coastal runoff impact study 11

7/28/2019 Coastal Runoff Impact Study 11

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Tidal Transport of Bacteria between the TalbertWatershed and the Ocean

Interim Report 1 for theUCI Coastal Runoff Impact Study (CRIS)

DRAFT I

Prepared For:

National Water Research Institute (NWRI)County of Orange Cities of Huntington Beach, Fountain Valley, Costa Mesa, Santa Ana, Newport Beach

Prepared By:

Stanley B. Grant, Ph. DAssociate ProfessorSchool of Engineering

University of California at Irvine

and

Brett F. Sanders, Ph. D

Assistant ProfessorSchool of Engineering

University of California at Irvine

January 21, 2000


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UCI Coastal Runoff Impact Study Interim Report 1 Draft 1 1/19/2000

1.1 Background ........................................................................................................................................................... 4

1.2 Tidal Transport Experiment................................................................................................................................ 4

1.2.1 Overview.........................................................................................................................................................4

1.2.2. Monitoring Station ......................................................................................................................................... 5

2.0 METHODS ............................................................................................................................................................ 6

2.1 Field Methods ........................................................................................................................................................7

2.1.1 Water Sample Collection................................................................................................................................. 7

2.1.2 Hydrodynamic Data Collection....................................................................................................................... 7

2.2 Laboratory Methods ............................................................................................................................................. 8

2.2.1 Enumeration of Bacteria in the Talbert Outlet Samples Total Coliform ......................................................... 8

2.2.2 Enumeration of Bacteria in Surfzone Samples................................................................................................ 8

2.2.3 Physical Measurements................................................................................................................................... 8

2.3 Characterization of Pump Station Forebay Water and Discharge Volumes .......... ........... ........... ........... ........ 8

3.0 RESULTS AND DISCUSSION ........................................................................................................................... 8

3.1 Tidal Transport of Total Coliform (TC)............................................................................................................. 9

3.1.1 Pump Station Inputs of TC.............................................................................................................................. 9

3.1.2 Oscillation in Tide Range................................................................................................................................ 9

3.1.3 Concentration of TC in the Talbert Outlet....................................................................................................... 9

3.1.4 Concentration of TC in Surfzone .................................................................................................................... 9

3.1.5 Interpretation of the TC Results .................................................................................................................... 10

3.1.6 Implications of the TC Results...................................................................................................................... 10

3.2 Tidal Transport of E.coli (EC)........................................................................................................................... 10

3.2.1 Pump Station Inputs of EC............................................................................................................................ 10

3.2.2 Concentration of EC in the Talbert Outlet..................................................................................................... 10

3.2.3 Concentration of EC (or FC) in Surfzone...................................................................................................... 11

3.2.4 Interpretation of the EC Results Interpretation:............................................................................................. 11

3.2.5 Implications of the EC Results...................................................................................................................... 11

3.3 Tidal Transport of Enterococcus (ENT)........................................................................................................... 12

3.3.1 Pump Station Inputs of ENT ......................................................................................................................... 12

3.3.2 Concentration of ENT in the Talbert Outlet .................................................................................................. 12

3.3.3 Concentration of ENT in Surfzone................................................................................................................ 12

3.3.4 Interpretation of the ENT Results.................................................................................................................. 12

3.3.5 Implications of the ENT Results ................................................................................................................... 13

3.4 Vertical Structure of the Water Column .......... ........... ........... ........... ........... .......... ........... ........... .......... .......... 133.4.1. Conductivity Data ........................................................................................................................................ 13

3.4.2. pH Data ........................................................................................................................................................ 14

3.4.3. Turbidity Data .............................................................................................................................................. 14

3.4.4. Arithmetic TC Data...................................................................................................................................... 14

3.4.5. Log Transformed TC Data ........................................................................................................................... 14

3.4.6. Arithmetic EC Data...................................................................................................................................... 14

3.4.7. Arithmetic ENT Data ................................................................................................................................... 14

3.4.8. Summary of Vertical Stratification Data...................................................................................................... 14


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4.0 SUMMARY OF FINDINGS .............................................................................................................................. 14

5.0 REFERENCES.................................................................................................................................................... 15


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1.0 Introduction

1.1 Background

The surf zone in Orange County, California, is routinely monitored for bacterial indicators of fecal pollution. During

the summer of 1999, elevated levels of indicator bacteria prompted health officials to restrict public access to a

nearly five mile stretch of Huntington Beach (HB). The beach closures and postings disrupted the local economy

and negatively impacted beach attendance.

