Source: SCPSM, Population includes the city and the Valley of Mexicali.
3. Human Health and Environment
5. Financial Feasibility and Project Management
Background It must be noted that the determination to develop and implement the works involved in the projects as well as their general costs are based on actions coordinated by the International Boundary Water Commission (IBWC) of Mexico and the United States, within the framework of the international agreements reached in Minutes 264 and 294. Both Commissions have developed coordinated actions to address the shared sanitation needs. In this regard, the Binational Technical Committee (BTC) was established in October 1996 to address the sanitation needs of Mexicali. The committee has the participation of local, state and federal authorities from both countries. BTC members defined the concept and monetary requirements for implementation of the sanitation actions which was to be submitted as Step I Format to BECC. This re-defined format was submitted to BECC on May 27, 1997, in which the Mexicali I System and Mexicali II System projects were bundled and totaled approximately $50 million dollars.
The 41 projects that will be implemented in the City of Mexicali, are part of the Mexicali Sanitation Program that consists in the following:
B.1. General Information
The National Water Commission (CNA) analyzed 9 different options for the wastewater conveyance, disposal, and reclamation. (See under Executive Project) It was determined to locate the Mexicali II System treatment plant 9.5 km. away from pumping station Nº 4 and treat wastewater to a level adequate for reclamation purposes in agricultural irrigation. The region has an extensive area for agricultural use in which treated effluent can be reclaimed. The quality standards used in designing the plant are NOM-001-ECOL-96 and the parameters defined in IBWC Minute 264. In this first stage of construction, the plant will have a treatment capacity of 880 liters/second.
Other program projects include construction of a sanitary sewer system to service over 46 housing developments, some of which have been without service over 35 years. Also included is the construction and rehabilitation of collectors in different areas of the city as well as the rehabilitation of pumping stations. At present, sanitary sewer service coverage is 90%; project implementation will increase coverage to 95% of the city population.
The sanitation program projects will resolve problems related to untreated wastewater discharges into the New River which are discharged by the City's sewer system, specifically, the area covered by the Mexicali II System. The projects will also increase the quality of wastewater treated by the Mexicali I System treatment plant, located at the Colonia Zaragoza. Collector rehabilitation and lining will eliminate problems in the drainage system and wastewater running through the storm water drains will no longer be necessary; therefore, the New River will no longer be an infectious foci affecting residents on both sides of the river bank throughout its course.
The construction of sanitary sewer in over 46 housing sites on the west side of the city will improve the quality of life of the residents and eliminate contamination due to latrines in the backyards and the risk of diseases and infections experienced among children and adults. Another benefit will be reflected in the reduction of gastrointestinal diseases and the risk of non-bacterial food diseases.
The Environmental Impact Statement (EIS) has been developed and approved by the Environmental Department of the State of Baja California, as well as the statement issued by the National Institute of Anthropology and History (INAH) stating no archeological ruins exist in the areas of interest.
The transboundary environmental impacts will be positive given that the wastewater from the city of Mexicali will be treated pursuant to quality standards agreed under IBWC Minute 264 and will benefit water resources on the US side of the border, since the New River crosses into the United States.
In determining the project's financial feasibility, the SPSCM and BECC evaluated different scenarios which consider funding by the US EPA, the Mexican federal government, and BEIF in accordance with NADBank regulations. These scenarios reflect the following premises:
Investment recovery and program to cover any increase in the O&M costs for the new structure is described below and make the project financially feasible.
1. With regard to the investment amount:
The SPSCM will recover the loan amount through the economic benefits resulting from the project. Users benefiting directly by the new service will be charged for construction costs and a connection fee which has already been established by the 1997 State Earnings and Expenditures Law.
2. With regard to the O & M costs:
The SPSCM has annual pre-authorizations for rate increases based on a formula that includes increases in the main O & M costs. This updating process is carried out monthly until the established limit is reached. When the accumulated rate and fee increases exceed the limit, approval by the State Congress is required.
The list below is the list of documents submitted to BECC by the SPSCM:
The city of Mexicali is divided in four large zones for the provision sanitary sewer services and the area and population estimated in 1996 in each of the four zones is listed below:
|
System |
Area (ha.) |
Population (residents) |
|
Mexicali I |
6,845 |
405,321 |
|
Mexicali II |
7,007 |
163,618 |
|
Mexicali III-A |
2,482 |
30,000 |
|
Mexicali III-B |
1,821 |
2,000 |
|
Total |
18,155 |
600,939 |
Source: SCPSM, Population includes the city and the Valley of Mexicali.
The project consists in the implementation of 40 works whose purpose is to address the lack of a sanitary drainage system in over 46 neighborhoods in the city; to meet this objective, construction of pumping stations, main collectors, as well as the construction and expansion of wastewater treatment plants, and the replacement and construction of collectors, and the rehabilitation pumping stations is required.
The projects that will be carried out are the following:
a) At the Mexicali I System:
b) At the Mexicali II System:
General Description of the project's main technical concepts:
a) Mexicali I System
a.1. Rehabilitation and expansion of the Mexicali I System Treatment Plant (Lagoons at the Colonia Zaragoza).
