G. Fred Lee, PhD, PE, President
and
R. Anne Jones, PhD, Vice-President
G. Fred Lee & Associates
El Macero, CA

on behalf of

The CA/NV American Water Works Association
Source Water Quality Committee

Summary

The current five year California drought is causing significant public health, aesthetic and other water quality problems for domestic water suppliers in the state. Of particular importance is the drought related problems associated with the deteriorated water quality of the Sacramento/San Joaquin River Delta to the domestic water utilities that use Delta water for all or part of their raw water supply. This source of supply provides domestic water for about 20 million people in the state. During periods of drought, increased use of Delta water as a raw water source is made by utilities in both the northern and southern part of the state. Many of those water utilities that have been using, or have had to switch to Delta water as a source during the drought have experienced significant increases in total trihalomethanes (TTHMs) and especially the brominated THMs. This increase is related to the drought related reduced availability of fresh water to prevent the up Sacramento River migration of marine waters from the San Francisco Bay system into the Delta. The increased marine water encroachment into the Delta during the drought has increased the bromide content of water exported from the Delta. The bromide reacts with disinfectants such as chlorine to produce bromine which in turn produces brominated THMs.

A number of domestic water utilities that obtain raw water from the Delta have also experienced increased TDS, system corrosion potential, algal related tastes and odors, hardness and sodium adsorption ratio.

The drought related decreasing water levels in Mono Lake and in the Owens Valley ground water have caused the courts to cause the Los Angeles Department of Water and Power (LADWP) to greatly curtail the amount of water available from these areas for the city of Los Angeles through the Los Angeles Aqueduct. This has required that LADWP use Delta water obtained from the Metropolitan Water District of Southern California (MWD) as a raw water source. The switch from Mono Lake tributary - Owens Valley water to Delta water has caused water quality deterioration in some of the waters provided by LADWP where increased algal related tastes and odors and algal derived THMs have been experienced

Several water utilities have experienced significant turbidity removal problems associated with increased turbidity in drawn down reservoirs. It has been found that the increased turbidity is difficult to remove by coagulation and filtration. This has caused some utilities to experience, for the first time, turbidity violations in their treated water.

The drought is causing a much greater demand for ground water as a source of domestic supply. The ground water resources of the state are the backbone of the domestic and agricultural water supplies during the drought. Prior to the drought, about 40% of the total waters used in the state are from ground water sources. During the drought, this percentage has increased to about 80%. Further, about 50% of the state population use ground waters for all or part of their domestic water supply. The drought has also stimulated a significant number of new well permits and well construction. In many areas, the drought is causing significant overdraft of the ground waters greatly reducing the water table. The reduced water table is creating a number of domestic water supply water quality problems such as salt water or brine intrusion in coastal and in some inland areas. Further, some utilities are experiencing migration of contaminated ground waters to domestic water supply wells. The slow movement of ground water would not be expected to have manifested all of the ground water quality problems that will occur under drawn down ground water table conditions.

The drawn down water table is leading to aquifer consolidation and the associated land subsidence. The land subsidence is causing fissures to develop in the soil surface, and has caused damage to well casings. Both the fissures and well casing damage coupled with the increased numbers of wells being drilled, associated with the drought, lead to increased potential for ground water pollution by surface derived contaminant migration down the bore hole or into the fissures. In the future, there will be increased recharge of ground water aquifers with surface waters as the drought ameliorates through conjunctive use of surface and ground waters. The increased ground water recharge is of concern since it provides an opportunity for aquifer contamination by contaminants present in the recharged surface waters.

California will continue to experience periodic droughts. The impacts of these droughts on domestic water supply water quality will become more frequent and in some instances more severe. The increased frequency will be associated with the rapidly increasing population in the state that will cause lesser droughts to cause water supply water quality problems that have in the past been experienced only with more severe droughts.

Domestic water utilities should carefully document the impact of the drought on domestic water supply water quality. Such documentation can be helpful in developing programs that will help to make the water supply raw water quality more drought resistant.

The current drought has had a well documented public health, aesthetic and other quality impacts on domestic water supply water quality for those utilities that use the Delta as a raw water source. The most significant of these appear to be the problems associated with the salt water encroachment into the Delta from the San Francisco Bay leading to increased total THMs and brominated THMs. It is estimated that if the peripheral canal system were in place during the current drought, that the total THMs that are being experienced by some utilities of 100 mg/L (the MCL for THMs) could be decreased to about 30 mg/L. With the US EPA to soon announce a potentially significantly reduced TTHM standard, there is increased justification for diversion structures such as the peripheral canal to improve domestic water supply raw water quality, especially during periods of drought. It is important to note that the drought related impacts on domestic water supply water quality are of importance to large numbers of people in both northern and southern California.

The construction of the peripheral canal would not however significantly change the algal related THM and taste and odor problems experienced by some water utilities during the drought since the point of proposed diversion of Sacramento River water is below the major domestic waste water sources of algal nutrients for the Delta system. It has been found that algal growth in the Delta is proportional to phosphorus added to the Delta from above Delta domestic waste water sources. Approximately 90% of this phosphorus can be removed from domestic waste water sources by well established technologies at a cost of about 4 cents/person/day for those who contribute domestic waste waters to the tributaries of the Delta. It is recommended that an evaluation be made of the potential benefits of practicing phosphorus removal from waste water sources that are tributary to the Delta in order to improve the algal related water quality for those utilities that use the Delta as a source of domestic water supply.

Those utilities that are experiencing turbidity removal problems associated with drought related drawn down reservoirs should undertake studies to determine the causes of the increased turbidity. It is possible that rough fish removal and/or baffling to reduce wave turbulence could significantly reduce the amounts of turbidity stirred into the water column in the drawn down reservoirs.

A potential problem that utilities with drawn down reservoirs will face as part of drought amelioration is the flooding of terrestrial vegetation beds that have developed in areas of the reservoir that are normally flooded each year under normal precipitation situations. The die off of large areas of terrestrial vegetation upon flooding can exert a significant oxygen demand on reservoir water to cause significant water quality problems. The management of the growth of terrestrial vegetation in drawn down reservoirs needs to be evaluated in order to avoid problems of this type.

The drought has emphasized the importance of protecting and where possible enhancing ground water quality in the state. It is evident that it is highly important that the state regulations governing the protection of ground water quality from land disposal of wastes such as municipal and industrial landfills be fully implemented. These regulations require that any land disposal of wastes prevent ground water pollution - impairment of uses for as long as the wastes represent a threat to the ground water quality. Since all municipal and many industrial landfills contain waste constituents that will be a threat to ground water quality forever, it is imperative that the siting, design, construction, operation, closure and post-closure care of landfills and other waste management units be conducted in such a way as to protect ground water quality forever.

