Storm effects on regional beach water quality along the southern California shoreline

23 © IWA Publishing 2003 Journal of Water and Health | 01.1 | 2003 Storm effects on regional beach water quality along the southern California shoreline Rachel T. Noble, Stephen B. Weisberg, Molly K. Leecaster, Charles D. McGee, John H. Dorsey, Patricia Vainik and Victoria Orozco-Borbón ABSTRACT Two regional studies conducted during dry weather demonstrated that the Southern California Bight (SCB) shoreline has good water quality, except near areas that drain land-based runoff. Here, we repeat those regional studies 36 h after a rainstorm to assess the influence of runoff under high flow conditions. Two hundred and fifty-four shoreline sites between Santa Barbara, California and Ensenada, Mexico were sampled using a stratified-random sampling design with four strata: sandy beaches, rocky shoreline, shoreline adjacent to urban runoff outlets that flow intermittently, and shoreline adjacent to outlets that flow year-round. Each site was sampled for total coliforms, fecal coliforms (or E. coli), and enterococci. Sixty percent of the shoreline failed water quality standards after the storm compared to only 6% during dry weather. Failure of water quality standards increased to more than 90% for shoreline areas adjacent to urban runoff outlets. During dry weather, most water quality failures occurred for only one of the three bacterial indicators and concentrations were barely above State of California standards; following the storm, most failures were for multiple indicators and exceeded State of California standards by a large margin. The condition of the shoreline in Mexico and the United States was similar following rainfall, which was not the case during dry weather. Key words | coliform, enterococcus, indicator bacteria, runoff, stormwater Rachel T. Noble (corresponding author) UNC at Chapel Hill, Institute of Marine Sciences, 3431 Arendell St., Morehead City, NC 28557, USA Tel.: +1 252 7266841 x150 Fax: +1 252 7262426 E-mail: rtnoble@email.unc.edu Stephen B. Weisberg Southern California Coastal Water Research Project, 7171 Fenwick Lane, Westminster, CA 92683, USA Molly K. Leecaster Idaho National Environment and Engineering Laboratory, Idaho Falls, ID, 83415, USA Charles D. McGee Orange County Sanitation District, 10844 Ellis Avenue, Fountain Valley, CA 92708, USA John H. Dorsey Department of Natural Sciences, Loyola Marymount University, One LMU Drive, Los Angeles, California 90045, USA Patricia Vainik City of San Diego Metropolitan Wastewater Department, 4918 North Harbor Drive, San Diego, CA 92106, USA Victoria Orozco-Borbón Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Km. 103 Carretera Tijuana-Ensenada, Ensenada, México INTRODUCTION Land-based runoff is increasingly being recognized as a Harbor, FL occur at sites near where urban streams enter source of fecal bacteria and a public health concern at the estuary. Mallin et al. (2000) found that fecal coliform swimming beaches. Noble et al. (2000) found that 60% of concentrations in South Carolina were directly correlated the Southern California Bight (SCB) shoreline areas with the percent of impervious surface in the watershed. receiving urban runoff fail State of California (CA) water Human viruses are consistently found in southern quality standards. Lipp et al. (2001a) demonstrated that California’s urban runoff (Jiang et al. 2001, Noble and the highest indicator bacteria concentrations in Charlotte Fuhrman 2001) and Haile et al. (1999) demonstrated that Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest 24 Rachel T. Noble et al. | Journal of Water and Health Regional microbiological studies | 01.1 | 2003 illness rates more than double when swimming at beaches sponding to four shoreline types: sandy beach, rocky near urban runoff outlets. shoreline, perennial urban runoff outlets, and ephemeral The effect of urban runoff on beach water quality is urban runoff outlets. Although the basic sample allocation even more severe following rain events. More than half of scheme was stratified random, a systematic component the beach water quality failures in Santa Monica Bay, was added to minimize clustering of sample sites along the California, are associated with rain events, even though it shore. This was accomplished using an extension of the typically rains less than 15 days per year (Schiff et al., in National Stream Survey sampling design of Messer et al. press). Several researchers have found significant correla- (1986) and Overton (1987). The term ‘urban runoff outlets’ tions between beach bacterial concentration and river is used to describe storm drains, creeks, and rivers that discharge (Solo-Gabrielle et al. 2000; Dwight et al. 2002). contribute freshwater/stormwater inputs to the coastal Rainfall effects are also apparent on an interannual basis Pacific Ocean. A total of 81 urban runoff outlets that as both Lipp et al. (2001b) and Boehm et al. (2002) have convey 99% of the total freshwater input to the SCB were demonstrated higher beach bacterial concentrations identified and differentiated as perennial or ephemeral during El Niño