Deep Flow System Research Articles

Identification of near-surface saline water in the Lake Kelemenszék area, Danube-Tisza Interfluve, Hungary

In the Danube Valley, a chain of saline lakes and a salinized area are situated in the discharge zone of two different waters. The two watertype were followed till the near surface by regional chemical and hydraulic investigations (Mádlné Szőnyi and Tóth 2009). The goals of this study were to prove the presence of these different waters in the near surface zone around the Lake Kelemenszék, and allocate their connection to the lake and to the salinized ground surface. Near-surface geophysical measurements (VES, RMT) supported the regional hydraulic and chemical results. The sediments are saturated by saline water down to 110 m beneath the lake, and to the east the fresh water is prevalent. The local chemical investigations strengthened this distribution. Highly saline water with Na-HCO3-Cl-type discharges into and around the lake. To the east there is a continuous change towards a (Ca,Mg)-(HCO3)2-type fresh water discharge. The interface between the two water types is a 2–3 km wide transition zone. The results of the investigations proved that the saline water of the deep flow system rises to the surface and provide salt for the salinization of the area.

Salt tectonics and shallow subseafloor fluid convection: models of coupled fluid‐heat‐salt transport

AbstractThermohaline convection associated with salt domes has the potential to drive significant fluid flow and mass and heat transport in continental margins, but previous studies of fluid flow associated with salt structures have focused on continental settings or deep flow systems of importance to petroleum exploration. Motivated by recent geophysical and geochemical observations that suggest a convective pattern to near‐seafloor pore fluid flow in the northern Gulf of Mexico (GoMex), we devise numerical models that fully couple thermal and chemical processes to quantify the effects of salt geometry and seafloor relief on fluid flow beneath the seafloor. Steady‐state models that ignore halite dissolution demonstrate that seafloor relief plays an important role in the evolution of shallow geothermal convection cells and that salt at depth can contribute a thermal component to this convection. The inclusion of faults causes significant, but highly localized, increases in flow rates at seafloor discharge zones. Transient models that include halite dissolution show the evolution of flow during brine formation from early salt‐driven convection to later geothermal convection, characteristics of which are controlled by the interplay of seafloor relief and salt geometry. Predicted flow rates are on the order of a few millimeters per year or less for homogeneous sediments with a permeability of 10−15 m2, comparable to compaction‐driven flow rates. Sediment permeabilities likely fall below 10−15 m2 at depth in the GoMex basin, but such thermohaline convection can drive pervasive mass transport across the seafloor, affecting sediment diagenesis in shallow sediments. In more permeable settings, such flow could affect methane hydrate stability, seafloor chemosynthetic communities, and the longevity of fluid seeps.

Flow and grain size control of depth‐independent simple subaqueous dunes

In the Grådyb tidal inlet (Danish Wadden Sea) simple medium to large dunes, which are superimposed on large to very large dunes, increase in size with decreasing grain size under quasi‐constant ebb dominated mean flow conditions. The mean height of the superimposed dunes increases from 0.1 m to 0.5 m and the mean dune length from 7 m to 12 m. This happens over a distance of 1.5 km from the inner to the outer part where mean depth (12 m) and the dominant ebb current (1.0 m s−1) remain constant. Over this reach, the grain size changes from 0.6 mm in the inner part to 0.3 mm in the outer part. As the water depth is constant and more than 1 order of magnitude larger than the height of the dunes, these are regarded as being depth‐independent. Relationships between dune dimensions and grain size established in previous studies are transformed into more general statements, bed form dimensions being directly related to the form‐corrected Shields parameter (θ′). In this way, dune dimensions and flow strength/grain size have, for the first time, been directly related to both bed load and free stream velocity in deeper flow systems. The former relationship is based on a recalibrated (form migration) version of the Meyer‐Peter and Müller bed load formula. Four diagrams describing flow conditions and dune migration rates as a function of grain size and dune length are presented.

