Border Environment Cooperation Commission
Comprehensive
Sewerage Collection and Treatment Systems Project in Piedras Negras, Coahuila
II. Human Health and the Environment
IV. Financial Feasibility and Project Management
Type
of Project. The project consists the
rehabilitation and expansion of the sanitary sewer system and the improvements
to the sewage treatment system.
Location
of Project. Piedras Negras is located
in the northern part of the State of Coahuila; it is the county seat for the
Municipality of the same name. It is
separated from Eagle Pass, Texas by the Rio Grande; therefore it is located
within the Border Region defined as the 100-km zone on both sides of the
border. The current population in
Piedras Negras is approximately 132,500, and is expected to reach 270,000
people by the year 2018
Description of Project and
Tasks The project consists of improving sewerage services to Piedras Negras,
including the construction of a wastewater treatment plant (WWTP), with a
capacity of 8.22 million galls per day (mgd). In 1998, it was estimated that sewage collection coverage was at
about 80%. The objective of this project is to reach 100% coverage.
The new WWTP will replace an
old oxidation lagoon system that was originally designed and built in the
1960s to handle 2.63 mgd. The existing
lagoon system is operating deficiently due to excessive clogging by
sediments. Additionally, the city has
encroached upon the existing WWTP site, which presents various negative human
health implications.
The population growth rate in
Piedras Negras in the last few years has surpassed the construction of
additional environmental infrastructure, particularly in the sanitary sewer and
sewage treatment. Furthermore, the
parts of the city that do have sewer service in most cases experience problems
because of the age of the system, clogging, lack of maintenance, negative pipe
slopes, and other factors.
The lack of a storm sewer
system is also a contributing factor to the deficient operation of the sewage
system, mainly due to infiltration, which causes overflows and backflows of raw
sewage during significant precipitation events.
The project contemplates the
closure of the existing WWTP, the construction of new collectors, trunk lines,
pump stations, and a new WWTP (activated sludge). The process is shown below.
Compliance with International
Treaties and Agreements. The project will have positive transboundary impacts,
since the effluent will be discharged into the Rio Grande. Its implementation will be in compliance
with the treaties between Mexico and the US, particularly those related to the
International Water and Boundary Commission.
II.
Human Health and the Environment
Human
Health/Environmental Needs. About 96%
of the population of Piedras Negras is served with drinking water through the
municipal public water distribution and supply systems. The water quality complies with Mexican
federal regulations, as set forth by the Mexican norm NOM-127-SSA1-1994. However, within the context of sewage
treatment, the community faces a problem, considering that about 80% of the
residents have sewage collection system. The portion of the population without the
service uses septic tanks and/or privies to dispose of their wastewater.
The Mexican National Water
Commission (C.N.A.) considers various parameters for assessing sanctions
relative to effluent discharge violations.
The effluent characteristics of the existing wastewater treatment
process exceed C.N.A.s discharge limits corresponding to Biochemical Oxygen
Demand (BOD). Additionally, in 1994 the
IBWC conducted a study and determined that wastewater treatment along the
US-Mexico border was deficient and needed to be improved. Thus, the Acuña project will address this
concern.
According to the Health
Department of Piedras Negras, from 1997 to 1998, the number of cases of seven
out of the 13 water-borne related diseases increased in some cases by as much
as 20%.
In 1979 the IBWC (U.S. and
Mexico) formulated Minute 261, which relates to the solution of sanitation
issues along the US-Mexico border. The
sanitation project of Piedras Negras complies with the recommendations
identified in Minute 261.
Environmental Assessment. As
part of the project studies, in February 1999, an Environmental Assessment (EA)
was prepared and submitted before the National Institute of Ecology (INE) of
the Secretariat of the Environment, Natural Resources, and Fisheries
(SEMARNAP). On April 14, 1999, the INE
issued its ruling authorizing the implementation of the sanitation project of
Piedras Negras. Additionally, a
document addressing the requirements established by the National Environmental
Policy Act (NEPA) was prepared.
Presently the United States
Environmental Protection Agency (EPA) has reviewed the above documents and
prepared an environmental assessment (EA) and a Finding of No Significant
Impact (FoNSI). The EA and the FoNSI
are currently undergoing a 30-day public review period. If there are no substantial negative comments
from the public, a final FoNSI will be issued.
It is necessary to have the FoNSI to enable the EPA to approve the
financial scheme relative to the Border Environmental Infrastructure Fund
(BEIF) proposed by the North American Development Bank (NADB).
