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Geologic Setting
Rock Analysis
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This study has shown that:

  1. Holocene sediment is the most significant confining bed in the offshore Florida Keys reef tract.
  2. Onshore and nearshore, where Holocene sediment is absent or thin, diagenetic processes such as development of soilstone and paleosols, along with boring and infilling have rendered the upper few feet (~1m) relatively impermeable. This surface therefore serves as a semi-confining bed.
  3. Onshore and nearshore, the Q3 unconformity between 25 and 35 ft deep (7.6-10.7 m) serves as a semi-confining bed.
  4. The Pleistocene limestone below and between confining beds is extremely porous and permeable and readily transmits fluids both vertically and horizontally.
  5. Tidal pumping serves both to diffuse, dilute and transmit fluids vertically where not confined by Holocene sediment or diagenetically altered unconformities.
  6. Chemical reactions between phosphorous and limestone are shown to be absent from the analyses done on selected samples, however, it may be possible for reactions to occur closer to the disposal wells.
  7. Nutrient levels in the offshore ground waters are elevated above those of overlying sea water.
  8. Nutrients can probably leak to the overlying sea water through Holocene reefs and wherever Pleistocene limestone is not covered by Holocene sediment.
  9. Because their levels increase offshore, the source of nutrients (mainly NH4) could not be directly linked to onshore disposal wells.
  10. Fecal bacteria were detected in ground waters from wells as far as 4 nmi offshore but were not detected in offshore surface waters at these sites. Fecal bacteria therefore may be the best indicators of lateral offshore movement of contamination from onshore sources.

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Last updated: 10 September, 2014 @ 12:20 PM (KP)