SUMMARY: In 1972 in the town of Woburn, Massachusetts, families of 13 different children who had contracted a rare form of childhood leukemia sued two large companies for the contamination of their community water supply wells. But the companies denied any responsibility, arguing that water originating from their plants may never be able to reach the community wells given the local hydrogeologic conditions. Instead, the companies blamed the heavily polluted Aberjona River as the source of contamination to the wells, given it's very close proximity to the community wells. You be the judge... who is responsible?!? Revisit the famous trial as modern-day ‘expert consultants’, addressing the debate issues based on the interpretation of groundwater flow and contaminant transport simulations. 

Figure 1: Woburn Superfund site. Right: Location of the known VOC sources during the trial. Adapted from: https://serc.carleton.edu/woburn/resources/Woburn_maps.html

Background & Arguments

In 1972 in the town of Woburn, Massachusetts, 13 children living in the same neighborhood contracted a rare form of childhood cancer (acute lymphocytic leukemia). The families wondered: is there something wrong with the water we drink of the air we breathe? That seemed to be the only thing they shared in common. The families complained to the local environmental health department, requesting that their community well water be tested. But nobody really listened. The response was that the water quality was perfectly fine based on their past well tests.

Until one day … a developer who was excavating a parcel of vacant land nearby accidentally discovered numerous 55-gallon drums containing toxic chemicals, causing significant subsurface contamination. The story immediately made the news the next day in the local paper. The shocked citizens thought “no wonder!” this place is so unfortunate! The inflicted families immediately hired a law firm and experts to get to the bottom of it. They identified a number of potential responsible parties, the biggest being the WR Grace company, a chemical manufacturing giant located less than half a mile up hill from the community wells, and Beatrice Food Inc., owners of the former J.J. Riley tannery properties.

A nasty legal fight ensued – one of the first major class-action, environmental lawsuits in US history. The citizens accused WR Grace of polluting their exclusive source of drinking water, because the chemical plant is uphill from their wells and groundwater moves from the plant towards their wells located in the valley below. They pointed out that the company uses the same chemicals that were found their wells. But the both the chemical company and the food processing plant denied any responsibility.

The argument from WR Grace:

It couldn’t possibly be us. The chemical plant had only been in operation since 1964. Groundwater moves very slowly and the soils underneath the plant are very tight – they don’t drain well. So, it may take decades before the groundwater originating from here to reach the valley. Even if there was an ‘infinite’ amount of time available, the hydrology is such that the water originating from our plant may never be able to reach both wells. And if you look around, there are other industries or places nearby that could be responsible:  Unifirst Corporation, a dry-cleaning facility; and the Olympia and Wildwood properties, formerly part of a tannery operation, which are much closer to the wells than our chemical plant is. Plus, Woburn has a legacy of industrial production since its founding in 1642. The Aberjona river was so polluted, collecting pollution effectively from everywhere - the entire watershed - and you were pumping right next to the heavily polluted river!

The argument from Beatrice Foods Inc.:

Although our properties are relatively close to your wells, we never used the chemicals found in the drinking wells in our operations. Most importantly, we are located on the other side of the Aberjona river, so we are hydraulically separated from the community wells – the Aberjona River is a hydraulic divide!  Water originating from our premises can never reach the other side of the river. That is just common sense and basic hydrogeology!

The plaintiff families countered and insisted that both WR Grace and Beatrice foods were contaminating their wells. To WR Grace they responded:

Our experts calculated that it only took months or – at most – a few years for the contaminated groundwater to flow from WR Grace to the community wells. You have been operating since 1964!

To Beatrice foods they responded:

Your property was formerly a tannery that used the same toxic chemicals found in the community wells. You inherited the liability when you purchased the property. And according to our experts, the river is a hydraulic divide only if the river is well connected to the aquifer. But the bottom of the Aberjona River is so full of fine sediments, muds and clays … that it is almost impervious, effectively sealing the river from the aquifer. The water pumped was not from the river!

Objective & Deliverable

In this project, you will be the judge... who is responsible?!?

Revisit the famous trial as modern-day ‘expert consultants’, addressing the debate issues based on the interpretation of groundwater flow and contaminant transport simulations. The key scientific issues to address include:

• Where does the water pumped come from?
• What is the area of contribution to wells G and H?
• Where do the spills from the various potential responsible parties go? - WR GRACE, the Beatrice Foods property, the dry cleaner, etc. - can they reach the wells?
• How long will it take for the spills to reach the wells from the various sources?

Prepare a 1-2 page report that summarizes your approach and findings. You should discuss your findings with regards to responsibility for the contamination. Include any detailed model results / graphics in support of your conclusions in an appendix. 

