Abstract The Chalk is a principal aquifer which provides an important resource in SE England. For two centuries, it allowed the establishment of a thriving watercress-growing industry, indirectly through diverted stream flow and directly through the drilling of flowing artesian boreholes. The distribution of artesian boreholes across different catchments, suggests a regional control of vertical groundwater flow within the New Pit and Lewes Chalk units. Interrogation of location-specific information points to the confining role of a few key marls within the New Pit Chalk Formation, which can be traced up-catchment to where they naturally outcrop or have been exposed by quarrying. Evidence is found in geophysical logging of a number of boreholes across catchments, confirming a consistent pattern of the spatial distribution of such key markers. When tectonic stress was applied to the various Chalk formations, the marl bands would have reacted, producing more plastic deformation and less fractures in comparison with rigid rock strata. Such a scenario would have created the conditions for secondary aquifer units, giving the Chalk confining or semi-confining hydraulic characteristics on a regional scale. This conceptual understanding helps explain why the river flow response to reductions in groundwater abstraction varies across the flow duration curve.

ABSTRACT The Edwards (Balcones Fault Zone) Aquifer is structurally controlled by the system of normal faults following the Balcones Escarpment, with major domains, including contributing, recharge (unconfined), and artesian (confined) zones, dictated by the large-displacement (50 m to >250 m throw) normal faults and depth of erosion. Faults and extension fractures, in many cases enhanced by dissolution, localize recharge and flow within the Balcones fault zone and into the subsurface of the artesian zone. Juxtaposition of the Edwards with other aquifers provides avenues for interaquifer communication, while juxtaposition against impermeable layers and concentration of clay and mineralization along faults locally produce fault seals for compartmentalization and confinement. Fault block deformation, including small faults and extension fractures, leads to aquifer permeability anisotropy. Faults also locally provide natural pathways for groundwater discharge through springs above the confined (artesian) zone. Although the importance of joints and faults in the Edwards (Balcones Fault Zone) Aquifer system is recognized, there has not been a systematic analysis of the meter-scale structures in the Edwards and associated confining units and their influence on groundwater flow. Here, we review evidence from several key areas showing that an analysis of faults and fractures in the Edwards (Balcones Fault Zone) Aquifer and associated aquifers and confining units is needed to characterize structural fabrics and assess the permeability architecture critical for the next generation of groundwater modeling of the aquifer.

ABSTRACT The Edwards Aquifer supports an important ecosystem with rarely seen faunas that have unique adaptations to a dark and thermally stable environment. We tallied over 60 species of aquifer-adapted (stygobitic) species in the Edwards Aquifer, and 30 more in other Texas aquifers, including snails, flatworms, worms, crustaceans, mites, and beetles. Exploration and research continue, with nine new species described in the last two years. Vertebrate species include Eurycea salamanders and ictalurid catfish, including a blind species ( Prietella phreatophila ) recorded for the first time in the United States from the Edwards–Trinity Plateau Aquifer in 2016. Contributing to the stygobite diversity are ten state or federally listed species, including the Texas blind salamander ( Eurycea rathbuni ), which was one of the first species to be listed as endangered by the U.S. Fish and Wildlife Service (USFWS) in 1970. Major springs of the Edwards (Balcones fault zone), Edwards–Trinity Plateau, Trinity, and other aquifers are under constant threat of drying due to aquifer overdraft and climate change. These springs provide habitat for 26 state or federally listed spring-adapted species. Aquifer species in general are known to provide ecosystem services, including water purification, nutrient cycling, and biological indication; however, the function and biology of these species in central Texas have not been studied. Considering the Edwards Aquifer ranks among the top aquifers in the world for number of species, the gaps in understanding remain enormous.

