Soil Vacuum Extraction of Perchloroethylene from the Borden Aquifer
Bibliographic record
Abstract
Abstract An assessment of a conventional soil vacuum extraction (SVE) system to remove perchloroethylene (PCE), a dense nonaqueous phase liquid (DNAPL), was conducted in a dewatered 9 × 9 m block of the surficial sand aquifer located at the Canadian Forces Base (CFB), Borden, Ontario. Approximately two years prior to the installation and operation of the SVE system, 1250 kg of PCE were released under saturated conditions into this experimental cell, forming a heterogeneous DNAPL distribution. Using ground penetrating radar and neutron probe data in conjunction with detailed soil core data, it was determined that approximately 600 kg of PCE were available for removal by the SVE system after dewatering. Performance assessment of this SVE system was based on soil core data and monitoring of in situ gas concentration and pressure, soil temperature, and moisture content. After the first 25 days of operation, the SVE system had removed 230 kg of PCE, during which time the off‐gas concentration decreased by 70% from an initial concentration of close to 3500 ppm Y After 432 days of operation, 63% (376 kg) of the estimated available mass was removed from the SVE target zone. In situ pressure measurements and sulphur hexafluoride tracer tests indicated that advective air movement occurred throughout the SVE target zone. Changes to the extraction well configuration and the use of short‐screened extraction drive points did not increase the mass removal performance. After 250 days of operation, eight soil cores were removed from the test cell, and bulk soil concentration and soil moisture content measurements were performed at 0.05 m increments along the length of each core. These data revealed zones where significant quantities of PCE remained, even though the cumulative mass removal profile for the SVE system was nonzero asymptotic. In general, these zones coincided with higher moisture content zones reflective of the heterogeneous nature of this porous medium. This investigation provides insight into some of the limitations of conventional SVE technology to clean up a sand aquifer contaminated with a DNAPL, given a reasonably good estimate of the before‐extraction mass conditions. In particular, the findings clearly show that the heterogeneous nature of the porous medium gives rise to a nonuniform moisture content, a heterogeneous pure phase distribution, and the development of preferential gas phase flow pathways. As a consequence, this will in general limit this technology to remove a considerable fraction of the DNAPL mass present. The results also shed light on the use of soil gas and bulk soil concentration data to provide a representative picture of the in situ mass distribution. And finally, an analysis of the system off‐gas data showed that continuous rather than pulsed operation of the extraction system increased mass removal.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.016 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".