U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5101

Prepared in cooperation with the

City of Baltimore, Baltimore County, and Carroll County, Maryland

The Water-Quality Monitoring Program for the Baltimore 

Reservoir System, 1981–2007—Description, Review 

and Evaluation, and Framework Integration for 

Enhanced Monitoring
Cover.  Map showing location of reservoirs and watersheds of the City of Baltimore, Maryland.
The Water-Quality Monitoring Program 

for the Baltimore Reservoir System, 

1981–2007—Description, Review and 

Evaluation, and Framework Integration 

for Enhanced Monitoring

By Michael T. Koterba, Marcus C. Waldron, and Tamara E.C. Kraus

Scientific Investigations Report 2011–5101

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

City of Baltimore, Baltimore County, and Carroll County, Maryland
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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Suggested citation:

Koterba, M.T., Waldron, M.C., and Kraus, T.E.C., 2011, The water-quality monitoring program for the Baltimore 

reservoir system, 1981–2007—Description, review and evaluation, and framework integration for enhanced 

monitoring: U.S. Geological Survey Scientific Investigations Report 2011–5101, 133 p.

ISBN 978-1-4113-3170-9
iii

Contents

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

Introduction.....................................................................................................................................................3

Baltimore Drinking-Water Reservoir System...................................................................................4

Watershed and Reservoir Characteristics .......................................................................................4

Reservoir Watershed Management and Reservoir Operation......................................................4

Overview of Water-Quality Concerns.........................................................................................................8

Long-Term Water-Quality Concerns ..................................................................................................8

Emerging Water-Quality Concerns ..................................................................................................11

Regulatory Concerns..........................................................................................................................12

The Water-Quality Monitoring Program...................................................................................................14

Description...........................................................................................................................................14

Historical Perspective (1981–2007).........................................................................................14

Current Perspective (as of 2007) .............................................................................................15

Liberty Watershed and Reservoir ..................................................................................18

Watershed Monitoring............................................................................................18

Reservoir Monitoring ..............................................................................................18

Ashburton Treatment Facility Monitoring............................................................19

Loch Raven Watershed and Reservoir..........................................................................19

Watershed Monitoring............................................................................................19

Reservoir Monitoring ..............................................................................................19

Montebello Treatment Facility Monitoring ..........................................................20

Prettyboy Watershed and Reservoir .............................................................................20

Watershed Monitoring............................................................................................20

Reservoir Monitoring ..............................................................................................20

Review and Evaluation.......................................................................................................................21

Quality of the Monitoring Database and the Data Collected..............................................21

Modeling to Address Water-Quality Concerns ....................................................................23

Monitoring to Address Individual Water-Quality Concerns ..............................................25

Long-Term Water-Quality Concerns ..............................................................................25

Eutrophication ..........................................................................................................25

Sedimentation ..........................................................................................................52

Distribution and Sources of Bacteria and Other Potential Pathogens...........58

Emerging Water-Quality Concerns ................................................................................58

Disinfection By-Products .......................................................................................58

Sodium and Chloride ...............................................................................................67

Effects of Climate.....................................................................................................71

Integrated Framework for an Enhanced Water-Quality Monitoring Program...................................75

Modified Monitoring Framework ....................................................................................................83

Enhanced Spatial and Temporal Resolution of Water-Quality Assessments ...........................86

Watersheds.................................................................................................................................86

Reservoirs ...................................................................................................................................90

Susquehanna River ...................................................................................................................93
iv

Enhanced Documentation of Data and Quality of Data Collection.............................................93

Benefits of an Enhanced Water-Quality Monitoring Program ....................................................94

Summary........................................................................................................................................................94

Long-Term and Emerging Water-Quality Concerns ......................................................................95

Description of Water-Quality Monitoring .......................................................................................95

Review and Evaluation of Monitoring .............................................................................................96

Quality of Monitoring Database and Data .............................................................................96

Monitoring to Support Modeling to Address Water-Quality Concerns ............................96

Monitoring to Address Individual Water-Quality Concerns ...............................................96

Long-Term Water-Quality Concerns ..............................................................................96

Emerging Water-Quality Concerns ................................................................................99

Framework Integration to Enhance Water-Quality Monitoring ................................................100

Framework Design...................................................................................................................100

Spatial and Temporal Resolution of Water-Quality Assessments ...................................100

Data Documentation and Quality .........................................................................................101

Implementation of Enhanced Monitoring .....................................................................................102

Acknowledgments.....................................................................................................................................102

References Cited........................................................................................................................................102

Appendix A: Water-Quality Monitoring to Support Watershed Restoration...................................109

Appendix B: Descriptions of Data Collected at Watershed Tributary and 

Reservoir Monitoring Stations ...................................................................................................117

Appendix C: Review of Baltimore Reservoir Ashburton and Montebello 

Treatment Facilities Laboratory Quality-Assurance Plans....................................................122

Appendix D: Plant Ecology Group (PEG) Model of Seasonal Succession of 

Plankton in Freshwater ...............................................................................................................131

Figures

1. Map showing location of reservoirs and watersheds for the City of 

Baltimore, Maryland.....................................................................................................................6

2. Diagram showing water-quality concerns related to impairments in 

watershed tributary, reservoir, or drinking-water quality and long-term 

monitoring in the Baltimore Reservoir System........................................................................9

3. Maps showing (A) tributary and (B) reservoir monitoring stations in the 

Baltimore reservoir watersheds ..............................................................................................16

4. Composite generalized seasonal depth profile of algal-impaired 

water-quality conditions in Liberty Reservoir—from turbidity, 

algal-count, color, and concentration data for chlorophyll-a, 

dissolved oxygen (DO), manganese (Mn), and iron (Fe) ......................................................27

5–18. Graphs showing—

5. Annual median ammonia-nitrogen concentrations in dry-weather 

flows at (A) Liberty and (B) Loch Raven Reservoir tributaries, 1982–91...................31
v

6. Nitrate-nitrogen concentrations in dry-weather flows at (A) Middle 

Run tributary in the Liberty Reservoir watershed, (B) Western Run 

tributary in the Loch Raven Reservoir watershed, and (C) Graves Run 

tributary in the Prettyboy Reservoir watershed, 1982–2000 .......................................32

7. Mean monthly nitrate- and nitrite-nitrogen concentrations in 

(A) upper (Reservoir station NPA0105), and (B) lower (Reservoir 

station NPA0059) parts of Liberty Reservoir, 1994–2001..............................................34

8. (A) Annual loads of total phosphorus and (B) proportion of total 

annual phosphorus load transported by dry-weather flows for six 

gaged streams and subbasins in the Loch Raven and Liberty 

Reservoir watersheds, 1983–90.......................................................................................35

9. (A) Mean annual total phosphorus concentration and (B) total 

annual phosphorus load for gaged streams and subbasins in the 

Loch Raven and Liberty Reservoir watersheds, 1983–90............................................36

10. Total phosphorus concentrations for dry-weather flows at selected 

subbasin tributaries in the Liberty Reservoir watershed and in the 

shallow surface (less than 30-foot depth) layer in the middle part 

of Liberty Reservoir, 1982–2000 .......................................................................................38

11. Total phosphorus concentrations for dry-weather flows at selected 

subbasin tributaries in the Prettyboy Reservoir, 1982–2000 .......................................38

12. Total phosphorus concentrations for dry-weather flows in the Loch 

Raven Reservoir watershed along Gunpowder Falls, from just below 

the Prettyboy Reservoir outlet to Loch Raven Reservoir, 1982–2000 ........................39

13. (A) Total algal counts (TAC) and (B) chlorophyll-a concentrations 

for shallow surface waters (less than 30 feet deep) at selected 

stations in the Liberty, Loch Raven, and Prettyboy Reservoirs, 

1981–2001 ............................................................................................................................40

14. Seasonal patterns in monthly total phosphorus concentrations and 

rates of dry-weather flow for tributaries in the Loch Raven Reservoir 

watershed, 1981–93...........................................................................................................42

15. Ratio of annual median dissolved phosphorus concentration to 

annual median total phosphorus concentration in gaged tributaries 

of the (A) Liberty and (B) Loch Raven Reservoir watersheds, 1982–92....................44

16. Mean monthly dissolved-oxygen depth-profile concentrations for 

(A) upper and (B) lower Liberty Reservoir, 1994–2001.................................................49

17. Monthly mean dissolved-oxygen concentrations in (A) epilimnetic 

waters and (B) hypolimnetic waters in lower Prettyboy Reservoir, 

1992–2004 ............................................................................................................................50

18. (A) Annual mean concentrations of suspended sediment, (B) total 

annual suspended-sediment loads and (C) proportion of total annual 

loads transported by dry-weather flows for six gaged tributaries in 

subbasins in the Loch Raven and Liberty Reservoir watersheds, 

1983–90 ................................................................................................................................54

19. Photographs showing terrestrial vegetation growing on exposed in-lake 

bed sediments in upper Prettyboy Reservoir in 2002............................................................57

20–32. Graphs showing—

20. Total trihalomethane concentrations at selected sampling locations 

in the water-supply distribution system from the (A) Ashburton 

(Liberty Reservoir) and (B) Montebello (Loch Raven Reservoir) 

treatment facilities, January 2003–July 2008 ................................................................62
vi

21. Total haloacetic acid concentrations at selected sampling locations 

in the water-supply distribution systems from the (A) Ashburton 

(Liberty Reservoir) and (B) Montebello (Loch Raven Reservoir) 

treatment facilities, January 2003–July 2008 ................................................................63

22. Concentrations of total organic carbon in the Baltimore Reservoir 

treatment facilities, April 2003–July 2008 ......................................................................64

23. Total concentrations of trihalomethanes for selected sampling 

locations in the Ashburton distribution system, and total organic 

carbon concentrations in raw intake and treated waters in the 

Ashburton treatment plant, April 2003–July 2008.........................................................66

24. Concentration of sodium in intake waters at the Montebello water 

treatment facility, Loch Raven Reservoir, January 1973–January 2004 ...................68

25. Mean annual chloride concentration in intake waters at the 

Montebello water treatment facility, Loch Raven Reservoir, 1925–67......................68

26. (A) Chloride concentrations, 1992–2000, and (B) conductivity, 

1984–2000, of in-lake shallow waters (less than 30 feet deep) in 

Liberty Reservoir................................................................................................................69

27. Examples of conductivity in shallow waters (less than 30 feet deep) 

of the Baltimore Reservoirs, and chloride concentrations in upstream 

tributary dry-weather flows, 1982–2000.........................................................................70

28. Relations between median concentrations of chloride in all dryweather tributary flows for selected time periods and selected 

1999 landscape characteristics in tributary subbasins of the 

Baltimore Reservoir watersheds, various years of record.........................................71

29. Chloride concentrations for finished supply waters at Montebello 

and Ashburton treatment facilities (1982–2004), reservoir tributaries 

(1982–2004), and selected Baltimore City streams (1997–2004).................................72

30. Long-term streamflow characteristics with major drought-recovery 

periods for U.S. Geological Survey station LIT0002 (Little Falls at 

Blue Mount, Maryland) in the Loch Raven Reservoir watershed, 

1941–2007 ............................................................................................................................73

31. Annual variation in surface-water elevation in Prettyboy Reservoir, 

indicative of releases to replenish Loch Raven Reservoir under 

normal and drought conditions, 1994–2004 ...................................................................73

32. Cumulative annual distribution of streamflow and time with selected 

high-flow (75th percentile or greater) statistics for six streamgages 

associated with monitoring stations in Liberty and Loch Raven 

Reservoir watersheds from 2001–06, including driest (2002) and 

wettest (2004) years ..........................................................................................................85

A1. Map showing Gunpowder Falls watershed monitoring sites within 

Loch Raven and Prettyboy Reservoir watersheds..............................................................112
vii

Tables

1. Reservoir and watershed characteristics for the City of Baltimore, 

Maryland, drinking-water supply system.................................................................................7

2. Federal Clean Water Act Section 303(d) impairments for Prettyboy, 

Loch Raven, and Liberty Reservoirs ........................................................................................13

3. Bioassay results for nutrient-spiked samples of Selanastrom capricornatum ...............29

4. Estimated average annual loads of nitrogen and phosphorus to the 

Baltimore reservoirs, various periods of record between 1973–97 ...................................29

5. Median ammonia- and nitrate-nitrogen concentrations in the Baltimore 

reservoirs, 1981–93.....................................................................................................................33

6. Mean total phosphorus and dissolved (orthophosphate) phosphorus 

concentrations and yields for Liberty Reservoir watershed tributaries, 

1981–93 .........................................................................................................................................43

7. Number of storm events with water-quality sampling, Loch Raven and 

Liberty Reservoir watersheds, 1994–2008 ..............................................................................45

8. Reservoir trophic conditions during mid to late spring through early fall, 

1981–2000 .....................................................................................................................................46

9. Annual maximum concentrations of total organic carbon, trihalomethanes, 

and haloacetic acids in raw and treated waters in the Ashburton treatment 

plant, Liberty Reservoir, 1997–2001...............................................................................................60

10. Summary statistics for annual concentrations of regulated total 

trihalomethanes and haloacetic acids in finished waters at the Montebello 

treatment facility, Loch Raven Reservoir, 1996–2003............................................................60

11. Number of sampling dates that U.S. Environmental Protection Agency 

Maximum Contaminant Levels for disinfection by-products were 

exceeded at one or more stations in the water distribution systems at 

the Ashburton or Montebello treatment facilities, 2003–08.................................................64

12. Possible improvements identified in scientific or technical investigations 

that address one or more water-quality concerns of the Baltimore Reservoir 

Watershed Protection Program and required data from the long-term 

monitoring program....................................................................................................................76

13. Modified monitoring network for reservoir watershed tributaries and 

reservoirs in the Baltimore, Maryland drinking-water supply system ..............................87

14. Modified data collection for hydrodynamic and water-quality constituents 

or characteristics at reservoir watershed tributary stations in the 

Baltimore, Maryland drinking-water supply system.............................................................89

15. Modified data collection for climatic, hydrodynamic, and water-quality constituents 

or characteristics at reservoir locations in the Baltimore, Maryland, drinking-water 

supply system..............................................................................................................................91

A1. Nutrient synoptic summaries for Liberty and Prettyboy Reservoir 

watersheds ................................................................................................................................113
viii

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

million gallons (Mgal) 3,785 cubic meter (m3)

billion gallons (Ggal) 3,785,000 cubic meter (m3)

Flow rate

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

cubic foot per second per square

mile [(ft3/s)/mi2]

0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

million gallons per day per 

square mile [(Mgal/d)/mi2]

1,461 cubic meter per day per square

kilometer [(m3/d)/km2]

billion gallons per day (Ggal/d) 43.81 cubic meter per second (m3/s)

billion gallons per day per square 

mile [(Ggal/d)/mi2]

1,461,000 cubic meter per day per square

kilometer [(m3/d)/km2]

Mass

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg)

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

 °F = (1.8 x °C ) + 32

Specific conductance (conductivity) is given in micromhos per centimeter (micromhos/cm).

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

or micrograms per liter (μg/L).

Water year for surface-water supply is the 12-month period October 1 through September 30. 

The water year is designated by the calendar year in which it ends and includes 9 of the 12 

months.
ix

α Accepted statistical significance level

BMC Baltimore Metropolitan Council

BMP Best Management Practice

CWA Clean Water Act

DBP Disinfection by-product

DPW Department of Public Works, Baltimore, Maryland

DEPRM Baltimore County Department of Environmental Protection and Sustainability 

 (formerly Resource Management)

HAA Haloacetic acid

ICPRB Interstate Commission on the Potomac River Basin

MDE Maryland Department of the Environment 

NPDES National Pollution Elimination Discharge System

p Statistical power of test

RTG Reservoir Technical Group

SDWA Safe Drinking Water Act

SRBC Susquehanna River Basin Commission

THM Trihalomethane

RWMA Reservoir Watershed Management Agreement

RWPC Reservoir Watershed Protection Committee (earlier version of RTG)

RWPS Reservoir Watershed Protection Subcommittee (earlier version of RWPC)

USEPA U.S. Environmental Protection Agency

WWTP Waste Water Treatment Plants

Abbreviations

The Water-Quality Monitoring Program for the Baltimore 

Reservoir System, 1981–2007—Description, Review 

and Evaluation, and Framework Integration for 

Enhanced Monitoring 

By Michael T. Koterba, Marcus C. Waldron, and Tamara E.C. Kraus

Abstract

The City of Baltimore, Maryland, and parts of five surrounding counties obtain their water from Loch Raven and 

Liberty Reservoirs. A third reservoir, Prettyboy, is used to 

resupply Loch Raven Reservoir. Management of the watershed conditions for each reservoir is a shared responsibility 

by agreement among City, County, and State jurisdictions. 

The most recent (2005) Baltimore Reservoir Watershed 

Management Agreement (RWMA) called for continued and 

improved water-quality monitoring in the reservoirs and 

selected watershed tributaries. The U.S. Geological Survey 

(USGS) conducted a retrospective review of the effectiveness of monitoring data obtained and analyzed by the RWMA 

jurisdictions from 1981 through 2007 to help identify possible 

improvements in the monitoring program to address RWMA 

water-quality concerns.

Long-term water-quality concerns include eutrophication 

and sedimentation in the reservoirs, and elevated concentrations of (a) nutrients (nitrogen and phosphorus) being transported from the major tributaries to the reservoirs, (b) iron 

and manganese released from reservoir bed sediments during 

periods of deep-water anoxia, (c) mercury in higher trophic 

order game fish in the reservoirs, and (d) bacteria in selected 

reservoir watershed tributaries. Emerging concerns include 

elevated concentrations of sodium, chloride, and disinfection 

by-products (DBPs) in the drinking water from both supply 

reservoirs. Climate change and variability also could be 

emerging concerns, affecting seasonal patterns, annual 

trends, and drought occurrence, which historically have led to 

declines in reservoir water quality.

Monitoring data increasingly have been used to support 

the development of water-quality models. The most recent 

(2006) modeling helped establish an annual sediment Total 

Maximum Daily Load to Loch Raven Reservoir, and instantaneous and 30-day moving average water-quality endpoints 

for chlorophyll-a (chl-a) and dissolved oxygen (DO) in Loch 

Raven and Prettyboy Reservoirs. Modelers cited limitations in 

data, including too few years with sufficient stormflow data, 

and (or) a lack of (readily available) data, for selected tributary and reservoir hydrodynamic, water-quality, and biotic 

conditions. Reservoir monitoring also is too infrequent to 

adequately address the above water-quality endpoints.

Monitoring data also have been effectively used to generally describe trophic states, changes in trophic state or conditions related to trophic state, and in selected cases, trends in 

water-quality or biotic parameters that reflect RWMA waterquality concerns. Limitations occur in the collection, aggregation, analyses, and (or) archival of monitoring data in relation 

to most RWMA water-quality concerns.

Trophic, including eutrophic, conditions have been 

broadly described for each reservoir in terms of phytoplankton production, and variations in production related to typical 

seasonal patterns in the concentration of DO, and hypoxic 

to anoxic conditions, where the latter have led to elevated 

concentrations of iron and manganese in reservoir and supply 

waters. Trend analyses for the period 1981–2004 have shown 

apparent declines in production (algal counts and possibly 

chl-a). The low frequency of phytoplankton data collection 

(monthly or bimonthly, depending on the reservoir), however, 

limits the development of a model to quantitatively describe 

and relate temporal variations in phytoplankton production 

including seasonal succession to changes in trophic states or 

other reservoir water-quality or biotic conditions.

Extensive monitoring for nutrients, which, in excessive 

amounts, cause eutrophic conditions, has been conducted in 

the watershed tributaries and reservoirs. Data analyses (1980–

90s) have (a) identified seasonal patterns in concentrations, (b) 

characterized loads from (non)point sources, and (c) shown 

that different seasonal patterns and trends in nutrient concentrations occur between watershed tributaries and downstream 

reservoirs. A lack of data for total nitrogen and (or) available 

phosphorus limits direct comparisons of temporal or spatial 

variations in nutrient availability (comparable forms or ratios) 

between watershed tributaries and reservoirs.
2 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Eutrophic conditions in the shallow water layer (30 feet 

in depth or less) in each reservoir have been assessed with four 

Carlson Trophic State Indices (TSIs)—derived from concentrations of chl-a, total phosphorus (TP), or DO, and (Secchi 

disc) transparency data. The frequency of eutrophic conditions 

for the entire period from 1982–2000 differed within each 

reservoir, and among the reservoirs, depending on which TSI 

index was used. The use of each index to compare trophic 

conditions among the reservoirs, however, possibly is biased 

because of the manner by which TSI data were collected, 

aggregated, or analyzed. In addition, no analyses of these 

indices were encountered that assessed possible trends in the 

frequency of eutrophic or mesotrophic conditions during this 

period.

Analyses of suspended-sediment data (1982–mid-90s) 

indicate that tributary concentrations and loads varied markedly within a year, and from year to year, but were clearly 

highest in wet years. Most sediment is carried by storm- as 

opposed to dry-weather (low) flow. Sediment transport has 

reduced reservoir capacity by 3 to 11 percent, and remains the 

major source of the TP load to the reservoirs. The role of this 

sediment as a source of available phosphorus (unmeasured) for 

phytoplankton production, however, has not been adequately 

addressed.

Manganese and iron are frequently monitored in watersupply intake waters during reservoir stratification and initial 

turnover. Elevated concentrations of these metals often occur 

at the supply intakes following their release from reservoir 

bed sediments under anoxic conditions, which can result from 

the decomposition of algal bloom residues. Monitoring in the 

reservoirs is too infrequent (monthly to bimonthly) to provide 

sufficient advanced warning of their occurrence at the intakes.

Elevated concentrations of mercury in game fish in the 

reservoirs are considered the end result of atmospheric deposition and beyond the control of RWMA jurisdictions. The 

submergence of terrestrial plants established on reservoir bed 

sediments exposed during droughts could enhance methylmercury production and biological uptake during reservoir 

recovery. However, this cannot be determined by conventional 

synoptic monitoring for mercury in game fish.

Fecal coliform bacteria have occurred at elevated counts 

in selected reservoir watershed tributaries, but counts in 

supply-reservoir intake waters consistently have been below 

the State recreational water-contact standard. Depending on 

results from synoptic surveys conducted by RWMA jurisdictions in the watersheds, the State could require routine monitoring of bacteria in the tributaries.

Among emerging concerns, trihalomethanes (THMs) and 

haloacetic acids (HAAs) are DBPs created by chlorination 

that are present in the drinking-water distribution systems of 

both supply reservoirs. Analysis of DBP data (2003–08) by 

the USGS indicates that the total concentrations of THMs and 

HAAs could exceed Federal standards under a pending rule 

change on approximately 19 percent and 40 percent of the 

sampling dates, respectively, at one or more monitoring stations in each water-distribution system. THM concentrations 

in drinking water varied seasonally, whereas HAA concentrations did not. There was little correlation between total concentrations of THMs and HAAs at a given monitoring station, 

or between monitoring-station concentrations of either DBP 

and total organic carbon (TOC) in intake waters. Monitoring 

of TOC alone will not identify intake waters associated with 

high concentrations of DBPs after chlorination.

In 2003, sodium and chloride concentrations at supply 

intakes were three-to-four-times greater than in the 1970s. 

Concentrations generally peaked during the winter months. 

Watershed and reservoir monitoring do not include the collection of sodium data. Monitoring also is too infrequent to 

provide either advanced warning of elevated sodium and chloride concentrations at the supply-reservoir intakes, or timely 

information on reductions in their concentrations if management activities are implemented to reduce road-salt use—the 

suspected source of the recent increases.

Projected changes combined with the inherent variability 

in climate in the Mid-Atlantic region indicate more intense 

storms with heavy precipitation and more frequent drought 

conditions. These changes imply increases in storm-borne 

contaminants (nutrient, sediment, salt, and bacterial loads), 

which could adversely affect reservoir water quality, particularly during recovery from drought conditions. Monitoring of 

stormflow does not appear to be adequate to address climate 

change and variability.

The 2007 Baltimore Reservoir System monitoring 

program could be improved in three major areas: (a) the 

monitoring design framework, (b) the temporal and spatial 

resolution of water-quality assessments in the major tributaries and reservoirs, and (c) the management and archival of 

data. Improvements in the framework design could include 

adoption of a quantitative phytoplankton model, such as the 

Phytoplankton Ecology Group model. Such models describe 

intra-seasonal, seasonal, and annual variations in phytoplankton abundance and succession. The model data can be 

analyzed in relation to temporal variations in nutrients or 

TSIs. The characterization of these biotic and water-quality 

conditions could be evaluated in relation to temporal variations in climate by the collection of climatic and water-quality 

data that reflect the full range in tributary flows and reservoir 

hydrodynamics within a year and from year to year. The 

minimal monitoring data would include daily temperature 

(mean), daily precipitation (total and type), continuous or 

partial records of streamflows depending on the type of tributary monitoring station, and daily water levels, withdrawals, 

and releases from each reservoir. To aid in this evaluation, 

the monitoring framework could incorporate the routine use 

of statistical and modeling methods to help define, aggregate, 

analyze, and interpret data.

Improvements in spatial and temporal assessments of 

water-quality conditions could be realized with two major and 

selected minor modifications to historical monitoring. First, to 

quantify water-quality conditions for the full range in tributary 

flows in the reservoir watersheds, sampling could include 3 to 

15 pre-defined high (or storm-) flows per year at each of seven 
Introduction 3

stations—three historical stations in each of the two supply 

reservoirs and one new station on a tributary to Prettyboy 

Reservoir. Pre-defined base-flow conditions could be sampled 

at each station on a monthly fixed time interval. Second, two 

fixed-station continuous monitors could be established in each 

reservoir to provide daily 5-foot-depth-increment profiles for 

selected parameters—water temperature, DO, pH, specific 

conductance, chl-a, turbidity, and depth of measurement. Data 

from these monitors could be transmitted to water-treatment 

staff to provide advanced warning of potential problems with 

supply intake waters.

A comprehensive quality-assurance program and plan 

(QAPP) with clear lines of responsibility could help ensure 

collection of the correct type and quality of data. The QAPP 

would include the following: (a) clear and concise definitions 

of the data and data-quality requirements for each water-quality concern; (b) field and laboratory methods and analytical 

procedures to obtain and provide the required data; (c) procedures to archive, clearly remark, and qualify data, including 

quality-assurance and control data; (d) procedures to routinely 

evaluate collected data in relation to data requirements; and 

(e) procedures to modify and document changes in field and 

laboratory methods.

Introduction

The City of Baltimore, Maryland (hereafter referred 

to as the City) supplies drinking water obtained from three 

reservoirs to approximately 1.8 million people in the City and 

parts of five Maryland Counties (Anne Arundel, Baltimore, 

Carroll, Harford, and Howard). Contributing watersheds 

to these reservoirs are primarily located outside the City in 

two Maryland counties (Baltimore and Carroll). The City 

is primarily responsible for managing and monitoring the 

reservoirs, monitoring in the major watershed tributaries, and 

assessing reservoir and major tributary conditions that affect 

the quality of drinking water. As the reservoir watersheds lie 

largely outside the jurisdiction of the City, however, managing 

and assessing reservoir-watershed conditions that could affect 

reservoir water quality is shared by City, County, and State 

governments. This shared responsibility is outlined in a voluntary Reservoir Watershed Management Agreement (RWMA) 

and related Reservoir Watershed Action Strategy (RWAS). 

Implementation of the RWMA and RWAS involves the 

Baltimore Metropolitan Council (BMC), which provides 

staff for RWMA coordination. Management of the RWMA 

is conducted by a Watershed Protection Committee (WPC), 

which informs the BMC (Management Committee) of ongoing 

work. The WPC also provides policy guidance to a Reservoir 

Technical Group (RTG), and reviews their technical work. The 

RTG, a professional advisory body, is responsible for guiding 

day-to-day operations of the RWMA under the RWAS. It also 

provides technical advice, assistance, and recommendations to 

the WPC and RWMA signatories or their designees.

The most recent (2005) RWMA and RWAS reflect knowledge gained in part from routine water-quality monitoring in 

the reservoirs and selected reservoir watershed tributaries, 

which began in the early 1980s. The resulting monitoring data 

have served a wide range of purposes. For example, data routinely collected by drinking-water purveyors, primarily on raw 

water obtained through intakes in each water-supply reservoir, 

coupled with knowledge gained from their long-term monitoring and treatment of reservoir waters, helps guide daily 

decisions on which intakes to use to withdraw water from the 

reservoirs in order to provide suitable potable water at reduced 

costs. Data obtained from routine monitoring in the reservoirs 

are used for periodic assessments of reservoir water quality in 

relation to designated recreational uses (water-contact activities such as fishing and non-motorized boating, where permitted) and in relation to the general ecological health or trophic 

state of each reservoir. Routine monitoring in the reservoirs 

and selected watershed tributaries provides data to periodically characterize states, changes, or trends in water quality 

in the reservoirs and tributaries, and target management and 

restoration activities in the watersheds. Monitoring data also 

have aided in the development of watershed-reservoir models, 

which are used to guide management strategies to improve 

water quality in the watersheds tributaries and reservoirs. 

As with most long-term monitoring efforts, the City and 

its RWMA partners recognize that the design and scope of the 

monitoring program require periodic evaluation. The purpose 

of this report is to aid the RWMA partners, and, in particular, 

the RTG, in an evaluation of the monitoring program as 

follows: 

a) To describe the long-term and emerging monitoringrelated RWMA water-quality concerns for the 

Baltimore reservoir system; 

b) To evaluate the historical (1981–2007) and current (as 

of 2007) monitoring program in relation to its ability to 

provide suitable, relevant, and technically sound data 

to characterize water-quality conditions directly related 

to long-term and emerging water-quality concerns and 

in relation to expressed 2005 RWMA goals and action 

strategies; and

c) To provide a framework to identify continuing and 

additional monitoring that could enhance the ability of 

the RWMA partners to address specific water-quality 

concerns.

The scope of this report focuses on monitoring that was 

conducted either in the reservoirs or on selected major tributaries (subbasins) of the reservoir watersheds chiefly from the 

early 1980s (1981 or 1982, depending on the water-quality 

parameter) through 2007. The scope of this report also is a 

retrospective by nature, in that the review and evaluation are 

conducted mainly on the basis of an examination of dozens 

of historical investigative and technical reports produced 

through 2007, which discussed the production, analysis, or 

utilization of monitoring data, described findings, and possibly 
4 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

recommended modifications to improve the monitoring 

program. 

The reports used in this retrospective review and evaluation were obtained during interviews and (or) by follow-up 

requests to agencies within or contracted under 2005 or past 

reservoir agreements and action strategies to provide data 

and (or) information relative to the Baltimore Reservoir 

Drinking-Water System. The reports include internal as well 

as published documents produced over several decades from a 

variety of agencies and organizations. As a result, the historical documents differed in the level of technical and scientific 

analysis, and in the manner and form in which monitoring data 

or interpretive analysis were reported and described (tables 

or figures). Limitations in the former are noted in this report 

where applicable. Modifications to the latter, where presented 

in this report for illustrative purposes, were minimal, and were 

used to improve visual quality and (or) maintain consistency 

in the names of reservoirs, reservoir watersheds, monitoring 

stations, or other place names used throughout this retrospective report.

Baltimore Drinking-Water Reservoir System

Drinking water for the City and all or parts of five 

Maryland counties is supplied by three surface-water reservoirs—Liberty, Loch Raven, and Prettyboy—and their 

contributing watersheds, which are entirely located in the 

Piedmont Physiographic Province in central Maryland (fig. 1). 

Water for consumptive use is withdrawn at intakes located in 

two of the reservoirs—Liberty and Loch Raven, which hereafter are collectively referred to as the water-supply reservoirs. 

The third reservoir, Prettyboy, is mainly used to provide additional storage and to re-supply the Loch Raven Reservoir. In 

addition, and generally during drought conditions, supplemental water supplies are obtained from the Susquehanna River 

upstream of Conowingo Dam, which is located approximately 

45 mi (miles) northeast of the City (fig. 1).

Watershed and Reservoir Characteristics

Liberty Reservoir watershed covers 164 mi2 (square 

miles; fig. 1, table 1), mainly in Carroll County and partly in 

Baltimore County, Maryland. Major land uses in the watershed 

are agriculture (43 percent), forest (32 percent), and developed 

land (22 percent; Maryland Department of Planning, 2000a; 

Winfield and Sakai, 2003). Agricultural lands are mainly 

cropland and pasture (37 percent and 6 percent, respectively). 

Developed lands include major transportation corridors and 

areas with predominantly industrial, commercial, and (or) residential infrastructure. Surface water to the reservoir is primarily supplied by the North Branch Patapsco River. Reservoir 

property covers 9,200 acres (table 1)—or 9 percent of the 

total watershed area—of which 3,100 acres is open water at 

reservoir capacity, estimated to be 37.7 Ggal (billion gallons) 

in 2001.

Loch Raven Reservoir watershed, excluding the 

Prettyboy Reservoir and watershed (fig. 1), covers 223 mi2

(table 1), mostly in Baltimore and Carroll Counties, with 

small parts in Harford County, Maryland and York County, 

Pennsylvania. Major land uses are forest (38 percent), agriculture (27 percent), developed (21 percent), and mixed open (15 

percent) (Maryland Department of Planning, 2000b; Maryland 

Department of the Environment, 2004a). Agricultural lands 

are mainly pasture and cropland (17 percent and 10 percent, 

respectively). Surface water to the reservoir is supplied primarily by the Gunpowder River. Reservoir property covers 

8,000 acres—or 5.7 percent of the total watershed area—of 

which about 2,400 acres is open water at reservoir capacity, 

estimated to be 19.1 Ggal as of 1998. 

Prettyboy Reservoir watershed covers 80 mi2 (table 1), 

mostly in Baltimore and Carroll Counties in Maryland, with 

a small part in York County, Pennsylvania (fig. 1). Major land 

uses in the Maryland part of the watershed include agriculture 

(50 percent), forest (38 percent), and developed (13 percent) 

lands (Baltimore County Department of Environmental 

Protection and Resource Management, 2008). Agricultural 

lands are primarily cropland and pasture (39 percent and 11 

percent, respectively). Surface water to the reservoir is supplied primarily by the Gunpowder River. Reservoir property 

covers 7,380 acres—or 14.3 percent of the total watershed 

area (table 1)—of which 1,500 acres is open water at reservoir 

capacity, estimated to be 18.4 Ggal in 1998.

Reservoir Watershed Management and 

Reservoir Operation

The City owns, and through its Department of Public 

Works (DPW), operates the three reservoirs to provide treated 

drinking water from the Liberty and Loch Raven water-supply 

reservoirs to approximately 1.8 million residents of the City 

and parts of five adjacent counties—Anne Arundel, Baltimore, 

Carroll, Harford, and Howard. Exclusive rights to surface 

water in the reservoirs and the Maryland part of their contributing watersheds have been granted to the City by the State 

legislature. However, only approximately 8 percent (table 1) 

of the total watershed area that drains into the three reservoirs 

actually is owned and under direct control of the City. Since 

the mid-1970s, the City DPW has been aided in its efforts 

to maintain the quality of water supplies by signatory City, 

County, and State organizations to a series of reservoir and 

watershed protection agreements and action strategies leading 

to the (2005) RWMA and RWAS. 

The water-quality related goals of the 2005 RWMA for 

the program are as follows (Reservoir Watershed Management 

Agreement, 2005, p. 5–6): 

a) To ensure the three reservoirs and their respective 

watersheds will continue to serve as:

1) Sources of high-quality raw water for the Baltimore 

metropolitan water-supply system; and
Introduction 5

2) Areas where the surface waters will continue to 

support existing environmental, wildlife-habitat, and 

aesthetic purposes, as well as beneficial recreational 

uses.

b) To ensure that water quality in the three reservoirs and 

their tributaries consistently meet all applicable waterquality standards established by Federal and State 

regulations.

c) To ensure continued satisfactory water quality in the 

reservoirs themselves, by adopting the following specific technical goals:

1) Maintain existing water quality in the reservoirs and 

their tributaries, and reduce phosphorus, sediment, 

bacterial, sodium and chloride loadings to the reservoirs (and their tributaries) to acceptable levels1

, in 

order to:

(i) Eliminate existing, and prevent future, waterquality impairments, as defined under the Federal 

Clean Water Act (CWA), Section 303(d);

(ii) Prevent health and nuisance (taste and odor) conditions from developing in the treated water; and

(iii) Assist Baltimore City and Anne Arundel, Carroll, 

Harford, and Howard Counties (as water providers) to meet the Federal Safe Drinking Water Act 

(SDWA) requirements.

2) To improve the safety and security of the metropolitan water supply by reducing the risk of hazardous 

material contamination of the reservoir watersheds.

d) To commit program participants to promote certain 

types of land use and certain stewardship practices 

within the watershed that are intended to minimize the 

delivery of certain types of pollutants (including sediment and nutrients) to the three reservoirs.

The 2005 RWMA is accompanied by the 2005 RWAS 

(Reservoir Watershed Management Agreement Action 

Strategy, 2005). This strategy includes and encourages program participants to continue a multi-decadal effort to promote 

land use and stewardship practices within the watersheds that 

are intended to reduce the delivery of selected pollutants (for 

example, nutrients and sediment) to the reservoirs.

Whereas the 2005 RWMA and RWAS are designed primarily for management of the reservoir watersheds, the City 

manages and operates the reservoirs to provide drinking-water 

supplies. Drinking water from Liberty Reservoir is produced 

at the Ashburton treatment facility, and drinking water from 

Loch Raven Reservoir is produced at the Montebello treatment 

facility.

1

 “Acceptable” is not explicitly defined in the agreement, but can be considered guided by elements (i), (ii), and (iii).

Water levels in the three reservoirs vary seasonally in 

response to climatic conditions and withdrawals for supplies. 

Summer seasonal drawdowns in water levels are a normal part 

of reservoir operations; however, recovery from high demand 

or climate stresses is slow, particularly in the case of Liberty 

Reservoir. For example, it can take several months or more for 

the reservoirs to recover after a substantial decrease in water 

levels (Valcik, 1975; Winfield and Sakai, 2003). Therefore, 

variations in water levels guide daily management decisions 

on withdrawals from each water-supply reservoir and releases 

of water from Prettyboy Reservoir. To reduce the duration 

and extent of drawdown in any reservoir, and particularly in 

Liberty Reservoir, the City employs what is officially referred 

to as their “firming program,” which represents the documented procedure that utilizes water levels to govern reservoir 

withdrawals (Loch Raven and Liberty Reservoirs) or releases 

(Prettyboy Reservoir) to meet supply demands (Winfield and 

Sakai, 2003). This term will be used hereafter in this report. 

Under the firming program, and assuming that all 

reservoirs have sufficient reserves, withdrawals for drinking 

water generally are made from both Liberty and Loch Raven 

Reservoirs. Daily withdrawals are incrementally reduced from 

Liberty Reservoir, however, as a function of seasonal demand 

and its water levels. For example, during the period of highest 

demand (generally June through September) and assuming 

all reservoirs are near capacity, withdrawals from Liberty 

Reservoir are typically 160 Mgal/d (million gallons per day) 

or more. Withdrawals from this reservoir are incrementally 

reduced, however, when the water level near the intakes in the 

lower part of this reservoir falls below 415 ft (feet) to as little 

as 60 Mgal/d if the water level falls below 370 ft. Increased 

withdrawals from Loch Raven Reservoir are used to make 

up the shortfall in demand. If demands result in water levels 

falling below approximately 236 ft near the intakes in the 

lower part of Loch Raven Reservoir, water is released from 

Prettyboy Reservoir, which is approximately 18 mi upstream 

on the Gunpowder River, to resupply Loch Raven Reservoir. 

The DPW also can release water from Prettyboy Reservoir as 

necessary during warmer low-flow periods to help maintain 

the aquatic habitat for stocked trout along the Gunpowder 

River between the two reservoirs.

The primary goal of the City in withdrawing water from 

either water-supply reservoir is to obtain the highest quality 

of raw water in order to minimize treatment costs (Winfield 

and Sakai, 2003). This is achieved by withdrawing water 

from one or more vertical intakes located at different depths 

at gatehouses in the middle (Loch Raven Reservoir only) and 

(or) at the lower end of each water-supply reservoir. City staffs 

at each reservoir treatment facility generally decide which 

intake(s) to use to withdraw raw water, and, if multiple intakes 

are used, the mixing ratio of intake waters. Their decisions 

are guided by routine (daily-to-weekly) monitoring of intake 

waters coupled with knowledge obtained from the long-term 

monitoring and treatment of reservoir waters. 

During extended dry periods, water demands could result 

in continued declines in water levels in all three reservoirs. 
6 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 1. Location of reservoirs and watersheds for the City of Baltimore, Maryland (modified from Baltimore Reservoir Technical 

Group, 2004).

The firming program generally has been able to circumvent 

this problem. Under extended withdrawals from all three 

reservoirs, water is released from Prettyboy Reservoir until the 

reservoir is at 50 percent of its capacity, whereupon the City 

can exercise its option to obtain water from the Susquehanna 

River at the Conowingo Dam (fig.1). Under an agreement 

with the Susquehanna River Basin Commission (2006), and 

dependent upon river flows to the Conowingo Dam, the City 

is permitted to pump from 64 to 240 Mgal/d on the basis of a 

30-day average. The drainage area of the Susquehanna River 

Basin is 27,510 mi2

 above the dam (Susquehanna River Basin 

Commission, 2006), therefore, the low-flow limitation on City 

withdrawals typically only becomes a factor under prolonged 

regional droughts. 

Generally it is the quality of the Susquehanna River 

water, and the added costs to the City to obtain, pump (transport), and treat this water, that limit its use. For example, during a severe drought in 2001–02, the City was able to obtain 

water of reasonably good quality from the Susquehanna River 

to help meet demands; nevertheless, major withdrawals and 

drawdowns ultimately occurred in all three reservoirs. During 

and upon recovery in 2003, however, the quality of water 

in the Baltimore Reservoirs declined in relation to selected 

water-quality conditions relative to pre-drought conditions 

(Baltimore Reservoir Technical Group, 2004). During a recent 

but less severe drought and recovery in 2005–06, the City 

also chose to use water from the Susquehanna River, but soon 

after the drought began, rather than withdrawing water solely 
Introduction 7

Table 1. Reservoir and watershed characteristics for the City of Baltimore, Maryland, drinking-water supply system.

Reservoir/watershed Characteristics1

Liberty Area of watershed: 164 square miles

Area of land owned by City: 9,200 acres or 14.4 square miles

Storage capacity: Initial (1913) estimate, 40.0 billion gallons

Storage capacity: Recent (2001) estimate, 37.7 billion gallons

Length of shoreline at crest elevation: 82 miles

Normal depth: 132.8 feet

Flooded area at crest elevation: 3,106 acres

Built: 1951–53, height 175 feet

Loch Raven Area of watershed: 223 square miles (less Prettyboy watershed area)

Area of land owned by City: 8,000 acres or 12.5 square miles

Storage capacity: Initial (1913) estimate, 21.4 billion gallons

Storage capacity: Recent (1997–98) estimate, 19.1 billion gallons

Length of shoreline at crest elevation: 50 miles

Normal depth: 76 feet

Flooded area at crest elevation: 2,400 acres

Built: 1912–14; crest raised: 1921–22, height 101 feet

Prettyboy Area of watershed: 80 square miles

Area of land owned by City: 7,380 acres or 11.4 square miles

Storage capacity: Initial (1933) estimate, 19.9 billion gallons

Storage capacity: Recent (1998) estimate, 18.4 billion gallons

Length of shoreline at crest elevation: 46 miles

Normal depth: 98.5 feet

Flooded area at crest elevation 1,500 acres

Built: 1933, height 155 feet

1

 Compiled from Ortt and others, 2000; Banks and LaMotte, 1999; Weisberg and others, 1985; and R. Ortt, Maryland Geological 

Survey, written commun., 2001. 

from the reservoirs. The quality of river water in 2005–06 

was notably poorer than the quality of river water in 2001–02, 

however, and use of this water was quickly discontinued 

(Michael Kohler, City of Baltimore, Department of Public 

Works, written commun., 2010).

As of 2007, the City firming program is under review 

(Michael Kohler, City of Baltimore, Department of Public 

Works, written commun., 2010). Decisions on when to begin 

reducing withdrawals from Liberty Reservoir, increase 

withdrawals from Loch Raven Reservoir, release water from 

Prettyboy Reservoir, or obtain water from the Conowingo 

Dam on the Susquehanna River, are still dependent upon the 

quality and available volumes of water. Comparing the costs to 

obtain, transport, and (or) treat each source of water for drinking water to provide the lowest-cost drinking water is becoming increasingly important to consider as part of the firming 

program. In addition, following the drought of 2001–02, the 

Susquehanna River Basin Commission (SRBC) initiated legal 

action to limit City withdrawals of water from the Conowingo 

Dam (Baltimore Reservoir Technical Group, 2004; Winfield 

and Sakai, 2003). The SRBC also is conducting an independent review of its basin management plan (Susquehanna River 

Basin Commission, 2006) because of increased demands for 

river water by upstream, in-lake, and downstream users, particularly during drought conditions.

Ultimately, how the City manages the reservoirs could 

possibly affect the quality of water in the reservoirs during 

their recovery following major droughts. During major 

droughts, the City maintains daily withdrawals of the best 

available quality of water for supplies to reduce treatment 

costs and limit consumer complaints about the quality of 

treated water. After recovery from droughts, there typically 

is a decline in the quality of reservoir waters, which could be 

exacerbated by the repeated removal of only the best available 

quality of water, as well as a considerable quantity of water, 

during drought conditions.
8 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Overview of Water-Quality Concerns

Water-quality issues of concern to the RWMA partners 

relate primarily to impairments in designated recreational 

uses for the watershed tributaries, designated recreational and 

supply uses for the reservoirs, and ultimately, impairments 

in the quality of drinking water (fig. 2). Most of the waterquality issues of concern also are interrelated. The appearance 

of impairment conditions associated with one concern often 

can be concomitant or precede the appearance of additional 

impairments associated with other concerns. 

For the purposes of discussion, the water-quality concerns identified by the 2005 RWMA can be grouped as 

long-term or emerging concerns. Long-term concerns include 

eutrophication and sedimentation in the reservoirs, and related 

to these concerns, elevated concentrations of (a) nutrients 

(nitrogen and phosphorus) being transported from the major 

tributaries to the reservoirs, (b) iron and manganese released 

from reservoir bed sediments during periods of deep-water 

anoxia, (c) mercury in higher trophic order game fish in the 

reservoirs, and (d) bacteria in selected reservoir watershed 

tributaries. Most of these concerns generally result, in part, 

from the initial creation of the reservoirs by the flooding of 

agrarian (mainly croplands) rather than undisturbed lands, and, 

in part, from subsequent decadal changes in land use and other 

human activities on the lands that remained. As a consequence 

of the former, the quality of reservoir waters was impaired in 

relation to most of these concerns from the start. As a result 

of the latter, there is evidence that the prolonged impairments 

in reservoir water and biotic quality have and will continue to 

make improvements to tributary and reservoir water quality in 

relation to these concerns a challenge. 

Emerging water-quality concerns include elevated concentrations of disinfection by-products (DBPs), sodium, and 

chloride in the drinking water from both supply reservoirs. 

Climate change and variability also could be emerging concerns, affecting seasonal patterns, annual trends, and drought 

occurrence, which historically have led to declines in reservoir water quality. These emerging concerns reflect relatively 

recent (within the decade) changes in tributary or reservoir 

water quality, or in Federal standards related to drinking-water 

quality. Thus, the factor(s) responsible for these emerging 

water-quality concerns are not necessarily well known or 

understood. 

Most long-term or emerging water-quality concerns have 

led to identified impairments in the designated uses for the 

reservoirs or their upstream tributaries. In turn, this has led to 

regulatory actions and concerns, which also influence monitoring and are described in detail later in this report. In addition, 

each of the long-term and emerging water-quality concerns is 

examined in detail later in this report in relation to the role that 

the long-term monitoring program has played in enabling the 

RTG to obtain the necessary data to understand and address 

each of these concerns.

Long-Term Water-Quality Concerns

Routine monitoring in the main tributaries in the reservoir watersheds and in-lake monitoring in the reservoirs 

only began in the early 1980s under the first formal voluntary 

agreement developed in the mid-to-late 1970s to manage the 

reservoir watersheds to maintain or improve the quality of 

water in the reservoirs. The main impetus for this agreement 

and monitoring was a host of reservoir and drinking-water 

impairments that occurred during a severe drought in the 

mid-to-late 1960s or during reservoir recovery in the early 

1970s, or were apparent even earlier on the basis of limited 

monitoring conducted by City staff at the reservoir watersupply intakes. Examination of the possible causes of these 

impairments has a direct bearing on most RWMA long-term 

water-quality concerns and the initial design of the long-term 

monitoring program. 

Amatayakul and others (1978), Amatayakul, Defries, 

and others (1978), Ortt and others (2000), Valcik (1975), and 

others describe the early Baltimore reservoir water-supply 

system from its inception to the creation of the first voluntary 

reservoir watershed protection agreement in the mid-1970s. 

The Baltimore reservoir system was created in the early 

through mid 20th century in a largely agrarian (cropland) 

landscape, which was mostly beyond the jurisdictional control 

of the City. Following creation of Loch Raven Reservoir 

(table 1, 1921–22), and up until World War II, most remaining 

croplands underwent conversion to pasture or woodlands. 

During World War II and thereafter, however, urban development (residential, commercial, and industrial) occurred in and 

near the reservoir watersheds, largely outward from the City 

along an arc on the southwest edge of the Liberty and Loch 

Raven Reservoir watersheds, and particularly in areas such 

as Towson, Maryland (fig. 1), and further north of Towson in 

Cockeysville and Timonium, Maryland. By the early 1970s, 

similar growth had occurred in reservoir watershed towns—

for example, Hampstead and Manchester, Maryland, which 

are located along the divide between the Liberty Reservoir 

and Prettyboy Reservoir watersheds. Expansion of these areas 

continued through the 1980s and 1990s. 

Stewart and others (2005) also noted that most of the 

aforementioned changes in land use occurred in the absence 

of environmental planning to protect tributary and reservoir 

water quality. For example, they estimated that 85 percent of 

all development in Baltimore County, which includes parts of 

all three reservoir watersheds (fig. 1), occurred before institutional programs were in place to mitigate potential adverse 

environmental impacts on streams or reservoirs. 

Thus, by the year 2000, the landscape in each contributing reservoir watershed was no longer cropland, but a composite of forest, agricultural, and developed lands. Although 

land-use composition differs among reservoir watersheds, as 

of 2000, no watershed contained more than approximately 

30–40 percent forest cover (see Watershed and Reservoir 

Characteristics, this report). Given the initial and subsequent 
Overview of Water-Quality Concerns 9 Figure 2. Water-quality concerns related to impairments in watershed tributary, reservoir, or drinking-water quality and long-term monitoring in the Baltimore Reservoir System (watershed graphic modified from The H. John Heinz III Center for Science, Economics, and the Environment, 2008).
10 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

changes in land use, most long-term water-quality issues of 

concern to the RWMA partners likely arose when the reservoirs were created, or evolved during development that 

occurred before institutional measures were in place to reduce 

its adverse effects on the quality of water and biota in the 

reservoirs.

Large-scale monitoring in the Baltimore Reservoir 

System began long after most changes in land use, and largely 

evolved in response to reservoir and drinking-water quality 

impairments that arose with the severe drought and recovery 

that occurred in the late 1960s and early 1970s. Initial studies 

of the drought and recovery identified the watersheds as the 

ultimate sources of the pollutants that cause most long-term 

water-quality impairments (Valcik, 1975; Amatayakul and 

others, 1978; Amatayakul, Defries, and others, 1978). For 

example, in relation to the major phytoplankton blooms that 

occurred during the 1960s and 1970s, Valcik (1975) summarized several 1970 sanitary surveys conducted by the 

Maryland Department of Health and Mental Hygiene for each 

Baltimore reservoir watershed. He noted that poor agricultural 

practices—for example, possible overuse of chemical fertilizers and poor management of livestock and livestock 

manure—likely contributed to excessive nutrient pollution. 

Industrial and domestic wastewater effluents also were cited as 

possible contributors, in particular, the wastewater treatment 

plant discharges into Loch Raven Reservoir tributaries from 

Hampstead and Manchester, which began operations in 1970 

and 1971, respectively. He also alluded to the high concentrations of nitrate found in groundwater in areas associated 

with these and other small towns and industries in Carroll and 

Baltimore Counties as sources of concern.

Further studies in the reservoir watersheds by the 

Baltimore City Department of Public Works (DPW) (1992, 

1996, 2000, 2001) and others from the 1980s through the 

mid-1990s utilized monitoring data from the major tributaries 

to characterize pollutant (for example, nutrient and suspendedsediment) concentrations, trends, and loads in and from the 

reservoir watersheds. In addition, tributary monitoring data 

were analyzed to identify patterns or relations between tributary and reservoir water quality. Beginning in the late 1980s, 

analyses of tributary monitoring data also helped enable 

characterizations and source-water assessments of the environmental state of the reservoir watersheds and their tributaries 

(Appendix A). These characterizations and assessments laid 

the foundation for subsequent (post-1990s) short-term and 

synoptic monitoring studies in each reservoir watershed to aid 

in (a) source-water assessments, (b) identification of nonpoint 

pollutant problems and source areas, and (c) development 

and implementation of targeted restoration strategies in each 

reservoir watershed, to improve tributary water and habitat 

quality and reduce pollutant loads (Appendix A). As of 2007, 

the long-term water-quality issues of concern to the RWMA 

in the watershed tributaries continue to be eutrophication and 

major algal blooms caused by excessive concentrations of 

nutrients (nitrogen and phosphorus), suspended sediment, and 

bacteria (fig. 2).

Problems with reservoir water quality due to sedimentation and eutrophication actually were apparent even before the 

major drought and recovery of the 1960–70s. Amatayakul and 

others (1978), Amatayakul, Defries, and others (1978), Ortt 

and others (2000), Valcik (1975), and others describe the early 

Baltimore reservoir water-supply system and water-quality 

concerns. In 1881, the first Loch Raven Dam was installed 

about 1,000 ft downstream of the present Loch Raven Dam. 

This initial dam impounded about 510 Mgal of water. Heavy 

sedimentation rates, however, prompted construction of the 

current Loch Raven Dam and reservoir upstream of this original dam in 1914 (table 1). In addition to sedimentation, other 

water-quality problems were evident soon after the raising of 

the Loch Raven Dam in the 1920s. Amatayakul, Defries, and 

others (1978) analyzed long-term monitoring data from the 

Loch Raven Montebello treatment facility, and found that total 

microscopic counts (TMCs, in numbers per milliliter), a reflection of phytoplankton productivity, increased and remained 

elevated for several years after the reservoir rose. They also 

found long-term positive exponential rates of increase in average annual TMCs and chloride concentrations from 1930–55, 

markers of water-quality degradation. Significant exponential 

rates of decline in mean annual turbidity, bacterial counts, and 

concentrations of iron and manganese, however, indicated 

some improvement in water quality during this period.

During the 1960–70s, Valcik (1975) described a marked 

decline in supply reservoir water quality that was associated 

with the severe drought and recovery during this period. From 

1963–70, total algal counts initially were low (approximately 

100 organisms per milliliter) at the Montebello treatment 

facility for Loch Raven Reservoir. No major water-treatment 

problems with phytoplankton were encountered. Despite 

drought conditions, the flows at Loch Raven Dam during this 

period were about 160 Mgal/d, and reservoir water detention 

time was estimated to be about 4 months. In the early 1970s, 

with reservoir recovery, algal counts from intakes near the 

dam began to markedly increase, as did visual sightings of 

algal blooms in the upper reservoir and headwaters (fig. 1, 

Western Run and Piney Run). Major algal blooms re-occurred 

in 1973, and, by mid-July 1974, serious algal-related problems 

occurred in the treatment of reservoir water. Attempts to 

utilize intakes from the lower reservoir to supply suitablequality water at low cost failed. Problems were encountered in 

the initial chlorination, alum coagulation, and sedimentation 

processes, with the removal of coagulated algal-alum residues, 

and with residual chlorination—all of which considerably 

increased the cost of potable water.

Valcik (1975) also described the deterioration of water 

quality in Liberty Reservoir. Under drought conditions from 

1963–70, chloride concentrations at the Ashburton treatment facility increased from about 5 mg/L (milligrams per 

liter) to 15 mg/L; nitrate concentrations, which were being 

measured during that period, also more than doubled from 

about 2.5 mg/L to 6 mg/L as nitrate. Total algal counts at 

the Ashburton treatment facility were about 200 organisms 

per milliliter, or double the counts found at the Montebello 
Overview of Water-Quality Concerns 11

treatment facility. Streamflow at the dam at Liberty Reservoir 

averaged only about 85 Mgal/d, or about half the flow found 

at the dam at Loch Raven Reservoir during this period. Low 

outflows coupled with the large storage capacity of Liberty 

Reservoir (table 1), which is about double the capacity of 

Loch Raven Reservoir, led to an estimated water detention 

time of 13 months, or more than three times the detention 

time for Loch Raven Reservoir during the drought period. 

Major seasonal algal blooms occurred in the upper Liberty 

Reservoir in 1963, 1965, 1968, and 1969. Despite re-occurring 

blooms, water-treatment problems were not encountered at 

the Ashburton treatment facility. Valcik (1975) suggested that 

the large capacity of this reservoir, combined with the use 

of deep intakes at the lower end of the reservoir, reduced the 

impact of blooms on the treatment of water. In fact, it appears 

multiple intakes were used, and that intake waters were mixed 

(Winfield and Sakai, 2003). Selected use of intakes, however, 

did not entirely eliminate adverse treatment consequences. 

Diatom blooms preferentially occurred in the deeper and 

cooler reservoir waters in 1967 and 1968. Their occurrence 

affected treatment operations, and increased treatment costs, 

but to a lesser degree than the costs that are typically incurred 

when treating waters with algal residues.

Subsequent bioassay and water-quality analyses by 

Amatayakul and others (1978) and Amatayakul, Defries, and 

others (1978) demonstrated (a) that additions of phosphorus 

and nitrogen to bioassay samples resulted in the greatest 

increase in phytoplankton production, and (b) that additions of 

phosphorus alone resulted in greater increases in phytoplankton production than additions of nitrogen alone. From these 

results, they concluded that phosphorus was the limiting metabolic nutrient. Amatayakul and others (1978) and Amatayakul, 

Defries, and others (1978) also analyzed a few reservoir 

profile samples from Loch Raven Reservoir. On the basis of 

the results, they concluded that bottom sediments were not a 

likely source of the phosphorus for algal blooms. 

Following the 1960s–70s drought-recovery period, the 

reservoirs continued to experience excessive algal blooms 

(Baltimore Reservoir Technical Group, 2004). For example, 

in 1981, a month-long blue-green algal bloom occurred in 

Loch Raven Reservoir that resulted in major odor and taste 

issues in treated water and over 1,800 customer complaints. 

Nevertheless, residential development continued in several 

rural areas serviced by wastewater treatment plants (WWTPs) 

in headwaters of the reservoir watersheds. Concerned about 

further nutrient enrichment in the reservoirs as a result of 

proposed expansions of WWTPs and contributions from agricultural lands, City, County, and State officials agreed in 1979 

to try to protect the reservoirs. Subsequent formal agreements 

and action strategies followed and led to the 2005 agreement 

and action strategy (Reservoir Watershed Management 

Agreement, 2005; Reservoir Watershed Management 

Agreement Action Strategy, 2005) described earlier in this 

report. 

Monitoring in the reservoirs under these agreements 

began in the early 1980s. The period of digitally available 

monitoring data relative to the age of the reservoirs (table 1), 

however, is relatively short, and the breadth of data is limited 

in scope. Nevertheless, considerable use has been made of 

these data to characterize the initial state of water quality in 

the reservoirs, identify possible seasonal and annual trends, 

and aid in the development of reservoir and watershed models 

that could help manage the reservoirs. The results of these 

efforts have been periodically summarized by the City and (or) 

the RTG, and are described in detail in relation to each longterm water-quality concern later in this report.

Emerging Water-Quality Concerns

Emerging concerns for the RWMA partners since 2000 

are the occurrence of elevated concentrations of DBPs, 

sodium, and chloride in treated water from each water-supply 

reservoir. These concerns chiefly reflect the need to address 

(a) the recent (2006) U.S. Environmental Protection Agency 

(USEPA) Safe Drinking Water Act (SDWA) Stage 2 rule 

change that limits concentrations of DBPs at specific locations, rather than on average throughout the drinking-waterdistribution system (U.S. Environmental Protection Agency, 

2006), and (b) the recent (2003) USEPA SDWA health advisory on sodium intake for individuals on restricted low-salt 

intake diets (U.S. Environmental Protection Agency, 2003).

Under the (2006) USEPA SDWA Stage 2 rule change, 

the 30-day moving averages for the total concentrations of 

selected trihalomethanes (THMs) and haloacetic acids (HAAs) 

cannot exceed the Maximum Contaminant Levels (MCLs) of 

80 μg/L (micrograms per liter) and 60 μg/L, respectively, at 

any monitoring station within the treated water distribution 

system of either water-supply reservoir. Preliminary studies 

indicate that the total concentrations of either THMs or 

HAAs occasionally could exceed their respective MCLs at 

one or more stations in either distribution system (Maryland 

Department of the Environment, 2004a; Winfield and Sakai, 

2003).

