Strategies for effective stormwater management

Horsley Witten Group
Sustainable Environmental Solutions

Decision Makers Workshop
Landscape Solutions: Strategies for effective
stormwater management and fertilizer use
March 20, 2013 - UMass Cranberry Station, East Wareham

Stormwater Management at Taunton Mill River Park

Speaker Profile: Workshop Packet Contents:
Rich Claytor, Principal • Restoring the Ponds in Roger Williams
Engineer at HW, has more Park Summary Plan
than 28 years of practical • Summary of Watershed Management
experience in civil and Plan for Rhode Islands Salt Ponds
water resource engineering. • Summary of Pleasant Bay Fertilizer
Rich has specific expertise Management Plan Final Report
in watershed planning and
management; stormwater
management practice design, policy
development and master planning; stream
and river geomorphology; water supply and
wastewater conveyance design; land use
planning, site design; drainage and erosion/
sediment control design. He has authored a
variety of publications on stormwater design
and implementation and presented in more
than 100 training workshop and conferences
over the last 20 years.

Sandwich, MA Boston, MA Newburyport, MA Providence, RI
508-833-6600 857-263-8193 978-499-0601 401-272-1717

www.horsleywitten.com

Summary Plan for Restoring the
Ponds in Roger Williams Park

Restoring the Ponds in Roger Williams Park:
Summary Plan
1.0 Introduction
Since the first plan for Roger Williams Park was
developed in 1878 by landscape architect
Horace Cleveland, the Park ponds have been
considered essential visual and recreational
elements in the Park’s design. Over the years,
the ponds have provided boating opportunities,
a place to fish, a home for wildlife, and a visual
refuge for urban dwellers looking for relief from
crowded city streets.

The Park ponds, however, have been suffering from algae problems, aquatic weed growth, and
sedimentation from road sand for many decades. In 1982 Park officials spent several hundred thousand
dollars to dredge 3 of the ponds in the pond system, but it didn’t solve the algae problem in the ponds
as phosphorous-laden storm water and road sand continued to flow unabated into the ponds. The
ponds were first listed in the Rhode Island Department of Environmental Management’s (RIDEM)
impaired water bodies list in 1992. The algae and aquatic weed growth in the ponds has been so severe
in the last 10 years, that RIDEM in 2007 released a report, Total Maximum Daily Load Report (TMDL), to
analyze 9 ponds in Rhode Island with the most challenging phosphorous problems. The Roger Williams
Park pond system was one of the pond systems highlighted for its worsening problems.

In 2010 with the urging and cooperation of the
Narragansett Bay Estuary Program (NBEP), the Parks
Department applied for and received an EPA Region
1 matching grant to comprehensively examine the
pond’s pollution problems, to suggest remedial
options, and to provide a plan for restoring the
ponds’ water quality. With the assistance of a
Technical Steering Committee, the firm of the
Horsley-Witten Group (HW) was selected to develop
a Water Quality Management Plan for the Park
ponds. The Committee has helped guide the work of
HW which began in July 2011.

Roger Williams Park
The project Steering Committee established the following goals for the
Ponds Restoration Project pond restoration project:
Technical Steering Committee
Roger Williams Park Ponds Restoration
Project Goals
 Providence Parks &
Recreation

 Narragansett Bay
Estuary Program  Improve water quality, habitat, and biodiversity within the
 U.S. Environmental ponds
Protection Agency Region
1  Improve the overall environmental quality and user experience
 US EPA Atlantic Ecology of the Park
Division
 Identify health risks associated with fish consumption; increase
 RI Coastal Resources
Management Council public awareness as warranted

 RI Department of Health
 Foster watershed awareness and environmental stewardship
 RI Department of among Park users and surrounding residents through a public
Environmental outreach campaign
Management

 RI Department of The first of these items—water quality restoration—is central to the
Transportation project. The HW firm undertook extensive investigations and completed
a water quality model and draft document for restoration of the ponds.
 Save the Bay
As a result of the HW work, it became clear that a significant reduction in
 Save the Lakes phosphorus pollution to the Ponds is necessary to achieve water quality
improvement. The sources of phosphorus include atmospheric
 US Fish & Wildlife Service
deposition, internal recycling within the Ponds, loading from waterfowl,
 USDA Natural Resources and stormwater runoff from upland sources. The City and Steering
Conservation Service Committee, therefore, established the following targets for phosphorus
pollution reduction in the Ponds, in order to improve water quality,
 University of Rhode
Island Watershed Watch habitat quality and aesthetics:

 RI Bass Federation Water Quality Restoration—Phosphorus Reduction Targets

 Environmental Justice  Reduce phosphorous loadings to the ponds by 20% in five years
League of Rhode Island
 Reduce phosphorous loadings to the ponds by 42% in ten years
 Serve Rhode Island

 Pawtuxet River Authority  Over the long term, 20-25 years, reduce phosphorus loadings
by up to 73%, a reduction which RI Department of
 RI Natural History Survey
Environmental Management suggests would allow the Park
 Urban Ponds Procession ponds to achieve a water quality that would be significantly
reduce seasonal algae and aquatic weed growth

2.0 Background
With the exception of Deep Spring Lake,
the Park ponds are man-made, and
consist of a series of seven interconnected
ponds. As the Park was developed in the
latter years of the 19th century,
Mashapaug Brook that ran from
Mashapaug Pond was used as the primary
water source to create the Park ponds.
This former location of the Brook in area
now constituting the Park is shown above.
The Brook was dammed near present day
Park Avenue at the southern end of what
is now Elm Pond. In conjunction with
considerable dredging that was done by
the hands of many immigrant laborers
over many years, several of the ponds
were literally carved out of the landscape.
Bridges were built to allow the ponds to
flow continuously from one to the other,
from Roosevelt Pond near the Casino to
Elm Pond near the Park Avenue entrance.

The general pattern of flow through the Park ponds is from the southern end of Roosevelt Lake where a
48 inch diameter pipe from Mashapaug Pond is located to the dam at the southern end of Elm Pond.
Once the water leaves the Park, it flows into Bellefont Brook into the Pawtuxet River and eventually to
Narragansett Bay.

