Artificial Recharge to a 

Freshwater-Sensitive Brackish-Water 

Sand Aquifer, Norfolk, Virginia 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 939 

Prepared in cooperation with the 

Department of Utilities, 

Norfolk, Virginia 

Artificial Recharge to a 

Freshwater-Sensitive Brackish--wrter 

Sand Aquifer, Norfolk, Virginia 

By DONALD L. BROWN and WILLIAM D. SILVEY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 939 

Prepared in cooperation with the 

Department of Utilities, 

Norfolk, Virginia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1977 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Brown, Donald L., 1938-

Artificial recharge to a freshwater-sensitive brackish-water sand aquifer, Norfolk, Virginia. 

(Geological Survey Professional Paper 939) 

Bibliography: p. 

Supt. of Docs. no.: I 19.16:939 

1. Water, Underground-Virginia-Norfolk region-Artificial recharge. 

I. Silvey, William D., joint author. II. United States Geological Survey. III. Norfolk, Va. Dept. of Utilities. IV. Title. 

V. Series; United States Geological Survey Professional Paper 939. 

TD404.B7 551.4'9 76-20538 

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

Washington, D.C. 20402 

Stock Number 024-001-02920-1 
CONTENTS 

Page 

English-metric equivalents .......................................................... . v Deterioration of aquifer hydraulic properties ............................ .. 

Abstract ....................................................................................... .. Head buildup .......................................................................... .. 

Introduction ................................................................................. . Excess head buildup due to temperature and viscosity ....... . 

Location of area ...................................................................... .. Excess head buildup due to hydraulic conductivity 

Previous investigations ............................................................ . 1 deterioration ...................................................................... . 

Acknowledgments .................................................................... . 2 Current-meter traverses ............................................................ . 

Well field ...................................................................................... . 3 Specific capacity ...... ~ ............................................................... . 

Injection well I (IW-1) ........................................................... .. 4 Conductivity surveys ............................................................... .. 

Injection well 2 (IW-2) ........................................................... .. 4 Aquifer heterogeneity .......................................................... .. 

Observation wells ..................................................................... . 4 Water quality ............................................................................... . 

Annular-space well (ASW) .................................................. .. 4 Comparison of the chemistry of city and formation water .... .. 

Observation well 2 (OW~2) .................................................. . 4 Water sampling ........................................................................ . 

Observation well 3 (OW-'3) ................................................. .. 4 Analytical results ...................................................................... . 

Test well 1 (TW-1) ............................................................... . 4 Changes in the concentrations of calcium, magnesium, and 

Geology and hydrology of the injection sand ........................... .. 4 sodium ............................................................................... . 

Aquifer tests ................................................................................. . 9 Effect of cation exchange on formation day during 

Injection system ........................................................................... . II injection ........................................................................... .. 

Pre-injection calibrations ........................................................... .. 12 Laboratory determination of hydraulic conductivity 

Current meter ........................................................................... . 12 deterioration ..................................................................... .. 

Transducers .............................................................................. . 14 Injection test 4 ............................................................................. . 

Turbidity .................................................................................. . 14 Injection specific capacity ....................................................... .. 

Water-quality monitor ............................................................. . 14 Current-meter traverses ............................................................ . 

Injection tests .............................................................................. .. 14 Cause of clogging of IW ...:2 during injection phase of test 4 

Injection test 1 ......................................................................... .. 14 Chemical effects observed during withdrawal phase of test 4 

Injection test 2 ......................................................................... .. 14 Analysis of project ...................................................................... .. 

Injection test 3 ......................................................................... .. 15 References cited ............................................................................ . 

ILLUSTRATIONS 

Page 

15 

16 

16 

17 

19 

28 

28 

31 

32 

32 

32 

33 

35 

36 

36 

39 

40 

42 

43 

46 

49 

53 

Page 

FIGURE I. Map showing location of test site.................................................................................................................................................... 2 

2. Sketch showing Norfolk injection project well field, Moore's Bridges Filter Plant ...................................................................... 3 

3. Diagrammatic sketch of injection well IW-'2 .................................................................................................................................. 5 

4. Geophysical logs and stratigraphy of test well TW-1..................................................................................................................... 6 

5. Graph showing composite cumulative curve of particle-size distribution of the injection sand................................................... 7 

6. Geophysical logs of injection zone, test well TW-1........................................................................................................................ 8 

7. Photograph showing thin section of a part of the injection sand (955 to 975 ft or 291 to 297 m)................................................ 10· 

8. Hydrograph of injection well IW-2 showing specific capacities derived from May 1970 step-drawdown test............................. 12 

9. Graph showing current-meter traverses in injection well IW,_2 prior to injection of freshwater.................................................. 13 

10. Graphs showing theoretical and measured head data for injection well IW-2 and observation well OW-'3, test 1 .................. ,... 18: 

11. Graph showing pre-injection and post-injection hydraulic gradients............................................................................................ 19 

12. Graph of current-meter traverses in injection well JW::o:2 of the pre-injection flow and the flow after 5 hours of injection 

during test 1 .. . ... . .. ... . ......... ...... .. .. . . .... ... . . . . .... ... .... . . .. .. ..... . . ............... .... . . . . . .... .. . . . . . .. .... . . . . .. .. .. . . . . . ...... . .... . . . . .... .. . . ......................... ... .. 20 

13. Graph showing current-meter traverses in injection well JW-:.2 of the pre-injection flow and the withdrawal flow during 

test 1............................................................................................................................................................................................... 21 

14. Grap~ .sh~wing ~rrent-meter traverses in injection well IW-2 of the pre-injection flow, test 2, and the flow after 24 hours 

of InJection durtng test 2 ............................................................................................................... ................... ............................ 23 

15. Graph showing current-meter traverses in injection well IW'-2 during the injection phase, test 2 ..................................... ......... 24 

16. Graph showing current-meter traverses in injection well IW-2 of the pre-injection flow and the withdrawal flow, 

test 2............................................................................................................................................................................................... 25 

17. Graph showing current-meter traverses in injection well JW...:2 of the pre-injection flow, test 2, and the flow after 75 

hours of withdrawal pumping during test 2. ........... ... .... . . . ... ........ .... . ... . . . ... .. . .. . .. . .. . .. . . . . . . . .. . . . . . ...... .... . .. .. ..... . . . .. .. ... .. .. . . ............ ... .. 26. 

III 
IV CONTENTS 

Page 

FIGURE 18. Graph shmying current-meter traverses in injection well IW-2 of the pre-injection, injection, and withdrawal flows, 

test 3............................................................................................................................................................................................... 27 

19. Graph showing changes in injection rate with time during tests l, 2, and 3 ................................................................................ 28 

20. Graph showing pre-injection withdrawal specific capacity of injection well IW-=2 and injection specific capacity during 

tests l, 2, and 3 .............................................................................................................................................................................. 29 

21. Graph showing conductivity profiles in observation well OW-3 during injection phase, test 2.................................................. 30 

22. Graph showing conductivity profiles in observation well OW-'3 and current-meter traverse in injection well IW-2, 

test 2............................................................................................................................................................................................... 31 

23. Graph of conductivity profiles in observation well OW.:..3, test 4................................................................................................... 32 

24. Graph of conductivity profiles in observation well OW-2, test 4................................................................................................... 33 

25. Lithologic section showing injection zone in injection well IW-2 and zones of detection of freshwater in observation 

wells in OW -'2 and OW -3 .. .. .... . .. . . ............ ..... .... .. ..................... ...... ... .............. ..... ..... ......... .... ......... .............. .... ... ......... .... . ......... 34 

26. Graph showing chloride, sodium, and dissolved solids versus specific conductance of recovered injected water from 

tests l, 2, and 3 .............................................................................................................................................................................. 35 

27. Graph showing calcium concentration and sodium to chloride ratio versus specific conductance during the recovery of 

injected water, tests l and 2 ... ....................................................................................................................................................... 37 

28. Graph showing effects on the hydraulic conductivity caused by injecting city water containing various chemicals into 

a core saturated with formation water.......................................................................................................................................... 38 

29. Graph showing variations in specific capacity of injection well IW-2 during injection tests...................................................... 40 

30. Graph showing specific capacity of injection well IW-2 prior to any injection of freshwater and variation of specific 

capacity during test 4.................................................................................................................................................................... 41 

31. Graph showing variation of specific capacity in injection well IW-2 for injection phases 5, 6, and 7, test 4 ............................. 42 

32. Graph showing variation of specific capacity in injection well IW-2 for injection phases, test 4 ............................................... 43 

33. Graph showing current-meter traverses in injection well IW-2 of pre-injection and injection flow, test 4................................. 44 

34. Graph showing current-meter traverses in injection well JW.:..2 of pre-injection, injection, and withdrawal flow, test 4 ........... 45 

35. Graph showing current-meter traverses in injection well IW-2 of withdrawal flow, test 4 .......................................................... 47 

36. Graph showing changes in injection and withdrawal flow and conductivity profile in injection well IW-2 after 8 Mgal 

(30,300 m3) withdrawn, test 4........................................................................................................................................................ 48 

37. Graph showing changes in injection and withdrawal flow and conductivity profile in injection well 1W-2 after 15.1 Mgal 

(57,150 m3) withdrawn, test 4......................................................................................................................................................... 49 

38. Graph showing changes in chloride concenu·ation with volume of water withdrawn, test 4 ............ ........................................... 50 

39. Sketch map showing possible well locations for a five-well injection field at Moore's Bridges Filter Plant............................... 52 

TABLES 

Page 

TABLE l. Heavy minerals identified from cores from injection zone of observation well OW-3.................................................................. 9 

2. Statistical parameters of the injection sand..................................................................................................................................... 9 

3. X-ray diffraction analysis of core samples from injection zone, observation well OW-3.............................................................. 9 

4. Thickness and sand-shale ratios for the injection zone within the well field................................................................................ 9 

5. Specific capacities at various pumping rates after l hour for the injection sand in test well TW-1 and injection well 

IW-2 .............................................................................................................................................................................................. ll 

6. Specific capacity of injection well IW-2 during the injection phase of tests l, 2, and 3............................................................... 30 

7. Concentration of major constituents from Moore's Bridges Filter Plant city water and formation water.................................... 32 

8. Variations in water chemistry of mixed freshwater and formation water during withdrawal, injection tests I and 2................. 36 

9. Sodium to chloride ratio and associated concentrations of calcium in samples collected during injection tests 1 and 2 ............ 36 

10. Effect of water chemistry on laboratory hydraulic conductivity for core samples from injection zoneof observation well 

OW-3 ..................................................................................................................................................................... :....................... 39 
CONTENTS 

ENGLISH-METRIC EQUIVALENTS 

[Although the conversion factors are shown to four significant figures, the metric equivalents in the text of this paper a~e 

shown only to the number of significant figures consistent with tht· values o( the English units] 

inch (in) 

foot (ft) 

gallon (gal) 

gallon (gal) 

English unit 

million gallons (Mgal) 

gallon per minute (gal/min) 

gallon per minute per foot (gal min-1ft-1)= 

foot per day (ft/d) 

cubic foot per day per foot (ft3d-1ft-1) 

pound per square inch (lb/in2) 

horsepower 

Metric equivalent 

25.4 

.3048 

3.785 

.003785 

3785 

.06309 

.207 

.3048 

.0929 

6.8948 

.7457 

millimetres (mm) 

metre (m) 

litres (I) 

cubic metre (m3) 

cubic metres (m3) 

litre per second (1/s) 

litre per second per metre (I s-1m-1) 

metre per day (m/d) 

cubic metre per day per metre (m3d-1m-1) 

kilopascals (kPa) 

kilowatt (kW) 

v 

ARTIFICIAL RECHARGE TO A FRESHWATER-SENSITIVE 

BRACKISH-WATER SAND AQUIFER, NORFOLK, VIRGINIA 

By DoNALD L. BROWN and WILLIAM D. SILVEY 

ABSTRACT 

During late 1971 and early 1972, three injection and withdrawal tests 

were made at the Norfolk, Va., injection site. In test 1, freshwater was 

injected at the rate of 400 gal/min (25 lis). The specific capacity of the 

well decreased from 15.4 to 9.3 gal min-1ft-1 or 3.2 to 1.9ls-1m-1 of drawdown at the end of 260 minutes of injection. In test 2, the initial injection 

rate of 400 gal/min (251/s) decreased to 215 gal/min (141/s) after 7,900 

minutes of injection. The specific capacity dropped from 14.2 to 3. 7 gal 

min-1ft-1 or 2.9 to 0.77 ls-1m-1 during the test. At the start of test 3, the 

aquifer accepted water at a maximum rate of 290 gal/min ( 181/s ), but the 

injection rate decreased to 100 gal/min (6.3 lis) within 150 minutes and 

continued to decrease to a low of 70 gal/min ( 4.41/ s) after approximately 

1,300 minutes. The specific capacity decreased from 3. 7 to 0.93 gal 

min-1ft-1 or 0. 77 to 0.19ls-1m-1. Attempts at redevelopment of the injection well failed to improve the specific capacity. 

Current-meter surveys made during injection and withdrawal 

pumping indicate that the reduction in flow and specific capacity were 

due to a uniform reduction in the hydraulic conductivity of all contributing zones in the aquifer and not to a complete shutoff of flow from 

selected parts of the aquifer. The hydraulic and chemical data indic;ate 

that the uniform loss of specific capacity of the contributing zones was 

due to dispersion of interstitial clay and that this clay would readily 

respond to chemical treatment for the purposes of decreasing or 

eliminating dispersion. 

Subsequently, a pre-flush of 3,000 gal ( 11 m3) of 0.2N calcium chloride 

solution was injected in front of the freshwater prior to injection test 4. 

The initial specific capacity was 4.3 gal min-1ft-1 or 0.89ls-1m-1 and, by 

redevelopment pumping during injection, the specific capacity was 

improved to 5.3 gal min-1ft-1 or l.l ls-1m-1. After injecting 4 Mgal 

(million gallons) (15,100 m3) of freshwater, an additional 3,000 gal (II 

m3) of 0.4N calcium chloride solution was added to the formation. A total 

of 20,146,100 gal (76,300 m~) of freshwater was injected during test 4. The 

specific capacity remained fairly constant throughout the injection of the 

first 16 Mgal (60,600 m3), indicating the stabilization of interstitial clay in 

the aquifer was accomplished. After 16 Mgal (60,600 m3) had been 

injected, particulate clogging began occurring, and the specific capacity 

fell to less than 3 gal min-1£t-1 or 0.62 ls:-1m-1. 

Current-meter traverses made during test 4 injection showed that 

because of the deterioration of aquifer properties caused by tests 1, 2, and 

3, the calcium chloride preferentially treated the most permeable part of 

the aquifer. As a result, a combination of dispersion and particulate 

clogging caused the lower 40ft (12m) of the aquifer to be plugged so that 

the freshwater selectively injected into the upper part of the aquifer. 

As withdrawal pumping began, the lower part of the aquifer became 

unclogged resulting in the brackish formation water mixing with the 

freshwater. Only 20 percent of the volume injected during test 4 was 

recovered as potable freshwater. Tests 1 and 2 showed that if clogging of 

the screen in the injection well can be prevented, as much as 85 percent of 

the injected water can be recovered and will remain within the drinkingwater standards of the U.S. Public Health Service (1962). 

Treatment of the injection well with a clay stabilizer prior to the injection of any freshwater will minimize clogging and increase recovery of 

freshwater. If plugging of the screen can be prevented so that injection 

and withdrawal flow patterns remain similar, the storage of freshwater in 

a brackish-water sand aquifer is feasible. 

INTRODUCTION 

The water supply for the city of Norfolk, Va., comes 

from surface impoundments in the independent cities of 

Nansemond, Norfolk, and Virginia Beach. During the 

winter months, when water demand is low and reservoirs 

are full, water must be diverted from the reservoirs and 

allowed to escape to the ocean with the potential use of the 

water unfulfilled. It has been estimated (Schweitzer, oral 

commun., 1968) that as much as 2.5 Bgal (billion gallons) 

(9,460,000 m3) of water per winter quarter could be avai1-

able for use if sufficient storage areas were available. 

The U.S. Geological Survey and the city of Norfolk 

entered into a cooperative program to determine if it 

would be possible to utilize the water presently flowing to 

waste by processing it in the treatment plants and storing 

it underground in aquifers containing saline water. The 

freshwater would then be retrieved during the summer 

months when peak water demands and low water levels in 

reservoirs place strains on the present water system. 

LOCATION OF AREA 

The Norfolk injection site is at Moore's Bridges Filter 

Plant, Norfolk, Va. (fig. 1). Excess water from the filter 

plant supplies the injection project. The water is taken 

from the treatment system after it has been chlorinated, 

settled, and filtered, but prior to the final chlorination and 

liming. 

PREVIOUS INVESTIGATIONS 

The first attempt at artificial recharge of freshwater into 

brackish-water aquifers in the Coastal Plain of Virginia 

was conducted by D. J. Cederstrom (Cederstrom, 1957) in 

1946 at Camp Peary. During that experiment, water was 

injected into a brackish-water aquifer over a period of 85 

days. The well into which the water was injected had 

screens in the intervals of 430 to 440ft (131 to 134m) and 

450 to 475 ft (137 to 145m) below land surface. The well 
2 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

\ 

0 1 000 2000 3000 FEET \ 

--~lr-~~~~1 \ 1 I \ 

0 300 600 900 METRES \ 

\ 

EXPLANATION. 

eiW-2 

Injection well and number 

eTW-1 

Test well and number 

eOW-3 

Observation well and number 

I 

r 

VIRGINIA /f' .. ~J / 

, 

< 

,A ,.._/ ...... J , \ " "' ~ "-"'" ~ ... 

I 

;' 

83° ... ~ 

37o +J~ 0 100 MILES 

,,. I I I I 

\ 

\ 

\ 

\ 

~ _________ r---z _______________________________ 0 100 KILOMETRES ___,. 

FIGURE I.-Location of test site. 

clogged during injection, but the withdrawal phase I ACKNOWLEDGMENTS 

indicated the concept of recharge into brackish-water Charla Smith must be singled out for her competent 

aquifers might be feasible. assistance in the field work and data compilation. Her 
WELL FIELD 3 

ability to keep the equipment functioning is directly 

responsible for much of the success of the project. The 

authors wish to acknowledge the assistance rendered by 

many Survey associates, but especially Robert L. Wait for 

his collaboration in the interpretation of current-meter 

data, Frank Koopman, Robert Wait, Jim Fickens, and 

Gordon Bennett for help in designing the injection 

system, Joe Pearson, Ivan Barnes, and Warren Wood for 

assistance in interpretation of geochemical data, and 

Francis Riley and John Roper for providing hydraulic 

conductivity tests on cores from the injection zone. Special 

thanks must also be given to former city councilman Paul 

Schweitzer and to James Kiracofe, chemist for the city of 

Norfolk, and to the personnel of the Norfolk Department 

of Utilities. Advice on the problems of clay dispersion was 

generously given by M. G. Reed, Chevron Oil Field 

Research; 0. C. Baptist, U.S. Bureau of Mines; Wayne 

Hower, Halliburton; Bill Coulter, Dowell Division of 

Storage 

Tanks 

OW-3 

Dow Chemical; and Charles Hewitt, Marathon Oil 

Company. Parts of the information used in this report has 

been previously published by the American Association of 

Petroleum Geologists as a paper by the authors entitled 

''Underground Storage and Retrieval of Fresh Water from 

a Brackish-Water Aquifer" (Brown and Silvey, 1973). 

Thanks are given to AAPG for use of these data in this 

report. 

WELL FIELD 

The well field (fig. 2) consists of the injection well 

(IW -2) and four observation wells. The observation wells 

are designated as follows: Annular-space well (ASW); 

observation well2 (OW-2); observation well3 (OW-3); and 

test well I (TW-1). All wells, with theexceptionofTW-1, 

were constructed of fiberglass casing with fiberglass or 

stainless-steel screens so that the materials used in the well 

construction would contribute no chemical influences in 

the experiment. 

I 

FIGURE 2.-Norfolk injection project well field, Moore's Bridges Filter Plant. 
4 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

INJECTION WELL 1 (IW1 1) 

IW-1 was the initial attempt at constructing an 

injection well. The 18-in (460-mm) fiberglass casing 

collapsed at a depth of about 51 ft (16 m) below land 

surface, prior to cerpenting the casing in place. Salvage 

attempts failed, and the well was abandoned and filled 

with cement. The well is 25ft (8 m) northeast of IW-2 and 

is in the same plane as IW-2, OW-3, and OW-2. 

INJECTION WELL 2 (IW-2) 

The design and construction of the injection well is 

shown in figure 3. The wall thickness of the 18-in (460-

mm) casing is 0.5 in ( 13 mm) and has a theoretical ultimate 

collapse strength of 70 lb/in2 (483 kPa). The wall thickness 

of the 8-in (200-mm) diameter casing is 0.4 in (10 mm) and 

has an ultimate collapse strength of 300 lb/in2 (2068 kPa). 

