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oL. 2
Republic of the PhilippinesLocal Water Utilities
Administration
SEWERAGE AND SANITATION PROJECTWATER DISTRICT DEVELOPMENT
PROJECT
WORLD BANk
ENVIRONMENTALASSESSMENT
lLoN REPORT
DAVAO CITW
Yp SA AS
_f 9 2_ ~DAVAOCITY
9wJINDAM ANXIOM ,9
March, 1997
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DAVAO ENVIRONMENTAL ASSESSMENT REPORT
ERRATA:
page 38, first paragraph: "Several potential sites... Planning
Department (see Figure 3."
page 38, first paragraph of B. Toril:"Two sites have been
identified (see Figure 3.2 by the City...."
page 58, first paragraph: "To evaluate the overall... district
in Table 4.5 CDM (1994)....
page 59, first paragraph somewhere past midway: Table 4.5 shows
that a conservative....
page 61, second paragraph, 2nd sentence: The coliform counts
reported in Table 2.6...
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* * 'iO..eA wB-
SCAIINNED
Republic of the PhilippinesLocal Water Utilities
Administration
SEWERAGE AND SANITATION PROJECTWATER DISTRICT DEVELOPMENT
PROJECT
WORLD BANK
ENVIRONMENTALASSESSMENT
UfON REPORT
b g DAVAO CITY
DAVAO
March, 1997
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TABLE OF CONTENTS
P_ge
EXECUTIVE SUMMARY I
Chapter I INTRODUCTION 12
Chapter 2 BASELINE ENVIRONMENT - DAVAO CITY 16
Section I Existing Environment 16Section II Environmental
Pollution 21
Chapter 3 PROJECT DESCRIPTMON AND ANALYSIS OF ALTERNATIVES
30
Section I Project Rationale and Objectives 30Section II
Sanitation 30Section m Overall Sewerage Scheme 32Section IV
Recommended Project Design for Davao City 49Section V No Project
Scenario 53
Chapter 4 ENVRONMENTAL IMPACTS 54
Section I Beneficial Impacts of the Project 54Section II Project
Iinplementation Impacts 63Section m Summary 66
Chapter 5 ENVIRONMENTAL MANAGEMENT PLAN 67
Section I Mitigation Plan 67Section II Monitoring Plan 69Section
III Implementation Arrangements 69
Appendices
I. Bibliography2. Climatological Normals (1961-1995)3. Typical
Noise Emissions of Construction Equipment4. Expected Noise Levels
at Various Distances from Construction Equipment5. Environmental
Quality Standards For Noise Maximum Allowable Noise Levels6. The
Advanced Integrated Pond System (AIPS) of Wastewater Treatment
Environmental Assessment Report: Davao Citv
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EXECUTIVE SUMMARY
Introduction
In the Philippines, the typical urban area/built-up area is
characterized by a heavy concentrationof activiies, both commecial
and industrial. It is also the area where the density of
populationis at its peak. These areas are also the sites where the
production and consunption of raw andprocessed materials could be
found. Consequetly the, pressure on the life support systems
inthese areas are far higher than the suburban and nual areas.
Advese environental conditonssuch as the generation and similarly
the discharge of wastes into the environment is common inurban and
built-up areas Unfortunately, the an, type and concenrion of
wastegencrated exceed the capability of the local environent to
absorb and assinilaethem. Thecariymg capacity ofthe life support
systems are stretched to the limits. The urgn ofestabhlishing
collection and tment methods which will preven adverse impacts to
thc healthand well-being of the residents, and to the ecological
systems which sustain them cannot beignored and overstated.
Most urban centers in the Philippines rely on individual septic
tank systems for thetreatment and disposal of wastewater from
domestic and commercial buildings. However,the designs for such
systems is often inadequate. Facilities for land disposal of
effluentsfrom the septic tanks are generally absent. Hence the
partialy treated septic tank effluentsflow directly into storm
drainage systems and other receiving bodies of water,
therebyexacerbating an already grave poilution situation.
There are several possible options for addressing this problem,
including improving thedesign of the septic tank system with the
installation of soil absorption systems. But anenvironmentally
sound alternative that is cost-effective and captures economies of
scale isto connect individual properties directly to a sewerage
system for the collection, treatmentand disposal of the urban
wastes.
The provision of a cost-effective centralized wastewater
collection, treatment, and disposal isthe pnmary objective of the
proposed Water DisicU Dewiopmnent Poject. The proposedproject will
assist the local governments of Dagupan, Calamba, Laguna, Cagayan
de Oro,Davao City and Cotabato City, in finding solutions to the
problern of sanitaLon.
Better sanitary conditions will thus be experienced in the areas
served by the sewerage,drainage and sanitation systems. This will
reduce water-borne pollution and water-loggingwithin the cities and
in the surrounding water bodies, thereby bringing health benefits
tolocal populations. In Davao, Cagayan de Oro and Calamba cities,
pollution from humanwastes have affected recreational areas, such
as beaches and lake front areas. Project
Environmental Assessment Report: Davao CitY I
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investments in wastewater collection and treatment will also
have positive benefits interms of improving prospects of saving the
remaining beaches for the city residents. Theconstruction of the
systems will protect shallow groundwater aquifers from
contarnination,particularly in Toril area of Davao city, which
forms the source of the city's water supplysystem.
Environmental Assessment Requirements
This Environment Impact Assesmen Report for Davao City has been
prepared inaccordance with the P*eldental Decree No 1586 otherwise
known as the EnvironmentlImpact Assessment Law and Department of
Environment and Natural Resources RevisedAMsinimaiw Order Nos 36,
the Rvised Water Usage and Clsszficataon/Water QualityCnteria and
RevisedEffluent Regulmions of 1990 rqsevely, and WorldBank
'sOperationalDirectie 4.01 on EnviromnentalAuesment. The revised
Administrative Order36 for Environmental Impact Statement System
issued in 1996 is comprehensive and iscompatible with the World
Bank's Operational Directive 4.01. It outlines the procedureto be
followed by environmental critical proiects (ECP) and project to be
located inenvironmental critical areas (ECA) in preparing
enviromnental impacts statement (EIS) .ECP and ECA are defined in
the AO It should also be noted that that local ordnances
andregulations goveng projects of such nature have been taken into
consideration in preparingtis report. Similar EIA reports are beng
prepared for the other 4 cities.
This report has been prepared by a team of local conslants under
the aegis ofthe Local WaterUtilities Adnwstration (LWUA) and the
Davao City Governent Much of the work relaingto the envionmental
impact analys was undertaken as part of the feasibility study done
by C.Lotti and Associati. Consultation with the community is an
on-going process. The sanitationcomponent of the project will be
exeated in a participatory manmer, and detailed guidelineshave been
speled out.
Selection of Priority Cities
The choice of the first batch of Philippine cities for sewerage
investments was made afteran initial screening at the national
level of urban areas facing the most serious problem ofpollution by
untreated wastes. Of the five cities, Davao and Cagayan de Oro
represent thelargest class of provincial cities with current
population estimates in the range of a millionand half a million
respectively. There are several major population concentrations in
thecity; each being a source of sewage contamination for nearby
surface and ground water.However, the largest volume of sewage is
generated by the largest consumers of pipedwater supply; in the
Central Business District or Poblacion area. Untreated
wastewaterfrom this area has polluted low-lying coastal areas, and
basically converted the principalrivers into open sewers.. The
scale of the pollution problem can be appreciated by the factthat
about 90 per cent of the daily water supply of 140,000 cubic meters
in Davao city and
Tius is the term used by DENR and refers to the standard
Environmcntal Assessment Reportrequired by the World bank as per OD
4.01
Environmental Assessment Report: Davao Citv 2
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76,000 cubic meters in Cagayan de Oro is being discharged as
untreated wastewater.Outside the Poblacion areas, there are pockets
of population concentrations pollutingnearby streams, creeks and
channels.
In the other three cities of medium size (Cotabato city, Calamba
and Dagupan), currentpopulation estimates are close to 200,000.
While the scale of urban pollution problems arenot comparable with
Davao and Cagayan de Oro, these cities are located close
toenvironmentally sensitive wetlands and water bodies. In Cotabato
city, the urban area isactually below the mean sea level, exposing
inhabitants to frequent waterlogging duringthe monsoon months.
Calamba is located on the shores of Laguna Lake, which
hasexperienced a rapid deterioration in water quality over the last
two decades. Dagupan cityis close to a large estuarine zone with
ecologically sensitive wetlands and fishponds. Ineach of these
cities, Mayors and city officials have recognized for some time
that unlesstheir complex environmental problems are tackled through
a strategic plan of handlingwaste disposal, sustainabiity of urban
growth could be seriously affected.
Overall Project Approach
The proposed project follows a demand-based approach, in the
sense that facilities will beconstructed only if they conform with
the preferences of local stakeholders, and servicesconform to their
respective willingness to pay. The stakeholders represent the
differenttiers of organizations from the City Council and Barangay
(part of the formal LGUsystem), to the more informal purok,
neighborhood and household levels. During projectpreparation, the
idea of involving communities in the planning process was
field-tested inthree barangays of Davao city, and found to be quite
successfil. The basic decision-making process is as follows:
For the capital-intensive trunk system, consisting of the main
transportationsewers, primary drains and wastewater treatment
facilities, the projectdesign and implemnentation plan has to be
approved by the City Council,because the latter is responsible to
repay the loan [see Annex 3 on FmancialAspects, Staff Appraisal
Report (SAR)].
