U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Maryland Department of the Environment

Maryland Department of Natural Resources

Maryland Department of Agriculture

Dorchester Soil Conservation District

U.S. Fish and Wildlife Service 

Geology, Hydrology, and Water Quality of 

the Little Blackwater River Watershed,

Dorchester County, Maryland, 2006–09

Scientific Investigations Report 2011–5054
Cover.  Aerial view of Little Blackwater River looking north. The Key Wallace Drive bridge is in the foreground.

Photograph by Jane Thomas, IAN Image Library (www.ian.umces.edu/imagelibrary/).
Geology, Hydrology, and Water Quality of 

the Little Blackwater River Watershed, 

Dorchester County, Maryland, 2006–09

By Brandon J. Fleming, Benjamin D. DeJong, and Daniel J. Phelan 

Scientific Investigations Report 2011–5054

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Maryland Department of the Environment

Maryland Department of Natural Resources

Maryland Department of Agriculture

Dorchester Soil Conservation District

U.S. Fish and Wildlife Service 
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Fleming, B.J., DeJong, B.D., and Phelan, D.J., 2011, Geology, hydrology, and water quality of the Little Blackwater 

River watershed, Dorchester County, Maryland, 2006–09: U.S. Geological Survey Scientific Investigations Report 

2011–5054, 82 p.

ISBN 978-1-4113-3123-5
iii

Contents

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

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

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

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

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

Groundwater and Surface-Water Monitoring Methods ................................................................2

Groundwater and Surface-Water Sampling Methods ...................................................................5

Geology............................................................................................................................................................5

Miocene Stratigraphy ..........................................................................................................................6

Pleistocene-Holocene Stratigraphy ..................................................................................................6

Hydrology ........................................................................................................................................................9

Groundwater-Flow System..................................................................................................................9

Surface-Water System ......................................................................................................................15

Water Quality................................................................................................................................................17

Data Quality Assurance.....................................................................................................................17

Blanks .........................................................................................................................................17

Duplicates ...................................................................................................................................18

Ion Balances...............................................................................................................................18

Groundwater Quality ..........................................................................................................................18

Inorganic Constituents..............................................................................................................18

Organic Constituents.................................................................................................................25

Surface-Water Quality .......................................................................................................................25

Inorganic Constituents..............................................................................................................25

Organic Constituents.................................................................................................................25

Summary and Conclusions.........................................................................................................................28

Acknowledgments.......................................................................................................................................29

Selected References...................................................................................................................................29

Appendix 1: Concentrations of inorganic constituents in groundwater samples, 

Little Blackwater River watershed, Dorchester County, Maryland.............................................32

Appendix 2: Concentrations of inorganic constituents in surface-water samples, 

Little Blackwater River watershed, Dorchester County, Maryland........................................37

Appendix 3: Concentrations of inorganic and organic constituents in equipment 

blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08 ..........57

Appendix 4: Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, 

Dorchester County, Maryland ......................................................................................................60

Appendix 5: Lithologic log of Maintenence Yard core, Blackwater National Wildlife 

Refuge, Dorchester County, Maryland .......................................................................................68

Appendix 6: Lithologic and geophysical logs of DO Cd 58 core, Little Blackwater 

River watershed, Dorchester County, Maryland........................................................................77

Appendix 7: Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater 

River watershed, Dorchester County, Maryland........................................................................78

Appendix 8: 2-D resistivity survey along the Egypt Road well transect B-B’, Little 

Blackwater River watershed, Dorchester County, Maryland..................................................82
iv

Figures

1–2. Maps showing—

1. Location of Little Blackwater River watershed study area, 

Dorchester County, Maryland............................................................................................3

2. Location of the Little Blackwater River drainage area and 

monitoring sites....................................................................................................................4

3–4. Photographs showing—

3. Miocene formations observed in cores collected in the 

study area: (A) Calvert Formation (97.9–99-feet depth in 

Kentuck core), and (B) Choptank Formation (approximately 

69–70.25-feet depth in Kentuck core)...............................................................................9

4. Examples of facies seen in Pleistocene sequences from the 

DO Dd 12 core: (A) fluvial (approximately 4–5.25-feet depth), 

(B) rising-stage (approximately 20–21.25-feet depth), and 

(C) estuarine-marine (41.75–43-feet depth)...................................................................10

5. Diagram showing stratigraphic contrast between DO Cd 58 (left) 

and DO Cd 66 (right)....................................................................................................................11

6. Photographs showing the Parsonsburg Sand as expressed in 

(A) 2.25–4-feet depth in the DO Dd 12 core, and (B) 8.5–9.5-feet 

depth in the Maintenence Yard core.......................................................................................12

7. Diagram showing generalized north-south hydrogeologic cross 

section through the Little Blackwater River watershed, Dorchester 

County, Maryland........................................................................................................................13

8. Graphs showing groundwater levels in (A) wells DO Cd 64 (screen 

interval 3–13 feet below land surface [fbls]), DO Cd 65 (screen 

interval 70–75 fbls), DO Cd 66 (screen interval 124–129 fbls), 

May 2008–August 2009, (B) wells DO Dd 12 (screen interval 

95–100 fbls) and DO Dd 13 (screen interval 2–12 fbls), September 

2007–September 2009, and (C) well DO Cd 1, 1960–2010, 

Dorchester County, Maryland...................................................................................................15

9. Graph showing (A) Groundwater levels in water-table wells, and 

cross sections showing (B) winter and (C) summer groundwaterflow directions, October 2007–July 2009, Little Blackwater River 

watershed, Dorchester County, Maryland .............................................................................16

10–12. Graphs showing—

10. Groundwater levels in wells DO Cd 58 and DO Cd 63, and 

surface-water elevations at the gage on the Little Blackwater 

River at Cambridge, Maryland, November 2007–May 2008........................................17

11. Comparison of (A) specific conductance at the Cambridge 

gage and Key Wallace Drive gage, Maryland, and 

(B) temperature and specific conductance at the Key Wallace 

Drive gage, Maryland, November 2006–November 2009............................................17

12. Discharge to and from the Little Blackwater River at Seward, 

Maryland on Key Wallace Drive, Dorchester County, Maryland, 

November 2006–September 2009....................................................................................17
v

13. Trilinear diagrams showing chemical characteristics of inorganic 

constituents in surface water and groundwater, Little Blackwater 

River watershed, Dorchester County, Maryland....................................................................23

14. Boxplots showing inorganic constituents in surface water and 

groundwater, Little Blackwater River watershed, Dorchester County, 

Maryland ......................................................................................................................................24

15. Graph showing pH compared to well depth for all groundwater 

wells sampled, Little Blackwater River watershed, Dorchester County, 

Maryland ......................................................................................................................................25

16–17. Boxplots showing—

16. Inorganic constituents at surface-water sites, Little Blackwater 

River watershed, Dorchester County, Maryland...........................................................26

17. Summer (June through November) and winter (December 

through May) inorganic constituents in the upper and lower 

basin, Little Blackwater River watershed, Dorchester County, 

Maryland .............................................................................................................................27

Tables

1. Geologic units described in previous investigations in the Coastal 

Plain of Delaware, Maryland, and Virginia...............................................................................7

2. Thickness and depth of geologic units in the Little Blackwater River 

watershed, Cambridge, Maryland ..............................................................................................8

3. Locations and descriptions of wells installed and monitored during 

the Little Blackwater River study, Dorchester County, Maryland ......................................14

4. Concentrations of organic compounds detected in surface-water 

and groundwater samples, Little Blackwater River watershed, 

Dorchester County, Maryland, June 2008...............................................................................19

5. Dissolved organic compounds analyzed for, but not detected, in 

surface-water and groundwater samples, Little Blackwater River 

watershed, Dorchester County, Maryland ..............................................................................22
vi

Conversion Factors and Datums

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

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

 °F = (1.8 × °C) + 32

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).

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

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

or micrograms per liter (μg/L).

The term “water year” is defined as the 12-month period from October 1 of any given year 

through September 30 of the following year. The water year is designated by the calendar year 

in which it ends and which includes 9 of the 12 months. Thus, the year ending September 30, 

2002, is called the “2002 water year.”


Geology, Hydrology, and Water Quality of 

the Little Blackwater River Watershed, 

Dorchester County, Maryland, 2006–09 

By Brandon J. Fleming, Benjamin D. DeJong, and Daniel J. Phelan

Abstract

The Little Blackwater River watershed is a low-lying 

tidal watershed in Dorchester County, Maryland. The potential exists for increased residential development in a mostly 

agricultural watershed that drains into the Blackwater National 

Wildlife Refuge. Groundwater and surface-water levels were 

collected along with water-quality samples to document 

hydrologic and geochemical conditions within the watershed 

prior to potential land-use changes. 

Lithologic logs were collected in the Little Blackwater 

River watershed and interpreted with existing geophysical 

logs to conceptualize the shallow groundwater-flow system. A 

shallow water table exists in much of the watershed as shown 

by sediment cores and surface geophysical surveys. Watertable wells have seasonal variations of 6 feet, with the lowest 

water levels occurring in September and October. Seasonally 

low water-table levels are lower than the stage of the Little 

Blackwater River, creating the potential for surface-water 

infiltration into the water table. 

Two stream gages, each equipped with stage, velocity, 

specific conductance, and temperature sensors, were installed 

at the approximate mid-point of the watershed and near the 

mouth of the Little Blackwater River. The gages recorded 

data continuously and also were equipped with telemetry. 

Discharge calculated at the mouth of the Little Blackwater 

River showed a seasonal pattern, with net positive discharge in 

the winter and spring months and net negative discharge (flow 

into the watershed from Blackwater National Wildlife Refuge 

and Fishing Bay) in the summer and fall months. Continuous 

water-quality records showed an increase in specific conductance during the summer and fall months. 

Discrete water-quality samples were collected during 

2007–08 from 13 of 15 monitoring wells and during 2006–09 

from 9 surface-water sites to characterize pre-development 

conditions and the seasonal variability of inorganic constituents and nutrients. The highest mean values of nitrogen are 

found in the deep groundwater system, with relatively low 

values in the water table. Surface-water-quality samples in the 

lower half of the basin show a significant increase in inorganic 

seawater constituents, especially in summer, corresponding 

with net negative discharge from the Little Blackwater River. 

Samples also were collected from nine wells and four 

surface-water sites for pesticides in June 2008. The herbicides 

atrazine, metolachlor, and simazine, and the insecticide fipronil were detected at each of the four surface-water sites, with 

concentrations less than 2 micrograms per liter. Concentrations 

of pesticides found in groundwater were typically one to two 

orders of magnitude lower than pesticide concentrations found 

in surface water of the Little Blackwater River.

Seasonal hydraulic-gradient reversals between the shallow groundwater system and the Little Blackwater River, 

coincident with the inflow of brackish water from Fishing Bay 

and Blackwater National Wildlife Refuge, indicate a potential 

for saltwater intrusion into the water table. The likelihood of 

saltwater intrusion into the water table is further supported 

by high chloride concentrations observed in water-table wells 

near the Little Blackwater River. 

Introduction

The U.S. Geological Survey (USGS), in cooperation with 

the Maryland Department of the Environment, the Maryland 

Department of Natural Resources, the Maryland Department 

of Agriculture, the Dorchester Soil Conservation District, 

and the U.S. Fish and Wildlife Service, began a study of 

the hydrology of the Little Blackwater River watershed in 
2 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Dorchester County, Maryland in September 2006. The study 

was designed to document the local geologic setting, measure seasonal groundwater and surface-water conditions, and 

analyze water quality in the drainage area of the Blackwater 

National Wildlife Refuge (BNWR) planned for municipal 

development.

The BNWR is located 12 mi (miles) south of Cambridge 

in Dorchester County, Maryland, and consists of over 25,000 

acres of freshwater impoundments, brackish tidal wetlands, 

open fields, and mixed evergreen and deciduous forests 

(fig. 1). The refuge was established in 1933 primarily as a 

wildlife sanctuary for migratory birds but is the home of other 

threatened species such as the Delmarva fox squirrel and bald 

eagle. In the 20th century, wetland plants have disappeared 

from the wetlands for a variety of reasons including the presence of nutria (Myocastor coypus)—non-native semi-aquatic 

rodents that overgraze native wetland plants. Residential 

development is planned in the Little Blackwater River 

watershed between the refuge and the City of Cambridge 

(fig. 2). County, State, and Federal regulators and agencies as 

well as public civic groups are concerned that an increase in 

development could have detrimental effects on the BNWR by 

changing groundwater-flow patterns, increasing runoff from 

areas treated with fertilizers, and increasing discharges from 

on-site wastewater systems into the tidal Little Blackwater 

River that flows into the Blackwater River and the BNWR. 

In an effort to minimize the potential effects of development 

on the BNWR, the State of Maryland purchased part of the 

proposed development area that directly borders the Little 

Blackwater River, and no development will be allowed on the 

state-owned property (fig. 2).

Purpose and Scope

This report describes (1) the geology of the Little 

Blackwater River watershed based on the drilling results from 

concurrent regional geological investigations, (2) the groundwater-flow system in areas adjacent to proposed development, 

(3) streamflow characteristics, and (4) groundwater and 

surface-water quality in the Little Blackwater River watershed 

from 2006 through 2009. Data presented in this report will 

provide a baseline of preexisting conditions for comparison 

with future post-development conditions.

Description of Study Area

The Little Blackwater River watershed is in Dorchester 

County, Maryland, on the Eastern Shore of the Chesapeake 

Bay. The watershed extends from the south side of Cambridge 

to the Blackwater River in the BNWR (fig. 2). The Little 

Blackwater River watershed drains approximately 27,748 

acres [43.3 mi2 (square miles)] that are used primarily for 

agriculture. Land use in the watershed in 2005 included 

approximately 1,276 acres of residential, commercial, and 

light industrial land, and 26,472 acres of cropland, woodland, 

forested and marshy riparian areas, and tidal wetlands (James 

Newcomb, Dorchester Soil Conservation District, oral commun., 2007). The watershed is relatively flat, with an elevation 

of 30 ft (feet) near Cambridge, to sea level at the confluence 

with the Blackwater River. The Little Blackwater River is 

tidally affected for much of its reach, and flows generally 

southward to discharge to the Blackwater River (fig. 2). 

Methods

Groundwater and surface-water levels were measured 

over a multi-year period to describe the seasonal hydrologic 

variation within the Little Blackwater River watershed. 

Water-quality parameters including major ions, nutrients, and 

pesticides were collected from groundwater and surface-water 

sampling sites to characterize water quality prior to changes in 

land use. 

Groundwater and Surface-Water Monitoring 

Methods

River conditions in the Little Blackwater River were 

monitored using two USGS gaging stations, station number 

1490120 (Little Blackwater River near Cambridge, Md.), 

located at the approximate mid-point of the watershed with 

a drainage area of 15.3 mi2, and station number 1490140 

(Little Blackwater River at Seward, Md.), near the confluence 

of the Little Blackwater River and the Blackwater River at 

Key Wallace Drive, with a drainage area of 30.2 mi2 (fig. 2) 

as calculated from a 30-m (meter) digital elevation model. 

These sites will hereafter be referred to as the Cambridge and 

the Key Wallace Drive gages. Both gages measured specific 

conductance, temperature, velocity, and river stage at 6-minute 

intervals. Discharge was calculated at Key Wallace Drive with 

an acoustic Doppler current profiler (ADCP), which measures 

both the velocity and the direction of flow.

The USGS installed a transect of three monitoring well 

nests (multiple wells screened at different depths at the location) consisting of eight wells, DO Cd 56-63, on the east side 

of Egypt Road in 2007, between the proposed development 

area and the Little Blackwater River (fig. 2). Another monitoring nest consisting of three wells, DO Cd 64-66, was installed 

about 0.4 mi farther south on the west side of Egypt Road in 

2008. The USGS also installed a pair of monitoring wells 

(DO Dd 12 and DO Dd 13) in the Kentuck Swamp near the 

BNWR in 2007 as part of a more regional assessment of the 

hydrogeology of the basin (fig. 2). Two wells, DO Cd 67 and 

DO Cd 68, were installed prior to the start of the study and 

were only monitored for water levels. Continuous sediment 

core was recovered from the deep well at each nest site and 

was used in this study as the basis for the geologic interpretation. Once the wells were installed, water levels were 

measured monthly and selected wells were instrumented with 

continuous pressure transducers. 
Methods 3

Figure 1. Location of Little Blackwater River watershed study area, Dorchester County, Maryland.
4 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 2. Location of the Little Blackwater River drainage area and monitoring sites.
Geology 5

Groundwater and Surface-Water Sampling 

Methods

Groundwater samples were generally collected using 

standard USGS sampling protocols (U.S. Geological Survey, 

variously dated) that were modified slightly because of the low 

permeability of the materials in which many of the wells were 

screened. Fultz groundwater sampling pumps were used and 

pumped at low-flow rates to minimize the drawdown in the 

wells so that well screens were not exposed to the atmosphere 

during the purging and sampling. For water-table wells, which 

had well screens that straddled the water table, the drawdown 

was minimized as much as possible, but some aquifer materials were exposed to the atmosphere. The intermediate-depth 

wells sampled in October 2007 along the transect (wells DO 

Cd 57, 60, and 62) had such low recovery rates that groundwater sampling pumps could not maintain flow rates high enough 

to recover sufficient volume for sampling. These wells were 

sampled with bailers during this sampling event, and were not 

sampled in June 2008.

The sampling procedure involved lowering the pump 

intake to the desired depth, and then pumping at a low-flow 

rate. Water-quality parameters were collected for pH, temperature, specific conductance, and dissolved oxygen during 

purging as the water was pumped through a flow-through 

cell. Parameter readings were taken every 5 minutes using 

YSI 6920 water-quality sondes until the change in parameter 

values between intervals reached stable values. Once stabilization was attained, defined as parameter values with less 

than a 5-percent change in six successive 5-minute intervals, 

sampling bottles for total (unfiltered) analyses were filled, then 

bottles for dissolved (filtered) analyses, followed by those 

requiring special sample-handling procedures, such as organic 

compounds. In-line filtration capsules were used to prevent 

atmospheric contact until the sample bottles were filled. All 

bottles were preserved, iced and processed, and shipped to the 

USGS National Water Quality Laboratory in Denver, Colorado 

within 48 hours.

Constituent group 

sampled for in study

Number of groundwater samples in 

study (including 

replicates and 

equipment blanks)

Number of 

surface-water 

samples in study 

(including 

replicates and 

equipment blanks)

Inorganic constituents 

including major 

ions, nutrients, and 

field parameters

20 71

Organic constituents 

including pesticides, 

fungicides, and 

insecticides

9 4

Surface-water-quality samples were collected using 

vertically integrated samplers at the approximate mid-stream 

location at each of the sampling points. Horizontal integration 

was not used due to the narrowness of the sampling locations. 

At two sampling locations (1490113 and 1490108) culverts 

were present under the roadways at each location. The culvert 

that had the most visual flow was sampled. Beginning on 

March 16, 2006, samples were collected from three surfacewater sampling sites (1490112, 1490116, and 1490120) and 

analyzed for nutrients, major ions, and field parameters 

(fig. 2) in cooperation with the USGS Priority Ecosystems 

Science (PES) Program. 

Two additional sampling locations (1490113 and 

1490140) were added for the next quarterly sampling effort 

(June 22, 2006, fig. 2). Additional sampling locations 

(1490108, 1490110, and 1490130) were added and quarterly 

sampling was maintained until October 29, 2007. A final 

sampling was conducted June 10, 2008 at eight of the surfacewater sites. Two storm-sampling events were also conducted 

on October 6, 2006 and April 16, 2007 to evaluate the impacts 

of major rain events when storm or wind surge was not bringing higher saline water from the Blackwater River or Fishing 

Bay into the Little Blackwater River watershed. The storm 

samples were collected following evaluations of the real-time 

discharge and specific conductance data in consultation with 

visual observations from staff from the BNWR. Groundwater 

and surface-water sampling sites, dates, and results of sampling are listed in Appendix 1 and 2. Also presented in 

Appendix 1 and 2 are the results of duplicate environmental 

samples and ion balances, with equipment blank results presented in Appendix 3 and described later in this report.

Geology

The Little Blackwater River watershed on the central 

Delmarva Peninsula is situated in the Atlantic Coastal Plain. 

The Coastal Plain is underlain by a wedge of Cenozoic 

and Mesozoic sediments that range in thickness from zero 

at the Fall Line west of the Chesapeake Bay in Virginia 

and Maryland to approximately 8,000 ft under the coast of 

Maryland at Ocean City (fig. 1), and is approximately 3,300 ft 

thick under the study area (Trapp and others, 1984). A study 

by Ator and others (2005) divides the surficial hydrogeology 

of the Mid-Atlantic Coastal Plain into seven sub-regions. The 

study area lies entirely within the coastal lowlands sub-region 

described by Ator and others (2005). The geological part 

of the current study is focused on both Pleistocene marine 

and non-marine deposits and Miocene substrates, which 

the Pleistocene deposits unconformably overlie. The subtle 

geomorphology of the area belies a complex stratigraphic 

sequence of laterally variable lithologies. The Delmarva 

Peninsula is highly sensitive to shifts in sea level because of 

its low relief and close proximity to the Atlantic. The complex 

sedimentology and stratigraphy of the region are evidence of 
6 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

constantly alternating processes of erosion and deposition. 

Quaternary deposits lie unconformably on middle Miocene 

sediments, a relation that reflects both deep erosion during 

the Pleistocene and a potential long (approximately 10–12 

million years) hiatus in deposition. The Miocene sediments 

are commonly shallow marine shelf facies with interbedded 

pro-delta deposits. The Miocene substrate is cut by numerous 

paleochannels of the Proto Chesapeake Bay and its tributaries. The channels are filled with the Pleistocene Kent Island 

Formation, an assemblage of cut-and-fill fluvial-to-marine, 

transgressive-regressive sequences locally overlain by a thin 

blanket of cold-climate modified sediments. This thin assemblage of surficial deposits is an artifact of a former landscape 

that was constructed, eroded, and modified by cold-climate 

processes during the late Pleistocene. When climate warmed 

at the beginning of the Holocene, the deeply incised drainages 

began to fill with fluvial-to-estuarine sediments as sea levels 

rebounded. Holocene sedimentation continues to fill the lower 

topography.

Miocene Stratigraphy

A core drilled to basement approximately 2 mi north 

of the study area placed the basal contact of the Miocene at 

345 ft (Trapp and others, 1984; table 1). Miocene deposits in 

this area include the fossiliferous sand, silt, and clay beds of 

the Calvert and Choptank Formations. These units have low 

permeability, and have even been referred to as the “upper 

confining unit” of the Piney Point aquifer (see Klohe and 

Feehley, 2001). 

The Calvert Formation is the oldest unit in the 

Chesapeake Group (table 1). The top of this unit was penetrated in several of the cores in the study area at elevations 

ranging from 48–87 ft bsl (below sea level) (table 2). In the 

study area, the Calvert Formation is generally composed 

of dark gray to olive gray very fine to medium sand with a 

variable abundance of fossils, including Chesapectinnefrens, 

barnacles, and small clams (fig. 3A). In a concurrent study, 

a sediment sample collected from this unit and analyzed for 

dinoflagellates in a core approximately 14 mi to the north of 

the study area (South Dover Bridge; SDB-1) (fig. 1), places 

this unit in the dinoflagellate cyst zone (DNZ) DN5 of 

deVerteuil and Norris (1996), and correlates this unit with 

Shattuck beds 14–16 (upper Calvert Formation; middle 

Miocene) of Gernant (1970) (Lucy Edwards, U.S. Geological 

Survey, oral commun., 2008). 

