POTENTIAL FOR CHEMICAL TRANSPORT BENEATH A 

STORM-RUNOFF RECHARGE (RETENTION) BASIN FOR AN 

INDUSTRIAL CATCHMENT IN FRESNO, CALIFORNIA

By Roy A. Schroeder

U.S. Geological Survey

Water-Resources Investigations Report 93-4140

Prepared in cooperation with the

FRESNO METROPOLITAN FLOOD CONTROL DISTRICT

rH 

I

Sacramento, California 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For sale by the

U.S. Geological Survey

Earth Science Information Center

Open-File Reports Section

Box 25286, MS 517

Denver Federal Center

Denver, CO 80225

For additional information write to: 

District Chief 

U.S. Geological Survey 

Federal Building, Room W-2233 

2800 Cottage Way 

Sacramento, CA 95825
CONTENTS

Abstract 1 

Introduction 1

Urban hydrology studies 1

Purpose and scope 2

Acknowledgments 2

Description of the study area 2

Geology, hydrology, and ground-water quality near the study area 4 

Field and analytical methods 6

Site selection, well installation, and soil coring 6

Sampling of sediment from the recharge basin 9

Chemical analysis of water, soil, and sediment 10 

Quality of recharge-basin water and ground water 13

Isotopic evidence for recharge 13

Major ions and trace elements 16

Organic priority pollutants and pesticides 17 

Chemical concentrations in sediment and soil 17

Inorganic elements 17

Organic chemicals 24

Assessment of anthropogenic inputs 25 

Laboratory elutriation experiments 26 

Transport and loading of contaminated sediment 31

Comparison of basin-sediment inventories and storm-runoff loads 32

Lead-210 constraints on origin and loading of contaminated sediment 34 

Summary and conclusions 35 

References cited 36

FIGURES

1. Map showing location of study area 3

2. Diagram showing recharge basin and location of test holes/monitor wells and sediment-sampling sites

in the recharge basin 5 

3,4. Graphs showing:

3. Relation between hydrogen and oxygen stable-isotope ratios in recharge-basin water and 

nearby ground water 16

4. Enrichment ratios for selected constituents in subbottom sediment at site 5 in the 

recharge basin 24

TABLES

1. Historical ground-water-quality data from well 14S/20E-24K1 near the study site 6

2. Particle-size distribution in soil cores from two test holes adjacent to the recharge basin 7

3. Geologic log for test hole 1 adjacent to the recharge basin 8

4. Sand, silt, and clay content of soil cores from two test holes adjacent to the recharge basin 9

5. Particle-size distribution in sediment beneath the recharge basin 11

6. Concentrations of dissolved inorganic and total-recoverable organic constituents in water from 

the recharge basin and from two nearby monitor wells 14

7. Concentrations of elements and radioisotopes in soil cores from test hole 1 adjacent to the 

recharge basin 18

Contents I
8. Concentrations of chemical constituents and radioisotopes in surface (0-1 cm) sediment from six 

sites in the recharge basin 19

9. Concentrations of chemical constituents and radioisotopes in sediment and substrata at site 5 in the 

recharge basin 21

10. Concentrations of extractable priority pollutants, organochlorine compounds, and organophosphorus 

insecticides in sediment from depths of 0-1 and 8-16 cm at site 5 in the recharge basin 23

11. Surface-enrichment ratios for selected elements and radioisotopes in sediment at site 5 in the recharge 

basin 26

12. Chemical concentrations in water from the recharge basin equilibrated (mixed for 0, 1,2, and 4 days) 

with surface (0-1 centimeter) sediment from near site 5 in the recharge basin 27

13. Chemical concentrations in water from the recharge basin equilibrated (mixed for 4 days) with 

aquifer soil from 10.9-11.3 meters in test hole 1, in deionized water equilibrated 

(mixed for 4 days) with surface (0-1 centimeter) sediment from near site 5 in the recharge 

basin, and in a deionized-water blank 28

14. Concentrations of elements in recharge-basin sediment and in aquifer soil used for the laboratory 

elutriation tests 29

15. Concentrations of chemical constituents in recharge-basin sediment and aquifer soil after the laboratory 

elutriation tests 31

16. Percent extractable for selected elements in recharge-basin sediment and aquifer soil by digestion with 

hydrogen peroxide plus mild acid 31

17. Annual loads to the industrial recharge basin determined from runoff monitoring and sediment 

inventories 32

CONVERSION FACTORS, VERTICAL DATUM, ABBREVIATIONS, AND WATER-QUALITY 

INFORMATION

Conversion Factors

Multiply By To obtain

centimeter (cm)

cubic centimeter (cm3)

centimeter per day (cm/d)

square centimeter (cm2)

gram (g)

gram per cubic centimeter (g/cm3)

hectare (ha)

kilogram (kg)

kilogram per year (kg/yr)

kilometer (km)

square kilometer (km2)

meter (m)

meter per kilometer (m/km)

meter per year (m/yr)

millimeter (mm)

square millimeter (mm2)

0.3937

0.06102

0.3937

0.155

0.03527

0.57808

2.471

2.205

2.205

0.6214

0.3861

3.281

5.2800

3.281

0.03937

0.00155

inch

cubic inch

inch per day

square inch

ounce (avoirdupois)

ounce per cubic inch

acre

pound (avoirdupois)

pound per year

mile

square mile

foot

foot per mile

foot per year

inch

square inch

Temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by the 

following equation:

°F=1.8(°C)+32.

IV Conversion Factors, Vertical Datum, Abbreviations, and Water-Quality Information
Vertical Datum

Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 a 

geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called Sea Level Datum of 1929.

Abbreviations

°C/min degrees Celsius per minute

dpm disintegrations per minute (radioisotope activity)

GC-FID gas chromatography with flame-ionization detection

GC-MS gas chromatography with mass spectrometric identification

keV thousand electron volt

M molar

meq/L milliequivalents per liter

mBq millibecquerels

MWL global meteoric water line

NURP Nationwide Urban Runoff Program (established in 1978 by U.S. Environmental Protection Agency)

permil parts per thousand

pCi/L picocuries per liter

TU tritium unit (1 tritium atom per 1018 hydrogen-1 atoms [approximately equal to 3.2 picocuries per

	liter]) 

urn micrometer (3.937 xlO'5 in.)

Water-Quality Information

Electrical conductivity is expressed as specific conductance, in microsiemens per centimeter at 25°C 

(uS/cm).

Trace-element and pesticide concentrations in water samples are given in micrograms per liter (ug/L). 

One thousand micrograms per liter is equivalent to 1 milligram per liter (mg/L). Micrograms per liter is 

approximately equivalent to "parts per billion" (ppb). Trace-element concentrations in sediment are given in 

micrograms per gram (ug/g). Micrograms per gram is equivalent to "parts per million" (ppm). Pesticide 

concentrations in sediment are given in micrograms per kilogram (ug/kg). One thousand micrograms per 

kilogram is equivalent to 1 microgram per gram (ug/g). Micrograms per kilogram is equivalent to "parts per 

billion" (ppb).

Conversion Factors, Vertical Datum, Abbreviations, and Water-Quality Information V
Well-Numbering System

Wells are identified and numbered according to their location in the rectangular system for the subdivision 

of public lands. Identification consists of the township number, north or south; the range number, east or west; 

and the section number. Each section is divided into sixteen 40-acre tracts lettered consecutively (except I and 

O), beginning with "A" in the northeast corner of the section and progressing in a sinusoidal manner to "R" in 

the southeast corner. Within the 40-acre tract, wells are sequentially numbered in the order they are inventoried. 

The final letter refers to the base line and meridian. In California, there are three base lines and meridians; 

Humboldt (H), Mount Diablo (M), and San Bernardino (S). All wells in the study area are referenced to the 

Mount Diablo base line and meridian (M) Well numbers consist of 15 characters and follow the format 

014S020E24L001M. In this report, well numbers are abbreviated and written 14S/20E-24L1. Wells in the same 

township and range are referred to only by their section designation, 24L1. The following diagram shows how 

the number for well 14S/20E-24L1 is derived.

R20E

RANGE

R19E R20E R2>i

i-^co$2co dIHSNMOl y

/ 

/ 

/ 

t

lil'IStetlil

/ 

/

/ 

/ 

/ 

/

T 

14 

S

6

7

18

19

30

31

5

8

17

20

29

32

4

9

16

21

28

33

3

10

15

22

27

34

2

11

14

23

26

35

1

12

13-'

111 N 

\

36

-24L1

VI Well-Numbering System
POTENTIAL FOR CHEMICAL TRANSPORT BENEATH A 

STORM-RUNOFF RECHARGE (RETENTION) BASIN FOR AN 

INDUSTRIAL CATCHMENT IN FRESNO, CALIFORNIA

By Roy A, Schroeder

Abstract

A wide variety of chemicals from urban 

runoff were found at elevated concentrations in 

sediment that accumulated in a storm-runoff 

recharge basin in an industrial part of the city of 

Fresno. The chemicals include as many as 

20 inorganic elements and about the same 

number of organic compounds, primarily organochlorine pesticides and polycyclic aromatic 

hydrocarbons. Most of these contaminants were 

found to be sorbed to the upper 4 centimeters of 

sediment, which also is the maximum depth to 

which atmospheric lead-210 penetrated. None of 

the contaminants were detected above backbackground concentrations in the sediment at 

depths greater than 16 centimeters. In shallow 

sediment, zinc is the inorganic element that was 

most enriched; its concentration was 38 times 

higher in surface sediment (0-1 centimeter) than 

in deeper strata (below 16 centimeters). 

Similarly, organic carbon enrichment was nearly 

1,000 times higher in the surface sediment.

Although batch-elutriation experiments 

demonstrated the potential for leaching of 

contaminants attached to sediments, a sharp 

decrease in concentrations with increasing 

sediment depth, and the extremely low level of 

contaminants in two monitor wells adjacent to 

the basin, confirmed the absence of contaminant 

transport to the water table. Continued long-term 

protection for ground water is afforded by an 

approximately 8-meter-thick unsaturated zone 

beneath the basin. Zinc, on the basis of its 

hundredfold-higher concentration in water from 

the recharge basin than in ground water, is 

indicated as the most sensitive surrogate for 

monitoring possible ground-water degradation by 

inorganic cations.

Results from this study were compared with 

previously published results from comprehensive 

monitoring of urban runoff to the basin during 

1981-83. The comparison revealed remarkably 

similar patterns of chemical contamination, although estimates of sediment quantity delivered 

to the basin differed by a factor of 1.8. The 

higher estimate of sediment quantity delivered 

obtained by this study likely reflects imprecision 

in the determination of sediment depths and an 

unusual open texture of the thin veneer that 

accumulated during the 4-year period the basin 

had been in existence. A technique using lead210 is illustrated that could, with adequate data 

collection, provide estimates of sediment and 

contaminant quantity delivered to recharge basins 

without the numerous analyses and samplecollection effort necessary to monitor runoff.

INTRODUCTION

URBAN HYDROLOGY STUDIES

In response to concerns that urban runoff may be 

a significant nonpoint source of contaminants, the 

U.S. Environmental Protection Agency (EPA) 

established the Nationwide Urban Runoff Program 

(NURP) in 1978 to characterize the quality of urban 

runoff and to determine the extent to which urban 

runoff might contribute to impairment of water 

quality in receiving water bodies (U.S. Environmental 

Protection Agency, 1983). Studies were done at 28 

urban areas throughout the Nation, and the U.S. 

Geological Survey (USGS) participated in 11 of the 

studies (Driver and others, 1985). At two study 

areas in Fresno, California (Oltmann and Shulters, 

1989), and Long Island, New York (Ku and 

Simmons, 1986) urban stormwater runoff is routed 

to constructed retention/recharge basins where it then 

percolates through the soil and recharges the aquifer.

Introduction 1
In the studies at Fresno and Long Island, it was 

concluded that properties of the soil beneath the 

basins are highly effective in retaining urban runoff 

contaminants, although the ability of the soil to 

continue to retain contaminants was said to be 

unknown (U.S. Environmental Protection Agency, 

1983).

Nightingale (1975; 1987a,b,c; 1989) showed that 

concentrations of several trace elements and synthetic 

organic compounds from urban runoff were elevated 

above background levels in near-surface sediments in 

recharge basins in residential and commercial parts of 

the city of Fresno, but that the concentrations 

decreased rapidly with increasing sediment depth and 

also generally were very low in interstitial water from 

the unsaturated zone and in ground water beneath the 

basins. The study reported here extends these previous 

investigations to a recharge basin in an industrial 

catchment where the Fresno NURP study found most 

contaminant concentrations to be several times higher 

than in runoff from residential and commercial 

catchments (Oltmann and Shulters, 1989). This study 

thereby completes the evaluation of these recharge 

basins in each of the major urban land-use categories 

(industrial, commercial, and residential). This 

investigation included analyses of numerous synthetic 

organic compounds, a broad suite of more than 40 

elements, and some stable and radiogenic isotopes. 

This study was done by the USGS in cooperation 

with the Fresno Metropolitan Flood Control District.

PURPOSE AND SCOPE

This report presents the results of a study during 

1986-87 whose purpose was to determine whether 

stormwater runoff to a recharge basin in an industrial 

part of the city of Fresno has caused, or has the 

potential to cause, degradation of the ground-water 

quality. The study included three approaches:

1. Comparison of chemical concentrations in 

water from the recharge basin to concentrations in water from an aquifer beneath the 

recharge basin,

2. Determination of chemical-concentration profiles in sediment beneath the recharge basin, 

and

3. Laboratory elutriation tests in which water 

was mixed with contaminated basin sediment 

or clean aquifer soil and reanalyzed.

This study builds on previous results of the 

Fresno NURP study for which contaminants in urban 

runoff were monitored during 1981-83. Results of the 

NURP study were published by Brown and Caldwell 

Consulting Engineers (1984), Fresno Metropolitan 

Flood Control District (1987), Nightingale (1987a,b,c; 

1989), Nightingale and others (1985), Oltmann and 

Shulters (1989), and Oltmann and others (1987).

ACKNOWLEDGMENTS

The author thanks Harry Nightingale of the U.S. 

Department of Agriculture in Fresno and Doug 

Harrison and Gerald Lakeman of the Fresno 

Metropolitan Flood Control District for helpful 

suggestions before and during the study. Removal of 

water from the recharge basin by the Fresno 

Metropolitan Flood Control District prior to sampling 

greatly facilitated the collection of sediment samples.

DESCRIPTION OF THE STUDY AREA

The city of Fresno is about 260 km southeast of 

San Francisco (about 180 km east of the Pacific 

coastline at Monterey Bay), in the San Joaquin Valley 

and between the San Joaquin River to the north and 

the Kings River to the south (fig. 1). Average annual 

rainfall in Fresno is about 25 cm, nearly all of which 

falls between October and April (Page and LeBlanc, 

1969). Topographic relief is low with an average 

gradient of only about 1.6 m/km. Because of the flat 

terrain and the lack of adequate water courses through 

the city, almost 100 stormwater retention/recharge 

basins (hereinafter referred to as "recharge basins") 

have been constructed to dispose of surface runoff 

and to recharge an aquifer that has been designated as 

a sole-source aquifer by the U.S. Environmental 

Protection Agency. The average size of the basins is 

4 to 6 ha, and the average size of the urban catchments served by the basins is about 2.6 km2 .

The industrial-catchment basin that was the 

subject of this study is in the southeast part of the 

Fresno metropolitan area (fig. 1). The area of the 

catchment is 113 ha, of which 34.2 percent is idle or 

vacant and 65.8 percent is used for industrial 

purposes. Impervious surface covers 52.5 percent of 

the catchment (Oltmann and Shulters, 1989). 

Industries present in the catchment include cotton 

mills, food processing, petroleum operations, chemical 

storage, carpet manufacturing, and light trucking 

(Brown and Caldwell Consulting Engineers, 1984).

2 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
INDUSTRIAL 

CATCHMENT

RECHARGE 

BASIN (Fig. 2)

Figure 1. Location of study area.

Introduction 3
Runoff is routed to a basin (approximately onehalf hectare) on the south side of the catchment. A 

detailed diagram of the basin and its immediate 

surroundings as they existed at the time of this study 

(1986) is shown in figure 2. Prior to this study, the 

basin was last dredged (scraped) in 1982, when it was 

deepened and rechannelized to its present form to 

facilitate sample collection for the NURP study (G.E. 