A vigorous program of well inspection and proper closure upon termination of use should be conducted in the state to prevent well bore holes from serving as a conduit for contaminant transport to ground water. Further, all surface waters incidently and deliberately recharged to ground water should be chemically analyzed and managed to prevent recharge waters from transporting contaminants from surface waters to aquifers.

Some water utilities are conducting extensive programs of contaminated ground water removal and treatment. It has been found in some parts of the state that contaminated ground waters can be treated and pumped at a cost that is less than the cost of imported waters into the area. Such programs should be encouraged to provide additional sources of domestic water supply especially during droughts and as part of ground water and aquifer clean up programs.

While not all domestic water utilities in California are experiencing deteriorated raw water quality as a result of the drought, the authors have found that many of the state water utilities are experiencing some domestic water supply raw water quality problems that are attributable to the drought. Further, it is concluded that the magnitude of these problems is such that many of the people in California are experiencing deteriorated domestic water quality due to the drought. It is apparent that water quality impacts of drought control programs should be carefully evaluated to where possible minimize the impacts of future droughts on domestic water supply raw water quality.

Introduction

The fifth year of drought in California is stimulating a variety of activities by regulatory-resource management agencies and water utilities to address issues of drought related water resources impacts and their management. The California/Nevada AWWA Source Water Quality Committee has elected to review the impacts of this drought on domestic water supply source water quality. Information has been obtained from a number of water utilities and other organizations on the impact of the current drought on source water quality. This paper presents a summary of the information that the authors have obtained from water utilities, regulatory-resource management agencies, and others on the impact of the current drought on domestic water supply raw water quality. Further, while not documented in the current California drought, this paper also discusses the experience of the authors and others on the expected impacts of the drought on source domestic water supply water quality.

This paper is intended to be an overview discussion of the types of problems that are being encountered by California domestic water utilities that influence the raw water quality that they have available to them during the current drought. The reviewers of the paper should contact the utilities or agencies mentioned for detailed information on the particular situation of interest.

Vaux (1991) in his opening remarks at the recently held 18th Biennial University of California Water Resources Conference devoted to the pros and cons of ground water regulation pointed out that the current five year drought situation is a preview of the situations that will become commonplace in the future associated with increased population pressures for domestic water supplies in the state. Barnett (1991) at the same conference pointed out that California is now increasing population at the rate of 720,000 people per year and that the population is expected to increase from the current approximately 30 million to the order of 36 million people by the year 2000. Barnett mentioned in the last prolonged drought of 1977-78, there were about 21 million people in California. During the 1959-61 drought, there were about 16 million people in California. Associated with this increased population will be significant increases in demands for municipal water supplies which in many locations are already being utilized to or near their limit. These increased demands for domestic water supplies will cause water quality problems that will adversely affect source and, in some instances, finished water quality.

Normally in the past during periods of drought, water managers and, for that matter, the public were most concerned about having water available to meet their needs. The issue of quality of this water was typically of secondary importance. As is sometimes said, the key issue during the drought was that "the water was wet." Today, however, with increasing attention being given to managing water quality from the protection of the public to health hazards associated with chemical contaminants in water supplies, much greater attention has been and will have to continue to be given to managing the impacts of droughts on municipal water supply source and finished water quality. It is apparent that those water utilities that have been affected by this drought should aggressively plan for increased drought impact frequency and take necessary steps to make their raw water quality as drought resistant as possible.

The impacts of drought on domestic water supply source water quality can be divided into the impacts on ground water quality and those on surface water quality. A summary of the measured and potentially expected impacts of the current drought on domestic water supply source water quality for surface and ground waters is presented below.

Impacts on Ground Water Quality

As would be expected, the current drought is placing increased demands for ground water. Hauge (1991) in a recent review of the importance of ground water to the state of California has reported that the ground waters of the state represent a very important buffer for protection against drought caused surface water supply shortages. He estimates that the ground water reserves represent about ten times the surface water reserves of the state. Hauge reports that typically that 40% of the water resources used in the state is derived from ground water sources. However, during periods of drought, this usage can increase to about 80%. Hauge reports that 50 to 60% of the state's population normally depend totally or in part on ground water supplies for domestic water supply purposes. He has recently reported that the number of ground water well permits issued for drilling of wells in the state has increased significantly during this drought. He has further reported that at many locations the ground water table elevation is dropping at a rapid rate associated with the increased use of ground waters during drought, and that decreased water tables tend to aggravate ground water quality problems.

Ground Water Pollution

Hauge (1991) expressed concern about the increased number of wells being constructed today leading to increased potential for ground water pollution. It is now recognized that one of the most significant pathways for ground water pollution by contaminants is associated with improperly constructed and maintained water wells. Not only does the increased number of wells, provide for a greater opportunity for contaminants present in surface waters to gain rapid access to the aquifer, but also there is a possibility of increased interaquifer transport of contaminants from one overlying to underlying aquifers by the bore hole.

Typically, because of the slow movement of ground water ranging from a few tenths of a foot to a foot or so a day, ground water quality does not change rapidly. However, when changes do occur such as associated with droughts, the rate of reversion of the change will also be very slow. It would be expected that during periods of drought that domestic water utilities that have part of their water supply derived from ground water sources will increase the pumping of ground water resulting in a decreased water table. According to the California Department of Water Resources State Drought Center, declining water tables are being experienced in many parts of the state associated with this drought. Associated with this decrease could be a number of source water quality problems. While thus far the authors have found few documented examples of decreasing water table causing a deterioration in ground water quality, it is reasonable to expect that problems of this type are occurring and that they will have a long term impact on ground water quality.

Noonan (1991) has reported a potential benefit associated with the drought lowering of the water table in the Fresno area of the San Joaquin Valley. He indicates that the increased agricultural pumping of ground water may be a benefit to domestic and municipal wells in the Fresno area by drawing more DBCP (dibromochloropropane) contaminated water into the irrigation wells where the presence of this contaminant is of lesser concern than in municipal wells. Todd (1991) has reported that the estimated time for clean up of the ground water in the Fresno area from DBCP contamination will be about 85 years. To the extent that Noonan's hypothesis that water table draw down associated with the current drought accelerates the removal of DBCP contaminated waters by agricultural wells, the clean up time of the aquifer could be shortened from the current estimated 85 years.

