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Dog Beach Landfill Shoreline Stabilization Pilot Study

Christopher J. Calabretta

Fort Monroe, Virginia

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Overview

History and background
Dog Beach Landfill shoreline stabilization
Living shorelines
Pilot study test plot construction
Initial monitoring results
Preliminary lessons learned
Next steps

Southern Cove, Dog Beach Landfill

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Fort Monroe: Background

565.5 acres on Old Point Comfort in Hampton, VA
Chesapeake Bay to the east and Mill Creek to the west
Closed under the 2005 BRAC Act

Source: U.S. Geological Survey 24k Topographic Data

Hampton, VA and Norfolk, VA North Quadrangles

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Dog Beach Landfill

Approximately 40-acre, unlined landfill

Northernmost area of Fort Monroe, west of Fenwick Road
Operated from 1930s to 1960s

Received unknown quantities of construction demolition debris, incinerator ash, and household solid waste

1957 U.S. Army map indicated 2 feet of soil cover would be placed over garbage and waste materials
It is unknown if or when this practice was used

Dog Beach

Landfill

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Dog Beach Landfill: Background

An incinerator used for on-post generated waste

Operated between 1940s and 1960s
Aerial photography shows ash disposal in southern part of the landfill

1945 Aerial View

Source: U.S. Army Topographic Engineering Center, August 2007

Dog Beach – Analysis of Historical Aerial Photography

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Dog Beach Landfill: Sampling Summary

2007: Site Inspection

Majority of screening criteria exceedances in southern ash disposal area

Further evaluation warranted

2009-2010: Initial sampling

No exceedances east of Fenwick Road
No unacceptable risks for planned future use (recreational)

Collect additional sediment and surface soil samples; evaluate unrestricted use risks in a Feasibility Study

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Dog Beach Landfill: Sampling Summary (continued)

2011-2012: Follow-on sampling

VDEQ requested sampling for polynuclear aromatic hydrocarbons (PAHs), pesticides, and polychlorinated biphenyls (PCBs) in three distinct areas

PAHs exceeded ecological screening in southwest cove
Pesticides detected at much lower concentrations around original sample
PCBs not fully delineated in west central cove

2016-2019: Follow-on sampling

Additional soil and sediment sampling to delineate the PCB contamination
Shallow test pitting to better understand the soil cover over the landfill
Following stakeholder input, additional data were collected from soil, surface water, sediment, and shellfish tissue to further define the extent of contamination and to fill data gaps

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Dog Beach Landfill: Field Activities

Collected 547 samples from 2007 to 2019:

Surface and subsurface soil, surface water, sediment, groundwater, biota (fish, crabs, shellfish)

Conducted various surveys:

Geophysical, topographical, wetlands, threatened and endangered species habitat, dune assessment

Dug 75 test pits:

Identify the presence/depth of waste materials

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Dog Beach Landfill: Feasibility Study

Chemicals of concern driving unacceptable risks for the proposed future recreational land use include:

Soil

Dioxins/Furans
PCBs
PAHs

Sediment

PAHs
PCBs

The U.S. Army will follow the Presumptive Remedy for Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Municipal Landfill Sites and Application of the CERCLA Municipal Landfill Presumptive Remedy to Military Landfills

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Presumptive Remedy

The presumptive remedy for a municipal landfill is source containment, which incorporates engineering controls to cover waste, eliminate exposure, and prevent migration of source material

Place 2-foot cap/cover to contain landfill contents, prevent direct contact, and reduce infiltration
Remove elevated concentrations of PCB hot spot, as defined under the presumptive remedy
Stabilize the shoreline to control erosion, surface water runoff, and contaminant release and migration

Actions Not Associated with Presumptive Remedy

Areas responsible for unacceptable risks that are not suitable for cap/cover (sediment and soil in wetlands) will be remediated

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Dog Beach Landfill Shoreline Stabilization

Located on a narrow sand bar between the Chesapeake Bay and Mill Creek, impacts from severe weather and sea-level rise are important considerations for the long-term success of future landfill containment measures

https://www.vims.edu/research/products/slrc/index.php

https://scijinks.gov/storm-surge/

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Dog Beach Landfill Shoreline Stabilization (continued)

The Mill Creek shoreline of Dog Beach Landfill consists of existing wetlands and tidal mudflats, with intermittent areas of exposed riprap and concrete rubble along its length

Steeper banks arise in the southern portion of the landfill, near the former incinerator and ash disposal area
This variability in shoreline profile will likely require the use of multiple methods of shoreline stabilization to provide long-term protection of Dog Beach Landfill

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Living Shorelines

“A living shoreline has a footprint that is made up mostly of native material. It incorporates vegetation or other living, natural ‘soft’ elements alone or in combination with some type of harder shoreline structure (e.g., oyster reefs or rock sills) for added stability. Living shorelines maintain continuity of the natural land–water interface and reduce erosion while providing habitat value and enhancing coastal resilience” (NOAA 2015).

