CHOLLAS CREEK BACTERIA TOTAL MAXIMUM DAILY LOAD 2015–2016 COMPLIANCE MONITORING REPORT · 2017-11-09 · CHOLLAS CREEK BACTERIA TOTAL MAXIMUM DAILY LOAD 2015–2016 COMPLIANCE MONITORING

CHOLLAS CREEK

BACTERIA TOTAL MAXIMUM DAILY LOAD

2015–2016 COMPLIANCE MONITORING REPORT

Submitted to the San Diego Regional Water Quality Control Board by:

City of San Diego

City of La Mesa

City of Lemon Grove

County of San Diego

San Diego Unified Port District

California Department of Transportation

Prepared by:

Amec Foster Wheeler Environment & Infrastructure, Inc.

San Diego, California

December 2016

Chollas Creek Bacteria TMDL 2015–2016 Compliance Monitoring Report December 2016

i

TABLE OF CONTENTS

Page

ACRONYMS AND ABBREVIATIONS ......................................................................................... v

EXECUTIVE SUMMARY ...................................................................................................... ES-1

1.0 INTRODUCTION ..........................................................................................................1-1

1.1 Document Overview ...........................................................................................1-2

1.2 Chollas Creek Watershed and Background of Bacteria Total Maximum

Daily Load ..........................................................................................................1-2

1.3 Compliance Timeline for Bacteria Total Maximum Daily Load ............................1-4

1.4 Compliance Requirements for Bacteria Total Maximum Daily Load....................1-6

1.4.1 Compliance Determination ......................................................................1-6

1.4.2 Receiving Water Limitations ....................................................................1-7

2.0 MONITORING AND ANALYTICAL METHODS ............................................................2-1

2.1 Compliance Monitoring Locations .......................................................................2-1

2.2 Wet Weather Compliance Monitoring .................................................................2-4

2.3 Dry Weather Compliance Monitoring ..................................................................2-4

2.4 Analytical Methods .............................................................................................2-4

2.5 Optional Field Measurements and Observations ................................................2-5

2.6 Measurement Quality Objectives ........................................................................2-6

2.7 Wet Weather Single-Sample Maximum Exceedance Frequency ........................2-7

2.8 Wet Season Geometric Mean and Exceedance Frequency ................................2-7

2.9 Dry Season Geometric Mean and Exceedance Frequency ................................2-8

2.10 Precipitation and Flow Data ................................................................................2-9

3.0 HYDROLOGY AND MONITORING SUMMARY ...........................................................3-1

3.1 Wet Weather: Hydrology and Monitoring Summary ............................................3-1

3.1.1 Wet Weather Event 1—November 4, 2015 .............................................3-3

3.1.2 Wet Weather Event 2—December 29, 2015 ...........................................3-5

3.1.3 Wet Weather Event 3—January 9, 2016 .................................................3-7

3.2 Dry Weather: Hydrology and Monitoring Summary .............................................3-9

4.0 MONITORING RESULTS .............................................................................................4-1

4.1 Wet Weather Fecal Indicator Bacteria Concentrations .......................................4-1

4.2 Dry Weather Fecal Indicator Bacteria Concentrations ........................................4-3

5.0 COMPLIANCE EVALUATION ......................................................................................5-1

5.1 Wet Weather Single-Sample Maximum Exceedance Frequencies .....................5-1

5.2 Wet Season Geometric Mean Exceedance Frequencies ....................................5-2

5.3 Dry Season Geometric Mean Exceedance Frequencies .....................................5-4

5.4 Progress Toward Attaining Interim and Final Receiving Water Limitations .........5-9

6.0 SUMMARY ...................................................................................................................6-1

6.1 Characterization of Current Fecal Indicator Bacteria Concentrations ..................6-1

6.2 Evaluation of Progress Toward Meeting Bacteria TMDL Numeric Targets .........6-1

7.0 REFERENCES .............................................................................................................7-1


TABLE OF CONTENTS (CONTINUED)

Page

ii

LIST OF TABLES

Table ES-1. 2015–2016 Bacteria TMDL Exceedance Frequencies in Chollas Creek........... ES-3

Table 1-1. Interim and Final Receiving Water Limitations for Creeks ...................................1-8

Table 2-1. Bacteria TMDL Compliance Monitoring Locations in Chollas Creek ....................2-2

Table 2-2. Fecal Indicator Bacteria Constituents ..................................................................2-5

Table 2-3. Optional In Situ Field Measurement Detection Ranges .......................................2-6

Table 3-1. Wet Weather Monthly Rainfall Summary .............................................................3-1

Table 3-2. Rainfall and Flow Totals for Monitored Events ....................................................3-2

Table 3-3. Dry Season Monthly Rainfall Summary ...............................................................3-9

Table 3-4. Dry Weather Sampling Summary and Antecedent Dry Days ............................. 3-11

Table 4-1. Wet Weather Analytical Results ..........................................................................4-2

Table 5-1. 2015–2016 Wet Weather Single-Sample Maximum Exceedance Frequencies .........................................................................................................5-2

Table 5-2. 2015–2016 Wet Weather Exceedance Frequencies and Compliance Reduction Milestones ...........................................................................................5-2

Table 5-3. 2015–2016 Wet Season Geometric Mean Exceedance Frequencies ..................5-3

Table 5-4. 2015–2016 Wet Season Exceedance Frequencies and Compliance Reduction Milestones ...........................................................................................5-3

Table 5-5. 2016 Dry Season Geometric Mean Exceedance Frequencies ............................5-5

Table 5-6. 2015 Dry Season Exceedance Frequencies and Compliance Milestones ...........5-5

Table 5-7. 2015–2016 General Progress Toward Interim and Final RWLs for Chollas Creek ...................................................................................................................5-9

Table 6-1. 2015–2016 Bacteria TMDL Exceedance Frequencies in Chollas Creek Watershed ...........................................................................................................6-3

LIST OF FIGURES

Figure 1-1. Chollas Creek Watershed ...................................................................................1-5

Figure 1-2. Compliance Monitoring Timeline .........................................................................1-6

Figure 2-1. Bacteria TMDL Compliance Monitoring Locations for Chollas Creek ..................2-3

Figure 3-1. Wet Weather 1 Photographs ...............................................................................3-3

Figure 3-2. Wet Weather 1 Hydrographs, SD8(1) and Z Street .............................................3-4

Figure 3-3. Wet Weather 2 Photographs ...............................................................................3-5



Figure 3-6. Estimated Percentage of Dry Weather Flow Days During the 2015–2016 Wet Season .............................................................................................................. 3-10

Figure 4-1. 2015–2016 Wet Weather Fecal Indicator Bacteria Concentrations .....................4-3

Figure 4-2 2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at CTL(1) ......4-4

Figure 4-3. 2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at SD8(1) ......4-5

Figure 4-4. 2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at Z Street .....4-6

Figure 5-1. 2015–2016 FIB Densities and Geometric Means—CTL(1)..................................5-6

Figure 5-2. 2015–2016 FIB Densities and Geometric Means—SD8(1) .................................5-7

Figure 5-3. 2015–2016 FIB Densities and Geometric Means— Z Street ...............................5-8


TABLE OF CONTENTS (CONTINUED)

Page

iii

LIST OF APPENDICES

Appendix A QUALITY ASSURANCE/QUALITY CONTROL SUMMARY

Appendix B 2015-2016 WET WEATHER FIELD AND ANALYTICAL RESULTS

Appendix C 2015-2016 DRY WEATHER FIELD AND ANALYTICAL RESULTS

Appendix D 2012–2015 HISTORICAL DATA RESULTS

Appendix E WET WEATHER ANALYTICAL LABORATORY REPORTS

Appendix F WET WEATHER FIELD DATA SHEETS

Appendix G BACTERIA TMDL AND MS4 PERMIT DISCREPANCIES


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v

ACRONYMS AND ABBREVIATIONS

> greater than

< less than

# number

% percent

°C degrees Celsius

303(d) List CWA Section 303(d) List of Water Quality Limited Segments

µS/cm microsiemens per centimeter

Amec Foster

Wheeler Amec Foster Wheeler Environment & Infrastructure, Inc.

Bacteria TMDL

A Resolution Amending the Water Quality Control Plan for the San Diego Basin

(9) To Incorporate Revised Total Maximum Daily Loads for Indicator Bacteria

Project I—Twenty Beaches and Creeks in the San Diego Region (Including

Tecolote Creek) (Regional Board, 2010)

Basin Plan Water Quality Control Plan for San Diego Basin (Regional Board, 2011)

Caltrans California Department of Transportation

cf cubic feet

cfs cubic feet per second

CFU colony-forming unit

CTL(1) compliance monitoring location in tidal prism of Chollas Creek

CWA Clean Water Act

DW dry weather

e estimated value

E. coli Escherichia coli

EMTS (City of San Diego) Environmental Monitoring & Technical Services Laboratory

FIB fecal indicator bacteria

L liters

MDL method detection limit

mL milliliters

MLS mass loading station

MPN most probable number

MQO measurement quality objective

MS4 municipal separate storm sewer system

MS4 Permit

National Pollutant Discharge Elimination System (NPDES) Permit and Waste

Discharge Requirements for Discharges from the Municipal Separate Storm

Sewer System (MS4) Draining the Watersheds Within the San Diego Region,

Order Number R9 2013-0001 (Regional Board, 2013)

NOAA National Oceanic and Atmospheric Administration

NPDES National Pollutant Discharge Elimination System

NR not recorded or value lost because of a database software malfunction

NTU Nephelometric turbidity unit

QA quality assurance


ACRONYMS AND ABBREVIATIONS (continued)

vi

QC quality control

REC-1 water contact recreation beneficial use

REC-2 noncontact water recreation beneficial use

Regional Board San Diego Regional Water Quality Control Board

Responsible

Agencies

City of San Diego, City of La Mesa, City of Lemon Grove, County of San Diego,

San Diego Unified Port District, and California Department of Transportation

RL reporting limit

RWL receiving water limitation

SD8(1) compliance monitoring location in north fork of Chollas Creek

SDIA San Diego International Airport

SM Standard Method

TMDL total maximum daily load

USEPA United States Environmental Protection Agency

WLA waste load allocation

WMA watershed management area

WQIP Water Quality Improvement Plan

WQBEL water quality-based effluent limitation

WQO water quality objective

WRCC Western Regional Climate Center

WW wet weather

Z Street compliance monitoring location in south fork of Chollas Creek


ES-1

EXECUTIVE SUMMARY

This report presents the 2015–2016 compliance monitoring data required by the Bacteria Total

Maximum Daily Load (Bacteria TMDL) for Chollas Creek, under Resolution No. R9-2010-0001 of

the San Diego Regional Water Quality Control Board (Regional Board) in 20101, as incorporated

into the Regional Board’s Order Number R9-2013-00012 (Municipal Separate Storm Sewer

System [MS4] Permit) in 2013. This report was developed to meet the assessment requirements

of the MS4 Permit.

The Bacteria TMDL monitoring program assesses the conditions of the receiving waters and has

the following objectives:

• Characterize levels of bacteria concentrations at compliance monitoring locations.

• Track progress toward meeting the Bacteria TMDL numeric targets.

Fecal indicator bacteria (FIB) sampling for the compliance monitoring season (October 2015–

September 2016) was conducted at three creek monitoring locations:

• CTL(1) (Chollas Creek tidal location)—the Chollas Creek tidal prism consists of primarily

brackish water and is located downstream of the confluence of the north and south forks.

• SD8(1) (north Chollas Creek location) and Z Street (south Chollas Creek location)—the

two mass loading stations (MLSs) in the north and south forks of Chollas Creek,

respectively, consist of freshwater when flowing.

Z Street was approved by the Regional Board prior to the start of the 2015–2016 wet season as a permanent replacement site for the former monitoring location (DPR3) because of channel restoration efforts at the DPR3 monitoring location. This report summarizes FIB concentrations and key hydrologic data by compliance monitoring

location and season for the 2015–2016 monitoring season (October 1, 2015 – September 30,

2016). Compliance is assessed by comparing analytical results for Enterococcus and fecal

coliform with applicable receiving water limitations (RWLs), in accordance with the Bacteria TMDL

requirements in Attachment E of the MS4 Permit. The RWLs are a combination of numeric targets

for bacteria density and allowable exceedance frequencies. The single-sample maximum numeric

targets are required to be achieved only during wet weather with a 22 percent final allowable

exceedance frequency. For dry weather days, the 30-day geometric mean numeric targets must

be achieved with a 0 percent exceedance frequency. The compliance schedule includes interim

milestones that must be achieved to demonstrate progress prior to attaining full compliance with

wet and dry weather total maximum daily loads (TMDLs).

