Aquidneck Island Drinking Water Assessment Results

de Islan
Department of
Safe and healthy lives in safe and healthy communities
Aquidneck Island Drinking
Water Assessment Results
The Newport Water Division maintains a system of seven interconnected surface water reservoirs that collect and store
stormwater runoff and infiltrating groundwater on Aquidneck
Island. These reservoirs serve the city of Newport and about
70 percent of residents in Middletown and Portsmouth. Three
quarters of the watershed – the area of land that drains to the reservoirs – is located within Middletown, with one quarter in Portsmouth.
Newport Water’s distribution network consists of two interconnected
systems. Water from North and South Easton Pond and other
Middletown reservoirs is treated at the main Newport Water treatment facility and distributed to Newport, Middletown, and the U.S.
Navy base. Water from the reservoirs located in Portsmouth is either
piped to Bailey Brook or treated at the Lawton Valley treatment plant
and distributed primarily by the Portsmouth Water and Fire District.
This system may be supplemented seasonally by Newport Water’s
Nonquit and Watson Reservoirs in Tiverton and Little Compton.* The
water service district includes most of the homes in the watershed.
N. Easton
Key Findings
Newport Water maintains an active watershed protection program
that includes watershed monitoring, land acquisition and retrofitting
storm drains to treat runoff. Yet much of the watershed is intensely
developed with serious pollution risks from urban development, active agriculture, and continued suburbanization.
Island reservoirs are showing signs of impact from watershed
pollutants and low flow. Newport Water’s state-of-the-art water
treatment plant ensures all drinking water standards are met.
However, sediment and aquatic plant matter reduces reservoir
capacity and can affect taste, odor and cost of water treatment.
Future conversion of farmland to medium density house lots,
with associated runoff-borne sediment and nutrients, is expected
to increase pollution risks slightly. Actual impacts are highly uncertain and depend on municipal development standards and
how landowners manage their property.
Enhanced watershed protection will reduce reliance on water
treatment to meet drinking water standards while also improving
aquatic habitat. Maintaining or restoring water quality will require
a combination of strategies to control existing pollution sources
and impacts of new construction and redevelopment.
Aquidneck Island water supply reservoirs
Source Water
The focus of this assessment is on public drinking
water supply “source” areas – the wellhead protection area that recharges a well or the watershed that
drains to a surface water reservoir. Source water is
untreated water from streams, lakes, reservoirs, or
underground aquifers that is used to supply drinking
This fact sheet summarizes results of a source water
assessment conducted for the city of Newport Water
Division. It identifies known and potential sources of
pollution to Aquidneck Island drinking water supplies
and ranks their susceptibility to future contamination.
The goal of this study is to help water suppliers, local
officials, and residents living in drinking water supply
areas to take steps to keep water supplies safe.
* Assessment results for the Newport Water and Stone Bridge Fire
District supplies in Tiverton and Little Compton are summarized in a
separate fact sheet.
Land Use Threats to Water Quality
Within a watershed, the quality of
groundwater and surface water is directly
related to land use activities. To locate
threats most likely to affect water quality,
the seven reservoir watersheds within the
Aquidneck Island water supply system
were evaluated and ranked based on
landscape features including: high
intensity land uses, unprotected shoreline
buffers, and estimated nutrient sources
such as septic systems and fertilizers. A rating from low to
high was assigned to each factor and summed to create an
average pollution risk score for each assessment area, and
an average susceptibility rank for the whole supply.
Susceptibility to Contamination
The results show that Newport Water’s Aquidneck Island
water supplies are moderately susceptible to contamination.
This is an average ranking for the entire system based on
land use and existing water quality. Individual subwatersheds may be more or less susceptible to
Note: A moderate ranking means that the water could become
contaminated one day. Protection efforts are important to assure
continued water quality.
Current Conditions
Land use throughout the watersheds is predominantly a mix
of agriculture and medium to high-density residential development. The Bailey Brook watershed, which feeds North
and South Easton Ponds, is the most urban with 20 percent
commercial land use. As a result, this area is at extreme risk
of contamination from polluted runoff, underground storage
tanks and businesses where hazardous materials may be
used. Because the Bailey Brook watershed makes up 40
percent of the total watershed system, these factors increase
pollution risks to the Newport Water supply overall.
Treated water meets all drinking water standards but
the RI Department of Environmental Management has
ranked all water supply reservoirs and tributaries as “impaired” due to poor habitat, high bacteria, or excessive
algae, at least partly due to low flow. Any additional runoff and associated pollutants with future development is
a concern given existing stresses.
Sewers in the Bailey Brook and half of the Maidford River
watersheds help to reduce risk of wastewater contamination provided sewer lines and pump stations are
checked for leaks. The Portsmouth reservoirs have the highest concentration of septic systems, underscoring the need
for proper septic system maintenance. Substandard systems
in shoreline buffers increase the risk that nutrients and bacteria will reach surface waters, especially in high water table
Newport Water has protected much of the land immediately
adjacent to the reservoirs, however, 50 percent of the critical shoreline buffers to surface waters and tributaries in the
watersheds has been converted to business, agriculture or
house lots, reducing natural treatment potential.
Aquidneck Island owes much of it’s unique scenic character
to it’s extensive farmland and nurseries, which covers almost 30 percent of the watersheds. Fertilizers and sediment
from tilled cropland is potentially a high risk to water quality
but actual impacts are highly variable and can be minimized
with good farming practices.
