NIWTP_Upgrade-Expansion_EA.pdf

ENVIRONMENTAL ASSESSMENT

for

NOGALES INTERNATIONAL WASTEWATER TREATMENT PLANT (NIWTP)

UPGRADE/EXPANSION

INTERNATIONAL OUTFALL INTERCEPTOR REPLACEMENT

WASTEWATER COLLECTION SYSTEM REHABILITATION

Nogales, Arizona and Nogales, Sonora

Prepared for

U.S. Environmental Protection Agency

Region IX

75 Hawthorne

San Francisco, CA 94105

Prepared by

U.S. Section International Boundary and Water Commission

4171 N. Mesa

The Commons Building C

El Paso, TX 79902-1441 and

Camp Dresser & McKee Inc.

177 North Church Street

Suite 800

Tucson, AZ 85701

CDM Camp Dresser & McKee S:\users\mklatt\projects\pmd99021\task8\working\ea120_new.wpd

List of Acronyms ADE� Arizona Department of Environmental �uality ADWR Arizona Department of Water Resources BECC Border Environment Cooperation Commission CE� Council on Environmental �uality CFR Code of Federal Regulations EA Environmental Assessment EI Environmental Inventory EIS Environmental Impact Statement EPA U.S. Environmental Protection Agency FONSI Finding of No Significant Impact IBWC International Boundary and Water Commission IOI International Outfall Interceptor NEPA National Environmental Policy Act NIWTP Nogales International Wastewater Treatment Plant PCE Tetrachloroethylene USIBWC U.S. Section, IBWC

CDM Camp Dresser & McKee

Section 1 Environmental Assessment

This Environmental Assessment (EA) is a stand-alone document developed parallel with and supportive of the Ambos Nogales Facilities Plan. This EA satisfies the requirements of the National Environmental Policy Act (NEPA) of 1969, the Council on Environmental Quality (CEQ) NEPA regulations (40 CFR Parts 1500–1508), the Environmental Protection Agency (EPA) NEPA regulations (40 CFR Part 6), the International Boundary and Water Commission (USIBWC) Final Operational Procedures for Implementing Section 102 of the National Environmental Policy Act, and the Border Environment Cooperation Commission (BECC). The primary purpose of the EA is to gather sufficient evidence and analysis for determining whether to prepare an Environmental Impact Statement (EIS) or a Finding of No Significant Impact (FONSI). An EIS is required if significant environmental impacts are anticipated.

1.1 Scoping

The international concerns and diversity of projects dictate that this EA incorporate analyses at a level generally associated with a NEPA EIS. This EA therefore meets the general requirements of an EIS and, as a component of the parallel Ambos Nogales Facilities Plan, considers NEPA requirements related to public involvement and community outreach. Public involvement is a component of this EA. This EA addresses all important potential impacts on the U.S. side of the international boundary, as well as transboundary impacts. Impacts in Mexico are covered in a Mexican environmental assessment, as appropriate.

1.2 Introduction

NEPA, along with subsequent amendments, requires that environmental considerations be given careful attention and appropriate weight in every recommendation or report on proposals for legislation and for other federal actions significantly affecting the quality of the environment. The requirements of NEPA are to be integrated with other planning and environmental review procedures required by law or by agency practice so that all such procedures run concurrently rather than consecutively. To meet these requirements, this EA is conducted concurrently with the Ambos Nogales Facilities Plan to evaluate the potential for identified project alternatives to adversely affect the local environment. As part of the facilities plan, an Environmental Inventory (EI) has been developed, and constitutes Section 6 of the facilities plan report.

The EI and other sections of the Ambos Nogales Facilities Plan provides details and much of the basis for the information presented in this EA. For example, the EI includes detailed descriptions of the local environment and habitats as well as discussions of the value of intermittent and ephemeral waters, the identification of important environmental resources, and the biology of important species. Other sections of the Ambos Nogales Facilities Plan provide detailed information on related issues such as socioeconomic issues and wastewater treatment processes.

The potentially affected environment is assessed in this EA as sixteen (16) individual components.

Fifteen of these components were previously identified in Element 6 of the Facilities Plan, the EI, CDM Camp Dresser & McKee

1-1 and include land use, geology and soils, topography, floodplains, surface water quality, groundwater aquifers, groundwater quality, biological resources (including threatened/endangered species), historic and cultural resources, public health and safety, air quality and odors, energy supply and natural resources, hazardous and solid waste, aesthetic resources, and parks. The category socioeconomics, which includes issues related to demographics, employment, and population growth, was not included in the EI. This category is also assessed in this EA. The EA therefore evaluates sixteen (16) resource categories, the fifteen (15) categories defined above and socioeconomics.

Another component discussed in the EI, applicable plans and policies, is not evaluated in the EA because it is not a component of the potentially affected environment. This EA does, however, consider how project actions and other related actions influence applicable plans and policies. No conflicts between applicable plans and policies and project actions or other related actions have been identified.

1.2.1 Purpose of the EA

The primary purpose of the EA is to determine if a FONSI can be prepared for the proposed action described in the following sections. A FONSI precludes the need to perform an EIS, while a finding of potentially significant impact dictates that an EIS is required. CEQ 40 CFR Part 1508.9 provides the following definition and requirements for an EA:

Environmental Assessment:

(a) Means a concise public document for which a Federal agency is responsible that serves to:

(1) Briefly provide sufficient evidence and analysis for determining whether to prepare an environmental impact statement or a finding of no significant impact.

