Thus, the current advance maintenance practice is considered a without project condition and is retained. A summary of this analysis is contained in a supplemental document on advance maintenance practices for Savannah Harbor. Therefore, the

operation and maintenance costs would remain the same as for the existing project, and no operation and maintenance costs have been assigned to the selected plan.

COST ENGINEERING

The cost estimate for construction of Plan 1-40 and Plan 1-42 reflect February 1992 price levels. For both Plan 1-40 and 1-42, the dredging estimate is based on utilizing 30-inch hydraulic pipeline dredges for the removal of material from the harbor channel and a 30-inch hydraulic pipeline dredge with a spider barge and dump scows for the jetties channel and bar channel. Table 45 presents a summary of the dredging requirements.

The material to be removed from the harbor channel harbor consists of silt, loose sand, and partially cemented rock-like (marl/hardpan), with disposal of the dredged material in existing diked upland disposal areas. Some of the material is classified as being rock-like, such as having cementation, induration, being ompacted or hard, or having high blow counts. However, these materials can be removed with a large hydraulic pipeline dredge without pretreating with blasting.

The material to be removed from the jetties channel and bar channel consists of silt, sand, and fat clay, with disposal in the ocean dumping site approved by the U.S. Environmental Protection Agency.

For both plans, the costs stated in the estimate represent dredging a box cut to the project depth, with an allowance of 85 percent of the available side slopes for sloughing. Authorized advanced maintenance is included, with no allowance for paid overdepth or rock tolerance.

Material percentages for new work dredging were derived from inspection of 64 of the new borings drilled between November 1991 and January 1992 and approximately 150 old borings drilled between 1966 and 1982. The materials in the logs were divided into discrete intervals consistent with their character. Each of these intervals was summed and then divided by the total interval from the top to the required depth to give a percentage. Detailed cost estimates were developed for each reach of the project using three 30-inch hydraulic pipeline dredges for the removal of maintenance and new work material for the total navigation channel. Cost estimates of the same level of detail were also developed using two 18-inch hydraulic pipeline dredges for each reach of the harbor channel and two medium class hopper dredges for the jetties channel and bar channel for the removal of maintenance material. The difference in the two cost estimates is the cost of the new work dredging.

The costs of mobilization and demobilization were developed for the three 30-inch hydraulic pipeline dredges being located within an 800 mile radius of the project, the two 18-inch hydraulic pipeline maintenance dredges being located within a 125 mile radius, and the two medium class hopper dredges located within 800 miles of the project. The cost of mobilization and demobilization for maintenance dredging has been deducted from the cost of mobilization for the new work dredging.

Environmental restrictions prohibit dredging above mile 5.0 from 16 March to 31 May. It is anticipated that the contractor would dredge below mile 5.0 (Station 26+400) during this time period and would not require any work stoppage or additional mobilization cost.

From 01 December to 31 March, support vessel speeds would be limited to less that 5 knots during nighttime operations. This restriction would not affect the contractor's operation since the vessel towing the dump scows is unable to achieve speeds greater than 5 knots.

The estimate contains an OMB escalation factor of 5.92 percent to the midpoint of construction, July 1993, for Plan 1-40, and an escalation factor of 6.23 percent to the midpoint of construction, August 1993, for Plan 1-42. The construction time of 13 months for Plan 1-40 and 15 months for Plan 1-42 is based upon the harbor channel, jetties channel, and bar channel being dredged concurrently.

Range

The estimate contains a contingency of 10 percent. estimating was performed using the 'Range Estimating Program' developed by Decision Sciences Corporation. Quantities and geological interpretations furnished by the Savannah District design elements were used to generate minimum and maximum estimates to the same level of detail as the Baseline Estimate. Probabilities of being over or under the Baseline Estimate were developed by Cost Engineering, based on information gained while preparing the Baseline Estimate. In general, it is believed that the assumptions used in developing the Baseline Estimate were conservative. The probability of the construction cost being within the Baseline Estimate is approximately 97.5 percent.

The estimate contains costs for acquiring real estate due to impacts of side slope instability on adjacent properties. It has been determined that no impacts on structures would occur. Relocating the bar channel buoy and establishing two new channel marker buoys would be accomplished by the U.S. Coast Guard and all costs associated with navigation aids are addressed in the estimate. New work dredging would not be required for centerline realignment or turning basins other than Kings Island Turning Basin. Georgia Port Authority docks are presently maintained at elevation -40 feet mlw and therefore would not require any new work dredging for Plan 1-40.

Alternate methods of dredging Stations -0+000B to -60+00OB were developed using hopper dredges and a clamshell dredge with dump scows. Due to costs and duration, it was determined that a 30-inch hydraulic pipeline dredge with spider barge was the most cost effective method of dredging the jetties channel and bar channel.

COST SUMMARY OF SELECTED PLAN

The following is a summary of the pertinent cost items for the Selected Plan.

Dredging

The Selected Plan provides for dredging the harbor channel and jetties channel to 42 feet and dredging the bar channel to 44 feet. Kings Island Turning Basin would also be dredged to 42 feet, and berthing areas at the Garden City Terminal and Ocean Terminal would be dredged to 42 feet.

Table 46 shows the total dredging costs for the Selected Plan. Costs also include water quality surveillance during dredging operations and navigation aids.

Table 47 provides a summary of all Engineering and Design work to be performed during Preconstruction Engineering and Design. The Engineering Appendix contains additional information on the Preconstruction Engineering and Design costs by Engineering Division.

Engineering Division has included a cost estimate for engineering during construction which amounts to $384,000 for the Selected Plan.

Construction Management

Construction Management costs for the Selected Plan includes Title II inspection costs and contract administration, based upon the simultaneous operation of four barges during dredging operations and continuous dredging. The total Construction Management costs are estimated to be $4,950 per day, which equals $2,213,000 for General Navigation and $45,000 for the berthing areas.

Navigation Aids

Cost estimates for the Selected Plan include $44,000 for the relocation of sea buoys.

Lands and Damages

Real estate requirements for the Selected Plan include the purchase of perpetual sloughing easements covering approximately 14 acres along both banks of the Savannah River. As was shown in Table 43, the land costs for the Selected Plan are $826,000.