China's Transboundary Groundwater Cooperation in the Context of Emerging Transboundary Aquifer Law

China shares more than 20 transboundary aquifers with its coaquifer states, but they have not exploited their transboundary groundwater resources, and these resources have not been governed by any international agreements. Given the close interaction between surface water and groundwater, and the growing demands for transboundary groundwater in China and its coaquifer states, there is increasing necessity for these countries to undertake international cooperation on this issue. This article overviews China's transboundary aquifers, reviews the duty to cooperate on China's transboundary groundwater as well as the emerging transboundary aquifer law. It concludes by providing some proposals on international cooperation in this context, based on the two theories of international water law—limited territorial sovereignty and common interests, taking into account the practicability of China's cooperation with its coaquifer states. The author suggests that China cooperates with its coaquifer states through such means as the exchange of data and information, joint monitoring, the conclusion of bilateral or multilateral aquifer agreements, the establishment of joint management mechanisms, and international technical cooperation.     

Economic Commission for Europe inventory of transboundary ground water in Europe

In Europe, a long history of cooperation over transboundary rivers--most notably the Rhine and Danube rivers--exists. To help foster cooperation and communication vis-à-vis transboundary ground water, the United Nations Economic Commission for Europe (UNECE), as part of its ground water program, conducted a survey on transboundary aquifers in Europe. The survey produced 25 responses from 37 countries and identified 89 transboundary aquifers. Respondents reported on the degree of ground water use within their own boundaries, transboundary aspects (agreements, joint commissions, etc.) of ground water, and transboundary aquifers themselves. The inventory proved useful, but a number of problems were identified: different map scales and symbols, difficulty in identifying transboundary aquifers, inconsistent labeling of aquifers, and data discrepancies. The UNECE ground water program also drafted guidelines for monitoring and assessment of transboundary ground water. These guidelines are not legally binding but have been adopted by 25 countries, deal mainly with monitoring and assessment, and are being implemented through a number of pilot projects. Other organizations-the United Nations Scientific, Educational and Cultural Organization, the Food and Agriculture Organization, the International Association of Hydrogeologists, and the European Union--are all supporting the investigation of transboundary aquifers in an effort to facilitate data sharing and coordinated management of these valuable resources.     

Transboundary aquifers: a global program to assess, evaluate, and develop policy

Transboundary aquifers are as important a component of global water resource systems as are transboundary rivers; yet, their recognition in international water policy and legislation is very limited. Existing international conventions and agreements barely address aquifers and their resources. To rectify this deficiency, the International Association of Hydrogeologists and UNESCO's International Hydrological Programme have established the Internationally Shared (transboundary) Aquifer Resource Management (ISARM) Programme. This multiagency cooperative program has launched a number of global and regional initiatives. These are designed to delineate and analyze transboundary aquifer systems and to encourage riparian states to work cooperatively toward mutually beneficial and sustainable aquifer development. The agencies participating in ISARM include international and regional organizations (e.g., Organization of American States, United Nations Environment Programme, United Nations Economic Commission for Europe, Food and Agriculture Organization, and South African Development Community). Using outputs of case studies, the ISARM Programme is building scientific, legal, environmental, socioeconomic, and institutional guidelines and recommendations to aid sharing nations in the management of their transboundary aquifers. Since its start in 2000, the program has completed inventories of transboundary aquifers in the Americas and Africa, and several ISARM case studies have commenced.     

Transboundary aquifers: conceptual models for development of international law

More than one-half of the world's population is dependent on ground water for everyday uses such as drinking, cooking, and hygiene. In fact, it is the most extracted natural resource in the world. As a result of growing populations and expanding economies, many aquifers today are being depleted while others are being contaminated. Notwithstanding the world's considerable reliance on this resource, ground water resources have long received only secondary attention as compared to surface water, especially among legislatures and policymakers. Today, while there are hundreds of treaties governing transboundary rivers and lakes, there is only one international agreement that directly addresses a transboundary aquifer. Given that many of the aquifers on which humanity so heavily relies cross international borders, there is a considerable gap in the sound management, allocation, and protection of such resources. In order to prevent future disputes over transboundary aquifers and to maximize the beneficial use of this resource, international law must be clarified as it applies to transboundary ground water resources. Moreover, it must be defined with a firm basis in sound scientific understanding. In this paper we offer six conceptual models is which ground water resources can have transboudary consequences. The models are intended to help in assessing the applicability and scientific soundness of existing and proposed rules governing transboundary ground water resources. In addition, we consider the development of international law as it applies to ground water resources and make recommendations based on the models and principles of hydrogeology. The objective is the development of clear, logical, and science-based norms of state conducts as they relate to aquifers that traverse political boundaries.     

