Appendix_A_Technical_Specifications_for_Dredging_and_Sediment_Removal.pdf

TECHNICAL SPECIFICATION

FOR

Charles County Government

Department of Public Works

Wheatley Dam Dredging Project

Charles County Project No. 23-32

Langan Engineering and Environmental Services LLC

1300 Wilson Boulevard

Arlington, VA 22209

October 2025

SECTION 02480

DREDGING AND SEDIMENT REMOVAL

PART 1 - GENERAL

1.1 Summary and Scope of Work

The Work includes all labor, materials, equipment, and services required to perform mechanical dredging and sediment removal within the Wheatley

Reservoir to restore capacity and maintain dam performance.

Major activities include:

1. Mobilization/demobilization of dredging and support equipment.

2. Mechanical dredging of accumulated sediment and debris within defined limits.

3. Transport, dewatering, and off-site disposal or beneficial reuse at an MDE-approved facility.

4. Implementation of erosion and sediment control and turbidity containment measures.

5. Post-dredge bathymetric surveys.

6. Site restoration and stabilization of disturbed areas.

Work shall comply with all MDE and USACE permits, including Wetlands and

Waterways, Dam Safety, and NPDES requirements.

1.2 Location and Site Description

A. The project is located at Wheatley Reservoir, an impoundment of approximately

2,454 acre-feet located near La Plata in 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.

B. 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.

C. The bathymetric and sub-bottom profiling surveys conducted in 2024 identified significant sediment accumulation in the northern and western 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 western 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.

D. 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.

E. 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.

1.3 Applicable Regulations and Permits

The Contractor shall perform all work in compliance with the following, including the most recent versions:

1. MDE Wetlands and Waterways, Nontidal, and Dam Safety regulations

(COMAR 26.17 and 26.23).

2. USACE Clean Water Act Section 404 and MDSPGP-6 Authorization for

Minor Dredging.

3. NPDES General Permit for Construction Activity (No. 23GP).

4. Maryland Standards and Specifications for Soil Erosion and Sediment

Control.

5. MDE Innovative Reuse and Beneficial Use of Dredged Material Guidance

(2019).

The Owner will obtain principal permits; the Contractor shall comply with all permit conditions and obtain any secondary approvals required for construction means and methods.

1.4 Contractor Qualifications and Coordination

The Contractor shall have completed at least three (3) comparable dredging projects within the last five (5) years and shall submit qualifications, references, and equipment lists as part of the Dredging Plan.

A pre-construction meeting shall be held with the Owner and Engineer to review permits, methods, and schedules. The Contractor shall coordinate site access, sequencing, and environmental controls throughout the Work and provide 72-hour advance notice prior to dredging.

1.5 Submittals

A. The Contractor shall prepare and submit all documentation, plans, and records necessary to demonstrate compliance with this Specification, the Contract

Drawings, and applicable permits. Submittals shall be transmitted to the

Engineer for review and approval prior to commencement of the associated work activity. Submittals shall be complete, clearly labeled, and include all supporting calculations, maps, and product data as required.

B. A comprehensive Submittal Register shall be provided at the pre-construction meeting, identifying all submittals required under this Specification, the responsible preparer, and the proposed submission and review dates. The

Contractor shall maintain and update the register throughout the project duration.

C. The following submittals shall be provided and approved prior to mobilization or initiation of dredging activities:

1. Dredging Plan – A detailed narrative describing the Contractor’s proposed equipment, methods, sequence of operations, dredge area limits, production rates, staging locations, and estimated schedule. The plan shall include:

a. Type and capacity of dredging and support equipment.

b. Anticipated dredge depths and control of over-dredging.

c. Proposed turbidity and environmental control measures.

d. Methods for material transport and containment.

e. Proposed working hours and sequencing of dredging zones.

2. Bathymetric Survey Plan – Description of the proposed survey equipment, methodology, control points, and deliverable formats for post-dredge surveys.

3. Health and Safety Plan – Site-specific plan meeting OSHA 29 CFR 1926 requirements, addressing over-water work, spill prevention, and emergency response procedures.

4. Project Schedule – A detailed schedule identifying mobilization, dredging, dewatering, disposal, restoration, and demobilization milestones.

5. Equipment Lists and Data Sheets – Manufacturer specifications and performance data for major dredging and dewatering equipment, pumps, and silt curtains.

6. Material Disposal Approval – Documentation of acceptance by the designated disposal or beneficial reuse facility, including MDE approval if required.

D. Dredging Phase Submittals

1. Daily Dredging Logs – Records of daily approximate production quantities, dredge locations, weather conditions, problems encountered, and any environmental control actions taken.