Salt Water Intrusion

Water utilities in several areas in the state especially in coastal areas face the possibility of increased salt water intrusion during drought. Further, some parts of the state have connate brackish water which represents a threat to fresh water quality under reduced water table conditions. Hurst (1991) has reported that Monterey County has experienced increased salt water intrusion into ground waters in the Salinas Valley-Castroville area. Hurst has also reported that one of the consequences of the drought has been inability to recharge the ground water aquifers in the Salinas Valley which has, in turn, promoted salt water intrusion. Essaid (1991) has recently discussed the mechanisms of salt water entry into the fresh water aquifers in that region of the state. Hurst (1991) has also expressed concern about ground water pollution by nitrate associated with the decreased water table in the Salinas Valley area.

A number of ground water management agencies are having to use increased amounts of reclaimed water derived from extensive treatment of domestic wastewaters as a barrier to salt water intrusion. This reclaimed water is therefore not available for use for other purposes.

Landfills and Other Waste Management Units

The greater draw down of the water table would accelerate the movement of contaminated ground waters from sources such as landfills to wells. This would cause even further spread of landfill leachate and other waste management system derived contaminants through the aquifer. Further, the lowered water table can reverse the direction of flow of contaminants so that the contaminants from the landfill or some other sources can enter a well used for domestic purposes in sufficient amounts to adversely affect water quality.

Another consequence of the prolonged drought is an inappropriate conclusion that certain types of waste disposal activities such as landfilling of municipal solid wastes will not result in ground water pollution due to the "arid" conditions that exist in California. During periods of drought less precipitation enters waste management units such as landfills which would likely result in less leachate being generated. Further, the leachate that is generated is likely more easily managed during drought periods. This could inappropriately cause regulatory agencies and others to incorrectly conclude that there is less need to protect ground water resources from landfill leachate in drought areas. However, as discussed by Lee and Jones (1991a), municipal landfills located in arid areas such as central and southern California while producing less leachate during drought periods than landfills located in the wetter parts of the state and country produce as much leachate as landfills located in these areas during non-drought periods. As discussed by Lee and Jones, the precipitation in a wet year in some parts of central or southern California is typically that of the normal precipitation of other "wet" parts of the country. Therefore, municipal landfills and some other waste management units whose rate of ground water pollution is a function of moisture entering the unit can and do significantly pollute ground waters in so-called "arid" areas.

This situation is exemplified in California by the Water Resource's Control Board's annual reports to the legislature on the Solid Waste Assessment Test (SWAT) program. According to the recently released SWAT report (WRCB, 1991), California has about 2,200 landfills of which 300 have been investigated thus far. Of this 300, 83% have been found to be polluting ground waters of the state. Many of these are located in the "arid" areas of the state indicating that these areas have sufficient precipitation during some years to result in sufficient leachate generation to pollute the ground waters in the vicinity of the landfill.

Conjunctive Use

It is likely as more water utilities and water purveyors increase conjunctive use of water, where during wet years surplus surface water is stored in an aquifer, ground water quality problems associated with drought years will become more common. It will then become even more important to manage ground water resources and especially waste management units to protect ground water and aquifer quality.

A potential consequence of the drought will be the increased recharge of surface waters into the aquifer at the end of the drought. There is concern that some of the recharge waters could contain contaminants that could lead to aquifer pollution. It will be important to carefully monitor all natural, as well as assisted aquifer recharge, to ensure that aquifer contamination by contaminants in the recharge water does not occur.

Evans (1991) has reported that some of the water utilities in the Santa Barbara area are experiencing potential problems with recharge of ground waters with treated domestic waste waters due to water conservation practices which have resulted in increased TDS content of the waste waters. Such practices could lead to having to treat the waste waters for salt removal using reverse osmosis before they could be recharged to the ground waters of the area.

Aquifer Consolidation and Subsidence

At the recent ground water management conference, Bertoldi (1991) has reviewed information on the impact of water table draw down on aquifer consolidation and the associated land surface subsidence. It is well known that decreased water tables cause aquifers to consolidate upon removal of the water which has lead to in some cases very significant subsidence of the land surface above the aquifer. While there is some rebound of the aquifer upon reintroduction of water into it, the aquifer never fully recovers from the water table draw down and therefore the aquifer experiences a loss in capacity for conjunctive use, i.e., the recharge and storage of surface waters in it. While the lost storage capacity is of significant concern to future water resource management, it is likely that the consolidation of the aquifer can cause a change in its chemical characteristics. The magnitude of significance of such changes would have to be determined on an aquifer specific basis.

Another potentially significant impact of water table draw down associated subsidence is the damage to water wells. It is possible that some of the damaged wells would provide a greater potential for ground water contamination from contaminants derived from surface sources or from upper aquifers to lower aquifers.

In some areas, such as the Antelope Valley near the Edwards Air Force Base, aquifer consolidation-subsidence associated with water table draw down is causing fissures to develop in the upper strata. Blodgett (1991) has expressed concern about the possibility that such fissures could extend to the water table and allow more contamination of the aquifer by surface derived contaminants.

 Treatment of Contaminated Ground Waters

The current prolonged drought has stimulated several domestic water utilities-agencies to investigate the feasibility of treating contaminated ground waters as an alternative source of water supply. The current drought conditions have limited the amount of water that can be imported into southern California from the northern part of the state and therefore treated contaminated ground waters represents a potentially highly valuable water supply source during droughts. Adams (1991) has reported that southern California derives about one third of its water from local sources, principally ground water. The other two thirds is derived from waters imported from other areas of the state such as from the Colorado River, the Mono Lake - Owens Valley areas and the Sacramento - San Joaquin River Delta. He further reports that southern California has about 3500 wells with about 38% of the wells being contaminated with chemicals that cause the water to have impaired use for domestic water supply purposes. The principal contaminants of concern are TDS, nitrate and chlorinated solvents (TCE and PCE).

In the past, water utilities on finding that the ground water well has been contaminated have abandoned or at least greatly reduced the use of contaminated wells in favor of drilling new wells in uncontaminated areas. This approach has lead to increased spread of the contaminated ground waters. Adams (1991) has discussed MWD's program which was stimulated by the current drought of encouraging water utilities to pump and treat contaminated ground waters as a domestic water supply source. It has been found that this approach can increase the amount of reliable domestic water supply during drought periods. Further, it tends to clean up the aquifer making it more usable for conjunctive use storage of surplus surface waters.

Mills (1991) has recently reported on a ground water clean up program that is being conducted by the Orange County Water District. He has found that in some instances, ground waters can be pumped and treated at less cost than the cost of purchasing imported water when it is available.