The Choptank Formation unconformably overlies the 

Calvert Formation as an onlap in this area and has a variable 

thickness (2–53 ft) that is attributed to local scouring by 

Pleistocene channels. A distinctive local facies in the upper 

part of this unit (“red and green bed”) ranges from gray fine 

sand to greenish, or reddish, gray silty clay or silty fine sand 

with local concentrations of whitish silty concretions and burrows; woody fragments and unoxidized iron sulfide growths 

also occur (fig. 3B). The lower part of this unit is generally 

a massive, dark gray clay with small (less than 1 inch) sand 

lenses. Two dinoflagellate samples collected from SDB-1 

bracket this unit. These well-preserved samples contain an 

assemblage that fits in the DNZ DN6 of de Verteuil and 

Norris (1996), which in turn correlates with Shattuck beds 

17–18 (Drumcliff and St. Leonard Members of the Choptank 

Formation; middle Miocene) of Gernant (1970) (Lucy 

Edwards, U.S. Geological Survey, oral/written commun., 

2008).

The upper Miocene St. Mary’s and Eastover Formations 

conformably overlie the Choptank Formation on the western 

side of the Bay (Gernant, 1970), but have not been observed in 

the study area east of the Bay. The absence of these overlying 

units indicates that they were stripped off the full extent of the 

Little Blackwater River watershed during repeated episodes of 

falling sea level in the Pleistocene.

Pleistocene-Holocene Stratigraphy

Climate variability during the Pleistocene was the 

dominant controlling factor on the stratigraphy and sedimentology in the Little Blackwater River watershed. The 

sea level was lowered as much as about 400 ft during glacial 

periods (Waelbroeck and others, 2002). These lower base 

levels greatly increased the erosive power of streams on 

the Delmarva Peninsula and caused deep incision of major 

rivers and their tributaries. Cold-climate processes and eolian 

sedimentation became extremely active while these cold, dry 

climatic conditions prevailed. During subsequent interglacial 

periods, climates warmed and sea level rose. River channels 

aggraded in response and filled the previously incised topography. The Pleistocene stratigraphy within the Little Blackwater 

River watershed is therefore largely defined by a variably 

thick package of transgressive-regressive sequences representing facies that range from cut-and-fill stream deposits to full 

estuarine fill, and have been capped with cold-climate-modified sediments.

Complete transgressive sequences from low stand 

(fluvial) to high stand (full estuarine) systems tracts can be 

seen in cores drilled near the center of paleochannels in the 

Little Blackwater River watershed (for example, DO Dd 12 

core, 17–30 ft; Appendix 4). The fluvial facies are generally 

characterized by open-water, very fine to coarse sand with silt, 

pebbles, and sparse cobbles (fig. 4A). Bedforms range from 

coarse lag deposits and braided channel cross-beds to silty, 

laminated fining-upward sequences on tops of flood plains. 

Intermediate, or rising stage, facies are predominantly silt and 

clay with thin sand lenses throughout, and local burrows and 

organic materials (fig. 4B). The fully estuarine facies is commonly characterized by burrowed-to-massive silty clay with 

local concentrations of organic materials (fig. 4C). Although 

these full, orderly fining-upward transgressive sequences are 

present near the center of paleochannels in the Kent Island 

Formation, small lenses of sand, silt, and clay facies are often 

interfingered with one another on channel margins and are 

not laterally continuous (for example, Maintenance Yard core, 

26–35 ft; Appendix 5). 
Geology 

7

Table 1. Geologic units described in previous investigations in the Coastal Plain of Delaware, Maryland, and Virginia.[USGS, U.S. Geological Survey; shaded areas indicate geologic units not included in study.]

System Series Trapp and others (1984) Cushing and others (1973) (Maryland names) Mixon and others (1989) (West side of Chesapeake Bay) Owens and Denny (1979) (Maryland and Delaware) Aleman and others, USGS, written commun., 2010 This study

Quaternary

Holocene Tidal marsh 

deposits

Holocene 

sediments

Pleistocene No name listed Columbia Group

Parsonsburg Sand

Kent Island Formation

Sinepuxent Formation

Ironshire Formation

Omar Formation

Pliocene ?Brandywine Formation?

Bacons Castle and 

Yorktown 

Formations

Walston Silt

Beaverdam Sand

Yorktown Formation

Tertiary

Miocene Chesapeake Group (lower part)

Chesapeake

Group

Yorktown Formation

Chesapeake

Group

Eastover 

Formation

Pensauken Formation

Chesapeake Group

[St. Mary’s Formation, 

Choptank Formation, 

Calvert Formation]

Chesapeake

Group

Choptank 

Formation

Chesapeake

Group

Choptank 

Formation St. Mary’s Formation

Choptank Formation St. Mary’s Formation Calvert 

Formation

Calvert 

Formation

Calvert Formation Calvert Formation

Oligocene Old Church Formation

Not penetrated in 

this study

Drummonds 

Corner beds

Not penetrated in 

this study

Eocene

Piney Point Formation Piney Point Formation Piney Point Formation Piney Point Formation

Nanjemoy Formation Nanjemoy Formation

Nanjemoy Formation Nanjemoy Formation

Marlboro Formation Marlboro Formation

Paleocene Aquia Formation Aquia Formation Aquia Formation Aquia Formation Brightseat Formation Brightseat Formation

Cretaceous

Upper 

Cretaceous

Severn and Matawan 

Formations,

undifferentiated

Monmouth Formation

Not penetrated in 

this study

Magothy Formation

Magothy Formation Raritan Formation

Lower 

Cretaceous

Potomac Group,

undifferentiated

Potomac

GroupPatapsco Formation Potomac Group, undifferentiated Arundel Formation Patuxent Formation
8 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

The lithologic contrast between two cores that were 

drilled less than 0.5 mi from one another (DO Cd 58 and 

DO Cd 66; Appendixes 6 and 7) clearly illustrates the high 

subsurface variability in this area. DO Cd 58 is located about 

one third of a mile from the Little Blackwater River and has 

an approximately 60-ft-thick section of Kent Island sediments, 

including a full transgressive sequence, a partial falling-stage 

sequence, and some minor wind-blown sands on the surface. 

These sediments rest unconformably over about 2 ft of the 

shallow, open-water facies of the middle Miocene Choptank 

Formation below. The Choptank Formation is conformable on 

the Calvert Formation at about 48 ft bsl. By contrast, DO Cd 

66 is about 0.5 mi from the Little Blackwater River channel 

and only includes about 14 ft of Kent Island fill that includes 

a partial rising-stage sequence capped by minor wind-blown 

sands. This thin package rests unconformably on about 55 ft 

of the shallow, open-water facies of the middle Miocene 

Choptank Formation. The Choptank Formation at DO Cd 66 

is conformable on the Calvert Formation at about 61 ft bsl. 

There are two possible explanations for the obvious lithologic 

contrast between these sediment records. The first explanation 

is that there could be a paleo-valley wall separating these two 

cores. In this scenario, the Kent Island sediments in DO Cd 58 

filled a paleochannel that had previously eroded the missing 

Miocene record in this location, but not the one located at DO 

Cd 66. Alternatively, geologic structure may be interpreted 

from the shallow geology between the two cores; a fault could 

be offsetting these cores so that DO Cd 66 is on the headwall 

and DO Cd 58 is on the footwall. If this were the case, the 

thicker Kent Island package in DO Cd 58 indicates more 

accommodation space (fig. 5). However, the elevation of distinctive shell beds within the Calvert Formation in these cores 

indicates that if there were ever any structures offsetting these 

cores, it would be opposite from the one that was described 

above, as this datum is about 13.5 ft lower in DO Cd 66 than 

in DO Cd 58 (fig. 5). 

As stated above, the uppermost Pleistocene sediments 

(the Parsonsburg Sand) were heavily impacted by cold-climate 

processes during glacial maxima. Cold, dense winds originating at the terminus of the Laurentide ice sheet (less than 150 

mi to the north) froze large parts of the emergent topography 

and transformed the central Delmarva Peninsula into a periglacial landscape that has been well documented by French and 

others (2009). Thermal-contraction cracks filled with eolian 

material have been observed in gravel pits about 15 mi to the 

north of the study area in Easton, Maryland and about 25 mi 

to the southeast near Salisbury, Maryland, for example. These 

cracks are found in association with thermokarst structures 

such as deformed and involuted near-surface soil horizons that 

result from thermal subsidence of underlying frozen ground 

(French and others, 2009; Smoot and others, 2009). The surface materials in which these phenomena occur are generally 

composed of silty sand containing scattered small pebbles 

(figs. 6A and B), and have been interpreted as a cover-sand 

unit and considered an analog to the cover sands found in 

Europe. This suite of cold-climate-derived features is indicative of permafrost and (or) deep seasonal frost (French, 2007). 

Additionally, large, currently inactive dune fields have long 

been recognized across the central Delmarva and attributed 

to processes active during colder, drier climates (Denny and 

Table 2. Thickness and depth of geologic units in the Little Blackwater River watershed, Cambridge, Maryland (from Trapp and 

others, 1984).

System Series Group or Formation Thickness

(feet)

Depth

(feet to base)

Quaternary Pleistocene/Holocene 48 48

Tertiary

Miocene Chesapeake Group

(lower part) 297 345

Eocene Piney Point Formation 192 537

Nanjemoy Formation 128 665

Paleocene Aquia Formation 124 789

Brightseat Formation 30 819

Cretaceous

Upper Cretaceous

Severn and Matawan 

Formations,

undifferentiated

46 865

Magothy Formation 132 997

Lower Cretaceous Potomac Group,

undifferentiated 2,302 3,299

Precambrian Basement complex
Hydrology 9

others, 1979; Sirkin and others, 1977). Recent Light Detection 

and Ranging (LIDAR)-based investigations carried out in both 

the central Delmarva Peninsula and west of the Chesapeake 

Bay confirm these observations and highlight the regional 

impact of these climates during this period (Markewich and 

others, 2009; Newell and Clark, 2008). 

Sea level has continued to rise since the Wisconsinan glaciation. As sea levels rose, the eroded Wisconsinan landscape 

filled with organic-rich silty peat, which is thickest in major 

river channels but also present in surficial wetlands.

Hydrology

The hydrology within the Little Blackwater River watershed is complex and variable, primarily due to lateral and vertical lithologic variability in the subsurface. Repeated climate 

oscillations during the Pleistocene caused both major stream 

incision into the existing Miocene land surface and subsequent 

backfilling of these channels with fluvial-to-estuarine sediments. Sediments that filled these stream channels represent a 

full range of sandy fluvial deposits to clayey estuarine-marine 

deposits that are interfingered throughout. The preferential 

flowpaths for shallow groundwater flow in this stratigraphy 

are extremely discontinuous. Although these sediments are 

young and non-indurated, they provide avenues for groundwater flow that are generally thin and lack significant lateral 

continuity (fig. 7). In many locations, erosion and deposition 

in the Pleistocene did not have an impact on the deeper strata. 

These locations have a thicker and more complete section of 

low permeability red and green beds of the upper Choptank 

Formation and are likely to create confining conditions in the 

Piney Point aquifer below.

Extensive ditching along agricultural fields can create 

artificial flowpaths that circumvent the typical topographically 

driven groundwater-flow system. The tidal nature of the Little 

Blackwater River affects groundwater fluxes, and because of 

the wide expanse of open water within the BNWR, southerly 

winds can increase river stage well into the headwater areas 

of the basin, creating temporary localized reversals in shallow 

groundwater-flow directions close to the river. Combined with 

the potential uptake of water during the growing season, all of 

these factors create a complex and dynamic hydrologic setting 

on the Delmarva Peninsula. 

Groundwater-Flow System

The USGS installed a transect of three monitoring well 

nests (multiple wells screened at different depths at the same 

location) consisting of eight wells, DO Cd 56-63 on the east 

side of Egypt Road in 2007, between the proposed development area and the Little Blackwater River (fig. 2). Another 

monitoring nest consisting of three wells, DO Cd 64-66 was 

installed about 0.4 mi farther south on the west side of Egypt 

Road in 2008 (table 3). The USGS installed a pair of monitoring wells (DO Dd 12 and 13) in the Kentuck Swamp near 

the BNWR in 2007 as part of a more regional assessment of 

the hydrogeology of the basin. The groundwater levels from 

September 2007 through September 2009 in wells DO Dd 

12-13, and from May 2008 through September 2009 in wells 

DO Cd 64-66 have consistently shown downward vertical 

gradients, indicating the potential for movement of shallow 

groundwater towards the deeper flow system (figs. 8A and B). 

Monitoring well DO Cd 1, located just west of the basin 

(fig. 2) and screened at 320 ft bls (below land surface) in the 

Piney Point aquifer, has water levels that are typically 

45–55 ft bsl (fig. 8C). These lower water levels, caused by 

(A) (B)

Figure 3. Miocene formations observed in cores collected 

in the study area: (A) Calvert Formation (97.9–99-feet depth 

in Kentuck core), and (B) Choptank Formation (approximately 

69–70.25-feet depth in Kentuck core). [Photographs by 

B.D. DeJong, USGS.]
10 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

(A) (B) (C)

Figure 4. Examples of facies seen in Pleistocene sequences from the DO Dd 12 core: (A) fluvial (approximately 

4–5.25-feet depth), (B) rising-stage (approximately 20–21.25-feet depth), and (C) estuarine-marine (41.75–43-feet 

depth). [Photographs by B.D. DeJong, USGS.]
Hydrology 11

Figure 5. Stratigraphic contrast between DO Cd 58 (left) and DO Cd 66 (right).

Lithology

 Depth

[feet below land 

surface (BLS)] Lithology

10

0

20

30

40

50

60

70

80

90

100

110

120

130

 DO Cd 58 DO Cd 66

 “Red/ Green Beds” of the upper

Miocene Choptank Formation

Pleistocene Fill

.47 mi

Distinctive shell bed layer in

the Calvert Formation
12 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

(A) (B)

Figure 6. The Parsonsburg Sand as expressed in (A) 2.25–4-feet depth 

in the DO Dd 12 core, and (B) 8.5–9.5-feet depth in the Maintenence Yard 

core. [Photographs by B.D. DeJong, USGS.]
Hydrology 13

regionally extensive water withdrawals from the Piney Point 

aquifer, indicate a large downward gradient between the shallow and deeper groundwater systems. 

The water-table wells, screened in the Parsonsburg Sand, 

generally have water levels slightly above sea level, with seasonal variations of several feet (fig. 9A). In winter and spring 

months, water-table well observations show groundwater 

gradients driven by the subtle topography, indicating potential 

flow towards the Little Blackwater River (fig. 9B). In summer 

and fall months, water-table well observations show groundwater levels that drop below the stage of the Little Blackwater 

River. These lower groundwater levels create gradient reversals with the potential for the Little Blackwater River to lose 

water into the water-table system (fig. 9C). This in turn creates 

the potential for infiltration of brackish river water into the 

shallow groundwater system close to the river, as evidenced 

by elevated chloride concentrations in monitoring wells DO 

Cd 61 and DO Cd 68 (see Appendix 1).

The deeper wells, screened in the Miocene sediments (at 

depths above the Piney Point aquifer, which is the primary 

groundwater supply in the area), generally have water levels 

that are several feet below sea level. Continuous water-level 

records from the deeper wells show a muted but instantaneous 

pressure response to tidal fluctuations observed at the 

Cambridge gage (fig. 10). Well DO Cd 58 is approximately 

2,500 ft from the Little Blackwater River and screened at 

89–94 ft bls, whereas well DO Cd 63 is 500 ft from the Little 

Blackwater River and screened at 47–52 ft bls. 

The response of the deeper wells to changes in tides may 

be caused by pressure loading as the high tides press down 

on the system, forcing water levels to rise in confined-aquifer 

wells. The same type of responses are typical in coastal areas 

and are observed in monitoring wells along tidal areas under 

both non-pumping and pumping conditions, such as in the 

Ocean City and Manokin aquifers (about 250–400 ft bls) near 

Ocean City, Maryland (Phelan, 1987, fig. 26). 

Geophysical (gamma) logs were collected in the deeper 

wells, and a 2-dimensional electrical resistivity survey was 

performed parallel to the well transect between Egypt Road 

and the Little Blackwater River. These logs (Appendixes 6 

and 7) and results from the survey (Appendix 8), combined 

with geologic core descriptions, are the basis for the crosssectional conceptual flow model of the water-table system 

for the Little Blackwater River (figs. 9B and C). In Appendix 

8, red colors indicate higher electrical resistivity, typically 

sands saturated with fresh water. Blue colors indicate values 

of lower electrical resistivity, typically of silts and clays. This 

interpretation is consistent with the sediment cores collected 

from the drilling of the wells along this cross section, however, 

the sands are poorly sorted and contain some silts and clays. 

The interpretation using gamma logs, electrical resistivity 

surveys, and lithologic logs confirms the presence of thin 

sandy deposits (10–20 ft) of the Parsonsburg Sand, which has 

a relatively higher permeability than the underlying silts and 

clays in this part of the watershed. 

Figure 7. Generalized north-south hydrogeologic cross section through the Little Blackwater River watershed, Dorchester County, 

Maryland.
14 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Table 3. Locations and descriptions of wells installed and monitored during the Little Blackwater River study, Dorchester County, Maryland. [USGS, U.S. Geological Survey; NAD83, North American Datum of 1983; NAVD88, North American Vertical Datum of 1988; PVC, polyvinylchloride; bls, below land surface] USGS well name USGS well number Local well name Latitude (decimal degrees, NAD83) Longitude (decimal degrees, NAD83) Casing diameter (inches) Type of casing Type of screen Altitude of ground surface (feet above NAVD88) Depth of borehole (feet bls) Depth to top of screen interval (feet bls) Depth to bottom of screen interval (feet bls) DO Cd 56 383122076055701 ERN-1-A 38.522778 -76.099167 2 PVC wire-wound 9.50 13.45 3.00 13.00 DO Cd 57 383122076055702 ERN-1-B 38.522778 -76.099167 2 PVC wire-wound 9.85 21.98 16.00 21.00 DO Cd 58 383122076055703 ERN-1-C 38.522778 -76.099167 2 PVC wire-wound 9.43 94 89.00 94.00 DO Cd 59 383118076054601 ERN-2-A 38.521667 -76.096111 2 PVC wire-wound 7.28 13.11 3.00 13.00 DO Cd 60 383118076054602 ERN-2-B 38.521667 -76.096111 2 PVC wire-wound 7.11 19.19 14.00 19.00 DO Cd 61 383112076053501 ERN-3-A 38.520000 -76.093056 2 PVC wire-wound 3.68 13.20 3.00 13.00 DO Cd 62 383112076053502 ERN-3-B 38.520000 -76.093056 2 PVC wire-wound 3.81 19.37 14.00 19.00 DO Cd 63 383112076053503 ERN-3-C 38.520000 -76.093056 2 PVC wire-wound 3.12 53.2 47.00 52.00 DO Cd 64 383100076061101 ERN-4-A 38.516667 -76.103333 2 PVC wire-wound 10.18 13.0 3.00 13.00 DO Cd 65 383100076061102 ERN-4-C 38.516667 -76.103333 2 PVC wire-wound 10.00 75 70.00 75.00 DO Cd 66 383100076061103 ERN-4-D 38.516667 -76.103333 2 PVC wire-wound 10.34 129.5 124.00 129.00 DO Cd 67 383139076053301 DW-1 38.527778 -76.092500 4 PVC wire-wound 2 15 5.00 15.00 DO Cd 68 383051076054201 DW-2 38.514167 -76.095278 4 PVC wire-wound 5 15 5.00 15.00 DO Dd 12 382718076062001 Kentuck-1 38.455000 -76.105556 2 PVC wire-wound 5.26 100 95.00 100.00 DO Dd 13 382718076062002 Kentuck-2 38.455000 -76.105556 2 PVC wire-wound 5.31 11.59 2.00 12.00
Hydrology 15

Surface-Water System

Over the period of record, specific conductance varies 

seasonally at the Cambridge and Key Wallace Drive gages, 

with maximum values in late October, and minimum values 

in May (figs. 11A and B). Annual peaks in specific conductance are observed approximately 2 months after annual peaks 

in surface-water temperature. These specific conductance 

patterns reflect the same seasonal trends typically seen in the 

Chesapeake Bay as the saltwater front moves up the Bay in 

the summer and out of the Bay in the spring in response to 

seasonal changes in freshwater inflow to the Bay. 

Specific conductance at the Key Wallace Drive and 

Cambridge gages ranged from 200 to 24,000 and 120 to 

13,000 μS/cm (microsiemens per centimeter), respectively 

(fig. 11A). For comparison, the specific conductance of 

seawater is typically about 50,000 μS/cm (Hem, 1985), and 

the range of specific conductance values in the freshwater 

portion of the Choptank River on the Delmarva Peninsula in 

685 samples between 1980 and 2009 ranged from 46 to 307 

μS/cm, with a median of 133 μS/cm (U.S. Geological Survey, 

2010).

Discharge calculated at Key Wallace Drive varies 

seasonally, with net negative discharge (more water flowing 

upstream than downstream) during the summer and fall 

seasons, and net positive discharge from the Little Blackwater 

River in the winter and spring (fig. 12). In water years 2008 

and 2009 (October 1, 2007 through September 30, 2009), 

annual net discharge was negative, meaning more water 

flowed into the watershed from the Blackwater River than 

flowed out to the Blackwater River. The annual net discharge 

in water year 2007 was positive, however. Given the high 

percentage of agricultural land use and significant amounts of 

riparian wetland vegetation, evapotranspiration (ET) is likely a 

major cause of groundwater flux out of the watershed. 

Figure 8. Groundwater levels in (A) wells DO Cd 64 (screen 

interval 3–13 feet below land surface [ft bls]), DO Cd 65 

(screen interval 70–75 ft bls), DO Cd 66 (screen interval 

124–129 ft bls), May 2008–August 2009, (B) wells DO Dd 12 

(screen interval 95–100 ft bls) and DO Dd 13 (screen interval 

2–12 ft bls), September 2007–September 2009, and (C) well DO 

Cd 1, 1960–2010, Dorchester County, Maryland.
16 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 9. (A) Groundwater levels in water-table wells, and cross sections of (B) winter and (C) summer groundwater-flow 

directions, October 2007–July 2009, Little Blackwater River watershed, Dorchester County, Maryland.
Water Quality 17

Water Quality

Water-quality samples were collected during 2007–08 

from 13 monitoring wells and during 2006–09 from 9 surfacewater sites to characterize pre-development conditions and 

seasonal variability. Continuous water-quality monitors were 

installed at both gaging stations (Cambridge and Key Wallace 

Drive) to measure temperature and specific conductance and 

observe the seasonality of brackish-water conditions in the 

Little Blackwater River between 2006 and 2009. 

Data Quality Assurance

Quality-assurance samples were collected during this 

study. Equipment blanks were collected to determine the 

potential for contamination of samples during the sampling, 

shipping, and laboratory handling procedures. Duplicate 

samples were collected to determine reproducibility, and ion 

balances were calculated to determine whether all appropriate 

major ions had been analyzed, and whether the analytical 

results were acceptable, and within generally accepted 

guidelines.

Blanks

Three field equipment blanks were collected during 

groundwater sampling, and one field equipment blank was collected during surface-water sampling to determine if there was 

a potential for contamination from the sampling equipment 

and filters, or if there was carryover contamination from previous samples (Appendix 3). One of the three blanks collected at 

the groundwater sites was analyzed for inorganic constituents 

Figure 10. Groundwater levels in wells DO Cd 58 and DO 

Cd 63, and surface-water elevations at the gage on the Little 

Blackwater River at Cambridge, Maryland, November 2007–

May 2008.

Figure 12. Discharge to and from the Little Blackwater River 

at Seward, Maryland on Key Wallace Drive, Dorchester County, 

Maryland, November 2006–September 2009.

