Drinking Water Protection: Waterline, Spring 2013 - EH: Minnesota Department of Health
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Stew Thornley

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Mammoth Main Break in Minneapolis

Minneapolis water main break - January 2013

Winter is a season for water main breaks. But the break in downtown Minneapolis the afternoon of Thursday, January 3, 2013 was distinctive for two reasons: though it happened in winter, it wasn’t the result of the stress of cold weather; in addition, the break occurred in a 36-inch pipe, bringing an unprecedented gusher with effects felt through a large portion of the city. Minneapolis distribution foreman Mark Ebert said it was the largest main break he has seen during his 33 years with the city.

The break occurred at a construction site at 2nd Street North and Hennepin Avenue when a private contractor ruptured the water pipe. The city lost more than 14 million gallons of water, much of which flooded streets down to the river and submerged a number of vehicles in the garage of the nearby post office. The cost of the lost water itself was $65,000.

Minneapolis Water Works crews followed procedures for isolating the area, but because of the size of the main, it took more than two hours to close the valves. Valves farther from the site had to be closed first to reduce the flow in the area of the break. By late afternoon, the affected area was confined to three blocks between 2nd Street and Washington Avenue and between Hennepin Avenue and Third Avenue North.

As distribution crews closed valves, others checked water pressure in the surrounding area, concerned that a drop below 20 pounds per square inch (psi) could cause back-siphonage issues. Although pressure dropped in buildings near the break site, the city confirmed that pressure had stayed above 20 psi in the nearby Federal Reserve Bank and Hennepin County Central Library.

Waterworks officials consulted with the Minnesota Department of Health (MDH), and the city issued updates on its web site and on Facebook while also communicating with local media. Workers delivered notices to buildings in the affected area with orders not to use the water.

By the weekend the city restored water to the three-block area with temporary lines from fire hydrants while crews continued to fix the broken pipe (shown above). Distribution crews bolted a pair of sleeves over a longer section of new pipe to replace the damaged portion.

The city flushed and disinfected the lines in the affected area and worked with MDH engineers Ike Bradlich and Lucas Martin to take bacteriological samples and to check the water for possible contamination from volatile organic chemicals. The samples came back clean. Within a week of the break, Minneapolis had restored all water service to the area and confirmed that the water was safe to drink.

The hole in the 36-inch water main
The hole in the 36-inch water main (above). A new pipe is lowered into place (below).
A new pipe is lowered into place

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Plate Settler Drops in on Eagan

Plate Settler being lifted into Eagan water plant
Having installed a plate settler in its North Water Treatment Plant in 2005, the city of Eagan recently added another to its South Plant. The challenges for installation and implementation were different, but newer technology and learning from the first experience have made the process at the South Plant a success. See below, Eagan Fills Its Plates, for the full story.

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John Blackstone Dies

John Blackstone
John Blackstone, a project engineer for St. Paul Regional Water Services (SPRWS), died of cancer November 20 at the age of 68. Blackstone had worked in the water industry for many years and came to St. Paul from the U. S. Army Corps of Engineers in 2004. “He had sterling recommendations,” said Dave Schuler, head of the engineering division at SPRWS, “and he lived up to his billing.” Blackstone worked on large projects for the utility, including meter replacement and lake reservoir restoration. “He was a master juggler [of projects] and a great communicator,” said Schuler. “You start everything with building relationships, and I don’t think I ever introduced him to someone he didn’t already know.” Blackstone is survived by his wife, Linda Kjerland, three children, and four grandchildren.

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MDH Updates and Reissues Press Release on Shady Sales of Water Treatment Devices

In response to continuing reports of deceptive and aggressive sales tactics by some sellers of home water treatment equipment, the Minnesota Department of Health has updated and reissued a press release, advising homeowners to beware of false claims, deceptive sales pitches, and scare tactics.

MDH had put out a press release in 2010 about the topic. Since then, police in Richfield alerted residents after some had bottles left at their doors with a request for a water sample. One Richfield resident, after providing a sample, said he was visited by a company’s representative with “an aggressive sales pitch for a treatment system costing more than $6,000 and had difficulty getting the salesman to leave.” Falcon Heights officials advised their citizens to call 911 if they saw anyone dropping off sales kits.

A few years ago MDH got a report of a sales rep telling a homeowner in the northern suburbs that he was working with the state health department, which had grant money available for homeowners needing home treatment equipment. This claim (which was false) led the sales rep to try to pressure the homeowner into a quick decision based on the possibility of the grant money no longer being available in the near future.

