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Monday, July 23, 2007

Deep Injection Wells - Detailed Information

The use of deep injection wells as a means by which to process the Marco Island sewage is another contentious issue. Part of this contention stems from the lack of information and misinformation being promulgated by the city and it's proponents of the STRP. Adding to the confusion are some anti-STRP activists making certain claims about the efficacy of deep injection wells.

The best judge of this issue will not be the "experts" - but as always - the public. The public should be informed on this (and all) issues. To that end, the following is a detailed explanation on deep injection wells are provided by the EPA. Additionally, information formulated by the Sierra Club from a near identical situation (in Miami) is also provided.

We urge that every citizen of Marco Island take the time to become informed on this very important environmental and social issue.

EPA - Deep Injection Wells (web based)
EPA - Deep Injection Wells (download the PDF)
Sierra Club Deep Injection Wells
Article of Interest ...

We trust that you find this information informative.


  • Fate and Pathways of Injection-Well Effluent in the Florida Keys

    Eugene A. Shinn1, Ronald S. Reese2, and Christopher D. Reich1

    1USGS Coastal Geology Center, St. Petersburg, Florida
    2USGS Water Resources Division Office, Miami, Florida

    Geologic Setting
    Rock Analysis
    Water Chemistry
    Ground Water
    Future Studies

    Executive Summary

    * Twenty-four wells (21 locations) were core drilled into the limestone beneath the Keys, reef tract, and outer reefs to determine if sewage effluents injected in Class V wells onshore are reaching offshore reef areas via underground flow. These wells were fitted with PVC casings and well screens and were sampled every three months for a period of one year. Analyses showed consistent hypersalinity in most wells and a marked increase in nitrogen (as ammonia) in offshore ground water. Other forms of nitrogen (NO2 and NO3) and phosphorous were not particularly elevated in offshore ground water but were above the levels found in surface marine water. The highest levels of nitrogen (NO2 and NO3) and phosphorous were in shallow onshore ground waters. Sources for the nutrients in the shallow onshore ground water consist of septic tanks and cesspools (@ 24,000 and 5,000 in the Florida Keys, respectively), agricultural fertilizers, and natural vegetation. Ammonia concentrations were low in shallow ground waters beneath the Florida Keys, probably because of oxidizing conditions.

    * Tidal pumping is particularly active, especially nearshore. Hydraulic heads sufficient to elevate well water as much as 7 cm above sea level during falling tides were detected in all nearshore wells. During rising tides, the situation was reversed and water flowed into the wells. Tidal pumping implies considerable water movement both in and out of the upper few meters of limestone. Tidal pumping is a likely mechanism for mixing and transferring nutrient-rich ground water into the overlying marine waters. Although tidal pumping should cause rather complete mixing and dilution of any freshwater-based effluents entering the limestone via the more than 600 disposal wells in the Florida Keys, the ground waters in the 30- to 40-ft-depth range (9-12 m) nevertheless remained slightly hypersaline relative to sea water throughout the year.

    * Fecal coliform and fecal streptococcal bacteria were associated with three Lower Keys offshore wells and two shallow onshore wells at Key Largo. On occasions, these bacteria were detected farther offshore, once in a well 4 miles off Key Largo. The bacterial analyses for Key Largo (both onshore and offshore) are supported by two independent bacteriological researchers using more sophisticated methods than the standard 100-ml membrane-filter method used in this study. Fecal bacteria can serve as tracers; thus, we conclude their presence is possible evidence for offshore transport of ground waters originating on Key Largo. Elevated nutrients (ammonia) and slightly elevated dissolved total phosphorous in offshore ground waters, however, cannot be tied to onshore sources with existing data.

