Evaluation of Sources of Nitrate Beneath Food 

Processing Wastewater-Application Sites near 

Umatilla, Oregon

Scientific Investigations Report 2009–5069

U.S. Department of the Interior

U.S. Geological Survey
This page intentionally left blank.
Evaluation of Sources of Nitrate Beneath 

Food Processing Wastewater-Application 

Sites near Umatilla, Oregon

By Lonna Frans and Anthony Paulson, U.S. Geological Survey; 

Phil Richerson, Oregon Department of Environmental Quality; 

Elise Striz and Curt Black, U.S. Environmental Protection Agency

Scientific Investigations Report 2009–5069

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Frans, Lonna, Paulson, Anthony, Richerson, Phil, Striz, Elise, and Black, Curt, 2009, Evaluation of sources of nitrate 

beneath food processing wastewater-application sites near Umatilla, Oregon: U.S. Geological Survey Scientific 

Investigations Report 2009-5069, 14 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Site Descriptions...................................................................................................................................2

Methods...........................................................................................................................................................2

Nitrate at Wastewater-Application Sites...................................................................................................5

Terrace Farm Site..................................................................................................................................5

North Farm Site .....................................................................................................................................8

Summary........................................................................................................................................................11

References Cited..........................................................................................................................................11

Figures

Figure 1. Map showing locations of the North Farm and Terrace Farm study sites in

the Umatilla River basin, Oregon ......................................................... 2

Figure 2. Map and cross section showing locations of (A) ground-water contours and

flow direction and (B) depths to water, nitrate concentrations, and apparent

recharge age at selected wells, Terrace Farm site, Umatilla River basin,

Oregon ....................................................................................... 3

Figure 3. Graph showing ratios of delta hydrogen-2 (δ2H) and delta oxygen-18 (δ18O)

for water samples from wells in the North Farm and Terrace Farm sites,

Umatilla River basin, Oregon ............................................................... 5

Figure 4. Graphs showing relations between (A) sulfate-chloride and (B)

calcium-delta oxygen-18 (δ18O) for water samples from wells, Terrace Farm

site Umatilla River basin, Oregon ......................................................... 6

Figure 5. Graph showing ratios of delta oxygen-18 (δ18O) and delta nitrogen-15 (δ15N)

for nitrates in samples compared with the range of ratios expected for

different sources of nitrate, Umatilla River basin, Oregon.............................. 7

Figure 6. Graph showing relation between nitrate delta nitrogen-15 (δ15N) and delta

oxygen-18 (δ18O) isotope ratios and fraction of water samples from wells,

Terrace Farm site, Umatilla River basin, Oregon ....................................... 8

Figure 7. Map and cross sections showing locations of (A) ground-water elevation

contours and flow direction and (B) depths to ground water, nitrate

concentrations, and apparent recharge age at selected wells, North Farm

site, Umatilla River basin, Oregon ......................................................... 9

Figure 8. Trilinear diagram showing cations for North Farm site water samples from

wells, Columbia River water, and process water from the wastewater-plant

clarifier, Umatilla River basin, Oregon ................................................... 9

Figure 9. Graph showing relation of sulfate and calcium from water samples from

wells at the North Farm site, Columbia River water, and process water from

the wastewater-plant clarifier, Umatilla River basin, Oregon ........................ 9

Figure 10. Graph showing relations between delta oxygen-18 (δ18O) and delta

nitrogen-15 (δ15N) of nitrate from water samples from wells, North Farm site,

Umatilla River basin, Oregon ............................................................... 10
iv

Conversion Factors, Datum, and Abbreviations and 

Acronyms

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

Volume

liter (L) 0.2642 gallon (gal)

cubic meter (m3) 264.2 gallon (gal) 

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter (m3) 0.0008107 acre-foot (acre-ft) 

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Tables

Table 1. Selected chemical and isotopic analyses and proportions of water attributed

to each end-member at the North Farm and Terrace Farm sites, Umatilla

River basin, Oregon ........................................................................ 4

Table 2. Difference of cations and anions in water from wells at the Terrace Farm

site, Umatilla River basin, Oregon ......................................................... 6

Table 3. Slope, intercept, and R2 value for EMMA-predicted versus actual

concentrations at the Terrace Farm site, Umatilla River basin, Oregon ............ 7

Table 4. Difference of cations and anions in water from well MW-10 compared to

wells MW-3, -4, -33 and 11-3 and -4 at the North Farm site, Umatilla River

basin, Oregon .............................................................................. 10
v

Conversion Factors, Datum, and Abbreviations and 

Acronyms—Continued 

Abbreviations and Acronyms

δ15N delta nitrogen-15 

δ18O delta oxygen-18 

‰ parts per thousand 

δ2H delta hydrogen-2 

3H/3He ratio of hydrogen-3 to helium-3

3H hydrogen-3

3He helium-3

δ3He delta helium-3

4He helium-4

N2 nitrogen gas

Ne neon

NH4 ammonium

NO3 nitrogen

mm micrometer

EMMA End-member mixing analysis

PCA principal component analysis 

SLAP Standard Light Antarctic Precipitation

USEPA U.S. Environmental Protection Agency

VSMOW Vienna Standard Mean Ocean Water
vi

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Abstract

Water samples from wells were collected beneath and 

downgradient of two food-processing wastewater-application 

sites near Umatilla, Oregon. These samples were analyzed 

for nitrate stable isotopes, nutrients, major ions, and agedating constituents to determine if nitrate-stable isotopes can 

be used to differentiate food-processing waste from other 

potential sources of nitrate. Major-ion data from each site 

were used to determine which samples were associated with 

the recharge of the food-processing wastewater. End-member 

mixing analysis was used to determine the relative amounts 

of each identified end member within the samples collected 

from the Terrace Farm site. The delta nitrogen‐15 (δ15N) of 

nitrate generally ranged between +2 and +9 parts per thousand 

and the delta oxygen-18 (δ18O) of nitrate generally ranged 

between -2 and -7 parts per thousand. None of the samples 

that were determined to be associated with the wastewater 

were different from the samples that were not affected by 

the wastewater. The nitrate isotope values measured in this 

study are also characteristic of ammonium fertilizer, animal 

and human waste, and soil nitrate; therefore, it was not 

possible to differentiate between food-processing wastewater 

and the other nitrate sources. Values of δ15N and δ18O of 

nitrate provided no more information about the sources of 

nitrate in the Umatilla River basin than did a hydrologic 

and geochemical understanding of the ground-water system 

derived from interpreting water-level and major-ion chemistry 

data.