Increase capacity from 980 liters/second to 1,300 lps
The works will consist in rehabilitation of 980 lps and an increase in the capacity of the treatment plant in 320 lps, from 980 lps to 1,300 lps, the current treatment system consists of 13 stabilization lagoons, three are anaerobic and 10 of the facultative. The operation is done by dividing the flow in order to operate at the same time with an "Australian" system; the distribution channels and the floodgates are in bad physical condition, causing the flow to be unevenly distributed. The hydraulic design has several short circuits with dead areas having no movement and causing the real retention time to be shorter than the estimated time. Furthermore, equipment to remove floating material is inadequate. In order to reach higher efficiency levels, actions to this effect are detailed in the technical chapter of this document.
Included in the works that will be carried out in the Mexicali II System, is construction of several collectors that will allow some areas currently discharging wastewater into the Mexicali I System to be conveyed to the Mexicali II System. This will provide the Mexicali I System Plant with a larger capacity to treat wastewater from the neighborhoods during the initial sewage works carried out on the western area of the city.
Sewer lines have collapsed in several parts of the city due to their age and because they are made of concrete. Furthermore, their location does not allow replacement by traditional methods. As such, lining the existing collector system has been determined to be the most appropriate solution.
In some areas of the city, the sewage collectors have collapsed due to age and pipe material, in addition silt deposits have accumulated over the years. These problems at times have made it necessary to divert wastewater to the storm water drainage system which in turn discharges into the New River. These replacements will be made of PVC pipelines.
In the area located to the west of the city of Mexicali, there are neighborhoods that are not provided with sanitary sewer service; there are several sub-divisions over 40 years old while others are experiencing rapid rates in population increases. Provision of services with systems discharging into the treatment lagoons of the Mexicali I System located in the Colonia Zaragoza is required.
Due to the age and the constant use of the pumping equipment immediate implementation and rehabilitation of the project is necessary for the lift stations. This involves replacing or repairing the motor pumps, replacing and repairing, if required, the reverse flow sectioning valves and air admission and expulsion valves; replacing pipelines, accessories and instrumentation damaged by corrosion; constructing gates and periphery fences to protect facilities which includes lighting, landscaping, and installing odor control devices, paving sidewalks, painting signage, etc. to not stand out against the surrounding residential area; as well as the general outfitting of the electrical installations, control systems, measurement boards, electrical substations, land systems, level controls, and security systems, etc.
b) System Mexicali II
The Mexicali II System Treatment Plant will be located approximately 9.5 km. to the south of Pumping Plant Nº 4 and will have a final capacity to treat 1,760 lps; currently construction of first stage to treat 880 lps.
The second stage of the project includes an average design flow of 1,760 lps through the year 2015, which will be applied in 4 modules using trickling filters preceded by the oxidation ponds which will have a design flow per module of 220 lps. This second stage is not included in this package of works submitted to BECC.
Pumping plant Nº 4 which will have an installed capacity of four 350 HP pumps in each of the two stages to overcome hydraulic charge of 33.50 m.c.a. and will pump 880 lps; it will recollect the untreated wastewater from the Mexicali II System and will be strategically located at the intersection of the road to San Felipe and the Dren Satélite which is a branch of the New River. Subsequently the water will be pumped and conveyed by a pressurized main collector to the future treatment lagoons. This plant consists in the connection of the collectors system to the pumping plant, plumbing, joint works, control room, electromechanical work, building for the electromechanical controls, building for the emergency plant, civil engineering for the lift station, sand trap and pumping equipment.
From pumping plant Nº 4 the wastewater will be conveyed by a pressurized main collector, approximately 9.5 km. in length and will be installed in the center median center of the road Mexicali - San Felipe. It consists in two steel pipelines with a diameter of 48", each one has a capacity to conduct 880 lps. At present the first line is in the process of being installed, with the CNA in charge of the project. This program only includes implementation of the second stage and will result in a total design capacity of 1,760 lps of final average flow.
This organization has developed a Master Plan for the Mexicali II System which includes the main collectors and subcollectors to provide required service coverage to the east and southeast area of the city of Mexicali. With these works, in addition to providing service to the are, several pumping sumps presently discharging into the González Ortega treatment lagoons will be eliminated.
The executive project for these collectors include the use of P.V.C. or polystyrene pipe, which is why the useful life is a minimum of 60 years.
b.5. Installment of telemetry equipment in at Mexicali II Plant System
The required equipment will be installed to monitor operation of the pumping equipment such as the R.P.M., amperage, discharge flow to lift stations, level at lift stations, and long distance equipment discharges.
Historically, the city of Mexicali has been characterized for its agricultural, industrial and more recently to manufacturing activities. In accordance with the 1990 Population and Housing Census by INEGI, 48.1% of the local population works in the 3rd sector (commerce and services). The estimated population in the area within the legal city limits (Fondo Legal) of Mexicali in 1996 was 600,939.
Due to its special geographic location in relation to the southern California market, and starting in 80's and through State Government policies that have encouraged industrial development, the city has become an area for industrial development of considerable importance for the regional and state economies. This phenomenon has resulted in the creation of a higher number of services and jobs in the community, which have in turn increased the demand for these by the community.
With recent growth in the maquiladora industry, growth in population during the last 5 years (according to estimates provided by the Population and Housing Counting of 1995) has increased at a higher than the prior two decades. This has intensified development of some areas which had not been included service planning/projections. Population projections based on the statistics provided by the census and the Population and Housing Counting of 1995 of the INEGI, establish that the population will increase at an annual rate near 3%, and will double from 507,000 in 1995 to over 1 million residents by the year 2020.