Lakeman, Fresno Metropolitan Flood Control District, 

oral commun., 1992). Although excavation of the 

basin exposed a highly permeable coarse sand, the 

very fine texture of muds that soon accumulate on the 

basin's floor may considerably reduce the effective 

area through which percolation takes place by 

restricting it to the sloping sides of the basin at highwater stages. Over a period of time, the structure 

increasingly functions as an evaporation (retention) 

pond as opposed to a recharge basin and must be 

scraped to again expose a more permeable bottom.

Vegetation on the rim of the basin is sparse and 

the water itself contains algae but no macrophytes. 

The area surrounding the basin is disked periodically 

to maintain a generally barren environment so as not 

to attract wildlife. The basin normally contains water 

to a depth of a meter or more, even during the dry 

summer months; however, it was pumped dry in July 

1986 to permit subbottom sampling on August 4, 

1986.

GEOLOGY, HYDROLOGY, AND GROUND-WATER 

QUALITY NEAR THE STUDY AREA

A general description of the geology, hydrology, 

and ground-water quality at the study area is inferred 

from Page and LeBlanc's (1969) summary for Fresno 

and its surrounding area. Their summary, in turn, was 

based on data and interpretations resulting from 

several regional studies in the Central Valley of 

California (Lippincott, 1902; Mendenhall and others, 

1916; Davis and Poland, 1957; Davis and others, 

1959, 1964; Olmsted and Davis, 1961; Meade, 1967; 

and Croft and Gordon, 1968).

The study area is in the Kings River high alluvial 

fan geomorphic unit. The water-bearing unconsolidated deposits of this unit (and of the adjacent units)

are underlain by a basement complex of consolidated 

rocks of pre-Teitiary age. Depth to bedrock at the 

study area is about 1,200 m. The unconsolidated finegrained continental deposits of Tertiary and Quaternary age, derived from weathering of crystalline rocks 

in the Sierra Nevada to the east, are overlain by 

coarser oxidized granitic alluvium of Quaternary age. 

Thickness of the alluvium is about 150 m at the study 

area, where it is capped by a veneer (a few meters 

thick, or less) of heavily reworked fine-grained soil.

Prior to development of the ground-water 

resources, the direction of ground-water movement in 

the Fresno area was toward the southwest; however, 

pumping has created a permanent cone of depression 

beneath the city of Fresno that now deflects groundwater movement toward the north in the vicinity of 

the study area (Mitten, 1984). A hydraulic gradient of 

2 m/km toward the west-northwest is inferred at the 

study site from water-level contours for 1963 and 

regional maps that show similar conditions prevailing 

in 1975 (Page, 1975). Although ground water is 

unconfined on a regional scale, local areas of 

confinement or partial confinement may exist beneath 

intercalated clay and silt lenses.

A trend toward higher dissolved-solids concentration, and dominance of sodium and chloride ions, 

with increasing depth probably exists throughout the 

Fresno area, particularly in the older, fine-grained 

continental deposits. The base of the freshwater 

(defined as water in which ionic concentration is less 

than 2,000 mg/L in NaCl equivalents) is estimated to 

be 400 m below sea level (about 500 m below land 

surface) at the study area. However, nearly all wells 

in the area penetrate only the younger alluvium, in 

which the alkaline earths (calcium or magnesium) and 

bicarbonate are the predominant ions. Ground water 

from a 65-m-deep (perforated to only 51 m) agricultural production well, 14S/20E-24K1, about 0.4 km 

east of the study area probably is representative of 

regional ground-water quality; data from a 1957 

analysis of water from this well are reproduced in 

table 1. Predominant ions are calcium, magnesium, 

and bicarbonate, and the dissolved-solids concentration of 226 mg/L is equivalent to a specific 

conductance of about 350 uS/cm (microsiemens per 

centimeter).

4 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
East Commerce Avenue

 Gate- -x x x x

M

M______ 71

"Stormdrain

Gate (6°-inch )

TEST HOLE 1 

(WELL14S/20E-24L1)

TEST HOLE 2 

(WELL14S/20E-24L2)

EXPLANATION 

Perimeter of flat bottom of basin 

Top of sloping walls of basin

4 0 Sediment-sampling site and number

50 METERS 

I_______I i I I

0 150 FEET

-X X X X X X X X XGate

 Gaging station 

(discontinued)

Chain

link

fence

-x x xEast Edgar A venue

Figure 2. Recharge basin and location of test holes/monitor wells and sediment-sampling sites in the 

recharge basin.

Introduction 5
Table 1 . Historical ground-water-quality data from 

well 14S/20E-24K1 near the study site

[Sample collected September 6, 1957, by the California 

Department of Public Health (Page and LeBlanc, 1969, 

tables 14 and 20). mg/L, milligram per liter; meq/L, 

milliequivalent per liter; , no data]

Concentration

Constituent

(mg/L) (meq/L)

Calcium (Ca)

Magnesium (Mg)

Sodium (Na)

Potassium (K)

Iron (Fe)

Bicarbonate (HCO3)

Sulfate (SO4)

Chloride (Cl)

Fluoride (F)

Nitrate (NO3 )

Dissolved solids

23

12

18

4

.08

140

7.2

14

.1

14

226

1.15

.99

.78

.10

~

2.29

.15

.39

.01

.23

pH=8.2 (standard units)

FIELD AND ANALYTICAL METHODS

SITE SELECTION, WELL INSTALLATION, AND SOIL 

CORING

Two test holes (fig. 2) were drilled: at latitude 

36°41'54"N, longitude 119°44'57"W; and at 

36°41'51"N, 119°44'56"W (about 100 m south of the 

first test hole). The holes were drilled with a 6-inchdiameter (15 cm) hollow-stem auger, and 2-inchdiameter (5 cm) PVC monitor wells, 14S/20E-24L1 

and 14S/20E-24L2, were installed in the holes.

As auger flights were pulled up and removed 

following insertion of the well casing in the hollow 

stem, the annulus between the walls of the test hole 

and the casing quickly was filled with a slurry of 

native material from the saturated zone. During this 

procedure the casing sank, exposing a much longer 

perforated interval (6 m) to the saturated zone than 

was intended (1-2 m). The wet, cohesionless sand 

(Durnford and others, 1991) below the water table 

rose several meters above the water table in the 

annulus. The remaining annulus above this sand was 

backfilled with a layer of bentonite pellets, then with 

drill cuttings from the unsaturated zone, and finally 

with a 1.5-m cement seal to land surface. Altitude of 

land surface is 86.5 m at well 14S/20E-24L1 (test 

hole 1) and 85.5 m at well 14S/20E-24L2 (test hole 

2). Both monitor wells are perforated (slotted) from

12 to 18 m below land surface. Because the casing 

sank during installation, the top of the perforated 

interval was only about 0.6 m above the water table 

at well 14S/20E-24L1 and was actually about 0.3 m 

below the water table at well 14S/20E-24L2 when 

samples for water-quality analysis were collected 

during summer and autumn 1986.

Both monitor wells are adjacent to the recharge 

basin (fig. 2) and, on the basis of regional groundwater-flow patterns discussed in the previous section, 

the first well installed (14S/120E-24L1) is believed to 

be downgradient of the basin. Irregular topography at 

this location precluded drilling the first test hole 

closer than about 50 m from the recharge basin. 

Flatter terrain to the south permitted drilling of the 

second test hole within a few meters of the edge of 

the recharge basin, thereby increasing the probability 

of intercepting any small ground-water mound should 

one extend only a short distance beyond the basin 

area. The second well also decreases the chance that 

a contaminant plume would be missed if the local 

hydraulic gradient were toward the southwest (the 

direction of the regional gradient prior to pumping in 

Fresno) for any reason, including pumping from any 

wells near the study area itself (see Mitten and Guay, 

1986, for a summary of municipal pumpage and 

location of wells). Although a monitor well upgradient of the basin would have provided information 

about the local hydraulic gradient and confirmation 

that water from the basin is reaching the water table 

and producing a ground-water mound, this study did 

not have sufficient resources to install a third well. 

Installation of lysimeters beneath the recharge basin 

itself, as in a previous study, would have been 

especially valuable but was precluded by concern that 

they would provide a pathway for enhanced transport 

of contaminants through the unsaturated zone.

Soil cores were recovered from selected depths 

during drilling of the test holes by lowering a 2-ft 

(0.6 m), split-spoon steel corer through the hollow 

drill stem. The depths selected for coring in test hole 

1 were based on field observations of change in 

texture as determined from drill cuttings brought to 

the surface by the auger and from the drill operator's 

perception of changes in drilling characteristics. 

Depths for coring in test hole 2 were chosen to 

confirm the presence of low-permeability zones found 

in test hole 1. Particle-size distribution in the core 

soils was determined using sieves for the sand-size 

fraction and hydrometers for the fine fraction using 

methods described by Guy (1969). The data are given 

in table 2.

6 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
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Field and Analytical Methods 7
Particle- size data were used in conjunction with racy of the logs relative to a fixed benchmark

field observations to compile the lithologic logs given probably is no better than 0.3 m. 

in table 3. Depths were recorded with a precision of

0.03 m during drilling; however, they were measured Although changes in color and texture commonly

relative to land surface that was highly irregular are gradual and subtle, three distinct zones of silty

because soil excavated to form the recharge basin had clay were found and correlated between the test holes:

been deposited near the test holes. Therefore, accu- at 7.2-7.3 m, 10.7-10.9 m, and 15.5-15.8 m in test

Table 3. Geologic log for test hole 1 adjacent to the recharge basin

[Rock-color terms are from Goddard and others, 1948. m, meter; mm, millimeter] _________ 

Depth (m) Thickness (m) _________ ____ Description _______

0.6 0.6 Fine sand, silt, and clay in about equal proportions, moderate-yellowish-brown (10 YR

5/4). Surface soil heavily reworked and mixed with soil excavated in construction of 

recharge pond.

2.5 1.9 Sand, fine to coarse, silty, moderate-yellowish-brown (10 YR 5/4) tending to darkyellowish-orange (10 YR 6/6). Numerous small concrete chips decreasing in abundance 

with depth, thin (1 mm) calcareous stringers and bands.

5.8 3.3 Sand, fine to coarse, pale-yellowish-brown (10 YR 6/2) with some moderate-yellowishbrown (10 YR 5/4) marbling. Biotite, quartz, and mica grains abundant. Measured 

10-percent silt and 90-percent sand. Becoming finer below 5.6 m.

6.2 .4 Silt, fine sand, pale-yellowish-brown (10 YR 6/2) with numerous small (1-3 mm) lightbrown (5 YR 5/6) blebs. Measured 70-percent silt.

6.4 .2 Sand, fine to medium, silt, pale-yellowish-brown (10 YR 6/2). Measured 15-percent silt. 

7.2 .8 Sand, fine, silty, moderate-yellowish-brown (10 YR 5/4). Measured 30-percent silt.

1 13 .1 Silt, clayey, moderate-yellowish-brown (10 YR 5/4) tending to dark-yellowish-brown

(10 YR 4/2). Measured 70-percent silt and 20-percent clay.

10.7 3.4 Fine sand, some silt, color fluctuating between moderate-yellowish-brown (10 YR 5/4)

and light-brown (5 YR 5/6) throughout interval. Measured 80-percent fine sand and 

10-percent silt.

H0.9 .2 Silt, clayey, pale-yellowish-brown (10 YR 6/2) to dark-yellowish-brown (10 YR 4/2).

Measured 60-percent silt and 20-percent clay.

13.0 2.1 Sand, fine to medium, with silt and clay, poorly sorted, light-brown (5 YR 5/6) blebs at

top of interval blending entirely into moderate-brown (5 YR 4/4) matrix below 1 1.6 m. 

Clay and silt decreasing and fine sand increasing slightly with depth. Measured 

15-percent clay and 20- to 30-percent silt. Bottom of interval in saturated zone.

15.5 2.5 Sand, fine to coarse, with silt and clay, (slightly coarser than interval above), changing

gradually from moderate-yellowish-brown (10 YR 5/4) at top of interval to light-brown 

(5 YR 5/6) at botton of interval.

45.9 .4 Sand, silty with greyish clay blebs, moderate-yellowish-brown (10 YR 5/4). Measured

35-percent silt and 15-percent clay.

18.3 2.4 Sand, fine to coarse, becoming coarser with increasing depth, moderate-yellowish-brown

(10 YR 5/4) tending to light-brown (5 YR 5/6). Biotite, quartz, and mica grains 

abundant (similar to 2.5-5.8 m interval). Measured 10-percent silt.

r, less-permeable zones visually identified during coring. 

8 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
hole 1; and at 6.4-6.5 m, 9.7-9.8 m, and 14.4-14.6 m 

in test hole 2 (table 4). Difference in the depth below 

land surface of these three zones matches closely the 

difference in land-surface altitude at the test holes. 

The water table was between the middle and deepest 

of these zones in each test hole.

SAMPLING OF SEDIMENT FROM THE RECHARGE 

BASIN

To facilitate sampling of accumulated sediment in 

the recharge basin, all water was pumped from the 

basin in mid-July 1986, and the exposed sediment 

was allowed to dry for about 3 weeks prior to 

sampling. As the fine-grained sediment covering the 

floor of the basin dried, shrinkage cracks formed thin 

polygonal plates. The plates were about 1 cm thick 

(although actual thickness is somewhat imprecise 

because the bottom surface of the plates was 

irregular) and represent the most recently deposited 

sediment that accumulated in the recharge basin.

Removal of the plates (the 0- to 1-cm depth 

samples) exposed an unusual geometric surface that 

bore a striking resemblance to a honeycomb, the individual cells of which were several millimeters across 

and deep. The sediment was strongly reduced, as 

indicated by its black color, except for a thin veneer 

of brown (oxidized) clay rimming the edge of each 

cell wall. It is suggested that the cells were formed by 

escape of gas bubbles as the mud was drying. Gas 

bubbles, accompanied by a small oil sheen, commonly were seen breaking the water's surface when 

the basin was flooded. This gas is presumed to be 

hydrogen sulfide, carbon dioxide, methane, and (or) 

nitrogen generated by microbial activity within the 

sediments. After the basin's water had been removed, 

the underlying sediment was exposed to air entering 

through cracks at the sediment surface, and oxidation 

produced the thin brown rind on the cells.

The 1-cm-thick surface-sediment plates were 

removed for analysis from six sites on the basin floor. 

The basin floor slopes gently downward from the

Table 4. Sand, silt and clay content of soil cores from two test holes adjacent to the recharge basin

[Contents, in weight-percent, calculated from data in table 2. m, meter]

T-V .1 Depth

interval

(m)

Coarse sand Medium sand Fine sand Silt Clay

1.2-1.8

3.1-3.7

4.9-5.5

5.8-6.2

6.2-6.4

6.4-6.7

6.7-7.2

!7.2-7.3

9.1-9.8

40.7-10.9

10.9-11.3

11.6-12.2

13.4-14.0

'IS.S-IS.S

16.5-17.1

'6.4-6.5

J9.7-9.8

10.1-10.4

10.4-10.7

44.4-14.6

15

26

48

1

15

17

1

0

1

1

4

7

11

8

24

2

2

9

5

5

Test Hole 1 (Monitor Well

20

43

30

1

39

11

7

1

7

4

13

22

19

18

40

Test Hole 2 (Monitor Well

5

5

21

16

11

14S/20E-24L1)

24

21

13

18

25

36

58

12

79

13

35

33

33

23

22

14S/20E-24L2)

22

28

35

21

12

29

8

7

72

16

28

30

67

10

63

28

23

25

35

11

62

43

23

37

59

6

2

2

8

5

8

4

20

3

19

20

15

12

16

3

9

22

12

21

13

'Finer, less-permeable zones visually identified during coring.

Field and Analytical Methods 9
northeast corner, where the storm runoff enters the 

basin, toward the south (fig. 2); therefore, a spatial 

gradation of increasing fines toward the south was 

anticipated. The particle-size data from the six sites 

that are presented in table 5 provide some evidence 

for such a trend, although the difference in percentage 

of fine fraction is small. Clay-plus-silt content ranges 

from 67 percent at sediment-sampling site 2 to 77 

percent at site 4; however, clay contents are about 10 

percent greater at sites 5 and 6 in comparison with the 

other four sites. In addition to the 0-1 cm (surfacesediment plate) samples, two successive thin layers, 

estimated to each be only about 1 mm thick, were 

scaped from the surface near site 5. Both were found 

to contain approximately equal proportions of clay 

and silt and virtually no sand (table 5). Accordingly, 

the small differences in the percentage of fine fraction 

between surface samples at the six sites could simply 

be due to varying proportions from the very thin layer 

of fine sediment at the surface (top few millimeters) 

and the coarser sediment immediately below the 

surface (to a depth of 1 cm).

