Geochemical Effects of Recharging 

the Magothy Aquifer, 

Bay Park, New York, 

With Tertiary-Treated Sewage 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 751-D 

Prepared in cooperation with the 

Nassau County Department of 

Public Works 

Geochemical Effects of Recharging 

the Magothy Aquifer, 

Bay Park, New York, 

With Tertiary-Treated Sewage 

By STEPHEN E. RAGONE 

DEEP-WELL ARTIFICIAL -RECHARGE EXPERIMENTS 

AT BAY PARK, LONG ISLAND, NEW YORK 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 751-D 

Prepared in cooperation with the 

Nassau County Department of 

Public Works 

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

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Ragone, Stephen E. 

Geochemical effects of recharging the Magothy aquifer, Bay Park, New York, with tertiary-treated sewage. 

(Deep-well artificial recharge experiments at Bay Park, Long Island, New York) (Geological Survey professional 

paper; 751-D) 

Bibliography: p. 

Supt. of Docs. no.: I 19.16:751-D 

1. Water chemistry. 2. Aquifers-New York (State)-Bay Park. 3. Sewage. 4. Water, Underground-New York 

(State)-Bay Park-Artificial recharge. I. Nassau Co., N. Y. Dept. of Public Works. II. Title. III. Series. IV. 

Series: United States. Geological Survey. Professional paper; 751-D. 

GB855.R34 627' .56 76-608223 

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

Washington, D.C. 20402 

Stock Number 024-oOl-03006-3 
CONTENTS 

Page 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D 1 

Introduction .......................................................................................... . 

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Previous studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Bay Park hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Bay Park sewage-treatment plant and demonstration tertiary-treatment plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Deep-well recharge facility ................................................................ ~.......... 4 

Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Chemical and physical characteristics of native water and reclaimed water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Clogging of the recharge well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Changes observed in the hydrochemical system during recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Iron-mobilization reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Cation-exchange reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Movement of pollutant-indicator constituents through the aquifer during recharge . . . . . . . . . . . . . . . . . . . . . 13 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map showing location of recharge site, Bay Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D2 

2. Sketch showing hydrogeologic section of artificial-recharge site showing vertical and horizontal 

distribution of the observation-well screens in relation to the injection-well screen . . . . . . . . . . 3 

3. Schematic drawing of water-reclamation process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

4. Sketch showing location of observation wells, structures, and external piping at the artificial-recharge 

site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

5-14. Graphs showing: 

5. Changes in iron concentration and pH as a function of the fraction of reclaimed water 

(f] )c1- at the 20-foot (6.1-meter) observation well during recharge . . . . . . . . . . . . . . . . 10 

6. Changes in iron concentration and pH as a function of the fraction of reclaimed water 

(f] )c1- at the 100-foot and 200-foot (30- and 61-meter) observation wells during 

recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

7. Changes in f] values for magnesium and calcium as a function of the fraction of reclaimed 

water (J:./ )c1

- at the 20-foot (6.1-meter) observation well during recharge . . . . . . . . . . . 12 

8. Changes in f] values for sodium, potassium, ammonium, and bicarbonate as a function of 

the fraction of reclaimed water (f] )c1- at the 20-foot (6.1-meter) observation well during 

recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

9. Changes in f] values for calcium and magnesium as a function of the fraction of reclaimed 

water (J:./ )c1- at the 100-foot (30-meter) observation well during recharge . . . . . . . . . . . 15 

10. Changes in f] values for sodium, potassium, ammonium, and bicarbonate as a function of 

the fraction of reclaimed water (f] )cr at the 100-foot (30-meter) observation well during 

recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

11. Changes in f] values for calcium and magnesium as a function of the fraction of reclaimed 

water (J:./ )c1

- at the 200-foot (61-meter) observation well during recharge . . . . . . . . . . . 17 

12. Changes in f] values for sodium, potassium, ammonium, and bicarbonate as a function of 

the fraction of reclaimed water ( J:.[ )cr at the 200-foot ( 61-meter) observation well during 

recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

13. Changes in MBAS, total phosphate, total nitrogen, and COD concentrations as a function of 

the fraction of reclaimed water (f] )c1- at the 20-foot (6.1-meter) observation well during 

recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

14. Changes in MBAS, total phosphate, total nitrogen, and COD concentrations as a function of 

the fraction of reclaimed water (f] )c1- at the 100- and 200-foot (30- and 61-meter) 

observation wells during recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

III 
IV CONTENTS 

TABLES 

Page 

TABLE 1. Lithologic profile of recharge zone, as determined from cores taken during drilling of the recharge well D4 

2. Recharge-test statistics at Bay Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Chemical and physical characteristics of native water from the Magothy aquifer and of reclaimed water 7 

4. Selected physical- and chemical-quality parameters of initially recovered water . . . . . . . . . . . . . . . . . . . 8 

5. Bacterial quality of water recovered after test RW4 in 1969 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

6. Effect of dissimilar treatments of reclaimed water and city water on the maximum iron concentration of 

the observed iron peak at the 20-foot (6.1-meter) observation well . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

7-9. Differences between observed and calculated concentrations of calci urn, magnesium, sodium, potassium, 

ammonium, and hydrogen ions in water from the: 

7. 20-foot (6.1-meter) observation well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

8. 100-foot (30-meter) observation well . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

9. 200-foot (61-meter) observation well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

CONVERSION FACTORS 

Factors for converting English units to metric units are shown to three or four significant figures. However, in the text the 

metric equivalents are shown only to the number of significant figures consistent with the values for the English units. 

bzgli.\h Multiply by Afrtric 

in (inches) 25.4 mm (millimeters) 

ft (feet) 3.048 X 10-l m (meters) 

mi (miles) 1.609 km (kilometers) 

gal (gallons) 3.785 1 (liters) 

gal/min (gallons per 6.308 X 10~2 lis (liters per 

minute) second) 

[(gallmin)/ft] (gallons 2.07 X 10" 1 [(1/s)/m] (liters per 

per minute per foot) second per meter) 

Mgal (million gallons) 3.785 mill (million liters) 

Mgalld (million gallons 4.381 X 10-2 m3/s (cubic meters 

per day) per second) 
DEEP-WELL ARTIFICIAL-RECHARGE EXPERIMENTS AT BAY PARK, LONG ISLAND, NEW YORK 

GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER, 

BAY PARK, NEW YORK, WITH TERTIARY-TREATED SEWAGE 

By STEPHEN E. RAGONE 

ABSTRACT 

A ground-water deficit of93.5 to 123 million gallons per day (4.10 to 5.39 

cubic meters per second) has been predicted for Nassau County, N.Y., by 

the year 2000 in a State report. Because of the predicted deficit, the U.S. 

Geological Survey, in cooperation with the Nassau County Department of 

Public Works, began an experimental deep-well recharge program in 1968. 

Thirteen recharge tests using tertiary-treated sewage (reclaimed water) and 

six tests usi!}g water from the domestic supply (city water) were completed 

between 1968 and 1973. Recharge was through an 18-inch (46-centimeter) 

diameter recharge well screened in the Magothy aquifer between depths of 

418 and 480 feet (127 and 146 meters) below land surface. Recharge rates 

ranged from about 200 to 400 gallons per minute ( 13 to 25 liters per second). In the longest test, reclaimed water was injected during 84.5 days of a 

199-day period. 

Although the iron concentration of native water in the recharge zone 

and of reclaimed water is less than 0.5 milligrams per liter, the iron 

concentration of samples collected from observation wells 20, l 00, and 

200 feet (6.1, 30, and61 meters) from the recharge well, and screened in the 

zone of recharge, approached 3 milligrams per liter at times. Iron massbalance calculations indicate that dissolution of pyrite and marcasite 

(FeS2) in the aquifer are the only known sources of iron that could 

explain the observed increase. Within a 20-foot (6.1-meter) radius of the 

recharge well, dissolved oxygen in the reclaimed water oxidizes pyrite 

and releases Fe+2 (ferrous iron) to solution. However, the amount of iron 

in water continues to increase with distance from the recharge well even 

though dissolved oxygen is no longer present in water reaching the 20-

foot (6.1-meter) radius; the mechanism by which iron continues to be 

dissolved is not quantitatively understood. 

Some cation exchange also occurs during recharge. Loss of ammonium and potassium cations in the water was balanced by an increase in H:, which at times caused pH to decrease by more than 1 pH unit. 

Tertiary treatment removes 90 to 98 percent of the phosphate, MBAS 

(methylene blue active substances), and COD (chemical oxygen 

demand), leaving an average of 0.17, 0.07, and 9 milligrams per liter, 

respectively. During recharge, phosphate concentrations remain at 

native-water levels at the20-, 100-, and200-£oot (6.1-, 30-, and61-meter) 

observation wells, which indicates phosphate retention by the aquifer. 

Some MBAS and COD are retained at the 100- and 200-foot (30- and 61-

meter) wells, presumably by adsorption reactions. 

INTRODUCTION 

Population of Nassau County, Long Island, N.Y. (fig. 

1) increased from 0.41 million in 1940 to 1.43 million in 

1970 and is expected to increse to between 1.63 and 1.85 

million by the year 2000 (Temporary State Commission on 

the Water-Supply Needs of Southeastern New York, 1972). 