1 A Resolution Amending the Water Quality Control Plan for the San Diego Basin (9) To Incorporate Revised Total

Maximum Daily Loads for Indicator Bacteria Project I—Twenty Beaches and Creeks in the San Diego Region (Including Tecolote Creek), February 10, 2010

2 National Pollutant Discharge Elimination System (NPDES) Permit and Waste Discharge Requirements for Discharges from the Municipal Separate Storm Sewer System (MS4) Draining the Watersheds Within the San Diego Region, May 14, 2013


ES-2

Wet weather samples were collected within the first 24 hours of the end of rainfall for three wet

weather events. Samples were analyzed for the FIB compliance constituents: fecal coliform and

Enterococcus, as well as for two additional constituents not required for compliance: total coliform

and Escherichia coli (E. coli). Dry weather samples were collected at least weekly between April 1

and October 31, and at least monthly on dry weather days from November 1through March 31.

Weekly monitoring was scheduled so that at least five samples were collected in each calendar

month.

Monitoring Results and Compliance Discussion

In accordance with the monitoring and assessment requirements in the MS4 Permit, three

separate weather-based evaluations were conducted to address the program objectives.

Table ES-1 summarizes the results and compares them with the allowable exceedance

frequencies.

Wet Weather Single-Sample Maximum Exceedance Frequencies

As described in the MS4 Permit, the wet weather exceedance frequency applies only to wet

weather days (days with 0.2 inch of rainfall or more plus the following 72 hours) between

October 1 and April 30 of each monitoring year. Wet weather exceedance frequencies for

Enterococcus and fecal coliform are derived by calculating the average result of wet weather

samples and applying that average to the remaining (not sampled) observed wet weather days.

Sampling results and the assigned averages are compared with single-sample maximum

exceedance frequencies, as established in the Bacteria TMDL and further clarified in the MS4

Permit (Regional Board, 2013).

The 2015–2016 wet season sampling included three monitored storm events. The averages of

the results of the three events were applied to the results for the remaining observed wet weather

days (days with greater than 0.2 inch of rainfall plus the following 72 hours) that were not sampled.

Wet weather results for the three compliance monitoring locations are as follows:

• Concentrations of Enterococcus and fecal coliform exceeded single-sample maximums

during all three wet weather events at two of three sites (CTL(1) and SD8(1)).

• For CTL(1) and SD8(1), the wet weather exceedance frequency was 100 percent for both

Enterococcus and fecal coliform.

Single-sample maximums for Enterococcus were exceeded at Z Street during all three

wet weather events; single-sample exceedances for fecal coliform occurred during two of

the three events.

• For Z Street, the wet weather exceedance frequency was 100 percent for Enterococcus

and 91 percent for fecal coliform.


ES-3

Table ES-1. 2015–2016 Bacteria TMDL Exceedance Frequencies in Chollas Creek

Location

ID

Bacteria

TMDL

Constituent

Wet Weather a Wet Season a,c Dry Season b

Single-Sample

Maximum

(CFU/100mL)

5-Sample

Geometric Mean

(CFU/100mL)

30-Day

Geometric Mean

(CFU/100mL)

2015–

2016 d

Exceedance Frequency

Numeric

Target

(MPN) f

Interim

Allowable

Frequency

Final

Allowable

Frequency

2015–

2016 e


Numeric

Target

(MPN) f

Interim

Allowable

Frequency

Final

Allowable

Frequency

2015–

2016 e


Numeric

Target

(MPN) f

Interim

Allowable

Frequency

Final

Allowable

Frequency

CTL(1) Enterococcus 100% 61 43% 22% 86% 33 50% 0% 24% 33 50% 0%

Fecal Coliform 100% 400 41% 22% 21% 200 50% 0% 0% 200 50% 0%

SD8(1) Enterococcus 100% 61 43% 22% 7% 33 50% 0% 10% 33 50% 0%

Fecal Coliform 100% 400 41% 22% 0% 200 50% 0% 0% 200 50% 0%

Z Street Enterococcus 100% 61 43% 22% 29% 33 50% 0% 0% 33 50% 0%

Fecal Coliform 91% 400 41% 22% 0% 200 50% 0% 0% 200 50% 0%

Notes: Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location

% = percent; CFU = colony-forming unit; mL = milliliters; MPN = most probable number

Bolded values = exceedance frequency is greater than the interim and final allowable limit established in the Bacteria Total Maximum Daily Load (TMDL). a. October 1, 2015–April 30, 2016 b. May 1, 2016–September 30, 2016 c. In accordance with the MS4 Permit, wet and dry weather FIB data were combined to calculate geometric means for the wet season and compared to the dry weather exceedance

frequencies as shown in Table ES-1. d. The exceedance frequency was derived by dividing the total number of wet weather days (days with 0.2 inch of rainfall or greater plus the following 72 hours) that exceeded the single-

sample maximum numeric target divided by the total number of wet weather days during the wet season. To determine exceedances for non-sampled wet weather days, the arithmetic mean of the analytical results from three monitored storm events was applied to the remaining observed wet weather days that were not sampled. The results from the total number of wet weather days, with either assigned averages or analyzed result values, were then compared with single-sample maximum numeric targets.

e. The exceedance frequency was derived by dividing the total number of geometric exceedances by the total number of geometric means calculated during the season. f. Numeric target are based on the freshwater water quality objectives (WQOs) in the Water Quality Control Plan for the San Diego Basin (Regional Board, 2011).


ES-4

Wet Season Geometric Means and Exceedance Frequencies

The wet season evaluation combines all dry and wet weather samples collected between

October 1, 2015, and April 30, 2016. Exceedance frequencies for Enterococcus and fecal coliform

are derived by calculating a rolling geometric mean using the most recent five sampling results.

The total number of geometric exceedances is divided by the total number of wet season

geometric means to derive an overall wet season exceedance frequency. Calculations for the

2015–2016 wet season included 14 geometric means.

Wet season results for the three compliance monitoring locations are as follows:

Chollas Creek Tidal Location (CTL(1)):

• CTL(1) is not hydrologically connected to the upper watershed during most dry weather

days. However, CTL(1) is tidally influenced, which allows for successful sampling year

round.

• CTL(1) location was successfully sampled during the 15 dry weather visits and the 3 wet

weather events during the wet season.

• The combined wet season exceedance frequencies for Enterococcus and fecal coliform

are 86 percent and 21 percent, respectively.

• CTL(1) is not currently achieving interim or final allowable exceedance frequencies for

Enterococcus.

• CTL(1) is achieving the interim allowable exceedance frequencies for fecal coliform, but

not the final allowable exceedance frequencies at this time.

North Chollas Creek Location (SD8(1)):

• During the wet season, three wet weather events were sampled at SD8(1).

• There was no measurable flow during the 14 scheduled dry weather events that occurred

during the 2015–2016 wet season (October 1 through April 30).

• The combined wet season exceedance frequencies for Enterococcus and fecal coliform

are 7 percent and 0 percent, respectively.

• SD8(1) is currently achieving interim allowable exceedance frequencies but not final

allowable exceedance frequencies for Enterococcus.

• SD8(1) is currently achieving both interim and final allowable exceedance frequencies for

fecal coliform.

South Chollas Creek Location (Z Street):

• During the wet season, three wet weather events were sampled at Z Street.

• Measurable flow was not observed during 11 of 14 scheduled dry weather events that

occurred during the wet season.

• Exceedance frequencies for compliance constituents Enterococcus and fecal coliform are

29 percent and 0 percent, respectively.


ES-5

• Z Street is currently achieving interim allowable exceedance frequencies but not final

allowable exceedance frequencies for Enterococcus.

• Z Street is currently achieving both interim and final allowable exceedance frequencies for

fecal coliform.

Dry Season Geometric Means and Exceedance Frequencies

The dry season is May 1 through September 30 of each monitoring year. Dry season exceedance

frequencies for Enterococcus and fecal coliform are calculated using a rolling geometric mean of

no fewer than five sampling results per 30-day period, as described in the Water Quality Control

Plan for the San Diego Basin (Basin Plan) (Regional Board, 2011). The dry season exceedance

frequency is calculated by dividing the total number of 30-day geometric means that exceed the

30-day geometric mean RWLs by the total number of geometric means calculated during the dry

season (Regional Board, 2013). When a compliance location had little or no flow, a value of 0.1

colony-forming units (CFU) was assigned as the concentration so that the dry conditions

associated with that sampling day were included in the overall compliance evaluation.

Dry season FIB exceedance results for the three compliance monitoring locations are as follows:

Chollas Creek Tidal Location (CTL(1)):

• The north and south fork compliance locations upstream of CTL(1) are typically dry on dry

weather days. However, CTL(1) is located in a tidally influenced segment of Chollas

Creek, which allows for successful sampling year round.

• The TMDL numeric target for Enterococcus was exceeded at CTL(1) on 5 of 21 calculated

geometric means during the 2016 dry season. However, the 5 exceedances were driven

by one elevated sample result.

• The maximum geometric mean value was 34.6 CFU/100mL, which slightly exceeds the

Bacteria TMDL numeric target of 33 CFU/100mL for Enterococcus in Creeks.

• The dry season exceedance frequencies for Enterococcus and fecal coliform were

24 percent and 0 percent, respectively.

• CTL(1) is not currently achieving interim or final allowable exceedance frequencies for

Enterococcus.

• CTL(1) is achieving both interim and final allowable exceedance frequencies for fecal

coliform.

North Chollas Creek Location (SD8(1)):

• Dry weather flows at this location were observed during five scheduled dry weather events.

• The exceedance frequency for Enterococcus was 10 percent.

• The exceedance frequency for fecal coliform was 0 percent.

• SD8(1) is achieving interim goals for Enterococcus and both interim and final goals for

fecal coliform during the dry season.


ES-6

South Chollas Creek Location (Z Street):

• Dry weather flows were not observed at this location during all 25 scheduled dry weather events.

• Exceedance frequencies for compliance constituents Enterococcus and fecal coliform

were both 0 percent.

• Z Street is achieving both the interim and final allowable exceedance frequencies for

Enterococcus and fecal coliform during the dry season.

Summary

During wet weather, the entire watershed is hydraulically connected and recreational water quality

standards are exceeded at all compliance monitoring locations. However, wet weather flows are

too high and dangerous for recreational activities to be safely performed. All locations have

elevated levels of FIB and are not currently meeting the wet weather RWLs.

During dry weather, the upper watershed is not typically hydraulically connected to the lower

segment of the creek. Few exceedances, if any, occur at the upstream MLS locations during the

dry season, because most days are observed to be dry at these locations. The lower portion of

the creek, below where the north and south forks converge, is tidally influenced and water levels

are sufficient to support recreational activities year round. The electrical conductivity

measurements taken at CTL(1), range from 43.3 to 60.3 milliSiemens per centimeter (mS/cm),

indicating that flows are brackish to pure saltwater during dry weather During most dry weather

days, the north and south fork compliance locations are dry with no flows reaching the CTL(1)

monitoring location. Despite brackish concentrations in the lower portion, Chollas Creek is listed

as a freshwater creek and thus results are compared with freshwater TMDL numeric targets.

Compliance monitoring data also indicate a greater likelihood for Enterococcus exceedances than

fecal coliform exceedances. This observation is typical in natural and urban environments shown

by data collected for other bacteria studies, as Enterococcus has been shown to persist and even

grow in the environment without a proximate or recent source of contamination (Byappanahalli et

al., 2012). Based on current monitoring, sources of dry weather exceedances at the Chollas Creek

tidal location (CTL(1)) are not known; potential sources may be land-use areas directly draining

to this segment of Chollas Creek or natural sources (regrowth) and wildlife, or the exceedances

may result from the hydrology and residence time of brackish water. It is evident that the upstream

portions of Chollas Creek are not typically contributing to exceedances at the Chollas Creek tidal

location during dry weather because the portions of the watershed are not hydraulically

connected.

The north and south Chollas Creek locations showed little to no flow during dry weather

conditions. During these extended dry periods, if water was present, it was for a short duration

and water levels were typically below 2 inches in depth and therefore too low to support water

contact recreation beneficial use (REC-1) or noncontact water recreation (REC-2) activities.

Overall, Chollas Creek is meeting the interim dry weather RWLs and making progress toward

meeting the final dry weather allowable exceedance frequencies. Most of the exceedances at the

compliance monitoring locations occur during the wet season because of residual storm flows.


