Source Water Assessment Program Fact Sheet

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FAIRFAX WATER

SOURCE WATER ASSESSMENT

FACT SHEET AND FREQUENTLY ASKED QUESTIONS 

 

INTRODUCTION 

Fairfax Water (FW) has completed a Source Water Assessment on portions of the Occoquan and Potomac watersheds that provide drinking water to FW customers in FWs legacy (original) and City of Fairfax service areas. For information on the Source Water Assessment covering areas that provide drinking water to FW’s customers in the Falls Church and Arlington Special service areas, please click here.

The purpose of a Source Water Assessment is to collect available information on activities and potential sources of contamination in source water areas. These include land use, point source discharges, hazardous waste sites, and other types of facilities that may affect the quality of raw water at a water supply intake. Fairfax Water’s Source Water Assessment is intended to provide guidance for prioritizing water quality protection efforts and to support the implementation of future source water protection strategies.

The final report for FW’s Source Water Assessment can be accessed here. Note that security concerns have constrained the release of some information to the public. That information has been redacted from the report. This Fact Sheet and Frequently Asked Questions document is intended to provide a summary of the Assessment

Frequently Asked Questions:

What is a Source Water Assessment?

Who is responsible for conducting the Assessment?

What information was collected during the FW Source Water Assessment?

            Delineation of Assessment Areas

Land Use Coverage

Inventory of Potential Sources of Contamination

BMP Inventory

Windshield Survey

How was susceptibility determined? 

Maps:

Occoquan Source Water Assessment Area

Potomac Source Water Assessment Area 

Data Summary Tables:

Occoquan Watershed Land Use

Occoquan SWAP Area Land Use

Occoquan SWAP Area Potential Sources of Contamination

Occoquan Watershed Best Management Practices

Potomac SWAP Area Land Use                                                                                 

Potomac SWAP Area Potential Sources of Contamination

Potomac SWAP Area Best Management Practices
 

WHAT IS A SOURCE WATER ASSESSMENT? 

The Federal Safe Drinking Water Act Amendments of 1996 require each state to develop a Source Water Assessment Program that: 

  • delineates the boundaries of the assessment areas from which one or more public water systems receive their drinking water supply, using all reliable and reasonably available hydrogeologic information deemed necessary to adequately determine such areas; and
  • identifies, for contaminants which are regulated and for which monitoring is required, (or any unregulated contaminants which the State has determined to present a threat to public health), to the extent practical, the origins within each delineated area of such contaminants to determine the susceptibility of the public water systems to such contaminants.

A Source Water Assessment includes delineation of the contributing watershed area upstream of a water supply intake, identification of potential sources of contamination, and determination of the susceptibility of the intake to contamination from those sources. 

WHO IS RESPONSIBLE FOR CONDUCTING THE ASSESSMENT? 

The Virginia Department of Health (VDH) is responsible for conducting Source Water Assessments in Virginia.  Although VDH is completing the majority of Assessments in the state, funds have been made available to more complex or larger systems to conduct their own Assessments.  As a result, FW applied for and received a grant to conduct the Assessment, and has completed the SWAP on behalf of VDH. 

FW conducted a Source Water Assessment of its Occoquan Reservoir and Potomac River intakes in accordance with Federal and State requirements, and collected some additional site-specific information with VDH approval. 

The Authority also owns several wells, which account for less than 1 percent of their water production.  VDH has conducted the Assessments for these wells. 

WHAT INFORMATION WAS COLLECTED DURING THE FW SOURCE WATER ASSESSMENT? 

The FW Source Water Assessment includes the following: 

·        delineation of  source water assessment areas for the FW Occoquan Reservoir and the FW Potomac River

·        land use coverage for the Source Water Assessment Areas and for the Occoquan Watershed

·        an inventory of potential sources of contamination

·        an inventory of Best Management Practices

·        a field survey on potential sources of contamination within a 5-mile radius upstream of each intake 

Delineation of Assessment Areas 

The assessment was conducted within defined portions of the watersheds above each intake.  The conditions and activities in these areas significantly impact water quality of the source water collected at the intake, before it is treated and distributed as drinking water. Assessment areas were identified based on a combination of operational experience and VDH guidance.  

The areas covered above each intake are: 

·        Occoquan Reservoir.    Map 1 shows the area covered for the Occoquan Reservoir intake.  This includes the 65 square mile area downstream of Lake Jackson and the free-flowing portion of Bull Run which is immediately adjacent to and drains directly into the reservoir. 

·        Potomac River.   Map 2 shows the area covered for the Potomac River intake.  This includes a 107 square mile area upstream of the intake defined by the Broad Run and Sugarland Run tributaries to the Potomac River.
 

