Robert A. Renken
United States Geological Survey
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Geological Society of America Bulletin | 2006
Kevin J. Cunningham; Michael C. Sukop; Haibo Huang; Pedro F. Alvarez; H. Allen Curran; Robert A. Renken; Joann F. Dixon
A combination of cyclostratigraphic, ichnologic, and borehole geophysical analyses of continuous core holes; tracer-test analyses; and lattice Boltzmann fl ow simulations was used to quantify biogenic macroporosity and permeability of the Biscayne aquifer, southeastern Florida. Biogenic macroporosity largely manifests as: (1) ichnogenic macroporosity primarily related to postdepositional burrowing activity by callianassid shrimp and fossilization of components of their complex burrow systems (Ophiomorpha); and (2) biomoldic macroporosity originating from dissolution of fossil hard parts, principally mollusk shells. Ophiomorpha-dominated ichnofabric provides the greatest contribution to hydrologic characteristics in the Biscayne aquifer in a 345 km 2 study area. Stratiform tabular-shaped units of thalassinidean-associated macroporosity are commonly confi ned to the lower part of upward-shallowing highfrequency cycles, throughout aggradational cycles, and, in one case, they stack vertically within the lower part of a high-frequency cycle set. Broad continuity of many of the macroporous units concentrates groundwater fl ow in extremely permeable passageways, thus making the aquifer vulnerable to long-distance transport of contaminants. Ichnogenic macroporosity represents an alternative pathway for concentrated groundwater fl ow that differs considerably from standard karst fl ow-system paradigms, which describe groundwater movement through fractures and cavernous dissolution features. Permeabilities were calculated using lattice Boltzmann methods (LBMs) applied to computer renderings assembled from X-ray computed tomography scans of various biogenic macroporous limestone samples. The highest simulated LBM permeabilities were about fi ve orders of magnitude greater than standard laboratory measurements using air-permeability methods, which are limited in their application to extremely permeable macroporous rock samples. Based on their close conformance to analytical solutions for pipe fl ow, LBMs offer a new means of obtaining accurate permeability values for such materials. We suggest that the stratiform ichnogenic groundwater fl ow zones have permeabilities even more extreme (~2‐5 orders of magnitude higher) than the Jurassic “super-K” zones of the giant Ghawar oil fi eld. The fl ow zones of the Pleistocene Biscayne aquifer provide examples of ichnogenic macroporosity for comparative analysis of origin and evolution in other carbonate aquifers, as well as petroleum reservoirs.
Environmental & Engineering Geoscience | 2005
Robert A. Renken; Kevin J. Cunningham; Michael R. Zygnerski; Michael A. Wacker; Allen M. Shapiro; Ronald W. Harvey; David W. Metge; Christina L. Osborn; Joseph N. Ryan
Proposed expansion of extractive lime-rock mines near the Miami–Dade County Northwest well field and Everglades wetland areas has garnered intense scrutiny by government, public, environmental stakeholders, and the media because of concern that mining will increase the risk of pathogen contamination. Rock mines are excavated to the same depth as the well fields primary producing zone. The underlying karst Biscayne aquifer is a triple-porosity system characterized by (1) a matrix of interparticle porosity and separate vug porosity; (2) touching-vug porosity that forms preferred, stratiform passageways; and, less commonly, (3) conduit porosity formed by thin solution pipes, bedding-plane vugs, and cavernous vugs. Existing ground-water flow and particle tracking models do not provide adequate information regarding the ability of the aquifer to limit the advective movement of pathogens and other contaminants. Chemical transport and colloidal mobility properties have been delineated using conservative and microsphere-surrogate tracers for Cryptosporidium parvum . Forced-gradient tests were executed by introducing conservative tracers into injection wells located 100 m (328 ft) from a municipal-supply well. Apparent mean advective velocity between the wells is one to two orders of magnitude greater than previously measured. Touching-vug, stratiform flow zones are efficient pathways for tracer movement at the well field. The effective porosity for a continuum model between the point of injection and tracer recovery ranges from 2 to 4 percent and is an order of magnitude smaller than previously assumed. Existing well-field protection zones were established using porosity estimates based on specific yield. The effective, or kinematic, porosity of a Biscayne aquifer continuum model is lower than the total porosity, because high velocities occur along preferential flow paths that result in faster times of travel than can be represented with the ground-water flow equation. Tracer tests indicate that the relative ease of contaminant movement to municipal supply wells is much greater than previously considered.
Water Resources Research | 2008
Robert A. Renken; Kevin J. Cunningham; Allen M. Shapiro; Ronald W. Harvey; Michael R. Zygnerski; David W. Metge; Michael A. Wacker
[1] The Biscayne aquifer is a highly transmissive karst limestone that serves as the sole source of drinking water to over two million residents in south Florida. The aquifer is characterized by eogenetic karst, where the most transmissive void space can be an interconnected, touching-vug, biogenically influenced porosity of biogenic origin. Public supply wells in the aquifer are in close proximity to lakes established by surface mining. The mining of the limestone has occurred to the same depths as the production wells, which has raised concerns about pathogen and chemical transport from these surface water bodies. Hydraulic and forced gradient tracer tests were conducted to augment geologic and geophysical studies and to develop a hydrogeologic conceptual model of groundwater flow and chemical transport in the Biscayne aquifer. Geologic and geophysical data indicate multiple, areally extensive subhorizontal preferential flow zones of vuggy limestone separated by rock with a matrix pore system. The hydraulic response from an aquifer test suggests that the Biscayne aquifer behaves as a dual-porosity medium; however, the results of the tracer test showed rapid transport similar to other types of karst. The tracer test and concurrent temperature logging revealed that only one of the touching-vug flow zones dominates transport near the production wells. On the basis of the rising limb of the breakthrough curve, the dispersivity is estimated to be less than 3% of the tracer travel distance, which suggests that the fastest flow paths in the formation are likely to yield limited dilution of chemical constituents.