Impacts on Surface Water Quality

The greatest immediate impact of the drought would be expected on surface water supplies. Since approximately two-thirds of the California population obtain their water supply from the Sacramento-San Joaquin River Delta, the impacts of the drought on Delta water quality is of particular importance.

Delta Water Quality

The Delta is particularly prone to water quality problems associated with drought. Of particular importance is that during periods of drought there is less fresh water available to prevent salt water intrusion into the Delta from the San Francisco Bay. Of particular concern is the presence of bromide in the marine waters which under various conditions of water disinfection with a strong oxidant such as chlorine or ozone leads to brominated trihalomethanes and other bromine containing disinfection by-products (DBPs).

Figure 1 presents the chloride concentrations at the Metropolitan Water District of Southern California (MWD) Jensen Filtration Plant influent. It is evident that over the past five years, the chloride content of the State Project water which is water derived from the Delta has shown a steady increase. Since chloride and bromide are major constituents of sea water which according to the Law of Constant Relative Proportions occur in constant ratios in sea water, it would be expected that the bromide content of this water would also have increased proportionately. Figure 2 presents THM species data for the MWD Jensen Filtration Plant which treats State Project water from the Delta. This data shows the increased amounts of total THM's and increased amounts of the brominated THM's especially the tribromo species (bromoform) during the current drought. Such an increase would be expected based on the increased chloride (bromide) content of the Delta waters during the drought. As the bromide concentration in the water that is disinfected increases, it is typically found that some of the chlorines in the THMs are substituted for by bromine. This kind of result is shown in Figure 2. The change in distribution from chlorinated to brominated species is of particular concern since there are some who feel that some of the brominated THM species may be of greater public health significance-hazard than the chlorinated species. This is under investigation by the US EPA at this time. Further, since THM's are regulated based on a weight basis, the formation of brominated THM's rather than chlorinated THM's makes it more difficult for the water utility to meet the total THM limits (MCLs).

California DWR (1990) has been investigating the characteristics and impacts of Delta island drainage waters on water supply water quality for several years. In June 1990, they released a report which presented a summary of their observations during the consecutive dry year conditions of 1987 and 1988. While the information available at the time of that report (June 1990) was not conclusive on the impacts of the drought on Delta water quality, it appeared that the drought could be exacerbating the water quality problems associated with the use of Delta waters for domestic water supply purposes for the approximately 20 million people that use Delta waters for this purpose. Agee (1991) has recently indicated to the authors that the current drought could be having a significant impact on Delta water quality associated with the impact of the agricultural drainage waters from the Delta islands. The management of water used for agricultural purposes within the Delta islands results in significant increases in the concentrations of inorganic salts and organic chemicals in the waters discharged from the Delta agricultural activities to the Delta channels.

The Delta channels transport the Sacramento and San Joaquin River waters through the Delta to San Francisco Bay or to the various water diversion projects. While the water is entering the Delta from upstream sources principally the Sacramento and San Joaquin Rivers contains a number of contaminants of concern for use of these waters for domestic water supply purposes, as the waters from these rivers passes through the Delta, the discharge of Delta island agricultural drainage waters causes significant deterioration in the Delta channel water water quality for use for domestic water supply purposes. According to Agee, the operation of the Delta islands during the drought results in the introduction of large amounts of organic and inorganic materials into Delta channels. With less water available for dilution as a result of the drought, contaminants discharged from Delta island agricultural drains could have an increased impact on domestic water supply water quality. Of particular concern would be the increased TDS and THM precursors. Further work needs to be done to specifically delineate the impact of drought conditions on the deterioration of Delta waters by Delta island agricultural drainage waters on the use of Delta waters for domestic water supply purposes.

Santa Clara Valley Water District

The Santa Clara Valley Water District (Haden, 1991) has reported that during 1990 that the drought has affected water quality in several ways including increased mineralization of the water where the concentrations of hardness, chloride, sodium, total dissolved solids, sodium adsorption ratio, etc., have increased above the normal historical values. Also, chloride and sulfate concentrations have increased requiring increased corrosion inhibitor doses. This district has also experienced increased brominated THM's which are now predominant during the drought where prior to it the chlorinated species dominated.

Contra Costa Water District

The Contra Costa Water District (CCWD), which derives water from the Delta, has experienced a number of the same problems as the Santa Clara Water District. According to Nelson (1991) the drought related impacts on the CCWD water quality include: extended periods of high TDS and high chloride in the source water; increased tendency to produce more THM's and increased tendency to produce brominated THM's; and a slight increase in the corrosiveness of the treated water.

San Diego County Water Authority

Buck (1991) has reported that the San Diego County Water Authority has experienced slight change in water quality since the drought began. The levels of many inorganic constituents have steadily increased since the drought began in 1987.

City of Sacramento

Meyer (1991) has indicated that during September 1991, the city of Sacramento Water Treatment Plant which uses the Sacramento River water as a raw water source has experienced significant increases in turbidity which he feels are related to up river rice farming activities. During September the rice farmers release water from their fields to the river. Associated with this water is elevated turbidity. Under normal flow - non-drought conditions, the turbidity is sufficiently diluted so that it does not cause water treatment problems for the city. However this year, because of the low flow conditions of the river, this turbidity has not been diluted and has caused some water treatment problems.

San Joaquin River Recirculation

Another problem associated with the drought in the Delta system is the increased concentrations of salts in the lower San Joaquin River system. According to Agee (1991), there is a growing consensus that San Joaquin River water is "recirculated" through the Delta Mendota Canal particularly through certain flow regimes. A short circuiting of San Joaquin River water through the southern Delta for export to the Central Valley Project where waters returned from this Project via the San Joaquin River are only partially diluted with Sacramento River water could result in an increased build-up of salts and other contaminants in the south-eastern part of the Delta. During periods of drought the dilution that the San Joaquin River water receives before it is again exported from the Delta to the Central Valley is reduced resulting in increased concentrations of contaminants in the San Joaquin River system. Agee (1991) points out, however, the principal cause of the increased salt build up in the San Joaquin River is likely the agricultural practices within the San Joaquin valley area of the project. Tamblyn (1991) has indicated that because of the limited water supply available during the drought, San Joaquin Valley farmers have had to apply less water per acre i.e. become more water efficient and therefore, the agricultural drainage reaching the San Joaquin River has most likely been more saline and has not been as diluted by tail water releases and operational spills. There is need for additional study to document the degree and factors influencing the impact of the drought on the waters short circuited through the lower Delta from the San Joaquin River to the Delta Mendota Canal.