As a result of population increase, gross pumpage from 

the ground-water system, the only source of public water 

supply to date (1977), has increased from 75 Mgal/d (3.29 

m~/s) in 1940 to 215 Mgal/d (9.42 m~/s) in 1970. Gross 

pumpage is expected to range from 258 to 313 Mgal/d (11.3 

to 13.7 m~/s) by the year 2000(Temporary State Commission on the Water-Supply Needs of Southeastern New 

York, 1972). The increased demand for water-together 

with decreased recharge resulting from the replacement of 

cesspools and septic tanks, which return effluents to the 

ground, with sewer systems, which discharge effluents 

offshore-is predicted to cause a water deficit in Nassau 

County of 93.5 to 123 Mgal/d(4.10to5.39m~/s) by the year 

2000 (Temporary State Commission on the Water-Supply 

Needs of Southeastern New York, 1972). 

PURPOSE AND SCOPE 

This report summarizes the geochemical effects of 

injecting reclaimed water (tertiary-treated sewage) into a' 

sand aquifer. Because of the very good chemical quality of 

the native water, as reflected by a dissolved-solids concentration of 22 to 25 mg/1 (milligrams per liter), it was necessary to determine the type and extent of any chemical 

reaction caused by artificial recharge that could lead to a 

degradation of water quality. The study began in 1964 and 

was completed in 1973 as part of a cooperative water-resources program between the U.S. Geological Survey and 

the Nassau County Department of Public Works. Thirteen 

Dl 
D2 ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

41° 

--~ ~!?· _,.. •• _... • • ~lshers\ , • • Island '. 

Plum lslandt( 

10 .Q 10 20 30 MiLES 

~1~0•~,~~~~lb~~2~b---3~b~K-I-LO_M_E~~ERS 

FIGURE I.-Location of recharge site, Bay Park, New York. 

tests using reclaimed water and six tests using city water 

(water from the domestic supply) were completed between 

1968 and 1973. Chemical and hydrologic data were 

collected from all the tests, but most of the geochemical 

data for this report were obtained from the last and longest 

recharge test, in which reclaimed water was injected 

during 84.5 days of the 199-day period from October 24, 

1972, to May 11, 1973. 

PREVIOUS STUDIES 

Several reports covering different aspects of the Bay Park 

project have been published. Details of design, construction, and operation of the recharge facility have been 

reported by Cohen and Durfor(1966and 1967), Perlmutter 

and others (1968), and Koch and others (1973). Several 

studies of the microbiological aspects of deep-well 

recharge have been reported by Vecchioli (1970), Vecchioli 

and others (1972), and Ehrlich and others (1972 and 1973). 

'Description of early findings are given in reports by 

Vecchioli and Ku (1972), Vecchioli (1972), and Vecchioli 

and others (1974). Some of the water-quality changes 

during recharge have been reported by Ku and others 

(1975), Faust and Vecchioli (1974), Ragone and others 

(1973 and 1975), and Ragone and Vecchioli (1975). The 

corrosivity of water with respect to metals was also 

reported by Vecchioli and Giaimo (1972), and a comprehensive review of the operation and general results of the 

Bay Park project is given by Vecchioli and others (1975). 

BAY PARK HYDROGEOWGY 

Long Island is underlain by consolidated bedrock, 

which, in tum, is over lain by a wedge-shaped mass of 

unconsolidated Pleistocene glacial deposits and Cretaceous fluvial or deltaic deposits. This unconsolidated 

material, which constitutes the ground-water reservoir for 

Long Island, ranges in thickness from 0 ft in northwest 

Queens County, where bedrock crops out, to more than 

2,000 ft (610 m) in southern Suffolk County (Cohen and 

others, 1968, p. 18). The ground-water reservoir consists of 

several aquifers, of which the Magothy aquifer is the 

principal water-supply source for Nassau County. 

The recharge well at Bay Park, N7884, is screened in a 

zone in the Magothy aquifer (fig. 2) that is semiconfined by 

beds of lower hydraulic conductivity. Static water level in 

this zone is approximately 5 ft (1.5 m) below land surface. 

In this zone, the aquifer consists of gray very fine to 

medium sand and contains some silt and clay layers (table 

1 ). X-ray analysis of a sample taken at a depth of 527ft (161 

m) during the drilling of the test hole that preceded 

drilling of the recharge well shows that the clay in this 

sample is composed of equal parts of kaolinite and illite 

(Vecchioli and others, 1974); presumably, therefore, clay is 

of this composition throughout the recharge.zone. Lignite 

occurs in layers and as disseminated particles. Pyrite and 

marcasite (FeS2) are also present and, in many places, are 

associated with lignite. Other accessory minerals include 

muscovite, tourmaline, garnet, zircon, andalusite, and 

sillimanite (Vecchioli and others, 1974). Carbonate miner-
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER D3 

ARTIFICIAL-RECHARGE PLANT 

ti:i 

w 

LL 

100 

z 200 

w .. (.) 

<( 

LL' 

a: 300 ::) 

en 

0 

z 

~ 

~ 0 

....J 

w 

CD 

400 

:I: 500 

h: 

w 

0 

s 

Magothy aqu1fer 

N7889 ~. N7888 ~ 

N7890~ 

, _ --~ N7885 

.l. 

N7891 :; N7887 ~ 

EXPLANATION 

D . 

. Sand and gravel 

Sand, silt, and clay 

Silt 

~ 

~ and clay 

.l. 

:; N7675 

Well screen and 

well number 

N 

30 

en 

a: 60 w 

1-

w 

~ 

z 

- 90 ui 

(.) 

<( 

LL 

a: 

::) 

en .. 0 J. z -- N8022 = <( 

. = ·. ....J 

.· --

150 ~ 0 l ....J 

w N2790 ~ CD 

:I: 

.180 h: 

w 

0 

40 FEET I I I I I 5 10 MITERS 

FIGURE 2.-Hydrogeologic section of artificial-recharge site showing vertical and horizontal distribution of the observation-well 

screens in relation to the injection-well screen (from Koch and others, 1973, fig. 9). 

als are absent from the vicinity of the recharge zone 

(Vecchioli and others, 1974). 

The predominant directions of ground-water movement are northward and southward from the groundwater divide near the central axis of the island. Detailed 

information about Long Island's hydrogeology is presented in several reports (for example, Franke and 

McClymonds, 1972; Perlmutter and Geraghty, 1963). Near 

the south shore of Long Island, the ground -water flow 

pattern is that of discharge-freshwater moves outward 

and upward into the bays and ocean. Thus, the water 

presently in the Magothy aquifer at this site is derived from 

precipitation that infiltrated the aquifer 1 mi (1.6 km) or 

more to the north hundreds of years ago (Franke and 

Cohen, 1972, p. C271). 

BAY PARK SEWAGE-TREATMENT PLANT AND 

DEMONSTRATION TERTIARY-TREATMENT 

PLANT 

The Bay Park sewage-treatment plant is a 60-Mgal/d 

(2.6-m11 /s ), conventional, activated-sludge treatment 

plant. About 1 percent of the secondary effluent from the 
D4 ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

TABLE I.-Lithologic profile of recharge zone, as determined from cores 

taken during drilling of the recharge well 

[From Vecchioli and others, 1974, p. C6] 

Thickness Depth below 

(feet) land surface 

Sand, gray, very fine to medium, slightly 

silty, lignitic, micaceous ...................... 36 392 

Sand, gray, very fine to fine, and gray 

silt, lignitic, micaceous; lignite 

layer at 402 feet; pyrite concentration at 435 feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 436 

Sand, gray, medium to coarse, clean to 

slighty silty, micaceous, lignitic, 

slightly pyritic .............................. 39 475 

Sand, gray, coarse to very coarse, silty, 

micaceous, slightly lignitic . . . . . . . . . . . . . . . . . . . . 7 482 

Sand, gray, very fine, silty, micaceous, 

lignitic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 490 

Bay Park plant is diverted to a 400-gal/min (25 lis) 

demonstration tertiary-treatment plant. There, the water 

receives physical-chemical treatment to produce virtually 

potable water (Peters and Rose, 1968). The general process 

is as follows (fig. 3). Influent from the activated-sludge 

plant enters a reactivator-clarifier tank, where it is treated 

with alum (aluminum sulfate) to precipitate phosphate 

and suspended solids. The supernatant liquid is then 

pumped through dual-media sand filters to remove 

additional suspended solids, then through from one to 

four activated carbon columns to remove dissolved 

organic materials. The final step in the tertiary-treatment 

process is chlorination. 

DEEP-WELL RECHARGE FACILITY 

Effluent from the tertiary-treatment plant is pumped 

approximately 0.5 mi (0.8 km) to the recharge site. 

Influent from 

activated sludge 

plant 

Alum 

Sludge to waste 

Detailed descriptions of design and operation of this 

facility are given by Koch and others (1973), Perlmutter 

and others (1968), and Cohen and Durfor (1966 and 1967); 

therefore, only a brief description is given here. 

The facility consists of (1) a 50,000-gal (189,000-1) 

storage tank; (2) a recharge well with an 18-in (46-cm)-

diameter fiberglass casing and a 16-in (41-cm) -diameter 

by 62-ft (19-m) -long stainless steel screen between depths 

of 418and480 ft(l27 and 146m); (3) various equipment for 

further treating reclaimed water or city water ( dechlorination, degassing, and Eh/pH adjustments); and (4) 18 

observation wells ranging from several inches to 200 ft ( 61 

m) from the recharge well and screened at various depths. 

Most of the data collected during the recharge tests were 

obtained from samples from the recharge well, N7884, and 

three observation wells that were screened within the zone 

of recharge; these wells are designated N7886, N7890, and 

N8022. Wells N7886 and N7890 are 20ft (6.1 m) and 100ft 

(30m) southwest of the recharge well, respectively (fig. 4). 

