Coastlines January/Febuary 1999- Santa Monica Bay Restoration Project

In addition, the bay supports a diversity of habitats and 

some 5,000 species, including biologically rich kelp 

forests the southern-most run of the endangered steelhead 

trout, submarine canyons and an extensive soft-bottom 

benthic community.

The Problem

Despite notable environmental improvements, the bay 

continues to face the challenges of health risks to 

recreational users and habitat degradation resulting from 

urban runoff pollution during both dry and wet weather.

Los Angeles County and the 21 cities in the watershed are 

grappling with implementing stormwater pollution 

reduction technologies, given limited financial resources 

and the lack of research on appropriate technologies for 

the climate and weather regime found in Southern 

California.

The Project

The purpose of this project was to demonstrate and evaluate the effectiveness of catchbasin retrofit 

devices in reducing pollutant loads to the bay. The focus was on devices requiring only minor structural 

modifications to existing catchbasins, costing no more than $500 to $1,000 per catchbasin and needing 

maintenance, on average, only once per year. Commercially available and easily constructed devices 

were evaluated in both wet and dry weather.

Introduction to Santa Monica Bay

Santa Monica Bay is a priceless resource, as vital to its marine life, birds, and other forms of resident and 

transient wildlife as it is to the nine million people who live within an hour's drive of its shores. 

However, it has long been adversely affected by the ills associated with its proximity to the heavily 

urbanized Los Angeles basin. While tremendous improvements have been made, stormwater and urban 

runoff remain significant uncontrolled sources of pollution to the bay. Reducing pollution from these 

sources is one of the highest priorities in the Bay Restoration Plan.

Indicative of the problems associated with stormwater and urban runoff are the findings of the landmark 

epidemiological study conducted by the Santa Monica Bay Restoration Project (SMBRP), linking 

increased illness rates to swimming near flowing storm drain outlets and at beaches with high bacterial 

indicator densities. Stormwater also carries massive trash loads to the bay, costing Los Angeles County 

taxpayers roughly $4 million in beach clean-up costs in 1997. Sediment contaminants (e.g., metals) are 

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Click on above image for larger picture.

elevated near stormwater discharges and 

urban runoff has been found to be toxic 

to portions of the bay's benthic 

community.

Overview of the Project

The Municipal Stormwater/Urban 

Runoff Pilot Project was initiated by the 

SMBRP, which awarded a $100,000 

challenge grant to the City of Santa 

Monica. With this money, Santa Monica 

led the effort to organize a consortium 

of agencies, including Los Angeles 

County, 13 municipalities, one industry 

partner and the SMBRP, to collectively 

undertake a study to evaluate the 

feasibility and effectiveness of retrofitting catchbasins to reduce pollutant loads to the bay. Catchbasins 

in Southern California typically are not designed to allow the solids to fall out, allowing sediments and 

their associated contaminants to wash down the drain. The consortium hired two consulting firms and 

two researchers from the University of California at Los Angeles to conduct a series of applied research 

studies to meet the project's goal.

Project Objectives

The goal of this project was to evaluate the feasibility and benefits of using catchbasin retrofit devices as 

one element in local stormwater management programs. Three main objectives (or tasks) were 

undertaken to achieve this goal: 

● characterizing local runoff and selecting target pollutants; 

● evaluating catchbasin retrofits, and 

● assessing the feasibility and potential environmental benefits of various inter-city catchbasin 

retrofit scenarios. 

Implementing the Project

Characterize Local Runoff and Select Target Pollutants

Limited sampling was conducted at four sites to confirm the types and concentrations of pollutants in 

local urban runoff and differences between land uses. Target pollutants met the following criteria: 

● present in local receiving waters in concentrations that threaten beneficial uses, 

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● discharged via municipal storm drains in significant quantities, and 

● can be removed or reduced by some type of catchbasin insert. 

Based on these criteria and the results of sampling conducted both prior to and as part of this project, the 

pollutants selected for study were total suspended solids, oil and grease, and trash and debris.

Evaluate Catchbasin Retrofits

Before conducting field and laboratory tests, a set of objectives for evaluating retrofits was established. 

The objectives addressed the cost of the devices and their ability to control the designated target 

pollutants, function as operationally practical components of the municipal stormwater collection system, 

and be used in certain municipal applications (i.e., with specific types of catchbasins and/or for specific 

types of land use).

Table 1: Comparative Pollutant Removal Effectiveness*

*Full report includes a similar comparison for all evaluation objectives.

**Commercial device consisting of an inlet screen panel, debris basket and oil sorbing columns. 

***"NR" indicates that the device is not recommended.

Based on previous 

research and limited 

modeling, a variety 

of catchbasin 

"inserts" was 

selected for further 

evaluation. Inserts 

are devices that 

attach to the 

catchbasin entrance 

or mount inside and 

thus are relatively 

easy and 

inexpensive to 

install. Inserts are 

designed to improve 

stormwater quality 

by either preventing 

debris and pollutants from entering the basin or by detaining and treating the water in the basin. Fieldtesting was conducted in two areas -- one having residential land use and the other commercial. 