(2) Aid an agency’s compliance with the Act when no environmental impact statement is necessary.

(3) Facilitate preparation of a statement when one is necessary.

(b) Shall include brief discussions of the need for the proposal, of alternatives as required by section 102 (2)(E), of the environmental impacts of the proposed action and alternatives, and a listing of agencies and persons contacted.

1.2.2 Project Identification and Location

Currently, domestic wastewater generated in Nogales Sonora, is conveyed north by a gravity collection system to Nogales, Arizona where it is combined with Arizona flows in the International Outfall Interceptor or IOI. Together, the combined wastewater flows from both cities continue northward via the IOI, along the Nogales Wash, to the Nogales International Wastewater Treatment Plant (NIWTP) where treatment takes place prior to discharge to the Santa Cruz River basin.

Due to deficiencies within the Sonoran collection system, a certain amount of untreated wastewater escapes into the Nogales wash, a tributary of the Santa Cruz river. In addition, seasonal increases in

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1-2 the water table caused by storm events account for a significant amount of infiltration especially into the IOI. This results in dilution of the wastewater as well as a reduction of hydraulic residence within the NIWTP. Both these factors can reduce the efficiency of treatment and may lead to the release of inadequately treated effluent to the Santa Cruz River.

The project area is located in southern Arizona and northern Sonora, Mexico. The northern boundary of the project area extends to the farthest reach of the Santa Cruz River with effluent–dominated surface flow (Figure 1). During most seasons and most years, this is near Tubac, Arizona, about 26 km (16 miles) downstream of the NIWTP. To the east, the project area is bounded by the Santa Rita and Patagonia Mountains, and to the west by the Pajarito Mountains. The southern boundary of the project area is delineated by the wellfields in the Los Alisos area of Sonora. Section 6.3 of the Facilities Plan (Topography) provides a more detailed description of the project area.

Specific sites identified in the Facilities Plan for the construction of treatment facilities under one or more alternatives include (1) the current NIWTP site near the confluence of the Nogales Wash and the Santa Cruz River; (2) at the Santa Cruz River between the NIWTP and Kino Springs near the intersection of Arizona State Route 82 and the Santa Cruz River; (3) the industrial site along River Road in the Rio Rico area. The disposal or discharge of treated wastewater generated at one or more of these WWTP sites requires an assessment of potential discharge locations. Several alternative sites were evaluated for wastewater discharge via direct discharge to the Santa Cruz River. Another potential discharge site was identified at Potrero Creek where discharge may be accomplished. At each potential discharge location, the added benefit of aquifer recharge is considered a positive secondary effect.

In Mexico, the initially selected sites of interest for treatment included (1) the Santa Cruz River at Mascareñas, east of Nogales; (2) the Santa Cruz River at El Mezquital, south of Mascareñas; (3) the Santa Cruz River at San Luis; (4) the Santa Cruz River at Paredes; and (5) two sites near the intersection of Rio Los Alisos and the Road to Saric south of Nogales, Sonora. These sites were also initially considered for their suitability for discharge of treated effluent, along with the added potential for aquifer recharge via direct discharge to the river followed by percolation. The parallel Mexican EA provides a detailed analysis of impacts to environmental resources in Mexico.

1.2.3 History of Proposed Action

There has been concern with pollution and public health issues along the U.S.–Mexico Border for several years. These concerns gained further importance in public opinion and the media during the negotiation of the North America Free Trade Agreement (NAFTA) which, according to some opponents, would increase the extent of contamination along the border as U.S. industries relocated to border areas in Mexico. A border sanitation problem has existed in Ambos Nogales since the 1940s, and has been attended to by the United States and Mexico by the construction of international outfalls and treatment plants; first, in the 1950s, then in the 1970s, and more recently in the 1990s. In Ambos Nogales, occurrences of raw or partially treated sewage in surface waters has been one of several border sanitation problems that threaten the health and well being of inhabitants along the border area. In 1995, the U.S. Congress passed an appropriations act, authorizing the U.S. Environmental Protection Agency (EPA) to spend US$47.4 million addressing

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Southern Pacific R.R. Sonoita Creek

Rio Rico

Discharge to Santa Cruz River

19 NIWTP Guevavi Creek

Santa Cruz River

Guevavi Ranch

289 Nogales Wash

River Road

International Outfall Interceptor

Kino Springs Duquesne Road

Arizona

Potrero Creek

Mariposa Road

Patagonia

Road

U N I T E D S T A T E S O F A M E R I C A

Buenavista

Sonora

NOGALES

Nogales, Sonora Collectors

Mascareña

M E X I C O

Nogales Wash

El Mezquital

Los Alisos River

Santa Cruz River

N

W

S

E Agua Zarca

Paredes

0 1 2 3 4 miles

Figure ES-1 CDM Camp Dresser & McKee Project Area sanitation problems on the border. EPA, Region IX, selected Ambos Nogales and Mexicali, Baja California for the development of sanitation facilities plans to develop alternative solutions for future implementation. Of these funds, EPA awarded US$33.6 million to USIBWC to develop facility plans and carry out selected wastewater sanitation improvements at Nogales and Mexicali.

