Water Quality
Bay Area Urban
Creeks - Diazinon and
(Approved 2007)
Total Maximum Daily Load (TMDL) Summary
Waterbody - 37 impaired urban creeks within seven counties in the San
Francisco Bay region (see map below). In addition, the TMDL states that
all Bay Area urban creeks likely receive pesticide discharges.
Implementation actions will work best if applied throughout the region,
so the TMDL strategy applies to all Bay Area urban creeks, including
those not identified as impaired.
o TMDL targets achieved
o Conditions improving
• Improvement needed
o Data inconclusive
Erin Foresman at (916) 930-3722 or
San Francisco Bay Water Board:
Jan O'Hara at (510) 622-5681 or

1)	Coyote Creek
2)	Arroyo Corte Madei
del Presidio
3)	Corte Madera Creek
4)	San Rafael Creek
5)	Callings Creek
6)	Miller Creek
7)	Novato Creek
8)	San Antonio Creek
9)	Petaluma River
10)	Ledgeuiood Creek
11)	Laurel Creek
12)	Suisun Slough
13)	Mt. Diablo Creek
14)	Pine Creek
15)	Walnut Creek
16)	Rodeo Creek
17)	Pinole Creek
13) San Pablo Creek
19)	Wildcat Creek
20)	San Leandro Creek
21)	San Lorenzo Creek
22)	Arroyo de las Positas
23)	Arroyo Mocho
24)	Arroyo del V^lle
25)	Arroyo de la Laguna
26)	Alameda Creek
27)	San Felipe Creek
23) Coyote Creek
29)	Guadalupe River
30)	Los Gatos Creek
31)	Saratoga Creek
32)	Calabaz as Creek
33)	Stevens Creek
34)	Permanente Creek
35)	Matadero Creek
36)	San Francisquito Creek
37)	San Mateo Creek

Urban Creeks Impaired due to Diazinon-Related Toxicity
Water Quality Goals
According to water quality objectives, all waters shall be maintained
free of toxic substances in concentrations that are lethal to or that
produce other detrimental responses in aquatic organisms.
The TMDL includes numeric targets to interpret this narrative objective:
There shall be no pesticide-related acute or chronic toxicity in urban
creek water and sediment in excess of 1.0 TUa or 1.0 TUC, where TU
is a toxic unit.
This means that no acute or chronic toxic effects should be observed when
compared to a control. This is determined through standard toxicity tests
such as sun'ival, growth, reproduction, and cell division.
Diazinon concentrations in urban creeks shall not exceed 100
nanograms per liter (ng/1) as a one-hour average.
This numeric target addresses both acute and chronic diazinon-related
Last Updated 6/15/2015

Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
These targets must be met at all locations in each urban creek, including near storm drain outfalls where urban
runoff enters the creeks.
Targeted Attainment Date - Not specified in the TMDL; however, the TMDL includes adaptive management
which entails taking actions commensurate with available information, reviewing new information as it becomes
available, and modifying actions as necessary based on the new information.
Water Quality Impairment -In the early 1990s, many Bay Area urban creek water samples were found to be toxic
to aquatic organisms (causing mortality or impacting reproduction, among other responses). Studies were
performed (toxicity identification evaluations) to identify the cause of toxicity. These studies found that
pesticides, particularly diazinon, caused the toxicity. Diazinon is an insecticide, which is a specific category of
pesticides, and has been found to be acutely toxic to aquatic life, wildlife, and humans. While pesticides are
intended to eliminate insects and other pests, they can be harmful to living organisms that are not considered
pests, particularly when rainwater or over-irrigation water carry the pesticide into a storm drain and creek.
Aquatic invertebrates appear to be the aquatic organisms most sensitive to diazinon exposure.
Data collected by several agencies document diazinon concentrations high enough to cause aquatic toxicity in
many urban creeks. Therefore, in 1998, a number of the Bay Area urban creeks were placed on the 303(d) list of
impaired waters due to toxicity attributed to diazinon. The results of recent monitoring efforts suggest that toxicity
occurs in urban creeks less frequently and diazinon concentrations are lower, when compared with conditions in
the early 1990s. While improvements have been noted, toxicity indicators above the numeric targets do still occur.
Urban creek waters that fail to meet these targets are not protective of cold and warm freshwater habitats. In 2004,
the product registration for most urban (non-agricultural) uses of diazinon were cancelled; thereby phasing out
urban diazinon use. Unfortunately, reducing diazinon use has increased reliance on other pesticides, which now
post a threat to water and sediment quality. To ensure protection of water quality, the TMDL is focused on the
attainment of pesticide-related toxicity targets (not just diazinon-related toxicity), regardless of which pesticide
causes the toxicity, in all urban creeks in the Bay Area. Given what is known about pesticide use trends, the
pyrethroid pesticide alternatives now pose the greatest concerns for water quality in urban creeks. For example,
Kirker Creek was found to be impaired by pyrethroid-related toxicity in 2010. Because this TMDL is applicable
to all urban creeks in the Bay Area, an additional TMDL was not necessary and the Kirker Creek impairment is
being addressed through implementation of this TMDL.
Pollutant Sources - Pesticides, including diazinon, enter urban creeks through urban storm water runoff and dry
weather discharges from storm drains, with a much smaller contribution from direct discharges (e.g., dumping or
riparian weed control). Storm drains are regulated and are owned and operated by municipalities, industrial and
construction dischargers, large institutions, and the California Department of Transportation (Caltrans). Urban
runoff contains pesticides that are purchased and applied by both businesses and individuals. Urban pesticides
uses include applications by professional pest control personnel, municipal workers, and homeowners to control
pests (aphids, spider mites, fleas, ants, roaches, and boring insects) on residential and commercial landscapes,
around building foundations and roadways, and at commercial and industrial locations. Pesticide use by structural
pest control professionals and use of products sold over-the-counter can be among the greatest contributors of
pesticides in urban runoff. In the nine Bay Area counties, roughly 93% of pesticides by weight are applied in
urban areas. Factors that affect pesticide concentrations in urban creeks include the amount used, the chemical and
physical properties of the pesticide and its product formulation, the sites of use (e.g., landscaping, lawns/turf, or
paved surfaces), and irrigation practices and precipitation.
Loading Capacity and Allocations - The loading capacity is the maximum amount of a contaminant or stressor
that can be assimilated by the waterbody without exceeding the TMDL numeric targets (which in this case are
interpretations of the narrative water quality objectives). The toxicity and diazinon loading capacity and source
allocations in this TMDL are toxic unit- and concentration-based limits. These limits are measured in receiving
waters and, for this TMDL, are equal to the numeric targets. Specifically, for urban creeks to assimilate diazinon

Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
and other pesticide discharges, water quality measurements in urban creeks must be below the numeric targets. By
expressing the loading capacity in terms of toxicity and diazinon concentrations, the TMDL automatically
considers seasonal and other critical conditions. Wasteload allocations (point sources) for each source are also
expressed in terms of toxic units and diazinon concentrations, and are the same as the numeric targets and the
loading capacity. The wasteload allocations address all urban runoff, including urban runoff associated with
municipal separate storm sewer systems, Caltrans facilities, and industrial, construction, and institutional sites.
Is Water Quality Improving?
Water quality is showing some improvement in the Bay Area urban creeks; however, additional effort is needed
to fully protect the freshwater habitat designated uses. Management efforts to reduce diazinon contamination have
been successful, including the cancellation of non-agricultural uses of diazinon and the subsequent reduction in its
application. There have been no diazinon measurements above the numeric target since the TMDL has been
approved (however, the California Environmental Data Exchange Network [CEDEN] dataset only included data
for Arroyo del Valle in the past five years, so exceedances may still be observed in other creeks).
Diazinon Concentration Trends in the Bay Area Urban Creeks


