Brine Seeps Research Articles

3D electromagnetic modelling in frequency domain - studies of underground measurements in a salt mine

In recent years efforts have been made to find underground sites suitable for waste disposals. A potential geological host rock for such a disposal is rock salt, which is used as a natural barrier separating the waste from the environment. To manifest the suitability of the location the geologic structure of the surrounding rock has to be investigated in detail. As only non-destructive methods have to be used to investigate the barrier system, geophysical methods seem to be suitable. Examinations were performed to determine whether the electromagnetic induction method in the frequency domain is a useful tool for such investigations. The measurements were carried out in a salt mine gallery. Brine seeps into it along a few meters of the profile. This marks a big brine reservoir imposing an anomaly on to the data set. Apart from this qualitative interpretation, studies were done to analyze the effect of the gallery, gallery crossings, voluminous brine zones and homogeneous areas. To analyze 3D structures like the gallery or voluminous brine scenarios, a numerical finite-difference modeling code was used. It is shown that in the homogeneous area the data can be interpreted with a full-space model. The influence of gallery crossings can be neglected. The explanation for the data of the anomalous zone lies in the existence of a brine reservoir close to the surface.

Salt Diapirs, Salt Brine Seeps, Pockmarks and Surficial Sediment Creep and Slides in the Canary Channel off NW Africa

Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, < 1km wide, with abrupt terminations and pockmarks associated with these mounds were probably eroded by dense brine and hydrocarbon seeps. The salt brines that eroded the gullies were formed where salt diapirs intersect the seafloor, or in the subsurface by circulating ground water heated by igneous activity along the Canary Ridge. If the brines originated in the subsurface they reached the seafloor along faults. Displacement of the surficial sediments by sliding and creep is probably the result of the expulsion of hydrocarbons and/or vertical motion of the Mesozoic evaporites. Microtopographic features along or near the east flank of the Canary Ridge are the creation of uplift of the ridge, hydrothermal activity, mass wasting processes and turbidity currents.

Evaporites, brines and base metals: Low‐temperature ore emplacement controlled by evaporite diagenesis

Salt beds and salt allochthons are transient features in most sedimentary basins, which through their dissolution can carry, focus and fix base metals. The mineralisation can be subsalt, intrasalt or suprasalt, and the salt body or its breccia can be bedded or halokinetic. In all these evaporite‐associated low‐temperature diagenetic ore deposits there are four common factors that can be used to recognise suitably prepared ground for mineralisation: (i) a dissolving evaporite bed acts either as a supplier of chloride‐rich basinal brines capable of leaching metals, or as a supplier of sulfur and organics that can fix metals; (ii) where the dissolving bed is acting as a supplier of chloride‐rich brines, there is a suitable nearby source of metals that can be leached by these basinal brines (redbeds, thick shales, volcaniclastics, basalts); (iii) there is a stable redox interface where these metalliferous chloride‐rich waters mix with anoxic waters within a pore‐fluid environment that is rich in organics and sulfate/sulfide/H2S; and (iv) there is a salt‐induced focusing mechanism that allows for a stable, long‐term maintenance of the redox front, e.g. the underbelly of the salt bed or allochthon (subsalt deposits), dissolution or halokinetically maintained fault activity in the overburden (suprasalt deposits), or a stratabound intrabed evaporite dissolution front (intrasalt deposits). The diagenetic evaporite ‐ base‐metal association includes world‐class Cu deposits, such as the Kupferschiefer‐style Lubin deposits of Poland and the large accumulations in the Dzhezkazgan region of Kazakhstan. The Lubin deposits are subsalt and occur where long‐term dissolution of salt, in conjunction with upwelling metalliferous basin brines, created a stable redox front, now indicated by the facies of the Rote Faule. The Dzhezkazgan deposits (as well as smaller scale Lisbon Valley style deposits) are suprasalt halokinetic features and formed where a dissolving halite‐dominated salt dome maintained a structural focus to a regional redox interface. Halokinesis and dissolution of the salt bed also drove the subsalt circulation system whereby metalliferous saline brines convectively leached underlying sediments. In both scenarios, the resulting redox‐precipitated sulfides are zoned and arranged in the order Cu, Pb, Zn as one moves away from the zone of salt‐solution supplied brines. This redox zonation can be used as a regional pointer to both mineralisation and, more academically, to the position of a former salt bed. In the fault‐fed suprasalt accumulations the feeder faults were typically created and maintained by the jiggling of brittle overburden blocks atop a moving and dissolving salt unit. A similar mechanism localises many of the caprock replacement haloes seen in the diapiric provinces of the Gulf of Mexico and Northern Africa. Evaporite‐associated Pb–Zn deposits, like Cu deposits, are focused by brine flows associated with both bedded and halokinetic salt units or their residues. Stratabound deposits, such as Gays River and Cadjebut, have formed immediately adjacent to or within the bedded salt body, with the bedded sulfate acting as a sulfur source. In allochthon/diapir deposits the Pb–Zn mineralisation can occur both within a caprock or adjacent to the salt structure as replacements of peridiapiric organic‐rich pyritic sediments. In the latter case the conditions of bottom anoxia that allowed the preservation of pyrite were created by the presence of brine springs and seeps fed from the dissolution of nearby salt sheets and diapirs. The deposits in the peridiapiric group tend to be widespread, but individual deposits tend to be relatively small and many are subeconomic. However, their occurrence indicates an active metal‐cycling mechanism in the basin. Given the right association of salt allochthon, tectonics, source substrate and brine ponding, the system can form much less common but world‐class deposits where base‐metal sulfides replaced pyritic laminites at burial depths ranging from centimetres to kilometres. This set of diagenetic brine‐focusing mechanisms are active today beneath the floor of the Atlantis II Deep and are thought to have their ancient counterparts in some Proterozoic sedex deposits. The position of the allochthon, its lateral continuity, and the type of sediment it overlies controls the size of the accumulation and whether it is Cu or Pb–Zn dominated.

