Friday, June 22, 2007

Does your Groundwater Taste Bad?

Expenditures to Eliminate Salt Water Intrusion

Whidbey Island, with its increasing population, has human-induced stress on its groundwater supply. This is a particular problem in coastal areas- where all want to live, because of the views of the Puget Sound (and its salt water).
The groundwater must remain in a steady state situation- where the precipitation must equal or surpass the usage- for inhabitants to depend upon a sufficient supply of fresh water. Groundwater existed before Man began to pump it, in a lens configuration. That is, a lens-shaped or elliptical layer of fresh water (which extends below sea level for part of the island) lay above the deeper brackish or salt water. The water-bearing layers (named aquifers) in an isolated lens occur within a portion of the island isolated by faults, on at least two sides. The other two edges of the lens generally exist at the beach, and the lens is the thinnest there. The lens is thickest in the center of the island. The faulting, which occurs every few miles on the island, acts as active slices or cuts in the layers containing the water, and these may isolate an area from neighboring lens. Water may move along the active fault, or cut, where it will create seeps or springs upon reaching the cliffs near the sea. This case is particularly obvious at Dugualla Bay, where an aborted ice lobe, from Glaciation times, has sliced the water-bearing layers to produce many springs (see the link labeled Bounty from the Earth to see one such spring bringing iron from the earth, at Penn Cove).
A proper analysis of the groundwater available for a particular neighborhood should first determine the lens and its boundaries of faulting and coastal saltwater. This costs the County time and Money, hence the workers are reluctant to undertake this requirement. Water should not be expected to cross the fault boundaries to recharge an adjoining lens. Whenever the permeable layers allow fresh water to cross from one lens to another, this is serendipity!
So long as Man used only spring water and cisterns, the natural lens configuration remained in a steady condition (or steady state in engineering notation). However, whenever man began to pump the fresh water, the equilibrium was disturbed. Several things then happened:
1. The lens became thinner (pressure dropped in the bottom of the well), causing the water table to lower, and the underlying mineralized water to rise to fill the bottom of the aquifer. In drastic cases, the underlying mineralized water forms a cone- rising to the level of the pump (smallest part of the cone pointing to the well);
2. Near the boundary or fault crossing the island, there is increased water movement as water pressure drops (due to loss of height or head);
3. The mineralized water, which exists along the fault and below the fresh water lens, moves toward the region of low pressure- this will be upward for the deeper non-fresh water and laterally for the case of faulting;
4. All of this causes a reduction of fresh water and an increasing content of mineralized water in the lens.
Faulting will exaggerate the influx of mineralized water, and if the fault connects with the sea, the water becomes more salty with time. It is not certain that the groundwater will become “salty” to the taste, since mineralized water from below may contain other objectionable minerals. This includes sulfate, which is attacked by bacteria to cause a stink. Iron will be associated with such deposits as the Esperance sand and the one causing the Penn Cove spring mentioned above. Other exotic ions cause strange tastes, and changes in Reduction potential and acidity or alkalinity create turbidity or precipitation of unsightly compounds in the water supply (most of which are measured in water quality tests).
Nearby faulting may cause the analyst to conclude that there is salt water intrusion, when the water merely exhibits its exotic contents. The county has undertaken to solve the mineralization problem, by looking only for chlorinity or salinity, while ignoring the minerals brought by faulting. This is now done by requesting that the landowner pay for an independant 24 hour production test, where a significant increase in the chloride ion condemns the well. The owner has to pay not only for the drilling but the testing of the well (as well), and he is not given a permit to build, when the production test indicates unsuitable water.
The easiest way to avoid appraising the groundwater purity in advance is to cause property owners to make expenditures to find whether there is high salinity present, which deters drilling in unknown areas. Rather than analyze the movement of exotic ions, it is simplest to categorize all abnormalities as Sea Water Intrusion, thereby minimizing county work.
Here is a method which will determine whether mineralization is from the sea, or from deeper zones- which have higher concentrations of undesirable ions or minerals at their original depth (greater depths of a drill hole encounters increasing temperatures, which generally produces higher concentrations of almost all soluble minerals):
a. For aquifers near faulted areas, the deeper warmer zones cause Potassium and Fluoride to diffuse upward along the fault. This does not mean that water is moving upward, but that the minerals are moving toward a region of lesser concentration (this is the normal occurrence for dissolved minerals, either Cations- positively charged, such as K+, potassium, or anions such as Fˉ, fluoride).
b. Groundwater with original exotic ions should be scrutinized for the pattern which it creates on a map, in as many locations as possible.When there is a linear arrangement of abnormal concentration of K or F on a map of an area containing more than 20 water wells, this suggests a faulted zone
a. Whidbey Island has most of the dominant faults tracing northwest to southeast, NW-SE, so that if this lineation is found on the map, there is a great likelihood that an active fault exists in the mapped area. Sometimes, the faulting lineation can be noticed on a topographic map, just by finding a creek which orients in this direction, e.g. Silver Creek.
b. Island County has such a data base already present due to the excellent collection by a hydro-geologist. However, after taking great pains to collect the data from water wells and to determine by GPS where the wells are located on the map, the chemical analyses are ignored.
c. Major faults exist on Whidbey Island in at least 10 areas, but the location of faulting sometimes may be found by simply looking at a topographic map- e.g. for Honeymoon Bay, the indentation is caused by three or more creeks making exit at a coastline where faulting caused unusual erosion. I have seen this small normal fault, which is just south of the bay, in the first cliffs adjacent to the indentation. Harrington Lagoon (indentation) is another suspect, which could easily be “rounded up” by making a map of K/Cl (potassium/chloride ions), to determine whether there is the usual NW-SE anomaly.
d. Whenever there is a fault indication on the topographic or K/Cl or F map, the proposed well location could then be assessed as to whether money should be spent before drilling. Requesting that a landowner pay for a pumping operation (requiring several thousand dollars), where the result could negate the use of the finished well is an easy way out for the county, and this could be avoided by use of data and workers already available to make an appraisal beforehand.
e. See the link: www.geocities.com/overtonharold/ for the original work done to establish this method. This work should be refined, to encompass the several thousand wells finished since the analysis was made 7 years ago. The work is referred to as Geochemical Mapping, K/Cl method, or Water well chemical analysis.
Note: 1 the original composition of the groundwater must be used for these analyses- since man can easily re-arrange the composition by pumping the well.
2. Ιt is normal for mineralized water to underlie the fresh water zone- the deeper one drills, the more exotic the water becomes.
More comments are to follow, in a subsequent Posting.