Page 1-1

1.0 INTRODUCTION

The Chollas Creek Watershed supports various beneficial uses, including noncontact water

recreation (REC-2), warm freshwater habitat, and wildlife habitat; water contact recreation

(REC-1) is listed as a potential beneficial use. In 2002, and again in 2010, the Clean Water Act

(CWA) Section 303(d) List of Water Quality Limited Segments (303(d) List) indicated that the

greatest cause of water body impairments in the San Diego region was elevated bacteria levels,

which impact recreational activities and cause potential for human health risks. Elevated bacteria

densities of Enterococcus and fecal coliform affect the beneficial uses of Chollas Creek and the

potential for water contact recreation.

The goal of the Bacteria Total Maximum Daily Load (Bacteria TMDL) (Regional Board, 2010) is

to restore recreational beneficial uses of Chollas Creek. The Bacteria TMDL compliance

monitoring program employs phased monitoring over the course of the compliance schedule to

evaluate receiving water conditions, identify potential sources, and develop compliance

strategies. The initial phase of the monitoring program focuses on characterizing bacteria

concentrations in the receiving water. After key compliance milestones, if exceedances persist in

the receiving water, the second phase will implement follow-up monitoring to determine whether

municipal separate storm sewer system (MS4) sources are causing the exceedances and then

implement strategies to control MS4 sources. Special studies will be implemented on the basis of

the available data and resources to address management questions regarding the Bacteria

TMDL.

This report presents the 2015–2016 Chollas Creek Bacteria TMDL compliance monitoring data,

in accordance with Attachment E.6 of Order Number R9 2013-0001, National Pollutant Discharge

Elimination System (NPDES) Permit and Waste Discharge Requirements for Discharges from the

Municipal Separate Storm Sewer System (MS4) Draining the Watersheds Within the San Diego

Region (MS4 Permit). Attachment E.6 presents the requirements for Resolution No. R9-2010-

0001, A Resolution Amending the Water Quality Control Plan for the San Diego Basin (9) to

Incorporate Revised Total Maximum Daily Loads for Indicator Bacteria Project I—Twenty

Beaches and Creeks in the San Diego Region (Including Tecolote Creek) (Bacteria TMDL) (San

Diego Regional Water Quality Control Board [Regional Board], 2013). Monitoring was performed

to meet the requirements of the MS4 Permit and to generate data to support the San Diego Bay

Water Quality Improvement Plan (WQIP) (San Diego Bay Municipal Agencies, 2016).

The Bacteria TMDL monitoring program assesses the conditions of the receiving waters and has

the following goals:

• Characterize levels of bacteria concentrations at compliance monitoring locations.

• Track progress toward meeting the Bacteria TMDL numeric targets.


Page 1-2

Sampling activities focused on the receiving water. Indicator bacteria sampling for the 2015–2016

compliance monitoring season was conducted at three compliance monitoring locations in the

lower portion of Chollas Creek during wet and dry weather, in accordance with the requirements

of Attachment E.6 of the MS4 Permit.

1.1 Document Overview

This report summarizes the 2015–2016 compliance monitoring conducted to meet the

requirements of the Bacteria TMDL in the MS4 Permit. The data generated will support the

Chollas Creek watershed source control planning and strategies to achieve compliance with the

Bacteria TMDL. This compliance monitoring report has six sections:

• Section 1—Introduction: Information on the Chollas Creek Watershed, beneficial uses,

the Bacteria TMDL, receiving water numeric targets and compliance schedule, and

program objectives;

• Section 2—Monitoring and Analytical Methodology: Overview of the compliance

monitoring locations, wet and dry weather sampling methodology, analytical methodology,

measurement quality objectives (MQOs), and MS4 Permit requirements;

• Section 3—Hydrology and Monitoring Summary: Hydrology summaries, event data,

and observations; and wet and dry weather monitoring results;

• Section 4—Monitoring Results: Fecal indicator bacteria (FIB) results from 2015–2016

and evaluation of seasonal patterns in FIB concentrations;

• Section 5—Compliance Evaluation: Evaluation of current receiving water conditions per

the MS4 Permit and comparison with the Bacteria TMDL receiving water limitations

(RWLs), based on 2015–2016 data;

• Section 6—Conclusions and Recommendations: Summary of current receiving water

conditions in Chollas Creek related to the program goals and recommendations for future

monitoring.

1.2 Chollas Creek Watershed and Background of Bacteria Total Maximum Daily Load

The Chollas Creek Watershed encompasses approximately 18,000 acres of mainly urbanized

land in the San Diego Mesa Hydrologic Area and is within the larger Pueblo San Diego Hydrologic

Unit. Located southeast of the downtown area of the City of San Diego, Chollas Creek has two

main tributaries, the north fork and the south fork. The drainage area of the north fork

(8,794 acres) is larger than that of the south fork (7,575 acres). The headwaters of the north fork

originate approximately 1.5 miles west of the jurisdictional boundary of the City of La Mesa. The

south fork flows to the west-southwest from its headwaters in the City of Lemon Grove, and is the

product of two smaller creek branches. The north and south forks merge approximately 0.8 mile

east of the mouth of Chollas Creek at San Diego Bay, in a tidally influenced section of the creek.


Page 1-3

The established beneficial use of Chollas Creek’s surface waters is REC-2, and REC-1 is listed

as a potential use. In 2002, contact recreation in the lower 1.2 miles of Chollas Creek was deemed

impaired by FIB and the water segment was placed on the 303(d) List. REC-1 and REC-2 are

defined in the Water Quality Control Plan for San Diego Basin (Basin Plan) as follows (Regional

Board, 2011):

• Water Contact Recreation (REC-1) uses of water are for recreational activities involving

body contact with water, where ingestion of water is reasonably possible. These uses

include, but are not limited to, swimming, wading, and fishing.

• Noncontact Water Recreation (REC-2) uses of water are for recreational activities near

water, but not normally involving body contact with water, where ingestion of water is

reasonably possible. These uses include, but are not limited to, picnicking, sunbathing,

hiking, sightseeing, and aesthetic enjoyment.

The Bacteria TMDL was developed by the Regional Board for impaired beaches and creeks on

the 2002 303(d) List to attain and maintain FIB water quality standards. Separate wet weather

and dry weather total maximum daily loads (TMDLs) were calculated for each FIB (total coliform,

fecal coliform, and Enterococcus). The Regional Board acknowledges that exceedances of the

REC-1 water quality objectives (WQOs) may be partially due to natural sources and so included

in the wet weather TMDLs an allowable exceedance frequency based on a reference system

approach. This approach accounts for bacterial loads contributed from natural sources and is

based on conditions at Leo Carrillo Beach in Los Angeles County, California. Each MS4

discharger has been assigned a waste load allocation (WLA) and will be responsible for reducing

its bacterial load and demonstrating that discharges are not causing exceedances of the numeric

WQOs and of allowable exceedance frequencies in the receiving water.

According to the Bacteria TMDL, MS4 discharges are “anthropogenic in nature and the most

significant controllable source of bacteria” (Regional Board, 2010). Each MS4 was assigned an

individual WLA for bacteria. The TMDL used a conservative approach by selecting the most

stringent numeric targets. For Chollas Creek, the TMDL numeric targets are based on REC-1

WQOs from the Basin Plan. According to the TMDL, “water quality objectives for REC-2 are less

stringent than the water quality objectives for REC-1; therefore, attainment of REC-1 objectives

through the implementation of the TMDLs will, a fortiori, provide the requisite water quality for

REC-2” (Regional Board, 2011).

The approved Bacteria TMDL identifies the Lead Agency and the Responsible Agencies

(excluding owners and operators of small MS4s) for the Chollas Creek Watershed, as follows:

• City of San Diego (Lead Agency)

• City of La Mesa

• City of Lemon Grove

• San Diego County

• San Diego Unified Port District

• California Department of Transportation (Caltrans)


Page 1-4

On May 24, 2013, the Regional Board incorporated the Bacteria TMDL into the MS4 Permit

(Regional Board, 2013). The MS4 Permit clarifies the final RWLs (as most probable numbers

[MPNs]) for Enterococcus and fecal coliform. (Total coliform has been removed from the RWLs

for creeks as a clarification to the TMDLs.)

The Responsible Agencies are collaborating to implement monitoring programs and management

strategies for the Chollas Creek Watershed. Figure 1-1 depicts the watershed boundaries, land

use within the watershed, and the jurisdictional boundaries of the Responsible Agencies.

1.3 Compliance Timeline for Bacteria Total Maximum Daily Load

The Bacteria TMDL compliance monitoring timeline outlines interim reduction milestones over the

20-year compliance period (2011–2031). The Bacteria TMDL compliance timeline began in

April 2011, after approval of the Bacteria TMDL by the State Water Resources Control Board

Office of Administrative Law. Compliance monitoring began in July 2013, after adoption of the

MS4 Permit. After the Dry Weather Exceedance Reduction Milestone in 2018, follow-up

monitoring will be implemented on the basis of annual exceedances of allowable exceedance

frequencies in Chollas Creek to investigate potential sources. The San Diego Bay WQIP

incorporates all of the requirements of the Chollas Creek Bacteria TMDL and provides a

comprehensive, watershed-based approach to management strategies designed to address

priority receiving water conditions, including approved TMDLs, draft TMDLs, and other

constituents of concern in the San Diego Bay WMA (San Diego Bay Municipal Agencies, 2016).

The ultimate goal of the San Diego Bay Water Quality Improvement Plan (WQIP) is to prevent

MS4 discharges from causing or contributing to beneficial use impairments in the San Diego Bay

Watershed Management Area (WMA). Currently, the Responsible Agencies are participating in

the San Diego Regional Reference Stream Study to determine the exceedance frequency of

bacteria in reference streams that is caused by natural sources. The study may be used to update

the scientific basis of numeric targets for the Bacteria TMDL reopener in 2018.


Page 1-5

Figure 1-1.

Chollas Creek Watershed


Page 1-6

The Responsible Agencies are participating in data assessments and coordination meetings with

the Regional Board and other Copermittees to determine the potential modifications to be

considered in the Bacteria TMDL Reopener. During the Bacteria TMDL Reopener, the Regional

Board will update the TMDL based on current data and United States Environmental Protection

Agency (USEPA) policy, which may lead to revised terms of compliance. The Bacteria TMDL

Reopener is in progress and is expected to be completed in 2018. Figure 1-2 provides the overall

timeline of the compliance monitoring program.

2010 2015 2020 2025 2030 2035

Notes: WQIP = Water Quality Improvement Plan; MS4 = municipal separate storm sewer system;

TMDL = total maximum daily load

Figure 1-2.

Compliance Monitoring Timeline

1.4 Compliance Requirements for Bacteria Total Maximum Daily Load

The MS4 Permit defines interim and final water quality-based effluent limitations (WQBELs) as

the basis of compliance (in Attachment E.6 of the MS4 Permit) and describes various ways to

achieve compliance. The WQBELs include RWLs for the 303(d)-listed creek segment and effluent

limitations for MS4 outfalls or discharges. The Bacteria TMDL compliance monitoring focuses on

the receiving water compliance monitoring locations, so this report addresses progress toward

achieving the RWLs, as presented in this section.

1.4.1 Compliance Determination

Compliance of the Responsible Copermittees with the final WQBELs may be demonstrated via

any one of the following conditions (Regional Board, 2013):

(a) There is no direct or indirect discharge from the Responsible Copermittees’ MS4 outfalls

to the receiving water; OR

(b) There are no exceedances of the final receiving water limitations under Specific

Provision 6.b.(2)(a) in the receiving water at, or downstream of, the Responsible

Copermittees’ MS4 outfalls; OR

Wet Weather

100%

Reduction:

April 2031

CLRP

Submitted:

October 2012

WQIP

Submitted:

June 2015

Dry Weather 50%

Reduction:

April 2018

Bacteria TMDL

Accepted:

April 2011

Dry Weather 100% Reduction &

Wet Weather 50% Reduction:

April 2021

2011–2031 COMPLIANCE MONITORING

MS4 Permit

Adopted:

May 2013

WQIP

Approved:

February 2016


Page 1-7

(c) There are no exceedances of the final effluent limitations under Specific

Provision 6.b.(2)(b)(i) at the Responsible Copermittees’ MS4 outfalls; OR

(d) The pollutant load reductions for discharges from the Responsible Copermittees’ MS4

outfalls are greater than or equal to the final effluent limitations under Specific Provision

6.b.(2)(b)(ii); OR

(e) The Responsible Copermittees demonstrate that exceedances of the final receiving

water limitations under Specific Provision 6.b.(2)(a) in the receiving water are due to

loads from natural sources AND pollutant loads from the Copermittees’ MS4 outfalls are

not causing or contributing to the exceedances; OR

(f) There are no exceedances of the interim receiving water limitations under Specific

Provision 6.c.(2)(a) in the receiving water at, or downstream of, the Responsible

Copermittees’ MS4 outfalls; OR

(g) The pollutant load reductions for discharges from the Responsible Copermittees’ MS4

outfalls are greater than or equal to the interim effluent limitations under Specific

Provision 6.c.(2)(b); OR

(h) The Responsible Copermittees have submitted and are fully implementing a WQIP that

is accepted by the Regional Board and provides reasonable assurance that the interim

TMDL compliance requirements will be achieved by the interim compliance dates.