The International Boundary and Water Commission (IBWC), represented by the United States and Mexico deliberated the terms of an international agreement made formal by IBWC Minute 294. This minute authorizes the formation of a multi-agency binational technical committee to coordinate the development of a wastewater facility plan facilitated by the IBWC. The Binational Technical Committee, as described in the following sections, represents federal, state, and local government agencies of both countries. In addition, the USIBWC retained the environmental consulting firm Camp Dresser & McKee Inc. (CDM) to act as an external consultant in the development of the Facilities Plan. It is expected that the responsible party or parties in the United States and Mexico will present the Facilities Plan to the BECC. If certified, the project would be eligible for North American Development Bank (NADBank) financing.

1.2.4 Relevant U.S. Lead and Cooperating Agencies

The IBWC under Minute 294 formed policy and technical binational committees to develop the Facilities Plan. The Binational Technical Committee is in charge of overseeing, providing guidance, and identifying relevant issues that require attention on a day–to–day basis. The Binational Policy Committee, on the other hand, is primarily responsible for decision making, but also provides directives on global or "big picture" issues. The binational committees are in turn divided into national committees. This section describes the members of the U.S. committees and their role in the Facilities Plan, followed by descriptions of Mexican agencies involved in the Facilities Plan.

International Boundary and Water Commission

The international coordinating agency for the facility plan development is the IBWC, an international organization established by the 1944 Water Treaty. The Governments of the United States and Mexico entrust to the IBWC the application of the 1944 Water Treaty (TS 944; 59 Stat 1219) and the regulation and exercise of the rights and obligations assumed by the two governments under this and other boundary and water treaties and agreements. The United States and Mexico obligations for the Nogales sanitation problem are in IBWC Minutes 227, 276 and 294. The IBWC is made up of two Sections, a United States Section (USIBWC) and a Mexican Section (MxIBWC) headed by an engineer commissioner appointed by the President of the respective country. Each Commissioner receives foreign policy guidance from his respective foreign office in those matters of joint action with the other country.

The IBWC may conduct studies and investigations on boundary and international water matters under the various boundary and water treaties and other international agreements in force between the United States and Mexico and as the two Governments may request.

The USIBWC has international oversight of the Nogales International Wastewater Treatment Plant (NIWTP), which has a design capacity of 754 L/s (17.2 mgd) average daily flow of which 320 L/s (7.3 mgd)is owned by Nogales, Arizona. Under Minute 276, 434 L/s (9.9 mgd) capacity was allocated to Nogales, Sonora. From 1954 to 1996, the City of Nogales operated and maintained the

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1-5 wastewater treatment plant under IBWC oversight and was reimbursed by the USIBWC for the cost of treating Nogales, Sonora sewage. At the request of Nogales, Arizona, in 1996, the USIBWC operates and maintains the wastewater treatment plant and is reimbursed by the Nogales, Arizona for the cost of treating Nogales, Arizona sewage.

As previously indicated, USIBWC has received funds from the EPA to act as Project Manager for the Ambos Nogales Facilities Plan in coordination with the agencies described below and the external consultant firm.

U.S. Environmental Protection Agency (EPA)

EPA is a federal entity in charge, among other things, of establishing and enforcing water quality standards, providing guidance for maintaining or improving water quality, and in some instances, providing funds for conducting studies and implementing water quality related projects.

The EPA awarded funds to the USIBWC through an interagency agreement to coordinate the development of the binational facility plan and selection of wastewater improvements for Nogales.

EPA funds are designated in this case for wastewater–related issues, e.g., for treatment and discharge of treated effluent.

Arizona Department of Environmental Quality (ADEQ)

The ADEQ was created in 1986 by the Arizona Environmental Quality Act. ADEQ is the primary agency responsible for all purposes of the Clean Water Act (CWA), the Safe Drinking Water Act (SDWA), the Resource Conservation and Recovery Act (RCRA), and other environmental programs in the State. ADEQ adopts water quality standards for navigable waters and aquifers. In addition, it requires programs to be adopted to control surface and ground water and to control point and nonpoint pollution discharges.

In Arizona, the National Pollutant Discharge Elimination System (NPDES) permits are issued by EPA rather than ADEQ. Nonetheless, ADEQ requires discharging facilities to obtain an Aquifer Protection Permit (APP).

ADEQ is an active member of the U.S. Committee dedicated to ensuring future effluent discharges comply with all state and federal laws. ADEQ has provided guidance throughout the facilities planning process to establish effluent water quality targets.

Arizona Department of Water Resources (ADWR)

In 1980, Arizona established the Groundwater Management Act (GMA) with the purpose of controlling overdraft of groundwater supplies. The GMA created the ADWR to manage groundwater resources and establish Active Management Areas (AMAs) in crucial areas where groundwater supplies were most threatened (SEAGO 1994).

"ADWR works to secure long–term water supplies for Arizona's communities. The Department administers state water laws (except those related to water quality), explores methods of augmenting water supplies to meet future demands, and develops policies that promote conservation and equitable distribution of water" (ADWR, December 17, 1997).