In addition to surface samples from the five sites, 

sediment and native soil to a depth of 1.5 m were 

collected at site 5 in the recharge basin. This site, 

which seemed to be the deepest part of the basin, was 

4.9 m below the top of the cement seal at well 

14S/20E-24L1 (test hole 1). Successive layers of 

sediment were exposed and collected at site 5 by excavating a rectangular pit with a small hand trowel. 

The pit was "telescoped" inward in a staircase 

arrangement to eliminate sloughing of overlying sediment as successive layers were uncovered. Excavation continued in this manner to a depth of 64 cm; 

the deepest sample, from 120 to 150 cm, then was 

obtained with a manually operated 2-inch-diameter(5 

cm) steel auger. Although the color of sediment 

samples lightened considerably with increasing depth, 

even the deepest sample had a grayish-tan color 

indicative of an anaerobic environment.

The particle-size-distribution data (table 5) for the 

subbottom-deposit samples collected at site 5 show 

the existence of a shallow zone, from the sediment 

surface to a depth of 8 cm, in which silt and clay 

predominate, and a deeper zone, below 16 cm, in 

which sand predominates (with little silt and clay present). The interval between 8 and 16 cm is a transition zone between the overlying sediment derived 

from outside the basin, presumably brought in 

by runoff from the catchment, and the underlying 

natural alluvium referred to throughout this report as 

"soils" or "substrata."

On the basis of the difference in altitude between 

test hole 1 and basin sediment-sampling site 5, one 

would expect the lithology of the basin deposits 

immediately below 16 cm to be similar to that of the 

test hole between 4.9 and 5.5 m. However, minor 

differences in particle-size distribution and in element 

concentrations suggest that the basin deposits below 

16 cm more closely resemble those from 5.5 to 5.8 m 

in test hole 1 (for which chemical data exist but 

particle-size data do not). Specifically, the basin 

deposits below 16 cm consist predominantly of a fineto-medium sand, whereas the soil from 4.9 to 5.5 m 

in test hole 1 consists predominantly of a coarse-tomedium sand (compare data in tables 2 and 5). In 

addition, comparison of selected element (Fe, Mg, 

Mn, Th, Ti, and V) concentrations (data given in 

tables 7 and 9 and discussed in later sections of this 

report) shows that basin deposits below 16 cm are 

closer in chemical composition to soils between 5.5 

and 5.8 m than to soils between 4.9 and 5.5 m in test 

hole 1. It should be noted, however, that chemical 

differences between the two soil samples are small 

and that the element arsenic presents a pattern 

opposite to that of the aforementioned six elements.

CHEMICAL ANALYSIS OF WATER, SOIL, AND 

SEDIMENT

A Teflon bailer with Teflon ball-check valve was 

used to collect ground-water samples from the two 

monitor wells installed for this study. Aliquots for 

analysis of inorganic constituents and nutrients were 

filtered through a membrane with 0.45-um pores. 

Aliquots for analysis of gross organic indicators (such 

as methylene blue active detergents, tannin plus 

lignin, and oil and grease) and specific organic 

compounds were not filtered. Samples for analysis of 

organic compounds were stored at temperatures near 

0°C and analyzed within a few days of their 

collection. Samples for analysis of cations and trace 

elements were stabilized by addition of nitric acid to 

pH approximately 2 and nutrients were preserved by 

addition of mercuric chloride and storage at temperatures near 0°C. Samples for trace-element analysis in 

the low-concentration (sub-ppb) range were acidified 

with ultrapure nitric acid and stored in Teflon bottles.

Grab samples of water from the recharge basin, 

and samples from the laboratory elutriation study 

(discussed in detail later in the "Laboratory Elutriation 

Experiments" section) were processed and analyzed in 

a manner similar to that used for the ground-water 

samples, except that collection and sample-preservation techniques for low-level (sub-ppb) trace10 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
D 

13

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Field and Analytical Methods 11
element samples described above were used for only 

some of the samples (readily recognized in data tables 

6, 12, and 13 by the reporting of significant digits to 

the tenths microgram-per-liter (sub-ppb) level for 

several trace elements). Solutions from the elutriation 

test were centrifuged rather than filtered.

Aqueous chemical constituents were analyzed by 

the USGS National Water Quality Laboratory in 

Arvada, Colorado, using methods described by 

Wershaw and others (1987) and Fishman and 

Friedman (1989). Tritium initially was analyzed at the 

University of California, San Diego, and these 

analyses later were confirmed at the USGS Isotope 

Laboratory in Reston, Virginia, using a liquidscintillation counting method. Stable isotopes of 

hydrogen and oxygen also were analyzed in the 

Reston laboratory.

Sediment and soil samples for determination of 

organic constituents were stored in glass jars at 

temperatures near 0°C until their analysis a few days 

after collection, or they were frozen for later use in 

the laboratory elutriation tests. Organic constituents 

and nutrients were analyzed by the USGS National 

Water Quality Laboratory using methods described by 

Wershaw and others (1987) and Fishman and 

Friedman (1989). Groups of organic compounds that 

were analyzed include the organochlorines, organophosphorous insecticides, chlorophenoxy-acid herbicides, and extractable priority pollutants. In addition 

to these specific compounds, extractable nonspecific 

organic compounds were analyzed by gas chromatography with flame ionization detection (GC-FID).

The GC-FID scans provide only a general 

indication of organic contaminant concentrations because total concentrations determined by GC-FID 

amount to only about 1 percent of total organic carbon (analyzed by combustion) in near-surf ace sediments from the basin. For GC-FID analysis, a 25-g 

(approximate dry weight) subsample of sediment was 

extracted with a methanol plus methylene chloride 

solvent mixture for 12 hours using continuous Soxhlet 

extraction. The extract then was concentrated using 

a Kuderna-Danish apparatus. Surrogate compounds 

were added prior to extraction to check recovery, and 

perdeuteronaphthalene (C10D8 ) was added as an 

internal standard to the extract just prior to GC-FID 

analysis. Chromatographic separation was done using 

a 25-m by 0.21-mm SE-54 fused silica capillary 

column held initially at 50°C for 5 minutes then 

increased to 300°C at 6°C/min. Concentrations were 

calculated relative to the response of the internal 

standard (as "C10D8 equivalents").

For the gas chromatography-electron impact mass 

spectrometric (GC-MS) analysis of two sediment 

samples (0-1 cm and 8-16 cm depths) from site 5, 

approximately 25 g (dry weight) of sediment was 

processed and chromatographed in the same way as 

for GC-FID analysis. However, the chromatography 

column was coupled directly to a mass spectrometer, 

which was set to analyze from 45-450 atomic mass 

units with a scan time of 0.25 second. Compound 

identifications were based on comparison of the gas 

chromatographic peak retention time and mass spectrum with similar data for standard compounds. In 

addition to priority pollutants, a computerized library 

search for nontarget compounds was done. Although 

many compounds were detected, especially in the 

surface sample, only a few could even be identified 

by the compound class to which they belong.

Analysis of soil and sediment samples for element 

concentrations was done in the USGS Analytical 

Facility in Denver using methods (Severson and 

others, 1987) identical to those also used for a 

multisite reconnaissance of irrigation drainage effects 

that was done concurrently with this study (see, also, 

Schroeder and others, 1988, and Arbogast, 1990, for 

details on analytical methods). The samples were 

prepared for analysis by drying at about 30°C and 

grinding to pass an 80-mesh (180 um) sieve. Virtually 

complete mineral digestion was effected with a combination of strong acids. Inductively coupled argonplasma atomic emission spectrometry (ICP) was used 

to analyze a broad suite of about 40 elements. Arsenic 

and selenium were analyzed using hydride-generation 

atomic absorption. Mercury was analyzed using 

flameless cold-vapor atomic absorption. Boron was 

analyzed on a hot-water extract. Uranium and thorium 

were analyzed using delayed-neutron activation.

Lead-210 (210Pb) and radium-226 (226Ra) were 

analyzed in 13 sediment samples from the recharge 

basin and in 2 soil samples from test hole 1. 

J.K. Cochran, at the State University of New York, 

Stony Brook, analyzed these samples using a nondestructive gamma-counting technique. About 90 to 

150 g dried sediment (or soil) was sealed in 100 cm3 

aluminum cans and stored for 2 weeks to allow 

gaseous radon-222 (222Rn) to reach decay equilibrium 

with 226Ra. Gamma emissions were counted on a 

1,000 mm2 ,10-mm-thick, Canberra Electronics planar 

germanium detector. The 46.5 keV (thousand electron 

volt) 210Pb peak and the 352 keV 214Pb peak were 

used to measure 210Pb and 226Ra activity, respectively. 

Counting time was about 24 hours. Detector 

efficiencies were determined using laboratory as well 

as National Bureau of Standards sediment standards.

12 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Corrections for sample self-absorption of gamma rays 

were made by measuring the attenuation of 210Pb and 

226Ra sources placed on the sample cans. Concentrations are reported in disintegrations per minute 

per gram dry sediment (dpm/g) with precision based 

on counting statistics.

QUALITY OF RECHARGE-BASIN WATER AND 

GROUND WATER

The most direct way of determining whether 

recharge from the study basin has impaired groundwater quality is to measure chemical concentrations in 

the basin sediment and concentrations in nearby 

ground water. Nightingale (1975, 1987a,b,c, and 

1989) found that several trace elements and synthetic 

organic compounds were strongly sorbed by soils 

beneath five recharge basins in residential and 

commercial parts of the city of Fresno and that their 

concentrations were low in soil moisture from the 

unsaturated zone and in ground water immediately 

below a basin. Accordingly, although contaminant 

levels in sediment were expected (and found) to be 

higher at the recharge basin in the commercial 

catchment that was the subject of this study, little or 

no effect on ground-water quality was anticipated.

An important consideration in evaluating the 

potential for ground-water contamination by urbanrunoff chemical constituents is establishing whether 

runoff in the basin actually reaches the water table 

below the basin in significant amounts. Measurement 

of soil-moisture content in the unsaturated zone and 

installation of several monitor wells to determine the 

local hydraulic gradient would provide direct evidence 

of recharge but were beyond the resources available 

for this study. Nevertheless, water-budget calculations 

indicate that the potential for substantial recharge 

exists. On the basis of mean annual rainfall of 26 cm, 

measured rainfall-runoff coefficient, soil-water 

capacity, and physical dimensions of the catchment 

and recharge basin (Oltmann and Schulters, 1989), 

mean annual runoff should be sufficient to saturate 

soil above the water table for a distance of about 

100 m beyond the basin's boundaries. Of course, this 

simplified calculation assumes symmetrical spreading 

beneath the recharge basin. On the basis of saturated 

hydraulic conductivities calculated from measured soil 

characteristics, Nightingale (1989) concluded that 

subsurface silt and clay strata (lenses) would cause 

lateral movement of water beneath a Fresno recharge 

basin that had a measured infiltration rate of 16 cm/d 

(almost 60 m/yr). If the soil deposits in the recharge 

area above the lenses are assumed to be isotropic and

homogeneous and the recharge rate is constant, then 

the radius of the area infiltrated must vary inversely 

with the square root of vertical hydraulic conductivity 

(Freeze and Cherry, 1979, p. 16). On the basis of this 

relation and the inferred variation in hydraulic 

conductivities (Nightingale, 1989), the water would be 

expected to spread laterally a distance of about three 

times the basin's diameter. The likelihood that 

recharge reaches the water table directly beneath and 

near (as opposed to some great distance from) the 

basin is inferred on the basis of arguments given 

above, along with the absence of significant lithologic 

discontinuities at the test holes.

Additional evidence that ground water at the 

water table has mixed with a substantial volume of 

water from the recharge basin was obtained from 

analysis of tritium and the stable isotopes of hydrogen 

and oxygen.

ISOTOPIC EVIDENCE FOR RECHARGE

Tritium, the radioactive isotope of hydrogen 

having a half-life of 12.43 years, is produced 

naturally by cosmic-ray interactions with the upper 

atmosphere. Atmospheric detonation of thermonuclear 

weapons produced large quantities of tritium with the 

result that tritium concentrations in precipitation 

began increasing above natural levels about 1950, 

reaching a peak that was 102-103 times natural levels 

in the mid-1960's, and then gradually declining 

following the international treaty that banned 

atmospheric testing by the major nuclear powers. 

Tritium in precipitation today remains several times 

higher than natural levels. It is this bomb-produced 

tritium transient that can be used to distinguish post1950 water from older water.

On the basis of nationwide maps of tritium deposition (Michel, 1989), it is estimated that average 

annual tritium concentration in precipitation at the 

city of Fresno was slightly greater than 10 TU 

(tritium units) at the time of this study. (One tritium 

unit is one tritium atom per 1018 hydrogen-1 atoms 

and equals approximately 3.2 picocuries per liter.) 

On the basis of physical properties of the aquifer 

(Williamson and others, 1989, and Hugh Mitten, 

USGS, written commun., 1986), it is concluded that 

regional ground water in the city of Fresno that 

originates as recharge in the Sierra Nevada foothills 

is unlikely to contain any tritium. The measured 

tritium concentration of 10.2 TU in the recharge basin 

(table 6) is close to the estimated tritium concentration in local precipitation. It is presumed that the

Quality of Recharge-Basin Water and Ground Water 13
Table 6. Concentrations of dissolved inorganic and total-recoverable organic constituents in water from 

the recharge basin and from two nearby monitor wells

[Water from recharge basin collected January 29,1986, except sample for analysis of isotopes, mercury, and bromide collected 

July 11, 1986. Monitor wells sampled August 4, 1986. MBAS, methylene blue active surfactants; PCBs, polychlorinated 

biphenyls; |aS/cm, microsiemen per centimeter at 25° Celsius; °C, degrees Celsius; mg/L, milligram per liter; |ag/L, microgram 

per liter; permil, parts per thousand; --, no data; <, less than indicated reporting limit]

Constituent

Major Constituents

Temperature (°C)

Specific conductance (|aS/cm)

pH (standard units)

Calcium (mg/L)

Magnesium (mg/L)

Sodium (mg/L)

Potassium (mg/L)

Chloride (mg/L)

Sulfate (mg/L)

Fluoride (mg/L)

Silica (mg/L as SiO2)

Alkalinity (mg/L as CaCO3)

Nutrients

Nitrite + nitrate (mg/L as N)

Ammonium (mg/L as N)

Kjeldahl nitrogen (mg/L as N)

Orthophosphate (mg/L as P)

Organic carbon (mg/L as C)

Trace Elements (|ag/L)

Arsenic (As)

Barium (Ba)

Boron (B)

Bromine (Br)

Cadmium (Cd)

Chromium (Cr)

Cobalt (Co)

Copper (Cu)

Iron (Fe)

Lead (Pb)

Manganese (Mn)

Mercury (Hg)

Molybdenum (Mo)

Nickel (Ni)

Selenium (Se)

Silver (Ag)

Strontium (Sr)

Vanadium (V)

Zinc (Zn)

Isotopes

8D (permil)

818O (permil)

3H (tritium units)

Recharge 

basin

--

360

6.9

13

5.3

14

18

23

32

.1

5.4

13

4.0

7.0

13

4.3

--

3

90

<10

1

<1

3

7

210

2

120

.1

10

4

<1

<1

170

~

130

-16.0

1.19

10.2±.8

Concentration, in indicated units

Well 

14S/20E-24L1

17

420

8.1

22

11

53

3.2

10

24

.1

49

171

4.0

.02

.6

.04

3.9

3

100

80

<10

.73

.50

1.0

3.5

16

<.08

210

<.l

15

6.8

<1

<.03

170

19

.5

-51.5

-7.20

6.4±.7

Well 

14S/20E-24L2

17

379

8.1

34

16

15

3.4

7.4

26

.1

49

~

4.8

.02

.7

.06

3.9

2

100

110

<10

1.1

.35

1.5

4.5

48

<.08

78

<.l

5

11

<1

<.03

220

15

.4

-49.5

-7.05

5.8±.6

14 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Table 6. Concentrations of dissolved inorganic and total-recoverable organic constituents in water from 

the recharge basin and from two nearby monitor wells~Con//nued

Concentration, in indicated units

Constituent Recharge 

basin

Well 

14S/20E-24L1

Well 

14S/20E-24L2

Broad Organic Indicators

Tannin and lignin (mg/L as

tannic acid)

Phenols (ug/L as phenol) 

MBAS detergents (mg/L)

Synthetic Organic Compounds (ug/L) 

1,2-Dichloroethane 

1,1,1 -Trichloroethane 

Dichlorodifluoromethane 

Lindane 

Endosulfan 

Malathion 

Parathion 

Diazinon

Purgeable priority pollutants 

Base/neutral-extractable

priority pollutants 

Acid-extractable priority

pollutants 

Organochlorine insecticides +

PCB's 

Organophosphorus insecticides

2.8

5 

.29

<3 

<3 

<3

.01

.01 

.01

<3

.11

.2 

.2

<.001 

.002

.01

C)

<.001

<1

.08

.2 

.2

<.001 

<.001

C)

<.001

'Value is less than reporting limit, which is 5 ug/L for most extractable organic priority pollutants.

basin contains a mixture of ground water used by 

industries in the catchment area and not discharged to 

a municipal treatment plant in addition to precipitation runoff, and that it is the precipitation runoff 

that was the principal source of tritium in the sample 

from the recharge basin collected January 29, 1986.

