By Hydrosimulatics INC  

SUMMARYCleanup Guru LLC won a major contract award to cleanup a groundwater contamination site – one of the largest under active remediation in the state. The project, however, did not go particularly well. In fact, the site owners who funded the contract accused the company of malpractice, arguing that the project which aimed to contain the plume actually accelerated the offsite migration to the creeks and to the wetlands and to the lakes downstream. Perform an independent assessment of the cleanup system and develop a new capture system that can contain the groundwater contamination.

Background and Dilemma

The site is within a 0.25 mile x 0.5 mile area of refineries in an industrial complex. The area was so polluted from decades of operations and accidental spills that multiple plumes co-mingled into one large oblong plume. The aquifer underground – sandy, unconfined, and relatively thin – essentially became a subsurface “gas storage tank”, with many of the monitoring wells show more than 1 ft of free product.

What further aggravated the problem was that, the site, though locally very flat, sits on a plateau which functions as a groundwater divide. Because of this, the plume expands with groundwater flow in multiple directions, toward a network of protected groundwater-fed wetlands and creeks surrounding the site. The creeks flow to a major lake used for recreation activities and as a source of water to domestic users around the lake.

The first order of business of the project required by the state Department of Environmental Quality (DEQ) is to stabilize the situation, i.e., prevent the plume from moving into the nearby surface water and wetlands. Once this is achieved, the site will need to be cleaned up (or remediated).

In a 5-year time-span, the Cleanup Gurus 1) excavated the contaminated soils; 2) created an above-ground bioreactor for treating the contaminated water; and 3) established a network of capture wells and injection wells that recirculates, flushes, and dilutes the contaminated water. The capture wells are located mostly on the perimeter of the site. The injection wells are largely located in the center of the contaminated site/plume. The captured contaminated water is immediately treated in the bioreactor and sent to the injection wells, forming a recirculation system.

Monitoring results clearly show that the chemical concentrations in in the aquifer have decreased over the years …. but the company did not seem to be able to achieve the first order goal: prevent the plume from migrating offsite to the wetlands and creeks.

“It just does not pass the eye and smell test!” one DEQ manager said. “One can visually see gas-laden water bubbling up at low elevations, on the slopes, and in the wetlands.”

“That was contaminated water that already escaped the site before we got started!” the Gurus argued.

Another year passed, and the situation got worse. While the concentration within the site area continued to decrease, the concentrations in the monitoring wells at lower elevation outside the site area had clearly increased. The DEQ ordered the operation to stop and initiated a complete reassessment. As part of this reassessment, the DEQ invited a retired professor – an expert in groundwater hydrology – to attend a presentation by the Gurus that summarized the work over the years. Immediately after the presentation, the professor said he think he knew what has been going on.

“The pump and injection system did not work. The conceptual design is flawed, and the contaminated water was not contained. In fact,” he said, “I can tell you exactly how much contaminated water escaped capture from day one – as soon as the remediation started – without doing any elaborate analysis. It is the same amount of water that migrates offsite before the remediation started. It is equal to whatever amount of water that infiltrates into the ground in the site area, except that the recirculation system changed the water quality dynamics by accelerating the mixing and increasing the concentration of the contaminated water moving offsite.  Initially, the water reached the site boundary was probably clean.”

After this, the site owners said they had heard enough.  The project which aimed to contain the plume actually accelerated the offsite migration to the creeks and to the wetlands and to the lakes downstream. They were furious and thought this amounted to malpractice, so they decided to sue the Cleanup Gurus LLC.

Objectives and Deliverable

You are asked to perform the following tasks as an expert witness:

  1. Present an independent assessment of the conceptual representation of the cleanup system.
  2. Develop a computer model to visualize how the groundwater flow and contaminant at the site responded to the Cleanup Guru’s remediation process.
  3. Quantify the flux offsite during the Guru’s remediation process.
  4. Develop a new capture system that can contain the groundwater contamination

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

A map of the site and the surrounding area is provided in the figure below. It includes a delineation of the areas consisting mostly of wetlands in between the Creek and River and the cliffs of the plateau.

Other pertinent information:

  • Plateau average elevation: 150 ft
  • Wetland area / Creek / River average elevation: 65 ft
  • Clay top average elevation: 0 ft
  • Wetland surface drainage leakance: 0.8 d-1
  • Hydraulic conductivity of sands in plateau area: 25 ft/d
  • Hydraulic conductivity of sands in wetland areas: 10 ft/d
  • Average recharge in plateau area: 16.5 in./yr.

Modeling / MAGNET hints:

  • Use ‘Synthetic mode’ in MAGNET to create a model domain with the same dimensions as shown in the map
  • Overlay the provided SiteMap image file included in the problem description. Choose ‘Use Domain Extent’ to fit the image to the established domain size.
  • The aquifer top can follow two constant elevations – one for the plateau area, one for the wetland areas
  • Conceptualize the model as 1-layer, unconfined aquifer, with the bottom of the model following the flat clay layer.
  • Assign a different hydraulic conductivity for the sand underling the wetlands / Creek / River than for the plateau area.
  • Conceptualize the Creek and River as constant head boundary conditions
  • Note that there recharge is negligible in the wetland areas