Well N8022 is 200ft (61 m) northeast of the recharge well. 

The recharge well and the observation wells are constructed of nonferrous or corrosion-resistant materials to 

minimize the possibility of chemical reaction of the 

reclaimed water with the wells (Cohen and Durfor, 1966). 

To permit additional experimentation, the system is 

designed to allow injection of city water as well as 

reclaimed water. 

Six recharge tests with city water and 13 recharge tests 

with reclaimed water were completed between 1968 and 

1973 (table 2). These tests ranged in length from 2 to84.5 

days; recharge rates were from about 200 to 400 gal/min 

(13 to 25 lis); and treatment process in the tertiary plant 

and (or) at the recharge site was also varied. Test RWIO 

consisted of two separate periods of recharge but is considered as one test because redevelopment between 

recharge periods was very slight and did not return the 

aquifer to natural conditions as it did after the other tests. 

To recharge facilities 

, REACTIVATOR-CLARIFIER DUAL MEDIA 

FILTRATION 

ADSOR_PTION ON 

ACTIVATED CARBON 

FIGURE 3.-Schematic drawing of water-reclamation process (from Vecchioli and others, 1975, fig. 1). 
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER 

I 

r 

r Fence~ 

r 

r 

I 

I 

N7678e 

eN2790 

N6928 ;N7675 

e e eN7676 

I 

I 

I 

I 

I 

I 

I 

I 

l 

I 

'-~1.-----------------------~ I XI ~From tertiary 

treatment plant 

Storage tank I 

r ~~-

r r XI N7680 XI 

e J N7889 and N7890 X N7891 

I 

N7682e e X 

X 

' • .N7679 I N7~81 

j 0 45 FE8 l I b 1

!

1

5 METERS I 

X N7682-Well numbe' r l__x-----x-----x-----x-----x-----x-----·x-----x-----x~ 

FIGURE 4.-Location of observation wells, structures, and external piping at the artificial recharge site (from 

Koch and others, 1973, fig. 8). 

D5 
D6 ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

TABLE 2.-Recharge-test statistics at Bay Park 

(CW, city water; RW, reclaimed water] 

Approximate Recharge Gallons Special 

treatment 

of water 

Test 

No. 

Date length rate recharged 

(days) (gal/min) (thousands) 

City water 

CW1 ..... Feb.27-29, 1968 ............. 2 190 570 Degassed, dosed 

with H2S04 and 

Na2S03. 

CW2 ..... Mar. 12-14, 1968 ............. 2 385 1,118 Dosed with H2S04 

andNa2S03. 

CW3 . . . . . Mar. 25-27, 1968 ............. 3 185 840 Degassed. 

CW4 ..... Apr. 16-19, 1968 ............. 3 390 1,655 None. 

CW5 ..... Feb. 17-19,1970 ••••••••• 0 ••• 2 400 1,200 Dosed with 

H3P04. 

CW6 ..... Sept. 13-17, 1971 . ........... 4 395 2,281 None. 

Reclaimed water 

RW1 ..... Oct. 8-10, 1968 •••• 0 ••••••••• 

RW2 ..... Dec. 10-12, 1968 ............. RW3 ..... Feb. 25-27, 1969 ............. RW4 ..... May 6-16, 1969 .............. RW5 ..... Sept. 15-25, 1969 ••• 0 •••••••• 

RW6 ..... Mar. 17-19, 1970 ............. RW7 ..... Apr. 14-May 17, 1970 

RW8 ..... Nov.30-Dec.9, 1970 0 •••••••• 

RW9 ..... Apr. 21-May 7, 1971 0 •••••••• 

RW10 .... Nov. 1-11, 1971 . .............. 

RW10A ... Jan. 10-14,1972 ••• 0 ••••••••• 

RW11 .... Mar. 6-16, 1972 .............. 

RW12 .... June 5-15, 1972 ••••••••••• 0 •• 

RW13 .... Oct. 24, 1972-

May 11, 1973 •••••••• 00 0. 00 

Effects of the different treatment processes are described 

where appropriate in the following sections. 

GEOCHEMISTRY 

CHEMICAL AND PHYSICAL CHARACTERISTICS OF 

NATIVE WATER AND RECLAIMED WATER 

Dissolved-solids concentration of native water in the 

Magothy aquifer ranges from 22 to 25 mg/1 (table 3), and 

pH ranges from 5.22 to 5. 72. Clay minerals, mainly 

kaolinite, control the concentration of the alkali and 

alkaline earth elements through cation exchange (Pearson 

and Friedman, 1970). Concentration of Si0 2 (silica) in 

solution approaches that in thermodynamic equilibrium 

with quartz. The concentrations of Fe+2 (divalent iron) 

and so4-2 (sulfate) in solution are controlled by thermodynamic equilibrium with pyrite (Vecchioli and others, 

1974; Faust and Vecchioli, 1974). The pH of the water is 

controlled by both the dissociation of HzC0 3 (carbonic 

acid) a·nd the silica-kaolinite equilibrium (Faust and 

2 200 616 Degassed. 

2 350 1,063 Degassed. 

2 350 1,066 None. 

10 360 5,247 None. 

10 350 5,117 Degassed. 

2 340 1,133 None. 

33 200 to 350 13,970 None. 

10 340 4,930 U nchlorinated. 

10 355 5,156 None. 

10 350 5,180 Bypassed carbon adsorbers. 

4 350 2,000 U nchlorinated. 

10 350 5,124 Dosed with 

Na2Sz03 • 5H20. 

10 355 5,050 Dosed with 

NaOH. 

84.5 355 41,695 None. 

Vecchioli, 1974). Carbon dioxide partial pressure of water 

in the recharge zone at Bay Park is one to two orders of 

magnitude greater than that of water in equilibrium with 

air (Faust and Vecchioli, 1974; Pearson and Friedman, 

1970); plant sources rather than carbonate minerals cause 

this increase (Pearson and Friedman, 1970; Vecchioli and 

others, 1974). DO (dissolved oxygen) concentration of 

native water is zero, and Eh (oxidation-reduction potential) of the water ranges from -0.03 to -0.10 volts. 

Concentrations of most constituents of the reclaimed 

water are greater than in native water from the Magothy 

aquifer (table 3). 

CLOGGING OF THE RECHARGE WELL 

Specific capacity at the end of each of the 13 recharge 

tests was less than at the start because of physical-chemical 

and (or) biological processes that caused entrapment of 

suspended material either in the gravel pack, at the well 

screen-aquifer interface, or within the first several inches 

of the aquifer. In physical-chemical clogging, suspended 
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER D7 

TABLE 3.-Chemical and physical characteristics of native water 

from the Mago~hy aquifer and of reclaimed water 

[All data in milligrams per liter unless otherwise indicated; N.D., not determined] 

:-.lative water 1 Reclaimed water2 

Range and( or) mean value Standard 

Minimum Mean Maximum Mean deviation 

Silica (Si02 ) •••••••••..••.•••••••••••••••••••• 7.2 13 1 

Iron (Fe), total,3 (~o~g/1) ......................... . 140 

7.4 

300 

300 

410 260 

Iron (Fe), dissolved,3 (1-'g/1) ..................... . 140 230 180 

Manganese (Mn), total, (1-'g/1) .......... , ....... . 

Calcium (Ca) ................................. . .4 

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

Sodium (Na) ................................. . 3.7 

Potassium (K) ................................ . .4 

Bicarbonate3 (HC03) .......................... . 4.5 

Sulfate (S04) ..•••••.•••••.•••••••••••••.•••••• 3.6 

Chlorine, total residuaP ....................... . 

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

Nitrate (N03), total ........................... . 

Nitrite (N02), total ........................... . 

Nitrogen, ammonia, total as NH4 .............. . .8 

Nitrogen, total organic as N ................... . .1 

Phosphorus (P04), total ....................... . .01 

Dissolved solids, residue at 180°C ............... . 

Dissolved solids, calculated (sum 

30 

.2 

40 

3.9 

0 

40 

N.D. 

1.4 

3.9 

.6 

7.5 

4.0 

4.9 

4.4 

.02 

75 31 

20 3 

6.4 2.1 

86 12 

13 1 

59 19 

160 20 

2.1 .5 

99 23 

.4 .2 

.3 .1 

30 2 

.6 .4 

.17 .24 

398 68 

of dissolved constituents) .................... . 22 25 463 48 

Specific conductance, 3 (micromhos/cm at 25°C) .. . 28 786 81 

pH3 ......................................... . 5.22 

32 

5.72 56.1 .2 

Water temperature,3 °C ........................ . 

Turbidity3 as Si02 ....•...••••••.••••••••.••••• 

Oxidation reduction potential3 

15 

40 

17.5 2.0 

.4 .3 

(Eh, in volts) ................................ . -.03 -.10 N.D. 

Dissolved oxygen3 (DO) ....................... . 40 4.5 1.6 

Chemical oxygen demand (COD) 

0.025N K2Cr20 7 ............................ . 40 9 5 

Detergents (MBAS) ........................... . 0 .07 .08 

1 After Vecchioli ahd others (1974), for samples taken from the 20-, 100-, and 200-ft (6.1-, 30-, and 61-m) 

observation wells before any recharge, unless otherwise stated. 