Land Use Coverage 

Detailed land use coverage, based on satellite photos, was developed for the SWAP areas.  Land use in this area was categorized according to the following land use classes: 

·        Agricultural

·        Barren/Transitional

·        Forest

·        Grassland

·        Commercial

·        Institutional

·        Office

·        Low, Medium, or High Density Residential

·        Highway/Transportation

·        Urban/Industrial/Central Business District 

A less detailed land use coverage was developed for the entire Occoquan Basin, and included agriculture, barren/transitional, forest, grassland, water, residential, and urban/industrial categories. 

Inventory of Potential Sources of Contamination 

Within the SWAP areas, an inventory of Potential Sources of Contamination (PSCs) was conducted.  The inventory of PSCs incorporated available Federal and State permit data and data available from local sources.  This includes information on wastewater discharges, hazardous materials sites, superfund sites, and other industrial and agricultural sites where chemical or biological materials are transported, used, stored or disposed. 

VDH provided data on the types of PSCs listed in Table 1.  

Potential Sources of Contamination

Superfund sites

NPDES (National Pollutant Discharge Elimination System) waste dischargers and no-discharge NPDES permitted facilities

Open solid waste disposal facilities

RCRA (Resource Conservation and Recovery Act) sites

Hazardous waste sites

Tire piles

Industry sites

Petroleum tank farms

Golf courses

Hospitals

Highways

Rail lines

Confined animal feeding operations

Military bases

Commercial and general aviation airports

Marinas

Table 1.  Data provided by the Virginia Department of Health. 

VDH also provided information on industrial facilities derived from Harris InfoSource, a commercially available database on U.S. manufacturing firms. 

In addition, local regulatory and commercial data base information was incorporated into the SWAP GIS/database.  This information included: 

·        Petroleum pipelines

·        Sanitary sewer lines

·        Sewer pumping stations

·        Boat Ramps 

BMP Inventory 

Available information on Best Management Practices in the Fairfax and Prince William County portions of the Occoquan Watershed and Loudoun County upstream of the Potomac intake was collected.  Authority staff worked with local stormwater management agencies to collect available information on urban BMPs, including wet pond and dry pond stormwater retention/detention ponds, infiltration facilities, underground storage facilities, trenches, filter strips/grass swales/sheet flow, non-structural facilities, bioretention facilities, and oil/grease collection inlets.  Available information on agricultural BMPs was also provided by the state Department of Conservation and Recreation.  

Windshield Survey 

A Windshield Survey was conducted within a 5-mile radius upstream of each intake.  During the survey, field staff identified land use activities and potential sources of contamination visible from publicly accessible areas.  The list of activities that may potentially cause contamination provided in VDH’s Source Water Assessment Plan  Table 1, Appendix F (available at http://www.vdh.state.va.us/ddw/index.htm), was used as a guide to identify activities.  The activities identified may or may not be associated with a permitting program or included in a State or Federal database.  Facilities of interest located by the windshield survey included above-ground storage tanks, car washes, dry cleaners, gas station/service centers, golf courses, marinas, parking lots, active pasture (grazing), photo processors/printers, salt storage sites, and stormwater ponds. 

HOW WAS SUSCEPTIBILITY DETERMINED? 

Virginia Department of Health Approach 

The VDH Guidance on conducting a Source Water Assessment categorizes any surface water intake with upstream potential sources of contamination as having a “high” susceptibility.  Based on this approach, the Authority’s intakes are considered to have a “high” susceptibility, as do the majority of surface water intakes in the Virginia Assessment. 

Additional FW Analysis 

FW and its consultant conducted additional analyses to provide information on the susceptibility of the Authority’s intakes to specific contamination sources.   

First, each of the industrial sites was assigned a contamination “risk code”, based on the Standard Industrial Code for that facility.  The risk codes are low, low-medium, medium, medium-high, and high.  Only low, low-medium and medium risk facilities were identified in the SWAP areas for the Authority intakes.  

Second, the distance from each contaminant site to the Authority’s intake was determined.  Both the overland flow distance and instream travel distance was determined for each PSC.  The PSCs within each category were ranked according to susceptibility based on the combined overland flow distance and stream distance.   For the industrial sites, the risk code was also taken into consideration for ranking.
 

MAPS 

            Maps 1 and 2 show the SWAP area delineated for the Occoquan Reservoir and Potomac intake, respectively.

Map 1.  SWAP area for Occoquan Reservoir.

 

Map 2.  SWAP area delineated for Potomac intake.

 

DATA SUMMARY TABLES 

            Tables 1 through 7 summarize the results of the SWAP.