Roger Williams Park
Pond System

Roger Williams Park Ponds Characteristics
Pond Average Depth Area Direction of Flow
(feet) (Acres)

Roosevelt 1.3 3.8 West to East then North to South
Willow 2.0 3.4 South to North and North to South
Polo 2.3 3.6 South to North
Pleasure 2.6 18.6 West to East
Edgewood 3.0 19.3 North to South
Cunliff 4.3 32.3 North to South
Elm 4.3 21.7 North to South

3.0 The Park Ponds are in Trouble Today
For almost six months a year the Park ponds appear as envisioned when the Park was built—free of
algae and weeds and reasonably normal in color and clarity. But those six months are generally from
November to April when the ponds are not actively used and overall park visitation is low. Beginning
generally in May every year, the shallow Park ponds began to heat up and to display a pea soup green
color culminating with floating algae and acres of weeds in July-October, this is known as eutrophic or
hypereutrophic conditions. Scientists typically look at a few key parameters to help assess water quality
conditions, including Chlorophyll a, total phosphorus concentration, and Secchi dish depth (a measure of
water clarity). As seen below, water quality data reflects the extent of water quality degradation in the
ponds. Even the casual Park visitor, without the benefit of scientific water quality data for the ponds,
can visually see the water quality degradation in the Park ponds.

Summary of Water Quality Data for Roger Williams Park Ponds (URI Watershed Watch 1993-2012)
Water Typical Average Value in Ponds by Year
Quality Threshold Pleasure Lake Roosevelt Lake Cunliff Elm Lake
Parameter for Lake
Eutrophic
Conditions
1993

1994

2001

2002

2005

2012

1993

1994

2012

2003

2012

2005

2012

Chlorophyll 7.2 to 30 22 28 20 46 57 55 17 26 31 54 55 56 58
a (ppm)
Total P 25 to 65 85 105 76 64 140 100 65 69 76 120 87 97 82
(ppm)
Secchi 6.5 to 2.5 5.2 4.6 3.0 2.0 1.6 2.6 5.2 5.2 1.6 2.3 2.6 2.0 3.0
Depth (ft)
Red Font = value exceeds outside range of Eutrophic Threshold

Why should we care about the poor water quality in the Park ponds?
The degraded water quality condition of the ponds in the summer and early fall months is troublesome
for many reasons:

 The boating experience on the ponds is diminished
 Biodiversity, particularly fish species, in the ponds is reduced
 Nearby shoreline activities, such as picnicking and gatherings, are unpleasant
 The overall perception of the park as an enjoyable family place to visit is negatively altered
 Finally, Roger Williams Park is the primary recreational area for thousands of Providence
families who do not have access to the state’s south county beaches and the restoration of
the Park’s water resources is a matter of environmental justice.

What is causing the water quality problems in the Park ponds?
The answer to that question is both simple and complex. To properly understand what is happening to
the ponds, it is useful to remember that the ponds are man-made. They are not natural geologically
formed deep lakes that you might find in western and northern Rhode Island. And because the Park
ponds are shallow, the ponds heat up quickly when the summer ambient air temperatures increase.

The shallow warm lakes when initially constructed probably did not exhibit today’s water quality
problems. The Park when it was built in the 1880’s and 1890’s was at the southern end of Providence
largely surrounded by vacant land. As the city’s population grew, the areas around the park were
developed into dense residential neighborhoods. Thousands of acres of vacant land became houses,
businesses, streets, sidewalks, driveways, and parking lots.

And when it rained, city engineers
provided these nearby
neighborhoods with storm
drainage systems with storm water
outfalls, many of which drained
into the Park ponds. Even the
Park’s principal source of flow—the
Mashapaug Brook—was at some
point channeled into a large storm
pipe before it enters Roosevelt
Pond. Throughout the 20th
century, park engineers also
drained Park roads and parking lots
into a storm drainage system which
today flows into the Park ponds via
many outfall pipes.

Not only did the areas around the Park develop, but the area around Mashapaug Pond and its feeder
ponds, Spectacle Pond and Tongue Pond, also were urbanized. Mashapaug Pond was relatively pristine
when its outflow from the pond, Mashapaug Brook was used to form the Park Ponds. Indeed, as late as
the early 20th century, Mashapaug Pond was a source of block ice for hundreds of Providence homes.

The accompanying aerial photograph shows the Park’s two main watershed areas—areas that are the
sources of storm water flowing into the Park ponds. The extent of development in the two watersheds
is pretty dramatic. And the graphic below illustrates the relationship of the Park ponds to its
watersheds.

Upper Watershed

Tongue Pond Spectacle Pond Mashapaug Pond
Watershed Watershed Watershed

Water
Tongue Spectacle Mashapaug
Pond Pond
Pond

Park Property
Watershed

Lower Watershed Roger Williams
Adjacent Park Ponds
Neighborhood
Watershed

Once dependent solely on Mashapaug Brook for its water source, the Park ponds became the
convenient receptacle for storm water from hundreds of acres of two nearby watersheds every time it
rained. This storm water is not clean. Anything on the impervious surfaces that drains into the Park
ponds—dirt, bird waste, pet waste, car chemicals, fertilizer, trash—is carried by the storm water into the
Park ponds.

Roger Williams Park Ponds Watersheds
Upper Watershed

Watershed Areas
Cranston/Providence
Upper—977 acres
Boundary
Lower—649 acres
Total—1,626 acres

Lower Watershed

The chemical culprit of particular concern in the storm water flowing into the
Park ponds is phosphorous.
A modest increase in phosphorous in a water body can, under the right conditions, set off a chain of
undesirable biological events that can accelerate algal blooms, undesirable plant growth, depletion of
dissolved oxygen, and the death of oxygen dependent fish. This process is known as eutrophication
which may take centuries to occur in undeveloped areas, but which in the Park ponds is accelerated by
the storm water entering the ponds after every rain event. The shallow warm Park ponds provide a
perfect situation for the significant amounts of phosphorous entering the ponds to stimulate algal
blooms and plant growth. See graphic below for the sources of phosphorous in the Park ponds.

