Ambient Groundwater Quality of the Sacramento Valley Basin: an ADEQ 1999 Baseline Study
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Ambient Groundwater Quality of the Sacramento Valley Basin: An ADEQ 1999 Baseline Study Chloride I, Introduction The Sacramento Valley Groundwater Basin (SVGB). located in northwestern Arizona (Figure 1), is an arid region with striking natural landscapes and a small, but rapidly growing population. The popularity of the area is influenced by its proximity to tourist destinations Sacramento Valley such as the Colorado River and Groun(Jwater Laughlin, Nevada, and by an abundance Basin of relatively inexpensive, undeveloped private land. Groundwater is the primary water source for municipal, domestic, industrial, mining, livestock, and irrigation in the basin. Population growth and the associated economic development in the SVGB will likely increase demand on groundwater and, over time, may influence water quality. These groundwater quality concerns prompted the Arizona Department of Environmental Quality (ADEQ) to conduct a regional groundwater quality study in 1999 to determine groundwater suitability for drinking purposes, appraise current baseline conditions, and examine spatial groundwater quality patterns. This factsheet is a summary of the more extensive hydrology report available from ADEQ (1). ^ 8 8 16 Miles Figure 1. Infrared satellite image (6/1993) of the Sacramento Valley groundwater basin (SVGB). Mountain forests appear crimson, upland areas are dark blue, and valley areas are beige/white. Inset map shows the location of the SVGB within Arizona. Inset photo shows a mural on an abandoned Route 66 gas station located in Yucca that reflects the intense desert conditions found in the basin. II. Background elevation, averaging 4 inches annually in the valley, 10 inches near the city of The SVGB encompasses more than Kingman, and more than 20 inches at 1,500 square miles in Mohave County, Hualapai Peak (2). Natural vegetation Arizona. It is bounded by the Cerbat, varies with topography and water Hualapai, and McCracken Mountains to availability. Creosote bush, cactus, the east, the Castaneda Hills and Mohave yucca, and Joshua trees grow in the Mountains to the south, the Colorado valleys, whereas juniper, pinyon pine, River and the Black Mountains to the and scrub oak are found at intermediate west, and an unnamed bajada to the elevations, and ponderosa pine forests north (Figure 1). Basin elevations range are abundant above 6,500 feet (2). from a high of 8,417 feet at Hualapai Peak to a low of 500 feet near the Colorado River and averages 2,500 feet. ^'Despite frequent water quality standard exceedances, sampled Surface topography consists of sloping sites in much of the SVGB met alluvial fans which extend from the drinking water standards." Figure 2. Twin windmills pump to a water surrounding rugged mountains to the tank in the southern Hualapai Mountains. valley floor. Precipitation increases with Basin communities include the historic No perennial streams exist within the mining town of Chloride, Golden Valley, SVGB. though a few watercourses flow the city of Kingman, Yucca, and the almost continuously in their upper Colorado River resort community of reaches (2). The main surface water Topock (Figure 1). Most land within drainage is the ephemeral Sacramento the SVGB. particularly rugged upland Wash, which originates north of Golden areas, are managed by the Bureau of Valley, tlows south, then west, and Land Management while private and eventually discharges an average of 500 State lands are common in valley areas. acre-feet per year into the Colorado River near Topock. III. Hydrogeology IV. Methods of Investigation The alluvium that underlies the valley floor and occurs within mountain This study was conducted by the ADEQ canyons is the most important aquifer in Groundwater Monitoring Program which the SVGB. These deposits are separated is authorized by the legislative into older, intermediate, and younger requirement in Arizona Re\ised Statute alluvium, based on their lithologic and VJ49-225 to monitor the quality of the hydrologic properties. The older allu\ial state's groundwater. To characterize aquifer yields and stores the greatest regional groundwater quality. 48 sites quantity of water in the basin. The (Figure 4) were sampled for inorganic intermediate and younger alluvium are constituents (field parameters, general less important hydrologically since these mineral characteristics, major ions, units lie predominantly above the water nutrients, and trace elements), volatile table (2). organic compounds (VOCs), perchlorate (a man-made inorganic salt), and The mountains that form the basin isotopes of hydrogen, oxygen, and ^ Primary MCL + Q % consist predominantly of granitic, nitrogen. At 40 sites, samples were also Secondary MCL volcanic, and metamorphic rocks with collected for radiochemistry analyses. limited outcrops of sedimentary rocks. O Secondary MCL While all rock types produce limited Of the 48 sampled sites. 