A SURVEY OF LITERATUREON GROUNDWATER RECHARGE AND SULFIDE GENERATION

by

James S. Kumagai

Technical Report No.5

Apri 1 1967

POLLUTION EFFECTS OF GROUND WATER RECHARGE IN HAWAII

OWRR Project No. A-001-HI, Grant Agreement No . 14 01-0001-781

Principal Investigators: L. Stephen Lau, Nathan C. Burbank, Jr.

May 15, 1965 to June 30, 1969

The programs and activities described herein were supported in part byfunds provided by the United States Department of the Interior as aut ho ­rized under the Water Resources Act of 1964, Public Law 88-379.

PREFACE

The literature r eview presented here is an outgrowth of the

author's examination of the extant literature related to sulfide

generation and sulfides as possible pollution agents. In the nor­

mal course of any research~ such a review is conducted to obtain

pertinent infor.mation of historica l aspects as wel l as t o ascer tain

current status of the work accomplished in a given field of re­

search. And such revi ews are normally published as pertinent infor ­

mation to add credence to the findings of the current r es earch

project.

However~ the author~ James S. Kumagai ~ conducted an unus­

ually extensive search in available publications~ resu lting in a

review of the literature which was significant enough to meri t

publication as a separate entity from the r es earch phase .

The Water Resources Research Cent er of the Univers i ty of

Hawaii feels that this summary wi l l be valuabl e t o other workers

in water resources res earch and contr ibute to ser vi ng a very real

need.

The EditorMarch 1967

iii

ABSTRACT

A critical appraisal of the extant l.i terature was made to

evaluate the various studies and concepts derived from t hese s tud­

ies pertinent to groundwater recharge with respect to treatment~

transport~ and storage of recharge water. The need f or more sci­

entific methods of underground disposal of waste waters~ concepts

of water filtration~ mechanisms of clogging~ and per co lati on studi es

is extensively reviewed. The extent of occurrence and optimum con­

ditions for sulfide generation was also traced hi s torically .

v

CONTENTS

Preface .••...............•.•.................... ................... iii

Abs tract .••.....••...•...•... ~ .........•.•...... ..................... v

INTRODUCTION ..•.•...••.....•........•• •••...... : 1

TREATMENT•••.•.•.•.••..•.........•.......•..•........................ 2

Intermittent Sand Filter .•.•...•..••........................•....... 2Septt c. Tanks and Cesspools ..•....•.................................. 4

HYDRAULIC CONSIDERATIONS ............. ....•.......................... 14

Some Concepts of Water Fi ltrati on 14The Perco1ati on Test .•.•.......•....•...•.......................... 17Relationship of Concepts of Filtration to Clogging and Reductionof Flows .............•.........· 18

Percolation Studies •.••.••.....•..•................................ 20Flow in Fine Grain Soils 22

CLOGGING .......•...........•...••................................... 27

Nature of Clogging Material at the Surface 30Mechanisms of Clogging ••.••........•......•........................ 30The Concept of "Incompatible Waters" 32

SUMMARY OF LITERATURE REVIEW 33

ACKNOWLEDGEMENTS •••...............•................................. 36

BIBLIOGRAPHy .••.•.........•.............•................... ........ 37

FIGURE

Figure 1. Assumed Equation of Pore Water Flow in a NormallyConsolidated Fat Clay Subjected to Small HydraulicGradi ents ••••.•.....•.. ................•.................. 24

TABLE

Table 1. Examples of Ground Water Recharge ............•...•........ 10

vii

I NTRODUCTI ON

Implementing waste reclamation concepts in a planned new com­

munity was perhaps bold, but it demonstrated the foresight of planners

and community leaders, and demonstrated confidence in water reclamation

research results and experience. The Irving project in Orange County,

California envisioned "University City," as an entirely new community,

with a projected population of 100,000, including a university. The

expected waste flow of 10 MGD, after treatment and prolonged storage,

was planned for reuse for agricultural and recreational purposes

(Ludwig and Feeney, 1965). Another project at Hemet, Riverside, Calif­

ornia, planned waste water reclamation for direct agricultural usage or

for ground water recharge by infiltration (Ludwig and Feeney, 1965).

Waste water reclamation or waste water reuse planned for these

two communities and possibly others came as a result of extensive re­

search in .California and elsewhere in water renovation and recharge

practice. Where procurement of water was costly, the logical direction

to be taken was water reuse as an economically favorable alternative

of resupply.

The purpose of ground water recharge with waste water was the

augmentation of natural recharge in the hydrologic cycle in such a

manner that the artificially recharged water blended with the existing

ground water and lost its identity. In an artificially recharged sys­

tem, the geology of a ground water basin not only dictated the occur­

rence and distribution of ground water, but provided for the treatment,

transportation, and storage of reclaimed water.

Further, ground disposal as a method of ultimate disposal of

waste was practiced as deep well injection, placement of waste waters

in subterranean caverns and tunnels, septic tanks, cesspools, lagoons,

and spray irrigation and contributed to ground water recharge. Ground

water pollution was evident from some of these practices in some locali­

ties while in other localities they provided a suitable means of ulti­

mate disposal.

The literature review is presented by bToad classifications as

(i) treatment, (ii) transportation and (iii) storage of recharged water.

2

TREATMENT

Ground disposal was a logical, and, perhaps, the best method

of waste disposal as standards of sanitation began to be upgraded.

The oldest anaerobic form of sewage treatment unit was probably the

cesspool (McKinney, 1962) which combined an air anaerobic treatment

process and percolation of waste water through soil as further treat­

ment. With this method, the use of soil, a porous media, as a treat­

ment unit had its beginning. But a more extensive and reliable docu­

mentary of the performance of a porous media as a treatment unit

appears to be the intermittent sand filter for sewage treatment which

was popular during the early part of this century . The performance

results and design criteria established for intermittent sand fil­

tration of sewage should be equally pertinent to treatment of wastes

in soil.

Intermittent Sand Filter

The history and performance of nearly 383 sand filtration plants

in 19 states prior to 1935 were reviewed and summarized by a committee

of the Sanitary Engineering Division of the American Society of Civil

Engineers with Professor W. E. Stanley as chairman (ASCE, 1937) .

The purpose of this study was the establishment of the controlling

factors in sand filtration of sewage to aid the design and operation

of such plants.

The Committee found that in general a high degree of purity could

be obtained by the intermittent sand filter but it was expensive. Early

work on intermittent sand filtration was credited to Sir Edward Franklin

by the report of the Rivers Pollution Commission of Great Britain for

1870. These experiments showed that the process was not mechanical, and

although biological action was not yet recognized, the necessity of rest­

ing and the need for oxygen were specified. The mechanism of treatment

was thought to be chemical.

The Committee further found that studies at Lawrence Experiment

Station of the Massachusetts State Board of Health in 1890 demonstrated

conclusively that the action within the filter was biological as well as

chemical. The essential feature was proper balance between the oxygen

3

supply and the organic matter applied. Hence, the filter treatment

method was recognized as an aerobic treatment process.

Essentially, the controlling factors of design of the operation

of sand filter beds pointed out by the Committee after review of per­

formance data could be grouped as (i) the porou~ media, (ii) the

characteristic of sewage and loading, and (iii) maintenance .

The porous media. The committee found that clogging or short circuit-I

ing by impurities such as fine clay, loam and silt in the sand resulted

in stratification or veins. Futher observations noted that clays and

loam tended to cement ' l ar ger particles together. To avoid stratifica­

tion and short circuiting, the committee recommended an effective grain

size of 0.20, to 0.50 mm with a conformity coefficient of less than 5.0.

The particles of porous media had to be inert with sufficient

porosity to allow aerobic conditions to prevail.

Sewage characteristics and loading. For normal strength sewage the

average loading limit appeared to be 150,000 gal/acre/day (0.46 ft/day).

It was found that design loadings based on complete inundation of the

filter to a depth of 3 inches intermittently gave good results.

Among the significant characteristics of sewage affecting s afe

loading were suspended solids. It was found that pretreatment to remove

suspended solids greatly increased permissible loading.

The wastes permitting increased loadings are listed in the order

of their allowable increase:

(1) raw sewage

(2) septic tank effluents

(3) freshly settled sewage

(4) secondary sewage

It was also found that loadings at 40,000 gal/acre/day resulted

in greater than 99% bacteria removals. The committee,howeve~ felt that

higher loadings and disinfection would be more economical.