1.4.2 Receiving Water Limitations

The RWLs are a combination of numeric targets for bacteria density and allowable exceedance

frequencies. The MS4 Permit clarifies the final RWLs for Enterococcus and fecal coliform, and

removes total coliform as a numeric target for creeks. Numeric targets for creeks are based on

freshwater WQOs in the Water Quality Control Plan for the San Diego Basin (Basin Plan)

(Regional Board, 2011).

Wet Weather

Per the MS4 Permit, interim compliance with the Bacteria TMDL requires a 50 percent reduction

in wet weather exceedance frequencies by 2021, resulting in a 43 percent allowable frequency

as the interim target for Enterococcus and a 41 percent allowable frequency for fecal coliform.

Full compliance with the TMDL requires a 22 percent maximum exceedance frequency for wet

weather by 2031. Interim and final wet weather exceedance frequency targets for both

constituents for Chollas Creek are presented in Table 1-1.

Dry Weather

The interim Bacteria TMDL allowable exceedance frequencies for Chollas Creek as provided in

the MS4 Permit require a 50 percent reduction in dry weather exceedances from the “existing”

dry weather exceedance frequencies by 2018. Based on data available between 1996 and 2002,

the City of San Diego estimated the historical exceedance frequency of the 30-day geometric

mean to be 100 percent in Chollas Creek, resulting in a 50 percent allowable exceedance

frequency as the interim target. Full compliance with the TMDL requires a 0 percent exceedance

frequency for dry weather by 2021. Interim and final dry weather exceedance frequencies for both

constituents for Chollas Creek are presented in Table 1-1.


Page 1-8

Table 1-1. Interim and Final Receiving Water Limitations for Creeks

(Maximum Bacteria Densities and Allowable Exceedance Frequencies)

Constituent

Wet Weather Days a Single-Sample Maximum

Dry Weather Days b 30-Day Geometric Mean

MPN/100mLc

Allowable

Exceedance

Frequency d MPN/100mLe

Allowable

Exceedance

Frequency

Interim Final Interim Final

Enterococcus 61 43% 22% 33 50% 0%

Fecal Coliform 400 41% 22% 200 50% 0%

Notes: Source (including footnotes): San Diego Regional Water Quality Control Board (Regional Board), 2010 and 2013.

% = percent; mL = milliliters; MPN = most probable number

a. A wet weather day is defined as a day with rainfall events of 0.2 inches or greater, plus the following 72 hours.

b. A dry weather day is defined as a day with less than 0.2 inch of rainfall observed on each of the previous 3 days.

c. Wet weather numeric target are based on the single-sample maximum (or equivalent) water quality objectives (WQOs) in the Water Quality Control Plan for the San Diego Basin (Regional Board, 2011). Compliance with the wet weather total maximum daily loads (TMDLs) in the receiving water is based on the frequency of the wet weather days in any given year exceeding the wet weather numeric target, but the 30-day geometric mean must also be met.

d. The wet weather allowable exceedance frequency is set at 22 percent. In the calculation of the wet weather TMDLs, the Regional Board chose to apply the 22 percent allowable exceedance frequency as determined for Leo Carrillo Beach in Los Angeles County. At the time the wet weather watershed model was developed, this 22 percent exceedance frequency was the only reference beach exceedance frequency that was available. The 22 percent allowable exceedance frequency used to calculate the wet weather TMDLs is justified because the San Diego Region watersheds’ exceedance frequencies will likely be close to the value calculated for Leo Carrillo Beach, and are consistent with the exceedance frequency that was applied by the Los Angeles Regional Board.

e. Dry weather numeric target are based on the 30-day geometric mean (or equivalent) WQOs in the Water Quality Control Plan for the San Diego Basin (Regional Board, 2011).


2-1

2.0 MONITORING AND ANALYTICAL METHODS

This section outlines the methods that were used in the monitoring program, laboratory analysis,

data assessment, and quality assurance and quality control (QA/QC) processes to meet the

program objectives. The Chollas Creek Diazinon, Dissolved Metals, and Bacteria TMDL

Monitoring Plan (Monitoring Plan) describes in detail the sampling, analytical, and QA/QC

procedures (Amec Foster Wheeler Environment & Infrastructure, Inc. [Amec Foster Wheeler],

2016a).

2.1 Compliance Monitoring Locations

Chollas Creek has two main stem tributaries that converge and discharge into San Diego Bay.

The Bacteria TMDL identifies the lower 1.2 miles of Chollas Creek as the targeted segment in the

TMDL. The MS4 Permit requires receiving water compliance monitoring to be at or near the mouth

of the creek and one or more locations upstream of the mouth. To adequately evaluate mass

loading from the watershed, the Responsible Agencies selected three monitoring locations.

• The first location, CTL(1), is near the mouth of the Creek, approximately 100 yards south

of the confluence of the north and south forks of Chollas Creek. CTL(1) (the Chollas Creek

tidal location), is centrally located in the Bacteria TMDL-listed segment and also reflects

the loading of the entire watershed. This tidal location is as far downstream as can be

accessed for monitoring within the City of San Diego’s jurisdiction. (The area below CTL(1)

cannot be monitored because it is accessible only via federal property, which is on both

sides of the Chollas Creek mouth and along the bay shoreline.)

• The two mass loading stations (MLSs) in the Chollas Creek Watershed, SD8(1) (north

Chollas Creek location) and Z Street (south Chollas Creek location), are located near the

upper boundary of the 303(d)-listed segment. The two stations depict the watershed

contribution from the two main stems. Z Street was approved by the Regional Board prior

to the start of the 2015–2016 wet season as a permanent replacement site for the former

monitoring location (DPR3) because of channel restoration at this monitoring location.

SD8(1) and Z Street are upstream of the tidally influenced section of Chollas Creek. Although the

exact extent of the tidal reach is not known, visual observations suggest the tidally influenced

portion of Chollas Creek extends roughly the same distance as the 303(d) listed segment.

Table 2-1 provides the site location, a description, and a photograph of each compliance

monitoring location.

Figure 2-1 is a map showing the compliance monitoring locations within the 303(d) listed segment

of the Watershed.


2-2

Table 2-1. Bacteria TMDL Compliance Monitoring Locations in Chollas Creek

Location Location ID Latitude Longitude Description Photograph

Chollas

Creek

Tidal

Location

CTL(1) 32.691270° -117.123510°

CTL(1) (Chollas Creek tidal

location) is within a segment of

natural channel of Chollas Creek

in the tidal prism, approximately

100 yards downstream of the

confluence of the north and south

forks, where the Main Street

bridge crosses the creek.

CTL(1) is in a tidally influenced

section of the creek.

North

Chollas

Creek

Location

SD8(1) 32.704932° -117.121121°

MLS SD8(1) (north Chollas Creek

location) is in a concrete trapezoidal

section of north Chollas Creek.

It is east of the intersection of 33rd

Street and Durant Street.

South

Chollas

Creek

Location

Z Street 32.692972° -117.109199°

MLS Z Street (south Chollas Creek

location) is in a vegetated

trapezoidal section of south Chollas

Creek.

It is located west on Z Street past the

cul-de-sac, off of the S 40th street

and Z Street intersection.


2-3

Figure 2-1.

Bacteria TMDL Compliance Monitoring Locations for Chollas Creek


2-4

2.2 Wet Weather Compliance Monitoring

Wet weather monitoring was conducted by Amec Foster Wheeler field teams during three storm

events during the 2015–2016 wet season (October 1 through April 30). The storms with greater

than 0.2 inch of rainfall were targeted for analysis. One grab water sample was collected per

storm within 24 hours after the end of rainfall. Bacteria grab samples were analyzed by the City

of San Diego Environmental Monitoring and Technical Services (EMTS) laboratory or Weck

Laboratories, Inc. Flow and rainfall data were collected for SD8(1) and Z Street as part of the

Diazinon and Dissolved Metals TMDLs (Regional Board, 2002 and 2007), and were used to

develop event hydrographs for the Chollas Creek Bacteria TMDL monitoring program. Collection

of rainfall and flow data is described in Section 2.10.

2.3 Dry Weather Compliance Monitoring

Dry weather monitoring was performed at the compliance monitoring locations from October 2015

through April 2016. Weekly dry weather monitoring was conducted during October 2015, and April

through September 2016, so that at least five samples were collected in each calendar month.

Although the MS4 Permit defines the dry season as between May 1 and September 30, the weekly

sampling was conducted during October and April to capture conditions during the time period

with greater potential for recreational activities. From November 2015 through March 2016, dry

weather monitoring occurred monthly, consistent with the requirements of the MS4 Permit.

Dry weather events may occur on dry weather days with an antecedent dry period of 72 hours

with less than 0.1 inch of rainfall. Grab water samples were collected only when measurable flow

was present. All dry weather samples were collected by City of San Diego Storm Water

Department staff. Bacteria samples were analyzed by the City of San Diego EMTS laboratory.

2.4 Analytical Methods

FIB are surrogates used to measure the potential presence of bacteria, fecal material, and

associated fecal pathogens. FIB such as Enterococcus and fecal coliform are part of the intestinal

flora of warm-blooded animals. Measurements of fecal indicator organisms have long been used

to protect swimmers from illnesses that may be contracted from recreational activities in surface

waters contaminated by fecal pollution. These organisms have been used as good indicators of

harmful pathogens that may be present in water bodies (Regional Board, 2011). As a clarification

to the TMDLs, the MS4 Permit clarified the final RWLs, which require the Bacteria TMDL

compliance samples to be analyzed for Enterococcus and fecal coliform; total coliform has been

removed from the RWLs for creeks. The analytical methods used generated comparable results.

The USEPA recommends using WQOs based on Escherichia coli (E. coli) for freshwaters

because E. coli is a better indicator of pathogens and so better protects human health (United

States Environmental Protection Agency [USEPA], 2012). Neither E. coli nor total coliform water

quality monitoring is required for Chollas Creek compliance monitoring locations. However, the

City of San Diego voluntarily elected to continue analyzing total coliform to maintain consistency

with the Bacteria TMDL and, per USEPA recommendations, added E. coli to begin developing a

dataset in anticipation of future requirements. The monitoring results for E. coli and total coliform

are provided as additional data in Appendices B, C, and D. Table 2-2 lists analytical constituents,

methods, method detection limits (MDLs), and target reporting limits (RLs).


2-5

Table 2-2. Fecal Indicator Bacteria Constituents

Constituent Method

Method

Detection

Limit a

Reporting

Limit a Units

Compliance Constituents

Enterococcus Enterolert b

USEPA 1600 c 1.0 1.0

MPN/100mL

CFU/100mL

Fecal Coliform SM 9222D

SM 9221E d 2.0 2.0

CFU/100mL

MPN/100mL

Additional Constituents

Total Coliform SM 9222B

SM 9221B d 2.0 2.0

CFU/100mL

MPN/100mL

Escherichia coli IDXX SM 9223B 1.0 1.0 MPN/100mL

Notes:

Compliance constituents are referenced as “compliance” for comparison purposes only. These constituents, as required by the MS4 Permit (Regional Board, 2013), do not pertain to these special study monitoring locations. Additional constituents are additional data collected above and beyond the scope of the Bacteria TMDL.

a. The table presents the lowest possible MDLs and RLs; actual RLs vary with the dilutions used to generate plates within the countable range.

b. Analytical method used for Wet Weather Event 1

c. Analytical method used for Wet Weather Events 2 and 3, and all dry weather events

d. Standard Methods 9221E and 9221B were used to analyze fecal/total coliforms for only one event, on October 20, 2015.

CFU = colony-forming unit; mL = milliliters; MPN = most probable number; SM = Standard Method; USEPA = United States Environmental Protection Agency

2.5 Optional Field Measurements and Observations

The Responsible Agencies elected to record in situ water quality (Table 2-3) and notable field

observations (i.e. creek odor, color, and clarity) with each sample collected, beyond the

requirements of the Bacteria TMDL. These optional data may be referenced to support key

findings or patterns indicated by the compliance analytical data. Event field measurements are

provided in Appendices B, C, and F.

Table 2-3 provides the range of accuracy of field meter in situ measurements.


