Post on 18-Jul-2018
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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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 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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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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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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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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“ It is far better to have an approximate answer to the right question than a precise answer to the wrong question.”