Prepared in cooperation with the Friends of Herring River

Hydrogeology and Interactions of Groundwater and Surface 

Water Near Mill Creek and the Herring River, Wellfleet, 

Massachusetts, 2017–18

Scientific Investigations Report 2019–5145

U.S. Department of the Interior

U.S. Geological Survey
Cover. Front: U.S. Geological Survey tide gage 011058798, Herring River at Chequessett Neck Road at Wellfleet, 

Massachusetts, December 2018. The tide gage measures water stage on the downstream side of the Herring River 

tide-control structure. Photograph by John Mullaney, U.S. Geological Survey. Back: Herring River and Mill Creek 

area, Wellfleet, Massachusetts, February 27, 2018. Image from Google, 2018.
Hydrogeology and Interactions of 

Groundwater and Surface Water Near Mill 

Creek and the Herring River, Wellfleet, 

Massachusetts, 2017–18

By John R. Mullaney, Janet R. Barclay, Kaitlin L. Laabs, and Katherine D. Lavallee

Prepared in cooperation with the Friends of Herring River

Scientific Investigations Report 2019–5145

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Mullaney, J.R., Barclay, J.R., Laabs, K.L., and Lavallee, K.D., 2020, Hydrogeology and interactions of groundwater 

and surface water near Mill Creek and the Herring River, Wellfleet, Massachusetts, 2017–18: U.S. Geological Survey 

Scientific Investigations Report 2019–5145, 60 p., https://doi.org/10.3133/sir20195145.

Associated data for this publication:

Mullaney, J.R., and Barclay, J.R., 2020, Data on tidally filtered groundwater and estuary water levels, and 

climatological data near Mill Creek and the Herring River, Cape Cod, Wellfleet, Massachusetts, 2017–2018: 

U.S. Geological Survey data release, https://doi.org/10.5066/P9T167II.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors would like to thank the Chequessett Yacht and Country Club for access to the 

Club property and assistance with logistics. The Friends of Herring River and the staff from 

the National Park Service, Cape Cod National Seashore, are thanked for providing support for 

groundwater monitoring.

The following U.S. Geological Survey employees made important contributions to the 

data collection and analysis in this report: Alana Spaetzel, Herring River stage monitoring; 

Michael Colombo, data processing and database assistance; Timothy McCobb, Amory Conant, 

and Nicholas Taylor, surveying; Robert “Quinn” Hull and Luan Tran, geologic logging, drilling, and 

well preparations; and James Caldwell, water-level data review and approval.

v

Contents

Acknowledgments����������������������������������������������������������������������������������������������������������������������������������������iii

Abstract�����������������������������������������������������������������������������������������������������������������������������������������������������������1

Introduction�����������������������������������������������������������������������������������������������������������������������������������������������������1

Purpose and Scope ������������������������������������������������������������������������������������������������������������������������������5

Site Description�������������������������������������������������������������������������������������������������������������������������������������6

Methods of Data Collection and Analysis �������������������������������������������������������������������������������������������������8

Drilling and Well Installation���������������������������������������������������������������������������������������������������������������8

Mill Creek and Herring River Stage Monitoring ������������������������������������������������������������������������������8

Measurement and Processing of Water-Level Data ��������������������������������������������������������������������11

Methods of Statistical Analysis of Groundwater-Level and Mill Creek Stage Data����������������11

Lithologic and Water-Level Data at the Mill Creek Study Area �����������������������������������������������������������14

Description of Site Geology ��������������������������������������������������������������������������������������������������������������14

Hydrologic Conditions Near the Mill Creek Study Area, June 1, 2017, Through 

June 14, 2018��������������������������������������������������������������������������������������������������������������������������16

Groundwater and Mill Creek Water Levels, June 1, 2017, Through June 14, 2018 ������������������16

Short-Term Tidal Fluctuations in Groundwater Levels �����������������������������������������������������������������22

Groundwater-Level Fluctuations Over Periods Longer Than Daily Tidal Cycles����������������������22

Factors Affecting Flooding in Mill Creek�����������������������������������������������������������������������������������������27

Summary and Conclusions�������������������������������������������������������������������������������������������������������������������������39

References Cited������������������������������������������������������������������������������������������������������������������������������������������40

Appendix 1. Graphs of Water Levels in Wells Monitored for the Study of the Mill Creek 

Study Area, June 2017–June 2018�����������������������������������������������������������������������������������������������43

Appendix 2. Regression Coefficients and Metrics for Linear Regression Models 

Describing the Variability in Groundwater Levels and Surface-Water Levels Near 

the Herring River, Wellfleet, Massachusetts, From June 2017 To June 2018�����������������������56

Figures

1. Map showing the location of the study area, Wellfleet, Massachusetts ���������������������������2

2. Map showing the data collection locations, in the Mill Creek study area, 

Wellfleet, Massachusetts������������������������������������������������������������������������������������������������������������3

3. Graph showing tidal stage and acres of submerged wetlands at mean spring 

high tide for incrementally restoring tidal flow in the Herring River, Wellfleet, 

Massachusetts������������������������������������������������������������������������������������������������������������������������������4

4. Photograph showing flooding at the Chequessett Yacht and Country Club in 

Wellfleet, Massachusetts, on May 1, 2018�������������������������������������������������������������������������������5

5. Map showing approximate location of former salt marsh areas and locations 

with lithologic information collected during this study and previous 

investigations, Wellfleet, Massachusetts���������������������������������������������������������������������������������7

6. Graph showing precipitation data for Cape Cod, Massachusetts, compiled from 

National Weather Service stations at Wellfleet and Camp Edwards, June 1, 

2017, to June 14, 2018�����������������������������������������������������������������������������������������������������������������14

7. Graphs showing groundwater levels at U.S. Geological Survey monitoring 

sites relative to long-term statistics, near the Mill Creek study area, Cape Cod, 

Massachusetts, 2017 to 2018 ����������������������������������������������������������������������������������������������������17
vi

8. Maps showing water-table altitude, depth to groundwater, and generalized 

flow direction at the Mill Creek study area, Wellfleet, Massachusetts ............................20

9. Map showing average amplitude of the M2 tidal harmonic for wells and rivers 

in the study area, Wellfleet, Massachusetts, June 1, 2017, through June 14, 2018 ........25

10. Graph showing relation of the amplitude of the M2 tidal harmonic to distance of 

the well from the nearest tidal waterbody, June 1, 2017, through June 14, 2018, 

Wellfleet, Massachusetts..........................................................................................................26

11. Graph showing tidally filtered water levels at the Herring River downstream 

from the tide-control structure (Wellfleet Harbor), tidally filtered water 

levels at well MA–WNW 158, and daily precipitation from December 2017 to 

January 2018, Wellfleet, Massachusetts ................................................................................28

12. Graphs showing water levels in Mill Creek at sites 1 and 2 from June 1, 2017, to 

June 14, 2018, Wellfleet, Massachusetts................................................................................29

13. Boxplots showing the distribution of groundwater levels at well MA–

WNW 157–0012 and 7-day precipitation under nonflooded and flooded 

conditions at the upstream site on Mill Creek, June 1, 2017, through June 14, 

2018, Wellfleet, Massachusetts................................................................................................32

14. Boxplots showing the distribution of groundwater levels at wells MA–

WNW 155–0017, MA–WNW 156–0010, MA–WNW 159–0012, and MA–

WNW 161; and distribution of 7-day precipitation under nonflooded and flooded 

conditions at the downstream site on Mill Creek, June 1, 2017, through June 14, 

2018, Wellfleet, Massachusetts................................................................................................34

Tables

1. Well characteristics, construction details, and general lithologic information 

for wells in the Mill Creek study area, Wellfleet, Massachusetts ........................................9

2. Groundwater, Mill Creek, and Herring River water-level statistics, June 1, 2017, 

to June 14, 2018, Mill Creek study area, Wellfleet and Truro, Massachusetts .................12

3. Information on lithology, thickness of marsh deposits, and estimated depth to 

the transition zone between fresh groundwater and saline groundwater, Mill 

Creek study area, Wellfleet, Massachusetts .........................................................................15

4. Tidal amplitudes of five tidal harmonics from regression using data from each 

well and the Herring River, Mill Creek study area, Wellfleet, Massachusetts .................23
vii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 hectare (ha)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

ounce, fluid (fl. oz) 29.57 milliliter (mL)

Pressure

pound per square inch (lb/in2) 6.895 kilopascal (kPa)

Precipitation

inch per day (in/d) 25.4 millimeter per day (mm/d)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Transmissivity

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

 °F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as 

 °C = (°F – 32) / 1.8.

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.
viii

Abbreviations

CYCC Chequessett Yacht and Country Club

GOES Geostationary Operational Environmental Satellite (National 

Oceanic and Atmospheric Administration)

lidar light detection and ranging

NPS National Park Service

NWIS National Water Information System

NWS National Weather Service

R2 coefficient of determination

USGS U.S. Geological Survey
Hydrogeology and Interactions of Groundwater and 

Surface Water Near Mill Creek and the Herring River, 

Wellfleet, Massachusetts, 2017–18

By John R. Mullaney,1 Janet R. Barclay,1 Kaitlin L. Laabs,1 and Katherine D. Lavallee2

Abstract

Groundwater levels and stream stage were monitored by 

the U.S. Geological Survey, in cooperation with the Friends of 

Herring River, at 19 sites in the Mill Creek Basin, a tributary 

of the Herring River in Wellfleet, Massachusetts, on outer 

Cape Cod, to provide baseline data prior to a proposed restoration of tidal flow to the Herring River estuary at the Cape Cod 

National Seashore. Tidal flow in the Herring River has been 

restricted by a tide-control structure since 1909. Baseline data 

are necessary to understand current conditions and provide 

information on water levels for comparison to future water 

levels under the proposed Herring River restoration, which 

includes restoration of salt marshes by enhancing tidal flow to 

the Herring River and construction of a tide-control structure 

on Mill Creek to prevent the flooding of upstream private 

properties, including a golf course.

Analysis of data collected during monitoring-well installation at eight locations on or near the golf course and Mill 

Creek, along with analysis of existing information, determined 

that parts of the study area are underlain by salt marsh deposits 

up to 18 feet (ft) thick. These marsh deposits are directly 

underlain by estuarine sediments, and adjacent upland areas 

are underlain by medium to very coarse sand. The freshwater 

lens on the golf course is 70 ft thick or more.

Groundwater levels at individual wells in the study area 

fluctuated by 1.3 to 2.6 ft during the study period (June 1, 

2017, to June 14, 2018). Total precipitation during this period 

was 60.8 inches, about 10 inches greater than the long-term 

(2000–17) annual average (50.3 inches). Groundwater levels 

on Cape Cod generally were normal to above normal during 

the study owing to the higher than normal precipitation. Tidal 

amplitudes of groundwater levels caused by daily fluctuations at nearby tidal waterbodies (M2 tidal harmonic) were 

as large as 0.12 ft at a well 105 ft from the tidally restricted 

Herring River and as large as 0.06 ft at a well 575 ft from 

Wellfleet Harbor. Tidal fluctuations in groundwater levels 

were generally limited to areas about 1,500 ft from the nearest 

tidal waterbody. Under the initial proposed restoration, where 

mean tides would be maintained similar to current conditions, 

tidal fluctuations would be restored to parts of Mill Creek, 

and subsequent tidal fluctuations in groundwater levels could 

increase at some of the areas closest to the proposed tidecontrol structure, but the fluctuations would be less than about 

0.06 ft in magnitude.

Regression models were used to describe the variability 

of daily mean tidally filtered groundwater levels and daily 

maximum stream stage in Mill Creek. Significant independent variables for the groundwater-level model included 

daily tidally filtered Wellfleet Harbor stage with a lag time of 

zero to 2 days, 7-day precipitation, the growing degree days 

(50 degrees Fahrenheit), and the quartile of groundwater levels 

relative to a long period of record at a nearby observation well.

Significant independent variables to predict the Mill 

Creek stage included daily mean groundwater levels in nearby 

wells, 7-day precipitation, growing degree days (50 degrees 

Fahrenheit), and a binary indicator of either a flooded or nonflooded condition on the golf course near Mill Creek. Flooding 

in Mill Creek occurred primarily when groundwater levels at 

nearby wells reached certain thresholds, when the precipitation in the preceding 7 days was at least 0.92–1.04 inches, and 

during the nongrowing season.

Introduction

The Herring River estuary is in the towns of Wellfleet and 

Truro, Massachusetts, on Cape Cod Bay (fig. 1). Prior to 1909, 

the Herring River estuary and flood plain was the largest tidal 

river and estuary complex on outer Cape Cod and included 

about 1,100 acres of salt marsh, intertidal flats, and open-water 

habitats (National Park Service and others, 2016). The natural 

tidal flow of the Herring River has been limited since the construction, in 1909, of a dike with tide gates (tide-control structure) near the mouth of the river at Chequessett Neck Road 

(fig. 2). Currently, the typical tide range on the upstream side 

of the Herring River tide-control structure is about 2.2 feet (ft), 

whereas on the downstream side of the tide-control structure 

(Wellfleet Harbor) it is about 10.3 ft. Consequently, the land in 

1U.S. Geological Survey.