2. Incident Reports – Documentation of spills, permit deviations, or noncompliance events within 24 hours of occurrence.

E. Post-Dredging Submittals

1. As-Built Drawings – Final bathymetric survey showing dredge limits, final grades, and extents of disturbed areas.

2. Final Quantities Report – Computed dredged volumes based on pre- and post-dredge survey data.

3. Disposal Documentation – Weight tickets, manifests, and acceptance certificates from the approved disposal or reuse facility.

4. Site Restoration Certification – Statement confirming all disturbed areas have been stabilized, seeded, and restored in accordance with the

Specification.

5. Permit Closeout Documentation – Copies of all correspondence, monitoring data, and certifications required by MDE or USACE for permit compliance and project closeout.

1.6 Environmental Protection and Safety Requirements

The Contractor shall implement all feasible measures to prevent turbidity, spills, and sediment migration.

1. Fueling shall occur at least 100 ft from water.

2. Spill kits shall be maintained on all vessels.

3. Work shall comply with OSHA 29 CFR 1926 and applicable USCG safety requirements.

4. No equipment or storage shall occur within 100 ft of wetlands.

1.7 Measurement and Payment Basis

Dredging shall be paid at the unit price per ton or cubic yard based on verified weight tickets and manifests dependent on the disposal location.

Mobilization/demobilization and restoration shall be paid as lump-sum items. No separate payment will be made for erosion control or variations in sediment moisture content.

PART 2 – MATERIALS AND DISPOSAL

2.1 Description of Sediment to be Removed

A. The material to be removed under this Contract consists of accumulated fine-grained sediments and organic deposits that have settled within Wheatley

Reservoir since its original impoundment. The dredging area includes the northern arm and western lagoons of the reservoir, where significant sediment deposition has occurred due to inflow transport and low circulation. The dredging limits are defined on the Contract Drawings.

B. Sediment Characteristics

1. Based on the 2024 bathymetric and sub-bottom profiling surveys and manual sediment probing, the accumulated sediment generally consists of soft, unconsolidated silts with moderate to high organic content and occasional fine clay layers.

2. Sediment thickness varies across the reservoir, ranging from 1 to 2 feet throughout most of the dredge area, with thicker deposits exceeding 2 feet in some areas.

3. Acoustic attenuation and field probing results suggest the underlying native substrate consists of dense silt or clay forming a distinct “hard bottom,” which shall not be disturbed during dredging.

C. Debris and Obstructions

1. Limited submerged debris, vegetation, and organic material (e.g., branches, roots, and leaves) were observed in the surveyed areas.

2. The Contractor shall remove incidental debris encountered during dredging and dispose of it at an approved off-site facility.

3. Should the Contractor encounter large obstructions such as stumps, boulders, or buried structures not identified in the Contract Documents, the

Contractor shall notify the Engineer and proceed with dredging in another location with the designated dredging area.

2.2 Material Characterization and Testing

The Contractor shall verify that dredged material is acceptable for disposal or reuse, perform all required sampling and testing per facility requirements, and provide analytical results and facility acceptance letters prior to transport.

2.3 Dewatering, Handling, and Disposal

A. General Requirements

The Contractor shall handle, dewater, and transport all dredged material in a safe and contained manner to prevent spillage, turbidity, or loss of fines. Handling operations include removal, conveyance, containment, drying, loading, and hauling to an approved disposal or beneficial reuse facility. All activities shall comply with

MDE permits, environmental protection requirements, and the Contractor’s

Dewatering and Return Water Management Plan.

B. Material Containment and Control

Dredged material shall be transferred from the dredging equipment to a containment system or designated staging area in a controlled manner to minimize suspended solids. Overflow or uncontrolled discharge is prohibited. Barges and containers shall be managed to prevent overtopping, and material shall not be placed outside approved containment or dewatering areas.

C. Dewatering and Temporary Storage

Material shall be transported to upland dewatering areas shown on the Drawings or approved by the Engineer. These areas shall allow natural drainage without creating ponding or erosion. Erosion and sediment control measures shall be installed per the approved plan and maintained in good condition. Return water shall pass through filtration or sediment control prior to discharge.

Material shall be placed in thin lifts not exceeding 18 inches and alternated between drying areas to promote drainage. The Contractor shall maintain containment berms or silt barriers, inspect them daily, and repair any damage. No material shall be placed within wetlands, floodplain zones, or within 100 feet of the reservoir shoreline without approval.

D. Drying, Loading, and Transport

Material shall remain until sufficiently drained to be handled without free water or sloughing. Material may be loaded when it supports equipment traffic with minimal rutting (≤3 inches) and can be bucketed without draining water. Under normal conditions, 1–3 days of drying per lift is expected. The Contractor may reshape piles to accelerate drying provided runoff remains contained.