The lowermost sections of both the 8-in (200-mm) and the 

1.5-in (38-rrnu) pipe have stainless-steel nipples wound 

into the fiberglass. The stainless-steel screens are welded to 

the nipples using stainless-steel welding rods. Eighty feet 

(24 m) of wire-wrapped, 40-slot, stainless-steel screen is 

attached to both the 8-in (200-mm) casing and the 1.5-in 

(38-mm) pressure-monitoring pipe. (The 1.5-in (38-mm) 

well is described in the section "Annular-Space Well".) 

Both screens have 10ft (3m) of blank stainless-steel pipe at 

the bottom for sand traps. The slot size of the screens was 

determined from mechanical analysis of the sand 

recovered from cores taken in the injection zone. The 

entire injection zone from 896 to 976ft (273 to 297m) below 

land surface was screened. 

A 4-in (100-mm) fiberglass instrument access pipe (fig. 

3) extends below the pump bow Is and is used for insertion 

and withdrawal of the current meter and other 

monitoring equipment as needed. Water is injected into 

the aquifer through a 4-in ( 100-mm) fiberglass line that 

enters the 18-in (460-mm) casing at a depth of 125ft (38m) 

below land surface. 

OBSERVATION WELLS 

ANNULAR-SPACE WELL (ASW) 

The purpose of the 1.5-in (38-mm) annular-space well 

(ASW) is to monitor pressure-head changes in the gravel 

pack of the injection well during injection and withdrawal tests. To accomplish this, the screen was attached 

parallel to, but separated from, the screen of the injection 

well (IW-2) by l-in (25-mm) wooden blocks. The screen is 

1.25 in (32 mm) in diameter, heavy-duty, wire-wrapped, 

40-slot, stainless steel. The entire injection zone is screened 

from 896 to 976ft (273 to 297m) below land surface, with a 

10-ft (3-m) fill-up pipe from 976 to 986ft (297 to 300m) that 

is a sand trap. 

OBSERVATION WELL 2 (OW-2) 

OW-2 is 75 ft(23 m) northeast of the injection well and 

lies in a plane t~rough IW -2 and OW'--3. The casing and 

screen are 4.37-in (111-mm) inner diameter, epoxy-resin 

fiberglass having a wall thickness of 0.25 in (6.3 mm). The 

screen was made by sawing horizontal slots 0.05 in (1.3 

mm) wide in a regular section of casing. The entire 

thickness of sand is screened from 900 to 990ft (274 to 302 

m) below land surface, and there is a 10-ft (3-mm) section 

of fill-up pipe from 990 to 1,000 ft (302 to 305 m) below 

land surface. The well is gravel packed to a height of 60ft 

(18m) above the screen and is cemented from that point 

upward to land surface. 

OBSERVATION WELL 3 (OW-3) 

OW-3 is50ft(l5m)southwestoftheinjection well. The 

construction of OW-'3 is identical to that of OW-2, with 

the exception that 81 ft (25 m) of saw-slotted screen was 

installed. The entire thickness of sand is screened from 900 

to 981ft (274 to 299m) below land surface, and there is a 10-

ft (3-m) fill-up pipe from 981 to 991ft (299 to 302m) below 

land surface. 

TEST WELL 1 (TW-1) 

TW-1 is 415ft (126m) northwest of the injection well. 

TW -1 was a test well originally drilled to a depth of 2,587 

ft (788 m) to determine the local geology, to define an 

injection zone, and to determine whether fresh ground 

water was present at depth (fig. 4). The water became 

increasingly saline with depth and was brine below 2,000 

ft (610 m). TW-1 was backfilled with cement to 1,000 ft 

(305 m) below land surface and was completed as an 

observation well, partially penetrating the injection zone. 

The hole was under-reamed to a diameter of 24 in (610 

mm) from 890 to 970ft (271 to 296m) below land surface. 

Sixty feet (18 m) of 6-in (150-mm) stainless-steel shutter 

screen (0.055-in or 1.4 mm openings) was set from 900 to 

960ft (274 to 293m) below land surface with a 10-ft (3-m) 

fill-up pipe from 960 to 970ft (293 to 296). Six-inch (150-

mm) mild steel casing extends from the screen to land 

surface. The casing is cemented from the top of the gravel 

pack to the surface. 

GEOLOGY AND HYDROLOGY OF THE 

INJECTION SAND 

The aquifer chosen for the injection zone is a 

moderately sorted, angular to sub-angular, fine- to 

medium-grained, poorly cemented quartz sand of 

Cenomanian-Albian age (Brown, 1971). Wood fragments, 

ostracodes, and foraminifers recovered in cores, as well as 

textural features of the sand, suggest it is marine and was 

deposited in a littoral environment, possibly a tidal flat. 

The size and angularity of the quartz grains indicate a 

lower energy level than would be expected in an open 

beach or bar environment and probably indicate a semiprotected shoreline. 

During coring attempts in TW-1, the sand in the injection zone was so unconsolidated that standard wire-line 

coring techniques did not obtain satisfactory core 

recovery. For this reason, a special "rubber sleeve" core 
GEOLOGY AND HYDROLOGY OF THE INJECTION SAND 5 

