U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007–3103

December 2007 Printed on recycled paper

Prepared in cooperation with Deschutes County and the Oregon Department of Environmental Quality

Questions and Answers About the Effects of Septic Systems on 

Water Quality in the La Pine Area, Oregon

The population of rural residential areas near La Pine in 

southern Deschutes County and northern Klamath County, 

Oregon, has grown rapidly since the 1960s. Most of these areas 

lie within a tract adjacent to the Deschutes and Little Deschutes 

Rivers that extends roughly 25 miles south of Sunriver (fig. 1). 

Existing and future homes on more than 9,300 residential lots in 

the area now use or will use individual, on-site septic systems for 

wastewater disposal and shallow wells for water supply. At least 

50 percent of these wells draw ground water from the upper 50 

feet of the shallow aquifer that underlies the area (Morgan and 

others, 2007).

Vulnerability of the shallow aquifer to contamination has 

led to concern by residents, County planners and resource 

managers, and State regulators that wastewater from septic 

systems may pose a threat to the primary drinking water supply 

if residential development continues at planned densities using 

conventional septic systems. Another concern is the quality 

of local streams (Hinkle, Morgan, and others, 2007). The 

Deschutes and Little Deschutes Rivers, which flow through the

developed areas near La Pine, already have excessive algae in

some reaches, possibly due to nutrient (nitrogen and phosphorus) 

contributions from ground water (Anderson, 2000; Jones, 2003).

Figure 1. Residential development near La Pine, Oregon, is proceeding at 

a rapid pace. This map of the area shows the boundary of a USGS study 

to examine the processes that affect the movement and chemistry of 

nitrogen in the ground-water system.

Nitrate levels in the ground-water aquifer underlying the central Oregon city of La Pine and 

the surrounding area are increasing due to contamination from residential septic systems. 

This contamination has public health implications because ground water is the sole source of 

drinking water for area residents. The U.S. Geological Survey, in cooperation with Deschutes 

County and the Oregon Department of Environmental Quality, studied the movement and 

chemistry of nitrate in the aquifer and developed computer models that can be used to predict 

future nitrate levels and to evaluate alternatives for protecting water quality. This fact sheet 

summarizes the results of that study in the form of questions and answers.

Septic system being installed near La Pine, Oregon.

Base modified from U.S. Geological Survey

1:500,000 state base map, 1982 with digital data from U.S. Bureau of the Census, TIGER/Line (R), 

1990 and U.S. Geological Survey Digital Line Graphs published at 1:100,000

Publication projection is Lambert Conformal Conic

Standard parallels 42o20' and 44o40', central meridian -120o30'

Datum is NAD83

T

19

S

T

20

S

T

21

S

T

22

S

T

23

S

R 9 E R 10 E R 11 E

DESCHUTES CO.

L A K E C O .

KLAMATH CO.

Paulina

River

RIVER

Deschutes

Little

Creek

Creek Crescent

River

Fall

Spring

River

Long

Creek

DESCHUTES

Wickiup

Reservoir

97

31 Masten

River

Spring

Century

South

Road

Road

Butte

Finley

Drive

Road

Road

Burgess

97

0 2 4 6 8 MILES

0 42 6 8 10 12 KILOMETERS

43°

35'

40'

121°40' 35' 30' 25' 121°20'

45'

50'

43°

55' Deschutes

Basin

La Pine

area

OREGON

Bend

EXPLANATION

Existing homes 

not served by 

sewer (2005)

Sewered area

Sewer under

construction (2007)

Long Prairie

La Pine 

core area

Wickiup 

Junction

La 

Pine

Sunriver
(R.J. Weick, ODEQ, written commun., 1998; Cole, 2006). 

The high concentrations were attributed to contamination by 

effluent from septic systems. 

