6_AMB_EA_Appendixes_April_2016_508_(1).pdf

National Park Service United States Department of the Interior

Environmental Assessment

The Arlington Memorial Bridge Rehabilitation

April 2016

Appendixes

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APPENDIX A: CONSULTATION LETTERS

Bran

Arlington Mem

APPENDIX B: WETLAND STATEMENT OF FINDINGS

STATEMENT OF FINDINGS

FOR

EXECUTIVE ORDER 11990 (PROTECTION OF WETLANDS)

THE ARLINGTON MEMORIAL BRIDGE REHABILITATION

GEORGE WASHINGTON MEMORIAL PARKWAY

Recommended:

Superintendent, George Washington Memorial Parkway Date

Certification of Technical Adequacy and Service-wide Consistency:

Water Resources Division Date

Approved: ____________________________________________________________________________ Regional Director, National Capital Region Date

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Arlington Memorial Bridge Rehabilitation Wetland Statement of Findings Table of Contents

TABLE OF CONTENTS

Introduction

Purpose of Proposed Action

Alternatives

No-Action Alternative

Elements Common to the Action Alternatives

Action Alternatives

Upland Staging Areas

Staging Areas Within the Potomac River

Causeways

Work Platforms

Temporary Trunnion Shoring

Site Description

Wetlands

Wetland Assessment Methodology

Wetlands within the Project Area

Evaluation of Wetland Functions and Values

Submerged Aquatic Vegetation Beds

Unconsolidated Bottom Habitat

Impacts to Wetlands/Waters

Justification for the Use of Wetlands

Mitigation Measures

Submerged Aquatic Vegetation Restoration Opportunities

Potomac River Mitigation Opportunities

Anacostia River Mitigation Opportunities

References

LIST OF FIGURES

Figure B-1: Project Area Map Figure B-2: Proposed Work Areas within the Potomac River Figure B-3: Location of SAV beds Figure B-4: Wetland Impact Areas Figure B-5: Key to SAV Restoration Opportunity Maps Figure B-6: Tile #1-Potential SAV Mitigation Opportunities i

Wetland Statement of Findings Table of Contents

Figure B-7: Tile #2-Potential SAV Mitigation Opportunities Figure B-8: Tile #3-Potential SAV Mitigation Opportunities Figure B-9: Tile #4-Potential SAV Mitigation Opportunities Figure B-10: Tile #5-Potential SAV Mitigation Opportunities Figure B-11: Tile #6-Potential SAV Mitigation Opportunities Figure B-12: Tile #7-Potential SAV Mitigation Opportunities Figure B-13: Tile #8-Potential SAV Mitigation Opportunities

LIST OF TABLES

Table B-1. Preferred Alternative Temporary And Permanent Impact Totals Table B-2. Impacts Resulting from Scour Countermeasures ii

Wetland Statement of Findings

INTRODUCTION

Executive Order 11990 - Protection of Wetlands (Published in 1977) requires the National Park Service (NPS) and other federal agencies to evaluate the likely impacts of actions in wetlands. NPS Director’s Order #77-1: Wetland Protection (effective October 2002) and Procedural Manual #77-1:

Wetland Protection (reissued in January 2012) provides NPS policies and procedures for complying with Executive Order 11990.

Pursuant to the National Environmental Policy Act of 1969, Section 101(2)(C) as amended, the National Park Service, in cooperation with the Federal Highway Administration, is evaluating the proposed rehabilitation of the Arlington Memorial Bridge. The historic bridge spans the Potomac River between the National Mall in Washington, DC, and Arlington National Cemetery in Arlington County, Virginia. The bridge, administered by the George Washington Memorial Parkway, is an important element to both the regional transportation network and the monumental core of Washington, DC. The Arlington Memorial Bridge is in need of repair to restore the structural integrity of the bridge. Therefore an Environmental Assessment is being completed to evaluate the impacts of several proposed alternatives.

This Statement of Findings for Wetlands was prepared per Director’s Order #77-1: Wetland Protection for the proposed Arlington Memorial Bridge Rehabilitation. A Statement of Findings has been completed because some of the proposed rehabilitation and reconstruction activities would take place in the Potomac River and would affect wetlands as defined by the National Park Service.

The project area is shown in Figure B-1.

PURPOSE OF PROPOSED ACTION

The purpose of the proposed action is to restore the structural integrity of the Arlington Memorial Bridge while protecting and preserving, to the extent feasible, its memorial character and significant design elements. The Arlington Memorial Bridge is more than 80 years old and has never undergone a major rehabilitation. Several temporary repairs have kept it operational to meet the needs of the traveling public. However, like many other older highway bridges across the nation, this bridge needs comprehensive repair to ensure its ability to provide adequate traffic service for decades to come.