In March, 1999, the
consulting firm of Consultores Mexicanos en Proyectos de Ingeniería prepared
an EA that was presented to the public on June 18, 1999, to inform the public
about the cumulative impacts of the project.
In the EA, it is mentioned
that some of the activities will take place in urban areas, while the WWTP site
is located in an agricultural field. To
mitigate the impacts, a reforestation program will be implemented to create a
buffer zone. The WWTP effluent will be
discharged into the Rio Grande. The impact of the effluent will be positive,
considering that the BOD5 (30 mg/l) and total suspended solids (30 mg/l) of the flow will
be lower than those currently being discharged. Additionally, the CNA established three sampling points for
determining current concentrations of BOD5 in the Rio Grande and at
La Amistad Dam.
In the EA, there are measures
identified for dust abatement, as well as traffic control measures during the
constructions stages. It is also
important to mention that the effluent (after evaporation adjustments are
applied) of the WWTP will be reused by Mexicos Comisión Federal de
Electricidad, downstream. This action
extends the water supply (from aquifers) for human consumption purposes in the
region.
Compliance with Ecology and
Cultural Laws and Regulations
As part of the environmental
review process by SEMARNAP and other agencies, the National Institute of
Anthropology and History issued a memorandum indicating that there was no
objection relative to the proposed WWTP site.
1.
Appropriate Technology. As part of the complementary report to the Master Plan
for improvements to the water, sewer, and wastewater treatment systems of
Piedras Negras, various alternatives were evaluated. The alternatives were developed and evaluated using a 20-year
planning horizon.
WASTEWATER
TREATMENT
In
accordance with chemical analysis conducted on the effluent, it was determined
that the BOD5
concentration (137.89 mg/l) and the TSS (182.35 mg/l) are within the typical
domestic values. These valves were taken into consideration in the WWTP design
and sizing. It is important to mention
that the WWTP will be financed under the Build-Operate-Transfer (BOT) scheme.
For the WWTP, four alternatives were evaluated, including the no-project
alternative.
Alternative
1 WWT System with Activated Sludge. The process units are as follows:
Influent
Train
Pretreatment,
inlet sump, primary settling tank, aeration tank, secondary settling tank, and
chlorination tank.
Sludge
Train
Aerobic digester, sludge
thickening, and drying bed or press filters.
Alternative 2 Oxidation
Ditch. This alternative is a variation
of the activated sludge process. The oxidation ditch features important
advantages over the oxidation/stabilization lagoon system, due to its high
performance and good removal levels of nutrients. The more notorious disadvantages are the need for qualified
personnel and a higher energy consumption level. Its train process consists of the following components:
Pretreatment, oxidation
ditch, clarifier or secondary settling tank, chlorination tank, sludge
recirculating tank, sludge thickening, and drying beds or press filters.
Alternative 3 Oxidation
Lagoons. The main process train of this alternative comprises pretreatment,
anaerobic lagoon, facultative lagoon, and stabilization lagoon. This method depends heavily on the water and
ambient temperatures. The lagoons,
after extended periods of time, can become clogged and saturated.
Alternative 4
No-project. This alternative was not
considered feasible given the current discharge conditions and the deficient
operation of the existing lagoons.
Excluding alternative no. 4,
the alternatives were evaluated using a matrix with the following parameters:
cost effectiveness, environmental considerations, effluent quality, expansion
features, compliance with C.N.A. regulations, operation requirements, and
public acceptance. Based on the technical analysis, alternative No. 1
(activated sludge) was selected.
SEWERAGE SYSTEM
The sewage collection system
covers just under 80% of the urban area.
The system is composed of 22,103 connections of pipeline and 384 km of
pipeline. The pipe diameters vary from
15 cm to 107 cm .
A study conducted under the
direction of the IBWC (Minute 294) diagnosed the condition of the environmental
infrastructure of Piedras Negras. This
study developed alternatives for the sewage system, using the Master Plan
prepared under the direction of the C.N.A. as the baseline. The Minute 294
study incorporated the recommendations submitted by the Binational Technical
Committee (BTC) of Piedras Negras. The
BTC is comprised of representatives of IBWC (both sections), C.N.A. (Border
Affairs and Regional), EPA, Sistema Municipal de Aguas y Saneamiento (SIMAS) of
Piedras Negras, Comisión Estatal de Aguas y Saneamiento (CEAS) del Estado de
Coahuila, NADB, and BECC.