In 1999, Deschutes County and ODEQ identified the need for a

better understanding of the processes that affect the movement 

and chemistry of nitrogen in the aquifer underlying the La Pine 

area in order to develop strategies for managing ground-water 

quality. In response, the USGS, in cooperation with Deschutes 

County and ODEQ, began a study in 1999 to examine the 

hydrologic and chemical processes that affect the movement 

and fate (chemical transformation) of nitrogen within the aquifer 

(Hinkle, Böhlke, and others, 2007; Morgan and others, 2007).

A primary objective was to provide tools for evaluating the 

effects of existing and future residential development on water 

quality. The study has provided area residents and local and 

State agencies the information and tools needed to make informed

decisions about the future of development in the La Pine area. 

Results from the study have been published in several reports (see 

References Cited). This fact sheet summarizes the results that 

relate to the effects of septic systems on water quality in the area.

Conventional residential septic systems are the principal 

source of nitrogen to the shallow aquifer in the La Pine area 

(Century West Engineering, 1982; Oregon Department of 

Environmental Quality, 1994; Hinkle, Böhlke, and others, 2007),

and the nitrate contribution (loading) to the aquifer from these 

septic systems has increased rapidly as a result of ongoing 

residential development (fig. 2). Conventional septic systems, 

including sand filter and pressure distribution systems, are 

not designed to remove nitrogen from wastewater. Nitrate is a 

human health concern because it can cause methemoglobinemia 

(Blue-Baby Syndrome) in infants (http://www.atsdr.cdc.gov/

HEC/CSEM/nitrate/). The U.S. Environmental Protection 

Agency has established 10 parts per million (ppm) of nitrogen 

as the maximum allowable nitrate concentration in drinking 

water for public water supply systems. Oregon law sets a nitrate 

concentration of 7 ppm as the level at which regulatory action 

must be taken to control water-quality degradation. 

The city of La Pine was the location of the first concentrated 

development within the area. The first building permits, 

recorded in what was then called the core area, date from 

1910. In 2006, the core area was incorporated as the City of 

La Pine. The Oregon Department of Environmental Quality 

(ODEQ) issued an administrative rule requiring community 

sewage treatment for the core area after studies in 1979 and 

1982 documented nitrate contamination in drinking water wells 

(Century West Engineering, 1982; Cole, 2006). 

Surveys of wells outside of the core area by ODEQ between 

1993 and 1995 found unnaturally elevated nitrate concentrations 

in several of the most densely developed parts of the region 

Figure 2. The rapid increase in nitrate loading to the aquifer that supplies 

drinking water to homes in the La Pine area is due to the rapid pace of 

residential development.

As part of the La Pine area ground-water study, the USGS drilled wells to collect 

geologic and water-quality data.

Geologists examined drill-core samples to define the geology at different depths.

OR19-00183_LaPineFS_fig 02

1960

140

120

100

80

60

40

20

0

160

1970 1980 1990 2000 2010 2020 2030 2040

NITRATE LOADING, IN THOUSANDS OF POUNDS OF 

NITROGEN PER YEAR

Historical loading

Projected loading

Loading if all planned homes use 

conventional septic systems

2
Why don’t more domestic wells in the area have high nitrate levels?

Ground water moves slowly through the shallow aquifer. Because ground water moves slowly, 

it takes a long time for nitrate to appear in well water.

For example, the severity of nitrate contamination in the La Pine core area did not become evident until 1979, nearly 

70 years after development of that area began. Away from the core area, most wells currently provide drinking water that 

percolated to the water table decades ago, when there were very few homes and septic systems. Nitrate plumes, however, 

are beginning to affect a significant number of drinking-water wells. Of nearly 200 well samples collected by ODEQ in 2000, 

over 10 percent had nitrate concentrations above 4 ppm, indicating contamination from septic systems.