ABSTRACT The Edwards (Balcones Fault Zone) Aquifer is a high-yield aquifer that provides water for municipal, military, irrigation, domestic, and livestock uses in south-central Texas, and it discharges to several springs that support groundwater ecosystems. Natural water cycling in the Edwards (Balcones Fault Zone) Aquifer is driven by recharge, which depends on precipitation and runoff over the catchment area and recharge zone of the aquifer. This chapter analyzes the water fluxes in the Edwards (Balcones Fault Zone) Aquifer and how they vary with climatic variability and might vary with modern-age climatic change. This work also evaluates the safe yield of the Edwards (Balcones Fault Zone) Aquifer under historic climatic conditions, which is ~400 thousand acre · feet, or 493 × 10 6 m 3 , annually. These results have implications for aquifer groundwater extraction and human and environmental water requirements, such that future groundwater extraction must be adaptive to precipitation and recharge fluctuations to preserve groundwater ecosystems.

ABSTRACT The San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer of south-central Texas is one of the most important and prolific karst aquifers in the United States. Extending from Kinney County (west) to Hays County (northeast), it is the primary source of water for the municipal and agricultural communities surrounding the greater San Antonio area. Deposited in Early Cretaceous time, rocks of the Edwards Group vary from 150 to 300 m thick and include eight members with highly variable hydraulic attributes and solubility. Its complex tectonic, weathering, and geologic history has allowed dissolution of the highly soluble members to form a highly transmissive karst aquifer. Regionally, the Balcones fault zone provides pathways that allow captured streams to flow into the aquifer in the contributing and recharge zones. Karstification of the aquifer has occurred by multiple processes, both epigenic and hypogenic, with visual documentation obvious in numerous caves of the area. Currently, overprinting of hypogenic systems by epigenic systems is common. The en echelon down-to-the-south faulting of the Balcones fault zone has resulted in deep burial of the aquifer in the artesian zone, with dissolution at depth driven by numerous processes, including infiltration of chemically aggressive surface water, hydraulic head, mixing corrosion, and biogenic acids. Well production in the artesian zone is commonly limited only by the discharge rate of the pump. The Edwards Aquifer is also noted for its diverse and widespread aquifer-adapted fauna, implying that the aquifer has a well-integrated karst conduit system.

ABSTRACT The Mitchell Plateau of south-central Indiana is one of the iconic karst landscapes of the United States. The sinkhole-dimpled forests, fields, and farms; the extensive cave systems; and the deep windows into the groundwater system have fostered curiosity, exploration, and publication since the mid-1800s. This paper is designed to complement a field excursion to the classic features of this landscape. Included are literature reviews focused on three karst basins of the Mitchell Plateau: Mill Creek–Mosquito Creek, Bluespring Caverns, and Lost River. Geomorphic, hydrologic, and geochemical data are synthesized in the modern context of our understanding of epigenetic karst. Revealed are three styles of karst basin: (1) small, shallow karst aquifers strongly controlled by meteoric recharge and epikarst percolation; (2) intermediate-size karst aquifers with significant base flow and surface-water–groundwater interaction; and (3) regional aquifer systems with outcrop belt recharge, downdip transport into confinement with long water-rock interaction times, and artesian flow or entrainment of mineralized waters through fractures into springs or surface waters. Quaternary glaciation has greatly influenced the vertical position of base level through river incision and sediment aggradation; conduit development is controlled by proximity to the major rivers and the stratigraphic position of conduits.

Abstract Relict glacial and periglacial environments are widespread, and the deposits that they are associated with mean it is inevitable that the design and construction of many projects will be influenced by their presence and nature. Tills and other glaciogenic deposits prove to be particularly challenging in this context for reasons that include: the spatial variability of the nature of the deposits; the wide range of particle sizes often included within a given soil, including large-sized particles; spatial variation in soil type and properties; variation in depth to rockhead and variable degrees of weathering and alteration; the presence of groundwater, that is misinterpreted as perched water, as well as sub-artesian and artesian conditions; the presence of solution features and fissures, partly or completely infilled with soft or loose material; and the presence of (often shallow) shear surfaces at residual strength. In this chapter, some of the more common problems and associated solutions associated with earthworks and man-made slopes, tunnels and underground structures, dams and reservoirs, foundations, and offshore engineering and installations are reviewed. It is important that great care is taken in addressing the influences of variability, complexity and uncertainty inherent in glacial/periglacial soil formations at all stages of the construction process, from feasibility to end-of-project activities, such as preparation of the as-built drawings.

