Ground Water and Used Water in Basin Recharge Areas Water stored in the underground basins of the river systems of Southern California is the principal source of water for urban, agricultural, and industrial purposes in the region. Under natural conditions, ground water accumulated from deep percolation of surface runoff and rainfall. Under present conditions of intensive development and the use of imported supplemental water, sanitary and industrial wastes and unconsumed irrigation water in basin recharge areas make important contributions to ground water. Conversely, increasing ocean disposal of sewage is a major factor in the depletion of coastal water basins. Return irrigation and waste water disposal in basin recharge areas are changing the character of receiving waters. Salinity and percentages of sodium have increased, and a build-up of chemical substances deleterious to quality of ground water has been observed in local water production zones. The disposal of spent waters, especially those derived from imported supplies, to afford the maximum quantity of water suitable for basin recharge consistent with the maintenance of safe quality in receiving waters is of paramount importance, and presents a major problem to industrial and sanitary engineers and water pollution control authorities. ROSS A. SHAFER, Tustin, Calif.
U
NDERGROUND water is the principal source of water supply in the drainage areas of the Los Angeles, San Gabriel, and Santa Ana river systems, which, with coastal fringe areas, comprise the metropolitan region of Southern California. Ground water also serves as the receiving water for increasing quantities of sanitary and industrial wastes and return irrigation water. Most of the cities and suburban communities and the agriculture of the region have no other sources of water supply immediately available; and t h e municipalities and municipal water districts which have access to imported water must continue to draw upon local ground waters for large or major portions of their water requirements to give flexibility, t o permit maximum usefulness of the imported supplies, to furnish standby reserves for use in times of drought in the foreign water source area8 or during unavoidable interruptions in aqueduct deliveries and for peaking purposes during the daily or seasonal periods when local demands exceed the rates at which imported supplies cafi be delivered. UNDERGROUND BASlNS
The structural nature of the underground basins and the movements of ground water within them are such t h a t they could be used effectively to distribute imported or reclaimed supplemental waters, which may be commingled with ground water in basinrecharging operations, to use areas which are not accessible to aqueducts and distributing pipelines. For these reasons, the use of the underground basins and waters of the region will continue to be indispensable to the water supply programs of the future. As of 1951-52, it is estimated that more than 70% of the water used for domestic, municipal, irrigation, and industrial purposes in the region was derived from ground water, and t h a t such water was in the order of 1,020,000 acre-feet,
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The principal ground-water bodies of the region are contained in pervious deposits of Recent and Pleistocene Ages which underlie the alluvial fans and the broad flood plains of the three river systems, and extend, in places, beyond the shore line under the ocean. Block faulting and deformations of the earth’s crust prior to the deposition of the recent fill created depressions, barriers, and constrictions athwart antecedent drainage troughs and formed the basins of the region. Between, over, and across such structural obstructions to stream flow, the troughs were filled with alluvial and marine sediments through which the ground waters percolate. I n every major basin of the region the bottom of the waterbearing sediments lies hundreds of feet lower than the outlet of the basin. This structural feature may be an insurmountable barrier to the basin drainage necessary to maintain salt balances in the basins. The underground basins are charged mith the waters they have absorbed over countless centuries from storm runoff, from tributary watersheds, and from the deep percolation of rainfall upon the valley floorp. Until they were exploited by pumping, the basins were full to overflowing; and losses of water by evaporation from moist lands and water surfaces, the use of water by phreatophytes, and the discharges of rising water from the basins increased or decreased with the rainfall cycle and the quantity of water in storage underground. Under prevailing conditions of land and water use, the drafts upon ground waters have exceeded the supplies of native waters available forbasin recharge and the natural processes of replenishment. Water deficits were appearing in some of the ground water basins prior to World War I1 as the result of overpumping to satisfy the demands for water to support a regional economy then dominated by irrigated agriculture. It is sometimes stated in respect to the water supplies of this
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Industrial Process Water
