Title : Sea water desalination system, McMurdo Type : Antarctic EAM NSF Org: OD / OPP Date : May 18, 1993 File : opp93104 INITIAL ENVIRONMENTAL EVALUATION REPLACEMENT OF THE SEA WATER DESALINATION SYSTEM, MCMURDO STATION, ANTARCTICA National Science Foundation Office of Polar Programs Washington, DC May 18, 1993 1. INTRODUCTION The U.S. Antarctic Program (USAP) is proposing to replace the Sea Water Desalination System at McMurdo Station, Antarctica, during the 1993-1994 season. Since 1986, the potable water supply at McMurdo Station has been produced using a multi-stage flash distillation system at the current location of Building 198. This system has been in continuous operation since its installation, and has in recent years shown signs of increasing deterioration due to corrosion and scale formation requiring significant increases in maintenance. The Supplemental Environmental Impact Statement (SEIS) on the USAP (NSF 1991) identified and discussed the technologies used at USAP stations and field camps to produce potable water. The purpose of this Initial Environmental Evaluation (IEE), the equivalent of an Environmental Impact Assessment, is to evaluate in more detail potential environmental impacts that might result from the installation, operation and maintenance at McMurdo Station of various potable water supply technologies. This IEE is prepared by USAP in compliance with the National Environmental Policy Act, the Antarctic Treaty, and the Protocol on Environmental Protection to the Antarctic Treaty (the Madrid Protocol) adopted by 26 countries in 1991. 1.1 BACKGROUND The National Science Foundation (NSF) is responsible for the USAP that supports a substantial national scientific research program in Antarctica, often in cooperation with other countries. The USAP maintains three year-round stations in Antarctica -- McMurdo Station on Ross Island, the Amundsen-Scott South Pole Station, and Palmer Station on the Antarctic Peninsula. McMurdo Station is the major base for providing logistic support to numerous scientific field camps on the continent each austral summer. Logistic and operational support is provided by the Department of Defense (Naval Support Force Antarctica, U.S. Army, and U.S. Air Force), the U.S. Coast Guard, and a civilian support contractor (currently Antarctic Support Associates, Inc). An essential component of USAP logistic support is the provision of a safe and healthful potable water supply for personnel working at McMurdo Station. Also, potable water is used in connection with the scientific research supported by the USAP. In a 1992 evaluation of the shell corrosion and status of operation of the multi-stage flash distillation system now in place and in operation, conducted by the original vendor, Beaird Industries, Inc., the inspector commented that repairs would be required within three years. More recent evaluation suggests that repairs would be required sooner. This has prompted the NSF's Office of Polar Programs to direct Antarctic Support Associates, Inc. (ASA) to conduct a design and procurement review for replacement water plant equipment. Any new desalination plant would be sized to provide potable water for an austral summer population of about 1300 people and an austral winter population of about 350. A consumption rate of 208 liters per person per day (270,628 L/d) would be used to determine the capacity of the new Water Plant. The new Water Plant would have a total austral summer capacity of approximately 360,000 L/d, based on a capacity load factor of 90%. Potable water consumption during the austral winter would be approximately 73,000 L/d. The specific location of the proposed activity would be Building 198, the Primary Distillation Water Plant, McMurdo Station, Antarctica (77deg51'S, 166deg40'E). (See Figure 1). No alternative locations were considered. An alternative location would require the construction of a new facility to house any new desalination equipment. The existing facility was constructed for this specialized function. 1.2 PHILOSOPHY OF THE U.S. ANTARCTIC PROGRAM IN MINIMIZING ENVIRONMENTAL IMPACTS Reducing human impacts on the antarctic environment is a major goal of the USAP. This philosophy of environmental protection embodies notions of human safety as well as support of scientific research of high value and quality. The operating philosophy of the USAP (Draggan and Wilkniss 1992) recognizes the potentially profound impacts that its presence and its activities can have upon Antarctica. This philosophy acknowledges the importance of the various components of the human environment, the antarctic environment, and the interactive processes that give structure to those environments. The philosophy goes further in affirming that USAP will use all practicable means and measures to foster and maintain Antarctica's natural conditions while promoting and supporting antarctic scientific endeavors in a manner that is safe and healthful for USAP participants. The USAP's operating philosophy is based upon several broad, yet reasonable and practical, assumptions. The assumptions are that: (1) the Antarctic Continent