The Federal Highway Administration regularly inspects the bridge in accordance with industry standard structural engineering guidelines and standards. These detailed structural inspections and studies have identified significant amounts of corroded steel and deteriorated concrete. The most critical elements needing repair are the concrete spans and the steel bascule (drawbridge) span.

Therefore, the project is needed to address the ongoing corrosion of steel structural members of the bascule span, deterioration of the concrete on the bridge’s approach spans, and deterioration of the sidewalks and wearing surface.

While the bridge is still considered safe for travel, the superstructure is deteriorating at an accelerated pace. The National Park Service, at the recommendation of the Federal Highway

Administration, has posted a 10-ton load limit across the entire length of the bridge. The load restriction, which has eliminated most bus traffic, would remain in effect until such time as the permanent rehabilitation project is complete. As the bridge continues to deteriorate, the National Park Service and the Federal Highway Administration may impose further weight restrictions or close the bridge.

Figure B-1: Project Area Map

ALTERNATIVES

No-Action Alternative

The No-Action Alternative describes the action of continuing present management operations and conditions. While the No-Action Alternative does not meet the purpose and need of the project, it provides a basis for comparing the management direction and environmental consequences of the Action Alternatives.

Under the No-Action Alternative, the National Park Service and Federal Highway Administration would not perform a major rehabilitation project on the Arlington Memorial Bridge and therefore there would be no resulting wetland impacts. Under the No-Action Alternative the load restriction would remain in effect indefinitely as no major repairs would be made to the bridge.

Elements Common to the Action Alternatives

There are several construction elements that are common to all the Action Alternatives that have the potential to impact wetland/waters within the Potomac River.

Repairs to the Concrete Arch Spans. The Arlington Memorial Bridge consists of 10 reinforced concrete arch spans that require varying levels of structural repair. The work needed to rehabilitate the concrete spans includes replacing the concrete deck, filling cracks with epoxy, patching concrete spalling with concrete repair compound, and replacing the concrete edge beams.

Repairs to the Concrete Bridge Piers. Several concrete bridge piers have cracking and scouring surrounding the piers that require repair below water. In order for structural repairs to occur, cofferdams would be installed to dewater the area around the bridge piers. Cofferdams are installed into the substrate and provide a barrier around the site to keep water from entering. This allows concrete repairs to be completed in a dry working environment. Cracks in the bridge piers/abutments would be filled using an epoxy suitable for underwater applications and then wrapped with fiber reinforced polymer. Undermined footing areas would be filled with grout, and scouring would be addressed by placing scour countermeasures around the piers for protection.

Action Alternatives

The Environmental Assessment presents four Action Alternatives all of which include the rehabilitation and repair of the concrete spans and associated bridge features. The four alternatives evaluate different ways to repair/replace the bascule span.

Alternative 1A. Alternative 1A involves the replacement of the existing bascule span with a new fixed span comprised of precast concrete box girders. Alternative 1A includes two potential construction methodologies; Construction Methodology A which requires full closure of the bridge for a portion of the construction period, and Construction Methodology B which includes partial closure of the bridge during construction.

Alternative 1B (Preferred Alternative). Alternative 1B would include the replacement of the existing bascule span with a new fixed span comprised of variable depth steel girders. Alternative 1B would also use one of two construction methodologies as described in Alternative 1A. The preferred construction methodology is Method A.

Alternative 2. Alternative 2 consists of replacing the existing bascule span with a new fixed arch span of welded steel truss construction that would visually replicate the construction of the existing span. Alternative 2 only has one possible construction methodology which includes full closure of the bridge for a portion of the construction period.

Alternative 3. Alternative 3 consists of repairing / rehabilitating all necessary elements of the existing bascule span in place. Alternative 3 construction methodology includes full closure of the bridge for a portion of the construction period.

The construction methodology would be determined by the selected contractor. The potential construction areas are described below. The preferred alternative includes construction activities within the upland staging areas, work zone which includes the causeway/platform area, Barge Staging Area 1 and the associated dredge area.

Upland Staging Areas

Four potential land-based staging areas, two on the west side of the bridge and two on the east side of the bridge may be used for any of the Action Alternatives. Staging Areas A, B, C and D are currently maintained grass areas that contain no jurisdictional wetlands.

