Monitoring Urban Pesticide Runoff in California 2008 - 2009 

Michael Ensminger and Kevin Kelley 

CALIFORNIA ENVIRONMENTAL PROTECTION AGENCY 

California Department of Pesticide Regulation 

Environmental Monitoring Branch 

Surface Water Protection Program 

1001 I Street, Sacramento, CA 95812 

March 2011 

Report 249 
i

ABSTRACT 

To determine the prevalent pesticides in urban surface waters in California, the California 

Department of Pesticide Regulation (CDPR) initiated a statewide urban surface water 

monitoring program in 2008. Water and sediment samples were collected at 25 sites in 

the Sacramento (SAC), San Francisco Bay (SFB), greater Los Angeles (Orange County), 

and San Diego (SD) areas. Samples were collected at stormdrain outflows and at 

receiving waters during rainy and during dryflow conditions. Water samples were 

analyzed for 63 pesticides or degradates. Sediment samples were only collected during 

dryflow and analyzed for pyrethroids and chlorpyrifos. In water samples, 18 insecticides 

and 12 herbicides or their degradates were detected above their reporting limits. Multiple 

detections were common; 50% of the samples had three or more pesticides and 25% had 

six or more pesticides. OC and SAC had the highest detection frequencies and SD had the 

fewest. The most frequently detected insecticides in water were bifenthrin, fipronil, 

fipronil sulfone, carbaryl, desulfinyl fipronil, and malathion. Chlorpyrifos and diazinon 

were detected, albeit infrequently, despite drastic reductions in urban use. Fipronil, 

fipronil sulfone, desulfinyl fipronil, and carbaryl were more frequently detected in OC 

than in other areas of the study. Other pyrethroids were infrequently detected in water 

samples but common contaminants of sediments. Half of the sediments contained five or 

more pyrethroids. The most common pyrethroids in sediments were bifenthrin, 

cyfluthrin, permethrin, deltamethrin, λ-cyhalothrin, and cypermethrin. Herbicides were 

detected at slightly higher frequencies than insecticides; the most frequently detected 

herbicides were 2,4-D, triclopyr, dicamba, diuron, MCPA, and pendimethalin. Except for 

bifenthrin, pesticides occurred with equal frequency in stormdrain outflows and in 

receiving waters. Bifenthrin was more frequently detected in stormdrain outflows than in 

receiving waters. Rain increased pesticide runoff for all of the pesticides but fipronil (and 

degradates). Fipronil appeared to have a continuous load dependent on use rather than 

rainfall. Detection of the herbicides diuron and pendimethalin also correlated with use but 

these herbicides are routinely applied during the rainy season when pesticide detections 

are generally highest. Bifenthrin, fipronil, and diuron were detected in water samples at 

concentrations that potentially could be toxic to aquatic organisms. 

ACKNOWLEDGEMENTS 

Many people have generously given their time to help this study succeed, especially the 

staff and of the Surface Water Protection Program of the Environmental Monitoring 

Branch of CDPR. We especially thank Kean S. Goh and Sheryl Gill for their support of 

this project, Carissa Ganapathy and Sue Peoples for sample coordination and 

organization between DPR and CDFG, to Jessie Ybarra for maintaining CDPR’s West 

Sacramento’s facility, and to Frank Spurlock for his critical review. In addition, we 

extend gratitude to Li-Ming He, currently at NOAA Fisheries, 650 Capitol Mall, 

Sacramento, CA for his early leadership in this project. 
ii

TABLE OF CONTENTS 

ABSTRACT..................................................................................................................................... i 

ACKNOWLEDGEMENTS............................................................................................................. i 

TABLE OF CONTENTS................................................................................................................ ii 

LIST OF FIGURES .......................................................................................................................iii 

LIST OF TABLES.........................................................................................................................iii 

I. INTRODUCTION....................................................................................................................... 2 

II. MATERIALS AND METHODS............................................................................................... 3 

III. RESULTS AND DISCUSSION............................................................................................... 5 

Pesticides detected in surface waters .......................................................................................... 5 

Pesticides detected in sediments ................................................................................................. 7 

The effect of waterbody type (storm drain vs. creek receiving water) on pesticide 

detections in urban surface waters. ............................................................................................. 8 

The effect of season (dryflow vs. rainstorm) on pesticide detections in urban surface 

waters. ......................................................................................................................................... 8 

Comparison of Pesticide Concentrations to Aquatic Toxicity Benchmarks............................... 9 

Water Quality............................................................................................................................ 11 

Quality Control ......................................................................................................................... 11 

IV. CONCLUSIONS .................................................................................................................... 11 

V. LITERATURE CITED ........................................................................................................... 13 

VI. APPENDIX I. DATA ............................................................................................................. 28 

VII. APPENDIX II. QUALITY CONTROL................................................................................ 53 
iii

LIST OF FIGURES 

Figure 1. Sampling sites for CDPR’s urban monitoring project in the Sacramento, San 

Francisco Bay, greater Los Angeles (Orange County), and San Diego areas, 

California. ............................................................................................................................. 20 

Figure 2. Cartoon depicting a storm drain outflow and receiving water. ..................................... 21 

Figure 3. Number of pesticides detected in water samples collected from urban creeks 

and storm drain outflows in the four different sampling areas of California........................ 22 

Figure 4. Detection frequency of insecticides from all sampling areas of California 

between April 2008 and August 2009 .................................................................................. 23 

Figure 5. Detection frequency of fipronil, fipronil sulfone, desulfinyl fipronil, and 

carbaryl in the four different sampling areas of California................................................... 23 

Figure 6. Detection frequency of herbicides from all sampling areas of California 

between April 2008 and August 2009 .................................................................................. 24 

Figure 7. Detections of pyrethroids in sediments from all sampling areas of California. ............ 24 

Figure 8. The influence of waterbody on frequency of pesticide detections................................ 25 

Figure 9. The influence of rain on frequency of pesticide detections........................................... 26 

Figure 10. PUR reported use of fipronil, diuron, pendimethalin, and synthetic auxin 

herbicides (2,4-D, dicamba, MCPA, and triclopyr) and their detection ratios. .................... 27 

LIST OF TABLES 

Table 1. Pesticides analyzed by the California Department of Food and Agriculture in 

water or sediment.................................................................................................................. 18 

Table 2. Detection frequencies (above reporting limit) of pesticides detected above US 

EPA benchmark or commonly accepted LC50 values in water samples............................... 19 
2

I. INTRODUCTION 

Annual California urban pesticide use is on the order of millions of kg of active 

ingredient (ai). Urban pesticide use includes structural pest control, landscape 

maintenance, rights-of-way and public health pest protection applications, as well as 

applications to commercial, institutional, and industrials areas, and residential home-andgarden applications. The California Department of Pesticide Regulation (CDPR) 

compiles pesticide use records for urban pesticide applications made by licensed 

applicators. Annually, professional applicators apply over 4 million kg ai of pesticides for 

urban (non-agriculture) pest control (CDPR 2010). However, urban pesticide use by 

individual homeowners is not reported, so that total urban use in California is greater than 

this reported use. Especially in dense urbanized areas, high homeowner pesticide use is 

anticipated. For example, a recent survey of four large home improvement stores in 

northern and southern California showed that 190 pesticide products, containing 79 

different ai’s, were being sold for outdoor use (Osienski et al. 2010). Other surveys have 

also shown that large numbers of pesticides are being sold in retail stores. Moran’s 

(2005) survey indicated that more than 320 pesticide products containing 99 different ai’s 

were being sold in the San Francisco Bay Area. Another survey in Sacramento, Stockton, 

and the San Francisco Bay area revealed 542 different products containing 112 different 

ai’s were available for sale (Flint 2003). Efforts have been made to estimate this nonreported urban pesticide use in California by comparing CDPR’s Pesticide Use Report 

(PUR) and sales database, but a recent analysis by Zhang and Spurlock (2010) 

demonstrated the high degree of uncertainty in those estimates. However, it has been 

estimated that non-agricultural pesticide uses account for approximately 20-25% of all 

total pesticide use in the United States; most of these uses are in urban areas (Aspelin and 

Grube 1999; Kiely et al. 2004). In 2009, excluding adjuvants, the total reported pesticide 

use in California was over 68 million kg ai (CDPR 2010). Thus, these data show that 

large amounts of pesticides are applied in California urban areas, although the exact 

amounts are unknown. 

Due to the high volume of urban pesticide use and perhaps lack of consumer awareness, 

urban pesticide runoff may exceed agricultural runoff (Wittmer et al. 2011). Pesticide 

runoff into urban creeks and rivers can occur via stormdrains during dryflow or with 

stormwater runoff leading to concentrations that may be toxic to aquatic organisms 

(Hoffman et al. 2000; Revitt et al. 2001; Schiff and Sutula 2004; Budd et al. 2007; 

Sprague and Nowell 2008; Weston et al. 2009; Oki and Haver, 2009). Many urban use 

pesticides have been detected at concentrations that are sufficient to cause toxicity in 

laboratory bioassays (Werner, et al., 2000; Schiff et al. 2002; Hunt, et al., 2003; Holmes 

et al. 2008; Mize et al. 2008; Lao et al. 2010; Weston and Lydy 2010). In addition, 

numerous urban creeks are listed on the 2006 Federal Clean Water Act Section 303(d) list 

due to the presence of organophosphorus (OP) pesticides that often originated in urban 

runoff (Cal/EPA 2009). Most of these listings are due to the presence of chlorpyrifos or 

diazinon. Chlorpyrifos and diazinon have been banned from most urban (residential) uses 

due to unfavorable human health and ecological risks. However, some urban uses of 

these two OP insecticides are still allowed so that their presence in urban waterways is 

still possible. For instance, chlorpyrifos is allowed for sale in indoor ant and roach baits 

in child resistant packaging, as a fogger adult mosquitocide (when applied by a public 
3

agency), and for use in golf course turf applications at reduced rates (US EPA 2010a). 

Currently in California, both chlorpyrifos and diazinon are used in urban areas for 

structural pest control, rights-of-way applications, and for landscape maintenance when 

applied by a licensed professional applicator. However, the overall urban use in 

California is less than 1% of the total usage prior to initiating the residential ban in 2000 

(CDPR 2010). 

Recent monitoring in California shows that urban waterways are frequently contaminated 

with pyrethroids, the OPs diazinon and chlorpyrifos, and fipronil (Oki and Haver, 2009; 

Weston et al. 2009; Weston and Lydy 2010; Lao et al. 2010). There is little or no 

published monitoring data for many other urban use pesticides in California, especially 

herbicides. Herbicides are often acutely toxic to algae, although the environmental 

impacts of herbicides on aquatic systems is not well understood (Jassby et al. 2003; 

Miller et al. 2005; Sommer et al. 2007). In addition, there are synergistic interactions 

between different pesticides to aquatic invertebrates (Lydy and Belden 2006). Additional 

monitoring of urban waterways is therefore needed in order to assess the potential 

impacts of urban pesticide use on urban surface waters. A consistent statewide 

monitoring program will provide useful data on the environmental fate of urban use 

pesticides and aid in the development and implementation of management measures. In 

2008, CDPR initiated a statewide urban monitoring project to address the problems of 

pesticides in urban waterways. Specific objectives of this study were fourfold: 1) 

determine what pesticides, at what concentrations, are present in urban runoff; 2) evaluate 

the magnitude of measured concentrations relative to water quality or aquatic toxicity 

benchmarks; 3) assess the effect of waterbody type (e.g., stormwater drain vs. creek); and 

4) assess the effect of season (dryflow vs. rainstorm). 

II. MATERIALS AND METHODS 

Study Area. Monitoring was conducted in four large metropolitan areas in northern and 

southern California. Twenty-five sites were sampled in total; four in the Sacramento area, 

seven in each of the San Francisco Bay, the greater Los Angeles, and San Diego areas 

(Figure 1). Water and sediment samples were collected from either stormdrain outflows 

or from downstream receiving waters (Figure 2); generally for each of the four main 

sampling areas, there were two or three stormdrain outflows for each receiving water site. 

Receiving waters comprised of: Pleasant Grove Creek (Sacramento [SAC] area), Grayson 

and Koopman/Martin Canyon Creeks (San Francisco Bay [SFB] area), and Wood 

Canyon and Salt Creeks (greater Los Angeles area, in Orange County [OC]), Lindo Lake 

(inflow), and the San Diego River (San Diego [SD] area). Two storm drain outflow sites 

at the San Diego River sites only contained water during rain events. Detailed 

information about the sampling sites can be found in Appendix I, Table A1. 

Field Sampling. This study was initiated in April 2008 and ended at the end of the 

August 2009. In northern California, four dryflow and four rainstorm sampling events 

were completed. However, due to limited rainfall in southern California, we were only 
4

able to sample one rain event during both the 2008 and 2009 water years1. To make up 

for the lack of rain sampling, we completed five dryflow sampling events. Pyrethroid 

monitoring was added about 10 months after this study was initiated, with sampling 

beginning in February 2009. Because of the limited rain in southern California, no 

pyrethroids were collected during rain events. We use the term dryflow for our base 

stream flow in urban surface waters as these waters likely never experience true 

baseflow, the condition where only groundwater contributes to surface water flow. Urban 

surface waters are augmented with water from other sources, as irrigation, washing of 

cars, etc. (Sprague and Nowell 2007). We will refer to dryflow conditions when surface 

waters receive no input from rain storms; usually in California from late April or early 

May through September or October. 