can be viewed, in the main, as a closed environment; (2) inputs to, and outputs from, the operating environments of the USAP (that is, its stations, field camps and vessels) can be controlled; (3) while all human activities entail some measure of change or impact to the environment, those changes and impacts can be minimized, mitigated, or controlled; and, (4) effective minimization, mitigation, and control of change or impact depends on information-intensive approaches that foster early consideration of potential changes or impacts. <++++++++++Figure 1++++++++++> In keeping with this philosophy, this IEE focuses on actions or changes to program activities that might: (1) reduce human impacts by reducing the need for antarctic personnel and non-science support operations; and (2) foster environmentally compatible use of such natural antarctic substrates as seawater, ice and snow. 1.3 SCOPE OF THE IEE This IEE evaluates the impacts associated with installing, operating and maintaining various seawater desalination technologies at McMurdo Station. The intent is to provide sufficient evaluation to ensure that adequate review of potential environmental impacts for planned developments of potable water production has been done and appropriate documentation prepared. This analysis will be reviewed for future developments, and supplemental analysis and documentation will be prepared for such developments as necessary. 2. THE PROPOSED ACTION AND ALTERNATIVES 2.1 PURPOSE AND NEED Specifically, the proposed action would replace the existing multi-stage flash distillation unit at McMurdo Station with a suitable alternative. The current system has been in a state of continual deterioration due to corrosion and scale formation. 2.1.1 Purpose The purpose of the proposed action is simple and straightforward: to assure the provision of a safe and healthful, year round supply of potable water for participants in the USAP. 2.2 ALTERNATIVE ACTIONS Alternatives considered in this IEE follow: (1) Multi-stage flash (MSF) distillation system; (2) Multi-effect flash distillation system (MED) ; (3) Vapor compression distillation plant; (4) Reverse osmosis desalination system (the preferred alternative); and, (5) the "No-action" alternative. These five alternatives are discussed in the following sections (and see Table 1). 2.2.1 Multi-Stage Flash (MSF) Distillation System Adoption of this system would provide, for all intents and purposes, a replacement of the existing system. This system produces potable water by heating salt water in a tubular heat exchanger using low- pressure steam from a boiler, or from a heat recovery system. It then passes the hot seawater to a separate chamber where a pressure lower than that in the heating tubes prevails. This causes some of the hot sea water to vaporize or flash. The vapor is then condensed by cooler incoming seawater to produce pure, distilled water. In a multi-stage flash distillation system, flash distillation is carried on at a number of successive stages (that is, the heated seawater flashes to vapor in a series of chambers -- each at a lower pressure than the preceding one). The greater the number of stages, the better the efficiency of the yield, overall. Flash distillation offers an advantage over submerged-surface distillation in that the heating of seawater without boiling causes less scale deposits. The multi-stage flash distillation system can use steam from a heat recovery system to heat seawater. The fuel required to operate a multistage flash distillation system with a heat recovery system providing heat for the process and a boiler to provide steam only for the steam ejectors is approximately 1.2 Liters of fuel per 3,785 liters of water produced. The fuel required to operate a multistage flash distillation system when waste heat is not used is approximately 52.2 Liters of fuel per 3,785 liters of water produced. Advantages of a multi-stage flash distillation system include: 1) a low operating cost when waste heat is used for the distillation process; 2) the quality of the feedwater is not as important when compared with the reverse osmosis system technology; and, 3) the multi-stage flash system has a high gain output ratio (GOR): that is, the ratio of pounds of water produced to pounds of steam condensed in the brine heater. <++++++++++Table 1++++++++++> Disadvantages of a multi-stage flash distillation system are a high operating cost when waste heat is not available for the distillation process and relatively high rates of corrosion and scale formation due to high operating temperatures. 