2National Park Service.
2 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

EXPLANATION

MA–TSW 89 U.S. Geological Survey long­term observation well and identifier

National Weather Service (NWS) weather station and identifier

Cape Cod National Seashore

MA–WNW 17

MA–BMW 22

MA–TSW 89

PLYMOUTH

BARNSTABLE

FALMOUTH

SANDWICH

BOURNE

TRURO

DENNIS

WAREHAM

MASHPEE

HARWICH

BREWSTER

YARMOUTH

WELLFLEET

CARVER

DUXBURY

MARSHFIELD

ORLEANS

EASTHAM

CHATHAM

KINGSTON

PROVINCETOWN

MARION

GOSNOLD

SCITUATE

70°30'0" W 70°0'0" W

42°0'0" N

41°40'0" N

CAPE COD BAY

Nantucket Sound

Vineyard Sound

Herring River

Cape Cod Canal

Wellfleet

Harbor

Buzzards

Bay

ATLANTIC OCEAN

Base from Massachusetts Bureau of Geographic 

Information (MassGIS) digital data

Community Boundaries (Towns), 1:25,000, 2014

Lambert Conformal Conic projection

North American Datum of 1983

Study

area

Cape

Cod Bay

42°30'

73° 72° 71°

41°30' 0 50 MILES

0 50 KILOMETERS

MASSACHUSETTS

0 6 12 18 24 MILES

0 8.5 17 25.5 34 KILOMETERS

NWS 191204

NWS 191203

NWS 191204

Figure 1. Location of the study area, Wellfleet, Massachusetts.
011058798

1

2 3

4

5

6

7

134 162

141

158

160

157

155

156

154

159

Mill Creek 2

Mill Creek 1

133–0030

161

Wellfleet Harbor Wellfleet Harbor

 70°3'30" 70°3'

41°56'

41°55'40"

011058798

Surface­water gage and numberApproximate boundary of the Chequessett 

Yacht and Country Club 

0 500 1,000 1,500 

0 120 240 360 480 METER

7

160

EXPLANATION

Well site

USGS Wellfleet well numberSite number (table 1) 

Base from U.S. Geological Survey, National Map, 2016, 1:24,000North American Datum of 1983

Chequessett Yacht and Country Club

Cape Cod National Seashore

Tide-controlstructure

Figure 2. Data collection locations, in the Mill Creek study area, Wellfleet, Massachusetts.
4 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

some low-lying areas of the Herring River watershed that previously flooded at high tide was developed, including private 

homes and a golf course along the Mill Creek tributary.

The Herring River is separated from Wellfleet Harbor by 

the Chequessett Neck Road dike. The dike has three 6-ft-wide 

box culverts, each with an attached flow-control structure. One 

culvert has an adjustable sluice gate that is currently set partially open at 2 ft and allows limited bidirectional tidal flow. 

The remaining two culverts have tidal flap gates, designed to 

permit flow only during outgoing (ebbing) tides (National Park 

Service and others, 2016).

The restriction of the tide in the Herring River has had 

numerous effects upstream from the Herring River tide-control 

structure, including, but not limited to, plant community 

changes, loss of estuarine habitat, degradation of water quality, 

and alteration of natural sediment processes, leading to marsh 

subsidence, nuisance mosquito populations, restriction of 

river herring migration, lack of carbon storage and consequent 

increases in methane emissions. The lower Herring River 

Basin currently contains subtidal, riverine, vegetated wetland, 

and fringing upland flood plains. Habitat in the Mill Creek 

Basin is primarily Phragmites marsh and disturbed, wooded 

wetland (National Park Service and others, 2016).

To eventually eliminate many of these problems, research 

and planning to restore the habitats upstream from the Herring 

River tide-control structure have been ongoing for several 

decades. In the Environmental Impact Statement/Report completed for the project (National Park Service and others, 2016), 

the goals include restoration of tidal flow to a large part of the 

1,100 acres of habitat that were degraded by the presence of 

the tide-control structure, with a minimal impact to private 

properties and cultural resources. Detailed restoration goals 

are described by the National Park Service and others (2016).

The current (2019) preferred restoration alternative in 

the Environmental Impact Statement/Report for the Herring 

River is identified as alternative D, which includes a new tidecontrol structure at Chequessett Neck Road and the installation 

of an additional tide-control structure on Mill Creek to prevent 

tidal flooding of the Chequessett Yacht and Country Club 

(CYCC) and some residential properties. The objective for 

alternative D is to fully open the new gates gradually to allow 

mean high water spring tides up to 5.6 ft above the North 

American Vertical Datum of 1988 (NAVD 88) and coastal 

storm-driven tides up to 7.5 ft above NAVD 88 in the Lower 

Herring River. Alternative D provides the highest possible 

altitudes of water surface at high tide, given the constraints 

of current land use in the flood plain (fig. 3). The gradual 

opening of the gates would allow for incremental evaluation 

of the effects of the higher tides on restoration objectives and 

private properties.

The tide-control structure to be constructed on Mill Creek 

would limit upstream movement of the tide, providing partial 

tidal restoration, while allowing freshwater to drain from the 

upstream Mill Creek Basin. To facilitate downstream movement of freshwater, a pumping system is being designed so 

that Mill Creek does not back up and cause nuisance flooding 

during high tides or during periods of high precipitation during storms.

-4

-3

-2

-1

0

1

2

3

4

5

0

100

200

300

400

500

600

700

Acres at mean high water spring tides

Mean tide level 

Mean low water

Mean high water

Water level, in feet above North American Vertical Datum of 1988

Incremental adjustments to the opening of the proposed Herring River tide-control structure

Area of restored tidal wetlands, in acres, at projected 

mean high water spring tides

EXPLANATION

Figure 3. Tidal stage and acres of submerged wetlands at mean spring high tide for incrementally restoring tidal flow in the Herring 

River, Wellfleet, Massachusetts.
Introduction 5

Parts of the CYCC currently flood periodically (fig. 4), 

affecting operations of the golf course during wet periods. 

Several of the fairways on the golf course are built on former low-lying salt marsh sediments that have compacted and 

caused land subsidence because of the loss of tidal flow to 

these areas. Although a mitigation plan that would elevate 

and regrade low parts of the golf course has been agreed to in 

concept, there is concern about increased flooding on the golf 

course caused by high groundwater levels or tidal flooding in 

Mill Creek.

To understand the hydrogeology of the Mill Creek/

Herring River area, the U.S. Geological Survey (USGS) 

entered into a cooperative agreement with the Friends of 

Herring River in 2016 to conduct a study of the area from 

June 1, 2017, to June 14, 2018. The study provides baseline information prior to the beginning of the Herring River 

restoration. The objectives of this study were to (1) determine 

water-table conditions and stream-aquifer interaction during 

the prerestoration period and (2) acquire additional subsurface 

geologic and aquifer data to better define the hydrogeologic 

framework in the study area. This information can be used 

if new groundwater-flow models need to be developed, or if 

existing models need to be revised, to aid in adaptive management planning and further evaluation of the effects of restoration scenarios.

Purpose and Scope

This report describes the hydrogeology of the Mill Creek 

area near the Herring River estuary on Cape Cod in Wellfleet, 

including the surficial geology, hydrologic properties of the 

aquifer, and fluctuations in groundwater and Mill Creek levels 

caused by precipitation and tidal fluctuations of the lower 

Herring River estuary upstream and downstream from a tidecontrol structure. The information in the report was collected 

from June 2017 to June 2018 and is intended to provide a 

baseline of the groundwater and surface-water levels in the 

study area prior to the restoration of the Herring River marsh. 

Figure 4. Flooding at the Chequessett Yacht and Country Club in Wellfleet, Massachusetts, on May 1, 2018, when the daily maximum 

stage at the Mill Creek downstream site was 1.33 feet above the North American Vertical Datum of 1988. Photograph by Katherine 

Lavallee, National Park Service.
6 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Information presented in this report may have applicability 

to similar geologic settings where the groundwater and tidal 

waterbodies interact. Data collected in this study are stored 

in the USGS National Water Information System (NWIS) 

database and publicly available (U.S. Geological Survey, 

2018), or are reported in a USGS data release Mullaney and 

Barclay (2020).

Site Description

The Herring River watershed is underlain by the Wellfleet 

plain glacial meltwater sediments described by Oldale (1992). 

These sediments were deposited by meltwater from the Cape 

Cod Bay and South Channel lobes of the glacial ice sheets 

that were retreating from Cape Cod about 15,000 years ago. 

The sediments were deposited as deltas in Glacial Lake Cape 

Cod, a lake that persisted in Cape Cod Bay when the ice from 

the retreating glacier blocked the northern part of the bay. The 

highest altitudes of the Wellfleet plain deposits near the mouth 

of the Herring River are currently about 80 ft above NAVD 88. 

The altitudes gradually increase to about 130 ft toward the east 

(Atlantic Ocean) side of lower Cape Cod. The lithology of the 

deposit is typically fine to coarse sand, with finer materials at 

depth (LeBlanc and others, 1986).

The Herring River and Mill Creek are in low-lying valleys thought to be created during deglaciation by the process 

of spring sapping, where a large volume of glacial meltwater 

was dammed by the outwash sediment, and a high volume of 

groundwater was forced through the sediments, causing erosion of these valleys (Oldale, 1992). The valleys now contain 

salt marsh sediments, the oldest of which were deposited more 

than 2,000 years before present (Oldale, 1992) as postglacial 

sea levels rose and inundated these low-lying coastal areas. 

The depth to bedrock in the area is about 490 ft based on 

information published by Lane and others (2008).

The Herring River drains parts of the towns of Wellfleet 

and Truro on lower Cape Cod to Wellfleet Harbor at the 

mouth, which is connected to Cape Cod Bay (fig. 1). The 

freshwater discharge in the Herring River system is dominated 

by groundwater flow; because of the permeable nature of 

sediments on lower Cape Cod, there is only a small amount 

of surface runoff. The Herring River drains a large part of the 

Chequessett groundwater-flow lens on Cape Cod as described 

by Masterson (2004). The estimated area contributing groundwater to the Herring River is about 7.4 square miles (mi2), 

based on modeling described in Carlson and others (2017). 

Mill Creek is a subbasin of the Herring River that has a surface drainage area of about 0.5 mi2; however, as is the case for 

the entire Herring River watershed, the discharge is dominated 

by groundwater flow and, because of the permeable nature of 

the sediments, the surface-water and groundwater basins are 

not coincident. The groundwater drainage divide between the 

Herring River and Mill Creek Basins and Wellfleet Harbor 

crosses the CYCC from east to west about 600–1,000 ft from 

Wellfleet Harbor (Carlson and others, 2017). The thickness 

of fresh groundwater (from the water table to salty groundwater) near the Herring River/CYCC study site ranges from 

37 ft at USGS well MA–WNW 133 to 55 ft at USGS well 

MA–WNW 134 (shown on fig. 2) (Masterson, 2004; Martin, 

2004, 2007).

Additional lithologic information for the study area is 

available from two recent studies. In March 2014, four borings were drilled at the site of a former dike (near the proposed future tide-control structure) on Mill Creek (Fuss and 

O’Neill, Inc., 2014). Borings were advanced to depths ranging 

from 41 to 71 ft. A piezometer was installed at one location 

(WNW 161, figs. 2 and 5) and screened at a depth of 8–18 ft, 

and slug tests were conducted to determine the hydraulic 

conductivity of aquifer materials. Hydraulic conductivity from 

these tests ranged from 5 to 14 feet per day (ft/d). A series 

of geotechnical tests were conducted on samples from these 

boring sites. Lithologic materials from these borings were 

typically fine to medium sand, but some silty and clayey layers 

were present.

A series of eight borings (fig. 5) was completed at the 

CYCC in 2009 (The Louis Berger Group, Inc., 2009). The 

purpose of the borings was to conduct geotechnical tests on 

the load-bearing properties of the soils in areas where filling 

and excavation have been proposed to eliminate flooding on 

the golf course under the preferred restoration alternative. A 

fine-grained silty organic layer 1–18 ft thick and containing 

peat (salt marsh deposits) was present at six of the eight locations. Beneath this layer was generally fine to medium sand, 

with some medium to coarse sand. The approximate area of 

the former salt marshes was determined through the use the 

information from the two studies described above, and from 

site visits to inspect the geology and landforms of the study 

area. The extent of former salt marsh was determined to be 

approximated by areas with altitudes less than 3.5 ft above 

NAVD 88 (fig. 5).
70°3'30" 

41°56'

41°55'50"

Base map data from Google, 2018, image from February 27, 2018Lambert Conformal Conic projection, North American Datum of 1983

133−0030

141

158

160

157

156

159

B−3

B−5

B−2

B−6

B−1

B−8

154

134

B−4

161

155

B−7

2

3

1

4

Herring River

0 425 850 1,275 1,700 FEET

0 110 220 330 440 METERS

EXPLANATION

U.S. Geological Survey well and number from MU.S. Geological Survey boring location and assBoring location and number from Fuss and O’NBoring location and number from The Louis Be

Altitude at or below 3.5 feet, North American V

B-1

158

141

4

Figure 5. Approximate location of former salt marsh areas and locations with lithologic information collected during this study and previous investigMassachusetts.
8 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Methods of Data Collection and 

Analysis

To establish a water-level network in the Herring River 

and Mill Creek study area, existing wells were inventoried. 

Four existing wells were located, including two USGS wells—

MA–WNW 141 and MA–WNW 134—installed during a 

study by Masterson (2004) (figs. 2 and 5). These wells were 

originally installed to determine the depth to the freshwater/

saltwater interface and were constructed with a deep sump and 

a shallow screen so that geophysical measurements could be 

made. In addition to the USGS wells, a well from a study of 

the subsurface of Mill Creek (Fuss and O’Neill, Inc., 2014, 

fig. 5) near the proposed Mill Creek tide-control structure 

and an additional well previously monitored by the National 

Park Service (NPS) on Old Chequessett Road (Martin and 

Medeiros, 2012) also were located (sites MA–WNW 161 and 

MA–WNW 162, respectively, fig. 2).

To collect lithologic information, and to establish baseline information on water-table altitudes, groundwater-level 

fluctuations, and fluctuations in stream stage in Mill Creek, 

new wells were installed at eight sites on the CYCC, including 

the replacement of one USGS well (MA–WNW 133) from a 

previous study, and sites were established to measure stream 

stage on Mill Creek at the CYCC and downstream from 

the golf course to improve understanding of the interaction 

between Mill Creek and groundwater levels.