Staging Areas within the Potomac River

Barge Staging Area 1 (Preferred Alternative). Barge Staging Area 1 would be used under all of the Action Alternatives and is located downstream from the bridge along the west bank of the Potomac River and the George Washington Memorial Parkway see Figure B-2. Approximately 225,000 square feet (5.2 acres) of area would be needed to accommodate the barges that would access this staging area. Barges would be secured with spud anchors, and a temporary piling-supported platform may be constructed for access to the barge from land.

Due to the shallow depths of the Potomac River within Barge Staging Area 1 access route, dredging of the river would be necessary (see Figure B-2 for river bathymetry). Approximately 10,000 cubic yards of sediment over an 11.2-acre surface area would need to be dredged to a depth of approximately 15 feet from the current river surface. Dredging activities would avoid areas where underwater cables and potential shipwrecks are located. Dredge material would be tested for contaminants and properly disposed of at an appropriate location determined by the contractor and with the approval of the Federal Highway Administration.

Barge Staging Area 2. Barge Staging Area 2 would be used for Alternatives 1A and 1B using Construction Method B which would allow the bridge to remain open to vehicular traffic for the duration of the construction. Approximately 100,000 square feet (2.3 acres) of area would be needed to accommodate the barges that would access Barge Staging Area 2.

Similar to Barge Staging Area 1, dredging would be required within the Barge Staging Area 2 access route. Approximately 80,000 cubic yards of dredge material over a 6.2-acre area would need to be dredge to a depth of approximately 15 feet from the current river surface. Dredging activities would avoid areas where underwater cables are located and the material would be tested for contaminants and properly disposed of at an appropriate location with the approval of the Federal Highway Administration.

Causeways. Up to four temporary causeways would be constructed from the east and west shores of the Potomac River. The causeways would extend between 250 and 750 feet into the river parallel to the north and south sides of the bridge. A filter fabric would be laid on the bottom of the river and the causeway built on top of the fabric. Appropriately sized pipes would be placed through the causeway to allow the river to continue to flow through the area. When construction activities are complete, the causeways would be removed and the river bottom restored to its current condition.

Work Platforms. Up to four temporary docks would be constructed from the east and west shores of the Potomac River to be used as work platforms. The docks would be built on temporary pilings and would extend approximately 250 to 750 feet into the river parallel to the north and south sides of the bridge. When construction activities are complete, the dock/work platforms would be removed and the river bottom restored to its current condition.

TEMPORARY TRUNNION SHORING

Regardless of the alternative selected, including the No-Action Alternative, immediate repairs to the bridge are needed. Each leaf of the bascule span consists of two main steel trusses that are supported by an axle, or trunnion, that rests on trunnion posts, which carry the load of the bridge down to the bridge abutments. Because the trunnion posts are critical to the structural integrity of the bascule span and due to the continuing deterioration of steel within the trunnion posts, temporary repairs to the posts are needed by approximately 2017. Under this action, Federal Highway Administration would install a shoring system to provide additional strength to the trunnions.

Installation of the shoring system would extend approximately 6 feet on each side of the trunnion posts. Depending on design, pilings may need to be placed in the Potomac River to support the bascule span during the period of these trunnion post repairs. These pilings would be placed in deep water and would not impact NPS defined wetlands/waters.

Figure B-2: Proposed Work Areas within the Potomac River

SITE DESCRIPTION

Wetlands

Wetlands associated with this project area are limited to the riverine habitat within the Potomac River below the mean high water line. The Potomac River is considered a riverine wetland, specifically Riverine Tidal Unconsolidated Bottom Vegetated (R1UBV) (USDOI 1979). The riverine system includes both wetland and deep water habitat. The boundary between wetland and deep water habitat in the riverine systems lies at a depth of 6.6 feet below low water (USDOI 1979).

Wetland Assessment Methodology

A wetland assessment was completed by a professional wetland scientist for the entire project area including the areas that lie outside the Potomac River. The wetland assessment utilized the Cowardin system from The Classification of Wetlands and Deepwater Habitats of the United States and the 1987 Corp of Engineers Wetland Delineation Manual and the Regional Supplement for the Atlantic and Gulf Coast Plain Region (USDOI 1979).

The wetland assessment verified that jurisdictional wetlands do not occur outside of the boundaries of the Potomac River. The Potomac River is considered jurisdictional by the National Park Service according to Procedural Manual #77-1: Wetland Protection including the unconsolidated bottom habitat and submerged aquatic vegetation (SAV) from a depth of 8 feet and shallower. The US Army Corp of Engineers also claims jurisdiction over the Potomac River as a navigable waterway. Actions that may reduce or degrade wetlands are governed by Section 404 of the Clean Water Act and Section 10 of the Rivers and the Harbors Act. At the federal level, the US Army Corps of Engineers regulates activities in navigable waters of the United States, which includes jurisdictional wetlands.