Figure 11. Comparison of (A) specific conductance at the 

Cambridge gage and Key Wallace Drive gage, Maryland, and 

(B) temperature and specific conductance at the Key Wallace 

Drive gage, Maryland, November 2006–November 2009.
18 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

only, and the other two blanks were analyzed for both organic 

and inorganic constituents. The surface-water blank was analyzed for inorganic constituents only.

The inorganic blank groundwater samples had detectable 

concentrations of dissolved calcium that ranged from 0.02 

to 0.1 mg/L (milligrams per liter) (Appendix 3) whereas the 

environmental calcium sample concentrations ranged from 

1.1 to 95.5 mg/L. This indicates that up to about 10 percent 

of only the lowest calcium concentration may have been 

affected by sampling, handling, or laboratory procedures. Four 

other inorganic compounds were detected in concentrations 

near detection levels in at least one of the four blank samples 

for potassium, alkalinity, silica, and ammonia plus organic 

nitrogen. The potassium detection in the blank was less than 

0.5 percent of the lowest environmental concentration. The 

acid-neutralizing capacity (ANC) in two blanks was detected 

at estimated concentrations (4 mg/L) below the minimum 

reporting level of 5 mg/L, but was about half of the concentration of the lowest environmental sample at 9 mg/L, indicating 

that very low ANC concentrations may be reported at almost 

twice the actual value. 

Dissolved organic carbon (DOC) was detected in one 

surface-water blank at a concentration of 0.6 mg/L, whereas 

environmental concentrations in surface water ranged from 

7.4 to 47 mg/L, indicating the potential to add greater uncertainty in samples with very low DOC concentrations. There 

were no detections of any organic compounds from the two 

groundwater equipment blanks. The lack of detections indicated that there was no contamination, but the unexpected 

analytical results of sulfometuron-methyl in a groundwater 

sample from DO Dd 12 may suggest otherwise. 

Duplicates

Two duplicate groundwater sample pairs were collected 

to determine reproducibility of the inorganic analyses 

(Appendix 1). Both duplicate pairs were sampled within 15 

minutes after the original sample. Most constituents were 

consistent between the duplicate samples, with the exception 

of well DO Cd 63, when sulfate concentrations nearly doubled 

(from 4.7 to 7.4 mg/L) between the first and second samples. 

Relative percent differences (RPDs) were calculated between 

duplicate pairs for each inorganic parameter that had measurable concentrations in both sample pairs to describe the reproducibility of the values. The formula for calculating RPD is:

1 2

1 2

C C

(C C )

2

−

− *100

(1)

where C1 is the concentration of the parameter in the original 

sample and C2 is the concentration of the same parameter 

from the duplicate sample. With the exception of the one 

sulfate concentration mentioned above, RPDs from inorganic 

constituents ranged from 0 to 16.4 percent, with an average of 

5.1 percent, indicating good reproducibility even after 15 

minutes of pumping. These results show good reproducibility 

at the non-detect levels, but cannot address the reproducibility 

of the detected concentrations as found in other samples.

Ion Balances

The accuracy of major dissolved-constituent values in 

a reasonably complete chemical analysis of a water sample 

can be checked by calculating the cation-anion balance (Hem, 

1985). If the analytical work has been performed accurately, 

and if all major ions were analyzed, the difference between 

the two sums will generally not exceed approximately plus or 

minus 5 percent. The cation-anion balances, given in percent differences between total cations and total anions when 

converted to milliequivalents per liter (meq/L), are presented 

for each groundwater and surface-water sample (inorganic 

constituents) from the Little Blackwater River watershed in 

Appendixes 1 and 2, respectively. Ion balances for 69 surfacewater samples ranged from -15.4 to 10.9 percent, and averaged 

1.7 percent. Nine surface-water samples had ion balances that 

exceeded 5 percent. Ion balances for 20 groundwater samples 

ranged from -6.9 to 3.8 percent, with an average of -2 percent. 

Five of the 20 samples had ion balances between 5 and 6.9 

percent.

Groundwater Quality

Groundwater-quality samples were collected from 

nine monitoring wells in October 2007. Several wells were 

installed in the winter and spring of 2008, and nine wells, 

including the newest, were sampled during June 2008. The 

sets of parameters analyzed varied between the groundwater 

sampling rounds, but both included major ions and nutrients. 

The samples collected during June 2008 also were analyzed 

for concentrations of pesticides, pesticide degradates, and 

other organic compounds. Concentrations of inorganic constituents in the groundwater samples are shown in 

Appendix 1. Concentrations of organic compounds detected 

in groundwater and surface-water samples are shown in 

table 4. A list of organic compounds that were analyzed for, 

but not detected, is shown in table 5 along with detection 

levels.

Inorganic Constituents

Results from all major ion analyses from both groundwater and surface-water samples are shown in trilinear diagrams 

(fig. 13). Several patterns are apparent. Samples are grouped 

into four categories: shallow groundwater, deep groundwater, surface water in the upper basin and surface water in the 

lower basin. Deep groundwater samples (black squares) have 

higher values of bicarbonate, whereas shallow groundwater 

samples (red squares) have little to no bicarbonate. Boxplots 
Water Quality 19

Table 4. Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland, June 2008.—Continued[USGS, U.S. Geological Survey; ft., feet; gal/min, gallons per minute; mi2, square miles; mm, millimeters; Hg, mercury; μg/L, micrograms per liter; %, percent; --, data not available; dark shaded couplets indicate duplicate samples; Md., Maryland; <, less than; E, quantified above the long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty]

Station 

name

USGS 

station number Date Time

Depth of 

well 

(feet below land 

surface)

Altitude 

of land 

surface 

(feet)

Water level, 

depth below 

measuring 

point 

(feet)

Flow 

rate 

(gal/min)

Pumping 

period 

prior to 

sampling 

(minutes)

Drainage 

area 

(mi2)

Sampling 

depth 

(feet)

Barometric 

pressure, 

(mm Hg)

2,4-D plus 2,4-

D methyl ester, 

sum on a molar 

basis, 

(μg/L as 2,4-D)

2,4-D 

(μg/L)

Surface-water sites

Christ’s Rock 01490112 6/10/2008 1230 -- 5 -- -- -- 8.29 -- 759 <0 <.02Maple Dam 

Bridge 01490113 6/10/2008 0740 -- 2.9 -- -- -- 1.46 -- 759 0.07 0.07

Tributary near 

Cambridge, Md.

01490116 6/10/2008 1245 -- 6 -- -- -- 4.19 -- 759 <0 <.02

River near 

Cambridge, Md.

01490120 6/10/2008 1130 -- -1.25 -- -- -- 15.3 -- 759 0.08 0.08

Groundwater sites

DO Cd 56 383122076055701 06/11/2008 0815 13.5 9.5 6.44 0.29 -- -- 11.5 -- <0 <.02DO Cd 59 383118076054601 6/10/2008 1520 13.1 7.28 -- 0.73 -- -- 13.1 -- <0 <.02DO Cd 61 383112076053501 6/10/2008 1100 13.2 3.68 4.05 0.572 0.5 -- 13.2 -- <0 <.02DO Cd 63 383112076053503 6/10/2008 1030 53.2 3.12 -- 0.83 50 -- 51.5 -- <0 <.02DO Cd 63 383112076053503 6/10/2008 1045 53.2 3.12DO Cd 64 383100076061101 06/11/2008 1555 13 10.18 -- -- -- -- 15 766 <0 <.02DO Cd 66 383100076061103 06/11/2008 1500 129.5 10.34 -- 4.68 -- -- 0 -- <0 <.02DO Cd 68 383051076054201 06/11/2008 1050 15 5 5.52 -- -- -- 0 -- <0 <.02DO Dd 12 382718076062001 06/09/2008 1345 99.7 5.26 15.04 0.88 -- -- 90 -- <0 <.02DO Dd 13 382718076062002 06/09/2008 1610 12 5.31 -- 1.09 -- -- 9.5 -- <0 <.02
20 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Table 4. Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland, June 2008.—Continued [USGS, U.S. Geological Survey; ft., feet; gal/min, gallons per minute; mi2, square miles; mm, millimeters; Hg, mercury; μg/L, micrograms per liter; %, percent; --, data not available; dark shaded couplets indicate duplicate samples; Md., Maryland; <, less than; E, quantified above the long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty] Station name 2-Chloro-4- isopropylamino-6- amino-s-triazine, (μg/L CIAT) 2-Chloro-6-ethyl- amino-4-aminos-triazine (μg/L) 2-Hydroxy-4-isopro- pylamino-6-ethyl- amino-s-triazine (μg/L) Aceto- chlor (μg/L) Ala- chlor (μg/L) Atrazine (μg/L) Caffeine (μg/L) Carbaryl1, (μg/L) Carbaryl2, (μg/L) Carbofu- ran (μg/L) Chlorimur- on-ethyl (μg/L) Desulfi- nylfipronil, μg/L Surface-water sites Christ’s Rock E.167 E.030 0.88 <.0164 0.016 0.732 E.05 <.04 E.01 <.02 <.08 E.002 Maple Dam Bridge E.023 <.08 <.04 <.006 <.006 0.044 <.06 E.01 E.01 <.02 <.08 E.007 Tributary near Cambridge, Md. E.210 E.050 0.84 <.006 <.006 0.917 0.07 <.04 <.06 <.02 E.02 E.002 River near Cambridge, Md. E.239 E.055 0.76 0.028 0.014 1.100 0.13 <.04 E.01 <.02 E.02 E.002 Groundwater sites DO Cd 56 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 59 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 61 <.014 <.08 <.04 <.006 <.006 0.009 <.06 <.04 <.06 <.0210 <.08 <.012 DO Cd 63 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 63 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 64 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 66 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Cd 68 E.009 <.08 <.04 <.006 <.006 0.019 <.06 <.04 <.06 <.02 <.08 <.012 DO Dd 12 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012 DO Dd 13 <.014 <.08 <.04 <.006 <.006 <.007 <.06 <.04 <.06 <.02 <.08 <.012
Water Quality 21

Table 4. Concentrations of organic compounds detected in surface-water and groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland, June 2008.—Continued[USGS, U.S. Geological Survey; ft., feet; gal/min, gallons per minute; mi2, square miles; mm, millimeters; Hg, mercury; μg/L, micrograms per liter; %, percent; --, data not available; dark shaded couplets indicate duplicate samples; Md., Maryland; <, less than; E, quantified above the long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty]

Station 

name

Disulfoton 

(μg/L)

Diuron 

(μg/L)

Desulfinyl 

fipronil 

amide 

(μg/L)

Fipronil 

sulfide

(μg/L)

Fipronil 

sulfone 

(μg/L)

Fipronil 

(μg/L)

Metolachlor 

(μg/L)

Picloram 

(μg/L)

Prometon 

(μg/L)

Siduron 

(μg/L)

Simazine 

(μg/L)

Sulfometuronmethyl

(μg/L)

Triclopyr

(μg/L)

Surface-water sites

Christ’s Rock <.04 E.0139 E.002 E.010 E.017 E.005 1.240 -- 0.034 <.02 0.239 <.06 <.08Maple Dam 

Bridge <.04 <.04 E.005 E.008 E.019 E.027 0.058 -- 0.064 0.04 0.015 <.06 E.0571

Tributary near 

Cambridge, Md.

<.04 E.0255 E.002 E.008 E.015 E.006 1.210 -- <.008 <.02 0.309 <.06 <.08

River near 

Cambridge, Md.

<.04 E.0217 E.002 E.007 E.011 E.006 1.260 -- <.008 <.02 0.391 <.06 <.08

Groundwater sites

DO Cd 56 <.04 <.04 <.029 <.013 <.024 <.02 <.010 -- <.008 <.02 <.006 E.08 <.08DO Cd 59 <.04 <.04 <.029 <.013 <.024 <.02 <.010 -- <.008 <.02 <.006 <.06 <.08DO Cd 61 <.04 <.04 <.029 <.013 <.024 <.02 0.030 <.12 <.008 <.02 <.006 <.06 <.08DO Cd 63 <.0863 <.04 <.029 <.013 <.024 <.02 <.010 <.12 <.008 <.02 <.006 <.06 <.08DO Cd 63 <.0863 <.04 <.029 <.013 <.024 <.02 <.010 <.12 <.008 <.02 <.006 <.06 <.08DO Cd 64 <.04 <.04 <.029 <.013 <.024 <.02 0.020 -- <.008 <.02 <.006 <.06 <.08DO Cd 66 <.04 <.04 <.029 <.013 <.024 <.02 <.010 -- <.008 <.02 <.006 <.06 <.08DO Cd 68 <.04 <.04 <.029 <.013 <.024 <.02 0.026 -- <.008 <.02 E.005 <.06 <.08DO Dd 12 <.04 <.04 <.029 <.013 <.024 <.02 <.010 <.12 <.008 <.02 <.006 0.10 <.08DO Dd 13 <.04 <.04 <.029 <.013 <.024 <.02 <.010 <.12 <.008 <.02 <.006 <.06 <.08

1 Carbaryl concentration from high-performance liquid chromatography (HPLC).2 Carbaryl concentration from gas chromatography-mass spectrometry (GCMS).

 Note: See table 5 for list of compounds that were not detected.
22 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Table 5. Dissolved organic compounds analyzed for, but not detected, in surface-water and groundwater samples, Little Blackwater 

River watershed, Dorchester County, Maryland.

[<, less than; all concentrations in micrograms per liter, filtered through glass-fiber filter with 0.7-micron opening; see Appendixes 1 and 2 for detected 

concentrations]

Compound

Minimum 

reporting limit

Compound

Minimum 

reporting 

limit

Compound

Minimum 

reporting limit

Compound

Minimum 

reporting limit

2,4-D methyl ester <.04 cis-Permethrin <.01 Lindane <.006 Parathion <.010

2,4-DB <.02 Cyanazine <.02 Linuron1 <.04 Pebulate <.004

2,6-Diethylaniline <.002 Cycloate <.02 Linuron2 <.06 Pendimethalin <.012

3-Hydroxy carbofuran <.04 Dacthal monoacid<.02 Malathion <.016 Phorate <.04

Acifluorfen <.04 DCPA <.003 MCPA <.06 Propyzamide <.004

Aldicarb sulfone <.08 Diazinon <.005 MCPB <.06 Propachlor <.006

Aldicarb sulfoxide <.06 Dicamba <.04 Metalaxyl <.02 Propanil <.006

Aldicarb <.12 Dichlorprop <.02 Methiocarb <.04 Propargite <.04

alpha-HCH <.002 Dieldrin <.009 Methomyl <.12 Propham <.04

Azinphos-methyl <.12 Dinoseb <.04 Methyl parathion <.008 Propiconazole <.04

Bendiocarb <.04 Diphenamid <.04 Metribuzin <.012 Propoxur <.04

Benfluralin <.004 EPTC <.002 Metsulfuron-methyl <.14 Tebuthiuron <.016

Benomyl <.04 Ethalfluralin <.009 Molinate <.002 Terbacil2 <.018

Bensulfuron-methyl <.06 Ethoprop <.012 N-(4-Chlorophenyl)-N’-methylurea<.12 Terbacil1 <.04

Bentazon <.04 Fenuron <.04 Napropamide <.018 Terbufos <.018

Bromacil <.02 Flumetsulam <.06 Neburon <.02 Thiobencarb <.010

Bromoxynil <.12 Fluometuron <.04 Nicosulfuron <.1 Triallate <.006

Butylate <.002 Fonofos <.01 Norflurazon <.02 Trifluralin <.006

Chloramben methyl 

ester

<.1 Imazaquin <.04 Oryzalin <.04

Chlorpyralid <.06 Imazethapyr <.04 Oxamyl <.12

Chlorpyrifos <.005 Imidacloprid <.06 p,p’-DDE <.003

1

 Concentration from high-performance liquid chromatography (HPLC).

2

 Concentration from gas chromatography-mass spectrometry (GCMS).
Water Quality 23

of samples grouped into the same categories in figure 13 are 

shown in figure 14. Silica shows the highest mean and range 

in both groundwater groups, as would be expected. Manganese 

and iron are highest in shallow groundwater. Calcium has the 

highest mean in deep groundwater, which is consistent with 

the shell material found in the deep cores. Deep wells (greater 

than 15 ft bls) have higher nitrogen concentrations (2.32–6.89 

mg/L) than shallow (less than 15 ft bls) wells (0.26–0.95 

mg/L). The exception is well DO Cd 66, screened from 

124–129 ft bls with a nitrogen concentration of 0.66 mg/L. 

The other inorganic constituents in figure 14 are relatively low 

compared to the lower basin surface-water samples.

The pH in shallow groundwater is relatively low—around 

4—and increases with depth to over 7 at 130 ft deep (fig. 15). 

Several samples collected from water-table wells screened 

in more silty sediments have pH values around 5 (fig. 15). 

As noted in Ator and others (2005), shallow groundwater 

quality in Coastal Plain lowlands can be acidic in areas with 

weathered organic matter and higher quartz content in sediments. These characteristics, along with the low observed dissolved oxygen and reducing conditions contribute to the low 

values of nitrate in the shallow groundwater. 

Chloride concentrations in the shallow groundwater 

increase with proximity to the Little Blackwater River. The 

wells closest to the river, DO Cd 61 and DO Cd 68, located 

500 and 250 ft from the Little Blackwater River, respectively, 

have chloride concentrations over 381 mg/L and 219 mg/L. 

For reference, the U.S. Environmental Protection Agency 

Secondary Maximum Contaminant Level (SMCL) for chloride 

based on taste is 250 mg/L (U.S. Environmental Protection 

Agency, 2009). In observed monthly water-level measurements, there are seasonal gradient reversals between the water 

levels in wells DO Cd 61 and DO Cd 68 and the stage of the 

Little Blackwater River. These higher chloride concentrations 

are likely caused by infiltration of brackish river water into the 

shallow groundwater-flow system close to the river.

Figure 13. Trilinear diagrams showing chemical characteristics of inorganic constituents in surface water and 

groundwater, Little Blackwater River watershed, Dorchester County, Maryland.
24 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 14. Boxplots showing inorganic constituents in surface water and groundwater, Little Blackwater River watershed, 

Dorchester County, Maryland.
Water Quality 25

Organic Constituents

Groundwater samples were collected and analyzed for 

pesticides from nine wells on June 9–11, 2008 (table 4). The 

commonly used herbicides atrazine, metolachlor, simazine, 

sulfometuron-methyl, and the atrazine degradate 2-chloro-4-

isopropylamino-6-amino-s-triazine (CIAT) were detected at 

low concentrations (0.03 mg/L or less) in up to three of nine 

shallow wells that ranged in depth from 12 to 15 ft (table 4). 

One deeper well (DO Dd 12, 99.7 ft) had a single detection 

(0.10 mg/L) of the herbicide sulfometuron-methyl. The 

detection of sulfometuron-methyl in well DO Dd 12 may be 

due to contamination during sampling or laboratory analysis, 

and should be confirmed with subsequent sampling because 

sulfometuron-methyl is used far less than the other herbicides 

in Dorchester County (Maryland Department of Agriculture, 

2002), and no other herbicides or insecticides were detected in 

that well. The detection was probably not caused by drilling 

because the shallow well at that location showed no concentrations of that compound. 

Surface-Water Quality

Surface-water-quality samples were collected during 

storm events and also on a seasonal basis. Storm event 

sampling occurred on October 6, 2006 and again on April 16, 

2007. Quarterly samples were taken from March 2006 through 

October 2007. A final sampling effort was conducted in June 

2008. 

Inorganic Constituents

Major ions were sampled in surface water at several 

sites within the watershed (fig. 2). Results of surface-water 

and groundwater inorganic analyses are plotted on a trilinear 

diagram (fig. 13). The samples are separated into four groups: 

shallow groundwater, deep groundwater, surface water from 

the upper basin, and surface water from the lower basin. 

Surface-water samples from the lower half of the Little 

Blackwater River watershed have consistently higher chloride 

concentrations than the upper part of the watershed, with a 

maximum concentration of 5,870 mg/L at the southernmost 

site, 01490140. The lower (southern) part of the watershed 

is under a strong tidal influence, not only in stage but also in 

terms of brackish-water mixing. Daily and seasonal variations in specific conductance at the mouth of the river (site 

1490140) and near the middle of the watershed (site 1490120) 

are shown in figure 11A. Both gage sites have strong seasonal 

variations in specific conductance, but the magnitude of the 

seasonal variation decreases further upstream in the watershed. Boxplots of selected inorganic constituents for surfacewater sampling sites are shown in figure 16. Sites 1490140, 

1490130, and 1490120, in the lower basin, show the greatest 

range of values for constituents associated with seawater. 

Ranges of silica, iron, and manganese are greatest at the 

surface-water sites in the upper basin where base flow from 

shallow groundwater contributes more significantly to overall 

streamflow. 

Surface-water samples are further grouped into summer 

(June through November) and winter (December through 

May) samples in the upper and lower basin (fig. 17). During 

the winter months, when the water table is higher, the Little 

Blackwater River is discharging freshwater. As such, upper 

and lower basin inorganic constituents do not vary significantly. However, in summer months, the upper basin has 

higher mean values for iron, manganese, and silica, likely 

caused by a greater portion of total streamflow coming from 

groundwater. 

There is a significant change in water chemistry in the 

lower basin from winter to summer. Constituents typically 

found in seawater are observed in much greater concentrations in the lower basin during summer (fig. 17). The source of 

seawater in the Little Blackwater River is from Fishing Bay, 

which flows through the BNWR. 

Organic Constituents

Surface-water samples were collected and analyzed for 

pesticides only once at four surface-water sites on June 10, 

2008 (table 4). This single sampling effort cannot address 

either variability or seasonality of the results, and is only representative of conditions at that time. The herbicides atrazine, 

metolachlor, and simazine, and the insecticide fipronil, were 

detected at each of the four surface-water sites. Atrazine, 

metolachlor, and simazine were 3 of 16 pesticides that were 

commonly found in surface waters of the Mid-Atlantic region 

Figure 15. pH compared to well depth for all groundwater 

wells sampled, Little Blackwater River watershed, 

Dorchester County, Maryland.
26 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Figure 16. Boxplots showing inorganic constituents at surface-water sites, Little Blackwater River watershed, Dorchester 

County, Maryland.
Water Quality 27

Figure 17. Boxplots showing summer (June through November) and winter (December through May) inorganic constituents in 

the upper and lower basin, Little Blackwater River watershed, Dorchester County, Maryland.
28 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

by Ferrari and others (1997), and were commonly used in 

Dorchester County in 2000, the latest date for which county 

pesticide usage data are available (Maryland Department of 

Agriculture, 2002). 

Atrazine is a commonly detected herbicide in surface 

water and was detected at concentrations up to 1.1 mg/L. 

In addition, three compounds that are atrazine degradates 

(2-Chloro-4-isopropylamino-6-amino-s-triazine [CIAT], 

2-Chloro-6-ethylamino-4-amino-s-triazine, and 2-Hydroxy-4-

isopropylamino-6-ethylamino-s-triazine) also were detected at 

three of the four sites. For comparative purposes, the USEPA 

Maximum Contaminant Level (MCL) for atrazine in drinking water is 3 mg/L (U.S. Environmental Protection Agency, 

2009). Commonly used pesticides in Dorchester County in 

2000 that were also detected in surface water during this study 

were alachlor, atrazine, metolachlor, and simazine (Maryland 

Department of Agriculture, 2002). Metalachlor and simazine 

are pre-emergent herbicides and are commonly used in much 

of the Delmarva Peninsula (Ator and others, 2004; Maryland 

Department of Agriculture, 1999, 2002). Fipronil is an insecticide commonly used on termites and fleas, and was found at 

estimated concentrations below the minimum reporting level. 

Fipronil was not reported to have been used in the County in 

2000, but was reported to have been used in adjacent counties 

(Maryland Department of Agriculture, 2002). Usage patterns 

may have changed between 2000, when the latest county-wide 

data on pesticide usage are available, and 2008, when samples 

were collected in the Little Blackwater River watershed.