In planning the required service capabilities, the city's current and expected distribution of sub-divisions in areas has been reviewed and divided for the provision of services: Mexicali I, the old central area experiences little growth; Mexicali II, the area with higher growth rates in recent years; and Mexicali III which will have the highest relative growth according to the planning horizons. The City is considered to under the marginality rate. In 1996, the minimum wage in the region's urban areas was $22.60/ day.
The information related whit the social-economical aspects of the city of Mexicali and it's future projections are described in more detail in the "Revised Master Plan for the Improvement of the Services of Potable Water sanitary Sewerage and Sanitation of the City of Mexicali, B.C." dated December 1996 and prepared for the General Sub-Directive of Construction of the National Water Commission by the firm Infrastructure and Services Consultants".
In order to carry out the construction and collector replacement project the works will be implemented in accordance with the procedures established by the SPSCM in this area which have proven to be the most convenient and causing less damage to the neighbors. They also make any excavations as narrow as possible and any material excavated is removed from the area as soon as possible once the ditches are filled in and the pavement has been replaced.
With regard to the lining the collectors, the method being considered has proven successfully in the area. Few disturbances are caused to area residents; the lining for the South collector which has 5.2 km. and crosses under the city's railroad station, which will not allow works to be carried out using traditional methods.
The sanitary sewer works and wastewater sanitation to be carried out will improve the environment as well as the quality of life for the residents on both sides of the border since it will improve the quality of wastewater that cross into the United States trough the New River.
Project execution is justified in accordance with the "Revised Master Plan for the Improvement of the Services of Potable Water sanitary Sewerage and Sanitation of the City of Mexicali, B.C.", dated December 1996, and prepared for the General Sub-Directive of Construction of the National Water Commission by the firm Infrastructure and Services Consultants".
Currently the city of Mexicali provides potable water services to 96% of the community and sanitary sewer services to 90% though it does not have sufficient capacity to provide treatment to all wastewater generated. It can provide treatment to 67%. This has caused untreated wastewater to be discharged into the New River causing an increase in contamination and bad odors along the New River area. The health of all residents of the city has also been affected. As commonly known, the New River is a natural valley drain that has been used as an agricultural drain for many years because it is the lowest geographic point in the area and thus receives wastewater discharged by the city. It also flows from South to North and then crosses the international boundary into the United States where it empties into Lake Salton.
Many areas of Mexicali do not have sanitary drainage service (approximately 10% of the population), resulting in residents installing latrines and/or septic tanks on their properties. This has become problematic because the lots are small and in the course of the years, space to build more latrines has been depleted resulting in diseases among children and adults due to the continuous contact with human waste which also contaminates to the subsoil.
The sanitary drainage of the city of Mexicali is in a state of major deterioration caused by the age of the pipelines or the materials used, making replacement necessary in order to prevent situations that pose risks to the community. When problems with the sewer system surface, wastewater must diverted to the storm water drain system and are then discharged into the New River.
Water that the Mexicali residents discharge into the New River must meet quality standards established by Mexican Laws as well as Regulations NOM-CCA-031-ECOL/1993, NOM-CCA-032-ECOL/1993, NOM-080-ECOL/1994, NOM-041-ECOL/1993, NOM-006-ECOL/1993, NOM-001-ECOL/1993, NOM-004-ECOL/1993, NOM-001-SEMP/1994 and NOM-001-ECOL/1996. Parameters must also conform to international agreements between Mexico and the United States making it critical that all wastewater discharged into the New River be properly treated.
Ninety percent of the city is provided with sanitary sewer services however only the Mexicali I System provides wastewater treatment. The system is located at the treatment plant in the Colonia Zaragoza on the outskirts of the city along the road between Mexicali and Tijuana.
The treatment lagoons in the Colonia Zaragoza require rehabilitation since they are working at maximum capacity and it has become necessary to clean them out and implement complementary works in order for them to be operated adequately. The edges and structures require corrective maintenance, existing shrub growth is affecting the lagoon hydraulics. The organic surface load in the anaerobic lagoons is higher than the recommended load; decomposition of organic matter produces unpleasant odors; the parallel operation does not permit higher efficiency levels, and hydraulic efficiency levels are not adequate. At present the lagoons provide service to 405,321 residents under Mexicali I which only represents 67.45% of the entire city.
The zone for the Mexicali II System (area east the city), does not provide treatment to its wastewater, meaning wastewater generated by 195,618 residents undergoes no treatment at all and is discharged directly into the drains leading to the Río Nuevo, causing contamination and health problems.
The zones for the Mexicali III-A and Mexicali III-B Systems do not provide sanitary sewer service. Residents must use septic tanks and latrines with the constant health risks involved. Which is why the Mexicali I System treatment plant will provide treatment to this water and also why this project includes providing sanitary sewer service to a large part of the zones already developed and rely on potable water services.
An important parameter with regard to human health needs is the reduction of gastrointestinal diseases caused by food products. The Secretary of Public Health published 1995 data regarding this issue and determined for the State of Baja California:
|
Disease |
Cases (residents) |
|
Acute Respiratory |
341.53 |
|
Gastro-intestinal diseases |
73.69 |
|
Helmintiasis |
11.62 |
|
Amibiasis |
6.23 |
|
Non bacteria food poisoning |
3.32 |
Source: Secretary of Health
As seen in this table, gastrointestinal diseases place second in the number of cases occurring. These figures are expected to decrease once the city is able to treat all wastewater generated in the city as well as provide sanitary sewer coverage at a similar level as the potable water coverage.