    * Rock analyses of material from our cores do not prove or disprove the hypothesis that limestone beneath the Keys or reef tract is serving as a sink for phosphorus or other nutrients. The data, however, do not rule out phosphorus uptake by limestone adjacent to disposal sources. For the purposes of this study, monitoring wells were not positioned sufficiently close to injection wells to determine if uptake of phosphorous is taking place. Ground waters were found to contain more dissolved solids than could be accounted for if hypersalinity resulted from simple evaporation of sea water. These data indicate that ground waters in the vicinity of our wells are dissolving solids from the rock rather than precipitating material within the rock framework; however, as mentioned above, our wells were not positioned sufficiently close to disposal wells to determine if localized uptake is occurring.

    * Examination of rock cores from these wells revealed a general distribution of reef- and grainstone-facies belts. The Upper and Middle Keys are composed of a thin coral reef facies that extends only a few hundred feet seaward of the Keys. Reef facies give way to mudstone facies within a few yards of shore on the Florida Bay side of the Keys. On the seaward side of the Keys, beneath Hawk Channel and White Bank, the Pleistocene limestone is a mixed grainstone, packstone, and wackstone facies. Corals are rare or absent. The Pleistocene limestone beneath the outer reefs 4 to 5 miles offshore, however, consists of reef facies with the same coral fauna as that found on Key Largo. This pattern of two major reef-facies belts separated by a 2- to 4-mile-wide belt of grainstone facies may have as yet undetermined effects on groundwater circulation beneath the Florida reef tract. Grainstone is approximately an order of magnitude less permeable than the coralline Key Largo Limestone facies.

    * The Q3 surface, a major subsurface unconformity thought to form an effective confining zone elsewhere in south Florida, was not detected in wells drilled more than 1 mile from shore. This unconformity, however, was detected in all wells drilled on or near the Keys. What was found to be a more effective and widespread confining layer is the Holocene sediment deposited on the Pleistocene limestone during the past 6,000 to 7,000 years. These relatively impermeable sediments are extensive, forming a belt up to 5 miles wide beginning about 0.5 mile offshore. Holocene sediments generally consist of low-permeability lime mud just above the Pleistocene surface, overlain by more permeable carbonate sands and reefs. Leakage of ground water by tidal pumping is not likely to occur through lime-mud-dominated areas such as Hawk Channel but is likely to occur through isolated porous and permeable Holocene reefs situated on Pleistocene limestone highs, and in places where Holocene sediment does not cover the limestone bedrock. Leakage is therefore limited to 1) a shallow-water 0.5-mile-wide nearshore belt of exposed Key Largo Limestone, 2) Holocene patch reefs, which grow on mud-free topographic rock highs, and 3) along the seaward side of the outermost reef in 35 to 65 ft (10-20 m) of water, where Holocene reef and sediment accumulations are thin or absent.

    * This study did not address direct measurements of lateral groundwater movement or a hydrologic mechanism for transporting hypersaline ground water away from the Florida Keys. More recent work, however (Halley et al., 1994), shows that sea level in Florida Bay is higher than on the Atlantic side of the Keys more than 50% of the time. Higher sea level on the bay side of the Keys provides a potential for groundwater flow toward the Atlantic most of the time. Use of tracers (dyes or harmless bacteriological tracers) injected into the center of tightly spaced clusters of monitoring wells is a simple way to ascertain the net direction and rate of groundwater movement. Knowing the direction and rate of groundwater movement is needed for prediction and modeling efforts in the future.

    Note - Research conducted in the Florida Keys has noted that isolates identified as coliforms on standard coliform media (mENDO, mFC, Marine Colilert) may instead be indigenous marine microbes, which are capable of utilizing the same substrates. Unless isolates are verified using more advanced media based assays (API or BioLog) or genetic sequencing (16S rDNA) there exists the possibility of recording false positive results.

    By Blogger Dr. Mario, at Tuesday, July 24, 2007 11:24:00 AM  

  • Conclusions

    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.

    By Blogger Dr. Mario, at Tuesday, July 24, 2007 11:31:00 AM  

  • source:

    By Blogger Dr. Mario, at Tuesday, July 24, 2007 11:33:00 AM  

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