Total Trihalomethanes (TTHM)

2019 2nd Quarter Testing Results - NO Violation

Why TTHM tests are required

The Texas Commission on Environmental Quality (TCEQ) requires all municipalities which source their drinking water from surface water i.e. rivers, to test for Trihalomethanes (TTHM). The samples are collected and tested quarterly throughout various locations in Kerrville. 

The sampling locations are selected as a result of a series of tests conducted from 2006 to 2013 in which TCEQ identified 4 locations where the City of Kerrville would be required to test TTHM levels. The locations were selected based on their distance from the Water Treatment Plant. Locations further away from the Water Treatment Plant have an increased likelihood of experiencing elevated TTHM levels. 

What is TTHM?

When chlorine is used for the disinfection of water, it reacts with organic matter in the water and creates a by-product. This by-product is called Total Trihalomethane and is the most common by-product formed during the disinfection process. 

Where else can you find TTHMs?

They can be found in swimming pools, soft drinks, coffee, tea, and some foods. TTHMs enter the body through inhalation during bathing/showering, skin contact during swimming and during food or drink consumption. 

What are the maximum contaminant levels and who establishes them?

The current maximum contaminant levels for TTHMs are .080 milligrams per liter (mg/L) which is equal to 80 parts per billion. These levels are established by the U.S. Environmental Protection Agency (EPA) and regulated by the Texas Commission on Environmental Quality (TCEQ).

What causes high TTHM levels?

Heavy rainfall can often introduce large amounts of organic matter into the water supply. When this organic matter reacts with chlorine during the disinfection process, it creates TTHMs. Additionally, when drought conditions and extremely high temperatures exist, the water becomes warmer than usual and requires more chlorine be used for disinfection.

What is the city doing to eliminate TTHMs?

In April 2017, the Kerrville City Council directed staff to move forward with the "Water Treatment Plant Trihalomethane Reduction Project". As the first step in the process, the council approved an engineering contract in the amount of $287,000 to study the issues and design improvements to reduce TTHMs. A project design has been completed and accepted. The project will include constructing granular activated carbon filters at the water production facility. The filters will remove any organic carbon from the drinking water prior to the sending it to distribution. This, in turn, will eliminate TTHM formation. Phase two is the construction phase. The winning bid was accepted from Dowtech Specialty Contractors, Inc. for $4 million. The construction began July 1st,  2019 and should be completed February 2020. 

However, even though the City's efforts should eliminate TTHM formation, TCEQ will still require testing as long as any municipality sources drinking water from surface water.