Introduction

Stable isotopes of nitrate have been used for more than 30 

years to determine nitrate sources in water supplies (Kohl and 

others, 1971; Kreitler, 1975; Kreitler and Jones, 1975; Kreitler 

and others, 1978; Gormly and Spalding, 1979; Kreitler, 

1979; Wolterink and others, 1979; Mariotti and others, 1980; 

Spalding and others, 1982; Heaton and others, 1983; Kreitler 

and Browning, 1983; Flipse and others, 1984; Heaton, 1984; 

Mariotti and others, 1984; Exner and Spalding, 1985; Flipse 

and Bonner, 1985; Heaton, 1986; Hubner, 1986; Amberger and 

Schmidt, 1987; Mariotti and others, 1988; Aravena and others, 

1993; Komor and Anderson, 1993; Clark and Fritz, 1997; 

Aravena and Robertson, 1998). Although the delta oxygen-18 

(δ18O) and delta nitrogen-15 (δ15N) of nitrate derived from 

various nitrate sources, including nitrate and ammonium 

fertilizers, soil nitrogen, precipitation, and manure and septic 

waste, are known (Kendall, 1998), values from nitrate derived 

from food-processing wastewater applications have not been 

published. 

Food-processing activities related to french-fry 

production generate large volumes of nutrient-rich wastewater 

on a daily basis (Grondin and Camacho, 1995). Foodprocessing wastewater often is applied as a treatment/

disposal method to crop land in the study area in north-central 

Oregon near Umatilla. Since the early 1980s, more than 1 

million pounds of nitrogen have been produced annually 

by food-processing activities in the Umatilla River basin. 

These activities are a potential source of nitrate to the groundwater system of the basin. The objective of this study was to 

measure the δ15N and δ18O of nitrate in ground water beneath 

food-processing wastewater application sites in the Umatilla 

River basin to determine if the nitrate resulting from the foodprocessing wastewater-application could be distinguished 

from other potential sources of nitrate.

Evaluation of Sources of Nitrate Beneath Food Processing 

Wastewater-Application Sites near Umatilla, Oregon

By Lonna Frans1, Anthony Paulson1, Phil Richerson2, Elise Striz3, and Curt Black3

1

U.S. Geological Survey

2

Oregon Department of Environmental Quality

3

U.S. Environmental Protection Agency
2 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

Site Descriptions

Two food-processing wastewater-application sites in 

the Umatilla River basin study area in north-central Oregon 

were studied (fig. 1): the Terrace Farm site and the North 

Farm site. At both sites, a shallow, unconfined aquifer occurs 

in the alluvial sediment that overlies the Columbia River 

Basalt Group; the sediment comprises primarily silt, sand, 

and gravel that resulted from the floods of glacial Lake 

Missoula (Wozniak, 1995). The aquifer mainly consists of 

basaltic fragments of plagioclase, pyroxene, and volcanic 

glass. Secondary minerals, such as calcite, smectite, gypsum, 

and dolomite, occur as well. The ground-water chemistry 

is generally classified as a mixed-cation/bicarbonate type 

(Grondin and Nelson, 1995). 

The Terrace Farm site is on an upland terrace between 

Emigrant Buttes to the east and the Butter Creek flood plain 

to the west (Richerson, 2004). The Hunt Irrigation Ditch 

runs along the western and northern edges of the site. Foodprocessing wastewater had been applied to the site since 1981 

on what previously was dryland and then irrigated farmland. 

Irrigated agriculture is the dominant land use upgradient 

of the Terrace Farm site. Immediately downgradient of the 

Terrace Farm site is a cattle-feedlot that has been in operation 

since before 1985. Columbia River water is the source of the 

process water for the Terrace Farm site.

The North Farm site is on a northeast/southwest trending 

topographic ridge that includes rangeland areas surrounding a 

landfill in the northwest section, the Umatilla Ordnance Depot 

to the west, and the North Farm wastewater-application areas 

to the east. Food-processing wastewater has been applied to 

the North Farm site since 1972 on land that previously was 

dryland (Richerson, 2004). The Umatilla Ordnance Depot 

landfill began accepting solid waste (mostly packing material) 

in 1968 and ceased receiving waste in 1993. Some munitionscontaminated soils that were solidified with cement were 

placed in the landfill in 1994. A slight downward vertical 

gradient generally has been observed beneath the wastewater 

application area (Phil Richerson, Oregon Department 

of Environmental Quality, written commun., September 

2005), which is consistent with recharge occurring due to 

the wastewater application. The vertical gradient on the 

western edge of the wastewater-application area, however, 

occasionally reverses itself indicating that there are brief 

periods of upward movement of water at that location. 

Food-processing wastewater, characterized by high levels 

of total Kjeldahl nitrogen (greater than 100 mg/L) and low 

amounts of nitrate (about 1 mg/L), was being applied to the 

two sites at the time of the study in 2004. The wastewater is 

sprayed on the crops by using center pivot sprinkler systems 

during the crop growing season, which typically runs from 

March through October. Various crops are grown, including 

corn, wheat, alfalfa, barley, forage grasses, potatoes, and peas. 