Methods of pretreatment to allow greater permissible loading in­

cluded primary sedimentation, trickling filters, and septic tanks. The

allowab~e loading from septic tank effluents was less than for fresh

settled sewage. Early review of performance by septic tanks indicated

/1

th at as a treatment unit t.he septi c tank was not e f f i c i en t . Ana erobic

proc es s es occur red resulting i n hi gh oxygen demand, pr obably f r om

sul fid es and n i t r i fication tog et he r with organic ma t ter. Report s of

sept ic t ank eff iciencies were r evi ewed and performance eff i ciencies

r cpo r-t cd .

It was apparent that pret reat ment was desi r abl e . The Commi t tee

O Il San itary Engi neeri ng Divi s ion s pe ci f i ed that increas ed l oadings can

be pract iced with pretreatment providing that nitrification is compl eted

by s ome other process. This stat ement implies that nitrificati on a s oxy­

gen demand was a crit i cal f actor in maint aining aerobic conditions i n the

filter.

Opcr'aUon and mai ntenance . The Committ ee a l s o found that the po or

performance of intermittent sand f iltration pl ants results from lack of

maint en ance. Weeds, l arge c l ogg i ng sol ids, etc. , result ed in ear ly

f ailur e. Clos e a t tenti on to maintenance as well as loading dosages was

necessary for proper performance.

The important parameters in the performance of intermitt ent s and

filtrat ion of s ewage were character ized from pl ant dat a and incorporated

i nt o a desi gn graph . Vari ous s afe l oadings were gi ve n in t erms of (i)

t ype of sewage (raw, s eptic, set t l ed ) , (ii) suspended s ol ids , ( i i i) BOD,

<Ind (iv) porous medi a e f fec ti ve grai n si ze.

The significant findings of sand filtration studies and plant

e xperi ence with s ewage were that the effective treatment process is

ae r ob ic, and at high BOD approaching 150 mg/l and at suspended s oli ds

approaching 280 mg/l the permissible loading was i ndependent of the grain

si ze of the s and filter, approaching a constant permis sible loading of

30,000 ga l /acre / day (0 . 09 ft/day).

Septic Tanks and Cesspools

Since th e acti on in both the septic t ank and c esspool as an an aer­

ohi c tre atment unit i s the s ame, the results and discus s ion can be app l i ed

t o hoth. No te, however, that the di scussion i nc l ude s the s epti c t ank,

pAr' Be , an d not the coniliined tank and leaching field performance.

Baumann &Babbi t (1953) studied the operation of six sept ic tanks and

5

found considerable difference in the effluent quality from day to day for

any particular tank. During the 8-month study they found that at best

85% of the suspended solids were removed and the poorest tank removed

68%. Gas "boils" allowed large amounts of solids to be carried over

with the effluent. Babbit and Baumann (1958) s~marized septic tank

performance by stating that the septic tank is not widely used in muni­

cipal practice because better results can be obtained by other processes.

The occasional discharge of sludge by septic "boiling" makes this processI

undesirable.

Winneberger, et aZ. (1962) in a study of a model septic tank with

detention times of 20 and 35 hours found that the effluent quality did

not depend as much on influent characteristics. The results when sub­

jected to a regression analysis approached an efficiency of 60% removal ;

Data showing removal efficiencies were scattered but the mean values

showed COD removals as 40% and suspended solids removal of 58% for a

35-hour detention time. At a 20-hour detention time, the mean COO per­

cent removal was 39% and suspended solids removals were 44%, all at

temperatures ranging from 460 to 790P. Little relationship was observed

between the removal efficiencies and temperatures.

Sedimentation studies by Winneberger, et aZ., (1960) with effluents

from laboratory septic tanks and aerobic aeration units showed that the

sedimentation of the septic tank effluent appeared to be colloidal solids.

The aerobic unit showed that 60% of the solids settled in six hours. Of

the remaining 40% only 16% of the suspended solids settled after 25 hours

of quiescent sedimentation. A review of the test procedure revealed

that the aerobic unit was run on a theoretical detention time of nearly

40 hours allowing ample opportunity for endogenous respiration, probably

with some diffused sludge. Otherwise, a more efficient sedimentation

of the aerobic unit sludge can be expected. The results indicated poor

efficiency in suspended solids removal.

A further report on septic tank efficiencies by Winneberger, e t aZ . ~

(1961) revealed that on the basis of BOD/COD ratios, a septic tank fed

with raw sewage (BOD/COD = 0.49) yielded a BOD/COD ratio of 0.67 after 1.5

days detention and at approximately 5 days detention the BOD/COD ratio

approached 1. The explanation given was that anaerobic treatment rendered

organics more suitable to aerobic degradation.

f\ morc fundamental e xp l ana t i on is needed to account for the bio­

logical action in ces spools and septic tanks. McKi.nney (1962) reported

that the organisms present in cesspools and septic tanks are the same,

e .g., acid and methane formers. The methane formers, McKinney (196 2)

further asserts, do not play an important role in cesspools and s ept ic

tanks because of the lack of controls. A given anaerobic population

consumes 5 times as much organic matter (McKinney, 1962, p. 252) as an

equitabl e aerobic population. This implies that concentrated organ ics

are a requisite for active methane formers. Optimum anaerobic treatment,

such as in anaerobic digestion, requires healthy methane producers which

seem to thrive best at ORP of -520 to -530 mv. A range of ~5l0 to - 540

mv, however, appear s to be safer for dependable gr owt h of meth an e organi­

sms (Buswell, 19(4). The major action, with slow build-up of methan e

formers, is hydrolysis whil e the organics are carried out into the s oil

wh ere ac rob i c bacteri a metabolize the soluble organics (McKinney, 1962).

The poor performances of septic tanks per se reported by Baumann and

Bahhit and by Winneberger, et aZ.~ can be explaineJ by the lack of

aJequate methane formers. Although there are instances of " boi l s " oc ­

curring in Sludge, indicating gas formation and the presence of methane

producing bacteria in significant numbers, the results of septic tank

performances are not consistent. Perhaps, as suggested by McKinney, the

lack of controls i n the treatment process may be a cause.

The literature reviewed, thus far, stresses the importance of

maintaining completely aerobic conditions for adequate organic removal.

With septic tanks and cesspools, the anaer obi c stage does not adequately

stabilize the wast e but depends on the soil for aerobic stabil i zation.

Therefore, the treatment process is not complete without the porous media.

Further, suspended sol ids removal from anaerobic effluents is

poor, indicating that sol ids are probably dispersed as colloids. It is

apparent that anaerobic pretreatment of a waste such as sewage is not an

eff i ci ent method for subsequent disposal in fi lters, leaching fie Ids, or

porous media in general.

!t'r.aerat i on and oxy gen demand i n porous medi a . Ample evidence exi s t s that

cesspool or sept i c tank effluents or other anaerobic effluents per mi t

solubl e organics to percolate to the ground water supply if an anaerobic

7

environment is maintained. The importance of soil reaeration to maintain

adequate aerobic conditions is apparent. The occurrence of pollutants

within the proximity of cesspool and septic tank areas underscores this

necessity.

Literature on the mechanisms of soil reae~ation and the fundamental

design factors is meager.

The mechanisms as discussed by McMichael and McKee (1965) included

the following possible mechanisms:I

(1) Dissolved air carried into soil by percolating water

(2) Hydrodynamic flow of air resulting from the "piston-like"

movement of a slug of water

(3) Diffusion of air into the soil mass when there is no standing

or ponded water on the ground surface.

The "hydrodynamic flow of air" described by McMichael and McKee (1965)

was also suggested to be the major factor in maintaining aerobic condi­

tions in the soil by McGauhey and Winneberger (1963).

The first method of reaeration is simply the carry-through of

dissolved air. The second method of the "piston action" dragging air

downward as the water recedes is an idealization. The importance of

this mechanism of reaeration was probably the criterion for complete

inundation of intermittent sand filters per dose I (ASCE, 1937). The

practice of main~aining unsaturated conditions by spraying by sprinkler

systems in a manner similar to a trickling filter spray may not be as

efficient as a method of inundation and draining in providing a piston­

type aeration. Furman, et al., (1955) employed this concept by loading

twice instead of once per day. BOD removal of 95% was obtained through

18 to 30 inches of sand beds of 0.25 to 0.31 mm sands. Improved per­

formance was reported for loadings of 100,000 to 300,000 gal/acre/day

(0.307 ft/day to 0.921 ft/day).