4-inch (100-mi//imetre) fiberglass 

__ _,..__ ___ --:,:injection line 

0 

4-inch (100-mi//imetre) fiberglass 

instrument access pipe 

1 ~-inch (38-miiJimetre) fiberglass 

pressure monitoring pipe 0 

L----==b::!Ji~rtt!-- 18-inch (460-mi//imetre) fiberglass casing 

~~~~~--L----==*===~~~lfr- 32-inch (810-mi//imetre) pit casing 

1-

w 

w 

u.. 

z 

ui 

(.) 

Lt 

a: 

::> 

(/) 

0 

z 

<X: 

.....J 

~ 

0 

.....J 

w 

(Il 

I 

1-

a_ 

w 

0 

Gravel pack 

8-inch (200-mi//imetre) fiberglass casing 

Cement grout 

• Wooden block and stainless-steel straps for fixing 

1 ~-inch (38-mi//imetre) pressure monitoring 

pipe to well easing 

8-inch (200-mi//imetre), heavy-duty, wire-wrapped, 

40-slot,stainless-steel screen 

1 ~-inch (38-mi//imetre), heavy-duty, wire-wrapped, 

40-slot,stain/ess-stee/ screen 

10 feet (3 metres) of blank stainless-steel pipe 

Gravel pack 

50 

(/) 

w 

100 a: 

1-

w 

~ 

z 

w 

(.) 

~ a: 

150 ::> 

(/) 

0 

z 

<X: 

.....J 

~ 

9 

w 

(Il 

200 

I 

1-

a_ 

w 

0 

250 

300 

Total Depth 990 feet (302 metres) 

FIGURE 3.-Diagrammatic sketch of injection well IW-2. 

barrel was employed to core the injection zone in OW-3. 

The tool is designed to take core in unconsolidated 

material by encasing the core in a rubber sleeve as the core 

is cut. Selected intervals of the core were submitted to the 

Geological Survey laboratory in Denver, Colo., for determination of clay type, grain size, porosity, hydraulic 

conductivity, and identification of mineral content of the 

sand. 

Table 1 lists the accessory minerals identified by 

William Lockwood of the laboratory. Figure 5 is a 
6 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

RESISTIVITY, IN 

SPONTANEOUS OHMS PER METRE GAMMA RAY 

AND CALIPER 

BULK DENSITY, IN GRAMS/cc 

1-

w 

w 

LL 

z 

_j 

w 

> 

w 

_J 

<( 

w 

Cl) 

z 

<( 

w 

~ 

~1 _J 

w 

co 

I 

1-

0.. 

w 

0 

387 

625 

682 

792 

+. 

< 

S2° ~ 

2 111 

~ 

..:. 

~ 

POTENTIAL SQUARED PER METRE 

20M .v- ~ 1.0 .. ].9 100 

2 

g ~'= ROCKS OF 

§ - f-- late MIOCENE AGE ~ 0 ~ ~~ 

-

----

= ~ I-- =~ --

~ !3!!! ROCKS OF --:c:-: middle MIOCENE AGE 

~ = f- --

-- _c:- '----~ 

~K.~ OF late t:OCE1'JE fJ 

g -

rc+f~ ROCKS OF - I-- c-- ~-- CENOMANIAN AGE 

g 

~ - --

~ ~ .-

I- - ! 

- g I ROCKS OF 

ENOMAN IAN ALBIA .. 

;;; 1- g AGE 

g I 

g -

~ 

g '--- = 

I 

g I 

i 

ROCKS OF g ALBIAN-APTIAN 

AGE ~ 

~ 

~ 

g 

~ CROCKS OF -

g I APTIAN NEOCOMIAN 

I 

AGE 9-

g -~'-

§ 

I r=t::: t:::~ ;I E 

:=t::: ~~ ~~ 1=;:::: ~ 

I 

, __ 

~( ,fI 

2.0 

2 

8, . -+e--+-

i ~~ .... 

g 

~ 1;:_: =-· 

~ 

~ 

~ 

~ 

~ :=i' 

~ =j--1 

---

.~ :=::=:~_, 

g 

g 

~ I"= 

1-=-

1::; I 

g 1-

§ 

~ 

g 1---:1 

~ I~ 

§ 

!!! 

g 

~ 1---: 

g --

g !=; 

- --=-- ~· r-= 

~ 

g 45 30 

2.5 

f-++-

--

~-

I-Ir--

1---

5 ) 

3. ,-,, -1 

=--

:_: 

F--

0 

118 

190 

208 

241 

en 

w 

a: 

1-

w 

~ 

z 

..1 

w 

> w 

_J 

<( 

w 

en 

z 

<( 

w 

469 ~ 

643 

:5: 

0 

--' 

w 

CJ 

J: 

1-

a.. 

w 

Cl 

15 

POROSITY, IN PERCENT 

FIGURE 4.-Geophysical logs and stratigraphy of test well TW-1. 
GEOLOGY AND HYDROLOGY OF THE INJECTION SAND 7 

w100 

N 

(j) v 0 

w 90 

~ 

~ 

0 

z 80 

j 

v 

z 

<( 

I 

I- 70 

II 

S2 

w 60 

s 

>- (]) 

a: 50 

w 

z 

lL 

(j) 40 

w 

_.J 

0 

i= 30 a: 

I 

I 

I 

J 

I <( 

0.... 

lL 

0 20 ~If I w 

<.9 

~ z 10 w 

0 

a: 

, ~~ 

,..., "" """""""' -""" ... -

___........,. I""""" 

w 

0.... 0 0 0 0 

0 

LD 

0 

0 0 

0 

LD 0 0 0 

(j) 0 LD 0 6 w 0 0 0 0 0 ,....: 

_.J 

0 w PARTICLE-SIZE DIAMETER, IN MILLIMETRES 

N I- (j) a: 

rE 0 

w 

CLAY SILT SAND 

Very fine Fine Medium Coarse Very Coarse GRAVEL 

>0.004 0.004-0.0625 lL 

0 I- 0.0625-0.125 0.125-0.25 0.25-0.50 0.5-1.0 1.0-2.0 <( 

w 0 (.? 0 

<( z 5.0 12.2 9.8 39.4 33.0 0.6 0.2 0 

fz 

w lL 

u 0 a: 

w 

a... 

FIGURE 5.-Composite cumulative curve of particle-size distribution of the injection sand. 

cumulative curve showing the distribution of grain sizes 

by percent of the total weight. The curve is a composite of 

particle-size analyses of four cores taken at selected depth 

intervals in the injection zone. Using figure 5 and the 

statistical parameters shown in table 2, a description of the 

injection sand can be obtained. 

The injection zone is bounded above and below by 

laterally persistent silty-day to clayey-silt confining beds 

(fig. 6). The clay in the confining beds was identified by Xray analysis as a multi-layered mixture of illite and montmorillonite, plus montmorillonite and minor amounts of 

kaolinite (table 3). 

Because the montmorillonite and mixed-layer clays are 

swelling clays, the amount of these clays present in the 

injection sand was of concern. If the clay percentage was 

significant and swelling occurred when the clay was subjected to freshwater, the hydraulic conductivity of the 

injection zone would be decreased. To determine the 

spacial relationship of the clay and sand, several thin 

sections were prepared by the laboratory from the OW-3 

core. A red thermosetting plastic was injected into the core 

under a vacuum while the core was still in the rubber 

sleeve. The "original" fabric, pore pattern, effective 

porosity, and interstitial relationship of the clay was thus 

preserved (fig. 7). 

Figure 7 shows slight cross-bedding and a minor 

amount of interstitial clay. Even though table 3 shows that 

the clay content in the injection sand is as high as 25 

percent, the interstitial clay content (fig. 7), which caused 

the clogging problems, is as low as 5 percent of the total 
8 

850 

900 

Iw 

w 

Ll.. 

z 

w 

u 

Lt 

a: 

:::> 

(/) 

0 

z 

<( 950 _j 

s 

0 

_j 

w 

m 

I 

I0... 

w 

0 

1000 

ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

DUAL INDUCTION LOG FORMATION DENSITY LOG 

GAMMA GAMMA 

SPONTANEOUS POTENTIAL 

RESISTIVITY, lN OHMS PER 

METRE SQUARED PER METRE BULK DENSITY, IN GRAMS/CC 

20MV- I- ...... 7 

I-- Cll / 

1- a. - E ' 1- " - (/) "' 1- / 

1- Q; \ 

- -ro 1- ' 3: -ll. 

' J / 

' l 

/ 

1/ 

" :) 

l....,..oo"' 

c 

' 

, -~~"' I 

- II" 

' 

... 

.., , 

......... I\. 

1/ 

/ 

1-1--Qj II' 

1- a. 1\ 

1-

1-- ' E J 

"' 1- Ll' (/) 

1- 1'-

" 1-

1- 2 \ 

1- "' / 

1-~ 

" ' ;' 

1/ 

" \ 

J 

( 

.... , ' 

I;' 

1\ 

' J.J 

"' 

' / 

~ 

... 

,..... 

r""ooo. 

.J .J 

/ 

_/ 

' 

/ ' 

-

f---~ -

Q) 

c 

0 

N 

c 

0 

-() 

Q) 

c 

1 0 10 20 IS ~ 

~ I--

7 

--. 

I 

I 

I , 

' 7 I I ...... I 

;.. 

! DEEP INDUCTIO 

ME?l~~RtNDUCTI LOG-8 .lo -1--- tr t#=-1· 1\ 

I. 

i\l ~ i '-IC: .... 1::1 

-. .Iii"" 

'.......,; , 

~ I' 

7 

r7 

rt: ,, 

II ' lo 

ri I 

I I ,, 

Iiiii! , 

c T 'I I ' I 

·~ I I 

~ 

~ 

I IJI• "lo. 

, 

~ I 

I 

J' .... 

'!!'., --, I I ~ 

I , !,_ ~ 

Ill- .\ ' r» 

I"' ; J ~ ' J" , 

I :LJ 

' t!! W". ~ 

. I 

11 

il J-1' 

• ' 1--'-

-~ 

-~ Yi.-' 

r-;.. - ...,_ " 

, ...... . I 

I' 

·II' 

' r 

l:J 

c 

cu 

(/) 

l:J 

c 

cu 

(/) 

I 

20 2 25 

1\: ~. --

~ c...-

~ ... . ' [j!. .. [';--~ }- l-~~ - 1-- -

11:' ~ 

~ !'{ 

~'= ~ .. { --- ~ 

" ~- ,.· " ~ 

--·- ----- - --- -- --~ 

1.- ----

• T ...., -~ . .., - "- -~ "ti 

-, -.. ,__ r.---' 

---=· r- ~ 

~ '-= _r. -c: 

_~;;po ....-. t: ~ t' lc:. ;. 

-

~ ..... ..., .... L. 

' -

f= ~- ~~- -- --- -

-- .,. f.-- -

~ ; 

-- ...... ~ ~ ~ .... --~ ~-<- . 

- ~ ..... 'f---

---..: rr -~' 

\ --...,;;;;; 

h ~..C r 

~ .;--: I--

~ !!> ---, --

--. IV 

~~ 1--f-- ~ 

"' t..: 'I; 

y T BULK DENSITY r .. -

''C ... 7 COMPENSATION 12 

~ :!> rc:..,; 

~ c:;;-, POROSITY 

.. ~~ ~<: r;--.. t--

c.,.s ..... ~ 

«::: 

-- --~~ ~ ~ 

I~ 1.-- I.:" 

~· ~·. 

1'-----. ~ \... 

h .. ..:, 

!!C- ~ 1-

lr.oil , r- ~ ... ~ ~ ,..J. ~- f-- ~--

~ :r 

'--~ .... ~ ~~ 1---I--

----~ ~ .. -. Ll 

')._ 

-

~~ ~- ~ 

:_.,;;; - ~ 

-r < C' .. ~ '}' 

.f ~ s .... f~ - ----

~ ~ 

r.-- .o::ll:,. 

--~-~-- ~ ~ - --

45 30 

POROSITY, IN PERCENT 

FIGURE 6.-Geophysicallogs of injection zone, test well TW-1. 

259 

274 

290 

304 

U) 

w 

a: 

Iw 

~ 

z 

u.J 

u 

<( 

LL 

a: 

:::> 

U) 

0 

z 

<( 

.....J 

s 

0 

.....J 

w 

co 

I 

Ic.. 

w 

0 
AQUIFER TESTS 9 

TABLE 1.-Heavy minerals identified from cores of injection zone of 

observation well OW-3 

Sample No. 

69Va-l 69Va-2 69Va-3 69Va-4 69Va-5 69Va-6 69Va-7 69Va-8 

Interval (ft) .................... 892- 912-- 975- 892- 912- 935- 955- 955-

912 932 995 912 932 955 975 975 Lithology ...................... clay clay clay sand sand sand sand sand 

Percent of sample 

Total heavy minerals 0.8 0.5 0.3 1.3 4.0 0.6 0.9 1.3 

Percent of total heavy minerals 

Apatite .......................... . <I Amphibole ................... . I Actinolite <1 

Tremolite .................... . <I Biotite............................ <I 13 

Chlorite ........................ . 12 I Diopside ....................... . <I <I I Epidote.......................... <I <I <I 5 Garnet .......................... . 5 <I 10 Hornblende .................. . <I I 

Hypersthene ............... . <I Kyanite ......................... . <I I Magnetite ..................... . II 24 23 Muscovite...................... I 4 8 2 Pyrite................... 85 4 9 7 

Rutile ........................... . <I <I Staurolite ...................... . 14 5 14 Titanite ........................ . 3 5 Tourmaline .................. . <I <I 2 Zircon ........................... . <I I Unidentifiable .............. . 35 45 28 

I 

4 19 

10 15 

<I I 

20 24 

9 I 

3 

22 12 

2 

<I I 

I 

30 18 

I 

2 

9 

5 

I 

27 

I 

10 

I 

25 

I 

I 

2 

21 

5 

15 

4 

I 

29 

2 

19 

14 

TABLE 2.-Statistical parameters of the injection sand 

Phi parameter 

Mean .................................... . 

Standard deviation .............. . 

Skewness coefficient. ........... . 

Kurtosis coefficient ............. . 

Value 

(phi units) 

2.3 

1.3 

0.46 

2.6 

Remarks 

Fine sand 

moderately sorted 

Slightly skewed (slightly 

poorer sorting in fine sizes) 

Moderately peaked (better 

sorted in the center than 

on the two ends) 

clay content. The relatively small amounts of interstitial 

clay present in the thin sections appeared to negate a 

clogging problem. However, it is now apparent that a very 

small percent of clay can significantly reduce hydraulic 

conductivity. Moreover, the injection well (IW-2) is in an 

area of facies change that has an increase in the percentage 

of silt and clay in the injection zone (table 4). The effect of 

the clay on the hydraulic conductivity will be discussed in 

detail later in the paper. 

The formation water in the injection zone is brackish 

having a dissolved-solids concentration of 3,010 mg/1 

(milligrams per litre). It is a sodium chloride bicarbonate 

type water having a chloride concentration of 1,360 mg/1. 

A detailed description of the chemkal quality of the 

native ground water is presented later in the paper. 

TABLE 4.-Thickness and sand-shale ratios for the injection zone within 

the well field 

Depth to top of Sand-shale ratio 

Well injection sand Thickness Total sand upper lower 

(ft below sea level) (ft) (percent) half half 

TW-1 885 I04 83.0 81.0 85.0 

OW-2 889 86 84.0 84.0 84.0 

OW-3 89I 82 83.0 76.0 90.0 

IW-1 89I 88 63.0 77.0 48.0 

IW-2 888 84 59.5 79.0 40.5 

AQUIFER TESTS 

Constant-rate and step-drawdown aquifer tests were 

made on IW-2 and TW-1. Consistent transmissivity 

values were not obtained from interpretations by the Theis 

method of analysis or by the "leaky aquifer" analysis. 

Slope changes indicating recharge boundary conditions 

TABLE 3.-X-ray diffraction analysis of core samples from injection zone, observation well OW-3 

[Results in percent] 

Depth' of Lithology Quartz Feldspar Kaolinite Illitic-mica Mixed-layer Montmoril- Chlorite Total sample (ft) clays lonite 

892-9I22 Clay 32 I6 5 I7 30 IOO 

975-9952 Sand 7I 6 4 6 I3 IOO 

975-9952 Sand 78 5 3 4 IO IOO 

892-9I23 Clay 20 12 I3 27 18 90 

892-9I23 Sand 52 24 3 3 I8 IOI 

935'-9553 Sand 67 23 I I 2 I 95 

955-9753 Sand 52 19 7 7 2 2 89 

'Core was recovered in 20-foot lengths and the lithology varies considerably within a cored interval. 

2Core analysis by Wayne Hower of Halliburton Company who reported that dye staining of consolidated fragments of the 

core showed the kaolinite was limited to isolated "clumps" whereas the mixed-layer clays were present in the waterways. In 

his opinion, the core would be "quite sensitive to freshwater" (Hower, oral commun., 1972). 

3Core analysis by Barbara Anderson, U.S. Geological Survey, Denver, Colo. 
10 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

FIGURE 7.- Thin section of part of the injection sand (955 to 975 ft or 291 to 297 m). 
INJECTION SYSTEM 11 

begin affecting the aquifer-test data after 10 minutes of 1 

pumping and continue to affect the logarithmic plots up 

to about 60 minutes. Apparent recharge occurs in the plot 

of both drawdown and recovery data and has been interpreted as indicating thickening of the producing aquifer 

or increased permeability in the aquifer away from the 

well field. 

On the basis of the aquifer-test data and an 

interpretation of the geology, a geologic model was made 

of the aquifer. This interpretation theorized a gently 

arcuate, concave west:;.~,mrd, sand buildup striking northnortheast lying to the we;:;t of the well field. The eastern 

limit of the buildup passes close to the western edge of the 

well field. 

Using the geologic framework and the aquifer-test data, 

0. J _ i:Osner of the Geologica~ Survey constructed a mathematical model of the hydrology of the well field. Values of 

transmissivity ranged from as low as 5,360 ft3d- 1£t- 1 or 498 

m3d- 1m- 1 in the injection well to 16,600 ft3d- 1ft- 1 or 1,540 

m3d-1m- 1 in the area of maximum sand buildup. In areas 

other than the sand b·uildup or the actual well field, a 

regional transmissivuy valu.e of 8,300 ft3d- 1ft- 1 or 770 

m3d- 1m- 1 was used. The digital model included a 20-ft (6-

m) layer of clay above the injection sand that had a vertical 

hydraulic conductivity of 1.4lxlo-s ft/d (4.3x10-6 m/d). 

The specific storage of the confining clay was assumed to 

be 4x10-5• The storage coefficient of the aquifer, determined from tests, was 1.5xl0-4• 

The model was verified by simulating drawdown and 

recovery curves obtained from a 48-hour aquifer test in 

which IW-2 was pumped at 800 gal/min (50 lis) and 

TW -1 was observed. The model shows that after pumping 

or injecting on a long-term basis (4 days or more), water 

levels would tend to stabilize because of leakage through 

the confining layers (Cosner, oral commun., 1970). No 

long-term aquifer tests were made to establish the validity 

of the model-derived hydraulic conductivity of the 

confining bed. 

Several constant-rate pumping tests and a 3-hour stepdrawdown test were made of IW -2 to determine specific 

capacities prior to any injection (table 5). Step-drawdown 

TABLE 5.-Specific ::apacities at various pumping rates after 1 hour for 

the injection sand on test well TJV-1 and injection well IW-2 

Screened imerval Pumping rate Specific 

Well Date Type of test capacity idepth in It) (gal/min) (gal min-lft-1) 

TW-1 3- 7-69 900-960 step drawdown 100 17.7 

TW-1 3- 7-69 900-960 step drawdown 150 13.7 

TW-1 3- 7-69 900-960 step drawdown 250 12.1 

TW-1 3-ll-69 900-960 constant rate 200 13.0 

IW:....2 5-20-70 896-976 step drawdown 250 16.2 

IW-"-2 5-20-70 896-976 step drawdown 500 15.8 

IW'-2 5-20-70 896-976 step drawdown 1000 13.4 

IW-2 5-21-70 896-976 constant rate 800 14.5 

tests were made to determine the well loss to be expected 

when withdrawing water at a rate double that of injection. 

Figure 8 is a hydrograph of the step-drawdown test made 

of IW-2 showing how the specific capacity values were 

derived. The well was pumped with a 10-in (250-mm) 

turbine pump, and the discharge measured by 10- by 6-in 

and 10- by 5-in (250- by 150-mm and 250- by 130-mm) 

orifice plates. Water-level measurements were made 

during pumping and recovery in the pumped well IW -2 

and in observation wells OW-2, OW-'-3, and TW-1. 

Comparison of the specific capacities obtained during 

withdrawal and injection tests will be presented later in 

the paper. 

INJECTION SYSTEM 

All pipes and valve~ are constructed of schedule 80-

polyviny I chloride. All waterways in the pumps are either 

rubber lined or epoxy coated so at no place in the system is 

there iron in contact with the injection or withdrawal 

water, except as stainless steel. Chemically stable materials 

were used to prevent extraneous sources of iron masking 

chemical reactions occurring within the aquifer. 

The city water is injected by a 10-horsepower (7.46 kW) 

centrifugal pump rated at 500 gal/min (31.51/s) against a 

total dynamic head of 30 ft (9 m). It operates at 800 

revolutions per minute. The pump will deliver 800 gall 

min (50.5 lis) to free discharge at the well house which is 

located 230ft (70m) from the centrifugal-pump vault. The 

pump vault is situated adjacent to a 60-in (1,520-mm) 

concrete line from which the injection water is supplied. 

The centrifugal pump has a rubber liner so that the city 

water is not in contact with any ferrous-metal surfaces 

prior to injection. 

The injected water is withdrawn by a 30-horsepower (22 

kW), 10-in (250-mm), vertical hollow-shaft turbine pump 

rated at800 gal/min (50.51/s) against a total dynamic head 

of 105ft (32m). It has 120ft (37m) of 8-in (200-mm) epoxycoated pump column and a four-stage stainless-steel 

pump-bowl assembly. All waterways are epoxy coated. 

The injection flow system is so arranged that water 

flows in the same direction through the metering system 

during either injection or withdrawal. The metering 

system consists of a 4.8-in (122-mm) stainless-steel orifice 

plate and a McCrometer1 Model MC 01400 saddle meter. 

One-inch (25-mm) diameter, thin wall, polyvinyl chloride 

pipes in 10-in (250-mm) lengths are cemented in the 6-in 

( 150-mm) flow line both upstream and downstream from 

the orifice to act as straightening vanes and eliminate 

turbulent flow through the orifice. Pressure changes 

between the upstream and downstream sides of the orifice 

are recorded by a differential pressure transducer. The 

orifice was calibrated in the laboratory prior to 

installation. 

'The use of trade names does not imply endorsement by the U.S. Geological Survey but is 

provided for complete description of the system. 
12 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

Step 1 

5 

Q = 250 gallons per minute 

( 15.8 litres per second) 

PRE- PUMPING WATER LEVEL 

1-

w 

w 

u... t.S1 = 15.48 feet (4.72 metres) Specific capacity= 16.2 gallons per minute per foot 

(/) 

w 

a: 

1--

z 

w 

() 

L£ 

a: 

:::) 

(j) 

0 

(3.35 litres per second per metre) 

Step 2 

Q = 500 gallons per minute 

(31.5 litres per second) 

___ 1 ______ _ 

t.S2 = 16.27 feet (4.96 metres) 

10 ~ 

~ 

w 

u 

<( 

LL 

15 ~ (/) 

z 

c::x:: 

...J 

Specific capacity= 15.8 gallons per minute per foot 

(3.25 litres per second per metre) 

_1 ___ _ 0 

z 

<( 

.....J s: 

9 

w 

m 

a: 

w 

~ 

Step 3 

Q = 1000 gallons per minute 

(63.1 litres per second) t.S3 = 42.78 feet (13.04 metres) 

~ 2og w 

OJ 

s: 

~ 

Specific capacity = 13.4 gallons per minute per foot 

(2.77 litres per second per metre) 

a: 

w 

I-

<( 

25~ 0 

II 

1-

0... 

s = -----=0=-------

p t.SI + t.S2 + ... t.Sn 

w 

0 Where Sp =Specific capacity 

100 Q = Discharge, in gallons per minute --- 30 

I 

1--

Q.. 

w 

0 

t.S = Change in water level after 1 hour of pumping 

35 

10 100 1000 

TIME AFTER PUMPING STARTED. IN MINUTES 

FIGURE 8.-Hydrograph of injection well IW-2 showing specific capacities derived from May 1970 step-drawdown test. 

The saddle meter registers both the rate in gallons per 

minute and the total flow. It was calibrated against the 

orifice in the laboratory prior to installation. The reproducibility of the saddle meter versus orifice data is accurate 

to a maximum positive deviation of 0.59 percent and a 

maximum negative deviation of 0.97 percent. 

PRE-INJECTION CALIBRATIONS 

CURRENT METER 

To determine if clogging was occurring during 

injection, it was necessary to determine which parts of the 

aquifer in IW -2 were contributing water during pumping 

of the well. Current-meter traverses were made of the 

screened interval in IW-2 before, during, and after injection tests to evaluate the clogging data. 

An Au deep-well impeller-type current meter was used 

for these tests. The current meter is in the top of a 3-ft (0.9-

m) tube. Water enters the bottom of the tube and flows 

vertically through it, causing the impellers to spin about 

the vertical shaft of the current meter. A magnetic switch is 

activated once each revolution and sends a signal through 

a single conductor cable to a counter at the surface. 

With the current meter hanging freely in the upper part 

of the screen that contribures no flow from the aquifer, the 

discharge was varied to calibrate the meter by establishing 

a revolutions-per-minute to gallons-per-minute relation. 

IW-2 was then pumped at a constant rate of 770 gal/min 

(49 lis), and a current-meter traverse was made of the 

screened part of the aquifer at 1-ft (0.3-m) increments. The 

traverse was repeated using a constant discharge rate of 400 

gal/min (25lls). These two traverses (fig. 9) show the preinjection flow patterns in the aquifer at the proposed 

injection rate (400 gal/min or 251/s) and withdrawal rate 

(770 gal/min or 49 lis). The traverses indicated that 45 

percent of the water came from the zone 908 to 923 ft (277 to 

281 m) and 39 percent from 950 to 972 ft (290 to 296 m) 

below sea level. Other minor zones of contribution were 

present. 
PRE-INJECTION CALIBRATIONS 13 

275 

Iw en w 280 w 

LL920 a: 

Iz w 

~ 

_j z 

w 

> _j w w _J 

> 

<( w 

~930 ...J 

<( 

z w 

en <( 

w z 

~ 285 <( 

w 

3:: ~ 

0 3: 

~940 0 

...J 

en w 

co 

I J: I- I- 0.... a.. w w 0 0 

950 

290 

295 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 9.-Current-meter traverses in injection well IW-2 prior to injection of freshwater. 
14 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

TRANSDUCERS 

Transducers were used to measure water-level changes 

during injection and withdrawal. Solid state, semiconductor pressure transducers with ranges of ±40 lb/in2 

(±276 kPa) were used in wells IW-2 and ASW. The 

transducers will measure a total change in water level of 

about 100ft (30m). The water level changes in OW-3 were 

not as great as in the pumped well; therefore, a± 15-lb/in2 

(± 103-kPa.) transducer was used. It will recorda total head 

change of about 30 ft (9 m). 

The transducer system of recording water levels or head 

changes did not prove reliable because they failed during 

long-term tests. The transducers were submerged during 