Methods

Ground-water levels and samples were collected from the 

shallow ground water at the Terrace Farm site in August 2004 

and at the North Farm site in January and April 2004. Samples 

were collected from the ground-water system, rather than 

directly from the process water, because the process water is 

nitrate poor and the isotopic values of the nitrate would change 

as the organic nitrogen undergoes nitrification to become 

nitrate.

Water samples from monitoring wells were collected 

by using submersible pumps. Each monitoring well had a 

screen-interval length of 3.0 m, and samples were collected 

at each well only after at least three casing volumes of water 

were purged and basic field parameters had stabilized. Water 

samples were collected from temporary push-probe wells at 

three Terrace Farm sites (Terrace-1, Terrace-2, and Terrace-3; 

fig. 2). 

Hydrogen-isotope ratios of water were analyzed by 

isotope-ratio mass spectrometry following hydrogen-water 

equilibration (Coplen and others, 1991) and are expressed 

relative to Vienna Standard Mean Ocean Water (VSMOW), 

tac09-0262_Figure01

Hunt Irrigation Ditch

UMATILLA

ORDNANCE

DEPOT

Cold

Springs 

Resevoir

U M A T I L L A C O U N T Y

Butter 

Creek

Umatilla

Hermiston

Emigrant

Buttes

Stanfield

Echo

Columbia

River

North 

Farm

site

Umatilla River

Umatilla

River

US

395

US

395

US

730

I

82

I

84

SR

207

SR

207

SR

320

Terrace

Farm

site

45°

45’

119°15’

O R E G O N

0 2 4 Study Area

0 2 4 6

6 8 MILES

8 KILOMETERS

Figure 1. Locations of the North Farm and Terrace 

Farm study sites in the Umatilla River basin, Oregon.
Methods 3

such that delta-2 hydrogen (δ2H) of Standard Light Antarctic 

Precipitation (SLAP) reference water is -428 parts per 

thousand (‰) (Coplen, 1996). Oxygen-isotope ratios of water 

were determined by the carbon dioxide-water equilibration 

(Epstein and Mayeda, 1953) and are expressed relative to 

VSMOW, such that δ18O of SLAP reference water is -55.5 ‰ 

(Coplen, 1996). 

Samples for hydrogen-3/helium-3 (3H/3He) age 

determination (3H, δ3He, 4He, and Ne analyses) were collected 

in 80-cm-long copper tubes with pinch-off clamps and 500 

mL plastic bottles, and analyzed by using mass-spectrometric 

procedures (Ekwurzel and others, 1994; Ludin and others, 

1998) at the Noble Gas Laboratory, Lamont-Doherty Earth 

Observatory, of Columbia University, Palisades, New York. 

Gases were extracted from the water samples in the copper 

sample tubes by using a vacuum extraction line and were 

transferred into flame-sealed glass ampoules. After separation 

of water vapor and dissolved gases into several cryogenic 

traps, He isotopes were measured on a VG 5400 mass 

spectrometer. After release from the cryogenic trap, neon was 

measured in a quadrupole mass spectrometer. The gas-free 

water sample was flame-sealed in a glass bulb, and after about 

6 months, the tritiogenic 3He was extracted from the glass 

bulb and measured using a mass spectrometer. The ratio of 

3H/tritiogenic 3He then was used to calculate the apparent 

recharge age of the water (Schlosser and others., 1988, 1989).

Unfiltered samples were analyzed for concentrations of 

nutrients and major ions by the U.S. Environmental Protection 

Agency (USEPA) Manchester Environmental Laboratory 

in Port Orchard, Washington. Samples for the analysis of 

nitrite-plus-nitrate, ammonia, and phosphate were preserved 

with sulfuric acid and analyzed by using USEPA Methods 

353.2, 350.1, and 365.1, respectively (U.S. Environmental 

Protection Agency, 1993). Samples for the analyses of 

magnesium, calcium, potassium, and sodium were preserved 

with nitric acid (pH less than 2) and analyzed by using USEPA 

Method 200.7 (U.S. Environmental Protection Agency, 

1991). Samples for the analysis of chloride and sulfate were 

untreated and were analyzed using USEPA method 300.0 (U.S. 

Environmental Protection Agency, 1993). Filtered water (0.45 

mm) was analyzed for isotope ratios of nitrogen and oxygen in 

dissolved nitrate by bacterial conversion of nitrate to nitrous 

oxide and subsequent measurement on a continuous-flow 

isotope-ratio mass spectrometer at the U.S. Geological Survey 

(USGS) Stable Isotope Laboratory (Sigman and others, 2001; 

Casciotti and others, 2002; Revesz and Casciotti, 2003). 

Nitrogen-isotope ratios were reported in parts per thousand 

relative to nitrogen gas (N2) in air (Mariotti, 1983). Oxygenisotopes of nitrate were expressed in the same manner as those 

tac09-0262_Figure02

MW-39 MW-40

Age=2.6 years

NO3 Age=1.9 years =28.9 mg/L

NO3

=13.4 mg/L Age=1.6 years

NO3

=53.5 mg/L Age=8.2 years

NO3=30.6 mg/L

MW-53

TERRACE-2

METERS

200

150

210

180

190

160

170

METERS

200

150

210

180

190

160

170

A'

SOUTH

A NORTH

0 0.5

0.5 1.0

1.0 MILE

0 KILOMETER Vertical scale greatly exaggerated

North American Vertical

Datum of 1988 (NAVD 88)

 WATER TABLE

LAND SURFACE

175

172

166

178

169

181

I

84

SR

207

CATTLE FEED LOT

STORAGE

LAGOON

Hunt Irrigation Ditch MW-38

MW-39

MW-51

MW-40

MW-22

MW-52

MW-14

MW-54

MW-53

TERRACE-1

TERRACE-2

TERRACE-3 Manns Pond A'

A

A.