Sediment samples were collected for pyrethroid and chlorpyrifos analysis. The collection 

of sediment sample timings differed somewhat from the water sample sampling. For 

pyrethroid analysis, sediments were collected twice during the study. In northern 

California, sediments were collected near the end of the rainy season and once in the 

summer. In southern California, sediments were collected in the late spring after the 

termination of the rainy season. Sediments were collected both from stormdrain outflows 

and, when feasible to do so, receiving waters. Sediments for chlorpyrifos analysis were 

only collected once, in the spring of 2009. 

Water samples from receiving waters were collected from stream banks close to 

midstream as feasible directly into 1-L glass amber bottles using an extendable pole and 

sealed with Teflon®-lined lids. Stormdrain outflows, generally with less flow, were 

collected by hand directly into 1-L amber bottles. However, dependent on flow and water 

depth, occasionally water samples from stormdrain outflows were collected into a 

stainless steel container and aliquots were poured into 1-L glass bottles. During the 

rainstorm event in OC, storm samples were collected as a composite sample with a HachSigma 900 Max automated sampler and split into 1-L amber bottles for transport. 

Sediment (up to a 2 cm depth) were collected using a stainless steel trowel or shovel, 

composited in a stainless steel container, and individual samples were placed into clear 

glass Mason® jars for later chemical analysis. Sediments could not be collected at all 

sites. Immediately after sampling, water and sediment samples were stored on wet ice for 

transport. Upon arrival at the laboratory, water samples were refrigerated (4°C) whereas 

sediments samples were frozen (–20°C) until chemical analysis. 

Total Suspended Solids and Total Organic Carbon. We analyzed total suspended 

solids (TSS) in water samples and total organic carbon (TOC) in both water and sediment 

samples. TSS was analyzed following US EPA method 160.2 (US EPA, 1971). Briefly, 

waters samples were filtered under vacuum through a Buchner funnel lined with a glass 

fiber filter, dried overnight at 103-105°C, and weighed. TOC was analyzed using a TOCV CSH/CNS analyzer (Shimadzu Corporation, Kyoto, Japan). 

 

1

A water year is from October of one year through September of the next; e.g., water year 2009 is from 

October 2008 through September 2009. 
5

Field Measurements. Water physiochemical properties (dissolved oxygen [DO], 

electrical conductivity [EC], pH, turbidity, and temperature) were measured in situ. 

Measurements were taken with a YSI 6920 V2 meter (YSI Incorporated, Yellow Springs, 

OH). The meter was calibrated prior to field use (Doo and Lee 2008). 

To get an estimate over overall pesticide load, flow data measurements were collected 

using a Global Flow Probe Flow Meter (Global Water, Gold River, CA). Flow could not 

be taken at all sites at all sampling dates, due to low or no flow or, in some cases, due to 

rapid flow in larger creeks. In specific cases, flow was estimated using the float method 

(timing the movement of an object on the surface) or by measuring volume over time 

(Appendix I). 

Analytical Chemistry. We analyzed for a total of 63 different pesticides, or pesticide 

degradates, in this study. Most of the analysis were from the following pesticide groups: 

pyrethroids, carbamates, OP, fipronil (FP) and FP degradates, synthetic auxin herbicides, 

triazines/triazinones/uracils/ureas (photosynthesis inhibitor herbicides [PI]), and 

dinitroaniline herbicides (Table 1). Although some of the pesticides included in the 

chemical analysis are not urban use pesticides, they were analyzed and reported by the 

laboratory from the same analytical method. 

We report the results as: 1) nd, not detected, concentrations below the minimum detection 

limit; 2) tr, trace detection, where in the chemist’s best professional judgment the analyte 

does exist between the reporting limit and the minimum detection limit; 3) a numerical 

concentration in ng L-1 (pyrethroid water samples), μg L-1 (all other water samples), or 

ng g 

-1 (dry weight; sediment samples). 

QA/QC for Water and Sediment Samples. Quality control for this study followed the 

CDPR SOP guidelines on Chemistry Laboratory Quality Control (Segawa, 1995). Quality 

control consisted of blind spikes, laboratory matrix spikes, method blanks, field 

duplicates, and field blanks. Propazine was also used as a surrogate spike in the PI 

analytical screen. Fifteen percent of the field samples were field duplicates, field blanks, 

or blind spikes. 

Statistics. Statistical analyses was conducted using the non-parametric Mann-Whitley 

mean comparison test, significance at the 0.05 level, with Minitab® Statistical Software 

(Release 15). Regression analysis was also determined using Minitab®, significance also 

at the 0.05 level. 

III. RESULTS AND DISCUSSION 

Pesticides detected in surface waters

Of the 63 pesticides or analytes in the chemical analysis, we detected 30 different 

pesticides (including degradates) above their analytical reporting limit (18 insecticides 

and 12 herbicides). Many pesticides in the analyses were not urban use pesticides and 
6

detections were not expected; nonetheless, 77% of the sampling sites contained at least 

one pesticide. Of the detected pesticides, OC and SAC had the highest detection 

frequency (24 and 20%, respectively), then SFB (14%) with SD having the fewest 

(4.5%). Frequently, more than one pesticide was detected in a water sample, which 

significantly differed among the four different study regions. OC had significantly higher 

median number of pesticides per water sample (6) than did SAC (4), which was 

significantly higher than SFB (2), which was significantly higher than SD (0; p=0.000-

0.135, Figure 3). OC residents tend to have slightly more pest problems than residents in 

northern California which may warrant more pesticide applications (Flint 2003). Our data 

would suggest higher use than the other areas of the study. SD may also have higher 

levels of pesticides in surface water; for example, the San Diego Storm Water 

Department (2010) has recently reported high levels of pyrethroids in this area. And, 

although we report fewer pesticides found at one time in urban streams than in a 10 year 

review by Gilliom et al. (2006), different analyses, sampling regimes, or differences in 

pesticide use (e.g., much reduced urban use of diazinon or chlorpyrifos) may account for 

the differences. 

The most frequently detected insecticides in surface waters were, in decreasing order, 

bifenthrin, fipronil (FP), FP sulfone, carbaryl, desulfinyl FP, malathion, and permethrin 

(Figure 4). Bifenthrin was the most frequently detected insecticide and second most 

detected pesticide in the study, with a 56% detection frequency. The high detection 

frequency was attributed to the high number of detections in SAC and SFB during rain 

runoff. For example, in northern California, bifenthrin dryflow detection frequency was 

27% but increased to 97% during rainstorm events. We had similar dryflow detections of 

bifenthrin in southern California (29%) but because bifenthrin was added later in the 

study, there is no rainstorm sampling of bifenthrin in this part of the state. Because 

rainfall greatly enhances bifenthrin detections, additional sampling during rainstorm 

events in southern California is needed to determine the full contamination of bifenthrin 

in the urban runoff. 

Other pyrethroids were detected in waters samples, albeit infrequently. The detection 

frequency of other pyrethroids in water samples: permethrin (both cis and trans isomers) 

9.7%; cypermethrin 4.2%; esfenvalerate/fenvalerate, cyfluthrin, and λ-cyhalothrin, 1.4%. 

All pyrethroids were detected above their analytical reporting limit. 

Fipronil and degradates were frequently detected. This group had a higher percentage of 

trace detections than detections above their analytical reporting limit. Fipronil had a 30% 

detection frequency; if trace detections are included, detection frequency increased to 

73%. This was also observed for the five degradates (percentage of detections above 

reporting limit, detections including trace detections): 

• FP sulfone (27%; 77%); 

• Desulfinyl FP (17%; 79%); 

• FP amide (4.5%; 64%); 

• Desulfinyl FP amide (3%; 42%); 

• FP sulfide (0.6%; 54%). 
7

Fipronil, FP sulfone, and desulfinyl FP had higher detection frequencies in OC than in 

other areas of California (Figure 5). 

Carbaryl was the fourth most frequently detected insecticide in surface waters (18% 

detection frequency, with trace detections, 28%). Carbaryl was also more frequently 

detected in OC than in other areas of the state (Figure 5). Three OPs were detected. 

Malathion was most frequently detected of these, with a 14% detection frequency (with 

trace detections, 25%). Diazinon and chlorpyrifos were also infrequently detected, with a 

6.5% and 4.5% detection frequency, respectively. The reduced urban detections of 

diazinon and chlorpyrifos over past sampling (Gilliom 2006) are likely due to the drastic 

reduction of these insecticides in urban areas (US EPA 2010a, 2010b). The only other 

insecticide detected in the study was oxamyl (a carbamate), detected once in a water 

sample from southern California. 

The most frequently detected herbicides were 2,4-D, triclopyr, dicamba, diuron, MCPA, 

and pendimethalin (Figure 6). 2,4-D was the most frequently detected pesticide in this 

study and as a group, the synthetic auxin herbicides (2,4-D, triclopyr, dicamba, and 

MCPA) were frequently detected in all areas but SDR. MCPA was also rarely detected in 

OC. For urban use, these four herbicides have similar uses and application timings. 

Frequency of detection ranged from 23% (MCPA) to 65% (2,4-D); detection frequency 

increased from 30% - 72% if trace detections are considered. Diuron was also frequently 

detected (30% detection frequency; with trace detections, 57%). 

The dinitroaniline herbicides pendimethalin, oryzalin, and prodiamine were also detected, 

albeit less frequently than the synthetic auxins and diuron. Their detection frequency 

ranged from 8% - 20% and if trace detections are considered, detection frequency 

increased to 21% - 37% (Figure 6). Of these, pendimethalin had much higher detection 

frequency in SAC (54% detection frequency) than in other areas (SFB was second 

highest, with 19% detection frequency). Prodiamine was only detected in northern 

California. Simazine, prometuron, and oxyfluorfen were detected less than 5% of the 

time. 

Pesticides detected in sediments

We did not detect chlorpyrifos in any sediment samples, but pyrethroids were abundant. 

All of the sediments contained at least one pyrethroid, over half contained at least five 

pyrethroids (median), and up to eight different pyrethroids were detected in one sediment 

sample (Figure 7, A). Bifenthrin was the most frequently detected pyrethroid; it was 

detected in all but two sediment samples. Sediment also commonly contained cyfluthrin, 

permethrin (both cis and trans isomers), deltamethrin λ-cyhalothrin, and cypermethrin; in 

addition esfenvalerate/fenvalerate and resmethrin were detected (Figure 7, B). 

Appendix I contains the complete analytical results (for both water and sediment) for the 

study (Tables A2-A10). 
8

The effect of waterbody type (storm drain vs. creek receiving water) on pesticide

detections in urban surface waters.

There were little differences between detection frequencies between storm drain outflows 

and receiving waters, with most pesticides having less than 10% difference between these 

two different water bodies (Figure 8). Bifenthrin was the main exception. Bifenthrin had 

a 64% detection frequency in stormdrain outflows but only a 36% detection frequency in 

receiving waters. Except for bifenthrin and pendimethalin, there were less than 10% 

differences between detections in receiving waters and stormdrain outflows. For most 

pesticides, sampling at stormdrain outflows gives a good representation of urban runoff 

and is often easier and safer to sample than from larger receiving waters. Other 

pyrethroids may behave like bifenthrin, but we did not have sufficient detections in water 

to make this determination. 

In addition, there were no significant differences in the median number of pesticides 

detected per sample between stormdrain outflows and receiving waters (median 3.0 and 

2.5, respectively; p=0.584). 

The effect of season (dryflow vs. rainstorm) on pesticide detections in urban surface 

waters.

Generally, we detected more pesticides during rainstorms than during dryflow sampling. 

Fipronil (and degradates) were a main contradiction; these were detected frequently 

during both dryflow and rainstorm events (Figure 9). This was biased by detections from 

OC, where dryflow sampling had high detections of fipronil (71% detection frequency) 

and its degradates (up to 77% detection frequency). Although first flush detections (first 

rainstorm of the water year) gave the highest detection frequencies in northern California 

and in San Diego, this was not true in Orange County. Detections of fipronil (and 

degradates) during the first flush in Orange County had similar detection frequencies as 

several of the dryflow sampling events. However, regardless of rain or dryflow sampling, 

detections from northern California correlated well with PUR use (r2

=75%; p=0.006) but 

detections from southern California did not (r2

=28%; p=0.08). The poor correlation in 

southern California was likely due to few detections with low to moderate use in San 

Diego and to high detections in Orange County with moderate use. Although fipronil 

runoff can be influenced by rainfall, it also behaves as other urban use pesticides that 

show a continuous load independent of rain events (Wittmer et al. 2011). The use of 

pesticides that have a continuous load into urban surface waters may be a concern. To 

prevent runoff, overall use would need to decrease, not just use during the rainy season. 

As fipronil use increases, runoff into urban surface waters will likely increase, regardless 

of season. 

All other detected pesticides had detection frequencies between 18-69% higher during 

rainstorm sampling than during dryflow sampling. Bifenthrin was most frequently 

detected pesticide during rainstorms. Although bifenthrin has higher reported use during 

dry weather than during the rainy season (CDPR 2010)2

, detections were higher during 

 

2

Although we cannot account for homeowner use, this use likely follows application timings made by 

professional applicators. 
9

rainstorm sampling. Bifenthrin had a 97% detection frequency during rain sampling 

compared to a 28% detection frequency during dryflow. Rain runoff may be initially 

driving bifenthrin into the water via sediment and organic carbon and keeping it 

suspended. Bifenthrin is known to be tightly bound to sediment and organic carbon. 

During rainstorm sampling events, the median concentrations of TSS, TOC, and turbidity 

were significantly higher than these parameters taken during dryflow sampling 

(p=0.0000-0.0035). 

