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Quagga Mussels
Population ConsiderationsThe Clean Colorado River Alliance, established by Arizona Governor Janet Napolitano, issued a 2006 report covering the most concerned threats to the Colorado River. Recognizing there are many potential threats to the river system, the Alliance decided to focus on what it perceived to be the seven most significant threats, nutrient loading, metals, endocrine disrupting compounds, perchlorate, pathogens/bacteria, salinity/total dissolved solids, and sedimentation, The report also highlights the need for better understanding of the interactions between the river and human activities through monitoring, data sharing, education programs, federal funding for mitigation, and interstate communications. Since the final report was published, the threat of perchlorates has waned due to significant mitigation efforts at the source in Nevada. However, another threat has emerged, the infestation of quagga mussels, which have the potential to alter the ecological balance in the river/reservoir system and could indirectly exacerbate the threat from pathogens/bacteria and more directly alter the threat of chemical compound contaminants through bio-concentration up the food chain. Yet another potential threat largely unstudied is the effect of hydrocarbons from recreational water craft in the river/reservoir system. Although each threat is significant and of great concern to our water supply, CRRSCo’s main emphasis has been on nutrient loading, specifically nitrate contamination.
Nitrates and Septic Systems
Nitrates cannot exceed 10 mg/L in a water source without treatment, based on federal standards. The Lower Colorado River has recorded well sites with nitrate values exhibiting highs from 20 to 40 mg/L. The primary source is the number and density of septic tanks utilized for wastewater treatment. Secondary non-point sources include agricultural areas and golf courses located adjacent to the river where fertilizers are applied.
An assessment of septic tank densities was made in 1999 by the engineering firm of Burns & McDonnell (hyperlink to the report) as part of a watershed planning document for the Colorado River from Bullhead City to Yuma, Arizona. The largest concentration of septic tanks is along the Colorado River, generally north of Interstate 10. In some instances, septic tank densities are three to four times greater than typically associated with current regulations in place for permitting septic systems. An update conducted in 2004 and included in the Bureau of Reclamation’s March 2007 report on the river found that the number of septic systems increased over the five-year period despite the addition and augmentation of some centralized collection systems
California communities along the Lower Colorado River have recorded large increases in septic systems installations, accounting for approximately 19 percent of the septic systems below Lake Mead and accounts for approximately 31 percent of those located in unincorporated areas.Due to past limits on funding and staff, California county regulators have been able to address septic system problems primarily when pollution was visible on the surface. However, the state is now taking a strong interest in septic systems because of fecal bacteria and nitrates leaking into surface water and groundwater. Instances of nitrate levels exceeding 100 mg/l have been identified and are attributable to septic tank contamination. With greater numbers of septic systems introduced, more nitrates are added to the connected hydrogeology of the Colorado River and the adjacent aquifer. The California Regional Water Quality Control Board members are concerned that in fast growing high desert areas developers are proposing septic systems despite the risk of aquifer contamination. The Board estimates that nearly 7 MGD of waste is discharged to septic systems, and only a small fraction of these tanks are regulated by the Board. Based on population information and septic tank data for the Lower Colorado River, CRRSCo estimates greater than 7 MGD are being discharged to this portion of the river aquifer system. This is a disproportionate value considering the limited land area involved along the Lower Colorado River.
On the Arizona side of the river, two communities with the highest septic tank densities, Lake Havsu City and Bullhead City have each taken the lead to mitigate against nitrate loading by expanding their sewer collection systems. Prior to these efforts, the number of pounds of nitrates accumulating in the aquifer adjacent to the river increased dramatically from 1981 to about 2005, particularly with the construction boom from 2000 to 2005. .Nitrate values recorded in monitoring wells in both areas over this period reflect increases and indicate a down gradient migration toward the Colorado River and Lake Havasu. Monitoring wells tested indicate increases from 4.3 mg/L to 8 mg/L to as much as 40 mg/L moving down gradient.