8 ¦ _

t at •! ~
• ~


Arroyo de las Positas
Arroyo del Valle
Arroyo Mocho
Coyote Creek
Guadalupe River
Mount Diablo Creek
Permanente Creek
Petaluma River*
San Leandro Creek
San Lorenzo Creek
San Mateo Creek
San Pablo Creek
Stevens Creek
Wildcat Creek

- Objective
In addition to diazinon concentrations, it is important to evaluate toxicity over time in the Bay Area urban creeks
to determine attainment of the water quality goals. Toxicity data can be difficult to interpret. Survival tests are one
metric that can be used to evaluate toxicity. For all percent survival data available at Bay Area urban creek
stations, the average value for each sampling date was calculated. Specifically, for each location-date
combination, there were multiple measurements - on different samples as well as survival tests on different
organisms. The average values were calculated and are graphed below overtime for Ceriodaphnia dubia (C.
dubia) and Hyalella ctztecct (H ctztecct).
C. dubia is sensitive to organophosphate pesticides, such as diazinon. The graph below illustrates that C. dubia
survival is not statistically different from the control, indicating that the samples are not toxic for that test
organism (using the 4-, 7-, or 8-day survival test). Since diazinon is phased out, this lack of toxicity in C. dubia is
Diazinon use has been replaced by pyrethroid pesticides in urban settings and these pesticides contribute to
sediment toxicity as they bind to sediment particles and do not readily partition to water. Therefore, it is important
to evaluate sediment toxicity associated with pyrethroid-sensitive test organisms, such as H. azteca. The percent

Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
survival of H. azteca was analyzed (in both 10- and 28-day survival tests) and is illustrated in the bottom graph
below. The non-toxic samples were not found to be statistically different than the control (based on the t test),
while the toxic and highly toxic results displayed statistically significant toxicity when compared to the control.
These toxic samples were then separated into toxic and highly toxic categories, where samples were identified as
highly toxic if the average percent survival was lower than the high toxicity threshold for H. azteca of 38.6
percent survival.
Over time, the range of sediment toxicity has remained about the same. However, the number of samples
characterized as highly toxic has increased in recent years. In addition, in the most recent three years of data, no
samples were characterized as non-toxic to H. azteca, suggesting that the use of pyrethroid pesticides is resulting
in sediment toxicity in urban creeks.
C. dubia Toxicity in Water in the Bay Area Urban Creeks
~ oo
o o
o Non-Toxic
¦ Toxic
H. azteca Toxicity in Sediment in th
100 ™DL
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80 	O	^	
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e Bay Area Urban Creeks

o Non-Toxic
8 $
_ o
¦ Toxic

O 1
A Highly Toxic


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Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
While conditions for diazinon impairment have improved considerably since implementation of the TMDL,
additional practices are needed to address sediment toxicity in the urban creeks and to restore the freshwater
habitat designated uses. Toxicity identification evaluations would be useful to identify the specific pollutants
causing sediment toxicity. If those pollutants are pesticides, then they could be addressed through implementation
of this TMDL.
TMDL Progress - Implementation activities and milestones
Implementation Activity
Target Date
Progress Details
Summarize pesticide
regulatory activities as they
relate to water quality, and
identify opportunities to
advise pesticide regulatory
oversight agencies regarding
future actions
Municipal stormwater Permittees' work
collectively through the Bay Area Stormwater
Management Agencies Association (BASMAA)
to comment on, and participate in, pesticide
regulatory actions, (summary table [linkl; full
report [linkl)
Summarize research and
monitoring data for
pesticide regulatory
oversight agencies and
others, and determine
where to focus future
monitoring efforts based on
critical data needs
Implementation activities include filling
information gaps monitoring to measure
implementation progress:
•	Summary of fipronil in San Francisco Bay
•	Surface Water Ambient Monitoring Program
(SWAMP) Toxicity Report (link)
•	Department of Pesticide Regulation (DPR)
Surface Water Protection Program
monitoring reports and related studies (link)
•	DPR webinars on monitoring surface water
for pesticides (link)
Describe urban pesticide use
trends and identify
pesticides likely to affect
water quality

