Evaluation and Impact of a Polluted Stream on the Integrated Management of a Drinking Water Resource: A Case Study of the Middle Vaal River, South Africa

摘要

The Koekemoerspruit is a possible pollution source of the Middle Vaal River, an important drinking water source in South Africa. This case study aimed to establish the water quality of the Koekemoerspruit, to evaluate the impact of the Koekemoerspruit on the Vaal River, and to use this information to identify shortcomings in the monitoring program. Monthly and weekly samples from both the Vaal River and the Koekemoerspruit were analyzed at an accredited testing laboratory based on ISO 17025 for 20 chemical methods. A dataset from 2002 to 2015 was statistically analyzed by means of Statistica software, the Mann-Kendall test and the Sens's slope to determine descriptive statistics and significant trends respectively. The sites' water quality was evaluated by comparison with both national drinking water standards and environmental target water quality objectives. Results indicated that the target water quality objectives for orthophosphate, nitrate and nitrite, and ammonia concentrations were considerably exceeded in the Koekemoerspruit. The drinking water quality of the Koekemoerspruit and the Middle Vaal was noncompliant with South African standards. Color, electrical conductivity, turbidity, sulfate, recoverable cyanide and arsenic at one site posed aesthetic, operational, acute and chronic health risks. Color, mean ammonia and total chlorophyll concentrations displayed significant trends of increase over time and increased drastically after 2012 at the site where water enters the Middle Vaal River. However, the Koekemoerspruit did not seem to have a significant impact on the overall water quality of the Middle Vaal River, except for total chlorophyll concentrations. Moreover, the review and recommendations for optimizing the water quality monitoring program proved that original moni- toring objectives have been achieved. The reviewed monitoring program has consequently been adopted in the water safety plan to address the shortcomings that were identified during this case study.