WQ1302: Ground Water Ammonia: A Minnesota Case Study
Speaker: David Schultz, PE
A Minnesota study found higher levels of ammonia and total organic carbon than expected in groundwater sources. During this session, we will identify the issues ammonia can cause in water distribution systems and develop a free ammonia management, disinfection, and/or nitrification control strategy to minimize undesirable consequences caused by these contaminants.
Minnesota Department of Health (MDH) has detected in Minnesota’s water systems ammonia concentrations as high as 8 mg/L. Since the mid 1990s, MDH engineers have speculated that many MN water systems may be affected by high levels of ammonia in their drinking water, causing problems such as nitrification, taste and odor, loss of chlorine residuals and microbial influenced corrosion in their water distribution systems. As Minnesota is the State with the highest number of copper action level exceedance, MDH has conducted many studies to understand and mitigate Minnesota’s copper corrosion problems. The Ammonia Study was conducted to:
1. understand the extent and impact of ammonia on Minnesota’s community water supplies and its effects on disinfection;
2. evaluate influence of free ammonia on distribution systems’ bio-stability;
3. associate Minnesota’s copper corrosion problems to the presence of free ammonia in water distribution systems or nitrification; and
4. seek solutions/strategies to manage ammonia in water and to control nitrification.
The study found statewide, wide spread, occurrences of Ammonia and higher than expected levels of TOC in Minnesota groundwater sources. Evidence of chlorine residuals loss due to the presence of free ammonia was observed in the majority of systems, and evidence of nitrification/de-nitrification was observed in water distribution systems investigated.
The study identified areas of concerns and problems need to be addressed relating to ammonia in groundwater. It is disquieting to realize the assumption that DBPs are more of a concern to the surface water supplies may not hold true in Minnesota (and possibly in other states). Since ammonia is an unregulated contaminant by the Environmental Protection Agency and groundwater systems are not required to monitor for TOC, there are limited data available to states on ammonia and TOC. Since both ammonia and TOC cause compliance concerns for the Disinfection By-Protect Rule (DBPR), Total Coliform Rule (TCR), and the Lead and Copper Rule (LCR), understanding their occurrence and fates is essential in developing a free ammonia management, disinfection, and/or nitrification control strategy to minimize undesirable consequences led by these contaminants.