the tests, and it was especially difficult to keep the 

electrical connections waterproofed under high heads in 

fresh water and also under static conditions in saline 

water. Their accuracy, when functioning properly, was 

reproducible within 0.1 percent of the total range. 

A 0 to 5 lb/in2 (0 to 34 kPa) variable reluctance differential transducer was located in the flow system to 

measure the change in head as the water passed through 

the orifice. The transducer box was connected to the 

upstream and downstream sides of the orifice by means of 

plastic tubes leading to taps installed in the 6-in ( 150-mm) 

pipe. The orifice was calibrated in the laboratory by a 

transducer system so that pressure changes may be directly 

converted to gallons per minute. 

TURBIDITY 

It was necessary to establish a relationship between 

turbidity recorded in Jtu's (Jackson turbidity units) and 

suspended solids to determine the volume of sediment 

being injected into or withdrawn from the aquifer. A Hach 

Model 1889 Surface Scatter Turbidometer was used to 

measure turbidity. Samples were collected at various Jtu 

values, then filtered, and the filtrate weighed to establish 

the relation. 

Turbidity was measured to determine if the particulate 

matter injected into the aquifer was recovered. It it could 

be shown that the volume of sediment recovered during 

withdrawal was less than was injected, it could be assumed 

that the aquifer was being clogged by particulate matter in 

the injection water. The amount of suspended sediment in 

the injection water is small (a maximum of 1 to 2 mg/1). 

WATER-QUALITY MONITOR 

The following parameters were measured by a waterquality monitor during both injection and withdrawal 

phases of any test: Conductivity, pH, Eh, temperature, 

dissolved oxygen (DO), turbidity, head changes in IW-2, 

ASW, OW-3, and orifice flow rate. Prior to each test, each 

sensor was calibrated to fit the expected range of values. 

The data were recorded by two systems. A Fisher & 

Porter Model 1542 digital punch records the data from 

the monitor on digital tape at either 15-, 30-, or 60-min 

intervals, depending upon the choice of the operator. It 

takes 45 seconds to monitor a parameter, punch it, and 

move to the next parameter. A 16-channel strip-chart 

recorder served as a backup system. The strip chart records 

a parameter every 15 seconds and has a complete cycle time 

of 4 min. Parameters that show considerable variations 

with time or pumping rate, such as conductivity or depth 

to water, were recorded more than once in the 4-min cycle. 

The strip-chart record has the advantage that changes in 

data can be observed directly, whereas the digital tapes 

must be processed. 

INJECTION TESTS 

It was originally planned to conduct successive 

injection tests with the emphasis on injection of a large 

quantity of water and storing it for a long period of time 

prior to withdrawal. Modification of these plans became 

necessary because the injection specific capacity of the 

aquifer became so low during injection test 3 that it was 

impractical to continue the test beyond 1,100 min. 

INJECTION TEST I 

The purpose of injection test 1 was to test the flow 

system and sensing apparatus; to determine the head 

buildup that would occur during long-term tests; to detect 

errors in calibration limits set for the monitoring 

equipment; to determine chemical reactions occurring 

during injection and withdrawal; and to establish the 

number of people required to conduct the tests. In 

accordance with these objectives, it was decided that the 

initial injection test would be of 8 hours duration. 

Injection was begun at 0900 hours on Nov. 22, 1971, at a 

rate of 400 gal/min (251/s). Thisratewasheld for 270min, 

after which the injection pump was shut down to allow 

insertion of the current meter into the screen of IW-2. 

After a shut-down of 35 min, injection continued at 400 

gal/min (25 lis) for an additional 205 min until shutdown at 1730 hours on Nov. 22, 1971. No redevelopment 

pumping was attempted during injection of the water. A 

total of 198,320 gal (750m3) of city water was injected into 

the brackish-water aquifer. The water remained in place 

for 15.5 hours before withdrawal began. 

Withdrawal of the injected water began at 0900 hours on 

Nov. 23, 1971, at a rate of 710 gal/min (451/s). The withdrawal rate gradually increased to 730 gal/min (461/s) by 

the end of the withdrawal phase (330 min of withdrawal) 

of test 1. A total of 250,210 gal (947m3) was withdrawn, or 

about 26 percent more water was removed than injected. 

During both injection and withdrawal, current-meter 

traverses were made of the screened section in IW -2 and 

conductivity profiles in OW-3 were made during the 

injection phase. 

INJECTION TEST 2 

The purpose of injection test 2 was to verify the 

chemical and physical data obtained in test 1. Although 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 15 

the results of test I were encouraging, the time span was so 

small that valid conclusions on long-term testing could 

not be made. Injection test 2 was designed to inject approximately 10 times the quantity of water of test I and to leave 

it in the aquifer for 48 hours. Conductivity surveys of the 

screened section of the nearest observation well (OW-3) 

were planned to determine the time of arrival of the 

injected water and to define the shape of the injection front 

at OW-3. 

Injection test 2 began at 1400 hours on Feb. 14, 1972, and 

concluded after a total of 7,906 min (5.49 days). Injection 

was interrupted for 250 min after continuously injecting 

for 5,340 min (3.71 days) because of repairs to the city filter 

plant. The initial injection rate was 410 gal/min (261/s), 

but it gradually decreased to 215 gal/min (14 1/s) after 

7,800 min (5.42 days) of injection. A total of 2,445,530 gal 

(9,260 m3) of treated city water was injected into the 

brackish-water aquifer without any redevelopment 

pumping during the injection period. The water 

remained in the aquifer for 50 hours (2.08 days). 

Withdrawal of the injection water began at llOO hours 

on Feb. 22, 1972, and ended Feb. 26, 1972, at 1100 hours. A 

total of 3,504,100 gal (13,260 m3) of water was withdrawn 

or about 43 percent more than was injected. Current-meter 

traverses of IW -2 and conductivity profiles of OW -3 were 

made during injection and withdrawal. 

INJECTION TEST 3 

The purpose of injection test 3 was to verify chemical 

and physical data obtained in tests I and 2 and to obtain 

additional data. The results of test 2, as in test I, were 

encouraging regarding the practical use of the aquifer for 

storage of freshwater. However, the decrease in the injection rate and the excess head buildup near the end of test 2 

were areas of concern. Injection test 3 was designed to 

inject about 10 times more water than in test 2 and to leave 

it in place a minimum of 2 weeks. Conductivity surveys of 

OW-·3 were planned to compare the shape of the injection 

front and arrival time with the data of test 2. 

Injection test 3 began at 1600 hours on Apr. 13, 1972. 

The injection rate dropped from an initial400 gal/min (25 

lis) to 115 gal/min (7.3 1/s) within 80 min, and gradually 

decreased to a low of 70 gal/min (4.41/s). After injecting 

for 20 min, pressure on the discharge side of the injection 

pump rose from a normal value of 12lb/in2 (83 kPa) to the 

maximum value of 20 lb/in2 (138 kPa). After 1,174 min 

(0.82 day) of constant injection, it was apparent that the 

aquifer would not take water in sufficient quantities to 

continue the test. 

A total of 132,700 gal (502 m3) of freshwater had been 

injected. In attempts to redevelop the well, water was 

alternately withdrawn and injected for a period of about 5 

hours, resulting in a net additional 13,300 gal (50m3) of 

water being injected for a total of 146,000 gal (553m3). The 

water remained in place for 76.5 hours (3.2 days). 

Withdrawal of the injected water began at 1000 hours 

on Apr. 17, 1972. A total of 318,000 gal (1,200 m3) of water 

was withdrawn or 46 percent more than was injectedt 

This total includes almost 95,000 gal (360 m3) recovered 

during redevelopment attempts during injection. Current-meter traverses of IW-2 were made during injection 

and withdrawal. 

At this point, a total evaluation of what was occurring 

within the aquifer had to be made before any additional 

injection tests could be attempted. 

DETERIORATION OF AQUIFER HYDRAULIC 

PROPERTIES 

It became increasingly apparent during the injection 

phase of test 3 that deterioration of the hydraulic 

properties was occurring because of injection of freshwater. Alteration of the aquifer and a resulting decrease in 

hydraulic conductivity was reflected by: (I) Excessive head 

buildup in the injection well and nearby observation 

wells; (2) alterations in flow gradients between wells; and 

(3) low injection rates into the aquifer. 

It has been shown by many investigators (Baptist and 

Sweeny, 1955, 1957; White, Baptist, and Land, 1962, 1964; 

Hewitt, 1963; Meade, 1964; Gray and Rex, 1966; Reed, 

1972) that a reduction in permeability of some aquifers 

occurs when the salinity of the pore water is altered. The 

reduction is greatest if the salinity is greatly reduced. A 

sand that exhibits this tendency is described as "water 

sensitive." 

The greatest deterioration of the hydraulic properties of 

the water-sensitive aquifer is usually a result of physical 

movement of interstitial clay particles rather than 

clogging by chemical precipitation. Land and Baptist 

(1965, p. 1213-1218) have demonstrated that most of the 

reduction in hydraulic conductivity is due to dispersion of 

clay particles rather than in situ swelling of the clay. 

Evidence of clay dispersion clogging versus in situ 

swelling is mostly indirect, but there are two criteria that 

may be used to determine which process is functioning: (I) 

Reduction in hydraulic conductivity due to swelling 

would be mostly reversible when original conditions were 

restored, whereas deterioration due to clay dispersion is 

largely irreversible. As the clay particles are dispersed, they 

move until they become lodged in pore constrictions, 

causing clogging. Returning the water chemistry to 

original conditions will not repack the clay in its original 

position. (2) If a section of core of the aquifer is saturated 

with formation water, then flushed with freshwater, a 

milky, turbid effluent accompanied by decreasing 

hydraulic conductivity usually results if clay dispersion is 

occurring. 

The mechanism for clay dispersion has been reported in 

detail by Meade (1964), Jones (1964), Gray and Rex (1966), 

and Reed ( 1972) and will be discussed here only in general 
16 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

terms. Clay dispersion is predominately a result of 

electrokinetic properties. The electrostatic attraction 

between negatively charged clay particles and exchangable cations is opposed by the tendency of the ions to 

diffuse and become uniformly distributed throughout an 

aqueous solution. 

Meade, Gray and Rex, and Reed all state that one of the 

most significant fac~ors causing dispersion is a change in 

the double-layer thickness surrounding a clay particle. 

The double layer exists because of a negative charge on the 

surface which attracts cations close to this surface. Because 

the fluid must retain its electrical neutrality, a more diffuse 

second zone of anions are attached to the attached cations. 

This forms a double layer of ions surrounding each 

particle. 

When the concentration of ions is large, as in the case of 

brackish water, the, double layer on the particle is compressed te a· small thickness. Compression of the double 

-layer permits clay particles to coalesce, due to interparticle attraction of van der Waals forces, and form larger 

aggregates that can overcome the disrupting Brownian 

movement and therefore promote gravitational settling. 

This is commonly called clay flocculation. When the 

concentration of ions in a fluid is low, as in the case when 

dilute freshwater enters the aquifer, the diffuse double 

layer expands, forcing the clay particles apart. This ex pansion prevents the clay particles from coming close together 

to aggregate, therefore keeping them dispersed and in 

suspension. This is commonly referred to as clay 

dispersion. 

The tendency to disperse is measured by the zeta 

potential 

z = 411"8q, 

D 

(1) 

where 8 =thickness of the zone of influence of the charge 

particle; 

q= charge on the particle before any cations are 

attached; 

D=dielectric constant of the liquid. 

For any given solution and colloid, reduction of the zeta 

potential is accomplished by reducing the thickness of 

the zone of influence. This is accomplished by increasing 

the charge density as close to the surface of the particle 

as possible by substituting small doubly or triply charged 

ions such as Al+3 or Ca+2 in place of large singly charged 

hydrated ions such as Na+1• This ionic substitution gives 

a smaller zeta potential and permits clay particles to 

coalesce. Highly hydrated ions, such as sodium, result in 

a clay-cation system with high zeta potential. The water 

of hydration prevents the cation from being closely 

adsorbed. ,These facts may account for the tendency of 

sodium to cause dispersion of clay colloids and for calcium to cause flocculation. 

Sands containing montmorillonite and mixed-layer 

clays that are small in size and have large surface charges 

are usually the most water sensitive. As little as 0.4 percent montmorillonite has caused a 55-percent reduction 

in hydraulic conductivity (Hewitt, 1963, p. 817). The clay 

present in the injection zone, as shown by X-ray studies 

(table 3 ), has sufficient quantities of montmorillonite, 

illite, and mixed-layer clays to account for the reduction 

in hydraulic conductivity that occurred during injection 

tests 1, 2, and 3. 

HEAD BUILDUP 

The first evidence of formation alteration due to injection of the freshwater was the excess head buildup that 

occurred in the injection well during injection test 1. The 

expected head buildup in each well was determined by 

a pre-injection pumping test in which IW -2 was pumped 

at 400 gal/min (25 1/s) for 8 hours. The inverse of the 

drawdown measured in each well was used to predict 

head buildup when the injection rate was 400 gal/min 

(25 1/s). 

EXCESS HEAD BUILDUP DUE TO TEMPERATURE 

AND VISCOSITY 

In the pumping well (IW-2) and annular space well 

(ASW), the effects of density and temperature were taken 

into consideration in calculating the expected head buildup using a method described by G. D. Bennett (written 

commun., 1969). The formulas for the radius of intrusion 

of the injection water and for the excess head buildup 

are as follows. 

The radius of intrusion can be derived from the formula for the radius of a cylinder: 

r=-~ T;T' 

where V=volume of the cylinder; 

h=height of the cylinder. 

(2) 

If a porosity factor (IJ) is used to compensate for the void 

spaces, the volume (V) is represented by the injection rate 

(Q) and length of injection (t-tc ), the length of the 

screened area (D) represents the height (h) of the cylinder, 

and the effect of the radius of the well ( rw) is considered, 

then equation 2 can be rewritten as follows: 

(3) 

where ri ( t)=the radius, in feet, of the injection water (colder water) at time (t); 

rw=the radius of the well, in feet; 

Q=the flow rate, in cubic feet per minute; 

t-tc=the time that the colder water has been in the 

aquifer, in minutes; 

D=the length of screen, in feet; 

()=porosity, expressed as a decimal. 

The excess head buildup can be calculated using a 

modification of the standard distance-drawdown formula; 

(4) 2.3Qlog10r2/rl T - , 27r(ScS2) 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 17 

where T=transmissivity, in cubic feet per day per foot; ' 

Q=rate of discharge of the pumped well, in gal/ 

m1n; 

r2=distance from the pumped well at which drawdown is desired, in feet; 

r1=radius of the well, in feet; 

s1 -s2=drawdown, in feet. 

If transmissivity is represented by the hydraulic conductivity (K) times the thickness of the aquifer screened (D), 

excess head buildup (SwTt -Swt) is substituted for drawdown (s 1-s2), and the radius of the injection front (ri (t)) 

is substituted for r2, then equation 4 can be rewritten as 

follows: 

SwTt-Swt= {_:__- __!__){ 2.

3

Q}(og ri (t) \ ' 

\K1c K1 \ 2-rrD 7 Yw J (5) 

where SwTt-Swt=excess head buildup, in feet, due to 

colder water (head buildup in IW-2 

for injection water of temperature T, 

at timet, minus head buildup in the 

well for the formation water at time 

t ); 

K1=horizontal hydraulic conductivity of 

the formation to formation water, in 

cubic feet per minute per square foot; 

K1c=horizontal hydraulic conductivity of 

the formation to freshwater at 

the injection temperature, in cubic 

feet per minute per square foot. Kleis 

defined as K 1(uluc ), where Uc is the 

viscosity of cold freshwater at injection temperature and u is the viscosity 

The following assumptions are used in making the calculations: The water moves into the formation in a horizontal, radial pattern; it remains confined in the 80-ft 

(24-m) zone in which the well screen is placed; accumulation of water in storage within the radius ri (t) is negligible 

for any time t during the test; and a definite interface exists 

between the colder denser injection water and the formation water. If the average transmissivity based on pumpingtest data between well OW-3 and IW-2 is taken as 7,075 

ft3d-1ft-I (657m.5d-Im-I ), the following substitutions can 

be made in equations 3 and 5: 

K1=0.061 ft3min-1ft- 2; 

Ku=0.041 ft3min- 1ft- 2, taking the water temperature of 

the injection water as I 0°C, its viscosity as 1.3 

cP (centipoises) and the viscosity of the formation water as 0.87 cP; 

Q=400 gal/min or 53.5 ft3 /min; 

D=80 ft; 

rw=0.33 ft; 

9=0.30 (the porosity of the injection sand was obtained from core analysis and interpretation of 

compensated gamma-gamma density logs. Both 

sources indicated an effective porosity of 35 to 

40 percent. A value of 30 percent is used here, 

as a part of the effective porosity is always occupied by essentially static water along the pore 

walls). 

After 1 minute of injecting 10°C water, the radius of the 

injection water from the well would be: 

r = .. / (53.5)(1) + (0.33)2 , 

i(t) 1{3.14)(80)(0.3) 

ri (t)=0.905 ft (0.28 m). 

Solving equation 5 gives: 

SwTt -Swt= (-1 ___ 1_). (2.3)(53.5) .log0.905 

0.041 0.061 (2)(3.14)(80) 0.33 

SwTt -Swt-0.87 ft (0.26m) of excess head buildup after 1 

minute due to colder water. 

The negative of the drawdown curve from a preinjection aquifer test was used as the head buildup to be 

expected in the wells. The calculations for excess head 

were added to the inverse drawdown plot in order to 

approximate head buildup changes with time and temperature. The equations were solved for excess head 

buildup changes with time and temperature. The equations were solved for excess head buildup at various temperatures and times so that predicted head buildup could 

be approximated prior to any injection test. The difference in temperature between the city water and formation water may vary as much as 20°C depending upon 

the season. 

Figure 10 shows plots for IW-2 and OW-3 of the theoretical head buildup divided by discharge and actual head 

buildup divided by discharge recorded during the first 270 

minutes of injection test 1. 

The figure shows that the theoretical data approach the 

empirical data in the observation well, but the head buildup divided by discharge in the injection well is far in 

excess of the predicted values. Plots of the values for tests 

2 and 3 gave similar results, but the excess head buildup 

in IW-2 and ASW became greater with successive tests. 

EXCESS HEAD BUILDUP DUE TO HYDRAULIC 

CONDUCTIVITY DETERIORATION 

The field data indicate that only a part of the excess 

head buildup can be explained by temperature and density differences. The balance must be associated either with 

hydraulic conductivity deterioration in the aquifer or 

with entrance losses due to clogging of the screen and 

gravel pack. As a first approach to estimating hydraulic 

conductivity alteration due to clay dispersion, equation 

5 may be solved for K10 the hydraulic conductivity of the 

aquifer to the injected water, and observed head differences may be inserted in place of the expression 
18 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

0.150 

~ Predicted head from negative of drawdown, measured 

during a pre-injection pumping test 0.72 

w 

1--

::J 

z 

~ Correction for excess head build-up due to temperature 

and viscosity differences between formation water and 0 

z 

~ 

city water, assuming a discharge of 400 gallons per minute. 

(25 litres per second) 

0 

u 

w 

(/) 

ffi 0.100 D... 

z 

9 

_J 

<( 

(,!) 

ffi 0.050 D... 

1--

w 

w 

0.48 

~ 

0.24 

a: 

w 

a.. 

w 

a: 

1-

_J 

a: 

w 

a.. 

(/) 

w 

a: 

1-

w 

~ 0.050.-------.----.--.--.-.-.-.~--------~--~--.--.-r-.~~-------.----.---.-~--~ .. ~ 0.24 ~ 

z ~ 

cf 

<( 

w 

I 

z 0.010 

w 

(,!) 

z 

<( 

I 

u 

0.005 

Well OW-3 

o o D. Data points 

0 

<( 

w 

I 

0.048 ~ 

w 

<.::J 

z 

<( 

I 

u 

0.024 

0.0 0 1 L_ ______ ..J.._ __ --l... __ __,f,____J____J.___J___J........L.....I _______ L.._ __ ---L,_ __ ,.L..___J....--L,.__J...._l.._J..,_J, ______ ___J. ___ ..,L_ __ L.__l..___J,_...J..._...L.....J.__J 0. 0048 

1 10 100 1000 

TIME SINCE PUMPING BEGAN, IN MINUTES 

FIGURE 10.-Theoretical and measured head data for injection well IW-2 and observation well OW-3, test I. 

(Swn-Swt)· That is, the difference between the head buildup actually measured during an injection test and the 

theoretical head buildup taken from the drawdown 

measured during pumping at an equal rate may be substituted for (Swn-Swt). This yields the equation: 

2.3Q (log ri(t))(Kl) 

27TD rw 

(6) 

where S inj =the head buildup measured after a time (t) 

of injection at the rate (Q); 

Sp =the drawdown measured after the same time 

during pumping at a rate (Q), prior to 

any injection; 

and the remaining terms are as previously defined. If no 

alteration has occurred in the aquifer and if entrance 

losses are negligible, equation 6 should yield a hydraulic 

conductivity equal to that calculated for the injection 

water from the relation KIC=K1(uluc ). Deterioration of 

the aquifer's hydraulic properties should be indicated by 

a lower hydraulic conductivity value. This approach 

assumes all excess head to be due to hydraulic conductivitv deterioration rather than to clogging of the screen. 

