2007-07-26 / Front Page

A scientific view of island water sources

By Sam Bari

Sources of ground water on Conanicut Island have long been a controversial issue. The sources of water, particularly ground water, can be easily explained and clearly defined, according to Daniel W. Urish, a certified professional hydrogeologist with a Ph.D. from the University of Rhode Island in civil and environmental engineering. He is presently a professor emeritus at URI, Kingston.

"By taking a scientific approach to the study of surface and ground water, sources of water can be easily identified in any given area," Urish said. Over the past 25 years, Urish has been the principal or co-principal investigator on 36 research projects, as well as author or co-author of more than 60 publications dealing with water resources, environmental issues and geophysics. His credentials as an authority on the subject of water resources are indisputable.

In a document titled "Origin and Fate of Precipitation on Conanicut Island," Urish explains the source of water and island hydrogeology.

His document says that all water on Conanicut Island comes from precipitation, whether it be rain, snow, dew or fog drip.

He also says that in terms of numbers for Conanicut Island, an average year produces about 43- inches of rainfall, 17- inches of surface runoff, seven-inches of groundwater recharge and 19- inches of evapo-transpiration from exposed surface water, plants and trees. He goes on to say, "For Conanicut Island it is important to note that surface water runoff collected in the reservoirs in the northern part of the island is exported to the southern part where it is a significant import."

Urish clarified the document by saying that, "The town water supply comes from reservoirs in the north end of the island that gather water from run-off. The reservoirs are not part of the aquifer. Residents in the south end who are using town water benefit from the north end surface water run-off because that is where the reservoirs and wells that supply town water come from. Water is pumped from the north end of the island to the south end and provides south end residents with town water, but not from the north end aquifer.

However, that is not to say that the island is a single source aquifer. In the aforementioned document, Urish also says that, "In terms of aquifer delineation and the fate of the precipitation, Conanicut Island is divided into three components, each with unique characteristics. Each is bounded by the bay shoreline and separated by a significant fault line manifested by a low topographic feature and salt marsh." Again he clarified the document by saying, "In other words, there are three aquifers on Conanicut Island."

The three aquifers were defined by Urish in the document as:

The northern aquifer in the area north of "Great Creek" is generally composed of old sedimentary rocks of predominately shale overlain by glacial till. Residents primarily obtain water from private wells and have individual septic systems effectively recycling water in localized areas.

The southern aquifer in the area south of the slough that originally joined Potter Cove and Dutch Island Harbor is composed of ancient metamorphosed and granite rocks overlain by a very thin glacial till mantle. While some wells might be successful for limited quantities of water, the primary source is the Jamestown public water supply system, with a public sewage collection system.

The southwest aquifer stretches from Beaverhead to Beavertail. This is the region separated by a narrow sand spit from the rest of the island. It has a very thin overburden and is composed of highly metamorphosed old rock, which may provide limited water to private wells. Water is returned in the ground through individual sewage disposal systems.

The document went on to say that in all zones, most of the available groundwater is obtained from fractures in the rock. Some older wells in the northern aquifer may be shallow, wide diameter dug wells in the till overburden, especially in the low topographic areas where the overburden is thicker and the water table less deep.

Urish said that individual deeper bedrock wells in the northern aquifer can typically produce three- to five- gallons per minute, a sufficient amount for a private household if an excess is not used for lawn watering or other non-essential purposes. The most promising areas for large quantity groundwater development are from major fracture zones that cross the island. Some of the more recently drilled town deep bedrock wells in recognized fracture zones are capable of producing 50 gallons per minute or more. Those wells are only used seasonally, during the summer months if the surface water run-off is not adequate to supply the reservoirs.

Surface water and groundwater are linked together in the hydrologic process. Surface water becomes soil moisture and groundwater as it seeps into the ground. But in other instances groundwater becomes surface water as it seeps out of the ground into low-lying wetlands. In the summer, much of the water in the ground returns to the atmosphere through the transpiration process in plants and trees, while surface water experiences direct evaporation, as much as three- inches per month.

Urish said that the replacement of groundwater, or the water that we drink, is a never-ending cycle. Probably the only water that has ever left the earth was in a few spaceships. However, we can, and do, contaminate the water that is available with pollutants and by overbuilding, which overtaxes the natural ability of any aquifer to recover and replenish itself.

Urish pointed out that contained in a separate document published by the United States Environmental Protection Agency titled "Sole Source Aquifer," the agency emphasizes that, "The Sole Source Aquifer program is not intended to be used to inhibit or stop development of landfills, publicly-owned treatment works or public facilities financed by non-Federal funds. Furthermore, the SSA program is not linked to other Federal environmental regulatory or remedial programs, except where Federal financial assistance is committed in a designated sole source aquifer area."

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