US Geological Survey professional paper | 2002
Robert A. Renken; W. C. Ward; I.P. Gill; Fernando Gómez-Gómez; Jesús Rodríguez-Martínez
Poorly lithified to unconsolidated carbonate and clastic sedimentary rocks of Tertiary (Oligocene to Pliocene) and Quaternary (Pleistocene to Holocene) age compose the South Coast aquifer and the North Coast limestone aquifer system of Puerto Rico; poorly lithified to unlithified carbonate rocks of late Tertiary (early Miocene to Pliocene) age make up the Kingshill aquifer of St. Croix, U.S. Virgin Islands. The South Coast aquifer, North Coast limestone aquifer system, and Kingshill aquifer are the most areally extensive and function as the major sources of ground water in the U.S. Caribbean Islands Regional Aquifer-System Analysis (CI-RASA) study area. In Puerto Ricos South Coast ground-water province, more than 1,000 meters of elastic and carbonate rocks of Oligocene to Pliocene age infill the South Coast Tertiary Basin. The pattern of lithofacies within this basin appears to have been controlled by changes in base level that were, at times, dominated by tectonic movement (uplift and subsidence), but were also influenced by eustiisy. Deposition of the 70-kilometer long and 3- to 8-kilometer wide fan-delta plain that covers much of the South Coast ground-water province occurred largely in response to glacially-induced changes in sea level and climate during the Quaternary period. Tectonic movement played a much less important role during the Quaternary. The North Coast ground-water province of Puerto Rico is underlain by a homoclinal coastal plain wedge of carbonate and siliciclastic rocks that infill the North Coast Tertiary Basin and thicken to more than 1,700 meters. A thin basal siliciclastic sequence of late Oligocene age is overlain by a thick section of mostly carbonate rocks of Oligocene to middle Miocene age. Globigerinid limestone of late Miocene to Pliocene age crops out and lies in the shallow subsurface areas of northwestern Puerto Rico. Oligocene to middle Miocene age rocks tentatively can be divided into five depositional sequences and associated systems tracts; these rocks record carbonate and minor siliciclastic deposition that occurred in response to changes in relative sea level. The Cibao Formation represents the most complex of these sequences and contains a varied facies of carbonate, mixed carbonate-siliciclastic, and siliciclastic rocks that reflect differential uplift, subsidence, and transgression of the sea. Uplift, graben formation, and gradual shallowing of the sea are reflected within the bathyal-dominated sedimentary facies of the Kingshill Limestone in St. Croix, U.S. Virgin Islands. Reef-tract limestone beds of Pliocene age were subject to exposure, resubmergence, and meteoric leaching of aragonitic skeletal debris; these beds contain patchy lenses of dolomite that are restricted to a small, structurally-controlled embayment. The South Coast aquifer, the principal water-bearing unit of Puerto Ricos South Coast ground-water province, consists of boulder- to silt-size detritus formed by large and small coalescing fan deltas of Pleistocene to Holocene age.
AWRA international symposium on Tropical hydrology | 1995
Robert A. Renken; Fernando Gómez-Gómez; Vicente Quinones-Aponte; Rafael Dacosta
Subsurface data and results of surface geologic mapping indicate that areal variations in hydraulic conductivity of water-bearing strata in the semiarid alluvial plain of southern Puerto Rico may be controlled by geologic structure and depositional patterns. Six fan-deltas coalesce to form a narrow, 3- to 8-km-wide alluvial plain that extends eastward 70 km from Ponce to Patillas. These unconsolidated coastal alluvial fan deposits consist of a moderately thick (50 to 1,000 m) clastic sequence of Holocene to Miocene(?) age. The fan-deltas are bordered to the north by foothills and mountains of the Cordillera Central and to the south by the Caribbean Sea. Bedrock hills protrude through thinner parts of the alluvial plain, and northwest-trending strike-slip faults and northeast-trending cross faults of the great southern Puerto Rico fault zone extend beneath the alluvial cover.
Water Resources Research | 2008
Ronald W. Harvey; David W. Metge; Allen M. Shapiro; Robert A. Renken; Christina L. Osborn; Joseph N. Ryan; Kevin J. Cunningham; Lee L. Landkamer
Special Paper of the Geological Society of America | 2006
Kevin J. Cunningham; Robert A. Renken; Michael A. Wacker; Michael R. Zygnerski; Edward Robinson; Allen M. Shapiro; G. Lynn Wingard
Water Resources Research | 2008
Allen M. Shapiro; Robert A. Renken; Ronald W. Harvey; Michael R. Zygnerski; David W. Metge
Circular | 2005
Robert A. Renken; Joann F. Dixon; John A. Koehmstedt; Scott Ishman; A.C. Lietz; Richard L. Marella; Pamela A. Telis; Jeff Rodgers; Steven Memberg
Water-Resources Investigations Report | 1996
Vicente Quinones-Aponte; Fernando Gómez-Gómez; Robert A. Renken