Herbicides were more frequently detected during rain sampling than during dryflow 

sampling. We had detection frequencies between 26-46% higher during rain sampling 

(Figure 9). In California, many herbicides are applied during the rainy season for residual 

weed control and would be less effective applied at other times of the year. Applications 

during the rainy season increase runoff into surface waters. Two of the herbicides we 

frequently detected, diuron and pendimethalin, had their highest use and detections 

during the rainy season (Figure 10). As use decreased in the spring through summer, the 

number of detections also decreased. Both diuron and pendimethalin had a good 

correlation between use and detections (r2

=85%, p=0.001 and r2=94%, p=0.01, 

respectively). Synthetic auxin herbicides also had higher detections frequencies when 

sampled during rainstorm events than during dryflow. Synthetic auxins are used late in 

the rainy season (March – May) to control flushes of germinated weeds but they also 

have use in the summer months. Although our detections frequencies are higher during 

rain runoff, we also detected synthetic auxins in dryflow sampling. We did not have a 

good correlation between reported use and detections, possibly due to unreported 

homeowner use or to the persistence of some of these herbicides when applied in the late 

summer (Figure 10; August, September) and then are detected in some of the first 

rainfalls of the season (October, November). 

Differences between the number of pesticides per sample during dryflow and rainstorm 

sampling give additional evidence that pesticides tend to runoff into urban surface waters 

when it rains. The median number of pesticides detected per sample during a rainstorm 

event was significantly greater than samples collected during dryflow (median 7.0 and 

1.0, respectively; p=0.000). 

Comparison of Pesticide Concentrations to Aquatic Toxicity Benchmarks

Established aquatic toxicity benchmarks can be used to interpret monitoring data and 

prioritize sites and pesticides for further investigation (US EPA 2010c). For this analysis, 

we used acute benchmarks available from US EPA OPP. But for pyrethroids we used 

established H. azteca LC50s (where available) due to the sensitivity of this organism to 

pyrethroids (Anderson et al. 2006, Weston and Jackson 2009). In water samples, we 

detected eleven pesticides above their benchmarks or LC50s (Table 2). In all, 76% of the 

sampling sites had at least one pesticide above its benchmark/LC50. This value 

comparable to the 83% value for urban streams as stated by Gilliom et al. (2006) during a 

10 year review (1992-2001) of USGS data. Any differences are likely due to changes in 

urban insecticide use that has occurred (decreased chlorpyrifos and diazinon use offset 

with increased pyrethroid use), as well as different sampling sites and monitoring 

regimes. Of OPs, we only detected chlorpyrifos twice above its benchmark value and 

malathion once, all in northern California. Pyrethroids (mostly bifenthrin), fipronil, and 
10

diuron were the only other pesticides detected at concentrations above their toxicity 

benchmarks. None of the other pesticides were detected above their benchmarks. 

Pyrethroids were frequently detected above their LC50s and this group of pesticides had 

the highest percentage of detections with the potential to be toxic to sensitive aquatic 

organisms. Pyrethroids are highly hydrophobic and associate with the dissolved organic 

carbon and suspended sediment in water samples which may limit their bioavailability. 

Taking these factors into consideration with the equation by Spurlock et al. (2005) and 

using the Koc value of 240000 (NPIC 2011), the bioavailability of bifenthrin ranged 

between 14% - 58% of the total concentrations. With these values, we would expect that 

approximately 20% of the bifenthrin detections would be toxic to H. azteca. However, 

Koc values are highly variable. For bifenthrin, Laskowski (2002) lists a range of Koc

values from 116000 – 888000 ml g-1. Based on this range of uncertainty in Koc, the 

estimated fraction of bifenthrin detections with bioavailable concentrations sufficiently 

high to cause toxicity to H. azteca ranged between 3% and 30%. We cannot know 

precisely what the overall toxic potential for bifenthrin was in the urban waterways where 

we sampled. However, it is likely that some of the bifenthrin would have been available 

for uptake and toxicity to sensitive aquatic species in these waterways. 

Although infrequently detected, cyfluthrin, cypermethrin, λ-cyhalothrin, and 

esfenvalerate were all detected above their respective benchmarks/LC50s. Half of all the 

permethrin detections were also above its benchmark (Table 2, estimated bioavailability) 

Fipronil had the second highest number of detections above its US EPA toxicity 

benchmark, with 20 detections (13% of all fipronil detections). Most of these detections 

above the benchmark (80%) were from OC, mostly during dryflow sampling. The 

fipronil degradates FP sulfone (MB46136) and FP sulfide (MB45950) are more toxic 

than fipronil itself (FAN 2010) even though fipronil has a lower benchmark. Using EPA 

benchmark values, Mize (et al. 2008) estimated LC50 values for the sulfone and sulfide 

degradates to be 0.06 and 0.22 μg L-1, respectively, for sensitive species. Using these 

LC50s, FP sulfone was detected 36 times (23% of FP sulfone total detections, mostly in 

OC) over its LC50. Likely FP sulfone has the potential to contribute to toxicity in these 

waters. No other fipronil degradates were detected above benchmarks (we could not find 

any toxicity values for desulfinyl FP or desulfinyl FP amide). This data also indicates that 

most of the potential toxicity of fipronil was in OC. 

Diuron was the only herbicide that was detected above its US EPA benchmark for nonvascular plants. Eight water samples (5% of total) contained concentrations above its 

benchmark; all were detected in northern California, mostly during rainstorm sampling. 

In past work, the potential importance of diuron toxicity to the overall food chain has 

been overshadowed by pesticides that cause toxicity to aquatic invertebrates (Munn et al. 

2006, Sprague and Nowell 2008). The ecological importance of diuron toxicity to 

phytoplankton is not well understood (Jassby et al. 2003, Miller et al. 2005, Sommer et 

al. 2007). 
11

In pesticide risk assessment, toxicity is usually based on exposure to one stressor or 

contaminate. However, it is more common for aquatic organisms to be exposed to 

multiple stressor or contaminants, often in complex mixtures of herbicides and 

insecticides. For example, our results show that 50% of the water from one site contained 

3 or more pesticides, 25% of the sites contained six or more pesticides, and 15% of the 

sites contained eight or more pesticides. Other work has shown similar results (Gilliom 

2006). The accumulated number of pesticides found at one time likely has a negative 

effect on overall stream health. Generally, pesticides within the same pesticide class (with 

a common mode of action) are likely to have an additive effect whereas pesticides from 

different chemistry classes are likely to have more varied effects, such as synergism or 

antagonism (Lydy and Belden 2006). However, little is known about interactions among 

multiple pesticides on the toxicity to aquatic organisms as all chemical combinations 

(pairs, triplets, etc.) are impossible to investigate (Lydy and Belden 2006). These 

combinations, in addition to other chemical contaminants (e.g., metals and salts) and 

physical stressors (as dissolved oxygen concentrations, temperature, and habitat 

degradation) likely interact to degrade natural habitats. Our work suggests that multiple 

pesticide stressors are common occurrences in urban surface waters and that toxicity tests 

should investigate these interactions. 

Water Quality

Water temperature, pH, EC, turbidity, DO, TSS, and TOC were measured in this study. 

DO, pH, and EC have specific water quality objectives and generally were within water 

quality objectives. DO exceeded water quality objectives 20% of the time but pH and EC 

only exceeded the objectives 2% and 9% of the time, respectively. Median concentrations 

of turbidity (3.1 NTU), TSS, and TOC were low (6.6 and 7.8 ppm, respectively). There 

were little differences in water quality between stormdrain outflows and receiving waters 

but there were some water quality differences between northern and southern California, 

and between dryflow and rain runoff. All of the water quality parameters can be found in 

the Appendix I, Tables A11 - A15. 

Quality Control

Quality control was acceptable for the study. Ninety-eight percent of all matrix and 

propazine spikes were recovered within acceptable levels and there were no detections in 

the lab blanks. Appendix II has more detailed information about quality control. 

IV. CONCLUSIONS 

The main conclusions from the study are listed below. 

1. Urban water bodies contain numerous pesticides at any given time. We detected 30 

different pesticides and degradates. The main insecticides detected in water samples 

were bifenthrin, fipronil, fipronil sulfone, carbaryl, desulfinyl fipronil, and malathion. 

The main herbicides detected were 2,4-D, triclopyr, dicamba, diuron, MCPA, and 

pendimethalin. 
12

2. Urban surface waters often contain more than one pesticide. Fifty percent of the 

sampled waters had three or more pesticides and 25% of the sampled waters had six 

or more pesticides. 

3. Fipronil, fipronil sulfone, desulfinyl fipronil, and carbaryl occur at higher frequencies 

in Orange County (greater Los Angeles area) than in other areas of California. 

4. San Diego area had fewer pesticide detections than did other areas of the study. 

5. Diazinon and chlorpyrifos are still detected in urban waters, albeit infrequently. 

6. Pyrethroids are found in urban surface waters. Bifenthrin is the main pyrethroid (56% 

detection frequency) followed by permethrin (10% detection frequency). In urban 

surface waters, only about one-third of the pyrethroid concentration is bioavailable to 

aquatic organisms. 

7. Sediments contain numerous pyrethroids and pyrethroids are more likely to occur in 

sediments than in water. Bifenthrin was most frequently detected (95% detection 

frequency), but cyfluthrin, cypermethrin, deltamethrin λ-cyhalothrin, and permethrin 

were common contaminants of urban sediments (32%-78% detection frequency). 

8. Rainstorms drive most pesticides into urban surface waters. Bifenthrin, diuron, 

MCPA, 2,4-D, malathion, dicamba, triclopyr, pendimethalin, and carbaryl are more 

frequently found during rain runoff than during dryflow sampling. 

9. Fipronil (and degradates) can be found frequently in urban surface waters during 

dryflow. Although rain may increase runoff, it is not needed to transport fipronil into 

urban surface waters. 

10. Pesticides are detected in storm drain outflows and receiving waters with about equal 

frequency, except for bifenthrin (and perhaps other pyrethroids). Bifenthrin is more 

commonly found in stormdrain outflows than in receiving waters. 

11. Bifenthrin, fipronil, and diuron are detected in water at concentrations that potentially 

could be toxic to aquatic life. Other pyrethroids are infrequently detected but at 

concentrations that potentially could be toxic to aquatic organisms. Fipronil sulfone 

may also have toxicological concerns. 

From this work, we can make recommendation for future research: 

1. Southern California, and especially the Orange County area, had high detections of 

insecticides. Other high urban use insecticides (i.e., imidacloprid) should be 

monitored to determine the extent of total insecticide runoff. We also had little storm 

runoff data for bifenthrin in Southern California; additional monitoring of bifenthrin 

during rainstorm events is warranted. Bioavailable concentrations of bifenthrin need 

to be estimated in monitoring studies. 

2. Determine if other high urban use pesticides, like the fungicide chlorothalonil, are 

common contaminants of urban surface waters. 

3. More work in the San Diego area is warranted to determine if the low level of 

detections are typical to this area. Future studies in the San Diego area should look at 

additional neighborhoods and creek sites to determine the extent of pesticide runoff. 

4. Additional monitoring of fipronil during dryflow is warranted to determine if runoff 

is related to use rather than rainfall. Sampling should occur monthly, at the end of the 

month, to correspond with PUR monthly use summaries. 

5. Determine if diuron and pendimethalin detections during rainy season occur only 

during rain runoff or if they are common in the rainy season when it is not raining. 
13

6. Conduct toxicity testing with two-way and three-way mixtures of pesticides 

commonly found in urban waters. Tests should include algae and aquatic 

invertebrates common to California. 

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18

Table 1. Pesticides analyzed by the California Department of Food and Agriculture in 

water or sediment, with their method detection and reporting limits, and holding times. 

Specific methods can be found at 

http://www.cdpr.ca.gov/docs/emon/pubs/em_methd_main.htm. 

Analyte Group (method) 

Method 

Detection Limit 

(μg L-1) 

Reporting 

Limit (μg 

L-1) 

Holding 

time 

(days) 

Carbamate Insecticides (HPLC; method EMON-SM 11.3) 

Analytes: aldicarb, aldicarb sufoxide, aldicarb 

sulfone, methomyl, carbofuran, 3-OH 

carbofuran, carbaryl, oxamyl, methiocarb 

0.01 – 0.02 0.05 28 

(acidified)

Fipronil Insecticides (GC/MSD in SIM mode; method EMON-SM 05-013) 

Analytes: fipronil (FP), desulfinyl FP, 

desulfinyl FP amide, FP sulfide, FP sulfone, 

FP amide 

0.003 – 0.005 0.05 14 

Organophosphorus Insecticides in Water (method EMON-SM 46-0) 

Analytes by GC/FPD: azinphos methyl, 

dichlorvos, dimethoate, disulfoton, ethoprop, 

fenamiphos, fonofos, malathion, 

methidathion, methyl parathion, phorate, 

profenofos, tribufos (plant growth regulator - 

defoliant) 

0.008 – 0.0142 0.03 – 

0.05 7 

Analytes by GC/MS: chlorpyrifos, diazinon 0.0008 – 0.0012 0.01 7 

Pyrethroid Insecticides (GC-ECD; water method, EMON-SM 05-003; sediment 

method EMON-SM 52.9) 

Water 0.001 – 0.008 0.005 – 

0.015 4 Analytes: bifenthrin, cyfluthrin, 

cypermethrin, 

deltamethrin/tralomethrin, 

esfenvalerate/fenvalerate, 

fenpropathrin, λ-cyhalothrin, 

permethrin (cis, trans), resmethrin 

Sediment 

(μg kg-1) 0.107 – 0.183 1.0 183 

Triazine/Triazinone/Uracil/Urea Herbicides (LC/MC/MC; method EMON-SM 62.9)

Analytes: atrazine, ACET (deisopropyl 

atrazine), bromacil, DACT (diamino 

chlorotriazine), DEA (deethyl atrazine),

diuron, hexazinone, metribuzin, prometon, 

prometryn, simazine and norflurazon (a 

phytoene desaturase inhibitor) 

0.01 – 0.04 0.05 14 
19

Table 1 continued. 