2-6

Table 2-3. Optional In Situ Field Measurement Detection Ranges

Parameter Method Range Units

Conductivity a Field Meter 0 to 200,000 µS/cm

pH a Field Meter 0 to 14 pH units

Temperature b Field Meter -5 to +75 °C

Turbidity c Field Meter 0 to 1,000 NTU

Notes:

µS/cm = microsiemens per centimeter; °C = degree Celsius; NTU = Nephelometric turbidity unit

Wet weather field measurements were collected with a calibrated Horiba U-52.

a. Dry weather field measurements were collected with Hanna HI 98130.

b. Dry weather field measurements were collected with YSI Pro ODO.

c. Dry weather field measurements were collected with Hanna HI 93703.

In addition to the conventional field observations, detailed trash surveys were conducted by field

crews during 2015–2016 wet weather sampling events. The trash surveys included categorizing

and quantifying visible trash and debris, and assigning numerical scores to seven separate trash

evaluations. The separate evaluations included observed threats to aquatic life and human health,

evidence of littering and dumping, and trash accumulation from storm drains and other outside

transport.

2.6 Measurement Quality Objectives

MQOs are quantitative and qualitative statements that define project objectives and specify the

acceptable ranges of field sampling and laboratory performance. QA/QC activities were

conducted with Chollas Creek compliance monitoring for comparison with relevant MQOs, as

defined in the project Monitoring Plan (Amec Foster Wheeler, 2016a). The QA/QC program

included both field procedures (which used field blanks and field duplicates) and laboratory

procedures (which used laboratory replicates, method blanks, and positive and negative controls).

All data met MQO and QA/QC requirements outlined in the project Monitoring Plan and were

included in the compliance evaluation. A detailed evaluation of the MQO analyses is provided in

Appendix A.

Several results reported by the City of San Diego EMTS Laboratory were estimated because

bacteria plate counts performed as part of the analytical method fell outside the ideal range in the

USEPA method guidelines. Those estimated results have been flagged with an “e” as estimated.

The flagged data are acceptable for comparison with TMDL numeric targets, but with a lesser

degree of confidence.

Results flagged with a “<” qualifier were non-detects, which are reported as the reporting limit.

During dry weather conditions, the majority of the results from CTL(1) were flagged as “<”

meaning the results were less than the reporting limit of 20 CFU/100mL. These results could have

been as low as 1 or 2 CFU/100mL; however, a value of 20 CFU/100mL was used for these results

in order to complete the geometric mean calculations, and may account for higher geometric

means above the TMDL numeric target for Enterococcus. If a lower reporting limit was achieved


2-7

for the same samples, the geometric mean would have likely been below the TMDL numeric

target.

2.7 Wet Weather Single-Sample Maximum Exceedance Frequency

Wet weather exceedances are based on a comparison of the frequency of exceedances of the

single-sample maximum numeric target to the allowable 22 percent exceedance frequency. Wet

weather events include the storm day(s) (0.2 inch of rainfall or greater) and the following 72 hours,

resulting in a minimum wet weather event duration of four days. Per the MS4 Permit, for monitored

storm events, the highest reported result from a storm event will be applied to each day for the

duration of that event. An inferred exceedance frequency must be calculated to account non-

monitored storm events.

For the remaining wet weather days that are not associated with a monitored event, the average

(arithmetic mean) of the highest reported results from each of the three monitored wet weather

events is assigned to the remaining wet weather days in the wet season.

Arithmetic Mean (�) = X1 + X2 + X3… Xn

n

where: Xn is the highest reported concentration of the monitored event

n is the number of monitored storm events

The wet weather exceedance frequency is then determined by dividing the number of wet weather

days that exceeded the single-sample maximum numeric target by the total number of wet

weather days observed during the 2015–2016 wet season. A list of observed wet weather days

for the 2015–2016 wet season, both monitored and observed, are presented in Appendix B.

Wet Weather Exceedance Frequency (%) = 100 ∗ �(WWD> Wet Weather Numeric Target)

ΣWWD

where: ΣWWD is the sum of wet weather days (0.2 inch of rainfall or more) and the

following 72 hours

A list of observed wet weather days for the 2015–2016 wet season, both monitored and observed,

is presented in Appendix B.

2.8 Wet Season Geometric Mean and Exceedance Frequency

Per the MS4 Permit, a wet season exceedance frequency was calculated using the combined wet

and dry weather results between October 1, 2015, and September 30, 2016, and was compared

with dry weather numeric targets. During the wet season, the amount of time summarized by each

geometric mean varies. Dry weather sampling was conducted weekly during the wet season in

October 2015 and April 2016, and monthly from November 2015 through March 2016. In addition,

three wet weather events were captured during the wet season; one sample was collected for

each wet weather event. A rolling geometric mean calculation was calculated from the five most

recent wet season samples. With each subsequent sample collected, the first sample from the

preceding five-sample geometric mean was dropped.


2-8

At SD8(1) and Z Street, when there was insufficient flow during dry weather, no sample was

collected or analyzed. The visits to a dry site were used in the wet season geometric mean

exceedance frequency evaluation because the site was dry and therefore not contributing a

bacteria load. To meet the prescribed dry weather geometric mean frequency, statistics were

calculated for dry events at SD8(1) and Z Street by assigning a concentration value of 0.1 colony-

forming unit (CFU) (rather than 0.0 CFU) when these sites were not flowing. A zero value is

undefined logarithmically and so would be unusable in the geometric mean calculation. The wet

season geometric mean is calculated as follows:

5-Sample Geometric Mean = ( )( )( )( )( )54321

n ΧΧΧΧΧ

where: n is the number of individual results used in the calculation

Xn is sample n result (e.g., X1 = November result, X2 = Wet Weather 1 Result)

A wet season exceedance occurs when a geometric mean exceeds the dry weather numeric

target. The first geometric mean was calculated after the fifth sample in October 2015. To

determine the wet season exceedance frequency, the number of wet season geometric means

that exceed the dry weather numeric target was divided by the total number of calculated wet

season geometric means, as follows:

Wet Season Exceedance Frequency (%) = 100 ∗ Wet Season Gn > DW

Wet Season Gn

where: Wet Season Gn is the number of dry season geometric means

DW is the dry weather numeric target

2.9 Dry Season Geometric Mean and Exceedance Frequency

Dry season geometric mean and exceedance frequency calculations are detailed below.

The MS4 Permit states that the geometric mean calculation should be consistent with the Basin

Plan (Regional Board, 2011). A 30-day rolling geometric mean calculation is based on a minimum

of five samples for any 30-day period, and is calculated as follows:

30-Day Geometric Mean = ( )( )( )( )( )54321

n ΧΧΧΧΧ

where: n is the number of individual results used in the calculation

Xn is week n result (e.g., X1 = week 1 result)

Dry season monitoring began in early May 2016; the first geometric mean was calculated after

the fifth sample in late May 2016. With each subsequent sample collected, the first sample from

the preceding five-sample geometric mean was dropped. Samples collected between May 1 and

September 30 are used in this calculation. At SD8(1) and Z Street, when there was insufficient

flow, no sample was collected or analyzed. The visits to a dry site were used in the dry weather

geometric mean frequency evaluation because the site was dry and therefore not contributing a

bacteria load. To meet the prescribed dry weather geometric mean frequency, statistics were

calculated for dry events at SD8(1) and Z Street by assigning a concentration value of 0.1 colony-


2-9

forming unit (CFU) (rather than 0.0 CFU) when these sites were not flowing. A zero value is

undefined logarithmically and so would be unusable in the geometric mean calculation.

A dry weather exceedance occurs when the geometric mean exceeds the dry weather numeric

target. The first exceedance frequency was calculated in late May 2016, after the first geometric

mean calculation. The number of geometric means that exceed the dry weather numeric target is

divided by the total number of calculated dry season geometric means to determine the dry

season exceedance frequency, as expressed below.

Dry Season Exceedance Frequency (%) = 100 ∗ Dry Season Gn > DW

Dry Season Gn

where: Dry Season Gn is the number of dry season geometric means

DW is the dry weather numeric target

2.10 Precipitation and Flow Data

Historical daily rainfall amounts generated by the National Weather Service were used to assess

annual rainfall and the historical average for San Diego County. The Monitoring Plan specifies to

use the San Diego International Airport (SDIA) rain gauge for mobilization of wet weather

sampling (Amec Foster Wheeler, 2016a). However, several storm events in the 2015–2016 wet

season were underrepresented by the SDIA rain gauge when compared with other rain gauges

in the San Diego region. Therefore, the 2015–2016 wet season rainfall data from SDIA were

averaged with rainfall data from Montgomery Field for better representation of unequal rainfall

distribution across several storm events. The average precipitation amounts measured by the

SDIA and Montgomery Field rain gauges were also used to determine the total number of

observed wet weather days during the 2015–2016 season.

Flow and rainfall data were collected for SD8(1) and Z Street as part of the Diazinon and Dissolved

Metals TMDLs (Regional Board Resolution Nos. R9-2002-0123 and R9-2007-0043, respectively),

and were used to develop event hydrographs for the Chollas Creek Bacteria TMDL monitoring

program (Amec Foster Wheeler, 2016b). Flow and rainfall data were logged in five-minute

intervals during each monitored event.

Flow was measured using a Sigma 950 area-velocity bubbler flow meter and a bubbler level

sensor. Flow was calculated in the flow meter using level data and a head-versus-flow table that

was developed for the Responsible Agencies’ compliance monitoring (Amec Foster Wheeler,

2016b). Rainfall was measured by a tipping bucket rain gauge at both SD8(1) and Z Street.


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3-1

3.0 HYDROLOGY AND MONITORING SUMMARY

This section summarizes wet and dry weather events, including hydrology, flow conditions, and

key observations. Field measurements and analytical results for wet weather are presented in

Appendix B; those dry for weather are in Appendix C.

3.1 Wet Weather: Hydrology and Monitoring Summary

Precipitation data from the SDIA and Montgomery Field were used to track the total number of

wet weather days, as defined in the MS4 Permit. Measured rainfall was compared with the

historical monthly averages recorded at SDIA from 1981 to 2010. This comparison will support

future evaluations of annual precipitation and potential effects on FIB concentrations, or the

assessment of exceedances. The historical data were accessed through the Western Regional

Climate Center (WRCC) website (WRCC, 2010, accessed in 2016).3

Total precipitation recorded at SDIA for the 2015–2016 wet season was 7.42 inches, which was

below the historical average of 9.92 inches (WRCC, 2016). Montgomery Field, however, recorded

approximately 2.5 inches more rainfall than SDIA, logging 10.03 inches of precipitation during the

2015–2016 wet season (National Oceanic and Atmospheric Administration [NOAA], 2016). The

disparity of the season totals between SDIA and Montgomery Field demonstrates the unequal

distribution of rainfall across the San Diego region.

Table 3-1 summarizes wet weather monthly precipitation data for SDIA for the 2015–2016 wet

season, and presents historical data for comparison.

Table 3-1. Wet Weather Monthly Rainfall Summary

Month

Rainfall (inches)

Montgomery Field SDIA

2015–2016 Monitoring Season

2015–2016 Monitoring Season

1981—2010 Historical Average

October 2015 0.69 0.43 0.54

November 2015 1.94 1.54 0.98

December 2015 1.58 0.88 1.65

January 2016 3.84 3.21 1.96

February 2016 0.02 0.05 2.21

March 2016 1.08 0.76 1.78

April 2016 0.88 0.55 0.79

Total Rainfall 10.03 7.42 9.92

Source: National Weather Service Notes: SDIA = San Diego International Airport

3 The WRCC website maintains climate data collected through a partnership of the National Oceanic and Atmospheric Administration (NOAA), the National Climatic Data Center, and the National Weather Service.


3-2

For the Bacteria TMDL compliance monitoring, a qualifying wet weather event occurs on days

with equal or greater than 0.2 inch of rainfall, preceded by at least 72 hours of less than 0.1 inch

of rainfall. Three storm events were successfully captured at all three compliance monitoring

locations. Wet Weather Event 1 was a medium- to large-sized storm event, with 1.12 inches of

recorded rainfall; Wet Event 2 was a small event, with 0.19 inch recorded; and Wet Event 3 was

a very large event, with nearly 3 inches of recorded rainfall.

The Chollas Creek watershed response varies throughout the wet season based on factors such

as antecedent soil moisture conditions, impervious area, rainfall amount, and rainfall intensity.

During larger storms, runoff from pervious surfaces can increase after soils are completely

saturated. Earlier in the season, the soil conditions throughout the watershed are drier and

increased infiltration results in less runoff. Later in the season, the ground is more saturated,

resulting in greater discharge volumes and peak flows. Storm flows were observed to be too

dangerous for recreational activities in the creek, especially in the concrete-lined segments.

