 2001 Prepared by: John Dadoly Oregon Department of Environmental Quality Environmental Cleanup Division Pendleton, Oregon 97801 Bretz Mine PA Report March 12, 2001 ECSI # 2493 GENERAL SITE DATA Site Name and Address: Bretz Mine, Section 3, T41S, R41E, W.M. Current Owner(s): U.S. Bureau of Land Management Current Operator(s): John Ruiz, Della Lossing, Sparks, NV Site Contact(s): David Rosenkrance Civil Engineer BLM Vale District Office 100 Oregon Street Vale, OR 97918 Latitude: 42 deg. 2’ 45.03” N Longitude: 117 deg. 54’ 3.46” W Legal Description: Section 3, T41S, R41E, W.M. Directions to site: County Road 592 west from McDermitt, Nevada approximately 10 miles, then north on road up Little Cottonwood Creek approximately 2 miles to Bretz Mine. 2 Bretz Mine PA Report March 12, 2001 ECSI # 2493 Table of Contents 1. INTRODUCTION 4 2. BACKGROUND 5 2.1 Site Description 5 2.2 Ownership and Operational History 5 2.3 Regulatory History 7 3. WASTE CHARACTERISTICS 7 3.1 Source Areas 7 3.2 Sampling Results 9 4. GROUNDWATER PATHWAY 10 4.1 Hydrogeologic Setting 10 4.2 Groundwater Targets 10 4.3 Groundwater Conclusions 11 5. SURFACE WATER PATHWAY 11 5.1 Hydrologic Setting 11 5.2 Surface Water Targets 11 5.3 Surface Water Pathway Conclusions 12 6. DIRECT CONTACT AND AIR PATHWAY 12 6.1 Physical Conditions 12 6.2 Direct Contact and Air Pathway Targets 12 6.3 Direct Contact and Air Pathway Conclusions 12 7. SUMMARY AND CONCLUSIONS 13 8. REFERENCES 14 APPENDIX A: LABORATORY DATA APPENDIX B: WELL LOGS APPENDIX C: CLIMATE DATA APPENDIX D: SITEINFO REPORT 3 Bretz Mine PA Report March 12, 2001 ECSI # 2493 1. INTRODUCTION This report presents the results of a Preliminary Assessment (PA) for the Bretz Mine site located in Malheur County, OR. The PA was conducted by the Site Assessment Program of the Oregon Department of Environmental Quality (DEQ). A PA is required by Oregon state law where a significant threat to human health or the environment is suspected from a release of hazardous substances (as defined in Oregon Revised Statutes (ORS) Chapter 465.200). Authority for conducting PAs is provided in ORS 465.245 and DEQ regulations, Oregon Administrative Rule (OAR) 340-122-072. This PA was designed to investigate chemical and waste handling practices, and to evaluate potential exposure pathways (surface water, air, groundwater and direct contact) for hazardous chemicals that may have been released to the environment from operations at the Bretz Mine facility. PAs are intended generally to identify potential hazards at a site, identify sites that require immediate action, and to establish priorities for sites requiring in depth investigations. The PA is not a full investigation or characterization of the site. The scope of the investigation includes review of available file information, interviews, a comprehensive target survey, and an on-site reconnaissance inspection. 4 Bretz Mine PA Report March 12, 2001 ECSI # 2493 2. BACKGROUND 2.1 Site Description The Bretz Mine is an inactive mercury mine located on public land administered by the Bureau of Land Management (BLM). It is located in the extreme southern end of Malheur County Oregon, approximately 10 miles northwest of McDermitt, Nevada (Figure 1). The area is within the Vale District of the BLM. The climate of the area is arid, and the sparse vegetation consists of grasses, sagebrush and other shrubs. Willows and other woody vegetation is present along many of the local creeks. The elevation of the site is approximately 5,400-5,500 feet above sea-level. The site is approximately 100 acres in size, and consists of two main mine pits, dozens of small exploratory prospect excavations, and several waste rock piles. The site history, which is detailed in the next section, gives no indications of on-site ore processing. However, there is an area located south of the two mine pits which contains four small retorts, a water storage tank, and the concrete foundations of other structures. Little Cottonwood Creek flows through the west pit, and an unnamed tributary flows along the west side of the east pit (Figure 2). There are at least four dikes across Little Cottonwood Creek which contain runoff and sediment from both pits. Adjacent land use mainly consists of livestock grazing, there are no residences or other structures within 4 miles of the site. Access to the site is unrestricted. 