Since the early 1970s, when sodium concentrations began 

to be routinely measured, concentrations of sodium have 

almost tripled in supply-intake water from Liberty Reservoir 

and almost quadrupled in supply-intake water from Loch 

Raven Reservoir (Baltimore Reservoir Technical Group, 

2004). Concentrations generally have peaked during the winter 

months. The suspected source of the recent increases is the use 

of sodium chloride (road salt) as a deicing agent (Winfield and 

others, 2006).

Although not formally considered an emerging concern 

by the RWMA partners, droughts and recoveries from drought 

have led to adverse water-quality conditions in the reservoirs 

as indicated above. Recent projected changes in climate, 

combined with the inherent variability in climate in the MidAtlantic region could lead to an increase in the number of 

intense storms with heavy precipitation and an increase in 

the frequency of extended dry periods or drought conditions 

(Intergovernmental Panel on Climate Change, 2007; Maryland 
12 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Department of the Environment, 2008). These changes imply 

that potential increases in storm-borne contaminants (nutrient, 

sediment, salt, and bacterial loads), could adversely affect reservoir water quality, particularly during recovery from drought 

conditions. Thus, the effects of climate are included as an 

additional emerging concern to be considered in this retrospective review of the monitoring program.

Regulatory Concerns

Water-quality concerns for the RWMA partners mainly 

relate to their goals, which include ensuring that SDWA and 

CWA Section 303(d) compliance continues. As of 2007, and 

except for periodic problems associated with color, odor, and 

taste, reservoir drinking-water supplies have routinely met 

the SWDA criteria for public water supplies. Also as of 2007, 

most water-quality concerns have led to impairments governed 

under Section 303(d) of the CWA, which provide general 

water-quality criteria that prohibit pollution of waters of the 

State of Maryland by any material in amounts sufficient to 

create nuisance or other interferences in designated uses (Code 

of Maryland Regulations (COMAR), 26.08.02.08). As of June 

2008 (COMAR 26.08.02.08J, K)2, the Maryland Water Quality 

Standards Stream Segment Designation for the reservoirs and 

their watershed tributaries can be described as follows:

a) Loch Raven and Prettyboy Reservoir Watersheds: Use 

III-P, all waters above the dam at Loch Raven, and 

therefore in the Loch Raven and Prettyboy Reservoir 

watersheds, are to be suitable for nontidal cold 

water (growth and propagation of trout, and supporting self-sustaining trout and their associated food 

organisms), as well as, for Use I-P, which implies 

suitable for recreation (water contact sports, fishing, 

and other play and leisure activities where individuals could come in direct contact with water surface), 

protection of nontidal warm-water aquatic life 

(growth and propagation of fish, other than trout), 

other aquatic life, and wildlife, and public water (as 

well as agricultural and industrial) supply; and 

b) Liberty Reservoir Watershed: Designated uses differ 

depending on water body, as follows:

1) Use I-P, Reservoir and above reservoir, and, except 

for tributaries designated uses III, III-P, or IV-P 

below, all tributaries to the West Branch and North 

Branch of the Patapsco River;

2) Use III, all tributaries to and the main branch of 

Roaring Run on North Branch Patapsco River, 

which implies they are to be suitable for nontidal 

cold water as well as Use I, which implies suitable 

2

 As of 2007, from the Maryland Department of Environment, accessed 

March 15, 2011 at http://www.mde.maryland.gov/programs/water/TMDL/

Integrated303dreports/Pages/303d.aspx.

for recreation, protection of nontidal warm-water 

aquatic life, other aquatic life, and wildlife; 

3) Use III-P, all tributaries and main branches of 

Beaver Run, Cooks Branch, East Branch Patapsco 

River, Keysers Run, Locust Run, Morgan Run, 

Norris Run on the West Branch Patapsco River, see 

a) above; and 

4) Use IV-P, main stems of West Branch Patapsco 

River (main stem only) and North Branch Patapsco 

River and Cranberry Branch and its tributaries (near 

Westminster, Maryland), above Liberty Reservoir 

are designated Use IV-P, which implies suitable for 

recreational trout waters (capable of holding and 

supporting adult trout for seasonal stocking and put 

and take fishing) and all uses under I-P, see a) above.

The inability of selected waters to fully meet the above 

designated-use criteria has led to CWA 303(d) listings of 

the impairments to reservoir watershed tributaries and (or) 

reservoirs, and of the progress made (as of 2007) to address 

each impairment (table 2). The Loch Raven and Prettyboy 

Reservoirs first appeared on the State 1996 Section 303(d) list 

as impaired by nutrients (mainly phosphorus), selected metals, 

and sediment (Loch Raven only). Listings for polychlorinated 

biphenyls (Loch Raven only) and mercury in fish tissue, bacteria, and biological communities were added in 2002.

Total Maximum Daily Loads (TMDLs) and final decision 

rationales for TMDLs for nutrients (phosphorus) and sediment 

for Loch Raven Reservoir, and nutrients (phosphorus) for 

Prettyboy Reservoir were approved by the USEPA (Maryland 

Department of the Environment, 2006). The specified waterquality goal of the nutrient TMDLs is to reduce the occurrence 

of high chlorophyll-a (chl-a) concentrations, which reflect 

excessive algal blooms, and to maintain dissolved-oxygen 

(DO) concentrations at levels supporting designated uses, in 

Loch Raven and Prettyboy Reservoirs. The water-quality goal 

of the sediment TMDL (28,925 tons per year, with 27,715 tons 

per year from nonpoint sources) for Loch Raven Reservoir is 

to increase the useful life of the reservoir for water supply by 

storage preservation.

Water-quality analyses for heavy metals (notably, chromium and lead) and polychlorinated biphenyls in fish tissue 

(only Loch Raven Reservoir), were completed and submitted 

to the USEPA for these reservoirs in 2003 (Maryland 

Department of the Environment, 2003 a,b). Results indicated 

that only manganese and iron, which are naturally abundant 

in watershed and reservoir sediments, occurred at elevated 

concentrations. As of 2007, it was anticipated that both reservoirs would be de-listed for polychlorinated biphenyls and the 

heavy metals in question, including chromium, lead, iron, and 

manganese.

The TMDLs for mercury in fish were completed for both 

reservoirs in 2002 (Maryland Department of the Environment, 

2002 a,b and 2004 b,c), and included evidence that atmospheric depositional sources largely beyond the jurisdictional 
Overview of Water-Quality Concerns 13

Table 2. Federal Clean Water Act Section 303(d) impairments for Prettyboy, Loch Raven, and Liberty Reservoirs1.

[MDE, Maryland Department of the Environment; TMDL, Total Maximum Daily Load; USEPA, U.S. Environmental Protection Agency; As, arsenic; 

Cd, cadmium; Cr, chromium; Cu, copper; Ni, nickel; Pb, lead; Se, selenium; Zn, zinc]

Reservoir Impairment category: 

constituent 

Year 

listed Comments

Liberty Nutrients: phosphorus 1996 Not fully addressed as of 2007

Sediments: suspended sediments 1996 Not fully addressed as of 2007

Metals: chromium and lead 1996 MDE submitted water-quality analysis to USEPA on September 

24, 2003 supporting delisting for chromium and lead

Metals: methylmercury—fish tissue 2002 MDE submitted TMDL to USEPA on December 27, 2002, with 

analysis supporting deferment and indicating chief sources are 

from atmospheric deposition

Bacteria—Escherichia coli sp. 2002 Additional data requested by MDE in 2003; as of 2007, MDE 

was analyzing these data

Biological communities 2002 Not yet addressed

Loch Raven Nutrients: phosphorus 1996 MDE submitted TMDL final decision rationale to USEPA on 

March 27, 2007

Sediments: suspended sediments 1996 MDE submitted TMDL final decision rationale to USEPA on 

March 27, 2007

Metals: As, Cd, Cr (total), Cu, Ni, 

Pb, and Se

1996 MDE submitted water-quality analysis to USEPA on September 

24, 2003 supporting delisting for heavy metals

Metals: methylmercury and polychlorintaed biphenyls (PCBs)—

fish tissue

2002 MDE submitted TMDL to USEPA on December 27, 2002, with 

analysis supporting deferment and indicating chief sources of 

mercury are from atmospheric deposition; as of 2003, reservoir 

was delisted for PCBs

Biological communities 2002, 2004 Not fully addressed as of 2007

Prettyboy Nutrients: phosphorus 1996 MDE submitted TMDL final decision rationale to USEPA on 

March 27, 2007

Metals: As, Cd, Cr (hexavalent), 

Cu, Ni, Pb, Se, and Zn

1996 MDE submitted water-quality analysis to USEPA on September 

24, 2003 supporting delisting for heavy metals

Metals: methylmercury—fish tissue 2002 MDE submitted TMDL to USEPA on December 27, 2002, with 

analysis supporting deferment and indicating chief sources are 

from atmospheric deposition

Bacteria—Escherichia coli sp. 2002 Additional data requested by MDE in 2003; as of 2007, MDE 

was analyzing these data

Biological communities 2002, 2004 Not fully addressed as of 2007

1

 Accessed December 29, 2010 at http://www.mde.maryland.gov/programs/water/TMDL/Integrated303dReports/Pages/303d.aspx.

control of the City accounted for most of the mercury input 

into each reservoir. As of 2004, it was anticipated that no 

further action on mercury in fish tissues would be required 

until such time as the USEPA completes a review of sources of 

atmospheric mercury. 

Listings for bacteria (Prettyboy only) and biological 

communities are mainly for watershed tributaries. As of 2007, 

action on both of these items awaited analysis of data by the 

Maryland Department of the Environment (MDE).

Liberty Reservoir first appeared on Maryland’s 1996 

Section 303(d) list of water quality-limited segments as 

impaired by nutrients (phosphorus), sediment, and metals 

(table 2). The listings for mercury in fish tissues, bacteria 

(tributaries only), and biological communities was added in 

2002. 

As of 2007, impairments for nutrients and sediment for 

Liberty Reservoir have yet to be addressed. Water-quality 

analyses for metals (in particular, for chromium and lead) were 

completed for this reservoir in 2003 (Maryland Department 

of the Environment, 2003c), and, as in the case of Prettyboy 

and Loch Raven Reservoirs, indicated that only manganese 

and iron, which are naturally abundant in reservoir sediments, 
14 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

occurred at elevated concentrations. The TMDL to address 

mercury was completed in 2002 (Maryland Department of the 

Environment, 2002c), with deferment anticipated for reasons 

similar to those noted above for Loch Raven and Prettyboy 

Reservoirs. Listings for bacteria and biological communities 

are awaiting action pending the collection and analysis of data 

by MDE. 

Addressing regulatory impairments for nutrients (phosphorus) and sediment in Loch Raven Reservoir and for 

nutrients (phosphorus) in Prettyboy Reservoir provides a basis 

for future monitoring requirements. The rationale presented 

and accepted by the USEPA (Maryland Department of the 

Environment, 2006) to control phosphorus is focused on chl-a

as the water-quality endpoint for the phosphorus TMDL. The 

chl-a concentration endpoints selected for the Loch Raven and 

Prettyboy Reservoirs are as follows:

a) A maximum permissible instantaneous chl-a concentration of 30 μg/L in surface layers; and

b) A 30-day moving average chl-a concentration not to 

exceed 10 μg/L in surface layers. 

Under the same rationale (Maryland Department of the 

Environment, 2006), the concentration of DO is the waterquality endpoint for proposed and accepted nontidal designated biotic and designated uses of the Loch Raven and 

Prettyboy Reservoirs, which are as follows:

a) Daily average of 5.0 mg/L throughout the reservoir 

water column during periods of complete and stable 

mixing;

b) Daily average of 6.0 mg/L in the mixed surface layers 

at all times; and 

c) Hypoxia in the deep water layers is to be addressed on 

a case-by-case basis, taking into account the morphology, degree of stratification or mixing of stratified 

waters in surface layers during lake turnover or drawdown, and given that seasonal hypoxia likely occurs 

regularly in both reservoirs in the hypolimnetic layer.

It also is apparent in the presented rationale that to the 

extent to which these TMDLs control excessive algal blooms, 

there is expected to be a corresponding reduction in the severity of DO sags, anoxic conditions, and the release of metals 

such as manganese and iron, as well as phosphorus, from 

bottom sediments. It is not apparent in the documentation how 

surface layers, mixed surface layers, or the hypolimnetic layer 

are to be defined, which is discussed later in this report.

In conjunction with excessive nutrients, it is assumed 

that the sediment impairment to Loch Raven Reservoir also 

would be addressed by the phosphorus TMDL. The underlying assumption is that the bulk of phosphorus entering this 

reservoir is bound to sediment. If true, then any control strategy directed toward reducing total phosphorus entering this 

reservoir also would help reduce sediment and vice versa. The 

MDE has adopted this rationale in all reservoirs and impoundments where both nutrient and sediment impairments exist.

The Water-Quality Monitoring Program

Water-quality monitoring in the Baltimore Reservoir 

System can be described in general terms from the formal 

implementation of the program in 1981–82 through 2007, 

as well as its current (2007) state. The effectiveness of this 

program can be described in relation to (a) a review and evaluation of the overall quality of the database and data collected 

during this period, (b) broad-based modeling attempts to 

describe and relate water-quality conditions in the reservoir 

watershed tributaries to water-quality and biotic conditions in 

the reservoirs, and (c) the use of monitoring data and information derived from the analyses of these data to describe spatial 

and temporal variations in water-quality parameters associated with each of the long-term and emerging water-quality 

concerns.

Description

Since its inception in the early 1980s, the long-term 

core monitoring network for the Baltimore Reservoir System 

generally has consisted of 21 nonpoint source (tributary or 

pond) and point-source water-quality monitoring stations in 

the reservoir watersheds, and 12 in-lake monitoring stations 

in the three reservoirs (fig. 3 and Appendix B). Use of this 

network and the data it has provided has varied over time. 

These variations are described in terms of a historical perspective (early1980s through 1990s or early 2000s) and a current 

perspective (chiefly as of 2007, given information provided by 

RWMA partners).

Historical Perspective (1981–2007)

Initially (1980s–90s), data from the core monitoring 

network were obtained and used mainly to define reservoir trophic conditions and their relation to drinking-water supplies, 

and describe variations in tributary water quality (Baltimore 

City Department of Public Works, 1992). By the mid-1990s, 

monitoring data were being used to describe and directly relate 

variations in tributary water quality to reservoir trophic conditions (Baltimore City Department of Public Works, 1996). It 

became apparent, however, that long-term monitoring would 

be required to detect trends that reflected the following: (a) 

the effect of management actions taken to reduce nonpoint 

sources of pollutants on tributary loads, (b) the effect of 

changes in tributary loads on reservoir trophic conditions, 

and (c) the effect of changes in reservoir trophic conditions 

on the quality of drinking-water supplies (Baltimore City 

Department of Public Works, 2000, 2001). The difficulty 

in the establishment of direct relations among tributary and 

reservoir water-quality conditions has been attributed in part 

to large variations in tributary and reservoir water quality due 

to year-to-year and within-year variations in streamflow, and 

in part to variations in in-stream and in-lake processing of pollutants. Nevertheless, the RWMA goals and action strategies 
The Water-Quality Monitoring Program 15

remained clear—to reduce nutrient and sediment loads, and 

address emerging drinking water-quality concerns (Reservoir 

Watershed Protection Committee, 2000). 

To help reduce nutrient and sediment loads and address 

these concerns, analysis of the monitoring data shifted in 

the mid-1990s from the initial emphasis on characterizing 

reservoir water quality to focus on tributary water quality 

and biotic conditions, and their relation to human activities in 

the watersheds (Baltimore City Department of Public Works, 

2000, 2001). Unfortunately, resource limitations also notably 

reduced storm monitoring after the mid-1990s, and it has 

been intermittent thereafter through 2007.3 Thus, characterizing and comparing water-quality tributary conditions among 

all subbasins in a reservoir watershed from the early 1980s 

through 1990s was done with data obtained from monthly dryweather-flow sampling, rather than data collected from annual 

storm- and dry-weather flows. Dry-weather-flow sampling, as 

its name implies, is performed at all tributary stations during 

generally low-to-possibly moderate, and likely wadeable, 

flow conditions. These conditions historically are referred to 

by the RTG as dry-weather flows, and the resultant data, as 

dry-weather-flow data. The same terminology is used in this 

report as these flows have not been routinely quantified since 

the mid-1990s.

Additional support in the development of watershed-restoration action strategies to address RWMA partner concerns 

has come from numerous short-term and synoptic monitoring 

efforts in each watershed (see Appendix A for details). Most 

of these efforts were conducted by the City, Baltimore or 

Carroll County, a State agency—for example, MDE or the 

Maryland Department of Natural Resources (MDDNR)—or as 

a collaborative effort. Most of these efforts were conducted on 

smaller representative areas in selected subbasins within each 

reservoir watershed, and at different times among the reservoir 

watersheds as resources became available. These short-term 

(single-year) and synoptic (low-flow) monitoring efforts, nevertheless, have aided the RWMA partners in the development 

of reservoir-watershed source-water assessments, characterization studies, and management plans with restoration strategies. 

The chief objectives of these efforts have been to help identify, 

prioritize, plan, implement, manage, and protect or restore 

subbasin conditions to reduce identified water-quality pollutant point and nonpoint tributary sources and loads, and to meet 

Federal requirements and State programs. 

The reservoir-watershed source-water assessments were 

conducted to evaluate the safety of all public drinking-water 

systems. Subsequent to or concomitant with the source-water 

assessments, selected RWMA partners conducted watershedcharacterization surveys, nutrient and biotic surveys, and 

stream-corridor and stability assessments, all of which were 

used to develop a watershed-restoration action strategy. The 

restoration action strategies have been used to direct resources 

towards restoration activities in each reservoir watershed. 

3

 William Stack, Baltimore City Department of Public Works, written commun., 2008.

All of the above assessments, surveys, or restoration action 

strategies largely were completed for the major part (Carroll 

County) of the Liberty Reservoir watershed by 2004, and 

the major part of the lower Loch Raven Reservoir watershed 

(Baltimore County part, below Prettyboy Reservoir) by 2005. 

The nutrient synoptic and stream-corridor surveys were completed for the Prettyboy Reservoir watershed in 2008, as were 

the watershed characterization and restoration action strategy.

Current Perspective (as of 2007)

The long-term monitoring network and strategy for 

the Baltimore reservoirs and their contributing watersheds 

were described in the latest recent Reservoir Watershed 

Management Agreement Action Strategy (2005)—a description which remains accurate as of 2007. The City DPW is 

responsible for conducting comprehensive water-quality 

monitoring at the watershed tributary stations and at the inlake stations of the three reservoirs (fig. 3, and Appendix B, 

table B1), and for the analysis of the monitoring samples for 

contaminants of concern (Appendix B, tables B2 through B4). 

They also are responsible for periodically analyzing and summarizing water-quality data for the RTG and RWMA partners 

on the status and trends in watershed tributary and reservoir 

water quality, including calculating annual loadings of selected 

pollutants—mainly suspended sediment and total phosphorus. 

Baltimore County is primarily responsible for selected chemical and biological monitoring in the tributaries in its parts of 

the three reservoir watersheds, and reporting the results annually in the County’s National Pollution Discharge Elimination 

System (NPDES) report to MDE. The U.S. Geological Survey 

(USGS) is mainly responsible for providing discharge data for 

the six tributary stations where sampling is conducted during 

selected storms as well as dry-weather flows.

As part of the 2005 Action Strategy, the RTG is responsible for initiating and overseeing the evaluation of reservoir 

monitoring programs, and determining the resources needed to 

develop and maintain an integrated, comprehensive monitoring program. The monitoring network as of 2007 will be 

examined in relation to the following abilities:

a) The ability to detect annual and long-term waterquality trends in the reservoirs and their contributing 

watersheds, emphasizing the reservoirs as a source 

of potable water and a habitat for desirable living 

resources;

b) The effectiveness of the monitoring network to support 

predictive tools (such as computer models) in helping 

to manage reservoir water quality;

c) The implementation of new technologies to improve 

the effectiveness of reservoir watershed-management 

efforts;

d) The ability to link various types of pollutant sources to 

2000 land use and land cover in the watersheds; and
16 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 3. (A) Tributary and (B) reservoir monitoring stations in the Baltimore reservoir watersheds (modified from Baltimore City 

Department of Public Works, 2000 and Winfield and others, 2006).
The Water-Quality Monitoring Program 17

Figure 3. (A) Tributary and (B) reservoir monitoring stations in the Baltimore reservoir watersheds (modified from Baltimore City 

Department of Public Works, 2000 and Winfield and others, 2006).—Continued
18 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

e) The suitability and adequacy of the areal extent of 

existing monitoring networks, and the need to sample 

additional areas in Carroll County or selected watersheds. 

In 2007, the RTG prepared an interim report that 

described the status of selected 2005 RWMA Action Strategy 

commitments in relation to monitoring (Baltimore Reservoir 

Technical Group, 2007). This interim report indicated that the 

DPW will continue to conduct comprehensive water-quality 

monitoring in the three reservoirs and in selected major tributaries. As part of this monitoring, key pollutants of concern 

will be measured, and estimated annual loadings of sediment 

and total phosphorus will be calculated. The DPW also will 

continue to collect water samples, and modify its cooperative 

agreement with the USGS to include the development of 

annual load estimates for sediment and nutrients to Loch 

Raven and Liberty Reservoirs.

As of 2007, the design of the long-term monitoring 

network for water quality in the Baltimore reservoir system 

includes parts of each reservoir and selected watershed tributaries supplying each reservoir (fig. 3). Although monitoring 

conducted within each reservoir-watershed system generally is 

similar (Appendix B), there also are some notable differences 

in the extent and type of monitoring conducted. 

In part, differences in monitoring reflect reservoir use. 

For the reservoirs used to directly provide drinking-water 

supplies, Loch Raven and Liberty, monitoring in three of the 

major tributaries for each reservoir includes storm- and dryweather flows, and, within the reservoirs, includes stations 

near the water-supply intakes, and analysis of additional (raw 

and treated) water parameters. Monitoring in the tributaries in 

Prettyboy Reservoir, which re-supplies Loch Raven Reservoir, 

is limited solely to dry-weather flows. Also, no monitoring 

data are collected in the upper part of Prettyboy Reservoir. 

Because releases from Prettyboy Reservoir also are used to 

support recreational use (fish habitat) downstream, monitoring 

is conducted on the water released from Prettyboy Reservoir.

In part, differences in monitoring among the reservoirs 

reflect differences in the need and ability to access areas 

within each reservoir to characterize water quality. During 

periods of stratification (generally mid-spring through early 

fall), and weather permitting, sampling in each reservoir is 

conducted more frequently (twice rather than once per month), 

and, weather permitting, by boat at sites within selected areas 

of the reservoir, or from bridges and intake gatehouses. During 

periods of lake turnover, roughly late fall through early spring, 

and given the weather limits access to some areas within the 

reservoirs, sampling frequency and the breadth of constituents 

covered is reduced, and monitoring to address Federal requirements and State programs is mostly done from bridges and 

gatehouses.

Liberty Watershed and Reservoir

Long-term monitoring in Liberty Reservoir can be 

described in relation to selected watershed tributaries, the 

reservoir, and the Ashburton treatment facility. Monitoring at 

all three locations has been conducted since the early 1980s. 

All laboratory analyses of tributary, reservoir, and treatment 

facility samples traditionally have been conducted in the 

Ashburton treatment facility laboratory, and in accordance 

with their laboratory protocols (Appendix C, QualityAssurance Plans, Ashburton treatment facility laboratory). 

From approximately 2005–08, renovations of this facility 

required analyses be performed by either a contract laboratory 

(chiefly tributary samples), or at the Loch Raven Reservoir 

Montebello treatment facility laboratory (chiefly reservoir 

samples).

Watershed Monitoring

City (Reservoir Natural Resources Section) staff 

conduct routine (monthly) dry-weather-flow sampling at six 

tributary sites (fig. 3), and, when discharging, at two NPDES 

sites within the watershed (Appendix B, table B1, Liberty 

Reservoir, Tributary and NPDES sites). In-field measurements taken at a single point in-stream with a multi-probe 

sonde include air and water temperature, pH, DO concentration (percent saturation is calculated), and specific conductance (Appendix B, table B2, Liberty Reservoir, Watershed 

Tributary Sites). Grab samples (at a single point in stream) 

are obtained for turbidity, solids, nutrients, alkalinity, and 

chlorides in low-density polyethylene bottles. If the site is colocated with a USGS streamgage, the stage height is recorded. 

The current-day and previous-day weather also are recorded.

Storm sampling is conducted by the City (Water-Quality 

Management Section) staff at three tributary sites for selected 

nutrients and solids (fig. 3 and Appendix B, table B2, Liberty 

Reservoir, Watershed Tributary Sites, parameters with E code). 

Although all three sites can be sampled for the same storm 

event, limitations in staff, equipment, and sampling logistics 

preclude sampling: (a) more than a few storms per site per 

year, (b) very large events, such as widespread flooding from 

a nor’easter or tropical cyclone, and (c) simultaneously for 

storms at these tributary sites and those tributary sites used 

for storm sampling in the Loch Raven Reservoir watershed. 

Sample collection also generally is limited to selected samples 

for solids and nutrients. Samples generally are obtained on an 

hourly basis with an ice-cooled automated sampler, which is 

temporarily installed before the anticipated storm event, and 

either activated after a pre-set elapsed time, or by a streamstage activator. Storm sampling occasionally is conducted 

manually.

Reservoir Monitoring

City (Reservoir Natural Resources Section) staff conduct 

routine sampling in the lower, middle, and upper parts of the 

reservoir (fig. 3 and Appendix B, table B1, Liberty Reservoir, 

Reservoir sites) at monthly (winter) to bimonthly (springsummer-fall) intervals for selected constituents (Appendix B, 

table B2, Liberty Reservoir, Reservoir sites). In the lower 

reservoir, sampling routinely is conducted throughout the year 
The Water-Quality Monitoring Program 19

at Reservoir site NPA0042, and additionally at Reservoir site 

NPA0059 by boat and weather permitting, which generally 

occurs during the spring-summer-fall period (April through 

November or December). Sampling in the middle part of the 

reservoir only is conducted at Reservoir Site NPA0067, and 

by boat, weather permitting. Sampling in the upper reservoir 

always is conducted at Reservoir Site NPA0105. Data from 

paired stations in the lower parts of this reservoir generally are 

combined for interpretive analysis.

In-field data collection at each Liberty Reservoir site 

includes multi-probe sonde readings of water temperature, 

pH, DO concentration (percent saturation is calculated), and 

specific conductance. These data are obtained during profile 

sampling at approximately 5-ft intervals from just below the 

lake surface to a depth of 60 ft, and then at 10-ft intervals until 

the sensor strikes the lake bottom. (Bottom readings are not 

recorded.) 

Algal and water-quality samples are collected for analysis 

at discrete depths at each reservoir monitoring site using a 

Kemmerer-style sampler. The samples for chl-a are collected 

at every site at 10-ft intervals starting from the surface to a 

depth of 50 ft. Samples for other chemical and additional 

analyses are obtained at each site as follows:

a) Site NPA0042: Surface, 10-ft, an elevation of 365 ft 

(to correspond with the 55-ft deep intakes), and an 

elevation of 320 ft (to correspond with the 100-ft deep 

intakes);

b) Site NPA0059 and Site NPA0067: Surface, and 10-, 

20-, 40-, and 80-ft depths; and

c) Site NPA0105: Surface, and 10-, 20-, and 40-ft depths.

Ashburton Treatment Facility Monitoring

Most of the data obtained by this City facility are used 

to enable water purveyors to assess recent and current (daily) 

water-quality conditions in order to help select intake depth(s) 

for raw-water supplies and determine the potential for nuisance problems in the treatment of this water or the finished 

water. Data used in this assessment include those routinely 

obtained by this facility (Appendix B, table B2, Liberty, 

Ashburton, TF, Raw) from samples delivered from gatehouse 

intakes. In addition, data used can include the most recent 

(monthly or bimonthly) and available reservoir water-quality 

data, mainly from the lower reservoir sampling locations 

(fig. 3 and Appendix B, table B1, Liberty Reservoir, Site 

NPA0042 and Site NPA0059). Sampling of treated water 

also is conducted by the Ashburton facility to assess residual 

chlorine and (or) the suitability of treated water for consumption (Appendix B, table B1, Liberty, Ashburton, TF, Treated). 

Most data obtained at this facility chiefly are used by water 

purveyors, but also ultimately can provide the RWMA partners 

with the most direct link between the quality of water in the 

lower Liberty Reservoir and the quality of treated or potable 

water.

Loch Raven Watershed and Reservoir

Long-term monitoring in Loch Raven Reservoir can be 

described in relation to selected watershed tributaries, the 

reservoir, and the Montebello treatment facility. Monitoring at 

all three locations has been conducted since the early 1980s. 

Traditionally, Loch Raven Reservoir dry-weather-flow samples have been analyzed by the Montebello treatment facility 

laboratory, in accordance with their laboratory protocols 

(Appendix C, Quality Assurance Plans, Montebello treatment 

facility laboratory). While the Montebello facility underwent 

renovations from 2005–07, samples were analyzed by either 

the Ashburton treatment-facility laboratory or a private contractor. Stormflow samples always have been analyzed by the 

Ashburton treatment-facility laboratory.

Watershed Monitoring

City staff (Reservoir Natural Resources Section) conduct 

routine (monthly) dry-weather-flow sampling at seven tributary sites (fig. 3), and, when discharging, at one irrigation pond 

and one NPDES site, within the watershed (Appendix B, table 

B1, Loch Raven Reservoir, Watershed, Tributary, Irrigation 

pond, and NPDES site). In-field measurements at a single 

point in-stream with a multi-probe sonde include air and 

water temperature, pH, DO concentration (percent saturation 

is calculated), and specific conductance (Appendix B, table 

B3, Loch Raven Reservoir, Watershed Tributary sites). Grab 

samples (at a single point in stream) are obtained for turbidity, solids, nutrients, alkalinity, and chlorides in low-density 

polyethylene bottles. If the site is co-located with a USGS 

streamgage, the stage height is recorded. Current-day and 

previous-day weather also are recorded.

Storm sampling is conducted by the City (Water-Quality 

Management Section) at selected (three) tributary sites for 

selected nutrients and solids (fig. 3 and Appendix B, table 

B1, Loch Raven Reservoir, Watershed Tributaries, parameters 

with E code). Although all three sites can be sampled for the 

same storm event, limitations in staff, equipment, and sampling logistics preclude sampling: (a) more than a few storms 

per site per year, (b) very large events, such as widespread 

flooding from a nor’easter or tropical cyclone, and (c) simultaneously for storms at these tributary sites and those tributary 

sites used for storm sampling in the Liberty Reservoir watershed. Samples are obtained in the same manner described 

above for storm sampling at selected watershed tributaries in 

Liberty Reservoir watershed.

 Reservoir Monitoring

City staff (Reservoir Natural Resources Section) conduct 

routine sampling in the lower, middle, and upper parts of 

the reservoir (fig. 3 and Appendix B, table B1, Loch Raven 

Reservoir, Reservoir sites) at monthly (winter) to bimonthly 

(spring-summer-fall) intervals for selected constituents 

(Appendix B, table B3, Loch Raven Reservoir, Reservoir 

sites). In the lower reservoir, sampling routinely is conducted 
20 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

throughout the year at Reservoir Site GUN0142. In the middle 

and upper parts of the reservoir, sampling is seasonally divided 

between paired sites (Appendix B, table B3, Loch Raven 

Reservoir, Reservoir Sites: Middle—Site GUN0156 (winter, 

from bridge) and Site GUN0171 (spring-summer-fall by boat), 

and Upper—Site GUN0174 (winter, from bridge) and Site 

GUN0190 (spring-summer-fall, by boat). Data from paired 

stations, in either the upper or middle part of the reservoir, are 

combined for interpretive analysis of that part of the reservoir.

In-field data collection at each Loch Raven Reservoir site 

includes multi-probe sonde readings of water temperature, 

pH, DO concentration (percent saturation is calculated), and 

specific conductance. Data are obtained at intervals similar to 

those described above for Liberty Reservoir. 

Algal and water-quality samples for analyses are 

collected at discrete depths at each reservoir site using a 

Kemmerer-style sampler. Samples for chl-a are collected at 

every site at 10-ft intervals starting from the surface to a depth 

of 50 ft. Samples for chemical and other analyses are obtained 

at each site at the surface and every 10 ft up to 60 ft.

Montebello Treatment Facility Monitoring

Most of the data obtained by this City facility are used 

to enable water purveyors to assess recent and current (daily) 

water-quality conditions in order to help select intake depth(s) 

for raw-water supplies and determine the potential for nuisance problems in the treatment of this water or the finished 

water. Data used in this assessment include those routinely 

obtained by this facility (Appendix B, table B3, Loch Raven 

Reservoir, Montebello, TF, Raw) from samples delivered from 

gatehouse intakes. This assessment also can include the most 

recent (monthly or bimonthly) reservoir water-quality data, 

chiefly from the lower reservoir sampling location (fig. 3 and 

Appendix B, table B1, Loch Raven Reservoir, Reservoir site 

GUN0142). Sampling of treated water also is conducted to 

assess residual chlorination, treatment results, and suitability 

of treated water for consumption (Appendix B, table B3, 

Loch Raven, Montebello, TF, Treated). As is the case for the 

Ashburton facility and Liberty Reservoir, data obtained at the 

Montebello facility is used primarily by water purveyors, but 

also could provide the RWMA partners with the most direct 

link between the quality of water in the lower Loch Raven 

Reservoir and the quality of treated or potable water.

Prettyboy Watershed and Reservoir

Long-term monitoring in Prettyboy Reservoir can be 

described in relation to selected watershed tributaries and the 

reservoir. Monitoring in the watershed and reservoir has been 

conducted since the early 1980s. Water-quality samples from 

Prettyboy Reservoir traditionally have been analyzed by the 

Montebello treatment facility laboratory, in accordance with 

their laboratory protocols (Appendix C, Laboratory Quality 

Assurance, Montebello treatment facility laboratory). While 

this facility undergoes renovation, samples are analyzed 

by the Ashburton treatment facility laboratory or a contract 

laboratory. Tributary samples from the Prettyboy Reservoir 

watershed have traditionally been analyzed by the Ashburton 

treatment facility laboratory, except during its renovation 

from approximately 2005–08, when samples were analyzed 

by the Montebello treatment facility laboratory or a contract 

laboratory.

Watershed Monitoring

City staff (Reservoir Natural Resources Section) routinely 

conduct only (monthly) dry-weather-flow sampling at three 

tributary sites (fig. 3), and, when discharging, at one NPDES 

site within the watershed (Appendix B, table B1, Prettyboy 

Reservoir, Tributary and NPDES Sites). In-field measurements 

are made at a single point in stream with a multi-probe sonde. 

Measurements include air and water temperature, pH, DO 

concentration (percent saturation is calculated), and specific 

conductance (Appendix B, table B4, Prettyboy, Watershed 

Tributary sites). Grab samples (at a single point in stream) 

are obtained for turbidity, solids, nutrients, alkalinity, and 

chlorides in low-density polyethylene bottles. If the site is colocated with a USGS streamgage, the stage height is recorded. 

Current-day and previous-day weather also are recorded.

Reservoir Monitoring

City staff (Reservoir Natural Resources Section) conduct 

routine sampling in the lower and middle parts of the reservoir (fig. 3 and Appendix B, table B1, Prettyboy Reservoir, 

Reservoir, Tributary, and NPDES sites) at monthly intervals 

for selected constituents (Appendix B, table B4, Prettyboy 

Reservoir sites). Sampling in the lower reservoir is conducted 

throughout the year at Reservoir site GUN0399, and additionally at Reservoir site GUN0401 by boat and weather permitting—generally during the spring-summer-fall period (April 

through November or December). Sampling in the middle part 

of the reservoir is conducted throughout the year at Reservoir 

site GUN0437. Data from paired stations in the lower part of 

the reservoir generally are combined for interpretive analysis.

In-field data collection at each Prettyboy Reservoir site 

includes multi-probe sonde readings of water temperature, 

pH, DO concentration (percent saturation is calculated), and 

specific conductance. Data are obtained at intervals similar to 

those described above for Liberty Reservoir. 

Algal and water-quality samples for analyses are collected at discrete depths at each reservoir site using a 

Kemmerer-style sampler. Samples for chl-a are collected at 

every site at 10-ft intervals starting from the surface to a depth 

of 50 ft. Samples for chemical and other analyses are obtained 

at each site as follows:

a) GUN0399 and GUN0401: Surface, and 10-, 20-, 40,- 

and 80-ft depths below the surface; and

b) GUN0437: Surface, and 10-, 20-, 40- and 60-ft depths 

below the surface.
The Water-Quality Monitoring Program 21

Review and Evaluation

The effectiveness of the monitoring program for the 

Baltimore Reservoir System was assessed in part through a 

review of the monitoring database and data as of 2007. The 

effectiveness of the monitoring program was partially assessed 

on the basis of the most recent (2006) attempt at broad-based 

modeling to describe and relate water-quality conditions in 

the Loch Raven and Prettyboy Reservoir watershed tributaries 

to water-quality and biotic conditions in these reservoirs. The 

effectiveness of the monitoring program also was assessed 

on the basis of the use of monitoring data and information by 

RWMA partners, the RTG, and others to describe spatial and 

temporal variations in water-quality parameters associated 

with each of the long-term and emerging water-quality 

concerns.

Quality of the Monitoring Database and the Data 

Collected

A key measure of the value of a monitoring program 

that needs to provide data over the long term for analysis and 

decision-making is the quality of the database and the data 

within that database. Often a critical determining factor as to 

whether both of the above are adequate is a quality-assurance 

plan and program (QAPP) that is sufficiently comprehensive 

and actively followed to ensure the following: 

a) A readily available complete and detailed description 

of the ongoing field and laboratory procedures and 

methods of data and sample collection for the monitoring program.

b) Definitions of the long-term data-quality requirements 

for the monitoring program, which include identification of the accuracy of the data (reporting level, precision, and bias) required or suitable for each constituent 

obtained by the monitoring program, and in particular, 

for those constituents that are used by the RTG as decision criteria (for example, to address SDWA or CWA 

303d regulatory standards).

c) Verification measurements of data quality from qualityassurance and control (QAC) samples, and the manner 

in which the QAC data routinely are obtained and digitally stored with the corresponding water-quality data.

d) Description and implementation of the procedures for 

the routine (for example, annual or biannual) analysis, 

review, verification, and evaluation of data quality on 

the basis of the QAC data, and the documentation of 

findings, to determine if data requirements are being 

met.

e) Description and implementation of procedures for the 

systematic modification of field or laboratory methods, 

and the digital documentation thereof, given that dataquality requirements, or methods or personnel used 

to obtain data under a long-term monitoring program 

invariably change.

The importance of the above elements in a QAPP cannot 

be underestimated. Long-term assessments of state, as well as 

trends, loads, and other interpretive measures of the physical, 

water-quality, and biotic conditions in the watershed tributaries and reservoirs related to RTG monitoring objectives are 

derived from analysis of long-term monitoring data. In turn, 

monitoring results guide RWMA action strategies and management decisions to meet RWMA goals.

In the absence of an adequate QAPP, it can be difficult to 

assess simple changes in state. For example, historically the 

RWMA partners and RTG had to rely on previous sediment 

bathymetric surveys to assess changes in reservoir storage 

capacity. Although several such surveys were conducted on the 

reservoirs, they were not adequately documented and archived 

in a manner that could be combined with recent RWMA 

surveys to determine periodic changes in reservoir storage 

capacities (Ortt and others, 2000). In addition, the lack of an 

adequate QAPP can result in considerable time and expense 

to address limitations in the quality of data if such limitations 

first become apparent during interpretative analyses.

In relation to the database and data obtained by the 

Baltimore Reservoir System long-term monitoring program, 

concerns such as those described above can be raised. The 

RTG has relied on biotic and chemical water-quality measurements and samples from the reservoirs and watersheds 

that are mainly collected by the City DPW Reservoir Natural 

Resources or Water-Quality Management Sections. The analyses of samples have been performed by the City at two different laboratories in the Ashburton or Montebello treatment 

facilities. Other contract laboratories also have been employed 

by the City for HAAs, suspended organic carbon, herbicides, 

metals, and cryptosporidium. Recent renovations involving 

both City water-treatment facilities (from 2005–09) resulted in 

first one and then the other treatment facility taking on added 

analyses, as well as an increased use of contract laboratories. 

With so many different groups involved in the collection and 

analysis of samples, the quality of the data being obtained by 

the monitoring program will likely come into question.

To determine the quality of database and data being used 

to address water-quality concerns, information was obtained 

from the City on the reservoir-monitoring locations and 

methods. A copy of the long-term monitoring database was 

obtained from the Baltimore City DPW, as were copies of the 

2007 Montebello and Ashburton treatment-facility laboratory 

QAC plans (Appendix C). Reviews of the database and facility QAC plans were conducted in relation to each of the five 

elements of the comprehensive QAPP described above. 

With respect to QAPP item a), and as of 2007, no single 

QAPP document was readily available from the RTG or City 

(DPW) that described in detail data- and sample-collection 

or sample-analyses procedures or protocols that included the 

monitoring locations, the types of data and samples collected, 

the frequency of their collection, and the specific methods, 
22 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

procedures, and equipment used in the field to obtain data 

and samples, or used by the laboratories to analyze samples. 

Thus, to aid the City, and this review, a fairly comprehensive 

description of the monitoring program (see Current 

Perspective, this report), and monitoring locations and data 

being collected by the City (Appendix B), were prepared with 

the assistance of City staff of the Water-Quality Management 

Section, DPW and brief descriptions found in historical 

reports. More detail is needed, however, on the specific procedures, methods, and equipment used to obtain samples in the 

reservoirs and watershed tributaries, and on the laboratories 

and methods used to analyze samples.

In relation to QAPP item b), and as of 2007, no description of specific data-quality objectives needed to meet the 

interpretive needs of the RTG or to guide agencies contracted 

to perform interpretive analyses for the RTG was found. 

Therefore, there are no clear data-quality requirements specified for the long-term monitoring data to guide the City DPW 

in the collection of data and samples or the City Ashburton 

and Montebello laboratories in the analysis of samples. That 

the lack of this information has occasionally affected the ability to analyze and interpret data is reflected in several studies 

that have noted selected data (historical or recent) were of 

unknown and questionable quality, and therefore, likely warranted caution in their use (Amatayakul, Defries, and others, 

1978; Walker, 1988; KCI Technologies, Inc., 2004; Interstate 

Commission on the Potomac River Basin, 2006). Whereas 

some recommendations by these investigators appear to 

have been adopted, others have not been fully addressed. For 

example, clearly articulated data-quality requirements still do 

not exist, which could aid the RTG and City in the reduction, 

if not elimination, of these types of data-quality concerns, 

regardless of who ultimately provides the required data.

 In relation to QAPP item c), a review of the 2007 QAC 

plans for both City laboratories (Appendix C) indicated that 

these plans are fundamentally different from what historically 

has been shown to be needed in a QAC plan for this longterm monitoring program. Both City laboratory plans focus 

chiefly on the performance of day-to-day analytical operations 

designed to assess the quality of water near or at the reservoir 

intakes for pending treatment, or the suitability of treated 

water for temporary storage, or immediate distribution and 

consumption. Data related to hydrodynamic conditions, such 

as reservoir water levels, are generally collected to meet these 

short-term needs, but not stored electronically. Water-quality 

samples are analyzed with Federal or State-approved procedures. However, these procedures are designed primarily for 

short-term needs to assess water-treatment requirements or 

compliance with Federal drinking-water standards, and are 

not generally well suited to the low concentrations of selected 

reservoir and watershed-tributary water-quality parameters—

for example, total phosphorus. Analytical method changes 

also do not require extensive comparative testing between 

the new and old methods or long-term documentation of 

method changes and differences. For a long-term monitoring 

program, if such steps are not taken, the changes in data due 

to method changes, and the lack of long-term documentation 

of such changes, can limit interpretations designed to assess 

changes in water-quality states or establish trends over decadal 

time periods (for example, see Eutrophication—Nutrients: 

Phosphorus Transport and Reservoir Recycling, this 

report). Also, archival of City laboratory QAC data is minimal 

if the analytical methods perform adequately that day; and, 

regardless of performance, these records are not required to be 

archived beyond a 5-year period. Hence, the City treatmentfacility laboratory QAC management plans cannot be expected 

nor used to meet the QAC requirements of a long-term monitoring program.

Also in relation to QAPP item c), other QAC issues 

arose from the review of the long-term monitoring program 

database. Most notable are differences in the number of total 

(significant and insignificant) figures reported for a given analytical constituent, and the inability to appropriately “remark” 

certain types of analytical data. For example, concentration 

values for total phosphorus (TP), a constituent of considerable 

concern to the RWMA partners, are not reported to the same 

number of total figures within or among the three reservoirs, 

despite both City laboratories using the same analytical 

procedures and methods for sample analysis. Values appear 

rounded to fewer total figures for some samples than others. 

For other constituents, for example, DO, the number of significant figures is used to identify the analytical method used 

to obtain the concentration of DO, but does not truly reflect 

the precision of the measurement. Fundamentally, data for 

a given constituent technically should be systematically and 

independently remarked, and reported to the number of figures 

warranted by the precision of its measurement, as determined 

from QAC samples obtained during data collection and during 

analysis of samples. For example, the U.S. Geological Survey 

National Field Manual (variously dated) provides guidance on 

how quality-control samples and data for common water-quality measurements can be obtained, reported, and remarked, 

assuming operation of the in-field sampling or measurement 

equipment provides data that fall within the manufacturerdesignated levels of precision. 

The ability to adequately remark data for long-term 

storage, or, more importantly, enable knowledgeable retrieval 

of that data, is critical. For example, measurements that fall 

below the reporting level of an analytical method routinely are 

remarked as less than (“<”). The City DPW, however, adopted 

a procedure early on to enter such data as one-half the value 

of the analytical method reporting level. Over time there have 

been changes to analytical methods with lower reporting levels. Thus, it is no longer possible to identify all historical “less 

than” values. This has led to interpretive studies that identified 

such outlier data as highly unusual and unexplainable, and as 

jeopardizing the ability to interpret the entire dataset (Walker, 

1998; KCI Technologies, Inc., 2004; Interstate Commission on 

the Potomac River Basin, 2006). 

In relation to item QAPP item d), as of 2007 no indication was found during this review that systematic summaries, 

evaluations, and reviews of the quality of the data being 
The Water-Quality Monitoring Program 23

collected are routinely (for example annually or bi-annually) 

performed and presented by the City as part of the monitoring 

program. A direct consequence of the above is that possible 

limitations in data quality can go undetected until long after 

data collection is complete, and only arise during subsequent 

independent analyses and interpretation of the data. In the 

absence of routine data-quality reviews, and because of the 

elapsed time involved, limitations in data discovered in this 

manner are unlikely to ever be clearly resolved (for example, 

see Eutrophication—Nutrients: Phosphorus Transport 

and Reservoir Recycling, and Sedimentation—Sediment 

Transport, this report).

In relation to item e), the responsibilities for the collection of data and samples in the field, as well as the analyses 

of the collected samples, have been conducted by different 

City staff or, for selected analyses, been contracted out to 

private laboratories over the course of long-term monitoring 

(early 1980s to present). However, there does not appear to be 

a concise description and manner of implementation for the 

systematic transfer of field or laboratory analysis and methods 

from one party to another, and the evaluation and documentation thereof. 

Collectively, the review of the database and data for 

the monitoring program for the Baltimore Reservoir System 

indicates that as of 2007, there was no single document that 

could describe how this monitoring program addressed each 

of five basic elements described above in the QAPP for longterm water-quality monitoring. Shortcomings in the Baltimore 

Reservoir System monitoring program appear in relation to 

each of the five elements. These shortcomings appear to have 

affected the quality of data collected, and (or) the ability of 

the RTG, or selected contractors, to effectively use that data to 

address selected RWMA water-quality concerns.

Modeling to Address Water-Quality Concerns 

The effectiveness of the monitoring network to support 

predictive tools, mainly computer models, to describe watershed and reservoir processes, or define TMDLs and related 

monitoring requirements, is critical to understanding and 

addressing long-term and emerging water-quality concerns 

and regulatory concerns (see Overview of Water-Quality 

Concerns, this report). Thus, there have been several modeling investigations directed toward relating water-quality 

conditions in the reservoir watershed tributaries to waterquality and biotic conditions in the reservoirs. Most notable in 

this regard was a recent study by the Interstate Commission on 

the Potomac River Basin (2006), which developed a modeling 

framework for simulating hydrodynamics and water quality in 

the Prettyboy and Loch Raven Reservoirs. Building upon earlier work by MDE, the Interstate Commission on the Potomac 

River Basin (2006) coupled a simulation model of the watersheds draining into Prettyboy and Loch Raven Reservoirs 

(Hydrological Simulation Program-Fortran, HSPF) with a 

two-dimensional simulation model to simulate the hydrodynamics and water quality of the reservoirs (U.S. Army Corps 

of Engineers CE-QUAL-W2). The primary purpose of the 

coupled models was to link nutrient loads, in particular, phosphorus loads, from the reservoir watersheds to algal biomass 

concentrations, represented by chl-a concentrations, in the 

reservoirs. A secondary purpose was to calibrate the relation 

between autochthonous and allochthonous organic matter and 

DO concentrations in the hypolimnetic layer. 

On the basis of comparisons of simulated and historical 

and long-term monitoring data from 1992–97, the Interstate 

Commission on the Potomac River Basin (2006) found and 

noted a number of limitations in the availability or quality of 

the long-term monitoring data in relation to their capability to 

simulate key reservoir water-quality constituents of concern, 

as follows:

a) Reservoir temperature: This physical parameter 

was among the most influential (and measureable) 

factors that affect the density of water and stratification, thus inhibiting the turbulent mixing between the 

epilimnetic, metalimnetic, and hypolimnetic layers. 

Among the most influential factors in the simulation of 

reservoir temperature was the elevation of the outflows 

from the reservoirs (measureable). During low-flow 

conditions into the reservoir, and high demands for 

water supplies, the elevation of outflows can be determined chiefly by reservoir withdrawals (measureable). 

Simulations were complicated by the lack of readily 

available data on the volumes of daily withdrawals 

for drinking water, and, when the reservoirs were at 

capacity, the lack of data on the daily volume of water 

releases from the supply reservoirs (measureable).

b) Reservoir water quality: The primary purpose of the 

water-quality simulation was to calibrate the relation 

between chl-a in each reservoir and TP loads from 

each reservoir watershed. A secondary purpose was 

to calibrate the relation between autochthonous and 

allochthonous organic matter and DO in the hypolimnetic layer. Four stages were used to simulate and 

validate these relations, which involved reservoir concentrations for TP (measured as orthophosphate phosphorus, in a persulfate-digested, raw-water sample), 

chl-a, DO, and ammonia- and nitrate-nitrogen (all four 

parameters being generally measureable and routinely 

monitored):

1) Total phosphorus: Concentrations of TP were 

simulated for reservoir surface and bottom conditions from simulated watershed TP loads in combination with reservoir settling rates for suspended 

sediment. Although simulated tributary loads for 

TP were reasonably accurate, the lack of tributary 

data for stormflows, particularly in the Prettyboy 

Reservoir watershed, limited model calibration and 

validation. Simulated reservoir surface and bottom 

concentrations for TP did not consistently match the 

variability in observed TP concentrations in either 
24 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

layer in either reservoir. In particular, monthly average surface TP concentrations were overestimated 

in 1993 and 1994, particularly for late fall storms 

in 1993, and notably underestimated in relation to 

major reservoir inflow events in 1996 and 1997. The 

inconsistencies were considered to be a function 

of the quality of the TP data and the quality of the 

model simulation. Regarding the latter, no data were 

available on dissolved organophosphate phosphorus 

(DOP, measured as orthophosphate phosphorus, in 

a filtered water sample) for model calibration, but 

DOP is the standard state variable for phosphorus in 

the reservoir water-quality model.

2) Chlorophyll-a: Concentrations of chl-a in the epilimnion were simulated for three seasons each year: 

(a) a mixed-species winter assemblage, (b) dominant 

spring algal taxa, and (c) dominant summer-fall 

algal taxa. The goal of the calibration was for the 

simulated chl-a concentration in each season to be 

at least as large as the observed chl-a concentration 

in that season (but not necessarily match by date 

and time). The resulting calibration was considered 

conservative. Ensuring that the simulated chl-a

peaks are at least as large as observed peaks helps 

guarantee that the models can be used to calculate 

what TP loads are compatible with the reservoirs 

meeting water-quality standards. Growth rates and 

temperature coefficients were varied in the simulation by year and season, reflecting the variety of 

dominant algal species and the variety of factors that 

determined species succession. Although the goals of 

the simulation were met, a wide variety of different 

algal species can assume dominance in Loch Raven 

Reservoir, and most every spring and summer season 

is dominated by a different species. (Although it 

was not specified, the variability in algal dominance 

could indicate that variations in the amount of available phosphorus (and (or) nitrogen) dictate what species dominates and the duration of its occurrence.) 

Notable in the case of both reservoirs was a lack of 

data on winter and early spring algal counts, and, for 

Prettyboy Reservoir, on taxa identification. 

3) Dissolved oxygen: Concentrations of DO were 

simulated for reservoir epilimnetic and hypolimnetic 

layers. Simulations were heavily dependent on the 

simulation of temperature, which determines density 

differences that inhibit oxygen transport through 

turbulent diffusion. Under stratification, simulated 

concentrations of DO in the water column were 

determined in relation to oxygen demands associated 

with the decomposition of labile dissolved organic 

matter (from autochthonous sources, algal detritus, 

and from allochthonous sources, tributary labile 

organic matter) and dissolved chemical biological 

oxygen demand. Nitrification of ammonia also 

was considered. Under stratification, bottom DO 

concentrations were assumed to be determined by 

sediment oxygen demand, and represented by a 

temperature-dependent first-order decay process of a 

single type of organic matter. Simulations of surficial 

and bottom DO matched observed DO in relation to 

seasonal trends and average monthly concentrations. 

Simulations tended to underestimate surface DO 

concentrations in Loch Raven Reservoir. Overall, 

simulations of chemical or chemical-biological oxygen demands could not be verified due to the lack of 

actual measurements on these oxygen demands. 

4) Ammonia- and nitrate-nitrogen: Concentrations 

of ammonia- and nitrate-nitrogen generally were 

assumed to occur in excess of aquatic needs, and 

available phosphorus was considered the limiting 

nutrient. In both Prettyboy and Loch Raven 

Reservoirs, approximately 93 percent of the surficial monitoring samples (10- and 20-ft depths) had 

nitrate-nitrogen to TP ratios of 10 or greater. The 

median nitrate-nitrogen to TP ratio in Loch Raven 

Reservoir was 38 and the median ratio in Prettyboy 

Reservoir was 47. The Interstate Commission on the 

Potomac River Basin (2006) concluded monitoring 

data overwhelmingly indicate that phosphorus is the 

limiting nutrient. Nevertheless, the simulation of 

nitrogen species was calibrated against the observed 

data. In general, model simulations had limited 

success in capturing the broad seasonal variability 

in either nitrate or ammonia nitrogen concentrations 

in either surface or bottom layers in either reservoir. 

Simulations also failed to capture the intra-seasonal 

variability concentrations of either nitrogen species 

in either surficial or bottom waters in either reservoir. The greatest deviations between simulated 

and observed values tended to occur in relation to 

extreme events—for example, in relation to storm 

events, or during very wet or dry years. A key limitation in the simulation of these nitrogen species was 

the lack of data on organic nitrogen.

The Interstate Commission on the Potomac River Basin 

(2006) noted that accurate simulations of water-quality conditions in Prettyboy and Loch Raven Reservoirs were limited 

by the lack of readily available data, or simply lack of data for 

selected hydrodynamic and biological parameters [see items 1) 

through 4) above]. Applying these limitations to modeling all 

three reservoir watersheds and reservoirs would indicate the 

following data are not obtained, obtained at too low a frequency, or obtained but not readily available:

a) Routine (daily) reservoir withdrawals (from Loch 

Raven and Liberty Reservoirs, not readily available), 

releases (from Loch Raven and Liberty Reservoirs, 

unavailable), and water levels from all three reservoirs 

(not readily available); 
The Water-Quality Monitoring Program 25

b) Routine measurements of reservoir water temperature 

(too low a frequency, requiring at least daily), which 

was found to be the most influential model parameter 

for the determination of reservoir stratification (epilimnion, metalimnion, and hypolimnion) or mixing;

c) Routine algal counts and taxa identification in winter 

and early spring [clearly a problem for Prettyboy 

Reservoir given evidence (chl-a) of blooms in late 

winter and early spring];

d) Routine measurements (unavailable) for DOP, total 

organic nitrogen, total organic carbon, and chemical 

and (or) biological oxygen demand;

e) Increased frequency of routine measurements for chl-a

(daily) and DO (possibly diurnal), given the TMDL 

endpoint criteria (see Regulatory Concerns, this 

report). 

The above measurements have been utilized in other 

model simulation studies developed with the U.S. Army 

Corps of Engineers CE-QUAL-W2 two-dimensional reservoir 

model to provide reasonably accurate simulations of waterquality and biotic conditions associated with seasonal algal 

blooms (Giorgino and Bales, 1997; Bales and Giorgino, 1998; 

Sarver and Steiner, 1998; Bales and others, 2001; Galloway 

and Green, 2004, 2006 a, b). All of these studies were able to 

simulate seasonal moderate to major algal blooms and their 

associated pre-, concomitant-, and post-bloom water-quality 

conditions in different lakes and reservoirs with reasonable 

accuracy and reliability. In all of the studies, simulations 

relied on the collection of reservoir data at similar to often 

higher frequencies (daily to monthly) than the frequency of 

data collection used in the long-term monitoring program 

for the Baltimore Reservoir System (generally monthly or 

bimonthly). In addition, these studies relied on measurements 

of DOP rather than just TP, as the former varied at times independently of the latter. It also was evident in several of these 

studies that DOP sources other than tributary inflows—for 

example, releases from nearby WWTPs and (or) reservoir bed 

sediments or previous phytoplankton blooms, likely contributed to phytoplankton production, and that reservoir DOP 

concentrations were not equal, or always directly proportional, 

to TP during the spring, summer, or fall, when phytoplankton 

blooms were most likely to occur.

Monitoring to Address Individual Water-Quality 

Concerns 

The ability of the monitoring program for the Baltimore 

Reservoir System to provide data for the reservoir watershed 

tributaries to (a) describe the state, and temporal variations in 

state—such as seasonal, annual, and long-term trends, in water 

quality (b) describe the areal extent of pollutant sources and 

their possible relation to land use and cover in the watersheds, 

and (or) (c) relate water-quality conditions in the tributaries 

to water-quality and (or) biotic conditions in the downstream 

reservoirs (fig. 3) were used to assess the effectiveness of this 

program to address each long-term and emerging RWMA 

concern. This assessment was conducted on the basis of a 

retrospective review of the 1980 through 2007 scientific and 

technical reports provided by the RTG partners or their contracted investigators. 

Long-Term Water-Quality Concerns

Long-term water-quality concerns addressed in this 

review and evaluation and described by the 2005 and earlier 

RWMAs include eutrophic conditions in the reservoirs that 

result in major algal blooms, which are attributed to elevated 

nutrient (nitrogen and phosphorus) loads from tributaries 

upstream of the reservoirs. In turn, algal bloom die-offs and 

decomposition can promote deep-water anoxia in the reservoirs, and the subsequent release of iron and manganese 

from reservoir bed sediments, which in addition to algal 

residues, can interfere with the treatment of reservoir water 

and quality of treated water for drinking water, and thus are 

of concern. Sedimentation is an additional long-term concern. 

It reflects overland and tributary in-stream bed and bank erosion, which degrade tributary stream-water-quality and biotic 

conditions and adversely affect the designated recreational 

uses of streams. The resultant sediment loads also reduce the 

storage capacity of the water-supply reservoirs, which impairs 

their designated use for such supplies, and is of concern. 

Transported sediment also is the major source of metals, 

including iron, manganese, and mercury, and a source of nutrients, including phosphorus, in the reservoirs. Mobilization of 

these metals and phosphorus is a concern. Fecal coliform and 

other bacteria are another long-term concern. Although these 

bacteria have not been found at concentrations that exceed 

State standards for recreational activities in the reservoirs, 

they have been found at elevated concentrations in selected 

tributaries, and their occurrence is cause for concern given the 

designated recreational uses that involve water contact in the 

tributaries.

Eutrophication

Eutrophication is the process that enhances the production of algal and higher plants in response to enrichment by 

the plant nutrients nitrogen and phosphorus (Phillips, 2010). 

In assessing eutrophic conditions and their impacts on the 

Baltimore Reservoirs, the reservoirs always have been and 

remain subject to nutrient enrichment and eutrophication 

(see Overview of Water-Quality Concerns, this report). 

Therefore, in addressing eutrophication in the Baltimore 

Reservoirs, it is important to note that the reduction in the 

occurrence of eutrophic conditions that result in major algal 

blooms is the primary goal for the RWMA partners.