2 Based on the weighted average of at least 33 daily or weekly composite samples. 

3 Measured or determined on site. 

4 Data from RWIO (reclaimed-water test 10). 

5 Mean calculated after converting pH values from logarithmic form to exponential form. 

material may originate in secondary sewage or may be 

formed during the tertiary-treatment process. Neither 

purely physical clogging caused by gas entrapment nor 

purely chemical clogging caused by chemical incompatibilities between the reclaimed water and native water and 

aquifer have been observed at Bay Park. Biological 

clogging has been observed (Ehrlich and others, 1973 ), but 

this type of clogging can be controlled by chlorination 

(Ehrlich and others, 1972 and 1973). 

Studies during tests R W 1 through R W7 (the first 7 of the 

13 recharge tests with reclaimed water) indicate a correlation between turbidity of the reclaimed water and the rate 

of well clogging (Vecchioli and Ku, 1972; Vecchioli, 1972; 

Vecchioli and others, 1975 ). The water initially repumped 

from the recharge well was turbid and, at times, odorous. 

Chemical and microbiological analyses indicated that it_ 

contained high concentrations of iron, phosphate, volatile 

and fixed suspended solids (table 4), and bacteria (table 5). 

Water quality improved markedly with continued 

repumping but often deteriorated after the pumping rate 

was rapidly varied. This suggests that material close to the 

well bore was being dislodged by the surging action. 

The high concentration of iron and phosphate in the 

repumped water suggests that iron hydroxy phosphates, 

which are formed in the coagulation step of tertiary 

treatment, pass through the sand filters (which are coarser 

than the aquifer material) and are trapped near the gravel 

pack-aquifer interface. Processing the chemical data by 

application of W ATEQ, the computer program of Truesdan and Jones (1974), showed that the repumped water 

was supersaturated with aluminum and iron hydroxy 

species and iron oxide species. Precipitation of some or all 
D8 ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

TABLE 4.-Selected physical and chemical-quality 

parameters of initially recovered water1 

[Analyses by Nassau County Department of Health. 

All constituents in milligrams per liter) 

RWI 

rurhidity . . . . . ................ 225 

rota! phosphate . . . . . . . . . . . . . . . . 30 

rota! iron . . . . . . . . . . . . . . . . . . . . . 45.5 

rota! solids .................... 672 

l'ota I su~pended 

\olid~ ....................... 321! 

l'otal dissolved 

•olids ....................... 344 

rotal volatile 

"'lids ....................... 171 

\'olatilt· suspended 

"'lids ....................... 116 

\'olatile dissolved 

"'lids ....................... 55 

l'otal fixed 

\olids ....................... 501 

Fixed "uspended 

"'lids ....................... 212 

Fixed dissolved 

"'lids ........................ 289 

( hygt•n consumed .............. 3 48 

1 Tablt· 6, from Vecchioli and Ku (1972). 

Test No. 

RW2 

78 

26 

RW3 RW4 

80 

1.44 19.6 

7.55 .08 15.1 

513 .......... 532 

136 

377 

146 

50 

96 

367 

86 

281 

35 

6 84 

381 448 

.......... 132 

.......... 37 

.......... 95 

......... .400 

.......... 47 

.......... 353 

15 36 

" Sample collected 5 minutes later than others. 

' Analysis for total organic carbon. 

RW5 

2 163 

43.5 

50.5 

686 

248 

438 

232 

82 

!50 

454 

166 

288 

2 21 

of these species probably explains the accumulation of 

iron- and aluminum-rich solids around the aquifer-well 

screen interface in previous recharge experiments. Ragone 

and others ( 1973) found that the amount of iron recovered 

from the recharge well during repumping after test RWlO 

was equal to the amount of colloidal iron in the reclaimed 

water initially recharged. 

Acid treatment of the recharge well rreatly improved 

specific capacity (Vecchioli, 1972). After test RW7, specific 

capacity was 2.5 (gal!min)/ft [0.52 (1/s)/m], down from 

23.5 (gal/min)/ft [4.9 (1/s)/m] at the start of the test. 

Stepwise surges in pumping at rates ranging from 300 

gal/min (191/s) to 1,000 gal/min (631/s) increased specific 

capacity to 18 (gal/min)/ft [3.7 (1/s)/m]. Approximately 

2,400 gal (9,084 1) of 32-percent commercial-grade 

hydrochloric acid was then pumped into the well and was 

pumped out after standing approximately 20 hours; this 

treatment increased specific capacity to 26.5 (gal/min)/ft 

(5.5 (1/s)/m]. 

A long-term redevelopment (pumping out) of the 

recharge well followed each recharge experiment in order 

to return the system to pretest condition. Nearly 50 percent more water had to be pumped out than had been 

injected in order to attain this. 

TABLE 5.-Bacterial quality of water recovered 

after test RW4 in 19691 

Date 

6-2-69 

6-3-69 

6-4-69 

6-5-69 

6-23-69 

6-27-69 

7-1-69 

7-15-69 

7-16-69 

8-6-69 

8-7-69 

[Analyses by Nassau County Department of Health. 

Intermittent pumping from 6-5 to 6-23; pauses from 

6-27 to 7-1, 7-1 to 7-15, 7-16 to 8-6) 

Cumulative 

gallons Standard plate 

withdrawn count at 35°C 

(thousands) (number/ml) 

····· ...... 2 >300 

6 >300 

24 >300 

86 >300 

........... 576 >300 

883 44 

........... 1,483 < 30 

1,699 < 30 

........... 2,299 < 30 

.......... 7,207 >300 

7,327 < 30 

.......... 10,580 < 30 

0 •••• 0 ••••• 10,586 >300 

10,676 < 30 

•••• 0 ••••• 10,682 >300 

10,778 88 

.......... 11,253 < 30 

........... 11,346 ............... 

11,438 ............... 

........... 11,918 ............... 

1 Table 7, from Vecchioli and Ku (1972). 

" Most probable number. 

Coliform 

confirmed 

(MPN2il00 ml) 

>240 

>240 

>240 

>240 

>240 

240 

240 

240 

38 

>240 

38 

5 

>240 

8.8 

>240 

2.2 

<2.2 

38 

<2.2 

<2.2 

CHANGES OBSERVED IN THE HYDROCHEMICAL 

SYSTEM DURING RECHARGE 

A simplified aquifer-flow model, although it does not 

exactly depict the actual flow, was used to define the 

movement of reclaimed water through the aquifer. With 

the model, reclaimed water is assumed to move radially 

away from the recharge well as an expanding cylinder the 

same height and at the same depth as the screened interval 

of the recharge well. Analysis of pumping-test data 

(Vecchioli and others, 1974) shows that within a 200-ft (61-

m) radius of the recharge well, flow follows a nearly horizontal-radial pattern. 

On the basis of the radial-flow model and on the 

assumption that the mineralogy of the screened interval is 

reasonably homogeneous within 200 ft (61 m) of the 

recharge well, water samples from the 20-, 100-, and 200-ft 

(6.1-, 30-, and 61-m) observation wells are considered to 

be representative of water everywhere on the circumference 

of the respective concentric cylinders. Expansion of the 

diameter of the cylinder is assumed to be proportional to 

the volume of water injected. In following discussions, 

chemical data on water from the observation wells are used 

to calculate the amount of specified constituents passing 

the respective concentric peripheries that circumscribe the 

recharge well. 
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER D9 

The flow system depicted by the hydraulic model is not 

firmly supported by water-quality data, however. Analysis 

of the breakthrough curve of specific conductance at the 

20-ft (6.1-m) well during test RWlO suggests that only 50 

percent of the reclaimed water remains in the recharge 

zone, but analysis of the breakthrough curve at the 200-ft 

(61-m) well suggests that nearly 100 percent of the 

reclaimed water remains in the recharge zone. Two factors 

may contribute to this anomaly: ( 1) various processes of 

dispersion produce a zone of diffusion and mixing 

between the reclaimed and native waters, so that the 

reclaimed water moves through the aquifer as an irregularly advancing front (F. J. Pearson, Jr., and G. D. Bennett, 

written commun., 1972); and (2) internal flow patterns 

observed at the 20-ft (6.1-m) observation well are complex 

and do not correspond to the steady-state, radially symmetric simulation (Vecchioli and others, 1974). Regardless of 

the exact nature of the flow pattern, the percentage of 

reclaimed water reaching the 200-ft (61-m) periphery is 

unlikely to be much different from that passing the 20-ft 

(6.1 m) periphery, because the screened interval behaves 

virtually as a confined zone within these distances from the 

recharge well. 

A flow net based on a steady-state, radially symmetric, 

electric-analog simulation of the well-aquifer system 

indicates that at 200ft (61 m) from the recharge well, 70 

percent of the flow is within the screened interval (Vecchioli and others, 1974). Thus, at a 20-ft (6.1-m) radius, the 

flow in the screened interval should be no less than 70 percent. 

To define the movement of reclaimed water through the 

aquifer, chloride concentrations of water samples were 

used to measure the extent of mixing between native and 

reclaimed waters. To do this, a mixing coefficient(~ )was 

calculated (F. J. Pearson, Jr., and G. D. Bennett, written 

commun., 1971) and is defined as: 

where 

VI 

es 

en 

ei 

VI = es -en 

ei- en (1) 

= in essence, the ratio of the concentration of a. 

given constituent in the water sample to the 

concentration of that constituent in the 

reclaimed water 

= the concentration of that constituent in the 

water sample 

= the concentration of that constituent 1n 

native water, and 

= the concentration of that constituent 1n 

injected water. 

The Ji; values calculated for other constituents in the 

footnote 1) indicates a concentration greater than can be 

explained by a simple-mixing model (equation 1 ), and a V1 

less than that for (li; )CI- indicates a concentration less than 

can be explained by the model. 