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ADWR intends to accomplish safe–yield of the aquifers of four of its five AMAs, including the Santa Cruz AMA, by the year 2050. Safe–yield is defined as a condition in which no more groundwater is being extracted than is being replaced. To achieve this, ADWR is interested in evaluating the potential for groundwater recharge, which is one of the components of all alternatives of the Facilities Plan. The rules for the use of renewable sources, such as effluent, are included in the Adequate Water Supply Program. Some of the provisions associated with recharge projects are included in the Groundwater Code of 1980 (ADWR, December 17, 1997).

Santa Cruz County

Santa Cruz County, through its Health Department, is a stakeholder in the Facilities Plan. One of the most important concerns of the County Health Department is the elimination of fugitive raw wastewater flows in the area to reduce potential public exposure to contaminated waters.

Additionally, the County is interested in guaranteeing that any groundwater recharge scheme would not compromise the quality of the receiving water.

City of Nogales

The City of Nogales, Arizona owns 42 percent of the capacity of the NIWTP, or approximately 320 L/s (7.3 mgd) daily average flow. In addition, the City owns the International Outfall Interceptor (IOI), which conveys raw wastewater originated in Ambos Nogales to the NIWTP. The City of Nogales also provides water and sewer service to its residents. The City of Nogales would act as a promoter of the project for purposes of BECC certification, as explained below.

The nearby residential area of Rio Rico, north of the City of Nogales, is served by Rio Rico Utilities, a private water and sewerage company. Currently, Rio Rico has an agreement with the City of Nogales by which Rio Rico is allowed to use 24 L/s (0.55 mgd) of treatment capacity at the NIWTP. Rio Rico is a stakeholder in the Facilities Plan mainly due to its current and potential future use of the NIWTP, and by the potential impact of the NIWTP discharge on its wells located along the Santa Cruz River, downstream of the NIWTP.

1.2.5 Relevant Mexican Lead and Cooperating Agencies

As previously indicated, these agencies are also members of the Mexican Policy Committee and the Mexican Technical Committee involved in the Ambos Nogales Facilities Plan. The functions of these committees are analogous to the functions of their U.S. counterparts. The Technical Committee is responsible for the day–to–day coordination and guidance, whereas the Policy Committee acts as a decision maker and provides guidance in global "big picture" issues. The Mexican committees are composed of federal and state government agencies as described below.

Comisión Internacional de Límites y Aguas

CILA (Comisión Internacional de Límites y Aguas) is an acronym for the Spanish name for the IBWC.

CILA has essentially the same role as USIBWC.

Comisión Nacional del Agua

The Comisión Nacional del Agua (CNA) is a federal entity charged with regulating water rights and water quality. The specific responsibilities of CNA include, among others:

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� To encourage and support the development of water, sewer, treatment, irrigation, and flood control programs

� To administer and protect the national waters, and to preserve and protect their quality, as well as to manage watersheds

� To plan, study, construct, operate, and maintain federal hydraulic projects or infrastructure

� To issue water allocations, concessions, permits and rights to act as an arbiter in water conflict resolution

� To promote the efficient use of water and its conservation in all phases of the hydrologic cycle

� To enforce the application of the Ley Nacional de Aguas (National Water Act) and to apply the appropriate sanctions in case of the violation of the law (CNA 1992).

For the case of the Ambos Nogales Facilities Plan, CNA has issued site specific standards referred to as condiciones particulares de descarga, as described in Section 9.3 of the Facilities Plan Report (Modifications for the Short List of Alternatives).

Secretaría de Infraestructura Urbana y Ecología (SIUE)

SIUE is a state government agency responsible for establishing infrastructure and environmental policies at the State level. SIUE also coordinates with COAPAES (described below) for planning water and wastewater infrastructure. In the case of the Facilities Plan, SIUE acts as the representative of the interests of the government of the State of Sonora to enhance the well–being of the residents of the State.

Comisión de Agua Potable y Alcantarillado del Estado de Sonora (COAPAES)

COAPAES, a decentralized agency of the State Government, whose responsibilities include: planning and budgeting of the hydraulic sector of the state; executing the State Government policies for the coordination of potable water and sewer systems; supporting and providing technical assistance to municipal operators; and acting as operator of the water and sewer systems in municipalities which do not have developed operating agencies. In the case of Nogales, Sonora, COAPAES is in charge of managing and operating the water and sewer systems (CNA 1996).

1.2.6 Relevant Binational Agencies

In addition to the national U.S. and Mexican agencies, there are two binational agencies, which are extremely important in ensuring the financial feasibility of the project. These two agencies are described below.

Border Environment Cooperation Commission (BECC)

The North American Free Trade Agreement (NAFTA) produced a side agreement related to the environment, referred to as the Border Funding Agreement between the United States and Mexico.

The signing of this agreement led to the creation of three binational institutions to address water, wastewater, and solid waste concerns: (1) the North American Commission on Environmental

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Cooperation (NACEC); (2) BECC; and (3) NADBank (ASCE and the U.S.–Mexican Policy Studies Program 1995).

The NACEC was created to settle trade disputes involving pollution or the enforcement of environmental laws and its members include Canada, the United States, and Mexico (ASCE and the U.S.–Mexican Policy Studies Program 1995), whereas the BECC and NADBank include only the U.S. and Mexico. These organizations are responsible for addressing environmental problems along the U.S.–Mexico border.

