Ground Waters of the HoustonMARGARET D. FOSTER United States Geological Survey, Washington, D. C.
tained from observations during 5 to 6 years, was made in 1937 (3). The present paper is largely a discussion of the findings of the investigation as they relate to the area.
Geologic Conditions The area included in the study is shown in Figure 1. It comprises Waller, Harris, Galveston, and parts of Fort Bend and Brazoria Counties. The area, which is Dart of the Gulf PAPERMILLAT HOUSTON USING20,000,000 GALLOXS OF GROUND WATERA DAY Coastal Plain, is underlain by beds of permeable sand, sandstone, and gravel, interbedded with layers of H E area in which Houston and Galveston are located is relatively impermeable clay, gumbo, shale, and marl. The structure of these beds and the order in which they occur is one of notable industrial development. Houston is one brought out graphically in Figure 2, which shows a generalized of the largest cities in the South, with a population of 318,000 in 1933. It is a leading seaport and manufacturing and railroad center. Galveston, with a population of 54,400 in 1935, also ranks high as a seaport. There are about twelve producing oil fields and eleven oil refineries in the area. The daily use of about 100,000,000 gallons of Farming is also important. The chief crops are rice, cotton, ground water for industrial purposes in sugar cane, and garden truck. the Houston-Galveston area is illustrative Large quantities of water are required for public water of the possibilities for development of supsupplies, oil refining, paper pulp manufacturing, ice manufacturing, cooling and other industrial uses, and for the irplies from the vast ground-water reserrigation of rice. The industrial plants and a large part of voirs of the Coastal Plain. In few places the rice-growing districts are comparatively remote from have ground waters been utilized so fully adequate supplies of surface waters suitable for their varied for industrial supplies. The ground-water requirements. With the development of industry and the conditions found here, the general chemical increase in population, the importance of the quantity and the quality of the available ground water in the area has character of the water, the change of become, therefore, increasingly apparent. As the continually character with depth, the artesian head, increasing demand for water has been met by greater and and the possibility, near the coast, of salt greater withdrawals of ground water, it has become a matter water contamination with overpumping, of public concern lest the supply be seriously overdrawn or are typical of general conditions throughthe wells become contaminated with salt water. I n response to public request, the United States Geological out the Coastal Plain. The large number Survey, in cooperation with the Texas State Board of Water of wells in the area affords an unusual Engineers, started in December, 1930, a survey of the water opportunity to study these ground-water resources of the area. The chief purpose of the investigation relations i’n detail. is to obtain data on which to estimate the practicable rate a t which water may be drawn from the underground reservoir. The survey covers various phases of the ground-water problem, such as quantity and quality of water a t different geologic cross section from a point about 50 miles north of depths a t different locations, its suitability for municipal Houston, southward to Galveston. I n general, the beds dip t o and industrial use and for irrigation, and the possibility of the south or southeast, which is also the general direction of the contamination by salt water. Some results of the investigation land slope. However, as Figure 2 shows, the dip of the beds were released in 1932 (1) and in 1933 ( d ) , and a progress is nearly everywhere steeper than the surface slope, and the report on the water resources of the mea, based on data ob-
T
1028
Chemical Character and Industrial Utility
Galveston Area
paper it will be termed the Willis (?) with the understanding that the problem is still uvsettled. The Willis (?) is predominantly a sand formation with interbedded clay lenses of merely local extent. It yields abundant supplies of water to shallow wells in the outcrop area and to deep wells whereever it is reached. The city wells of Houston and many privately owned deep wells used for industrial purposes and for rice irrigation draw heavily from the Willis (?) sands. The next outcrop encountered in crossing the area from nortli to south is the Lissie. The Lissie is predominantly a sandy formation like the Willis (?),but it is finer textured and carries less gravel and more disseminated clay, particularly in the upper part of the formation. The sands in this formation yield large supplies of water to shallow wells in the rice irrigation districts in the outcrop area and to fairly deep industrial wells from Houston southward. The Beaumont is the youngest formation exposed in the area, aside from superficial deposits of Recent age along the coast and in the valleys of the major streams. The Beaumont occupies the area southward from Houston. The basal 200 feet of the formation consists largely of sand, but the middle and upper parts are predominantly calcareous clay and marl, with some lenses of sand, The sand beds, particularly those in the lower part of the formation, supply large quantities of water to wells in the area south of Houston. In the outcrop areas of the waterbearing beds the water is generally unconfined and there is a water table. But as the water-bearing beds are interbedded with relatively impermeable clay and shale, the water in the sands down the dip, where they are under cover, is generally confined under artesian pressure. In wells sunk into these beds through the overlying confining beds, the water rises approximately to the level of the water in the outcrop. Because the land surface slopes gently from the outcrops toward the Gulf, the artesian water in some places is under sufficient head to rise to the surface and produce flowing wells.