International borders, ground water flow, and hydroschizophrenia

A substantial body of research has been conducted on transboundary water, transboundary water law, and the mitigation of transboundary water conflict. However, most of this work has focused primarily on surface water supplies. While it is well understood that aquifers cross international boundaries and that the base flow of international river systems is often derived in part from ground water, transboundary ground water and surface water systems are usually managed under different regimes, resulting in what has been described as "hydroschizophrenia." Adding to the problem, the hydrologic relationships between surface and ground water supplies are only known at a reconnaissance level in even the most studied international basins, and thus even basic questions regarding the territorial sovereignty of ground water resources often remain unaddressed or even unasked. Despite the tensions inherent in the international setting, riparian nations have shown tremendous creativity in approaching regional development, often through preventive diplomacy, and the creation of "baskets of benefits," which allow for positive-sum, integrative allocations of joint gains. In contrast to the notion of imminent water wars, the history of hydropolitical relations worldwide has been overwhelmingly cooperative. Limited ground water management in the international arena, coupled with the fact that few states or countries regulate the use of ground water, begs the question: will international borders serve as boundaries for increased "flows" of hydrologic information and communication to maintain strategic aquifers, or will increased competition for shared ground water resources lead to the potential loss of strategic aquifers and "no flows" for both ground water users?     

Investigation and water management aspects of a Hungarian-Ukrainian transboundary aquifer

In the framework of an EEA Norway and EU grants project involving industrial and scientific partners, complex hydrogeological investigation and groundwater modeling of a regional transboundary aquifer between Hungary and Ukraine were carried out in 2010. To find a common groundwater management strategy, this challenging cooperation work was completed by an EU country and a non-EU country. This pilot project demonstrated how the EU Water Framework Directive and some other legal aspects can be applied for a regional scale transboundary aquifer between Hungary and Ukraine. The transboundary aquifers play significant role in Hungary because the country land is mainly located in a deep and closed basin called Carpathian. After finalizing the watershed management plans in 2009, it turned out that 40 from the total 185 groundwater bodies are classified as transboundary in Hungary. The authors were involved to participate in an earlier NATO Science for Peace Project, which investigated a transboundary aquifer between Hungary and Romania some years ago. The special experience gained that time was utilized in the current project.     

Investigating Groundwater Flow Between Edwards and Trinity Aquifers in Central Texas

Understanding the nature of communication between aquifers can be challenging when using traditional physical and geochemical groundwater sampling approaches. This study uses two multiport wells completed within Edwards and Trinity aquifers in central Texas to determine the degree of groundwater inter‐flow between adjacent aquifers. Potentiometric surfaces, hydraulic conductivities, and groundwater major ion concentrations and Sr isotope values were measured from multiple zones within three hydrostratigraphic units (Edwards and Upper and Middle Trinity aquifers). Physical and geochemical data from the multiport wells were combined with historical measurements of groundwater levels and geochemical compositions from the region to characterize groundwater flow and identify controls on the geochemical compositions of the Edwards and Trinity aquifers. Our results suggest that vertical groundwater flow between Edwards and Middle Trinity aquifers is likely limited by low permeability, evaporite‐rich units within the Upper and Middle Trinity. Potentiometric surface levels in both aquifers vary with changes in wet vs. dry conditions, indicating that recharge to both aquifers occurs through distinct recharge areas. Geochemical compositions in the Edwards, Upper, and Middle Trinity aquifers are distinct and likely reflect groundwater interaction with different lithologies (e.g., carbonates, evaporites, and siliceous sediments) as opposed to mixing of groundwater between the aquifers. These results have implications for the management of these aquifers as they indicate that, under current conditions, pumping of either aquifer will likely not induce vertical cross‐formational flow between the aquifers. Inter‐flow between the Trinity and the Edwards aquifers, however, should be reevaluated as pumping patterns and hydrogeologic conditions change.     

