Water Closure Public Sector ( X )

Wastewater ( X ) Rehabilitation ( X ) Private Sector

Municipal Solid Waste Expansion ( X ) Public/Private Venture

Other New Plant ( X )

Lic. Luis Gerardo Higareda Adam, General Manager.

Comisión Municipal de Agua Potable y Alcantarillado de Reynosa, Tamps. (COMAPA)

Pánuco y J. Escandón, Col. Longoria

C.P. 88660, Cd. Reynosa, Tamps. México

Tel. (89) 24-33-16

Fax. (89) 23-34-63

The City of Reynosa lies south of the United States and north of the city of Méndez; the City of Rio Bravo lies east, while the City of Díaz Ordaz and the State of Nuevo León lie west of Reynosa. It is located 26º 04’ 24’’ latitude north and 98º 17’ 12’’ longitude west, and 125 feet above sea level.

The Reynosa sewage system was designed in a separate mode, however absence of a storm water drainage system results in large amounts of rainwater being incorporated into the system. It has both main and secondary collectors in need of repair or replacement due to their age, state of deterioration, corrosion, and obstructions

Approximately 25 percent of the lots that have municipal sewage services provided continue to dispose of their raw sewage via septic tanks and cesspools. These methods must be eliminated in order to avoid further contamination to underground resources and at the same time improve public health.

There are currently thirteen lift stations. Occasionally, when the lift station is overloaded, the collectors operate with a hydraulic load; by reducing the leakage rate, solid waste is then deposited and decomposed causing foul and unpleasant odors as well as corrosion to the pipes. Furthermore, in some cases, when the collectors go into the hydraulic load mode, they leak into public areas. Several lift stations, such as No. 3 and No. 10, have surplus lines that discharge raw wastewater into the collecting bodies.

The City of Reynosa currently relies on an oxidation pond system for treatment of its wastewater and the plant's current capacity has been determined to be inadequate. As such, the water currently being discharged into the Rio Grande River does not comply with required norms. In the future, the treatment plant effluent will not be discharged into the Rio Grande River. The effluent will be conveyed via the Anzaldúas and Rodhe Canals to the irrigation districts.

Rehabilitation and expansion of the sewage system is required and involves replacement of the damaged pipes in the primary and secondary systems; implementation of a maintenance system; expansion of the system to provide service to the subdivisions lacking service and which will use a conventional gravity sewage system; and implementation of a program to incorporate areas that have yet to be connected to the sewage system.

With regard to the wastewater pump stations, rehabilitation and expansion of the plant's capacity is required. Both the electrical/mechanical as well as the civil engineering components must be considered. Also required is the rehabilitation, replacement or expansion of the pressure lines that discharge into the current treatment plant into the new plants.

The current WWTP exceeds its design capacity and requires rehabilitation. In addition, construction of two additional plants will help meet the future planning demands (through the year 2016). The proposed treatment consists in anaerobic ponds followed by a facultative treatment process, similar in design to Treatment Plant No. 2.

Rehabilitation and expansion projects for the municipal drainage system and the treatment plants could be carried out during the course of a 20-year period in four stages:

* The O&M costs are discussed in the financial section of this document

Location of the new wastewater treatment plants has been determined based on the sewage system needs as well as the availability of space. The first criterion used for (site) selection was the plant's location in proximity to these facilities. The second criterion relates to the availability of surface area for construction. Design needs and operational-economical aspects require a large surface area. For this reason, WWTP No. 1, built in 1970, was built at the existing location and there are no plans to change this site in the future. Another advantage to this site is that discharging the water into the Anzaldúas Canal does not present a problem and also avoids adverse transboundary effects by discharging the treated effluent into the Rio Grande River. In addition, the location and design of this facility, ensures that under flooding conditions the Plant will operate safely.

With regard to WWTP No. 2, the drainage system is distributed to convey wastewater to the selected site; this area currently has lots available for construction. Different localization options were analyzed in accordance with the following conditions: extension, location outside city limits, future population growth, urban growth trends, etc. After analysis of the aforementioned conditions, the most appropriate location for WWTP No. 3 was determined to be on the far east area of the city, close to the Reynosa/Pharr International Bridge, outside of the .flooding protected area boundaries.

Location of WWTP's #2 and #3 was determined in the Sub-Regional Territorial Ordinance Plan for Reynosa-Rio Bravo, Tamaulipas, prepared in October 1991. Some advantages to the location of the plants include discharging the treated effluent into the Anzaldúas and Rodhe drains and thus avoiding negative transboundary effects. In addition, the drains are in close proximity to the plants.

Treatment of the municipal wastewater can be carried out efficiently via secondary or biological, and was selected as the most appropriate because it does not require a highly specialized workforce for operation and maintenance. Another contributing factor was its cost effectiveness since, aside from the pumping system for the raw wastewater, does not require electro-mechanical equipment.

A computerized hydraulic model was developed to review operations of the sanitary sewage facilities in Reynosa. This model was used to evaluate the existing system's capacity and to determine what facilities and hydraulic capacity are required to handle the projected flows. The model focuses on the main collector system and incorporates data from the primary sewage system, manholes, and surveys taken with the Global Positioning System (GPS), land use projections, lift station evaluations, lift station discharge pipes, and flow monitoring results.

Similar to the primary system, rehabilitation and expansion sites of the secondary system cannot by defined. In order to provide wastewater collection services, project needs have indicated that the systems must be laid along the city streets to make connections to the different domestic, commercial, service, and industrial users feasible

Due to its characteristics and availability in Reynosa and after extensive evaluations, it was concluded that the most appropriate material for rehabilitation and expansion of the secondary system is PVC. Future assumptions have indicated that the sewage system must be built with tighter restrictions to minimize flow into the collectors.

Immediate consequences of not implementing measure to rehabilitate the current systems will be reflected in the bad condition and low efficiency levels of the pumping systems, sewage system and wastewater treatment system. This situation has a direct impact on human health and the community's surroundings. Leaks tend to flow into the natural ground, contaminating underground resources; water quality will not be adequate for irrigation and will cause diseases in the farming community as well as in the consumers of these products.

In conclusion, not implementing the project will have serious impacts on human health and the environment. Specifically, discharging raw wastewater into the Rio Grande River will create transboundary effects.

The relationship between the environment and community's health/disease level is undeniable. Studies and experiences in countries where high levels of basic service coverage, such as waster, sanitary sewage, wastewater treatment collection and treatment, and solid waste management, among others exist, have demonstrated a significant decrease in the prevalence of infectious/contagious diseases, specifically gastrointestinal diseases. On the other hand, in countries and cities, like the City of Reynosa, where provision of these services is not adequate, high levels of these diseases are present.