Yet, testing of wells within a thousand feet of Lake Havasu indicates a decrease in nitrate concentrations. Modeling of the river aquifer system indicates the decreased concentrations are due to dilution occurring in an aquifer mixing zone created by diurnal and seasonal fluctuations in the reservoir’s water level. The water level changes are due to varying magnitudes of Bureau of Reclamation water releases from Lake Mead to satisfy delivery orders for customers down river or for maintenance or power generation management. When lake levels are high, lake water tends to migrate inland and serves to dilute the nitrates moving down gradient. When lake levels are low, nitrate-rich groundwater moves toward the lake. This same situation is likely occurring at other locations along the Colorado River system where highly concentrated nitrate in aquifers interfaces with fluctuating levels of lake and river water. Current drought conditions reflected in the levels of Lake Mead and Lake Powell exacerbate the situation. With lake levels around 50 percent of the normal full capacity, levels in the downstream river system will tend to exaggerate the changing water levels. There is little that can be done to change drought conditions, but we can move to reduce nitrates by reducing the septic systems.
Arizona Department of Environmental Quality studies in 1995 and 1999 in the Bullhead City and Mohave Valley areas noted that local geology controls the hydrology and the water quality of the area, particularly correlating elevated nitrate concentrations with high-density population areas using subsurface, on-site septic systems. Discharging wastewater migrates down gradient toward the Colorado River. Representatives of the California State Water Board in Sacramento confirm that septic wastewater plumes can travel much farther than previously thought; up to 300 feet at dangerously elevated levels. Data developed for the Lake Havasu City area indicates 400 feet lateral migration in a year’s time.
Although Lake Havasu City and Bullhead City have taken large strides in the past few years in eliminating septic tanks (up to 23,000 as of November 2008), many more are still in place within these communities and in surrounding unincorporated areas adding nitrate to the Colorado River aquifer system.
The Atlas Corporation's uranium tailings pile in Moab, Utah, contains approximately 10.5 million tons of uranium mill wastes, including 426 million gallons of highly contaminated liquid which is seeping from the unlined site.
This 130-acre site, where rich uranium to abandon the site. The company regulatory commission agreed to a plan that would minimize Atlas’ expense for cleanup by capping the tailings, covering them with rock and sand instead of moving the tailings away from the Colorado River.
A 1998 report by the Oak Ridge National Laboratory calculated that even if Atlas’ plan is implemented, the uranium-contaminated liquid will leak into the Colorado River for approximately the next 270 years. The EPA states that uranium can cause toxic damage to the kidneys and increases the risk of bone and liver cancer and blood diseases such as leukemia.
The U.S. Department of Energy took over the site in 2001 and in September 2005, approved a plan by which almost 16 million tons of radioactive waste will be moved from the banks of the Colorado River to a site at Crescent Junction, more than 30 miles to the northwest. Amendments to that plan schedule the removal to begin in the spring of 2009 with an original projected project completion date of 2028. The process could be accelerated to be done as early as 2019 if sufficient funding is available.
Residents along the Colorado River have growing concerns regarding chromium and the potential for surface and groundwater contamination.
The pollution began decades ago when the Pacific Gas & Electric Company (PG&E), which serves central and northern California, used hexavalent chromium to control corrosion and mold in water-cooling towers at an isolated natural gas compressor station south of Needles. From 1951 to 1964, PG&E dumped untreated wastewater into percolation beds in a wash across from its Topock Natural Gas Compressor Station.
A groundwater plume contaminated with chromium was discovered on the California side of the river near PG&E's Topock site and is being cleaned up under the direction of the California Department of Toxic Substance Control. Contaminated water is being trucked more than 200 miles to treatment facilities in California and Arizona, according to DTSC spokesperson Ron Baker.
The plume was estimated to contain at least 108 million gallons with chromium concentrations as high as 12,000 parts per billion (ppb) — California’s drinking
water standard is 50 ppb — and had reached within 125 feet of the Colorado River. To date, no chromium contamination has been detected in the river, but DTSC has estimated that the plume is moving at about one foot per year.The Arizona Department of Environmental Quality (ADEQ) is working with California officials to characterize the full extent of contamination and reduce the potential threat to public health and the environment.
The ADEQ has sampled more than 20 potable water supply wells in the area, and collected water level measurements to determine the direction of groundwater flow along the river. Although hexavalent chromium was found in all wells sampled by ADEQ, chromium concentrations detected in the study wells were well below the Arizona drinking water standard of 100 ppb.
A subsurface chromium plume emanating from the now defunct McCulloch Corporation boat motor manufacturing plant in Lake Havasu City is about one mile from Lake Havasu. Previous exploration work defines two plume levels beneath the water table and about 150 feet below ground level. Groundwater is slowly migrating towards the lake, A full scale remediation program is now in the planning stages.