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region that “transition from agriculture to municipal use can be made without affecting the volume of water required for a definite area.” This requires qualification. Under agricultural use, the difference between the duty of water (the quantity required t o serve a n area) and the consumptive use of water (the quantity consumed by the life processes of plants and animals plus evaporation and transpiration) usually returns to ground water and becomes available for re-use. If the spent waters from municipal use were disposed of by export through sewers, the element of return water would be lost to the basin, and, while the volume of water to serve the area might not be affected, a loss of water would result from the transition from agricultural to municipal use. As a result of increased demands for water and the growing trend toward the ocean disposal of spent waters, which have accompanied the unprecedented wartime and postwar urban and industrial development of the region, overdrafts upon underground water have become general. With the notable exception of the San Fernando Basin, which has been recharged by the deep percolation of irrigation, sanitary, and industrial wastes derived from the use of water imported by the city of Los Angeles, all of the major ground-water basins have been so depleted, or are so physically related to depleted basins into which they discharge, t h a t ground-water production cannot safely be expanded, and litigation and legislation to limit withdrawals to the safe yields of the basins are being seriously considered. No official estimates of the over-all deficit in the ground waters of the region have been published. However, by using as guides recent estimates of annual overdrafts of 57,000 acre-feet in the West Coast Basin ( S ) , 77,000 acre feet in the Central Coastal Basin ( 2 ) , and 67,000 acre feet in the Orange County Coastal Basin (7), i t appears probable that the total annual overdraft upon t h e ground-water basins of the region exceeds 300,000 acre-feet, and that the accumulated total of such deficits exceeds 1,300,000 arrefeet. The deficits are increasing at accelerated rates and are now approximately 29% of the total annual use of ground water in the region. Because the basins of a stream system occupy the troughs traversed by the present streams, the surface flows of the streams and the waters in storage underground are interdependent. During storm runoff, the surface streams may be continuous across their basins from the mountains to the ocean. During t h e remainder of the year the rivers and their tributaries usually appear as surface streams only where they debouch from t h e mountains or where they show as rising waters near the lower lips of upstream basins and flow for short distances until they percolate into the absorptive sands of the basins next below. In addition to the surface flows of the streams, the ground waters of the basins move slowly under the influence of their hydraulic gradients from basin’intake areas toward basin outlets, where they rise to form surface streams or discharge across the basin boundaries as underflows. Thus in the intake areas of the basins, influent surface streams replenish ground water, and in the areas of rising waters, ground water supports the surface streams. Because the perennial surface flows and the percolating underground waters of a river system are so closely interrelated t h a t water in its passage down the river may occur as a surface stream in reaches of surface flow, and as ground water in the intervening basin areas, i t follows that changes in the quality of one will eventually be reflected downstream in the quality of the other. QUALITY OF WATER
Under natural conditions the quality of ground water was determined by the mineral character of the deposits which filled the basins and the tributary areas from which influent drainage was derived, and by the degree to which basin waters were concentrated by surface evaporation and transpiration by plants.
December 1953
The settlement of the region has brought additional influences
to bear upon the quality of the native waters, and in every basin in the region the effects of urban, suburban, agricultural, and industrial development are noticeable in the degradation of the quality of both surface and ground waters. As the continued availability of usable underground water is an indispensable requirement in providing adequate water supplies to support the development of the region, it is important to know what has happened to the quality of the native waters under past conditions in order to plan for the future use and preservation of this essential natural resource.
TABLE I. FIFTEEN-YEAR INCREASE IN SALINITY OF SANTA ANA RIVER (On basis of single yearly samples in late spring and summer)
Sampling Point 1. Inflow to San Bernardino basin NE. of Redlands 2 . Discharge from S.B. basin E. Street, San Bernardin0 3. Discharge from Riverside basin in Narrows (influent fresh water enters stream from Chino basin between 2 and 4) 4. Hamner Ave. bridge inflow to Prado basin (saline water from Corona basin and fresh water from Chino basin enter stream between 4 and 5) 5. Orange Co. line inflow
Total Dissolved Solids, P.P.M. 1931-32 1947
I~~~~~~~or Decrease, P.P.M.