Quantifying temporal variations in water resources of a vulnerable middle eastern transboundary aquifer system

Freshwater resources in the arid Arabian Peninsula, especially transboundary aquifers shared by Saudi Arabia, Jordan, and Iraq, are of critical environmental and geopolitical significance. Monthly Gravity Recovery and Climate Experiment (GRACE) satellite‐derived gravity field solutions acquired over the expansive Saq transboundary aquifer system were analysed and spatiotemporally correlated with relevant land surface model outputs, remote sensing observations, and field data to quantify temporal variations in regional water resources and to identify the controlling factors affecting these resources. Our results show substantial GRACE‐derived terrestrial water storage (TWS) and groundwater storage (GWS) depletion rates of ?9.05 ± 0.25 mm/year (?4.84 ± 0.13 km³/year) and ?6.52 ± 0.29 mm/year (?3.49 ± 0.15 km³/year), respectively. The rapid decline is attributed to both climatic and anthropogenic factors; observed TWS depletion is partially related to a decline in regional rainfall, while GWS depletions are highly correlated with increasing groundwater extraction for irrigation and observed water level declines in regional supply wells.     

Sustainability of groundwater usage in northern China: dependence on palaeowaters and effects on water quality,quantity and ecosystem health

A synthesis of groundwater ages, recharge rates and information on processes affecting groundwater quality in northern China highlights the major challenges faced for sustainable management of the region's groundwater. Direct recharge rates range from hundreds of millimetres per year in the North China Plain, to tens of millimetres per year in the Loess Plateau to less than 4 mm/year in the arid northwest. Recharge rates and mechanisms to deep semiconfined and confined aquifers are poorly constrained; however, on the basis of available data, these are likely to be mostly negligible. Severe groundwater level declines (0.5–3 m/year) have occurred throughout northern China in the last three to four decades, particularly in deep aquifers. Radiocarbon dating, stable isotope and noble gas data show that the most intensively extracted deep groundwater is palaeowater, recharged under different climate and land cover conditions to the present. Reservoir construction has reduced surface runoff in mountain‐front areas that would naturally recharge regional Quaternary aquifers in many basins. In combination with intensive irrigation practices, this has resulted in the main recharge source shifting from surface runoff and mountain‐front recharge to irrigation returns. This has reduced infiltration of fresh recharge at basin margins and rapidly increased nitrate concentrations and overall mineralisation in phreatic groundwater over wide areas (in some cases to >400 mg/l and >10 g/l, respectively). In some basins, there is evidence that poor quality shallow water has leaked into deep layers (>200 m) via preferential flow, mixing with palaeowaters stored in semiconfined aquifers. High concentrations of naturally occurring fluoride and arsenic (locally >8.5 and >4 mg/l, respectively) have recently lead to the abandonment of numerous supply wells in northern China, creating further pressure on stressed water resources. Increasing water demand from direct and indirect consumption poses major challenges for water management in northern China, which must consider the full water cycle. Copyright © 2012 John Wiley & Sons, Ltd.     

Stack unit mapping of coastal aquifer to predict and control sea water intrusion using remote sensing and a geographical information system

Aquifers are inherently susceptible to contamination and coastal aquifers in specific are highly vulnerable to sea water intrusion. For efficient planning and management of coastal aquifers in Kayalpattu and Tiruchopuram villages, which extend over 4·05 km², it is essential to delineate and predict the extent of intrusion into the shallow aquifer. Management of ground water in coastal aquifers is composed of major elements that should be properly evaluated, and special attention is given to the sea water intrusion problem. Different data, like hydro‐geomorphological and depth‐wise iso‐apparent resistivity, are integrated spatially using a geographical information system. The stack‐unit mapping approach is used to delineate the zones with iso‐apparent resistivity of less than 10 Ω m have been found to be increasing in areal extent with reference to depth. Copyright © 2003 John Wiley & Sons, Ltd.     

