U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2008-1106

In cooperation with the Pennsylvania Department of Environmental Protection 

Development of the Water-Analysis Screening Tool Used in 

the Initial Screening for the Pennsylvania State Water Plan 

Update of 2008

Development of the Water-Analysis 

Screening Tool Used in the Initial 

Screening for the Pennsylvania State 

Water Plan Update of 2008

By Marla H. Stuckey 

In cooperation with the Pennsylvania Department of Environmental Protection

Open-File Report 2008–1106

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Stuckey, M.H., 2008, Development of the Water-Analysis Screening Tool used in the initial screening for the Pennsylvania State Water Plan update of 2008: U.S. Geological Survey Open-File Report 2008-1106, 9 p.
iii

Contents

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

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

Development of the Water-Analysis Screening Tool...............................................................................2

Inventory of Water-Use Data..............................................................................................................2

Estimated Unregistered Water-Use Data ................................................................................3

Residential ...........................................................................................................................3

Non-Residential ..................................................................................................................3

Irrigation...............................................................................................................................4

Livestock...............................................................................................................................5

Golf Courses ........................................................................................................................5

Consumptive Use .........................................................................................................................6

Initial Screening Criteria......................................................................................................................6

Water-Analysis Screening Tool...................................................................................................................7

Assumptions ..........................................................................................................................................8

Limitations and Accuracy....................................................................................................................8

Summary..........................................................................................................................................................9

References Cited............................................................................................................................................9

Tables

1. Total water use by source of data .............................................................................................2

2. Estimated unregistered water use by category ......................................................................3

3. North American Industry Classification System used in estimation of 

non-residential water use ...........................................................................................................4

4. Water-use factors used in the estimation of irrigation water use .......................................5

5. Estimated water required for livestock for selected counties..............................................6

6. Trout-stream classifications and requirements for Pennsylvania streams........................7
iv

Conversion Factors and Acronyms

Multiply By To obtain

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

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

Flow rate

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

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

Acronyms

7Q10 7-day, 10-year low flow 

CAFO Concentrated Animal Feeding Operation 

CWPA Critical water-planning area 

DMR Discharge monitoring report

GIS Geographic Information System

Gpcd Gallons per day per capita

ISC Initial screening criteria

NAICS North American Industry Classification System

NHD National Hydrography Dataset 

NW Net withdrawals

SI Screening indicator

SIP Screening indicator as a percentage

WAST Water-analysis screening tool
Abstract

The Water Resources Planning Act, Act 220 of 2002, 

requires the Pennsylvania Department of Environmental 

Protection (PaDEP) to update the State Water Plan by 2008. 

As part of this update, a water-analysis screening tool (WAST) 

was developed by the U.S. Geological Survey, in cooperation 

with the PaDEP, to provide assistance to the state in the identification of critical water-planning areas. The WAST has two 

primary inputs: net withdrawals and the initial screening criteria. A comprehensive water-use database that includes data 

from registration, estimation, discharge monitoring reports, 

mining data, and other sources was developed as input into the 

WAST. Water use in the following categories was estimated 

using water-use factors: residential, industrial, commercial, 

agricultural, and golf courses. A percentage of the 7-day, 

10-year low flow is used for the initial screenings using the 

WAST to identify potential critical water-planning areas. This 

quantity, or initial screening criteria, is 50 percent of the 7-day, 

10-year low flow for most streams. Using a basic water-balance equation, a screening indicator is calculated that indicates 

the potential influences of net withdrawals on aquatic-resource 

uses for watersheds generally larger than 15 square miles. 

Points representing outlets of these watersheds are coloredcoded within the WAST to show the screening criteria for each 

watershed.

Introduction

The Water Resources Planning Act, Act 220 of 2002 

[Water Resources Planning Act of 2002 (P.L. 1776, No. 220)], 

requires the Pennsylvania Department of Environmental 

Protection (PaDEP) to update the State Water Plan by 2008. A 

Statewide Water Resources Committee and six Regional Water 

Resources Committees have been created to oversee and provide guidance to the process of updating the State Water Plan. 

The Statewide Water Resources Committee establishes guidelines and policies that will be used as part the State Water Plan 

update. The State Water Plan update, among other things, will 

result in the identification of areas where the demand for water 

exceeds available supplies. These areas will be designated as 

Critical Water-Planning Areas (CWPA) and will serve as a 

planning boundary for the creation of a more detailed Critical 

Area Resource Plan (Pennsylvania Department of Environmental Protection, 2006a).

A water-analysis screening tool (WAST) was developed 

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

the PaDEP, to provide assistance to the state in the identification of CWPAs. The WAST compares water-use information 

to an initial screening criteria (ISC), resulting in a screening 

indicator (SI) for influences of net withdrawals on aquaticresource uses. The ISC is a percentage of the 7-day, 10-year 

low-flow statistic (7Q101). A screening indicator as a percentage (SIP) is determined for over 10,000 watersheds across the 

state, generally larger than 15 mi2, and is color-coded within 

the WAST for each watershed at its outlet (termed the “pour 

point”). This allows for watersheds to be easily identified for 

further evaluation. After this initial screening of watersheds 

using the WAST, areas with potential conflicts between water 

use and aquatic-resource needs will be selected for further 

evaluation, and CWPAs will be identified. 