years. based upon whether water flowed year-round or season- While these studies have demonstrated increases ally, respectively. Sample sites within the perennial and in bacterial concentration associated with wet weather ephemeral water outlet strata were selected using two runoff, they are mostly based on integrating existing public methods. First, sites were selected at a random distance health monitoring data, which are focused on high use within 100 m of the mouth of the outlet (random sites). beaches and not designed to assess the spatial extent of Second, a site was placed on the beach at a location as stormwater influence. The question of spatial extent is close to the mouth of the outlet as possible (referred to as particularly important in southern California, where the the point zero site). At the perennial urban runoff outlets, rainfall influence on beach water quality is perceived as random sites were placed around 39 of the 40 outlets, and severe enough that the health departments routinely issue point zero sites were placed at 30 of the 40 perennial warnings to avoid recreational water contact for at least outlets. At the ephemeral outlets, 36 random sites and 3 days following a storm. Here, we present a survey in 29 point zero sites were sampled from the 41 possible which 1000 km of the SCB shoreline was synoptically systems. sampled the day after a storm to assess the spatial influence of rainfall on regional water quality. Samples were collected in sterile sample bottles or Whirl-Pak bags from ankle-deep water on an incoming wave just prior to receding, with the sampler positioned downcurrent from the bottle and the mouth of the bottle facing into the current. After the sample was taken, the bottle was tipped to decant enough sample to ensure 2 to METHODS 5 cm of airspace in the sample bottle. The bottle was then tightly capped, stored on ice in the dark, and returned to Samples were collected along the shoreline of the SCB at the laboratory in time to begin analysis within 6 h of 254 sites between Point Conception, California, and Punta sample collection. All samples were tested for total Banda, Mexico (Figure 1). All sites were sampled between coliforms (TC), fecal coliforms or E. coli (FC), and 06.00 and 10.00 h on 22 February 2000, approximately enterococci (EC). Collection and processing of samples in 36 h after a storm that deposited ca. 3–7 cm of precipita- a short period was accomplished through cooperative tion over the entire study region. These were the same sites efforts of 21 organizations that conduct routine monitor- sampled by Noble et al. (1999, 2000) during two previous ing of southern California’s beaches. Each participating dry weather regional water quality surveys along the laboratory used their established analytical methods for shoreline of the SCB (Figure 1). These sites were selected sampling processing, which include membrane filtration using a stratified random approach, with strata corre- (MF), multiple tube fermentation (MTF), and the defined Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest 25 Rachel T. Noble et al. | Figure 1 | Journal of Water and Health Regional microbiological studies | 01.1 | 2003 Map of the Southern California Bight depicting the shoreline, counties, and land features of southern California and sampling sites (black dots). substrate technology test kits, Colilert® and Enterolert Methods (1995) or following manufacturer’s instructions. (IDEXX Laboratories, Inc., Portland, ME). All analyses Comparability among laboratories and among methods were performed using techniques as outlined in Standard was confirmed prior to the study through a series of intercalibration studies (Noble et al. 2003). To enhance reliability of comparisons between studies conducted Table 1 | State of California single sample daily bacterial indicator thresholds during wet and dry conditions, each laboratory processed samples from the same sites as they did in the Daily limits Indicator (cfu or MPN per 100 ml)* Total coliforms 10,000 Fecal coliforms 400 Enterococci 104 two previous dry weather regional surveys (Noble et al. 1999, 2000). Total coliform:fecal coliform ratio When total coliforms are > 1,000, and TC:FC≤10 The assessment of shoreline condition focused on estimating the percent of shoreline miles that exceeded a threshold of concern. The State of CA daily single-sample water quality standards for TC, FC, EC and the TC:FC ratio were used as thresholds (Table 1). The percent of shoreline exceeding the thresholds was estimated for each strata and for the shoreline as a whole using a ratio *cfu: colony forming units; MPN: most probable number Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest estimator (Thompson 1992). 