Border Environment Cooperation Commission

Replacement of a Potrero Wellfield Well in Nogales, Arizona


General Criteria

Human Health

Technical Feasibility

Financial Feasibility

Public Participation

Sustainable Development



I. General Criteria

1.     Type of Project.  The project consists of the construction of a drinking water well in Nogales, Arizona.

2.     Location of Project.  The City of Nogales is located in Santa Cruz County, in South-Central Arizona. Nogales is located along the U.S.-Mexico border, 62 miles South of Tucson, Arizona. Nogales, Sonora, its sister City is located just south of the border from Nogales, Arizona. The project is located within the 100 km border region as defined by the La Paz agreement. According to U.S. Census 2000 data, the population in Nogales, Arizona is approximately 21,000. The project consists of the construction of a new drinking water well to substitute the City’s Meadow Hills #2 well, currently contaminated with trichloroethylene (TCE), trichloroethane (TCA), dichloroethane (DCA), and dichloroethylene (DCE). Well #2 has an extraction capacity of 800 gallons per minute (gpm). The water consumption per capita is 85 gallons per day for the domestic sector, and 187 gallons per capita per day considering the commercial, governmental, and industrial sectors.














Description of Project and Tasks.  The project considers the construction of a new drinking water well with a total extraction capacity of 1,200 gallons per minute (gpm) as well as all necessary accessories, including a pump and a main to connect to the City’s distribution system.

Compliance with International Treaties and Agreements.  There are no applicable international treaties or agreements regarding water extraction in Nogales, Arizona. The only international agreement between Nogales, Arizona and Nogales, Sonora relates to the operation of the Nogales International Wastewater Treatment Plant (NIWTP.) The operation of the NIWTP is responsibility of the International Boundary and Water Commission (IBWC.)



II. Human Health and Environment

1.      Human Health/Environmental Needs. The City of Nogales, Arizona proposes to construct a water supply well to replace Well No. 2 in Meadow Hills, which has been taken offline from the municipal potable water system. This action was necessary to minimize the potential for interception of existing groundwater Volatile Organic Compounds (VOC) pollution. The proposed well will guarantee the Arizona Department of Water Resources 100-year assured water supply.

The project will address serious health concerns stemming from a VOC contamination plume that has been identified near the Meadow Hills well area. Contamination of the aquifer accessed by the Meadow Hills Well No. 2 includes dichloroethylene (DCE), dichloroethane (DCA), trichloroethane (TCA), and trichloroethylene (TCE). The source of this plume has been traced to United Musical Instruments (UMI), a musical instrument manufacturing company. Contamination of groundwater was discovered by UMI in 1985 during work on an on-site pond. The site was previously declared an Arizona Water Quality Assurance Revolving Fund (WQARF) site. UMI received a Poor Water Quality Permit from ADWR with instructions to remediate VOC-contaminated groundwater. The groundwater treatment process for Well No. 2 is an air stripping treatment process that transfers VOCs from the liquid phase to the gaseous phase. The treated water is then sent to a lined pond where it is extracted and used for irrigation on the Palo Duro golf course.

Volatile Organic Compounds are known carcinogens and allowable levels in drinking water are extremely low by Arizona State and Federal standards. Administration of VOCs to mice induces neoplasms in the liver, and TCE has been found to cause pulmonary adenocarcinomas and hepatocellular carcinomas in mice.

The Arizona Department of Health Services completed a Community Health Survey in Decmeber 1994 and found that the excess occurrence of Systemic lupus erythematosus (SLE) and multiple myeloma, and the prevalence of Anti-Nuclear Antibodies (ANA) in Nogales as compared to Patagonia, a neighboring community, is strong evidence that adverse health effects have occurred in Nogales. The report states: “The concordance of these observations is strong evidence that adverse health effects have occurred in residents of Nogales, Arizona and that these health effects may be the result of complex environmental exposures to biologic or chemical agents.”

The proposed well will supply water to the existing City of Nogales potable water system, provide consistent water quality and is anticipated to supply a capacity equal to the capacity of the well replaced.

2.      Environmental Assessment. An environmental assessment (EA) was prepared by the City of Nogales. Since the project sponsor is not seeking federal funding for the construction of the well, the environmental review does not need to comply with the National Environmental Policy Act (NEPA). However, the EA does comply with the Border Environment Cooperation Commission environmental review guidelines as established in the Project Certification Criteria. As part of the evaluation, the impacts were assessed for the following environmental parameters: topography, geology and soils, climate and air quality, drainage, groundwater resources, and floodplain. The proposed well site will not have any impacts on the existing upper aquifer, since it will be over 1,000 ft deep to gauge the aquifer potential of the deeper sediments that make up the Nogales Formation.  The project does not have transboundary impacts.