The Coastal Runoff Impact Study (CRIS) was funded November 1, 1999 by the National Water Research Institute to

investigate the impact of watershed runoff on indicator bacterial levels at HB. Matching funds and/or in-kind

support was provided by the County of Orange, the Orange County Sanitation District (OCSD), the California

Department of Parks and Recreation, and the cities of Huntington Beach, Fountain Valley (FV), Costa Mesa, Santa

Ana, and Newport Beach. In the first phase of CRIS, which was carried out between November 1, 1999 and January

8, 2000, the tide induced transport of indicator bacteria between the Talbert Watershed and the nearshore area at HB

was characterized.

The Talbert Watershed (TW) encompasses 12 square miles in HB and Fountain Valley (FV). The watershed

contains three flood control channels, including the Talbert Channel, HB Channel, and FV Channel (Figure 1).

These channels are tidally influenced, which means ocean water flows into the channels during- flood tides and back

out during- ebb tides. This tide-induced transport of water in the channels may impact water quality at the beach, by

acting as a mechanism for carrying watershed runoff to the nearshore. One of the primary objectives of this transportexperiment was to test the validity of this hypothesis. Current land use in the TW is primarily residential in nature,

although portions of the watershed are zoned for industrial or agricultural purposes.

Both controlledand uncontrolledsources of runoff enter the TW flood control channels. Controlledsources drain

from the street level to one of several forebays. When a forebay pump station is activated, water is transferred from

the forebay to the channel network. The City of HB operates seven (7) pump stations and the Public Facilities and

Resources Department of the County of Orange (PFRD) operates one (1) pump station that discharge into the

channel network. The location of each pump station is noted in Figure 1. Uncontrolledsources, on the other hand,

drain by gravity from street level, through closed conduit collection lines, and then into the channel network. Once

runoff enters the channel network, it travels under gravitational and tidal forces toward the coast, passing through a

constructed wetland (Talbert Marsh) before it enters the ocean approximately 1000 feet upcoast of the Santa Ana

River (SAR) in the City of HB.

1.2 Tidal Transport Experiment

1.2.1 OverviewThe tidal exchange experiment was designed, organized, and carried out by Professors Stanley B. Grant and Brett F.

Sanders of the University of California at Irvine (UCI). The experiment would not have been possible without the

help of personnel from (in alphabetical order) the California Department of Parks and Recreation (CDPR), the City

of Huntington Beach (HB), Orange County Health Care Agency (OCHCA), Huntington Beach Wetlands

Conservancy, Orange County Public Facilities and Resources Department (PFRD), Orange County Sanitation

Districts (OCSD), Surfrider Foundation, and UCI.

The goal of the experiment was to determine if the TW is a significant source of indicator bacteria (total coliform,

E.coli, and enterococcus) to the nearshore area in HB. Indicator bacteria are groups of bacteria that may indicate the

presence of fecal pollution. To achieve this goal, a monitoring station was constructed at the outlet of the TW,located approximately 1000 feet up-coast of the SAR outlet (Figure 1). Over a two-week period beginning

December 7, 1999, this monitoring station was used to simultaneously characterize the hydrology, bacteriology, and

chemistry of water flowing in and out of the TW. Data was collected at the station every hour, 24 hours per day, for

the entire two- week period.

In many ways the experiment replicated the conditions that existed over the summer:

(1) There was no precipitation during the two-week study;


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(2) High levels of indicator bacteria in the surfzone prompted County officials to post portions of the beach twiceduring the study period;

(3) The postings occurred up-coast of the TW outlet, in the same general area where beach closures occurred theprevious summer;

(4) Two large tidal excursions occurred during the study; a moderate excursion at the beginning of the study and anextreme excursion at the end of the study.

At the outset of this study, pump stations operated by the City of HB and OC PFRD were in a diversion mode.