Change in % Sodium
176
174
-2
+s
273
478
$205
-F 25
615
668
+53
-1
490 553
638 658
4-148
-6 -1
f105
Conditions in the basins of the Santa Ana River may be con sidered as typical of the other river basins of the region. The headQaters of thia etream rise on the southern and western slopes of the San Gabriel, San Bernardino, and San Jacinto mountains. The main stream traverses the San Rernardino, Colton, Riverside, Prado (Chino), Canyon and Coastal basins for some 70 miles on its way from the San Bernardino Mountains to the ocean. The river is flanked by the tributary Chino basin on the north, and the Arlington and Corona basins on the south. Except during times of storm runoff, the streams of this system flow on the surface only in their mountain canyons and at points of spill from upper t o lower basins. Early.analyses of basin waters showed wide variations in the quality of water from basin to basin and significant differences between the influent and effluent waters of the individual basins. I n the Chino and San Bernardino basins a t the foot of the mountains, the waters were relatively low in dissolved solids, with influent surface waters containing 150 to 175 p.p.m and ground waters in the central portion of the basin containing less than 200 p.p.m., with a build-up to around 300 p.p.m. in. the effluent waters. In the tributary basins south of the river, which receive their waters from the spills of the upper basins and from drainage from the old sedimentary formations which outcrop about midway between the mountains and the ocean, the mineral content of the waters ranged from about 450 p.p.m. to more than 1200 p.p.m. of dissolved solids. I n the Coastal Basin, whose influent waters are a composite of all of these plus substantial runoff from the surrounding hills and the seaward slopes of the Santa Ana Mountains as well as rainfall on the intake area of the basin, early analyses of ground waters in the central portion of the basin showed about 300 p.p.m. with greater concentrations of salts t o 600 or 700 p.p.m. in the rising waters which flowed from the coastal swamp areas t o the ocean. The settlement of the Santa Ana River drainage area has greatly modified conditions which affect the quality of its native waters. As of 1950, there were 275,000 acres (1)under irrigation
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in the Santa Ana River basins, 38 sewered communities were disposing of the sewage and industrial wastes from a combined population of 218,900 persons into surface streams or basin recharge areas, and the domestic sewage from 239,000 persons living outside the sewered areas was disposed of in cesspools and septic tanks tributary to ground water ( 5 ) . The effect of the return of used waters to the basins and the surface flons of the Santa Ana River upon the salinity of the surface stream in and between the ground-water basins, in the 15-year period 1931-32 to 1947, is shown in Table I (4). The increasing salinity of the surface stream a t the Orange County line is believed to be a fair index of the composite effect of return water upon the water supplies of the upstream basins. The average annual increase in the salinity of the summer stream a t the County Line Station, over the 15-year period covered by Table I, was 7.0 p.p.m. An unpublished tabulation of analyses (6) of the waters of the Santa $na River a t the count) line, based upon 12 monthly samplesper year for the 5-year period from 1936 e0 1941, shows an increase in the yearly means of total salines from 440 p.p.m. in 193B to 518 p.p.m. in 1941, which is an increase of 78 p.p.m. in 5 years, or 15.6 p.p.m. per year. As these analyses cover the entire year, the results are believed to be more indicative of the actual build-up of salts in the basins of the river than the results tabulated in Table I from single yearly samples. Table I1 shows the increase or decrease of salinity in ground water pumped from representative wells of the basiris of the Santa Ana River system.
TABLE11. FIFTEEN-YEARCHANGESIN SALINITYOF \TELL WATERIK BASINSOF SANTA ANARIVERSYSTEM Total Dissolved I~~~~~~~ or Decrease, Change in Well Locationa 1932 1947 P.P.M. 70 Sodium San Bernardino basin 1. E. of 6an Bernardino 339 459 +l20 -6 2. W. of San Bernardino 374 400 +26 -1 Riverside basin 3. E. of Riverside 302 877 +75 - 12 Arlington basin 3.5. SW. of Arlington 854 0 937 83 Prado (Chino) basin 4. W.of Norco 650 655 +5 +6 Corona basin 1252 1146 106 4.3. N. of Coronab +Q Chino basinC 605 433 4.6. E. Of Chino 172 0 Coastal basin 388 403 5 . S. of Anaheim +I5 -2 Numbers indicate a r e a corresponding t o Table I. b Decrease in salinity in water from this well is believed to have resulted from the imDortation and use of water from the San Bernardino Basin f n r irrigation in'the area around this well in lieu of more saline water formerly used and from the effects of a series of wet years 0 Decreased salinity probably resulting from abandonment of the disposal of beet sugar factory nastes in this area and leaching away of salts by the deep percolation of irrigation water and rainfall.
