Module 3: Understanding the Geology

Woburn Resources across the site

Overarching Questions: Expert Witness
Key Issues in the Trial: Woburn Water Supply; Exploration and Construction of Wells G & H
Resource Collections: Historic Air Photos; Well Data

Module Goals:

Familiarize students with the basic geology of the study site.
Gain experience completing cross sections and contouring geologic data.

Student Assignment

Overview

In response to the lawsuit, both plaintiffs and the defense completed extensive investigations of the geology in the Woburn Massachusetts area. Understanding the unique aspects of the geology were important to both the plaintiff and the defense's case strategies.

Overview of the Woburn geology

Woburn lies within the glaciated portion of the northeast Massachusetts. Bedrock that occurs in this area consist primarily of igneous granite and metamorphic schists. The bedrock surface undulates, and does not have any consistent surface within the Woburn area. Atop the bedrock lies thick sequences of sands and gravels and glacial tills. A relatively thick sequence of peat occurs just beneath the Aberjona River. The USGS provided an extensive investigation of the subsurface, surface water and groundwater in the vicinity of Wells G and H. The USGS report can be viewed at this link.

The relation between the Aberjona River and regional geology

The Aberjona River is part of the Mystic River drainage basin. The Aberjona River's relatively small drainage area occurs in the headlands of the larger Mystic River drainage system. The Mystic River drainage system is one of several drainage areas that empty into Boston Harbor, long recognized as one of the most polluted bodies of water in the United States. Defining the connection between the Aberjona River and the subsurface geology was disputed by the USGS, the plaintiffs and the defense.

Creating geologic cross sections

Creating a visual slice of the earth is achieved by constructing a geologic cross-section. Cross sections are completed by taking geologic data at a specific locations, typically a boring location, arranging the data to a vertical and horizontal datum and then correlating like units spatially between the boring log datasets. After reviewing the attached reference, site-specific boring log data and a map showing the location of the boring logs are presented on the assignment page along with instructions for creating geologic log of the Woburn area.

Student Assignment

Data for Making Cross-Sections

The following link contains sample well log data for construction of a cross-section in the Aberjona Valley. A map showing the locations of the wells is available at this link ( 246kB May7 07)