In the press release MDH outlined some of the sales tactics used by some companies, explained the standards that are used for testing public water systems and that residents can be confident in the safety of their water unless told otherwise by their utility, and made recommendations for those considering the purchase of a home system.

The press release resulted in a number of stories, including in the St. Paul Pioneer Press and on Minnesota Public Radio and the Minnesota News Network.

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School Water Poster Contest Underway

The Minnesota Department of Health is working with H2O for Life, Dow Water and Process Solutions, Bongard Corporation/Elkay, and the Minnesota Section of American Water Works Association on a contest within Minnesota schools to have students develop posters about drinking water.

Funded by grants from the participating organizations, a bottle filling station will be awarded to the schools of the students who produce the winning posters. Four filling stations will be awarded, one each for the winning entry from an elementary school, middle school, and high school as well as for the best overall poster. In addition, a $50 check will be awarded to the four student winners.

image of poster
Funded by grants from the participating organizations, a bottle filling station will be awarded to the schools of the students who produce the winning posters. Four filling stations will be awarded, one each for the winning entry from an elementary school, middle school, and high school as well as for the best overall poster. In addition, a $50 check will be awarded to the four student winners.

The winners will be announced in conjunction with World Water Day March 22 and will also be celebrated during Safe Drinking Water Week in May.

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Eagan Fills Its Plates

Eagan South Water Treatment Plant

Plate settlers continue a new trend in water treatment optimization processes. “Once the domain of the wastewater industry as a means of reducing the footprint required for clarification and solids consolidation,” said Todd Butz of Treatment Resources, Inc. of Minneapolis, “the process has found a new niche as an efficient method of recovering backwash water that is benefitting more and more water treatment plants.” Water conservation is one reward, allowing treatment plants to recover more than 95 percent of their wastewater, but the benefits go beyond that.

“Beyond savings on sewer charges, the bigger impact is operational flexibility and the ability to more quickly turn around a sequence of filter backwash events,” said Steve Gilberg, the water production supervisor for the city of Eagan, Minnesota, which recently added plate settlers to its South Water Treatment Plant. Gilberg explained that conventional backwash systems, using backwash tanks, required a polymer to bind with the sludge. “There is a settling time where the sludge particulates must grow and sink to the bottom of the tank—in our case it took about three to four hours. Now, with our plate settler in place, we use far less polymer and can start the reclaim process immediately after backwashing.

“Before, we could do four backwashes a day, and all the backwash tanks would be full. We’d have to wait three to four hours for the poly to settle out. We would then start to pump down our tanks; this would take another two hours for a total turnaround time of six hours. Before the addition of the settler, we could get three to four days of filter run time in the summer if we’re lucky. This summer [2012] we increased that nearly 100 percent to six or seven days of run time per filter.”

What changed to create such a long filter run time? Gilberg said, “By having a plate settler, less wastewater is recycled back into the splitter box at the head of the plant. With less waste recycled, the filters are less likely to bind, giving us longer filter run times.”

Steve Nelson of Bolton & Menk, Inc. noted, “The plate settlers also enabled Eagan to more easily optimize their polymer addition because the solids concentration is uniformly blended prior to the polymer being added. This helps prevent the intermittent overfeed of polymers that had the tendency to carry over onto the filters and contribute to partial filter blinding and decrease filter runs. Jar testing and assessing the current mass balance of solids and desired plant operations was the key to the successful renovation.”

South of the Minnesota River amid the also-burgeoning suburbs of Burnsville, Apple Valley, and Lakeville, Eagan has grown from a small community to one of the 10 largest cities in Minnesota. Transportation improvements, including a new Cedar Avenue (Minn. Hwy. 77) bridge and the completion of Interstate 35E across the river, have contributed to more commuters settling in Eagan. In addition, the city has a number of large employers of its own, including the bulk-mail center for the post office, Blue Cross Blue Shield, and West Publishing (now part of Thomson Reuters). It was also home to the world headquarters for Northwest Airlines.

As has been the case with other outer-ring suburbs, Eagan has had to build its municipal services to match population growth, which has more than tripled to 64,000 people since 1980. With water coming in from 21 wells, in 2012 Eagan produced nearly 4 billion gallons of drinking water for its residents and commercial users.

Public water wells began replacing private supply systems in the 1960s, and Eagan put its first water treatment plant into service in 1985. In 1991, another plant was added a few miles to the south, and, like the north facility, removes iron and manganese.

