ABSTRACT

Concentrations of arsenic that exceed the proposed New Jersey State Cleanup Criterion for residential soils of 20 parts per million (20 mg/kg (milligrams per kilogram)) have been measured in soil samples from two residential and farm properties (referred to as the “Texas Road site”) that abut Birch Swamp Brook immediately south of Texas Road and downstream from the Imperial Oil Company Superfund site in Monmouth County, New Jersey. Concentrations of arsenic that exceed the proposed cleanup criterion also have been measured in sediments along the banks and point bars of Birch Swamp Brook and in the organic soils through which the brook runs. The brook drains areas of contamination about 0.5 miles upstream that are associated with the Superfund site, where arsenical pesticide production (1917-45) and waste-oil processing (1950-69) took place. Prior to the current study, the Imperial Oil Company Superfund site was the only known major upstream source of contaminants, which include arsenic, petroleum, and polychlorinated biphenyls, but past use of arsenical pesticides had been shown to contribute substantial amounts of arsenic to the soils in the area. The source of the arsenic in the residential and farm soils was unknown, however.

The soils adjacent to the stream are organic-rich wetland soils, known as humaquepts, with areas of recent sand and clay fill, which overlie sands of the Englishtown Formation. Samples of soils and sediments were collected and analyzed for major cations, trace elements, and total organic carbon. Results of the chemical analyses indicate that arsenic concentrations are substantially larger (4.7-139 mg/kg) in the humaquepts than in the underlying sand of the Englishtown Formation (less than 0.64-7.6 mg/kg). Areas of sand and silt along the stream bank and on point bars contain elevated (greater than 20 mg/kg) arsenic concentrations that range up to 2,570 mg/kg. Similar arsenic levels, typically accompanied by petroleum and polychlorinated biphenyl contamination, have been measured in previous investigations.

Samples of humaquepts were collected from other, nearby watersheds in the New Jersey Coastal Plain and analyzed for arsenic, metals, and total organic carbon. Arsenic concentrations in these samples, which represent local ambient conditions, ranged from 4.9 to 43.1 mg/kg and include background arsenic levels and various anthropogenic inputs. These concentrations are similar to those measured in many of the humaquept samples from the Texas Road site, but statistically significant differences in calcium, barium, magnesium, and chromium concentrations are indicative of different chemical inputs to the other watersheds.

A ground-penetrating-radar survey of the Texas Road site revealed the presence of a buried stream channel between the present-day channel and the house nearest Tesas Road. Because the buried channel probably existed before the beginning of the 20th century, widespread arsenic contamination of the humaquept soils did not result from floodwaters emanating from a channel located elsewhere on the property. The rate of deposition of the humaquepts, determined by analysis of the samples for the isotope lead- 210, indicates that the humaquepts were deposited over a period of at least 1,000 years; therefore, arsenic measured at or near the bottom of the humaquepts is unlikely to be derived from the Superfund site wastes or from pesticide applications unless it has leached from the land surface. An increase in arsenic and iron concentrations and a decrease in lead and copper concentrations with depth in the humaquepts at the Texas Road site indicate probable redistribution of surficially deposited arsenic by geochemical processes.

Anecdotal evidence for arsenical pesticide use on the farm fields indicates that some of the arsenic measured in soils at the Texas Road site probably is attributable to these pesticides. Given the small size of the basin and little recent history of major flooding along Birch Swamp Brook, arsenic from an upstream source would have been deposited on the fields only during major floods, such as those during the hurricane of 1938. The presence of elevated arsenic concentrations in association with petroleum and polychlorinated biphenyl contamination along the stream provides considerable evidence for stream-sediment contamination that is derived from the Superfund site, whereas the arsenic in the humaquept soils is probably derived, in part, from pesticide use, as well as from contaminated sediment originating at the Superfund site that was deposited during an extreme flood.

First posted March 2, 2011