Environmental Isotopes as Indicators for Ground Water Recharge to Fractured Granite

To assess the contribution of accumulated winter precipitation and glacial meltwater to the recharge of deep ground water flow systems in fracture crystalline rocks, measurements of environmental isotope ratios, hydrochemical composition, and in situ parameters of ground water were performed in a deep tunnel. The measurements demonstrate the significance of these ground water recharge components for deep ground water flow systems in fractured granites of a high alpine catchment in the Central Alps, Switzerland. Hydrochemical and in situ parameters, as well as delta(18)O in ground water samples collected in the tunnel, show only small temporal variations. The precipitation record of delta(18)O shows seasonal variations of approximately 14% and a decrease of 0.23% +/- 0.03% per 100 m elevation gain. delta(2)H and delta(18)O in precipitation are well correlated and plot close to the meteoric water line, as well as delta(2)H and delta(18)O in ground water samples, reflecting the meteoric origin of the latter. The depletion of 18O in ground water compared to 18O content in precipitation during the ground water recharge period indicates significant contributions from accumulated depleted winter precipitation to ground water recharge. The hydrochemical composition of the encountered ground water, Na-Ca-HCO3-SO4(-F), reflects an evolution of the ground water along the flowpath through the granite body. Observed tritium concentrations in ground water range from 2.6 to 16.6 TU, with the lowest values associated with a local negative temperature anomaly and anomalous depleted 18O in ground water. This demonstrates the effect of local ground water recharge from meltwater of submodern glacial ice. Such localized recharge from glaciated areas occurs along preferential flowpaths within the granite body that are mainly controlled by observed hydraulic active shear fractures and cataclastic faults.

Evolution of Qinling Mianlue Belt: Evidence from Sedimentology and Tectonics of the Northern Yangtze, China

Evolution of Qinling Mianlue Belt: Evidence from Sedimentology and Tectonics of the Northern Yangtze, China

The role of subsurface runoff through bedrock on storm flow generation

AbstractThe influence of bedrock subsurface flow on storm runoff generation was investigated in Japan in two regions in Japan underlain by three bedrock types. One region, with approximately 2500 m of relief, is located in the Japan Alps, central Japan (In a region), where six small forest‐covered watersheds underlain by granite and Mesozoic shale were studied. Two of these watersheds were instrumented to monitor stream discharge and the other four are springs occurring at the bedrock exposure. The other study area is in northern Kyoto prefecture, western Japan (Oe region). Here, spring distribution and seasonal flow were monitored in two steep basins underlain by serpentinite rocks. Distinctly different runoff responses were observed: the granite watershed exhibited a large and rapid runoff peak that coincided with the rainfall peak (type 1); and the shale and serpentinite basins exhibited small initial runoff peaks followed by a maximum peak discharge five to ten times greater with a convex recession limb (type 2). Runoff response from bedrock springs had characteristics similar to type 1 hydrographs; however, discharge increased only when the antecedent precipitation index was large and the runoff peak was delayed between 10 h and 1 week after rain events. The specific discharge of the springs decreased with increase in altitude in the Oe region, especially in dry periods. This decline in discharge with elevation suggests that a deep subsurface flow system through bedrock fissures contributes to the storm water flow in serpentinate basins. When comparing runoff response and spring discharge, slow or double peak runoff response may be a good indicator of the influence of bedrock subsurface outflow on storm runoff generation in steep mountainous regions. Copyright © 2001 John Wiley & Sons, Ltd.

Isotopic composition and origin of geothermal waters at Caldetes (Maresme—Barcelona)

Several thermal springs occur within the Catalan Coastal Ranges, mainly located along bounding faults of horst–graben systems. Most of the springs are located in the Vallès-Penedès graben, where they correspond to local topography-driven flow systems. The Caldetes thermal water spring cannot be explained easily in these terms. From the chemical and isotopic composition of these waters, a recharge area at an elevation of at least 600m is inferred, most likely in the Montseny massif some 20km NW of Caldetes. We propose a deep flow system with infiltration of meteoric fluids from the Montseny massif. Fluids then pass through tertiary units of the Vallès-Penedès graben and infiltrate faults and fracture zones that are connected to the bounding faults of the Barcelona halfgraben. Fluids finally ascend along these faults and are discharged as thermal waters at Caldetes.