Material shall be hauled using watertight, covered trucks or trailers to prevent leakage and dust generation. All trucks shall be cleaned prior to exiting the site.

The Contractor shall comply with applicable transportation, weight, and safety regulations.

E. Weather and Site Management

Placement shall be suspended during heavy rainfall or when saturation prevents stable handling. If one area becomes unworkable, operations shall shift to an alternate drying area. The Contractor shall prevent rutting, compaction, or disturbance beyond designated limits.

F. Spill Prevention and Cleanup

The Contractor shall maintain spill prevention measures for all equipment and conveyance systems. Any accidental spill, leak, or loss of material outside containment shall be immediately contained, recovered, and reported to the

Engineer and Owner. The Contractor is responsible for full cleanup and restoration of affected areas at no cost to the Owner.

G. Records and Documentation

The Contractor shall maintain daily records including dredging and transport volumes, dewatering methods, return water testing, and trip counts. Each truckload shall have a manifest or weight ticket showing date, time, truck number, driver, weight or volume, destination, and receiving facility signature. Copies of manifests and test results shall be submitted weekly to the Engineer and Owner.

2.4 Beneficial Reuse or Off-Site Disposal

A. General Requirements

Following dewatering, all dredged material shall be transported for beneficial reuse or off-site disposal in accordance with MDE regulations and the Contractor’s approved Material Disposal Plan. The Contractor shall not dispose of material within the project limits, floodplain, or wetlands unless expressly approved by the

Engineer and MDE. The method of reuse or disposal shall be determined based on analytical results and acceptance by an authorized receiving facility.

B. Beneficial Reuse

Beneficial reuse shall conform to MDE’s Innovative Reuse and Beneficial Use of

Dredged Material Guidance (2019) or latest revision. Acceptable reuse applications include:

1. Upland fill, grading, or construction backfill (non-structural uses).

2. Mine reclamation or industrial site restoration.

3. Soil amendment or manufactured soil meeting unrestricted use criteria.

4. Habitat creation, shoreline stabilization, or wetland restoration approved by

MDE.

The Contractor shall submit documentation verifying suitability and authorization prior to reuse, including:

5. Analytical results confirming material meets reuse criteria.

6. Written acceptance from the reuse facility or landowner.

7. MDE concurrence or permit modification authorizing reuse.

8. Certification from the receiving facility confirming delivery and placement quantities.

C. Off-Site Disposal

If beneficial reuse is not feasible, material shall be disposed of at an MDE-permitted solid waste or dredged material containment facility. The Contractor shall identify the facility in the Dredging Plan and provide:

1. Facility name, address, and permit number.

2. Written acceptance documentation and fee schedule.

3. Transportation plan showing haul routes and safety measures.

Each load shall be accompanied by a manifest or weight ticket that includes the date, time, truck ID, driver name, quantity, and signature of the receiving facility representative. Copies shall be submitted weekly to the Engineer.

D. Transportation and Handling Requirements

Hauling vehicles shall be watertight, covered, and maintained to prevent leakage or loss of material. The Contractor shall comply with all state and county haul permits, load limits, and safety regulations. Any spillage on public roads shall be immediately cleaned. Damage to roadways, drainage systems, or property caused by transport operations shall be repaired at no additional cost to the Owner.

E. Environmental Compliance

All reuse or disposal activities shall occur only at MDE-authorized facilities per

COMAR 26.04.07 and 26.23.05. No discharge, dumping, or unauthorized placement shall occur outside approved sites. Any violation, spill, or complaint from a regulatory agency or property owner shall be reported immediately to the Engineer and corrected at the Contractor’s expense. If contamination is discovered during transport or at the receiving facility, the Contractor shall suspend operations and coordinate corrective actions with the Engineer and MDE.

F. Final Documentation

Upon completion of reuse or disposal activities, the Contractor shall submit a Final

Disposal Summary Report that includes:

1. Total quantities of material reused or disposed.

2. Copies of all manifests, weight or volume tickets, and acceptance receipts.

3. Description of the final disposition for each material type and facility.

4. Photographic documentation of completed site conditions.

The Final Disposal Summary Report shall be reviewed and approved by the

Engineer prior to project closeout.

2.5 Erosion and Sediment Control Materials

A. General Requirements

The Contractor shall furnish, install, and maintain all erosion and sediment control

(E&S) materials necessary to prevent sediment migration, turbidity, or off-site runoff from dredging, dewatering, and material handling operations.