Sources of Phosphorous

in the Roger Williams Park Ponds

Atmospheric Deposition

(64 lbs/yr)

Upper Watershed Storm

Water

(360 lbs/yr) Roger Williams Park
Roger Williams Park Ponds Waterfowl
Lower Watershed Storm

Water (128 lbs/yr) (154 lbs/yr)

(216 lbs/yr)

As seen above, a major source of phosphorous in the ponds is not just the drainage system, but the
number of Canada geese that have taken up residence in the Park.  For decades Canada geese migrated
south and stopped along their journey in the Park ponds.  Once the ponds began to freeze, the geese
would continue their journey south.  Because of relatively recent climate changes, however, the Park
ponds no longer consistently freeze in the December‐March months.  Gradually, large numbers of geese
simply wintered over in Roger Williams Park.  As the resident geese population increased, park visitors
unfortunately began to fed them bread from home.  And feeding the geese bread continued throughout
all months of the year.

While well‐intentioned, public feeding of the
geese in the Park is misguided and as recently
as July 2012 resulted in over 700 resident
geese living in the Park.  Unknown to most of
the Park visitors, the gaggles of geese in the
Park have been an environmental and public
health nightmare for the Park because of the
sheer volume of fecal matter produced by the
geese on park lawns and in the park ponds.
Park officials began a comprehensive geese
management strategy in the last 6 months of
2012, including signs instructing the public
not to feed the geese.  This short‐term effort has drastically reduced the geese population.in the Park to
approximately 60‐75 birds.

3.0 What Can Be Done: Best Management Practices
The Horsley-Witten (HW) study of the Park ponds outlines scores of potential remedies to reduce
phosphorous loadings entering the ponds. The study recommends everything from cleaning the street
catch basins more frequently to re-directing existing storm water flows to educating nearby
homeowners to reduce pollution that washes into the Park ponds.

Outlined below are some of the principal categories of best management practices that potentially may
improve the water quality of the Roger Williams Park ponds:

4.1 Structural Storm Water System Changes

 Storm Water System Retro Fits—the HW study examined about 30 places in the Park where
the existing storm water pipes could be diverted and re-engineered to enable storm water
to flow into bio-retention vegetated areas and swales before entering the groundwater into
the ponds. This technique essentially allows the storm water to be intercepted and to be
treated before it enters the pond system. The graphic below illustrates a typical storm
water treatment design. The picture below shows a bio retention area being constructed
near the Carousel which now drains a major portion of the Carousel parking lot.

 Pavement Reduction—A very basic method
for reducing storm water pollution in the ponds is to reduce the amount of impervious
surfaces—primarily parking lots and roadways—in the Park to reduce the amount of storm
water flow. While the Park has many stretches of wide roads that could be narrowed, this
type of structural change needs to consider parking and traffic issues very carefully. Thus,
Park staff will examine where pavement can be reduced at a reasonable cost without
affecting normal Park use. The current storm water retro fit project along Roosevelt Pond
involves the removal of almost 40,000 sq. ft of road area.

 Curb Removal—Roger Williams Park, unlike the large state parks in Rhode Island, has miles
of curbing along the sides of its roads. This curbing is a legacy of work done by the Works
Progress Administration in the 1930’s and was a well intentioned effort to channel storm
water into catch basins to flow into the ponds. There are lots of opportunities in the Park to
selectively remove curbing to allow storm water to flow into existing grass areas and to be
absorbed into groundwater.

 Disconnecting Building Down Spouts—Another storm water practice implemented in
Providence in the early 20th century was to have building down spouts connect directly into
underground drainage lines that then directed storm water into the street drainage system.
This practice also occurred in the Park
and in the watersheds draining into
the Park. The roof areas in the Park
total over 100,000 sq. ft and thus
send a lot of storm water into the
ponds. These down spouts can be
disconnected relatively easily from
the underground pipes and then the
down spouts can be altered to divert
the storm water into adjacent
planting areas. This has been
successfully done in a demonstration
at the Botanical Center already as
seen in the accompanying photo.

This practice also offers significant potential in the upper and lower watersheds where
neighborhoods, according to the HW study, have generally 50-60% of houses with down
spouts directly connected to underground storm water pipes.

4.2 Non Structural Practices

While some of the above structural practices will involve considerable capital costs, there are scores of
non structural practices, much less costly, that can be implemented in the Park and in the nearby
watersheds draining into the Park to reduce storm water loadings.

 Operations and Maintenance Practices—Daily operations in Roger Williams Park and the
abutting watersheds can be altered and adjusted to reduce storm water pollution. Here are
the most significant practices that should be considered:

--Catch Basin Cleaning: Catch basins in the street “catch” storm water flowing on the street
and then through gravity flow discharge the flows from the catch basin through a pipe into a
nearby water body. As seen in the accompanying sketch, catch basins are designed to settle
out solids before the storm water flows into the discharge pipe. These solids are loaded

with nutrients and thus catch basins can potentially be a significant method for reducing
storm water pollution flowing into the Park ponds, if the catch basins are periodically
cleaned of the settled solids.

If the catch basin solids are not cleaned in a timely manner,
they eventually fill up the catch basin and storm water
events flush the solids into the discharge pipe into the
nearby water body. Roger Williams Park has approximately
45 catch basins and there are perhaps a few hundred in the
upper and lower watersheds outside of the park. The Parks
Department does not have its own vacuum truck to clean
out catch basins—it depends on an already strapped
Providence Department of Public Works (DPW) to
periodically clean Park catch basins as well as the catch
basins in the upper and lower watersheds. This catch basin
cleaning does not consistently occur because does not have
the resources to clean approximately 20,000 catch basins
throughout the City.

Park officials are examining how to become self-sufficient
for catch basin cleaning.

--Street Sweeping: One way to reduce the amount of solids and trash on Park and
watershed streets from flowing into the storm water drainage system is to sweep the
streets more frequently. The Parks Department does not own a street sweeper and
depends on Providence DPW to sweep the 10 miles of roads in Roger Williams Park twice a
year. Park officials need to figure out how to supplement the DPW services with private
vendors or how to contract DPW services more frequently.

--Mowing Operations: When the Park was designed in the Victorian era of the late 19th
century, the Park design emphasized grass lawns coming right to the edge of the water.
Several thousand feet of shoreline in the Park have this look as seen in the photo below.
Unfortunately, while this design and practice presents an aesthetically pleasing appearance,
it is not a wise water quality management
practice: it allows geese to easily go
between the ponds and the shoreline
making the Park an attractive place to
stay; it provides no natural vegetative
buffer to absorb pond nutrients; and it
leads to shoreline erosion in steep slope
areas that are difficult to mow.