Reservoirs

The DWR Drought Information Center (DWR, 1991) has reported that the statewide average of the states 155 reservoirs was at 65% of their storage capacity on July 1, 1991. This same percentage applied to the Sacramento Basin which provides water supplies for two-third of all Californians. A number of source water quality problems associated with the draw down of reservoirs during the drought would be expected for water utilities that use reservoirs as their primary source of their domestic water supply water. As reservoir levels decrease, there would be expected increases in turbidity due to the mixing of the fine grained sediments, which are normally below the wave influence zone, into the water column. The increased turbidity of a water supply reservoir could lead to a water utility having to spend more money for inorganic turbidity removal. In addition to wind stirring of sediments into the water column, some reservoirs with substantial rough fish populations, such as carp, could have significantly increased turbidity due to their stirring of sediments. As discussed by Lee (1973), it is well known that the removal of carp from a shallow waterbody increases the waterbody's water clarity.

According to O'Bleness (1991) the San Juan Suburban Water District and other water utilities that derive their raw water from Folsom Reservoir on the American River experienced severe coagulation problems during this past spring and summer. The characteristics of the inorganic turbidity changed during the severe draw down of Folsom Reservoir so that it was extremely difficult to obtain adequate coagulation of the turbidity. Very high doses of alum and/or polymer were used in an effort to improve coagulation of the turbidity. Even at high doses, poor coagulation was achieved where the floc readily penetrated the filter beds. The problem persisted after Folsom Reservoir filled during the March 1991 rains until July 1991.

Mullane (1991) has reported that the San Francisco Water Department experienced significant turbidity removal problems during the current drought which were related to a drawn down reservoir. He indicated that SFWD experienced the first violation of the turbidity standard during the current drought.

Reduced water levels in reservoirs are known to cause a number of water quality problems associated with the growth of planktonic algae and macrophytes. With respect to the latter, the depth to which macrophytes develop in a reservoir or lake is a function of sunlight penetration. Decreased water depths could stimulate the growth of macrophytes and attached algae at depths at which they have not occurred previously (see discussion by Lee, 1973). However, as noted above, the finer grain sediments that are typically associated with deeper waters of lakes and reservoirs would be more readily stirred into the water column. This would tend to decrease light penetration and therefore the depth in the water column to which macrophytes develop.

There have been instances (Beron, 1984) where during periods of drought terrestrial plants developed in the exposed sediment areas which upon re-flooding were killed. These plants as they decay exerted a very high oxygen demand on the reservoir and released significant amounts of nutrients which in turn stimulated algal growth. A recent visit by the authors to Lake Shasta led us to believe that a problem of this type could develop in that lake whenever the large areas of terrestrial weed beds that have developed on what are normally submerged lands are again flooded.

Salazar (1991) has recently reported that the Empresas Publicas de Medellin in Colombia, South America has successfully modeled the deoxygenation of a reservoir upon flooding of terrestrial vegetation. In this case, a new reservoir was constructed without removal of terrestrial vegetation. It was predicted through the use of models that extensive deoxygenation of the reservoir waters would occur in the first year due to death and decay of the vegetation. This is what was found upon filling of the reservoir.

The exposure of sediments to dry conditions tends to cause a release of phosphorus which can stimulate algal growth. This phosphorus release is typically associated with aerobic mineralization of phosphorus containing organic chemicals and the loss of the phosphorus binding capacity of iron in sediments. Overall, decreased water levels in reservoirs would be expected to increase algal productivity. Ramos (1991) has indicated to the authors that the Vista Irrigation District has experienced increased aquatic plant growth in its reservoirs associated with the drought. As discussed by Jones and Lee (1986), shallower waterbodies tend to produce more aquatic plants and algae. The most significant impact of lowering the water level in a reservoir occurs when the water level is lowered sufficiently so that the permanent thermocline that develops in the reservoir, if one develops, is lost during the summer months. Under these conditions, there is much more efficient recycling of nutrients released from sediments through mineralization processes back to the euphotic (lighted) zone.

Ordinarily, the thermocline in a reservoir is a fairly efficient barrier to nutrient transport to the surface waters during the summer months. The Vollenweider-OECD eutrophication model relating normalized phosphorus loads to planktonic algal chlorophyll can be used to predict the impact of decreased water depth on the phytoplankton productivity in waterbodies since one of the normalization factors is the waterbodies' mean water depth. While this relationship works well for relating shallow and deep waterbodies to their productivity, it is important to use this relationship cautiously for drawn down reservoirs since, as discussed above, the draw down can have pronounced impacts on nutrient availability which could overshadow any impacts of depths on productivity.

Lee and Jones (1991b) have discussed the potential importance of phosphorus in Delta waters as a cause of algal related tastes and odors, THM precursors, etc., for domestic water supplies that utilize Delta waters as a source. The draw down of the reservoirs that are tributary to the Delta impact on phosphorus concentrations of the reservoir water could contribute to increased algal related water quality problems for those water utilities that are utilizing Delta waters as a source.

LADWP Mono Basin-Owens Valley Water

One of the most significant consequences to Southern California of the current drought is the reduction of water available to the city of Los Angeles Department of Water and Power (LADWP) from its watersheds on the eastern slopes of the Sierra Nevadas in the Owens Valley and Mono Basin areas. The current drought is causing restrictions in the amount of surface waters diverted by LADWP from tributaries of Mono Lake and from ground waters in the Owens Valley. Since this water, especially the Mono Lake tributary water, which is delivered by the Los Angeles Aqueduct (LAA) is of very high quality, the substitution of other sources to compensate for the supply deficiency significantly impacts the quality of the water supply of the City. To make up for the shortfall in LAA supply, LADWP has taken delivery of large quantities of MWD (Delta) water. The latter source tends to have a higher algal nutrient content and may have contributed to the increased algae growth and higher trihalomethane levels that have been experienced in some of the LADWP reservoirs. As reported by Kriami and Singer (1991), Heyer (1991), and discussed by Lee and Jones (1991b), the change from Mono Lake tributary water to water derived from the MWD (Delta) water is believed to have affected the growth of algae in Silver Lake Reservoir, which is a part of the LADWP municipal water supply system. The MWD supplied water is believed to have caused an increase in trihalomethanes, in parts of the LADWP municipal water supply system fed by Silver Lake Reservoir. The increased THMs is believed to be derived from the increased algal growth.

One of the consequences of the LADWP utilization of increased amounts of MWD water has been a change in the approach used by MWD for water treatment. Previously, MWD had been using chloramine treatment of its waters in order to minimize THM formation. LADWP on the other hand has been chlorinating to produce a free chlorine residual. Now that MWD is providing increased water to LADWP (maximizing use of Colorado River Water, which has not been reduced by the drought), MWD has modified its water treatment to be compatible with LADWP producing a free chlorine residual. This has adversely affected the THM's present in the water treated by this approach.