The Integral Sanitation Project for the City of Reynosa, Tamaulipas, will clearly address the sanitation problems by providing 100 percent treatment to its wastewater and reach high coverage levels for drainage and potable water. In addition, the treated effluent will comply with Official Mexican Norm 001-ECOL-96, for irrigation purposes.

In the City of Reynosa, gastrointestinal diseases and parasite related diseases have been placed third under general disease rates and are the frequent cause of death among children under the age of five. The first most common disease is respiratory ailments caused by severe changes in temperature and the generation of dust. The ratio between the rates of intestinal diseases and respiratory diseases is approximately 1:5.

The Integral Sanitation Project for the City of Reynosa, Tamaulipas has also complied with the required environmental evaluation issued by the appropriate natural resource authorities. The Environmental Impact and the Finding of No Significant Impact on Cultural and Historical Resources has also been issued.

The project will however cause adverse effects during the construction stages and operation and maintenance of the drainage systems and the wastewater treatment plants. However, the majority of the impacts can be mitigated and prevention and control measures will be undertaken as part of the project.

Transboundary environmental impacts will be positive since the project will not cause potential contamination to the soil or underground or surface water resources.

Specific design criteria have been developed to ensure that changes to the system, such as design, construction, and operation will be maintained throughout the project's projected useful life. In this manner, sewage system service with a useful life over 50 years for the different structural components (pipes, manholes, pump stations, etc.) can be assured and a useful life of more than 20 years can be assured for mechanical equipment.

The estimated current wastewater flow exceeds nominal capacity at the existing wastewater treatment plant (WWTP). Based on service area flow projections, the need for WWTP #2 is immediate while WWTP#3 will be required within the next 5 years.

Development of the Final Design of the Treatment Plant Rehabilitation and Expansion Project also provided analysis of both the treatment plant influent and effluent. Wastewater characterization, drilling, and tests to determine design constants resulted in the modification being proposed for WWTP #1. After evaluating the alternatives, it was concluded that the best option for rehabilitating the existing system was the option consisting in the expansion of the anaerobic ponds followed by facultative ponds modified to piston flow. This option has been developed through the Final Design stages.

In accordance with the information collected during field visits, population projects, potable water and sewage services, city growth plans, land use at feasible treatment sites, and the area topography, different alternatives to expand the treatment system were established. It was determined that the best option for WWTP No.2 is the alternative consisting of anaerobic ponds followed by facultative ponds.

By the year 2001 it has been determined that a third wastewater treatment plant will be required to treat a portion of the 53.6 mgd average wastewater flow that is expected to be generated through the year 2016. WWTP #3 has been designed conceptually and its location will be east of the Reynosa-Pharr Bridge. It will have the capacity to treat 19.4 mgd. The treatment process will be similar to the pond systems and as such, will require approximately 198 acres for construction.

Pursuant to the Ley de Equilibrio Ecológico y de Protección al Ambiente del Estado de Tamaulipas (Environmental Protection Laws of the State of Tamaulipas), the Environmental Department of the State, the Environmental Department of the City and the Potable Water and Sewage Board of the City of Reynosa, Tamps., developed a Wastewater Reduction and Pre-Treatment Program. The program basically consists in the development of a discharge register, follow up activities on discharge quality and quantity; control via implementation of pretreatment systems, and imposing sanctions or incentives based on compliance or non-compliance with requirements.

The primary sewage system in Reynosa is approximately 64 miles in length and includes a sewage drain pipe system whose diameter is 10 in wider. The sites requiring project work were established based on the drainage system evaluation which includes: revision of wastewater plans and system information; field measurements collected with the Global Positioning System (GPS) of manholes in the primary system, and conventional measurements of the system's other components, interviews and field visits with COMAPA staff, inspections and evaluations of the man holes and lift stations, rainfall and duct flow monitoring, system inspections via Closed Circuit TV (CCTV), a Closed Circuit Sonar Inspection Technique (CCSIT), corrosion, sulfur, and hydrogen samples, and a system simulation through the load model.

After reviewing these factors and materials, it was concluded that the most appropriate materials for construction and rehabilitation of the system was PVC and reinforced concrete. Materials used to manufacture PVC and reinforced concrete must comply with CNA standards.

The main corrosion-causing agent in the sewage system is sulfuric acid. Rehabilitation of the sewage system will help reduce the production of sulfuric acid by avoiding water settling and turbidity in the water. However several areas have been identified were this situation may continue to occur and an additional protective coating must be utilized. In areas where corrosion is likely to occur, it is necessary to increase the concrete thickness of the pipe, between the steel and pipe interior, in order to increase useful life. All concrete pipes without the epoxy layers must have a thick wall to provide the concrete with the required "endurance".

To ensure compliance with minimum requirements, several detailed and specification plans for each of the projects (both construction and rehabilitation) must be prepared. The plans must be reviewed prior to construction stages to ensure compliance.

There are approximately 1,400 manholes in the Reynosa sewage system. The manholes are generally made of brick (98% of the total) or concrete. Based on the analysis, the manholes will be made of prefabricated concrete or brick. An epoxy covering will also be provided in case they are exposed to turbidity or corrosion. Manholes will have to be replaced in sections where original pipes are rehabilitated. To increase ventilation in the system and avoid corrosion, manhole lids must have vents, except in highly populated areas or environmentally protected areas, or areas susceptible to flooding.

Based on the project useful life of the exiting pipes, estimates indicate that the complete system will require structural improvements by the year 2016. Improvements do not include the new proposed pipes to improve the load capacity or to avoid structural faults in the short term. Over 34 miles of the primary gravity system require rehabilitation improvements to extend the system's useful life.

The small drain system collects domestic, commercial, and industrial discharges. The system's length exceeds 425 miles. Approximately 92 miles require rehabilitation due to the infrastructure's age and corrosion; it is distributed in 14 subdivisions.

In addition, the sewage system must be expanded in 16 subdivisions.

Also, 37 subdivisions require to regulate discharges from lots that are not connected to the sanitary sewage system:

Pump stations are the essential component of the drainage system, as such, any faults or problems affect the entire system. The age of the pump stations ranges from one to thirty years. General recommendations were developed based on the analysis of the pump stations in order to provide immediate corrective measures to the structural, electrical, and most critical hydraulic problems.

COMAPA will be responsible for the operation and maintenance of Reynosa's potable water and sewage systems. Due to the high rate in population growth, infrastructure development and maintenance has not been sufficient to satisfy all needs.

