10.4122/1.1000000451
French, Helen K.
Helen K.
French
helen.french@jordforsk.no
Forquet, Nicolas
Nicolas
Forquet
nforquet@engees-e.u-strasbg.fr
Robertsen, Knut-Robert
Knut-Robert
Robertsen
knutr.robertsen@asplanviak.no
Mæhlum, Trond
Trond
Mæhlum
trond.mahlum@jordforsk.no
French, Helen K.
Helen K.
French
helen.french@jordforsk.no
Flow and transport in a constructed infiltration system for wastewater treatment characterised by electrical resistivity and 2D numerical unsaturated zone modeling.
XVI International Conference on Computational Methods in Water Resources
2006
2006
Disposal of domestic sewage effluents in soil has been used for several decades in
Norway and more than 100000 constructed systems for wastewater purification have
been built with capacities between 5 and 8000 pe (person equivalent). However, the
infiltration of wastewater effluents into soils and the estimation of application
rates for a given system design and environmental setting are extremely complex and
often poorly understood and oversimplified (Siegrist, 2004). The infiltration system
presented here consists of 26 horizontal distribution pipes separated by 1.25 m over
an area of 1100m2. The distribution pipes are placed in a coarse gravely
distribution layer at about 1m depth. A pump ensures regular injection of wastewater
into the system. Below the distribution layer there is a 20 cm thick layer of local
natural soil, which is a coarse sandy soil with gravel, followed by a 25 cm thick
layer of light weight aggregates (LWA). Below the LWA layer there is natural soil
and the water drains freely to the groundwater at about 5m depth. Hence the
retention time and flow pattern are key factors determining whether phosphates are
retained and organic components are degraded before water leaves the filter system
or enters the phreatic level. In this study a combination of time lapse electrical
resistivity (ER) measurements and numerical modeling of an unsaturated system have
been performed in order to examine the wastewater distribution and its potential
effect on flow and transport in a 2D unsaturated layered profile. Measurements were
performed in June 2005. In addition to the ER measurements, an inactive tracer was
applied and the breakthrough curve monitored at three depths below the constructed
filter. Temporal changes in electrical resistivity revealed spatial patterns
coinciding with the locations of the pipes, hence suggesting a heterogeneous
distribution of waste water. The numerical simulations show the importance of the
hydraulic conductivity of the distribution layer, and support the conclusion that
the distribution may be non uniform over the area, hence causing preferential flow
paths in the filter system.
References
Siegrist R.L. McCray J.E., Lowe K., 2004, Wastewater Infiltration into soil and the
effects of infiltrative surface architecture, Small flows quarterly Vol. 5 No. 1,
pp. 29-39.