Drilling and Well Installation

Wells were installed at seven of the eight sites by use of 

a direct-push drilling technique during the week of May 15, 

2017. At each location, a continuous core was collected to 

the approximate depth of the freshwater/saltwater transition 

zone. The core was logged, and subsamples were retained. To 

identify the top of the transition zone from freshwater to saltwater, specific conductance of pore water from each core was 

measured. In addition to measuring the specific conductance 

of the pore water, specific conductance also was measured in 

the field and in the laboratory by adding deionized water to 

subsamples of core material. The sample was prepared by adding 50 milliliters (mL) of sediment and adding enough deionized water so that the total volume was 150 mL. The specific 

conductance was then measured in the water/sediment slurry. 

Whereas the first method to measure specific conductance 

was done in situ and provided actual measurements of specific 

conductance of pore water, the second method was used to 

verify changes that might indicate the position of the top of the 

transition zone.

Following the collection of the continuous core, the 

direct-push drill rig was fitted with a temporary steel casing 

that was driven to the depth of interest for well installation. A 

2-inch-diameter flush-jointed polyvinyl chloride casing and 

a 5-ft-long 0.010-inch-slot (number 10) screen were set in 

the temporary steel casing, which was then withdrawn from 

the boring.

Wells were installed at multiple depths at four sites 

(sites 2, 3, 4, and 6, fig. 2). At three of the sites (sites 2, 3, 

and 6, fig. 2), shallow and deep wells were installed, the former near the top of the saturated zone and the latter just above 

the transition zone from freshwater to saltwater. The depths of 

the well screens were selected based on the geology identified 

in the core samples. At site 4 (fig. 2), a third well was installed 

that penetrated through the transition zone to allow future 

electromagnetic borehole logging. This well was installed 

with a deep sump and screened at an intermediate depth to 

ensure that there was only freshwater in the well. Wells were 

completed by retrieving the temporary casing and allowing 

the formation to collapse around the well screens. A bentonite 

seal was emplaced near or at the water table, and the well was 

finished, depending on the location at the CYCC, with a standpipe or a flush-mounted well cover set in a concrete pad.

An additional well was installed near the Herring River 

(site 1, fig. 2) by using hand tools because the site was not 

accessible to vehicles. The well was installed with the use of 

a hand auger and was driven to additional depth by using a 

posthole driver. The well was constructed of 1.5-inch-diameter 

stainless steel casing and a 2.5-ft-long wire-wound 0.010-inchslot (number 10) screen (site 1, fig. 2).

The altitude of the measuring point on each well installed 

at the CYCC or near the Herring River was determined by 

using a differential laser-level survey. The laser-level survey 

was tied to NAVD 88 by using altitudes established by the 

NPS at the existing Herring River tide-control structure. All 

wells were developed by pumping and monitoring recovery to 

verify if there was a connection to the aquifer, and therefore 

responsive to water-level change in the formation. Information 

on the well characteristics, well construction, and lithologic 

logs is presented in table 1.

Mill Creek and Herring River Stage Monitoring

Two locations for monitoring stream stage were established on Mill Creek: an upstream site between two fairways 

at the CYCC (Mill Creek 1), and a downstream site in the Mill 

Creek Marsh about 800 ft upstream from the Herring River 

(Mill Creek 2, fig. 2). The upstream location was installed by 

using a standpipe that was attached to a bridge that is part of 

a golf cart path at the CYCC. At the downstream location, no 

fixed points were available to attach equipment to monitor 

water stage; therefore, a fixed point was established by driving two sections of angle iron to a depth of 10 ft, where firm 

sediment was encountered. A well screen was pushed into the 

sediment and attached to the angle iron as a housing to measure stage. Reference points were established at both locations 

for determining water-surface altitude. These points were tied 

to the survey of the measuring points for the wells installed for 

the study.
Table 1. Well characteristics, construction details, and general lithologic information for wells in the Mill Creek study area, Wellfleet, Massachusett[Dates are given in year, month, and day (yyyymmdd). Latitude and longitude are given in degrees (°), minutes (′), and seconds (′′) referenced to the North American Datum of 1Geological Survey; ft NAVD 88, foot above the North American Vertical Datum of 1988; ft rls, foot relative to land surface; ft bls, foot below land surface; MA, Massachusetts; 

Site 

no. 

(fig. 2)

USGS local identifier Station identifier

Date of 

construction Latitude Longitude

Altitude 

(ft NAVD 88)

Height 

of measuring 

point 

(ft rls)

Depth 

of well 

(ft bls)

Screen internal 

(ft bls) 

Measuring 

point

Land 

surface Top Bottom

1 MA–WNW 154 

WELLFLEET, MA

415556070033501 20170531 41°55′55.82′′ 70°03′34.65′′ 7.83 5.43 2.4 10.1 7.6 9.6 

2 MA–WNW 155–0035 

WELLFLEET, MA

415557070032301 20170516 41°55′56.69′′ 70°03′22.95′′ 3.31 3.78 −0.47 34.54 29.54 34.54 

MA–WNW 155–0017 

WELLFLEET, MA

415557070032302 20170516 41°55′56.69′′ 70°03′22.95′′ 3.45 3.83 −0.38 16.98 11.98 16.98 

3 MA–WNW 156–0037 

WELLFLEET, MA

415557070031701 20170516 41°55′57.03′′ 70°03′16.8′′ 4.74 5.14 −0.4 37.41 32.41 37.41 

MA–WNW 156–0010 

WELLFLEET, MA

415557070031702 20170516 41°55′57.03′′ 70°03′16.8′′ 4.63 5.05 −0.42 10.55 5.55 10.55 

4 MA–WNW 157–0033 

WELLFLEET, MA

415600070030701 20170517 41°56′00.31′′ 70°03′07.31′′ 4.04 4.4 −0.36 32.71 27.71 32.71 

MA–WNW 157–0070 

WELLFLEET, MA

415600070030702 20170519 41°56′00.31′′ 70°03′07.31′′ 4.24 4.54 −0.3 67.6 15 25 

MA–WNW 157–0012 

WELLFLEET, MA

415600070030703 20170517 41°56′00.31′′ 70°03′07.31′′ 3.96 4.3 −0.34 11.74 6.74 11.74 

5 MA–WNW 158 

WELLFLEET, MA

415549070031401 20170515 41°55′49.26′′ 70°03′13.52′′ 2.85 3.17 −0.32 9.52 4.52 9.52 

6 MA–WNW 159–0035 

WELLFLEET, MA

415552070031701 20170518 41°55′51.99′′ 70°03′17.03′′ 2.99 3.43 −0.44 32.9 27.9 32.9 

MA–WNW 159–0012 

WELLFLEET, MA

415552070031702 20170518 41°55′51.99′′ 70°03′17.03′′ 6.44 3.34 3.1 11.79 6.79 11.79 

7 MA–WNW 160 

WELLFLEET, MA

415544070033301 20170515 41°55′44.49′′ 70°03′33.01′′ 5.33 5.74 −0.41 12.18 7.18 12.18 
Table 1. Well characteristics, construction details, and general lithologic information for wells in the Mill Creek study area, Wellfleet, Massachusett[Dates are given in year, month, and day (yyyymmdd). Latitude and longitude are given in degrees (°), minutes (′), and seconds (′′) referenced to the North American Datum of 1Geological Survey; ft NAVD 88, foot above the North American Vertical Datum of 1988; ft rls, foot relative to land surface; ft bls, foot below land surface; MA, Massachusetts; 

Site no. (fig. 2) USGS local identifier Station identifier Date of construc­ tion Latitude Longitude Altitude (ft NAVD 88) Height of mea­ suring point (ft rls) Depth of well (ft bls) Screen internal (ft bls) 

Measur- ing point Land sur­ face Top Bottom na MA–WNW 133–0030 WELLFLEET, MA 415550070032202 20170518 41°55′50.67′′ 70°03′22.75′′ 12.81 13.15 −0.34 29.62 24.62 29.62 

na MA–WNW 141 WELLFLEET, MA 415556070030601 20040909 41°55′55.68′′ 70°03′05.8′′ 44.29 44.67 −0.38 135.38 50.38 55.38 na MA–WNW 161 WELLFLEET, MA 415559070032601 20140317 41°55′59.32′′ 70°03′26.38′′ 2.94 0.39 2.55 17.15 7.15 17.15 na MA–WNW 134 WELLFLEET, MA 415605070032001 20030911 41°56′05.02′′ 70°03′20.12′′ 5.27 5.51 −0.24 104.21 9.21 14.21 na MA–WNW 162 WELLFLEET, MA 415605070031301 na 41°56′04.98′′ 70°03′13.06′′ 3.99 3.51 0.48 4.87 na na 
Methods of Data Collection and Analysis 11

Data for the Herring River stage (tidal gage 011058798, 

fig. 2) were collected by the USGS for another project to 

monitor water quality in the Herring River system. Stage data 

were collected from the upstream side of the Herring River 

tide-control structure (Herring River) at 5-minute intervals 

by using a pressure transducer and bubbler system. These 

data were available during the entire study. Data on Herring 

River stage downstream from the Herring River tide-control 

structure (Wellfleet Harbor) were collected beginning in 

September 2017 at 15-minute intervals by using a radar system over the water. The stage data were used in the analysis 

of the effects of the Herring River and Wellfleet Harbor tidal 

fluctuations on groundwater levels in the study area. Data 

were transmitted to the USGS National Water Information 

System (NWIS) database either by mobile phone modem or 

satellite transmitter and ground station to the National Oceanic 

and Atmospheric Administration (NOAA) Geostationary 

Operational Environmental Satellite (GOES).

Measurement and Processing of Water-Level 

Data

Continuous water-level monitoring began at most 

groundwater sites as well as the two Mill Creek sites at the 

beginning of June 2017. Water levels were monitored using 

HOBO U20–001–04–TI unvented submersible pressure 

transducers, which measure the absolute pressure of the water 

and atmosphere. The typical error for this sensor for water 

levels is 0.01 ft (Onset Computer Corporation, 2019a). The 

transducers were suspended in the wells at set depths and 

programmed to measure pressure at 15-minute intervals. To 

correct for variations in atmospheric pressure, barometric 

pressure was monitored by using HOBO U20L–04 pressure 

transducers set to read at 15-minute intervals at two locations 

within the CYCC (sites 6 and 7, fig. 2). The maximum error 

for pressure for this sensor is 0.063 pound per square inch 

(Onset Computer Corporation, 2019b). To relate the pressure readings from the transducers to the groundwater levels, 

reference water-level measurements were made either by NPS 

or USGS personnel every 4 to 6 weeks by using a calibrated 

electric tape. Reference water levels (tape-down measurements to verify transducer calibration) were measured by 

using procedures outlined in Cunningham and Schalk (2011). 

The electric tapes used for the measurements were calibrated 

according to the guidance of the USGS tape calibration program (U.S. Geological Survey, 2013). Reference water levels 

were stored in the USGS program SVMobileAQ, which is an 

interface to the NWIS database. SVMobileAQ stores a copy 

of the database of groundwater-level measurements, as well 

as pertinent information regarding the measuring point of the 

well and the tape calibration adjustment for each water-level 

tape. It then provides a file output that is loaded directly into 

the NWIS database. All measurement data were uploaded 

within 1 week of each site visit.

Well MA–WNW 159-0012 (site 6, fig. 2) was instrumented with a vented transducer, which required no barometric correction. Data were transmitted directly to NWIS through 

transmission to the GOES satellite, and ground station. Data 

for this site were collected at 15-minute intervals and made 

available in near real time on the public web portal for NWIS.

Data from the HOBO loggers and the real-time site were 

downloaded in the field during each site visit. Data from 

the sites with HOBO loggers were corrected for barometric 

pressure, and then these time-series data were loaded into 

the USGS AQUARIUS database, analyzed, and approved 

by using the procedures outlined in U.S. Geological Survey 

(2017a). Time-series data were analyzed every 1–3 months, 

and any necessary corrections, based on field readings, 

were applied.

Reference water levels were collected at the two waterlevel stage sites on Mill Creek by measuring with an engineer’s tape to the water surface from a reference point with 

a known altitude. Tape-down measurements were made just 

after a 15-minute time interval to correlate with the HOBO 

time-series data. Reference measurements at the Herring River 

tidal gages were made with a staff gage on the upstream side 

that was read at each site inspection on a 5-minute time interval. At the downstream site (harbor side), an engineer’s tape 

and a 1-ft-long brass weight were used to tape down from a 

reference point to the water surface on a 15-minute time interval. Data collected at these sites were analyzed and approved 

by using the guidance in U.S. Geological Survey (2017b). Any 

corrections to time-series data were made based on field tapedown readings.

Methods of Statistical Analysis of 

Groundwater-Level and Mill Creek Stage Data

As part of the data analysis, summary statistics were 

computed for the groundwater sites and the Herring River and 

Mill Creek monitoring sites. Summary statistics consist of the 

minimum, median, mean, and maximum water levels during 

the study period from June 1, 2017, through June 14, 2018 

(table 2).