The following maintenance plans were developed and must be extensively developed and include operation manuals in the final design projects:

1. Start Up Operation Plan.
2. Contingency Plan.
3. Safety Plan.
4. Quality Assurance Plan
5. Pollution Prevention Plan.

In developing the existing projects, the following land use plans have been taken into consideration:

• Municipal Urban Development Plan
• State Master Plan for Urban Development
• State Environmental Ordinance Plan

Development of the wastewater system is required to utilize design norms and applicable regulations by stage agencies. The Integral Sanitation Project complies with the following evaluation and design criteria:

1. "Lineamientos Técnicos para la Elaboración de Estudios y Proyectos de Agua Potable y Alcantarillado Sanitario" CNA, México 1994. (Technical Guidelines for Development of Water and Sanitary Sewage Studies and Projects)
2. "Especificaciones Generales para la Construcción de Sistemas de Agua Potable y Alcantarillado" CNA, México 1993. (General Specifications for Construction of Potable Water and Sewage Systems)
3. "Manual de Especificaciones Generales y Técnicas de Construcción de Sistemas de Agua Potable y Alcantarillado" SEDUE, México 1986. (General Specifications Manual for Construction of Potable Water and Sewage Systems)
4. "Normas de Proyecto para Obras de Alcantarillado Sanitario en Localidades Urbanas de la República Mexicana", SAHOP, México 1979. (Project Norms for Sanitary Sewage Projects in Urban Locations in the Republic of Mexico)
5. "Guía General para la Elaboración de Proyectos de Ingeniería de Sistemas de Agua Potable y Alcantarillado", SAHOP, México 1979. (General Guide for the Development of Water and Sewage Engineering Projects)
6. "Manual de Diseño para Lagunas de Estabilización" CNA, México 1994. (Design Manual for Stabilization Ponds)

With regard to the pump stations, recommendations address the pumping equipment and electrical system in accordance with NOM-001-SEMP-1994. The main specifications used are:

1. Electric Equipment Selection, CNA, Mexico, 1994,
2. Mechanical Facilities Design and Selection of Mechanical Equipment, CNA, Mexico, 1994.

Norm NOM-001-SEMP-1994, issued by the Secretary of Energy, Mines, and (Para) State Industry (SEMIP) established technical specification that electrical energy facilities must meet.

In this manner, assurances that project will be carried out in conformance with issued authorizations in order to comply with Official Mexican Norms will be undertaken. COMAPA participation during manufacturing and test processes to ensure compliance with the aforementioned norms is important.

The project was analyzed to determine its financial impact on COMAPA. Additionally, the project in and of itself would have to be capable of generating the necessary cash flow and revenues. Based on population projections, planned coverage, and estimated allowances, water demand projections were prepared for Reynosa. This demand would increase from 23 mgd in 1996 to 54 mgd by the year 2016. Three alternative scenarios were developed; they vary according to the amount of grants and loans the project might receive. The analysis of the pro forma financial statements for each of these scenarios determined that the project is financially feasible if a strict prioritization order is maintained in the investment program. It involves a total investment of $660 million pesos, which represents almost the totality of Reynosa’s investment for the 1998-2001 period.

A set of financial models were obtained from the three scenarios considered. They resulted in different rate/fee structures that can support the project’s financial viability. As such, real annual increases of 10 and 15% to water and wastewater collection fees allow the utility to cover future operating and maintenance costs, and obtain the necessary cash flow to amortize the debt and cover physical infrastructure replacement costs. It must be noted that COMAPA’s fee increases must correspond to the final project funding structure, considering grants, loans and COMAPA’s own funds.

It would be convenient for COMAPA to initiate the following actions to consolidate the utility and ensure the project’s financial viability: a) Establish an institutional capacity building program, including the reduction of water losses and the reinforcement of its commercial area to recover backlogs and improve collection efficiency; b) Develop a periodic program to update its user registry.

The Citizen's Committee was created on August 25, 1997. IBWC (CILA), BECC, and local Government officials were present during its creation.

Since its inception, the Committee has held ten meetings; 9 meetings were regular meetings and one was a special meeting. The Committee has been in charge of the public review process and has reviewed, discussed, and approved several key issues such as the comprehensive community participation plan, the outreach and media campaign, internal guidelines, appointment of its Chairperson, Co-Chairperson, and Secretary. It also approved and held neighborhood meetings and two public meetings. Other actions undertaken by the Committee include the development of a promotional video and flyers regarding project actions. During the public review process all project information was made available to the community and access to information was guaranteed. Based on surveys taken, results demonstrated the community at large supports the project.

Based on the Comprehensive Community Participation Program, a total of 46 meetings were held throughout the community in the different neighborhoods, including the Citizen's Committee meetings and included the majority of the community's social sectors. Two of the meetings were held with the media and one of the two meetings was held in McAllen. The information provided to the McAllen business community, the International Environmental Committee, and the McAllen Environmental Development Committee, and the media was extensive. The experiences gained have demonstrated the project which was strongly supported b the Citizen's Committee, is supported by the community.

The use of a special bus with television sets and VCRs was implemented in order to take project information to low-income neighborhoods. At universities, 26 detailed video presentations of the project were made. Brochures were also distributed and surveys from the student body were taken to determine their opinion on the project

The television was also used for broadcasting 28 sixty-second infomercials during prime time viewing (AAA). Three interviews on informational talk shows were also part of the program. The highlight of the campaign was to include community involvement and promote community members to provide input at the Information Center of the Integral Sanitation Program. The community's response to these measures was significant.

The radio was used to transmit 324 sixty-second informational spots regarding the project. The community was also requested to provide their input at the Information Center. Eight live interviews provided extensive coverage of the Citizen's Committee's activities.

COMAPA customer bills were used to distribute a total of 20,000 flyers. An additional 10,000 double sided promotional flyers printed on both sides were also distributed. Distribution also included 1,000 posters and 5,000 full-page surveys. Outreach activities in the press included eight full-page articles in the newspaper, which described the Committee's main activities.

A telephone information line was also established and 200 calls requesting project information were received.

The following aspects were presented during the public meetings:

• Technical Presentation of the Integral Sanitation Project, Saturday, October 4^th;
• Financial Presentation of the Integral Sanitation Project, Friday, October 17^th;

During the course of the public meetings, a one-question survey was distributed to all the attendees: Would your support the Integral Sanitation Project?, and the response was positive.

All input received from the surveys, public meetings, neighborhood meetings, and media campaigns has indicated that the community strongly supports the project. The community does however demand a high quality project and intends to follow up with organized efforts.

The Comprehensive Sanitation Project, fully complies with the principle of conservation oriented social and economic development based on the protection and rational use of natural resources, considering the needs of the present without compromising the ability of future generations to meet their own needs.