Each monitored storm event is described in detail in the following sections.

Table 3-2 presents the precipitation and flow summaries for the three monitored wet weather

events at SD8(1) and Z Street. These flow and rainfall data, collected as part of the Diazinon

TMDL and the Dissolved Metals TMDL (Amec Foster Wheeler, 2016b) provide a hydrologic

overview of wet weather events. However, these data are not required to be collected for the

Bacteria TMDL Compliance Program.

Table 3-2. Rainfall and Flow Totals for Monitored Events

Event Date SDIA Rain (inches)

Montgomery Field Rain (inches)

Location a

North Chollas Creek Location, SD8(1) b

South Chollas Creek Location, Z Street b

Rain (inches)

Estimated Flow (cf)

Rain (inches)

Estimated Flow (cf)

Wet Weather

Event 1 11/4/2015 1.12 1.41 1.27 15,800,000 1.40 16,100,000

Wet Weather

Event 2 12/29/2015 0.19 c 0.24 0.18 1,080,000 0.24 314,000

Wet Weather

Event 3 1/9/2016 2.98 3.40 3.07 86,100,000 2.36 d 40,600,000

Notes: cf = cubic feet

a. Compliance monitoring location CTL(1) is not listed because it is a tidally influenced location and freshwater flows cannot be accurately recorded.

b. Precipitation and flow data are recorded at SD8(1) and Z Street as part of the Diazinon TMDL and the Dissolved Metals TMDL (Amec Foster Wheeler, 2016b). These data are not a requirement of the Bacteria TMDL compliance monitoring program.

c. Wet Weather Event 2 did not exceed 0.2 inch at SDIA or the SD8(1) rain gauge. However, Montgomery Field and other rain gauges in the Chollas Creek Watershed exceeded the 0.2-inch target.

d. The rainfall data suggests the tipping bucket rain gauge at Z Street may have become clogged with debris during Wet Weather Event 3; therefore, total rainfall may not be accurately represented for the south Chollas Creek MLS area during.


3-3

3.1.1 Wet Weather Event 1—November 4, 2015

A qualifying wet weather event occurred on November 3–4, 2015. Isolated showers began the

afternoon of November 3, 2015, with the heaviest periods of rainfall occurring during the evening

of November 3, 2015. Isolated cells brought additional rainfall to the area during the early morning

hours of November 4, 2015. Over the course of the storm, SDIA recorded 1.25 inches of rainfall,

SD8(1) recorded 1.27 inches of rainfall, and Z Street recorded 1.40 inches of rainfall.

This storm was the first monitored event of the 2015–2016 wet season. Bacteria grab samples,

in situ field measurements, and field observations were collected at the three compliance

monitoring locations: CTL(1), SD8(1), and Z Street. Wet weather samples were collected at each

compliance monitoring location within 24 hours after the end of rainfall. Bacteria grab samples

were collected at the Chollas Creek compliance monitoring locations between 11:30 and 13:30

on November 4, 2015.

Figure 3-1 presents event photographs taken on November 3–4, 2015. Figure 3-2 shows the

SD8(1) and Z Street hydrographs during this event.

CTL(1) (Chollas Creek Tidal Location),

November 4, 2015

SD8(1) (North Chollas Creek Location),

November 4, 2015

Z Street (South Chollas Creek Location),

November 4, 2015

Figure 3-1.

Wet Weather 1 Photographs


3-4

Notes: SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location; cf = cubic feet; cfs = cubic feet per second; in. = inch

Figure 3-2.

Wet Weather 1 Hydrographs, SD8(1) and Z Street


3-5

3.1.2 Wet Weather Event 2—December 29, 2015

The season’s second monitored wet weather event occurred on December 28–29, 2015. Showers

began the afternoon of December 28, 2015, and continued intermittently through

December 29, 2015, with the most intense rainfall occurring in the evening on

December 28, 2015. Over the course of the storm, SDIA recorded 0.22 inch of rainfall, SD8(1)

recorded 0.18 inch of rainfall, and Z Street recorded 0.24 inch. Wet weather samples were

collected at each compliance monitoring location within 24 hours after the end of rainfall. Bacteria

grab samples were collected at the SD8(1) and Z Street compliance monitoring locations between

10:00 and 11:00 on December 29, 2015.

Figure 3-3 presents photographs of Wet Event 2 taken on December 29, 2015. Figure 3-4

presents the hydrographs from SD8(1) and Z Street during this event.

CTL(1) (Chollas Creek Tidal

Location), December 29, 2015

SD8(1) (North Chollas Creek


Z Street (South Chollas Creek


Figure 3-3.

Wet Weather 2 Photographs


3-6


Figure 3-4.



3-7

3.1.3 Wet Weather Event 3—January 9, 2016

The third and final monitored event of the 2015–2016 wet season occurred on January 4–9, 2016.

Showers began the evening of January 4, 2016, and continued intermittently through the late

morning of January 8, 2016, with the heaviest rainfall occurring during the afternoon of

January 5, 2016. Over the course of the storm, SDIA recorded 3.35 inches and SD8(1) recorded

3.07 inches. The Z Street rain gauge recorded 2.36 inches of rainfall; however, the data indicate

that the rain gauge may have become clogged during the storm event.

Wet weather samples were collected at each compliance monitoring location within 24 hours after

the end of a storm event. Bacteria grab samples were collected at the Chollas Creek compliance

monitoring locations between 04:15 and 04:45 on January 9, 2016.

Wet Weather Event 3 photographs are not presented because sample collection occurred before

sunrise and clear photographs could not be obtained. Figure 3-5 presents the hydrographs from

SD8(1) and Z Street during this event.


3-8


Rainfall data at Z Street indicate that the rain gauge may have become clogged during the January 9, 2016, storm event.

Figure 3-5.



3-9

3.2 Dry Weather: Hydrology and Monitoring Summary

Per the MS4 Permit, dry weather days occur on days with less than 0.1 inch of rainfall observed

on each of the previous three days. The Chollas Creek compliance monitoring locations were

visited during 40 dry weather events from October 1, 2015, through September 30, 2016. Each

location was visited at least weekly in October 2015, and April 2016 through September 2016;

from November 2015 through March 2016 each location was visited monthly.

Unlike the 2015 dry season, which recorded well above average dry season rainfall, the 2016 dry

season was much more comparable to historical seasonal averages. Table 3-3 summarizes total

monthly rainfall for the 2016 dry season compared with the 2015 dry season (characterized as a

large El Niño year) and the historical average.

Table 3-3. Dry Season Monthly Rainfall Summary

Month

SDIA Rainfall (inches)

2015 Dry Season 2016 Dry Season 1981—2010

Historical Average

May 2015 2.20 0.44 0.12

June 2015 0.05 0.00 0.08

July 2015 1.70 0.00 0.04

August 2015 0.01 0.00 0.04

September 2015 1.24 0.32 0.16

Total Rainfall 5.20 0.76 0.44

Source: National Weather Service

SD8(1) and Z Street had little or no flow during a majority of dry weather sampling events.

Measurable flow was present at SD8(1) during 5 of the 40 dry weather sampling events. Of those

five dry weather events, only one event, on October 20, 2015, occurred during the wet season,

and the source of the dry weather flow during that event was not identified. The remaining four

dry weather events occurred in May 2016 (one event) and August 2016 (three events). City of

San Diego staff identified the outfall discharging to Chollas Creek on May 23, 2016, but were

unable to identify the upstream source. The City of San Diego was able to identify and address

the three events that occurred during August 2016; the source was likely the result of construction

activities occurring immediately upstream of the north fork compliance point.

Measurable flow was present at Z Street during three of 40 dry weather monitoring events, each

of which occurred during the wet season. Successful dry weather sampling occurred during

December 2015, January 2016, and March 2016; each of those events had an antecedent dry

period of approximately 5 days. Antecedent dry days were calculated on the basis of the number

of days since the last day with 0.1 inch of rainfall or more. If feasible, flow volumes were estimated

by the City of San Diego Stormwater Department staff. However, in most cases, flows were too

low to estimate. The duration of the observed dry weather flows was not recorded. It was not

confirmed whether the dry weather flows reached CTL(1) (the tidal monitoring location) on these

occasions.


3-10

CTL(1) has year-round flows, which allowed successful sampling during each event for a total of

40 dry weather events. However, hydrologic connectivity with the upper watershed was not

observed during most of the monitored events. With the absence of flow from the upper

watershed, specific conductivity measurements indicated that samples collected at the location

are predominantly brackish; the continuous tidal exchange is likely the source of water during dry

weather conditions. Notable field observations were excessive trash and algae in the channel,

and biological elements, such as abundant bird counts and the presence of fish, snails, and

insects.

SD8(1) and Z Street are upstream of the tidally influenced section of the Creek. Although the

exact extent of the tidal reach is not known, visual observations suggest the tidally influenced

portion of Chollas Creek extends roughly the same distance as the 303(d) listed segment. Figure

3-6 illustrates the apparent lack of hydrologic connectivity between the upstream compliance

monitoring locations SD8(1) and Z Street and the tidal creek mouth location CTL(1) on dry

weather days during the wet season. The pie charts were derived using the continuous flow data

collected as part of the Diazinon and Dissolved Metals TMDLs monitoring program (Amec Foster

Wheeler, 2016b). Flow days were determined by evaluating days where average daily flow met

or exceeded 0.001 cubic feet per second (cfs) (equivalent to 0.44 gallon per minute); daily

averages below 0.001 cfs were assumed to be dry because ponding and trickle flows are often

too low to be identified on the basis of the resolution of the flow data collection equipment. The

47 days associated with wet weather events (as presented in Appendix B) were excluded from

the analysis. Continuous flow data are not collected between May 1 and September 30, so an

evaluation during the dry season could not be performed.

Figure 3-6.

Estimated Percentage of Dry Weather Flow Days During the 2015–2016 Wet Season

Table 3-4 presents sampling event information (flow, tidal stage, and total antecedent dry weather

days before each event). Note that tidal stage (not flow value) is used at CTL(1) because of its

daily tidal exchanges. Dry weather results for FIB concentrations and field measurements for

2015–2016 monitoring year are in Appendix C.

21%

79%

SD8(1)

Flowing Dry

7%

93%

Z Street

Flowing Dry

100%

0%

CTL(1)

Flowing Dry


3-11

Table 3-4. Dry Weather Sampling Summary and Antecedent Dry Days

Date Visited

Location Sampled Tide Height b

(feet)

Antecedent Dry Days c

CTL(1) Estimated Flow a

SD8(1) Z Street <0.1 inch <0.2 inch

10/12/2015 Yes No Flow No Flow 6.61 7 7


10/19-20/2015 d,e Yes d 200.6 e No Flow d 5.22 14 d/15 e 14 d/15 e




12/2/2015 Yes No Flow Ponded 3.81 5 29












5/23/2016 Yes 2.7 No Flow 4.08 17 17












8/3/2016 Yes Ponded No Flow 4.70 89 89







9/19/2016 Yes 7.5 No Flow 6.36 136 136



Notes: Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location DW = dry weather; Ponded = Flows too low to estimate.

Blue-shaded dates are dry weather events that took place during the wet season. a. Flow values are in-field estimations and apply only to the non-tidal monitoring locations, SD8(1) and Z Street. b. Source: NOAA, 2016a. Tidal height is approximate and pertains to the CTL(1) tidally influenced sample time (nearest hour). c. Source: NOAA, 2016b. NWS archived rain gauge data for the SDIA were used to determine antecedent dry days. d. Sample event date for CTL(1) and Z Street occurred on October 19, 2016.


3-12

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4-1

4.0 MONITORING RESULTS

This section presents FIB data collected from October 2015 through September 2016.

Additionally, historical FIB data collected beginning in 2012 are provided in Appendix D.

Appendix B presents additional wet weather data, including analytical results, optional field

measurements, and observed wet weather days, for the 2015–2016 wet season. Appendix E

contains the 2015–2016 wet weather laboratory reports. Appendix F contains the wet weather

field data sheets.

4.1 Wet Weather Fecal Indicator Bacteria Concentrations

Elevated FIB concentrations were detected in all three monitored storm events of the 2015–2016

storm season. Long-term FIB concentration trends have not been evaluated. The extended

periods of drought during winter months may influence seasonal results, because the watershed

system as a whole is flushed out less frequently than in years with normal rainfall. Fecal coliform

concentrations tend to decrease later in the wet season. Concentrations of Enterococcus, which

is thought to replicate and persist in extra-enteric environments and may be more resistant to

harsh environments than other indicator species, did not decrease later in the season

(Byappanahalli et al., 2012).