To analyze the daily tidal fluctuations in water levels at 

the wells and Herring River sites, a Godin filter (Godin, 1972) 

was applied to the 15-minute data for each site (Paul Work, 

U.S. Geological Survey, written commun., 2017). The filter 

removes the variation in the data caused by daily tidal fluctuations with three passes of 24, 24, and 25 hours. A record of the 

daily tidal fluctuations was created by subtracting the filtered 

result from the original unfiltered data. To determine the magnitude of daily tidal fluctuations on the groundwater levels, 

the daily fluctuations component for each well was regressed 

on five common tidal and solar harmonics (M2, principal 

lunar semidiurnal constituent; N2, larger lunar elliptic semidiurnal constituent; S2, principal solar semidiurnal constituent; O1, lunar diurnal constituent; and K1, lunar diurnal 
Table 2. Groundwater, Mill Creek, and Herring River water-level statistics, June 1, 2017, to June 14, 2018, Mill Creek study area, Wellfleet and Truro, [no., number; USGS, U.S. Geological Survey; ft NAVD 88, foot above the North American Vertical Datum of 1988; ft bls, foot below land surface; Min, minimum; Med, mediaMA, Massachusetts; na, not available] Site no. (fig. 2) USGS local identifier Site type Station identifier Water-level altitude (ft NAVD 88) Depth (f

Min Mean Med Max Min Mean 

1 MA–WNW 154 WELLFLEET, MA Well 415556070033501 −0.25 0.29 0.25 1.44 3.99 5.14 2 MA–WNW 155–0035 WELLFLEET, MA Well 415557070032301 0.97 2.03 2.03 3.44 0.34 1.75 

MA–WNW 155–0017 WELLFLEET, MA Well 415557070032302 0.92 2.09 2.09 3.56 0.27 1.74 

3 MA–WNW 156–0037 WELLFLEET, MA Well 415557070031701 1.21 1.73 1.7 2.72 2.42 3.41 

MA–WNW 156–0010 WELLFLEET, MA Well 415557070031702 1.29 1.77 1.73 2.73 2.32 3.28 

4 MA–WNW 157–0033 WELLFLEET, MA Well 415600070030701 1.44 1.91 1.87 2.84 1.56 2.49 

MA–WNW 157–0070 WELLFLEET, MA Well 415600070030702 1.44 1.90 1.87 2.82 1.72 2.64 MA–WNW 157–0012 WELLFLEET, MA Well 415600070030703 1.42 1.91 1.87 2.82 1.48 2.39 

5 MA–WNW 158 WELLFLEET, MA Well 415549070031401 0.95 1.66 1.64 2.88 0.29 1.51 6 MA–WNW 159–0035 WELLFLEET, MA Well 415552070031701 1.06 1.67 1.64 2.76 0.67 1.76 

MA–WNW 159–0012 WELLFLEET, MA Well 415552070031702 1.06 1.64 1.62 2.73 0.61 1.70 

7 MA–WNW 160 WELLFLEET, MA Well 415544070033301 0.53 1.17 1.15 2.38 3.36 4.57 

na MA–WNW 133–0030 WELLFLEET, MA Well 415550070032202 0.98 1.52 1.49 2.65 10.5 11.63 na MA–WNW 141 WELLFLEET, MA Well 415556070030601 1.33 1.84 1.8 2.9 41.77 42.83 na MA–WNW 161 WELLFLEET, MA Well 415559070032601 0.2 1.14 1.19 1.98 −1.59 −0.75 na MA–WNW 162 WELLFLEET, MA Well 415605070031301 0.58 1.39 1.45 1.93 1.58 2.12 na MA–WNW 134 WELLFLEET, MA Well 415605070032001 1.15 1.58 1.55 2.49 3.02 3.93 

Mill Creek 1 MILL CK AT CHEQUESSETT YT & GOLF WELLFLEET MA Stream/ estuary 415601070030701 0.39 1.28 1.37 2.06 na na Mill Creek 2 MILL CREEK US HERRING RIVER AT WELLFLEET MA Stream/ estuary 415560070032501 0.08 1.04 1.13 1.67 na na Upstream HERRING R AT CHEQUESSETT NECK RD AT WELLFLEET, MA Estuary 011058798 −3.82 −0.76 −0.73 1.31 na na Downstream1 HERRING R AT CHEQUESSETT NECK RD AT WELLFLEET, MA Estuary 011058798 −3.71 0.27 0 9.76 na na 

1Data for downstream side of the Herring River tide-control structure only available from September 27, 2017, to June 14, 2018.
Methods of Data Collection and Analysis 13

constituent) (Foreman and Henry, 1989; National Oceanic and 

Atmospheric Administration, 2018) by using the TideHarmonics package for R statistical software (Stephenson, 2016).

An additional analysis was done to examine the factors that affect groundwater-level fluctuations at time periods longer than the daily tidal fluctuations in the study area. 

Regression models were created for each well to describe the 

variability in water levels. Groundwater-level and water-level 

data from the Herring River were filtered by using the Godin 

filter described above. The dependent variable for each model 

was daily mean tidally filtered water level at each well. The 

independent variables included daily mean tidally filtered 

water levels in the Herring River downstream (Wellfleet 

Harbor) and upstream from the Herring River tide-control 

structure (Herring River), precipitation, the growing degree 

days (50 degrees Fahrenheit [°F], the base temperature), 

and the quartile of groundwater levels in nearby long-term 

USGS observation wells. Precipitation data and other weather 

characteristics were downloaded from the Western Regional 

Climate Center (2018). Data in this database were downloaded 

for the Wellfleet weather station (National Weather Service 

[NWS] 191203) and were supplemented with data from the 

Cape Cod site at Camp Edwards (NWS 191204) (fig. 1) if 

there were missing or erroneous values for any days (fig. 6) 

(Mullaney and Barclay, 2020). Data from nearby USGS 

long-term monitoring sites were downloaded from NWIS 

(U.S. Geological Survey, 2019).

To determine which variables in the regression models 

were the most important, the standardized coefficients for 

each model also were determined. Standardization was done 

using the lm.beta package in R (Behrendt, 2014). Standardized 

coefficients were calculated by subtracting the mean of 

each variable from each observed value and then dividing 

by the standard deviation of the variable. This allowed for 

the absolute values of the coefficients of each variable to be 

directly compared.

Additional regression models were developed to describe 

the variability in daily maximum water levels at the upstream 

and downstream sites on Mill Creek. The regression models 

were designed to identify factors that may be affecting water 

levels and the frequency of flooding at these sites. The independent variables tested included groundwater levels at nearby 

wells, precipitation, the growing degree days, and indicators of 

a flooded condition at each site. Standardized coefficients also 

were calculated as described above.
14 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

0

1

2

3

4

5

Precipitation, in inches per day

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

Date

Figure 6. Precipitation data for Cape Cod, Massachusetts, compiled from National Weather Service stations (NWS) 191203, at 

Wellfleet, supplemented with data from station NWS 191204 at Camp Edwards, June 1, 2017, to June 14, 2018.

Lithologic and Water-Level Data at the Description of Site Geology

Mill Creek Study Area

The following sections summarize new and existing data 

on lithology, hydrologic conditions, and groundwater and 

surface-water levels in the study area. Statistical models relating fluctuations in groundwater levels over daily tidal cycles 

and longer periods to ancillary data are described. Statistical 

models relating ancillary data to water levels and flooding in 

Mill Creek also are discussed.

Data collected from the coring and well installation and 

from previous geotechnical studies of the subsurface at the 

CYCC were used to delineate the areas that were formerly 

salt marshes, show the lithology of the glacial deposits, and 

indicate the approximate depth to the top of the transition zone 

from fresh to saline groundwater (table 3). Of the new locations cored for this investigation, only the core at site 2 (well 

cluster MA–WNW 155, figs. 2 and 5) fully penetrated 15 ft 

of salt marsh deposits. The salt marsh deposits at this location contain organic material (peat) as well as clay. Additional 

data on the thickness of the salt marsh deposits were collected 

during a geotechnical investigation done as part of a study to 
Table 3. Information on lithology, thickness of marsh deposits, and estimated depth to the transition zone between fresh groundwater and saline groarea, Wellfleet, Massachusetts.[ft, foot; na, not applicable]

Site identifier 

(fig. 5) General description of site lithology

Thickness of 

salt marsh 

sediments (ft)

Approximate 

depth to top of the 

transition zone to 

saltwater (ft)

Sou

Fuss and O’Neill boring 2 Fine to medium sand, silt and clay 0 na Fuss and O’Neill, Inc. (2014Fuss and O’Neill boring 3 Fine sand, silt and clay 0 na Fuss and O’Neill, Inc. (2014Fuss and O’Neill boring 4 Fine sand, silt and clay 0 na Fuss and O’Neill, Inc. (2014Louis Berger Group B–1 Marsh deposits over medium sand 4 na The Louis Berger Group, InLouis Berger Group B–2 Marsh deposits over fine sand 4 na The Louis Berger Group, InLouis Berger Group B–3 Marsh deposits over fine to medium sand 13 na The Louis Berger Group, InLouis Berger Group B–4 Fine to medium sand over coarse sand 0 na The Louis Berger Group, InLouis Berger Group B–5 Marsh deposits over medium sand 18 na The Louis Berger Group, InLouis Berger Group B–6 Marsh deposits over fine to medium sand 18 na The Louis Berger Group, InLouis Berger Group B–7 Fill over marsh deposits over fine sand 7 na The Louis Berger Group, InLouis Berger Group B–8 Medium to fine sand 0 na The Louis Berger Group, InMA–WNW 133 Medium to coarse sand 0 43 Well was redrilled for this s

depth to transition zone f

MA–WNW 134 Fine to very fine sand 0 59 Masterson (2004).MA–WNW 141 na 0 95 Masterson (2004).MA–WNW 155 (site 2) Marsh deposits over very fine to medium sand 15 60 naMA–WNW 156 (site 3) Medium to coarse sand 0 >65 naMA–WNW 157 (site 4) Very coarse sand 0 >70 naMA–WNW 158 (site 5) Medium to very coarse sand 0 40 naMA–WNW 159 (site 6) Fine to coarse sand 0 >45 naMA–WNW 160 (site 7) Medium to very coarse sand 0 40 naMA–WNW 161 Marsh deposits over fine sand 2 15 Information from Fuss and 
16 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

determine whether fairways and other parts of the golf course 

could be filled to raise the land-surface altitude to mitigate 

flooding following the proposed restoration of tidal flow to 

the Herring River (The Louis Berger Group, Inc., 2009). The 

study indicated that salt marsh deposits are as much as 18 ft 

thick at other locations at the CYCC. The area at the CYCC 

that is underlain by former salt marsh deposits is roughly 

coincident with the area where the land-surface altitude is 

less than about 3.5 ft (fig. 5). Deposits directly underlying the 

marsh sediments are typically finer grained than the sediments 

in the adjacent upland areas. These underlying sediments are 

likely estuarine sediments (alluvium and mudflats) that predate 

the marsh sediments. The sediments in the upland areas are 

typically coarse grained and represent collapsed facies of the 

Wellfleet plain deposits.

The estimated depths to the transition zone at the CYCC, 

based on the drilling information collected in 2017, ranged 

from 40 ft at site 5 (MA–WNW 158, figs. 2 and 5) to greater 

than 70 ft at site 4 (MA–WNW 157–0070, figs. 2 and 5). The 

range in the depths to the transition zone from new and existing data was from 15 to 95 ft below land surface (table 3).

Hydrologic Conditions Near the Mill Creek 

Study Area, June 1, 2017, Through June 14, 2018

The hydrologic conditions during the study period were 

characterized by several large precipitation events during the 

summer of 2017, with three events exceeding 2 inches and 

two of these events exceeding 3 inches of precipitation (fig. 6). 

During the fall, a large storm on Cape Cod on October 25–26 

produced 4.8 inches of rainfall. This storm was followed by 

a strong coastal storm on October 29–30 that produced an 

additional 1.9 inches of precipitation. The winter of 2017–18 

had several powerful coastal storms in January, February, and 

March. In addition to substantial precipitation, these coastal 

storms caused higher than normal tides in Wellfleet Harbor. 

The total precipitation for the period of the study from June 1, 

2017, through June 14, 2018, was about 60.8 inches, based on 

data from the Wellfleet weather station and supplemented with 

data from the Camp Edwards station (data downloaded from 

the Western Regional Climate Center [2018]). The total study 

precipitation compares with an average annual precipitation of 

50.3 inches for the period of 2000–17.

During the study, three long-term USGS monitoring 

wells on this part of Cape Cod (Wellfleet, MA–WNW 17; 

Truro, MA–TSW 89; and, Brewster, MA–BMW 22, fig. 1) had 

groundwater levels that were generally in the normal to above 

normal range during the summer of 2017. Because of the large 

amount of precipitation during the study period, groundwater 

levels ranged from above normal to much higher than normal 

during the spring of 2018, with record high monthly groundwater levels documented at the Brewster site during March 

and April (figs. 7A–C).

Groundwater and Mill Creek Water Levels, 

June 1, 2017, Through June 14, 2018

Data on depth to groundwater, groundwater altitude, and 

Mill Creek water-level altitude from June 1, 2017, through 

June 14, 2018, are summarized in table 2. The highest groundwater levels were measured near Mill Creek in the shallowest well at site 2 (fig. 2), with water levels as high as 3.56 ft 

above NAVD 88 in March 2018. The range in groundwater 

levels during the study period observed at individual wells 

in the Mill Creek study area was smallest—1.34 ft—at 

well MA–WNW 134 on the north side of Mill Creek and 

largest—2.64 ft—at site 2 (MA–WNW 155–0017; fig. 2, 

table 2). The depth to water in most of the wells near the 

CYCC was typically 1–4 ft below land surface, except in wells 

drilled at higher altitudes in the study area (table 2). Graphs 

of the water levels for all sites monitored during the study are 

shown in appendix 1. The analysis of short-term tidal fluctuations is given in the next section of this report.