Ator and others (2004) analyzed the seasonal variability 

of atrazine and metalachlor in two streams on the Delmarva 

Peninsula, and found that seasonal variability in pesticide 

concentrations in surface water is related to application patterns and that concentrations were generally highest in the 

growing season but were detectable throughout the year. 

Concentrations of pesticides found in the Little Blackwater 

River during this study were similar to concentrations found 

by Ator and others (2004) in the Pocomoke River between 

Wicomico and Worcester Counties, and in Chesterville Branch 

in Kent County, Maryland. 

Summary and Conclusions

 The goals of this study were to (1) document geochemical conditions in the shallow groundwater system and the 

Little Blackwater River prior to potential land-use changes, 

and (2) characterize the hydrology of the watershed, looking 

at both the tidal and seasonal variability of surface water and 

groundwater. The lithologic variability in the subsurface of the 

Little Blackwater watershed suggests an inherently complex 

hydrogeologic regime. Preferential pathways for groundwater 

flow in the shallow sediments are generally quite thin and 

lack significant lateral continuity. Areas where Pleistocene 

erosion and deposition did not have an impact on the deeper 

stratigraphy have a thicker and more complete section of the 

low-permeability beds of the upper Choptank Formation.

Much of the complexity within the shallow groundwater 

system is due to the heterogeneous nature of the surficial sediments. Extensive ditching along agricultural fields can create 

artificial flowpaths that circumvent the typical topographically 

driven groundwater-flow system. The tidal nature of the Little 

Blackwater River also affects groundwater fluxes, and because 

of the wide expanse of open water within the Blackwater 

National Wildlife Refuge, southerly winds can increase river 

stage well into the headwater areas of the basin, creating 

temporary, localized reversals in shallow groundwater-flow 

directions close to the river. 

Water-table wells in the study area generally have water 

levels slightly above sea level, with seasonal variations of 

several feet. Horizontal hydraulic gradients are persistent 

throughout all seasons and indicate groundwater flow towards 

the Little Blackwater River. Lower seasonal groundwater 

levels in shallow wells close to the river during late summer 

and fall indicate a localized gradient reversal from the Little 

Blackwater River. 

Discharge calculated at the lower gage varies seasonally, 

with net negative discharge (more water flowing upstream than 

downstream) from June through November and net positive 

discharge from the Little Blackwater River from December 

through May. Given the high percentage of agricultural land 

use and significant amounts of riparian wetland vegetation, 

evapotranspiration is likely the major flux of freshwater out 

of the watershed during the summer. In the summer months, 

brackish water encroaches up the Little Blackwater River from 

the Blackwater National Wildlife Refuge and Fishing Bay. 

Water samples were collected during 2007–08 from 13 

monitoring wells and during 2006–09 from 9 surface-water 

sites to characterize pre-development conditions and seasonal 

variability of inorganic constituents and nutrients. Pesticide 

samples were collected from nine wells and four surfacewater sampling sites in June 2008. The herbicides atrazine, 

metolachlor, and simazine, and the insecticide fipronil, were 

detected at each of the four surface-water sampling sites. 

With the exception of sulfometuron-methyl, concentrations of 

pesticides found in the groundwater were typically one to two 

orders of magnitude lower than pesticide concentrations found 

in the Little Blackwater River during the same time period. 

Concentrations and the type of compounds found in the Little 

Blackwater River were similar to concentrations and compound types found in other investigations in the Pocomoke 

River between Wicomico and Worcester Counties, and in 

Chesterville Branch in Kent County, Maryland. Nitrogen concentrations were higher in deep groundwater than in shallow 

groundwater. Chloride concentrations in the water-table wells 

increase with proximity to the Little Blackwater River.

It is unclear what implications land-use change from 

agricultural to residential would have on the water quality in 

the Little Blackwater River watershed. Changes in land use 
Selected References 29

will likely affect the applications of pesticides, road salts, and 

nutrients within the watershed. These potential impacts are 

subjects for future studies. 

Seasonal hydraulic-gradient reversals between the Little 

Blackwater River and the water table, coincident with a 

seasonal increase in specific conductance and chloride in the 

Little Blackwater River, along with elevated chloride in nearriver water-table wells indicate saltwater intrusion into the 

shallow groundwater system during summer and fall months. 

Sea level rise could exacerbate the impacts to saltwater 

intrusion in the future. However, the mechanisms affecting 

saltwater intrusion into the shallow groundwater system are 

beyond the scope of this study and can be the subject of further investigations. 

Acknowledgments

The authors would like to thank the Edgar family for 

allowing us to install and maintain a stream gage on their 

property, and USGS employees Jessica Teunis, Deborah 

Bringman, Michael Brownley, Anthony Tallman, and Douglas 

Yeskis for their sampling and data-collection efforts, and 

Wayne Newell for technical input for the geologic interpretation. The authors would also like to thank Michael Brayton 

and Gary Lauben of the USGS for assistance with geophysical 

surveys. The authors also thank the following personnel from 

other agencies and organizations who assisted in field logistical support and provided technical input during the completion 

of this project: Diane Cole and James Newcomb (Dorchester 

Soil Conservation District); Rebecca Fox and Thomas Fisher 

(University of Maryland, Horn Point Laboratory); William 

Giese, Dixie Birch, and Suzanne Baird (U.S. Fish and Wildlife 

Service, Chesapeake Marshlands Wildlife NWR Complex); 

and Gary Setzer (Maryland Department of the Environment).

Selected References

Ator, S.W., Denver, J.M., and Brayton, M.J., 2004, Hydrologic 

and geochemical controls on pesticide and nutrient transport 

to two streams on the Delmarva Peninsula: U.S. Geological 

Survey Scientific Investigations Report 2004–5051, 34 p., 

available online at http://pubs.usgs.gov/sir/2004/5051/.

Ator, S.W., Denver, J.M., Krantz, D.E., Newell, W.L., and 

Martucci, S.K., 2005, A surficial hydrogeologic framework 

for the Mid-Atlantic Coastal Plain: U.S. Geological Survey 

Professional Paper 1680, 44 p., available online at 

http://pubs.usgs.gov/pp/2005/pp1680/.

Cole, W.D., 2008, The Little Blackwater River watershed 

management plan: From city headwaters to National 

Wildlife Refuge: Cambridge, Maryland, Dorchester Soil 

Conservation District, 58 p., accessed October 27, 2009, at 

http://www.ci.cambridge.md.us/uploads/images/Planning_

Zoning/Draft_Little_Blackwater_Mgmt_Plan.pdf.

Cushing, E.M., Kantrowitz, I.H., and Taylor, K.R., 1973, 

Water resources of the Delmarva Peninsula: 

U.S. Geological Survey Professional Paper 822, 58 p. 

deVerteuil, L., and Norris, G., 1996, Miocene dinoflagellate 

stratigraphy and systematics of Maryland and Virginia: 

Micropaleontology, v. 42, supplement, p. 1–172.

Denny, C.S., and Owens, J.P., 1978, Sand dunes on the central 

Delmarva Peninsula, Maryland and Delaware: 

U.S. Geological Survey Professional Paper 1067–C, 15 p.

Denny, C.S., Owens, J.P., Sirken, L.A., and Rubin, M., 1979, 

The Parsonsburg Sand in the central Delmarva Peninsula, 

Maryland and Delaware: U.S. Geological Survey 

Professional Paper 1067–B, 16 p.

Ferrari, M.J., Ator, S.W., Blomquist, J.D., and Dysart, J.E., 

1997, Pesticides in surface water of the Mid-Atlantic 

Region: U.S. Geological Survey Water-Resources 

Investigations Report 97–4280, 12 p.

French, H.M., 2007, The periglacial environment (3d ed.): 

Chichester, United Kingdom, John Wiley and Sons Ltd., 

458 p. 

French, Hugh, Demitroff, Mark, and Newell, W.L., 2009, 

Past permafrost on the Mid-Atlantic Coastal Plain, eastern 

United States: Permafrost and Periglacial Processes v. 20, 

no. 3, p. 285–294, DOI: 10.1002/ppp.659.

Gernant, R.E., 1970, Paleoecology of the Choptank Formation 

(Miocene) of Maryland and Virginia: Maryland Geological 

Survey Report of Investigations No. 12, 90 p.

Hem, 1985, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey WaterSupply Paper 2254, 263 p.

Klohe, C.A., and Feehley, C.E., 2001, Hydrogeology and 

ground-water quality of the Piney Point-Nanjemoy and 

Aquia aquifers, Naval Air Station Patuxent River and 

Webster Outlying Field, St. Mary’s County, Maryland: U.S. 

Geological Survey Water-Resources Investigations Report 

01–4029, 51 p., available online at http://pubs.usgs.gov/wri/

wri01–4029/.

Larsen, Curt, Clark, Inga, Guntenspergen, Glenn, Cahoon, 

Don, Caruso, Vincent, Hupp, Cliff, and Yanosky, Tom, 

2004, The Blackwater NWR inundation model. Rising sea 

level on a low-lying coast: Land use planning for wetlands: 

U.S. Geological Survey Open-File Report 04–1302, online 

only, available at http://pubs.usgs.gov/of/2004/1302/.
30 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Markewich, H.W., Litwin, R.J., Pavich, M.J., and Brook, 

G.A., 2009, Late Pleistocene eolian features in southeastern 

Maryland and Chesapeake Bay region indicate strong 

WNW–NW winds accompanied growth of the Laurentide 

Ice Sheet: Quaternary Research, v. 71, no. 3, p. 409–425, 

doi: 10.1016/j.yqres.2009.09.003.

Maryland Department of Agriculture, 1999, Maryland 

pesticide statistics for 1997: Maryland Department of 

Agriculture Report MDA–265–99, 56 p.

Maryland Department of Agriculture, 2002, Maryland 

pesticide statistics for 2000: Maryland Department of 

Agriculture Report MDA–265–02, 45 p.

Milheim, L.E., Jones, J.W., and Barlow, R.A., 2007, 

Development of an impervious-surface database for the 

Little Blackwater River watershed, Dorchester County, 

Maryland: U.S. Geological Survey Open-File Report 

2007–1308, 6 p., available online at http://pubs.usgs.gov/

of/2007/1308/ofr2007-1308.pdf.

Mixon, R.B., Berquist, C.R., Jr., Newell, W.L., Johnson, 

G.H., Powars, D.S., Schindler, J.S., and Rader, E.K., 1989, 

Geological map and generalized cross sections of the 

Coastal Plain and adjacent parts of the Piedmont, Virginia, 

IMAP: U.S. Geological Survey Numbered Series, 1 sheet.

Newell W.L., and Clark Inga, 2008, Geomorphic map of 

Worcester County, Maryland, interpreted from a LIDARbased digital elevation model: U.S. Geological Survey 

Open-File Report 2008–1005, 34 p., 2 pls., available online 

at http://pubs.usgs.gov/of/2008/1005/.

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits 

of the central Delmarva Peninsula, Maryland and Delaware: 

U.S. Geological Survey Professional Paper 1067–A, 28 p.

Owens, J.P., and Denny, C.S., 1986, Geologic map of 

Dorchester County, Maryland: Baltimore, Maryland, 

Maryland Geological Survey, 1 sheet, scale 1:62,500.

Phelan, D.J., 1987, Water levels, chloride concentrations, and 

pumpage in the coastal aquifers of Delaware and Maryland: 

U.S. Geological Survey Water-Resources Investigations 

Report 87–4229, 106 p.

Sirkin, L.A., Denny, C.S., and Rubin, M., 1977, Late 

Pleistocene environment of the central Delmarva 

Peninsula, Delaware-Maryland: Geological Society 

of America Bulletin, v. 88, no. 1, p. 139–142, doi: 

10.1130/0016-7606(1977)88<139:LPEOTC>2.0.CO;2

Smoot, J.P., Newell, W.L., and DeJong, B.D., 2009, 

Investigation into the origin and character of surficial 

sedimentary deposits at the Midshore Regional Solid Waste 

Facility near Easton, Maryland: U.S. Geological Survey 

Open-File Report 2009–1052, 64 p., available online only at 

http://pubs.usgs.gov/of/2009/1052/.

Trapp, Henry, Jr., Knobel, L.L., Meisler, Harold, and Leahy, 

P.P., 1984, Test Well DO-Ce 88 at Cambridge, Dorchester 

County, Maryland: U.S. Geological Survey Water-Supply 

Paper 2229, 48 p.

U.S. Environmental Protection Agency, 2009, 2009 Edition 

of the drinking water standards and health advisories: U.S. 

Environmental Protection Agency, EPA 822-R-09-011, 

Office of Water, accessed February 02, 2011, at http://water.

epa.gov/action/advisories/drinking/drinking_index.cfm.

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9, available online at http://pubs.water.usgs.

gov/twri9A.

U.S. Geological Survey, 2010, National Water Information 

System data available on the World Wide Web (Water 

Data for the Nation), accessed January 20, 2010, at http://

waterdata.usgs.gov/nwis/.

Waelbroeck, C., Labeyrie, L., Michel, E., Duplessy, J.C., 

McManus, J.F., Lambeck, K., Balbon, E., and Labracherie, 

M., 2002, Sea-level and deep water temperature changes 

derived from benthic foraminifera isotopic records: 

Quaternary Science Reviews, v. 21, nos. 1–3, p. 295–305, 

doi: 10.1016/S0277-3791(01)00101-9.
Appendixes 1–8 31

Appendixes 1–8
32 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 1. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland. [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; CaCO3, calcium carbonate; SiO2, silica; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Water Quality Laboratory] USGS well number USGS well name Date Time Depth of well (feet below land surface) Altitude of land surface (ft) Water level, depth below measur- ing point (ft) Pump flow rate (gal/ min) Pump period (minutes) Sampling depth (ft) Turbidity (FNU) Carbon dioxide, dissolved (mg/L) Dissolved oxygen (mg/L) pH, field pH, lab 383122076055701 DO Cd 56 10/30/2007 1135 13.5 9.50 8.48 -- -- -- -- -- 1.2 4.2 3.8 383122076055701 DO Cd 56 06/11/2008 0815 13.5 9.50 6.44 0.3 -- 11.5 -- -- 0.9 4.1 3.9 383122076055702 DO Cd 57 10/31/2007 1240 22.0 9.85 8.4 -- -- -- -- -- 2.8 6.3 6.5 383122076055703 DO Cd 58 10/30/2007 1515 94.0 9.43 14.9 0.3 -- -- -- -- -- 7.3 7.2 383118076054601 DO Cd 59 10/30/2007 1445 13.1 7.28 8.53 0.1 -- -- -- -- 0.1 5.1 3.7 383118076054601 DO Cd 59 06/10/2008 1520 13.1 7.28 -- 0.7 -- 13.1 -- -- 0.4 4.2 4.1 383118076054602 DO Cd 60 10/31/2007 1158 19.2 7.11 7.75 -- -- 7.8 -- 0.9 6.2 6.2 383112076053501 DO Cd 61 10/31/2007 1110 13.2 3.68 -- 0.2 -- -- -- -- -- 4.0 3.9 383112076053501 DO Cd 61 10/31/2007 1115 13.2 3.68 -- -- -- -- -- -- -- -- 3.9 383112076053501 DO Cd 61 06/10/2008 1100 13.2 3.68 4.05 0.6 0.5 13.2 -- -- 2.3 3.8 4.0 383112076053502 DO Cd 62 10/31/2007 1029 19.4 3.81 4.61 -- -- 9 -- -- 6.3 6.5 383112076053503 DO Cd 63 10/31/2007 1225 53.2 3.12 8.01 1.1 -- 46.18 6 -- -- 7.1 7.5 383112076053503 DO Cd 63 06/10/2008 1030 53.2 3.12 -- 0.8 50 51.5 -- 95 0.2 7.1 7.3 383112076053503 DO Cd 63 06/10/2008 1045 53.2 3.12 -- 0.1 65 51.5 -- -- 0.0 7.1 7.3 383100076061101 DO Cd 64 06/11/2008 1555 13.0 10.18 -- -- -- -- -- 124 0.7 5.3 5.8 383100076061103 DO Cd 66 06/11/2008 1500 129.5 10.34 -- 4.7 -- -- -- 46 0.1 7.4 7.5 383051076054201 DO Cd 68 06/11/2008 1050 15.0 5.00 5.52 -- -- -- -- -- 0.3 4.3 3.9 382718076062001 DO Dd 12 10/31/2007 0915 99.7 5.26 16.01 0.4 -- 5.47 -- -- -- 7.3 7.4 382718076062001 DO Dd 12 06/09/2008 1345 99.7 5.26 15.04 0.9 -- 90 -- 64 0.3 7.1 7.3 382718076062002 DO Dd 13 06/09/2008 1610 11.6 5.31 -- 1.1 -- 9.5 -- 97 0.4 5.2 5.6
Appendixes 1–8 33

Appendix 1. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; CaCO3, calcium carbonate; SiO2, silica; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Water Quality Laboratory]

USGS 

well name Date Time

Specific 

conductance, lab 

(μS/cm)

Specific 

conductance, 

field 

(μS/cm)

Temperature, 

water 

(°C)

Hardness 

(mg/L as 

CaCO3)

Noncarbonate 

hardness, 

dissolved, 

field (mg/L 

as CaCO3)

Noncarbonate 

hardness, 

dissolved, 

lab (mg/L 

as CaCO3)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Potassium, 

dissolved 

(mg/L)

Sodium, 

adsorption 

ration

Sodium 

fraction of 

cations (% 

equivalent 

of major 

cations)

DO Cd 56 10/30/2007 1135 657 606 14.7 173 -- -- 19.1 30.4 4.0 1.0 26.9DO Cd 56 06/11/2008 0815 724 677 19.8 120 -- -- 14.9 20.0 2.9 2.7 54.7DO Cd 57 10/31/2007 1240 400 443 17.1 118 -- -- 19.9 16.6 8.3 1.3 34.7DO Cd 58 10/30/2007 1515 1,204 1,192 15.1 466 55.2 -- 95.5 55.2 22.6 1.6 26.3DO Cd 59 10/30/2007 1445 626 546 16.7 114 99.1 -- 19.1 16.0 3.9 1.4 39.2DO Cd 59 06/10/2008 1520 518 542 22.2 115 -- -- 15.6 18.3 2.4 1.6 41.9DO Cd 60 10/31/2007 1158 376 439 18.0 103 -- -- 18.9 13.4 6.1 1.3 38.1DO Cd 61 10/31/2007 1110 1,062 1,059 18.9 96 -- -- 11.8 16.1 4.4 6.1 74.6DO Cd 61 10/31/2007 1115 1,060 -- -- -- -- -- 13.5 16.8 4.4 -- --DO Cd 61 06/10/2008 1100 1,370 1,320 21.4 132 -- -- 15.4 22.8 4.7 6.9 74.1DO Cd 62 10/31/2007 1029 1,013 1,048 18.5 77 -- -- 13.6 10.4 6.8 9.1 82.4DO Cd 63 10/31/2007 1225 1,205 1,217 15.2 199 -- -- 36.1 26.4 17.4 6.1 66.1DO Cd 63 06/10/2008 1030 1,220 1,241 19.6 205 -- -- 36.5 27.7 18.7 6.0 65.4DO Cd 63 06/10/2008 1045 1,230 1,240 19.6 -- -- -- 37.7 28.8 19.0 -- --DO Cd 64 06/11/2008 1555 231 231 23.2 43 -- 34.2 5.7 7.0 2.6 1.3 47.6DO Cd 66 06/11/2008 1500 1,110 1,089 15.6 141 -- -- 28.7 16.9 12.6 7.8 74.6DO Cd 68 06/11/2008 1050 795 762 19.2 96 -- -- 10.6 16.8 2.9 3.6 64.2DO Dd 12 10/31/2007 0915 1,070 1,063 15.8 170 -- -- 37.8 18.3 12.9 5.9 67.2DO Dd 12 06/09/2008 1345 917 907 18.0 206 -- -- 46.1 22.1 15.3 3.5 52.7DO Dd 13 06/09/2008 1610 150 161 21.9 10 -- -- 1.1 1.8 0.3 3.4 83.5
34 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 1. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; CaCO3, calcium carbonate; SiO2, silica; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Water Quality Laboratory] USGS well name Date Time Sodium, dissolved (mg/L) Acid-neu- tralizing capacity, lab, total (mg/L as CaCO3

)

Alkalinity, lab, 

dissolved 

(mg/L as 

CaCO3

)

Alkalinity, field, 

dissolved 

(mg/L as 

CaCO3

)

Bicarbonate, 

field, 

dissolved 

(mg/L)

Bromide, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Fluoride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L as 

SiO2

)

Sulfate, 

dissolved 

(mg/L)

Residue, 

dissolved, 

sum of constituents 

(mg/L)

DO Cd 56 10/30/2007 1135 30.0 -- -- -- -- 0.07 93.9 0.60 70.2 146 --DO Cd 56 06/11/2008 0815 68.5 -- -- -- -- -- 80.7 0.41 56.3 199 --DO Cd 57 10/31/2007 1240 31.5 -- -- 172 209 0.09 18.2 0.27 57.4 14.9 285DO Cd 58 10/30/2007 1515 81.0 -- -- 411.2 500.6 0.06 16.8 0.30 50.4 244 E822DO Cd 59 10/30/2007 1445 35.1 -- -- 14.3 17.6 0.08 58.1 0.15 58.1 138 357DO Cd 59 06/10/2008 1520 39.0 -- -- -- -- -- 47.1 0.19 59.0 174 --DO Cd 60 10/31/2007 1158 31.2 -- -- 129.3 157.7 0.11 21.4 0.16 50.1 44.9 286DO Cd 61 10/31/2007 1110 137 -- -- -- -- 1.02 285 0.71 51.4 37.4 --DO Cd 61 10/31/2007 1115 138 -- -- -- -- 1.05 297 0.77 49.7 39.0 --DO Cd 61 06/10/2008 1100 181 -- -- -- -- -- 381.1 0.92 49.7 49.8 --DO Cd 62 10/31/2007 1029 184 -- -- 159.5 194.4 0.31 61.0 0.27 47.6 238 668DO Cd 63 10/31/2007 1225 198 -- -- 585.6 712.6 <.02 51.0 0.32 56.4 1.2 E754DO Cd 63 06/10/2008 1030 199 605 606 -- -- -- 49.6 0.32 58.3 4.7 E777DO Cd 63 06/10/2008 1045 200 621 614 -- -- -- 49.0 0.32 57.6 7.4 --DO Cd 64 06/11/2008 1555 19.4 11 9 -- -- -- 25.6 0.19 41.8 48.4 E161DO Cd 66 06/11/2008 1500 212 605 603 -- -- -- 20.0 0.41 59.8 0.5 E716DO Cd 68 06/11/2008 1050 82.0 -- -- -- -- -- 219.6 0.22 17.8 17.8 --DO Dd 12 10/31/2007 0915 176 -- -- 474.4 577.1 E.016 68.5 0.29 29.0 1.1 E634DO Dd 12 06/09/2008 1345 116 397 392 -- -- -- 67.7 0.20 29.6 E.17 E541DO Dd 13 06/09/2008 1610 24.5 8 13 -- -- -- 9.7 0.15 66.4 37.3 155
Appendixes 1–8 35

Appendix 1. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; CaCO3, calcium carbonate; SiO2, silica; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Water Quality Laboratory]

USGS 

well name Date Time

Residue, 

dissolved 

(tons per 

acre-foot)

Residue 

on evaporation, 

dissolved 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

total (mg/L 

as N)

Ammonia, 

dissolved 

(mg/L as 

NH4)

Ammonia, 

dissolved 

(mg/L as N)

Nitrate 

plus nitrite, 

dissolved 

(mg/L as N)

Nitrate, 

dissolved 

(mg/L)

Nitrate, 

dissolved 

(mg/L as N)

