Geotechnical Report Army Materials Technology Laboratory Watertown, Massachusetts

As part of the remedial investigation and feasibility study being conducted at the Army Materials Technology Laboratory in Watertown, Massachusetts, Arthur D. Little, Inc., conducted a program of physical characterization and sampling of the site. The geology and hydrology of the site was summarized using data from 17 soil borings, one of which was cored 15 feet into bedrock, physical testing of soil samples, water level measurements and determination of in situ hydraulic conductivity from 16 monitor wells, a seismic refraction survey to determine depth to bedrock and stratigraphic variation, and two borehole geophysical surveys. Bedrock at the site consists of the Pennsylvanian Cambridge Argillite, a dense, finely laminated siltstone. The siltstone is overlain by a basal, bouldery till with a gray green, silt-rich sandy to gravelly matrix. Laying on top of the till is a laminated, silty sand found across the site, which is composed of moderately well sorted, very fine to fine-grained sand, with a clayey-silty matrix. Overlying the silty sand is a texturally variable layer of medium to coarse-grained sand and gravel, which is not found over the entire site. It is absent in the northwest corner of the site and grades to a gravelly sand eastward. The coarser sand-gravel unit is generally overlain by fill of disturbed gravel with exotic debris (concrete, brick, ceramic, etc.). Surface run-off across the site is to the south, toward the Charles River, which is within 100-400 feet of the site. Groundwater flow estimated by water level data, is to the south. The gradient averages 0.03 across the site, but in the southeast corner it decreases to 0.003. In situ hydraulic conductivities (k) were determined by falling head and rising head tests. For the silty sand, k ranges from 7.06 x 10(exp -4) to 1.30 x 10(exp -2) cm/sec and averages 6.4 x 10(exp -2) cm/sec.

Prepared in cooperation with EG&G Idaho, Inc., Idaho Falls, ID.