Eagan completed an expansion of the north plant in 2005, doubling its number of filters to 16 and increasing its capacity by more than 80 percent to 22 million gallons per day. The project also included upgrades to the chemical feed systems and sludge handling, the latter in response to more stringent regulations regarding the discharge of backwash water.

Plate settlers were added with the expansion at the North Plant as they were in a later upgrade at the South Plant, but with a key difference. “The North Plant and the South Plant achieved blending in an existing backwash tank,” said Nelson, who led the design of both plant renovations. “The difference is that the South Water Plant also converted one of the existing backwash tanks into a plate settler room. This also required the addition of a second story over the buried backwash tank (a new plate settler room) that allows for easy observation and access to the plates, mixers, and flocculator.”

“That was the biggest hurdle,” said Gilberg of the retrofit. “You don’t mess with your backwash tanks. If anything, you want more.”

Nelson added, “This was a hurdle in that it seemed intuitively like the city would be losing backwash capacity by losing one of their three backwash tanks. However, the net effect was a great enhancement in the ability to handle backwash water.”

The South Plant had three tanks performing conventional backwash. The utility cut off the top of Tank A to fit the plate settler in it. “From our filter cells, we dumped everything into the C tank,” explained Gilberg of the process that is now operating. “From the C tank, we pump the waste into the plate settler.”

Gilberg said the South Plant benefitted from advances in technology in the years following the expansion at the North Plant as well as learning from the experiences at the North Plant. “If we could do it, we wanted a physical break from the plate settler into the system, so we ran the effluent of the plate settler into the B tank. That was a big thing for us.”

Gilberg and Nelson have been tracking the gains in recovery from the plate settler. “We are now recovering 98-plus percent of the backwash water from the filters and are able to reintroduce it into our system,” said Gilberg. “Before that, it was about 60 percent, with the rest going down the sewer.

“The turnaround time for filter cells backwashed to Tank C is about two hours. We’ll initiate a backwash and dump that water into the C tank. There is a pressure transducer in the C tank that allows us to see the level we want our plate settler feed pump to run. This allows us the flexibility to run the plate settler summer and winter. The plate settler effluent then flows to the B tank, a physical break because if the plate settler would malfunction (usually a polymer issue), we would have time to settle the sludge out in this tank. From the B tank, or effluent tank, we pump clean water back to the splitter box at the head of the plant. The net effect is a 50 percent reduction in time required to backwash water and reclaim eight filter cells.”

Diagram of process flow at Eagan Water Plant

The plate settler at the South Plant was installed in the summer of 2010, and the utility made adjustments over the next few months. It was fully operational throughout 2012, and Gilberg said, “With the hot, dry summer, it was a great year to really show how this plate settler works.

“It was a benefit to have a plate settler at the North Plant. We had some operational pitfalls with the North Plant settlers, and the improvement from the North Plant was applied to the plate settler at our south facility.”

“The way the flocculation chamber ties together with the sludge hopper was carefully specified during the design,” added Nelson. “As a result, the plate settlers at the South Plant do not have the tendency to plug up with the filter media.”

Gilberg and Nelson said the benefits include a:

  • decrease in filter down time as the filters can be backwashed and the water recycled in continuous succession if necessary, effectively reducing the time required to turn over all eight cells by about 50 percent.
  • decrease in polymer from .9 milligrams/liter (mg/L) to .2 mg/L.
  • 100 percent increase in length of filter run time.
  • decrease in energy costs because the motors are running fewer hours.
Eagan plate settler
The plate settler at the South Plant was shipped in pieces and had a unitized tank construction. Nelson said the design allows for the removal of single plates from the plate settler.

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High-hazard Cross Connections as Significant Deficiencies—Part 6

How Does MDH Expect Public Water Supplies to Address High Hazard Cross-Connections?

Sixth in a series by MDH engineer David Rindal

The year 2013 introduces the use of the term “significant deficiency” to the distribution system portion of the typical MDH sanitary survey at community public water supplies (PWSs). Specifically, water operators will be asked “Do you know of any inadequately protected high hazard cross-connections in the distribution system?” The term “high hazard” has been defined by the MDH Community PWS Unit as a situation that would require a reduced pressure zone (RPZ) backflow preventer or air gap. Although many PWS operators will answer “No” or “I don’t know,” this article focuses on options a PWS may pursue if the answer to the above question is “Yes” and adequate progress has not been made to correct the significant deficiency.

