Arsenic Concentration and Mass Flow Rate in Natural Waters of the Valles Caldera and Jemez Mountains Region, New Mexico
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Arsenic concentration and mass flow rate in natural waters of the Valles caldera and Jemez Mountains region, New Mexico Kevin D. Reid, Shaw Environmental and Infrastructure, Inc., 335 Central Park Square, Los Alamos, NM 87544, [email protected]; Fraser Goff and Dale A. Counce, LA-UR-03-2357, MS-D462, Los Alamos National Laboratory, Los Alamos, NM 87545, [email protected] Abstract addition to review, the act required a pro- Arsenic chemistry posed MCL by January 1, 2000, and imple- This paper details the spatial and temporal mentation of the final MCL by January The stable forms of arsenic in solution are occurrence of arsenic concentrations and 2001. The review included an evaluation arsenate (As5+) or arsenite (As3+) (Hem, mass flow rates along the Jemez River and of: human health effects of consuming 1992). Unless these species are analyzed the Rio Grande in north-central New Mexi- separately, chemical analyses report only co. Samples of river water, hot springs, and arsenic, risks associated with consumption cold springs were collected at 25 locations of different concentrations of arsenic in the total concentration of elemental during November 1994, March 1996, and drinking water, technology for removal of arsenic. In waters between pH 3 and 7 the – June 1996. Arsenic and other trace metal arsenic from drinking water, and occur- dominant anion of arsenic is H2AsO4 ; analyses were performed by graphite fur- rence and sources of arsenic in the United between pH 7 and 11 the divalent species 2– nace and hydride generator atomic absorp- States. In January 2001 the EPA lowered HAsO4 is favored (Hem, 1992). Arsenic tion spectroscopy for acidified unfiltered the MCL to 10 µg/L (EPA, 2001). concentrations in water decrease as a result samples. Concentrations along the Jemez In northern New Mexico, arsenic con- of many inorganic processes including: River ranged from 2 to 300 micrograms per centrations between 2,000 and 7,000 µg/L adsorption or coprecipitation by hydrous liter (µg/L). Seven of ten locations exceeded the current EPA arsenic drinking water stan- are found as a natural constituent dis- iron oxide, adsorption onto aluminum dard of 10 µg/L. These seven locations were solved in the 200–300°C geothermal reser- hydroxide and clays, coprecipitation or at or downstream of the Jemez Springs area voir of the Valles caldera (Fig. 1; Goff and combination with sulfide in reduced bot- where roughly 1,500 L/min of thermal water Gardner, 1994). These high-temperature tom mud, and by isomorphous substitu- enters the river from the Valles caldera geo- fluids circulate in caldera fill ignimbrites tion for phosphate in various minerals thermal system. In the Jemez Springs area, and precaldera rocks at depths of (Hem, 1992; Nagorski and Moore, 1999). the thermal water can be sampled directly 500–1,500 m (1,640–4,921 ft) and drain Organic and biochemical mechanisms can from Soda Dam hot spring and Travertine from the caldera along the south-south- also reduce arsenic concentrations in Mound hot spring. Discharge from these hot west-trending Jemez fault zone forming a water. Biologically mediated methylation springs flows directly into the Jemez River. From Soda Dam hot spring, the arsenic con- classic hydrothermal outflow plume (Goff can transform inorganic arsenic species to centration was 1,770 µg/L and the mass flow et al., 1988). The reservoir fluids mix with organic species. This is accomplished by a rate was 0.02 kg/day. The Travertine Mound other ground waters and issue as hot sequence of five reduction reactions where hot spring arsenic concentration was 830 springs primarily at Soda Dam and Jemez arsenic acid [H3AsO4] transforms to µg/L, and the mass flow rate was 0.001 Springs. Discharge temperatures at these trimethylarsine [(CH3)3As] (Matisoff et al., kg/day. The highest arsenic mass flow rate springs range from 30° to 75°C. The hot 1982; Nagorski and Moore, 1999). on the Jemez River was approximately 6 spring system at Soda Dam has created an kg/day at a location below Soda Dam hot extensive multi-tiered travertine deposit Anthropogenic sources of arsenic spring and decreased to 0.1 kg/day below and has been episodically active for the the Jemez Canyon Dam. All six sampling locations along the Rio Grande between past 1 m.y. (Goff and Shevenell, 1987). At Several studies have reported high concen- Espa˜nola and Bernalillo had arsenic concen- least 1,500 L/min of hot spring discharge trations of arsenic in the United States, par- trations less than 10 µg/L. The Rio Grande enters the Jemez River at the Soda Dam ticularly in the Southwest (Welch et al., showed no difference in arsenic concentra- area (Trainer, 1984), and a similar amount 2000). There are several factors both tions above and below the confluence with enters the river at Jemez Springs. An anthropogenic and natural that contribute