40 were random • None amounts of water, especially where sites and 8 were targeted sites. Sampling Granitic Rock extensively fractured, volcanic rocks are protocol followed the ADEQ Quality the most important source in mountain Assurance Project Plan. Interpretation areas supplying large quantities of water of quality control data indicated that the Figure 4. Water quality exceedances most for use in Kingman (2). sampling equipment and laboratory commonly occur near the town of Chloride, in procedures had no significant effects on granitic areas of the Hualapai Mountains, and in downgradient areas of the basin near Topock. For this study, the older, intermediate, the analytical results. and younger alluvium are considered the alluvial aquifer. Granitic, volcanic, V. Water Quality Sampling Results sampled. 28 exceeded Secondary MCLs metamorphic, and sedimentary rock are including total dissolved solids or TDS Groundwater sample results were considered the hardrock aquifer. (24 sites), fluoride (16 sites), sulfate (7 compared to federal Safe Drinking sites), chloride (7 sites), manganese (3 Water (SDW) quality standards. sites), and iron (2 sites) (Figure 4). Primary Maximum Contaminant Levels (MCLs) are enforceable, health-based, VOCs were not detected at any sample water quality standards that public water site. Perchlorate, an inorganic salt used systems must meet when supplying in the manufacmre of solid fuel water to customers (3). Primary MCLs propellants and explosives, was are based on a lifetime consumption of detected in the northwest part of the two liters of water per day (3). Of the 48 sites sampled. 22 had constituents basin at four sites. All perchlorate that exceeded a Primary MCL (Figure detections were at concentrations below 4). Constituents with Primary MCL the Arizona provisional Drinking Water exceedances included gross alpha (18 Health-Based Guidance Level of sites), nitrate (6 sites), fluoride (4 sites), 31 micrograms per liter (A/g/1). radium-226+228 (4 sites), and antimony (2 sites). ^'Sample sites exceeding Secondary MCLs are unenforceable, water quality standards aesthetics-based, water quality generally occurred in three areas: guidelines for public water systems (3). (1) near the town of Chloride, Water with Secondary MCL (2) in the central and southern exceedances may be unpleasant to drink Hualapai Mountains, and and/or create unwanted cosmetic or laundry effects but is not considered to (3) near the town of Topock." Figure 3. A domestic well house and water tank arc situated in the shadow of Thimble Mountain, be a health concern (3). Of the 48 sites a famous Route 66 landmark west of Kingman. VI. Groundwater Composition concentrations of various constituents. Depending on the dominant cation, there In general, groundwater in the SVGB is were two general patterns. With slightly alkaline (pH > 7 standard units), calcium, correlations occurred among fresh (TDS < 1000 milligrams per liter or magnesium, bicarbonate, sulfate, mg/1), and ranges from moderately hard hardness (all positive), and pH to very hard. Groundwater chemistry is (negative). With sodium, positive frequently of a calcium-bicarbonate correlations occurred with boron type, however, calcium-sulfate and (Figure 5) as well as with chloride, sodium-bicarbonate sites were also sulfate, and fluoride (Pearson identified. The only sodium-sulfate Correlation Coefficient test. p< 0.05). samples were collected at the two most downgradient sites near Topock. Nitrate These test findings support the observed (as nitrogen) concentrations were greater flowpath evolution in the SVGB. Along than 3 milligrams per liter (mg/1) at 42 the groundwater flowpath, that parallels percent of sites, which may indicate the course of Sacramento Wash (2), impacts from human acti\ities. Most calcium, magnesium, bicarbonate, and trace elements such as aluminum, hardness concentrations generally antimony, barium, beryllium, cadmium, decreased downgradient. In contrast, iron, lead, manganese, mercury, silver, sodium, chloride, fluoride, and boron and thallium were rarely detected. concentrations initially decreased, and Arsenic, boron, chromium, copper, then increased dramatically in fluoride, selenium, and zinc were the downgradient areas. These flowpath only trace elements detected at more than changes appear to indicate that the 10 percent of the sites. SVGB is largely a chemically closed basin, or one in which the aqueous VII. Groundwater Spatial Patterns chemistry is determined mainly by the reactions of recharge waters with the Bicarbonate, calcium, gross beta, various in situ minerals and gases as the hardness, magnesium,