IRON-MOBILIZATION REACTIONS 

Although iron concentrations of reclaimed water and 

native water in the recharge zone are less than 0.5 mg/1 

(table 3), the iron concentration of samples taken during 

test RW13 from the 20-, 100-, and 200-ft (6.1-, 30-, 61-m) 

observation wells at times approached 3 mg/1. Most of the 

earlier tests were too short for reclaimed water to reach the 

100- and 200-ft (30- and 61-m) wells, but increased iron 

concentrations were observed at the 20-ft (6.1-m) well in 

several tests (table 6). Iron mass-balance data indicate that 

TABLE 6.-Effect of dissimilar treatments of reclaimed 

water and city water on the maximum iron concentration 

of the observed iron peak at the 20-foot 

Recharge 

test 

( 6.1-meter) observation well 

Treatment 

RWlO, part I Carbon filters bypassed; 

Maximum iron 

concentration 

(mg/1) 

high COD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.05 

RWlO, part II Unchlorinated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.20 

R Wll Dechlorinated using sodium 

thiosulfate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.60 

RW12 Raised pH to 8 using sodium 

hydroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.37 

RW13 Normal treatment (see section 

"Bay Park sewage-treatment 

plant and demonstration 

tertiary-treatment plant") . . . . . . . . . . . . . . . . . 2.88 

CW6 . . . . . . do . . . . . . . . . . . . . . . . No change from 

native water. 

iron-bearing minerals must be dissolving. and that ·pyrite 

and marcasite (FeS2) are the only source of iron present in 

sufficient quantity to have caused the increased iron 

concentration (Ragone and others, 1973 ). Within a 20-ft 

(6.1-m) radius of the recharge well, dissolved oxygen in 

the reclaimed water oxidizes FeS2 and releases Fe+2 to 

solution. However, the fact that the dissolved iron content 

of water passing cylindrical sections of radii 100 and 200ft 

(30 and 61 m) from the recharge well is greater than that of 

water passing a cylindrical section of radius 20ft (6.1 m) 

from the recharge well, even though dissolved oxygen does 

not reach the 20-ft (6.1-m) radius, indicates that other 

factors must be controlling the addition of iron to the 

system. 

Changes in iron concentration and pH as functions of 

the fraction of reclaimed water in water samples at the 20-, 

water sample indicate their reactivity compared with that 1. This term distinguishes the VI o£ chloride from the VI of other 

of Cl- (chloride). A Ji; value greater than thatfor(~)cr (see constituents. 
DlO ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

100-, and 200-ft (6.1-, 30-, and 61-m) observation wells 

are given in figures 5 and 6. With the arrival of reclaimed 

water at the observation wells, iron increases and pH 

decreases simultaneously. At the 20- and 100-ft (6.1- and 

30-m) wells, iron concentration reaches a maximum of 

nearly 3 mg/1 at (~)c values of 0.4 and 0.5, respectively, 

then decreases as (~ )CI- approaches 1. This suggests that 

the increase in iron concentration occurs in the reclaimedwater front as the reclaimed water displaces native water. 

Native water at a radius of 200 ft (61 m) was not 

completely displaced by reclaimed water because the test 

was not long enough (fig. 6). Whether the 3-mg/1 iron 

concentration observed at the end of the test is the 

maximum concentration, or whether it would have 

increased with continued recharge, is not known. 

The pH of samples from the 20- and 100-ft(6.1-and30-

m) wells decreased with the arrival of reclaimed water, 

reached a minimum at about the same time that iron 

concentration reached a maximum, and then increased 

(figs. 5 and 6). At the 200-ft (61-m) well (fig. 6), the pH 

decreased until the end of the test. The minimum pH was 

successively lower at the 20-, 100-, and 200-ft (6.1-, 30-, 

and 61-m) wells. 

Iron-mass balance calculations showed that the 

increased amount of iron in water passing a cylindrical 

section of radius 20ft (6.1 m) from the recharge well could 

not be accounted for by iron in the reclaimed water 

(Ragone and others, 1973 ). Iron content of the mixed water 

passing cylindrical sections of greater radii continues to 

increase-going from 6.4 x 107 mg at 20ft (6.1 m) to 20.1 x 

107 mg at 100ft (30m) and to (see footnote 2) 18.5 x 107 mg 

at 200ft (61 m); this increase indicates that the source of 

dissolved iron is in the aquifer. These values represent the 

areas under those parts of the iron-concentration curves in 

figures 5 and 6 that exceed native-water concentrations. 

Because pyrite and marcasite are the only known iron 

minerals in the recharge zone, the increase in iron 

concentration within 20ft (6.1 m) of the recharge well was 

probably caused by oxidation of these minerals by dissolved oxygen in the reclaimed water (Ragone and others, 

1973). DO concentration of the first 2 Mgal (7.6 mill) of 

reclaimed water injected during test R W 13 was 5 mg/1. On 

the basis of this value, the concentration of Fe+2 produced 

by oxidation reaction 

(2) 

2. This is a minimum value, as reclaimed water did not completely displace native water at the 

radius of 200ft (61 m). 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS 

a: 2 5 10 20 50 100 w 1.2 3 I-

<(w 

3=-.J z a.. a: 0~ 'w 

W<( Zl-

~en 0.8 2 Q ::i 

<Co: ~ a: -.Jw a: W· 

U!- I- a.. W<( 

a:~ z en w LL u ~ 

0~ <( 0.4 1Z ·a a: 

z I u (!) 

0 u ::i - ·- z _J I- ~- 0 ~ ~ g; a: 

LL 0 

7 

:a 6 • 

0.2 0.5 2 5 10 20 50 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE 5.-Changes in iron concentration and pH as a function of the fraction of reclaimed water ( 11 Jcr at the 20-toot (6.1-meter) 

observation well during recharge. 
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS .. -

a: 

w 1.2 

I-

<( w 

~ ..J 

a.. 

0 ::2 w <( 

::2 en 0.8 <:( a: ..J w u 

w 

a: ~ 

~ u. 

0 z 

0.4 

z I 

0 32 i= :::;-

~ a: 

u. o~ 

4 

~a: 'w Zl- 3 

O::::i 

~ a: 

w ,a: a.. IZen 

w::2 u<C 

za: 

0(!) 

U-..J 

z ..J 

0 :E Q;; 

6~------------------------------------------------------------------------------~ 

:a 5 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE 6.-Changes in iron concentration and pH as a function of the fraction of reclaimed water(Vt h:J- at the 100-foot and 200-foot (30-

and 61-meter) observation wells during recharge. 

Dll 

is 2.5 mg/1. This calculation agrees well with the observed 

value of 2.9 mg/1. A similar correlation between DO 

concentration and iron concentration was observed during test RW10 (Ragone and others, 1973). However, water 

reaching the 20-ft (6.1-m) well had no detectable DO 

concentration; therefore oxidation of FeS2 by DO in the 

reclaimed water cannot explain the increase in iron 

· observed at the 100- and 200-ft (30- and 61-m) wells. It 

may be that other factors, such as organic complexing and 

auto-oxidation of divalent iron by Fe+3 (trivalent iron), 

contribute to the continued mobilization of iron. 

CATION-EXCHANGE REACTIONS 

Higher concentrations of alkali and alkaline earth 
012 

0 

z· 

<{ b 

:!~ 

2a: u w 1.6 

_.1-

<Cc:J:: u3: 

co 

zw 

<(~ 

~­

::>~ 

en~ 

~a: 

(!)U.. <( 0 0.8 

~z 

a:Q 

01-

u..u 

(/)<{ 

~a: -IW 

<(J: >IARTIFICIAL-RECHARGE EXPERIMENTS. BAY PARK, LONG ISLAND. NEW YORK 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS 

EXPLANATION 

• (V,lcl-

• Mg+2 

• ca'+2 

0.2 0~5 j_ _2 5 1 0 20 50 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE 7.-Changes in r-] values for rpagnesium and calcium as a function of the fraction of reclaimed water(~ )c1- at the 20-foot (6.1-

meter) observation well during recharge. 

metals and NH/ (ammonium) in the reclaimed water the (li; )CI- curve has (fig. 7). During the period when 

than in native water, and the presence of clay minerals in reclaimed water is displacing native water from the 

the recharge zone, seem to cause some cation exchange vicinity of this well, that is, when(~ Jcc is greater than zero 

during recharge; that is, a loss of NH4+ and K+ (potas- · but less than 1, concentrations of Mg+2 and Ca+2 exceed 

sium) from solution seems to be balanced by an increase in those predicted by the simplified aquifer-flow model deH+ (hydrogen ion). scribed earlier. With continued injection, V1 values for 

~ curves for Mg+2 (magnesium) and Ca+2 (calcium) at Mg+2 and Ca+2 decrease below that of (~)CI-, then 

the 20-ft (6.1-m) well do not have the usual S-shape that approach the (~)cf curve near the end of the test (fig. 7). 

RECLAI!YlED WATER RECHARGED, IN MILLIONS OF _!liTERS 

: 1 

EXPLANATION 

• (V,)cl-

.& Na+ 

• K+ 

• Nl-+.t 0 'HCOf 

50 

~._----~--~~~~_.~2-LL------~----L--L-J-J~~~1~o------~--~--~~5o 

0.1' 0.2 Jl.5 ....L 5 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE M.-Changes m ~ values for sodium, potassium, ammonium, and bicarbonate as a function of the fraction of reclaimed water(~ Jcr at 

the 20-foot (6.1-meter) observation well during recharge. 
GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER Dl3 

The increase in the concentration of Mg+2 and Ca +2 is 11 

mg/1 and 24 mg/1, respectively, as compared with the 

average dissolved-solids concentration of 463 mg/1 of 

reclaimed water, and represents only a small percentage of 

the dissolved-solids load. 

