Location:
Steak and Ale, 3030 S. Post Oak (not 3300 Post Oak)
Social: 5:30 pm
Dinner: 6:00 pm
Presentation: 7:00 pm
Topic:
Landfill Siting Criteria with Emphasis on Karst Hydrogeology
[Chairman's note: We would like to thank Faizur R. Khan, P.E., Project Manager for Laidlaw Environmental Services Columbia Engineering Department (Houston), for substituting at the last moment for October's speaker. His talk was entitled "Cut-Off Wall System for Subsurface Liquid Containment."]
Authors:
by Allan Biddlecomb,P.G., Diane Yeager, P.G.,* and Laurie Irwin
* Denotes speaker other than senior author.
Abstract:
Karst landscapes result from the subsurface solution of rock and are usually
characterized by sinkholes, caverns, and drainage of surface water to the
subsurface. Karst terrane covers an estimated 15 percent of the earth's land
surface and is usually associated with carbonate rock.
Once these surfaces become buried, they may comprise very prolific aquifers. Karst may continue to develop (in areas where the groundwater table is near the surface and unconfined) after the rock has been buried and becomes the matrix for the aquifer. An example of this type of aquifer is the Floridan Aquifer located throughout most of central and north-central Florida.
Where the karst aquifer is near surface or relatively unprotected by thin soils, impacts to the aquifer are likely. In areas where the limestone is buried beneath a thick sequence of clay (example: Hawthorn Formation, Florida), the groundwater is confined and the aquifer is generally perceived as protected from surface influences. However, the paleo-karst development within the limestone may breach the clay unit and fill with permeable sediments such as sands and silts. These breaches are also avenues for contamination to enter the aquifers and are not easily mapped from surface features. Other karst features, such as fractures and conduits, do not have predictable patterns, are difficult to trace, and enhance the aquifer's porosity (secondary porosity).
In many areas of the country, landfills have been built over these karst aquifers. Where the landfills have been constructed prior to establishing landfill siting criteria, drinking water supplies (recovered from the karst aquifers) have most likely been impacted. For example, several landfills in north Florida have impacted the Floridan Aquifer and numerous potable drinking water wells. Contaminants impacting the karst aquifer tend to migrate rapidly in both the lateral and vertical directions. The impacted area of the aquifer makes active remediation impractical. Once these aquifers become impacted, alternative drinking water supplies need to be established for the population and the aquifer monitored for contaminant migration.
For these reasons, establishing practical landfill siting criteria is critical. In karst hydrogeologic environments geologic investigations should provide the necessary detail to determine if paleo-karst has breached clay units and other features that cannot easily be established from surface mapping. Other siting features are inherently related to the hydrogeologic environment and should be considered prior to conceptual development of the landfill design.
Biographical Sketches:
Diane Yeager has worked in the environmental arena for approximately 10 years
focusing on hydrogeology. Ms. Yeager obtained her B.S. in geology at Ball State
University in Muncie, Indiana. She studied civil engineering at the University
of Florida and has her professional registration in Florida. She has worked as
both a consultant and government contractor to NASA in California and Florida.
As a government contractor at the Kennedy Space Center, Ms. Yeager oversaw the
hydrogeology compliance issues affiliated with the Space Center's landfill
closure and construction. Her work with Allan Biddlecomb, P.G., of Jones
Edmunds & Associates, Inc. included landfill siting investigations in north
Florida that are the basis of this paper. Ms. Yeager is currently with Dames
& Moore in Houston, Texas, working on a variety of environmental projects.
Laurie Irwin is the manager of the Geosciences Unit at Dames & Moore Houston, Texas. Ms. Irwin has worked in the environmental field for 15 years. She has a wide variety of experience with solid waste facilities throughout the U.S. with emphasis on hazardous waste landfills.
Allan Biddlecomb has an M.S. degree in hydrogeology from the University of Florida (Gainesville). He has worked as a consultant for JEA in Gainesville for approximately 10 years. His current work involves a variety of hydrogeologic investigations for landfill sitings, closures, and contamination investigations. Mr. Biddlecomb has his professional registration in the States of Florida and Georgia.
Location:
Westchase Hilton, 9999 Westheimer.
Social Hour and Posters or Demonstrations 5:30 PM, Dinner and Talk 6:30 PM.
Poster Session:
Come and see large sets of important data with expert interpretation.
Talk:
"Geologic Evolution Of Conjugate Volcanic Passive Margins:
Influence on the Petroleum Systems of the South Atlantic"
Speaker:
Vitor Abreu, Peter R. Vail,
Albert Bally; Rice University, and
Edith Wilson, Amoco
Abstract:
Two contrasting types of passive margins are 1) thick-crusted volcanic margins
and 2) thin-crusted nonvolcanic margins. Examples of conjugate nonvolcanic
margins in the South Atlantic Ocean are the Santos and Campos basins along
the Brazilian margin and Kwanza and offshore Lower Congo basins along the
African margin (Fig. 1).
In these basins, the ocean-continent transition is marked by crustal thinning caused by to extensional deformation preceding the continental breakup. During extension, normal synthetic faulting generated half-graben systems in Campos Basin and offshore Lower Congo and Kwanza basins during the Neocomian (Fig. 2), with deposition of thick syn-rift fluvio-lacustrine deposits (Syn-Rift I). A second phase of rifting, developed during the Barremian (Syn-Rift II), is marked by thermal subsidence and minor extension (Fig. 2). The Syn-Rift II sediments are referred to as the Lagoa Feia Formation in the Campos Basin (Brazil) and Sag phase (e.g., Henri et al., 1995) or Pre-Salt Wedge (e.g., Wilson et al., in press) along the African margin and are characterized by transitional sediments with increasing marine influence in the upper portion (e.g., Rodrigues and Takaki, 1988; Silva-Telles, 1996; Wilson et al., 1997). The rift deposits are the major source of hydrocarbons in the South Atlantic. After breakup, evaporites were deposited during the early drift phase. Salt movement during Cretaceous and Cenozoic generated salt pillows and domes, deforming the sediments deposited during the drift phase.
