As mentioned above most of the City's water supply is diverted from the Colorado River system via the horizontal collector well (HCW), which is located at London Bridge Beach on the Island. This well consists of a 16 feet diameter concrete conduit called a caisson and is 103 feet deep. Close to 90 feet down the well, there are 14 horizontal "tunnels" called laterals, about 12" in diameter that extend from the caisson in all directions up to 220 feet away from the well (Figure 2).
There are three water pumps in this well, which can withdraw up to 26 million gallons per day on a consistent basis (Figure 4). Currently though, a typical daily pump range is between 14 and 17 million gallons. There are usually one to two pumps operating at any given time with the third acting as a backup if one of the other two needs repair. Water is pumped out of the well through any of three 30" pipes (Figure 5) that lead to one 48" pipeline underground. That main transmission line goes northward under the Bridgewater Channel and continues a few miles to the City's Water Treatment Plant. The City is currently looking for another location to possibly construct a second HCW. If the current well for whatever reason cannot pump water, the older backup wells will not be able to pump enough to keep up with current demand.
The Lake Havasu city water treatment plant is located a few miles north of the HCW. Water transported through the 48" transmission line from the HCW ends at the City's Water Treatment Plant (WTP) where it first passes through a flow meter that records the volume of water received at the plant and then ascends a few feet above ground into an aeration tower (Figure 5).
The City constructed a biological filtration water treatment facility to extract dissolved manganese and arsenic from the water. This type of facility is rather uncommon in the United States. Those residents that have lived in Lake Havasu City for more than a decade know well that manganese can turn clothes, toilets, sinks and tubs brown. The City also had to regularly flush fire hydrants to keep the distribution lines from clogging with heavy manganese sludge. A lot of water was wasted in that process.
In order to follow along with each of the following sections, a schematic map of the water treatment process is presented in Figure 5.
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North, central and south main transmission lines are in place to transport water to storage tanks positioned around town. Since Lake Havasu City lies on an alluvial fan slope, that is sand, gravel, cobbles and boulders eroded and deposited from the hills and mountains on the city's eastside, water has to be pumped up hill. Initially, the high service pumps at the water treatment plant deliver water to the first set of tanks (Figure 23). These tank locations also have booster pumps that can further deliver water to higher sections of the city.
The water storage tanks range in size from 0.5 to 2 million gallons capacity and reside at an elevation higher than the area they serve because they deliver water to customers only using gravity. Water delivered to a particular range of elevations is called a pressure zone and there are seven water pressure zones within the city (Figure 1). Those customers that are at the top of a pressure zone typically have water pressures at their meter of around 40-50 psi. The water pressure increases with distance down slope from the top of the pressure zone. The bottom of some pressure zones can be well over 100 psi (up to 150 psi). Residences or commercial buildings with water pressures higher than about 65-70 psi definitely need a pressure regulator on the water line going into the structure to prevent damage to pipes and appliances inside.
Water is either used at any location in which the water is captured by the municipal wastewater system, is percolated into the subsurface, is consumed into a product or is evaporated. Percolation, product consumption and evaporation represent one time use of water. Irrigation is the largest use of potable water, about 70% of the total treated, at the home, at commercial landscaping and in our parks and other public landscaped areas. Some of the other 30% is also lost through leaks and the other process just mentioned, but about 25% of the water is cycled through the sewer system via toilets, sinks, showers, and washing machines of various sorts. This is the water we will now follow through the wastewater system.