Summary (Baltimore City Department of Public Works, 

1996, 2001; Baltimore Reservoir Technical Group, 2004) 

and other reports (Valcik, 1975; Winfield and Sakai, 2003; 

Interstate Commission on the Potomac River Basin, 2006) 
26 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

have utilized algal counts and taxa identification data from 

the long-term monitoring program (Appendix B) to describe 

phytoplankton production and bloom characteristics in the 

reservoirs. These reports all generally indicate that although 

algal counts appear to have declined (at least over the period 

from 1980–2001, and particularly through the 1990s), all three 

City reservoirs appear to remain subject to the effects of ongoing eutrophication. The use of the terms “apparent” or “appear 

to” here and throughout the remainder of this report indicates 

reported trends, seasonal patterns, or other relations where no 

statistical analyses were used to verify the trend, pattern, or 

relation.

Under what might be best termed typical mesotrophic 

conditions, which generally can be defined as average nutrient 

conditions, and average to above-average clarity, the aforementioned reports indicate phytoplankton production increases 

in the spring as daylight length increases and water temperature rises, and thermal stratification of each reservoir begins. 

Production generally builds to a maximum in the shallow 

reservoir waters—defined by the City, and for the purposes of 

this report, as waters up to 20–30 ft below the reservoir water 

surface—in the late summer to early fall, and then generally 

declines with reduced daylight length and temperature and 

reaches a minimum by late fall or early winter, coincident with 

lake turnover.

Long-term (1992–2004) data for Loch Raven and 

Prettyboy Reservoirs on routine algal counts and taxa identification from reservoir monitoring (Appendix B) were analyzed 

by the Interstate Commission on the Potomac River Basin 

(ICPRB) (2006). Their report indicated that for Loch Raven 

Reservoir, the relative abundance of taxa follows a typical seasonal spring-summer-fall succession. Golden-brown algae and 

diatoms generally dominate in the spring (February through 

April), and can continue their dominance until about mid-summer (approximately July). Green algae then briefly dominate 

until late summer to early fall (August through September), 

when, absent conditions for a major algal bloom, diatoms 

resume dominance. Throughout the summer, dinoflagellates 

can account for 15–25 percent of the algal count.

Also, according to the ICPRB report (2006), and except 

for the lack of occurrence of golden-brown algae, Prettyboy 

Reservoir exhibits a spring-summer-fall seasonal succession 

in the relative abundance of taxa similar to that described for 

Loch Raven Reservoir. In addition, although data on algal 

count and taxa identification only routinely were collected 

from these reservoirs from April or May through September, 

and sampling in Prettyboy Reservoir is only conducted 

monthly, the ICPRB noted that other monitoring data (chl-a) 

indicate major phytoplankton blooms (taxa and counts 

unknown) occur in Prettyboy Reservoir in late winter to early 

spring. 

Long-term data on routine algal counts and taxa identification from reservoir monitoring for Liberty Reservoir 

(Appendix B) were analyzed by Winfield and Sakai (2003). 

Their results indicate that phytoplankton production in this 

reservoir typically follows a bimodal (spring and late-summerfall) seasonal succession. Surface-water inflows and complete 

mixing of the reservoir during the winter are considered the 

source of nutrients for a spring bloom (February through April 

or May), which typically is dominated by diatoms and green 

algae. As the reservoir stratifies, phosphorus in the shallow 

reservoir waters is reduced, and temperatures in shallow 

waters become warmer. These conditions are considered by 

Winfield and Sakai (2003) as unfavorable to continued phytoplankton in the spring bloom, which declines in production 

(generally May through June). Decomposition of the spring 

bloom, in combination with nutrient loads from surface-water 

inflows, is presumed to provide the nutrients (chiefly phosphorus) for the late summer bloom, dominated by blue-green and 

green algae, that begins mid-summer and continues in the late 

summer and fall (August through about October). 

Winfield and Sakai (2003) also noted that the bimodal 

pattern in phytoplankton production is observed throughout 

Liberty Reservoir. In their report, however, algal counts and 

chl-a data indicate that the magnitude in productivity clearly 

follows a longitudinal gradient—greatest in the upper part, and 

smallest in the lower part, of the reservoir. By way of contrast, 

no studies were encountered during this review that addressed 

in detail whether or not marked spatial differences occur in the 

relative abundance (by counts) or type of taxa in either Loch 

Raven or Prettyboy Reservoirs.

Whereas the studies by ICPRB and Winfield and Sakai 

describe general seasonal phytoplankton production and 

succession characteristics for the three reservoirs, excessive 

algal-bloom production under eutrophic (elevated nutrient) 

conditions and its impact on reservoir water quality have only 

been described in detail for Liberty Reservoir. Under the right 

conditions, which Winfield and Sakai (2003) indicate relate 

to phosphorus availability, excessive blooms occur in Liberty 

Reservoir. Most often, these major blooms involve the typical 

taxa—green algae in mid-summer, and (or) blue-green algae 

in the late summer and early fall (Valcik, 1975; Winfield and 

Sakai, 2003; Baltimore Reservoir Technical Group, 2004; 

Interstate Commission on the Potomac River Basin, 2006). 

Less common major blooms have occurred in the fall, winter, 

or spring. For example, during the latter phase of the drought 

in the 1960s, and possibly related to excessive reservoir drawdown, major diatom blooms occurred in Liberty Reservoir in 

the spring of 1967 and spring of 1968; a major golden-brown 

algal bloom occurred in Loch Raven Reservoir in the spring of 

1996. 

Winfield and Sakai (2003) created a conceptual depth 

profile that illustrates temporal water-quality conditions 

related to excessive algal blooms in Liberty Reservoir (fig. 4). 

This illustration can serve as a model of this phenomenon for 

all three reservoirs, although the taxa, and actual timing, spatial extent, and magnitude of the changes in water quality that 

result from a major bloom can vary among the reservoirs.

In Liberty Reservoir, major blooms are most often distinguished by elevated algal counts and high concentrations of 
The Water-Quality Monitoring Program 27

Figure 4. Composite generalized seasonal depth profile of algal-impaired water-quality 

conditions in Liberty Reservoir—from turbidity, algal-count, color, and concentration data 

for chlorophyll-a, dissolved oxygen (DO), manganese (Mn), and iron (Fe) (modified from 

Winfield and Sakai, 2003).

chl-a in shallow reservoir waters. Phytoplankton photosynthesis during these blooms can lead to (daytime) supersaturated 

DO concentrations and increases (spikes) in pH in the shallow 

reservoir waters. Algal respiration, and ultimately die-off and 

residue decomposition that follow a major bloom, appear to 

create a high biochemical oxygen demand, which Winfield and 

Sakai (2003) indicate leads to oxygen and pH sags (reduced 

concentrations of DO and lowered pH), and high color and 

turbidity, which generally are most pronounced in deep reservoir waters—here, and hereafter, in this report, defined as 

waters 30 ft or more below the reservoir water surface—in the 

late fall and early winter (fig. 4). With lake turnover in the late 

fall or early winter, only the deepest reservoir waters remain 

highly turbid into the late winter and early spring.

Winfield and Sakai (2003) also note that the decomposition of algal residues does appear to occasionally lead to 

anoxic conditions in surficial bottom sediments, which result 

in the release of manganese and iron presumably by sediment 

diagenesis. This release would account for the elevated concentrations of these two metals often observed in reservoir 

intake waters after excessive blooms die off, and DO declines 

at deep depths, as these metals are naturally abundant in 

origin, and found at elevated concentrations in all reservoir 

sediments (Ortt and others, 2000). In addition, iron mobilization is thought to be accompanied by the release of phosphorus, which Winfield and Sakai (2003) also noted was observed 

for a number of years at elevated concentrations primarily in 

deep reservoir waters following major blooms. As in the case 

of manganese and iron, reservoir bottom sediments also contain abundant phosphorus, which largely is bound to iron (Ortt 

and others, 2000). 

Ultimately, algal bloom die-off and decomposition that 

leads to hypoxic to anoxic conditions also is assumed by 

the Baltimore Reservoir Technical Group (2004) to produce 

physical and chemical conditions that adversely affect biota, 

including higher trophic sport-fish populations. In addition, 

the physical and aesthetic conditions associated with blooms 

and their decay is assumed to reduce recreational opportunities 

such as fishing and other water-contact activities, which are 

designated uses for all three reservoirs.

In addition to the impact on reservoir biota and recreational uses, the impact of excessive blooms on drinking-water 

supplies is also of concern. Although such blooms tend to 

occur in association with, they are not limited to, reservoir 

recovery after droughts and major drawdowns (Valcik, 1975; 

Winfield and Sakai, 2003; Baltimore Reservoir Technical 
28 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Group, 2004). Whether their occurrence is widespread, or 

simply near the water-supply intakes, eutrophic conditions 

(fig. 4) that result in excessive algal blooms can reduce the 

quality and quantity of reservoir water available for potable 

supplies. Among the taxa associated with these blooms, bluegreen and green algae appear to create the broadest array of 

water-treatment problems and subsequent nuisance complaints 

regarding odor, color, and taste (Valcik, 1975; Winfield and 

Sakai, 2003; Baltimore Reservoir Technical Group, 2004). 

Winfield and Sakai (2003) indicate reservoir withdrawals 

of water during or after such blooms preferentially are made 

from the intake(s) whose depth(s) provide water(s) that are 

the least affected by algal blooms or their die-off in order to 

reduce treatment costs and possible problems with color, odor, 

and (or) taste of treated water. Withdrawing such water in sufficient quantities, however, can be difficult, and occasionally 

not possible. Major algal blooms can occur from May through 

November, depending on the supply reservoir, which covers 

the period of highest annual daily demands—late spring 

through early fall. The range of depths at which relatively 

unimpaired supply waters are available can narrow markedly 

through time (fig 4.), however, as a major bloom progresses, 

dies off, and decomposes, and oxygen depletion related to 

decomposition results in elevated concentrations of metals at 

depth. Elevated concentrations of algal matter in any state at 

any depth, and elevated concentrations of iron and manganese 

at depth, both interfere in the treatment of water, and with 

treated water color, odor, and (or) taste. 

Overall, the long-term monitoring network has provided 

the City and the RTG with the data to generally (a) describe 

seasonal phytoplankton production during lake stratification in 

each reservoir and either mesotrophic conditions or eutrophic 

conditions associated with major algal blooms, (b) relate broad 

seasonal patterns in the occurrence of phytoplankton (taxa 

and abundance) to their effect on other current or subsequent 

water-quality conditions (measured parameters) in each reservoir, and (c) identify bloom-related water-quality impairments 

to recreational uses in the reservoir under eutrophic conditions 

with major algal blooms. Under these conditions, and in the 

case of the water-supply reservoirs, the City also can identify 

the related water-quality impairments to supplies, and operate 

supply-reservoir intakes to reduce bloom effects on watertreatment costs and the quality of treated water.

Long-term monitoring data, or the analysis of these data, 

have not enabled the RTG to relate changes in phytoplankton 

taxa or abundance to water-quality conditions antecedent to 

their occurrence. Thus, water-quality conditions such as the 

concentrations of phosphorus and (or) nitrogen in the reservoir that lead to excessive algal blooms, or specific types of 

taxa blooms, are unknown. Long-term monitoring also has 

not adequately addressed, through algal taxa and counts, the 

blooms that occur in the winter and early spring in Prettyboy 

Reservoir. Nor could it be established via any received RTG 

report that monthly sampling for algal and taxa counts is sufficient to accurately characterize phytoplankton abundance or 

succession, particularly in Prettyboy Reservoir.

Nutrients

Eutrophic conditions that result in excessive algal blooms 

are considered by the RTG (2004) to be caused by excessive 

levels of nutrients entering a reservoir, and the amounts of 

nutrients (nitrogen and, in particular, phosphorus) transported 

from the Loch Raven (including Prettyboy) and Liberty 

Reservoir watersheds to their respective reservoirs are therefore a concern (fig. 2). It also should be noted that the occurrence of elevated concentrations of nutrients in streams have 

been cited as a possible contributing factor to excessive algal 

blooms in selected major tributaries (Valcik, 1975), which also 

could affect stream aquatic habitats and designated recreational uses, such as fishing.

To reduce nutrient concentrations in streams and loads to 

the reservoirs requires quantifying their transport within and 

from the reservoir watersheds, identifying their main sources 

within the watersheds, and reducing nutrient concentrations 

from these sources. Data from long-term monitoring in the 

watershed tributaries has been used to estimate nutrient loads, 

concentrations, and trends, and identify possible source areas 

on a subbasin scale.

Nitrogen Transport and Reservoir Cycling

Elevated nitrogen concentrations could play a role in 

phytoplankton production. Although Amatayakul and others 

(1978) concluded that phosphorus was the limiting nutrient 

in Baltimore reservoir waters, their greatest increase in assay 

algal production was in response to samples in which both 

concentrations of nitrogen and phosphorus were elevated 

(table 3). Also, increases in nitrate contributions from known 

point sources (WWTPs) to tributary streams were observed 

in the mid-1980s, just before major blooms occurred in Loch 

Raven and Liberty Reservoirs (Baltimore City Department of 

Public Works, 1996).

Before implementation of the long-term monitoring 

network, Amatayakul, Defries, and others (1978) provided and 

compared estimates for total nitrogen loads with earlier load 

estimates for Loch Raven Reservoir (table 4). They noted a 

lack of spatial and temporal coverage in the monitoring data; 

for example, nitrogen data only were available in subbasins 

representing 27 percent of the reservoir watershed area. Thus, 

their load estimates for the entire watershed were largely 

derived in the absence of actual measurements of nitrogen in 

most subbasins. In addition, they cited several known WWTPs 

whose effluents likely contributed to the nutrient load but also 

were unmeasured. Their monitoring recommendations for 

nutrients included year-round data collection at known major 

point-source discharges and in storm- and base flows on all 

major subbasins in the reservoir watershed.

The long-term monitoring network created in the early 

1980s did include monitoring at known major point sources in 

the major tributaries for nitrogen but chiefly in forms available for biological uptake—ammonia, nitrate, and nitrite 

nitrogen, hereafter referred to as available forms of nitrogen in 
The Water-Quality Monitoring Program 29

Table 3. Bioassay results for nutrient-spiked samples of Selanastrom 

capricornatum (from Amatayakul, Defries, and others, 1978).

[mg/L, milligrams per liter]

Nutrient-spiked sample concentration

(mg/L)

Maximum algal yield

(mg/L, dry weight)

Control 1.0

Phosphorus 0.05 8.1

Phosphorus 0.05, Nitrogen 1.00 14.7

Nitrogen 1.00 1.2

Table 4. Estimated average annual loads of nitrogen and phosphorus to the Baltimore reservoirs, various periods of record between 

1973–97.

[kg/yr, kilograms per year; ---, unavailable]

Constituent Reservoir/

watershed

Estimated average annual load to the reservoir on basis of cited water years 

(kg/yr x 1,000)

1973–741 1975–782 1983–19--3 1983–904 1988–915 1992–976

Nitrogen Liberty --- --- --- --- --- ---

Loch Raven 625 774, 744 --- --- 3,450 717

Prettyboy --- --- --- --- --- 287

Phosphorus Liberty --- --- 31.2 44.6 --- ---

Loch Raven 11.1 14.7, 21.3 48.9 64.0 49.0 49.7

Prettyboy --- --- --- 17.6 --- 22.9

1

 Amatayakul, Defries, and others (1978), National Eutrophication Study, Report for Loch Raven Reservoir, Environmental Protection Agency, Region III, 

Working Paper No. 358, Corvallis, Oregon—likely few stormflows, load estimates for ungaged subbasins, with loads derived from normalized flow-concentration curves, and annual mean concentration.

2

 Amatayakul, Defries, and others (1978), includes some stormflows, load estimates for ungaged subbasins, with load estimates derived from flow-duration 

and concentration curves (first value) or annual mean flow and concentration (second value).

3

 Baltimore City Department of Public Works (1992), computed from statement that 1983–90 load estimates (see footnote 4, below) reflect a 30-percent 

increase for Loch Raven Reservoir and a 43-percent increase for Liberty Reservoir compared to prior published estimates. No information is available on how 

these prior estimates were computed, or publication source or date.

4 Baltimore City Department of Public Works (1992), includes stormflows, load estimates for point and nonpoint sources, and assumes estimates from flowduration and concentration curves.

5 Maryland Department of the Environment (2003d), includes stormflows, load estimates for total phosphorus from point and nonpoint sources, including 

gaged and ungaged subbasins, for 10-year synthetic period under existing conditions generated from U.S. Environmental Protection Agency Storm Watershed 

Management Model, calibrated and validated with data from water years 1988–91. 

6

 Interstate Commission on the Potomac River Basin (2006), load estimates from point and nonpoint sources for ungaged subbasins created with the 

Hydrological Simulation Program–FORTRAN (HSPF) model, and calibrated with data from water years 1992–97.

this report. As of 2007, no or few data have been collected on 

Kjeldahl or organic nitrogen.

The RTG and others have used data on the available 

forms of nitrogen and improved models to provide more 

accurate estimates of total annual loads of these nitrogen species to the reservoirs (table 4); these estimated loads generally 

are greater than the loads initially estimated by Amatayakul, 

Defries, and others (1978). 

Monitoring data also have been used to describe and 

compare concentrations of available forms of nitrogen from 

point sources (NPDES includingWWTPs) among subbasins 

within a given reservoir watershed, or, on the basis of data 

from dry-weather-flow stations, as form-specific areal nitrogen 

loads. For example, upgrades to the WWTPs to reduce effluent nutrient loads were begun in the late 1970s and continued 

through the 1980s. Using data provided by the long-term 
30 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

monitoring network for NPDES sites, the City reported that 

initially there appeared to be no substantial reductions in total 

available nitrogen, but that there were shifts in the proportion 

of the forms of available nitrogen—from ammonia to nitrite 

and (or) nitrate nitrogen in WWTP effluents. By the mid1990s, however, the monitoring data indicated a reduction in 

total available nitrogen loads at two WWTPs—Dutterers and 

Manchester—in Prettyboy and Loch Raven Reservoir watersheds, and an increase in load at a third WWTP—Hampstead 

(Baltimore City Department of Public Works, 1996, fig. 9.1). 

Monitoring in Liberty Reservoir watershed also indicated 

total available nitrogen loads eventually declined at its 

three WWTPs—Congoleum, Montrose, and Roy F. Weston 

(Baltimore City Department of Public Works, 1996, fig. 9.2). 

The documented reductions in available nitrogen from WWTP 

discharges demonstrated the effectiveness of the long-term 

monitoring program to track changes in known point-source 

loads for the available forms of this nutrient through the 

USEPA NPDES program.

Data obtained from the long-term monitoring network 

have been used to indicate apparent annual trends in ammonia, 

and apparent annual trends and seasonal variations in nitrate, 

nitrogen in the watershed tributaries. Decreases in annual 

median ammonia-nitrogen concentrations were observed in 

dry-weather flows at all tributary monitoring stations during the 1980s (fig. 5), which continued through the 1990s 

(Winfield and Sakai, 2003). The apparent declines in ammonia-nitrogen concentrations for most tributary stations in the 

Loch Raven Reservoir watershed eventually were verified 

to be statistically significant (Maryland Department of the 

Environment, 2003d, Kendall trend test, accounting for autocorrelation, p less than 0.05, data from 1981–95).

During the 1980s through the mid-1990s, concentrations 

of nitrate nitrogen appeared to increase at most tributary monitoring stations, and more so in the Liberty Reservoir watershed 

than in either the Loch Raven or Prettyboy Reservoir watersheds, but by 2000, they had appeared to level off (fig. 6). The 

apparent increasing trends in nitrate-nitrogen concentrations 

for the tributary stations in the Loch Raven Reservoir watershed eventually were statistically verified by MDE (Maryland 

Department of the Environment, 2003d).

Dry-weather flow monitoring data have been used to 

indicate seasonal patterns in tributary nitrate-nitrogen concentrations. Except for those tributaries overly influenced by 

WWTP effluent, or Prettyboy Reservoir outflow (for example, 

at Gunpowder River at Falls Road), mean-monthly nitratenitrogen concentrations for dry-weather flows in watershed 

tributaries cycle from winter highs to summer lows—a pattern 

attributed to greater riparian or in-stream biotic uptake or 

abiotic sequestration of nitrate during summer compared to 

winter months (Baltimore City Department of Public Works, 

1996, fig. 9.11). 

Monitoring data for dry-weather flows have been used 

to relate differences in nitrate-nitrogen concentrations among 

streams to differences in land cover. The City illustrated that 

long-term median nitrate-nitrogen concentrations in a stream 

appeared to decrease as a function of the amount of forested 

land in the subbasin draining to that stream (Baltimore City 

Department of Public Works, 2001, fig. 44). No statistical 

analyses were conducted, however, to determine the strength 

of this relation or its level of statistical significance.

Given the aforementioned apparent or confirmed annual 

trends observed in ammonia- and nitrate-nitrogen concentrations in the reservoir watershed tributaries, the question 

arose as to whether similar trends could be discerned in the 

reservoirs. Overall, City DPW summary and other reports 

(Baltimore City Department of Public Works, 1996, 2000, 

2001; Winfield and Sakai, 2003) note from graphical analysis 

that concentrations of ammonia-nitrogen appeared to decline 

in the reservoirs, as well as in the streams draining into the 

reservoirs from the 1980s through the 1990s. They also 

noted that in-lake nitrate-nitrogen concentrations appeared to 

increase in Liberty Reservoir, as well as in its watershed tributaries, but that despite the apparent increase in nitrate-nitrogen 

concentrations noted in the Loch Raven and Prettyboy 

Reservoir watershed tributaries, no clearly discernible and 

consistent in-lake trends in nitrate concentrations were apparent in either reservoir.

Although no statistical analyses were conducted for 

ammonia- and nitrate-nitrogen concentrations in Liberty 

Reservoir and its watershed tributaries, trend analyses were 

conducted for Loch Raven and Prettyboy Reservoirs and 

their watershed tributaries (Maryland Department of the 

Environment, 2003d). Ammonia-nitrogen concentrations did 

significantly decline in dry-weather flows in most Loch Raven 

and Prettyboy Reservoir watershed tributaries, but significant 

declines in ammonia-nitrogen concentrations occurred at only 

two stations (fig. 3B, Station GUN0171 and GUN0156) in the 

middle-to-lower part of Loch Raven Reservoir (Kendall trend 

test, with autocorrelation, p less than 0.05, with data from 

1981–95). Statistical analyses also revealed positive significant trends in nitrate-nitrogen concentrations in dry-weather 

flows in the Loch Raven and Prettyboy Reservoir watershed 

tributaries, but no significant trends in nitrate-nitrogen concentrations were observed in either reservoir.

The lack of a direct correspondence between observed 

patterns, and in at least some cases, verified trends, in ammonia- or nitrate-nitrogen concentrations in watershed tributaries and reservoirs is not unexpected. First and foremost, the 

patterns observed in the tributaries only reflect available forms 

of nitrogen in dry-weather flows. Measurements of ammoniaand nitrate-nitrogen in the reservoirs, however, could reflect 

not only available nitrogen from dry-weather flows but also 

stormflows. Although the latter would be expected to have 

similar or lower concentrations than dry-weather flows, they 

nevertheless would increase available nitrogen loads to the 

reservoirs. Reservoir concentrations also could reflect nitrogen made available from organic sources in streamflows (not 

measured) or within the reservoir through in-lake abiotic 

and biotic, and (or) hydrodynamic processes—for example, 

through the release of ammonia-nitrogen from bottom sediments under hypoxic and stratified conditions.
The Water-Quality Monitoring Program 31

Figure 5. Annual median ammonia-nitrogen concentrations in dry-weather flows at (A)

Liberty and (B) Loch Raven Reservoir tributaries, 1982–91 (modified from Reservoir Watershed 

Protection Subcommittee, 1992).

Reservoir processes likely do play a role in the determination of in-lake available nitrogen concentrations. For 

example, monitoring data indicate both ammonia- and 

nitrate-nitrogen concentrations are considerably lower in the 

reservoirs than in streams (table 5), an indication of considerable in-lake nitrogen processing and recycling. In addition, 

concentrations of available forms of inorganic nitrogen appear 

to be governed in part by reservoir hydrodynamics. During 

lake stratification, they generally are stratified. Nitrate nitrogen 

is highest in shallow oxic waters, whereas ammonia nitrogen 

is highest in deep hypoxic waters (Baltimore City Department 

of Public Works, 1996). Additional evidence that in-lake processes influence concentrations of available nitrogen is seasonally apparent. As noted earlier, nitrate-nitrogen concentrations 

in most tributaries tend to peak in the winter months and then 

gradually decline to their lowest values during the summer 

months. Concentrations of nitrate nitrogen in the reservoirs, 

however, tend to peak in the late spring to early summer and 

then decline (for example, fig. 7), presumably because of midsummer in-lake primary production. 
32 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 6. Nitrate-nitrogen concentrations in dry-weather 

flows at (A) Middle Run tributary in the Liberty Reservoir 

watershed, (B) Western Run tributary in the Loch Raven 

Reservoir watershed, and (C) Graves Run tributary in the 

Prettyboy Reservoir watershed, 1982–2000 (modified from 

Baltimore City Department of Public Works, 2001).

Phosphorus Transport and Reservoir Cycling

Considerable attention and effort have been paid to the 

reduction of phosphorus loads to the Baltimore City reservoirs. Amatayakul and others (1978) provided the initial laboratory bioassay studies that led them to conclude that stoichiometric increases in phosphorus rather than nitrogen produced 

the greatest increase in algal production in euphotic water 

samples from Loch Raven Reservoir (table 3). Monitoring 

data also have been used by the RTG and others as evidence 

from the field that phosphorus possibly is the limiting nutrient (Amatayakul and others, 1978; Interstate Commission on 

the Potomac River Basin, 2006). Various ratios of nitrogen to 

phosphorus (N:Ps) have been calculated and reported (10-to100 or more to one) for shallow surface waters in the Loch 

Raven and Prettyboy Reservoirs, and have been reported to 

typically exceed the Redfield (16:1) ratio (Redfield, 1958), the 

ratio of total nitrogen to total phosphorus found in phytoplankton when neither nutrient is limiting. The reported ratios, however, utilize available nitrogen, or modeled estimates of total 

nitrogen, rather than actual measurements of total nitrogen. 

Hence, the actual total N: total P ratios in reservoir surface 

waters could differ from the reported ratios. In addition, the 

Redfield ratio was developed from marine not artificial freshwater (reservoir) environments, and the variations in this ratio 

could be more important to consider than a single ratio value 

when assessing nutrient limitations and phytoplankton production in fresh waters (Downing and others, 2001; Arrigo, 2005).

Amatayakul, Defries, and others (1978) also provided 

and compared estimates for TP, with the earliest load estimates 

for Loch Raven Reservoir (table 4). As is the case with nitrogen loads described earlier (see Eutrophication—Nutrients: 

Nitrogen Transport and Reservoir Cycling, this report), 

they noted a lack of spatial and temporal coverage in the TP 

data required to estimate loads. Their monitoring recommendations for phosphorus included year-round data collection 

in the reservoir watersheds for point sources (for example, 

WWTPs) and in major tributary storm- and base flows to the 

reservoir.

The long-term reservoir watershed monitoring network 

created in the early 1980s included monitoring at known major 

point sources for phosphorus (NPDES WWTPs), in the reservoir watershed tributaries during storm- and base flows, and in 

the reservoirs. Analyses for phosphorus initially included TP 

at all monitoring sites, and through the early 1990s, additional 

analyses for DOP for storm- and selected dry-weather flows at 

the three gaged tributary stations in each supply reservoir. The 

measurement of DOP was used to approximate bioavailable 

phosphorus. No DOP measurements were routinely obtained 

in the reservoirs, mainly because TP concentrations in the reservoirs often approached or were below the laboratory method 

reporting levels at the water-treatment facilities (Robert 

McAuley, Baltimore City Department of Public Works, written commun., 2008). Thus, long-term tracking of phosphorus 

has mainly relied on TP data alone from dry-weather flows to 

describe concentrations and (or) compute areal-weighted loads 
The Water-Quality Monitoring Program 33

Table 5. Median ammonia- and nitrate-nitrogen concentrations in the Baltimore reservoirs, 1981–93 (adapted from Baltimore City 

Department of Public Works, 1996).

[mg/L, milligrams per liter]

Nutrient Time

period

Reservoir 

location

Reservoir

waters1

Median concentration

(mg/L)

Liberty Loch Raven Prettyboy

Ammonianitrogen

Year-round Lower Shallow 0.04 0.05 0.04

Growing season Lower Shallow 0.03 0.03 0.04

Growing season Headwaters Shallow 0.05 0.04 0.03

Year-round Lower Deep 0.06 0.11 0.05

Nitratenitrogen 

Year-round Lower Shallow 1.53 1.43 1.69

Growing season Lower Shallow 1.81 1.50 1.74

Growing season Headwaters Shallow 2.04 1.68 1.78

Year-round Lower Deep 0.14 0.11 0.05

1

 Shallow waters are 30 feet deep or less; deep waters exceed 30 feet in depth. 

at all dry-weather-flow tributary stations, or from storm- and 

dry-weather flows to describe concentrations or total loads, or 

compute flow-concentration curves, at each of the three gaged 

tributary stations in the supply-reservoir watersheds.

After WWTPs were identified early on as likely sources 

of phosphorus that contributed to excessive algal blooms 

(Valcik, 1975), upgrades to the WWTPs were made during the 

late 1970s through mid-1980s. Data provided by the long-term 

monitoring network through the 1980s to mid-1990s were 

used to document substantial reductions in TP effluent loads 

following WWTP renovations in the late 1970s through 1980s 

(Reservoir Watershed Protection Committee, 2000, fig. 12). 

Summary and other reports (Baltimore City Department of 

Public Works, 1996; Winfield and Sakai, 2003) indicate that 

within the Liberty Reservoir watershed, total annual loads 

of TP in WWTP effluents decreased 95 percent to approximately 28 kg/yr (kilograms per year) for 1989–94, from 

approximately 512 kg/yr for 1983–86. In the Loch Raven and 

Prettyboy Reservoir watersheds, the WWTP effluent loads for 

TP decreased 71 percent during the same period.

Annual TP loads from WWTPs are a small part of the 

total annual watershed tributary TP loads to the reservoirs. 

For example, the TP loads from the WWTPs to the streams in 

Loch Raven Reservoir watershed in what was then considered 

a wet water year (1984) represented only approximately 3 

percent, and in a dry water year (1986), only approximately 9 

percent, of the estimated total annual tributary load of TP from 

the three gaged subbasins to the reservoir in each of these 

water years (Baltimore City Department of Public Works, 

1996, fig. 10.1). Nevertheless, reductions in effluent TP loads 

were considered important (Baltimore City Department 

of Public Works, 1996, 2000, 2001). The WWTP effluents 

contained available forms of nitrogen—ammonia, nitrite, and 

nitrate—and possibly contained high concentrations of DOP 

(Baltimore City Department of Public Works, 1996). The 

documented reductions of TP in WWTP effluents also demonstrated that the long-term monitoring program effectively 

can track changes in known point-source TP load through the 

NPDES program.

Given that effluent loads from suspected major point 

sources accounted for only a small fraction of the total annual 

tributary loads for TP, it was suspected by the RTG that the 

major portion of tributary loads was largely from unregulated 

nonpoint sources. Thus, the RTG and others periodically have 

used long-term monitoring data to estimate TP loads to the 

reservoirs (table 4); the estimated loads are generally greater 

than the loads initially estimated by Amatayakul, Defries, and 

others (1978). It should be noted, however, that all TP load 

estimates, regardless of when they were computed, reflect TP 

monitoring data obtained before the year 2000, which will be 

discussed further below.

Monitoring data for TP from the early 1980s to mid1990s have been used to assess annual variations and differences in TP concentrations and loads among and from 

the six gaged tributaries and their subbasins (figs. 8A and 

B; Reservoir Watershed Protection Subcommittee, 1992). 

Summary reports for this period note that mean total annual 

TP concentrations and loads varied for each subbasin 

(Baltimore City Department of Public Works, 1992, 1996; 

Reservoir Watershed Protection Subcommittee, 1992). The 

reports also noted that the high variability in TP loads was 

likely the result of climatic variation—concentrations and 

loads being notably higher in wet years than in dry years 

(fig. 9, for example, 1984 and 1986, respectively), and, within 

a given year, to flow regime. Most of the TP load in the gaged 

tributary subbasins did indeed appear to be carried by storm-, 

as opposed to dry-weather, flows, with the latter, depending on 

the tributary, accounting for no more than 15–30 percent of the 

total annual TP load (fig. 8B).
34 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 7. Mean monthly nitrate- and nitrite-nitrogen concentrations in (A) upper (Reservoir station NPA0105), and 

(B) lower (Reservoir station NPA0059) parts of Liberty Reservoir, 1994–2001 (modified from Winfield and Sakai, 2003). 
The Water-Quality Monitoring Program 35

Figure 8. (A) Annual loads of total phosphorus and (B) proportion of total annual phosphorus load 

transported by dry-weather flows for six gaged streams and subbasins in the Loch Raven and Liberty 

Reservoir watersheds, 1983–90 (modified from Reservoir Watershed Protection Subcommittee, 1992, 

and Baltimore City Department of Public Works, 1996)
36 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 9. (A) Mean annual total phosphorus concentration and (B) total annual phosphorus load for gaged streams and 

subbasins in the Loch Raven and Liberty Reservoir watersheds, 1983–90 (modified from Reservoir Watershed Protection 

Subcommittee, 1992).
The Water-Quality Monitoring Program 37

Monitoring data for TP in storm- and dry-weather flows 

during the 1980s at the six major tributaries in the supply 

reservoir watersheds were used to provide the first spatial load 

assessments among major subbasins. On the basis of arealweighted TP (storm- and dry-weather flow) loads or yields 

(Baltimore City Department of Public Works, 1996, table 

10.1), the three major subbasins within each supply reservoir 

could be ranked to help identify high TP source areas for 

management of this nutrient (Baltimore City Department of 

Public Works, 1996, 2000, 2001). Although not statistically 

confirmed in these reports, for the Loch Raven Reservoir 

watershed, Western Run appeared to have the highest yield 

among the three tributaries, despite the variability yields, 

which appeared similar among the three tributaries. Apparent 

differences in yields among the three major Liberty Reservoir 

watershed subbasins were considered relatively minor and 

insufficient to warrant ranking given the high variability in 

yields at all three subbasins.

The long-term monitoring data also have enabled subbasin TP yield comparisons among all reservoir watersheds to be 

computed, but solely with dry-weather-flow data (Baltimore 

City Department of Public Works, 1996, fig 9.5). Western Run 

again appeared to have the highest yields among all monitored 

subbasins in the Loch Raven Reservoir watershed, as did 

Georges Run in the Prettyboy Reservoir watershed, and Bonds 

Run and the North Branch of the Patapsco River at Route 91 

in the Liberty Reservoir watershed. Overall, dry-weather-flow 

TP yields among subbasins, however, also were highly variable, and average yields among subbasins within a reservoir 

watershed differed by less than 5 to 10 kg/m2

/yr (kilograms 

per square meter per year) (Baltimore City Department of 

Public Works, 1996, table 10.1). Whether or not these differences in yields were statistically different among subbasins 

was not determined.

Dry-weather flow TP data also have been used on a 

limited basis to assess apparent relations between tributary 

TP concentrations and subbasin land use and cover characteristics—forested, agricultural, or residential (Baltimore 

City Department of Public Works, 2001, fig. 27, fig. 30, and 

fig. 38). Median TP concentrations for dry-weather flows in 

1999 for each subbasin were found to be inversely related to 

the proportion of the subbasin in forest cover. (Presumably 

this relation holds true for most other years as well.) Median 

TP concentrations in 1990 and 1999 for each subbasin also 

appeared to be positively related to the proportion of the subbasin in agricultural land use, and the difference in median TP 

concentrations from 1990 and 1999 appeared to be positively 

related to the number of low-density residential housing units 

without sewer hook-up per square mile of subbasin constructed during the 1990s. The latter relation was taken by the 

RTG to indicate that construction operations (for example, cut 

and fill, and septic-system installation) associated with new 

residential units could result in sediment transport or have 

some other type of transient effect on TP concentrations in 

streams. Although the above apparent TP and land-use relations did not consider stormflow, it was inferred they could 

be considered in the development of management activities 

to reduce phosphorus loads in selected individual subbasins 

(Reservoir Watershed Protection Committee, 2000).

Tributary dry-weather-flow data for TP have been 

analyzed to assess annual trends and seasonal variations. 

Summary and other reports (Baltimore City Department of 

Public Works, 1992, 1996, 2001; Winfield and Sakai, 2003) 

describe apparent decreases in TP concentrations at most dryweather tributary stations. The apparent decline in TP in the 

Liberty Reservoir watershed tributaries began in the 1980s and 

continued through the 1990s—for example, at Little Morgan 

and Middle Runs (fig. 10). Similar apparent trends were 

noted for tributaries in the Prettyboy Reservoir watershed—

for example, Gunpowder Falls and Georges Run (fig. 11). 

Declines in TP concentrations were not apparent for tributaries 

flowing into Loch Raven Reservoir—for example, at three stations on the Gunpowder Falls (fig. 12).

The City (Baltimore City Department of Public Works, 

2001) noted that the apparent declines in TP concentrations for 

dry-weather flows in Liberty Reservoir and Prettyboy watersheds (fig. 10, fig. 11) appeared to be accompanied by apparent declines observed in algal counts and, to a less apparent 

degree, concentrations of chl-a, in the reservoirs (fig. 13). In 

addition, despite no apparent declines in TP concentrations 

in tributaries in Loch Raven watershed, there were apparent 

declines in total algal counts and concentrations of chl-a in the 

reservoir (fig. 13).

To substantiate whether there were significant trends in 

TP, at least in relation to the Loch Raven Reservoir watershed, 

the Maryland Department of the Environment (2003d) conducted statistical trend analysis on the tributary dry-weatherflow and reservoir in-lake TP data collected from 1983–92. 

Their results revealed that among the tributaries, only two 

stations (Dulaney Valley Branch and Gunpowder Falls at 

Falls Road just below Prettyboy Reservoir) showed significant negative trends whereas the remaining four tributary 

stations indicated no significant trend in TP concentrations. 

In the reservoir, only one in-lake station in the lower part of 

the reservoir (fig. 3B, Reservoir station GUN0142) showed 

a significant decline in TP. All other reservoir stations (four) 

had no significant trends. Overall, the investigation concluded 

that for the period of record examined, there generally were no 

significant declines in TP concentrations at most reservoir and 

tributary stations. Thus, changes in TP concentrations, at least 

on the basis of dry-weather-flow data, could not account for 

the apparent long-term declines in reservoir total algal counts 

or concentrations of chl-a. 

Assuming that the apparent declines in algal counts 

and chl-a concentrations in the reservoirs from 1981–2001 

could be statistically verified in all three reservoirs, which is 

necessary, they could reflect trends in environmental factors 

other than TP that influence phytoplankton production. For 

example, if phosphorus is not truly solely limiting phytoplankton production, the declines in ammonia nitrogen in the 

reservoir tributaries described earlier could have led, or helped 

lead, to the declines in algal counts and chl-a concentrations 
38 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 10. Total phosphorus concentrations for dry-weather 

flows at selected subbasin tributaries in the Liberty Reservoir 

watershed and in the shallow surface (less than 30-foot depth) 

layer in the middle part of Liberty Reservoir, 1982–2000 (modified 

from Baltimore City Department of Public Works, 2001).

Figure 11. Total phosphorus concentrations for dry-weather 

flows at selected subbasin tributaries in the Prettyboy 

Reservoir, 1982–2000 (modified from Baltimore City Department 

of Public Works, 2001).

in the reservoirs (see Eutrophication—Nutrients: Nitrogen 

Transport and Reservoir Cycling, this report). Other 

environmental factors could influence phytoplankton production, but possibly were not fully investigated. For example, 

there is evidence of reductions in suspended sediment (a 

potential source of phosphorus) in tributary flows (see 

Sedimentation—Sediment Transport, this report).

Perhaps as important, studies conducted after the investigation by MDE indicate that problems in the monitoring 

methods for phosphorus could play a role in the inability to 

explain the differences in apparent trends in TP in the watershed tributaries and for tributaries and in-lake concentrations 

of TP, chl-a, and algal counts. Among the monitoring issues 

raised are the quality of the TP data, the reliance on measurements of only dry-weather-flow TP concentrations (instead 

of storm- and base-flow TP concentrations and loads), and 

the measurement of only TP (rather than some form of 

phosphorus that could possibly better represent bioavailable 

phosphorus, for example, DOP, or total dissolved phosphorus, 

TDP, measured as orthophosphate phosphorus in a filtered and 
The Water-Quality Monitoring Program 39

persulfate-digested sample) (Baltimore City Department of 

Public Works, 1992, 1996, 2001; Winfield and Sakai, 2003; 

Interstate Commission on the Potomac River Basin, 2006). In 

addition, there is a lack of information on phosphorus cycling 

in the reservoirs, including in-lake sources of bioavailable 

phosphorus possibly released from sediment, and (or) from 

early season algal bloom die-offs. 

Notable among the concerns raised regarding the limitations in phosphorus monitoring is the quality of the TP data 

obtained through the long-term monitoring network. Shortly 

after the completion of the Maryland Department of the 

Environment (2003d) study, KCI Technologies, Inc. (KCI 

Technologies, Inc., 2004) presented its findings on an examination of trends in TP for all three reservoirs. Using monitoring data obtained from 1981 to 2003, they examined the extent 

to which non-systematic variations, such as step changes or 

outliers, influenced the ability to detect trends in TP concentrations in the reservoirs and their tributaries. They found that all 

or almost all stations in each reservoir and reservoir watershed 

would exhibit statistically significant declines in TP during all 

or most of the period of record, except for two unusual anomalies in the TP data. The first anomaly was an inexplicable step 

change (increase) in TP concentrations that occurred in June–

July 1995. The step changes were most pronounced in the 

TP data for monitoring stations in Loch Raven and Prettyboy 

Reservoirs, and ranged from approximately 40–100 μg/L. The 

pronounced step changes were suspected of being the result 

of an undocumented change in the analytical procedures at 

the Montebello water-treatment laboratory. The second data 

anomaly was the occurrence of extreme (generally low) TP 

values in the data record. At least some of these low values 

were suspected of being TP concentrations that were less than 

the laboratory reporting levels (LRLs) for the Montebello and 

Ashburton treatment-facility laboratories, which historically 

were stored in the monitoring database as real number values 

corresponding to one half the LRL with no additional remarks. 

Other studies have questioned the quality of the TP 

data possibly because of one or both of the above anomalies 

(Walker, 1988; Interstate Commission on the Potomac River 

Basin, 2006). The lack of sufficient field and laboratory QAC 

information and data in relation to laboratory methods used 

and possible changes in methods, and the manner in which 

concentration data below the LRL historically were stored, 

again were cited as shortcomings in the data-collection program. As of 2007, neither of these issues appears to have been 

fully and adequately addressed.

From an environmental perspective, limitations in monitoring phosphorus solely as TP can be illustrated by results 

obtained by the RTG to characterize seasonal variations in TP 

in the tributaries and reservoirs. Concentrations of TP in the 

reservoir watershed tributaries in dry-weather flows have been 

shown to vary seasonally. Peak intra-annual (monthly) median 

concentrations of TP appear to occur in the summer months 

and are at least 2 to 5 times greater than median monthly TP 

concentrations during most of the rest of the year (for example, Loch Raven watershed, fig. 14).

Figure 12. Total phosphorus concentrations for dry-weather 

flows in the Loch Raven Reservoir watershed along Gunpowder 

Falls, from just below the Prettyboy Reservoir outlet to Loch 

Raven Reservoir, 1982–2000 (modified from Baltimore City 

Department of Public Works, 2001).
40 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 13. (A) Total algal counts (TAC) and (B) chlorophyll-a concentrations for shallow surface waters (less than 30 feet deep) at 

selected stations in the Liberty, Loch Raven, and Prettyboy Reservoirs, 1981–2001 (modified from Baltimore City Department of Public 

Works, 2001).
The Water-Quality Monitoring Program 41

The elevated concentrations of TP in summer flows 

have been cited as a concern possibly warranting further 

investigation (Baltimore City Department of Public Works, 

1996, 2001). Their arrival does occur just before most major 

mid-to-late summer algal blooms begin in the supply reservoirs, and when epilimnetic conditions such as light intensity 

and penetration and water temperature are conducive to algal 

blooms. Because of these conditions, it was noted in the above 

reports that identification of subbasins with the highest peak 

summer TP concentrations possibly could be used to help 

focus management activities in these subbasins to reduce summer TP inflows, and thus possibly reduce mid-to-late-summer 

phytoplankton production.

Whether or not the summer peaks in dry-weather-flow 

TP concentrations do contribute to mid-to-late-summer algal 

blooms is uncertain. They could possibly act as a tipping 

point, or add to the available phosphorus pool and possibly 

exacerbate algal blooms, since their arrival does coincide with 

a period when epilimnetic water temperatures and microbial 

activity are elevated. But peak summer TP dry-weather-flow 

concentrations correspond to low flows, and thus loads. For 

example, areal-weighted median or average summer dryweather flows (at least based on measured values at the time 

of dry-weather sampling) only are on the order of a cubic foot 

per second per square mile (fig. 14), or, in terms of streamflows, in flows of a few tens of cubic feet per second or less.

Adding to the uncertainty of the effect of peak TP 

dry-weather flows on summer algal blooms is that there is 

no corresponding TP summer peak observed at most in-lake 

stations. Reservoir TP concentrations generally are similar 

in magnitude to dry-weather TP concentrations. If tributary 

inflows exerted that much influence, some elevation in TP 

concentrations in reservoir stations closest to tributary inflows 

would be anticipated. Elevated reservoir TP concentrations in 

Loch Raven Reservoir, however, only appear to occur in the 

shallow surface water of one reservoir station (Baltimore City 

Department of Public Works, 1996, fig. 9.10) at the expected 

May-June TP peak for tributaries to this reservoir (fig. 14). 

Elevated TP concentrations do not appear in upper Liberty 

Reservoir shallow headwaters in August (Winfield and Sakai, 

2003, fig. 7-4d), where tributary-inflow effects are most 

pronounced, and when seasonal summer peaks are observed 

at the dry-weather-flow tributary in the watershed for this 

reservoir. Also, in neither case do the tributary dry-weatherflow seasonal patterns in TP to either water-supply reservoir 

explain the seasonal variations, or annual TP peak concentrations, that occur generally in the fall, in both the headwaters 

and elsewhere, at most stations in these reservoirs (Baltimore 

City Department of Public Works, 1996, fig. 9.10; Winfield 

and Sakai, 2003, fig. 7-14d). These seasonal peaks in the 

reservoirs could reflect phosphorus release from algal bloom 

die-offs or sediment, and the beginning of lake turnover. Thus, 

reservoir abiotic and biotic, and hydrodynamic, processes 

likely determine, in whole or at least in part, the availability of 

phosphorus, and concentration of TP, in the reservoirs. 

Without measurements of bioavailable phosphorus (for 

example, DOP or TDP) in the tributaries and reservoirs, 

however, one cannot determine if the seasonal variations in TP 

in both the tributaries and reservoirs truly reflect variations in 

bioavailable phosphorus. Nor can one determine the relative 

contributions of bioavailable phosphorus in the reservoirs 

from tributaries and in-lake sources.

The RWMA partners initially did attempt to quantify 

bioavailable phosphorus by monitoring DOP during the 1980s 

through the early 1990s. From 1981–93, concentrations of 

DOP were more or less routinely determined as part of storm 

sampling, less frequently determined for dry-weather-flow 

sampling, and as noted earlier, seldom if ever determined in 

the reservoirs. Monitoring data for TP and DOP at the three 

gaged watershed tributaries in Liberty Reservoir were summarized by Winfield and Sakai (2003). Long-term average TP and 

DOP concentrations in tributary stormflows were 0.38–0.42 

mg/L and 0.08–0.15 mg/L, respectively, and for dry-weather 

flows were 0.02–0.05 mg/L and 0.02–0.03 mg/L, respectively 

(table 6). On average, for the period from 1981–93, and 

depending on the tributary, only a small fraction of tributary 

stormflow TP was DOP—approximately 4 to 21 percent; 

however, approximately 75 to 81 percent of dry-weather-flow 

TP was DOP.

Relative to the period during which DOP data were collected, there also was a notable change in the ratio of DOP to 

TP in tributary flows. About mid-way through the 1981—93 

monitoring period, there was an abrupt decline in the ratio 

of annual median DOP concentrations to annual median TP 

concentrations in gaged tributary flows (fig. 15). What caused 

the decline in this ratio is not known. The City (Baltimore City 

Department of Public Works, 1992) thought that the decline in 

the ratio could reflect a combination of watershed best management practices, including changes in agricultural methods 

or practices, modifications to WWTPs, and a statewide ban 

on phosphates in detergents. They also noted, however, that 

the decline was being investigated to determine if it was due 

to a bias in the sampling method used during stormflows 

up through 1986. No further results from this investigation 

were encountered in any subsequent reports obtained for this 

review. The decline in the DOP:TP ratio after 1986 implied 

that the median annual DOP concentration accounted for no 

more than approximately 40 percent of the median annual TP 

from gaged tributary storm- and dry-weather flows; before 

1987, the median annual DOP concentration had accounted for 

at least 40 percent or more of the median annual TP concentration at most of the gaged tributary sites.

The combination of finding a relatively high ratio of 

DOP to TP (DOP:TP) in dry-weather flows from 1980–93, 

combined with the low ratio of DOP:TP in storms after 1986, 

possibly contributed to the shift in the focus of the monitoring 

program in the early 1990s—from monitoring of DOP and 

TP in storm- and dry-weather flows to monitoring just TP in 

dry-weather flows as a means of tracking changes in phosphorus in the reservoir watershed tributaries. It also was apparent that dry-weather-flow monitoring of TP, which contained 
42 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 14. Seasonal patterns in monthly total phosphorus concentrations and rates of dry-weather flow for tributaries in the Loch 

Raven Reservoir watershed, 1981–93 (modified from Baltimore City Department of Public Works, 1996).
The Water-Quality Monitoring Program 43

Table 6. Mean total phosphorus and dissolved (orthophosphate) phosphorus concentrations and yields for Liberty Reservoir 

watershed tributaries, 1981–93 (modified from Winfield and Sakai, 2003).

[ft3/s, cubic feet per second; mg/L, milligrams per liter; kg/km2, kilogram per square kilometer; ---, unavailable]

Station

Number of samples Tributary discharge Concentration Yield

Total 

phosphorus

Dissolved

(orthophosphate)

phosphorus

Mean

(ft3

/s)

Maximum

(ft3/s)

Total

(mg/L)

Dissolved

(orthophosphate)

(mg/L)

Total

(kg/km2)

Dissolved

(orthophosphate)

(kg/km2

)

Dry-weather flows

Beaver Run at Hughes 

Road 113 27 12 42 0.025 0.020 7.2 6.5

Morgan Run at London 

Bridge Road 113 30 24 115 0.021 0.017 6.1 4.8

North Branch Patapsco 

River at Route 91 110 27 41 145 0.045 0.034 15.3 12.0

Stormflows

Beaver Run at Hughes 

Road 173 78 91 1, 917 0.382 0.080 --- ---

Morgan Run at London 

Bridge Road 179 80 201 2, 985 2.64 0.097 --- ---

North Branch Patapsco 

River at Route 91 167 79 401 6, 173 3.22 0.152 --- ---

considerable DOP, also would provide data for comparisons 

among more subbasins than TP monitoring for storm- and dryweather flows (Reservoir Watershed Protection Subcommittee, 

1992).

Despite the possible advantages of just dry-weatherflow TP monitoring, the reliance on this type of monitoring, 

and the reduction in stormflow TP monitoring, possibly have 

limited the ability of the RTG to address RWMA concerns. 

Dry-weather-flow monitoring presents a challenge in formally 

defining what constitutes a dry-weather flow—to date, these 

flows have not been well-defined and described in any RWMA 

partner reports beyond 1993 (fig. 14). More importantly, monitoring for only TP in dry-weather flows could lead to erroneous conclusions regarding changes or comparisons in TP and 

thus presumably DOP among subbasins if the DOP:TP ratio 

changes markedly for one or more subbasins through time. 

Evidence presented above indicates this ratio changed considerably in the mid-1980s, and for reasons that have never been 

fully understood. Given that no DOP data have been routinely 

collected for the watershed tributaries since the early 1990s, 

the DOP:TP ratios are unknown for the watershed tributaries 

after 1986, and thus after nearly two additional decades 

(1990–2007) of efforts to reduce phosphorus loads from the 

watersheds. 

 Ultimately, if the main concern with phosphorus in the 

tributaries is DOP rather than TP, the mean annual concentration of DOP in stormflows is at least five times greater than the 

mean annual concentration of DOP in dry weather flows (table 

6). Thus, the major portion of the DOP load from the tributaries to the water-supply reservoirs in all but the driest years 

likely occurs from storm- and not dry-weather flows, and the 

frequency and timing of those storms could have considerable 

influence on reservoir phytoplankton production. 

There have been other major limitations introduced by 

the reduction in monitoring storms in the mid-1990s. The 

decline in frequency of storm monitoring after about 1995 

(table 7) means tributary TP loads, as well as any other type of 

load estimates, to the reservoirs in relation to storm- and dryweather flows will be a challenge to estimate for any reservoir 

tributary. In turn, models designed to estimate phosphorus 

loads to either supply reservoir could have too few storm 

events since 1995 for calibration and validation purposes—for 

example, see Interstate Commission on the Potomac River 

Basin (2006). 
44 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 15. Ratio of annual median dissolved phosphorus concentration to annual median total 

phosphorus concentration in gaged tributaries of the (A) Liberty and (B) Loch Raven Reservoir 

watersheds, 1982–92 (modified from Baltimore City Department of Public Works, 1992).
The Water-Quality Monitoring Program 45

Table 7. Number of storm events with water-quality sampling, Loch Raven and Liberty Reservoir watersheds, 

1994–2008 (data courtesy of Baltimore City Department of Public Works, Baltimore, Maryland).

Reservoir/

watershed

Water year

1994 1995 1996 1997 1998 1999 2000

Loch Raven 5 0 0 0 4 4 0

Liberty 5 0 0 0 0 0 3

Reservoir/

watershed

Water year

2001 2002 2003 2004 2005 2006 2007 2008

Loch Raven 3 1 3 3 3 4 3 2

Liberty 2 0 0 1 4 1 4 3

To illustrate the potential importance of modeling to the 

ultimate goals of the Baltimore Reservoir Program, and the 

need for adequate data in order to estimate loads, one can 

examine the results from several chronological studies that 

at least in part aimed to estimate phosphorus loads for the 

Baltimore reservoirs (table 4). The most recent annual load 

estimates (Maryland Department of the Environment, 2003d; 

Interstate Commission on the Potomac River Basin, 2006) 

are 4 to 5 times greater than the earliest estimated loads. 

The most recent TP load estimates relied on more advanced 

models, but calibration of those models has been based on 

storm- and dry-weather flow data mostly collected before the 

latter part of the 1990s, as storm monitoring was discontinued 

in the mid-1990s, and has only partially been restored since 

the year 2000 (table 7). Furthermore, in the case of Prettyboy 

Reservoir watershed, all load estimates are truly estimates as 

no stormflow data have ever been obtained to at least partially 

validate estimated loads for the three major tributaries that 

supply this reservoir. Despite these limitations, accurate load 

estimates minimally are necessary to help establish suspendedsediment and phosphorus TMDLs for Liberty Reservoir (see 

Regulatory Concerns, this report).

In addition to the reduction in monitoring TP in stormflow, the cessation of monitoring DOP in any tributary flows 

has further limited the ability of the RTG to address RWMA 

concerns. Despite the long-term decision to rely primarily 

on TP as the measurement for phosphorus, the importance of 

bioavailable phosphorus, estimated by either DOP or TDP, to 

algal production in the reservoirs has been raised by the City 

DPW and others. Summary and other reports (Baltimore City 

Department of Public Works, 1992, 1996, 2001; Winfield and 

Sakai, 2003; Interstate Commission on the Potomac River 

Basin, 2006) have outlined concerns regarding the role of and 

possible need to resume measurements of bioavailable phosphorus (for example as DOP or TDP). Use of TP data alone 

could be misleading in relation to:

a) Identifying high-phosphorus-source subbasins within 

the watersheds, and within those subbasins, the landscape conditions and human activities that contribute 

the most bioavailable phosphorus (not just TP) to 

watershed tributaries, to better target management 

activities to reduce phosphorus;

b) Describing the states and trends in watershed conditions in relation to bioavailable phosphorus (not just 

TP) in the watershed tributaries, in order to better 

relate watershed tributary contributions of bioavailable 

phosphorus to in-lake bioavailable phosphorus concentrations and phytoplankton production (algal counts 

and chl-a concentrations), and 

c) Determining the levels and relative source contributions of not just tributary, but in-lake biotic (for 

example, algal decomposition) or abiotic (for example, 

bottom sediment release), contributions to bioavailable phosphorus (not just TP) in the reservoirs to better 

identify the in-lake phosphorus sources that possibly 

contribute to the occurrence of major algal blooms.

In addition, the above reports reveal a less than complete and 

possibly necessary understanding of nutrient cycling—for 

nitrogen, as well as phosphorus—in the reservoirs, and of the 

role that nutrient cycling processes in the reservoirs, as well 

as tributary loads, play in the timing, occurrence, intensity, 

duration, and type of algal blooms associated with eutrophic 

compared to mesotrophic conditions.
46 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Trophic State of Reservoirs

The Carlson Trophic State Index, or TSI (Carlson and 

Simpson, 1996), is a multimetric index that has been used by 

the RTG to assess eutrophication in the reservoirs. The TSI 

value of most concern for the RTG is that which marks the 

change during mid-to-late spring through early fall (approximately April through September) from moderately impaired 

(mesotrophic) to severely impaired (eutrophic) conditions 

(Baltimore Reservoir Technical Group, 2004). Threshold 

values for the Baltimore reservoirs that correspond to this transition have been determined by the RTG for shallow surfacewater concentrations of chl-a, DO, and TP, and for water 

transparency using Secchi depth (Winfield and Sakai, 2003). 

Using these TSI indicators, the Baltimore Reservoir Technical 

Group (2004) determined that each reservoir exhibits some 

degree of eutrophication during the mid-spring through early 

fall. The degree of impairment among the reservoirs differs, 

however, depending upon the TSI index used (table 8). These 

differences are examined in relation to the manner of data collection, aggregation, and analysis for each of the TSI indices.

Phytoplankton and Chlorophyll-a

The concentration of chl-a is an indicator of the 

abundance of phytoplankton algae, and appears to be a 

sensitive indicator of algal productivity. The TSI index 

threshold concentration used to distinguish eutrophic from 

mesotrophic conditions in the shallow surface layer for chl-a

is 10 μg/L. On the basis of this threshold concentration, the 

Baltimore Reservoir Technical Group (2004) considered 

Prettyboy Reservoir to have the highest frequency of eutrophic conditions (be the most impaired), followed by Loch 

Raven Reservoir, and then Liberty Reservoir (table 8). In 

addition, and subsequent to the publication of these data, the 

Baltimore Reservoir Technical Group (2004) also noted that 

mean monthly chl-a concentrations (and total algal counts) 

appeared to decline at most monitoring stations in all three 

reservoirs during the 1980s–90s (fig. 13), but increased during 

1999–2003, possibly due to drought and recovery conditions. 

Winfield and Sakai (2003) and the Interstate Commission on 

the Potomac River Basin (2006) also indicated that differences 

in chl-a (or algal counts) occur not only among the reservoirs, 

but within a reservoir, over time. They indicated that these differences reflect variations in the individual hydrodynamics, the 

magnitude, timing, and duration of peak algal growth periods, 

and the diversity of taxa among the reservoirs.

There are limitations in the manner the RTG has used 

chl-a as a TSI indicator of mesotrophic and eutrophic conditions. These limitations relate to differences in the frequency 

and location of sampling of chl-a among the reservoirs, and 

the manner in which the resultant data have been aggregated. 

Sampling for chl-a was only conducted monthly, and only 

in the lower and middle parts of Prettyboy Reservoir, but 

bimonthly and throughout each supply reservoir, during periods of stratification. It is not known whether these differences 

in sampling frequency and the extent of sampling for chl-a

among the reservoirs affected the frequency of occurrence in 

eutrophic conditions among the reservoirs on the basis of the 

results for the TSI chl-a index (table 8).

In relation to the depths used to define shallow- and 

deep-water conditions to aggregate chl-a data (table 8), the 

Interstate Commission on the Potomac River Basin (2006) 

noted that the actual epilimnion for Loch Raven and Prettyboy 

Reservoirs derived on the basis of reservoir temperature 

Table 8. Reservoir trophic conditions during mid to late spring through early fall, 1981–2000 (from Baltimore City Department of Public 

Works, 2001).

