New publications on Arizona water and environment

Sharon Megdal, Director of the University of Arizona Water Resources Research Center, passed along this news about the release of three new publications related to water and the environment in Arizona.

The Arizona Environmental Water Needs Assessment (AzEWNA) Report and the Arizona Environmental Water Needs Assessment Methodology Guidebook explore and synthesize efforts to quantify the water needs of river systems in Arizona.

The Report summarizes the state of knowledge about environmental water needs in Arizona, explores the information gaps in Arizona environmental flow studies, and contains maps and graphics to help readers visualize the extent of the inventory.

The Guidebook describes the methods employed to quantify Arizona’s environmental flows and provides decision trees and other tools for those designing environmental flow studies.

The AzEWNA Report and Methodology Guidebook are available at http://cals.arizona.edu/azwater/programs/AzEWNA/index.html.

"The Forgotten Sector: Arizona Water Law and the Environment," by Sharon B. Megdal, Joanna B. Nadeau and Tiffany Tom, has been published in the Arizona Journal of Environmental Law & Policy. This paper examines the extent to which the environment as a water-using sector is recognized in Arizona water law. The paper also highlights opportunities for giving the environment a place at the table within the current legal context. This paper can be accessed online at http://www.ajelp.com/.

Why we map, #3: Upper Gila River and Safford area

The third area proposed for mapping under the next round of funding for the STATEMAP program is the upper Gila River region in eastern Arizona. AZGS geologists Jon Spencer and Phil Pearthree made the case to the USGS on why this is important to the National Cooperative Geologic Mapping Program. New mapping was proposed around the town of Safford because of Quaternary faulting, opening of a new and very large copper mine in a belt of similar copper deposits, associated development in the Safford area, and geomorphic and hydrologic features along the Gila River and tributaries. Phil will lead our mapping effort in this area.

The upper Gila River area in southeastern Arizona was identified as a long-term priority for new mapping by the Arizona Geologic Mapping Advisory Committee (GMAC) in 2009. Although no STATEMAP mapping has been done in this area, the GMAC gave it high priority largely because of environmental and water resource issues in Gila and San Simon Valleys and because of expected increasing development and population growth associated with recent opening of the Safford mine in the Lone Star mining district. Critical geologic issues affecting this area include groundwater availability for agriculture, urban development, and mining, water quality, surface water / groundwater interactions, seismic hazards, potentially unstable substrate, the nature and timing of development of the through-going Gila River in this area, and several issues surrounding the geology of mineral deposits and environmental geology of mine development and closure.

Location and Geologic Setting

The proposed map area covers a swath across Gila Valley and northernmost San Simon Valley, including some limited bedrock areas on the basin flanks. It is located in the southern Basin and Range province on the margin of the Transition Zone. Bounding mountain ranges are the Gila Mountains to the northeast and the high Pinaleño Mountains (up to 10,720 feet) to the southwest. The valley axes are dominated by the Gila River, a large, perennial river that heads in New Mexico and drains a significant fraction of southeastern Arizona and southwestern New Mexico, and San Simon River, a large ephemeral tributary that enters the valley from the south. The Gila River has flooded numerous times historically, resulting in widespread inundation and substantial channel change and bank erosion (Burkham, 1972; Klawon, 2003). The Gila River has downcut through the Quaternary, resulting in the formation of prominent stream terraces and extensive exposures of basin-fill deposits. Valley piedmonts contain beautiful, stair-stepped suites of alluvial deposits and associated alluvial surfaces ranging in age from Holocene to early Pleistocene (Menges and McFadden, 1981); these relict alluvial fans and terraces developed in response Gila River downcutting and climate changes. Most of the proposed map area is underlain by thousands of feet of middle to late Cenozoic sediment, possibly including evaporites (Richard et al., 2007). Quaternary normal faults along the west side of San Simon Valley separate the Pinaleño Mountains, a horst of Proterozoic crystalline rocks, from the deep, valley-filling, clastic sediments that make up the hanging wall. Other Quaternary faults have been identified closer to the center of the valley (Machette et al., 1986).

Purpose and Justification

The proposed mapping area is in Graham County, which has grown from a population of 14,000 in 1960 to approximately 39,000 in 2008. Population growth is due to a number of factors, including the area’s scenic character and diverse economic activity including agriculture, mining and small businesses. The basin aquifer beneath Gila Valley is utilized by agricultural interests, mines, and the towns of Safford, Thatcher, and Pima. Water-table drawdown has been less of an issue in Gila Valley than in many other basins in Arizona, in part because of recharge from the Gila River (average 300,000 acre-feet/year), but understanding flow paths and recharge rates in the valley will become increasingly important as development continues. Geologic mapping will assist in identification of geologic resources such as aggregate that will aid future development in Gila Valley, and it will provide critical data to avoid flooding and erosion hazards and potential unstable substrate issues as that development occurs.

