40 FEBRUARY 2025 WorldWide Drilling Resource® Environmental Engineers Making a Difference Adapted from Information by GeoEngineers Based in Washington, GeoEngineers is an employee-owned engineering and earth science consulting firm. Back in 2017, the company began investigating the site of a former dry cleaning business where tetrachloroethylene, or PCE, had been found. The goal was to assess soil and groundwater conditions in anticipation of an upcoming acquisition and future redevelopment plans. As part of this process, remedial investigations were conducted due to the levels of chlorinated solvents in the groundwater. In September 2024, the evaluation to further assess the extent of contamination downgradient of the site started. This project became an excellent example of remedial investigations and the important role groundwater monitoring and sampling play as environmental engineers and environmental geologists work to understand the scale and scope of subsurface contamination at similar sites across the country. The project kicked off with a crucial task, determining the perfect location for the monitoring wells, strategically downgradient from the main contamination source (the former dry cleaning business). When placed correctly, monitoring wells can help determine how far contamination might extend, and in what concentrations. Using hollow stem augers, the monitoring wells were installed reaching depths of 40 feet. The company wanted the wells to sit on the top of a confining silt layer approximately 40 feet belowground. Once the wells tapped into the groundwater, on top of a confining silt layer, they began to dance in harmony with the flow - driving deeper into the earth due to their weight compared to water. With the well screens installed at the bottom 20 feet of the well and groundwater successfully drawn, it was time to prepare the well for taking samples. After drilling, it was time to ensure the monitoring wells were in pristine condition. Well development clears out any silt or fine particles introduced during drilling, as well as those in the aquifer surrounding the well screen. To achieve this, a number of different pumps were used to reduce the turbidity of the water. This clarity helped minimize sediment extraction during sampling and established a direct connection between the well and the aquifer. Once the wells were developed, it was time to capture a snapshot of the groundwater conditions. Following a 72-hour resting period, sampling was conducted. There were a variety of pumping techniques available, but for this project, a bladder pump and low-flow purge sampling technique was used. By stabilizing key parameters such as pH, dissolved oxygen, conductivity, and temperature, they were able to ensure the water was in equilibrium with its surroundings. Engineers observed how water levels exhibited significant variances within a mere 15-20 feet of distance, shedding light on the dynamic nature of groundwater in the area. These fluctuations not only impacted groundwater characteristics but also had noticeable effects on the concentrations of contaminants. The collected data will be carefully analyzed by the rest of the environmental team, and the picture it paints of subsurface contamination - location, concentrations, and even dynamic changes in the aquifer - will be used in the development of a remedial action plan to clean up the site. Groundwater monitoring programs are one of the most common, and critical, data collection methods for environmental engineers. When developed and maintained correctly, monitoring wells can continue to provide reliable information about subsurface conditions for years as contamination is treated or removed. Across the country, many former dry cleaner locations have left PCE contamination behind in soil and groundwater. Environmental agencies like the Washington Department of Ecology are working to investigate, characterize, and clean up these sites - and environmental engineers help them do it. ENV
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