Microbiological Effects of Recharging 

the .l\1agothy Aquifer, 

Bay Park, New York, 

With Tertiary-Treated Sewage 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 751-E 

Prepared in cooperation with the 

Nassau County Department 

of Public Works 

Microbiological Effects of Recharging 

the Magothy Aquifer, 

Bay Park, New York, 

With Tertiary-Treated Sewage 

By GARRY G. EHRLICH, HENRY F. H. KU,JOHN VECCHIOLI, and THEODORE 

A. EHLKE 

DEEP-WELL ARTIFICIAL RECHARGE EXPERIMENTS 

AT BAY PARK, LONG ISLAND, NEW YORK 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 751-E 

Prepared in cooperation with the 

Nassau County Department 

of Public Works 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON:l979 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

Library of Congress catalog-card No. 79-600110 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-03210-4 
CONTENTS 

Page 

Abstract ------------------------------------------------------------------------- E 1 

Introduction -------------------------------------------------------------------- 1 

Purpose and scope ------------------------------------------------------ 1 

Water-reclamation and artificial-recharge facilities----------- 1 

Geohydrology of recharge site-----------------------------------·-

Previous work------------------------------------------------------------ 2 

Acknowledgments------------------------------------------------------- 4 

Methods of investigation ---------------------------------------------7------ 4 

Injection procedures --------------------------------------------------- 4 

Bacterial enumeration and identification------------------------- 6 

Bacterial clogging of well--------------------------------------------------

Injection of chlorinated reclaimed water------------------------

Injection of unchlorinated reclaimed water---------------------

Injection of dechlorinated reclaimed water---------------:-------

Effect of nutrient level-----------------------------------------------

Long-term injection test---------------------------------------------

Bacterial alterations of water quality----------------------------------

Public health considerations --,...-------------------------...: ________________ _ 

Summary -----------------------------------------------------------------------

References cited-------------------------------------------~-------...: _________ _ 

ILLUSTRATIONS 

Page 

E7 

7 

9 

10 

11 

12 

12 

15 

17 

17 

Page 

FIGURE 1. Map showing location of study site, Bay Park, N.Y.------,---------------------------------------------------------------------------- E2 

2. Diagram showing location of observation wells, structures, and external piping at artificial-recharge site ---------------------- 3 

3--7. Graphs showing: 

3. Decrease of specific capacity of injection well with time during test RW7, with chlorinated water----------------------- 7 

4. Head in relation to turbidity during test RW7, with chlorinated water---------------------------------------------------- 8 

5. Head as a function of time at the injection well during: (1) test RW8, with unchlorinated water and (2) tests RW4, 

RW5, and R W9, with chlorinated water ------------------------------------------------------~--------------------------------- 9 

6. Head buildup as a function of time at injection well, an observation well in fllterpack, and an observation well 20 feet 

from the injection well during test RW8, with unchlorinated water--------------------------------------------------------- 10 

7. Changes in concentration of total nitrogen, total phosphate, MBAS, COD, and chloride at observation well20 feet 

from injection well during recharge ---------------~-----------------------------------------.:...---------------------------------------- 13 

TABLES 

Page 

TABLE 1. Data on injection tests at Bay Park, N.Y., 1968-72---------------------------------------------------------------------------~----------------------- E5 

2. Injection data from test RW13, October 1972 to May 1973 ----------------------------------------------------------------------------------------- 5 

3. Chemical and physical quality of typical reclaimed water------------------------------------------------------------------------------------------- 6 

4. Chemical composition of water from observation wells at Bay Park artificial-recharge site---------------------------------------------- 6 

5. Bacterial counts in water recovered from injection well after test RW7, with chlorinated water--------------------------------------- 8 

6. Genera of bacteria isolated from repumped water 2 days after cessation of test RW7, with chlorinated water-------------------- 8 

7. Turbidity of reclaimed water during selected injection tests--------------------------------------------------------------------------------------- 9 

8. Bacterial content of injectant during test RWll, with dechlorinated water------------------------------------------------------------------ 10 

9. Bacterial quality of injectant during test RW10, with carbon filtration omitted------------------------------------------------------------- 11 

10. Bacterial counts of water repumped from injection well during three redevelopment cycles, test RW13----------------------------- 12 

11. Bacterial counts observed in injection well during 2-month resting phase, test RW10 ----------------------------------------------------- 14 

12. Bacterial counts in observation well 20 feet from injection well during initial injection phase, resting phase, and after final 

redevelopment phase of tests RW10 and RW10A----------------------------------------------------------------------------------------------- 14 

13. Mass-balance data on chloride, total nitrogen, methylene blue active substances, and chemical oxygen demand, tests RW10 

and RW10A---------------------------------------------------------------------------------------------------------------------------------------------- 14 

14. Microbiological quality of water from observation wells 20 feet and 100 feet from injection well, test RW13--------------------- 15 

15. Bacterial colony counts of water sampled during and after test RW8, with unchlorinated water-------------------------------------- 16 

III 
IV 

Metric unit 

millimeter ( mm) meter <m) 

kilometer ( km) 

Hauare meter (m~) 

Hquare kilometer tkm2) 

lwctare ( ha) 

cubic centim,eter ( cm3) 

liter (L) 

cubic meter (m") 

cubic meter cubic hectometer (hm:J) 

liter 

liter 

liter 

cubic meter 

cubic meter 

gram (g) 

gram 

metric tons (t) 

metric tons 

kilogram per square 

centimeter (kg/cm2) kilogram per square 

centimeter 

cubic meter per second 

( m:1/s) 

CONTENTS 

CONVERSION FACTORS 

Inch-Pound equivalent Metric unit Inch-Pound equivalent 

Length Specific combinations-Continued 

0.03!)37 inch (in) 

3.28 feet (ft) 

.62 mile (mi) 

Area 

10.76 

.386 

:2.47 

Volume 

0.061 

6\1.08 

35.31 

.00081 

=810.7 

2.113 

1.06 

.26 

.00026 

6.290 

Weight 

o.o:-:5 

.0022 

1.102 

0.9842 

square feet (ft2) 

square mile tmi2 ) 

acres 

cubic inch (ina) 

cubic inches 

cubie feet (ft3) 

a<>re-foot (acre-ft) a ere-feet 

pints (pt) 

quarts (qt) 

gallon (gal) 

million gallons (1\Igal or 106 gal) 

barrels (bbl) (1 hbl=42 gal) 

ounce, avoirdupois (oz avdp) 

pound, a voirflupois (lb a vdp) 

tons, short (2,000 lb) 

ton, long (2,240 lb) 

Specific combinations 

0.96 

.98 

35.3 

atmosphere (atm) 

bar (0.9·869 atm) 

cubic feet per second (fta;s) 

liter per second (L/s) 

cubic meter per second 

per square kilometer 

[(ma;s)/km2] meter per day (m/d) 

meter per kilometer 

(m/km) 

kilometer per hour 

(km/h) 

meter per second (m/s) 

meter squared per day 

(m2/d) 

cubie meter per second 

(n1'1 /S) 

cubic meter per minute 

(m3 /min) 

liter per second (L/s) 

liter per second per meter [(L/s)/m] 

kilonwter per hour 

(km/h) 

meter per second (m/s) 

gram per cubic 

centimeter (g/cma) 

gram per square centimeter (g/cm2) 

gram per square 

centimeter 

degree Celsius (°C) 

degrees Celsius 

(temperature) 

.0353 

91.47 

3.28 

5.28 

.9113 

3.28 

10.764 

22.826 

=264.2 

15.85 

4.83 

.G2 

2.237 

6:2.43 

2.048 

cubic foot per second 

cubic feet per second per 

square mile [ (ft3js) jmi2] 

feet per day (hydraulic 

conductivity) (ft/d) 

feet per mile (ft/mi) 

foot per second (ft/s) 

feet per second 

feet squared per day (ft2/d) 

(transmissivity) 

million gallons per day (Mgaljd) 

gallons per minute (gal/min) 

gallons per minute 

gallons per minute per foot 

[ (gal/min)/ft] 

mile per hour (mi/h) 

miles per hour 

pounds per cubic foot (lbjft3) 

pounds per square foot (lb/ft2) 

.0142 pound per square inch (lb/in2) 

Tern perature 

1.8 degrees Fahrenheit (°F) 

= [ (1.8 X °C) +32] degrees Fahrenheit 
DEEP-WELL ARTIFICIAL RECHARGE EXPERIMENTS AT BAY PARK, LONG ISLAND, NEW YORK 

MICROBIOLOGICAL EFFECTS OF RECHARGING THE MAGOTHY 

AQUIFER, BAY PARK, NEW YORK, WITH TERTIARY-TREATED 

SEWAGE 

By GARRY G. EHRLICH, HENRY F. H. Ku, JoHN VECCHIOLI, and THEODORE A. EHLKE 

ABSTRACT 

Injection of highly treated sewage (reclaimed water) into a sand 

aquifer on Long Island, N.Y., stimulated microbial growth near the 

well screen. Chlorination of the injectant to 2.5 milligrams per liter 

suppressed microbial growth to the extent that it did not contJ,ibute 

significantly to head buildup during injection. In the absence of chlorine, microbial growth caused extensive well clogging in a zone immediately adjacent to the well screen. 

During a resting period of several days between injection and well 

redevelopment, the inhibitory effect of chlorine dissipated and mi,crobial growth ensued. The clogging mat at the welVaquifer interface was 

loosened during this period, probably as a result of microbial activity. 

Little microbial activity was noted in the aquifer beyond 20 feet from 

the well screen; this activity probably resulted from small amounts of 

biotransformable substances not completely filtered out of the injectant 

by the aquifer materials. 

Movement of bacteria from the injection well into the aquifer was not 

extensive. In one test, in which injected water had substantial totalcoliform, fecal-coliform, and fecal-streptococcal densities, no fecal-coliform or fecal-streptococcal bacteria, and only nominal total-coliform 

bacteria, were found in water from an observation well 20 feet from the 

point of injection. 

INTRODUCTION 

Continuing population growth in Nassau County, a 

suburb of New York City, has been accompanied by increased withdrawals of ground water, the only source of 

public-supply water for the area. 

