HORIZONTAL COLLECTOR WELL

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. There are three water pumps in this well, which can withdraw up to 26 million gallons per day on a consistent basis. Currently though, a typical daily pump range is around 12 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 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.

WATER TREATMENT PLANT

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. 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. When the Lake Havasu City plant was finished in 2004, it was the largest of only six such plants in North America and the second in the United States. Those residents that have lived in Lake Havasu City for more than a few decades 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 below.

CASCADE AERATION TOWER

The aeration tower cascades water down four different stair-step like ladders to encourage oxygen from the atmosphere to entrain (mix) with the water so that a specific type of bacteria can start cleaning the water. Screened netting over the cascading water is present to discourage birds from landing in the water and to keep algae from growing. 

The cascading water flows to a small basin on one side of the tower that leads to a conduit underground. Ferric chloride is added to the water in this basin to react with and precipitate arsenic, an element that can cause detrimental effects on humans. Ferric chloride is fed to the aeration tower from nearby storage tanks. The pH of the water is also monitored at in the aeration tower basin to make sure the water is neither too alkaline nor too acidic. The pH of the water is usually between the neutral point of 7.0 and 8.0, which is slightly alkaline. The oxygenated water traveling through the underground pipeline flows to the next treatment step, the biological sand filter beds. 

BIOLOGICAL SAND FILTRATION BEDS

There are four filter bed basins that are 46’ long x 31’ wide x 18’ deep (Figures 10 and 11).  Figure 11 displays the components of filter beds. The actual sand beds (or Biolite™ filter media) containing the bacteria in the basins are 7’ deep. Naturally occurring filamentous bacteria, such as those in genera of Leptothrix, Gallionella, Crenothrix, Hyphomicrobium, Siderocapsacaes, Siderocystis, Metallagenium and Pseudomonas manganoxidan, reside within the sand and they metabolize manganese and iron to separate those elements from the water in the form of solid iron hydroxide.

Below is a picture demonstrating examples of the bacterias and in the case of Leptothrix, some of the manganese oxide clumps it creates. The hydroxide is a brown solid and the dioxide is a black solid, both that remain in the filter media until the filter is backwashed. The microbes need no special nutrients added to the water to help them grow. They do very well on their own, but need to have the water with a pH higher than 7.4 in order to best remove the manganese. Fortunately, our water is above this mark and it is oxygenated, which keeps chemicals out of the water such as hydrogen sulfide and ammonia that could kill bacteria.

Water in these beds usually stays in the basin for a few minutes before being transferred via an underground pipeline to be sanitized by ultraviolet radiation. Periodically, the sand filter beds need to be cleansed of the solid byproducts by backwashing. Two filter beds are backwashed at a time and the process usually takes approximately 1.5 hours, once to twice a week, depending on the season.

UV DISINFECTION VAULT

Water travels out of the filter beds and through one of two banks of high intensity ultraviolet light reactors that are approximately 15 feet below the ground surface.  There are 72 bulbs per reactor. These ultraviolet sources are along the pipeline, so water is not temporarily stopped, it just flows through at rates up to 13 million gallons per day.  

CHLORINE CONTACT BASIN

After the ultraviolet radiation treatment, water is delivered into the backwash pump basin prior to entering the chlorine contact basin. Water in the backwash pump basin is used for the backwash process discussed soon. Water enters the subsurface contact basin through weirs that direct water to one of its two sides. The weirs control the water level of the backwash pump basin. The contact basin is approximately 154’ wide, 130’ long and 22’ deep and holds a maximum of 2.5 million gallons of water. Chlorine gas is injected into the basin to make sure no live bacteria are present in the water. The chlorine concentration must be maintained to last throughout the distribution system; however, chlorine byproducts that can create health issues may form, so the chlorine levels are watched very closely. Each side of the basin consists of baffles that direct water back and forth in a snake-like fashion and usually takes from 71 minutes to 3 hours for the water to travel through, depending if the backwash process is operating. Each side can be closed for maintenance without the other side affected. 

CHLORINE GAS TANKS

Chlorine gas tanks contain canisters of chlorine gas and the delivery of the gas is controlled by computerized instrumentation.