26 Table 2 Rachel T. Noble et al. | | Journal of Water and Health Regional microbiological studies | 01.1 | 2003 Rainfall quantity for locations in Southern California (in centimetres) and duration (in hours) for the storm sampled during the Storm Study (2/20/00–2/21/00). Also included is antecedent rainfall information Location Time rain started (2/20) Time rain stopped (2/21) Duration of storm (h) Rainfall (cm) San Ysidro 6:00 am 9:00 pm 40 7.19 Plaza Bonita Rd 6:00 am 4:00 am* 47 3.91 Fashion Valley 5:00 am 8:00 pm 40 5.11 San Onofre 5:00 am 9:00 pm 41 Encinitas 5:00 am 1:00 am* Carlsbad 5:00 am Oceanside Days since last rain Duration of most recent storm (h) 0.41 9 0.41 23 3 0.71 23 2.79 3 0.30 21 46 2.69 3 0.41 14 12:00 am 44 4.09 3 0.51 21 5:00 am 4:00 pm 36 3.63 3 0.30 15 Santa Ana River 6:00 am 4:00 pm 34 4.09 NA 0.00 Coyote Creek 6:00 am 3:00 pm 33 3.23 NA 0.00 Point Vicente 6:00 am 8:00 pm 39 3.91 3 1.30 14 Malibu 7:00 am 5:00 pm 35 5.61 3 1.30 18 Oxnard Airport 5:00 am 11:00 am 31 7.06 3 0.43 14 Ventura 4:00 am 12:00 pm 33 7.21 3 0.84 14 Sea Cliff 4:00 am 12:00 am 45 7.47 3 1.09 13 Lechuza Patrol 6:00 am 12:00 pm 31 7.80 3 1.30 17 Point Hueneme 4:00 am 11:00 am 32 4.75 3 0.33 17 Santa Barbara 4:00 am 3:00 am* 48 6.88 3 0.94 13 UCSB 5:00 am 10:00 pm 42 7.34 > 19 0.00 31–48 h 2.69–7.8 cm 3 days 0–1.3 cm Overall range 3 Rainfall from most recent storm (cm) 2.5 9–23 h *Rain stopped on 2/22. NA: No data available RESULTS of the rainfall event averaged 39 h. A smaller storm that produced rainfall quantities between 0.1 and 1.25 cm The rainfall event that preceded sampling deposited preceded this storm event by 3 days. between 2.5 and 7.0 cm throughout the study area, More than half (58%) of the SCB shoreline exceeded with the highest quantity measured near the Los at least one of the indicator bacteria thresholds (Table 3). Angeles–Ventura County border (Table 2). Duration Beach areas immediately in front of perennially flowing Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest 27 Rachel T. Noble et al. Table 3 | | Journal of Water and Health Regional microbiological studies Fecal coliforms Total coliforms Total:fecal ratio<10 Any indicator Ephemeral point zero 52 26 11 22 52 Ephemeral 38 13 3 11 38 Rocky 34 19 6 7 34 Sandy 59 42 31 18 62 Perennial 67 28 20 17 67 Perennial point zero 87 43 33 30 87 All SCB 56 36 24 16 58 | 01.1 | 2003 Percent of shoreline miles that exceeded State of California water quality standards in the Southern California Bight Enterococci Table 4 | Percent of shoreline that exceeded single or multiple bacterial indicator standards Any indicator Only one indicator Any two indicators Any three indicators All four indicators Ephemeral point zero 52 19 11 19 4 Ephemeral 38 13 14 8 3 Rocky 34 8 19 4 5 Sandy 62 14 10 33 5 Perennial 67 29 13 18 8 Perennial point zero 87 40 3 27 17 All SCB 58 15 12 26 5 urban runoff outlets had the highest frequency of highest frequency of multiple indicator threshold failures threshold failures (87%). The rocky shoreline strata had occurred at the perennial point zero sites (Table 4). the lowest frequency of failures (34%). The vast majority of water quality exceedences, EC was the indicator bacteria that exceeded state regardless of indicator type, were significantly above the water quality standards most often, with nearly 100% water quality thresholds. Using method-specific estimates of the samples that failed standards exceeding for EC of laboratory variability developed during the intercalibra- (Table 3). EC exceeded water quality standards at twice tion exercise (Noble et al. 2003), we found that 77% of the the frequency of FC. Approximately three-quarters of the samples exceeding water quality standards for EC did so samples failed water quality standards for more than one by more than one standard deviation of measurement bacterial indicator during the Storm Study (Table 4). The error. Similarly, 42% and 53% of the TC and FC failures Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest 28 Rachel T. Noble et al. Table 5 | | Journal of Water and Health Regional microbiological studies Comparison of the percentage of total shoreline miles that failed State of California water quality standards in Mexico and the United States following a storm event Enterococci Fecal Total coliforms coliforms Mexico Table 6 | | 01.1 | 2003 Median indicator concentrations in the United States and Mexico following a storm (reported as MPN or cfu/100 ml) Enterococci Total Fecal coliforms coliforms Beach Sandy beach 63 32 11 Mexico 330 Point zero 80 50 20 United States 130 900 80 Entire shoreline 66 36 15 Mexico 310 1,450 515 United States 228 1,400 80 66 42 31 Point zero 87 43 33 Entire shoreline 61 36 24 220 Urban Runoff Outlets United States Sandy beach 490 Kachel, in press). Moreover, southern California has an arid environment with a short rainy season and long dry periods when the rivers provide minimal runoff. Thus, exceeded the standard by more than a standard deviation bacteria and other contaminants accumulate on land of measurement error. between storms, enhancing runoff quality concerns com- The failure of California’s water quality standards pared to temperate areas where rainfall is more frequent. along the Mexican shoreline were similar to that found in The storm effect on water quality is well illustrated by the United States (Table 5). For example, 63% and 66% of comparison with results from the two dry weather regional the shoreline along beaches failed the EC threshold in surveys that sampled at the same sites (Noble et al. 