Synthetic Auxin Herbicides (GC/MS; method EMON-SM 05-012) 

Analytes: 2,4-D, dicamba, MCPA, triclopyr 

0.064 0.1 12 

Dinitroaniline Herbicides (GC/TQMS or LCQ; method EMON-SM 05-006) 

Analytes: benfluralin, ethalfluralin, oryzalin, 

pendimethalin, prodiamine, trifluralin, 

oxyfluorfen (diphenyl ether herbicide) 

0.0048 – 0.015 0.05 14 

Table 2. Detection frequencies (above reporting limits) of pesticides detected above US 

EPA benchmark or commonly accepted LC50 values in water samples (N = 155; 

pyrethroids, N = 72). 

Detection Frequency (DF) 

Pesticide Benchmark 

(μg L-1)

A

DF for the Study DF greater than 

benchmark or LC50

Diuron 2.4 30% 5% 

Fipronil (FP) 0.11 30% 13% 

FP sulfone 0.36 27% 0.6% 

Chlorpyrifos 0.05 4.5% 1.3% 

Malathion 0.3 14% 0.6% 

Benchmark or 

LC50 (ng L-1) 

--Pyrethroid DF above 

estimated bioavailable 

concentrationE

-- 

BifenthrinB 7.7 56% 20% 

PermethrinA,C 10 11.1% 5.6% 

CyfluthrinB 2.3 1.4% 1.4% 

λ-CyhalothrinA 3.5 1.4% 1.4% 

CypermethrinB 2.3 4.2% 4.2% 

EsfenvalerateA, D 25 1.4% 1.4% 

A Lowest acute fish or invertebrate benchmark (US EPA 2010c) 

B Hyalella azteca LC50 (Weston and Jackson 2009) C Both cis and trans isomers 

D Analysis does not differentiate between esfenvalerate and fenvalerate 

E Using equation from Spurlock et al. (2005) and Koc values from PPDB (2011) and NPIC (2011).
20

Figure 1. Sampling sites for CDPR’s urban monitoring project in the Sacramento, San 

Francisco Bay, greater Los Angeles (Orange County), and San Diego areas, California. 
21

Figure 2. Cartoon depicting a storm drain outflow and receiving water (from

http://www.stormwater.co.trumbull.oh.us/).

storm drain outflow

storm drain 

receiving water 
22

Figure 3. Number of pesticides detected in water samples collected from urban creeks 

and storm drain outflows in the four different sampling areas of California (Sacramento 

[SAC], San Francisco Bay [SFB], greater Los Angeles [OC], and San Diego [SD] areas 

of California, USA) and in samples combined from all four sampling areas. All 

detections were above the analytical reporting limit; * indicates the median number of 

pesticides detected per water sample.

0%

5%

10%

15%

20%

25%

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Percentage of samples

SAC

*

0%

5%

10%

15%

20%

25%

0 1 2 3 4 5 6 7 8 9 10 11 12 13

OC *

0%

5%

10%

15%

20%

25%

30%

35%

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Number of Pesticides Detected in Water Samples

Percentage of samples

SFB

*

0%

5%

10%

15%

20%

25%

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Number of Pesticides Detected in Water Samples

Percentage of Samples

All Areas

*

0%

10%

20%

30%

40%

50%

60%

70%

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Number of Pesticides Detected in Water Samples

* SD
23

0%

10%

20%

30%

40%

50%

60%

70%

Bif FP FP

So

Carb Ds

FP

Mala Per Diaz Chlr FP

Am

Cyp DsFP

Am

 FP 

Si

Detection Frequenc

y

Detection > RL Trace Detection (MDL-RL)

Figure 4. Detection frequency of insecticides from all sampling areas of California 

between April 2008 and August 2009. Bif, bifenthrin; FP, fipronil; FP So, FP sulfone; 

Carb, carbaryl; Ds FP, desulfinyl FP; Mal, malathion; Per, cis and trans-permethrin; Diaz, 

diazinon; Chlr, chlorpyrifos; FP Am, FP amide; Cyp, cypermethrin; Ds FP Am, DSFP 

amide; FP Si, FP sulfide. There was also one detection each of cyfluthrin, λ-cyhalothrin, 

esfenvalerate/fenvalerate, and oxamyl. RL, reporting limit; MDL, minimum detection 

limit. 

Figure 5. Detection frequency of fipronil, fipronil sulfone, desulfinyl fipronil, and 

carbaryl in the four different sampling areas of California (Sacramento [SAC], San 

Francisco Bay [SFB], greater Los Angeles [OC], and San Diego [SD] areas of California, 

USA). All detections were above the analytical reporting limit.

0%

20%

40%

60%

80%

Detection Frequency

Fipronil

0%

20%

40%

60%

80%

Fipronil 

Sulfone

0%

20%

40%

60%

80%

SAC SFB OC SDR

Detection Frequency

Desulfinyl 

Fipronil

0%

10%

20%

30%

40%

SAC SFB OC SDR

Carbaryl
24

0%

10%

20%

30%

40%

50%

60%

70%

2,4-D Tric Dica Diur MCPA Pend Oryz Prod Simz Prom Oxyf

Detection Frequenc

y

Detection > RL Trace Detection (MDL-RL)

Figure 6. Detection frequency of herbicides from all sampling areas of California 

between April 2008 and August 2009. Tric, triclopyr; Dica, dicamba; Diur, diuron; Pend, 

pendimethalin; Oryz, oryzalin; Prod, prodiamine; Simz, simazine; Prom, prometon; Oxyf, 

oxyfluorfen. There was also one detection of ACET (deisopropyl atrazine), one trace 

detection of bromacil, and one trace detection of trifluralin. RL, reporting limit; MDL, 

minimum detection limit. 

Figure 7. Detections of pyrethroids in sediments from all sampling areas of California. 

A, percentage of pyrethroid detections per sample (* indicates the median number of 

pyrethroids detected). B, detection frequency of pyrethroids in sediment samples (Bif, 

bifenthrin; Cyf, cyfluthrin; Cyp, cypermethrin; Del, deltamethrin; Esf, 

fenvalerate/esfenvalerate; λ-Cyh, λ-cyhalothrin; cPer, tPer, cis- and trans- permethrin; 

Res, resmethrin). 

0%

5%

10%

15%

20%

25%

30%

0123456789

Number of Pyrethroids Detected in one Sediment Sample

Percentage of Samples

*

A

0%

20%

40%

60%

80%

100%

Bif Cyf Cyp Del Esf λ-Cyh cPer tPer Res

Pyrethroids Detected in Sediment Samples

Detection Frequency

B
25

-10%

0%

10%

20%

30%

Bif Pend FP 2,4-D MCPA FP So Mala Dica DsFP Carb

Pesticide

Detection Frequency (DF) Difference

(DF stormdrain outflow samples - 

DF receiving water samples) i

positive value = higher DF in stormdrain outflows (by the indicated value)

negative value = higher DF in receiving waters (by the indicated value)

Diur Tric

Figure 8. The influence of waterbody on frequency of pesticide detections. Detection 

Frequency (DF) differences were determined by subtracting the detection frequency of 

stormdrain outflow samples from the detection frequency of receiving water (DF 

receiving water – DF stormdrain outflow). Thus, a positive value on the y-axis (Detection 

Frequency Difference) indicates higher detection frequency in stormdrain outflows and a 

negative value indicates a higher detection frequency in receiving waters. Bif, bifenthrin; 

Pend, pendimethalin; FP, fipronil; FPSo, FP sulfone; Mala, malathion; Dica, dicamba; 

DsFP, desulfinyl FP; Carb, carbaryl; Diur, diuron; Tric, triclopyr. Only pesticides or 

degradates detected with a greater than 10% detection frequency during the entire study 

are included in the figure. 
26

-20%

-10%

0%

10%

20%

30%

40%

50%

60%

70%

80%

Bif Diur MCPA 2,4-D Mala Dica Tric Pend Carb FP FPSo DsFP

Pesticide

Detection Frequency (DF) Difference 

(DF rain samples - DF dryflow samples) i

positive value = higher DF during rainstorm events (by the indicated value)

negative value = higher DF during dryflow events (by the indicated value)

Figure 9. The influence of rain on frequency of pesticide detections. Detection Frequency 

(DF) differences were determined by subtracting the detection frequency of dryflow 

samples from the detection frequency of rainstorm samples (DF rainstorm – DF dryflow). 

Thus, a positive value on the y-axis (Detection Frequency Difference) indicates higher 

detection frequency during rainstorm sampling (by the indicated value) and a negative 

value indicates a higher detection frequency during dryflow sampling). Bif, bifenthrin; 

Diur, diuron; Mala, malathion; Dica, dicamba; Tric, triclopyr; Pend, pendimethalin; Carb; 

carbaryl; FP, fipronil; FPSo, FP sulfone; DsFP, desulfinyl FP. Only pesticides or 

degradates detected with a greater than 10% detection frequency during the entire study 

are included in the figure.
27

Figure 10. PUR reported use of diuron, pendimethalin, and synthetic auxin herbicides 

(2,4-D, dicamba, MCPA, and triclopyr) and their detection ratios. The detection ratio is 

the number of detections (greater than the reporting limit) per number of sampling events 

for that particular month. A detection frequency of 1.0 indicates that one pesticide was 

detected at one site. PUR use data was an average of 2008 – 2009 for the counties 

sampled, except: point a (pendimethalin), sampled only in southern California, x 

indicates actual use for the collected samples and this data was used in the correlation. 

0

400

800

1200

1600

2000

J FMAMJ J ASOND

Month

Pendimethalin Use (lb ai) i

0

0.1

0.2

0.3

0.4

0.5

0.6

Detection Ratio

a

0

3000

6000

9000

12000

J FMAM J J ASOND

Month

Diuron Use (lb. ai)

0

0.2

0.4

0.6

0.8

Detection Ratio

0

500

1000

1500

2000

2500

3000

3500

4000

4500

J FMAMJ JASOND

Month

Synthetic Auxin Use (lb ai) i

0

0.5

1

1.5

2

2.5

3

3.5

Detection Ratio

3

4

5

Use Detection Ratio
28

VI. APPENDIX I. DATA Appendix I contains data for the urban study, April 2008 – August 2009. Abbreviations commonly used in the Appe

Abbreviation Definition FP fipronil mv missing value, not data available or site not sampled nd not detected ppm parts per million (mg L-1) RW receiving water StDr storm drain outflow tr trace detection (below the reporting limit but above the 

minimum detection limit). 
29

Table A1. Characteristics of the sampling sites in Study 249. 

Datum: WGS84 (De

degrees) Watershed Site Location Site ID Site Type Urban Land Use 

Approximate 

Area 

(Acres) 

Approximate 

Residence 

Number Longitude Latitu

Grayson 

Creek 

Shadowood Park 

between 

Chilpancingo 

Parkway and 2nd 

Avenue South 

GRY010 Storm Drain 

Mixed 

residential 

and 

commercial 

320 600 37.97967 -122.0

Grayson 

Creek 

Blackwood Ave. and 

2nd Ave South GRY020 Storm Drain 

Mixed 

residential 

and 

commercial 

670 1200 37.98097 -122.0

Grayson Creek 

Grayson Creek at Center Avenue GRY030 Receiving Water 

Mixed residential and commercial 

37.983549 -122.0

Martin 

Canyon/ 

Koopman 

Canyon 

Creek 

Donohue Drive at 

Fire Station MCC010 Storm Drain Mostly residential 500 1300 37.70922 -121.9

Martin 

Canyon/ 

Koopman 

Canyon 

Creek 

End of Millbrook 

Avenue MCC020 Storm Drain Mostly residential 225 650 37.71668 -121.9

Martin 

Canyon/ 

Koopman 

Canyon 

Creek 

Dublin Blvd by 

Safeway and I-680 MCC030 Storm Drain 

Mixed 

residential 

and 

commercial 

290 450 37.70686 -121.9

Martin 

Canyon/ 

Koopman 

Canyon 

Creek 

Dublin Blvd by 

Safeway and I-680 MCC040 Receiving Water 

Mixed 

residential 

and 

commercial 

 37.706412 -121.9

Pleasant 

Grove 

Creek 

Dr. Paul J. Dugan 

Park on Diamond 

Woods Circle 

PGC010 Storm Drain Mostly residential 50 250 38.80477 -121.3
30

Table A1 continued.

Watershed Site Location Site ID Site Type Urban Land Use 

Approximate 

Area 

(Acres) 

Approximate 

Residence 

Number 

Datum: WGS84 (De

degrees) 

Pleasant 

Grove 

Creek 

Opal and Parkside 

Way, righthand side 

of stream 

PGC020 Storm Drain Mostly residential 150 450 38.80232 -121.3

Pleasant 

Grove 

Creek 

At Crocker Ranch 

Road PGC030 Storm Drain Mostly residential 85 300 38.79908 -121.3

Pleasant 

Grove 

Creek 

At Veteran's 

Memorial Park PGC040 Receiving Water Mostly residential 38.79857 -121.3

Salt Creek South neighborhood (contributing) SC 1 Storm Drain Mostly residential 96 460 33.50908 -117.6Salt Creek North neighborhood (contributing) SC 3 Storm Drain Mostly residential 120 245 33.51197 -117.6Salt Creek Below Niguel Road bridge SC 5 Receiving Water Mostly residential 33.50547 -117.