The third method, diffusion, is discussed by McMichael and McKee

(1965). The gas transfer rate through a porous media is given by Fick's

Law as the following:

q = -D grad C.p

(1)

The term 0p

in free space (0 )o

effective porosity

8

where q

op

grad C

transfer rate/unit area

= molecular diffusion coefficient for the soil body, and

= concentration gradient.

is related empirically to the diffusion coefficient

by the relationship 0 = 0.66 P 0 where P is thep 0

and 0 is the diffusitivity in free air (Penman,o

1940, 1940a).

Together with the integral form of Fick's law, McMichael and Mc­

Kee (1965) present a numerical example to illustrate time for reaera­

tion in soils:

C = Co [1 - erf x 12.fiG

P(2)

where C concentration of oxygen

Co = surface atm concentration of oxygen (330 ppm)

0p = diffusivity of 02 in soil body

x = distance from surface, and

t = time.

Using handbook values for Do of 02 as 1.62 m2/day,

and assuming these

values:

Porosity = .40

50% saturation P = .40 x .5 = 202 2o = 0.66 x .20 x 1.62 ft /dat = 0.214 m /day

p

Co = 300 mg/1.

Substituting values into Equation (2) and calculating t for x = 0.5

meters and C/Co = 0.544, t = 1 day. When x = 5.0 meters, t = 100 days.

This numerical example indicates that to attain an oxygen concentration

of 54.4% of atmospheric at a depth of 0.5 meters, the time required would

be 1 day. But to reach the same oxygen concentration at a depth of 5

meters, the time required would be 100 days. This numerical example

selected by McMichael and McKee (1965) amply demonstrates the slow

process of oxygen diffusion through soils. The selection of 50% satura­

tion value is realistic for sand filters with effective grain size of

9

0.25 mm where a typical value of specific retention is 20% for sand fil­

ter of 44% porosity (Todd, 1959). These values would apply .to

operating intermittent sand filters with moisture retained against in­

fluence of gravity.

Further, the time required to reach a par~icular concentration is

a function of (x2/D ).p

Because of the slow diffusion of oxygen through a porous media,

depletion created by oxygen-demanding substances such as ammonia nitrates,I

organics, and sulfides is likely. McMichael and McKee (1965) asserted

that the behavior of carbonaceous and nitrogenous materials was not

similar to trickling filters because of oxygen limitations. Because

the travel and storage of recharged water were slow and involved great

lengths of time, oxygen depletion by nitrification was critical . This

was also brought out by the ASCE (1937) work with sand filtration

of sewage. The Whittier Narrows project intermittently percolating

highly treated activated sludge effluents (BOD > 5 mg/l) produced oxygen

depletion (Range 0.0 to 8.6 mg/l) in the ground water body as indicated

by data from sampling wells (McMichael and McKee, 1965). The ammonia

nitrogen data of the effluent showed a mean of approximately 16 mg/l.

The results of some recharge studies are given in Table 1. Sewage

recharge studies indicated that highly treated waste water greatly im­

proved infiltration rates. The order of magnitude of infiltration rates

through sandy soil was about 1 ft/day. For the Whittier Narrows project,

the mean rate of infiltration was 1.61 ft/day at a ponding depth r anging

from 0.5 to 2.0 ft/day through silty fine and medium sand. A complete

mechanical analysis of the soil was not given.

A noteworthy result was the performance at Lodi (Orlob and Butler,

1955). Intermittent spreading with an approximate loading of 0.5 ft/day

gave results of satisfactory chemical quality and produced a bacteria­

safe percolate through at least four feet of soil. The soil characteris­

tics showed that Hanford Fine Sandy Loam had a modal grain si ze of 0. 210

mm and 6% clay. This loading of '0.5 ft/day compared favorably with load­

ings of .i nt er mi t t ent sand filtration of sewage at approximately 0.46 ftl

day with filter-effective grain size ranging from 0.20 to 0.40 mm. As

McMichael and McKee (1965) had suggested, soil percolation can be likened

to intermittent sand filtration. The experiments at Lodi showed similar

!O

TABLE 1. EXAMPLES OF GROUND WATER RE CHARGE

I.()U\ T JON DATE

HYPFRION l q~5

PlANT,CALII"ORNJ A

1961

TYPE

INJECTI ON

INJECTI ON

TREATMENT REMARKS

ACTIVATED SLUDGE AND PERCO LATION THROLGH SAND DU/'£SAT 1 FTIDAY TO POLISH EFFLUENT .

RAPID SAND FILTRATION AND DI ATOMITE FILTRATION TOPOLISH EFFLUENT.

RE FERENCES

MCM1CHAEL & MCKEE. 1965

1949

ENr.LM.O

INTERM ITTENTSPRFADIf\GSO IL

INT ERMI TTENTPERCOLATIONIN SOIl.

INTERMI TTENT SPREADlf\G OF TREATED SEWAGE AT 1 FTIDAY MCM ICHAEL & MCKEE, 1965YIEWED COLIFORM FREE EFFLUENT IN 7 FT. OF SO IL.BOD < 0.5 mg/1 WHEN AEROBI C. LOADING RATE: 0. 5FTI DAY .

RIVER WATER WITH SEWAGE. BOD REMOVAL 80- 90%. ALMOST MCMI GiAEL & MCKEE, 1965Al.L ORGAN IC NI TROGEN TO NITRATE. COLIFORM RF.MOVALIN 1 OR 2 FEET. NO CHANGE IN DISSOLVED SOl.IDS , HARD­NESS, Mg, Ca, 5°4, C1. COMPLETE l.Y REMOVED Ni, Cr , Zn ,Pb, Cu.

l.OO I,CALIFORNIA

WHITTI ERNARROiI'> r

CALIFORNIA

PI OR II\./I I I ~ J() I ';

1950

1'162-65

1'1'11 TOPRESENT

SEWAGESPREAD lf\G

INTERMI TTENTSPREADINGRECLAIMEDWATER

HANFORD SANDY l.OAM AT RATES APPROXIMATE LY 0 .5 FT/ DAY. ORl.OB s BUTl.ER, 1955BACTER IALLY SAFE WATER WITH FINAL EFFLUENT OR PRIMARYSETTl.ED WATER IN AT LEAST 4 FEET OF SOIl.. SATISFAC-TORY CHEMICAL QUALITY FROM NORMAL DOMESTIC SEWAGESOIL. SUBSURFACE DRA INAGE GOOD.

CLAY 6%SILT, 0.002-0 .05mm 21%VERY FINE SAND, 0.05-0 .1mm 16%FINE SAND, 0.1-0 .2 mm 25%MEDI UM SAND, 0 .2-0 .5mm 29%COARSE SAND, > 0 .5mm 3%

UNIFOP~ITY COEFFICIENT, 24. 9 .MODAL SIZE, 0.21 0mm .

ACTIVATED SLUDGE EFFLUENT. BOD < 5. 0 mg/1 . WELL MCMICHAE L &MCKEE, 1965OPERATING PLANT. GOOO SUBS~FA CE ORA INAGE . FIRST,SURFACE FINE TO MEDI UM SILTY SAND AND SOIL TO 2-FooTDEPTH. THEN, FINE TO MEDIUM SAND. PONDING AT 0. 5 FT.TO 2.0 FT. MEAN RATE, 1.61 FT/DAY. DRYING TIME ONORDER OF 10 HOURS . INCREASE IN DI SSOLVED SOLIDS WITHC€PTH AND IN SOME CAS ES INCREASE IN COD.

TEST PIT IN 1955- 1957 USING ILLINOI S RIVER WATER WI TH SUTER &H~SON, 1960TURBIDITY ON THE ORDER OF 100. TEST PIT 10' X 50 'BOTTOM WI TH 3:1 SIDE SLOPES. TWELVE-I NCH PEA GRAVE LIN MAXIMUM DEPTH OF 10' . INITIAL RATES GREATER THAN200 FT/DAY . AFTER TEN MONTHS OPERAT ION 100 FT/DAY.RATES WHEN STOPPED IN 1957, 54 FT/DAY. WATER REMOVEDMn , 50% REDUCTI ON IN TOTAL MINERALS, INCREASE IN C1 ,5°4, F, NO] , and DO .

11

results.

Anaerobiasis. McMichael and McKee (1965) and others observed that with

laboratory columns, anaerobic conditions under high loadings resulted in

putrid effluents. Orlob and Butler (1955) foun9 increases in BOD in the

percolate from laboratory columns. The percolates of the Whittier Nar­

rows Study (McMichael and McKee, 1965) showed increases in COD with depth

with some oxygen depletion, but they were still aerobic. However, theI

method of collecting samples of percolate for D.O. as noted by McMichael

and McKee was open to question. Septic tank studies (Baumann, and Babbit,

1953, 1958; Winneberger, et al., 1962; and McKinney, 1962) further assert­

ed that under anaerobic conditions organics can percolate through soil

and pollute ground water supplies.