"The purpose of BECC is to help preserve, protect, and enhance the environment of the border region in order to advance the well–being of the people of the United States and Mexico" (BECC 1996). In keeping with its mission, the BECC is responsible for evaluating the feasibility, efficiency, and effectiveness of proposed water, wastewater, and solid waste infrastructure projects within a 100 km region along both sides of the U.S.-Mexico border. Projects must comply with criteria established by the BECC. A project would then be eligible for possible funding from the NADBank. The certification criteria established by BECC are classified as follows (BECC 1996):

� Human health and Environment � Technical feasibility � Financial feasibility and Project Management � Community participation � Sustainable development

The Ambos Nogales Facilities Plan is the planning document that will be used to identify a wastewater infrastructure project for Nogales, Arizona, and Nogales, Sonora that will be submitted to BECC for certification. Once certified, the proposed projects would be eligible for NADBank financing. The following paragraph summarizes briefly the role of the NADBank as a financing institution for environmental infrastructure projects along the border.

North American Development Bank (NADBank)

NADBank was also created as part of the Border Funding Agreement. "The purposes of NADBank are to use a small amount of federal capital to leverage a large volume of private–sector lending; to make effective use of local grants and loans from federal and state sources; and to involve financial participation of local citizens" (ASCE and the U.S.–Mexican Policy Studies Program 1995). In addition, the NADBank was established to: "provide financing for projects certified by BECC, as appropriate, and at the request of the BECC, to otherwise assist the BECC in fulfilling its purposes and functions”;

and "to provide financing endorsement by [either the United States or Mexico] for community adjustment and investment in support of the purposes of the NAFTA" (Holub 1997).

1.3 Statement of Purpose and Need

Some of the concerns identified in Section 1.2.3 are a result of inadequate or incomplete coverage of the sewer system in Nogales, Sonora. According to the operating agency, COAPAES, there were in December 1997 a total of 23,699 registered connections to the sewer system. Multiplying the number of connections by the average residential population density provided by Instituto Nacional de Estadístion, Geografía e Informática (INEGI) of 4.3 people per household, and dividing

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1-9 by the CNA population estimate for the same year of 187,820 people, indicates that only about 54 percent of the population has access to the sewer system. In addition to the incomplete coverage of the system in Nogales, Sonora, many sewer lines in Ambos Nogales are in less than optimal condition, as observed during the infiltration/inflow investigations conducted in both communities (Section 3 of the Facilities Plan). Moreover, the capacity of the IOI, which conveys Ambos Nogales wastewater flows to the NIWTP, is limited by several bottlenecks. Flows in excess of the IOI capacity result in overflows of untreated sewage into the Nogales Wash. Incomplete coverage coupled with less than optimal conditions of the sewer system in its upstream sections also result in fugitive flows, which in most circumstances travel from Mexico into the United States via the Nogales Wash. These fugitive flows are an important public concern, as evidenced by the frequent publication of articles in local newspapers.

In addition to the fugitive flow problem, the hydraulic capacity of the NIWTP is near its limit. As population grows, the remaining capacity of the NIWTP will be exhausted. Furthermore, water supply and consumption and the accompanying wastewater production are expected to grow in the near future as the acuaférico project is implemented in Nogales, Sonora. The acuaférico project would increase the amount of water delivered, the level of coverage of the water system, and the per capita water consumption (Section 5 of the Facilities Plan).

From a water quality perspective, the effluent quality limits for the NIWTP are currently being revised (Section 2.3 of the Facilities Plan). The proposed permit calls for the reduction of potential toxicity to aquatic life, which implies a reduction in ammonia concentrations. Additionally, there is a concern about the potential impact of effluent with high total nitrogen concentrations, since nitrogen could potentially be transformed to nitrate [(NO3)

-], affecting the potable water wells located downstream of the wastewater treatment plant, such as those serving Rio Rico. As a result of these new regulatory requirements, the wastewater treatment plant will require upgrading in the near future regardless of concerns with capacity limitations.

1.4 Project Description

Sections 9.1 and 9.2 of the Facilities Plan present a detailed discussion of preliminary screening of alternatives and plan selection, respectively. As indicated in the Facilities Plan, seventy–six (76) alternatives were developed and evaluated. These seventy–six alternatives can be grouped into six (6) conceptual alternatives.

Following standard NEPA practice, this EA evaluates three action alternatives and a “no action” alternative, for a total of four evaluated alternatives. The three Action Alternatives for the EA are associated with changes to the wastewater treatment system currently in place. EA Alternatives A, B, and C were originally identified as conceptual Alternatives 3, 4, and 6, respectively. The No Action Alternative (D) assumes no changes to the current system, and corresponds to conceptual Alternative

5. Each of these alternatives are described below and the three action Alternatives (A, B, and C) are graphically presented as Figures 2, 3, and 4, respectively.

Alternative C is the recommended alternative. Alternative C, like Alternatives A and B, includes components in Nogales, Arizona and Nogales, Sonora. Construction of the different components may be phased, depending on funding availability and other factors.

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1.4.1 Environmental Assessment Alternatives

The descriptions of the four environmental alternatives are presented below.