Wood 

Canyon 

Above constructed 

wetland WC 1 Storm Drain Mostly residential NA1 NA 33.58247 -117.7

Wood 

Canyon 

Below constructed 

wetland WC 2 Storm Drain Mostly residential 194 283 33.58155 -117.7

Wood 

Canyon 

South neighborhood 

(contributing) WC 3 Storm Drain Mostly residential 66 307 33.58158 -117.7

Wood 

Canyon 

Receiving water 

below storm drains AV01 Receiving Water Mostly residential 33.58131 -117.7

San Diego 

River 

At Fashion Valley 

Road SDR101 Receiving Water 

Mixed 

residential 

and 

commercial 

 32.76436 -117.1

San Diego 

River 

Above Fashion Valley 

Road SDR102 Storm Drain 

Mixed 

residential 

and 

commercial 

NA NA 32.76528 -117.1

San Diego 

River 

At Camino de la 

Reina SDR103 Storm Drain Commercial NA NA 32.76568 -117.1

San Diego 

River 

Camino de la Reina 

& Camino Del Arroyo SDR104 Storm Drain 

Mixed 

residential 

and 

commercial 

NA NA 32.76679 -117.1
31

Table A1 continued.

Watershed Site Location Site ID Site Type Urban Land Use 

Approximate 

Area 

(Acres) 

Approximate 

Residence 

Number 

Datum: WGS84 (De

degrees) 

Lindo 

Lake At Lindo Lake SDR151 Storm Drain Mostly residential NA NA 32.85731 -116.9

Lindo 

Lake At Lindo Lake SDR156 Storm Drain Mostly residential NA NA 32.85724 -116.9

Lindo 

Lake At Lindo Lake SDR158 Receiving Water Mostly residential 32.85715 -116.9

1Data not available Table A2. Detections of insecticides in water samples from Sacramento area sampling sites. Concentrations are in μg 

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

Carbaryl 

Desulfinyl 

fipronil 

Desulfinyl FP 

amide 

Fipronil 

Fipronil 

amide 

Fipronil 

sulfide 

Fipronil 

sulfone 

Chlorpyrifos 

Malathion 

Bifenthrin 

(ng L-1) 

Cyfluthrin 

4/21/2008 PGC010 StDr Dryflow nd tr nd tr nd nd tr nd nd mv m4/21/2008 PGC020 StDr Dryflow 0.065 tr nd tr nd nd tr nd tr mv m4/21/2008 PGC030 StDr Dryflow nd 0.054 tr 0.064 tr tr 0.118 nd nd mv m4/21/2008 PGC040 RW Dryflow nd tr tr tr tr tr 0.078 nd nd mv m6/23/2008 PGC010 StDr Dryflow nd tr tr tr tr tr tr nd nd mv m6/23/2008 PGC020 StDr Dryflow tr tr tr 0.164 tr tr tr nd nd mv m6/23/2008 PGC030 StDr Dryflow nd tr nd tr nd nd tr nd nd mv m6/23/2008 PGC040 RW Dryflow nd tr nd tr nd nd tr nd nd mv m

8/4/2008 PGC010 StDr Dryflow nd tr tr tr tr tr 0.064 nd nd mv m8/4/2008 PGC020 StDr Dryflow nd tr tr tr tr tr tr nd nd mv m8/4/2008 PGC030 StDr Dryflow nd tr tr 0.066 tr tr tr nd nd mv m8/4/2008 PGC040 RW Dryflow nd tr tr 0.061 tr tr tr nd nd mv m

11/1/2008 PGC010 StDr Rain tr tr tr 0.107 tr tr 0.059 nd tr mv m11/1/2008 PGC020 StDr Rain 0.129 tr tr 0.146 tr tr 0.064 nd 0.357 mv m11/1/2008 PGC030 StDr Rain nd tr tr 0.064 tr tr tr nd tr mv m11/1/2008 PGC040 RW Rain tr tr nd tr tr tr tr nd tr mv m2/13/2009 PGC010 StDr Rain nd tr tr 0.057 tr tr tr nd tr 203 n
32

Table A2 continued.

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

Carbaryl 

Desulfinyl 

fipronil 

Desulfinyl FP 

amide 

Fipronil 

Fipronil amide 

Fipronil sulfide 

Fipronil 

sulfone 

Chlorpyrifos 

Malathion 

Bifenthrin 

(ng L-1) 

Cyfluthrin 

2/13/2009 PGC020 StDr Rain nd tr tr 0.118 tr tr 0.058 nd 0.040 48.5 n2/13/2009 PGC030 StDr Rain nd tr tr 0.067 tr nd tr nd nd 43.6 n2/13/2009 PGC040 RW Rain nd tr nd tr nd nd tr nd nd 17 n

4/7/2009 PGC010 StDr Rain nd tr nd tr nd nd tr nd 0.048 98.5 n4/7/2009 PGC020 StDr Rain nd tr nd tr nd nd tr nd 0.121 19.2 n4/7/2009 PGC030 StDr Rain nd tr nd tr tr nd tr nd nd 46.7 n4/7/2009 PGC040 RW Rain nd tr nd tr tr nd tr nd nd 7.74 n

4/13/2009 PGC010 StDr Dryflow mv mv mv mv mv mv mv mv mv 25.7 n4/13/2009 PGC020 StDr Dryflow mv mv mv mv mv mv mv mv mv 8.58 n4/13/2009 PGC030 StDr Dryflow mv mv mv mv mv mv mv mv mv 20.8 14/13/2009 PGC040 RW Dryflow mv mv mv mv mv mv mv mv mv nd n

5/1/2009 PGC010 StDr Rain tr tr nd tr nd nd tr nd 0.068 20.3 n5/1/2009 PGC020 StDr Rain nd tr nd tr nd nd tr nd 0.064 14.5 n5/1/2009 PGC030 StDr Rain nd tr nd tr tr nd tr 0.012 0.192 20.1 n5/1/2009 PGC040 RW Rain tr tr nd tr nd nd tr nd 0.040 8.87 n

8/27/2009 GRY010 StDr Dryflow nd nd nd nd tr tr tr nd nd nd n8/27/2009 GRY020 StDr Dryflow nd nd nd nd nd tr nd nd nd nd n8/27/2009 GRY030 RW Dryflow nd tr nd nd nd nd nd nd nd nd n8/27/2009 MCC010 StDr Dryflow nd nd nd nd tr nd nd nd nd nd n8/27/2009 MCC020 StDr Dryflow nd nd nd nd nd nd tr nd nd nd n8/27/2009 MCC030 StDr Dryflow nd nd nd nd tr nd nd nd nd nd n8/27/2009 MCC040 RW Dryflow nd nd nd nd tr nd nd nd nd nd n
33

Table A3. Detections of insecticides in water samples from San Francisco Bay area sampling sites. Concentrations aspecified. 

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

Carbaryl 

Desulfinyl 

fipronil 

Desulfinyl FP 

amide 

Fipronil 

Fipronil amide 

Fipronil sulfide 

Fipronil 

sulfone 

Chlorpyrifos 

Diazinon 

Malathion 

4/22/2008 GRY010 StDr Dryflow nd nd nd tr tr tr tr nd nd nd 4/22/2008 GRY020 StDr Dryflow nd nd nd nd nd nd nd nd nd nd 4/22/2008 GRY030 RW Dryflow nd tr nd nd nd nd nd nd nd nd 4/22/2008 MCC010 StDr Dryflow nd nd nd nd tr nd nd nd nd nd 4/22/2008 MCC020 StDr Dryflow nd nd nd nd nd nd tr nd nd nd 4/22/2008 MCC030 StDr Dryflow nd nd nd nd nd nd nd nd nd nd 4/22/2008 MCC040 RW Dryflow nd nd nd nd nd nd nd nd nd nd 6/24/2008 GRY010 StDr Dryflow tr nd nd tr nd tr nd nd nd nd 6/24/2008 GRY020 StDr Dryflow nd nd nd nd nd nd nd nd nd nd 6/24/2008 GRY030 RW Dryflow nd nd nd tr nd nd nd nd nd nd 6/24/2008 MCC010 StDr Dryflow nd nd nd nd tr nd nd nd nd nd 6/24/2008 MCC020 StDr Dryflow nd tr nd nd nd nd nd nd nd nd 6/24/2008 MCC030 StDr Dryflow nd nd nd nd nd nd nd nd nd nd 6/24/2008 MCC040 RW Dryflow nd nd nd nd tr nd nd nd nd nd 

8/6/2008 GRY010 StDr Dryflow nd tr nd tr tr tr tr nd nd nd 8/6/2008 GRY020 StDr Dryflow nd tr nd tr tr tr tr nd nd nd 8/6/2008 GRY030 RW Dryflow nd tr nd tr tr tr tr nd nd nd 8/5/2008 MCC010 StDr Dryflow nd tr tr tr tr tr tr nd nd nd 8/5/2008 MCC020 StDr Dryflow nd tr tr tr tr tr tr nd nd nd 8/5/2008 MCC030 StDr Dryflow nd tr tr tr tr tr tr nd nd nd 8/5/2008 MCC040 RW Dryflow nd tr nd tr tr tr tr nd nd nd 

11/1/2008 GRY010 StDr Rain nd tr nd 0.061 tr tr tr nd nd nd 11/1/2008 GRY020 StDr Rain 0.294 0.059 nd 0.458 tr tr 0.085 nd nd nd 11/1/2008 GRY030 RW Rain 0.28 tr nd tr tr tr tr nd nd nd 11/1/2008 MCC010 StDr Rain nd tr nd 0.05 tr tr tr nd nd 0.075 11/1/2008 MCC020 StDr Rain nd tr nd tr tr tr tr nd nd tr 11/1/2008 MCC030 StDr Rain tr tr nd 0.078 tr tr tr nd nd tr 11/1/2008 MCC040 RW Rain nd tr nd tr tr tr tr nd nd nd 2/15/2009 GRY010 StDr Rain nd tr nd tr tr tr tr 0.0104 nd nd 2/15/2009 GRY020 StDr Rain nd tr nd tr tr tr tr nd 0.0547 nd 2/15/2009 GRY030 RW Rain nd tr nd tr tr nd tr 0.0228 0.0388 nd 2/15/2009 MCC010 StDr Rain nd tr nd tr tr nd tr 0.014 0.0414 nd 
34

Table A3 continued.

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

Carbaryl 

Desulfinyl 

fipronil 

Desulfinyl FP 

amide 

Fipronil 

Fipronil 

amide 

Fipronil 

sulfide 

Fipronil 

sulfone 

Chlorpyrifos 

Diazinon 

Malathion 

2/15/2009 MCC020 StDr Rain nd tr tr tr tr nd tr 0.0229 0.0432 nd 2/15/2009 MCC030 StDr Rain nd tr nd tr nd nd tr 0.0539 0.0458 nd 2/15/2009 MCC040 RW Rain nd tr nd tr nd nd tr 0.0507 nd nd 

4/7/2009 GRY010 StDr Rain nd tr nd tr tr nd tr nd nd 0.079 4/7/2009 GRY020 StDr Rain nd tr nd tr tr nd tr nd nd 0.06 4/7/2009 GRY030 RW Rain 0.094 tr nd tr tr nd tr nd nd 0.055 

4/14/2009 GRY010 StDr Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 GRY020 StDr Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 GRY030 RW Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 MCC010 StDr Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 MCC020 StDr Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 MCC030 StDr Dryflow mv mv mv mv mv mv mv mv mv mv 4/14/2009 MCC040 RW Dryflow mv mv mv mv mv mv mv mv mv mv 

5/1/2009 GRY010 StDr Rain tr tr nd 0.067 tr tr tr nd nd nd 5/1/2009 GRY020 StDr Rain 0.069 tr nd tr tr tr tr nd nd nd 5/1/2009 GRY030 RW Rain 0.187 tr nd tr nd nd tr nd nd tr 5/1/2009 MCC010 StDr Rain tr tr nd tr nd nd tr nd nd tr 5/1/2009 MCC020 StDr Rain tr tr nd tr nd nd tr nd nd nd 5/1/2009 MCC030 StDr Rain 0.119 tr nd tr nd nd tr nd nd nd 5/1/2009 MCC040 RW Rain 0.369 tr nd tr nd nd tr nd nd tr 

8/27/2009 GRY010 StDr Dryflow nd nd nd nd tr tr tr nd nd nd 8/27/2009 GRY020 StDr Dryflow nd nd nd nd nd tr nd nd nd nd 8/27/2009 GRY030 RW Dryflow nd tr nd nd nd nd nd nd nd nd 8/27/2009 MCC010 StDr Dryflow nd nd nd nd tr nd nd nd nd nd 8/27/2009 MCC020 StDr Dryflow nd nd nd nd nd nd tr nd nd nd 8/27/2009 MCC030 StDr Dryflow nd nd nd nd tr nd nd nd nd nd 8/27/2009 MCC040 RW Dryflow nd nd nd nd tr nd nd nd 0.0105 nd 
35

Table A4. Detections of insecticides in water samples from Orange County area sampling sites. Concentrations are i

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

Carbaryl 

Oxamyl 

Desulfinyl 

fipronil 

Desulfinyl FP 

amide 

Fipronil 

Fipronil amide 

Fipronil sulfide 

Fipronil 

sulfone 

Diazinon 

Malathion 

Bifenthrin 

(ng L-1) 