The alternatives evaluated
included the BOT project with modifications.
Alternative 1
This alternative utilizes the BOT as the baseline, and would provide 100%
coverage for the current needs.
The cost for this alternative
was estimated at US$13.4 M.
Alternative 2 This alternative includes the BOT works in
addition to those proposed in the study prepared under Minute 294. Coverage
under this alternative is 100% for the planning horizon. The estimated cost for
this alternative is US$36.1 M.
Based on the BTC analysis,
Alternative 1 is the recommended option.
O&M Plan. This plan identifies the requirements of
O&M of all unit processes, including human resources, the frequency of
maintenance, and cost estimates. Before start-up of the WWTP and pump/lift
stations, there should be a final O&M plan in place that should include the
sewage collection system.
Compliance with applicable
design norms and regulations. The requirements for construction of the sewer
system have been validated by C.N.A. and corroborated by the BTC.
IV.
Financial Feasibility and Project Management
Financial
Feasibility.
The
NADB is currently analyzing the project to determine its financial feasibility. This analysis will help determine the
contributions for each funding source, as well as credit and/or grant
components, and the ultimate rate structure.
The results of the analysis were presented in a public meeting held on
August 13, 1999.
The
table below summarizes the project construction costs, for the components,
identified by the BTC in June 1999.
Estimated
cost (dollars)
|
Phase I Concession (BOT) |
$23,214,376 |
|
WWTP |
$ 8,036,243 |
|
Lift Station |
$ 651,120 |
|
Interceptor/collectors |
$
14,527,031 |
|
Phase II Mid Range |
$ 8,988,097 |
|
Lift Station |
$ 640,952 |
|
Interceptors, collectors,
laterals, subcollectors |
$ 8,347,145 |
|
Phase III Long Range |
$24,616,165 |
|
Lift Station |
$ 640,952 |
|
Interceptors, collectors,
laterals, subcollectors |
$
23,975,213 |
|
Institutional development |
$ 598,691 |
|
TOTAL |
$57,417,329 |
The required investments for
funding the WWTP and associated collector, subcollectors, and pump stations
have been obligated by the BOT concessionaire.
Estimated O&M Costs
Yearly (dollars)
Concept
|
WWTP |
Included
in BOT works |
|
Personnel services |
$1,216,162 |
|
General services |
$1,150,665 |
|
Maintenance |
$ 646,857 |
|
Supplies and materials |
$ 479,855 |
|
O&M Sewer |
$ 196,471 |
|
O&M Water Supply |
$ 10,321 |
|
TOTAL |
$3,700,331 |
|
|
|
Based on the analysis
developed by the consultant, NADB determined the grant and loan amounts for the
project. For access to each one of the funding sources, their corresponding
authorization processes must be followed.
Financial
Structure
|
Source (dollars) |
|
|
Concession |
$23,214,376 |
|
CNA, State and Local Goverments |
$ 8,401,065 |
|
NADB -BEIF |
$ 8,401,065 |
|
NADB Credit |
$16,802,132 |
|
NADB IDP |
$ 250,000 |
|
Desarrollo Institucional (Otros) |
$ 348,691 |
|
TOTAL |
$57,417,329 |
|
|
|
|
|
|
Rate
Model: The rate model prepared by the consultant was utilized to determine the
impact that the proposed project would have on the user rates, considering
various grant and loan combinations.
The rate model that was prepared by the consultant was reviewed by the
NADB. With the proposed financial
structure, the rates must be increased by 42% over an 8-year period. Thereafter, the rates need to be adjusted
accordingly to accommodate inflation and cost of living. This rate increase will allow the public
utility to face its responsibilities of
O&M, liabilities, investments, and reserves. The average rate will increase from 2.54
pesos/m3 to 3.62 pesos/m3.
Project
Management. The project will be managed by the SIMAS Piedras Negras that has
operated the public utility for several years.
The SIMAS is the agency that will adopt the rate adjustments. The system
is expected to operate in a self-sufficient manner, supporting itself through
user fees.
Comprehensive Public Participation Plan. The objectives of the Comprehensive
Community Participation Plan (Plan) are to ensure that the community
understands and supports the environmental, health, social, and financial
benefits and costs of the project, as well as any changes in user fees. The City of Piedras Negras, with important
contribution of the steering committee, submitted a Public Participation Plan,
which includes the following activities: develop a steering committee to lead
the implementation of the plan, identify and meet with local groups and
organizations, hold two public meetings (one has already taken place) and
develop and final report documenting public support for the project. The
activities carried out thus far in fulfillment of this Plan are detailed below.