Nitrite, 

dissolved 

(mg/L)

Nitrite, 

dissolved 

(mg/L as 

N)

Organic 

nitrogen, 

dissolved 

(mg/L)

DO Cd 56 10/30/2007 1135 -- 412 -- 0.61 0.47 0.12 0.52 0.12 0.01 0.00 0.15DO Cd 56 06/11/2008 0815 -- -- 0.39 0.28 0.22 0.13 0.57 0.13 0.01 0.00 0.20DO Cd 57 10/31/2007 1240 0.39 287 -- 3.55 2.75 <.04 -- -- 0.01 0.00 --DO Cd 58 10/30/2007 1515 1.16 853 -- 4.57 3.55 <.04 -- -- E.006 E.00197 --DO Cd 59 10/30/2007 1445 0.54 397 -- 0.93 0.72 <.04 -- -- -- <.002 --DO Cd 59 06/10/2008 1520 -- -- 0.37 0.37 0.29 0.04 E.186 E.043 E.003 E.001 0.11DO Cd 60 10/31/2007 1158 0.37 269 -- 2.66 2.07 <.04 -- -- 0.01 0.00 --DO Cd 61 10/31/2007 1110 -- 542 -- 0.31 0.24 0.04 E.176 E.041 E.004 E.00122 0.13DO Cd 61 10/31/2007 1115 -- 575 -- -- 0.28 E.03 -- -- -- E.002 --DO Cd 61 06/10/2008 1100 -- -- 0.43 0.41 0.32 <.04 -- -- -- <.002 --DO Cd 62 10/31/2007 1029 0.92 679 -- 3.07 2.38 <.04 -- -- 0.01 0.00 --DO Cd 63 10/31/2007 1225 1.04 764 -- 7.99 6.20 <.04 -- -- E.004 E.00128 --DO Cd 63 06/10/2008 1030 E1.1 -- 6.85 8.08 6.27 <.04 -- -- E.005 E.002 --DO Cd 63 06/10/2008 1045 -- -- 6.90 -- 6.36 <.04 -- -- -- E.002 --DO Cd 64 06/11/2008 1555 E.22 -- 0.30 0.19 0.15 <.04 -- -- E.006 E.002 --DO Cd 66 06/11/2008 1500 E.97 -- 0.65 0.62 0.48 <.04 -- -- E.003 E.001 --DO Cd 68 06/11/2008 1050 -- -- 0.21 0.16 0.12 0.11 E.488 E.112 E.006 E.002 0.10DO Dd 12 10/31/2007 0915 0.92 678 -- 3.20 2.48 <.04 -- -- E.005 E.00148 --DO Dd 12 06/09/2008 1345 E.74 -- 3.09 3.22 2.50 <.04 -- -- E.004 E.001 --DO Dd 13 06/09/2008 1610 0.21 -- 1.06 0.21 0.16 0.14 -- -- -- <.002 0.33
36 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 1. Concentrations of inorganic constituents in groundwater samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; gal/min, gallons per minute; FNU, formazin nephelometric units; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; CaCO3, calcium carbonate; SiO2, silica; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; M, present but not quantified; U, deleted value by lab; --, data not available; USGS, U.S. Geological Survey; shaded couplets indicate duplicate samples; NWQL, National Water Quality Laboratory] USGS well name Date Time Organic nitrogen, total (mg/L) Total nitrogen (NO2+NO3

+

NH4+N), 

dissolved, 

analytically 

determined 

(mg/L)

Total 

nitrogen, 

total 

(mg/L)

Orthophosphate, 

dissolved 

(mg/L)

Orthophosphate, 

dissolved 

(mg/L as P)

Phosphorus, total 

(mg/L as 

P)

Hydrogen 

ion, total, 

calculated 

(mg/L)

Organic 

carbon, 

total 

(mg/L)

Hydrogen 

sulfide, 

total 

(mg/L)

Iron, 

dissolved 

(μg/L)

Manganese, 

dissolved 

(μg/L)

Cation/ 

anion 

balance 

(% difference)

DO Cd 56 10/30/2007 1135 -- 0.75 -- 0.03 0.01 -- 0.06 -- -- 2,496 404 -6.5DO Cd 56 06/11/2008 0815 0.18 0.55 0.52 0.04 0.01 0.01 0.09 3.4 -- 2,900 233 -6.7DO Cd 57 10/31/2007 1240 -- 3.18 -- 2.95 0.96 -- 0.00 -- -- 7,477 729 -1.5DO Cd 58 10/30/2007 1515 -- 3.93 -- 0.43 0.14 -- 0 -- -- 5,081 122 -0.7DO Cd 59 10/30/2007 1445 -- 0.95 -- 0.04 0.01 -- 0.01 -- -- 18,690 954 -2DO Cd 59 06/10/2008 1520 0.08 0.44 0.42 0.05 0.02 E.0071 0.07 2.0

U 5,100 569 -6.9

DO Cd 60 10/31/2007 1158 -- 2.32 -- 0.33 0.11 -- 0.00 -- -- 18,190 772 1.4DO Cd 61 10/31/2007 1110 -- 0.41 -- 0.02 0.01 -- 0.10 -- -- 2,217 416 -3.9DO Cd 61 10/31/2007 1115 -- 0.47 -- -- 0.01 -- -- -- -- 2,550 454 -5.3DO Cd 61 06/10/2008 1100 0.12 0.45 -- 0.04 0.01 E.0057 0.15 2.3

U 4,870 511 -3.7

DO Cd 62 10/31/2007 1029 -- 2.80 -- 0.41 0.13 -- 0.00 -- -- 6,660 606 0.5DO Cd 63 10/31/2007 1225 -- 6.53 -- 5.87 1.91 -- 0 -- -- 2,617 379 -0.2DO Cd 63 06/10/2008 1030 0.57 6.89 -- 5.72 1.87 1.98 0.00 8.3

M 4,990 546 -0.7

DO Cd 63 06/10/2008 1045 -- -- -- -- 2.20 2.14 -- 9.8

M 5,090 577 -0.7

DO Cd 64 06/11/2008 1555 0.15 0.26 -- 0.03 0.01 0.02 0.01 2.5 -- 4,240 223 -0.5DO Cd 66 06/11/2008 1500 0.17 0.66 -- 0.18 0.06 0.06 0.00 7.1 -- 2,680 18.5 -0.8DO Cd 68 06/11/2008 1050 0.09 0.34 0.32 0.02 0.01 <.008 0.06 1.1 -- 5,860 890 -5.9DO Dd 12 10/31/2007 0915 -- 2.88 -- 0.60 0.19 -- .000 -- -- 3,160 49.6 -0.1DO Dd 12 06/09/2008 1345 0.59 3.05 -- 2.05 0.67 -- 0.00 10.2 -- 4,020 62.6 -0.3DO Dd 13 06/09/2008 1610 0.90 0.64 1.20 0.14 0.05 0.31 0.01 14.4

M 4,290 27.7 3.8
Appendixes 1–8 37

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date Time Tidal cycle

Altitude 

of land 

surface 

(ft)

Gage 

height 

(ft)

Discharge 

(ft3/s)

Drainage 

area 

(mi2)

Barometric 

pressure 

(mm Hg)

Carbon 

dioxide, 

dissolved 

(mg/L)

Dissolved 

oxygen 

(mg/L)

Dissolved 

oxygen (% 

saturation)

pH, 

field

pH, 

lab

Specific 

conductance, 

lab 

(μS/cm)

Specific 

conductance, 

field 

(μS/cm)

Little Blackwater River at Stone Boundary Rd. near Cambridge, Md.

01490108 12/06/2006 1400 H 12 -- -- 3.7 770 12.9 9.5 75 6.6 6.7 192 18601490108 03/13/2007 0900 L 12 -- 1.36 3.7 768 29.9 11 -- 6.5 7.1 313 --01490108 04/16/2007 0915 H 12 -- 177 3.7 741 10.1 9.3 79 6.3 6.3 57 5301490108 07/10/2007 1045 L 12 -- 0.321 3.7 762 30.1 0.7 9 6.5 7.2 316 33001490108 10/29/2007 1300 L 12 -- 0.6 3.7 769 7.7 4.7 46 6.9 7.0 171 17101490108 06/10/2008 0910 R 12 -- -- 3.7 759 26.8 0.9 12 6.4 7.1 164 169

Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md.

01490110 12/06/2006 1300 H 14 -- 0.108 0.2 770 40.5 9.3 75 6.5 6.9 320 30901490110 12/06/2006 1305 H 14 -- -- -- -- -- -- -- -- 7.3 320 --01490110 03/13/2007 1000 L 14 -- 0.08 0.2 768 13.5 12.7 -- 6.8 7.1 295 --01490110 04/16/2007 1030 H 14 -- 12.4 0.2 741 7.4 9.1 79 6.6 7.1 78 7601490110 10/29/2007 1330 L 14 -- 0.076 0.2 769 11.2 6.8 65 6.5 6.9 129 13001490110 06/10/2008 0710 L 14 -- 0.2 759 55.0 1.8 22 6.5 7.0 352 353

Little Blackwater River at Maple Dam Rd. near Cambridge, Md.

01490111 06/10/2008 0815 L 7 -- -- -- -- 45.6 0.3 -- 6.1 7.0 124 128

Little Blackwater River near Christs Rock, Md.

01490112 03/16/2006 1215 L 5 -- -- 8.3 -- 16.7 8.5 -- 6.5 7.0 201 20201490112 06/22/2006 1050 L 5 -- -- 8.3 767 -- 1.4 17 6.1 6.9 544 53701490112 09/13/2006 1030 R 5 -- -- 8.3 767 13.8 0.9 10 6.7 7.1 173 16901490112 10/06/2006 1310 R 5 -- -- 8.3 -- 10.7 7.2 74 6.5 7.1 108 6501490112 12/06/2006 1045 R 5 -- -- 8.3 757 12.0 6.5 53 6.6 7.2 142 14201490112 03/12/2007 1226 R 5 -- -- 8.3 772 7.2 11.6 104 6.7 7.7 133 12101490112 04/16/2007 1215 F 5 -- -- 8.3 741 -- 6.6 61 6.3 7.1 134 12501490112 07/10/2007 0945 L 5 -- -- 8.3 762 30.0 2.3 30 6.4 7.1 369 35301490112 10/29/2007 1015 F 5 -- -- 8.3 769 19.6 4.2 38 6.3 6.8 565 55301490112 06/10/2008 1230 R 5 -- -- 8.3 759 52.0 0.2 3 6.1 7.2 137 143
38 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Time Tidal cycle Altitude of land surface (ft) Gage height (ft) Discharge (ft3/s) Drainage area (mi2

)

Barometric 

pressure 

(mm Hg)

Carbon 

dioxide, 

dissolved 

(mg/L)

Dissolved 

oxygen 

(mg/L)

Dissolved 

oxygen (% 

saturation)

pH, 

field

pH, 

lab

Specific 

conductance, 

lab 

(μS/cm)

Specific 

conductance, 

field 

(μS/cm)

Maple Dam Branch at Rt. 16 at Cambridge, Md.

01490113 06/22/2006 1615 ND 2.9 -- -- 1.5 767 -- 2.3 28 6.4 7.7 246 24801490113 09/13/2006 1300

H 2.9 -- -- 1.5 767 10.4 0.98 10 7.0 7.2 218 220

01490113 10/06/2006 1430

R 2.9 -- -- 1.5 -- 5.0 8.2 83 7.0 7.1 110 100

01490113 12/06/2006 1210

R 2.9 -- -- 1.5 770 13.6 8.8 68 6.8 7.2 262 254

01490113 03/13/2007 1030

R 2.9 -- 1.26 1.5 768 5.1 -- -- 7.1 7.8 319 309

01490113 04/16/2007 1100

H 2.9 -- 11.2 1.5 741 7.6 9 78 6.7 7.5 90 91

01490113 07/10/2007 1135

R 2.9 -- 0.475 1.5 762 19.6 5.6 72 7.0 7.4 319 335

01490113 10/29/2007 1400

L 2.9 -- -- 1.5 769 10.4 6.7 64 6.9 7.3 187 188

01490113 06/10/2008 0740

L 2.9 -- -- 1.5 759 26.4 0.6 8 6.6 7.1 203 209

Little Blackwater River tributary near Cambridge, Md.

01490116 03/16/2006 1250

L 6 -- -- 4.2 -- 10.4 -- -- 6.7 7.0 180 182

01490116 06/22/2006 1110 F 6 -- -- 4.2 767 -- 1.4 17 6.1 7.1 204 19101490116 09/13/2006 1000

R 6 -- -- 4.2 767 13.2 1.5 17 6.7 7.0 186 180

01490116 10/06/2006 1320

R 6 -- -- 4.2 -- 11.5 6.8 68 6.6 7.1 151 136

01490116 12/06/2006 1100

R 6 -- -- 4.2 757 10.2 7.1 57 6.8 7.1 215 210

01490116 03/12/2007 1242

R 6 -- -- 4.2 772 5.3 12.3 108 7.0 7.8 231 209

01490116 04/16/2007 1225 F 6 -- -- 4.2 741 9.1 7.9 73 6.6 6.8 81 7801490116 07/10/2007 0930

L 6 -- -- 4.2 762 28.8 2.7 35 6.4 7.5 465 444

01490116 10/29/2007 1000 F 6 -- -- 4.2 769 27.5 2.2 20 6.2 6.8 2,030 4,22001490116 06/10/2008 1245

R 6 -- -- 4.2 759 36.1 0.5 7 6.3 7.5 150 167

01490116 06/10/2008 1250

R 6 -- -- -- -- -- -- -- -- 7.2 153 --
Appendixes 1–8 39

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date Time Tidal cycle

Altitude 

of land 

surface 

(ft)

Gage 

height 

(ft)

Discharge 

(ft3/s)

Drainage 

area 

(mi2)

Barometric 

pressure 

(mm Hg)

Carbon 

dioxide, 

dissolved 

(mg/L)

Dissolved 

oxygen 

(mg/L)

Dissolved 

oxygen (% 

saturation)

pH, 

field

pH, 

lab

Specific 

conductance, 

lab 

(μS/cm)

Specific 

conductance, 

field 

(μS/cm)

Little Blackwater River near Cambridge, Md. gaging station

01490120 03/16/2006 1130 L -1.25 0.37 -- 15.3 -- 6.9 9 -- 6.8 6.7 297 29801490120 06/22/2006 1020 F -1.25 -- -- 15.3 767 -- 5.7 73 5.8 7.3 2,140 2,16001490120 09/13/2006 0915 R -1.25 2.3 -- 15.3 767 2.3 6.8 77 7.5 7.2 519 50901490120 10/06/2006 1245 R -1.25 -- -- 15.3 5.9 8.5 88 7.0 7.1 225 21901490120 12/06/2006 1000 R -1.25 1.44 -- 15.3 757 7.9 10.5 85 6.9 7.1 226 22301490120 03/12/2007 1204 R -1.25 0.71 -7.48 15.3 772 4.5 9.9 87 6.9 7.4 186 17101490120 04/16/2007 1240 F -1.25 2.06 -- 15.3 741 8.7 8.9 79 6.3 6.7 73 6901490120 07/10/2007 1230 R -1.25 -- -- 15.3 762 3.5 5.8 80 7.2 7.9 155 1,46001490120 10/29/2007 1030 F -1.25 -- -- 15.3 769 15.3 6.4 62 6.6 6.9 4,140 4,11001490120 06/10/2008 1130 R -1.25 -- -- 15.3 759 16.4 3 41 6.6 7.4 169 175

Little Blackwater River near Seward, Md.

01490130 09/13/2006 0845 R 5 -- -- 28.2 767 0.0 8.2 93 9.3 7.3 6,130 6,21001490130 10/06/2006 1230 R 5 -- -- 28.2 0.9 9.8 101 8.1 7.5 2,940 2,94001490130 12/06/2006 0940 R 5 -- -- 28.2 757 4.1 11.3 92 7.2 7.0 736 70501490130 03/12/2007 1138 R 5 -- -- 28.2 773 0.5 7.8 68 7.8 7.4 542 57401490130 04/16/2007 1300 F 5 -- -- 28.2 741 2.4 10 89 7.0 7.2 149 14701490130 07/10/2007 1510 H 5 -- -- 28.2 762 0.0 9.6 138 9.3 8.6 7,020 7,00001490130 07/10/2007 1515 H 5 -- -- -- -- -- -- -- -- 8.9 7,020 --01490130 10/29/2007 1100 F 5 -- -- 28.2 769 2.7 8.9 90 7.7 7.2 E14,900 14,910
40 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Time Tidal cycle Altitude of land surface (ft) Gage height (ft) Discharge (ft3/s) Drainage area (mi2

)

Barometric 

pressure 

(mm Hg)

Carbon 

dioxide, 

dissolved 

(mg/L)

Dissolved 

oxygen 

(mg/L)

Dissolved 

oxygen (% 

saturation)

pH, 

field

pH, 

lab

Specific 

conductance, 

lab 

(μS/cm)

Specific 

conductance, 

field 

(μS/cm)

Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive)

01490140 06/22/2006 0900 F 5 -- -- 30.2 767 -- 6.1 81 5.2 7.2 E15,300 15,47001490140 06/22/2006 1520 ND 5 -- -- 30.2 767 -- 10 145 7.7 8.0 E15,300 15,66001490140 09/13/2006 1200

R 5 -- -- 30.2 767 0.3 8.5 99 8.6 7.3 E12,900 13,000

01490140 10/06/2006 1215

R 5 -- -- 30.2 -- 3.5 8.3 89 7.5 7.5 5,230 5,225

01490140 12/06/2006 0901

R 5 2.18 18 30.2 757 5.4 11.1 91 7.2 7.7 4,880 4,840

01490140 03/12/2007 1045

R 5 1.52 -195 30.2 772 1.5 11.4 98 7.5 7.3 2,603 2,450

01490140 04/16/2007 1340 F 5 2.68 450 30.2 741 1.9 9.9 88 7.1 7.4 287 21501490140 07/10/2007 1730 F 5 2.44 356 30.2 762 2.3 6.5 93 7.6 7.8 E12,970 12,90001490140 10/29/2007 1115 F 5 -- -- 30.2 769 -- 7.9 82 -- 7.4 E17,540 17,50001490140 06/10/2008 1050

R 5 -- -283 30.2 759 0.3 10 141 8.5 7.6 1,784 1,870
Appendixes 1–8 41

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Temperature, 

air 

(°C)

Temperature, 

water 

(°C)

Hardness 

(mg/L as 

CaCO3)

Noncarbonate 

hardness, 

dissolved, field 

(mg/L as CaCO3)

Noncarbonate 

hardness, 

dissolved, lab 

(mg/L as CaCO3)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Potassium, 

dissolved 

(mg/L)

Sodium, 

adsorption 

ratio

Sodium 

fraction of 

cations (% equivalent 

of major 

cations)

Sodium, 

dissolved 

(mg/L)

Little Blackwater River at Stone Boundary Rd. near Cambridge, Md.

01490108 12/06/2006 9 5.5 51.5 26.0 25.5 12.5 4.9 3.6 0.83 34.6 13.601490108 03/13/2007 13.5 9 74.1 25.7 32.4 18.2 6.9 3.2 1.61 47.0 31.901490108 04/16/2007 10 7 16.6 -- 6.6 4.4 1.4 2.4 0.34 25.7 3.101490108 07/10/2007 -- 29 83.7 29.6 -- 21.9 7.1 11.2 1.02 32.2 21.401490108 10/29/2007 -- 15 47.8 16.6 -- 12.8 3.9 9.7 0.53 23.2 8.301490108 06/10/2008 31.5 28.5 52.6 -- 13.9 13.4 4.7 4.5 0.64 28.3 10.6

Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md.

01490110 12/06/2006 10 6.5 76.6 14.2 10.3 19.3 6.9 4.5 1.43 43.2 28.701490110 12/06/2006 -- -- -- -- -- -- 6.9 4.4 -- -- 28.901490110 03/13/2007 9 7.5 69.5 26.0 23.4 17.0 6.6 3.0 1.54 46.7 29.601490110 04/16/2007 9.5 8 20.5 -- 6.0 5.3 1.8 2.9 0.47 30.5 4.901490110 10/29/2007 14 14 32.3 18.4 -- 8.3 2.8 3.9 0.78 37.4 10.201490110 06/10/2008 31 24 97.8 -- 4.9 25.0 8.6 3.8 1.32 38.9 30.0

Little Blackwater River at Maple Dam Rd. near Cambridge, Md.

01490111 06/10/2008 -- 25.5 36.5 -- 4.5 8.9 3.5 7.3 0.44 22.5 6.1

Little Blackwater River near Christs Rock, Md.

01490112 03/16/2006 12 -- 40.8 -- -- 8.7 4.6 4.3 1.25 46.2 18.301490112 06/22/2006 -- 26.5 70.0 -- -- 13.5 8.8 9.2 3.43 63.7 66.001490112 09/13/2006 21 20 37.2 2.7 0.6 8.1 4.1 8.0 0.90 36.7 12.701490112 10/06/2006 -- 14 19.6 -- 2.4 4.4 2.1 7.1 0.79 37.8 8.001490112 12/06/2006 8.5 6 35.0 10.4 10.4 7.7 3.8 5.7 0.73 33.8 9.901490112 03/12/2007 -- 11 33.2 16.0 15.0 7.6 3.4 3.7 0.80 37.6 10.501490112 04/16/2007 11 10.5 37.0 -- 25.0 8.8 3.6 5.1 0.50 25.8 7.001490112 07/10/2007 -- 30 55.3 15.1 -- 11.7 6.3 8.5 2.54 58.8 43.401490112 10/29/2007 -- 11 89.3 -- -- 19.6 9.8 8.5 3.38 61.4 73.401490112 06/10/2008 -- 27.5 37.7 -- 2.3 8.9 3.8 7.7 0.56 26.5 7.9
42 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Temper- ature, air (°C) Temper- ature, water (°C) Hard- ness, (mg/L as CaCO3

)

Noncarbonate 

hardness, 

dissolved, 

field 

(mg/L as CaCO3

)

Noncarbonate 

hardness, 

dissolved, 

lab 

(mg/L as CaCO3

)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Potassium, 

dissolved 

(mg/L)

Sodium, 

adsorption 

ratio

Sodium 

fraction of 

cations (% 

equivalent 

of major 

cations)

Sodium, 

dissolved 

(mg/L)

Maple Dam Branch at Rt. 16 at Cambridge, Md.

01490113 06/22/2006 -- 26 67.6 -- -- 20.8 3.8 5.0 1.04 36.7 19.701490113 09/13/2006 21 18.5 60.2 8.5 5.2 18.1 3.7 4.7 0.81 32.0 14.401490113 10/06/2006 -- 16 34.3 -- 8.2 10.1 2.2 6.3 0.28 16.2 3.801490113 12/06/2006 8.5 5 70.9 29.9 27.5 19.5 5.4 3.3 1.03 36.6 20.001490113 03/13/2007 9 8.5 77.0 43.4 44.1 19.9 6.6 2.7 1.37 42.7 27.601490113 04/16/2007 10.5 8 31.1 -- 12.0 9.1 2.0 2.2 0.35 22.3 4.501490113 07/10/2007 -- 28 62.4 -- -- 18.3 4.0 5.4 2.23 55.9 40.401490113 10/29/2007 14 14 49.8 8.8 -- 15.0 3.0 5.1 0.84 34.4 13.601490113 06/10/2008 32 26.5 60.9 -- 7.1 18.2 3.7 4.6 0.73 30.0 13.1

Little Blackwater River tributary near Cambridge, Md.

