A whimsical comment by the author Michael McClary compels one to realize that more intuitive processes can be overlooked when considering technology’s abilities to improve our natural environments. He said: “Irrigation of the land with seawater desalinated by fusion power is ancient. It’s called rain.”
In situ treatment of contaminated groundwater may be one such intuitive approach worth more regular consideration these days. This field of environmental science has been well-proven to effectively address sites impacted with a wide range of COIs, such as petroleum hydrocarbons, PAHs, and BTEX, often at a fraction of the cost of more ubiquitous long-term methods such as “pump and treat”.
In addition, application of in situ treatment is non-invasive and causes minimal disruption of normal site operations, injections can be made through roads, parking lots and in many cases through base floors of existing buildings. Subsequent operations and maintenance (O&M) requirements for in situ applications are limited to periodic sampling for monitoring purposes, which is significantly less expensive than operating pump and treat systems.
This article presents a recent case study from a project that employed an oxygen releasing compound for aerobic treatment of petroleum compounds. It also seeks to provide general information on how a typical in situ treatment project is conducted in North America, including cost information and some technical details.
Groundwater was impacted by petroleum volatile organic carbons (PVOCs) at a site in Kenosha, Wisconsin, as a result of a leaking underground storage tank (LUST). The tank had been removed during the 1970s and the groundwater subsequently treated in 2004 using a then-common oxygen releasing compound. In early 2005, PVOCs were still detected at significant levels by STS Consultants, Ltd. In August of 2005, STS performed a second round of injections, this time using Adventus’ oxygen slow-release product labeled EHC-O™. This technology was chosen for several reasons:
- It contains >15% oxygen, thus at $5.29/lb, is a more cost-efficient source of controlled release oxygen than alternatives.
- It releases between 80% and 90% of its content within 120 days.Independent data have shown that other oxygen release compounds exhibit the same release characteristics, regardless of their “advanced” status.
- It is buffered and contains inorganic nutrients, these factors are critical to soil microbiology but are often disregarded during the formulation of other oxygen release compounds.
- Its pH buffering component reduces self-encapsulation of the active ingredients.
At Kenosha, results from the spring 2005 sampling event indicated that groundwater was impacted with up to 2,300 ppb of PVOCs, including BTEX, naphthalene, MTBE and rimethylbenzene. The chemical oxygen demand (COD) was measured at between 36 and 90 ppm. The groundwater table was approximately 5 ft (1.5 m) below ground surface (bgs) and the impacts extended down to approximately 15 ft (4.6 m) bgs. The lithology of the targeted treatment depth consisted of silty clay with occasional trace gravel. The redox potential was +21 mV and the pH was 6.65. The treatment goal was to reduce the PVOC concentrations to below their respective groundwater quality standards in a timely manner to facilitate development of the site.