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Title: Effects of Natural Environmental Changes on Soil-Vapor Extraction Rates

Abstract

Remediation by soil-vapor extraction has been used for over a decade at Lawrence Livermore National Laboratory (LLNL). We have found that natural changes in environmental conditions affect the rate of soil-vapor extraction. Data on flow rate observations collected over this time are compared to in-situ measurements of several different environmental parameters (soil-gas pressure, soil-temperature, soil-moisture, Electrical Resistance Tomography (ERT), rainfall and barometric pressure). Environmental changes that lead to increased soil-moisture are associated with reduced soil-vapor extraction flow rates. We have found that the use of higher extraction vacuums combined with dual-phase extraction can help to increase pneumatic conductivity when vadose zone saturation is a problem. Daily changes in barometric pressure and soil-gas temperature were found to change flow rate measurements by as much as 10% over the course of a day.

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
894334
Report Number(s):
UCRL-CONF-220094
TRN: US200701%%381
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: Remediation of Chlorinated and Recalcitrant Compounds, Montery, CA, United States, May 22 - May 25, 2006
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ELECTRIC CONDUCTIVITY; FLOW RATE; LAWRENCE LIVERMORE NATIONAL LABORATORY; PNEUMATICS; SATURATION; TOMOGRAPHY

Citation Formats

Martins, S, and Gregory, S. Effects of Natural Environmental Changes on Soil-Vapor Extraction Rates. United States: N. p., 2006. Web.
Martins, S, & Gregory, S. Effects of Natural Environmental Changes on Soil-Vapor Extraction Rates. United States.
Martins, S, and Gregory, S. Thu . "Effects of Natural Environmental Changes on Soil-Vapor Extraction Rates". United States. doi:. https://www.osti.gov/servlets/purl/894334.
@article{osti_894334,
title = {Effects of Natural Environmental Changes on Soil-Vapor Extraction Rates},
author = {Martins, S and Gregory, S},
abstractNote = {Remediation by soil-vapor extraction has been used for over a decade at Lawrence Livermore National Laboratory (LLNL). We have found that natural changes in environmental conditions affect the rate of soil-vapor extraction. Data on flow rate observations collected over this time are compared to in-situ measurements of several different environmental parameters (soil-gas pressure, soil-temperature, soil-moisture, Electrical Resistance Tomography (ERT), rainfall and barometric pressure). Environmental changes that lead to increased soil-moisture are associated with reduced soil-vapor extraction flow rates. We have found that the use of higher extraction vacuums combined with dual-phase extraction can help to increase pneumatic conductivity when vadose zone saturation is a problem. Daily changes in barometric pressure and soil-gas temperature were found to change flow rate measurements by as much as 10% over the course of a day.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 23 00:00:00 EST 2006},
month = {Thu Mar 23 00:00:00 EST 2006}
}

Conference:
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  • A model for soil vapor extraction (SVE) is developed which includes evaporation of nonaqueous phase liquid (NAPL) and mass transport of dissolved volatile organic compounds (VOCs) through low-permeability lumps, lenticular structures, and discontinuous layers of clay by means of a distributed diffusion approach. The configuration modeled is that of a single vertical well screened a short length near its bottom. The model exhibits high off-gas VOC concentrations initially (while NAPL is being evaporated), followed by rapid drop-off to a relatively long period of tailing, the extent of which is highly variable and determined by (1) the thickness of the low-permeabilitymore » layers from which diffusion is occurring, and (2) the period after the spill which elapsed before SVE was initiated. The results agree with previous models in that they indicate that one cannot predict SVE cleanup times from data taken in short-term pilot-scale experiments removing only 5-25% of the VOC present in the domain of influence of the well. The rebound of soil gas VOC concentration after well shutdown is explored; soil gas VOC levels measured under such static conditions are much more informative than levels measured during well operation.« less
  • Simulations of soil-heated vapor extraction have been performed to evaluate the NAPL removal performance as a function of borehole vacuum. The possibility of loss of NAPL containment, or NAPL migration into the unheated soil, is also evaluated in the simulations. A practical warning sign indicating migration of NAPL into the unheated zone is discussed.
  • In early 1990, during the removal of an underground gasoline tank, field observations showed the presence of soil contamination. Subsurface investigations were performed to delineate the extent of petroleum hydrocarbons in soil and ground water beneath the site and vicinity. A feasibility study was performed to identify, select, and implement appropriate measures to remediate the site. This paper presents a brief description of the subsurface contamination conditions, the remedial measures implemented, and the effectiveness of these measures in achieving the required cleanup levels.
  • The selection and design of an effective soil vapor extraction system is dependent upon data generated from pilot testing. Therefore, it is critical to understand factors that may affect the testing prior to selecting or designing a system. In Sebago Lake Village, Maine, two adjacent gasoline stations experienced a release. Gasoline migrated through fine sand into the groundwater and discharged to a small stream. Soil vapor extraction was investigated as a remedial alternative to reduce volatile organic compounds in the unsaturated soil. Three soil vapor extraction pilot tests were performed at one of the sites and one test at themore » other site. The results of the testing varied. Data collected during a summer test indicated soil vapor extraction was less likely to work. The wells tested were installed using an excavator. An adequate surface seal was not present in any of the tested wells. An additional test was performed in the winter using wells installed by a drill rig. Winter test results indicated that soil vapor extraction could be effective. Another test was performed after a horizontal soil vapor extraction system with a surface seal was installed. The results of this testing indicated that soil vapor extraction was more effective than predicted by the earlier tests. Tests performed on the other property indicated that the horizontal wells were more effective than the vertical wells. Testing results were affected by the well installation method, well construction, proximity to manmade structures, and the season in which testing was performed. Understanding factors that affect the testing is critical in selecting and designing the system.« less
  • Soil-vapor extraction systems are used to remediate soils contaminated with volatile organic compounds. SVE systems operate by drawing air through the contaminated zone and a dry well to the surface. The air evaporates the VOCs and provides oxygen for in situ biodegradation. Most SVE systems use high flow rates (100 cubic feet per minute) and pumps of several horsepower to achieve VOC removal. However, increasing evidence suggests that lower flow rates (10--20 cfm) can remediate soils efficiently and economically, and may even achieve more rapid cleanup. Moreover, low flow-rate systems require pumps of one-quarter horsepower or less, minimizing initial capitalmore » and operating costs, and can be used with low-cost treatment systems for offgases, such as mobile biofilters. Estimates of VOC removal rates from SVE systems usually are based on pump tests conducted when the system is installed. VOC concentrations initially are high, because VOC-contaminated air is drawn from advective zones. After the air in these relatively small zones is displaced several times, a rapid SVE rate draws more air through already clean pores. The removal rate is controlled by the VOC`s rates of diffusion and migration into the soil`s advective zones.« less