Application of equation 6 at several different time 

values during injection test I yielded a hydraulic conductivity of about half that calculated from the relation 

K 1c=K1 (uluc ). Application of the equation in later tests 

yielded even lower hydraulic conductivity values, but it is 

believed that these later results may reflect the results of 

screen clogging as well as hydraulic conductivity 

deterioration. 

Figure 11 shows distance-drawdown plots from two 

aquifer tests-one prior to any injection, and one 

following test 3, after removal of all injection water and 

extensive redevelopment to remove screen-dogging 

particles. Both tests were made at a discharge rate of 400 

gal/min (25 1/s). Calculation by the distance-drawdown 

method using the gradient between ASW and OW-3 

shows that the average lateral hydraulic conductivity 

following the three injection tests was about 50 percent of 

the original value. The value agrees with the estimates 

obtained from test 1 using equation 6. The fact that the 

redevelopment pumping did not restore the hydraulic 

conductivity to its original value illustrates the irreversible 

nature of the deterioration. 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 19 

DISTANCE FROM PUMPING WELL, IN METRES 

o~----~--~~~~,~~~--~--~~~~~~3~.o~--~----~~~~.r~----.---r-.-.-r~-.n 

10 

I- 20 LlJ 

LlJ 

LL 

z 

(f) 

LlJ 

I- 30 ::> 

~ s ~ (f) 

0 <( 

0 N ~ I 

I-

<{ 40 s 

z H 

s 

0 WELLS 

0 

s 

<{ 

cc 

IW-2-ASW 

ASW-OW-3 

N 

C0 I 

I S 

s 0 

0 

GRADIENT PER LOG CYCLE 

Pre-injection Post-injection 

11.3 feet 3.4 metres 60.3 feet 18.4 metres 

8.3 feet 2.5 metres 18.3 feet 5.6 metres 

5 

en 

w 

a: 

1-

w 

~ 

z 

en 

w 

1-

10 ~ 

~ 

0 

0 

"'" 1-

4: 

z 

$ 

0 

0 

$ 

4: 

a: 15 0 0 50 OW-3-0W-3 4.4 feet 1.3 metres 7.2 feet 2.2 metres 

OW-2-TW.-1 2.6 feet 0.8 metre 2.6 feet 0.8 metre 

60 

20 

7QL-----~--~-L-L-L.~~------L---~~-L~LL~------~--L-~~~~~----~--~--~~~~ 

0.1 1.0 10 100 

DISTANCE FROM PUMPING WELL, IN FEET 

FIGURE H.-Pre-injection and post-injection hydraulic gradients. 

Figure 11 shows that after injection of freshwater, the 

hydraulic gradient steepened greatly near the pumping 

well and has, in fact, been modified as far as 50ft (15m) 

from the pumping well. The hydraulic gradient steepened 

between OW-3 and OW-2 but not between OW-2 and 

TW-1. This is because freshwater was injected slightly 

beyond the radius of OW-~1 but not as far as OW-2. Everywhere that the freshwater displaced the brackish water, 

deterioration of the aquifer hydraulic conductivity 

occurred. It can be shown, by plotting head buildup versus 

distance for each injection test, that the deterioration 

becomes more severe with each test and does not improve 

significantly with development pumping. The greatest 

amount of deterioration, as would be expected, is close to 

the injection well. 

CURRENT -METER TRAVERSES 

Figure 12 shows the flow pattern of water entering the 

screen during test 1 and the flow pattern during pumping 

before any injection tests. Minor clogging occurred in two 

zones; 917 to 923ft (280 to 281 m) and 951 to 961ft (290 to 

293 m) below sea level. A decrease in flow of 14 percent in 

the upper zone and 15 percent in the lower zone is believed 

to have resulted from clogging of the injection sand by 

particulate matter. Agitation of the drilling mud, silt, and 

sand in the fill-up pipe or movement of drilling mud not 

removed from the filter pack by development may have 

been the source of the material. During the withdrawal 

phase, the clogged zones became productive again, and the 

flow pattern reverted to the pre-injection condition (fig. 

13). 
20 

1--

w 

w 

LL 

z 920 

_j 

w 

> 

w 

_j 

ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

<( 

~93oh444444.+.44?4444+.44202002l.W~i.0GS0.0$.4~44~44~44.4444WW 

z 

<( 

w 

~ 

~ 

0 

~940Hfff+Rff+ff§&.ff484444:4~4.444.4:4+8f++f84+8488f842+4+8f+H Ill 

I 

1--

a... 

w 

0 

ZONE CLOGGED 

275 

(/) 

w 

280~ w 

~ 

z 

_j 

w 

> 

w 

_j 

<( 

w 

(/) 

z 

285 <( 

w 

290 

295 

~ 

~ 

9 

w 

Ill 

I 

1--

a... 

w 

0 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 12.-Current-meter traverses in injection well IW-2 of the pre-injection flow and the flow after 5 hours 

of injection during test 1. 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 

1- (/) 

w w 

w a: 

LL 2801-

z 920 w 

~ 

_J z 

w 

> _J 

w w _J > 

w 

_J 

<( 

z w 

<( (/) 

w z ~ 285<( w 

~ ~ 

0 

_J ~ w 940 

a:l 9 

w 

I a:l 

1-

a.. I 

w 1-

0 a.. 

w 

0 

290 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 13.-Current-meter traverses in injection well IW-2 of the pre-injection flow and the withdrawal flow 

during test 1. 

21 
22 ARTIFICIAL RECHARGE TO A BRACKISH·WATER AQUIFER, VIRGINIA 

During injection test 2, the flow pattern deviated from 

that determined by pre-injection tests (fig. 14). The change 

was not so much in the minor zones that clogged, but 

rather in a new zone that developed and began taking 

water. The sand from 898 to 906ft (274 to 276m) below sea 

level took nearly 20 percent of the total flow by the end of 

24 hours of injecting. 

In all the pre-injection test I traverses, the sand zone 

from 897 to 917ft (273 to 280m) below sea level contributed 

virtually no water from the aquifer. In tests I, 2, and 3, but 

especially in test 2, as pressure became greater in the injection well and sand zones began clogging, the 897- to 917-ft 

(273- to 280-m) zone began taking water. In test 2, this zone 

began taking water after 35 minutes of injection and 

continued taking water in the lower part for the remainder 

of the test. The lower part of the sand zone contributed 

water during the withdrawal phase of test 2 and remained 

open throughout test 3. 

Examination of the drill cuttings and geophysical logs 

indicates that the sand zone from 897 to 917ft (273 to 280 

m) is clean, moderately sorted, porous, and permeable and 

should have contributed water since the initial development of the well. Probable causes for the lack of contribution from this zone are either clogging by drilling mud 

that was not removed from the gravel pack during 

development or by cement implaced during the 

construction of the well. 

Evidence that drilling mud remained in the gravel pack 

consists of glauconite grains and Miocene microfossils 

recovered in the turbid water pumped during the with· 

drawal phase of test 2. Both items are foreign to the 

injection zone. The pH data observed prior to any 

injection tests present strong evidence supporting the 

theory of cement influence of water in IW-2. Injection 

well 2 was completed in May 1970 and was not pumped 

between May 1970 and July 1971. Water samples gathered 

by a thief sampler in December 1970 had a pH of II. 7 

compared with a normal formation water pH of 7.8. 

During subsequent test pumpings over a period of several 

months, the pH was never above 7.8 even when the well 

was idle for as long as a month. These facts indicate that 

the cement reaction had gone to completion before 

injection test I began. 

Nine current-meter traverses were made in IW-2 during 

the injection phase of test2 (fig. 15). I tis significant to note 

that the plot of traverses I through 9 nearly parallel each 

other even though the injection rate decreased from a high 

of 400 gal/min (251/s) during traverse I to 240 gal/min ( 15 

lis) during traverse 9. If the reduction in the ability of the 

aquifer to accept the water was caused by physical 

clogging with particulate matter, the flow pattern could 

be expected to change with time. Clogging would be most 

severe in the zones initially accepting the most water; 

deterioration of these zones would then force flow into the 

less permeable zones. Figure 15 supports the alternate 

theory that the reduction in acceptance of water is due to 

rather uniform reduction in hydraulic conductivity of the 

entire screened interval. 

Figures 16 and 17 illustrate the flow patterns during the 

withdrawal phase of test 2. The percentage of total flow 

from individual sections of the aquifer did not change 

appreciably with time, even though the flow increased 

from 575 to 670 gal/min (36 to 421/s). Traverse 6 (fig. 17) 

more nearly matches the pre-injection flow pattern than 

traverse 1 (fig. 16), probably because of the increased 

percentage of formation water being pumped. Base 

exchange again occurred as the brackish formation water 

replaced the injected water in the formation and increased 

the hydraulic conductivity, although not to its original 

value. 

During injection in test 3, the flow pattern shows a 

drastic variation from those established during injection 

in tests I and 2 (fig. 18). The entire basal section of the 

aquifer, from 945 to 972 ft (288 to 296 m) below sea level, 

took less than 10 percent of the total recharge. In the preinjection traverse, this same zone contributed about 32 

percent of the total flow. Moreover, the zone from 923 to 

945 ft (281 to 288 m) below sea level, which in the preinjection traverse contributed only 10 percent of the total 

flow, took 41 percent of the flow. The flow at the time of 

the traverse was 70 gal/min (4.4 lis). This plugging of 

selected zones and development of less permeable zones 

during injection conforms to the expected pattern of 

changes due to clogging by particulate matter.' 

During test 3, the post-injection withdrawal flow 

pattern roughly parallels the pre-injection flow pattern. 

The reason the traverses do not match is that the lower 

section of the aquifer had failed to develop during the 

period of withdrawal pumping prior to making the screen 

traverse. 

The injection current-meter traverse (fig. 18) could not 

be made until the injection rate stabilized. The initiallOO 

min of injection accounted for nearly all the decrease in 

the rate of injection (fig. 19). By the time the injection 

traverse was made, the acceptance rate of the formation 

had nearly stabilized; particle clogging had effectively 

reduced the input into the more permeable zones, forcing 

water to enter less permeable zones, and causing correspondingly higher injection heads. 

The origin of this particulate clogging may have been 

fine material that accumulated at the bottom of the well 

during the extensive redevelopment pumping following 

test 2. This material may have been agitated into 

suspension at the start of injection in test 3 and lodged in 

the screen and gravel pack. Another explanation might be 

that material from horizons above the screen sifted downward through breaches in the gravel pack around the 

screen, causing some choking of the upper part of the 

screen. 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 

ZONE DEVELOPED 275 

I- (f) 

w w 

w 

LL 280 ~ w z ~ 

_J z 

w 

> _J 

w w _J > 

<( w 

w _J 

(f) <( 

w z (f) <( 

w z ~ 285 <( 

w 

S: ~ 

0 S: _J 

w 0 (]) _J 

w 

I (]) 

I-

(L I 

w I0 (L 

w 

0 

290 

295 

Bottom of s 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 14.-Current-meter traverses in injection well IW-2 of the pre-injection flow, test 2, and the flow after 24 

hours of injection during test 2. 

23 
24 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

275 

(f) 

1- w 

w a: 

w 280 ILL w 

z 2 

z _j 

w _j 

> 

w w _j > 

w 

<( _j 

w 

(f) <( 

w 

z (f) 

<( 

w z 

2 285 <( 

w 

S: 2 

9 

w S: 

(l) 0 

_j 

I w 

1- (l) 

Q_ I w I- 0 Q_ 

w 

0 

950 

295 

290 

0 40 80 120 160 200 

REVOLUTIONS PER MINUTE 

FIGURE 15.-Current-meter traverses in injection well IW-2 during the injection phase, test 2. 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 25 

275 

{f) 

I- w 

w a: 

w ILL 280 w 

z 920 ~ 

z _J 

w 

> _J 

w w _J > 

w 

<( _J 

w 

{f) <( 

w 

z {f) 

<( 

w z 

2 285 <( 

w 

~ ~ 

0 

_J ~ w 940 0 

(I) _J 

w 

I (I) 

I-

(L I 

w I0 (L 

w 

0 

950 

290 

295 

Bottom of screen~ 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 16.-Current-meter traverses in injection well IW-2 of the pre-injection flow, and the withdrawal flow, test 2. 
26 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

275 

1-- (j) 

w w 

w 280 g: IJ... 920 w 

z ~ 

_j z 

w 

> _j 

w w .....J > 

w 

<( .....J 

w 930 (j) <( 

w 

z (j) 

<( 

w z ~ 285 <( 

w 

~ ~ 

0 

.....J ~ w 940 

co 9 

w 

I C) 

1--

0... I w 1-- 0 0... 

w 

0 

290 

295 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 17.-Current-meter traverses in injection well IW-2 of the pre-injection flow, test 2, and the flow after 

75 hours of withdrawal pumping during test 2. 
_J 

w 

> 

w 

_J 

<( 

DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 

~930~------------~~~--~--------~~~~~~~=-----------~ 

z 

<( 

w 

~ 

~ 

0 

~940pjf:tf74titf:jtfjjjitf:t77btf:tti77Ft7:7:77:7tttftttttttttttttJ (() 

I 

f0.... 

w 

0 

ZONE DEVELOPED 

ZONE CLOGGED 

960~--~~--------------------------------------------------~ 

z 

_J 

w 

> 

w 

_J 

<( 

w 

(/) 

z 

<( 

285W ~ 

~ 

0 

_J 

w 

(() 

I 

f0.... 

w 

0 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 18.-Current-meter traverses in injection well IW-2 of the pre-injection, injection, and withdrawal flows, 

test 3. 

27 
28 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

70 

65 

60 

w 55 

1-

::J 

0 

0 

0 

0 

0 

z 

~ 50 

a: 

~ 45 0 

(/) 

I I I I I I I I I I 

/Test 1~ 

./ 

/ ..0.. ~ 

~ 

I I I I I I I I I I I 

o o r:,. Data points 

I I I I I 

-

r40 

Cl 

z 

0 

0 

w 30 (/) 

a: 

w 

a.. 

5 40 _J 

_J 

0 ----

(/) 

w 

a: 

<3 35 

z 

30 w 

I-

<( 

a: 25 

z 

0 

I- 20 

0 

w 

' z 15 

10 

5 

0 

0 

0~ 

0 

~Test3 

0 ~ 

0 ~ 

0 

0 I I I I I I I I I 

~ Test 2 

~ 

~ ~ 

I I 1 1 _I I I I I I I I I I I I I 

I-

-' 

z 20-

w 

~ a: 

z 

0 

1--

0 

w 

10 :i 

10 100 1000 

0 

10.000 

TIME SINCE PUMPING BEGAN, IN MINUTES 

FIGURE 19.-Changes in injection rate with time during tests I, 2, and 3. 

SPECIFIC CAPACITY 

Figure 20 shows the change of InJection specific 

capacity with time (see table 6). It illustrates, as did the 

decline in injection rate, the progressive deterioration of 

the aquifer hydraulic conductivity with successive tests. 

Neither development nor withdrawal pumping returned 

the specific capacity of the well to pre-test levels, 

indicating permanent deterioration of the aquifer 

properties. Moreover, after the first few minutes, decline in 

specific capacity during injection continued at nearly the 

same rate as established in the previous injection test. 

Figure 20 shows that a definite departure from the preinjection specific capacity pattern occurred in all three 

injection tests. The test 2 line falls between test 1 and the 

pre-injection line rather than between the lines for tests 1 

and 3 because the head values for the annular-space well 

(ASW) had to be used rather than those of the injection 

well due to failure of the transducers in IW-2. The slope of 

the line is valid, however. Figure 20 suggests that if additional injection tests were made under the same conditions as the previous tests, further deterioration of the 

specific capacity of the well could be expected. 

CONDUCTIVITY SURVEYS 

During the injection phase of test 1 and the injection 

and withdrawal phases of test 2, conductivity traverses 

were made in the screen of OW-3 using a downhole probe 

to detect the arrival and movement of freshwater. The 

background conductivity along the traverse in OW-3 was 

4,800 micromhos on a scale of 0 to 6,000. Changes of 50 

micromhos were considered significant. No apparent 

freshening of the water in OW -3 occurred during test 1. 

The first definite detection of freshwater in OW-3 was 

during test 2 after 5,433 min (3.77 days) of injection (fig. 

21). Approximately 1.8 Mgal (6,800 m!S) of freshwater had 

been injected at that time. The freshwater first appeared 

at the depth interval of 895 to 899 ft (273 to 274 m) below 

sea level, near the top of the injection zone. 

Figure 21 indicates that there may have been some 

internal flow within OW-3 during the injection test 

caused by small vertical head differences in the aquifer; 

uncertainty regarding such internal movement 

complicates the interpretation of the breakthrough curves. 

Nevertheless, there appear to be two additional zones in 

which breakthrough of freshwater occurred as the 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 29 

r18r---------------------------------------------------------------------------------~ w 

0 ~ 0 Pre- inject ion test 1 withdrawal r ~ w 

(temperature corrected) ~ 

~16~----~~----------~------------------------------------------------------------~ 

a.. • o o 6 Data points ~ 

w -3~ r 

~14~----------~~'=--~~~~~~~~ .. ~~--------------------------------~ ~ 

~ 8 ~ ~ ~12r-----~u-~~------------------~~----------------------------------------------~ ~ 

~ w 

z a.. 

0 ~ j10r-----------------------------~~~~------~~----------------------------------~ 2~ 

~ r ~ ~ 

~8 z 

r r 

r r 

~6 ~ a.. a.. ~ ~ u u 

~4 u ~ ~ 

u Test 3 u 

w w 

~2 ~ 

OL-------~--~--~~~~_L~~------L----L--~-L~-L~~------~----~--L-~_L_L~LLQ 

10 100 1000 10,000 

TIME SINCE INJECTION BEGAN, IN MINUTES 

FIGURE 20.-Pre-injection withdrawal specific capacity of injection well IW-2 and injection specific capacity during tests 1, 2, and 3. 

injection continued. The zones are from 908 to 916ft (277 

to 279m) and 932 to 941 ft (284 to 287m) below sea level. 

Figure 22 illustrates that the section of the aquifer taking 

57 percent of the total flow in IW-2 is the same interval in 

which the dominant freshwater breakthrough occurred in 

OW-3. Noapparentfresheningofthewaterin OW-2, 75ft 

(23 m) from the injection well, occurred during test 2. 

During injection test 4, which will be described in a subsequent section, conductivity surveys were made in both 

OW-3 and OW-2 (figs. 23 and 24). Freshwater was 

detected in OW-3 after 1.82 Mgal (6,890 m3) had been 

injected, virtually the same volume as was injected during 

test 2. The freshwater was again detected in virtually the 

same intervals as in test 2, indicating that the flow pattern 

between the injection well and OW-3 was repeatable. 

Freshwater was detected in OW-2 after 6.67 Mgal (25,250 

m3) of freshwater had been injected in IW-2. 

Figure 25 is a lithologic section of a part of the well field 

showing the zones taking water in the injection well 

during injection test 4 and the zones of detection in the 

nearby observation wells. It demonstrates the continuity of 

sand lenses within the injection zone. The clay and silt 

beds from about 880 to 890ft (268 to 271m) and 975 to 985ft 

(297 to 300m) below sea level in OW-2 are the confining 

beds of the aquifer. 

There is good correlation between the intervals of high 

input in the injection well and the intervals of freshwater 

breakthrough in the observation wells, suggesting that the 

flow occurred in a virtually horizontal pattern. 

If it is assumed that the injection front moves outward 

in the aquifer in the form of a cylinder, the radius of the 

freshwater zone, neglecting hydrodynamic dispersion, is 

given at any time by the equation: 

7:-(t)=~rv-' (7) 2 ,-;;;;o 

where V=volume of water that has been injected up to 

timet, in cubic feet; 

m=thickness of aquifer, in feet; 

o=porosity. 

Equation 7 is equivalent to equation 3 except that rw 

is considered to be negligible, V is used in place of 
30 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

860.--------------------------------------------------------------------------------------. 

870r------------------------------------------------------------------------------------r265 

t = 5433 minutes, (3.77 days) 

1.81 million gallons, t=6525 minutes, (4.53days) (/) 

w 

a: 

1-

270~ 

~ 880 (6850 cubic 

w metres) injected lL 

~8901-----------+~--~::::::::::~----------------~~---------------­

1=6936 minutes, ( 4.82 days) 

2.20 million gallons, (8330 

cubic metres) injected z 

_j 

w 

> 

w 

_J 

w 

> 

~ 9001----------

<( 

w 

(/) 

z 9101----------

<( 

w 

~ 

s 920 

0 

_J 

w 

m g3o t----------

I 

1-

0... 

~ 9401-----------

950~--------------

275....J 

<( 

w 

(/) 

z 

<( 

w 280~ 

s 

0 

_J 

w 

co 

285~ 

290 

0... 

w 

0 

960~------------------------------------------------------------------------------------~ 

~ 

DECREASING CONDUCTIVITY 

FIGURE 21.-Conductivity profiles in observation well OW-3 during injection phase, test 2. 

TABLE 6.-Specific capacity of injection well IW-2 during the injection TABLE 6.-Specific capacity of injection well IW-2 during the injection 

phase of tests 1, 2, and 3 phase of tests 1, 2, and 3 -Continued 

Injection rate Time since Water-level Specific capacity Injection rate Time since Water-level Specific capacity change in change in (gal/min) injection began IW=2 (gal min=1ft=1) (gal/min) injection began IW=2 (gal min=1ft=l) 

(min) (ft) (min) (ft) 

Injection Test I Injection Test·3 

400 6 26.0 15.4 245 20 66.7 3.7 

400 10 29.5 13.6 240 32 69.4 3.5 

400 20 33.1 12.1 215 40 75.6 2.8 

400 30 33.9 11.8 185 50 72.9 2.5 

400 40 34.5 11.6 175 60 75.8 2.3 

400 50 34.8 11.5 155 67 75.8 2.0 

400 60 35.5 11.3 135 73 75.8 1.8 

400 90 37.0 10.8 125 77 75.8 1.6 

400 120 38.7 10.3 115 90 75.9 1.5 

400 160 40.0 10.0 105 120 76.2 1.4 

400 180 40.0 10.0 90 250 84.0 1.1 

400 220 41.0 9.8 70 900 72.9 0.96 

400 260 43.0 9.3 70 1020 75.9 0.92 

70 llOO 75.4 0.93 

Injection Test 21 

400 35 28.1 14.2 1Change in water level measured in ASW rather than in IW-2. 

400 145 32.0 12.5 

375 560 39.5 9.5 Q(t-tc ), and it is recognized that the thickness of aquifer, 335 1380 44.3 7.6 

330 1440 44.6 7.4 m, accepting flow may differ from the screen length, D. 

295 2790 49.7 5.9 

At the time of detection of freshwater in OW-3 during 

285 3030 50.6 5.6 test 2, a total of 1,813,000 gal (6,860 m3) had been injected. 

270 4290 52.1 5.2 Using equation 7 and this volume, expressed in cubic feet, 220 6681 55.9 3.9 

215 7896 57.8 3.7 and using m=80 ft (24m), 6=0.30, ri ( t) is calculated as 56.7 
DETERIORATION OF AQUIFER HYDRAULIC PROPERTIES 31 

860 

870 

880 

tu 890 w 

u.. 

z 

- 900 

...J 

w 

~ 910 ...J 

<( 

w 

C/) 920 z 

<( 

w 

~ 930 

~ 

0 

...J 

~ 940 

I 

1-

Q_ 

~ 950 

960 

970 

980 

I 

IW-2 

50 feet, (15 metres) 

Percentage of total flow entering screen 

after 4290 minutes (3.04days) of injection test 2. 0=270 gallons per 

minute, ( 17 litres per second). 

1.48 million gallons, (5600 cubic 

metres) injected. 

32 percent 

25 percent 

I 5 percent 

I 6 percent 

112 percent 

.......... percent 

16 percent 

T 

OW-3 

\ Conductivity profile after 6936 minutes, 

(4.82 days) of injection test 2. 

.,)!! 2.2 million gallons, (8330 cubic 

:::: metres) injected. 