Option A: Cross-connection control program initiation or development to add or improve:
 • Authority to implement and enforce the program.
 • Certification of backflow assembly device tester personnel.
 • Reporting and recordkeeping.
 • Public notification of backflow events.

Option B: Work with the cross-connection owner to correct the hazard.
 • Notify owner within 30 days of receiving MDH significant deficiency notification.
 • Request the owner correct the cross-connection within 30 days of notification.
 • Confirm the cross-connection has been corrected within 60 days of notification.

Option C: Notify a responsible licensing authority if the owner is a business.
• MDH for food, beverage, or lodging establishments and health care facilities
• Minnesota Department of Agriculture for in-store delis, grocery stores, butcher stores, bakeries, and convenience stores
• U.S. Department of Agriculture for food processing facilities
Confirm the cross-connection has been corrected within 90 days of notifying a responsible licensing authority.

Option D: Adopt local enforcement authority for the Minnesota Plumbing Code.
• Adopt code authority within 90 days of receiving MDH significant deficiency notification.
• Notify owner within 30 days of adopting code authority.
• Request the owner correct the cross-connection within 30 days of notification.
• Confirm the cross-connection has been corrected within 30 days of notification.

Option E: Implement RPZ testing and rebuilding program at cross-connection site.
• Meet with owner within 30 days of being notified by MDH of the significant deficiency.
• Test RPZ backflow preventer annually and rebuild the device every five years.

As always, community PWSs are welcome to adopt more comprehensive approaches, addressing all cross-connections as part of a cross-connection control program.

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    To Systems That Chlorinate . . .

    By Mackenzie Hales
    Minnesota Department of Health
    Community Water Supply Unit

    The Minnesota Department of Health (MDH) has been issuing a lot of easily avoidable notices of violation for missing disinfectant residual (DR) results. A few tips to avoid having this happen to your system:

  1. Always write the chlorine residual in the proper area on the lab form. Do not write the chlorine residual on the bottle; there is no guarantee that the lab will record it for you. Bottles get thrown away, so there is no record of it left behind.
  2. Keep a copy of the lab form you send into the lab with your samples. That way, if the lab fails to report the chlorine residual, you have proof that you recorded it and can avoid a violation.
  3. If a lab returns the bacteriological/disinfectant residual report to you without the DR and you have proof that you provided the DR to the lab, please contact us proactively with that information.

    Note on properly filling bacti sample bottles: MDH has been receiving a lot of bacti samples with insufficient volume for total coliform/E. coli analysis. When filling up your bacti sample bottles, make sure you fill them up so the bottom of the meniscus is at the top of the 100 milliliter fill line.

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    Drinking Water Institute to be Held in Rochester in August

    Water Works! A Drinking Water Institute for Educators will be held in Rochester this summer from Monday, August 5 to Wednesday, August 7. Each year Minnesota science teachers attend the three-day Institute, learning about drinking water and about ways to develop inquiry-based activities that can be incorporated into their existing science curriculum. The program is free to interested teachers, who will receive college credit for their participation.

    Water Works! is sponsored by the Minnesota Department of Health and the Minnesota Section of AWWA and is conducted through a partnership with Hamline University’s Center for Global Environmental Education.

    Water Works! A Drinking Water Institute for Educators.

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Words to Live By

Before you speak, make sure it’s an improvement on silence.

To profit from good advice requires as much wisdom as to give it.

Opportunities multiply as they are seized, die when neglected.

It’s always easy to see both sides of an issue we are not particularly concerned about.

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Reminder to All Water Operators

When submitting water samples for analyses, remember to do the following:

  • Take coliform samples on the distribution system, not at the wells or entry points.
  • Write the Date Collected, Time Collected, and Collector’s Name on the lab form.
  • Write the Sample Point on lab forms for bacteriological and fluoride samples.
  • Attach the label to each bottle (do not attach labels to the lab form).
  • Include lab forms with submitted samples.
  • Do not use a rollerball or gel pen; the ink may run.
  • Consult your monitoring plan(s) prior to collecting required compliance samples.

If you have questions, call the Minnesota Department of Health contact on the back of all sample instruction forms.

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Operator training sponsored by the Minnesota Department of Health and the Minnesota AWWA will be held in several locations this spring.

Upcoming water training schedule


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Updated Wednesday, June 14, 2017 at 08:04AM