It can be assured that the construction and operation of the sanitation system will promote a reduction in the rate of diseases directly related to water use and consumption, wastewater collection and treatment, and reuse of treated wastewater. The project guarantees an adequate treatment of wastewater generated by both the existing population and that expected by the year 2016.

The comprehensive management of water and treated wastewater considers the environmental protection principle an integral part of the development process. It enhances the condition of water bodies existing at the locality and those located along the U.S.-Mexico border.

Different institutions that participate in environmental, social and economic improvement efforts have been involved in planning the wastewater collection, treatment and reuse system. Additionally, their experience has been taken into account to achieve a well balanced planning and obtain the maximum benefit from existing resources.

Through the Instituto Mexicano de Tecnología del Agua (IMTA) and with support from the North American Development Bank (NADB), COMAPA is currently developing the "Project for Locating and Recovering Losses at the Reynosa Water System’s Granjas Sector". The benefits of this program must be analyzed within two contexts: economic and non economic benefits. In fact, the latter falls within the area of resource conservation and sustainable development. As such, projects for the rest of the city areas are scheduled to be developed in the short term, and they should help strengthen the utility.

The Plan Subregional de Ordenamiento Territorial for Reynosa-Río Bravo, Tamps. (Subregional Territorial Organization Plan), is part of the State’s Urban Development Plan included in the National Planing System. The plan’s main objectives are: to manage population distribution in the local territory, and economic activities developed in areas with more potential; promote a comprehensive and balanced development of population centers, improve and preserve the environment at settlements; promote favorable conditions that enable residents to solve their urban development, housing, public utilities, and urban equipment needs.

COMAPA will implement a strategy to regulate domestic discharges generated by households not connected to the wastewater collection system, and those outside the service area.

1. GENERAL INFORMATION

1. Project Type

The project falls under the Wastewater Treatment priority and consists of Rehabilitation of the Current Wastewater Treatment Plant and Construction of (2) New Treatment Plants, Rehabilitation of the Wastewater Pump Stations, and Rehabilitation and Expansion of the Sanitary Sewage System.

2. Project Location

The City of Reynosa lies south of the United States and north of the city of Méndez; the City of Río Bravo lies east, while the City of Díaz Ordaz and the State of Nuevo León lie west of Reynosa. Regional maps indicate the location of the City of Reynosa.

The project is located within the 62 mile border region between Mexico and the United States, in the city of Reynosa, Tamaulipas. It is located 26º 04’ 24’’ latitude north and 98º 17’ 12’’ longitude west, and 125 feet above sea level. The City covers approximately 15 x 9.4 miles, an area that extends from the highway to Monterrey, (western perimeter), to the Pharr International Bridge, (eastern perimeter) next to the airport, and to the Rio Grande River (northern perimeter). It extends 9.4 miles to the south parallel to the Anzaldúas Canal. The site map provides details of the planning zone.

The Rehabilitation of the Wastewater Pump Stations and Rehabilitation and Expansion of the Sanitary Sewage System projects are located within the city limits.

The Wastewater Treatment Plant Rehabilitation project (WWTP I) planning area is located to the east of the City of Reynosa, on the Reynosa-Rio Bravo highway, at 2.2 miles. marker and is bordered to the north by the Rio Grande River, approximately 6.2 miles from the International Bridge. The railroad line to Matamoros and the Anzaldúas Canal border the project to the south, while the Industrial Paraíso and Delicias Addition subdivisions are located to the west.

The lot being considered for expansion of the current treatment plant (WWTP II), is located 9.4 miles from Reynosa, at the Monterrey-Río Bravo and Canal Rodhe intersection, and covers a total area of 183 acres. It is located southeast of the City, on the edge of the Rodhe Canal, and in close proximity to the Cereso Dos. (Federal Prison).

The lots for the new treatment plant (WWTP III) are located east of the City, in close proximity to the Reynosa/Pharr International Bridge.

 

 

 

3. Project Description and Work Tasks.

Design of the Reynosa sewage system is separate however absence of a storm water drainage system results in large amounts of rainwater being incorporated into the system. It has both main and secondary collectors in need of repair or replacement due to their age, state of deterioration, corrosion, and obstructions. Sections of the primary distribution system have exceeded their original design parameters, specifically the lines close to the lift stations. This situation is causing leaks into the ground, resulting in long term contamination of the sub soil and decrease in soil capacity due to the loss of natural material. As such, the pipes may collapse due to any overflow in the pipes.

Approximately 25 percent of the lots having municipal sewage services continue to dispose of their raw sewage via septic tanks and cesspools. These methods must be eliminated in order to avoid further contamination to underground resources and at the same time improve public health.

There are currently three lift stations, two of which operate at intervals with mobile equipment. Equipment and fitting is currently being undertaken and the Roma lift station is also currently under construction. Occasionally, when the lift station is overloaded, the collectors operate with a hydraulic load; as such, a reduction in the rate of leaks, both inorganic and organic solid waste is deposited, causing anaerobic decomposing of the waste. This situation causes foul and unpleasant odors as well as corrosion to the pipes. Furthermore, in some cases, when the collectors go into the hydraulic load mode, they leak into public areas. Several lift stations, such as No. 3 and No. 10, have surplus lines that discharge raw wastewater into the collecting bodies. The area being served by the Roma lift station, currently discharges in the El Anhelo Drain and La Escondida Lagoon.

The City of Reynosa currently relies on an oxidation pond system for treatment of its wastewater. In accordance with population demands, consumption based on user type and current distribution zones the plant's current capacity has been determined to be inadequate. As such, the water currently being discharged into the Rio Grande River does not comply with required norms.

It must be noted, that the future treatment plant effluent will not be discharged into the Rio Grande River. The effluent will be conveyed via the Anzaldúas and Rodhe Canals to the irrigation districts.

Due to the aforementioned reasons, rehabilitation and expansion of the sewage system is required. This process involves replacement of the damaged pipes in the primary and secondary systems; implementation of a maintenance system based on degritting and construction of special structures (to avoid importation of sand into the system); and expansion of the secondary system in subdivisions that lack service, based on a conventional gravity sewage system.

Implementation of a program to incorporate lots not connected to the sewage system requires development of a manual describing those requirements needed to comply with national norms.

With regard to the wastewater pump stations, rehabilitation and expansion of the plant's capacity is required. Both the electrical/mechanical as well as the civil engineering components must be considered. Also required is the rehabilitation, replacement or expansion of the pressure lines that discharge into the current treatment plant, and in the future, into the new plants.

The aforementioned needs are described in the studies carried out by the International Boundary & Water Commission (IBWC/CILA) through the U.S. based company Montgomery Watson, for the City of Reynosa in 1997.