The primary purpose of mapping is to characterize and accurately depict alluvial deposits and surfaces, identify faults, characterize and map exposed basin deposits, and map bedrock and surficial deposits along the highly mineralized southwest side of the Gila Mountains. (1) Detailed surficial geologic mapping will allow better characterization of potential for large earthquakes in this area. Quaternary faults have been mapped in the area on a reconnaissance basis, but need careful evaluation of deposits and geomorphic features that may reveal their age of most recent movement. (2) More detailed depiction of surficial and basin deposits and faults will allow for development of more realistic groundwater flow models, which will serve the interests of property owners in obtaining long-term water supplies and will provide a better foundation for decisions that affect water use and riparian and aquatic habitats along the Gila River. In addition, these models may improve understanding of moderate-temperature geothermal systems that exist in the valley (Stone and Witcher, 1982). (3) Detailed surficial geologic mapping will assist in identification of potentially flood-prone areas on piedmonts and along the axial rivers. (4) Fine-grained deposits exposed extensively across much of the valley may pose potential hazards due to shrink-swell or hydrocompaction, and gypsum dissolution may also pose hazards. (5) Mapping of Gila River deposits of various ages will assist in the identification of potential aggregate resources. (6) Little research has been done into the timing of initial development and the subsequent evolution of the Gila River, but the proposed map area has the potential so shed considerable light on this subject through better dating of deposits that pre-date and post-date development of the through-going river. (7) The proposed map area is downslope from mines and mine facilities under development in the Lone Star mining district. Proposed mapping will contribute to understanding the regional hydrologic setting of open-pit mines and facilitate mine-complex design that minimizes adverse hydrologic consequences.

Quaternary faulting and earthquake hazards. The Pinaleño Mountains, which form the footwall to the normal-fault zone at the southwest margin of the Safford basin, included mylonitic crystalline rocks at the foot of the range that formed down-dip from a normal fault or fault zone during regional Oligo-Miocene extension (Naruk, 1987; Long et al., 1995). Quaternary normal faulting appears to represent the modern incarnation of this faulting, with continued exhumation of a metamorphic core complex adjacent to a listric normal fault and a deep sedimentary basin (Kruger et al., 1995). Several Quaternary fault zones have been identified in or near the foot of the range (Machette et al., 1986; Houser et al., 2004), but none have been mapped in detail. New detailed surficial geologic mapping will document faulted and unfaulted alluvial deposits and thus provide age constraints on the Quaternary faulting history, long-term slip rates, and age of most-recent rupture. In addition, the fault zones themselves will be mapped in much greater detail, which will better define their length. This will be useful in estimating the magnitudes of paleoearthquakes on these faults.

Basin geology and groundwater flow models. Basin geology exerts controls on groundwater recharge and groundwater circulation systems that feed moderately hot springs at several locations in the map area (Stone and Witcher, 1982). Groundwater in the Gila Valley is undoubtedly recharged through several mechanisms, including infiltration along the Gila River and infiltration of local runoff on piedmonts. Due to orographic effects, the high parts of the Pinaleño Mountains receive upwards of 60 cm of average annual precipitation, whereas the adjacent valleys receive 25‐30 cm/yr. Some of this montane precipitation is transferred to the adjacent valley via moderately large, east‐flowing drainages, and some water may flow into the basin via fractures in bedrock. A number of springs with water as warm as 46 °C are found within 10 km east of the mountain front. Stone and Witcher (1982) suggested that these warm springs result from recharge in coarse alluvial fan deposits along the mountain front, circulation into the basin to sufficient depth to heat the water, and confinement of groundwater in sand and gravel beds between finer‐grained beds. The higher altitude of the recharge input along the mountain front would provide the hydrostatic head to drive the system. Detailed mapping of alluvium of various ages will delineate areas of young deposits associated with montane drainages and the river system, where most recharge occurs.

Flood hazards and debris flows. Flood hazards in the area exist along major drainages and their tributaries throughout the proposed map area (e.g., Klawon, 2001). Lateral bank erosion during floods is a significant hazard along major rivers and desert washes, and is especially likely along banks formed in weakly cohesive Holocene terrace deposits. Mapping of active and abandoned channels and Holocene terraces along these streams defines the corridor that is most likely to be subjected to flooding or bank erosion. Flash floods generated by thunderstorms can cover broad portions of piedmonts with sheet wash in areas of active alluvial fans. Such floods are infrequent and of short duration, but are potentially devastating to homes because of the extent of inundation and the potential for developing new channels. Areas that are covered by young deposits are, or have recently been, part of active fluvial systems, whereas areas covered by Pleistocene deposits have not been subject to significant inundation for at least 10,000 years. Thus, the surficial mapping component of our mapping effort will outline areas where flooding along major drainages may occur as well as potential alluvial-fan flooding areas on piedmonts.
Soil and substrate problems. Unstable soil clays and near-surface compaction of some sediment types due to wetting or loading can cause cracking or destruction of overlying buildings. In addition, poorly compacted, low-density, fine-grained alluvial deposits have been the source of piping problems in desert soils. Fine-grained basin-fill deposits and Quaternary deposits reworked from basin deposits are candidates for these kinds of problems. Gypsum content is fairly high in some of the fine-grained deposits, and this may make them even more prone to subsidence or collapse due to dissolution if they are wetted. Mapping of surficial deposits generally outlines surficial geologic units that may be characterized by problem soils, and provides a template with which to evaluate the spatial distribution of existing and potential substrate problems.