beds are beveled a t their outcrops by the land surface. In crossing the area from north to south, therefore, the outcrops of successively younger formations are encountered. The outcrop areas of the formations exposed in this area are shown in Figure 1. The oldest formation exposed is the Lagarto, of Miocene (?) age, which outcrops in the northern part of the area. The Lagarto is predominantly clay and is not important as a source of water for industrial or municipal purposes in the middle and southern parts of this area, and few analyses were made of the water. There is considerable controversy regarding the next younger formation exposed in the area. In the opinion.of some geologists it is the Goliad; others think that the Goliad is completely overlapped in this area by younger sediments which they call the Willis sand, but that the Goliad may be present in subsurface. In the recent geologic map of Texas published by the Geological Survey (1937) the outcrop is mapped as the Willis. In this
Chemical Character of the Waters
FIGURE 1. MAPOF HOUSTON-GALVESTON AREA 1029
To study the chemical character of the waters at different depths in the different formations, more than one hundred analyses and more than four hundred field tests were made of waters from wells in the area. Most of the analyses were made in the Water Resources Laboratory in Washington, al-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1030
VOL. 31, NO. 8
I (1 to 4). Below 100 feet, however, the waters in the upper part of the Lissie tend to become more uniform in mineral content and more comparable to those in the lower part (compare Figure 4, J , K , and L , and Table I, 5 to 7). The shallow waters in the Beaumont clay, like those in the upper part of the Lissie, differ greatly in content and character of dissolved mineral matter (Table I, 8 to 10). On the whole, however, they are more highly mineralized and harder than the shallow waters in the upper part of the Lissie. Those analyzed contained from 300 to more than See Level 2000 p. p. m. of dissolved mineral matter and had 14x' from about 200 to 750 p. p. m. of hardness. Korth and west of South Houston most of the 2000 10 2oMI'Les 0 shallow waters in the Beaumont are low in chloI ride, but south and east of South Houston many GEOLOGIC SECTION FROM A POINT ABOUT50 MILES FIGURE 2. GENERALIZED are hiah in chloride: the amountof in NORTH OF HOUSTON SOUTHWARD TO GALVESTOK solution increases with greater proximity to the coast. Some of the'shallow waters contain so much chloride that this is the predominant acid constituent. analyses indicate that the shallow waters (those from less The principal soluble material in the sediments is calcium than a 150-foot depth) of the area are characterized by their content of calcium bicarbonate. The quantity of calcium carbonate, with some magnesium carbonate. The clastic constituents of the sands and clays consist of the weathered bicarbonate, or more inclusively, of t#otalhardness, differentiresidues of older igneous and sedimentary rocks and as such ates the shallow waters of the different formations. This is have already been more or less altered by hydrolysis and brought out in Figure 3, in which the shallow waters of the different formations are plotted according to their content of total hardness. The Willis (?) sand, in its outcrop, yields soft waters of low mineral content. Analyses of typical 25 %shallow Willis (1) waters are shown in Figure 4,A and B. Of the fifteen shallow waters analyzed, only three contained BEAUMONT d I more than 150 parts per million of dissolved mineral matter. 25%. Sandy phase C l a y e y phase These three waters were very high in nitrate content, one -, having more than 300 p. p. m. They had apparently been LESE-polluted by household or barnyard wastes and are not typical 25 % of the formation. Only four of the fifteen waters had more than 150 p. p. m. of total hardness. Thirty samples tested -. WlLLlS (?) in the field likewise were low in hardness. 