01490116 03/16/2006 12 44.3 -- -- 10.1 4.7 4.7 0.92 37.9 14.101490116 06/22/2006 -- 24 46.1 -- -- 11.0 4.5 6.3 1.06 40.0 16.601490116 09/13/2006 20 21 37.1 2.7 0.6 7.8 4.3 8.0 1.02 39.6 14.301490116 10/06/2006 -- 15 33.6 -- 10.2 7.9 3.3 9.1 0.69 30.5 9.101490116 12/06/2006 9 6 56.9 24.9 23.8 14.1 5.3 5.0 0.84 33.4 14.601490116 03/12/2007 -- 10 58.7 34.1 31.8 14.4 5.5 3.7 1.05 38.9 18.501490116 04/16/2007 -- 10.5 25.4 -- 7.5 7.1 1.9 2.4 0.36 24.3 4.201490116 07/10/2007 -- 29.5 61.5 22.1 -- 12.6 7.3 8.0 3.14 63.2 56.701490116 10/29/2007 -- 10 218.4 -- -- 33.9 32.5 16.2 8.71 72.9 295.801490116 06/10/2008 -- 30 39.5 -- 2.1 9.3 3.9 7.8 0.63 28.5 9.001490116 06/10/2008 -- -- -- -- -- -- 4.0 7.9 -- -- 9.1
Appendixes 1–8 43

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Temperature, 

air 

(°C)

Temperature, 

water 

(°C)

Hardness 

(mg/L as 

CaCO3)

Noncarbonate 

hardness, 

dissolved, field 

(mg/L as 

CaCO3)

Noncarbonate 

hardness, 

dissolved, lab 

(mg/L as CaCO3)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved, 

mg/L

Potassium, 

dissolved 

(mg/L)

Sodium, 

adsorption 

ratio

Sodium 

fraction of 

cations 

(% equivalent of major 

cations)

Sodium, 

dissolved 

(mg/L)

Little Blackwater River near Cambridge, Md. gaging station

01490120 03/16/2006 12 11.5 55.9 -- -- 11.4 6.7 5.2 1.81 52.0 31.201490120 06/22/2006 -- 28 204.1 -- -- 25.8 33.9 16.6 9.71 75.5 31901490120 09/13/2006 20 21.5 61.9 27.5 24.3 8.8 9.7 9.9 3.37 64.0 61.001490120 10/06/2006 -- 17 36.7 -- 5.9 7.0 4.7 9.1 1.63 50.4 22.601490120 12/06/2006 9 6 46.5 17.0 14.0 9.5 5.5 6.3 1.28 44.4 20.001490120 03/12/2007 -- 10 39.7 24.1 21.4 8.6 4.4 4.0 1.22 46.2 17.701490120 04/16/2007 10.5 9 18.4 -- 10.2 4.2 1.9 3.0 0.46 30.5 4.501490120 07/10/2007 -- 32.5 135.6 115.9 -- 18.7 21.6 14.8 8.12 75.4 21701490120 10/29/2007 12 14 409.5 384.0 -- 47.9 70.4 28.9 13.42 75.3 62401490120 06/10/2008 34 31.5 39.4 -- 6.0 8.2 4.6 7.9 0.92 36.7 13.2

Little Blackwater River near Seward, Md.

01490130 09/13/2006 20 21 586.2 544.4 541.6 43.6 116 41.1 17.46 76.8 97101490130 10/06/2006 -- 17 289.9 -- 237.8 23.1 56.4 22.5 10.93 74.5 42801490130 12/06/2006 8.5 6 84.7 52.7 48.9 8.8 15.2 9.7 4.54 68.3 96.001490130 03/12/2007 9 10 67.3 48.4 49.5 8.7 11.1 6.3 3.82 67.5 72.001490130 04/16/2007 -- 9 29.3 -- 15.9 5.3 3.9 4.6 1.19 47.8 14.801490130 07/10/2007 -- 33.5 689.1 658.7 -- 56.8 133 52.3 18.02 75.8 1,08701490130 07/10/2007 -- -- -- -- -- 131 53.0 1,10001490130 10/29/2007 13 14 1,654.4 1,599.5 -- 121.3 328.2 99.6 28.82 76.7 2,694
44 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Temper- ature, air (°C) Temper- ature, water (°C) Hardness (mg/L as CaCO3

)

Noncarbonate 

hardness, 

dissolved, field 

(mg/L as 

CaCO3

)

Noncarbonate 

hardness, 

dissolved, lab 

(mg/L as CaCO3

)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved, 

(mg/L)

Potassium, 

dissolved 

(mg/L)

Sodium, 

adsorption 

ratio

Sodium 

fraction of 

cations 

(% equivalent of major 

cations)

Sodium, 

dissolved 

(mg/L)

Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive)

01490140 06/22/2006 -- 28 1,579.5 -- -- 111.9 315.7 94.2 26.88 75.9 2,45501490140 06/22/2006 -- 33 1,654.1 -- -- 116.7 330.9 98.6 27.81 76.1 2,59901490140 09/13/2006 21 21 1,321.8 1,269.3 1,264.8 90.7 266.0 82.4 25.04 76.1 2,09201490140 10/06/2006 -- 17 507.3 -- 455.4 37.9 100.2 35.0 15.11 75.5 78201490140 12/06/2006 8.5 5.8 459.9 418.1 416.0 32.1 92.2 32.0 14.69 75.9 72401490140 03/12/2007 9.5 9 256.0 233.9 229.9 21.6 49.1 17.6 10.83 75.7 39801490140 04/16/2007 -- 9 37.8 -- 23.0 5.0 6.2 5.3 2.47 63.0 34.901490140 07/10/2007 -- 32 1,366.3 1,317.9 -- 98.6 272.0 98.7 25.38 75.9 2,15601490140 10/29/2007 13 14.5 1,905.5 1,842.3 -- 135.9 380.3 115.1 31.39 77.0 3,14901490140 06/10/2008 37 33 160.7 -- 112.0 12.8 31.3 18.3 9.35 76.3 272
Appendixes 1–8 45

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Acidneutralizing 

capacity, 

lab, total 

(mg/L as 

CaCO3)

Alkalinity, lab, 

dissolved 

(mg/L as 

CaCO3)

Alkalinity, field, 

dissolved 

(mg/L as 

CaCO3)

Bicarbonate, 

field, 

dissolved 

(mg/L)

Bromide, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Fluoride, 

dissolved 

(mg/L)

Silica, 

dissolved, 

(mg/L as 

SiO2)

Sulfate, 

dissolved 

(mg/L)

Residue, 

dissolved, 

sum of 

constituents 

(mg/L)

Residue, 

total 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

total 

(mg/L as N)

Little Blackwater River at Stone Boundary Rd. near Cambridge, Md.

01490108 12/06/2006 26.5 26.0 25 31 -- 21.3 0.18 19.46 22.8 116 <10 1.0701490108 03/13/2007 48.8 41.7 49 59 -- 38.1 0.18 7.70 35.9 172 38 0.8401490108 04/16/2007 10.4 10.0 -- -- -- 4.7 <.10 4.26 5.5 33.5 24 1.1901490108 07/10/2007 49.1 -- 54 66 -- 30.1 0.32 2.04 37.8 E167 54 3.1101490108 10/29/2007 31.5 -- 31 38 <.02 11.8 E.110 8.07 26.1 E103 52 1.4301490108 06/10/2008 34.7 38.6 -- -- -- 15.9 0.16 16.2 10.4 E105 42 2.53

Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md.

01490110 12/06/2006 66.2 66.2 63 76 -- 35.3 0.21 17.0 27.7 179 12 0.9301490110 12/06/2006 67.0 -- 63 77 -- -- 0.22 16.9 27.7 -- 15 0.9401490110 03/13/2007 44.1 46.1 43 53 -- 35.6 0.15 7.71 34.5 161 32 E1.00601490110 04/16/2007 15.2 14.5 -- -- -- 8.0 E.065 2.95 6.9 E43.0 <20 1.3501490110 10/29/2007 18.2 -- 14 17 E.0149 12.5 E.076 4.79 21.6 E73.2 <20 0.7501490110 06/10/2008 89.8 92.8 -- -- -- 34.2 0.25 17.75 24.1 E204 24 1.77

Little Blackwater River at Maple Dam Rd. near Cambridge, Md.

01490111 06/10/2008 31.8 32.0 -- -- -- 11.2 0.12 8.31 6.0 74.3 26 2.16

Little Blackwater River near Christs Rock, Md.

01490112 03/16/2006 27.2 -- -- -- -- 34.5 0.15 1.16 7.3 96.7 -- --01490112 06/22/2006 -- -- -- -- -- 132 0.18 3.32 6.6 -- -- --01490112 09/13/2006 35.7 36.6 34 42 -- 22.4 0.12 6.67 6.8 92.8 <20 1.6701490112 10/06/2006 17.5 17.2 -- -- -- 15.9 E.084 2.92 3.4 E55.4 <16.7 0.8001490112 12/06/2006 24.7 24.7 25 30 -- 18.3 0.10 12.41 8.2 82.8 <20 1.0201490112 03/12/2007 18.5 18.2 18 21 -- 17.6 0.12 0.65 11.9 66.6 <10 0.9901490112 04/16/2007 -- 12.0 -- -- -- 12.9 0.11 4.88 14.6 76.0 118 2.4601490112 07/10/2007 38.9 -- 40 49 -- 76.6 0.19 3.16 5.7 E182 36 2.8701490112 10/29/2007 20.2 -- -- -- 0.598 195 E.101 6.58 59.2 E386 <10 0.9301490112 06/10/2008 33.8 35.4 -- -- -- 13.7 0.14 8.41 5.1 81.7 <20 2.09
46 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Acid- neutralizing capacity, lab, total (mg/L as CaCO3

)

Alkalinity, lab, 

dissolved 

(mg/L as 

CaCO3

)

Alkalinity, field, 

dissolved 

(mg/L as 

CaCO3

)

Bicarbonate, 

field, 

dissolved 

(mg/L)

Bromide, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Fluoride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L as 

SiO2

)

Sulfate, 

dissolved 

(mg/L)

Residue, 

dissolved, 

sum of 

constituents 

(mg/L)

Residue, 

total 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

total 

(mg/L as N)

Maple Dam Branch at Rt. 16 at Cambridge, Md.

01490113 06/22/2006 -- -- -- -- -- 14.6 0.26 2.78 29.4 -- -- --01490113 09/13/2006 53.5 55.0 52 63 -- 13.4 0.16 10.06 26.0 122 30 0.7601490113 10/06/2006 26.0 26.1 -- -- -- 5.3 E.074 4.47 11.7 E62.2 46 1.2601490113 12/06/2006 44.3 43.4 41 50 -- 21.4 0.18 18.79 39.6 155 30 1.0701490113 03/13/2007 33.4 32.9 34 41 -- 37.0 0.19 15.72 58.7 191 12 0.6401490113 04/16/2007 19.7 19.1 -- -- -- 6.1 E.074 4.36 11.5 E52.7 66 0.9401490113 07/10/2007 101.1 -- 93 113 -- 16.4 0.33 3.18 29.4 174 158 1.5301490113 10/29/2007 42.8 -- 41 50 0.029 8.3 0.16 4.06 30.1 106 32 0.9901490113 06/10/2008 54.3 53.8 -- -- -- 12.4 0.15 10.59 23.5 E121 46 1.80

Little Blackwater River tributary near Cambridge, Md.

01490116 03/16/2006 27.0 -- -- -- -- 25.9 0.15 0.53 10.9 88.7 -- --01490116 06/22/2006 -- -- -- -- -- 24.0 0.21 5.54 9.9 -- -- --01490116 09/13/2006 34.1 36.5 34 42 -- 25.9 0.12 6.45 6.8 97.1 20 1.8501490116 10/06/2006 23.7 23.4 -- -- -- 22.5 E.077 4.46 6.2 E78.5 <20 0.8901490116 12/06/2006 33.2 33.1 32 39 -- 23.3 0.12 14.91 24.4 E122 <10 0.8701490116 03/12/2007 27.2 26.9 25 30 -- 27.4 0.14 1.89 31.9 E119 <10 0.7401490116 04/16/2007 18.7 17.9 -- -- -- 5.6 E.073 3.55 9.4 E46.3 24 0.9601490116 07/10/2007 37.3 -- 40 48 -- 105 0.22 2.39 8.6 E227 20 3.0001490116 10/29/2007 22.5 -- -- -- 1.828 576 0.13 5.83 66.1 E1,043 11 1.2701490116 06/10/2008 37.2 37.5 -- -- -- 15.5 0.17 7.41 6.8 87.2 20 2.0501490116 06/10/2008 37.0 -- -- -- -- -- 0.16 7.50 7.1 -- 20 2.00
Appendixes 1–8 47

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Acidneutralizing 

capacity, 

lab, total 

(mg/L as 

CaCO3)

Alkalinity, lab, 

dissolved 

(mg/L as 

CaCO3)

Alkalinity, field, 

dissolved 

(mg/L as 

CaCO3)

Bicarbonate, 

field, 

dissolved 

(mg/L)

Bromide, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Fluoride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L as 

SiO2)

Sulfate, 

dissolved 

(mg/L)

Residue, 

dissolved, 

sum of 

constituents 

(mg/L)

Residue, 

total 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

total 

(mg/L as N)

Little Blackwater River near Cambridge, Md. gaging station

01490120 03/16/2006 22.4 -- -- -- -- 55.6 0.17 0.77 23.0 148 -- --01490120 06/22/2006 -- -- -- -- -- 629 0.21 2.64 36.0 -- -- --01490120 09/13/2006 37.5 37.6 35 42 -- 122 0.13 4.79 12.8 251 22 2.4501490120 10/06/2006 30.4 30.8 -- -- -- 41.1 0.12 4.50 4.4 113 <20 1.6101490120 12/06/2006 32.6 32.5 30 36 -- 36.4 0.13 13.27 9.3 E120 E23.3 1.4101490120 03/12/2007 18.6 18.3 16 19 -- 28.9 0.11 2.91 17.6 94.3 15 1.1301490120 04/16/2007 9.0 8.2 -- -- -- 7.5 E.063 4.86 7.6 E41.1 98 1.3601490120 07/10/2007 28.4 -- 20 24 -- 431 0.23 4.05 30.1 E751 62 4.2601490120 10/29/2007 31.4 -- 26 31 4.076 1,256 0.14 3.26 103.4 E2,160 40 2.3501490120 06/10/2008 33.7 33.4 -- -- -- 22.2 0.15 5.92 7.4 E92.9 <20 1.75

Little Blackwater River near Seward, Md.

01490130 09/13/2006 50.2 44.7 42 51 -- 1,837 0.25 3.98 219.5 E3,260 32 3.6401490130 10/06/2006 55.3 52.1 -- -- -- 821 0.15 0.84 83.2 E1,470 82 2.9001490130 12/06/2006 33.3 35.8 32 39 -- 174 0.14 9.88 23.6 358 E36.7 2.6501490130 03/12/2007 17.4 17.8 19 23 -- 131 0.12 1.85 30.9 E273 45 1.4701490130 04/16/2007 12.2 13.5 -- -- -- 23.8 0.10 2.24 13.8 77.8 200 2.7001490130 07/10/2007 41.5 -- 30 37 -- 2,101 0.31 5.49 261.5 E3,720 100 5.5801490130 07/10/2007 42.0 -- -- -- -- -- 0.30 5.60 261.0 -- 92 2.4001490130 10/29/2007 71.3 -- 55 67 16.395 4,906 0.34 0.26 611.5 E8,810 24 2.74
48 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Acid- neutralizing capacity, lab, total (mg/L as CaCO3

)

Alkalinity, lab, 

dissolved 

(mg/L as 

CaCO3

)

Alkalinity, field, 

dissolved 

(mg/L as 

CaCO3

)

Bicarbonate, 

field, 

dissolved 

(mg/L)

Bromide, 

dissolved 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Fluoride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L as 

SiO2

)

Sulfate, 

dissolved 

(mg/L)

Residue, 

dissolved, 

sum of 

constituents 

(mg/L)

Residue, 

total 

(mg/L)

Ammonia 

plus organic 

nitrogen, 

total 

(mg/L as N)

Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive)

01490140 06/22/2006 -- -- -- -- -- 4,974 0.37 0.52 680.6 -- -- --01490140 06/22/2006 -- -- -- -- -- 5,058 0.38 0.40 692.0 -- -- --01490140 09/13/2006 58.5 56.9 53 64 -- 4,099 0.35 2.01 514.0 E7,180 26 2.2201490140 10/06/2006 56.7 51.9 -- -- -- 1,522 0.19 1.38 167.5 E2,680 48 2.9501490140 12/06/2006 44.4 43.9 42 51 -- 1,411 0.21 4.35 165.4 E2,490 E46.0 1.9301490140 03/12/2007 24.5 26.1 23 27 -- 750 0.15 1.70 109.2 E1,360 13 1.9801490140 04/16/2007 12.3 14.9 -- -- -- 57.6 E.099 1.99 18.3 E140 330 3.2701490140 07/10/2007 46.9 -- 48.3 59 -- 4,094 0.40 1.15 583.6 E7,330 48 2.4101490140 10/29/2007 72.3 -- 63 77 19.525 5,874 0.35 <.20 738.1 E10,500 32 1.8701490140 06/10/2008 51.1 48.6 -- -- 479 0.23 0.63 56.0 E901 62 3.08
Appendixes 1–8 49

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Ammonia, 

dissolved 

(mg/L as 

NH4)

Ammonia, 

dissolved 

(mg/L as N)

Nitrate 

plus nitrite, 

dissolved 

(mg/L as N)

Nitrate, 

dissolved 

(mg/L)

Nitrate, 

dissolved 

(mg/L as N)

Nitrite, 

dissolved 

(mg/L)

Nitrite, 

dissolved 

(mg/L as N)

Organic 

nitrogen, 

total 

(mg/L)

Total nitrogen 

(NO2+NO3+NH4+N), 

dissolved, analytically 

determined 

(mg/L)

Total nitrogen, 

total 

(mg/L)

Little Blackwater River at Stone Boundary Rd. near Cambridge, Md.

01490108 12/06/2006 0.11 0.083 0.208 0.897 0.203 0.018 0.005 1.053 1.34 1.27401490108 03/13/2007 0.08 0.061 0.096 0.41 0.093 0.011 0.003 0.823 0.98 0.93101490108 04/16/2007 0.06 0.048 0.17 0.732 0.165 0.016 0.005 1.057 1.28 1.36201490108 07/10/2007 1.30 1.009 E.052 E.178 E.040 0.039 0.012 E2.82 3.83 E3.1601490108 10/29/2007 0.13 0.102 0.361 1.508 0.341 0.067 0.020 1.325 1.79 1.7901490108 06/10/2008 0.43 0.337 E.029 E.101 E.023 0.02 0.006 E2.06 2.40 E2.56

Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md.

01490110 12/06/2006 0.13 0.103 0.281 1.218 0.275 0.019 0.006 0.867 1.25 1.2101490110 12/06/2006 0.101 0.28 -- -- -- -- 1.21 --

01490110 03/13/2007 0.08 0.064 0.089 0.379 0.086 0.011 0.003 0.901 1.05 E1.1001490110 04/16/2007 0.32 0.247 0.175 0.746 0.168 0.022 0.007 1.112 1.53 1.5301490110 10/29/2007 E.022 E.017 E.020 E.074 E.017 0.011 0.003 E.803 0.80 E.76801490110 06/10/2008 0.39 0.301 E.031 E.109 E.025 0.021 0.006 E1.39 1.69 E1.80

Little Blackwater River at Maple Dam Rd. near Cambridge, Md.

01490111 06/10/2008 0.44 0.338 <.04 -- -- 0.011 0.003 1.819 2.08 --

Little Blackwater River near Christs Rock, Md.

01490112 03/16/2006 -- <.04 <.060 -- -- -- <.008 -- 1.40 --01490112 06/22/2006 0.26 0.198 <.060 -- -- 0.034 0.010 -- 2.63 --01490112 09/13/2006 0.21 0.163 <.060 -- -- 0.009 0.003 1.505 1.70 --01490112 10/06/2006 -- <.04 0.072 0.301 0.068 0.013 0.004 -- 0.97 0.87401490112 12/06/2006 0.09 0.069 <.060 -- -- 0.014 0.004 0.947 0.96 --01490112 03/12/2007 -- <.02 <.060 -- -- 0.007 0.002 -- 1.04 --01490112 04/16/2007 0.52 0.403 2.371 10.214 2.307 0.209 0.064 2.07 4.84 4.8301490112 07/10/2007 -- <.02 <.060 -- E.006 E.0018 -- 3.06 --01490112 10/29/2007 0.09 0.072 0.042 0.17 0.038 0.012 0.004 0.882 1.00 0.97301490112 06/10/2008 0.47 0.365 <.04 -- -- 0.015 0.005 1.73 1.98 --
50 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Ammonia, dissolved (mg/L as NH4

)

Ammonia, 

dissolved 

(mg/L as N)

Nitrate 

plus nitrite, 

dissolved 

(mg/L as N)

Nitrate, 

dissolved 

(mg/L)

Nitrate, 

dissolved 

(mg/L as N)

Nitrite, 

dissolved 

(mg/L)

Nitrite, 

dissolved 

(mg/L as N)

Organic 

nitrogen, 

total 

(mg/L)

Total nitrogen 

(NO2+NO3+NH4+N), 

dissolved, analytically 

determined 

(mg/L)

Total nitrogen, 

total 

(mg/L)

Maple Dam Branch at Rt. 16 at Cambridge, Md.

01490113 06/22/2006 0.05 0.039 <.060 -- -- 0.012 0.004 -- 3.07 --01490113 09/13/2006 0.06 0.047 0.06 0.255 0.057 0.008 0.003 1.031 1.14 0.81901490113 10/06/2006 -- <.04 0.335 1.449 0.327 0.025 0.008 -- 1.48 1.5901490113 12/06/2006 0.04 0.032 0.302 1.307 0.295 0.022 0.007 1.013 1.35 1.37201490113 03/13/2007 0.03 0.021 0.29 1.265 0.286 0.014 0.004 0.558 0.87 0.93301490113 04/16/2007 0.03 0.021 0.191 0.826 0.187 0.014 0.004 0.949 1.16 1.1401490113 07/10/2007 0.10 0.073 <.060 -- -- 0.007 0.002 1.454 1.70 --01490113 10/29/2007 0.15 0.119 0.218 0.921 0.208 0.033 0.010 0.823 1.16 1.201490113 06/10/2008 0.46 0.354 E.034 -- -- -- <.006 E1.76 2.12 E1.83

Little Blackwater River tributary near Cambridge, Md.

