Prepared in cooperation with the Connecticut Department of Energy and 

Environmental Protection

Evaluation of the Effects of Sewering on Nitrogen 

Loads to the Niantic River, Southeastern 

Connecticut, 2005–11

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5011
Cover. Photograph of the Niantic River, southeastern Connecticut; Smith Cove is in the foreground. Saunders Point and Pine Grove are in the 

middle of the photograph. Courtesy of the Office of Long Island Sound Programs, Bureau of Water Protection and Land Reuse, Connecticut 

Department of Energy and Environmental Protection.
Evaluation of the Effects of Sewering 

on Nitrogen Loads to the Niantic River, 

Southeastern Connecticut, 2005–11

By John R. Mullaney

Prepared in cooperation with the 

Connecticut Department of Energy and Environmental Protection

Scientific Investigations Report 2015–5011

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Mullaney, J.R., 2015, Evaluation of the effects of sewering on nitrogen loads to the Niantic River, southeastern Connecticut, 2005–11: U.S. Geological Survey Scientific Investigations Report 2015–5011, 30 p., 

http://dx.doi.org/10.3133/sir20155011.

ISSN 2328-0328 (online)
iii

Acknowledgments

The author would like to thank members of the Connecticut Nitrogen Credit Advisory Board and 

the Pine Grove Niantic Association, Kelly Streich of the Connecticut Department of Energy and 

Environmental Protection, and Paul Stacey formerly of the Connecticut Department of Environmental Protection for their assistance. Timothy Frick of the U.S. Geological Survey completed 

extensive sampling efforts for this project, and Denis LeBlanc and Tristen Tagliaferri of the 

U.S. Geological Survey provided technical reviews of this report.

v

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Description of the Study Area ............................................................................................................2

Methods of Data Collection and Analysis .................................................................................................4

Drilling and Well Installation...............................................................................................................4

Water-Quality Field Measurement and Sampling Procedures .....................................................4

Laboratory Measurements..................................................................................................................4

Water-Level Measurements ...............................................................................................................6

Water-Use Estimation ..........................................................................................................................6

Estimation of Nitrogen Loads From Pine Grove...............................................................................7

Estimates of Nitrogen Loads From Groundwater Discharge From Other Regions of the

Lower Niantic River ................................................................................................................7

Hydrogeology and Direction of Groundwater Flow .................................................................................8

Water Quality in the Pine Grove Area ......................................................................................................13

Water Quality Before Installation of Sewers .................................................................................13

Nutrients......................................................................................................................................13

Dissolved Gases.........................................................................................................................13

Major Ions and Field Measurements .....................................................................................13

Water Quality After Installation of Sewers.....................................................................................19

Estimated Nitrogen Loads From Groundwater to the Niantic River....................................................21

Nitrogen Loads Estimated for Pine Grove ......................................................................................21

Predicted Future Nitrogen Loads From Pine Grove ......................................................................22

Comparison of Nitrogen Loads From Pine Grove and Other Niantic 

River Subwatersheds ...........................................................................................................22

Summary and Conclusions.........................................................................................................................25

References Cited..........................................................................................................................................26

Appendix 1. Dissolved Gas Measurements in Groundwater Samples From Pine Grove and 

Sandy Point, Niantic River, Connecticut, August and September 2005 ................................30

Figures

1. Map showing the Pine Grove area of the Niantic River Estuary, southeastern

Connecticut, and the locations of U.S. Geological Survey (USGS)

groundwater-quality monitoring sites and generalized surficial geology ..........................3

2. Schematic cross-section A–A’ through the Pine Grove study area showing the

position of the transition zone between freshwater and saltwater in July and

August 2005....................................................................................................................................9

3. Maps showing the water-table configuration in A, July 2007 and B, November 2010

at the Pine Grove, Connecticut, study area............................................................................10

4. Graphs showing water-table fluctuations in wells A, CT–ELY 67 and B, CT–ELY 81 in

Pine Grove and Saunders Point, Connecticut, in August and September 2011 ...............12

5. Piper diagram showing relations among major anions and cations in water

samples from wells at Pine Grove and Sandy Point on the Niantic River,

Connecticut, in August and September 2005 .........................................................................16
vi

6. Graph showing the relation of chloride-to-bromide ratio to chloride concentration

in groundwater samples collected during August and September 2005 at Pine

Grove and Sandy Point on the Niantic River, Connecticut, and binary mixing curves

representing various potential sources of chloride..............................................................17

7. Graph showing the relation between boron and nitrite plus nitrate nitrogen

concentrations in groundwater samples collected during August and September

2005 at Pine Grove and Sandy Point on the Niantic River, Connecticut............................18

8. Boxplots showing the distributions of total dissolved nitrogen concentrations for

presewering, transition, and postsewering periods at the Pine Grove, Connecticut,

study area ....................................................................................................................................19

9. Map showing total dissolved nitrogen load estimates from groundwater to the

lower Niantic River, Connecticut .............................................................................................23

Tables

1. Site data for wells in Pine Grove, Sandy Point, and Saunders Point on the Niantic

River, Connecticut.........................................................................................................................5

2. Analytes for groundwater samples and analytical methods, Niantic River, 

Connecticut....................................................................................................................................6

3. Statistics for groundwater levels, Pine Grove, Sandy Point, and Saunders Point on

the Niantic River, Connecticut, September 2005 to December 2011....................................9

4. Water-quality analyses of groundwater samples from August and September 2005

from Pine Grove and Sandy Point Niantic River, Connecticut ............................................14

5. Median and mean concentrations of total dissolved nitrogen in groundwater

samples from wells at Pine Grove, Sandy Point, and Saunders Point on the Niantic

River, Connecticut, before, during, and after sewering was completed at 

Pine Grove ...................................................................................................................................20

6. Water use at Pine Grove, Connecticut, 2006–10 ...................................................................21

7. Estimates of total dissolved nitrogen load from the Pine Grove peninsula area to

the Niantic River Estuary, Connecticut, before and after sewering and after total

dissolved nitrogen concentrations have stabilized ..............................................................21

8. Total dissolved nitrogen loads from groundwater discharge for the lower Niantic

River, Connecticut, estimated for 2011....................................................................................24
vii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

inch (in.) 2.54 centimeter (cm)

Area

acre 0.4047 hectare (ha)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2

)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3

)

Flow rate

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

Datum

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

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Supplemental Information

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

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25°C).

Abbreviations

CTDEEP Connecticut Department of Energy and Environmental Protection

NOAA National Oceanic and Atmospheric Administration

PVC polyvinyl chloride

TDN total dissolved nitrogen

USGS U.S. Geological Survey

Evaluation of the Effects of Sewering on Nitrogen Loads to 

the Niantic River, Southeastern Connecticut, 2005–11

By John R. Mullaney

Abstract

Nitrogen concentration data were collected from 20 wells 

near the Niantic River Estuary, during 18 sampling periods 

from 2005 through 2011, as part of a study to determine 

changes in nitrogen concentrations and loads as a result of 

sewering on the Pine Grove peninsula in Niantic, Connecticut. 

The Pine Grove peninsula area is a neighborhood of 35 acres 

containing 172 residences with onsite wastewater treatment 

systems at the beginning of the study in 2005. From 2008 

through 2009, the residences were connected to a newly 

installed sewer system. Water-quality data collection continued from 2010 through 2011, after the sewers were installed.

The peninsula is underlain by glacial stratified deposits. The freshwater in this aquifer ranges from 10 to 45 feet 

(ft) in thickness and overlies saline groundwater. The mean 

water-table altitude was from 0.09 to 0.97 ft above the North 

American Vertical Datum of 1988, with a horizontal hydraulic 

gradient of 0.0004 to 0.0005.

Initial sampling of the wells included analysis for 

nutrients, major ions, boron, bromide, and dissolved gases. 

Concentrations of nitrate plus nitrite nitrogen from the initial 

sampling ranged from 0.94 to 20 milligrams per liter (mg/L) in 

samples collected spatially and with depth in the aquifer. The 

mean concentration of total dissolved nitrogen before the sewers were installed was 7.5 mg/L, and dissolved gas analyses 

indicated little or no denitrification in the aquifer. Chloride to 

bromide ratios and boron analysis of the initial water samples 

confirmed that wastewater was a source of groundwater 

recharge to most of the wells. Annual recharge from onsite 

wastewater-disposal systems in 2006 was 4.98 inches, based 

on analysis of water-use data.

Concentrations of total dissolved nitrogen decreased following sewering in samples from most of the wells that were 

identified as having nitrogen related to wastewater discharge. 

Concentrations of total dissolved nitrogen in individual wells 

decreased by as much as 11.7 mg/L between the periods 

before and after the sewers were installed, and the mean concentration of total dissolved nitrogen in all wells decreased by 

2.3 mg/L to a mean concentration of 5.2 mg/L.

Nitrogen loads from groundwater in the Pine Grove peninsula area were estimated for three time periods by using the 

measured mean concentrations of total dissolved nitrogen and 

estimated recharge rates. The estimated nitrogen load before 

sewering was 1,675 pounds per year (lb/yr) and following 

sewering was 963 lb/yr. Mean concentrations of total dissolved nitrogen were assumed to have been reduced to 1.1 to 

2.3 mg/L after the aquifer had stabilized and sewage-related 

nitrogen had been completely discharged from the system, 

with an estimated future load of 202 to 423 lb/yr.

Nitrogen loads from groundwater discharge to the 

Niantic River Estuary from the lower part of the Niantic 

River watershed, including Pine Grove, were estimated to be 

18,800 pounds (lb) in 2011. This compares with an additional 

51,000 lb from the surface-water tributaries to the estuary and 

an unknown quantity of nitrogen load from stormwater runoff 

in the lower Niantic watershed.

Introduction

Septic systems have been long recognized as a source of 

excess nitrogen to estuaries, although the contribution as part 

of the overall nitrogen budget to embayments and the ocean is 

poorly understood. Estimates of the contribution of nitrogen 

from septic systems in the lower part of the Long Island Sound 

watershed are as high as 17 percent of the annual nonpoint 

source load (Georgas and others, 2009). These contributions 

may be locally important as a source of nitrogen to some 

embayments and their associated ecosystems (Valiela and others, 1990). Information is currently lacking on the importance 

of the contribution of nitrogen loads from groundwater, and 

specifically septic systems, to Long Island Sound (Latimer and 

others, 2014). 

The Niantic River is an estuary at the mouth of a developed 30.2-square mile (mi2

) coastal basin in southeastern 

Connecticut on Long Island Sound (fig. 1). The eelgrass beds 

of the Niantic River function as a nursery and feeding ground 

for a number of recreationally and commercially important bird, 

shellfish, and finfish species. Many people enjoy the recreational 
2 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

opportunities afforded by the river, including boating, kayaking, sailing, swimming, fishing, and shellfishing. Although 

the Niantic River continues to serve all these functions, it has 

experienced fluctuations in water quality during the past few 

decades. The river once supported a major recreational scallop 

fishery that has declined drastically (Marshall, 1994). Episodic 

summertime hypoxia events in bottom waters of the upper estuary have occurred.

The presence of so-called nuisance macroalgae in the 

Niantic River indicates that nitrogen loads are relatively high, 

though currently low enough to provide a suitable environment 

for eelgrass (Jamie Vaudrey, University of Connecticut, written 

commun., April 2012). Excessive nitrogen loading to the Niantic 

River is considered to be a major cause of the decline and 

variability in the density of eelgrass populations (Connecticut 

Department of Environmental Protection, 2006b). Currently, the 

Niantic River one of the first areas in Long Island Sound where 

eelgrass is present when moving from west (New York City area) 

to east along a gradient of improving water quality (Latimer and 

others, 2014). Therefore, the Niantic River is currently thought 

to have marginal water quality with respect to eelgrass habitat.