A more dramatic difference in treatment during percolation under

anaerobic and aerobic conditions was shown with ABS removal from the soil.

Under anaerobic conditions ABS will pass through soil unadultered (Mc­

Michael and McKee, 1965). They further reasoned that although absorption

and ion exchange phenomenon associated with clays are important, these

processes possess finite capacities. This is especially significant since

recharge and ground water movement and storage are long term occurrences.

Therefore, the significant mechanism of ABS and LAS removal in soil is

biological action under aerobic conditions. McMichael and McKee (1965)

demonstrated this in laboratory columns using microorganisms subjected to

long-term acclimation to ABS.

The degradation of ABS was demonstrated with long-term BOD tests

in the order of 100 days. The calculation of the long-term biochemical

oxygen demand of ABS can be made by determining the COD and calculating

the oxygen for nitrification of ammonia to nitrate. 1 The sum of the two

will give the long term BOD. The long term BOD performance of ABS with

COD of 40 mg/l showed a 5-day BOD of 2.7 mg/l and a lOa-day BOD of 154

mg/l. The nitrification stage was calculated to be 115 mg/l BOD and

combined with the COD gave 155 mg/l as opposed to 154 mg/l observed at

100 days (McMichael and McKee, 1965).

lSuggested by Dr . William Samples, Assistant Professor, California Insti­tute of. Technology.

12

The California Institute of Technology tests demonstrated that ABS

was degraded aerobically under long term. incubation and that nitrification

was the significant oxygen consuming potential. That ABS was degraded in

soils under aerobic condition was also demonstrated by a worker at the

Taft Sanitary Engineering Center in Cinncinati (Robeck, e t al., 1963).

Other studies on ABS with percolating water were conducted by the

Berkeley group (Klein, et al., 1961 and 1962). But in a critical review

of the literature on ABS and CAS removals, McMichael and McKee (1965)

pointed out that the Berkeley sttidies were criticized because of satur­

ated anaerobic columns and insufficient time to permit an aerobic culture

to develop. But no mention was made of further studies by the Berkeley

group (Klein and McGauhey, 1964; and Klein, 1965) obtaining similar re­

sults as in earlier studies of ABS degradation (Robeck, et al., 1963; and

McMichael and McKee, (1965). It was found that only 2% of the ABS degraded

in the septic tank while ABS degradation was 35% in laboratory trickling

filters and 45% by laboratory standard-rate activated sludge.

McMichael and McKee (1965) stressed the importance and necessity

of a bacteriologically active bed in porous media with proper acclimation

and sufficient time for development. Robeck, et al. (1963), suggested

that in a new percolation bed, a transplant of about ~" from a biologi­

cally active bed be used initially.

Calaway, et al.. (1952), and Calaway (1957) investigated the

biologically active 30" sand filter bed and found that zoogleal bacteria

predominated in the top 6" and Flavobacterium was second. Zoogleal

bacteria was found in less significant numbers with depth. Alcaligenes

and Bacillus were found below the 18" level. In general, it was found

that increasing the dosing rates increased the bacterial population. At

high rates, the species Flavobac terium predominated at low loading rates

(150,000 gal/acre/day), Bacillus exceeded it. It should be noted that what

Calaway, et al.. (1952) called "low" loading was the average permissible

loading rate for intermittent sand filters (ASCE, 1937).

From the literature reviewed on treatment, evidence strongly indi­

cated that aerobic conditions were mandatory for organic stabilization.

Therefore, from the standpoint of organic pollution, anaerobic conditions

were undesireable. It was further apparent that principles of biological

treatment in sanitary engineering were applicable; the principal dif­

ference being the limitations of oxygen in the porous media. Evidence

in literature indicated that certain inorganics are not removed and may

percolate freely to ground water supplies. Absorption or ion exchange

possess a finite capacity, above this capacitY' ,inorganics as well as

organics may percolate to the ground water. When these processes pre­

dominate, lengths of travel of pollutants become exceedingly important.

13

14

HYDRAULIC CONSIDERATIONS

Since soil reaeration has been intimately related to hydraulic

loading and the manner of loading and moisture content, consideration

of hydraulics is necessary. Further, hydraulics are often the limiting

factor in the economics of the recharging system (Koenig, 1964).

Design consideration of recharging systems includes the quantity of

reclaimed water as a significant factor, often dictating the economic

success of the system. Together with hydrologic factors, the balance

between recharge water and volume of ground water is a necessary con ­

sideration for dilution. Bonderson (1964) estimated that, whereas, the

dilution factor was large in the instance of the Whittier Narrows project,

the waste water recharge volume to the natural recharge for the Hemet

project (Ludwig and Feeney, 1965) was sufficient to alter the ground water

quality.

Aside from the volumes and rates of flow significant on a basin­

wide basis, the movement of ground water and percolating water may be

affected by chemically or biologically induced resistance to flow. Fur­

ther, physical aspects of the porous media, such as stratification,

channeling, etc., affect flows as indicated by performances of intermit­

tent sand filters (ASCE, 1937).

Some Concepts of Water Filtration

Since it was apparent that suspended solids played an important

part in the clogging of infiltration and percolation systems, it is

necessary to review some of the literature in the area of rapid sand

filtration in water treatment.

Much work has been done on water filtration since Stein (1940) and

Eliassen's (1941) work, and the surunary by Ives (1964).

There are many theories of the mechanism of removal of suspended

matter by filtration through porous media. Each appears to apply to a

particular range of interest and some times even seem to be in conflict

with each other. It is not the purpose of this review to evaluate all

theories, but to point out some that appear to be particularly pertinent

15

to cloggi ng and/or movement of ce rta'i.n par t i cul at es thr ough por ous medi a

as they may af fect permeab i l i t y or wat er quality.

It was i ni t i ally poi nted out (Ryon ' s percolation tests) that the

extent of c l oggi ng depended on the cloggi ng material . Further work re­

vealed that ef f l uents , aer obic or anaer obi c , pr~duced suspended solids

of different charact er and si ze that exhi bited clogging char acter i s t i cs

influenced by the pore size of the por ous medi a. Never t heless , both

produce~ clogging in t he l ong r un. Un l ike water f iltration pract i ces , the

leaching field or per colation bed f or r ec har ge cannot be backwashed .

But work in wat er fi l tration concluded that i t was dependent on the

physical and chemi ca l pr operties of both the porous med i a and t he suspen­

sion. A paper reviewed which was f elt to be applicable and whi ch gave

credence to Winneber ger , et a l. , (1960) and Orl ob and Butler (1955) was

the report of the work by Cur r y, e t aZ . (1965) . Thi s paper summar ized

some theories re l at ing to fi ltrat i on of so lids with r espect to the physi­

cal, chemi cal , and electroki neti c pr operties of co lloida l s uspens i ons

and porous medi a .

It was f el t by Cur ry, et al . (1965) that the s t udy of flow of

col l oi da l sus pensions through porous media had particul ar app l i cat i on in

water fil trat ion, gr oundwat er r echarge, infiltration i n the soi l , and seal­

ing methods fo r reser voirs and canals. They cited works by Riddi ck (1961)

and Jordan (1963) as demonstrat i ng the usefulness of t he knowl edge of

electroki netic ph enomena i n wat er filtrat i on . Raush (1963) demons t r at ed

that f or a porous medium, carbor undum, t he amount of seal ing increased

with a decrease in zet a potential s by changi ng the elect ro l yt e concent r a­

tion which also changed the viscosity of the suspension.

Curr y, et aZ. (1965) conduct ed a ser i es of labor a t or y exper i ment s

using beads , s and , and carbor undum with bentonite suspens i on (s odi um

montmorillini te) . Carbor undum and glass beads used i n experiment had

zeta potentials i n the order of - 100 my . Bentonite su sp en s i ons had nega­

tive potent i als. Cur ry , et aZ . (1965) sur mi s ed that a r epuls i on exi s t ed

between pa rt icles dur ing f l ow and a part icul ar chemi cal charact er i s t i c of

the sys t .em dictated t he ze t a potent i al whi ch in turn dic t ated the reten­

tion of t he c l ay in the filter . From t he i r experiments it was concluded

that :

16

(a) the principal process was mechanical filtering,

(b) the degree of sealing increased with particle size,

(c) the degree of sealing increased with increasing hydraulic

gradients,

(d) the shape of particles in the media had considerable effect

on the degree of sealing and the hydraulic characteristics,

(e) sharp angular material in porous media removed more material

than the spherical glass beads, and

(f) data from experiment seem to indicate that the magnitude of

the difference in the negative potential of clay and carborun­

dum would control amount of retention of solids in the media,

other factors being constant.

