TRACING HISTORICAL LANDFILL LEACHATE TRANSPORT THROUGH THE USE OF DENDROCHRONOLOGY AND DENDROCHEMISTRY AT BATTIS ROAD LANDFILL, MERRIMAC, MA

Landfill leachates pose a threat to groundwater quality, which can negatively impact drinking water. Where long term monitoring of groundwater chemistry is unavailable, dendrochronology and dendrochemistry can be utilized to provide an archive of historical contamination events. One such landfill is the capped Battis Road landfill, in Merrimac, MA, which began operation in 1960 as an open burning site and after 1979 was used for residential refuse. In December of 2015, groundwater data from wells around the landfill showed concentrations of As, Mn, and Fe above the reportable concentration standards. Data was collected from oak tree cores to supply a historical assessment for potential leachate contamination to determine if the landfill has been contributing dissolved metals to the groundwater.

Groundwater flows from southwest to northeast. Trees downgradient from the landfill should contain a higher concentration of metals than the upgradient trees. To test this, oak cores were extracted up and downgradient from the landfill. The cores were split into increments of ten years and analyzed by pED-XRF spectroscopy. Results indicate that the concentrations of metals are equivalent in up and downgradient trees, with the exception of Cl and Cu, whose concentrations were higher in the downgradient trees. The data also indicates a recent increase in concentrations of Mn, Zn, and Rb, occurring in up and downgradient trees.

The equivalency of metal concentrations in up and downgradient trees suggests that the source of these metals is not leachate from the landfill. The metals could be naturally occurring within the soil horizons and derived from the underlying igneous rocks. The elevated Cl and Cu in the downgradient trees could indicate that the source of these elements is leachate from the landfill. However, it’s possible that Cl and Cu is due to runoff from road activities such as road salt applications and the wearing of brake pads. The increase in the concentrations of Mn, Zn and Rb from 2005-2015 could be the product of a more recent change to groundwater chemistry but the presence of these elements in up and downgradient trees suggest the source is not the landfill. Future work includes extracting cores as well as collecting road runoff and sediment samples to fingerprint this alternative source of trace elements in the system.