Tritium concentrations of about 6 TU in both 

monitor wells (table 6) seem to indicate significant 

recharge from the basin. However, the evidence is 

compromised by the recent finding of tritium in many 

wells throughout the San Joaquin Valley, including 46 

TU in well 14S/20E-34G1, a 124-foot well about 3 

km southwest of the study site (Shelton and Miller, 

1991). Recharge by extensive irrigation with surface 

water likely is the source of tritium in ground water 

throughout the San Joaquin Valley; in the city of 

Fresno, artificial recharge also is a potential source of 

tritium.

Stable-isotope ratios of hydrogen (2H/!H or D/H) 

and oxygen ( 18O/16O) also can be used to infer

recharge and possibly to place constraints on the 

timing of such recharge from the basin. Both isotope 

ratios are expressed here as permil in the commonly 

used 8 (delta) notation relative to the Vienna-Standard 

Mean Ocean Water (V-SMOW) standard. The general 

relation between hydrogen- and oxygen-isotope ratios 

in precipitation is shown by the global meteoric-water 

line (MWL) in figure 3 (Craig, 1961). This line has 

a slope of 8, and the isotopic composition of waters 

that have undergone evaporation typically fall to the 

right of this line; that is, they are enriched in 18O 

relative to deuterium. This deviation from the MWL, 

as well as relatively high values of 8D and 818O, 

indicates that water in the recharge basin at the time 

of sampling for stable isotopes on July 11, 1986, was 

highly evaporated.

The hydrogen-isotope ratio of precipitation in the 

city of Fresno can be inferred, from regional-scale 

data along an east-west traverse between the Pacific 

Coast and Nevada, to be about -80 permil (Ingraham 

and Taylor, 1991). Ground water from most wells in

Quality of Recharge-Basin Water and Ground Water 15
-20

-40

E -60 

cc

<

 I

Q -100

-120

l I I r

,0;%; Well 14S/20E-24L1 

Well 14S/20E-24L2

Fresno 

precipitation

- - - "Mixing" lines

Well 14S/20E-34G1

I_____L

-14 -12 -10 -8 -6 -4 -2 0 +2 

DELTA OXYGEN-18, IN PERMIL

Figure 3. Relation between hydrogen and 

oxygen stable-isotope ratios in recharge-basin 

water and nearby ground water.

the vicinity of the city of Fresno has a 8D slightly 

less than -90 permil. Even the isotopic composition of 

water from well 14S/20E-34G1 (alluded to in the 

earlier discussion on tritium), at 8D=-91.5 permil and 

818O=-12.3 permil, does not differ greatly from the 

composition expected for ground water free of local 

recharge by surface water or irrigation apparently 

because the local recharge has not undergone 

substantial evaporation. As can be seen in figure 3 

(dashed lines), there is no way the isotopic 

composition measured in the two monitor wells can 

be obtained by mixing regional ground water or local 

precipitation with recharge-basin water in varying 

proportions. On the basis of this departure from a 

simple two-member mixing model, it is concluded 

that one or more of the following conditions are 

necessary to explain the isotopic composition found 

in the monitor wells:

1. The 8D of precipitation may have been higher

(less negative) at the time of this study than 

the inferred estimate of -80 permil.

2. The D and 18O contents of regional ground 

water at the study site may be higher than 

represented by well 14S/20E-34G1. D and 18O 

contents are reported to be higher in some 

wells several kilometers from the study area 

(Shelton and Miller, 1991).

3. Recharge in the basin might be occurring 

during periods when the basin's water has 

undergone less evaporation, such as during the 

winter; as a result, ]H and 16O concentrations

ordinarily would be considerably higher (2H 

and 18O would be lower) than during summer 

when the basin was sampled. It is reasonable 

that recharge should be much greater following 

winter storms when the basin was observed by 

the author to be fuller than during the dry 

summer season when it contains less water.

Although the relative importance of each of the 

above explanations cannot be evaluated without 

frequent monitoring over a period of time, the fact 

that 8D and 818O values in the monitor wells 

generally are less negative than in other wells in the 

Fresno area argues strongly that recharge from the 

basin is reaching the water table locally.

The stable-isotope data, together with the tritium 

data, suggest that basin recharge is comparable in 

importance at the study site to regional ground-water 

flow from the Sierra Nevada foothills, so that any 

storm-runoff contaminants not effectively removed by 

the soil beneath the basin should be easily detectable 

by means of shallow monitor wells such as those that 

were installed for this study. Nevertheless, the sparse 

isotope data presented do not support quantitatively 

apportioning ground water at the monitor wells 

between regional flow and basin recharge. Apart from 

the limitations discussed above, seasonal and annual 

isotope variations in precipitation are likely to be 

quite large. For example, mean annual tritium 

concentration in precipitation during 1980-81 is nearly 

double that of the near-record wet period of 1982-83 

(Michel, 1989). Also, mean annual 8D in precipitation 

was found to vary as much as 40 permil between 

1981 and 1989 at some sites in a monitoring network 

that included 32 locations in southeastern California 

and adjacent parts of Nevada and Arizona (Friedman 

and others, 1992).

MAJOR IONS AND TRACE ELEMENTS

Comparison between water samples from the 

recharge basin and the monitor wells (table 6), and 

comparison of both with regional ground-water 

composition listed in table 1, reveals little difference 

in such broad measures of water quality as dissolvedsolids concentration and specific conductance. For 

chloride, which is an ideal unreactive tracer (as are 

isotopes), differences are larger but still too small to 

be useful. Although differences are large for silica 

and bicarbonate (alkalinity), precipitation and dissolution reactions make both unsuitable as tracers. Of 

the major ions, potassium (K) is the most useful 

indicator of whether cationic contaminants in the re16 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
charge basin reach the water table. Aqueous potassium concentrations are about 5 times higher in the 

recharge basin than in either regional ground water 

(table 1) or the nearby monitor wells (table 6) 

indicating that there is no discernible transport of this 

cation to the water table. Profiles of dissolved- and 

exchangeable-cation concentrations beneath a recharge 

basin in the city of Fresno show that removal of 

dissolved potassium in percolating recharge water 

occurs through ion-exchange reactions with clay 

minerals in the soil (Nightingale, 1989).

Zinc is potentially an even more sensitive surrogate than is potassium, as the concentration of zinc is 

more than 100 times higher in the recharge basin than 

in the monitor wells (table 6). Motor vehicles, and 

especially motor oil, have been implicated as the 

major source of zinc in the urban environment 

(Wigington and others, 1983). The reason for such a 

large enrichment (comparative concentration ratio) for 

aqueous zinc in the recharge basin is unknown; 

however, it may be related partly to its role as 

a biological micronutrient and partly to its greater 

solubility than other heavy metals with large 

anthropogenic inputs (Harter, 1983; Wigington and 

others, 1983). (These same reasons can be used to 

explain the high concentrations of potassium.) In any 

case, because the available data show that trace metals 

in urban runoff have not affected ground-water 

quality at this site, monitoring for zinc would be very 

effective in demonstrating continued absence of 

impairment by trace-metal cations.

ORGANIC PRIORITY POLLUTANTS AND PESTICIDES

Water from the recharge basin and from monitor 

wells was analyzed for three gross organic indicators: 

tannin and lignin, total phenols, and methylene blue 

active surfactant (MBAS) detergents. All were 

reported present in the recharge basin and some also 

were detected in the monitor wells (table 6). 

However, the baseline for colorimetic detection of 

these analytes in dissimilar waters is likely to be 

variable and is sufficiently uncertain that their 

reported detection at very low levels in the monitorwell samples is not conclusive evidence for their 

actual presence (that is, the levels detected likely 

represent "false positives").

Several groups of synthetic organic chemicals also 

were analyzed: purgeable and extractable priority 

pollutants, organochlorine compounds, and organophosphorous insecticides. Only a few were found and, 

because their reported aqueous concentrations were at

the laboratory reporting limit, their presence should 

not be inferred without further sampling.

Organic (and trace-metal) concentrations generally 

are much higher in sediments than in water and, for 

this reason, the sediment (soils) data presented in the 

next section of this report provide a much more 

sensitive indicator of organic contaminant migration 

than do the aqueous-phase data.

CHEMICAL CONCENTRATIONS IN 

SEDIMENT AND SOIL

Chemical analysis of sediment beneath the 

recharge basin and of soil from test holes provides 

this study with the strongest evidence that sorption by 

the solid phase is a very effective mechanism for 

removal of inorganic and organic contaminants, and 

that only a very small fraction of the available 

capacity for removal is used after a few years. Results 

of these analyses are presented in tables 7 to 10, and 

in table 14 (results reported in table 14 are discussed 

later, in the "Laboratory Elutriation Experiments" 

section). The results given in these tables indicate 

marked attenuation in concentration of numerous 

elements and synthetic organic chemicals within the 

top few centimeters beneath the recharge basin.

INORGANIC ELEMENTS

The determination of "background levels" is more 

difficult for inorganic elements than for synthetic 

organic chemicals; whereas the former occur naturally 

in variable concentrations, the latter are completely 

absent in soil and sediment known to be free of 

human influence.

Comparisons of trace-element data show that 

natural variability far exceeds any differences 

resulting from sampling and analytical imprecision. 

The range in concentration for 43 elements analyzed 

in five soil cores from test hole 1 exceeds 10 percent 

for all 32 of the elements whose concentrations 

exceed reporting limits (table 7). This contrasts 

markedly with the nearly identical concentrations 

measured for sediment samples collected immediately 

adjacent to one another from depths of 0 to 1 cm 

(table 8) and 120 to 150 cm (tables 8 and 9) at site 5 

in the recharge basin. For the highly contaminated 

surficial samples, measurable concentrations are 

identical for 20 elements and differ by more than 10 

percent for only 4 elements (molybdenum, potassium, 

thorium, and ytterbium). For the background-level

Chemical Concentrations in Sediment and Soil 17
Table 7. Concentrations of elements and radioisotopes in soil cores from test hole 1 adjacent to the 

recharge basin

[Element concentrations in micrograms per gram dry weight and radioisotope concentrations in disintegrations per minute per 

gram dry weight. --, no data; <, less than indicated reporting limit]

Element/isotope

Aluminum

Arsenic

Barium

Beryllium

Bismuth

Boron

Cadmium

Calcium

Cerium

Chromium

Cobalt

Copper

Europium

Gallium

Gold

Holmium

Iron

Lanthanum

Lead

Lithium

Magnesium

Manganese

Mercury

Molybdenum

Neodymium

Nickel

Niobium

Phosphorus

Potassium

Scandium

Selenium

Silver

Sodium

Strontium

Tantalum

Thorium

Tin

Titanium

Uranium

Vanadium

Ytterbium

Yttrium

Zinc

Lead-210

Radium-226

Lead-210 excess

Symbol

Al

As

Ba

Be

Bi

B

Cd

Ca

Ce

Cr

Co

Cu

Eu

Ga

Au

Ho

Fe

La

Pb

Li

Mg

Mn

Hg

Mo

Nd

Ni

Nb

P

K

Sc

Se

Ag

Na

Sr

Ta

Th

Sn

Ti

U

V

Yb

Y

Zn

210pb

226Ra

21 °Pbxs

4.9-5.5

69,000

1.2

1,000

1

<10

<0.4

<2

17,000

35

16

4

4

<2

12

<8

<4

13,000

21

24

11

3,400

230

<.02

<2

14

7

5

300

30,000

3

<.2

<2

22,000

360

<40

7.74

<10

1,300

1.57

29

<1

9

22

2.01±.24

1.43±.05

.58±.25

Depth 

5.5-5.8

73,000

4.5

900

1

<10

<.4

<2

18,000

50

20

7

8

<2

14

<8

<4

23,000

29

19

17

5,700

400

<.02

<2

20

10

9

400

29,000

5

<.2

<2

23,000

350

<40

13.9

<10

2,100

3.10

54

1

13

38

__

~

Concentration

(meters below land 

5.8-6.2

82,000

9.5

830

2

<10

<.4

<2

23,000

63

26

9

12

<2

16

<8

<4

25,000

36

23

24

8,200

560

<.02

<2

25

12

11

800

28,000

8

<.2

<2

26,000

380

<40

19.3

<10

3,000

3.52

63

2

18

53

~

surface) 

6.2-6.4

70,000

3.9

820

1

<10

<.4

<2

19,000

54

29

6

6

<2

13

<8

<4

23,000

31

16

14

5,200

390

<.02

<2

22

10

8

300

27,000

4

<.2

<2

23,000

350

<40

12.8

<10

2,100

2.53

56

2

14

33

2.95±.32

2.70±.21

.25±.38

10.9-11.3

89,000

4.2

510

<1

<10

1.9

<2

24,000

37

140

19

26

<2

16

<8

<4

38,000

19

14

30

15,000

590

<.02

<2

18

140

5

300

18,000

14

<.2

<2

19,000

280

<40

4.7

<10

3,100

2.24

91

2

17

69

~

18 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Table 8. Concentrations of chemical constituents and radioisotopes in surface (0-1 cm) sediment from 

six sites in the recharge basin

[Chemical concentrations in micrograms per gram dry weight; radioisotope concentrations in disintegrations per minute per 

gram dry weight. GC-FID, gas chromatography with flame-ionization detection, cm, centimeter; , no data; <, less than 

indicated reporting limit]

Symbol 

Constituent (where 

applicable

Aluminum

Arsenic

Barium

Beryllium

Bismuth

Boron

Cadmium

Calcium

Cerium

Chromium

Cobalt

Copper

Europium

Gallium

Gold

Holmium

Iron

Lanthanum

Lead

Lithium

Magnesium

Manganese

Mercury

Molybdenum

Neodymium

Nickel

Niobium

Phosphorus

Potassium

Scandium

Selenium

Silver

Sodium

Strontium

Tantalum

Thorium

Tin

Titanium

Uranium

Vanadium

Ytterbium

Yttrium

Zinc

Nitrite+nitrate

(asN)

Ammonium (as N)

Phosphorus (as P)

Organic carbon

(asC)

Al

As

Ba

Be

Bi

B

Cd

Ca

Ce

Cr

Co

Cu

Eu

Ga

Au

Ho

Fe

La

Pb

Li

Mg

Mn

Hg

Mo

Nd

Ni

Nb

P

K

Sc

Se

Ag

Na

Sr

Ta

Th

Sn

Ti

U

V

Yb

Y

Zn

Concentration at site:

) 1

59,000

5.3

580

1

<10

7.9

<2

28,000

42

44

10

63

<2

12

<8

<4

22,000

24

91

20

10,000

490

.07

2

17

31

8

1,500

19,000

6

.4

<2

20,000

410

<40

12.7

<10

2,300

5.08

59

1

13

590

10

1,800

2,000

170,000

2

66,000

17

650

1

<10

5.6

<2

27,000

46

59

10

74

<2

13

<8

<4

23,000

26

92

24

11,000

490

.06

<2

17

33

7

1,200

21,000

7

.6

<2

20,000

370

<40

12.3

<10

2,500

4.64

64

1

13

490

23

1,400

1,700

95,000

3

70,000

6.9

680

1

<10

5.4

<2

22,000

52

61

13

64

<2

15

<8

<4

30,000

30

110

33

12,000

600

.10 '3

21

43

8

1,500

22,000

9

.5

<2

18,000

340

<40

19.7

<10

2,900

4.78

75

2

14

510

11

830

1,800

100,000

4

71,000

9.0

680

1

<10

3.6

<2

19,000

53

71

14

97

<2

16

<8

<4

34,000

31

130

37

12,000

560

.11

3

21

51

7

1,800

22,000

9

.7

<2

16,000

290

<40

21.4

<10

3,000

5.70

83

2

14

750

7

1,400

1,900

130,000

5 1

70,000

18

640

1

<10

3.9

<2

17,000

54

83

17

140

<2

16

<8

<4

38,000

31

170

45

14,000

640

.22

6

20

66

7

2,200

18,000

10

1.0

<2

13,000

270

<40

20.6

<10

2,900

11.6

94

1

14

1,200

8

1,100

87

160,000

5 1

70,000

17

680

1

<10

3.9

<2

17,000

53

84

17

140

<2

16

<8

<4

39,000

31

170

45

14,000

650

.23

5

20

68

7

2,300

21,000

10

1.0

<2

13,000

270

<40

30.1

<10

3,100

11.3

94

2

14

1,200

--

--

--

6

72,000

16

680

<1

<10

4.3

<2

17,000

54

86

17

130

<2

17

<8

<4

40,000

32

160

46

14,000

650

.19

6

20

68

8

2,400

22,000

10

.9

<2

13,000

270

<40

25.1

<10

3,200

10.0

97

2

14

1,200

3

990

2,800

150,000

Footnote at end of table.