It was also brought out by Curry, et: al . (1965) that zeta potential

measurements and correction factors have not been agreed on. It

was further noted from the experiment that washing did not appreciably

affect clay (Curry, et aZ.~ 1965), but details of the manner and extent

of washing were not given.

Other mechanisms of suspended matter removal, largely clay suspen­

sions, were discussed (Curry, et aZ.~ 1965). In summary, it was presented

by the authors as two mechanisms: (i) removal at the surface probably

as mechanical or interstitial securings, and (ii) removal below the sur­

face probably as a combination of diffusion and gravitational settling

within the pores.

ASCE (1937) in working with radioactive ferric chloride suspen­

sions found that deposited floc did not dislodge or move deeper into the

filter bed. rves (1961) working with radioactive algae felt that these

mechanisms were pertinent to filtration:

1) Amount of material removed from suspension is proportional to

concentration of suspension.

2) At close range Van der Waal's forces predominate.

3) Removal depends on these porous media and flow characteristics:

a) surface area of the media particles,

b) tortuosity of flow path,and

c) interstitial velocity.

17

Curry, et a1,. (1965 ) from a review of other research and from

their own laboratory work felt that these factors were pertinent:

1) Mechanical sieving or straining is the principal mechanism of

the removal of particles in suspension by porous media when

the pores are smaller than 200~.

2)lfuen the particle size is greater than 200~, or when the flow

rate is low, gravitational settling may be the principal

mechanism.

3) Zeta potentials, size, and shape of the media, hydraulic

gradient, and solid concent r at i on are factors which influ­

ence the amount of clay retained in the column.

The Percolation Test

The percolation t est was a design aid devised by Ryon in 1926

while he was affil iated with the New York Engineers Office and with the

State Department of Public Works as senior sanitary engineer. From a

study of cesspools and septic tank, Ryon devised the percolation test.

For a time, this was the only criterion for relating soil characteris­

tics to leaching field performance (McGauhey, et al.~ 1958).

As a result of the FHA approved research, performed by the Public

Health Service (Coulter, et a l . ~ 1958; Sullivan, G.M., 1959;

Coulter, et al.~ 1960; Bendixen, et al.~ 1962) and the University of Cali­

fornia, Berkeley (McGauhey, e t a l . ~ 1958 and 1959; Winneberger, e t al.~

1960; Winneberger, et al.~ 1961; and Winneberger, et al.~ 1962), the

validity of Ryon's percolation test for cesspool leaching fields was

questioned.

McGauhey and Winneberger (1963) summarized their previous work

while outlining objections to Ryon's percolation test :

a. Insuffici en t dat a . The test was formulated by too few ob­

servations, and as an empirical method, the range of values of percola­

tion rates did not extend over the range of designs for which it was

used. Only 27 tile fields and 21 cesspools were involved in Ryon's

studies from which not more than 14 tile fields and not more than 8 or

9 cesspools were used to draw determinative conclusions. The range of

18

percolation r ates was 5 to 15 min/in (well-drained ). Although Ryon

drew failure envelopes for his data, two points were still valid.

b. Clear water infi l t rat i on rate. The major fallacy was i n the

underlying assumption that the short term clear water infiltration r ate

was on the s ame order as the long term rate. The r esults of l at er work

poi nted out the fallacy of this assumption.

e . Inua l.i d curves . Another fallacy was the assumption that the

one set of curves wer e valid for all soil types. During the course of

critical evaluation of Ryon's percolation test, much of the work done by

others in other processes came to light. All of these, however, were

concerned fundamentally with flow through porous media.

d. Fi eld tes t s . Allison (1947) described field studies of gr ound

water recharge in Kern County, California, applying Kern River wat er on

Exeter and Hespera sandy loams. The studies indicated that initial r ates

were satisfactory at 3 to 4 ft/day, but the rates decreased with time

sharply at first, then gradually until the infiltration was but a few

in/day. For a l l practical purposes, the pond became impermeable. As a

result, Allison (1947) undertook laboratory studies to determine the

nature and cause of this behavior.

This phenomenon was not pred icted by Ryon's percolation t est and

deviations from his results may be more significant with soils l ess

permeable than those suggested in the original range of percolation rates.

Relationship of Concepts of Filtration to Clogging andReduction of Flows

Ryon's percolation test and the underlying assumption that the

initial clear water infiltration r,te was a measure of the long term

clogging rate were invalid from the standpoint of water filtration concepts.

Ryon's percolation tests were, perhaps, at best special cases of a more

general theory. The work of Grlob and Butler (1955) and McGauhey, et al .

(1958) resulted in an improvement of the concepts of clogging material

and a l ong with water filtration concepts a more complete theory may be

formulated to provide a rational approach to design and operation.

The predominant action depicted by water filtration theories ap-

Zeta potential

chemical factors as they affect Zeta potential

surface area of media

19

peared to be mechanical s eiving or interstitial straining. This was also

found in the results obtained by Winneberger, et al. (1960) with lysime­

ters and Millipore filter . Both phenomenon can be described by Blake's

formula used by chemical engineers in filtration tests. Other factors

are involved especially with suspended solids r~movals within the bed.

Water filtration is affected by the degree of suspended solids removal,

with a corresponding effect on hydraulic conduction. The factors influ­

encing solids removal coincidentally are factors influencing clogging.,Based on results of water filtration studies, the filtration and

clogging of solids are dependent on these factors:

Fluid:

(1) Zeta potential of particles

(2) chemical properties as they affect Zeta potential and

viscosity

(3) particle size

Porous media:

(1)

(2)

(3)

(4) shape of particles in porous media (structure)

(5) pore size

(6) tortuosity

Hydraulics:

(1) interstitial velocity

(2) hydraulic gradient

These factors, derived from studies directed at suspended solids

removal, are the same ones that influence clogging since the solids tend

to reduce the effective flow area and to resist flow.

It was found that solids resulting from anaerobic or aerobic treat­

ment had different settling characteristics and that anaerobic effluent

appeared to be more dispersed than the aerobic effluents (Winneberger,

et al. (1960). Since much of the anaerobic effluent solids appear to be

colloids and that part of both anaerobic and aerobic effluent solids re­

main in suspension as colloids, studies relating Zeta potentials to known

parameters will contribute to a more complete theory of filtration and

clogging.

20

Percolation Studies

Ryon's assumption that his percolation tests applied to all soil

types was not valid in the light of results of further work. As Allison

(1947) had summarized, the first phase decrease in permeability may be

due to swelling of clays and other changes in structure not recognized by

Ryon's test, but noted in later investigaticn s by others (Winneberger,

e t al.. 1958) .

As a result of ground-surface sewage disposal system failures by

clogging, it became apparent that fluids, other than clear water, exhibited

clogging characteristics of a different nature than with the "clear-water"

type experiments by Allison (1947). Sewage effluents contained organics

and suspended solids in higher concentrations.

Soi l Zysime t ers . The experiments by Orlob and Butler (1955) demonstrated

that the rate limiting factor was the clogging material and not the

porous media. Using soil lysimeters containing soils of various sizes,

Orlob and Butler (1955) found that each lysimeter clogged to a similar

rate with settled sewage independent of the initial clear-water rate.

Other experiments (McGauhey, et aZ. 1959) (Winneberger, e t a l. 1960)

conf i r med the findings of Orlob and Butler (1955). Subsequent experiments

!lroved that clogging was dependent not only on the porous media, but also

on the nature of the clogging materi al as we 11. The flow rate was inde­

pendent of the clear-water infiltration rate determined by Ryon's tests.

Winneberger, e t al., (1960) studied the clogging aspects of sewage

effluents characterized as anaerobically or aerobically treated sewage.

The results indicated that the anaerobic effluent clogged finer pored

soil more rap idly than the aerobically treated sewage. Conversely, the

soils possessing larger pores clogged faster with the aerobically treated

e f f l uent s than with the anaerobically treated effluents.

