Solutions to High Groundwater Elevations in Queens, New YorkCity: Groundwater Modeling Applications

Groundwater has been pumped for potable and industrial use in Queens, New York City, since the late 1800s. Historically, groundwater withdrawals in Queens reached peak rates in the mid-1980s, averaging 70 million gallons per day (mgd) and peak summer withdrawals approaching 100 mgd.  In the 1990s, groundwater was phased out as a potable supply source in Queens.

During periods of high pumping, the water table was considerably lower than it is today. As pumping rates were reduced, the water table responded and began to recover to near pre-pumping levels, recovering more than 35 feet in portions of Queens. This rise in the water table is believed to have caused or exacerbated basement flooding in areas where new infrastructure was built during the previous quarter-century (high-pumping period). High groundwater also occurs in various subway/bus tunnels and infiltration/inflow (I/I) studies have indicated infiltration rates exceeding 2 mgd in sewer lines.

In response, facility planning activities were conducted to combine potential future water supply pumping with groundwater control in areas of Queens affected by the rise in the water table. These included groundwater model simulations to evaluate several future water supply pumping scenarios that would also maintain the groundwater table at a depth of 20 feet below the surface in some areas. A target depth of 20 feet below ground surface (bgs) should alleviate groundwater problems in residential buildings, schools, hospitals, and banks, as well as reduce flow in I/I areas.

Model simulations indicated that 22 shallow extraction wells pumping 1 mgd each would be sufficient to increase the simulated depth of water within the control target zone to greater than 20 feet bgs, without causing saltwater intrusion. The location of the target zone was chosen based on data from a 1997 flood survey and historical groundwater elevation and pumping data.