Introduction to ‘A tribute to Edward P. Glenn (1947–2017): A legacy of scientific environmental assessment and applications in hydrological processes’

This special issue (SI) ‘A Tribute to Edward P. Glenn (1947-2017): A legacy of Scientific Environmental Assessment and Applications in Hydrological Processes’ is a celebration of the extensive work of Dr. Ed Glenn that was instrumental across multiple sub-disciplines of hydrology. The SI highlights four primary areas of hydrological processes that are cornerstones of Ed Glenn's over four decades of research. These contributions cover the following specialties: (i) Hydrology in the Colorado River Delta; (ii) Riparian ecosystem water use; (iii) Riparian Plant ecophysiology and ecohydrology; and (iv) Methods and models to characterize evapotranspiration. Since Ed was passionate about the dryland delta at the end of the Colorado River, we begin with four research studies that focus on this special region on the U.S.–Mexico border which encompasses four states (Baja and Sonora in Mexico and California and Arizona in United States) as well as tribal communities in the transboundary area. The Colorado River delta reaches the Northern Gulf of California in the Sea of Cortez which has been designated as a UNESCO international biosphere reserve (‘Reserva de la Biosfera El Pinacate y Gran Desierto de Altar’), which includes the Upper Gulf of California and Delta of the Colorado River (‘Reserva de la Biosfera Alto Golfo de California y Delta del Río Colorado’). Ed spent the majority of his last three decades on water balance studies and on ground-based transpiration quantification for validation of satellite and airborne remote sensing methods. We wrap up the special issue with contributions related to improving satellite and airborne remote sensing estimation of actual evapotranspiration. It is our pleasure to summarize the 16 research studies contributed to the special issue to honour Ed Glenn's research interests.     

The effects of Hurricane Irene and Tropical Storm Lee on the bed sediment geochemistry of U.S. Atlantic coastal rivers

Hurricane Irene and Tropical Storm Lee, both of which made landfall in the U.S. between late August and early September 2011, generated record or near record water discharges in 41 coastal rivers between the North Carolina/South Carolina border and the U.S./Canadian border. Despite the discharge of substantial amounts of suspended sediment from many of these rivers, as well as the probable influx of substantial amounts of eroded material from the surrounding basins, the geochemical effects on the <63‐µm fractions of the bed sediments appear relatively limited [<20% of the constituents determined (256 out of 1394)]. Based on surface area measurements, this lack of change occurred despite substantial alterations in both the grain size distribution and the composition of the bed sediments. The sediment‐associated constituents which display both concentration increases and decreases include: total sulfur (TS), Hg, Ag, total organic carbon (TOC), total nitrogen (TN), Zn, Se, Co, Cu, Pb, As, Cr, and total carbon (TC). As a group, these constituents tend to be associated either with urbanization/elevated population densities and/or wastewater/solid sludge. The limited number of significant sediment‐associated chemical changes that were detected probably resulted from two potential processes: (1) the flushing of in‐stream land‐use affected sediments that were replaced by baseline material more representative of local geology and/or soils (declining concentrations), and/or (2) the inclusion of more heavily affected material as a result of urban nonpoint‐source runoff and/or releases from flooded treatment facilities (increasing concentrations). Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Complexities in Hindcasting Models—When Should We Say Enough Is Enough?

Groundwater models are routinely used in hindcasting applications to predict the past concentration levels in contaminated aquifers. These predictions are used in risk assessment and epidemiological studies, which are often completed either for resolving a court case or for developing a public‐policy solution. Hindcast groundwater modeling studies utilize a variety of computer tools with complexity levels ranging from simple analytical models to detailed three‐dimensional, multiphase, multispecies, reactive transport models. The aim of this study is to explore the value of using complex reactive transport models in hindcasting studies that have limited historic data. I review a chlorinated solvent exposure problem that occurred at a U.S. Marine Corp Base in Camp Lejeune, North Carolina and use it as an example to discuss the limits of hindcasting modeling exercises. The lessons learned from the study are used to reflect upon the following questions related to model complexity: How should we decide how much is enough? Who should decide when enough is enough?     