Much of the nitrate in the aquifer currently is confined to plumes less than about 30 feet below the water table, so not all 

supply wells are drawing water from affected areas of the aquifer (fig. 3). As development proceeds and the nitrate plumes 

expand and move deeper into the aquifer, more wells will be affected. Age dating of ground water in the La Pine area provides 

additional insight into this process. USGS scientists determined the age of ground water by sampling special monitoring wells 

and analyzing the water for tracers called chlorofluorocarbons (common refrigerant gases found in the atmosphere). These 

tracers indicate that nitrate from septic systems is moving downward into deeper parts of the aquifer where more wells will 

be affected in the future (Hinkle, Böhlke, and others, 2007; Morgan and others, 2007).

Is shallow ground water in the vicinity of La Pine vulnerable to contamination from 

on-site wastewater systems?

Yes, several factors contribute to the vulnerability:

1. The ground-water table is shallow, typically less than 20 feet below land surface and seasonally rising to within 

2 feet in low-lying areas (fig. 3). 

2. The sandy soils allow rapid infiltration of septic system effluent to the water table.

3. The amount of rain and snowmelt that enters the aquifer is small, which limits dilution of septic system effluent.

4. Most existing drinking-water wells draw water from shallow sand and gravel deposits within 50 feet of land surface. 

These deposits form the primary aquifer in the area. 

5. Fifty-eight percent of lots are less than 1 acre and 82 percent are less than 2 acres, making residential densities 

relatively high for an area where homes are dependent on individual septic systems and wells. 

Figure 3. Wastewater from septic systems contains nitrogen in the forms of ammonia and organic nitrogen. As wastewater leaves the septic 

system drainfield and percolates through the unsaturated zone, these forms of nitrogen are converted to nitrate. When the wastewater reaches 

the water table it forms plumes of elevated nitrate within the aquifer. The plumes move downward with the ground water and slowly spread. 

Currently, relatively few wells have water with high nitrate concentrations because these plumes have not had time to reach the depths where 

most domestic supply wells draw water. As more homes are built, and as plumes move deeper and spread, many more supply wells will be affected.

DIAGRAM NOT TO SCALE

Septic

tank

Drain line

Screen

Well

Plume

Well

Screen

3
4

Could other sources of nitrate, like agriculture, animals, golf courses, or lawns, 

cause water-quality problems?

Probably not. Several lines of evidence point to septic systems as the main source of the nitrate 

(Hinkle, Böhlke, and others, 2007):

1. Agriculture (primarily pasture) represents only about 4 percent of the study area. The four golf courses in the area 

cover less than 0.4 percent of the study area and are located where they would affect few if any wells. Animal waste 

contribution is much less than that of humans, and it is deposited on the land surface, where various processes 

remove nitrogen. Most homes in the area have natural landscaping or small lawn areas; assuming fertilizer is applied 

at recommended rates, very little nitrogen infiltrates below the root zone and into the ground water.

2. Nitrogen isotope (15N) concentrations can be used to identify the source of nitrate in ground water; nitrogen isotope 

data for the La Pine area indicate that septic systems are the source of nitrate in the shallow ground water. 

3. The occurrence of nitrate in distinct plumes is consistent with localized sources (individual septic systems) and is not 

consistent with dispersed sources, such as agricultural fields, golf courses, or livestock pasture. 

4. Chloride, a wastewater component, is present in the shallow aquifer at higher concentrations than seen outside of the 

La Pine area or in deep ground water beneath the area. Other sources of chloride, such as agriculture or road salt, 

are not common in the area. Therefore, the elevated chloride concentrations indicate that the shallow ground water 

contains a proportion of septic system effluent.

What will happen to water quality if nitrate loading from septic systems continues 

at projected rates?

Large areas of the shallow aquifer will have nitrate concentrations above 10 ppm, and more nitrate will be 

carried into streams by ground water.

If residential development proceeds as planned and no efforts are made to reduce the rates of nitrate loading from septic systems,

loading is projected to increase 52 percent above 2005 rates (fig. 2). Computer model simulations of this future scenario show that:

1. Peak nitrate concentrations will exceed 10 ppm over large areas of the shallow aquifer (fig. 4). On average, drinking 

water in those areas will be composed of at least 22 percent septic system effluent. 

