City Council
Report
City Council Meeting: September 26, 2017
Agenda Item: 8.A
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To: Mayor and City Council
From: Susan Cline, Director, Public Works, Water Resources Subject: Approval of Sanitary Sewer System Master Plan
Recommended Action
Staff recommends that the City Council approve the 2017 Sanitary Sewer System Master Plan.
Executive Summary
The 2017 Sanitary Sewer System Master Plan (SSSMP) (Attachment A) provides the City with a tool for planning sanitary sewer collection system infrastructure improvements. The primary purpose of this Master Plan is to evaluate the capacity of the City’s existing sanitary sewer system under current conditions and plan for the capacity required by future conditions associated with anticipated development projects, including the Land Use and Circulation Element (LUCE) and the Downtown Community Plan (DCP). In order to analyze the impacts of existing and future sewer flows, a numerical hydraulic model was developed. The analysis found that the City’s sewer system performs well under both existing and future conditions. Existing conditions show a 1% shortfall in sewer flow capacity citywide, and under future build out conditions, only 3% of the modeled pipelines exhibited a capacity deficiency.
The ability of the sewer collection system to meet future conditions with only modest investments in sewer upgrades paid for by development fees means these improvements can be incorporated into the City’s existing $3 million per year sewer main replacement Capital Improvement Program forecast, as presented below.
Description FY
2018/19
FY 2019/20 FY 2020/21 FY
2021/22
FY2022/23
Capacity Improvements $2,000,000 $1,200,000 $1,600,000 $2,000,000 Field Review Services $100,000 $80,000
Pipeline Replacements $900,000 $1,800,000 $1,400,000 $2,920,000 $1,000,000 2 of 9
TOTAL ANNUAL CIP $3,000,000 $3,000,000 $3,000,000 $3,000,000 $3,000,000 Background
Santa Monica’s wastewater system includes a collection system including gravity sewers, force mains, monitoring stations and a lift station to help convey sewage to the City of Los Angeles’ Hyperion Water Reclamation Plant in El Segundo for treatment and disposal. The City’s sanitary sewer facilities include approximately 152 miles of pipelines, 2,800 maintenance holes, two permanent flow monitoring and sampling stations, and one 26-million-gallons-per-day (MGD) pumping station, referred to as the Moss Avenue Pump Station (MAPS), located at 1623 Appian Way. The City’s sanitary sewer system is shown in Figure 1.
Prior studies included the development of a limited model assessing the capacity of the trunk sewer used to discharge brine (the wastewater produced as a by-product of potable water treatment process) from the City’s water treatment plant into the sewer system at 19th and Broadway (2011), and a Sewer System Management Plan (2012) which addressed sewer system organization and management, operations and maintenance, overflow response plans, and water quality monitoring programs. The last comprehensive Sewer Master Plan for the system was conducted in 1992. The findings and recommendations of the 1992 Master Plan were mostly not implemented, however, as the 1994 Northridge Earthquake caused considerable damage to the sewer system, after which approximately 80% of the system was rebuilt and rehabilitated.
Discussion
This 2017 Sanitary Sewer System Master Plan (SSSMP) was prepared to reflect current conditions in the City and anticipated future developments coincident with the LUCE and DCP planning horizons of year 2030, and to provide the City with a tool for planning improvements needed for sanitary sewer collection system infrastructure. The Downtown Community Plan EIR includes mitigation measure MM U-4 which states: “In addition to the improvements to the water delivery system described in the MM U-1, the City shall ensure adequate financing for funding of infrastructure improvements to the wastewater system. The DPIFP described in MM U-1 shall determine the costs of and establish a funding program for the following capital improvements to wastewater 3 of 9
conveyance as needed to serve the demands of new projects occurring under the Downtown Community Plan.”
The primary purpose of this planning document is to evaluate the capacity of the City’s sanitary sewer system under current conditions and plan for any necessary improvements in capacity to accommodate anticipated new development in the City.
These improvements would be implemented within the City’s Capital Improvement Program (CIP).
To fully assess existing conditions in the sewer collection system and plan for the future capacity needs of the sanitary sewer system, future flow estimates incorporate the changes in sanitary flows that would be generated by anticipated development and the additional water that enters the sewer system from storm-related events. The additional sanitary sewer flows associated with these development projects are derived by applying the applicable sewer discharge factors for the land use types and densities of each planned development project. Future development projects and their status in the development process are depicted graphically on Figure 2. Based on these factors, future average dry weather flows are projected to increase from 14.4 million to 16.5 million gallons per day (MGD), an increase of approximately 14 percent. About half of this increase is projected to occur in the downtown area. 4 of 9
Figure 1
Figure 2
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Recent and near-term actions planned by the City continue to support the City’s 6 of 9
sustainability goals and minimize the projected increase of sewage generation related to new development in the City. Foremost among these programs is the recently adopted Water Neutrality Ordinance and the programmatic efforts of the Sustainable Water Infrastructure Project (SWIP). Each of these programs will help in reducing the projected overall increase in sewer flows and are summarized below.