For the feeder system, consisting uf collector sewers, secondary
drains and on-sitesanitation facilities, barangays and local
neighborhoods will be associatedwith the planning and
implementation program. The design criteria havebeen simplified, so
that the feeder system can respond to local preferencesand
willingness to pay, rather than be bound by any conventional
sewerdesign criteria used in industrialized countries. Detailed
design will beconducted through a participatory process described
in Annex 13, SAR_
Given the capital-intensive nature of the investments, the
proposed project is only theinitial phase of a program to improve
the sanitation infrastructure through a strategicplanning approach
that involves a mix of on-site and off-site wastewater
collection,treatment and disposal. Choice of initial service areas
for sewerage has been confined tothe Central Business Districts or
Poblacion areas because these are the major contributors
Environmental Assessment Report: Davao Citv 3
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to municipal wastewater pollution. The only exception made is in
the case of Davao City,where a second area of high growth prospects
(TorI) has also been included on therequest of the LGU.
The project will construct a sewer network that will discharge
sewage to a verticallyintegrated pond system designed to treat both
sewage and septage. In each of the cities,with the exception of
Davao, the treatment site was selected in areas free
fromencumbrances.
For the sanitation and drainage components, the entire city has
been included in theproject area, with final selections being made
on the basis of demand. On-site treatmentsystems through the
construction of VIP latrines, pit latrines, pour flush toilets and
septictanks will also be constructed if there is demand from
property owners. For thoseproperties with uncertain land tenure (as
in squatter settlernents), the project will financethe construction
of communal toilets, to be managed by NGOs and/or the private
sector.The specific location of these facilities will be driven by
the willingness to pay for theservices by beneficiaries at the
barangay leveL provided of course that these are
technicallyfeasible.
Analysis of Alternatives
The recommended solutions for wastewater treatment were arrived
at after an intensiveprocess of evaluating alternatives during the
project preparation in order to achieve costeffectiveness and
acceptability. The alternatives considered were
anaerobic/facultativePonds, modified lagoon systems and mechanical
treatment. The evaluation of alternativesindicated that the
modified lagoon systems, despite having a higher O&M costs
comparedto anaerobic/facultative ponds (as it requires mechanical
aerators and recirculation pumps)was appropriate. The selected
option met the foliowing criteria the effectively:
irnimize overall pond area required
Minimize odor production
Meet DENR effluent quality criteria, including fecal coliform
reduction
Minimize sludge production rate
Maximize potential to use surrounding land for recreational
purposes
Environmerral Assessment Report: Davao Cirv 4
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Summary Information on Project Cities
Davao Cagaan de Or o Cal D
Poqulation(1990) 849.947 339,598 127.065 173.453 12S.ooo
Housnng 163329 47.724 21.5S1 32109 21.219
Sizeof'CIaa 1000 l eOOOh 400hbecaa 120bc 95bets 50bedaeB
_S~Diarc(CBD)
Morbiditv rae per 95 for 733 for diarrhta 3050 for diith 3l 2
for puastim 523 for pgi-10.000 f diseam diuXagturd (tird re*) (rtun
ran) (second ra*) enteritis (thd
Ta-k ar" rank)diseases)
Wer bodies at risk DSaW nu ad Csapr nvrad About 50% of cty
Laguna Lake About 50% of cItybecane of _cul a8 bead. claw adjondug
beace a us- of am am wdilmds.poihg to city no it for on Mpajlsw Bay
wdand fib ma l usd for fish
rea_ahal udit for pondse ad midity sidid farusug
P,_mpo bmmo(feesI_ _ ~~~~~~~~~~~~~~~~onnm tof n
The urban area/built-up area in the project cities is
characterized by a heavy concentrationof commercial and industial
activities. It is the area where population density is
highest.These areas are also represent the bulk of economic
activity in the informal sector - suchas, the production and
consumption of raw and processed food, light
manufacturingactivities and retail distribution. A large proportion
of piped water supply from the localWater District is also consumed
in the Central Business District. Consequently, thepressure from
both solid and liquid wastes in these areas greatly exceed the
capability ofthe land and water resources to absorb, assimiate and
recycle them.
Davao City
Impact Dunng Construction Phase
The implementation of the project and-its components is
projected to produce onlyminimal adverse environmental impacts. The
socio-economic impacts will be beneficiaLand will result in a
better standard of living for the municipalities and cities
concerned. Inthe short-term the project will provide emnployment
and livelihood opportunities to thepopulation of the surrounding
communities through the jobs generated during theconstruction
phase. In the long-term, better sanitary conditions will reduce
sicknessescaused by water-related problems. Thus an improvement of
the existing environmentalconditions is expected. The project will
undertake mitigating measures to minimize, or ifat all possible,
eliminate adverse impacts.
Air Quality. The implementation of the project will result in an
increase in the ambientconcentration of suspended particulates in
the vicinity of the project site. This would be
Environmental/Assessment Report: Davao Cirv 5
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attributed to dust from land clearing and excavation activities,
which expose soil to windand vehicular traffic over unpaved
road.
Water Quality. Excavation activities in the project sites could
also loosen soils andtransport of these materials to any surface
waters, thereby increasing siltation andturbidity.
During the rainy season, surface runoff may increase total
suspended solids, and causetemporary stress at the discharge
points. However, the impact will be locaiized, and whenthe
vegetative cover returns, impact on the receiving body of water
caused by surface run-off will be eliminated.
Noise. The noise irnpact during the construction stage is
expected to be generally minimaland will not require any special
noise abatement measure. The treatment plant sites shallhave a
setback away from residential clusters, which will definitely
provide the necessary'buffer to reduce noise impact during
construction of the modified lagoon systems.
During the pipe-laying, some noise will be generated due to the
construction activities andthe temporary operation of heavy
equipment. Noise from breaking concrete pavement andsidewalks may
also pose a temporary problem. However, the noise level at the
streets isexpected to be within the ambient noise quality
standards.
Socio-economic. The only potentially adverse impact is likely to
be in the Davao sewagetreatment site, where approximately 15
squatter structures are located in the vicinity of thetreatment
plant site. The treatment plant, can, however, be constructed
without affectingthese structures, and hence no resettlement action
plan will be required. The CityGovernments will be requested at
appraisal to indicate how they plan monitoringpotentially adverse
impacts in the project cities.
Ecological Effects. As there are no rare, endernic species of
flora and fauna in any of theproject area, project implementation
has minimal impact on the terrestrial ecc!ogy.Vegetative cover
shall be unavoidably cleared during civi works.
Impacts During Operation Phase
Air Quality. The operation of the wastewater treatment facility
will have minimal impacton the air quality of the area. Aside from
the occasional odor nuisance, it is not projectedto have adverse
effect at all.
Water Quality. The implementation of the project will be
beneficial to the general envi-ronment of participating cities and
their environs. Discharging of untreated domesticwaste water from
the high volume consumers in each city's Central Business Districts
intonearby bodies of water would thus be minimized or eliminated.
However, operations andmaintenance failures may result in
occasional discharges.
Environmental .4ssessment Report: Davao City 5
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Socio-economic. The provision of sanitation facilities in the
project cities wouldundoubtedly benefit the general populace of
these areas. The occurrence of epidemic-scale diseases caused by
current unsanitary conditions will be reduced. This will result in
amore healthy and productive population.
Sludge Disposal. The modified lagoon system or Advanced Improved
Ponds System(AIPS) will require sludge disposal at very infrequent
intervals. The sludge in theanaerobic pond/s remains for an
extended period continuously undergoing organicdecomposition. This
may take place over a 20-30 year period. One system in operation
inthe U.S. has not been desludged in thirty years. Recent testing
of this system has indicatedthat the sludge is well-digested and
very stable. If desludging does become due,arrangemnents can easily
be made with the city environment office for disposal at
thesanitary landfill.
Mitigating measures to mininize, or if possible, eliminate
adverse impact will beimplemented. Measures to enhance the existing
environmental conditions in the projectsite shall be implemented to
maintain the enviromnental sustainability of the area.
Theimplementation of the project wilL inevitably produce impact,
both adverse and beneficial.Table I shows the potential impact,
risks and the proposed mitigating action.
Implementation and Monitoring of Management Plan
The PMO, with the assistance of LWUA-CPSO and consultants, would
monitorcompliance with the ECC and carry out the requisite data
collection. Monitoring reportswould be submitted to DENRIEMB and
the World Bank periodically. Whileresponsibility for the various
mitigation activities have been identified, the PMO willensure that
the requirements are complied within addition, feedback from
comnunities,city officials, NGOs, etc. wiU be pro-actively sought
through the city public affairsprograms, regular monthly meetings
of barangay captains and other methods. Funally,DENR, through its
planned PPA system, would also periodically monitor and
auditcompliance with the ECC, assisted by independent
contractors.
Table 2 summarizs the responsibilities and timetable for the
Mitigation Plan.
Environmental Assessment Report: Davao City 7
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Table 1: Mitigation Actions
Construction Phase
Potential Impma & Risks Mitigation Action
* Poor qualty of consuon * Design and supevision contra will be
separated from supplyand installation contract as a means of
assuring quality ofconstrucion. Works engineers, with a relatively
indepe tsource of information on construction progress, will be
hired.
Air Polluion * Careful consructon planning and work phasiLg,
specificationsand constrion methods to reduce the length of time
that the
* Constuction equipment and soil is cxposed to the
enviromentvehicles may cause higher * Provision of adequately and
propely tainmtad storge forsuspended particult, odors and
construction materials and equipmnfumes emissions - COt. CO, NO, *
Expeditious and prompt removal of cvatd materials or
dedged spoils from construction sites.* Exposure of fine-grain
particles to * Replar d andequate sprinkling of water on
dust-generating
wind and vehicular traflic will mnds/piles resulting from
eardhnoving activities and civillikely rsult in a decrease in air
wrks.quality. * Good housekeepgi for all constructiwo affected as
and
workpla.* Control of motor vehidcle and equipment ions* Use of
protective gear by all workers.