Runoff collected at each of the stations was diverted into the sanitary sewer system and subsequently treated at

OCSD facilities. This mode of operation was initiated during August of 1999 when runoff from the TW was

suspected of contributing to elevated levels of bacterial pollution at HB, and diversions continued into the fall and

early winter months. While the diversion mode cannot continue through storm periods when runoff volumes are

considerably larger, the absence of significant precipitation this year allowed diversions to continue up to the study

period. Midway through our study, on December 13, pump stations in the TW went out of diversion mode, and the

discharge of runoff into the channel network resumed. The timing of the operational change allowed the exchange of

bacteria between the watershed and the ocean to be characterized both with and without the contribution of

controlled runoff sources.

To summarize, the City of HB and OC PFRD operated their pump stations in two different modes during the studyperiod:

(1) During the first week of the study, the pump stations operated in a diversion mode. In this mode, runoff thataccumulated in the pump station forebays was diverted to the sanitary sewer system;

(2) During the second week of the study, the pump stations operated in a discharge mode. In this mode, runoff thataccumulated in the pump station forebays was pumped directly into the flood control channels following normal

operating procedures.

1.2.2. Monitoring StationWith the assistance of the OC PFRD and CDPR, a monitoring station was built on the bridge that spans the Talbert

Outlet at Huntington State Beach. An automated data collection system was installed inside a fenced staging area to

collect water samples and simultaneously collect information about flow conditions in the Talbert Outlet.

In designing the water collection system, several issues were considered:

(1) Studies conducted the previous summer by OCSD suggested that the concentration of bacteria in the outlet ofthe Talbert and SAR channels sometimes varied with horizontal position across the channel; in particular, the

bacterial concentration was sometimes high in the center of the channels and low at the edges, or vice versa.

(2) The spatial pattern of beach closures over the summer prompted speculation that indicator bacteria may havebeen concentrated in freshwater lenses that originated when urban runoff from the Talbert and/or SAR

watersheds flowed out to the ocean. If true, then the concentration of bacteria at our sampling station should

vary significantly with vertical position in the water column, with the highest concentrations located near the

air/water interface where freshwater lenses would be located.

(3) There is substantial evidence that indicator bacteria can be associated with fine particles and sediments (1,2).Furthermore, aerial photography from the previous summer showed turbidity plumes exiting the outlets of theTalbert Channel and SAR watersheds and spreading up-coast along the area impacted by high concentrations of

indicator bacteria. Considered together, these two observations suggest that high levels of indicator bacteria in

the surfzone may have been particle-associated. If true, then the concentration of bacteria at our sampling

station might be vertically stratified, with the highest concentrations appearing near the bottom of the water

column where the particle concentration is highest.

To characterize the vertical distribution of bacteria at the Talbert Outlet, the sampling station was designed to

collect water from four different depths in the water column. Two of the sampling points were located a fixed


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distance (3 and 1-3) below the air/water interface; the other two sampling points were located a fixed distance

above the channel bed (1'-7" and 2'- 11).

The sampling system is illustrated in Section AA' of Figure 1. Each sampling point consisted of a strainer that was

connected by vinyl tubing to an ISCO sampler located in the staging area on the overhead bridge. The fixed-

elevation strainers were attached with brackets to a 4" stainless steel pipe supported by the bridge above, and braced

against shear by a collar inserted into the sand below. The floating strainers were supported by a buoyant platform

(see lower-right inset in Figure 1) that was designed to slide up and down a 1" stainless steel pipe installed parallel

and approximately 3 feet away from the 4" pipe. The following numbering convention was adopted for the sampling

points:

Sampler 1 (S1): Fixed strainer located l'-7" above the channel bed.

Sampler 2 (S2): Fixed strainer located 2'-11" above the channel bed.

Sampler 3 (S3): Floating strainer located 15" below the air/water interface.

Sampler 4 (S4): Floating strainer located 3" below the air/water interface.

An ISCO acoustic Doppler velocimeter and pressure transducer were installed at the base of the 4" pipe to measure

and record water depth, index velocity, and flow direction (ebb or flood). A YSI water chemistry sonde was also

installed to measure the temperature, dissolved oxygen concentration, pH and salinity of the water. These physical

and chemical parameters were monitored and recorded every minute, 24 hours per day, for 14 days. These data were

stored on site in a data logger, and then downloaded onto a portable PC for further processing.

