Filter media plays a very important role in water treatment plants because it is the fundamental right of every individual to have safe and clean drinking water. In Walla Walla, the members of its City Council voted to change the plans on how its drinking water will be purified in the coming years. The council voted 5 to 2 to for ultraviolet filtration system instead of slow sand filtration system.
The ultraviolet filtration system is expected to cost about $24 million compared to slow sand filtration system that costs $34 million. The cost of construction for the ultraviolet system is projected at $17.4 million with an additional $6.5 million for permits, studies, loan fees, design costs and other expenses. The projected costs for construction for slow sand filtration system are $27.2 million and another $7.7 million for additional expenses.
The new water treatment process will replace the current ozone treatment system that was constructed in 1998 to purify water coming from Mill Creek. This is the source of 89% of the city’s drinking water. The new water treatment filtration system is expected to be completed by 2017.
Going for the less expensive ultraviolet system will allow the city to have the financial capacity to tackle its leaky distribution system which at this point, the city cannot account for 29% of the water in its distribution system. The city’s water system has a water loss issue due to miles of old corroded and leaking pipes. Its utility rates are also pretty high compared to other cities.
The council actually preferred slow sand filtration system because of its ability to filter excess sediment in water but it would result into a major fire in Mill Creek watershed. Studies indicate sediment levels will drop faster than previously anticipated after a fire but this would depend on the severity of the fire.
According to the US Forest service, recovery of the watershed would be from 0 to 5 years and recovery will depend on fire size, post fire weather patterns and mitigation techniques. However, ultraviolet filtration system will not effectively remove cryptosporidium, fecal coliform, biological pathogens and other chemicals which can effectively be dealt with through slow sand filtration system.