GROUNDWATER RESPONSE TO UNUSUAL WEATHER EVENTS – A CASE STUDY FROM STATEN ISLAND

The USGS makes data from their groundwater wells available to the public via the National Water Information System. Using data from the six wells on Staten Island it is possible to examine the effects of Hurricane Irene, Tropical Storm Lee and other unusual weather events during 2011 on the groundwater of Staten Island. The sites encompass a range of locations and altitudes on Staten Island, although all are located in glacial moraine deposits. All of the sites show similar average annual trends with the water table being lowest during the late fall, climbing to a late spring peak during May or June and slowly falling back to the November or December low point. However, during 2011 the water table elevations deviate considerably from this trend, both in the timing of the peaks and the heights of the highest levels. At most sites, the year started with levels lower than average, possibly because most of the winter precipitation was in the form of snow that remained frozen at the surface for longer than usual. By late spring and during the summer levels were close to the average at all sites. On August 28 Hurricane Irene deposited 5.4 inches of rain, followed by 2.6 inches from Tropical Storm Lee on September 6, and then 1.7 inches on September 23 (the 3^rd wettest day of the year). The groundwater response to this rainfall is not immediate, but by the end of September levels had risen at all sites, and peaked during October or November. The water table elevations at this time were 1 – 3 feet above the summer peaks. The main concerns with changes to the water table on Staten Island relate to the impact this may have on surface water drainage and the response of streams to further rainfall, and also whether the water table will rise far enough to interact with waste disposal sites and contaminated sediments from past industrial operations.