From 2002 to 2011 Lake Havasu City undertook an unprecedented wastewater expansion program to sewer about 85% of the City. There are now approximately 420 miles of pipe in the ground. The additional capacity of the system necessitated the renovation and expansion of the City's two existing wastewater treatment plants (Island and Mulberry Wastewater Treatment Plants - ITP and MTP, respectively) and building a third, the North Regional Wastewater Treatment Plant (NRP) just south of the airport to accommodate the greater wastewater flows. The 2.5 million per day capacity ITP and the 2.2 million gallons per day capacity MTP facilities are extended aeration sludge treatment plants that treat the wastewater on multiple levels. The 3.5 million gallons per day capacity NRP uses an ultra-filtration membrane system to rid the treated wastewater, called effluent, of particulates down to 0.4 microns (0.4 millionths of a meter). This virtual trip will cover both treatment technologies. The treatment process must meet many state regulations to achieve A+ status, the highest grade of treated wastewater recognized by the state's Department of Environmental Quality. A+ status means that the treated wastewater is safe for body contact (essentially bacteria free and nitrate-nitrogen concentrations less than 10 mg/l (10 parts per million)). Fecal coliform bacteria analyses must indicate non-detect per 100 milliliters, four days out of every seven the water is tested to comply with A+ standards. Turbidity (measure of the water clarity) of the water must be < 2 turbidity units (ntu) over a 24 hr average and have a daily maximum of <5 ntu.
Wastewater collected from homes and businesses flows mostly by gravity through the sewer system to respective wastewater treatment plants. Along the way at several locations throughout the city; however, some sewer lines cross a topographic low point and the wastewater needs a boost upslope get it to the appropriate place. Fifty-six sewer lift stations of various capacities have been constructed in the sewer system to accomplish this task. Odor control in the sewer collection system is accomplished by adding a chemical called calcium nitrate to facilitate aerobic conditions in the wastewater and inhibit hydrogen sulfide gas development.
Since the ITP and MTP have the same treatment technology; they will be treated as one. Figure 24 exhibits a general wastewater process flow that is characteristic of both plants. Click for details
Treated wastewater (also known as effluent) is the finished liquid product of the wastewater treatment process. About 2/3 of this water is used to irrigate three golf courses in or near the city and a few other small landscape areas on the Island. The rest of the effluent is disposed by either surface percolation in ponds at the ITP, or injected into the subsurface for storage by special wells adjacent to the NRP.
Treated wastewater exits each treatment plant a little differently. Effluent at MTP falls into a small contact basin after the ultraviolet treatment (Figure 49). This basin was formerly a place for chlorine injection into the water to disinfect the water prior to the establishment of the ultraviolet process. The basin is now used to pump effluent to the ITP percolation ponds when conditions merit or to more normally let the effluent flow over a weir into the adjacent commingling pond (Figure 50). The commingling pond at the MTP is not intended for use as a percolation pond. With a muddy bottom, little water is actually lost from the pond by this process. Effluent is pumped from the commingling pond (Figure 51) through purple pipe (that particular color is conventionally used throughout the industry to indicate effluent) to help irrigate the fairways and greens of the 36-hole London Bridge Golf Course.
During the warmer months, irrigation demands may and frequently do exceed the available effluent in the pond. The City has taken care of this shortage by constructing the City's only surface water intake from the lake (yes, it counts against the City's annual water allocation). The untreated lake water is pumped to the commingling pond to supplement the effluent volume and mixes with it as well, lowering the total dissolved solids concentration. This pond attracts birds like herons as fish have been introduced.
After treated wastewater runs through the ultraviolet light bank at the ITP, it can be either sent to a plastic lined holding pond for reuse (Figure 52) or diverted into the first of three percolation ponds located adjacent to the plant facility (Figure 53). Effluent is pumped from the lined pond to irrigate the Nautical Island Golf Course, a couple of ball fields and several small landscape areas. If this pond is full, then excess effluent generated from the plant is delivered the percolation pond (Movie 3). If that one fills up, there are connections to the second two percolation ponds to surface spread the effluent. These ponds have sandy bottoms that periodically need to be churned (scarified) to keep clays or organic material from plugging up the bottoms. These ponds have been in operation for about 40 years and are still capable of accepting 1-2 million gallons per day from the treatment plant. The main pond has been stocked with gold fish, which has attracted many kinds of birds. In fact, the ITP is a listed spot for winter bird watching on the Arizona Field Ornithologists website. The one main down side for Lake Havasu city of using these ponds is that the effluent is lost to the Colorado River and cannot be reused. The Central Arizona Project likes this as they can then divert the same amount of water for their use.