~ 

IJitm 

:;:;:;:;:: I =;::::;:::;: ::::::::::: 

~ 

DECREASING CONDUCTIVITY 

-

-~-

f--

-

-

-

f--

265 

270~ ([ 

1-

w 

~ 

z 

275 ...J 

w 

> 

w 

...J 

<( 

280W C/) 

z 

<( 

w 

~ 

285~ 

9 

w 

CD 

I 

1-

Q_ 

290~ 

295 

FIGURE 22.-Conductivity profiles in observation well OW-3 and current-meter traverse in injection well IW-2, test !~. 

ft (17.3 m). However, the current-meter traverses show 

that only about 60 ft (18m) of the injection-well screen 

was taking water; if m is taken as 60ft (18m) rather than 

80 ft (24 m), ri (t) is calculated as 65.5 ft (20 m). Again, 

the current-meter traverses show that 40 percent of the 

total inflow occurred in the sand between 900 and 920 

ft (274 to 280 m) below sea level, which correlates with 

the intervals of early breakthrough in OW-3. If equation 

7 is solved using 40 percent of the injected volume and 

using m=20 ft (6 m), Ti (t) is calculated to be about 72 ft 

(22 m). Thus, the injected water should have reached 

OW-3, at a distance of 50ft (15m) from the injection well, 

from 1 day to more than 2 days prior to actual detection, 

depending upon the assumptions used. 

The calculations indicate that the injection front 

probably did not move out equally in all directions and 

form a cylinder. Subsequent calculations relating to the 

arrival time in OW-2, 75ft (23m) from the injection well, 

confirm this interpretation. A possible alternative is that 

the front may have had an elliptical form, as should be 

expected if the aquifer were homogeneous but anisotropic. 

However, comparison of the arrival times in OW-3 and 

OW-2 during test 4 rules out this possibility. It does seem 

clear, however, that the injection front was elongate in a 

direction roughly normal to the line through OW-2, 

OW-3, and the injection well. Trial calculations show 

that this elongation could not be due to superposition of a 

radial flow on the original hydraulic gradient in the 

aquifer, as this original gradient was very sn1all. 

AQUIFER HETEROGENEITY 

A reasonable explanation of the arrival time data can be 

offered on the basis of the geology. The zone of greatest 

hydraulic conductivity in the upper part of the aquifer is 

probably a channel-fill or a shoestring sand. A deposit of 

this type would have the coarsest material along the center 

of the channel, with transition to progressively finer 

material along the sides. The average hydraulic 

conductivity across the channel would accordingly be 

lower than that along the channel axis, and injected water 

would tend to follow the channel axis. The channel would 

have a meandering orientation, but presumably its overall 

lineation would be at some angle to a line through OW-2, 

OW-3, and the injection well (IW-2). This interpretation 
32 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

860r---------------------------------------------------------------------------------~ 

870r-----------------------------------------------------------------------------------r265 

1-

w 

w 

880r---------------------------

t= 9935 minutes, (6.90 days) 

1.82 million gallons, (6890 

cubic metres) injected 

t=10,130 minutes.(7.03days) 

1.84 million gallons, (6960 

cubic metres) injected 

t=11,700 minutes. (8.12days) 

2.02 million gallons.(7650 

cubic met res) injected (/) 

270W a: 

1-

w 

~ 

LL 890 z 

....J 

~ 900r---------------~~---­ w 

....J 

<X: 

~ 910r-----------~L---------~::;::;:;: 

z 

<X: 

z 

275_j w 

> 

w 

....J 

<X: 

w 

(/) 

~ 920r--------==-------------~::::::~--------------------E:::::::::::r---------------------------------~ 280 2 

<X: 

w :s: ~ 0 Lti 93or---------------------~ 

OJ 

I 

~ 940r----------------------~l~:;: w 

0 

:s: 

0 

285 Lti 

290 

295 

OJ 

I 

1-

0.. 

w 

0 

970~--------------------------------------------------------------------------------~ 

~ 

DECREASING SPECIFIC CONDUCTANCE 

FIGURE 23.-Conductivity profiles in observation well OW-3, test 4. 

is supported by aquifer-test data, which indicate that the 

specific capacities of wells IW -2 and TW -1 are higher 

than those of OW-3 and OW-2. 

WATER QUALITY 

COMPARISONOFTHECHEMISTRYOFOT\' AND 

FORMATION WATER 

The city water is a calcium sulfate chloride type, and the 

formation water is a sodium chloride bicarbonate type. 

The major constituents are listed in table 7. The dissolvedsolids concentration of the city water varied between 110 

and 190 mg/1, and the formation water contained about 

3,000 mg/l. 

WATER SAMPLING 

Prior to injecting any freshwater into the host formation, consideration was given to the possibility of 

chemical reactions which might interfere with the injection process. For example, the freshwater to be injected 

was generally saturated with dissolved oxygen while the 

formation water contained none. Thus, if high concentrations of iron and manganese were present in the 

formation water, precipitation of iron or manganese 

TABLE 7.-Concentration of major constituents from Moore's Bridges 

Filter Plant city water and formation water. 

[Values given in mg/1 unless otherwise noted) 

Constituents Formation water City water 

Silica (Si02) ................................................ .. 

Calcium (Ca) .............................................. .. 

Magnesium (Mg) ......................................... . 

Sodium (Na) ............................................... .. 

Potassium (K) ............................................. .. 

Bicarbonate (HCO~) ................................... .. 

Sulfate (S04) ................................................ . 

Chloride (Cl) .............................................. .. 

Nitrate (NOs) .............................................. . 

Phosphate (P04) ......................................... . 

Boron (8) ..................................................... . 

Fluoride (F) ................................................. . 

Dissolved solids .......................................... .. 

pH ............................................................... . 

Specific conductance (micromhos) ............ .. 

13 

l4 

8.7 

1,140 

25 

624 

136 

1,360 

.1 

.28 

3.4 

1.4 

3,010 

7.9 

5,000 

3.8 

17 

2.6 

9.5 

1.6 

9.0 

36 

21 

1.2 

.00 

.04 

.1 

Ill 

5.8 

190 

hydroxides could occur within the formation when the 

freshwater was injected, resulting in loss of hydraulic 

conductivity of the aquifer. Chemical analysis, however, 
WATER QUALITY 33 

870.---------------------------------------------------------------------------------~ 

880r---------------------------------------------------------------------------------~ 

z 

t= 31 days 

6.67 million gallons, 

(25,250. cubic met res) 

injected 

ui 91 01-----------1----------

> 

UJ 

~ 

~ 920t---------

(/) 

z 

~ 9301--------------------

::2: 

5 9 9401------------------~: UJ 

Ill 

I 

~ 9501-------------------

UJ 

0 

t = 40 days 

8.77 million gallons, 

(33,190 cubic metres) 

injected 

t = 41 days 

9.06 million gallons, 

(34,290 cubic metres) 

injected 

t=45 days 

270 

(j) 

UJ 

a: 

rUJ 

275::2: 

z 

....J 

UJ 

> 

UJ 

....J 

280<{ 

UJ 

(j) 

z 

<t: 

UJ 

285::2: 

5 

9 

UJ 

Ill 

I 

290b:: 

UJ 

0 

980~--------------------------------------------------------------------------------~ 

~ 

DECREASING SPECIFIC CONDUCTANCE 

FIGURE 24.-Conductivity profiles in observation well OW-2, test 4. 

indicated that the iron and manganese concentration in 

the formation water is too small (less than 0.1 mg/1 to 

account for significant loss in hydraulic conductivity 

because of precipitation. Another possible chemical 

reaction was precipitation of calcium carbonate. 

However, studies carried out by Ivan Barnes (written 

commun., 1968) indicated that the concentration of 

calcium in both the freshwater and formation water was 

below equilibrium (saturation) values, and no preci)litation would occur when the two waters mixed. 

After examining the data, it was believed that when 

injection occurred, the major chemical effect would be 

simple dilution; in which case, three chemical zones 

would be formed around the wellbore. These include, in 

order of decreasing distance from the well bore: (I) 

Undiluted formation water; (2) mixed formation and 

freshwater; and (3) freshwater. In order to chemically 

define these zones during the freshwater withdrawal 

phase, water samples were collected for chemical analysis 

whenever a change in specific conductance occurred 

(increase in specific conductance of 200 to 500 micro mhos. 

The range in specific conductance was approximately 200 

micromhos in freshwater to 5,000 micromhos in 

formation water. It was also believed that in collecting 

samples with respect to changes in specific conductance, 

the resulting chemical data would indicate not only when 

unsuspected reactions occurred, but also which 

constituents were involved. Unfortunately, as will be 

discussed later, some reactions took place when there was 

little or no change in specific conductance, and the withdrawn water was still virtually fresh. 

ANALYTICAL RESULTS 

It was previously stated that the formation water is 

predominately a sodium chloride type containing approximately 1,100 and 1,400 mg/1 ,sodium and chloride, 

respectively. The freshwater contained 9.5 and 2 .I mg/1 of 

sodium and chloride, respectively. It was assumed that as 

these two waters mixed a dilution would occur, and the 

analytical data as shown in table 8 tended to support this 

assumption. However, when these data concerning 

variations in the concentrations of sodium, chloride, and 

dissolved solids were plotted against specific conductance 

(fig. 26), the assumptions weakened. For example, the 

chloride values produced almost a straight-line relationship with respect to specific conductance, but sodium and 
34 

1-

w 

w 

u.. 

z 

_j 

w 

> 

w 

....J 

<( 

w 

Cf) 

z 

<( 

w 

~ 

s 

0 

....J 

w 

Ill 

I 

1-

a.. 

w 

0 

870 

900 

910 

920 

930 

940 

950 

960 

970 

980 

990 

1000 

ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

DISTANCE, IN METRES 

25 20 15 10 5 0 5 10 15 

OW-2 IW-1 IW-2 OW-3 

80 70 60 0 10 

EXPLANATION FEET 

F~\'::::~/?riLA Sand 

§----=---==@ CIa y 

I 

I 

Zone taking 90 percent of flow during injection test 4, (based on 

current- meter traverse). 

Zone where injected water appeared in observation wells during 

injection test 4 (based on conductivity profiles). 

20 

255 

260 

265 

Cf) 

w 

a: 

1-

270 ~ 

z 

....J 

275 ~ 

w 

....J 

<( 

UJ 

280 Cf) 

z 

<( 

w 

~ 

285 s 

0 

....J 

w 

Ill 

290 I 

fa.. 

w 

0 

295 

300 

305 

FIGURE 25.-Lithologic section showing injection zone in injection well IW-2 and zones of detection of freshwater in observation 

wells OW-2 and OW-3. 
WATER QUALITY 35 

SODIUM CONCENTRATION. IN MILLIEOUIVALENTS PER LITRE 

0.5 1.0 5.0 10 

U) 

w 

w 

a: 

Cl 

w 

0 

L() 

N 

I-

~ 

U) 

0 

I 

~ 

~ 1000 

u 

~ 

z 

w 

u 

z 

~ 

t; 500 

::J 

0 

z 

0 

u 

~ 

u. 

u 

w 

a... 

U) 

o Data point 

J 

DISSOLVED SOLIDS 

50 100 500 1 000 5000 10.000 

CHLORIDE AND DISSOLVED SOLIDS CONCENTRATION, IN MILLIGRAMS PER LITRE 

FIGURE 26.-Chloride, sodium, and dissolved solids versus specific conductance of recovered injected water from tests I, 2, and 3. 

the dissolved solids did not. Sodium and dissolved-solids 

concentrations tended to increase at a greater rate than 

changes in specific conductance or chloride, which 

indicated that sodium ions were being evolved by chemical 

reaction. The dilution concentration of other 

constituents, such as calcium and magnesium, indicated 

that there was little or no relationship between variations 

in concentration with respect to changes in specific 

conductance. 

CHANGES IN THE CONCENTRATIONS OF CALCIUM, 

MAGNESIUM, AND SODIUM 

The concentrations of calcium and magnesium in city 

water were 17 and 2.6 mg/1, respectively, and in formation 

water averaged 14 and 8.7 mg/1, respectively. The calcium 

and magnesium values in table 8 indicate that the concentrations of these two constituents in the mixed water were 

at times much lower or higher than their concentrations in 

either city or formation water. The water containing the 

low concentrations, however, was still virtually 

freshwater. During the later periods of withdrawal, when 

formation water became dominant in the mixture, the 

calcium and. magnesium concentrations began to increase 

and were greater than could occur in a simplle mixture. 

Near the end of withdrawal in test 1, the concentration of 

calcium was almost twice that in either city water or 

formation water. There appeared to be little doubt that 

calcium and magnesium were involved in some form of 

reaction as the freshwater entered the formation and that 

the reaction was reversible (fig. 27). 

If calcium and magnesium concentrations were not 

decreasing as a result of calcite precipitation, then the 

decrease must have been due to simple cation exchange 

with the sodium-saturated clay within the formation. 

When calcium in the freshwater was exchanged onto the 

clay, exchangeable sodium from the clay should be 

released into the water. Thus, there should be an excess of 

sodium in the water when calcium concentrations 

approach minimum values. Figure 27 shows that calcium 

from the water was being lost (sorbed onto the clays) when 

the water was still fresh. As the percentage of formation 

water increased (based upon specific conductance), the 

calcium was exchanged from the clay into the water. 

Because of the small amount of sodium exchanged 
36 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

TABLE B.-Variations in water chemistry of mixed freshwater and 

formation water during withdrawal, injection tests 1 and 2 

Specific Formation . . . . conductance water Calcmm Magnesmm.Sodmm PotassiUm Bicarbonate Sulfate Chloride 

(micromhos) (percent) (mg/l) (mg/l) (mg/l) (mg/l) (mg/1) (mg/1) (mg/1) 

Freshwater 

180 0.0 17 2.6 9.5 1.6 9 36 21 

Injection test I 

290 1.0 6.2 2.0 48 8.4 60 34 35 

370 2.0 4.0 2.1 72 8.8 73 35 49 

840 11 8.0 2.3 160 13 129 45 170 

2000 35 23 8.0 400 26 272 75 500 

3400 61 31 12 710 35 422 100 860 

4600 93 23 ll 1000 40 582 130 1300 

Formation water 

5000 100 l4 8.6 1200 40 618 150 1400 

Freshwater 

180 0.0 17 2.6 9.5 1.6 9 36 21 

Injection test 2 

190 0.3 10 3.2 17 2.9 8.0 36 24 

245 .5 20 3.8 20 3.7 31 42 27 

360 1.8 5.6 1.3 63 8.6 67 40 46 

460 3.3 5.3 l.l 85 8.9 81 40 67 

1400 14 10 2.5 220 13 256 52 220 

1800 28 16 4.8 360 15 228 48 410 

2300 36 16 5.5 460 17 274 66 520 

2600 43 16 6.0 530 19 312 71 620 

2900 51 17 6.4 590 21 352 74 720 

3200 58 19 7.2 680 23 400 69 820 

3800 68 24 8.8 800 25 456 81 960 

4900 96 22 10 1000 29 620 63 1200 

Formation water 

5000 100 15 8.8 llOO 29 608 69 1300 

compared to the total in the water, the sodium data do not 

show clearly that there was excess sodium during the 

periods when calcium was being lost from the water. 

There is a slight change in the slope of the sodium curve 

(fig. 26) at low concentrations, indicating that the concentration of sodium was increasing at a greater rate than the 

specific conductance of the mixed waters. 

An indirect technique to show that cation exchange was 

occurring was attempted based on the assumption that ( 1) 

chloride ions do not enter into any reactions during either 

the injection or withdrawal of the fresh water (fig. 26) and 

(2) sodium was irtvolved in only the cation-exchange 

reaction. The ratio of sodium to chloride in city water is 

0. 71 and in formation water is 1.30. The ratios obtained 

from all the analytical data indicated that the sodium to 

chloride ratio was never less than 0.71, but was frequently 

more than 1.30. Furthermore, when the ratio was more 

than 1.30, the calcium concentration was much less than 

that of either the city or formation water, as shown in table 

9. If a comparison is made between the calcium concentration data and the sodium to chloride ratios shown in 

figure 27, it can be seen that, with respect to specific 

conductance, excess sodium concentrations occurred 

TABLE 9.-Sodium to chloride ratio and associated concentrations of calcium in samples collected during injection tests 

1 and 2. 

Specific 

conductance Sodium-chloride ratio Calcium 

(micro mhos) (meq/1) (mg/1) 

Injection test I 

290 2.11 6.2 

370 2.27 4.0 

840 1.45 8.0 

2000 1.23 23 

3400 1.27 31 

4600 1.19 23 

5000 1.30 14 

Injection test 2 

190 1.09 10 

245 1.14 14 

360 2.11 5.6 

460 1.96 5.3 

1380 1.54 10 

1800 1.35 16 

2300 1.36 16 

2600 1.32 16 

2900 1.26 17 

3200 1.11 19 

3800 1.29 24 

4900 1.29 22 

5000 1.30 15 

during the withdrawal periods when calcium concentrations were approaching minimum values. 

EFFECT OF CATION EXCHANGE ON FORMATION CLAY 

DURING INJECTION 

It is unlikely that cation exchange during the injection 

phases had any effect except to slightly lower the zeta 

potential (tendency to disperse) of the clays. If the sodium 

montmorillonite-illite clay were going to disperse when 

subjected to freshwater, the exchange of calcium for 

sodium would only slightly lower this tendency. The 

chemical data were actually showing a solution to the 

problem rather than a cause of clogging. The fact that even 

low concentrations of calcium would exchange for 

sodium on the clay indicated that the clay would respond 

to chemical treatment. 

LABORATORY DETERMINATION OF 

HYDRAULIC CONDUCTIVITY DETERIORATION 

In order to substantiate the hypothesis that clay 

dispersion caused hydraulic conductivity deterioration in 

the aquifer, core samples of the injection sand taken 

during the drilling of OW -3 were sent to the hydrologic 

laboratory to determine if the aquifer was "water 

sensitive." Testing procedures were similar to the 

techniques described by Hewitt ( 1963 ). The cores were 

saturated with formation water for 24 hours prior to 

testing. Hydraulic conductivity was determined by 

running formation water through the core until the values 
DETERMINATION OF CONDUCTIVITY DETERIORATION 37 

(/) 

:::::> 

(/) 5000 _J 

w 

0 

(/) 

w 

w 

0: 

C9 

w 

0 

1.!) 

N 

I-

<( 

(/) 

0 

I 

~ 

~ 1000 

0 

~ 

z 

u.i 

0 

z 

~ 0 

:::::> 

0 

z 

0 

0 

~ 

LL. 

0 

w 

0... 

(/) 

Concentration of calcium 

in format ion water 

Beg1n Withdrawal 

TEST 1 

o c Data points 

Concentration of 

in formation 

water 

Concentration of sodium 

in fresh water 

100L---------~-----L--~--~-J--L-~~--------~ 

0.1 0.5 1.0 2 0 1 2 3 

CALCIUM CONCENTRATION, IN 

MILLIEQUIVALENT$ PER LITRE 

SODIUM TO CHLORIDE RATIO. IN 

MILLIEQUIVALENT$ PER LITRE 

FIGURE 27.-Calcium concentration and sodium to chloride ratio versus specific conductance during the recovery of injected water, tests 1 

and 2. 

stabilized. City water was then introduced into the core, 

displacing the formation water. Hydraulic conductivity 

was measured until the value stabilized (table 10). 

Laboratory results matched the field tests in that the 

hydraulic conductivity of the sand was irreversibly 

reduced. Reductions in hydraulic conductivity ranged 

from 50 percent to over 70 percent/The aquifer, on the 

basis of Hewitt's 1963 classification (water permeabilityKlinkenberg (gas) permeability is less than 0.3), would be 

classified as strongly sensitive to freshwater. 

Various chemicals were added to the city water to 

prepare a pre-flush prior to injection in an attempt to 

overcome the dispersion problem (table 10 and fig. 28). 

Sodium hydroxide and sodium carbonate were added to 

adjust the pH of the city water to values similar to, or 

greater than, that of the formation water. Deterioration of 

the hydraulic conductivity was not prevented by this treatment. Sodium hexametaphosphate, a compound used to 

clean wells that have had excessive invasion of drilling 

mud, was introduced into the core as a mixture in the city 

water. The compound did not prevent reduction .in the 

hydraulic conductivity, and, because it acts as a dispersant, 

probably magnified the damage. 

The fact that a turbid effluent resulted when either 

untreated or chemically treated city water was introduced 

into the core saturated with formation water indicates 

dispersion was occurring. When the city water wastreated 

with calcium chloride, the double layer around the clay 

particles-and consequently the zeta potential-was 

reduced. No reduction in hydraulic conductivity occurred, 

and the effluent was clear, indicating dispersion and 

migartion of clay did not occur in any significant amount. 

When a calcium chloride pre-flush was used (fig. 28, 

sample 73Va9), followed by untreated city water, a 

reduction in hydraulic conductivity of only 11 percent 

occurred. Reed (oral commun., 1973) has found that all-
38 ARTIFICIAL RECHARGE TO A BRACKISH-WATERAQUIFER, VIRGINIA 

0 

z 

SAMPLE 73Va5 

Formation water. 1400 milligrams 

per l1tre Cl-1 

SAMPLE 73Va7b 

0.0 0.05 0.01 0.15 0 20 0.25 0.30 0.0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 

HYDRAULIC CONDUCTIVITY, IN METRES PER DAY 

SAMPLE 73Va9 

SAMPLE 73Va6 

0.0 0.05 0.10 0.15 0.20 0.25 0.30 0.0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 

HYDRAULIC CONDUCTIVITY, IN METRES PER DAY 

FIGURE 28.-Effects on the hydraulic conductivity caused by injecting city water containing various chemicals into a core saturated with 

formation water. 

to 12-percent reduction in hydraulic conductivity occurs 

in wells treated with polymeric-hydroxy aluminum in 

water-flood projects and should be expected if either the 

calcium or aluminum treatment is used to stabilize clay. 

The core was resaturated with formation water, then 

injected with untreated city water. Clogging did occur, 

and the effluent was slightly turbid, indicating the 

calcium for sodium cation exchange is a reversible 

reaction. The reduction in hydraulic conductivity was not 

so severe as in previous tests, suggesting that the cation 

exchange may not be as complete when exchanging 

sodium for calcium at the concentrations used in this 

experiment. This is to be expected, as the calcium ion is 

held more tightly than the sodium ion. 
INJECTION TEST 4 39 

TABLE 10.-Effect of water chemistry on laboratory hydraulic conductivity for core samples from 

injection zone of obsewation well OW-3 

Laboratory Depth Klinkenberg Water Water Input Hydraulic Effluent sample permeability conductivity 

number (ft) (millidarcy) (m/d) type modification pH (mid) condition 

73Va2a 892-912 1050 8.7xl0-1 formation none 8.5 4.2xl0- 1 clear 

2a city none 6.5 2.15xl0-1 turbid 

2a formation none 8.5 2.42xl0-1 clear 

2b 892-912 formation none 8.3 4.98'xl0- 1 clear 

2b city Na0H1 8.35 2.25xl0- 1 turbid 

2c 892-912 formation rione 8.3 1.34 clear 

2c city Na2C03

2 10.2 4.52xl0- 1 turbid 