A graphical approach for documenting peatland hydrodiversity and orienting land management strategies

This study focuses on the development of an approach to document the hydrological characteristics of peatlands and understand their potential influence on runoff processes and groundwater flow dynamics. Spatial calculations were performed using geographic information systems data in order to evaluate the distribution of peatlands according to (a) neighbouring hydrogeological units and (b) their position within the hydrographic network. The data obtained from these calculations were plotted in a multiple trilinear diagram (two ternary plots projected into a diamond‐shaped diagram) that illustrates the position of a given peatland within the hydrogeological environment. The data allow for the segregation of peatlands according to groups sharing similarities as well as the identification of peatlands that are most likely to have similar hydrological functions. The approach was tested in a 19,549 km² region of the southern portion of the Barlow‐Ojibway Clay Belt (in Abitibi‐Témiscamingue, Canada) and lead to a conceptual model representing the hydrological interactions between peatlands, aquifers, and surface waters. This approach allows for a geographic information systems‐based differentiation of headwater peatland complexes that are likely to interact with aquifers and to supply continuous baseflow to small streams from lowland peatland complexes of the clay plain that are isolated from surrounding aquifers but that can act as storage reservoirs within the hydrographic network. The typology is further used to discuss land management strategies aimed at preserving peatland hydrodiversity within the study region. The proposed approach relies on widely applicable hydrogeological and hydrographic criteria and provides a tool that could be used for assessing peatland hydrodiversity in other regions of the planet.     

Arsenic Geochemistry and Hydrostratigraphy in Midwestern U.S. Glacial Deposits

Arsenic concentrations exceeding the U.S. EPA's 10 μg/L standard are common in glacial aquifers in the midwestern United States. Previous studies have indicated that arsenic occurs naturally in these aquifers in association with metal-(hydr)oxides and is released to groundwater under reducing conditions generated by microbial oxidation of organic matter. Despite this delineation of the arsenic source and mechanism of arsenic mobilization, identification of arsenic-impacted aquifers is hindered by the heterogeneous and discontinuous nature of glacial sediments. In much of the Midwest, the hydrostratigraphy of glacial deposits is not sufficiently characterized to predict where elevated arsenic concentrations are likely to occur. This case study from southeast Wisconsin presents a detailed characterization of local stratigraphy, hydrostratigraphy, and geochemistry of the Pleistocene glacial deposits and underlying Silurian dolomite. Analyses of a single core, water chemistry data, and well construction reports enabled identification of two aquifers separated by an organic-rich aquitard. The upper, unconfined aquifer provides potable water, whereas arsenic generally exceeds 10 μg/L in the deeper aquifer. Although coring and detailed hydrostratigraphic characterization are often considered impractical, our results demonstrate that a single core improved interpretation of the complex lithology and hydrostratigraphy. This detailed characterization of hydrostratigraphy facilitated development of well construction guidelines and lays the ground work for further studies of the complex interactions among aquifer sediments, hydrogeology, water chemistry, and microbiology that lead to elevated arsenic in groundwater.     

River flood seasonality in the Northeast United States: Characterization and trends

The New England and Mid‐Atlantic regions of the Northeast United States have experienced climate‐induced increases in both the magnitude and frequency of floods. However, a detailed understanding of flood seasonality across these regions, and how flood seasonality may have changed over the instrumental record, has not been established. The annual timing of river floods reflects the flood‐generating mechanisms operating in a basin, and many aquatic and riparian organisms are adapted to flood seasonality, as are human uses of river channels and flood plains. Changes in flood seasonality may indicate changes in flood‐generating mechanisms, and their interactions, with important implications for habitats, flood plain infrastructure, and human communities. I applied a probabilistic method for identifying flood seasons at a monthly resolution for 90 Northeast U.S. watersheds with natural, or near‐natural, flood‐generating conditions. Historical trends in flood seasonality were also investigated. Analyses were based on peaks‐over‐threshold flood records that have, on average, 85 years of data and three peaks per year—thus providing more information about flood seasonality than annual maximums. The results show rich detail about annual flood timing across the region with each site having a unique pattern of monthly flood occurrence. However, a much smaller number of dominant seasonal patterns emerged when contiguous flood‐rich months were classified into commonly recognized seasons (e.g., Mar–May, spring). The dominant seasonal patterns identified by manual classification were corroborated by unsupervised classification methods (i.e., cluster analyses). Trend analyses indicated that the annual timing of flood‐rich seasons has generally not shifted over the period of record, but 65 sites with data from 1941 to 2013 revealed increased numbers of June–October floods—a trend driving previously documented increases in Northeast U.S. flood counts per year. These months have been historically flood‐poor at the sites examined, so warm‐season flood potential has increased with possible implications for aquatic and riparian organisms.     

