The American shad ascends the river to spawn well upstream of the harbor; therefore, the eggs and larvae of these species are not expected to come in contact with the dredge or its plume. However, the striped bass primarily spawn in the Little Back River. The eggs and larvae of this species have a high potential for contact with the dredge and possible entrainment by the dredge. Striped bass and their eggs and larvae also have a high potential for coming in contact with the increased suspended sediment loads of a dredge plume. Based on studies to date, all life stages of estuarine dependent and anadromous fish species appear to be very tolerant of elevated suspended sediment concentrations.

In all probability, species that utilize naturally turbid habitats as spawning and nursery grounds are adapted to, and highly tolerant of, elevated suspended sediment concentrations and, in some cases, their migration corresponds to periods of highest suspended sediment levels. Such conditions would not be expected to prevail at a hydraulic pipeline dredge site for sufficient lengths of time to merit special concern (LaSalle 1989). In order to avoid any possible impacts to striped bass, as well as other species which spawn in the spring, dredging schedules will be arranged to limit dredging activities to the lower harbor (mile 5.0 to 0.0.) during the period of 15 March to 31 May of each year.

The same is true for Plan 5; however, this plan would result in higher increases in suspended solid levels since overflow filling of the dump scows would be necessary in the inner harbor. The filling of the scows in this area would result in increased suspended solids levels throughout the water column since the silt laden water would enter from the surface, whereas Plan 1 would result in increases mainly near the river bottom. In view of this, Plan 5 would have a higher potential for impacting fish at all life stages.

Impacts on fisheries due to the disposal operation for Plan 1 would be minimal, since existing high ground disposal areas would be used for the inner harbor sediments and only the unpolluted sandy bar channel material would be placed in the ocean disposal area. However, Plan 2 would result in the loss of 664 acres of nursery habitat for creation of the new disposal area. Plan 5 would expose the existing fishery at the ocean disposal site to any pollutants contained in the inner harbor sediments which have not been tested

for ocean disposal. To determine the potential impact of disposal of these sediments, testing would have to be conducted in accordance with the EPA regulations on ocean disposal (40 CFR 220-229). Bioassays as well as bioaccumulation studies may be required.

The primary concern for fisheries with either proposal would be related to salinity increases caused by dredging.

Implementation of the Section 1135 project modification will result in reduced salinities in the estuary, which will in turn result in increases in freshwater habitat in the upper estuary and a downstream shift in the areas of brackish and saline marshes. Deepening of the harbor would reduce the extent of these changes and thereby impact any fish species which would have used these converted areas of marsh. The area of saline/brackish to freshwater marsh conversion would be reduced by a maximum of 560 acres for either a two or four foot deepening.

This impact of the deepening project would have very little or no impact on fish due to the reduced habitat conversion, since the deepening project would likely be constructed before the predicted conversion would occur. Even if the conversion did occur prior to project construction, there is little potential for impact to fisheries due to habitat modification.

The main impact of channel deepening would be to the striped bass which spawn in the Back River. According to the U.S. Fish and Wildlife Service, salinity levels of 1.7 ppt or less present optimum spawning conditions for striped bass. After implementation of the Section 1135 project modification, such conditions will exist above mile 20.1 in the Back River when flows are 6,000 cfs. If the harbor is deepened by two or four feet, such levels would exist only above approximately Mile 20.6.

Therefore, the increase in optimum spawning habitat for the striped bass which is expected to result from the Section 1135 project modification would be reduced by approximately one-half mile by either a two or four foot deepening during flows of 6,000 cfs. This impact is not significant in view of the approximate 8 miles of optimum spawning habitat which would remain upstream of this point. Also, flows of 6,000 cfs or less seldom occur during the spawning season.

As indicated in the Final EIS, striped bass recruitment, as opposed to insufficient spawning grounds, is thought to be the problem in the Savannah Harbor. Studies indicate that, without the Section 1135 project modification, striped bass eggs and larvae were swept out into the Front River through New Cut where they encountered adverse water quality conditions. The Section 1135 project modification will eliminate this impact.

The other impact to the eggs and larvae results from their encountering salinity levels of 10 ppt or higher. Under the without project conditions, such levels would not be encountered in the Back River during flows of 6,000 cfs or greater. These levels would occur in the Front River below Mile 12.5 when flows are 6,000 cfs.