FINISHED WATER CLEAR WELL

The finished water clear well is just downstream from the chlorine contact basin for temporarily storing the water as it waits to be pumped into the water distribution system. This well or subsurface tank has the same dimensions and holds the same water volume as the chlorine contact basin.  Water is also divided into two sides that each feed the water into 48” pipes that lead to the high service pumps.

HIGH END SERVICE DISTRIBUTION PUMPS

There are 12 high service pumps, six that pump water to the north and central part of the city and six that deliver water to the southern third. These are vertical turbine pumps, some with fixed speed and some variable speed motors that can pump up to 3,500 gallons per minute. The distribution system pipelines going away from the water treatment plant to the rest of the city are 30” and 36” in diameter.

BACKWASH SYSTEM

The backwash process consists of flushing the sand filter beds of the precipitated solids and organic debris. Non-chlorinated water from the backwash pump station just beyond the ultraviolet disinfection vault is used so as not to kill the bacteria that remove the manganese and iron. Water from the filter beds is pumped out at a rate of almost 10,000 gallons per minute into a pipeline to silver geodesic like domes called filter backwash wastewater holding tanks. Excess water in these holding tanks is decanted and sent back to the aeration tower and cycled back through the plant.  This process results in low water losses, about 3% of the total water that enters the plant. 

The left over sludge is directed into a thickening clarifier and small holding tank/pump station that then delivers the sludge to a belt filter press. The last water in the residual sludge is squeezed out by the press screen conveyor system. 

Residual solids are then dropped onto another conveyor belt that takes the material to a trailer to be transferred to the Municipal Landfill. Approximately 4 tons of solid waste is produced every week.

WATER DISTRIBUTION SYSTEM

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. 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. They then deliver water to customers downhill using gravity. Water delivered to a particular range of elevations is called a pressure zone; there are seven water pressure zones within the city (refer to image below). 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 need a pressure regulator on the water line going into the structure to prevent damage to pipes and appliances inside.

WASTEWATER TREATMENT

Sewer 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 sewer 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 gallon per day capacity MTP facilities are extended aeration sludge treatment plants that treat the wastewater on multiple levels. The 3.5 million gallon 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 hour 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.

Island and Mulberry Wastewater Treatment Plants - Since the ITP and MTP have the same treatment technology; they will be treated as one. Wastewater influent enters a plant through subsurface sewer lines  and is first pretreated in the headworks or screens building. This building contains a trash rack  that collects as much of the larger solids in the water as possible (i.e. diapers, rags, paper etc.). This is the one part of the entire tour that reading this online is far less offensive to your olfactory system than being onsite.

For the MTP only, water flows into a grit chamber underneath the building after the trash rack, which slows the water flow to allow more solids like small pieces of glass, rock and sand to settle. The solids from the trash rack and grit chamber are transferred to a trash bin that is picked up by Allied Waste and transferred to our municipal landfill. The trash rack screen mesh size for the ITP and NRP is much finer (0.006 inch mesh) than at MTP, which does the same job as the grit chamber at MTP. So there are no grit chambers at either ITP or NRP. In any case, the water still has plenty of small suspended solids (mostly organic) in it after the pretreatment process, but those will be taken care of in the next couple of treatment steps. Wastewater is sent from the headworks building to a flow equalization tank, which regulates the flow of wastewater into the rest of the plant. This is a very important step because if too much flow comes in at once, the system would be overwhelmed and a spill could take place. 

These next treatment steps involve biochemistry, and more specifically, the action of bacteria to change the water chemistry. There are many types of bacteria in the wastewater that cumulatively can accomplish several steps in the treatment process. The flow-controlled wastewater is sent to an aeration basin, in which different types of aerobic (oxygen loving) bacteria do their magic on the wastewater by consuming much of the organic material. The wastewater industry calls this soupy brew of water and minute organic solids, mixed liquor, and it is certainly not the type anyone would want to drink. Since the bacteria can quickly use up the dissolved oxygen in the basin, more oxygen must be provided to the bacteria by blowing air into the tank. A large bridge stirrer that has paddles in the basin rotates around the basin once every 2.5 minutes to keep the solid particulates from settling to the bottom of the basin. 

