Michael D. White and Cheryl M. Hart
Ogden Environmental and Energy Services Co., Inc.
Table of Contents
BACKGROUND AND PROJECT SETTING
In 1993, the counties of Riverside and Imperial, the Imperial Irrigation District (IID), and the Coachella Valley Water District (CVWD) entered into a Joint Powers Agreement, creating a public agency known as the Salton Sea Authority. The Salton Sea Authority directs and coordinates actions relating to improvement of water quality, stabilization of water elevation, enhancement of recreational and economic development potential of the Salton Sea, and other beneficial uses, recognizing the importance of the Salton Sea to the dynamic agricultural economy in Imperial and Riverside counties. In 1994, the Salton Sea Authority received a grant from the U.S. Environmental Protection Agency's (USEPA) Clean Lakes Program to conduct environmental and economic analyses of salinity and elevation management options for the Salton Sea. The general goal or purpose of the management project is to stabilize the salinity and elevation of the Salton Sea at levels that maximize the economic, environmental, social, and cultural attributes of the region. This document, the Final Report for the Clean Lakes Grant, summarizes management alternatives proposed to date, screens these proposed alternatives against criteria established by the Salton Sea Authority, and presents environmental scoping issues raised during the public review period.
The Salton Sea is the largest lake in California and is a regionally important feature from both environmental and economic standpoints. It is located in the southeastern corner of the state within the geologic feature known as the Salton Basin, a natural basin located approximately 278 feet below mean Sea level (-278 feet msl). The Salton Sea receives drainage from approximately 8,000 square miles of Riverside, Imperial, and San Diego counties and the Republic of Mexico. It is a closed basin; water only leaves the Sea via evaporation. Inflow to the Salton Sea consists of agricultural drainage, storm water, and wastewater and is generally in hydrologic balance with evaporative losses. The closed nature of the system has resulted in changes in the salinity and water surface elevation of the Salton Sea over time. The salinity of the Sea is currently 44 parts per thousand (ppt) and is expected to continue to rise. The increasing salinity is due mainly to high evaporation rates, low rainfall, and the discharge of saline agricultural wastewaters into the lake. Elevation of the Sea varies as a result of changes in inflows and weather conditions that alter its hydrologic balance.
The Salton Sea and surrounding area provides important habitat for many wildlife species. The Salton Sea is characterized by both terrestrial and freshwater wetland vegetation communities. Typical vegetation communities occurring in the Salton Sea area include Sonoran creosote bush scrub, desert saltbush scrub, desert sink scrub, stabilized and partially stabilized desert dunes, tamarisk scrub, freshwater marsh, cismontane alkali marsh, Sonoran cottonwood-willow riparian forest/nonnative tamarisk scrub intermediate, open water, mud flats, ruderal, and agricultural lands. Sensitive habitats are those which are considered rare within the region or that support sensitive plants or animals. Sensitive habitats found in the Sea area include wetlands and non-vegetated aquatic habitats ("waters of the U.S."), which include freshwater marsh, cismontane alkali marsh, Sonoran cottonwood-willow riparian forest/nonnative tamarisk scrub intermediate, open water, and mud flat habitats.
There are numerous invertebrates, amphibians, reptiles, fish, birds, and mammals that are found in aquatic and terrestrial habitats adjacent to the Sea and in the surrounding Imperial and Coachella valleys. The Sea and adjacent wetlands, river systems, natural habitats, and agricultural fields provide foraging and roosting opportunities for large numbers of migrant and resident birds. There are also important fishery resources present in canals, irrigation ditches, rivers, and the Sea itself. The Salton Sea is currently reported to support eight species of fish, including the federally endangered desert pupfish (Cyprinodon macularius) and four important sport fishes, tilapia (Oreochromis mossambiqus), bairdiella (Bairdiella icistia), sargo (Anisotremus davidsoni), and orangemouth corvina (Cynoscion xanthulus). There are also several sensitive fish, reptile, bird, and mammal species found at the Sea and adjacent areas.
The Regional Water Quality Control Board, Colorado River Region has designated a number of beneficial uses for the Salton Sea. These include aquaculture; water contact recreation; non-contact water recreation; warm freshwater habitat; wildlife habitat; and preservation of rare, threatened, or endangered species. Industrial service supply is designated as a potential beneficial use.