Laboratory testing included shake tests, bench-scale column tests, and a full-scale simulation in a 

fabricated, aboveground catchbasin. Table 1 summarizes the results of the field and full-scale laboratory 

tests for the candidate devices.

Assess Inter-city Implementation Scenarios

Several inter-city implementation scenarios were considered, including citywide implementation, 

implementation at high opportunity sites, land-use specific implementation, and implementation in 

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catchments discharging to sensitive or targeted receiving waters. 

For example, for the land-use specific scenarios, the expected reduction in the target pollutant load was 

estimated using data on the number of catchbasins associated with the particular land use(s): the 

predicted pollutant removal efficiency for retrofitted catchbasins and the estimated pollutant load for the 

area under that land use. These calculations are illustrated for free oil and grease removal in Table 2. 

Calculations were also made for removal of trash and debris and total suspended solids under various 

scenarios.

Table 2: Estimated Results of Sedimentation Baffle Retrofit for Free Oil and Grease Removal 

Based on this pilot 

project, a decision 

framework for 

evaluating retrofit 

options was 

developed to help 

municipalities select 

catchbasin retrofit 

devices taking into 

account local 

conditions and 

priorities. The first 

"decision tree" 

includes four steps:

1. Determine 

which pollutants are of concern (e.g., which impair or threaten beneficial uses), 

2. Identify the catchbasins to be controlled (e.g., those discharging to sensitive water bodies), 

3. Decide whether to focus on dry-weather or wet-weather discharges or both, and 

4. Select appropriate devices (e.g., boardovers or screens to control dry-weather pollutants). 

Another decision tree with supporting information helps planners evaluate different devices based on 

their technical feasibility, pollutant removal effectiveness, cost, and operation and maintenance 

considerations.

Success Stories

● This pilot project is the first to systematically test stormwater treatment devices under the climate 

and weather regime found in Southern California (i.e., arid climate, clearly defined wet and dry 

seasons, and high-intensity winter storms). 

● The project's findings are transferable to coastal Southern California and other arid regions of the 

U.S. and, in addition, the implementation scenarios can be easily updated with new information. 

● The project's findings are providing a timely impact on disbursement of county bond funds for 

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capital improvements to reduce stormwater pollution -- and should prove valuable to 

municipalities as they formulate capital project proposals. 

● Inlet screen panels and boardovers are a very effective and inexpensive way to prevent nearly all 

debris from entering catchbasins during dry weather. In addition, they do not interfere with street 

sweeping; in fact, tests showed that the street sweeper picked up 95% of the accumulated debris in 

front of the catchbasin. 

● Debris baskets are equally effective in both dry and wet weather; they did not impede flow in field 

tests, require no catchbasin modifications and can be easily cleaned out. Furthermore, they can 

hold oil sorbents to control oil and grease. These are probably used most effectively in 

commercial areas, which typically generate about three times the trash as other areas. 

Prototype box-shaped debris basket

Lessons Learned

When evaluating stormwater 

treatment devices, planners should 

make sure that devices have been 

tested based on pollutant 

concentrations typically found in 

urban runoff. Many sorbers, for 

example, had been tested based on oil 

and grease concentrations in the 

thousands of milligrams per liter 

rather than the more appropriate 10 to 

35 mg/l range typical of urban runoff.

Catchbasins should be evaluated in 

the context of all of the elements of a 

watershed-based stormwater 

management program. When 

considering the use of catchbasin inserts, it is important to recognize that there are practical limits on 

which pollutants can be controlled, what degree of control is possible, and what is truly "practicable" 

given that catchbasins must still perform their function of flood control.

For oil and grease removal, the most cost-effective land use-based approach is to target commercial, 

multi-family and industrial areas. Reducing the number of retrofits by 44%, but focusing on the land uses 

that generate more oil and grease, still affords a pollutant load reduction of 67% of the baywide scenario 

(see Table 2). 

The volume of most Southern California catchbasins is large enough to allow significant capture of total 

suspended solids and fine particulate-related pollutants. The most cost-effective scenario for controlling 

total suspended solids is to focus on catchbasins where pollutant removal would be highest (e.g., those 

with larger volume to tributary area and imperviousness ratios).

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A "boardover" used to physically block the curb inlet of the catchbasin

For Further Information

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Environmental Protection Agency's Office of Wetlands, Oceans, & Watersheds

URL: http://www.epa.gov/owow/estuaries/coastlines/janfeb99/center/insert.html

Revised March 2, 1999

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