3.      Compliance with Ecology and Cultural Laws and Regulations. The environmental assessment presented by the project sponsor complies with the BECC project certification criteria. Also, the construction of the well does not present a potential impact to any environmental resources in the project site.


III. Technical Feasibility


1.      Appropriate Technology. The final design for the construction of the Potrero Well has been finalized. Drilling of the well is underway. The final design was based on hydrogeologic investigations performed at the project site. The well is being drilled using reverse circulatory rotary drilling, a method typically used in the construction of potable water wells. 

The investigation showed that the project site is an appropriate location for the well and that the aquifer is capable of providing adequate capacity to replace the Meadow Hills Well No. 2. The factors considered in the selection of the site include: ease of access, proximity to a water line serving a nearby reservoir, availability of electrical power, adequate separation of the well site from sources of contamination of pollution, easement and land acquisition, and location in relation to the floodplain. The design of the well includes a 20-foot minimum surface seal, appropriately sized slotted perforations, sounding, gravel and vent tubes, concrete pump pedestal, and gravel pack and annular grout seal. The well will be equipped with a vertical turbine pump and motor and the well site will be equipped with a hydropneumatic pressure tank with air compressor, sampling taps, air release-vacuum relief valve, shutoff valves, flow meter, and check valve.

Construction components and techniques selected for the project have been used on numerous well sites in Nogales and throughout southern Arizona. The well site will require minimal operator interaction. Controls will be based on reservoir level, which is affected by the demand in the system. The system will be tied into the City’s Supervisory Control and Data Acquisition System (SCADA), which will allow the remote monitoring, and control of the well operation.


2.      O&M Plan.   The City of Nogales water system operation and maintenance program has been established and is currently used for all wells in the system. The same procedures will be used for the Potrero Replacement Well. Typical procedures for operation and maintenance of wells, and other facilities in the water system, are contained in several manuals prepared by the California State University, Sacramento, entitled “Small Water System Operation and Maintenance” and “Water Distribution System Operation and Maintenance.” These manuals provide the basic outline for the operation and maintenance program followed by the City of Nogales. In order to provide a summary of the operation and maintenance concerns and procedures for wells in the City of Nogales water system, the following information is provided, as outlined in the O&M manuals.

a.      Start-up Operation Plan. Chlorination and new source testing is required per the ADEQ Engineering Bulleting No. 10. Following satisfactory compliance with new source testing requirements, ADEQ will grant permission for the well to be placed in service, at which time the City may begin pumping water from the well into the water system.

b.      Contingency Plan. Numerous options are available to the City if unforeseen circumstances affect the operation of the well site. During construction and during normal operation of the site, onsite personnel and operators must be aware of unusual conditions or changes in the characteristics of the well, such as water quality, water production, and operation of the pump and motor. In the event that there is an unexpected change in the operation of the well, the exact procedure will depend upon the conditions, and are based primarily on the operators knowledge of the system. The City of Nogales will respond to emergency conditions in accordance with the City of Nogales Water Department Emergency Operations Plan.

c.       Safety Plan. Safety issues are addressed in safety training provided by the City of Nogales to water system personnel and are discussed extensively in the O&M manuals. The operation safety program includes such topics as safe work practices, driving safety, hazardous chemicals, use of monitoring equipment and protective clothing, slips and falls, handling and lifting, and electrical safety.

d.      Quality Assurance Plan. All operators have a responsibility to exercise due care and diligence to protect the water sources in the system, effectively operate and maintain the facilities, and take corrective action as necessary to assure that safe and potable water in adequate quantity and pressure is supplied to the community. All operators will have a working knowledge of all component parts of the wells and completely understand the role of each part in the operation of the well.

The well will be checked often enough to assure that the facilities are receiving proper service, maintenance functions are performed as needed, facility components are operating properly and capable of producing safe water, and that the well site is secure. The site will be inspected visually for condition and proper operation every day. When the operator enters the well site, a complete visual inspection of the facility will be made, including listening for any unusual noises and feeling for vibrations on equipment.

The maintenance of proper records pertaining to operation and maintenance is critical to the proper operation of a well site. An operational record will be maintained for the well, and will be completed each time the operator visits the facility either for routine service or for other purposes. Items noted in the records will include the date and time of the service visit, well meter reading, electric power meter reading, oil level, amount of lineshaft oil added, greasing frequency, air level in the pressure tank, static water level in the well, and general operation and appearance of the facility. Some of these data will also be logged automatically by the telemetry system, which reports directly to the main City of Nogales Water Department computer.