Hydrogeochemistry in two adjacent areas in the Pannonian Basin (Southeast-Hungary)

Groundwaters from the Quaternary, Pliocene and Pontian layers in two adjacent basin areas of Hungary (Szeged and Körös) and from the intermediate basement high, all belonging to the central part of the Pannonian Basin, have been investigated chemically and isotopically. Most of the waters are NaHCO 3 type with significant quantitative and qualitative regional differences for the Szeged and Körös areas, the intermediate high, and the deepest studied lithostratigraphic zone (the base of the Pontian stage). Hydrogen and oxygen isotopes indicate that most of the waters have a paleometeoric origin. The period of infiltration for the entire studied depth interval (75–2500 m) was within the last cold period in the Szeged and intermediate areas, and during a preceding warmer period in the Körös area. Over the entire studied region, waters in the deepest lithostratigraphic position are mixtures of paleometeoric waters and deep waters squeezed out from the thick sequence of fine-grained (Pannonian) sediments that underlie the Pontian thermal water aquifer. In the Szeged and intermediate areas, the effect of the upward seepage from the deeper (Pannonian) layers was overprinted by the recharge in the last cold period. In the Körös area, due to the lack of infiltration during the last cold period, the mixing with Pannonian waters is seen up to a depth of 1000 m. Based on 87 Sr/ 86 Sr ratios, water flow systems were separated. In the Szeged and intermediate areas, a shallower and a deeper flow systems were distinguished, one in the Pleistocene and Pliocene formations, and another in the Pontian layers. In the Körös area, most of the waters belong to the same flow system that occupies the depth interval from the base of the Pontian (about 2500 m) up to 1000 m. The two shallowest samples studied (above a depth of 1000 m) show lower 87 Sr/ 86 Sr ratios.

Isotope hydrology of southern Nevada groundwater: Stable isotopes and radiocarbon

A new δ18O map of southern Nevada groundwater shows a systematic decrease in δ18O of ∼5‰ from 36° to 39°N latitude. The variation is consistent with higher‐latitude recharge following continuous flow paths along north‐south trending graben valleys and systematically increasing in δ18O due to mixing with lower‐latitude, higher‐δ18O recharge. The data do not suggest that large masses of groundwater with unusually low δ18O values were recharged during the last pluvial period as suggested by previous workers. Many δ18O‐δD pairs in groundwater indicate variable amounts of evaporation relative to the global meteoric water line. The precipitation rate and type (rain versus snow) for a given geographic area controls the extent of evaporation. A “model” δ18O value was calculated from evaporated groundwaters by subtracting postcloud evaporation. The distribution of these model δ18O values suggest new regional groundwater flow paths previously undocumented. Dissolved inorganic carbon in groundwaters collected from deep regional flow systems typically has low 14C concentrations (≤12% modern carbon). In contrast, groundwaters collected from the carbonate rock of the Spring Mountains and alluvium of Forty Mile Canyon have higher 14C contents, indicating more recent recharge. Because of nonlinear mixing of 14C, groundwater in the regional flow system likely acquired most of its observable 14C from mixtures of young, locally recharged groundwater.

Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams

Groundwater and stream water data collected at three headwater catchments in the Neversink River watershed indicate that base flow is sustained by groundwater from two sources: a shallow flow system within the till and soil and a deep flow system within bedrock fractures and bedding planes that discharges as perennial springs. Data from eight wells finished near the till/bedrock interface indicate that saturated conditions are not maintained in the shallow flow system during most summers. In contrast, the discharge of a perennial spring remained constant during two summer rainstorms, providing evidence that the deep flow system is disconnected from the shallow flow system in summer. Discharge from perennial springs was the principal source of streamflow in a headwater reach during low flow. Mean NO3− concentrations were 20–25 μmol L−1 in five perennial springs during the summer but only 5–10 μmol L−1 in shallow groundwater. Thus the deep flow system does not reflect typical NO3− concentrations in the soil during summer. A hydrologic budget at a headwater drainage reveals that March and late fall are the principal groundwater recharge periods. Residence time modeling based on analyses of 18O and 35S indicates that groundwater in the deep flow system is 6–22 months old. These data indicate that summer base flow largely originates from previous dormant seasons when available soil NO3− is greater. In these Catskill watersheds, high base flow concentrations of NO3− during summer do not provide sufficient evidence that the atmospheric N deposition rate exceeds the demand of terrestrial vegetation.

Zonation hydrogéochimique verticale dans l'aquifère karstique du Cid (Alicante, Espagne)

Study of hydrochemical data, conductivity and temperature logs and the samples taken at different depths reveals a marked hydrogeochemical vertical zonality in the Cid karst aquifer. Most saline waters lie in the deepest parts of the aquifer, while those of lowest mineralization occupy the areas of the saturated zone closest to the surface. The hydrodynamic system thus formed is considered to be influenced by two flows: a more superficial one, presenting a lower level of water mineralization; and a deep flow system in which the water, due to contact with Triassic evaporitic materials, experiences a considerable increase in mineralization.