In addition, within the District of Columbia, the Department of Energy and Environment is responsible for issuing water quality certifications and would therefore regulate waters within the Potomac within the boundaries of the District of Columbia.

Submerged aquatic vegetation was delineated using the most recent 2014 SAV data layer provided by the Virginia Institute of Marine Science (VIMS). The Virginia Institute of Marine Science is an established and reputable program that has been mapping submerged aquatic vegetation since the late 1970s. The SAV program uses fly-over aerial photography and ground-truthing information, when available, to map SAV beds within the Chesapeake Bay and its tributaries (VIMS, 2014).

In addition to delineating the SAV bed boundaries, the Virginia Institute of Marine Science provides an estimate of SAV density within each bed. This is accomplished by visually comparing each bed to an enlarged crown density scale similar to those utilized for estimating crown cover of forest trees from aerial photography. Bed density is categorized into four classes based on a subjective comparison with the density scale. The four categories include: 1) very sparse (<10% coverage); 2) sparse (10 to 40%); 3) moderate (40 to 70%); or 4) dense (70 to 100%). The classification is assigned to the whole bed or the bed is divided into subsections if there is variation in coverage (VIMS, 2014).

Wetlands within the Project Area

Wetlands in the project area are limited to deepwater and wetland riverine habitat within the Potomac River. By definition, the NPS jurisdictional wetland habitat is located along both the eastern and western shorelines in areas less than 8 feet in depth. The wetland habitat consists of both SAV beds and unconsolidated bottom habitat.

Established beds of submerged aquatic vegetation are located along the western and eastern shorelines of the river. The 2014 data for these beds is preliminary, but the outline of the beds was available for reference although the coverage and composition has not yet been released. During a previous survey in 2013, the bed along the western shoreline was characterized as having 70 to 100% coverage. According to the Maryland Department of Natural Resources, hydrilla (Hydrilla verticillata), coontail (Ceratophyllum demersum) and watermilfoil (Myriophyllum spicatum) were the most frequently reported of the eight common species found during ground-truthing by citizens and the US Geological Survey (MDDNR 2015). The bed along the eastern shoreline was not identified during the 2013 mapping effort; therefore, the coverage and composition are unknown. Figure B-3 shows the location of the submerged aquatic vegetation as mapped by the Virginia Institute of Marine Science.

The areas not mapped as submerged aquatic vegetation are understood to be unconsolidated bottom habitat, which is most prevalent in this type of environment. There are no other mapped habitat types, such as oyster beds, in the vicinity of the project area. The upper Potomac River is considered a non-shellfish area by the Maryland Department of the Environment (MDDOE 2015).

Figure B-3: Location of SAV beds

EVALUATION OF WETLAND FUNCTIONS AND VALUES

Submerged Aquatic Vegetation Beds

The SAV beds within the Potomac are understood to be high quality beds based on the coverage and information received from the Virginia Institute of Marine Science. Submerged aquatic vegetation provides a series of functions including habitat, water quality enhancement, and sediment stability.

SAV beds provide habitat for a number of species. Crab and fish species find protective nurseries in bay grass beds. Microscopic zooplankton, an important component of the food chain, feed on the decaying bay grasses, thereby keeping the bed healthy and free of waste. Bay grass stems and leaves are often covered with small invertebrates that attach to and feed on the grass. In addition to marine species, migratory waterfowl feed on bay grasses and the animals that live in the bay grass beds (Chesapeake Bay Program 2012a).

Submerged aquatic vegetation is an ecological indicator of water quality that provides a quick and visible monitoring method for water quality degradation. Ecosystem services of submerged aquatic vegetation include absorption of nitrogen and phosphorus, release of dissolved oxygen from photosynthesis, sediment trapping, and reduce excess nutrients that would otherwise further impair the Chesapeake Bay watershed (Chesapeake Bay Program 2012a).

SAV beds attenuate wave action and water velocity which decreases turbidity in the water column and can benefit the animals in the area as well the submerged aquatic vegetation itself. The submerged aquatic vegetation acts as a natural filter which traps sediment reducing adverse impacts of sedimentation. The roots of the vegetation provide stability at the bottom of the Bay and its tributaries thereby reducing erosion and further sediment pollution (Virginia Department of Education 2013).