2594 u l l o w waters in the outcrop of the lower or more sandv Dhase of the Lissie formation are lower in content of dissolved mineral matter than those in the outcrop of the upper or more clayey phase. The former generally contain less than 250 p, p. m. of dissolved mineral matter; the latter generally contain more than 275 p. p. m. The analyses of shallow waters from the lower part of the formation indicate a relation between depth and mineral content; there is an apparent increase in bicarbonate content and in hardness with leached of their soluble materials. The solution of calcium depth to about 150 feet (Figure 4, F , G, H , and I ) . The and magnesium carbonate is, therefore, the primary action shallow waters in the upper part of the formation differ when meteoric waters containing in solution carbon dioxide considerably in total mineral content and show no relation between mineral content and depth. Analyses of typical derived from the air and soil pass down through such sedimentary deposits. The amount of these carbonates taken waters in the upper part of the formation are given in Table though a few analyses by commercial laboratories were also accepted. The field tests which included total hardness, sulfate, and chloride, were made by Samuel F. Turner in the course of geologic work in the area. Turner also collected most of the samples for analysis and collaborated in the early studies of the data upon which this paper is based. The
I
--
TABLE I. ANALYSESOF GROUNDWATERS FROM THE UPPER PART OF THE LISSIEFORMATION AND HOUSTON-GALVESTON AREA(IN PARTS PER MILLION) No.
Depth, Feet
Si02
1 2 3 4 5 6 7
28 41 57 94 174 340 537
.. ., .. ,. .,..
Fe
Ca,
Mg
Na
+K
HC0a
FROM THE
C1
NO3
4 4.4 19 13 3.8 12 13
18 59 59 39 62 48 30
0.30 12 0.0 0.30 0.20 0.0
14 7 2.2 1.2 1.6 2.6
50 137 171 114 162 422
6.2 1.1 4.5 0.25 0.12 0.38
904
BEAUMONT CLAY I N THE
Total Dissolved Solids
Total Hardness as CaCOa
...
288 188 301 227 221 212 121
546
326 318 196 121 32 98
Upper Part of Lissie Formation
8 9 10 11 12 13
35 87 117 185 611 843
.. .. .. .. 22
..
0:02 0.05 0.92 0.04 0.14 0.56
..
57 73 75 74 62 32
.. 11
29 9.6 8.7 14 10
... 34 83 30 39 41 58
407 200 462 271 262 270' 234
0.0
276 49 1 300 317 310 258
Beaumont Clay 0.08 3.6 0.89 0.59 0.82 0.15
83
29
49 22 7.7 26
18 16 3 1 8.0
..
..
98 274 223 Na305, K 3 . 8 356
648 476 664 542 578 333
...
846 644 811 979
AUGUST, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
1031
OIL REFINERY NEdR HOUSTON USING 14,500,000 GALLONS O F GROUND WATER A DAY waters in the Willis (?) formation this alteration in type is acinto solution depends on the carbon dioxide content of the companied by a continuous increase in total mineral content by percolating waters as well as on the calcium and magnesium the addition of sodium bicarbonate; the hardness, and the carbonate content of the sedimentary beds. content of the other constituents remain practically the same In deposits that are relatively calcareous, the capacity of (Figure 4, A , B , C, D, and E ) . But in waters in the Lissie and the percolating waters to take calcium and magnesium carBeaumont formations there is a gradual decrease in calcium bonate into solution by virtue of their content of carbon and magnesium accompanied by a gradual increase in sodium dioxide is exhausted a t shallow depths. In general, waters equivalent to the decrease in calcium and magnesium, the from such formations do not increase in mineral content with bicarbonate and total mineral content remaining the same. increasing depth in the formation. Wells 20 to 40 feet deep This phenomenon, which is exhibited particularly well by in these formations yield water containing as much dissolved mineral matter as those several hundred feet deep. This is waters in the lower part of the Lissie formation is shown true of waters in the Beaumont clay and in the upper clayey graphically in Figure 4, I , J , K , and L. The depth a t which phase of the Lissie formation. In formations that contain softening begins differs in the different formations. In the Willis (?) sand (as has already been shown) the waters are little calcareous material, however, the waters must travel never very hard. In the lower part of the Lissie the waters farther to exhaust their capacity to take calcium carbonate apparently begin to soften at about 600 feet, in the upper into solution. Water from shallow depths in such formations is usually low in dissolved mineral matter. As the waters part of the Lissie, at about 500 feet; in the lower part of the Beaumont between 200 and 300 feet, and in the upper percolate downward, they continue to dissolve calcium and part of the Beaumont, a t about 150 feet. magnesium carbonates until their carbon dioxide content is The change of character of the waters appears to be the exhausted. With greater depth the mineral content then t e n d s to r e m a i n result of a secondary relatively constant. action between the The watkrs from the waters and the rock L lower part of the materials-exLissie f o r m a t i o n change, of calcium i give an excellent and magnesium in e x a m p l e of t h i s solution i n t h e phenomenon (Figwaters for sodium of base-exchange minure 4, F , G, H, I , and J ) . erals in the sediAs the waters pass mentary beds. The down the dip of the depth at which sofwater-bearing beds t e n i n g begins dethey appear to unpends upon the reladergo a gradual altive proportion of teration in chemical calcium and magnecharacter, changing sium carbonates to from calcium bicarbase-exchange minbonate, which charerals in the beds acterizes the shallow through which the waters, tosodium biIf water passes. c a r b o n a t e , which the base-exchange FIGURE 4. COMPOSITION OF TYPICAL WATERS FROM DIFFERENT DEPTHSIN THE WILLIS(?) AND LISSIEFORMATIONS IN THE HOUSTOX-GALVESTON AREA c h a r a c t er i a e s the minerals are present deeper waters. In in an amount at Kumbers above columns refer to depths of wells