2.2.2 Multi-effect Flash Distillation System Multi-effect flash distillation systems produce potable water by boiling seawater to create freshwater vapor. The vapor produced in each "effect" is condensed on the system's cooler tube-bundle surfaces, where it is collected as high purity distillate. The multi-effect evaporator employs two or more evaporator effects, each operating at successively lower temperature and pressure (that is, vacuum). The process is repeated several times, multiplying the effectiveness of the original heat supplied in the first effect, thereby giving the process its name. The first effect is heated by steam or hot water on the inside of the evaporator effect bundle. Incoming seawater is sprayed on the outside surface of the tube bundle in each effect. In order to reuse the heat of vaporization and condensation, the pressure in each effect is reduced relative to the preceding effect. The boiling occurs at lower and lower temperatures as the feed water passes through subsequent effects. The distillate collects in a trough that flows from the first effect to the last. The multi-effect flash distillation system can use waste heat from a heat recovery system. Fuel requirements for multi-effect flash distillation with, and without, waste heat would be about the same as that for multi-stage flash dis- tillation. Advantages of multi-effect flash distillation systems include: 1) a low operating cost when waste heat is used for the distillation process; 2) the quality of the feed water is not as important as for a reverse osmosis system; 3) the multi-effect flash system has a high GOR, and 4) the multi-effect flash system can utilize hot water instead of steam for the distillation process. Hot water temperature is less affected by changes in the power plant generator load than steam production. Disadvantages of multi-effect flash distillation systems include: 1) high operating costs when waste heat is not available for the distillation process; and, 2) the multi-effect flash system operates at high temperatures that increase corrosion and scale formation. 2.2.3 Vapor Compression Distillation Plant Vapor compression distillation systems use the energy supplied by a compressor that takes vapor from boiling seawater and compresses it to a higher pressure and temperature -- furnishing heat for vaporization of more seawater. In so doing, the vapor is condensed to yield distilled water. Theoretically, vapor compression is more efficient than other desalination methods. The vapor compression distillation system requires a small amount of heat to preheat seawater, and electrical energy for the compressor motor. The fuel required to operate a vapor compression distillation system is approximately 15.14 liters of fuel per 3,785 liters of water produced. Advantages of vapor compression distillation systems include: 1) the operating costs are low compared to multi-stage or multi-effect flash distillation systems and 2) the equipment is smaller than the multi-stage flash or multi-effect flash distillation systems. Disadvantages of vapor compression distillation systems include: 1) maintenance on compressors and heat exchangers is greater than those of other systems; 2) energy consumption is high; and, 3) capital costs are high. Because of the last two reasons, vapor compression was dropped from further consideration (see Table 2). <++++++++++Table 2++++++++++> 2.2.4 Reverse Osmosis Desalination System In the natural process of osmosis, when a seawater solution and pure water are separated by a semi- permeable membrane, the pure water will pass through the membrane to the seawater solution side. The natural driving force is osmotic pressure. This process can be reversed and pure water can be made to pass from the salt water solution to the pure water solution. This is accomplished through the application of pressure to the salt water solution in excess of the osmotic pressure: that is, reverse osmosis. The reverse osmosis system does not require heat to produce potable water. Reverse osmosis membranes can be used for feedwater temperatures between 1degC and 32degC but operate most efficiently at 25degC. As the feedwater temperature goes down, the viscosity of the water increases and more membranes are required for the same feedwater flow. Heat from a waste heat recovery system can be used to preheat the feed water to increase efficiency. Reverse osmosis systems require electrical energy for the high pressure pump. Fuel required to operate a reverse osmosis system is approximately 9.1 liters of fuel per 3,785 liters of water produced. Advantages of reverse osmosis systems include: 1) reverse osmosis systems operate at ambient seawater temperatures, reducing corrosion and scale formation; 2) capital equipment costs are lower; 3) lower operating costs and energy savings when waste heat is not available for distillation processes; 4) equipment size is smaller; 5) equipment can be delivered in four or five months after receipt of a factory order; 6) start-up time for each unit is usually less than one hour; and, 7) a steam boiler or heat recovery system is not required. Disadvantages of reverse osmosis systems when compared with flash distillation systems include: 1) the system's high pressure pump creates vibrations that may require special foundations; 2) high pressure salt water requires special materials for the system's high pressure piping; and, 3) feedwater quality must be very good or membranes and multi-media filters will foul and not operate properly. The feedwater pretreatment system must remove colloidal materials, microorganisms, organics, iron and chlorine from the sea water to prevent membrane fouling and deterioration. In addition, chlorination as a pretreatment mechanism also may require increased monitoring to assure that trihalomethane formation is not occurring. 