The Arcediano Dam Project

Background Information

The Arcediano Dam, whose construction is promoted by the Jalisco State Commission for Water and Sanitation (CEAS), would be situated on the Santiago River, 350 meters downstream from its confluence with the Verde River, just below the location of the Arcediano Bridge.

The dam wall will measure 125 m in height and the consequent reservoir will have a storage capacity of 404 million cubic meters. The project includes a pumping station to transport 10.4 m3 of water per second from the bottom of the canyon to the purification plant 580 m above. The CEAS estimates the Arcediano dam project would cost approximately US$300 million. Sixty percent of the cost will be covered by the state government while the remaining forty percent will be obtained from federal sources.

As justification for this major engineering project, the CEAS calculates that the Suburban Area of Guadalajara requires 12.5 m3 of water per second. Its current sources – Lake Chapala, the Calderón Dam and various wells supplying groundwater – provide 9.0 m3 per second which government sources claim results in a deficit of 3.5 m3 per second.

From the beginning, this project has been questioned by diverse groups including academics, researchers and members of civil society organizations. Critiques have focused on the selection process for the project, the analysis of water quality, the cost of the project and the lack of information regarding the proposed process for purification of the water. The following paragraphs will present some of the essential information key to understanding the health risk which the Arcediano Dam Project represents. It also indicates the information that the authorities have failed to supply to the population that would be affected by project.

Health Issues

The main concern is related to the possible impact on the health of the over three million residents of the Guadalajara Suburban Area who would receive water from the dam. This concern is due to the high levels of water pollution in the Santiago River. In 2001, the National Water Commission (CNA) stated that it considered the Santiago River unsuitable as a source of raw water to supply drinking water; despite this official proclamation, the Arcediano Dam Project proposes this very use.

The Santiago River, from its source in Lake Chapala to the Arcediano site, receives wastewater from both domestic and industrial sources. A total of approximately 2,316 liters per second of untreated wastewater is discharged from the Suburban Area of Guadalajara directly in the Rio Santiago or via the Ahogado Dam before the Arcediano site. This same river also receives untreated sewage from towns such as Ocotlán and El Salto.

The Santiago River receives industrial wastewater from industries based in Ocotlán, from the industrial corridor which runs from the Guadalajara Industrial Park alongside the road to El Salto and La Capilla, and the industrial zone situated along the ring road to the south of the city of Guadalajara. A large number of significant industrial installations are also situated outside of these industrial zones.

In Mexico, water quality is measured using a Water Quality Index (ICA). The National Water Commission (CNA) requires untreated water proposed as a source for drinking water purification to have an ICA value of at least 50. The Santiago River, at the site for the proposed construction of the Arcediano Dam, according to the CEAS has a value of 33 in the dry season and of 48 in the rainy season. A level of 33 is considered unacceptable and 48 dubious as a source of water to be purified for human consumption.

Therefore, the studies which the CEAS itself has presented reveal the following:

  • While the Verde River contributes 70% of the volume of water, the Santiago River provides 67% of the pollution.
  • Wastewater of industrial, commercial and service sector origin is discharged from the Suburban Area of Guadalajara containing organic pollutants and heavy metals which do not easily break down and are not easily assimilated. These pollutants are harmful to aquatic ecosystems and local populations.
  • The CEAS concludes that the presence of these unconventional pollutants, from non-domestic facilities including industries, that discharge into the Santiago River, present a potential risk for water quality, given their resistance to processes used in the purification of drinking water, and their resistance to assimilation and bio-depuration.

Furthermore, the data presented by the CEAS indicate that due to the presence of excess nitrogen and phosphates in the river basin, conditions for eutrophication will develop in the reservoir, even when the proposed wastewater treatment plants are taken into account. Eutrophication, or the increase of nutrients in freshwater lakes or reservoirs, provokes an excess of phytoplankton and can cause severe deoxigenation of the water which is linked to human health problems. Eutrophication stimulates the growth of cyanobacteria, and the presence of cyanobacterial toxins has been linked to liver cancer.

Based on another study requested by the CEAS1, Mercedes Lu, Technical Advisor of eLAW (Environmental Law Alliance Worldwide) of the United States, evaluated the water quality data for the Verde and Santiago rivers as well as the viability of the construction of the dam. Lu underlines the fact that the studies found highly toxic substances, including benzene, toluene, trichloroethane and heavy metals such as chromium, cobalt, mercury, lead and arsenic; several of these substances are known carcinogens. Based on her analysis, Lu concludes the following:

"The technical report presented by the CEAS lacks information which would guarantee, technically and objectively, that the quality of the water to be distributed to the citizens from the Verde and Santiago rivers will be safe for the population.

It also lacks a technical and economic study of water treatment to efficiently and effectively remove the toxic compounds, such as heavy metals, benzene, polycyclic aromatic hydrocarbons and other substances of known toxicity found in the results of the water analyses.

Without detailed knowledge of the technical proposals and of the projected costs of water treatment for the waters to be stored in the Arcediano, it is not possible to determine the effectiveness of the water treatment methods, nor the viability of the use of this water for human consumption."