Aggregate resources. Large quantities of aggregate are required for concrete and asphalt that are essential to housing and infrastructure development. All major aggregate operations in central and southern Arizona are located along major regional drainage systems like the Gila River, where gravel has been transported some distance and contains a wide mix of rock types. No large aggregate operations currently exist in the proposed map area, but large-scale deposits associated with the Gila River are likely to be present. Sand and gravel production has become controversial in Arizona because expanding suburbs encroach on quarry operations, and new residents complain of associated dust and noise. If locations of potential resources are identified before development occurs in an area, they can be factored into management decisions regarding land use.

Development of the Gila River. The Gila River developed sometime after the late Miocene through a series of formerly closed basins, including Gila Valley. Detailed analysis of the Duncan Valley, the next basin upstream, indicates that it was a closed basin in the late Miocene (Reid and Buffler, 2002). Major incision of the valley began after the basin was integrated downstream. The situation in Gila Valley was probably similar, but the age of drainage integration is poorly constrained. Very high and old alluvial fan remnants on the north side of the Pinaleno Mountains may record the level of maximum valley filling, prior to the beginning of Gila River downcutting. Several prominent Gila River terraces record the downcutting history, and the 640 ka Lava Creek B tephra has been found in one of the lower Pleistocene Gila River terrace gravels (Houser et al., 2004), implying that substantial river downcutting occurred in the early Pleistocene. Better dating of basin deposits that predate river development, the beautiful suite of terraces on the north side of the Gila River, and the highest preserved alluvial fan surfaces on the valley flanks has the potential to substantially improve our understanding of the timing and nature of river development in this area.

Metallic mineral deposits. A string of copper deposits northeast of Safford that make up the Lone Star mining district (Langton and Williams, 1982) form one of the largest copper districts in the world (11th on the list compiled by Cooke et al. [2005], 4th in North America). Open-pit mining began in 2007 and is expected to continue for decades.

Development of multiple, large open-pit mines will have long-term consequences for groundwater hydrology. A standard plan in closing an open-pit mine in the arid Southwest is to leave a pit lake that will evaporate, thus producing a cone-of-depression in the water table. The cone-of-depression will draw in sulfate-bearing groundwater and associated cations and prevent flow of contaminants off-site. Proper understanding of groundwater behavior is necessary to implement procedures that will minimize groundwater contamination and evaporative loss from pit lakes after mine abandonment. While proposed mapping is not directly in the area of mining, it covers the river valley that is downslope from the mining district. Proposed mapping will improve understanding of regional hydrology and may influence plans for mining-facility development, environmental remediation, and mine abandonment.

A potpourri of geo-news

Some interesting Arizona themed items that you may not have seen today -

SRP sets goal of 20% renewable energy to include hydro and out of state credits

Construction delayed on trailhead to Scottsdale's Marcus landslide

New Master's degree in Climate Science & Solutions at NAU

Geology of National Parks online course includes the Grand Canyon

Why we map, #2: Prescott - Chino valleys

This is the second in a 3-part series explaining the basis for AZGS geologic mapping under the STATEMAP component of the National Cooperative Geologic Mapping Program, administered by the USGS. We were notified last week that partial funding was approved for three areas proposed by AZGS based on recommendations from the Arizona Geologic Mapping Advisory Committee. Here is the description by AZGS geologists Jon Spencer and Phil Pearthree of the mapping project in the Verde River area:

Mapping the region near the city of Prescott was given high priority largely because of concerns about groundwater depletion and renewed concern about arsenic in municipal water supplies. This area has been a GMAC priority in three previous years, and AZGS geologists will have mapped six quadrangles in this area by the end of the current STATEMAP project.

New geologic mapping in the upper Verde River area is consistent with the goals of the Water for America initiative. Proposed mapping is partly directed at better understanding of the surface geology and its relationship to the stratigraphy and structure of groundwater basins, groundwater flow paths, and geologic sources of natural contaminants in groundwater (especially arsenic in the upper Verde River area). Indeed, most of the STATEMAP project areas recommended for by the Arizona GMAC over the past several years were identified because of issues associated with groundwater availability and quality, preservation of riparian habitat, aggregate potential along river beds and flood plains, and flood hazards.

Proposed project #2 map area is within the third province, known as the Transition Zone, which stretches northwest to southeast across central Arizona and lies between the other two provinces. Bedrock consists largely of Proterozoic crystalline rocks that are contiguous with those beneath the Paleozoic sedimentary rocks of the Plateau, with a significant cover of upper Cenozoic volcanic rocks. These rocks are locally broken by Miocene to Quaternary normal faults that have produced generally shallow extensional basins that contain most of the areas groundwater resources. The physiography of the Transition Zone varies from gently sloping basin fill to very rugged bedrock, and the region is drained by several large river systems that supply much of the water for urban and agricultural uses in Arizona.

