Nitrogen in Groundwater Washington State Department of Health

March 6, 2013

Nancy Darling, LHG, CPSS Office of Shellfish and Water Protection

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Source

Soils

Aquifer

Nitrogen in Groundwater

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Sources in Scatter Creek Agriculture Residential Fertilizer On-Site Sewage Systems Natural Sources

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Contaminants in WastewaterOn-Site Sewage Systems Pathogens - Fecal Coliform Viruses Emerging Contaminants (ECOC’s) Nitrogen Phosphorus

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Wastewater Characteristics Waste VolumeWaste Strength (mg/liter or ppm) Location

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Wastewater Volume 3 bdrm home is 360 gpd Four schools - 3900 gpd * 8900 gpd RV park - 5800 gpdMobile home park - 5040 gpd

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Wastewater Strength Domestic nitrogen is 45-60 mg/L Schools can be closer to 100 mg/L RV Parks usually over 100 mg/L

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Source Location

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ground-water flow

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Source

Soils

Aquifer

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Role of Soils in On-site Sewage

Disposal for wastewater Treatment for wastewater

contaminants: pathogens viruses organic matter ECOCs phosphates, & nitrogen

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Soil Characteristics Depth – Upper five to six feet

Soil Texture – Loamy soils with low gravel

Soil Structure – not dense or compact

Drainage – not excessively or slowly drained

* The ideal soil is deep, well drained and medium texture.

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How Soils Treat Wastewater

Physically trap large pathogens and organic matter Natural microbes out-compete pathogens for food React with soils by chemical or physical adsorption Biomat – forms under conventional drainfield

High zone of physical and reactive treatment

Minor amount of plant uptake

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How Soils Treat Wastewater (cont.)

Nitrogen Some organic nitrogen is trapped in biomat Ammonium (NH4+) weakly adsorbed on soil Most N converted to nitrate (NO3-) Not adsorbed by soil Minor plant uptake Minor denitrification (wet conditions) Most leaches to ground water (NO3, TKN)

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Nitrogen Cycle

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Nitrates Not Held in Soil

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The good…. Excellent for disposal Loose and well aerated Deep soils

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Scatter Creek Soils Sand and Gravel

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Scatter Creek Soils

The bad…. High rock content means less soil for

treatment Coarse soils = low reactive surface High permeability means less retention Less developed biomat Good aeration means minimal denitrification

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Scatter Creek SoilsThe ugly… High rainfall leaches the nitrates and other

contaminants not retained in the soil to the shallow groundwater.

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Source

Soils

Aquifer

2020

Scatter Creek Aquifer• High producing sand and gravel aquifer• Flows east to southwest towards Chehalis River

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Scatter Creek Aquifer:Two-Part Concern#1 Highly Susceptible to Land-Use Shallow Water Table (< 50 ft.) Unconfined aquifer Nitrates detected in localized areas

#2 Single Aquifer

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Hydraulic Conductivity (K)

K is the aquifer’s (media) ability to transmit water (ft/day)

Q (flow)=kia

High K = Dilution

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Nitrate PlumesMinimal Dispersion

24 http://pubs.usgs.gov/fs/2007/3103/

Note: Output values for example only.

Note: Output values for example only.

Note: Output values for example only.

Note: Output values for example only.

Note: Output values for example only.

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“ It is far better to have an approximate answer to the right question than a precise answer to the wrong question.”

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