B.

0 0.5

0.5 1.0

1.0 MILE

0 KILOMETER

EXPLANATION

MW-38

520

Land-application field

Terrace Farm boundary

Ground-water elevation contour

 Contour interval 3 meters

Irrigation canal

Transect

Sampled well location and No.

Ground-water fow direction

 Perpendicular to contours

A A'

Figure 2. Locations of (A) ground-water contours 

and flow direction and (B) depths to water, nitrate 

concentrations, and apparent recharge age at selected 

wells, Terrace Farm site, Umatilla River basin, Oregon.
4 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

of water and were corrected for drift, blank, and exchange 

with water by using USGS 34 and USGS 35 (Böhlke and 

others, 2004). Data from field and laboratory measurements 

for sites listed in table 1 are available at http://waterdata.usgs.

gov/wa/nwis/qw. Major ions and nutrient results from samples 

collected from the Umatilla Ordnance Depot landfill wells on 

the North Farm site were obtained from SCS Engineers (Mark 

Varljen, SCS Engineers, written commun., November 2004).

End-member mixing analysis (EMMA) (Christophersen 

and Hooper, 1992) was used to estimate the water contribution 

to each well sample from the various end members determined 

at each site. The EMMA model was developed by: (1) 

constructing constituent-constituent plots to estimate the 

number of identifiable end members present at each site and 

the representative solute concentrations of each end member; 

(2) completing a principal component analysis (PCA) (SAS 

Institute, 1990) for various constituent combinations; (3) 

selecting constituents with the largest proportion of variance 

explained by the first two components for the end-member 

mixing analysis; (4) determining the proportions of each end 

member in each well sample by using a Microsoft EXCEL 

spreadsheet (available at www.cof.orst.edu/cof/fe/watershd/

Documents/Shortcourses/shortcourse/EMMA.xls; and (5) 

comparing the concentrations predicted by EMMA with the 

measured concentrations by using linear regression. 

USGS station 

No.

Well

identification

No.

Elevation 

of water 

table (m)

Top of 

screen in 

relation 

to water 

level (m)

NO3

(mg/L)

δ15N 

(‰)

δ18O 

(‰)

Tritium 

(TU)

Recharge 

age 

(years)

Proportion of water from each end 

member

Upgradient 

ground 

water

Western 

ground water 

affected by 

irrigation 

canal leakage

Terrace 

Farm 

water

Terrace Farm site

454625119192101 MW-14 170.5 -7.7 41.5 4.87 -3.82 0.05 48.9 0.11 0.89 0.00

454604119195501 MW-22 173.9 – 30.1 4.49 -3.01 – – .01 .99 .00

454636119184101 MW-38 171.6 .5 14.7 3.54 -2.91 – – .64 .31 .05

454612119184101 MW-39 179.2 -4.8 13.4 7.55 -5.80 .92 1.9 1.00 .00 .00

454546119181401 MW-40 181.2 -3.9 28.9 8.51 -5.99 .43 2.6 .92 .08 .00

454551119201001 MW-51 176.4 .6 9.95 4.39 -2.16 – – .58 .00 .42

454628119195301 MW-52 170.2 .8 36.1 4.24 -2.10 – – .00 1.00 .00

454638119190901 MW-53 166.6 .2 53.5 2.36 -2.06 4.03 1.6 .00 .00 1.00

454546119193901 MW-54 177.8 -.5 22.0 6.27 -4.12 – – .19 .81 .00

454700119193501 Terrace-1 165.8 -2.1 46.1 5.87 -2.87 4.58 7.8 – – –

454657119192501 Terrace-2 165.8 -3.4 30.6 4.62 -3.25 2.8 8.2 .15 .82 .03

454656119190801 Terrace-3 165.9 -2.5 28.2 4.56 -3.42 – – .24 .72 .04

North Farm site

455128119224901 MW-3 171.9 -17.1 8.58 3.40 -4.08 – –

455150119221901 MW-4 172.1 -17.9 25.9 4.95 -3.53 – –

455128119224301 MW-101 171.6 -3.1 48.0 6.27 -3.06 6.7 5

455100119234101 MW-331 156.8 -7.7 15.4 4.20 -5.40 .04 >50

455104119235401 MW-34 155.1 -5.1 13.9 – – – –

455102119235501 MW-35 154.7 -2.9 10.3 – – – –

455106119234901 MW-36 156.7 -5.5 14.1 – – – –

455111119235401 11-1 156.3 -4.0 16.6 – – – –

455046119235001 11-2 153.8 1.0 17.7 – – – –

455058119232401 11-31 160.9 -1.7 12.5 4.52 -4.96 .04 >50

455115119232401 11-4 164.3 -5.0 10.2 1.87 -5.67 –

455106119234401 11-5 157.8 -5.7 11.9 – – – –

455054119242101 11-6 153.2 -.2 11.0 – – – –

455058119240701 11-71 154.5 -1.6 14.9 6.24 -6.33 .07 >50

455107119240701 11-8 154.9 -1.0 13.6 – – – –

455045119240801 11-9 154.0 .1 13.6 4.06 -6.56 – –

455040119235701 11-10 153.9 -.7 6.29 3.07 -5.39 – –

1

Nitrate and isotope values are average of January and April samples.

Table 1. Selected chemical and isotopic analyses and proportions of water attributed to each end-member at the North Farm and 

Terrace Farm sites, Umatilla River basin, Oregon.