This report presents the methodology used to develop the 

WAST and the supporting data used as input into the WAST 

for the initial screening for the Pennsylvania State Water Plan 

update. A comprehensive water-use database that includes data 

from registration, estimation, discharge monitoring reports 

(DMRs), mining data, and other sources is described. Wateruse data were estimated for the following categories: residential, industrial, commercial, agricultural, and golf courses. The 

ISC are determined using regression equations developed by 

Stuckey (2006). The assumptions and limitations of the WAST 

also are presented.

1

The 7-day, 10-year low flow; the lowest consecutive 7-day mean flow 

expected on average every 10 years. 

Development of the Water-Analysis Screening Tool Used 

in the Initial Screening for the Pennsylvania State Water 

Plan Update of 2008

By Marla H. Stuckey
2 Development of the Water-Analysis Screening Tool for the Pennsylvania State Water Plan Update of 2008

Development of the Water-Analysis 

Screening Tool

A water-use database consisting primarily of registrations, DMRs, and available mining data was developed as part 

of the update process for the State Water Plan. Water use was 

estimated, where necessary, to complete the database. The 

ISC used in the statewide initial screening were determined 

from low-flow regression equations as described by Stuckey 

(2006). The WAST uses the total withdrawals minus the total 

discharges, or net withdrawals, of ground water and surface 

water and the ISC for a watershed to determine a SI for potential influences of net withdrawals on aquatic-resource uses. 

Watersheds with a negative SI may indicate areas where the 

net withdrawals are negatively impacting aquatic resources.

Inventory of Water-Use Data

As part of the State Water Plan update, substantial effort 

has been made to compile a comprehensive water-use database to be used in the statewide identification of CWPAs. 

All water users withdrawing or using more than 10,000 gal/d 

averaged over a 30-day period and all public water agencies 

and hydropower facilities were required to register their water 

use with PaDEP. The comprehensive water-use database used 

to perform the initial screening originated from the following 

information: Act 220 registration, estimation, DMRs, mining data, and “other.” These sources of water-use information 

are described in more detail in the following sections. The 

169,700 records that comprise the water-use database are summarized by category in table 1. 

The 7,339 registered water users reported water use in 

agricultural, commercial (which includes golf courses), industrial, water supply, power generation, and mineral extraction. 

More detailed descriptions of these categories can be found in 

Ludlow and Gast (2000). Registered water use is from 2003 

because the records for that year were more complete than 

previous years, in part because of the passing of the Act 220 

legislation. Water use, especially in the non-residential categories and in agriculture, can differ depending on the amount 

of precipitation in a given year. Because the precipitation was 

above average in 2003, the water use reported may be different 

during periods of drought. Information on registered use was 

determined by actual days used, rather than average annual 

use. This may result in a higher value than if water use was 

calculated on an average annual rate. For example, if a facility used 10 Mgal of water for 180 days, the actual days-used 

value is 0.06 Mgal/d. The average annual use for the same 

facility would be 0.03 Mgal/d. Actual days used was utilized 

in the WAST to capture demands that may only use water during the summer months, such as golf courses and irrigation for 

agricultural uses. 

Unregistered withdrawals were estimated to address 

data gaps in water-use categories with water use known to 

be under-reported. The categories requiring estimates were 

self-supplied residential, industrial, commercial, agricultural, 

and golf courses. The methodology used to estimate water use 

is described in more detail in the following section. A total 

of 158,662 records was estimated as part of this process. The 

individual quantities estimated are relatively small, averaging 

1,238 gal/d. Another category requiring estimation was mining, but because withdrawals for mining vary widely and are 

dependent on such factors as type of mineral, type of processing, and need for dewatering, a consistent methodology could 

not be determined.

In addition to withdrawals, flow contributions in the form 

of discharges also were tabulated. Discharges were compiled 

for major basins by the Delaware River Basin Commission 

(DRBC), the Susquehanna River Basin Commission (SRBC), 

and PaDEP primarily through DMRs. DMRs are monthly 

reports submitted by wastewater permittees that summarize the 

quality and quantity of treated water that is discharged. DMRs 

were compiled from 2000 through 2004, resulting in up to 60 

entries for a single facility. Water use was determined for each 

month using monthly quantities excluding any zero, missing, 

or unreported months. This resulted in an actual days-used 

quantity per year. The 2003 actual days-used discharge for 

each facility was used in the statewide compilation of water 

use to be consistent with registration water use. In the event 

that a facility did not have 2003 data, 2002 or 2004 data were 

used. A sensitivity analysis was done using discharges in the 

Codorus Creek watershed in York County as a pilot study 

to determine whether there were any significant differences 

between the discharges for 2000, 2001, 2002, 2003, and 2004. 

