What is land subsidence? NOAA defines it this way: Land subsidence is a gradual settling or sudden sinking of the Earth’s surface. ADWR states: “Land subsidence in the basins of Arizona is generally due to compaction of the alluvium caused by lowering of the water table. As the water table declines, pores in the alluvium once held open by water pressure are no longer supported and collapse.” This results in a lowering of the elevation of the land.
ADWR (Arizona Department of Water Resources) has identified that Wenden is in a subsidence bowl. Their satellite imaging system identified that Wenden and the surrounding area has sunk 3.89 feet in the last 15 years and continues to sink at the rate of 2.2 inches per year. This has happened because of the significant amount of ground water that has been pumped from the aquifer over the years, including a significant increase of ground water pumping over the last five years.
Here is a satellite image, provided by ADWR, of Wenden’s subsidence bowl.
Please note the location of Alliance Metals property. It is in the subsidence bowl meaning that the property is sinking and is subject to the consequences of subsidence.
Land subsidence usually manifests itself in some pretty obvious ways. The first thing that becomes apparent is that the subsidence increases the frequency and severity of flooding. The flood of 2000 was said to be a 100-year flood, meaning it is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. A flood of that severity is rare, but not in the case of Wenden…it happened again in 2010 and 2014. With increased frequency, the probability is very likely for more 100-year floods to occur in Wenden, because the town is going to sink further and further every year.
The second way that it sometimes appears in southwest Arizona is when well casings start to stick up above the ground such as in the picture below. The concrete pad in this picture originally was at ground level but as the ground sunk the well casing and the concrete pad did not. This has actually happened in Wenden at the Water Department. Several times over the past few years the Department has had to have the well casings, that were sticking up above the ground, cut off and the well head reset at ground level.
The third way that subsidence makes itself known, without using satellites or other complicated equipment to detect it, is through the appearance of earth fissures and sinkholes. Some of these open gradually while others can happen very suddenly. This is a picture of an example of an earth fissure. This picture was taken in McMullen Valley, near the town of Wenden by the Arizona Geological Survey.
What this all means is that the Alliance Metals property is subject to more frequent and severe flooding than in past years. It also means that earth fissures and or sinkholes can open at any time. There is no way to predict these events or their severity. There is no guarantee that either earth fissures and/or sink holes won’t open under the furnace building, the chlorine storage tank or the storage area where dross and salt cake are stored. If an event such as this were to occur under this facility, the results could be catastrophic polluting the air, the land and the aquifer below.
This all comes back to one point that we keep talking about. This property is the wrong location for this kind of facility. The risk is just too high. None of this was taken into account when Alliance purchased the property meaning that the company was extremely haphazard with their due diligence process. McMullen Valley and its residents should not be held accountable for Alliance Metals short sightedness and be forced to live with a facility that most of the community does not want.