73Va5 955-975 1320 l.l formation none 7.5 2.43xl0- 1 clear 

5 city none 6.5 6.49xl0-2 turbid 

5 formation none 7.5 7.2xl0-2 clear 

73Va6 955-975 2150 1.8 formation none 7.5 2.56xl0- 1 clear 

6 city none 6.5 7.76:xl0-2 turbid 

6 city Na(P03 )n3 7.48xl0-2 turbid 

6 formation none 7.5 7.77xl0-2 clear 

73Va7b 955-975 formation none 7.0 6.2xlO-I clear 

7b city NaOH4 7.3 2.7xl0- 1 turbid 

7b formation none 7.0 2.5xl0- 1 clear 

73Va9 955-975 formation none 2.08xl0- 1 clear 

9 city CaC12

5 2.08x10-l clear 

9 city none l.86xl0- 1 clear 

9 formation none 2.20xl0- 1 clear 

9 city 

'Enough added to bring pH equal to or greater than 8.3. 

240 mg ;J added. 3 100 mg-'1 added. 

INJECTION TEST 4 

A fourth injection test was made to determine the 

effectiveness of chemically treating the clay to prevent 

dispersion under field conditions. Because the damage to 

the aquifer from clay dispersion during the first three tests 

severely reduced the capacity of the well to accept water, it 

was decided to use an inexpensive, nonpermanent, 

calcium chloride pre-flush treatment to stabilize the clay. 

As the pre-flush moves away from the well screen, the 

calcium ions in the solution are exchanged onto the clay 

replacing the sodium ions. The pre-flush becomes a 

sodium chloride solution with time due to addition of 

sodium ions exchanged by the clay. Once the calcium ions 

in the pre-flush solution are reduced and reach the 

concentraticn of the formation water, the effectiveness of 

the pre-flush is negated, and dispersion, migration, and 

particle plugging occur in the aquifer. Thus, a decrease in 

injection rate and increase in injection head buildup will 

occur when the freshwater enters the untreated part of the 

aquifer away from the well. 

It is neither practical nor necessary to treat the entire 

area that will come into contact with the injected water. In 

any problem of flow toward a well, the cross-sectional area 

of flow decreases sharply as the well is approached, and the 

greatest head losses occur close to the well. This can be 

shown by a simple application of Darcy's law, which states 

that as the cross-sectional area of flow decreases, the 

none l.74xl0- 1 slightly 

turbid 

4Enough added to modify pH to between 7.0 am:l8.0. 5 1.375 grams per litre (0.14 percent solution) added. 

hydraulic gradient must increase, other factors remaining 

equal. In the present problem, this leads to the conclusion 

that if the area immediately around the well can be treated, 

most of the increased head losses, due to hydraulic 

conductivity deterioration, can be avoided. The exact 

distance from the well to which the treatment should 

extend is controversial; however, discussions with 

personnel from oil field service companies indicate that 

the preferred radius of treatment lies within the limits of 3 

to 10 ft (0.9 to 3 m) from the borehole. 

Injection test 4 was begun Nov. 24, 1972. A pre-flush of 

3,000 gal (11 m3) of 0.2N calcium chloride was injected in 

front of the city water. Based on current-meter data, this 

volume would theoretically treat the aquifer to a radius of 

8ft (2 m) in the most permeable zones. 

The injection rate stabilized at 185 gal/min ( 121/s) after 

10 minutes and was maintained at that rate for 115 minutes. The hydraulic gradient declined throughout this 

time indicating that the treatment was working effectively. 

After 115 minutes, the injection rate began to decline 

slowly, and the injection head pressure began to increase 

slowly. At this point, over 20,000 gal (76 m3) had been 

injected, and the freshwater was beyond the area of 

treatment. 

It was suspected that redevelopment pumping would 

increase the specific capacity of the well, but redevelopment pumping could not be attempted until a sufficient 
40 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

quantity of freshwater was injected to ensure that 

formation water was not brought back into the vicinity of 

the wellbore. Because the calcium for sodium base 

exchange is reversible, if formation water were brought 

into contact with the "desensitized clay," it would return 

them to a water-sensitive condition. 

Continuous injection of 398,000 gal (1,510 m3) was 

made over a 2,580-min (1.79-day) period before any 

redevelopment pumping was attempted. Water was then 

injected for periods of 11,380 min (7.9 days), 10,025 min 

(6.96 days), 2,495 min (1.73 days), 2,695 min (1.87 days), 

and 20,450 min (14.2 days) between redevelopment 

pumpings. After the 20,450-min injection phase, 

redevelopment pumping was done on a daily basis. 

Thirty-nine injection phases were used over a period of95 

days in order to inject a total of 20,146,100 gal (76,250 m3) 

of freshwater into the brackish-water aquifer. 

INJECTION SPECIFIC CAPACITY 

Figure 29 shows the injection specific capacity of 

IW-2 during the early part of test 4 as compared to the 

specific capacity measured during pre-injection and 

injection tests 1, 2, and 3. In the first 1,000 min, the 

decrease in specific capacity was 51 percent in test 2, 75 

percent in test 3, and only 32 percent in the initial phase of 

test 4. A 40-percent decrease in specific capacity occurred 

during the initial 260 minutes of test 1. The expected 

decrease in specific capacity with time, based on preinjection aquifer test data, is about 15 percent. 

After the initial injection phase of test 4, the decrease in 

specific capacity during the first 1,000 min of injection for 

each new injection period following redevelopment 

ranged from 3 to 20 percent. The variation in percentage of 

decrease reflects the effectiveness of redevelopment 

pumping. A decrease of 11 to 12 percent per initial 1,000 

min of injection is an average value for test 4. This value 

agrees with the decrease Reed (oral commun., 1973) found 

to occur in treated water-flood wells and with the decrease 

in laboratory hydraulic conductivity when freshwater was 

injected into core treated with a calcium chloride pre-flush 

(table 10). 

Figure 30 shows that each redevelopment pumping 

period increased the specific capacity of the injection well. 

After discharging the water standing in the well casing 

(about 3,000 gal or 11 m3), the water first pumped from the 

4 

r 18~------------------------------------------------------------------------------------~ 

0 

0 

LL PRE -INJECTION TEST 1 WITHDRAWAL 

(Temperature corrected) 

o Data point 

z 

~ 

r 

0 

~ 6~------------------------------------------------------------------~~--------------~ 

<( 

0 

0 

LL 

0 

w 

Q_ 

(f) 

TEST 4 Phase 1 

OL_ ______ l_ __ _L __ ~_L_L_LJ_LL ______ ~ ____ L__i __ L_~~_L~~----~--~--~~~~~~ 

10 50 100 500 

TIME SINCE INJECTION BEGAN, IN MINUTES 

FIGURE 29.-Variations in specific capacity of injection well IW-2 during injection tests. 

.....J 

z 

>-=" 

r 

0 

<( 

CL 

<( 

10 

0 

LL 

0 

w 

Q_ 

(f) 
INJECTION TEST 4 41 

3.4 

16.0~----------------------------------------------------------------------------------~ 3.3 

o Data point 

PRE-INJECTION WITHDRAWAL 

15 .0~------~~------------(~T_e_m~p~e~r~a_t~u_re~c~o_r_re_c~t~e~d~) ______________________________________ _ Q_ 

w 

r14.5~--------------~~-------------------------------------------------------------------~ 

:::::> 

z 

~14.0~----------------------~~------------------------------------------------------T 

cr. 

w 

Q_13.5~----------------------------------~~~----------------------------------------------r 

Cf) 

z 

913.0 

_j 

<( 

~12.5L-----J---~-L~_L~LLL_ ____ J_ __ ~_L~_LJ-LLL_ ____ J_ __ J_~~-LJ-LLL-----J---~~~~-~~ 

z 5.5~----~--~~~~~~~----~--~~~~~~~----~--~~~-r~~.-----.---.--.-.~ 

>--

~ 

u 

<( Q_ 

<( 

u 

u 

LL 

u 

w Q_ 

Cf) 

5.0 

4.5 

4.0 

3.5 

u 

0.8 LL 

u 

w 0.7 Q_ 

Cf) 

0.6 

2.5L-----J---~-L~-L~LLL_ ____ J_ __ ~_L~-LJ-LLL-----~--J_~~_LJ_LLL-____ J_ __ J-~~-L~~ 

10 1 00 1000 10,000 100,000 

TIME SINCE INJECTION BEGAN. IN MINUTES 

FIGURE 30.-Specific capacity of injection well IW-2 prior to any injection of freshwater and variation of specific capacity during test 4. 

aquifer contained sand, clay, and mica in excess of 360 

mg/1. The water was heavily laden with sediment for 5 to 6 

minutes during the first redevelopment pumping, but the 

large sediment concentration had decreased until it existed 

for less than a 1-minute duration after the fourth 

redevelopment pumping. The sediment coming from the 

well contained microfossils and glauconite particles that 

are foreign to the aquifer. This material probably 

represented drilling-mud invasion into the gravel pack 

and formation during construction of the well. The clay 

particles coming from the well were flocculated and 

probably represented material lossened during treatment 

by the calcium chloride. 

Sediment was noticed in the redevelopment discharge 

from IW-2 following injection test 2. Development 

pumping, by alternately surging and injecting water, 

produced large concentrations of sand prior to and after 

test 3. The sediment recovered during that development 

attempt was identical to that recovered during test 4, with 

the exception that the clay was in a dispersed state prior to 

test 4. 

The specific capacity of IW -2 improved with redevelopment pumping, and the amount of sediment discharged 

decreased during the redevelopment pumping of injection 

test 4. It was believed that the well yield could be further 

improved if sediment movement could be prevented 

completely. Coppel (oral commun., 1973) stated that treatment to desensitize water-sensitive aquifers has reduced or 

prevented sand production in wells that had a history of 

sand production. Reed (oral commun., 1973) suggested 

that the 0.2N solution of calcium chloride pre-flush was 

not the most efficient concentration to stabilize the clay 

and recommended the injection of another pre-flush using 

a OAN solution. After 4.04 Mgal (15,290 m3) had been injected, 3,000 gal (11 m3) of a 0.4N calcium chloride solution was injected in front of untreated city water. 

Figure 31 shows the injection specific capacity for the 

calcium chloride water, and the specific capacity recorded 

after two subsequent redevelopment periods. The specific 

capacity during injection phase 5 showed a marked 

improvement for about 60 minutes following the treatment with the calcium chloride solution but then declined 

at a greater rate (27 percent between 60 and 1,000 min) than 

the 11- to 12-percent average decrease. The specific 

capacity for the injection phases 6and 7 ranged from 3.3 to 

5.8 gal!min- 1ft- 1 (0.68 to 1.2 ls-1m-1) and decreased at a 
42 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

rate similar to that of phase 4 (fig. 30). Thus, the aquifer 

characteristics did improve significantly with the additional treatment but clogged again sometime after 120 min 

of injection. The sand flow during the redevelopment 

periods diminished but did not completely stop. 

Figures 30 and 31 show that an optimum specific 

capacity value can be maintained if the injection period is 

limited to about 1,440 min (I day). In IW-2, considering 

the altered condition of the aquifer and the sediment 

discharge, the most efficient method was to inject for 

about I ,440 min, withdraw for 30 min to clear the screen of 

sediment, wait 1 hour to allow the water level to approach 

static conditions, and then begin the next injection. 

Figure 32 illustrates that the injection specific capacity 

did not vary significantly from the time 9.05 Mgal (34,250 

m3) had been injected through the time 15.87 Mgal (60,070 

m3) had been injected. After injecting 16.35 Mgal (61,890 

m3), the specific capacity deteriorated and redevelopment 

pumping could not restore it. 

CURRENT-METER TRAVERSES 

Figure 33 shows the pre-injection test 4 flow pattern and 

the flow patterns observed during the injection phase of 

test 4. The injection flow pattern shows that essentially no 

water is entering the aquifer deeper than 930ft (283 m) 

below sea level. This interval, based on the pre-injection 

test-4 traverse, should have been taking about 45 percent of 

the total flow. The flow pattern suggests particulate 

clogging in the screen and gravel pack rather than the 

uniform reduction in flow percentages that occurred when 

clay dispersion affected the hydraulic conductivity of the 

aquifer as shown in tests 1 and 2. The withdrawal currentmeter traverses (fig. 34) show that the flow pattern returns 

to the pre-injection test 4 pattern, indicating that the 

sediment lodged in the screen was removed during the 

initial surge of withdrawal pumping. 

Within the zones taking water, little clogging occurred 

during the injection of the first 15 Mgal (56,800 m3) of 

freshwater (fig. 33). The current-meter traverses show that 

in the zone taking the highest percentage of the water at 

the start of the test (903 to 915ft or 275 to 279m below sea 

level) only 3ft (0.9 m) at 912 to 915ft (278 to 279m) below 

sea level had clogged after nearly 63 days of injecting. 

During the first 63 days of injecting, the specific capacity 

of the well had remained rather uniform. When the 

specific capacity of IW-2 began declining rapidly (after 16 

Mgal or 60,600 m3 had been injected), it was suspected that 

1.6 

o Data point 

b 1.5W 

2 7r-------------~--~~-------------------------------------------------------------~ ~ w a: 4.65 million gallons, (17,600 cubic metres) 1.4 ~ 

~ injected including 3000 gallons, ( 11 cubic a: 

w metres) of 2.8 percent CaCI 2 pre-flush 1.3 ~ 

~ 6r---~~------------------------~--------------------------------------------------~ 0 

z z PHASE 6-5.20 million gallons, 1·

2 0 

~ (19,680 cubic metres) ~ ffi injected 1.1 (f) 

~5 ffi 

~ 1.0 ~ 

0 (f) 

~ w ~ 0.9 a: ~ ~ 

~ 4r---------------~----------------------------------------~~~--------------------~ ....J 

z 0.8 z 

~ PHASE 7-8.76 million gallons, >= ~ (33,160cubicmetres) 0.7!:::: 

O injected u ~3 ~ ~ 0.6 ~ 

u u 

0 Q5g ~ ~ 

~ 2 0.4 ~ ~ ~ (f) (f) 

0.3 

100 1000 10,000 100,000 

TIME SINCE INJECTION BEGAN, IN MINUTES 

FIGURE 31.-Variation of specific capacity in injection well IW-2 for injection phases 5, 6, and 7, test 4. 
INJECTION TEST 4 43 

8 

1.6 

I- PHASE Million 

0 gallons Cubic metres 1.5~ 07 I- u... 8 9.05 34,250 w 

a: 10 9.71 36,750 1.42 

w a: 0... 20 13.76 52,080 w 

w 1.3 0... 

~6 23 15.87 60,070 0 

27 16.85 61,880 z ~ 1.20 

() 2 28 17.32 65,560 w 

a: (f) 

w 39 20.15 76,270 1.1 a: 0... 5 w (f) 1.0 0... z (f) 0 w __J 

0.9 g: __J 

<( __J (.!)4 

z 0.8~ 

>-- ~ 

I- 0 7 t:: 

() ·o 

~3 ~ <( 0.6 <( 

() () 

() () 

u... 0 Data point 0.5 i:L 

~ 2 

() 

0.4 ~ 0... (f) (f) 

0.3 

1 

10 50 100 500 1000 5000 10,000 

TIME SINCE INJECTION BEGAN, IN MINUTE 

FIGURE 32.-Variation of specific capacity in injection well IW-2 for injection phases, test 4. 

clogging was occurring within the aquifer above the depth 

of 930 ft (283 m) below sea level. The current meter was 

inoperative at this time, however, and traverses could not 

be made to confirm the suspicion. 

Prior to treatment of the aquifer with the calcium 

chloride, the zone from 904 to 922ft (276 to 281m) below 

sea level accepted a maximum of 50 percent of the water 

injected. After treatment with a calcium chloride solution, 

the zone took between 80 and 90 percent of the water 

injected. This fact suggests that the treatment may have 

operated preferentially in this zone. It was the most 

permeable zone and would accept most of the calcium 

chloride solution and show the greatest improvement in 

hydraulic conductivity. The preferential treatment of this 

zone may have taken so much of tahe calcium chloride 

solution that only a token amount reached the aquifer 

below 922 ft (281 m). Therefore, when the pre-flush was 

followed by freshwater, dispersion and clogging by sand 

and clay particles occurred below 922 ft (281 m). 

CAUSE OF CLOGGING OF IW-2 

DURING INJECTION PHASE OF TEST 4 

The quantity of sediment produced during the 

redevelopment phases up through 16.35 Mgal (61,880 m3) 

injected in test 4 usually diminished after about 1 or 2 

minutes of redevelopment pumping. After injecting 16.35 

Mgal (61,880 m3) of freshwater, the heavy discharge of 

sediment obtained during the daily redevelopment lasted 

for 8 to 10 minutes. Not only had the quantity of sediment 

increased, but the character of the sediment also changed. 

It consisted predominately of clay granules with some 

colloidal clay and silt to fine-grained particles of quartz 

and mica. The granules consist of flocculated clay and silt. 

The colloidal clay remained in suspension for several 

hours in undisturbed water but not for days, as it had 

before treatment. 

A possible cause for the large amount of sediment 

discharge and the subsequent decrease in specific capacity 

may have been due to disturbance of the gravel pack, so 

that its effectiveness as a filter was decreased. During the 

redevelopment cycle, a combination of injection and withdrawal pumping was ernployed; this practice tends to 

agitate the gravel pack of the well. It was after this 

vigorous redevelopment pumping that the sediment discharge during withdrawal became noticeably larger and 

lasted up to 15 minutes before diminishing. 

The appearance of some dispersed clay and the overall 
44 

_J 

w 

> 

w 

_J 

z 

<( 

w 

~ 

ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

275 

(f) 

w 

280 ~ w 

~ 

z 

_J 

w 

> 

w 

_J 

<( 

w 

(f) 

z 285 <( 

w 

~ ~ 

g 

w 940H&------------------~~----------------------------------~ 

~ 

g co 

I 

1-

0.... 

w 

0 

Pre-injection withdrawal, test 4 

0=560 gallons per minute 

(35 litres per second) 

950~----------------~----------------------------------~ 

ZONE CLOGGED 

960~----~----------------------------------------------~ 

o o e:. Data points 

290 

295 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 33.-Current-meter traverses in injection well IW-2 of pre-injection and injection flow, test 4. 

w 

co 

I 

1-

0.... 

w 

0 
INJECTION TEST 4 45 

275 

I- (f) 

w w 

w 280g: 

u.. 920 w 

z ~ 

_J z 

w _j > 

w w _J > 

w 

_J 

<( 

w 

z (f) 

<( 

285~ w 

~ w 

~ ~ 

g ~ w 

CD 9 

w 

I CD 

Ia.. I 

w I0 a.. 

w 

0 

290 

295 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 34.-Current-meter traverses in injection well IW-2 of pre-injection, injection, and withdrawal flow, test 4. 
46 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

decrease in size of the sediment indicated that the sediment 

may have been coming from the aquifer below 922ft (281 

m) below sea level, which did not receive effective calcium 

chloride treatment. During redevelopment pumping, the 

higher pumping rates produced appreciable water from 

the lower part of the aquifer with enough velocity to move 

clay and silt in to the borehole. As pumping continued and 

the rate fell off, the velocity of the water coming from the 

lower section was not sufficient to move the sediment into 

the borehole. 

The sand trap below the screen may have been the source 

of most of the sediment that caused particulate clogging. 

As injection began, after each phase of redevelopment 

pumping in test 4, the surge of water into the well bore and 

screen could agitate the material into suspension, so that 

injection of sand and clay particles into the screen and 

gravel pack could take place. During redevelopment, the 

curre::':t meter indicated water movement in the bottom 40 

ft (12 m) of the well, but during injection it indicated no 

water movement even though the pumping rates were 

comparable. 

The phenomenon may occur because the screen is 

designed for withdrawal pumping. The openings of the 

screen are V-shaped with the open end of the V facing 

inward. During normal withdrawal pumping, particles 

passing through the smallest opening enter the well and 

are removed, provided the well is pumping at sufficient 

rates to keep the sand in suspension. However, if the 

sediment clogging the well is coming from agitation of an 

internal source (such as the fill-up pipe) while injection is 

occurring, the sand would lodge in the screen and block 

the flow of water. Upon withdrawal pumping, the shape 

of the openings would allow easy removal of the material 

and open the screen to flow from the aquifer. 

Figure 35 shows that below 950 ft (290 m) below sea 

level, the screen in IW -2 contributed a larger percentage 

of the total flow as withdrawal pumping progressed, indicating that development occurred within the zone. The 

flow from 946 to 960ft (288 to 293m) increased from 23 

percent to 36 percent of the total flow after 26.3 Mgal 

(99,550 m3) had been withdrawn. At the same time, the 

percentage of total discharge from 910 to 922 ft (277 to 

281 m) below sea level decreased from 41 to 13 percent. 

Both the chemical and hydraulic data suggest that the 

clay in the gravel pack in the 910- to 922-ft (277- to 281-

m) zone was exposed to the brackish water, which resulted 

in repacking, which, in turn, reduced the flow from that 

zone. 

CHEMICAL EFFECTS OBSERVED DURING 

WITHDRAWAL PHASE OF TEST 4 

Chemically, the following sequence of events were 

predicted during the withdrawal phase of test 4: (1) The 

specific conductance of the first water withdrawn would 

be about equal to the input value; (2) the specific conductance would remain below 1,000 micromhos until approximately 17 Mgal (64,300 m3) was withdrawn; and (3) the 

calcium concentration in the repumped water would 

remain at 15 to 17 mg/1, assuming that most of the calcium 

in the calcium chloride solution was exchanged by the 

clay. There would be some increase in the concentration of 

sodium at the outer edges of the freshwater zone, 

corresponding to periods in which the calcium chloride 

was injected (calcium for sodium exchange). The calcium 

concentration in the repumped water would not increase 

above 17 mg/1 until the concentration of sodium in the 

mixed freshwater and formation water rose to between 600 

and 700 mg/1. At that point, a reverse exchange would 

occur, which would indicate the return to a high 

percentage mixture of native water, including some 

exchanged sodium. 

During this later period of pumping, the calcium 

concentration would remain relatively high until most of 

the exchanged calcium had been replaced by sodium from 

the formation water. These events were predicted on the 

basis of data observed during withdrawal phases of tests 1 

and 2. 

The authors were aware that most of the water was 

injected selectively in the interval 910 to 930ft (277 to 283 

m) below sea level. It was expected that the stabilization of 

the clay in that zone, combined with the clogging in the 

bottom of the aquifer, would cause the withdrawal flow 