Design and costs for a system to reduce chloride levels in the Red River by shallow-well collection and deep-well disposal

The Red River drains 242000 km2 with 90% of this area being downstream of discharges from naturally occurring brine seeps and springs. The upstream area has been designated as a major chloride emission area in Texas and Oklahoma. Ten major brine source emission areas along the tributaries to the Red River were identified by U.S. Public Health Service and U.S. Army Corps of Engineers. Eight of these areas were deemed suitable for the control of brine emissions by structural methods including a ring dike to enclose brine springs; low flow dams to capture and divert stream flows with high chloride content to evaporation lakes; and shallow aquifer brine collection wells with a deep-well disposal system. Two adjacent emission areas, designated as Areas XIII and XIV, contribute 500 metric tons of salt per day to the Red River. These areas, along Jonah Creek and Salt Creek, tributaries to the Prairie Dog Town Fork of the Red River were selected for investigation to control brine emission by utilization of shallow collection wells and disposal by deep injection wells. Drilling programs and pumping tests were performed to determine the number and location of shallow collection wells. Eighteen wells with 12 operating full time, will be located in the primary emission areas. The collected brine will be conveyed through corrosion-resistant pipelines to a treatment facility for filtration at a rate of 300 l/s. Additional pipelines will convey the filtered brine to deep injection wells for disposal. Nine deep wells will be installed with seven operating full time. Design criteria for the project are 100-year life expectancy and automated operation with minimum supervision and maintenance. The required minimum operating, maintenance and supervision coupled with 100-year life expectancy of the project added significantly to the estimated US $58 million capital cost of the project. However, the reduction in annual cost for labor, repairs and replacement of the component of the system should result in a lower life cycle cost. The estimated annual operating and maintenance cost is US $4.7 million.

The Geochemistry of Hydrothermal Vent Waters from Milos Island, Hellenic Volcanic Arc

The Hellenic Volcanic Arc is a tectonically and volcanically active part of the earth's crust, situated above the subduction zone of the African plate under the Aegean. The arc extends from the Methana peninsula (NE Peloponese) through the greek islands Milos, Santorini, Kos, Nisiros and Yali to the Bodrum peninsula, Turkey (e.g. Fytikas et at., 1986). Hydrothermal venting has been reported from Nisiros, Yali (Varnavas and Cronan, 1991), Santorini (Varnavas and Cronan, 1988) and Milos (Fytikas, 1989). The island of Milos, at the central west part of the volcanic arc, is dominated by volcanic and voIcaniclastic rocks, with the exception of minor occurrences of metamorphic basement rocks and Neogene sediments outcropping at the south part of the island, underneath the volcanics (Fytikas et al., 1986). Submarine and, later, sub-aerial extrusive sequences formed during a prolonged period of volcanic activity (3.5 to 0.1 Ma, Fytikas, 1989). Geochemically, the Milos volcanics show a calcalkaline character and comprise andesites, dacites and ryolites (Fytikas et al., 1986). Hot water springs and fumaroles occur at several localities around the island. In submarine settings, hot fluids exit through the sandy seafloor, often in the form of a mixed liquid/ gas phase; as a result, venting can be located due to the visually impressive presence of streams of gas bubbles. In the most hydrothermally active south-east part of the island (Palaeohori bay), extensive areas of bacteria mats are associated with submarine hydrothermal brine seeps (Fitzsimons et al., 1997). Field observations and sampling