Generalized contour maps were created to show the 

altitude of the water table, the depth to groundwater, and the 

direction of groundwater flow under both dry and wet conditions (figs. 8A–B). Data for both conditions were analyzed for 

a specific time of day, and not daily means; therefore, water 

levels may be affected by the tidal fluctuation. The dry period 

was analyzed by using data from August 18, 2017, during 

one of the driest periods in the study. Data from February 27, 

2018, were used for the wet period. Although water levels 

were not the highest on this date, February 27 was selected 

because of the availability of satellite imagery showing the 

extent of surface flooding at the CYCC.

The configuration of the water table for these two periods 

indicates that the directions of groundwater flow generally 

were to the west toward the Herring River, northwest toward 

Mill Creek, and southwest toward Wellfleet Harbor. The 

altitude of the water table at wells measured for the periods 

shown in figures 8A and 8B was from −0.13 to 1.48 ft above 

NAVD 88 during the dry period and from 0.44 to 2.52 ft above 

NAVD 88 during the wet period. During wet periods, the highest groundwater levels were measured in the shallow well at 

site 2 (MA–WNW 155–0017, fig. 2), indicating a local area of 

high groundwater levels. The high groundwater levels in this 

area may indicate that groundwater is flowing laterally from a 

high point in some of the adjacent upland deposits. It is possible that groundwater levels are higher in some of the coarsegrained deposits that make up the uplands on the CYCC 

because of higher recharge rates in these well-drained materials. The configuration of the water table under these deposits 

is difficult to determine because of the lack of measurement 

points in these upland areas.
Lithologic and Water-Level Data at the Mill Creek Study Area 17

 7

 8

 9

10

11

12

13

Groundwater levels, in feet below land surface

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

Monthly statistics from Nov. 29, 1962, to Dec. 31, 2017

A.

Minimum and maximum 

25th and 75th percentiles

Median

EXPLANATION

MA−WNW 17, Wellfleet, Mass.

Date

End of month daily mean value, 2017–18 

Figure 7. Groundwater levels at U.S. Geological Survey monitoring sites relative to long-term statistics, near the Mill Creek study area, 

Cape Cod, Massachusetts, 2017 to 2018: A, Wellfleet, B, Truro, C, Brewster. 
18 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

 7

 8

 9

10

11

12

13

Groundwater levels, in feet below land surface

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

Monthly statistics from Sept. 26, 1962, to Dec. 31, 2017

B.

EXPLANATION

MA−TSW 89, Truro, Mass.

Minimum and maximum 

25th and 75th percentiles

Median

End of month daily mean value, 2017–18 

Date

Figure 7. Groundwater levels at U.S. Geological Survey monitoring sites relative to long-term statistics, near the Mill Creek study area, 

Cape Cod, Massachusetts, 2017 to 2018: A, Wellfleet, B, Truro, C, Brewster. —Continued
Lithologic and Water-Level Data at the Mill Creek Study Area 19

28

29

30

31

32

33

34

Groundwater levels, in feet below land surface

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

C. MA−BMW 22, Brewster, Mass.

EXPLANATION

Minimum and maximum 

25th and 75th percentiles

Median

End of month daily mean value, 2017–18 

Monthly statistics from Nov. 29, 1962, to Dec. 31, 2017

Date

Figure 7. Groundwater levels at U.S. Geological Survey monitoring sites relative to long-term statistics, near the Mill Creek study area, 

Cape Cod, Massachusetts, 2017 to 2018: A, Wellfleet, B, Truro, C, Brewster. —Continued
20 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Base map data from Google, 2018, image from February 27, 2018

Lambert Conformal Conic projection, North American Datum of 1983

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.17

0.4 Water­table contour and

 altitude—Contour 

 interval 0.2 foot

Well or Mill Creek site, 

 and water altitude, 

 in feet, on August 18, 2017, 

 at 18:30 eastern 

 standard time

PRIMARY MAP EXPLANATION

INSET MAP EXPLANATION

0.41

1.48

1.4

0.09 0.24

0.95 1.38

1.31

1.17

1.34

0.91

­0.13

70°3'30" W 70°3'20" W 70°3'10" W

41°56'0" N

41°55'40" N

A

0 450 900 1,350 1,800 FEET

0 110 220 330 440 METERS

Flow direction

0

>0 to 0.5

>0.5 to 1

>1 to 5

>5

Depth to water, in feet 

 below land surface

Inset from rectangle above

Wellfleet

Harbor

Figure 8. Water-table altitude, depth to groundwater, and generalized flow direction at the Mill Creek study area, Wellfleet, 

Massachusetts, A, during a dry period, August 18, 2017, and B, during a wet period, February 27, 2018.
Lithologic and Water-Level Data at the Mill Creek Study Area 21

Base map data from Google, 2018, image from February 27, 2018

Lambert Conformal Conic projection, North American Datum of 1983

Water­table contour and

 altitude—Contour 

 interval 0.2 foot 

INSET MAP EXPLANATION

1.8

1.53

1.94 1.31

1.48

2.52 1.76 0.44

1.61

1.48

1.64

1.04

70°3'30" W 70°3'20" W 70°3'10" W

41°56'0" N

41°55'40" N

B

PRIMARY MAP EXPLANATION

0.6

0.8

1.0

1.2

1.2

1.4

1.6

1.8

1.6

1.8

2.0

2.2

1.4

Well or Mill Creek site, 

 and water altitude, in

 feet on February 27, 2018, 

 at 12:00 eastern 

 standard time

1.4

0 450 900 1,350 1,800 FEET

0 110 220 330 440 METERS

Flow direction

0

>0 to 0.5

>0.5 to 1

>1 to 5

>5

Depth to water, in feet 

 below land surface

Inset from rectangle above

Wellfleet

Harbor

Herring

River

Figure 8. Water-table altitude, depth to groundwater, and generalized flow direction at the Mill Creek study area, Wellfleet, 

Massachusetts, A, during a dry period, August 18, 2017, and B, during a wet period, February 27, 2018.—Continued
22 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Short-Term Tidal Fluctuations in Groundwater 

Levels

Daily tidal fluctuations were observed in water levels at 

most of the wells monitored for this study, because they are 

near tidal waterbodies, including Wellfleet Harbor and the 

Herring River. Groundwater levels in the wells exhibited daily 

fluctuations as well as longer term fluctuations related to lunar 

tidal cycles and to other ocean, harbor, and Herring River 

water-level fluctuations.

The amplitudes of the tidal signals for the five common tidal and solar harmonics at the wells and sites on the 

Herring River monitored for this study are shown in table 4

and figures 9 and 10. The tidal amplitude is the “half range” 

from the low to the high tide. The coefficient of determination 

(R2) (table 4) is a measure of how much of the variability in 

water level is explained by the statistical models using the five 

different tidal harmonics. For sites with a very low R2, either 

(1) the wells are too distant from the tidal waterbody for water 

levels to be affected by ocean tides, (2) interactions between 

tides from the Herring River and tides from Wellfleet Harbor 

affect the periodicity of the tidal harmonics, (3) the tidal signal 

is of a similar order of magnitude to the noise in the data and 

instrument accuracy (less than 0.01 ft), or (4) water-level fluctuations are affected by other unidentified processes.

Amplitudes of the M2 harmonic (the largest tidal signal 

in the data) generally decreased with increasing distance 

from the tidal source (fig. 10). The strongest tidal signal was 

observed at MA–WNW 154 (site 1; amplitude=0.12 ft), which 

is about 105 ft from the Herring River. Water levels in wells 

at sites MA–WNW 161, MA–WNW 141 (shown only on 

fig. 9), and at MA–WNW 155 (both shallow and deep wells; 

site 2) showed less tidal influence than expected based on their 

proximity to tidal waterbodies (fig. 10). In contrast, the tidal 

response in the deep well at site 3 (MA–WNW 156–0035) 

was greater than expected, given the relation between distance 

from a tidal waterbody and M2 tidal amplitude shown in 

figure 10. Water levels in wells at site 2 (fig. 2), and the water 

levels at the nearby downstream monitoring site on Mill Creek 

showed little tidal influence. The greater response in some 

wells is likely related to the degree of hydraulic connection 

between the tidal waterbody and the aquifer and to the degree 

of confinement in the aquifer.

In the study area around the CYCC and Mill Creek, the 

tidally influenced water-level fluctuations in the wells were 

effectively limited to the area within about 1,500 ft from tidal 

waterbodies. The influence of the tidal fluctuations in the 

Herring River (upstream from the tide-control structure) were 

observed at site 1 (MA–WNW 154) and MA–WNW 134. 

Tidal fluctuations in water levels in wells likely caused by the 

Herring River tide also were observed at site MA–WNW 161 

and at site 2 (MA–WNW 155, both shallow and deep wells), 

but the regressions on the tide harmonics had a low R2 of 

less than 0.3 (fig. 10). The fluctuation in groundwater levels 

caused by tidal fluctuations in the Herring River was limited 

to short distances from the river, with the exception of well 

MA–WNW 134. Possible causes include the smaller average 

tidal amplitude of the Herring River (1.08 ft) than Wellfleet 

Harbor (4.04 ft) (table 2) and the hydraulic properties of the 

marsh deposits and fine-grained estuarine sediments underlying the Herring River and Mill Creek. The amplitude of the 

tidal fluctuations at MA–WNW 134 was greater than expected 

based on the general relation shown in figure 10. This amplitude may indicate locally confined conditions in the aquifer 

at this location, which would allow the effects of the tidal 

fluctuations to propagate further inland.

Under the proposed initial restoration scenario (fig. 3) 

(little to no change in mean tide, about zero ft above 

NAVD 88), the amplitude of the tidal fluctuation in the 

Herring River upstream from the control structure would 

increase to about 2.5 ft. The increased tidal fluctuations would 

be as much as 700 ft closer to the areas on the CYCC that 

presently flood and would also extend to the downstream side 

of a proposed tide-control structure on Mill Creek. Under 

these conditions, the daily tidal fluctuations in groundwater levels on parts of the CYCC nearest to the river could 

increase, depending on the degree to which the underlying 

lithology facilitates the interaction with the tides. Because the 

maximum observed tidal amplitude in well MA–WNW 158 

at site 5 was about 0.06 ft in response to a tidal amplitude 

of 4.04 ft in Wellfleet Harbor 575 ft from the site, the future 

daily average groundwater tidal amplitude under the restoration scenario on the CYCC would likely be less than 0.06 ft. 

However, if the proposed tide-control structure is adjusted to 

allow the mean tide of the Herring River to an altitude greater 

than the current mean tide (about zero ft above NAVD 88, 

fig. 3), groundwater levels could rise at the locations nearest to 

the proposed tide-control structure on Mill Creek, as the water 

level in the aquifer adjusts to the new equilibrium between 

Herring River and Wellfleet Harbor tides.

Groundwater-Level Fluctuations Over Periods 

Longer Than Daily Tidal Cycles

Water levels in the aquifer in the study area respond to 

daily tidal fluctuations and longer-term variations in the stage 

of Wellfleet Harbor that are associated with the recurrence and 

magnitude of the spring and neap tides. In addition, they are 

affected by other fluctuations in Wellfleet Harbor stage caused 

by short-term (storm surges) and long-term weather patterns, variations in barometric pressure, and the direction and 

strength of prevailing winds. The groundwater levels also are 

affected by precipitation, resulting in groundwater recharge, as 

well as evapotranspiration.

Tidally filtered water levels at MA–WNW 158 (site 5, 

fig. 2) follow the general pattern of tidally filtered Wellfleet 

Harbor water levels, with an apparent time lag. The effect of 

the Wellfleet Harbor stage on groundwater levels is difficult 

to separate from aquifer recharge events because precipitation 

often occurs during times of high mean Wellfleet Harbor stage.
Lithologic and Water-Level Data at the Mill Creek Study Area 23

Table 4. Tidal amplitudes of five tidal harmonics from regression using data from each well and the Herring River, Mill Creek study 

area, Wellfleet, Massachusetts.

[ft, foot; R2, coefficient of determination; M2, principal lunar semidiurnal constituent; N2, larger lunar elliptic semidiurnal constituent; S2, principal solar semidiurnal constituent; O1, lunar diurnal constituent; K1, lunar diurnal constituent]

Site (fig. 2)

Distance from nearest or 

tidal waterbody affecting 

groundwater levels

Harmonic

Amplitude (ft),

rounded to nearest 0.01 ftPhase (degree) Adjusted R2

Herring River upstream

011058098

0 M2 1.08 58.15 0.94

N2 0.16 31.83

S2 0.1 96.81

O1 0.09 179.83

K1 0.12 196.91

Herring River downstream

011058098

0 M2 4.04 353.88 0.95

N2 0.78 326

S2 0.57 25.09

O1 0.32 149.48

K1 0.39 152.04

MA–WNW 133–0030 1,140 M2 0.02 135.29 0.31

N2 0 108.87

S2 0 219.5

O1 0.01 286.71

K1 0 252.7

MA–WNW 134 980 M2 0.04 106.5 0.57

N2 0.01 83.72

S2 0 165.53

O1 0.01 262.75

K1 0.01 262.42

MA–WNW 154

Site 1

105 M2 0.12 91.05 0.87

N2 0.02 62.01

S2 0.01 133.11

O1 0.01 232.94

K1 0.02 239.84

MA–WNW 155–0017

Site 2 (shallow well)

910 M2 0.01 110.84 0.06

N2 0 107.13

S2 0 182.71

O1 0 277.66

K1 0.01 277.43

MA–WNW 155–0035

Site 2 (deep well)

910 M2 0.02 117.38 0.11

N2 0 103.67

S2 0 184.14

O1 0.01 275.65

K1 0.01 284.25

MA–WNW 156–0010

Site 3 (shallow well)

1,400 M2 0.01 141.15 0.1

N2 0 124.05

S2 0 220.32

O1 0 301.62

K1 0.01 288.13

MA–WNW 156–0035

Site 3 (deep well)