01490116 03/16/2006 -- <.04 <.060 -- -- -- <.008 -- 1.33 --01490116 06/22/2006 0.60 0.466 <.060 -- -- 0.017 0.005 -- 1.61 --01490116 09/13/2006 0.23 0.178 <.060 -- -- 0.009 0.003 1.667 2.02 --01490116 10/06/2006 -- <.02 E.039 E.161 E.036 0.008 0.003 -- 1.05 E.93201490116 12/06/2006 0.19 0.146 E.040 E.154 E.035 0.017 0.005 E.663 0.81 E.90701490116 03/12/2007 -- <.02 <.060 -- -- E.004 E.0013 -- 0.74 --01490116 04/16/2007 0.04 0.033 0.151 0.646 0.146 0.017 0.005 0.924 1.11 1.1101490116 07/10/2007 -- <.02 <.060 -- -- E.006 E.0019 -- 2.66 --01490116 10/29/2007 0.10 0.076 E.035 E.141 E.032 0.01 0.003 E1.254 1.33 E1.3001490116 06/10/2008 0.41 0.320 <.04 -- -- 0.026 0.008 1.73 1.89 --01490116 06/10/2008 -- 0.349 <.04 -- -- 0.008 -- 2.07 --
Appendixes 1–8 51

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Ammonia, 

dissolved 

(mg/L as 

NH4)

Ammonia, 

dissolved 

(mg/L as N)

Nitrate 

plus nitrite, 

dissolved 

(mg/L as N)

Nitrate, 

dissolved 

(mg/L)

Nitrate, 

dissolved 

(mg/L as N)

Nitrite, 

dissolved 

(mg/L)

Nitrite, 

dissolved 

(mg/L as N)

Organic 

nitrogen, 

total 

(mg/L)

Total nitrogen 

(NO2+NO3+NH4+N), 

dissolved, analytically 

determined 

mg/L)

Total nitrogen, 

total 

(mg/L)

Little Blackwater River near Cambridge, Md. gaging station

01490120 03/16/2006 -- <.04 <.060 -- -- -- <.008 -- 1.88 --01490120 06/22/2006 0.01 0.010 <.060 -- -- E.005 E.0014 -- 4.33 --01490120 09/13/2006 0.02 0.012 <.060 -- -- 0.007 0.002 2.439 2.28 --01490120 10/06/2006 -- <.04 0.073 0.306 0.069 0.013 0.004 -- 1.70 1.6801490120 12/06/2006 0.34 0.261 E.043 E.161 E.036 0.022 0.007 E1.181 1.44 E1.4501490120 03/12/2007 0.06 0.047 <.060 -- -- 0.011 0.003 1.078 1.34 --01490120 04/16/2007 0.09 0.068 0.379 1.615 0.365 0.046 0.014 1.574 2.02 1.7401490120 07/10/2007 0.04 0.031 <.060 -- -- E.006 E.0017 4.228 4.56 --01490120 10/29/2007 0.11 0.088 E.029 E.113 E.025 0.012 0.004 E2.419 2.51 E2.3801490120 06/10/2008 E.02 E.013 <.04 -- -- 0.01 0.003 E1.75 1.71 --

Little Blackwater River near Seward, Md.

01490130 09/13/2006 0.03 0.024 <.060 -- -- -- <.002 3.615 3.56 --01490130 10/06/2006 E.036 E.028 <.060 -- -- E.004 E.0013 E2.901 3.44 --01490130 12/06/2006 0.70 0.543 0.087 0.321 0.073 0.047 0.014 1.695 2.33 2.7401490130 03/12/2007 -- <.02 <.060 -- -- E.005 E.0016 -- 2.00 --01490130 04/16/2007 0.23 0.180 0.111 0.456 0.103 0.026 0.008 4.296 4.59 2.8101490130 10/29/2007 1.00 0.774 E.032 E.106 E.024 0.026 0.008 E2.035 2.81 E2.77
52 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Ammonia, dissolved (mg/L as NH4

)

Ammonia, 

dissolved 

(mg/L as N)

Nitrate 

plus nitrite, 

dissolved 

(mg/L as N)

Nitrate, 

dissolved 

(mg/L)

Nitrate, 

dissolved 

(mg/L as N)

Nitrite, 

dissolved 

(mg/L)

Nitrite, 

dissolved, 

(mg/L as N)

Organic 

nitrogen, 

total 

(mg/L)

Total nitrogen 

(NO2+NO3+NH4+N), 

dissolved, analytically 

determined 

(mg/L)

Total nitrogen, 

total 

(mg/L)

Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive)

01490140 06/22/2006 0.03 0.021 <.060 -- -- E.005 E.0014 -- 2.06 --01490140 06/22/2006 0.03 0.022 <.060 -- -- E.004 E.0013 -- 2.07 --01490140 09/13/2006 E.036 E.028 <.060 -- -- -- <.002 E2.217 1.89 --01490140 10/06/2006 -- <.04 0.065 0.278 0.063 0.007 0.002 -- 3.14 3.0101490140 12/06/2006 0.30 0.231 E.053 E.204 E.046 0.023 0.007 E1.726 1.96 E1.9801490140 03/12/2007 E.015 E.011 <.060 -- -- E.005 E.0015 E1.975 2.22 --01490140 04/16/2007 0.32 0.248 0.241 1.011 0.228 0.041 0.013 6.218 6.71 3.5101490140 07/10/2007 0.08 0.062 <.060 -- -- E.004 E.0014 2.349 2.36 --01490140 10/29/2007 0.53 0.412 E.024 E.085 E.019 0.016 0.005 E1.726 2.14 E1.8901490140 06/10/2008 E.020 E.015 <.04 -- -- 0.009 0.003 E3.077 3.21 --
Appendixes 1–8 53

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Orthophosphate, 

dissolved 

(mg/L)

Orthophosphate, 

dissolved 

(mg/L as P)

Phosphorus, 

total 

(mg/L as P)

Hydrogen ion, 

total, 

calculated 

(mg/L)

Organic 

carbon, 

dissolved, 

(mg/L)

Organic 

carbon, 

total, 

(mg/L)

Iron, 

dissolved 

(μg/L)

Manganese, 

dissolved 

(μg/L)

Cation/anion 

balance 

(% difference)

Little Blackwater River at Stone Boundary Rd. near Cambridge, Md.

01490108 12/06/2006 0.206 0.067 0.274 0 21.3 26.4 1,411 92.3 5.001490108 03/13/2007 0.037 0.012 0.219 0 16.6 22.4 383 149.9 2.701490108 04/16/2007 0.31 0.101 0.232 0.001 22.0 22.7 543 37.8 8.701490108 07/10/2007 0.496 0.162 1.197 0 21.0 28.7 591 361.6 3.401490108 10/29/2007 1.13 0.368 0.647 0 12.5 15.4 292 69.5 1.701490108 06/10/2008 0.971 0.317 0.865 0 38.4 44.9 4,412 452.3 10.9

Little Blackwater tributary at Stone Boundary Rd. near Cambridge, Md.

01490110 12/06/2006 0.066 0.021 0.298 0 12.0 16.3 405 77.2 0.801490110 12/06/2006 -- 0.021 0.295 -- 11.9 16.2 370 77.1 0.101490110 03/13/2007 0.057 0.019 0.226 0 13.3 17.2 514 145.2 3.401490110 04/16/2007 0.257 0.084 0.302 0 14.0 E14.8 312 14.6 2.401490110 10/29/2007 0.186 0.061 0.166 0 11.3 9.2 407 10.1 5.301490110 06/10/2008 0.705 0.230 0.587 0 22.0 23.7 2,860 586.9 2.1

Little Blackwater River at Maple Dam Rd. near Cambridge, Md.

01490111 06/10/2008 1.09 0.355 0.972 0.001 28.7 30.3 1,815 374.4 7.5

Little Blackwater River near Christs Rock, Md.

01490112 03/16/2006 0.478 0.156 0.362 0 -- -- 785 80.4 2.201490112 06/22/2006 0.662 0.216 0.849 0.001 -- -- 394 343.1 7.801490112 09/13/2006 1.48 0.482 0.762 0 17.1 22.2 1,474 154.9 3.201490112 10/06/2006 0.472 0.154 0.275 0 11.2 15.5 402 33.1 3.601490112 12/06/2006 0.571 0.186 0.304 0 22.1 25.0 1,069 26.3 5.001490112 03/12/2007 0.187 0.061 0.150 0 18.9 22.4 515 31.8 5.401490112 04/16/2007 0.41 0.134 0.599 0.001 17.3 21.4 343 43.9 4.601490112 07/10/2007 1.06 0.346 0.856 0 22.8 34.6 797 225.2 2.401490112 10/29/2007 0.235 0.077 0.221 0.001 13.9 19.3 713 317.3 -15.401490112 06/10/2008 1.62 0.530 0.999 0.00 27.3 34.8 2,340 500.0 7.2
54 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Orthophosphate, dissolved (mg/L) Orthophosphate, dissolved (mg/L as P) Phosphorus, total (mg/L as P) Hydrogen ion, total, calculated (mg/L) Organic carbon, dissolved (mg/L) Organic carbon, total, (mg/L) Iron, dissolved (μg/L) Manganese, dissolved (μg/L) Cation/anion balance (% differ- ence) Maple Dam Branch at Rt. 16 at Cambridge, Md. 01490113 06/22/2006 0.03 0.010 0.480 0 -- -- 56 95.5 -- 01490113 09/13/2006 0.028 0.009 0.235 0 6.4 8.2 121 259.1 -0.1 01490113 10/06/2006 1.16 0.378 0.544 0 8.9 12.8 97 37.3 3.9 01490113 12/06/2006 0.055 0.018 0.205 0 10.6 13.2 613 203.3 2.6 01490113 03/13/2007 0.03 0.010 0.108 0 7.5 8.8 468 212.3 -2.5 01490113 04/16/2007 0.197 0.064 0.252 0 15.3 E16.4 316 59.0 4.4 01490113 7/10/2007 0.094 0.031 0.465 0 13.3 13.9 64 174.7 3.3 01490113 10/29/2007 0.257 0.084 0.267 0 6.6 7.4 80 147.4 0.7 01490113 06/10/2008 0.33 0.107 0.407 0.00 13.2 15.2 1,480 334.0 1.2 Little Blackwater River tributary near Cambridge, Md. 01490116 03/16/2006 0.537 0.175 0.362 0 -- -- 956 71.4 4.7 01490116 06/22/2006 1.8 0.587 0.881 0.001 -- -- 379 274.1 -- 01490116 09/13/2006 1.36 0.444 0.830 0 18.1 25.2 1,049 162.8 1.6 01490116 10/06/2006 0.903 0.294 0.450 0 -- -- 511 51.0 3.3 01490116 12/06/2006 0.165 0.054 0.224 0 12.1 E15.3 245 55.1 2.6 01490116 03/12/2007 0.094 0.031 0.123 0 12.3 14.0 238 73.9 3.4 01490116 04/16/2007 0.291 0.095 0.261 0 11.9 14.3 218 23.6 2.4 01490116 07/10/2007 1.03 0.336 0.749 0 21.8 32.0 1,070 285 -0.1 01490116 10/29/2007 0.134 0.044 0.354 0.001 13.0 15.3 420 663.0 -1.1 01490116 06/10/2008 2.05 0.668 0.930 0.00 22.8 30.7 1,870 371 4.5 01490116 06/10/2008 -- 0.680 0.990 -- 23.4 32.2 2,000 353 7.1
Appendixes 1–8 55

Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued[ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data]

USGS 

station 

number

Date

Orthophosphate, 

dissolved 

(mg/L)

Orthophosphate, 

dissolved 

(mg/L as P)

Phosphorus, 

total 

(mg/L as P)

Hydrogen ion, 

total, 

calculated 

(mg/L)

Organic 

carbon, 

dissolved 

(mg/L)

Organic 

carbon, 

total, 

(mg/L)

Iron, 

dissolved 

(μg/L)

Manganese, 

dissolved 

(μg/L)

Cation/anion 

balance 

(% difference)

Little Blackwater River near Cambridge, Md. gaging station

01490120 03/16/2006 0.221 0.072 0.351 0 -- -- 484 119 2.401490120 06/22/2006 0.149 0.049 0.591 0.002 -- -- 119 382 -0.301490120 09/13/2006 1.14 0.372 0.650 0 15.6 25.0 439 95.3 -2.801490120 10/06/2006 0.599 0.195 0.410 0 14.3 25.4 498 79.8 2.501490120 12/06/2006 0.814 0.265 0.452 0 20.8 26.3 842 90.1 4.301490120 03/12/2007 0.129 0.042 0.185 0 16.1 18.0 455 64.0 5.401490120 04/16/2007 0.192 0.062 0.369 0.001 18.7 E25.6 549 43.5 7.801490120 07/10/2007 0.526 0.171 0.586 0 23.1 39.5 386 129 -2.501490120 10/29/2007 0.095 0.031 0.344 0 16.2 28.5 299 777 -2.701490120 06/10/2008 1.62 0.527 0.745 0.00 21.0 29.7 1,480 198 5.5

Little Blackwater River near Seward, Md.

01490130 09/13/2006 0.028 0.009 0.307 0 16.0 28.1 E21.6 3.4 -2.001490130 10/06/2006 0.13 0.042 0.441 0 14.8 28.8 41 3.6 -1.901490130 12/06/2006 0.443 0.144 0.372 0 18.1 29.7 380 30.0 0.701490130 03/12/2007 0.034 0.011 0.231 0 15.3 21.6 203 27.3 -0.801490130 04/16/2007 0.278 0.091 0.717 0 16.8 47.2 271 6.2 4.501490130 07/10/2007 0.837 0.273 0.730 0 22.4 35.2 <30 10.9 -2.301490130 07/10/2007 0.295 0.720 -- 24.4 35.7 <30 11.5 -2.301490130 10/29/2007 0.176 0.057 0.194 0 20.0 24.1 <120 322 0.2
56 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 2. Concentrations of inorganic constituents in surface-water samples, Little Blackwater River watershed, Dorchester County, Maryland.—Continued [ft, feet; ft3/s, cubic feet per second; mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; %, percent; μg/L, micrograms per liter; mi2, square miles; mm Hg, millimeters mercury; --, data not available; CaCO3, calcium carbonate; SiO2, silicate; N, nitrogen; NH4, ammonia; NO2, nitrite; NO3, nitrate; P, phosphorus; <, less than; E, estimated; USGS, U.S. Geological Survey; dark shaded couplets indicate duplicate samples; H, high; L, low; R, rising; F, falling; ND, no data] USGS station number Date Orthophosphate, dissolved (mg/L) Orthophosphate, dissolved (mg/L as P) Phosphorus, total (mg/L as P) Hydrogen ion, total, calculated (mg/L) Organic carbon, dissolved (mg/L) Organic carbon, total, (mg/L) Iron, dissolved (μg/L) Manganese, dissolved (μg/L) Cation/anion balance (% differ- ence) Little Blackwater River at Seward, Md. gaging station (at Key Wallace Drive) 01490140 06/22/2006 E.013 E.004 0.156 0.006 -- -- <60 51.8 -4.7 01490140 06/22/2006 E.010 E.003 0.140 0 -- -- <60 38.8 -2.8 01490140 09/13/2006 E.015 E.005 0.094 0 13.9 21.6 <90 <9.0 -3.2 01490140 10/06/2006 E.012 E.004 0.316 0 13.7 23.9 21 6.8 -2.6 01490140 12/06/2006 0.027 0.009 0.184 0 14.3 E25.8 96 7.0 -3.0 01490140 03/12/2007 E.017 E.005 0.200 0 12.9 23.8 112 36.5 -2.2 01490140 04/16/2007 0.404 0.132 0.848 0 17.3 E66.6 289 9.5 2.0 01490140 07/10/2007 0.037 0.012 0.186 0 15.4 23.9 <60 75.4 -2.0 01490140 10/29/2007 0.038 0.012 0.128 -- 14.8 17.7 <120 104 -1.2 01490140 06/10/2008 0.803 0.262 0.587 0 21.1 39.2 299 6.5 -0.4
Appendixes 1–8 57

Appendix 3. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08.—Continued[mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25°C; %, percent; μg/L, micrograms per liter; <, less than; --, data not available; E, estimated]

Station number Local identifier Date Sample start time

Specific 

conductance 

(μS/cm)

2,4,5-T

(%)

a-HCH-d6

(%)

Barban

(%)

Caffeine13C

(%)

Diazinond10

(%)

Residue

(mg/L)

Residue, 

total 

(mg/L)

Calcium

(mg/L)

Magnesium

(mg/L)

1490140

Little 

Blackwater 

River at 

Seward, 

Md.

03/12/2007 1230 6 -- -- -- -- -- -- <10 E.02 <.014

382718076062001 DO Dd 12 06/09/2008 1234 <8 89.1 113 85.3 87.2 123 -- -- 0.1 <.020382718076062002 DO Dd 13 06/09/2008 1500 <8 77.7 105 94.2 81.8 116 -- -- 0.08 <.020383122076055703 DO Cd 58 10/30/2007 1023 4 -- -- -- -- -- <10 -- 0.05 <.020

Date Potassium (mg/L) Sodium (mg/L) CaCO3 (mg/L) Silica (mg/L) Sulfate (mg/L) NH3+orgN (mg/L as N) Ammonia (mg/L as N) NO3+NO2 (mg/L as N) Nitrite (mg/L as N)

Orthophosphate

(mg/L as 

P)

Phosphorus 

(mg/L)

Total 

nitrogen

(mg/L)

Total 

nitrogen

(mg/L)

03/12/2007 <.04 <.20 <5 <.2 <.18 0.49 <.020 <.06 <.002 <.006 <.008 -- <.0606/09/2008 <.02 <.12 E4 <.2 <.18 <.14 <.020 <.04 <.002 <.006 <.008 <.06 --06/09/2008 E.01 <.12 E4 E.1 <.18 <.14 <.020 <.04 <.002 <.006 <.008 E.03 --10/30/2007 <.02 <.12 -- <.02 <.18 -- <.020 <.04 <.002 <.006 -- <.06 --

Date Iron (μg/L) Manganese (μg/L)

2,4-D 

methyl 

ester

(μg/L)

CIAT

(μg/L)

CEAT

(μg/L)

OIET

(μg/L)

3-Hydroxy 

carbofuran

(μg/L)

Acetochlor 

(μg/L)

Acifluorfen 

(μg/L)

Alachlor

(μg/L)

Aldicarb 

sulfone

(μg/L)

Aldicarb 

sulfoxide 

(μg/L)

Aldicarb

(μg/L)

03/12/2007 <6 <.2 -- -- -- -- -- -- -- -- -- -- --06/09/2008 <8 <.4 <.040 <.014 <.08 <.040 <.040 <.006 <.040 <.006 <.08 <.060 <.1206/09/2008 <8 <.4 <.040 <.014 <.08 <.040 <.040 <.006 <.040 <.006 <.08 <.060 <.1210/30/2007 <8 <.4 -- -- -- -- -- -- -- -- -- -- --
58 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09 Appendix 3. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08. —Continued [mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25°C; %, percent; μg/L, micrograms per liter; <, less than; --, data not available; E, estimated] Date alpha-HCH (μg/L) Atrazine (μg/L) Azinphos- methyl (μg/L) Bensul- furon- methyl (μg/L) Bentazon (μg/L) Bromacil (μg/L) Bro- moxynil (μg/L) Butylate (μg/L) Carbaryl1 (μg/L) Carbaryl2 (μg/L) Carbofu- ran (μg/L) Carbofu- ran (μg/L) Chlo- ram- ben ME (μg/L) 03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- 06/09/2008 <.002 <.007 <.120 <.06 <.04 <.02 <.12 <.002 <.04 <.060 <.020 <.020 <.10 06/09/2008 <.002 <.007 <.120 <.06 <.04 <.02 <.12 <.002 <.04 <.060 <.020 <.020 <.10 10/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- Date Chlorimur- on-ethyl (μg/L) Chlor- pyrifos (μg/L) cis-Per- methrin (μg/L) Dacthal- monoacid (μg/L) DCPA (μg/L) Desulfi- nylfipronil amide (μg/L) Desul- finylfi- pronil (μg/L) Diazinon (μg/L) Dicamba (μg/L) Dichlor- prop (μg/L) Dieldrin (μg/L) Dinoseb (μg/L) Di- phena- mid (μg/L) 03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- 06/09/2008 <.080 <.005 <.010 <.02 <.003 <.029 <.012 <.005 <.04 <.02 <.009 <.04 <.04 06/09/2008 <.080 <.005 <.010 <.02 <.003 <.029 <.012 <.005 <.04 <.02 <.009 <.04 <.04 10/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- Date Disulfoton (μg/L) Diuron (μg/L) EPTC (μg/L) Fipronil sulfide (μg/L) Fipronil sulfone (μg/L) Fipronil (μg/L) Flumet- sulam (μg/L) Fluome- turon (μg/L) Fonofos (μg/L) Imaza- quin (μg/L) Imazetha- pyr (μg/L) Imida- cloprid (μg/L) Lin- dane (μg/L) 03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- 06/09/2008 <.04 <.04 <.002 <.013 <.024 <.020 <.06 <.04 <.010 <.04 <.04 <.060 <.006 06/09/2008 <.04 <.04 <.002 <.013 <.024 <.020 <.06 <.04 <.010 <.04 <.04 <.060 <.006 10/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- Date Linuron (μg/L) Linuron (μg/L) Malathion (μg/L) Methio- carb (μg/L) Methomyl (μg/L) Methyl parathion (μg/L) Meto- lachlor (μg/L) Metribuzin (μg/L) Metsul- furon- methyl (μg/L) Molinate (μg/L) N(4Chloro- phenyl) N’methyl- urea (μg/L) Naprop- amide (μg/L) Ne- buron (μg/L) 03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- -- 06/09/2008 <.02 <.060 <.016 <.040 <.120 <.008 <.010 <.012 <.14 <.002 <.12 <.018 <.02 06/09/2008 <.02 <.060 <.016 <.040 <.120 <.008 <.010 <.012 <.14 <.002 <.12 <.018 <.02

10/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- --
Appendixes 1–8 59

Appendix 3. Concentrations of inorganic and organic constituents in equipment blanks, Little Blackwater River watershed, Dorchester County, Maryland, 2007–08.—Continued[mg/L, milligrams per liter, °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25°C; %, percent; μg/L, micrograms per liter; <, less than; --, data not available; E, estimated]

Date

Nicosulfuron 

(μg/L)

Norflurazon 

(μg/L)

Oryzalin 

(μg/L)

Pebulate 

(μg/L)

Pendimethalin 

(μg/L)

Phorate 

(μg/L)

Picloram 

(μg/L)

Prometon 

(μg/L)

Propachlor 

(μg/L)

Propanil 

(μg/L)

Propargite 

(μg/L)

Propham 

(μg/L)

Propiconazole 

(μg/L)

03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- --06/09/2008 <.10 <.02 <.04 <.004 <.012 <.040 <.12 <.01 <.006 <.006 <.04 <.040 <.0406/09/2008 <.10 <.02 <.04 <.004 <.012 <.040 <.12 <.01 <.006 <.006 <.04 <.040 <.0410/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- --

Date Propoxur (μg/L) Propyza- mide (μg/L) Siduron (μg/L) Terbacil1 (μg/L) Terbacil2 (μg/L) Terbufos (μg/L) Thioben- carb (μg/L) Triallate (μg/L) Triclopyr (μg/L) Triflura- lin (μg/L) Sum 2,4-D + 2,4-D ME (μg/L) Caffeine (μg/L) Or- ganic carbon (mg/L)

03/12/2007 -- -- -- -- -- -- -- -- -- -- -- -- 0.606/09/2008 <.040 <.004 <.02 <.018 <.040 <.02 <.010 <.006 <.08 <.006 <.02 <.060 --06/09/2008 <.040 <.004 <.02 <.018 <.040 <.02 <.010 <.006 <.08 <.006 <.02 <.060 --10/30/2007 -- -- -- -- -- -- -- -- -- -- -- -- --

1 Concentrations from high-performance liquid chromatography (HPLC).2 Concentrations from gas chromatography-mass spectrometry (GCMS).
60 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.

Peat

Silt and clay

Sandy clay

Medium sand

Fine sand and silt

Clay

Coarse sand/ gravel

Pebbles

Iron stains/mottles

Wood fragments

Burrows

No data

LithologyFeatures

Comments Comments

2

0-0.5 Yellowish brown (10YR 5/4) f-vc subangularsubrounded quartz sand (roadfill)

0.5-1.2 Very dark grayish brown (10YR 3/2) 

organic-rich silty clay. Small pods of dark gray 

(10YR 4/2) silt

1.2-1.6 Gradual transition to black (10YR 4/2)

peaty silt

3.9-5.5 Light brownish gray (10YR 6/2) openwork f-m angular-subangular quartz sand

9.3-10.0 Pebble gravel in a matrix of dark gray m sand fining upwards to dominantly m sand

10.0-14.7 Very dark gray (10YR 3/1) clayey silt. Large sand-filled burrows in upper ~5 in. 

Roots

Shells/shell fragments

LEGEND

1.6-2.5 Very dark grayish brown (10YR 4/2) to 

gray (10YR 5/1) organic-rich clay. Abundant

oxidized zones; detrital limonite?