Preliminary observations on biological communities at shallow hydrothermal vents in the Aegean Sea

Abstract Hydrothermal vents, at depths varying from the littoral zone to water depths of 115 m, have been explored around the islands of Milos and Santorini in the Hellenic Volcanic Arc. The biota were surveyed by scuba divers and with a remote operated vehicle as well as by soft-bottom sampling with grabs and corers. No species specific to hydrothermal areas were found at any of the sites investigated. Animals in the immediate vicinity of the vents belonged to opportunistic species, such as the polychaetes Capitella capitata, Microspio sp. and Spio decoratus . The nassariid gastropod Cyclope neritea was the dominant macrofaunal species found in the bacterial mat areas at Milos which overlay hot brine seeps. At all rocky hydrothermal sites deeper than 35 m water depth the echiuran Boniellia cf. viridis was observed. Around the periphery of the seeps the meiofaunal community was dominated by the nematode Onchlaimus camplyoceroides . Few nematodes were found in the centre of the hydrothermal brine areas. At Santorini the bacteria at the venting sites were dominated by iron bacteria, whereas at Milos large globular sulphur bacteria, Achromatium volutans , covered the hydrothermal brine seeps. Unlike deep-sea vents, little of the biomass production was due to symbiotic associations between animals and chemoautolithotrophic bacteria, although a few stilbotnematine nematodes were found at the periphery of the brine seeps at Milos. Macrofaunal biomass reached a maximum of 80 g m −2 around the vents, compared with ≥c 500 g m −2 at hydrothermal vents elsewhere. Much of the bacterial biomass appeared to be exported from the sites.

Sulphide tolerance and adaptation in the California killifish, Fundulus parvipinnis, a salt marsh resident

Hydrogen sulphide is a toxicant naturally produced in hypoxic marine sediments, hydrocarbon and brine seeps and hydrothermal vents. The California killifish, a salt marsh resident, is remarkably tolerant of sulphide. The 50% lethal concentration is 700 μM total sulphide in 96 h, and 5 mM in 8 h (determined in flow‐through, oxygenated sea water). Killifish exposed to sulphide produce thiosulphate which accumulates in the blood. The cytochrome c oxidase (a major site of toxicity) of the killifish is 50% inhibited by &lt;1 μM sulphide. Killifish liver mitochondria are poisoned by 50–75 μM sulphide but can oxidize 10–20 μM sulphide to thiosulphate. Sulphide causes sulphhaemoglobin formation (and impairment of oxygen transport) at 1–5 mM in vitro and to a small extent at 2 mM in vivo. Killifish blood neither catalyses sulphide oxidation significantly nor binds sulphide at environmental (low) sulphide concentrations. Exposure to 200 μM and 700 μM sulphide over several days causes significant increases in lactate concentrations, indicating shift to anaerobic glycolysis. However, individuals with the most lactate die. In terms of diffusible H2S, the killifish can withstand concentrations two to three orders of magnitude greater than would poison cytochrome c oxidase. The high sulphide tolerance of the killifish, particularly of concentrations typical of salt marshes, can be explained chiefly by mitochondrial sulphide oxidation. Sulphide tolerance and mitochondrial sulphide oxidation in the killifish have a constitutive basis, i.e. do not diminish in fish held in the laboratory in sulphide‐free water for 1–2 months, and are improved by prior acclimation.