2.2.5 No Action The "no-action" alternative would force continued use of the existing multi-stage flash distillation unit. This unit's components exhibit extensive internal damage due to corrosion and scale formation. The components have been repaired several times in the past to correct leaks due to corrosion; extreme metal fatigue, however, makes continued repairs difficult to execute. The units have a very short life expectancy. This places the population at McMurdo Station in jeopardy of not being able to produce an adequate supply of safe and healthful drinking water. 3. AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES 3.1 MCMURDO STATION 3.1.1 Affected Environment McMurdo Station (77deg51'S, 166deg40'E) is the major support station for the USAP. The station is located on Ross Island and consists of more than 100 structures, extensive storage yards, an ice pier, an annual sea-ice runway, a skiway, a helicopter landing area, and other ancillary structures and features (e.g., communications antennas and roads). During recent years, the austral winter (late February through early October) population at McMurdo has ranged from 100 to more than 250 people, depending on the amount of science, construction, and renovation going on. The U.S. Navy began constructing McMurdo Station during the 1955þ1956 season. Because it was intended to be used solely as a logistical support base, and because the United States' presence was considered expeditionary at the time, McMurdo's early development consisted of the construction of temporary structures. By the mid-1960s, however, it was evident that the U.S. presence at McMurdo was to be more permanent, and the Navy began to construct steel-frame buildings. By the time NSF assumed the management of McMurdo in 1970, the station had evolved from a temporary logistical support base into an established station responsible for both logistic support and scientific research. Because of the need for facilities in which to conduct research, in addition to those facilities required for support, many of McMurdo Station's original temporary structures have been replaced, and some new ones have been erected to help alleviate overcrowding. Patterns of currents in McMurdo Sound were studied by the Raytheon Service Company for consideration in designing new wastewater outfalls and water intakes (Raytheon 1983). McMurdo Sound in the vicinity of McMurdo Station is covered with sea ice that breaks up only for brief periods in some years. Tides follow a 13-day cycle, with daily variations in water surface elevation ranging from about 0.1 to 1 m through the cycle. Directions and speeds of currents vary greatly among sites along the Ross Island coast and over time during the tidal cycle. In general, researchers believe there is a net southward flow in the central and eastern Sound and a northward flow in the western Sound (Barry and Dayton 1988a). Current meters deployed by Raytheon (1983) showed net flows in the immediate vicinity of McMurdo station that appear to follow a counterclockwise eddy, with northward flows immediately offshore. Net flows are very low, ranging from about 10 to 150 m/d. More recent study of current patterns of McMurdo's nearshore environment are on- going, with results expected after the 1993-1994 austral summer season. Very little flow occurs in Winter Quarters Bay. McMurdo Sound is affected by the annual formation of sea ice, and has high salinity (34 to 35 ppt) and cold temperatures (about þ2degC). There is little vertical variation in temperature and salinity in winter and spring, but some stratification occurs in summer (Barry and Dayton 1988b). Although water quality results of the Raytheon study (1983) are of questionable reliability and limited use, they indicate that: 1) high coliform bacteria concentrations are found off McMurdo Station, indicating that these organisms (which may indicate the presence of sewage contamination) survive in the Sound; 2) relatively high ammonia concentrations occur both inshore near the wastewater discharge and offshore; and, 3) wastewater discharged from surface outfalls tends to follow the tidal cracks around the edge of the Sound. Ambient water quality characteristics are available from Raytheon (1983) and from research studies conducted in McMurdo Sound. The Raytheon values presented are from a site near the present sea water intake jetty where samples were taken at the surface, mid-depth, and bottom, on two different dates. Barry and Dayton (1988) conducted hydrographic studies of McMurdo Sound in the spring and summer. His study showed that nutrient concentrations are high and uniform in the spring, prior to a summer bloom in plankton productivity. In the late summer, nitrate and phosphate concentrations were about two-thirds of the spring values, while nitrite concentrations were several times higher in summer. Also, this study showed that dissolved oxygen concentrations were uniform in spring at