Aquidneck Island’s Water Resources Impaired by Runoff

The primary causes of water impairments on Aquidneck Island are total phosphorus, total organic carbon, and bacteria. Bailey’s Brook and the Maidford River, which feed multiple reservoirs, are listed as impaired by enterococcus and fecal coliform. (DEM)

The primary causes of water impairments on Aquidneck Island are total phosphorus, total organic carbon, and bacteria. Bailey’s Brook and the Maidford River, which feed multiple reservoirs, are listed as impaired by enterococcus and fecal coliform. (DEM)

By ecoRI News staff


MIDDLETOWN, R.I. — Aquidneck Island’s fresh and saltwater resources are immensely valuable for drinking water and recreation and are the foundation of a three-municipality coastal economy. But the island’s geography, geology, and land uses make these waters vulnerable to pollution from stormwater runoff.

During periods of heavy rain, as the region experienced on Jan. 24, excess stormwater carries toxic pollutants through drinking water supplies and overflows into recreational coastal waters.

The Aquidneck Island Planning Commission (AIPC) has a set of plans, called the Island Waters project, to collect and treat stormwater runoff, reducing harmful pollutants that enter the island’s water system.

Impervious cover is any land surface covered by asphalt, concrete, brick, or similar material that doesn't allow rainwater to infiltrate into the soil. (AIPC)

Impervious cover is any land surface covered by asphalt, concrete, brick, or similar material that doesn't allow rainwater to infiltrate into the soil. (AIPC)

With support from the Environmental Protection Agency (EPA), AIPC is expected to start breaking ground on a series of projects beginning this spring. Island Waters intends to promote a healthy water system for the 70,000 residents in Portsmouth, Middletown, and Newport. The goal of the project is “to work with the communities and residents of Aquidneck Island to protect and improve the quality of our water system,” according to John Shea, AIPC’s executive director.

The Rhode Island Department of Health closes recreational beaches when fecal bacterial levels are too high. During the past five years, beaches on the island have been closed an average of 12 days a year during an approximate 100-day beach season.

Aquidneck Island is also the only East Coast island that relies almost entirely on surface reservoirs for its drinking water, according to AIPC.

The greater the area of land covered by impervious surfaces, the greater the amount of runoff volume generated during rainfall. (AIPC)

The greater the area of land covered by impervious surfaces, the greater the amount of runoff volume generated during rainfall. (AIPC)

Land use on Aquidneck Island is diverse, ranging from forested and agricultural uses to high-density residential and commercial uses. Across the island, residential land of variable density represents the single-largest land use (36 percent), followed by forest and brushland (17 percent), agricultural (12 percent) and commercial (5 percent).

Impervious cover on island watersheds that drain directly to drinking water supplies is below the 10 percent degradation threshold for Gardiner, Nelson, and St. Mary’s ponds, higher than the 10 percent threshold for the Lawton Reservoir and Maidford River, and greater than the 25 percent threshold for Bailey Brook. On a broader scale, all watersheds on the island are above the 10 percent impact threshold, and the Lower East Passage of Narragansett Bay, Mount Hope Bay, and Coastal Aquidneck subwatersheds are beyond the 25 percent threshold.