The following pages describe how toxic vapors can enter your living space from the subsurface
The following pages describe various methods to prevent toxic vapors entering your living space from the subsurface
The following pages describe basic groundwater flow
The following pages describe basic contaminant transport by groundwater
The following page describes how products like gasoline sink below water when it normally floats
The following page illustrates the importance that contaminated soils are often composed of three different populations
The following page illustrates the mechanism for chemicals as a separate phase to directly, not dissolved in water, contaminate soils
The following page illustrates the mechanism for chemicals, dissolved in water, to contaminate soils
The following page provides definitions of terms used on this website
This page is an in depth overview describing the objectives of this website
It is probably best to first explore the other links; however, the Table of Contents page is a must see: many more pages are available than the few hyperlinks displayed in this column
This page provides some useful links to interesting sites on the web


"the environmental ombudsman"
Environmental Justice Plus Equity - prescriptions (Rx) for
a cleaner environment

Influencing Clean Groundwater to Flow Beneath Your Home to Curtail Vapors in Your Basement Resulting from Off Gassing of Seeps of Groundwater Contamination

Eliminating Vapors in Your Home Caused by Seepage into Your Basement of Dissolved Phase Contamination: containing products such as gasoline, fuel oil, MTBE, benzene, toluene, ethylbenzene, xylene, TCE, and PCE

It has been previously noted that it is possible to split a plume into two separate plumes. In many subsurface cleanups, but not all, there is value in splitting a plume into two portions. When vapors result from the off gassing of contaminated groundwater seeping into your basement, shouldn't the objective of this type cleanup be to ensure that only clean groundwater flows under your home? This clean groundwater will eventually flush much of the contamination from below your home. Splitting the plume to redirect the natural groundwater flow regime and thereby, induce clean groundwater to flush contamination from below your home will be illustrated. A previous figure has illustrated vapor generation in a home from the off gassing of seepage of contaminated groundwater (such as dissolved product) into the basement when the water table is above the basement slab.

The first figure on this page depicts an extensive plume of contaminated groundwater engulfing this residence with the water table higher than the basement slab so that seepage of contaminated water into the basement occurs. The plume of contamination that is dissolved in the water table is being transported with the groundwater as it moves from a point of higher hydraulic head to a lower hydraulic head (generally put, but not quite correct - groundwater and the product dissolved in it are moving from points on the water table that have a higher elevation to those points of lower elevation - similar to the groundwater rolling downhill). Notice that the plume of contaminated groundwater is not that extensive across the transverse-lateral extent (width and depth) of the plume. Just outside the perimeter defining the transverse-lateral extent of the plume is where clean groundwater can be found. The objective of splitting the plume into two portions is to influence, by the pumping of groundwater, these outer flowpaths that are free of contamination to flow under your home flushing any remaining contamination off in a downgradient direction.

The objective of hydraulic control is to influence clean groundwater to flow under your home. Do I need to add: that this should be accomplished in a timely manner. Generally, this definition does not need much time to accomplish. In the second figure, the recovery well is installed sufficiently upgradient of the house so that the downgradient extent of the capture zone, known as the stagnation point, is located at the upgradient side of the house. The stagnation point should be located sufficiently close to and upgradient of the house so that the clean ground water from just outside the sidegradient extent and below the vertical extent of the plume is induced to flow the shortest distance to the upgradient side of the house through those soils contaminated by dissolved product.  Once the soils on the upgradient side and just under the upgradient side of the house are flushed of their contaminant load, the clean ground water, which originated from just beyond the sidegradient extent of the plume, can now flush the contaminant load in the more distant, downgradient soils under the basement as will be depicted next.

The second figure depicts early capture of the plume just after the plume splitting is effectuated. The next figure depicts a later stage of the plume splitting when the objective of inducing clean ground water to flow beneath your home is achieved. The objective of inducing clean ground water to flow beneath your home is to rid those soils and waters underlying your home of contamination. Since we are addressing
remediation of dissolved phase seeps into your basement, please remember that those soils surrounding your home were contaminated by contact with dissolved phase contamination, and not by contact with a separate phase which might include such products as gasoline, MTBE, TCE, PCE, or some other toxic substance or mixture. In other words, this discussion applies to soils contaminated by contacting ground water that has first been contaminated by the dissolution of product into the water and not by product directly contacting the soil. Inducing clean ground water to flow beneath your home may not be the best remedy if the soils proximate to your house have been contaminated by contact with separate phase, unless these soils have been exhausted of their contaminant load (mass) given sufficient time or some other remedial action. Dissolved product contaminated soils (I call them solusols - for solute contaminated soils) can be flushed with clean water to remediate them. It may take eight or nine flushes with clean ground water to exhaust these soils of the contamination load (mass). Separate phase contaminated soils (I call them produsols - for product contaminated soils) can require in excess of 400 flushes of the pore volume to exhaust contaminants from them. Splitting a plume into two parts can be accomplished relatively quickly when the transverse-lateral extent of the plume is limited; the permeability of the soil to transmit water is adequate; and, the soils surrounding your home are comtaminated by dissolved product. When these conditions are met, splitting the plume and flushing the plumelet beyond your basement can be measured in timeframes of months, and not years, when the recovery well is properly installed to locate the stagnation point of the capture zone just upgradient of the your home.

Unfortunately, in practice, many recovery wells have not been located in similar fashion to that depicted in the second and the third figures. Mislocation of recovery wells will not abate the vapor problem and possibly make it worse.