Water Treatment Wetlands at Reasure Island

[ARC Ecology <arc@igc.org>]

The following is an Executive Summary of a study done to create water
treatment wetlands at Treasure island. The full study (in hard copy
format) can be purchased ($10) by contacting Arc Ecology at
<arc@igc.org>. An email version is also available free of charge.

**** WARNING: This is a long file ****

>CREATING WATER TREATMENT WETLANDS AT TREASURE ISLAND:
An Exploration of Opportunities and Feasibility

EXECUTIVE SUMMARY
>As scientists have learned how natural wetlands purify water, they
developed technologies to reproduce this ability in constructed wetlands and
applied them to treating storm runoff and sewage. By the late 1980s, the
fundamentals of using treatment wetlands for water quality improvement were
well understood, and the Environmental Protection Agency (EPA) began
promoting such systems as alternatives to conventional engineered solutions
(e.g., EPA, 1987; EPA, 1988).
>
>Water Treatment
>This report explores the feasibility parameters of constructing a 10-20
acre wetland on the eastern edge of Treasure Island to treat stormwater
before it is released to the Bay. Currently Treasure Island's stormwater is
discharged directly to San Francisco Bay through at least 40 existing
outfalls located around the perimeter of the island. Six stormwater lift
stations assist in the transfer of stormwater to the various outfalls.
>
>The current Storm Water Pollution Prevention Plan for Treasure Island
outlines, at best, a minimal program for controlling pollution in stormwater
runoff. The program emphasizes primarily on-site "best management
practices" and outfall monitoring, with little emphasis on treating the
stormwater to remove pollutants before discharging to the Bay. The current
plan does not incorporate any of the technologies currently available and
typically implemented by other cities, such as detention basins, grassy
swales, and infiltration ditches which help remove pollutants before
discharging to a water body. In light of the inadequacy of the current
SWPPP, constructing treatment wetlands on Treasure Island would contribute
substantially to improving the quality of water that Treasure Island
discharges to the Bay
>
>This stormwater treatment project may be expanded later to include wetland
polishing of secondary-treated sewage effluent. Treasure Island would be
well suited to such a concept because it would improve the quality of
stormwater discharged to the Bay in the short run; and since long range
redevelopment calls for replacement of the sewage treatment plant, money
could be saved on plant construction by designing the system to complete the
wastewater treatment using wetlands instead of engineered technology.
Together with a tidal saltmarsh, the wetland habitat would be on the order
of 40 acres, and would provide wildlife benefits.
>
>A Treasure Island stormwater treatment wetland would include:
>
> Runoff collected from the area surrounding the wetland.
>
> A series of ponds located on the eastern edge of the island, in which
the stormwater would accumulate and settle. The ponds provide a growth
medium for plants that take up pollutants, as well as slow the flow of water
to encourage sedimentation processes. The water progresses through the
ponds, becoming progressively cleaner.
>
> A simple system for discharging the treated water to the Bay, or into a
reservoir for reuse in landscaping or fire fighting.
>
>Wildlife
>A primary and well-documented benefit of constructed wetlands is the
creation of valuable habitat for wildlife (Benson and Foley, 1956).
Features to maximize wetland functions for wildlife habitat are now well
understood (Weller, 1990; Kent, 1994) and therefore, treatment wetlands can
be designed to provide valuable habitat for wildlife. Treasure Island,
located along the Pacific Flyway, is well situated to attract migrating
birds, as well as year-round birds and other wildlife.
>
>The wildlife, as well as the opportunity to understand the wetland's water
treatment function, would become an important educational resource for
children and adults.
>
>Economics
>The opportunity to view this wildlife at close range in the attractive
setting of the wetland would in turn generate economic benefits by
attracting visitors to Treasure Island. These economic benefits would be
realized without the major capital investment that buildings require because
of seismic and soil instability issues.
>
>The area that the wetland would occupy is not ideal for development. The
island was constructed through the placement of sandy fill material over a
shoal which is underlain by compressible bay mud. This history means that
Treasure Island -- especially along its perimeter -- is vulnerable to the
