EPA Science Inventory

Model Test of Proposed Loading Rates for Onsite Wastewater Treatment Systems

Citation:

Radcliffe, D. AND J. Bradshaw. Model Test of Proposed Loading Rates for Onsite Wastewater Treatment Systems. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL. Soil Science Society of America, Madison, WI, 78(1):97-107, (2014).

Description:

State regulatory agencies set standards for onsite wastewater treatment system (OWTS), commonly known as septic systems, based on expected hydraulic performance and nitrogen (N) treatment in soils of differing texture. In a previous study, hydraulic loading rates were proposed for four categories of soils ranging from Group I (sands) to Group IV (clays). Our objective was to use a HYDRUS model to test the hydraulic performance and N treatment for all 12 soil textural classes using 2 yr of weather data. The model simulated water, N, and temperature dynamics in a two-dimensional space surrounding a drain-field trench. It was calibrated in a previous field study on a clay soil and included water content dependent N transformations. In terms of hydraulic performance, we found that the proposed loading rates were adequate except for the sandy clay textural class in which the rate was too high and caused continuous ponding in the trench. Nitrogen treatment varied widely among soils with denitrification losses ranging from 1% in the Group-I sand to 75% in the Group-IV sandy clay, due to water content limits on denitrification. Leaching losses were inversely related to denitrifcation losses, ranging from 97% in the sand to 27% in the sandy clay. Plant uptake and soil storage accounted for 5% or less of the N losses. The shape of the unsaturated hydraulic conductivity curve and water retention curve were important in determining the prevailing pressure head in the soil and the degree to which denitrification was inhibited in the various soil classes.

Purpose/Objective:

Article published in Soil Sciences Society of America Journal

URLs/Downloads:

https://www.soils.org/publications/sssaj/abstracts/78/1/97   Exit

Record Details:

Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Start Date: 06/20/2014
Completion Date: 06/20/2014
Record Last Revised: 06/20/2014
Record Created: 06/20/2014
Record Released: 06/20/2014
OMB Category: Other
Record ID: 279054

Organization:

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF RESEARCH AND DEVELOPMENT

NATIONAL EXPOSURE RESEARCH LAB

ECOSYSTEMS RESEARCH DIVISION