The following table indicates the main causes in the rate of morbility. This data was provided by the Coordinated Services of Public Health of the State of Baja California for 1995.
|
Disease |
Cases (inhabitants) |
|
Acute Respiration |
163.59 |
|
Gesture-intestinal |
18.08 |
|
Helmintiasis |
2.7 |
|
Amibiasis |
2.1 |
|
Nourishing Intoxication non bacterial |
1.0 |
Source: Health Secretary
To comply with information requested by the State Environmental Agency of the State of Baja California Public Service Commission of Mexicali, through official notice Nº DGE-MXL-578/97 dated June 17, 1997, wherein the agency determined that the proposed project would have a positive impact on the sanitation of the city of Mexicali.
The private firm CH2MHILL developed and prepared the Environmental Assessment regarding the effects caused by the Rio Nuevo Program project in the United States. These works were carried out as an option by the SPSCM to comply with BECC requirements in accordance with its Project Certification Criteria.
The assessment evaluated four long term alternatives for improvement of the wastewater treatment systems of the city of Mexicali, meant to increase wastewater collection, conveyance, and treatment. And also meant to improve the level of sanitation in the city as well as improve the quality of the treated wastewater being discharged into the New River.
ALTERNATIVE Nº 1.- Alternative selected for application to BECC.
Based on analysis of the Environmental Assessment, the proposed alternative reaches a high level of environmental protection due to the following reasons:
2.a. Transboundary Environmental Impacts
2.a.1.Background
The treated wastewater of the city, in the case of the Mexicali I System is discharged into the New River and with the rehabilitation works for the treatment Plant located in the Colonia Zaragoza, the quality of this wastewater will dramatically improve. This will lead to a reduction in the contamination of the New River with improvement to the environment on the U.S. side as well as the Mexican side of the border.
In the case of the Mexicali II System, wastewater discharges are diverted to drain without any treatment; the drain leads to the New river, causing constant contamination problems. Project implementation will avoid untreated water being discharges and the water quality of the New River will improve. Environmental conditions along both the U.S. and Mexican side of the border will also increase.
The New River flows north out of Mexico and into the United States into the Colorado River Basis. Part of the Basis is located in the southeast region of the state of California. The area of Colorado River Basin in the United States covers approximately 13 million acres (20,000 sq. miles), which includes the Salton Sea a salt water lake into which the New River discharges. In Mexico the extension of the New River covers the area known as the Hydrological Region RH-7 and has a surface are of 5,923 Km2 , (see attached plan 3.C.1.)
The New River was formed in approximately 1840 due to floods in the Colorado River. Floods were intermittent until the practice of the agriculture was developed in Mexico around 1950.
The main water currents in the region are the Colorado River, Hardy River, and the New River. The first one has an annual flow into Mexico in the amount of 1,850,234,000 cubic meters, in accordance with the agreement reached with the United States, The currents of the Hardy River are a result of the mountain stream runoff which are located on the western edge of the valley (Cucapah and El Mayor). In the case of the New River, it feeds of the agricultural drains from the Valley of Mexicali.
Both in the United States as well as in Mexico, the New River is used as a drainage. In the United States it is utilized as an agricultural drain serving the western zone of the Imperial Irrigation District (IID) which periodically drains a third part of all of the water used for irrigation into the New River and which in turn discharges into Lake Salton.
In accordance with provisions contained in the Environmental Assessment prepared by CH2MHILL, Section 3.- Affected Environment, Chapter 3.1.2.- Quality of the Water, states that the New River receives water from the agricultural drains consisting mainly of underground drains which reduce the salinity and problems related to the quality of the underground water. The water from the agricultural drain discharged into the New River causes it to rise up to three times its normal flow between the border line and the outfall into Lake Salton. This situation indicates that the flow sent by Mexico is only 25% of the total water discharged by the New River into Lake Salton.
In accordance with the Colorado River Basin Plan, beneficial uses have been designated for the bodies of water. These include use by man, vegetation and wild life. The beneficial uses for rivers and drains in the Imperial County and for Lake Salton are also established pages 3-10 of the study. The large amount of the uses are designed for agriculture, recharging fresh water supplies, non contact recreational activities, and wild life habitats. Lake Salton is appropriate for fresh water recharging since water from the New River has been designated as water that cannot be used for contact and non contact recreational purposes.
The quality standards established for monitoring of quality of New River waters are based on IBWC Minute 264 which were approved in December 1980.
The quality standards established under Minute 264 for the New River are the following:
The Rehabilitation of the Mexicali I System wastewater treatment plant is necessary given that the capacity of design of the plant is 22.4 MGD and the capacity required is 30 MGD. The works encompasses installation of baffles, deeper facultative lagoons up to 1.70 meters, and modification of the hydraulic operation which involves modifying the existing parallel system to a serial flow system.
Implementation of these measures will provide an increased retention time which will result in a more efficient treatment process in order to comply with the specific discharge conditions established for the City of Mexicali. These measures will be reflected in improved conditions of the New River.