Chemical Concentrations in Sediment and Soil 19
Table 8. Concentrations of chemical constituents and radioisotopes in surface (0-1 cm) sediment from 

six sites in the recharge basin-Continued

Constituent

Inorganic carbon

(asC)

Oil and grease

GC/FID (as C10D8

equivalents)

Aldrin

Lindane

Chlordane

DDD

DDE

DDT

Dieldrin

Endosulfan

Endrin

Heptachlor

Heptachlor

expoxide

PCB

PCN

Lead-210

Radium-226

Lead-210 excess

Symbol 

("where

applicable) 1

200

24,000

370

<.0005

.001

.13

.064

.065

.0050

.0021

<.0005

.0025

<.ooo?

.031

<.005

210Pb 5.18±.17

226Ra 2.70±.10

210Pbxs 2.48±.20

Concentration

2

100

13,000

370

<.001

<.0011

.14

.005

.043

.0041

.0041

<.0011

.0031

<.0011

.021

<.010

5.40±.18

3.03±.ll

2.37±.21

3

100

17,000

1,300

<.001

<.0011

.64

.060

.070

<.001 1

.0051

<.001

<.0011

.0031

<.0001

.033

<.010

6.92±.21

3.33±.12

3.59±.24

4

100

16,000

1,400

<.001

.0011

.20

.005

.071

.012

.0061

<.0011

.0031

<.0011

.030

<.010

8.81±.29

4.71±.18

4.09±.34

at site:

5 1

200

22,000

1,500

<.0005

.0011

.21

.035

.040

<.0005

<.0005

<.0005

.0021

<.0051

.039

<.005

10.1±.3

5.10±.15

5.00±.34

5 1 6

300

20,000

2,700

<.0005

<.0005

.18

.032

.077

<.0005

.0015

<.0005

<.0005

.0031

<.0005

.040

<.005

10.9±.3

5.15±.19

5.75±.36

*Two adjacent samples at site 5 were analyzed.

samples from the deepest interval, measurable 

concentrations are identical for 13 elements and differ 

by more than 10 percent for only 3 elements (nickel, 

niobium, and thorium).

Such small differences between duplicate sediment 

analyses provides strong evidence that the much 

larger site-to-site differences in surface sediments 

from the recharge basin (table 8) are real. Many of 

the trace elements whose concentrations are highest at 

the surface have concentrations at sites 5 and 6 that 

are about double those at sites 1 and 2. This trend of 

increasing concentration toward the south end of the 

recharge basin and away from the discharge pipe is 

consistent with a similar trend of increasing 

percentage of clay (table 5) to which these 

contaminants could be expected to adsorb.

Although the sediment at site 5 shows a marked 

decrease in many chemical concentrations with 

increasing depth (table 9 and fig. 4), the rather large 

variability in natural abundances and sharp change in 

lithology (from fine to coarse sediment) several 

centimeters below the recharge basin makes the 

assignment of background values somewhat uncertain. 

This variability in background concentrations is

especially evident from the chemical differences 

between soil cores at five different depths (table 7), 

all of which must represent uncontaminated natural 

conditions. The concentrations of several elements are 

highest in the core interval from 10.9 to 11.3 m, 

which likely is related to the increased proportion of 

clay and silt in this sample relative to the other four 

samples (table 4). Radium-226 provides similar 

evidence of natural variability that probably implies 

differences in mineral assemblage. Concentrations of 

this naturally occurring radioisotope differ substantially between two of the soil cores (table 7), between 

the six surface-sediment sites in the recharge basin 

(table 8), and at different subbottom depths from site 

5 beneath the recharge basin. On the basis of the 

particle-size distributions and selected chemical 

concentrations, as was noted in the section "Sampling 

of Sediments from the Recharge Basin," it was 

concluded that recharge-basin sediment below 16 cm 

is chemically most similar to soil between 5.5 and 5.8 

m in test hole 1. However, the fact that chemical 

concentrations for a number of elements vary by a 

factor of 2 or more in uncontaminated soil from 

various depths in test hole 1 indicates that "background" for fine-grained basin deposits above 16 cm 

may be quite different from "background" for coarse20 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Table 9. Concentrations of chemical constituents and radioisotopes in sediment and substrata at site 5 

[Chemical concentrations 

also are given in table 8.

in micrograms per gram dry weight; isotope concentrations in disintegrations per minute per gram 

cm, centimeter; ~, approximate value; , no data; <, less than indicated reporting limit]

Symbol 

Constituent (where 

applicable)

O3-

<D

O

Q

9

3

O 

<D

3

I

0

tn

3

«£

a 

3

<D

2-

Q

3

a

Aluminum

Arsenic

Barium

Beryllium

Bismuth

Boron

Cadmium

Calcium

Cerium

Chromium

Cobalt

Copper

Europium

Gallium

Gold

Holmium

Iron

Lanthanum

Lead

Lithium

Magnesium

Manganese

Mercury

Molybdenum

Neodymium

Nickel

Niobium

Phosphorus

Potassium

Scandium

Selenium

Silver

Sodium

Strontium

Tantalum

Thorium

Fnntnntp at <mH n

Al

As

Ba

Be

Bi

B

Cd

Ca

Ce

Cr

Co

Cu

Eu

Ga

Au

Ho

Fe

La

Pb

Li

Mg

Mn

Hg

Mo

Nd

Ni

Nb

P

K

Sc

Se

Ag

Na

Sr

Ta

Th

f tflhlf

Depth interval below recharge basin (cm)

O-l 1

70,000

18

640

1

<10

3.9

<2

17,000

54

83

17

140

<2

16

<8

<4

38,000

31

170

45

14,000

640

.22

6

20

66

7

2,200

18,000

10

1.0

<2

13,000

270

<40

20.6

O-l 1

70,000

17

680

1

<10

3.9

<2

17,000

53

84

17

140

<2

16

<8

<4

39,000

31

170

45

14,000

650

.23

5

20

68

7

2,300

21,000

10

1.0

<2

13,000

270

<40

30.1

1-2

79,000

13

740

1

<10

2.4

<2

17,000

63

87

17

120

<2

18

<8

<4

44,000

36

160

53

15,000

700

.22

4

25

70

7

2,100

24,000

11

<1.0

<2

13,000

280

<40

29.9

2-4

82,000

9.5

800

1

<10

1.4

<2

21,000

67

54

13

52

<2

18

<8

<4

34,000

39

88

39

12,000

620

.13

<2

26

39

10

1,200

26,000

10

.8

<2

21,000

340

<40

23.6

4-8

86,000

3.7

900

2

<10

<.4

<2

24,000

66

24

10

13

<2

17

<8

<4

22,000

39

22

27

9,800

550

<.02

<2

27

12

12

1,000

31,000

9

<.2

<2

27,000

410

<40

25.9

8-16

82,000

1.2

840

2

<10

<.4

<2

23,000

58

26

8

10

<2

16

<8

<4

19,000

33

19

21

7,500

450

<.02

<2

23

11

9

700

27,000

7

<.2

<2

27,000

400

<40

15.2

16-32

75,000

1.0

800

1

<10

<.4

<2

21,000

59

21

6

6

<2

14

<8

<4

19,000

36

19

15

5,500

370

<.02

<2

24

10

8

500

27,000

5

<.2

<2

25,000

. 380

<40

15.6

ro
IO

10

Table 9. Concentrations of chemical constituents and radioisotopes in sediment and substrata at site 5 

Continued

<D 

Q 

3" 

O 

<D

<D

I

(A

O

TO

C

i

TO 

<D 

O

Q 

CD 

<D

So

Q.

Q

§O 

<D

 n

5 

</»

O

Symbol 

Constituent (where 

applicable)

Tin Sn

Titanium Ti

Uranium U

3.08

Vanadium V

Ytterbium Yb

Yttrium Y

Zinc Zn

Nitrite+nitrate

(asN)

Ammonium (as N)

Organic nitrogen

(asN)

Phosphorus (as P)

Organic carbon

(asC)

Inorganic carbon

(asC)

Oil and grease

GC/FID (as C10Dg

equivalents)

Aldrin

Lindane

Chlordane

ODD

DDE

DOT

Dieldrin

Endosulfan

Endrin

Heptachlor

Heptachlor expoxide

PCB

PCN

Lead-210 210Pb

Radium-226 226Ra

Lead-210 excess 210Pbxs

Depth interval below recharge basin (cm)

O-l 1 O-l 1

<10 <10

2,900 3,100

11.6 11.3

94 94

1 2

14 14

1,200 1,200

8

1,100

-

87

160,000

200

22,000

1,500

<.0005

.001 1

.21

.035

.040

<.0005

<.0005

<.0005

.0021

<.0051

.039

<005

10.1±.3

5.10±.15

5.00±.34

1-2

<10

3,500

8.73

100

2

15

760

<2

960

~

2,600

150,000

300

24,000

600

 c.OOll

.0071

.35

.055

.072

.10

.055

<.001

.085

.0021

<.001 1

.06

<.01

9.19±.23

3.54±.ll

5.65±.25

2-4

<10

3,500

4.81

84

2

17

390

<2

560

-

990

50,000

200

11,000

380

<.0001

.0032

.20

.067

.048

.0021

<.0001

<.0001

<.0001

<.0001

<.0001

.04

<.001

6.68+19

3.92±.ll

2.76±.22

4-8

<10

3,300

3.11

59

2

18

71

<2

230

-

1,300

800

100

1,000

4.2

<.0001

.0003

.001

<.0001

.0004

.0001

.0001

<.0001

<.0001

<.0001

<.0001

<.001

<.001

2.42±.ll

2.48±.09

-.06±.14

8-16

<10

2,800

3.32

51

2

16

49

3

97

43

730

-600

<100

<1,000

1.7

<.0001

<.0001

.001

.0001

<.0001

<.0001

<.0001

<.0001

<.0001

<.0001

<.001

<.001

2.17±.09

2.53±.08

-.36±.12

16-32

<10

2,200

2.98

50

2

15

31

2

32

--

690

-200

<100

<1,000

2.9

<.0001

<.0001

<.001

<.0001

<.0001

<.0001

<.0001

<.0001

<.0001

<.0001

<.0001

<.001

<.001

2.57±.10

2.58±.08

-.01±.13

'Analysis of two samples collected next to one another.
Table 10. Concentrations of extractable priority pollutants, organochlorine compounds, and organophosphorus insecticides in sediment from depths of 0-1 and 8-16 cm at site 5 in the recharge basin

[Concentrations in micrograms per gram dry weight, cm, centimeter; ; <, less than indicated reporting limit]

Concentration Concentration

Organic constituent

0-1 cm 8-16 cm

Organic constituent

0-1 cm 8-16 cm

Extractable Priority Pollutants

Acenaphthylene <0.2

Acenaphthene <.2

Anthracene .46

Benzo (a) arthracene 3.9

Benzo (b) arthracene 9.2

Benzo (k) fluoranthene 6.4

Benzo (g,h,i) perylene 11

Benzo (a) pyrene 6.5

bis (2-Chloroethyl) ether <.2 

bis (2-Ethylhexyl) phthalate 6.2

Chrysene 9.7

Diethylphthalate <.2

Dimethylphthalate <.2

di-n-Butyl phthalate <.2

Fluoranthene 9.4

Fluorene <.2

Hexachlorobenzene <.2

Hexachlorobutadiene <.2 

Hexachlorocyclopentadiene <.2

Hexachloroethane <.2

Indeno (l,2,3,ed) pyrene 9.5

Isophorone <.2

n-Nitrosodi-n-propylamine <.2

n-Nitrosodiphenylamine < 1.5

n-Nitrosodimethylamine <.2

Naphthalene . 15

Nitrobenzene <.2

p-Chloro-m-cresol <.6

Phenanthrene 2.7

Pyrene 15

1,2-Dichlorobenzene <.2

1,2,4-Trichlorobenzene <.2

1,2,5,6-Dibenzanthracene <.4

1.3-Dichlorobenzene <.2

1.4-Dichlorobenzene <.2

2-Chloronaphthalene <.2

2-Chlorophenol <.2

2-Nitrophenol <.2

Di-n-octylphthalate <.4

2,4-Dichlorophenol <.2

2,4-Dinitrotoluene <.2

2,4-Dinitrophenol <.6

2,4,6-Trichlorophenol <.6

<0.2

2,6-Dinitrotoluene <0.2 

4-Bromophenyl phenyl ether <.2 

Chlorophenyl phenyl ether <.2

4-Nitrophenol <1.2

4,6-Dinitro-o-cresol <.6

Phenol <.2

Pentachlorophenol <.6

Organochlorine Compounds

Aldrin <0.0005

Lindane .0011

Chlordane .21

DDD .035

DDE .040

DDT <.0005

Dieldrin <.0005 

Endosulfan

Endrin <.0005

Ethion <.0005

Toxaphene <.05

Heptachlor .0021

Heptachlor epoxide .0051

Methoxychlor <.025

Mirex <.0005

Perthane <.005

PCB .039

PCN <.005

Organophosphorous Insecticides

Malathion <0.0005

Parathion <.0005

Diazinon <.0005

Methyl parathion <.0005

Methyl trithion <.0005

Trithion <.0005

2,4-D

Dicamba

2,4-DP

Pichloram

Silvex

2,4,5-T

Chlorophenoxy Acid Herbicides

<0.0001 

<.0001

<.0001 

<.0001 

<.0001

<0.2

<0.0001 

<.0001 

.001

.0001 

<.0001 

<.0001 

<.0001 

<.0001 

<.0001

<.0001

<.0002

<.0001

<.0001

<.001

<.001

<.001

<0.0001 

<.0001 

<.0001 

<.0001 

<.0001 

<.0001

<0.0001 

<.0001

<.0001 

<.0001 

<.0001

grained basin deposits below 16 cm. Sampling of 

near-surface soil in the vicinity of the study basin that 

could have established more suitable background 

levels for the shallower basin sediment was not done. 

Extensive tilling and grading in the area indicated that

nearby soil would not have been suitable for direct 

comparison because reworking is likely to have mixed 

contaminated (by atmospheric deposition) and 

uncontaminated soil, and soil of differing texture, in 

variable proportions.

Chemical Concentrations in Sediment and Soil 23
500

200

100

50

<

DC

LU

20

I 

o 

E 10

z

LU

0.5

0.2 0.5 1 10 20 50 100 200

DEPTH TO MIDDLE OF SEDIMENT INTERVAL, 

IN CENTIMETERS

Figure 4. Enrichment ratios for selected constituents in subbottom sediment at site 5 in the recharge basin.

ORGANIC CHEMICALS

The results for organic carbon, oil and grease, 

GC-FID organic carbon, and organochlorine compounds in near-surf ace (0-1 cm) sediments at the six 

recharge-basin sites are given in table 8. Table 9 

gives results for the same suite of organic constituents 

with increasing subbottom depth at site 5. Results for 

analysis of extractable priority pollutants, organochlorine compounds, organophosphorus insecticides, 

and chlorophenoxy-acid herbicides at depths of 0 to 

1 cm and 8 to 16 cm at site 5 are given in table 10. 