Variable‐density flow in the midcontinent basins and arches region of the United States

Basins in the midcontinent basins and arches region of the United States are typical of many sedimentary basins containing a diverse assemblage of lithologies that have been deformed at various stages in their geologic history and now transmit fluids of varying density. On the basis of the synthesis of geologic data from more than 500 wells, specific‐gravity data from more than 1800 samples, fluid‐pressure data from nearly 40 deep wells, and hydraulic‐conductivity data from core analyses of more than 35 wells, the midcontinent basins and arches region is conceptualized as a layered, heterogeneous, hydrologically mature region containing 11 hydrostratigraphic units that have undergone various periods of deformation and comprise a sequence of aquifers and confining layers with fluid‐density variations ranging from freshwater to brine. An interpretative, threedimensional, steady state, variable‐density, finite difference flow model was constructed to organize the field data and to evaluate various controls on regional flow patterns. Simulation results indicate that flow directions in the shallow hydrostratigraphic units are controlled by local surface elevations. The deeper flow systems, however, show the influence of regional structural features, such as the Cincinnati Arch, that control the locations of regional groundwater divides. The amount of downward cross‐formational flow into the older hydrostratigraphic units is greatest along the area of the Cincinnati and Findlay Arches where the Mt. Simon Sandstone is relatively shallow and fracturing and faulting are more common. Spatial variations in fluid density are a significant influence on vertical cross‐formational flow in regions where salt‐bearing units are present.

Study of the microbial dynamics in the root environment of closed, hydroponic cultivation systems for tomato using phospholipid fatty acid profiles.

A more basic understanding of the microbial dynamics of closed, hydroponic cultivation systems is needed. We therefore initiated a study of the microbial community inhabiting the root environment, using phospholipid fatty acid (PLFA) profiles, and started to examine whether changes in the microbial population structure would result from the introduction of selected isolates of plant growth-promoting rhizobacteria (PGPR). Tomato were cultured in deep-flow systems with circulating nutrient solution. Bacteria were sampled from tomato roots at three locations, longitudinally, in the gutters of a control system and in two systems inoculated with PGPR. In the beginning of the gutters the PLFA profiles were similar in all systems, whereas the profiles differed in the gutter ends (following the direction of flow). In the control system, and in a treatment inoculated with two Gram-negative and one Gram-positive PGPR strain, the relative proportion of PLFAs characteristic to Gram-positive bacteria was highest at the end of the gutter. In a treatment inoculated only with a Gram-negative PGPR strain, the relative proportion of PLFAs characteristic of Gram-negative bacteria was highest at the end of the gutter. The results indicate a complex situation with different micro-environments distributed along the root mat. It can also be concluded that PLFA profiles may be useful tools in the study of the microbiology of closed hydroponic plant cultivation systems.

Importance of the vertical component of groundwater flow: a hydrogeochemical approach in the valley of San Luis Potosi, Mexico

Fractured volcanics exert a control on groundwater flow in the San Luis Potosi (SLP) valley. The chemical composition and temperature of water pumped from boreholes partially penetrating the fractured volcanics indicate that the produced water originates from an upward vertical flow. Most of the thermal groundwater has been detected in areas related to regional faults and lineaments. Intensive and uncontrolled pumping from the upper 1 4 of the aquifer (total depth > 1500 m) causes the rise of water from a deep regional flow system that mixes with the shallower waters. The deep waters contain high fluoride concentrations that contaminate the mixture and cause substantial health related effects. The recharge controls on the regional flow system require further research; however, hydrogeochemical evidence supports the view that the origin of this recharge is limited to the western bounding Sierra Madre Occidental. Higher levels of dissolved Na +, Li +, F − (and SO 4 −2) derived from Tertiary volcanics have been introduced into the exploited region; the concentrations indicate lengthy and deep circulation flow. Li + concentration was used as an indicator of groundwater residence time, and therefore of the length of the groundwater flow path. Hydrogeochemical interpretation indicates the presence of three flow systems: a shallow local one controlled by a clay layer that subcrops most of the valley floor, an intermediate system in which water infiltrates just beyond the boundary of the clay layer, and a deep regional system which originates outside the surface catchment. The local and intermediate systems circulate through materials with comparatively low hydraulic conductivity. Low Cl − concentrations suggest rapid flow in the regional system. Concentrations of Li + and F − can be used to calculate percentages of waters in mixtures of regional and intermediate flows. Concentrations of Na +, Ca 2+ and SO 4 −2 appear to be controlled by water-rock reactions. Uncontrolled pumping increases will tend to enhance fluoride concentration and its undesirable effects. Lack of management of aquifers in basins similar to the SLP valley can result in groundwater contamination, not only from surface anthropogenic sources, but also from natural water-rock interactions.