The Connecticut Department of Energy and Environmental Protection (CTDEEP) has listed the Niantic River on the 

impaired waters list of the State of Connecticut (Clean Water 

Act, 33 U.S.C. §§1313 and 1315); the river is impaired as a 

habitat for marine fish, other aquatic life, and wildlife. The listed 

potential causes for this impairment include eutrophication 

resulting from nutrients, with sources such as industrial pointsource discharges, illicit discharges, remediation sites, groundwater contamination, and insufficient septic systems (Connecticut Department of Energy and Environmental Protection, 2012, 

table 3–4). Other more general sources of elevated nutrients 

include atmospheric deposition, stormwater runoff, and groundwater discharge from developed areas, including discharge from 

septic systems adjacent to the Niantic River. During the past 

two decades, point-source nutrient loads associated with failing, 

privately maintained, onsite septic systems have been reduced 

along most of the developed shoreline of the Niantic River 

through the installation of municipal sewer systems (Connecticut Department of Environmental Protection, 2006b).

The Pine Grove neighborhood, a residential area on a 

peninsula in the Niantic River (fig. 1), contains 172 homes 

on an area of about 35 acres. In 2004, the town of East Lyme, 

Connecticut, approved sanitary sewers for the Pine Grove 

neighborhood. Sewer installation began in 2006, and the 

majority of residences were connected from 2007 through 

2009. The sewering project presented an opportunity to document changes in nitrogen concentrations and loads to improve 

the understanding of management alternatives for reducing 

nitrogen loads in similar unsewered areas, which are common 

in the coastal areas of Long Island Sound.

In 2005, the U.S. Geological Survey (USGS) entered 

into a cooperative agreement with the CTDEEP to document 

groundwater-quality conditions and loading of nitrogen from 

groundwater in Pine Grove in 2005 and subsequent to sewering until at least 2010. 

Purpose and Scope

This report provides information on the concentrations of 

nitrogen and major ions in the groundwater of the Pine Grove 

neighborhood in Niantic, Conn., and the process of denitrification in the groundwater during the early part of the study. 

The report also provides information on the concentrations 

of nutrients in the groundwater at this study area from 2005 

through 2011 and estimates of the groundwater discharge of 

nitrogen leaving the Pine Grove area before and after sewers 

were installed. The report also provides estimates of the load 

of nitrogen from groundwater discharge in other regions of the 

Niantic River watershed that are adjacent to the Niantic River 

as part of the overall nitrogen budget.

Description of the Study Area

The Niantic River Basin in coastal southeastern Connecticut drains an area of 30.2 mi2

 and lies between the Connecticut River Basin on the west and the Thames River Basin on 

the east (fig. 1). The Niantic River Estuary is primarily a saltwater environment that covers an area of 1.25 mi2

 at the mouth 

of the basin. The lower part of the Niantic River basin has a 

4.1 mi2 area downstream from streamgages established by the 

USGS on the three major tributaries from 2007 through 2012 

(Mullaney, 2013). The altitude of this lower watershed area 

ranges from sea level to about 270 feet (ft) above the North 

American Vertical Datum of 1988 (NAVD 88). Mean annual 

precipitation at nearby New London, Conn., is 48.7 inches per 

year (in/yr; Brown and others, 2011).

The surficial geology of the Niantic River Basin includes 

deposits of glacial till of varying thickness that underlie 

63 percent of the lower watershed and coarse-grained glacial 

stratified deposits that underlie 37 percent of the watershed in 

areas next to the Niantic River (Stone and others, 1992). The 

surficial geology controls whether groundwater discharge or 

overland runoff is the dominant source of water and nutrients 

to surface waters in different regions of the basin. Areas with 

coarse-grained glacial stratified deposits have higher groundwater recharge rates than areas with glacial till and consequently provide an important source of groundwater discharge 

to estuaries or other surface-water bodies (Thomas, 1966).

As of 2005, the only areas with municipal sewer systems 

were in the town of Waterford, Conn., on the eastern side of 

the Niantic River and at Camp Niantic, a Connecticut National 

Guard training site on the western side of the Niantic River. 

Sewering of the Pine Grove neighborhood began in 2006 

and was completed in 2009. Most of the lower Niantic River 

watershed is also served by public water supplied from outside 

the watershed. The newly installed sewers flow to the New 

London wastewater treatment facility where the treated wastewater is discharged to the Thames River.

The Pine Grove neighborhood is on a peninsula in the 

Niantic River on an area of about 35 acres. The entire peninsula is underlain by coarse-grained glacial stratified deposits. All the 172 residences in the area were served by septic 
Introduction 3

Figure 1. The Pine Grove area of the Niantic River Estuary, southeastern Connecticut, and the locations of U.S. 

Geological Survey (USGS) groundwater-quality monitoring sites and generalized surficial geology. Ave, avenue; 

Cem, cemetery; Ct, court; Dr, drive; N, north; Pkwy, parkway; Rd, road; S, south; St, street.

72°12' 72°10'30" 72°9'

41°21'

41°19'30"

Niantic Bay

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

CONNECTICUT

1 2 3

4 5 6

7 8

9

10

Areas with glacial stratified deposits or alluvium

8 Well or well cluster location and map number

Niantic River watershed 

Base from U.S. Geological Survey GeoPDF, 2011, 1:24,000 scale Geology modified from Stone and others, 1992

Niantic River

EXPLANATION

Waterford

East Lyme

11

Lower Niantic River watershed 

A

A'

A A'

Line of section—See figure 2
4 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

systems and public water supply at the beginning of this study. 

The study area was originally developed from the late 1800s to 

the 1930s; homes were initially served by onsite shallow wells 

but were connected to the public water supply from outside 

of the watershed in about 1970; many of these residences are 

only used seasonally in this coastal community. The area is 

bordered on the south by Camp Niantic.

Methods of Data Collection and 

Analysis

Data collection for this project included drilling and 

well installation to obtain groundwater samples from the 

Pine Grove area as well as Saunders Point and Sandy Point. 

Groundwater-quality data were collected during 18 different sampling periods between August 2005 and December 

2011. During the first sampling of the wells, the samples were 

analyzed for nutrients, major anions and cations, bromide, 

boron, and dissolved gases. During the remaining 17 sampling 

periods, samples were analyzed only for nutrients.

Nitrogen concentration data were analyzed to determine 

if concentrations had changed as a result of the completion 

of the sewering project. Nitrogen loads from the study area 

from groundwater were estimated by multiplying estimated 

recharge rates and mean concentrations of total dissolved 

nitrogen (TDN) both before and after the sewering project 

was completed. Recharge rates before the installation of 

sewers included the discharge of water from septic systems 

at residences served by public water supply. Water-use data 

were analyzed to determine additional recharge inputs from 

septic systems.

Nitrogen loads to the Niantic River from other parts of 

the lower Niantic River Basin were estimated by using available nitrogen concentration data from this study and other 

studies, along with estimated recharge rates and estimated 

water use in areas with septic systems.

Drilling and Well Installation

Drilling sites were selected in order to characterize 

groundwater quality in the middle of the Pine Grove peninsula, 

along the coastline, and with depth in the aquifer (table 1). 

Test holes were drilled with the use of a truck-mounted auger 

drilling rig and hollow-stem augers for geologic sampling and 

well installation. Drilling proceeded in a sequential manner 

at each location. At selected depths, the geologic materials 

were sampled by use of a split-spoon sampler. After each 

geologic sample was recovered, the specific conductance was 

measured inside the hollow stem of the auger with a downhole 

conductivity probe. The conductance data were used qualitatively to determine the depth at which the water in the aquifer 

was becoming brackish, indicating the transition from fresh 

to saline groundwater. Wells were set at one to three depths 

in the aquifer. The deepest well at each location was set by 

using schedule 40 polyvinyl chloride (PVC) casing and 2 feet 

of number 10 slotted PVC well screen. At four locations, a 

second sampling point was set at a shallower depth (ranging from 7 to 25 feet above the well screen; table 1) by using 

0.25-inch (in.) inside diameter polyethylene tubing. The tubing 

was attached to the outside of the deepest well, and the tip of 

the tubing was covered with a nylon mesh to screen out the 

aquifer materials. These sampling ports were designed to be 

sampled with a peristaltic suction pump. At two locations, a 

third well was installed just below the water table. Wells were 

finished with a bentonite seal above any screened sections or 

sampling ports (near the water table) and with concrete and a 

flush-mounted well box at the land surface.

Water-Quality Field Measurement and Sampling 

Procedures

Groundwater samples were collected from all wells during 18 different sampling periods between September 2005 

and December 2011. Field sampling procedures were based on 

the methods described in U.S. Geological Survey (undated b). 

The general water sampling methods are described below.

At each site, the water level in the well was measured 

before sampling. The volume of water in the casing and screen 

of each well was determined, and the well was sampled by 

using a positive displacement gear-drive pump. The sampling 

points constructed with 0.25-in.-diameter tubing were sampled 

by using a peristaltic pump that was connected directly to the 

top of the tubing. Before sample collection, wells were purged 

at a low-flow pumping rate until three to five casing volumes 

had been removed from the well and the field measurements 

for specific conductance, temperature, and dissolved oxygen 

concentration had stabilized. Similarly, the sampling points 

were purged at a low-flow rate until approximately 2 to 3 gallons of water had been pumped and the field water-quality 

characteristics had stabilized. Samples for nutrients and major 

ions were filtered with use of a 0.45-micrometer capsule filter.

Methods used to collect water samples during one 

sampling event in 2005 for analysis of dissolved gases are 

described in U.S. Geological Survey (undated a).

