USGS Water-Year Summary for Site 01646000

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	Available Parameters
	00010 Temperature, water(Max.,Min.,Mean,Med.)
	00060 Discharge(Mean)
	00095 Specific cond at 25C(Max.,Min.,Mean,Med.)
	00300 Dissolved oxygen(Max.,Min.,Mean,Med.)
	00400 pH(Max.,Min.,Med.)
	63680 Turbidity, Form Neph(Mean,Med.,Max.,Min.)
	63680 Turbidity, Form Neph(Min.,Med.,Max.) [(2)]
	99133 NO3+NO2,water,insitu(Max.,Min.,Med.)

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Water year 2023: 2022-10-01 to 2023-09-30

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USGS Water-Year Summary 2023

01646000 DIFFICULT RUN NEAR GREAT FALLS, VA

LOCATION - Lat 38°58'33", long 77°14'46" referenced to North American Datum of 1927, Fairfax County, VA, Hydrologic Unit 02070008, on right bank 250 ft downstream from bridge on State Highway 193, 300 ft downstream from Rocky Run, 0.7 mi upstream from mouth, and 1.5 mi southeast of Great Falls.

DRAINAGE AREA - 57.8 mi².

REVISIONS HISTORY - WSP 951: 1936(M), 1937-38, 1939-40(M). OFR 2006-1308: Drainage area.

SURFACE-WATER RECORDS

PERIOD OF RECORD - April 1935 to current year. Monthly discharge only October 1934 to March 1935, published in WSP 1302.

GAGE - Water-stage recorder. Datum of gage is 150.85 ft NAVD of 1988.

WATER-QUALITY RECORDS

PERIOD OF RECORD - October 2006 to September 2008, July 2011 to current year.

PERIOD OF DAILY RECORD -
DISSOLVED OXYGEN: October 2012 to current year.
NITRATE: October 2012 to current year.
pH: October 2012 to current year.
SPECIFIC CONDUCTANCE: October 2006 to September 2008, October 2012 to current year.
TURBIDITY: October 2012 to current year.
WATER TEMPERATURE: October 2006 to September 2008, October 2012 to current year.

COOPERATION - Daily records October 2007 to April 2009 were provided by the Virginia Department of Environmental Quality - Water Division.

INSTRUMENTATION - Water-quality and nitrate monitors. Electronic data logger with 15-minute recording interval. Specific conductance and water temperature monitor October 2006 to September 2008.

EXTREMES FOR PERIOD OF DAILY RECORD -
DISSOLVED OXYGEN: Maximum: 15.2 mg/L, Feb. 16, 2015, but may have been higher during periods of missing record; minimum: 1.1 mg/L, Apr. 26, 2014, but may have been lower during periods of missing record.
NITRATE: Maximum: 2.68 mg/L as N, Feb. 14, 2016, but may have been higher during periods of missing record; minimum: 0.12 mg/L as N, May 16, 2014, but may have been lower during periods of missing record.
pH: Maximum: 8.6 standard units, June 23, 2013, but may have been higher during periods of missing record; minimum: 5.5 standard units, Feb. 3, 4, 2015, but may have been lower during periods of missing record.
SPECIFIC CONDUCTANCE: Maximum: 8710 microsiemens/cm, Feb. 16, 2016, but may have been higher during periods of missing record; minimum: 42 microsiemens/cm, Sept. 6, 2008, but may have been lower during periods of missing record.
TURBIDITY: Maximum: 1,380 NTU, June 24, 2015, but may have been higher during periods of missing record; minimum, 0.0 NTU on several days.
WATER TEMPERATURE: Maximum: 28.8°C, Aug. 13, 2016, but may have been higher during periods of missing record; minimum, -0.2°C, on several days.