The Impact of Nonpoint Source Contamination on the Surficial Aquifer of the Delmarva Peninsula

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1 The Impact of Nonpoint Source Contamination on the Surficial Aquifer of the Delmarva Peninsula Judith M. Denver National Water-Quality Assessment Program (NAWQA) September 28,2010 U.S. Department of the Interior U.S. Geological Survey

2 Delmarva Peninsula Soils and aquifer sediments are generally sandy Water table is shallow; about 15 inches of recharge/year The surficial aquifer is susceptible to contamination from human activities Because agriculture is the predominant land use (48%), most groundwater contamination is related to agricultural activities Concentrations of nitrate and herbicide compounds are among the highest in the Nation

3 Nitrate - Spatial Trends Elevated concentrations throughout Delmarva Above background in 68 percent of sampled wells Above MCL in about 33 percent of sampled wells Median concentrations similar at all depths 5.4 mg/l, beneath agricultural land use (median 22 feet) 5.5 mg/l, randomly located, all land uses (median 45 feet) 5.2 mg/l, public supply wells (median 85 feet)** (**public supply wells not included in Delmarva stats above)

4 Aquifers of the Delmarva Peninsula

5 Typical Shallow GW Flow Paths Surficial Aquifer Groundwater flows from upland recharge areas along flowpaths of different lengths to discharge areas in local streams and coastal areas. The residence time of groundwater in the surficial aquifer ranges from a few years to several decades.

6 Factors Affecting Groundwater Transport of Contaminants Land use and land-use change Hydrogeology Geochemical environment (redox) Climate (recharge) Change in chemical applications over time

7 Picture of interspersed land use with chicken houses

8 Relation Between Land Use and Nitrate Concentration in Groundwater 1 to 3 miles CORN CORN SOYBEANS OR SMALL GRAINS Stream to 80 feet SURFICIAL AQUIFER 5 5 CONFINING UNIT VERTICAL SCALE GREATLY EXAGGERATED NOT TO SCALE EXPLANATION UNSATURATED ZONE SURFICIAL AQUIFER CONFINING UNIT CONTOUR OF NITRATE CONCENTRATION IN GROUND WATER, IN MILLIGRAMS PER LITER AS NITROGEN GENERALIZED DIRECTION OF GROUND-WATER FLOW WATER TABLE

9 SUSQUEHANNA RIVER GENERALIZED PENNSYLVANIA MARYLAND FALL LINE C & D CANAL RIVER DELAWARE NEW JERSEY Hydrogeomorphic Regions, Delmarva Pilot ( ) D E L A W A R E B A Y EXPLANATION C H E S A P E A K E B A Y MARYLAND VIRGINIA DELAWARE MARYLAND A T L A N T I C O C E A N CONCENTRATION OF NITRATE AS NITROGEN, IN MILLIGRAMS PER LITER WELL-DRAINED UPLANDS POORLY DRAINED UPLANDS MCL LABORATORY REPORTING LIMIT POORLY DRAINED LOWLANDS AND FINE-GRAINED LOWLANDS SURFICIAL CONFINED REGION 12 MCL NUMBER OF SAMPLES (in 8B) MAXIMUM 75TH PERCENTILE 50TH PERCENTILE 25TH PERCENTILE MINIMUM U.S. ENVIRONMENTAL PROTECTION AGENCY'S MAXIMUM CONTAMINANT LEVEL TOTAL NUMBER OF SAMPLES IN WHICH MCL IS EXCEEDED (in 8A) TOTAL NUMBER OF SAMPLES MILES HYDROGEOMORPHIC REGIONS (HGMR's) KILOMETERS EXPLANATION HYDROGEOMORPHIC REGIONS (HGMR's) POORLY DRAINED UPLAND SURFICIAL CONFINED REGION WELL-DRAINED UPLAND POORLY DRAINED LOWLAND INNER COASTAL PLAIN FINE-GRAINED LOWLAND OTHERS - Beaches, tidal marshes, lagoons, and barrier islands

10 Redox Affects Nitrate Concentrations Nitrate significantly higher in: Oxygen-rich areas throughout surficial aquifer Well-drained areas in shallow network Positively correlated with percent agricultural land use

11 13 Trends in Nitrate, Locust Grove Study area Nitrate concentrations in groundwater increase with increases in rate of nitrogen fertilizer application CONCENTRATION OF NITROGEN IN FERTILIZER, IN GRAMS PER SQUARE METER PER YEAR Concentration of nitrogen in fertilizer Concentration of nitrate in ground water EPA Maximum Contaminant Level = 10 mg/l nitrate CONCENTRATION OF NITRATE IN GROUND WATER, IN MILLIGRAMS PER LITER From Bohlke and Denver, RECHARGE DATE

12 Locust Grove 1989/1999

13 Nitrate from Groundwater Enters Streams

14 Nitrate Concentration in Stream Base Flow Related to Hydrogeology and % Agricultural Land Use SUSQUEHANNA RIVER GENERALIZED C H E S A P E A K E B A Y PENNSYLVANIA MARYLAND FALL LINE C & D CANAL RIVER DELAWARE NEW JERSEY DELAWARE MARYLAND D E L A W A R E B A Y MARYLAND VIRGINIA CONCENTRATION OF NITRATE AS NITROGEN, IN MILLIGRAMS PER LITER EXPLANATION EXPLANATION HYDROGEOMORPHIC REGIONS (HGMR's) INNER COASTAL PLAIN POORLY DRAINED UPLAND SURFICIAL CONFINED REGION WELL-DRAINED UPLAND A T L A N T I C O C E A N MILES KILOMETERS HYDROGEOMORPHIC REGIONS (HGMR's) POORLY DRAINED UPLAND SURFICIAL CONFINED REGION WELL-DRAINED UPLAND POORLY DRAINED LOWLAND INNER COASTAL PLAIN FINE-GRAINED LOWLAND OTHERS - Beaches, tidal marshes, lagoons, and barrier islands PERCENTAGE OF AGRICULTURAL LAND USE IN WATERSHED

15 Groundwater Impacts on Surface Water Groundwater provides 50% or more of flow to streams on the Delmarva Peninsula Groundwater is the major source of nitrate in streams Average age of groundwater discharging to streams is about 15 years Concentrations of nitrate increasing in some streams on the Delmarva Peninsula as groundwater with higher concentrations reaches stream discharge areas. Changes that occur at the land surface take time to reach streams Important factor to consider for local TMDLs

16 Implications for NPS Groundwater Contamination by Nitrate (From Kauffman and others, 2001)

17 Delmarva Peninsula Nitrate Trends no data

18 Implications National NAWQA Results Nitrate concentrations are likely to increase in aquifers used for drinking-water supplies during the next decade or longer as shallow groundwater with high concentrations moves downward into the groundwater system. Improvements in nutrient management practices on the land surface will likely take years to decades to result in lower nitrate concentrations in groundwater used for drinking water because of the slow rate of groundwater flow. Similar time delays also expected for streams that receive considerable groundwater discharge.

19 Sources of Information New publication: Nutrients in the Nation s Streams and Groundwater, ; USGS Circular

20 Picture with thanks Thanks!