I
I
, ~
+
l:, 'e
3
1032
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURE 5. SODIUM AND BICARBONATE CONTENT AND HARDNESS OF GROUND WATERSAT DIFFERENT DEPTHS AT HOUSTON
least proportional to the carbonates, the two processes are probably almost simultaneous, the calcium being exchanged almost as soon as it is taken into solution. This seems to explain the increase in sodium bicarbonate content in the Willis (?) waters more reasonably than to assume that sodium bicarbonate is taken into solution as such. If the carbonates are present in the rock materials in amounts more than equivalent to the exchange minerals, or if the exchange capacity of the base-exchange minerals has been exhausted in the shallower materials, the ground waters must travel farther before being softened, as in the Lissie formation.
Water Supplies in Houston Houston is situated a t the landward edge of the Beaumont outcrop. The total hardness, bicarbonate and sodium content of water that would be encountered a t different depths by a well drilled in the Houston district are shown in Figure 5. The first water the well would encounter would be in shallow water-bearing sands in the Beaumont and in the upper part of the Lissie. The waters in these sands differ in mineralization and in total hardness, but they are, in general, high in dissolved mineral matter and hard. The sodium content is generally fairly low. As the well is drilled deeper into the Lissie formation, the waters encountered are progressively softer with depth in the formation; a t the same time they contain increasing amounts of sodium. The bicarbonate tends to remain fairly uniform. These waters are lower in
VOL. 31, NO. 8
total dissolved mineral matter than most of the shallow waters. Still deeper the well enters the Willis (?) sand and encounters waters which are very soft, but are high in sodium and bicarbonate and in total mineral content. The municipal water supply of Houston is furnished by nineteen wells (in service in November, 1937) 900 to 2040 feet deep, located at seven pumping plants in different parts of the city. The system is only partially interconnected. The wells are not all in service a t one time, and the quality of water delivered to the taps by a pumping plant is dependent on the wells in service. All of the wells are screened opposite several water-bearing horizons in order to increase the yield. Consequently the water delivered by a given well is a composite of waters from the several horizons screened. The quality of the water is dependent upon which horizons are cased off and which are screened. For example, one well, 1664 feet deep and screened only below 1080 feet, draws water from the deep Willis (?) strata and yields water with only 4.5 p. p. m. of total hardness. Another well, 1037 feet deep and screened from 513 feet downward, draws from lower Lissie and Willis (1) beds and yields water with 116 p. p. m. of hardness. A third well, 558 feet deep and screened below 114 feet, draws from shallower Lissie strata. The water from this well has a hardness of 215 p. p. m. The city water is used principally for domestic use and for office buildings. Industrial requirements for water are supplied largely by privately owned wells. It is estimated that altogether there are about two hundred and thirty wells in use in the Houston district. The heaviest consumers are a paper pulp mill, oil refineries, ice plants, railroads, and laundries, but large quantities of water are also used for cooling in connection with the air conditioning of office buildings and theaters. The availability of different kinds of waters a t different depths enables industrial users to make some selection of the waters best suited to their needs. For some uses all the types of waters are equally suitable, but for others, certain types are distinctly superior. The laundries regularly utilize waters from wells in which all but the 1300-1400 foot horizons are cased off, so that only the very soft Willis (?) waters enter the wells. More than half of the water pumped in Houston comes from the deeper beds in the Lissie formation and from beds in the Willis (?) sand that lie below 900 feet.