A Kruskall-Wallis test (Helsel and Hirsch, 2002) was used to 

compare the datasets, and the results indicated that discharges 

for all the years are statistically equivalent (p-value = 0.9461).

Active mine operations can withdraw and return large 

amounts of water to a system. To ensure a balance between the 

withdrawals and discharges from mining operations, registered 

mining withdrawals were examined for an associated discharge. If no discharges were found for a particular miningoperation facility, a discharge that assumed 8 percent consumptive use was estimated. For mining-operation facilities 

involving only mineral preparation, a discharge that assumed 

17 percent consumptive use was estimated. Details describing the mining operations for facilities were obtained from 

registration reports. A consumptive-use factor of 8 percent 

was obtained from the last water-use compilation for PennsylTable 1. Total water use by source of data.

[Mgal/d, million gallons per day]

Data source Total number 

of sources

Total water use 

(Mgal/d)

Registration 7,339 8,731

Estimation 158,662 196

Discharge monitoring reports 3,453 8,147

Mining 89 85

Other 157 1,059
Development of the Water-Analysis Screening Tool 3

vania completed by the USGS (Ludlow and Gast, 2000) and 

a consumptive-use factor of 17 percent was determined using 

mining water-use data from the PaDEP water-use database. 

These additional mining discharges are herein referred to as 

“mining.” 

An ongoing quality-control program revealed that 

additional withdrawals and discharges have been missed or 

not reported. As these water-use facilities are found, they are 

added to the statewide water-use database and are termed 

“other.” Examples of “other” water use include power generators, water purveyors, mining, and sewage-treatment plants. 

Some of these facilities may have registered or submitted a 

DMR, but the reports may have been misplaced, may have 

included erroneous information, were not filed on time, or 

were unavailable to staff during times of collection.

Estimated Unregistered Water-Use Data

Unregistered withdrawals were estimated to fill data gaps 

in water-use categories with water use known to be underreported. These categories are primarily self-supplied users 

and include residential, industrial, commercial, agricultural, 

and golf courses water use. The estimated unregistered water 

use by category is shown in table 2. The methodology used to 

estimate unregistered water use was modified from procedures 

developed by Camp, Dresser, and McKee, in cooperation with 

the DRBC and the PaDEP (David Sayers, Delaware River 

Basin Commission, written commun., 2005). Water use was 

estimated using a point approach to represent a larger area, 

resulting in a unique spatial location necessary for inclusion in 

the WAST.

Residential

Self-supplied residential use refers to households outside 

of public-water-supply service areas that are assumed to 

rely on private wells. Data from the 2000 census were used 

to determine populations outside of the service areas (U.S. 

Census Bureau, 2000). Service-area boundaries were supplied 

by PaDEP. Revised 2000 population data were obtained from 

PaDEP, and blocks with zero populations were removed. A 

population density (person per square meter) was calculated 

for each census block. A Geographic Information System 

(GIS) was used to determine census blocks that were outside 

the service areas. In cases where the service areas crossed a 

census block, the population was adjusted by multiplying the 

population density by the area of the census block outside the 

service area. Centroids of the census blocks outside of service 

areas were determined and assigned with associated population attributes. These points represent the combined household 

population residing in a particular census block. 

An attempt was made to determine a water-use factor using statewide data from selected public water suppliers, including population served and quantity of water used. 

However, there was wide variance in the data, and a conclusive water-use factor could not be determined (Michael 

Hill, Pennsylvania Department of Environmental Protection, 

written commun., 2006). A water-use factor of 80 gallons per 

capita per day (gpcd) was determined by Camp, Dresser, and 

McKee as part of a pilot study conducted in the Lehigh River 

watershed (David Sayers, Delaware River Basin Commission, 

written commun., 2005). This factor was based on data from 

21 public water suppliers. Because this value of 80 gpcd was 

similar to the results of the statewide effort, and a conclusive 

statewide water-use factor could not be determined, the value 

of 80 gpcd was applied to each point representing the population residing in one particular census block to determine the 

estimated water use. 

Non-Residential

Non-residential points were assumed to be places of 

employment outside of public-water-supply service areas. 

These non-residential points are industrial and commercial 

facilities relying on private wells or other sources to meet 

their water needs. Employment data were obtained by PaDEP 

from the Pennsylvania Department of Labor and Industry. Of 

the total employment sites included in the Labor and Industry 

data, 42 percent had either missing or incorrect spatial data. 

For those sites without valid spatial data, attempts were made 

to assign latitude and longitude designations on the basis of 

the centroid of the associated census block. In cases where 

the service areas crossed a census block, the employment was 

adjusted by area distribution. Of the employment sites without 

spatial data, approximately 20 percent did not have censusblock information or could not be matched to the 2000 census 

blocks and were not included in the analysis. A GIS was used 

to identify those points outside of the service areas. North 

American Industry Classification System (NAICS) codes 

Table 2. Estimated unregistered water use by category.

