Hastings City Council was briefed on the results of the feasibility study in a workshop meeting Jan. 22.

The study, performed by the city's water consultant Stantec, aimed to look into different options for disinfecting the city's water after an E. coli contamination in September. The city began administering low levels of chlorine into the system since.

The study looked at eight different alternatives and analyzed the pros, cons and costs of each alternative.

Council members will continue to meet and discuss the various options. The city intends to hold a public open house prior to City Council making its final decision. No dates or times for the meetings and open house have been decided at this time.

More information on disinfection alternatives from Stantec report

Chlorine gas disinfection

• Can be accurately metered, highly effective, consistent

• Doesn't degrade over time

• Inexpensive compared to some alternatives

• Storing of chlorine gas requires high attention and precautionary measures, meaning higher capital expenses versus other alternatives

Liquid chlorine solution

• This is the current process being used by the city to disinfect the water system

• Storage poses fewer hazards than chlorine gas, causes advantages in retrofitting the existing system

• Lower capital costs than chlorine gas

• Can be accurately metered, but degrades over time. This requires adjustments to be made in dosing of the chlorine to maintain constant disinfection

• A liquid chlorine solution tends to cost more than chlorine gas

Ozone disinfection with chlorine residual

• Higher inactivation of viruses and parasites than chlorine-based disinfectants

• Improved color, taste and odor of water

• Very expensive, higher level of skill and training required to operate

• Ozone systems must be paired with another disinfection system, making them more costly

• Usually desirable for systems with a low-quality water source - Hastings' source water is already high quality

Ultraviolet light disinfection with chlorine residual

• No chemicals added to the water supply

• Requires high-quality source water

• Must be paired with a chlorine-based disinfectant, making it more costly

• Due to water hardness, a prefilter may be required

Shock chlorination disinfection

• This is the process that the city used to flush the water system after the E. coli contamination was found

• City water would be unusable for a period of time

• Does not provide continuous disinfection, therefore does not treat recurring contamination

Filtration

• Physically removes pathogens from water

• Does not provide a residual disinfectant, and would have to be paired with a chlorine-based system, adding costs

• Requires more space than other alternatives. Might require building expansions and increase costs

Inspection and maintenance program

• Does not disinfect the system

• Implements a program that increases the inspection and maintenance of the water system

• The city would enforce inspections of backflow prevention devices more actively

• The city has over 7,800 metered connections, the city would need roughly four full-time staff members to check every connection each year

• Impossible to stop all contamination events with a program like this

Do nothing

• Hastings did not disinfect in the past

• Goes against Minnesota Department of Health recommendations

• MDH would require the city to continuously disinfect if contaminations continue to happen

For more information on the final report from Stantec, visit www.hastingsmn.gov/residents/water-advisory-event-recap/chlorination-in-....