M1: l. l .ipox:e membrane f i l.ter , Sedimentation tests with both types of

effluents, aerobic and anerobic, showed that only 16% of the suspended

solids settled after 24 hours of quiescent standing for the anaerobic

effluent as previously stated in this review. It was postulated that the

21

dispersed solids clogged individual pores more readily in finer grained

soils than the aerobically treated flocculant solids did. The flocculant

solids were large enough that "bridging" over the pores resulted. For

large-grained soils with larger sized pores, the dispersed solids pene­

trated into the porous medium and the larger flocculant solids were

strained out causing physical clogging. To test this hypothesis, the

Millipore membrane filter (0.4S~) was used. The clogging phenomenon was

related to Blake's formula in chemical engineering for filtration as:

where T = time since start of filtration,

V = volume

A = x-section area, and

C = constant.

The clogging phenomenon in the soil lysimeter and the Millipore

membrane filter could be described by Blake's formula indicating that

the clogging phenomenon in the lysimeter was similar. Further, the

membrane filters clogged faster with the anaerobic effluent than with

the aerobically treated effluent. These results tended to confirm the

postulated phenomenon derived from soil lysimeter studies. But with

time, Winneberger, et al., (1960) concluded that there was l i tt l e prac­

tical difference in the clogging aspects between the aerobically and

anaerobically treated sewage.

Effect of pore s~ze. It was evident, however, that the clogging capacity

of aerobically or anaerobically treated effluents depended on the size of

the pores because of the size of the suspended solids. Removal of sus­

pended solids by flocculation and sedimentation using polyelectrolytes

was satisfactory for only 5 of 17 coagulants tested. The results of

these studies indicated that septic tank particles were negatively

charged (Winneberger, et aI., 1963). It should be noted that the manner

in which the coagulation tests were performed was not according to the

standard jar-test experiments. Coagulant addition with inflow to the

septic tank was simulated by gentle mixing. More effective mixing and

flocculation periods may have fielded better results.

Later experiments by Jones and Taylor (1965) showed that clogging

was not reduced by using coarse and fine sand lysimeters. The differ­

ence with the experiments by Orlob and Butler (1955) and Jones and

Taylor (1965) was in the hydraulic head or gradient and in the manner of

expression of results.

Loading. Orlob and Butler (1955) used settled sewage ponded at I-foot

depths. Negative heads at levels below the soil surface indicated un­

saturated conditions when clogged. Jones and Taylor (1965) used septic

tank effluents with variable gradients ranging from 0.4 to 3.0. Jones

and Taylor also used intermittent dosages as did Orlob and Butler (1955).

Orlob and Rutler (1955) demonstrated that the final rate of infiltration

was independent of the initial clear water rate, and Jones and Taylor

(1965) demonstrated that permeability was a fraction of the initial per­

meahility, and these results tended to support Ryon's underlying assump­

tion for his percolation tests.

Orlob and Rutler did not vary the depth of the gradient to

simulate sewage spreading for sewage recharge. Jones and Taylor used

Darcy's Law:

v = k grad H

and related initial k and final k values while varying the gradient.

A criticism of Jones and Taylor's work in using Darcy's Law was

that the authors did not first establish the validity of Darcy's Law

for the clogged state. Insufficient data were presented to evaluate this

aspect. Further, the data presented indicated instead that Darcy's Law

was not applicable since for 2 different gradients, the same flow rates

were measured. Perhaps more work is needed along this line.

Flow in Fine Grain Soils

McGauhey and Winneberger (1963) discussed the validity of the per­

colation tests in clays. They felt that because of the widely varying

structure and nature of clays in states of consolidation, the percolation

test would be almost meaningless. Winneberger, et a l., (1960) cited an

23

example of percolation field tests in Tennessee in an area 30' x 300'.

The results indicated that the maximum infiltration rate was 40 times

the least rate determined. This example illustrated the widely varying

conditions found in the field.

Muskat (1937) gave examples of varying co~paction stages with

clays. For freshly deposited clay particles, the porosity may be as

high as 80%. The same sample when compacted and dried may have porosi-

ties of about 40 to 45%. Some shales with overburden of 3000 feet

had porosities of only 5%.

McGauhey and Winneberger (1963) stated that much work has been

done in sandy soil with a low clay content, such as those listed by

Orlob and Butler (1955) for some California soils that have clay con­

tents from 3 to 10%, ie., Yolo Oakley, Hanford, Hespera, and Columbia

soils. Studies with clay soils are lacking. Since the filtration theory

outlined some of the important characteristics of the porous media, the

clogging or suspended solids removal action can be expected to be differ­

ent. Clays are fine-grained soils, hence, clogging may be due predomi­

nantly to mechanical sieving or interstitial straining.

But there are other factors that influence permeability in fine

grained soils, resulting in deviation from Darcy's Law.

Deviations from Darcy's Law were observed before the turn of this

century (Mitchell and Younger, 1966). Mitchell and Younger reviewed the

current studies of the non-Darcy behavior of flow through fine grained

soils and related their own laboratory studies of flow through kaolinite

and silty clay soils.

No flow occurred through fine soils at gradients of about 1. Many

mechanisms explaining this behavior have been advanced by various workers.

Among the mechanisms were (1) the quasi-crystalline theory, (ii) biologi­

cal clogging, (iii) particle migration and consolidation, (iv) abnormal

water properties, ego increases in fluid viscosity, (v) flocculation and

deflocculation, and (vi) the electroviscosity theories (Mitchell and

Younger, 1966). Some of the results were discounted as experimental

errors arising from measuring flows by the capillary tubes that could

influence the order of magnitude necessary to imply a threshold.

But Olsen's (1965) work can not be used to discount all results as

24

possible experimental erro r.

lIansbo (1960) fo und t hat deviations f rom Darcy 's Law resulted

Jur i ng t he consolidation process . He further des cr i bed t he behavior

of t he proces s i n r el at i vely simple mathemat i cs . As depic ted by Figure

1, the deviation f r om Darcy 's Law appear to be the greates t at gradi ents

less than about S. Above this, the behavior closely f ollowed the l inear

re lation of Darcy 's Law.

Han sbo (1960) favored the partic le migration theory as an exp lana­

tion of t he non-Darcy beh avi or. Further, Hansbo (1960) did not fi nd a

t hresho ld gradient.

Mitche l l and Younger (1960) fo und th at sil ty c l ay fl ow rates de ­

creased or increased with time . They studied the possibi l i ty of thr es­

hol d gradient by using the capillary tube method to measure f l ow r at es.

~ Vo-.J1.L.

a:::wl­e:(

~

wa:::oa..

io i,HYDRAULIC GRADIENT

FIGURE I: ASSUMED EQUATION OF PORE WATERFLOW IN A NORMALLY CONSOLIDATED FATCLAY SUBJECTED TO SMALL HYDRAULICGRADIENTS .

25

Although the results show a mark ed deviation of flow r ates suggesting a

threshold gradient, Mitchell and Younger (1966) noted that f low did oc ­

cur even at lower gradients . It m~y be that the threshold gr adi ent is a

matter of semant i cs, and for all practical purposes a threshold grad ient

did occur. Mit chell and Younger (1966) also stated that the Russians

accept the concept of the threshol d gradient and have used it for s ome time .

Rut they caut ioned that there i s insufficient f i eld data to decisively

confirm or r efute the concept of threshold gradi ent and the deviations

from Darcy 's Law.

Mit chell and Younger (19 66) expr es sed great e xper i ment a l difficul­

ti es assoc i a t ed with low flows in the labor a t or y and the time necess ary

to properly s t udy f l ow through clays at low gradients . They support the

v i ew of part i cl e migrat i on or rearrangement of structure as interpreted

hy their r esults. The pore water pressures, measured by e lect r i c pres ­

sure transducers located throughout the length of the soil column varied

wi t h time . They reasoned that the app l i c at i on of a hydraulic gr ad i en t

r esulted in d ifferent pore pressures , and therefore, changed the effec ­

tive s t res s es a t different points along the length of the sample. As a

r esult, non -un iform void ratios dev eloped . This phenomenon changed with

the magn i tud e o f the hydraulic gradient . Further, they found that r atios

were l es s f or d enser mat erial, and re asoned that for denser materi al s, the

soi l particl es were involved in a load carrying capacity and were not

fr ee t o move.

The s igni f i cance of the results of these studies on the (i) thres­

hold grad i ent , and (i i) the non-Darcy beh avior espec i ally in consolidat ion

o f c lay i s that ponding e xpe r i ment s occur approximately at a gradient of

1 whi ch appear s to be ne ar the threshold gr adient of s ome clays. Further,

th e devi ation from Darcy's Law with the consolidation process can be

l i ken ed to th e c l ogg i ng process whi ch in effect is reducing the pore geo­

metry . The method of appl icat ion of Darcy 's Law by Jones and Taylor (1965)

i s questi onabl e .

