U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 072–03

January 2004

Prepared in cooperation with the

Lower Platte South Natural Resources District, the Lower Platte North Natural Resources District, the Papio-Missouri River Natural 

Resources District, and the Lower Platte River Corridor Alliance

Is Septic Waste Affecting Drinking Water From Shallow 

Domestic Wells Along the Platte River in Eastern Nebraska?

By Ingrid M. Verstraeten1, Greg S. Fetterman2, Sonja K. Sebree3, M.T. Meyer4, and T.D. Bullen5

Printed on recycled paper

Significant Findings

The quality of drinking water from shallow 

domestic wells potentially affected by seepage from 

septic systems was assessed by analyzing water samples 

for substances derived from septic systems. The effects 

of septic systems on water from domestic wells was 

demonstrated using several tracers including bacteria, 

virus indicators, dissolved organic carbon, nitrogen 

species, nitrogen and boron isotopes, and organic 

compounds such as prescription and nonprescription 

drugs. Domestic wells seemed to be most vulnerable to 

septic-waste contamination when they were sand-point 

wells within 100 feet of a septic system and were less 

than 45 feet deep in a shallow, thin aquifer. 

Introduction

More than 100 million people in the United States use 

ground water as their source of drinking water (Tuthill and 

others, 1998), and about one-third of the rural and water-front 

population (25 to 30 percent of the households) in the United 

States uses septic systems for wastewater disposal (Robertson 

and others, 1991; McAvoy and others, 1994; U.S. Environmental Protection Agency, 2000). Septic tanks serve primarily as 

settling chambers removing solids from the sewage (fig. 1). In 

sand and gravel aquifers characterized by large pore sizes that 

allow for relatively easy and rapid transport of water and contaminants, concentrated plumes of dissolved constituents from 

septic systems can occur in the shallow part of the aquifer and 

can affect the quality of drinking water withdrawn from domestic wells. In Nebraska, a large number of shallow sand-point 

wells are used to obtain drinking water in private households, 

even though their construction for consumptive uses has been 

banned since 1987 (Nebraska Department of Health and Human 

Services, 2002). Sand-point and cased wells within 15 feet of 

septic systems are used for drinking-water supplies in a few 

cases. 

A study conducted by the U.S. Geological Survey (USGS), 

in cooperation with the Lower Platte South Natural Resources 

District (NRD), the Lower Platte North NRD, the Papio-Missouri River NRD, and the Lower Platte River Corridor Alliance, 

was done in 2001 and 2002 to assess the quality of drinking 

water from shallow domestic wells potentially affected by 

seepage from septic systems. Water samples were analyzed for 

traces of certain substances that indicate the presence of water 

and constituents from septic systems.

1 U.S. Geological Survey, 8987 Yellow Brick Road, Baltimore, MD 21237.

2 Lower Platte River Corridor Alliance, Lincoln, NE 68501.

3 U.S. Geological Survey, Federal Building, Centennial Mall North, 

Room 406, Lincoln, NE 68508.

4 U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, KS 66049.

5 U.S. Geological Survey, Building 15, McKelvey Building, Menlo Park, CA 

94025.

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Figure 1. Diagram of a typical septic system.
The study area covers approximately 300 square miles in 

eastern Nebraska extending from Columbus to the Platte River’s 

confluence with the Missouri River and is defined as the 100-

year flood plain plus a 1-mile buffer on both sides of the Platte 

River (fig. 2). In the study area, depth to the water table generally is less than 10 feet. Wells are completed in sand and gravel 

deposits along the river. Some silt and clay also occur at depths 

of less than 100 feet.

Water samples were collected from 26 domestic wells 

including both sandpoint (no casing) and 

cased (with casing) 

wells (see fig. 3). 

Wells less than 

120 feet deep and 

within 250 feet of 

a septic tank were 

selected within 

the study area and 

were sampled when 

permission from the 

well owners could 

be obtained. The 

water samples were 

analyzed for bacteria, 

coliphages (indicators 

of viruses), forms 

of nitrogen, and 

nitrogen and boron 

isotopes (isotopes 

are different forms 

of an element with 

the same nucleus but 

differing number of 

neutrons), prescription and 

nonprescription drugs, and 

organic contaminants thought 

to be present in wastewater. 

These and other tracers are 

useful for determining whether 

drinking water from domestic 

wells has been affected by 

water and constituents from a 

septic system. Samples were 

analyzed at the Nebraska 

Department of Health, the 

USGS National Water Quality 

Laboratory, and several USGS 

research laboratories.