Sulphide tolerance and adaptation in the California killifish, Fundulus parvipinnis, a salt marsh resident

Hydrogen sulphide is a toxicant naturally produced in hypoxic marine sediments, hydrocarbon and brine seeps and hydrothermal vents. The California killifish, a salt marsh resident, is remarkably tolerant of sulphide. The 50% lethal concentration is 700 μM total sulphide in 96 h, and 5 mM in 8 h (determined in flow-through, oxygenated sea water). Killifish exposed to sulphide produce thiosulphate which accumulates in the blood. The cytochrome c oxidase (a major site of toxicity) of the killifish is 50% inhibited by <1 μM sulphide. Killifish liver mitochondria are poisoned by 50–75 μM sulphide but can oxidize 10–20 μM sulphide to thiosulphate. Sulphide causes sulphhaemoglobin formation (and impairment of oxygen transport) at 1–5 mM in vitro and to a small extent at 2 mM in vivo. Killifish blood neither catalyses sulphide oxidation significantly nor binds sulphide at environmental (low) sulphide concentrations. Exposure to 200 μM and 700 μM sulphide over several days causes significant increases in lactate concentrations, indicating shift to anaerobic glycolysis. However, individuals with the most lactate die. In terms of diffusible H2S, the killifish can withstand concentrations two to three orders of magnitude greater than would poison cytochrome c oxidase. The high sulphide tolerance of the killifish, particularly of concentrations typical of salt marshes, can be explained chiefly by mitochondrial sulphide oxidation. Sulphide tolerance and mitochondrial sulphide oxidation in the killifish have a constitutive basis, i.e. do not diminish in fish held in the laboratory in sulphide-free water for 1–2 months, and are improved by prior acclimation.

Morphological development of the Florida Escarpment: observations on the generation of time transgressive unconformities in carbonate terrains

An unconformity of 100 m.yr magnitude continues to form on the western edge of the Florida-Bahama Platform, near 26°N, where distal Mississippi Fan sediments are progressively burying the Florida Escarpment. Multiple perspectives of the developing unconformity's morphology are revealed using available technologies including GLORIA images of the entire platform's edge, Seabeam bathymetric contours, and Deep-Tow's high resolution side-scan data calibrated with bottom photographs. The structure and stratigraphy of the buried escarpment and the associated unconformity are resolved by airgun, sparker, and Deep-Tow's 4 kHz seismic reflection data; we summarize the morphological data on the exposed part of the unconformity and the sedimentary deposits accumulating in the basin above the unconformity. The exposed cliff face is composed of a staircase of bedding-plane terraces which are developed along joint planes. The terraces extend 100–1000 m along the escarpment's face, and the intervening vertical walls are up to 100 m high. The jointed morphology of this Mesozoic limestone cliff apparently reflects erosional exposure of its interior anatomy rather than its accretionary shape. The change in slope between the platform face and the abyssal plain is very abrupt. In places along the contact between the escarpment and fan sediments, reduced chemical-charged brine seeps occur, which locally cause carbonate dissolution and precipitation, sulfide mineralization, and the deposition of a fossiliferous and organic carbon-rich lens associated with chemosynthetic communities. These seep deposits and escarpment-derived megabreccias intercalate with basinal sediments that overlie the unconformity. Because surface seismic reflection data do not produce images of the escarpment's face that closely reflect the exposed escarpment's morphology, they must also be of limited value in characterizing the surface of similar steeply dipping buried escarpments. Thus, the downslope extent of the heavily eroded platform edge is unclear.

Biogenic methane from abyssal brine seeps at the base of the Florida escarpment

Dissolved methane is present at concentrations exceeding 10mM in the pore waters of sulfidic, salt-brine-enriched sediments underlying chemosynthetic communities at the base of the Florida escarpment. Light hydrocarbon samples were obtained from brine seep sediments by means of an in situ probe and push cores deployed by the deep submersible Alvin. Pore-water methane had a {delta}{sup 13}C value of {minus}83.3 {plus minus}7.0 (Peedee belemnite, N = 17), contained < 1.3% modern carbon, and was enriched over ethane concentrations by 10{sup 3} to 10{sup 5}; these results all indicate a fossil, biogenic carbon source within the Florida platform. Methane-rich brine fluids arriving at seep sites are depleted in dissolved sulfate, although they have been diluted twenty-fold with sulfate-rich seawater during transit. It appears that sulfate reduction and methano-genesis are important processes within the platform.