Ground‐Water Quality and Flow in a Shallow Glaciofluvial Aquifer Impacted by Agricultural Contamination

AbstractThe Prairie Ronde fan, a discrete glaciofluvial deposit in southwestern Michigan, contains a productive but highly vulnerable unconfined aquifer used for irrigation, municipal, and domestic supply. A comprehensive hydrogeological study of the aquifer delineated shallow, local flow systems that interact with ponds and wetlands on the fan surface, overlying a deeper intermediate/regional flow system extending to the base of the glacial drift. Ground water within the shallow flow systems contains tritium concentrations indicative of a post‐bomb age and is heavily impacted by nonpoint source contamination. Nitrate commonly exceeds drinking water standards in the shallow flow system. Although no continuous physical barrier separates the two flow systems, the deeper flow system is generally lacking in tritium as well as nonpoint source contaminants derived from surface land uses. High capacity pumping from the deeper flow system, however, will likely draw contaminants downward from the shallow flow system.Background‐water quality in the aquifer is controlled by equilibrium with calcite and slight undersaturation with respect to dolomite. No spatial trends in major ions were observed, suggesting that carbonate mineral equilibrium is achieved rapidly in the vadose zone and further chemical evolution along ground‐water flow paths is minimal. Iron concentrations are highly variable in the aquifer and not correlated with depth. Recharge from lakes and wetlands is a significant cause of elevated iron concentrations in the shallow flow systems.

Fracture detection and groundwater flow characterization using He and Rn in soil gases, Manitoba, Canada

Surveys of the distribution and migration of He and Rn were carried out in the well-characterized granitic terrane of the AECL Underground Research Laboratory (URL), Manitoba as part of a joint AECL Research, United Kingdom Department of the Environment, and United States Department of Energy research initiative. The investigations were designed to determine whether concentrations of He and Rn in soil gases could be used to identify locations of groundwater recharge and discharge from bedrock fractures. The results obtained indicate that subsurface transport of He and possibly Rn in this setting appears to be controlled largely by the groundwater flow system in the bedrock. Release of dissolved gases near the ground surface causes soil gas anomalies, which reflect discharge from the deeper flow system. In the recharge area of the deep groundwater flow system at the URL site, He abundances are close to the atmospheric level, but the discharge area of the deep flow system is characterized by significant He anomalies (up to 0.5 ppm above atmosphere levels). For Rn, the recharge area has broadly distributed high concentrations, probably caused by local Rn production in U-rich overburden, while the discharge area has only localized concentrations of Rn, which are not at the same location as the He anomalies. The general nature of the groundwater flow regime in both areas is reflected in the presence and distribution of the soil gas anomalies. In addition, major fractures in bedrock, which act as preferential groundwater flow paths, have been located from soil gas anomalies, even when obscured by overburden of variable thickness and character. The distribution of He in soil gas appears to be most representative of groundwater recharge and discharge conditions in the granitic rock, while Rn may be useful for locating specific channels where more rapid groundwater discharge is occurring from deep fracture zones.

Deep Burial Dolomitization Driven by Plate Collision: Evidence from Strontium-Isotopes of Jurassic Arab IV Dolomites from Offshore Qatar

The use of strontium-isotope ratios of dolomites to constrain timing and mechanism of diagenesis has been investigated on Jurassic Arab IV dolomites from offshore Qatar. Reservoir quality is determined by two types of dolomites, which were differentiated geochemically (cathodoluminescence, fluid inclusions, and carbon and oxygen stable isotopes): (1) stratigraphically concordant sucrosic dolomites with high porosity formed during early near-surface diagenesis (Jurassic) and (2) stratigraphically discordant cylindrical bodies of massive, porosity-destroying dolomites formed late during deep burial diagenesis (Eocene-Pliocene). Detailed Sr-isotope analysis of dolomites from the Arab IV confirms an Early Jurassic age of the sucrosic, high porosity dolomites ({sup 87}Sr/{sup 86}SR = 0.70707 for NBS 987 = 0.71024) with magnesium and strontium being derived from Jurassic seawater. Late Tertiary compressional orogeny of the Zagros belt to the north is proposed to have caused large-scale squeezing of fluids from the pore system of sedimentary rocks. A regional deep fluid flow system developed dissolving infra-Cambrian evaporites upflow and causing large-scale deep burial dolomitization downflow.