Water Polution and Soil Erosion * Provide tempowy dainage and
stoage failities for excavtionsoils, for fuel and oils needed for
equipment
* Siltation * Carehfl and rational plnning of construction and
post-construction phases of the prcect
* Maintesnce of adeae drnagp system.
* Noise from operation of construc- * Eect temporay sound barrie
around the work sites; avoidtino equipnt woud be about 70-
simultaneous use of heavy equipment; limit Jaytime work,80 dBA at
10 m; 50-70 dBA at 30 vebicle speed at 20 kph; egular maintenac of
quipmetm. * Use of apppruiate mufflers and sound proofing of
construction
machineies, quipment, and engies Use of apprpriate
shock-absorbing mountings for mwainy.
. Establshment of buffer zones and noie zones
* Temporary Dlisruption of Traffic * To the extent possible,
feeder and coUecon sewer lins will beFlow located along secondary
sbeets
* Scheduling and increasing input resources so that period
oftmffic disruption in primay roads are reduced.
* Coordinate with city tmtEc management office and the PNPTrafic
Management Command
* Clear diretional signs and barriers in case traffic rerouting
isneeded.
* Public Information campaign.
Environmental A.ssessment Report: Davao Citv 8
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________________________ Operation PhasePotntial Impact &
Risks MltigaZion Action
* Envuroncntal hazards due to * Carefully designed
post-construction mantenance, contingencvaccidnts and man-made or
natural and momtonng programs.disasters. * Well designed plan for
detection of accident or natwal events
* Breakdown or malfunction of the including precautionary and
remedial measures to besewer lift station will increase level
taken/obsavednof pollution at the mouth of Davao * Adequate plans
for environmental rehabilitation, clean-up,River as raw sewage will
have to be restoraton, and disposition of temponary strcures and
facilitiesdumped directv. nstIled dng the construition phase.
Water Pollution * Upgrade laboratory facilities of the Davao
City Water Distnc tobe able to undrtake waster analysis.
* The effluent dischage point of the * Following the bubble
concept, wastewater discharged into Davaotreaument plant is
affected by tidal River shaL in the lng-tem, conform to the water
qualityconditions (estuary). sadards established by the Department
of Envionment and
Natual Resources as set foath in DAO No. 34 and 35, RevisedWate
Usage nd Clasification/Water Quality Standards andRevised Effluent
Regaltions of 1990, respectivly.
* A dispersion/dilution modelig study will be conducted to
priorto cating the outall. Treted effluet discharge to Davao
Rivershall be timed based on tidal conditions. The adopton of
theAUPS pmcess for the treat plants should result intoatainment of
effluent stands.
* Investiating the possibility of rchbaging the acquifer
withurated wastewate fmn Toril teament plant
* Noise would be at about 65495 * Establshment of buffer zones
and noise zones.dBA, pnncipally coming frotmsptage trucks unloading
at theponds-
* Odors (organic and sulfit com- . Maintenance of greenbeit
zones and vegetation.poumds mainly from the trucks * Pvison of
ladscaped open sscs which wiU impWrove theunloading seWe) aesthtch
of the ae by plantiung the gen stnps with approprate
plant or tre speci
Manasement and O&M of the System Institutional:* Management
Conttact with DCWD which has proven utility
* Poor maintenance of pumps management and operations capacity.*
User consltation at detailed engining d...agn stage to isure
* Low connections COODeCtiOn.* Sewerage stcharge should be
sufficient to provide inctives for
DCWD to maintan system.* Requie M&E repoing to the DENR and
LWUA.* Explore feasibility of BOO/BOT contrats for recretional
actvities in unused lands at treatmet sites.* Provide adequate
training of DCWD and city staff.Retulatory:
* Require compulsory connection for all commecial, indusial
andhigh domestic water users.
* Utilize Public Perfornance Auditing system being set up byDENR
to monitor advere impacts.
Technical:* Provision of adequate maintenance eqwupment and
spares with
DCWD.
Environmental Assessment Report: DavaooCity 9
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Monitoring and Implementation Arrangements
Construction Phase
Ambient air quality measurements will be undertaken near
construction sites. This will bemostly near locations where sewer
network is being laid and treatment plant sites. Whenselecting
sites due consideration will be given to sensitive receptors like
schools, hospitals,houses etc. Total suspended particulates (TSP)
will be measured once a fortnight, for 8 or24 hours, over the
construction period.
Noise wiU measured at the same locations as TSP. Leq and L9o
values will be measuredand recorded.
Overation Phase
Receiving water quality will be monitored by the Environmental
Management andProtected Areas Service of DENR. The local Regional
Technical Directorate agency iscurrently monitonng the status of
Davao river and estuarne water quality on a monthlybasis. PMO will
collect information on present conditions, observed changes in
pollutionloads etc. It should be noted that all the pollution load
will not be removed and theproposed sewerage infiastucture will
greatly reduce the problemn. Once the plan becomesoperational, the
operator would be required to set-up a laboratory and measure
theefflluent quality.
Treatment Plant Operator will institute a monitoring program to
measure the effluentdischarge. Daily representative values of PHK
5-day BOD, COD, Total Nitorgen andTotal Phosphorus will be measured
during the start-up period. Once the plant operationsstabilize,
weekly measurements (24-hourly basis) will be taken.
Quaterly reports showing the trends of effluent discharge and
receiving water quality willbe reported to the PMO and DENR
Regional Office.
Environmental Assessment Report: Davao City 10
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Table 2Summary of Responsibilities and Timetable for the
Mitigation Plan
Actiw* P-R_PM t Sbu Camp'
Sewoe ECC clec fSom DENR. CPSO-LW%'A De.itre 196 mUrdh 1997
CoUsei refe ce amb.a ai poamasi City PMU. wih DENR ional Mwdh
1997 May 1997dthe Propose nm pit aim at office
Pmj cti
Enae that the bid doamui imcue PMO Mwrb 1997 Mav 1997p-v for
mnuution ndr the reap-d-lity ofthe comacor re,w coeuataoe workpait
to amin co.qgiwAnc with -kvirunatal inupon- Pisa -_ _ _ _ _ _ _Tram
opwann on O&M paciem & hw_h% PMO and CPSO-LWUA Deember 1997
April 1998
the Dano City Wer Dwit Dina_
Conduct mi. coemutwicsod udennatn Pn je City PMU. with ance May
197 DeaihercaNVIFg ofNGO. 1997
Monitor and repwt on co_pliance. PMO Bi-anl basis Bial bai
LWUAI,vrC:.tIWDDP%SOICM.W* 19. 19974:224 PM
Environmental Assessment Report: Davao Citv 1
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I I
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1. INTRODUCTION
In the Plilippines, the typical urban aea/built-up arm is
characteized by a heavy concentrationof actives, both conmiercal
and industrial. It is also the area where the dnsity of
populationis at it's peak- These areas are also the sites where the
production and consumption of raw andprocessed materials could be
found. Consequently the, pressr on the life support systems inthese
areas are far hgh than the suburban and nual areas. Adverse
eirmnmental conditionssuch as the generation and similarly the
diLharge of wastes into the envirornent is common inurban and
built-up areas. Unfortuatey, the amount, type and concention of
wastegenemed exceed the capabiity ofthe local evronm to absorb and
assimilate then. Thecariying capacity ofthe life support systems
are streched to the limits. The urgency ofestabishing colection and
treatment methods which will prevent adverse impacts to the
healthand well-being ofthe residets, and to the ecological systens
which sustain them cannot beignored and ovated.
The provision of a cost-efective calized watewater coDection,
treament, and disposal isthe primary objective of the proposed
WacrDi0is DewlopmaU Project. The proposedproject will assist the
local goverets of Dagupan, Calamba, Laguna, C4gayan de Oro,Davao
City and Cotabato City, in finding solutions to the problem of
sanitation.
Most urban centers in the Philippines rely on individual septic
tank systems for thetreatment and disposal of wastewater from
domestic and commercial buildings. However,the designs for such
systems is often inadequate. Facilities for land disposal of
effluentsfrom the septic tanks are generally absent. Hence the
partially treated septic tank effluentsflow directly into stormn
drainage systems and other receiving bodies of water,
therebyexacerbating an already grave pollution siuation.
There are several possible options for addressing this problem,
including imnproving thedesign of the septic tank system with the
installation of soil absorption systems. But anenvironmentally
sound alternative that is cost-effective and captures econonies of
scale isto connect individual properties directly to a sewerage
system for the collection, treatmentand disposal of the urban
wastes.
Better sanitary conditions will thus be experienced in the areas
served by the sewerage,drainage and sanitation systems. This will
reduce water-bome pollution and water-loggingwithin the cities and
in the surrounding water bodies, thereby bringing health benefits
tolocal populations. In Davao, Cagayan de Oro and Calamba cities,
pollution from humanwastes have affected recreational areas, such
as beaches and lake front areas. Projectinvestments in wastewater
collection and treatment wi1l also have positive benefits intermns
of improving prospects of saving the remaining beaches for the city
residents. The
Environmental Assessment Report: Davao City 12
-
construction of the systems will protect shallow groundwater
aquifers from contamination,particularly in Toril area of Davao
city, which forms the source of the city's water supplysystem.
Overad Approach of the Proposed Project
The proposed project follows a demand-based approach, in the
sense that facilities will beconstructed only if they conform with
the preferences of local stakeholders, and servicesconform to their
respective willingness to pay. The stakeholders represent the
differenttiers of organizations from the City Council and Barangay
(part of the formal LGUsystem), to the more informal purok,
neighborhood and household levels. During projectpreparation, the
idea of involving communities in the planning process was
field-tested inthree barangays of Davao city, and found to be quite
successfil. The basic decision-making process is as follows:
(a) For the capital-intensive trunk system, consisting of the
maintransportation sewers, primary drains and wastewater treatment
facilities,the project design and implementation plan has to be
approved by the CityCouncil, because the latter is responsible to
repay the loan (see Annex 3 onFinancial Aspects).
