Cape Cod, Massachusetts

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Large-Scale Natural Gradient Tracer Test in Sand and Gravel, Cape Cod, Massachusetts: 1. Experimental Design and Observed Tracer Movement

LeBlanc et al., 1991. Water Resources Research, 27(5):895-910

Denis R. LeBlanc (1)

Stephen P. Garabedian (1)

Kathryn M. Hess (1)

Lynn W. Gelhar (2)

Richard D. Quadri (1)

Kenneth G. Stollenwerk (3)

Warren W. Wood (4)

(1) U.S. Geological Survey, Marlborough, Massachusetts

(2) Dept. of Civil Engineering, Massachusetts Institute of Technology, Cambridge

(3) U.S. Geological Survey, Lakewood, Colorado

(4) U.S. Geological Survey, Reston, Virginia

Abstract: A large-scale natural gradient tracer experiment was conducted on Cape Cod, Massachusetts, to examine the transport and dispersion of solutes in a sand and gravel aquifer. The nonreactive tracer, bromide, and the reactive tracers, lithium and molydate, were injected as a pulse in July 1985 and monitored in three dimensions as they moved as far as 280m down-gradient through an array of multilevel samplers. The bromide cloud moved horizontally at a rate of 0.42 m per day. It also moved downward about 4 m because of density-induced sinking early in the test and accretion of areal recharge from precipitation. After 200 m of transport, the bromide cloud had spread more than 80 m in the direction of flow, but was only 14m wide and 4-6m thick. The lithium and molybdate clouds followed the same path as the bromide cloud, but their rates of movement were retarded about 50% relative to bromide movement because of sorption onto the sediments.