23 Geologic Aspects of Environmental Problems in the Northeast

Tuesday, 13 March 2001
8:15 AM - 12:15 PM

OCCURRENCE OF ARSENIC AND LEAD IN UNCONSOLIDATED SOILS IN CENTRAL MASSACHUSETTS

Paper number: 23-10
Program: THEME SESSIONS
Time: 8:15 AM – 12:15 PM

Authors

Abstract

Elevated arsenic values in glacial deposits and other unconsolidated soils of Central Massachusetts are often observed with a particular attention drawn to "spiked" values that have a very sporadic occurrence pattern. Geologic framework of the source bedrock are formations of the Merrimack Belt located on the western side of the Clinton - Newbury fault. Associated with same formations elsewhere within the belt are numerous cases of natural contamination of arsenic in water supply wells. The same general area also hosts numerous apple orchards known for a widespread applications of lead arsenate as the pesticide of choice during the first forty years of the twentieth century. In this context, Central Massachusetts is a region where it may be rather difficult to relate elevated arsenic levels to either the anthropogenic or the natural sources.

In this study we report on concentrations of As, Pb, Fe, Cr and Co in soil profiles obtained from up to 20 ft long soil cores from several selected sites in Worcester County. From each site we obtain composite soil samples in two foot intervals that are analyzed by acid digestion for the same suite of metals via ICP. This methods allows identification of metals that are readily available for the uptake by ground water without the need for chemical weathering as the releasing agent. Metal profiles with depth confirms the presence of the above mentioned anomalous "hot" spots for arsenic with values exceeding 250ppm. Typical background values for arsenic in the analyzed samples are in the 30 to 60ppm range. The data does not correlate with lead suggesting that the arsenic source is of natural origin. We attribute the spotty spike levels to random presence of arsenic bearing sulfides, now all oxidized, that can contain up to 49 % of arsenic by weight. Soil sampling that includes a few of these grains will show elevated levels whereas soil samples that miss these grains will have background levels.