The current treatment plant exceeds its design capacity. As such, requires rehabilitation. In addition, construction of two additional plants will help meet the future planning demands (through the year 2016). The proposed treatment consists in anaerobic ponds followed by a facultative treatment process, similar in design to Treatment Plant No. 2.

The Infrastructure Improvement Program presents the projects required to provide structural integrity and adequate capacity to the existing drainage system. It also satisfies the City's expected growth needs.

Based on available economic resources, rehabilitation and expansion projects for the municipal drainage system and the treatment plants could be carried out during the course of a 20-year period.

The Infrastructure Improvement Program is divided into four stages based on the year scheduled for project construction:

• Stage I 1997 to 2001
• Stage II 2002 to 2006
• Stage III 2007 to 2011
• Stage IV 2012 to 2016

* The O&M costs are discussed in the financial section of this document

Based on statistical information reported by the National Institute on Statistics, Geography, and Information, the Municipality of Reynosa experienced an annual growth rate of 3.57 percent during the 40-year period between 1950-1990, while the City of Reynosa experienced a 5.27 percent annual growth rate during the same period.

The population projection period covers 20 years, between 1997 and 2016, and is based on the report, "Master Plan for Consolidation and Institutional Development of the Water and Sewage Operating System Municipal Commission of the City of Reynosa, Tamaulipas, carried out by the National Water Commission in 1996. In determining future population, six forecast methods were developed and are based on statistical data included in the VIII, IX, X and XI General Population and Housing Census. The following table illustrates the results:

Based on the results obtained by applying the forecast methods, it was determined to use a population base through the year 2016 the results obtained with the "method average" method, which established a population of 1,003,916 and a 4.45 percent annual growth rate.

It must be noted that demographic growth does not maintain the same growth rate constant and that it tends to decrease. For this reason, the project population should include intermediate growth rates at five-year plans as described below in the Five Year Plan Method:

POPULATION PROJECTIONS 1997-2016
INHABITANTS	AVERAGE ANNUAL GROWTH RATE (%)
420,294
446,104	6.14
473,500	6.14
502,577	6.14
533,441	6.14
566,199	6.14
592,767	4.69
620,582	4.69
649,702	4.69
680,188	4.69
712,105	4.69
739,152	3.80
767,226	3.80
796,367	3.80
826,614	3.80
858,010	3.80
885,387	3.19
913,638	3.19
942,791	3.19
972,873	3.19
1´003,916	3.19

In conclusion, once the Comprehensive Sanitation Project is carried out the actual population affected by the project will be 420,294 inhabitants equal to the entire population.

In determining the design flow for rehabilitation of the Reynosa sanitation system, the City currently has 420,294 inhabitants and will reach 1,003,916 inhabitants at the end of the project's financial term, the year 2016.

The Rio Grande River provides potable water to the City of Reynosa. Collection is carried out at the Anzaldúas Deviation Dam where it is pumped to the treatment plants, Loma Linda and Benito Juárez. The treatment process consists in a pre-chlorination process, turbidity removal, flocculation, coagulation, filtering, and chlorination; a physical-chemical-bacteriological analysis of the untreated and treated water is carried out daily.

The water is then stored in two tanks. One is an surface tank that has a 7.9 million gallons capacity and the other is an underground tank with a 1.3 million gallons capacity. There is an additional underground tank with a 4 million gallons capacity that will be placed in operation in the near future. After these two tanks, pumping is carried out directly into the five distribution sectors. Metering exists for the pumped water volume at the treatment plants. COMAPA is currently developing a micro-metering project that will determine the metering points and necessary equipment.

Distribution is carried out via differential pumping based on user needs and any tank surplus. Due to the absence of regulating tanks, services are not adequately provided to the "high" sub-divisions or those located at distance from the treatment plants. Studies and projects required to address these problems are currently being undertaken.

The distribution system is currently 594 miles length and covers 90 percent of the city's needs. Based on population, it is estimated that 92.24 percent of the population is provided with potable water services while the remaining population receives its water supply via hydrants and water tank trucks.

The sewage system was designed and built to collect only wastewater, though it does have some rain water collection units included in the system. As of December 1996, there was a total of 51,777 domestic hook ups, providing service to 239,180 inhabitants, and equal to 57 percent coverage. At present, three wastewater lift stations are in operation.

As stated earlier, the City of Reynosa relies on an oxidation pond system for wastewater treatment. The ponds are located in the Northeast area, between the Anzaldúas Canal and the Rio Grande, in close proximity to the Matamoros highway extending alongside the Rio Grande River.

Location of the new wastewater treatment plants has been determined based on the sewage system needs as well as the availability of space. The sewage system requires areas in close proximity to the pump/lift station in order to meet both treatment and reuse components.

The first criterion used for (site) selection was the plant's location in proximity to these facilities.

The second criterion relates to the availability of surface area for construction. Design needs and operational-economical aspects require a large surface area. For this reason, WWTP No. 1, built in 1970, was built at the existing location and there are no plans to change this site in the future. Another advantage to this site is that discharging the water into the Anzaldúas Canal does not present a problem and also avoids adverse transboundary effects by discharging the treated effluent into the Rio Grande River. In addition, the location and design of this facility, ensures that under flooding conditions the Plant will operate safely.

With regard to WWTP No. 1, the drainage system is distributed to convey wastewater to the selected site and this area has lots available for construction. Different localization options were analyzed in accordance with the following conditions: extension, locations outside city limits, future population growth, urban growth trends, etc.

After analysis of the aforementioned conditions, the most appropriate location for WWTP No. 3 was determined to be on the far east area of the city, close to the Reynosa/Pharr International Bridge, outside of the .flooding protected area boundaries.

Location of WWTP's #2 and #3 was determined in the Sub-Regional Territorial Ordinance Plan for Reynosa-Río Bravo, Tamaulipas, developed in October 1991.

Some advantages to the location of the municipal wastewater plants include discharging the treated effluent into the Anzaldúas and Rodhe drains and thus avoiding negative transboundary effects. In addition, the drains are in close proximity to the plants.

Treatment of the municipal wastewater can be carried out efficiently via secondary or biological, aerobic and anaerobic treatment systems, such as activated sludge (in one of its many forms), rotating discs, mechanically aerated ponds, spraying filters, stabilization ponds, elevated flow anaerobic reactors, or a combination of any one of these.

These systems, though simple in their general conception, require highly specialized personnel for operation and maintenance. The system that has been selected to treat Reynosa's wastewater is a biologic or secondary treatment system. It was selected because the need for specialized personnel for the facilities' operation and maintenance is minimal and also because of its cost effectiveness. Electrical-mechanical equipment will only be required for pumping the raw wastewater.

