Septic Design and Master Site Plan of Polifuncional Calama School
Santa Cruz, Bolivia
(resumens de los informes en Espaņol (PDF)

Melissa Trahan, Civil Engineering
Mary Anderson, Environmental Engineering
Kasey Cornwell, Environmental Engineering

International Senior Design, CE 4990 & 4905
August 2005

The Project Background

In 2001, Michigan Technological University (MTU) sent groups of students to developing countries as part of a flagship International Senior Design Class (ISD). Most recently, in the summer of 2005, two groups of students traveled to Santa Cruz Bolivia.
LSS Engineering was among these students. They chose two schools to evaluate, Polifuncional Calama in UV 125 and Oscar Ungaza de la Vega in UV 127. Upon further analysis and scrutiny of the toilet room and septic system problems, the project was narrowed down to include only Calama. This decision was made after interviewing school staff and students.

(1) LSS interviewing Calama Director Anivar Rocha.

(2) Calama school yard, facing the stage.

(3) Watching water table soil boring.

(4) Calama toilet room with visible upwelling around building.

(5) Standing water on toilet room floor.

The Trouble With Calama

Site Exploration:

Site analysis revealed standing water in and around the toilet rooms. The water was assumed to be upwelling from the existing septic system and runoff from the toilet room floors. The septic tank fills so fast that it needs to be pumped every three months. When the school can’t afford it themselves the parents pay for it. To slow the filling of the tank the water to the toilets is turned off and they are flushed manually when necessary. This allows the toilets to fill with human waste.

(6) Septic upwelling along student walkway.

(7) septic up welling at base of toilet room.

(8) Septic upwelling along student walkway.

(9) Collecting a soil sample from the soil auger.

(10) Water testing results, light brown color shows presence of coliforms, indicating human waste contamination.

(11) Surveying at Camala

The Master Site Plan

The current and future site plans for Calama can be seen to the left. Changes made to the current design include:

Completion of brick area in front of stage.
Additional classrooms
New location for bathrooms
New septic system
Study area
Volleyball pit

 

 

Traditional Bolivian System

The Traditional Bolivian System consists of three parts in the following order: a sedimentation tank, septic tank (camera septica), and dry well (pozo ciego) and is currently being used. The system is failing because the soil surrounding the dry well is not permeable enough to handle the school’s wastewater load and the septic tank cannot not be pumped as frequently as necessary due to lack of funds.

Holding Tank

The Holding Tank alternative is comprised of a large sedimentation tank which acts as a holding tank, needing to be pumped at designated intervals. Though a holding tank would overcome the problem of soil permeability at Calama, this is not a feasible option due to the large maintenance costs.

Subsurface wetland

The Subsurface Wetland alternative consists of a sedimentation tank and constructed subsurface wetland and performs the same functions as a traditional system. This is a feasible design for Calama, however it is limited by cost of materials and land availability on site. Off site there is enough land available but the ownership is unknown.

The Recommended Solution

The recommended design is one which utilizes a sand filter. The system will be gravity fed and will run the wastewater effluent through two parallel septic tanks before being dosed on the sand filter by a siphon. The filter effluent will be collected in an underdrain and will need to be piped to an existing ditch just beyond the Calama site walls to the east. The effluent will have an approximate pathogen removal of 99%, and secondary BOD5 and TSS removal to compliment that accomplished in the septic tanks. The sand filter will be open at the top and therefore it was recommended that a fence be used to keep students from playing in it.

The sand filter design accommodates 30% growth over the next 10 years. If the sand filter is properly maintained it is possible for it to have a life of up to 20 years. Backwash pipes have been included to allow for periodic cleaning of the system.

Although the sand filter is more costly to build then a traditional Bolivian system, it will be more cost effective in the long run because the traditional system will need to be pumped every few weeks. Also it has been recommended that the school and community push to have their location incorporated into Santa Cruz, sanitary sewer system. The city supplies water to the school and legally for this reason they should be removing the water as well. See the tables above for system advantages and disadvantages and a cost analysis comparison

The Community Connections

While visiting Calama, LSS made connections with faculty, students and community members. Although none extended their welcome with as much enthusiasm as the current senior class. Pictured with LSS to the immediate left. As part of their senior gift to the school they were working to beautify the school yard. This included planting flower beds, organizing an open air study area and sand volleyball court. They worked with LSS to incorporate their ideas into a master site plan seen to the far left.
LSS also met with parents and staff who discussed their dedication to helping make Calama a better place for the students. They even committed to helping with the construction of the new septic system.

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