Results from First Direct Observation and Sampling of a Gulf of Mexico Basin Floor Salt Dome, Green Knoll

ABSTRACT In April 1990 DSV ALVIN, the deep-diving research submersible, was used to investigate the lower continental slope and adjacent basin floor off Louisiana. Green Knoll, a salt diapir with over 400 m relief above the flat-lying Gulf bottom, was a focal point of interest in the dive program. The dome is seaward of the Sigsbee Escarpment in the Walker Ridge lease block area. Seismic profiles run across this feature suggest salt at or near the sea floor. Although salt exposures were not observed, a brine pool and several active seeps were found on the east side near the crest of the dome where seismic data suggested exposure or near exposure of salt. A brine layer 12 feet thick collected in a bowl-shaped depression with steep sides. The feature was interpreted to be the result of a large sediment failure which created a cirque-like depression. Brine seeps originated in the steep walls of this feature presumably near the salt core of the dome. Elevated sodium and chloride levels in the brine suggest an origin related to the dissolution of salt. Downslope transport of brine (salinity to 7.2 higher than normal GOM water) from these seeps created drainage patterns similar to braided streams. These transport pathways were floored by bright red/orange sediments, presumably oxidized iron-rich clays. Sediment evacuation scars, gullies, shattered and deformed sediment masses, vent-like dewatering structures, stress fractures/cracks associated with incipient failures, and exaggerated slopes linked to recent episodes of mass movement were all common features of the dome flank and crest. This family of features emphasizes the importance of mass movement processes to the current configuration of the dome. Hydrocarbon seeps and commonly associated chemosynthetic communities plus authigenic carbonates were not found on top or upper flanks of the dome. End_of_Record - Last_Page 563-------

Old carbon in living organisms and young CaC03 cements from abyssal brine seeps

ABYSSAL brine springs at the base of the Florida Escarpment in the Gulf of Mexico (∼3,280 m, 26° O2' N 84° 55' W) are surrounded by communities of abundant heterotrophic organisms1–4 and carbonate-cemented crusts5. These organisms are apparently supported by local chemosynthetic primary production because the 13C content of their tissues is lower than that found in typical photosynthetically fixed organic carbon6, and the enzymes associated with chemosynthetic metabolism are present in their tissues7,8. Here we report that fossil methane is the dominant source of carbon found in living tissues and recent authigenic carbonate minerals associated with abyssal brine seeps at the base of the Florida Escarpment. Most organic carbon and authigenic carbonates adjacent to the seeps contain progressively less modern carbon as their 13C contents approach that of methane carried in the brine. Incorporation of fossil methane (⩾=1.3% modern carbon) into living tissues and carbonate cements results in recently formed materials which are depleted in 14C. Therefore, 14C cannot be used to indicate the age of authigenic materials produced at the pore-water-seepage environments that speckle the continental margins of the world.

Multiple trophic resources for a chemoautotrophic community at a cold water brine seep at the base of the Florida Escarpment

The biological community that surrounds the hypersaline cold water brine seeps at the base of the Florida Escarpment is dominated by two macrofaunal species: an undescribed bivalve of the family Mytilidac and a vestimentiferan worm, Escarpia laminata. These animals are apparently supported by the chemoautotrophic fixation of carbon via bacterial endosymbionts. Water column and sediment data indicate that high levels of both sulfide and methane are present in surface sediments around the animals but absent from overlying waters. Stable isotopic analyses of pore water indicate that there are two sources of sulfide: the first is geothermal sulfide carried in groundwater leaching from the base of the escarpment, and the second is microbial sulfide produced in situ. The vestimentiferan E. laminata, and the mytilid bivalve (seep mussel) live contiguously but rely on different substrates for chemoautotrophy. Enzyme assays, patterns of elemental sulfur storage and stable isotopic analyses indicate that E. laminata relies on sulfide oxidation and the seep mussel on methane oxidation for growth.

Mussel Periostracum from Deep‐Sea Redox Communities as a Microbial Habitat: The Scalloping Periostracum Borer

Abstract. A complex and highly unusual eukaryotic microorganism was discovered to be penetrating and removing the periostracum of deep‐sea mussels from the Florida Escarpment brine seeps at a depth of 3266 m. These brine seeps support a chemolithoautotrophic redox community similar to those known from Pacific hydrotherma! vents. This microorganism of unknown taxonomic affinity is filamentous and coenocytic, with a simple plasma membrane and no cell wall. It forms prostrate, radiating systems of branched tunnels, 8–15 u.m in diameter. The surface of the tunnels is sculptured by helically organized, scale‐like depressions, which are left as scars in the process of periostracum removal by the organism. Periostracum is removed in discrete pieces (scallops) at the ends of the tunnels. This organism has been found at three Atlantic deep‐sea redox communities, but not in similar communities of the Pacific.

