Another sampling in Rye Brook also came up with a positive result, as did several in the Bronx near the Westchester border.

The area's proximity to the Westchester border increases the traffic of illicit activity, residents and the police say.

When the projects are done, there will be a 15-mile greenway linking parts of the Bronx waterfront to Randalls Island and the Westchester border.

"The Gillespie case was five miles from the Westchester border," said Paul L. Shechtman, the director of Criminal Justice Services.

They traced the pollution to the Westchester border, and then contacted Yonkers and the State Department of Environmental Conservation.

The 911 operator sent the police to the Burtons' three-bedroom, second-floor apartment at 3515 Eastchester Road, not far from the Westchester border.

It is now effectively possible to follow the original aqueduct from the Westchester border through Van Cortlandt Park and all the way down to Bryant Park.

The third-ranked site is in Phillipstown, but not near the Westchester border.

Moreover, Westchester borders on the Bronx, and big-city problems, from crack to homelessness, are painfully familiar.

"Caution dictates that it would be better to continue to go further north toward the Westchester border along the water."