Keeping Ahead of Groundwater Quality Questions
by Robert D. Libra
|Emmetsburg Municipal Well #4 is 35 feet deep and taps gravel deposits along the Des Moines River valley. The well has been sampled periodically as part of a long-standing cooperative program with the U.S. Geological Survey. Photos by Dave Conell (USGS).|
Results from this cooperative monitoring network are a key part of our knowledge about the state’s groundwater quality. They allow for prediction of natural and contaminant-related water quality of our major aquifers, and thus let us know whether their quality will support various uses. Is the water too hard for a boiler, or does it have too much sulfate for supplying a dairy? Would we need to purge the iron and hydrogen sulfide to make it palatable? Will the water meet public drinking water standards? Will the quality pose odor problems if used with an anaerobic lagoon?
Many such questions are known to the water supply industry. However, new questions always arise, and one of the most important uses of groundwater monitoring information is to supply answers for questions that haven’t been asked before.
For example, nitrogen in the form of ammonia may undergo troublesome reactions during some types of water treatment, and even have a negative effect on the treatment process itself. In the past, water supply wells were rarely analyzed for ammonia, based on the “conventional wisdom” that ammonia doesn’t occur in significant amounts in groundwater, unless it is grossly polluted. When a water supply did show measurable ammonia, the search was on for the contamination source. The usual suspects, such as nearby septic systems, leaking sewer lines, or livestock manure, would be rounded up, examined, and typically found innocent. Information from the groundwater monitoring was used to explain the situation. Ammonia does indeed occur naturally in high enough concentrations in some groundwaters to cause treatment problems. This occurs fairly commonly, and predictably more so in some aquifers than others. There is no contaminant source to search for.
Other such questions are being raised. Researchers are coming to realize that relatively low concentrations of phosphorus impact stream and lake environments, so we need to assess the natural background levels in groundwater feeding streams and lakes. Also, there has been a long discussion about lowering the drinking water standard for arsenic. What would be the impact on Iowa water suppliers if this happens? Beyond answering the questions we know about, we need to continue keeping our monitoring efforts a step ahead – collecting answers before the questions are asked.