The City is trying to solve two long standing problems for our water supply. This project will increase the amount of water available for use during drought (reliable yield) while simultaneously providing a method to lower the concentration of nitrates when they are elevated in our reservoirs. Since the Illinois Environmental Protection Agency (IEPA) developed and began enforcing the nitrate regulation for drinking water supplies over 35 years ago, the City has actively pursued practices and actions to assure meeting this regulation.        

As part of an enforceable compliance agreement with the IEPA in the mid-1980’s, the City stated that it would solve the nitrate problem by blending water from its reservoirs to stay below the nitrate regulation. This has worked fairly well for the City through the years, simply because of the principle of dilution. Both reservoirs can absorb a fair amount of nitrates from the agricultural watershed before the water in the reservoir is at or above the nitrate standard. However, there is always a point that, as the reservoirs continue to be filled with high nitrate water from the watershed, they reach or exceed the nitrate standard. While Lake Bloomington can seasonally exceed the limit, Evergreen Lake will generally exceed the limit only after periods of extended drought. This usually occurs in the Lake Bloomington reservoir because it has a larger watershed in relation to the reservoir volume. High nitrates tend to occur less frequently in the Evergreen Lake reservoir as it has a smaller watershed and a larger volume of reservoir.        

Thus, it is a much more likely occurrence for the Lake Bloomington reservoir to exceed the nitrate standard.  We normally observe a seasonal cycle whereby the nitrate levels are elevated in both reservoirs in the spring, generally decline through the summer, and reach their lowest levels in the early fall.        

That means that the sole source for water with a nitrate level below the standard is the Evergreen Lake reservoir or Lake Bloomington reservoir water blended with the lower nitrate Evergreen Lake reservoir water. Again, historically, blending lower nitrate water from the Evergreen lake reservoir with the higher nitrate water from the Lake Bloomington reservoir has worked through the years. The City has an active source water protection program with the McLean County Soil and Water District and in cooperation with producers and landowners in the watersheds to decrease the amounts of nitrates and other nutrients entering our reservoir.        

However, following the drought of 1988-89, the City exceeded the 10 mg/l nitrate nitrogen standard. Both reservoirs were down by billions of gallons of water and when the rains did come again, they filled both reservoirs with high nitrate water. Since there was not as much low-nitrate water already in the reservoirs, the ability to dilute the high nitrate water coming into the reservoirs was limited and the reservoirs were overwhelmed with high nitrate water. The Lake Bloomington reservoir easily exceeded the nitrate standard in 1989 and the Evergreen Lake reservoir was above the nitrate standard for months.        

This experience could happen again. The City simply wants a cost-effective solution, kind of an insurance policy, against this happening again.

The process can be broken into several distinct steps. The first step in the process is to review all available information about the subsurface conditions, such as the location of existing wells, depth to the bedrock, existing aquifers, etc. This is done from existing public records and any research that has previously completed. The Illinois State Water Survey (ISWS) has completed this work.         

The St. Peter Aquifer is generally around 1600 feet deep in this area and residential wells are less than 500 feet deep in the glacial till.  The St. Peter sandstone formation is separated from the private well aquifer by alternating shale and carbonite layers which form impervious barriers known as aquitards.  These impervious layers prevent any change in water levels in the St. Peter aquifer from affecting the water levels in the upper aquifers.  The St. Peter Aquifer is currently used to supply the City of Minonk and the City of Chenoa as well as many Illinois municipalities farther to the north.        

The next step is to drill test well(s) in the areas where additional information is desired on the water quality and production capacity of the aquifer at this location. Because of the depth of the St. Peter Aquifer the test well(s) will be drilled at a production well diameter.  During the drilling process, careful attention is paid to the various layers of material that the drill passes through. The careful recording of this information develops what is known as the well “log”.        

The well will include a welded steel casing pipe from the surface down to the bedrock layers to isolate the shallower aquifers.  The test well is developed like a production well except it is intended for testing purposes to begin with.  The well will be pumped by a test pump which is generally smaller than the actual production pump. The test pumping is designed to determine the reaction of the aquifer to the effects of different rates of pumping over different periods of time and to gauge any potential influence on surrounding wells.

Test Well > Analysis > Process and Pipe Design > Permitting > Construction > Production Well      

The test well(s) will be constructed and tested during the summer and fall of 2017.  Well water quality and capacity testing will be used to design and permit any piping and plant modifications necessary to add the water to production.  Construction of production infrastructure improvements would occur during the summer of 2018.

The idea of the well testing program is to scientifically catalogue the response of nearby wells to either test pumping or production pumping if the City is able to develop a production well. This information will go a long way towards identifying any cause and effect relationship between the City pumping water and any influence on nearby wells.        

Wells that are monitored will have a detailed record of their response to normal weather conditions (amount of precipitation and the wells response to those conditions), and test or production pumping. This record will make it easier to determine the extent, if any of influence from the City’s pumping and may indicate the best course of action the City would take to minimize that influence.        

By not participating in the well testing program, a well owner can still make a claim against the City, but with the lack of information about the historical conditions of the well and the water levels in that well over a variety of conditions, it may be more difficult to relate the cause and effect of the City’s pumping and any influence on the well. That being said however, any claim of influence on a residents well will be taken seriously and responded to promptly.