[μg/L, micrograms per liter; mg/L, milligrams per liter; ≥, greater than or equal to; ≤ , less than or equal to <, less than; >, higher frequency of impairment 

than]

Water-quality index, 

mesotrophic-eutrophic, 

or other quality threshold

Frequency (in percent) of all samples that 

indicate eutrophic conditions Relative order of reservoir 

impairment Period of data2

Liberty Loch Raven Prettyboy

Shallow-water1 chlorophyll-a, 

≥ 10 μg/L 9.9 19.8 26.2 Prettyboy > Loch Raven > Liberty 1985–2000

Shallow-water total phosphorus, 

≥ 26 μg/L 15.7 57.2 55.5 Loch Raven > Prettyboy > Liberty 1982–99

Secchi depth, ≤ 6.10 feet 5.8 7.9 7.3 Loch Raven > Prettyboy > Liberty 1983/84–2000

Shallow-water dissolved 

oxygen, < 5 mg/L 10.9 15.7 8.2 Loch Raven > Liberty > Prettyboy 1981/82–2000

Deep-water1 dissolved 

oxygen, < 1 mg/L 12.0 48.1 24.6 Loch Raven > Prettyboy > Liberty 1982–2000

1

 Shallow water is up to 30 feet deep; deep water (dissolved oxygen) exceeds 30-foot depth.

2

 Secchi-depth and dissolved-oxygen data collection for Prettyboy Reservoir began 1 year later than data collection at other reservoirs. 
The Water-Quality Monitoring Program 47

profile data and simulations of mixing in the reservoirs is 

approximately 15–20 ft for a number of years of record, not 

the 30 ft or less used by the City to define the shallow surficial layer of the reservoirs (for example, Baltimore City 

Department of Public Works, 2001; Winfield and Sakai, 2003). 

Thus, only historical data from the near surface, 10-ft depths, 

and on occasion, the 20-ft depths, likely reflect the true epilimnetic layer in each reservoir for a number of years of record. 

The inclusion of the 20-ft and 30-ft measurements in the 

shallow-water layer likely biases the chl-a trophic summary 

data in relation to the true epilimnetic and hypolimnetic layers 

(table 8). The shallow-water layer chl-a data systematically 

include measurements made at 20-ft and 30-ft depths, which 

exceed the depth of the modeled epilimnion.

Aggregation of TSI chl-a data over each entire reservoir 

and from all years of data collection could mask noteworthy 

differences in the degree of eutrophic impairment in the 

actual epilimnion within, as well as among, the reservoirs. For 

example, the concentrations of chl-a (and algal counts) have 

been shown to be greatest and extend over greatest depths in 

the upper part of Liberty Reservoir, where tributaries enter 

the reservoir (Winfield and Sakai, 2003). Thus, the upper part 

of this reservoir could experience eutrophic conditions much 

more frequently, and the lower part of this reservoir much less 

frequently, than the aggregated TSI chl-a data for this reservoir imply (table 8). 

In relation to analyses conducted, no analyses of the 

TSI chl-a index data were encountered in RTG, City, or other 

reports on spatial differences in the frequency of occurrence 

of mesotrophic or eutrophic conditions within a reservoir. Nor 

were any analyses encountered on annual trends or seasonal 

variations in the frequency of occurrence of mesotrophic or 

eutrophic conditions, within and among the reservoirs. Thus, it 

is not known whether there has been a decline in the frequency 

of eutrophic conditions throughout or in parts of any reservoir 

through the 1980s–90s despite an apparent decline in chl-a

and algal counts during this period (fig.13).

It should be noted that the aforementioned limitations 

described for the manner in which the TSI chl-a index data 

were collected, aggregated, and (or) analyzed also apply to 

other reservoir TSI indices. The parameters used in other TSI 

indices (see Eutrophication—Trophic State of Reservoirs: 

Phosphorus, Dissolved Oxygen, and Water Transparency, 

this report) also were only collected on a monthly basis, and 

only in the lower and middle parts, of Prettyboy Reservoir. 

The use of the fixed 30-ft or less depth layer to distinguish 

between shallow and deep reservoir waters for the TSI chl-a

index also was used to partition monitoring data composed of 

incremental depth measurements for the TSI-TP and TSI-DO 

indices. In addition, aggregation of data for each of the three 

other TSI indices (using TP, DO, and Water Transparency 

data) was done over an entire reservoir (table 8), which could 

mask important differences in the frequency of eutrophic conditions in the epilimnion or hypolimnion within a reservoir on 

the basis of each of these other indices.

Phosphorus

In theory, phosphorus could serve as a sensitive indicator 

of eutrophic conditions. Reports by the RWMA partners and 

others have emphasized that it could be the limiting nutrient to 

phytoplankton productivity (see Eutrophication—Nutrients: 

Phosphorus Transport and Reservoir Recycling, this 

report). 

In relation to the Carlson TSI, a TP concentration of 26 

μg/L marks the threshold between eutrophic and mesotrophic 

conditions for the Baltimore reservoirs (table 8). Relative 

to this threshold, the Baltimore Reservoir Technical Group 

(2004) found that Loch Raven Reservoir, followed closely 

by Prettyboy Reservoir, both appear markedly more impaired 

than Liberty Reservoir. Relative to this finding and assuming 

the trend analyses for TP corrected for possible laboratory 

and data management errors is valid, concentrations of total 

TP have been shown to decline at most tributary and reservoir 

stations during the 1980s–90s, but most notably in Liberty 

Reservoir and watershed (see Eutrophication—Nutrients: 

Phosphorus Transport and Reservoir Recycling, this report

and KCI Technologies, Inc., 2004). 

It also was noted by the Baltimore Reservoir Technical 

Group (2004), and later substantiated by the Interstate 

Commission on the Potomac River Basin (2006), that estimated tributary TP yields are greater per acre to Liberty 

Reservoir than to Loch Raven Reservoir. To explain how 

greater loads could result in less impairment, the Baltimore 

Reservoir Technical Group (2004) indicated Liberty Reservoir 

has about twice the volume of the other reservoirs, but only 

about half the watershed area (see table 1). This implies that 

Liberty Reservoir provides a greater potential for dilution of 

tributary inputs, and because of its longitudinal shape, for the 

settling of any solids (for example, sediment or algal residues 

associated with TP) than either of the other two reservoirs. 

Despite the implications of the TP trend and spatial 

analyses described above, no analyses of the TSI-TP index 

data were encountered in RTG, City, or other reports on annual 

trends or seasonal variations in the frequency of eutrophic 

or mesotrophic conditions within a reservoir. Nor were any 

analysis of the TSI-TP data encountered on whether spatial 

differences occur in the frequency of eutrophic or mesotrophic 

conditions within a reservoir.

Dissolved Oxygen

Data for DO concentrations, routinely collected as part 

of the monitoring program, are used in conjunction with the 

following adopted standards for DO to develop a TSI-DO 

index to assess reservoir biotic health (Baltimore Reservoir 

Technical Group, 2004):

a) Shallow surface-layer water maintains a DO concentration of at least 5.0 mg/L, a State water-quality 

standard considered adequate to support fish life; and

b) Deep-water layer maintains a DO concentration of at 

least 1.0 mg/L, a RTG water-quality standard, consid-
48 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

ered adequate and reflective of mesotrophic (rather 

than eutrophic) lake conditions, although this level is 

generally not supportive of normal aquatic life.

On the basis of the TDI-DO index, shallow surface 

waters for Loch Raven Reservoir appear to be the most 

impaired, shallow surface waters in Liberty Reservoir are at an 

intermediate level of impairment, and for Prettyboy Reservoir, 

they are the least impaired (table 8). Deep waters, however, 

indicate a high degree of impairment compared to shallow 

waters for Loch Raven and Liberty Reservoirs, which alters 

the relative order of impairment—Loch Raven Reservoir 

being the most impaired, Prettyboy intermediate, and Liberty 

Reservoir the least impaired.

Whereas the use of DO concentrations and TSI-DO index 

threshold in the manner described above allows for simple 

comparisons among reservoirs or between shallow- and deepwater layers within a reservoir, the results (table 8) do not fully 

illustrate differences in DO concentrations and impairments 

within a reservoir. First and foremost, all DO measurements 

in the reservoirs are exclusively made during daylight hours. 

Measured shallow-water DO concentrations likely reflect phytoplankton production, and could be positively biased because 

of photosynthetic activity. Hence, the frequency of eutrophic 

conditions derived from the TSI-DO index could be underestimated in the shallow-water layer of all three reservoirs.

From a broad perspective, the analyses of temporal 

variations (mean monthly) and spatial differences (by location 

and within location by depth) of actual DO concentrations 

within each reservoir indicate that the degree of impairment 

due to low-DO (eutrophic) conditions is considerably more 

spatially complex than the generalized analysis of the TSI-DO 

index data indicates (table 8). All three reservoirs appear to 

exhibit DO impairments on a seasonal basis for most years 

of record. For example, Winfield and Sakai (2003) describe a 

temporal pattern in DO concentrations for Liberty Reservoir, 

which is similar to the patterns observed in Loch Raven and 

Liberty Reservoirs (Interstate Commission on the Potomac 

River Basin, 2006, Appendix C). From January through 

April, Liberty Reservoir waters have fairly homogeneous and 

elevated DO concentrations (fig. 16). As thermal stratification 

begins in the spring (roughly May), the DO concentrations, 

particularly in the deep-water layer, begin to decline. They 

continue to decline throughout the summer, presumably 

because of an increase in biological oxygen demand as a 

result of phytoplankton residue decomposition, and possibly 

an increase in water temperatures at depth. The decline in DO 

is most pronounced in the deepest waters, but occasionally 

extends into shallow surface waters, which Winfield and Sakai 

(2003) considered included DO measurements at the 20–30-ft 

depths. Minimum DO concentrations frequently occurred in 

the late summer to mid fall (generally August to November). 

Also during this period, episodic cooling of reservoir waters 

resulting from variably autumnal weather can introduce 

episodic thermal mixing, which eventually evolves to persistent cooler temperatures and turnover to re-establish elevated 

and relatively uniform DO concentrations throughout the 

reservoir. (Although evidence of this episodic cooling before 

turnover commences has not been fully documented in Liberty 

Reservoir, it clearly is evident in Loch Raven and Prettyboy 

Reservoirs; see Interstate Commission on the Potomac River 

Basin, 2006).

In the case of Liberty Reservoir, the aforementioned 

seasonal pattern in DO concentrations follows a longitudinal 

gradient in the reservoir. The largest range of variation in the 

seasonal cycle of mean monthly DO concentrations appears to 

occur in the upper part of the reservoir, and the smallest range 

in variation in the lower part of the reservoir (Winfield and 

Sakai, 2003). Given the above, and that the range in annual 

variation chiefly relates to the extent of DO depletion, which 

reaches its maximum in the late summer to early fall, the frequency of severe DO biotic impairments (eutrophic conditions 

indicated by a TSI-DO index) in both shallow and deep layers 

would be expected to occur with the greatest frequency in the 

upper part of the reservoir, and with the least frequency in the 

lower part of the reservoir. This longitudinal pattern in severe 

DO impairments is not evident if TSI-DO index data are 

aggregated for the entire surface- or deep-water layers across 

the entire reservoir (table 8). 

Oxygen impairment differs markedly between Prettyboy 

Reservoir or Loch Raven Reservoir and Liberty Reservoir in 

spatial extent, frequency of occurrence, and, to some extent, 

timing. A study by the Interstate Commission on the Potomac 

River Basin (2006) showed spatial differences in the degree of 

DO impairment in Prettyboy Reservoir occur primarily in late 

summer and early fall, with impairments most often occurring 

only in the deep-water layer in the lower and middle parts of 

the reservoir Prettyboy Reservoir (fig. 17). (Given no DO data 

have ever been collected in the upper part of this reservoir, it 

cannot be determined if these DO impairments occur in deep 

water throughout the reservoir.) In the case of Loch Raven 

Reservoir, annual variations in monthly mean DO concentrations for the period of record (Maryland Department of the 

Environment, 2006, Appendix A) indicate impairments also 

occur in the late summer to early fall, and routinely (almost 

every year) in the deep waters in the lower, mid, and upper 

parts of the reservoir, as well as in the shallow waters in most 

years, but slightly more often in the lower than middle or 

upper parts of the reservoir.

Relative to their evaluation of the monitoring data for 

DO concentrations for Prettyboy and Loch Raven Reservoirs, 

the Interstate Commission on the Potomac River Basin (2006) 

also noted that the use of a fixed-depth definition of 20–30 ft 

for shallow surface-layer waters (for example, table 8) can 

result in an inaccurate representation of DO concentrations 

in the true epilimnion, particularly in the fall (September 

through November). They found that water temperatures 

are an extremely sensitive indicator of stratification in these 

reservoirs, and modeled temperature profiles indicate that the 

well-mixed surface layer (epilimnion) is often less than 20 ft 

thick, and not up to 30 ft in depth. They also noted that the 

DO concentration for the surficial layer is lower if the greater 

depth interval is used to represent the epilimnion. This bias 
The Water-Quality Monitoring Program 49

Figure 16. Mean monthly dissolved-oxygen depth-profile concentrations for (A) upper and (B) lower Liberty 

Reservoir, 1994–2001 (modified from Winfield and Sakai, 2003). 
50 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 17. Monthly mean dissolved-oxygen concentrations in (A) epilimnetic waters and 

(B) hypolimnetic waters in lower Prettyboy Reservoir, 1992–2004 (modified from Interstate 

Commission on the Potomac River Basin, 2006). [Epilimnetic and hypolimnetic waters are 

defined by measured and modeled temperature gradients and simulated reservoir stratification 

and turnover.]
The Water-Quality Monitoring Program 51

is particularly apparent during the fall because of episodic 

autumnal cooling. The cooling appears to result in temporary 

stabilization of the thermocline, which results in the entrainment of low-DO (metalimnetic) water into waters 20–30 ft 

below the lake surface, and thus the surface layer as traditionally defined by the City. Furthermore, in the case of Prettyboy 

Reservoir, the Interstate Commission on the Potomac River 

Basin (2006) indicated that similar problems appeared during 

the severe drought of 2002–03 (fig. 17) as a result of water 

releases from the reservoir. 

As part of the effort to model DO concentrations in these 

two reservoirs, the Interstate Commission on the Potomac 

River Basin (2006) showed that the annual variation in DO 

concentrations, and the seasonal sags in DO, could be conditions indicative of internal reservoir hydrodynamics and 

therefore unlikely to change. This conclusion has important 

implications that go beyond the use of DO concentration data 

to determine trophic state to assess reservoir eutrophication 

and ecological health. 

If seasonal DO sags are to be the norm, with deep-water 

DO concentrations falling below 1.0 mg/L, then addressing 

several questions raised earlier in this report takes on added 

significance: specifically, whether deep-water oxygen depletion results in anoxic conditions and iron, manganese, and 

phosphorus releases from bed sediments, and whether that 

released phosphorus routinely becomes available for future 

phytoplankton production. If these processes do occur as a 

result of natural hydrodynamic conditions, it could take a 

considerable reduction in TP tributary loads to reduce phytoplankton production as reservoir sediment contains an appreciable amount of bound phosphorus (see Eutrophication—

Nutrients: Phosphorus Transport and Reservoir Recycling, 

and Sedimentation—Reservoir Storage Capacity, this 

report). 

The TSI-DO index data to characterize the frequency 

of eutrophic and mesotrophic conditions (table 8) are likely 

biased—positively by only daytime DO measurements, and 

negatively by the manner in which DO data are aggregated 

and analyzed. The analysis of DO concentration data reveals 

temporal trends, seasonal variations, and spatial differences in 

DO, which likely influence the TSI-DO frequency of eutrophic 

conditions within each reservoir and among the reservoirs. 

None of the latter are apparent, however, given the manner in 

which the TSI-DO index data have been analyzed.

Water Transparency

Water transparency (as determined by Secchi disc depth 

to extinction) is used as an independent TSI indicator of 

ecological health in the Baltimore reservoirs (table 8). The 

Secchi-depth value corresponding to the Carlson TSI boundary between mesotrophic and eutrophic conditions is 6.1 ft. 

Application of this threshold to reservoir waters through late 

spring, summer, and early fall from the 1980s through the 

1990s revealed each of the three reservoirs seldom exhibited a 

reduction in transparency that would correspond to eutrophic 

conditions (table 8). In relation to other TSI indices, the 

Baltimore Reservoir Technical Group (2004) noted that 

transparency is the least sensitive indicator of TSI impairment 

during the spring-summer growing season (table 8).

Among the three reservoirs, the Baltimore Reservoir 

Technical Group (2004) and the Baltimore City Department of 

Public Works (2000) noted that water transparency appeared 

to decline in Prettyboy Reservoir during the 1980s through 

1990s, but that there were no apparent trends in transparency 

in either of the other two reservoirs for the same data period. 

They postulated that the apparent decline in transparency in 

Prettyboy Reservoir could be the result of increased suspended 

sediment. The lack of stormflow monitoring data for tributaries to Prettyboy Reservoir, however, makes it difficult to test 

this hypothesis. They also did not address why this reservoir 

would not have a positive trend in transparency, or why no 

positive trends were observed in transparency in either supply 

reservoir, given that all three reservoirs appear to have had 

declining trends in algal counts and (or) chl-a concentrations 

throughout the 1990s (see Eutrophication, this report).

Seasonal patterns in transparency have been observed in 

all three reservoirs. The Interstate Commission on the Potomac 

River Basin (2006) described seasonal transparency patterns 

in Loch Raven and Prettyboy Reservoirs. Transparency 

generally was highest in the summer (typically approaching 

about 18 ft in depth in June and July), and then declined (by 

about two thirds) with lake turnover to its lowest levels in the 

winter or early spring (typically about 8 ft in depth or less 

from November through March) in both reservoirs. A similar 

annual pattern was observed in Liberty Reservoir (Winfield 

and Sakai, 2003), with the most pronounced seasonal differences in transparency occurring in the upper part of the 

reservoir. This result is consistent with seasonal and longitudinal patterns for chl-a concentrations (and algal counts), and 

for turbidity (suspended sediment), and likely reflects the fact 

that the major tributaries all discharge into the upper part of 

this reservoir.

A significant finding by the Interstate Commission on the 

Potomac River Basin (2006) in the transparency results for 

all three reservoirs is that light penetration likely only limits 

phytoplankton production throughout the epilimnetic layer 

(typically 20 ft or less) in the early spring. This result would 

explain why the TSI transparency index is not a very sensitive 

indicator of eutrophic conditions associated with major algal 

blooms in this layer compared to other TSI indices.

It also should be noted that the Interstate Commission 

on the Potomac River Basin (2006) studies of water transparency in Loch Raven and Prettyboy Reservoirs indicate there 

is an inconsistency between trends in transparency and trends 

in other water-quality indicators that should strongly correlate 

with transparency in the reservoirs. Transparency ought to be 

determined by turbidity caused by algal growth and reservoir 

turnover in combination with sediment transport by tributary 

watersheds. Thus, measurements such as chl-a, color, and 

turbidity should each be directly correlated with, and collectively explain most of, the variability in transparency. The 
52 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Interstate Commission on the Potomac River Basin (2006) 

essentially tested this hypothesis. Using an epilimnetic layer 

of 20 ft and mean monthly data for the above parameters from 

1992–2004, they found that color or chl-a (algal source) and 

then turbidity (from non-algal sources, for example, suspended 

sediment) most likely account for reductions in transparency 

in Loch Raven Reservoir, and that turbidity, and then chl-a or 

color, most likely account for reductions in transparency in 

Prettyboy Reservoir. They also found that measurements of 

color, chl-a, and turbidity each accounted for no more than 

about 45 percent, and, collectively, accounted for only about 

54 percent, of the total variability in transparency, in Loch 

Raven and Prettyboy Reservoirs. Thus, about half of the variability in water transparency in these two reservoirs cannot be 

explained. 

One likely source of the unexplained variability in transparency could be differences in the measurement methods. 

Transparency data reflect a single depth-integrated monthly or 

bimonthly measure of the depth at which the Secchi disk disappears from view to an observer at each reservoir monitoring 

site. It is in effect a single continuous depth-integrated measurement, and, to a degree, a subjective (operator-sensitive) 

measurement. Measurements of chl-a, color, and turbidity are 

determined at a similar frequency, but each is an average value 

derived from discrete samples and instrumental measurements 

obtained at possibly three (near-surface, 10-ft, and 20-ft depth) 

discrete depths in the epilimnion at each reservoir monitoring 

site. 

Because half of the variation in transparency in Loch 

Raven and Prettyboy Reservoirs cannot be explained by 

individual or collective measurements of turbidity, chl-a, 

and color, further investigation of measurement methods 

for all four parameters could be warranted. Studies of lakes 

or impoundments in North Carolina, Florida, and New 

Hampshire have found relatively high (individual or multivariate) correlation coefficients (ranging from approximately 

50–90 percent) between transparency and one or more of these 

parameters (Caffrey and others, 2007; Schloss, 2002; Weiss 

and Kuenzler, 1976). For example, it could be that transparency measurements are not consistently obtained to visible 

extinction, or are obtained in a manner that introduces considerable variations in this measurement.

Sedimentation

The occurrence of elevated concentrations of suspended 

sediment in Baltimore Reservoir watershed tributaries and 

their contribution to sediment loads to the reservoirs are 

concerns for the RWMA partners (fig. 2). Elevated concentrations of suspended sediment in the tributaries reflect excessive 

losses of soil due not only to inadequately managed agricultural and urban lands, but also to the erosion of streambeds 

and banks mainly as a result of inadequately managed stormwater flows (Appendix A). The resultant damages to stream 

habitat and ecosystem health are considered impairments to 

designated recreational use of the tributaries, such as fishing 

(see Regulatory Concerns, this report). 

The subsequent transport of tributary sediment to the reservoirs can lead to the loss of storage capacity—a designated 

use for the supply reservoirs. Sediment transported into each 

reservoir also can increase in-lake turbidity, which affects the 

cost of water treatment, and thus impairs the designated use of 

supply reservoirs for drinking-water supplies. Sediment deposited in the supply reservoirs also is a major potential source 

of iron and manganese (Ortt and others, 2000), metals, that 

when mobilized (see Sedimentation—Sediment Diagenesis 

and Mobilization of Metals and Phosphorus, this report), 

can increase the costs to treat water, as well as raise color and 

taste issues with treated water, which are considered impairments in the quality of reservoir water used for supplies 

(see Regulatory Concerns, this report). Recently deposited 

sediment, particularly during reservoir recovery following 

droughts, combined with the submergence of vegetation 

established on reservoir beds during droughts, also provides 

a readily available source of mercury for methylation and 

biological uptake. The mobilization, methylation, and uptake 

of this mercury could increase mercury concentrations in 

higher trophic order game fish. Although elevated concentrations of mercury in game fish is already a known impairment 

of designated recreational uses for all three reservoirs (see 

Regulatory Concerns, this report), this pathway of biological 

uptake has not been considered nor adequately investigated by 

the RTG. Sediment deposited in the reservoirs also contains 

elevated concentrations of phosphorus (Ortt and others, 2000), 

which if mobilized and available to phytoplankton, can help 

promote eutrophic conditions and excessive algal blooms in 

the reservoirs, which can cause additional impairments in designated recreational and water-supply uses for the reservoirs 

(see Eutrophication, this report). 

To address most sedimentation-related concerns minimally requires quantifying sediment transport, identifying 

the main sources of sediment, and reducing sediment from 

these major sources. Thus, monitoring to describe sediment 

transport in the reservoir watersheds and to assess reservoir 

storage capacity is of critical importance to the City, RTG, and 

RWMA partners.

Sediment Transport

Development of the long-term watershed tributary 

monitoring network for suspended-sediment transport followed from the initial work of Amatayakul and others (1978), 

and Amatayakul, Defries, and others (1978), who provided 

some of the first estimates of total average annual loads for 

suspended sediment to Loch Raven Reservoir (table 4). In so 

doing, they noted a paucity of data for storms. They also cited 

a host of assumptions, other data limitations, and the need to 

rely on empirical data and methods from studies conducted 

elsewhere, to estimate loads. To address the above, they 

recommended a long-term monitoring program be designed 

and implemented. To accurately estimate loads and trends in 

loads, this program was to provide year-round collection of 

suspended-sediment samples for storm- and base flows on the 

major tributaries supplying the reservoir.
The Water-Quality Monitoring Program 53

The recommendations of Amatayakul and others (1978) 

and Amatayakul, Defries, and others (1978) helped guide 

development of the long-term reservoir-watershed tributary 

monitoring network established in the early 1980s (fig. 3, and 

Appendix B). The resulting tributary monitoring network 

includes six gaged watershed water-quality monitoring 

stations for storm- and dry-weather flows, and nine additional 

dry-weather-flow tributary stations. The monitoring network 

also is used for sampling at selected point-discharge sites, 

including WWTPs, and at containment ponds if discharging, 

during routinely scheduled visits (Appendix B). In relation to 

the major subbasins that drain into each reservoir (fig. 3), the 

network includes water-quality monitoring for storm- and dryweather flows at three large subbasins in each supply reservoir. 

Additional dry-weather-flow monitoring stations are used for 

selected small subbasins in the two supply reservoirs, and for 

the three major subbasins that drain into Prettyboy Reservoir. 

No monitoring occurs in small subbasins that are in close 

proximity and independently drain into each reservoir. The 

quality of water in most of these small subbasins occasionally 

or periodically has been monitored as part of short-term or 

synoptic studies conducted at different times by the State, or 

Baltimore or Carroll Counties (Appendix A). 

The long-term monitoring of suspended sediment in the 

watershed tributaries has been useful in providing data and 

information on suspended-sediment concentrations, loads, 

trends, and potential source areas of sediment (among major 

subbasins). Tributary monitoring from the early 1980s to mid1990s yielded data to assess annual variations in suspendedsediment concentrations and loads at each of the three major 

subbasins in each supply-reservoir watershed (figs. 18a and 

b). Summary reports indicate that the annual mean concentrations and total annual loads of suspended sediment markedly 

vary for each subbasin (Baltimore City Department of Public 

Works, 1992, 1996). This variability was attributed to climatic 

variation—concentrations and loads being notably higher in 

wet years compared to dry years (figs. 18a and b, for example, 

1984 and 1986, respectively), and within a given year, to flow 

regime—notably more sediment being carried by stormflows 

as opposed to dry-weather flows, with the latter accounting for 

only 10 percent or less of the total annual sediment load 

(fig. 18b). 

Suspended-sediment loads derived for the three major 

subbasins in each supply reservoir watershed during the 1980s 

also enabled the first spatial comparisons of loads. On the 

basis of areal-weighted loads (yields), subbasins within each 

supply reservoir were ranked to help identify major sedimentsource areas and initially guide management to reduce sediment transport [Baltimore City Department of Public Works, 

1996 (table 10.1), 2000, 2001]. For example, for the Loch 

Raven Reservoir watershed, it was noted that yields at the 

Gunpowder Falls at Glencoe station indicate that Prettyboy 

Reservoir captures most of the suspended sediment upstream 

from this station, and thus reduces the sediment load delivered 

to Loch Raven Reservoir. Therefore, management activities 

to reduce sediment loads to Loch Raven Reservoir could be 

directed towards the main sources of sediment—the Beaver 

Dam and Western Run subbasins, and the lower Gunpowder 

River Basin between Prettyboy and Loch Raven Reservoirs 

(Maryland Department of the Environment, 2003d; Reservoir 

Watershed Protection Committee, 2000).

Monitoring data have been used to assess apparent trends 

in suspended-sediment concentrations and loads for the gaged 

tributaries. Suspended-sediment concentrations, and notably 

loads, appeared to decline after 1987 (figs. 18a and b). A visual 

comparison of suspended-sediment concentration-discharge 

curves constructed from monitoring data from 1983–85 and 

from 1986–90 for each of six major subbasins indicated less 

sediment was being transported throughout most of the range 

in flows after 1985 (Baltimore City Department of Public 

Works, 1992). No statistical tests accompanied the visual 

comparisons, however, to determine if the curves were significantly different. 

The apparent decrease in sediment concentrations and 

loads, and downward shift in sediment rating curves, for both 

water-supply reservoirs were considered possible outcomes 

of a decade of best management practices (BMPs) that in 

part were designed and implemented to reduce erosion and 

improve agricultural and urban sediment control (Baltimore 

City Department of Public Works, 1992, 1996, 2000). It also 

was noted, however, that they could possibly reflect a bias due 

to the manner in which suspended-sediment data for storms 

were collected (Baltimore City Department of Public Works, 

1996). No subsequent reports were encountered that indicated 

the nature of this change in methods, however, nor whether or 

not a change in monitoring methods was the cause or contributed to the decline in suspended-sediment concentrations, 

yields, or rating curves. Also, the alternative to tracking sediment-load reductions by tracking BMP installations and determining their efficiency (in the absence of relevant pre- and 

post-stream monitoring) proved difficult, and this accounting 

approach to sediment-load reductions resulting from BMPs 

was abandoned (Baltimore City Department of Public Works, 

1996). Therefore, it was not possible to independently determine if the aforementioned decline in the concentrations, 

loads, and rating curves for suspended sediment truly resulted 

from the implementation of BMPs. 

As noted earlier in this report, from about 1995 to 2004, 

monitoring of storm events was markedly reduced (table 7). 

The decline in stormflow data leaves a discontinuity in longterm records of total annual suspended-sediment loads from 

the three major subbasins in each supply reservoir watershed. 

Thus, advanced models to estimate suspended-sediment loads 

have few events for calibration or validation during most of 

this period—none in a number of years—despite almost an 

additional decade of BMP implementation to reduce sediment 

loads. For example, direct and local assessment of BMPs to 

demonstrate their effectiveness in reducing sediment transport, such as the recent study by Stewart and others (2005) 

on stream buffer restoration, strengthen the argument for the 

continued widespread monitoring and modeling of suspendedsediment concentrations to estimate loads. 
54 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 18. (A) Annual mean concentrations of suspended sediment, (B) total annual suspended-sediment loads and 

(C) proportion of total annual loads transported by dry-weather flows for six gaged tributaries in subbasins in the Loch 

Raven and Liberty Reservoir watersheds, 1983–90 (modified from Reservoir Watershed Protection Subcommittee, 1992, 

and Baltimore City Department of Public Works, 1996).
The Water-Quality Monitoring Program 55

A reasonably accurate and complete sediment record on 

major reservoir tributaries to properly calibrate and validate 

load-estimation models is vital to the RWMA partners. 

Modeled total annual suspended-sediment loads to Loch 

Raven Reservoir based on calibration periods of 1988–91 

(Maryland Department of the Environment, 2003d) and 

1992–97 (Interstate Commission on the Potomac River Basin, 

2006) are approximately a thousand times greater than the 

initial estimates based on 1975–78 data from Amatayakul and 

others (1978) and Amatayakul, Defries, and others (1978) 

(table 4). In part, the differences in the estimated loads could 

reflect differences in the periods of record used for comparisons. Improvements in hydrologic and suspended-sediment 

records, combined with improvements in modeling, however, 

also likely resulted in more accurate load estimates that 

were substantially higher than earlier and less accurate load 

estimates.

Although storm sampling has been limited since 1995 

(table 7), dry-weather monitoring of suspended-sediment 

concentrations and flows, which also began in 1983, generally 

has continued almost uninterrupted at all stations in the three 

reservoir watersheds. Because dry-weather-flow data represent 

just part of the overall flow and sediment-transport regime, 

their utility is limited (Baltimore City Department of Public 

Works, 1992, 1996, 2000, 2001). For the three major subbasins in each supply reservoir watershed, the dry-weather 

flow data have enabled the determination of the proportion of 

the total annual sediment load actually transported by dryweather flows (fig. 18b). These data also were used to derive 

suspended-sediment concentration-discharge curves for the six 

major subbasins, which were described above and indicated a 

reduction in sediment loads after 1986. 

Suspended-sediment data from dry-weather flows also 

have been used to compare annual yields from subbasins in all 

three reservoir watersheds to assess apparent seasonal variations or annual trends among the subbasins, and whether these 

apparent variations or trends relate to trends in reservoir water 

quality (Baltimore City Department of Public Works, 1992, 

1996, 2000, 2001). Inherent in the use of dry-weather-flow 

suspended-sediment data for the above purposes, however, is 

the assumption that they have and remain highly, positively, 

and similarly correlated with the corresponding yields, seasonal variations, and trends in suspended sediment associated 

with storm- and dry-weather flows at each dry-weather-flow 

monitoring station. No analyses were encountered in this 

retrospective review that validate these assumptions. The historical and continued use of dry-weather-flow suspended-sediment data for the above purposes requires that such correlations be demonstrated. Historically, it is already apparent that 

there has been at least one indication that the proportion of the 

total sediment load carried by dry-weather flows has changed 

(fig. 18c). If this change can be statistically verified, and it 

is due to BMPs rather than sample-collection methods, then 

additional changes in the proportion of suspended sediment 

carried by dry-weather flows could be expected. Such a finding also would preclude the use of dry-weather flows for the 

above purposes. 

Accurate estimates of seasonal variations in suspendedsediment concentrations, and computation and comparisons 

of annual trends in loads or yields, generally require the 

measurement of suspended-sediment concentrations during 

both storm- and dry-weather flows at a majority of, if not all, 

reservoir watershed subbasins. For example, Gellis and others 

(2005) indicated that comparisons of loads and yields among 

Chesapeake Bay watershed tributaries generally required each 

tributary have suspended-sediment records for at least 3 consecutive years that included approximately 10 storms per year. 

Reservoir Storage Capacity

Summary interim and final reports from the City 

Department of Public Works (Baltimore City Department 

of Public Works, 1996, 2000, and 2001) and the Baltimore 

Reservoir Technical Group (2004) indicate that sedimentation 

in the reservoirs is a long-term and continuing concern. Recent 

bathymetric surveys (1998–2000) indicate all three reservoirs 

have lost some storage capacity since their initial construction—from about 3 percent to 11 percent depending on the 

reservoir (table 1). In at least the case of the Loch Raven 

Reservoir, sediment deposited by the year 2000 likely had 

filled available storage in the lower parts of the watershed 

tributaries and certain upland parts of the upper reservoir (Ortt 

and others, 2000). 

One main implication and concern is that future sediment 

transport and deposition could occur further into the reservoir, 

and accelerate the loss in reservoir capacity. Therefore, the 

RTG plans to monitor the loss in the storage capacity of Loch 

Raven Reservoir and the other two reservoirs through future 

surveys conducted every 10–15 years (Baltimore Reservoir 

Technical Group, 2004). As part of their findings, and in 

regard to these future surveys, Ortt and others (2000) indicated 

that their surveys were hampered by submerged aquatic 

vegetation because they were conducted during the summer 

months. They also noted that they were unable to locate or 

utilize historical bathymetric survey data from several previous surveys because of the inadequate manner in which survey 

data were archived, and survey methods were documented. 

Another implication and concern regarding sedimentation 

expressed by the Baltimore Reservoir Technical Group (2004) 

is that the dispersion of sediment further into the reservoir 

could increase the potential mobilization of metals including 

iron, manganese, and mercury, as well as nutrients such as 

phosphorus, which all occur in reservoir sediment (Ortt and 

others, 2000). On the basis of this review, the decreased storage is almost certain, but the possible increase in metal and 

phosphorus availability requires the RTG to address the larger 

question of the extent to which metal and phosphorus mobilization from sediment occurs in the reservoirs in general. 
56 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Sediment Diagenesis and Mobilization of Metals and Phosphorus

How available are the metals and phosphorus associated 

with sediment transported and deposited in the reservoirs? 

The answer is not clear. Ortt and others (2000) established that 

reservoir sediments contain elevated concentrations of metals 

such as iron and manganese and elevated concentrations of 

phosphorus, which appears mainly bound to iron in these 

sediments. 

Except for manganese and iron in reservoir intake 

waters, and possibly mercury in game fish, summary and 

other reports (Baltimore City Department of Public Works, 

1996, 2001; Maryland Department of the Environment, 2003 

a,b,c; Baltimore Reservoir Technical Group, 2004) indicate 

that heavy metals are not a concern in reservoir waters (see 

Regulatory Concerns, this report). Elevated concentrations 

of iron and manganese in reservoir intake waters can lead to 

nuisance problems in the treatment of water, and odor, taste, 

and appearance issues in finished water. Their origin and 

pattern of occurrence as elevated concentrations in reservoir 

waters have been discussed (see Overview of Water-Quality 

Concerns, this report). Their primary source appears to be the 

release of iron and manganese as a result of sediment diagenesis under anoxic conditions. Anoxia occurs with deep-water 

DO depletion caused at least in part by the decomposition of 

algal residues following major blooms and die-offs (Winfield 

and Sakai, 2003). Thus, reductions in impairments to drinking 

water caused by iron and manganese largely will be controlled by the degree to which eutrophic conditions that lead 

to excessive algal blooms can be reduced. Reducing major 

algal blooms will help reduce deep-water DO depletion during 

bloom decomposition, and thus reduce the anoxic conditions 

that lead to the release of these metals from reservoir 

sediments.

Elevated concentrations of mercury have been found 

in upper-trophic-level game fish in all three reservoirs, and 

notably in largemouth bass (Micropterus salmoides) tissues. 

Bass fish-tissue concentrations in the reservoirs range from 

minimums between approximately 50–100 μg/kg (micrograms 

per kilogram) to maximums between approximately 400–800 

μg/kg; the geometric mean concentrations for fish tissues in 

the three reservoirs ranges from approximately 260–310 μg/

kg (Maryland Department of the Environment, 2002 a,b,c; 

2004 b,c). Mercury concentrations in game fish tissue exceed 

the Maryland State (235 μg/kg) and Federal (300 μg/kg) 

CWA standards. Combined with an upward revision in risk 

assessment for mercury consumption, the City had to take 

action (Maryland Department of the Environment, 2002 a,b,c; 

2004 b,c). In addressing this reservoir impairment, the City 

provided data that indicated the bulk (85–95 percent) of the 

mercury delivered to the reservoirs and watersheds is from 

atmospheric deposition, and argued that the source of this 

mercury is regional and largely beyond control. As of 2007, 

the City findings were under review by the USEPA.

Not considered in the arguments presented by the City 

but worthy of note is that during periods of low water levels 

in the reservoirs, such as those that occur following prolonged 

withdrawals during drought conditions, exposed reservoir bed 

sediments can be oxidized, and subject to extensive re-vegetation by terrestrial plants (fig. 19). The area of exposed and 

potentially vegetated and oxidized bed sediments in the City 

reservoirs during prolonged droughts is considerable given the 

extent of reservoir shorelines (table 1, fig. 3B). Submergence 

of this vegetation and oxidized sediments during reservoir 

recovery could lead to what has been described as a first-flush 

release of nutrients (Newman and Pietro, 2001) and trace 

metals, including mercury, from recently deposited reservoir 

bed sediments (Dmytriw and others, 1995; Rawlick, 2001). In 

the presence of freshly released and elevated concentrations 

of oxidized carbon, sulfur, iron, and bioavailable Hg (II), there 

can be an acceleration in methylmercury production (Morrel 

and others, 1998; Krabbenhoft and others, 2000; Krabbenhoft 

and Fink, 2001), leading to increased biological uptake. 

Whether this process is an internal contributing factor to the 

elevated concentrations of mercury found in game fish in the 

City reservoirs cannot be determined without adequate data 

being obtained before (baseline) and after (within first 2 years 

of) recovery conditions in those areas of the reservoir where 

terrestrial vegetation is inundated. In general, the occasional 

monitoring of mercury in game fish in the reservoirs is inadequate in terms of timing and spatial distribution to determine 

whether enhanced mercury methylation occurs in those shallow areas of the reservoirs subject to exposure, re-vegetation, 

and subsequent re-inundation during drought and recovery 

periods. It also is unlikely that the answer to this question can 

be inferred from other Maryland lakes or reservoirs. There is a 

markedly wide range in the concentrations of methylmercury 

found in game fish in most Maryland lakes and reservoirs that 

cannot be explained, and likely indicates highly variable rates 

in regional atmospheric deposition and (or) reservoir response 

(Sveinsdottir and Mason, 2005).

Mobilization of phosphorus from reservoir sediments 

has been of concern to the RTG because of its possible role 

as the limiting nutrient in phytoplankton production (see 

Eutrophication—Nutrients: Phosphorus Transport and 

Reservoir Recycling, this report). Four studies have discussed 

its potential occurrence; but collectively the results of these 

four studies are ambiguous in terms of whether phosphorus 

release occurs, and if it occurs, whether the released phosphorus becomes available for phytoplankton production. In the 

first of these studies, Amatayakul and others (1978) conducted 

an analysis of Loch Raven Reservoir water-column data from 

which they concluded that bottom sediments were not a likely 

source of the phosphorus for algal blooms. From the concentrations of TP observed at depth, they concluded that reservoir 

bottom sediments appeared to release phosphorus. But they 

also argued that the released phosphorus likely would be 

unavailable, because during the summer months, stratification 

would prevent its utilization in the epilimnion, where algal 

blooms most often occur. Furthermore, they theorized that 

during lake turnover in the fall and winter, this phosphorus 

could reach shallow depths, but the reduced temperatures and 
The Water-Quality Monitoring Program 57

Figure 19. Terrestrial vegetation growing on exposed in-lake bed sediments in upper Prettyboy Reservoir in 2002. [Photographs by 

Wendy S. McPherson and Michael T. Koterba, U.S. Geological Survey.]

day length would limit bloom occurrence. Their study, however, was limited in a number of ways. Most of their conclusions were drawn from only a few samples collected in 1 year 

(1973). The samples were analyzed for just TP, and not bioavailable phosphorus. The samples reflected selected depths at 

just three sites in just Loch Raven Reservoir. Although these 

samples were collected before and during reservoir stratification, examination of the data indicates that the concentrations 

of DO were measurable at all sampled depths in the hypolimnion. Hence, the anoxic conditions that were suspected to 

occur at depth in the reservoirs in association with the die-off 

of major algal blooms, and which are necessary for the release 

of phosphorus from reservoir sediments, actually were not 

truly investigated. Finally, in generalizing their findings, the 

authors did not know at the time that major algal blooms can 

occur in Prettyboy Reservoir during the late winter or early 

spring (Interstate Commission on the Potomac River Basin, 

2006), which could reflect phosphorus released from bottom 

sediments and made available through lake turnover the preceding fall and winter. 

In the second study, Winfield and Sakai (2003) noted that 

for a number of years from 1981–93, concentrations of TP 

in deep water (greater than 30 ft deep) exceeded concentrations of TP in shallow waters (30 ft deep or less) in Liberty 

Reservoir. They interpreted elevated TP concentrations at 

depth to be the result of phosphorus released from reservoir 

bottom sediments. They indicated that the typical spring 

blooms in this reservoir could be in response to nutrients possibly made available from lake turnover the preceding fall and 

winter.
58 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

In the third study, Ortt and others (2000) found that sediments in all three reservoirs contained abundant phosphorus, 

and that surficial bottom sediments appeared to be enriched in 

phosphorus. Sediment phosphorus concentrations were high, 

and highly correlated with those of iron, and, therefore, likely 

bound to iron. They did not postulate whether this phosphorus 

would become available for algal blooms.

In the fourth study (Interstate Commission on the 

Potomac River Basin, 2006), the investigators found that 

anoxic conditions (no measureable DO) did occur at depth 

during the late summer and early fall in both Loch Raven and 

Prettyboy Reservoirs (for example, see fig. 16B), indicating 

that iron-bound phosphorus could be released under these conditions. They noted that this would occur, however, only after 

oxic nitrogen species (for example, nitrate) are reduced (see 

also Hem, 1970; Wetzel, 2001). But they also pointed out that 

nitrate generally was always present at measurable (above 0.5 

mg/L) concentrations at reservoir-bottom monitoring stations. 

They theorized that if nitrate is sufficiently abundant to serve 

as the preferred electron acceptor over ferric iron, iron would 

not be mobilized, and phosphorus would remain bound to iron 

in bottom sediments in the reservoir. They do not consider, 

however, whether the measurements taken at only a few locations in the deep parts of these reservoirs adequately reflect 

bottom conditions throughout the entire reservoir. Is nitrate 

present at all depths throughout each reservoir during periods 

of anoxia?

Collectively, these four studies appear to leave several 

unanswered but critical questions. What are the sources of 

available phosphorus that lead to algal blooms, and do they 

include the carryover of bioavailable phosphorus from one 

year to the next? For example, does lake turnover mobilize 

phosphorus from biomass decay or sediment release in one 

year to contribute to spring algal blooms in the following year, 

or is the source of the bioavailable phosphorus just winter and 

spring streamflows? Within a year, are mid-to-late summer 

algal blooms the result of bioavailable phosphorus released in 

part by decay of biomass from earlier algal blooms and (or) 

released from bed sediments in late summer? The answers 

to these questions are not known with any certainty because 

other than TP, no long-term routine measurements have been 

made in both the tributaries and reservoirs of bioavailable 

phosphorus, such as DOP or TDP.

Distribution and Sources of Bacteria and Other Potential 

Pathogens

Summary reports (Baltimore City Department of Public 

Works, 1996, 2001; Baltimore Reservoir Technical Group, 

2004) indicate that although bacteria have been found at 

elevated counts in selected locations in the watershed tributaries, the Baltimore reservoirs appear to function in an effective 

manner to reduce microbial contaminants at supply intakes. 

Individual sample values and monthly averages for fecal 

coliform bacteria counts in raw water from Liberty and Loch 

Raven Reservoirs consistently fall below and well below, 

respectively, the State water-quality recreational water-contact 

standard (200 Most Probable Number per milliliter). As of 

2007, selected watershed tributaries in each reservoir watershed had bacterial concentrations that exceeded this standard, 

and MDE had requested additional data be collected and 

analyzed (see Regulatory Concerns, this report). Pending the 

outcome of this request, long-term monitoring in the reservoir 

watershed tributaries could require the collection of fecalcoliform or other bacterial data. The design of the bacterial 

monitoring program for the reservoir watershed tributaries (if 

it follows other similar multi-watershed-scale studies) could 

depend on the type and levels of bacteria found, their spatial 

and temporal distribution, and their potential sources (Francy 

and others, 2000). For the Baltimore Reservoir System watersheds, likely potential source areas include agricultural as well 

as (sub)urban lands, with potential sources being livestock 

and pet wastes (manure), aging septic systems (rural), sewer 

and outfall lines [(sub)urban, residential, commercial, and 

industrial], storm drains and lines [rural and (sub)urban)], and 

WWTP storm-related overflows (Valcik, 1975).

Emerging Water-Quality Concerns

Emerging water-quality concerns addressed in this review 

and evaluation and described in recent (post-2000) RWMAs 

include the occurrence of elevated concentrations of DBPs 

in treated water in the distribution systems associated with 

both water-supply reservoirs. Recent increases in sodium and 

chloride in reservoir and treated waters are another emerging 

concern, and presumably result from the increased use of 

sodium-chloride salt as a deicing agent. In addition, although 

not formally recognized in the RWMAs as an emerging concern, the effects of climate are considered in this review and 

evaluation as an emerging concern. The projected changes in 

climate combined with the inherent variability in climate in 

the region could produce marked fluctuations in tributary and 

reservoir water quality, and therefore need to be considered in 

relation to current and future monitoring.

Disinfection By-Products

Disinfection by-products (DBPs) are an emerging 

concern at the City water-treatment plants because of recent 

(2006) changes to the manner in which the USEPA SDWA 

standards governing the concentrations of these compounds 

must be applied to treated drinking water (see Regulatory 

Concerns, this report). As of 2007, little is known about 

the source(s) of organic carbon found in Baltimore reservoir 

intake waters, which form DBPs during or after the initial 

disinfection (chlorination) of raw intake water or the residual 

chlorination of water after coagulation and filtration, which is 

used to maintain the quality of water as it moves through the 

City water-distribution system.

DBPs typically form when organic carbon, both dissolved 

and particulate, reacts during or after chlorination to form 

chlorinated and brominated compounds, which have been 

shown to be harmful to human health. From an operational 
The Water-Quality Monitoring Program 59

standpoint, total organic carbon (TOC) is employed by the 

City as a surrogate for the organic matter that reacts upon 

chlorination to form DBPs. A TOC concentration exceeding 

2.0 mg/L in reservoir intake waters is the action level that 

requires treatment-plant operations be undertaken to reduce 

TOC, and thus possibly DBP formation.

Although there are a wide array of DBPs potentially 

formed during treatment-plant operations (Krasner and others, 2006), only two of the major categories of DBPs—trihalomethanes (THMs) and haloacetic acids (HAAs)—and 

only the total concentration of the most commonly observed 

compounds in each of these classes—are regulated by USEPA 

SDWA standards.

Because regulations regarding DBPs relate to total THM 

and total HAA concentrations found in drinking-water distribution systems, most of the THM and HAA data routinely 

obtained by the City DPW reflect finished-water samples collected after treatment, and within the water-supply distribution 

systems. Therefore, the reported DBP concentrations reflect 

variations in the quantity of carbon that forms DBPs in raw 

intake waters, and variations in treatment-plant operations. 

For the City treatment-plant operations, the latter typically can 

include the initial chlorination, coagulation, and filtration of 

water, as well as the possible temporary storage and possible 

re-chlorination of finished water, and ultimately the transport 

of the treated water through the water distribution system.

The occurrence of DBPs in the Baltimore reservoir watersupply system is an emerging concern because of the need to 

adopt changes in Federal regulations regarding the reporting 

of total THMs and total HAAs in public water-supply distribution systems. Under the existing Federal rule, routine monitoring by the City DPW for DBPs indicates that the 30-day 

moving-average total concentrations of THMs or HAAs have 

not exceeded their respective USEPA MCLs of 80 μg/L and 

60 μg/L, respectively (Baltimore Reservoir Technical Group, 

2004). The City DPW has noted, however, that summer-to-fall 

mean THM concentrations in the distribution system during 

the mid-1990s sometimes approached the 80 μg/L USEPA 

MCL for THMs, and that during 1995–2001, total THM 

and or HAA concentrations at selected stations occasionally 

exceeded their respective USEPA MCLs under what would 

be the revised reporting rules. Revised rules will require the 

MCLs be applied to the 30-day moving average of total THMs 

or total HHAs at each point of sampling within the waterdistribution system.

The Baltimore Reservoir Technical Group (2004) 

indicated additional studies were needed to identify sources 

of DBP precursors. In support of these studies, Winfield 

and Sakai (2003) provided some initial DBP-related data on 

Liberty Reservoir intake waters at the Ashburton treatment 

facility (table 9). MDE (2004a) also summarized DBP data for 

the Loch Raven Reservoir Montebello treatment facility 

(table 10).

The data from Winfield and Sakai (2003) indicate that, 

except for 1998, water treatment at the Ashburton plant, which 

utilizes water from Liberty Reservoir, reduced the initial 

concentration of TOC by approximately 30 percent, but that 

considerable TOC, approximately 1.7–2.9 mg/L, still remained 

in the water after coagulation and filtration (table 9). Also the 

concentrations of total THMs and total HAAs encountered in 

finished waters appear to be solely a result of the treatment 

process, as no THMs or HAAs were detected in raw intake 

waters.

Data on DBPs and TOC in finished waters analyzed 

by the Maryland Department of the Environment at the 

Montebello treatment facility (table 10) generally reflect 

water from Loch Raven Reservoir, or from the Susquehanna 

River when the reservoir water levels are low (see Reservoir 

Watershed Management and Reservoir Operation, this 

report). The DBP data from the Montebello treatment facility 

are consistent with data presented above for the Ashburton 

treatment facility. Overall MDE found that the average annual 

total concentration of THMs or HAAs from all samples collected at all stations were below the respective USEPA MCLs. 

Maximum annual concentrations, which reflect conditions at 

individual stations, exhibited total THM and HAA concentrations that would have exceeded the respective USEPA MCLs 

under the revised rules. MDE (2004a) also summarized data 

on a quarterly basis that indicate about 30 percent of the TOC 

in raw supply waters at the Montebello treatment facility was 

removed by coagulation and filtration. 

To aid in understanding the occurrence of elevated DBPs 

in the City water-supply distribution system, the USGS conducted an analysis of recent (2003–08) data provided by the 

City DPW on THMs, HAAs, and TOC. The purpose of this 

retrospective analysis was twofold: 

a) To describe and characterize the THM, HAA, and TOC 

data, in relation to concentrations and trends at each 

water-treatment facility, and 

b) To identify in the broadest terms the potential sources 

(reservoir or watershed) of carbon that forms DBPs.

There are inherent limitations in the analyses of the City DBP 

and TOC data. Whereas TOC is routinely monitored at the 

reservoir intakes, there has been no routine long-term inlake or tributary monitoring for TOC specifically focused on 

the identification of the carbon that forms DBPs in finished 

waters. Nor has the timing and frequency of routine sampling 

used by the City DPW specifically been designed to relate the 

TOC concentration found in an intake water to the total THM 

or HAA concentrations in this water after it has been treated 

and distributed. Thus, although sampling for TOC and DBPs 

could have been conducted on the same day, the intake water 

that was collected and analyzed for TOC is not necessarily the 

finished water that was sampled for DBPs. 

Also relative to the THM, HAA, and TOC data that have 

been collected, much of the detailed ancillary information on 

variations in actual plant operations that could influence DBP 

formation is unavailable. In the case of the Baltimore watersupply system and treatment-plant operations these variations 

include:
60 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 9. Annual maximum concentrations of total organic carbon, trihalomethanes, and haloacetic acids in raw and treated waters in 

the Ashburton treatment plant, Liberty Reservoir, 1997–2001 (modified from Winfield and Sakai, 2003).

(TOC, total organic carbon; THMs, trihalomethanes; HAAs, haloacetic acids; mg/L, milligrams per liter; μg/L, micrograms per liter; ND, not detected)

Year

Annual maximum concentrations

TOC, 

raw water 

(mg/L)

TOC, 

treated water

(mg/L)

THMs1, 

raw water

(μg/L)

THMs, 

treated water

(μg/L)

HAAs2, 

raw water

(μg/L)

HAAs, 

treated water

(μg/L)

1997 2.54 1.69 ND 40.0 ND 35.0

1998 2.00 2.70 ND 27.0 ND 46.0

1999 2.62 1.38 ND 36.0 ND 38.0

2000 3.42 2.30 ND 36.0 ND 33.0

2001 3.10 2.92 ND 19.5 ND 34.0

1

 Sum of the concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform.

2

 Sum of the concentrations of mono-, di-, and tri-chloroacetic acids and mono- and di-bromo acetic acids.

Table 10. Summary statistics for annual concentrations of regulated total trihalomethanes and haloacetic acids in finished waters at 

the Montebello treatment facility, Loch Raven Reservoir, 1996–2003 (modified from Maryland Department of the Environment, 2004a).

[All concentrations are in micrograms per liter; ---, unavailable]

Year

Concentration of trihalomethanes1 Concentration of haloacetic acids2

Average Maximum Minimum Number of 

samples Average Maximum Minimum Number of samples

1996 45 82 20 96 --- --- --- ---

1997 40 84 17 45 --- --- --- ---

1998 40 77 15 54 33 58 16 35

1999 47 93 15 36 19 41 2 27

2000 41 80 23 36 48 102 1 28

2001 50 100 22 18 28 53 7 16

2002 52 87 17 42 26 58 0 42

2003 33 54 21 11 40 59 13 11

Total 44 100 15 338 31 102 0 159

1

 Sum of the concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform.

2

 Sum of the concentrations of mono-, di-, and tri- chloroacetic acids and mono- and di- bromo acetic acids.
The Water-Quality Monitoring Program 61

a) Variation in the sources of raw water, which in the case 

of the Montebello treatment facility, generally is from 

Loch Raven Reservoir but occasionally, and particularly during droughts, could include water from the 

Susquehanna River; 

b) Variation in treatment plant operations, including the 

levels of chlorination and possibly re-chlorination, 

given the latter is sometimes required;

c) Variation in the residence time of stored treated 

water, which for each treatment facility can be held in 

outdoor finished-water ponds for up to several days, 

before it is possibly re-chlorinated, and then placed 

into the distribution system;

d) Variation in the travel (residence) times of the treated 

water after it enters the distribution system; and

e) Variation in the formation and degradation rates of 

THMs or HAAs.

Since there is no permanent documentation on the long-term 

history of these variations at each treatment plant, there also is 

no way to rank them according to their relative importance to 

DBP formation. It generally is known, however, that variations 

in each of the above factors can affect the concentrations of 

total THMs or total HAAs found in finished water within different parts of a large water-supply distribution (storage and 

pipeline) system (Singer and others, 2002).

Given these limitations, the monitoring data for DBPs 

for individual stations and TOC in raw intake waters only can 

be summarized, described, and analyzed in a broad manner. 

For the period of record (January 2003–July 2008), the total 

concentrations of THMs and HAAs in finished-water samples 

periodically exceeded the USEPA MCLs at one or more stations in each water-supply distribution system (figs. 20 and 

21). The total concentration of THMs at one or more stations 

exceeded 80 μg/L on approximately 19 percent of the samplecollection dates for either distribution system; the total concentration of HAAs exceeded 60 μg/L at one or more stations 

on approximately 43 percent and 38 percent of the samplecollection dates for the Ashburton and Montebello distribution 

systems, respectively (table 11). In addition, for most sampling 

dates, about the same number of stations in both distribution 

systems were likely to have total THM (fig. 20) or HAA 

(fig. 21) concentrations that exceeded their respective USEPA 

MCLs on that date.

The concentrations of THMs in finished waters associated with either treatment plant appear cyclic in nature on a 

seasonal basis (fig. 20). For the period of record, the highest 

THM concentrations, and thus frequency of exceedances of 

the USEPA THM MCL, generally occurred each year from 

mid-summer through early fall (July–September). MDE 

(2004a) found a similar cyclic pattern for THM exceedances 

for 1995–2003 DBP data collected from the Montebello distribution system. 

The repeated frequencies with which the total THM 

concentration exceeds the USEPA MCL for THMs at the same 

stations during mid-summer through early fall indicate that 

it is during this period that a 30-day moving average THM 

concentration at these stations is most likely to exceed the 

USEPA for THMs under the pending rule change. In contrast, 

seasonal trends in the total concentration of HAAs are not 

readily apparent (fig. 21). Elevated total concentrations of 

HAAs often occur at the same stations, but at different times 

in different years. Thus, it is uncertain whether there will be no 

periods, or occasional but random periods, during a given year 

or from year to year during which a 30-day moving average 

HAA concentration at each of these stations is likely to exceed 

the USEPA MCL for HAAs under the pending rule change.

Interpretation of the likelihood that the 30-day moving 

average for the total concentration of either THMs or HAAs 

will exceed their respective USEPA MCL is further complicated by the fact that in either distribution system, the total 

concentrations of THMs and HAAs during the period of 

record (January 2003–July 2008) at a given station are largely 

independent of one another. There is little to no significant 

linear correlation between the total concentration of THMs 

and the total concentration of HAAs at a given distribution 

station. For 19 stations, linear correlation coefficients (R2) for 

most (17/19) stations were less than or equal to 0.10, with p 

values equal to or greater than 0.10; for two stations, the R2

values were between 0.30–0.40, and p values were less than 

0.002, but linearity was largely the result of one or two outlier 

values (linear regression analysis, Helsel and Hirsch, 2002). 

This result is not atypical given that THMs generally form and 

degrade more quickly than HAAs in large distribution systems 

(Xie, 2004).

As for the sources of carbon that form DBPs, concentrations of TOC are the only routinely measured form of carbon 

that can serve as a potential indicator of the occurrence of 

DBP precursors in the City water-supply distribution systems. 

Excluding an extreme outlier value of 9.6 mg/L recorded on 

October 13, 2005 at the Montebello treatment facility, concentrations of TOC at the two treatment facilities generally were 

similar. For the period of record, at the Montebello facility, 

they ranged from 1.3 to 3.5 mg/L and averaged 1.9 ± 0.3 

mg/L; at the Ashburton facility, they ranged from 1.2 to 3.0 

mg/L and averaged 2.0 ± 0.3 mg/L. 

For the period of record, variations in the concentration 

of TOC in treated water were generally similar to variations in 

the concentration of TOC in raw-intake waters at either treatment facility (fig. 22). The main difference in these two measurements of TOC is that treated-water TOC concentrations 

were consistently lower than raw-water TOC concentrations. 

The treatment process, which typically involves chlorination, 

coagulation, and then filtration, routinely removed about onethird of the total carbon found in raw-intake waters. This result 

is similar to results described earlier by Winfield and Sakai 

(2003) for the Ashburton treatment facility from 1997–2001, 

and by MDE (2004a) for the Montebello treatment facility for 

TOC data collected from 1996–2003.
62 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 20. Total trihalomethane concentrations at selected sampling locations in the water-supply distribution system from the 

(A) Ashburton (Liberty Reservoir) and (B) Montebello (Loch Raven Reservoir) treatment facilities, January 2003–July 2008. 

(Data provided by the Baltimore City Department of Public Works, Environmental Division, Baltimore, Maryland).
The Water-Quality Monitoring Program 63

Figure 21. Total haloacetic acid concentrations at selected sampling locations in the water-supply distribution systems from the 

(A) Ashburton (Liberty Reservoir) and (B) Montebello (Loch Raven Reservoir) treatment facilities, January 2003–July 2008. 

(Data provided by the Baltimore City Department of Public Works, Environmental Division, Baltimore, Maryland).
64 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 11. Number of sampling dates that U.S. Environmental Protection Agency Maximum Contaminant 

Levels for disinfection by-products were exceeded at one or more stations in the water distribution systems 

at the Ashburton or Montebello treatment facilities, 2003–08.

