By Terry Engelhardt
It is a challenging time in America, and the water industry is going to be busy helping authorities struggle with questions about how safe our nation's drinking water is from criminal acts. The people who oversee the more than 54,000 public and private community water systems are at the front lines of public focus on the system, and Americans are looking for reassurance.
How should water professionals approach this challenge, particularly in an environment where resources to make the system more secure are limited? The answers aren't always totally clear, but the best approaches for finding the answers are becoming clearer.
Since long before September 11, researchers at the 55-year-old Hach Company have been helping municipal and private water authorities expand monitoring of the drinking water system, to better reassure the public that they're safe. Hach manufactures and distributes analytical instruments and reagents used to test the quality of water and other aqueous solutions.
As calls began coming in to Hach's customer service lines after the attack on America, the company issued general guidelines - "guidelines that we're glad have been circulated widely, regardless of what water monitoring supplier a public or private water system does business with," said Vice President Jon Chamberlain. In brief, those guidelines included understanding the current values of individual systems, discrete sampling, post-effluent monitoring, and maintaining adequate chlorine levels.
Laboratory and on-line testing are both key to monitoring water quality.
Knowing your current values is what professionals in the monitoring industry all know as baseline monitoring. And that's not properly done by just looking at water for a week. It's done by knowing your water over an extended period, because of seasonal fluctuations and periodic loading of organic and inorganic materials within systems.
"If you look at water today, and let's say for the next week, you won't know your water well enough to have a solid baseline," Chamberlain said. "Water composition may change seasonally, and if you don't know, for example, that you're going to experience manganese loading at a certain time of the year, your monitoring could suddenly show something you might misinterpret as an unnatural intrusion. When possible, on-line continuous monitoring should be employed to capture daily fluctuations in quality due to demand and other normal factors as well as seasonal changes."
When possible, on-line continuous monitoring should be employed to capture daily fluctuations in water quality.
Discrete sampling, meanwhile, involves being able to isolate a sample from the time frame when a deviation occurred. Automatic samplers can be set to take discrete samples periodically throughout the day. With such a sample, you can then perform advanced analysis to know what caused the change detected by monitoring. It also allows managers to isolate the period of time the excursion occurred and thus more easily identify the probable source.
Chlorine is still the most common disinfectant used for killing or inactivating microbiological contaminants. Security monitoring must include chlorine, or other disinfectant, monitoring not only at treatment but also in the distribution system with field or on-line testing equipment. At Hach, experts recommend water systems strongly consider increasing the frequency of chlorine measurements, wherever possible with continuous on-line monitoring.
Post-effluent monitoring, the last of Hach's major recommendations, is extraordinarily important. As professionals know, it is arguable that the greatest vulnerabilities America faces in drinking water security exist downstream of the treatment process. What are the right tests post-effluent? Again, the answer to this has been a constantly changing one as technology advances. But a reliable and respected set of parameters that Hach recommends for monitoring are outlined here. This battery of tests won't tell a manager what has changed in the water if there is a sudden change. But they will identify a sudden change in the water that demands attention:
Total Organic Carbon. On-line and laboratory TOC methods are both effective tests for detecting contamination from organic compounds. As a result of accidental spills or leaks or potentially deliberate acts, industrial organic wastes, pesticides or other toxics may enter the water supply pre- or post-treatment. Such contaminants may not be removed by treatment, or could be introduced post-treatment.
TOC monitoring is a speedy way of determining the degree of organic contamination. A carbon analyzer using an infrared detection system is used to measure total organic carbon. In the test, organic carbon is oxidized to carbon dioxide. The CO2 produced is carried into an infrared analyzer that measures the absorption wavelength of CO2. The instrument will calculate the concentration of carbon based on the absorption of light in the CO2. The amount of carbon will be expressed in mg/L.
Two other test methods that offer organic contamination information are biochemical oxygen demand (BOD) and chemical oxygen demand (COD), but only TOC is readily available in an on-line format.
Turbidity. A unit of measurement (in Nephelometric Turbidity Units, or NTUs) quantifying the degree to which light traveling through a water column is scattered by suspended organic and inorganic particles. Turbidity, in the simplest sense, is a measure of how clear the water is. Post-treatment, a sudden change in turbidity could indicate a routine operational concern (sudden increase in flow due to normal demand) or it could be an introduction of a foreign substance that could be of real concern.
Chlorine Residual. On-line chlorine monitors can perform frequent analysis to ensure that free or total residual chlorine levels are adequate. Chlorine residuals ensure disinfection is maintained. A sudden change in the residual indicates a potential problem which must be investigated. Whether the apparent residual increases or decreases, one needs to determine the cause.
pH, Alkalinity and/or Conductivity. These tests detect a change in water due to a dissolved substance, and serve as an early warning indicator. The pH of a sample of water is a measure of the concentration of hydrogen ions: at higher pH there are fewer free hydrogen ions; at lower pH there are more ions. Substances with a pH of less than 7 are acidic, and substances with a pH higher than 7 are basic. The pH of water impacts the solubility of substances in the water and also the level of such substances as nutrients like phosphorus, nitrogen and carbon and heavy metals like lead and copper. In a well buffered water, however, large amounts of a substance may be added and not affect the pH. Thus, alkalinity of water should be regularly monitored.
In drinking water, alkalinity is most simply defined as the buffer capacity of the water or the ability of the water to neutralize acids. It is a measure primarily of bicarbonate, carbonate and/or hydroxide ions. Certain salts of weak acids, such as borates, silicates and phosphates may also contribute to alkalinity. In one city in the eastern United States, a significant storm event poured several inches of rain into a watershed in just a few hours. The quantity of rain was sufficient to cause dilution of the normally well-buffered (high alkalinity) water without significantly affecting pH. However, the change in alkalinity was sufficient to cause significant operational problems at the water treatment facility.
Many water utilities take conductivity for granted. It is not a parameter that provides much day-to-day operational information. However, that may be its greatest value in monitoring for introduction of foreign substances. Sudden changes in conductivity should be investigated.
These are good examples of why no one parameter or set of parameters will be appropriate for every utility to monitor. Each utility must determine which parameters will be the most useful based on their unique knowledge of their utility and water supply. Companies like Hach Company can serve as a resource to utilities to discuss monitoring alternatives based on local conditions.
Simple test kits also can be useful. ToxTrak, a Hach Company product, is used by wastewater utilities to assess presence of toxic materials (organic or inorganic) that may be present in sewage. Since the wastewater treatment process relies on healthy microorganisms to treat the waste, toxic material can severely affect the wastewater treatment process. This same kit can be used full in monitoring for the presence of toxic materials in the raw water before water treatment and treated water in the distribution system.
Again, experts at Hach do not believe that running these tests solely within the treatment regime will give water managers great security throughout the system. They should be run downstream of treatment in order to ensure that no hazardous materials are introduced after water leaves treatment.
There are plenty of unanswered questions in this field as America moves forward, and innovations are on the horizon that will help water managers protect the people they serve. But America has the technology to improve the safety of our drinking water. To water managers, that may be preaching to the choir - but all Americans are going to be listening to those managers much more attentively in the months and years ahead.
About the Author:
Terry Engelhardt, Market Development Manager for The Hach Company, has worked in water plant operations and been a plant operations trainer for more than 20 years. He is an active member of the American Water Works Association (AWWA) , the Water Environment Federation and the American Filtration and Separations Society. He currently serves on the Rocky Mountain Section Research Committee of the AWWA.