How preferential flow delivers pre‐event groundwater rapidly to streams

Groundwater often accounts for a substantial fraction of flood hydrographs, but the processes responsible for this have been unclear. However, many aquifers have preferential flow and this explains how aquifers can be so responsive. In bedrock aquifers, weathering enhances the connectivity and apertures along the most efficient flow paths and hence enhances the permeability. This results in celerities and velocities of the preferential flow in these dual‐porosity aquifers that are two to three orders of magnitude higher than if the aquifers behaved as single‐porosity media. The celerities have been determined from artificial and natural flood pulses, from tidal lags, and from pumping tests. Preferential‐flow velocities have been calculated from tests using applied tracers. Celerities in bedrock aquifers are typically one to two orders of magnitude faster than velocities. The ubiquitous preferential flow in aquifers provides an additional explanation, besides groundwater ridging, for the rapid release of groundwater to streams during storm events.     

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south‐central New York. All samples were collected ?1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [⁴He], thermogenic [CH₄], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon‐rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.     

Boundary depletion rate and drawdown in leaky wedge‐shaped aquifers

This study presents analytical solutions of the three‐dimensional groundwater flow to a well in leaky confined and leaky water table wedge‐shaped aquifers. Leaky wedge‐shaped aquifers with and without storage in the aquitard are considered, and both transient and steady‐state drawdown solutions are derived. Unlike the previous solutions of the wedge‐shaped aquifers, the leakages from aquitard are considered in these solutions and unlike similar previous work for leaky aquifers, leakage from aquitards and from the water table are treated as the lower and upper boundary conditions. A special form of finite Fourier transforms is used to transform the z‐coordinate in deriving the solutions. The leakage induced by a partially penetrating pumping well in a wedge‐shaped aquifer depends on aquitard hydraulic parameters, the wedge‐shaped aquifer parameters, as well as the pumping well parameters. We calculate lateral boundary dimensionless flux at a representative line and investigate its sensitivity to the aquitard hydraulic parameters. We also investigate the effects of wedge angle, partial penetration, screen location and piezometer location on the steady‐state dimensionless drawdown for different leakage parameters. Results of our study are presented in the form of dimensionless flux‐dimensionless time and dimensionless drawdown‐leakage parameter type curves. The results are useful for evaluating the relative role of lateral wedge boundaries and leakage source on flow in wedge‐shaped aquifers. This is very useful for water management problems and for assessing groundwater pollution. The presented analytical solutions can also be used in parameter identification and in calculating stream depletion rate and volume. Copyright © 2011 John Wiley & Sons, Ltd.     

Potassium, uranium, thorium radiogenic heat contribution to heat flow in the precambrian and younger silicic rocks of the Zuni and Florida mountains, New Mexico (U.S.A.)

High heat flow in the Zuni Mountains, New Mexico, U.S.A., has been explained by the possible presence of a buried felsic pluton. Alternately, high K, U, Th abundances have been proposed to account for part of the high heat flow. The mean radiogenic heat contribution for 60 samples of Precambrian core rocks is 7.23 μcal/gm-yr, which is slightly higher than the average for western U.S.A. granitic rocks and significantly higher than the average for continental “crust”; hence, the K, U, Th radiogenic contribution from Precambrian rocks to the overall heat flow is significant. Radiogenic K, U, Th heat for 32 samples for the Florida Mountains, New Mexico, U.S.A., yields a lower mean of 5.46 μcal/gm-yr. This value is somewhat anomalous in that the predominantly syenitic rocks commonly yield higher values. Furthermore, heat flow is higher in areas distant from the Floridas and the radiogenic heat contribution is considered small.