208 Days of DPE Operation Achieves Residential Case Closure at a Former Gasoline UST Site
A former floor service business occupied a site in San Jose since 1948 and had a 550-gallon gasoline underground storage tank (UST) for fueling company vehicles. The UST was abandoned in place in 1979. The business continued operations until 2012, then leased the property as warehouse space. A developer purchased the property as part of a larger residential development project in 2013.
GeoRestoration, Inc. (GRI) conducted dual-phase extraction (DPE) from October 2012 to June 2013 for a total of 208 days of run time. A total of 134 gallons of hydrocarbon mass was removed during this period. While the extraction rate was relatively low, with less than 1 gallon of mass removed per day, significant reductions in groundwater and soil vapor concentrations were achieved (see the table below). The reductions in soil were more limited, with reductions between 23 and 90 percent. Ethylbenzene in groundwater also increased slightly, which can occur during remediation as higher concentrations are drawn into wells. Additional run time would have continued to reduce concentrations in soil, groundwater, and soil vapor.
Although some elevated concentrations remained, the limited DPE event was sufficient to achieve residential closure conditions under the Low-Threat UST Case Closure Policy, with the closure letter issued in 2016. The site is now part of a large residential development.
As with many hydrocarbon sites, GRI’s portable DPE systems are able to achieve case closure, especially under the Low-Threat UST Case Closure Policy, in less than one year of run time. This limited run time allows GRI’s DPE systems to be significantly more cost efficient than a permanent DPE system. When shorter run times are needed, GRI’s portable DPE systems can be less than the cost just to design a new permanent system.
| Analyte | Before | After | % Reduction |
|---|---|---|---|
| Soil | (mg/kg) | (mg/kg) | (%) |
| TPHg | 21,000 @24 ft | 9,400 @25 ft; 1.3 @<10 ft | 55.2 |
| Benzene | 13 @24 ft | 1.3 @30 ft; ND<0.0058 @<10 ft | 90.0 |
| Toluene | 400 @24 ft | 290 @25 ft; ND<0.0058 @<10 ft | 27.5 |
| Ethylbenzene | 390 @24 ft | 300 @25 ft; 0.011 @<10 ft | 23.1 |
| Total Xylenes | 2,700 @24 ft | 1,600 @25 ft; 0.081 @<10 ft | 40.7 |
| Groundwater | (µg/L) | (µg/L) | (%) |
|---|---|---|---|
| TPHg | 98,000 in 2012 | 18,000 in 2014 | 81.6 |
| Benzene | 5,200 in 2007 | 230 in 2014 | 95.6 |
| Toluene | 14,000 in 2012 | 160 in 2014 | 98.9 |
| Ethylbenzene | 3,000 in 2012 | 3,200 in 2014 | -6.7 |
| Total Xylenes | 14,000 in 1998 | 3,100 in 2014 | 77.9 |
| Soil Vapor | (µg/m3) | (µg/m3) | (%) |
|---|---|---|---|
| TPHg | 860,000 in 2009 | 5,200 in 2015 | 99.4 |
| Benzene | 2,000 in 2009 | 420 in 2015 | 79.0 |
| Toluene | 42,000 in 2009 | 190 in 2015 | 99.5 |
| Ethylbenzene | 48,000 in 2009 | 600 in 2015 | 98.8 |
| Total Xylenes | 180,000 in 2009 | 900 in 2015 | 99.5 |
Contact GRI today to save time and money on your next DPE project!
Phone: 408-779-5533 · Email: main@georestoration.com