4/8/2008 AV01 RW Dryflow 0.159 nd 0.060 tr 0.232 tr tr 0.107 nd nd mv 4/8/2008 SC1 StDr Dryflow 0.078 nd tr tr tr tr tr 0.051 nd nd mv 4/8/2008 SC3 StDr Dryflow tr 0.112 tr tr tr tr tr 0.068 nd nd mv 4/8/2008 SC5 RW Dryflow nd nd tr tr 0.052 tr tr 0.060 nd nd mv 4/8/2008 WC1 StDr Dryflow nd nd tr tr tr tr tr tr nd nd mv 4/8/2008 WC2 StDr Dryflow 0.197 nd tr tr 0.140 tr tr 0.092 nd nd mv 4/8/2008 WC3 StDr Dryflow nd nd 0.118 0.072 0.359 0.145 tr 0.187 nd nd mv 

5/13/2008 AV01 RW Dryflow 0.091 nd 0.053 tr 0.099 tr tr 0.064 nd nd mv 5/13/2008 SC1 StDr Dryflow nd nd tr tr tr tr tr tr nd tr mv 5/13/2008 SC3 StDr Dryflow nd nd 0.126 tr 0.391 tr tr 0.110 nd tr mv 5/13/2008 SC5 RW Dryflow tr nd tr tr tr tr tr tr nd nd mv 5/13/2008 WC1 StDr Dryflow 0.682 nd tr tr tr tr tr 0.053 nd nd mv 5/13/2008 WC2 StDr Dryflow 0.086 nd 0.056 tr 0.106 tr tr 0.066 nd nd mv 5/13/2008 WC3 StDr Dryflow 0.130 nd 0.056 0.062 0.094 0.101 tr 0.104 nd 0.057 mv 6/13/2008 SC1 StDr Dryflow 0.108 nd tr tr 0.076 0.051 tr 0.070 nd tr mv 6/13/2008 SC3 StDr Dryflow nd nd 0.167 tr 0.175 nd tr 0.140 nd nd mv 6/13/2008 SC5 RW Dryflow nd nd tr tr 0.062 tr tr 0.056 nd 0.232 mv 6/14/2008 AV01 RW Dryflow 0.111 nd 0.061 tr 0.063 tr tr 0.082 nd nd mv 6/14/2008 WC1 StDr Dryflow nd nd 0.111 tr 0.179 tr tr 0.080 nd tr mv 6/14/2008 WC2 StDr Dryflow 0.161 nd tr tr 0.059 tr tr 0.060 nd nd mv 6/14/2008 WC3 StDr Dryflow nd nd 0.093 0.078 0.064 0.113 tr 0.171 nd nd mv 

11/26/2008 AV01 RW Rain 0.109 nd 0.085 0.058 0.164 0.088 tr 0.141 nd tr mv 11/26/2008 SC1 StDr Rain 0.088 nd tr tr 0.103 tr tr 0.076 nd 0.109 mv 11/26/2008 SC3 StDr Rain 0.057 nd 0.050 tr 0.148 tr tr 0.061 nd 0.168 mv 11/26/2008 SC5 RW Rain 0.129 nd 0.059 tr 0.120 tr tr 0.077 0.064 0.119 mv 11/26/2008 WC2 StDr Rain tr nd tr tr 0.076 tr tr 0.091 nd tr mv 11/26/2008 WC3 StDr Rain 0.180 nd 0.093 tr 0.196 0.064 tr 0.160 nd nd mv 

5/5/2009 AV01 RW Dryflow nd nd 0.053 tr 0.072 tr tr tr nd nd nd 5/5/2009 SC1 StDr Dryflow nd nd 0.069 tr 0.085 tr tr 0.064 nd nd nd 5/5/2009 SC3 StDr Dryflow nd nd 0.129 tr 0.099 tr tr 0.077 nd nd 26.4 5/5/2009 SC5 RW Dryflow tr nd tr tr tr tr tr tr nd tr nd 5/5/2009 WC1 StDr Dryflow nd nd tr tr tr tr tr tr nd nd 12.3 5/5/2009 WC2 StDr Dryflow nd nd 0.051 tr tr tr tr tr nd nd nd 
36

Table A4 continued.

Sample Date 

Site ID 

Waterbody 

Sampling Event 

Carbaryl 

Oxamyl 

Desulfinyl fipronil 

Desulfinyl FP amide 

Fipronil 

Fipronil amide 

Fipronil sulfide 

Fipronil sulfone 

Diazinon 

Malathion 

Bifenthrin (ng L-1) 

5/5/2009 WC3 StDr Dryflow nd nd 0.061 tr 0.464 tr tr 0.069 0.015 nd 5.18 8/1/2009 SC1 StDr Dryflow nd nd tr tr tr tr tr tr nd nd nd 8/1/2009 SC3 StDr Dryflow nd nd 0.144 0.063 0.518 tr tr 0.244 0.029 tr 23.7 8/1/2009 SC5 RW Dryflow nd nd 0.064 tr 0.132 tr tr 0.072 nd nd nd 8/1/2009 WC2 StDr Dryflow tr nd 0.061 tr 0.126 tr tr 0.07 nd nd nd 8/1/2009 WC3 StDr Dryflow nd nd 0.102 tr 2.11 0.094 0.057 0.546 nd nd 11.7 
37

Table A5. Detections of insecticides in water samples from San Diego area sampling sites. Concentrations are in μg 

Sample 

Date Site ID Waterbody 

Sampling 

Event Carbaryl 

Desulfinyl 

fipronil 

Desulfinyl 

fipronil 

amide Fipronil 

Fipronil 

amide 

Fipronil 

sulfide 

Fipr

sulf

4/7/2008 SDR101 RW Dryflow nd nd nd nd nd nd n4/7/2008 SDR102 StDr Dryflow 0.05 nd nd nd nd nd n4/7/2008 SDR151 StDr Dryflow nd nd nd nd nd nd n4/7/2008 SDR156 StDr Dryflow nd nd nd nd nd nd n4/7/2008 SDR158 RW Dryflow nd nd nd nd nd nd n

5/12/2008 SDR101 RW Dryflow nd tr nd nd nd nd t5/12/2008 SDR102 StDr Dryflow nd nd nd nd nd nd n5/12/2008 SDR151 StDr Dryflow nd nd nd nd nd nd n5/12/2008 SDR156 StDr Dryflow nd nd nd nd nd nd n5/12/2008 SDR158 RW Dryflow nd nd nd nd nd nd n5/12/2008 SDR159C StDr Dryflow nd nd nd nd nd nd n6/12/2008 SDR151 StDr Dryflow nd nd nd nd nd nd n6/12/2008 SDR156 StDr Dryflow nd tr nd nd nd nd n6/12/2008 SDR158 RW Dryflow nd nd nd nd nd nd n6/13/2008 SDR101 RW Dryflow nd tr nd nd nd nd t6/13/2008 SDR102 StDr Dryflow nd nd nd nd nd nd n

11/26/2008 SDR101 RW Rain tr tr tr tr tr nd t11/26/2008 SDR102 StDr Rain nd tr nd tr tr nd t11/26/2008 SDR103 StDr Rain nd tr nd nd nd nd n11/26/2008 SDR104 StDr Rain nd tr tr tr tr nd t11/26/2008 SDR151 StDr Rain 0.066 tr tr 0.053 tr tr 0.011/26/2008 SDR156 StDr Rain 0.055 tr tr tr tr tr t11/26/2008 SDR158 RW Rain 0.066 tr tr 0.058 tr tr 0.0

5/6/2009 SDR101 RW Dryflow nd tr nd nd nd nd t5/6/2009 SDR102 StDr Dryflow nd nd nd nd nd nd n5/6/2009 SDR156 StDr Dryflow nd tr nd nd tr nd t5/6/2009 SDR158 RW Dryflow nd tr nd nd nd nd t8/1/2009 SDR101 RW Dryflow nd tr nd nd nd nd n8/1/2009 SDR102 StDr Dryflow nd nd nd nd nd nd n8/1/2009 SDR156 StDr Dryflow nd tr nd tr nd nd t8/1/2009 SDR158 RW Dryflow nd tr nd nd nd nd n
38

Table A6. Detections of herbicides in water samples from Sacramento area sampling sites. Concentrations are in μg 

Sample Date 

Site ID 

Waterbody 

Sampling Event 

2,4-D 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Oxyfluorfen 

Pendimethalin 

4/21/2008 PGC010 StDr Dryflow 1.29 0.25 nd tr nd nd 0.232 04/21/2008 PGC020 StDr Dryflow 2.51 0.73 tr 0.101 nd nd 0.067 4/21/2008 PGC030 StDr Dryflow 2.4 tr nd nd nd nd 0.396 4/21/2008 PGC040 RW Dryflow 0.48 0.071 nd tr nd nd tr 5/27/2008 PGC010 StDr Dryflow 11.475 0.296 nd 0.059 nd nd 0.051 5/27/2008 PGC020 StDr Dryflow 8.22 3.07 tr 13.59 nd nd 0.07 5/27/2008 PGC030 StDr Dryflow 1.494 tr nd nd nd nd 0.05 5/27/2008 PGC040 RW Dryflow 0.747 0.069 nd nd nd nd nd 6/23/2008 PGC010 StDr Dryflow 0.3 tr nd nd nd nd tr 6/23/2008 PGC020 StDr Dryflow 3.622 0.114 nd nd nd nd nd 6/23/2008 PGC030 StDr Dryflow 0.079 nd nd nd nd nd 0.349 6/23/2008 PGC040 RW Dryflow 1.228 nd nd nd nd nd nd 11/1/2008 PGC010 StDr Rain 0.209 0.186 tr 0.061 nd nd tr 11/1/2008 PGC020 StDr Rain 0.697 0.069 tr tr tr nd nd 11/1/2008 PGC030 StDr Rain 0.221 0.058 nd tr nd nd nd 011/1/2008 PGC040 RW Rain 0.214 tr tr 0.086 nd nd nd 2/13/2009 PGC010 StDr Rain 3.51 tr 0.214 tr tr nd 0.051 02/13/2009 PGC020 StDr Rain 2.01 0.401 tr 1.05 1.04 nd 0.094 02/13/2009 PGC030 StDr Rain 0.147 0.096 tr 0.175 0.151 nd tr 02/13/2009 PGC040 RW Rain tr nd 0.429 nd 0.194 nd tr 

4/7/2009 PGC010 StDr Rain 10.4 0.947 tr 3.3 tr nd 0.163 4/7/2009 PGC020 StDr Rain 1.27 0.135 17.6 0.268 tr nd 0.161 4/7/2009 PGC030 StDr Rain 3.46 0.189 0.134 nd tr nd 0.096 4/7/2009 PGC040 RW Rain 1.02 0.085 6.76 0.141 tr nd tr 5/1/2009 PGC010 StDr Rain 0.429 0.079 nd 0.082 nd nd 0.067 5/1/2009 PGC020 StDr Rain 0.37 0.167 0.921 0.103 tr nd 0.064 5/1/2009 PGC030 StDr Rain 0.196 0.355 tr 0.44 tr nd 0.084 
39

Table A6 continued.

Sample 

 Date 

Site ID 

Waterbody 

Sampling Event 

2,4-D 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Oxyfluorfen 

Pendimethalin 

5/1/2009 PGC040 RW Rain 0.479 0.114 0.135 0.266 tr tr nd 

8/28/2009 PGC010 StDr Dryflow 0.164 0.118 nd nd mv mv mv 8/28/2009 PGC020 StDr Dryflow 0.127 0.075 tr nd mv mv mv 8/28/2009 PGC030 StDr Dryflow 0.162 0.07 nd nd mv mv mv 8/28/2009 PGC040 RW Dryflow nd 0.543 nd nd mv mv mv Table A7. Detections of herbicides in water samples from San Francisco Bay area sampling sites. Concentrations are 

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

2,4-D 

ACET 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Oxyfluorfen 

Pendimethalin 

4/22/2008 GRY010 StDr Dryflow nd nd nd tr nd nd nd tr 4/22/2008 GRY020 StDr Dryflow nd nd nd 0.11 nd nd nd nd 4/22/2008 GRY030 RW Dryflow 0.163 nd nd nd nd nd nd nd 4/22/2008 MCC010 StDr Dryflow 0.905 nd tr 0.088 nd nd nd nd 4/22/2008 MCC020 StDr Dryflow 0.101 nd nd 0.477 nd nd nd nd 4/22/2008 MCC030 StDr Dryflow nd nd nd tr nd nd nd nd 4/22/2008 MCC040 RW Dryflow 10.1 nd 0.544 1.7 nd nd nd nd 5/28/2008 GRY010 StDr Dryflow 0.069 nd nd tr nd nd nd nd 5/28/2008 GRY020 StDr Dryflow 0.069 nd nd tr nd nd nd nd 5/28/2008 GRY030 RW Dryflow 0.073 nd tr nd tr nd nd nd 5/28/2008 MCC010 StDr Dryflow 0.052 nd nd nd nd nd nd nd 5/28/2008 MCC020 StDr Dryflow 0.047 nd nd 0.072 nd nd nd nd 5/28/2008 MCC030 StDr Dryflow tr nd nd tr 0.063 nd nd nd 5/28/2008 MCC040 RW Dryflow nd nd nd 3 0.071 nd nd nd 6/24/2008 GRY010 StDr Dryflow nd nd nd nd nd nd nd nd 6/24/2008 GRY020 StDr Dryflow nd nd nd nd nd nd nd nd 6/24/2008 GRY030 RW Dryflow 0.284 nd nd tr nd nd nd nd 6/24/2008 MCC010 StDr Dryflow nd nd nd nd nd nd nd nd 6/24/2008 MCC020 StDr Dryflow 0.142 nd tr 0.148 nd nd nd nd 
40

Table A7 continued.