Unconsolidated Bottom Habitat

Although focus is often placed on SAV beds, soft sediment habitat is typically the most common habitat type in bays and estuaries. Unconsolidated bottom habitats include environments where the bottom consists of fine grain sediments, sand and mud. Their biodiversity and productivity vary depending upon depth, light exposure, temperature, sediment grain size and abundance of microalgae and bacteria (Ocean Health Index 2015). This habitat typically supports high densities of clams, worms, crustaceans, and other benthic invertebrates. Benthic microalgae are also present in this habitat when shallow enough that light can penetrate to the bottom (VIMS 2015). The organisms that dwell in this habitat are important to the overall food chain and diversity of the system.

IMPACTS TO WETLANDS/WATERS

Potential impacts to the wetlands within the Potomac River related to the Arlington Memorial Bridge Rehabilitation are anticipated to be both temporary and permanent. Permanent and temporary impacts resulting from dredge and fill activities were calculated for National Park Service jurisdictional area less than 8 feet in depth within the impacted areas. The preferred alternative (Alternative 1B) and associated construction methodology would include temporary and permanent impacts within the work zone, Barge Staging Areas 1 and 2, and the associated dredge footprint.

Temporary impacts would result from construction activities, while permanent impacts would result from bridge pier stabilization.

Temporary impact calculations have been determined for both submerged aquatic vegetation and unconsolidated bottom habitat for areas that would be disturbed under all of the Action Alternatives (e.g. barge staging areas and associated dredge areas, the east and west causeway/platform areas, and the areas where scour countermeasures would be placed) (see Table 1). It is assumed that the entire area within these areas would be temporarily impacted in order to account for all possible construction activities. Due to the assumption that the entire area within the work areas outlined above could be potentially impacted it was not necessary to calculate impacts from specific activities such as cofferdams. Figure B-4 graphically represents the impact areas presented in Table B-1.

TABLE B-1. PREFERRED ALTERNATIVE TEMPORARY AND PERMANENT IMPACT TOTALS

Total Impacts

Impact Area

Temporary Submerged

Aquatic Vegetation

(Acres)

Permanent Submerged

Aquatic Vegetation

(Acres)

Temporary Unconsolidated Bottom (Acres)

Permanent Unconsolidated Bottom (Acres)

Barge Staging Area 1 0.0 0.0 2.6 0.0

East Causeway/Platform Area 0.0 0.0 1.3 0.0

West Causeway/Platform Area 2.7 0.0 1.2 0.0 Scour Countermeasures (Pier #5 and

#6) 0.0 1.4 0.0 0.0

Barge Staging Area 2 3.3 0.0 2.9 0.0

Total Impact 6.0 1.4 8.0 0.0

Permanent wetland impacts are limited to the scour countermeasures that could be installed at the base of the bridge piers. The necessity of the installation of the countermeasures would be based on the extent of damage and scour observed around each individual pier. The calculations are limited to the two piers on the western side of the bridge (Pier #5 and #6) that are located in NPS defined Wetlands. Table B-2 demonstrates the total permanent impacts resulting from the scour countermeasures which were calculated using the guidelines outlined in Publication No. FHWA-NHI- 09-112, Design Guidelines 11: Rock Riprap at Bridge Piers. Standard riprap scour countermeasure dimensions where used to calculate the total impact along with the size of the piers.

TABLE B-2. IMPACTS RESULTING FROM SCOUR COUNTERMEASURES

Pier Width

Riprap scour Placement Width (ft)

Area of Pier (sf)

Total Area (sf)

Area of Scour Protection (sf)

Area of Scour Protection (ac)

Pier 5 28 56 3,724 34,300 30,576 0.70

Pier 6 27 54 3,591 34,464 30,464 0.70

Total 61,040 1.40

Approximately 1.4 acres of SAV habitat would be impacted around Pier #5 and #6. It is understood that this area is currently colonized by submerged aquatic vegetation based on the information gathered from the Virginia Institute of Marine Science.

JUSTIFICATION FOR THE USE OF WETLANDS

The purpose of the project is to restore the structural integrity of the Arlington Memorial Bridge.

The project is needed to address the ongoing corrosion of steel structural members of the bascule span, deterioration of the concrete on the bridge’s approach spans, and deterioration of the sidewalks and wearing surface.