Net withdrawals from the ground-water system have 

resulted in declining ground-water levels and decreased 

streamflow (Franke, 1968) and in local landward movement of salty ground water (Lusczynski and Swarzenski, 

1966; Cohen and Kimmel, 1970). Net withdrawals are expected to increase with the rising population, per-capita 

water use, and percentage of population served by sewers. These growth factors indicate a water-supply deficit 

of between 71.1 and 91.1 Mgal/d by 1990 (Temporary 

State Commission on Water Supply Needs of Southeastern New York, 1972, p. 142-144). 

PURPOSE AND SCOPE 

Artificial recharge of the ground-water reservoir with 

water reclaimed from sewage is one of several alternatives under examination by Nassau County to meet the 

anticipated water-supply deficit (Peters and Rose, 1968). 

From 1968 to 1973, the Nassau County Department of 

Public Works operated a pilot advanced waste-treatment 

plant at Bay Park, N.Y., near the south shore of Nassau 

County (fig. 1). Reclaimed water from this plant was 

used in a series of 13 deep-well artificial-recharge experiments made by the U.S. Geological Survey, in cooperation with the Nassau County Department of Public 

Works, to provide some of the scientific and engineering 

data needed to evaluate (1) the degree and causes of well 

clogging that resulted from injection of reclaimed water, 

and remedies for the clogging, and (2) the geochemical 

compatibility of the reclaimed water with the aquifer. 

This report, the filth chapter in Professional Paper 

751, "Deep-Well Artificial-Recharge Experiments at Bay 

Park, Long Island, New York," summarizes the results 

of microbiological investigations carried out during those 

tests. The geochemical aspects of injection of reclaimed 

water are described in the previous chapter (Ragone, 

1977). 

Microbial activity associated with artificial recharge 

may have three principal effects: (1) bacteria ~ay grow 

near the well screen and cause a gradual reduction of 

aquifer hydraulic conductivity in the immediate vicinity 

of the well; (2) microbial activity may produce substances 

·that adversely affect the taste and odor of injected water 

later recovered from the aquifer; and (3) pathogenic organisms in the injected water may travel through the 

aquifer and cause illness when the water is later recovered for domestic use. 

WATER-RECLAMATION AND ARTIFICIAL-RECHARGE 

FACILITIES 

Reclaimed water for injection was obtained by tertiary-stage treatment of 0.6 Mgal/d of effluent from ail 

activated-sludge-type, 60-Mgal/d sewage-treatment plant 

(Peters and Rose, 1968; Peters, 1968; V ecchioli, Oliva, 

Ragone, and Ku, 1975). This treatment consisted of (1) 

coagulation and sedimentation, (2) primary filtration 

El 
E2 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

73° 

ATLANTIC OCEAN 

10 0 10 20 30MILES 

FIGURE !.-Location of study site, Bay Park, N.Y. 

through a dual-media sand-anthracite filter, (3) second-. 

ary filtration through one to four activated carbon· columns, and (4) chlorination. Additional treatments (degasification, pH adjustment, and dechlorination) were 

applied for comparison at selected times at the recharge 

facility 1,000 feet from the sewage-treatment plant. 

Major components of the recharge facility include (1) a 

50,000-gallon storage tank into which either public-supply water or reclaimed water can be delivered; (2) a vacuum-operated degasifier; (3) injection and redevelopment pumps with automatic-flow controls; (4) an injection 

well consisting of an 18-inch-diameter fiberglass casing 

above a 16-inch diameter stainless-steel well screen set 

at 418 to 480 feet below land surface, (5) 18 observation. 

wells, some of which are equipped with water-level-recording equipment, and (6) equipment for monitoring 

several chemical and physical characteristics of the water. 

(See fig. 2.) 

GEOHYDROLOGY OF RECHARGE SITE 

The recharge site is in the Atlantic Coastal Plain and 

is underlain by about 1,250 feet of unconsolidated deposits of Pleistocene and ·Late Cretaceous age, which, in 

turn, overlie crystalline bedrock of Precambrian age. 

The injection well is screened within the lower part of 

the Magothy aquifer of Late Cretaceous age at a· depth 

of 418 to 480 feet below land surface. The screened interval (injection or receiving zone) consists primarily of 

stratified fine to medium quartz sand sandwiched between and semiconfined by Magothy beds of lesser hydraulic conductivity. At Bay Park, the Magothy aquifer 

is confined below by the Raritan clay, also of Late Cretaceous age, but is virtually unconfined above owing to 

the generally coarse-grained character of the overlying 

. Pleistocene deposits. Lateral hydraulic conductivity of 

the stratified injection zone averages 940 (gal/d)/ft or 126 

ft/d, but flowmeter surveys indicate considerable variation within the interval. The hydraulic characteristics of 

the aquifer system were determined by standard aquifer-test methods and were later simulated by electric analog-model studies. 

PREVIOUS WORK 

The geology and ground-water conditions in southern 

Nassau and southeastern Queen~ Counties, which en-· 

compass the Bay Park area, were discussed by Perlmutter and Geraghty (1963). Lusczynski and Swarzenski 

(1966) gave a detailed description of the hydrologic environment in_southeastern Nassau County. General discussions of mor~ regional hydrologic conditions were given 

by Cohen, Franke, and Foxworthy (1968). The geohy-

. drology of the Bay Park site was described in brief by 

Perlmutter and others (1968) and in detail by V ecchioli, 

Bennett, Pearson, and Cerillo ·(1974). 

Scope and objectives of the Bay Park wastewater-reciamation and artificial-recharge project have been described by Cohen and Durfor (1967) and by Peters and 

Rose (1968). These reports also contain general descriptions of the facilities. A detailed description of the inj ection well was given by Cohen and Durfor (1967). Koch 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER 

eN2790 

N6928 'N7675 e eN7676 

I 

I 

I 

I 

I 

X 

I 

X 

I 

I 

X 

l 

I 

'-~~--------------------~ I 

15 0 15 30 45 FEET 

FIGURE 2.-Location of observation wells, structures, and external piping at artificial-recharge site. (Modified from Koch and others, 1973.) 

E3 
E4 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

and others (1973) described in detail the design and operation of the entire recharge facilities, including the injection well. 

Many progress reports have dealt with all or most aspects of the project in varying detail. Peters (1968) commented on the project overall, including some discussion 

of early operations of the treatment and injection plants. 

Vecchioli and Ku (1972) presented preliminary results of 

early injection experiments. These early results were 

later updated and summarized by Vecchioli (1972). Principal conclusions drawn from all tests were discussed in 

brief by Vecchioli and others (1975). Significant features 

of the longest recharge experiment (41. 7 Mgal) were reported on by Sulam (1973). 

Reports dealing specifically with geochemical aspects 

of the recharge experiment include V ecchioli and Giaimo 

(1972) on potential corrosion of metals; Faust and Vecchioli (1974) on several problems; Ragone, Vecchioli, and 

Ku (1973), Ragone and Vecchioli (1975), and Ragone, Ku, 

and V ecchioli (1975) on dissolution of iron from the aquifer; and Ku, Vecchioli, and Ragone (1975) on movement 

of sewage-related substances through the aquifer. Ragone (1977) presented a comprehensive discussion of all 

geochemical problems studied. 

Bacterial growth around the injection well and the significance thereof was reported on by V ecchioli ( 1970) and 

Ehrlich, Ehlke, and Vecchioli (1972, 1973). Movement of 

bacteria through the aquifer along with the injected 

water was discussed by V ecchioli, Ehrlich, and Ehlke 

(1972). 

ACKNOWLEDGMENTS 

Individuals who had a major role in the design and construction of the injection facilities include John H. Peters, former Commissioner of the Nassau County Department of Public Works; John L. Rose, formerly of 

Burns and Roe, Inc.; Philip Cohen and Bruce L. Foxworthy, Geological Survey; and Charles N. Durfor, forme1ly 

with the Geological Survey. Particular recognition is 

given Messrs. Cohen and Durfor, whose efforts early in 

the project made possible the detailed testing of the Hydraulics and hydrochemistry of the aquifer system that 

followed. 

Installation and early testing of the wells was done under the joint direction of Messrs. Cohen and Durfor. 

Most of the credit for the design of the operating controls 

and monitoring instrumentation of the injection facilities 

belongs to Mr. Durfor. In preparation for the injection of 

reclaimed water Gordon D. Bennett of the Geological 

Survey directed extensive hydraulic testing of the inj~ction facilities, the injection well, and the aquifer; many of 

the test procedures developed by him were followed wi'th 

little modification throughout the project. Bennett and 

F. J. Pearson, Jr., also directed the early recharge tests 

with public-supply water; some of the data from those 

tests are included in this report. 

The authors are especially grateful to former Commissioner Peters and Deputy Commissioner James S. Gillen, 

Nassau County Department of Public Works, for making 

available the physical and human resources of the department throughout the project. Particular thanks are 

given also to Francis J. Flood, former Superintendent of 

Operations and Maintenance, James A. Oliva, Sanitary 

Engineer, and to many others in the department for coordinating water-treatment operations with the injection 

experiments, for providing assistance in making modifications to the injection equipment, and in helping to 

make various measurements during the experiments. 

Louis S. Guaracini of the Department of Public Works 

provided numerous chemical analyses throughout the 

course of the project. 

Several members of the Geological Survey assisted in 

making test measurements and in reducing and compiling the data acquired. Particular recognition in this respect are given Anthony A. Giaimo, Dennis J. Sulam, 

and Lillian B. Maclin for their assistance throughout the 

project. The authors are grateful to all who assisted. 

METHODS OF INVESTIGATION 

INJECTION PROCEDURES 

Reclaimed water from the tertiary-treatment plant 

was injected into the well under positive head at a rate 

of about 350 gal/min, except in the first and part of the 

seventh tests (tests RWI and RW7), when the injection 

rate was 200 gal/min. Pertinent information about the 13 

recharge tests is given in tables 1 and 2. 

Chemical and physical properties of typical reclaimed 

water, and their values recorded during the study, are 

listed in table 3; except where otherwise stated, reclaimed water used in the tests conformed closely to 

these values. Chemical composition of water from observation wells at the site before injection began is presented in table 4. 