about 7 mg/L, and in summer were about 8-9 mg/L near the surface. In general, the ocean waters at McMurdo Station can be described as cold, nutrient rich, with relatively high dissolved oxygen concentrations. New water quality studies were begun during the 1992-1993 austral summer season and, currently, results are being analyzed and interpreted. Regardless of the system chosen to replace the existing multi-phase flash distillation unit, environmental impacts associated with construction activities would be less than minor and less than transitory as the new system would be installed inside the existing Water Plant. All work would occur within this structure. No building addition, requiring earth work, would be needed . A portion of the skin of the Water Plant Building would be removed so the existing desalination system could be removed from the building. All new equipment would be moved into the building and assembled on-site. The building would then be reassembled. Little to no waste would be created during this process and all of the old desalination equipment would be retrograded from Antarctica. Impacts on the population during construction of a replacement facility have also been considered. It is anticipated that a replacement unit would be purchased to be sent via vessel in February of 1994. Construction would take place during the austral winter when the population is at its lowest. Replacing the existing flash evaporation unit with a like system (multi-stage or multi-effect distillation) would require a shut-down of the Water Plant and the use of the standby Water Plant located in Building 126 while the old equipment is removed and new equipment is installed. Installation of a reverse osmosis unit would not require the use of the standby Water Plant -- water could be supplied to residents with little disruption. The civilian support contractor's McMurdo Operations and Maintenance staff have reviewed the alternatives and anticipate no difference in the number of personnel required to operate and maintain equipment regardless of the system chosen to replace the existing unit. Currently, it is expected that six people are required; nonetheless, operating staff may be reduced to three or four. No impacts, therefore, are expected from an increase in station population. 3.1.2 Potential Environmental Consequences of a Reverse Osmosis Unit The proposed alternative being considered is installation.,operation and maintenance of a Reverse Osmosis Desalination System using three reverse osmosis units having a daily output of approximately 151,400 L/d each. No direct, adverse environmental impacts are anticipated for the use of reverse osmosis, as long as the system is properly operated and maintained. Some chemicals are used in reverse osmosis desalination plants, however, that are not required with the other alternatives. These substances include such sequestrants as polyacrylic acid -- to be added to the feedwater to prevent the buildup of scale deposits on reverse osmosis membranes; and, sodium bisulfite -- to remove any dissolved oxygen or halogens. Environmental contamination from chemicals -- concen- trated corrosives -- normally used in on-site cleaning of the reverse osmosis membranes would be precluded by sending the membranes off-site for cleaning. The system would be designed, however, with a closed-loop, cleaning option to capture substances used in cleaning in the unlikely event that there may be a need to clean the membranes on-site. Impacts on water supply during construction would be mitigated by performing the work in phases. Construction would begin during the 1994 austral winter with one reverse osmosis unit being placed within the Water Plant addition. One unit is capable of producing enough water to supply the needs of a winterover population having a daily consumption requirement of 72,861 L. Upon testing and startup of the first unit, additional units would be set in place in the main building as the flash evaporators are removed. The standby Water Plant would be readied for emergency operation in the event of equipment failure. The proposed site for the desalination equipment does not serve as habitat for any significant assemblages of antarctic wildlife. The marine environment that would receive its brinewater effluent does support an abundance of marine organisms. The effluent brine would be discharged along with the station's wastewater effluent. The wastewater effluent is freshwater and would serve to decrease the salinity of effluent brine. No long-term aesthetic impacts are anticipated should the proposal proceed. There would be some temporary aesthetic impacts associated with construction activities, particularly when portions of the Water Plant siding are removed to install new equipment. 