[Mgal/d, million gallons per day]

Estimated unregistered

water-use category

Total 

number of 

estimated 

points 

Total 

estimated 

water use 

(Mgal/d)

Residential 114,950 20.9

Industrial 3,021 67.8

Commercial, excluding golf courses 36,563 16.5

Irrigation 1,595 39.3

Livestock 2,112 23.0

Golf courses 421 28.8
4 Development of the Water-Analysis Screening Tool for the Pennsylvania State Water Plan Update of 2008

(U.S. Department of Commerce, 2002) were used to identify 

the industrial (manufacturing) and commercial (non-manufacturing) employment sites (table 3). 

An attempt was made to determine a water-use factor 

using statewide data from registered industrial and commercial facilities, including number of employees and quantity 

of water used. However, there was wide variance in the data, 

and a conclusive water-use factor could not be determined 

(Michael Hill, Pennsylvania Department of Environmental 

Protection, written commun., 2006). Water-use factors of 

665 gal/d per employee and 42 gal/d per employee for industrial and commercial sites, respectively, were determined by 

Camp, Dresser, and McKee as part of a pilot study conducted 

in the Lehigh River Watershed (David Sayers, Delaware River 

Basin Commission, written commun., 2005). These factors 

were based on data from 16 and 21 public water suppliers, 

with standard deviations of 815 gal/d and 57 gal/d for industrial and commercial facilities, respectively. Because the 

water-use factors developed by Camp, Dresser, and McKee 

were similar to the results of the statewide effort and new 

values could not be determined, these water-use factors were 

used to estimate water use for industrial and commercial sites. 

These water-use factors were applied to known and approximate locations outside of public-water-supply service areas. 

Duplicate values for the same non-residential facility may 

exist as a result of both registration and estimation. Insufficient information from the Labor and Industry data resulted 

in the inability to check for duplicate values on a statewide 

basis. Before a watershed is identified as a CWPA, verification 

would be needed to ensure there are no duplicate values for 

estimated unregistered facilities with large registered withdrawals outside of service areas.

Irrigation

Irrigation water use was estimated for the top 10 counties 

identified from the 2002 agriculture census (U.S. Department 

of Agriculture, 2004) that accounted for about 60 percent of 

irrigated water use in the state. Irrigation water use in Lancaster, Franklin, Adams, Erie, Berks, Schuylkill, Lebanon, 

Chester, Lycoming, and York Counties was estimated. Water 

use was estimated for points within these counties on the basis 

of total irrigated cropland, which was determined using a ratio 

of irrigated cropland to total cropland as reported in the 2002 

agricultural census (U.S. Department of Agriculture, 2004). 

Data were compiled for the 2002 agricultural census through 

the use of mailed questionnaires to farm and ranch owners 

and operators. Land-use categories were used to determine the 

Table 3. North American Industry Classification System used in estimation of non-residential water use.

North American Industry 

Classification System

 (NAICS)

Description

Manufacturing

31-33 Manufacturing

Non-manufacturing

22 Utilities

23 Construction

42 Wholesale Trade

44-45 Retail Trade

48-49 Transportation and Warehousing 

51 Information

52 Finance and Insurance

53 Real Estate and Rental and Leasing 

54 Professional, Scientific, and Technical Services

55 Management of Companies and Enterprises 

56 Administrative and Support and Waste Management and Remediation Services

61 Educational Services

62 Health Care and Social Assistance 

71 Arts, Entertainment, and Recreation

72 Accommodation and Food Services

81 Other Services (except Public Administration)

921 Public Administration

1

NAICS code 99 was used in the Labor and Industry database but did not have a corresponding NAICS code in the Workforce 

Investment Area Data; after discussion with Pennsylvania Department of Environmental Protection, data from NAICS code 92 

was substituted for NAICS code 99. 
Development of the Water-Analysis Screening Tool 5

location of cropland within the counties.Total cropland for 

Lancaster, Franklin, Adams, Berks, Schuylkill, Lebanon, and 

Lycoming Counties was determined from row crops (Pennsylvania State University, 2003); total cropland for Erie and York 

Counties was determined from row crops, grain, hay, seeds, 

and other crops (U.S. Department of Agriculture, 2006); and 

total cropland for Chester County was determined from row 

crops, grain, hay, and seeds (U.S. Department of Agriculture, 

2006). The areas of cropland computed using these geospatial data layers were compared to the 2002 agriculture census 

total cropland for the counties, and the two areas were within 

12 percent. The cropland was then determined in a GIS for the 

subbasins used in the WAST, and the centroids of the subbasins were generated. 

As a result of the GIS analysis described in the preceding 

paragraph, each centroid point has a corresponding amount of 

cropland representing a portion of the total cropland for the 

county. This cropland amount was then adjusted on the basis 

of a ratio of total cropland to irrigated cropland (table 4) determined from the 2002 agriculture census (U.S. Department 

of Agriculture, 2004). Water use was then estimated using a 

water-use factor based on irrigated cropland in acres generated 

by Dr. Albert R. Jarrett from the Pennsylvania State University 

in conjunction with PaDEP (Dr. Albert Jarrett, Pennsylvania 

State University, written commun., 2007). The water-use factors for the counties with estimated water use are provided in 

table 4. These water-use factors were determined on the basis 

of the growing season, using a 31-day August average with 

average precipitation. Actual water used for irrigation during 

drought years may be greater than the quantities determined 

using the water-use factors shown in table 4 and may need 

to be further evaluated before a watershed is identified as a 

CWPA.