(b) For the feeder system, consisting of collector sewers,
secondary drains andon-site sanitation facilities, barangays and
local neighborhoods will beassociated with the planning and
implementation program. The designcritena have been simplified, so
that the feeder systenm can respond to localpreferences and
willingness to pay, rather than be bound by anyconventional sewer
design critena used in industrialized counties. Detaileddesign will
be conducted through a participatory process.
Given the capital-intensive nature of the investments, the
proposed project is only theinitial phase of a program to improve
the sanitation infrastructure through a strategicplanning approach
that involves a mix of on-site and off-site wastewater
collection,treatment and disposal. Choice of initial service areas
for sewerage has been confined tothe Central Business Districts or
Poblacion areas because these are the major contributorsto
municipal wastewater poliution. The only exception made is in the
case of Davao City,where a second area of high growth prospects
(Torii) has also been included on therequest of the LGU.
The project will construct a sewer network that will discharge
sewage to a verticallyintegrated pond system designed to treat both
sewage and septage. In each of the cities,with the exception of
Davao, the treatment site was selected in areas free
fromencumbrances.
For the sanitation and drainage components, the entire city has
been included in theproject area, with final selections being made
on the basis of demand. On-site treatment
Environmental Assessment Report: Davao City 13
-
systems through the construction of VIP latrines, pit latrines,
pour flush toilets and septictanks will also be constructed if
there is demand from property owners. For thoseproperties with
uncertain land tenure (as in squatter settlements), the project
will financethe construction of communal toilets, to be managed by
NGOs and/or the private sector.The specific location of these
facilites will be driven by the willingness to pay for theservices
by beneficiaries at the barangay level, provided of course that
these are technicallyfeasible.
The reconmnended solutions for wastewater treatment were arrived
at after an intensiveprocess of evaluating alternatives during the
project preparation in order to achieve costeffectiveness and
acceptability. The altemnatives considered were
anaerobic/facultativePonds, modified lagoon systems and mechanical
treatment. In all the five cities evaluationof alternatives
indicated that the modified lagoon systems, despite having a higher
O&Mcosts compared to anaerobic/facultative ponds (as it
requires mechanical aerators andrecirculation pumps) was
appropriate. Details are available in project files. The
selectedoption met the following criteria the effectively:
(a) Minimize overall pond area required
(b) Minimize odor production
(c) Meet DENR effluent quality criteria, including fecal
coliform reduction
(d) Minimize sludge production rate
(e) Maxize potential to use surrounding land for recreational
purposes
Environmental Impact Assessment
This Environmental Inpact Asmnent Report for Davao City has been
prepared inaccordance with the PresidentialDecre No. 1586 othewise
known as the Env SnenatImpact Assesment Law and Deprtent f
bironment and Natol Resoucs RevisedAdmirnew Order Nos 36, the
Revired Water Usage and Clamfication/Water QuabtyCriteria and Rev
sed Effluent Regulations of 1990 respectivd, and World
Bank'sOperatonal Directve 4.01 onEfvirnraentAsessmeni. The revised
Administrative Order36 for Environmental Impact Statement System
issued in 1996 is comprehensive and iscompatible with the World
Bank's Operational Directive 4.01. It outlines the procedureto be
followed by environmental critical proiects (ECP) and projects to
be located inenvirornental critical areas (ECA). in preparing
environmental impacts statement (EIS)'.ECP and ECA are defined in
the AO It should also be noted that that local ordinances
andregulations governing projects of such nature have been taken
into consideration in preparingthis report. Similar EIA reports are
being prepared for the other 4 cities.
This is the tenn used bv DENR and refers to the standard
Environmental Assessment Reportrequired by the World bank as per OD
4.01
Environmental Assessment Report: Davao Citv 14
-
Ths report has been prepared by a team of local conltants under
the aegis of the Local WaterUtilities Adminisration (LWUA) and the
Davao City Govenunent. Much of the work relaingto the environmental
impact analysis was undertaken as part of the feasibility study
done by C.Lotti and Associati. Consultation with the community is
an on-going process. The sanitationcomponent of the project will be
executed in a participatory manner, and detailed guidelineshave
been spelled outL
LWTUAJJaC. IWDDPiCK PJDOCAc 19, 197 4.26M
Environmental Assessment Report: Davao Cty i5
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2. BASELINE ENVRIONMENT - DAVAO CITY
Introduction
This chapter is in two sections. Section I profiles the existing
environmental situation inDavao and Section 2 analyses the water
pollution impacts (historical) of uncontrolledsewage discharge.
Section I - Existing Environment
2.1 Land Reources and Use
Davao City, the major development center in Mindanao, is among
the highly urbanizedcities in Mindanao. The city is situated in the
west central portion of Region x) inSouthern Mindanao, bounded in
the north by the Municipality of Kapalong, Davao Pro-vince; in the
northeast by the municipality of Panabo, Davao Province; in the
south by themunicipality of Sta Cruz, Davao del Sur; in the east by
the Davao Gulf, in the west by Mt.Apo and North Cotabato; and in
the northwest by the province of Bukidnon.
Davao City is approximately 950 kdloneters southeast of Manila
It is the largest city inthe Philippines in terms of land area
(244,000 has.). The city is divided into threecongressional
districts which is further sub-divided into eleven (11)
administrativedistricts: Poblacion, Talomo, Agdao, Buhangin,
Bunawan, Paquibato, Toril Tugbok,Calinan, Baguio, and Marilog for
efficient and expedient delivery of basic services. It hasa total
of 180 barangays. (See Figure 2.1)
Table 2.1 shows the Land-Use in Davao City based on aerial
photos taken in 1994 and asplotted by the City Planning and
Development Office, Davao City. Table 2.2 presents theUrban
Land-Use in the city.
2.2 PhvsioMraohv and GeoloRy
The topography of the area is relatively flat and rolling. The
soil is very rich and fertile asevidenced by the agricultural
activities in the area. The area has undergone physiographicchanges
in recent times with the southern portion expanding due to
deposition and thenorthem portion being eroded. These natural
processes were direct results of the actionof the Davao River.
Environmental Assessment Report: Davao Citv 16
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T Canowo C. * /X" ngan~~~~~jnmnI,-
TogokpcA a~~~~~ mips .. . -/~No,uuIgngo ~ ~ ~ ~~
~~~~~~~~~~~~~~~~~~ancoGlugn SinfOl 7;019
-do" %,~~~~~~~' ~gbnc~
*\'..lManmwbbuIon s VacuA ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ %
a vane ~~~~~~~~~~* AIO \:-N~~~~~~~~~~~~~~.~~~4~~~ , Miasma
~~~~~~~ ~ i/hre\¶ind-
gokp- rm~~~~~~~~~~~~~~ u Mandul "'.0 ribun~~~~~~
af .2-8 ~ ~ I*AII I~If
A0~~~~~~~~~~~~~~~~~~~~~oi
0 foe"'liLn~ ~ ~ ~ ~ ~ ~~~~~~~~~~~OTNiA EWRG%
%~~~~~~~~~~~~~~~~~~~~~~EVC RA
-
Clastic sedimentary rocks are the most common outcrops in the
City. Limited outcrops ofvolcanic rocks are found in the extreme
western part of the City. The most imposinggeological
characteristics within the city are Mt. Apo and Mt. Talomo. These
inactivevolcanoes account for the steep slopes west of the city and
also the radial drainagepatterns found along the slopes.
The geologic history of Davao City could be traced back to the
pre-Tertiary period ascharacterized by the basement complex rock
unit located in the northernmost section ofthe city. The basement
complex was exposed during the pre-Tertiary period and remainedso
until the sea covered the area during the mid-Tertiary period
resulting to the depositionof the Kabigtican Sandstone. Further
encroachment of the sea resulted to the depositionof the Upian
Lirnestone and the Masuhi Sandstone. During a period of regression
in thelate-Tertiary period the Mandog Sandstone was deposited.
The volcanic activity of Mt. Apo and Mt. Talomo, as well as of
other peaks to the north,dominated the post-Tertiary environment
resulting to broad expanses of volcanicdeposition west of the city
(CDM, 1994).
2.3 Climate
Davao City is characterized by a mild tropical climate with no
pronounced dry or wetseason, suitable for year round agricultural
production. The lowland areas are faidywarm, however, the
hinterlands, especially in the areas of high elevations, such as
Calinan,Baguio, Paquibato and Marilog districts experience cooler
temperatures throughout theyear.
The average annual rainfall is 1,749.8 mm and is evenly
distributed throughout the year.The City being situated outside the
typhoon belt, makes it an ideal place for the culture ofexotic
fuiits such as durian, mangosteen, marang, pomelo and other
agricultural produce.The City has an average of 168 days of
rainfall. Appendix 2 shows the climatologicalnormals for the city
of Davao.
2.4 Hvdrologv and Water Ouality
The receivin; body of water for the treatment plant is the Davao
River. As per the De-partment of Environment and Natural Resources
Classification, the upstream portion ofDavao River is classified as
Class A while the downstream portion is classified as Class B.
The portion of the river where the discharge point of the
proposed treatment plant shall belocated exhibits the
characteristics of an estuary. The area is highly influenced by
tidalfluctuations, i.e. the flow of the river reverses during high
tide. Table 2.3 shows the waterquality of the Davao River as
monitored by the Environmental Management Sector of theDepartment
of Environment and Natural Resources Region 11. Sampling data
extendfrom February 1990 to May 1996 at irregular intervals. Hence
a time series could not beconstructed.