In all tests except RW8, RW10A, and RW11, reclaimed water used for injection was chlorinated. In tests 

RW8 and RW10A, chlorination was omitted; in test 

RW11, chlorinated water from the treatment plant was 

treated with sodium thiosulfate to remove all traces of 

free and available combined chlorine before injection. In 

test RW10, the secondary filtration through activated 

carbon was omitted to test the aquifer response to the 

inclusion of phosphate, chemical oxygen demand (COD), 

and methylene blue active substances (MBAS) in injection water. In test RW12, sodium hydroxide was added 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E5 

TABLE 1.-Data on injection tests.at Bay Park, N.Y., 1968-1972 

Test 1 Date Approximate Injection Gallons Special 

length of test rate injected treatment 

(days) (gal/min) (thousands) of water 

RW1----- 10-8-68 to 10-10-68 2 200 616 Degasified. 

RW2----- 12-10-68 to 12-10-68 2 350 1,063 Do. 

RW3----- 2-25-69 to 2-27-69 2 350 1,066 None. 

RW4----- 5-6-69 to 5-16-69 10 360 5,247 Do. 

RW5----- 9-15-69 to 9-25-69 10 350 5,117 Degasified. RW6----- 3-17-70 to 3-19-70 2 340 1,133 None. 

RW7 2 ---- 4-14-70 to 5-17-70 33 350 13,970 Do. 

and 200 

RW8----- 11-30-70 to 12-1D-70 10 340 4,930 Unchlorinated. 

RW9----- 4-27-71 to 5-7-71 10 355 5,156 None. 

RW10---- 11-1-71 to 11-11-71 10 350 5,180 Bypassed carbon 

adsorbers. 

RW10A--- 1-10-72 to 1-14-72 4 350 2,000 Unchlorinated. 

RWll---- 3-6-72 to 3-16-72 10 350 5,124 Dosed with 

RW12---- 6-5-72 to 6-15-72 10 355 5,050 

Na 2 S2 03 • 5H2 0 

Dosed with 

NaOH. 

RW133 --- 10-24-72 to 5-11-73 84.5 355 41,695 None. 

1 RW, reclaimed water. 2 Injection rate reduced after 19 days because output from treatment plant had been reduced. 3 Injection done intermittently. See table 2. 

to the reclaimed water to increase pH. In test RW13 (the 

longest test), the injection was not continuous as a result 

of weekend shutdowns, equipment breakdowns, and short 

periods of backflushing for well redevelopment. The injection period in test RW13 was divided into 18 separate 

segments. (See table 2.) 

Samples for chemical and microbiological testing were 

taken at frequent intervals. Injection water was sampled 

TABLE 2.-lnjection data from test RW13, October 1972 to 

May 1973 

[From Sulam, 1973. Injection rate 350 gal/min unless otherwise noted] 

Segnent Date Date Total Total Cumulative No. started ended number gallons ga 11 ons of days injected injected 

1------ 10-24-72 10-27-72 3 1, 598,400 1, 598,400 

2------ 11- 7-72 11-17-72 10.5 5,192,400 6,790,800 

3------ 11-20-72 11-22-72 2. 5 1,213,600 8,004,400 4------ 11-27-72 12- 8-72 11.5 5,657,300 13,661,700 5------ . 12-13-72 12-15-72 2. 5 1,246,800 14,908,500 6------ 12-19-72 12-21-72 2.5 1,255,400 16,163,900 7------ 1- 3-73 1-12-73 9.5 4, 706 '700 20,870,600 8------ 1-15-73 1-19-73 4.5 2, 246,600 23,117,200 

9------ 1-29-73 2- 4-73 6.5 3, 206,300 26,323,500 10------ 2- 6-73 2- 9-73 3 1, 470,600 27' 794,100 11------ 2-10-73 2-10-73 .33 149,400 27,943,500 

121 ----- 2-12-73 2-13-73 .67 324,700 28,268,200 13------ 3-12-73 3-16-73 4.5 2,207' 700 30,475,900 14------ 3-19-73 3-30-73 11.5 5,678,200 36,154,100 

15------ 4- 2-73 4- 6-73 4 1, 964,000 48,117,100 16------ 4- 9-73 4- 9-73 .5 233,500 38,350,600 17------ 5- 2-73 5- 4-73 2. 5 1,177,400 39,528,000 18------ 5- 7-73 5-11-73 4. 5 2, 166,700 41,694,700 

1

Injection rate reduced to 200 gal/min. 

at least daily, with few exceptions, for microbial analysis 

during all tests except R W12. Water samples were also 

taken from observation wells at appropriate times. Sam~ 

pies were collected in sterile containers from flowing 

streams of water pumped from the observation wells. 

Bacterial population of the aquifer near the well screen 

during tests RW7, RW8, RW11, and RW13 was determined by evaluating the contents of a specially designed 

probe that was lowered into the gravel pack during injection. The probe was built from a piece of stainless-steel 

well screen 2 inches in diameter and 27 inches long. Before each test, it was filled with sand from the aquifer 

and autoclaved for 30 min at 121 oc. To assure sterility of 

sand in the probe after autoclaving, samples of its contents were inoculated into tubes of sterile nutrient broth. 

Absence of microbial growth in the broth after 48 hours 

indicated the absence of viable microorganisms in the 

probe. If growth developed, the autoclaving and testing 

cycle was repeated until growth did not appear in the 

broth. Immediately before each test, the probe containing sterile sand was lowered approximately 450 feet into 

the observation well. It was removed immediately after 

injection ceased (Ehrlich and others, 1972). 

Mter each test, the injection well was pumped until at 

least 1.5 times the volume of water injected had been 

removed. Samples for bacterial analyses were collected 

at appropriate intervals. 
E6 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

TABLE 3.-Chemical and physical quality of typical reclaimed 

water 

[Modified from Vecchioli and others, 1975] 

Constituent or characteristic 

(1) 

Number 

of deter- minations (2) 

Silica (SiO, )-------------------- 35 Aluminium (Al), total------------ 22 Iron (Fe), total----------------- 35 

Iron (Fe), dissolved------------- 35 

Manganese (Mn), total------------ 35 

Manganese (Mn), dissolved-------- 35 Calcium (Ca), dissolved---------- 33 

Magnesium (Mg), dissolved-------- 34 Sodium (Na), dissolved----------- 33 

Potassi urn (K), di sso 1 ved--------- 33 Bicarbonate (HCO, ), dissolved---- 33 Sulfate (SO,), dissolved--------- 35 Chlorine, total residual--------- 207 Chloride (Cl), dissolved--------- 34 Fluoride (F), dissolved---------- 35 

Organic nitrogen (N), dissolved-- 35 

Nitrogen (N), total-------------- 35 Nitrite nitrogen (N), dissolved-- 35 Ammonia nitrogen (N), dissolved-- 34 

Nitrate nitrogen, dissolved------ 35 Phosphorus, as P, total---------- 35 

D i sso 1 ved solids, residue 180' C-- 33 Dissolved solids, calculated from determined constituents--- 33 

Total solids residue, volatile--- 33 Hardness, as CaCO, (Ca, Mg)------ 33 Noncarponate hardness------------ 33 Specific conductance (~'mho/em 

at 25"C)----------------------- 35 

pH------------------------------- 210 Temperature, in 'C--------------- 211 

Turbidity, as SiO, --------------- 385 Dissolved oxygen (DO)------------ 204 C hemi ca 1 oxygen demand (COD) 

(0.025 N K,Cr,O, )-------------- 35 

Detergents (MBAS) ---------------- 35 

Observed values' 

Max1mum M1 n1mum (3) (4) 

15 

400 

1,300 

780 

210 

210 

32 

10 

110 

15 

108 

210 

3. 5 

150 0.8 

1.1 

27 

. 0.02 

26 

0.1 

0.48 

519 

571 

52 

121 

96 

970 

6.6 

21 

1.9 

8.0 

21 

0.36 

12 

0 

100 

70 

30 

30 

16 

5.2 

72 

11 

30 

120 

0 

65 

0.1 

0 

21 

0 

20 

0.0 

0.01 

298 

393 

15 

63 

0 

720 4.8 

15 

0 

0 

2 

0.02 

Weighted 

average' 

(5) 

13 

100 

410 

230 

75 

72 

20 

6.4 

86 

13 

59 

160 

2.1 

99 

0.3 

0.60 

24 

0.01 

23 

0.1 

0.08 

398 

463 

33 

79 

32 

786 6.1 

17.5 

0.4 

4. 5 

9 

0.07 

'Observed values are based on daily or weekly composite samples, consisting of four aliquots daily except for temperature, turbidity, chlorine residual, 

pH, and dissolved oxygen, which were determined at least twice daily onsite. Values for aluminum, iron, and manganese are in micrograms per liter; all 

other values except those for pH, specific conductance, and water temperature are in mi 11 i grams per 1 iter. 

'Weighted average is equal to (concentration 1 times injected volume 1 plus 

concentration 2 times injected volume 2, and so forth, to concentration n times injected volume_!!) divided by total injected volume. -

BACTERIAL ENUMERATION AND IDENTIFICATION 

Total coliform determinations during tests RW1 

through RW6 were made by the multiple tube technique 

(American Public Health Association and others, 1971, 

p. 662-678). In all other tests, total-coliform, fecal-coliform, and fecal-streptococcal counts were made by the 

membrane-filter method (American Public Health Association and others, 1971, p. 678-688; p. 690-691). 

Total bacterial counts were made by the Standard 

Plate Count Method (American Public Health Association and others, 1971, p. 660-662) and by the following 

membrane filtration procedure: Total aerobic bacteria 

counts were made by filtering measured volumes of samples through membrane filters (mean pore size 0.45 (JLm). 

The filters were placed on plates of plate count agar or 

tryptone-glucose-yeast extract agar (American Public 

Health Association and others, 1971, p. 651) with the 

bacteria-laden side up and were incubated at 30°C for 48 

hours. To enhance visibility of colonies on the membrane 

filters, the filters with attached colonies were placed together on a pad saturated with dilute methylene blue dye 

solution before counting (Committee on Bacteriologic 

.Technique, 1957, p. 13). Counting was done with a lowpower binocular microscope. 