A detailed review of the options analyzed for the treatment process is included in the technical feasibility section.

The U.S. company Montgomery-Watson developed a computerized hydraulic model to review operations of the sanitary sewage facilities in Reynosa. This model was used to evaluate the existing system's capacity and to determine what facilities and hydraulic capacity is required to handle the projected flows. The model focuses on the main collector system and incorporates data from the primary sewage system, manholes, and surveys taken with the Global Positioning System (GPS), land use projections, lift station evaluations, lift station discharge pipes, and flow monitoring results.

Based on several meetings held with the Binational Technical Committee (coordinated by the International Boundary & Water Commission), key parameters in hydraulic analysis were defined:

• Manning roughness coefficient
• Hydraulic capacity loss due to clotting
• Definition of construction practices for future projects
• Overloading conveyance lines
• Contributions to the system
• Speed and minimal ground slope
• Design Storm

After analysis of the possible design options, and considering technical and financial aspects, the Technical Committee proposed forming two design storm options:

• The first option is defined by a design storm with a peak factor of 5:1, which means that any water down river of the system will produce a peak flow during the monsoon season five times the average daily flow (return period is two years).
• The second option considers that the gravity system will be designed to maintain conditions without any overload during daily peak flow times and during low water seasons and with maximum flow design of 3:1 (return period is 8 months) for the lift stations (in order to include a safety factor for the monsoon season). The scenario determined the minimum size for the system to operate through the year 2016.

Furthermore, the following system conditions were analyzed during the simulation with the model.

1. The existing system under low water conditions.
2. The existing system in the year 2016 under a storm and with a 2 year return period (low water peak factor 5:1)
3. The existing system with the proposed required improvements to manage a storm with a two year return period through the year 2016 (without going into load).
4. The existing system with the proposed required improvements to maintain load conditions, during low water periods through the year 2016. Under this scenario, capacity of the lift stations was evaluated as they relate to a design storm with an 8 month return period, and represents a 3:1 peak factor for the system.
5. The existing system with the proposed required improvements to avoid overload conditions during low water conditions through the year 2016, and with the existing degritting level.

Results of the five scenarios were utilized for the following:

• Locate points where overloading in the system may occur; identify problem areas.
• Propose and design new installations in order to alleviate any system limitations.
• Obtain service area limits for the existing WWTP and proposed WWTP's.
• Prioritize proposed facilities in order to establish a construction calendar in stages.

Scenario #4 was selected as a base for the proposed Infrastructure Improvement Program (low water flow by the year 2016, and with a peak storm flow with an 8 month return period for the lift stations).

Similar to the primary system, rehabilitation and expansion sites of the secondary system cannot by defined. In order to provide wastewater collection services, project needs have indicated that the systems must be laid along the city streets to make connections to the different domestic, commercial, service, and industrial users feasible. As such, the line sites is required and no other site selection alternatives are available.

Due to its characteristics and availability in Reynosa and after extensive evaluations, it was concluded that the most appropriate material for rehabilitation and expansion of the secondary system is PVC.

It has been assumed that in the future, all new sewage systems shall be built in accordance with tighter restriction standards in order to minimize any matter flowing into the lines. The Technical Feasibility sections provides a detailed overview of the advantages.

Growth in urban zones, specifically in areas where access to potable water and sanitation services is difficult, has caused a significant reduction in the efficiency and capacity levels of these services.

With regard to the sewage system, lack of maintenance and adequate treatment of wastewater discharges has caused serious contamination problems, requiring rehabilitation and expansion of the existing systems. These efforts must include a maintenance program to address current needs and any that may arise in the future. This situation has a direct affect effect on public health.

Immediate consequences of not implementing measure to rehabilitate and improve the current systems will be reflected in the efficiency levels of the systems, the bad condition and inadequate service provided by the lift stations, the sewage system, and the wastewater treatment system. This situation has a direct impact on human health and the community's surroundings. As such, it is feared that discharges tend to leak into the natural ground, contaminating underground resources; water quality will not be adequate for irrigation and will cause diseases in the farming community as well as in the consumers of these products.

In conclusion, not implementing the project will have serious impacts on human health and the environment. Specifically, discharging raw wastewater into the Rio Grande River will create transboundary effects.

The Governments of the United States and Mexico have undertaken efforts of cooperation for the protection of the environment and natural resources along the border shared by these two countries. The two governments signed the Agreement for the Protection and Improvement of the Environment of the Border Region between the United States and Mexico in 1983 (The La Paz Agreement). This Agreement established the basis that provides the framework for environmental cooperation efforts.

Agenda XXI is the result of the United Nations Conference on the Environment and Development held in Rio de Janeiro in 1992. The Agenda defines a series of environmental objectives on an international level which provide general guidelines for sustainable development on a global level. It also encourages communities and the different levels of government to establish specific programs that promote sustainable development in their own communities. The Comprehensive Sanitation Program for Reynosa conforms to these objectives.

Binational agreements have continued to move cooperation efforts forward, such as the 1994 North American Free Trade Act (NAFTA). This cooperation effort seeks to improve the environment and public health while also encourages sustainable economic growth.

The Commissioners determined that the International Boundary & Water Commission (IBWC) will support border communities in their planning efforts and those communities interested in submitting wastewater management projects for certification by the BECC in order to access financing by the North American Development Bank (NADBank) or any international financing institution. This Commission established that in order to receive financial support, border sanitation problems must present any one of the following conditions:

1. Risks to human health.
2. Beneficial use of international waters is obstructed.
3. A community is affected.
4. The community supports the project.
5. The community does not have the capacity to cover the costs required for to have project certified by the BECC.

After review of the water quality monitoring results obtained from testing water along the U.S.-Mexico border, and in accordance with the terms established in Minute 289, "Conformance with Water Quality along the U.S.-Mexico Border" it was determined to give priority to the community of Reynosa, Tamaulipas.

IBWC is in charge of coordinating, consulting, administering, operating, and maintaining the sanitation and infrastructure projects along the border. IBWC, along with the State and Municipal Government and the COMAPA, has supported the Comprehensive Sanitation Program. Support documents are included in Commission Meeting Minutes, and in Minute 294, "Project Consolidation Program for Solution to Border Sanitation Problems" dated November 24, 1995.

