Formatted Title
In-Well Stripping of Petroleum and Chlorinated Hydrocarbons during Two-Phase Extraction (TPE) and Recirculation
Background/Objectives
Two-phase extraction (TPE) is extraction of both vapor and liquid in a common flow stream using a drop tube and vacuum source from wells (subsurface). It is documented that TPE also strips volatile organic compounds (VOCs) from water during extraction and increases dissolved oxygen (DO) content of the extracted water by simply entraining air in water. This paper presents a summary of three pilot tests involving TPE, in-well stripping (by TPE) and recirculation and setting up air-stripping recirculation cells in a large open top tank. Three pilot tests were performed using TPE and in-well striping. Two of the tests were performed for petroleum hydrocarbon sites and one for chlorinated hydrocarbon sites. The TPE is implemented using a drop tube with openings on the sides and bottom to draw air and water as a response to a vacuum applied at the wellhead. The extraction drop tube will act as an air stripper removing up to 99% of the VOCs from liquid to vapor phase. Extracted vapor is then treated using thermal oxidizer or granular activated carbon.
Approach/Activities
Three tests were performed on different settings at three different sites. The first test was performed in New York using two separate monitoring wells for TPE and recirculation (extraction and injection wells); the second test was performed in California using a single well for TPE and recirculation with two separate screen intervals (shallow and deep screen intervals) and the third test was performed in California using monitoring wells for TPE and a stripping-recirculation cell set up in a storage tank to remove residual PCE and TCE after in-well stripping. Pre-test and post-test groundwater samples were collected from each test. Additional groundwater samples were collected during recirculation from extraction and injection portions of the recirculation cell to collect data in VOC reductions, dissolved oxygen increases and temperature changes.
Results/Lessons Learned
The results indicated that there is a significant reduction (up to 99%) in VOC concentrations during TPE and recirculation and significant increases in dissolved oxygen concentrations. Additionally, reduction in Fe2, BOD and COD was observed in the second test. Some scaling in the extraction tube was also observed that require a control solution or frequent maintenance.