problems and hazards associated with earthquakes, including soil
liquefaction and lateral spreading, failure of perimeter dikes,
consolidation of recent bay sediments, the effects of differential
settlement, and building failure. The areas of the island that have the
greatest potential for damage resulting from earthquakes are found in a band
within 500 feet of the shoreline. The cost for addressing the
geotechnical/seismic constraints on Treasure Island to meet current
development standards is estimated to equal $325 million (ROMA Design Group,
1995).
>
>Reserving the perimeter for open space, including wetlands, would
contribute to overall financial feasibility of Treasure Island
redevelopment. To the extent that Treasure Island can host additional
development, it makes sense to locate it centrally where it would be
grounded in more stable soils and still enjoy spectacular views. This study
explored the island's eastern edge as a location for the wetland in order to
reserve the west-facing views towards San Francisco for commercial 
enterprises.
>
>Design
>Because of its flat topography, Treasure Island is ideal for treatment
wetlands in terms of grading/construction. For typical siting studies for
treatment wetlands, one of the primary design factors is to locate the
system at or near the downstream end of drainages and wetlands (Hammer,
1989). At Treasure Island, natural wetlands and drainages are not present.
The only hydrologic consideration is to locate the treatment wetland near
the periphery of the island to minimize infrastructure (e.g., pipes)
expenses for discharging the treated water into the Bay. As previously
discussed, geotechnical considerations demonstrate the advantages of
locating the system in an area where the costs of buildings would be high
because of seismic-requirements. At Treasure Island, the treatment wetlands
could be safely placed in a seismically unstable zone without the need for
expensive solutions because the wetlands do not need extensive 
infrastructure.
>
>Public Policy
>The use of treatment wetlands for advanced treatment of stormwater
strengthens the overall goals and objectives, and the feasibility of the
Draft Base Reuse Plan for Treasure Island. The presence of wetlands will
enhance and reinforce the feasibility of other uses provided for by the
Plan. Furthermore, one of the sites identified in this report as a potential
location for the wetland is already designated in the Plan as an open space
area.
>
>The wetland is also highly compatible with the Public Trust Doctrine that
applies to Treasure Island. The wetland utilizes the site's proximity to the
Bay, and benefits future as well as current California generations.
>
>Toxics and Cleanup
>Treasure Island requires a substantial investment in toxic soil remediation
and seismic safety. To the extent that the Base Cleanup Plan may require
excavation of contaminated soil from some very contaminated sites and its
replacement with clean material, a treatment wetland could provide a cost
effective solution, because the excavated area would not need to be
refilled. The savings could be applied to cleanup costs (since clean fill
would not have to be imported) and also to the costs of constructing the
treatment wetland (since the initial excavation work would be charged to
cleanup).
>
>Potential Sites
>The treatment wetland example explored in this report is approximately 10
acres. It would draw on a watershed of 45-75 acres. If subsequent analysis
suggests that the optimum area of the stormwater treatment wetland should be
larger, the runoff from a correspondingly larger watershed would be
delivered. To enable a future decision to modify and enlarge the stormwater
treatment wetland to include wastewater treatment, additional land could be
reserved as open space (an option consistent with the Reuse Plan).
Regardless of the sequence of the construction of the wetland habitat
components, portions of the site could serve as parkland in the interim.
>
>The two sites described below illustrate feasibility options for locating a
stormwater treatment wetland on Treasure Island. See Figure 1 on page 28.
>
>Site 1
> Drainage Area:
>Three contiguous drainage areas (Drainage Areas 3, 4, and 5 as shown on
Figure 1) totaling approximately 75 acres contribute to the overall
watershed for this site. This drainage area is located on the eastern side
of the island south of the existing sewage treatment plant and is currently
served by approximately 95 catch basins and six stormwater outfalls.
>
> Hazardous Waste/Installation Restoration Sites:
>The contributing watershed contains four sites where cleanup is in process
(Installation Restoration sites) and two hazardous waste generation activity
areas which include the following: Pesticide Storage, Bus Painting Shop,