Impacts to the Potomac River result from several site and construction limitations. Due to the weight of some equipment and bridge materials including precast concrete bridge decking and the new bascule span, they cannot be moved over land and brought onto the bridge utilizing the existing bridge superstructure; rather they must be brought to the bridge via the Potomac River. Because of the shallow water depths on both sides of the Potomac River approaching and surrounding the bridge, dredging is necessary to move the equipment and materials to and within the bridge work zone. In addition, some work on the bridge must be performed from below the bridge deck, and causeways or work platforms in the shallow portions of the river are needed to hold equipment for this work. In addition, scour countermeasures are needed to protect bridge piers. Piers 5 and 6 are located in wetland areas and the scour countermeasures for these two piers must be placed within these wetlands.

Figure B-4: Wetland Impact Areas

MITIGATION MEASURES

The activity of rehabilitating the bridge would result in unavoidable impacts to 15.4 acres of riverine wetlands (7.4 acres of submerged aquatic vegetation and to 8.0 acres of unconsolidated bottom wetlands). The construction contractor would be encouraged to minimize impacts to wetlands where feasible, and construction methodologies would need to be approved by the National Park Service and the Federal Highway Administration.

In accordance with Procedural Manual #77-1, mitigation is required for both temporary and permanent impacts. No compensatory mitigation for impacts to unconsolidated bottom wetland areas would be required. The 8.0 acres of disturbed unconsolidated bottom area would be restored to pre-disturbance elevations and recolonization of invertebrates and other substrate fauna is expected to occur rapidly.

Mitigation measures for temporary impacts to submerged aquatic vegetation would include restoration of the areas to pre-construction elevations and re-establishing submerged aquatic vegetation in the areas previously colonized. The areas would be replanted with the same species composition and planted to a greater density of plant cover than what existed prior to disturbance.

Compensatory mitigation would be undertaken for impacts to submerged aquatic vegetation at a 2:1 ratio for all permanent and temporary impacts. A compensatory mitigation plan would be developed before the project begins and approved by NPS, Water Resources Division staff. The applicant would identify existing areas of submerged aquatic vegetation within the river, that have medium to low cover density submerged aquatic vegetation, and that can be enhanced by infill planting of the same species. The areas would be planted with the same species composition and planted to a density of plant cover that would infill to a high level of canopy density.

The preferred alternative requires compensatory mitigation for 1.4 acres of temporary impacts and

6.0 acres of permanent impacts within the causeway/platform areas, Barge Staging Areas 1 and 2, and associated dredging area. The construction contractor may propose to avoid utilizing Barge Staging Area 2. However, the assumption at this point is that Barge Staging Area 2 would be dredged.

The construction contractor would be required to develop a restoration plan approved by the NPS and obtain all required regulatory permits. A total of 14.8 acres of existing, degraded submerged aquatic vegetation habitat would be identified for vegetation restoration. The areas proposed for compensation would be within NPS regulation boundaries, i.e. within reaches of the Potomac and/or the Anacostia river that are under NPS management. The areas designated for compensatory mitigation would need to be assessed for potential impacts to natural and cultural resources including potential for impacts to underwater archeology. It is understood that additional mitigation may be required by the US Army Corp of Engineers or the DC Department of Energy and the Environment.

The submerged aquatic vegetation restoration plan would include a description of how restoration enhancement areas were selected and the parameters used to select the most appropriate areas for replanting (including location within the riverine system, water chemistry, hydraulic and geomorphologic conditions at the sites; and the individual species present, species density and cover, and delineation of the replanting areas). The plan would also include planting/seeding, 5-year monitoring plans, and a contingency replanting plan to ensure successful reestablishment. The details of this plan would be formulated once a submerged aquatic vegetation survey is completed during the permitting phase of the project and the current species makeup and percent cover is known.

Submerged Aquatic Vegetation Restoration Opportunities

The National Park Service has investigated possible in-kind mitigation opportunities within the Potomac and Anacostia rivers to restore submerged aquatic vegetation. Potential sites have been identified within the Potomac River based on depth and locations in which grasses historically occurred. The 2010 SAV maps from the Virginia Institute of Marine Science were used to identify areas within the Potomac that were previously colonized by submerged aquatic vegetation. These areas were then further refined to only include locations within the boundaries of NPS jurisdiction and within a river depth of 6 feet or less. The potential sites along the Anacostia were identified based only on the boundaries of NPS jurisdiction and river depth because SAV coverage has not been present, with the exception of some small patches in 1993, since 1971. The Virginia Institute of Marine Science does not have historic SAV data available for the Potomac River or Anacostia River dating earlier than 1971.

