The land utilized for sediment storage and dewatering could benefit from the
reclaimed topsoil if the dried sediment is graded properly after the dredging project has
been completed. For a project of this size, one to two years after dredging is complete
is a normal time period to allow sufficient drying time prior to site grading and
reclamation. The dredged sediments can also be land applied and beneficially reused
as fertile agricultural soil and/or fill. Further evaluation and analysis will be required to
find a suitable location(s) for a detention site(s).
The laboratory analyses of two sediment core samples collected by HDR│CWI
indicated a very high percentage of fine grained silt and clay particles (see Appendix),
which typically remain in suspension for long periods of time and re-suspend easily
when agitated in shallow water. Although preliminary laboratory analysis indicated no
elevated chemical constituents, a polymer or flocculent will likely be required during
dredging in order to satisfy Illinois EPA effluent discharge requirements for total
suspended solids (TSS) at the sediment storage and dewatering site. The flocculent
would be a minimal additional cost to the overall dredging project.
The scope of engineering services for a typical dredging project include planning,
design, permitting, bid document preparation and coordination of potential bidders, and
construction phase oversight. Table 7 summarizes work tasks that would be required
for a sediment removal project and an opinion of the estimated costs for completion
based on removal of an estimated 64,498 cubic yards from Lake Hillsboro.
Table 7. Estimate of Probable Sediment Removal Costs
Work Task Quantity
Dredging Lake Segments ($5.00/cy) 64,498 cu. yds. $322,490
Dredge Mobilization and Demobilization 1 Lump Sum $50,000
Polymers / Flocculants for Effluent Water ($0.50/cy) 1 Lump Sum $32,249
Construct Sediment Retention/Dewatering Facility * 1 Lump Sum $75,000
Contingency (10%) $47,974
Engineering and Permitting (15%) $71,961
Illinois EPA Permit Fees (i.e. dredging, stormwater) 1 Lump Sum $4,725
Total Estimated Cost for Dredging $604,399
Probable Site Reclamation Cost 1 Lump Sum $50,000
* Approximately a 10 acre site
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