Park officials need to commit to letting a large amount of shoreline to go “natural” and not
mow up to the water’s edge.

--Maintenance Operations “Hot Spots”: The HW study identified several areas in non-
public maintenance areas where the operations required better “housekeeping” by Park
staff to minimize pollution from entering the ponds after rain events. Both the area
Grounds Maintenance yard and the Mounted Command facility on Noonan Island need to
develop best management practices to avoid waste from flowing into the ponds.

 Geese Management—As pointed out in Section 2, the resident Canada geese have long
contributed to the phosphorous loadings that are harming the Park ponds. In 2012 the first
steps to comprehensively manage the resident geese were undertaken: addling all of the
geese eggs in the Park nests; removing several hundred geese under contract with the US
Department of Agriculture; installing “geese education signs” in key geese feeding areas of
the Park; and public education of park visitors by summer high school interns. The 2012
effort has reduced the resident Canada geese in the Park to approximately 60 geese.
This comprehensive effort needs to continue for several years to keep the resident Canada
geese population in check.

 Shoreline Buffer Planting—To
accelerate natural vegetation along the
shorelines, it will be useful to pro-
actively plant native plant species
along many of the Park shorelines. This
will have many water quality
management benefits as discussed
above under “Mowing Operations”.

 Steep Slope Stabilization—While most of the sediment that is in the Roger Williams Park
Ponds is the result of sand washed into the ponds from the upper and lower watershed
storm drainage systems, a small amount of pond sediment is from erosion of sloped lawn
areas that have lost their grass cover for one reason or another. These steep slope areas
with bare soil should be systematically re-seeded with appropriate erosion control matting
in September of each year.

 Making a Difference: The Public—Clean water in Roger Williams Park is not just a municipal
or public sector responsibility and it will not occur if total responsibility is left with
government actions. Park users, and particularly upper and lower watershed residents,
need to do their part to improve the ponds water quality. The HW study indicates that
upwards of 60-65% of the phosphorous loads coming into the ponds causing the water
quality problems come from outside the Park. Watershed residents and businesses will

need to be continually engaged to learn what they do on their properties affects the storm
water flowing into the Park.

Park officials also need to ramp up
efforts to inform and inspire Park
visitors about restoring the water
quality and biodiversity in the Park
ponds. A significant education and
information program will need to be
developed to develop a constituency
for clean ponds.

4.3 In-Pond Options

While the above land-based options and public outreach will significantly reduce pollution loads
entering the pond, many of the actions will be expensive and will not make a major difference
immediately in the ponds. The in-pond management options discussed below should be considered in
the mix of actions to be implemented.

 Chemical Treatment of Aquatic Weeds and Algae—Park officials have been chemically
treating aquatic weeds and algae, under RI DEM permit procedures, for approximately 20
years. Aquatic herbicides are used to treat
rooted aquatic weeds and copper sulfate is
used to treat algal blooms. The doses for
these applications are governed by time of
year and water temperature, are relatively
inexpensive--about $5,000-7,000 per year,
and provide temporary relief for algae and
aquatic plants during the Park’s busy time
of year.
 Dredging of Pond Sediment—In the early 1980’s Park officials spent considerable funds
dredging Roosevelt Pond, Willow Pond, and Polo Pond to address the water quality
problems that existed in the ponds at that time. While well-intentioned, it was a very
expensive short-term solution. Because nothing was done to control the sediment and
phosphorous coming in from the upper watershed into Roosevelt Pond, all three ponds have
long since lost the pond depth that was achieved in 1982. In addition, Pleasure Pond has
also lost considerable pond depth.

The lesson from the early 1980’s dredging effort is that water quality improvements have to
be sequenced properly or else the cost benefit of these actions will be significantly reduced.
Dredging will need to be done again at some point in at least 3 or 4 of the Park ponds, but
land based efforts and upper watershed efforts need to be done first.

 Chemical Treatment of Exiting Sediment in the Ponds—One of the issues unresolved by the
HW study is the extent to which existing sediment in the ponds releases phosphorous into
the water column under certain depth and dissolved oxygen conditions. This phenomenon
is called “internal recycling” and it may be a significant contributor to phosphorous in the
Park’s deeper ponds, i.e., Cunliff, Elm and Edgewood. When existing phosphorous loads
coming into those ponds from the lower watershed are substantially reduced, water quality
testing will need to determine if internal recycling is an issue. At that point Park officials
may consider treating the sediment with aluminum sulfate or sodium sulfate. This is a
relatively expensive treatment—about $1,500/acre, however, and will require careful
dosing to not harm existing fish in the ponds.

4.4 Mashapaug Pond Flow into the Park: Options

The HW study recognized that the long term goal of reducing phosphorous from the upper watershed
that flows into the Park ponds via Mashapaug Pond will be daunting to achieve. Two cities are involved;
three water bodies; scores of dense residential neighborhoods with no common identity or track record
of working together; one industrial park; and hundreds of stand-alone businesses. While all of the
above discussed structural, non-structural, and public outreach efforts need to be started and pushed
forward, the pace of implementation in the upper watershed will likely be far more challenging than the
efforts in the lower watershed.

In the meantime, phosphorous loadings from Mashapaug Pond—the major source of pollution for Roger
Williams Park—will continue to diminish the other efforts in the lower watershed to reduce storm water
pollution in the Park ponds. What can be done in the interim, before the hundreds of pollution
reduction actions are implemented in the upper watershed? The HW study suggests three important
small scale solutions that will need considerably more study, but which appear to be promising.

 Chemical Dosing Station—The 48” pipe that carries the Mashapaug Brook and the storm
water flows from the upper watershed is essentially a point source of pollution for the Park
ponds. The HW study recognized this and suggests chemical treating of the water coming
out of this point source should be considered as an interim measure until solutions in the
upper watershed to reduce pollution are implemented. Their suggestion: a dosing station
that would treat the phosphorous and suspended solids.

One or more aluminum compounds via a drip line feed dosing station, either at the
discharge point in Roosevelt Pond or upstream of the Park, would bind up the phosphorous
and suspended solids precipitating a resultant floc that would fall out of the flow into the
pond. HW recognizes the need for a study to examine the permitting for such a dosing
study, operational requirements, maintenance requirements, treatment protocol, and
disposal of the precipitated floc.

