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The geology of Staten Island is varied and complex, ranging from artificial fill, various glacial deposits including glacial till and glacial outwash, as well as exposed bedrock including ancient serpentines. The geothermal designer, with respect to particular locations in Richmond County, has the option of completing wells in the outwash deposits in eastern Staten Island or the completion of bedrock wells throughout most of the remainder of the borough. Portions of Staten Island are artificially filled wetlands and coastal areas that may contain transmissive deposits. However, it is more likely that the fill materials used are not sufficiently transmissive for water production.

The outwash deposits located in eastern Staten Island are similar to the outwash deposits found in southern Brooklyn and Queens. Both units are capable of ground water yields in the hundreds of gallons per minute to thousands of gallons per minute. However, unlike the Long Island outwash deposits, the outwash on Staten Island are limited to a maximum of 125 feet. The proximity of the outwash deposits to New York Bay places this aquifer in danger of salt water intrusion from over pumping. Therefore, a system of five New York City drinking water wells was limited to pumping less than 5 million gallons of water per day, although the wells were capable of significantly higher yields. These wells have not been operated since the early 1970's. Geothermal systems return the water pumped out to the aquifer, so they should not increase the risk of saltwater intrusion. Salty or contaminated water will increase the maintenance required for wells and well pumps.

The terminal and ground Moraines of Staten Island are generally composed of glacial till, a material that results from the grinding of rocks by the advancing glacial ice. The material, till, appears to be a hard clay with various amounts of sand and gravel mixed in. Till has poor hydraulic conductivity and should not be considered as a source of ground water. Occasionally sandy till is encountered. These deposits, although more productive than the clay tills discussed above, are still limited to about ten gallons per minute, on average (Soren 87-4048, 1988).

The Raritan Formation underlies the outwash deposits of eastern Richmond. Wells tapping this formation, which includes the Lloyd, or Farrington as it is referred to in New Jersey, have yields as high as 200 gallons per minute. This formation appears to be confined, separated from the water table aquifer, but insufficient data exists to fully make that determination.

The bedrock units underlying Richmond include the Newark Supergroup (shales, sandstones and limestones), the Palisades Diabase, the Manhattan Schist and the Staten Island Serpentine. Ground water data from the Staten Island portion of the Newark Supergroup is not generally available and, therefore, the yield of this formation within Richmond is not known. However the Newark formations is tapped extensively in Rockland County New York and is found to have an average yield of 83 gallons per minute (Permutter, 101-120, 1959). This average yield is based on a list of wells, which include mostly municple wells, including a well yielding a reported

1,515 gallons per minute. If all wells, including domestic wells, tapping this formation were included in the average, the average yield for the formation will be found to be considerably lower, more in the range of 10's of gallons per minute.

The Palisades Diabase is considered a poor water producing formation with yields limited to less than 10 gallons per minute. The Manhattan Schist unit in Richmond is not generally used for water supply due to the existence of more productive unconsolidated deposits. However, wells drilled in the Manhattan Schist in Manhattan and Westchester generally produce yields of between 5 and 50 gallons per minutes, with some wells yielding as high as 150 gallons per minutes. The productivity of this unit is completely dependant on the existence of faults and fractures that may be tapped by the well.

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