[Abbreviations: USGS, U.S. Geological Survey; m, meter; mg/L, milligram per liter; ‰, per mil; –, not determined; NA, not available; >, greater than]
Nitrate at Wastewater-Application Sites 5

Nitrate at Wastewater-Application 

Sites

Terrace Farm Site

Water levels measured from wells at the Terrace Farm 

wastewater-application site indicated that ground water 

generally flows towards the northwest (fig. 2A). Depths to 

water at the Terrace Farm site ranged from about 15 m at well 

MW-40 to 26 m at well MW-53 and then shallowed to around 

8 m below land surface downgradient of the cattle feedlot 

(fig. 2B). 

Apparent recharge ages ranged from 1.6 to 49 years in 

water samples from wells in the wastewater-application site 

and averaged about 8 years for water samples from wells 

downgradient of the feedlot (fig. 2; table 1). Apparent recharge 

ages were uncorrected for terrigenic helium because the 

samples may have been fractionated. The tritium concentration 

values were consistent with piston flow at several of the 

wells (Terrace-1, Terrace-2, and MW-53) because the tritium 

concentration values were about equal to those expected in 

precipitation for their given recharge year. 

 Conversely, at wells MW-39 and MW-40, the tritium 

concentration values indicated a mixture of young and old 

waters. The δ18O and δ2H ratios of water sampled from wells 

were along the local meteoric water line (constructed from 

samples collected from nearby rivers and streams), indicating 

that the aquifer water was not notably affected by evaporation 

(fig. 3). 

Constituent-constituent plots that were constructed 

for relatively conservative ions at the Terrace Farm site 

indicated that three identifiable, potential end members were 

present (fig. 4). The end members included a group with 

low concentrations of sulfate, chloride, and calcium (less 

than 100 mg/L) and low δ18O of water; a group with higher 

concentrations of sulfate, chloride, calcium and slightly higher 

δ18O of water; and Terrace Farm water, which had a high 

concentration of sulfate, but a low concentration of chloride 

and a much higher δ18O of water. The median concentrations 

of constituents in water from wells MW-39 and MW-40 were 

selected to represent the group with lower concentrations 

of sulfate, chloride, and calcium. This end member likely is 

representative of the upgradient ground water because these 

wells generally are on the upgradient side of the study area 

and away from the irrigation canal. The median concentrations 

of constituents in water from wells MW-22 and MW-52 were 

selected to represent the water with higher concentrations of 

sulfate, chloride, and calcium and slightly higher δ18O ratio 

of water. The source of this end member is unknown, but 

may be ground water flowing from west of the site, and (or) 

may be affected by irrigation canal leakage or application 

of road salt because these wells are screened near the water 

table and are near the irrigation canal and road. On a molar 

scale, the largest increase in concentration was for the chloride 

ion (4.5 millimolar) between wells MW-22 and MW-52 

relative to wells MW-39 and MW-40 (table 2). Additionally, 

the increases in concentrations of calcium, magnesium, 

alkalinity, and sulfate were not consistent with the dissolution 

of a combination of carbonate minerals and gypsum. It is 

unlikely that geochemical reactions with aquifer minerals were 

responsible for the increases in the concentrations of most 

major ions in water from wells MW-22 and MW-52. 

-120

-115

-110

-105

-100

-95

-90

-16 -15 -14 -13 -12 -11 -10

DELTA HYDROGEN-2, IN PARTS PER THOUSAND

DELTA OXYGEN-18, IN PARTS PER THOUSAND

North Farm wells

Terrace Farm wells

Local meteoric

 water line

Figure 3. Ratios of delta hydrogen-2 (δ2H) and delta 

oxygen-18 (δ18

O) for water samples from wells in the 

North Farm and Terrace Farm sites, Umatilla River 

basin, Oregon.
6 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

Well MW-53 was selected to represent the Terrace Farm 

water and because it was geochemically isolated from other 

wells sampled. The water in well MW-53 likely represents the 

ground water from the wastewater application on the Terrace 

Farm, because of its young apparent age, lack of mixing with 

older waters, and heavier δ18O and δ2H values, which may 

indicate recharge during summer when the wastewater is 

applied. The increase in calcium and sulfate concentrations in 

water from well MW-53 relative to wells MW-39 and -40 is 

consistent with the dissolution of about 230 mg/L of gypsum. 

Terrace-1 was excluded from the EMMA because it seemed 

to be affected by heterogeneity or a possible fourth source of 

water that may originate from the west side of the study area; 

Terrace-1 frequently plotted outside the mixing lines for the 

other three end members. 

The PCA selected for use in the EMMA incorporated 

four constituents (calcium, chloride, sulfate, and δ18O 

of water) for the Terrace Farm site because the first two 

principal components explained about 99 percent of the 

variability, and the remaining conservative constituents were 

strongly correlated with at least one of the four incorporated 

tac09-0262_Figure04

Terrace Farm

water

Upgradient ground water

SULFATE, IN MILLIGRAMS PER LITER

CALCIUM, IN MILLIGRAMS PER LITER

CHLORIDE, IN MILLIGRAMS PER LITER

50 100 150 200 250

50

100

150

200

250

MW-53 MW-22 MW-52

MW-14

MW-54

Terrace-2

Terrace-1

Terrace-3

MW-38

MW-51

MW-39 MW-40

Terrace Farm

water

Upgradient ground water

A. B.

Terrace-1

MW-53

MW-51

MW-39

MW-40

MW-38

Terrace-3

Terrace-2

MW-54

MW-14

MW-52

MW-22

-14.5 -14.0 -13.5 -13.0 -12.5

50

100

150

200 affected by canal leakage

DELTA 18 OXYGEN, IN PARTS PER THOUSAND

Western ground water

Western ground water

 affected by canal leakage

Figure 4. Relations between (A) sulfate-chloride and (B) calcium-delta oxygen-18 (δ18O) for water samples from wells, Terrace 

Farm site Umatilla River basin, Oregon. (Probable end-members are at the three points of each triangle.)