Salt Water Contamination Southeastward from Houston to the coast the contamination of the ground waters by sea water from the Gulf becomes a factor of increasing importance in the determination of the chemical character of the waters and their suitability for municipal and industrial use. The chloride content of waters from different depths a t selected locations between Houston and Galveston is shown in Figure 6, in which the chloride content of the waters is plotted against depth and location on a generalized geologic section from Houston to Galveston. The values shown for the chloride content of the shallow waters are averages of all the waters tested from a depth of less than 150 feet a t each location. Some of the values given for the deeper waters are averages, others are single values, depending on the amount of data available for a given depth a t a given location. The shallow waters at each location differ greatly in chloride content, For example, a t Texas City-Lamarque the chloride in the shallow waters ranged from 65 to 265 p. p. m., a t Webster-League City from 45 to 645, and a t Houston from 36 to 180. IT the c h ~ ~ ~ ~ i ~ ~ ~ o ~ - d ofi sea f f u s water t h r o u g m e r m e a b l e shallow m a t e r j - ~ a n ~ r ~ r n -ton Bay or f r ~ W e ~ ~ & ~the~waters ~ ~ n a€ any particular locat%-Kwould be expected to show more -- -\-
---_-I/-
AUGUST, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
uniformity in chldidgcontent anbh&ain-chlo_ride m n l a n d , Some of the shallow waters for which compIete analyses were available were high in nitrate as well as chloride. It UKoJeble, therefore, that in scme 01theseshallow- w z r s high & i a n T e S s to pollutioe; in others it may be derived from some other local source of cop&@nation. Because of the comparatively small number of shallow waters tested at any particular locality, except a t Houston, and because of the liability-cL.&aJlow wells ha. local pollution, the averages g i v e n c t h e shallow waters may n t t b e representative of the chloride content at any point. In this connection it may be pointed out that the values given for the chloride content of waters at a depth-of 200 to 250 feet a t ea%- uint is lesj-than that given for the shallow w - d a t e r s at this depth represent a mixture of tlie waters entering the outcrop and are less liable to reflect merely local contamination. At Houston, where data on the chloride content of the waters are available to a depth of 1750 feet, the chloride decreases from 60 p. p. m. in the upper Lissie to 35 p. p. m. in the middle Lissie, and then gradually increases to 50 in the basal Lissie, and from 45 to 110 p. p. m. in the Willis (?). In the horizon which is 200-250 feet below the surface a t Houston the water i n c r e a m - n chloridETC€Fn€AfiYEi-60 p,-pxn?at Houston to 90 at Webster-League City, 758 a t Texas City-Lamarque, and 3380 a t Galveston. There is definite salt water contamZation in this hohzon4 tJiiEG&,s atvEZ&CZ-azIri I exas City-Lamargue and perhaps a l m x e - & ~ I - t a E t ~ t Y o 5a-t Webster.,T%e 200-250 foot hm%3in-iXW6T%€Z~Lc~gueCity yYeTds w_ater containing 170 p. p. m. of chloride at__thatpoint~Laf&i&veston, a n d 3 2 & i r t ? ~ f X t ~ ~ L a m ~ u eThis . horizon is apparently not contaminze-a water on the mainland but is somewhat. co%aiiiiEata a t Galveston. In an intermediatee ddori$e--c~Zii-WViiTGaterincreases from 94 p. p. m. a t Webster-League City to 305 a t Texas City-Lamarque and 830 af-Galveston. Ti&KYiZFizons all belong to the Beaumont or upper cissie formations. Unfortunately no data are available on the lower Lissie or the Willis (?) formations coastward from Houston. The lack of data is due largely to the custom of stopping drilling and pulling back a well if salt water is encountered while drilling and of abandoning
1033
or plugging a well that goes salty on pumping. This very lack of data is therefore a fairly good indication that these horizons yield salty water southeast of Houston. An analysis published in 1914 showed that a sample of water from a 1020-foot well a t League City contained 870 p. p. m. of chloride.