Ed-
+
-
(1
An investigation of changes in the quality of ground water from 1931 to 1946-52 by the engineers of the San Bernardino County Flood Control District has disclosed numerous areas in the basins of Riverside and San Bernardino Counties where the salinity of ground water has increased significantly. Many of these foci of pollution can be readily associated with farming and industrial practices or the disposal of sewage wastes in the areas in which they occur. For others the causes are obscure. The changes observed in the investigation have occurred in a 20-year period, during which the economy of the subject area was largely agricultural and rural, where the water used was from native sources, and when the wartime and postwar expansion of urban and industrial development was just beginning. Maps showing changes in quality of ground water, prepared by Lloyd Martin, hydrologist, under the direction of R. V. Ward,
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assistant engineer of the San Bernardino County Flood Control District (8)indicate ground-water degradation conditions believed typical of those that have developed in the other basins of the region in Los Bngeles and Orange Counties. They exemplify conditions which, if not corrected in time, could destroy the usefulness of the ground water basins. The phenomenal increase in urban and industrial development now occurring, and the necessary resort to the use of more saline imported waters to supplement the native supplies, will inevitably accelerate the rate of degradation of basin ground ~ a t e r s . The degradation of ground-water quality in the Santa Ana River basins is the result of the use and disposal of native waters. The combined annual overdraft upon ground water in these basins is now estimated as in excess of 100,000 acre-feet. Increasing importations of supplemental n.ater in exceSs of that amount will be required to sustain the gron ing urban, suburban residential, and industrial development n hich has been imposed upon the mature agricultural economy of the area, and to restore safe fresh water lepels along the coast. These conditions are similar to those which prevail in the basins of the other river systems of the region. The disposal in recharge areas of spent Inters resulting from the use of imported supplies could make important contributions to ground water. However, because the imported waters now available carry from 1.5 to 3 times the concentrations of minerals present in the underground waters of the principal basins, their use and disposal in the basins will further increase the salinity of the receiving waters. LIuch investigation and rescai ch have been directed toward determining the effects of saline ryaters upon irrigated crops and croplands, and the irrigation requirements for maintaining favorable salt balances in the crop root zones. There have been occasional references in scientific reports and discussions to the necessity for wasting sufficient water from the underground basins to flush out accumulated salts and maintain the salt balances of the basins. How such flushing can be accomplished in the overdraa n basins of the region, whose characteristic structure is such that their deeper waters accessible to pollution lie below the basin outlets, has not been determined nor suggested. The inevitable increase in the salinity of ground waters, which are subject to recharge by waste and return waters, poses a serious question of our ability to preserve the usefulness of the basins and their aaters over the long future. The solution of the problem appears to require prevention rather than cure, for it is doubtful that pollution once established in the deep basin waters could be flushed out. The aspects of its long-range effects upon the stability of the cconomy of the region indicate t h a t the prevention of irreparable damage to basin xaters by pollution is the most important R-ater problem of today, and by far the most difficult t o solve. LITERATURE CITED
(1) Division of Water Resources, State of California, Bull. 53 (1947). (2) Division of Water Resources, State of California, Central Basin
Investigation, hlarch 1952. (3) Division of Water Resources, State of California, Report of Referee, West, Coast Basin Reference, February 1952. (4) Division of Water Resources, State of California, unpublished data, 1931-32 to 1947. (5) Federal Security Agency, Public Health Service, Report on W a t e r Pollution Control, Santa Ana River Basin, March 1, 1951. ( 6 ) Netropolitan Water District of Southern California, unpublished analyses, 1942. (7) Orange County Water Basin Conservation Committee, estimate by C. R. Browning, August 1952. (8) San Bernardino County Flood Control District, California, Map Showing Ground Water Quality, 1952. RBCBIVED for review April 10.1953.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTED October 9, 1953.
Vol. 45, No. 12