Steering Committee: A steering committee was
formed in 1996 as part of the BECC certification process to guide the public
participation component. The committee
has been responsible for disseminating project information and scheduling the
public meetings. Committee members also
met as necessary to follow-up with the public information campaign regarding
the project and related activities.
Local Organizations: The City and the steering
committee have met with business, civic, community and neighborhood
representatives to present the project and request support for the
project.
Public Information: Information about the
project has been provided to the public in the utility bills and at the public
and neighborhood meetings. Information
about the financial aspects of the project was provided to the residents during
the second public meeting held on August 13, 1999. The project sponsor made available to the public the
Comprehensive Sanitation Master Plan and BOT designs, and environmental
information documents 30 days before the public meeting. This information was available at the
offices of the SIMAS. A public meeting
was held on June 18, 1999. There were
over 100 people in attendance.
Public Meetings: Two public meetings have been
conducted. The first public meeting was
held on June 18, 1999, and was properly advertised 30 days in advance. The meeting
covered the technical aspects of the project. The second public meeting was
conducted on August 13, 1999.
Definition and
Principles. The project complies with
BECCs definition of Sustainable Development:
An
economic and social development based on the conservation and protection of the
environment and the rational use of natural resources, but considering current
and future needs, as well as present and future impacts of human activities.
All the environmental parameters have been met
and the culture of reuse of treated water has been realized through the sale of
the effluent to Comisión Federal de Electricidad (Mexico's Power Company). This action will help manage the Rio Grande
Conchos watershed, as well as downstream resources in a more sustainable
pattern. The improvements will help preserve aquatic life in the Rio Grande,
considering that the effluent will have lower BOD and TSS concentrations than
those required by C.N.A.
The
principles of sustainable development are satisfied. These include: Human
beings are the central point of all concerns for sustainable development; they
have the right to a healthy and productive life in harmony with nature. The project complies with the principles
objectives, which are to solve human health problems by improving the sanitary
sewage collection system, and decreasing pollution of the environment and
health risks to the population, through sewerage improvements and sanitation of
wastewater.
Institutional
and Human Capacity Building. For the optimum operation of the Utility an
investment of about $600,000 dollars will be required for the purpose of
increasing the institutional capacity of the Utility (SIMAS). Further, the transition from a lagoon system
to a mechanical technology (activated sludge) will require the training of
personnel. The increase in treatment
capacity will prevent potential sanctions that could occur without the proposed
capacity.
Conformance
with Applicable Local/Regional Conservation and Development Plans. The project will not modify any land use
patters or zones, since most of the sewer lines will be constructed on already
impacted and improved areas. The site
of the WWTP will be re-landscaped to provided for a buffer zone to mitigate the
impacts resulting from its construction.
Border
XX1, a regional environmental plan established by the United States and Mexico,
utilizes as project sustainability indicators the percentage of collected and
treated wastewater, and the population percentage served with water sewer
service. For 1998, these figures were 96% and 80%, respectively.
Natural
Resource Conservation. With the water
leak detection program, water losses are anticipated to drop from 41% to
25%. Furthermore, with the installation
of water meters and water conservation campaigns there will be better results
associated with the conservation of natural resources.
Additionally, there is a contract with C.F.E. for
the sale of treated wastewater to be used in the cooling process of the power
plant. The reused treated volume will
reduce the water drawn from surface or underground sources allocated in the Rio
Grande basin.
Energy
Conservation The selected sewer system alternative will require less energy
since only three pump stations will be needed, which is less than the original
BOT proposal. Although the WWTP will
require a power generation substation, energy conservation measures will be
implemented, whenever feasible.
Community
Development. The new project, with an
investment of $57.4 million dollars, will ensure compliance with federal
regulations for water quality and will benefit the community. The project will also improve the quality of
life and health in the community.
Presently, the existing lagoons pose a health hazard to the neighbors,
considering that the growth of the city has exceeded the treatment capacity of
the plant. The project will help reduce
and eliminate the health biological hazards for the residents and will eliminate
bad odors, biological hazards, and infectious diseases.
Furthermore,
with the construction of the new WWTP, the effluent quality discharged into the
Rio Grande will be improved.