Figure
1
Figure
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Tierras
Nuevas Onsite Wastewater Treatment Design
Santa Cruz, Bolivia
International Senior Design
August 2006
Bailey
Gamble – Project Manager
Amanda Kohler- CAD specialist
Jeff Dambrun – Translator and Field Engineer
Introduction
Tierras Nuevas is a public school located in UV 135, District 10
of Santa Cruz, Bolivia. The school contains two sites; the main
primaria/secundaria location and the newer, smaller kinder location
attended by 2300 and 110 students respectively. Two traditional
Bolivian septic systems (Figure 1) serve the main site. Neither
system is large enough to meet current demands. Wetness resulting
from overflow can be observed in surrounding soil. A traditional
Bolivian system is currently malfunctioning at the kinder site as
well. Students, who suffer from stomachaches, diarrhea, and infection,
congregate in contaminated areas (Figure 2). All three of these
systems pose serious health risks to the students.
Ernesto
Engineering spent 2 weeks in Santa Cruz working with the faculty
and community members involved with Tierras Nuevas. Need for and
support of the project were strong so engineers collected the necessary
data and designed an alternative wastewater treatment system. |
Methods
and Procedures |
Figure
3 Surveying (Click to enlarge)
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Surveying
Surveying data was collected at both sites in order to acquire information
on system dimensions, space available for design, and general layout
of the schools.
Figure
3 at right shows the layout of the main site created using survey
data.
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Water
Quality Testing
Hach Coliform Presence/Absence tests (Figure 4) and 3M Petrifilm tests
(Figure 5) were performed to determine the presence and amount of
coliforms. Samples were collected at both sites from standing water
puddles, wet soils, and tap water. All samples, except for tap water
and a control sample, tested positive for coliforms including E. coli.
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Usage
Surveys
Surveys were distributed to a sample population of 288 students
in order to determine the following statistics:
75% of students
prefer the west toilet room
Students use toilet rooms an average of 1.5 times per day
97% of student wash hands
37% of students use soap
Stomachache frequency (Figure 6) |
Figure
7a
Figure
7b
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Soil
Analysis
Engineers performed three soil borings (Figure 7a,b,c) near each
of the distribution systems. Borings were taken to depths of 7 ft.
at the main site and 9 ft. at the kinder site with samples being
collected each time soil texture or color changed (Figure 8). Engineers
determined the seasonal high water table to be located at 1.5 m
due to visible mottling in the soil.
Soils consisted mainly of loamy sand with small amounts of clay
present in some layers. Visual analysis and hydrometer jar tests
(Figure 9) were used to draw these conclusions.
Figure
7c |
Design
Alternatives |
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The main factors influencing design for Tierras Nuevas’ septic
systems were flow, soil type and conditions, appropriate technology,
and sustainability. With this in mind, nine design alternatives
were considered. Seven were eliminated for reasons stated below.
Two were utilized in final design.
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Final
Design
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Primaria/Secundaria Site
This site had good soil conditions and abundant space available.
The septic tanks in both systems are too small to support the student
populations. Final design recommendations include larger septic
tanks and a gravity fed drainfield (Figure 10) for each system.
Sample design drawing (Figure 11) and proposed layout (Figure 12)
are shown below.
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Kinder
Site
Final design recommendations are to first investigate the connection
between the septic tank and pozo ciego (dry well) then install a
small gravity fed drainfield off the pozo ciego. Proposed layout
is shown at right (Figure 13)
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Conclusion |
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Implementation of the final design recommendation will provide the
treatment capacity needed at the two Tierras Nuevas locations and
create a safer environment for children to play in. The design utilizes
appropriate technology and is cost effective, however it provides
temporary solution. The best solution for Tierras Nuevas is to connect
to a sanitary sewer when the option becomes available.
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