Border Environment Cooperation Commission
Construction of
a Wastewater Treatment Plant in Somerton, Arizona
General Criteria
1.
Type
of Project. The project consists of the construction
of a wastewater treatment plant in Somerton, Arizona.
2.
Location
of Project. The City of
Somerton is located in Yuma County, Arizona, approximately 10 miles [16 km]
southwest of Yuma, Arizona, 10
miles [16 km] south of the California/Arizona border, and 10 miles [16 km]
north of the southern Arizona/Mexico border. The project is located within
the 100 km border region as defined by the La Paz agreement. The City of
Somerton is a community of approximately 7,500 residents and the population is
expected to reach 16,000 by the year 2020 (4.2% annual increase). The City
limits bound an area of approximately one square mile. The City of Somerton is
shown in the figure below:
Description
of Project and Tasks. The
project consists of constructing a sequencing batch reactor (SBR) wastewater
treatment plant with a total treatment capacity of 0.8 million gallons per day
(MGD) to replace the existing lagoon system.
Compliance
with International Treaties and Agreements. The project will not have any international
impacts as all construction, maintenance, and project effects will occur within
U.S. territory in a very localized zone. The wastewater treatment plant
discharge is to the Yuma Drain Canal, that eventually flows into Mexico and is
used for agricultural reuse. The new wastewater treatment plant will guarantee
that the effluent discharged complies with U.S. standards for protection of
water bodies and its subsequent use for irrigation in Mexico.
Human Health/Environmental Needs. This project will address human health and environmental concerns by providing improved wastewater treatment that conforms to current US standards. Although there is currently no evidence of health effects from the deteriorated standards of the current treatment plant, it is subject to violation of the NPDES permit.
The construction and operation of the new wastewater treatment plant will result in water quality improvements in the Yuma Drain Canal surface waters and the underlying groundwater aquifer by reducing levels of conventional pollutants (BOD5 and TSS) and of total nitrogen. Potential increased volume of discharged chlorinated wastewater effluent can be mitigated the establishment and proper monitoring of a Mixing Zone. The new plant will also eliminate current seepage of approximately 30,000 gpd from the lagoons into the groundwater.
The plant will be a good neighbor. Foul odors generated from the lagoon system adversely impacting the adjacent residential area will cease. The elimination of gaseous chlorine as a disinfectant agent will reduce the public health and safety risk to plant staff, farm workers on the adjacent agricultural fields, and nearby residential areas.
Environmental Assessment. An Environmental Assessment (EA) was performed in compliance with BECC Project Certification Criteria and EPA 40 CFR Part 6 requirements. The assessment considered the following criteria:
· Discussion of the direct, indirect, cumulative and short-term positive and negative effects of the project on the environmental components of the affected area (e.g. ecosystem integrity, biological diversity, sensitive environmental habitats, and human health);
· Description of unavoidable negative impacts and actions to be taken to mitigate these impacts;
· Discussion of the environmental benefits, risks, and costs of the proposed project as well as the environmental standards and objectives of the affective area.
Significant transboundary effects are not likely.
EPA has reviewed the EA and issued a Finding of No Significant Impact on mid-May, 2002.
Compliance
with Ecology and Cultural Laws and Regulations. A
consultation with the Arizona State Historic Preservation Office and with
different Arizona tribes was performed as part of the environmental assessment
process. The environmental evaluation of the process indicated that there are no
potential impacts, direct or indirect, to any historical, cultural, and/or
archaeological resources in the area.
Appropriate Technology. The selected alternative is a Sequencing
Batch Reactor system, which is described below.
a)
Project
Specifications
The recommended activated sludge treatment process
in Hazen and Sawyers report is the sequencing batch reactor due for a variety
of reasons with the cost effectiveness, process flexibility, and ease of modular
expansion being the primary selection factors.
The sequencing batch reactor (SBR) process is a
cyclic activated sludge treatment process.
Multiple reactors are provided to treat the wastewater in batches. Somertons sequencing batch reactors will be
and operated to oxidize the carbonaceous BOD, nitrify the ammonia, and
denitrify to reduce the total nitrogen to a level that meets the permit
limits.
All treatment processes including equalization,
aeration, denitrification, and sedimentation, and decanting occur in the SBRs
eliminating the need for separate clarification and return activated sludge
systems.
The typical SBR treatment sequence for
nitrification-denitrification systems is as follows:
1.
The reactor is allowed
to fill with raw wastewater. The
filling phase is often divided into stages that include aeration to reduce BOD
and to nitrify ammonia and then mixing without aeration to promote
denitrification (removal of nitrogen).
2.
A reaction phase is
generally provided to promote additional treatment.
3.
A settling or
quiescent phase then follows to allow the biological solids to settle.
4.