Treated wastewater generated at the NRP not sent to the Refuge Golf Course for irrigation, is either injected into the ground via wells adjacent to the plant or is sent to the ITP for disposal in the percolation ponds. The injection wells are 180 feet in depth and four feet in diameter. Underlying groundwater though is about 400 feet below ground surface. Water pumped into these wells migrates downward and outward through once dry sediments, forming a water mound on top of the groundwater (Figure 54). The water slowly moves towards the lake 2.5 miles away and is at an elevation from which it can be recovered without counting against the City's water allocation (i.e. - the water can be recovered in addition to water we divert from the river and is not under federal or state control). The City is currently evaluating the feasibility of recovering that water during the summers when irrigation demand is high so that parks and other public landscape areas can be irrigated with effluent instead of potable water. This effectively adds to the City's water supply.
The virtual tour is intended to show the process steps involved to accessing, using and disposing municipal water and to prep the reader for a possible on-site tour.
The basic on-site tours include visiting the Horizontal Collector Well, the Water Treatment Plant and the Mulberry Wastewater Treatment Plant and Lab, which usually takes about 3-4 hours, including travelling to these sites. The time of the tour can vary depending what your group wants to see. For example, the North Regional Wastewater Treatment Plant and effluent recharge site could be substituted for the Mulberry Wastewater Treatment Plant and Lab, but this will take about 40 minutes longer due to the increased travel time. Please note that the tours are available only during staff hours between 7am to 1pm Monday through Friday. The City at this time does not provide transportation to and from any of the sites.
Tours for groups can be arranged by calling Doyle Wilson, Water Resources Coordinator, at 855-3999 or by email at firstname.lastname@example.org. In addition, the City is in the process of establishing two days each year for the general public to attend a tour. Dates are to be announced.
This virtual field trip is intended to give residents of Lake Havasu City an idea of the origin, pre-use treatment process, distribution, post-use treatment process and reuse of the City's Colorado River water supply. The City has a contracted directly with the U. S. Department of Interior through the Bureau of Reclamation (Reclamation) or subcontracted indirectly through the Mohave County Water Authority, 28,319 ac-ft of 4th priority Colorado River water. Each year the City determines how much of that allocation is needed to supply city's needs and submits a request to Reclamation to withdraw that amount over the calendar year.
How does the City get the water from the lake? Although there is one surface water intake pump offshore of Body Beach, which is used to help with golf course irrigation (more on this near the end of the tour), all other water is pumped by wells on shore. These wells have been drilled to the aquifer that is hydrologically connected to the lake. This means the water in the lake percolates into the sediments below and adjacent to the lake, saturating them and creating the aquifer. The City uses wells instead of surface intake pipes because the water has a chance to filter through the sand and gravel in the aquifer, leaving behind bacteria that cannot get through the sediments. However, certain chemicals can move through with the water and that is why we have a special type of water treatment plant (more on that soon). The City used to be dependent on a number of conventional water wells, but found that the demand for water was going to be larger than these wells could produce. In 2001, the City built a first of its kind in Arizona, a horizontal collector well. This well today produces about 98% of all the water we use at our homes and businesses, including irrigation at our schools and other public places.
The virtual tour is not intended to replace the actual tour, which is primarily given to 6th grade and Mohave Community College chemistry students (though the tour can accommodate other groups as well), but can be used as a preparation of that tour to better understand the processes and effort involved in getting water through the municipal system. The virtual tour does include some components not covered in a typical field tour because there would be a significant amount of required travelling. The following virtual tour begins at the horizontal collector well, continues to the water treatment plant and the water distribution system, follows the used water through the wastewater treatment process and finally ends with what is done today and what may be done in the future with the treated wastewater (Figure 1).