the Jemez River. Discharge of the Rio Grande equivalent volume of mixed geothermal to the elevated arsenic levels in the south- was about 30 times greater than the Jemez fluid circulates at depth adjacent to the western states. The most common anthro- River. The arsenic mass flow rate of the Rio fault zone (Goff et al., 1988). The hot spring pogenic sources are related to mining Grande during June 1996 was approximately waters are revered for their therapeutic 6 kg/day. activities (Nagorski and Moore, 1999; value and are consumed by the public in Shevenell et al., 1999; Welch et al., 2000). small quantities. The aquifer is tapped by Arsenic is concentrated in many hydro- Introduction wells and used for drinking and other thermal ore deposits, especially those with domestic purposes. sulfides and sulfo-salts (Boyle and Jonas- Arsenic is an element of environmental The object of this paper is to examine the son, 1973). Arsenic is used during concern worldwide because of its known temporal and spatial changes in the chem- prospecting as an indicator or path finder toxicity. In the United States the Environ- istry of surface waters in the north-central element for economic deposits of copper, mental Protection Agency (EPA) has region of New Mexico with particular silver, gold, zinc, cadmium, mercury, ura- reviewed the drinking water standard for attention to arsenic. Thorough documenta- nium, tin, lead, phosphorus, antimony, bis- arsenic beginning in the late 1990s (EPA, tion of the concentrations and mass flow muth, sulfur, selenium, tellurium, molyb- 2001; Wust, 2001). Since 1974 the maxi- rates of arsenic in surface waters in the denum, tungsten, iron, nickel, cobalt, and mum contaminant level (MCL) for arsenic Jemez Mountain region are lacking. This platinum (Boyle and Jonasson, 1973; in drinking water has been 50 µg/L. An study focuses on arsenic because of the Nicholson, 1993). Arsenic-bearing miner- amendment to the Safe Water Drinking Act potential of many different anthropogenic als are widespread in igneous, sedimenta- in 1996 required the EPA to review the and natural processes to have contributed ry, and metamorphic rocks (Boyle and drinking water standard for arsenic. In to elevated arsenic levels in surface waters. Jonasson, 1973; Matisoff et al., 1982; Baker August 2003, Volume 25, Number 3 NEW MEXICO GEOLOGY 75 FIGURE 1—Inset map shows location of the Jemez Mountains region. Principal map shows sample localities in yellow. Base map reproduced with permission ©1988, revised 1991, Raven Maps & Images. et al., 1998; Shevenell et al., 1999; Welch, arsenic-bearing mineral, pyrite, can occur additives, pharmaceuticals, chemical wea- 1999; Oremland et al., 2000; Welch et al., (Boyle and Jonasson, 1973; Hem, 1992; pons, riot control agents, metallurgical 2000). Baker et al., 1998; Shevenell et al., 1999). additives, burning of coal, and waste dis- Mining is the most widespread anthro- Additionally, arsenic commonly exists in posal (Aurilio et al., 1995; Welch et al., pogenic contributor of arsenic to the envi- high concentrations in both gold and coal 2000; EPA, 2001). ronment. Mining disaggregates the host deposits. Other anthropogenic arsenic rock and brings it to the surface where oxi- sources include: insecticides, herbicides, dation and mobilization of the principal crop desiccants, wood preservatives, feed 76 NEW MEXICO GEOLOGY August 2003, Volume 25, Number 3 Natural sources of arsenic ed sediments. The catchment of the Rio appendix). Discharge on the Jemez River Grande in the study area is mostly was measured using a Pygmy meter. On Sources of arsenic in natural waters Miocene to Pliocene basin fill sediments the Rio Grande discharge values were include discharges from hot and cold with exposures of Precambrian basement obtained at three locations where United springs in active volcanic terrains, and sol- rocks and Quaternary volcanic tuffs and States Geological Survey (USGS) stream ubilization resulting from the reduction of lava flows. Land use in the Jemez River gages are located. An error of 10% was ferric iron arsenate or arsenite and reduc- region includes ranching, some agricul- assumed for Pygmy meter discharge meas- tion to arsine or methylarsines (Clement ture, very localized logging, and sparsely urements (S. Woods, pers. comm. 2003), and Faust, 1981; Hem, 1992; Nagorski and populated communities of less than 800 and a 5% error was assumed for USGS Moore, 1999). Natural releases into the people. The Rio Grande study region is stream gage discharge measurements (F. atmosphere result from the venting of vol- located between the communities of D. Byrd, pers. comm. 2003). canic gases and the volatilization of Española (1998 estimated population of For trace metal analysis, samples were arseniferous compounds by bacteria, 9,000) and Bernalillo (1998 estimated pop- collected, acidified, and stored in a cooler fungi, and other microorganisms in soils, ulation of 7,500). Land use on this section before delivery to an analytical laboratory.