Water samples were collected from each sampling point every hour, 24 hours per day for two weeks. To obtain an

"average" measure of the water quality over the hour-long sampling interval, the ISCO samplers were programmed

to deposit 200 mL of water every 15 minutes. Hence, each 800 mL water sample was a composite of four 200 mL

samples collected over an hour-long period from a particular depth in the water column. This sampling protocol

generated a total of approximately 1,000 water samples for analysis.

Standard Methods requires that all bacteriological sample analyses be carried out within 8 hours of collection,

although 24 hours is allowed (3). Consequently, water samples were collected from the site every 8 hours, and

transported to the Microbiology Laboratory at OCSD for analysis. At OCSD, the water samples were immediately

analyzed for the following:

(1) Indicator Bacteria-Total Coliform (TC),

-E.coli (EC),

-Enterococcus bacteria (ENT)

(2) Turbidity,

(3) Conductivity, and

(4) pH.

The samples were later analyzed for total suspended solids (TSS), and a subset of the samples were archived to

permit later analysis for male-specific bacteriophage. The laboratory procedures used to carry out the water analyses

are described next in the methods section.

2.0 Methods

The sampling approach adopted for this study was designed to quantify the transport of bacteria between the TW

and the ocean with: (1) a sufficiently small time-resolution to capture both intra-tidal and inter-tidal variations in

bacteria concentration and bacterial flow, and (2) a sufficiently small vertical resolution through the water column to

characterize the vertical variation in bacterial concentration.

The study period encompassed a two-week period beginning December 7 and ending December 21, 1999. Methods

were employed to obtain hourly measurements of water level, index velocity, concentration of three indicator

bacteria, and four physical water properties. Water samples were collected 24 hours a day during the study period at

four y elevations within the water column.


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2.1 Field Methods

2.1.1 Water Sample CollectionThe timing and number of water samples associated with this study necessitated an automated approach for water

sample collection in the field. The monitoring station consisted of four ISCO programmable samplers (three model-

3700 and one model-6700) connected to " vinyl tubing that reached into the channel water and terminated in either

a fixed-elevation or floating strainer, as described earlier and illustrated in Figure 1. Two fixed-elevation strainers

were set 1-7 and 2'-11" above the initial bed elevation. The elevation of the bed was estimated to be -2'-8" (MSL)

at the outset of the experiment; however, sediment scouring, around our sampling equipment resulted in a lowering

of the channel bed as the experiment progressed. Two floating-strainers were suspended 3" and 1'-3" below the

water surface. A detailed sketch of the floating strainer apparatus is presented in the lower portion of Figure 1. The

ISCO samplers were filled with ice to keep the water samples near 4C until a servicing crew arrived. Crews

serviced the automated samplers at 6:00, 14:00, and 20:00 each day and transported the samples to OCSD for

immediate analysis.

Hourly water samples from each strainer were composited into a single bottle using the strategy described earlier.

To minimize the potential for cross-contamination between samples, a purge cycle was executed before and after

each sampling event. Because of the configuration of the ISCO samplers relative to the tubing, the purge cycle did

not completely remove all water from the tubing line. However, a small (


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cycle. Intermediate values were interpolated by hand recognizing that the day-to-day tidal variations are remarkably

similar. Index velocity was estimated by using the tide levels and the recorded velocity data for the following day

(12/17/1999-12/18/1999).

2.2 Laboratory Methods

Water samples were analyzed for three indicator bacteria: Total Coliform, E.coli and Enterococcus; samples were

also analyzed for four physical characteristics including pH, Conductivity, Turbidity and Total Suspended Solids

(TSS).

2.2.1 Enumeration of Bacteria in the Talbert Outlet Samples Total Coliform(TC) and E.coli (EC) were quantified using the IDEXX Colilert-18 test. Enterococcus (ENT) counts were

determined using the IDEXX Enterolert test. Sample processing followed manufacturer's recommendations.

Briefly, the Colilert tests were incubated 18 hours at 35C and Enterolert tests were incubated for 24 hours at 41C.

For comparison purposes, 10% of all samples were analyzed in parallel using the multiple tube fermentation method

for TC (3). The MTF data were not available as of the date of this report, but these data will be included in a later

version.

