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Monitoring and Modeling Support of Management Activities in the Occoquan Watershed Virginia Section AWWA Water Resources & Environment Committee Sprin...
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Monitoring and Modeling Support of Management Activities in the Occoquan Watershed Virginia Section AWWA Water Resources & Environment Committee Spring Seminar Thomas J. Grizzard, Ph.D, P.E. Occoquan Laboratory Director Professor of Environmental Engineering Virginia Tech Manassas VA Manassas, 12 April, 2011

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Outline of Presentation • History of the watershed and reservoir • Water quality quality, wastewater disposal disposal, and water supply issues • The Occoquan Policy • Water reclamation and reuse • Land use decisions • Monitoring support for management decisions • Modeling support to help future decisionmaking

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Urbanization Trends Increase Pressure on Water Supply • In 2007, for the first time, half the earth’s population resided in cities • Over half the US population resides in the coastal margin, which is 20%of the continental land mass • Expect a 40% increase in water consumption by 2025. • Today 1.2 billion people do not have adequate access to drinking water and 2 2.4 4 billion people not connected to waste water systems. 2025, one third of the world‘s world s population will be • By 2025 affected by water shortages and by 2050, 60 percent.

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Importance of Water and Population Distribution • Per capita rainfall statistic: – Annual rainfall multiplied by drainage area and divided by population  Per Capita Rainfall= Rainfall

(Annual Rainfall) x (Land Area) x CF Population

– m3/capita/yr gallons/capita/yr. – World variability Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Per Capita Rainfall Comparisons

C Country t or Region R i

Annual R i f ll Rainfall

Land A Area

Pop.

Per Capita R i f ll Rainfall

(inches)

(sq. mi.)

(millions)

(10 Gal/cap/yr)

Saudi Arabia Arizona U S Average U.S. Potomac Watershed Singapore

Per Capita R i f ll Rainfall

3

3

3

(10 m /cap/yr)

40 4.0

900 004 900,004

21 1 21.1

2 959 2,959

11 20 11.20

13.1

113,642

5.1

5,043

19.09

7 789 7,789

29 48 29.48

-

-

-

~ 40.0

14,670

5.0

2,039

7.72

86 6 86.6

267

44 4.4

91

0 35 0.35

Note: Singapore calculation does not include Johor catchments

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Management Issues in the Occoquan Watershed • Multi-jurisdictional watershed – 4 counties and 2 cities – One jurisdiction doesn’t rely on the water source

• Indirect p potable reuse – Water reclamation agency – Water purveyor

• Availability of high quality of reclaimed water has changed the view of wastewater – More M off a resource than th a problem bl – Reduces a barrier to additional watershed development • More urban runoff problems Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

The Occoquan Reservoir: History and Statistics • Occoquan High Dam constructed in 1957 • Fairfax Water operates water treatment works on both Potomac River and Occoquan Reservoir q mi. watershed lies in four counties and two cities • 570 sq. • 8.2 BG (US) usable storage measured in year 2000 • Currently a major component of water supply system serving nearly 2,000,000 Northern Virginians • Watershed also supports a variety of human activity – Population of ~400,000 – Agricultural, residential, commercial, industrial activity Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Reservoir Statistics • • • • • • • • •

Length: Dam Distance from AWT Discharge Maximum Width: Surface Area: Maximum Depth: Mean Depth: Storage Capacity (2000): Average Annual Natural Inflow: Average g residence time:

14 miles 18.6 miles 900 feet 1,540 acres 65 feet 14 feet 8 3 BG (US) 8.3 550 cfs 3 weeks

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Northern Virginia satellite image showing location of Occoquan Reservoir Reservoir, 1994

Potomac River Goose Creek Reservoir

Dulles Airport

Lake Barcroft Burke u e Lake a e Lake Manassas

O Occoquan Reservoir R i

Potomac Estuary

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Reservoir, 1994

Source: MS Terraserver

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

The Occoquan Watershed in the Post-WWII Years • Start of urban growth of DC area during World War II • In post post-war war decades, pace of development continued in Northern Virginia suburbs • Watershed water quality impacted by existing agricultural runoff and new urban runoff sources • Sanitary wastewaters treated with small plants discharging into reservoir tributaries – By 1970, 11 small secondary treatment plants in service – Flows totaled 2.9 mgd (US) Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Resulting Reservoir Water Quality Problems • • • • • • • •

