skip navigation

What’s in Your Water Mains?

July 23, 2014 by John W. Carpita, PE
Category: Water Utilities

What’s in Your Water Mains?

An article in the April 2014 AWWA Opflow magazine caught my eye, particularly as the City of Longview is featured. The article is entitled: “The New Ice Age: Pigging Effectively Cleans Water and Wastewater Pipelines." First of all, what is a “pig?” For eons, it seems, utilities of all sort have been cleaning the insides of their pipelines with rubber and metal tools of varying degrees of sophistication that are sent down a pipeline and propelled by the pressure of the product flow in the pipeline itself. According to Wikipedia, originally pigs were made from straw wrapped in wire. They made a squealing noise while traveling through the pipe, sounding to some like a pig squealing, which gave pigs their name.{C}

The Opflow article referenced the use of ice pigging (see "Ice Pigging" sidebar below) in the City of Longview in the spring of 2013, which prompted telephone and email exchanges with Jacki Masters, Longview’s Utilities Manager, and a site visit to the Utilities Operation Center and Mint Farm Water Treatment Plant. As it turns out, the use of ice pigging was just the tip of the iceberg (pun intended). Here is - the rest of the story (as Paul Harvey used to say).

Having spent most of my pre-MRSC public works career in design and management of capital project construction, I’ve installed bright, shiny, new water, sewer, and storm drainage pipes (along with streets and bridges, etc.). I spent far less time in the operation and maintenance arena. The inside of a new water main is clean and pristine. How does a near 100-year-old water main look, particularly if it is galvanized iron exposed to groundwater containing iron and manganese for much of its life? Well, look at the eight-inch pipe section in Figure 1 and the two-inch pipe in Figure 2, both from Longview’s water system.

Figure 1P1030254

Lest you think that this is unique to Longview, Jacki Masters noted that iron and manganese are commonly found in groundwater. While they create objectionable taste, color, and odor problems, these minerals pose no health threat at the concentrations normally found in groundwater. Longview has a great set of fact sheets on manganese, iron, silica and hard water. And, aside from the obvious capacity issue in the two-inch pipes (which are being replaced), the hardened scale in the mains posed no problems in terms of actual or perceived water quality issues until the city’s Mint Farm Regional Water Treatment Plant was placed into service in January 2013. Then all proverbial heck broke loose, along with small chunks of dissolving scale from the inside of older galvanized and cast iron water mains. These older mains were mostly found in an older residential area in the southeast portion of the city. Some of these are being replaced on a fast-tracked, emergency basis. The city flushed and re-flushed the mains and installed automatic flushers to increase flow in this area, provided water bottled at the treatment plant to customers who requested it (to bypass the older mains causing the water quality problems), and offered rate reductions and other, very proactive customer service initiatives to customers in that area.

In ice pigging, an ice slurry is used to scour pipe walls. The slurry is loose enough to flow through the pipe and navigate obstacles but firm enough to scour loose material and biofilm from the pipe walls. Ice is injected into a water main through a hydrant, if available, or through a two-inch tap. If hydrants are used, no digging is required. A downstream hydrant is opened, and system pressure pushes the pig through the main. Disposal of the used slurry and its collected sediments can be placed in the nearest sewer main or into a tanker for disposal offsite. Use of the ice slurry in sewer force mains is similar, but sometimes inventive methods of injection are needed.

So, what happened, and why did the city resort to ice pigging? A quick timeline is necessary at this point.

  • Longview was incorporated in 1924. Its water supply at the time and up until 1947 consisted of shallow wells, with iron and manganese present in the groundwater. Over those years, scale from these minerals built up onto the inside of galvanized and cast iron mains.

  • In 1947, the city built an intake and treatment plant on the Cowlitz River. The treated river water provided a safe and reliable supply for many years, including recovering after the major disruption when Mount St. Helens erupted in 1980. While the city was able to restore and rehabilitate the intake and treatment plant after the eruption, by 2005 increased demand beyond the plant’s capacity, the age of the facility, dredging costs, and a host of other issues led to consideration of a different water source. It should be noted that the river water source had little effect on the already hardened deposits in the water mains.

  • In 2006, consideration of alternatives to the Cowlitz River source began in earnest. Of the alternatives considered, a well field and treatment plant at the city’s Mint Farm Industrial Park was not only the least expensive but offered an almost unlimited water supply from a protected aquifer. After extensive water quality testing and due consideration of all alternatives, the city proceeded with drilling four wells and construction of a very sophisticated water treatment plant, which went into operation in January 2013.

In anticipation of the change in water source, city staff worked hard to analyze and develop contingency plans for changes in three major areas: flow reversal (from east to west due to the new plant location across town); increased pressure (the new plant location requires slightly higher discharge pressure); and the chemical makeup of the new source. Two years in advance of the change in source, the City implemented an extensive flushing program to mitigate the flow reversal impacts. To minimize mixing the source waters when the switch occurred, the City lowered reservoir levels, used fluoride as a tracer, and aggressively flushed water to replace the surface water in the distribution system with the new groundwater in less than 24 hours. They also enlisted “citizen sentinels” to regularly report on water quality and help with tracking problems as they arose. Despite this advance planning, more than 550 complaints about dirty or discolored water, chlorine taste, and white spotting or film from the older section of the city came in the first three months after the source change.

Figure 3 Figure 3

The city responded by flushing the mains in this area frequently. Staff noticed that instead of large tubercles typical of the scale found in the pipes, small, pebbly sized granules appeared during flushing, which meant that the chemical composition of the new water source was causing the tubercles to disintegrate (see Figure 3) and cause the issues described above. The city didn’t want to further disturb the tubercles but only remove the deteriorating material, so they contracted with a firm to do ice pigging (described as a “big slushy” pushed through the system by water pressure). They were hoping for several months of relief to give the system time to re-equilibrate. However, the effect was short lived – only about two weeks before water quality issues returned.

City staff, with the assistance of Confluence Engineers, developed a four-pronged approach to addressing the issues: tweaking the treatment process and water chemistry; community outreach; water main flushing; and water main replacements, including improved interconnections.

In a May 2014 water quality update, city staff noted that water quality complaints had dropped to an average of five per week, that bottled plant water is being delivered to 10-15 homes, that emergency main replacements were completed in April, and that chemical parameter monitoring indicates that the system continues to stabilize. Ongoing efforts include evaluation of dissolved oxygen injection to supplement pH and chlorine adjustments to prevent iron and manganese release from water mains that still contain the scale.

Note that the above description of Longview’s “trial by water” relates to scale in existing water mains in the distribution system and that the new regional water treatment plant is quite effective at removing iron and manganese from the source groundwater (see Figures 4 and 5). The black gunk in Figure 4 is iron/manganese removed from the source water after dewatering in the bladder bags shown in Figure 5. Four of these bladders have been filled since the treatment plant went into operation last year.

P1030257 Figure 4

P1030259 Figure 5

MRSC is a private nonprofit organization serving local governments in Washington State. Eligible government agencies in Washington State may use our free, one-on-one Ask MRSC service to get answers to legal, policy, or financial questions.

About John W. Carpita, PE

John was MRSC’s resource for many years on engineering design, purchasing and contracting issues, local improvement districts, and other infrastructure issues. He had a widely varied career as a consultant, county engineer, city engineer and project manager. He is now retired.



Blog Archives


Follow Our Blog