 Mashapaug Brook Weir Box Re-engineering—When Route 10 was constructed, some of the
flows from Mashapaug Pond were altered to go through a weir box (just east of RT 10 and

south of the Calart Building) into a 72” pipe that bypasses the Park ponds. Currently all of
the low flows and smaller storm flows are directed towards the Park ponds through the 48”
pipe into Roosevelt Pond. The HW study speculates that if the weir box is modified to divert
more of the storm events into the 72” pipe that bypasses the Park ponds this might reduce
the phosphorous loads that come into Roosevelt pond after storm events. A detailed
engineering study to examine the feasibility of this weir box modification is needed.

 Chemical Treatment of Sediment in Mashapaug Pond—RI Department of Environmental
Management indicates in its 2007 report on Mashapaug Pond that “internal recycling” of
phosphorous in Mashapaug Pond maybe a a major contributor to the phosphorous loads
originating from Mashapaug Pond and flowing into the Roger Williams Park ponds during
the summer months. The conditions in Mashapaug Pond in the summer months—relatively
deep pond, high water temperatures, and low dissolved oxygen levels—allow the release of
phosphorous into the water column. Thus, treating portions of Mashapaug Pond during
summer months with some type of aluminum compound may be able to inactivate
phosphorous and bind to the pond sediment impinging the ability of the phosphorus to be
released. A detailed study of this treatment is obviously needed since it may require several
acres of Mashapaug Pond to be treated.

4.0 What Can Be Done: Recommendations
While the Horsley-Witten study outlines an impressive array of best management practices for reducing
storm water pollution in the Park ponds, it is clear that some significant findings should guide Park
officials in deciding how to proceed during the next eight to ten years.

A Long-Term Commitment to Managing the Water Quality in the Park Ponds Is Needed. A
year-by-year set of cost effective solutions for the next several years will be required that
takes advantage of available scarce resources. There are no quick and easy solutions. Park
officials need to plug away each year targeting a sequence of activities to reduce storm water
pollution entering the ponds.

Engineering Solutions Alone Will Not Clean Up the Park Ponds—Public Attitudes Need to be
Changed. The Horsley-Witten looked at 35 structural storm water retro-fit projects to
address the storm water pollution from existing storm water outfalls in the Park(not
including the pipe from Mashapaug Pond) and the total cost was estimated at around $1.8-
2.0 million. The Park can’t simply buy its way out of the pollution problem in the ponds
because these infrastructure projects are expensive and will not address all of the
phosphorous loadings flowing into the ponds. Many of the sources of phosphorous coming
into the Park ponds are the result of human behavior, such as feeding the geese and
residential fertilizer practices in watershed areas near the Park. A consistent public outreach
program is needed to change public behavior and attitudes about the Park ponds.

Water Quality Management Improvements Start at Home. There are a number of
operational and maintenance tasks that Park staff need to focus on to help reduce pond
pollution, including:

o systematic catch basin cleaning
o educating park visitors about geese feeding and littering
o providing shoreline buffer vegetation
o allowing leaves to remain in wooded hillside areas
o diligently addressing slope erosion issues as they develop each year.

We Will Need Additional Study to Determine Long Term Solutions for Some of the Pond
Water Quality Issues. We not only need to provide an annual water quality sampling program
in the ponds to monitor the effectiveness of our on-going efforts, we also need to look at the
following un-resolved and/or on-going storm water issues:

 Is it possible to treat the storm water coming into Roosevelt Pond from the Mashapaug
Pond watershed to reduce phosphorous? What are capital and operating costs for such a
system?

 To what extent is the existing sediment that is in the Park ponds releasing phosphorous into
the ponds and under what conditions? Is it cost effective to selectively treat the sediment
in some of the ponds? Is it cost effective to treat sediment in Mashapaug Pond?

 What would it cost to dredge selective Park ponds and what will be the pollution reduction
from such an effort?

 Can storm flows (and the resulting phosphorous loads) from Mashapaug Pond be diverted
away from the 48” pipe entering Roosevelt Pond?

 Is it feasible for the City to develop an overall Regional Storm Water Management District
to fund city wide storm water flow and pollution reduction?

The following Roger Williams Park Pond Restoration actions are recommended to be implemented
during the 2013 – 2020 period. Depending on the number of actions implemented and the ability to
reduce phosphorous from the Mashapaug Pond inflow into Roosevelt Pond, these actions will reduce
the phosphorous loadings into the Park ponds by 20 to 50%.

Summary of Watershed Management
Plan for Rhode Islands Salt Ponds

Horsley Witten Group
Sustainable Environmental Solutions
90 Route 6A • Sandwich, MA • 02563
Phone - 508-833-6600 • Fax - 508-833-3150 • www.horsleywitten.com

Final Watershed Management Plan
Executive Summary
for Green Hill and Eastern
Ninigret Ponds, South Kingstown and
Charlestown, Rhode Island

April 18, 2007

Submitted to:

Rhode Island Department of Environmental Management;
the Salt Ponds Technical Advisory Committee;
and the Salt Ponds Coalition

i. EXECUTIVE SUMMARY

INTRODUCTION

This Watershed Management Plan for Green Hill and eastern Ninigret Ponds is an action
plan to guide residents, watershed groups, and local, state and federal governments on
how to reduce both nutrients and bacteria loadings to Green Hill Pond and eastern
Ninigret Pond in order to restore and maintain water quality levels suitable for fishing
and swimming. This plan is also intended to provide a model for other salt pond
watersheds within the state.

The plan includes an introduction section that describes the planning area, a description
of the watersheds, partners involved in development of the plan, and a water quality
analysis that identifies water quality goals, sources of pollutants, and current loads and/or
concentrations. An assessment section documents existing programs and management
options for wastewater management, stormwater management, regulatory programs,
public education and outreach, and increasing flushing to Green Hill Pond. The
management plan presents specific measures for reducing pollutant sources and presents
implementation measures that specify what is required, who is responsible, a timeframe
for implementation, and how such implementation might be funded. A monitoring plan
is provided to measure interim progress of plan implementation and to provide a
framework for adjusting management measures in the future.