The U.S. Department of Health and Human Services has determined that some chromium compounds are known to cause cancer in humans. The Agency for Toxic Substances and Disease Registry, meanwhile, states that ingesting large amounts of chromium can cause stomach upsets and ulcers, convulsions, kidney and liver damage, and even death.
(back to top)A number of other contaminants — both organic and inorganic — further contribute to pollution on the Lower Colorado River and threaten the water supply.
Organic contaminants are usually carbon-based chemicals, such as solvents and pesticides, that can get into water through runoff from cropland or discharge from factories. Municipal wastewater discharge from treatment plants and stormwater runoff frequently contain numerous organic contaminants stemming from the use of pesticides, pharmaceuticals and personal care products, petroleum derivatives, cleaning agents and other household products.
The emergence of organic compounds in streams is a relatively recent phenomenon, and there are many uncertainties regarding their effects. Most are not regulated by the EPA.
Pesticide residues have been detected in the Lower Colorado River at Imperial Dam and the Northern International Boundary. In 1968, the Federal Water Pollution Control Administration concluded that the use of pesticides on irrigated lands was causing contamination problems, a 1973 EPA analysis concluded that pesticide contamination was not a problem on the Lower Colorado River. Nonetheless, fish tissues collected there exceeded California’s maximum tissue residue level for several pesticide constituents.
Pharmaceuticals and personal care products are emerging contaminants found in wastewater streams and have been detected at very low concentrations in Lake Mead and Lake Havasu. Several compounds are known to cause endocrine and physiological disruptions (such as sex changes) in aquatic species and many more compounds are being studied for their potential to cause similar responses in humans. The group under investigation includes both prescription and nonprescription drugs, steroids, insect repellents, fragrances and solvents. Most are not regulated by the EPA. They generally are difficult to remove through conventional treatment methods and, consequently, are highly persistent in the environment.
Industrial contaminants include compounds such as polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons which once were used as coolants and lubricants in transformers, capacitors and other electrical equipment. PCBs, which the EPA has identified as carcinogens and priority pollutants, do not readily break down in the environment and may remain there for very long periods of time.
Inorganic contaminants are compounds that typically do not contain the element carbon in their structure. They can become dissolved in water from natural sources or as the result of human activity. Though they occur naturally, they are regulated in public water supplies due to their ability to cause acute poisoning, cancer and other health effects.
Inorganic contaminants also include a variety of metallic and basic ions that collectively make up the salinity of Colorado River water. They stem from compounds of metals such as sodium, calcium and magnesium and of bases such as carbonates, sulfate and chlorides. Salinity can affect the palatability of drinking water, the durability of appliances and fixtures, agricultural productivity and the amount of water needed for irrigation.
The river’s salinity is being addressed by the Colorado River Salinity Control Program, a partnership effort involving agricultural interests, federal agencies and the seven Colorado River Basin states. The program includes numerous projects to reduce inflow of natural saline springs and seeps and to reduce the salts contained in return flows from irrigation and domestic use.
Since the discovery of quagga mussels in Lower Colorado River reservoirs in early 2007, observations show an explosion in growth and distribution within these reservoirs and connecting canals and reservoir systems that draw water from river. These mussels are growing on any substrate or surface they can find (except copper pipes) and are rapidly clarifying the waters in the reservoirs. As their discovery in the arid southwest is so recent, very little scientific research has been concluded concerning this species, yet managers of water delivery systems and federal, state, and local agencies have scrambled to implement mitigating measures to control and limit the further spread of these mussels. Most North American scientific research on quagga mussels and its close relative, the zebra mussel, has been focused in the Great Lakes region, although published studies from other areas in the eastern United States have shed light on the adaptability of these mussels to new environments. The two mussels belong in the genus, Dreissena, whose name will be used in this summary to encompass research information related to both species.
