Sanitary Survey Checklist

The U.S. Environmental Protection Agency (USEPA) defines a sanitary survey of a water system as an “…on-site review of a public water system’s water source, facilities, equipment, operation, and maintenance.”  For a community water system, they require that a survey be done at least every three years.  They further go on to identify eight areas that are covered by the sanitary survey:

• water sources
• treatment
• distribution systems
• finished water storage
• pumps, pump facilities and controls
• monitoring, reporting and data verification
• water system management and operations
• operator compliance with state requirements 

Most if not all states will have similar requirements for periodic sanitary surveys covering these same elements as a part of implementing the Federal Groundwater Rule, compliance with which was to have begun on December 1, 2009. 

A large part of any sanitary survey is the inspection of treatment and distribution system equipment to ensure there are no defects that could compromise the quality or reliability of the water being served to the public.  Water systems should take a very proactive approach to these inspections, conducting periodic in-house inspections in addition to the inspections done by state or other regulators.  Many industry professionals think having an operator go to each plant site every day is sufficient, but operators are busy people and may not have time to inspect all the elements involved in a thorough sanitary survey.  And it’s always good to have someone besides the operator conduct the survey; a fresh set of eyes and a different perspective can often turn up issues that may otherwise have gone unintentionally overlooked.

It always helps in this sort of effort to have a good checklist you can work off of that covers all or most of the basic elements to be reviewed.  A checklist will help make sure nothing is missed and that the surveys are conducted consistently between plant sites and over time for the same plant site.  That last point is important to make sure any issues discovered in the survey are being addressed and not resulting in repeat deficiencies. To help me with the sanitary surveys I conduct in California, I went through a long list of references, including the California Title 22 regulations; Department of Water Resources well construction bulletins; and AWWA standards, and came up with my own checklist.  Those are available in this Excel file for you to look over, use, share, or modify to meet your needs.

This checklist also includes some basic health and safety elements, along with some hazardous material and hazardous waste elements that your local CUPA might inspect for.  For each item in the checklist, I've included the reference.   If there is no reference, that means either I couldn't find one, of that the item is just what I feel is a best management practice and doesn't have a regulatory reference.  If you can’t access the checklist for some reason, of if it’s in a format you can’t read, just contact me and I’ll try to provide the information for you in a different way.

I’d really appreciate any feedback you have on this checklist, including any suggestions for improvements or just comments on what you think in general. You can either comment right on this blog, or send me an e-mail.  Hopefully this check list will help keep your water systems running smoothly.

A Chloramine Primer

In my last post, I wrote about using the power of chlorine contained in sodium hypochlorite to inactivate microbial contaminants; give residual protection in the distribution system; and oxidize inorganic contaminants.  This time, we’ll look at using another chlorine containing compound, monochloramine, to do the first two of those three jobs.

The use of monochloramine as a drinking water disinfectant residual is nothing new; Denver, Colorado has been using it since 1917.  Monochloramine has a chemical formula of NH₂Cl.  It’s created by mixing the correct ratios of chlorine and ammonia, usually somewhere in a range from 3:1 to 5:1, chlorine:ammonia by weight.  The chemical reaction, using our old friend sodium hypochlorite for the source of the chlorine, looks like this:

HOCl + NH3 → NH2Cl + H2O

The reaction of monochloramine is also very dependent on the pH level.  Where a typical pH in any free chlorinated system is usually around 7, chloraminated systems usually have a pH closer to 8.

Monochloramine, also referred to as just chloramine, does not have the same inactivation or disinfecting “power” of free chlorine, due primarily to the fact that it is not as strong an oxidizer.  Some sources estimate that monochloramine is 200 times less effective as a disinfectant than free chlorine.  For that reason, chloramine levels need to be higher than free chlorine levels.  Many systems that run free chlorine often maintain a residual level of 0.5 to 1.0 mg/L, but chloraminated systems often run at 2.0 to 3.0 mg/L total chlorine. 

Without very careful monitoring of monochloramine formation, chloraminated systems can also have significant taste and odor issues.  This can result from the formation of di-chloramine (NHCL2) and tri-chloramine (NCL3), compounds similar to monochloramine but with additional chlorine atoms added.  These compounds have a very strong chlorine taste and odor.  Their formation is generally tied to an incorrect chlorine:ammonia ratio.  Specifically, there is too much chlorine for the given amount of ammonia.