-
OIL REFINERYON
.. -"M
F
[
186
Ob-
162
I -
I800
"0
52
ie
44
.
\
40
36 32 28 24 do 16 MILES INLAND FROM GALVESTON
,
a
400
a30t
305
IZ
LV"
; 1800 4
FIGURE 6. GENERALIZED SECTION FROM GALVESTON TO HousTON
SHOWING THE CHLORIDE CONTENT OF THE GROUND WATERS
At Galveston all the water below a shallow surface layer 5 to 15 feet deep is salty. The water supply for the city is furnished by seven wells, 828 to 888 feet deep, at Alta Loma on the mainland. An analysis of a tap samp1e;f the w a c r is shown in Table I, 13. The water is soft but contains about 420 p. p. m . w i d g k -- - _ _-__.
-
----I--
--_I
_ I
Artesian Head
The probability of salt water contamination of waters in a given formation near the coast depends on the relation between the fresh water head in a formation and the salt water head at its possible submarine outcrop. If the head of fresh water in the formatibn is sufficient to balance the head of heavier salt water, which tends to force salt water into the formation up the dip from its submarine outcrop, salt water will not enter the formation. If, however, the fresh water head is not sufficient, sea water will enter the formation to the point where it is balanced by the fresh water head. If this point lies somewhere inland from the coast line, salty waters will be encountered by wells drilled into the formation between this point and the coast. Whether salt water will be encountered in a given formation, therefore, depends on the head of fresh water as determined by the altitude of the outcrop that forms the intake area; on the amount of water entering the intake area to replenish the reservoir; on the permeability of the confining beds, which may permit upward percolation of water, with consequent loss of head; and on the amount of water withdrawn from the formation as opposed to the head of heavier sea water, which is determined by the depth of the submarine outcrop. All these factors are rather definitely fixed for a given formation except the SHIP CANALAT HOUSTON USINQ 5,000,000 GALLONS OF amount of water entering the outcrop, which GROUND WATERA DAY
INDUSTRIAL AND ENGINEERING CHEMISTRY
1034
varies from year to year and the amount of water withdrawn, which is the only factor under the control of the users. If the amount of water withdrawn lowers the fresh water head sufficiently, salt water will move up the formation. In the early days of Houston, flowing wells could be obtained almost anywhere within the present city limits, and the artesian head in some wells was sufficient to raise the water from 15 to 30 feet above the ground. Kow the artesian head is about 80 feet below the surface in the downtown part of Houston. Between 1920 and 1931 the decline in artesian head averaged about 4 feet a year. Between 1931 and 1936 there was little decline in artesian head in the heavily pumped Houston-Pasadena district. In the area to the south and southeast of Houston, however, the artesian head declined markedly. In 1937 new wells were put down in Pasadena which are reported to have a combined capacity of 20,000,000 gallons a day, an increase of about 40 per cent over the average pumpage for 1931-36. From March, 1937, when these wells were put into operation, to March, 1938, there was a pronounced decline in water levelsh observation wells in the Houston-Pasadena district, particularly in those within 4 miles of the new wells. In two wells, 6/8 and 13/4 miles distant, respectively, the decline in water level was 35 feet in the 12-month period. * yu-ia-lie e a r distant down th-jg-ihe-deeper beds, from which _ I _ _ . . -
VOL. 31, NO. 8
a large part of the water in the Houston district is drawn. There is, therefore, a distinct possibility that any large decline in artesian head may result in the encroachment of salty water into the wells of the district. Fortunately such an encroachment is likely to be slow, and can be watched and to a degree anticipated if proper observations are made. The progress report on the ground water resources of the Houston district (S), published in March, 1937, recommends there sh@d be no increase in pumpingjL&-on IS net, ( b ) a d ~ X i K ~ i T t waterZ d & o d d be o m n e d a t a sufficient distance f i m h e - t o avoid undue inJt=&on--Qf ~ a ~ ~ t h ~ ~ s - ; ‘ ~ ~ I the e n iground B h i nwater g reservoir in the heavily pump$ Hguton-Pasadena area, and (c) p r o d i a and w B f i l 5 i e x water should be eIiEiEated, .--_ I _
””
-
.