Laboratory Measurements

The analytical methods used to analyze groundwater 

samples for nutrients and major anions and cations at the 

USGS National Water Quality Laboratory are summarized in 

table 2. Analytical results were entered into the National Water 

Information System database by laboratory personnel. Major 

anions and cations and dissolved gases were analyzed only 

for the first round of sampling that occurred in August and 

September 2005. TDN was determined from the sum of nitrite 

plus nitrate nitrogen and dissolved ammonia plus organic 

nitrogen. If dissolved ammonia plus organic nitrogen was less 

than the reporting limit, then only nitrite plus nitrate values 

were used.
Methods of Data Collection and Analysis 

5

Table 1. Site data for wells in Pine Grove, Sandy Point, and Saunders Point on the Niantic River, Connecticut.[Latitude and longitude are in degrees, minutes, and seconds. fig., figure; USGS, U.S. Geological Survey; ID, identification number; NAVD 88, North American Vertical Datum of 1988; --, no data; pt, no well screen, point interval]

Site 

number 

(fig. 1)

USGS local 

ID Station ID

Date of 

construction Latitude (° ’ “) Longitude (° ’ “)

Altitude of 

land surface, 

in feet above 

NAVD 88

Depth of 

well, in feet 

below land 

surface

Screened interval, in feet below 

land surface

Geologic materials in contact 

with the well screen

11 CT–WT 62 412101072105501 8/24/2005 41 21 01.7 72 10 54.8 22.8 57.9 55.9–57.9 Coarse to very coarse sand11 CT–WT 63 412101072105502 8/24/2005 41 21 01.7 72 10 54.8 22.8 29.75 27.75–29.75 Coarse to very coarse sand, granule gravel

9 CT–ELY 63 412005072110501 7/19/2005 41 20 05.2 72 11 04.8 13.40 36.77 34.77–36.77 Coarse to very coarse sand9 CT–ELY 65 412005072110503 7/19/2005 41 20 05.2 72 11 04.8 13.70 22.82 20.82–22.82 Medium to coarse sand, little pebble gravel, 

little fine to medium sand

3 CT–ELY 66 412014072110701 7/20/2005 41 20 14.3 72 11 07.2 17.31 22.86 20.86–22.86 Coarse to very coarse sand2 CT–ELY 67 412014072111001 7/20/2005 41 20 13.9 72 11 10 19.85 28.08 26.08–28.08 Medium to coarse sand, some fine sand6 CT–ELY 68 412010072110401 7/21/2005 41 20 10.5 72 11 04.4 13.68 25.59 23.59–25.59 Very fine to fine sand1 CT–ELY 69 412013072111701 7/21/2005 41 20 13.2 72 11 17.4 20.20 32.75 30.75–32.75 Very coarse sand, gravel1 CT–ELY 70 412013072111702 7/21/2005 41 20 13.2 72 11 17.4 6.00 23 pt Very coarse sand, pebble gravel4 CT–ELY 71 412006072111801 7/22/2005 41 20 05.8 72 11 17.5 6.00 28.3 26.3–28.3 Coarse to very coarse sand, medium sorted4 CT–ELY 72 412006072111802 7/22/2005 41 20 05.8 72 11 17.5 -- 10 pt Coarse to very coarse sand5 CT–ELY 73 412007072111001 7/25/2005 41 20 06.6 72 11 09.7 20.49 62.21 60.21–62.21 Fine to medium sand5 CT–ELY 74 412007072111002 7/25/2005 41 20 06.6 72 11 09.7 -- 45 pt Coarse to very coarse sand5 CT–ELY 75 412007072111003 7/25/2005 41 20 06.6 72 11 09.7 20.47 28.63 26.63–28.63 Coarse to very coarse sand7 CT–ELY 76 412002072111601 7/27/2005 41 20 01.7 72 11 16.4 12.58 51.25 49.25–51.25 Medium to coarse sand, some gravel to 1 inch7 CT–ELY 77 412002072111602 7/27/2005 41 20 01.7 72 11 16.4 12.58 22.87 20.87–22.87 Coarse to very coarse sand8 CT–ELY 78 412001072110701 8/23/2005 41 20 01.1 72 11 07.3 16.93 54.27 52.27–54.27 Fine to medium sand8 CT–ELY 79 412001072110702 8/23/2005 41 20 01.1 72 11 07.3 16.93 41 pt Coarse to very coarse sand, some pebble gravel8 CT–ELY 80 412001072110703 8/23/2005 41 20 01.1 72 11 07.3 16.89 28.45 26.45–28.45 Fine to medium sand

10 CT–ELY 81 412023072111101 7/28/2005 41 20 22.7 72 11 10.9 14 23.2 21.2–23.2 Fine to coarse sand, pebble gravel
6 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Dissolved gas measurements (nitrogen, argon, oxygen, 

carbon dioxide, and methane) were used to determine excess 

air and recharge temperature of the groundwater and whether 

excess nitrogen gas, which is an indicator of denitrification in 

the groundwater-flow system (Lindsey and others, 2003), was 

present. Samples were analyzed by using methods described 

by Busenberg and others (1998). Excess nitrogen gas was 

estimated by using the procedure outlined in Lindsey and others (2003, p. 14). Dissolved gas measurements are shown in 

appendix 1.

Water-Level Measurements

Water-level measurements were made at all wells before 

water-sample collection. Continuous water-level data were 

collected with the use of submersible pressure transducers 

in five wells for different periods of time. Water levels were 

measured in two wells (CT–ELY 67 and CT–ELY 81) intermittently from 2006 through 2011 in order to understand the 

long-term trends in fluctuation at Pine Grove and in an area 

that was not undergoing sewering (Saunders Point; fig. 1). 

Additional manual water-level measurements were made at 

the wells where pressure transducers were installed as part 

of the overall data collection and as a check to determine if 

the transducers were reading accurately. The altitudes of the 

measuring points of the wells in Pine Grove were surveyed 

and referenced to a benchmark on the newly constructed sewer 

pumping station.

Water-Use Estimation

Water-use data were analyzed to estimate the amount of 

recharge from onsite wastewater treatment systems before the 

installation of sewers. This information was used as an input 

for the estimation of recharge associated with wastewater and 

nitrogen loads discharged to the groundwater at the study site. 

The water-use data were compiled for the period from 2006 

through 2010 from meter readings for individual properties 

in the study area (Brad Kargl, East Lyme Water and Sewer 

Department, written commun., 2011). It was assumed, based 

on information from the USGS water-use program (U.S. 

Geological Survey, 1995), that consumptive water use was 

14 percent and that 86 percent of the water used was returned 

to the aquifer via septic systems.

Table 2. Analytes for groundwater samples and analytical methods, Niantic River, Connecticut.

Analyte Reporting limit, 

in milligrams per liter Reference to methodology

Nitrogen, ammonia, filtered 0.01 Fishman (1993)

Nitrogen, ammonia and organic, filtered 0.07 Patton and Truitt (2000)

Nitrogen, nitrite, filtered 0.001 Fishman (1993)

Nitrogen, nitrite and nitrate, filtered 0.04 Patton and Kryskalla (2011), Fishman (1993)

Phosphorus, filtered 0.003 U.S. Environmental Protection Agency (1993)

Phosphorus, phosphate, ortho, filtered 0.004 Fishman (1993)

Bromide 0.01 Fishman and Friedman (1989)

Boron 2 Struzeski and others (1996)

Calcium 0.022 Fishman (1993)

Chloride 0.06 Fishman and Friedman (1989)

Fluoride 0.04 Fishman and Friedman (1989)

Iron 4 Fishman (1993)

Magnesium 0.011 Fishman (1993)

Manganese 0.16 Fishman (1993)

Potassium 0.03 Clesceri and others (1998)

Residue, 180 degrees Celsius (total dissolved solids) 20 Fishman and Friedman (1989)

Silica 0.018 Fishman (1993)

Sodium 0.06 Fishman (1993)

Sulfate 0.09 Fishman and Friedman (1989)
Methods of Data Collection and Analysis 7

Estimation of Nitrogen Loads From Pine Grove

Nitrogen loads from Pine Grove to surrounding surfacewater discharge areas were estimated from rates of natural 

recharge from precipitation, artificial recharge from septic 

systems, and the mean nitrogen concentrations in the groundwater with time. It was assumed that nitrogen loads can be 

represented by the following equation:

Nt

R R n s Navg = ( ) + ×

106

, (1)

where

Nt = estimated nitrogen load from the Pine 

Grove area at time t,

Rn = the mean annual effective recharge from 

precipitation,

Rs = the combined rate of recharge from onsite 

wastewater treatment systems, and

Navg = the mean concentration of nitrogen in the 

aquifer at time t.

Nt was converted from kilograms to pounds for consistency 

with previous reports (Mullaney, 2013).

Natural recharge was estimated by using a relation 

between recharge rate and mean annual runoff that was developed by Mazzaferro and others (1979). The relation as applied 

to the Pine Grove study area, which is completely underlain 

by glacial stratified deposits, indicates that the recharge rate 

is about 95 percent of the mean annual runoff. The mean 

annual runoff for this area was previously calculated to be 

24.4 in/yr (Weiss, 1983), yielding a recharge rate of 23.2 in/yr 

based on the 95 percent figure. During October 2008 through 

September 2011, the runoff from Stony Brook, a tributary 

of the Niantic River that is unaffected by water diversions, 

ranged from 27.3 to 40.7 in/yr (Mullaney, 2013), indicating 

that runoff conditions were higher than normal for that period.

Recharge rates to the Pine Grove area can be reduced 

by impervious cover that diverts water to storm drains and 

reduces the infiltration of the water through the unsaturated 

zone. It was estimated that about 23 percent of the study area 

is covered with impervious surfaces, potentially reducing natural rates of recharge by as much 23 percent. The impervious 

area was estimated by use of an impervious surface analysis 

tool developed by Chabaeva and others (2004), with impervious surface coefficients for Connecticut developed by Prisloe 

and others (2003). In reality, not all precipitation that falls on 

impervious surfaces is discharged to storm drains; much of it 

runs off of these surfaces and infiltrates the well-drained soils 

in the study area.

Estimates of Nitrogen Loads From Groundwater 

Discharge From Other Regions of the Lower 

Niantic River

Estimates of nitrogen load from groundwater discharge 

were similarly calculated for other regions of the lower Niantic River (fig. 1) by multiplying estimated recharge rates by 

measured or estimated nitrogen concentrations in groundwater 

or stream base flow. Nitrogen concentration data from three 

sources were used to make these estimates: (1) groundwater 

samples that were collected on Sandy Point and Saunders 

Point and analyzed for TDN as part of this study, (2) stream 

base flow samples that were collected by Mullaney (2013) in 

two small subbasins of the lower Niantic River, and (3) shallow groundwater samples that were collected by the University of Connecticut from shallow wells temporarily installed 

at 60 locations around the perimeter of the Niantic River in 

2003 (Jamie Vaudrey, University of Connecticut, Department 

of Marine Sciences, written commun., April 2012). In a case 

where there were no nitrogen concentration data corresponding to an area, concentrations of TDN were estimated by 

extrapolation of data from the above sources on the basis of a 

qualitative comparison of land-use characteristics and whether 

or not the area was sewered.

The lower basin of the Niantic River (downstream from 

the streamgages installed for another study; Mullaney, 2013) 

was divided into basin segments based on surficial geology 

(glacial till or stratified deposits). Two of the segments were 

existing surface-water sampling sites where nitrogen and flow 

data were reported in Mullaney (2013).

Estimates of nitrogen loads from each segment were 

calculated by multiplying the estimated recharge rates (23.2 in. 

for glacial stratified deposits, 8.6 in. for glacial till) by the 

estimated TDN concentration; these values were confirmed by 

using the method described in Mazzaferro and others (1979). 

Recharge rates were adjusted for areas served by septic 

systems because the water for domestic use is imported from 

outside the drainage basin of the Niantic River. Estimates of 

water use in these areas were based on the number of residences (assuming two persons per household) and per capita 

water-use data from U.S. Geological Survey (1995).
8 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Hydrogeology and Direction of 

Groundwater Flow

The logs from the well drilling indicate that the Pine 

Grove area is underlain by generally coarse-grained sand and 

gravel with a maximum thickness of 64 ft at well CT–ELY 73 

(fig. 1, site 5). At this location, glacial till was encountered 

from 64 to 68 ft below land surface. The change in electrical 

conductivity in the water in the bottom of the hollow-stem 

auger during drilling indicated a gradual transition from freshwater to saltwater (fig. 2).

In July and August 2005, the thickness of the freshwater 

layer (difference between the altitude of the water table and 

top of the transition zone to saltwater) at Pine Grove ranged 

from about 10 ft at the northern end of the study area (well 

CT–ELY 66; fig. 1, site 3) to about 45 ft at the southwestern 

side of the study area (well CT–ELY 76; fig. 1, site 7) and 

averaged 27 ft. On Saunders Point (fig. 1, site 10), saltwater 

was not encountered during drilling. On Sandy Point, the 

freshwater thickness was about 43 ft (fig. 1, site 11). The top 

of the transition zone was identified by a change in specific 

conductance to greater than 1,000 microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25°C ).