Furthermore, based on the aforementioned agreements, the "Joint Report by the Principal Engineers and Technical Advisors Regarding the Development of the Work Plan for the Comprehensive Sanitation Projects in Cd. Acuña and Piedras Negras, Coahuila and Reynosa, Tamaulipas" dated, March 11, 1997, was prepared. The report outlines the work plan for the Comprehensive Sanitation Project for the City of Reynosa, in accordance with the agreements established in IBWC Minute 294. As stipulated in the work plan, the Binational Technical Committee was established; the committee is comprised of representatives from the responsible agencies from both countries. The scope of work were also established and constitute the framework for implementation of this project.

2. HUMAN HEALTH AND THE ENVIRONMENT.

During the last four decades we have seen an accelerated growth in our country’s population. This phenomena has been more intense in large urban concentrations, which has caused severe coverage and quality problems in its main services, among which we have potable water, drainage and sewage.

The growth in the majority of the urban concentrations, specially the zones with difficult access for services such as potable water, has given rise to the adoption of temporary solutions that later on try to be considered as definite. This reduces the efficiency and causes the distribution systems to reach a high complexity, making its operation and maintenance difficult.

The coverage of potable water and drainage services in the City of Reynosa are represented in the following table, to December 31, 1996 there were 82,257 water intakes, classified as follows:

If you consider that the number of service intakes to houses (domestic, housing units, apartments and retirees), this means 77,537 intakes and an accumulation index of 5 persons per housing unit, it is determined that for the month of December 1996, 387,685 inhabitants were supplied at the residential intake level, that with regards to the population of 420,294, it turn out that 92% of the population receives potable water through the system and the remaining 8% of the population obtains its water from hydrants and water tank trucks.

The drainage system is of a separate type, this means, it is designed and built exclusively to capture waste water, even though it has storm water discharges connected to the system.

To December 31, 1996 a total of 51,777 drainage discharges were installed, classified as follows:

The number of discharge service to houses (domestic, housing units, apartments, and retirees), this represents 47,836 discharges and an accumulation index of 5 persons per housing unit, up to the month of December 239,180 inhabitants had drainage service, this represents a service coverage of 57%.

The sewerage service covers 70% of the urban area with drainpipes system. The system is designed to capture only wastewater, even though it has some storm water discharges connected to the system. The service as was mentioned covers 57% of the population, this indicates that the system is under used, that there are vacant lots connected to the system of that there are too many illegal discharges.

The City of Reynosa, Tamps., has a wastewater treatment plant with oxidation ponds, located on the Northeast end of the city, between the Anzalduas Canal and the Rio Grande. The National Water Commission, carried out an executive project in order to rehabilitate the current treatment plant, according to measurements made at the lake system’s main pumping sumps the design characteristics have been exceeded, since it was constructed to treat a flow of 703 lps, and during the sampling period it was observed that there was a volume of flow of 745 lps, this represents an overflow of 6%. Based on the information gathered and on population planning, potable water and sewerage services expansion and plans for urban area growth, an executive project was prepared for the expansion of the wastewater treatment system.

One of the most important aspects related to the potable water, drainage and sewerage systems is Public Health.

The potable water supply source for the City of Reynosa is the Rio Bravo, whose intake work is located at the Anzalduas Deviation Dam from where it is pumped to the potabilizing plants that are designed to eliminate water cloudiness and pathogens, through chlorine gas desinfection. The quality of potable water produced at the plants is adequate for human use and for consuming, as it complies with the Department of Health’s standards.

As can be noted, the free chlorine waste, in the potabilized water, exceeds the permissible limit for over chlorinated waters, this does not mean a health risk for the users, since this insures a chlorine residue that prevents any water contamination from the plant to the users home. The Magnesium concentration exceeds the permissible limits; therefore it will have to be eliminated from the water. The same thing happens with the parameter that sanctions the concentration of Active Substances at Methylene Blue, which is the active part of the detergents. Appearing in the human use water could have several explanations: laboratory error; sampling problems and probable natural water contamination by waste water discharges. It would be necessary to make a greater number of analytical determinations before having a reliable answer, that would allow taking the necessary measures for the case.

The relationship that exists between the environment and the health-disease relationship in a community is undeniable. In studies and experience from countries that have reached high coverage of basic services such as: potable water, drainage, treatment and disposal of treated waste water and adequate management of waste, among others, we have seen an important decrease in the prevalence of infectious-contagious diseases, specially gastrointestinal diseases. On the contrary it can be proven that countries and urban zones like the City of Reynosa, that have difficulties in providing these services adequately, there is a high rate of the diseases mentioned.

The Comprehensive Environmental Health Project for the City of Reynosa,
Tamps., as was mentioned previously, includes works that will be developed in the drainage system as well as consistent with the rehabilitation and expansion of pumping sumps, such as the rehabilitation of the current oxidation ponds and the expansion of the waste water treatment system and the reuse of treated water for agriculture irrigation, therefore expecting to improve the levels of quality of life for the city’s population.

The gastrointestinal diseases and parasitoid in the municipality of Reynosa, occupy third place within the general morbidity and they are the cause for frequent deaths among five year olds and younger population. The acute respiratory infections have first place in morbidity, which are caused by sudden changes in temperatures and dust generation. The ratio between intestinal infections and respiratory infections is approximately 1 to 5.

From the information gathered in relation to the incidence of gastrointestinal and parasite diseases, from 1990 to 1997, obtained from the health sector through its source SSA EPI-1-85 and EPI-1-95 SPESCIFIC PROGRAMS, where morbidity due to transmissible diseases is reported and, at a jurisdiction IV level – Reynosa, there is an increase in the growth trend rate for these diseases.

From this information we have selected the diseases that have a direct relation to water, through which it is ingested, or the one discharged from the housing unit or from the one reused. The intestinal infections are highlighted due to their importance, followed by amebiasis, ascariasis and oxyuriasis. The first disease registers 65% of the total of gastrointestinal diseases.

The total morbidity annual rates for gastrointestinal diseases vary from 549 in 1992 to 840 in 1995 (cases per 10,000 inhabitants).

It should be clarified that the rate 1996 was also considered for 1997S for the following transmissible diseases: hepatic abscess, taeniasis, basilar dysentery and trichuriasis and that the rates were extrapolated from the information obtained for that year’s first semester.

Comparing the infectious-contagious disease rates from 530 persons from the City of Reynosa, for 1996, with Rio Bravo and Diaz Ordaz, in the same State of Tamaulipas, that mount to 2,098 and 616, the great disparity of these values can be observed and the rate for the City of Reynosa is the lowest one. A similar comparison with the towns of Guadalupe D.B. and Praxedis G. Gro. in the Municipality of Cd. Juarez, State of Chihuahua, whose rate for 1995 is 151, this represents 28.5% of the existing rate in the City of Reynosa for the same year and for 1996 is 198 which represents 37% of that registered in Reynosa. There is no explanation of why this in this Municipality the morbidity rate is so low compared to the ones for the City of Reynosa.