~ values for Na+ (sodium), K+, NH/, and HC03

-

(bicarbonate ), on the other hand, remain below that of 

(~ )CI- (fig. 8), which indicates that concentrations ofthese 

constituents of the water at the 20-ft (6.1-m) well are less 

than predicted by the simplified aquifer-flow model. The 

~ curve for HC03- indicates that this constituent has the 

lowest ~ of that group. The HC03- curve indicates 

changes in H+ concentration in solution (Faust and 

Vecchioli, 1974) and, in calculations that follow, the 

amount of HC03- lost from solution is equated to the 

amount of H+ added to solution. 

The extent to which the noted excesses of Ca +2, Mg +2, 

and H+ and the deficits of NH/ and K+ are caused by 

cation exchange was determined by comparing the concentrations of cations added to the reclaimed water with 

the concentrations of those removed from the water. To do 

this, actual concentrations of the constituents of the water 

samples were compared with concentrations that were 

calculated from the simplified aquifer-flow model (table 

7 ). The calculated concentrations were determined by 

solving equation 1 for C sand using (~)cr values for J:-j to 

obtain 

( CJ = [( ~) C( ][ c rC nl + c n• (3) 

After 0.6 Mgal (2.3 mill) recharge the volume at which 

the ~ for Ca+2 and Mg+2 is greatest (fig. 7), 1.32 meq/1 

(milliequivalent per liter) more cations have been added to 

solution than have been removed (table 7). This value is 

too large to result from experimental or sampling error 

and suggests that other reactions besides cation exchange 

may be occurring as well. As Ca +2 and Mg+2 are the only 

cations whose concentrations significantly increase, they 

must be entering solution through some mechanism that 

has not been explained by available data. Deleting these 

cations and Na+ (see footnote 3) from the cation balance 

produces a good agreement between added and subtracted 

constituents-NH/ and K+ account for a 0.94 meq/lloss 

from solution, and H+ accounts for a 0.91 meq/1 gain to 

solution. 

The balance for added and substracted cations at 0. 7 

Mgal (2.6 mil 1) and at 0.74 Mgal (2.8 mill) recharge is 

similar to that for 0.6 Mgal (2.3 mill) recharge (table 7). 

Again, deleting ea+2, Mg+2, and Na+ from the cation 

balance produces excellent agr~ement between added and 

3. Sodium ion was not included in the mass bal ance because the difference between observed 

and calculated concentrations is relatively small and varies erratically from a positive to negative 

deviation. This suggests analytical errors rather than real changes. 

subtracted cations; the difference is 0.01 at 0.7 Mgal (2.6 

mill) and 0.00 at 0.74 Mgal (2.8 mill). Although the differences between observed and calculated concentrations 

of ea+2 and Mg+2 decrease substantially as recharge 

increases, differences between observed and calculated 

concentrations of K+, NH4 +, and HC0 3 - remain relatively large. This supports the earlier suggestion that 

cation exchange does not explain the large net increases in 

concentrations of Ca +2 and Mg+2 as reclaimed water 

displaces native water from the vicinity of the 20-ft ( 6.1-m) 

well. The increase in Ca +2 and Mg +2 cannot be explained 

by dissolution of carbonate minerals because none were 

found during mineralogical investigations of cores from 

the recharge well. The large net increases may, however, 

result from the dislodgment of calcium and magnesium 

salts that were entrapped near the recharge well in earlier 

tests, that is, salts that were not completely removed 

during well redevelopment. 

The balance of the cations NH4 +, K+, and H+ observed 

for samples collected through 0.74 Mgal (2.8 mil 1) 

recharge is poor for samples collected after 1.3 Mgal (4.9 

mil 1) recharge (table 7), which suggests that cationexchange reaction involving these constituents has 

stopped. 

Of all the constituents determined at the 100-ft (30-m) 

well, only Mg+2 shows an excess in concentration (figs. 9 

and 10). 

Cation-balance calculations indicate that relationships 

observed at the 100-ft (30-m) well (table 8) are similar to 

those described for the 20-ft (6.1-m) well-the increase in 

H+ is balanced by a decrease in NH4 + and K+ through 15 

Mgal (57 mill) of recharge. After this amount of recharge, 

poor correlation suggests cessation of cation exchange. 

As at the 100-ft (30-m) well, only Mg+2 concentration 

exceeds the concentration calculated from the simplified 

aquifer flow model at the 200-ft (61-m) well (figs. 11 and 

12). The HC03

- values are low and often zero; thus it is not 

known whether the decrease in HCO 3

- concentration 

equals an increase in H+ concentration, and, consequently, the mass-balance calculations cannot be made. 

However, the relatively large decrease in concentrations of 

K+ and NH4+ (table 9) suggest that NHt and K+ may also 

be involved in cation exchange at the 200-ft (61-m) well. 

MOVEMENT OF POLLUTANT-INDICATOR CONSTITUENTS 

THROUGH THE AQUIFER DURING RECHARGE 

Nitrogen, phosphorus, and organic constituents of 

water are often used as pollution indicators; that is, these 

constituents are present in chemical and microbiological 

reactions that degrade water quality. In addition, nitrate 

has been linked to methemoglobinemia in infants (Walton, 1951 ). 

Tertiary treatment at Bay Park removes 98 percent of the 

phosphorus from secondary sewage (Vecchioliandothers, 
Constituents 0.60 

Diffe~ncr I Ptt=~se difference 

ea+2 ••••••••••.•••. +0.66 

Mg+2 ............... + .58 

Na+ ................ + .11 

K+ ................. - .11 

NH4+ .............. - .83 

H+ (see footnote 1) ... + .91 

Gain or loss2 ...... + 1.32 

+ 68 

+ 83 

+ 4 

- 69 

-110 

+150 

TABLE 7.-Differences between observed and calculated concentrations of calcium, 

magnesium, sodium, potassium, ammonium, and hydrogen ions in water 

from the 20-foot (6.1-meter) observation well, in milliequivalents per liter 

\'olume o[ water injected, in millions o[ gallons 

0.70 0.74 13 2.2 

Qiff= I Pttc~- difference 

Diflerentt I Pe~bg< difference Diffcr~cr I """"""'" difference 

Diffe~cr I Ptt=bge 

difference 

+0.24 

+ .20 

- .19 

- .16 

-1.00 

+ 1.15 

+ .24 

+ 25 

+ 31 

- 6 

76 

92 

+144 

+0.12 

+ .16 

- .30 

- .17 

- .95 

+ 1.12 

- .02 

+ 13 

+ 25 

- 9 

-77 

- 82 

+130 

-0.20 

- .15 

+ .42 

- .05 

- .29 

+ .57 

+ .30 

- 29 

- 30 

+ 12 

- 18 

- 18 

+ 48 

-0.21 

- .03 

- .22 

- .03 

- .42 

+ .58 

- .33 

- 30 

8 

7 

- 10 

- 28 

+ 49 

1 H +gained by solution assumed equal to HC03-lost from solution. 

2 Plus sign indicates that cations have been added to solution; minus sign 

indicates that cations have been removed. 

9.1 

Diffe=cr I Pe<e~<age difference 

-0.10 

- .02 

+ .11 

+ .03 

- .07 

+ .34 

+ .29 

- 11 

- 4 

+ 3 

+ 9 

5 

+ 49 

22 

Diffe~ncr I Pe=bge 

diHerence 

-0.25 

- .03 

- .05 

+ .02 

0 

+ .16 

- .15 

- 33 

7 

2 

+ 7 

0 

+ 21 

'=' :; 

:.> 

~ 

~ 

:;; 

r; 

> t""' 

~ tTl 

(') 

:I: 

:.> 

~ 

() 

tTl 

tTl 

:X 

'"d 

tTl 

~ 

i: 

tTl 

z 

~ 

!;J1 

~ 

> ""'!'! 

'"d 

> 

~ 

r 

t""' 

0 

z 

() 

-'J) 

~ z 

5:' 

z 

tTl 

~ 

""'!'! 

0 

~ 

~ 
1.6 

0 

z I <( .2 

:E:::;-

:::>- 1.2 -a: Uw ...Jt- <(<( 

u~ 

0 

z 0 

<( w 

:E 

:E 

:::> 3 

Ci5 u 0.8 

w ~a: 

(!)U. 

<(0 

:E z 

a: 0 

0 ~ u. u 

(/) <( 0.4 

w a: 

u. :::> ...J w <( :I: 

> .... :::; 

J5/ 

GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS 

1.0 '2o' 50 JOO· 

EXPLANATION 

A Mg+2 

e (V,)cl-

• ca+2 

2 5 10 20 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

50 

FIGURE 9.-Changes in r; values for calcium and magnesium as a function of the fraction of reclaimed water (V, h:1· at the 100-foot 

(30-meter) observation well during recharge. 

:E 

RECLAIMED WATER RECHARGED, IN MILLIONS. OF LITERS 

5 

:::> 1.2 

z 

oz 

:Eo 

:E~ EXPLANATION 

<(U !_ 

.. <( ~ • (V,)cl·- :E,fE~ ANa+ :::> - (j)Wa: 

cn::r:w 0.8 • K+ <( ........ 

t-o~ .j. NH/ 

oz 

·9 HC03 0..<( - 0 :EWW 

2~~ oz<( oo...J 

cnmtd 0.4 

a:a:a: 0<( u. u.~ 0 a:l 

ffio 

:::>Z 

;i_<( 

> 

:::;- 0. 