1,400 M2 0.04 96.3 0.62

N2 0.01 72.44

S2 0 150.95

O1 0.01 258.47

K1 0.01 255.73
24 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Table 4. Tidal amplitudes of five tidal harmonics from regression using data from each well and the Herring River, Mill Creek study 

area, Wellfleet, Massachusetts.—Continued

[ft, foot; R2, coefficient of determination; M2, principal lunar semidiurnal constituent; N2, larger lunar elliptic semidiurnal constituent; S2, principal solar semidiurnal constituent; O1, lunar diurnal constituent; K1, lunar diurnal constituent]

Site (fig. 2)

Distance from nearest or 

tidal waterbody affecting 

groundwater levels

Harmonic

Amplitude (ft),

rounded to nearest 0.01 ftPhase (degree) Adjusted R2

MA–WNW 157–0012

Site 4 (shallow well)

1,520 M2 0.01 147.64 0.07

N2 0 137.27

S2 0 194.52

O1 0 294.24

K1 0 276.59

MA–WNW 157–0033

Site 4 (intermediate well)

1,520 M2 0.01 146.46 0.08

N2 0 136.46

S2 0 192.32

O1 0 296.6

K1 0 278.71

MA–WNW 157–0070

Site 4 (deep well)

1,520 M2 0.01 147.09 0.08

N2 0 147.2

S2 0 212.29

O1 0 297.79

K1 0 293.31

MA–WNW 158

Site 5

570 M2 0.06 88.78 0.75

N2 0.01 56.49

S2 0.01 137.59

O1 0.01 259.06

K1 0.01 259.48

MA–WNW 159–0012

Site 6 (shallow well)

945 M2 0.03 108.41 0.68

N2 0.01 81.01

S2 0 147.76

O1 0.01 263.16

K1 0.01 257.67

MA–WNW 159–0035

Site 6 (deep well)

945 M2 0.03 103.12 0.59

N2 0.01 75.6

S2 0 162.4

O1 0.01 267.49

K1 0.01 261.51

MA–WNW 160

Site 7

1,000 M2 0.02 118.41 0.46

N2 0 93.81

S2 0 184.05

O1 0.01 281.3

K1 0.01 277.53

MA–WNW 161 560 M2 0.02 116.94 0.15

N2 0 100.25

S2 0 173.47

O1 0 255.69

K1 0.01 264.29
Base map data from Google, 2018, image from February 27, 2018 Lambert Conformal Conic projection, North American Datum of 1983 0.02

0.06

0.02

0.03

0.03

0 0.12

0.04

0.01

0.02

0.01

0.02

0

0.01

0.01

0.01

0

0.04 0

70°3'30" W 

41°56' N

41°55'50" N

0.01

0 425 850 1,275 0 110 220 330 

Well, Herring River, or Mill Creek site,  and amplitude of the M2 harmonic,  in feet, June 2017–June 2018

EXPLANATION

0.04

0.01

0.01

Deep well averageIntermediate well averageShallow well or Mill Creek

average

Mill Creek

Herring

Rive

r

Herring

Rive

r

Mill Creek 1

Mill Creek 2

Figure 9. Average amplitude of the M2 tidal harmonic for wells and rivers in the study area, Wellfleet, Massachusetts, June 1, 2017, through June 14
26 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

0.001

0.003

0.010

0.030

0.100

0.300

M2 tidal amplitude, in feet (unrounded)

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

Distance to tidal waterbody, in feet

Tidal waterbody likely causing fluctuation

Wellfleet Harbor

Herring River

Wellfleet Harbor, R2

 <0.3

EXPLANATION

Herring River, R2 <0.3

WNW 154

WNW 158

WNW 134 WNW 156–0035

WNW 159–0012

WNW 159–0035

WNW 160

WNW 161 WNW 133–0030

WNW 155–0017

WNW 155–0035

WNW 156–0010

WNW 157–0033

WNW 157–0012, 0070

Figure 10. Relation of the amplitude of the M2 tidal harmonic to distance of the well from the nearest tidal waterbody, June 1, 2017, 

through June 14, 2018, Wellfleet, Massachusetts. R2, coefficient of determination.

A storm surge on January 4, 2018, during a large coastal To understand the factors that affect groundwaterstorm resulted in a maximum storm tide of 9.76 ft above 

NAVD 88 in Wellfleet Harbor, which resulted in a storm 

surge of about 2.64 ft above the predicted high tide. This 

maximum was just higher than the storm of record of 9.70 ft 

above NAVD 88 that occurred during the blizzard of early 

February 1978 (National Park Service and others, 2016). The 

effect of the surge on groundwater levels was complicated 

by precipitation during the event. The precipitation may not 

have contributed to the rise in groundwater levels because the 

air temperatures leading up to the storm event were below 

freezing, likely leading to frozen ground conditions and 

limited infiltration.

level fluctuations (excluding daily tides) in the study area, 

regression models were developed for each well. The 

dependent variable was the daily mean tidally filtered 

groundwater level (meanFiltGWalt) at the wells of interest. 

The independent variables selected included the following: 

daily mean tidally filtered Herring River water levels upstream 

(meanHerringAlt) and downstream (meanHarborAlt) of the 

tide-control structure; total precipitation during the preceding 

7 days (precip7day); the growing degree days 50 °F (GDD50); 

and the quartile of monthly groundwater levels at USGS well 

MA–WNW 17 in Wellfleet (longtermGW) relative to the 

long-term water level record at the well.
Lithologic and Water-Level Data at the Mill Creek Study Area 27

As noted previously, there was a lag time between waterlevel fluctuations in Wellfleet Harbor and water-level fluctuations in wells in the study area. The lag time was determined 

for each well by use of a sensitivity analysis that tested 

different lag times. The best model for each well was selected 

by maximizing the R2 and minimizing the Akaike information 

criterion (Akaike, 1988) while varying the lag times from zero 

to 3 days, in half-day increments.

The independent variables used in the regressions were 

selected for their potential effects on groundwater levels. The 

variations in the stage in Wellfleet Harbor were consistent 

with fluctuations observed in the groundwater levels (fig. 11). 

The wells in the study area are all near tidal waterbodies that, 

as surface-water boundaries, strongly influence groundwater 

levels. The precipitation relates to the potential for recent 

groundwater recharge. The GDD50 accounts for evapotranspiration that reduces recharge from precipitation and increases 

water loss by evapotranspiration from wetland areas hydraulically connected to the groundwater system. The status of 

water levels in a long-term well (longtermGW) indicates 

whether regional groundwater levels on this part of Cape Cod 

are above, at, or below normal (values 1–4, representing the 

four quartiles in the long-term monthly data) relative to the 

long-term record at the well. The status at the long-term well 

is a potentially important consideration in the evaluation of 

future groundwater levels in the study area during and after 

the restoration phase.

The coefficients of determination (R2) indicate that these 

regression models describe about 63 to 81 percent of the variability in the water levels in each well (appendix 2, table 2.1). 

The variables shown in table 2.1 are all significant at or less 

than p=0.05.

The meanHarborAlt variable explained more variability 

in the tidally filtered daily water levels mean (FiltGWalt) than 

the meanHerringAlt variable at most of the wells tested. In two 

locations, the models using the meanHerringAlt data explained 

more variability in a total of three wells, indicated by an R2

value higher than that of the model that used meanHarborAlt

as the independent variable (sites MA–WNW 155–0017, 

MA–WNW 155–0035, and MA–WNW 161, fig. 2, table 2.1). 

Models for sites identified as having tidal influence from 

the Herring River (fig. 10) are included in table 2.1. Models 

using the meanHerringAlt data typically had higher variance 

inflation factors and larger residual standard error than models 

using the filtered meanHarborAlt data. This indicates a greater 

multicollinearity in the models using the Herring River data. 

The Herring River data are affected by freshwater discharge 

that causes temporal change in Herring River height, which is 

not evident in the Wellfleet Harbor data.

The absolute values of the standardized model coefficients for these models were largest for the variable meanHarborAlt (daily mean tidally filtered Wellfleet Harbor 

altitude) at many of the wells; however, this was not the case 

for wells along the Mill Creek corridor. The variables with 

the largest influence on the daily tidally filtered water levels 

along the Mill Creek corridor were (1) longtermGW (quartile 

of long-term groundwater levels) at well WNW 161, site 4 

wells (WNW 157–0012, 0033, 0070), and well WNW 134 

and (2) GDD50 (growing degree days [50 °F]) at site 2 wells 

(WNW 155–0017 and 0035) and site 3 well WNW 156–0010 

(shallow well). The standardized coefficients are shown in 

appendix 2, table 2.2.

Factors Affecting Flooding in Mill Creek

Two areas on the CYCC near Mill Creek routinely flood, 

limiting use and causing temporary closures of the golf course. 

Water-stage data collected at upstream and downstream locations on Mill Creek, analysis of photographs taken during 

several flooding events, and survey information and altitude 

data from lidar (light detection and ranging) indicate that the 

flooding threshold elevations for Mill Creek at these two areas 

on the CYCC can be approximately determined. Near the 

upstream monitoring site (Mill Creek 1, fig. 2), the altitude of 

a low part of the golf cart path is about 1.5 ft above NAVD 88, 

from analysis of the lidar data. Mill Creek stages at or above 

1.5 ft are associated with conditions when there is standing 

water in this area (fig. 12A). An analysis of the data for Mill 

Creek at the upstream site determined that the daily maximum 

stage was at or higher than 1.5 ft on 146 of 377 days (39 percent) monitored from June 2017 to June 2018.

In the area that frequently floods at the CYCC near the 

downstream monitoring site for Mill Creek (Mill Creek 2, 

fig. 2), it was determined that the altitude of the golf cart path 

was about 1.4 ft above NAVD 88. This was confirmed by a 

laser-level survey during May 2018. The downstream monitoring site on Mill Creek, however, is at a slightly lower altitude 

than the area that floods on the golf course. An analysis of Mill 

Creek stage data and photographs of flooding taken at different 

times during the study indicate that the area floods when the 

stage at the downstream Mill Creek monitoring site exceeds 

about 1.3 ft above NAVD 88 (figs. 4 and 12B). The daily 

maximum stage equaled or exceeded 1.3 ft on 118 of 377 days 

(31 percent), according to monitoring data from June 1, 2017, 

through June 14, 2018 (fig. 12B).

Likely factors affecting water levels in Mill Creek include 

local groundwater levels, recent precipitation, and evapotranspiration. Recent precipitation not only recharges the local 

groundwater system but also provides overland runoff, which 

contributes directly to flooding and contributes inflow of water 

from the drainage basin to Mill Creek upstream from the 

CYCC. High groundwater levels contribute discharge to Mill 

Creek through multiple pathways, including discharge to Mill 

Creek upstream from the study area, direct seepage of groundwater into low-lying drainage areas (former salt marsh areas) 

adjacent to Mill Creek, and direct discharge of groundwater 

to Mill Creek from the subsurface. High groundwater levels 

contribute to overland runoff during precipitation events by 

causing ponding in areas where the water table is at the land 

surface, thereby exacerbating the flooding. Evapotranspiration 

removes water from surface runoff, groundwater recharge, 
28 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

−1.0

−0.5

 0.0

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

 0.0

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

Water level, in feet above the North American Vertical Datum of 1988 

Daily precipitation, in inches per day

December January

2017 2018

Tidally filtered water level

Daily precipitation

MA−WNW 158 (site 5)

Wellfleet Harbor 

EXPLANATION

Date

Figure 11. Tidally filtered water levels at the Herring River downstream from the tide-control structure (Wellfleet Harbor), tidally 

filtered water levels at well MA–WNW 158, and daily precipitation from December 2017 to January 2018, Wellfleet, Massachusetts.

downstream sites on Mill Creek was 0.24 ft (table 2), indicating a gradient of about 0.00013, based on the approximate 

distance between the sites along the creek (1,814 ft).

To describe the variability in Mill Creek stage, regression models to account for some of the factors discussed 

above were created for the two sites on Mill Creek. The daily 

maximum values for Mill Creek stage at either site were 

used as the dependent variable in the regressions. Daily mean 

groundwater-level data (meanGWalt) from nearby wells were 

used as the primary independent variable. The daily mean 

values of groundwater-level data were used in this model, 

rather than the tidally filtered daily mean used in the regressions to evaluate factors related to groundwater levels, as 

described in the section “Groundwater-Level Fluctuations 

and groundwater discharge near the wetland areas around Mill 

Creek, potentially reducing the severity of flooding during the 

growing season. Another factor that affects the water levels 

in Mill Creek is the resistance to flow in the channel of Mill 

Creek, which causes backwater that exacerbates flooding, and 

likely causes additional increases in groundwater levels near 

the creek. The resistance to flow is likely to vary seasonally 

as the growth of wetland plants such as the nonnative reed 

Phragmites australis increases during the growing season. The 

water in Mill Creek from storms drains away slowly because 

of the small gradient in the watercourse. The mean difference in the water-surface altitude between the upstream and 
Lithologic and Water-Level Data at the Mill Creek Study Area 29

0.0

0.5

1.0

1.5

2.0

2.5

Water level, in feet above the North American Vertical Datum of 1988

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

A. Mill Creek 1, upstream

Estimated flooding threshold

Date

Figure 12. Water levels in Mill Creek at A, site 1, upstream at Chequessett Yacht and Country Club, and B, site 2, downstream, from 

June 1, 2017, to June 14, 2018, Wellfleet, Massachusetts.
30 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

Estimated flooding threshold

B. Mill Creek 2, downstream

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 12. Water levels in Mill Creek at A, site 1, upstream at Chequessett Yacht and Country Club, and B, site 2, downstream, from 

June 1, 2017, to June 14, 2018, Wellfleet, Massachusetts.—Continued
Lithologic and Water-Level Data at the Mill Creek Study Area 31

Over Periods Longer Than Daily Tidal Cycles.” The other 

variables included the total precipitation during the preceding 7 days (precip7day), the growing degree days (50 °F) 

(GDD50), and a binary variable based on whether Mill Creek 

is considered above (1) or below (0) the flooding thresholds 

described above (flooded). This variable was used to account 

for the change in relation between groundwater levels and Mill 

Creek stage when the channel overflows and water spreads 

over the flood plain.