The mean depth to the water table (for manual waterlevel measurements made from 2005 through 2011) in wells 

at Pine Grove ranged from 5.26 to 19.92 ft below land surface; 

the differences in mean depth to the water table were related 

primarily to differences in the land-surface altitude, which 

ranged from 6.00 to 20.49 ft above NAVD 88. The mean 

altitude of the water level in individual wells, (for measurements made from 2005 through 2011) ranged from 0.09 ft 

(CT–ELY 66; fig. 1, site 3) to 0.97 ft (CT–ELY 78; fig. 1, site 

8). Mean sea level for the Niantic River was estimated from 

the published values for the nearby National Oceanic and 

Atmospheric Administration (NOAA) tidal station at New 

London, Conn. (National Oceanic and Atmospheric Administration, undated). Mean sea level in the Niantic River at Pine 

Grove is estimated to be –0.30 ft below NAVD 88.

The annual fluctuations in the water table during the 

study period were typically less than 0.5 ft, as determined by 

the interquartile range of water levels (table 3). The maximum 

change in water level in the wells was about 2 ft during early 

spring 2010, in response to recharge from a large precipitation 

event of 9.2 in. on March 30, 2010 (Mullaney, 2013).

The water-level altitude data were mapped for 2007 and 

2010 coincidentally with the sampling activities in order to 

determine groundwater flow directions and the horizontal 

hydraulic gradient of the water table (fig. 3A, B). Fluctuations 

in water levels owing to variations in recharge from precipitation and tides may affect these maps because the measurements were made when water samples were being collected 

over a 2-week period. The time periods selected were those 

with little precipitation in order to minimize the fluctuations. 

Water levels in the wells at Pine Grove fluctuate in response 

to the tides, making it difficult to get an accurate snapshot in 

time. Continuous water-level data from selected wells indicate the daily tidal response. Typical daily fluctuations in well 

CT–ELY 67, which is in the northern end of the study area and 

adjacent to the Niantic River (fig. 1, site 2) were in the range 

of 0.3 to 0.5 ft (fig. 4A). In the middle of the Pine Grove study 

area at well CT–ELY 73 (fig. 1, site 5), water-level fluctuations 

owing to tidal influence were apparent, but only on the order 

of 0.01 ft (hydrograph not shown). The water levels in the 

wells at Pine Grove also responded to a storm surge on August 

28, 2011, during tropical storm Irene. Water levels rose by 

about 1.5 ft in well CT–ELY 67 and 0.5 ft in well CT–ELY 81 

(fig. 4A, B) in response to a storm surge that reached a 

maximum altitude of 5.07 ft above NAVD 88 at nearby New 

London (McCallum and others, 2012).

The configurations of the water table in July 2007 

and November 2010 indicate groundwater-flow directions 

predominantly toward the north, with components toward 

the Niantic River and Smith Cove. The horizontal gradient is 

shallow during these two time periods, ranging from about 

0.0004 to 0.0005, likely indicative of the high hydraulic 

conductivity of the coarse-grained sand and gravel deposits at 

Pine Grove.
Hydrogeology and Direction of Groundwater Flow 9

Distance, in feet

-70

-80

-50

-30

-40

-60

-10

-20

10

0

30

20

50

60

40 CT−ELY 78−80 CT−ELY 73−75

CT−ELY 67

CT−ELY 81

Pine Grove

Saunders 

Point

Altitude, in feet above NAVD 88

Niantic River

0 500 1,000 1,500 2,000 2,500 3,000

?

A A'

CT–ELY 73 Well and identification number

Saltwater level—Top of transition zone to saltwater level in July and August 2005; 

specific conductance greater than 1,000 μS/cm at 25 °C. Dashed where 

inferred; question mark where uncertain 

Freshwater level

Land surface

EXPLANATION

Figure 2. Cross-section A–A' through the Pine Grove study area showing the position of the transition zone between 

freshwater and saltwater in July and August 2005. μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; NAVD 88, 

North American Vertical Datum of 1988.

Table 3. Statistics for groundwater levels, Pine Grove, Sandy Point, and Saunders Point on the Niantic River, Connecticut, 

September 2005 to December 2011.

[fig., figure; USGS, U.S. Geological Survey; ID, identification number; NAVD 88, North American Vertical Datum of 1988]

Site number 

(fig. 1) USGS local ID Number of measurements

Mean depth to groundwater, 

in feet below land surface

Mean altitude of groundwater, 

in feet above NAVD 88

Interquartile range, 

in feet 

11 CT–WT 62 25 22.25 0.55 0.27

11 CT–WT 63 18 22.26 0.54 0.45

9 CT–ELY 63 29 13.03 0.37 0.53

9 CT–ELY 65 21 13.09 0.61 0.24

3 CT–ELY 66 21 17.22 0.09 0.34

2 CT–ELY 67 41 19.55 0.30 0.38

6 CT–ELY 68 20 13.23 0.45 0.3

1 CT–ELY 69 19 19.92 0.28 0.3

3 CT–ELY 71 26 5.26 0.74 0.37

5 CT–ELY 73 27 19.65 0.84 0.36

5 CT–ELY 75 20 19.71 0.76 0.36

7 CT–ELY 76 18 11.62 0.96 0.44

7 CT–ELY 77 18 11.62 0.96 0.48

8 CT–ELY 78 18 15.96 0.97 0.4

8 CT–ELY 80 18 15.93 0.96 0.38

10 CT–ELY 81 35 13.80 0.20 0.36
10 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

0.45 Water table contour and

 altitude—Datum is NAVD 88.

 Contour interval 0.1 ft

0.55

0.45

0.35

0.25

0.15 -0.05

-0.15

-0.05

0.05

Base from Esri ArcGIS, 2014

72°11'30" 72°11'

41°20'

41°20'15"

0 0.05 0.1 0.2 MILE

0 0.05 0.1 0.2 KILOMETER

Smith

Cove

Niantic 

River

Well or well cluster

A

EXPLANATION

Figure 3. The water-table configuration in A, July 2007 and B, November 2010 at the Pine Grove, Connecticut, study area. ft, feet; 

NAVD 88, North American Vertical Datum of 1988. Satellite imagery is the intellectual property of Esri and is used under license; 

copyright © 2014 Esri and its licensors.
Hydrogeology and Direction of Groundwater Flow 11

0.5

0.4

0.3

0.2

0.1

0.0

72°11'30" 72°11'

41°20'

0.7

Water table contour and

 altitude—Datum is NAVD 88.

 Contour interval 0.1 ft.

 Dashed where inferred

Base from Esri ArcGIS, 2014

0.7

0.6

Smith

Cove

Niantic 

River

B

72°11'30" 72°11'

41°20'

41°20'15"

0 0.05 0.1 0.2 MILE

0 0.05 0.1 0.2 KILOMETER

EXPLANATION

Well or well cluster

Figure 3. The water-table configuration in A, July 2007 and B, November 2010 at the Pine Grove, Connecticut, study area. ft, feet; 

NAVD 88, North American Vertical Datum of 1988. Satellite imagery is the intellectual property of Esri and is used under license; 

copyright © 2014 Esri and its licensors.—Continued
12 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Figure 4. Water-table fluctuations in wells A, CT–ELY 67 (site 2 on figure 1) and B, CT–ELY 81 (site 10 on figure 1) in Pine 

Grove and Saunders Point, Connecticut, in August and September 2011. NAVD 88, North American Vertical Datum of 1988.

Aug. 1 Aug. 8 Aug. 15 Aug. 22 Aug. 29 Sept. 5 Sept. 12 Sept. 19 Sept. 26

2011

20.0

19.5

19.0

18.5

18.0

17.5 2.35

1.85

1.35

Water level, in feet below land surface 

CT−ELY 67

2011

13.8

13.6

13.4

13.2

13.0

Water level, in feet below land surface

CT−ELY 81

A

B

14.0

Aug. 1 Aug. 8 Aug. 15 Aug. 22 Aug. 29 Sept. 5 Sept. 12 Sept. 19 Sept. 26

Water level, in feet above or below NAVD 88

0.85

0.35

-0.15

1.0

0.8

0.6

Water level, in feet above or below NAVD 88

0.4

0.2

0
Water Quality in the Pine Grove Area 13

Water Quality in the Pine Grove Area

Changes in nitrogen concentrations were analyzed from 

2005 through 2011. The initial water-quality data from the first 

sampling period (2005) included concentrations of nutrients, 

dissolved gases, major ions, bromide, and boron. Data for the 

other 17 sampling periods included only nutrient analyses.

Nitrogen loads from the study area were estimated for 

2006 and 2011 and for a future time when nitrogen concentrations have stabilized at lower values than before sewers were 

installed in the study area. Regionally, nitrogen loads from 

groundwater to the Niantic River were estimated for 2011 on 

the basis of data from this and previous studies.

Water Quality Before Installation of Sewers

The initial water-quality samples were collected in 2005 

at all wells installed on the Pine Grove peninsula and at two 

wells installed at different depths on Sandy Point. Waterquality samples were not collected from the single well on 

Saunders Point because the well had not yet been installed 

at the time the initial water-quality samples were collected. 

Samples were analyzed for field water-quality characteristics 

and concentrations of nutrients, major ions, and dissolved 

gases. Selected water-quality analyses from the first round of 

samples are shown in table 4.

Nutrients

The focus of this study was on nitrogen because of the 

concerns that excessive nitrogen loading was affecting the 

habitats along the Niantic River. Most of the nitrogen in the 

groundwater samples was in the form of nitrate nitrogen, 

suggesting that ammonification and subsequent nitrification 

of the organic nitrogen in wastewater had occurred in the 

septic systems and unsaturated zone. Concentrations of nitrite 

were generally below the reporting limit. Nitrate plus nitrite 

nitrogen ranged from 0.94 to 20 milligrams per liter (mg/L, as 

nitrogen), with a median value of 3.29 mg/L and a mean value 

of 6.7 mg/L. These values are in the range of those reported 

by Weiskel and Howes (1991) for areas of high-density septic 

systems on Cape Cod, Massachusetts. Nitrate plus nitrite 

concentrations are not related to the depth of the sample in 

the aquifer. Samples from shallow, intermediate, and deep 

depths in the aquifer had concentrations that exceeded the 

U.S. Environmental Protection Agency maximum contaminant level for drinking water of 10 mg/L nitrate plus nitrite as 

nitrogen. Dissolved ammonia plus organic nitrogen concentrations ranged from less than 0.06 to 0.15 mg/L and represented 

a small part of the TDN. The mean and median concentrations 

of TDN were 7.5 mg/L and 4.8 mg/L, respectively, during the 

period before sewering (2005–7), based on the statistics from 

102 samples. Concentrations of dissolved phosphorus in the 

groundwater were low, ranging from below the reporting limit 

of 0.004 to 0.021 mg/L (as phosphorus).

Dissolved Gases

Dissolved gas measurements (appendix 1) were used to 

determine if denitrification was occurring in the groundwater 

at Pine Grove and at one well cluster on Sandy Point. These 

samples were collected at all wells; however, the analysis of 

samples from the polyethylene tubing attached to the casing 

at four wells showed evidence of stripping of dissolved gases, 

which renders the samples unusable. These samples had been 

collected by using a peristaltic (suction) pump.