Lake Tahoe

Lee and Jones (1991b) have discussed the water quality problems that some domestic water utilities are experiencing with the use of Lake Tahoe's water as a source. The drought caused lowering of this lake is associated with taste and odor production in some utilities' waters. This is the first time that these utilities have experienced this problem. As discussed by Lee and Jones it is not clear that the problem is due exclusively to lower water levels, it may also be due to increased algal growth that is occurring in the lake in both open waters and near shore areas due to increased nutrient inputs to the lake.

Impact on Algal Growth

MWD (1991) has recently indicated that the growth of algae in Lake Mathews associated with the drought is causing increased water supply taste and odors. In the past MWD has been able to blend Delta water with Colorado River water to compensate for increased algal growth. However the reduced availability of State Project water from the Delta has reduced MWD's ability to blend waters to dilute the algal caused taste and odors.

In some reservoirs, there is evidence that during drought periods there is a change in the numbers and types of algae which adversely affects the water quality more than that predicted by an increase in algal productivity-biomass. Certain kinds of algae, such as bluegreen algae, tend to cause more domestic water supply water quality problems per unit chlorophyll than other types of algae. Silvey (1975) indicated that he felt that in some water supply reservoirs drought periods tend to promote increased algal and other organism type tastes and odors than those that occur under full pool conditions. He thought that this may be related to the algae and other organisms, such as actinomycetes and bluegreen algae, tending to grow in the small shallow pools along the water's edge. He indicated that these pools tend to be more prevalent during droughts.

Miscellaneous Impacts

Another potential impact of drought on domestic water supply water quality occurs in association with the increased potential for fire in the watershed. Burned areas tend to increase nutrient fluxes from them which would increase algal growth in downstream reservoirs. Also there would be increased erosion of burned areas. Several papers concerned with the effects of fire in watersheds on nutrient and erosional material transport from burned areas were published in the Proceedings of the California Watersheds at the Urban Interface Symposium (DeVries and Conard, 1991).

Another expected impact of the drought is to damage the ability of vegetation in a water supplies watershed to limit erosion and nutrient transport. The State Drought Office has reported that vegetation in the Sierras is under significant stress because of the drought. Since the presence of healthy vegetation is the key to erosion control it would be expected that the drought would be adversely effecting the amount of erosion, nutrient, and other contaminant transport from the watershed. It would also be expected that during the prolonged drought animal grazing, logging, and other activities in the watershed which promote erosion would be more severe than during normal precipitation. This would be the result of adverse impacts of grazing, logging, etc. on vegetation which is already stressed because of the drought.

A possible positive impact of the drought would be for those water utilities that have acid mine drainage problems in their watershed. The production of acid water by some mines would be expected to be reduced during periods of drought due to reduced water input to the mine. This may, however, lead to severe acidity problems at the time of the next major precipitation event.

In a survey of its members of the 1991 drought management practices conducted by the Californian Urban Water Agencies it was found that a number of water utilities are utilizing sources of water that have been used to a limited extent in the past. This situation may cause domestic water supply water quality problems since the water utilities may find that these other sources are of overall poor quality and are of a more variable quality. Variable source water quality can be a particularly significant problem for water utilities since it often means that the finished (treated) water delivered to the consumers is also of variable quality. It is well known that the public tends to respond adversely to changes in water quality. Often a change in water quality will bring complaints even though the change is not adverse to the use of the water for domestic water supply purposes.

Algal Nutrients and Delta Water Quality

A number of water utilities have experienced increased algal related water quality problems during the drought which are associated with the use of Delta waters. As discussed above, these problems are primarily arising from substitution of Delta water for other waters which typically had lower algal nutrient content. It does not appear from the information available at this time that more algae are developing in the Delta waters during the drought than developed during non-drought periods. Sutcliffe (1991) has reported that algal related tastes and odors in the Santa Clara Valley Water District surface waters, which are derived from the Delta, have not increased during the drought.

Lee and Jones (1991b) have discussed the algal nutrient (N and P) situation for the Delta. They have concluded that the Delta receives sufficient quantities of nutrients from above Delta sources to cause sufficient algal growth within the Delta and in reservoirs that are filled with Delta water to impair the use of the water for domestic water supply uses. They further point out that the growth of algae in the Delta typically follows the same pattern found for most waterbodies throughout the world as being proportional to the normalized phosphorus loads to the Delta. They have found that during the summer months, which is the critical period for impacts of algae on domestic water supply water quality, over 95% of the phosphorus loads for the Delta which stimulate algal growth within the Delta or downstream reservoirs is derived from domestic waste water sources discharged to tributaries of the Delta (Sacramento and San Joaquin Rivers). As Lee and Jones (1991b) point out, there are over 50 million people in the world treating their domestic waste waters for phosphorus removal at a cost of about 4 cents per person per day who contribute waste waters to the waste water treatment plant. They conclude that if phosphorus treatment were practiced for the waste waters discharged to the Delta tributaries that this would significantly improve Delta algal related water quality in such areas as tastes and odors and for some utilities reduced THM precursors.

It is Lee and Jones' preliminary assessment based on the hydrology of the Delta that such treatment may only have to be practiced in late spring and summer thereby reducing the overall annual cost significantly. From the information collected in this review, it appears that treatment for phosphorus removal may be particularly important during periods of prolonged drought in order to minimize the algal related problems reported above by some water utilities associated with increased use of Delta water during the drought.

Management of Source Water Quality During Droughts

The water quality problems that have occurred for a number of water utilities in this state during the drought raises questions about whether those utilities that have experienced such problems could make their raw water quality more drought resistant. It is evident that since large numbers of people in both northern and southern California's domestic water supply water quality who use the Delta as a water source has been adversely affected during the drought, that considerable consideration should be given to the water quality that would be present if the water supply diversion structure (peripheral canal) had been operational during this drought. It is now well established through DWR studies that the Delta agricultural practices contribute significant amounts of THM organic precursors to the Sacramento River as it passes through the Delta before discharge to the San Francisco Bay system, or is exported from the Delta. Not only do the Delta island farm practices add substantial amounts of THM precursors, it has been found according to Agee (1991) that the organic THM precursors added from agricultural drains within the Delta are particularly potent precursors. The drainage from the peat soils and the agricultural as well as other plant residues that develop on Delta islands tends to form more THMs per unit organic carbon than the organic precursors found in the tributaries of the Delta. Therefore, the proposed peripheral canal system could significantly reduce the potential for THM formation in the exported-diverted water.