2.2.2 Enumeration of Bacteria in Surfzone SamplesSurfzone samples were collected at 18 stations up- and down-coast of the Talbert Outlet once per day, and these

samples were analyzed for bacteria at either OCSD or the OC Health Care Agency (OCHCA). The multiple tubefermentation (MTF) procedure (3) was used to analyze surfzone samples for TC at both OCHCA and OCSD.

OCHCA used the IDEXX Colilert-18 test and the Enterolert test to analyze for EC and ENT. OCSD, on the other

hand, used an MTF procedure to analyze for fecal coliform (FC), and a membrane filtration (MF) technique to

analyze for ENT. A recent study compared these different methodologies for detecting indicator microorganisms,

and found that their results were intercomparable (4). Specifically, MTF estimates of FC are comparable to Colilert-

18 estimates of EC, and MF estimates of ENT are comparable to Enterolert estimates of ENT.

2.2.3 Physical MeasurementsUpon arrival at the laboratory, the volume of each sample was recorded and a 200 mL aliquot was poured off for

physical characterization. 100 mL of the aliquot was used to measure conductivity, pH, and turbidity, which were

carried out immediately. Another 100 mL was stored at 4C for later TSS analysis. Water pH and conductivity were

measured using, respectively, an Orion SA520 pH meter and an Orion 160 Conductivity meter. Water turbidity was

measured using a HACH 21000N. TSS was measured by filtering a well mixed portion of the sample through aWhatman 934-AH glass fiber filter disc. The filter disc was dried at 103-105C for one hour, and TSS was

calculated from the increase in weight and the volume of the sample used. Some of the water samples were not

processed for TSS within the 10 day window specified for NPDES monitoring. The TSS data were not available as

of the date of this report, but these will be included in a later version.

2.3 Characterization of Pump Station Forebay Water and Discharge Volumes

During the study period, the City of HB contracted Truesdail Laboratores, Inc (Tustin, CA.) to characterize forebay

water from each of the City's seven pump stations in the TW. Water samples were collected once per day from each

of the pump station forebays operated by the City, and these samples were subsequently analyzed for physical

properties (pH, conductivity, turbidity) and bacteriology (TC, EC, and ENT) using the same procedures described

above for the Talbert Outlet samples (Sections 2.2.1 and 2.2.3). In addition, the City of HB recorded the timing of

each pump station event, and provided an estimate of the total volume of runoff that was discharged into thechannel. The discharge volumes were calculated from time histories of the water level recorded for each forebay.

3.0 Results and Discussion

The results are organized as follows. The tidal exchange data for the three indicator bacteria (TC, EC, and ENT) are

presented first. This is followed by an analysis of the vertical distribution of bacteria and physicochemical

parameters in the water column.


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3.1 Tidal Transport of Total Coliform (TC)

3.1.1 Pump Station Inputs of TCThe tidal exchange data for TC are graphically summarized in Figure 2. The top panel indicates the timing, location,

and magnitude of pump station discharges of runoff into the channel network. The circles in this plot are color coded

to indicate the pump station (see Figure 1 for the geographic location of each pump station). The vertical position of

the circles indicates the volume of runoff discharged into the channel; the diameter of the circles indicates the

concentration of TC in the forebay water prior to the discharge event. For example, just after midnight on Monday

(12/13), the Indianapolis Street pump station discharged approximately 1 million gallons of stored runoff into the

Talbert channel, and the concentration of TC in that water was between 104 and 105 most probable number (MPN)

per 100 mL of sample. Altogether, over 11 million gallons (or 33 acre-feet) of runoff was discharged into the

channel network in the second week of the study, and the majority of that runoff had TC concentrations exceeding

105 MPN per 100 ml. For comparison purposes, the total watershed encompasses an area of approximately 7,700

acres.

3.1.2 Oscillation in Tide RangeThe next panel in Figure 2 displays the water level recorded by our instrumentation at the Talbert Outlet (black line)

and the tide level predicted for the Balboa Pier (red line) by the computer program WXTide32 (copyright, Michael

Hopper, 1999). Because southern California has markedly asymmetrical semidiurnal tides (mixed tides) (Emery and

Aubery, 1991), the tide range oscillates over time with a fairly long (~2 week) period. This oscillation in the tiderange can be clearly seen in the second panel of Figure 2: the tide range is large at the onset of the study, small at the

beginning of the second week, and large again at the end of the study. The water elevation at the Talbert Outlet is

relatively constant (~ l'-10" above channel bed) at the low tide mark, even when the water elevation predicted for the

Balboa Pier is much lower. This is because, during a low tide, a critical flow section exists between the monitoring

station and the surfzone. This critical flow section leaves the TW hydraulically isolated from the tide level during

low-tide periods.