The selected models explained about 76 percent of the 

variability in daily maximum water levels at the upstream site 

and about 61–89 percent of the variability in daily maximum 

water levels at the downstream site, based on the coefficients 

of determination for each model (appendix 2, table 2.3). The 

meanGWalt variable for wells near each site on Mill Creek 

explained about 31 and 26–75 percent, respectively, of the 

variability in daily maximum water levels at the upstream and 

downstream sites. The other variables accounted for additional 

variability in daily maximum water levels at each site on Mill 

Creek. This was confirmed with an analysis of the standardized coefficients in these regression models, which indicated 

the relative importance of each variable in the regression 

models (appendix 2, table 2.4).

For the upstream site on Mill Creek, the order of the 

absolute magnitude of the standardized regression coefficients 

was GDD50>precip7day>flooded>meanGWalt (table 2.4). For 

the downstream site, the absolute magnitude of the standardized coefficients was largest for the meanGWalt variable for 

wells MA–WNW 155–0017 and MA–WNW 161, indicating 

that these wells are important in predicting the likelihood of 

flooding (table 2.4). These two regression models had the 

highest R2 values of 0.81 and 0.93, respectively (table 2.3).

The general relations between the stage of Mill Creek 

and nearby groundwater levels can be summarized as follows: 

at the upstream site on Mill Creek, the water level rises to or 

above 1.5 ft above NAVD 88 when the groundwater level in 

the nearby well (MA–WNW 157–0012, site 4) reached about 

1.89 ft (25th percentile, fig. 13A). This occurred primarily 

when the 7-day precipitation was at least 0.92 inch (25th percentile, fig. 13B) and when the GDD50 value was low or zero.

At the downstream site, the water level rises to or above 

1.3 ft above NAVD 88 when the groundwater levels in nearby 

wells (MA–WNW 155–0017, MA–WNW 156–0010, and 

MA–159–0012, MA–WNW 161) generally reached 2.33, 1.78, 

1.60, and 1.38 ft above NAVD 88, respectively (25th percentile, figs. 14A–D). This occurred primarily when the 7-day 

precipitation was at least 1.04 inches (fig. 14E).

In addition to the thresholds for nearby groundwater 

levels and 7-day precipitation, the GDD50 variable helped 

explain some of the variability, as most of the flooding during 

the study period was during the nongrowing season. Flooding 

events during the growing season and during times when 

groundwater levels were low were typically short-duration 

events caused by recent heavy precipitation. Flooding events 

during the nongrowing season tended to last longer, as groundwater levels remained above the thresholds described previously (figs. 12A and B).
32 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

1.0

1.5

2.0

2.5

3.0

3.5

231 146

Well MA–WNW 157–0012

Not flooded Flooded

Water-level altitude, in feet above the North American Vertical Datum of 1988

A.

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Flooding condition 

Figure 13. The distribution of A, groundwater levels at well MA–WNW 157–0012 and B, 7-day precipitation under nonflooded and 

flooded conditions at the upstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.
Lithologic and Water-Level Data at the Mill Creek Study Area 33

−2

 0

 2

 4

 6

 8

228 145

Not flooded Flooded

B.

7-day precipitation, in inches

Mill Creek 1, upstream

Flooding condition

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Figure 13. The distribution of A, groundwater levels at well MA–WNW 157–0012 and B, 7-day precipitation under nonflooded and 

flooded conditions at the upstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.—Continued
34 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

259 118

Well MA–WNW 155–0017

Not flooded Flooded

Water-level altitude, in feet above the North American Vertical Datum of 1988

A.

Flooding condition

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Figure 14. The distribution of groundwater levels at A, well MA–WNW 155–0017, B, well MA–WNW 156–0010, C, well MA–

WNW 159–0012, and D, well MA–WNW 161; and E, distribution of 7-day precipitation under nonflooded and flooded conditions at the 

downstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.
Lithologic and Water-Level Data at the Mill Creek Study Area 35

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

1.0

1.5

2.0

2.5

3.0

254 113

Well MA–WNW 156–0010

Not flooded Flooded

B.

Water-level altitude, in feet above the North American Vertical Datum of 1988

Flooding condition

Figure 14. The distribution of groundwater levels at A, well MA–WNW 155–0017, B, well MA–WNW 156–0010, C, well MA–

WNW 159–0012, and D, well MA–WNW 161; and E, distribution of 7-day precipitation under nonflooded and flooded conditions at the 

downstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.—Continued
36 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

1.0

1.5

2.0

2.5

3.0

260 118

C. Well MA–WNW 159–0012

Water-level altitude, in feet above the North American Vertical Datum of 1988

Not flooded Flooded

Flooding condition 

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Figure 14. The distribution of groundwater levels at A, well MA–WNW 155–0017, B, well MA–WNW 156–0010, C, well MA–

WNW 159–0012, and D, well MA–WNW 161; and E, distribution of 7-day precipitation under nonflooded and flooded conditions at the 

downstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.—Continued
Lithologic and Water-Level Data at the Mill Creek Study Area 37

0.0

0.5

1.0

1.5

2.0

2.5

260 118

D. Well MA–WNW 161

Water-level altitude, in feet above the North American Vertical Datum of 1988

Not flooded Flooded

Flooding condition

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Figure 14. The distribution of groundwater levels at A, well MA–WNW 155–0017, B, well MA–WNW 156–0010, C, well MA–

WNW 159–0012, and D, well MA–WNW 161; and E, distribution of 7-day precipitation under nonflooded and flooded conditions at the 

downstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.—Continued
38 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

−2

 0

 2

 4

 6

 8

256 117

7-day precipitation, in inches

E. Mill Creek 2, downstream

Not flooded Flooded

Flooding condition

32 Number of days

90th percentile

75th percentile

50th percentile (median)

25th percentile

10th percentile

EXPLANATION

Figure 14. The distribution of groundwater levels at A, well MA–WNW 155–0017, B, well MA–WNW 156–0010, C, well MA–

WNW 159–0012, and D, well MA–WNW 161; and E, distribution of 7-day precipitation under nonflooded and flooded conditions at the 

downstream site on Mill Creek, June 1, 2017, through June 14, 2018, Wellfleet, Massachusetts.—Continued
Summary and Conclusions 39

Summary and Conclusions

The Herring River estuary is in the towns of Wellfleet 

and Truro, Massachusetts, on Cape Cod Bay. The natural tidal 

flow of the Herring River has been limited since the construction of a dike with tide gates (tide-control structure) near the 

mouth of the river at Chequessett Neck in 1909. The National 

Park Service has a goal to restore tidal flow to a large part 

of the 1,100 acres of habitat that have been degraded by the 

presence of the tide-control structure, with a minimal impact 

on private properties and cultural resources. Restoration will 

be done by replacing the existing tide-control structure with a 

new structure that will allow for incremental adjustment of the 

tide range.

There is concern about increased flooding, under the proposed restoration plan, resulting from high groundwater levels 

on the golf course at the Chequessett Yacht and Country Club 

(CYCC), which was built on some low-lying areas, including 

former salt marshes. A new tide-control structure also would 

be constructed on the Mill Creek tributary to block upstream 

movement of the tide, when the tide range is increased in the 

Herring River, to protect private properties.

To monitor the water levels near the Mill Creek area 

prior to restoration activities, the U.S. Geological Survey, in 

cooperation with the Friends of Herring River, established a 

monitoring network that included new and existing wells. New 

wells were drilled at eight locations, including four locations 

with wells installed at multiple depths.

Surface-water-level monitoring sites were established at 

upstream and downstream locations on Mill Creek, and tidal 

fluctuations were measured at existing sites on the Herring 

River upstream and downstream from the existing tide-control 

structure. Groundwater levels and water levels in Mill Creek 

were monitored from June 2017 to June 2018. Water levels in the Herring River were monitored for the same time 

period upstream from the tide-control structure and from 

September 2017 to June 2018 at the downstream side of the 

tide-control structure (Wellfleet Harbor).

From new and existing information on site geology, it 

was determined that salt marsh deposits at the CYCC range 

from zero to 18 feet (ft) thick. The deposits directly underlying 

the marsh sediments are typically finer than the sediments in 

the adjacent upland areas and are likely estuarine sediments. In 

the adjacent upland areas at the CYCC, away from the former 

salt marsh deposits, the glacial deposits are primarily medium 

to very coarse sand. The depth to the transition zone from 

freshwater to saltwater ranged from 15 to 95 ft, depending on 

location and altitude of each site.

The water levels from short-term tidal fluctuations at 

individual wells and the Herring River were analyzed by filtering the tidal signal from the groundwater levels and regressed 

on five common tidal harmonics, and the amplitude and phase 

of each of the tidal components were determined. The largest amplitude (0.12 ft) in the M2 (principal lunar semidiurnal 

constituent) was observed at site 1 (MA–WNW 154), adjacent 

to the Herring River. The next largest amplitude (0.06 ft) was 

observed at site 5 (MA–WNW 158), which is the well closest 

to Wellfleet Harbor. Short-term tidal fluctuations (greater than 

0.01 ft) were generally limited to an area within 1,500 ft of 

Wellfleet Harbor.

Under the proposed initial restoration scenario (little or 

no change in mean tide), the amplitude of the tidal range in the 

Herring River would increase to 2.5 ft, and the tidal influence 

would move closer to the CYCC by about 700 ft. The tidal 

fluctuations in Mill Creek would extend to the downstream 

side of a proposed tide-control structure on Mill Creek. Under 

these conditions, it is possible that the daily tidal fluctuations 

in groundwater levels on parts of the CYCC nearest to the 

proposed tide-control structure could increase; however, they 

should be limited to less than 0.06 ft, the maximum tidal fluctuation observed in well MA–WNW 158, which was nearest to 

Wellfleet Harbor, under the influence of the full tidal range of 

Wellfleet Harbor.

Regression models were developed to describe the variability in groundwater levels at individual wells and at the 

upstream and downstream monitoring sites on Mill Creek. For 

the groundwater levels, a tidal filter was used to remove the 

effects of the daily tidal fluctuations. The daily mean tidally 

filtered groundwater level was the dependent variable. The 

significant independent variables included daily mean filtered 

Herring River (downstream or upstream) stage lagged in 

time by zero to 2 days, precipitation in the preceding 7 days, 

growing degree days (50 degrees Fahrenheit), and the quartile 

of local groundwater storage for a long-term monitoring site 

(well MA–WNW 17). An analysis of the standardized coefficients for these models indicated that for wells away from 

the Mill Creek corridor, the variable with the largest absolute 

value was the tidally filtered water level in Wellfleet Harbor. 

For wells along the Mill Creek corridor, the variables with 

the largest absolute values were the growing degree days 

(50 degrees Fahrenheit) and the quartile of the long-term 

groundwater levels.

For the monitoring sites upstream and downstream on 

Mill Creek, approximate flooding thresholds were established. 

At the upstream site on Mill Creek, the flooding threshold was 

met or exceeded on about 39 percent of the days monitored 

during the study period from June 1, 2017, through June 14, 

2018. At the downstream site on Mill Creek, the flooding 

threshold was met or exceeded on about 31 percent of the days 

during the study period.

Regression models were developed to explain the 

variability of daily maximum water levels at both sites on 

Mill Creek. The independent variables included daily mean 

groundwater levels in nearby observation wells, precipitation 

in the preceding 7 days, growing degree days (50 degrees 

Fahrenheit), and a binary variable indicating whether the 

Mill Creek stage at each site was above the estimated flood 

stage. The models explained about 76 percent of the variability in daily mean water levels at the upstream site and about 

61–89 percent of the variability in daily mean water levels at 

the downstream site. Based on an examination of the standardized coefficients for these models, the daily mean groundwater 
40 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

levels were the variable with the largest absolute coefficients 

for two of the closest wells at the downstream site, whereas, at 

the upstream site, the variable for the daily mean groundwater 

levels had the smallest absolute coefficient.

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alternatives analysis, Herring River Restoration Committee, 

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Friends of Herring River, 34 p. plus attachments.

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Toronto Press, 264 p.

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adjacent to Herring River and Mill Creek, Cape Cod 

National Seashore: National Park Service Technical 

Report NPS/NRWD/NRTR–2004/319, 25 p. plus figures, 

accessed September 6, 2019, at https://www.nps.gov/

caco/learn/nature/upload/herringrivergroundwatereffect.pdf.

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Cod National Seashore: National Park Service 

Natural Resource Report NPS/NRPC/WRD/

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monitoring in shallow wells in the Herring River Basin, 

Cape Cod National Seashore: 15 p., accessed September 6, 

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groundwater and estuary water levels, and climatological data near Mill Creek and the Herring River, Cape Cod, 

Wellfleet, Massachusetts, 2017–2018: U.S. Geological 

Survey data release, https://doi.org/10.5066/P9T167II.

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Harmonic constituents for 8447173, Sagamore, Cape Cod 

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water level (13 ft) data logger: Onset Computer 

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evaluation Chequessett Yacht and Country Club, proposed 

Herring River restoration project, Wellfleet, MA: Technical 

memorandum, variously paginated.

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checks of steel and electric groundwater level measurement tapes: U.S. Geological Survey Office of Groundwater 

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approving and auditing of groundwater-level records: 

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approving and auditing of stage or elevation records: U.S. 