1999, Mexico and the United States, respectively. Median indi- 2000). The extent of shoreline that exceeded water quality cator concentrations of samples that failed standards were standards during this study was nearly 10 times higher also similar between the United States and Mexico, except than in the two dry weather studies (Figure 2). This for FC. FC concentrations were noticeably lower in the increase was observed across all shoreline types and United States at both urban runoff outlets and beaches among all bacteria indicator types (Figures 2 & 3). More- (Table 6). over, the magnitude of the exceedences was much greater during this study. During dry weather, two-thirds of the threshold failures were attributable to failure of a single bacterial indicator and most of those failures were barely above the indicator threshold. In contrast, two-thirds of DISCUSSION the threshold failures during wet weather were for Non-point runoff concerns are exacerbated in southern multiple indicators in which at least one indicator was California because its rivers are highly modified storm- twice the allowable standard (Figure 4). Because we used a water conveyance systems that are independent of the regionally applied, stratified-random sampling design, we sewage flows have not only further demonstrated the importance of unimpeded to the ocean. When storm events occur, runoff rainfall as a component of urban runoff, but we have also plumes can become large oceanographic features that demonstrated that rainfall events have region-wide extend for many kilometers (Bay et al. 1999, Hickey and impacts on coastal water quality in southern California. treatment systems, so urban Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest runoff 29 Rachel T. Noble et al. Figure 2 | | Regional microbiological studies Journal of Water and Health | 01.1 | 2003 The extent of water quality threshold exceedences in the Southern California Bight during the summer and winter studies (dry) compared with the present storm study (wet), by shoreline type. Figure 3 | The extent of water quality threshold exceedences among indicator bacteria in the Southern California Bight during the summer and winter studies (dry) compared with the storm study (wet). Another difference between wet and dry weather con- between Mexican and the United States. While the better ditions was the comparability in water quality between dry weather water quality in the US is probably a reflec- Mexican and US waters. During dry weather, water quality tion of their more extensive sewage treatment systems, the standards were exceeded five times more often on comparable wet weather water quality probably reflects Mexican beaches than on US beaches (Noble et al. 2000). the lack of urban runoff treatment in either country. Still, In contrast, we found that during wet weather there was there were some differences between the countries during no difference in the percentage of impacted shoreline wet weather. Median FC and EC levels were higher along Downloaded from http://iwaponline.com/jwh/article-pdf/1/1/23/393255/23.pdf by guest 30 Rachel T. Noble et al. Figure 4 | | Journal of Water and Health Regional microbiological studies | 01.1 | 2003 Relative frequency of single and multiple bacterial indicator threshold exceedences in the Southern California Bight during the summer and winter studies (dry) compared with the storm study (wet). Mexican shoreline, regardless of whether samples were evaluate the health effects of wet-weather urban runoff are taken at an open beach or near an urban runoff outlet advisable to further support these management actions. (Table 6). These results could be due to the fact that Mexican runoff contains contributions of fresh human fecal contamination from untreated sewage (Noble et al. CONCLUSIONS 2000). • The public health risk of the high indicator bacteria concentrations observed in this study are unclear, particularly if the source material has a large animal contribution. beach water quality of southern California. • source of bacteria is human sewage rather than urban weather. • conducted in Santa Monica Bay, CA and was limited to The indicator bacteria, enterococci, exceeded State of California water quality standards more often runoff. The only epidemiological study that focused on the human health concerns associated with urban runoff was During large storm events, indicator bacteria levels are orders of magnitude higher than during dry Most studies relating bacterial indicator levels to illnesses rates have been conducted at locations where the primary Storm events have a dramatic regional effect on the than total coliforms or fecal coliforms. • Urban runoff outlets, both in Mexico and the United States, are primary sources of contaminated runoff, assessing health effects of dry-weather runoff (Haile et al. with 90% of sites near urban runoff outlets failing 1999). Currently, most public health agencies in southern water quality standards during a storm event. CA issue countywide warnings to avoid recreational water contact following all storms of 1.25 cm or greater. 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