[μg/L, micrograms per liter]

Treatment facility

Ashburton Montebello 

Number of sampling dates that concentration of trihalomethanes 

equalled or exceeded 80 μg/L at one or more stations

7 7

Total number of sampling dates 37 37

Frequency of exceedances, in percent 18.9 18.9

Number of sampling dates that concentration of haloacetic acids 

equalled or exceeded 60 μg/L at one or more stations

16 14

Total number of sampling dates 37 37

Frequency of exceedances, in percent 43.2 37.8

Figure 22. Concentrations of total organic carbon in the Baltimore Reservoir treatment facilities, April 2003–July 2008 (Data 

provided by the Baltimore City Department of Public Works, Baltimore, Maryland).
The Water-Quality Monitoring Program 65

Temporal variations did occur in concentrations of TOC 

during the period of record (fig. 22). At the Ashburton facility, 

the highest TOC concentrations occurred from mid-2003 to 

early 2004, which reflects reservoir recovery waters after the 

severe drought from 2000–02. Elevated TOC concentrations 

also occurred during the reservoir recovery period in late 

2005–early 2006, and following a less severe drought in early 

2005. These elevated concentrations of TOC possibly could 

reflect increases in carbon from the watershed tributaries in 

recovery flows, and (or) from algal blooms, or the decomposition of terrestrial vegetation established in the reservoirs 

during the droughts. Elevated TOC concentrations also 

occurred in the early fall in 2004 and in 2008. The elevated 

concentrations of TOC in 2004 again could reflect the continuation of increased levels of carbon in tributary flows, the 

decomposition of algal blooms, and (or) the decomposition of 

terrestrial vegetation established on reservoir bed sediments 

during the drought but then submerged during reservoir 

recovery. Concentrations of TOC in the Montebello facility, 

which generally reflect Loch Raven Reservoir water, but also 

occasionally reflect Susquehanna River water (see Reservoir 

Watershed Management and Reservoir Operation, this 

report), also appear to vary temporally throughout the period 

of record. Elevated TOC concentrations occurred during the 

drought-recovery periods noted above, as well as in the fall 

or winter—January 2004, October 2005, December 2006, 

and October 2007 (fig. 22). As was the case with Liberty 

Reservoir and the Ashburton facility, the periods of elevated 

TOC concentrations in the Montebello facility could, in 

part, reflect increases in carbon from Loch Raven Reservoir 

watershed tributary flows, reservoir algal blooms, and (or) the 

decomposition of terrestrial vegetation in the reservoir, during 

the recovery from drought conditions. The other periods of 

elevated TOCs, during the fall and winter months, could 

reflect increased carbon loads from the reservoir watershed 

tributaries, for example, leaf-litter contributions (October 

months) or lake turnover (January–December months), respectively. The variations in TOC at this facility in part also could 

reflect the use of Susquehanna River water—for example, during the severe drought and recovery from drought in 2000–04, 

and the moderate drought-recovery period from 2005–06 

(see Reservoir Watershed Management and Reservoir 

Operation, this report).

Temporal variations in the concentrations of TOC were 

compared to either total THM or total HAA concentrations 

for the period of record. Although the monitoring of TOC in 

relation to THM and HAA concentrations was not specifically designed to relate the former to the latter, such comparisons are useful for illustrative purposes. In the case of the 

Ashburton facility, and except for 2003–04, the concentration 

of TOC bore no apparent relation to the total concentration 

of THMs during the period of record (fig. 23). Similar results 

were obtained for TOC and HAAs at this facility and for 

TOC in relation to THMs or HAAs at the Montebello facility. Variations in the amount and (or) types of carbon that 

form DBPs possibly are insufficient in magnitude to notably 

influence the concentrations of TOC, or if there is such a 

correspondence, it is not apparent because of the limitations 

inherent in trying to compare these TOC and DBP data (see a) 

through e), p. 61).

The Baltimore Reservoir Technical Group (2004) recognized the need to determine the sources of carbon (rather than 

TOC) entering or generated within a reservoir that contribute 

to DBP formation. As such, future monitoring for in-stream 

and in-lake sources of carbon that form DBPs needs to take 

into account that the differences in the temporal patterns of 

elevated THMs or HAAs in finished waters in the water-supply distribution system could reflect different carbon sources. 

Assuming that the variations in THM concentrations 

reflect variations in the concentrations and types of reactive 

carbon that form THMs, and not variations in treatment plant 

operations, freshly created TOC from phytoplankton can have 

a high propensity to form DBPs, and phytoplankton residues 

are not necessarily removed during coagulation and filtration 

(Graham and others 1998; Jack and others, 2002; Kraus and 

others, 2011). Elevated THM concentrations in finished water 

in the water-distribution system from the Ashburton facility 

and Liberty Reservoir generally do appear in mid-summer 

to early fall in most years of record, which corresponds with 

the period when algal blooms and die-offs most often occur 

in the reservoir. A similar pattern generally holds true for 

seasonal patterns in THM occurrence associated with the 

Montebello distribution system. In the case of this distribution 

system, however, the source of the finished waters generally 

is from Loch Raven Reservoir; but when reservoir water 

levels are low, the source of the finished waters could be the 

Susquehanna River.

In relation to major hydrologic events and sources of 

DBP precursors, and in the case of THMs, the drought-recovery periods (in 2003–04 and again in 2005–06) correspond to 

periods when relatively high THM concentrations occurred 

in finished waters at selected stations in both the Ashburton 

and Montebello distribution systems. These types of droughtrecovery periods are known or suspected to be marked by 

intense algal blooms (Baltimore Reservoir Technical Group, 

2004; Valcik, 1975). These blooms could result from tributary 

waters enriched in nutrients (Kaushal and others, 2008), and 

possibly also enriched in organic residues that contribute 

to DBP formation. In addition, terrestrial vegetation established on extensive areas of reservoir bed sediments exposed 

by repeated drawdowns during drought conditions (fig. 19) 

constitutes another potential DBP carbon source when this 

vegetation is submerged during reservoir recovery (Fram and 

others, 2001).

In the case of HAAs, elevated total HAA concentrations 

do not generally co-occur with elevated total THM concentrations in finished waters associated with either treatment plant, 

nor do they generally co-occur with elevated TOC concentrations in finished or treated waters. They also tend to occur 

at the same stations, but at different times in different years. 

These findings indicate that the sources and types of carbon 

that lead to elevated HAA concentrations could differ from the 
66 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 23. Total concentrations of trihalomethanes for selected sampling locations in the Ashburton distribution 

system, and total organic carbon concentrations in raw intake and treated waters in the Ashburton treatment 

plant, April 2003–July 2008 (Data provided by the Baltimore City Department of Public Works, Baltimore, Maryland).

sources and types of carbon that form THMs, and, as in the 

case of THMs, are not of sufficient magnitude in concentration to lead to elevated concentrations of TOC. The sporadic 

nature of observed elevated concentrations of HAAs suggests 

these different sources and types of carbon are associated with 

relatively short and discrete biological and (or) hydrodynamic 

events whose nature is largely unknown.

In relation to future monitoring to determine in-stream 

and in-lake sources of reactive carbon that form DBPs, 

consideration needs to be given to the effect of the treatment 

process on DBP formation. The DBPs that form during initial 

chlorination of raw intake waters may or may not reach the 

distribution system. For example, research has shown that 

aromatic organic compounds more readily form DBPs than 

non-aromatic compounds, but that aromatic compounds often 

are effectively removed by coagulation (Fram and others, 

2001, Singer, 1999; Wu and others, 2000. 

In addition, future monitoring could be guided by a number of recent and ongoing studies. The USEPA rule change 

on DBPs has generated considerable interest, discussion, and 

study to identify the sources and types of carbon that lead 

to DBPs in finished waters (Bergamaschi and others, 1999; 

Fram and others, 2001; Mash and others, 2004; Xie, 2004, 

Bergamaschi and others, 2005; Kraus and others, 2008; Kraus 

and others, 2010; Kraus and others, 2011). On the basis of 

these studies, the following findings could be relevant to the 

Baltimore reservoir system and City water-treatment process, 

and help guide monitoring to identify the sources of carbon 

that form DBPs within the Ashburton and Montebello waterdistribution systems:

a) DBP carbon sources can be autochthonous—for 

example, from reservoir phytoplankton or aquatic 

plants, and (or) allochthonous—for example, from 
The Water-Quality Monitoring Program 67

humic, silt, or colloidal detritus (plant or animal) matter transported by tributaries.

b) Autochthonous sources could include vegetation 

initially established on bed sediments during a drought, 

and subsequently submerged during reservoir recovery.

c) The source of carbon that leads to DBP formation 

could be allochthonous, and not be found to form 

DBPs if exposed to chlorination; but this carbon could 

undergo transformations as it is transported through the 

reservoir in a manner that enhances its ability to form 

DBPs.

d) Differences in the physical and chemical characteristics of autochthonous and allochthonous source materials can aid in their identification as DBP precursors.

e) The types of DBPs that enter, or form afterwards 

in, the distribution system depend upon the watertreatment process; variations in that treatment process—including levels of initial chlorination, coagulation and filtration; the length of time finished water is 

stored, and its manner of storage; the re-chlorination 

of finished water before it is placed in the distribution 

system; and the amount of time finished water resides 

in the distribution system.

f) Accurate assessment requires that potential DBP source 

waters be sampled and tested using treatment and posttreatment processes with residence times similar to that 

used when treating and distributing water for consumptive use.

g) Reducing DBP formation from a confirmed source, 

often requires determining at what point(s) in the treatment process that source forms DBPs, and how quickly 

the DBPs form and decompose.

h) In areas with heavy use of road salt (sodium chloride) 

as a deicing agent, bromide (a residual contaminant in 

road salt) could contribute to elevated DBP concentrations as brominated DBP compounds have an appreciably greater mass than chlorinated DBP compounds.

Given all of the above factors, continuous-monitoring parameters and procedures are being identified and developed to help 

identify DBP precursors in source waters, which effectively 

monitor for more than TOC. Effective monitoring generally 

(a) begins with the determination of concentrations of aromatic and aliphatic carbon in raw reservoir intake waters, (b) 

follows with treatment of samples to determine the relative 

contributions of aromatic and aliphatic carbon to DBP formation, (c) extends to backtracking to identify reactive carbon 

source(s) in the reservoir and its tributaries, and (d) extends 

to forward tracking of these reactive carbon compounds to 

determine if these compounds occur in proximity to where the 

DBPs form in the distribution system.

Sodium and Chloride

Elevated concentrations of sodium and chloride in 

potable water supplies are emerging water-quality concerns 

for the RWMA partners. Since the early 1970s, when sodium 

concentrations began to be routinely measured, concentrations 

of sodium have almost tripled in the supply-intake water from 

Liberty Reservoir, and almost quadrupled in the supply-intake 

water from Loch Raven Reservoir (Baltimore Reservoir 

Technical Group, 2004). In 1999 and 2003, sodium concentrations in treated waters from Loch Raven Reservoir often 

exceeded 20 mg/L—the USEPA (2003) non-regulatory health 

advisory for consumers on restricted low-salt-intake diets (500 

mg/d or milligrams per day). During the same period, sodium 

concentrations in treated waters from Liberty Reservoir 

ranged from 10–16 mg/L, exceeding almost all previous 

measurements.

Chloride concentrations also have increased in reservoir 

intake waters since the early 1970s from about 15 mg/L to as 

high as 25 to 30 mg/L by the year 2000. Although still well 

below the USEPA SWDA health advisory (2009), which is 

250 mg/L, the increase in chloride concentrations has raised 

RWMA partner concerns, as indicated in their most recent 

RWMA 2005 (see Reservoir Watershed Management and 

Reservoir Operation, this report).

In relation to monitoring, sodium has not been extensively and continuously monitored by the City. Although 

routine monitoring for sodium began in 1973 in finished 

waters at the intakes of both water-supply reservoirs, the 

data largely remained unpublished until the 1990s. Up to this 

period, sodium concentrations were well below the USEPA 

SDWA secondary standard for taste set for the general population (30–60 mg/d). Thus, it was only recently that MDE 

(2004a) provided some historical data on finished waters at 

the Montebello treatment facility (fig. 24). The data illustrate 

the rise in sodium concentrations described above by the RTG 

for finished waters from 1973–2004. As will be discussed 

in greater detail below, the source of the recent increase in 

sodium concentrations has been attributed to the use of salt 

(sodium chloride) as a deicing agent in high-density parking 

and transportation corridors (Reservoir Watershed Protection 

Committee, 2000; Baltimore Reservoir Technical Group, 

2004). The basis for this conclusion is that recent sodium 

concentrations are roughly proportional to the increases in 

chloride concentrations and conductance levels—both of 

which have been monitored extensively and for long periods 

of time in the reservoir watersheds and (or) reservoirs.

From a historical perspective, chloride concentrations in 

the Montebello treatment facility intake waters were routinely 

monitored beginning soon after the reservoir was created. Data 

provided by Amatayakul, Defries, and others (1978) show that 

chloride generally increased from the 1930s to 1970s (fig. 25). 

The initial upward trend in chloride concentrations to the mid1940s likely reflected runoff from agricultural development 

(livestock and animal waste) and human septic and sewered 

wastes. Following World War II, increases in urban residential, 
68 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 24. Concentration of sodium in intake waters at the Montebello water treatment facility, Loch Raven Reservoir, 

January 1973–January 2004 (modified from Maryland Department of the Environment, 2004a).

Figure 25. Mean annual chloride concentration in intake waters 

at the Montebello water treatment facility, Loch Raven Reservoir, 

1925–67 (modified from Amatayakul and others, 1978).

commercial, and industrial growth likely contributed to the 

sharp rise in chloride concentrations that continued up to the 

mid-1960s. By then, and just before the first major sewage 

WWTPs came on line in the watershed (at Hampstead in 1969 

and at Manchester in 1970), chloride concentrations at the 

reservoir intake had risen from approximately 5 mg/L in the 

1930s to 14 mg/L.

From the mid-1970s through the 1980s, chloride monitoring was intermittent, and not performed as part of routine 

reservoir in-lake monitoring. Up until this period, it was primarily used as a surrogate for nutrient (primarily nitrate) concentrations; a use which was halted because of concerns that 

natural sources of chloride (for example, sea spray) rendered 

its use as a surrogate for nutrients suspect. In addition, analytical methods to directly measure nutrients became available in 

the late 1960s.

Since 1982–83, chloride and conductance data were 

again collected by the City at selected reservoir and watershed 

tributary stations. A comparison of selected time-series data 

for in-lake conductivity and chloride concentrations (fig. 26), 

as well as in-lake conductivity in the reservoirs and chloride 

concentrations in the upstream tributaries (fig. 27), indicate 

apparent positive trends in chloride and conductivity, and that 

the chloride concentrations in the reservoirs have continued 

to increase in reservoir waters (Baltimore City Department of 

Public Works, 1996, 2001; Winfield and Sakai, 2003).

Since 1992, dry-weather-flow data indicate chloride concentrations also apparently have increased in most, but not all, 

of the reservoir subbasins. For the Loch Raven and Prettyboy 
The Water-Quality Monitoring Program 69

Figure 26. (A) Chloride concentrations, 1992–2000, and (B)

conductivity, 1984–2000, of in-lake shallow waters (less than 

30 feet deep) in Liberty Reservoir (modified from Baltimore City 

Department of Public Works, 2001).

Reservoir watersheds, and except for Beaver Dam Run, all 

the monitored subbasins show apparent increases in chloride 

concentrations; in the Liberty Reservoir watershed, and except 

for the stations at Beaver Run and the North Branch of the 

Patapsco River, all dry-weather-flow tributary stations also 

show apparent increasing trends (Baltimore City Department 

of Public Works, 1996; Winfield and Sakai, 2003).

Monitoring data have indicated that conductivity and 

chloride concentrations in the tributaries and shallow reservoir 

waters have varied seasonally, and have been subject to periodic spikes (figs. 24, 26, and 27). The highest conductivity and 

chloride concentrations typically occurred in the late winter 

or early spring, whereas the lowest conductivity and chloride 

concentrations typically occurred in the summer months 

(Baltimore City Department of Public Works, 1996). 

Winter maxima in chloride concentrations appear related 

to subbasin land use. Using data from the 1999 water year, 

which had the highest winter chloride concentrations on 

record at supply-reservoir intakes, annual median chloride 

concentrations in dry-weather flows for subbasin tributaries 

were found to be most significantly (p < 0.0054) correlated to 

the areal extent of commercial and industrial land use within a 

subbasin (fig. 28). The median chloride concentration in dryweather flows for the winter (January through March) periods 

of 1996–99 also were found to significantly correlate with the 

road length per unit area (p < 0.0313) in a subbasin (fig. 28). 

In addition, the difference in the 1999 and 1990 median 

annual chloride concentrations in dry-weather tributary flows 

were significantly correlated (p < 0.0116) with one landscape 

characteristic—declining agricultural land use (fig. 28). 

Further evidence that urban settings possibly contributed to a 

disproportionately high amount of chloride in the reservoirs 

was provided by Winfield and others (2006). They found an 

increasing pattern in chloride concentrations from reservoir 

intakes to upstream urban areas (fig. 29).

Monitoring for chloride in the watershed tributaries and 

at the reservoir intakes, and to a lesser extent, for sodium in 

finished drinking waters, has enabled the RWMA partners to 

determine that the recent increases in sodium and chloride 

were cause for concern. As of 2007, monitoring has shown 

that sodium in reservoir intake waters has approached concentrations that occasionally exceed Federal guidelines for 

individuals on low-sodium intake diets. Chloride concentrations also have increased at rates similar to those observed 

for sodium. The analysis of recent apparent trends in the 

monitoring data with land use also has enabled the identification of road-salt use as a deicing agent, particularly in residential, institutional, commercial, and industrial areas with a 

high density of impervious parking areas and roads, as likely 

being responsible for the enhanced elevated concentrations 

of sodium and chloride in finished water supplies during the 

winter months. 

As of 2007, monitoring cannot provide a timely advance 

warning to water purveyors (at the Ashburton and Montebello 

treatment facilities) of potentially high sodium concentrations. 

Sodium is not routinely or frequently measured in either the 

reservoirs or in the tributary watersheds. Nor does chloride 

sampling occur with sufficient frequency during the winter 

months to use as a surrogate for sodium. In general, monitoring for either sodium or chloride concentrations in winter 

months in both the reservoir watersheds and reservoirs also 

is insufficient to readily detect reduced concentrations should 

actions be taken to reduce sodium-chloride road-salt use in the 

subbasins. It could take years for such reductions to become 

truly apparent given the type and frequency of sampling 

being conducted. It also is unclear whether or not sodium 

and chloride concentrations will decline or simply increase 

at a reduced rate following a major reduction in road-salt 

use because there are other sources of sodium and chloride 

in the reservoir watershed. For example, watershed populations are expected to continue to increase, which either likely 

will increase sodium and chloride loads to WWTPs, or from 

additional septic systems, which in either case, do not remove 

sodium or chloride, and eventually likely lead to increased 

concentrations being observed in reservoir-watershed tributary 

streams. 
70 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 27. Examples of conductivity in shallow waters (less than 30 feet deep) of the Baltimore Reservoirs, and chloride 

concentrations in upstream tributary dry-weather flows, 1982–2000 (modified from Baltimore City Department of Public Works, 

2001).
The Water-Quality Monitoring Program 71

Figure 28. Relations between median concentrations of 

chloride in all dry-weather tributary flows for selected time 

periods and selected 1999 landscape characteristics in tributary 

subbasins of the Baltimore Reservoir watersheds, various years 

of record (modified from Baltimore City Department of Public 

Works, 2001).

Effects of Climate

Climate has a marked effect on the quality as well as 

quantity of water in the tributaries and reservoirs of the 

Baltimore Reservoir System. The climate of the Mid-Atlantic 

region over short time periods is inherently quite variable. 

This variability is apparent in the within-year and year-to-year 

variations in streamflows, tributary concentrations and loads, 

and reservoir water quality for most pollutants of concern (for 

examples, see Eutrophication—Nutrients, Sedimentation—

Sediment Transport, and Sodium and Chloride, this report). 

In terms of short-term climatic variations, those that are 

possibly most critical are potential changes in water quality 

associated with major storms and droughts and recoveries 

from droughts (see Overview of Water-Quality Concerns, 

this report). Within the last decade, however, there have been 

at least two moderate to severe droughts that have affected 

reservoir water quality and operations, and that were largely 

terminated by major storms—a pattern that could reflect recent 

long-term forecasts of the effects of climate change on the 

Mid-Atlantic region. As of 1995, however, the monitoring 

program does not appear to be well suited to ensuring that the 

effects of climate variability and climate change on the quality 

of water in the watershed tributaries and reservoirs can be 

clearly assessed and differentiated from the effects of watershed and reservoir management activities designed to address 

RWMA water-quality concerns.

Climate Variability

Whereas year-to-year and within-year variations in 

tributary and reservoir water quality inherently have been 

characterized by the monitoring program to a degree, there are 

two aspects of climate variability—storms and droughts—for 

which the effects on watershed tributary and reservoir water 

quality have not been well characterized. 

Monitoring of stormflows declined in the mid-1990s, 

and as of 2007, and except perhaps for drought years, the 

subsequent monitoring of stormflows within a year and 

from year to year likely has been insufficient to characterize 

stormflow water quality and pollutant loads of interest (see 

Eutrophication—Nutrients: Phosphorus Transport 

and Reservoir Recycling and Sedimentation—Sediment 

Transport, this report). However, even the storm-related 

data collected before the decline in stormflow monitoring 

possibly were insufficient as suggested by the most recent and 

advanced attempt to characterize the effects of tributary flows 

and water quality on reservoir water quality and biota (see 

Modeling to Address Water-Quality Concerns, this report). 

According to the ICPRB, there appears to be insufficient 

data to determine if the effect of storms on reservoir water 

and biotic quality is simply minimal and transient (Interstate 

Commission on the Potomac River Basin, 2006). Historical 

monitoring of tributary stormflows, and in the reservoirs, has 

been too infrequent. Reservoir monitoring at selected sites 

also is limited by boat and weather permitting (see Current 

Perspective, this report).
72 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure 29. Chloride concentrations for finished supply waters at Montebello and Ashburton treatment 

facilities (1982–2004), reservoir tributaries (1982–2004), and selected Baltimore City streams (1997–2004) 

(modified from Winfield and others, 2006).

The effects of droughts and recoveries from droughts 

represent another form of short-term climatic variability for 

which the effect on watershed tributary quality, and reservoir 

water and biotic quality, also is not well known. Anecdotal 

evidence provided during the late 1960s drought and 1970s 

recovery (Valcik, 1975), and also more recently by Winfield 

and Sakai (2003), the Baltimore Reservoir Technical Group 

(2004), and MDE (2004a), for the 2000—03 drought-withdrawal-recovery event, indicates that algal blooms could be 

enhanced during a major drought and (or) during the recovery 

from drought conditions. Reservoir withdrawals during prolonged droughts could be a contributing factor because of the 

City firming program which aims to always withdraw the best 

quality of water (see Reservoir Watershed Management and 

Reservoir Operation, this report).

Beginning in the summer of 1999 until the spring of 

2003, the reservoir watersheds experienced moderate and 

then severe drought conditions marked by episodic periods 

of relatively low streamflow (fig. 30). Although precipitation, 

such as the nor’easter in the winter of 1999, which resulted 

in a major snowfall in the region, was initially sufficient to 

reduce the impact of the drought, drought conditions intensified and persisted until 2003. Final cessation of the drought 

and full recovery in the reservoirs began with Hurricane Isabel 

in September 2003, and was enhanced by two nor’easters that 

produced major snowfalls in the region in December 2003 and 

February 2004. 

During the drought-recovery period, and due to the 

City firming program, it is evident that annual releases from 

Prettyboy Reservoir increased in magnitude each year until 

drought recovery (fig. 31), and in response to major withdrawals and drawdowns each year from Liberty and then Loch 

Raven Reservoirs, in the absence of full reservoir recovery. 

Ultimately, the City obtained water from the Susquehanna 

River (see Reservoir Watershed Management and 

Reservoir Operation, this report), but not before reservoir 

withdrawals led to parts of each reservoir being drained, and 

covered by terrestrial vegetation (for example, see fig. 19). 
The Water-Quality Monitoring Program 73

Figure 30. Long-term streamflow characteristics with major drought-recovery periods for U.S. Geological Survey station 

LIT0002 (Little Falls at Blue Mount, Maryland) in the Loch Raven Reservoir watershed, 1941–2007 (modified streamflow records 

from U.S. Geological Survey Maryland-Delaware-D.C. Water Science Center).

Figure 31. Annual variation in surface-water elevation in Prettyboy Reservoir, indicative of releases to 

replenish Loch Raven Reservoir under normal and drought conditions, 1994–2004 (modified from Interstate 

Commission on the Potomac River Basin, 2006).

Upon submergence during reservoir recovery, the decomposition of this vegetation potentially could have led to elevated 

concentrations of mercury methylation and biological uptake 

in the reservoirs and elevated concentrations of DBPs in drinking water (see Sedimentation—Sediment Diagenesis and 

Mobilization of Metals and Phosphorus and Disinfection 

By-Products, this report). In addition, the absence of large 

volumes of water in the reservoirs likely contributed to the elevated concentrations of sodium and chloride that occurred in 

reservoir supply intake waters in 1999 and 2003–04 (Maryland 

Department of the Environment, 2004a). The source of this 

sodium and chloride is likely from road-salt use associated 

with the major snowfalls produced by the nor’easters that 

occurred in December 1999, December 2003, and February 

2004 (see Sodium and Chloride, this report).

There also may have been no prolonged recovery as 

another moderate drought and recovery occurred in 2005–06. 

During this drought-recovery period, however, reservoir 

withdrawals initially were reduced by taking water from 

the Susquehanna River before major declines had occurred 

in reservoir water levels. However, the poor quality of this 

river water led to a decline in the quality of treated water, 

and its use was discontinued (see Reservoir Watershed 

Management and Reservoir Operations, this report). 

Fortunately, the drought was short-lived, with recovery in 

2006 being aided by Tropical Storm Ernesto (September 2006) 

and two back-to-back nor’easters in November 2006. 

During this review, no studies were encountered that 

specifically analyzed changes in reservoir watershed tributary, 

or reservoir biotic and water-quality conditions associated 

with major storms or drought-drawdown-recovery events in 

the Baltimore reservoir system during the past decade. Nor 

does the City firming program appear to have been reviewed 

to determine whether or not the extended withdrawals of the 

best available water affect the determination of subsequent 

reservoir water quality during recovery from drought 

conditions.
74 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

It is possible that reservoir water-supply systems such 

as the Baltimore reservoir system are particularly vulnerable 

to extended periods of dry weather followed by reservoir 

recovery aided by intense storms. During droughts there are 

increased demands for water supplies, particularly during 

extended dry periods that include the spring, summer, and 

early fall. Under the City firming program, initial drawdown 

of either supply reservoir is somewhat mitigated, but under 

extended dry periods with continuing demands, reservoir 

withdrawals eventually remove major quantities of the best 

quality water from one and progressively both water-supply 

reservoirs, with the remaining water possibly trending towards 

poorer quality. Continued withdrawals also ultimately produce 

major declines in reservoir volumes, and possibly in the quality of water that remains. Thus, recovery, even if temporary, 

occurs with increased tributary inflows, likely enriched in 

nutrients and sediment, into reservoirs with reduced dilution 

volume and buffering capabilities, creating conditions favorable for algal proliferation.

Documentation of the individual or combined effects of 

major storms and droughts, withdrawals, and recoveries on 

water quality in the reservoirs is lacking. The historical and 

current monitoring program appears to lack sufficient spatial 

and temporal resolution to accurately characterize intra-seasonal changes in reservoir biotic and water-quality conditions 

that likely result from these types of events (for example, see 

Modeling to Address Water-Quality Concerns, this report).

Climate Change

The last decade could be an indicator of the future effect 

of climate change on the Baltimore Reservoir system given 

that the forecasted regional effects of climate change are an 

increase in the frequency of moderate-to-severe droughts 

punctuated by an intense increase in storms. As of 2007, 

detailed analysis of long-term monitoring and modeling 

results provided by the Intergovernmental Panel on Climate 

Change (IPCC) predicts future increases in both precipitation 

and hydrologic extremes for the Mid-Atlantic region 

(Intergovernmental Panel on Climate Change, 2007). The 

IPCC has concluded that the frequency of drought conditions 

is likely to increase (66–90 percent probability) in the MidAtlantic region and that these conditions are very likely 

(90–99 percent probability) to be interspersed with periods of 

heavy precipitation—for example, due to tropical storms and 

nor’easters as described above. Assuming climate-change predictions are accurate, and depending upon the climate scenario 

adopted, recent studies indicate that Maryland could receive 

about 10 percent more precipitation in winter and spring 

(Maryland Department of the Environment, 2008). Because of 

warmer temperatures overall, however, it was noted that rainfall could be more intermittent, extreme events more likely, 

and drought durations of several weeks to months in duration 

could be common during what amounts to an extended and 

dry “summer” season.

The effects of these climate-related changes, combined 

with the accelerated conversion of land to human-dominated 

uses (Vitousek and others, 1997) could result in notable 

increases in contaminant loads to reservoir-tributary rivers 

and streams in the form of intense storm events. Kaushal 

and others (2010) documented the extent of this climate-land 

use interaction in the Chesapeake Bay watershed, where the 

extreme drought (1999–2002) and recovery (2003) ultimately 

led to near record freshwater inflows to the Bay. The result 

was an increased flux of nitrogen to the Bay that coincided 

with phytoplankton blooms, severe hypoxia, and elevated 

mortality of fish and other aquatic species (Acker and others, 

2005; Miller and others, 2006). Kaushal and others (2008; 

2010) concluded that nitrogen stored in tributary watersheds 

during the extended dry period was flushed into the waterways 

by the intense rainfall and runoff. They also found that agricultural, and in particular urban, areas had accelerated rates 

of nutrient transport and reduced retention capacities, to the 

extent that, even after a return to more typical streamflow conditions in 2004, the flux of nitrogen remained high.

Other studies have further highlighted the combined 

effects of development, and in particular, urbanization, and 

increased climate variability on water resources in the eastern 

United States. Langland and others (2007) provided evidence 

that sediment loads in the Potomac River near Washington, 

D.C. could be increasing in response to increased variability 

in streamflow since the 1970s. Wall and others (2008) showed 

that recent high-flow events in the Hudson River estuary 

produce elevated inputs of sediment over short time intervals. 

In addition to increased nutrients and sedimentation, drinkingwater supply reservoirs and rivers in the region could be especially vulnerable if climate change also results in increased 

snowfall. The latter would require increased applications of 

road deicing salts in urban and suburban areas, which could 

possibly increase pulses of sodium and chloride (Kaushal and 

others, 2008). 

Kaushal and others (2010) have indicated that increases 

in the frequency and magnitude of contaminant pulses will 

require major changes in existing water-quality monitoring 

programs, including the need for high-resolution, continuous 

and (or) high frequency monitoring and event sampling. 

Continuous monitoring of specific conductance, for example, 

is a relatively inexpensive surrogate for sodium and chloride 

measurements (Granato and Smith, 1999); and increased 

episodic or event sampling, although costly, is essential to 

quantifying the effects of intense precipitation on contaminant 

loading (Lindenmayer and Likens, 2009; Palmer and others, 

2008).

The monitoring requirements described above differ 

markedly from the trend in monitoring in the Baltimore 

Reservoirs and their contributing watersheds since the mid1990s and at least through 2007, which generally has emphasized monthly dry-weather tributary sampling and intermittent 

monthly to bimonthly reservoir monitoring. Major sediment 

and nutrient-laden stormflows generally are not adequately 
Integrated Framework for an Enhanced Water-Quality Monitoring Program 75

monitored. However, they can reach one of the Baltimore 

Reservoirs in a matter of hours (see Appendix A—Watershed 

Characterizations, this report). Their effect on reservoir 

hydrodynamic, water-quality, and biotic and conditions is not 

well understood. Their initial arrival and subsequent impact 

likely often go undetected because of the relatively low 

(monthly or bimonthly) frequency of monitoring in the reservoirs (see Modeling to Address Water-Quality Concerns, 

this report), which is further limited by the inability to access 

selected monitoring sites except by boat and weather permitting (see Current Perspective, this report).

Integrated Framework for an Enhanced 

Water-Quality Monitoring Program

The design and evaluation of an integrated framework for 

a comprehensive water-quality monitoring program begin with 

a clear definition of goals and objectives (Reinelt and others, 

1988). The goals guide the development of the entire monitoring-program process, including its design, implementation, 

and evaluation. Ideally, the data obtained effectively meet the 

monitoring objectives. An effective water-quality monitoring 

program typically provides answers to the following types of 

questions (Intergovernmental Task Force on Monitoring Water 

Quality, 1995): What is the condition of the source water? 

Where, how, and why are water-quality conditions changing 

over time? What problems are related to source-water quality? 

Where are these problems occurring, and what is causing 

them? Are programs to prevent or remediate problems working effectively? Are water-quality goals and standards being 

met?

Specific goals of the RWMA partners and objectives of 

the RTG incorporate these questions as follows:

a) To characterize the condition of the water supply with 

regard to contaminant occurrence, sources, causative 

agents, and potential threats.

b) To detect annual and long-term trends in water-quality 

and biotic conditions in the reservoirs and their contributing watershed tributaries.

c) To provide data, interpretations from analysis of the 

data, and (or) conceptual or simulation models to support development and verification of predictive tools 

for use in managing the watersheds, reservoirs, and 

water supply.

d) To demonstrate that restorative and protective actions 

actually result in reduction or elimination of contaminants or other adverse impairments to the water supply.

e) To demonstrate that RWMA goals and Federal [SDWA 

and CWA 303(d)] and State standards are being met 

in the watershed tributaries, the reservoirs, and the 

finished water supply.

On the basis of the preceding discussions on waterquality monitoring in both the watersheds and reservoirs, 

it is evident that the RTG has made considerable progress 

in achieving their monitoring objectives and enabling the 

RWMA partners to address their water-quality concerns. It 

also is evident that the RTG recognizes that to fully meet the 

RWMA goals and their objectives ultimately requires (a) the 

identification and implementation of restorative actions, and 

(b) that these restorative efforts in the reservoir watersheds 

could take years to reduce concentrations of nonpoint source 

contaminants (for example, sediment, nutrients, sodium, and 

chloride) in the tributaries and reservoirs to the point that their 

influence on watershed or reservoir water and biotic quality 

are no longer of concern. Furthermore, in the case of emerging water-quality concerns, such as DBPs, it is recognized 

that considerably more work needs to be done to identify the 

sources of organic carbon that lead to elevated DBP concentrations in finished waters in the City water-supply distribution 

system.

Along with these successes and pragmatic limitations 

in achieving RWMA goals and meeting RTG objectives, it is 

evident from the preceding discussions that the design of the 

monitoring program warrants modifications if continued progress is to be made. Possible improvements in the monitoring 

program can be described in relation to three broad areas: a) 

the monitoring design framework, b) the spatial and temporal 

resolution of water-quality assessments in the major tributaries 

and reservoirs, and c) the management and archival of data. 

The improvements in these three areas incorporate suggested modifications to the monitoring program that were 

described and warranted on the basis of previous studies, but 

appear to not have been adopted, and (or) reflect inadequacies 

identified as a result of this retrospective review (table 12). 

The first two tabulated modifications are broad in scope—to 

modify monitoring to provide improved temporal and spatial 

coverage of water quality and biotic conditions associated 

with intra-seasonal, seasonal, and annual variations in climate, 

streamflow, and reservoir hydrodynamics, and to develop 

a comprehensive QAPP. Adoption of these modifications 

could help improve the ability to describe, model, compare, 

and address water-quality and biotic conditions associated 

with every long-term, emerging, and (or) regulatory (TMDLrelated) water-quality concern. The remaining proposed 

modifications are narrow in scope, and focus on individual 

long-term and (or) emerging water-quality concerns (table 12). 

Adoption of one of these concern-specific modifications without the adoption of the two initial broad modifications could 

limit improvements in the ability to address that water-quality 

concern. Also, no attempt was made to prioritize one concernspecific modification over another as this would require a 

prioritization of RTG objectives and RWMA water-quality 

concerns, which is beyond the scope of this report.
76 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Monitoring Program Data Requirements 

and Data Quality: To improve ability 

to readily and adequately understand 

the quality of the archived monitoring 

data and their suitability for interpretive 

purposes, and ability to readily understand the monitoring program design 

and data-quality requirements, which are 

both necessary in order to review, modify, 

or execute any major aspect of program.

Current and sufficiently detailed descriptions of the data-quality requirements, 

quality-control and assurance procedures 

and data, and state of documentation of data 

in the long-term monitoring database were 

found to be inadequate. Long-standing dataquality issues do not appear to have been 

adequately addressed. 

Framework: Develop a description of the monitoring program with specific quality-assurance and 

control plan that includes descriptions of the station networks, methods of data and sample collection, sample analyses, data-quality evaluation and 

verification, and data archival. Populate archival 

database using data with appropriate qualifying remarks and significant figures and related qualitycontrol data.

Review and Evaluation: 

Quality of the Monitoring Database and the Data Collected
Integrated Framework for an Enhanced Water-Quality Monitoring Program 77

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

General: To improve capability to assess 

effects of episodic or intra-seasonal 

climatic variations on watershed and 

reservoir hydrodynamics and associated 

water-quality and biotic conditions.

Episodic-event and intra-seasonal pulses of 

contaminants appear to have an influence on 

most water-quality issues of concern, and 

will likely become increasingly important to 

consider given recent climate variability and 

forecasts for climate change. Addressing 

these limitations also will address most of 

the limitations in monitoring related to (a) 

describing and relating tributary water-quality and biotic conditions to watershed landuse activities, and management of those 

activities to reduce pollutant loads, and (b) 

relating tributary water-quality conditions to 

reservoir water-quality and biotic conditions 

either directly or through improving the data 

necessary for modeling these relations.

Watershed Tributaries: Collect high-flow (storm) 

samples (5-15 per year) and monthly fixedtime interval low-flow samples (12 per year) 

for water-quality and biotic conditions at seven 

continuous-discharge tributary monitoring sites 

in the reservoir watersheds; collect similar 

samples monthly (fixed-time interval, variable 

flow) at eight additional partial-discharge-record 

monitoring stations in the reservoir watersheds. 

Collect continuous depth-profile measurements 

for selected parameters at each monitoring site at 

onset of sampling.

Reservoirs: Collect bimonthly fixed-time intervals 

and thermocline-dependent fixed-depth intervals 

samples for water-quality and biota at eight stations in three reservoirs during reservoir stratification; collect similar samples monthly (fixed-time 

interval) at these same stations during reservoir 

turnover. Collect continuous depth-profile data for 

selected water-quality and biotic parameters at six 

of the eight stations in the three reservoirs. 

Hydrodynamics: Obtain (a) continuous stream-discharge measurements for monitoring stations that 

include storm sampling; (b) partial-record streamdischarge measurements for monitoring stations 

that do not include storm sampling; (c) daily water 

levels, and volume of withdrawals, and, when applicable, releases, from each reservoir. Obtain the 

daily total amount and type of precipitation.

Review and Evaluation: 

Modeling to Address WaterQuality Concerns and Monitoring to Address Individual 

Water-Quality Concerns, all 

concerns
78 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Eutrophication: To improve ability to 

quantitatively describe eutrophication 

in relation to mesotrophic and eutrophic 

phytoplankton conditions and waterquality (nutrient) and hydrodynamic 

(stratification) processes that affect 

phytoplankton production. Limited ability 

to relate short-term or long-term changes 

in phytoplankton taxa or abundance to reservoir water-quality conditions antecedent to 

their occurrence. Levels of available phosphorus and (or) nitrogen in the reservoir that 

lead to excessive algal blooms, or specific 

types of taxa blooms are unknown. Most 

of the annual load in available nutrients is 

transported during stormflows, which are insufficiently monitored to provide reasonably 

accurate estimates of storm loads. Whether 

or not there are in-lake sources of available 

nutrients promoting phytoplankton production has not been adequately assessed. Algal 

taxa and counts that occur in the winter and 

early spring are not adequately characterized, especially in Prettyboy Reservoir. Data 

limitations prevent accurate (a) comparisons 

among subbasins on basis of total yields, 

(b) estimation of tributary nutrient loads, (c) 

estimation of the available nutrients in the 

reservoirs and their influence on phytoplankton production, and (d) adequate characterization of reservoir hydrodynamics. All 

of the above also limit the ability to model 

the influence of tributary nutrient loads 

and possible in-lake sources on reservoir 

phytoplankton production, and the ability 

to identify what levels of available nutrients 

lead to excessive algal blooms. Sampling 

and data collection during stratification in 

actual epilimnetic layer possibly limited to 

only two depths. Insufficient monitoring 

frequency for chl-a and DO to address phosphorus TMDL endpoints for Loch Raven 

and Prettyboy Reservoirs. 

Framework: Consider adoption of a broad descriptive model for seasonal phytoplankton production 

(taxa and abundance); evaluate model on the basis 

of monitoring data; define and describe stratification (epilimnion, metalimnion, and hypolimnion) 

on the basis of actual thermocline; describe mesotrophic and eutrophic conditions for each reservoir 

(a) on the basis of trophic indices determined for 

actual epilimnion and hypolimnion, (b) in relation 

to spatial differences within the reservoir, and (c) 

temporally—seasonally and as long-term trends; 

utilize watershed reservoir model to link nutrient 

loads from tributaries to reservoir trophic conditions.

Watersheds: Collect nutrient (total, total dissolved, 

and dissolved phosphorus; total Kjeldahl, nitrate 

(plus nitrite), and ammonium nitrogen) samples 

during all sampling at seven continuous-discharge 

tributary monitoring sites in the three reservoir 

watersheds; collect similar samples and data during monthly sampling at all eight partial-record 

stations in the three reservoir watersheds. Obtain 

continuous depth-profile measurements for water 

temperature, DO, specific conductance, pH, chl-a, 

and turbidity during each sampling event at every 

station. Collect similar samples and data for all 

reservoir releases.

Reservoirs: Collect nutrient (see Watersheds, above) 

and chemical oxygen demand samples during 

depth-profile sampling at all eight stations in three 

reservoirs; obtain continuous (daily) depth profile 

measurements for water temperature, DO (diurnal, 

during stratification), specific conductance, pH, 

chl-a, turbidity, and transparency at six of eight 

reservoir stations; obtain intermittent depth-profile 

measurements for these same parameters during 

sampling at remaining two reservoir stations. Sampling in actual epilimnetic layer should include 

three depths. Collect manganese and iron samples 

during collection of hypolimnetic samples at all 

eight stations. 

Review and Evaluation: Modeling to Address Water-Quality 

Concerns and Monitoring to 

Address Individual WaterQuality Concerns, Long-Term 

Concerns, Eutrophication
Integrated Framework for an Enhanced Water-Quality Monitoring Program 79

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Sedimentation: To improve ability to quantify sediment transport in the watershed 

tributaries and its influence on reservoir 

water quality and storage capacity. From 

the mid-1980s to mid-1990s, 90 percent or 

more of the annual sediment load from six 

major subbasins was transported in storms. 

There has been a lack of adequate tributary 

storm data for suspended sediment in supply 

reservoir watersheds since 1995, and possibly to date. Lack of data limits (a) comparisons of reservoir subbasins as source or 

restored areas, and (b) estimation of annual 

loads, either directly or model-aided for 

all tributaries, and (c) determination of the 

effects of suspended sediment on reservoir 

water-quality and biotic conditions. Model 

simulations also are needed to help establish 

TMDLs for Liberty Reservoir and indicate compliance with existing TMDLs for 

sediment loads to Loch Raven Reservoir. 

No storm sampling has been conducted on 

any major tributary to Prettyboy Reservoir. 

Increases in turbidity at Prettyboy Reservoir 

indicate that establishment of a sediment 

TMDL could eventually be necessary.

Framework: Upgrade at least one tributary monitoring station on Prettyboy Reservoir watershed to 

act as a continuous-discharge monitoring site.

Watersheds: Conduct suspended-sediment and 

turbidity-depth profiles during all sampling at 

seven continuous-discharge tributary monitoring 

sites in the three reservoir watersheds; collect 

similar samples and data during monthly sampling 

at eight partial-record stations in the three reservoir watersheds.

Reservoirs: Conduct suspended-sediment sampling 

during all sampling at eight reservoir stations; 

obtain continuous (daily) profile monitoring 

for turbidity at six of these eight stations, and 

intermittent profile monitoring for turbidity during 

sampling at remaining two reservoir stations.

Review and Evaluation: Modeling to Address Water-Quality 

Concerns and Monitoring to 

Address Individual WaterQuality Concerns, Long-Term 

Concerns, Sedimentation
80 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Mercury in Higher Trophic Order Game 

Fish: To improve understanding of internal reservoir biotic and hydrodynamic 

processes that contribute to mercury 

methylation and biotic uptake. Sources of 

mercury for reservoirs were shown to likely 

be predominantly atmospheric and from 

regional sources beyond reservoir watershed 

boundaries. Enhanced mercury methylation 

and biological uptake, however, could 

occur during reservoir recovery following 

severe drought and reservoir drawdown in 

reservoir areas where terrestrial vegetation 

became established on exposed lake bed 

sediments. Current monitoring is insufficient to determine whether or not this 

occurs. Current lack of understanding of 

the factors that affect mercury methylation 

and biological uptake in Maryland lakes and 

reservoirs makes it difficult to determine 

without adequate monitoring whether or 

not enhanced methylation and uptake of 

mercury occurs during recovery in the Baltimore reservoirs.

Framework: Routinely sampling young of year 

trophic game fish in reservoir areas where bed 

sediments likely will become exposed and covered 

by terrestrial vegetation is necessary to provide a 

baseline before drought occurs. Given that drought 

conditions lead to the establishment of terrestrial 

vegetation, resampling during the year of recovery 

and year thereafter would provide the data needed 

to determine whether these conditions lead to enhanced mercury methylation and biological uptake 

in trophic game fish.

Review and Evaluation: Monitoring to Address Individual 

Water-Quality Concerns, 

Long-Term Concerns, Sedimentation, Sediment Diagenesis, and Mobilization of Metals 

and Phosphorus
Integrated Framework for an Enhanced Water-Quality Monitoring Program 81

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Disinfection By-Products (DBPs): To 

improve capability to identify sources of 

carbon that form DBPs. DBPs do not appear 

in raw water. Reducing the amount of TOC 

in raw intake waters at treatment plants 

by approximately one-third is insufficient 

in the prevention of DBP formation after 

chlorination in the distribution system at 

selected stations at concentrations that likely 

will exceed pending Federal drinking-water 

standards, particularly for total trihalomethanes. Current monitoring of only TOC 

appears insufficient to show that elevated 

levels of carbon that form DBPs are present. 

Sampling of TOC routinely has not been 

conducted on raw-intake water that subsequently is treated and then sampled for TOC 

and ultimately for TOC and DBPs in the 

distribution system. 

Framework: The amount and type (brominated or 

chlorinated) of trihalomethanes formed is highly 

dependent on variations in (a) the types and levels 

of carbon that form DBPs, which may or may 

not be reflected by similar variations in the level 

of TOC, and (b) the treatment process, including 

the levels of initial chlorination, whether or not 

any DBPs that form during initial chlorination are 

reduced by coagulation and filtration, and whether 

or not finished water is initially stored, the length 

of time it is stored, and the manner of storage, 

whether or not stored water is re-chlorinated before it is placed in the distribution system, and the 

length of residence or traveltime the finished water 

travels in the distribution system. Minimally, sampling for TOC in raw water, sampling for TOC in 

treated water, and sampling for TOC and DBPs in 

the distribution system all must involve generally 

the same water if the use of TOC as a surrogate for 

DBP forming carbon, and, in particular trihalomethanes, is to be evaluated. Indirect evidence 

presented in this report indicates that possible 

sources of carbon that form trihalomethanes could 

routinely include phytoplankton (residues) in the 

reservoirs. An additional source of carbon could be 

terrestrial vegetation that grows on reservoir bed 

sediments exposed by excessive drawdowns during severe droughts that is then submerged during 

reservoir recovery.

Review and Evaluation: Monitoring to Address Individual 

Water-Quality Concerns, 

Emerging Concerns, Disinfection By-Products
82 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Table 12. Possible improvements identified in scientific or technical investigations that address one or more water-quality concerns 

of the Baltimore Reservoir Watershed Protection Program and required data from the long-term monitoring program.—Continued

[TMDL, total maximum daily load; chl-a, chlorophyll-a; DO, dissolved oxygen; TOC, total organic carbon]

Focus area(s) identified 

for improvements

Modification(s) to monitoring 

program framework

Report subsection(s) that further 

describe limitations addressed by 

modifications

Sodium and Chloride: To improve ability 

to characterize and track changes and 

trends in sodium and chloride concentrations in watershed tributaries and 

reservoir waters. Historical data released 

from the monitoring study to date have not 

clearly defined the strength of correlations 

among conductance and the concentrations 

of chloride and sodium. Presumably this 

could be done for historical conditions. To 

determine the current strength of these correlations, however, monitoring data could 

be obtained for all three of these parameters 

as part of a monitoring program designed 

for that purpose. Current monitoring design 

is inadequate to provide early warning to 

water purveyors of the potential rise in 

sodium, and also inadequate to rapidly 

determine changes in sodium and chloride 

if management activities are introduced to 

reduce sodium chloride use as a deicing 

agent. If road deicing is no longer done with 

sodium chloride salt over the long term, 

there remains the larger question of whether 

sodium, chloride, or both will still continue 

to rise. Long-term data on chloride indicate 

it has steadily risen in concentration since 

the 1930s. 

Framework: Select subbasin in each supply 

reservoir thought to contain smaller subbasins 

with high use of sodium-chloride salt as a deicing 

agent. Conduct baseline data collection for several 

years in smaller subbasin, at major subbasin, and 

in supply reservoirs at station closest to subbasin 

tributary. Implement management procedures to 

reduce salt use in smaller subbasins and continue 

monitoring to determine effect of reduced salt use. 

Ideally, subbasins selected lead to tributary inflows 

near reservoir station with continuous depthprofile monitoring.

Watersheds: Collect sodium, chloride, and conductance samples as part of routine winter (November 

through March) monitoring in smaller and larger 

subbasin.

Reservoirs: Collect sodium and chloride samples as 

part of all winter sampling conducted at reservoir 

station closest to tributary subbasin inflows. 

Include conductance in continuous depth-profile 

monitoring, or intermittent depth-profile monitoring, depending on reservoir station chosen. 

Review and Evaluation: Monitoring to Address Individual 

Water-Quality Concerns, 

Sodium and Chloride
Integrated Framework for an Enhanced Water-Quality Monitoring Program 83

Modified Monitoring Framework 

On the basis of this review, major modifications to the 

monitoring framework design for the Baltimore Reservoirs 

that could be considered to improve the ability of the RTG to 

address the water-quality concerns of the RWMA partners are 

as follows:

a) The adoption of a formal phytoplankton model for the 

reservoirs, such as the Plankton Ecology Group (PEG) 

model (Appendix D), which could be used to quantitatively describe intra-seasonal changes in taxa, their 

abundance, and succession in relation to variations in 

nutrient availability;

b) The collection of PEG-model compatible (total and 

available) nutrient (phosphorus and nitrogen) data in 

the reservoirs and watershed tributaries. These data 

could be used to improve load estimates, modeling of 

tributary loads and reservoir nutrient recycling, and 

relate changes in nutrient concentrations, loads, or 

ratios to temporal changes in phytoplankton production 

as described by the PEG model; 

c) The collection of the appropriate hydrologic data to 

link hydrodynamic processes with water-quality, abiotic, and biotic processes. Collection of these hydrodynamic data would meet recommendations from modeling studies that indicated these data are necessary 

to accurately model, and to verify modeled reservoir 

watershed runoff, tributary flows, and reservoir hydrodynamics over the full flow regime of each watershed 

major subbasin tributary, and reservoir hydrodynamic 

response to releases or withdrawals and tributary flow 

regime, and

d) The use of statistical and modeling methods, in 

addition to graphical analysis, to provide scientifically defensible support to descriptions of changes in 

state, trends, or relations among watershed, tributary, 

and reservoir characteristics that involve the use of 

monitoring data given that the results of these analyses 

are used to promote action strategies that affect human 

activities in the reservoir watersheds. 

A long-standing water-quality concern of the RWMA 

partners and therefore, area of investigation for the RTG, is 

reservoir eutrophication accompanied by major algal blooms. 

To address this issue directly, consideration could be given to 

the adoption of a formal model for phytoplankton production 

in the reservoirs. Such a model could provide a framework to 

not only describe taxa and their abundance, but intra-seasonal, 

seasonal, year to year, and multi-year changes in phytoplankton production and succession, and help to distinguish mesotrophic conditions from eutrophic conditions with excessive 

algal blooms in relation to variations in nutrient (phosphorus 

and nitrogen) availability. The PEG Model (Appendix D) by 

Sommer and others (1986) describes patterns in phytoplankton 

succession that are similar to those described earlier in this 

report (see Eutrophication, this report). In addition, the PEG 

model takes into account that succession often is governed by 

variations in nitrogen, as well as phosphorus, availability, and 

other biotic processes. 

Although the PEG model (or a similar phytoplankton 

model) could provide a useful reservoir framework for the 

Baltimore Reservoirs, the benefits from the use of this model 

described above require the collection of comparable and 

compatible nutrient data that can quantify either the total or 

available concentrations of nutrients in the reservoir-watershed 

tributaries and reservoirs. The comparable and compatible 

data include total Kjeldhal or organic nitrogen, in addition to 

available ammonia- and nitrate-plus-nitrite-nitrogen, and bioavailable phosphorus [DOP and (or) TDP] in addition to TP. 

Collection of these data also would enhance modeling capabilities to link water-quality conditions in the reservoir watershed tributaries to water quality and phytoplankton production 

and succession in the reservoirs (Interstate Commission on the 

Potomac River Basin, 2006). 

Data obtained on variations in the concentrations and 

ratios of either total N to total P (or available forms of N to 

available forms of P) could be used to help explain observed 

PEG patterns in the seasonal succession of phytoplankton and 

(or) major bloom occurrence and dominance of selected taxa 

among phytoplankton communities in each of the reservoirs. 

This approach has proven to be useful as a diagnostic and 

management tool (Rast and Lee, 1978; Ryding and Rast, 1989; 

Levich, 1996; Bulgakov and Levich, 1999; Tõnno, 1999; 

Downing and others, 2001). 

In addition, the above studies are highly relevant to concerns raised by the RTG that phosphorus is the limiting nutrient, and blue-green algal blooms create the greatest problems 

in the treatment of reservoir water and nuisance problems in 

treated water. For example, Rast and Lee (1978) and Ryding 

and Rast (1989) pointed out that the limiting nutrient can 

best be determined by measurements of available phosphorus 

(for example, DOP and (or) TDP) and nitrogen (for example, 

ammonia- plus nitrate plus nitrite nitrogen) during the period 

of maximum algal biomass. This has never been done in the 

Baltimore Reservoirs. Downing and others (2001) found 

that blue-green algal bloom abundance in 99 lakes correlated 

more strongly with variations in nitrogen and phosphorus, and 

standing algal biomass, than the simple single ratio of total N 

to total P. They also found that high standing algal biomass 

correlates with a high likelihood of blue-green algal dominance. The variations in available nutrients and in standing 

algal biomass with blue-green algal bloom occurrence have 

never been directly investigated for the Baltimore Reservoirs.

The collection of comparable types of nutrient data without the relevant and related hydrologic data could severely 

limit the use of the nutrient data. On the basis of reviews 

conducted on modeling studies (see Modeling to Address 

Water-Quality Concerns, this report), the availability of 

nitrogen in its various forms is governed by reservoir stratification. Available phosphorus also could be governed by 
84 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

reservoir stratification. Hence, the routine determinations of 

the thicknesses of the epilimnion, metalimnion, and hypolimnion are needed to accurately characterize nutrient availability 

for phytoplankton production. Reservoir water temperature is 

among the most influential and measureable factors that affect 

stratification. The elevation of reservoir water levels is among 

the most influential and measureable factors influencing reservoir temperature. Precipitation, tributary inflows, water withdrawals, and reservoir releases are among the most influential 

factors governing reservoir water levels. Thus, collection of all 

of the above climate and hydrologic data on a daily-to-weekly 

basis generally is considered a standard requirement to obtain 

the data necessary for reasonably accurate two-dimensional 

model simulations of the hydrodynamics and water-quality 

conditions of Mid-Atlantic Coast lakes and reservoirs using 

U.S. Army Corps of Engineers CE-QUAL-W2 (Giorgino and 

Bales, 1997; Bales and Giorgino, 1998; Sarver and Steiner, 

1998; Bales and others, 2001; Galloway and Green, 2004, 

2006 a,b). 

For the RTG to be able to fully address RWMA concerns, 

it is equally important that the collection of biotic and waterquality data within each of the major reservoir watershed tributaries adequately reflect the range in tributary flows within 

a year and from year to year. This coverage could become 

increasingly critical in the future. Changes in climate and 

climatic variability (see Effects of Climate, this report) imply 

longer warmer and drier periods, punctuated by more intense 

storms. These changes combined with an ever-increasing population, and thus demand for water, could lead to reservoirs 

that are frequently drawn down to low levels, with recovery 

waters being of poor quality. This type of tributary flow coverage clearly has been a challenge for the Baltimore Reservoir 

monitoring program. Nevertheless, most of the water-quality 

concerns of the RWMA can be linked to excessive nutrient, 

sediment, salt, and other loads from the watershed tributaries. 

Without the ability to accurately assess the onsite effectiveness 

of BMPs to reduce loads, the most reliable means to assess 

whether these practices are effective is to measure downstream 

loads. On the basis of this review, the bulk of the annual loads 

to the Baltimore Reservoirs are transported during storm- or 

high flows. 

Water-quality conditions associated with high flows 

have not been adequately covered by the Baltimore Reservoir 

monitoring program. To illustrate, sampling of stormflow in 

the Baltimore Reservoir watershed tributaries is generally 

conducted with automated samplers, or manually if necessary. Storm sampling involves the collection of water-quality 

samples at a gaged tributary within a single day. To assess 

the adequacy of this type of sampling, stream discharge 

from 2001–06 was summarized for each of the three major 

gaged tributary subbasins in each water supply reservoir. The 

summary, which includes the drought-recovery period from 

2001–04, describes the proportion of each year in percent or 

number of days represented by the 75th percentile or higher 

streamflows (or generally the annual streamflow that reflects 

high flows), hereafter, referred to as high-flow days (fig. 32). 

For example, for the period of record, and depending on the 

year, 25 percent of the annual flow at Morgan Run tributary in 

Liberty Reservoir watershed occurred during 4–11 percent (or 

15 to 40 high-flow days) of the year. Monitoring records, however, indicate that for this entire period (4 years), water-quality 

data were only collected for seven storms, or approximately 

7 high-flow days (table 7). In particular, during the driest 

year (2002), there were from 22–46 high flow days in 2002, 

depending on the tributary (fig. 32). Only one storm (1 highflow day), however, was monitored at the three stormflow stations in Loch Raven Reservoir watershed, and no storms were 

monitored at the three stormflow stations in Liberty Reservoir 

watershed. However, monthly monitoring of dry-weather 

flows at all stations in 2002 could have included additional 

high-flow days because it was a very dry year. A different 

picture of high-flow coverage emerged during the wettest year 

of record (2004). There were from 14–36 days of very high 

flow, depending on the tributary (fig. 32). Only three storms 

(3 high-flow days) were monitored, however, at the stations in 

Loch Raven Reservoir watershed, and only one storm 

(1 high-flow day) was monitored at the three stations in 

Liberty Reservoir watershed. It is unlikely that monthly dryweather flow monitoring included any additional high-flow 

days given the magnitude of high flows. Even if five storms 

(5 high-flow days) had been monitored during 2004 at each 

tributary station, it is unlikely that the full range in high-flow 

conditions was adequately represented at all six stations.

Adequate coverage of high flows within a year generally 

implies sampling is needed throughout the year and that consideration is given to the types, not just the number, of storms 

that occur. Typical storms that can occur over the Baltimore 

Reservoir watersheds are thunderstorms, nor’easters, and 

tropical storms (Mogil and Seaman, 2009). The origin and 

nature of these storms differ markedly in their spatial extent, 

duration, and the intensity and amount of precipitation, which 

can lead to marked differences in runoff response. They also 

are likely to occur at different times of the year. 

To adequately reflect water-quality conditions associated 

with high and low flows, or the flow regime, within a given 

year, it is proposed that monitoring be conducted for both 

types of flows at sufficient frequency throughout the year at 

selected tributary stations in each reservoir watershed. It also 

is proposed that monitoring at the remaining traditional dryweather flow stations continue to be conducted on a monthly 

fixed-time interval, regardless of flow condition. Details 

are provided below (see Enhanced Spatial and Temporal 

Resolution of Water-Quality Assessments, this report).

Sampling to adequately reflect the full range in flows 

within a given year, and from year to year, could markedly 

improve load estimates. It also could enhance the ability of the 

RTG to detect annual, seasonal, and discharge-related components in the water-quality and biotic variables of primary 

interest to the RTG. For example, Hirsch and others (2010) 

recently simultaneously identified long-term increasing or 

decreasing trends, seasonal variations, and major flow-related 

changes in biotic and water-quality conditions in nine large 
Integrated Framework for an Enhanced Water-Quality Monitoring Program 85

[ft3/s, cubic feet per second]

Morgan Run 

near 

Louisville, 

Md.