Further, the cons ol i da t i on process observed with laboratory lysi­

meters may be strictl y a laboratory phenomenon . As a result , indiscri ­

min at e app l ica ti on of l aboratory flow data to the field is dangerous.

Caut ion is es pe c ially warranted since clays taken to the laboratory are

disturbed samples and cannot be expected to reproduce the widely varying

consolidated state found in the field. For example, results of percola­

tion rates found in field studies (Winneberger, et aZ.~ 1960) in Tennes­

see depicted differences in infiltration rates on the order of 40 times,

implying that conditions in the field are markedly different, unless com­

posed of sandy soil or sand.

As a result, infiltration and percolation of reclaimed waste waters

in fine ground soils are still subjected to other complications that af­

fect the behavior of the flow of reclaimed sewage through these soils.

27

CLOGGING

Early experience with ground water recharging systems indicated a

reduction of flow occurred in various systems. In seepage pits (Suter

and Harmeson, 1960) in Peoria, Illinois, reduction occurred in infiltra­

tion rates of more than 200 ft/day initially to 100 ft/day after 10

months. But in 2 years, the rate fell to 54 ft/day. The reclaimed water

was obtained from the Illinois River and operation of the pits continued

without interruption.

The reduction of flows in injection wells in Kentucky was cited

by Suter and Harmeson (1960) to illustrate the reduction of their re­

charge capacity to 50% of their initial recharge capacity. A highly

clarified effluent is necessary for a successful injection recharge

system, making this alternative unfavorable for the Peoria recharge vol­

ume requirement utilizing the turbid Illinois River water . Surface

ponding was not believed to be suitable for the recharge requirement of

3 to 5 MGD. For the particular situation in Peoria, the recharge seepage

pit i n gravels was considered the best system (Suter and Harmeson, 1960).

Failures, especially in septic tanks, were problems which were mag­

nified with the increased septic tank installations paralleling the post­

World War II building boom. The design criteria and guides were inade­

quat e and at times based on meager scientific facts drawn from inadequately

documented experience (McGauhey and Winneberger, 1963). Because of the

magnitude of the problem, when the Federal Housing Administration (FHA)

assumed the responsibility of being the federal agency for housing and

the principal insurer of home loans, it was forced to initiate research.

The public health hazard created by the malfunctioning septic tank systems

added urgency to the problem (McGauhey and Winneberger, 1963) and resulted

in a series of studies conducted at the University of California at Berke­

ley (Winneberger, e t al.~ 1960).

Although the Berkeley studies emphasized investigations of septic

tank systems, they contributed much to the study of flow in porous media,

in particular, infiltration and filtration. Since flow in porous media

i s a study in many unit operations in sanitary engineering, including

intermittent sand filtration, rapid sand filtration, ion exchange, activa-

t ed carbon beds, vacuum and pressure filtration, as well as water r ecl a­

mati on by gr ound water r echarge, studies contributing to the i dent i f i ca­

t i on of fund ament a ls and the expression ·of results in terms of t hes e

fund ament als are r equ is ites to a sound desi gn appr oach .

Clogg ing in sep tic tank l eaching f i elds. A review of septic tank designs

and the i r construct ion practices (McGauhey, et a l. . , 1958; and McGauhey

and Winneb erger, 1963) r eveal ed that they received littl e engine ering at­

tention in the past . Engineers have been too busy with other major prob­

l ems created by popul ation growth to be concerned with the septic t ank

(McG auhe y and Winneberger, 1963).

Trying to r elated performance against certain fundamental s from

f i eld dat a was diff i cult. Poor construct ion methods as well as mis repre­

sent ation of f i eld percolat ion tests by contractors were exampl es of gr oss

negl i gence of regu latory agenci es and unethical conduct of contracto rs.

It was report ed that i n s ome instances, contractors did not perform pe r ­

co l ation tests, but pres ented falsified data to receive favorable act i on .

r ur t he r , it was found that the smearing of the side walls of the trenches

by the d i ggers and compaction of the bottom by construction equipment con­

tributed to ear ly fai l ure . The contractors at times cheated on grave l

fills as well (McGauhe y and Winneberger, 1963). McKinney (1962) on the

other hand, felt that there were many well operating septic tanks and that

the problem was i n the misuse instead of the use of the septic tanks.

With cleaning eve r y two or three years and proper design, the septic tank

can be an effici ent treatment system according to McKinney. However, he

fa il ed to point out what was considered a good design, nor di d he gi ve an

examp le of one on which to base future designs. The att empt to r el at e

fi eld performance agai ns t more fundamental factors led to difficulties be­

cause of i nadequa te ly documented r esults in design and in fi eld t est s.

Ferrous sulfide c l ogging . In their work with septic tank effluents,

Winneber ger, et al. . (1960) found that f errous sulfide precipitat es con­

tr ibuted to c l ogg i ng . For one study (Winneberger, et a l . ~ 1960 ) su l f i des of

3.1 mg/l i n a nine-day old s eptic tank effluent account ed for 18. 8% of

the s uspe nde d so l i ds as fe r r ous sulfide precipitates. Others obs erved

29

simil ar c l oggi ng with the occurrence of the leach precipitates (Jones

and Taylor , 1965; and Thomas, et al . ~ 1965). An estimate of the signi­

ficance was given as 40% in a study by McGauhey and Winneberger (1963).

In the studi es by Winneberg~r, et a l . ~ (1960) including ana er obi c

and aer obic effluent e f f ect s on clogging, sulfide concentrations were

not adequa te ly documen ted . The study concl uded that there was littl e

practical difference between the effluents on percolat ion and infiltrat ion

characteristics, assuming that the sulfide concentrations wer e on the or­

der of 3.1 mg/l or less . At the t ime of comparison, the theoretical de­

tention time was on the order of 40 hours, whereas , the 3.1 mg/l of sul­

fides wer e value s from a 9-day old septic tank ef f l uent . Therefore, if

the sulfide concentrations were higher, the difference between the infil­

t rat ion characte r i s tics of the aer obic and an aerob ic effluents would have

he en significant.

Summary of eeiaaqe c l oggi ng . A r ev i ew of pe r colat i on t est s, including

clogging with r espect to septic tank ef f l uen t s and ae r obi cal ly treated

effluents as primary e f f l uents , revealed that the clogging was dep endent

on the clogging material and not dependent on the initial clear water

r ate. This was the major criticism of Ryon's percol at ion t est. Wi nne­

berger, e t al . (1960) also pointed out that anaerobic and aerobic e f ­

fluents had different actions on porous media depending on the pore si ze.

Fur t he r , it was found that ferrous sulfide was a s ignificant factor as a

precipitate which contributed to c l oggi ng. Resting and exposure to at ­

mosphere discolored the black precipitate, sugge st ing oxidation of f er­

rous sulfid e .

It was further appar ent that suspended solids led to early clogging,

not only on a wei ght basis but on s ize distribution as well. Little at ­

tent ion was paid t o microbi al gr owt h caus ed by hi gh concentration of

organics and its contributions to clogging. To s t udy the significance of

microbial growth i n clogging, Winneberger, e t al . (1960) ran exper imen t s

using sterile f eeds, but results did not appear conclusive . There was

only a 10% difference in the final percolation r ates between sterile and

non-ster i l e te sts. Nevertheless, Winneberger, e t al. , (1960) concluded

that microbi al clogging was appar ent on the basis of tests whi ch were

conouct ed f or l ess th;ln ten days.

Nature of Clogging Material at the Surface

Studies were conducted by Thomas, et al . (1965) to investigat e the

sit e and nature of soi l - pore clogging under sewa ge loading. Soil cores

were anal y zed for sulfide, phosphate, iron, total organic matter, poly­

sacch aride, and polyuronide to evaluate causative relationship at the

s i te of cl ogging.

It was f ound that clogging was limited to the top 1 em and that the

concentrat ion of all the parameters increased in proportion to clogging

except the polys accharides. When the soil was rested, sulfides dissipated

ano total organic matter de clined 40% while iron, phosphate and polyuro­

nides r emaineo undiminished.

Although Martin (1945 and 1946) depicted the polysaccharides as a

cause of s ealing and soil aggregation, the results of Thomas, e t al. . (1965)

indicated that polyuronides may be of greater significance with sewa ge

effluent. Espec i a l ly noteworthy was the fact that the total organic mat-I

ter concentration decreased and the permeability recovered when the soil

was rested.

