Source Water Assessment Program Fact Sheet
SOURCE WATER ASSESSMENT
FACT SHEET AND FREQUENTLY ASKED QUESTIONS
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:
Data Summary Tables:
The Federal Safe Drinking Water Act Amendments of 1996 require each state to develop a Source Water Assessment Program that:
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.
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.
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
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
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:
· Low, Medium, or High Density Residential
· 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.
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.
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
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.
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.
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 1 and 2 show the SWAP area delineated for the Occoquan Reservoir and Potomac intake, respectively.
Map 2. SWAP area delineated for Potomac intake.
Tables 1 through 7 summarize the results of the SWAP.
Table 1. Occoquan Watershed Land Use Summary.
Table 2. Occoquan SWAP Area Land Use Summary.
Table 3. Occoquan SWAP Area Potential Sources of Contamination.
Table 4. Urban Stormwater Best Management Practices
located within the Occoquan Watershed
(Note: Fauquier County was not inventoried for urban BMPs).
Potomac SWAP Area Land Use Summary.
Table 6. Potomac SWAP Area Potential Sources of Contamination.
Table 7. Urban Stormwater Best Management Practices
located within Potomac SWAP Area.
Fairfax County Water Authority
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