3.1.3 Indirect and Cumulative Environmental Impacts Direct and indirect costs for all alternatives have been evaluated in a study conducted for ASA by Holmes & Narver, Inc./1/(see endnotes) Other indirect costs of the proposed activity would be associated with the proposed alternative's impacts on existing facilities and proposed construction or development projects. One such project impacted by the proposed and preferred alternative would be the human waste disposal facility. This facility is designed to dispose of human waste (urine only) collected in 208-L drums. The facility proposes to use the hot brine from existing flash evaporators to melt the drum's frozen contents and to wash out emptied drums. Reverse osmosis would eliminate the production of hot brine produced by flash evaporation. The hot brine from the flash distillation units is approximately 32.2degC. The proposed reverse osmosis system would use waste heat from the power plant generators to preheat the seawater. This would produce a brine water with a temperature of between 1.7degC and 4.4degC. This temperature range would be sufficient for washing the human waste barrels and would also suffice in melting the contents, although this process would take more time and energy than using hot brine from the existing flash evaporators. Also, the civilian support contractor is proposing and assessing a plan for advanced wastewater treatment at McMurdo Station. A possible alternative under this plan would be tertiary wastewater treatment with the potential for effluent water reuse for either human consumption or for growing plants hydroponically. It is unknown how effective reverse osmosis would be as part of a wastewater reuse system to provide water of sufficient quality to meet either of these applications. Another indirect cost would be associated with providing training for operators who have no experience operating reverse osmosis units. The present system of flash evaporation provides a virus-free, drinking water without any filtration or disinfection -- although McMurdo Station does employ chlorine disinfec- tion to provide an added degree of health protection. Reverse osmosis would not deliver the same quality of water without disinfection. Operators would require additional training to ensure that the proper level of disinfection is maintained. Also, particular attention must be paid by operators to biological fouling of the reverse osmosis membranes. Chemical and biological fouling of the membranes can sharply reduce the cost- efficiency of the reverse osmosis process and can cause serious public health problems and risks. Operators would need to be sufficiently trained in the operations and maintenance of the system to control fouling of the membranes. The proposed, preferred alternative, reverse osmosis, would engender several potential indirect environmental changes near McMurdo Station. One such change would be the addition of cooler brine water to the station's wastewater effluent. The current flash distillation unit releases to the nearshore marine environment brinewater at a temperature between 33.3degC and 39.4degC./2/ It is estimated that the brine water discharged from a reverse osmosis unit would be approximately 1.7degC. A brinewater discharge at this temperature would further cool the wastewater effluent and may provide increased dispersion by reducing the rapid rise of the effluent plume to the ice surface. It has been pointed out, however, in the Final Supplemental Environmental Impact Statement that dilution of McMurdo's wastewater with desalinator brine is expected to provide little wastewater effluent quality improvement through increase dilution. The higher flow rate created by the addition of brinewater is said to reduce the mixing that takes place as the heated plume rises from the submerged outfall to the surface ice. It has been suggested, therefore, that it may be more beneficial to use the brine water for other purposes such as fire fighting. Construction of a wastewater treatment facility would greatly reduce environmental concerns regarding the effect of the brine discharge on the effluent dispersion. Another environmental change would be a reduction in fuel usage for potable water production. The current flash distillation system uses an average of 26,226 L of fuel per week to generate potable water using steam boilers (See Table 3). Reverse osmosis has been calculated by ASA's Engineering Division to have a lower energy demand than flash evaporation (see Attachment 1). The result would be decreases in fuel usage, in air emissions from combustion, and in potential spills associated with fuel distribution. Energy demand has been calculated by ASA's Engineering Division be lessened with the use of reverse osmosis. It has been calculated that the preferred alternative would require a total of 98.4 Kw to operate 3 reverse osmosis units simultaneously. Flash evaporation has been calculated to require 106 Kw of power to operate two plants (see Table 1). In addition, reverse osmosis would eliminate the need for an average of 26,226 L of fuel per week which is required to operate the existing flash evaporators. The characteristics of the neighboring terrestrial environment are dominated by activities supporting USAP operations at McMurdo Station and are suitable for the proposed activity. The location is also close to sea level and does not require energy to pump the effluent to a higher elevation for discharge. Disposal of