The document Evaluation of the Viability of the Arcediano Dam Project prepared by the Technical Analysis Committee of the Arcediano Project, an interdisciplinary committee formed of researchers from the University of Guadalajara, indicates several of the projects’ associated health risks. This evaluation indicates that:

  • At the site of the Arcediano Dam Project, "there is no complete characterization of the presence, distribution and potential migration of high-risk chemicals present in the . . . sediments of the riverbed . . . it is clear that the cost of cleaning the riverbed is not included in the budget."
  • "There has been no evaluation of the potential impact of the Arcediano system on public health that analyses the categories of health damage associated with the building and operation of the dam."
  • ". . . the high volume of discharges of chemical residues in the Santiago river basin means some sections of the river contain high concentrations of polluting elements, principally highly toxic, high risk heavy metals such as lead, arsenic, mercury, aluminum, as well as cyanide.
  • The consequences of the ingestion, absorption or inhalation of these metals include: "altering of the reproductive and nervous systems, learning difficulties, memory loss, cancer and altering of bone tissue, mainly in children, pregnant women and the elderly."
  • "Given the agricultural activity in the area there is a high possibility that the course of the river is contaminated with highly toxic pesticides, which are used in large quantities."

The study indicates the striking lack of consideration given to the participation of the health sector in the design of the project. This indicates that if the highly deficient sanitary conditions present in the Verde and Santiago rivers are taken into account, this deficiency: "will convert the Arcediano site into a risk for the population if a dam is built in this location."

The known pollution of the Santiago River puts into question the proposal of the Arcediano Dam Project. Even if it were technically and economically possible to succeed purifying the water, it is not an option that meets international standards, as is indicated below:

  • "International best practices indicate that treated wastewater is not recommended for use as drinking water, due to possible risks to human health that an eventuality could imply, such as the presence of an unknown pollutant or the malfunctioning of a water treatment plant. They therefore suggest that wastewater be used for human consumption only as a last resort."
  • Taking into consideration this recommendation, the lack of information about the way in which the water will be purified must be highlighted, as well as the costs implied by the maintenance and operation of the treatment plants.

Economic Issues

The Arcediano Dam Project has been promoted as an economical water source for the Suburban Area of Guadalajara; however, there are many points on which to question this affirmation. The dam will be built with public finances and will implicate public debt. For this reason it is essential to analyze the operation and maintenance costs as well as the cost of construction of the dam.

Cost of the Dam

The facts that CEAS have presented about the cost of the project have been considered totally inadequate. The Technical Analysis Committee of the Arcediano Project indicates that, "the budget presented is not sufficiently precise, clear nor complete". They therefore conclude that, "they do not consider that there exists a sufficiently solid base to determine with the necessary precision the amount of capital needed for the Arcediano Dam, for example the current budget of US$300 million". Furthermore, seeing as the budget is incomplete, it has been confirmed that, "significant areas have not been included in the total cost and will affect the financial viability of the project". They indicate that, for example, the cost of cleaning the riverbed of the Santiago has not been taken into account.

Cost of the Water

The problematic situation of serious pollution of the water that would reach the dam has already been mentioned. Although it is, in theory, possible to purify all grades of water, due to the fact that the precise levels of pollution of the waters that will feed Arcediano are unknown, it is impossible to calculate the resources, both economic and technological, needed to make the water suitable for human consumption.

The cost of the required electricity has been presented in an inconsistent manner. Academics from the University of Guadalajara estimated that to pump 10 m3 of water per second to a height of 580 m, 69 megawatts of electrical energy would be required. This quantity is equivalent to 11% of the current energy consumption of Guadalajara. This energy consumption is equivalent to 36million dollars per year or nearly a hundred thousand US dollars a day!

From a more inclusive perspective, taking into account the growing awareness of the limited supply of freshwater both within Mexico and worldwide, this highlights the government's focus on supplying the city with more water through large-scale engineering works. An approach is lacking that takes into account the loss of water through the distribution network, even when these loses account for forty to forty-five percent of the total of water supplied to the Suburban Area of Guadalajara. Nor has a reduction in demand through environmental awareness campaigning been considered.

Ecological Issues

The Arcediano Dam, as has been previously mentioned, will be built in the Oblatos-Huentitlán canyon, an area of high biodiversity; rich in flora and fauna including various endangered and endemic species. Around 400 species of plant have been recorded in the area planned for the reservoir. It is important to underline the uniqueness of the ecosystem along the length of the canyon due to the combination of altitude and humidity from the Pacific. At over 1,000 m above sea level the canyon represents a micro-climate which serves as a climate regulator for Guadalajara as well as a natural barrier limiting the city's growth.

For these very characteristics, in 1997 the canyon was declared a Protected Natural Area by Guadalajara City Council subject to ecological conversation. In 1934, it had previously been declared a Zone of Protected Forest. The construction of the dam would mean the deforestation of over 1,300 hectares of land followed by the flooding of 800 hectares and the great loss of biodiversity including unique species.


  1. Results of the analyses of the Verde and Santiago rivers, undertaken by the University Center for Exact Sciences and Engineering (CUCEI) of the University of Guadalajara for the CEAS.