1.4.1.1 Environmental Assessment Alternative A

Alternative A was originally identified as conceptual Alternative 3. This alternative would retain the NIWTP, which would be upgraded and used exclusively for treating flows from Mexico conveyed by the existing IOI, which will also be rehabilitated. Upgrade of the NIWTP will be accomplished by converting the aerated lagoon system to a conventional activated sludge system with sludge recirculation. Existing basins will be retrofitted to an activated sludge process using nitrification and denitrification, and secondary clarifiers will be added. The new system will allow the facility to increase the removal of nitrogen as well as Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). The capacity of the upgraded NIWTP will be 412 L/s (9.4 mgd).

Mexican flows in excess of the IOI and/or NIWTP capacity would be conveyed to a new WWTP in Mexico located adjacent to Los Alisos River. A pumping system will be in place in Nogales, Sonora, based on a series of pump stations capable of handling Mexican flows in excess of the Mexican allocation to the NIWTP. The wastewater treatment plant in Los Alisos under this alternative would be based on an activated sludge system with biological nutrient removal. The biological treatment would be accomplished by means of an oxidation ditch, and the wastewater treatment plant would include headworks, clarifiers and disinfection, as well.

Wastewater originating in Arizona would be treated at a new WWTP at the Nogales, Arizona Industrial Site. Associated with the new Arizona WWTP would be the construction of a new interceptor that would convey wastewater from Nogales, Arizona to the new WWTP at the Industrial Site. Treated effluent would be pumped to the Santa Cruz River near Kino Springs or to Potrero Creek for discharge in Arizona. Mexico would discharge at the new WWTP site at Los Alisos directly to the Los Alisos River. The wastewater collection systems in Nogales, Arizona and Nogales, Sonora, as well as the IOI, would also be rehabilitated under this alternative.

Currently, the NIWTP discharges an average of about 504 L/s (11.5 mgd) to the Santa Cruz River at the existing outfall. Under Alternative A, flows to the NIWTP would drop to approximately 412 L/s (9.4 mgd) in 2020. The effluent from the NIWTP would contain reduced concentrations of total nitrogen, BOD, and TSS, under this alternative.

1.4.1.2 Environmental Assessment Alternative B

Alternative B was originally identified as conceptual Alternative 4. Under this alternative, the NIWTP and the IOI would be upgraded as necessary to collect and treat all flows from Nogales, Arizona. The IOI and the wastewater collection systems in Nogales, Arizona and Nogales, Sonora would be replaced or rehabilitated as needed. Effluent treated at the upgraded NIWTP would be discharged to the Santa Cruz River using the existing outfall. All wastewater originating in Mexico would be collected in Mexico near the International Border and pumped back to Los Alisos for treatment and subsequent discharge directly to the Los Alisos River.

Upgrade of the NIWTP would also be accomplished by converting the aerated lagoon system to a conventional activated sludge system with sludge recirculation. Existing basins will be retrofitted

CDM Camp Dresser & McKee 1-14 to an activated sludge process employing nitrification/denitrification and secondary clarifiers would be added. The new system will allow the facility to reduce the overall nitrogen as well as biochemical oxygen demand (BOD) and suspended solids (SS). The capacity of the upgraded NIWTP would only be required to be 202 L/s (4.6 mgd) based on the projected wastewater production of Nogales, Arizona for the year 2020. The wastewater treatment plant in Los Alisos would incorporate the same process train proposed for Alternative A, and only the capacity would be different. Under this alternative, the Mexican wastewater treatment plant would have an average capacity of about 1,117 L/s (25.5 mgd). Wastewater would be delivered to the wastewater treatment plant by means of a pumping scheme, similar to the system described under Alternative A. This pumping system, however, would incorporate a pump station at the U.S.-Mexico border, and multiple pump stations would be required for appropriate conveyance of all the Mexican flows to Los Alisos.

Implementation of this alternative would then reduce the volume of water currently discharged from the NIWTP to the Santa Cruz River from approximately 504 L/s (11.5 mgd) to the 202 L/s (4.6 mgd) referenced above. The effluent from the NIWTP would also contain reduced concentrations of nitrogen (overall), BOD, and TSS under this alternative. The effluent from the NIWTP would also contain reduced concentrations of total nitrogen, BOD, and TSS, under this alternative.

1.4.1.3 Environmental Assessment Alternative C

Alternative C was originally identified as conceptual Alternative 6. Under this alternative, the existing IOI would be replaced with a new enlarged version and the NIWTP will be upgraded and expanded in capacity. The NIWTP will continue to service the wastewater generated in both the communities of Nogales, Arizona and Sonora. In addition, the wastewater collection systems in Nogales, Arizona and Nogales, Sonora would be rehabilitated.

The respective allocations to Nogales, Sonora, defined in a binational agreement will remain at 434 L/s (9.9 mgd). The remainder of the current capacity, 320 L/s (7.3 mgd), is reserved for Arizona.

Mexican flows in excess of that treated at the NIWTP would be conveyed to a new WWTP in Mexico at Los Alisos. Effluent from the new Los Alisos WWTP would be discharged directly to the Rio Los Alisos.

