– Chris McCue
Remediation systems are a viable means to remove contamination from soil and groundwater in situ. If properly designed, installed and operated the benefits can be lower costs, lower carbon footprint, reduced liability, and lower accident frequency compared to other remediation methods such as dig and dump.
In comparison to dig & dump a remediation system is a much safer alternative for remediation. OSHA reports the fatality rate for excavation work is 112% higher than the rate for general construction. In addition, once the excavators and dump trucks are removed from the picture the overall carbon footprint of the project is greatly reduced, and liability is reduced when soil remains in place.
Though safer and more sustainable, the down side of remediation systems is remediation can take longer and dedicated operation is required. An inefficient system will have an increased carbon footprint, and budget! Three crucial elements must be considered to ensure a successful remediation system project; right site, right technology, and right operator.
Determining if the site is right requires collection and interpretation of data. The contaminant plume must be delineated both horizontally and vertically, the concentration of contaminant must be determined, and soil & groundwater characteristics must be assessed – drill, sample, pilot test, assess, assess, assess. Sandy sites can have great radius of influence, but add silt lenses or layers and you can find yourself in a nightmare. Clean silt above contaminated sand can be a dream. Every site is different!
The right technology includes all elements of the system; piping, wellheads and equipment. Piping and equipment must be sized adequately, and a little too big is usually better than a little too small, though not so for the bottom line! Wellheads can be the difference between a stalled well with little or no drawdown and a fully evacuated well with excellent radius of influence.
On one such site, multi-phase extraction wells installed in tight glacial till soil were found to be stalling. The former operator’s solution was to raise drop tubes until sufficient air was available to allow water to move up the drop tubes. The problem was the drop tubes were raised higher than the static groundwater level to account for mounding created by the applied vacuum. The mounding caused free phase product to move away from the system wells and migrate further from the system. Our engineers designed new wellheads for the existing system that overcame stalling and allowed the wells to be fully evacuated. Free phase product moved back towards the system wells and was captured by the system.
The right operator is one who understands the site, the technology, and the project objectives. Operation is the responsibility of the project manager and field personnel. Good communication between the field and office is key to success and ensures the system continues to move toward the project objectives. During a recent audit of a client operated remediation system, our engineers determined that the sparge blower was operating at a pressure too low to evacuate groundwater from the well and allow for air flow. The system had been operating this way for 5 years!
Neglect one of these three elements and likely a remediation system will fail to reach the site objective, or take a very, very long time to do so. But under the right circumstances and with good planning, a remediation system can rapidly remove contaminants and achieve the site objective in a cost effective, safe and sustainable manner.
For a more in depth look at this topic, don’t miss our presentation entitled “10 Questions to Ask About Your Remediation System”