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On April 29, 2004, the Village of Rye Brook Police Department received a report of a mercury spill along a paved walkway in the Village of Rye Brook owned by the Condominium Association of the Arbors at Rye Brook (Arbors). The Westchester County Health Department and EPA were contacted and responded to the reported spill. In early May 2004, EPA cleaned up visible elemental mercury found along the walkway and excavated approximately one ton of soil in the vicinity of the mercury spill. Soil containing elemental mercury was loaded into drums and stored at the Village Police Department shed pending future disposal. In May, June, and July 2004, EPA collected surface soil samples from the Arbors property in the area of the path in order to delineate the area of mercury contamination. Upon determining that the mercury contamination was present in the soil on a few neighboring properties beyond the area of the spill, EPA expanded its investigation to several neighboring properties. A comprehensive investigation of air, surface and subsurface soil, storm drainage system sediment, and groundwater began on September 15, 2004 and was completed on December 17, 2004.
The investigation revealed that surface soil in some areas of the Arbors property common area and on 55 Hillandale Road are contaminated with mercury above the EPA Site cleanup level of 10 parts per million (ppm). The contamination appears to emanate from three primary source areas, a rock pile on the Arbors property and from two vaults on the 55 Hillandale Road property. One of the vaults exhibited the highest overall mercury concentration. The highest mercury concentration adjacent to the paved walkway on the Arbors property was 1,300 parts per million (ppm). Elevated levels of mercury in the surface soils were also found in other isolated areas, at the base of three large trees on the Arbors property and at depressions in the soil surface. Generally, analytical results reveal that mercury is not present in soils at depths greater than one foot in depth at concentrations above 10 ppm, with the exception of soil in and around the main source areas and in areas around the base of the three trees discussed above. Mercury concentrations in the subsurface soil ranged from non-detect to 160 ppm, adjacent to the paved walkway on the Arbors property.
Two subsurface vaults filled with vessels which may have contained or may contain mercury, were discovered during the assessment at 55 Hillandale Road. One vault that is suspected of being a former hand-dug well, was located adjacent to the rear patio. The other vault, located in the front of the property is a former septic tank. Both vaults were opened and found to contain numerous bottles, cylinders and other laboratory containers which were determined to be of the type used for transporting and handling elemental mercury. Analytical results of water and soil samples collected from the former hand dug well revealed mercury concentrations significantly greater than any other samples collected on-Site. Additionally, seven piezometers (micro-wells) in the vicinity of this abandoned well had elevated concentrations of mercury in groundwater. It is clear that this vault represents a significant source of mercury contamination.
Mercury contamination in sediments that exceed the Site specific cleanup level of 10 ppm was identified in all thee small ponds, i.e., two ponds on 51 Hillandale Road and in one pond on 20 Hillandale Road. There are also isolated locations in a stream channel that is part of the storm drainage system where mercury concentrations in sediment exceed 10 ppm. Mercury concentrations in sediments ranged from non-detect to 1,900 ppm, the later value being detected in the 51 Hillandale Road pond that’s closer to the spill area.
In October 2004, EPA conducted indoor air screening inside 16 single-family homes on Hillandale Road and inside four condominiums at the Arbors. Only 55 Hillandale Road contained levels over EPA’s indoor air cleanup goal of 0.3 µg/m3. In response to the elevated mercury vapor levels inside 55 Hillandale Road, EPA installed a mercury air filter and a heat recovery ventilation system in the basement, sealed the walls and floors of the basement with water sealant paint and fabricated a cover for the basement sump. Subsequent indoor air sampling within 55 Hillandale Road indicates that these actions effectively reduced the mercury levels. However, there is a concern that higher mercury readings may occur in the air when warmer weather arrives in summer (most screening events have been in late fall/early winter, during cool temperatures).