 

Land Use

Acres

Percent

Agriculture

94,754

25

Barren/Transitional

350

0

Forest

160,288

42

Grassland

41,892

11

Water

3,910

1

Residential

51,648

14

Urban/Industrial

25,900

7

Total

378,741

100

Table 1.  Occoquan Watershed Land Use Summary.

 

 

Land Use

Area (acres)

Percentage of Total Area in this Use

Percent Impervious for this Use

Agricultural

1,120

3%

2%

Barren/

Transitional

342

1%

5%

Commercial

285

1%

52%

Forest

14,387

35%

0%

Grassland

556

1%

3%

Institutional

435

1%

34%

Office

53

0%

32%

Residential HDR

891

2%

29%

Residential MDR

4,007

10%

17%

Residential LDR

16,892

41%

4%

Highway (Primary)

457

1%

64%

Urban/

Industrial

45

0%

42%

Water

1,545

4%

100%

Total Area

41,015

100%

10%

Table 2.  Occoquan SWAP Area Land Use Summary.


 

 

Potential Sources of Contamination                                                  

Number of facilities

Superfund sites

1 upstream of SWAP boundary

NPDES (National Pollutant Discharge Elimination System) Permitted Facilities

1

Sanitary Sewers:

12” or larger, within 500 ft of stream

Pumping stations, within 500 ft of stream

 

14 miles

5

Open solid waste disposal facilities                                                                   

0

RCRA (Resource Conservation and Recovery Act) sites

0

Hazardous waste sites

0

Tire piles

1 at upstream edge of watershed boundary

Industry sites:

Low-medium risk                                                                                                  

Medium risk                                                                                                         

 

 

8

2 Additional sites located outside SWAP area in vicinity of Manassas

Petroleum Facilities:

Tank farms

Petroleum pipelines                                                                                    

 

0

6 miles

Golf courses                                                                                                        

1 Additional sites located outside SWAP area

Hospitals                                                                                                              

0  1 hospital outside of SWAP area but within watershed

Highway stream or tributary crossings                                                            

9

Rail lines

Just upstream of SWAP area boundary

Confined animal feeding operations                                                                   

0

Military bases

0 1 outside of SWAP area

Commercial and general aviation airports                                                            

0 Dulles within watershed, upstream of SWAP area

Marinas and boat ramps                                                                                       

3

Table 3.  Occoquan SWAP Area Potential Sources of Contamination.


 

County

Number of facilities

Prince William

406

Fairfax

 209

Loudoun

5

Total

620

Table 4.  Urban Stormwater Best Management Practices

located within the Occoquan Watershed

(Note:  Fauquier County was not inventoried for urban BMPs). 

 

Land Use

Area (acres)

Percentage of Total Area in this Land Use

Percent Impervious for this Use

Agricultural

9,622

14%

1%

Barren/

Transitional

1,389

2%

9%

Commercial

1,412

2%

65%

Forest

21,440

31%

2%

Grassland

3,320

5%

4%

Institutional

2,127

3%

28%

Office

2,983

4%

52%

Residential HDR

3,718

5%

49%

Residential MDR

13,298

19%

31%

Residential LDR

3,470

5%

8%

Highway (Primary)

3,535

5%

56%

Urban/

Industrial

1,642

2%

43%

Water

455

1%

100%

Total Area

68,411

100%

19%

Table 5.  Potomac SWAP Area Land Use Summary.
 

 

Potential Sources of Contamination                                                  

Number of facilities

Superfund sites

0

NPDES (National Pollutant Discharge Elimination System) Permitted Facilities

5

Sanitary Sewers:

12” or larger, within 500 ft of stream

Pumping stations, within 500 ft of stream

 

82

0

Open solid waste disposal facilities                                                                   

1 in VDH database, but existence could not be verified

RCRA (Resource Conservation and Recovery Act) sites

0

Hazardous waste sites

0

Tire piles

0

Industry sites:

Low

Low-medium risk

Medium risk

 

9

117

41

Petroleum Facilities:

Tank farms

Petroleum pipelines                                                                                    

 

2

15

Golf courses                                                                                                        

3

Hospitals                                                                                                              

1

Highway stream or tributary crossings                                                            

48

Rail lines

Upstream of SWAP area boundary

Confined animal feeding operations                                                                   

0

Military bases

0

Commercial and general aviation airports                                                           

1

Marinas and boat ramps                                                                                       

1

Table 6.  Potomac SWAP Area Potential Sources of Contamination.

 

 

County

Total

Prince William

0

Fairfax

92

Loudoun

136

Total

228

Table 7.  Urban Stormwater Best Management Practices

located within Potomac SWAP Area.

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