Long-Term Natural Attenuation of Carbon and Nitrogen within a Groundwater Plume after Removal of the Treated Wastewater Source

Abstract

Disposal of treated wastewater for more than 60 years onto infiltration beds on Cape Cod, Massachusetts produced a groundwater contaminant plume greater than 6 km long in a surficial sand and gravel aquifer. In December 1995 the wastewater disposal ceased. A long-term, continuous study was conducted to characterize the post-cessation attenuation of the plume from the source to 0.6 km downgradient. Concentrations and total pools of mobile constituents, such as boron and nitrate, steadily decreased within 1-4 years along the transect. Dissolved organic carbon loads also decreased, but to a lesser extent, particularly downgradient of the infiltration beds. After 4 years, concentrations and pools of carbon and nitrogen in groundwater were relatively constant with time and distance, but substantially elevated above background. The contaminant plume core remained anoxic for the entire 10-year study period; temporal patterns of integrated oxygen deficit decreased slowly at all sites. In 2004, substantial amounts of total dissolved carbon (7 mol C m(-2)) and fixed (dissolved plus sorbed) inorganic nitrogen (0.5 mol N m(-2)) were still present in a 28-m vertical interval at the disposal site. Sorbed constituents have contributed substantially to the dissolved carbon and nitrogen pools and are responsible for the long-term persistence of the contaminant plume. Natural aquifer restoration at the discharge location will take at least several decades, even though groundwater flow rates and the potential for contaminant flushing are relatively high.

Occurrence and Turnover of Nitric Oxide in a Nitrogen-Impacted Sand and Gravel Aquifer

“…At that time, the contaminant plume was undergoing largescale changes due to removal of the wastewater source in 1995 (29). This removal resulted in significant decreases in the total inorganic nitrogen load and DOC in the vicinity of F575 in 1999-2001 (29). Therefore, these NO decreases may have been related to the source removal.…”

“…This study was conducted within a transect of wells situated along a groundwater flow path starting from the contaminant source to a point 0.6 km down gradient (see the map in ref 29). The primary location for this study was well site F575, which is located about 0.4 km from the contaminant source and consists of a cluster of 10 15-port multilevel samplers (MLS), 9 of which have screens within the same 7.1 m vertical interval.…”

Dynamic sorption of ammonium by sandy soil in fixed bed columns: Evaluation of equilibrium and non-equilibrium transport processes

“…During treated wastewater infiltration in unsaturated subsoil layers, a significant quantity of ammonium is transformed biologically to nitrites and nitrates. However, infiltrating a large quantity of ammonium through low-thickness unsaturated zone raises the groundwater pollution magnitude (Bouwer, 2000;Repert et al, 2006). According to the Tunisian wastewater reuse norms (NT106.02), the maximum ammonium concentration allowed for indirect aquifer recharge is relatively low (1 mg L À1 ).…”

Catchment tracers reveal discharge, recharge and sources of groundwater-borne pollutants in a novel lake modelling approach

“…Thus, in the case of 305 northern Europe, sampling during late winter might be the best solution because soils are generally wet at this time of year (Sand-Jensen and Lindegaard, 2004). Previously polluted areas, for example from wastewater infiltration, with increased concentrations of DOC and nutrients are likely to be in a state of imbalance resulting in a reduction in concentrations over time (Repert et al, 2006). In these areas, it is therefore important to have temporal sampling following decreases in concentrations and to relate them to lake concentrations during sampling.…”