Environmental Assessment Report: Davao Citv 18
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Table 2.1: General Land-Use
Land-Use Area (in Has)
Built-up 10,195
Agricultural 187,480
Forest Land 46,325
Total 244,000
Table 2.2 - Urban Land-Use
Land-Use Area (in Ha)
Residential 4,055.25
Conunercial 782.24
Industrial/Agro-Industrial 836.48
AgrialturalIdletVacant 21,648.78
Marine/Fishponds 179.20
Institutional 477.60
Open Spaces, RecreationaL etc. 196.80
Structures/Utilities 48.00
Dumpsites 1.28
Total 28,225.61
Sourc City Deveopmmt PIamg Offwr, Davao CitY
Environmental Assessment Report: Davao City 19
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Table 2.3
Results of Physical and Chemical Analysis of Water
Davao River, Davao City
Date Sampled August 28 1996
Station ID 1: S0m. from the confluence w/ Tamugan River
2: Tamugan River, approx. S0m. upstream from the confluence w/
Davao
River
3: 800m. downsrem from the confluence w/ Davao River
4: Davao River, Mandug Area
S Davao River, Diversion Bndge, Ma-a
6: Davao River, Gov. Genmeso Bridge
7: Davao River, Bolton Bridge
8 Mouth of the River
CharcterisIics 1 2 3 4 5 6 7 18
Color Units 25 10 20 20 20 20 20 20
Tenatue, C° 29 29 29 29 29 29 29 29
pH 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0
Dissolved Oxygen. n's/L 7.1 8.0 7.8 7.6 7.3 7.0 6.6 6.6
BODS. mg/L I
-
2.5 VeUctation and Wildlife
The proposed site for the wastewater treatment plant along the
Davao River is situated ina built-up area. Portions of the site is
planted to cash crops such as coconut trees, rice,fruit trees,
etc.
The floral and faunal characteristics of the area has been
highly controlled by human in-terference. Domesticated animals,
such as dogs, cats, goats, chickens, are found in thearea. There
are no significant, endangered nor rare species of flora and fauna
existing inthe area.
2.6 Socio-economic Aspects
The population of Davao City is distinct because of its highly
heterogenous composition.This was a direct result of the influx of
nigrant settlers from Luzon, Visayas and the otherprovinces of
Mindanao. Based on the 1990 census undertaken by the National
StatisticsOffice, Davao City has a population of 849,947.
The 1990 census listed 159,976 households with an average of 5.4
persons per household.Davao City accounts for 19.0 % of the total
regional population of 4,457,076. As of1990, the population density
of the City is 347.82 persons/sq.km. The urban populationof Davao
City accounts for 73.5% of the total population. This has brought
on increasedpressure for the provision of basic services by the
city.
Section II- Environmental Pollution
As in most other major cities, the urban area/built-up area in
Davao City is characterizedby a heavy concentraton of conmnercial
and industrial activities. It is also the area wherepopulation
density is highest. These areas are also the sites where the
production andconsumption of raw and processed materials could be
found. Consequently, the pressureon the environment in these areas
are far higher than the suburban and rural areas.Adverse
environmental conditions such as the generation and discharge of
wastes onto theenvironment are common in urban and built-up areas.
Unfortunately, the amount, typeand concentration of waste generated
exceed the capability of the local environment to ab-sorb and
assimilate them. The carrying capacity of the life support systems
are stretched.
2.7 Water Pollution in Davao City
The basic geography of Davao City is illustrated in Figure 2.2.
There are several majorpopulation concentrations in the city, each
a source of sewage contamination For nearbysurface and ground
waters. Undoubtedly, the largest volume of sewage is generated in
thearea of Poblacion and Agdao. There are three main drainage
canals in the Poblacion area,all of which empty directly into the
Gulf of Davao. Two smaller drains flow into theDavao River, which
flows into the Gulf between Poblacion and Matina. Agdao Creek,which
extends west to east in the area immediately behind the Agdao
Public Market, also
Environmental Assessment Report: Davao Cutv 21
-
serves as a drainage area as well as a receptacle for sewage
disposal before it flows intothe Gulf.
Squatter settlements in Poblacion are undoubtedly major sources
of sewagecontamination. The highest concentration is in Piapi,
fronting the Gulf, but there are othersettlements lining the Davao
River as far north into Poblacion as the public market
atBankerohan. Before it passes between Poblacion and Matina, the
Davao River traversesseveral heavily-populated zones to the north.
These factors make the river a likely conduitfor large volumes of
sewage.
Other streams drain into the ocean northeast and southwest of
the central city areas, andsome of them pass through significant
population concentrations. Sewage volume in theTori area is already
large, and promises to grow rapidly as population expands
westwardfrom the central city area.
Figure 2.2: The Basic Geography of Davao
Coastal Population Clusters inDavao City
= Population Cluster]Davao R.
aon
. 1Gulf of Davao
Envwronmental Assessment Report Davao Citv 22
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2.8 Environmental Impact of Uncontrolled Sewage Discharge
To analyze the impact of uncontrolled sewage discharge, four
factors were considered:human health, fisheries, recreation, and
land values. The available data is sparse and everyeffort has been
made to capture the magnitude of the problem. The description
follows.
2.9 Health Problems faced by Davao Residents
Sewage contaniination is a prime cause of diarrheal diseases, so
it is not surprising thatthey have been ranked third among causes
of morbidity in Davao City since 1991.However, official estimates
of the actual incidence vary by two orders of magnitude. In1995,
the Davao City Health Office (DCHO) reported a total of 73
medically-confirmedcases of diarrheal disease. For the same period,
the Philippines Department of Health(PDOH) reported a total of 6012
cases - greater than the DCHO estimate by a ratio of82:1!
Comparison with other cities was used for arrived at one set of
estimates. PDOHnumbers have been chosen, because they yield
incidence rates similar to those for Cagayande Oro.
The DCHO has reported diarrhea cases by district. Assuming the
same rate ofunderreporting in each district, the district-level
estimates are given in Table 2.4. Theyindicate a roughly constant
rate of infection (6 per 1,000) across districts, with thepossible
exceptions of Matina and Bunawan. This is confirmed visually by the
scatter plotin Figure 2.3, which shows an approximately
straight-line relationship between populationand PDOH-reported
cases of diarrheal disease. Analysis demonstrates, the critical
pointis simply that health-related priority for sewage projects is
roughly proportional todistrict population.
Table 2.4: Population and Iltestidal Disease by District, Davao
City
Population Diarrheal InfectionPopulation Density Disease
Rate
District 1995 (/hectare) Cases (/100,000
Matina 60,886 34.1 574 940Bunawan 78,563 10.5 328 420Agdao
85,998 154.0 492 570Tonil 94,227 6.3 574 610Buhangin 135,346 12.8
820 610Talomo 148,534 16.6 820 550Poblacion 161,146 137.2 902
560
Environmental Assessment Report. Davao CUty 23
-
Figure 2.3: District Populatioo vs. Diarrheal Disease, 1995
1000
900 . - . -1-- . . ... ........800. . ... :...... .
o .: - -. - .... ~~~~~~~~~..... .. ---.,-,.- + ...:-: * °500 ---
:
Q ~~~~~~~~~~.- :. :.- . :-.-. .-.-.::.----. ... .. :z O
,......................~~ ~~~................
O :- '.' ,,.'. ,,.,-'.,-- '.. ..... .. .. .. ;'
l : ~~~~~~~~~~.:. :-.::-. .:. ... :O -: - - ~~~~~~~~~~~~. --.
--. :.:-:.;.; .-. ; :., -,,-,----. - - . . -.....-
300
200 ... .. . ....
100
00 20,000 40.000 60,000 80,000 100.000 120,000 140,000 160.000
180,000
2.10 Drinkins Water Contamination
Protection of drinking water from natural sources is another
health-related issue which isof concem to the city. The aquifer
basin located in Dumoy (Figure 2.2) is the main sourcefor the Davao
City Water District (DCWD). Its water is notable for purity, and is
ofcommercial interest because it has attracted bottling plants for
several national bea andsoft drink companies. Although the city
could combat contamination with chlorination,this would greatly
reduce the appeal of the aquifer water for the bottling firms.
Almost aOlof the expansion that the DCWD has planned over the next
10 years involves sinking morewells in the aquifer near Toril. When
the assessment began, the city govermment wasconcerned about sewage
contamination of the aquifer. The aquifer is located at a depth
ofat least 800 feet, underneath a layer of hard rock. The technical
consensus at the DCWDis that the aquifer is in no real danger from
sewage contamination by an expanding Torilpopulation. It is
well-protected by its depth.
The situation in Bunawan, however, may be more serious. Bunawan
is in the northeasternarea of Davao City, somewhat removed from the
other populous districts. It sits on top ofthe Mt. Apo catchmnent
basin, which currently provides water for the district through
wellsand springs. The DCWD's master plan doesn't anticipate
extension of water service toBunawan until 2010, so the condition
of the Mt. Apo basin water is a matter of concern.Recent chemical
analysis performed by the DCWD has detected the presence of
fecalmatter in this basin, including fecal coliform and
enterococcus. Although the DCWDreports that contamination is not at
unacceptably high levels, Bunawan has had outbreaksof cholera in
both of the past two years. They may or may not connected to
fecalcontamination in the basin water, but the correlation is at
least suggestive.
Environmental .4ssessment Report: Davao c'tv 24
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2.11 Damnaee to Fisheries
Data for the Gulf of Davao show a significant decrease in the
productivity of localfisheries during the past 10 to 15 years.
Originally, the impact of sewage contaminationon the Gulf fisheries
was considered to be of concern. However, the reported decline
isfor the entire Gui£ including waters well outside any possible
influence from organiccontamination by sewage. It seems mostly
attributable to overfishing, both legal and byillegal means which
include dynamiting and fine-mesh netting. Therefore,
fecalcontamination of coastal waters is probably not significantly
affecting the catch. Theremay well have been some contamination of
fish caught near the city shore, but the impactis difficult to
assess.'