3.      Compliance with applicable design norms and regulations. The well has been designed and will be constructed in accordance with all applicable local design regulations and standards, as developed by the Arizona Department of Environmental Quality and presented in ADEQ Engineering Bulletin No. 10, “Guidelines for the Construction of Water Systems.


IV. Financial Feasibility and Project Management

1.      Financial Feasibility. 

BECC prepared a financial analysis for submittal to the NADB (see Appendix A). The financial analysis includes an evaluation of cash flow, system revenues, debt service, and capital improvement program. As part of the investment program, only the construction of the Potrero Well is considered. Other projects, currently being developed as part of the Water and Wastewater Master Plan are not being considered as part of the Capital Improvement Program. These projects will be considered at a later date, once those projects are proposed for BECC certification. The City of Nogales expects to pay for the construction of the well with a NADB loan and municipal bonds. 


Project Cost


Amount (US$)



Engineering and testing




BECC Documents

Well construction





Contingencies (10%)








Current Water Expenses (Annual)


Amount (US$)


Water Office







Financial Structure


Amount (US$)


NADB Value lending program



Municipal bonds








Rate Model: The loan will be paid with an increase in new water connection fees. The user fees will not be increased to service the debt of the loan for the construction of the well. The City of Nogales is considering a rate increase to pay for other projects in the Capital Improvement Program. The increase for the average user will increase a total of $6.71 per month, or 31 percent. The average water bill assumes a monthly consumption per household of 9,500 gallons per month (at $1.68 per every 1,000 gallons) and a monthly base fee of $5.60. In the year 2006, the rates will increase an additional 2.3 percent to a monthly average of $28.97. Currently, the average water bill is $21.60 per month.







Average Monthly Water Bill

$ 21.60

$  28.31

$ 28.31





  Average Monthly Water Bill

$ 28.31

$ 28.97

$ 28.97







2.      Project Management. The City has adequate personnel to handle the proposed infrastructure and to respond to any potential emergency that might arise during operation and maintenance of the project. 



V. Public Participation

Comprehensive Public Participation Plan. The City of Nogales and the steering committee submitted a public participation plan (Plan) to BECC on February 6, 2000, which was approved two days later.  The Plan described the step the committee will take to comply with the objectives of public participation, identify and meet with local organizations, organize an informational outreach campaign, hold public meetings and develop and final report documenting public support for the project.

Steering Committee: The steering committee was formed on January 5, 2000 and included:  Maria Gómez-Murphy, president; Anita Jones, Isabel Leal, Leonor Sesteaga, Norma Cárdenas, Shirley Macias, Maria Antonieta Pérez and Gloria Rosas, of the Way of the Heart Promotora Institute of Nogales. The committee counted with the support and advice of Gerardo Calza, Engineering Department City of Nogales and Kara Festa, consulting engineer.  


Local Organizations: The steering committee contacted health groups, social and civic organizations and local churches to present the project and solicit public support for it.  


Public Information: The certification, environmental and engineering documents, were available for public review at the public library, Public Works Department, and Way of the Heart Promotora Institute during and after work hours and during the public meetings.  Four 45-minute radio programs were aired with a broadcast footprint from the border to Tucson, House to house visits were held in neighborhoods located near the wellhead such as Meadow Hills, Vista del Cielo and Monte Carlo, as well as in other neighborhoods in Nogales. Public meeting notices were published in the Nogales International and a bilingual fact sheet was developed and handed out to residents. 


Public Meetings: Two public meetings were held per BECC requirements.  The first meeting was held on March 6, 2000 at the Way of the Heart Promotora Institute – Nogales Neighborhood Center. About 50 people attended the meeting. The second public meeting will take place on May 1st, 2002.  



VI. Sustainable Development

1.      Definition and Principles.  The project complies with BECC’s definition of Sustainable Development:  “An economic and social development based on the conservation and protection of the environment and the rational use of natural resources, but considering current and future needs, as well as present and future impacts of human activities”.

The construction of the well is centered on providing an improved quality of life for human beings.

The project provides environmental protection by replacing a contaminated water supply.

Stakeholders for this project include the Public Works Department, and members of the steering committee that have been active in the public outreach for the project.


2.      Institutional and Human Capacity Building.   An aspect of this project that will build institutional capacity is the creation of reserves for any potential emergencies.


3.      Conformance with Applicable Local/Regional Conservation and Development Plans.  The project is required to comply with the Arizona Department of Water Resources 100-year assured water supply.


4.      Natural Resource Conservation. The Meadow Hills Well No. 2 is being treated by United Musical Instruments via an air stripping process that converts volatile organic compounds from liquid to gaseous phase. The treated water is being used for irrigation of the Palo Duro golf course.


5.      Community Development. Without a clean water source and an assured 100-year water supply, a number of negative impacts to the community will continue, hindering community development.