First Use of Drop Hose Technology For A Municipal Well in Iowa

The City of Washington, Iowa, has 3 deep Jordan wells that provide drinking water supply.  Two wells are needed to keep up with the City’s water demand and a third is a standby well.  In July 2015, the submersible well pump and motor failed.  As is frequently the case with these deep wells, the factors which contributed to the failure could be traced back to corrosion.

The ground water in the well is typically 23 degrees Celsius (74 degrees Fahrenheit) year-round, total dissolved solids about 1600 ppm, sodium 197 ppm, sulfate 579 ppm, chloride 62 ppm, total hardness of 433 ppm, and a pH of 7.35.  This water has a Ryznar Index of 6.9 and a Larson-Skold index of 3.4.  While the Ryznar Index number is not particularly bad for well water, the Larson-Skold Index, which considers sulfate, indicates that high levels of corrosion could occur.

The casing in Well 6 was televised and visually indicated a lot of corrosion on the steel casing and a large amount of debris floating in the water. In the past, city staff had pulled the well pumps in each well about once a year or every other year to inspect and replace the steel drop pipe. Since the pump setting was at about 400 feet in the casing, this method became expensive as the costs of mobilizing a well pump crew and their equipment, plus the labor on site, increased.

Budgets became tight and the frequency of pulling well pumps was reduced. About ten years ago, city staff were reminded of the corrosive nature of the well environment as one of the well pumps separated from the drop pipe and fell to the bottom of one of the other 1800-feet deep wells.

In an effort to prevent the loss of well pumps in the future, city staff decided to use stainless steel drop pipe and all stainless-steel pump and motor equipment. Stainless steel drop pipe certainly has the benefit of corrosion resistance but it is difficult to work with. Steel or stainless steel drop pipe comes in sections of 20 feet and almost always has threaded joints.

When a pump is pulled and the stainless-steel drop pipe sections are separated, the stainless steel threads often are damaged beyond repair.  When that happens, the well contractor typically cuts the threaded end off, re-threads the remaining end, and continues with installation. An additional stick of pipe is added to make up for all the pipe cut offs. The cost of stainless steel drop pipe can be almost double the cost of (black) steel drop pipe or almost $100 per foot in this well. Frustrated with the expensive options using steel and stainless steel, city staff considered an alternative to rigid drop pipe.

A Different Technology

Drop hose technology has been frequently used by the mining industry due to its strength, ease of installation and retrieval, and the fact that it does not corrode. The drop hose is one continuous length of product from the well head down to the submersible pump / check valve without joints every 20 feet.

One section of drop hose has the potential to save a considerable amount of time during installation since a threaded joint does not need to be secured every 20 feet during installation. Some installers wrap the hose around a reel and drop it into the well in a matter of an hour.  (Dozens of YouTube videos are available for by going to Hose Solutions’ website and looking for the Boreline® product.)

According to the manufacturer, the drop hose is made of circular, woven, high-strength polyester and is encapsulated with a polyurethane lining. Their specifications indicate that the material does not corrode, is not susceptible to biological attack, and is resistant to scaling. A 6-inch diameter Boreline™ hose is manufactured to have a theoretical tensile strength of 44,000 pounds, an operating pressure of 310 psi, a theoretical burst pressure of 800 psi, and a head loss which equals or exceeds that of new plastic pipe.

In Well 6, the expected weight of the pump equipment, check valve, the drop hose, and the water in the line is expected to be about 7600 pounds. By dividing the theoretical tensile strength of 44,000 pounds by 7600 pounds, the result is a safety factor of 5.7. The calculated working pressure at the pump was expected to be 210 psi, and considering the product’s 310 psi maximum working pressure, a safety factor of 1.5 is theoretically possible. The Boreline™ drop hose product is NSF61 approved which is required by the Iowa Department of Natural Resources. The manufacturer, Hose Solutions, places a 50-year warranty on the product.

Study/report phase and contacting Boreline™ references

Since this was a new product to municipal wells in Iowa, well contractors were understandably skeptical.  City staff directed FOX Engineering to study the product and interview contractors with experience using the product.