The continued rise in salinity and variable elevation threaten the region's environmental, recreational, and economic values associated with the Salton Sea. The Sea currently serves many important functions such as serving as a drainage basin for agricultural run-off of Coachella and Imperial valleys; providing important habitat for both resident and migratory wildlife species as well as several endangered species; providing recreational values such as fishing, hunting, boating, camping, nature study, bird-watching, and sightseeing; providing for growth of commercial resources and residential developments; and providing flood control measures by serving as a repository for stormwater run-off. The Salton Sea Authority is evaluating alternatives that have the ability to manage salinity and elevation of the Sea in order to protect the beneficial uses of the Sea.
In order to evaluate the efficacy of various potential management alternatives, salinity and elevation management goals or targets were established. Three quantitative criteria for screening potential management alternatives include, a target salinity range of 35 to 40 ppt, a target elevation range of -230 to -235 feet msl, and operation and maintenance cost that does not exceed $10,000,000 per year. Additionally, the Salton Sea Authority decided that the alternatives must make use of currently available, proven technologies. Any alternative that does not meet these criteria will be eliminated from consideration in further environmental reviews.
PROPOSED MANAGEMENT ALTERNATIVES
A wide variety of alternatives have been proposed over the years to manage the salinity and surface elevation of the Salton Sea. The various management alternatives have been grouped into six general categories: 1) diked impoundments within the Salton Sea; 2) pump-out of Salton Sea water to another area (e.g., dry lake beds, onshore evaporation ponds, the Gulf of California, or the Pacific Ocean); 3) a combination of alternatives consisting of diked impoundments, onshore evaporation ponds, and a pipeline/canal system to transport concentrated brine to Laguna Salada/Gulf of California, among others; 4) removal of salts from inflowing water before it enters the Sea (e.g., desalination plant, biological filters, or special pre-treatment reservoirs); 5) use of imported water to dilute the Sea; and 6) other proposed alternatives that do not specifically address the problem of stabilizing salinity or surface elevation.
Managing salinity with diked impoundments is based on removing salts from the Sea and decreasing the volume of the lake, which results in greater dilution of the remaining Salton Sea water by inflowing fresh water. The diked impoundment acts as an evaporation basin, isolating and concentrating the brine by evaporating Salton Sea water within the impoundment (USDOI and RAC 1969, 1974; Aerospace Corporation 1971; CVWD pers. comm. 1995). Although the effective volume of the lake would be reduced by the volume of the impoundment, which would result in a rising lake level given the same fresh water inflow, a volume of Salton Sea water equal to the freshwater inflow can be let into the impoundment to evaporate away, thereby controlling lake elevation. Eventually, the impoundment would fill with salts, and salt disposal would be necessary.
Numerous diked impoundment alternatives have been proposed over time. The major differences in these options include size of the impoundment, location of the impoundment, and the type of dike structure and design. Nine locations were first studied, with impoundment sizes ranging from 20 to 50 square miles. Since then, CVWD has updated the descriptions of various diked impoundment options and evaluated their efficacy in managing the Sea's salinity. Selected alternative configurations included in this discussion are: 1) a 50-square-mile diked impoundment at the southern end of the lake, 2) a 40-square-mile diked impoundment at the southern end of the lake, 3) two impoundments, one at the southwestern and on at the southeastern end of the lake, totaling 50 square miles, 4) diking off the northern third of the lake, 5) diking off the northern half of the lake, 6) parallel dikes forming 47-square miles of impoundment, and 7) a phased zoning concept. In general, the smaller diked impoundments have been placed in the southern portion of the Sea because the slope of the Sea's bottom and average depth of water is less in the southern end than the northern end. Larger impoundments that dike off one third to one half of the Sea would be located at the northern end of the Sea because the majority of fresher water inflows (New and Alamo rivers) are located in the southern end of the Sea. In addition to these configurations, many other sizes and locations are possible. In general, proposed sizes of the impoundment have ranged from approximately 8 to 50 percent of the surface area of the Salton Sea, and proposed impoundment locations have included all sectors of the lake.