Parameter |
Unit |
NOM-001-ECOLMonthly average at discharge |
Minute 264in the New River |
Ph |
Uph |
--- |
6.0 to 9.0 |
Floating matter |
|
none |
none |
Sedimentable solids |
ml/l |
2 |
Absent |
Oil and grease |
mg/l |
25 |
--- |
Total suspended solids |
mg/l |
175 |
--- |
Total BOD5 |
mg/l |
200 |
30 |
Total QOD |
mg/l |
--- |
100 |
Ntk |
mg/l |
25 |
--- |
P total |
mg/l |
5 |
--- |
Dissolved Oxygen |
mg/l |
--- |
5.0 |
Fecal Coliforms |
NMP/100 ml |
1,000 |
30,000 |
Receiving Bodies
The New River is the receiving water body. Currently it receives the water produced by the agricultural drain and surplus from the Colorado River Irrigation District 014. It also receives about 9 MGD of improperly treated wastewater from the González Ortega lagoons (Mexicali II zone). Furthermore, 26.3 MGD flow into the river coming out from the Mexicali I zone. From that figure, approximately 2.3 MGD spills from the sanitary collectors to the storm water sewer system.
The receiving waters of the effluent of the González Ortega plant is the Tula agricultural open channel. The channel runs across the project area from east to west and eventually discharges to the New River.
Mexicali I and Mexicali III Systems
In 1985 CNA implemented a reclamation project to use the treated effluent for agricultural irrigation of 2,792 ha.
Mexicali II System
For this zone, the CNA carried out studies that resulted in two alternatives for reclamation of the Mexicali II effluent. Both alternatives discharge into the Hardy River, one of them includes partial reuse in irrigation while the other includes irrigation and agricultural return.
However, the Master Plan developed by the CAN recommends disposal of wastewater flow surpluses as a combination of reclamation and discharge to receiving waters. For the receiving waters use of the New River as opposed to the Hardy River was recommended.
With regard to the technical process of the Mexicali II WWTP:
Based on the "Revision of the Executive Project of the Mexicali II System Wastewater Treatment Plant", developed by the National Water Commission and the firm Montgomery Watson Mexico, S.A. de C.V., under the contract Nº SGC-AP-96-238-I in June 1997, the process selected for wastewater treatment of the Mexicali II System, was determined to include two phases. The first stage would consist in a natural lagoon system with a 34 day delay period.
The Phase II has taken provisions in land required and the necessary preparations for the head-works. The second stage of operations would include a biological process for BOD rough dressing based on a percolated filters or a high rate activated sludge and the possible inclusion of a floating process with dissolved air. This second stage will be required approximately by the year 2008. Relevant design parameters are described below:
Parameter |
Unit |
Influent |
Effluent |
||
|
|
|
|
Anaerobic |
Facultative. |
Maturate. |
Flow |
l/s |
880 |
880 |
880 |
880 |
BOD5 Influent |
mg/l |
250 |
250 |
138.5 |
26.5 |
Temperature |
C |
12.3 |
12.3 |
12.3 |
12.3 |
Volumetric Charge |
g/m3-d |
- |
49 |
7.0 |
2.5 |
Area |
ha. |
- |
9.7 |
88.34 |
88.4 |
Depth |
m |
- |
4.00 |
1.70 |
0.90 |
Delay Time |
days |
- |
5.1 |
19.6 |
10.5 |
BOD5 Effluent |
mg/l |
- |
138.5 |
26.5 |
12.2 |
Fecal Coliforms |
NMP/100ml |
1.0 E+07 |
2.16E+07 |
1.09E+05 |
2.37E+03 |
TSS |
mg/l |
210 |
60 |
60 |
60 |
Parameter |
Unit |
Effluent |
BOD5 calculated |
mg/l |
18 |
TSS |
mg/l |
45 |
Detention Time Module A |
days |
21 |
Detention Time Module B |
days |
19 |
Total Coliforms |
NMP/100ml |
1.8E+06 |
Fecal Coliforms |
NMP/100ml |
1.8E+06 |
A certain amount of sludge will be deposited in the lagoons, the largest amount is expected in the anaerobic lagoons. After the maximum period of sludge storage, when these residues are stabilized, the removal, collection and disposal will be the next step, using the methodology and considerations described below. Removal will be carried out every 5 or 10 years and will be transported to the final disposal site that will be determined by regulating authorities.
Sludge generated during the operation of the treatment plant will not require an additional treatment process. The majority of the suspended solids will be deposited on the bottom of the anaerobic lagoons. The anaerobic decomposition process of the sedimented sludge will also take place in the lagoons.
The anaerobic lagoons were designed to have a volumetric charge lower than the one specified for these units, resulting in a higher value than required. In this manner an additional volume in the lagoon where the generated sludge will be processed and stored will be ensured, thus avoiding that any space to be occupied by the residues affect the efficiency of the lagoons.
Treatment of sludge stored at the bottom of the anaerobic lagoons is done without oxygen but with anaerobic and facultative microorganisms that digest the organic matter. Sludge processed by this method presents relatively stable characteristics and reaches a low level of decomposition with minimum odors; with these characteristics sludge management can be permanent without causing adverse conditions on the environment.
Emptying water in the lagoon.
Once the estimated time for the stabilization of the sludge of the lagoon has elapsed, pretreatment works of the anaerobic lagoons will be regulated so that the flow of incoming water into the lagoon which is in the emptying process, will be blocked. In this manner, the flow will be distributed in equal portions to the anaerobic lagoons in operation. The mechanism utilized to remove the water from the lagoons will be a siphon line, complemented with other pumping systems. The discharge site, of the siphon as well as the pumping line, will be the anaerobic lagoon adjacent to the one described below. Another option is the distribution channel of the facultative lagoons.
Sludge Extraction
Extraction of the sludge deposited in the lagoon previously discharged, will be carried out with mechanical equipment that will collect and transport the sludge from the bottom of each lagoon up to the loading area where vehicles will transport it to the appropriate site. Operators will remove and pile any sludge that the machine is not able to collect, specifically, from corners and the area next to the feeding pipes.