3.1.3 Concentration of TC in the Talbert OutletThe third panel in Figure 2 shows the depth-averaged concentration of TC measured at the Talbert Outlet. To

indicate which direction the water was flowing, the TC concentrations were multiplied by a +1 if the water was

flowing from the watershed into the ocean (ebb tide), and a -1 if the water was flowing from the ocean into the

watershed (flood tide). TC concentrations at the Talbert Outlet were fairly low (


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large pulses of TC on 12/18 and 12/19 left the watershed during periods of time when no surfzone samples were

collected. Hence, the impact of these pulses on TC levels in the surfzone cannot be determined from this data set.

3.1.5 Interpretation of the TC ResultsInterpretation:

Runoff discharged from pump stations markedly increases the nearshore loading of TC from the TW, but

only at the end of the ebb tide and when the tide range is large (>2.5').

Evidence:

(1) The pump station discharges contributed significant levels of TC to the channel network. Dischargevolumes routinely exceeded 105 gallons and TC concentration in forebay water was routinely greater

than 105 MPN/100 mL.

(2) The TC pulses occurred after the pump stations began discharging, and they coincided with the end ofthe ebb tide and a decrease in conductivity, implying an upstream freshwater origin. This set of

observations is consistent with a pump station source of TC.

3.1.6 Implications of the TC ResultsThe diversion of runoff to the sewer system has a positive impact on beach water quality, by reducing the loading of

TC to the nearshore. However, the TC concentrations leaving the watershed during the study period never exceeded

4,000 MPN/100 mL. These values are significantly below the California ocean water standard for single samples of10,000 MPN/100 mL (California AB 411).

When runoff is not diverted, the time at which the TC pulses leave the TW for the nearshore may be predictable;

namely, the peak concentrations occur at the end of the ebb tide when the tide range is large. Because the tide levels

can be predicted far in advance, it may be possible to forecast when TC pulses are likely to impair beach water

quality. Further analysis and studies are necessary to address this issue.

Finally, these results suggest that the timing and magnitude of bacterial pulses flowing out of the TW are controlled

by the tide range. When the tide range is small (e.g., 12/12-12/17) there is little tidal exchange of water in the

channels, and the addition of runoff leads to an accumulation of contaminants in the channels. As the tide range

picks up, tidal exchange of the channel water causes a sudden release of bacteria to the nearshore, as observed in the

early morning hours on 12/18 and in the afternoon on 12/19. This "tidal pumping" of contaminants out of low lying

urban watersheds could be a significant source of coastal pollution not accounted for in standard models ofwatershed hydrology.

3.2 Tidal Transport of E.coli (EC)

3.2.1 Pump Station Inputs of ECThe tidal exchange data for EC are graphically summarized in Figure 4. Comparing the top panels in Figures 4 and

6, we find that the EC concentration in the forebays is about 100 times lower than the TC concentration. Hence, the

discharge of runoff from pump stations should have a proportionally smaller impact on the concentration of EC in

the channel water. The California ocean water standards for fecal coliform (FC)which is a group of bacteria that

includes ECare much more stringent than the standards for TC. For example, the single sample standard for FC is

400 MPN/100 mL, while the single sample standard for TC is 10,000 MPN/100 mL. Consequently, the level of EC

detected in the forebay water, while much lower than TC, is still significant relative to current ocean water

standards.

3.2.2 Concentration of EC in the Talbert OutletThe depth-averaged concentration of EC at the Talbert Outlet is illustrated in the third panel of Figure 4. While EC

appears to be flowing primarily from the watershed to the ocean (i.e., there is more red than blue in Figure 4), the

EC concentrations are generally low (


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In general, all of the depth-averaged EC values recorded at the Talbert Outlet were below the California single

sample standard for FC (400 MPN/100 mL) and below the geometric mean standard for FC (200 MPN/ 100 mL).