Pure cultures from isolated colonies on membrane 'filters and standard plate count plates were obtained by 

picking with a sterile needle and streaking on plates of 

plate count agar. The process of picking and streaking 

was repeated at least three times after the initial isolation or until only one type of colony appeared on the 

streak plates. Material from one colony of each final isolation plate was transferred to Plate Count Agar Slants 

with monthly transfers. 

Characterization of pure cultures was done according 

to methods described by the Committee on Bacteriologic 

Technique (1957) and Skerman (1967). 

Bacterial densities of the sand probe after each test 

were determined in the following way: A portion of material from the center of the probe was suspended in sterile buffered dilution water, and the suspension was shaken 

vigorously to dislodge attached bacteria. Samples of this 

suspension and serial dilutions thereof were tested for 

total aerobic count as described above. Sand was collected on a preweighed filter and dried at 105°C. The 

weight of sand was obtained as the difference between 

the weight of dry sand and filter and the weight of the 

filter alone. Bacterial density was calculated from estimated pore volume based on sample weight and an assumed porosity of 30 percent and bulk ~ensity of 2 g/cm3 • 

TABLE 4.-Ghemical composition of water from observation 

wells at Bay Park artificial-recharge site 

[From Vecchioli and others, 1974. Chemical analyses by U.S. Geological Survey. All values in milligrams per liter unless otherwise noted] 

Characteristic or Well number' 

constituent N7886 N7890 N8022 

Silica (SiD,), d i sso 1 ved---------- 7.2 7.5 7.4 

Ferrous iron (Fe)----------------- .30 .14 .14 

Total iron (Fe)------------------- .30 .14 .14 

Total manganese (Mri )-------------- .03 .03 .03 

Calcium (Ca), di sso 1 ved----------- .37 1.39 .87 

Magnesi urn (Mg), di sso 1 ved--------- .22 .21 .24 

Sodium (Na), di sso 1 ved------------ 3. 90 3.82 3.68 

Potassi urn (K), di sso 1 ved---------- .53 .62 .44 

Bicarbonate (HCO, ),dissolved------ 4.5 7.5 6.0 

Sulfate (SO,), di sso 1 ved---------- 3. 55 3.95 3. 75 

Chloride ~Cl ), dissolved---------- 3. 90 3.90 3.85 Fluoride F), dissolved----------- .13 .13 .13 

Nitrate (NO,), d i sso 1 ved---------- .00 .00 .00 Phosphate (PO,), dissolved-------- .02 .005 .015 

Hydrogen sulfide ( H, S) ,dissolved .4 .0 .0 

Dissolved solids------------------ 22 25 23 Specific conductance (~'mho/em 

at 25 ° c)------------------------ 28 32 23 

pH-------------------------------- 5.22 5. 72 5.45 Oxidation-reduction potential 

(YO 1 ts) ------------------------- -.03 -.10 -.06 

Hydrogen sulfide (H S)------------ .4 .0 .0 Temperature ('C)---~-------------- 15 15 15 

'Locations of wells are shown in figure 2. N7886 is 20ft from injection 

well; N7B90 is 100ft from injection well; N8022 is 200ft from injection well. 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E7 

Denitrifying bacteria counts were determined by the Elemental chlorine was selected as a bacterial growth 

method described by Alexander (1965). inhibitor at the start of the injection program. To critiPresence of sulfate-reducing bacteria was determined cally evaluate its effectiveness as a control agent, two 

by the method described by the American Petroleum In- comparative tests (RW7 and RW8) were run. In RW7, 

stitute (1959). chlorinated reclaimed water was injected. Mter removal 

Anaerobic bacterial testing was done by two methods: of the chlorinated injectant and restoration of the origi-

(1) 0.1 mL of water sample was spread over the surface nal specific capacity of the well, test RW8 was run with 

of a plate of predried Anaerobic Agar (BioQuest, Divi- unchlorinated injectant. Results of the two tests are desion of Becton Dickinson and Co. 1

); (2) exposed mem- ~.scribed in the following sections. 

brane filters were laid on plates of Anaerobic Agar. 

Plates and membrane filters were inoculated under oxygen-free conditions in Gas Pak Jars (BioQuest, Division 

of Becton Dickinson and Co.) at room temperature. 

BACTERIAL CLOGGING OF WELL 

Several investigations, including those of the California State Water Pollution Control Board (1954), Snie- . 

gocki (1963), Rebhun and Schwartz (1968), and Vecchioli 

and others (1975), have shown that suspended inorganic 

and organic particulate matter in the injectant collects 

and forms a mat at or near the well screen. Although the 

mat was never directly observed in these studies, it is 

expected to be similar to those formed on the surface of 

rapid sand filters. 

Most of the deposit is assumed to be at the interface 

and to penetrate the interstices of the sand for only short 

distances. The effect of this mat in an injection well is the 

same as its effect on a filter, namely, to block pores and 

reduce hydraulic conductivity. 

The California State Water Pollution Control Board 

(1954, p. 165) and Ehrlich and others (1972) found that 

the rate of clogging is directly proportional to the amount 

of solids injected in any period of time. The California 

State Water Pollution Control Board (1954) concluded 

that biological activity within the mat reduces the rate of 

clogging by breaking down the organic matter held in the 

mat. In contrast, Rebhun and Schwartz (1968) suggested that bacterial growth together with associated 

slimes enhance the rate of solids buildup and therefore 

increase the rate of well clogging. 

Effects of microbial activity on the performance of the 

injection well at Bay Park were under investigation since 

the beginning of the program. V ecchioli and Ku (1972) 

suggested that bacterial growth may have contributed to 

well clogging observed during early tests. Treatment of 

the injection well after test RW4 with a biocidal agent 

resulted in a small improvement in well capacity, which 

suggests that biota had contributed to the head buildup 

observed in that test. 

INJECTION OF CHLORINATED RECLAIMED WATER 

In test RW7, reclaimed water of virtually the same 

composition as that described in table 3 was injected. Residual chlorine level was maintained at about 2. 5 mg/L 

(minimum 0 mg/L; maximum 4. 0 mg/L ). Specific capacity 

of the injection well decreased from about 24 (gal!min)/ft 

at the start of the test to 2.5 (gal!min)/ft at the end, 33 

days later. Specific capacity as a function of time is depicted in figure 3; cumulative plots of turbidity values 

(suspended-solids concentration) in relation to head 

buildup are shown in figure 4. A rapid rise in head 

buildup followed a sharp increase in turbidity in the injectant from about the 14th to the 20th day. This correlation of decreased specific capacity with increased cumulative particulate matter was characteristic in all tests. 

The first water recovered during redevelopment of the 

injection well during tests RW7 and RW8 was grayish 

tan, opaque, and very turbid. The volatility of the suspended matter was 25 percent, which indicates that it 

(/) 25 z 

0 

...Jf-

...JQ 

;3 ~ 20 

Zo:: 

-w 

>-' 0. 

!::: w 15 01--

<C::J 

~~ 0:2; 

0 0:: 10 

U::w 

(30. 

w 

0. 

(/) 5 

0 6 12 18 24 30 36 

TOTAL TIME OF INJECTION, IN DAYS 

FIGURE 3.-Decrease of specific capacity of injection well with time 

• Use of trade names is for identification purposes only and does not imply endorsement by during test RW7, with chlorinated water. (Modified from Ehrlich 

the U.S. Geological Survey. and others, 1972, fig. 1.) 
E8 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

0.40 

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w 

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...J 

...J 

<( 

<.!' 

a:: 

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<.!' 

a:: 

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I 0.10 u 

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TOTAL TIME OF INJECTION, IN DAYS 

FIGURE 4.-Head in relation to turbidity during test RW7, with chlorinated water. A, head buildup divided by injection rate; B, cumulative maximum turbidity. (Modified from Ehrlich and others, 1972, 

fig. 2.) 

was composed primarily of inorganic materials. The bacterial plate count of the first opaque, turbid water was 

near 5 x 103 cells per 100 mL. 

Clarity of repumped water gradually improved with 

pumping, and visible turbidity disappeared within several hours. After 30 minutes of pumping, the bacterial 

count had increased to 5 x 106 cells per 100 mL (table 5). 

After 4 and 24 hours of pumping, bacterial counts remained at essentially that level. 

The injection water contained significant concentrations of dissolved oxygen. (See table 3.) Water pumped 

from the formation immediately after cessation of injection had virtually the same dissolved-oxygen content as 

the injectant, but, as pumping continued, dissolved oxygen gradually decreased until it was no longer detectable. In a later test (Ragone and others, 1973), it was 

TABLE 5.-Bacterial counts in water recovered from injection 

well after test R W7, with chlorinated water 

[Total bacteria and coliform counts given as cells per 100 mL; denitrifying bacteria given as most probable number per 100 mL] 

determined that dissolved oxygen persists in the injectant to about 12 feet laterally into the formation. At 

greater distances, the water is essentially oxygen free. 

Two factors can account for the loss of oxygen from the 

injectant as it moved from the injection well into the 

aquifer. 

1. Ragone and others (1973) and Ragone and V ecchioli (1975) suggested that oxygen in the injectant reacts 

with pyrite in the formation to produce ferrous iron, sulfate, and hydrogen ions according to the equation: 

FeS2 + 7/202 + H20 = Fe+2 + 2S042 + 2H+. 

2. Microbial respiration can deplete dissolved oxygen. Apparently, only small amounts of soluble biotrans 

formable compounds entered the aquifer with the injec 

tant, but work by Moffett and Williams (1967) and Favaro 

Petersen, Boyer, Carlson, and Bond (1971) has shown 

that substantial bacterial populations can arise in very 

dilute nutrient media. Therefore, it is possible that mi 

crobial activity was sufficient to account for a major part 

of the observed oxygen depletion. However, despite the 

potential for microbially induced oxygen depletion, the 

relative importance of this mechanism, as compared to 

other oxygen sinks, such as pyrite oxidation, cannot be 

assessed. Evidence presented later in this section sug 

gests that microbial activity in the formation was re 

stricted and that bacterial respiration would, therefore 

be only a minor factor in oxygen uptake. 

Several bacterial strains were isolated from the sand 

probe and from water pumped from the aquifer at se 

lected times during initial well redevelopment. Twenty 

five isolated colonies from the plate-count tests were 

identified as to genus. Sources and identity of isolates 

are given in table 6 (from Ehrlich and others, 1972). 