The proposed mapping areas are in Yavapai County, which has grown from a population of 31,000 in 1960 to approximately 215,500 in 2008. This rapid population growth is due to a number of factors, including the area’s scenic character, and elevations of 4500-5500 feet above sea level which result in cooler weather than in the low deserts where most Arizonans live. The basin aquifer beneath Little Chino Valley, which is utilized by Prescott and the town of Chino Valley, had been depleted at such a high rate by 1999 that the State declared the aquifer to be in an overdraft situation. The City of Prescott and the Town of Chino Valley are now attempting to develop well fields in more distant Big Chino Valley and Williamson Valley. Water-table drawdown in Big Chino Valley might, however, affect water discharge at springs along the perennial Verde River, which would have serious environmental consequences. The quality of water in the basin aquifers is also less than ideal, primarily because of elevated arsenic concentrations. Prescott is currently installing arsenic-removal equipment on six city wells located in Little Chino Valley. Many of the wells in Big Chino Valley contain arsenic above the 10 ppb level allowed by federal guidelines (Blasch et al., 2005).

A primary purpose and justification of new mapping is to identify fault zones and rock units that could serve as conduits for groundwater movement and that should be factored into groundwater flow models. More geologically realistic flow models will serve the interests of property owners in obtaining long-term supplies of clean water, and will provide a better foundation for decisions that affect riparian and aquatic habitats along the Verde River. A Quaternary fault identified in Little Chino Valley by recent STATEMAP mapping (Gootee et al., 2010) projects beneath the Verde and Granite Creek river beds where springs provide most of the recharge in the approximately 15 km reach of the Verde River below Big Chino Valley. The fault may provide a conduit for groundwater movement from the sediment-filled valley to the Verde River. Additional justifications for proposed mapping are as follows: (1) Identification of geologic factors that affect arsenic content of well water, such as association of arsenic with volcanic rocks and derivative sediments. (2) Further characterization of potential earthquake hazards. Quaternary faults have been mapped in the area on a reconnaissance basis, but need careful evaluation of deposits and geomorphic features that may reveal their age of most recent movement. (3) Identification of potentially flood-prone areas in the valleys based on the distribution and nature of young alluvial deposits. (4) Identification of areas with potential for base and precious metal mineralization as revealed primarily by evidence of ancient hydrothermal activity. Existing bedrock geologic maps (Krieger, 1965, 1:48,000 scale; Krieger, 1967a, b, 1:62,500 scale; DeWitt et al., 2008, 1:100,000 scale) are not very detailed.

Groundwater resources. Population growth around Prescott Valley and Chino Valley has placed increasing pressure on groundwater supplies. As a result of concerns that groundwater would be depleted, the Little Chino Valley drainage basin was made part of an Active Management Area (AMA) by the Arizona Department of Water Resources in 1980. The Prescott AMA has a statutory goal of achieving basin-wide safe-yield, balancing annual groundwater withdrawal with natural and artificial recharge, by 2025. According to the legal framework of Arizona water law, recharging water in one part of an AMA can offset groundwater-level declines in another portion of the AMA. In spite of AMA management, however, the water table is declining in 90% of the groundwater wells in the AMA, with an average rate of decline of 2.7 feet per year. Water pumping is now estimated to be 45% greater than recharge.

Knowledge of rates of recharge depends in part on understanding the surficial geology well enough to be able to identify areas of recharge. Proposed detailed geologic mapping will improve recognition of areas where surface water recharges groundwater. This useful aspect of detailed geologic maps was specifically identified by John Rasmussen of the Yavapai County Water Advisory Committee, who indicated his support for detailed geologic mapping in Little Chino Valley and Big Chino Valley. Calculations of changes to the water table resulting from groundwater pumping, and resulting from modifications to the amounts and locations of recharge, require understanding of underground flow paths. Understanding flow paths depends on understanding subsurface basin geometry, the distribution and character of aquifer materials, and potential conduits such as faults.

Proposed geologic mapping is intended to refine understanding of basin-margin geometry as revealed by basin-margin faults and depositional contacts, by recognizing incised basin-filling sedimentary units that represent exposed basin stratigraphy, and by identifying faults in bedrock that are potential conduits for water flow. This will allow better approximation of subsurface basin geology and improved groundwater flow models. Discovery of a Quaternary fault zone on the northeast flank of Little Chino Valley during recent STATEMAP mapping (Gootee et al., 2010) will affect representation of basin geometry in groundwater flow models by creating possible flow paths from basin aquifers to the Verde River.