Annual streamflow characteristics

Water year

Mean 

daily 

flow

(ft3/s)

Coefficient of 

variation

(percent)

Total of 

mean 

daily 

flows

(ft3/s)

Annual high-flow 

(75th-percentile flow or greater) 

characteristics 

2001 20 85 7,315 25 percent of annual streamflow occurred in just 31 high-flow 

(39 ft3/s or higher) days, or during less than 10 percent of the year

2002 10 69 3,506 25 percent of annual streamflow occurred in just 39 high-flow 

(15 ft3/s or higher) days, or during less than 11 percent of the year

2003 50 113 18,417 25 percent of annual streamflow occurred in just 22 high-flow 

(109 ft3/s or higher) days, or during less than 6 percent of the year

2004 54 162 19,859 25 percent of annual streamflow occurred in just 15 high-flow 

(146 ft3/s or higher) days, or during less than 4 percent of the year

2005 34 128 12,589 25 percent of annual streamflow occurred in just 18 high-flow 

(84 ft3/s or higher) days, or during less than 5 percent of the year

2006 34 116 11,335 25 percent of annual streamflow occurred in just 24 high-flow 

(60 ft3/s or higher) days, or during less than 7 percent of the year

Reservoir/ 

watershed

U.S. Geological Survey 

streamgage1

Selected streamflow characteristics for dry (2002) and wet (2004) water years

Annual streamflow characteristics

(ft3/s)

Number of days with high 

flows (75th-percentile flow 

or greater) (ft3/s)

Percentage of year with 

high flows (75th-percentile flow or greater)

Mean 

daily 

flow 

(2002)

Mean 

daily 

flow 

(2004)

Total of 

mean 

daily 

flows 

(2002)

Total of 

mean 

daily 

flows 

(2004)

2002 2004 2002 2004

Liberty 

Reservoir

Beaver Run near Finksburg, Md.

5 25 1,971 9,038 31 (33 ft3/s 

or higher) 

25 (208 ft3/s 

or higher)

9 7

Morgan Run near Louisville, Md.

10 54 3,506 19,859 39 (15 ft3/s 

or higher)

15 (146 ft3/s 

or higher)

11 4

North Branch Patapsco River at Cedarhurst, Md.

20 104 7,359 38,043 31 (33 ft3/s 

or higher) 

25 (208 ft3/s 

or higher)

9 7

Loch Raven 

Reservoir

Beaverdam Run at Cockeysville, Md.

13 42 4,567 15,507 20 (32 ft3/s 

or higher)

14 (146 ft3/s 

or higher)

5 4

Western Run at Western Run, Md.

20 103 7,427 37,515 46 (30 ft3/s 

or higher)

30 (175 ft3/s 

or higher)

12 8

Little Falls at Blue Mount, Md.

23 123 8,495 44,800 39 (34 ft3/s 

or higher)

31 (187 ft3/s 

or higher)

10 9

Gunpowder Falls at Glencoe Road, Md.2

91 343 33,381 125,301 44 (152 ft3/s 

or higher)

36 (564 ft3/s 

or higher)

12 10

1 Streamgage names can differ from monitoring station names because of small differences in location.2 Flows in 2002 notably reflect releases from Prettyboy Reservoir to resupply Loch Raven Reservoir.

Figure 32. Cumulative annual distribution of streamflow and time with selected high-flow (75th percentile or greater) statistics for six streamgages associated with monitoring stations in Liberty and Loch Raven Reservoir watersheds from 2001–06, including driest (2002) and wettest (2004) years [Data from U.S. Geological Survey Maryland-DelawareD.C. Water Science Center].
86 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

tributaries in the Chesapeake Bay using weighted regression 

analysis. Their work focused on many of the same water-quality parameters monitored in the Baltimore Reservoir system 

over approximately the same time period (1978–2008).

The work by Hirsch and others (2010) also illustrates the 

last major modification proposed for the design framework. 

The use of statistical analysis to characterize and compare 

changes in states, assess trends, describe seasonal variations, 

and (or) other relations among watershed, tributary, and 

reservoir characteristics could improve the RTG’s ability and 

efficiency in understanding, identifying, and (or) managing 

the reservoir watersheds in relation to the RWMA concerns. 

Examples were presented in earlier sections of this report in 

which conclusions related to the above likely were drawn 

solely on the basis of appearance (graphical analyses) and not 

statistically verified. In selected cases, the lack of thorough 

statistical analyses early on led to the subsequent expenditure 

of considerable resources by contracted studies that possibly 

could have been avoided (for example, see Eutrophication—

Nutrients: Phosphorus Transport and Reservoir Recycling, 

this report.) Additional examples that illustrate statistical 

analyses can be a useful tool to the RTG were also presented, 

including the following:

a) That there were significant declines in the concentrations of ammonia nitrogen at most tributary and 

reservoir stations throughout the 1980s–90s (see 

Eutrophication—Nutrients: Nitrogen Transport 

and Reservoir Cycling, this report), which indicates 

management activities to reduce the transport of 

nutrients, at least for this form of available nitrogen, do 

appear to be working; 

b) That the lack of significant trends in TP at most 

tributary and reservoir stations likely reflected a step 

change and data outliers (see Eutrophication—Nutrients: Phosphorus Transport and Reservoir Cycling, 

this report), which indicated the need for improved 

documentation of changes in methods and archival of 

data, and

c) That the recent increases in sodium and chloride can be 

correlated with high road density in selected developed 

areas, and likely reflects the use of sodium-chloride 

salt as a deicing agent (see Sodium and Chloride, this 

report), which clearly helped the RTG identify a source 

that possibly could be managed to reduce sodium and 

chloride in drinking water.

In considering the proposed modifications, it also became 

apparent during this review that it could take considerable 

time, even with improvements in monitoring, before notable 

reductions in the frequency of eutrophic conditions and (or) 

major algal blooms can be statistically documented. For 

decades, elevated and varying concentrations of nutrients have 

entered the reservoirs through tributary inflows. This has led 

to the development of a fairly robust, diverse, and abundant 

phytoplankton community in the reservoirs, to the extent that 

different algal taxa dominate in different years (see Modeling 

to Address Water-Quality Concerns, this report). Padisák 

(2004) noted that algal abundance and diversity provides for 

community resiliency; namely, a large standing and taxonomically diverse phytoplankton population has a finite but potentially large capability to absorb declines in levels of external 

resources, such as nutrients, without undergoing a substantial 

reduction in biomass.

Given that appreciable reductions in the frequency of 

eutrophic conditions and major algal blooms could take time, 

it is important that the monitoring program consider the above 

modifications to provide the type and quality of data most 

needed, and that the data be analyzed in a sound scientific 

manner. In the interim, adoption of the above modifications 

combined with improved statistical methods and models could 

enable the RTG to provide interim indications that management strategies are improving water-quality conditions in 

the tributary watersheds and water-quality and biotic conditions in the reservoirs. In addition, the information generated 

could help the RTG develop improved RWMA action strategies to reduce nutrient loads associated with the full range 

in hydrodynamic processes related to possible changes in 

climate, rather than chiefly in relation to dry-weather flows. 

Collectively, the interim results also could possibly encourage 

reservoir watershed residents to adopt management strategies 

long before the full benefits of those strategies clearly can be 

seen in the reservoir watershed tributaries, or ultimately in the 

reservoirs.

Enhanced Spatial and Temporal Resolution of 

Water-Quality Assessments

Modifications to improve the spatial and temporal resolution of water-quality assessments in the major tributaries and 

reservoirs of the Baltimore reservoir system can be described 

by use of a framework (table 13) similar in form, but modified 

in content, from the framework used for the existing monitoring design (Appendix B). The proposed framework reflects 

modifications to the existing monitoring in the reservoir watersheds and reservoirs which could improve the RTGs ability to 

address all RWMA water-quality concerns. 

Watersheds

The proposed improvements to water-quality monitoring 

in the reservoir watersheds would utilize 15 of the tributary 

monitoring stations historically used in the monitoring network (table 13).4

 There would be six tributary stations in the 

4

 Sampling of National Pollution Discharge Elimination System Sites or 

ponds (wastewater treatment plants or other point sources), when discharging, would continue as before but include any new water-quality parameters 

described for the reservoir watershed tributaries.
Integrated Framework for an Enhanced Water-Quality Monitoring Program 87

Table 13. Modified monitoring network for reservoir watershed tributaries and reservoirs in the Baltimore, Maryland drinking-water 

supply system.1

[---, not applicable; TBD, to be determined]

Reservoir/

watershed Station location Tributary station name Station identifier2

Continuous 

profile 

monitoring

Fixed interval 

sampling3

Storm 

sampling4

Liberty Upper reservoir Liberty at Nicodemus/Deer Park Bridge NPA0105 X X ---

Middle reservoir Liberty at Oakland Road Point, near 

intake 

NPA0067 --- X ---

Lower reservoir Liberty at gatehouse or Route 26 bridge 

(TBD)2

NPA0042 or 

NPA0059

X X ---

Tributary Beaver Run at Hughes Road BEA0015 X X X

Tributary Morgan Run at London Bridge Road MOR0040 X X X

Tributary North Branch Patapsco River at 

Route 91

NPA0165 X X X

Tributary Middle Run at Louisville Road MDE0026 --- X ---

Tributary Little Morgan Run at Bartholow Road LMR0015 --- X ---

Tributary (Pond) Bonds Run at Hollingsworth Road UZP0002 X

Loch Raven Upper reservoir Loch Raven at Dulaney Valley Bridge or

power lines (TBD)2

GUN0174 or 

GUN0190

X X ---

Middle reservoir Loch Raven at Loch Raven Drive Bridge 

or between picnic and golf course areas

GUN0171 --- X ---

Lower reservoir Loch Raven at gatehouse GUN0142 X X ---

Tributary Beaver Dam Run at Beaver Run Lane BEV0050 X X X

Tributary Gunpowder Falls at Glencoe Road GUN0258 X X X

Tributary Western Run at Western Run Road WGP0050 X X X

Tributary Dulaney Valley Branch at Loch Raven 

Drive

DVB0000 --- X ---

Tributary Gunpowder Falls at Falls Road GUN0387 --- X ---

or Tributary Gunpowder Falls below Prettyboy Dam GUN0398 --- X ---

Tributary Little Falls at Blue Mount Road LIT0002 --- X ---

Prettyboy Middle reservoir Prettyboy at Beckleysville Road Bridge GUN0437 X X ---

Lower reservoir Prettyboy at gatehouse or 1,000 feet 

upstream of dam (TBD)2

GUN0399 or 

GUN401

X X ---

Tributary Georges Run at Georges Creek Road GOB0017 X, one 

station, 

TBD

X X, one 

station, 

TBD Tributary Graves Run at Gunpowder Road GRG0013 X

Tributary Gunpowder Falls at Gunpowder Road GUN0476 X

1

 Sampling also would be conducted at National Pollution Elimination Discharge Sites in each reservoir watershed if discharging, on a fixed interval 

(monthly) basis.

2

 For selected Liberty and Loch Raven Reservoir locations, the City of Baltimore and Baltimore and Carroll Counties, in consultation with the Reservoir 

Technical Group, need to determine which of the two stations would employ continuous profile monitoring. In a similar manner, the City and Counties would 

need to determine which tributary in Prettyboy Reservoir would have continuous monitoring and storm sampling.

3

 For reservoirs, bimonthly sampling during stratification, otherwise monthly. For tributaries with no storm sampling, conducted regardless of flow conditions. For tributaries with storm sampling, conducted at low-flow conditions.

4

 Conducted at high-flow conditions throughout the year, 5 to 15 samples per year.
88 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Liberty Reservoir watershed, six tributary stations in the Loch 

Raven Reservoir watershed, and three tributary stations in the 

Prettyboy Reservoir watershed. 

Sampling for high-flow conditions would be conducted at 

the three stations historically used for storm- and dry-weather 

flow sampling in each supply reservoir watershed, and in addition at one station in Prettyboy Reservoir watershed, which 

could be determined by the RTG. Upgrading one historical 

tributary station from dry-weather to full-flow monitoring 

in the Prettyboy Reservoir watershed is essential to address 

limitations noted in the attempts to describe water-quality 

and biotic changes in state, assess trends, estimate loads, or 

model tributary water quality (table 12). There simply are no 

long-term water-quality data for high flows on any Prettyboy 

Reservoir watershed tributary. 

The seven tributary-monitoring stations targeted for highflow sampling would be monitored for 5 to 15 storm events 

per station, selecting storms distributed throughout the year. 

Stormflow conditions at each station could be defined by the 

RTG on the basis of long-term existing streamflow records. 

Monthly fixed-time interval sampling also would be conducted 

during base flow at each of these seven stations. Base-flow 

conditions for each station could be defined by the RTG on 

the basis of historical flow records. In addition, continuous 

streamflow records would be maintained for these seven 

stations.

Monitoring at the remaining and historically dry-weatherflow stations in each reservoir watershed would be conducted 

on a monthly fixed-time interval, but regardless of flow 

conditions (table 13). Thus, monitoring at these stations over 

the course of each year would include base and high flows. In 

addition, partial streamflow records would be maintained for 

these stations.

To ensure results from stations within a given reservoir 

watershed are comparable, all stations within a given reservoir 

watershed that are sampled at high flows would be sampled 

for the same storm event. Minimally this would include all 

stations defined as storm-sampling stations in that reservoir 

watershed. It also could include additional stations sampled at 

monthly-fixed intervals depending on when the storm occurs 

during the month. 

Water-quality samples collected at each and all monitoring stations for every sampling event would reflect representative samples for suspended sediment, or constituents 

for which concentrations could depend in part on suspended 

sediment, such as TP, total carbon, and total Kjeldahl nitrogen. Representative samples would require the collection of 

a depth- and width-integrated sample, unless it can be demonstrated that a single vertical depth-integrated sample or 

automated-sampler point sample is representative of the flow 

(Wilde, 2006). The latter sample-collection methods can be 

used if it is determined by a comparison of methods that they 

can provide a reasonably representative sample for the above 

constituents across the general range in streamflows at a station. No information was encountered in any report to indicate 

that such a comparative study has been done or if done was 

ever repeated. Absent this information, any notable spatial 

bias in the quality of water flowing throughout the cross section could lead to a bias in the water-quality data collected 

from that cross section (Wilde, 2006). This bias could lead to 

misinterpretations when data from this monitoring station are 

compared to data from other monitoring stations, and could 

lead the RTGs to erroneous decisions, for example, in ranking 

subbasins for restorative action strategies.

To further help ensure that sample and data collection 

for every sampling event at each tributary monitoring station 

is representative, sampling at a station initially would include 

at least a mid-stream depth-profile (equidistant measurements 

throughout stream depth, minimum of three depths) for field 

measurements of water temperature, DO, conductance, pH, 

and turbidity using a portable multi-parameter water-quality 

monitoring system (table 13). These measurements could aid 

in the assessment of the uniformity of water-quality conditions throughout the depth of flow, and provide instantaneous 

values, for stream conditions associated with sampling. 

Representative water samples collected and analyzed for 

every sampling event at a station could include samples for 

concentrations of not only suspended sediment, but sodium 

(minimally late October through early March), chloride, total 

and dissolved organic carbon, total, total-dissolved, and dissolved phosphorus, and total Kjeldahl- or organic-, nitrate 

(plus nitrite)-, and ammonia-nitrogen (table 14). Monitoring 

for dissolved carbon, total-dissolved and dissolved phosphorus, and total Kjeldahl (or organic) nitrogen addresses inadequacies in monitoring of total and dissolved forms of all three 

nutrients, which are described in earlier discussions in this 

report (table 12). 

Monitoring of sodium in addition to chloride could be 

limited to winter months. Monitoring for sodium also could 

be limited if need be to selected subbasins within one supply 

reservoir watershed to establish baseline conditions before 

the implementation of any strategy designed to limit sodiumchloride use as road deicing agent. For example, one subbasin could be chosen and remain the control, and a second 

adjacent or nearby subbasin could be monitored for several 

years before and after being targeted for reductions in road 

salt use. Although strategies to reduce road-salt use could be 

implemented in all subbasins except for the control subbasin 

in this and the other two reservoir watersheds, the control and 

treated subbasins would provide the data needed to evaluate 

the rapidity and magnitude of change in sodium and chloride 

concentrations related to the reduction strategy. 

To help ensure the quality of data and samples obtained 

from a tributary station, water-quality monitoring instrumentation for depth-profile measurements would be calibrated and 

operated according to manufacturer specifications. In addition, 

selected quality-assurance (QA) samples would be collected 

during each of two monthly fixed-interval sampling events per 

year (table 13), and at a randomly selected tributary station for 

each monthly fixed interval. Similar QA samples also would 

be collected for one storm event per year at one randomly 

selected tributary station. The QA samples would consist 
Integrated Framework for an Enhanced Water-Quality Monitoring Program 89

Table 14. Modified data collection for hydrodynamic and water-quality constituents or characteristics at reservoir watershed tributary stations in the Baltimore, Maryland drinking-water supply system.[X, representative sample; ---, not collected; ft3/s, cubic feet per second; °C, degrees Celsius; mg/L, milligrams per liter; μmhos/cm, micromhos per centimeter; TBD, to be determined (dependent upon sensor type)]

Hydrodynamic or water-quality 

constituent or characteristic

Sampling frequency1

March April May June July August September October November December January February

Data collected at a tributary station during intermittent or storm sampling

Streamflow, ft3/s

X

X

X

X

X

X

X

X

X

X

X

X

Temperature, air, °C

X

X

X

X

X

X

X

X

X

X

X

X

Temperature, water, °C

X

X

X

X

X

X

X

X

X

X

X

X

Dissolved oxygen, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Specific conductance, μmhos/cm

X

X

X

X

X

X

X

X

X

X

X

X

pH, standard units

X

X

X

X

X

X

X

X

X

X

X

X

Turbidity, TBD

X

X

X

X

X

X

X

X

X

X

X

X

Samples collected at a tributary station during intermittent or storm sampling2

Suspended sediment, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Chloride, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Sodium, mg/L

X -- -- -- -- -- -- --

X

X

X

X

Total organic carbon, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Dissolved organic carbon, mg/LTotal phosphorus, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Total dissolved phosphorus, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Dissolved phosphorus, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Total organic or Kjeldahl nitrogen, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Nitrate-nitrogen, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Ammonia nitrogen, mg/L

X

X

X

X

X

X

X

X

X

X

X

X

Quality-assurance samples obtained during intermittent sampling3 -- ..........X.......... -- -- -- -- ...............X............... -- --Quality-assurance samples obtained during storm 

sampling for storm during designated period4 

--- --- --- --- ....................X.................... --- --- --- --- ---

1 Data and samples collected at National Pollution Discharge Elimination System sites and during supply reservoir releases and should include data and samples listed here.2 Storm sampling would be conducted for up to 12 (monthly) storm events per year at stations on three selected tributaries in Loch Raven Reservoir watershed, on three selected tributaries in Liberty 

Reservoir, and on one selected tributary in Prettyboy Reservoir watershed. If storm samples are collected using an automated sampler at a station, a visit would need to be made during the rising limb of storm runoff to obtain data normally collected during on-site sampling. If this is not possible, the following data normally collected on site—specific conductance, pH, and turbidity—would need to be obtained from measurements made on samples within 24 hours of collection.

3 Obtained at one randomly selected station within each indicated 2-month period. Samples for suspended sediment would be collected; data compared to tubidity data. Field blanks and replicate water 

samples are collected for all constituents that will be obtained from the laboratory analyses of the collected water-quality samples. Include blind standard reference samples for as many of the constituents as possible that will be obtained from the laboratory analyses of the collected water-quality samples.

4 Obtained at one randomly selected station within the 3-month period. Samples for suspended sediment would be collected; data compared to tubidity data. Field blanks and replicate water samples are 

collected for all constituents that will be obtained from the laboratory analyses of the collected water-quality samples. If automated system used for sample collection, blank is collected from system in field before storm; replicate samples automatically would be collected during storm.
90 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

of field blanks and replicate samples for all water-quality 

constituents determined by laboratory analysis. Field blanks 

would be collected on site before tributary sampling, with the 

sampling equipment used for tributary sampling, and for all 

constituents for which water-quality samples are sent for analyses. Replicate tributary (split or sequential) samples would be 

submitted for all constituents in water-quality samples sent for 

analyses.

In addition, and to the extent they are available at the 

appropriate concentrations, standard reference samples would 

be obtained and submitted as blind samples to the laboratories 

analyzing water-quality samples. These reference samples 

would be analyzed for concentrations of sodium, chloride, 

total and dissolved organic carbon, total, total-dissolved, and 

dissolved phosphorus, and total Kjeldahl- or organic-, nitrate 

(plus nitrite)-, and ammonia-nitrogen.

Reservoirs

In the modified network, there would be eight reservoir 

monitoring locations—the upper, middle, and lower parts of 

Liberty and Loch Raven Reservoirs, and the middle and lower 

parts of Prettyboy Reservoir (fig. 3, table 13). Monitoring 

locations in the lower part of each reservoir at or near each 

of the three reservoir gatehouses, in the upper parts of 

Liberty and Loch Raven Reservoirs, and in the middle part 

of Prettyboy Reservoir, would be equipped with continuous 

multi-parameter water-quality monitoring systems. Each of 

these systems would obtain daily depth-profile logs (minimum 

5-ft intervals to 30 ft below water surface, and to-be-determined intervals below 30 ft) during daytime and (possibly 

nocturnal, for DO) during periods of stratification for seven 

parameters (table 15)—water temperature (°C or degrees 

Celsius), DO concentration (mg/L), specific conductance 

(microsiemens per centimeter), pH (standard units), chl-a

concentration (fluorescence units), turbidity (to be determined, 

units dependent upon sonde probe type), and depth of measurement (ft) via an array of sensors automatically raised 

and lowered through the water column. The remaining two 

reservoir-monitoring locations would be in the middle parts 

of Liberty and Loch Raven Reservoirs (fig. 3). At these stations, depth profiles similar to those described above would 

be obtained bimonthly from March through October, and 

monthly from November through February, during the day. 

Transparency (Secchi-disc depth to extinction) would be measured at all stations during routine water-quality sampling.

Intermittent sampling would be conducted at all eight 

reservoir-monitoring locations (table 13). During periods 

of thermal stratification (March through October, table 15), 

samples would be collected twice monthly at each station at 

sufficient selected fixed depths similar to those used historically to characterize water quality associated with epilimnion, 

thermocline (metalimnion), and hypolimnion; during periods 

of thermal turnover (November through February), samples 

would be collected monthly at each station at similar depths 

to those used under the existing design with one exception. 

During the period of general stratification, an additional 

sample would be collected at the 15-ft depth to ensure at least 

three samples are collected in the epilimnetic layer, which the 

Interstate Commission on the Potomac River Basin (2006) 

indicated could be shallower than 20–30 ft in thickness. 

Samples collected at each depth would be analyzed for 

a variety of constituents (table 15), including concentrations 

of sodium (late October through early March only), algal taxa 

and counts (mid-March through October only), and concentrations of total and dissolved organic carbon, total, total-dissolved, and dissolved phosphorus, total Kjeldahl- or organic-, 

nitrate (plus nitrite)-, and ammonia-nitrogen, and chemical 

oxygen demand. In the hypolimnion, an additional sample 

would be collected for total manganese and total iron. 

Among the proposed modifications to reservoir monitoring, the use of continuous multi-probe depth profilers could 

represent the most significant change in monitoring technology. Continuous-monitoring data are used elsewhere by reservoir and watershed managers. When used on a daily basis, 

they can provide the short-term water-quality data for key 

parameters necessary to relate watershed tributary-reservoir 

hydrodynamics and the associated water-quality and biotic 

conditions in response to major storm events, and seasonal and 

annual variations in climate, including drought and recovery 

conditions (Rasmussen and McAllister, 2005; Rowland and 

others, 2006). 

Continuous water-quality monitoring instrumentation 

would be calibrated and operated according to manufacturer 

specifications. Well-developed guidelines and procedures 

address the installation, operation, and routine maintenance 

of continuous water-quality monitors, and describe how to 

address and verify the quality of the resultant data, which can 

be excellent with proper routine (typically bimonthly) field 

maintenance (Rowland and others, 2006; Wagner and others, 

2006). 

Selected QA samples would be collected during each of 

two fixed time periods (table 15), and at a randomly selected 

reservoir station for each fixed time interval. The QA samples 

would consist of field blanks and replicate samples for all 

water-quality constituents determined by laboratory analysis. 

Additional water-quality samples would be obtained for 

comparative analysis between sonde measurements for chl-a

(fluorescence units) and chl-a analysis (in μg/L), and possibly 

for sonde turbidity measurements (dependent upon probe type 

used). In addition, standard reference samples to the extent 

they are available would be obtained and submitted as blind 

samples for the analyses of as many water-quality constituents 

as possible, including concentrations of sodium, chloride, 

total-, total dissolved-, and dissolved phosphorus, total and 

dissolved organic carbon, and total Kjeldahl- or organic-, 

nitrate (plus nitrite)-, and ammonia-nitrogen.

The improved framework for the collection of waterquality data needs to provide the hydrodynamic data necessary 

to relate watershed-reservoir hydrodynamic and water-quality 

conditions with reservoir hydrodynamic, water-quality, and 

biotic conditions (table 15). Thus, each reservoir would be 
Integrated Framework for an Enhanced Water-Quality Monitoring Program 91

Table 15. Modified data collection for climatic, hydrodynamic, and water-quality constituents or characteristics at reservoir locations in the Baltimore, Maryland, drinkingwater supply system.—Continued[D, daily; TDAP(6), twice daily automated profile measurement at six locations; TMMP(2); twice monthly manual profile measurement at two locations; DAP(6), daily automated profile measurement at six locations; MMP(2), manual monthly profile measurement at two locations; SDP, sampling depth profile; SB, sampling bimonthly, water samples collected between 3 feet below surface to 3 feet above bottom; S, sampling monthly, water sample(s) collected between 3 feet below surface to 3 feet above bottom; X, quality-assurance sample; ---, not sampled; in., inches; ft, feet Mgal/d, million gallons per day; °C, degrees Celsius; mg/L, milligrams per liter; μmhos/cm, micromhos per centimeter; TBD, to be determined (dependent upon sensor type); #/mL, number per milliliter]

Location/constituent 

or characteristic

Sampling method and frequency

March April May June July August September October Novem- ber Decem- ber January February

Stratified reservoir Non-stratified reservoir

At reservoir gatehouse or outlet1

Precipitation, total (in.) and form

D

D

D

D

D

D

D

D

D

D

D

D

Water levels, ftWater withdrawals and releases, 

Mgal/d

Reservoir surface elevation, ftTemperature, air, °C

At reservoir monitoring location, 

and with multiprobe sonde or 

Secchi disc2

Depths of measurement profile, ft

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

TDAP(6) 

or 

TMMP(2)

DAP(6) 

or 

MMP(2)

DAP(6) 

or 

MMP(2)

DAP(6) 

or 

MMP(2)

DAP(6) 

or 

MMP(2)

Temperature, water, °CDissolved oxygen, mg/LSpecific conductance, μmhos/cmpH, standard unitsChlorophyll-a, fluorescenceTurbidity, TBDTransparency (Secchi disc), ft
92 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007 Table 15. Modified data collection for climatic, hydrodynamic, and water-quality constituents or characteristics at reservoir locations in the Baltimore, Maryland, drinking- water supply system.—Continued [D, daily; TDAP(6), twice daily automated profile measurement at six locations; TMMP(2); twice monthly manual profile measurement at two locations; DAP(6), daily automated profile measurement at six locations; MMP(2), manual monthly profile measurement at two locations; SDP, sampling depth profile; SB, sampling bimonthly, water samples collected between 3 feet below surface to 3 feet above bottom; S, sampling monthly, water sample(s) collected between 3 feet below surface to 3 feet above bottom; X, quality-assurance sample; ---, not sampled; in., inches; ft, feet Mgal/d, million gallons per day; °C, degrees Celsius; mg/L, milligrams per liter; μmhos/cm, micromhos per centimeter; TBD, to be determined (dependent upon sensor type); #/mL, number per milliliter] Location/constituent or characteristic Sampling method and frequency March April May June July August September October Novem- ber Decem- ber January February Stratified reservoir Non-stratified reservoir At reservoir monitoring station, and with discrete-depth sampler Depths of sampling profile, ft SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP SDP DP DP Sodium, mg/L S --- --- --- --- --- --- --- --- --- --- --- --- --- --- S S S S S Total algal count, #/mL SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB --- --- --- --- Algal taxa identification SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB --- --- --- --- Chloride, mg/L SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB SB S S S S Dissolved organic carbon, mg/L Total organic carbon, mg/L Total phosphorus, mg/L Total dissolved phosphorus or orthophosphate phosphorus, mg/L Total organic nitrogen, mg/L Nitrate-nitrogen, mg/L Ammonia nitrogen, mg/L Chemical oxygen demand, mg/L Hypolimnion, Manganese, mg/L

Hypolimnion, Iron, mg/LQuality-assurance samples ............X3............ ............X3............ ............X ............

1 Water purveyors collect a variety of water-quality samples at or near the Loch Raven and Liberty reservoir intakes. To the extent that the reservoir monitoring station at or near the gatehouse can provide 

suitable data from profiles and interval sampling, their sampling requirements can be reduced. Conversely, if water purveyors can provide suitable data from their routine sampling, interval sampling at the lower end of each reservoir can be reduced.

2 Historical monitoring in reservoirs has included dissolved solids (mg/L), and hardness and alkalinity (mg/L, as calcium carbonate), which could be included in interval sampling, but they have not 

appeared to be critical assessment parameters in relation to water-quality issues of concern.

3 Quality-assurance samples are collected within each designated period, at one randomly selected station. Chlorophyll-a and suspended-sediment samples would be collected; data would be compared to 

chlorophyll-a and turbidity measured with multi-parameter sonde. Field blanks and replicate water samples are collected for all constituents that will be obtained from the laboratory analyses of the collected water-quality samples. For one randomly selected period, include blind standard reference samples for as many of the constituents as possible that will be obtained from the laboratory analyses of the collected water-quality samples. 
Integrated Framework for an Enhanced Water-Quality Monitoring Program 93

characterized with respect to daily water levels, releases, and, 

in the case of the drinking-water reservoirs, withdrawals. 

Each reservoir system also would be characterized with 

respect to mean daily air temperature and precipitation, with 

the latter including daily totals and form (rain or snow). 

Depending on the reservoir watershed, climate stations could 

be installed within the reservoir property controlled by the 

City, or within reservoir watershed property controlled by 

either Carroll or Baltimore Counties. Obtaining these data in 

proximity to the reservoirs and reservoir watersheds would 

improve modeling capabilities (see Modeling to Address 

Water-Quality Concerns, this report).

Susquehanna River

If the ongoing review of the City firming program results 

in an increased use of the Susquehanna River as a primary 

source of drinking water, and the SRBC agrees to this increase 

in use, then the RTG and City would need to determine the 

implications of this decision with respect to its long-term 

monitoring program. Use of Susquehanna River water as a 

drinking-water source will complicate the identification and 

management of source waters that lead to water treatment 

and finished water impairments. For example, concentrations 

of DBPs in finished waters in the City water-distribution 

system from the Montebello treatment facility could reflect 

treatment of waters obtained from Loch Raven Reservoir, 

the Susquehanna River, or both sources. Minimally, the RTG 

needs to ensure that periods of Susquehanna River water use 

are documented and archived for easy reference. 

Enhanced Documentation of Data and Quality of 

Data Collection

Regardless of whether the monitoring network is modified as a consequence of this review, the RWMA requires 

that long-term (multi-decadal) monitoring be performed to 

obtain the data necessary to address its goals and water-quality 

concerns. Inherent in this effort is the need to be able to access 

data from the entire period during which they have been collected. It also is critical that the data are of known quality. 

Invariably, field and laboratory personnel as well as 

the methods used to collect data and samples in the field or 

analyze samples in the laboratory change with time. To ensure 

these changes do not adversely affect the ability to obtain and 

use these data, and that the quality of the data being used is 

known or can be determined over an indefinite period of time, 

implies that data obtained in the field or from a laboratory 

be stored in a well-maintained and supported database with 

the appropriate qualifications (units, significant figures, and 

remarks). It also generally implies that the quality of the data 

entered be determined through the independent collection of 

QA data in the field and laboratory, and that these QA data be 

stored in a similar fashion, ideally either in the same database 

or at least a similarly supported companion database. These 

operational objectives generally are successfully completed if 

they are guided by a single comprehensive QAPP. 

On the basis of a review of available (2007) documents 

on data-collection methods, QAC plans, and the database, it is 

apparent that a single comprehensive QAPP would be of great 

benefit to the RWMA program. For this QAPP to be effective 

and eliminate the shortcomings identified in this review, it 

would need to include the following elements:

a) A description of the field and laboratory procedures 

and methods and organizations responsible for the 

collection of data and samples for the monitoring 

program.

b) Definitions of the long-term data-quality requirements 

for the monitoring program, including the identification of the appropriate reporting level, precision, and 

bias required (determined suitable) for each hydrodynamic, water-quality, or biotic parameter stored in the 

database.

c) A description of the required quality-assurance and 

control measurements (QAC data), the agencies 

responsible for their collection and entry, and the 

manner in which they routinely will be obtained and 

digitally stored along with the corresponding hydrodynamic, water-quality, or biotic parameters.

d) A description of the procedures for the routine (annual 

or biannual) summary, review, analysis, and evaluation 

of the QAC data, the agencies responsible for conducting these activities, and the documentation of findings, 

to determine if data requirements are being met.

e) A description of procedures for the systematic transfer 

or modification of field or laboratory methods, and 

required documentation thereof, and the responsible 

agencies for overseeing this activity given that dataquality requirements and (or) methods invariably 

change.

To be most effective, this QAPP would be developed and 

implemented by the RTG partners, and include the DPW and 

Baltimore County field operations and the DPW treatment 

facility staff and contract laboratory staff that analyze longterm monitoring samples.

Examples of comprehensive QAPPs, and the parts of 

these QAPPs that routinely undergo periodic change, for other 

long-term monitoring programs can be found in the following 

resources:

a) Quality Management Plans: U.S Environmental 

Protection Agency (2008) National Risk Management 

Research Laboratory’s (NRMRL) Quality Management 

Plan (QMP); 

b) Quality Assurance Program Plans: California Water 

Resources Control Board (2008) Surface Water Ambient Monitoring Program (SWAMP), with guidance 

from Keith (2006); or the Chesapeake Bay Program 
94 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

(2008) non-tidal monitoring quality plan, which is 

modeled after the U.S. Environmental Protection 

Agency (2001) quality assurance program plan for 

measurement projects; and

c) Environmental Sampling Protocols Documentation: 

The U.S. Geological Survey National Field Manual 

for Water-Quality Sampling (U.S. Geological Survey, 

variously dated).

In addition, examples of the types of quality-control samples that can be collected as part of routine monitoring were 

described for the watershed tributaries (table 14) and reservoirs (table 15). The blind standard-reference samples referred 

to in these examples are available from inter-laboratory verification programs and commercial vendors. Two examples of 

regional and national programs that provide standard reference 

samples for water-quality parameters of interest to the RWMA 

partners are (a) the Split and Blind Sample Program of the 

Chesapeake Bay Program (Chesapeake Bay Program, 2010), 

and (b) the Inter-Laboratory Comparison Program of the 

USGS Branch of Quality Systems (Glodt and Pirkey, 1998).

Benefits of an Enhanced Water-Quality 

Monitoring Program

The proposed improvements to the long-term monitoring 

network reflect the combined recommendations or address the 

notable limitations described in the preceding discussions on 

the use of monitoring data to address watershed and reservoir 

water-quality issues of concern, and the monitoring-related 

objectives of the RTG. The improved monitoring design can 

provide the RTG with the type and quality of data needed to 

improve upon spatial and temporal assessments under potentially rapid changes to long-term changes in hydrodynamic 

and associated water-quality and biotic conditions. In particular, they would help the RTG to:

a) Describe states, changes, and trends in the concentrations and loads for the water-quality parameters used 

to address the water-quality concerns in the reservoir 

watersheds;

b) Describe states, changes, and trends in the concentrations of water-quality parameters used to assess, or 

compute indices to assess, water-quality and biotic 

conditions that reflect water-quality and biotic concerns in the reservoirs;

c) Describe states, changes and trends in the concentrations of water-quality and biotic parameters used by 

City water purveyors to identify reservoir intake(s) for 

raw-water withdrawals for water treatment, and (or) to 

reduce or eliminate potential impairments in finished 

drinking water; 

d) Describe modeled states, changes, or trends in the 

concentrations or loads of water-quality and biotic 

parameters required to develop (Liberty Reservoir 

and watershed) or improve upon (Loch Raven and 

Prettyboy Reservoirs and watersheds) simulations of 

hydrodynamics and associated water-quality conditions 

in the reservoirs; 

e) Quantify states, changes, and trends in concentrations 

and loads associated with water-quality and biotic 

parameters used to address regulatory requirements, 

including TMDLs, or water-quality parameters used as 

TMDL endpoints in the reservoirs;

f) Assess water-quality conditions associated with emerging water-quality issues of concern—concentrations 

and sources of DBPs and of sodium and chloride;

g) Improve understanding of the effects of climate (variability and change) on water-quality conditions in the 

reservoir tributaries, and water-quality and biotic conditions in the reservoirs associated with each long-term 

and emerging water-quality concern; and 

h) Improve the reservoir-monitoring framework to provide continuous profile data possibly in real time, and 

at a higher frequency if needed, for water purveyors to 

provide advance warning of changes in the quality of 

reservoir water in the upper part of each water-supply 

reservoir that could imply eventual changes in water 

quality in the lower parts of each reservoir near the 

intakes used to withdraw water for drinking-water 

supplies.

Summary

The City of Baltimore, Maryland, and parts of five surrounding counties obtain water from Loch Raven and Liberty 

Reservoirs. A third reservoir, Prettyboy, is used to resupply 

Loch Raven Reservoir. Management of the watershed conditions in all three reservoirs is a shared responsibility among 

City, County, and State representatives under the Baltimore 

Reservoir Watershed Management Agreement (RWMA), 

which is guided by voluntary agreements and action strategies. 

Management of the reservoirs is chiefly the responsibility of 

the City. Withdrawals for supplies vary markedly in response 

to seasonal demands, and routinely aim to withdraw only the 

best quality of water for supplies to reduce treatment costs and 

complaints about the quality of treated water. However, they 

must be managed to reduce major drawdowns in all three reservoirs. Reservoir recovery, particularly for Liberty Reservoir, 

can take months following major withdrawals and drawdowns, 

and major drawdowns possibly can result in reductions in the 

quality of reservoir water during recoveries.
Summary 95

A major purpose of these RWMA agreements is to 

address long-term and emerging water-quality concerns. The 

2005 RWMA action strategy called for continued comprehensive water-quality monitoring in the reservoirs and selected 

watershed tributaries related to these concerns, and indicated 

that monitoring could be revised as needed based on an evaluation of: a) its ability to detect changes in state or trends, b) 

its suitability in relation to the areal extent and adequacy of 

monitoring to provide the type and quality of needed data, and 

c) its effectiveness in helping to understand and manage the 

reservoir watersheds and reservoirs to address water-quality 

concerns. To aid in this effort, the U.S. Geological Survey 

conducted a review of the effectiveness of the monitoring 

program from its inception in 1982 through 2007 in relation to 

the above criteria.

Long-Term and Emerging Water-Quality 

Concerns

The long-term water-quality concerns of the RWMA 

partners include eutrophication and sedimentation in the reservoirs, and elevated concentrations of (a) nutrients (nitrogen 

and phosphorus) transported from the major tributaries to the 

reservoirs, (b) iron and manganese released from reservoir bed 

sediments during periods of deep-water anoxia, (c) mercury 

in higher trophic order game fish in the reservoirs, and (d) 

bacteria in selected reservoir watershed tributaries. Emerging 

concerns include elevated concentrations of sodium, chloride, 

and disinfection by-products in the drinking water from both 

supply reservoirs. Climate variability and climate change 

also could be emerging concerns. The inherent variability in 

climate could affect within-year and year-to-year variations 

in water quality in the tributaries and reservoirs. Projected 

changes in climate in the region include an increased frequency in drought conditions punctuated by an increased 

frequency in intense storms.

Eutrophic conditions that lead to major algal blooms 

are presumed to be caused by elevated nutrient (nitrogen and 

phosphorus) concentrations and loads from the major tributaries to the reservoirs. Elevated concentrations of iron and 

manganese are released from bed sediments under hypoxic 

reservoir conditions, which often follow the die-off and 

decomposition of major algal blooms. Sedimentation in the 

reservoirs largely is caused by elevated suspended-sediment 

concentrations and loads from the reservoir watersheds. Major 

sediment loads reflect overland as well as in-stream bed and 

bank erosion. Sediment transported to the reservoirs reduces 

reservoir storage capacity, increases in-lake turbidity, and is 

the major source of iron and manganese as well as a potential 

source of available phosphorus to the reservoirs. Elevated 

concentrations of mercury, which occur in higher trophic order 

game fish in the reservoirs, likely result from regional sources 

that are presumed to be beyond the control of the RWMA 

partners. Elevated concentrations of bacteria also occur in 

selected tributaries. As of 2007, their occurrence and sources 

were being investigated.

Emerging water-quality concerns (primarily related to 

drinking water) include elevated concentrations of disinfection by-products measured at selected times and monitoring 

stations in the water-supply distribution systems of both 

supply reservoirs. Concentrations of disinfection by-products 

could exceed Federal drinking-water standards upon implementation of a recent rule change. The source(s) of the carbon 

compounds that form these by-products, however, are largely 

unknown. Elevated concentrations of sodium, presumably 

from increased use of sodium-chloride salt as a deicing agent, 

also recently have approached or exceeded the Federal standard for individuals on low-sodium diets in drinking water 

from both supply reservoirs. Although not formally considered by the RWMA partners as an emerging concern, climate 

variability and climate change were considered in this review 

as emerging concerns. Climate variability in the Mid-Atlantic 

region already notably affects within-year and year-to-year 

variations in the quantity and quality of tributary and reservoir 

waters. Climate change for the Mid-Atlantic is projected to 

result in an increase in the frequency and length of hot dryweather periods and in an increase in the number of intense 

storms. Historical patterns indicate the quality of waters in 

the reservoirs can decline during droughts that result in major 

drawdowns and (or) following the recovery of the reservoirs 

from such drought conditions.

Description of Water-Quality Monitoring 

The chief purpose for monitoring in the Baltimore 

Reservoir System has been to provide data to describe, assess, 

and relate changes in the state of water-quality and biotic 

conditions in the major reservoir watershed tributaries and 

reservoirs associated with long-term and emerging RWMA 

water-quality concerns. In addition, monitoring has been 

conducted to support the development of models that could 

help the RWMA partners relate watershed and tributary conditions to reservoir conditions, in order to better identify either 

effective watershed management activities, or better assess the 

effectiveness of activities already performed, to address their 

water-quality concerns. 

Since its inception in the early 1980s, the long-term 

core monitoring network for the Baltimore Reservoir System 

generally has consisted of approximately 21 nonpoint-source 

(tributary or pond) and point-source water-quality monitoring 

stations in the reservoir watersheds, and 12 in-lake monitoring 

stations in the three reservoirs. As of 2007, there were few 

changes in the network. The most notable documented 

changes in monitoring include a decline in the frequency of 

storm sampling in 1995, and the discontinuance of monitoring 

for bioavailable (dissolved phosphate) phosphorus in 1993. 

Undocumented or never fully explained changes in monitoring 

include the manner in which storm samples were collected in 

the mid-1980s, and the manner in which phosphorus samples 

were collected in the mid-1990s.
96 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Review and Evaluation of Monitoring

The review and evaluation of the monitoring program 

included (a) a broad review of the quality of the monitoring 

database and dated collected from the inception of data collection in 1982 through 2007, (b) a review of the monitoring 

program and data in relation to their ability to support modeling to address water-quality concerns, and (c) a review of the 

monitoring program and data to support analyses that address 

each individual long-term and major water-quality concern.

Quality of Monitoring Database and Data

During the course of this review, concerns were encountered by RWMA partners or contractors about the quality of 

monitoring data. At least four investigative studies actually 

published those concerns as part of their investigative work. 

A broad review of the related database documentation as of 

2007 revealed no single quality assurance program and planning (QAPP) document was readily available that described 

in sufficient detail the current reservoir monitoring program 

from data collection to archival. No document was found that 

describes the data-quality requirements for the monitoring 

program, or indicates that routine reviews with summaries are 

conducted by the Reservoir Technical Group (RTG) on the 

quality of data being collected by the monitoring program. It 

also was apparent that the quality-assurance and control plans 

for City water-treatment facility laboratories, which analyze 

most monitoring samples, cannot be expected nor used to meet 

the quality-assurance and control requirements of a long-term 

monitoring program. In addition, responsibilities for data collection and analysis for the Baltimore Reservoir monitoring 

program have been distributed among different City staff, City 

partners, or private contractors, leading to difficult data-quality 

issues that can arise long after the data have been collected.

Monitoring to Support Modeling to Address 

Water-Quality Concerns

Monitoring data were reviewed in relation to their ability 

to support the development of models that could help identify 

effective watershed management activities, or assess the 

effectiveness of activities already undertaken. Such modeling 

is viewed by the RTG, as an effective means to help address 

existing and future RWMA partner water-quality concerns. 

To date, model development has been a challenge because 

of a lack of required data or limitations in the availability 

of required data. A review of the most recent and comprehensive modeling effort was conducted as part of this study. 

A computer simulation model of the watersheds draining 

into Prettyboy and Loch Raven Reservoirs (Hydrological 

Simulation Program—Fortran, HSPF) coupled with a twodimensional lake computer simulation model (U.S. Army 

Corps of Engineers CE-QUAL-W2) was used to simulate the 

hydrodynamics and water quality of the reservoirs. Use of this 

coupled model was adequate to link nutrient loads, specifically phosphorus loads, from the Loch Raven and Prettyboy 

Reservoir watersheds to algal biomass concentrations (represented by chlorophyll-a or chl-a concentrations) in the 

reservoirs, and to calibrate the relation between autochthonous 

and allochthonous organic matter and dissolved oxygen (DO) 

concentrations in the hypolimnetic layer. The models could be 

improved, however, with the addition of the appropriate data. 

Limitations in data noted by the modelers were considerable. 

In brief, they included (a) a limited number of years with sufficient stormflow water-quality data for model calibration and 

validation, and (b) a lack of selected nutrient and other data for 

the watershed tributaries and the reservoirs. There also was a 

lack of data, or readily available data, on tributary or reservoir 

water-quality and biotic conditions, including (a) bioavailable, 

rather than just total, phosphorus, (b) total and (or) organic, in 

addition to inorganic, forms of nitrogen, (c) dissolved, as well 

as total, organic carbon, and (e) data on chemical, or biological and chemical, oxygen demand.

Monitoring to Address Individual Water-Quality 

Concerns

The monitoring program and use of monitoring data 

were reviewed in relation to their ability to address individual 

long-term and emerging water-quality concerns. For each 

water-quality concern, this review included an assessment of 

the ability of RWMA partners or their contractors to describe 

(a) the state, changes in state or trends, in key water-quality 

conditions in either the reservoir watershed tributaries or their 

downstream reservoirs, (b) relate general patterns in land-use 

conditions or human activities to the water-quality conditions 

in the reservoir tributaries, and (or) (c) relate tributary waterquality conditions to reservoir water-quality or biotic conditions in the reservoirs.

Long-Term Water-Quality Concerns

Eutrophication accompanied by major algal blooms is 

a long-term water-quality concern. Long-term monitoring 

data (approximately 1982–2003) on algal taxa identification 

and abundance (counts) have been used by RWMA partners 

to describe seasonal patterns in phytoplankton diversity and 

production characteristics in each reservoir in relation to 

eutrophic and mesotrophic conditions. Seasonal patterns of 

phytoplankton (taxa and abundance), and their die-off and 

decomposition, have been linked to seasonal patterns in concentrations of DO, hypoxic to anoxic conditions, and concentrations of iron and manganese in reservoir waters. Analysis of 

time-series data have been used to illustrate apparent declines 

in algal counts and possibly concentrations of chl-a from the 

early1980s through 1990s. Except for one modeling study 

(described above), there has been limited success relating 

intra-seasonal variations or annual trends in water-quality 

conditions in the reservoir watershed tributaries to seasonal 

or annual trends in water-quality conditions, or phytoplankton 
Summary 97

production and succession in the reservoirs. Comparisons of 

phytoplankton data among reservoirs also have been complicated by the lack of data for the upper part of Prettyboy 

Reservoir, and for major blooms that likely occur in at least 

the mid-to-lower part of this reservoir in the late winter and 

early spring.

Eutrophic conditions in the reservoirs, and adjoining portions of selected tributaries supplying the reservoirs, generally 

are considered to result from excessive nutrients—nitrogen, 

and in particular, phosphorus—which are long-term waterquality concerns. Extensive monitoring for nitrogen and 

phosphorus has been conducted in the tributaries, in relation to 

point and nonpoint sources, and in the reservoirs. Monitoring 

data from the 1980–90s for nitrogen, exclusively in available 

forms (ammonia, nitrate, and nitrite), have been used to 

describe and assess total and form-specific concentrations or 

loads of nitrogen in the tributaries, their relation to point and 

nonpoint sources in the reservoir watersheds, and nitrogen 

concentrations in the reservoirs. Monitoring has documented 

that wastewater treatment plant (WWTP) upgrades led to the 

reduction of all forms of available nitrogen in effluents by the 

late 1990s. Concentrations of total available nitrogen in dryweather (generally unquantified low) flows also were shown to 

increase with the extent of agricultural land use, and decrease 

with the extent of forest cover in a reservoir watershed subbasin. Seasonal but different patterns were shown to occur in 

concentrations of nitrate nitrogen in the watershed tributaries 

and reservoirs. But mid-summer annual lows in tributary 

dry-weather flows were not observed in the reservoirs, where 

annual nitrate-nitrogen concentrations actually tend to peak in 

the spring or early summer. Trend analysis indicated ammonia 

nitrogen appeared to decline, and nitrate nitrogen appeared to 

increase, and then possibly leveled off, in dry-weather flows 

at most tributary stations, whereas only ammonia appeared to 

decline in the reservoirs. Statistical analysis, limited to Loch 

Raven and Prettyboy Reservoirs and watersheds, confirmed 

the trends for ammonia and nitrate nitrogen in the tributaries, 

but showed that only ammonia nitrogen declined, and at just 

two stations in Loch Raven Reservoir. The reasons for the 

differences in nitrate seasonal patterns, or the above trends or 

lack thereof, in ammonia- and nitrate-nitrogen in the tributaries and reservoirs are unknown. But reservoirs receive both 

organic (not measured) and inorganic nitrogen loads from 

storm- (limited sampling after 1995) as well as dry-weather 

flows. Concentrations of both forms of available nitrogen also 

generally are lower in the reservoirs compared to dry-weather 

flows in the tributaries. They also appear to be governed 

by reservoir stratification, with nitrate nitrogen primarily 

occurring in the epilimnion and ammonia nitrogen primarily 

occurring in the hypolimnion. Thus, seasonal patterns, and 

possibly trends, in available nitrogen likely are determined 

by nutrient-cycling (abiotic and biotic) and hydrodynamic 

processes (stratification and turnover) in the reservoirs and not 

just tributary inflows.

Phosphorus is considered to be the limiting nutrient in 

phytoplankton production. Monitoring data mainly from the 

1980s–90s, primarily for concentrations of total phosphorus 

(TP), have been used to describe and assess concentrations 

of phosphorus in the tributaries, their relation to point and 

nonpoint sources in the reservoir watershed subbasins, and 

TP concentrations in the reservoirs. Concentrations and total 

annual loads of TP from three major subbasins in each supply 

reservoir from the 1980s to the mid-1990s were shown to be 

highly variable within a year and from year to year presumably because of variations in climate and flow regime. Loads 

were markedly elevated in wet years compared to dry years. 

Most of the TP load was carried by stormflow; dry-weather 

flow accounted for only 15–30 percent of the total annual load 

depending upon the tributary. Only a relatively small fraction 

of stormflow TP appeared to be dissolved (orthophosphate) 

phosphorus (4–21 percent); a higher fraction of the TP in 

dry-weather flows appeared to be dissolved orthophosphate 

phosphorus or DOP (75–81 percent). However, concentrations 

of DOP in stormflows are at least 5 times greater than concentrations of DOP in dry-weather flows. 

By the late 1990s, plant upgrades had reduced TP in 

wastewater effluents by 71–95 percent. For Loch Raven 

Reservoir, loads from the Western Run subbasin were markedly higher than loads from the other two major subbasins, 

which indicated that activities to reduce TP loads could focus 

on this subbasin.

Stormflow and DOP sampling were reduced and discontinued, respectively, by the mid-1990s. Thus, long-term 

characterizations of the temporal variations of phosphorus in 

the tributaries, and comparisons of phosphorus in the tributaries and reservoirs were made with TP data primarily obtained 

from dry-weather flows. During the 1980s–90s, seasonal, but 

different, patterns in concentrations of TP were observed in 

the tributaries and reservoirs. Apparent mid-summer peaks 

in TP in most tributary dry-weather flows were not apparent 

in the reservoirs, where peak TP concentrations generally 

appeared in late summer or early fall. Attempts to characterize and compare long-term trends in the concentrations of TP 

also have proven difficult. Concentrations of TP appeared to 

decline in dry-weather flows during the 1980s–90s at most 

tributary stations, but trends could not be statistically verified. 

Subsequent studies on TP data collected from 1981–2003 

revealed that a step change in June or July 1995, and extreme 

outliers, particularly low TP values in the early data record, 

complicated trend analysis. The step change could reflect a 

change in laboratory methods; the outliers could reflect the 

manner in which immeasurable concentrations of TP data 

were stored. The documentation of methods and remarking of 

data, however, are insufficient to confirm either of the above. 

These types of problems have led to questions on the overall 

quality of the data in the database (see below). From a broader 

perspective, the sole reliance on TP analyses coupled with the 

monitoring of primarily dry-weather flows after 1995, and 

at least through 2007, likely has and will continue to hinder 

the ability to estimate loads, to discern patterns and relations 

among phosphorus concentrations among the tributaries and 

reservoirs, to describe phosphorus cycling in the reservoirs, 
98 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

and to relate phosphorus to other markers of eutrophication in 

the reservoirs.

In relation to eutrophication, the frequency of eutrophic 

compared to mesotrophic conditions in each reservoir is a 

major water-quality concern, and has been assessed with 

Carlson Trophic State Indices (TSIs) derived from concentrations of chl-a, TP, or DO, and (Secchi disc) transparency data 

collected from 1982–2000. The frequency of eutrophic compared to mesotrophic conditions observed in the shallow water 

layer (defined to be 30 feet or less in depth) of each reservoir 

differed within a given reservoir, and among the reservoirs, 

depending upon the TSI index used. Among the four TSIs, the 

TSI chl-a index could be a highly sensitive (trend and relative) indicator of the frequency of eutrophic conditions with 

major algal blooms among the reservoirs. The TSI-DO index 

also could be a sensitive (trend and relative) indicator of the 

frequency of hypoxic conditions that result from major algal 

blooms among the reservoirs. The TSI-transparency index 

appears to be the least sensitive indicator of eutrophic conditions as the data from 1992–2004 indicate that light penetration is highest in the summer (approaching approximately 20 

feet), and lowest in the winter to early spring as a result of lake 

turnover. 

Whereas the analysis of reservoir trophic conditions 

using the TSI indices indicate that they could help assess the 

frequency of eutrophic and mesotrophic conditions in the 

reservoirs, no study was encountered during this review that 

examined the (1982–2000) trend in results for each index. In 

addition, there are a number of inadequacies in the monitoring, aggregation, and analyses of the TSI indices data. For 

most TSI indices, data are collected only monthly throughout 

the year in Prettyboy Reservoir but bimonthly in the supply 

reservoirs during periods of reservoir stratification. There also 

has been no monitoring for chl-a data for the upper part of 

Prettyboy Reservoir, and insufficient monitoring of chl-a data 

for the late winter and early spring in the middle and lower 

parts of this reservoir. Thus, the TSI index comparisons of 

the frequency of eutrophic or mesotrophic conditions in this 

reservoir to the frequency of these conditions in the two supply reservoirs is questionable. Measurements of DO, which 

serve as the basis of the TSI-DO index comparisons, primarily 

occur only in the daytime in all three reservoirs. During major 

algal blooms, these measurements could be positively biased 

by phytoplankton photosynthesis. Questions concerning the 

quality of TP data through time already have been noted, 

which could affect results obtained for the TSI-TP indices—

most notably in Loch Raven and Prettyboy Reservoirs. As for 

transparency, only one-half of the variability in transparency 

in Loch Raven and Prettyboy Reservoirs can be explained by 

parameters directly related to light penetration (color, turbidity, and chl-a), which is low compared to other studies. In 

addition, the TSI results for chl-a, TP, and DO for the shallowwater layer (defined as 30 feet or less in depth) likely include 

samples at depths (20 to 30 feet) beyond the determined 

epilimnion and euphotic layers in at least two of the three 

reservoirs. Subsequent to the analyses of the TSI-based frequency of eutrophic conditions, the epilimnetic layers, at least 

for Loch Raven and Prettyboy Reservoirs, were shown to be 

15–20 feet in depth for most years of record. In addition, for 

each of the four TSI indices, the aggregation of sample data 

over an entire reservoir could mask important spatial differences in the frequency of eutrophic conditions within different 

parts of each reservoir.

Sedimentation is a long-term water-quality concern. 

Long-term monitoring in the watershed tributaries has been 

used to provide data and information on suspended-sediment 

concentrations, loads, trends, and potential source areas 

of sediment (among major subbasins). Mean total annual 

suspended-sediment concentrations and loads markedly varied 

but were notably higher in wet compared to dry years for 

each of the three major subbasins monitored in each supplyreservoir watershed during the 1980s through the mid-1990s. 

More sediment also was carried by stormflow as opposed to 

dry-weather flow, with the latter accounting for only 10 percent or less of the total annual sediment load. On the basis of 

areal-weighted dry-weather-flow loads (yields), Beaver Dam 

and Western Run subbasins, and the lower Gunpowder River 

subbasin between Prettyboy and Loch Raven Reservoirs were 

identified as areas for management activities to reduce yields. 

Suspended-sediment concentrations, and notably loads, also 

appeared to decline during the mid-1980s. A comparison of 

suspended-sediment concentration-discharge curves constructed using data from 1982–86 and from 1986–90 for each 

of three major subbasins in each supply reservoir watershed 

also indicated less sediment was being transported in each 

subbasin throughout most of the range in flows after 1985. 

No statistical analysis was used to confirm the above, nor 

could these changes be clearly linked to management activities designed to reduce sediment loads as they could reflect 

a possible change in storm-sampling methods. Since 1995, 

the reduction in storm sampling has made and will make it 

difficult to obtain reasonably accurate estimates of annual 

sediment loads to the reservoirs. Use of dry-weather-flow suspended-sediment data, however, is inadequate as these flows 

account for very little of the total annual sediment load. After 

the early 1990s, the magnitude of these flows has been largely 

unquantified. The transport of sediment to the reservoirs has 

reduced reservoir storage capacity since their creation. Recent 

bathymetric surveys (1998–2000) have shown the loss in 

storage capacity since reservoir construction is 3–11 percent, 

depending on the reservoir. For Loch Raven Reservoir, which 

lost 11 percent of its capacity, sediment has filled available 

storage in the lower parts of the reservoir watershed tributaries 

and downstream parts of the reservoir. These recent surveys 

are the starting point for trend assessments on losses in reservoir capacity. Historical (pre-1980s) survey data could not 

be used because of inadequate documentation of methods and 

archival of survey data. 

Elevated concentrations of manganese and iron in intake 

waters of both supply reservoirs are a long-term water-quality 
Summary 99

concern. Monitoring of manganese and iron in intake waters is 

routinely done by water purveyors only at the water treatment 

facilities associated with each supply reservoir. Elevated concentrations of these metals have been shown to generally occur 

following the die-off and decomposition of major algal blooms 

that contribute to anoxic conditions at depth and the mobilization of these metals from reservoir bed sediments. Monitoring 

for these metals in the supply reservoirs (bimonthly) is not 

frequent enough to provide a timely warning of their ultimate 

occurrence at the intakes in the water-supply reservoirs.

Elevated concentrations of mercury in game fish are a 

long-term-water-quality concern. Given the initial sources of 

mercury to the reservoir watersheds and reservoirs appears 

regional in scope, the concentrations of mercury in game fish 

occurrence have been largely considered beyond the control of 

the City or the other RWMA partners. Following droughts that 

lead to extended withdrawals of water for supply, however, 

exposed reservoir bed sediments can be covered by dense 

stands of terrestrial vegetation. Upon reservoir recovery, the 

submergence of this vegetation could lead to conditions that 

enhance methylmercury production and biological uptake. 

