PURPOSE

 

To provide Council with an update on the status of the City of Burbank�s wastewater collection and treatment system and provide a summary of the recently completed Sanitary Sewer System Evaluation and Capacity Assurance Plan (SECAP).

 

BACKGROUND

 

 

Each day, Burbank residents and businesses generate approximately eleven million gallons of wastewater.  This wastewater is collected and conveyed through privately owned building sewers to publicly owned sewer mains. The majority of wastewater generated within the City is treated at the Burbank Water Reclamation Plant (BWRP). Effluent produced at the BWRP is either provided to Burbank Water and Power for sale as recycled water or discharged to the Burbank Western Channel. Sludge is conveyed from the BWRP out of the City via the City of Los Angeles� (Los Angeles�) North Outfall Sewer (NOS).

 

The City�s existing wastewater system includes three types of facilities: (1) wastewater collection system pipelines and maintenance holes, (2) wastewater pump stations, and (3) the Burbank Water Reclamation Plant.

                                  

Wastewater Collection System

The existing wastewater collection system within the City contains approximately 224 miles of underground sewer pipelines. City-owned pipelines range from 8 inches to 36 inches in diameter. The vast majority of the City�s wastewater collection system (over 98%) is composed of vitrified clay pipe (VCP). Due to the inert nature of VCP, it is generally considered to provide one of the longest useful lives of materials commonly used in sewer pipeline construction. VCP pipelines are generally considered to provide reliable service for 80 to 100 years, provided they are properly designed, constructed, and maintained.

 

In January 1994, the Northridge earthquake caused severe damage to the City�s sewer system. Through video inspection, the majority of the City�s sewer system was investigated to determine locations requiring repair.  The damaged sewer pipes were repaired using approximately $14 million dollars in funding from the Federal Emergency Management Agency (FEMA). These extensive repairs have resulted in a wastewater collection system that is in good physical condition.

 

Wastewater Pump Stations

Wastewater generated in the northern half of the City flows by gravity to the BWRP while wastewater generated in the southern half flows into the Beachwood Pump Station, which lifts it to the BWRP. Wastewater generated along the extreme southeastern edge of the City flows to the Mariposa Pump Station, where it is lifted to the Beachwood Pump Station before being lifted a final time to the BWRP for treatment. In addition to the wastewater generated within its borders, the City conveys and treats a small section of Los Angeles� wastewater that is adjacent to Burbank�s northwestern border (Figure 1).

 

Burbank Water Reclamation Plant (BWRP)

The BWRP is a tertiary wastewater treatment plant that is rated for an average design flow of 9 million gallons of water per day (MGD).  The plant was originally built in 1966 as a secondary treatment facility with a 6 MGD flow capacity.  In 1971, the plant was expanded to 9 MGD and tertiary filtration was added to improve effluent quality. 

 

Three recent upgrades have significantly improved the quality of effluent and the safety at the BWRP.  These upgrades have been: (1) 1999 Operational Upgrade � new filters and numerous electrical and chemical improvements, (2) Biological Nutrient Removal Package A � effluent ammonia concentration was greatly reduced by converting the biological process, and (3) Biological Nutrient Removal Package B � replaced chlorine gas disinfection with liquid sodium hypochlorite for enhanced safety.

 

REGULATORY ISSUES

 

Although the United States Environmental Protection Agency is the ultimate authority for water quality in this country, the California State Legislature has entrusted the California State Water Resources Control Board (State Board) and nine Regional Water Quality Control Boards (Regional Boards) with the authority to preserve and protect the state's waters. 

 

The Regional Board regulates the water quality of discharge from the BWRP into the Burbank Western Channel through a National Pollution Discharge Elimination System (NPDES) permit. Compliance with this permit requires extensive monitoring, frequent capital projects and diligent oversight of the plant�s operation.
 

Figure 1.

 

In addition to this NPDES permit, the State Board has recently promulgated regulations in the form of Waste Discharge Requirements (WDRs) for wastewater collection systems.  The WDRs approved by the State Board will extend to every city and agency in the state that owns a wastewater collection system. Burbank�s wastewater collection system will be directly regulated for the first time.

 

The WDRs proposed by the State Board focus on the creation and implementation of a Sanitary Sewer Management Plan (SSMP).  An SSMP is a comprehensive plan created by each city or agency that addresses how the wastewater collection system will be maintained to eliminate all preventable wastewater overflows. The System Evaluation and Capacity Assurance Plan (SECAP) recently completed for the City is one of the major components of an SSMP.  Other elements of an SSMP include: legal authority documentation, schedule of cleaning, training goals, and overflow response plans.

