Fate of trace organics during rapid infiltration of primary wastewater at Fort Devens, Massachusetts

Abstract

Transport and fate of trace organics were studied during rapid infiltration of primary wastewater at a land application facility in Fort Devens, Massachusetts. A preliminary sampling trip was made to compare trace organic concentrations in the infiltrating wastewater and in ground water samples from three monitoring wells around the site. Trace organic concentrations were reduced by the rapid infiltration process. However, significant concentrations of specific compounds could be detected in ground water down-gradient of the site. Therefore, a field study was undertaken to determine the primary region where trace organics were removed in the system. Teflon monitoring wells were installed at a depth of 1.2 m in one of the basins at the site prior to flooding. Flooding was initiated and samples of the raw wastewater, the wastewater entering the basin, the infiltrate at 1.2-m depth and the ground water down-gradient of the site were analyzed for six compounds selected for the study. Results from replicate samples during the 6-day flooding period demonstrated that most of the removal for the six compounds occurred in the top meter of the soil, although concentrations of each compound increased substantially in the basin infiltrate from two of the sample points after the fourth day of flooding. No removal of p-dichlorobenzene, p-(I,1,3,3-tetramethylbutyl)phenol and 2-(methylthio)benzothiazole was apparent in the aquifer itself, as indicated by relatively high concentrations of these compounds in the contaminated monitoring well down-gradient of the site. These data indicate that trace organic concentrations in primary effluent can be reduced by rapid infiltration and that most of the removal occurs in the top meter of the soil during the early phase of the flooding cycle. This removal capability can rapidly diminish, however, and result in ground water contamination by trace organics above background levels.