3.2.3 Concentration of EC (or FC) in SurfzoneAs described earlier (see Section 2.2.2), different methodologies were employed to analyze the surfzone samples,

depending on whether they were analyzed at OCHCA or OCSD. Specifically, OCHCA reported Colilert estimates of

EC, while OCSD reported multiple tube fermentation (MTF) estimates of FC. A recent study (4) found that there

was not a statistically significant difference between the bacterial concentrations estimated by these two techniques.

In this report we have pooled the data from OCHCA and OCSD into one data set that we refer to below as "EC (or

FC)".

The EC (or FC) concentration detected in the surfzone (bottom panel of Figure 4) was high several times during the

study period: once at Station 2N on 12/8 (368 MPN/100 mL) and two times at stations ON-4N on 12/18 and 12/20

(approximately 200 MPN/100 mL). However, the depth-averaged EC concentration leaving the watershed on 12/8

was much lower (


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mL). Indeed, all of the EC concentrations recorded in this study fell below the California ocean water standard for

single samples.

3.3 Tidal Transport of Enterococcus (ENT)

3.3.1 Pump Station Inputs of ENTThe tidal exchange data for ENT are graphically summarized in Figure 6. Comparing the top panels in Figures 4, 6

and 8, we find that the ENT concentration in the forebays is about the same as the EC concentration. Furthermore,

the forebay concentration of both ENT and EC are about 100 times lower than the forebay concentration of TC.

Hence, the discharge of runoff from pump stations should have approximately the same impact on the concentration

of EC and ENT in the channel water.

3.3.2 Concentration of ENT in the Talbert OutletThe depth-averaged concentration of ENT at the Talbert Outlet (third panel in Figure 6) reveals that two large pulses

of ENT flowed out of the watershed during the study period: one in the afternoon on 12/10 and another in the late

evening on 12/16.Importantly, the first large pulse of ENT left the watershed before the pump stations began

discharging runoff. Hence, the source of this first ENT pulse is not related to pump station discharges.

Insight into the probable source of these two large ENT pulses can be obtained by comparing the depth-averaged

ENT data with the water elevation and depth-averaged conductivity measured at the Talbert Outlet (Figure 7).

Focusing on the afternoon of 12/10, the onset of the pulse begins immediately after the start of the ebb tide. Thisimplies that the source of the ENT is immediately upstream of the sampling station, most likely in the Talbert Marsh

(see Figure 1). The peak concentration of this ENT pulse (650 MPN/100 mL) is significantly higher than the

California ocean water standard for a single sample of 104 MPN/100 mL.

The second event in the evening of 12/16 begins with an ENT pulse flowing into the watershed from the ocean

(peak concentration 300 MPN/100 mL). This is followed by a ENT pulse that flows from the watershed back to the

ocean (peak concentration 420 MPN/100 mL). It is possible that these two pulses are actually a single plume of ENT

that was advected into the watershed during the flood tide, and advected back out to the ocean during the following

ebb tide.

3.3.3 Concentration of ENT in SurfzoneThe spatiotemporal patterns of ENT and EC in the surfzone are very similar. The surfzone concentration was high

for both groups of bacteria twice during the study period: once at Station 2N on 12/8, and later at Stations ON-4N on12/18 through 12/20. The surfzone concentration of ENT recorded during these events exceeded the California

standards for ocean water, and prompted the OC Health Care Agency to post the beach. Importantly, the

concentration of ENT detected in the surfzone at Station 2N on 12/8 (990 MPN/100 mL) was significantly higher

than the concentration of ENT leaving the TW during same period of time (


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Interpretation:

The Talbert Marsh is the source of the large ENT pulse that left the TW on 12/10.

Evidence:

(1) The large pulse of ENT that left the TW on 12/10 coincided with the beginning of

the ebb tide, implying that the source of the ENT was immediately upstream of the sampling station in the

general vicinity of the Talbert Marsh.

Interpretation:

The Talbert Marsh is not the only source of ENT in the nearshore.

Evidence:

(1) The peak ENT concentration in the surfzone (990 MPN/100 mL) was significantly higher than the ENT

concentrations observed at the Talbert Outlet around the same time (


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(3) There is no evidence of vertical stratification at any point in the tide cycle.

The absence of vertical stratification in conductivity would appear to rule out the existence of fresh water lenses.