 

In general, the City has been proactive in most areas required by the new WDRs. Many of the required elements of the SSMP have already been created and will only need minor modifications before adoption. On the other hand, certain elements in the WDRs may require Burbank to purchase additional equipment and increase staffing in the future. For example, an additional vacuum truck and two person crew may be needed to respond to wastewater overflows in the manner desired by the State Board. 

 

The State Board has estimated that the average monthly cost of compliance with the new collection system WDRs will add $6 per household per month. Considering that Burbank�s current monthly sewer service charge per single family dwelling is $16 per month, this would represent an increase of 37% in the monthly bill for these new regulations. As stated above, the City has been proactive in many of the required elements and does not anticipate sewer rates to increase by the full $6 per month that other cities or agencies may face.  As Public Works moves closer to the completion of the SSMP, any sewer service charge increases will be brought before the Council for approval.

 

SYSTEM EVALUATION AND CAPACITY ASSURANCE PLAN (SECAP)

 

The System Evaluation and Capacity Assurance Plan (SECAP) recently completed for the City is a major element of the required SSMP.  It focuses on a hydraulic evaluation of the existing sewer pipelines, maintenance holes, and pump stations, and includes reliability assessment of these facilities through the development of an appropriate ongoing capital repair and replacement program.

 

Infrastructure Inventory

The first step in a SECAP was the verification of the wastewater collection system infrastructure inventory.  A comprehensive reconciliation of the entire sewer system was performed and integrated in the Geographic Information System (GIS) database.  Although this data checking procedure was time consuming, the accuracy of the GIS data directly impacts the ability to create an accurate hydraulic model for the wastewater collection system.  Another benefit of this exercise was that it allowed the City to create updated sewer maps through the GIS system.

 

Hydraulic Analysis of Existing Wastewater Flows

The next step was to evaluate existing wastewater flows through water usage information and flow monitoring.  The data collected through these tasks allow for a high degree of confidence in the resulting hydraulic model.

 

Wastewater discharge was first determined by utilizing utility billing data so that the water usage from the monthly water billing records could be attached to each individual parcel. Each parcel was then assigned a return-to-sewer (RTS) ratio based on zoning classification. The RTS ratio refers to the fraction of each gallon of water reaching a parcel that enters the wastewater collection system. The RTS ratios were based upon industry standards but calibrated specifically to the City using flow monitoring data.  Knowing the amount of water delivered to a parcel in combination with the calibrated RTS ratios provided an initial estimate of wastewater within each pipe in the wastewater collection system.

 

The next step was to conduct a flow monitoring program. The wastewater collection system was divided into a total of twenty basins requiring twenty-five flow monitoring sites. The flow monitoring program was conducted from February 10, 2003 through April 20, 2003.  This time period was chosen due to the high likelihood of rain events during these months, which allow for an analysis of the amount of rain water that enters the wastewater collection system.  Although wastewater collection systems are designed to convey a limited quantity of rain water, excessive rain water can reduce collection system capacity, increase the probability of sanitary sewer overflows and increase treatment costs.

 

The flow monitoring program resulted in several important areas of information and data. The data gathered through this monitoring included: (1) average and peak flow values under dry and wet conditions, (2) effects of various storm events on each monitored area or basin, and (3) general flow conditions at specific sites to compare with the hydraulic model output.  These data allows the City to make an assessment of existing and future capacity deficiencies within the wastewater collection system.

 

Potential deficiencies determined though the modeling process do not indicate that there will be overflows in these locations, but rather indicate that the desired depth to diameter (d/D) ratios will be exceeded. Pipelines in the City�s wastewater system are considered to have a potential deficiency with a d/D greater than 75%. Pipes with a diameter of 18 inches or less are considered to have potential capacity concerns with a d/D value between 50% and 75% (Figure 2).

 

 

Figure 2

Pipeline Loading Conditions

 

 

 

Hydraulic Analysis Conclusions

 

The hydraulic analysis revealed that the City�s wastewater collection system is in relatively good shape in regards to capacity. There are only a few pipelines with current capacity deficiencies.  Of immediate concern are pipelines with capacity deficiencies under current average dry-weather flow.  The SECAP has identified only two pipelines which exhibit this level of deficiency: 150 feet of pipe on San Fernando east of Cedar, and 150 of sewer pipe on Cedar south of San Fernando. Parallel pipelines are already scheduled for construction as a part of the South San Fernando Streetscape Improvement Project. 