As with many successful exotic species placed in a new environment, Dreissena have had a pronounced ecological effect through its feeding habits. These mussels are extremely efficient, but selective filter feeders of phytoplankton, zooplankton, and other organic and inorganic debris. In doing so, they expel both pseudofeces, unused material mixed with mucus, and feces, processed nutrients and waste products. The pseudofeces provide a desirable nutrient source for protozoan organisms and also contain unwanted cyanobacteria, blue-green algae that can create toxic conditions in the water column if they occur in mass. Filtering algae out of the water essentially clears the water column allowing sunlight to penetrate to deeper levels in the aquatic system. More sunlight, coupled with increased nutrients such as nitrates, leads to more aquatic plant growth on the lake bottom. Green, filamentous algae is the most commonly reported plant group that establish the once barren surface. Some species like Cladophora (which is beginning to grow on the reservoir bottoms as the water clarifies), have contributed to deteriorating environmental conditions by fouling water as it decays and by harboring and promoting E. coli bacterial growth. Fewer phytoplankton translates to less overall food and to changes in types of dominant plankton species that are generally less nutritious for higher level organisms. These conditions have been known to lead to degraded fish size and populations. Less food has also led to significant population declines of other filter feeding mollusks such as Unionids in the Great Lakes and Orbiculas in Lake Havasu. Quagga mussels have even out-competed their zebra mussel relative in the Great Lakes. Several predators feed on Dreissena, yet the predation rate is far less than the mussel’s reproduction rate, leaving mussel populations largely unaffected.
As Dreissena depends on the availability of phytoplankton, it indirectly is dependent on the amount of nutrients available in the aquatic system for plankton production. Their feeding habits also modify an aquatic system’s nutrient cycle by redistributing the availability of nitrogen, phosphorus, and dissolved organic carbon (including chlorophyll). Although nitrogen and phosphorus is regenerated on the lake bottom from protozoan activity on pseudofeces, phosphorus regeneration may be limited if the aquatic environment is phosphate limited. Modifying the nutrient cycle affects the natural balance in which many species depend. Once dominant species may be reduced or replaced by species previously not well suited in the environment.
Without a continuous input of these nutrients, phytoplankton production could decrease enough to negatively affect the Dreissena population. Outside sources of nitrogen, in the form of nitrates, and phosphorus, in the form of organic orthophosphates, include septic tanks, effluent disposal, and urban run off. Large amounts from these sources can lead to over production of phytoplankton and other aquatic plants, which can, in turn, enhance mussel proliferation. Algal blooms, such as the blue-green algae, Microcystis, may also develop when these nutrients are released into the water column from protozoans grazing on the mussel pseudofeces. These blooms may lead to oxygen depletion of the aquatic system when the algae die and decay, killing fish and other aquatic organisms. As noted above, toxic conditions may also develop during these blooms. Research suggests that limiting nutrient loading may help control mussel populations.
Most mollusks, including Dreissena, have the capacity to absorb and concentrate contaminants from the aquatic environment. Dreissena also concentrate contaminants in their pseudofeces. In either case, the contaminants may be passed up the food chain to further concentrate the pollutants to levels toxic to higher organisms, including humans. Types of pollutants that have been found in these mussels include chlorinated hydrocarbons, pesticides and herbicides, and heavy metals such as mercury, arsenic, and cadmium.
The relationship between Dreissena feeding habits, nutrient loading and cycling, ecological shifts, and the bioaccumulation of contaminants all result in changes of water quality and a potential threat to the health of the ecosystem, including sport fish and humans. A key to slowing the potential environmental alteration due to the presence of quagga mussels in the Lower Colorado River is to limit the mussel’s food source by controlling outside nutrient loading.
Population Considerations
Explosive population growth has occurred along the Lower Colorado River. In 1999, when the original watershed study was completed, population data available indicated a projected population in 2005 of 240,000 for the study area. Information developed in 2004 with U.S. Census data from 2000 and updated information from communities, however, shows a 2005 population of 330,000. This represents a 38 percent increase over what previously was projected for a five-year period. Although growth has temporarily slowed beginning in 2006 due to a national economic downturn, the planning area is expected to resume its rapid growth as people continue to be attracted to the desert climate.
The above population numbers do not include the large influx of winter visitors to the area who call the Lower Colorado River home for several months each year. Populations swell in some areas, such as Quartzite, Arizona, which explodes from a few thousand to over one million people during this period.
Population growth is too large to stop, and turning people away is not the answer. The influx of people has been good for the economic conditions of communities and counties in California, Arizona and Nevada. But the downside is that they are moving into areas already being served by outdated wastewater technology and septic tanks that can no longer function to treat wastewater without creating a nitrate contamination problem.
Action is needed now. The dynamics of all the factors at work contributing to the need for increased wastewater system facilities to meet the needs of the population can not be changed to reduce the wastewater treatment requirements.
The only solution is to deal with the lack of adequate state-of-the-art systems and assist in funding programs to allow for their implementation.
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