Monochloramine

In any chloraminated system, there is also the presence of some level of ammonia.  The more closely controlled the process of chloramine formation, the less ammonia should be present.  But even with low levels of ammonia, under the right conditions, certain bacteria can use that ammonia for a food source and produce as by-products both nitrite and nitrate in a process called nitrification.  Nitrite in particular can become a problem because the Maximum Contaminant Level (MCL) is so low, only 1.0 mg/L.  Once the nitrification process gets established, it will also cause the chloramine residual level to drop, allowing for the formation of hard to treat biofilms in the distribution system.

With all of these issues with the use of chloramines, why would anyone want to use them?  Under the right conditions, a chloramine residual will last longer in the distribution system than a free chlorine residual.  If you have a very large distribution system, or very long transmission lines, using chloramines can provide better protection.  Another common reason for the use of chloramines is the fact that they can result in the formation of fewer disinfection by-products, particularly trihalomethanes (THMs) and haloacetic acids (HAAs).  The implementation of the Stage 2 Disinfectants and Disinfection Byproducts Rule resulted in a great number of utilities that could no longer meet the MCLs for THMs and HAAs like they could under the Stage 1 Disinfectants and Disinfection Byproducts Rule.  As a result, many of these utilities switched from free chlorine to chloramination.  Chloramines can also combat biofilms better than free chlorine, as long as nitrification is kept under control.  Free chlorine can’t penetrate through the outer layer of the biofilm very well, while monochloramine does a better job, resulting in increased inactivation of the organisms within the biofilm.  Since free chlorine and monochloramine each have their own pluses and minuses when it comes to combating biofilms and inactivating microorganisms, many utilities that routinely chloraminate make a yearly switch to free chlorine for several weeks to try and utilize the benefits of both types of disinfectants.

For a more detailed discussion of free chlorine, chloramines, and related disinfection topics, please check out these additional sources:

·          HACH has a very good discussion of all these topics located here - http://www.hach.com/DisinfectionSeries

·          HACH also has a very nice video on You Tube – http://www.youtube.com/watch?v=3rXZg6VDVRQ

A Bit About Sodium Hypochlorite Chemistry

In this post we’ll take a look at one of the major chlorine based disinfectants that we are most likely to deal with and how it reacts when we add it to water.  This will involve a bit of chemistry, but don’t be afraid.  It won’t hurt, I promise!

Sodium hypochlorite is a very commonly used disinfectant in drinking water systems.  The chemical formula for sodium hypochlorite is NaOCl, which means it has one sodium atom (Na); one oxygen atom (O); and one chlorine atom (Cl) all bound together.  This chemical is commonly purchased as a concentrated solution that contains about 12% sodium hypochlorite by weight.  So if you took 1 gallon of the stuff, which weighs about 10 pounds, then 1.2 pounds would be sodium hypochlorite, another 2 ounces would be sodium hydroxide (NaOH), and the rest would be water.

In a typical situation which we will use as an example, this concentrated chemical would be diluted.  It would be fed at a controlled rate into water being pumped from a well before it goes into the distribution system.  In this situation, the sodium hypochlorite reacts with water and forms two new chemicals: Hypochlorous acid (HOCl) and sodium hydroxide (NaOH).  The equation looks like this:

NaOCl + H₂O → HOCl + NaOH

Sodium hydroxide is a base, meaning it will raise the pH of the water.  This is the opposite of an acid, which lowers pH.  pH, without getting too technical, is just a scale to measure how acidic or basic something is.  Hypochlorous acid in water partially comes apart, or dissociates, into ions, which are just atoms or molecules that have an electrical charge.  In this case, it dissociates into a hydrogen ion (H⁺) and a hypochlorite ion (OCl⁻), like this:

Hypochlorite anion

HOCl → OCl⁻ + H⁺

The hypochlorite anion (a negative ion) that results is what we are after.  Because of its negative charge and the oxygen atom hanging off one end, this ion is very reactive and can cause changes to many other molecules it comes into contact with.  It is known as a strong oxidizer, which just means it can force changes to other atoms or molecules by either adding an oxygen atom to them, or by stealing electrons from them.  So what does that mean in more practical terms?  Let’s look at the function of the hypochlorite ion as a disinfectant – how does it actually kill bacteria?  It might surprise you to know that no one actually knows for sure.  There are lots of theories and the reality is probably a combination of some or all of them, but for all of our scientific prowess we still aren’t exactly sure.  Some of the ways in which it has been proposed that it works is by punching holes in the bacterial cell wall and membrane, causing too much water to flow in and other cell contents to flow out; slicing up the cell’s DNA; or inhibiting glucose metabolism, causing near instant starvation.  Sounds brutal!

Sodium hypochlorite is one way of using the oxidizing capabilities of chlorine based chemicals to, among other things, help keep our drinking water free of microbiological organisms.  Next time, we’ll take a look at chloramines and see how they perform a similar function.