2.12 Loss of Recreational Amenities
The beaches of Davao City have traditionally served the city as
major sources ofrecreation. They may have been particularly
important for poor families who cannotafford travel to more distant
sites in the Gulf For this reason, the contamination ofoffshore
waters by sewage is an important political and social issue in
Davao City.For the Times Beach area which abuts Poblacion and
Matina, it is also not a new issue.In 1985, water samples drawn at
three offshore points yielded the total coliform countsreported in
Table 2.5.2
Table 2.5: Total Coliforn Counts (MPN/100), rimes Beach,
1985
Station I Station 2 Station 3Average 3,263 | 2,692 | 1,784
|Standard Deviation 5,943 5,977 2,293
In Table 3.2, the size of the standard deviations registers the
effect of extremely highcoliform counts in some daily sample
results. Variation of this type is typical, :-4 even inbeach areas
with high average contamination, some days have safe readings
because of thecombined effects of wind and tide. Unfortunately,
there is no way of predicting such days,or informing the public in
a timely fashion. Average coliform counts are therefore taken
asgood indicators of risk, with numbers above 1,000 considered
unsafe for swimming. Thenumbers in Table 2.5 make it clear that the
beach area of central Davao City had becomeunsafe for swimming by
1985, when its population was considerably smaller than it is
now.
lIn a recent survey (Whittington et. al., 1993), the residents
of several districts were asked for their assement oftrends in the
quality and size of fish caught during the preceding 20 years.
Almost half the respondents saidboth quality and size were -much
worse,' but there was no imputation of cause to pollution as
opposed to over-fishing.
The t 98 5 samples were drawn at uitervals between lanuarv 8 and
August 18. 1985.
Environmental .4ssessment Report: Davao Citv 25
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In 1992, public concern mounted with publication of sampling
results for eleven of Davao'smain beaches by the Philippines
Enviromnental Management Bureau (EMB).3 The resultsare tabulated in
Table 2.6 and displayed in Figure 2.4.
Table 2.6: Total Coliform Counts for Selected Davao Beaches,
1992
Beach Average Total StandardColiforms Deviation
Kalayaan 1757 1698Villa Victoria 654 1060Seagull 821 1044Times
(between Saavedra & 1999 2452Bonguyan)Times (in front of
Liberty Beach) 3568 8509Times (in front of Marina Azul) 1607
1158Coaco 1011 828
After the EMB results were published in the local press,
recreational use of Times Beachdropped sharply. Less attention was
apparently paid to the results for other beaches,although some also
registered dangerous levels of contamination. Seagull and
CoacoBeaches had average coliform counts at or near the critical
threshold, and Kalayaan Beachwas substantially beyond it.
Figure 2.4: Population Clusters and Beach Coliform Conuts,
1992
Davao R.
X 0 *0b,4~~~011Coaco
35686 Times Beach
175 Vila Seaul (Liberty)
Kalayaan Victoria Gulf of Davao
3 The samples were drawn between July 7 and November 22. 1992.
at intervals of roughly 4-5 days.
Environmental Assessment Report: Davao City 26
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Since population clusters are the source of sewage
contamination, it is logical to supposethat the condition of
Davao's beaches is closely related to the size of the
hinterlandpopulations whose waste drains into the Gulf Figure 2.5
plots beach contaminationagainst hinterland population and confirms
that the relationship is a relatively close one. Itsuggests that
installation of sewerage and treatment in any of the more populous
coastalareas would significantly reduce the level of risk
associated with swimming at the localbeach.
The study began with the assumption that upstream communities
along the Davao Rivershould be counted as part of the Times Beach
'hinterland,' because the river transportstheir sewage to its mouth
near the beach area. The policy implication of this assumption
issignificant: If upstream contamination were a significant factor,
installation of sewerage inPoblacion and Matina alone would leave
rimes Beach highly contaminated. This wouldeliminate an important
reason for an exclusive focus on sewering Poblacion and Matina
inthe first phase of the project.
However, water quality infornation for the Davao River provided
by EMB suggest.P thatthe original assumption was incorrect.' The
data suggest that coliforn counts are likely tobe in the safe
range, even at the mouth of the river after it has traversed all
the unseweredpopulation clusters.5 By implication, contamination of
Times Beach is due to drainage
from Poblacion and Matina, not to upstream contamination of the
Davao River.
By accepted international standards, the pollution levels
recorded offshore from severalDavao beaches are dangerous for
swimmers. For days with particularly high coliformcounts, one can
expect to see a heightened incidence of waterborne disease or
skinirritation among people swimming at the affected beaches.
However, examination of theavailable clinical health records from
the beach areas shows no signs of such outbreaks.There are at least
two possible interpretations of this finding: First. the people of
Davaomay be accustomed to low-level intestinal disease because
sewage contamination hasmade it endemic. If so, people would not
regard post-swimming episodes of diarrhea asworth a clinic visit.
Secondl] the traditional standards for safe swinniing may simply
betoo conservative, so health damage is minimal. In any case, the
people of Davao Cityhave already registered their own judgment on
the matter. The use of beaches aroundDavao City, and particularly
Ttmes Beach, has decreased considerably in recent yearsbecause
people know that fecal contamination levels are high.
4 Sampling data provided by EMB extend from Fenuxary 1990 to May
1996 at irregu1ar intervais. There arereadings for almost everv
month in 1990 but only for one month, February, in 1995.
5 While the EMB data do not include coliform counts, they do
record measures of organic pollution and dissolvedoxygen. There is
known to be a close relationship between these measures and
coliform counts when the majorsource of water pollution is human
waste. Even at the mouth of the Davao River, the results show
levels ofdissolved oxygen and organic pollution which are well
within the safe range. Thus, fecal coliform pollution atthe mouth
of the nver is unlikelv to be at dangerously high levels.
Environmental Assessment Report: Davao Citv 27
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Figure 2.5: Hinterland Population and Beach Contamination,
1992
Population vs.Average Total Coliforms
3.21.
3.2--.-.1e -/
l g 3.3 .. ............................. - --
]~~~~~~~~~~~M........
2.9
2. . ......2 ....... .........--..
2 54 4.2 4.4 4.0 4.8 5 5.2 5.4
Log Populbtion
2.13 Reduced ftDortunities for Commercial Development
Accelerated high-rise construction and sharp increases in
property values haveaccompanied the installation of sewerage in the
Makati district of Manila and the centralbusiness district of
Jakarta, Indonesia In somne Latin American cities,
central-ctyproperty values are reported to have increased by as
much as 20%/ after sewerage wasinstalled. It would not be
surprising to see similar results in Davao City if sewerage
wereinstalled in the Poblacion distfict. Davao is well-positioned
to become a conmercial hubfor its region, and the city teadership
cleary aspires to this role for the city. Rapidexpansion of
high-rise commercial activity in Poblacion seems very unlikely
unless the areais served by a sewer system.
2.14 Summary of Findings of the Existing Environment
Health-related problems related to sewage contamination are of
uncertain magnitude, butare an important consideration for the city
leadership. The available evidence suggeststhat the rate of
infection is roughly constant across populous districts with the
possibleexceptions of Matina and Bunawan.
The evidence suggests that the absorptive capacity of the Davao
River is quite high, sinceits dissolved oxygen and organic
pollution readings are well within the safe range even atthe
river's mouth. The river does not seem to be adding significantly
to the pollution ofTimes Beach.
Environmental .4ssessment Report: Davao City 28
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Pollution of Davao Gulf near each beach is closely related to
drainage from theneighboring population. Times and Kalayaan Beaches
presently have the worstcontamination. Pollution reduction will
depend on the proportion of the local populationwhose sewage is
treated or safely removed from septic tanks.
There is no concrete evidence of health damage from beach
pollution, even at levels whichare quite high by international
standards. Nevertheless, there has been a sharp reductionin beach
visits as Davao's residents have become aware of the contamination
problem.
Dumoy Aquifer is in no danger of contamination, so Davao's main
drinking water sourceand commercial beverage production are not
likely to be threatened by sewage for theforeseeable future. The
Mt. Apo catchment basin, which serves Bunawan, is alreadysomewhat
contaminated; there have been two cholera outbreaks in the district
during thepast two years.
Fishing productivity in the Gulf of Davao has declined, but
sewage contamination has notbeen a significant factor.
Commercial development in the Poblacion is repressed by the
absence of sewerage.Installation of a system would permit high-rise
construction and a significant increase inproperty values.
LWTVAICrC:1WDDPHAPhR.ZDOCIaRdk 19. 97 4:25 PM
Environmental Assessment Report: Davao Citv 29
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3. PROJECT DESCRIPTION AND ANALYSIS OFALTERNATIVES
Introduction
This chapters begins with an explanation of the rationale of the
proposed project and thengoes onto describe the project. The main
components - sanitation and scheme aredescribed separately.
Descziption includes the analysis of alternatives considered
inamving at the final choice. The chapter concludes with the
recommended design and plan.
Section I - Project Rationale and Objectives
Chaper 2 describes the existing enviromnental sintation in
Davao, and illsrates theworsening health impacts caused by the
uncontrolled discharge of sewage. Less than 1%of urban Davao has
piped sewerage. There are no treatnent and disposal facilities
forseptage removed from septic tanks. Septic tank soakaways and
overflows enter the drainsand the groundwater.