The pump-out alternatives are based on the concept of removing Salton Sea water (and its associated salts) from the lake. This would provide, in effect, an outflow from the lake and change the system from a closed terminal lake to an open flowing system. Salts would be exported with the outflow rather than being retained in the lake when water evaporates. In addition to salts being exported from the Sea with a pump-out alternative, the lake's total volume is reduced as a result of pump-out (inflow no longer equal to outflow), which would result in a salinity decline from dilution with inflowing fresher water and a drop in the Sea's elevation. Surface elevation can only be maintained by importing water back to the Salton Sea. For example, water from the Gulf of California or the Colorado River could be used, in concept, to replace an amount of Salton Sea water that is pumped-out.
All of the pump-out alternatives are based on exporting saline water out of the Salton Sea. The major differences between different pump-out alternatives are the amount of water removed each year, the location to which Salton Sea water would be pumped, and whether water is pumped back to the Salton Sea to control elevation. The pump-out rate will be dependent upon the salinity of the Sea when initiation of pumping begins, the desired target salinity, the desired time to reach that target salinity, and cost considerations. The alternative pump-out locations proposed to date include pump-out to a dry lake bed (Palen Dry Lake will be used as an example, but other dry lakes such as Clark and Ford are considered options), evaporation ponds, Laguna Salada, the Gulf of California, the Pacific Ocean, or onshore treatment/filtration units.
The pump-out to onshore evaporation alternative involves pumping Salton Sea water into evaporation ponds located on the lake's shore, where the water evaporates leaving behind saline residue. Saline water would be removed from the lake at a predetermined rate until the desired salinity was reached. At this point, pump-out would continue at a rate such that salts removed by pump-out each year would equal the annual inflow of salts to the lake. Eventually, the evaporation ponds would fill with salts, and disposal would be necessary. Areas on the southeastern shore, between Bombay Beach and Red Hill, have been suggested as a potential location for onshore evaporation ponds).
Most evaluations of evaporation ponds have concluded that evaporation ponds on land are not economical because of the high costs of acquiring sufficient land around the lake. However, developments in solar pond technology, such as an enhanced evaporation system (EES), where salt water is pumped through an elevated spray system, producing increased evaporation rates, appear to require less land than standard evaporation ponds. The original volume of removed water is reduced by 90 percent with the enhanced evaporation system. The remaining saline water is pumped to conventional evaporation ponds for further evaporation. With the use of enhanced evaporation, Ormat anticipated the need for only 10 percent of the land area necessary for conventional evaporation ponds. The need for salt disposal still exists because the evaporation ponds would eventually fill with salt. Furthermore, there is more energy needed for the pumping and spray system associated with enhanced evaporation.
Evaporation ponds could be used for other purposes, such as using the saline residue in a solar plant for generation of electricity or using Sea water for aquaculture by first pumping the water to a series of aquaculture ponds and then to a series of evaporation ponds. In both cases, the principles for salt removal are essentially the same as described above for onshore evaporation ponds. These additional options represent a potential means to generate monies to offset construction, or operation and maintenance costs.
The pump-out of saline Salton Sea water to the Gulf of California alternative would transport Salton Sea water via a series of canals and pipelines to Laguna Salada and then to the Gulf of California. Canals would be used when transporting water downgradient, and pipelines would be used when pumping water uphill or for outfalls. Another option would be to carry water only to Laguna Salada and allow water to evaporate and the salts to remain. However, the consent of the Mexican government would be required for this option.
An additional option is to construct a return canal/pipeline to transport less saline Gulf of California water to the Salton Sea. Water from the Gulf of California would be pumped over the mountains to Laguna Salada and then gravity-fed to the Salton Sea. The amount of Gulf water pumped to the Sea would equal the amount pumped from the Sea to the Gulf, stabilizing the Sea's elevation.
Construction of an inland seaport at Laguna Salada has been discussed by both the Mexican and United States governments. A canal would be constructed to carry sea water from the Gulf of California to Laguna Salada, which would replenish the dry lake. This canal would be large enough for both freight and pleasure ships to navigate. This proposal could benefit the Salton Sea area by providing for an outlet from the lake. If approval from the Mexican government were obtained, Salton Sea water could be pumped from the Salton Sea to the inland seaport. This alternative is essentially the same as a pump-out alternative to Laguna Salada or the Gulf of California, but the canal/pipe system would extend only to the northern terminus of the navigable waterway. It has also been suggested that a navigable waterway with a lock system could be constructed from Laguna Salada into the United States, providing for economic growth to both the United States and Mexico.