The sludge has the potential of being utilized in the following areas: composting for use in agriculture. They may be applied in liquid form or after being composted. Another possibility is to apply them in landfills, evaporation lagoons, or in soil mixtures.
Additionally, it will be necessary to take samples of the sludge at the plant to perform laboratory tests (CRETIB) in order to determine the existence of hazardous wastes. If required, sludge will be handled and disposed in accordance whit the appropriate sludge management regulations.
With regard to the wastewater treatment plants, the training program may be classified in two fundamental aspects:
The wastewater treatment process based on a lagoon system requires little operation and maintenance. All essential equipment for continuous operations will have replacement and support parts in stock. In the case of an emergency, system operations will not be interrupted.
The personnel will receive accident prevention and security training in order to reduce any work hazards. The security system will include fire extinguishers in areas where equipment is located; a telephone or two-way radio should be available for communications in case of an emergency.
Visible warning signs will be posted in the appropriate places as well as in the lagoon area to ensure that all persons entering the area are aware of risks involved should contact with wastewater occur.
All personnel shall be provided with safety equipment including gloves, safety belts, protective eyewear, safety boots and uniforms.
In accordance with how the lagoons function and because they do not become obsolete and are no longer able to function on a specific date no closure plan has been established. Lagoons can be maintained at the initial design efficiency levels with proper maintenance.
The designated area for the lagoons is in the Urban Development Program of Population Center 1993-2007, and has a protective barrier around them.
C. Conformance with all Applicable Design Norms and Regulations
The National Water Commission (CNA) issued Official notice Nº BOO.E.31.2/715 dated August 4, 1997, regarding the Mexicali I Wastewater Treatment Plant project. Approval and authorization was given to the project.
Included in the Urban Development Program of Population 1993-2007 carried out by the XV City Council of the City of Mexicali, which regulates and establishes land use for urban structure of the area as well as the policies and programs that consolidate the urban development of the city, the selected area for the expansion of the capacity of the Mexicali I System wastewater treatment plant, located in the Col. Zaragoza, it's designated for this use considering the creation of a protection zone around the plant in order to mitigate the impacts produced in the process, the Treatment Plant of Mexicali II System is located outside of the urban area.
The project will comply with applicable design norms from the beginning of the works and will be regulated by State Construction Regulations and the guidelines established by the Cadastre Dept. of the City of Mexicali, under the building permits area.
Within the Ley de Equilibrio Ecológico and Environmental Protection of the State of Baja California and in accordance with the Article 5, sections V and VII of the Regulations of the Ley de Equilibrio Ecológico and Environmental Protection of the Baja California State in environmental impact matter, the project is considered as a sanitation project.
As such, the region is considered to have sufficient technical capacity and experience required for project implementation which will rely on the most advanced existing technology required to comply with national environmental regulations as well as regulations established in international agreements.
It must be noted that the determination to develop and implement the works involved in the projects as well as their general costs are based on actions coordinated by the International Boundary Water Commission (IBWC) of México and the United States, within the framework of the international agreements reached in Minutes 264 and 294.
Both Commissions have developed coordinated actions to address the shared sanitation needs. In this regard, the Binational Technical Committee (BTC) was established in October 1996 to address the sanitation needs of Mexicali. The committee has the participation of local, state and federal authorities from both countries.
BTC members defined the concept and monetary requirements for implementation of the sanitation actions which was to be submitted as Step I Format to BECC. This re-defined format was submitted to BECC on May 27, 1997, in which the Mexicali I System and Mexicali II System projects were bundled and totaled approximately $50 million dollars which included a preliminary grant proposal with equal contributions by México - United States.
Total project costs have experienced several changes in accordance with completion of the preliminary projects and executive projects, specifically the Mexicali II WWTP executive project which was concluded on August, 1997 by the C.N.A.. Taxes and construction administration have also affected final project costs.
BECC as well as SPSCM, both sections of IBWC and NADBank collaborated in the review and analysis of final project costs. The costs presented in this document were calculated in Mexican currency based on the exchange rate effective April 1997, and based on the index costs of the National Water Commission (CNA). In obtaining the index costs, the most recent and accurate information has been used however, once the executive project is completed these figures will reflect more accurate information.
After review and discussion, the final amount of $398,126,479 pesos was estimated on April, 1997, equivalent to $50,395,757 dollars. The following table shows the breakdown of these amounts divided for the Mexicali I and Mexicali II projects.
Source: SCPSM
Currency exchange rate: 7.9 pesos/dollar
The project's financial feasibility was determined through the analysis of the information provided in the historical financial statements of the State Public Service Commission of Mexicali (SPSCM). Analysis of these considers the income statement, historical earnings and disbursements, and the project costs for both the Mexicali I and Mexicali II Systems.
The financial analysis of the project has given consideration to an $8.70 million contribution by the US EPA through IBWC Minute 294 Minute and a contribution by the State Government of Baja California which will be defined through the Public Works and Human Settlements Secretary of the State (SAHOPE) and the SPSCM. Another possible contribution may come from the Mexican federal government grants through the CNA and a possible contribution by the USEPA.
The SPSCM and BECC carried out the "Study to Determine Payment Capacity for the Sanitation Works of Mexicali". Several scenarios with possible grant programs, loans, project completion dates, rate and fee increases and interest rates.