The loss of nitrate through denitrification would be 

evidenced by low nitrate concentrations, low dissolved oxygen concentrations, and excess nitrogen gas in the samples. 

Denitrification is a biologically mediated reduction of nitrate 

through a series of intermediate steps to nitrogen gas (Kendall 

and Aravena, 2000) and typically requires a carbon source as 

an electron donor.

Analysis of the data show oxic conditions (dissolved 

oxygen greater than 2 mg/L) in the samples from most of the 

wells, indicating a low potential for denitrification. Samples 

from wells CT–ELY 73 and CT–ELY 78 (fig. 1, sites 5 and 8) 

had low dissolved oxygen concentrations of less than 2 mg/L. 

Excess nitrogen gas was estimated to be present in samples 

from these wells at low concentrations ranging from 0.2 to 

1.2 mg/L. Both of these wells are screened in the in the upper 

part of the transition zone between fresh and saline groundwater, as indicated by specific conductance values greater 

than 1,000 μS/cm at 25 °C. The saline water that has mixed 

with the groundwater may be more depleted in oxygen than 

the local groundwater and may provide an additional organic 

carbon source.

The results of the dissolved gas sampling indicate that 

nitrate-nitrogen is generally not being attenuated by denitrification in the aquifer. Denitrification is still possible along 

the flow paths that pass under the Niantic River on the way 

toward discharge to the saltwater environment, especially if 

the groundwater discharges through organic muds that might 

be present on the bottom of the Niantic River.

Major Ions and Field Measurements

The analyses of water from the wells on Pine Grove and 

Sandy Point provide additional evidence of the influence of 

human activities on the groundwater quality. The dominant cations detected were sodium and magnesium, and the dominant 

anions were nitrate and chloride (fig. 5). The water-quality data 

(table 4) also show the influence of seawater on groundwater, 

particularly for wells CT–ELY 73 and CT–ELY 78, which are 

screened in the top of the transition zone between freshwater 

and saltwater and have high chloride concentrations.

Information on the source of recharge in the study area 

can be obtained by plotting the chloride to bromide ratio 

against the chloride concentrations, as was done in Mullaney 

and others (2009) and seen in figure 6. The curves represent 

binary mixtures of dilute groundwater with halite (road salt), 

sewage and animal waste, and seawater (fig. 6). 
14 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Table 4. Water-quality analyses of groundwater samples from August and September 2005 from Pine Grove and Sandy Point on the Niantic 

[Laboratory analyses by USGS National Water Quality Laboratory; fig., figure; USGS, U.S. Geological Survey, ID, identification number; μS/cm at 25 °C, microsiemens 

per liter; <, less than; e, estimated]

Site 

number 

(fig. 1)

USGS local 

ID Station ID Date

Dissolved 

oxygen, 

water, 

unfiltered

pH, water, 

unfiltered, 

field, 

in standard 

units

Specific conductance, water, unfiltered, 

in μS/cm at 

25 °C

Temperature, water, 

in °C

Calcium, 

water, 

filtered, 

in mg/L

Magnesium, 

water, 

filtered, 

in mg/L

Potassium, 

water, 

filtered, 

in mg/L

11 CT–WT 62 412101072105501 9/2/2005 9.1 5.3 185 11 5.3 2.77 2.91 

11 CT–WT 63 412101072105502 9/2/2005 9.7 5.3 93 11.7 8.29 1.36 1.25 

9 CT–ELY 63 412005072110501 8/17/2005 12.8 5.6 640 12.8 27.3 11.5 2.8 

9 CT–ELY 65 412005072110503 8/17/2005 14.1 5.9 81 14.9 8.83 0.761 1.36 

3 CT–ELY 66 412014072110701 8/18/2005 11 4.6 282 13 15.6 2.61 9.29 

2 CT–ELY 67 412014072111001 8/17/2005 8.5 5.4 485 13.7 23.2 6.39 10.3 

6 CT–ELY 68 412010072110401 8/23/2005 7.1 5.6 242 15.4 9.98 3.42 3.32 

1 CT–ELY 69 412013072111701 8/18/2005 9.7 5.4 449 12.1 15.4 3.31 9.7 

1 CT–ELY 70 412013072111702 8/18/2005 9.2 5.3 740 13.7 16.4 4.04 7.41 

4 CT–ELY 71 412006072111801 8/23/2005 6.2 5.2 236 12.9 12.4 2.69 4.43 

4 CT–ELY 72 412006072111802 8/23/2005 5.6 5.1 290 17.6 10.4 2.56 3.65 

5 CT–ELY 73 412007072111001 8/19/2005 2 5.9 3,580 12.5 274 126 11 

5 CT–ELY 74 412007072111002 8/19/2005 3.7 5.4 451 15.5 27.4 6.46 7.35 

5 CT–ELY 75 412007072111003 8/19/2005 7.7 5.1 292 12.7 13 2.63 8.87 

7 CT–ELY 76 412002072111601 8/24/2005 5.6 5.8 406 13.1 21.8 7.56 2.96 

7 CT–ELY 77 412002072111602 8/24/2005 8.1 5.9 309 14.6 17.6 2.69 4.54 

8 CT–ELY 78 412001072110701 9/1/2005 2.6 5.6 1,010 13.2 62.4 19 5.72 

8 CT–ELY 79 412001072110702 9/1/2005 6.7 5.7 323 17.6 15.8 3.29 5.38 

8 CT–ELY 80 412001072110703 9/1/2005 9 5.2 160 12.5 6.99 1.27 3.66 
Water Quality in the Pine Grove Area 15

River, Connecticut.

per centimeter at 25 degrees Celsius; °C, degrees Celsius; mg/L, milligrams per liter; SiO2, silicon dioxide; N, nitrogen; P, phosphorus; μg/L, micrograms 

Sodium, 

water, 

filtered, 

in mg/L

Bicarbonate, water, 

filtered, inflectionpoint titration method 

(incremental titration 

method), field, 

in mg/L

Bromide, 

water, 

filtered, 

in mg/L

Chloride, 

water, 

filtered, 

in mg/L

Silica, water, 

filtered, 

in mg/L as 

SiO2

Ammonia plus 

organic nitrogen, 

water, filtered, 

in mg/L as N

Nitrate plus 

nitrite, water, 

filtered, 

in mg/L as N

Phosphorus, 

water, filtered, 

in mg/L as P

Boron, water, 

filtered, 

in μg/L

21.2 21 0.051 29.4 12.9 < 0.1 0.94 0.021 22

4.72 15 0.035 5.28 9.99 e 0.07 3.29 0.008 19

66.2 12 0.524 158 14.2 < 0.1 3.26 e 0.003 35

3.83 18 0.023 3.6 6.39 < 0.1 2.33 0.005 11

21.6 5 0.067 28.5 12 0.11 13.8 < 0.004 82

45.4 17 0.162 62.5 19 < 0.1 20 e 0.003 188

24.9 19 0.022 50 9.92 < 0.1 2.15 e 0.003 26

51.4 11 0.09 81.3 14.4 e 0.06 10.6 < 0.004 56

110 16 0.135 179 14.8 0.14 1.95 0.005 43

21.1 13 0.064 36.7 13.2 e 0.07 7.29 e 0.002 45

32.7 6 0.041 59.1 10.6 0.15 5.84 < 0.004 30

163 19 4.07 1,120 31.5 0.12 3.24 0.004 e 18

34.9 21 0.133 67.2 16 0.12 15.5 0.006 49

28.3 11 0.075 39.4 12.7 e 0.1 9.29 e 0.003 42

31.9 16 0.347 93 13.9 < 0.1 1.36 < 0.004 40

31.5 49 0.037 58.4 11.3 e 0.07 0.96 0.006 11

83.4 20 0.67 248 16.8 < 0.1 17.1 0.006 58

32.2 15 0.094 71.6 12.2 e 0.08 5.29 e 0.003 40

16.8 15 0.038 21.6 9.08 e 0.06 3.21 0.02 27
16 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Percent

Calcium

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20 

 40 

 60 

 80 

 100 

Sodium plus potassium

Chloride, fluoride, nitrite plus nitrate

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 

Carbonate plus bicarbonate

 100 

 80 

 60 

 40 

 20 

 0 

Sulfate

 0 

 20 

 40 

 60 

 80 

 100 

Sulfate plus chloride

 0 

 20 

 40 

 60 

 80 

 100 

Calcium plus magnesium

 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

Percent

Percent

Figure 5. Relations among major anions and cations in water samples from wells at Pine Grove 

and Sandy Point on the Niantic River, Connecticut, in August and September 2005.
Water Quality in the Pine Grove Area 17

10 100 1,000 10,000

Chloride, in milligrams per liter

1

10

100

1,000

10,000

Chloride-to-bromide ratio

0.1 1

Approximate range for dilute groundwater

1. Dilute groundwater/halite deicing salt, high range

2. Dilute groundwater/halite deicing salt, low range

3. Dilute groundwater/sewage or animal waste, high range

4. Dilute groundwater/sewage or animal waste, low range

5. Halite deicing salt/sewage or animal waste, high range

6. Halite deicing salt/sewage or animal waste, low range

7. Sewage or animal waste, low range/seawater

8. Dilute groundwater/seawater

1.

Binary mixing curves

EXPLANATION

2.

3.

4.

5. 6.

7.

ELY 73 8.

ELY 78

ELY 76 ELY 63

ELY 67

ELY 70

ELY 69

ELY 79

ELY 72

ELY 68

ELY 65

WT 63

ELY 80

WT 62 ELY 71

ELY 75

ELY 77

Samples from wells—Size of circle is proportional to the total dissolved nitrogen 

 concentration. Letter/number designation is local CT well identifier

ELY 78

Figure 6. The relation of chloride-to-bromide ratio to chloride concentration in groundwater samples collected during August and 

September 2005 at Pine Grove and Sandy Point on the Niantic River, Connecticut, and binary mixing curves representing various 

potential sources of chloride. mg/L, milligrams per liter; TDN, total dissolved nitrogen. See table 1 for a list of wells. From Mullaney and 

others (2009).
18 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

The plotted positions of the samples in figure 6 indicate 

that the source of water for many of the samples is dominated 

by sewage and animal waste (wastewater). The majority of 

these samples plot near the sewage and animal waste end 

members for mixtures of dilute groundwater and sewage and 

animal waste, indicating a substantial contribution of water 

from wastewater.

Four of the samples show the influence of seawater, 

although one sample (from well CT–ELY 78) may indicate 

seawater and wastewater sources. Three of the samples (from 

wells CT–ELY 63, CT–ELY 65, and CT–ELY 68) show 

little or no influence of wastewater in their water chemistry. 

These samples also are associated with the lowest nitrite 

plus nitrate concentrations, indicating that few or no septic 

systems are likely in the recharge areas for these wells. Wells 

CT–ELY 63 and CT–ELY 65 are in a park on Pine Grove and, 

based on the configurations of the water table (fig. 3A, B), 

may receive recharge from the undeveloped lawn areas within 

the park. These samples have some of the lowest nitrate plus 

nitrite concentrations, ranging from 2.2 to 3.3 mg/L, in the 

study area.

Boron concentrations are generally considered to be an 

indicator of wastewater (LeBlanc, 1984; Katz and others, 

2011). Domestic wastewater typically contains elevated concentrations of boron because of the use of sodium perborate 

in laundry detergents. Nitrate plus nitrite and dissolved boron 

data from the initial sampling of the wells in the study area 

are generally positively correlated and demonstrate that boron 

appears to be an indicator of the wastewater influence on the 

water quality in many of the wells in the study area (fig. 7). 