2.2 Ownership and Operational History The deposit was discovered in 1917 by William S. Bretz. Assessment work was done for many years before high grade mercury ore was discovered in 1931. The mine was then sold to the Bradley Mining Company, operators of the Opalite mercury mine, which is located approximately 6 miles west of the Bretz Mine (Schuette, 1938). The Bretz Mine was actively worked by the Bradley Mining Company from 1931 through 1936. All ore was shipped to the Opalite Mine for processing during this period. At the end of the 1936 mining season the option to purchase the Bretz mine was released, and Bradley Mining apparently stopped work there (Schuette, 1938). Production values reported by Brooks, 1971, indicate that further mining occurred after 1936. The total mercury production given by in Brooks, 1971 was 15,185 flasks, and the last year of production recorded was 1968. A flask of mercury is equivalent to 76 pounds. The presence of processing equipment (observed June 6, 2000), suggests that some processing may have occurred at the site. 5 Bretz Mine PA Report March 12, 2001 ECSI # 2493 6 Bretz Mine PA Report March 12, 2001 ECSI # 2493 There are currently several active mining claims on and nearby the site. According to the BLM Vale District Office, the claimants are performing exploratory work for potential gold mineralization and no recent mercury mining has occurred at the site. 2.3 Regulatory History Other than regulation of mining claims by the BLM, there appears to be no regulatory history at the site. The significant mining operations that have occurred pre-date both state and federal mining regulations. 3. WASTE CHARACTERISTICS 3.1 Source Areas Based on the site visit performed by DEQ in June, 2000 several source areas were identified: • Mine pits - Mineralized rock is exposed in the mine pits. This material is a potential source of mercury and other heavy metals. Sulfide minerals that may be present are also a potential source of Acid Rock Drainage (ARD). Little Cottonwood Creek flows through the west pit and an unnamed tributary of Little Cottonwood Creek flows through the east pit. • Waste Rock Dumps - This material is likely to contain mercury and other heavy metals and to also be a source of ARD. • Impoundments – There are at least four impoundments constructed in Little Cottonwood Creek downstream of the mine (Figure 3). The dikes which were constructed across the stream channel may be composed of waste rock and could be a source of metals and ARD. The sediment accumulated behind the dikes is likely to contain mercury and other heavy metals. • Ore Processing Areas – Approximately ¼ mile south of the west pit is an area which contains evidence of ore processing. There is a large steel tank (Figure 4) which was apparently used for water storage along with four small retorts (Figure 5). Retorts are ovens which are used to liberate mercury vapor from ore. The mercury condenses in tubing after it leaves the retort. Other contaminants of concern may be present at the processing areas. An empty 55-gallon drum, riddled with bullet holes and labeled “Carbon Tetrachloride” was present in this area. 7 Bretz Mine PA Report March 12, 2001 ECSI # 2493 Figure 3. Photograph of Bretz Mine from south, looking up Little Cottonwood Creek. Dikes across creek channel are in foreground, mine pits are in background. The ore processing area is in the left center. Figure 4. Photograph of Ore Processing area showing retorts on left and steel tank in center. 8 Bretz Mine PA Report March 12, 2001 ECSI # 2493 Figure 5. Photograph of four retorts in ore processing area. 3.2 Sampling Results Two samples of what appeared to be ore material were collected during the June, 2000 site visit. One sample was collected from what appeared to be a low-grade ore stockpile, and one sample was collected from inside one of the retort furnaces. Both samples were analyzed for total mercury. A mercury concentration of 168 mg/kg was detected in the low-grade ore sample and a mercury concentration of 1370 mg/kg was detected in the retort sample. These levels are in excess of the EPA Region 9 Preliminary Remediation Goal (November, 2000) value for total mercury in a residential setting (23 mg/kg). The retort sample is also above the PRG value for an industrial setting (610 mg/kg). The total mercury concentrations detected are also well in excess of the State of Oregon Level II Ecological Screening Benchmark Values for Terrestrial Receptors (DEQ, 1998). The screening value for plants is 0.3 mg/kg and the screening value for invertebrates is 0.1 mg/kg. The toxicity and bioavailability of mercury is complicated and strongly dependent on the chemical species of the mercury present at the site. Further characterization is necessary before conclusions can be drawn. The analytical report for these samples is included in Appendix A. 9 Bretz Mine PA Report March 12, 2001 ECSI # 2493 4. GROUNDWATER PATHWAY 4.1 Hydrogeologic Setting The Bretz Mine is located in the northern extension of the Basin and Range physiographic province of Oregon, Nevada, Utah, Idaho, Arizona, California, New Mexico, and Mexico.
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