Date of Award

Spring 2018

Access Restriction

Thesis

Degree Name

Master of Science

School or College

Seaver College of Science and Engineering

First Advisor

John H. Dorsey

Second Advisor

Joseph C. Reichenberger

Abstract

Biofiltration systems like rain gardens and bioswales are an important tool for capturing and
infiltrating polluted runoff, but little data exists on their efficiencies within Mediterranean
climates. A two-year study initiated in 2015 investigated water retention and pollutant loading
and retention in the Ballona Creek Rain Garden (BCRG). This 300 by 3 m biofiltration system
was constructed by The Bay Foundation in 2011 along Ballona Creek in Culver City, Los Angeles
County, California. The purpose of the garden was to capture and infiltrate runoff from light
industrial and commercial operations bordering the Creek, thus reducing pollutants entering
this waterway and flowing into Santa Monica Bay 9 km downstream. During storm events,
runoff enters the garden via five inlets, and when filled, flows into the creek via two outlets.
The goal of this study was to sample flows and pollutant concentrations in runoff entering and
leaving the garden and then integrate these to calculate mass loading estimates. Flows were
measured at all inlets and outlets using 90° V-notch weirs outfitted with Hobo water level
sensors to produce hydrographs. The following pollutants were measured at all flowing inlets
and outlets two to three times per storm depending on its duration and intensity: fecal
indicator bacteria (E. coli and enterococci), total suspended solids, metals (copper, zinc, and
lead), and semivolatile hydrocarbons (polyaromatic hydrocarbons, diesel hydrocarbons, and
motor oil hydrocarbons). The summation of load method was used to calculate the mass of
contaminants entering and leaving the garden for each storm event, and their percent capture
within the garden. The BCRG was very effective at infiltrating runoff and sequestering
pollutants. The garden’s infiltration rates ranged from 73% to 100% (with 100% for many of the
smaller storms <1-in). Results for pollutant loading and retention indicated that the average
percent retentions were in the 80-90% range for all pollutants, with an average of 90% for all
nine pollutants sampled. This suggests rain gardens and other Low Impact Development (LID)
systems can be used successfully in urban Mediterranean climates like Los Angeles to promote
infiltration, capture pollutants, and prevent polluted stormwater from reaching impaired water
bodies.

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