The pump-out to the Pacific Ocean alternative is similar to the pipeline/canal to the Gulf of California alternative, except a link between the Salton Sea and the Pacific Ocean would be established. The exact route has not yet been selected but would be dependent upon cost and engineering considerations. Ocean water would be carried to the Salton Sea, and Salton Sea water would be transported to the Pacific Ocean via the shortest and least expensive route. The distance between the two is estimated at about 100 miles. This exchange of water between the ocean and the Sea would eventually stabilize the salinity and elevation.
A number of proposed alternatives rely on treating or filtering Salton Sea water. Water would most likely be pumped to a filtering unit or plant to remove salts and other constituents. Many of these alternatives rely on developing or unproven and therefore could not be considered viable management alternatives.
Combinations of Impoundment and Pump-out Alternatives
The combination of alternatives use various combinations of the previously described alternatives and some enhancement options not yet mentioned. They may include all or some of the following options: diked impoundments, onshore evaporation ponds, shoreline enhancement areas, constructed wetlands, stabilizing dikes, solar pond and power generation plant, canal/pipeline with or without storage facilities. Some of the combined alternatives proposed thus far include:
an in-Sea diked impoundment, on-shore evaporation ponds, and a pipeline to the Gulf of California;
an in-Sea diked impoundment and a pipeline to the Gulf of California;
on-shore evaporation ponds and a pipeline to the Gulf of California;
a stabilizing dike, solar pond power generation, and constructed wetlands;
a stabilizing dike, solar pond power generation, constructed wetlands, and pumped storage facility to the Gulf of California; and
a joint USA/Mexico solar power generation and pumped storage to Laguna Salada.
These alternatives combine various options already discussed. A diked impoundment adjacent to the shoreline would serve to control elevation, allowing water in and out of the impoundment as needed, as well as manage the salinity. An onshore evaporation pond would serve to manage salinity and could potentially be used for solar pond power generation. A pipeline could be used to transport concentrated brine to another area (e.g., Laguna Salada, the Gulf of California, or the Yuma desalting plant discharge canal). The combined alternative offers the advantage of optimum control of salinity and elevation while also solving the problem of salt disposal. Any combination, such as a diked impoundment and pipeline; evaporation ponds and a pipeline; or a diked impoundment, evaporation ponds, and a pipeline, could be used to manage salinity and elevation.
Other options that could be coupled with these three options described above include, constructed wetlands and shoreline enhancement projects. This would serve to improve water quality and could potentially help to filter out contaminants as they enter the Sea. A stabilizing dike could be used to decrease the overall volume of the Sea and help to control elevation. This differs from the diked impoundment in that there is no enclosure and evaporation of water. Instead a dike is constructed at the southern end of the Sea to reduce the overall volume of the lake, helping to stabilize the surface elevation. A pumped storage facility could be constructed at the highest point of the canal/pipeline. This would allow for more control of the transportation of water, allowing pumping at night when electricity rates are the lowest.
Another proposed solution is to import fresh water to the Sea, diluting the Sea water to a desired salinity. It is unlikely sufficient fresh water is available to dilute the Sea to the desired salinity, nor does this solution address elevational control. However, many of the management alternatives discussed above, especially pump-out alternatives, call for the removal of Salton Sea water, which will lower the lake's elevation. The only way to stabilize surface elevation would be to add an equal amount of water to the lake to replace that which is removed. This would also help to decrease the Sea's salinity if the replacement water has low salinity relative to the Sea's water.
Identified sources of replacement water include Colorado River water and the Gulf of California water. Colorado River water could be delivered through existing canals or expanded canal systems only in years when surplus water is available. Gulf of California water could be delivered through constructed pipeline/canal systems. The latter option is more expensive, but potentially more reliable.
Other Proposed Options
Other proposed alternatives do not specifically address the problem of stabilizing salinity or surface elevation. Since these alternatives do not meet the purpose and need of the project, these alternatives can not be considered viable management alternatives.