Constituent 

MW-22 and 52 

compared with 

MW-39 and 40

MW-53 

compared with 

MW-39 and 40

Cations (millimolars)

Calcium 2.97 1.87

Magnesium 1.34 .60

Potassium .03 .12

Sodium .35 .85

Total milliequivalents 8.99 5.91

Anions (millimolars)

Alkalinity 0.70 -0.42

Chloride 4.46 .93

Sulfate 1.50 1.68

Nitrate .19 .52

Total milliequivalents 8.35 4.39

Table 2. Difference of cations and anions in water from wells at 

the Terrace Farm site, Umatilla River basin, Oregon.
Nitrate at Wastewater-Application Sites 7

constituents. For each constituent included in the EMMA, the 

linear-regression relations between the predicted and measured 

concentrations produced slopes between 0.93 and 1.0 and 

coefficient of determination (R2) values between 0.98 and 

0.99 (table 3). The R2 values and slopes close to 1 indicated 

that the EMMA model is a strong predictor of ground-water 

concentrations for the conservative solutes. To determine 

how robust the analysis was, the results from the EMMA also 

were used to predict concentrations for constituents that were 

not included in the EMMA. The conservative constituents 

(magnesium, bromide, and δ2H) had high R2 values and 

slopes near 1, similar to the constituents that were included 

in the EMMA. Bicarbonate, nitrate, sodium, and potassium, 

however, had much lower slopes and R2 values, indicating that 

these constituents probably were nonconservative. 

EMMA indicated that most samples included a mixture 

of water from upgradient and western ground water that 

was affected by irrigation-canal leakage. A large proportion 

of water from Terrace Farm (table 1) was inferred by the 

EMMA only in samples collected from two wells (MW-51 

and MW-53). The sample from well MW-51 contained a mix 

of about 60 percent upgradient ground water and 40 percent 

Terrace Farm water, which is consistent with its location on 

the upgradient side of the study site next to the wastewaterstorage lagoon. As much as 5 percent of water from the 

Terrace Farm was detected in three wells (MW-38, Terrace-2, 

and Terrace-3). All these wells were on the downgradient side 

of the wastewater-application area.

The δ15N of nitrate generally ranged between +2 and +9 

‰ and the δ18O of nitrate generally ranged between -2 and -6 

‰ (table 1). Well MW-53, which represented the wastewater, 

had a δ15N of +2.36 ‰ and a δ18O of -2.06 ‰. The measured 

isotope values at well MW-53 overlap with previously 

reported values for soil nitrogen (N), animal and septic 

waste, and ammonium fertilizer (fig. 5). Values in this range 

generally are the result of nitrification. Isotope values resulting 

from nitrification of organic nitrogen in the food-processing 

wastewater determined in this study also are in this range. 

Table 3. Slope, intercept, and R2 value for EMMA-predicted 

versus actual concentrations at the Terrace Farm site, Umatilla 

River basin, Oregon.

[Abbreviations: EMMA, end-member mixing analysis; δ18O, delta 

oxygen-18; δ2H, delta hydrogen-2]

Constituent Slope Intercept R2

Bromide 0.98 0.00 0.95

Bicarbonate .12 2.70 .03

Calcium .95 .17 .99

Chloride .93 .30 .99

δ18O 1.00 .04 .98

δ2H .86 -14.00 .84

Magnesium .90 .23 .97

Nitrate .44 19.00 .45

Potassium .66 .08 .56

Sodium .37 1.61 .44

Sulfate .97 .06 .98

30

25

20

15

10

5

-10

-5

0

-10 -5 0 30252015105

Manure and 

septic waste

Ammonium

and rain

Nitrogen fertilizer

Soil

nitrogen

DELTA OXYGEN-18, IN PARTS PER THOUSAND

DELTA NITROGEN-15, IN PARTS PER THOUSAND

North Farm wells

Terrace Farm wells

in fertilizer

Figure 5. Ratios of delta oxygen-18 (δ18O) and delta 

nitrogen-15 (δ15N) for nitrates in samples compared 

with the range of ratios expected for different sources 

of nitrate, Umatilla River basin, Oregon. (Ranges are 

from Kendall, 1998.)
8 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

Because of the overlap in the potential nitrate sources, 

the proportion of each sample attributed to the Terrace Farm 

ground water was compared to the isotope values to determine 

any statistically significant relation (fig. 6). No significant 

relation was determined between either δ15N or δ18O and 

the proportion of the Terrace Farm water (p-values = 0.68 

and 0.07, respectively). For water samples from wells in the 

wastewater-application area with no Terrace Farm water, 

the nitrate-isotope values likely were primarily the result of 

ammonium fertilizer or nitrification of soil N. 

North Farm Site

Interpretation of water-quality data from the North Farm 

site was more difficult than interpretation of water-quality data 

from the Terrace Farm site because the types and amounts of 

water applied to the North Farm site changed over time. From 

0 0.1 0.2 0.3 0.4 0.5

FRACTION OF SAMPLE WITH TERRACE FARM WATER SAMPLES

-6

-4

-2

0

2

4

6

8

ISOTOPE RATIO, IN PARTS PER THOUSAND

Terrace 2

All others

(mean ± standard deviation) y = -1.2x + 4.8

p-value = 0.68

R2

 = 0.06

y = 3.5x - 3.6

p-value = 0.07

R2

= 0.71

MW-51

MW-38

Terrace 3

All others

(mean ± standard deviation)

δ15N

δ18O

Standard deviation

Regression line

EXPLANATION

Figure 6. Relation between nitrate delta nitrogen-15 

(δ15N) and delta oxygen-18 (δ18O) isotope ratios and 

fraction of water samples from wells, Terrace Farm site, 

Umatilla River basin, Oregon.