Table 4-1 lists the current wet weather analytical results at the three Chollas Creek compliance

monitoring locations. With the exception of fecal coliform detected at Z Street during Wet Weather

Event 2, the FIB concentrations at all compliance monitoring locations exceeded the single-

sample maximum numeric target for all three wet weather events monitored, as presented in

Figure 4-1.

Chollas Creek Bacteria TMDL 2015–2016 Compliance Monitoring Report November 2016

4-2

Table 4-1.

Wet Weather Analytical Results

Analyte Unit Numeric

Target Method

Reporting

Limit a

WW1, 11/4/2015 WW2, 12/29/2015 WW3, 1/9/2016

CTL(1) SD8(1) Z Street CTL(1) SD8(1) Z Street CTL(1) SD8(1) Z Street

Enterococcus CFU/

100mL 61

SM 9230C b 20–1000 28,000 13,000 34,000 9,800 3,200 3,200 1,300 1,600 1,100

USEPA 1600 c

Fecal Coliform CFU/

100mL 400 SM 9222D d 20–1000 66,000 54,000 58,000 2,000 2,200 320 2,500 1,100 1,400

Notes: Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location; CFU = colony-forming unit; mL = milliliters; RL = reporting limit; SM = Standard Method; USEPA = U.S. Environmental Protection Agency Bolded values indicate that the value exceeds the single-sample maximum numeric target. a. Reporting limit values vary with the dilutions used to generate plates within the countable range. b. Analytical method used for Wet Weather Event 1. c. Analytical method used for Wet Weather Event 2 and Wet Weather Event 3. d. Analytical method used for all Wet Weather Events.


4-3

Figure 4-1.

2015–2016 Wet Weather Fecal Indicator Bacteria Concentrations

4.2 Dry Weather Fecal Indicator Bacteria Concentrations

SD8(1) location had flow during five dry weather monitoring events during the 2015–2016 season.

Prior to October 20, 2016, the first of those events, dry weather flows had not been observed

since December 2013. During dry weather, the creek at Z Street was most likely to flow from

residual stormwater runoff. The south Chollas Creek location was typically dry with flow observed

only 8 of the 40 dry weather events and 7 of the 8 monitored dry weather events occurred within

seven days after a storm event. The weekly monitoring records show that these dry weather flows

were short-lived at the south Chollas Creek location. Prior to this monitoring period, no dry

weather flows had been observed at this location since December 2013.

Figures 4-2 through 4-4 depict each dry weather monitored event in the 2015–2016 monitoring

season and the reported FIB concentrations for dry weather samples collected. The blue-shaded

areas represent dry weather results that occurred during the wet season, when greater

concentrations were more likely to occur. During the dry season, the majority of CTL(1) results

were qualified as less than the reporting limit of 20 CFU/100mL. Since a lower reporting limit could

not be achieved, the results are presented as 20 CFU/100mL.

1

10

100

1,000

10,000

100,000

1,000,000

CTL(1) SD8(1) Z Street CTL(1) SD8(1) Z Street CTL(1) SD8(1) Z Street

Co

nc

en

trati

on

(C

FU

/10

0m

L)

Wet Weather 1 November 4, 2015

Wet Weather 3 January 9, 2016

Wet Weather 2December 29, 2015


4-4

Notes: Blue-shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliters

Concentrations presented as 20 MPN/CFU/100mL were qualified as estimated or less than the Reporting Limit.

Figure 4-2

2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at CTL(1)

0

1

10

100

1,000

10,000

100,000

1,000,000

MP

N/C

FU

/ 1

00

mL


4-5

Notes: Blue shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliter


Figure 4-3.

2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at SD8(1)

0

1

10

100

1,000

10,000

100,000

1,000,000

MP

N/C

FU

/ 1

00

mL


4-6

Notes: Blue shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliter


Figure 4-4.

2015–2016 Dry Weather Fecal Indicator Bacteria Concentrations at Z Street

0

1

10

100

1,000

10,000

100,000

1,000,000

MP

N/C

FU

/ 1

00

mL


5-1

5.0 COMPLIANCE EVALUATION

This section presents the results of the compliance evaluation for wet and dry seasons in

accordance with the assessment requirements in Attachment E.6 of the MS4 Permit. FIB data

collected between October 2015 and September 2016 were used to assess compliance in

accordance with the MS4 Permit. Separate evaluations were completed using single-sample

maximum exceedance frequencies for wet weather results and geometric mean exceedance

frequencies for both combined wet weather and dry weather results during the wet season and

dry weather results collected during the dry season. Several inconsistencies were identified in

Attachment E.6.6 of the MS4 Permit that may affect the interpretation of compliance; these

inconsistencies are explained in detail in Appendix G.

5.1 Wet Weather Single-Sample Maximum Exceedance Frequencies

Per the MS4 Permit assessment requirements, the wet weather exceedance frequency is inferred

from the three sampled wet weather events. A wet weather day, as defined in the MS4 Permit,

includes any wet weather storm event with more than 0.2 inch of rainfall, plus the following

72 hours. The 2015–2016 wet season had a total of 47 wet weather days. Wet weather days

identified during the 2015–2016 wet season are detailed in Appendix B. For each compliance

monitoring location, this assessment applied the arithmetic mean of the three wet weather sample

results to each non-sampled wet weather day. A total of 14 of the 47 wet weather days were

associated with sampled storm events (three storm events plus the following 72 hours per event)

and the average of the results was assigned to each of the remaining 33 wet days. This

assessment resulted in an exceedance frequency of 100 percent of wet weather numeric targets

at all compliance sites.

Table 5-1 presents the wet weather numeric target and exceedance days for each compliance

monitoring location, as well as exceedance frequencies. Additional results, including optional field

measurements and observed wet weather days for this monitoring year, are presented in

Appendix C.

Table 5-2 compares the wet weather exceedance frequencies with wet weather compliance

interim and final reduction milestones.


5-2

Table 5-1. 2015–2016 Wet Weather Single-Sample Maximum Exceedance Frequencies

Site ID Analyte

Single-Sample Maximum

(CFU/MPN / 100mL) Exceedance

Days

Total Wet Weather

Days

2015–2016 Wet Weather Exceedance Frequency Numeric Target

CTL(1) Enterococcus 61 47 47 100%

Fecal Coliform 400 47 47 100%

SD8(1) Enterococcus 61 47 47 100%


Z Street Enterococcus 61 47 47 100%


Notes:

Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location

% = percent

Bolded values = exceedance frequency is greater than final allowable limit established in the Bacteria TMDL.

Table 5-2. 2015–2016 Wet Weather Exceedance Frequencies and Compliance Reduction Milestones

Site ID Analyte

2015–2016

Exceedance

Frequency

Interim Allowable

Exceedance

Frequency

Final Allowable

Exceedance

Frequency

Interim

Milestone

Achieved?

Final

Milestone

Achieved?

CTL(1) Enterococcus 100% 43% 22% No No

Fecal Coliform 100% 41% 22% No No

SD8(1) Enterococcus 100% 43% 22% No No


Z Street Enterococcus 100% 43% 22% No No


Notes:


% = percent


5.2 Wet Season Geometric Mean Exceedance Frequencies

Higher exceedance frequencies of the geometric mean numeric target are expected during the

wet season with the inclusion of storm samples. At the Chollas Creek tidal location (CTL(1)), the

exceedance frequency for Enterococcus was 86 percent and the exceedance frequency for fecal

coliform was 21 percent during the wet season. Despite exceedances, the Chollas Creek mouth

does not appear to be hydrologically connected to the upper reaches of the watershed during

most of the dry weather events that occur in the wet season. This finding is supported by lack of

flow at the north Chollas Creek location (SD8(1)) and south Chollas Creek location (Z Street)

during dry weather in the wet season and the specific conductivity recorded at the Chollas Creek

tidal location that reflect a primarily brackish condition.


5-3

Measureable dry weather flows occurred only one time at the SD8(1) during the wet season. For

dry weather sampling events where no flow was observed, no samples were collected or analyzed

and a value of 0.1 CFU was assigned. The exceedance frequencies for Enterococcus and fecal

coliform were 7 percent and 0 percent, respectively, at SD8(1). Measureable dry weather flows

were observed during only three sampling events at Z Street during the wet season, and each of

those days occurred within the wet season. The wet season exceedance frequencies at Z Street

were 29 percent for Enterococcus and 0 percent for fecal coliform.

Table 5-3 presents the wet season geometric mean exceedance frequencies for the compliance

monitoring locations, including the number of geometric means calculated from the results, the

number of geometric means that exceeded the numeric target, and the maximum geometric

mean. Table 5-4 compares the wet season exceedance frequencies with wet season compliance

interim and final reduction milestones.

Table 5-3. 2015–2016 Wet Season Geometric Mean Exceedance Frequencies

Site ID Analyte

5-Sample Geometric Mean

(CFU/MPN / 100mL) Number of Geometric

Means

Number of Exceedances

2015–2016 Wet Season Exceedance Frequency Numeric

Target

Maximum Geometric

Mean

CTL(1) Enterococcus 33 844 14 12 86%

Fecal Coliform 200 831 14 3 21%

SD8(1) Enterococcus 33 58 14 1 7%


Z Street Enterococcus 33 204 14 4 29%

Fecal Coliform 200 139 14 0 0% Notes:

Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location % = percent


Table 5-4. 2015–2016 Wet Season Exceedance Frequencies and Compliance Reduction Milestones

Site ID Analyte 2015–2016


Interim Allowable


Final Allowable


Interim Milestone Achieved?

Final Milestone Achieved?

CTL(1) Enterococcus 86% 50% 0% No No

Fecal Coliform 21% 50% 0% Yes No

SD8(1) Enterococcus 7% 50% 0% Yes No

Fecal Coliform 0% 50% 0% Yes Yes

Z Street Enterococcus 29% 50% 0% Yes No


Notes: Site IDs: CTL(1) = Chollas Creek tidal location, SD8(1) = north Chollas Creek location, Z Street = south Chollas Creek location % = percent Bolded values = exceedance frequency is greater than final allowable limit established in the Bacteria TMDL.


5-4

5.3 Dry Season Geometric Mean Exceedance Frequencies

For each compliance monitoring location, 30-day rolling geometric means were calculated using

Enterococcus and fecal coliform results and compared with the dry weather numeric targets per

analyte, as presented in Table 5-5. Despite brackish concentrations in the mouth, Chollas Creek

is listed as a freshwater creek and thus results are compared with the freshwater TMDL numeric

targets. The dry season exceedance frequency for Enterococcus was 24 percent at CTL(1).

However, the exceedance frequency was largely driven by one elevated sample result. The

maximum geometric mean value was 34.6 CFU/100mL, which slightly exceeds the Bacteria

TMDL numeric target of 33 CFU/100mL for Enterococcus in Creeks. During dry weather, the

majority of results from CTL(1) were non-detects but flagged by the laboratory as less than the

reporting limit of 20 CFU/100mL. A value of 20 CFU/100mL was used for these results in order to

complete the geometric mean calculations, and may account for higher geometric means above

the TMDL numeric target for Enterococcus. If a lower reporting limit was achieved for the same

samples, the geometric mean would have likely been below the TMDL numeric target.

For fecal coliform, the Chollas Creek tidal location achieved a 0 percent exceedance frequency.

Based on current monitoring, sources of elevated FIB concentrations at CTL(1) are not known;

however, monitoring observations indicate that the mouth of Chollas Creek is rarely hydrologically

connected to the upper watershed during the dry season. Potential sources may include land

areas draining directly to this segment of Chollas Creek, natural sources (regrowth and wildlife),

and the result of the hydrology and residence time of brackish water.

Enterococcus exceedance frequencies for at the north and south Chollas Creek locations (SD8(1)

and Z Street, respectively) were 10 percent and 0 percent, respectively; both locations achieved

0 percent exceedance frequencies for fecal coliform. The three Chollas Creek compliance

monitoring locations are in compliance with interim allowable exceedance frequencies during the

dry season. Only Z Street achieved final exceedance frequency goals during the 2016 dry season.

Table 5-6 compares the dry season exceedance frequencies to dry weather compliance interim

and final reduction milestones.


5-5

Table 5-5. 2016 Dry Season Geometric Mean Exceedance Frequencies

Site ID Analyte

30-Day

Geometric Mean

(CFU/MPN / 100mL)

Number Of Geometric

Means

Number of

Exceedances

2016

Dry Season

Exceedance

Frequency Numeric

Target

Maximum

Geometric

Mean

CTL(1) Enterococcus 33 35 21 5 24%


SD8(1) Enterococcus 33 90 21 2 10%


Z Street Enterococcus 33 0 21 0 0%



% = percent


Table 5-6. 2015 Dry Season Exceedance Frequencies and Compliance Milestones

Site ID Analyte 2015


Interim Allowable


Final Allowable


Interim Milestone Achieved?