Future Threats
Under current zoning, one half of the
agricultural land in the reservoir watersheds could be converted to home sites,
with up to two thirds lost in the heavily
agricultural Maidford River watershed.
Pollution sources are expected to
increase only slightly but runoff,
lawn fertilizers, and septic systems
will become more significant
sources. Actual impacts are highly
uncertain and may be much greater
if landowners develop their properties intensively and if highly marginal
sites are developed.
Most of the remaining vacant land
is wet, with water tables within 3 feet
or less from the ground surface.
These areas require careful design
to prevent increased runoff volume.
In addition, advanced wastewater
treatment systems used to build on
wet sites are sure to fail without routine maintenance.
Estimated Percent Impervious Surface Area,
Aquidneck Island Reservoir Watersheds
St. Mary’s
Impervious cover is a catch-all term for pavement, rooftops and other impermeable surfaces that
prevent water from seeping into the ground. Many studies have linked the extent of impervious surfaces to declining habitat quality in streams and wetlands.
This chart shows that average impervious levels in Aquidneck reservoir watersheds represent a high
risk to stream quality, with Bailey Brook well above the extreme risk threshold. Many watersheds are
still near or below the 10 percent level considered safe for stream quality. Future development is
expected to result in at least minor increases in most areas. Management options to maintain future
water quality include limiting impervious cover at present levels, controlling runoff volume with new
construction, and in developed areas, retrofitting stormwater systems to treat pollutants.
The streamside zone is a critical water
quality protection zone. Although forest
cover is ideal, natural grass buffers also
remove pollutants provided they are not
fertilized or disturbed. Runoff from
roads and parking lots should be treated
before discharge to the buffer.
Maidford River, Middletown.
St. Mary’s Pond.
Constructed wetland in the
Bailey Brook watershed
helps treat runoff from the
roads and parking lots.
Photo courtesy RI Sea Grant
What You Can Do to Protect Water Quality
Municipal Boards and Government
Water Supplier
Portsmouth and Middletown have adopted watershed protection measures
and have a history of regional cooperation through the Aquidneck Island
Planning Commission. Continued cooperation in updating plans and development standards will better protect future water quality with continued
Town planning and land use ordinances
Designate a committee to review assessment results, select priorities, and incorporate key recommendations into town plans and ordinances. Work with the Aquidneck Island Planning Commission to
implement a regional water supply protection strategy.
Continue regional open space planning to prioritize land protection
immediately adjacent to water supplies and tributaries. Coordinate
drinking water protection with Phase 2 Stormwater Plans.
Expand community pollution prevention education. Start by mailing
this fact sheet to watershed residents and water users. Adopt model
practices at municipal garages, schools and parks.
Controlling runoff and nutrients
Use zoning setbacks for maximum protection of small headwater
streams and wetlands.
Set targets for maximum impervious cover at current levels or no
more than 10 percent in less developed areas; limit site disturbance
and keep runoff volume at pre-development levels; update site design
and stormwater runoff controls using state-of-the-art practices.
Develop standards for redevelopment and infill to limit impervious
cover, retrofit storm water systems and restore wetland buffers.
Use creative development techniques to preserve farmland and open
Apply strict erosion controls. Assign field inspectors in erosive sites.
Restrict use of hazardous materials,
Managing wastewater/keeping septic systems functioning
Inspect and maintain sewers to prevent leakage and infiltration.
Adopt septic system management programs requiring regular
inspection and maintenance. Phase out cesspools in critical areas.
Restrict new alternative systems on highly marginal land.
This assessment was conducted by the University
of Rhode Island Cooperative Extension with
funding from the R.I. Department of Health,
Source Water Assessment Program, established
under the 1996 amendments to the Federal Safe
Drinking Water Act.
Cooperative Extension in Rhode Island provides
equal opportunities in programs and employment
without regard to race, color, national origin, sex
or preference, creed or disability. University of
Rhode Island, U.S. Department of Agriculture,
and local governments cooperating. This is
contribution #3986 of the College of the
Environment and Life Sciences, University of
Rhode Island.
Implement recommendations of the latest water supply system management plan.
Continue to acquire land for protection, focusing on intake areas and tributary buffers.
Work with local officials to implement land use protection measures and
education programs.
Inspect water supply and protection area regularly for potential pollution
Expand reservoir sampling to monitor nutrient enrichment levels, track
frequency and duration of algal blooms.
Maintain wooded buffers or restore natural vegetation along wetlands or
watercourses that run through your property. Reduce fertilizer and pesticide
use. Limit watering. All septic systems need regular care to function properly,
keep your well safe, and avoid costly repairs. Inspect annually and pump tank
when needed, usually every 3-7 years. For information about protecting your
well contact URI Home*A*Syst (401) 874-5398,
Farmers and Landowners
Work with the USDA Natural Resource Conservation Service to develop a conservation plan that addresses proper nutrient, manure, pest, and irrigation water
management. Contact them at (401) 828-1300,
Commercial and Industrial Businesses
Adhere to all laws, regulations, and recommended practices for hazardous
waste management, above and underground storage tanks, and wastewater
discharges. Check local regulations with city/town hall and state regulations
with the R.I. Department of Environmental Management, Office of Water Resources (401) 222-4700,
For More Information
• R.I. Department of Health, Office of Drinking Water Quality, (401) 222-6867,
• URI Cooperative Extension Nonpoint Education for Municipal Officials (NEMO)
(401) 874-2138,
• Newport Water (401) 847-0154,
Report prepared by URI Cooperative Extension, NEMO program
Editing and graphic design by Rhode Island Sea Grant (2003).