Effects of Historic Mining on Groundwater and Surface Water Item Type text; Proceedings Authors Rösner, Ulrike Publisher Arizona-Nevada Academy of Science Journal Hydrology and Water Resources in Arizona and the Southwest Rights Copyright ©, where appropriate, is held by the author. Download date 01/10/2021 03:54:55 Link to Item http://hdl.handle.net/10150/297004 EFFECTS OF HISTORIC MINING ON GROUNDWATER AND SURFACE WATER Ulrike Rösner1 Ore mining developed into a booming business in the stream flow in the valley and its margins is the southwestern United States in the second half ephemeral. of the last century, with innumerable small mines The hydrogeologic situation comes about opening and mining towns sprouting up almost through the difference between range and basin everywhere. However, most of the smaller mines (Figure 2). The igneous and metamorphic rocks were given up at some stage before the late 1940s (granite, gneiss, shist) of the range generally do for a variety of quite different reasons. not yield water except along fractures and in A typical example for the boom and bust of ore weathered zones. Wells located at the foot of the mining in the Southwest can be found in the Cer- Cerbat Mountains are completed in the zone of bat Mountains, Mohave County, Arizona (Figure fractured /weathered rocks. The principal aquifer 1). Small mines were to be found particularly in the Sacramento Valley region is the older allu- frequently in the areas east and southeast of the vium (Gillespie and Bentley 1971; ADWR 1990). little town of Chloride. The miners were looking for gold and silver, and later on also for lead, zinc, Methods and copper (Dings 1951). Some of the mines -pri- Field work was carried out in spring and fall of marily the Tennessee Mine, which was the largest 1995. Twenty-seven water samples were then producer at that time -even processed the ore on analyzed at McKenzie Laboratories, Phoenix, for site. Today the mines are abandoned, but numer- their general chemistry and for 12 heavy metals ous tailings and waste rock dumps remain. (As, Ag, Cd, Cr, Cu, Hg, Ni, Pb, Se, Zn, Fe, Mn). Strange- colored deposits can easily be recog- Judging from background samples (WP 8, WP 11, nized in several streambeds below the old tail- and WP 17), the water in the Cerbat Mountain area ings -fine sediments washed out from the tailings probably met drinking water quality before min- and dumps during heavy rains. In the light of this ing started. Drinking water standards were there- evident pollution and considering the widespread fore used as a comparative basis: first the official mining activities, the question arises: to what DWS = Domestic Water Source standards, enforce- degree could the remnants of the deserted mines able standards published in the Arizona Admini- affect the groundwater and the surface -water strative Code (AAC) (ADEQ 1995); second the quality in this historical mining district? Health -Based Guidance Levels (HBGLs) for But before going into the investigation results, a drinking water and soil, non -enforceable levels set brief survey of the main physicogeographical facts by the Arizona Department of Health Services of the study area seems to be appropriate. (ADEQ 1992). The Study Area Results The Cerbat Mountains and the western adjacent Only some examples of the study can be discussed Sacramento Valley Basin are part of the Basin and in this short paper (for complete data concerning Range Province. The climate is arid to semi -arid the water quality see Wisner 1995). with average precipitation rates of 6 to 10 inches at Surface Water the western foot and 12 to 20 inches in the moun- tains above 4,000 feet. The stream flow in the The first indications of a contamination are ob- upper reaches of the Cerbats is intermittent - tained by field measurements of the electrical con- flowing continually for several months - whereas ductivity (EC) and the pH values. The EC values in the Tennessee Wash (Figure 3) gradually increase on its way through the canyon, 1Department of Geography, University of Erlangen -Nürnberg, Kochstrasse 4, 91054 Erlangen, Germany. in which one abandoned mine closely follows the 82 Effects of Mining on Water 1 40 1 2, 1100 370 A Kingman @Flagstaff 350 °Holbrook i Prescott PHOENIX Gila 330 Yuma ()Tucson Nogales o 100 miles Figure 1. Map showing area of report (shaded) in Mohave County, Arizona. PEDIMENT 7 GROUNDWATER V LEVEL ALLUVIUM '7 7 V. 4 L 'I UPPER UNIT . A 7 ......r.; '7 A L. A V r. - 4 4.BASIN-FILL DEPOSITS L. A .1 AQUIFER".... > 1- A . A A c 4, .,, -, L. L. A > L. L. A A MOUNTAIN- A A BLOCK L. > COMPLEX A A t, > A A a i` 4 r- 1. r, L A Figure 2. Basin and Range hydrogeologic section (after ADWR 1990). Rösner 83 Mine N Prospect 545 \ 545 EC in pS /cm . Tennessee Mine > Tailings 1.41675 d'o O. d ' . , \ X" / XX J!