REMEDIATION OF TOXIC VAPORS RESULTING FROM PRODUCT SEEPS
 
DEWATERING THE WATER TABLE AND VACUUM EXTRACTION
 
By the earthDr!
 
It is necessary to incorporate both pumping of the ground water and soil vapor extraction to remedy vapors resulting from seeps of separate phase product (use the back button on your browser or click on the Table of Contents to relocate yourself back to this page should you choose to review the earlier page). Don't assume that the objective of pumping of ground water for this situation is the same as for remedying vapors from seeps of dissolved product
as was illustrated on the earlier webpage. The initial objective is not to influence clean ground water to flow beneath the structure. The objective is to dewater the ground-water table so that soil vapor extraction can be more effective. Normally, it is necessary to pump appreciably more ground water to accomplish dewatering of the ground-water table, than it is to influence clean ground water to flow beneath a structure. Significant drops in the water table elevation are not needed to influence clean, outer ground-water flowpaths to flow beneath the structure. Dewatering normally requires more extensive drops. Obviously, increasing drops of the water table require ever increasing ground-water pumping rates. When the water table is dropped by the pumping of ground water, more volumes of contaminated soil can be exposed to the effects of soil vapor extraction.

The figure to the left depicts a simplified version of both dewatering of the water table and soil vapor extraction. A recovery well is used to dewater the water table in this figure. A blower is used to pull a vacuum and any toxic vapor clouds from the soil atmosphere. It operates similar to an exhaust fan. A vacuum is applied to the unsaturated zone to reduce soil atmospheric pressure below atmospheric pressure. When this is achieved, air will flow from the basement into the soils surrounding the basement.

Air flow is reversed from that depicted on the previous webpage illustrating venting of the soil atmosphere into a structure. It is this reversal of air flow that will prevent vapor clouds from entering a basement or crawl space. Air flow is now from the basement into the soil atmosphere. It doesn't make sense to place an exhaust fan in a basement window and exhaust the basement air to the outside atmosphere, because this action would decrease the basement atmospheric pressure; thereby, further increasing the difference between soil atmospheric pressure and the basement atmospheric pressure driving more contaminated air from the soil atmosphere into the basement.

 
 
 
   
VAPORS VAPORIZING FROM SEEPS OF PRODUCT INTO A BASEMENT
   
         
 
TABLE OF CONTENTS
TREATISE - VAPOR REMEDY FOR SEEPS OF CONTAMINATED GROUND WATER
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TREATISE - REMEDIATION OF VAPORS RESULTING FROM VENTING OF THE SOIL ATMOSPHERE CONTAINING A VAPOR CLOUD
   
         
   
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