The identified isolates were obligate aerobes and fa 

cultative anaerobes. Under the oxygen-poor conditions 

in the formation, only sparse growth of obligate aerobes 

such as Alcaligenes, Micrococcus, Flavobacterium, and 

Acinetobacter would be expected as was the case. A few 

genera of facultative anaerobes such as Proteus, Aero 

TABLE 6.-Genera of bacteria isolated from repumped water 2 

days after cessation of test RW7, with chlorinated water 

[From Ehrlich and others, 1972] 

Number of times isolated In sand- In water samples filled Pu~ing time 1 Genus in minutes 

probe 0 30 240 1,440 

Pseudomonas, type 1-------

Pseudomonas, type 2------- 1 0 0 0 0 1 0 0 0 0 

Pumping time 

(min) 

Total bacteria 

count Denitrifying bacteria count 

Col iform Pseudomonas, type 3------- 0 0 4 2 0 

count Micrococcus--------------- 0 1 0 0 0 

----------------------- :l~~~~~~~~~i~;============ 0 2 1 0 1 

0 1 0 0 0 

3

t::::::::= 5 X 10' 0 Acinetobacter-------------

240---------- ~ ~ }g: ~ ~ }g: ~~ ~~~~~~=~================= 1, 440---------- 5 x. 10' 5 X 10• 90 Proteus-------------------

0 1 0 0 3 

0 0 1 1 0 

0 0 2 0 0 

0 0 0 2 1 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E9 

monas, and Serratia were found; these can grow under 

anaerobic conditions if suitable fermentable substrates 

are available. Denitrifying strains of Pseudomonas jluorescens can grow under anaerobic conditions by using nitrate as a terminal electron acceptor. Although nitrate 

concentration was typically only about 0.4 mg/L, this 

concentration could sustain a small denitrifying bacterial 

population. Coliform (lactose-fermenting) bacteria were 

present in only small numbers in the repumped water. 

Several Pseudomonas species, including P. fluorescens, P. aeruginosa, P. putida, P. alcaligenes, and P. 

pseudoalcaligenes, are able to sustain themselves under 

anaerobic conditions by decomposing arginine, an amino 

acid, through a process known as substrate level phosphorolation (Stanier, Douderoff, and Adelberg, 1970). 

The relative importance of arginine hydrolysis is unknown because no data on arginine concentrations are 

available. 

INJECTION OF UNCHLORINATED RECLAIMED WATER 

Results of test RW7, with chlorinated water, showed 

that the rate of clogging depended mainly on the concentration of suspended solids in the injectant. Suspended 

solids in the water frrst repumped from the injection well 

were mostly nonvolatile, which indicates that little organic matter had accumulated near the well. 

In the next test (RW8), about 5 Mgal unchlorinated 

reclaimed water of nominally the same composition as 

that in test RW7 (table 3) was injected. After 10 days of 

injection, specific capacity of the injection well had decreased from 26 (gal!min)/ft of head buildup to 11 (gall 

min)/ft. A curve showing rate of head buildup in this and 

three other tests is shown in figure 5. Turbidity of the 

injectant was consistently low in test RW8 (table 7) and 

averaged less than in other tests. Thus, the increased 

rate of head buildup observed in test RW8 could not be 

ascribed to physical clogging by inert particulate matter 

alone. 

In all tests but RW8, head buildup in the observation 

well (well N7885) within the filter pack of the injection 

well was virtually the same as that in the injection well. 

In test RW8, however, after the second day of injection, 

the head in the injection well rose at a more rapid rate 

than in the observation well (fig. 6) and, near the end of 

the test, the head in the injection well was nearly 12 feet 

higher than in the observation well. This increase in head 

suggests that much of the clogging occurred in the filter 

pack immediately adjacent to, or on, the injection-well 

screen. A lesser amount of clogging probably also developed behind the filter pack at the aquifer face, where 

most of the clogging had been noted in other tests. 

The water first recovered from the formation after the 

end of test RW8 was moderately turbid and showed little tendency for settlement of suspended material on 

w 

f-

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Test 5 Test 8--.... ... ···· i -

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8 4 L_ /~ ... ::~------ ~ 

~ I ~ 

i 1_. i __ ~_l-~ _ __1__ ___ __,_1 - j 0 2 4 6 8 -- 10 

TOTAL TIME OF INJECTION. IN DAYS 

FIGURE 5.-Head as a function of time at the injection well during: 

(1) test RW8, with unchlorinated water, and (2) tests RW4, RW5, 

and RW9, with chlorinated water. (Modified from Ehrlich and others, 1973, fig. 2.) 

standing. Approximately 75 percent of the suspended 

material was volatile at 550°C, which suggests that the 

material was largely oxidizable organic matter. In test 

RW7 (with chlorin&ted water), the volatility of comparable suspended matter was only about 25 percent. Because the injectant had received virtually the same treatment before both tests (except for chlorination), the 

threefold increase in volatile matter in the particulate 

material recovered after test RW8 cannot be attributed 

solely to differences in preinjection treatment. 

Bacterial counts in the water first recovered from the 

filter pack after test RW8 were much higher than in 

comparable samples from test RW7 with chlorinated 

water (2.0 x 107 cells per 100 !JlL in RW8 as opposed to 

5 x 105 cells per 100 mL in RW7). This greater fraction 

of volatile matter in the residue after test RW8 suggests 

a larger bacterial biomass in the organic mat after test 

RW8. 

TABLE 7 .-Turbidity of reclaimed water during selected injection tests 

[In milligrams per liter as Si02 ] 

Test 

RW4--------------------------------- RW5--------------------------------- RW8--------------------------------- RW9---------------------------------

Range 

0.2-1.8 

.1-1.6 

0 -0.3 

0 -1.5 

Turbidity 

Average 

0.9 

.6 

·.1 

.3 
ElO DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

30 

. '0'0"" 

~'I 

fw 

w 

LJ.. 

20 l 

10 J r----- N7886 

i 

o~~-~1--~--~- ' I _______ l_ _ ____L_ _ _j 

o 2 4 6 8 10 

TOTAL TIME OF INJECTION. IN DAYS 

FIGURE 6.-Head buildup as a function of time at injection 

well, an observation well in filter pack, and an observation 

well 20 feet from the injection well during test RW8, with 

unchlorinated water. (Modified from Ehrlich and others, 

1973, fig. 2.) 

After test RW8, the sand-filled probe, which had been 

suspended in the observation well tapping the filter pack 

during injection, was coated with a slimy, gelatinous material that cemented some of the sand grains into larger 

aggregates. Such slime had not been observed in the 

probe after test RW7, in which chlorinated water had 

been used. Material from the center of the probe had a 

bacterial density of 1.0 x 108 cells per 100 cm3 of pore 

volume, about 500 times that of both the injectant and 

the water repumped after injection. The coliform bacteria count in the probe was about 10 times that of the injectant and the first repumped water, but fecal-coliform 

and fecal-streptococcal counts were about the same in 

the probe, the injectant, and the first repumped water. 

Coliform bacteria, which formed approximately half 

the total bacterial count of the injectant during much of 

test RW8, constituted only 1 percent of the bacterial 

population in the probe. It was assumed that the ratio of 

coliform bacteria to total bacteria captured in the probe 

by filtration would be representative of the ratio in the 

injectant; therefore, the lower ratio noted in the probe 

must have resulted either from a more rapid die-off, or 

slower multiplication, of coliforms than of other bacterial 

species. In any event, coliform bacteria during test RW8, 

in which the injectant was not chlorinated, were less significant. 

From the preceding discussion, one can conclude that 

the impact of bacterial clogging is reduced in the presence of an effective bacteriostatic or bactericidal agent 

such as chlorine. When residual chlorine was maintained 

at a level of about 2.5 mg/L in the injected water, bacterial growth and attendant clogging did not occur either 

in the filter pack or at the formation face. 

INJECTION OF DECHLORINATED RECLAIMED WATER , 

In test RW11, reclaimed water was dechlorinated with 

sodium thiosulfate before injection, so that the effects of 

chlorine on microbial growth could be studied further. 

The injection water was similar in chemical quality to 

that used in earlier tests (table 3). During test RW11, 

residual chlorine could not be detected in the injectant. 

Total bacterial and total coliform counts in the injectant were monitored throughout test RW11 (table 8). 

Coliforms were detected only once, and total bacterial 

count never exceeded 37 cells per 100 mL. Specific capacity decreased from 24.9 (gal/min)/ft at the start of the 

test to 22.8 (gal/min)/ft after 10 days of injection. This 

relatively small (10-percent) loss of specific capacity contrasts sharply with the 58-percent loss observed in test 

RW8, in which unchlorinated water was injected. 

Head buildup in test RW11 was moderate but less than 

expected. By analogy with test RW8, which had used 

unchlorinated water, accelerated clogging from accumulation of bacterial cells in the filter pack had been expected to appear during the first week. Chemical oxygen 

demand (COD) levels in the injectant were comparable 

in tests RW7 and RW11; therefore, about equal amounts 

of carbon and energy sources were available for cell 

building in the two tests. 

Percentage volatiles content of solids recovered from 

the well and cell count of the sand probe were determined after test RW11. Solid material obtained during 

TABLE B.-Bacterial content of injectant during test RWll, 

with dechlorinated water 

[Total bacteria and coliform counts given as cells per 100 mg/L] 

Days since beginning Total bacteria of test count 

1------------------------------- 37 

2-----------------------,-------- 14 

3------------------------------- 2 

4------------------------------- 1 

5------------------------------- 2 

6------------------------------- 2 

7-----------------------------:-- 2 

8------------------------------- 1 

9------------------------------- 23 10-~----------------------------- 4 

Total coliform 

count 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 . 1 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER Ell 

redevelopment after test RW11 contained 86 percent 

volatile materials, which compares closely with.the 68 

percent found after test RW8 and is significantly greater 

than the 25 percent found after test RW7 (Ehrlich and 

others, 1972, p. 242). This high percentage shows that 

the clogging mat near the well was composed primarily 

of organic matter. 

