When experts in the water sector talk about improving the infrastructure in a given city or region, we hear a lot about the importance of pipe condition assessment, leak detection and how to deal with major concerns like corrosion. Despite the dry, desert climate of southern Nevada, the Las Vegas Valley Water District (LVVWD), which supplies water to millions of annual visitors, is known for having significantly low water loss rates. So how do they do it? UIM sat down with Charles Scott, engineering project manager for the LVVWD to discuss their current state of infrastructure. Scott has over 30 years of experience in the industry, working in maintenance engineering and maintenance and asset management for various specialty and commodity chemical plants.?????
Tell us about the state of the water system in the Las Vegas Valley District. What is the age of the infrastructure and what is your rate of replacement??
The LVVWD distributes potable water to over one million residents and 36 million annual visitors in the metropolitan Las Vegas and unincorporated Clark County area. Although the LVVWD began distributing water in 1954, due to the phenomenal growth Las Vegas experienced over the past two decades, the age of LVVWD?s infrastructure is only about 19 years old. Consequently, we have relatively low water losses, and low break rates at less than 70 breaks a year per 4,500 miles of pipe. Our pipe replacements or renewals are prioritized by risk. Of the pipe we have assessed so far, we have prioritized about nine miles as potential renewal candidates over the next 10 years.
Are there any special considerations you make in operating a water system in a desert environment? What are the challenges?
Las Vegas is located in the Mojave Desert, one of the hottest and driest deserts on Earth. Our average rainfall is less than 5 in. per year, with temperatures ranging from below freezing in the winter, to over 110 degrees in the summer. Our seasonal demand varies between 170 million gallons per day (mgd) in the winter to over 400 mgd in the summer.
About 90 percent of our water comes from Lake Mead, which currently sits at an elevation of 1,119 ft and is about 30 miles from our nearest turn-out reservoir. The Las Vegas valley is bowl-shaped with elevations ranging from 1,845 to 3,550 ft. Being able to move between 170 to 400 mgd from a lake located nearly 30 miles away from our closest turn-out and distributing it over an elevation range of 1,700 ft is our biggest day to day challenge.
The LVVWD is known for having low loss rates, as you confirmed earlier. What else helps you accomplish that?
As with most things, if you don?t measure it, you can?t improve it. To address our apparent losses, we developed an economic meter replacement strategy. To go after our unknown system leaks, the LVVWD employs fixed acoustic monitoring devices for small service line leaks and a sophisticated acoustic leak detection program for large (12-in. and above) diameter piping. Having a 19 year old distribution system also helps.
Why did LVVWD decide to go with acoustic technology?
We wanted a leak-detection system that could locate un-surfaced leaks on large diameter (mostly steel) pipelines that would be non-intrusive, cost-effective and one we could employ with minimal outside technical assistance. The acoustic leak detection system meets those criteria.
What does a water utility need to consider before deciding to implement a service like this?
If a utility intends to do some or most leak detections in-house (as we do), they should consider the staffing requirements. This is technically challenging work that requires a lot of training and experience to get good results.
Utilities need to have as much detailed information about their systems as possible. At a minimum they should know pipe size, material and locations of services, pressure regulating valves, air-vacs, low-point drains, etc. Locating leaks is largely dependent on record drawing accuracy. Nothing kills a leak detection program quicker than digging a bunch of dry holes.
Tell us about the kinds of pipe materials LVVWD uses. Is corrosion a big concern?
We have about 4,500 miles of pipe (4-in. and larger) in our distribution system. About 51 percent is PVC, 35 percent ACP, 10 percent steel (mortar lined steel cylinder, bar-wrapped, etc.), 3 percent ductile iron, and less than 1 percent cast-iron.
Corrosion is a concern due to our soils. Our soils are not only corrosive to steel, but can also affect our AC pipes. We have found through our assessment program, AC pipe degradation varies widely based on soil types. Prior to the early 1970s, about 100 miles of our steel pipe was installed without corrosion protection. After the 1970?s, steel pipe was installed with cathodic protection test stations, and (as needed) sacrificial anodes. Today we read and maintain over 2,600 cathodic protection test stations each year and work to develop corrosion mitigation plans. The ultimate goal of our corrosion control program is to extend the life of our steel pipes and other steel structures.
What are some of your goals for the future in terms of improving conservation efforts and overall infrastructure in the district?
Our goal is to cost effectively maintain acceptable service levels through a well thought out and executed asset management program. Our underground infrastructure asset management strategy can be summed up as: protect, assess, renew.
