Lake Management Plan
|
 |
 |
 |
 |
 |
 |
 |
 |
Questions? |
5.3.2 Wells
Most wells around Pelican Lake are for domestic use with a few for irrigation. Wells for domestic use are usually 50-200 feet in depth. Wells for irrigation are much shallower usually 25-75 feet. There is one observation well near the North East section of the lake at over 300 feet.
Fig 5.6 Well use.
5.3.3 Water Table Pollution
Pelican Lake has a moderate to high ground water pollution susceptibility (from the Minnesota Environmental Atlas and based on aquifers in the region). The highest potential is at the east and west end of the lake where the Pelican River and Bob Creek inlets are found.
Fig. 5.7 Ground water pollution susceptibility.
In the Ganges Plain of northern India and Bangladesh, severe natural pollution by arsenic affects 25% of water wells in the shallower of two regional aquifers. The pollution occurs because aquifer sediments contain organic matter (dead plant material) that generates anaerobic (an environment without oxygen) conditions in the aquifer. These conditions result in the microbial dissolution of iron oxides in the sediment and thus the release of the arsenic, normally strongly bound to iron oxides, into the water. As a consequence, arsenic-rich groundwater is often iron-rich, although secondary processes often obscure the association of dissolved arsenic and dissolved iron.
Arsenic and many of its compounds are especially potent poisons. Arsenic kills by massively disrupting the digestive system, leading to death from shock.
Elemental arsenic and arsenic compounds are classified as toxic and dangerous for the environment. The International Agency for Research on Cancer recognizes arsenic and arsenic compounds as group 1 carcinogens, and the European Union lists arsenic trioxide, arsenic pentoxide and arsenate salts as category 1 carcinogens.
Not all groundwater problems are caused by over-extraction. Pollutants dumped on the ground or in landfills may leach into the soil and work their way down into aquifers. Movement of water within the aquifer is then likely to spread the pollutant over a wide area, making the groundwater unusable. Areas of karst topography on limestone bedrock are especially vulnerable to surface pollution. Sinkholes and underground caverns allow direct groundwater flow without the filtering effect of a permeable aquifer.Pelican Lake Arsenic
During the spring and summer of 2003 many lakes area residents became aware of high levels of Arsenic in their deep-water wells. Because of this drinking water concern, data has been collected from Pelican Lake property owners about their individual well tests. This information is also being reported back to the Directors of PGOLID and PLPOA.
Arsenic is measured in micrograms per liter (ug/L, or as ppb, parts per billion). There have been about 25 well tests received, as well as verbal input on several dozen other water tests. Around Pelican lakes, there has been arsenic numbers from a low of less than 2.5 ug/L (the lowest number reported in most tests), to a high of 75 ug/L. The acceptable standard for arsenic in drinking water is 10 ug/L, and is set by the US Environmental Protection Agency (EPA). This standard was lowered from 50 ug/L to 10 ug/L in March of 2001 because of concerns the EPA had with recent research on the effects of arsenic in drinking water.
Several lake residences have done repeated tests on the same well. The results can change from an existing well based on the time of year, well usage, and other factors. One lake resident tested his well in October and had a 37.2 ug/l reading, but the same well had a 14.0 ug/L in April. The accuracy and repeatability of the arsenic test procedure itself is good, meaning the same water sample, if taken to different labs on different days, should come back with results within less than 1% error.
A water softener will make no difference on the arsenic level in your water. RO (reverse osmosis) filter systems do help with one report showing a 14.0 to 6.3 ug/L change, a second lake resident saw his level drop from 14 to 3 ug/L after RO. This same lake resident went on to purchase a special RO filter system that was rated to remove arsenic, a follow up test on this system showed his arsenic level dropped to 0 (zero).
The arsenic is occurring in deep wells (deep wells are usually considered over 90 feet deep) and the arsenic problem does not usually, and has never been reported here, to occur in sand point wells. Arsenic is naturally occurring mineral in soil and bedrock, and the elevated readings in the area are not believed to be associated with any man made problem. Many arsenic tests in deep wells within a 20-mile radius of the lakes are coming back with readings in the 90-110 ug/L range.
Arsenic water tests can be processed through several water testing labs in the area.