The bacterial density of the sand-filled probe after test 

RW11 was 1.4 x 104 cells per 100 mL-significantly 

greater than the median bacterial counts of the injectant 

(table 8) and the probe after test RW7, but orders of 

magnitude less than the 1.0 x 108 cells per 100 mL observed after test RW8. The high volatiles content of solids in water pumped after test RW11, and the nearly 

10,000-fold increase of cells in the sand probe, suggest 

that bacterial growth had occurred both in the filter pack 

and the formation near the well during test RW11, although not nearly as rapidly as during test RW8. 

A clogging mat did not form during test RW11. Its 

development may have been delayed by an initial lack of 

significant numbers of viable cells in the injectant because the rate of clogging-mat formation by bacteria and 

their associated slimes depends on the number and types 

of cells in the injectant as well as the quality and quantity 

of assimilable carbon sources. Inoculum size has long 

been known to be a major determinant of the rate of industrial fermentation processes; large inocula are generally administered to minimize the time required for the 

microbial population to build up to a high level. 

The bacterial' density of the injectant in test RW11 was 

consistently less than 100 cells per 100 mL, whereas in 

test RW8 it had been consistently greater than 1 x 105 

cells per 100 mL. The cell counts in. the sand-filled probe 

after tests RW11 and RW8 (1.4 x 104 and 1.0 x 108 colonies per 100 mL, respectively) indicate an increase of 

three to four orders of magnitude in each test. Thus, the 

absence of clogging during test RW11 may be attibuted 

to a lower original count in the injectant. Had the test 

continued, a rapid increase in head buildup might have 

ensued. 

EFFECT OF NUTRIENT LEVEL 

Results of test RW7, with chlorinated water, suggest 

that the bacterial-growth-inhibiting effects of residual 

chlorine were exerted only over a short distance (less · 

than 20ft) within the formation. Once the chlorine had 

dissipated, microbial growth could proceed freely. Thus, 

it is possible that if a high level of soluble organic matter 

were introduced with the injectant, some of it would penetrate into the formation and support microbial growth. 

To determine the effect of elevated nutrient levels in 

the injectant, the carbon filtration step was omitted from 

the tertiary-treatment process in test RW10. Water was 

taken from the sand filters and chlorinated to a level of 

about 2.5 mg/L, and 5 Mgal was injected at a rate of 350 

gal/min for 10 days. Chemical oxygen demand (COD) and 

methylene blue active substances (MBAS) concentrations were from two to eight times the concentrations 

usually observed in reclaimed water filtered through activated carbon. Nitrogen and phosphate concentrations 

were unaffected, and the bacterial count of the injectant 

was low (table 9). 

Specific capacity of the well in test RW10 decreased 

from 26 (gal!min)/ft at the start of the test to 15.2 (gall 

; min)/ft after 10 days of injection. Pumping from the well 

was started shortly after the end of the injection period. 

The bacterial count of water was 1,400 cells per 100 mL 

after 14 minutes of pumping and 1,000 cells per 100 mL 

after 90 minutes, when pumping was discontinued. The 

bacterial count of the initially sterile sand probe suspended in the gravel pack was relatively low (300 cells 

per 100 mL), which indicates that little microbial growth 

had occurred in the vicinity of the well during the 10-day 

injection period. 

Immediately after cessation of the 90-minute repumping cycle, the well was allowed to remain idle for 35 days. 

At the end of this time the well was again pumped, and 

the specific capacity of the well had increased from 15.2 

(gal/min)/ft at the end of the injection test to 26 (gal/min)/ 

ft, or roughly the same value as that at the start of injection. Bacterial counts in water. pumped from the well 

after the 35-day rest period were in excess of 105 cells 

per 100 mL, as compared to 1,000 cells per 100 mL immediately after cessation of injection. The bacterial aftergrowth is consistent with observations of Rebhun and 

Schwartz (1968) and V ecchioli (1970), who found greatly 

increased coliform densities in water repumped from injection welb after long pauses between injection andredevelopment. 

Restoration of specific capacity to pretest levels indicates that the clogging mat, which had accumulated during the injection phase and was not removed during the 

TABLE 9.-Bacterial quality of injectant during test RWl 0, 

with carbon filtration omitted 

[Total bacteria and coliform counts given as c~lls per 100 mL] 

Days si nee beginning of test 

1----------,..----------------·---- 2------------------------------- 3-------------------------------

4--------..; ____ ------------------ 5-------------------------------

6-------------------------------

7------------------------------- 8------------------------------- 9-------------------------------

i 0-------------------------------

Total bacteria 

count 

12 

9 

7 

6 

7 

28 

15 

19 

10 

28 

Total coliform count 

<1 

3 

2 

4 

2 

2 

<1 

2 

2 

<1 
E12 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

initial 90-minute repumping cycle, had changed sufficiently to be removed during the 60-minute repumping 

cycle after the 35-day rest period. 

LONG-TERM INJECTION TEST 

Test RW13, the final test of the series, ran from October 24, 1972, to May 11, 1973. Recharge was intermittent, and the total volume of chlorinated reclaimed water 

injected during the test was 42 Mgal. Some of the waterquality aspects of test RW13 have been discussed by Ragone and others (1975) and Vecchioli and others (1975). 

About two-thirds of the way through the test, after injection of slightly more than 28 Mgal of reclaimed water, 

the sand-filled probe was removed from the observation 

well in the gravel pack. The bacterial count of the sand 

was 1 x 10;, cells per 100 mL of free pore volume-considerably more than that observed in the probe after any 

of the shorter tests with chlorinated water-which indicates that bacterial growth may occur in the proximity of 

chlorinated water. 

During test RW13, the injection well was redeveloped 

by pumping whenever specific capacity decreased to 6 

(gal!min)/ft. This was done seven times during the test. 

On three occasions, samples of repumped water were 

analyzed for bacterial count. Results are given in table 

10. 

The sample of December 11, 1972, taken 3 days after 

the cessation of injection, showed that bacterial populations increase rapidly during idle periods. The bacterial 

count was very high at first but decreased with pumping. 

Sulfate-reducing bacteria appeared after 60 minutes of 

pumping on February 14, 1973, but were present in the 

initial water repumped from the well on April 6, which 

shows that microbial growth occurred near the well even 

in the presence of residual chlorine. Apparently, this 

growth did not contribute significantly to well clogging. 

The appearance of sulfate-reducing bacteria near the 

TABLE 10.-Bacterial counts of water repumped from injection well during three redeveloped cycles, test RW13 

[Total bacteria counts given as cells per 100 mL; sulfate reducing bacteria given as most probable number per 100 mL. N D, not determined] 

Date Runnin~ time Total bacteria Sulfate-reducing (m1n) count bacteria 

count 

12-11-72-------- 10 100,000 NO 30 3,400 NO 60 260 NO 2-14-73-------- 12 200 <50 30 2 <60 60 2 8 4- 6-73-------- 12 64 43 30 NO 9 60 54 4 'Surge 380 23 

'Pump turned off then c;m at short intervals over a 10-minute period. 

well bore toward the end of the test suggests that a nutrient buildup was occurring near the well, but at a sufficient distance to be in an anoxidative zone, since sulfate-reducing bacteria are obligate anaerobics. 

BACTERIAL ALTERATIONS OF WATER 

QUALITY 

Reclaimed water contains higher concentrations of 

most chemicals than native water from the Magothy 

aquifer. Chemical oxygen demand (COD) of reclaimed 

water from the tertiary-treatment plant was typically 9 

mg/L, whereas COD of native water from the aquifer is 

below measurable levels. In addition, the concentrations 

of essential microbial nutrients such as NHH, P04- 3, 

Mg+2 , K+, and Fe+2 in reclaimed water are sufficient to 

allow a considerable amount of microbial growth. 

Abundant evidence has been presented to show that 

microbial growth supported by nutrients in the injectant 

occurs in the clogging mat, particularly in the absence of 

chlorine. During the process of microbial assimilation, 

part of an organic substrate will be used for energy and 

part will be incorporated into new cell mass. Simpler 

molecules are produced in the heterotrophic utilization of 

organic compounds, and sometimes these products of 

metabolism produce undesirable tastes and odors in the 

water. 

Many microorganisms can cause transformations of organic compounds, although they cannot use these compounds as carbon and energy sources. This phenomenon, 

called cometabolism, can produce undesirable products 

from relatively innocuous substances. 

During the evolution of any microbiological ecosystem, 

the rate of cell death will at some time equal or exceed 

the rate of new cell formation. Mter death, cells lyse and 

release their contents to the environment, where some 

of them may cause unpleasant tastes and odors. 

Both particulate and soluble organic materials are 

present in reclaimed water. Although significant amounts 

of particulate materials are filtered from the injectant 

near the well screen at or near the well bore/aquifer interface, a small fraction of particulate matter is probably 

also carried into the formation, where it can provide nutrients for microbial growth. 

The fate of dissolved organic substances is uncertain. 

Sorption processes could concentrate dissolved organic 

nutrients previously too dilute for microbial assimilation 

into local, highly concentrated areas on solids, where 

they might then be utilized by microbes. Kaolinite, illite, 

and lignite, which are present in the Magothy aquifer at 

Bay Park, are known to have sorptive capacity for organic molecules. However, no measurements of the sorptive · capacity of materials in the Magothy aquifer have 

been made. 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E13 

To investigate the effects of microbial activity on organic substances in the formation, a recharge test involving injection of reclaimed water having higher than average COD levels was run. In test RW10 (described 

above), 5 Mgal of reclaimed water having an average 

COD of 22 mg/L and a MBAS concentration of 0.55 mg/L 

was injected at a rate of 350 gal/min for 10 days. The 

injected water subsequently was repumped briefly on 

five occasions over a 2-month period. A second period of 

recharge followed, in which an additional 2 Mgal of reclaimed water with a COD of 9 mg/L and MBAS concentration of 0.07 mg/L was injected; this was followed by 

another repumping period to remove the injected water 

from the aquifer. 

Ku and others (1975) presented graphs showing concentrations of nitrogen, phosphate, chloride, COD, and 

MBAS at the observation well 20 feet from the recharge 

well (well N7886) as the reclaimed water moved through 

the formation (fig. 7). 

