Arendal municipality has used Lake Rore as a water source since 1973. The water is taken from a depth of 30 m. The quality of the water is fairly good, but the water is very soft and the acidity is low (pH-value about 5,5). This causes that the water is aggressive towards common pipe materials as iron, cement, and copper.

The old treatment plant included filtering of the water, disinfecting with chlorine and a reduction of acidity by adding lye, so that the pH-value was raised to about 8 in the outlet water from the plant. This has satisfied the previous demands from the government.

Recently one has realized that such a treatment is not good enough to avoid corrosion in the water pipes. In addition, rusts and mud was found in the pipes. This led to extensive cleaning procedures of parts of the network to avoid problems with discolored water for the consumers.

To improve the water quality, Arendal municipality built a new water treatment plant in 1998. The purpose is to give the water a quality so that corrosion of the pipe materials is reduced to a minimum, and to secure the subscribers drinking water which satisfies the new quality requirements imposed by the governmental health authorities.

New water treatment plant at Rore.

The new treatment plant is located close to the old plant near Rore. The old water intake is still used, and the water is pumped into the new plant from the existing intake chambers.

The water is then filtered through several cubic meters of crushed marble, which is placed in eight parallel filter reservoirs. The lime in the marble will dissolve in the water. The calcium content in the water will then increase, so that the water will become less soft. At the same time the pH-value increases to 7,5-8,5. To make the releasing of the crushed marble adequate, carbonic acid is added to the water on beforehand.

The result is a drinking water which is considerably "nicer" towards pipe material, and the quality of the water is a lot better throughout the network than before.

As the quantity of marble is reduced, new masses are added a couple of times a year. Periodically, the marble reservoirs are cleaned by retrograde pumping of water.

The filtering through the crushed marble also reduces the amount of microscopic particles from the raw water. In addition, the content of aluminum in the drinking water will be reduced.

Finally, the water is added small amounts of chlorine for disinfection. For the future, the new plant is prepared for disinfection with ultra violet light.

After treatment the water is pumped to the consumers via new pumps in the plant.

Facts on Rore water treatment plant:

• Building ground area: 470 sq. metros
• Construction costs: 20 mill.kr.
• Costs per liter: 0,05 øre/liter
• Finished: 1998
• Subscribers: 35 000
• Maximum capacity: 44 000 subscribers
• Annual production: 7,5 mill. cubic meters
• Production: 240 l/s
• Amount of marble: 760 tons
• Filtration area: 134 sq. meters
• Responsible for operation: Arendal municipality

What is obtained with the new plant?

• An increase of the pH-value to 7,5-8,5 without adding lye.
• An increase of the alcality to 0,6-1,0 mmol/l. This ensures that the pH-value is maintained throughout the network.
• A content of calcium is increased to 15-25 mg/l, and thereby a slight increase of the hardness of the water.
• A reduction of the aluminum content.
• Increased lifetime of the network by reducing corrosion problems.
• Reduced dissolvement of heavy metals from the water pipes and household installations.
• Less mud and rusts in the pipes, and thereby considerable fewer problems with discolored water.
• Less need for cleaning of the pipe network.
• A stabile and good water quality that satisfies the demands of the government for drinking water.
• Increased stability of water supply

OTHER WATERWORKS.

Kilsund waterworks.
This waterworks take water from Lake Vindkoll. The quality of this water is not good enough to fill the present requirements of drinking water. Kilsund waterworks delivers water to about 1.000 subscribers. When a new pipe of supply from the Rore Waterworks is established, the Kilsund waterworks will be shut down.

Strengereid waterworks.
This is run and used by Norton A/S, a metallurgic company.

THE PIPE NETWORK.
In 1998 the pipe network was 361 km long. There are 21 pump stations for pressure improvement, in addition to several water basins located on ridges. The Steinsaas water basin is the largest one, with a volume of 16.000 cubic meters.

Key figures of the network:
Length of main distribution pipes:

• Pipe length Rore-Hoelen: 13,2 km.
• Pipe length Hoelen-Steinsaas: 12,0 km.
• Pipe length Steinsaas-Saltroed: 6,6 km.