The pattern of results for organic chemicals generally

is similar to that shown by inorganic elements, 

although there exists considerably less uniformity in 

either the areal trend (table 8) or the profile (table 9) 

for the organic chemical constituents. No pesticides 

were detected below 16 cm at site 5, and only two, 

chlordane and DDE, were identified (at their reporting 

limits of 0.001 ug/g and 0.0001 ug/g, respectively) in 

sediment from the 8- to 16-cm interval.

The only pesticides that were found in basin 

sediment are the long-lived organochlorine compounds. It was anticipated that some of the more 

widely used organophosphorus insecticides, on the

24 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
basis of their abundance in rainfall and runoff 

(Oltmann and Shulters, 1989), also might be present 

in sediment, but none were detected (table 10). 

Similarly, their absence in sediment from five 

recharge basins in residential and commercial 

catchments during the Fresno NURP study was 

attributed to probable degradation (Nightingale, 

1987c). A large number of phosphorus-containing 

organic compounds were reported during the gaschromatographic analyses for this study, but they 

could not be specifically identified because of poor 

resolution and many interferences (M.P. Schroeder, 

USGS, oral commun., 1987). High organic content 

and the anaerobic nature of the sediment which 

made cleanup of the sample extracts difficult and may 

have interfered with detection of organophosphorus 

insecticides is the cause of the variable analytical 

reporting limits for the organochlorine compounds 

that are listed in the tables.

Chlordane was the organochlorine compound 

reported in highest concentration, a finding similar to 

that obtained during monitoring for the NURP study 

(Oltmann and Shulters, 1989). However, one of the 

more puzzling results obtained by this study is the 

finding of DDT itself as opposed to only its 

metabolites, DDD and DDE, which are more 

commonly present in environmental samples today. 

The highest DDT concentration of 0.10 ug/g was 

found not in surface sediment but rather in sediment 

from a depth of 1 to 2 cm at site 5. Use of DDT was 

banned in the United States about 10 years prior to 

the Fresno NURP study and the operation of this 

recharge basin in its present configuration. 

Confirmation of DDT's presence is strong, as shown 

by its detection in several of the sediment samples 

analyzed (tables 8 and 9). Furthermore, the Fresno 

NURP study found that DDT concentrations 

consistently exceeded DDD and DDE concentrations 

in street sweepings from residential, commercial, and 

industrial catchments (Oltmann and Shulters, 1989).

Of 50 extractable organic priority pollutants 

analyzed, 13 including 12 polycyclic aromatic 

hydrocarbons and 1 phthalate ester were detected in 

surficial sediment from site 5 (table 10). None were 

detected in sediment from the 8- to 16-cm interval. 

Total concentration of all the identified organic 

compounds in the surficial interval is slightly less 

than 100 ug/g, nearly all of which consists of the 

polycyclic aromatic hydrocarbons listed in table 10. 

Comparison with data given in table 9 shows that this 

represents only about 5 percent of the organic carbon 

reported by the GC-FID analysis, and less than 0.1 

percent of total organic carbon. Although two additional polycyclic aromatic hydrocarbons (dimethylsubstituted napthalenes) and at least 20 compounds 

belonging to the broad classes of alkanes and alkenes 

(or cycloalkanes) were identified by GC-FID analysis, 

virtually all the organic matter in the basin sediment 

remains uncharacterized. It seems likely that much of 

it may be generated by biological activity in the 

overlying water column; however, the organic nitrogen data that might have supported this assertion with 

the observation of low carbon/nitrogen ratios are 

lacking because all sediment samples but one listed in 

table 9 were accidentally destroyed in the laboratory 

during analysis.

ASSESSMENT OF ANTHROPOGENIC INPUTS

Chemical profiles that show a decrease in 

concentration with increasing sediment depth not only 

are strong evidence for sorptive removal of contaminants but also can be used, with some assumptions, 

to quantify the relative importance of anthropogenic 

(human-related) and natural (background) sources. 

The concept of enrichment ratios, defined herein as 

the concentration in a particular sediment interval 

divided by the mean concentration for all intervals 

below a depth of 16 cm (considered background concentration), is useful for this discussion. Profiles of 

enrichment ratios for selected constituents are shown 

in figure 4. If the surficial (0 to 1 cm) sediment is 

presumed to represent the combined inputs of current 

anthropogenic and natural sources, then decreases 

below this depth represent removal of contaminants, 

and possibly dilution by mixing with deeper soil that 

is free of anthropogenic influence. As expected, for 

rare-earth elements such as lanthanum, which has 

very few industrial uses, the concentration profile 

shows no change and represents only the natural 

abundance of this element. Two other rare earths that 

are present above reporting limits, cerium and 

neodymium, also show no change in concentration 

with depth (table 9).

Surface-enrichment ratios for all elements were 

calculated and are reported to the nearest whole 

number in table 11 for those values that differ from 

1. These values include about half the elements 

analyzed. For those elements not listed in table 11, 

either there is no anthropogenic source or (1) 

concentrations are uniformly below detection, (2) 

natural levels are so high that they mask any anthropogenic input, or (3) variability in mineralogy or 

lithology exerts the predominant influence on concentrations. Just as an enrichment ratio of 1 does not 

preclude an anthropogenic component conversely, an

Chemical Concentrations in Sediment and Soil 25
Table 11 . Surface-enrichment ratios for selected 

elements and radioisotopes in sediment at site 5 

in the recharge basin

[Surface-enrichment ratio is concentration of 0-1 centimeter 

interval divided by mean concentration of all intervals 

below 16 centimeter. >, greater than indicated value]

Constituent

Arsenic

Boron

Chromium

Cobalt

Copper

Iron

Lead

Lithium

Magnesium

Maganese

Mercury

Molybdenum

Nickel

Phosphorus

Scandium

Selenium

Thorium

Uranium

Vanadium

Zinc

Lead-210

Radium-226

Symbol

As

B

Cr

Co

Cu

Fe

Pb

Li

Mg

Mn

Hg

Mo

Ni

P

Sc

Se

Th

U

V

Zn

210pb

226Ra

Enrichment 

ratio

16

>9

5

3

25

2

9

3

3

2

>11

>2

7

5

2

>5

2

4

2

38

4

2

enrichment ratio greater than 1 is not necessarily conclusive proof of anthropogenic contamination, 

especially when these ratios are low. Such results 

could be an artifact of natural variability, as already 

discussed, or the results could be unique to the 

geochemical behavior of individual elements.

Despite these limitations on interpretation, it is 

clear from some of the very large enrichment ratios 

listed in table 11 that anthropogenic fluxes to the recharge basin far exceed natural fluxes for several 

trace metals that are in widespread industrial use. 

Results for three elements at this recharge basin 

(copper=25, lead=9, and zinc=38) can be compared 

with the enrichment ratios for these same elements 

(Cu=6, Pb=15, and Zn=5) in sediment from Irondequoit Bay, New York (Schroeder, 1985), which also 

was one of the NURP study sites (Kappel and others, 

1986).

The results for four elements (As, Cu, Pb, and Ni) 

from this study also can be compared with those from 

a previous investigation at five other recharge basins 

in the city of Fresno, the oldest of which has been in 

use for about 20 years. The five basins are in

predominantly residential catchments that include 

some commercial land use and minimal industry. 

Surface-enrichment ratios, calculated by comparing 

published data for depths of 0-2 and 90-120 cm in the 

five basins (Nightingale, 1987b), range from 1 to 18 

for arsenic, 3 to 13 for copper, 60 to 400 for lead, 

and 2 to 4 for nickel. Values for this study (table 11) 

are arsenic =16, copper = 25, lead = 9, and nickel = 

7. Enrichments are greater for the trace metals copper 

and nickel and much less for lead in the industrial 

catchment in comparison with the residential/commercial catchments, a pattern which is similar 

to that found during direct monitoring of runoff in the 

NURP study (Oltmann and Shulters, 1989).

Surface-enrichment ratios can be calculated 

similarly for organic priority pollutants and organochlorine compounds; however, the calculations yield 

only minimum estimates of 102 and 103, respectively, 

because these compounds are below detection levels 

in the deeper sediment. Organic carbon, analyzed by 

combustion and by GC-FID (fig. 4 and table 9), also 

yields surface-enrichment ratios of almost 103 ; for 

organic carbon, detectable concentrations exist below 

16 cm for both methods of analysis.

The data presented and the foregoing discussion 

indicate that a wide variety of trace elements and synthetic organic chemicals from the industrial catchment 

are removed within the top 16 cm of sediment in the 

recharge basin. Given the existence of nearly 8 m of 

soil between the basin and the water table and such 

effective removal of contaminants for the 4 years of 

operation in the basin's current configuration (since 

last scraped), local ground-water quality should be 

afforded protection during continued operation of the 

basin for a very long time. A similar inference can 

be made on the basis of results of studies at five other 

recharge basins in the city of Fresno (Nightingale, 

1987a,b,c, and 1989) although it was suggested by 

Nightingale (1989) that periodic monitoring of 

organic contaminants in soil would be advisable 

because of their known presence in storm runoff.

LABORATORY ELUTRIATION EXPERIMENTS

The potential for movement of urban-runoff 

contaminants through the unsaturated zone can be 

evaluated by means of laboratory experiments that 

simulate processes of sorption from the aqueous onto 

the solid phase and desorption from the solid into the 

aqueous phase. Both types of experiments were done 

for this study. As conducted, the experiments were 

intended to provide only a qualitative rather than a 

quantitative assessment. They, were adapted from

26 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Table 12. Chemical concentrations in water from the recharge basin equilibrated (mixed for 0, 1,2, and 

4 days) with surface (0-1 centimeter) sediment from near site 5 in the recharge basin

[Water from recharge basin collected April 29, 1986, and stored frozen until beginning of laboratory experiment 4 months 

later. jaS/cm, microsiemens per centimeter at 25° Celsius; mg/L, milligrams per liter; Mg/L, micrograms per liter; --, no data; 

<, less than indicated reporting limit]

Constituent

Equilibration time

Oday 1 day 2 days 4 days

Specific conductance ((aS/cm)

pH (standard units)

Calcium (mg/L)

Magnesium (mg/L)

Sodium (mg/L)

Potassium (mg/L)

Chloride (mg/L)

Sulfate (mg/L)

Silica (mg/L as SiO2)

Alkalinity (mg/L as CaCO3)

Ammonium (mg/L as N)

Kjeldahl nitrogen (mg/L as N)

Nitrate + nitrite (mg/L as N)

Orthophosphate (mg/L as P)

Organic carbon (mg/L as C)

Arsenic (Mg/L)

Boron ((Mg/L)

Cadmium (Mg/L)

Chromium (Mg/L)

Cobalt (Mg/L)

Copper (Mg/L)

Iron (Mg/L)

Lead (Mg/L)

Manganese (Mg/L)

Mercury (Mg/L)

Molybdenum (Mg/L)

Nickel (Mg/L)

Zinc (Mg/L)

Tannin & lignin (mg/L as

tannic acid)

Phenols (Mg/L as phenol)

MBAS detergents (mg/L)

346

6.2

8.0

5.0

16

26

21

33

5.9

7

11

15

<.l

5.0

24

3

80

1.4

2.2

.5

10.0

140

1.4

40

.1

2

5.7

30

4.3

2

.09

638

7.7

29

--

22

--

23

120

11

8

26

48

<.l

2.7

--

--

-

-

--

-

--

6,300

~

370

--

--

--

540

--

--

--

660

6.9

25

--

21

--

22

120

14

8

25

42

.2

3.5

--

~

--

--

--

4,300

330

-

-

290

-

--

~

696

7.3

29

13

22

30

24

110

16

--

29

41

<.l

4.2

66

11

620

.15

2.1

1.5

3.1

1,000

2.7

290

<.l

9

10

110

9.0

18

.27

methods commonly used to determine sorption 

isotherms (Harter, 1983) and from elutriation tests 

used to determine short-term water-quality conditions 

associated with dredging operations (Fuhrer and 

Rinella, 1983; Palermo, 1986). In one set of 

experiments, samples of highly contaminated surface 

sediment from the recharge basin were mixed with 

water from the recharge pond to test the ability of the 

sediments to desorb contaminants into the water with 

which it is in contact. In another experiment, water 

from the recharge basin was mixed with clean soil 

from the unsaturated zone deep beneath the recharge 

basin to examine the potential for removal of aqueous 

contaminants by the soil.

Water for the experiment was collected from the 

recharge basin on April 29, 1986, and stored frozen 

until its use 4 months later. It generally was similar in 

composition to water collected from the basin on 

January 29, 1986, as indicated by comparison of 

chemical concentrations in tables 6 and 12 (in table 

12, see values for zero-day equilibration time). The 

most obvious difference between the two samples is 

the absence of nitrate (plus nitrite, which likely is 

negligible) in the water used for the laboratory 

experiment. Although this difference may be a 

consequence of seasonal variations, it seems more 

likely that it is the result of biological degradation 

because the water used for the laboratory experiment

Laboratory Elutriation Experiments 27
Table 13. Chemical concentrations in water from the recharge basin equilibrated (mixed for 4 days) with 

aquifer soil from 10.9-11.3 meters in test hole 1, in deionized water equilibrated (mixed for 4 days) with 

surface (0-1 centimeter) sediment from near site 5 in the recharge basin, and in a deionized-water blank

[uS/cm, microsiemens per centimeter at 25° Celsius; mg/L, milligrams per liter; ug/L, micrograms per liter; , no data; <, 

less than indicated reporting limit. MBAS, methylene blue active surfactants.]

Constituent

Specific conductance ((iS/cm)

pH (standard units)

Calcium (mg/L)

Magnesium (mg/L)

Sodium (mg/L)

Potassium (mg/L)

Chloride (mg/L)

Sulfate (mg/L)

Silica (mg/L as SiO2)

Alkalinity (mg/L as CaCO3)

Nitrite + nitrate (mg/L as N)

Ammonium (mg/L as N)

Kjeldahl nitrogen (mg/L as N)

Orthophosphate (mg/L as P)

Organic carbon (mg/L as C)

Arsenic (ug/L)

Boron (|ig/L)

Cadmium (ug/L)

Chromium (ug/L)

Cobalt (ug/L)

Copper (ug/L)

Iron (ug/L)

Lead (ug/L)

Manganese (ug/L)

Mercury (ug/L)

Molybdenum (ug/L)

Nickel (ug/L)

Zinc (ug/L)

Tannin & lignin (mg/L as

tannic acid)

Phenols (ug/L as phenol)

MBAS detergents (mg/L)

Basin water 

equilibrated 

with 

aquifer soil

548

7.8

35

18

29

14

27

130

38

139

<.l

13

20

2.1

39

35

320

.66

1.2

10

4.5

150

.30

890

--

18

58

30

4.1

6

.09

Deionized water 

equilibrated 

with basin 

sediment

197

7.1

10

5.0

4.0

7.8

3.5

11

9.9

82

<.l

12

20

3.9

16

12

60

.4

2.2

1.0

4.5

850

3.4

140

<.l

5.0

8.6

50

7.4

4

.36

Deionizedwater 

blank

2

6

<.l

<.l

.4

.3

<.l

.2

<.l

2

<.l

.03

.7

.041

--

<1

10

.02

.06

<.20

--

10

.20

<10

<.l

<1

<.5

<10

--

--

was neither preserved with the mercuric chloride 

biocide nor filtered prior to its storage for later use.

One experiment was carried out by using a 

magnetic stirrer to continuously mix recharge-basin 

water and recharge-basin surficial sediment, in an 

approximately 10-to-l gravimetric ratio, for as long as 

4 days. The sediment-water slurry was contained in a 

covered, cylindrical glass chromatography jar and was 

continuously bubbled with nitrogen gas to maintain an 

oxygen-free environment throughout the experiment. 

Aliquots for chemical analysis were removed after 1, 

2, and 4 days. The aliquots (also the initial, or zeroday, water) were centrifuged for 1 hour at 5,000 times

gravity, but they were not filtered. Although the 

solutions appeared visually to be free of suspended 

solids, the possible presence of colloidal material 

cannot be excluded. The increase in specific conductance from 346 to 638 uS/cm after 1 day, and a 

smaller increase to only 696 uS/cm after 4 days (table 

13) shows that dissolution is initially rapid and then 

slows.

