Scottish Water was fined £6,500 at Alloa Sheriff Court on Monday for allowing chlorinated water to discharge from a reservoir into an Alva Burn, resulting in the death of over 1,000 fish.

Scottish Water pled guilty to causing pollution of the water environment following the discharge of chlorinated water to the Alva Burn.

On 31 August 2013 SEPA received a number of complaints from members of the public regarding dead fish at the Alva Burn. A SEPA Officer attended and found approximately 50 dead fish along a 400 metre stretch of the burn.

A follow-up investigation on 2 September found hundreds of dead fish along a 500 metre stretch of the burn. Scottish Water staff were carrying out repair work nearby at the Alva Service Reservoir and admitted to SEPA officers that the reservoir had been discharging chlorinated water over the weekend and that it was also continuing to do so.

SEPA Officers voiced their concerns that no steps had been taken to neutralise the chlorine in the discharge and that there were no chemicals on site for this purpose. It was only after SEPA’s intervention that chemicals were sourced and the discharge neutralised - however this was after the discharge had stopped.

When SEPA ecologists surveyed the burn on 2 September they found that there were approximately 1,400 dead fish, consisting of juvenile trout and salmonids (young of that year) as a result of the pollution incident.

Discussions between Scottish Water and SEPA revealed that the discharge to the Alva Burn was a result of the Service Reservoir’s east inlet control valve failing to close and although the west inlet valve was shut, it was also not working properly. As a result of the increased, unmitigated flows into the reservoir, there was a constant flow of chlorinated water into the Alva Burn.

Steps were taken by Scottish Water to repair the internal mechanisms within the east inlet, but the west inlet valve was not fully repaired until 6 September 2013.

The pollution event and fish deaths were significant. Chlorine is extremely toxic to fish causing severe and rapid irritation and damage to gill muscles and the mucous membranes around the fish skin. The chlorine levels measured in the burn were over 10 times those which have shown to be lethal to salmonoids.

In addition, the chlorine impacted other life within the burn and dead earth worms, slugs and invertebrates were found. This is significant as such invertebrates are less susceptible to the effects of chlorine than fish and shows that the level of pollution was too high. It will take several years for the natural regeneration of fish stocks

Callum Waddell, SEPA’s investigating officer, said:

“This pollution could have been avoided if sodium thiosulphate had been on site, with appropriate apparatus to treat the water before it was discharged. A wide range of dosing equipment and chlorine monitors are available, but the method being used by Scottish Water at this site was essentially a bucket sized container which would dose the chlorinated water discharge with sodium thiosulphate once. This would not treat any type of continuing discharge, and as such falls far short of the standard required for an incident such as this.

“It is also disappointing that Scottish Water on becoming aware of the discharge did not think it was ’their job’ to consider the overflow and the impact that the discharge could have on the water environment . Staff failed to recognise environmental harm, or to mitigate pollution risks. In addition, sodium thiosulphate was not obtained until after SEPA told Scottish Water to obtain some. Scottish Water staff ought to know what to do in situations like this, otherwise valuable time can be lost."