If the harbor is deepened by four feet, salinities of 10 ppt or higher would exist below Mile 12.6 in the Back River and below Mile 14 in the Front River. Therefore, a 1.5 mile stretch of the river would be impacted when flows are 6,000 cfs.

Deepening of the harbor by two feet would impact approximately a 1 mile stretch of the river under these flow conditions. The impact of harbor deepening would be diminished at higher flows, such as those which normally occur during the spawning season (11,000 18,000 cfs) since adverse salinity conditions would be shifted downstream.

This was shown in Figures 20 through 22, which indicated the impact of flow on salinity levels predicted to result from a 4 foot deepening. At a flow of 12,000 cfs, salinities of 10 ppt or higher would not occur in the Back River and would not occur in the Front River until Mile 10.

Based on conversations with the Georgia Department of Natural Resources, past striped bass egg and larvae sampling in the river has seldom found eggs or larvae below mile 13. Therefore, there is little potential for impact to eggs and larvae due to the upstream shift in salinity levels due to either a two or four foot deepening. Based on the above, there would be no significant impacts to striped bass or other fish species due to the proposed deepening.

Benthics

Benthic communities in the area of channel deepening would be physically disturbed by the dredging activities. This impact would be most noticeable in areas where the channel has to be widened to accommodate the deepened channel, since this would involve dredging in previously undisturbed areas. Most of the benthic communities would be lost from the dredging. After construction, the channel area would be available for recolonization. The extent to which recolonization would occur would depend on the amount of maintenance dredging required. Those areas dredged frequently (1-2 times per year) would probably not be able to support stable benthic communities. Other potential impacts to benthic assemblages are impacts related to the resuspension of sediments by the dredge.

The major impacts of this resuspension are possible burial of organisms and the impacts increased sediment loads may have on feeding, respiration, and/or photosynthetic activity. The benthic organisms of the Savannah Harbor area are adapted to, and highly tolerant of, naturally elevated suspended sediment concentrations for short periods of time. According to Hayes 1986, a hydraulic dredge operating in the Savannah Harbor results in increases in

suspended sediments of less than 200 mg/1. Naturally occurring storm events often increase suspended sediments in the harbor well beyond the increase created by a hydraulic dredge.

Therefore, the existing benthic community in the Savannah Harbor would not be impacted by the resuspension of sediments in the harbor due to Plans 1 and 2. Plan 5-40 has a greater potential for impacting benthic communities, since suspended sediment levels would be greater at the dredge site in the inner harbor due to overflow filling of the dump SCOWS. This impact would be throughout the water column and would have a greater liklihood of impacting benthic communities. Impacts to the benthic community due to the predicted 0.0-1.02 ppt salinity increase that would result from a 2-foot deepening and the 2.03 ppt increase predicted to result from a 4-foot deepening would be minor. This increase would only occur during low flow conditions, which have occurred for only 7 percent of the last 35 years.

Most estuarine organisms are of marine origin (Gunter 1956b, 1961a, Pearce and Gunter 1957) and almost all can live in full sea water, but the lower limits of salinity are limiting or lethal (Gunter 1973). Review of past literature on this subject indicates that, in most cases, organisms living in estuaries can withstand large upward shifts in salinity with little impact on their growth or survival. Sessile organism, due to their immobility, usually have larger ranges of salinity tolerance. Therefore, it is expected that they would be able to survive the predicted increases in maximum salinities, unless a particular species is already living very near its salinity tolerance limits, which is unlikely. mobile species could move to avoid any salinity increases. fact, young mobile animals distribute themselves in the lower salinities and migrate toward the sea as they grow, so that size gradient corresponds to salinity gradient (Gunter 1961b).

Water Quality Surveillance

1.

All
In

To monitor the quality of weir effluent, a water quality sampling program would be conducted during the construction period of Plan Water quality data would be taken in accordance with the schedule indicated below by a qualified independent laboratory or Savannah District employee. If a laboratory is used, the contractor would be responsible for providing this data to the Contracting Officer's Representative (COR). Test results indicating a violation of State Water Quality Standards would be reported immediately to the COR. Results of all other available tests would be sent telephonically on the day the samples are taken. Written confirmation of all the test results would be provided to the COR within 7 days of the sampling, unless laboratory analysis requires extension of this reporting period.