FOX also contacted Iowa well contractors to understand their questions and concerns prior to the study. Many were not sure what rigging and equipment would be used with this product, how the hose would be connected to the pump and check valve, would the hose twist during pump starts, and if the hose could be damaged rubbing up against a rough well casing wall during installation and retrieval.

FOX discussed the product and how it was used with references from Nebraska, Missouri, and Indiana.  The drop hose was used in Hastings, Nebraska, in wells with concrete encasement which were not straight, or plumb. This would cause rubbing of the hose against the casing during installation. The utility’s owner found that the drop hose worked better than a rigid steel product in this case because it was flexible during installation. Later, after retrieval of the pump, the hose did not show wear from rubbing against the casing.

Utility staff did not think that pump starts caused any twisting of the hose. Representatives from Hose Solutions confirmed that the hose does not twist significantly during pump starts because the hose behaves like a rigid wall pipe once the water inside reaches its operating pressure. Constant speed pumps were used in this installation.

The contractor installing the drop hose in these wells had no prior experience with the drop hose and found it to be easy and not difficult to learn.  They used a typical pump installation truck and straight truck with a reel on the end for the installation.

A well contractor in Indiana was also contacted. His company has used the drop hose in 4-inch to 6-inch diameter wells ranging from 100 feet to 400 feet deep. Due to the difficulties of working with threaded joints for stainless steel pipe, it is their standard to use drop hose in corrosive wells, or wells which would require uncoated schedule 80 drop pipe to be replaced every 3 to 5 years. They have not had any failures with their drop hose installations. This contractor uses the two-clamp rigging system provided by Hose Solutions.

The rigging clamp of the two-clamp rigging system has two halves.  The drop hose is clamped or “sandwiched” between the two halves without damaging it (clamp holds by friction). Then nuts and bolts are fastened on either side of the hose and tightened to a torque specified by Hose Solutions. The crane then can pick up a clamp and lift the full weight of the hose, pump, and water. The clamp is much wider than diameter of the well, so that it will not go down the hole with the hose. Instead, the clamp spans the well hole like a bridge and secures the pump equipment and hose in the well.  A second clamp is attached further up the hose.  When it is picked by the crane and is carrying the full load, then the first clamp can be removed. The hose is installed using the two clamps in a “leap frog” fashion, with the contractor making sure that there is always one clamp on the hose. It follows that taller cranes will permit shorter installation times. The contractor in Indiana has access to 2 cranes, one with a boom of 70 feet and another with a boom of 100 feet. A three-person crew is used.

A third reference from Wichita, Kansas had experience with using the Boreline™ product and had used Boreline™ products up to 8-inch diameter in wells up to 150 feet deep. They felt more comfortable with using a 165 boom crane to install the drop hose in one pick rather than using the dual clamp rigging system. This crew also managed to cause wear in the drop hose product through abrasion and had problems attaching the pump motor power cable to the hose. The wear caused a small amount of leakage (water drops on the outside of the hose), so Hose Solutions provided a full replacement under the product warranty. The power cable issues were resolved by using a different tie to fasten the cable to the hose, which is now a standard with a new Boreline® product.

One key to installation is ensuring that the power cable is attached to the hose securely once every 3 feet of hose and that there is enough slack in the cable. The pump must be supported by the hose and not the cable, so about 3% more cable length is required to be installed in the well, relative to the hose length. The hose comes with straps already attached to it for securing the power cable.

During pump retrieval, the inline check valve installed just above the pump can be specified to have a “break away” plug.  A well tool can be extended down through the well head and hose to break away the plug. This causes the water to drain out of the section of hose above the check valve. Pulling up the pump and hose without the water avoids the mess of water coming out on the ground surface as the hose is pulled out. Draining the water also greatly lightens the load to be lifted since the weight of the water in the hose contributes the most to the overall weight being lifted.

The pump discharge head and check valve(s) are attached to the drop hose using a simple two-piece, threaded hose coupling.  According to the manufacturer, they know of no installation in which a pump was dropped into the well due to a failure of the coupling or the drop hose. The coupling can only be assembled one way.