Mechanisms of Clogging

From his revi ew of possible mechanisms of clogging, Allison (194 7)

summari zed what was then gene r ally accepted. The common behavior

pattern was divided into three distinct phases depending on the permeabi­

l it y of the soi l :

Phase 1 . Initi al percolation decrease is caused by structural

changes in the soil par t l y from the swelling of dry soil upon wetting and

by dispers i on. A decrease in the electrolyte content of the soil solu­

tion results and may last from 10 to 20 days in relatively impermeable

soils.

Phas e 2. Entrapped air in pores dissolves and is removed while

permeability in creas es to a maximum when nearly a l l of the air is r e­

moved.

31

Phas n 3. The maximum permeability decre ases with time. In 2 to 4

weeks, the rate i s but a fraction of the initial rate . The contributing

causes arc as fo l lows:

(1 ) Sl ow physical dis integration of s ol i ds under prolonged sub­

mergence.

(2) Biological clogging of s oi l pores with microb ial cells and

their s ynt hes i s products.

(3) Dispersion due to attack of micro-organisms on organic mat erial

which bind soil together.

(4) Combinat ion of all factors.

Exper i ment s on steril e and non-sterile systems were performed using

synthetic t ap water dos ed on Hanford, Exeter, and Hespera soils. Hanford

soil was considered fairly rich in organic matter and estimated to contain

an act ive microflora . From these experiment s , Allison ( 1947) was able

to show that clogging was microbially i nduced . Low rates of infiltration

were exper i enced aft er 60 to 70 days. However, when sucrose was add ed to

the ponded water, the l ysimeters became impermeable in 2 days.

Microbial "gwns." The work of Allison (1947) pointed out the signi fi­

cance of microbial activity to flow in porous media, particularly for

the specific case of the Kern County land spreading recharge study . This

work also contributed to the previous work by Martin (1945 and 1946 ) who

studied the significance of microbial "gums" or polysaccharides in soil

aggregation which improved soil-water movement upon drying. The results

of studies by Allison (1947) and Martin (1945 and 1946) and others empha­

sized the significance of organics and the resulting microbial act ivity

which affected soil -water movement. The organics may be res idual organics

in the soil or may be added to the soil system with the percolating f l ui d .

The results, translated into soil percolation terms , meant that

under continous ponding, the pores may seal as a result of microbial

"gums" or polysaccharides, as Martin suggested. Upon drying and rest­

ing, the "gurns fl caused soil particle aggr egat i on and subsequent wat e r

dosing improved permeabil it ies. In this way, infiltration and percolation

rat es were dependent on the organics present in the syst em as well as on

the hydraulic loading.

The Concept of "Incompatible Waters"

In a recent publication (Warner, 1966), the effect of reactions

resulting in precipitate formation by recharged and interstitial waters

was discussed. He studied theoretically and experimentally, the factors

<lffecting both phenomena. "Incompatible" waters are related to the pre­

cipitate formations such as FeCI 3, CaS04, FeS, etc. upon mixing. The

particular problem studied was related directly to well injection, but

it has relevance to ground water recharge in general.

By a modification of the dispersion equation, Warner (1966) was

ahle to calculate the dispersion characteristics of the porous media as

it was significant in the mixing characteristics; and, hence, could de­

termine the precipitate formation which caused clogging within the porous

media. By the use of a buffer water separating the two "incompatible"

waters, the thickness of which was shown to be calculable by the disper­

s ion equation, he showed that it was possible to prevent adverse reac­

tions. The precipitates influenced the extent of clogging with FeCl 3exhibiting the most pronounced effect.

Warner's (1966) results expressed the occurrence of the adverse

effects of clogging by precipitates from "incompatible" waters in more

fundamental terms as (i) the nature of the precipitate, (ii) dispersion

characteristics of the porous media, and (iii) the resulting mixing pat­

tern. As a possible remedy for the prevention of undesirable precipitate

formation, Warner (1966) suggested and studied the feasibility of inject­

ing a body of good quality water to act as a buffer. His method of

calculating the necessary quantity of buffer water required and his

laboratory study demonstrated that this practice was feasible. This con­

cept of buffer-water safeguard ag~inst early clogging by precipitate

formation in saline and brackish ground water was also reported as an in­

tended practice before injection-well disposal by the Holland-Suco Color

Company (1966) in Michigan. Prior to waste disposal, a one million gallon

buffer water injection was planned to prevent possible chemical reactions

between the waste liquors and the brine.

33

SUMMARY OF LITERATURE REVIEW

From the results of existing studies it is apparent that for

grounJ water recharge systems the following are controlling factors:

Water quality:

(1) Anaerobi.c conditions yield poor results of organic

stabilization allowing materials such as ABS to per­

colate to ground water supplies essentially unchanged.

Aerobic conditions must prevail within the system to

afford adequate treatment .

(2) From the results of work related to inorganic materials,

it is apparent that water quality may be seriously al­

tered by the inorganic content of recharge water. Ab­

sorption and ion exchange capacities of the soil sys­

tem have finite capacities and in the long run, these

processes may be strained to their limits and inorganic

pollution may eventually occur.

(3) For infiltration and percolation systems, the loading

rates for settle sewage in well-drained sandy soils

appear to be about O.S ft/day while highly treated

effluents can be spread at rates of about 1.62 ft/day.

(4) Oxygen depletion from nitrification is significant and

contributes to anaerobic conditions in long-termed action.

Nitrification by pretreatment is necessary before recharge

to maintain adequate aerobic conditions.

Hydraulic:

(1) The hydraulic considerations which limit flows or the

hydraulic capacity of the system are physical, chemical,

and biological characteristics of the porous media as

well as the recharged fluid. Further, the hydraulic

characteristics, intluding the gradient and initial

velocity contribute to the performance of the system si­

milar to filtration or consolidation of clays.

(2) Organics in the soil or fluid provide energy sources for

microorganism producing biochemical degradation products

that s eal t he pores of porous med i a. Thes e products may

be ce lls , or microb ial "g ums , " or similar material.

(3) Changes in s oil structure may have a s i gnificant effect

on permeability. Among these ar e floc culation and de ­

flocculation of soil s by the electrolyte content of the

sys t em . Bre akdown of soil structure, st r atifi cat ion , and

veins af fe ct hydraulic charact eristics of the soi l .

(4 ) Suspended sol ids remov al and clogging ar e r elated t o

these factors:

(a) Zet a potent i al

(b) chemical and physical characteristics affecting Zet a

potent i al and viscosity .

(c) sh ape of the porous particles

(d) por e size of the porous medium

(e) s i ze and shape of the suspended matter

(f) sur face ar ea of the media

(g) tortuosity of the porous medi a

(h) hydraulic gradient, and

(i) interstitial velocity.

(5) A s ucces s f u l system dep ends on a highl y clarified ef f l uent .

But it must not be organically rich nor contain electro­

l yt es which may cont r i bute to precipitate f ormat i on. The s e

react ions may be due to the r eaction within a f lu i d sy s t em

due t o biological r eact ions, such as FeS or the r echarge

fluid may r eact with interstit ial waters to form precipi­

tat es. In the l att er cas e, the mixing and dispersing

character of the po.r ous media and the nature and t ype of

precipitates are the important factors.

(6) For c lays, the results of i nf i l t r ati on and percol ati on

can be expected to vary widely within the field. Tests

on disturbed samples of clay cannot be related to the

field unless studies are expressed in terms of fundam ental

soil-water param eters: structure, consolidation, mo isture

retention properties, and soil organics as they may con­

tribute to microbial s ealing .

3S

(7) Laboratory samples may give variations in flows due to

consolidations as well as other factors mentioned pre­

viously. The variations may be a significant laboratory

phenomenon and not established in the field . . Hydraulic

gradient is an important factor.

(8) Laboratory samples may exhibit threshold gradients

erroneously implying sealing from other factors. In

field flows the path of least resistance and earth

"channels" and veins may dictate the flow patterns.

(9) Soil re-aeration is dependent on effective porosity

which is in turn dependent on moisture retention charac­

teristics of the sample.

36

ACKNOWLEDGEMENTS

The aut hor gratefully acknowledges the assistance of the following

persons who aided materially in this research project: John DeBoic e ,

senior in civil engi neer i ng ; Martin McMorrow, assistant in sanitary en­

gineering, Water Resources Research Center; and Bernadino Cagauan, j uni or

soil sc i entist, Water Resources Research Center.

Thanks are also due to Dr. Reginald H. F. Young for his critical

appraisal of this report and the many suggestions made by him that are

incorporated into it and Mrs. Rose T. Pfund, for her editorial assistance.

37

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