Assessment of 1,4 Dioxane in Private Drinking Water Wells
Related to Town Landfill, Eastham, MA
MassDEP’s Division of Solid Waste required the Town of Eastham to conduct sampling for 1,4 Dioxane under their Landfill Monitoring Plan. In 2012, 1,4 Dioxane was detected in drinking water from several private wells downgradient of the Town's landfill. Since the Town was not yet served by a municipal water system, private well water was the only source of drinking water for Eastham residents. ES&M was retained by the Town to determine the extent of 1,4 Dioxane so that the affected residences could be provided bottled water. ES&M also evaluated water treatment technologies that would successfully remove 1,4 Dioxane from water, and studied other sources of 1,4 Dioxane.
The chemical and physical properties of 1,4 Dioxane make it difficult to remove from water, which renders most conventional water treatment technologies ineffective. Because it does not adsorb onto soil and does not biodegrade or volatilize, it is very persistent and mobile in groundwater.
ES&M implemented a focused private well sampling program to identify residential drinking water wells impacted by 1,4 Dioxane related to the landfill. We also conducted a background study to better understand the distribution of this compound in groundwater outside of the study area. Our laboratory utilized the most up-to-date analytical methods to detect 1,4 Dioxane below the newly promulgated drinking water standard. We collected samples from over 300 private wells and managed the analytical results in an extensive database that allowed for thorough evaluation of the data and prompt reporting of the results to residents. The results of this study were used to define the area of 1,4 Dioxane impact from the landfill and to ensure that residents’ drinking water was safe.
We also studied extensively the occurrence of 1,4 Dioxane in consumer products. Because all of the homes in the study area had septic systems (in addition to private wells), it was suspected that commonly used products such as soaps, shampoos and detergents that contain 1,4 Dioxane were confounding the site assessment of the landfill. We conducted a septic study to prove that 1,4 Dioxane from homeowner use was impacting the shallow aquifer, and we also showed that private wells were ‘recirculating’ impacted water from deeper zones into shallow zones.
ES&M initiated an additional comprehensive site assessment with the goal of defining the horizontal and vertical extent of 1,4 Dioxane in groundwater originating from the landfill. We completed a soil conductivity boring to define low permeable confining layers, and installed seven temporary vertical profiling wells to identify specific zones where 1,4 Dioxane is present. The profiling work entailed groundwater sample collection from multiple zones (as dictated by the conductivity borings) down to 200 feet. We completed several comprehensive water level/piezometric gauge events (which included two ponds) to better understand vertical and horizontal groundwater flow patterns in multiple aquifer zones. Using this data, ES&M was able to identify which private wells were screened within the landfill’s 1,4 Dioxane plume and would have to be abandoned in order to eliminate the Critical Exposure Pathway.
We developed a Conceptual Site Model for the landfill to illustrate how 1,4-dioxane migrated throughout the study area. Groundwater profiling work defined source areas of 1,4 Dioxane and showed that downward groundwater gradients were allowing the plume from the landfill to migrate to deep aquifer zones. The septic studies helped us to understand why 1,4 Dioxane was being detected in the shallow zones. The reason for this work was to develop the Town’s policies regarding mandated connections to the forthcoming municipal water system. In 2015, Eastham residents voted to construct a Town-wide Municipal Water Supply system. The Critical Exposure Pathway was eliminated once the residences within the defined mandatory zone were connected to the MWS.