Livestock

Water use for livestock was estimated for the top 

12 counties that accounted for about 60 percent of water used 

for livestock in the state (Dr. Albert Jarrett, Pennsylvania 

State University, written commun., 2007). These included 

Lancaster, Franklin, Lebanon, York, Berks, Bradford, Adams, 

Cumberland, Chester, Somerset, Perry, and Snyder Counties. 

An analysis of land use and locations of Concentrated Animal 

Feeding Operations (CAFOs) showed that the majority of 

these locations were in land-use areas categorized as row crops 

(Pennsylvania State University, 2003). The livestock areas 

were therefore assumed to be located in the row-crop areas, 

and row crops were determined in a GIS for the subbasins 

used in the WAST. The percentage of row-crop area within 

each subbasin to total county row-crop area was determined 

for each subbasin. The centroids of the subbasins with row 

crops were determined. Each centroid was assigned a wateruse quantity representing a particular subbasin on the basis 

of the percentage of row-crop area and water-use factors for 

the county. The water use required for livestock per county is 

shown in table 5 (Dr. Albert Jarrett, Pennsylvania State University, written commun., 2007). 

Golf Courses

According to an extensive search by DRBC in conjunction with PaDEP, 421 golf courses did not register water use 

in 2003 (David Sayers, Delaware River Basin Commission, 

written commun., 2006). These golf courses account for about 

60 percent of all golf courses in the state. Using registered 

golf courses as a reference, a consistent methodology was 

determined to estimate water use at the unregistered courses. 

Water used at each registered golf course varied widely and 

depended on such factors as expanse of facility and grounds, 

Table 4. Water-use factors used in the estimation of irrigation water use.

County Rank

Irrigated 

lands1

(acres)

Total 

cropland1

(acres)

Ratio of 

irrigated land to 

total cropland

Water-use

 factor2

(gallons per day 

per acre)

Lancaster 1 6,051 333,009 0.01817 2,467

Franklin 2 2,712 191,112 .01419 1,836

Adams 3 2,656 135,040 .01967 1,867

Erie 4 2,302 106,364 .02163 2,506

Berks 5 1,914 173,223 .01105 2,653

Schuylkill 6 1,876 78,347 .02394 2,727

Lebanon 7 1,857 102,547 .01811 2,512

Chester 8 1,846 124,322 .01485 2,689

Lycoming 9 1,770 103,763 .01706 997

York 10 1,689 222,789 .00758 2,245

1

U.S. Department of Agriculture (2004). 

2

Dr. Albert Jarrett, Pennsylvania State University, written commun., 2007.
6 Development of the Water-Analysis Screening Tool for the Pennsylvania State Water Plan Update of 2008

amenities, and number of holes. A relation between the 

number of holes and the water used on registered golf courses 

statewide was developed to estimate water use at the unregistered golf courses; a water-use factor of 4,270 gal/d per 

hole was used. Further analysis could be applied to refine the 

water-use factor to a smaller scale, basing it on counties or 

census information rather than on the entire state.

Consumptive Use

Consumptive use is the part of withdrawn water that is 

consumed and is removed from the immediate water system 

(Solley and others, 1998). The water may be consumed by 

humans or livestock, or incorporated into products or crops, 

making it unavailable for immediate use. Consumptive use 

is incorporated into the database through related registered 

withdrawal and discharge points. The difference between the 

amount of water a facility withdraws and the amount returned 

as a discharge is essentially the consumptive use. 

However, the estimated withdrawals do not have corresponding estimated discharges, because discharges, as a 

whole, were not estimated. All estimated withdrawals, with the 

exception of residential, are assumed to have a consumptive 

use of 100 percent. Although that assumption may be realistic 

for some water-use categories, such as irrigation where historically most of the water applied is evapotranspired, it may not 

be realistic for all categories. Estimated residential water use 

was adjusted to account for consumptive use of 10 percent, 

resulting in 90 percent of the water used being returned to the 

system. Previous studies in Pennsylvania support a consumptive-use factor of 10 percent for self-supplied residential, 

including the last compilation completed by the USGS (Solley 

and others, 1998) and an analysis done by DRBC (David 

Sayers, Delaware River Basin Commission, written commun., 

2007).