Literature Cited (1) White, W. N., Livingston, Penn, and Turner, S. F., U. S. Dept. Interior, Press Mem. 66,553 (1932). (2) White, W. N., and Livingston, Penn, Ibid., 79,241 (1933). (3) White, W. N., Turner, 9 F , and Livingston, Penn, U. S. Geol. Survey, mimeographed rept., March 1, 1937
PRESBNTED before the Divlsion of Water, Sewage, and Sanitation a t the 95th Meeting of the American Chemical Soaiety, Dallas, Texas. Published by permission of the Director, Geological Survey, United States Department of the Interior.
-------*
Mass Transfer between Phases ROLE OF EDDY DIFFUSION T. K. SHERWOOD AND B. B. WOERTZ Massachusetts Institute of Technology, Cambridge, Mass.
I
KTERPHASE transfer of material is a process of considerable engineering importance, as illustrated by the unit operations of drying, gas absorption, and humidification. In some cases of mass transfer between a solid or liquid and a fluid moving in turbulent motion, much of the resistance to diffusion is encountered in a region very near the boundary between phases. According to the simple film concept the entire resistance to interphase transfer of material is represented by a stagnant fluid film a t the interface through which the diffusing substance must pass by the slow process of molecular diffusion. It is generally recognized that the concept of a single stagnant film constituting the entire resistance is an oversimplification of the situation, and that much of the resistance may be in the eddy zone or “core” of the turbulent stream. Any analytical treatment of the whole process may be subject to serious error if it does not allow for the resistance to eddy diffusion, which is a process fundamentally different in character from molecular diffusion. A previous paper (IO) reported a study of eddy diffusion of carbon dioxide and hydrogen in a turbulent air stream. The results show that the rate of eddy diffusion is proportional to the concentration gradient, and that the proportionality constant, or “eddy diffusivity,” is independent of the nature of the diffusing gas. The study was made in the central third of a large round duct and shed no light on the nature of eddy diffusion in the vicinity of the wall. The present study is concerned with the
over-all process of transfer between a liquid surface and a turbulent air stream.
Turbulence and Eddy Diffusion Largely because of its application in aeronautics, the science of fluid mechanics has been developed materially in recent years. The nature of turbulence has received special attention, and many of the concepts and theories (3) proposed bear directly or indirectly on the question of mass transfer in a turbulent fluid. It is impossible to summarize this work briefly, and the reader is referred to the general papers of vcn Karman (6),Rouse (8), Izakson (4), and Bakhmeteff (1). A recent paper by Dryden ( 2 ) gives an excellent summary, with particular reference to diffusion. Turbulent motion is characterized by the random motion of the particles constituting the fluid stream. Individual particles move irregularly in all directions with respect to mean flow, and it is convenient to think of a fluid in turbulent flow as having a mean velocity, U , in a direction, x, with a superimposed random motion resulting in instantaneous deviations from U a t any point. This instantaneous deviating velocity a t any point has components u, u, and w in the x, ?J, and z directions. Techniques have been developed for measuring u’, which is the root mean square average u(u’ = and the “per cent turbulence” is u’expressed as a percentage of mean velocity U a t the point.
dm),