2. The highest nitrate concentrations will be near the water table, but many wells that draw water from the upper 50 feet 

of the aquifer will be at risk for nitrate contamination. 

3. It will take decades for peak concentrations to occur and decades for concentrations to subside if nitrate loading 

is reduced.

4. Increasing amounts of nitrate from septic systems will be carried into the Deschutes and Little Deschutes Rivers by 

ground water.

The computer model integrates the current understanding of nitrogen geochemistry, hydrology, and geology of the

aquifer underlying the La Pine area. The model was tested by simulating past ground-water levels, ground-water travel 

times, ground-water discharge to streams, and ground-water-quality conditions and then comparing the model results

with measurements made in the study area. The simulated conditions, including past ground-water nitrate concentrations,

matched measured conditions within acceptable limits. These results indicate that the model has sufficient accuracy

to be a valid tool for evaluating the potential effects of septic systems on future ground-water quality. 

The USGS measured water levels in the aquifer under the La Pine 

area to determine the direction of ground-water flow.

These scientists are measuring the flow of ground water into the 

Little Deschutes River through the streambed.
5

Figure 4. Ground water in much of the shallow aquifer underlying residential areas will exceed State and Federal water-quality 

standards for nitrate if existing and future homes continue to use conventional septic systems.

OR19-00183_LaPineFS_fig 04

Base modified from U.S. Geological Survey 1:500,000 state base map, 1982 

with digital data from U.S. Bureau of the Census, TIGER/Line (R), 1990 and

U.S. Geological Survey Digital Line Graphs published at 1:100,000.

Publication projection is Lambert Conformal Conic

Standard parallels 42o20' and 44o40', central meridian -120o30'

Datum is NAD83

T 23 S

T

19

S

T

20

S

T

21

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T

22

S

T

23

S

R 9 E R 10 E R 11 E

DESCHUTES CO.

L A K E C O .

KLAMATH CO.

Spring

River

Fall

River

Crescent Creek

Creek

Little

Deschutes

DESCHUTES

RIVER

River

Paulina

Creek

Long

Wickiup

Reservoir

97

97

31

Burgess

Road

Drive

Finley

Butte

Road

Road

South

Century

Spring

River

Masten

Road

SunriverSunriver

La 

Pine

43°55'

50'

45'

121°40' 35' 30' 25' 121°20'

40'

43°35'

Extent of study area model

EXPLANATION

0

5

10

20

50

100

Nitrate concentration

near the water table,

in milligrams N per liter

0 2 4 6 8 MILES

0 42 6 8 10 12 KILOMETERS
For more information, contact:

U.S. Geological Survey

Oregon Water Science Center

2130 SW 5th Ave., Portland, OR 97201

(503) 251-3200 http://or.water.usgs.gov

References Cited

Anderson, C.W., 2000, Framework for regional, coordinated 

monitoring in the middle and upper Deschutes River basins, 

Oregon: U.S. Geological Survey Open-File Report 00-386, 81 p.

Century West Engineering, 1982, La Pine aquifer management 

plan: Bend, Oregon, Century West Engineering, 597 p.

Cole, D.L., 2006, Groundwater quality report for the Deschutes 

basin, Oregon: Oregon Department of Environmental Quality 

Laboratory and Water Quality Division, 54 p.; also available 

online at http://www.deq.state.or.us/lab/techrpts/groundwater/

dbgroundwater/dbgwreport.pdf, last accessed November 9, 2007.

Hinkle, S.R., Böhlke, J.K., Duff, J.H., Morgan, D.S., and Weick, R. 

J., 2007, Aquifer scale controls on the distribution of nitrate 

and ammonium in ground water near La Pine, Oregon, USA: 

Journal of Hydrology, v. 333, p. 486–503.