Continental margin brine seeps: their geological consequences : Paull, C.K. and A.C. Neumann, 1987. Geology, geol. Soc. Am., 15(6):545–548

Continental margin brine seeps: their geological consequences : Paull, C.K. and A.C. Neumann, 1987. Geology, geol. Soc. Am., 15(6):545–548

Vent-type taxa in a hydrocarbon seep region on the Louisiana slope

Recent discoveries on the northern Gulf of Mexico continental slope have altered our understanding of biological and chemical processes occurring in the deep ocean. A biological community of hydrothermal vent-type organisms was recently discovered at the base of the Florida Escarpment1, where the fauna are apparently nourished by hydrogen sulphide-rich hypersaline water seeping out onto the sea floor. Dense colonies of deep living chemosynthetic benthic organisms were first discovered during investigations of warm water anomalies along the axis of the Galapagos Rift in the Pacific Ocean in 19772—4, and this first discovery of clusters of clams, tube worms and other filter feeders in the immediate proximity of warm water vents has been followed by the discovery of a number of other hydrothermal vent sites, for example Guaymas Basin, East Pacific Rise at 21° N. The dense population assemblages at these sites are apparently restricted to small areas of the ocean floor where hydrogen sulphide-rich water is escaping from spreading centres, but the Florida Escarpment discovery indicates that these communities can also exist on passive margins. Here we report the discovery of dense biological communities associated with regions of oil and gas seepage on the Louisiana continental slope. These communities of large epi- and infaunal organisms are similar to those associated with the vents of the Pacific and the hypersaline brine seeps of the Florida Escarpment. Carbon isotope analyses suggest that these communities are chemosynthetic and derive their energy from hydrogen sulphide and/or hydrocarbons. Similar communities may be widely distributed on the sea floor in other oil-producing regions of the ocean.

Evaporite dissolution and development of karst features on the rolling plains of the texas panhandle

AbstractMore than 400 dolines, consisting of collapse sinkholes and closed depressions, occur in Hall and Briscoe Counties, Texas. Of these, at least 36 sinkholes and two depressions formed between 1940 and 1972. Collapse sinks are typically circular and range up to 100 m in diameter and 15 m in depth. Closed depressions are irregularly‐shaped, internally‐drained depressions up to 2.4 km in length. Surface fractures up to 1.5 km in length are associated with certain closed depressions.Karst features are forming as a result of intrastratal dissolution of Upper Permian evaporites, primarily halite and secondarily gypsum. Salt dissolution and overburden collapse are evident from geophysical log cross‐sections and occur at depths ranging from 195 to 275 m. Dissolution is progressing down dip and mean dissolution rates for salt beds in the Hall County area range from 0.29 to 7.73 cm/yr.The valley of the Prairie Dog Town Fork of the Red River is an area of ground‐water discharge for flow systems moving eastward from topographically high areas of the Rolling Plains and from the eastern rim of the High Plains. Halite beds in contact with these waters undergo dissolution. Salt springs and brine seeps, some associated with sinkholes and depressions, occur in the discharge area and indicate that dissolution is an ongoing process.

Control of Natural Chloride, Arkansas-Red Rivers

Natural mineral pollution si rendering water unusable in portions of the Arkansas and Red River Basins. Stream flows are high in chloride because of brine springs and seeps emitting directly into major tributaries of the two rivers. Two large reservoirs on the streams are polluted by chlorides to the extent that stored water is unfit for municipal and industrial use. The Corps of Engineers has proposed structural controls for the two river systems. The Great Salt Plains, Oklahoma on the Salt Fork of the Arkansas River, presents an unusual ground-water problem as related to structural measures for control of natural chlorides. Geographical explorations have shown that source of the pollution is in the bedrock. Artesian conditions force the higher concentrated salt brine into the reservoir and the alluvium. The brine has formed a broad expanse of salt flats at the reservoir perimeter of some 30 sq miles. An average of 1,440 tons per day of chloride ions enter the stream through the geological formations and the ground-water system in the area.