1972 to 1992, about 3.4 million m3 of process water were 

applied each year to the North Farm site with an additional 

33,300 m3 of supplemental surface-water application. 

The alluvial wells at the wastewater-processing plant are 

the original sources of pre-processed water. Beginning in 

1992, the amount of processed water applied annually to 

the North Farm wastewater-application site decreased to 

284,000–370,000 m3 with an additional 1.4–1.9 million m3

of supplemental surface-water application (Emmett Walker, 

ConAgra Foods, oral commun., July 2006). Because the 

source of water has changed over time, application of the 

EMMA would not be appropriate at this site. Piper diagrams 

and constituent-constituent plots were examined to determine 

which wells, if any, were affected by the wastewater 

applications. 

Ground-water levels collected at the North Farm 

wastewater-application site indicated that ground water flowed 

radially away from the center of the ground-water mound 

beneath the site with a southwesterly flow direction beneath 

the general study area (fig. 7A). Depths to water generally 

ranged from about 26 m on the edge of the wastewater 

application area to more than 45 m southwest of the Umatilla 

Ordnance Depot landfill (fig. 7B). Unlike the water samples 

from wells collected at the Terrace Farm site, several samples 

collected downgradient of the North Farm site were below the 

local meteoric water line and may be affected by evaporation 

(fig. 3). Whether the evaporative signal of these samples was 

the result of changes to the ground water prior to pumpage 

and use in food processing or changes to the water after it was 

applied to the site is not known. 

Wastewater applied at the North Farm site is particularly 

rich in potassium and sodium (fig. 8) compared with most of 

the ground-water samples. Wells MW-3, MW-4, MW-33, and 

11-5 all appear to be affected by the processed water because 

they plot between the wastewater samples and remaining well 

samples as shown in figure 8. 

Sulfate levels generally were low in the wastewater 

and supplemental surface-water irrigation (fig. 9). With the 

exception of samples from well MW-10, the samples clustered 

into two groups: (1) wells with low sulfate concentrations, 

which seemed to be affected by the wastewater, and (2) 

wells with high sulfate concentrations, which did not seem 

to be affected by the wastewater. Samples from wells 11-3, 

11-4, 11-5, MW-3, MW-4, and MW-33 all had calcium and 

sulfate concentrations that were between those detected in the 

wastewater and those in the supplemental-irrigation water. 
Nitrate at Wastewater-Application Sites 9

tac09-0262Figure07

I

82

153

156

159

162

165

168

171

0 0.5 1 MILE

0 0.5 1.0 KILOMETER

LANDFILL

Coyote Coulee

UMATILLA

ORDNANCE

DEPOT

A.

B.

11-9 11-2

11-10

11-6

11-7

11-1

MW-34 11-8

MW-35 MW-33

11-3

11-5

MW-36

11-4

MW-3

MW-4

MW-10

EXPLANATION

165

Land-application field

North Farm boundary

Ground-water elevation contour

 Contour interval 3 meters; 

 dashed where uncertain

Transect

Ground-water flow direction

 Perpendicular to contours

MW-36 Sampled well location and No.

A A'

A'

A

Vertical scale greatly exaggerated

North American Vertical

Datum of 1988 (NAVD 88) 0 0.5

0.5 1.0

1.0 MILE

0 KILOMETER

150

210

200

180

190

160

140

130 130

170

150

210

200

180

190

160

140

170

METERS

A'

NORTH

METERS

A SOUTH

NORTH FARM

LAND APPLICATION

LANDFILL

NO3 = 25.9 mg/L

NO3

 = 8.58 mg/L

Age > 50 years

NO3

 = 12.6 mg/L

11-7

MW-33

MW-3

MW-10 MW-4

11-3

Age > 50 years

NO3 Age > 50 years = 15.5 mg/L

NO3

 = 15.1 mg/L

Age = 5 years

NO3

 = 48 mg/L

WATER TABLE

Figure 7. Locations of (A) ground-water elevation 

contours and flow direction and (B) depths to ground 

water, nitrate concentrations, and apparent recharge 

age at selected wells, North Farm site, Umatilla River 

basin, Oregon. 

11-4

11-10

11-9

11-3

11-7

11-1

11-2

11-5

11-6

11-8

MW-3

MW-33

MW-4

MW-10

MW-34

MW-35

MW-36

Columbia

 River water

Process

 water

EXPLANATION

80

60

40

20

100

Magnesium (Mg)

0

100 80 60 40 20 0

80

60

40

20

100

Percentage of

milliequivalents

per liter

0

Calcium (Ca)

Sodium (Na)+Potassium(K)

Mg

Ca Na+K

C A T I O N S

Figure 8. Trilinear diagram showing cations for North Farm 

site water samples from wells, Columbia River water, and 

process water from the wastewater-plant clarifier, Umatilla 

River basin, Oregon.

MW-10 

MW-34

MW-35

MW-10 

MW-36

MW-3 MW-33

MW-4

11-3 11-5

11-4

11-6

11-7

11-8

11-1

11-9

11-10

11-2

Columbia

River

water

Process

water

0 20 806040 100 120 140 0

20

40

60

80

(January)

(April)

CALCIUM, IN MILLIGRAMS PER LITER

SULFATE, IN MILLIGRAMS PER LITER

Not effected by wastewater

Effected by wastewater

Source water

Well screened in silt layer

Figure 9. Relation of sulfate and calcium from water 

samples from wells at the North Farm site, Columbia River 

water, and process water from the wastewater-plant 

clarifier, Umatilla River basin, Oregon.
10 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

Well MW-10 is on the edge of the wastewater-application 

area and is screened within a silt layer. Compared to wells 

affected by wastewater (low sulfate and high potassium), 

the water chemistry of this young water (5 years) from the 

shallow well MW-10 is perplexing. The highest concentrations 

of calcium, magnesium, alkalinity, chloride, and nitrate were 

detected in water from well MW-10 for the North Farm 

site, but potassium concentrations were within the range 

determined for wells affected by the wastewater. When 

compared to the wastewater affected wells, water from well 

MW-10 contained significantly more calcium, magnesium, 

alkalinity, and nitrate with lesser amounts of chloride and 

sulfate (table 4). The confinement of this water in the silt layer 

may have allowed geochemical reactions such as dissolution 

of gypsum and calcium-magnesium carbonates and the 

remineralization of total Kjeldahl nitrogen to nitrate to proceed 

faster relative to the flow of water. The addition of significant 

amounts of calcium, magnesium, and alkalinity shifted 

MW-10 water to a mixed-cation/bicarbonate type (fig. 8). 