Summer blooms of Blue-Green algae (cyanobacter) Frequent taste & odor episodes in water treatment Treatment problems from algal mats in raw water Oxygen loss and and fish kills in Reservoir Sulfide presence in deep water from Reservoir Increased organic matter in the reservoir system Viruses detected in streams and reservoir During u g low o flow, o , poo poorly y ttreated eated wastewater aste ate was as a major part of inflow

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Algal Bloom at Jacob’s Rock on 06/24/69

Source: Metcalf & Eddy

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Algal Bloom in Occoquan Reservoir: Summer, 1973

Source: OWML

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Algal Bloom in Occoquan Reservoir: Summer, 1973

Source: OWML

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Algal Bloom in Occoquan Reservoir: Summer, 1973 Source: OWML

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Responses to Water Quality Deterioration • Sewer connection moratorium imposed by the Virginia ( ) State Water Control Board (VaSWCB) • In 1968-69, Metcalf & Eddy conducted comprehensive study of the Occoquan Watershed and Reservoir – Point and nonpoint source pollution contributed to water quality degradation – Principal sources were found to be discharges from 11 secondary sewage treatment plants in the watershed – Study provided three principal recommendations to protect reservoir and insure future availability of adequate potable water supply Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Metcalf & Eddy 1969 Study Recommendations • Option 1 – Export all wastewater for treatment outside the watershed – Rejected because of loss of reclaimed water outside watershed

• Option 2 – – – –

Provide highest treatment technically achievable P Pump reclaimed l i d water t di directly tl tto WTP ffor potable t bl reuse Limit watershed population to those who use reclaimed water Rejected because of “direct” reuse component

• Option 3 – – – –

Provide highest treatment technically achievable Discharge reclaimed water to the Occoquan Reservoir Li it B Limit Basin i P Population l ti tto 100 100,000 000 With exception of population limit, this solution was adopted

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Why was a Reuse Solution Chosen? • At the time (1970), conventional practice would have been to: – Treat the wastewater with standard (secondary) technology – Export E port the treated wastewater aste ater from the water ater ssupply ppl watershed

• Noman Cole (chairman of the SWCB) concluded (over 40 years ago) that Northern Virginia would eventually t ll need d th the water, t and dh he advocated d t d adoption of reuse technology Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

The Adopted Solution: The Occoquan Policy • Adopted by VaSWCB in 1971; revised in 1981, 1991 • Required state-of-the-art water reclamation plant with: – Standby treatment units – Emergency holding basins – Three independent electrical power sources

• Independent water quality monitoring program • Limit of 3, but “preferably no more than 2” WRF’s in watershed Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Current UOSA Reclaimed Water Discharge Limits

• Reclaimed water discharge requirements: – COD – TN* – MBAS

10 mg/L 1 mg/L 0 1 mg/L 0.1

- TSS (current) - TP - Turbidity

1 mg/L 0.1 mg/L 0 5 NTU 0.5

*Notes: 1. TN standard currently interpreted as total unoxidized N (TKN) 2. Process operated to maintain < 5 mg/L NO3-N at raw water intake 3 Future treatment requirements set by Chesapeake Bay restoration 3. may require N removal

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Upper Occoquan Service Authority The Millard H. Robbins, Jr. Water Reclamation Plant (An abbreviated tour)

UOSA Aerial View, 2003

Storage Reservoir

Discharge

Ballast Ponds

ERP ERP

Chemical Treatment

Chemical Treatment

Filtration & GAC

Secondary Settling

Primary

Secondary Settling Biological Process

Primary

The 10 Second UOSA Tour

Indirect Potable Reuse in Northern Virginia, USA Fairfax Water Potomac River water treatment/distribution Potomac River

Potable water Wastewater W t t Reclaimed water Dulles Airport

Upper Occoquan Service Fairfax County AuthorityGeneration/collection Collection/Reclamation of Wastewater; Discharge to of wastewater Occoquan Reservoir

Lake Manassas

Manassas/ Manassas Park

Lake Manassas water treatment/distribution

Prince William County

Fairfax Occoquan Water an Occoq Occoquan Reservoir Reservoir Occoquan Watershed Laboratory treatment/distribution

The Via Department of Civil and Environmental Engineering

Daily Disch D harge, mgd d

Reclaimed Water Discharges to Occoquan Reservoir

35 30 25 20 15 10 5 0

T t l Total UOSA Other POTW's 72 75 78 81 84 87 90 93 96 99 02 05 08 Year

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

25

0

20

30

15

60

10

90

5

120

0

An nnual Rainfa all, inches

UOSA Annu ual Percentag ge of Total Re eservoir Inflo ow

Occoquan Watershed Rainfall & Reclaimed Water Percentages

150 78

80

82

84

86

88

90

92

94

96

98

00

02

04

06

08

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

IPR Increased Occoquan Reservoir Safe Yield • Safe Yield from Natural Streamflow:

