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Articles in support of small community water and wastewater operators.

Common Distribution System Deficiencies

This article was first published in the Winter 2012 issue of Spigot News, the Ohio EPA's drinking water program newsletter. Many thanks for allowing us to republish it! You may also be interested in the articles Common Source Water Deficiencies and Common Treatment Deficiencies

This article is a continuation of the series on common deficiencies, covering source, treatment and distribution deficiencies. This article covers different aspects of the distribution system, including cross-connection, backflow, depressurization events, water age and infrastructure deterioration. 

Cross-connection
A “cross-connection” occurs in areas of the plumbing system where non-potable water comes in contact with potable water. There are two types of cross-connections: direct and indirect cross-connections. 

Direct cross-connections – the potable system is permanently connected to a non-potable system (for example a submerged inlet pipe for a chemical feed system). 

Indirect cross-connections – there is a potential for a connection of the potable system to a non-potable system (for example, a garden hose connected to an outside hose bid without a vacuum breaker or a bidet with a douche sprayer or jet that fills the bowl below the rim). 

Establish cross-connection control ordinances for municipalities with diligent inspections of new and existing plumbing to prevent possible cross-connection issues. These issues may be identified during a sanitary survey or when real estate is bought and/or sold within the municipality. 

Backflow and Backsiphonage
A “backflow event” is when non-potable water is forced by pressure into the potable water supply due to a direct cross-connection. All distribution systems must maintain a minimum pressure of 20 psig and a 35 psig working pressure during all water demands including fires. Distribution systems that fall below these minimum pressures may experience a backflow event if an overpowering pressure differential is experienced by a competing cross-connection within the system. 

A “backsiphonage event” is when water flows backward in the water distribution system from a vessel or other contamination source because the distribution system has lost, created or reduced pressure. 

Backflow devices (backflow preventers, double check valves, testable reduced pressure zone device, etc.) are required on certain businesses that pose the most threat to a potable water system, but municipalities can require all businesses and homes within their jurisdictions to install and inspect backflow devices every 12 months. Another preventative measure may be to conduct a hydraulic assessment of the distribution system to identify those areas at most risk of a backflow event. Once identified, these areas can be targeted for improvement.  

Depressurization Events
System-wide depressurization events are rare but can occur when mains break or electrical power is lost. When an event occurs, it is strongly recommended to issue a boil alert to those affected. Public water systems can issue a boil alert without consulting Ohio EPA, but boil alerts that affect a major portion of the distribution system must be reported within 24 hours. The municipality may lift voluntary boil alerts after the system is pressurized and the designated operator clears the system for providing drinking water. (Editor's Note: Please see your state agency for reporting requirements that affect you.)

The best way to avoid a depressurization is to keep the water and power flowing. When all power is lost through the electrical grid an alternate source of energy that will run the treatment plant and the distribution system critical components, such as a generator, is an excellent choice. 

Water main breaks are resolved by isolating the break quickly while maintaining water pressure to the rest of the system. This approach works well when all valves are accurately identified and working properly. A valve exercising program identifies the valves and keeps them working correctly in case they are needed. 

Water Age
The issues related to water age are directly attributable to water quantity and quality needs. These vital needs are always in conflict because quantity objectives dictate excessive storage issues while quality strives to minimize storage time while maintaining appropriate disinfectant residuals. Public water systems must strike a balance to minimize water age, effectively limit the formation of disinfection by products (DBPs) such as HAA5s and TTHMs, and keep disinfectant residuals within regulatory limits. 

A Distribution System Optimization Plan (DSOP) offers a mix of options for public water systems to meet quantity and quality standards by optimizing treatment and storage capabilities. OAC Rule 8745-81-78 (Note: This is for regulated entities in Ohio.) details the DSOP requirements and options. For more on sanitary surveys for small water systems, read Preparing for a Sanitary Survey for Small Public Water Systems.

Operator Math Part 3: Continuous Education

This is the third and final installment of our operator math series, and we’re closing with an eye to the future. When the exams are done and you’re thrown back into the stress of daily operations, it’s easy for math skills to get a little rusty.

Here are some great videos, blog series, and more to help you test and strengthen your knowledge of commonly—and not so commonly—used formulas and functions. And many of these resources can also double as exam prep, making them something you can turn to again and again.

Beginner Skills Check

Pinpoint your math weak spots with these five sample problems designed to test your familiarity with unit conversions, and calculations related to area, volume, flow rate, chlorine dosage, and pressure. Developed by the engineering firm Souder, Miller & Associates, this skills check also includes an answer sheet.

 

Problem of the Day

Wastewater Technology Trainers gives you a keep your skills sharp and review at your own pace with their Problem of the Day blog series. Each problem is provided in the form of a downloadable document containing a page or two about working in the wastewater treatment industry followed by the sample problem. Although each of the documents appear similar at first, you’ll find the problems generally begin on the second or third page following a schedule of problems provided on earlier dates. 