Whether or not this occurs cannot be indirectly determined 

from recent regional knowledge on the occurrence of mercury 

in game fish in Maryland lakes and reservoirs. Routine synoptic monitoring for mercury in reservoir game fish also cannot 

address this question. It lacks focus on these reservoir areas 

prone to bed-sediment exposure and the establishment and 

eventual submergence of terrestrial vegetation. It also occurs 

too infrequently to provide suitable comparative data before 

and after drought events in these areas. 

Fecal and other bacteria have been found at elevated 

counts in selected reservoir watershed tributaries, and are a 

long-term water-quality concern. The reservoirs, however, 

appear to function in an effective manner to reduce microbial 

contaminants at supply intakes. Individual intake sample 

values and monthly averages for fecal coliform bacteria 

counts in raw water from Liberty and Loch Raven Reservoirs 

consistently fall below and well below, respectively, the State 

water-quality recreational water-contact standard (200 Most 

Probable Number per milliliter). As of 2007, selected watershed tributaries in each reservoir watershed had bacterial 

concentrations that exceeded this standard, and the Maryland 

Department of the Environment requested and is reviewing 

additional bacterial data from the reservoir watersheds. Longterm monitoring in the reservoir watershed tributaries eventually could require the collection of fecal-coliform or other 

bacterial data.

Emerging Water-Quality Concerns

Trihalomethanes (THMs) and haloacetic acids (HAAs) 

are disinfection by-products (DBPs) created by the chlorination of raw supply water, and both are considered to be 

emerging water-quality concerns. Analysis of monitoring data 

collected after the late 1990s indicates that DBPs generally 

form and thus occur in the City water-distribution systems 

after water treatment. Under a pending rule change, the 30-day 

moving average concentrations of these DBPs cannot exceed 

the Federal standards at any monitoring station in either supply reservoir treated water distribution system. An analysis 

of data from 2003–08 indicates that the total concentration 

of THMs at one or more distribution monitoring stations 

exceeded the Federal standard (80 μg/L or micrograms per 

liter) on approximately 19 percent of the sample-collection 

dates in both the Loch Raven Reservoir and Liberty Reservoir 

water-supply distribution systems, and that the total concentration of HAAs exceeded the Federal standard (60 μg/L) at one 

or more stations on approximately 43 percent and 38 percent 

of the sample-collection dates in the Loch Raven Reservoir 

and Liberty Reservoir water-supply distribution systems, 

respectively. Concentrations of THMs in finished waters also 

varied seasonally. The highest THM concentrations often 

occurred from July to September, when algal blooms and 

die-offs also occur most often in the reservoirs. High THM 

concentrations also occurred during two drought-recovery 

periods, which likely also were marked by algal blooms and 

possibly submerged terrestrial vegetation. There was no correlation between concentrations of THMs and HAAs at a given 

monitoring station, nor any apparent seasonal trend in HAA 

concentrations in either water distribution system. Elevated 

concentrations of HAAs tended to occur at the same monitoring stations in each water distribution system, but at different 

times in different years. Their occurrence possibly reflects 

short-term but currently unknown hydrodynamic and (or) 

biological events. Concentrations of THMs (or HAAs) also 

bore little relation to concentrations of total organic carbon in 

raw intake waters, or concentrations of organic carbon after 

removal of one third of the total carbon in raw intake waters. 

Hence, monitoring of total carbon alone likely will not identify 

intake waters that contain elevated concentrations of carbon 

that form either type of DBP.

Recent increases in the concentrations of sodium and 

chloride in treated water are emerging water-quality concerns. 

Monitoring data indicate that sodium concentrations in 2003 

were three-to-four-times greater than sodium concentrations in 

raw waters at the intakes of the supply reservoirs. During the 

winters of 1999 and 2003, sodium in treated waters from Loch 

Raven Reservoir often exceeded 20 mg/L (milligrams per 

liter)—the U.S. Environmental Protection Agency non-regulatory guideline limit for consumers on restricted low-salt-intake 

diets (500 milligrams per day) diets. During the same period, 

sodium in treated waters from Liberty Reservoir ranged from 

10–16 mg/L, exceeding almost all previous measurements. 

Chloride concentrations, which have been monitored at supply 

reservoir intakes since the early 1930s and at tributary dryweather flow stations since 1982, also have steadily risen in 

both intake waters and the tributaries throughout these periods. 

Recently, however, the highest chloride concentrations have 

occurred during the winter months. The suspected cause for 

the recent increase in both sodium and chloride concentrations 
100 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

is road-salt use as a deicing agent. As of 2007, however, 

watershed and reservoir monitoring is too infrequent and lacks 

inclusion of sodium, and therefore cannot provide a timely 

assessment of the occurrence of elevated sodium or chloride 

concentrations in the tributaries or reservoirs before that water 

reaches the intakes. For the same reason, monitoring likely 

cannot provide a timely indication of any reductions in sodium 

or chloride that could result from management activities that 

could eventually be taken to reduce the use of sodium-chloride 

salt as a road deicing agent.

Climate variability and climate change could exacerbate 

withinin-year and year-to-year variations in water-quality 

conditions associated with most water-quality concerns, and 

in relation to future monitoring, were addressed as emerging 

water-quality concerns. Seasonal patterns and year-to-year 

variations in water-quality conditions associated with longterm concerns, such as eutrophication and sedimentation, as 

well as emerging concerns, such as DBP and sodium-chloride 

concentrations, can be linked to the inherent seasonal patterns 

and annual variability in climate in the Mid-Atlantic region. 

Recent climate change studies predict increases in both the 

intensity and frequency of major storms and the duration of 

periods of hot dry weather for the Mid-Atlantic region. The 

projected climate changes could imply more frequent drought 

conditions alleviated by more frequent intense storms with 

heavy precipitation. Historically, droughts have led to major 

reservoir withdrawals for supplies, and generally have been 

followed by a decline in the quality of reservoir water during 

recovery. The droughts that occurred during the last decade are 

no exception. The projected climate-related changes described 

above could result in marked increases in storm-borne contaminants (nutrient, sediment, salt, and bacterial loads) to the 

tributaries and reservoirs during storm events that lead to reservoir recovery. As of the mid-1990s, the monitoring design, 

which relies chiefly on dry-weather-flow monitoring, cannot 

adequately quantify the effects of drought-recovery episodes 

on tributary and reservoir biotic and water-quality conditions, 

and thus address most water-quality concerns, particularly if 

recovery periods increasingly are the result of intense rainfall 

or snow storms.

Framework Integration to Enhance WaterQuality Monitoring

Collectively, and as of 2007, the reservoir monitoring 

system could be improved in several key areas to obtain the 

data necessary to address long-term and emerging waterquality concerns. Improvements could be made in three major 

areas: (a) the monitoring design framework, (b) the spatial 

and temporal resolution of water-quality assessments in the 

major tributaries and reservoirs, and (c) the management and 

archival of data, including data-quality and methods verification and documentation.

Framework Design

The framework design could include a formal phytoplankton model, such as the Phytoplankton Ecology Group 

model. This model not only would describe seasonal taxa and 

their abundance, but intra-seasonal variations in phytoplankton 

succession. Data from this model could be analyzed in relation to intra-seasonal data on bioavailable (dissolved and total 

dissolved) as well as total nutrients and trophic indices to (a) 

improve the RTG’s understanding of reservoir water-quality 

and biotic conditions, (b) help identify nutrient concentrations 

associated with major algal blooms and their taxa, (c) help 

identify whether phosphorus and (or) nitrogen are limiting 

nutrients, and, with time, (d) help identify whether the frequency of eutrophic conditions and (or) occurrence of major 

algal blooms is declining, and why.

The framework design generally could benefit from 

alterations in monitoring to improve the characterization of 

water-quality conditions associated with intra-seasonal and 

annual variations in climate. This would require monitoring to 

collect water-quality and biotic data for the full range in flows 

in tributaries within a year and from year to year. 

The framework design could benefit from the aggregation, and as necessary, collection, of the basic hydrodynamic 

data necessary to quantitatively describe the full range in 

temporal variations in seasonal and annual climatic and 

hydrologic conditions for each reservoir watershed and reservoir. The minimal monitoring data required would include 

daily temperature (mean), daily precipitation (total and type), 

continuous or partial records of streamflows depending on the 

type of tributary monitoring station, and daily water levels, 

withdrawals, and releases from each reservoir. 

The framework design generally could benefit from an 

increased use of statistical methods to help define, aggregate, 

analyze, and interpret data. Numerous examples where interpretive data appeared in reports but statistical analyses were 

lacking are presented throughout this review. Although waterquality models have been developed for the Loch Raven and 

Prettyboy watersheds and reservoirs, these models could be 

improved, and a similar improved model could be developed 

for the Liberty watershed and reservoir. 

Spatial and Temporal Resolution of Water-Quality 

Assessments

To illustrate that tributary monitoring falls short in the 

representation of annual (water year) streamflow in perhaps 

all but the driest of years, the annual flow regimes for the six 

gaged tributaries from 2000–06 were examined in relation to 

daily mean flows, and in particular, the number of days of high 

flows (75th percentile flows or greater) per year. The period 

of record chosen reflects several extremely wet as well as dry 

years. The resultant data indicate that sampling just five stormflow events per year along with monthly dry-weather flows is 

likely to cover the annual flow regime in only the driest years 

of record. 
Summary 101

To adequately address tributary flow regime in all three 

reservoir watersheds, it is proposed that sampling for predefined high (or storm-) flow conditions could occur at seven 

stations (historical stormflow stations in the supply reservoirs 

and one new station on a tributary to Prettyboy Reservoir) for 

3–15 high-flow conditions per station distributed throughout 

the year. Predefined base-flow conditions would be sampled 

at each station within a monthly fixed time interval. Sampling 

at all of the other tributary (remaining historical dry-weatherflow as well as wastewater treatment plant or WWTP) stations 

would be sampled monthly during a fixed time interval, but 

regardless of the magnitude of flow condition at each station.

Other changes could be made to improve the spatial 

and temporal resolution of assessments of water-quality and 

biotic conditions in the reservoir watershed tributaries and in 

the reservoirs and thus in relation to modeling or statistical 

assessments related to most water-quality concerns. Tributary 

monitoring (including WWTPs) that could address all waterquality and biotic parameter limitations described in this 

review include in-stream measurements of temperature, pH, 

DO, conductance, and turbidity. These measurements initially 

could help determine what methods could be used to collect 

a representative sample, and ultimately help characterize 

stream-water-quality conditions at the time of sampling. It 

also would include the collection at the appropriate times of 

samples for suspended sediment, sodium, chloride, total and 

dissolved organic carbon, total-, total dissolved-, and dissolved 

phosphorus, and total Kjeldahl- or organic-, as well as nitrate 

plus nitrite-, and ammonia-nitrogen. Reservoir monitoring 

(generally monthly or bimonthly) at eight historical reservoirmonitoring locations (and as appropriate for the Susquehanna 

River if it is used) that could address all of the water-quality 

and biotic parameter limitations noted earlier in this review 

would include the collection at the appropriate times (generally monthly or bimonthly, but in selected cases, less frequently) of samples for suspended sediment, sodium, chloride, 

total and dissolved organic carbon, total-, total dissolved-, 

and dissolved phosphorus, and total Kjeldahl- or organic-, as 

well as nitrate plus nitrite-, and ammonia-nitrogen. In addition, bimonthly sampling would include samples for algal taxa 

identification and counts and chemical oxygen demand at all 

eight reservoir-monitoring locations. Sampling at each reservoir station also would be conducted at depths similar to those 

used under the ongoing monitoring design, but also at the 

15-foot depth during reservoir stratification to ensure sufficient 

data are obtained in the epilimnion (defined by temperature 

and transparency conditions). 

In addition, a major change that could be implemented 

with respect to monitoring reservoir water quality could be the 

use of water-quality profile monitors to provide the short-term 

data for key parameters necessary to relate watershed tributary-reservoir hydrodynamics and the associated water-quality 

and biotic conditions that reflect major storm events, and 

seasonal and annual variations in climate, including drought 

and recovery conditions. Two fixed-station continuous monitors could be established in each reservoir. Each fixed-station 

monitor could provide daily 5-foot depth-increment profiles 

for at least seven parameters—water temperature, DO, pH, 

specific conductance, chl-a, turbidity, and depth of measurement. If upgraded to real-time, these reservoir monitors also 

could provide the data needed to provide advance warning of 

potential problems in treated waters. 

In relation to sedimentation and specifically future 

bathymetric surveys, the latter could be conducted in the late 

fall or early spring to reduce interference problems in past 

surveys caused by submerged aquatic vegetation. The most 

recent (1998–2000) and future survey results could be checked 

periodically to verify they are properly documented and that 

survey data remains properly archived for possible reuse. The 

most recent survey is the starting point to assess trends in each 

reservoir. As of 2007, surveys are to be conducted every 10–15 

years. Thus, the first real opportunity to determine actual 

trends in the loss of reservoir storage capacities will be after at 

least three surveys are completed, which would be sometime 

in 2030–45.

Data Documentation and Quality 

To ultimately reduce the likelihood of future data-quality 

issues, a comprehensive quality-assurance program and plan 

(QAPP) plan could be created by the RTG with clear lines of 

responsibility defined for each QAPP activity. On the basis of 

the general activities addressed in most standard QAPPs for 

long-term monitoring programs, such a plan could address all 

of the limitations identified in the review of the monitoring 

database and related documentation, through the inclusion of 

the following:

a) Clear and concise definitions of data-quality requirements for each hydrodynamic or water-quality parameter to be obtained;

b) A comprehensive description of the field and laboratory methods and procedures used to obtain and 

provide data, including the required quality-assurance 

and control data;

c) A comprehensive description of procedures for the 

archival and remarking of all data;

d) A comprehensive description of procedures for routine 

annual or bi-annual evaluation of the data collected, 

including quality-assurance and control data, to determine if data requirements are being met; 

e) A comprehensive description of procedures for modifying any of the above items (a through d) and documenting the changes; and 

f) Designation of the organization(s) that will carry out 

each of the above items. 
102 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Implementation of Enhanced Monitoring

The described modifications to the long-term monitoring 

network for the Baltimore Reservoir System are intended to 

be comprehensive in nature and address all long-term and 

emerging water-quality concerns. Prioritization and implementation of selected modifications to the monitoring program 

would require prioritization of RTG objectives, and ultimately 

RWMA water-quality concerns. The proposed modifications 

could be implemented as a pilot or trial effort in one of the 

supply-reservoir watershed systems. Routine monitoring then 

could conducted for at least several years, to obtain data over 

at least a range of climatic conditions, and the resultant data 

reviewed and analyzed to determine the real benefits compared to the expected benefits. On the basis of this pilot or trial 

effort, the resultant monitoring design could be implemented 

throughout the Baltimore Reservoir System.

Acknowledgments

This report is a product of a cooperative investigation 

between Baltimore City, Carroll and Baltimore Counties, and 

the U.S. Geological Survey (USGS). To aid in the preparation 

of this report, interviews were conducted with the following 

Reservoir Technical Group (RTG) personnel, whom we 

thank for providing historical and recent technical information related to the reservoir-monitoring program: Ralph 

Cullison, Chief, Environmental Services Division, Department 

of Public Works, City of Baltimore Bureau of Water and 

Wastewater; and within this division, William P. Stack, former 

Program Administrator, and Robert McAulay, Data Manager, 

Water-Quality Management Section, Eugene J. Scarpulla, 

Watershed Manager, Reservoir Natural Resources Section 

of the Department of Public Works, Baltimore City; Lisa 

Jones, Analyst, Montebello Water-Quality Laboratory, and 

Savita Bagel, Analyst, Ashburton Water-Quality Laboratory, 

Baltimore City Department of Public Works, Baltimore 

City; Thomas Devilbiss, Deputy Director, Hugh Murphy, 

Hydrogeologist, Bureau of Resource Management, and 

James Slater, Compliance Officer, Office of Environmental 

Compliance, Carroll County Department of Planning, 

Westminster, Maryland; Stephen Stewart, Manager, Watershed 

Management Section, Department of Environmental 

Protection and Sustainability, Baltimore County, Towson, 

Maryland; Gould Charshee, Chair of the Reservoir Technical 

Group, Baltimore, Maryland; Timothy C. Rule, Chief, 

Nutrient and Bacteria Division, Total Maximum Daily Load 

Technical Development Program, and Charles Poukish, Chief, 

Biological Assessments Division, Environmental Assessments 

and Standards Program, Science Services Administration, and 

Gul Behsudi, Water Resources Engineer, Source Protection 

and Appropriation Division, Water Supply Program, Water 

Management Administration, Maryland Department of the 

Environment, Baltimore, Maryland.

The authors also wish to sincerely thank USGS colleagues W. Reed Green and Douglas B. Chambers, and 

William P. Stack, Ellicott City, Maryland, for their peer 

reviews. We also appreciate the reviews of earlier drafts 

provided by Jerad Bales, USGS, Reston, Virginia, and the following RTG staff or their designees: William P. Stack, Robert 

McAulay, Thomas Devilbiss, Hugh Murphy, Stephen Stewart, 

Gould Charshee, and Clark Howells and Duncan Stewart, 

Department of Public Works, Baltimore County. In addition, 

the authors thank the following USGS Maryland-DelawareD.C. Water Science Center (WSC) staff: James M. Gerhart, 

retired WSC Director, for reviewing and assisting on earlier 

report drafts, and Robert J. Shedlock and Matthew Pajerowski 

for their supervisory assistance in arranging meetings with the 

RTG personnel and staff members of their respective organizations. The authors also thank the following members of the 

USGS Office of Communications and Publishing, Science 

Publishing Network: Valerie Gaine, Editor, and Timothy Auer 

and Gloria Jean Wilson, Visual Information Specialists, who 

aided in the preparation of this report.

References Cited

Acker, J.G., Harding, L.W., Leptoukh, G., Zhu, T., and 

Shen, S., 2005, Remotely-sensed chl a at the Chesapeake 

Bay mouth is correlated with annual freshwater flow to 

Chesapeake Bay: Geophysical Research Letters, v. 32, 

L05601, 4 p., DOI:10.1029/2004GL021852.

Amatayakul, P., Cox, R., Defries, R., Delatour, R., Moy, W., 

Shobrys, D., Boland, J., and Chamberlin, C., 1978, Jones 

Falls and Loch Raven Watersheds: Baltimore, Maryland, 

Johns Hopkins University Department of Geography and 

Environmental Engineering, Final Report to Regional 

Planning Council, 111 p.

Amatayakul, P., Defries, R., Shobrys, D., Boland, J., and 

Chamberlin, C., 1978, Jones Falls and Loch Raven 

Watersheds: Baltimore, Maryland, Johns Hopkins 

University Department of Geography and Environmental 

Engineering, Interim Report to Regional Planning Council, 

57 p. 

Arrigo, K.R., 2005, Marine microorganisms and global 

nutrient cycles: Nature, v. 437, p. 349–355, DOI:10.1038/

nature04159.

Bales, J.D., and Giorgino, M.J., 1998, Lake Hickory, North 

Carolina: Analysis of ambient conditions and simulation 

of hydrodynamics, constituent transport, and water-quality 

characteristics, 1993–94: U.S. Geological Survey WaterResources Investigations Report 98–4149, 62 p.
References Cited 103

Bales, J.D., Sarver, K.M., and Giorgino, M.J., 2001, Mountain 

Island Lake, North Carolina: Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics, 1996–97: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4138, 85 p.

Baltimore City Department of Public Works, 1992, Appendix 

C: Reservoir watershed management progress report, 

Baltimore, Maryland, in Reservoir Watershed Protection 

Committee, 2000, Action report for reservoir watersheds: 

Baltimore, Maryland, 70 p., plus appendixes. 

Baltimore City Department of Public Works, 1996, Volume 

I: Selected graphics, report conclusions, and discussion: 

Baltimore, Maryland, Reservoir Watershed Management 

Progress Report, 128 p.

Baltimore City Department of Public Works, 2000, Appendix 

C: Reservoir water quality assessment for Loch Raven, 

Prettyboy and Liberty reservoirs, Interim Report, 

Department of Public Works, in Action report 2000 for the 

reservoir watersheds: Baltimore, Maryland, Watershed 

Protection Committee, 37 p.

 Baltimore City Department of Public Works, 2001, Reservoir 

water quality assessment for Loch Raven, Prettyboy, and 

Liberty reservoirs: Baltimore, Maryland, 39 p.

Baltimore County Department of Environmental Protection 

and Resource Management, 2008, Prettyboy reservoir 

watershed characterization report, Baltimore County: 

Towson, Maryland, 101 p. 

Baltimore Reservoir Technical Group, 2004, Water quality 

assessment, targeted studies and ongoing water quality 

issues in the Baltimore metropolitan water supply reservoirs and their watersheds: Baltimore, Maryland, Reservoir 

Program Technical Report, 46 p. 

Baltimore Reservoir Technical Group, 2007, Implementation 

of the 2005 reservoir watershed action strategy for calendar 

year 2006, Partial Progress (Interim) Report: Baltimore, 

Maryland, Reservoir Technical Group, 11 p.

Banks, W.S.L., and LaMotte, A.E., 1999, Sediment accumulation and water volume in Loch Raven Reservoir, 

Baltimore County, Maryland: U.S. Geological Survey 

Water-Resources Investigations Report No. 99–4240, 1 pl., 

accessed March 15, 2011 at http://md.water.usgs.gov/

publications/wrir-99-4240/.

Bergamaschi, B.A., Fram, M.S., Kendall, C., Silva, S.R., 

Aiken, G.R., and Fujii, R., 1999, Carbon isotopic constraints on the contribution of plant material to the natural 

precursors of trihalomethanes: Organic Geochemistry, 

v. 30, no. 8, p. 835–842, DOI: 10.1016/

S0146-6830(9a)00066-2.

Bergamaschi, B.A., Kalve, Erica, Guenther, Larry, Mendez, 

G.O., and Belitz, Kenneth, 2005, An assessment of optical properties of dissolved organic material as quantitative 

source indicators in the Santa Ana River Basin, Southern 

California: U.S. Geological Survey Water-Resources 

Investigations Report 2005–5152, 38 p., available online at 

http://pubs.usgs.gov/sir/2005/5152/sir_2005-5152.pdf.

Bulgakov, N.G., and Levich, A.P., 1999, The nitrogen: phosphorus ratio as a factor regulating phytoplankton community structure: Archiv für Hydrobiologie, v. 146, no. 1, 

p. 3–22.

Caffrey, A.J., Hoyer, M.V., and Canfield, D.E., Jr., 2007, 

Factors affecting the maximum depth of colonization 

by submersed macrophytes in Florida lakes: Lake and 

Reservoir Management, v. 23, p. 287–297. 

California Water Resources Control Board, 2008, Quality 

assurance program plan: Sacramento, California, Surface 

Water Ambient Monitoring Program, Final Technical 

Report, 190 p.

Carlson, R.E., and Simpson, J., 1996, A coordinator’s guide to 

volunteer lake monitoring methods: North American Lake 

Management Society, 96 p., accessed March 15, 2011 at 

http://www.secchidipin.org/tsi.htm.

Chesapeake Bay Program, 2008, Chapter V: Non-tidal water 

quality monitoring: Annapolis, Maryland, Chesapeake Bay 

Program, 17 p., accessed March 15, 2011 at http://archive.

chesapeakebay.net/pubs/subcommittee/msc/amqawg/

Chapter%205%20Nov%2008%20Final.pdf.

Chesapeake Bay Program, 2010, Chesapeake Bay Program 

split sample program implementation guidelines, Revision 

4, 17 p., accessed March 15, 2011 at http://archive.

chesapeakebay.net/pubs/quality_assurance/CSSP_

Guidelines_12-17-10.pdf.

Downing, J.A., Watson, S.B, and McCauley, Edward, 2001, 

Predicting Cyanobacteria dominance in lakes: Canadian 

Journal of Fisheries and Aquatic Sciences, v. 58, no. 10, p. 

1,905–1,908, DOI: 10.1139/cjfas-58-10-1905.

Dmytriw, R., Mucci, A., Lucotte, M., and Pichet, P., 1995, 

The partitioning of mercury in the solid components of dry 

and flooded forest soils and sediments from a hydroelectric 

reservoir, Quebec (Canada): Water, Soil, and Air Pollution, 

v. 80, nos. 1–4, p. 1,099–1,103, DOI: 10.1007/BF01189770.

Fram, M.S., Bergamaschi, B.A., and Fujii, Roger, 2001, 

Improving water quality in Sweetwater Reservoir, San 

Diego County, California: Sources and mitigation strategies 

for trihalomethane (THM)-forming carbon: 

U.S. Geological Survey Fact Sheet 112–01, 4 p., available 

online at http://pubs.usgs.gov/fs/fs-112-01/.
104 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Francy, D.S., Myers, D.N., and Helsel, D.R., 2000, 

Microbiological monitoring for the U.S. Geological Survey 

National Water-Quality Assessment Program: 

U.S. Geological Survey Water-Resources Investigations 

Report 00–4018, 31 p., accessed June 15, 2011 online at 

http://oh.water.usgs.gov/reports/wrir/wrir.00-4018.pdf.

Galloway, J.M., and Green, W.R., 2004, Water-quality 

assessment of Lakes Maumelle and Winona, Arkansas, 

1991 through 2003: U.S. Geological Survey Scientific 

Investigations Report, 2004–5182, 46 p., available online at 

http://pubs.usgs.gov/sir/2004/5182/.

Galloway, J.M., and Green, W.R., 2006a, Analysis of 

ambient conditions and simulation of hydrodynamics and 

water-quality characteristics in Beaver Lake, Arkansas, 

2001 through 2003: U.S. Geological Survey Scientific 

Investigations Report, 2006–5003, 55 p., available online at 

http://pubs.usgs.gov/sir/2006/5003/.

Galloway, J.M. and Green, W.R., 2006b, Application of a 

two-dimensional reservoir water-quality model of Beaver 

Lake, Arkansas, for the evaluation of simulated changes in 

input water quality, 2001–2003: U.S. Geological Survey 

Scientific Investigations Report 2006–5302, 31 p., available 

online at http://pubs.usgs.gov/sir/2006/5302/.

Gellis, A.C., Banks, W.S.L., Langland, M.J., and Martucci, 

S.K., 2005, Summary of suspended-sediment data for 

streams draining the Chesapeake Bay watershed, water 

years 1952–2002: U.S. Geological Survey Scientific 

Investigations Report, 2004–5056, 59 p., available online at 

http://pubs.usgs.gov/sir/2004/5056/.

Giorgino, M.J., and Bales, J.D., 1997, Rhodhiss Lake, North 

Carolina: Analysis of ambient conditions and simulation 

of hydrodynamics, constituent transport, and water-quality 

characteristics, 1993–94: U.S. Geological Survey WaterResources Investigations Report 97–4131, 62 p.

Glodt, S.R., and Pirkey, K.D., 1998, Participation in performance-evaluation studies by U.S. Geological Survey 

National Water-Quality Laboratory, Denver, Colorado: 

U.S Geological Survey Fact Sheet FS–23–98, 6 p., 

accessed January 13, 2010 at http://nwql.usgs.gov/rpt.

shtml?FS-023-98.

Graham, N.J.D., Wardlaw, V.E., Perry, R., and Jiang, Jia-qian, 

1998, The significance of algae as trihalomethane precursors: Water Science and Technology, v. 37, no. 2, p. 83–89. 

Granato, G.E., and Smith, K.P., 1999, Estimating concentrations of road-salt constituents in highway-runoff from measurements of specific conductance: U.S. Geological Survey 

Water-Resources Investigations Report 99–4077, 

22 p., available online at http://pubs.usgs.gov/wri/

wri99-4077/.

Helsel, D.R, and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 522 p.

Hem, J.D., 1970, Study and interpretation of the chemical 

characteristics of natural waters, 2d ed.: U.S. Geological 

Water Supply Paper 1473, Washington, D.C., U.S. 

Government Printing Office, 383 p.

Hirsch, R.M., Moyer, D.L., and Archfield, S.A., 2010, 

Weighted regressions on time, discharge, and season 

(WRTDS), with an application to Chesapeake Bay 

river inputs: Journal of the American Water Resources 

Association, v. 46, no. 5, p. 857–880. 

Intergovernmental Panel on Climate Change, 2007, Climate 

Change 2007: Synthesis report summary for policymakers: 

Intergovernmental Panel on Climate Change Plenary 

XXVII, Valencia, Spain, November 12–17, 2007, 22 p.

Intergovernmental Task Force on Monitoring Water Quality, 

1995, The strategy for improving water-quality monitoring 

in the United States—Final Report of the Intergovernmental 

Task Force on Monitoring Water Quality: U.S. Geological 

Survey Open-File Report 95–742, 25 p. 

Interstate Commission on the Potomac River Basin, 2006, 

Modeling framework for simulating hydrodynamics and 

water quality in the Prettyboy and Loch Raven reservoirs, 

Gunpowder River basin, Maryland: Rockville, Maryland, 

Interstate Commission on the Potomac River Basin, 230 p., 

plus appendixes. 

Jack, J., Sellers, T., and Bukaveckas, P.A., 2002, Algal production and trihalomethane formation potential: an experimental assessment and inter-river comparison: Canadian 

Journal of Fisheries and Aquatic Sciences, v. 59, no. 9, p. 

1,482–1,491.

Kaushal, S.S., Groffman, P.M., Band, L.E., Shields, C.A., 

Morgan, R.P., Palmer, M.A., Belt, K.T., Swan, C.M., 

Findlay, S.E.G., and Fisher, G.T., 2008, Interaction between 

urbanization and climate variability amplifies watershed 

nitrate export in Maryland: Environmental Science & 

Technology, v. 42, no. 16, p. 5,872–5,878, DOI: 10.1021/

es800264f.

Kaushal, S.S., Pace, M.L., Groffman, P.M., Band, L.E., 

Belt, K.T., Mayer, P.M., and Welty, C., 2010, Land use 

and climate variability amplify contaminant pulses: Eos 

Transactions, American Geophysical Union, v. 91, no. 25, p. 

221–222, DOI: 10.1029/2010EO250001.

KCI Technologies, Inc., 2004, Total phosphorus in three 

Baltimore City reservoirs, variations and trends: Baltimore, 

Maryland, 35 p.
References Cited 105

Keith, L.D., 2006, Environmental monitoring and measurement advisor, Instant Reference Sources, Inc., Monroe, 

Georgia, accessed March 15, 2010 at http://www.emmaexpertsystem.com/.

 Krabbenhoft, D.P., and Fink, L.E., 2001, The effect of 

dry down and natural fires on mercury methylation in 

the Florida Everglades, Appendix 7–8 in Everglades 

Consolidation Report: West Palm Beach, Florida, South 

Florida Watershed Management District, 14 p., accessed 

March 15, 2010 at http://my.sfwmd.gov/portal/page/portal/

pg_grp_sfwmd_sfer/portlet_prevreport/consolidated_01/

chapter%2007/chapter%207%20appendices/a07-08.pdf.

Krabbenhoft, D.P., Fink, L.E., Olsen, M.L., and Rawlick, P.S., 

II, 2000, The effect of dry down and natural fires on mercury methylation in the Florida Everglades, in Proceedings 

of the International Conference on Heavy Metals in the 

Environment, August 6–10, 2000, Ann Arbor, Michigan.

Krasner, S.W., Weinberg, H.S., Richardson, S.D., Pastor, S.J., 

Chinn, R., Sclimenti, M.J., Onstad, G.D., and Thurston, 

A.D., Jr., 2006, Occurrence of a new generation of disinfection byproducts: Environmental Science & Technology, 

v. 40, no. 23, p. 7,175–7,185, DOI: 10.1021/es060353j.

Kraus, T.E.C., Anderson, C.A., Morgenstern, Karl, Downing, 

B.D., Pellerin, B.A., and Bergamaschi, B.A., 2010, 

Determining sources of dissolved organic carbon and 

disinfection byproduct precursors to the McKenzie River, 

Oregon: Journal of Environmental Quality, v. 39, no. 6, 

p. 2,100–2,112, DOI: 10.2134/jeq2010.0030.

Kraus, T.E.C., Bergamaschi, B.A., Hernes, P.J., Doctor, D., 

Kendall, C., Downing, B.D., and Losee, R.F., 2011, How 

reservoirs alter drinking water quality: Organic matter 

sources, sinks, and transformations: Lake and Reservoir 

Management, v. 27, no. 3, p. 205–219.

Kraus, T.E.C., Bergamaschi, B.A., Hernes, P.J., Spencer, 

R.G.M., Stepanauskas, R., Kendall, C., Losee, R.F., and 

Fujii, R., 2008, Assessing the contribution of wetlands 

and subsided islands to dissolved organic matter and 

disinfection byproduct precursors in the Sacramento-San 

Joaquin River Delta: A geochemical approach: Organic 

Geochemistry, v. 39, no. 9, p. 1,302–1,318, DOI: 10.1016/j.

orggeochem.2008.05.012.

Langland, M.J., Moyer, D.L., and Blomquist, Joel, 2007, 

Changes in streamflow, concentrations, and loads in 

selected nontidal basins in the Chesapeake Bay watershed, 

1985–2006: U.S. Geological Survey Open-File Report 

2007–1372, 76 p., available online at http://pubs.usgs.gov/

of/2007/1372/.

Levich, A.P., 1996, The role of nitrogen-phosphorus ratio in 

selecting for dominance of phytoplankton by cyanobacteria 

or green algae and its application to reservoir management: 

Journal of Aquatic Ecosystem Stress and Recovery (formerly Journal of Aquatic Ecosystem Health), v. 5, no. 1, 

p. 55–61, DOI: 10.1007/BF00691729.

Lindenmayer, D.B., and Likens, G.E., 2009, Adaptive monitoring: a new paradigm for long-term research and monitoring: Trends in Ecology and Evolution, v. 24, no. 9, p. 

482–486.

Maryland Department of the Environment, 2002a, Total 

maximum daily load for mercury in Loch Raven reservoir, 

Baltimore County, Maryland, Final Report and Final 

Comments: Baltimore, Maryland, Maryland Department of 

the Environment, 55 p.

Maryland Department of the Environment, 2002b, Total 

maximum daily load for mercury in Prettyboy reservoir, 

Baltimore County, Maryland, Final Report and Final 

Comments: Baltimore, Maryland, Maryland Department of 

the Environment, 55 p.

Maryland Department of the Environment, 2002c, Total maximum daily load for mercury in Liberty reservoir, Baltimore 

County, Maryland, Draft Report for Comments: Baltimore, 

Maryland, Maryland Department of the Environment, 50 p.

Maryland Department of the Environment, 2003a, Water 

quality analysis of heavy metals for the Loch Raven reservoir impoundment in Baltimore County, Maryland, Final 

Report: Baltimore, Maryland, Maryland Department of the 

Environment, 22 p.

Maryland Department of the Environment, 2003b, Water 

quality analysis of heavy metals for the Prettyboy reservoir 

impoundment in Baltimore County, Maryland, Final 

Report: Baltimore, Maryland, Maryland Department of the 

Environment, 20 p.

Maryland Department of the Environment, 2003c, Water quality analysis of chromium and lead for the Liberty reservoir 

impoundment in Baltimore and Carroll Counties, Maryland, 

Final Report: Baltimore, Maryland, Maryland Department 

of the Environment, 20 p.

Maryland Department of the Environment, 2003d, Water 

quality and management plan for the Loch Raven watershed 

study area in Baltimore County, Maryland: Annapolis, 

Maryland, Maryland Department of the Environment, 

180 p.

Maryland Department of the Environment, 2004a, Source 

water assessment for Loch Raven watershed: Baltimore, 

Maryland, Maryland Department of the Environment, 99 p., 

plus additional appendixes.
106 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Maryland Department of the Environment, 2004b, Approval 

and rationale of total maximum daily load for mercury 

in Loch Raven reservoir, Baltimore County, Maryland: 

Baltimore, Maryland, Maryland Department of the 

Environment, 14 p.

Maryland Department of the Environment, 2004c, Approval 

and rationale of total maximum daily load for mercury 

in Prettyboy reservoir, Baltimore County, Maryland: 

Baltimore, Maryland, Maryland Department of the 

Environment, 14 p.

Maryland Department of the Environment, 2006, Total maximum daily loads of phosphorus and sediments for Loch 

Raven reservoir and total maximum daily loads of phosphorus for Prettyboy reservoir, Baltimore, Carroll and Harford 

Counties, Maryland, Final Report, 2006: Baltimore, 

Maryland, Maryland Department of the Environment, 

135 p., plus appendixes. 

Maryland Department of the Environment, 2008, Integrated 

report of surface water quality in Maryland: Baltimore, 

Maryland, Maryland Department of the Environment, 

188 p., plus additional tables.

Maryland Department of Planning, 2000a, Maryland 

Department of Planning land use and land cover data from 

year 2000, Annapolis, Maryland, unnumbered table, 

p. 28, in Maryland Department of Natural Resources, 2002, 

Liberty Reservoir watershed characterization: Annapolis, 

Maryland, 61 p., plus additional maps.

Maryland Department of Planning, 2000b, Maryland 

Department of Planning land use and land cover data from 

Land Cover Map Series 2000, Annapolis, Maryland, fig. 4, 

p. 5 in Maryland Department of the Environment, 2007, 

Total maximum daily loads of phosphorus and sediments 

for Loch Raven reservoir and total maximum daily loads 

of phosphorus for Prettyboy reservoir, Baltimore, Carroll 

and Harford Counties, Maryland, Final Report: Baltimore, 

Maryland, 42 p. 

Mash, H., Westerhoff, P.K., Baker, L.A., Nieman, R.A., and 

Nguyen, My-Lihn, 2004, Dissolved organic matter in 

Arizona reservoirs: assessment of carbonaceous sources: 

Organic Geochemistry, v. 35, no. 7, p. 831–843, DOI: 

10.1016/j.orggeochem.2004.03.002.

Miller, W.D., Harding, L.W., Jr., and Adolf, J.E., 2006, 

Hurricane Isabel generated an unusual fall bloom in 

Chesapeake Bay: Geophysical Research Letters, v. 33, 

L06612, 4 p., DOI: 1029/2005GL025658.

Mogil, H.M., and Seaman, K.L., 2009, The climate and 

weather of Delaware, Maryland, and Washington, D.C.: 

Weatherwise, July–August, p. 16–24.

Morrel, F.M.M., Kraepiel, A.M.L., and Amoyt, Marc, 1998, 

The chemical cycle and bioaccumulation of mercury: 

Annual Review of Ecology and Systematics, v. 29, 

p. 543–566.

Newman, S., and Pietro, K., 2001, Phosphorus storage and 

release in response to flooding: implications for Everglades 

stormwater treatment areas: Ecological Engineering, v. 18, 

no. 1, p. 23–28, DOI: 10.1016/S0925-8574(01)00063-5.

Ortt, R.A., Jr., Kerhin, R.T., Wells, Darlene, and Cornwell, 

Jeff, 2000, Bathymetric survey and sedimentation analysis 

of Loch Raven and Prettyboy Reservoirs: Maryland 

Geological Survey, Coastal and Estuarine Geology File 

Report Number 99–4, 56 p., plus appendixes, accessed 

March 15, 2011 at http://www.mgs.md.gov/coastal/pub/

FR99-4.pdf .

Padisák, J., 2004, Phytoplankton, chapter 10, in O’Sullivan, 

P.E., and Reynolds, C.S., eds., 2004, The lakes handbook: 

limnology and limnetic ecology, volume 1: Malden, 

Massachusetts, Wiley-Blackwell Publishing Company, 

p. 251–308. 

Palmer, M.A., Liermann, C.A.R., Nilsson, C., Florke, M., 

Alcamo, J., Lake, P.S., and Bond, N., 2008, Climate change 

and the world’s river basins: Anticipating management 

options: Frontiers in Ecology and the Environment, v. 6, 

no. 2, p. 81–89.

Phillips, G.L., 2010, Eutrophication of shallow temperate 

lakes, chapter 10, in O’Sullivan, P.E., and Reynolds, C.S., 

eds., 2004, The lakes handbook: limnology and limnetic 

ecology, volume 2: Malden, Massachusetts, WileyBlackwell Publishing Company, p. 261–278.

Rasmussen, P.P., and McAllister, D.H., 2005, Monitoring the 

water quality of Lake Olathe, Johnson County, Kansas: 

U.S. Geological Survey Fact Sheet 2005–3093, 2 p., available online at http://pubs.usgs.gov/fs/2005/3093/.

Rast, W., and Lee, G.F., 1978, Summary of analysis of the 

North American (U.S. portion) OECD Eutrophication 

Project: Nutrient loading—Lake response relationships 

and trophic state indices: Corvallis, Oregon, U.S. 

Environmental Protection Agency Report Number EPA600/3-78-008, 453 p. 

Rawlick, P., 2001, Stormwater treatment area 1 west: 

Results of startup mercury monitoring, appendixes 7–14, 

in Everglades Consolidated Report: West Palm Beach, 

Florida, South Florida Watershed Management District, 

12 p., accessed March 15, 2011 at https://my.sfwmd.gov/

portal/page/portal/pg_grp_sfwmd_sfer/portlet_prevreport/

consolidated_01/index.html.
References Cited 107

Redfield, A.C., 1958, The biological control of chemical factors in the environment: American Scientist, v. 46, 

p. 205–221.

Reinelt, L.E., Horner, R.R., and Mar, B.W., 1988, Nonpoint 

source pollution monitoring program design: Journal of 

Water Resources Planning and Management, v. 114, no. 3, 

p. 335–352.

Reservoir Watershed Management Agreement, 2005, 

Baltimore management agreement: Baltimore, Maryland, 

Reservoir Watershed Protection Program, Baltimore, 

Maryland, 10 p.

Reservoir Watershed Management Agreement Action 

Strategy, 2005, Action strategy for the reservoir watersheds: 

Baltimore, Maryland, Baltimore Reservoir Management 

Program, Baltimore, Maryland, 13 p.

Reservoir Watershed Protection Committee, 2000, Action 

report for reservoir watersheds: Baltimore, Maryland, 

Reservoir Watershed Protection Committee, 70 p., plus 

additional appendixes.

Reservoir Watershed Protection Subcommittee, 1992, Action 

report for the reservoir watersheds: Baltimore, Maryland, 

Reservoir Watershed Protection Subcommittee, 17 p., plus 

additional appendixes.

Rowland, R.C., Westenburg, C.L., Veley, R.J., and Nylund, 

W.E., 2006, Physical and chemical water-quality data 

from automatic profiling systems, Boulder Basin, Lake 

Mead, Arizona and Nevada, water years 2001–04: U.S. 

Geological Survey Open-File Report 2006–1284, 27 p., 

available online at http://pubs.usgs.gov/of/2006/1284/.

Ryding, O.E., and Rast, W., eds., 1989, The control of eutrophication in lakes and reservoirs: Paris, France, Man and 

the Biosphere Series, v. 1, United Nations Educational, 

Scientific, and Cultural Organization (UNESCO), 314 p.

Sarver, K.M., and Steiner, B.C., 1998, Hydrologic and waterquality data from Mountain Island Lake, North Carolina, 

1994–97: U.S. Geological Survey Open-File Report 

98–549, 165 p.

Schloss, Jeffrey, 2002, Murky waters: Gaining clarity on 

water transparency measurements in The clean water 

team guidance compendium for watershed monitoring 

and assessment: Durham, New Hampshire, University of 

New Hampshire, Cooperative Extension and the Center for 

Freshwater Biology, State Water Resources Control Board, 

Division of Water Quality, 12 p.

Singer, P.C., 1999, Humic substances as precursors for potentially harmful disinfection by-products: Water and Science 

Technology, v. 40, no. 9, p. 25–30.

Singer, P.C, Weinberg, H.S, Krasner, S., Harish, A., and Najm, 

I., 2002, Relative dominance of HAAs and THMs in treated 

drinking water: Denver, Colorado, American Water Works 

Association and Research Foundation, 293 p.

Sommer, U., Gliwicz, Z.M., Lampert, W., and Duncan, A., 

1986, The PEG-model of seasonal succession of planktonic 

events in fresh waters: Archiv für Hydrobiologie, v. 106, 

no. 4, p. 433–471.

Stewart, S., Gemmill, E., and Pentz, N., 2005, An evaluation 

of the functions and effectiveness of riparian forest buffers: Alexandria, Virginia, Baltimore County Department 

of Environmental Protection and Resource Management, 

Report to the Water Environment Research Foundation, 

123 p., plus additional appendixes. 

Susquehanna River Basin Commission, 2006, Conowingo 

pond management plan: Harrisburg, Pennsylvania, 

Susquehanna River Basin Commission Publication Number 

242, 153 p. 

Sveinsdottir, A.Y., and Mason, R.P., 2005, Factors controlling 

mercury and methylmercury concentrations in largemouth 

bass (Micropterus salmoides) and other fish from Maryland 

reservoirs: Archives of Environmental Contaminant 

Toxicology, v. 49, no. 4, p. 528–545. 

The H. John Heinz III Center for Science, Economics, and the 

Environment, 2008, The state of the nation’s ecosystems 

2008: Focus on nitrogen: Washington, D.C., Fact Sheet, 

6 p., accessed June 26, 2011 at http://www.heinzctr.org/

ecosystems/2008report/pdf_files/Nitrogen_Fact_Sheet.pdf.

Tõnno, I., 1999, The impact of nitrogen and phosphorus concentration and N/P ratio on cyanobacterial dominance and 

N2 fixation in some Estonian Lakes, Tartu: Estonia, Spain, 

University Press, 46 p. 

U.S. Environmental Protection Agency, 2001, Requirements 

for quality-assurance project plans EPA QA/R-5: 

Washington, D.C., Office of Environmental Planning, 

U.S. Environmental Protection Agency Report 

EPA/240/B-01/003, 24 p., plus appendixes, accessed March 

15, 2011 at http://www.epa.gov/quality1/qs-docs/r2-final.

pdf. 

U.S. Environmental Protection Agency, 2003, Drinking 

water advisory: Consumer acceptability advice and health 

effects analysis on sodium: U.S. Environmental Protection 

Agency, Office of Water, Washington, D.C., Report Number 

EPA 822-R-03-006, 29 p.
108 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

U.S. Environmental Protection Agency, 2006, National 

Primary Drinking Water Regulations: 40 CFR Parts 9, 

141, and 142, Stage 2 Disinfectants and Disinfection 

Byproducts Rule: Final Rule, in Federal Register, National 

Archives and Records Administration, v. 72, no. 2, p. 

392–436, accessed March 15, 2011 at http://frwebgate.

access.gpo.gov/cgi-bin/getdoc.cgi?dbname=2006_

register&docid=fr04ja06-14.pdf.

U.S. Environmental Protection Agency, 2008, National Risk 

Management Research Laboratory’s quality assurance 

program plan requirements for measurement projects, 2 p., 

accessed March 15, 2011 at http://www.epa.gov/nrmrl/qa/

pdf/MeasurementQAPPNRMRLrev0.pdf.

U.S. Environmental Protection Agency, 2009, Drinking water 

standards and health advisories, 2009 edition: Washington, 

D.C., U.S. Environmental Protection Agency, Office of 

Water, Report Number EPA 822-R-09-011, 12 p.

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.

Valcik, J.A., 1975, Algae in Baltimore’s reservoirs: Journal of 

American Water Works Association, v. 67, no. 3, 

p. 109–113.

Vitousek, P.M., Mooney, H.A., Lubchenco, Jane, and Melillo, 

J.M., 1997, Human domination of Earth’s ecosystems: 

Science, v. 277, no. 5325, p. 494–499.

Wagner, R.J., Bougler, R.W., Jr., Oblinger, C.J., and Smith, 

B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors: Station operation, record 

computation, and data reporting: U.S. Geological Survey, 

Techniques and Methods Report 1–D3, 51 p., plus attachments, available online at http://pubs.usgs.gov/tm/2006/

tm1D3/.

Walker, W.W., Jr., 1988, Evaluating watershed monitoring 

programs, Report to Bureau of Water and Waste Water: 

Baltimore, Maryland, 87 p., plus additional appendix.

Wall, G.R., Nystrom, E.A., and Litten S., 2008, Suspended 

sediment transport in the freshwater reach of the Hudson 

River estuary in eastern New York: Estuaries and Coasts, 

v. 31, no. 3, p. 542–553, DOI: 10.1007/s12237-008-9050-y.

Weisberg, S.B., Rose, K.A., Clevenger, B.S., and Smith, J.O, 

1985, Chapter III: Dams with potential for hydroelectric 

power, in Inventory of Maryland Dams and Assessment 

of Hydropower Resources: Columbia, Maryland, Martin 

Marietta Environmental Systems, Report Number PPSP-85-

02, p. 4–9.

Weiss, C.M., and Kuenzler, E.J., 1976, The trophic state of 

North Carolina lakes: Chapel Hill, North Carolina, Water 

Resources Research Institute of the University of North 

Carolina, Report Number 119, 224 p.

Wetzel, R.G., 2001, Limnology: lake and river ecosystems, 3d 

ed.: New York, Academic Press, Elsevier Science Imprint, 

1,006 p.

Wilde, F.W., ed., 2006, Collection of water samples (ver. 2.0): 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A4, September 2006, available 

online at http://pubs.water.usgs.gov/twri9A4/.

Winfield, G.L., and Sakai, J., 2003, Task 6: Final Liberty 

watershed assessment: Baltimore, Maryland, Department of 

Public Works, Bureau of Water and Wastewater, Project No. 

812 On-Call Engineering Services 110 p., plus additional 

appendix.

Winfield, G.L., Sakai, J., and Stack, W., 2006, Road salt 

contamination of the Baltimore metropolitan reservoirs, 

Potomac River Drinking Water Source Protection 

Partnership Meeting Proceedings, February 15, 2006, 

Interstate Commission on the Potomac River Basin, 

Rockville, Maryland, 18 figs.

Wu, W.W., Chadik, P.A., and Davis, W.M., 2000, The effect of 

structural characteristics of humic substances on disinfection by-product formation in chlorination, chapter 8, 

p. 109–121, in Barrett, S.E., Krasner, S.W., and Amy, G.L., 

eds., 2000, Natural organic matter and disinfection byproducts: Characterization and control in drinking water: 

Washington, D.C., American Chemical Society Symposium 

Series 761, 163 p.

Xie, Y.F., 2004, Disinfection byproducts in drinking water: 

Formation, analysis, and control: Boca Raton, Florida, 

Lewis Publishers, CRC Press, 160 p.
Appendix A 109

Appendix A: Water-Quality Monitoring to 

Support Watershed Restoration

Contents

Introduction.................................................................................................................................................110

Source-Water Assessments....................................................................................................................110

Watershed Characterization Studies .....................................................................................................110

Short-Term Stream Monitoring Studies .................................................................................................111

Stream Surveys..........................................................................................................................................113

Synoptic Surveys for Nutrients ......................................................................................................113

Stream Corridor and Stability Surveys..........................................................................................114

Stream Habitat and Biological Surveys ........................................................................................115

References Cited........................................................................................................................................116

Figure

A1. Map showing Gunpowder Falls watershed monitoring sites within Loch Raven 

and Prettyboy Reservoir watersheds....................................................................................112

Table

A1. Nutrient synoptic summaries for Liberty and Prettyboy Reservoir watersheds............113
110 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Introduction

Baltimore City is primarily responsible for managing and 

monitoring water-quality conditions in the City water-supply 

reservoirs, and in selected tributaries in the reservoir watersheds. Because the reservoir watersheds lie largely outside the 

jurisdiction of the City, however, managing and assessing reservoir-watershed conditions that could affect reservoir water 

quality is shared by City, County, and State governments. 

Management of the reservoir watersheds has been guided 

by characterizations and source-water assessments that reflect 

the environmental state of the reservoir watersheds and their 

tributaries. These characterizations and assessments have been 

helped or were followed by short-term and synoptic studies 

conducted on tributary streams in each reservoir watershed to 

identify nonpoint pollutant problems and their source areas, 

to develop and implement stream restoration strategies, and to 

improve tributary water and habitat quality and reduce pollutant loads. These activities are described using representative 

examples below. In each case, the descriptions are illustrative 

of these activities and are not a comprehensive summary of all 

activities that have been conducted in the reservoir watersheds 

by agencies of the State of Maryland or Baltimore and Carroll 

Counties.

Source-Water Assessments

Amendments to the 1996 Safe Drinking Water Act 

(SWDA) required states to conduct source-water assessments 

to evaluate the safety of all public drinking-water systems. 

These assessments are to include a comprehensive characterization of each reservoir watershed as well as the reservoir 

to better enable strategies to be developed to maintain or 

improve the quality of water, biota, and habitat in streams and 

reservoirs. The source-water assessment studies for both the 

Liberty and Loch Raven Reservoir watersheds were completed 

in 2003 and 2004, respectively (Winfield and Sakai, 2003; 

Maryland Department of the Environment, 2004). As part of 

these assessments, water-quality data from the core monitoring 

program were analyzed and summarized to describe point and 

nonpoint sources of pollutants. Information from these assessments has been used throughout this retrospective review. 

Relevant to the retrospective review of the monitoring 

program, source-water assessments provided time-of-travel 

studies. These studies indicate that low flows can travel from 

the headwaters of tributaries to the reservoirs within approximately half a day to 2 days. High flows, however, such as 

those associated with storms, likely reach a reservoir fairly 

quickly, in less than a quarter to a half day. 

The rapid traveltimes of storms have implications for 

long-term monitoring. Unless a storm runoff event is large 

enough to displace a major portion of the stored reservoir 

water, and in-lake monitoring occurs shortly afterwards, the 

direct impact of the storm on the reservoir is not measured. 

As noted by the Interstate Commission on the Potomac River 

Basin (2006), in-lake monitoring by the Reservoir Watershed 

Management Agreement (RWMA) partners is simply too 

infrequent (monthly to bi-monthly). By design, storm-related 

reservoir sampling also generally does not occur if reservoir 

conditions are unsafe for sampling, such as during storms. 

Thus, the probability of capturing the impact of a major stormrunoff event on the reservoirs is low. When a storm occurs 

and at least some of its effects on reservoir water quality are 

measured, the resultant data complicate analyses of long-term 

trends as well as modeling of water quality in the reservoir 

because few events are in fact adequately captured.

A consequence of the current reservoir monitoring is 

that the influence of storms on reservoir water quality, such as 

sedimentation and turbidity, nutrient enrichment (phosphorus), 

and changes in dissolved-oxygen concentrations, in both the 

epilimnetic and hypolimnetic layers also are poorly understood, and therefore, difficult to accurately model (Interstate 

Commission on the Potomac River Basin, 2006). The ability 

to obtain water-quality data for storm events in both the 

watershed tributaries and reservoirs is desirable to accurately 

assess conditions of state, changes in state, trends, and loads, 

and improve modeling to determine whether progress is being 

made towards addressing RWMA partner water-quality concerns and technical goals.

Other aspects of the source-water assessments that 

involve monitoring to address RWMA partner concerns, and 

achieve RWMA goals, are short-term studies conducted by 

RWMA partners that focus on the watershed tributaries. These 

studies are designed to describe the conditions of streams, to 

identify impaired streams, to identify actions needed to reduce 

impairments, and to prioritize impaired streams for restoration. 

They also are important to the large-scale long-term monitoring program. The source-water assessments include identification of areas impaired by agricultural or urban development. 

For those areas that are upstream of the long-term monitoring 

stations, their restroation could lead to detected improvements 

in tributary water-quality conditions. In addition, source-water 

assessments can help identify impaired areas, such as eroded 

streambeds and banks, or degraded forest areas, for restoration, that generally would not be identified and restored by use 

of traditional best-management practices (BMPs) that focus on 

agricultural or urban land use and land owners, which could 

also lead to improvements in monitored reservoir watershed 

tributary conditions.

Watershed Characterization Studies

As part of the source-water assessment studies, watershed-characterization studies have been conducted on the 

reservoir watersheds (Maryland Department of Natural 

Resources, 2002a; Maryland Department of the Environment, 

2003; Baltimore County Department of Environmental 

Protection and Resource Management, 2008). These studies 
Short-Term Stream Monitoring Studies 111

were conducted to partially fulfill Federal requirements under 

the National Storm Discharge Elimination Site (NPDES) 

Municipal Stormwater Discharge Permit, and State programs, such as the 1998 Maryland Clean Water Action Plan 

(Maryland Department of Natural Resources, 1998). Under 

the latter, the Liberty and Loch Raven-Prettyboy Reservoirs 

and their watersheds were designated as watersheds within the 

state that have the highest priority for protection and restoration, and warrant a comprehensive watershed-restoration 

action plan. 

As part of each watershed characterization, information 

was compiled on land use and land cover and known or potential point and nonpoint sources of pollutants. Most nonpoint 

sources of pollutants actually are defined in relation to land 

use and land cover, on the basis of early studies that compared 

different types of land use and land cover to water-quality data 

obtained from the long-term tributary dry-weather monitoring 

program (Baltimore City Department of Public Works, 1996, 

2000, 2001). In addition, short-term monitoring and synoptic 

studies were used to help characterize water quality in relation 

to land use within selected reservoir watershed subbasins. 

The selected subbasins include subbasins identified by the 

long-term monitoring network as source areas for elevated 

nutrient and sediment loads, as well as subbasins not covered 

by the long-term monitoring network—for example, within 

close proximity to the reservoirs. Examples of monitoring 

data collected, and information provided from the analysis of 

these data, are provided as part of this retrospective to show 

(a) that impairment conditions in tributary streams directly 

relate to RWMA goals and water-quality concerns, and (b) that 

the location of impaired streams and plans to restore impaired 

streams have a bearing on the design of the long-term monitoring network.

Short-Term Stream Monitoring Studies

Short-term monitoring (typically 1–2 years) of streamwater quality is conducted by RWMA partners to address 

water-quality conditions in the small subbasins within each 

reservoir watershed. Using the Loch Raven Reservoir watershed as an example, short-term (1-year) monitoring was 

conducted at over two dozen stream sites in the lower part of 

this watershed in 1998 (fig. A1). The monitoring stations were 

used in part to assess source-water conditions, and most were 

established around the periphery of the reservoir in subbasins 

not covered by the long-term monitoring network in the reservoir watersheds (see Main Report, fig. 3). Selected monitoring stations were located in Piney Run primarily to address 

concerns with effluent discharge by the wastewater treatment 

plant (WWTP) at Hampstead, Maryland.

The purposes of this monitoring network were to provide 

data to: (a) address potential risks to drinking-water quality 

and aquatic health from pollutants—nutrients, metals, and 

bacteria or other pathogens—in stream base- and stormflows; 

(b) calibrate a model to estimate loads by land use, to further 

aid the identification of excessive pollutant-source areas; and 

(c) for Piney Run, to determine if the Hampstead WWTP 

effluent impacted downstream water quality and quantity. 

From the monitoring data, the State and Baltimore County 

(Maryland Department of the Environment, 2003) determined 

that:

a) Subbasins where development reflected urban and residential land use produce elevated base and stormflows 

relative to rural subbasins with agricultural or forested 

land use.

b) Subbasins with developed land use had elevated nitrogen and phosphorus concentrations in base and stormflows compared to subbasins with appreciable forest 

cover. Nitrate concentrations were elevated at 13 of 15 

sites under low-flow conditions, indicating widespread 

contamination of groundwater.

c) Selected agricultural and urban sites had high concentrations of fecal coliform bacteria during low flow, 

which was attributed to livestock operations at the 

agricultural sites, but elevated concentrations also were 

found at selected urban sites for unknown reasons. 

Cryptosporidium was not detected. Giardia cysts were 

detected by presumptive and definitive tests, but at 

concentrations well below levels related to an infectious dose of 150 cysts.

d) Arsenic, barium, chromium, and nickel did not exceed 

water-quality standards during base or stormflows, 

but two metals (copper and lead) were considered a 

potential threat to aquatic life at two locations, likely 

as a result of livestock operations, with the highest 

concentrations occurring during stormflows.

e) Stream pH was within the acceptable range (6.5–8.5 

standard units), except in areas underlain by limestone 

karsts, where base-flow pH was likely to exceed 8.5.

f) Concentrations of dissolved oxygen typically were 

above the 5.0 mg/L (milligrams per liter) RWMA 

standard. Biological oxygen demand, chemical oxygen 

demand, and total organic carbon concentrations 

indicated little potential for oxygen depletion in these 

streams.

g) Although storm data were limited, atrazine concentrations did not appear to pose a health risk in either base 

or stormflows.

h) Hampstead WWTP effluent constituted approximately 

82 percent of base flow in the headwaters of Piney 

Run and effluent quality determined stream-water 

quality downstream. During recorded stormflows (peak 

discharges of 20–40 ft3/s, or cubic feet per second), the 

WWTP flow was only 4 ft3/s, and had considerably less 

influence on stream-water quality.
112 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Figure A1. Gunpowder Falls watershed monitoring sites within Loch Raven and Prettyboy Reservoir watersheds (modified 

from Baltimore County Department of Environmental Protection and Sustainability, formerly Baltimore County Department of 

Environmental Protection and Resource Management, 1998).
Stream Surveys 113

Stream Surveys

Three types of stream surveys have been used to characterize water-quality conditions in subbasins in the Baltimore 

Reservoir watersheds, and include synoptic surveys for nutrients (nitrogen and phosphorus), stream corridor and stability 

surveys, and stream habitat and biological surveys.