California Stormwater Quality Association
(CASQA) Pesticides Subcommittee developed a
report entitled Preventing Urban Pesticide
Pollution in Stormwater, including a Pesticide
Watch List (link).
Notify pesticide regulatory
oversight agencies if water
quality standard violations
exist or are likely to exist in
the future due to pesticide
At least annually

•	As of 2009, diazinon and associated toxicity
in urban creeks were no longer observed
•	By 2011, toxicity found in urban creeks was
related to pyrethroid pesticides, which have
largely replaced urban uses of diazinon (link).
Identify waters impaired by
pesticide-related toxicity
and waters where there is a
potential for impairment
• Kirker Creek exhibited pesticide-related
impairments and was subsequently added to
the 303(d) list and is being addressed by this
TMDL (link).

Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
Implementation Activity
Target Date
Progress Details
Meet or correspond with
pesticide regulatory
oversight agencies regarding
their roles in protecting
water quality
At least annually
• San Francisco Bay Regional Water Quality
Control Board (Water Board) staff, as well as
wastewater and stormwater discharger
groups, work with DPR and the U.S.
Environmental Protection Agency (EPA) to
bring the potential threats to water quality
to the forefront during pesticide evaluation
and registration processes (see regulatory
programs [link]).
Place required actions in
National Pollutant Discharge
Elimination System (NPDES)
stormwater permits
No later than
five years from
effective date of
• Incorporated into Municipal Separate Storm
Sewer System (MS4) permit as per Order R2-
2009-0074 (link). This permit will be reissued
in 2015 with similar requirements for
pesticide-related toxicity control.
Report implementation
status to Water Board
• Municipalities submit Annual Reports to
document compliance with implementation
requirements (link).
What Next?
Water quality goals are currently being achieved for diazinon but overall aquatic toxicity appears to be unchanged
since the adoption of the TMDL. Cancellation of residential uses of diazinon has mitigated risks to aquatic life
from this pesticide in urban areas but new pesticides, such as pyrethroids and fipronil, have emerged which also
cause aquatic toxicity. Additional implementation activities for this TMDL associated with pyrethroid pesticides
may be necessary to reduce sediment toxicity and achieve the toxicity water quality goals. Likely, new pesticides
will emerge in the future and continued monitoring for aquatic toxicity will be the most efficient way to assess
pesticide impacts overtime. During pesticide registration and registration review, aquatic life risk mitigation
strategies are developed into pesticide use instructions that must appear on product labels and must be followed
by pesticide applicators. Increased coordination between State and Federal water quality and pesticide use
regulators will help to achieve the long term goal of improved aquatic health.
Information Source Documents
•	San Francisco Bay RWQCB website for the Diazinon and Pesticide-Related Toxicity in Urban Creeks
TMDL (link)
•	Total Maximum Daily Load (TMDL) Report for Diazinon and Pesticide-Related Toxicity in Urban Creeks
•	San Francisco Bay RWQCB TMDL Resolution - Amending the Water Quality Control Plan for the San
Francisco Bay Region to Establish a Water Quality Attainment Strategy and Total Maximum Daily Load
(TMDL) for Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks (link)
•	California Department of Pesticide Regulation adopted regulations (link)
http: //www. cdpr. ca.gov/docs/emon/surfwtr/reg_index.htm
•	NPDES MS4 Permit - California Regional Water Quality Control Board San Francisco Bay Region,
Municipal Regional Stormwater NPDES Permit, Order No. R2-2009-0074, NPDES No. CAS612008 (link)

Progress Report: Diazinon and Pesticide-Related Toxicity in Bay Area Urban Creeks
• Information on permit reissuance, including the draft permit is available on the San Francisco Bay Water
Board website (link)
•	Annual Reports for Municipal Regional NPDES Permit (Bay Area Stormwater Management Agencies
Association and Individual MRP Permittees) (link)
•	EPA Aquatic Life Common Effects Methodology (link)