Bob Arrington comments on Williams air sparging

The area of the underground hydrocarbon plume is outlined in yellow. This map is dated April 30, 2013

The area of the underground hydrocarbon plume is outlined in yellow. This map is dated April 30, 2013

The process of air sparging is where a recharging stream works against Williams. The water table has the relatively impervious rock of valley floor and valley sidewalls confining the water table below the stream and the vadose zone(1). It is putting hydraulic head (pressure) in the horizontal plane as well as the hydraulic head of topographic elevation fall. If the topography flattens out as in a stream oxbow area and resistant compaction faces the stream causing turnback, then those pressure heads bring the water table back up to the stream level (i.e. marshy ground, wet sand bar deposits) like a dam. That is why the benzene found the stream where it did because the vadose zone became saturated.

The stream, vadose zone, and valley formations confine the water table to the stream’s delta of alluvial deposits making it in effect a “confined aquifer”(2). But when the conditions bring the ground water (water table) to the surface, it is locally no longer a “confined aquifer.” However, if sparging trenches do not go deep enough to the “bedrock” or across the whole delta, they can, with the air pressure of sparging, push the plume and saturated ground water table flow out and around or down and under their sparging trenches.

Williams is gambling the majority of the hydrocarbons are floating at the surface of the water table as opposed to being soluble in the water. It is also the strategy of diluting the tracer benzene readings to an insignificant number. But this sparging does not do that much for the other hydrocarbons that are more plentiful and heavier like the toluene, xylene and gasoline and they will travel further. Eventually, all becomes spread out over a downstream zone (volume) that the “leading edge” becomes negligible to detect with dilution: Fick’s Second Law(3)

If you noticed their yellow line plume maps first came up to the “oxbow”, but now they show the plume as having gone under the stream, again, in recent maps. But with no replenishment of hydrocarbons from a source, it becomes a slow washout of the hydrocarbons through evaporations and water carry, but at levels that are very minute and below any measure limits.

The problem is you still have contamination that was just pushed into another sector of the environmental makeup by sparging. It is not collecting or actual removal of hydrocarbons; it is a transfer to another part of the environment and they are becoming available to create ozone and emission effects. The missing element is vapor collection that has been used in other systems.

Back in the early days of smokestack abatement of pollutants there was the advocating of two methods. Collect the pollutants which was more expensive or “build a taller stack” which was cheaper. The argument of a taller stack, which put out the same amount of pollution, was it would disperse it over a greater area. Spread the problem around more area became a laugher to reasonable people, but it was practiced and allowed for “economic” consideration until it became obvious that acid rain and associated impacts were costing more.

You have raised good questions [Day 96], as to Williams’ plan, approach, and shortcomings of their process. What they are doing will slow and make the growth of affected land areas less by transferring contamination to the air, but the only removal is happening with their water treatment of collected water and, depending on soil treatments, what they do there.

(1) vadose zone: the zone between land surface and the water table within which the moisture content is less than saturation (except in the capillary fringe) and pressure is less than atmospheric. Soil pore spaces also typically contain air or other gases. The capillary fringe is included in the vadose zone.

(2) confined aquifer: a fully saturated aquifer overlain by a confining layer. The potentiometric surface (hydraulic head) of the water in a confined aquifer is at an elevation that is equal to or higher than the base of the overlying confining layer. Discharging wells in a confined aquifer lower the potentiometric surface which forms a cone of depression, but the saturated media is not dewatered.

(3) Fick’s Second Law: an equation relating the change of concentration with time due to diffusion to the change in concentration gradient with distance from the source of concentration.

(4) free product: a petroleum hydrocarbon in the liquid (“free” or non-aqueous) phase (see also non-aqueous phase liquid, NAPL).

*Bob Arrington is a retired engineer and the Battlement Mesa citizen representative on Garfield County’s Energy Advisory Board (EAB). He also represents the Grand Valley Citizens Alliance and the Battlement Concerned Citizens.

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One Comment on “Bob Arrington comments on Williams air sparging”

  1. Tod Tibbetts Says:

    I find it interesting that when this disaster first came to light, using the information provided by Williams, you compared the size of the plume to the Glenwood Pool and were soundly criticized for that characterization. Now we finally know why, because it is 35 times the size of the Glenwood Pool !!!!

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