The proposed project is, therefire, aimed at addressing the
problems of inadequatesanitation and sewerage in the City of Davao
by providing sustainable sanitation andsewerage fcilities, thereby
reducing public health risks and environmental poilution
fromwastewater sources. The project is designed also to provide a
learning experience forfuture expansion of sustainable sanitation
services for tne city as well as for other cities.The selection of
final project design is driven by: (i) demand-based approach, (C)
level ofwastewater treatment to be achieved; and (iii) the need for
protecting the enviromnent.
Section II - Sanitation
Proposed Facilities
The sanitation component will include the construction of 140
communal toilets in thePoblacion area. The sanitation works were
based upon an identified deficit of sanitationfacilities of 37%.
The location of the communal toilets is not defined yet and will
dependon the consultation of potential beneficiaries. The areas to
be served by the communaltoilets may include public areas such
markets and low-income squatters or blighted areas.
Envwronmental Assessment Reporr: Davao City 30
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The possibility to construct on-site facilities is site
specific. As the majority of squattersare located on government
owned property, that is, along river banks and shoreline it
isunlikely that communal toilets, with on-site disposal will be
technically feasible. In theselocations communal toilets will only
be feasible if there can be a direct discharge to aproposed
sewer.
The sizing of the facility is dependent upon the depth to
groundwater, the permeability ofthe ground and the availability and
cost of land.
The objective is to construct the communal toilets in areas
where, through publicconsultation, there is an established demand
and willingness to pay for the service.
The arrangements for construction and operation could take many
forms such as:
(i) City constructs and operates;
(ii) City constructs and contracts out the operations either to
a private company or tothe local conumunity the facility is serving
through a leasing arrangement;
(iii) Construction and operation contracted through a concession
arrangement.
It is recommended that arrangement (d) be given preference over
the others, particularly ifthe local community is willing to
operate the facility.
The different arrangements should be eamnined following
consultation between the Cityand users, in order to implement the
preferred option. Then following a monitoringpeniod, the more
successful operation can be repeated. A balance has to be
soughtbetween affordability to construct (the quality) and
willingness to pay. The facility has tobe made "attractive" to the
users and provide the service they require and, therefore,
inselecting the option the following aspects should be
considered:
D Site - central location to proposed users (designed to serve
250 users, orapproximately more than 40 properties);
- proximity to a proposed sewer line, if any, of the land area
required(including for septic tank/soakaway)
- availability of water supply,
- availability of power supply;
- area not prone to flooding.
* Services - need for inclusion of showers/laundry
facilities.
* Design - attractive to users;- clean, odor/insect free;
- well lit; good security;
- facilities designed for intense usage; need to be functional
and durable.
Environmental Assessment Report: Davao City 31
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Cost Estimates
A. Capital Cost
The capital cost for the sanitation component is as follows:
Facifity ~ costBefiarsFacility (P million) | l
Communal Toilets- Construction 44.57 35,000
-Land 8.30Total 52.87
The construction cost includes 5% physical contingencies. The
cost of engineering hasnot been considered on the assumption that
the design and construction supervision can behandled directly by
the City's concerned department because of the simplicity of
thestructures.
B. Operation and Maintenance Cost
Annual O&M costs for each communal toilet has been estimated
at P192,780. This wouldrequire an user fee of about PL .20-1.40 per
visit- on the the assumption of 250 personsusing the facility twice
daily. It is intended that the cost of O&M plus the operator's
feehave to be covered by the users.
ImDlementation Schedule
It is assumed that all 140 communal toilets will have to be
constructed during the 5 yearsimnplementation period of the
project. Therefore, an average of 28 communal toiletswould be
constructed annually including the required time for consulation
and design.
Section III - Overall Sewerage Scheme
C'issification
Sewerage refers to the collection and treatment, at a single
location, of water-borne waste(sewage) discharged from individual
properties. It includes the collection and treatment of"domestic"
sewage only and not for any "industrial" waste discharge.
Environmental Assessment Report: Davao Citv 32
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The sewage is collected and transported through a network of
underground pipes, orsewers, to a WWTP, where the sewage is treated
to produce an effluent that can bedischarged to a receiving water
body (river, sea, etc.).
Sewage flows along the sewers by gravity, that is, the pipes are
laid at a slope or gradientwhich is sufficient to ensure that the
sewage will flow without causing blockage.
To minimize depth of excavation, sewers, generally, should
follow the slope of theground, that is, they go downhill. If the
depth of a sewer becomes too deep (greater than5 m) a pump station
would be used to elevate the sewage, either to another sewer or
tothe WWTP. The sewers are divided into two classifications:
* coHlector sewers - sewers connecting an individual property or
group of severalproperties to a sewer located in the street or
right-of-way,
* transportation sewers - those sewers receiving the sewage flow
from the"collection" sewers and transporting the sewage to the
WWTP.
The transportation sewers can be considered as the "main road",
with the collector sewersacting as the "feeder roads".
Seiction of Service Areas
A. Poblacion
The Poblacion area is considered a priority area for the
following factors:
* increasing population density and limitations for on-site
sanitation;
e presence of large commercial establishments, and institutions
such as schools,universities, college, government offices and
hospitals;
* health hazard and ris' posed by Ehe increasing wastewater flow
on the municipaldrainage system;
* high level of urban development with a population density
capable of payingwastewater service charge;
* biological degradation of Davao City beaches. The DENR found
that the majority ofbeaches in the city are polluted with human
excreta and that tests performedindicated positive for fecal
coliforms. This pollution is being caused by the lack ofon-site
sanitation facilities in the peri-urban areas as well as discharge
or disposal ofseptic tanks effluent to the main drainage
interceptor along Dacudao Avenue, andM. Roxas Street, and raw
sewage along the Davao River.
Environmental Assessment Report: Davao Citv 33
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The identified Initial Service Area (ISA) comprises a total of
40 barargays with an area of1,109 ha and a total population of
about 213,000 in 1995 projected to increase to about300,000 in
2015. The ISA is bounded on the west by the Davao River, on the
north by theCircumferential Road, on the east by Cabangui St. and
on the south by the Davao Gulf.
As shown in Figure 3.1, the ISA is subdivided into three stages
of implementation.
Stage I Service Area has been outlined to include those areas
which can provide thehighest impact in terms of improvements to the
environment as well as to the social andeconomic conditions of the
City. The areas included are:
* the city's center including the Central Business District
where commnercial andinstitutional establishments, such as
universities, hospitals, and offices are located;
* the barangays that are highly urbanized and densely populated,
extending tobarangays in Agdao District;
The Poblacion Stage I Service Area has a land area of 486 ha
with a population of about105,000 in 1995 projected to increase to
about 121,400 in the year 2002 (starting ofoperations) and to
147,300 in 2015.
The population which will connect to the system has been
estimated at 60% of the servicearea population. At the starting of
operations, in the year 2002, the system will serveabout 72,800
users, with 13,480 connections, projected to increase to about
88,400 usersin 2015 with 16,370 connections.
The figure that 600/o of service area population will connect to
the system is based on theassumption that 85% of the population
(year 2015) would be connected to the DCWDsupply system, and of
those, 70% would be connected to the sewer. Expansion of thesystem
would be dependent upon the number of sewer connections and the
sewage flowfrom each co.nection. The capacity of WWTPs and pump
stations would have to beincreased once the 60% design flow is
reached. This .aay or may not correlate to theactual connected
population.
B. Toril
Toril district was declared an environmentally critical area by
the City because its aquiferis the source of the water system
operated by the DCWD. The majority of the populationin Davao City,
including the Poblacion and Toril areas, rely on the water supphed
by theDCWED for domestic use, which is drawn from the Toril
wellfields. Its selection was,therefore, based on the priority need
to protect the aquifer and on the long-term benefitsto the
environment, and to the people that may be adversely affected by
the impact ofwastewater polluting the aquifer taking also into
account the rapid urbanization of Torildistrict.
Environmental Assessment Report: Davao Cutv 34
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lli AcJ ' i
,2~ ~ ~ ~ ~ ~~~g .1,j. VL,YN A I>&f-
ri- . 'Mr.,SnirE t
6L~~~~~~~~ :_ ___ _ .~~5.
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~~~~~~~~~~~~~~~~~~~~~.r
*-~~~~.I5
/ 7P4~ 'I , I I ..I-t V 1.4
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;i .. :e VWTP~ ~ ~ ~ ~~~~~~~~~~~~~~I TI.s-09
RECLAMIATION " ~ ii"reIPLIEo IS'
- I .~~~~~~~~~ DivA.) ~~~~~~~~~~~~IiLF ~~~~~~Figure 3.1
C ~~~~WWTP ... .PIIU (ION S['A[RAGF.
SEVIWIE AnEA
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~~ % !1 -. ' i,,X>X. s s A'tt'
.E.,;~~~~~~~~~~~~~~~~~~~~~~~~~
W - > - . ;r - X j ̂ . a % S. j;. X ,,--$ J *
-~~~~~~~~~~~~~~~~~~~oo-3 * rJ l t ** > "vx,*wx1,-w.,, ,^^> ,_
¢ | 0+~~~~~~~~~1i ,1 .3] \. "\ 28'9A N }} X~~A
B '; I \ >8; lty
-
The identified Tori ISA includes the three barangays of Toril
District, namely, BarangaysToriL Daliao and Bayabas Crossing. It is
bounded on the north and west by LipadasRiver, on the east by
Barangays Lubogan and Talomo, and on the south by the DavaoGulf. It
has a total land area of 707 ha and 1995 population of about
30,500. The area isa typical residential area with scattered
commercial and institutional establishments.
As shown in Figure 3.2, the Toril ISA is subdivided into three
priority stages ofimplementation.
The Toril Stage I Service Area has been outlined to include
those barangays that: (a) arehighly urbanized and densely
populated, where the commercial and institutionalestablishments are
located; and (b) can provide the highest impact in terms
ofimprovements to the environment as well as to the social and
economic conditions of thedistrict.