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

2,4-D 

ACET 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Oxyfluorfen 

Pendimethalin 

6/24/2008 MCC030 StDr Dryflow tr nd nd 0.233 nd nd nd nd 6/24/2008 MCC040 RW Dryflow tr nd nd 2.68 tr nd nd nd 11/1/2008 GRY010 StDr Rain 0.093 nd nd 0.391 nd nd nd 0.115 11/1/2008 GRY020 StDr Rain 0.209 nd 0.096 0.414 0.207 nd nd 0.05 11/1/2008 GRY030 RW Rain 0.408 nd 0.064 0.169 0.127 0.116 nd 0.057 11/1/2008 MCC010 StDr Rain 0.186 nd tr 0.054 0.157 0.077 nd nd 11/1/2008 MCC020 StDr Rain 0.613 nd tr 3.9 0.088 nd nd nd 11/1/2008 MCC030 StDr Rain 0.103 nd nd 0.306 0.098 tr nd tr 11/1/2008 MCC040 RW Rain 0.173 nd tr 6.82 0.151 nd 0.07 tr 2/15/2009 GRY010 StDr Rain tr nd nd tr nd tr nd tr 2/15/2009 GRY020 StDr Rain tr nd nd 0.445 nd tr nd 1.02 2/15/2009 GRY030 RW Rain 0.118 nd tr 0.26 tr 0.096 nd 0.073 2/15/2009 MCC010 StDr Rain 1.107 nd tr tr 0.167 0.129 nd nd 2/15/2009 MCC020 StDr Rain 0.461 nd 0.111 0.209 0.052 tr nd nd 2/15/2009 MCC030 StDr Rain 0.121 nd tr tr 0.082 0.11 nd 0.604 2/15/2009 MCC040 RW Rain 0.28 nd tr 0.709 0.077 nd nd 0.651 

4/7/2009 GRY010 StDr Rain 0.102 nd 0.054 nd nd 0.06 nd nd 4/7/2009 GRY020 StDr Rain 0.251 nd 0.065 0.162 nd nd 0.052 nd 4/7/2009 GRY030 RW Rain 0.423 nd 0.102 0.104 0.143 0.41 nd 0.675 5/1/2009 GRY010 StDr Rain 0.094 0.086 tr nd nd nd nd nd 5/1/2009 GRY020 StDr Rain 0.439 nd 0.101 tr 0.275 nd nd tr 5/1/2009 GRY030 RW Rain 0.131 nd tr tr nd nd nd tr 5/1/2009 MCC010 StDr Rain 0.339 nd 0.063 tr 0.079 tr nd nd 5/1/2009 MCC020 StDr Rain 0.524 nd 0.05 27.6 0.212 nd nd nd 5/1/2009 MCC030 StDr Rain 0.141 nd tr 0.377 nd nd nd tr 5/1/2009 MCC040 RW Rain 0.275 nd 0.055 10.9 0.122 tr nd tr 

8/27/2009 GRY010 StDr Dryflow nd nd nd nd nd mv mv mv 8/27/2009 GRY020 StDr Dryflow tr nd nd nd nd mv mv mv 8/27/2009 GRY030 RW Dryflow nd nd nd nd nd mv mv mv 8/27/2009 MCC010 StDr Dryflow nd nd nd nd nd mv mv mv 8/27/2009 MCC020 StDr Dryflow 0.075 nd nd nd nd mv mv mv 8/27/2009 MCC030 StDr Dryflow nd nd nd nd nd mv mv mv 8/27/2009 MCC040 RW Dryflow nd nd nd 1.49 nd mv mv mv 
41

Table A8. Detections of herbicides in water samples from Orange County sampling sites. Concentrations are in μg L

Sample Date 

Site ID 

Waterbody 

Sampling 

Event 

2,4-D 

Dicamba 

Diuron 

MCPA 

Oxyfluorfen 

Pendimethalin 

Prodiamine 

4/8/2008 AV01 RW Dryflow 0.39 nd 0.054 nd nd tr nd 4/8/2008 SC1 StDr Dryflow 0.052 nd tr nd nd nd nd 4/8/2008 SC3 StDr Dryflow 0.144 0.06 0.099 nd tr 0.138 nd 4/8/2008 SC5 RW Dryflow 0.151 nd tr nd nd nd tr 4/8/2008 WC1 StDr Dryflow 0.096 nd tr nd nd tr nd 4/8/2008 WC2 StDr Dryflow 0.573 nd 0.051 nd nd tr nd 4/8/2008 WC3 StDr Dryflow 0.136 nd tr nd nd 0.077 nd 

5/13/2008 AV01 RW Dryflow nd 0.056 tr nd nd tr nd 5/13/2008 SC1 StDr Dryflow nd tr tr nd nd nd nd 5/13/2008 SC3 StDr Dryflow nd tr 0.05 nd nd tr nd 5/13/2008 SC5 RW Dryflow nd 0.117 nd nd nd nd nd 5/13/2008 WC1 StDr Dryflow nd nd tr nd nd tr nd 5/13/2008 WC2 StDr Dryflow nd nd tr nd nd nd nd 5/13/2008 WC3 StDr Dryflow nd nd tr nd nd nd nd 6/13/2008 SC1 StDr Dryflow 0.256 nd tr nd nd nd nd 6/13/2008 SC3 StDr Dryflow 0.058 nd nd nd nd nd nd 6/13/2008 SC5 RW Dryflow 0.1 0.062 nd nd nd nd nd 6/14/2008 AV01 RW Dryflow 0.152 nd tr nd nd nd nd 6/14/2008 WC1 StDr Dryflow 0.711 0.169 tr 0.482 nd nd nd 6/14/2008 WC2 StDr Dryflow 0.276 tr tr nd nd nd nd 6/14/2008 WC3 StDr Dryflow 0.409 0.17 tr nd nd nd nd 

11/26/2008 AV01 RW Rain 0.1657 0.054 0.22 nd nd nd nd 11/26/2008 SC1 StDr Rain 0.547 tr 0.271 nd nd nd tr 11/26/2008 SC3 StDr Rain 0.111 nd 0.132 nd nd 0.215 nd 11/26/2008 SC5 RW Rain 0.204 nd 0.228 tr nd nd nd 11/26/2008 WC2 StDr Rain 1.571 0.369 tr tr nd nd nd 11/26/2008 WC3 StDr Rain 0.191 tr 0.273 nd nd tr nd 

5/5/2009 AV01 RW Dryflow 0.182 nd nd nd nd tr nd 5/5/2009 SC1 StDr Dryflow 0.57 0.314 nd nd nd nd tr 5/5/2009 SC3 StDr Dryflow 0.969 nd nd nd nd nd nd 5/5/2009 SC5 RW Dryflow 0.406 tr nd nd nd nd tr 5/5/2009 WC1 StDr Dryflow tr nd tr nd nd nd nd 5/5/2009 WC2 StDr Dryflow 0.351 nd tr nd nd tr nd 
42

Table A8 continued.

Sample Date 

Site ID 

Waterbody 

Sampling Event 

2,4-D 

Dicamba 

Diuron 

MCPA 

Oxyfluorfen 

Pendimethalin 

Prodiamine 

5/5/2009 WC3 StDr Dryflow 0.196 nd nd nd nd 0.292 nd 8/1/2009 AV01 RW Dryflow 0.324 0.088 tr nd mv mv mv 8/1/2009 SC1 StDr Dryflow 0.065 tr nd 0.238 mv mv mv 8/1/2009 SC3 StDr Dryflow 1.454 0.517 nd 0.424 mv mv mv 8/1/2009 SC5 RW Dryflow tr tr nd tr mv mv mv 8/1/2009 WC2 StDr Dryflow 0.745 0.150 0.063 nd mv mv mv 8/1/2009 WC3 StDr Dryflow 0.330 0.193 tr nd mv mv mv 

Table A9. Detections of herbicides in water samples from San Diego Sampling sites. Concentrations are in μg L-1. 

Sample 

Date 

Site ID 

Waterbody 

Sampling 

Event 

2,4-D 

Bromacil 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Prodiamine 

Prometon 

4/7/2008 SDR101 RW Dryflow 0.052 nd nd nd nd nd nd tr 4/7/2008 SDR102 StDr Dryflow nd nd nd nd nd nd nd nd 4/7/2008 SDR151 StDr Dryflow nd nd nd nd nd nd nd nd 4/7/2008 SDR156 StDr Dryflow nd nd nd nd nd nd nd nd 4/7/2008 SDR158 RW Dryflow nd nd nd nd nd nd nd nd 

5/12/2008 SDR101 RW Dryflow nd nd nd nd nd nd nd nd 5/12/2008 SDR102 StDr Dryflow nd nd nd nd nd nd nd nd 5/12/2008 SDR151 StDr Dryflow nd nd nd nd nd nd nd nd 5/12/2008 SDR156 StDr Dryflow nd nd nd nd nd nd nd nd 5/12/2008 SDR158 RW Dryflow nd nd nd nd nd nd nd nd 5/12/2008 SDR159C StDr Dryflow nd nd nd nd nd nd nd nd 6/12/2008 SDR151 StDr Dryflow nd nd nd nd nd nd nd nd 6/12/2008 SDR156 StDr Dryflow nd nd nd nd nd nd nd nd 6/12/2008 SDR158 RW Dryflow nd nd nd nd nd nd nd nd 
43

Table A9 continued.

Sample Date 

Site ID 

Waterbody 

Sampling Event 

2,4-D 

Bromacil 

Dicamba 

Diuron 

MCPA 

Oryzalin 

Prodiamine 

Prometon 

6/13/2008 SDR101 RW Dryflow tr nd nd nd nd nd nd nd 6/13/2008 SDR102 StDr Dryflow nd nd nd nd nd nd nd nd 

11/26/2008 SDR101 RW Rain 0.085 tr nd tr nd 0.383 nd 1.34 11/26/2008 SDR102 StDr Rain nd nd nd 2.03 nd nd nd nd 11/26/2008 SDR103 StDr Rain nd nd nd nd nd nd nd nd 11/26/2008 SDR104 StDr Rain tr nd nd 0.059 nd 0.208 nd nd 11/26/2008 SDR151 StDr Rain 0.261 nd 0.053 0.234 0.11 nd nd nd 11/26/2008 SDR156 StDr Rain 0.132 nd nd nd nd nd nd tr 11/26/2008 SDR158 RW Rain 0.339 nd 0.07 0.238 nd tr nd nd 

5/6/2009 SDR101 RW Dryflow nd nd nd nd nd nd nd nd 5/6/2009 SDR102 StDr Dryflow nd nd nd nd nd nd nd nd 5/6/2009 SDR156 StDr Dryflow nd nd nd nd nd nd nd nd 5/6/2009 SDR158 RW Dryflow nd nd nd nd nd nd nd nd 8/1/2009 SDR101 RW Dryflow nd nd nd nd nd mv mv nd 8/1/2009 SDR102 StDr Dryflow nd nd nd nd nd mv mv nd 8/1/2009 SDR156 StDr Dryflow nd nd nd nd nd mv mv nd 8/1/2009 SDR158 RW Dryflow nd nd nd nd nd mv mv nd 
44

Table A10. Detections of pyrethroids in sediments (units, μg kg-1 dry wt.). All sediments were collected during dryfl

Site ID 

Area 

Waterbody 

Sample Date 

Bifenthrin 

Cyfluthrin 

Cypermethrin 

Deltamethrin 

Fenvalerate/ 

esfenvalerate 

Lambdacyhalothrin 

Permethrin cis 

Phi

PGC010 SAC StDr 8/4/2008 438.4 75.2 45.3 13.2 nd 8.1 89.2 3PGC020 SAC StDr 8/4/2008 196.2 13.2 6.7 2.8 nd 2.6 16.7 PGC020 SAC StDr 8/4/2008 101.1 28.6 10.2 nd nd 6.9 66.9 4PGC020 SAC StDr 8/4/2008 605.6 14.7 19.7 nd nd nd 22.6 PGC030 SAC StDr 8/4/2008 63.5 9.8 4.6 2.1 nd 2.0 45.0 2PGC010 SAC StDr 4/13/2009 679.8 148.6 53.6 20.3 nd 14.8 113.1 5PGC010 SAC StDr 4/13/2009 41.5 5.5 nd 2.0 nd nd 3.4 PGC020 SAC StDr 4/13/2009 61.4 4.4 nd nd nd nd 7.4 PGC020 SAC StDr 4/13/2009 323.5 83.7 22.7 7.5 4.9 4.1 40.7 3PGC020 SAC StDr 4/13/2009 267.9 49.6 22.6 14.0 nd 5.8 58.2 3PGC030 SAC StDr 4/13/2009 24.0 2.9 nd nd nd nd 5.2 MCC010 SFB StDr 8/5/2008 37.5 23.4 nd 7.2 nd nd 5.0 MCC020 SFB StDr 8/5/2008 0.1 18.9 nd nd nd nd nd MCC030 SFB StDr 8/5/2008 25.5 19.6 nd 5.2 nd nd 3.8 GRY010 SFB StDr 8/6/2008 7.8 nd nd nd nd nd nd GRY020 SFB StDr 8/6/2008 13.1 2.9 nd 1.8 nd nd 4.6 GRY030 SFB RW 8/6/2008 8.9 1.9 nd nd nd nd 2.2 GRY030 SFB RW 8/6/2008 9.3 nd nd nd nd nd 2.8 GRY020 SFB StDr 4/14/2009 17.9 2.1 nd nd nd nd 3.3 GRY030 SFB RW 4/14/2009 26.8 7.1 nd 2.3 nd nd 7.0 GRY030 SFB RW 4/14/2009 23.0 5.8 nd nd nd nd 5.7 MCC010 SFB StDr 4/14/2009 11.9 4.3 nd nd nd 1.5 4.3 SC1 OC StDr 6/13/2008 45.0 14.1 nd 2.2 nd nd 23.5 2SC3 OC StDr 6/13/2008 39.7 38.2 nd 26.8 nd 4.6 45.3 4SC5 OC RW 6/13/2008 25.2 7.0 nd 4.7 nd 1.9 11.5 AV01 OC RW 6/14/2008 236.5 44.6 nd 12.3 9.4 21.6 45.7 2WC1 OC StDr 6/14/2008 323.7 89.3 18.2 15.7 4.0 31.9 149.0 2WC2 OC StDr 6/14/2008 141.0 39.0 nd 6.9 6.6 31.0 62.6 6WC3 OC StDr 6/14/2008 207.6 67.2 22.0 50.7 20.3 30.1 171.0 2SC1 OC StDr 5/5/2009 14.2 3.7 nd 5.8 nd nd 16.4 SC3 OC StDr 5/5/2009 nd nd nd 2.7 nd 7.5 6.8 SC5 OC RW 5/5/2009 nd nd nd nd nd 3.1 2.2 SDR151 SD StDr 6/12/2008 3.3 nd 1.9 nd nd nd nd 
45

Table A10 continued. 

