Dredging_Contract_Special_Provisions_12.12.25kr.docx

SPECIAL PROVISIONS

1.0 - General

1.1 Project Description

The primary purpose of this service is for the Contractor to provide sediment dredging, sediment hauling, sediment disposal, and possible barging services for Wheatley Dam reservoir. Wheatley Dam, constructed in 1968, is one of three earthen dams within the Gilbert Run Watershed located near Charlotte Hall, Maryland. The dam is listed within the National Inventory of Dams https://nid.sec.usace.army.mil/nid/#/dams/system/MD00060/summary.

The initial service event may consist of one or two areas of work at the Wheatley Dam reservoir: the northern end of the reservoir and the western cove (bisected by a footbridge). Please see Appendix B: Drawings for approximate locations and general geography. Currently, there is no established total number of dredging service events for this contract. The dredging services are recommended maintenance by the Maryland Department of the Environment (MDE) and the Natural Resource Conservation Service (NRCS). The reservoir has never been fully dredged to the best of the County’s knowledge.

1.2 Project Background

Wheatley Dam’s initial purpose was flood control. The project is located at Wheatley Reservoir, an impoundment of approximately 2,454 acre-feet located near Charlotte Hallin Charles County, Maryland. The reservoir is a non-tidal freshwater waterbody formed by Wheatley Dam; an earthen embankment regulated by the Maryland Department of the Environment (MDE) Dam Safety Division. The drainage area feeding the reservoir encompasses roughly 1,832 acres, and the reservoir discharges southward to tributaries of the Gilford creek watershed.

The normal pool elevation of the reservoir is approximately 95 feet (NAVD 88), with a minimum pool elevation of about 92.5 feet and a maximum pool elevation of approximately 110.7 feet during the design storm event. The water level at the time of the December 2024 bathymetric survey was about two feet below normal due to dry seasonal conditions. Please see Appendices: C, D, E, F, & G.

The bathymetric and sub-bottom profiling surveys conducted in 2024 identified significant sediment accumulation in the northern and eastern portions of the reservoir. Manual sediment probing confirmed unconsolidated deposits averaging 1 to 2 feet in thickness in most areas, with thicker deposits (greater than 2 feet) found in the upper north and eastern lagoon areas. In contrast, the central and southern basins near the dam contain only a thin surface layer of fine material, indicating that much of the original reservoir bottom remains exposed or covered by partially consolidated sediment. Some localized “crunchy” resistance was reported in the probe logs, suggesting layers of cohesive or compacted material beneath the upper silt layer.

The sediment composition is inferred from acoustic attenuation and probe feedback to be fine-grained silt and organic matter, with minimal sand content. The material exhibits high water content and poor strength in shallow deposits, consistent with organic accumulation over time. Due to its fine texture, sediment in the southern basin may be partially transported through the principal spillway during high-flow events, potentially contributing to a gradual loss of reservoir storage capacity.

The surrounding property is composed primarily of wooded parkland and open space managed by Charles County. All work shall be performed in a manner that protects adjacent natural resources and prevents the release of sediment or turbidity into downstream waters. The Contractor shall maintain compliance with all applicable MDE Wetlands and Waterways, Water Quality, and Erosion and Sediment Control permit requirements throughout the dredging operations. Please see Appendix H: Wetland Pre-App.

1.3 Project Timeline

Due to the reservoir’s location within a recreational park and future retrofitting construction of the embankment, coordinated planning is essential. The Contractor shall provide an estimated timeline of the major phases of each dredging service event. Mobilization of a dredging service event must happen within thirty (30) consecutive days after the Contractor has been given notice for an event. It shall be the responsibility of the Contractor to provide revised updated timelines if the timeline estimations change significantly.

Dredging, hauling, and any other disruptive activity must be limited to daytime workdays, Monday through Friday, 7:00 am to 4:00 pm, unless otherwise agreed upon. Dredging service events must be completed before Memorial Day or start after Labor Day of the current calendar year. Park operations may influence the availability of the Contractor to perform dredging-related activities. The County shall provide the Contractor advance notice of any dates on which dredging service events cannot occur.

2.0 Scope of Services

Please see Appendix A: Technical Specifications for Dredging and Sediment Removal.

3.0 BID ITEM DESCRIPTIONS

Prices quoted on base bid items shall include everything necessary for the execution and completion of the work including, but not limited to, finishing all materials, equipment, tools, all management, superintendence, and labor.

3.1 BASE BID ITEMS

3.1.1 Base Bid Item A1: Mobilization & Demobilization

The Contractor shall perform mobilization activities before and demobilizing activities after each dredging service event. Multiple concurrent mobilizations and/or demobilizations are not permitted. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-1 of the Bid Form establishes a per service event unit cost for a mobilization and a demobilization.

3.1.2 Base Bid Item A-2: Reservoir Sediment Dredging

The Contractor shall perform mechanical dredging of accumulated sediment and debris within defined limits. The quantities shall be based on financial resources and with a minimum of 3,000 cubic yards of sediment removed per service event. Implementation of erosion and sediment control and turbidity containment measures are required. Site restoration and stabilization of disturbed areas is required. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-2 of the Bid Form establishes a per cubic yard unit cost for a reservoir sediment dredging.

3.1.3 Base Bid Item A-3: Hauling Sediments

The Contractor shall be responsible for all transport, dewatering, and off-site disposal or beneficial reuse at an MDE-approved facility. The quantities of sediment will be based on financial resources and with a minimum of 3,000 cubic yards of sediment per service event. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-3 of the Bid Form establishes a per cubic yard unit cost for a reservoir sediment hauling.

3.1.4 Base Bid Item A-4: Beneficial Reuse or Disposal Fees

Beneficial reuse or disposal fees of the dredged sediments will be the responsibility of the Contractor. The Contractor will be responsible for sediment sampling analysis. The quantities of sediment will be based on financial resources and with a minimum of 3,000 cubic yards of sediment. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-4 of the Bid Form establishes a per cubic yard unit cost for sediment disposal or beneficial reuse.

3.1.5 Base Bid Item A-5: Post-dredging Bathymetric Survey

Post-dredge bathymetric survey shall be performed, upon request, to record and confirm the change in elevation after a dredging service event. The post-bathymetric survey will be restricted to the areas which had been recently dredged. Post-dredging bathymetric surveys will be performed if the County requests one after a dredging event. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-5 of the Bid Form establishes a per service event unit cost for post-bathymetric surveying.

3.1.6 Base Bid Item A-6: Barge Usage

Barge usage, as needed, may be used by the Contractor to access service areas and transport dredged sediments to staging areas. Technical Specifications for Dredging and Sediment Removal in Appendix A is available for reference.

Base Bid Item A-6 of the Bid Form establishes a per service event cost for barge usage.