ENVIRONMENTAL IMPACT IDENTIFICATION AND POSSIBLE MITIGATING STRATEGY FOR BORALESGAMUWA LAKE

Abstract

The degradation of lake environments and resources is now a world-wide issue.Efforts urgently have to be made to restore the friendly coexistence of lakes andhumankind through appropriate management of lake/watershed systems to assurethe sustainable use of their resources.ln this project the Boralesgamuwa Lake,which is one of the most distinctive landmarks within the town limits ofMaharagarna had been studied. The rapid urbanization of the town has led to theenvironmental deterioration of the lake exacerbated by numerous out fallsdischarging nutrient rich water into this stagnant body of water.

Objectives of the study were identification of sources of polluting theBoralesgamuwa lake, significant impact of pollution, and designing anddeveloping a suitable mitigating strategy. There isn't any water quality monitoreddata relating to the Boralesgarnuwa lake. During this study, pH, conductivity,temperature, DO, BOD, COD, nitrate, phosphate and the coliform levels of thelake water were examined & also several sources of polluting the lake wereidentified. About 30 surface water samples were analysed during Feb. 2000 toJuly 2000. Heavy metal pollution of the lake was also examined.Physicochemical characteristics of the Boralesgamuwa lake water showedsignificant site-specific & time-bound variations during the study period.

The phosphate concentration in surface water close to wastewater dischargingpoint of one garment factory is comparatively high. During the month of Aprilphosphate concentration at that point was comparatively low, because at that timethe factory was not working. At the point, where the urban waste water drainageline is entering the lake, the nitrate concentration is fairly high. Most of the lakesurface is covered with macrophytes and with very high amount of the waterhyacinth (Eichorniai. The coli form count of the lake is also very high. TheMPN (Most Probable Number) is more than 1000 per 100 ml for the most of thelocations. The faecal coli form count is also very high. Unauthorized settlers andenchroachments are common factors of the lake reservation.

The industry concerned is already doing primary treatments and they aredischarging their effluents according to the CEA standards. But the problem isstill there. There are no industrial effluent standards for phosphate in Sri Lanka.Proposed mitigating strategies for these negative impactsl.For phosphate reduction

1.1Chemical treatment

1.2Biological treatment

2.For urban waste water

2.1 A central waste water treatment plant should beinstalled

3.For reduction of faecal contamination

3.1 A sewerage system should be designed

4.Unauthorized settlers and enchroachments

4.1 Unauthorized settlers andenchroachers should be resettled.