Navy Exchange Service Station, New Fuel Farm, NTTC Fire Fighting School, and
PWC/Paint Solvent Storage.
>
> Aboveground/Underground Storage Tanks:
>A total of ten aboveground fuel storage tanks currently exist within the
drainage area. Six additional aboveground tanks in the vicinity of the New
Fuel Farm have been removed. All ten underground fuel storage tanks that
existed within the drainage area have been previously removed. With a few
exceptions, most of the removed aboveground and underground storage tanks
within the contributing watershed are associated with the New Fuel Farm and
Navy Exchange Service Station IR sites. In addition, approximately 1250
linear feet of underground fuel line is present within the drainage area.
>
> Planned Reuse:
>The location of Site 1 is shown as open space in the DBRP.
>
>Site 2
> Drainage Area:
>The drainage area for Site 2 totals approximately 45 acres and is composed
of four contiguous drainage areas (Drainage Areas 7, 8, 9, and 10 in Figure
1) at the southeastern corner of Treasure Island. Approximately 104 catch
basins and six outfalls currently facilitate drainage of this area.
>
> Hazardous Waste/Installation Restoration Sites:
>A total of four cleanup sites and one hazardous waste generation activity
area exist within the drainage area. These sites include the following: Old
Boiler Plant, Old Fuel Farm, Tanks 103 and 104, Fifth Street Fuel Releases
(Dry Cleaning Facility), and the Main Boiler plant.
>
> Aboveground/Underground Storage Tanks:
>A total of twelve aboveground storage tanks are present within the Site Two
drainage area. Several of these tanks are associated with the Old Boiler
Plant IR site. Only one of two underground tanks remain within the limits
of the drainage area. This drainage area also has approximately 4000 linear
feet of underground fuel line.
>
> Planned Reuse:
>A second alternative for the stormwater treatment site, Site 2, is the
location for a theme park in the DBRP.
>
>Costs
>Based on a 10-acre treatment wetland, the approximate estimated cost for
construction of the type of treatment wetland described for Treasure Island
would equal approximately $1.1 million dollars ($110,000/acre). The actual
cost may be lower (or possibly higher) depending on the specific site
conditions, the level of contaminated soils, and the amount of additional
piping to be installed for redirecting stormwater flows into the treatment
wetland. Estimated maintenance cost would be approximately $4,000 per year
($400/acre).
>
>Conclusions
>In summary, a wealth of experience is available to inform the design of
constructed wetlands for the effective treatment of stormwater runoff on
Treasure Island. The benefits are many and diverse:
>
>The presence of contaminated soils and groundwater, as well as the
inadequate SWPPP currently in place, create strong incentives to construct
such a treatment wetland in order to improve Bay water quality. If soil
needs to be excavated to remediate the site of the wetland, there could be
substantial savings both to the cleanup effort and the cost of constructing
the wetland.
>
>There are at least two areas where a treatment wetland could be
constructed, both on the eastern edge that is generally less attractive to
development than the west-facing areas. Using either of the two sites, the
wetland would not compete for sites that are most valuable for commercial
development --generally those in the central, higher portion of the island
and along the western edge, commanding the best views.
>
>The wetland would help to sustain existing wildlife and would attract new
wildlife to the area by providing much needed habitat.
>
>The recreation and wildlife viewing opportunities for the public, that
could be constructed at relatively modest cost, would generate significant
economic return. Incorporation of the treatment wetland into the
redevelopment effort should result in increased economic potential for the
overall redevelopment project.
>
>The wetland would provide educational opportunities for schools and the
general public about the ecology of the Bay.
>
>The stormwater wetland could be supplemented in future years to treat
sewage effluent as well, potentially creating savings in the costs of a new
sewage treatment plant. A muted tidal (saltwater) wetland also could be
added. Together, the treatment wetland and the tidal marsh would attract a
great diversity of wildlife.
>
>There are also possibilities for water conservation -- using the treated
effluent for landscaping and fire fighting backup.
>
>Construction of a treatment wetland on Treasure Island would create a
highly visible model of 21st century sustainable development that will
benefit existing and future generations in the San Francisco Bay Area and
all of California. .
>
>