Hinkle, S.R., Morgan, D.S., Orzol, L.L., and Polette, D.J., 2007, 

Ground water redox zonation near La Pine, Oregon—Relation 

to river position within the aquifer–riparian zone continuum: 

U.S. Geological Survey Scientific Investigations Report 

2007–5239, 28 p.; last accessed November 9, 2007, at http://

pubs.usgs.gov/sir/2007/5239/.

Jones, Lesley, 2003, Characterization of select water quality 

parameters within the upper Deschutes and Little Deschutes 

study areas: Upper Deschutes Watershed Council Bend, 

Oregon: 2003, 127 p.

Morgan, D.S., Hinkle, S.R., and Weick, R.J., 2007, Evaluation 

of approaches for managing nitrate loading from on-site 

wastewater systems near La Pine, Oregon: U.S. Geological 

Survey Scientific Investigations Report 2007–5237, 64 p.; also 

available online at http://pubs.usgs.gov/sir/2007/5237/, last 

accessed November 9, 2007.

Oregon Department of Environmental Quality, 1994, Statewide 

groundwater monitoring program, La Pine area groundwater 

investigation, Deschutes County, Oregon: Portland, Oregon 

Department of Environmental Quality, v. II, variously paginated.

How much nitrate can be put into 

the aquifer while still protecting 

water quality?

The computer model is a tool that can be used to 

help answer this question.

The capacity of the aquifer to receive nitrate

varies throughout the area and depends on factors 

related to geology, climate, chemistry, and nearby 

development. These factors are accounted for by the 

model, allowing it to compute the maximum sustainable 

nitrate loading capacity in each of 95 subareas ranging 

in size from 160 to 640 acres. The maximum sustainable 

loading capacity also depends on the water-quality 

protection goals for the aquifer. Model users set 

the values of water-quality goals, which can be the 

maximum acceptable nitrate concentration in ground 

water, the maximum acceptable discharge of nitrate to 

streams, or both. Goals that are more protective, such 

as limiting nitrate concentrations in ground water to 7 

ppm instead of 10 ppm, reduce the sustainable loading 

capacity of the aquifer (fig. 5). The model can be used

to examine the trade-offs between more stringent 

water-quality goals and the costs of limiting nitrate 

loading. Planners and resource managers also can use 

the model to identify areas where loading from planned 

or existing development exceeds the sustainable nitrate 

loading capacity of the aquifer and devise appropriate 

strategies for reducing loading.

Figure 5. This graph shows the relation between maximum 

acceptable nitrate concentration in ground water and the 

sustainable nitrate loading capacity of the aquifer, as determined 

using the computer model. The graph illustrates that there is a 

trade-off between the sustainable loading capacity and 

water quality goals.

John S. Williams, David S. Morgan, and Stephen R. Hinkle

Illustrations by Jacqueline Olson and Robert Crist

Editing by Debra Grillo

Graphic Design by Bill Gibbs

Base modified from U.S. Geological Survey

1:500,000 state base map, 1982 with digital data from U.S. Bureau of the Census, 

TIGER/Line (R), 1990 and U.S. Geological Survey Digital Line Graphs published at 1:100,000

Publication projection is Lambert Conformal Conic, Standard parallels 42o20’ and 44o40’, 

central meridian -120o30’. Datum is NAD83

Base Credits for figures 1 and 4.

6

MAXIMUM ACCEPTABLE GROUND WATER NITRATE CONCENTRATION, 

IN PARTS PER MILLION

SUSTAINABLE NITRATE LOADING CAPACITY, 

IN THOUSANDS OF POUNDS PER YEAR

0

0

5 10 15 20

20

40

60

80

100

120

140

160

25

Loading if all planned homes use conventional septic systems

Estimated 2005 loading

Sustainable loading for maximum 

nitrate concentration of 

10 parts per million 

Sustainable loading for maximum 

nitrate concentration of 

7 parts per million