Water Neutrality
In May 2017, the Santa Monica City Council adopted a Water Neutrality Ordinance to require that new development offset water use on site or off site, or alternately, pay the City an in-lieu fee to fund retrofitting of plumbing fixtures offsite. The ordinance would prohibit a new development from exceeding the water use of the existing development on that property. If that requirement could not be met onsite, the excess water demand would have to be offset by reducing the water demand (through fixture replacement) at other sites within the City. Given this water neutrality requirement, much if not all of the projected overall increase in future sewage flow should be offset through this growthfunded plumbing fixture retrofit program.
It should be noted that while this water neutrality program may offset an increase in overall sewage flows, Water Neutrality may still allow for an increase in flows at any specific site. With this program provision, some of the large future developments could still have a substantial point load increase in sewage discharges. To plan for this potential increase associated with these developments and to assure adequate capacity in the sanitary sewer system collection system network, the impact of site specific increases has been incorporated in the hydraulic model. Proceeding in this manner, the assessment included some anticipated impact from new development to reduce the risk of sanitary sewer overflows.
SWIP – Water Reclamation Facility (WRF)
The City of Santa Monica Sustainable Water Infrastructure Project (SWIP) will provide for the treatment and reuse of brackish/saline impaired groundwater, recycled municipal wastewater and stormwater runoff. In addition, the SWIP will help improve the water quality in the Santa Monica Bay by reducing urban runoff into the Bay. 7 of 9
The Water Reclamation Facility (WRF) component of the SWIP will have the greatest benefit to the City’s sanitary sewer system. The WRF will remove 1 MGD of sewage from the sewer collection system in the area. This will provide additional pipeline capacity and reduce the cost of wastewater treatment and disposal currently charged by the City of Los Angeles.
Assessment Modeling
To support the evaluation of the City’s sanitary sewer system for both existing and future conditions, a hydraulic model was developed. The hydraulic model development activities included a comprehensive review of system data including Geographic Information System (GIS) mapping, Supervisory Control And Data Acquisition (SCADA), NorthStar billing system statistics, sewer flow analysis and allocation, elevation extraction for the model facilities based on survey data, diurnal (daytime/nighttime) pattern assignments, analysis of dry and wet weather peaking factors and model calibration based on flow monitoring data.
The calibrated sanitary sewer system hydraulic model was used to perform a comprehensive capacity analysis of the sewer system under current and future conditions. These modeling simulations determined the adequacy of the system capacity under dry weather and wet weather conditions, and subsequently identified parts of the systems where improvements will be required for anticipated development.
Findings
The analysis found that the City’s sanitary sewer system performs exceedingly well, and there are very limited areas where the hydraulic capacity of the existing sewer system may fall short of the applicable evaluation criteria. These evaluation criteria comprise two factors used in sewer flow analysis in pipelines:
depth of flow equal to or less than half of the pipe diameter; and average flow velocity equal to or greater than 2 feet per second.
For maintenance hole performance, surcharge relates to the depth of wastewater in the 8 of 9
maintenance hole relative to the street elevation in the event of a sewage backup.
Under existing conditions, approximately 1% of the system may experience a capacity shortfall. In utilizing the model to simulate future conditions, the City’s sewer system continues to perform well. In fact, under future conditions, only 3% of the modeled pipelines exceeded the evaluation depth of flow criteria (depth of flow greater than half of the pipe diameter). Although 1% existing and 3% future capacity shortfall results represent a favorable outcome of this analysis, any Sanitary Sewer Overflow which occurs can become an environmental hazard to the coastal environment. By addressing problem areas proactively, spills may be prevented and hazards avoided.
The condition of the existing system and its ability to address future conditions with relatively modest investment lead to a proposed 5-year Capital Improvement Program.
The annual expenditures in the proposed CIP coincide with historical $3 million per year sewer main replacement budgets. In addressing needed improvements in the immediate five-year planning horizon, capacity to serve future conditions will be in place in advance of the build-out of the DCP/LUCE. The proposed five-year CIP schedule is provided below.
Description FY
2018/19
FY 2019/20 FY 2020/21 FY
2021/22
FY2022/23
Capacity Improvements $2,000,000 $1,200,000 $1,600,000 $2,000,000 Field Review Services $100,000 $80,000
Pipeline Replacements $900,000 $1,800,000 $1,400,000 $2,920,000 $1,000,000 TOTAL ANNUAL CIP $3,000,000 $3,000,000 $3,000,000 $3,000,000 $3,000,000 Capacity improvements are those projects identified in the SSSMP, which were found through the hydraulic modeling to be in need of replacement due to insufficient capacity to meet existing and/or future conditions.
Field review services include projects or activities that are needed to further refine the sewer system hydraulic model from additional field investigations, in the form of facility information validation or flow verification, to confirm pipeline and maintenance hole data and obtain new information on actual sewer flow conditions in various areas of the City.
The results of this effort may enable the City to reduce the identified capacity-related 9 of 9
improvements provided herein.
Pipeline replacements include those pipelines identified through ongoing maintenance activities (e.g., sewer jetting and video inspections) for the annual sewer main replacement program.
Financial Impacts and Budget Actions
There is no immediate financial impact or budget action necessary as a result of the recommended action. Projects identified in the plan will be incorporated into future Capital Improvement Program budgets.
Prepared By: Gil Borboa, Water Resources Manager
Approved Forwarded to Council
Attachments:
A. Sanitary Sewer System Master Plan - Draft - August 2017 B. Powerpoint Presentation