Decision to use drop hose in Well No. 7, Washington, Iowa

Not long after the pump and motor in Well No. 6 failed, the pump and motor failed in Well No. 7 in March 2016. Since two wells are required to meet the community’s water demand, a well contractor was called and installed a temporary pump in Well No. 6.  The well pump in Well 7 had failed due to electrical grounding failures associated with the submersible motor. Well No. 7 was televised and no serious issues were found with its casing, other than the wear that any well casing of its age (47 years) would have. It was determined that the submersible well pump and motor would be replaced, as soon as possible.

Quotations were obtained from well companies and the lowest responsive quotation was accepted.  The technical specifications required the contractor to install a new submersible well pump and motor, and 420 feet of drop hose. The specification also required use of the couplings supplied by Hose Solutions and for a Hose Solutions representative to be present during the installation preparation of the drop hose and the installation of the pump and drop hose at Well 7.

The installing contractor decided to use their standard well pump installation truck, the dual clamp rigging system provided by Hose Solutions, and a flat bed trailer.

Preparation of the drop hose

The drop hose was prepared at the contractor’s shop. Here the hose was stretched out and the power cable was laid next to it with the prescribed slack. The drop hose manufacturer’s representative was present to instruct the pump installation crew on how to properly fasten the power cable to the drop hose.  Attaching in advance of pump installation at the well site was found to save time, according to the drop hose manufacturer’s representative. The pump, motor, and well head are also prepared for installation at this time.

Once the power cable was attached to the 6-inch diameter drop hose, the contractor tried to roll the assembly on the largest reel available, but the power cable did not seem to be flexible enough; so, instead, they decided to lay the drop hose assembly on a flat bed trailer. After the assembly was transported to the site in Washington (about a two-hour drive), the contractor washed down the drop hose assembly to remove any dust which may have accumulated.

Drop Hose Assembly on Trailer

Drop Hose Assembly on Trailer

Installation of the drop hose and pump assembly in Well 7

The contractor and drop hose manufacturer’s representative arrived at the site around 10:30 AM. After the well house roof and wall were removed, the well contractor inserted the calcium hypochlorite tablets into the well for disinfection. The contractor brought their typical pump installation truck which had a boom of 32 feet. The contractor used the two-clamp system for rigging but only chose to lift the hose in segments of 25 feet. The time to install the pump at a setting of 420 feet deep was about seven hours; it would have been faster with a three-person crew and a crane with a longer boom.

Attaching Clamps

Attaching Clamps

Time was used to by the crew to figure out the clamping procedure, but they realized how simple it was after using the clamps 3 or 4 times. The only user error was facing the clamp the wrong direction. The crew took their time and methodically repeated the clamping procedure to install the pump and drop hose.  The hose was transferred directly from the trailer to the hole by the crane, but there were a few occasions where the hose assembly touched the ground. A high strength solution of sodium hypochlorite was sprayed on the drop hose assembly before it went down the hole to protect against contamination. This ground contact could have been avoided if a third crew member was used, and if the trailer was parked in a better location. The crew became faster as the work proceeded – the first 100 feet took two hours to drop and the last 100 feet took 30 minutes.  At the end, the crew had some difficulty sliding the drop hose over the nipple on the well head, but eventually obtained a tight fit and well mounted coupling.

Lifting Pump

Lifting Pump

2nd clamp up

2nd clamp up

Well Head

Well Head

After installation, the well was test pumped and bacteria test results returned negative.  The cost savings to provide this well with a drop hose that will not corrode is approximately $26,000 or a savings of about $60 per foot, assuming difference in the labor and installation costs for a first-time drop hose installer.  (Subsequent installations would theoretically be lower.)  Since there is less friction from water flowing through drop hose, relative to the friction loss associated with steel pipe, approximately $900 a year is saved in pumping costs for Well 7.  Given the success of using the drop hose in Well 7 so far, the city plans to use the Boreline in Well 6 next year.

 

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.