Proposed recommendations of the aquifer committee

MEMORANDUM

DATE:             September 5, 2000

TO:                  Dr. Chris Schuberth, Chair, SEG Aquifer Committee

FROM:                        The Undersigned

SUBJECT:            Proposed Recommendations of the Aquifer Committee to the SEG

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The Aquifer Committee (AC) was created by the Stakeholder Evaluation Group (SEG) as the result of new concerns about the structural integrity of the Miocene confining unit overlying the upper Floridan aquifer.  Of particular concern is the high potential for the confining unit to contain fractures, causing the hydraulic conductivity of the confining unit to be significantly higher than previously determined from drilling cores and thereby greatly increasing the estimated flow rate (leakage) of seawater into the Floridan aquifer.  As established during the first meeting of the AC on 26 June 2000, the purpose of the Committee is fourfold:

  1. To establish what impact, if any, deepening of the Savannah Harbor from 42 feet (with depths in places currently at 50 feet) to as much as 48 feet (with depths in places in excess of 48 feet) will have on the upper Floridan aquifer.
  2. To recommend a “Scope of Work” (SOW) and/or other recommendation(s).
  3. To recommend the SOW and/or other recommendation(s) to SEG.
  4. To establish the impact, if any, the current depth may have on the upper Floridan aquifer.

Although a 1998 US Army Corps of Engineers (USACE) study of the potential groundwater impacts of the Savannah Harbor expansion concluded that “…the proposed dredging will have no noticeable effect on the quality and quantity of groundwater within the upper Floridan aquifer….,” concern remained that further studies were needed to assure that conclusion.  Relevant to this concern, the City of Savannah had the USACE report critiqued by HydroVision, an Atlanta consulting firm.  The resulting report was distributed to AC members and the second meeting of the AC, on 21 August 2000, was largely given over to a presentation by Rick Krause, co-author of the HydroVision report.  In essence, the HydroVision report indicated that the level of confidence as concluded in the 1998 USACE report was not justified.  Krause cited two specific points of concern:  (1) that the leakage calculations were based on averaged geotechnical properties rather than using the worst-case scenario, and (2) that core-sample hydraulic conductivities (permeabilities), calculated by laboratory analysis, are much less definitive of actual conditions than in-situ aquifer (pumping) tests.  Krause then proposed studies that would provide a greater level of confidence as to the potential effects of harbor deepening on the aquifer.

From the foregoing, we have derived four alternative actions that should be considered as a means of better assessing the risk of seawater intrusion associated with harbor deepening:

1. No further studies needed as “...the proposed dredging will have no noticeable effect...” (1998 USACE Report, p. 39, #7).

That conclusion “cannot be made” (HydroVision Report, p. 3 #4).  Furthermore, Ram Arora, co-author of the HydroVision report, stated in a letter (April 5, 2000) to Mr. Kenny Dumas, Director of Water Operations for the City of Savannah, “We have reviewed the report and concluded that sufficient study has not been done.  Substantial additional work would be required to answer the question regarding the impact of proposed harbor dredging on groundwater in the Savannah area.”

 

2.     Recalculate the 1998 USACE Report’s core hydraulic conductivity (permeability) data using the worst-case scenario.

The HydroVision Report stated that this option would not solve the need for in-situ leakage analyses.

3.     Carry out a “Phase 2” study as described in the HydroVision Report (p. 4) and by Rick Krause during the 21 August AC meeting.

4.     Carry out a “Phase 2” study using a different, but appropriate, methodology if one exists.

In considering these alternatives, it is imperative that we have the highest possible level of confidence that no harm will be done to the aquifer, because if seawater intrusion results from deepening, remediation is unlikely both technically and economically.  We cannot afford to make a mistake.  It is also worth considering that except for perhaps the most seaward portion, all of the channel is within the cone of depression of the upper Floridan aquifer.  Here, the gradient, and hence the flow, is downward from the surface to Savannah’s critical water-supply wells located within the aquifer.

We most strongly feel that additional studies are required to insure, insofar as possible, that the proposed dredging will indeed have no noticeable effect on the quality and quantity of groundwater within the upper Floridan aquifer, and so present this recommendation to the AC as an action consistent with the purpose and objectives of the committee and the Sound Science Initiative.  We further recommend that either Alternative 3 or Alternative 4 be employed to develop a statement of work.  And, we further recommend that a highly qualified independent firm be selected to carry out the work and that the work undergoes peer review by appropriate entities.

 

Dr. Clark R. Alexander                                                                                Dr. Anthony M. Foyle  

Skidaway Institute of Oceanography                                                            Georgia Southern University

 

Dr. Vernon J. Henry                                                                                    Dr. James S Reichard        

Georgia Southern University                                                                        Georgia Southern University

 

Dr. Fredrick J. Rich

Georgia Southern University