Given information

You are provided with the following information that was collected during and after the lawsuit.

Site Hydrogeology

Wells G and H are located east-central Woburn, MA - about 10 miles (16 km) northwest of Boston - in a gently sloped valley with a large stream, the Aberjona River, flowing through it from roughly north to south. A number of small tributaries contribute to upstream flow of the Aberjona River. Flanking either side of the Aberjona River are a collection of wetlands, throughout much of which peat deposits occur near the surface. Much of the land outside of the wetland areas is developed, an intermix of industrial, commercial and residential properties.

The river and its surrounding lowlands are underlain by 0.5- to 1.0 mile-wide stratified (layered) glacial deposits primarily consisting of sand and gravel, but also clays and silts.  These deposits fill a basin-shaped, buried bedrock channel (see below).  In some places, glacial till separates the stratified drift and the bedrock, and is exposed at the land surface in the upland areas.  Recharge to the stratified drift is from precipitation. 

Figure 2: Conceptual 3D view of the groundwater at the Superfund site.

Field Data / Information

The top boundary of surficial/unconfined aquifers follows the land surface, which can be represented with detailed 10m Digital Elevation Models (DEMs).

The depth to the bedrock surface ranges from close to zero to 240 ft near the central part of the valley. Wells completed in the bedrock typically yield relatively small amounts of water (e.g., a few GPM). The shape of the bedrock surface is available from the the global bottom elevation data layer available on the MAGNET server.

Like many glaciated environments, the lithology of the stratified drift can be separated generally into four layers on the basis of the principal lithology in each layer:

• In the deep, central part of the aquifer, coarse sands of about 15m thickness sit on top of fine-grained sands and silts. The hydraulic conductivity of the coarse sands is estimated at 5 m/d.
• Above the layer of coarse sands and gravel is a layer of fine-to-coarse sand with a thickness of about 20m and a hydraulic conductivity estimated as 3 m/day.
• The uppermost layer, occupying the top 27m (or so) of the aquifer is a mix of sand, silt, clay, and – where the wetlands are present – deposits of peat. The hydraulic conductivity of this layer was estimated as 0.5 m/day.

Long-term average recharge to the stratified drift aquifer is estimated to be 20 in./year.

Wells G and H (see below) are screened in the drift aquifer and reach a depth below land surface of 26 ft and 27 ft, respectively. Until they were closed down in 1979, they pumped at an average rate of 700-800 GPM (well G) and 400 GPM (well H).

Two industrial wells southwest of the Aberjona River have long extracted groundwater from the drift aquifer to support the tannery operations associated with John J. Riley Tannery. The first well (industrial well 1) began operating in 1954 while the 2^nd well (industrial well 2) began operating in 1958. Industrial wells 1 and 2 were estimated to operate at 70 GPM and 200 GPM, respectively.

Figure 3: Study area extent, with locations of Wells G and H and the industrial wells shown. Also shown are the approximate wetland areas

Further Hints and Suggestions (MAGNET-related)

• The suggested conceptual model is summarized in Figure 4 below.
• A georeferenced image file of the site map is available for overlaying in the MAGNET modeling environment (‘Other Tools’ > ‘Utilities’ > ‘Overlay myImage’). It is included in the problem posting on the MAGNET Curriculum Network.
• Also included is the ‘base_map_wetlands_extent.txt’ file which includes the image spatial extents needed for overlaying in the modeling environment.
• Conceptualize the model with 3 aquifer layers – one for each of the glacial drift layers described above.
• The approximate extents of each of the three layers is shown in Figure 5 below.
• Treat the domain boundaries as ‘no-flow’ boundaries. The extent of the first layer follows the boundary between the uplands and the glacial drift valley.
• The uplands are underlain by thin layers of till over low permeability bedrock, and thus, negligible flow in this area is expected.
• Conceptualize the Aberjona River as a head-dependent boundary condition where the stage follows the aquifer top (DEM from land surface) and the leakance is 2 d^-1.
• Treat the wetland areas as a one-way drain, allowing water to leave the aquifer in places where the head exceeds the land surface elevation. Typically, a leakance of 1 d^-1 is appropriate.
• The approximate extents of the wetland areas is shown in the site map (Figure 3)
• Add the wells in the locations indicated in the site map (Figure 3). Assign steady pumping rates using the information provided above.
• Use particle tracking applications on your simulated flow patterns to track the movement of groundwater flow or potential contaminants.

Figure 4: Suggested conceptual model.

Figure 5: Model layer extents.

Disclaimer: Although this project is based on a real-world story, some information has been simplified, modified, or omitted to make the problem suitable for educational application. The results and interpretations of this project are not meant to be liable assessments of the real-world contamination problem.