It has been documented that submerged aquatic vegetation within the Chesapeake Bay area are limited to waters less than 6.0-foot depth due to their light requirements. This was used as a guidance to preliminarily select potential restoration locations with the understanding that light availability is site specific and depends largely on localized water quality parameters. Water quality parameters such as dissolved inorganic nitrogen and phosphorus, water column light attenuation coefficient, planktonic chlorophyll and total suspended solids affect not only SAV physiology and ecology but also strongly influence the plant’s light climate. It is important to recognize that easily available water clarity data obtained from a secchi disk does not take into account light attenuation by epiphytes on SAV leaves which is a dominant factor in regulating plant growth (Kemp, et al 2004).

Mitigation for SAV impacts resulting from the Woodrow Wilson Bridge project included planting 90,000 shoots of eelgrass (Zostera marina) at Piney point in the lower Potomac River estuary. The planting occurred between 2003 to 2005 and was completely gone by the end of the summer of 2007.

Prior to planting, the project team undertook extensive analysis including a habitat evaluation using a Preliminary Transplant Suitability Index and test to determine the likelihood of success. The suitability index looked at historical SAV distribution, current SAV distribution, water depth, water quality, sediment composition, proximity to natural bed, and shoreline configurations. The transplant grass experienced season summer mortality which is common in the Chesapeake due to the large seasonal temperature fluctuations, but unlike natural beds the grass never recovered. The failure is attributed to high temperatures, hypoxic conditions, low percent light at leaf level and a heavy epiphyte load (Chesapeake Bay Program 2010).

The localized water quality plays a large role in the design of the restoration plan (i.e. which species to plant) and the ultimate success of the restoration. In addition to the parameters previously discussed, salinity is important in deciding which species to plant and varies within the different reaches of the Potomac and Anacostia Rivers. Salinity tolerances have been established for the most commonly found species in Chesapeake Bay and its tributaries. Although generally understood for the Potomac and Anacostia Rivers, salinity can vary seasonally and experience large fluctuation resulting from high rain years. It has been hypothesized that this was also the cause of failure for a 2002 seagrass transplant that was being monitored by the US Geologic Survey in 2003 and 2004 in the mesohaline waters of the Potomac River. This was a transplanting project for the destruction of

33.7 acres of submerged aquatic vegetation in Alexandria, Virginia. The transplanted eelgrass was completely gone by the end of 2004 and it was determined that water clarity and light penetration were sufficient. The transplant failure may be attributed to above average precipitation which drove salinity below eelgrass tolerance limits (10 ppt) percent of the time at the transplant site. Other factors that have could have contributed to the failure includes low sediment nutrient concentration and poor substrate (Schenk and Rybicki 2006).

Some shallow areas that meet the water quality requirements are subject to high currents and wave action or contain sediments that are high in organic content and may not have potential for SAV growth. Therefore it is important to have a complete understanding of the area sediment composition and water velocity. Areas historically colonized with submerged aquatic vegetation are much more likely to have the necessary growth conditions. It is important to recognize that conditions could have changed and that there is likely a reason that they are no longer present in that area.

A decline in water quality has been identified as the primary cause for the overall decline in submerged aquatic vegetation in the lower Potomac River and Chesapeake Bay in the last century.

Due to this a large component of the overall Bay restoration plan includes measures to improve overall water quality by decreasing nutrients and suspended solids. Since 2000, the overall SAV restoration goal established by the Chesapeake Bay Program has been decreasing. Between 2003 and 2013 approximately 173 acres of grasses were planted in the Chesapeake Bay and have met mixed success. The National Oceanic and Atmospheric Administration’s Chesapeake Bay Office and US Army Corps of Engineers Engineer and Research and development Center have funded almost all of the large-scale plantings in the region. They have since not been able to increase funding enough to meet the annual planting need. Large scale bay grass plantings have become rarer as the managers continuing to evaluate the best and most cost-effective methods for planting bay grasses (Chesapeake Bay Program 2012b).

Potomac River Mitigation Opportunities

As discussed above, Chesapeake Bay SAV restoration efforts have focused on the mesohaline portion of the Potomac River. There were a number of federally funded restoration projects conducted by the US Army Corp of Engineers and the National Oceanic and Atmospheric Administration between 2003 and 2006 that included the planting of 32.75 acres of eelgrass in the Potomac River. Several different collection and planting methodologies were employed with mixed results. The potential sites identified for this project include this area but also the areas upstream closer in location to the project area.

Figure B-5 provides a key to the maps that follow. Figure B-6 through Figure B-10 show the potential restoration areas identified based on previous SAV colonization and depth. A total of 882 acres has been identified.