The contaminant possibly of the greatest concern in the Delta that is affected by the drought is bromide. The bromide is introduced into the Delta through marine water intrusion from the San Francisco Bay system. If the peripheral canal had been operational during the current drought, then the increase in total THMs and the brominated THMs would not have occurred since the bromide content of the Sacramento River water is low and leads to only small amounts of brominated THMs. It is estimated by MWD representatives that considering current water treatment methodology, the total THMs in the waters taken from the Sacramento River system via the peripheral canal would have been on the order of 30 mg/L with little or no brominated THMs rather than the 100 mg/L that have been found during the past summer. This would obviously be a significant improvement in the domestic water supply water quality for those water utilities that would obtain waters from the peripheral canal system.

The US EPA's 1992 release of proposed new regulations governing the MCLs for disinfection by-products in domestic water supplies which will likely, based on preliminary information released by the US EPA, reduce the total THM MCL as well as possibly place specific MCLs on certain of the DBPs. Reducing the THMs form in the water from 100 to 30 mg/L associated with the construction of a peripheral canal, could play a major role in enabling water utilities to meet the new US EPA MCLs. As discussed above, this is of importance to large numbers of people in both northern and southern parts of the state. It is evident that further work should be done to evaluate the potential benefits of a peripheral canal or other diversionary system which would take Sacramento River water around the Delta so that it would not be contaminated by Delta island agricultural drainage, San Joaquin River agricultural drainage which at times adds significant amounts of contaminants to the exported water from the Delta and most importantly, the bromide associated with the salt water intrusion into the Delta from the San Francisco Bay.

Another significant problem associated with Delta waters is the high algal nutrients (nitrogen and phosphorus compounds) present in these waters. These lead to algal related tastes and odors and under some situations, elevated algal derived THMs. The peripheral canal system as originally proposed, would take water from the Sacramento River below the waste water treatment plant discharges from the metropolitan Sacramento area which is one of the major sources of nitrogen and phosphorus for the Delta waters currently exported in the State Water Project. A review of the phosphorus data for Green's Landing on the Sacramento River, which is typical of the characteristics of the water that would be diverted in the peripheral canal, shows that in general, during the summer months, the concentrations of phosphorus at this location are the same as those found at the Clifton Court Forebay where the waters are currently diverted from the Delta for the State Water Project. Therefore, the peripheral canal diversion of Sacramento River water would not be expected to significantly change the algal related taste and odor problems that the water utilities in both northern and southern California are experiencing in association with the use of Delta water as a raw water supply.

The authors (Lee and Jones) have concluded that there is considerable merit to developing phosphorus removal programs at the domestic waste water treatment plants that contribute phosphorus to the Delta. The removal of phosphorus from domestic waste water is a widely practiced technology in many parts of the world that could be implemented at those waste water treatment plants that discharge to the Sacramento River system above the intake for the peripheral canal. Adopting such practices would, in the opinion of the authors, significantly improve the algal related domestic water supply water quality for the water utilities that would use the peripheral canal supplied Sacramento River water. A possible alternative is to divert the Sacramento River water above the metropolitan Sacramento area. This would significantly reduce the amounts of nitrogen and phosphorus added to this water from waste water sources. It could also reduce the amounts of organic THM precursors added to the Sacramento River from urban storm water drainage and domestic waste water sources. The agricultural practices such as rice farming that take place above the city of Sacramento are likely significant sources of organic THM precursors for the Sacramento River. Lee and Jones (1991b) have discussed the importance of evaluating the current significance of above Delta THM precursor sources in developing management programs or THM problems associated with the use of the Sacramento River as a domestic water supply source.

It is evident that much greater consideration needs to be given to how to operate the State Water Project exported waters from the Delta as it relates to minimizing algal related domestic water supply water quality problems than has been done thus far. This will be especially true if the proposed off-stream reservoir systems such as the Los Banos Grandes Reservoir is constructed. Considerable experience exists in other parts of the US and other countries in minimizing algal related water supply problems through management of reservoir systems. The critical factors governing the growth of algae for waters of the type present at Green's Landing on the Sacramento River during the summer months are water mean depth in the reservoir, water hydraulic residence time in the reservoir and the areal algal available phosphorus loadings to the reservoir. The biomass of algae can be reliably predicted based on the Vollenweider-OECD eutrophication study results to estimate the biomass of algae that would develop in a waterbody with sufficient reliability to make management decisions on proposed management options. The algal related water quality could be significantly improved if the operation of the State Water Project reservoirs were such that the waters with high concentrations of nutrients could be stored in a off-line reservoir for at least two weeks during the summer before transmission to the reservoirs in the southern part of the state. This is a result of algal growth significantly reducing the phosphorus content of the water and incorporating the phosphorus into the sediments. Typically from 50 to 80% of the phosphorus entering a reservoir is removed via algal growth during the summer months. Jones and Lee (1986) have discussed the use of this approach for this purpose. It is now based on a data base of about 750 waterbodies located in various parts of the world and has been demonstrated to have a high degree of predictive capability.

Those water utilities that are experiencing elevated THMs due to the presence of algae in the water could consider storing the water for a period of time to allow the algal derived THM precursors to decay. As discussed by Lee and Jones (1991b) it appears that THM precursors derived from terrestrial plants which contain lignin produce a more refractory THM precursor than the THM precursors derived from algae. The algal derived THM precursors appeared to be highly labile and are converted to non-THM precursor compounds after a few weeks in many aquatic systems. Lee and Jones suggest that water utilities that have significant parts of their THM precursor material derived from algae could modify their water treatment to enhance biological transformation of the algal derived precursor materials.

Gregg (1991) has discussed the Contra Costa Water District's (CCWD) development of the Los Vaqueros off stream storage reservoir. The development of this reservoir would greatly improve the raw water quality that CCWD obtains from the Delta. It should also help make the CCWD raw water quality much more drought resistant, especially as it relates to increased THMs, increased brominated THMs, increased TDS, algal tastes and odors, etc.

The other drought associated surface water problem that has affected a number of water utilities is the increased turbidity of drawn down reservoirs. It would be important for water utilities that have experienced such problems to understand whether rough fish populations in the reservoir are a significant cause of the increased water turbidity. Fish census techniques can readily be used for this purpose. If large numbers of rough fish are found in the reservoir, then they can be readily removed. This would not only improve the water clarity, but also the game fisheries of the waterbody.