In determining the project's financial feasibility, the SPSCM and BECC evaluated different scenarios which consider funding by the US EPA and the Mexican federal government. These scenarios reflect the following premises:
Premises:
Investment recovery and coverage of the increase in operation and maintenance costs are based on the new infrastructure.
The SPSCM will recover the loan amount through the economic benefits resulting from the project. Users benefiting directly by the new service will be charged for construction costs and a connection fee which has already been established by the 1997 State Earnings and Expenditures Law.
The SPSCM has annual pre-authorizations for rate increases based on a formula that includes increases in the main O & M costs. This updating process is carried out monthly until the established limit is reached. When the accumulated rate and fee increases exceed the limit, approval by the State Congress is required.
In this manner, the capital and/or loans contributed by the SPSCM do not affect the rates and fees charged to the general public. Rates will only be affected by an increase in O&M costs already included in the Organism's Earnings Law.
Evaluation results were submitted at the 2nd public meeting held by the SPSCM in the city of Mexicali at the CANACO Auditorium on October 9. At the meeting concerns of over 300 attendees were addressed. In addition, public approval regarding the rates and fees to be applied was obtained.
This proposed financial structure makes the project financially feasible, maximizing potential benefits while also utilizing available SPSCM resources as well as projected earnings.
An important result of the financial runs made is that while grant funding sources are reduced, the project's construction period is extended from the original three years up to 15 years.
It must also be noted that the project will be defined by NADBank in conjunction with the US Environmental Protection Agency and the Mexican federal government.
In conclusion, quantities used in the analyses are in pesos at April 1997 prices. When funding application occurs, prices must be revised to reflect any increase in the Consumer Price National Index (INPC) which could affect the project.
The next table shows preliminary in which components of the Mexicali I & II Systems would funding sources be applied.
The operation and maintenance costs, both historical and projected, are shown in the attached "Study to Determine Payment Capacity for the Sanitation Works of Mexicali". The study determined the O&M costs for the new Mexicali II wastewater treatment plant to treat in its initial stages 880 l/s. The cost is $0.35 pesos per cubic meter of treated water. Added to this cost was the estimated cost for operation of Pumping Station Nº 4 as well as some of the complementary works. This cost was finally estimated at $0.50 pesos per cubic meter of treated water.
In addition to this O&M cost, an incremental cost was also added to the general O&M expenses of the SCPSM. The additional cost reflects the increase incurred with the new infrastructure and includes both potable water as well as sanitary sewer services resulting from the system's normal expansion required to maintain coverage.
Projections were made through a 25 year period in order to cover the loan terms to be negotiated by the SPSCM.
The sensitivity analysis carried out considers the impact the project will have with changes in the critical variables described below:
The major sensitivity indicator was obtained with a variation in grant funding. In this regard, if grant funds are reduced by 10%, the SPSCM will be forced to delay the construction period for one year in order to obtain funding from the State during the next fiscal year. With a 20% decrease, it is delayed 1½ years. The less attractive scenario does not include grant funds, which would result in the extension of the construction period to more than 15 years.
This scenario would be presented should there be an increase in the contribution made by the SPSCM in the order of $1 million dollars. As such, in the financial structure proposed herein the SPSCM contributes $6.50 million dollars, and with an increase to $7.5 million, the project would require elimination of the loan amount in order to make the project financially feasible.
The following table shows the historical rate model for 1996 as well as the current 1997 rates charged to the users by the SPSCM for both potable water services and sanitary sewer services:
The SCPSM has pre-authorized rate increases based on a formula that includes the main O&M costs experienced. This revision is done on a monthly basis until the established limit is reached. When the accumulated rate and fee increases exceed the limit, approval by the State Congress is required.
ITEM |
PERCENTAGE |
Wages |
46.0% |
Electrical Energy |
10.0% |
Fuel and lubricants |
3.0% |
Chemical substances, materials and supplies |
35.0% |
C.N.A. Rights |
6.0% |
TOTAL |
100.0% |
The SCPSM has technical and administrative capacity to carry out its functions. Over the last several years it has applied an improvement program to increase operational and commercial efficiency levels, as well as to increase collection efficiency and the recovery of late payments. In recent years, audited financial statements of the SCPSM have shown positive figures, which highlights that the new administration that took office in 1996 has been working on the organization for several years which ensures the continuity of these programs and their effectiveness.
In this regard, the SPSCM has its own Institutional Strengthening Program which includes and adheres to several aspects of the BECC criteria.
Furthermore, it must be noted that the NADBank is working in coordination with the CNA and the SPSCM on an Institutional Development Plan through the PRODIN, in the amount of $250,000 dollars. The Plan will be scheduled over two fiscal Bank years and with funding provided by the C.N.A.
A. Comprehensive Community Participation Plan
On July 10, 1997, the SPSCM submitted a Comprehensive Community Participation Plan to the BECC. The purpose of the Plan is to fully inform the community of Mexicali regarding the proposed project as well as ensure community wide approval. The Plan was approved by the Community Outreach Section.
On July 14, 1997, the Steering Committee was created with representatives of several sectors including the industrial, commercial, services, academic, as well as three representatives of the NGO's, professional associations, and neighborhood representatives.
The Community Participation Plan includes information strategies through meetings with sectors and the media. Some of the Plan actions include:
Committee participation included representatives from communities in Imperial County acting as observers. A community meeting in Imperial was held on October 3rd and a second community meeting will be held on October 16th at the same location.