What We Found Out

The study illustrates that 

shallow wells, whether sandpoint wells or cased wells, can 

be affected by septic waste if 

constructed near a septic field, 

the water table is shallow, and 

the saturated media consist 

mainly of sand and gravel. The 

study results also indicate that bacteria and nitrate concentrations may not always be the best indicators of contamination of 

drinking water with water and constituents from septic systems 

and that other indicators may be more valuable in some cases.

Bacteria and Viruses 

Bacteria, commonly used as indicators of fecal contamination, were not detected. The lack of detections indicates that 

the time required for water to travel from the drain field to the 

well may have been long enough to allow bacteria to die or 

adsorb to sediment because of the presence of iron or ammonium (Gerba and Bitton, 1984). Indicator viruses (male-specific 

coliphages) were detected in 2 of 19 samples. The detections of 

male-specific coliphages in these two water samples indicate the 

presence of fecal contamination in water, perhaps due to short 

traveltimes from the drain fields to the wells.

Nitrogen, Oxygen, and Boron Isotopes

Nitrogen species can change from one compound to another 

through biochemical reactions during infiltration and movement within the sediment as shown in figure 4. Water samples 

from 4 of 26 wells exceeded the U.S. Environmental Protection Agency’s Maximum Contaminant Level of 10 milligrams 

per liter of nitrate as nitrogen (NO3- -N) (U.S. Environmental 

Agency, 2000) (table 1). 

When oxygen is abundant in the ground water, ammonia 

changes to nitrate over short distances through nitrification. In 

the absence of oxygen in the ground water, denitrification can 

occur, and nitrate is changed to nitrogen gas (fig. 4). In water 

from 12 of 19 wells, the presence of ammonia may indicate 

that the distances from septic tank to domestic well were short 

enough that ammonia did not have the opportunity to be transformed to nitrate or nitrogen gas in these cases. In water from 

6 of 19 other wells, the absence of ammonia and presence of 

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Douglas 

Cass 

Saunders 

Lancaster 

Platte 

Polk 

Washington

Colfax Dodge

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Sand-point well Cased

well

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Figure 3. Diagrams of a sand-point well and 

a cased well such as those typically used in 

the study area.

Figure 2. Study area showing general location of shallow domestic wells.
nitrate in water are consistent with sufficient transport time and 

oxygen being available to change ammonia to nitrate through 

nitrification. In water from 1 of 3 wells, the absence of nitrate 

and presence of nitrogen gas are consistent with complete conversion of nitrate to nitrogen gas through denitrification. Finally, 

at two locations, ground water had intermediate oxygen concentrations with both nitrate and nitrogen gas present indicating 

that the denitrification process was incomplete.

Ammonia concentrations seem to be related to well type, 

well depth, and distance of the well to the laterals of a septic 

system. The shallower the sand-point well and the shorter the 

distance from this well to a 

septic system drain field, the 

higher the concentrations of 

ammonia (fig. 5). 

Typically, water affected 

by wastewater has an isotopic 

value of boron of +5 per 

mil or less (Vengosh and 

others, 1994). In this study, 

two of five samples suspected 

to be affected by seepage from 

septic systems on the basis 

of nitrogen concentrations, 

nitrogen isotopes, organic 

carbon concentrations, general 

hydrogeologic and land-use 

setting, and well construction 

had values of -0.2 and 0.7 per mil consistent with the presence 

of septic effluent.

Organic Compounds

Prescription and nonprescription drugs can be indicators of 

wastewater contamination in water from wells. However, these 

organic compounds can be biodegraded or can be adsorbed 

to aquifer media. Eight nonprescription drugs were detected 

in water from 12 of 19 domestic wells at concentrations of as 

much as 0.13 microgram per liter. There are no Maximum ConTable 1. Generalized statistical information of selected variables of interest

[MRL, minimum reporting level; ft, feet; --, not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; <, less than] 

Constituent 

(unit of measure) MRL 

Number 

of samples Minimum Mean Median Maximum

Well depth (ft) -- 26 15 34 29 100

Distance of well to laterals of 

 septic drain field (ft)

 -- 26 25 85 65 250

Dissolved oxygen (mg/L) 0.05 25 .06 1.12 .17 12.0

pH (standard units) .20 26 6.3 7.2 7.2 7.8

Specific conductance (μS/cm) 26 285 550 570 710

Organic carbon, dissolved 

 (mg/L)

 .20 14 .5 2.8 3.1 4.3

Ammonia as nitrogen (mg/L) .04 19 <.04 .40 .17 1.39

Nitrate as nitrogen (mg/L) .05 26 <.05 4.39 <.05 38.7

Nitrite as nitrogen (mg/L) .006 19 <.006 .004 <.006 .09 ��������������

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Nitrite

Nitric oxide

Nitrogen gas

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Figure 4. The nitrification and denitrification processes (from Havlin and others, 1999, p. 87. Adapted by permission of Pearson Education, Inc., Upper 

Saddle River, New Jersey).
taminant Levels for drinking water established by the U.S. Environmental Protection Agency for these compounds. However, 

occurrence of these contaminants in water from a domestic well 

can indicate the presence of local septic waste in the drinking 

water of the household. Whether the source is the owner’s own 

septic field or a neighbor’s septic field was not resolved during 

this study.

