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Update: Despite dredging Lake Decatur, city to spend millions to increase water supply

On Monday, September 26, the Decatur City Council held a study session to receive updates on water projects and discuss additional water supply options.  Below is an update to a previous post.  It has come to my attention that there were some inaccuracies in the original post, and I apologize.   

The city of Decatur will spend over $160 million to dredge Lake Decatur when interest, fees, and the costs of a previous dredging attempt are incorporated into the costs.  Despite dredging, the city does not have the water supply it needs to withstand the most severe drought.  This reduced drought resiliency appears to be a result of a water supply gap that was not fully overcome by dredging, a 2022 agreement with ADM allowing it to sell/give away water, and additional future water projects. 

After completion of dredging, the city of Decatur continues to have a supply gap of 107 days (3.1 billion gallons of water needed in the event of the most severe drought) assuming a lake level at a minimum elevation of 607 ft (data from Intera Inc. December 2021 memo).  In August 2022, the city council approved an amended agreement with ADM that allows it to sell, transfer, or give away a portion of the 24 million gallons per day (mgd) of non-potable water from Lake Decatur that it is allocated (the average demand of ADM’s North Water Treatment Plant in 2017 was 15.9 mgd).  Thus, in theory, ADM could sell, transfer, or give away 8 mgd of non-potable water.  If ADM fully uses its allocation, the supply gap for the lake increases from 107 to 156 days (5.4 billion gallons needed).  It was also revealed at the study session that industrial customers could require an additional 7-12 mgd in the future, a net increase of up to 4.1 mgd assuming ADM fully utilized its 24 mgd allotment resulting in a further increase in the supply gap of >179 days (>6.3 billion gallons needed). 

To increase water supply, the city of Decatur is proposing to use the former Vulcan Pit, Lake Toko, and the DeWitt Well Field which will substantially if not completely eliminate the supply gap if ADM were only using 15.9 mgd.  However, if the city and its industrial partners require more water (i.e., projected 7-12 mgd), the city will have to develop new water sources to be drought resilient.  Moreover, depending on whether the water comes from the city’s South Water Treatment Plant (potable water) or ADM’s North Water Treatment Plant (non-potable water) will determine whether a new water main needs to be installed in the NE quadrant of the city.  Collectively, these projects will likely cost tens of millions of dollars.

It is important to note that while the city will spend over $160 million to have dredged Lake Decatur, and millions, if not tens of millions, more will be spent with additional water supply and distribution projects, Lake Decatur continues to fill with sediment (albeit at a slower rate than during the first part of the lake’s history).  According to the report “Lake Decatur Watershed Management Plan & Initiative – Long-Term Strategy”, the majority of sediment settling in Lake Decatur originates from within Macon County.  Thus, the final resting place for the best farmland on planet Earth continues to be the bottom of Lake Decatur, and our taxpayers will continue to pay millions of dollars to increase water supply to a lake whose water capacity is continuously shrinking. 

The study session memo provided to the city council claims that “Providing sufficient water, sewer, broadband and transportation access … can be expected to bring more investment to Decatur, add to the population over time, and thereby improve city revenues.”  While there is no doubt that significant industrial investment has been made in recent years, the city’s population has declined every year since dredging began, the labor force has declined even faster, and water rates are increasing substantially.  It will be incumbent on city staff to accurately estimate water demands.  Incorrect assumptions could result in tens of millions of taxpayer dollars being spent unnecessarily. 

Horn for Decatur
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