The Tori Stage I Service Area has a land area of 215 ha with a
population of about14,000 in 1995 projected to increase to about
15,900 in the year 2001 (starting ofoperations) and to 19,700 in
2015.
The population which will connect to the systetn has been
estimated at 63% of the servicearea population at the starting of
operations, in the year 200 1, or about 10,1 00 users with1,868
connections. In the year 2015 100% of the service area population
will be servedwith 3,642 connections.
For Tori the connection factor applied is to gradually increase
the connected populationto reach I00% in the year 2015. The aim of
this scheme is the protection of theunderlying aquifer, therefore,
the system has been designed for the connection of allproperties to
the sewer system.
Potential Treatment Plant Sites
A. Poblacion
The strategy to identify potential treatment plant sites for
Stage I was:
* take advantage on the availability of small parcel of lands
with minimal number ofsettlers, if not totally vacant;
* divide the system, as recommended in the 1994 Feasibility
Report, into smallercatchment areas considering the potential
treatment plant sites, as well astopography and drainage
characteristics.
Availability of land for a wastewater treatment plant to serve
the Poblacion Area is amajor issue in planning the sewerage system.
Potential lands are either occupied withnumerous squatters, as in
the case of the original Bucana site, or, owned by private
Environmental Assessment Report: Davao Citv 37
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individuals who either have no intention to sell or are
demanding a high price. Other siteshave limited area which could
not accommodate the treatment plant proposed in the 1994Feasibility
Report.
Several potential sites, including a reclamation area along the
Davao Gulf shore, have beenidentified and their suitability and
availability reviewed with the City Planning Department(see Figure
3.1 (4.2). Most of the identified sites were of a small area and
have high landvalue. On the overall, the site along the Davao River
appears to be a good option sincethe area is sparsely populated and
requires minimal resettlement which can be achievedwithin the samne
area.
To evaluate alternative schemnes the following sites have been
considered:
(i) Bucana which was proposed in the Feasibility Report and, as
already mentioned,would require the relocation of a large number of
families. The land value of thearea has been indicated by the City
Planning Department at PIO,000/sq.m;
(ii) Davao River which, as discussed above, would require a
minimal resetdement offamilies with a land value of A1,000/sq.m as
indicated by the City PlanningDepartment;
(iii) Davao Gulf shore which is an area intended for reclamation
by private investors.The land that can be made available for a WWTP
would be limited at an estimatedcost of 10,000/sq.m.
B. Toril
Two sites have been identified (see Figure 3.3 (4.3)) by the
City Planning Department, asfoilows:
• Daliao - Located southeast of Toril, the site is owned by the
National Govermnent.There are several large warehouse structures
located on the site. However, theWWTP can be located to mininize
the need for demolition The City believes thatthe site can be
acquired from the National Goverranent at reasonable cost. A strip
ofland between the site and the coast nas residential development.
A portion of landwill have to be acquired for the construction of
the outfall from the treatment plantto the Davao Gulf
* Lizada - Located west of Toril. The City has proposed to
purchase the area for useas a sanitary land fill where a WWTP could
also be located. Effluent from theWVWTP could be discharged to the
Lipadas River.
The land value of both sites as been indicated at
l1,000/sq.m.
Environmental Assessment Report: Davao Citv 38
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Treatment Process Oitions
For the treatment of sewage to be collected from the Stage I
service area, utilizing eitherone or twvo treatment plants, three
process options were assessed, as follows:
* anaerobic/facultative lagoons;
* modified lagoons;
* mechanical activated sludge.
1. Anaerobic/Facultative Lagoons
This sytem comprises of two or more ponds in series: the initial
anaerobic pondfollowed by facultative pond(s). Each pond is defined
as follows:
* Anaerobic Pond - used primarily as a pre-treatment process for
high-strengthwastewater. They may be used for septage, night-soil"
and high-strengthdomestic sewage. The advantages of using anaerobic
ponds are that theyeffectively decrease the land requirements of
subsequent facultative andaerobic ponds and the accumulation of
large sludge banks in subsequenttreatment ponds is avoided.
- Facultative Pond - are the most common type used for
wastewater treatment.Raw wastewater enters at one end of the pond
and suspended solids settle tothe pond bottom. Over a period of
time, a sludge layer develops that is voidof dissolved oxygen. The
bottom sludge decomposes anaerobically. Abovethe sludge layer, the
pond has a facultative layer that alternates from aerobic,during
daylight hour, to anaerobic at night. The upper layer of the pond
isaerobic at all times due to oxygen supplied primarily by
photosynthesis andwind action. Facultative pond effluent would have
to be further treated forthe removal of suspended solids before
discharging to the receiving water tomeet the effluent discharge
standards.
The Feasibility Report selected this process for the initial
septage treatment facilityand for identifying the land area
requirement for the deferred sewage treatmentplant.
Envur-nmental Assessment Report: Davao Citv 39
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The design criteria for the process is as follows:
* Anaerobic Ponds
- Dual ponds; depth of 4.0 m, side slopes of 3:1; rectangular
with length of 1.5to 2 x width.
- Organic loading of 0.3 kg of BOD/day per cu.m of pond volume.-
Detention time at least 1.5 days.
- Pond volume to be determined by the higher value.
- Assumed BOD removal for subsequent treatment of 65%.
Facultative Ponds
Dual ponds in series; depth 1.5 m side slopes 3:1; rectangular
shape, withlength 2 x width.
Organic loading rate of 400 kg of BOD/day per hectare of pond
surface area(based on 40 g of BOD per capita and 10,000 persons per
ha). Loading rate tobe applied to residual BOD in effluent from
anaerobic ponds.
Detention time to be 6 days, total for all ponds in series.
- Pond volume to be determined by the higher value.
- Estimated BOD remnovals of 70%/o of influent BOD (overall BOD
remnovalsestimated at 900/.).
While providing a treatment system that has a reduced land take
(compared toa complete facultative lagoon system) and utilizes no
mechanical equipment,there are concerns as to its ability to
operate satisfactordy. Concerns raisedinclude:
* Anaerobic Pond
- Will produce odors - particularly if sulfates are present in
the influent.
- Sometimes difficult to manage if pH varies on the acid side.
Processeffectiveness decreases or fails completely. Short detention
period uds toreduce buffer capacity. Once the system becomes acid,
it must be treated withlime or some other chemical to neutralize
the system.
- Removal of sludge required. Frequently depends on severity of
the solids -BOD loading and nature of composition (sludge disposal
was not addressed inthe Feasibility Report).
- Ability to treat low strength domestic sewage and variable
rates of flow.
Environmental Assessment Report: Davao Citv 40
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* Facultative Pond
- Shallow ponds at depths of 1.5 to 1.75 meters subject to
turnover because oftemperature variations or wind and wave action.
Temperature not as much ofa factor in areas of low
fluctuations.
- Anaerobic and aerobic processes tend to be in state of flux
and vacillatebetween stages reducing treatment effectiveness.
- Tends to increase land requirements because of the relatively
shallow depth.
- Limited detention period will not ensure the removal of fecal
coliforms to anacceptable level.
2. Modified Lagoens
The modified lagoon system is a non-structural design which
utilizes earthenconstruction practices to simplify and reduce
construction costs. The system isdesigned to optimize natural
biological processes in order to improve treatmenteffectiveness and
reduce power requirements and chemical additives while limitingland
requirements. The design concept is to minimize sludge production,
eliminatedaily sludge handling and restrict desludging to a long
term 20- to 30-year cycle.
The modified lagoon system is an integrated, multi-stage
biological reactor systemtreating municipal, agricultural and
industrial wastewater. The reactors may berelatively deep and
constructed of compacted earth as open surface pond areas.The
biological reactor has discrete and isolated biological zones
integrated into asingle unit; a deeper anaerobic cell(s) at the
bottom of the reactor, sludge blanketsuspended over the deepened
zone and an overlying aerobic zone comprised ofaerobic bacteria,
algae and a saturated oxygen media provided by a combination
ofalgae and surface aeration.
In many cases the initial reactor is followed by a similar
second reactor operatingin series with the provision to recirculate
to .ne first pond depending on conditionsand circumstances.
Recirculation lends flexibility and buffer (shock loading)capacity
and adsorption abilities with highly variable hydraulic or organic
loadingsor where there is a potential for receiving toxic
spikes.
The primary facultative pond with an aerobic surface and
extremely anoxic internalcells for sedimentation and fermentation
is the initial treatment element in the seriestreatment train. In
this element raw or screened wastewater is introduced directlyinto
the bottom of a relatively deep internal cell(s) where settable
solids aredigested anaerobically. The overflow velocity in the cell
is maintained at a lowrate such that the suspended solids and BOD5
removal efficiency approach 100and 65%. respectively. These rates
are maintained at less than the settlingvelocities of helminth ova
and parasite cysts. Consequently, the majority of these
Environmental Assessment Report: Davao Citv 41
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organisms remain in the cells and are permanently removed from
the effluent.Settled solids in the anoxic cells ferment to the
extent that only ash remains due tothe large cell volume. Hence,
sludge removal is seldom required.
The rising gases and upwelling of wastewater from the anaerobic
cell pass througha thick anaerobic sludge blanket, that is formed
as a result of the fermentationprocess, and remains suspended above
the anaerobic cell. The hydraulic detentiontime in this anaerobic
zone and corresponding rise velocity is variable by designand
nature of the waste stream.
Treatment of soluble waste continues in the overlying aerobic
zone, comprised ofaerobic bacteria and algae. These organisms are
maintained in an oxygenated stateby photosynthesis, recirculation
and surface aeration. The nature of the surfaceaeration creates a
circular motion over the entire pond surface area which in
turnensures an oxygen rich continuity.
Soluble wastewater componen