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Posted on: March 26, 2021

Drinking water TOC treatment technique not met for City of El Dorado

Water Systems with surface water and/or groundwater under the influence of surface water treatment plants are required by federal rule to monitor the water every month for Total Organic Carbon (TOC), which is a disinfection by-product precursor. Compliance is determined each calendar quarter by a 12 month running annual average (RAA).  For TOC, we are required to achieve a RAA removal ratio of at least 1.00 every quarter.  At the end of the 1st Q2020 and 2nd Q2020 samples show our water system’s TOC removal ratio RAA was 0.90.    

Even though this is not an immediate risk, as our customers you have the right to know what happened and what we did to correct it.  This is not an immediate risk and your water is safe to drink.  If it had been, you would have been notified immediately.  Total Organic Carbon (TOC) has no health effects. However, TOC provides a medium for the formation of disinfection by-products trihalomethanes (THM’s) and haloacetic acids (HAA5’s). Drinking water containing HAA or TTHM in excess of the Maximum Contaminant Level (MCL) may lead to adverse health effects, liver or kidney problems, and may lead to increased risk of cancer.  The Maximum Contaminant Level of THM’s is 80 ppb and for HAA5’s 60 ppb. El Dorado’s drinking water is well below these MCL’s with THM and HAA5’s both around 30 ppb, and have been well below the MCL’s for as long as these contaminants have been monitored. 

Several circumstances led to us not being able to meet the TOC removal regulation.  First, an all-time record setting rainfall during the fall of 2018 and the spring/summer of 2019, caused El Dorado Lake to experience high concentrations of Naturally Occurring Organic Matter (NOM) flowing into the Lake.  Prior to this large inflow of NOM, the Lake was at a low elevation which encouraged vegetation growth along the shorelines.  As lake levels increased and flooded green shorelines, the vegetation decayed releasing natural organic matter into the water, further elevating TOC levels.  The El Dorado Water Treatment Plant took all the necessary steps to reduce TOC levels by increasing dosages of Sodium Permanganate (an oxidant) and activated carbon (for adsorption), but we could not remove all the TOC.  The TOC levels are naturally coming down now, which has allowed us to come into compliance as of the 3rd Q2020. 

The city’s drinking water is safe to drink and TOC has no health effects.  For more information, please contact Brett Perry at (316) 322-4441, or by mail at 220 E. First, El Dorado, KS 67042.  Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in apartments, nursing homes, schools, and businesses). You can do this by posting this notice in a public place or distributing copies by hand or mail.

This notice is being sent to you by the City of El Dorado, Federal ID# KS2001511

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