ARSENIC IN MUNICIPAL SOLID WASTE LANDFILLS LEACHATE PLUMES IN CENTRAL MASSACHUSETTS

Many landfills located in a northeasterly trending zone in Central Massachusetts had been previously noted for elevated levels of arsenic in groundwater down gradient from the landfill sites. We present here data on yet another landfill, not previously reported, which is proximally located to a fault line separating two distinct major geotectonic zones. The Clinton-Newbury fault system separates Nashoba Block to the east and Merrimack Belt to the west. The studied landfill site lies in the Town of Clinton just a short distance west of the Clinton – Newbury fault. All other earlier noted landfills are located some distance west of the fault within the Merrimack Zone as well. Water quality data for groundwater and from surface water discharge points down gradient from this landfill indicate very high concentrations of iron (up to 70 ppm) and arsenic (up to 4000 ppb). The landfill is located on a grade fill over marshes in some location which were erected during the construction of Wachusett reservoir in the early part of the 20th century (work on the reservoir was completed in 1905). The raised water level in the reservoir also reversed ground water flow in the direction away from the reservoir. Combination of buried marshes and the landfill reducing leachate mobilize hydrous ferric oxide (HFO) coatings on the underlying glacial material. Arsenic correlates with iron providing further evidence for the source of arsenic coming from the release of adsorbed arsenic on the HFO surfaces. The amount of arsenic adsorbed at the HFO surfaces appears to be sensitive to the geotectonic context of the underlying bedrock. We report also data on one more landfill which is located within the Nashoba Belt east of the Clinton – Newbury fault line in the Town of Millbury. Samples of water collected down gradient from this site show similar high iron concentrations but by contrast arsenic is about a factor 20 lower by comparison with water samples from landfill sites within the Merrimack Zone.