Protecting Curb Boxes in Acidic Soils

For municipal waterworks supervisors, keeping curb boxes in good working order is critical. But this job can become even more complicated by the prevalence of acidic soils across the U.S., which accelerates corrosion along with costly repair and replacement.

Traditionally, a curb box is composed of a metal tube that connects the cast iron base to a cast iron lid/cap. It is necessary for water line repairs (or shut off in case of non-payment) and is typically buried 6-8 ft below ground, beneath the frost line. Curb boxes are found on every residential water line that connects a home to a city water main. The challenge is that many areas across the U.S. – including the East Coast, South, upper Midwest, and Pacific Northwest – have acidic soil that rapidly corrodes cast iron infrastructure, including curb boxes. Soil with a pH of 6 or less is considered acidic.

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While soil can typically range in acidity from 2.5 to 10, pH levels of 5 or below can lead to extreme corrosion rates and premature pitting of cast iron infrastructure and curb boxes buried in the soil. Even coatings intended to protect cast iron begin to dissolve when soil pH is around 4, which leaves curb boxes vulnerable to corrosion that makes them unusable.

“We have an electrolysis problem in the acidic soil here, and it eats up the pipe. Even though we put a stainless steel rod on it [the curb box], that stainless steel rod doesn’t do any good when you have a pipe that’s rotting out where we can’t get to it,” said Bob Krueger, a systems operator at Waverly Sanitary District in Menasha, Wisconsin, which had hundreds of curb boxes in need of repair.

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Fortunately for municipal waterworks departments, a repair method that takes minutes can prolong curb box service life using polyurethane parts that do not corrode even in acidic soil.

Because corrosion due to acidic soil can also compromise the entire curb box/curb stop apparatus, a growing number of industry professionals are also turning to replacement kits that utilize polyurethane, which can make the whole system impervious to corrosion and premature replacement.

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Stop Acidic Soil Corrosion, Prolong Service Life

The more acidic the soil, the sooner cast iron curb box caps will corrode, making it potentially difficult to access the water shut off valve.  Typically, the curb box cap will seize due to corrosion. Then when a waterworks technician tries to remove the cap, he or she will either break the nut or the cap.

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The common curb box cap repair procedure is to dig a wide, deep hole around the broken equipment, cut the cast iron tube below the affected area, and splice an extension (either by manually threading the broken pipe and using a threaded coupler or by using a coupler with two set screws then replacing the cast iron top). However, this can be time-consuming and exposes the curb box to the possibility of corroding again.

If acidic soil corrosion has affected the curb stop, the lower portion of the curb box that houses the water shut off valve, then a more extensive repair is required. Often, this can require a work crew using heavy equipment like a backhoe to dig out and replace the entire curb box/curb stop apparatus, requiring additional labor.

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In response, Krueger and the Waverly Sanitary District first turned to a non-corroding, quick repair curb box product made of polyurethane called Speedy Sleeve from Argonics, a Michigan-based design and manufacturing firm specializing in high-performance materials.

The product enables repairs of the corroded or broken top portion of curb boxes in minutes to provide access to the water shut off valve, and was specifically engineered for extended use, low maintenance, and easy installation.  The polyurethane is superior to cast iron because it will not rust or corrode in acidic soil. It will not shatter or crack like plastic, cannot be damaged from impact with lawnmowers or plows, and despite extreme cold it remains pliable.

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The sleeves are 6 to 18 in. in length with two small fins. The top opening is sealed with a cap that will not seize.  To install, cut off the top of the old pipe and then slip on the sleeve.  To get a snug fit at an appropriate level—above or below ground—dig out around the pipe and then tap down with a hammer.  The fins stabilize the device in the soil so that it won’t twist or move due to frost heaving.  They are always easy to locate because the cap is designed with an embedded magnet.

After successful use of the sleeves for quick repairs, Kreuger and the Waverly Sanitation District also utilized Speedy Sleeve poly curb box systems to replace a large number of systems that had corroded and were no longer viable. When used with off-the-shelf PVC piping, these replace the entire curb box/curb stop apparatus with a polyurethane alternative to cast iron that will not corrode in acidic soil.

The Waverly Sanitary District installed the poly curb box systems because the acidic soil was corroding their cast iron curb boxes, requiring them to be replaced every 5-10 years.

“We were looking for something [curb box] with a lot more lifespan than 10 years,” says Krueger.  “We like it [the curb box] because…it’s a non-corrosive product…and because of the ease of installation.  These boxes installed easily, they’re easy to adjust, and they don’t rely on metal threaded couplings.”

The simplicity of the design enables easily adjusting the height of the Speedy Sleeve repair kit and complete curb box system to the desired final grade. Both are engineered to be installed with ease in concrete driveways and sidewalks.

Unlike proprietary cast iron repair tops and bottoms which often vary in thread pitch so they cannot be mixed and matched, the Speedy Sleeve units have a universal design that accommodates most industry variations and adjusts to height, which minimizes required inventory space.

With the lifespan of aging municipal waterworks infrastructure being shortened by acidic soil conditions in many parts of the country, proactive supervisors will increasingly extend service life, reduce maintenance, and ease installation by turning to polyurethane alternatives that will not corrode.

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