Verde River base flow. Base flow, which is the amount of flow in a river that results from groundwater inflow and is unrelated to prompt runoff from precipitation, increases along a several-mile stretch of the Verde River in the Chino Valley North 7.5' Quadrangle (Wirt, 2004b). Springs in the streambed, primarily near Upper Verde River Springs and above the Paulden gauging station, emanate from an area of faulted Paleozoic sedimentary units and sustain a base flow of about 25 ft3/s. This base flow maintains critical habitat for the threatened spikedace minnow (Meda fulgida). The Arizona Game and Fish Department recently acquired 796 acres along the upper Verde River in order to protect the area’s native fish (Wirt, 2004b), including at least six native fish species. Proposed mapping is not directly related to the problem of identifying the source of Verde River recharge, but it is directed at better understanding of the basins upstream and up gradient from the springs. Proposed mapping will contribute to a better understanding of regional groundwater behavior and so may influence decisions regarding water use.

Arsenic in groundwater. A recent compilation of well-water chemistry in the Prescott – Chino Valley area outlined the areal extent of wells with elevated arsenic levels (data from Blasch et al., 2005). The highest arsenic levels are within the southeastern end of Big Chino Valley. High levels are also apparent in some spring discharges; all nine samples analyzed from Upper Verde River Springs contained 13 to 29 ppb As. The Quail Ridge Domestic Water Improvement District at the east edge of the Sullivan Buttes 7.5' Quadrangle recently installed arsenic removal equipment in order to reduce arsenic concentrations to below 10 ppb.

Elevated arsenic levels are thought to be derived from lower Paleozoic aquifer units and from fine-grained, basin-interior sediments in Big Chino Valley (Wirt, 2004a). We suspect that Cenozoic volcanic rocks, which are common in the area of elevated arsenic concentrations, could play a currently unappreciated role in contributing contaminants to groundwater. These volcanic rocks are dominated by the Sullivan Buttes latite, a widespread sequence of mafic to intermediate composition volcanics (51-68% SiO2, n=22) with elevated K2O (2.7-6.5%, n=22) and locally abundant lower crustal and upper mantle xenoliths (Tyner, 1984). As part of proposed mapping, we will map the Sullivan Buttes 7.5' Quadrangle and obtain trace-element geochemical analyses, including arsenic, of the latite. (We could not find any geochemical measurements of arsenic from the Sullivan Buttes latite and related volcanic rocks in available geologic literature).

Quaternary faulting. Quaternary normal faults are present in the Jerome Canyon 7.5' Quadrangle and possibly extend northward but are unidentified in the Sullivan Buttes 7.5' Quadrangle. Minor historic seismicity is inferred to reflect approximately east-west crustal extension southward from the more active Hurricane fault and related faults near the edge of the Colorado Plateau in northwestern Arizona (Pearthree and Bausch, 1999). Reconnaissance investigations of the Big Chino fault zone indicate that it has had substantial activity in the middle and late Quaternary (Pearthree et al., 1983). Fault identification is also significant because of implications for groundwater flow.

Flood hazards. Potential flood hazards exist along piedmont drainages throughout the proposed map area. Big Chino, Little Chino, and Prescott Valleys are generally dry, but drainages of all sizes are subject to infrequent to rare floods with deep, high velocity flow. In addition, lateral bank erosion and drastic changes in channel position may occur during floods, especially along banks formed in weakly cohesive Holocene terrace deposits. Mapping of active and abandoned channels and Holocene terraces along these streams defines the corridor that is most likely to be subjected to flooding or bank erosion. In low-relief portions of valleys, sheetflooding on active alluvial fans can cover broad portions of piedmonts. Such floods are infrequent and of short duration, but are potentially devastating to homes because of the extent of inundation and the potential for developing new channels. Mapping surficial deposits on piedmonts will document extensive areas that are covered by young deposits, and thus may be prone to sheetflooding.

Mineral deposits. Mineral deposits and old mining camps are abundant in eastern Yavapai County, and have much to do with the original settlement of the area. The Big Bug and Ticonderoga mining districts at the south edge of the Prescott Valley South 7.5' Quadrangle each have millions of pounds of historic copper production and hundreds of thousands of ounces of historic gold production, as well as substantial lead, zinc, and silver. Better geologic understanding of the bedrock geology in the area could lead to new exploration efforts.

Iron King Mine – Humboldt Smelter superfund site. Arsenic and lead contamination associated with historic mining and smelting activities have resulted in contamination around the Iron King Mine at the extreme southeastern corner of the Prescott Valley South 7.5' Quadrangle and the Humboldt smelter located about a mile down Chaparral Creek and just outside the proposed map area (EA Engineering, Science, and Technology, Inc., 2010). Proposed mapping will clarify the structural geology and rock types under the superfund site area, which will improve understanding of potential pathways for groundwater movement and dispersal of pollutants.


Preliminary Results and Prior Work

The proposed map area was mapped previously at 1:48,000 scale (Krieger, 1965) or 1:62,500 scale (Krieger, 1967), but the Quaternary deposits in the map area were subdivided into only two map units. We will provide much greater differentiation and detail to Quaternary map units. We expect to divide Tertiary volcanic rocks into more units, and to more finely divide other bedrock units if hydrologic properties are likely to be different within previously combined units. Faults also will be mapped with much greater detail. Proterozoic metamorphic rocks in the Prescott Valley South 7.5' Quadrangle are mapped well at 1:48,000 scale (Krieger, 1965), but we expect to add significant detail at 1:24,000 scale.