Some aerobic bacteria in the mixed liquor of the aeration basin oxidize nitrogen ions, primarily found in the compound ammonia (NH₃ – this is one nitrogen atom bonded with three hydrogen atoms). This two step process called nitrification, is a great example of bacteria using dissolved oxygen. First, Nitrosomonas sp. bacteria metabolically convert the ammonia into nitrite (NO₂^-) by adding oxygen.  Once nitrite is formed, Nitrobacter sp. bacteria quickly add more oxygen to convert the nitrite into nitrate (NO₃^-).

It is good to rid the mixed liquor of ammonia (it is poisonous and smells bad), but nitrate as well as nitrite can create health problems when consumed. Nitrate is a regulated contaminate under the Safe Drinking Water Act that is supposed to be kept to concentrations less than 10 mg/l or 10 parts per million. This law carries over to disposing the finished product at the end of the treatment process, called wastewater effluent, into a groundwater aquifer or surface water system. In order to keep the wastewater effluent concentrations below 10 mg/l, another set of bacteria is used (including Paracoccus sp.) to reduce the nitrate to nitrogen gas (N₂ – this composes 78% of the Earth’s atmosphere) that harmlessly escapes into the atmosphere. This process is called denitrification. The bacteria that does this work also utilizes oxygen like the others, but when dissolved oxygen is not available, they can also breakup nitrate to get the oxygen they need. As the nitrate concentration in the aeration basin rises, the blower is turned off, bacteria quickly consume the available dissolved oxygen, and reducing conditions develop. These conditions push the bacteria to do the required work of denitrifying the mix liquor. When the dissolved oxygen concentrations drop, usually between 0.5-3 mg/l, the blower turns on again. The on-off process is automatically controlled using a combination of timers set by wastewater staff (based on lab results of daily nitrate and ammonia concentrations in the aeration basin) and sensors that detect the dissolved oxygen levels in the mix liquor. There are also many microorganisms in the mixed liquor that work on the organic molecules to break them up into carbon dioxide (CO₂) and water (H₂O).

The aeration basins at the various wastewater treatment sites have holding capacities between 1.5 to 2.7 million gallons of mixed liquor. At any of the sites, the hydraulic retention time is about 24 hours before it is transferred to a secondary tank, called a clarifier. As the name implies, solids are allowed to settle to the bottom, clearing the water of most particulates. 

The clarifier is smaller than the aeration basin and has sludge collectors at the tank bottom that rotate only once per hour. The sludge collectors push the sludge along the bottom of the tank so it does not stick and accumulate. The solids remain in the tank for about 20 days and are then returned to the aeration basin as a return activated sludge (active because the microbes are actively working to break up the molecules). 

Every so often though, when the sludge accumulation begins to exceed the desired concentration in the aeration basin, the solids are diverted instead to an aerobic digester tank as waste activated sludge.

The odor in the digester tank is also very strong for those who dare to enter during the onsite tour.  Solids are thickened in the digester and once every couple of days, they are pumped out of the bottom of the tank and are taken to a filter press (Figure 36) very similar to that located at the water treatment plant. A polymer is added to the sludge to help separate the solid phase from the water before it is pressed to drive as much water out as possible. The separated, moist solids fall onto a conveyor belt that transfers the material to a City dump truck. All of the recovered solids are transferred to the city landfill. The squeezed water is piped back to the aeration tank for reuse. Water in the digester is decanted out after about one to three hours to the aeration tank for recycling.

Water in the clarifier has undergone quite a bit of biological treatment to this point. As water from the aeration basin flows into the clarifier, it displaces the existing water, which flows over a weir into a pipeline that connects to either to “fuzzy” filters of synthesized material or to sand filters (ITP), which capture what they can of leftover solid particulates. The water continues through a series of high intensity ultraviolet lights at both plants and is discharged to ponds for either reuse or percolation. The ultraviolet lights provide disinfection treatment of the water, similar to that at the water treatment plant; they disinfect the water of many pathogens. Post ultraviolet water samples are collected to test for fecal coliform bacteria as regulated by law.