A simple linear regression fits a line through these data, with a 

coefficient of 0.1191 and an intercept of 1.4251.

Figure 7. The relation between boron and nitrite plus nitrate nitrogen concentrations in groundwater samples collected during 

August and September 2005 at Pine Grove and Sandy Point on the Niantic River, Connecticut. mg/L, milligrams per liter. See table 1 

for a list of wells.

Boron, in micrograms per liter

0

5

10

15

20

Nitrate plus nitrite nitrogen, in milligrams per liter

25

CT−WT 62

CT−WT 63

CT−ELY 63

CT−ELY 65

CT−ELY 66

CT−ELY 66

CT−ELY 67

CT−ELY 68

CT−ELY 69

CT−ELY 70

CT−ELY 71

CT−ELY 72

CT−ELY 73

CT−ELY 74

CT−ELY 75

CT−ELY 76 CT−ELY 72

CT−ELY 78

CT−ELY 79

CT−ELY 80

0 25 50 75 100 125 150 175

EXPLANATION

Sampled wells, 

 with site identifiers 
Water Quality in the Pine Grove Area 19

Postsewer

Presewer

Transition

10

15

20

25

30

x

x

x

x

x

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

119

x

x

x

102

x

x

x

x

x

85

5

0

Total dissolved nitrogen, in milligrams per liter

85

EXPLANATION 

Number of values

75th percentile

Largest value within 1.5 times

Mean

interquartile range above

75th percentile 

25th percentile

Interquartile 

range

50th percentile

(median)

Smallest value within 1.5 times

interquartile range below

25th percentile

Outside value—Value is greater

 than 1.5 and less than 3 times 

 the interquartile range beyond 

 either end of the box

o Outlier

x

Figure 8. The distributions of total dissolved nitrogen concentrations for presewering (2005–7), transition (2008–9), and postsewering

(2010–11) periods at the Pine Grove, Connecticut, study area. mg/L, milligrams per liter.

Water Quality After Installation 

of Sewers

Concentrations of TDN were generally lower during 

the transition time period, when the sewers had been connected to residences, than during the period before sewering 

(fig. 8) and were lowest during the period after sewering. The 

mean and median concentrations of TDN were 6.7 mg/L and 

3.5 mg/L, respectively, in the transitional period (85 samples) 

and 5.2 mg/L and 3.1 mg/L, respectively, during the monitoring period after sewering (119 samples). The decrease in the 

mean concentration of TDN during the study period (2005–11) 

was 2.3 mg/L. The significance of the decrease in the concentrations of TDN before and after sewering was evaluated 

with the use of a Wilcoxon rank-sum test, which indicated 

that the groups of data were significantly different at a p-value 

of 0.0002.

When comparing the changes among individual wells, 

sample numbers were generally too few for any statistical 

comparison tests. Therefore, the means and medians for each 

of the three periods described above were compared qualitatively (table 5). Of the wells sampled on Pine Grove, only two 

had medians and three had means that were larger at the end 

of the study (postsewer period) than at the beginning of the 

study (presewer period). Of these three wells, samples from 

two wells had very small differences, likely indicating no 

significant change. Concentrations of TDN at well CT–ELY 67 

(fig. 1, site 2) increased by more than 1 mg/L. Concentrations 

of TDN remained above 20 mg/L at this location, indicating 

a continuing source of nitrogen or insufficient groundwatertravel time for a difference to be observed.

The wells with some of the smallest decreases or 

increases, including wells CT–ELY 63, CT–ELY 68, CT–ELY 

73, and CT–ELY 76, are where the sources of water as indicated in figure 6 were less likely to be sewage or animal-waste 

related. The possibility that the source was not onsite sewage 

disposal could explain the absence of changing TDN concentrations at these wells in the period after sewering.

The wells with the largest decreases in TDN concentrations between presewer and postsewer periods included wells 

CT–ELY 66, CT–ELY 70, CT–ELY 74, CT–ELY 75, and 

CT–ELY 80. The well cluster that includes wells CT–ELY 78, 

CT–ELY 79, and CT–ELY 80 (fig. 1, site 8) had decreases 

in TDN in all three wells at deep, intermediate, and shallow 

depths in the aquifer. This likely represents groundwater entering the Pine Grove neighborhood from Camp Niantic to the 

south, where sewers were connected before the beginning of 

this study.
20 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Table 5. Median and mean concentrations of total dissolved nitrogen1 in groundwater samples from wells at Pine Grove, Sandy 

Point, and Saunders Point on the Niantic River, Connecticut, before, during, and after sewering was completed at Pine Grove.

[Sites shaded in gray are at Sandy Point and Saunders Point. fig., figure; USGS, U.S. Geological Survey; ID, identification number, hyperlinked to data for each well; No., number of samples; TDN, total dissolved nitrogen; mg/L, milligrams per liter]

Site 

number 

(fig. 1)

USGS local 

ID

Presewering Transitional period Postsewering Difference in 

medians, 

presewer to 

postsewer, 

in mg/L

Difference in 

means, 

presewer to 

postsewer, 

in mg/L

No.

Median 

TDN,

in mg/L

Mean 

TDN, 

in mg/L

No.

Median 

TDN,

in mg/L

Mean 

TDN, 

in mg/L

No.

Median 

TDN,

in mg/L

Mean 

TDN, 

in mg/L

9 CT–ELY 63 6 3.48 3.47 5 3.28 2.80 7 3.43 3.13 0.05 0.34

9 CT–ELY 65 6 3.22 3.62 5 3.28 3.24 7 2.26 2.57 0.96 1.05

3 CT–ELY 66 6 9.33 9.44 5 12.95 16.06 7 4.53 5.11 4.79 4.33

2 CT–ELY 67 6 21.07 21.27 5 23.41 22.06 7 22.18 22.69 -1.12 -1.43

6 CT–ELY 68 6 2.36 2.32 5 2.25 2.33 7 2.39 2.38 -0.03 -0.06

1 CT–ELY 69 6 12.53 12.17 5 10.69 11.03 7 8.25 10.00 4.28 2.17

1 CT–ELY 70 6 4.45 5.37 5 5.22 4.86 7 2.51 2.79 1.94 2.58

4 CT–ELY 71 6 4.62 4.13 5 1.86 2.01 7 2.28 2.33 2.34 1.80

4 CT–ELY 72 6 4.76 4.55 5 5.16 5.25 7 3.43 3.77 1.33 0.78

5 CT–ELY 73 6 3.53 3.51 5 3.42 3.45 7 3.45 3.23 0.08 0.28

5 CT–ELY 74 6 15.80 15.20 5 8.00 8.97 7 3.33 3.51 12.47 11.69

5 CT–ELY 75 6 9.47 10.48 5 2.87 4.75 7 2.08 2.22 7.39 8.26

7 CT–ELY 76 6 1.52 1.52 5 1.34 1.37 7 1.26 1.59 0.26 -0.07

7 CT–ELY 77 6 0.95 0.94 5 0.54 0.68 7 0.55 0.60 0.41 0.34

8 CT–ELY 78 6 19.92 19.55 5 19.70 19.47 7 18.58 18.29 1.34 1.26

8 CT–ELY 79 6 4.77 4.56 5 4.10 3.88 6 2.71 2.90 2.07 1.66

8 CT–ELY 80 6 3.75 5.40 5 2.32 2.38 7 2.12 2.11 1.63 3.29

11 CT–WT 62 6 0.98 1.00 5 1.01 1.13 7 1.61 1.69 -0.63 -0.69

11 CT–WT 63 6 3.80 3.74 4 5.15 5.11 6 3.66 3.72 0.14 0.03

10 CT–ELY 81 4 6.41 6.37 6 6.71 6.68 6 6.06 6.43 0.35 -0.06

1

TDN was determined from the sum of nitrite plus nitrate nitrogen and dissolved ammonia plus organic nitrogen. If dissolved ammonia plus organic nitrogen was less than the reporting limit, only nitrite plus nitrate values were used.
Estimated Nitrogen Loads From Groundwater to the Niantic River 21

Estimated Nitrogen Loads From 

Groundwater to the Niantic River

Estimates of nitrogen load from groundwater discharge 

from the study area were made for three time periods: (1) 

before the installation of sewers in 2006, (2) after installation 

of sewers in 2011, and (3) in the future when concentrations 

of nitrogen have stabilized. Loads were estimated by using 

estimated effective recharge rates from precipitation and septic 

systems combined with mean TDN concentrations in the aquifer and estimated future TDN concentrations. Nitrogen loads 

from groundwater were estimated for other regions of the 

Niantic River by using estimated recharge rates and measured 

or estimated TDN concentrations for different regions of the 

lower watershed.

Water use in the Pine Grove study area ranged from 

5.41 to 5.51 million gallons per year [Mgal/yr]) from 2006 

through 2010 (table 6; Brad Kargl, East Lyme Water and 

Sewer Department, written commun., 2011). Water-use values 

from 2006 were used to estimate recharge from septic systems 

because these data precede the connection to sewers. Water 

use during 2006 was 5.51 million gallons (Mgal). It was 

assumed that 86 percent (U.S. Geological Survey, 1995) of 

the water used, or 4.7 Mgal, was returned to the aquifer. When 

distributed evenly over the 35-acre study area, this wastewater discharge is equivalent to 4.98 in. of recharge. Therefore, 

before the installation of sewers, the total estimated recharge 

from precipitation (23.2 in/yr) and artificial recharge from 

septic systems (4.98 in/yr) totaled 28.2 in.

Following the installation and connection by 2009 of 

all properties in the area to the sewer system, discharge from 

septic systems had ended, and recharge rates had dropped to 

23.2 in. The effect of eliminating the discharge from septic 

systems should be to reduce the rate of discharge of freshwater 

from the Pine Grove study area to the coast, thereby reducing 

nitrogen loads to the adjacent surface-water bodies even in the 

absence of changing concentrations of TDN.

Nitrogen Loads Estimated for Pine Grove

At the beginning of this study, before the extension of 

the municipal sewer system to the Pine Grove area, the mean 

concentration of TDN in samples from all wells was 7.5 mg/L, 

based on data from 2005 through 2007 (102 samples). If this 

mean concentration is representative of the concentration of 

TDN for the fresh groundwater in the study area, and taking into account that the recharge rate before sewering was 

28.2 in/yr on 35 acres, then the estimated dissolved nitrogen 

load to the surrounding surface waters before sewering was 

about 1,675 lb/yr. This value compares well with estimates 

made on the basis of the estimated return flow multiplied by an 

assumed concentration of total nitrogen in septic system leachate. Concentrations in the literature vary, but the CTDEEP 

summarized data from around the United States and estimated 

the mean concentration of total nitrogen to be 50.9 mg/L 

in residential septic tank effluent (Connecticut Department 

of Environmental Protection, 2006a). This compares with 

45 mg/L as reported by the U.S. Environmental Protection 

Agency (1980). Using these concentrations multiplied by the 

return flow to the aquifer in 2006 (table 7) produces load estimates of 1,780 to 2,012 lb/yr, which compares well with the 

values calculated for this study.

Table 6. Water use at Pine Grove, Connecticut, 2006–10.