All materials and installations shall conform to the Maryland Standards and

Specifications for Soil Erosion and Sediment Control (latest edition) and the project’s approved Erosion and Sediment Control Plan. Where this Specification is silent, the Maryland standards shall govern.

B. Materials and Installation

E&S materials may include silt fence, super silt fence, compost filter logs, straw bales, turbidity curtains, and other measures as required by the site-specific plan.

The Contractor shall install each device per the Maryland standards and maintain it in good condition until disturbed areas are stabilized. Sediment shall be removed when accumulation reaches one-half of the barrier height.

C. Maintenance and Removal

E&S controls shall be inspected daily during active work and after any rainfall event exceeding 0.5 inch. Damaged or displaced controls shall be repaired immediately.

Upon final stabilization and acceptance, the Contractor shall remove temporary

E&S devices and properly dispose of used materials off-site.

PART 3 – EXECUTION

3.1 General Requirements

All dredging, dewatering, and disposal operations shall be performed safely, efficiently, and in full compliance with this Specification, the Contract Drawings, permits, and the Contractor’s approved Dredging Plan. The Contractor shall coordinate continuously with the Engineer and Owner and maintain compliance with all environmental and safety regulations throughout construction.

3.2 Site Preparation

Prior to commencing dredging, the Contractor shall:

1. Verify access, water levels, and site conditions.

2. Install all required erosion and sediment control measures.

3. Establish upland containment and dewatering areas.

4. Set and verify survey control points and benchmarks.

All preparatory work shall be approved by the Engineer prior to mobilization of dredging equipment.

3.3 Environmental and Erosion Control

The Contractor shall maintain all erosion and sediment control measures per the approved plan and Maryland Standards. Turbidity curtains shall be deployed as required to isolate work zones and protect adjacent wetlands.

1. Inspect and maintain all controls daily and after rainfall events.

2. Repair damaged barriers immediately and remove sediment buildup when it reaches half the control height.

3. Prevent discharge of dredged water or slurry directly into surface waters without prior treatment.

4. Maintain fueling and hazardous material handling areas at least 100 feet from the reservoir.

5. Immediately notify the Engineer and MDE if any inadvertent disturbance to wetlands occurs and implement corrective actions as directed.

3.4 Wetland Protection and Exclusion Zones

A. General

1. Jurisdictional wetlands and waters of the State have been identified adjacent to the dredging areas as documented in the MDE Wetland

Delineation and Assessment Report (included as an appendix to this

Specification).

2. The approximate boundaries of these wetlands are shown on the Contract

Drawings and shall be clearly marked in the field prior to dredging.

3. The Contractor shall not enter, disturb, or perform any dredging, excavation, staging, or equipment operation within delineated wetland areas unless specifically authorized in writing by the Engineer and the

Maryland Department of the Environment (MDE).

B. Compliance and Coordination

1. All work shall comply with the approved MDE Wetlands and Waterways

Permit, and the Contractor shall adhere strictly to the wetland limits established in the MDE Wetland Assessment appended to this

Specification.

2. The Contractor shall immediately notify the Engineer and MDE of any inadvertent encroachment or disturbance to delineated wetlands.

3. The Contractor shall be fully responsible for any restoration or mitigation required as a result of unauthorized disturbance to regulated wetland areas.

C. Prohibited Activities

1. No equipment storage, fueling, or maintenance shall occur within 100 feet of delineated wetlands.

2. No temporary access routes, dewatering areas, or stockpiles shall be placed within wetland boundaries.

3. No alteration of wetland vegetation, soil, or hydrology shall occur except as expressly permitted by MDE.

3.5 Dredging Execution and Grading

Dredging shall be performed only within the authorized limits shown on the

Drawings and as approved by the Engineer. The Contractor shall:

1. Remove accumulated soft sediment down to firm substrate or until the specified removal quantity is reached.

2. Maintain uniform bottom conditions and side slopes not steeper than

3H:1V.

3. Avoid disturbing wetlands, embankments, or existing structures.

4. Terminate dredging at least 5 feet waterward of delineated wetland boundaries unless otherwise approved by MDE and the Engineer.

5. Conduct operations in controlled, uniform lifts to minimize turbidity and resuspension.

6. Coordinate sequencing to ensure containment and dewatering capacity are not exceeded.

All dredging shall proceed systematically, generally from upstream to downstream, and shall be suspended during unsafe water levels, excessive turbidity, or severe weather. The Engineer may direct adjustments to sequencing or limits as necessary.

3.6 Dredging Operations

A. Method of Dredging

Dredging shall be performed using a barge-mounted, amphibious, or long-reach hydraulic excavator, or equivalent equipment approved by the Engineer. The equipment shall safely and efficiently remove soft sediment while maintaining precise depth control and minimizing turbidity, resuspension, and water quality impacts.

