Dumping pump and treat: rapid cleanups using thermal technology Page: 18 of 26
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rate was set to equal the rate at which water was injected as steam). The majority of the
product was removed in the vapor phase.
Second Steam Pass
The amount of water and gasoline vapor removed during the first steam pass (-6400 liters)
was limited by the capacity of the vapor treatment system (-95 liters/day); subsequently, the
vapor treatment was redesigned to increase its capacity. After a 3-month shutdown, during
which the effluent treatment facility was upgraded and the in-process sampling and analysis
procedures were improved, the second steam pass was conducted from May into July, 1993.
The previous liquid-ring-pump-based vacuum system was replaced with an internal
combustion engine system in which the applied vacuum came from the engine manifold.
Thus, the applied vacuum and total vapor extraction rates were lower in the second pass,
although the total gasoline removal was much higher due to the increased treatment capacity.
Extraction rates were high at the beginning of this pass, because residual heat in the soil had
vaporized much of the remaining gasoline during the shutdown period. During the second
steam pass, operations were conducted in a "huff-and-puff" manner, alternating steam
injection and vacuum-only phases on a five- to six-day cycle (Figure 9). The extraction rate
varied considerably depending on the amount of steam injected and the total vacuum applied;
more gasoline was extracted when steam was not being injected and thus the vacuum effect
was greater. During this pass, the average extraction rate was more than 380 liters/day of
gasoline (compared to 3 liters/day for pump-and-treat).
As during the first pass, extracted water and vapor temperatures are limited to the boiling
point of water after steam breakthrough to the extraction well. During the second pass, the
amount (and location) of injected steam was varied, while the extraction system remained at
full capacity. This resulted in a "huff and puff' operation, reflected in the amounts of
extracted vapor and in the temperature variations not seen in the first pass where steam was
injected continuously. On day 20, the steam recovery rate was at a maximum, and steam
injection was slowed to maximize gasoline recovery. This also occurred on days 28 and 36,
each time with a corresponding rapid rise in the amount of recovered gasoline vapor.16
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Newmark, R. L. & Aines, R. D. Dumping pump and treat: rapid cleanups using thermal technology, article, March 11, 1997; California. (https://digital.library.unt.edu/ark:/67531/metadc691700/m1/18/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.