The Chesapeake Bay impact structure is a late Eocene complex crater that was excavated ~35 Ma ago in a continental shelf environment at the Atlantic margin, in Virginia. It is the largest impact structure in the United States and the seventh largest on Earth. It has an average diameter of ~85 km and is centered near Cape Charles. The scientific well Eyreville B drilled within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the deep crater moat ~9 km from the center of the structure. Core holes drilled in impact structures are especially suited for investigations of the influence of lithological heterogeneities on petrophysical properties and the thermal field. In the Eyreville B core hole, two high-resolution temperature-logging campaigns and a petrophysical profile measured on core samples spaced at ~10 m intervals were recorded. The temperature values of the first campaign in December 2005 were heavily disturbed by outflow of artesian water and could only be used for an estimation of the depth where the fluid originated. For the second campaign in May 2006, a riser was constructed to enable measurements in standing (equilibrated) fluid of the well without opening the well head. This construction yielded a measurement of the undisturbed temperature profile as well as recognition of thermal relaxation after some outflow of artesian water, which heated the surrounding rock. The data allowed determination of (1) the origin of the artesian water, (2) equilibrium temperatures derived from the relaxation process, (3) microclimatic effects at the nearby test well STP2, (4) lateral heterogeneities in the core holes STP2 and Eyreville B, and (5) a profile of vertical heat-flow density in the Eyreville B core. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on core samples, a mean heat-flow density of 65 ± 6 mW/m 2 in the 440–1100 m depth interval was determined. These data and results are now available for application in numerical models of the local and regional geologic, hydrologic, and geothermal regimes.

ABSTRACT Steens Mountain, a fault-block in the northern Basin and Range Province, rises 1.7 km above flanking basins and drives hydrologic systems that include hot springs, fresh-water streams, and cold artesian wells in the Alvord Valley. It also feeds freshwater streams, desert wetlands, and shallow fresh-water and alkali lakes in the Harney Basin. Steens Mountain melt water from the winter snow pack partitions to surface-water and groundwater systems. How the composition of these fluids evolve along the various flow paths as a result of differences in the geology, interaction with geother-mal aquifers, surface storage time, degree of evaporation, and biology will be examined. Deep-seated flow paths feed Alvord Valley hot springs, which discharge to the east, in the rain shadow of Steens Mountain. The largest of these hot spring systems— Borax Lake—along with features at Mickey Hot Springs, offer ample opportunity to investigate how biosignatures form and become preserved in hydrothermally precipitated sinter deposits. Surface water moving off the westward-dipping slope of Steens Mountain passes through wetland environments to Malheur Lake in Harney Basin. This key point along the Pacific flyway provides wonderful wildlife viewing and the chance to ponder the impacts of biology on lake chemistry. Finally, we will visit the saline-alkaline Harney Lake, the terminal sump for the water moving through Malheur Lake and all of the nearly 40,000 km 2 Harney Basin. At this locale, the focus will be on the influence of evaporative processes on water composition.

Abstract Over the past four decades, ongoing deformation of an 18-m-thick peat deposit within the flat-lying Mercer Slough has resulted in damaging deflections, and near-collapse in three cases, of pile-supported Interstate 90 bridges and a major water line on the east side of the slough. The peat is partially underlain by a dense sand unit, which includes a highly pressurized aquifer that produces artesian flow 1–2.5 m above the ground surface. Inclinometers on the east side of the slough show the peat flowing toward the structures and then apparently directed west along the interstate centerline. Large displacements recorded in several inclinometers near the center of the slough suggest a length of deforming peat that approaches 600 m, which is likely initiating retrogressively. Potential causal mechanisms include poor engineering characteristics of the peat, presence of high hydrostatic pressure transmitted within and beneath the peat, seasonal water-level variations of Lake Washington and induced hydraulic gradients within the peat, dredging of the Mercer Slough channel, puncturing of the underlying aquifer by numerous pile foundations, and fill placement along the eastern margin of the slough. The peat is flowing around the pile/shaft foundations; however, excessive lateral loads are still being applied to the foundations in a poorly understood and unpredictable manner. The most severe deflections have occurred in the outermost structures where the peat is primarily flowing transverse to the structures.