Linda debrewer shenandoah valley water conference october 28 2008
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Linda Debrewer Shenandoah Valley Water Conference October 28, 2008. Trends in Water Quality Great Valley Carbonate Region. Water-Quality Trend Studies NAWQA Program.

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Linda Debrewer Shenandoah Valley Water Conference October 28, 2008

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Linda debrewer shenandoah valley water conference october 28 2008

Linda Debrewer

Shenandoah Valley Water Conference

October 28, 2008

Trends in Water QualityGreat Valley Carbonate Region


Water quality trend studies nawqa program

Water-Quality Trend StudiesNAWQA Program

Long-term goal: to describe changes in the quality of the Nation’s water resources over time and to provide scientific understanding of the primary natural and human factors contributing to these changes

Decadal sampling in networks representing major aquifers and river basins and different land-use settings

Biennial sampling at a subset of wells

Local-scale flow system studies


Factors affecting trends in ground water quality

Factors Affecting Trends in Ground-Water Quality

  • Hydrogeology

  • Geochemical environment

  • Land use and land-use change

  • Change in chemical applications

  • Climate


Great valley carbonate region hydrogeologic setting

Great Valley Carbonate Region Hydrogeologic Setting

Carbonate bedrock

Well-drained soils

Ground water flows through regolith and along fractures, bedding planes, and solution channels (well-mixed)

Ground water is susceptible to contamination


Linda debrewer shenandoah valley water conference october 28 2008

Great Valley Carbonate Region

  • Median nitrate: 5.1 mg/L

  • National median: 3.4 mg/L in agricultural settings

  • Potomac River Basin median: 1.8 mg/L

  • Oxygen-rich system throughout


Great valley carbonate region 1993 to 2002

Great Valley Carbonate Region1993 to 2002

  • No significant change in nitrate

  • Reflects relatively steady nitrogen fertilizer use over past several decades

  • Also may reflect differences in climate during sampling periods


Linda debrewer shenandoah valley water conference october 28 2008

Great Valley Carbonate Region1993 to 2002


Linda debrewer shenandoah valley water conference october 28 2008

Great Valley Carbonate Region1993 to 2002

  • Wide range of ages and large overlap in recharge dates relative to the 9 year sampling interval

  • Age is mixture of pre-1940s and recently recharged. Young fraction ranges from 16% to 96% (median 68%). Typically less than 30 years.

  • Drought conditions during later sampling period: larger influence of older water in 2002 sampling


Linda debrewer shenandoah valley water conference october 28 2008

Great Valley Carbonate Region1993 to 2002

  • Pesticides detected in 89% of wells (frequencies among the highest in the Nation)

  • Mixtures commonly detected

  • Decreasing atrazine, deethylatrazine, and prometon concentrations reflect changes in use despite higher percentage of older water sampled in 2002

  • Limited use data shows decrease in atrazine and prometon between sampling periods


Linda debrewer shenandoah valley water conference october 28 2008

Great Valley Carbonate Region1993 to 2002

  • Detecting trends in ground water is complicated by long open boreholes which facilitate ground-water mixing

  • Trends may be more apparent over multiple decades or with controlled tracking of change along specific flow paths


Linda debrewer shenandoah valley water conference october 28 2008

Muddy Creek at Mt. Clinton, Virginia

Watershed is 68% agriculture, with no apparent point sources

Poultry, cattle, corn, soybeans

Routine and storm samples: 1993 to 1997

Fixed interval samples: 1997 to 2005 (long term trends approach)

Currently on 4 year cycle: 30 samples ( monthly and more frequently during growing season)


Muddy creek at mt clinton virginia

Muddy Creek at Mt. Clinton, Virginia

Nitrate

  • Detected throughout the year

  • Little seasonal pattern

  • Exceeds ecoregion criteria of 0.01 mg/L


Linda debrewer shenandoah valley water conference october 28 2008

Muddy Creek at Mt. Clinton, Virginia

Phosphorus highest during base flow, April-Sept; exceeds criteria of 0.01 mg/L.


Linda debrewer shenandoah valley water conference october 28 2008

Pesticides

A variety of pesticides detected

Present in surface water year-round

Concentration generally increases with flow during application period and diluted by runoff during remainder of year

Pattern typical of most NAWQA sampling

Issues:

fate of compounds (parent and degradate showing up in streams)

transport (in streams from ground water at low flow and from runoff)

persistence (all year, not just during application)

Muddy Creek at Mt. Clinton, Virginia


Linda debrewer shenandoah valley water conference october 28 2008

Atrazine

Detected in every sample to date

Higher concentration during application period

Muddy Creek at Mt. Clinton, Virginia


Linda debrewer shenandoah valley water conference october 28 2008

Deethylatrazine

Detected in every sample to date

Concentrations increasing over time

Pesticide degradates are transported primarily by ground water

Muddy Creek at Mt. Clinton, Virginia


Linda debrewer shenandoah valley water conference october 28 2008

Metolachlor

Detected in most samples to date

Higher concentration during application period

Muddy Creek at Mt. Clinton, Virginia


Future nawqa study of gw trends

Future NAWQA Study of GW Trends

  • Status and Trends

    • Continue study of temporal changes (trends) in water quality in response to changing land use, chemical use, or agricultural-management practices.

  • Understanding

    • Continue study to identify natural and human-related factors that govern the degree, direction, periodicity and amplitude of changes observed in water quality.

  • NEW: Simulation and Forecasting

    • Reproduce observed water-quality measurements, and forecast future conditions based on anticipated changes in land or chemical use.


Simulation and forecasting studies

Simulation and Forecasting Studies


For more information

For more information:

Recent publication:

JEQ Supplement, Special Submission, Sept-Oct 2008,

Temporal Trends in Nitrate and Selected Pesticides in Mid-Atlantic Ground Water

http://jeq.scijournals.org/cgi/reprint/37/5_Supplement/S-296

Contacts:

  • Linda Debrewer, Hydrologist

    [email protected], (443) 498-5562

  • Judith Denver, Potomac River Basin and Delmarva Peninsula NAWQA Chief

    [email protected], (302) 734-2506 x229

  • Bruce Lindsey, NAWQA Ground Water trends coordinator

    [email protected],(717) 730-6964


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