Initial Screening Criteria

The ISC were established in cooperation with the CWPA 

Subcommittee, a subcommittee of the Statewide Water 

Resources Committee, for purposes of identifying potential 

CWPAs. CWPAs are areas where existing or projected withdrawals are likely to cause irreparable or unmitigated impacts 

to reasonable and beneficial withdrawal and non-withdrawal 

uses (Pennsylvania Department of Environmental Protection, 

2006b). Cumulative unmitigated net withdrawals in CWPAs 

exceed, or result in, at least one of the following values or conditions (Pennsylvania Department of Environmental Protection, 2006b):

•	 Repeated acute dewatering, 

•	 5 percent mean annual habitat loss for Class A trout 

streams underlain by carbonate bedrock, 

•	 5 percent mean annual habitat loss for Class A trout 

streams in noncarbonated areas,

•	 10 percent mean annual habitat loss for Class B trout 

streams underlain by carbonate bedrock,

•	 15 percent mean annual habitat loss for Class C and D 

trout stream underlain by carbonate bedrock,

On the basis of an analysis by the Pennsylvania Fish and 

Boat Commission for the CWPA Subcommittee and PaDEP, it 

was determined that a percentage of the 7Q10 may be used for 

the initial screenings to satisfy the requirements listed above 

(Leroy Young, Pennsylvania Fish and Boat Commission, oral 

commun., 2005). This quantity, or the ISC, was determined 

to be 50 percent of the 7Q10 flow for all streams except 

those designated as a Class A trout stream in areas of carbonate bedrock; 30 percent of the 7Q10 flow is used for those 

streams. Trout-stream classifications and requirements are 

shown in table 6. The 7Q10 is computed by regional regression equations developed by the USGS (Stuckey, 2006). All 

7Q10 values determined using the regression equations are 

greater than zero. After the initial screening using a percentage 

of 7Q10, if a watershed is prioritized for further study, the ISC 

will be reevaluated using other methods where applicable. For 

example, a percentage of mean annual habitat loss as determined using Pennsylvania Instream Flow Incremental Methodology developed by SRBC (1998) could be compared to the 

ISC and used in the WAST. 

Regulated flow from flood-control reservoirs and other 

lakes and ponds may alter downstream streamflow. Conservation releases or pass-by flows requiring permits were not 

included in the initial screening using the ISC as a percentage of 7Q10. In addition, net withdrawals and the ISC were 

computed as stand-alone values in the initial screening without 

Table 5. Estimated water required for livestock for selected 

counties.

[Mgal/d, million gallons per day]

County Rank1

Water 

required1

(Mgal/d)

Lancaster 1 8.771

Franklin 2 3.469

Lebanon 3 2.248

York 4 1.868

Berks 5 1.860

Bradford 6 1.710

Adams 7 1.660

Cumberland 8 1.287

Chester 9 1.231

Somerset 10 1.130

Perry 11 1.060

Snyder 12 1.055

1

Dr. Albert Jarrett, Pennsylvania State University, written commun., 2007.
Water-Analysis Screening Tool 7

regard to the effects or implications from the conservation 

releases, pass-by flows, or other mitigation efforts. Information on the actual quantity, timing, and operation of conservation releases would be collected as part of the detailed 

verification required before a watershed is designated as a 

CWPA. Because conservation releases and pass-by flows are 

an important component of the water balance for a particular 

watershed, efforts should be made to compile known releases 

into a statewide database.

Water-Analysis Screening Tool

The WAST is a watershed-based geospatial program 

developed by the USGS to evaluate potential influences of 

net withdrawals on aquatic-resource uses. The WAST is used 

as an initial screening for the state as part of the process of 

identifying CWPAs and can later be used to refine the inputs 

for a particular watershed to more closely replicate actual conditions. The WAST has two primary inputs: net withdrawals 

and the ISC, both defined in previous sections. Assuming the 

surface-water and ground-water resources are one resource, 

total withdrawals include both surface-water and ground-water 

withdrawals, and assuming unmitigated withdrawals for initial 

screening purposes, the potential influence of net withdrawals 

on aquatic-resource uses is defined as the SI. A basic waterbalance equation is used in the determination of SI, as shown 

in equation 1.

SI = ISC – NW , (1)

where:

SI is a screening indicator of the potential 

influence of net withdrawals on aquaticresource uses for a watershed, in million 

gallons per day;

ISC is the initial screening criteria for a watershed 

as determined by a percentage of the 7Q10, 

in million gallons per day; 

and

NW is the net withdrawal for a watershed as 

determined by total withdrawal minus total 

discharge, in million gallons per day.

SI is calculated at pour points across the state representing watersheds generally larger than 15 mi2

. To correlate and 

compare estimated SIs between different watersheds with differing drainage areas and natural flows, a dimensionless SIP is 

computed. SIP is determined using equation 2.

SIP = [(ISC – NW) / ISC] × 100 , (2)

where:

SIP is the screening indicator of the potential 

influence of net withdrawals on aquaticresource uses for a watershed, as a 

percentage;

ISC is the initial screening criteria for a watershed 

as determined by a percentage of the 7Q10, 

in million gallons per day; 

and

NW is the net withdrawal for a watershed as 

determined by total withdrawal minus total 

discharge, in million gallons per day.

Table 6. Trout-stream classifications and requirements1 for Pennsylvania streams.