A decanting phase is
provided to draw off the clarified effluent from the upper portion of the
reactor.
5.
Often a small idle
phase is provided to allow time for miscellaneous operations that may need to
occur to keep the reactors in sequence.
Wasting of the biological solids that are produced
by converting BOD to bacteria needs to occur periodically to maintain the
design mixed liquor concentration and sludge age. Wasting can occur at anytime in the process sequence. Frequently, wasting is performed following
the decant phase when the sludge concentration is highest.
The Hazen and Sawyer Report recommended a two SBR
basin configuration. While economical,
the two SBR configuration does not provide much operational flexibility and
process redundancy. Two methods are
commonly used if one of the reactors is removed from service for cleaning or
repairs. The first method is to convert
the remaining in-service reactor to a continuous flow operation. This is viable for short periods of time
especially when the system is well below its design loadings. As loadings approach design loads, achieving
treatment objectives by this method becomes difficult. The second method is to provide an aerated
and mixed basin where the flow can be stored during the cycling of the
in-service reactor.
Stanley Consultants proposes to provide four basins
for Somerton. The four-basin configuration
offers much more process flexibility and redundancy. One of the four basins can be taken out of service without severe
impact to the three remaining in-service basins. The design will be set up so the four basins can be paired
together for dual cell cycling during normal operations. In the event a basin needs to be taken
out-of-service, the remaining three basins can be cycled independently.
The SBRs will be equipped with
diffused aeration, mechanical mixers, and decanting facilities. A submersible pump will be provided in each
basin to pump waste solids to the sludge thickener. Jet mixing, a type of aeration system offered by some vendors,
will not be utilized on this project based on poor experiences at other
facilities.
The discharge from SBR systems is higher than the
inflow because the same volume of water that entered the SBR is discharged over
a shorter time period. Flow
equalization downstream of the SBRs was considered to dampen the discharge
flows from the SBRs. Separate flow
equalization was found to cost more than sizing the disinfection facilities for
the higher peak flows.
A. Major
Equipment
1. SBR Design Criteria
|
Average Flow: |
0.8 mgd |
|
Maximum Day Flow: |
1.6 mgd |
|
BOD5 |
225 mg/l avg, 270 mg/l sustained peak |
|
TKN |
39 mg/l average, 47 mg/l sustained |
|
NH3N |
29 mg/l average, 33 mg/l maximum |
|
SRT |
16 to 19 days |
|
Volumetric Loading |
10 lbs BOD/1000 CF |
|
Hydraulic Retention Time |
29 hrs |
|
Dissolved Oxygen |
2.0 mg/l minimum during aerobic phase |
|
O2 Requirements BOD |
1.1 lb O2 per lb BOD5 |
|
O2 Requirements NH3N |
4.56 lb O2 per lb NH3N |
|
Oxygen Transfer Efficiency |
25% |
|
(Based on new, clean water transfer efficiency) |
|
2. SBR Design
|
Number of Basins: |
4 |
|
Capacity, Each: |
0.2 MG |
|
Nominal Length: |
39 feet |
|
Width: |
39 feet |
|
Maximum SWD: |
21 feet |
|
Normal SWD: |
17.5 feet |
|
Minimum SWD: |
14 feet |
|
Freeboard at maximum water depth: |
2 feet |
|
Number of Cycles per basin: |
5 per day |
|
Cycle Time: |
4.8 hours |
|
Actual Oxygen Required: |
3541 lb day |
|
Est. Net Sludge Yield: |
0.701 lbs. WAS/lb BOD |
|
Waste Sludge, mass |
579 lb/day |
|
Waste Sludge, % solids |
0.35 |
|
Waste Sludge, Flow |
162 to 196 gpm |
|
Number of WAS pumps per Basin: |
1 |
|
Type: |
Submersible |
|
Flow: |
200 gpm |
|
Number of Mixers per Basin: |
1 |
|
Mixer Horsepower: |
10 hp |
|
Note one uninstalled mixer and one uninstalled WAS pump will be
provided for redundancy. |
|
3. Aeration
System
|
Diffuser Type: |
Fine Bubble Diffused Air |
|
Air flow per Basin, SCFM |
TBD |
|
Number of Blowers: |
3 |
|
Blower Capacity, ea. |
TBD |
|
Blower Horsepower: |
100 |
|
Blower Type: |
Positive Displacement |
Decant devices vary significantly from
vendor to vendor. An appropriate decant
mechanism will be provided to decant clarified treated wastewater from the
SBR. The decant mechanism will have provisions
for accounting for varying liquid levels and will minimize entrance of solids
into the mechanism during all phases of operation or will automatically flush
solids accumulated in the mechanism prior to discharge.
O&M Plan. The Operation and Maintenance(O&M) Manual will be prepared by the design engineer upon completion of the construction of the plant with support from the construction contractor and equipment manufacturers. Development of this manual is not possible at this time since no equipment has been selected or installed.