A watershed quality improvement plan was developed by the Rhode Island Department
of Environmental Management (DEM) that specifies maximum allowable bacterial levels
in the ponds and their tributaries. This is referred to as a total maximum daily load
(TMDL) and the bacteria management recommendations are intended to support the
TMDL (approved in 2006). Since a nutrient TMDL has not been developed for the
ponds, the nitrogen loading calculations and management recommendations presented in
this report are intended to be the equivalent of a TMDL.

Watershed Description

The so-called Charlestown lagoon system is located on the southern coast of Rhode
Island and consists of two major basins, Ninigret Pond and Green Hill Pond. Both of
these shallow coastal lagoons receive restricted tidal flushing through one narrow man-
made breachway between Ninigret Pond and the ocean.

Green Hill Pond is located primarily in the southwestern corner of the Town of South
Kingstown, Rhode Island with a small portion of the pond extending into southeastern
Charlestown, Rhode Island. Green Hill Pond has a surface area of approximately 380
acres and a watershed area of approximately 3,400 acres. Ninigret Pond is located
entirely within the Town of Charlestown and is bounded on its northern side by Route 1
and the Charlestown end moraine. It has a surface area of approximately 1,600 acres and
a watershed area of approximately 6,000 acres.

Final Watershed Management Plan for i Executive Summary
Green Hill and Eastern Ninigret Ponds Horsley Witten Group, Inc.
South Kingstown and Charlestown, RI April 18, 2007
J:4095 R.I. South Shore Salt PondsReportsFinal Management PlanFinal Executive Summary 4-18-07.doc

Over the years, the water quality of Green Hill Pond and eastern Ninigret Pond has
diminished. Scientists use a variety of specific measures to gage water quality and/or
chemistry including measures such as dissolved oxygen concentration, fecal coliform
concentrations, Secchi dish depth, nitrogen concentrations, or Chlorophyll a
concentration. Green Hill Pond and eastern Ninigret Pond are listed on the Rhode Island
2006, 303(d) list as being impaired for pathogens and a final TMDL was developed by
the Rhode Island Department of Environmental Management (DEM) and approved by
the U.S. Environmental Protection Agency (EPA) in February 2006. Green Hill Pond is
also listed as impaired for dissolved oxygen (DO), a consequence of excessive nitrogen
loading and poor tidal flushing.

Bacteria Sources and Concentration Reduction Requirements

Green Hill and Ninigret Ponds are designated as Class SA waters. Class SA waters are
defined as suitable for shellfish harvesting for direct human consumption, bathing and
contact recreational use, and providing habitat for fish and wildlife. Class SA waters
must meet a standard for fecal coliform (fc) bacteria of 14 fc/100 ml and no more than
10% of samples can exceed 49 fc/100 ml and a dissolved oxygen standard of not less than
4.8 mg/L at any place or time. Green Hill Pond and eastern Ninigret Pond do not meet
the required fecal coliform standard due to elevated levels of fecal coliform bacterial
concentrations.

In 2002, as part of the TMDL development, DEM used a DNA-based technique to
conduct a bacteria source tracking assessment. Sources of fecal coliform bacteria were
determined to include humans, wildlife, waterfowl, and domestic pets with the major
pathway being the stormwater conveyance system. Septic systems were determined to be
the source from humans. Development of the TMDL utilized sampling stations that were
located in several locations in Teal Brook, Factory Pond Brook, which are tributaries to
Greenhill Pond, Green Hill Pond and eastern Ninigret Pond. The TMDL report cites
required reductions in fecal coliform concentrations to comply with water quality
standards. Factory Brook and Teal Brook need the greatest reductions in fecal coliform
of 95% and 93% respectively based on a mean of all sampling locations.

Nitrogen Loading and Water Quality Assessment

The other major pollutant source to coastal lagoons such as Green Hill and Ninigret
Ponds is nitrogen, which is acknowledged to contribute to impaired water quality by
stimulating algae/plant growth in the water column and along the pond’s bottom. Several
researchers have developed nitrogen loading estimates to the Salt Ponds over the past
several years that evaluate the sources of loads, that documented the elevated loading and
concentrations of nitrogen in the ponds, and that report the negative consequences of too
much nitrogen loading.

In October of 2006, DEM issued a report entitled Determination of Nitrogen Thresholds
and Nitrogen Load Reductions for Green Hill and Ninigret Ponds. This report
established an appropriate nitrogen loading “target” for each pond to ensure a predictive

Final Watershed Management Plan for ii Executive Summary

level of water quality. The management plan partners selected a nitrogen loading and
management approach based on a method originally developed by the Buzzards Bay
National Estuary Program (BBNEP). The BBNEP method uses sampled water quality
data to derive an empirical relationship between watershed mass loading of nitrogen as
related to estuary flushing rate and water quality measures of eutrophication. The
BBNEP approach characterizes estuarine response as a Eutrophication Index (EI) that is a
function of five factors: the mean value of the lowest 20% of dissolved oxygen percent
saturation values, mean dissolved inorganic nitrogen (DIN) concentration, mean Secchi
depth, mean chlorophyll a concentrations, and mean total organic nitrogen (TON).

Eutrophication Indices, calculated using available physical and chemical data collected
from the Salt Ponds Coalition Volunteer Water Quality Monitoring Program (Pond
Watchers) and DEM were determined to be an average of 45 for Green Hill Pond and an
average of 67 for Ninigret Pond.

Eutrophication Index Scores of 65 to 100 are considered “good to excellent” water
quality, 35 to 65 are considered “fair to good” water quality, and less than (<) 35 are
considered typical of eutrophic conditions. Both Green Hill and Ninigret Ponds have
been designated by DEM as Special Resource Protection Waters (SRPW) and therefore
should have an EI goal of 65 or greater (higher).

Applying this approach to Green Hill and Ninigret Ponds, DEM calculated a target
nitrogen loading for Special Resource Protection Waters. These targets and existing
loads are summarized in Table E1.