If the increased turbidity in a drawn down reservoir is primarily due to the wind mixing of fine grain sediments into the water column, then floating baffles or other structures to dissipate wind-wave energy could be used to reduce wind stirring of sediments. It may also be possible to treat the reservoir with alum to remove turbidity. Such treatment would also remove phosphorus and thereby help in reducing any algal related quality problems that are occurring in the reservoir. Considerable experience has been gained as part of the US EPA's lake restoration program in the treatment of whole lakes and reservoirs to improve water quality. Cooke et al. (1986) have summarized the work that has been done in this topic area.

The city of Sacramento's problem with increased turbidity apparently due to rice farmers discharge of turbid waters in September, 1991 could be controlled through requiring that such discharges be settled and/or treated before discharge. While the treatment of irrigation drainage waters has typically not been required in the past, it is likely that such discharges will be considered as waste waters and therefore have to be treated to the same degree as other municipal, industrial and commercial waste water discharges to prevent the agricultural drainage water from impairing the beneficial uses of surface waters of the state.

Lee and Jones (1991d) have discussed the approach that the water utilities that used Lake Tahoe water as a source that are experiencing algal related tastes and odors should consider in developing programs to minimize problems of this type. Lee and Jones suggest that the focus should be on limiting the algal nutrients entering the lake. They suggest that an evaluation be made of the potential significance of NOx omitted from automobiles, buses and trucks within the Lake Tahoe Basin serving as a source of atmospheric nitrogen for the lake. If on the order of 10% or so of the NOx emitted is converted to nitrate and ammonia within the Tahoe Basin, then banning the use of internal combustion engines within the basin could be a highly effective method of reducing the atmospheric nitrogen loads to the lake. The atmospheric nitrogen load is estimated by Lee and Jones (1991d) to be the dominant source of nitrogen for the lake. Adoption of a light rail system or similar public conveyance system and thereby eliminating or at least greatly reducing automobile, bus and truck use within the Lake Tahoe watershed could be a highly effective way to significantly reduce the deteriorating water quality in the open waters of the lake arising from increased growth of algae.

The near shore water quality problems of Lake Tahoe can be managed through limiting the use of irrigated and fertilized non-native vegetation such as lawns. There is considerable evidence for fertilizers applied to lawns being transported via the irrigation water used on the lawns to the near shore waters where this water enters the lake as springs, stimulating algal growth at the point of entry. For further information on eutrophication management in Lake Tahoe, consult Lee and Jones (1991d).

The current drought has emphasized the importance of protecting and where possible enhancing ground water quality in the state. It is evident that it is highly important that the state regulations (Water Resources Control Board, Chapter 15) governing the protection of ground water quality from land disposal of wastes such as municipal and industrial landfills be fully implemented. These regulations require that any land disposal of wastes prevent ground water pollution - impairment of uses for as long as the wastes represent a threat to the ground water quality. Since all municipal and many industrial landfills contain waste constituents that will be a threat to ground water quality forever, it is imperative that the siting, design, construction, operation, closure and post-closure care of landfills and other waste management units be conducted in such a way as to protect ground water quality forever not for just a few tens of years as now typically proposed.

The authors have found that at this time in California inadequate attention is being given to the long-term ground water quality impacts of municipal landfills. During the past several years, landfills have been approved which almost certainly will result in ground water pollution at some time in the future. As discussed by Lee and Jones (1991c), once ground waters are polluted by municipal landfill leachate, the ground water and part of the aquifer that was polluted cannot be used again for domestic water supply purposes. It is imperative that water utilities take a highly aggressive role in reviewing the siting of lined landfills of the type being constructed today to ensure that future generations will not have the uses of their ground waters impaired by landfill leachate. Lee and Jones (1991b) have provided guidance to water utilities on the approach that they should consider in protecting the ground water resources of their area from contamination by landfill leachate.

A vigorous program of well inspection and proper closure upon termination of use should be conducted in the state to prevent well bore holes from serving as a conduit for contaminant transport to ground water. Further, all surface waters incidently and deliberately recharged to ground water should be chemically analyzed and managed to prevent recharge waters from transporting contaminants from surface waters to aquifers.

The current programs being practiced by some water utilities and agencies of pumping and treating contaminated ground waters should be encouraged. This approach not only provides additional sources of domestic water supply especially during droughts, but also can be a key part of ground water and aquifer clean up programs.

Conclusions

The current five-year drought in California is having a significant adverse impact on domestic water supply source water quality. Some of the most significant impacts are associated with water utilities that use Delta waters as a source of supply. Increased total THM's and brominated THM's, algal related tastes and odors, turbidity, TDS, etc., are being experienced. Other impacts which are less well documented are also expected for both surface, and especially ground water quality. The increased population pressures with the associated increased demand for municipal water will make the impacts of droughts on municipal water quality a more frequent occurrence. It will become increasingly important that increased attention be given to, not only supplying water to meet municipalities' needs during droughts, but also to protect water supplies from deteriorated water quality during periods of drought. Water utilities should, as part of developing information that can lead to minimizing the impact of prolonged periods of drought, carefully document the impacts when they occur so that the information can be used by the utility regulatory agencies and the public in order to gain the necessary support for drought mitigating practices. Water utilities should also understand the factors that caused deteriorated water quality during the drought, and take action to make their water supply water quality more drought resistant.

Acknowledgments

The authors wish to acknowledge the assistance of many individuals who provided information that served as a basis for this review. These included L. Hoag, Executive Director of the California Water Agencies; Roger James and J. Sutcliffe, Operations and Water Quality Manager and Supervising Engineer of the Santa Clara Valley Water District; M. O'Bleness, Water Quality Superintendent for the San Juan Suburban Water District; V. Driver and B. Buck, Manager Water Quality and Director of Water Resource Planning of the San Diego County Water Authority; B. Deprimio, Los Angeles Department of Water and Power; G. Deatherage, California Department of Water Resources; T. Tamblyn, Bay-Delta Engineering Unit, CA Water Resource Control Board; A. Nelson, Director of Water Resources, Contra Costa County Water District; B. Agee and R. Woodard, Division of Local Assistance, California Department of Water Resources; R. Meyer, City of Sacramento Water Treatment Plant; T. Maddock, Chairman of the California Chamber of Commerce Water Resources Committee; M. Beuhler, Associate Director of Water Quality, Metropolitan Water District of Southern California, B. Brickson of the Water Education Foundation and the members of the CA/NV AWWA Source Water Quality Committee especially L. Hoag, J. McElroy, J. King, and E. Archibald. While several of the CA/NV Source Water Quality Committee members and others provided significant input to this discussion, the views expressed in this paper are those of the authors and not necessarily those of the Committee or its members.

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