As noted above, just-completed STATEMAP mapping (Gootee et al., 2010) identified a Quaternary fault zone that projects beneath springs in the Verde River bed that contain elevated arsenic and that provide habitat for native fish. High arsenic levels suggest that spring water is derived from Big Chino Valley, but chemical analysis of water by Wirt et al. (2004a) suggest that spring water is derived from Little Chino rather than Big Chino Valley. Water flow paths may be more complicated than previously appreciated, and perhaps involve subsurface mixing from multiple sources. Further evaluation and study are warranted.

Congressional hearing on future of Navajo generating station

Arizona congressmen Trent Franks and Paul Gosar called on the House Natural Resources Subcommittee on Water and Power and the Subcommittee on Indian and Alaska Native Affairs, to hold a hearing this Tuesday, to question EPA's requirement that the Navajo Generating Station use state-of-the-art air scrubbers rather than much cheaper alternatives that the plant owners and power users argue will do just as good a job.

This is one more step in an ongoing battle. The plant owners, Salt River Project, warn that the EPA mandated costs of $1.1 billion might force the plant to shut down. The Page plant not only is a major contributor to the economy of the Navajo Nation, the low-sulfur bituminous coal is mined from the Kayenta mine 78 miles to the southeast on the Hopi Reservation.

The Central Arizona Project is the largest user of electricity from the NGS. They argue against the EPA requirements:

Last year, CAP used 2.8 million megawatt hours to deliver more than 500 billion gallons of Colorado River water to a service area that includes more than 80% of the state’s population.

Why so much power? Because between Lake Havasu and the end of the CAP system south of Tucson, Colorado River water flows 336 miles and ends its journey nearly 3,000 feet higher than where it started. Almost all of the power CAP uses to move this water comes from the coal-fired Navajo Generating Station near Lake Powell. Because the Navajo plant is near a dozen or so National Parks, monuments and wilderness areas, controlling emissions released from the plant into the air has been a priority for CAP and the power plant owners for decades. In the 1990s, the plant owners invested more than $400 million in scrubbers that take out sulfur dioxide (SO2), a gas that can cause acid rain.

In 2008, installation began on Low-NOx burners to reduce emissions of smog-forming nitrogen oxide, also known as NOx. The job will be finished in 2011 at a cost of approximately $45 million. The U.S. EPA is in the process of setting rules to control NOx emissions at coal-burning power plants like Navajo to protect visibility in the region. The EPA is looking at the Low-NOx burners. They are also considering a very different NOx control system known as Selective Catalytic Reduction (SCR). An SCR system could cost more than $1 billion, at least 15-20 times more than the Low NOx burners.

There is debate within the Navajo and Hopi communities over the economic benefits of the plant and mine versus concerns of lung disease, asthma, and visual pollution from burning coal.

Horseshoe 2 fire seen from space station

This photo of the Horseshoe 2 fire in the Chiricahua Mountains was just posted on Spaceref.com. It was taken by the crew on the International Space Station on May 15. At that time the fire had burned approximately 8,900 hectares, or 22,110 acres. They report that the smoke plume extends to the east-northeast over a distance of at least 60 kilometers (approximately 40 miles). "As of May 19, 2011, the fire had burned an area of nearly 14,000 hectares (approximately 34,400 acres) of grasses, shrubs, and trees along the mountain slopes."

Willcox Playa is visible in the upper left. I was told the black smoke in the lower/southern portion of the burn is the location of Sulpher Draw which is reported as heavily charred. The whiter smoke is more typical of a less intense fire.

Why we map, #1: Artillery Mountains, Western Arizona

Geologic mapping is one of the primary functions of the AZGS. For the past 15 years, we have been aggressive participants in the USGS-run National Cooperative Geologic Mapping Program, especially in the Statemap component that matches state and federal funds. We just got notice of our funding award for FY12 so I thought it would be valuable to explain why we will be mapping the areas selected. This is part 1 of a 3-part series on next years plans, drawn from Jon Spencer's and Phil Pearthree's successful proposal to USGS. Our priority areas were recommended by the Geologic Mapping Advisory Committee (GMAC). The following is taken from the AZGS proposal written by Jon and Phil:

The Arizona GMAC recommended that the Arizona Geological Survey map the Artillery Mountains area because of its large, low-grade manganese and uranium deposits. These deposits are incompletely mapped and studied, and significant questions surround their genesis. New mapping is intended to clarify models for deposit genesis and estimates of deposit extent.

The Artillery Mountains are located in the low-elevation, dry desert region of western Arizona, which is very sparsely populated except along the Colorado River. The Artillery Peak 7.5' Quadrangle includes Lake Alamo, a water-storage reservoir and popular fishing area at the confluence of the Big Sandy and Santa Maria rivers. The surrounding area contains abundant manganese, uranium, and Cu-Pb-Zn-Ag-Au deposits.