Table E1. Nitrogen Loading Targets for Green Hill and Ninigret Ponds

Parameter Green Hill Pond Ninigret Pond
Pond Area (km2) 1.70 7.38
Average Pond Depth (m) 0.80 1.35
EI Goal1 65 65
1
Current EI 45 67
1
Current Annual Nitrogen Load (lb) 30,386 79,384
Target Load (lb)1 6,078 84,450
Required Percent Reduction1 80% 0%
1
(DEM, 2006)

The nitrogen loading target identified above was derived using an EI score of 65 which is
predictive of “good to excellent” water quality and is the ultimate objective of this
management plan. As it will take time and a significant investment to achieve an 80%
reduction in nitrogen loading to Green Hill Pond, this plan also recommends a phased or
adaptive management approach to watershed planning, where ultimate goals are
established based on water quality standards and criteria and interim goals are also
defined. An interim goal of reaching an EI score of 50 (associated with the Class SA
water use designation) would result in predictive water quality in the “fair to good”
Final Watershed Management Plan for iii Executive Summary

condition range and allow for a higher nitrogen loading target of 18,234 lbs/year or
require a nitrogen load reduction of 12,152 lbs/year (or approximately 40%) below
existing levels for Greenhill Pond. There is currently no nitrogen load reduction needed
for Ninigret Pond. However, it is prudent to continue to mange nitrogen loadings to
maintain good water quality.

ASSESSMENT SUMMARY

This section provides a summary of the watershed assessment for the Green Hill and
eastern Ninigret Ponds. Given the water quality impairment currently experienced in the
ponds, the assessment focused on two contaminants: fecal coliform bacteria and nitrogen.
The assessment focuses on current and potential future wastewater management
programs, stormwater management programs and options, regulatory programs, public
education and outreach methods, other pollutant sources, and the potential for increased
flushing of Green Hill Pond.

A summary of the analysis for each of two primary contaminants is described below. In
addition, a brief summary of recommended additional studies is provided at the end of
this section.

Nitrogen

Nitrogen enters the ponds through groundwater and surface water, with groundwater
sources representing approximately 75% of the total load to the ponds. Loadings from
individual ISDSs within the watershed are the greatest contributor of nitrogen to the
ponds (approximately 74% of the load provided through groundwater and 60% of the
total load to Green Hill Pond). As a result, a series of wastewater alternatives were
evaluated to develop recommendations to reduce nitrogen inputs. The options considered
include:

• Upgrading all ISDSs according to current DEM regulations;
• Upgrading all ISDSs with alternative nitrogen reducing systems;
• Community or cluster systems for six service areas within the study area; and
• The use of nitrogen treatment trenches along the pond shoreline.

The nitrogen reductions provided by these options were then compared to the nitrogen
loading target for Green Hill Pond (the pond most severely impacted by nitrogen). None
of the wastewater options, on their own, reduce nitrogen loading enough to reach the
targeted 80% nitrogen reduction (although the load reduction of the nitrogen treatment
trenches was not specifically quantified). The community or cluster treatment alternative
comes the closest, providing approximately 16,700 lbs/year of the necessary nitrogen
reduction (36% of the total nitrogen load to Green Hill Pond). The community treatment
option is similar in cost to the on-site denitrification system option. Both cost in the
range of $20,000 to $35,000 per lot. The community system is more attractive because it
provides a greater reduction of nitrogen, and eliminates the need for management of
hundreds of different on-lot denitrification systems. However, there are still issues with
Final Watershed Management Plan for iv Executive Summary

this approach. The potential disposal areas identified in this plan still need to be
confirmed with field testing, and may, or may not, provide adequate sites for disposal.
The community system may foster the development of existing lots of record that are
currently unbuildable given existing DEM regulations on ISDSs. There are significant
political and institutional hurdles to overcome regarding who would manage the system,
who would pay for it, and how it would be financed.

An alternative approach of nitrogen removal is also identified in the report. In this
approach, a porous reactive “barrier” or treatment trench is constructed in the ground
perpendicular to the direction of groundwater flow at a depth sufficient to intercept and
interact with the groundwater. The trench is filled with woodchips, which serve as a
carbon or food source for denitrifying bacteria. As nitrate-bearing groundwater filters
through the trench, the bacteria denitrify the nitrate, causing a decrease in nitrate
concentrations. These nitrogen treatment trenches appear to offer a significant benefit to
reducing nitrogen loading to the ponds. Further investigations are needed to see if this
approach is feasible. There is a need for further data to define the watershed treatment
area and the amount of groundwater that flows to the trenches, and there is a need for
more research to confirm the long-term treatment efficiency they provide. Engineering
and maintenance considerations also need to be fully vetted. However, the trenches have
the potential to provide the greatest nitrogen reduction at the least cost. In addition, the
approach is attractive because it treats all sources of nitrogen in groundwater that pass
through the barrier and because it can have an immediate impact on the quality of
groundwater entering the pond (as opposed to other options that will only affect water
quality over the long term). The towns of South Kingstown and Charlestown are in the
process of further assessing the most appropriate wastewater treatment options in a
pending wastewater treatment facilities plan. This plan is scheduled to be completed by
December 2007.

Although stormwater is a major contributor of bacteria and other pathogens, nitrogen
loading from stormwater is not as significant as the loading from other sources in the
watershed, particularly wastewater sources. The results of the MANAGE model show
that surface runoff load is not reduced significantly by the handful of structural end-of-
pipe practices. However, the implementation of small-scale practices across the
watershed can make a significant reduction in nitrogen loading. Although there are few
“centralized treatment options” for stormwater in this watershed, the small-scale
solutions, in conjunction with end-of-pipe solutions, will help reduce nitrogen loads
incrementally over time.

Another option to reduce the impacts of nitrogen loading is to increase the flushing
within Green Hill Pond. This could be done through the construction of a new opening
from Green Hill Pond across the barrier beach into the ocean. This direct opening would
allow a greater exchange of water than is currently provided through the single opening
in Ninigret Pond. The opening could be permanent, or periodic (seasonal). The creation
of a permanent opening would require significant armoring, at tremendous expense, to
prevent the new entrance from closing, shifting or filling in with sediments from coastal
erosion. The creation of a new opening would require a complex environmental analysis

Final Watershed Management Plan for v Executive Summary

and permitting process through the CRMC and the Army Corps of Engineers. The
analysis would have to consider the benefits of the increased flushing versus potential
changes in habitat in the pond due to changes in water level, salinity, and other potential
factors. A breachway would also require an suitable parcel of land. The parcel with the
best potential is owned by DEM, however it appears that the deed would preclude
constructing a breachway.