Synoptic Surveys for Nutrients

Spring low-flow nutrient synoptic surveys, in lieu of 

short-term monitoring, are another method used to determine 

relations between land use and land cover (human activities) 

and nutrient loads, and help identify pollutant source areas 

on a subbasin scale. By design, these surveys were conducted 

in the spring—in April 2002 for the Carroll County parts 

of the Liberty Reservoir watershed (Maryland Department 

of Natural Resources, 2002b) and in April 2006 for the 

Prettyboy Reservoir watershed (Maryland Department of the 

Environment, 2006a). Although total phosphorus concentrations are not highest in reservoir tributaries in the spring, 

nitrate concentrations and dry-weather flows are on average 

highest in April. Thus, nitrogen and phosphorus dry-weather 

loads were expected to be at or near their annual highs in 

April.

Within each watershed, synoptic data were used to 

describe and compare low-flow nutrient concentrations and 

loads among subbasins (table A1). For the Liberty Reservoir 

watershed, and according to synoptic-survey criteria, among 

the 41 synoptic sites, all sites exhibited elevated nitrogen—59 

percent (25/41) had high to excessive nitrogen concentrations, 

and 15 percent (6/41) of the sites also had high to excessive 

(instantaneous) areal-weighted nitrogen loads or yields 

(Maryland Department of Natural Resources, 2002b). For 

orthophosphate-phosphorus, only 8 percent of the survey sites 

had concentrations that were considered high to excessive, but 

none of the sites had phosphorus loads that exceeded baseline 

conditions (0.0005 kilograms per hectare per day or less). 

The Middle Run and Western Run subbasins had the greatest 

number of internal subbasins with high to excessive low-flow 

nutrient concentrations. In addition, most sites in the four 

sub-watersheds covered by this survey (which also included 

Snowden Run and Roaring Run tributaries) that had high to 

excessive nutrient concentrations were in developed headwater 

subbasins.

For the Prettyboy Reservoir watershed, all but 1 of the 

68 nutrient synoptic sites exhibited excessive nitrate-nitrite 

concentrations at low flows compared to the survey baseline 

standard, and most (88 percent or 60/68) sites had concentrations that were considered high to excessive 

Table A1. Nutrient synoptic summaries for Liberty and Prettyboy Reservoir watersheds (from Maryland Department of Natural 

Resources, 2002b and Maryland Department of the Environment, 2006a).

[%, percent, equals the ratio of the number of sites with either baseline to moderate, or high to excessive, nitrate-nitrite or orthophosphate concentrations (or 

loads) to total number of synoptic sites, multiplied by 100; N, nitrogen; P, phosphorus; <, less than; >, greater than; mg/L, milligrams per liter; kg/ha/d, 

kilograms per hectare per day]

Reservoir/

watershed

Date of 

synoptic

Synoptic 

site 

distribution

Number 

of 

synoptic 

sites

Proportion of total number of synoptic sites (%)

With nitrate-nitrite 

N concentrations 

within the specified 

range 

With nitrate-nitrite N

areally weighted 

loads within the 

specified range 

With orthophosphate 

P concentrations 

within the specified 

range 

With orthophosphate 

P areally weighted 

loads within the 

specified range 

Baseline 

to 

moderate 

(<1 to 3 

mg/L)1

High to 

excessive

(3.1 

to >5 

mg/L)2

Baseline 

to 

moderate 

(<0.01 to 

0.02 

kg /ha/d)1

High to 

excessive 

(0.021 to 

>0.03 kg /

ha/d)2

Baseline 

to 

moderate 

(<0.005 

to 0.010 

mg/L)1

High to 

excessive 

(0.011 to 

>0.015 

mg/L)2

Baseline 

to 

moderate 

(<0.0005 

to 0.001 

kg/ha/d)1

High to 

excessive 

(0.0015 to 

>0.003 

kg/ha/d)2

Liberty April 

2002

Among 

four 

subbasins

41 41 59 85 15 70 8 100 0

Prettyboy April 

2006

Throughout 

watershed 68 12 88 4 96 93 7 100 0

1

 First value defines baseline concentrations, which are less than the specified numerical value; moderate values lie between the defined upper threshold for 

baseline values up to the second value specified. Ranges were defined by Frink (1991) for the Chesapeake Bay watershed.

2

 High concentrations are those that occur at the first value and up to the second value; excessive concentrations are those that exceed the second value. 

Ranges were defined by Frink (1991) for the Chesapeake Bay watershed.
114 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

(table A1). Furthermore, approximately 96 percent of the sites 

had basin-area-weighted-flow (instantaneous) nitrogen loads 

that were excessive. Only about 8 percent of the subbasins had 

high to excessive orthophosphate-phosphorus concentrations, 

and none of the sites had high to excessive phosphorus loads. 

Subbasins with high to excessive nitrate-nitrite concentrations 

often were clustered together, and chiefly occurred in two subbasins—Georges Creek and Prettyboy Branch sub-watersheds 

(Maryland Department of the Environment, 2006a). High to 

excessive nutrient concentrations were associated with agricultural and developed subbasins, mainly row-crop and livestock 

agriculture and low-density residential communities on septic 

systems. 

Collectively, the synoptic surveys were shown to be 

useful in the identification of subbasins within each reservoir 

watershed that were potential source areas for high to excessive nutrient (primarily nitrogen) concentrations and, in some 

cases, nutrient loads, at low flows. Results from the two 

synoptic surveys, however, cannot be compared to prioritize 

subbasins among reservoir watersheds as the synoptic in each 

reservoir watershed occurred in different years with different 

hydrologic conditions. The Liberty Reservoir watershed 

synoptic was conducted in 2002 during a very dry spring. 

Surveyed low-flow nutrient concentrations were lower than 

the typical annual averages for streams in this and other 

watershed areas (Maryland Department of Natural Resources, 

2002b). The Prettyboy Reservoir watershed synoptic occurred 

in 2006 during a very wet spring. Surveyed low-flow nutrient 

concentrations were higher than typical averages for streams 

in this and other watershed areas (Maryland Department 

of the Environment, 2006a). For reasons similar to those 

described above, results cannot be combined for the synoptic 

and short-term monitoring. The short-term monitoring in the 

Loch Raven Reservoir watershed was conducted in 1988, a 

relatively dry year. 

Stream Corridor and Stability Surveys

In addition to nutrient surveys, stream corridor and stability surveys have been developed and used to assess the impact 

of land use and land cover (human activities) on the physical 

condition of streams in the reservoir watersheds, and aid in the 

development of RWMA watershed restoration action strategies 

and priorities (Maryland Department of Natural Resources, 

2002c; Maryland Department of the Environment, 2004, 

2006b). Collectively, these surveys have provided a wealth of 

data and information in relation to both of these objectives, 

including the following:

a) Information on the occurrence, extent, and possible 

causes of observed instabilities in third- and lowerorder streams, including bed incision or aggregation 

and bank erosion (widening or mass wasting) or deposition, and the potential for continued erosion and, if 

performed, effective restoration;

b) Information on the integrity of the riparian zone adjacent to the stream, including the type, width, density, 

and appearance of vegetation; and

c) Information on stream-corridor biotic and waterquality indicators, including physical habitat, and the 

occurrence and conditions that result from stormwater 

BMPs, storm-drain outfalls, roadways, construction, 

exposed sewer lines, non-permitted discharges, and 

trash or dumping.

Corridor and stability surveys used in the Baltimore 

reservoir watersheds differed in that the former primarily 

obtained information through visual observation, were more 

qualitative than quantitative in nature, and thus enabled coverage of a greater number of streams in a subbasin than the latter. Stream-corridor studies generally were conducted before 

stream-stability surveys over large areas of the reservoir 

watersheds. The information obtained from corridor studies 

allowed the RWMA partners to make general comparisons of 

stream conditions among major, and within a major, minor, 

subbasins within the reservoir watersheds. In this regard, they 

helped identify small subbasins within a major subbasin whose 

stream corridors appeared to be impaired.

On the basis of information obtained from the streamcorridor surveys, stream-stability surveys were developed 

mainly to further examine streams in the subbasins. The subbasins surveyed for stability generally had a high frequency 

of potentially moderately to highly impaired water-quality 

conditions. The objectives of stream-stability surveys were to 

provide detailed information on: (a) the current morphological 

states of the small (generally first- and second-order) stream 

corridors within a targeted subbasin, (b) the likelihood these 

streams would maintain their current morphology or undergo a 

change in morphology, and (c) if their morphological condition was unstable, whether or not stream restoration was warranted, and what it likely would require. 

Stability surveys appear to be an effective monitoring 

tool for the RWMA partners to help determine what restorative 

actions on which streams would be most effective in a surveyed subbasin. Because of the quantitative data requirements 

of stream-stability surveys, however, they generally have been 

conducted in only a few major subbasins in each reservoir 

watershed, and within each major subbasin, generally on some 

but not all small subbasins within a major subbasin. 

Collectively, the stream-corridor and stability surveys 

(Maryland Department of Natural Resources, 2002c; 

Maryland Department of the Environment, 2004, 2006b) have 

shown that highly unstable (eroding) and chiefly first- and 

second-order stream corridors occur in a variety of different 

but mostly headwater settings in surveyed subbasins in all 

three reservoir watersheds. These settings range from reaches 

without any riparian (forested) buffer lying adjacent to developed lands to the presence of more than adequate riparian 

buffers that are subject to inadequately controlled stormwater runoff. Where stream erosion is observed, channels are 

most often undergoing incision, or if already incised, are 
Stream Surveys 115

widening through bank cutting; many of the stream corridors 

undergoing degradation (incision, widening, or both) are in 

upland headwater basins, and these eroding streams likely 

are a major source of sediment to downstream tributaries and 

inevitably the watershed reservoirs. The RWMA partners 

have identified and prioritized stream reaches for restoration 

activities throughout the surveyed subbasins in each reservoir 

watershed.

Stream Habitat and Biological Surveys

Two types of monitoring surveys have been used to 

assess the habitat conditions related to the biotic health of 

reservoir watershed tributary streams. Initial stream-habitat 

assessments were frequently conducted as part of the streamcorridor and stability studies. The results from these surveys 

have provided site-specific information that is useful in the 

characterization of the suitability of streams to support designated uses related to recreational fishing, and to sustain native 

and stocked trout populations.

Stream habitat surveys identified fish-migration barriers. 

Barriers most often consisted of debris blockages or limited 

flow and depth conditions, but included human-constructed 

structures that could interfere with fish migration.

Although information was not available for the lower 

Loch Raven Reservoir watershed, during stream corridor 

surveys for the Liberty Reservoir watershed, survey crews 

identified 32 such barriers (Maryland Department of Natural 

Resources, 2002c). The majority of these barriers (22/32) 

blocked the entire width of the stream. Artificial barriers (23) 

dominated, and included dams (9), pipe crossings (5), road 

crossings (5), concrete debris (3), and a streamgage. Natural 

barriers (9) included beaver dams (3), natural falls (3), and an 

in-stream pond, a channelized stream, and a large rock. On a 

sub-watershed basis, West Branch, Middle Run, and Snowdens 

Run had 18, 9, and 5 barriers, respectively. 

For the Prettyboy Reservoir watershed, stream-corridor 

survey crews identified 17 fish migration barriers (Maryland 

Department of Natural Resources, 2006b). Most of the barriers 

were artificial (12/17), and included road crossings (10) and 

dams (2). Natural barriers consisted of natural falls (2) and 

debris dams (2). 

Stream-stability surveys also provided a more detailed 

assessment of stream characteristics related to biological habitat for generally small (first- and second-order) streams. On 

the basis of surveys conducted in the lower Loch Raven and 

Prettyboy Reservoir watersheds, and in addition to intermittent 

fish barriers, the most commonly encountered habitat impairments that would limit fish migration and populations were 

low-flow (shallow depth) conditions and a lack of in-stream 

epifaunal vegetation and attached or fixed woody debris. Both 

of these conditions led to poor to very poor Physical Habitat 

Index values based on the Maryland Biological Stream Survey 

(MBSS) protocols (Kayzak, 2001) for about one-third of the 

stream reaches surveyed in the lower Loch Raven Reservoir 

sub-watersheds, and about one-tenth of the reaches surveyed 

in the Prettyboy Reservoir sub-watersheds. On the other hand, 

fish barriers were more likely to restrict fish migration at sites 

surveyed in the Prettyboy Reservoir watershed than at sites 

surveyed in lower Loch Raven Reservoir watershed.

Additional information on the physical habitat conditions 

related to the biotic health of streams has been obtained 

through the MBSS. The MBSS surveys were conducted in 

the Baltimore reservoir watersheds in 1994, 1997, and 2000. 

Although the results of the MBSS surveys for the Loch Raven 

or Prettyboy Reservoir watersheds were not readily available 

at the time of this review, results for the Carroll County part 

of the Liberty Reservoir watershed were summarized as part 

of the watershed characterization (Maryland Department 

of Natural Resources, 2002a). In addition, the MBSS 2000 

survey in the Liberty Reservoir watershed was augmented by 

MBSS Stream Waders, which nearly doubled the number of 

surveyed sites.

On the basis of the MBSS results, physical habitat conditions in the Liberty Reservoir watershed for most stream 

sites were rated fair to good. Only 5 of nearly 100 assessed 

sites were rated as poor and only 1 site as very poor. Based 

on habitat conditions, Liberty Reservoir watershed streams 

scored an average of 6.47 on a scale of 1 (worst) to 10 (best). 

For this size watershed, a score of 6.0 or less implies restoration is needed and a score of 8 or greater implies protection is 

recommended. 

Two other measures of tributary biotic conditions in 

the Baltimore reservoir watersheds have been provided by 

routine benthic and fish surveys conducted as part of the 

MBSS. On the basis of surveys conducted in 1994, 1997, and 

2000 in the Liberty Reservoir watershed, with the latter being 

augmented by additional data collection through the MBSS 

Stream Waders program, the Maryland Department of Natural 

Resources and Carroll County summarized survey findings as 

listed below (Maryland Department of Natural Resources and 

Carroll County, 2002a).

In relation to benthos integrity, the MBSS Program 

assessed 58 monitoring sites throughout the Liberty Reservoir 

watershed between 1995 and 2000. An additional 52 sites were 

sampled by citizen volunteers in 2000. Relative to reference 

streams, about 53 percent of the sites were considered good 

(or minimally degraded) with respect to reference stream conditions. A total of 16 sites (28 percent) were rated poor, with 

degraded conditions in relation to reference sites.

In relation to macro-invertebrate communities, Liberty 

Reservoir watershed streams scored an average of 6.89 on a 

scale of 1 (best) to 10 (worst). For nontidal watershed areas of 

this size, a score of less than 6 implies restoration is needed 

and a score of 8 implies protection is recommended.

In relation to fish communities, most streams in the 

Liberty Reservoir watershed were rated fair to good on the 

basis of MBSS data obtained between 1995 and 2000. The 

rating fair to good implies a generally diverse range of fish 

species are present at a site. Only a few sites were rated as 

poor.
116 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

In relation to fish communities, the Liberty Reservoir 

watershed streams generally are in good condition. The average site score of 8.87 on a scale of 1 (worst) to 10 (best) for 

streams in the Liberty Reservoir watershed implied that individual sites with scores of 8 or greater should be protected.

Although MBSS summaries were not available for 

the Loch Raven and Prettyboy Reservoir watersheds, these 

surveys form an important part of the Baltimore reservoir 

long-term monitoring strategy. The surveys provide the opportunity to periodically assess the biotic health of the reservoir 

watershed streams in a systematic and well-documented manner. Although surveys have been conducted since 2000 in all 

three reservoir watersheds, results have not been summarized. 

Ultimately, however, the MBSS data will provide for trend 

analysis related to the biotic health of reservoir streams.

Whereas the long-term monitoring program has helped 

identify subbasins that appeared to be sources of excessive 

nutrients and sediment, the collective components of the 

source-water assessments—watershed characterizations, shortterm monitoring and synoptic surveys, stream-corridor and 

stability studies, and stream-habitat and biota surveys—enable 

the RWMA partners to describe the state of the watershed tributaries within these subbasins, identify impaired tributaries, 

develop restoration activities to address those impairments, 

and prioritize impaired streams for restoration. From these collective studies, however, it also is apparent that most impaired 

streams are located in headwater areas. Given their general 

location, the intensity of survey efforts to correctly identify 

the nature of stream impairments, and the resources required 

for reducing or eliminating impairments, it likely will take 

considerable time to restore impaired streams. Therefore, it is 

important to realize that it is likely to take considerable time 

before the full effects of restoration activities become apparent 

at the downstream tributary monitoring stations operated as 

part of the long-term monitoring program for major subbasins 

within each of the reservoir watersheds. 

References Cited

Baltimore City Department of Public Works, 1996, Volume 

I: Selected graphics, report conclusions, and discussion: 

Baltimore, Maryland, Reservoir Watershed Management 

Progress Report, 128 p.

Baltimore City Department of Public Works, 2000, Appendix C: 

Reservoir water quality assessment for Loch Raven, Prettyboy 

and Liberty reservoirs, Interim Report, in Action report 2000 

for the reservoir watersheds: Baltimore, Maryland, Watershed 

Protection Committee, 37 p.

 Baltimore City Department of Public Works, 2001, Reservoir 

water quality assessment for Loch Raven, Prettyboy, and 

Liberty reservoirs: Baltimore, Maryland, 39 p.

Baltimore County Department of Environmental Protection and 

Resource Management, 1998, Gunpowder watershed characterization: Research design and monitoring procedures: 

Towson, Maryland, Baltimore County, 13 p. 

Baltimore County Department of Environmental Protection and 

Resource Management, 2008, Prettyboy Reservoir watershed 

characterization report: Towson, Maryland, 101 p. 

Frink, C.F., 1991, Estimating nutrient exports to estuaries: 

Journal of Environmental Quality, v. 20, no. 4, p. 717–724.

Interstate Commission on the Potomac River Basin, 2006, 

Modeling framework for simulating hydrodynamics and 

water quality in the Prettyboy and Loch Raven Reservoirs, 

Gunpowder River basin, Maryland: Rockville, Maryland, 230 

p., plus appendixes.

Kayzak, P.F., 2001, Maryland Biological Stream Survey sampling manual: Annapolis, Maryland, Maryland Department of 

Natural Resources, 83 p.

Maryland Department of the Environment, 2003, Water quality 

and management plan for the Loch Raven watershed study 

area in Baltimore County, Maryland: Annapolis, Maryland, 

180 p.

Maryland Department of the Environment, 2004, Source water 

assessment for Loch Raven watershed: Baltimore, Maryland, 

99 p., plus appendixes.

Maryland Department of the Environment, 2006a, Nutrient synoptic survey in the Prettyboy watershed, Baltimore and Carroll 

Counties, Maryland, 2005, as part of a Watershed Restoration 

Action Strategy: Baltimore, Maryland, 20 p.

Maryland Department of the Environment, 2006b, Stream corridor assessment survey for the Prettyboy reservoir watershed: 

Baltimore, Maryland, 59 p. 

Maryland Department of Natural Resources, 1998, Maryland 

clean water action plan, final (1998) report on unified watershed assessment, watershed prioritization and plans for restoration action strategies: Annapolis, Maryland, Clean Water 

Action Plan Technical Workgroup, 39 p., plus appendixes.

Maryland Department of Natural Resources, 2002a, Liberty 

reservoir watershed characterization-Carroll County portion, 

Maryland Department of Natural Resources: Annapolis, 

Maryland, and Carroll County, Maryland, 96 p.

Maryland Department of Natural Resources, 2002b, Nutrient and 

biological synoptic surveys in portions of the Carroll County 

drainage to Liberty reservoir: Annapolis, Maryland, 38 p.

Maryland Department of Natural Resources, 2002c, Liberty 

reservoir stream corridor assessment: Annapolis, Maryland, 

103 p.

Winfield, G.L., and Sakai, J., 2003, Task 6: Final Liberty watershed assessment: Baltimore, Maryland, Department of Public 

Works, Bureau of Water and Wastewater, Project No. 812 

On-Call Engineering Services, 110 p., plus appendix.
Appendix B 117

Appendix B: Descriptions of Data Collected at 

Watershed Tributary and Reservoir Monitoring 

Stations

Appendixes

B1. Baltimore City monitoring network station locations, 2007 ...............................................118

B2. Baltimore City monitoring for Liberty Reservoir: treatment facility, reservoir, 

and tributaries—sample location, water-quality parameters, and frequency ..............119

B3. Baltimore City monitoring for Loch Raven Reservoir: treatment facility, 

reservoir, and tributaries—sample location, water-quality parmeters, 

and frequency ...........................................................................................................................120

B4. Baltimore City monitoring for Prettyboy Reservoir: reservoir and tributaries—

sample location, water-quality parameters, and frequency .............................................121
118 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007 Appendix B1. Baltimore City monitoring network station locations, 2007. [N, north; W, west; NPDES, National Pollutant Discharge Elimination System; USGS, U.S. Geological Survey; WP, weather permitting, usually April through November or December] Watershed Station type Reservoir location Station identifier Latitude, N Longitude, W Station location Associated USGS gage Comment (degrees, minutes, seconds) Liberty Reservoir Lower NPA0042 39 23 20.00668 76 52 51.61888 Liberty Gatehouse, maximum depth 105 feet Lower NPA0059 39 23 48.47139 76 53 10.61397 Liberty at Route 26 Bridge, mid-channel WP, requires boat Middle NPA0067 39 25 04.09886 76 52 56.28529 Liberty at Oakland Road Point, near intake WP, requires boat Upper NPA0105 39 26 56.59918 76 52 40.35257 Liberty at Nicodemus/Deer Park Bridge, mid-channel Tributary BEA0015 39 29 22.55919 76 54 10.28399 Beaver Run at Hughes Road 01586210 LMR0015 39 25 36.29438 76 57 37.85655 Little Morgan Run at Bartholow Road MDE0026 39 27 45.72575 76 54 27.22165 Middle Run at Louisville Road MOR0040 39 27 07.22750 76 57 18.84300 Morgan Run at London Bridge Road 01586610 NPA0165 39 30 03.78299 76 53 00.61143 North Branch Patapsco at Route 91 (below outfall) 01586000 UZP0002 39 29 47.68237 76 52 12.78678 Bonds Run at Hollingsworth Road NPDES STP7704 39 30 14.34065 76 53 08.64558 Effluent Congoleum manufacturing plant Grab, if discharge STP8000 39 35 14.32810 76 51 06.05665 Effluent Roy F. Weston manufacturing plant Grab, if discharge Loch Raven Reservoir Lower GUN0142 39 25 50.86953 76 32 39.57712 Loch Raven Gatehouse Middle GUN0156 39 26 50.67932 76 33 20.68793 Loch Raven at Loch Raven Drive Bridge Bridge access Middle GUN0171 39 27 04.77082 76 34 08.44553 Loch Raven between picnic and golf course areas WP, requires boat Upper GUN0174 39 27 46.16274 76 34 49.59077 Loch Raven at Dulaney Valley Road Bridge Bridge access Upper GUN0190 39 29 00.28084 76 34 53.65176 Loch Raven at power lines WP, requires boat Tributary BEV0005 39 29 08.36173 76 38 44.59508 Beaver Dam Run at Beaver Run Lane 01583600 DVB0000 39 27 58.10206 76 32 43.51881 Dulaney Valley Branch at Loch Raven Drive GUN0258 39 32 59.29999 76 38 09.95642 Gunpowder Falls at Glencoe Road 01582500 GUN0387 39 37 08.38463 76 41 26.10235 Gunpowder Falls at Falls Road 01581920 GUN0398 39 37 08.62153 76 42 23.89133 Gunpowder Falls 500 feet below Prettyboy Dam (Pond) JNR0003 39 28 02.09216 76 33 29.69286 Jenkins Run at Dulaney Valley Road Grab, if flow

LIT0002 39 36 07.34671 76 37 19.03368 Little Falls at Blue Mount Road 01582000

WGP0050 39 30 38.38894 76 40 36.83822 Western Run at Western Run Road 01583500

NPDES STP8005 39 35 50.14921 76 50 03.52134 Effluent Hampstead Wastewater Treatment Plant Grab, if discharge

Prettyboy Reservoir Lower GUN0399 39 37 11.37820 76 42 26.02913 Prettyboy Dam Gatehouse

Lower GUN0401 39 37 14.12232 76 42 36.07822 Prettyboy 1,000 feet upstream of Prettyboy Dam WP, boat

Middle GUN0437 39 38 52.33959 76 45 19.25522 Prettyboy at Beckleysville Road Bridge Bridge access

Tributary GOB0017 39 37 33.47745 76 46 22.06942 Georges Run at Georges Creek Road 01581870

GRG0013 39 39 16.99906 76 46 46.13531 Grave Run at Gunpowder Road 01581830

GUN0476 39 41 20.98079 76 46 49.77908 Gunpowder Falls at Gunpowder Road 01581810

NPDES STP8006 39 39 27.88889 76 52 46.84074 Effluent Manchester Wastewater Treatment Plant Grab, if discharge
Appendix B 119

Appendix B2. Baltimore City monitoring for Liberty Reservoir: treatment facility, reservoir, and tributaries—sample location, water-quality parameters, and frequency. [NPDES, National Pollutant Discharge Elimination System; TF, treatment facility, R, raw, or T, treated, water sample or measurement, taken in facility; raw-water sample or measurement taken at all other locations; D, daily; W, weekly; M, monthly; 2xW, twice weekly; 2xM, twice monthly; (S), spring-summer-fall (approximately April through November); (W), winter (approximately December through March); E, storm event; *, permitted discharge, grab sample, if flow; ---, not sampled; °C, degrees Celsius, mg/L, milligrams per liter, μg/L micrograms per liter; L, liter; mL, milliliter; #, number; MP, most probable; μmhos/cm, micromhos per centimeter; CaCO3, calcium carbonate]

Water-quality parameter

Liberty Reservoir

Ashburton Reservoir site identifier Watershed tributary site identifier NPDES site identifier

TF, 

Raw

TF, 

Treated1 NPA0042 NPA0059 NPA0067 NPA0105 BEA 0015 LMR 0015 MDE 0026 MOR 0040 NPA 0165 UZP 0002 STP7704* STP8000*

Temperature, air, °C --- --- 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) M M M M M M M MTemperature, water, °C D D 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) M M M M M M M MColor (True), color units 2xW 2xW 2xM(S), M(W) --- --- --- --- --- --- --- --- --- --- ---Secchi disc, meters --- --- 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) --- --- --- --- --- --- --- ---Turbidity, nephelometric units D D 2xM(S), M(W) M(S) M(S) M M M M M M M M MTotal solids, mg/L M M --- --- --- --- M M M M M M M MTotal suspended solids, mg/L --- --- --- --- --- --- M, E M M M, E M, E M M MVolatile suspended solids, mg/L --- --- --- --- --- --- E only --- --- E only E only --- --- ---Chlorophyll-a, μg/L --- --- 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) --- --- --- --- --- --- --- ---Total algal count, #/mL W W 2xM(S), M(W) M(S) M(S) M --- --- --- --- --- --- --- ---Algal identification W W 2xM(S), M(W) M(S) M(S) M --- --- --- --- --- --- --- ---Total and fecal coliforms, MP#/100 mL D D --- --- --- --- --- --- --- --- --- --- --- ---Cryptospiridium and Giardia, #/L M --- --- --- --- --- --- --- --- --- --- --- --- ---Specific conductance, μmhos/cm --- M 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) M M M M M M M MDissolved solids, mg/L --- M 2xM(S), M(W) M(S) M(S) M M M M M M M M MHardness, mg/L as CaCO3 D D M M(S) M(S) M --- --- --- --- --- --- --- ---pH, Standard units D D 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) M M M M M M M MAlkalinity, mg/L as CaCO3 D D 2xM(S), M(W) M(S) M(S) M M M M M M M M MDissolved oxygen, mg/L 2xW 2xW 2xM(S), M(W) 2xM(S) 2xM(S) 2xM(S), M(W) M M M M M M M MManganese, mg/L D D 2xM(S), M(W) M(S) M(S) M --- --- --- --- --- --- --- ---Iron, mg/L 3xW 3xW M M(S) M(S) M --- --- --- --- --- --- --- ---Phosphorus, total, mg/L M M 2xM(S), M(W) M(S) M(S) M M, E M M M, E M, E M M MNitrogen, nitrate, mg/L M M M M(S) M(S) M M, E M M M, E M, E M M MNitrogen, ammonium, mg/L M M M M(S) M(S) M M M M M M M M MNitrogen, total Kjeldahl, mg/L --- --- --- --- --- --- E only --- --- E only E only --- --- ---Carbon, total organic, mg/L 2xM 2xM --- --- --- --- --- --- --- --- --- --- --- ---Trihalomethanes, μg/L M M --- --- --- --- --- --- --- --- --- --- --- ---Haloacetic acids, μg/L M M --- --- --- --- --- --- --- --- --- --- --- ---Sodium, mg/L M M --- --- --- --- --- --- --- --- --- --- --- ---Chloride, mg/L M M 2xM(S), M(W) M(S) M(S) M M M M M M M M M

1 Additional constituents only for treated water: calcium, magnesium, potassium, aluminum, arsenic, sulfate, silica, fluoride, residual chlorine, and selected metals, radionuclides, and synthetic and volatile organic 

compounds.
120 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007 Appendix B3. Baltimore City monitoring for Loch Raven Reservoir: treatment facility, reservoir, and tributaries—sample location, water-quality parmeters, and frequency. [NPDES, National Pollutant Discharge Elimination System; TF, treatment facility, R, raw, or T, treated, water sample or measurement, taken in facility; raw-water sample or measurement taken at all other locations; D, daily; W, weekly; M, monthly; 2xW, twice weekly; 2xM, twice monthly; (S), spring-summer-fall (approximately April through November); (W), winter (approximately December through March); E, storm event; *, grab sample, if flow; **, permitted discharge, grab sample, if flow; ---, not sampled; °C, degrees Celsius, mg/L, milligrams per liter; μg/L, micrograms per liter; L, liter; mL, milliliter; #, number; MP, most probable; μmhos/cm, micromhos per centimeter; CaCO3, calcium carbonate] Water-quality parameters Loch Raven Reservoir Montebello Reservoir site identifier Watershed tributary site identifier NPDES site identifier TF, Raw TF, Treated1 GUN 0142 GUN 0156 GUN 0171 GUN 0174 GUN 0190 BEV 0005 DVB 0000 GUN 0387 GUN 0256 WGP 0050 LIT 0002 GUN 0398* JNR 0003* STP 8005*, ** Temperature, air, °C

D

D 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S)

M

M 2xM

M

M

M

M

M

M

Temperature, water, °C

D

D 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S)

M

M 2xM

M

M

M

M

M

M

Color (True), color (apparent) units

D

D 2xM(S), M(W) M(W) M(S) M(W) M(S) --- --- --- --- --- ---

M --- ---

Secchi disc, meters --- --- 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S) --- --- --- --- --- --- --- --- ---Turbidity, nephelometric units

D

D 2xM(S), M(W) M(W) M(S) M(W) M(S)

M

M

M

M

M

M

M

M

M

Total solids, mg/L

M

M --- --- --- --- ---

M

M

M

M

M

M ---

M

M

Total suspended solids, mg/L --- --- --- --- --- --- --- M, E

M

M M, E

M

M ---

M

M

Volatile suspended solids, mg/L --- --- --- --- --- --- ---

E --- ---

E

E --- --- --- ---

Chlorophyll-a, μg/L --- --- 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S) --- --- --- --- --- --- --- --- ---Total algal count, #/mL

W

W 2xM(S), M(W) --- --- --- --- --- --- --- --- --- --- --- --- ---

Algal identification

W

W 2xM(S), M(W) --- --- --- --- --- --- --- --- --- --- --- --- ---

Total and fecal coliforms, MP#/100 mL

D

D --- --- --- --- --- --- --- --- --- --- --- --- --- ---

Cryptospiridium and Giardia, #/L

M

M --- --- --- --- --- --- --- --- --- --- --- --- --- ---

Specific conductance, μmhos/cm

M

M 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S)

M

M 2xM

M

M

M

M

M

M

Dissolved solids, mg/L

M

M --- --- --- --- ---

M

M

M

M

M

M ---

M

M

Hardness, mg/L as CaCO3 D

D --- --- --- --- --- --- --- --- --- --- --- --- --- ---

pH, Standard units

D

D 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S)

M

M 2xM

M

M

M

M

M

M

Alkalinity, mg/L as CaCO3 D

D 2xM(S), M(W) M(W) M(S) M(W) M(S)

M

M

M

M

M

M

M

M

M

Dissolved oxygen, mg/L

D D2 2xM(S), M(W) M(W) 2xM(S) M(W) 2xM(S)

M

M 2xM

M

M

M ---

M

M

Manganese, mg/L

D

D 2xM(S), M(W) M(W) M(S) M(W) M(S) --- --- --- --- --- ---

M --- ---

Iron, mg/L 3xW 3xW --- --- --- --- --- --- --- --- --- --- --- --- --- ---Phosphorus, total, mg/L

M

M 2xM(S), M(W) M(W) M(S) M(W) M(S) M, E

M

M M, E M, E

M

M

M

M

Nitrogen, nitrate, mg/L

M

M 2xM(S), M(W) M(W) M(S) M(W) M(S) M, E

M

M M, E M, E

M

M

M

M

Nitrogen, ammonium, mg/L

M

M 2xM(S), M(W) M(W) M(S) M(W) M(S)

M

M

M

M

M

M

M

M

M

Nitrogen, total Kjeldahl, mg/L --- --- --- --- --- --- ---

E --- ---

E

E --- --- --- ---

Carbon, total organic, mg/L 2xM 2xM --- --- --- --- --- --- --- --- --- --- --- --- --- ---Trihalomethanes, μg/L

M

M --- --- --- --- --- --- --- --- --- --- --- --- --- ---

Haloacetic acids, μg/L

M

M --- --- --- --- --- --- --- --- --- --- --- --- --- ---

Sodium, mg/L

M

M --- --- --- --- --- --- --- --- --- --- --- --- --- ---

Chloride, mg/L

M

M --- --- --- --- ---

M

M

M

M

M

M ---

M

M

1 Additional constituents for treated water: calcium, magnesium, potassium, aluminum, arsenic, sulfate, silica, fluoride, residual chlorine, and selected metals, radionuclides, and synthetic and volatile organic 

compounds.
Appendix B 121

Appendix B4. Baltimore City monitoring for Prettyboy Reservoir: reservoir and tributaries—sample location, water-quality parameters, and frequency. [NPDES, National Pollutant Discharge Elimination System; M, monthly; (S), spring-summer-fall (approximately April through November); (W), winter (approximately December through March); **, permitted discharge, grab sample, if flow; ---, not sampled; °C, degrees Celsius, mg/L, milligrams per liter; μg/L, micrograms per liter; L, liter; mL, milliliter; #, number; MP, most probable; μmhos/cm, micromhos per centimeter; CaCO3, calcium carbonate]

Water-quality parameters

Prettyboy Reservoir

Reservoir site identifier Watershed tributary site identifier NPDES site identifier

GUN0399 GUN0401 GUN0437 GOB0017 GRG0013 GUN0476 STP8006**

Temperature, air, °C M(W) M(S) M M M M MTemperature, water, °C M(W) M(S) M M M M MColor (True), color units M(W) M(S) M --- --- --- ---Secchi disc, meters M(W) M(S) M --- --- --- ---Turbidity, nephelometric units M(W) M(S) M M M M MTotal solids, mg/L --- --- --- M M M MTotal suspended solids, mg/L --- --- --- M M M MVolatile suspended solids, mg/L M(W) M(S) M --- --- --- ---Chlorophyll-a, μg/L M(W) M(S) --- --- --- --- ---Total algal count, #/mL M(W) M(S) --- --- --- --- ---Algal identification --- --- --- --- --- --- ---Total and fecal coliforms, MP#/100 mL --- --- --- --- --- --- ---Cryptospiridium and Giardia, #/L M(W) M(S) M M M M MSpecific conductance, μmhos/cm --- --- --- M M M MDissolved solids, mg/L --- --- --- --- --- --- ---Hardness, mg/L as CaCO3 M(W) M(S) M M M M MpH, Standard units M(W) M(S) M M M M MAlkalinity, mg/L as CaCO3 M(W) M(S) M M M M MDissolved oxygen, mg/L M(W) M(S) M --- --- --- ---Manganese, mg/L --- --- --- --- --- --- ---Iron, mg/L M(W) M(S) M M M M MPhosphorus, total, mg/L --- --- --- --- --- --- ---Nitrogen, nitrate, mg/L M(W) M(S) M M M M MNitrogen, ammonium, mg/L M(W) M(S) M M M M MNitrogen, total Kjeldahl, mg/L --- --- --- --- --- --- ---Carbon, total organic, mg/L --- --- --- --- --- --- ---Trihalomethanes, μg/L --- --- --- --- --- --- ---Haloacetic acids, μg/L --- --- --- --- --- --- ---Sodium, mg/L --- --- --- --- --- --- ---Chloride, mg/L --- --- --- M M M M
122 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Appendix C: Review of Baltimore Reservoir 

Ashburton and Montebello Treatment Facilities 

Laboratory Quality-Assurance Plans

Contents

Introduction.................................................................................................................................................123

Ashburton Laboratory Quality-Assurance Plan, Revision 3, 2007 .....................................................123

Montebello Laboratory Quality-Assurance Plan, Revision 3, 2007....................................................127
Appendix C 123

Introduction

The following quality-assurance (QA) plans for the Ashburton and Montebello treatment facility laboratories were 

requested and reviewed as part of the retrospective review, and are included in this Appendix. Except for minor reformatting, the 

plans are presented as they were received. For selected headings, no additional text appears in plan after the heading. 

Ashburton Laboratory Quality Assurance Plan, Revision 3, 2007

This plan was obtained in March 2007 from Savita Bagel, Laboratory Manager, Ashburton Laboratory, Baltimore, 

Maryland. It has been minimally reformatted for inclusion in this Appendix.

1. Organization Chart, Line Authority - see list (attached list not requested)

2. 

3. Analytical Procedures (see the Standard Operating Procedures (SOP) manual)

4. Sample Handling Procedures

Sample Acceptance and Logging—There is a sample log for all samples coming into the laboratory. All samples must 

be collected, stored and preserved in accordance with EPA guidelines. More specific instructions are in the SOPs.

Sample Rejection—Samples are rejected for improper labeling, collection, storage or holding times.

Sample Disposable—Samples are disposed of after all analyses are completed or at the end of the holding time.

Sample Storage—Chlorine and pH analyses must be done immediately when the sample comes into the lab. For most 

other analyses the samples are stored in the refrigerators before analysis. For metals analyses the samples should be 

preserved with nitric acid to less than pH 2.

Sample Tracking—All samples should be recorded in the sample log book.

Chain of Custody—Is needed for samples being transported to or from Montebello, including samples for metals 

analysis.

5. Sampling Procedures

Containers—The container must be appropriate for the intended analysis and must be labeled with the location, date and 

time of collection. Sterile bottles with sodium thiosulfate are used for micro samples. Acid-washed bottles are needed 

for metal analyses. 

Preservation—All, except samples for metal analysis, must be kept on ice or refrigerated until analyzed. If analyses for 

nitrate, ammonia and phosphates cannot be completed within 48 hours, the samples are preserved by acidifying to < 

pH 2 with concentrated sulfuric acid. Samples for metal analysis should be acidified to < pH 2 with concentrated nitric 

acid. They must be held for 16 hours after acidification and then can be held for up to 6 months. If the turbidity is > 1 

NTU, the sample must be digested. (see SOPs.)

QC Samples—Should be done quarterly for fluoride, nitrites, and nitrates and as many other parameters as possible. The 

complete analysis should be done on the yearly Performance Evaluation samples each spring. As many analysts as possible should complete each analysis.

Documentation—All samples must be logged into the sample log book and/or have a paper form with the required information. Included must be the name of the sampler, date and location of the sample and a list of parameters for analysis.

Special Instructions—Care must be exercised to take samples that will be representative of the water being tested and to 

avoid contamination of the sample at the time of collection or in the period before analysis.

Plant Process Samples—Samples can be taken from the sink taps, anytime, except when the water flow thru the plant 

has been changed recently. A change in flow may affect the water quality temporarily. Samples should be analyzed 

immediately when possible.
124 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Metals Analyses Samples—The tap should be opened and the water allowed to run to waste for 2 to 3 minutes or for a 

sufficient time to permit clearing of the service line. Chlorine and pH determinations must be done at this time. The 

flow from the tap should then be restricted to one that will permit filling the bottle without splashing. The bottles can 

be filled almost to the top leaving enough air space to permit mixing. For a first draw sample for lead analysis, the line 

should be thoroughly flushed and then allowed to sit unused for 6 to 8 hours. The sample should then be collected as 

soon as the tap is opened.

Utility Maintenance Samples—There are no restrictions on these samples except that we need to know the location and 

the time collected. These analyses are not done by approved methods and are only an approximation, but good enough 

to tell whether city water, sewage or ground water is involved.

Watershed Samples—Are collected by the watershed samplers.

Water Quality Management Samples—Storm water runoff samples for nutrient analyses are preserved before they 

come to the lab.

Distribution Samples—Must be collected by a State Certified Sampler and are almost always analyzed at Montebello.

Waste Lake Samples—All composite samples must be analyzed each week to meet the requirements of the NPDES 

permit for the plant.

6. Calibration Procedures

Standards Source—ERA, NSI, SPEX, Fisher, Perkin Elmer.

Comparability Checks—New standards are run against old standards with a QC sample.

Frequency—The pH meter is calibrated each morning and afternoon with three certified buffers. The calibration is 

checked with each use. The balance calibration is checked monthly. All turbidimeters in the plant are calibrated each 

month by the Instrumentation group. Calibration of other instruments is done each day of use. A set of at least 3 standards and a blank must be used. An appropriate standard or QC sample must be checked after a set number (usually 

10) of samples. Standards and QC samples must be run again at the end of the run. More specific instructions are in 

each SOP.

7. Documentation 

There are calibration books for pH and fluoride as well as for the digital berets and balances. For other analyses the analyst keeps the calibration documentation with the sample results.

8. Data Reduction, Validation and Reporting

Calculations

Units Units must be clearly marked as to mg/L or (text ends here)

Transcription/Transfer Each analyst records their results on the report form.

Report Format The report format varies with the type of sample. 

Documentation 

9. QC Checks—see SOPs for specific instructions.

Reagent Blanks—Are done for each set of analyses.

Replicate Analyses—At least 10 % of samples must be duplicated. 

Check Sample Recoveries

Matrix Spike Recoveries—Are done for every sample analyzed by graphite furnace. For fluorides, the spikes are done 

each day. For nitrates, the spikes should be done on at least 10 % of the samples or whenever the matrix changes.

Instrument Control Standard Response
Ashburton Laboratory Quality Assurance Plan, Revision 3, 2007 125

Internal Standard Response

Control Charts—Are done for fluoride, nitrates, nitrites and all metal analyses.

Documentation—If the QC is not acceptable, the samples must be run again. Any out of control sample or standard on 

the control charts must be documented with the corrective action: The sample could be rerun or recalibration was done 

or maintenance of the instrument was needed. 

10. Specific Routine Procedures

Accuracy—All graphite furnace samples are spiked. 10% of other samples are spiked.

Precision—Duplicates are done to demonstrate precision.

Completeness

Timeliness—All samples must be analyzed within the approved holding time unless clearly marked on the report of 

results. Compliance samples must always be done within the approved holding time.

Legibility

Clarity

11. Schedules of internal and external system and data quality audits and inter laboratory comparisons.

The EPA performance evaluation samples for chemistry are done each year for all analyses that are done in the lab. At 

least once each quarter, QC samples are done for nitrates, nitrites and fluorides. QC samples are included for each of 

the metals analyses each time they are run.

12. Preventive Maintenance

Operating Manuals—There is a file drawer for operating manuals and instruction books for most equipment. A file 

folder of instructions and a record of repairs and replacement parts will be included there.

Service Schedule—Both balances are cleaned and calibrated each year by American Scale. Class S weights are used to 

check the balance calibration each month.

Spare Parts Inventory—Some spare parts are kept on hand including parts for the glass still and various bulbs for the 

spectrophotometer and the turbidimeter. Backup equipment is available for the ion meter, the pH meter, the turbidimeter and the spectrophotometer. There is cooperation with the Montebello Lab for emergencies.

Service Agreements—The annual service contract agreement for the Perkin Elmer Atomic absorption spectrometer 

includes two preventive maintenance visits each year. 

Documentation—All service and repairs should be documented in the appropriate file folder in the equipment file. 

Records for the AA are in the desk nearest the AA.

13. Corrective Action

QC Failure—If the QC results are not acceptable, the analysis must be repeated.

PE Failure—Every aspect of the analysis must be examined to determine the problem. Correction must be as soon as 

possible and steps taken to ensure that the problem will not occur again.

Audit Deficiency—Must be corrected as soon as possible.

Complaint

14. Record Keeping Procedures

Keep original data for at least 5 years. Monthly reports are kept on disk (two copies) and at least one paper copy is in the 

lab as well. As needed, reports are kept on disk as well as on paper. Reports are distributed as needed to other people.
126 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Montebello Laboratory Quality Assurance Plan for Chemical Analysis, 

Revision 3, 2007

This plan was obtained in March 2007 from Lisa Jones, Laboratory Manager, Montebello Laboratory, Baltimore, Maryland. 

It has been minimally reformatted for inclusion in this Appendix.

1. Organization Chart

INEZ HAWK, LABORATORY TECHNICAL ADMINISTRATOR

LISA JONES, LABORATORY TECHNICAL SUPERVISOR

DEBORAH PITTS, MICROBIOLOGIST SUPERVISOR

JOSEPH BRENNAN, CHEMIST II

OMACHILE TAUPYEN, CHEMIST I

MARIA REED, MICROBIOLOGIST II

KAREN CAMPBELL, LAB ASSISTANT II

JOHN HOHMAN, POLLUTION CONTROL ANALYST II

RICHARD NUSS, CHEMIST III

THO NGUYEN, CHEMIST III

All of the chemists have at least 20–30 hours of college level chemistry courses. Each new analyst is trained and checked 

by a senior analyst. The laboratory supervisor is responsible for implementing the QA plan. Each analyst is responsible 

for doing analyses with the required quality control.

The laboratory supervisor is responsible for making sure that all personnel are updated on changes in regulations and 

methodology. The analysts should be able to make the necessary changes with minimal assistance.

The Microbiologists have a Microbiological Quality Control and Procedures Manual. The Microbiologist Supervisor 

makes changes in methods and procedures. Now, while that position is vacant, the laboratory supervisor will make 

changes when necessary.

On weekends and holidays, one analyst does both the routine chemistry and microbiology. Therefore, all chemists and 

microbiologists must demonstrate the ability to perform the routine chemical and microbiological analyses that are 

done on weekends and holidays. This is done before they work a weekend.

2. Data Quality Objectives:

Compliance samples are done with approved methods and all appropriate quality control, being careful to observe 

required holding times. Plant process samples occasionally can be done more informally; e.g., manganese. Waste lake 

samples need to be done as quickly as possible with screening tests that do not necessarily require all the usual quality 

control.

3. Analytical Procedures-Dates of Revision (see the SOP manual)

Alkalinity-titration method-2/28/97

Ammonia-Electrode method-11/9/98

Calcium Carbonate Stability-2/11/97

Carbon dioxide-titrimetric method-12/20/95

Chloride-argentometric method-12/95

Chloride-see ion chromatography method-11/5/98
Montebello Laboratory Quality Assurance Plan for Chemical Analysis, Revision 3, 2007 127

Chlorine-amperometric titration-2/27/97

Color-Visual comparison-11/6/98

Dissolved Oxygen-electrode-12/95

Fluoride-ion selective method-10/95

Hardness-EDTA titration-2/28/97

Iron-Phenanthroline method-12/95

Ion Chromatography for nitrate, chloride and sulfate-11/5/98

Jar test procedure-3/22/96

Manganese for plant process-11/6/98

Nitrate-electrode method-11/4/98

Nitrate-see ion chromatography method-11/5/98

Nitrite-colorimetric method-3/16/98

PH-electrometric-11/19/96

Phosphate-total-ascorbic acid method-11/16/95

Silica-molybdosilicate-12/95

Sulfates-see ion chromatography method-11/5/98

Threshold odor number (TON)-12/19/95

Total Organic Carbons 4/2000

Total suspended solids-Dried at 180oC-4/2002

Total Solids-11/3/98

Turbidity-Nephelometric Method-3/20/97

Volatile solids-11/3/98

Organics:

Trihalomethanes EPA 524.2

HAA’s EPA 552

VOC’s EPA 524.2

EDB, DBCP EPA 504

Organohalide Pesticides EPA 505

Chlorinated Pesticides EPA 508, 515.1

TTHM Formation Potential EPA 510.1

4. Sampling Procedures

Containers—The container must be appropriate for the intended analysis and must be labeled with the location, date, 

time of collection and collector. Sterile bottles with sodium thiosulfate are used for micro samples. Acid-washed (25% 

HNO3) bottles are needed for metal analyses. Leak samples are collected in clean glass pint bottles. Watershed samples 

are collected in acid (50% HCI) rinsed plastic liter bottles.
128 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Preservation—All samples, except samples for metal analysis, must be kept on ice or refrigerated until analyzed. If 

analyses for nitrate, ammonia and phosphates cannot be completed within 48 hours; acidifying to < pH with concentrated sulfuric acid preserves the samples.

Samples for metal analysis should be acidified to pH 2 with concentrated trace metal grade nitric acid. They must be held 

for 16 hours after acidification and then can be held for up to 6 months.

Special Instructions—Care must be exercised to take samples that will be representative of the water being tested and to 

avoid contamination of the sample at the time of collection or in the period before analysis. Paperwork must be filled 

out in ink.

Plant Process Samples—Samples can be taken from the sink taps, anytime, except when the water flow through the 

plant has been changed recently. A change in flow may affect the water quality temporarily. Samples should be analyzed immediately when possible. Chlorine and pH must be done immediately. Immediately is considered to be within 

15 minutes.

Metals Analyses Samples—The tap should be opened and the water allowed to run to waste for 2 to 3 minutes or for a 

sufficient time to permit clearing of the service line. Chlorine and pH determinations must be done at this time. The 

flow from the tap should then be restricted to one that will permit, filling the bottle without splashing. The bobbles can 

be filled almost to the top leaving enough air space to permit mixing. For a first draw sample for lead analysis, the line 

should be thoroughly flushed and then allowed to sit unused for 6 to 8 hours. The sample should then be collected as 

soon as the tap is opened.

Watershed Samples—Are collected by the watershed samplers and will come with all needed paperwork.

Organic Bottles—Must be cleaned according to the appropriate EPA protocol for each method.

Distribution Samples—Must be collected by a Certified Sampler and are always analyzed at Montebello. 

5. Sample Handling Procedures

Sample Acceptance and Logging

All samples must be recorded in the sample log book and/or have a paper form with the required information. Included 

must be the name of the sampler, date and location of the sample and a list of parameters for analysis. All samples 

must be collected, stored and preserved in accordance with EPA guidelines. More specific instructions are in the SOPs. 

Samples from the Ashburton Lab should have a chain of custody with the appropriate information.

Sample Rejection—Samples are rejected for improper labeling, collection, storage or holding times.

Sample Storage—Chlorine and pH analyses must be done immediately when the sample comes into the lab. This means 

they must be done within 15 minutes of collection. For most other analyses the samples are stored in the refrigerators 

before analysis. For metals analyses the samples are to be preserved with nitric acid to less than pH 2 and then can be 

held at room temperature.

Sample Disposal—Samples are disposed of after all analyses are completed or at the end of the holding time.

Sample Tracking—All samples are to be recorded in the sample logbook. Microbiological samples for coliform analysis 

must be logged into the micro book and stored in the Micro refrigerator on the shelf for coliform samples.

Chain of Custody—Is needed for samples being transported to or from Ashburton, including samples for metals 

analysis.

6. Calibration Procedures

Standards Source ERA, SPEX, Fisher

Comparability Checks New standards are run against old standards with a QC sample.

Frequency The pH meter is calibrated each morning with two certified buffers. The calibration is checked with each use. 

The balance calibration is checked monthly. All turbidmeters in the plant are calibrated quarterly by the Instrumentation group. Calibration of other instruments is done each day of use. A set of at least 3 standards and a blank must be 
Montebello Laboratory Quality Assurance Plan for Chemical Analysis, Revision 3, 2007 129

used. An appropriate standard or QC sample must be check after a set number (usually 10) of samples. Standards and 

quality control samples must be run again at the end of the run. More specific instructions are in each SOP.

Documentation There are calibration books for pH and fluoride and balances. For other analyses the analyst keeps the 

calibration documentation with the samples results. 

7. Analytical Procedures

Standard Operating Procedures are in SOP manual and should be reviewed by the analysts frequently. The complete 

method citation is included at the beginning of the SOP. The date of the last revision is at the bottom of the SOP.

8. Data Reduction, Validation and Reporting

Units Units must be clearly marked.

Transcription/Transfer Each analyst records his or her results on the report form.

Report Format The report format varies with the type of sample.

Documentation results can only be reported if all the QC has been satisfactory.

9. QC Checks see SOPs for specific instructions.

Reagent Blanks are done for each set of analyses.

Replicate Analyses at least 10% of samples must be duplicated.

Check Sample Recoveries The required percentage range varies with the type of analyses.

Matrix Spike Recoveries For fluorides, the spikes are done each day. For nitrates the spikes should be done on at least 

10% of the samples or whenever the matrix changes.

Instrument Control Standard Response varies for each instrument.

Control Charts are done for fluoride, nitrates, and nitrites.

Documentation If the QC is not acceptable, the samples must be run again. Any out of control recovery on the control 

charts must be documented with the corrective action:

The sample was rerun or recalibration was done or maintenance of the instrument was needed.

Accuracy 10% of all samples are spiked for certified analyses.

Timeliness All samples must be analyzed within the approved holding time unless results are clearly marked on the 

report. Compliance samples must always be done within the approved holding time.

Method Detection Limits (MDL) must be done at least annually by each new analyst.

Quality Control procedures for microbiology are included in the Microbiology Manual.

10. Schedules of internal and external system and data quality audits and inter-laboratory comparisons.

The EPA Performance Evaluation samples for chemistry are done each year for all analyses that are done in the lab.

As many analysts as possible should complete each analysis. At least once each quarter, QC samples are done for nitrates, 

nitrites and fluorides. QC samples are included for each of the ORGANICS analyses each time they are run.

11. Preventive Maintenance

Operating Manuals There is a file drawer for operating manuals and instruction books for most equipment. A file folder 

of instructions and a record of repairs and replacement parts for each instrument are included there.

Service Schedule All balances are cleaned and calibrated each year by American Scale. Class 1 weights are used to 

check the analytical balance calibration each month.
130 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

Spare Parts Inventory Some spare parts are kept on hand including parts for the glass still and various bulbs for the 

spectrophotometer and the turbidimeter. Backup equipment is available for the ion meter, the pH meter, the turbidimeter and the spectrophotometer. There is cooperation with the Ashburton Lab for emergencies.

Service Agreements The Ion Chromatograph is covered by a service contract with preventive maintenance visits. The 

same applies to the autoclave, dishwasher, and the Total Organic Carbon Analyzer. Service contracts are generally in 

effect for the GC/MS.

All service and repairs should be documented in the appropriate maintenance log book near the equipment.

12. Corrective Action

QC Failure- If the QC results are not acceptable, the analysis must be repeated. If the holding time has expired, the 

sample cannot be rerun and the results must re-check the SOP to see if everything was done correctly. Check to be sure 

that all reagents are correct. Depending on the type of analysis, recalibration might be required. Dilution of the sample 

might be helpful. Check with the laboratory supervisor or chemist III for more suggestions.

PE Failure every aspect of the analysis must be examined to determine the problem. Corrective action must be taken 

as soon as possible to ensure that the problem will not occur again. Check the SOP. Reagents should be checked. The 

instrument used may need to be serviced. Preventive maintenance procedures should be reviewed. The results of the 

investigation should be written up and given to the laboratory supervisor to be sent in the response to the State. 

Audit Deficiency must be corrected as soon as possible.

13. Record Keeping Procedures

Original data in workbooks is kept for at least five years. Copies of the weekly Watershed data are sent to the watershed 

section.

Plant monthly reports are kept on disk (two copies) and at least one paper copy is in the lab as well. Copies are sent to the 

State MDE, to the Water System Manager, Water Systems Assistant Manager, the Water Quality Laboratory Administrator and the Water Quality Lab Supervisors.

Microbiological results are reported by telephone. The paperwork is filed for future reference.
Appendix D 131

Appendix D: Plant Ecology Group (PEG) 

Model of Seasonal Succession of Plankton in 

Freshwater
132 The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007

The Plankton Ecology Group (PEG) model sequentially describes the general trend of a spring bloom of small diatoms, 

followed by the progression during summer from large colonial green algae to large diatoms, then large dinoflagellates and (or) 

finally blue-green algae (Sommer and others, 1986). In so doing, the PEG model incorporates the relative importance of physical 

factors, nutrients (nitrogen and phosphorus), and grazing in shaping phytoplankton community structure throughout the growing 

season in freshwater lakes, as follows (from Sommer and others, 1986, with modified formatting):

a) Towards the end of winter, nutrient availability and increased light permit unlimited growth of the phytoplankton. A 

small crop of fast-growing algae, for example golden-brown (Cryptophyceae sp.) and centric diatoms develops.

b) This crop of small algae is grazed upon by herbivorous zooplanktonic species, which become abundant due to hatching 

from resting eggs and to high fecundity by high levels of edible algae.

c) Planktonic herbivores with short generation duration times increase their populations first and are followed by slower 

growing species.

d) The herbivore populations increase exponentially up to the point at which their density is high enough to produce a community filtration rate, and so cropping rate, which exceeds the reproduction rate of the phytoplankton.

e) As a consequence of herbivore grazing, the phytoplankton biomass decreases rapidly to very low levels. 

f) There then follows a ‘clear-water’ equilibrium phase which persists until inedible algae species develop in significant 

numbers. Nutrients are re-cycled by the grazing process and can accumulate during the ‘clearwater’ phase.

g) Herbivorous zooplanktonic species become food-limited and both their body weight per unit length and their fecundity 

declines. This results in a decrease in their population densities and biomasses.

h) Fish predation accelerates the decline of herbivorous planktonic populations to very low levels and this trend is accompanied by a shift towards a smaller average body size amongst the surviving crustaceans.

i) Under the conditions of reduced grazing pressure and sustained non-limiting concentrations of nutrients, the phytoplankton summer crops start to build up. The composition of the phytoplankton becomes complex due to both the increase in 

species richness and to the functional diversification into small ‘undergrowth’ species, which are available as food for 

filter-feeders, and into large ‘canopy’ species, which are only consumed by specialists such as raptors or parasites. 

j) At first, the edible algae (such as golden-brown (Cryptophyceae sp.) and inedible colonial green algae become predominant. They deplete the soluble reactive phosphorus to nearly undetectable levels.

k) From this time onwards, the algal growth becomes nutrient-limited and this prevents an explosive growth of ‘edible’

algae. Grazing by predator-controlled herbivores balances the nutrient-limited growth rate of edible algal species.

l) Competition for phosphate leads to a replacement of green algae by large diatoms, which are only partly available to 

zooplankton as food. 

m) Silica-depletion leads to a replacement of the large diatoms by large dinoflagellates and/or blue green algae (Cyanophyta 

sp.).

n) Nitrogen depletion ultimately favors a shift to nitrogen-fixing species of filamentous blue-green algae.

o) Larger species of crustacean herbivores are replaced by smaller species and by rotifers. These small species are less 

vulnerable to fish predation and are less affected by interference with their food collecting apparatus which can be caused 

by some forms of inedible algae. Accordingly, their population mortality is lower and their fecundity is higher than that 

of the larger species.

p) The smaller species of herbivores coexist under a persistent fish predation pressure and the increased possibility of food 

partitioning, which is associated with the greater species complexity of the phytoplankton.

q) The population densities and species composition of the zooplankton fluctuate throughout the summer, the latter being 

also influenced by temperature. 

r) The period of autogenic succession is terminated by factors related to physical changes, which includes increased mixing 

depth resulting in nutrient replenishment and a deterioration of the effective underwater light climate.
Appendix D 133

s) After a minor reduction in algal biomass, an algal community develops which is adapted to being mixed. Large unicellular or filamentous algal forms appear. Among them diatoms become increasingly important with the progress of autumn.

t) This association of poorly-ingestible algae is accompanied by a variable biomass of small, edible algae.

u) This algal composition together with some reduction in fish predation pressure leads to an autumnal maximum of zooplankton which includes larger forms and species.

v) A reduction of light energy input results in a low or negative net primary production and an imbalance with the algal 

losses, which causes a decline of algal biomass to the winter minimum.

w) Herbivore biomass decreases as a result of reduced fecundity due both to lower food concentrations and to decreasing 

temperature.

x) Some species in the zooplankton produce resting stages at this time, whereas other species produced resting stages earlier.

y) At this period in the year, some cyclopoid species ‘awake’ from their diapauses and contribute to the over-wintering 

populations in the zooplankton.

Reference Cited

Sommer, U., Gliwicz, Z.M., Lampert, W., and Duncan, A., 1986, The PEG-model of seasonal succession of planktonic events in 

fresh waters: Archiv für Hydrobiologie, v. 106, no. 4, p. 433–471.

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
Koterba, M.T., and others—The Water-Quality Monitoring Program for the Baltimore Reservoir System, 1981–2007—Scientific Investigations Report 2011–5101

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