The proposed map area includes part of the Harcuvar metamorphic core complex, which is the largest known terrestrial core complex on Earth (a larger core complex is present beneath the Philippine Sea). The Buckskin and Rawhide Mountains, located to the west of and within the map area, consist largely of Paleoproterozoic to Miocene granitic and gneissic rocks with a strong, middle Tertiary, mylonitic fabric. These rocks form the footwall to the Buckskin-Rawhide detachment fault, a subhorizontal to gently dipping normal fault that was active in Oligo-Miocene time and accommodated many tens of kilometers of top-ESE displacement. The three large antiforms that make up most of the Buckskin and Rawhide Mountains are enormous grooves in the detachment fault. Rocks above the fault include 27-12 Ma, syntectonic strata that were generally tilted to the southwest during faulting, with dips decreasing up-section. The proposed map area also includes the western end of Date Creek basin, a large, deep, dissected, roughly east-west-trending sedimentary basin that developed in conjunction with Oligo-Miocene detachment faulting. The proposed map area consists primarily of bedrock, with lesser amounts of dissected basin deposits and Quaternary surficial deposits.

Geologic background - Harcuvar core complex. The Harcuvar metamorphic core complex is associated with Earth’s greatest known concentration of mineral deposits related to detachment faults (Spencer and Welty, 1986, 1989). Core complexes consist of middle crustal rocks that were exhumed by large displacement below moderately to gently dipping normal faults. Exhumation and uplift of large core complexes was sufficiently rapid that, in some cases, the core complexes formed large thermal anomalies during and immediately after uplift (e.g., Scott et al., 1998). Detachment faults were conduits for ascent of hydrothermal fluids, with fault permeability maintained by repeated faulting and fault-zone crushing of hydrothermal minerals. Syntectonic ascent of hot (225-325°C) basin brines along detachment faults produced abundant specular hematite and common sulfide minerals along and adjacent to the Buckskin-Rawhide detachment fault and related faults (Wilkins and Heidrick, 1982; Wilkins et al., 1986). A few deposits related to detachment faults include substantial silica and economic concentrations of gold (Spencer et al., 1988). [right, five types of Oligo-Miocene mineralization and alteration phenomena that occurred in association with extensional detachment faulting and basin genesis in the Buckskin-Rawhide-Harcuvar Mountains area. Widespread potassium metasomatism, especially of mafic lava flows within basin sediments, is suspected to have been a source of base and precious metals that were deposited along detachment faults during extensional faulting (Hollocher et al., 1994). Chloritic breccias, characteristic of detachment-fault footwalls, are probably not geochemically related to the others, as indicated by oxygen isotope data (Smith et al., 1991).]

Geologic background - Artillery manganese deposits. The Artillery mining district is the most historically productive manganese district within the western Arizona manganese province (Spencer, 1991). Total historic manganese production in the province is about one hundred thousand metric tons, with 40% derived from the Artillery mining district. All of the deposits are Miocene in age, and most are vein deposits. The Artillery manganese district contains primarily stratabound manganese (Lasky and Webber, 1949), as do a few of the other districts in the province.

Tilted Oligo-Miocene strata of the Artillery Mountains area were deposited in a syntectonic basin directly above the gently northeast-dipping Buckskin-Rawhide detachment fault (Spencer et al., 1989). The large, low-grade, stratabound Artillery Mountains manganese deposits were deposited at Earth’s surface as very fine clastic material in the upper part of the tilted clastic sequence (Lasky and Webber, 1949). The geochemically similar elements iron and manganese are present in crustal rocks at ratios of roughly 50:1. Many manganese deposits are thought to have developed under conditions where iron- and manganese-bearing aqueous solutions gradually lost iron but retained manganese until manganese was deposited from solutions that had lost all of their iron. Under a significant range of ambient conditions, acidic solutions that react with carbonate to increase solution pH will precipitate iron and retain manganese (Krauskopf, 1957). Detachment-fault-related deposits typically contain abundant hematite or specular hematite (Fe2O3). Spencer and Welty (1989) suggested that mineralizing hydrothermal fluids that yielded iron, copper, and associated metals along detachment faults retained manganese until reaching Earth’s surface and deposited manganese in shallow veins or as clastic material.

Derivation of the Artillery stratabound manganese deposits from fluids that formerly yielded voluminous iron along detachment faults is appealing for a number of reasons, but has been difficult to confirm. Fluid-inclusion studies indicate that detachment-fault related deposits were derived from hydrothermal fluids with 12 to 24 wt. % NaCl equivalent (Wilkins and Heidrick, 1982; Wilkins et al., 1986) whereas four minor manganiferous vein deposits with associated calcite, barite, and quartz in the Artillery Mountains area were derived from fluids with 0-3 wt. % NaCl equivalent (Spencer et al., 1989). These four vein deposits are younger than the stratabound manganese in the Artillery Mountains and their genesis may have involved different processes. It is clear, however, that the relationship between manganese mineralization and detachment-fault mineralization is not well established, even though these deposits are the same approximate age and are near each other (or were before significant fault displacement).

