Seniors Erica Montgomery and Sara Tichenor spent the summer of 1995 analyzing the structural geology and aqueous geochemistry of the ground water aquifers in Zimapán, Mexico. They were working under the direction of Lois Ongley, a professor of geology at Bates, Aurora Armienta (National Autonomous University of Mexico, Mexico), Alison Lathrop (Millersville University, Pa.) and Helen Mango (Castleton State College, Vt.).

The drinking water in Zimapán has an average arsenic concentration of 0.3 mg/L. The World Health Organization drinking water standard is 0.05 mg/L. The residents of Zimapán are beginning to show ill health effects of chronic arsenic poisoning which include skin cancer and kidney and liver disease. Montgomery and Tichenor are trying to determine the source of the arsenic and the pathway by which it enters the groundwater supply.

Montgomery made a geologic map of the area of El Muhi, near the public water supply well with the highest concentration of arsenic (1.1 mg/L). Tichenor was part of a team that sought out sources of drinking water (wells and springs) to analyze the water chemistry. A significant result of this work is that the municipal authorities have closed the El Muhi well and opened another, the San Pedro Profundo, whose water has much less arsenic (0.006 mg/L).

Montgomery, a resident of Lancaster, Pa., plans to become a secondary school teacher after graduation. Tichenor, from Washington, D.C., is planning a career in geochemistry.