1. FOR/GEOG 5104 Predicting NPS Nutrient Pollution in the Occoquan Watershed Mark Dougherty PhD Candidate Civil & Environmental Engineering April 2, 2001

2. General Research Goals To develop a more accurate predictive model of the NPS contribution to stream nutrients within the Occoquan watershed. To enhance regional efforts to plan future waste treatment needs to respond to changing storm runoff quality. To demonstrate that land-use planning in the Occoquan basin should target (or at least not ignore) streamside management zones. To develop a predictive model of land use change for the Occoquan basin, based on projected population.

3. Where is the Occoquan Watershed?

4. Occoquan Reservoir Lake Manassas

5. Occoquan Watershed Source: FCWA HIGH GROWTH AREA: City of Fairfax Town of Vienna Loudon County Warrenton Reservoir Lake Jackson Lake Brittle Germantown Lake Lake Manassas Occoquan Reservoir

6. The Occoquan Reservoir Impounded in 1957 by Alexandria Water Company. Ownership transferred to Fairfax County Water Authority in 1967 (current owner). Reservoir Drainage Area: 1475 km 2 (570 mi 2 ). Encompasses all or part of six counties and cities. Original Storage: 37 mil m 3 (9.8 x 10 9 gallons). Dam height increased in 1982, and storage raised to 42.4 mil m 3 (11.2 x 10 9 gallons). Major component of water supply for over 1,000,000 northern Virginians.

7. Occoquan Reservoir

8. Landsat 7 land cover map Chesapeake Bay watershed Source: Mid-Atlantic Regional Earth Science Applications Center (RESAC), 1998 Occoquan Dam

9. Washington, D.C. Potomac Estuary

10. 1 km

12. Water Quality Problems in the Occoquan Reservoir, 1960s Frequent and intense algal blooms, particularly of the genus Cyanobacter, in mid-1960s. Frequent taste and odor episodes were experienced in water treatment. Treatment problems from algal mats in raw water. O 2 depletion and fish kills in Reservoir. Sulfide presence in deep water from Reservoir. Increased organic matter in the reservoir system. Active viruses detected in streams and reservoir.

13. Causes of Eutrophication in the Reservoir: Study by Metcalf & Eddy (1970) cited high nutrient concentrations from 11 POTW’s within the basin. Study warned that conditions will become progressively worse as population increases. In 1971, the SWCB adopted the Occoquan Policy. A Monitoring Subcommittee was created. Occoquan Watershed Monitoring Laboratory (OWML) was established to conduct ongoing sampling and analysis of waters within the basin.

14. 1 km Sampling stations

15. Water quality parameters measured at Occoquan Reservoir sampling stations, 1980 Source: Randall et al. (1980) C – continuously; W – weekly; R – runoff ; BiM - bimonthly

16. Daily Occoquan Basin Rainfall: 1951 - 1997 Source: OWML

17. 21 sub-basins of the Occoquan watershed

18. Bull Run sub-basin

19. Broad Run sub-basin

20. Occoquan Creek sub-basin

21. Total basin area = 1475 km 2 (570 mi 2 ). Historic land use in the Occoquan watershed (1977-1989), as percentage of watershed area. Randall and Grizzard (1995). Total basin area = 1475 km 2 (570 mi 2 ).

22. Wastewater Flows in the Occoquan Basin: 1972 - 1997 Source: OWML

23. UOSA Wastewater Treatment Process on-line July, 1978 Solids Separation: grit removal; primary; secondary Biological Treatment (nitrifying A/S w/denitrification capability) Chemical Precipitation (high lime phosphorus treatment and ancillary disinfection) Mixed Media Filtration Granular Activated Carbon Adsorption Chlorination and Dechlorination System-wide flow storage and final effluent reservoir STATE OF THE ART – ADVANCED TREATMENT POINT SOURCE NUTRIENT CONTROL

24. Load sources and pollutant retention/conversion in Occoquan Reservoir, 1983-1991. Source: Randall and Grizzard (1995). POINT SOURCE NUTRIENTS

25. Nonpoint source pollution control in the early 1980’s Mandated construction of wet and dry stormwater detention ponds for commercial and suburban areas. Swale drains rather than curb-and-gutter construction in residential subdivisions. Porous pavements and subsurface drains for commercial parking lots. Restrictions on cluster development regulations in Fairfax County. SWCB imposed sewer moratoriums in some areas.

26. Summary of the Occoquan Experience to Date The institution of AWT practices and NPS controls have ameliorated extremely poor water quality conditions of the 1960s and 1970s. The reservoir remains eutrophic but the enrichment rate is substantially lower. Continued care in management of point and non- point sources maintains acceptable source quality while allowing a variety of basin land uses and activities. Source: Godrej (2000)

27. Current Nitrogen Issues in the Occoquan Reservoir OWML & UOSA have monitoring ‘trigger points’ to initiate N removal at the wastewater treatment plant. (OWML monitors NO 3 - -N, and calls for N removal at plant if NO 3 - -N levels near 10 mg/L.) RESEARCH RESPONSE: More accurate prediction of nonpoint pollution loads into the Occoquan basin (as a result of changing land use or seasonal weather conditions) will enhance regional efforts to plan future treatment needs to respond to changing storm runoff quality.

28. Nitrogen, Phosphorus, and Sediment Loads as Functions of Basin Rainfall Source: OWML

29. Current Phosphorus Issues in the Occoquan Reservoir TP concentrations are generally lower in Bull Run (during base flow) than in Occoquan Creek. RESEARCH RESPONSE: Better determination of nonpoint phosphorus sources in the large Occoquan Creek sub-basin can be used to more effectively control entry of this limiting nutrient into the reservoir. (Use this opportunity to compare urban vs. non- urban potential for NPS nutrient export.)

30. Occoquan Creek sub-basin Bull Run sub-basin

31. Additional Research Objectives To develop a predictive model of land use change for the Occoquan basin, based on projected population, increased probability by adjacency, zoning restrictions, and site limitations. To demonstrate that land-use planning in the Occoquan basin should target (or at least not ignore) streamside management zones.

32. Example of forest buffering of agricultural land Source: RESAC

33. Example of building encroachment on stream buffer Source: RESAC

34. The End Questions?