ALTERNATIVES EVALUATION AND SCREENING
The primary objective of the management project is to stabilize the salinity and elevation of the Salton Sea at levels that maximize the economic, environmental, social, and cultural attributes of the region. To focus future studies and environmental analyses on those alternatives that are most likely to meet the objectives of the project, the Salton Sea Authority set management targets that were used to screen potential alternatives. These targets included the ability to maintain salinity in a range of 35 to 40 ppt, maintain surface elevation in range of -230 to -235 feet msl, have an annual O&M cost less than $10,000,000, and rely on proven technologies. The ability of proposed management alternatives to meet these criteria are summarized below.
A number of alternatives, such as research or enhancement projects, did not address the problem of stabilizing salinity or surface elevation, and were not considered further as management alternatives. Alternatives that did not meet the established screening criteria include alternatives that propose to remove salts before water enters the Salton Sea. While many of the specifics of these alternatives were not available, it is unlikely that the various proposed alternatives could remove the 4,000,000 tons of salt that enter the Salton Sea each year, except at enormous cost, most likely exceeding the established annual O&M cost target. In addition, these alternatives do not manage surface elevation.
Alternatives that import water also do not appear to be an effective method to manage salinity of the Salton Sea. Sufficient volumes of water from the Colorado River do not appear to be available at a frequency to allow management of the Sea's salinity. Gulf of California water could be used to replenish water removed as part of a pump-out alternative, but pipeline/canal systems to the Gulf of California have been estimated to exceed the established annual O&M cost target.
Pump-out options, which do not incorporate water imports, do not manage surface elevation. Pump-out options which do incorporate water imports have the capability of managing salinity, elevation, and solve the problem of salt disposal. However, pipeline/canal alternatives are relatively expensive to operate and maintain, and are generally estimated to exceed the O&M target. In addition, the majority of pump-out options involve siting project components in Mexico, which would result in a loss of control over the project and greater uncertainty in the environmental process for the Salton Sea Authority. Similarly, combinations of alternatives that rely on pump-out or transport of Salton Sea water from the Salton Basin have the same problems as the pump-out alternatives; although the specifics of many of these combinations of alternatives are presently not available. Many of the remaining pump-out options rely on unproven technology or lack sufficient information to adequately evaluate their ability to meet screening targets. However, since the specifics of some of the pump-out and combinations of alternatives are not available, some of these alternatives were not eliminated by the screening process.
Diked impoundments appear to have the greatest potential for meeting the project objectives while satisfying the established Salton Sea Authority's screening criteria. In general, diked impoundments have the ability to manage both salinity and surface elevation and are relatively inexpensive to operate and maintain. However, the diked impoundment alternatives store the salts within the impoundment and salt disposal will be necessary at some point within the life of the project. A value engineering evaluation of alternative dike structures concluded that excavation, haul, and dump dike construction is the most flexible, reliable, and cost-effective method. Combinations of alternatives that make use of diked impoundments and certain pump-out alternatives also appear to meet established screening criteria, except O&M costs of these alternatives have not been estimated. Based on the projected O&M costs for pipeline/canal systems, combinations of alternatives that utilize both diked impoundments and pipeline/canal systems are unlikely to meet the established O&M target; however, the O&M costs of many of these systems are uncertain at this time.
A number of environmental scoping issues, raised during the public review process, were identified for the project. All of the proposed alternatives will have potential environmental consequences that have not been addressed in this report. Potential impacts include construction or operational impacts to sensitive resources (e.g., wetlands, endangered species, and migratory birds); the potential for creating or exacerbating problems with toxic substances; and potential impacts to Mexican resources. Other issues include the need for and cost of land acquisition, right-of-way requirements, and environmental permitting requirements. Comments were also received regarding the need for refinement of the project's purpose and need, how management targets were established, the need for comprehensive water quality analyses, and making use of long-term inflow data and inflow variability (wet and dry cycles) for environmental analyses.
Ogden Environmental and Energy Services Co., Inc. 1996. Salton Sea Management Project, Evaluation of Salinity and Elevation Management Alternatives. Prepared for the Salton Sea Authority. June.
Michael D. White
Ogden Environmental and Energy Services Co., Inc.
5510 Morehouse Drive
San Diego, CA 92121