Operation and maintenance manuals for each piece of equipment should also be maintained. Each of these should contain the following for each system component:
· Specifications and cut sheet drawings
· Maintenance schedules
· Replacement parts list.
The O&M manual for the treatment plant as a whole should include the following elements:
|
Plan
Element |
|
Description |
|
Start-Up Operation Plan |
|
The Operation Plan will be developed by the design engineer to ensure that Treatment plant staff understand how to properly start-up and operate the facility. Traditionally, the contractor and equipment supplier conduct the initial start-up of plant equipment to permit the detection that equipment is installed and started properly. Start-up operations and training of the permanent staff should be part of this activity. |
|
Contingency Plan |
|
The Contractor will be required to submit an emergency response and contingency plan covering the construction and start-up phase, upon the issuance of the contract award notice. This plan will be updated and maintained by Publilc Works Division personnel to cover any emergency that might occur during normal operation. |
|
Safety Plan |
|
A safety and health plan will be developed by the WWTP Superintendent and implemented by all Public Works Division personnel involved with plant operation and maintenance. It should include safety training before start-up, with periodic refresher training. |
|
Quality Assurance Plan |
|
The quality assurance plan should be developed during the start-up |
|
Pollution Prevention Plan |
|
The construction operator will provide a Pollution Prevention Plan, including a Storm Water Pollution Prevention Plan required by the NPDES permit. |
|
Facility Closure Plan and Post-Closure Plan |
|
The existing lagoons will be decommissioned during and after the start-up of the new facilities. A closure plan will be submitted to ADEQ with the facility closure application. |
Compliance with applicable design norms and regulations. Currently, Stanley Consultants is under contract to the City of
Somerton, Arizona to prepare final design for the wastewater treatment plant. Sixty
percent design has been completed. Also, a Value Engineering was performed to
the final design.
Financial Feasibility and Project
Management
1.
Financial
Feasibility.
The
NADB completed the financial analysis to determine the funding structure of the
project and the user rates to guarantee the financial sustainability of the
operating agency.
The project costs are
as follows:
|
Capital
Cost Estimate New
Wastewater Treatment Plant City
of Somerton |
|
|
Construction |
6,424,389 |
|
Administration |
488,325 |
|
Engineering
Fee |
973,979 |
|
Legal
Fee |
15,000 |
|
Contingency |
642,439 |
|
CONSTRUCTION
COST |
8,544,132 |
Funding
sources for the project are as follows:
Financial
Structure
|
Source |
Amount (US$) |
% |
|
Loan Component |
4,400,000 |
51 |
|
BECC |
436,779 |
5 |
|
City of Somerton |
32,000 |
1 |
|
NADB - BEIF |
3,675,353 |
43 |
|
Total |
$8,544,132 |
100% |
The
NADB also awarded a $864,168 BEIF transition assistance grant in order to make
the user fees affordable based on the City's Median Household Income.
2.
Rate
Model: The NADBank prepared a rate study to determine the
water user fees that will guarantee the financial sustainability of the
project. The proposed water user fees are presented below.
Public Participation
Public
Participation Plan. The City of Somerton submitted a public
participation plan to BECC on November 21, 2000 and was approved on the 27th of
that month.
Steering
Committee:
The steering committee was formed on
October 12, 2000. Its membership is composed of: Oscar Joanicot, citizen; Fred
Gloria, Accountant; Enrique Porchas, Equipment Salesman and Luis Heredia, Oscar
Sanchez, and Carmen Juarez, local
citizens. The steering committee has a technical support group composed of
Eddie Mendez, Public Works Director, Leo Lomelí, City Water Specialist and
Cliff O'Neill, Community Development Director.
The committee was responsible for the development of the public participation
plan and met ten times since its formation to follow-up on the public process.
Local Organizations:
The Somerton School
Parents League, Somerton Rotary Club, Somerton Merchants, Senior Nutrition
Center, and the Immaculate Heart of Mary Catholic Church were contacted to
present the proposed project and solicit their support. Approximately one
hundred people attended these meetings.
Public
Information: The project proposal was available at the
Somerton City Hall and after work hours at the Somerton Police Station. The
Yuma Daily Sun published articles on the city's efforts to improve the
wastewater plant Feb. 7, April 6, and May 16, 2001. Committee members and
volunteers delivered to about 900 customers a flyer that contained information
on the election, and a project fact sheet. Additional flyers were handed out at
the Immaculate Heart Catholic Church with meeting notices included in the
church bulletin. The engineering consultant provided the technical presentation
at the Feb.8, 2001 public meeting.