North Regional Wastewater Treatment Plant – The NRP has a similar flow and biological treatment design as the ITP and MTP, but differs in a significant way by utilizing membrane basins in place of a clarifier basin and tertiary filtration. Also unlike the other two plants, the aeration basins are rectangular and closed to the atmosphere to prevent birds from congregating in the area. This plant is just south of the City’s airport and of course, birds and planes do not mix very well. There are two basins, each 154’ long x 21’ wide x 18’ deep, which together can hold almost 1.8 million gallons. 

Water entering a membrane basin from the aeration basins is forced through 0.4 micron holes by applying a vacuum in the hollow core membrane fibers that are draped into the basin. This process effectively separates the solids from the water. The membranes need periodic cleaning and the plant has a membrane air scour and chemical feed system for this purpose. Once the treated wastewater has been filtered through the membranes, it is pumped through ultraviolet lights and discharged temporarily into a 250,000 gallon reuse tank. Effluent is then pumped from this tank for either irrigation use, injected into the subsurface via wells, or is transferred to the ITP percolation ponds.

MULBERRY LAB

Part of the wastewater treatment process includes monitoring the environmental conditions of key process steps to make sure the system is operating properly. Additionally, Arizona State law dictates that the City hold Aquifer Protection Permits (APP) for the disposal of effluent at each treatment plant.  APP’s, as regulated through the Arizona Department of Environmental Quality (ADEQ), require monitoring of wastewater prior to leaving the plant and groundwater surrounding the treatment plants, including collecting and analyzing groundwater samples. Lake Havasu City operates a laboratory at the MTP to handle most of the voluminous water samples required to be analyzed. The lab is accredited by the Arizona Department of Health Services to conduct specific analytical analyses for water and wastewater samples and is annually audited by the department to make sure they are in compliance with state regulations.

Under the APP, water samples are collected daily at different stages of the treatment process at each treatment plant to check for appropriate levels of turbidity, fecal coliform counts, various types of nitrogen concentrations, and other chemical parameters (pH, alkalinity, total dissolved solids, chemical oxygen demand and biological oxygen demand). The operators of the plants need this information to properly operate the wastewater treatment process. Further monthly and quarterly sampling is required from point of compliance groundwater monitoring wells adjacent to the treatment plants to make sure the effluent is not negatively impacting the environment. Those parameters that the MTP lab cannot analyze, such as various types of metals and volatile hydrocarbon compounds, are sent to commercial labs. 

The lab also can identify what types of organisms that are involved in the wastewater digestion process and through a method known as Most Probable Number (MPN), how many fecal coliform bacteria are in the finished product. These tests use a Quanti-tray unit that isolates wastewater in small wells for the growth of bacterial colonies. This method uses an incubator to heat the wells to 44.5^oC to encourage bacterial growth. Note that during the on-site tour, a microscope is often set up to show the microorganisms in action that are present in the aeration basins. The lab must submit quarterly Self-Monitoring Report Forms (SMRF) of the lab results to ADEQ.

The MTP also analyzes water samples submitted by the City’s Water Division. ADEQ regulations for operating the water treatment plant and water distribution system also require monitoring, particularly for total coliform bacteria. Alkalinity, dissolve oxygen, pH, total dissolved solids, ammonia, hardness and calcium concentration are also analyzed at the laboratory.

Neighboring communities and entities also submit water and wastewater samples to the MTP lab for analyses. Included are Kingman, Parker, Arizona State Parks, Colorado River Sewage Systems Joint Venture, and Yucca.

TREATED WASTEWATER DISPOSAL AND REUSE

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. 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 let the effluent flow over a weir into the adjacent commingling pond. 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 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. 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 or diverted into the first of three percolation ponds located adjacent to the plant facility. 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. 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. If fact, the ITP is a listed spot for winter bird watching on the Arizona Field Ornithologists website. The one main downside for Lake Havasu City of using these ponds is that the effluent is lost to the Colorado River and cannot be reused.

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. 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.