B. Equipment Requirements

1. Dredging Excavator:

a. Shall be barge-mounted, amphibious, or long-reach type with sufficient reach to excavate the full dredge prism from designated positions.

b. Equipped with a smooth-edged or sealed environmental bucket to minimize water entrainment and turbidity.

c. Bucket size and cycle rate shall balance production with environmental compliance.

d. Hydraulic systems shall be leak-free and maintained in good condition;

biodegradable fluids shall be used where practical.

2. Support Barges and Platforms:

a. Floating work platforms shall be stable under loaded conditions and comply with U.S. Coast Guard standards.

b. Sufficient freeboard shall be maintained to prevent overflow or loss of material.

c. A push boat or tender shall be provided for barge positioning and maneuvering.

C. Operations and Controls

1. Dredging shall proceed systematically in uniform lifts, removing sediment in layers not exceeding 1 foot per pass.

2. The bucket shall be raised slowly to minimize suspended solids; rinsing or agitation below the water surface is prohibited.

3. Each load shall be placed into a barge, scow, or hopper in a controlled manner to prevent spillage or overflow.

4. No mechanical agitation or jetting shall be permitted unless specifically approved by the Engineer.

5. Dredging shall progress from upstream to downstream or as directed by the Engineer to maintain water quality and containment capacity.

D. Material Handling and Offloading

1. Dredged material shall be transferred at designated shoreline or containment areas approved by the Engineer.

2. Transfer shall be continuous to avoid overloading barges and minimize free water loss.

3. Offloading shall be performed in a controlled manner to prevent spillage or overflow, maintaining safe draft and stability at all times.

4. Return water decanted from barges shall be directed through approved treatment or settlement structures prior to discharge.

E. Equipment Maintenance and Inspection

1. The Contractor shall maintain all dredging and support equipment in proper working order, free from leaks and defects.

2. Daily inspections shall include hydraulic systems, fuel lines, alarms, lighting, pumps, and ballast systems.

3. Fluid changes, fueling, and maintenance shall occur at designated fueling areas located at least 100 feet from the reservoir unless otherwise approved.

4. Spill containment kits shall be kept on each vessel and inspected daily.

F. Production and Environmental Control

1. Production rates shall not exceed containment or dewatering capacity.

2. Turbidity and water quality shall be monitored regularly; production rates, bucket size, or lift thickness shall be adjusted as needed to maintain compliance.

3. The Contractor shall keep daily records of dredging volume, equipment hours, and environmental readings.

G. Equipment Movement and Access

1. Movement of floating equipment shall be planned to minimize disturbance of the reservoir bottom and shoreline.

2. Anchoring or spudding shall occur only in approved locations.

3. The Contractor shall coordinate movement near the dam, spillway, and outlet works with the Owner to avoid interference with operations.

4. Access routes and launch areas shall be restored to original condition upon project completion.

H. Noise and Vibration Control

1. Engines, pumps, and mechanical systems shall be equipped with mufflers or sound-dampening devices to limit disturbance to adjacent parklands and wildlife.

2. Equipment shall be operated to minimize vibration transmission through the water and substrate.

3. Any noise or nuisance complaints shall be investigated promptly, and corrective actions implemented as directed by the Engineer or Owner.

I. Shutdown and Emergency Procedures

The Contractor shall maintain a written Emergency Shutdown Plan addressing equipment malfunction, barge instability, spills, turbidity exceedances, or unsafe weather or water conditions. Upon any such event, dredging shall immediately cease, containment measures implemented, and the Engineer and

Owner notified. Work shall not resume until corrective actions are approved.

J. Daily Operational Logs

The Contractor shall maintain a Daily Dredging Log including:

1. Date, weather, and water level.

2. Equipment in operation and crew on site.

3. Dredging area and estimated volume removed.

4. Turbidity and water quality data.

5. Maintenance actions, incidents, or corrective measures.

Logs shall be submitted weekly to the Engineer as part of project documentation.

3.7 Site Restoration and Cleanup

Upon completion of dredging and hauling:

1. Remove temporary containment and E&S measures.

2. Regrade disturbed areas to pre-work contours.

3. Apply topsoil and seed per the Maryland E&S Manual.

4. Repair any rutting or damage to access routes, park surfaces, or vegetation.

5. Remove all temporary facilities, debris, and unused materials from the site.

Pre- and post-construction photographs shall document restoration. Final payment will not be made until the Engineer verifies that all restoration, stabilization, and documentation requirements have been met.

END OF SECTION 02480