Indigo Water Group Math Videos

This series of 13 videos walks through the procedures for solving common water or wastewater math problems. Viewers are able to learn how to solve problems in a step-wise process by following along with the video, which demonstrates and explains each step. The series contains three unit conversion tutorials, five geometry tutorials, three dosing tutorials, one that calculates pump run time to reduce MLSS concentration, and one that calculates VSS loading rate to an anaerobic digester.

CAwastewater.org Math Videos

These 19 HD-quality videos were created by operators for operators. They provide instruction, examples, and advice on math topics covered by the Grads 1-5 exams offered in California.

Big Books of Math Problem Generator

Also from Indigo Water Group, this tool gives you a new set of problems with every click. Each set is provided as an Excel spreadsheet, allowing you to easily work through the solutions at your own pace. Click on the “Math Problem Generator” link at the bottom of the page.

 

Skills Builder

This webpage allows you to test your knowledge of wastewater and laboratory topics using Skills Builder—a set of quizzes provided by WEF as a free resource for operator education. The quizzes incorporate math, safety, and a variety of other topics. Skills Builder provides feedback on your answers as well as references for follow-up study sources. Results are completely confidential and are not recorded. 

 

Industry groups and not-for-profits, including our partners at the Rural Community Assistance Partnership, also regularly host operator math training courses and webinars. Learn about these and other training opportunities with our Event Calendar.   

Operator Math Part 2: Online Tools and Apps

Last week, we shared a few basic tips to help you master some of the calculations used in day-to-day operations. Understanding these and other functions and formulas is an integral part of the job, but working through the problems can be intimidating. Fortunately, there is a large bank of online tools and apps geared toward water and wastewater professionals that puts solutions literally at your fingertips. 

Of course, mobile technology is fast-moving and new tools are being released almost daily. Here are just a few of the ones available at no cost right now.

Online tools

From the Pennsylvania Department of Environmental Protection:

From the Missouri Rural Water Association:

Device apps

From the Missouri Rural Water Association:  

From Georg Fischer AG:

From Thermo Fisher Scientific:

  • Process Water Products – Apple

From Hydromantis ESS, Inc.:

From Pipeflowcalculation.com:

  • Pipe Diameter Calculator – Android

From Fleming Training Center:  

Be sure to check back here next week for the last post in our operator math series. We’ll have resources to help you keep your calculation skills sharp.

Operator Math Part 1: Practical Guidelines

Mathematical calculations can be a challenge for even for the most veteran of water and wastewater operators. The formulas for volume, chemical dosage, filtration, pipe velocity, and other daily problems vary of course, but there are a few underlying guidelines that can help you make sure your answer is correct regardless of the calculation you’re working on. 

This is the first in a three-part series dedicated to operator math. The tips below are adapted from information provided by the South Dakota Department of Environmental and Natural Resources.

  1. Learn what a formula means, not just when it is used. This will help you remember when to use πR2H to calculate the volume of a cylinder instead of 2πRH—the formula for measuring the surface area of a cylinder’s sides.
  2. Use unit labels throughout your calculation to help you easily see whether you need to multiply or divide.
  3. Always convert percentages to decimals.
  4. Convert “inches” to “feet” unless you’re trying to solve a pressure problem. Using “inches” in any other problem will almost always leave you with the wrong answer.
  5. Make sure the units you end with match the problem you are trying to solve. If a volume calculation results in a “square feet” or “square yards” answer, something went wrong along the way.
  6. Trust your suspicions. If the answer doesn’t seem right, check that you used the right formula and units before running the problem again.

For those looking for more detailed and specific instruction, our documents database is a great place to start. Here are some of the resources you’ll find if you search “math.”

Basic Math Handbook

This 24-page handbook is a basic math study tool. It provides formulas for basic geometry, velocity & flow rates, and pressure, force & head, and contains several typical water problems that show users how to apply the formulas in real-world scenarios. 

Formula and Conversion Sheet for Drinking Water Treatment and Distribution

This 1 page document provides conversions and formulas for water treatment & distribution operators in studying for a certification exam. 

 

Chlorine Contact Time Calculations

This 7-page document provides guidelines on how to solve math problems that deal with calculating chlorine contact time. It includes important equations and practice problems with solutions. 

 

Industrial Math Formulas

This 7-page document provides a list of valuable formulas and conversion factors important for wastewater operators. 

 

Intermediate Water Math

This 37-page study guide contains 82 intermediate water math questions. Solutions to the problems are provided at the end of the document. 

 

Advanced Wastewater Math

This 29-page study guide contains 35 advanced wastewater math questions. Solutions to the problems are provided at the end of the document. 

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