Fecal Coliform

Results from the Green Hill Pond bacteria source tracking project conducted by DEM in
the fall of 2002, suggest that waterfowl and wildlife are a major source of fecal coliform
to the pond. Stormwater runoff can act as the delivery mechanism for much of this
animal-derived bacteria. The study also found evidence of human sources of fecal
coliform but not at as high a frequency as other animal sources. The study was
conducted during a drier than normal period. Failing septic systems may play a more
significant role in pollutant loadings to the ponds in wetter years and when groundwater
is elevated.

All of the wastewater management options will also help to reduce bacterial
concentration to the ponds, with the exception of the nitrogen treatment trenches.
Currently, properly functioning ISDSs are already reducing bacterial concentration.
Given the current relatively low hydraulic failure rate of ISDSs in both Charlestown and
South Kingstown, it is unlikely that wastewater is the primary source of bacterial
concentration to the ponds. Future ISDSs failures, outbreak and overflow events, pipe
breaks, as well as overflows associated with the community sewerage options may
continue to contribute a modest level of bacterial concentration, but this contribution is
probably negligible when compared to the contribution from stormwater runoff.

Bacteria can be removed to a certain extent through structural stormwater practices such
as infiltration, constructed wetlands, water quality swales, and bioretention, with
infiltration being the most effective structural control. However, since infiltration is not
feasible in areas adjacent to the end-of-pipe outfalls to Green Hill and Ninigret Ponds, the
most effective method to reduce fecal coliform levels is by implementing a combination
of structural controls combined with source controls. Non-structural stormwater source
controls and habitat modifications, including wildlife management, are therefore
important measures and receive significant attention in the watershed management plan.

Recommendations for Additional Studies

While numerous studies have been performed for the Rhode Island South Shore Salt
Ponds, the watershed assessment revealed the need for other studies that would aid in the
decision making process for implementation of watershed plan recommendations. A
preliminary list of additional recommended studies includes, but is not limited to:

• Further analysis of groundwater flow and capture amount to the nitrogen
treatment trenches;

Final Watershed Management Plan for vi Executive Summary

• Developing a wastewater management facilities plan (which is Pending);
• Conducting a review of waterfowl/wildlife management strategies that focuses on
nuisance waterfowl and wildlife (e.g. raccoons, skunks, and foxes) and better
control measures; and
• A study that evaluates the effectiveness of existing regulations, such as
determining how many existing sites comply with current CRMC buffer
regulations.

Regulatory programs and public education and outreach currently provide a range of
measures to minimize nitrogen loading and fecal coliform concentrations to the ponds.
These include regulations at the federal and state level, including the total maximum
daily load (TMDL) program, the Rhode Island Pollution Discharge Elimination System
(RIPDES) Phase II Stormwater program, Coastal Resources Management Council
(CRMC) regulations for activities on or within 200 feet of a shoreline feature, the CRMC
Special Area Management Plan (SAMP) for the Salt Ponds Region, and Rhode Island
Division of Fish and Wildlife nuisance species control programs. Local regulations
include controls in the local zoning ordinances in both South Kingstown and
Charlestown. Both towns have adopted local Watershed Management Districts that
provide for mandatory inspection and maintenance programs of ISDSs, and both towns
are subject to RIPDES Phase II requirements to implement stormwater controls to reduce
nitrogen loading.

Public education and outreach programs are generally voluntary at the town level (with
the exception of Phase II stormwater program requirements). The Salt Ponds Coalition
provides significant educational and outreach programming. Key educational areas
include:
• Waterfowl and wildlife management;
• Lawn care management;
• Pet waste management;
• Stormwater management; and
• Septic system maintenance.

MANAGEMENT AND IMPLEMENTATION RECOMMENDATIONS

The watershed plan presents a phased or adaptive management approach to improve
water quality in the ponds. The first step is to increase water quality to a “good” level by
implementing near-term actions. The next step is to implement a second level of actions,
such that “excellent” pond conditions that can be achieved by actions considered more
long-term.

The watershed management plan presents a suite of available options pertaining to
wastewater management, stormwater management, regulatory mechanisms, public
education and outreach, and other management of pollutant sources. All of these options
are presented in a Watershed Management Toolbox in Appendix L of this plan, with the
preferred recommendations presented as an implementation plan. This plan also presents
a Watershed Monitoring Plan that outlines existing monitoring programs and
Final Watershed Management Plan for vii Executive Summary

recommended monitoring indicators. The watershed management implementation
measures are summarized in Table E2. Detailed descriptions of the proposed
management and implementation measures are provided in Section 3 of the watershed
plan.

Final Watershed Management Plan for viii Executive Summary

Table E2. Watershed Management Implementation Plan Summary
Action Item Responsible Party Term Target
Pollutant
Near Long Nitrogen Bacteria
Wastewater Management
Wastewater Facilities Town Councils of South X X X
Plan Kingstown and Charlestown
Stormwater Management
Site 3: Elm Road Retrofit South Kingstown Town Council X X

Site 6: Dawley Road South Kingstown Town Council X X
Retrofit
Site 2: Shore Road Retrofit Charlestown Town Council X X
Site 1: Arches Road Retrofit Charlestown Town Council X X
Sites 7&8: Matunuck South Kingstown Town Council X X
School House Road and GH
Beach Rd.
On-lot, Community and Individual homeowners, X X X
Roadway Stormwater Neighborhood or Condominium
Treatments Associations, Town Councils
Regulatory Programs
Overlay Districts Planning Commission/Town X X X
Councils of each town
Subdivision and Land Planning Commission/Town X X X
Development Councils of each town
Ordinance/Regulations
Phase II Stormwater Planning Commission/Town X X X
Management Ordinance Councils of each town
Stormwater Management South Kingstown – Dept of X X X
Program Plan (in Public Services, Charlestown –
accordance with Phase II) Dept. of Public Works
Performance Based South Kingstown – Conservation X X X
Wastewater Treatment Commission, Charlestown
Standards Wastewater Management
Commission
Public Education and Outreach
Education of Local Officials Salt Ponds Coalition, DEM, X X X
CRMC
Annual Watershed Salt Ponds Coalition X X X
Awareness Day
Adopt-a-Pond Organization Salt Ponds Coalition X X X
Demonstration Projects Town Public Service/Public X X X
Works
School Watershed Science Town School Committees, X X X
Programs Teachers
Other Pollutant Sources
Wildlife Management Study DEM. X X X

Final Watershed Management Plan for ix Executive Summary

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