By Russell Ford CH2M HILL Vice President, Senior Principal Technologist, and Deputy Global Service Leader for Drinking Water Infrastructure
As I was working during Drinking Water Week, I got to thinking about the drinking water regulations that are upcoming. I still run across utilities that are working on getting into compliance with the Stage 2 Disinfectant/Disinfection By-Products (D/DBP) Rule. The most important change in the rule is that utilities are required to measure total trihalomethanes (THMS) and haloacetic acid (HAA5) at specific locations within the distribution system that represent the worst case. This new sampling is called the locational running annual average (LRAA). The previous approach allowed for averaging over the entire distribution system for running annual average. In the end, the Stage 2 D/DBP Rule is geared toward protecting our drinking water, so it is really a good thing. The compliance dates for the new rule are:
-Systems serving greater than 100,000 persons – April 1, 2012
-Systems serving between 50,000 and 99,999 persons – October 1, 2012
-Systems serving between 10,000 and 49,999 persons – October 1, 2013
In addition, utilities that have determined that they need to make major capital improvements can petition their primacy agency to get a 2-year extension before they have to start compliance monitoring.
Another little surprise in the regulation is something called an Operational Evaluation Level (OEL). The OEL requires utilities to “estimate” the worst case DBP formation once they have three quarters worth of compliance data and to do this every quarter thereafter. The purpose of this OEL is to catch any potential trouble areas before they become compliance trouble spots. This is a good approach, but utilities need to stay on top of this data and if the OEL anticipates a problem, the utility will need to provide the primacy agency with an action plan to address this before the next compliance sampling date.
The good news to all of this is that DBP compliance can usually be achieved with simple methods such as replacing pre-chlorination with another preoxidant such as potassium permanganate (KMnO4) or chlorine dioxide; optimizing coagulation for organics removal by either switching coagulants or utilizing acid or base to obtain the proper coagulation pH without using excessive amounts of coagulant; and/or optimizing the distribution system to reduce the residence time (i.e. getting those distribution tanks to turnover on a more frequent basis).
When those simple methods are not enough to achieve the goal, then there are other options such as the use of Ozone, Ion Exchange (MIEX and/or Anion Exchange), biologically active carbon, granular activated carbon, High Pressure Membranes (Nanofiltration or Reverse Osmosis). The implementation of these processes are usually paired or with other improvements to provide the lowest life cycle cost for the utility.
One common element is to consider changing the residual disinfectant in the distribution system from chlorine to chloramines. This will usually result in DBP compliance, but is also important to note that this implementation requires additional steps. You must consider the distribution system as a unit process and develop specific operating procedures to halt nitrification within the distribution system. Once again, the good news is that many systems have successfully done this with great success.
So in the end, there is still time to investigate DBP compliance issues and implement a simple solution. However, if the solution requires a major capital improvement, then additional planning, testing, permitting, design and construction must be incorporated into the implementation schedule.
Dr. Russell Ford has more than 23 years of experience in developing, evaluating, and designing treatment processes to remove a variety of contaminants from drinking water.