Title

Water Infiltration and Pollutant Rentention Efficiencies in the Ballona Creek Rain Garden

Date of Award

Spring 2018

Access Restriction

Thesis

Degree Name

Master of Science

Department

Environmental Science & Civil Engineering

School or College

Seaver College of Science and Engineering

First Advisor

John H. Dorsey, Ph.D.

Second Advisor

Joseph C. Reichenberger, P.E.

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

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