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Abstracts:
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1.  "Prospecting for Ground Water Contamination from On-Site Wastewater Systems in New Mexico"  

2. " Flow Variation in Design of Advanced Onsite Systems" 

3.  "Performance Evaluation of a Wastewater Treatment Facility Using A Low Speed Rotating  Aerator" 

4.  "Simplified Design of ET beds for groundwater protection in the Arid Southwest"

1. Prospecting for Ground Water Contamination from On-Site Wastewater Systems in New Mexico
Bruce Thomson[1], Gwinn Hall[2], John Stormont1, Jeff Peterson[3], Adrian Hanson[4]

Abstract:

While on-site wastewater treatment and disposal systems are frequently blamed for groundwater contamination, few hydrogeologic investigations have actually been conducted to quantify their impact.  Fewer still have been done in arid environments that are characterized by high evaporation, low rainfall, porous soils, and large depths to ground water.  This paper describes a field investigation to measure the impacts of high densities of septic tank systems on ground water quality near Albuquerque, NM.  Surprisingly little contamination was found including very low concentrations of nitrate.  One mechanism for nitrogen removal may be subsurface nitrification-denitrification in deep unsaturated soils.  The implications for development densities in unsewered communities will be discussed.



[1] Dept. of Civil Engineering, University of New Mexico, Albuquerque, NM 87131

[2] Daniel B. Stephens & Associates, Albuquerque, NM 87110

[3] Dept. of Public Works, Bernalillo County, Albuquerque, NM 87102

[4] Dept. of Civil, Agricultural & Geological Engineering, New Mexico State University, Las Cruces, NM 88003

 
2.    Flow Variation in Design of Advanced Onsite Systems

 A. Hanson, Ph.D., PE, L. E. Mimbela, R. Polka, W. Zachritz1

New Mexico State University, Las Cruces, NM 88003

1Currently at the Dry Lands Research Institute, Las Vegas, Nevada.

 

There is an increase in use of advanced home scale wastewater treatment systems to protect sensitive environmental areas.  In the arid southwest these are both shallow ground waters used for drinking water, fractured bedrock areas, and riparian areas.  Standard septic tank systems are relatively insensitive to flow variation, but the advanced systems are extremely sensitive to large fluctuations in flow.  This paper will present a detailed flow study from 3 homes.  It will compare the peaks day during the week as well as hourly peak flows to the typical values presented in engineering design literature.  Flow values are measured at the septic tank effluent not coming out of the house so hydraulic damping by the septic tank is accounted for. 

 

3.  Performance Evaluation of a Wastewater Treatment Facility Using A Low Speed Rotating  Aerator

Robert Richardson, PE

Bohannan Huston Inc. * 425 S. Telshor Ave * Ste. 103C * Las Cruces * NM * 88011

Phone. 505.532.8670 * Fax. 505.532.8680 * rrichard@bhinc.com

 

Ege Richardson, PhD, PE

Bohannan Huston Inc. * 425 S. Telshor Ave * Ste. 103C * Las Cruces * NM * 88011

Phone. 505.532.8670 * Fax. 505.532.8680 * eegemen@bhinc.com

 

Adrian Hanson, PhD, PE

New Mexico State Univ. * Civil and Agricultural Eng Dept * PO Box 30001 * MSC. 3CE * Las Cruces * NM * 88003

Phone. 505.646.3032 * Fax. 505.646-3032 * athanson@nmsu.edu

  

 The treatment system was designed to treat a medium flowrate, at present the facility treats 10,000 gpd.  Influent wastewater enters an equalization basin, which is continuously mixed.  The treatment unit consists of two BiowheelsTM, a final clarifier, and a chamber type drainfield. The effluent is pumped from the wet well to the  chambers (InfiltratorsTM ), which are placed in six different zones that can be isolated using manual valves.  The contaminant of interest for removal is nitrogen.  This paper will present performance of this facility from start-up to the present.  The presentation will include the problems encountered during the start-up as well as the influent and effluent data collected.  Facility photos will also be presented.  Photo 1 below is taken across the treatment system, and Photo 2 is the subsurface drainfield with tumble weeds growing over the drainfield.

  

Photos 1&2.  The left hand picture is the treatment system taken from behind the bio-wheel across the clarifier.  Right hand picture is the drainfield.  The vegetation in the front of the picture is native without the addition of the discharge water to the subsurface.

 

4.  Simplified Design of ET beds for groundwater protection in the Arid Southwest

 

  1. Hanson, Ph.D., PE, P. King, Ph.D., PE, S. Bawazir, Ph.D., PE

NMSU Civil Engineering Department Las Cruces NM 88003

 

With the continuing drought and increasing populations, there is growing concern in the arid southwest over contamination of groundwater with nitrogen.  One of the suggested solutions has been the use of ET beds.  The Southwest is the obvious place to use this technology, but this region has had a long history of technology failures.  The failures have been caused by the design approach, which sizes the systems based on an average annual evapotranspiration rate.  Techniques have been proposed that designed the systems based on computer modeling, but this is not practical for most on-site installers.  This paper will present a simplified design procedure that accounts for climactic impacts on ET bed design.  Issues to be addressed in design are water balance, need for supplemental irrigation, and plant selection. 

 

 

 

 

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