[cm, centimeter; kg/ha, kilogram per hectare; —, does not apply]

Stream 

classification

Trout

species

Total biomass 

of species

Total biomass 

less than 15 cm

Species percentage of 

total trout biomass

A Wild brook 30 kg/ha or greater 0.1 kg/ha or greater 75% or greater

Wild brown 40 kg/ha or greater .1 kg/ha or greater 75% or greater

Mixed wild brook and 

brown

40 kg/ha or greater .1 kg/ha or greater less than 75% brook trout and 

less than 75% brown trout

Wild rainbow — 2.0 kg/ha or greater —

B Brook 20 kg/ha or greater and 

less than 30 kg/ha

— —

Brown or mixed brown 

and brook

20 kg/ha or greater and 

less than 40 kg/ha

— —

C All species 10 kg/ha or greater and 

less than 20 kg/ha

— —

D All species less than 10 kg/ha — —

1

 Russel Greene, Pennsylvania Fish and Boat Commission, written commun., 2008.
8 Development of the Water-Analysis Screening Tool for the Pennsylvania State Water Plan Update of 2008

The pour points are displayed in the WAST and colorcoded on the basis of the SIP as determined from equation 2. 

Green is used for watersheds where net withdrawals are less 

than the ISC, indicating the potential of adequate water to 

meet the demands of aquatic-resource uses. Yellow is used for 

watersheds where net withdrawals are greater than the ISC, 

indicating potential areas of conflicts with aquatic-resource 

uses. Some of these potential conflict areas may eventually 

become designated CWPAs. White is used for watersheds that 

can not conclusively be labeled as having a high or low potential for conflicts with aquatic-resource uses. 

Assumptions

At times of severe drought, it is assumed that the only 

flow in a stream is attributed to ground-water base flow, which 

is sustained by ground-water discharge. Gaining reaches in a 

stream are those in which ground-water discharge is supplementing the natural streamflow. Losing reaches in a stream are 

those in which streamflow is exiting the stream channel and 

entering the ground-water system. The ISC may need to be 

adjusted in areas of losing reaches because the 7Q10 as computed from regression equations assumes gaining reaches. 

A one-to-one relation between ground water and surface 

water is assumed; that is, if 1 gal is pumped from ground 

water, it is assumed to be equivalent to 1 gal removed from a 

stream. This assumption does not factor in ground-water storage, the time-response delay due to the distance a well is from 

a stream, or the loss due to ground-water evapotranspiration. 

The water-use data, based on 2003 data, are assumed 

to be comparative to water-use data recorded during other 

years. Because 2003 was a year with above-average precipitation and streamflow, the actual water use may change during 

drought conditions, particularly in the categories of industrial, 

commercial, and agricultural. The water-use factors used to 

estimate irrigation water use were based on a year with average precipitation.

Methodology used in the placement of water-use points 

using the centroid approach for estimated residential, commercial, and industrial use assumes a uniform distribution of 

population within the census blocks. Methodology used in the 

placement of water-use points using the centroid approach for 

estimated agricultural use assumes a uniform distribution of 

irrigated land within the row crops. In addition, livestock is 

assumed to be within areas of row crops.

Estimated water use for commercial, industrial, agricultural, and golf courses is assumed to be 100 percent consumptive, in which no water is returned to the system. Although 

that may be realistic for some water-use categories, such 

as irrigation where historically most of the water applied is 

evapotranspired, this assumption may not be realistic for the 

other categories. Estimated residential water use was assumed 

to have a 10-percent consumptive use on the basis of previous 

studies in Pennsylvania. Depending on the number of residential sand mounds, which return less water to the water system 

than septic systems because of evaporation, and the number of 

households with private wells that are connected to a public 

sewer system, the consumptive-use factor for estimated residential use within a particular watershed may be higher. Lack 

of comprehensive maps outlining the service areas for sewagetreatment plants hinders establishing the relation between 

public-water-supply service areas and sewage-treatment-plant 

service areas.

Limitations and Accuracy

Aquatic resources depend on water quantity and quality. 

Clean and abundant water is necessary for most users of water, 

from ecological uses to water purveyors. The WAST only 

identifies watersheds with areas of concern based on net withdrawals. There may be watersheds not identified by the WAST 

where there may be potential conflicts with aquatic resources 

because of the quality of the available water. Water quality can 

limit the types of uses of the available water. 

The WAST includes watersheds with drainage areas of 

generally about 15 mi2 to about 2,000 mi2. Watersheds outside 

of this range may have aquatic-resource concerns not captured 

by the WAST. Not all watersheds within this range of drainage areas are included in the WAST because of the automated 

processing used to generate the pour points. Watershed 

boundaries may have errors in the delineations because of 

problems with the underlying National Hydrography Dataset 

(NHD) or the digital elevation model. GIS processing involved 

in the WAST used the centerline flow from the NHD, which 

can result in skewed watershed delineations near major rivers. 

Incorrect watershed delineations could result in inaccuracies in 

the calculations of ISC, SI, and SIP.