concentrated brinewater into the local aquatic environment has occurred for a number of years. In recent years this brinewater has been hot and has been used to dilute McMurdo Station's wastewater effluent in order to provide a greater degree of dispersion and increased assimilative qualities. Environmental impacts associated with this activity have been presented in previous assessments and discussed in a paper /3/ prepared by Steven Railsback of the Oak Ridge National Laboratory; the outcomes of which revealed the neighboring marine environment is suitable for such an activity. Scientific studies at and near McMurdo are not expected to be affected by adoption of the reverse osmosis technology. The discharge of brinewater in combination with McMurdo's wastewater would be monitored to predict impacts to the local environment and to scientific research in the area. <++++++++++Table 3++++++++++> 4. IMPACT MITIGATION 4.1 Impact and Pollution Prevention and Environmental Management 4.1.1 Marine Environment No new construction would be required, so no construction wastes or one-time-use materials would require disposition. The old flash evaporation equip- ment that would be removed from the Water Plant would be staged and prepared for retrograde to the United States for disposition through the military reutiliza- tion system. Any other construction related waste would be treated in a similar manner. Protection of human health is the main consideration regardless of the method of water production chosen. Flash evaporation is known to destroy enteric viruses without the need for chemical disinfection. Post-chlorination has been used at McMurdo Station as a secondary safeguard. Tables 4A and 4B shows the results of a study conducted during the 1992-1993 austral summer to evaluate the presence of enteric viruses in McMurdo Station's potable water supply. No viruses were detected in three separate sampling events conducted in three separate months. When considering the use of reverse osmosis in water production, several concerns were addressed to ensure that the safest water would be produced and delivered. These included pretreatment of the feedwater to prevent biological fouling of the mem- branes and post-treatment of the permeate water. Pre- treatment of feedwater was considered by the Contractor to avoid membrane biofouling. Pretreatment approaches typically include continuous or intermittent disin- fection of the feedwater stream, or filtration of the feedwater stream, to remove microorganisms and other colloidal particles that can promote membrane biofouling.Disinfection by chlorination, ozonation and iodination of reverse osmosis feedwater are viewed as the most economical methods of chemical disinfection. Reverse osmosis membranes can be irreversibly damaged, however, by such oxidizing disinfectants. Where chlorination is used, damage to the membranes may be mitigated through dechlorination of the feedwater prior to its entrance into the reverse osmosis system. De- chlorination methods include passage of the water through granular, activated carbon or the addition of sodium thiosulfate or biosulfate to the feedstream. <++++++++++Table 4A++++++++++> <++++++++++Table 4B++++++++++> Pretreatment using chlorination enhances, however, the possibility of trihalomethane production due to chlorine coming into contact with humic and fulvic acids from the decomposing organic matter that may be present in feedwater. In this case, the presence of marine phytoplankton in the source water would be of concern. Because trihalomethane formation was an important concern to USAP, other pretreatment alterna- tives were considered. Some studies have shown ozonation to be superior to chlorination as a pretreatment method. However, it has some serious consequences. Ozone is one of the most powerful oxidizers known and must be handled as a hazardous material. In order to protect workers from exposure to ozone, additional safety equipment must be installed to monitor for accidental discharges in equipment rooms. Additional equipment may be required to destroy excess ozone which may be present after water's passage through a purification system's ozone contact chamber to insure that no ozone would leak into the ambient atmosphere during normal operations. The use of ultraviolet irradiation is also an alternate method of pretreatment. It has the advantages of being relatively self-contained and requires little maintenance. The disadvantages are: 1) many bacteria are UV-resistant; and, 2) ultraviolet irradiation does not provide a continuously available disinfectant residual on reverse osmosis membrane surfaces, where it is most needed. Prefiltration using submicron filters is also an alternative. However, the economics of this method has been questioned due to the increased maintenance required to continually keep the filters clean. This often offsets the advantages it has in controlling biofouling of reverse osmosis membranes/4/. A reverse osmosis system maintenance firm, Argo Scientific, has advised ASA, after reviewing the analyses of feedwater from McMurdo Sound, that no form of pretreatment