Even though the respective allocations for Nogales, Sonora and Nogales, Arizona will remain the same (434 L/s [9.9 mgd] and 320 L/s [7.3 mgd], respectively) for a total capacity of 754 L/s (17.2 mgd), this alternative provides for expansion of the NIWTP to accommodate potential flows from Mexico in excess of their allocation as a result of storm events, system failures and until later phases of the Mexican wastewater system are implemented. In addition, projected water system improvements in Nogales, Sonora will possibly lead to increased wastewater flows ahead of the pumping system improvements associated with this alternative. Although the exact amount of expansion is undetermined at this time, it is anticipated that the NIWTP capacity may be increased by 131 L/s (3 mgd) to 219 L/s (5 mgd).

This increase in the NIWTP capacity is not necessarily associated with an immediate increase in the amount of effluent discharged to the Santa Cruz River from the wastewater treatment plant. Over time, as the increased treatment capacity is utilized, the volume of effluent discharged to the Santa Cruz River would increase. Therefore, increases in effluent discharged to the river would be realized only gradually as human population and water use increased.

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Upgrade of the NIWTP would also be accomplished by converting the aerated lagoon system to a conventional activated sludge system with sludge recirculation. Existing basins will be retrofitted to an activated sludge process employing nitrification/denitrification and secondary clarifiers would be added. The new system will allow the facility to reduce nitrogen as well as BOD and TSS.

The wastewater treatment plant in Los Alisos, under this alternative, will be based on a natural system. The treatment train will consist of a series of lagoons (deep facultative, high algae growth, settling, and maturation/filtration), with configuration known as Advanced Pond Systems. These ponds will be capable of lowering the concentration of BOD, TSS and, to a varying degree, total nitrogen, to comply with the site specific discharge conditions issued by the Mexican government for this site, as described in Section 9 of the facilities plan (Plan Screening and Selection). Under this alternative, a pumping system very similar to the system described under Alternative A, would be required for wastewater conveyance to Los Alisos. In this case, however, the pump stations would have the capacity to pump only the average flows in excess of the Mexican allocation to the NIWTP.

Peak flows associated to storm events would not be pumped to Los Alisos, and would be bypassed to the gravity system, allowing them to flow north, cross the border and be conveyed to the NIWTP.

Under this scheme, additional hydraulic capacity would be provided in the gravity lines downstream of the pump stations (Mexican collectors and the IOI), to assure appropriate conveyance of the peak flows to the NIWTP.

Implementation of this alternative would not decrease the volume of water currently discharged from the NIWTP. Typical current discharge flows are based on the minimum (386 L/s (8.8 mgd)) and maximum (701 L/s (16.0 mgd)) average monthly flows measured during the 1994–1997 time period.

The average discharge flow (504 L/s (11.5 mgd)) is the overall 4–year average daily flow measured at the NIWTP. Effluent volume leaving the NIWTP would be maintained at levels equal to or exceeding the current minimum monthly flow of 386 L/s (8.8 mgd). The new system will allow the facility to reduce the overall nitrogen as well as biochemical oxygen demand (BOD) and suspended solids (SS).

1.4.1.4 Environmental Assessment Alternative D (No–Action Alternative)

Implementation of this alternative would result in no major upgrades and/or expansions to the existing infrastructure or wastewater treatment processes. Currently, all wastewater generated in Ambos Nogales is conveyed to the NIWTP where it undergoes aerated lagoon–based treatment, sludge retention and polishing, prior to discharge to the Santa Cruz River just downstream of the NIWTP. Any current beneficial or adverse environmental effects would remain under this alternative.

The population projections performed under this facility plan indicate that the average daily flow of domestic wastewater generated in Ambos Nogales will increase from its present level of 504 l/s (11.5 mgd) to 1,207 l/s (29 mgd) by the year 2020. Under this option, no improvements would be made to the IOI and wastewater from Sonora would be crossing the international border by gravity under increasingly surcharged conditions on its way to the NIWTP. This is because a constriction in the IOI itself exists near the border to limit the flow from Mexico. As a result, sewer overflows on the Mexican side will become more frequent, and increasing amounts of raw or untreated wastewater would be discharged to the Nogales Wash and the Santa Cruz River. Under this scenario, the overall annual loadings of BOD, SS and nutrients to the environment will most likely incur a steady increase in Arizona over time. This would occur as a result of the following factors; 1) Increased flows to the NIWTP which would lower detention time and therefore reduce treatment; 2) increased fugitive flows

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1-16 as a result of wastewater backup as described in section 1.3; 3) higher volume of exfiltration from the interceptor lines in areas and/or periods of lower water table.

The frequency of NIWTP effluent limit violations could potentially increase for BOD, solids and coliform organisms and the concentration of ammonia would not be significantly reduced prior to discharge. Since people use the river for recreational or other purposes, there would be increased potential to be subjected to exposure to a harmful constituent. An increased risk for exposure to bacterial and/or viral pathogens would also result with regard to increased fugitive flows.

With respect to the aquatic environment and especially the water quality of the Santa Cruz River immediately downstream of the NIWTP discharge point, water quality would become increasingly worse as the relative contribution of untreated wastewater is increased over time. From an ecosystem habitat standpoint, however, the average increase in volume of water discharged will most likely result in an increase of the available amount of habitat for aquatic species. In addition, the vegetation of the riparian habitat particularly the willow trees, could actually be enhanced by increased nutrient loading. From a public health perspective, the chance of exposure to hazardous constituents would increase for those who use the river for recreational or other purposes(dermal and inhalation routes).