Alternatively, water from MW-10 may reflect flow from 

surface-water irrigation applied north of the North Farm site. 

The apparent-recharge age of the water just downgradient 

of the wastewater-application area in water samples from 

well MW-10 was 5 years. Further downgradient from the 

wastewater-application area, the apparent recharge dates of the 

three Umatilla Ordnance Depot wells, wells 11-3, 11-7, and 

MW-33, were greater than 50 years (table 1). The old apparent 

recharge age in these wells likely is because the source of 

most of the water applied to the North Farm site originally 

was ground water, which in this case appears to be tritium 

dead. The young age of the water in well MW-10 likely was 

due to surface-water irrigation either on the North Farm or 

the area north of the North Farm site. The lack of tritium in 

water samples from wells MW-33, 11-3, and 11-7 combined 

with δ18O and δ2H ratios of water below the local meteoric 

water line indicated that the water in these wells did not have 

a substantial amount of supplemental surface-water irrigation. 

The water in these wells likely was from the wastewater 

applied prior to 1992 when the supplemental surface water 

application amounts were less than 1 percent of the total water 

applied.

The δ15N of nitrate in sampled wells generally ranged 

between +2 and +6 ‰ and the δ18O of nitrate generally 

ranged between -3 and -7 ‰ (fig. 10). The heaviest isotope 

values, with a δ15N of +6.27 ‰ and a δ18O of -3.06 ‰, and 

the highest nitrate concentration were detected in the water 

sample collected from well MW-10. The samples from wells 

MW-3, MW-4, MW-33, 11-3, and 11-4, which are believed 

to be affected by the process water, also had slightly heavier 

values of δ18O than the remaining downgradient samples, 

but the values of δ15N were similar. The samples affected by 

wastewater generally did not have distinctly different isotope 

values of nitrate when compared with samples that were not 

affected by wastewater. As at the Terrace Farm wastewaterapplication site, the measured isotope values at the North Farm 

wastewater-application site overlap with previously reported 

nitrate isotope values for soil N, animal and septic waste, and 

ammonium fertilizer (Kendall, 1998) (fig. 5). 

Constituent Difference 

(millimolars)

Cations

Calcium 2.37

Magnesium 2.79

Potassium -.00

Sodium -.41

Total milliequivalents 9.91

Anions

Alkanity 5.50

Chloride 1.31

Sulfate .25

Nitrate .54

 Total milliequivalents 7.83

Table 4. Difference of cations and anions 

in water from well MW-10 compared to 

wells MW-3, -4, -33 and 11-3 and -4 at 

the North Farm site, Umatilla River basin, 

Oregon.

1 2 3 4 5 6 7

-7

-6

-5

-4

-3

MW-10

48 mg/L 

MW-4

25.9 milligrams per

 liter (mg/L) MW-3

8.58 mg/L 

11-3

12.5 mg/L

11-7

14.9 mg/L

MW-33

15.4 mg/L

11-9

13.6 mg/L

11-10

6.29 mg/L 11-4

10.2 mg/L 

DELTA OXYGEN-18, IN PARTS PER THOUSAND

DELTA NITROGEN-15, IN PARTS PER THOUSAND

Effected by wastewater

Well screened in silt layer

Not effected by wastewater

Figure 10. Relations between delta oxygen-18 (δ18O) 

and delta nitrogen-15 (δ15N) of nitrate from water samples 

from wells, North Farm site, Umatilla River basin, Oregon.

(Symbols are labeled with the nitrate concentration of each 

sample.)
References Cited 11

Summary

End-member mixing analysis (EMMA) was used to 

determine the relative mixing amounts of water samples 

collected from wells at the Terrace Farm site and was robust in 

predicting the concentrations of the conservative solutes. The 

relative proportions of each end member were not inconsistent 

with the hydrogeologic setting. Nitrate and several other major 

ions (potassium and sodium), however, did not appear to be 

conservative. 

Piper diagrams and constituent-constituent plots were 

used to determine which samples were affected by the 

wastewater at the North Farm application site.

The delta nitrogen-15 (δ15N) of nitrate generally ranged 

between +2 and +9 parts per thousand and the delta oxygen-18 

(δ18O) of nitrate generally ranged between -2 and -7 parts 

per thousand. No relation was determined between δ15N 

and δ18O values and the proportion of a sample attributed to 

food-processing wastewater at the Terrace Farm application 

site. Additionally, no differences in nitrate-isotope values 

were detected between samples affected by the wastewater 

at the North Farm application site and samples that were not 

affected by the wastewater. These observations indicated that 

the nitrate derived from the food-processing wastewater likely 

was not distinct from other nitrate, because it overlaps with 

nitrate from ammonium fertilizer, animal and septic waste, 

and soil nitrogen. Values of δ15N and δ18O of nitrate provided 

no additional information about sources of nitrate in the 

Umatilla River basin than did a hydrologic and geochemical 

understanding of the ground-water system derived from 

interpreting water-level and major-ion chemistry data.

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14 Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

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 Frans and others— Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon—SIR 2009–5069