1 2 5 10 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

50 

FIGURE 10.-Changes in V, values for sodium, potassium, ammonium, and bicarbonate as a function of the fraction of reclaimed water 

(V, )e~- at the 100-foot (30-meter) observation well during recharge. 

Dl5 
TABLE B.-Differences between observed and calculated concentrations of calcium, magnesium, sodium, 

potassium, ammonium, and hydrogen ions in water from the 

100-foot (30-meter) observation well 

Volume of water injected, in millionso! gall<ms 

Constituents 3.7 4.3 5.3 6.3 !Lj 

Difference 

I·~=~"' Dill•=« I P=m~ge Difference I-. ..... Diff=re I Pttttn~ge Differentt I Pe>ttn~!!" difference difference difference difference difference 

ea+2 ............... +0.03 + 24 +0.03 + 13 +0.01 + 3 -0.17 - 45 -0.38 -64 

Mg+2 ............... + .02 + 29 + .13 + .63 + .11 + 40 + .13 + 39 - .08 - 19 

Na+ ................ - .11 - 29 + .07 + 8 - .05 - 3 - .10 - 6 - .60 - 24 

K+ ................. - .02 - 67 - .03 - 46 - .10 -100 - .12 - 86 - .13 - 58 

Nn1+ .............. - .12 -171 - .31 -138 - .59 -i30 - .57 -101 - .59 - 62 

H+ (see footnote 1) ... + .1 0 + 67 + .37 +140 + .40 +174 + .48 +178 + .69 +184 

Gain or 1oss2 ...... - .10 .... + .26 .... - .22 . ... - .35 -1.09 

Volume of water injected, in million of gallons-Continued 

Constituents 15 19 26 35 42 

DU!erenre I ~'fire•~ .. Difference 

difference ll'ff=~..- difference Difle~ntt I Percentage difference 

Diff=re I P=~ge difference DU!== I -----

ea+2 ............ -0.23 - 28 -0.33 - 43 -0.23 - 28 

Mg+2 ............ - .04 - 8 - .03 - 6 - .01 - 2 

Na+ ............. - .27 - 8 - .27 - 8 - .18 - 5 

K+ .............. - .11 - 43 - .04 - 15 - .06 - 8 

NH4+ ........... - .63 - 48 - .41 - 29 - .20 - 13 

H+ (see footnote 1) + .79 +160 + .74 +144 + .63 +110 

Gain or loss2 ..... - .49 .... - .34 ...... - .05 . ... 

1 H +gained by solution assumed equal to HC03- lost from solution 

2 Plus sign indicates that cations have been added to solution; minus sign 

indicates that cations have been removed. 

-0.40 - 47 -0.47 

- .26 - 42 - .10 

-1.04 - 22 + .27 

- .08 - 25 + .30 

- .06 - 4 - .06 

+ .44 + 73 + .52 

-1.40 . ... + .46 

Difference 

-0.21 

- .04 

- .14 

- .14 

- .63 

+ .71 

- .45 

Percentage 

difference 

- 43 

- 16 

+ 7 

+ 65 

- 4 

+ 93 

10 I P=en~ge difference 

- 28 

- 9 

- 5 

- 70 

- 57 

+163 

0 

;: 

;.:r.. 

~ ::;:; 

5 

F 

~ Ci 

:I: 

;.:r.. 

~ 

'"' tTl 

tTl 

>:: 

"'0 

tTl 

~ 

~ tTl 

z 

~ 

$'1 

t::d 

;.:r.. 

><: 

"'0 

> 

~ 

?! 

t""' 

0 

z 

'"' c;; 

~ z 

~ 

z 

tTl 

:E 

><: 

0 

~ 

:r:: 
5 

GEOCHEMICAL EFFECTS OF RECHARGING THE MAGOTHY AQUIFER 

RECLAIMED WATER RECHARGED, IN MLLLIONS OF LITERS' 

10 

EXPLANATION . 

._ Mg+2 

• (V,)cr-

• ca+2 

2-6 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE I I.-Changes in· r'[ values for calcium and magnesium as a function of the fraction of reclaimed water(r'[ h:r- at the 200-

foot (61-meter) observation well during recharge. 

~ 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS 

? 1() 20 100 

2 1.2 

z 

O'Z 

:::!":0 

::.:!:~ <(U !_ EXPLANATION .. <( u 

~a:--::: LL~ • (14kr- :::> - -:W ._ N~+ ~: J: ffi j0.8 <(1-1- • K+ 1-c<C • NH/ .. oz~ C..<( • .. c o HC03- ::!:WW 

:::>1-::.:!: • 

-<C- • cz<C 

Ood 

en m w 0.4 

a: ~.a: 

OuLL LLaiO 

ffic 

:::>Z 

<t<C 

> -

$" 0 

1 I : 2 5 10 20 

RECLAIMED WATER RECHARGED, IN MILLIONS OF': GALLONS 

FIGURE 12.-Changes in r'[ values for sodium, potassium, ammonium, and bicarbonate as a function of the fraction of reclaimed water 

(r'[ )CI- at the 200-foot (61-meter) observation well during recharge. 

017 
Constituents 

TABLE 9.-Differences between observed and calculated concentrations of calcium, magnesium, sodium, 

potassium, ammonium; and hydrogen ions in water from the 

200-foot (61-meter) observation well 

Volume of water injected, in m_illion of gallons 

13 16 20 22 25 27 

---

Difference Diff~-re] I·=·- Diff= ll'firenrng< Diff<re~ l""'"""' Diff~re 1 P=n,.g< Percentage Diff~re I Pnren,.g< 

difference difference difference difference difference difference 

<::a+ 2 ............... 0 0 -0.05 - 22 -0.02 - 6 -0.03 - 9 -0.06 

Mg+2 ............... -.67 -151 + .07 + 40 + .13 + 55 + .12 + 48 + .12 

Na+ ................ -.13 - 27 - .17 - 21 + .01 + 1 + .04 + 3 - .09 

K+ ................. -.04 -100 - .07 -112 - .07 - 82 - .06 - 67 - .08 

NH4+ .............. -.19 -181 - .33 -169 - .36 -106 - .36 - 92 - .44 

H+ (see footnote 1) ... +.14 +140 + .15 +143 + .31 +177 + .33 +178 + .41 

Gain or loss2 ........ - .89 ... . - .40 ... . 0 . ... + .04 . ... - .14 

Volume of water injected, in millions of gallons-Continued 

Constituents 29 32 36 

~' Diff~·" I Percentage Di·~, I Pttren- n•rere~ I Pe=rnge difference difference difference 

----------

Ca+2 .............. -0.07 - 17 -0.06 - 11 -0.11 

Mg+2 .............. + .04 + 11 + .08 + 18 + .13 

Na+ ............... - .04 - 2 + .36 + 18 + .46 

K+ ................ - .06 - 50 - .07 - 52 - .06 

NH4+ ............. - .38 - 75 - .43 - 70 - .42 

H + (see footnote 1) . . + .40 +182 + .48 +200 + .45 

Gain or loss2 ....... - .11 ... . + .36 .... + .45 

1 H+ gained by solution assumed equal to HC03- lost from solution, but not 

necessarily true in this case (see text). 

2 Plus sign indicates that cations have been added to solution; minus sign 

indicates that cations have been removed. 

- 20 

+ 25 

+ 21 

- 38 

- 60 

+164 

. ... 

38 

Diff~~ I ·~ .. .., difference 

-0.21 - 35 

+ .19 + 35 

+ .47 + 21 

- .05 - 30 

- .41 - 55 

+ .55 +200 

+ .54 . ... 

- 16 -0.01 - 2 

+ 43 + .16 + 52 

- 6 + .01 + 1 

- 73 - .06 - 50 

- 94 - .36 - 67 

+200 + .40 +174 

.... + .14 

42 

Diff<=re I PB='""' 

difference 

----------

-0.06 - 8 

+ .19 + 38 

- .03 - 1 

- .07 - 40 

- .38 - 46 

+ .58 +200 

+.23 

8 

00 

~ 

~ :;; 

c=; 

> t'"" 

~ C) 

::c 

~ 

:;d 

~ 

tTJ 

tTJ 

., 

~ 

tTJ 

:;d 

~ tTJ 

z 

~ 

sn 

1;1::1 

~ 

><: 

., 

~ 

:;d 

r: 

t'"" 

0 

z 

~ 

(;; 

~ z 

~ 

z 

tTJ 

~ 

><: 

0 

:;d 

~ 
ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK Dl9 

1975) but an average concentration of 0.17 mg/1 phosphorus (as P04) remains. Concentrations of MBAS (methylene 

blue active substance) and COD (chemical oxygen 

demand) are also substantially decreased by tertiary 

treatment-MBAS by 98 percent and COD by 90 percent 

(Vecchioli and others, 1975)-which leaves average concentrations of 0.07 mg/1 and 9 mg/1, respectively. Denitrification is not included in tertiary treatment at Bay Park. 

Total N (total nitrogen) concentration of the reclaimed 

water aYerages 24 mg/1 (as N). Of this, 23 mg/1 (as N) is in 

NH4+ form, 0.59 mg/1 (as N) is in N03- (nitrate) form, and 

0.01 mg/1 (as N) is in N02- (nitrite) form. 