2.5-3.0 Gray (10YR 5/1) sandy (vf ) clay. Abundant

roots

3.0-3.9 Gray (10YR 5/1) to dark gray (10YR 4/1)

silty vf-f sand. Granules common and less silt

toward base

5.5-7.0 Color change to dark brown (10YR 3/3); appears stained by humate. Horizontally bedded and alternates between

more brown and more gray colors 

No recovery

Silt 

4

6

8

10

12

0 Depth [feet below 

land surface (BLS)]
Appendixes 1–8 61

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

14.7-15.0 Dark gray (2.5 Y 4/0) clayey silt. Large sand-filled burrows in upper ~.4 in. 

15.0-15.2 Small lag of c sand to pea gravel composed of rounded-well rounded quartz and chert with silt between clasts

15.2-16.2 Dark gray (2.5Y 4/0) silty m-vc subangular-well rounded quartz sand and ~7% black chert. Several 

pea gravel clasts in lower ~.5 in.

16.4-17.0 Dark gray (2.5Y 4/0) silty m-vc subangular-well rounded quartz sand and ~7% black chert

16.2-16.4 Gravel lag composed of well-rounded quartz clasts up to 4 cm in diameter

17.0-18.0 Dark gray (2.5Y 4/0) heavily burrowed silt. Burrows filled with sand from above; also abundant macro organic

fragments

18.0-20.0 Dark gray (2.5Y 4/0) silty clay with several accumulations of peaty material

20.0-22.6 Very dark gray (10YR 3/1) peaty silty clay (~30% peat)

22.6-24.0 Very dark gray (10YR 3/1) silty clay with ~15% peat

Lithology

Features

Comments

12

14

16

18

20

22

24 Depth [feet below 

land surface (BLS)]
62 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

24.0-24.4 Very dark gray clay with few small shell fragments near base

28.4-28.7 Dark gray (10YR 4/1) peaty silty clay

27.9-28.4 Black (10YR 2/1) peat

29.2-44.3 Gray (5Y 4/1; more blue in upper ~7.0 ft) clay with abundant roots. ~2 in. concretion at 31 ft

28.7-29.2 Gravel lag (to 28.9) composed of .4-1.2 in. well-rounded quartz and black chert with a matrix 

of grayish brown (2.5Y 5/2) silty f-vc subangular-well rounded quartz sand w/ few black chert fragments

24

26

28

30

32

34

Lithology

Features

Comments

36 Depth [feet below 

land surface (BLS)]
Appendixes 1–8 63

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

44.3-45.0 Olive gray (5Y 4/2) clay

45.0-46.5 Olive gray (5Y 4/2) clay with abundant organics

46.5-47.8 Gray (5Y 5/1) clay. Silty near the middle of unit, and oxidized in lower ~10 in., possibly in association with small 

limonite concretions

47.8-49.6 Gray (5Y 5/1) silty f angular-subangular quartz sand with few mica flakes. Color changes to dark gray (5Y 4/1) at 48.5 ft

36

38

40

42

44

46

36.1 Color changes to gray (10YR 5/1) 

36.1-44.0 Color varies to gray (10YR 5/1; 5Y 5/1) to dark gray (5Y 4/1) 

Lithology

Features

Comments

48 Depth [feet below 

land surface (BLS)]
64 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

48

50

52

54

56

58

49.6-64.8 Color changes to dark grayish brown (2.5Y 4/2) and silt disappears 

Lithology

Features

Comments

60Depth [feet below 

land surface (BLS)]
Appendixes 1–8 65

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

64.8-64.9 Gravel lag composed of rounded, but chipped, red-stained quartz pebbles, with a .8-in. clay lense directly underlying 

64.9-65.4 Dark grayish brown (2.5Y 4/2) micaceous vf-f sand. No opaques 

19.93-20.13 Dark gray (5Y 4/1 - 10YR 4/1) clay (alternates between more red and more green hues) with small vf sand lenses 

composed of above sand. Small light brownish gray (2.5Y 6/2) mud balls present from ~65.5 to 69.0 ft 

60

62

64

66

68

70

72 Depth [feet below 

land surface (BLS)]

Lithology

Features

Comments
66 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

79.2-84.0 Very dark grayish brown (10YR 3/2) clay with several vf sand stringers and 

numerous mud balls (”little white balls”)

-reddish color fades and disappears here

74

76

78

80

82

84

Lithology

Features

Comments

72 Depth [feet below 

land surface (BLS)]
Appendixes 1–8 67

Appendix 4. Lithologic log of DO Dd 12 core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

84.0-91.7 Dark gray (5Y 4/1) clay continues without sand, except that which fills burrows

-alternations between red and green reappears

91.7-92.0 Dark gray (5Y 4/1) heavily oxidized sandy clay - clayey vf-f angular-subangular quartz sand with minimal mica; 

small fragments of pectin shells near base

92.0-92.3 Dark grayish brown (2.5Y 4/2) vf-f angular-subangular quartz sand with minimal mica; micro and macro organics

92.3-96.0 Dark olive gray (2.5Y 3/2) vf-m angular-rounded quartz sand with minimal chert grains. Abundant pectin shell

fragments down to 95.6 ft; potentially burrowed

86

88

90

92

94

96

Lithology

Features

Comments

84 Depth [feet below 

land surface (BLS)]
68 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.

Peat Clay with some silt

Medium sand Silt with some clay

Fine sand and silt

Clay Coarse sand/ gravel

Pebbles Iron stains/mottles

Wood fragments Burrows

No data

LithologyFeatures

Comments Comments

0-.70 Grayish brown peat rich in 

grasses and roots with vf-m quartz 

sand and silt. Soil has a medium-thick

platy structure

.70-2.0 Gray vf sand with silt and traces

of m-c sand, heavily mottled

2.0-4.0 Gray vf sand and silt coarsening 

upwards to dominantly vf sand

4.0-4.5 Gray vf-m angular-well rounded

sand coated with silt fining upwards to

vf sand and silt

7.4-9.3 Gray f-m subangular-well rounded quartz sand with evidence of redox features

9.3-10.0 Pebble gravel in a matrix of dark gray m sand fining upwards to dominantly m sand

10.0-10.7 Pebble gravel in a matrix of dark gray m sand fining upwards to m sand

10.7-11.5 Rounded-well rounded and flattened pebble gravel with interstitial dark gray subangular-well 

rounded vf-vc silt coated sand 

11.5-11.8 Dark gray silty clay and vf sand mixed with vf-c sand fining up to dark gray clay with a pocket of

vf-c sand, likely from sediment overloading

11.8-12.6 Dark gray clay with a pocket of f sand-pebbles, likely from sediment overloading

Roots Shells/shell fragments

NO RECOVERY

LEGEND

CoreSection

2

4

6

8

10

12

0 Depth [feet below 

land surface (BLS)]
Appendixes 1–8 69

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

12.6-12.9 Dark gray clay rich in root fragments;. This layer dries out much more quickly than the underlying 

clay; sharp boundary between them

12.9-17.7 Dark gray clay with a small amount of organic material and associated redox features. small roots

observed in core interior

22.9-23.9 Dark gray clay continues with abundant oyster shell fragments (>60%) with no apparent preferred 

orientation

12

14

16

18

20

22

Lithology

Features

24

Comments

Depth [feet below land surface (BLS)]
70 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

23.9-24.4 Very dark gray clay with few small shell fragments near base

24.4-24.8 Dark gray clay with abundant oyster shell fragments (>60%) with no apparent preferred 

orientation

24.8-28.1 Very dark gray clay with abundant organic material and charcoal

28.1-28.2 Lense of angular-subangular vf-c sand

28.4-29.2 Black peat with charcoal fragments interrupted by a 1 cm sand lense of dark gray vf-vc 

subangular-well rounded sand

28.2-28.4 Black clay coarsening up to sandy peat

29.2-30.2 Black vf-vc subangular-rounded sand rich in opaque minerals and likely stained by humate. 

Small charcoal fragments present. Fine silt binds grains together 

* 29.5-29.9 Very dark grayish brown 

*29.9-30.2 Light gray-dark gray; sharp basal contact 

30.2-31.0 Light gray vf-m angular-subrounded sand with sharp basal contact

31.0-31.2 Dark gray - gray clay with small non-extensive sand laminae 

31.2-31.3 Dark gray angular-subrounded vf-f sand

31.3-31.33 Dark gray clay bed with two thin sand lenses

31.33-31.6 Dark gray angular-subrounded vf-f sand

31.6-31.7 Dark gray clay and vf-f sand alternating every 1/2 cm

31.7-31.8 Dark gray clay with small vertical sand inclusions, possibly from burrow infilling

31.8-32.3 Dark gray clay and light gray finely laminated vf-f sand alternating every .2-.8 in.

32.3-32.4 Light gray vf sand and silt; oxidized 

*32.4-34.9 Missing 2.5’ of core according to labels on rods

34.9-35.1 Light gray vf sand and silt; oxidized

35.1-35.5 Dark gray clay with finely laminated beds of light gray sand; overall coarsening upward

trend. Heavily oxidized disturbed laminae shows evidence of sediment loading 

35.5-36.0 Dark gray with very thin (.25-.5 cm) fine sand & silt laminae

NO DATA

26

28

30

32

34

24

36 Depth [feet below 

land surface (BLS)]Lithology

Features

Comments
Appendixes 1–8 71

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

36.0-36.1 Dark gray fine sand/silt

36.1-36.5 Dark gray clay with non-continuous sand pockets ~.4-.6 in. in diameter. Sharp basal contact

36.5-36.7 Dark gray sand bed with small interstitial clay pockets

36.7-36.9 Dark gray clay with .1-in. thick vf sand beds spaced 1.5 cm apart

36.9-37.2 Dark gray sand bed with coarse mottling (~.4 in.)

37.2-37.5 Dark gray clay with small vertical sand inclusions; likely infilled burrows

37.5-38.0 Discrete packages of dark gray clay alternating with dark gray sand with sharp contacts 

38.0-38.4 Gray vf-f sand bed with a 1.5-cm clay horizon diagonally bedded 

38.4-38.6 Dark gray clay with small sand pockets; overall fines up. Possible bivalve traces

38.6-39.0 Gray vf-f sand bed with slight fining upward trend and bioturbated (vertical oxidized zones)

39.0-39.3 Dark gray clay interfingering with/coarsening upward to vf-f sand

39.3-39.5 Dark gray clay 

39.5-39.7 Discontinuous light gray vf-f sand locally pinching to 0 thickness

surrounded by dark gray clay 

39.7-39.9 Dark gray clay with vertical sand intrusions (filled burrows?)

39.9-40.1 Light gray vf-f sand

40.1-40.6 Gray clay that oxidizes quickly upon exposure; possible bivalve trace

40.6-41.0 Dark gray clay; massive

41.0-41.8 Dark gray f sand with possible bioturbation (discolored) bound by abrupt contacts

41.8-44.8 Very dark gray clay with repeating flasers of vf-f very dark gray sand

44.8-44.9 Dark gray vf-f sand

NO DATA- BETWEEN VIBRACORE AND B40

38

40

42

44

46

Lithology

Features

36

48 Depth [feet below 

land surface (BLS)]

Comments
72 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

55.0-60.0 Very dark gray (5Y 3/1) angular-rounded f quartz sand

NO DATA- BETWEEN VIBRACORE AND B40

*Begin B40 Auger Hole Data

50

52

54

56

58

48

60Depth [feet below 

land surface (BLS)]Lithology

Features

Comments
Appendixes 1–8 73

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

60.0-66.0 Very dark grayish brown (2.5Y 3/2) clay with vf-f quartz sand stringers (oxidized)

66.0-70.0 Very dark gray (5Y 3/1) clay with vf-f quartz sand stringers 

70.0-72.0 Very dark gray (5Y 3/1) silty vf-f sand

62

64

66

68

70

Lithology

Features

60

72Depth [feet below 

land surface (BLS)]Comments
74 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Features

72.0-75.0 Very dark grayish brown (2.5Y 3/2) clay with abundant m-vc sand grains

75.0-77.0 Very dark grayish brown (2.5Y 3/2) clay 

77.0-80.0 Dark gray (10YR 4/1) clay with small sand lenses/stringers

80.0-96.8 Very dark grayish brown (10YR 3/2) clay with several vf sand stringers and 

numerous mud concretions

72

74

76

78

80

82

84 Depth [feet below 

land surface (BLS)]

Comments
Appendixes 1–8 75

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued Lithology Features

96.8-94.0 Dark gray (5Y 4/1) - very dark gray (5Y 3/1) clay

84

86

88

90

92

94

96Depth [feet below 

land surface (BLS)]

Comments
76 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 5. Lithologic log of Maintenence Yard core, Blackwater National Wildlife Refuge, Dorchester County, Maryland.—Continued

94.0-99.0 Very dark gray (5Y 3/1) well-laminated silty vf sand

99.0-100.0 Black (5Y 2.5/2) vf sand

100.0-101.5 Very dark grayish brown (2.5Y 3/2) clay

101.5-103.0 Very dark grayish brown (2.5Y 3/2) well-laminated sand

103.0 Very dark grayish brown (2.5Y 3/2) clay

96

98

100

102

LithologyFeatures

103 BOCDepth [feet below 

land surface (BLS)]Comments
Appendixes 1–8 77

Appendix 6. Lithologic and geophysical logs of DO Cd 58 core, Little Blackwater River watershed, Dorchester County, Maryland.

Lithology Description

10

0

20

30

40

50

60

70

80

90

1.0-2.0 Plowed horizon

Gamma Log

2.0-11.8 Silty vf sand transitioning to silty sand and gravel

11.8-12.0 Small pea gravel lag

12.4-16.0 Silty clay

12.0-12.4 Silty sand continues

16.0-18.5 Dark brown clay

18.5-19.5 Poorly sorted f-fc sand and granules

19.5-21.5 Dark brown clay continues

21.5-22.0 vf-m sand and silt

22.0-28.0 Brown clay rich in organics

28.0-43.0 Gray clay with variable organic content

43.0-50.0 Gray silty/sandy clay package

*Wet; Small aquifer in upper part

50.0-53.0 Open-work sand package rich in quartz and black chert

53.0-55.0 Brownish gray clay

55.0-89.5 Gray silty/sandy clay with large shell hash to 64.7 ft

Diminishing shells 64.7-89.5 ft

0 100 API-GR

*6.0-8.0 Possible limonite nodules oxidizing

Depth [feet below 

land surface (BLS)]
78 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland.

Lithology Description

0-6” Black (10YR 2/1) plowed horizon

6”-2’4” Yellowish-grayish brown (10YR 6/2-5/6) locally oxidized, rooted, and burrowed silt. More oxidized towards the base

2’4”-4’9” Dark yellowish brown (10YR 3/4) diamict. Vf-f sand matrix with increasing amounts of floating pebbles towards the

 base. Pebbles are generally angular-well rounded quartz and chert. Several are tubular, a couple flattened. 

6’6”-9’1” Dark olive heavily burrowed silty clay and sand. Several .4-.6 in pebbles in matrix.

4’9”-6’6” Dark grayish brown-v. dark grey (10YR 4/1-2) silty vf-f micaceous sand with several matrix supported granules 

and one 1-cm rounded quartz pebble. Upper ~8” mottled, several oxidized zones.

9’6”-11’10” Dark olive gray (5Y3/2) silty f-m sand with few clay rip-ups. Several small (<.5 cm) pebbles from 9’7”-9’9”. 

Fines increase at 11’10” (vf sand and clayey silt). 12’6”-14’3” : Unconformity lag; several large (.4-.2.75 in.) 

angular-rounded pebbles and many clay rip-ups.

14’3”-30’8” Gray (5YR 5.5/1) clay unit with many flaser beds begins (For details, see inset 1). 

30’8”-34’6” Very dark grayish brown (2.5Y3/2)-dark olive gray (5Y3/2) laminated and heavily burrowed vf sand and silty clay. 

34’6”-36’10” Grayish brown (2.5Y 5/2) open work fine sand package. Angular quartz sand with ~5% unidentified opaques.

-41’6”-41’8.5” V. dark grayish brown (2.5Y3/2) well-sorted f quartz sand. Well-laminated and angular; possibly

some small bits of charcoal.

47’2”-62’6” “Red clay” unit returns: V. dark grayish brown (2.5Y3/2) - dark grayish brown (10YR 4/2) silty clay. Heavily

burrowed (filled with sand) with many flasers. Sand component is micaceous angular quartz (either rosy or 

stained) silty vf sand (for details, see inset 2). 

62’6”-62’11” Sandy (f-m) silt with several floating angular-rounded granules (white and black quartz) 

62’11”-64’2” Dark gray (5Y4/1) clay with floating granules and vf micaceous quartz sand flasers

36’10”-47’2” Dark olive gray (5Y3/2) silty f sand. Heavily burrowed/bioturbated with burrows oxidizing upon exposure.

Well-laminated unit with a couple of ~1-2” clay horizons around 40’. Fines increase to the base.

64’2”-67’11.5” Olive gray (5Y5/2) silty vf-f sand and clay. Heavily bioturbated/burrowed

67’11.5”-68’5” vf-m angular-well rounded quartz sand with ~3% opaques and ~3% shell fragments in the sand fraction. 

Shell fragments appear at 68’ and remain minimal to 68’5”. Clay horizon from 68’3”-68’5”. Several sand-filled 

burrows precipitating sulfates.

68’5”-75’11”* Dark grayish brown (2.5Y4/2) shell hash. Dense shell layer in silty vf sand. Shells include pectin, isognomen, 

barnacles, and more. (*missing 69’6”-74’6”; assume shell hash continues)

75’11”-79’6” Dark greyish brown (2.5Y4/2) angular vf-m massive sand. Shells are minimal, but few horizontally lying clams 

“float” in matrix. 

79’6”-82’6” Dark grayish brown (2.5Y4/2) angular vf-m massive sand continues, with shell proportion increasing once again to 

become a dense shell hash. 

Inset 1

Inset 2

ERN-4

* First occurence Pterocarya pollen grains; MIOCENE

10

0

20

30

40

50

60

70

80

0 200

GAMMA

API-GR

Depth [feet below 

land surface (BLS)]
Appendixes 1–8 79

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland.

—Continued

82’6”-89’6” Olive gray (5Y4/2) angular-subrounded m quartz sand with few clams and other bivalves in matrix suspension. 

 Small clay films throughout.

89’6”-100’10”* Olive gray (5Y4/2) massive/bioturbated m quartz sand with minimal shells (*99’6”-100’10”. missing).

100’10”-104’6”* Olive gray (5Y4/2) m quartz sand with high proportion of shells. Appears fragmented; storm surge?

 (*101’-104’6” missing)

104’6”-107’ Olive gray (5Y4.5/2) silty vf-f quartz sand with high proportion of shells. The fine fraction appears to be made up

largely of ground-up shell material that fizzes violently with HCL.

-Top ~3” indurated fossiliferous limestone clast (likely small portion of 101‘-104’6” interval).

107’-108’9” Dark gray (5Y4/1) f-m silty quartz sand with several shell fragments in suspension; mostly pectin and isognomen.

108’9”-113’6”* Grayish brown (2.5Y5/2) vf-f quartz sand with fewer shells. Some organic material (roots?) (*113’6”-115’6” missing)

-110’4”-111’6” ~50% shells with long axes in horizontal position.

-111’6”-111’11” Open-work concentration of organics with oxidation stains and a couple of small pectin fragments.

113’6”-116’1” Brown (10YR4/3) Indurated zone; disaggregated shells.

116’1”-119’6” Olive gray (5Y4/2) f angular quartz sand with many large clams both stacked and in suspension in horizontal 

orientation. Indurated from 117’-117’8”; shells minimal below 118’4”

119’6”-123’8” Sand continues with increasing shell accumulation. Dense pectin and pearly isognomen.

123’8”-127’5” Dark greyish brown (2.5Y4/2) silty vf-f sand. Massive or structure destroyed by drilling. Shells minimal.

127’-129’6” Olive gray (5Y5/2) silty vf-f sand with variable induration. Generally well-laminated with bioturbation.

Soft Sediment Deformation

Glauconite

Shells/Shell Fragments

Pebbles

Burrows/Bioturbation

Oxidation stain

Clay

Sand

Silty sand

Silty clay and sand

EXPLANATION

Lithology Description

80

90

100

110

120

130

0 200

GAMMA

API-GR

Depth [feet below 

land surface (BLS)]
80 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland.

—Continued

14’3”-14’11” Gray (5YR5.5/1) clay with several small flasers.

14’11”-15’3” Dark grayish brown (2.5Y4/2) vf sand

15’3”-15’6” Heavily burrowed gray (5YR5.5/1) clay. ~2 cm burrows and many flaser beds

15’6”-16’11” Gray (5YR5.5/1) clay. ~2 cm burrows and many flaser beds. Large burrows

 drop out.

16’11”-17’3” Light olive brown (2.5Y5/4) well-laminated, vf, angular quartz sand.

17’3”-18’2” Interbedded clay and sand; sand has very clear laminae.

18’2”-19’5” Dark gray (5YR4/1) clay cyclically interrupted by oxidized silty vf sand beds.

19’5”-19’11.5” Light olive brown (2.5Y5/4) vf well-laminated sand. 

19’11.5”-21’10.5” Dark gray (5YR4/1) clay with sand flasers throughout.

21’10.5”-22’9” Interbedded clay and sand on ~3’ intervals. Some charcoal bits at the base.

 Sand part is well laminated.

22’9”-26‘ Dark gray (5YR4/1) clay with multiple vf sand flasers and ~1” sand beds.

26‘-26’1” Dark olive gray (5Y3/2) angular-subrounded micaceous vf quartz sand.

26’1”-27’6” Clays and vf sands with soft-sediment deformation (due to drilling?)

27’6”-30’8” Dark gray (5YR4/1) clay. The most “pure” clay in the package; flasers throughout, 

but less common and smaller. Colors vary from above to grayish brown (2.5Y4/2).

Lithology Description

16

14

18

20

22

24

26

28

30

0 200

GAMMA

API-GR

Depth [feet below 

land surface (BLS)]
Appendixes 1–8 81

Appendix 7. Lithologic and geophysical logs of DO Cd 66 core, Little Blackwater River watershed, Dorchester County, Maryland.

—Continued

47’2”-51’6” Very dark grayish brown (2.5Y3/2) silty clay. 

 Heavily burrowed, multiple flasers, two sand excursions.

54’6”-52’8” Very dark grayish brown (2.5Y3/2) vf sand and silt.

52’8”-54’1” Very dark grayish brown (10YR3/2) heavily burrowed clay. Filling sands

 are micaceous angular quartz silty vf sand.

54’1”-54’8” Dark brown (10YR3/3) angular micaceous f sand excursion; possibly glauconitic.

54’8”-55’6” Very dark grayish brown (10YR3/2) clay with 2 small well-laminated silty f sand

 beds. 

55’6”-56’ Dark brown (10YR3/3) vf sand package. Micaceous quartz with possible charcoal

 in upper ~1”. 

56’-57’6” Dominant clays and sands “swirled” together. Bioturbated? Soft sediment 

 deformation? Disturbed by drilling?

57’6”-62’6” Brown (10YR4/3) clay with less sand/silt; also slightly less “red”. Few burrows. 

Lithology Description

49

47

51

53

55

57

59

61

63

0 200

GAMMA

API-GR

Depth [feet below 

land surface (BLS)]
82 Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09

Appendix 8. 2-D resistivity survey along the Egypt Road well transect B-B', Little Blackwater River watershed, Dorchester County, 

Maryland.
Prepared by USGS West Trenton Publishing Service Center.

Edited by Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

or visit our Web site at:

http://md.water.usgs.gov
Fleming, B.J., and others—Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006–09—Scientific Investigations Report 2011–5054

Printed on recycled paper