Inflow and infiltration used to be an issue in Coon Rapids. Now, not so much. The Minnesota municipality has been aggressive with system rehabilitation and is reaping the rewards of its progressive approach.
Coon Rapids, in Anoka County, is a northern suburb of Minneapolis with a population just over 60,000. It is largely residential but also has industrial and commercial areas. The collections system, operated by Public Works department’s Utilities Division, includes about 240 miles of sewer, 80 miles of which is clay tile. The system isn’t especially old — the clay tile was installed from the 1950s into the early 1970s. The rest of the system is PVC, installed from the mid-‘70s on. The utility maintains its own collections system, but all treatment is handled by the Metropolitan Council in St. Paul. The council also maintains the interceptor lines that carry wastewater from Coon Rapids’ system to the plant in St. Paul.
The utility has worked hard to eliminate sources of I&I, particularly in the older parts of its system, where heavy root intrusion caused frequent sewer backups. From 2008 through 2013, the utility lined approximately 240,000 feet of sewer.
“It’s something we’ve gone after,” says Rick Bednar, operations supervisor with Coon Rapids Utilities. “We fix whatever we can find.”
Falling in line
In 2007, with the help of a local engineering firm, Coon Rapids prioritized its system for lining. Sewer lines were prioritized for the lining process based on how much time crews spent on cleaning operations in those areas along with the specific problems. The next year, they began lining pipes in the areas where they had been having the most frequent problems.
“We started with the bad areas and we’ve been working toward the better areas, but we’re still going to keep lining for another couple years,” Bednar says.
In some cases, pipes need to be dug up and repaired before they can be lined. Over the 40,000 feet they’re rehabilitating annually, Bednar says there are approximately eight to 10 sections that require repair. For this reason, he says larger general contractors frequently bid on the jobs and hire someone else to do the lining. Insituform has been the main provider.
The city is spending about $1 million per year on sewer lining right now. When the process is complete, Bednar says they will have lined a majority of the 80 miles of clay pipe, and the entire system will be in good shape for years to come.
Lateral lines have not been a significant issue. In areas served by clay tile line, the laterals are also clay, but the property owners are responsible for those lines from the main to the house. Everything has been televised, and while there are a lot of root problems in the laterals, there is very little I&I. Since the Metropolitan Council closely tracks the volume of metered water used by Coon Rapids customers and the volume of wastewater flowing to its plant, assessing I&I levels is fairly easy, and Bednar says the laterals haven’t been a big factor.
Bednar says with the frequency of the utility’s sewer cleaning schedule, regular pipe inspection isn’t necessary.
“We have what we call our spot check list that we go through every month — problem areas. You’re always going to have your smaller lines flowing into bigger lines, 90 degree turns in manholes, things like that. We look at about 200 manholes every month, and there are some we have on a quarterly list.”
They’ve had to replace the rings on some manholes, but they haven’t had to deal with many structural issues. They’ve also lined some manholes, typically where I&I or root intrusion has become a problem, using a variety of spun epoxy systems depending on the contractor.
While lining has been the primary rehab method in Coon Rapids, the utility has also done some pipe bursting, including a 4,000-foot section of thin-walled PVC that had become egg-shaped. The pipe ran through a business area and was replaced with HDPE. The pipe’s shape made it impossible to reline, and the traffic and congestion made pipe bursting the only viable option. “It was quite successful,” Bednar says.
The utility has also been spending about $600,000 per year on lift station projects, and the last one slated for reconstruction will be finished in 2014. These are significant projects, with some stations as deep as 40 feet, so the work is contracted out.
“We’ve replaced a sewer lift station every year since 2006,” he says. “We’re completely rebuilding them, with new wet wells, pumps, control panels, everything. We have standby portable generators on the ones we have trouble getting to in a power outage, or ones that we don’t have a lot of time to get to in a power outage. We have three portable generators that we can take out and hook up to lift stations, but the high flow stations and the ones that are a ways away, we’ve put in permanent generators.”
The Twin Cities area doesn’t feature a lot of topographic relief, but the lift stations are all in low spots and are required to move the wastewater to points where gravity flow can be restored.
Roots, grease and non-flushables
Coon Rapids had been active in cutting and removing roots from its own lines, twice a year in some areas. The issues were primarily in the clay tile lines, but most of those pipes have since been lined, and roots are no longer a significant problem.
PVC lines, which comprise the other 160 miles in the system, are also cleaned on a regular basis. The Utilities Division tackles that task with a Vactor combo unit and a jet truck from Sewer Equipment Co. of America, which also includes an Aries camera. The utility tackles about a third of the system, or 80 miles, every year.
“We’re out there almost every day,” Bednar says. “We jet them, and if we pull anything back we vacuum it out through the manhole.”
One of the common problems they encounter is large root balls that have been cut and flushed out of the laterals. Bednar says if they are unaware of these situations, they can lead to backups.
“We encourage customers through quarterly newsletters to let us know if they have their services cleaned, but if we don’t know, sometimes we get backups from service roots that get pushed out in the main.”
The utility always tells customers that the first thing they should do when they have a backup is notify the utility so they can make sure it’s not an issue in the city line.
“We go out and check right away,” Bednar says. “When somebody calls in saying they’re having a sewer backup, we go check our lines to make sure that’s not the problem.”
The utility also urges customers to notify them if they’ve had their sewer cleaned so they can go out and make sure there are no clogs or root problems in the main. And they include information about what not to put down their drains — grease and “flushable” wipes.
“We try to educate everybody that way,” Bednar says. “It’s been pretty effective.”
Coon Rapids hasn’t had too many sewer backups related to flushable wipes because pump stations have two pumps.
“People have been pretty good about it, but you’re always going to have your problems,” he says.
With a large number of restaurants in town, FOG is a concern, but the utility has been proactive about addressing and preventing problems. Some traps are cleaned regularly. Others haven’t been too big of an issue, and Bednar says cleaning lines in problem areas twice a year has been a big help.
“We have a list of restaurants we clean in the spring and fall to make sure there’s no grease in the lines,” Bednar says. “We catch the stuff before it becomes too much of a problem.”
FOG has also been an issue in a few residential areas. “We can usually run a camera up and find out which service it’s coming from, so we either knock on the door or send them a letter if they’re not home,” Bednar says. “It helps.”
The city does have a grease ordinance, but some restaurants don’t have grease traps, so the ordinance spells out the amount of grease in parts per million that’s allowable in the city lines. Business owners are notified if they’re in violation of the ordinance, but there is no real enforcement mechanism.
“Most of them are pretty good about capturing that stuff before it gets in the line,” Bednar says.
“I got here nine years ago and we were having sewer backups multiple times a week,” Bednar says. “Last year we had six sewer backups that were our responsibility, and those came from roots that had been pushed out by a service cleaning.”
When Bednar first arrived in Coon Rapids, he says the League of Minnesota Cities, which insured the utility, was going to cancel their insurance because there were so many claims. He met with them and spelled out the plan — lining, cleaning, spot-checking, grease traps — to improve the system and reduce backups.
“We laid out what we planned to do, and it’s worked,” Bednar says. “We got back in their good graces and they’re insuring us and we don’t have any trouble anymore. It’s really worked out pretty well.”