Antibiotics were detected in water from 3 of 26 shallow 

domestic wells. These detections occurred in developments 

at sandpit lakes or small towns. At these three locations, 

residences have their own water supply and septic systems 

and are located far from animal feeding operations. Antibiotics that were detected included ciprofloxacin, enrofloxacin, 

sarafloxacin, sulfamethoxazole, trimethoprim, and a degradation product of erythromycin. These antibiotics generally are 

used by humans, but at times also are used to prevent disease in 

livestock at animal feeding operations. Concentrations varied 

from traces of ciprofloxacin to 0.75 microgram per liter of an 

erythromycin degradation product.

What the Results Mean

Water from several domestic wells contained tracers that 

were probably derived from seepage from septic systems. Water 

from domestic wells completed in a shallow (depth to water less 

than 10 feet) were most likely to show evidence of an effect by 

seepage from a septic system and seemed to be more vulnerable to septic-waste contamination if they were sand-point wells 

within 100 feet of a septic-tank system or were less than 45 feet 

deep. Results from this study indicate that drinking water from 

some domestic wells in sandy soil with a shallow aquifer that 

are close to septic drain fields may be affected by seepage from 

septic systems. Under these conditions, lot sizes, densities of 

septic-tank systems, and well construction could be evaluated to 

prevent contamination of drinking water with septic waste. 

Acknowledgments

The authors thank the well owners for participating in the 

project and giving permission to sample their domestic wells. 

We also acknowledge the support from the Nebraska Department of Health, the constructive comments of many other 

Nebraska State and local agencies, and the contributions of Matt 

Landon, JohnKarl Böhlke, Michael Doughten, Steven Zaugg, 

and Jeffrey Cahill of the USGS.

References

Gerba, C.P., and Bitton, Gabriel, 1984, Microbial pollutants—their survival and transport pattern to groundwater, in

Bitton, Gabriel, and Gerba, C.P., eds., Groundwater pollution 

microbiology: New York, John Wiley and Sons, p. 65–88.

Havlin, J.L., Tisdale, S.L., Nelson, W.L., and Beaton, J.D., 

1999, Soil fertility and fertilizers—an introduction to nutrient 

management: Upper Saddle River, New Jersey, Prentice Hall, 

499 p. 

McAvoy, D.C., White, C.E., Moore, B.L., and Rapaport, R.A., 

1994, Chemical fate and transport in a domestic septic system—sorption and transport of anionic and cationic surfactants: Environmental Toxicology and Chemistry, v. 13, no. 2, 

p. 213–221.

Nebraska Department of Health and Human Services, 2002, 

Regulations governing water well construction, pump installation and water well decommissioning standards: Department of Health and Human Services Regulation and Licensure, Title 178B, chap. 12, sec. 004.01. 

Robertson, W.D., Cherry, J.A., and Sudicky, E.A., 1991, 

Ground-water contamination from two small septic systems 

on sand aquifers: Ground Water, v. 29, no. 1, p. 82–92.

Tuthill, M.S., Meikle, D.B., and Alavanja, M.C.R., 1998, 

Coliform bacteria and nitrate contamination: Environmental 

Health, April 1998, p. 16–20. 

U.S. Environmental Protection Agency, 2000, Current drinking 

water standards—national primary and secondary drinking water regulations: Office of Ground Water and Drinking Water, accessed December 27, 2000, at URL: http//

www.epa.gov/safewater/standards.html

Vengosh, A., Heumann, K.G., Juraske, S., and Kasher, R., 1994, 

Boron isotope application for tracing sources of contamination in groundwater: Environmental Science and Technology, 

v. 28, p. 1968–1974.

For further information contact:

U.S. Geological Survey 

Federal Building, Room 406 

100 Centennial Mall North 

Lincoln, NE 68508 

(402) 437–5082

USGS Nebraska District Home Page: http://ne.water.usgs.gov

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Interquartile

range

1.5 x interquartile

range above box

1.5 x 

interquartile

range 

below box

75th percentile Outlier

50th percentile

(median) Number of

samples

25th

percentile

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Figure 5. Ammonia concentration by distance of well to laterals of septic 

system.