Final Milestone Achieved?

CTL(1) Enterococcus 24% 50% 0% Yes No


SD8(1) Enterococcus 10% 50% 0% Yes No


Z Street Enterococcus 0% 50% 0% Yes Yes


Notes:


% = percent


Geometric means for the 2015–2016 monitoring year are presented graphically in Figures 5-1

through 5-3. FIB concentrations in wet and dry weather are indicated with blue triangles and

yellow circles, respectively. Wet season geometric means are illustrated using a blue line with

blue markers throughout the blue areas (wet season), which reflects the rolling geometric mean

using the last five samples. Dry season geometric means are illustrated using a red line with green

markers, which reflects the rolling 30-day geometric means throughout the dry season (May 1

through September 30). Wet weather and dry weather Bacteria TMDL numeric targets are

illustrated with a blue dashed line and an orange dotted line, respectively.


5-6

Notes: Site ID: CTL(1) = Chollas Creek tidal location; Blue shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliter;

MPN = most probable number

Figure 5-1.

2015–2016 FIB Densities and Geometric Means—CTL(1)

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00

mL E

nte

roc

oc

cu

s

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00

mL

Fe

ca

l Co

liform


5-7

Notes: Site ID: SD8(1) = north Chollas Creek location; Blue shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliter;


Figure 5-2.

2015–2016 FIB Densities and Geometric Means—SD8(1)

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00

mL E

nte

roc

oc

cu

s

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00

mL F

eca

l Co

liform


5-8

Notes: Site ID: Z Street = south Chollas Creek location; Blue shaded area = dry weather samples collected during the wet season; CFU = colony-forming units; mL = milliliter;


Figure 5-3.

2015–2016 FIB Densities and Geometric Means— Z Street

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00m

L En

tero

co

ccu

s

0

1

10

100

1,000

10,000

100,000

1,000,000

CF

U/M

PN

/ 1

00

mL F

eca

l Co

liform


5-9

5.4 Progress Toward Attaining Interim and Final Receiving Water Limitations

Table 5-7 depicts the general progress toward meeting interim and final numeric targets by

season for each compliance monitoring location in the Chollas Creek Watershed. This table

indicates whether targets for collective FIB have been met (●), have been partially met (��), or

have not yet been met (X). A partially met goal means that at least one of the FIB constituents is

meeting the RWL.

Table 5-7. 2015–2016 General Progress Toward Interim and Final RWLs for Chollas Creek

Monitoring Location

2015–2016 Wet Weather

Sample Maximum RWLs

2015–2016 Wet Season

RWLs

2016 Dry Season

RWLs

Interim Final Interim Final Interim Final

CTL(1) X X �� X � �� SD8(1) X X � �� Z Street X X � ��

Notes:


● = Currently, interim or final receiving water limitations (RWLs) have been fully achieved.

� = Currently, interim or final RWLs have been partially achieved, but not all compliance constituents have attained the RWLs.

X = Currently, no fecal indicator bacteria (FIB) constituents meet Bacteria Total Maximum Daily Load (TMDL) RWLs.


5-10



6-1

6.0 SUMMARY

This section summarizes current receiving water conditions in Chollas Creek related to the project

goals. The monitoring program has generated sufficient data to evaluate the project goals on the

basis of current conditions.

6.1 Characterization of Current Fecal Indicator Bacteria Concentrations

During storm events, the entire watershed is hydraulically connected and recreational water

quality standards are exceeded at all compliance monitoring locations. However, wet weather

flows are too high and dangerous for recreational activities to be safely performed. All locations

have elevated levels of FIB and are not currently meeting the wet weather RWLs.

Monitoring data indicate that the upper watershed is not typically hydraulically connected to the

lower segment of the creek during dry weather. Few exceedances, if any, occur at the upstream

MLS locations during the dry season, because most days are observed to be dry at these

locations. The lower portion of the creek, below where the north and south forks converge, is tidal

and water levels are sufficient to support recreational activities year round. Both the lack of dry

weather flows at the upstream MLS locations and the electrical conductivity measurements taken

at CTL(1), ranging from 43.3 to 60.3 milliSiemens per centimeter (mS/cm), suggest that flows are

or are close to pure saltwater during dry weather, fed by tidal fluctuations. Despite brackish

conditions in the lower portion of Chollas Creek, results are currently compared to freshwater

TMDL numeric targets.

Compliance monitoring data also indicate a greater frequency for Enterococcus exceedances

than fecal coliform exceedances. This observation is consistent with data collected for other

bacteria contamination studies, as Enterococcus has been shown to persist and even grow in the

environment without a proximate or recent source of contamination (Byappanahalli et al., 2012).

Sources of dry weather exceedances at the Chollas Creek tidal location (CTL(1)) are not known;

potential sources may be land-use areas directly draining to this segment of Chollas Creek or

natural sources (regrowth) and wildlife, or may result from the hydrology and residence time of

brackish water. It is evident that the upstream portions of Chollas Creek may not be contributing

to exceedances at the Chollas Creek tidal location during dry weather conditions because the

portions of the watershed are not hydraulically connected.

Overall, Chollas Creek is meeting the interim dry weather RWLs and making progress toward

meeting the final dry weather allowable exceedance frequencies. A majority of exceedances at

the compliance monitoring locations occur during the wet season as a result of residual storm

flows.

6.2 Evaluation of Progress toward Meeting Bacteria TMDL Numeric Targets

Interim and final RWLs for wet weather were not attained this year for all compliance monitoring

location. However, Chollas Creek is making progress toward meeting the dry weather RWLs. The

three compliance monitoring locations are meeting both interim dry weather RWLs. The 2015–

2016 monitoring results are summarized below.


6-2

Wet Weather Single Sample Maximum Comparison

• Currently, no compliance monitoring locations achieved interim or final wet weather RWLs

for Enterococcus or fecal coliform.

Wet Season Geometric Mean Comparison

• Two of three compliance monitoring locations attained the interim dry weather RWLs for

Enterococcus and fecal coliform during the wet season.

• None of the compliance monitoring locations attained final dry weather RWLs for

Enterococcus and fecal coliform during the wet season.

Dry Season Geometric Mean Comparison

• The south Chollas Creek location (Z Street) attained the interim and final dry weather

RWLs for Enterococcus and fecal coliform during the dry season.

• The north Chollas Creek location (SD8(1)) and Chollas Creek tidal location attained

interim dry weather RWLs for Enterococcus and fecal coliform and final dry weather RWLs

for fecal coliform

Table 6-1 presents the exceedance frequencies by season in the Chollas Creek Watershed.


6-3

Table 6-1.

2015–2016 Bacteria TMDL Exceedance Frequencies in Chollas Creek Watershed

Site ID

Bacteria

TMDL

Constituent

Wet Weather a Wet Season a,c Dry Season b

Single-Sample

Maximum

(CFU/100mL)

5-Sample

Geometric Mean

(CFU/100mL)

30-Day

Geometric Mean

(CFU/100mL)

2015–

2016 d


Interim

Allowable

Frequency

Final

Allowable

Frequency

2015–

2016 d


Interim

Allowable

Frequency

Final

Allowable

Frequency

2015–

2016 d


Interim

Allowable

Frequency

Final

Allowable

Frequency

CTL(1) Enterococcus 100% 43% 22% 86% 50% 0% 24% 50% 0%

Fecal Coliform 100% 41% 22% 21% 50% 0% 0% 50% 0%

SD8(1) Enterococcus 100% 43% 22% 7% 50% 0% 10% 50% 0%

Fecal Coliform 100% 41% 22% 0% 50% 0% 0% 50% 0%

Z Street Enterococcus 100% 43% 22% 29% 50% 0% 0% 50% 0%

Fecal Coliform 91% 41% 22% 0% 50% 0% 0% 50% 0%


% = percent

Bolded values = exceedance frequency is greater than the interim and final allowable limit established in the Bacteria Total Maximum Daily Load (TMDL). a. October 1, 2015–April 30, 2016 b. May 1, 2016–September 30, 2016 c. In accordance with the MS4 Permit, wet and dry weather FIB data were combined to calculate geometric means for the wet season and compared to the dry weather exceedance frequencies

as shown in Table ES-1. d. The exceedance frequency was derived by dividing the total number of wet weather days (days with 0.2 inch of rainfall or greater plus the following 72 hours) that exceeded the single-

sample maximum numeric target divided by the total number of wet weather days during the wet season. To determine exceedances for non-sampled wet weather days, the arithmetic mean of the analytical results from three monitored storm events was applied to the remaining observed wet weather days that were not sampled. The results from the total number of wet weather days, with either assigned averages or analyzed result values, were then compared with single-sample maximum numeric targets.

e. The exceedance frequency was derived by dividing the total number of geometric exceedances by the total number of geometric means calculated during the season.


6-4



7-1

7.0 REFERENCES

Amec Foster Wheeler, Environment & Infrastructure, Inc. (Amec Foster Wheeler). 2015. Chollas

Creek Bacteria Total Maximum Daily Load 2014–2015 Compliance Monitoring Report.

Prepared for: Amec Foster Wheeler Environment & Infrastructure, Inc. December.

Amec Foster Wheeler. 2016a. Chollas Creek Diazinon, Dissolved Metals, and Bacteria TMDLs

Monitoring Plan. Prepared for the City of San Diego. Prepared for: City of San Diego,

County of San Diego, Unites States Navy, San Diego Unified port District, City of La Mesa,

City of Lemon Grove, and the California Department of Transportation (Caltrans). January.

Amec Foster Wheeler. 2016b. Chollas Creek Dissolved Metals Total Maximum Daily Load 2015–

2016 Compliance Monitoring Report. Final. Prepared by Amec Foster Wheeler

Environment & Infrastructure, Inc. June.

Byappanahalli, Muruleedhara N.; Nevers, Meredith B.; Korajkic, Asja; Staley, Zachery R.; and

Harwood, Valerie J, 2012. Enterococci in the Environment. Microbiology and Molecular

Biology Reviews. 76(4): 685-706.

City of San Diego. 2012. Chollas Watershed Comprehensive Load Reduction Plan. Prepared by:

Tetra Tech, Inc. July.

National Oceanic Atmospheric Administration (NOAA), 2016a. Tides and Currents.

http://tidesandcurrents.noaa.gov/waterlevels.html?id=9410170. Website accessed in

October 2016.

NOAA, 2016b. Western Regional Headquarters. Annual Daily Rainfall Archive.

http://www.wrh.noaa.gov/sgx/obs/rtp/rtpmap.php?wfo=sgx. Website accessed in

September 2016.

San Diego Regional Water Quality Control Board (Regional Board). 2002. Resolution R9-2002-

0123. Total Maximum Daily Load for Diazinon in Chollas Creek Watershed, San Diego

County. August.

Regional Board. 2007. Resolution No. R9-2007-0043. A Resolution Adopting an Amendment to

the Water Quality Control Plan for the San Diego Basin (9) to Incorporate Total Maximum

Daily Loads for Dissolved Copper, Lead, and Zinc in Chollas Creek, Tributary to San Diego

Bay.

Regional Board. 2010. Resolution No. R9-2010-0001, A Resolution Amending the Water Quality

Control Plan for the San Diego Basin (9) to Incorporate Revised Total Maximum Daily

Loads for Indicator Bacteria Project I—Twenty Beaches and Creeks in the San Diego

Region (Including Tecolote Creek) (Bacteria TMDL) February 10.

Regional Board. 2011. Water Quality Control Plan for the San Diego Basin (9) (Basin Plan).

Regional Board. 2013. Resolution No. R9-2013-0001, National Pollutant Discharge Elimination

System (NPDES) Permit and Waste Discharge Requirements for Discharges from the

MS4s Draining the Watershed in the San Diego Region (MS4 Permit). May 14.


7-2

San Diego Bay Municipal Agencies. 2016. Water Quality Improvement Plan: San Diego Bay

Watershed Management Area. Final. February.

United States Environmental Protection Agency (USEPA). 2012. 2012 Recreational Water Quality

Criteria. EPA 820-F-12-061. Washington, DC.

Western Regional Climate Center (WRCC). San Diego WSO Airport, California (047740). Period

of Record Monthly Climate Summary. Period of Record: January 1981 to December 2010.

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca7740. Website accessed in September

2016.

Documents

CHOLLAS CREEK BACTERIA TOTAL MAXIMUM DAILY LOAD 2015–2016 COMPLIANCE MONITORING REPORT · 2017-11-09 · CHOLLAS CREEK BACTERIA TOTAL MAXIMUM DAILY LOAD 2015–2016 COMPLIANCE MONITORING