[Data were compiled for the period from 2006 through 2010 from meter 

readings for individual properties in the study area (Brad Kargl, East Lyme 

Water and Sewer Department, written commun., 2011)]

Year Gallons

2006 5,506,351

2007 5,414,971

2008 5,498,900

2009 5,250,995

2010 5,046,200

Table 7. Estimates of total dissolved nitrogen load from the Pine Grove peninsula area to the Niantic River Estuary, Connecticut, 

before and after sewering and after total dissolved nitrogen concentrations have stabilized.

[in., inches; TDN, total dissolved nitrogen; mg/L, milligrams per liter; lb/yr, pounds per year]

Time period

Annual recharge rate 

(in.) Mean measured or 

estimated TDN

concentration 

(mg/L)

Estimated TDN 

load

Natural (lb/yr) From septic 

systems

Recharge over entire area

Presewer (2005–07) 23.2 4.98 7.50 1,675

Postsewer (2010–11) 23.2 0.00 5.24 963

After stabilization of total dissolved nitrogen concentrations 23.2 0.00 2.30 423

No recharge over impervious areas

Presewer (2005–07) 17.8 4.98 7.50 1,358

Postsewer (2010–11) 17.8 0.00 5.24 742

After stabilization of total dissolved nitrogen concentrations 17.8 0.00 2.30 326
22 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Immediately following installation of the sewers and connection of most residences to the system (2010–11), the mean 

concentration of TDN decreased to 5.24 mg/L, which indicates 

that some changes to concentration had occurred as a result 

of the sewer system installation. The load from the study area 

during this period was estimated by multiplying the recharge 

rate of 23.2 in/yr, which is solely from precipitation, by the 

area of the study site and the mean concentration for the postsewering period. The estimated load of TDN for the postsewering period is 963 lb/yr. This reduction from the presewering 

period is caused by the decrease in concentrations of TDN and 

a reduction in the water discharge as a result of sewering.

Predicted Future Nitrogen Loads From

Pine Grove

As the aquifer beneath the Pine Grove area adjusts to a 

new steady state from the changes in nitrogen loading and the 

discontinuation of wastewater discharge to the subsurface, 

concentrations of TDN are likely to continue to decrease. The 

long-term changes in the loading of nitrogen to the Niantic 

River are dependent on the travel time of groundwater across 

the study area, the time for any nitrogen stored in the unsaturated zone to be flushed from the system, the final steady-state 

concentrations of TDN in the groundwater, and the length 

of additional pathways of discharge beneath the estuary that 

continue beyond the shoreline.

Based upon the mean saturated thickness of freshwater 

(27 ft) when the wells were drilled in 2005, a land area of 

about 35 acres, and an estimated porosity of 0.3, the freshwater zone in the study area contains approximately 12.3 Mgal 

of water in storage. The mean recharge rate of 23.2 in/yr is 

equivalent to 2.9 Mgal/yr over the study area of 35 acres. This 

indicates that the mean replacement time for the total annual 

recharge volume of water in the aquifer underlying the study 

area is about 4.2 years, excluding groundwater flow from 

upgradient areas. The associated residence time of TDN in the 

aquifer is likely longer than the replacement time for recharge 

due to hydrodynamic dispersion.

Groundwater enters the study area from the south from 

Camp Niantic. The estimated annual flow across the southern 

boundary of the study area is 5.5 to 13.8 Mgal/yr, some of 

which discharges into the Niantic River and some of which 

mixes with the recharge from precipitation in the study area. 

This conclusion is based the use of Darcy’s law, and the typical range in gradient (0.0004–0.0005), the estimated hydraulic 

conductivity of the glacial stratified deposits (100–200 feet per 

day, based on the material composition and associated values 

in Mazzaferro and others [1979]), and the mean thickness 

of the freshwater layer of 37 ft across the southern boundary (1,370 ft) of the study area. This additional water likely 

decreases the residence time of recharge to the study area but 

also adds additional nitrogen. Sewers were installed at Camp 

Niantic in 2000, and concentrations of TDN in the groundwater (fig. 1, site 8, with three wells) on the northern part of 

Camp Niantic have been decreasing.

The groundwater travel time across the longest dimension 

of the study area can be estimated on the basis of the typical 

water-table gradient, the travel distance from the Camp Niantic boundary to the northern end of the peninsula (1,400 ft), 

and an estimated mean hydraulic conductivity. Assuming a 

porosity of 0.3 and mostly horizontal flow, the estimated travel 

time across the longest dimension of the study area ranges 

from 11.5 to 29 years. Most groundwater flow paths from the 

study area to the shore of the Niantic River are shorter than 

1,400 ft, so travel times will be less than this estimate (less 

than 6 to 15 years). However, some flow paths may extend 

some distance beneath the Niantic River rather than ending at 

discharge points at the shoreline. Therefore, it is difficult to 

estimate the overall timing of the decrease in nitrogen loading 

to the river owing to the installation of the sewer system.

Concentrations of nitrogen in groundwater in the future 

are estimated to be similar to those in other parts of Connecticut with high density of development and sanitary sewers. 

Grady (1994) determined that the median nitrate plus nitrite 

concentration in groundwater in glacial stratified deposits 

beneath 21 sewered areas in Connecticut was 2.3 mg/L. This 

compares with a value of 1.1 mg/L of nitrate plus nitrite 

beneath undifferentiated urban areas in the Connecticut River, 

Housatonic River, and Thames River Basins (Grady and Mullaney, 1998). These concentrations are higher than those for 

undeveloped or forested areas where median values for nitrate 

plus nitrite ranged from 0.11 to 0.14 mg/L. When the range 

of values for typical urban areas are applied to the analysis of 

the potential for future nitrogen loads, the range in estimated 

future nitrogen loads to the Niantic River from the study area 

is 202 to 423 lb/yr. Remaining sources of nitrogen input to the 

groundwater at Pine Grove include atmospheric deposition, 

lawn fertilizers, and pet and animal wastes.

The method used to estimate the nitrogen loads described 

above and in the following section has several limitations 

resulting from the assumptions used in the analyses. These 

assumptions include that concentrations of TDN measured in 

the wells are representative of the concentrations in the study 

area, both vertically and areally, and that concentrations of 

TDN from different depths in the aquifer have equal weight 

(contribute equally to the load) in the analyses. The use of this 

method assumes a discharge of water from the study area that 

is equivalent to the estimated annual recharge from precipitation and septic systems.

Comparison of Nitrogen Loads From Pine Grove 

and Other Niantic River Subwatersheds

Estimates of the nitrogen loads that discharge directly 

to the Niantic River were made for other regions abutting the 

Niantic River. These estimates were made by using a combination of estimated recharge rates, which varied by surficial geology type (glacial till or glacial-stratified deposits), 

and measured or estimated nitrogen concentrations (fig. 9; 

table 8). Estimates from each region were summed for a total 

load to the river. The total annual estimated nitrogen load from 
Estimated Nitrogen Loads From Groundwater to the Niantic River 23

72°13'30" 72°9'

41°22'30"

41°19'30"

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

EXPLANATION

0−200

>200−400

>400−700

>700−1,500

>1,500−4,300

Estimated total dissolved nitrogen load, in pounds 

 per year—Number is basin segment, as listed in table 8

12

2

4

13

5 6

5 14

18

8

10

7 16

17

1 9

15

20

21

19

3

22

Site where well(s) were installed for this study

Groundwater-quality data site—From 2003 

011277918 0112779165

011277918 Base flow water-quality site and number 

Base from Esri World Topographic Map, 2013 Groundwater-quality data by Jamie Vaudrey, University of Connecticut, 2012

Base flow water quality sites by Mullaney, 2013

1

Figure 9. Total dissolved nitrogen load estimates from groundwater to the lower Niantic River, Connecticut. >, greater 

than.

[http://goto.arcgisonline.com/maps/World_Topo_Map]
24 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Table 8. Total dissolved nitrogen loads from groundwater discharge for the lower Niantic River, Connecticut, estimated for 2011.

[fig., figure; TDN, total dissolved nitrogen; mg/L, milligrams per liter; lb, pounds; USGS, U.S. Geological Survey; GSD, glacial stratified deposit; NA, not 

applicable]

Map 

number

(fig. 9)

Surficial 

geology

TDN concentration 

(estimated 

or measured), 

in mg/L

Size of 

basin 

segment, 

in acres

Recharge 

from 

septic 

systems,

in inches

Recharge, 

in inches

Estimated 

number of 

residences using 

septic 

systems

Estimated 

per household water 

use, 

in gallons 

per day

Estimated 

percentage 

of water 

from septic 

systems 

returned to 

aquifer

Estimated 

annual 

load of 

TDN, 

in lb1

Other USGS 

station 

identification number2

1 Till 1.2 98.3 0.15 8.75 0 NA NA 234 NA

2 GSD 4.0 31.7 0 23.20 0 NA NA 666 NA

3 GSD 1.6 2.7 0 23.20 0 NA NA 22 NA

4 GSD 1.6 84.9 0 23.20 0 NA NA 714 NA

5 GSD 1.5 187.1 0 23.20 0 NA NA 1,475 NA

6 GSD 0.8 116.4 0 23.20 0 NA NA 490 NA

7 GSD 1.5 17.0 0 23.20 0 NA NA 134 NA

8 GSD 6.5 87.6 2.71 25.91 130 160 0.85 3,350 NA

9 GSD 6.0 94.6 0 23.20 0 NA NA 2,974 NA

10 GSD 4.0 186.1 2.12 25.32 216 160 0.85 4,272 NA

11 GSD 0.0 11.6 0 23.20 0 NA NA 0 NA

12 Till 0.2 344.0 0 8.60 0 NA NA 147 NA

13 Till 0.5 290.6 0 8.60 0 NA NA 283 NA

14 Till 1.5 88.3 0 8.60 0 NA NA 258 NA

15 Till 0.1 435.3 0.27 8.87 65 160 0.85 79 NA

16 Till 3.3 14.6 0 8.60 0 NA NA 94 NA

17 Till 3.3 9.7 0 8.60 0 NA NA 62 NA

18 Till 0.8 89.0 0 8.60 0 NA NA 139 NA

19 GSD and Till 0.5 191.8 0 23.2/8.6 0 NA NA 216 011277918

20 GSD and Till 2.4 149.2 0 23.2/8.6 0 NA NA 1,181 0112779165

21 GSD 5.3 35.3 0 23.20 0 NA NA 970 NA

22 GSD 4.0 51.6 0 23.20 0 NA NA 1,084 NA

1

Data are presented unrounded.

2

From Mullaney (2013).
Summary and Conclusions 25

groundwater discharge from the areas identified in table 8 is 

18,800 lb/yr, including the nitrogen loads estimated for Pine 

Grove in 2011. Data and analyses in Mullaney (2013) indicate 

that the mean total of nitrogen loads from the tributaries of the 

Niantic River from 2009 through 2011 was about 51,000 lb/yr. 

With the additional estimated total nitrogen load from direct 

groundwater discharge of 18,800 lb, the combined total 

nitrogen load to the Niantic River is greater than 69,800 lb/yr. 

The only component not accounted for in this total nitrogen 

load estimate is direct overland runoff from the areas of the 

watershed that are downstream of the USGS water-quality 

monitoring stations.

The predicted change in nitrogen load from the system 

resulting from the sewering at Pine Grove is about 1,250 lb/yr, 

representing about 1.8 percent of the estimated nitrogen load 

from upstream watershed and lower watershed groundwater 

sources combined.