Geothermics and the deep flow-system of the Hungarian Basin

The Hungarian Basin is a large depression. The deep multilayer flow-system of this basin represents a thermal circulation in equilibrium under natural conditions. The terrestrial heat-flow of the basin can be considered balanced, therefore, any geothermal anomaly is of convective origin. Negative geothermal anomaly and low salinity of the water characterize the recharge area and positive anomaly and high salinity the discharge belt. All is proved by geothermal, hydrochemical and hydrodynamic maps of the thermal water aquifer. Deep flow through thick and highly permeable deposits of the main recharge area cause strong negative anomaly and very low salinity. Extreme anomalies are of tectonic origin.

Ground-Water Circulation in the Meade Thrust Allochthon Evaluated by Radiocarbon Techniques

The Meade thrust, in southeastern Idaho, is a major element of the Western Overthrust Belt. The allochthon is of geo-economic importance both as a potential hydrothermal area and as the principal mining area within the Western Phosphate Field. To assist in the development of these two resources, an understanding of the regional ground-water circulation was sought. Geologic and hydrologic data from boreholes in this area are virtually nonexistent. Waterwell development in the area has not occurred because of the abundance of springs and only a few hydrocarbon exploration boreholes have been drilled. Thus, the problem lends itself to evaluation by isotope hydrologic and geochemical methods. Ten springs from within the thrust block and around its periphery were sampled for major ions, 2H/18O, and 14C/13C analysis. Data from these analyses and from field geologic evidence have identified two distinct flow regimes within the Meade thrust allochthon. Shallow flow systems lie above the impermeable Phosphoria Formation, usually within a few hundred meters of the surface. Most of the spring waters from this system are recent and cool. In all cases, they have mean subsurface residence times of less than a few hundred years. The deeper flow systems which lie below the Phosphoria formation are hydraulically isolated from the shallow system. Warm waters from these springs have 14C contents suggesting mean ground-water residence times on the order of 15,000 years. Although these waters could have circulated to as deep as 1900m, 2H/18O results show that high temperatures were never reached. There is no evidence to suggest that water from beneath the Meade thrust has contributed to the circulation in the allochthon.

Utility of Computerized Data Bases of Drill-Stem Test Information in Hydrogeologic Studies: ABSTRACT

The Palo Duro basin, a subbasin of the Permian basin, is being investigated by the Bureau of Economic Geology at The University of Texas at Austin as a potential site for the location of a nuclear waste repository. As the program changes from a regional to a site-specific investigation, it becomes necessary to optimize the expenditure of funds for drilling and testing. Hydrogeologic information is of critical importance in evaluating the long-term stability of a potential repository; consequently, deep multipurpose wells should be drilled in locations that maximize the opportunity to obtain both hydraulic and geochemical data. Prior to our own borehole testing, the only hydrogeologic data available came from petroleum exploration activities, namely, drill-stem test (DST) pressure measurements and brine samples collected with the test. Computer data files of DST information were purchased from commercial sources or obtained directly from operators who had worked in the basin, and the data were merged into a master file. Approximately one thousand tests have been sorted according to geologic formation and lithology. The DST data were then screened and ranked according to their level of confidence based on shut-in pressure characteristics, fluid recoveries, and flowing times. Automatic computer contouring of the selected data produced an unsatisfactory map because of the varied quality of the tests. An objective geostatistical method was subsequently employed to map the regional pressure or hydraulic head distribution in the basin. Geostatistical analysis of the data revealed that a spatial dependency existed which could be modeled by a two-dimensional spherical variogram. The method of kriging was then applied to the data to estimate the regional hydraulic head surface. A chemical equilibrium computer program was used to determine the reaction state of the deep basin flow system, using as input data the chemical composition of the brines collected during drill-stem testing. The program then incrementally added the CO2 lost during collection back into the initial brine composition until it reached the calcite phase boundary. This mass transfer approach results in the computation of the most likely mineral constraints on the brine at measured formation temperatures, pressures, and computed pH conditions. The results of these studies provide interpretations of the regional hydrogeologic processes. Consequently, exploration decisions can be made concerning the location of future test wells to further define the geologic, hydrologic, and geochemical characteristics in this sedimentary basin. End_of_Article - Last_Page 546------------