Figure B-5: Key to SAV Restoration Opportunity Maps

Figure B-6: Tile #1-Potential SAV Mitigation Opportunities

Figure B-7: Tile #2-Potential SAV Mitigation Opportunities

Figure B-8: Tile #3-Potential SAV Mitigation Opportunities

Figure B-9: Tile #4-Potential SAV Mitigation Opportunities

Figure B-10: Tile #5-Potential SAV Mitigation Opportunities

Anacostia River Mitigation Opportunities

The Anacostia River has been devoid of submerged aquatic vegetation since before 1971 as demonstrated by the VIMS historical aerial maps. The absence is largely attributed to poor water quality. High levels of suspended solids and nutrients flow into the Anacostia River from the surrounding watershed. Restoration efforts have focused almost exclusively on improving the water quality of the system. Recently the Anacostia Watershed Society has received a permit to establish a 400 square foot test bed in the tidal Anacostia primarily wild celery (Vallisneria Americana). Due to the infancy of the research in establishing grass beds within the Anacostia River it is important to understand the risks. Extensive data would be necessary to further understand the water quality, light penetration, water velocity, and sediment composition. Potential locations based only on water depth have been called out on Figure B-11 and Figure B-12. A total of 240 acres has been identified.

Figure B-11: Tile #6-Potential SAV Mitigation Opportunities

Figure B-12: Tile #7-Potential SAV Mitigation Opportunities

Figure B-13: Tile #8-Potential SAV Mitigation Opportunities

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REFERENCES

Chesapeake Bay Program

2010 Christopher Tanner, Sarah Hunter, Justin Reel, Thomas Parham, Mike Naylor and Lee Karrh. Evaluating a Large-Scale Eelgrass Restoration Project in the Chesapeake Bay.

Restoration Ecology, 538-548.

2012a Bay Grasses. Accessed December 8, 2015. Chesapeake Bay Program:

http://www.chesapeakebay.net/issues/issue/bay_grasses#inline

2012b Chesapeake Bay Program. Accessed March 3, 2016. Planting Underwater Bay Grasses:

http://www.chesapeakebay.net/indicators/indicator/planting_bay_grasses

Edward R. Schenk and Nancy B. Rybicki

2006 Exploring Causes of a Seagrass Transplant Failure in the Potomac River. Ecological Restoration, 116-117.

W. Micael Kemp,Richard Batiuk, Richard Bartleson, Peter Bergstrom, Virginia Carter, Charles L. Gallegos, William Hunley, Lee Karrah, Evamaria W. Koch, Jurate M. Landwehr, Kenneth A.

Moore, Laura Murray, Michael Naylor, Nancy B. Rybick, J. Court Stevenson, and David J.

Wilcox.

2004 Habitat Requirements for Submerged Aquatic Vegetation in Chesapeake Bay: Water Quality, Light Regime, and Physical-Chemical Factors. Estuaries, Vol. 27, No. 3, 363-377.

Ocean Health Index

2015 Soft Bottom Habitats (subtidal). Accessed March 2, 2016.

http://www.oceanhealthindex.org/methodology/components/soft-bottom-habitats

Maryland Department of the Environment

2015 Maryland’s Shellfish Harvesting and Closure Area Map. Accessed September 15, 2015.

http://www.mde.state.md.us/programs/Marylander/CitizensInfoCenterHome/Pages/ci tizensinfocenter/fishandshellfish/pop_up/shellfishmaps.aspx

Maryland Department of Natural Resources

2015 About Bay Grasses. Accessed September 1, 2015.

http://www.dnr.state.md.us/bay/sav/about.asp

U.S. Department of the Interior

1979 Classification of Wetlands and Deepwater Habitats of the United States. Washington, DC.

Virginia Department of Education

2013 Grasses, grasses, everywhere. Retrieved March 01, 2016.

http://www.doe.virginia.gov/instruction/science/elementary/lessons_bay/lesson_plans/grass es_everywhere/grasses.pdf

Virginia Institute of Marine Science

1979 Decline of Submerged Plants in Chesapeake Bay. Accessed December 8, 2015.

http://www.fws.gov/chesapeakebay/savpage.htm

2014 SAV in Chesapeake Bay and Coastal Bays. Accessed December 4, 2015.

http://web.vims.edu/bio/sav/sav13/index.html

2015 Shallow Water Habitats. Accessed December 9, 2015.

http://web.vims.edu/bio/shallowwater/physical_characteristics/habitat_types.html

As the nation’s principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering sound use of land and water resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The department assesses our energy and mineral resources and works to ensure that their development is in the best interests of all our people by encouraging stewardship and citizen participation in their care. The department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.

GWMP 850/131908 April 2016

United States Department of the Interior ‒ National Park Service

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