pattern to be the same as the injection flow pattern. 

However, this did not occur during test 4 withdrawal, and 

the flow pattern reverted to the pre-injection flow pattern 

(fig. 35 ), causing many of the predicted chemical reactions 

to be masked. 

After 8 Mgal (30,300 m3) of water had been withdrawn, 

the zone that had taken 80 percent of the water during 

injection (904 to 915ft (276 to 279m) below sea level) was 

yielding less than 10 percent (fig. 36). Further, it can be 

seen that zones that took little or no freshwater began to 

develop and were yielding formation water. As pumping 

continued and after 17 Mgal (64,300 m3) of water had been 

withdrawn, more than 50 percent of the water coming out 

of the well was formation water (fig. 37). Based on the 

chloride concentration, less than 20 percent of the water 

recovered was potable (U.S. Department of Health, 

Education, and Welfare, 1962) (fig. 38). 

The net result of this differential yield between injected 

and withdrawn freshwater was that predicted chemical 

observations were obscured by the preponderance of 

formation water. The specific conductance was above 

1,000 micromhos after only 4.2 Mgal (15,900m3) was withdrawn instead of 17 Mgal (64,300 m3), as was predicted. 

The calcium content did show some deficiency in the first 

water withdrawn, indicating some base exchange still 

occurred in test 4. The deficiency of calcium in test 4 was 

minor compared to the calcium deficiency recorded in the 

first three tests, and was further evidence that treatment of 
INJECTION TEST 4 47 

I- C/) 

w UJ 

w a: lL.. I920 w 

z ~ 

_j z 

w _j 

w 

> w _J > 

w 

<( _J 

w 

(/) <( 

w 

z C/) 

<( 

w z ~ <( 

w 

~ ~ 

9 ~ w 0 

IIl _J 

w 

I IIl 

IQ_ I 

w f- 0 Q_ 

w 

0 

0 20 40 60 80 100 

PERCENTAGE OF TOTAL FLOW 

FIGURE 35.-Current-meter traverses in injection well IW-2 of withdrawal flow, test 4. 
48 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

Injection current meter 

traverse in I W -2. 

Conductivity profile in 

IW-2. 

Withdrawal current meter 

traverse in IW-2. 

14.8 million gallons, (56,000 

cubic metres) injected 890.---------~~--,----. 

8.0 million gallons, (30,300 

cubic metres) withdrawn 

Water 

sa£12Pies 

8.4 million gallons, (31,800 

cubic metres) withdrawn 

_j 

w 

> 

~ 920~--------------------~ 

<( 

w 

(/) 

z 930~------------------~ 

<( 

w 

~ 

s: 940 

g 

w 

m 950~---------------------1 

:r: 

fa.. 

~ 960~------------------~ 

• 

• 

• 

(/) 

w 

275 g: 

w 

~ 

z 

....I 

280 ~ ~0+~----------------~ w 

....I 

<( 

w 

(/) 

285 ~ w 

~ 

s: 

g 

290 ~ 

:r: 

fa.. 

w 

0 

295 970L---~----~----~--~ 

0 20 40 60 80 

PERCENTAGE OF TOTAL FLOW 

~ 

DECREASING CONDUCTIVITY 

0 20 40 60 80 

PERCENTAGE OF TOTAL FLOW 

WATER SAMPLES COLLECTED BY THIEF SAMPLER. 5-30-73 

Depth below mean Chloride Specific conductance 

sea level (mg/1) ( Micromhos) 

Feet Metres 

901 275 670 2900 

907 276 700 3100 

917 280 880 3800 

957 292 1200 4800 

FIGURE 36.-Changes in injection and withdrawal flow and conductivity profile in injection well IW-2 after 8 Mgal (30,300 m3) withdrawn, 

test 4. 

the lower 40ft (12m) of the aquifer by the calcium chloride 

pre-flush was not complete. 

The variation in concentration of calcium and sodium 

indicated a reversible reaction was occurring in test 4. As 

shown in tests 1 and 2, this reaction normally begins to 

take place at low conductivity values. The immediate 

influx of formation water from the lower40 ft (12m) of the 

aquifer raised the conductivity and dissolved-solids 

concentration of the first water withdrawn to such an 

extent that a clear definition of the reactions was not 

possible. 

In all the previous tests, the temperature functioned as a 

straight-line dilution and apparently continued to do so in 

test 4. The pH data, however, did show the effects of 

stabilization of the clay. In tests 1, 2, and3, water of pH 5.4 

to 6.0 was injected into the formation, displacing water of 

7.9 pH. When the water was withdrawn, the pH was 

between 9 and 10 until the percentage of formation water 

in the mixture became greater than the percentage of freshwater. It was suspected that this condition was a result of 

cation exchange whereby one equivalent of sodium 

carbonate in the freshwater would produce a higher pH 

than one equivalent of calcium bicarbonate. As the saltwater was drawn back into the well and the base exchange 

reversed, the pH returned to the original formation value. 

When the clay was stabilized in test 4 and cation exchange 

was confined to the partly treated lower part of the aquifer, 

the pH of the first water withdrawn did not rise above 8.0. 

Dissolved oxygen, which ranged between 8 and 11 mg/1 

during all tests, was lost during each ,test. The immediate 

assumption was that the dissolved oxygen was involved in 

reactions with iron or manganese or some organic 

material. However, there was less than 0.1 mg/1 iron or 

manganese in either the injected freshwater or formation 

water. The organic content, in terms of chemical-oxygen 

demand, was exceedingly low (less than 2 mg/1). The loss 
ANALYSIS OF PROJECT 49 

880 

Injection current meter 

traverse in IW-2 

14.8 million gallons, (56,000 

cubic metres) injected 

Conductivity profile in IW-2 

15.1 million gallons, (57,150 cubic 

metres) withdrawn 

Water 

samples 

Withdrawal current meter 

traverse in IW-2 

17.24 million gallons, (65,250 

cubic metres) withdrawn 

1-

UJ 

890 

~ 900 

z 

~ 910 

> UJ .....1 

~ 920 

(/) 

z 

~ 930 ~ 

~ 9 940 

w 

m 

~ 950 a. 

UJ 

0 

960 

970 

:::::::::::: 

@]_ 

I I I 

-

• ::::::::::::::::::: -

::::·····:·:·:·:·:··· •. ·.:W::.::::::••:::-··•·.:::.:.:.:1 

~ 

1-

-

- I I I 

r-

•:::> :::::1 

r- • 

J 

-

1 

j • -

r-

• r270 

(/) 

UJ 

0: 

1-

UJ 

275~ 

z 

.....1 

UJ 

> 

UJ 280.....1 

<{ 

UJ 

(/) 

z 

<( 

UJ 

285~ 

§ 

UJ 

m 

290~ a. 

UJ 

0 

295 

0 20 40 60 80 

PERCENTAGE OF TOTAL FLOW 

~ 

DECREASING CONDUCTIVITY 

0 20 40 60 80 

PERCENTAGE OF TOTAL FLOW 

WATER SAMPLES COLLECTED BY THIEF SAMPLER 5:...30-73 

Depth below mean Chloride Specific conductance sea level 

Feet Metres (mg/1) ( M icromhos) 

902 275 880 3800 

909 277 880 3700 

932 284 1200 4900 

962 293 1400 5800 

FIGURE 37.-Changes in injection and withdrawal flow and conductivity profile in injection well IW-2 after 15.1 Mgal (57,150 m~) withdrawn, 

test 4. 

of dissolved oxygen is an immediate reaction during 

injection but has little effect on the potability of the water. 

Although plugging by gas bubbles is a possibility, saturation and head data suggest that the hydraulic properties of 

the aquifer were not noticeably affected by the loss of 

dissolved oxygen. 

ANALYSIS OF PROJECT 

The Norfolk injection project has demonstrated that the 

sand aquifers containing saline water in the Norfolk area, 

and quite likely throughout the Coastal Plain, are water 

sensitive and must be treated as such if they are to be 

recharged with freshwater. Moreover, if physical clogging 

of the screen of the injection well can be prevented during 

injection of freshwater, the percentage of recoverable 

potable water is sufficient to make the proposal of underground storage and retrieval of freshwater from a brackish 

aquifer feasible. 

During injection tests I and 2, 65 percent of the water 

recovered was within Public Health Service standards, and 

as much as 85 percent of the mixed water recovered could 

be used if necessary. During these two tests, the clogging of 

the aquifer, due to clay dispersion, caused a uniform 

reduction in aquifer hydraulic conductivity. 

The first three injection tests were conducted prior to 

identifying the water-sensitive nature of the aquifer. Consequently, deterioration of aquifer properties as a result of 

injecting freshwater was irreversible, and original condi-
50 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

1400 378.5 

VOLUME WITHDRAWN, IN CUBIC METRES 

3785 

~ 1200 

1--

_J 1100 

a: 

w 

a.. 1000 

(/) 

~ 

<( 

a: 

(!) 

_J 

_J 

~ 

z 

z 

0 

~ 600 

a: 

1--

z 

w 

() 

z 

8 

w 

0 

a: 

g 

I 

() 

o Data point 

0~----~--~~~~LLLL----~---L~L-~-L~~----~--~-L-L~~~----~~~--~~~~ 

0.01 0.1 1 1 0 1 00 

VOLUME WITHDRAWN. IN MILLIONS OF GALLONS 

FIGURE 38.-Changes in chloride concentration with volume of water withdrawn, test 4. 

tions could not be restored. Treatment of the clay to 

prevent further deterioration of the aquifer hydraulic 

properties was possible, as evidenced by the injection 

phase of test 4. However, the aquifer deterioration had 

progressed to the point that physical clogging of the screen 

and the gravel pack was the dominant factor in the 

injection process. 

Current-meter traverses made during injection and 

withdrawal in tests I and 2 showed that zones taking water 

during injection gave up water during withdrawal in 

approximately the same percentage of the total discharge. 

That is, a zone that took 10 percent of the water injected 

also yielded 10 percent of the water during withdrawal. 

This demonstrates that the injection front was predictable, provided that clogging did not occur and cause 

variations in flow patterns between injection and 

withdrawal. 

The importance of preventing clogging can be seen 

from the low recovery percentages of potable water during 

tests 3 and 4. Because of the water sensitivity factor, the 

deterioration of the aquifer had progressed to the extent 

that clogging by sand and clay particles became the 

dominant factor in the injection process. Current-meter 

traverses showed that the injection flow patterns had 

changed drastically from those of tests I and 2. Zones that 

had taken water during injection tests I and 2 clogged 

completely during tests 3 and 4, resulting in localized 

rather than uniform injection of freshwater. 

Current-meter traverses made during withdrawal 

pumping are consistent and similar to those made prior to 

injection of any freshwater. Zones that clog during 

injection become productive during withdrawal and 

produce nearly the same percentage of the total discharge 

from the well as was produced during pre-injection 

conditions. As a result, when withdrawal pumping 

commenced in tests 3 and 4, flow came not only from the 

zones that took freshwater but from the previously clogged 

zones that contained formation water. Consequently, only 

20 percent of the water recovered in test 4 was potable. 

Sand production during withdrawal and development 

pumping in IW-2 after test 2 was coincident with the 

particulate clogging on the screen and in the gravel pack. 
ANALYSIS OF PROJECT 51 

It is unclear, at this time, whether clay dispersion and 

repacking within the aquifer allowed the gravel pack to 

settle below the top of the screen, thereby allowing movement of aquifer sand into the screen. The sand produced 

during redevelopment pumping contains glauconite and 

Miocene fossil material foreign to the aquifer. There is 

some evidence that the high injection heads during test 3 

may have caused a channel along the boundary of the 

gravel pack and well screen so that sand and clay from an 

overlying formation could move downward through the 

channel into the screen. The younger material is probably 

best explained by incomplete development pumping 

during the construction of the well, resulting in drilling 

mud being left in the gravel pack. The majority of sand 

production, on the basis of examination of the screen by 

down-hole television during test 4 withdrawal, appears to 

be coming from a breach in the gravel pack below a depth 

of 972 ft (296 m) below sea level. 

The obvious question is whether the sand production 

and resulting clogging could have been prevented if the 

formation had been treated with clay stabilizers prior to 

injection of any freshwater. The question cannot be 

answered definitely unless a new well is drilled. Based on 

published data and observations made through long 

exposure to the problems of the injection project, we 

believe that physical clogging can be minimized provided 

proper well construction and formation treatment are 

utilized. X-ray and thin sections of core samples indicate 

that the consolidation factor is very low and that the 

bonding agent is essentially the clay surrounding the 

quartz grains. If dispersion of the clay is prevented prior to 

injection of freshwater by treatment with trivalent cations, 

such as aluminum, clogging by sand should be a minor 

problem in a properly developed well. 

The chemical quality of water recovered indicated that 

the injection and retrieval of freshwater from an aquifer 

containing brackish water is entirely feasible. During this 

study, only 15 percent of the injected water was considered 

not potable according to U.S. Public Health Service 

standards (chloride more than 250 mg/1). Further, adverse 

chemical reactions (deterioration in water quality or large 

scale chemical precipitation) did not occur as a result of 

injection and withdrawal of the freshwater from the 

brackish -water sand. The freshwater injected contained no 

coliform bacteria, and biological contamination was not 

found in the water withdrawn. 

Chemical measurements, such as those for pH and 

dissolved oxygen, indicated that reactions other than 

simple silution were occurring when the water was 

injected. The pH effect was eliminated by pre-treatment of 

the formation clay with calcium chloride; however, the 

cause of the loss of dissolved oxygen is unclear at this time. 

Laboratory experiments (Kimbler, Kazmann, and 

Whitehead, 1973) have suggested that the density difference between freshwater and saltwater would cause vertical movement, which could affect the recovery of the 

injected freshwater. The conductivity profiles and currentmeter traverses made in this investigation suggest that 

under injection conditions the flow was essentially horizontal. Natural stratification within the aquifer may prevent upward migration of freshwater, but not enough 

evidence is available, especially regarding Jong-term 

storage under static conditions, to warrant any conclusions. Also, the effect of injection on the natural movement of water could not be fully evaluated. The injected 

water was not left in residence long enough and the 

observation-well network was not dense enough to 

observe the effect, if any, ,injection has on the movement 

of formation water. 

An injection well field at Moore's Bridges Filter Plant, 

ideally, would have at least 4 wells; each capable of 

injecting 1,000 gal/min (63 1/s) and withdrawing 2,000 

gal/min (126 1/s). Injection would be continuous until 

a sufficient quantity had been injected so that withdrawal 

demands would not remove more than 60 percent of the 

injected freshwater. 

Invasion of drilling fluids into the sediments usually 

occurs during hydraulic rotary drilling. In a withdrawal 

well this is normally not a problem, but in an injection 

well, where clay dispersion is a possibility and prevention 

of clogging is essential, invasion of drilling fluids can 

jeopardize the life of the well. Therefore, to minimize the 

invasion of drilling mud into the aquifer, a proposed 

injection zone could be drilled using a hydraulic reverse 

rotary method. 

The Norfolk study has shown that clogging of the 

formation by iron precipitation is not sufficient to prevent 

the use of steel casing, although a stainless-steel screen 

would probably be required because of the brackish water. 

If a different aquifer or well field location were chosen, 

then new calculations of the iron reactions would have to 

be made. The advantages or disadvantages of a gravel pack 

have been widely published for withdrawal wells, but, 

because of the serious problems that can be caused by 

clogging in the gravel pack of an injection well, natural 

completion (no gravel pack) using a wire-wrapped screen 

may help to minimize clogging problems. A screen with a 

round or square wire, rather than a V-shape, may reduce 

internal clogging. 

To effectively inject 1,000 gal/min (63 1/s) and withdraw 2,000 gal/min (126 1/s), the specific capacity of an 

injection well would be in the range of 20 to 30 gal 

min-lft- 1 or4.1 to6.2ls- 1m- 1• In theNorfolkarea,inorder 

to obtain a specific capacity within that range at the 

proposed pumping rates, more screened aquifer is 

required than was used in IW-2. Test drilling in the 

vicinity of IW-2 has shown that the sand from 

approximately 750 to 1,000 ft (229 to 305 m) below land 

surface and the chemical quality of the water in this 

interval are rather uniform. Using electric-log and coresample data to determine screen placement, this entire 
52 ARTIFICIAL RECHARGE TO A BRACKISH-WATER AQUIFER, VIRGINIA 

section could be selectively screened in order to obtain the 

desired specific capacity. 

Immediately after setting the screen, development 

pumping exceeding maximum operational rate would 

continue until sand pumping ceased. At this time treatment of the formation to prevent clay dispersion would 

begin-before freshwater is introduced into the well. The 

detailed method of treatment is available from several oil 

field service companies. 

The design of an injection well would be more efficient 

than that of IW -2 if the same size casing extended from the 

surface to the top of the screen. This would allow the 

installation of additional pump column and provide for 

greater drawdown. With such construction, the screen 

may be adjusted or even removed and replaced if necessary. 

The design also could provide access for a current meter in 

order that changes in the injection flow pattern from that 

of the pre-injection pattern could be detected. 

Storage 

Tanks 

• 0 

Withdrawal pumps on the first injection well would be 

capable of pumping at least 2,000 gal/min (126 lis) 

against a total dynamic head of 300ft (91 m). Aquifer-test 

data could then be used to refine pump requirements for 

subsequent wells. The only special construction requirement for a withdrawal pump would be to have stainlesssteel line-shaft, epoxy-coated column pipe, and an allbronze bowl assembly. Each well would be equipped with 

its own injection pump located at the freshwater 

collection point. The injection pump would be capable of 

pumping more than 1,000 gal/min (63lls) against a total 

dynamic head of 120ft (37m). The water injected, ideally, 

would contain the least possible amount of particulate 

matter. 

Spacing in a well field is normally based on hydraulic 

characteristics of the aquifer in that the wells are spaced far 

enough apart to prevent serious hydraulic interference 

when several wells are pumping. In an injection well field, 

.. 

0 - Possible well location 

FIGURE 39.-Possible well locations for a five-well injection field at Moore's Bridges Filter Plant. 
REFERENCES CITED 53 

however, two additional considerations are of equal 

importance: (I) The distance from the source for injection 

water, and (2) the shape of the injection front. 

Injection tests 2 and 4 demonstrated that the spread of 

water from the injection well is non-radial and is 

elongated roughly in a northwest direction. Wells placed 

perpendicular to the long axis of the injection front in the 

shape of an expanded W, with a minimum of 600ft ( 183 m) 

between the wells, would make efficient use of space 

available (at the Filter Plant for instance) and the 

hydraulic properties of the aquifer could be achieved (fig. 

39). This spacing and well configuration would only 

apply to the area under investigation. If a well field were to 

be located in a different area, an analysis of the hydraulic 

properties of the aquifer at that location would be 

necessary. Using this spacing, and assuming an aquifer 

thickness of 150 ft (46 m), approximately 100 Mgal 

(378,000 m3) of freshwater could be stored by each well in 

the area of the Filter Plant before well interference became 

serious. 

REFERENCES CITED 

Baptist, 0. C., and Sweeney, S. A., 1955, Effects of clays on the permeability of reservoir sands to various saline waters, Wyoming: Bureau 

of Mines Rept. Inv. 5180, 23 p. 

---1957, Physical properties and behavior of the Newcastle oilreservoir sand, Weston County, Wyo: Bureau of Mines Rept. Inv. 

5331, 43 p. 

Brown, D. L., 1971, Techniques for quality of water interpretations 

from calibrated geophysical logs, Atlantic Coastal area: Ground 

Water, July-August, v. 9, no. 4, 13 p. 

Brown, D. L., and Silvey, W. D., 1973. Underground storage and retrieval of fresh water from a brackish-water aquifer: in Second 

International Symposium on Underground Waste Management 

and Artificial Recharge, New Orleans, La. Reprints, vol. 1, p. 

379-419, Am. Assoc. Petroleum Geologists. 

Cederstrom, D. J., 1957, Geology and ground-water resources of the 

York-James peninsula, Virginia: U.S. Geol. Survey Water-Supply 

Paper-1361, 237 p. 

Coppel, C. P., Jennings, H. Y., and Reed, M. G., 1972, Field results 

from wells treated with hydroxy-aluminum: SPE-AIME, San 

Antonio, Texas. ' 

Gray, D. H., and Rex, R. W., 1966, Formation damage in sandstones 

caused by clay dispersion and migration: Clays and Clay Minerals, 

14th Nat. Con£., Pergamon Press, London, 10 p. 

Hewitt, C. H., 1963, Analytical techniques for recognizing water 

sensitive reservoir rocks: Jour. Petrol. Tech., August, p. 813-818. 

Jones, T. 0., 1964, Influence of chemical composition of water on 

clay blocking of permeability: Jour. Petrol. Tech., No. 16, p. 

441'-446. 

Kimbler, 0. K., Kazmann, R. G., and Whitehead, W. R., 1973, Saline 

aquifers-future storage reservoirs for fresh water?: Underground 

Waste Management and Artificial Recharge, 2nd International 

Symposium, vol. 2, AAPG, New Orleans, La. 

Land, C. S., and Baptist, 0. C., 1965, Effect of hydration of montmorillonite on the permeability to gas of water-sensitive reservoir 

rocks: Petrol. Transactions, Oct., p. 1213-1218. 

Meade, R. H., 1964, Removal of water and rearrangement of particles 

during the compaction of clayey sediments-Review: in Mechanics of Aquifer Systems, U.S. Geol. Survey Prof. Paper 497-B, p. 

B2-B23. 

Reed, M. G., 1972, Stabilization of formation clays with hydroxyaluminum solutions: Jour. Petrol. Tech. July. 

U.S. Department of Health, Education, and Welfare, 1962, Drinking 

water standards, 1962: Public Health Service Pub. 956, 61 p. 

White, E. J., Baptist, 0. C., and Land, C. S., 1962, Physical properties 

and clay mineral contents affecting susceptibility of oil sands to 

water damage, Powder River Basin, Wyoming: Bureau of Mines 

Rept. lnv. 6093, 20 p. 

__ 1964, Formation damage estimated from water sensitive tests, 

Patrick Draw Area, Wyoming: Bureau of Mines Rept. Inv. 6520, 

20 p. 

• 1 ,.,vernment Prlntltl Office 1977-n7-612