/ \ . Dardanelles \ ine XX\ X X , Argyle Mine l / XX'610\?Ci X x, X iechenecaady-- ©Mine/ Elkhart Mine x ,730. X x Schuylkill Mine I p X Distaff Mine / Bullion Mine ° 730 (, ' Tennessee Mine Chloride 830 q.} I4 830 o MILE 0.5 U. ROESNER 1995 Figure 3. EC values along Tennessee Wash (March 1995). other (starting from 545 µS /cm). The maximum of mines such as the Cyprus Mineral Park Mine. Both 1,050 gS /cm is reached below the confluence, with the EC values and the pH values point to a small washes flowing directly through the area of contamination, but they do not say anything about the Tennessee Mine tailings and the western adja- the nature, the degree, and therefore the danger- cent mines. Further downstream the electrical ousness of the water pollution. This information conductivity decreases again to 810 µS /cm. Conse- can be obtained by the heavy -metal concentra- quently, this steady increase of EC values indicates tions. that chemical substances are being washed out of Table 2 (for location of samples see Figure 4) the tailings and are entering the surface water. shows heavy -metal concentrations in the surface Similar tendencies are shown by the pH values water of the Chloride mining district east of Chlo- (Table 1). They are considerably lower in tunnel or ride. The samples exceed the standards for arsenic, tailings discharges or in discharges from active cadmium, chromium, copper, nickel, zinc, iron, and 84 Effects of Mining on Water Table 1. Surface water pH values in the western Mine \.1 Schenectady - Cerbat Mountains mining area. X Prospect Mine / aTennessee Mine Elkhart Mine Tailings X Water Source pH Groundwater sample X x Schuylkill Mine X OSurface water sample Distaff Mine Bullion Mine Clear surface water 7.0-8.3 Discharge of old tailings 4.9-7.0 X Discharge of old tunnels 3.0-6.6 Mine Discharge from the operation Chloride site and the tailings of the Cyprus Mineral Park Mine 2.6 -3.2 0 manganese in different combinations and propor- tions. Samples WP 21 and WP 5 in particular -the x sampling sites from right beside and just down- x stream of the big Tennessee Mine tailings -show MILE 0.5 very heavy contaminations. These results prove U. ROESNER 1995 that remarkable amounts of heavy metals are be- ing washed out of the old tailings by heavy rains Figure 4. Location of surface water and ground- or are entering the surface water from polluted, water samples in the Chloride mining district and shallow groundwater. in Chloride itself. The surface water was also found to be polluted in canyons that were not as heavily mined as Tennessee Canyon. In the case of Eureka Canyon (Figure 5), the streambed was covered with a light - ID Cd Cu Ni Zn Fe Mn blue, soft deposit in the lower section, the color of 26 0.0190 1.20 8.40 which is most likely due to its extremely high 27 0.1600 41.00 0.73 23.00 81.0 8.60 content of copper: 1,000 mg /L. 28 0.0220 2.20 8.60 2.5 0.75 The discharge of an old tunnel (WP 27) flowing into Eureka Wash has a particularly high heavy - DWS 0.0050 1.00 0.14 5.00 NA NA metal load which pollutes the streamflow of the HBGL 0.0035 1.30 0.14 1.40 0.3* 0.70 main wash below the confluence (WP 28 com- N brown G;r/ pared to WP 26). For example, the level of cadmi- Tunnel 6 um is 32 times higher than the DWS standard, and 27 ' copper is 41 times higher (WP 27). Even after dilu- .1b tion with cleaner water from the upper canyon, the heavy -metal concentration still clearly exceeds 9reeni'sh °" 9¡eSy Y 0 MILE 0.2 ROSNER1995 appropriate levels. l/' Such tunnel discharges can occur several times in a single canyon (e.g. the canyon of the Golconda Figure 5. Heavy -metal concentrations in the sur- mining area south of the Chloride mining district). face water of Eureka Canyon exceeding DWS and Consequently, the streamflow is repeatedly en- HBGL standards (units are mg /1). riched by heavy metals on its way through the canyon. The same effect occurs when several tail- ings in a canyon line up along a wash; in contrast Groundwater to that, simple waste -rock dumps have a negligible When the surface water is already more or less effect on the water quality. contaminated, the following question arises: to When some of the water samples show a higher what extent are the pollutants from the mining reading for certain heavy metals but do not exceed areas indeed entering the groundwater? standards, one has to keep in mind the fact that Comparative investigations of a well outside the heavy rains on the days before sampling will any influence of former mining activities proved presumably have diluted the load of pollutants.