Also of interest is the fact that diurnal declines in conductivity were recorded during the first week of the study

when runoff in the pump stations was being diverted to OCSD. The source of this fresh water signal is currently not

known. One possible source of fresh water is the uncontrolled runoff entering the channel network. Alternatively,

there may be a significant source of groundwater input into the TW, perhaps through the earthen bottom of the

Talbert Marsh.

3.4.2. pH DataThe vertical structure of the pH data is presented in Figure 9. There is an abrupt change in the pH of the water after

12/9, from approximately pH 8.4 to 7.8. This change in pH is not corroborated by in situ measurements of pH

obtained from the YSI sonde (data not shown). Therefore, this change in pH is most likely a laboratory artifact

(laboratory workers report that the pH meter used at the outset of the experiment may not have been reliable and was

therefore replaced). There is no evidence of vertical stratification in the pH data.

3.4.3. Turbidity DataThe vertical structure of the turbidity data is presented in Figure 10. These data reveal that the turbidity of the water

is maximum when the water level is low, and is minimum when the water level is high. Surprisingly, there is no

evidence of vertical stratification in turbidity. Presumably, the turbulent eddies at the Talbert Outlet are sufficiently

strong to keep particles suspended and well mixed over the depth.

3.4.4. Arithmetic TC DataThe vertical structure of the TC data is presented in Figure 11. In this figure, the TC data are plotted arithmetically

to accentuate the large events. These data do not reveal any significant vertical stratification. Some vertical

variability in the TC concentration can be observed on 12/18 at an elevation of about 2' (middle panel); however,

close examination reveals that this apparent stratification is an artifact of the interpolation procedure used to

generate the plot.

3.4.5. Log Transformed TC DataThe vertical structure of the log-transformed TC data is presented in Figure 12. The color representation of the TC

data appears mottled during the first week of the study due to the normal sample-to-sample variability that occurs

when the TC concentration dips below 100 MPN/ 100 mL. The large TC events beginning on 12/17 are uniformly

distributed over the depth. Also note that the baseline level of TC appears to increase about the same time that thelarge pulses of TC left the watershed.

3.4.6. Arithmetic EC DataThe vertical structure of the EC data is presented in Figure 13. Because the EC concentrations observed at the

Talbert Outlet were generally small (


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The primary findings of this study are summarized as follows:

(1) Pump station discharges increased the nearshore loading of TC during the study period. The timing andmagnitude of the nearshore loading appears to be affected by tidal conditions, pump station release times,

discharge volumes, and discharge concentrations.

(2) While pump station discharges increased the nearshore loading of TC during this study, the peak TCconcentrations at the Talbert Outlet were. below the California standard for single samples of ocean water.

(3) The Talbert Marsh appears to be a significant source of episodic nearshore loading of ENT. The ENT pulse thatleft the watershed on 12/10 had a peak concentration well above the California standard for single samples of

ocean water. Therefore, ENT loading from the Talbert Marsh was a significant source of nearshore pollution

during the study period.

(4) The TW is not the only source of EC and ENT. Other sources may account for the elevated surfzoneconcentration of these bacteria observed during the study period.

(5) The water at the Talbert Outlet is well mixed over the depth. There is no evidence for the existence offreshwater lenses, and bacteria did not appear to be concentrated near the top or bottom of the water column

during the study period.

5.0 References

1. Gannon, J.J. et al. (1983) Wat. Res. 11: 1595

2. Mitchell R., Chamberlin, C. (1978) inIndicators of Viruses in Water and Food(Berg, G., Ed.), pp. 15-37. Ann

Arbor Science, Ann Arbor, MI.

3. APHA/AWWA/WPCF 1995 Standard Methods for the Examination of Water and Wastewater, 19th Edition,

American Public Health Association, Washington D.C.

4. McGee, C.D., Leecaster, M.K., Vainik, P.M., Noble, R.T., Walker, K.O., and Weisberg, S.B. Comparison of

Bacterial Indicator Measurements Among Southern California Marine Monitoring, Southern California CoastalWater Research Project Annual Report, 1997-1998, pp. 187-198.

5. Emery K.O., Aubrey, D.G. (1991) Sea levels, land levels, and tide gauges. Springer-Verlag,

New York, pg. 16.

coastal runoff impact study 11

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