Long Island Concerns on the level

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Long IslandConcerns on the level

Newsday

town geology leaves little recourse where water table has yet

to subside since storms of 2005

BY JENNIFER SMITH

For most Long Islanders, effects from two weeks of torrential rains

in October 2005 subsided when the puddles dried. But in two low-

lying areas of town, the repercussions to local groundwater

have resulted in an enduring, mold-spotted dankness for those whose

homes now sit on, instead of above, the water table.

Groundwater levels from Westbury to Westhampton Beach surged after

the 2005 rains as the deluge of water worked its way down through

the sand, silt and clay of Long Island's underground aquifers. " You

saw a big jump in all areas of the island, " said Busciolano,

supervisory hydrologist and data chief at the Coram office of the

U.S. Geological Survey.

After the rains, groundwater in some places sank back to more

moderate levels. But in a number of other locations - including much

of town - the water table remains higher than usual, according

to USGS well data.

That's not unusual. While depth to groundwater varies from place to

place, fluctuations generally reflect precipitation patterns -

rising in wet times and dropping during drought. That's especially

true in areas such as central and eastern Suffolk County, where the

lack of sewers means most of the water pumped up for consumption is

returned to the soil through septic systems.

Changes in impact

Still, the impact of those changes differs dramatically depending on

how close the water table is to the surface. Even a big leap won't

mean much to residents whose basements stand 30 feet above

groundwater or those who live in Nassau, where sewer systems have

caused an overall drop in the water table. But in areas where

groundwater lurks just feet from the surface, big downpours can mean

big trouble for residents.

Bill Hillman, the chief engineer for Suffolk County's department of

public works, said that since the October 2005 storms his office has

gotten complaints, mostly during or immediately after rain, about

rising groundwater from a handful of residents in town,

Babylon, Patchogue and Yaphank. " The majority were adjacent to

bodies of freshwater, " Hillman said. When rain swelled the surface

waters, the water table associated with them also rose, and flooding

ensued.

But in parts of town, elevated groundwater from the storms has

stayed high.

More than a year later, the water table around Lake Ronkonkoma

remains near record levels, Busciolano said. On a cul-de-sac just

north of the lake, wetlands continue to engulf yards and swamp

cesspools. When it rains, underground lakes pooling in basements

near s Pond overwhelm homeowners' pumps that once kept the wet

at bay.

Hydrologists think the problems stem in part from the area's unique

and complex geology, which was shaped by the glaciers that once

covered Long Island.

Below the surface in parts of town, layers of clay sit between

the topmost Upper Glacial aquifer and the deeper Magothy aquifer.

Those layers, known as the town clay, make it harder for

rainwater to flow down through the aquifer system - the process

scientists call " recharge. "

" When it rains, the water sort of pools on top " of the clay,

Busciolano said. " It either has to seep down around the clay, or

slowly percolate through. "

Recharge too slow

Scientists don't know precisely where the clay is because the area's

soil is complex and has not been studied in detail. But USGS staff

say local topography and evidence from old soil maps indicate it is

probably making it harder for the ground to absorb high volumes of

rainwater.

" It's the recharge, " said Terracciano, head of USGS's Coram

office. " Because it happens rather slowly, increased precipitation

raises the water table to the point where it starts intercepting

basements. "

Complicating the picture are homes that sat close to the water table

even in dry weather. Both areas have low elevations. A former stream

bed winds through neighborhoods by s Pond. The swampy area

that abuts the damp homes on Court sits at the same

elevation as the surface of Lake Ronkonkoma, just across the street.

In many places on Long Island, the groundwater starts at 40 feet and

deeper. But at its 30-year low, groundwater measured at one USGS

well south of s Pond was still only about 4.7 feet

underground, enough to soak a basement. After 2005, groundwater

levels there have mostly hovered between three and a half feet and

the new historic high reached this year: a depth down to groundwater

of only 2.8 feet.

Records from another well just west of Lake Ronkonkoma show that in

some years the water table all but lapped at the surface and even

flooded up inches above at one point in 1991. In mid-2005, the depth

to groundwater was one and a half feet. No subsequent measurements

exist - the well was taken offline soon after because of flooding.

It's unclear just how effective local efforts to alleviate the

problem through engineering may be. The town of town has plans,

which Suffolk is partially funding, to remove silt from s Pond

and a nearby tributary of the Nissequogue River in hopes that such

work would lower nearby groundwater. Some had suggested pumping

water out of Lake Ronkonkoma. But it seems more likely that the

flooded nearby homes will either be abandoned or bought by the

county, which has taken steps toward purchasing one home there.

" People don't understand, they think that we can just fix this

problem by pumping a lake or dredging a stream, " Hillman said. " You

dig a hole, you're going to hit groundwater somewhere. "

Clogging the drain

Heavy rains in October 2005 caused water levels to rise, creating

flooding issues in the Town of town that continue today. No

precise cause has been cited, but scientists do have a possible

explanation for the waters' failure to recede.

Flood Points

Water level measurements near two chronically flooded areas in the

Town of town

MILLERS POND

(Village of the Branch)

- Current: 2.8 feet below surface (historic high)

- Previous 30-year-high: 3 feet

- Previous 30-year-low: 4.7 feet

CHARLES COURT

(Lake Ronkonkoma)

- Last measurement: 1.5 feet below surface

Previous 30-year-low: 5 feet

A theory

1. Heavy rains fall in October 2005; precipitation runs off into

lakes, streams and ground.

2. As water seeps below surface into the Upper Glacial Aquifer, it

comes into contact with layers of clay deposited long ago by

glaciers.

3. Clay layers are less permeable than soil in other parts of Long

Island. Rainwater is slower to flow down through the aquifer system,

similar to a clogged drain.

SOURCES: UNITED STATES GEOLOGICAL SURVEY, NEWSDAY