Surface-water and ground-water resources and drainagebasin divides are not differentiated in the screening tool and, 

therefore, all relevant water use in a watershed may not be 

captured. In areas where there are probable discrepancies 

between the divides, such as areas with karst topography or 

coal-mining areas, the results of the WAST should be reviewed 

carefully. 

The registered water use was determined from 2003 registrations because that year was the most complete compared 

to previous years. However, this does not necessarily mean 

that the 2003 registrations capture all the water users in the 

state. Estimates were used to fill in these data gaps and build 

a comprehensive water-use database. Additional water users 

not captured as part of the registration process or estimation 

can only be identified at a local scale. The use of 100-percent 

consumptive use for estimated water use, with the exception of 

the residential category, may result in a lower SI than expected 

for a watershed because no water is returning to the system.

The WAST was developed to provide an initial screening 

of the potential influence of net withdrawals on aquatic-resource uses. From this initial screening, areas of the state can 

be identified that have potential conflicts between water-use 

demands and aquatic-resource needs and further work can be 
Summary 9

prioritized. Further investigation into the water use, ISC, and 

mitigation efforts would be needed before a watershed can be 

designated as a CWPA. The accuracy of the WAST depends 

on the accuracy of the input data, specifically the water-use 

information and the ISC. Data from each watershed should be 

carefully examined for accuracy. 

Summary

The WAST was developed by the USGS to provide 

assistance to PaDEP in the identification of critical waterplanning areas as required by the Water Resources Planning 

Act. The WAST compares water-use information to an ISC 

based on the 7Q10, resulting in a SI for potential influences of 

net withdrawals on aquatic-resource uses. The SIP is displayed 

in the WAST by a range of colors at pour points representing the outlets of watersheds generally larger than 15 square 

miles. Green is used for watersheds where net withdrawals are 

less than the ISC, indicating the potential of adequate water 

to meet the demands of aquatic-resource uses. Yellow is used 

for watersheds where net withdrawals are greater than the ISC, 

indicating potential areas of conflicts with aquatic-resource 

uses. Some of these potential conflict areas may eventually 

become designated CWPAs. White is used for watersheds that 

can not conclusively be labeled as having a high or low potential for conflicts with aquatic-resource uses.

A comprehensive water-use database that includes data 

from registration, estimation, DMRs, mining data, and other 

sources was developed as input into the WAST. The registered 

water-use data and DMRs were reported in actual days used 

rather than as an annual average. This allows for a more direct 

comparison between water use and the 7Q10. Estimated water 

use includes data from the following categories: residential, 

industrial, commercial, agricultural, and golf courses. Consumptive use is assumed to be 100 percent for all estimated 

water-use categories except residential, which uses a 10-percent consumptive-use factor. 

The WAST was developed to provide an initial screening of the potential influence of net withdrawals on aquaticresource uses. Users should familiarize themselves with the 

assumptions and limitations described in this report before 

assessing the results displayed in the WAST. The accuracy of 

the WAST depends on the accuracy of the input data, specifically the water-use information and the ISC. Data from each 

watershed should be carefully examined for accuracy. 

References Cited

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. 

Ludlow, R.A., and Gast, W.A., 2000, Estimated water withdrawals and use in Pennsylvania, 1995: U.S. Geological 

Survey Fact Sheet 174-99, 4 p.

Pennsylvania Department of Environmental Protection, 2006a, 

The Pennsylvania State Water Plan and Act 220 of 2002: 

3920-FS-DEP 3155, 2 p.

Pennsylvania Department of Environmental Protection, 2006b, 

Guidelines for identification of Critical Water Planning 

Areas: Document 392-2130-014, 17 p.

Pennsylvania State University, 2003, Pennsylvania land cover, 

2000: accessed September 12, 2007, at http://wiz.pasda.

psu.edu/uci/MetadataDisplay.aspx?entry=PASDA&file=pal

anduse2000.xml&dataset=464.

Solley, W.B., Pierce, R.R., and Perlman, H.A., 1998, Estimated use of water in the United States in 1995: U.S. 

Geological Survey Circular 1200, 71 p. 

Stuckey, M.H., 2006, Low-flow, base-flow, and mean-flow 

regression equations for Pennsylvania streams: U.S. Geological Survey Scientific Investigations Report 2006-5130, 

84 p.

Susquehanna River Basin Commission, 1998, Instream flow 

studies Pennsylvania and Maryland: Susquehanna River 

Basin Commission Publication 191, 309 p.

U.S. Census Bureau, 2000, United States Census 2000: 

accessed August 22, 2007, at http://www.census.gov/main/

www/cen2000.html. 

U.S. Department of Agriculture, 2004, 2002 Census of 

Agriculture Pennsylvania: National Agricultural Statistics 

Service, Agricultural Statistics Board.

U.S. Department of Agriculture, 2006, 2002 MidAtlantic 

Cropland Data Layer: National Agricultural Statistics Service, Agricultural Statistics Board.

U.S. Department of Commerce, U.S. Census Bureau, 2002, 

North American Industry Classification System – United 

States, 2002: Springfield, Va., 1419 p.