There was extensive coordination with the Bi-national Technical Committee which is made up of representatives from appropriate agencies from both countries who are in charge of carrying out follow up activities for the development of the Integral Sanitation Project of Mexicali, B.C. Members of the committee were invited to attend the project follow up meeting.
A.1. Public Meetings
The first Public Meeting was held at the CANACO Auditorium with 700 people in attendance. At the meeting it was determined that the majority of the population supports the project. However, a group of local farmers from the Farm El Choropo, though they support the project, raised their concern regarding the location of the Mexicali II treatment plant. The Ejido, located between 500 and 1,000 meters away from the plant site, is home to approximately 250 residents. It was apparent there was a lack of information among this group of local farmers, represented at the meeting by almost 20 people. It must be noted that this village is located outside the city limits, approximately 10 km away.
On October 9th a meeting with representatives of Ejido El Choropo was held. The meeting was held after BECC staff member, Ing. Edgar Tovilla, SPSCM officials and an IBWC engineer visited the area on Saturday, October 4th. At this meeting the National Water Commission provided a detailed presentation of the selection process and reviewed the 12 options evaluated. It was further explained that the plant does not have any negative impacts on the human health and that it does not generate bad odors. In addition, coordinated actions among appropriate agencies to regulate irregular discharges caused by a local slaughterhouse and an egg farm located next to this village which represents a source of contamination.
The 2nd Public Meeting was held with 300 persons in attendance. The meeting was held in order to present the financial aspects of the Integral Sanitation of Mexicali. The project's financial program was presented which includes approximately $50 million dollars in project costs; the presentation also covered project impact on users and new service connections. Public comments reflected approval of the financial and cost recovery program.
Later during the meeting, residents from the Ejido El Choropo raised their concerns with signs and comments. They presented their opposition to the location of the treatment plant. The technical presentation regarding the project site and the benefits on human health was also made. Most of the public comments made were in the context of the position taken by the residents of the Ejido El Choropo.
The Community Participation Report which was submitted by the SCPSM on October 11th, shows that the community was properly informed, that access to project information was guaranteed, and with regard to the survey results, the majority support the project and has an understanding of its benefits and impacts.
It was recommended the community continue addressing the concerns raised by the group of local farmers from the Ejido El Choropo by taking measures described below:
The SPSCM prepared and submitted a written report to the BECC in which successful implementation of the Comprehensive Community Participation Plan is detailed. The report includes all support information, a list of Steering committee members and the activities carried out by each, a list of the local meetings carried out, copies of the public meeting announcements, the Minutes of the public meetings, videos of the main events, and other documents that demonstrates the extensive scope of the Plan.
The report shows that the public understands and supports the project's environmental, health, social, and financial costs and benefits. The preliminary evaluation of the surveys carried shows that between 83% and 93% of the community supports the project.
As a fundamental principle, this project focuses on human beings as the central point of all the objectives of sustainable development, who have the right to lead a healthy and productive life in harmony with nature.
Project implementation will contribute substantially to the reduction of the contamination levels in the New River. Discharges of untreated wastewater into the channels that flow to the New River will be halted. Improvement to the surrounding environment of the New River as well as benefits in both countries will be experienced.
The quality of life of residents of Mexicali will improve substantially once sanitary sewer services are provided and the use of latrines and septic tanks that have constantly caused health problems to nearby inhabitants will be eliminated.
Construction, rehabilitation and lining of collectors will prevent problems in the system that presents risks to the health of the residents.
With the rehabilitation of the pumping station, equipment failure will be avoided and the discharge of untreated wastewater into the New River will be prevented, so the conditions in the river will be maintained within the established parameters.
The conditions along the New River will improve once the Mexicali II System no longer discharges raw wastewater directly into the Mexicali drain. This drain flows to the New River; raw wastewater will instead be conveyed to the new Mexicali II wastewater treatment plant for treatment and will contribute to the decontamination and environmental recovery of the river on both sides of the international border.
The project will meet the present and future needs related to wastewater treatment for the city of Mexicali, which presently has 90% coverage of the sanitary sewer and intends to increase coverage to a percentage similar to the potable water which is 95% at the present.
In order to build the organization's capacity, the SPSCM has developed the following programs:
The rehabilitation and expansion project for the Mexicali I Wastewater Treatment Plant, as well as construction of the Mexicali II Wastewater Treatment Plant, take into consideration reforestation of areas adjacent to the plant and mitigation actions for any possible impacts caused to the dispersion of odors.
In this section is important to point out that the elements that contemplate the Industrial Discharge Control Program were established in coordination between both State agencies directly involved with its control, the State Ecology Department and the SCPSM. In that program the following points are stressed:
The impact caused by project implementation will be definitively beneficial to the community. There will be an improvement in the quality of life of the residents of the colonias where the sanitary sewer service will be introduced, health problems will be reduced to the minimum and there will be an increase in land space allowing for residents to expand use of their homes.
Furthermore, with the introduction of sanitary sewer services, in 3 years it will be necessary to connect close to 7,500 hook ups in addition to the 4,200 hookups that the SCPSM annually serves. The SPSCM will undertake a Program aimed at new users that includes a focus on the community with the new infrastructure, information to potential new users, the procedure and mechanism for establishing connections, the payment for services, as well as a program of connections to the system. The next table is a projection of new users that will be benefited.
New Users |
1998 |
1999 |
2000 |
2001 |
Nº of houses |
5,811 |
5,976 |
4,582 |
4,715 |
Inhabitants |
21,791 |
22,410 |
17,183 |
17,681 |