TASK ORDER NO. 5
CITY OF PACIFICA
AND
DHI WATER & ENVIRONMENT, INC.
SECTION 1 – PURPOSE
The purpose of this Task Order is to authorize and direct DHI WATER & ENVIRONMENT, INC. to proceed with the work specified in SECTION 2 below, in accordance with the provisions of the Master Agreement for Consultant Services between the City of Pacifica (“CITY”) and DHI WATER & ENVIRONMENT, INC. (“CONSULTANT”) hereto dated JANUARY 24, 2025 (“MASTER AGREEMENT”)
SECTION 2 – SCOPE OF WORK
The items authorized by this Task Order are presented in Attachment “A” – Scope of Services, which is attached hereto and incorporated by this reference.
SECTION 3 – COMPENSATION AND PAYMENT
Compensation shall be as provided in the MASTER AGREEMENT. Compensation for services as set forth in SECTION 2 shall be as set forth in Attachment “B” – Compensation, which is attached hereto and incorporated by this reference. Total compensation for all services provided under this Task Order shall not exceed Twenty-Four Thousand Eight-Hundred Dollars ($24,800.00) (“Cost Ceiling”).
SECTION 4 – TIME OF PERFORMANCE
The services described in SECTION 2 of this Task Order shall be completed by December 31, 2027 or as extended in writing by the City Manager.
SECTION 5 – ITEMS AND CONDITIONS
All terms and conditions contained in the MASTER AGREEMENT are incorporated by reference and remain in full force and effect.
Approved this ___24th__ day of _January_, __2025_.
[Signatures on Next Page]
OAK #4818-2196-0582 v1
CITY OF PACIFICA
By: Date
Kevin Woodhouse, City Manager
Approved As To Form
By: Date
Michelle Marchetta Kenyon, City Attorney
CONSULTANT
DHI WATER & ENVIRONMENT, INC.
By: Date
Thomas L. Johnson, COO
1 September 2026
ATTACHMENT “A”
SCOPE OF SERVICES
TO5: Custom SBR Controller Design
Objective: Consolidate the findings from the modeling exercises into an SBR control narrative that could be scripted and implemented at the CCWRP.
The TO5 scope is designed to convert preferred scenarios from the simulations into practical control methods that can then be implemented at the CCWRP to optimize the SBRs in real-time. While DHI offers controller implementation technology and services for WRPs, the intent of this TO5 is to design and outline recommended control methods to be implemented at the City of Pacifica’s discretion.
The following subtasks describe DHI’s proposed workflow for TO5.
Combined Scenario Analysis
DHI will execute a simulation combining the recommendations from all previous scenarios into a single operating strategy. The results can be used by CCWRP process staff to evaluate the value of implementing advanced controllers and to guide the following controller design tasks.
Aeration Cycle Length Control
The aeration cycle length is the main driver for aeration energy savings and process optimization of the CCWRP. The method for determining when to stop aeration in an SBR determines the sensors requirements impacts further operation of the SBRs such that the method will be isolated and prioritized.
DHI will draft a control narrative for determining the aeration cycle length, likely based on a combination of ORP, pH, DO, and NH4 sensors in one or more SBRs. This control narrative will be customized and presented to CCWRP operations staff to assess feasibility, practicality, and necessary limits or interlocks.
Fill Fraction Optimization
From the simulation exercise, the SBR fill fraction was determined to have a high impact on overall plant capacity. The more the SBR are decanted, the more volume available for the next cycle. However, the decant level depends on the sludge settleability. The control method may rely on a comparison of realtime sludge blanket level calculations based on SVI and MLSS data to sludge blanket level meters for realtime monitoring of settling to safeguard against sludge carryover. The settling characteristics may also be impacted by additional considerations discussed in the following Aerobic SRT Control section. DHI will develop a control method to automatically determine the optimal decant level and present the resulting control narrative to CCWRP process and operations staff.
Aerobic SRT Control
The required aerobic SRT for nitrification in a specific activate sludge is governed by the wastewater temperature. Too high of aerobic SRT results in unnecessarily high total SRT, sludge hydrolysis, and additional aeration requirements while too low of aerobic SRT is likely to washout nitrifiers. The cyclic nature of SBRs along with dynamic aeration cycle lengths and fill fractions indicate a need for automated control of solids wasting rate (waste activated sludge, WAS) to maintain a steady aerobic SRT. A data preprocessing methodology and aerobic SRT calculation will be designed to allow for dynamic WAS settings to maintain a stable aerobic SRT.
Example dashboard for an aerobic SRT controller designed and implemented by DHI for a WRP with both hydrocyclone- and RAS-base wasting.
Sensor Network Evaluation
DHI will combine the relevant control methods in a holistic SBR optimizer method for review. These control narratives and diagrams will be used to list sensor requirements with the objective of minimizing online sensors to be installed. While sensors are critical for advanced control, data quality is equally critical and can deteriorate when too many sensors are installed and maintenance costs are underestimated.
DHI will deliver a final controller design including recommended sensors and next steps to implementation.
This task will be aided by a site visit with operations and controls workshops to train operations staff in the intent of the control methods, evaluate feasibility and practicalities, and plan for implementation and integration with existing control structures.
ATTACHMENT “B”
COMPENSATION
Project Cost
The estimated project costs, to be invoiced as a lump sum upon delivery of each Task Order, are tabulated below. The project terms and conditions are outlined in the Master Agreement for Consultant Services between DHI and the City of Pacifica dated January 24, 2025.
Advanced SBR Modeling and Controller Design
DHI Cost Estimate
TO5 Custom SBR Controller Design $ 24,800