Summary and Conclusions

A study of the concentration and estimated loads of 

nitrogen to adjacent surface waters before, during, and after 

sewers were installed was conducted at the Pine Grove neighborhood on the Niantic River Estuary in southeastern Connecticut. The study was conducted from 2005 through 2011 

by the U.S. Geological Survey (USGS) in cooperation with 

the Connecticut Department of Energy and Environmental 

Protection (CTDEEP).

The Niantic River Estuary is impaired through excessive nitrogen loading, which is considered to be a major 

cause of the decline and fluctuation in the density of eelgrass 

populations. The CTDEEP has listed the Niantic River on the 

impaired waters list of the State of Connecticut and considers the river to be an impaired habitat for marine fish, aquatic 

life, and wildlife. Excess nitrogen in groundwater discharge 

from developed lands, including onsite wastewater treatment 

systems, has been implicated as a cause in the decline of the 

eelgrass habitats.

The Pine Grove neighborhood has 172 homes on the 

northern part of a peninsula, which is surrounded by the 

Niantic River. In 2005, all residences were served by septic systems and public water supply. In 2006, a project was 

begun to install sanitary sewers. The project was completed 

by connecting all residences to the sewer system from 2007 

through 2009.

The USGS installed 17 wells throughout the neighborhood and 3 wells in two other regions adjacent to the Niantic 

River. The wells were sampled 18 times over the course of the 

study, primarily for analysis of nutrients but also for analysis 

of dissolved gases, bromide, boron, and other major ions during the first sampling period in 2005. Water levels were measured periodically at all wells and continuously at selected 

sites. The drilling and water-level monitoring indicated the 

Pine Grove area has a freshwater layer from 10 to 45 feet (ft) 

thick. Mean water levels ranged from 5.26 to 19.92 ft below 

land surface, or from 0.09 to 0.97 ft above the North American 

Vertical Datum of 1988. Groundwater flow directions were 

toward the north and toward the shorelines of Pine Grove. The 

horizontal hydraulic gradient is shallow, ranging from 0.0004 

to 0.0005.

At the beginning of the study in 2005, analyses of water 

samples indicated that nitrate nitrogen was the primary component of the total dissolved nitrogen (TDN) in the groundwater. Nitrate plus nitrite concentrations ranged from 0.94 to 

20 milligrams per liter (mg/L), with dissolved ammonia plus 

organic nitrogen concentrations ranging from less than 0.06 

to 0.15 mg/L. The dissolved gas measurements indicated that 

the samples from most of the wells were oxic and denitrification was not a widespread process. Nitrate plus nitrite nitrogen 

concentrations were positively correlated with boron, which is 

an indicator of a wastewater source.

Chloride to bromide ratios were used along with chloride concentrations to understand sources of water entering 

the aquifer at Pine Grove. Many of the samples plotted near 

the binary mixing line for dilute groundwater and sewage or 

animal waste, indicating likely substantial input from septic 

systems. Five samples showed the influence of seawater, 

which likely is due to the proximity of the sampling depth to 

the transition zone between freshwater and saltwater.

TDN concentrations were compared for samples from 

all wells across the presewering period, the transitional period 

when residences were being connected to the sewer system, 

and the postsewering period when almost all residences had 

been connected. Mean and median TDN concentrations began 

to decrease during the transitional period and continued to 

decrease in the postsewering period. A Wilcoxon rank-sum 

test indicated a significant difference between the sample 

concentrations of TDN before and after sewering. The mean 

concentration of TDN for groundwater samples collected 

during the presewering period was 7.5 mg/L and for samples 

collected during the postsewering period was 5.2 mg/L. The 

median and mean TDN concentrations decreased in 14 of the 

17 wells between the presewering and postsewering periods. 

Decreases in mean concentrations of TDN ranged from 0.34 to 

11.7 mg/L.

Nitrogen loads from groundwater in the Pine Grove area 

were calculated for the periods before and after sewering and 

estimated for the future when nitrogen concentrations have 

stabilized to levels typical of similarly developed sewered 

areas. Estimated TDN loads were calculated by using estimates of recharge under presewering and postsewering conditions and mean measured or estimated future TDN concentrations. Water-use records from 2006 were used to calculate 

an estimated recharge from septic systems of 4.98 inches 

per year (in/yr) for the presewering period. Recharge from 

precipitation for the presewering period was estimated to be 

23.2 in/yr. Given the combined recharge rate of 28.2 in/yr, an 

area of 35 acres, and a mean TDN concentration of 7.5 mg/L, 

the estimated TDN load from the Pine Grove area before 

sewering was 1,675 pounds per year (lb/yr).

Following the sewer installation, the estimated combined recharge rate was reduced to 23.2 in/yr, and the mean 
26 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

concentration of TDN was 5.2 mg/L, yielding an estimated 

TDN load of 963 lb/yr. The timing of the eventual stabilization 

of TDN concentrations in the aquifer at Pine Grove to steadystate, lower values, reflecting the new sewered hydrologic system, is dependent on the amount of residual nitrogen from septic systems remaining in the saturated and unsaturated zones 

and the travel time and residence time of water in the aquifer. 

The mean replacement time for the zone of freshwater was 

estimated to be about 4.2 years based on estimated recharge 

rates and the volume of freshwater in the aquifer but is probably less because of inflow from upgradient areas. The longest 

flow paths across the study area were estimated to have travel 

times of 11.5 to 29 years based on measurements of the watertable gradient and estimates of the hydrologic properties of 

the aquifer materials. When concentrations of TDN reach new 

quasi-stable values, reflecting the sewered condition, they are 

estimated to be in the range of 1.1 to 2.3 mg/L based on previous studies in Connecticut. Therefore, the estimated annual 

TDN load from the study area in the future could be as low as 

202 to 423 lb/yr.

Nitrogen load estimates from groundwater discharge 

were made for other areas of the lower Niantic River watershed adjacent to the river. Estimates were made by applying 

recharge rates for different geologic materials (23.2 in/yr for 

glacial stratified deposits and 8.6 in/yr for till) to previously 

measured or estimated nitrogen concentrations to determine loads for selected areas. The estimated TDN load from 

groundwater discharge for the lower watershed, including the 

Pine Grove study area, for 2011 was 18,800 lb/yr, compared 

with 51,000 lb/yr from the tributaries computed in a previous study (2009–11). The predicted change in nitrogen load 

from the system resulting from the sewering at Pine Grove is 

1,250 lb/yr, representing about 1.8 percent of the estimated 

nitrogen load from upstream watershed and lower watershed 

groundwater sources combined. Further research is needed to 

confirm these estimates of TDN load for the lower watershed 

and the remaining TDN loads to the Niantic River from stormwater surface runoff from the lower watershed.

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Appendix 1. Dissolved Gas Measurements 

in Groundwater Samples From Pine Grove and 

Sandy Point, Niantic River, Connecticut, August 

and September 2005
30 Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11

Table 1–1. Dissolved gas measurements, August and September 2005. 

[Laboratory analyses by the U.S. Geological Survey, Chlorofluorocarbon Laboratory, Reston, Virginia. USGS, U.S. Geological Survey; ID, identification number; °C, degrees Celsius; mg/L, milligram per liter; N2, nitrogen; Ar, argon; O2

, oxygen; CO2, carbon dioxide; CH4, methane; cm3 STP/L, cubic centimeters at 

standard temperature and pressure per liter; --, no excess N2]

USGS 

local 

identifier

Date 

collected

Time 

collected

Field 

temperature 

(°C)

N2

(mg/L)

Ar 

(mg/L)

O2

(mg/L)

CO2

(mg/L)

CH4

mg/L

Estimated 

excess N2

(mg/L)

Recharge 

temperature, 

(°C)

Excess 

air

(cm3 

STP/L)

CT–ELY 63 08/17/05 1005 12.9 18.4 0.7 6.7 28.8 0.000 -- 12.4 1.1

CT–ELY 63 08/17/05 1005 12.9 17.9 0.7 6.4 29.4 0.000 -- 12.2 0.6

CT–ELY 65 08/17/05 1210 14.9 17.8 0.7 8.8 21.0 0.000 -- 12.2 0.4

CT–ELY 65 08/17/05 1210 14.9 18.0 0.7 8.9 20.4 0.000 -- 11.8 0.5

CT–ELY 66 08/18/05 915 13.0 18.1 0.7 5.8 56.6 0.000 -- 12.8 1.0

CT–ELY 66 08/18/05 950 13.0 18.0 0.7 5.8 56.5 0.000 -- 12.3 0.7

CT–ELY 67 08/17/05 1350 13.7 17.2 0.6 4.7 84.9 0.000 -- 13.7 0.3

CT–ELY 67 08/17/05 1350 13.7 17.5 0.6 3.2 85.9 0.000 -- 13.8 0.7

CT–ELY 68 08/23/05 955 15.4 17.5 0.6 6.6 31.8 0.000 -- 12.9 0.3

CT–ELY 68 08/23/05 955 15.4 17.4 0.7 6.5 32.2 0.000 -- 12.7 0.3

CT–ELY 70 08/18/05 1110 13.7 18.3 0.7 4.2 99.1 0.000 -- 11.7 0.8

CT–ELY 70 08/18/05 1110 13.7 18.3 0.7 4.2 101.9 0.000 -- 11.6 0.7

CT–ELY 71 08/23/05 1210 12.9 18.8 0.7 5.2 41.6 0.000 -- 13.4 1.9

CT–ELY 71 08/23/05 1210 12.9 18.2 0.7 5.4 39.6 0.000 -- 13.8 1.4

CT–ELY 73 08/19/05 1055 12.5 20.2 0.7 0.1 27.2 0.003 1.2 10.9 1.3

CT–ELY 75 08/19/05 1205 12.7 17.9 0.7 7.0 61.1 0.000 -- 13.0 0.8

CT–ELY 75 08/19/05 1205 12.7 17.9 0.7 7.0 60.8 0.000 -- 13.0 0.8

CT–ELY 76 08/24/05 935 13.1 18.9 0.7 5.2 18.2 0.001 -- 10.7 1.0

CT–ELY 76 08/24/05 935 13.1 18.9 0.7 5.3 18.4 0.001 -- 10.8 1.0

CT–ELY 77 08/24/05 1110 14.6 18.3 0.7 7.0 43.6 0.000 -- 12.5 1.1

CT–ELY 77 08/24/05 1110 14.6 18.0 0.7 6.6 43.8 0.000 -- 12.8 0.9

CT–ELY 78 09/01/05 1000 13.2 18.5 0.7 1.6 34.9 0.000 0.2 12.5 1.3

CT–ELY 78 09/01/05 1000 13.2 18.4 0.7 1.6 35.5 0.000 0.2 12.8 1.3

CT–ELY 80 09/01/05 1150 12.5 16.9 0.6 7.7 35.8 0.000 -- 14.5 0.3

CT–ELY 80 09/01/05 1150 12.5 17.2 0.6 7.6 36.4 0.000 -- 14.6 0.6

CT–WT 62 09/02/05 1005 11.0 20.1 0.7 7.5 52.4 0.000 -- 7.9 1.1

CT–WT 62 09/02/05 1005 11.0 20.0 0.7 7.9 52.3 0.000 -- 7.7 0.9
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Office Chief

U.S. Geological Survey

New England Water Science Center 

Connecticut Office

101 Pitkin Street

East Hartford, CT 06108

dc_ct@usgs.gov

or visit our Web site at:

http://ct.water.usgs.gov
Mullaney—Evaluation of the Effects of Sewering on Nitrogen Loads to the Niantic River, Southeastern Connecticut, 2005–11—Scientific Investigations Report 2015–5011

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155011