is required. They predict that the system would perform well without pretreatment for approximately three years before the membranes would require cleaning. Eliminating pretreatment using chlorination of the feedwater would also eliminate the chances of trihalomethane production. Chlorination would only be required to disinfect the potentially potable permeate water to destroy pathogens and to control microbial growth in the potable water distri- bution system. Following this guidance, two sets of membranes would be purchased to use on a rotational schedule. Fouled membranes would be sent to the U.S. for cleaning. These would be replaced with membranes cleaned off-site . Although this method would increase the cost of maintaining the reverse osmosis system, it would preclude the need for importing into Antarctica substances containing hazardous constituents (that is, the chemicals used to clean the membranes and the need to pretreat the water by chlorination. Post-treatment would consist of two injection systems; one for chlorine injection to disinfect the water to World Health Organization standards, and another for sodium bicarbonate injection to maintain a pH of 8 to 8.5. The proposed activity would not change surface water flow or drainage at McMurdo. As discussed previously, there may be some positive impacts associated with improved dispersion of McMurdo's sewage effluent due to the reduction in its temperature. The effect of reduced wastewater effluent temperature is more fully explained in the final Supplemental Environmental Impact Statement. 4.1.2 Air Environment A reduction in fuel usage, under adoption of the preferred alternative, would positively impact the ambient air quality by reducing air emissions. Based upon the calculations presented in Table 3, when compared to a similar sized flash evaporation unit, reverse osmosis represents an energy demand approximately 7% less than that of flash evaporation. 4.1.3 Terrestrial Environment Should the proposed activity be decommissioned in future, all materials would be disassembled and retrograded from Antarctica and the site would be returned to as close to original condition as possible. 5. FINDING The finding of this IEE is that development and subsequent use and maintenance of a reverse osmosis water desalination system at McMurdo Station would have less than minor or transitory environmental impacts (that is, no significant environmental impacts are anticipated). Accomplishment of the proposed action would benefit the program. The benefits of the proposed action include continuing provision of a safe and healthful source of potable water to personnel and scientific research projects working at McMurdo. The proposed action would allow for: 1) removal of seawater from McMurdo Sound; 2) production of potable water and residual brine; and, 3) return of residual brine with the station's wastewater effluent to McMurdo Sound. In all instances, save bona fide emergencies, fouled reverse osmosis membranes would be sent to the U.S. for cleaning; they would be replaced with membranes cleaned off-site. 5. LITERATURE CITED Barry, J. 1988a. Current patterns in McMurdo Sound, Antarctica, and their relationship to local benthic communities. Polar Biology 8:367-376. Barry, J. and P. Dayton. 1988b. Hydrographic patterns in McMurdo Sound, Antarctica, and their relationship to local benthic communities. Polar Biology 8:377-391. Draggan, S., and P. Wilkniss. 1992. An Operating Philosophy for the U.S. Antarctic Program. Marine Pollution Bulletin 25 (9-12): 250-252 National Science Foundation. 1991. Final Supplemental Environmental Impact Statement on the U.S. Antarctic Program. Division of Polar Programs, Washington, D.C. (October). Raytheon Service Company. 1983. Report on the McMurdo Station Water Quality Study. Middletown, RI. Attachment: Memorandum From M. Lesiak/ASA to W. Koleto/ASA on: Power Consumption Comparison - Flash Evaporator and RO. 6. LIST OF PREPARERS NATIONAL SCIENCE FOUNDATION, OFFICE OF POLAR PROGRAMS PANEL Dr. Sidney Draggan, Panel Chairperson Dr. Jane Dionne, Co-Chairperson Dr. Harry Mahar Mr. Frank Brier ANTARCTIC SUPPORT ASSOCIATES Mr. Terry Johnson Ms. Carol Andrews Mr, Craig Martin Mr. William Koleto Mr. Matt Lesiak OAK RIDGE NATIONAL LABORATORY Assessment Support:: Dr. Robert M. Reed Mr. Lance B. McCold Mr. J. T. Ensminger Dr. J. Warren Webb Mr. Jeremy Holman Notes /1/ Holmes & Narver, Inc., 1993, Water Desalination Plant Study, McMurdo Station, Antarctica, Albuquerque, NM, February. /2/ National Science Foundation, 1991, Final Environmental Impact Statement, Washington, DC, October. /3/ Railsback, S. F. 1991. Dispersion and Fate of Wastewater Released from Submerged and Surface Discharges at McMurdo Station, Antarctica. Session on "Measuring the Fate, Behavior and Effects of Contaminants in Polar Environments" at the First International Ocean Pollution Symposium. April 28-May 2, 1991, Mayaguez, Puerto Rico. /4/ Source: Mittleman, Marc W. and G. G. Geesey. 1987. Biological Fouling of Industrial Water Systems: A Problem Solving Approach. Water Micro Associates. <++++++++++Attachment 1++++++++++>