Volcanic passive margins are a major type of large igneous provinces, characterized by seaward-dipping reflectors (SDRS), normally associated with subaerially emplaced basalt flows and intercalated at least in part with continental sediments. In the South Atlantic, the volcanics extend laterally for hundreds of kilometers and can reach a thickness of about 15 kilometers. A number of questions remain concerning their formation. These include the influence of hotspots, the timing of volcanic emplacement with respect to continental breakup, the nature of the crust associated with the volcanics, and the symmetry of the volcanics with respect to the breakup axis.
The Paran-Etendeka flood basalts and the SDRS of the Pelotas and Walvis basins (Fig. 1) are the result of the rifting and subsequent breakup of the South American and African plates under an initial influence of the Tristan da Cunha hotspot. The SDRS wedges were probably emplaced after continental breakup at least partially over an extended continental crust. The Pelotas and Walvis SDRS wedges are part of two major SDRS provinces in the South Atlantic: Santos-San Jorge (South America) and Walvis-Orange (Africa) provinces (Fig. 1). These provinces form a broad and symmetrical volcanic complex, extending over more than 3,000 km linearly in the South Atlantic. It is proposed that these SDRS provinces were emplaced as a subaerial oceanic ridge, representing the initial stage of formation of the oceanic crust in most passive margins.
The subsidence in the Pelotas and Walvis basins started in the continental/initial oceanic crust transition. The oceanic crust kept close to sea level or in shallow water depths almost until the Turonian, at least in the northern portion of the Pelotas and Walvis basins. The subsidence close to the continental crust generated a narrow seaway parallel to the coast in both margins. The initial oceanic crust formed a broad and shallow platform in both margins since the Barremian, creating a barrier between the South Atlantic and the Southern Ocean during the early Aptian.
During the Barremian, while continental breakup started in Pelotas and Walvis basins with the emplacement of a subaerial mid-oceanic ridge, the second phase of rifting (Syn-Rift II or Pre-Salt Wedge) dominated the northern basins of the South Atlantic. Geochemical and paleontological data from the Brazilian margin (Rodrigues and Takaki, 1987; Silva-Telles, 1996) and observations from Angola (Burwood et al., 1992; Wilson et al., in press) suggest an increase of marine influence toward the top of the section in a time that precedes continental breakup and oceanic crust formation in the Campos and Kwanza basins. One explanation for the presence of marine strata in the rift section of Campos and Kwanza basins is the fast subsidence rate during the Syn-Rift II combined with marine invasions through the seaways in the Pelotas and Walvis basins during periods of high sea level in the Barremian. Marine waters could invade the northern basins of the South Atlantic during the sea-level high in the Barremian, transgressing over transitional sediments and infilling depressions formed by the second phase of rifting, allowing restricted deposition of marine evaporites and carbonates.
Limited circulation occurred along the seaways and the sides of the shallow oceanic ridge since the Barremian in the Pelotas and Walvis basins. After continental breakup and oceanic crust emplacement in the Campos and Kwanza basins, periods of low sea level during the early Aptian would practically have isolated the South Atlantic from the Southern Ocean, allowing sea-water evaporation and salt precipitation in a broad area along the South Atlantic continental margins (Fig. 3).
Biographical Sketch:
Vitor Dos Santos Abreu received his B.S. (1984) and M.S. (1989) at the Federal University
of Rio Grande do Sul in Brazil. Abreu has worked for Petrobras since 1987 and
was previously the manager of biostratigraphy and paleoecology. Currently,
Abreu is at Rice University studying for a Ph.D. on the topic "Geologic
Evolution in Conjugate Volcanic Passive Margins: Pelotas Basin, Brazil, and
offshore Namibia, Africa." His research interests include sequence stratigraphy
in passive margins and stable isotope stratigraphy.
References:
Burwood, R., Leplat, P., Mycke, B., and Paulet, J., 1992, Rifted margin source
rock deposition: a carbon isotope and biomarker study of a West African
Lower Cretaceous "lacustrine" section, Organic Geochemistry, v. 19,
p. 41-52.
Henri, S. G., Brumbaugh, W., and Cameron, N., 1995, Pre-salt source rock development on Brazil's conjugate margin: West African example, 1st Latin American Geophysical Conference, Abs.
Rodrigues, R., and Takaki, T., 1987, O Cretaceo Inferior nas bacias sedimentares da costa sudeste do Brasil: analise isotopica e suas implicacoes ambientais. Revista Brasileira de Geociencias, v. 17, n. 2, p. 177-179.
Silva-Telles, A. C., Jr., 1996, Marine ingression events of Jiquia age (early Aptian) in the Afro-American rift system from the viewpoint of tectono-eustasy, Congresso Brasileiro de Geologia, 39, Bahia, Anais, p. 360-363.
Wilson, E., Abreu, V. S., Asley, M. P. Brandao, M., and Telles, A. S., in press, Lower Cretaceous stratigraphy and source rock distribution in the South Atlantic: Comparison of Angola and southern Brazil, South Atlantic Source Rocks, AAPG/SBG Meeting, Rio de Janeiro.