Calcium and sulfate were the main contributors to 

the increase in specific conductance. Despite a very 

large increase in dissolved (supernatant after centrifugation) iron and manganese during the experiment, 

the increase in all other cationic trace-metal concen28 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
trations, with the exception of zinc, was 

comparatively modest. Most chemical concentrations 

changed little between days 1 and 4. Iron is an 

obvious exception its concentration decreased from 

6.3 to 1.0 mg/L during this period. Failure of the 

needle valve that regulated release of nitrogen gas 

several hours before termination of the experiment 

may have allowed entrance of some oxygen to the 

chamber, with the consequent precipitation of iron.

Increases were measured in tannin and lignin, 

total phenols, and MB AS detergents during the 4-day 

experiment. However, given the potential for 

analytical artifacts in the colorimetric methods used 

for these broad-indicator constituents (Wershaw and 

others, 1987), their precise concentrations and 

detection at these low concentrations is uncertain. 

Nightingale (1989) reported the movement of phenols 

in soil moisture beneath one recharge basin in the city 

of Fresno that had very coarse substrata. The 

solubility and negative polarity of phenols make them 

one of the few relatively mobile classes of compounds 

analyzed for in this study. However, specific phenols 

were not detected in sediment samples from the 

recharge basin (table 10) and, therefore, their presence 

and downward transport remain uncertain.

Surficial sediment for the laboratory experiment 

was taken from a location near site 5 in the recharge 

basin and was collected in a slightly different manner 

than was used for all other samples of surficial 

sediment described elsewhere in this report. Instead of 

removing the entire 1-cm-thick polygonal plate, the 

sample was obtained by scraping the sediment surface 

with a Teflon-coated spatula at several locations over 

a wide area near site 5. Chemical composition of this 

composite sample (table 14) is remarkably similar to 

composition of the duplicate samples from 0 to 1 cm 

at site 5 (tables 8 and 9). For 35 detectable elements, 

the average (unsigned) difference in concentration is 

5.4 percent between the duplicate samples and only 

slightly larger at 7.7 percent between the composite 

sample and the mean value of the duplicate samples.

In addition to the equilibration between surface 

sediment and water from the recharge basin, the 

sediment also was mixed with deionized water for 

about 4 days as a further check for desorption of 

contaminants into the aqueous phase. The results 

given in table 13 (results for a deionized-water blank 

also are shown in the table) lead to the conclusion 

already stated that evidence exists for possible transfer 

of some chemical constituents from sediment to the 

aqueous phase. Wigington and others (1983) also 

reported the potential for leaching of four inorganic

Table 14. Concentrations of elements in 

recharge-basin sediment and in aquifer soil used 

for the laboratory elutriation tests

[Concentrations in micrograms per gram dry weight. 

Sediment is from top 1 centimeter near site 5; soil data, 

also given in table 7, are from depth of 10.9-11.3 meters in 

test hole 1. <, less than indicated reporting limit]

Concentration

Element

Aluminum

Arsenic

Barium

Beryllium

Bismuth

Boron

Cadmium

Calcium

Cerium

Chromium

Cobalt

Copper

Europium

Gallium

Gold

Holmium

Iron

Lanthanum

Lead

Lithium

Magnesium

Manganese

Mercury

Molybdenum

Neodymium

Nickel

Niobium

Phosphorus

Potassium

Scandium

Selenium

Silver

Sodium

Strontium

Tantalum

Thorium

Tin

Titanium

Uranium

Vanadium

Ytterbium

Yttrium

Zinc

Symbol

Al

As

Ba

Be

Bi

B

Cd

Ca

Ce

Cr

Co

Cu

Eu

Ga

Au

Ho

Fe

La

Pb

Li

Mg

Mn

Hg

Mo

Nd

Ni

Nb

P

K

Sc

Se

Ag

Na

Sr

Ta

Th

Sn

Ti

U

V

Yb

Y

Zn

Basin 

sediment

74,000

18

710

1

<10

2.6

2

16,000

57

87

17

140

<2

17

<8

<4

38,000

33

170

46

14,000

630

.27

4

21

66

7

2,000

22,000

10

.8

<2

14,000

270

<40

29.0

<10

3,200

11.4

97

2

15

1,200

Aquifer 

soil

89,000

4.2

510

<1

<10

1.9

<2

24,000

37

140

19

26

<2

16

<8

<4

38,000

19

14

30

15,000

590

<.02

<2

18

140

5

300

18,000

14

<.2

<2

19,000

280

<40

4.7

<10

3,100

2.24

91

2

17

69

urban contaminants (Cd, Cu, Pb, and Zn) from 

sediment in a recharge basin in Washington, D.C. 

They found that as much as 2 percent of these

Laboratory Elutriation Experiments 29
elements was removed by a 0.01 M Ca(NO3)2 solution; 

of the four elements tested, zinc was the most readily 

solubilized. Because solid-phase concentrations 

typically exceed aqueous concentrations by three 

orders of magnitude or more, the amount leached 

during the experiment represents a very large input to 

the aqueous phase. However, their experimental 

procedure likely overstates the potential for leaching 

in the environment because Ca(NO3 )2 is expected to 

hydrolyze to form a weakly acidic solution.

For the laboratory experiment in which water 

from the recharge basin was mixed with natural uncontarninated soil, the core from a depth of 10.9-11.3 

m in test hole 1 was selected. Soil from this depth 

was chosen because its generally higher silt-plus-clay 

content in comparison with other, sandier, core 

samples (table 4) would be expected to favor 

increased sorption. Results from this experiment to 

check for removal of aqueous contaminants by clean 

soil were inconclusive. An increase in mineral 

dissolution, as indicated by the increase in specific 

conductance from 346 (table 12) to 548 uS/cm (table 

13), was measured. The major ions that showed the 

largest increase are calcium, sulfate, and bicarbonate 

(alkalinity).

Concentrations of many minor constituents, 

including tannin and lignin and MBAS detergents, 

changed little. Some constituents, such as phenols and 

arsenic, actually show substantial increases. The 

increase from 2 to 6 ug/L for phenols is, if anything, 

another indication of the uncertainty in the colorimetric test for phenols at this low level. And the 

increase in arsenic from 3 to 35 ug/L indicates the 

potential for leaching of selected trace elements from 

even uncontaminated soil.

In summary, the batch-elutriation experiments 

done for this study demonstrate the potential for 

leaching of urban-runoff contaminants as water in 

recharge basins infiltrates the basin's sediment. 

However, the results of similar experiments to test the 

ability of uncontaminated substrata to remove those 

contaminants were inconclusive in part, because of 

the significant natural abundances of some inorganic 

elements; because of limitations on the colorimetric 

methods used to analyze broad organic indicators; and 

because of the possible presence of colloidal material

in the centrifuged elutriate itself. Theoretical consideerations based on the physical and chemical properties 

of contaminants in a circumneutral (or slightly 

alkaline) environment and monitoring of soil moisture 

and ground-water chemistry provide more reliable 

support for evaluating transport of urban-runoff 

contaminants to the water table than do the results of 

these elutriation experiments. The observation that 

concentration gradients show a sharp decrease in 

sediment beneath the recharge basin, and the likelihood that water-infiltration rates are sufficiently slow 

for the soil moisture to, in effect, undergo a series of 

"batch-removal" processes as it percolates downward 

through the soil, ensures the effective removal of all 

urban runoff contaminants, with the possible 

exception of those having negative charge (anions) or 

negative polarity.

Perhaps the most important finding obtained from 

these laboratory experiments comes from analyses of 

the sediment and soil before (table 14) and after (table 

15) the elutriation tests. The data in table 14 were 

obtained from complete mineral digestion with strong 

acids, whereas those in table 15 are based on 

oxidation of organic matter with H2O2 followed by 

only partial digestion with 0.3M HCL (Fishman and 

Friedman, 1989). The mild-acid digestion is intended 

to remove only surface layers while leaving the 

aluminosilicate mineral matrix itself largely intact. 

Among the alkali- and alkaline-earth elements, the 

mild-acid treatment removed virtually no calcium, 

magnesium, and sodium but did leach a substantial 

proportion of the total potassium. Percent recoveries 

from the contaminated basin sediment at 0 to 1 cm 

near site 5 and from clean aquifer soil at 10.9-11.3 m 

in test hole 1 can be obtained by dividing 

concentrations for partial digestion (table 15) by 

concentrations for complete digestion (table 14). 

Results of this calculation for several elements are 

summarized in table 16. These results show that a 

number of elements having high enrichment ratios 

(the contaminants in urban runoff) are almost entirely 

recoverable by the mild treatment and therefore are 

presumed to be present in surface coatings on mineral 

grains and in organic matter (Horowitz and Elrick, 

1987). Percent recoveries for mild-acid digestion of 

the uncontaminated aquifer soil are somewhat less, 

but they also indicate that a substantial proportion of 

selected trace elements is likely associated with

30 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
Table 15. Concentrations of chemical constituents in recharge-basin sediment and aquifer soil after the 

laboratory elutriation tests

[Element concentrations, in micrograms per gram dry weight, are based on analysis of mild-acid leachate from sediment 

and soil. Pesticide concentrations are in micrograms per kilogram dry weight.]

Basin sediment 

Constituent equilibrated with 

deionized water

Calcium 

Magnesium

Sodium

Potassium

Aluminum

Arsenic

Boron

Cadmium

Chromium

Cobalt

Copper

Iron

Lead

Manganese

Mercury

Molybdenum

Nickel

Zinc

Nitrite + nitrate

(asN)

Ammonium (as N)

Kjeldahl nitrogen

(asN)

Phosphorus (as P) 

Organic carbon

(asC)

Inorganic carbon

(asC)

Oil and grease

10

<10

8,400

22,000

15

20

5

40

<50

180

36,000

200

580

.24

3.8

50

1,600

6,000

380

13,000

2,300 

140,000

100

20

Aquifer soil 

equilibrated with 

basin water

Basin sediment Aquifer soil 

Constituent equilibrated with equilibrated with 

deionized water basin water

<10 Organochlorine Compounds

<10

3,300

8,200

4

<10

<1

20

<50

17

13,000

<10

260

.02

<1

60

35

3,000

160

460

1,000 

3,000

100

<1

Aldnn

Lindane

Chlordane

DDD

DDE

DDT

Dieldrin

Endosulfan

Endrin

Ethion

Toxaphene

Heptachlor

Heptachlor epoxide

Methoxychlor

PCN

PCB

<0.1 <0.1

51 <.l

<1 1

17 .8

50 .6

.6 <.l

5.3 <.l

10 <.l

<.l <.l

<.l <.l

<10 * <10

52 <.l

8.1 <.l

<.l <.l

<1 <1

26 <1

Organophosphorus Insecticides

Malathion

Parathion

Diazinon 

Methyl parathion

Mirex

Ethyl trithion

Methyl trithion

Perthane

<0.1 <0.1

<.l <.l

<1 <1

<.l <.l

<.l <.l

<.l <.l

<1 <1

Table 16. Percent extractable for selected 

elements in recharge-basin sediment and aquifer 

soil by digestion with hydrogen peroxide plus mild 

acid

[Calculated from data in tables 14 and 15. Basin 

sediment is from top 1 centimeter near site 5, and aquifer 

soil is from 10.9-11.3 meters in test hole 1. >, greater 

than; <, less than; , indeterminate value]

Element

Aluminum (Al)

Arsenic (As)

Chromium (Cr)

Copper (Cu)

Iron (Fe)

Lead (Pb)

Manganese (Mn)

Mercury (Hg)

Nickel (Ni)

Potassium (K)

Zinc (Zn)

Percent

Basin

sediment

30

83

46

>100

95

>100

92

89

76

38

>100

extractable

Aquifer

soil

9

>100

14

69

34

<71

44

43

18

51

hydrous ferromanganese oxides present either as 

coatings on mineral grains or disseminated throughout 

the uncontaminated soil.

TRANSPORT AND LOADING OF 

CONTAMINATED SEDIMENT

When results of this study are compared with 

results from the NURP study, some differences 

emerge that raise questions about how contaminants 

in the urban environment are delivered to the recharge 

basin and about the quantity of contaminants actually 

present in the basin. Although these are important 

questions, it is emphasized that they do not change 

this study's principal conclusion that urban contaminants are not reaching the ground water, nor do they 

affect sediment-disposal considerations (following 

periodic scraping of the basin's floor) that are based 

on compliance with sediment-quality criteria or 

standards.

Transport and Loading of Contaminated Sediment 31
Table 17. Annual loads to the industrial recharge basin determined from runoff monitoring and sediment 

inventories

[Annual loads in kilograms per year. Inventory loads are converted to values based on mild-acid, partial digestion (see text) 

for direct comparison with runoff loads, adjusted to mean annual rainfall in Fresno, obtained by Oilman and Shulters (1989)]

Element

Aluminum (Al)

Arsenic (As)

Organic carbon (as C)

Chromium (Cr)

Copper (Cu)

Iron (Fe)

Lead (Pb)

Manganese (Mn)

Mercury (Hg)

Nickel (Ni)

Zinc (Zn)

Sediment

Annual

Runoff

340

.93

11,000

1.1

3.5

570

4.5

19

.013

1.3

26

30,000

load, determined from:

Inventory

1,300

.57

5,700

1.8

5.1

2,000

7.0

33

.0088

2.3

38

56,000

Inventory/runoff 

ratio

3.7

.6

.5

1.6

1.5

3.5

1.6

1.8

.7

1.8

1.4

1.8

COMPARISON OF BASIN-SEDIMENT INVENTORIES 

AND STORM-RUNOFF LOADS

Storm-runoff loads to the industrial basin, calculated from average-annual constituent loads estimated 

by Oltmann and Shulters (1989, table 25) on the basis 

of monitoring for the NURP study during the 1981-82 

and 1982-83 wet seasons, are given in table 17. 

Quantities of constituents found in this study to have 

accumulated in the recharge-basin's sediment during 

operation in its present configuration from 1982 to 

1986 also are given in the table. In order to compare 

annual loads estimated by means of the two methods, 

it is necessary to adjust the sediment inventories for 

differences in recovery between the mild-acid 

digestion used during the NURP study to analyze 

runoff samples and the complete mineral digestion 

used in this study to analyze basin sediment. This was 

done by multiplying total-constituent amounts mea 

sured in the sediment by recovery percentages from 

the "Basin sediment" column in table 16, thereby 

providing a comparison that is based on element 

recoveries from the partial-digestion analytical 

method. [Alternatively, an equivalent comparison 

could be based on loads determined from completedigestion methods by dividing the runoff-load values 

of Oltmann and Shulters (1989) reproduced in table 

17 by the recovery percentages.] Complete recovery 

(100 percent) was used in the calculation for organic 

carbon, copper, lead, and zinc. The concentration

profiles at site 5, given in table 9, were 

used to calculate constituent quantities in the basin 

sediment. Quantities are calculated by multiplying 

concentrations, basin area, sediment dry-bulk density, 

and subbottom depth. The error that is propagated by 

uncertainty in each of these parameters is discussed 

below.

The uncertainty in element concentrations that 

results from analytical imprecision is small: an 

average of only about 5 percent on the basis of 

analysis of duplicate samples. The error that results 

from spatial variability in concentration is much 

greater: as much as a factor of about 2 (100 percent) 

for many of the urban contaminants in surface 

sediment (0-1 cm) at six locations in the recharge 

basin (table 8). However, the effect of such large 

spatial variability is deceptive because nearly all of 

the basin floor's area is in the south end, where the 

variability obtained by comparing surficial 

concentrations at sites 5 and 6 is only about 5 percent 

(table 8), and by comparing concentrations at site 5 

with those from a broad area near site 5 (table 13) is 

only about 8 percent. The area of the basin floor that 

contains contaminated sediment is difficult to estimate 

because the sediment reaches an indeterminate 

distance up the sloping sides of the basin. The basinfloor area was measured in the field to be about 

3.72xl07 cm2 (40,000 ft2 or about 1 acre) with a 

possible error of about 25 percent.

32 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, industrial Catchment, Fresno
Sediment dry-bulk density (p in equation 1 later) 

was not measured in this study, but a value of 1.5 

g/cm3 was chosen because it was measured by 

Nightingale (1989) for a sediment with similar grainsize distribution from another recharge basin in the 

city of Fresno. True density of well-homogenized 

sediment samples is likely to differ little from this 

estimate, although minor fluctuations with depth can 

be expected. A far greater error arises from the 

unusual open texture of sediment in the top few 

centimeters referred to in the "Sampling of Sediment 

from the Recharge Basin" section of this report.

These irregularities in sediment texture, and 

thinning of the contaminated zone along the 

sideslopes and channel in the northern part of the 

basin, create a rather large uncertainty in precise 

assignment of subbottom depths as well as some 

ambiguity in choosing the maximum depth to be used 

in calculating sediment inventories. Four centimeters 

was chosen as the maximum depth to use because 

sediment below this depth contained no excess 

(atmospheric) lead-210 (210Pbxs).