~65 mgd

• Estimated future safe yields: 2010 2020 2030 2040 2050

79 mgd 86 mgd d 95 mgd 103 mgd g 110 mgd

Note: Flows given in million US gal/day Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Watershed Monitoring Program • Mandated by Virginia State Water Control Board Occoquan Policy in 1971 • Operated p by y Virginia g Tech Department p of Civil and Environmental Engineering • Provide unbiased water quality information to decisionmakers with the goal of protecting the reservoir for water supply and other beneficial uses

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Monitoring System Components • 39 year period of record • 14 titipping i b bucket k t rain i gages di distributed t ib t d iin watershed t h d • 1 full meteorological station near basin centroid • 8 automated gaging/water quality monitoring stations – Web-enabled water quality data access downstream of UOSA

• 7 key reservoir monitoring stations

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Stream Monitoring and Rain Gauging g g Network

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Monitoring Station: Bull Run at Route 28

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Flow Gauging Equipment at Bull Run

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Automated Sampling Equipment

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Web-based Access to Hyrdology and Water Quality

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Annual Stream Loadings as a Function of Rainfall (1983 – 2009) 1.0E+09

Total Load, lb./yrr.

1.0E+08

Sediment

1.0E+07

2009

Nitrogen Phosphorus

1.0E+06

1 0E+05 1.0E+05

1.0E+04 1.0E 04 20

25

30

35

40

45

50

55

60

Occoquan Watershed Laboratory Theissen Average Annual Rain, inches

The Via Department of Civil and Environmental Engineering

Occoquan Reservoir Showing OWML Monitoring Stations

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Trends in Reservoir Phosphorus Concentrations RE02: Occoquan Dam RE15: Ryan's Dam RE30 B RE30: Bullll R Run M Marina i RE35: Occoquan Creek at Ravenwood Bridge

Total Phossphorus, mg/L

1 RE35 0.8 RE30

0.6 04 0.4

RE15

0.2

RE02

0 73 75 77 79 81 83 85 87 89 91 93 95 97 99 01 03 05 07 09

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Local Government Land Use Decisions • 1982 - Fairfax County downzoning – Protection of the drinking g water supply pp y – Supported by water quality data and modeling – Several court challenges

• 1990’s – Prince William County Rural Crescent – Low density uses in western county

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Fairfax County DownZoning in the Occoquan Watershed • 1982 action ti reduced d d density of 41,000 acres to 1 du/5 acres • Created 63,000 acre water supply overlay where strict stormwater management required • Decision relied heavilyy on water quality data and Occoquan Model simulations Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Prince William County Rural Crescent • Designated g rural area • Evolved in Comprehensive Plans from 1974 - 1998 • 80,000 acres • Low development Density – Default is 1 du/10 acres

Modeling

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

The Occoquan Model • Originally developed at NVRC to support land use decision-making in Fairfax County – HSPF Watershed Model – Simple completely-mixed reservoir model

• Transition to complexly-linked watershed-reservoir model – – – –

Virginia Vi i i T Tech h CEE D Department t t 6 HSPF (Hydrologic Simulation Procedure – Fortran) 2 CE-QUAL-W2 for reservoir simulation Models are linked and calibrated together to observed hydrology and water quality in watershed and reservoir Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Calibration and Verification

• HSPF

• CE CE-QUAL-W2 QUAL W2

– Flow Balance – Sediment Loads – Water Quality

– Surface Elevation – Heat Balance – Water Quality

• Orthophosphate Phosphorus • Ammonium Nitrogen • Nitrate Nitrogen • Organic Matter (BOD)

• DO • Orthophosphate O th h h t Phosphorus • Ammonium Nitrogen • Nitrate Nitrogen • Algae

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering

Model Applications • Evaluation of land use change – Modeling future/alternative zoning scenarios – Modeling proposed large projects (developments)

• Ch Changes in i discharge di h ((quantity tit and d quality) lit ) ffrom permitted facilities – Management of nitrate discharge from UOSA

• Changes in climate and meteorological patterns • Development of non-expert stakeholder interface

Occoquan Watershed Laboratory The Via Department of Civil and Environmental Engineering