Replacement of native water by reclaimed water at 

the observation well 20 feet from the injection well, as 

indicated by chloride concentrations, was complete after 

5 x 105 gal had been injected. After that, chloride concentration at the observation well remained essentially 

constant at a value close to that of the injected water. 

Total nitrogen concentration approached the nitrogen 

level of the injectant, but at a slightly slower rate than 

the chloride. MBAS and COD concentrations were about 

half their respective concentration in the injected water. 

After the initial injection of 5 Mgal of reclaimed water, 

the injection well was left idle for 2 months except for 

brief pumping episodes. Analysis of water samples from 

the injection well 35 days after cessation of injection 

showed concentrations of dissolved iron, total organic 

carbon (TOC), and COD of 40 mg/L, 21 mg/L, and 50 mg/ 

L, respectively. Concentrations of dissolved iron, TOC, 

and COD in the reclaimed water were 0.2 mg/L, 6 mg/L, 

d' z 0.. 

AMOUNT OF WATER INJECTED, IN MILLION LITERS 

~ iii 0 0 1- 1-

a: 

w 

1-

::::i 

a: 

w 

a.. 

(/) 

~ 

<( 

a: 

(!) 

::::i 

...J 

~ 

~ 

~ z 

w 

::J 

1::: 

In 

z 

0 

u 

0 

u 8 

or-________ _,5~--------~~~o----------~~~5------~~~.~lr9~2=0~--------~2r5 __________ ~ 

RW 10 

,.....--...._ __ ..._ COD ----- / .....___.... .___---....... ...... ___...,.. ,_. 

~ 

RW lOA 

" 

~ 

' ' 

"'MBAS 

' ' "" ' ' "" ' ' 

-. ____ CQD ____ _ 

3 4 5 5 

AMOUNT OF WATER INJECTED, IN MILLION GALLONS 

30 

0.25 25 

0 0 

FIGURE 7.-Changes in concentration of total nitrogen, total phosphate, MBAS, COD, and chloride at observation well N7886, 20ft from 

injection well during recharge. (Modified from Ku and others, 1975.) 
E14 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

TABLE 11.-Bacterial counts observed in injection well during injection phase, the resting phase, and the final inJ"ection 

2-month resting phase, test RWJ 0 phase of tests RW10-10A (table 12). Water from that 

. [Total bacteria counts given as cells per 100 mL; denitrifying bacteria well during the resting period showed that total N and 

and sulfate reducers given as most probable number per 100 mL] COD concentrations had decreased slightly, whereas the 

Date Total bacteria 

count Denl.trl·fyl·ng 5 

lf t MBAS concentration had dropped from 0.27 mg/L to 0.17 u a e reducers 1 

ba~~~~ia count , mg/L. The COD decrease was about 2 mg/L, which sug-

-----------------------, gests that some degradation of organic matter took place; 

11-11-71--------- 1 X 10' 

11-23-71--------- 9 X 108 

12- 7-71--------- 5 X 10 • 12-14-71--------- 4.3 X 10' 

12-15-71' -------- 7.5 X 10' 

12-15-71' -------- 2.5 X 10' 

140 

400 

2.4 X 10' 

>2.4 X 10' 

'Taken 14 minutes after onset of pumping. 

'Taken 60 minutes after onset of pumping. 

4.6 X 10' 

4.6 X 10' 

and 22 mg/L, respectively. Results of bacterial counts 

made during the resting period are given in table 1L 

This approximate tripling of the TOC and doubling of 

COD indicates that the concentration of soluble organic 

compounds in the water near the well was increasing, 

probably at the expense of insoluble particulate organic 

matter in the filter mat. 

The increase of Fe-t 2 concentration in the area near the 

well was similar to the increase of Fe-t 2 in soils shortly 

after waterlogging. Although the exact mechanism of 

this transformation is not known, it has been shown to 

be a consequence of bacterial metabolism (Alexander, 

1961). . 

Many genera of bacteria are able to induce the reduction of Fe+3 in compounds such as Fe(OH)3 , FeOOH, 

FeP04, and FezOa. Included in table 11 are several genera reported to be active iron reducers. Tests of the ironreducing ability of isolates from tests RW7 and RW8 

were made by the method described by Ottow (1968). 

Several isolates of Pseudomonas type 2 showed small 

but definite iron-reducing activity. Pseudomonas type-2 

organisms are also vigorous denitrifiers. This is in agreement with the observations made by Ottow (1968) that 

organisms having inducible nitrate-reductase activity 

frequently also showed iron-reducing activity. 

Samples of water from the observation well 20 feet 

away were analyzed for bacterial count during the initial 

TABLE 12.-Bacterial counts in observation well 20 feet from 

injection well during initial injection phase, resting phase, 

and after final redevelopment phase of tests RWJ 0 and 

RWJOA 

Date 

11- 4-71------------ 11- 6-71------------ 11- 8-71------------

11-11-71------------

11-23-71------------

12- 1-71------------

12-14-71------------

2-23-72------------

Phase 

Initial injection-----------

Initial injection--------~-­

Initi al injection-----------

Initial injection-----------

Resting---------------------

Resti ng--------------------- Resti ng--------------------- Fi nal redevelopment---------

Total bacterial count (cells per 100 mL) 

3,150 

2,600 

5,000 

5,800 

1,000 

13,100 

3, 700 

5,400 

: however, a significant increase in bacterial numbers was 

: not noticed. 

At the end of the 2-month resting stage, an additional 

2 Mgal of reclaimed water was injected. The carbon filtration stage was employed during this phase, and COD 

and MBAS concentrations were 9 and 0.07 mg/L, as opposed to 22 and 0.55 mg/L during the first phase. COD 

concentration at the well 20 feet away did not change 

during the second phase, although MBAS concentration 

declined linearly from nearly 0.17 mg/L at the start of 

the second phase to about .0.07 mg/L after the injection· 

of 2 Mgal. 

A volume of water about 1.5 times the volume injected 

was withdrawn from the injection well after the second 

phase to restore the ground-water quality to pretest conditions. Ku and others (1975) calculated mass balances 

for the constituents as shown in table 13. 

The near-total recovery of nitrogen suggests only limited assimilation by microbes during the· test. If it is assumed that microbial assimilation and mineralization accounted for the entire COD loss and that the pertinent 

reactions involved carbon at the oxidation level of a carbohydrate, then the calculated amount of carbon assimilated in these processes was 172 lb. According to Stanier 

and others (1970), the maximum cell yield is at most 50 

percent of the total of carbonaceous substrate converted 

by combined respiration and cell synthesis; hence, the 

microbial cell mass produced was no more than 86 lb. 

Since the carbon/nitrogen ratio in bacterial cells is normally about 8, it is seen that only about 11lb of nitrogen 

could be accounted for in this way, although the total loss 

was 368lb. 

TABLE 13.-Mass-balance data on chloride, total nitrogen, 

methylene blue active substances, and chemical oxygen demand, tests RWJO and RWJOA 

[Modified from Ku and others, 1975] 

Constituent 

Ch 1 ori de---------------

Total nitrogen (N)-----

Methylene blue active 

substances (MBAS)----

Chemi cal oxygen 

demand (COD)---------

Mass, in kilograms In water In water injected recovered 

2,100 

755 

11.2 

494 

1, 780 

588 

4. 9 

207 

Percentage In water In water injected recovered 

84 

78 

43 

42 

(assuming 

100-percent 

recovery of ' 

chloride) 

100 

93 

51 

50 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E15 

Because MBAS and COD concentrations at the 20- high bacterial densities would be expected. However, 

foot-distant observation well changed little during the 2-

month resting period, it is concluded that the major part 

of the microbial activity associated with the system remained in the near vicinity of the injection well. Apparently, significant concentrations of soluble and particulate organic materials capable of sustaining anaerobic 

microbes did not travel as far as 20 feet into the formation. 

· the above test results suggest that little soluble biotransformable material remained in the reclaimed water. 

Sulfate-reducing bacteria were detected in half the 

samples collected during test RW13. The presence of 

H2S in native formation water suggests that sulfate-reducing bacteria might be indigenous to the aquifer. The 

effect of an increased potential nutrient supply upon the 

! activity of these organisms is not clear from the results 

of these tests. It is possible, however, that an increased 

I level of H2S could result if a higher level of nutrients 

j were available to those organisms. Also, the presence of 

• sulfate-reducing bacteria indicates a relatively low Eh, 

The final injection test (RW13) began on October 24, 

1972, and ended on May 11, 1973. Results of test RW13 

are given in V ecchioli and others (1975), and a summary 

log of the test was presented by Sulam (1973). In general, the results of test RW13 were similar to those of 

most earlier tests. Reclaimed water had effectively displaced the formation water at the observation well 20 1 

feet from the injection well after 5 x 105 gal had been 

injected. Some difficulties with COD measurement arose 

during the test, but the MBAS. measurements indicated 

that both substances traveled at roughly the same rate 

as the reclaimed-water front. The steady-state concentration of MBAS at the observation wells 20 feet and 100 

feet away was close to that in the injected water. Total 

nitrogen levels in water at both observation wells were 

close to those in the injected water. 

Total bacteria count was measured in both observation 

wells during test RW13 (table 14). 

Bacterial densities in the observation wells were highly 

variable during test RW13. Densities were generally 

higher at the well 20 feet away than at the well 100 feet 

away, and densities at the nearer well were generally 

somewhat lower during test RW13 than during test 

RW10, which may reflect the reduced COD levels in the 

injectant during test RW13. If large amounts of microbial nutrients had been transported into the formation, 

TABLE 14.-Microbiological quality of water from observation 

wells 20 and 100 feet from injection well, test RW13 

[Total bacteria counts given as cells per 100 mL; sulfate reducers given 

as most probable number per 100 mL. ND, not determined] 

Well N7886 Well N7890 

Date Total Sulfate Date Total Sulfate bacteria reducers bacteria reducers 

11- 7-72---- 320 

11-12-72-'--- 70 

11-21-72---- 1 <30 -- -- 11-29-72---- 1,400 NO 11-28-72 4 NO 

12-15-72---- 6,700 40 12- 5-72 400 30 

12-20-72---- 1 30 12-19-72 2 30 1- 3-73---- 2,000 Nb 1-10-73---- 5 30 1- 9-73 73 

1-17-73---- 14 40 -- -- 1-31-73---- 30 186 1-30-73 14 80 . 