Also, the nitrogen present in the effluent may cause nitrate levels in the downstream aquifers to rise to levels that exceed primary drinking water standards.

1.4.2 Historical and Projected Flows

To fully understand the potential impacts of each alternative on Ambos Nogales environmental resources, the flow to each WWTP and the corresponding discharge point(s) must be known. To assess potentially significant changes in NIWTP discharge flows, typical discharges for the four–year time period from 1994 to 1997 were evaluated. Data from years earlier than 1994 are not included because beginning in late 1993 there was a substantial increase in water supply in Nogales, Sonora.

The earlier data would therefore not be adequately representative of current conditions. Over the four–year period, the minimum monthly flow was 386 L/s (8.8 mgd), while the maximum monthly flow was 701 L/s (16.0 mgd). Therefore, flows of 386 to 701 L/s (8.76 to 15.98 mgd) are considered representative of current conditions. The average daily flow over the entire time period was 504 L/s (11.5 mgd). The fact that the overall average is closer to the minimum monthly flow than the maximum monthly flow is indicative of the high–flow storm events that occur occasionally throughout the monsoon season, driving up maximum monthly flow numbers. It is important to note that monthly average discharges from the NIWTP varied by as much as 90 L/s (2 mgd) from one month to the next during the study period.

In addition to the amount of water discharged to the stream, the length of the aboveground flowing portion of the Santa Cruz River downstream of the NIWTP is also influenced by spatially and temporally variable parameters such as storm events and groundwater hydrology as well as effluent volumes. Precise control of the NIWTP effluent volume therefore does not guarantee a specific number of miles of flow in the Santa Cruz River downstream of the NIWTP. It is clear, however, that during the vast majority of the time, the primary contributor to surface flow downstream of the NIWTP is the volume of effluent discharged to the Santa Cruz River.

Table 1 summarizes recently measured and projected future wastewater flows for the year 2020 for Ambos Nogales for each of the four Environmental Assessment alternatives. Recently measured data

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1-17 presented in this table were collected at the NIWTP influent structure and at the International Boundary from 1994 through 1997. Under Alternative A, discharge from the NIWTP site would be limited to about 412 L/s (9.4 mgd). However, depending on the discharge location selected for the new Arizona wastewater treatment plant, another 163 L/s (3.7 mgd) could be discharged to the Santa Cruz at Kino Springs. Under Alternative B, discharges to the Santa Cruz at the existing NIWTP outfall would decrease substantially since this discharge would consist only of treated wastewater from Arizona.

For Alternative C, as long as the inflow of wastewater to the NIWTP remains within its present capacity of 754 L/s (17.2 mgd), average discharges from the NIWTP to the Santa Cruz River at the existing outfall would be maintained within the 386 L/s (8.8 mgd) to 701 L/s (16.0 mgd) range described above. However, if the NIWTP expanded capacity is used, the volume of effluent discharged to the Santa Cruz River would increase to 973 L/s (22.2 mgd) (average flow) in the most extreme case. As previously mentioned, such increases would be gradual, paralleling the population growth in Nogales, Sonora.

Alternative D (no action) would result in increasing untreated NIWTP discharge flows to the Santa Cruz at the existing outfall because existing capacity would soon be exceeded.

1.5 Summary of the Environmental Assessment

This section describes the general approach for conducting the EA, identifies the major environmental resources that may be at risk, and provides recommendations based on the conclusions of the EA.

1.5.1 General Approach

The Environmental Assessment is based on an assessment of the potential effects to each of the sixteen

(16) previously identified environmental resource categories from implementation of Alternatives A, B, C, and D, presented in Section 1.4. These sixteen resource categories are not equal with regard to likelihood or severity of effects that may be experienced. Certain resource categories are therefore deemed more vulnerable or important than others.

For example, it is clear that the resource category identified as Topography is less likely to exhibit measurable effects than Surface Water Quality. The unique potential for each alternative to cause adverse environmental effects suggests that, although all resource categories are assessed, the EA can and should focus on selected environmental resources that are especially vulnerable or important.

The most vulnerable or important resource categories are described below, along with a statement of why these particular resources are considered the most important with regard to this Ambos Nogales project.

Table 1

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1.5.2 Major Environmental Resources

All sixteen identified categories of environmental resources have at least some potential to be affected by implementation of the alternatives. Those resource categories considered most likely to be affected by the project are defined as primary environmental resource categories. These are listed below.

� Surface Water Quality (directly affected by treated effluent quality and potential untreated wastewater overflows and directly affects aquatic habitat quality)

� Groundwater Aquifers (seasonally affected by surface water quantity and directly related to surface discharge and water availability)

� Groundwater Quality

(directly affected by treated effluent quality and surface water/groundwater interface)

� Biological Resources [biota (including threatened/endangered species), habitats, surface water quantity; (directly affected by quality and quantity of treated effluents, potential untreated wastewater overflows and by surface discharge of effluent)]

� Public Health and Safety

(directly affected by treated effluent quality and potential untreated wastewater overflows)

� Energy Supply/Natural Resources

(directly related to power availability for operation of a new WWTP or pump station)

Other resource categories are considered secondary based on the assumption that impacts to these categories are either unlikely or, if impacts occur, they are expected to be minor or unmeasurable.

These categories are listed below.