Geologic background - Potassium metasomatism. We also propose geochemical analysis of common brick-red sandstones and associated altered basalts that might have been greatly modified by potassium metasomatism. The brick red color of sandstone that hosts the Artillery stratabound manganese deposits is typical of K-metasomatism, which can convert sandstone to an assemblage of quartz, adularia, and hematite (Chapin and Lindley, 1986; Roddy et al., 1988). This process is known to liberate manganese, copper, and zinc, probably during low-temperature diagenesis by alkaline, saline fluids (Roddy et al., 1988; Hollocher et al., 1994). Circulation of these metal-bearing brines during detachment faulting and core-complex exhumation is a possible source of both detachment-fault related mineral deposits and manganese deposits (Spencer and Welty, 1986, 1989).

Geologic background - Uranium deposits. Whereas manganese deposits in the Artillery Mountains are hosted by clastic sedimentary rocks near the top of the tilted Oligo-Miocene sedimentary sequence, uranium deposits are associated with lacustrine strata near the base of the sequence. Basal arkosic sandstone and minor conglomerate grade upward into finer grain sandstone, siltstone, and mudstone, which in turn are overlain by lacustrine mudstone and limestone with locally interbedded rock-avalanche breccia (Yarnold, 1994). In the Anderson Mine area, located at the northeastern upturned margin of Date Creek basin, lacustrine strata include carbonaceous mudstone with plant material, lignitic coal seams, and limestone and marl that contain freshwater gastropods, ostracods, and pelecypods (Otton et al., 1990). The lacustrine strata are overlain by sandstone, conglomerate, rock avalanche breccia, tuff, and basalt.

Calcareous and carbonaceous strata at the northern margin of Date Creek basin, which includes the Artillery Mountains area, commonly contain elevated uranium concentrations, typically within <3m thick zones in carbonaceous mudstone and associated marl, limestone, and tuffaceous mudstone. In areas of greatest uranium mineralization near Anderson Mine, uranium-bearing strata are up to 15 m thick, with unoxidized uranium in concentrations of 0.3-0.8% U3O8. Where oxidized in near-surface environments, uranium concentrations are up to 30% U3O8 (Sherborne et al., 1979; Mueller and Halbach, 1983). Uranium mineralization has been attributed to (1) alteration of uraniferous tuff beds (Sherborne et al., 1979), (2) derivation of uranium from surrounding bedrock and transport by groundwater to reducing environments in carbonaceous lacustrine strata (Mueller and Halbach, 1983), or (3) direct precipitation of uranium from anoxic lake-bottom water (Otton, 1981).

Justification for proposed mapping. The proposed map area (Rawhide Wash and Artillery Peak 7.5' Quadrangles) is centered on the Artillery manganese district, which contains the largest known manganese deposit in the United States. The only previous mapping study specifically directed at the manganese deposits was done by the U.S. Geological Survey during World War II as part of an assessment of strategic and critical minerals (Lasky and Webber, 1949). Manganese is necessary for steel production, and has a variety of other uses. We propose to map the Artillery Mountains primarily because of the potential economic significance of the manganese deposits. We especially hope that new mapping will identify manganiferous veins around the bedded deposits, and that we will be able to clarify the nature of mineralizing fluids by studying the veins. Ideally we will identify fluid conduits for suspected spring systems that delivered manganiferous hydrothermal fluids to Earth’s surface and produced the sedimentary manganese deposits. Better understanding of flow pathways for mineralizing solutions will potentially lead to improved mineral exploration strategies in this area.

Furthermore, we intend to map the eastern Rawhide Mountains to clarify the structural and lithologic setting of Fe-Cu-Pb-Zn-Ag-Au deposits. While this deposit type is moderately well understood (Spencer and Welty, 1989), these specific deposits in the Rawhide Mountains are not well mapped or studied. Some aspects, such as the presence of peripheral manganese mineralization that might reveal aqueous-solution pathways following iron deposition, will be carefully evaluated.

We propose to map facies in lacustrine and related strata to determine the setting of uranium mineralization. This will include data collection for radiation derived from uranium daughters, using a portable gamma-ray spectrometer, to identify uraniferous units and their distribution. Previous studies of the Anderson Mine area were not extended westward to the Artillery Mountains, even though many claims for uranium have been staked in the area and it is well known that the lacustrine strata are mildly to moderately uraniferous.

Finally, we will map exposed basin-fill deposits, surficial deposits, and river deposits. The sedimentology, clast composition, and ages of these various deposits may shed light on the timing and character of the development of the Bill Williams - Big Sandy - Santa Maria River system, which drains much of west-central Arizona and is a tributary to the Colorado River. In addition, we may find deposits along the river that were emplaced by very large early historical floods that have been reported for this river system (Pope et al, 1998).