As reclaimed water reaches the 20-ft (6.1-m) well, 

concentrations of total Nand MBAS increase (fig. 13). The 

MBAS curve reaches reclaimed-water levels at nearly the 

same time that (~)cr reaches 1, which indicates littl~ 

MBAS retention by the formation. The total N curve 

reaches reclaimed-water concentration after(~ )cr reaches 

1, which indicates some retention. Because most of the 

total N is composed of NH/, the observed retention is 

explained by cation exchange, as described previously. 

Insufficient data are available to show changes in COD 

during recharge. The P04

- 3 curve indicates that at the 20-

ft ( 6.1-m) well the concentration ofthis constituent is only 

RECLAIMED WATERL RECHARGED, IN MILLIONS OF'·LITERS 

z 

c 

w 

~ 

·3 ~~0.8 u. u 

~g. 

~~~ 6'~ 0.4 

~ LL 

w a: 

~ z-~ 0 -~:J _u_z a: 

~(/)~ (!)<((/) 

~:z·~ t-0<( 

zi=a: 

...J ~ ~ 10 

<(•1-•...J 

b ~ 1-

2 --5 10 -26 50\ 100 

AVERAGE INPUT CONCENTRATION=24 mg/1 

AVERAGE INPUT CONCENTRATION=0.07 mg/1 

______ i_~~-~---------~--?~ 

0 

00 

AVERAGE INPUT CONCENTRATION=9 mg/1 ~ fv _________________ AVERAGE INPUT CONCENTRATION~0.17 mg/1 -.. _____ _ 

1 2 5 10 20 

RECLAIMED WATER RECHARGED. IN MILLIONS OF GALLONS 

soFIGURE 13.-Changes in MBAS, total phosphate, total nitrogen, and COD concentrations as a function of the fraction of reclaimed water 

(fl )cT at the 20-foot (6.1-meter) observation well during recharge. 
D20 ARTIFICIAL-RECHARGE EXPERIMENTS, BAY PARK, LONG ISLAND, NEW YORK 

RECLAIMED WATER RECHARGED, IN MILLIONS OF LITERS .. T -5 1lJ """""2(] 50 100 

~ ·o· 6 .,o.a wZ ·~·:;; o--

i=::Sa: U·U W 

~~ ~ LL. ~ i0.4 

z.z 

wo 

. (!) i=' CJ) 

0 <C::Z. ~ a: O:a:-<( w !::: 1- ~ a: 1-

zr5zS2 ::::i 

...~ u.~ ...~ a: <(z ::! w 1-o ~ a.. 

~u 

w w CJ) CJ) z~~~~~ a: 

w 0.1 ~uzz ~<( !::: >-<(~~~~ ..J 

:I:wCJ)Z-::J a: tu::::~mo~...~ w 

~ffi~U~~ a.. 

CJ) a: ..J "~ 

() r5 ~<( w 1- -(!)<(0: ::::i 

wxw..J ~>-~~ a: 5oo:::! w 

a.. ~ 

~ • zl~ 

~ot ..J<(Z- <( :I: w -~ ,<( 1-a..uza: QCJ)ZQS2 

~~8~~ a.. f!:~ 1 2 5 10 20 50 

RECLAIMED WATER RECHARGED, IN MILLIONS OF GALLONS 

FIGURE 14.-Changes in MBAS, total phosphate, total nitrogen, and COD concentrations as a function of the fraction of reclaimed water 

(Tj hr at the 100- and 200-foot (30- and 61-meter) observation wells during recharge. 

slightly greater than the 0.01- to 0.02-mg/1 concentration 

in native water but is significantly below the 0.17 mg/1 

average for reclaimed water. 

Changes in the concentrations of total N, MBAS, COD, 

and total P04-3 at the 100-ft (30-m) and 200-ft (61-m) 

wells during recharge are plotted in figure 14. Total N 

behaves as described at the 20-ft (6.1-m) well. MBAS and 

COD do not reach reclaimed-water levels by the end of the 

test, which suggests some retention by the aquifer. Total 

P04 -.3 remains approximately at native-water levels. 

Evidently, some pollution-indicator constituents are 

selectively removed in the Magothy aquifer during 

recharge. Total N, mainly as NH/, is removed by cation 

exchange, as described earlier. P04

-3 is presumably 

removed by precipitation with ca+2, Al+3, or Fe+3, all of 

:which are very insoluble salts at prevailing pH values 

(Leckie and Stumm, 1970), or by adsorption on clay in the 

aquifer. Decreases in concentrations of MBAS and COD 

can also probably be attributed to adsorption. 

SUMMARY 

Determination of the kind and extent of chemical 

reactions between reclaimed water and native water and 

aquifer minerals was one phase of the experimental 

recharge studies at Bay Park. 

Secondary-treated sewage was diverted from the Bay 

Park sewage-treatment plant to a pilot tertiary-treatment 

plant, where physical and chemical treatment produced 

an effluent that met virtually all standards for drinking 

water, as established by the U.S. Public Health Service 

(1962). 
GEOCHEMICAL EFFEGrS OF RECHARGING THE MAGOTHY AQUIFER D21 

Tertiary-treated effluent was pumped 0.5 mi (0.8 km) to 

the recharge facility, which included an 18-in (46-cm)-

diameter recharge well screened at a depth of 418 to 480ft 

(127 to 146m), and 18 observation wells ranging from several inches to 200 ft (61 m) from the recharge well and 

screened at different depths above, below, and in the 

recharge zone. 

Thirteen recharge experiments with reclaimed water 

and six with city water were completed between 1968 and 

1973. Most of the data reported were collected during the 

last and longest test, in which reclaimed water was injected 

on 84.5 days of a 199-day period between October24, 1972, 

and May 11, 1973, but additional data from other tests are 

also included. Most of the samples were taken from three 

wells located 20, 100, and 200 ft (6.1, 30, and 61 m), 

respectively, from the recharge well. Test results are summarized as follows: 

1. Samples taken from three wells screened in the 

recharge zone 20, 100, and 200ft (6.1, 30, and 61 m) from 

the recharge well indicated that chemical reactions were 

altering the reclaimed water passing through the aquifer. 

2. The observed increase in iron concentration from less 

than 0.5 mg/1 to 3 mg/1 in the reclaimed-water front 

indicates interaction between a constituent of the 

reclaimed water and the pyrite and marcasite (FeS:J in the 

aquifer. Pyrite and marcasite are the only sources of iron 

large enough to provide the amount taken into solution. 

Iron was taken into solution near the 20-ft (6.1-m) well by 

reaction of FeS2 with dissolved oxygen in the reclaimed 

water, but, as reclaimed water becomes devoid of oxygen 

beyond the 20-ft (6.1-m) well, the continued pickup of 

iron is not quantitatively understood. 

3. There seems to be an exchange between NH/ and K+ 

in the water and H+ on the clays. Concentrations of Ca +2 

and Mg+2 are greater than had been predicted from a 

simplified aquifer flow model. 

4. Movement of pollutant-indicator constituents 

(MBAS, COD, and P04- 3) was monitored. P0 4

- 3 was 

retained by the aquifer. MBAS and COD were partly 

. retained at distances of 100 and 200ft (30 and 61 m) from 

the recharge well. 

REFERENCES CITED 

Cohen, Philip, and Durfor, C. N., 1966, Design and construction of a 

unique injection well on Long Island, N.Y., in Geological Survey 

research 1966: U.S. Geol. Survey Prof. Paper 550-D, p. D253-D257. 

--- 1967, Artificial-recharge experiments utilizing renovated 

sewage-plant e££luent-a feasibility study at Bay Park, New York, 

U.S.A.: Intemat. Assoc. Sci. Hydrology Pub. 72, p. 194-199. 

Cohen, Philip, Franke, 0. L., and Foxworthy, B. L., 1968, An atlas of 

Long Island's water resources: New York State Water Resources 

Comm. Bull. 62, 117 p. 

Ehrlich, G. G., Ehlke, T. A., and Vecchioli, john, 1972, Microbiological 1 

aspects of ground-water recharge-injection of purified chlorinated 

sewage effluent in Geological Survey research 1972: U.S. Geol. 

Survey Prof. Paper 800-B, p. B241-B245. 

___ 1973, Microbiological aspects of ground-water rechargeinjection of purified unchlorinated sewage e££Iuent at Bay Park, 

Long Island, New York: U.S. Geol. Survey Jour. Research, v. I, no. 

3, p. 341-344. 

Faust, S. D., and Vecchioli, John, 1974, Chemical problems associated 

with the injection of highly treated sewage into a deep-sand aquifer: 

Am. Water Works Assoc. Jour., v. 66, no. 6, p. 371-377. 

Franke, 0. L., and Cohen, Philip, 1972, Regional rates of ground-water 

movement on Long Island, New York in Geological Survey research 

1972: U.S. Geol. Survey Prof. Paper 800-C, p. C271-C277. 

Franke, 0. L., and McClymonds, N. E., 1972, Summary ofthe hydrologic 

situation on Long Island, New York, as a guide to water-management alternatives: U.S. Geol. Survey Prof. Paper 627-F, 59 p. 

Koch, Ellis, Giaimo, A. A., and Sulam, D. J ., 1973, Design and operation 

of the artificial-recharge plant at Bay Park, New York: U.S. Geol. 

Survey Prof. Paper 751-B, p. Bl-B14. 

Ku, H. F. H., Vecchioli, John, and Ragone, S. E., 1975, Changes in 

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