2- 7-73---- 30 2- 6-73 3 40 

2-13-73---- 690 NO 2-12-73 167 NO 3- 4-73---- 49 NO 3-20-73 7,100 NO 

3-29-73---- 136 23 3-28-73 38 23 

4- 3-73 206 NO 4-11-73 4 

5- 2-73---- 12 ND 5- 3-73 220 43 

5- 9-73---- 340 NO 

i which indicates that oxygen and chlorine were absent. 

PUBLIC HEALTH CONSIDERATIONS 

Introduction of pathogenic organisms and their dis-

. semination through the surrounding aquifer is one of the 

primary concerns when treated sewage is injected directly into ground-water bodies. The movement of hac-

. teria through aquifers has been thoroughly studied. 

' Romero (1970) summarized the characteristics of bacterial movement through porous media. A partial listing of 

these characteristics follows: 

1. Bacteria travel with the flow of water; they do not 

move against the hydraulic gradient. 

2. The rate of bacterial removal by filtering is a function of the nature of the aquifer materials. Aquifer 

materials best suited for removal of biological contaminants are silt and fine sand with high clay content. 

3. The rate of bacterial removal by filtering can be 

characterized by a function called the filter efficiency of the aquifer (called filterability by California State Water Pollution Control Board, 1954, 

and Romero, 1970). 

4. Typically, the maximum distance that bacteria 

travel in porous materials ranges from 50 to 100 

feet. 

5. Under favorable conditions (not necessarily applicable to the Magothy aquifer), bacteria may survive as long as 5 years. 

In December 1970, during test RW8, unchlopnated 

reclaimed water containing substan'tial numbers of total 

coliforms, fecal coliforms, and fecal streptococci was injected for a 10-day period. Water from the observation 

well N7886, 20 feet from the injection well, was monitored for specific conductance to determine the arrival of 

injected water. Results showed that the injected water 

had almost displaced the native water at the nearest observation well after the second day of injection. 

Neither fecal-coliform nor fecal-streptococcal bacteria 

were found in any samples collected from the observation 
E16 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

TABLE 15.-Bacterial colony counts of water sampled during 

and after test RWB, with unchlorinated water 

[From Vecchioli and others, 1972. All results in number of cells per 

100 mL; (e), estimated count based on nonideal colony count] 

Date 

12- 1-70--------

12- 2-70--------

12- 3-70-------- 12- 4-70--------

12- 5-70-------- 12- 6-70--------

12- 7-70-------- 12- 8-70-------- 12- 9-70--------

12-10-70--------

1- 5-71--------

12- 1-70-------- 12- 2-70-------- 12- 3-70-------- 12- 4-70-------- 12- 5-70-------- 12- 6-70-------- 12- 7-70-------- 12- 8-70-------- 12- 9-70--------

12-10-70--------

1- 5-71--------

12- 1-70 12- 2-70-------- 12- 3-70-------- 12- 4-70--------

12- 5-70-------- 12- 6-70-------- 12- 7-70-------- 12- 8-70-------- 12- 9-70--------

12-10-70--------

1- 5-71--------

Volume of 

injected 

water 

(gal) 

9, 700 

27,000 

10,000 

47,000 

60,000 

61,000 

60,000 

54,000 

55,000 

200 

1,200 

2,000 

1, 500 

750(e) 

1,100 

2,200 

960 

1(e) 

80 

ll(e) 

39 

31 

30 

10(e) 

15(e) 

22 

Observation wells 

20 feet 

from 

injection 

well 

Total coliform 

19 

'<1 

<1 

<1 

1(e) 

1(e) 

1(e) 

<1 

<1 

--

4(e) 

Fecal coliform 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

Fecal streptococcus 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

100 feet 

from 

injection 

well 

<1 

<1 

1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

<1 

Injection 

well' 

83,000 

3,200 

2,800 

10(e) 

57 

32 

'Water repumped from injection well after end of injection on Dec. 10, 1970. 

'All counts reported as <1 represent no colonies counted in a 100-mL sample. 

wells during test RW8 (table 15). Low numbers of total 

coliform bacteria were found in the observation well on 

the 2d, 6th, 7th, and 8th days of the test and also in a 

sample obtained from that well 26 days after the end of 

the test. 

Rate of travel of bacterial cells through an aquifer is 

controlled by complex interactions of physical, chemical, 

and biological factors. Nevertheless, in an investigation 

of the travel of pollutants, the California State Water 

Pollution Control Board (1954) found that, at maximum 

penetration of coliforms into the aquifer, the logarithm 

of the coliform density decreased linearly with. distance 

from the injection well. The Board called this property of 

impeding bacterial travel the filterability of the aquifer, 

herein called the coefficient of filter efficiency. 

The filter efficiency of the aquifer is defined by the following equation: 

Log,N2>, = LogN~\- F (r2 - r1) 

where: 

N 1 = most probable number of organisms at any 

sampling point in the aquifer (r1); 

N2 =most probable number at any other point (r2); 

r1, r2 =distance between sampling points and. point of 

injection with r2>r1; and 

F = coefficient of filter efficiency of the aquifer. 

When the equation is applied to the Bay Park observations with values of 50,000 cells per 100 mL for the 

water injected (r1 = 0), and 1 cell per 100 mL for water 

from the observation well 20 feet from the injection well 

(r2 = 20), the calculated coefficient of filter efficiency of 

the Magothy aquifer is 0.23/foot. The coefficient is conservatively low because the coliform density used in the 

calculation (1 per 100 mL) was the highest count observed during the test. The high first-day count was not 

included in the interpretation. 

Fractional reduction in bacterial density per foot of 

travel may be determined from the following formula 

(California State Water Pollution Control Board, 1954, 

p. 106): 

-F = log(1-R) 

where R = fractional reduction of bacteria per foot of 

travel. With an F value of 0.23, the computed R value is 

0.41. This is interpreted as a 41-percent reduction in bacterial count per foot of travel. 

In the California study, the coefficient of filter efficiency varied somewhat with direction of water movement from the injection well, but the average R values 

ranged from 19 to 24 percent (California State Water 

Pollution Control Board, 1954, p. 107). The aquifer under 

test in the California study, a stratum of sand and pea 

gravel, had a hydraulic conductivity of about 250 ft/d. 

The injection zone in the Magothy aquifer at Bay Park, 

a slightly silty fine to medium sand with thin beds of 

coarse sand, had an average hydraulic conductivity of 

about 130 ft/d (G. D. Bennett, written commun., 1970). 

On the basis of grain size and hydraulic conductivity, the 

greater fractional reduction values found for the Magothy aquifer seem reasonable. 

The California State Water Pollution Control Board 

Study of 1954 noted that coliform counts in water from 

observatiqn wells reached maximum values and then decreased as injection continued, possibly because of the 

filtering effect of a mat that formed in the vicinity of the 

injection well during injection. Some bacteria in the injectant were presumably captured by the filter mat, 
EFFECTS OF RECHARGING THE MAGOTHY AQUIFER E17 

which consisted of solids accumulated at the interface between the injection well and the aquifer (California State 

Water Pollution Control Board, 1954, p. 153). Formation 

of a filter mat and (or) microbial slime deposits was noted 

also in the Bay Park study. Bacterial capture by the filter mat complicates evaluation of computed aquifer filter 

efficiency. However, this effect can be minimized by using bacterial-density data from earlier in the injection period, before the filter mat had developed appreciably. 

The computed coefficient of filter efficiency for the early 

period would approximate the filtration component related to the effective porosity of the aquifer. 

In this study, a significant number of indicator bacteria survived for at least 26 days in the vicinity of the 

injection well. Virtually undiluted injected water reached 

the observation well20 feet from the injection well within 

2 days. Only a nominal coliform count was observed in 

this water. If the bacterial cells had been traveling at a 

rate comparable with that of the injectant, significant 

coliform counts should have been observed on the second 

day. Large diminution of counts as a result of die-off 

would not be expected in only 2 days because the bacteria could survive for as long as 100 days (Romero, 1970, 

p. 42). Therefore, filtration phenomena rather than organism die-off were probably the primary reason for the 

large reduction in numbers. Similar conclusions were 

reached by the California State Water Pollution Control 

Board (1954, p. 113). 

The results of the Bay Park study are consistent with 

the conclusion reached in other studies (Romero, 1970) 

that coliform bacteria travel only short distances in finegrained material. Comparatively little work has been 

done with bacterial species other than coliform. Results 

of such studies suggest, however, that other species behave in the same way as the coliforms, and there is no 

reason to suppose that they would be more mobile than 

the coliforms. 

SUMMARY 

· Tertiary-treated sewage (reclaimed water) was injected into a fine to medium sand aquifer through a well. 

As long as a chlorine residual of 2.5 mg/L or greater was 

maintained in the injectant, interference from biological 

growth was minimal. The effect of residual chlorine did 

not extend more than 12 feet into the aquifer from the 

injection well, as indicated by the isolation of significant 

numbers of bacteria in water recovered from the injection well after relatively short pumping periods. 

The composition of the bacterial population in the formation is not the same as that in the injectant. The proportion of coliform bacteria in the aquifer population was 

consistently much lower than in the injectant. 

During injection, essentially aerobic assimilation of organic matter filtered from the injectant occurs in the vicinity of the well bore/aquifer interface. Continued microbial activity after cessation of injection leads to 

establishment of anaerobic conditions and the appearance of obligate anaerobic bacteria. Biotransformation 

under anaerobiosis can decompose the mat and thereby 

diminish the effects of clogging built up during injection. 

Soluble organic material in the reclaimed water may 

be adsorbed onto clay and lignite in the formation. Additional soluble organic matter may be released by microbial action onto insoluble particulate organic matter in 

the clogging mat. The soluble matter could support an 

indigenous microbial population in the formation. 

Travel of bacterial cells in the Magothy aquifer at Bay 

· Park during injection was found not to exceed distances 

of 20 feet laterally from the injection point. 

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E18 DEEP-WELL RECHARGE AT BAY PARK, N.Y. 

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-r:. U.S. Government Printing Office: 1979-281-359/80