Different trends could be found by adjusting the values for morbidity rates, and the most significant ones are the ones represented in the previous figure where if an adjustment is made with a potential curve one would obtain a pessimistic planning and a growing trend could be observed, which would mean that by the year 2016 the morbidity rate for the population of the City of Reynosa would be 3,788 cases per 10,000 inhabitants. A less pessimistic planning, considering only the data signaling the decrease of these diseases in the last few years, has been called current trend and it would be expected that by the year 2016 it would reach a value of 1,004 cases per 10,000 inhabitants. If on the other hand one takes into consideration the impact the environmental projects will have on the population, one could expect an optimistic projection that would start decreasing in 1998 from a rate of 791 to one of 612, which means a cut down of 12% in this rate; later it has been considered that this rate is reduced annually 7% annually, reaching the year 2,016 with a value of 163.

Many factors should influence the environmental health issue in order for the previous proposal to became a reality, among which are outstanding: improvement of public services, nutrition, hygiene habits, healthy environment at home and a growth in the economic perception levels.

To that effect COMAPA from the City of Reynosa, will implement a strategy to normalize residential discharges from the lots that have not yet been connected to the sewerage system, as well as those that are in the areas where the service will expand. This strategy will involve the following activities:

• identification and lot regulating program; if it is true that we have information lots that are not connected to the sewerage system, and of those that do not have potable water service, it is necessary to update the information in order to insure the success of the regulating program. For this project we will have administrative information, from the operating organism, and information that would have to be gathered from the field. In the operating organism, we have information from the lots where discharge connections have been made according to payment control or rights exemption due to hook-ups and/or by materials’ control leaving the warehouse for hook-up work. Filed information refers to the list of potable water users from the organism, which is always updated. However, during the updating activities the necessary information will be gathered regarding water discharge from lots and we will take advantage of the support from personnel assigned to taking the readings from the meters-recorders for potable water from homes and personnel assigned to the repair and/or replacement program of damaged meters, previous training.
• residential discharge regulation; manuals with materials and projects specifications will be prepared or updated for sewerage and potable water facilities within the lot and the techniques to be used for canceling latrines and black wells, in order for them to meet the national standards required. Due to its importance, it is necessary to take into consideration in the regulation, the corresponding sanctions in order to guarantee the success of the regulation. The sanctions could be fining and suspension of potable water service. Also, it would be necessary to update the regulations in order to foresee the incorporation of discharges from the lots in the zones that are being developed.
• awareness program and inspection work; the program will be promoted before it begins, highlighting the benefits it will provide to the population, emphasizing the improvement of human conditions and inviting the users to register with the program. The lots that are not hooked up will be visited, in order to verify the information recorded and invite users to update their records with this institution and/or register in the regulation program.
• marketing; taking into consideration that the user will have to make improvements to the sewerage installation in his/her lot, that this program is for the benefit of the community and that the population involved is the one that has less economic resources, around 92%, it is suggested that 50% of the cost of the program be absorbed by the operating organism (COMAPA) and the other 50% by the user who will receive the benefit, giving him/her a year to pay the debt, with the condition of canceling the latrine or black well.
• investments; in order not to increase the current expense, due to the fact that the program is transitory, it is proposed that it be executed by contracting a specialized company.

2. Environmental Assessment.

The project requires the submittal to the Office of Ecology from the Secretariat of Social Development (SEDESOL) in the state, an environmental assessment, for which a final document was prepared and the final report of the Environmental Impact Manifestation (EIM) as a General Mode for the Comprehensive Environmental Health Project for the City of Reynosa, Tamps., issued by SEDESOL in the state.

The most significant environmental effects are outlined and analyzed in detail in section V (Identification of Environmental Impacts) from E.I.M. for the Comprehensive Environmental Health Project for the City of Reynosa, Tamps., whose information is valid and applicable according to an evaluation made by SEDESOL in the state. For more details reference these documents that have been presented to the Border Environmental Cooperation Commission (BECC).

As is described in the E.I.M. previously mentioned the benefit for the community and the ecosystem en general with the Comprehensive Environmental Health for the City of Reynosa is undoubtable.

To emphasize the beneficial effect that this project will have in the comprehensive environmental health project for the City of Reynosa with regards to water quality from the Rio Grande Basin, the following is an analysis with water quality results that the National Water Commission, through its Water Quality and Sewerage Management has generated since the beginning of the sixties.

As has already been mentioned in the hydraulic region Num. 24b, Lower Bravo, it covers a surface of 136,196 Km², and it includes part of the states of Coahuila (81,902), Nuevo Leon (36,513) and Tamaulipas (17,781). The most important cities are Monterrey, Saltillo, Reynosa, Montemorelos, Monclova, Nueva Rosita, Sabinas Hidalgo, Piedras Negras and the City of Acuña.

The most important hydraulic works are the dams Falcon (Mexico), its main purpose is irrigation, electricity generation and avenue control; Marte R. Gomez (El Azucar) and Venustiano Carranza for irrigation and avenue control and El Retamal.

The diagnosis for water quality in the surface water bodies is carried out through the use of data from the National System Monitoring. In this region, the System operated until 1995, with 55 stations located in 23 bodies of water. To estimate water quality CNA uses the Water Quality Index (WQI), which provides the degree of water contamination to the sampling date and it is expressed in adimentional units, as ratio of the water being studied to pure water. Therefore, highly contaminated water will have a WQI closer or equal to zero and water with excellent conditions a value close to 100. The mathematical ratio that defines this index is:

WQI = (å Ii Wi) / (å Wi )

where:

WQU = Water Quality Index, adimensional.

Ii = Quality Index for parameter i.

Wi = Weight Average Coefficient for parameter i.

n = Total number of parameters

The number of parameters that are considered in order to determine WQI is 18; dissolved oxygen and the biochemical oxygen demand are the parameters with more weight in the WQU value. The following table includes the weight average coefficients for each one of the parameters:

In order to evaluate the quality that the national surface waters have shown, monitored by the National System; three intervals have been established in the WQI scale; WQI values between 0 and 40 is considered that water quality is bad; between 40 and 70 regular and between 70 and 100 good. The WQI value for the stations of interest for this study, is the average obtained since the monitoring started until 1995.

The following table shows the location of the monitoring stations in question.

The following table and graph shows the distance as well as its WQI value, from monitoring stations from Falcon Dam to the station at the Nuevo Progresso International Bridge, going through the City of Reynosa International Bridges and the station located downstream from the Anhelo drain at the Rio Grande.