When each of the various sources of error is 

considered, the accuracy of calculated annualcontaminant inventories in the sediment is thought to 

be no better than a factor of 2 or 3. As noted, most of 

the imprecision is attributable to uncertainty in the 

determination of depth and bulk density related to the 

unusual sediment texture. Guay and Smith (1988) also 

recognized the large error in simulating a relation 

between quantity and quality of storm runoff in the 

industrial catchment and therefore developed 

simulations for residential and commercial catchments 

only. Failure of their model for the industrial 

catchment may be caused by discharge from large 

point sources unrelated to rainfall, in contrast to 

residential and commercial catchments, where 

nonpoint (as numerous small-point) contributions 

predominate. Median errors using data from 

individual storms for their simulation in a commercial 

catchment were 11 percent for lead and 54 percent for 

suspended sediment. However, even these rather large 

errors in estimating urban-runoff loads are much less 

than differences between the results obtained using 

the two methods described in this report. The 

differences for selected constituents are expressed as 

a ratio between the sediment-inventory and runoffmonitoring load and are given in table 17. Possible 

reasons for the differences include: (1) errors in one, 

or both, of the methods used to estimate annual loads; 

(2) real differences between the period of storm 

monitoring during 1981-83 and the period of sediment

accumulation during 1982-86; and (3) substantial 

delivery of sediment containing urban contaminants 

by some mechanism in addition to storm runoff, such 

as overland flow and erosion on the perimeter of the 

basin or atmospheric transport (dryfall).

Contaminated sediment contained in the recharge 

basin exceeds the amount delivered as suspended 

sediment in storm runoff by a factor of 1.8 (table 17). 

The difference is only slightly less for several 

elements (Cr, Cu, Pb, Mn, Ni, and Zn), possibly 

reflecting minor dilution with sediment (soils or 

substrata) containing little or no urban contaminants. 

The close similarity in loading patterns for these 

elements and for sediment is especially surprising 

given the very different procedures and assumptions 

used to obtain the two estimates. These results 

suggest that a single explanation may exist for the 

differences, such as a systematic error in the estimated 

quantity of sediment. Furthermore, there are simple 

explanations to reconcile inventory-runoff differences 

that are either much greater (aluminum and iron) or 

much less (arsenic, organic carbon, and mercury) than 

1.8 for five other elements.

The amount of recoverable aluminum and iron 

contained in basin sediment relative to runoff 

apparently is overestimated because the digestion 

procedure produced uncharacteristically high 

recoveries for the strongly anaerobic sediments from 

the basin in comparison with the much lower 

recoveries of both aluminum and iron for clean 

aquifer soil (table 16). Possible explanations for those 

elements that appear to be depleted in the basin 

sediment (arsenic, organic carbon, and mercury) are 

much more varied.

The subbottom concentration profile from site 5 

(table 9 and fig. 4) clearly shows that some arsenic 

has migrated beyond the 4-cm depth. The amount of 

arsenic that migrated was not included in the 

inventory calculation, which was cut off at 4 cm to 

maintain internal consistency among all elements. The 

greater mobility for arsenic, in comparison with many 

other trace elements that exist as cations, may be 

attributed to its possible existence as the more soluble 

oxyanion.

Mercury concentrations are so low that analytical 

errors and loss during storage and processing of the 

sediment samples must be considered; however, 

natural loss by volatilization of the element or its 

methylated form within the basin (Compeau and 

Bartha, 1985) also is possible.

Transport and Loading of Contaminated Sediment 33
Because the concentration of dissolved organic 

carbon in soil water (and ground water) generally is 

low and sorption of organic carbon to solid-particle 

surfaces typically is high, transport of organic carbon 

with downward-percolating recharge is likely to be a 

minor mechanism for its removal. The main removal 

mechanism for organic carbon is believed to be 

biological degradation within the subbottom sediment; the data in table 17 indicate that at least onehalf the organic carbon delivered in runoff must be 

decomposed. In fact, the fraction of organic carbon 

actually mineralized (degraded) must be even greater 

than one-half because not only allochthonous carbon 

in runoff but also autochthonous carbon produced 

biologically within the pond itself is delivered to the 

subbottom sediment. The basin receives an average 

annual load of 730 kg total nitrogen. Dissolved 

phosphorus also was noted to be especially high in 

runoff from the industrial catchment in comparison 

with runoff from the residential and commercial 

catchments (Oltmann and Shulters, 1989). It is this 

rich supply of nutrients which results in the deep 

green color (from algae) of the pond itself and in the 

existence of strongly anaerobic sediment beneath the 

basin, and which provides an environment that 

supports extensive degradation of organic carbon.

LEAD-210 CONSTRAINTS ON ORIGIN AND LOADING 

OF CONTAMINATED SEDIMENT

Lead-210 occurs naturally as a product of the 

uranium-238 decay series and has a half-life of 22 

years. Lead-210 has been used widely for dating 

lacustrine and coastal sediments that have 

accumulated during the last 100 years (Faure, 1977). 

For this study, the primary purpose in obtaining 210Pb 

data was to ascertain the maximum depth at which 

inorganic elements from urban runoff occur in basin 

sediment. This radioisotope is especially well suited 

to this purpose because (1) its chemical and physical 

properties are expected to be similar to those of other 

inorganic cations, especially nonradiogenic lead, and 

thus it would be expected to transport similarly and 

(2) that portion of the sedimentary 210Pb derived from 

atmospheric fallout, the 210Pbxs (excess lead-210), will 

be completely absent in the much older substrata that 

lie beneath the basin's recently deposited sediment if 

no downward transport of the isotope has occurred. 

Lead-210 also may provide useful insight into the 

origin (mechanism of delivery) and loading of urbancontaminated sediment to recharge basins.

Atmospheric 210Pb is produced when 226Ra in the 

Earth's crust decays to 222Rn, an inert gas that effuses 

into the atmosphere, where it subsequently decays 

through a series of very-short-lived daughters to 210Pb 

and falls back to the Earth's surface. Because secular 

(long-term) equilibrium is presumed to exist between 

sedimentary (or soil) 226Ra and its decay products, the 

210Pbxs activity can be calculated as total 210Pb activity 

minus 226Ra activity (see Graustein and Turekian, 

1986, for a more complete discussion). For this study, 

activities are given in dpm (disintegrations per 

minute), which can be converted to other units of 

activity commonly used in the literature with the 

relation: 1 pCi (picocurie) = 2.2 dpm = 37 mBq 

(millibecquerels). Crustal variations in concentration 

of the parent isotope from which 210Pb is derived and 

rapid removal of 210Pb from the atmosphere in 

comparison with global circulation times causes 

regional variations in the flux of atmospheric 210Pb. 

On the basis of measurements in soil and 

precipitation, Moore and Poet (1976) reported values 

of 0.53 to 1.0 (dpm/cm2)/yr for oceanic fluxes, 0.8 to 

2.0 (dpm/cm2)/yr for continental fluxes in the north 

temperate zone, and 1.6 (dpm/cm2)/yr from surfacesoil profiles in Colorado, Texas, and Kansas. 

Graustein and Turekian (1986) reported values 

ranging from 0.6 to 1.2 from undisturbed soil in 19 

locations throughout the central and eastern United 

States. Published data from several locations on the 

west coast yield a range of about 0.2 to about 0.7 

(dpm/cm2)/yr, with latitude, longitude, and precipitation quantity influencing the flux (Fuller and 

Hammond, 1983) and a value of about 6 

(dpm/cm2)/yr in Emerald Lake (calculated from data 

in Holmes and others, 1989, fig. 2). Although 

Emerald Lake is only 110 km east-southeast of Fresno 

in an alpine watershed on the west slope of the Sierra 

Nevada, its high ratio of watershed to lake area 

(almost 50) and the steep slopes of this cirque lake 

are likely to result in an anomalously high 

atmospheric-flux estimate. Although data are not 

available for the city of Fresno, proximity to the 

Pacific Ocean suggests that the 210Pb flux should be 

near the low end of the range of continental values 

and likely no greater than about 1 (dpm/cm2)/yr. Data 

from undisturbed soil or from atmospheric precipitation (wet and dry deposition) in the Fresno area 

would be needed to determine the local flux more 

accurately.

Annual deposition of 210Pbxs in a sediment profile 

can be calculated from:

34 Potential for Chemical Transport Beneath Storm-Runoff Recharge (Retention) Basin, Industrial Catchment, Fresno
210Pb flux =

l-e

where A, is the decay constant (0.0311 yr" 1 ), p is dry: 

bulk density (1.5 g/cm3), t is 4 years, and the other 

terms are defined in the following paragraph. The 

above formulation yields the same result as an 

alternative method chosen to illustrate more clearly 

the effect of errors in basin area and sediment mass 

on the result. The method also is analogous to that 

used for calculating element inventories in table 17.

Annual deposition of 210Pbxs to the basin also can 

be calculated by substituting data (in table 9) from 

site 5, where a complete activity profile exists, into 

the equation:

210Pbxs flux = xs t-A-L rPbJL, , (2)

where [21°Pbxs] 

A

L

M 

t

is the activity in sediment interval i, 

is the length of sediment interval i 

is the sediment depth (4 cm) to which

210Pbxs is present, 

is mass of sediment in the basin, 

is length of time (4 years) the basin has

been operated since last scraped, and 

is area of the basin (3.72xl07 cm2).

Using the estimated sediment-accumulation rate (M/t) 

of 56,000 kg/yr given in table 17, and adjusting 

upward for the small amount of decay that took place 

during 4 years, yields a 210Pbxs deposition rate of 6.4 

(dpm/cm)2/yr. This value is markedly higher than the 

expected atmospheric flux of about 1 (dpm/cm2)/yr. 

Fluxes determined from sediment data in surfacewater bodies often are higher than atmospheric 

deposition rates and the difference is attributed to 

sediment "focusing" the preferential scavenging on 

fine-grained material at the location of the cored 

sediment. For example, in four cores from the NURP 

study site in Irondequoit Bay, New York, fluxes were 

found to range from about 1 to 3 (dpm/cm2)/yr 

(Schroeder, 1985). The spatial trend shown by 

surficial activities that are given in table 8 provides 

evidence that focusing occurs in the recharge basin.

However, the equation above hints at a simpler 

explanation that reconciles the difference a decrease 

in the sediment mass by a factor of 2 and an increase 

in the effective basin area by a factor of 3.

Monitoring of suspended-sediment concentration 

in runoff yielded the lower estimate (in relation to 

inventory estimate) for average annual sediment 

delivered to the recharge basin, and because total 

rainfall in Fresno during 1982-86 was only a little 

above average, annual sediment deliveries during this 

period also should be near the annual average. 

Erosion from the sideslopes and perimeter to the floor 

of the recharge basin plausibly could increase the 

effective area of deposition by a factor of 3 (compare 

total basin area to bottom area in figure 2). Such 

sediment may have been deposited initially as dryfall, 

whose contribution must be small in comparison with 

that of runoff, or the pattern and level of 

contamination in the dryfall and overland flow on the 

sideslopes must be similar to that in runoff in order to 

maintain the similarity in pattern shown by several 

different elements that is indicated in table 17.

The discussion above illustrates how, with 

relatively few measurements in comparison with much 

more intensive monitoring of runoff, reasonable 

estimates can be obtained for the quantity of 

contaminated sediment in an urban-runoff recharge 

basin. More detailed studies are needed to refine and 

test the validity of the method. Such studies might 

preferably be done in turfed basins that have been 

operated for a much longer time than was the subject 

basin in this study, thereby minimizing possible 

effects of erosion from the sides of the basin and 

providing a much thicker sediment veneer in which 

depths and bulk density could be measured more 

accurately.

SUMMARY AND CONCLUSIONS

Previous monitoring of storm-runoff quantity and 

quality, during 1981-83, in Fresno revealed elevated 

concentrations of urban contaminants in residential, 

commercial, and industrial catchments. The monitoring was accompanied by studies that confirmed the 

presence of these contaminants within the top few 

centimeters of sediment beneath recharge basins 

constructed to dispose of runoff from residential and 

commercial catchments. This study extends those 

previous studies to a 0.4-ha industrial-catchment basin 

where some urban contaminants were expected to be

Summary and Conclusions 35
present at even higher concentrations than in 

residential- and commercial-catchment basins. This 

study also shows that a wide variety of inorganic and 

organic contaminants generated in the 1.13-km2 

industrial catchment are removed by sorption within 

the top 4 cm of sediment in the recharge basin, and 

that the contaminants have not degraded ground-water 

quality beneath the basin.

The absence of local ground-water-quality 

impairment is documented by comparing chemical 

concentrations in two water-table monitoring wells to 

aqueous concentrations in the recharge basin. Shallow 

ground water near the basin contains a significant 

proportion of partly evaporated runoff from the basin 

as shown by measured delta-deuterium values of 

about -50 permil in both monitor wells in comparison 

with reported values of about -90 permil in regional 

ground water and -16 permil in the recharge basin 

itself. Because aqueous zinc concentration is about 

100 times higher in the recharge basin than in the 

monitor wells, this element is an especially sensitive 

surrogate for assessing potential ground-water degradation by inorganic cations. Organic contaminants 

either were absent or were detected at such low 

concentrations (near reporting limits) that evidence for 

their presence in the monitor wells is questionable.

The range in chemical concentration of many 

urban contaminants in surface (0-1 cm) sediment from 

six locations on the floor of the recharge basin was a 

factor of about 2. Concentrations were lowest in 

channels at the north end of the basin nearest the pipe 

from which runoff discharges, and highest at the 

south end in the broad, topographically lowest part of 

the basin. The proportion of fine sediment also is 

highest at the south end, as would be expected. 

Profiles at a representative location in the south end 

of the basin show that concentrations of nearly all 

contaminants decrease to background levels at a depth 

of 4 cm, which also was the maximum depth to 

which atmospheric 210Pb (excess 210Pb) penetrates; no 

contaminants generated in the urban environment 

were detected below a depth of 16 cm.

Surface-enrichment ratios, defined as the ratio of 

concentrations in the top centimeter to concentrations 

in substrata below 16 cm, provide a quantitative 

means to compare anthropogenic (human related) and 

natural sources. Accordingly, a ratio of 2 is consistent 

with equal inputs from human and natural sources. 

Twenty inorganic elements were found to have 

enrichment ratios of 2 or greater. The value for zinc, 

which had the highest ratio, was 38. Values for several other elements were: arsenic=16, chromium=5,

copper=25, lead=9, mercury>ll, nickel=7, phosphorus=5, and organic carbon«103 .

Enrichment ratios cannot be calculated for the 

approximately 20 organic compounds identified in 

sediment because the compounds are absent at depth. 

Nearly all the organic compounds detected in 

sediment are either organochlorine pesticides or 

polycyclic aromatic hydrocarbons. Among compounds 

in these two groups, chlordane and pyrene show the 

highest concentrations. Curiously, concentrations of 

the banned pesticide DDT exceed those of its possible 

metabolites DDD and DDE, a finding also noted in 

previous studies of urban runoff in the city of Fresno.

Estimates of sediment quantity and element load 

(total recoverable by mild-acid digestion) loads obtained in this study from a single core in the recharge 

basin exceed previously published estimates that were 

based solely on storm-runoff monitoring by a factor 

of 1.8. Possible explanations for this study's higher 

estimates are imprecision in the determination of 

sediment depths, the unusually open texture of the 

sediment veneer that had accumulated during the 4- 

year period the basin was operating, and thinning of 

the sediment layer in parts of the basin.

The flux of atmospheric 210Pb, calculated to be 6.4 

 (disintegrations per minute/cm2)/yr using data from 

the only core obtained in the basin, is much higher 

than the maximum expected atmospheric flux of 

about 1 (disintegrations per minute/cm2)/yr. This 

difference can be reconciled if 1982-86 sediment contained in the basin is reduced by half and if the 

effective area of deposition is increased to 3 times 

larger than the approximately 0.4-ha floor of the 

basin. Erosion from the perimeter and sideslopes of 

the basin could provide the additional area required. 

This discussion illustrates how acquisition of 210Pb 

data can be used to check estimated loads of sediment 

and urban contaminants delivered to recharge basins 

without the numerous analyses and intensive sample 

collection necessary to monitor runoff itself. However, 

additional data collection is needed to confirm and 

refine the method.

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