Public
Meetings: Public meetings were held on October 30, 2000, January 29 &
30, Feb. 8, March 12 & 15, and April 11, 2001 to present the technical aspects,
project costs, and ballot information to local residents. A final public
meeting was held on April 30, 2003 to present the rates to the residents of the
city.
Election Authorization: At a General Election on May 15, 2001,
local voters authorized the City to incur indebtedness in an amount not to
exceed $4.4 million to improve and expand the wastewater system. The election
results were 180 in favor and 26 opposed.
1.
Definition
and Principles. The project complies
with BECCs 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 Wastewater Treatment Plant Replacement Project was developed in full conformity with the following four principles of sustainable development:
Principle 1 - Human beings are at the center of concerns for sustainable development.
They are entitled to a healthy and productive life in harmony with nature.
Principle 2 - The right to development must be fulfilled so
as to equitably meet developmental and environmental needs of present and
future generations.
Principle 3 - In order to achieve sustainable development,
environmental protection shall constitute an integral part of the development
process and cannot be considered isolation from it.
Principle 4
- The stakeholders (e.g. groups and
individuals impacted by, and having an impact on development projects, must be
part of any related activity.
Specifically, this means that: Border residents experiencing
environmental problems first hand must be given the opportunity to participate
in the decision-making process on ways to protect, manage, and employ
environmental resources in their communities; and the efforts and expertise of
the different institutions involved in environmental, social, and economic
endeavors within all sectors of the society must be brought together for better
balanced development planning and better use of scarce resources.
The project will improve the quality of life in the community by ensuring the capacity to properly treat the effluent generated by Somertons growing population, before its discharge, thus avoiding the human health and environmental problems associated with a degradation of the water quality of the receiving Yuma Main drain.
2. Institutional and Human Capacity Building. The new wastewater treatment plant will be operated and maintained by the Citys Water and Sewer Division personnel. For this purpose, the Public Works Department will need to hire one new operator, increasing the capabilities of the Division as a whole. Either this operator or one of the current operators will need to achieve a Grade III certification according to the Arizona Administrative Code.
Somerton has a history of providing training opportunities to their operators and encouraging them to attain higher certification levels. The current operators have begun the certification process and undoubtedly will be able to advance concurrently with the anticipated increase of certification level required for the new facility.
As has been noted throughout this document, the project will require a series of additional capacity building activities in addition to the hiring and grade certification of their operators. These are summarized below:
· An Operation and Maintenance (O&M) Manual will be developed with project funding for the new treatment plant. This manual will be a reference document for setting up routine maintenance and for trouble-shooting non-routine maintenance, thereby improving the capabilities of the Public Works Department.
· Start-up training in treatment plant operation will be offered by the contractor and equipment providers to Public Works Department staff.
· A work safety and health training program below project start-up, followed by periodic refresher courses.
In general, the advancement of administration and operations personnel is supported by available training programs, such as those offered by the ADEQs Outreach Program. The selected treatment facility will provide the ability to serve an increased client base, which in turn generates greater revenues for the City through user charges.
Finally,
the update of the NADBank rate study will allow the City to make the necessary
adjustments to the rate design currently being implemented so as to improve its
institutional and financial capacity.
3. Conformance with Applicable
Local/Regional Conservation and Development Plans. The project complies with the City of Somerton
General Plan.
4. Natural Resource Conservation. The construction of a new SBR treatment plant to replace the current lagoon system will allow the City to effectively treat the influent sewage flows to their facility. The existing plant has not been able to maintain NPDES compliance and has been cited for other violations of applicable environmental regulations. The existing plant is also not capable of handling expected future flows that will accompany population growth. The new plant will improve the quality of surface water in the Yuma Main Drain and the quality of groundwater by eliminating the current seepage from the lagoons.
The project will have no impact on available land or biological resources as the new plant will be constructed on a filled lagoon and will not require additional land.
5. Community Development. The City of Somerton has a significant recurring unemployment problem as employment is centered on the highly seasonal agricultural industry. Reported unemployment rates are have surpassed 50%. Somertons household income is also quite low, ranking 150 out of Arizonas 176 cities and unincorporated areas.
The new wastewater treatment plant can have a positive impact on these weak economic indicators by helping to provide improved services and environmental conditions that can attract new businesses, which in turn can have a multiplier effect on the local economy through payrolls, taxes and additional housing requirements.
Potential negative effects of building the new treatment plant are primarily related to an increase in utility rates. The net effect of the new project is to increase average monthly residential and commercial sewer bills by approximately 35% to 40% over the next 5 years, which could offset the indirect development impact of improved service. But these negative effects could be mitigated by the fact that the total projected water and sewer bills will still be competitive with many other representative cities in the state.
·
Environmental Assessment
·
Finding of No Significant
Impact
·
Project Certification
Document
·
Preliminary Engineering
Report
·
Value Engineering Report
·
60 percent design drawings.