Geological Survey time-series guidance, accessed July 17, 

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the Nation: U.S. Geological Survey National Water 

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Massachusetts—Groundwater, in USGS water data for the 

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Appendix 1 43

Appendix 1. Graphs of Water Levels in Wells Monitored for the Study of the 

Mill Creek Study Area, June 2017–June 2018
44 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

−1

 0

 1

 2

 3

 4

Water level, in feet above the North American Vertical Datum of 1988

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

MA−WNW 154 (site 1)

EXPLANATION

Date

Figure 1.1. Water levels at well MA–WNW 154 (site 1) from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 1 45

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 155−0017 (site 2, shallow)

 MA−WNW 155−0035 (site 2, deep)

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.2. Water levels at well MA–WNW 155–0017 and MA–WNW 155–0035 (site 2) from June 2017 to June 2018, Mill Creek study 

area, Wellfleet, Massachusetts.
46 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 156−0010 (site 3, shallow)

 MA−WNW 156−0037 (site 3, deep)

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.3. Water levels at well MA–WNW 156–0010 and MA–WNW 156–0037 (site 3) from June 2017 to June 2018, Mill Creek study 

area, Wellfleet, Massachusetts.
Appendix 1 47

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 157−0012 (site 4, shallow)

 MA−WNW 157−0070 (site 4, deep)

 MA−WNW 157−0035 (site 4, intermediate)

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.4. Water levels at well MA–WNW 157–0012, MA–WNW 157–0070, and MA-WNW 157–0035 (site 4) from June 2017 to 

June 2018, Mill Creek study area, Wellfleet, Massachusetts.
48 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 158 (site 5)

EXPLANATION

−1

 0

 1

 2

 3

 4

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.5. Water levels at well MA–WNW 158 (site 5) from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 1 49

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 159−0012 (site 6, shallow)

 MA−WNW 159−0035 (site 6, deep)

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.6. Water levels at well MA–WNW 159–0012 and MA–WNW 159–0035 (site 6) from June 2017 to June 2018, Mill Creek study 

area, Wellfleet, Massachusetts.
50 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 160 (site 7)

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.7. Water levels at well MA–WNW 160 (site 7) from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 1 51

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 133−0030

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.8. Water levels at well MA–WNW 133–0030 from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
52 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 134

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.9. Water levels at well MA–WNW 134 from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 1 53

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 141

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.10. Water levels at well MA–WNW 141 from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
54 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 161

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.11. Water levels at well MA–WNW 161 from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 1 55

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

2017 2018

 MA−WNW 162

−1

 0

 1

 2

 3

 4

EXPLANATION

Water level, in feet above the North American Vertical Datum of 1988

Date

Figure 1.12. Water levels at well MA–WNW 162 from June 2017 to June 2018, Mill Creek study area, Wellfleet, Massachusetts.
Appendix 2. Regression Coefficients and Metrics for Linear Regression 

Models Describing the Variability in Groundwater Levels and Surface-Water 

Levels Near the Herring River, Wellfleet, Massachusetts, From June 2017 To 

June 2018

56 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River
Table 2.1. Coefficients and other regression metrics for linear regression models used to describe the variability in daily mean tidally filtered groundwells near the Herring River, Wellfleet, Massachusetts, from June 2017 to June 2018.[Dependent variable name: meanFiltGWalt, daily mean groundwater altitude for each well, daily tidal effects filtered from dataset. Independent variables: meanHarborAlt, daily River downstream from tide-control structure, daily tidal effects filtered from dataset; meanHerringAlt, daily mean water altitude at Herring River upstream from tide-control strfiltered from dataset; precip7day, sum of precipitation in the preceding 7 days; GDD50, growing degree days (base temperature 50 degrees Fahrenheit); LongtermGW, quartile oU.S. Geological Survey MA–WNW 17 (1, ≤25th percentile; 2, ≤50th percentile, 3, ≤75th percentile; 4, >75th percentile). SE, standard error; R2, coefficient of determination; --, 

Well (meanFiltGWalt)

meanHarbor

Alt

SE

meanHerringAlt SE precip­ 7day SE GDD50 SE Long term GW SE Constant SE Obser- vation (day)

Selecte

lag time f

groundw

ter data

in days

MA–WNW 154 0.304 0.021 -- -- 0.093 0.007 −0.011 0.001 0.113 0.009 −0.148 0.027 242 1 MA–WNW 154 -- -- 0.640 0.051 0.042 0.008 −0.003 0.001 0.085 0.010 0.516 0.063 268 1 MA–WNW 155–0017 0.226 0.044 -- -- 0.172 0.016 −0.037 0.003 0.214 0.019 1.504 0.057 246 1 MA–WNW 155–0017 -- -- 0.577 0.117 0.121 0.018 −0.022 0.002 0.193 0.024 2.035 0.143 295 1 MA–WNW 155–0035 0.245 0.039 -- -- 0.154 0.014 −0.033 0.003 0.200 0.017 1.468 0.050 250 1 MA–WNW 155–0035 -- -- 0.587 0.106 0.104 0.016 −0.020 0.002 0.176 0.021 2.032 0.130 286 1 MA–WNW 156–0010 0.300 0.027 -- -- 0.074 0.010 −0.015 0.002 0.146 0.011 1.274 0.035 245 2 MA–WNW 156–0037 0.335 0.025 -- -- 0.060 0.009 −0.012 0.002 0.141 0.010 1.235 0.032 245 2 MA–WNW 157–0012 0.261 0.026 -- -- 0.067 0.009 −0.016 0.002 0.182 0.011 1.339 0.033 249 2 MA–WNW 157–0033 0.264 0.025 -- -- 0.066 0.009 −0.016 0.002 0.190 0.011 1.320 0.032 249 2 MA–WNW 157–0070 0.265 0.025 -- -- 0.062 0.009 −0.016 0.002 0.187 0.011 1.334 0.033 245 2 MA–WNW 158 0.517 0.024 -- -- 0.047 0.009 −0.005 0.002 0.079 0.010 1.273 0.031 242 1.5 MA–WNW 159–0012 0.432 0.025 -- -- 0.055 0.009 −0.010 0.002 0.093 0.010 1.250 0.032 249 2 MA–WNW 159–0035 0.438 0.024 -- -- 0.054 0.010 −0.010 0.002 0.104 0.010 1.248 0.031 245 2 MA–WNW 160 0.507 0.026 -- -- 0.057 0.009 −0.005 0.002 0.081 0.011 0.751 0.033 249 2 MA–WNW 161 0.106 0.024 -- -- 0.108 0.009 −0.026 0.002 0.148 0.010 0.786 0.031 246 1 MA–WNW 161 -- -- 0.235 0.072 0.108 0.011 −0.019 0.001 0.149 0.015 0.945 0.089 287 1 MA–WNW 133–0030 0.435 0.026 -- -- 0.059 0.009 −0.012 0.002 0.103 0.011 1.180 0.033 249 2 MA–WNW 134 0.188 0.020 -- -- 0.078 0.007 −0.013 0.001 0.190 0.009 1.000 0.026 247 1 MA–WNW 134 -- -- 0.414 0.053 0.044 0.008 −0.003 0.001 0.161 0.011 1.454 0.066 280 1 MA–WNW 141 0.387 0.028 -- -- 0.048 0.010 −0.016 0.002 0.157 0.012 1.334 0.035 245 2.5 
58 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Table 2.2. Standardized coefficients for independent variables used to describe the variability in daily mean tidally filtered 

groundwater levels in monitoring wells near the Herring River, Wellfleet, Massachusetts, from June 2017 to June 2018.

[Dependent variable name: meanFiltGWalt, daily mean groundwater altitude for each well, daily tidal effects filtered from dataset. Independent variables: meanHarborAlt, daily mean water altitude at Herring River downstream from tide-control structure, daily tidal effects filtered from dataset; meanHerringAlt, daily 

mean water altitude at Herring River upstream from tide-control structure, daily tidal effects filtered from dataset; precip7day, sum of precipitation in the preceding 7 days; GDD50, growing degree days (base temperature 50 degrees Fahrenheit); LongtermGW, quartile of monthly groundwater levels at U.S. Geological 

Survey MA–WNW 17 (1, ≤25th percentile; 2, ≤50th percentile, 3, ≤75th percentile; 4, >75th percentile); --, not applicable]

Well (meanFiltGWalt) meanHarborAlt meanHerringAlt precip7day GDD50 LongtermGW Constant

MA–WNW 154 0.4735 -- 0.3908 −0.2230 0.4192 0

MA–WNW 154 -- 0.5305 0.2019 −0.1131 0.3142 0

MA–WNW 155–0017 0.2064 -- 0.4056 −0.4429 0.4504 0

MA–WNW 155–0017 -- 0.2230 0.2831 −0.3858 0.3373 0

MA–WNW 155–0035 0.2381 -- 0.3958 −0.4274 0.4601 0

MA–WNW 155–0035 -- 0.2501 0.2638 −0.3755 0.3367 0

MA–WNW 156–0010 0.4239 -- 0.2801 −0.2751 0.4837 0

MA–WNW 156–0037 0.4876 -- 0.2338 −0.2379 0.4827 0

MA–WNW 157–0012 0.3584 -- 0.2455 −0.2961 0.5910 0

MA–WNW 157–0033 0.3566 -- 0.2389 −0.2923 0.6064 0

MA–WNW 157–0070 0.3643 -- 0.2279 −0.2920 0.6037 0

MA–WNW 158 0.7137 -- 0.1736 −0.0964 0.2558 0

MA–WNW 159–0012 0.6287 -- 0.2129 −0.1823 0.3195 0

MA–WNW 159–0035 0.6267 -- 0.1834 −0.1888 0.3488 0

MA–WNW 160 0.6876 -- 0.2085 −0.0813 0.2594 0

MA–WNW 161 0.1532 -- 0.4116 −0.4947 0.4975 0

MA–WNW 161 -- 0.1272 0.3516 −0.4733 0.3608 0

MA–WNW 133–0030 0.6029 -- 0.2193 −0.2179 0.3385 0

MA–WNW 134 0.3066 -- 0.2949 −0.2721 0.6571 0

MA–WNW 134 -- 0.3181 0.1959 −0.1168 0.5561 0

MA–WNW 141 0.5037 -- 0.1693 −0.2689 0.4798 0
Table 2.3. Coefficients and other regression metrics for linear regression models used to describe the variability in daily maximum altitude of water Creek, Wellfleet, Massachusetts, from June 2017 to June 2018.[Shading indicates significance p at less than 0.01. Dependent variable: maximum daily stage (altitude) of Mill Creek, in feet above the North American Vertical Datum of 1988 ables: meanGWalt, daily mean groundwater altitude, in feet above NAVD 88; precip7day, sum of precipitation in the preceding 7 days; GDD50, growing degree days (base tempflooded, Mill Creek flooded (1) or not flooded (0). SE, standard error; R2, coefficient of determination]

Site Well (data used in meanGWalt) mean­ GWalt SE precip­ 7day SE GDD50 SE flooded SE Constant SE Obser- vation (day) 

Mill Creek 1

(upstream)

(Site 4)

MA–WNW 157–0012

0.228 0.040 0.093 0.009 −0.018 0.001 0.187 0.026 0.878 0.074 373 0

Mill Creek 2

(downstream)

(Site 2)

MA–WNW 155–0017

0.429 0.024 0.068 0.008 −0.009 0.001 0.013 0.024 0.180 0.050 373 0

Mill Creek 2

(downstream)

(Site 3)

MA–WNW 156–0010

0.389 0.048 0.088 0.010 −0.017 0.001 0.102 0.031 0.405 0.082 367 0

Mill Creek 2

(downstream)

(Site 6)

MA–WNW 159–0012

0.291 0.047 0.089 0.010 −0.018 0.001 0.151 0.030 0.602 0.075 373 0

Mill Creek 2

(downstream)

MA–WNW 161 0.871 0.023 0.040 0.005 −0.002 0.001 −0.034 0.015 0.077 0.027 373 0
60 Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River

Table 2.4. Standardized coefficients for independent variables used to describe the variability in daily maximum altitude of water 

levels at two sites on Mill Creek, Wellfleet, Massachusetts, from June 2017 to June 2018.

[Shading indicates significance p less than 0.01. Dependent variable: maximum daily stage (altitude) of Mill Creek, in feet above the North American Vertical 

Datum of 1988 (NAVD 88). Independent variables: meanGWalt, daily mean groundwater altitude, in feet above NAVD 88; precip7day, sum of precipitation in 

the preceding 7 days; GDD50, growing degree days (base temperature 50 degrees Fahrenheit); flooded, Mill Creek flooded (1) or not flooded (0)]

Site Well (data used in meanGWalt) meanGWalt precip7day GDD50 flooded Constant

Mill Creek 1

(upstream)

(Site 4)

MA–WNW 157–0012

0.174 0.308 −0.481 0.259 0

Mill Creek 2

(downstream)

(Site 2)

MA–WNW 155–0017

0.622 0.234 −0.248 0.018 0

Mill Creek 2

(downstream)

(Site 3)

MA–WNW 156–0010

0.296 0.291 −0.470 0.137 0

Mill Creek 2

(downstream)

(Site 6)

MA–WNW 159–0012

0.213 0.305 −0.480 0.205 0

Mill Creek 2

(downstream)

MA-WNW 161 0.895 0.135 −0.059 −0.047 0
For more information about this report, contact:

Director, New England Water Science Center

U.S. Geological Survey

331 Commerce Way, Suite 2

Pembroke, NH 03275

dc_nweng@usgs.gov

or visit our website at

https://www.usgs.gov/centers/new-england-water

Publishing support provided by the

Pembroke and Rolla Publishing Service Centers
Mullaney and others—Hydrogeology and Interactions of Groundwater and Surface Water Near Mill Creek and the Herring River—SIR 2019–5145

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20195145