https://www.habitatblueprint.noaa.gov/living-shorelines/

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Living Shorelines (continued)

Living shorelines provide resiliency by attenuating wave energy, reducing erosion rates and storm damage, and absorbing storm surge and flood waters
Living shorelines become more stable over time and outperform hardened shorelines during storm events
Wave energy dissipation causes increased sediment deposition, resulting in vertical and horizontal accretion that will enable a salt marsh to maintain surface elevation relative to sea level rise
Living shorelines provide ecosystem services, including improved water quality and enhanced aquatic habitat

Source: https://oceanservice.noaa.gov/facts/living-shoreline.html

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Shoreline Stabilization Pilot Study

The goal of the pilot study is to find the best stabilization options to enhance resilience along the landfill shoreline and provide an additional layer of protection from erosion during the remedial design stage of the CERCLA work

Survey (topography and bathymetry) along 1,200 linear feet of Mill Creek shoreline in southern landfill
Install four different types of test plots (hardscapes and softscapes/living shorelines)
Monitor plots for 20 months

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Pilot Study Test Plots

Test plots were installed May/ June 2022
Monitoring initiated in July 2022
Local tide gauge was installed

Plot A

Plot B

Plot C

Plot D

Control

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Test Plot Construction

Design phase considered sustainability requirements in FAR Part 23 and other green technologies
Worked to achieve low-impact environmental goals consistent with coastal resilience objectives
Construction approach minimized overall project carbon footprint and impacts on existing conditions

Use of long reach excavator replaced several pieces of equipment required with conventional techniques
Low-impact mud mats minimized impacts to existing vegetation and shoreline

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Test Plot Construction�(continued)

Construction sequence:

Rock (Plot B) and oyster (Plot C) sills; rip rap (Plot A)
Sand fill for Plots B and C
Plot D coir log and sand fill
Wetland planting

Tradeoff for efforts to reduce environmental impacts from conventional heavy equipment was an expanded construction schedule

Increase in manual labor
Although materials were delivered point of construction by the long reach excavator, many materials required hand placement (e.g., oyster castles)

Plot B

Plot C

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Test Plot Construction� (continued)

Installing the rock (Plot B) and oyster sills (Plot C) first allowed for more accurate sand backfill placement

Reduced the overall amount of fill required
Reduced the amount of fuel required to deliver backfill

Since backfilling occurred over several tidal cycles, allowed the team to evaluate performance and make real-time design changes to enhance performance and minimize construction change orders and schedule impacts

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Test Plot Construction� (continued)

Rock for traditional rip rap sized to meet site parameters

Existing historical remnants of rock rip rap and concrete rubble incorporated into final revetment
Larger surface pieces in Plots A, B, and C resized with hydraulic hammer

Plot A

Existing concrete rubble

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Wetland Test Plots

Constructed wetlands are 60 feet wide and extend approximately 20 feet from shore
Plots B and C grade from MHW at shoreline to approximately -0.5 feet NAVD88 at sill
Plot D ties into existing wetland grade at shoreline

Plot B

Plot C

Plot D

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Typical Test Plot Monitoring Locations

Permanent photo marker for wetland hydrology
Sample quadrats for vegetation community
Photo quadrats for oyster settlement
Sediment plates
Sediment pins

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Initial Monitoring Results

After 5 months, retention of imported sand is good and established slopes remain intact
Plant survival and growth is good; new stems and seed heads were observed in all three wetland test plots
No evidence of persistent ponding, puddling, or erosive channels was found

Photos from October 2022

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Initial Monitoring Results (continued)

Rip rap and sills remain intact and appear to be unchanged
Oyster settlement is occurring on both sills and rip rap; oyster growth appears greatest at deepest sill depth
Test plots survived wind/weather/flood conditions associated with first major storm event since construction

Photos from October 2022

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Initial Monitoring Results (continued)

Remnants of Hurricane Ian brought wind, rain, and tidal flooding to region 9/30-10/1
Moved offshore and formed a nor’easter that returned 10/3-10/4
Flooding captured on Dog Beach Landfill tide gauge
Plots held up well; no noticeable effects observed during the 10/10 monitoring event
Data show no evidence of storm-related sedimentation or erosion

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Preliminary Lessons Learned

After 4 months of sun exposure, herbivory controls had deteriorated and required replacement

Mill Creek tides are strongly influenced by weather; can cause highs and lows that depart from predictions

Extremely high tides during the week of 5/8 caused flooding on the James River
This will impact project execution and may impact plant survival if plants have not had sufficient time to establish themselves at the site before conditions occur

https://www.weather.gov/marfc/

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Next Steps

Herbivory controls will be replaced in December
Test plot monitoring continues through February 2024

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Questions?

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