 

In addition to the analysis of dry-weather wastewater flows, pipeline capacity was examined for wet-weather conditions. In general, flow monitoring revealed that the City�s sewer system is sealed relatively well. This was confirmed during the record shattering 2004-05 rain year in that there were no storm related wastewater collection overflows.  Nevertheless, rain water entering the system must be accounted for in the hydraulic modeling to prevent future overflows during storm events.  For planning purposes, a 5-year storm event has been included in the model to determine capacity deficiencies.

                                                                                   

Looking toward the future, the SECAP used growth and land use projections provided by the Community Development Department (CDD) and the Southern California Association of Governments (SCAG).   These projections of future land use and population were used to establish the general trends and locations of growth and to project future wastewater flows and requirements in the City�s collection system.  The target year of 2025 was used to assess growth related impacts.

 

Based on growth projections and wet-weather considerations, the hydraulic model indicates that there are 37,600 lineal feet of sewer pipeline that will potentially have capacity deficiencies. The majority of these potential deficiencies are located in the central and southern areas of the City.  In addition, the hydraulic model indicated another 45,200 lineal feet of sewer pipeline that will be over 50% full which the City should reexamine in the future.

 

The capacity deficiencies indicated by the hydraulic analysis indicate where action may need to be taken to prevent future sewer system problems within the City. Such action may include replacing the existing wastewater pipeline with a larger diameter pipeline or parallel construction of existing wastewater pipelines.  Due to the expense of replacing or constructing new sewer pipelines, alternate solutions will be explored first.

 

The general strategy of the SECAP is to have a dynamic plan that can be used by the City to make informed decisions.  The following steps will be taken before replacing or constructing new sewer pipelines: (1) confirmation of capacity deficiency, (2) assessment of diversion opportunities, or (3) analysis of system connectivity possibilities.

 

Although additional investigation will be performed to determine which of the identified sewer upgrade projects are needed, initial analysis has determined that not all of the identified potential capacity deficiencies can be eliminated. Therefore, Public Works is programming $750,000 each year toward the upgrade of the wastewater collection system.  In addition to these funds, any significant increase in wastewater flow caused by new development will require that the developer help to pay a portion of the upgraded sewer pipelines that would serve that facility.  

 

Sewer rates are not anticipated to increase due to the programming of funds for capital improvements of our sewer collection system.  Recent upward pressure on sewer rates has been primarily based on maintaining a positive operating budget rather than the cost of capital improvement projects.

 

BWRP Equalization Basin Project

 

In addition to evaluating the wastewater collection system, Public Works has also been investigating future opportunities at the treatment plant.  The BWRP is what is often referred to as a �skimmer� plant in that it selectively receives, treats and discharges as much, or as little raw wastewater as the plant operating system allows. The BWRP is rated for a daily process capacity of 9 million gallons per day (MGD), and has been treating an average of 8.7 MGD over the past couple of years.  The plant receives this flow at a higher flow rate during the day (as high as 12 MGD during the day) and significantly less flow at night (as low as 4 MGD).  Thus, the diurnal flow pattern stresses plant capacity during the day but underloads the plant during the night (Figure 3).

 

 

                                                                 Figure 3     

Diurnal Wastewater Flow Patterns

 

During the day, when flow is received into the BWRP at peak capacity, a portion of raw wastewater is bypassed to Los Angeles for treatment. For this treatment, the City pays Los Angeles a service charge proportional to the flow and strength of wastewater discharged into their system. 

 

An equalization basin project is currently in design for the BWRP that would virtually eliminate this diurnal flow of wastewater treatment at the BWRP.  An equalization basin would store wastewater during the daytime peak hours that exceed the plant�s operational capacity and treat it during the nighttime hours when unutilized capacity exists.  Although the BWRP can continue to treat wastewater under the current diurnal flow pattern, there are a number of benefits for constructing an equalization basin that would create a more constant flow of wastewater into the facility.

 

The benefits of this project include increased recycled water availability, reliability of wastewater treatment, and cost savings to Los Angeles for wastewater treatment.

               

Burbank Water and Power currently uses an average of over 1.6 million gallons of recycled water each day. Other than the power plant, which is the single largest user of recycled water, all other uses are for irrigation.  The most desirable time for use of recycled water for irrigation is during early morning  hours. Unfortunately, these are also the hours when available recycled water is at its lowest.  The equalization basin project would provide recycled water when it is desired most, during the early morning.  This availability of recycled water will allow the City to expand its use of this valuable alternate water source and lessen its use of imported water.