Site ID 

Area 

Waterbody 

Sample Date 

Bifenthrin 

Cyfluthrin 

Cypermethrin 

Deltamethrin 

Fenvalerate/ 

esfenvalerate 

Lambdacyhalothrin 

Permethrin cis 

SDR158 SD RW 6/12/2008 1.3 nd nd nd nd nd nd SDR101 SD RW 6/13/2008 0.1 nd nd nd nd nd nd SDR102 SD StDr 6/13/2008 0.1 2.0 nd nd nd nd 1.7 SDR101 SD RW 5/6/2009 3.8 nd nd nd nd nd nd SDR101 SD RW 5/6/2009 4.6 nd nd nd nd nd nd SDR102 SD StDr 5/6/2009 3.2 3.1 nd nd nd nd 6.5 SDR156 SD StDr 5/6/2009 8.3 4.2 7.9 nd nd nd 3.2 SDR158 SD RW 5/6/2009 10.7 6.0 4.0 1.8 nd nd 2.1 
46

Table A11. Summary of the water quality parameters for the entire study. 

 pH EC (mS 

cm

-1) 

DO 

(mg L1

) 

Temperature (°C) Turbidity 

(NTU) 

TSS (mg 

L-1) 

TOC (mg 

L-1) 

Median 7.6 1.0 8.4 16.9 3.1 7.2 7.8 

Range 6.1 – 

8.6 

0.06 – 

4.47 

1.5 – 

18.3 6.9 – 25.9 0 – 236.6 0 – 844.3 1.2 – 106.4 

Criteria 

for 

water 

quality1

6.5 – 

8.5 

> 3.0 

(severe) < 5.0 

15.6 – 23.9 

(seasonal), 

or not 

2.8°C 

above 

natural 

levels 

> 1 NTU or 

20% based 

on natural 

levels2

Shall not 

cause a 

nuisance 

or 

adversely 

affect 

beneficial 

uses. 

-- 

Percent 

outside 

criteria 

2% 9% 20% -- 

Background 

natural 

levels 

unknown 

unknown 

1

Criteria from Central Valley Regional Water Quality Board, Water Quality Control Plan for the 

Sacramento and San Joaquin River Basins, 

http://www.waterboards.ca.gov/centralvalley/water_issues/basin_plans/; The San Diego Regional Water 

Quality Board, San Diego Region Basin Plan, 

http://www.waterboards.ca.gov/sandiego/water_issues/programs/basin_plan/; San Francisco Bay Area 

Regional Water Quality Control Board, basin plan, http://www.swrcb.ca.gov/rwqcb2/basin_planning.shtml

2

Determined based on medians of sampling sites. If NTUs medians were between 1 – 5, and increase of 1 

NTU over the median was an exceedance. If the medians were between 5 – 50 NTUs, an increase of 20% or 

more was an exceedance. Most exceedances (70%) were during rainstorm sampling and in stormdrain 

outflows (67%). 

Water Quality Parameters by Category 

There generally were little differences in water quality parameters between stormdrain outfalls and 

receiving waters. However, storm drain outflows had significantly higher DO and lower conductivity (EC) 

than receiving waters (p=0.0031-0.0163; Table A11). Rainfall was the biggest factor influencing differences 

between these water quality parameters. With dryflow conditions EC and temperature values were 

significantly higher than those observed with rainstorm events (p=0.000), whereas during rain events, DO, 

turbidity, TSS, and TOC were significantly higher than during dryflow (p=0.000-0.0035; Table A12). 

Between areas of the state, northern California had significantly higher DO (p=0.000) whereas southern 

California had significantly higher conductivity and temperature (p=0.000; Table A13). These may be 

rainfall effects. 
47

Table A12.Water quality median concentrations between stormdrain outflows and receiving waters. 

 pH EC (mS 

cm

-1) 

DO 

(mg L1

) 

Temperature (°C) Turbidity 

(NTU) 

TSS (mg 

L-1) 

TOC 

(mg L-1) 

Stormdrain 

outflows 7.63 0.82 8.4 17.2 2.6 7.1 7.3 

Receiving 

waters 7.67 1.43 6.9 18.0 3.9 6.1 8.8 

Significant 

p values n.s. 0.0031 0.0163 n.s. n.s. n.s. n.s. 

Table A13. Water quality median concentrations between dryflow and rainstorm sampling. 

 pH EC (mS 

cm

-1) 

DO 

(mg L1

) 

Temperature (°C) Turbidity 

(NTU) 

TSS (mg 

L-1) 

TOC (mg 

L-1) 

Dryflow 7.69 1.46 7.3 18.6 1.1 4.4 6.9 

Rainstorm 7.62 0.29 9.0 15.8 17.4 31.1 9.5 

Significant 

p values. n.s. 0.000 0.000 0.000 0.000 0.000 0.0035 

Table A14. Water quality median concentrations between northern and southern California. 

 pH EC (mS 

cm

-1) 

DO 

(mg L1

) 

Temperature (°C) Turbidity 

(NTU) 

TSS (mg 

L-1) 

TOC 

(mg L-1) 

Northern 

California 7.7 0.37 8.7 16.7 2.9 7.1 6.9 

Southern 

California 7.56 1.73 7.1 18.6 2.7 6.1 9.1 

Significant 

p values n.s. 0.000 0.000 0.000 n.s. n.s. n.s. 
48

Table A15. Water quality parameters at the individual sampling sites of the urban study. Region Area 

Sample 

Date Site ID 

Water 

Body 

Sample 

Event 

Flow 

(cfs)1 pH EC (mS cm-1) DO (mg L-1) Temp (°C) 

NoCal SAC 21-Apr-08 PGC010 StDr Dryflow nf 7.29 0.167 5.88 13.34 NoCal SAC 21-Apr-08 PGC020 StDr Dryflow 0.23 7.04 0.217 5.43 11.03 NoCal SAC 21-Apr-08 PGC030 StDr Dryflow fl 7.66 0.143 9.28 15.17 NoCal SAC 21-Apr-08 PGC040 RW Dryflow fl 7.75 0.487 7.75 13.58 NoCal SAC 27-May-08 PGC010 StDr Dryflow nf 7.35 0.183 8.33 17.66 NoCal SAC 27-May-08 PGC020 StDr Dryflow nf 7.06 0.193 4.45 16.15 NoCal SAC 27-May-08 PGC030 StDr Dryflow 0.015 7.75 0.198 8.43 19.01 NoCal SAC 27-May-08 PGC040 RW Dryflow nf 7.74 0.508 5.8 17.45 NoCal SAC 23-Jun-08 PGC010 StDr Dryflow nf 7.11 0.215 4.3 21.89 NoCal SAC 23-Jun-08 PGC020 StDr Dryflow 0.05 6.82 0.176 3.2 20.78 NoCal SAC 23-Jun-08 PGC030 StDr Dryflow 0.035 7.5 0.144 7.52 23.65 NoCal SAC 23-Jun-08 PGC040 RW Dryflow nf 7.57 0.369 4.24 22.78 NoCal SAC 04-Aug-08 PGC010 StDr Dryflow nf 7.24 0.182 4.96 22.4 NoCal SAC 04-Aug-08 PGC020 StDr Dryflow 0.13 6.77 0.316 4.87 19.81 NoCal SAC 04-Aug-08 PGC030 StDr Dryflow 0.0142 7.64 0.181 7.37 24.47 NoCal SAC 04-Aug-08 PGC040 RW Dryflow nf 7.22 0.338 3.53 21.24 NoCal SAC 01-Nov-08 PGC010 StDr Rain fl 7.22 0.198 9.06 16.64 NoCal SAC 01-Nov-08 PGC020 StDr Rain 2.22 7.59 0.15 8.13 16.68 NoCal SAC 01-Nov-08 PGC030 StDr Rain 1.28 7.7 0.135 9.47 17.31 NoCal SAC 01-Nov-08 PGC040 RW Rain fl 7.52 0.313 6.47 15.88 NoCal SAC 13-Feb-09 PGC010 StDr Rain 2.49 7.62 0.113 11.26 6.94 NoCal SAC 13-Feb-09 PGC020 StDr Rain 4.99 7.57 0.204 11.02 7.47 NoCal SAC 13-Feb-09 PGC030 StDr Rain 4.66 7.73 0.277 11.93 8.5 NoCal SAC 13-Feb-09 PGC040 RW Rain 135.98 7.68 0.174 10.57 7.8 NoCal SAC 07-Apr-09 PGC010 StDr Rain fl 7.4 0.129 8.5 13.47 NoCal SAC 07-Apr-09 PGC020 StDr Rain fl 7.35 0.96 9.3 13.57 NoCal SAC 07-Apr-09 PGC030 StDr Rain fl 7.67 0.105 9.91 14.23 NoCal SAC 07-Apr-09 PGC040 RW Rain fl 7.76 0.385 8.02 14 NoCal SAC 13-Apr-09 PGC010 StDr Dryflow nf 6.99 0.184 1.5 14.23 NoCal SAC 13-Apr-09 PGC020 StDr Dryflow nf 6.78 0.352 2.1 13.8 NoCal SAC 13-Apr-09 PGC030 StDr Dryflow fl 7.48 0.173 7.4 16.66 NoCal SAC 13-Apr-09 PGC040 RW Dryflow fl 7.1 0.22 2.43 14.85 NoCal SAC 01-May-09 PGC010 StDr Rain 1.4 7.67 0.076 8.79 18.04 NoCal SAC 01-May-09 PGC020 StDr Rain 1.25 7.47 0.078 8.62 17.68 NoCal SAC 01-May-09 PGC030 StDr Rain fl 7.38 0.063 9.57 16.8 NoCal SAC 01-May-09 PGC040 RW Rain fl 7.89 0.267 8.72 16.56 NoCal SAC 28-Aug-09 ANT001 StDr Dryflow 0.02 7.99 0.493 7.24 24.46 
49

Table A15 continued. Region Area 

Sample 

Date Site ID 

Water 

Body 

Sample 

Event 

Flow 

(cfs)1 pH EC (mS cm-1) DO (mg L-1) Temp (°C) 

NoCal SAC 28-Aug-09 FOL001 StDr Dryflow 0.02 6.61 0.201 6.69 21.46 NoCal SAC 28-Aug-09 FOL002 StDr Dryflow fl 8.03 0.28 8.19 20.55 NoCal SAC 28-Aug-09 NAT001 StDr Dryflow fl mv mv mv mv NoCal SAC 28-Aug-09 PGC010 StDr Dryflow nf 6.96 0.206 2.11 23.37 NoCal SAC 28-Aug-09 PGC020 StDr Dryflow 0.01 6.74 0.153 1.17 21.1 NoCal SAC 28-Aug-09 PGC030 StDr Dryflow fl 7.59 0.193 6.95 25.28 NoCal SAC 28-Aug-09 PGC040 RW Dryflow nf 7.18 0.348 3.65 20.88 NoCal SFB 22-Apr-08 GRY010 StDr Dryflow 0.44 8.04 2.22 9.58 13.11 NoCal SFB 22-Apr-08 GRY020 StDr Dryflow 0.33 8.12 1.883 10.59 14.02 NoCal SFB 22-Apr-08 GRY030 RW Dryflow 5.53 8.36 1.581 14.77 17.12 NoCal SFB 22-Apr-08 MCC010 StDr Dryflow 0.41 8.25 1.822 12.6 15.86 NoCal SFB 22-Apr-08 MCC020 StDr Dryflow fl 8.17 1.84 10.4 11 NoCal SFB 22-Apr-08 MCC030 StDr Dryflow 0.33 8.24 1.087 9.75 15.68 NoCal SFB 22-Apr-08 MCC040 RW Dryflow fl 7.82 1.641 8.53 12.88 NoCal SFB 28-May-08 GRY010 StDr Dryflow 0.05 7.97 1.861 8.62 15.72 NoCal SFB 28-May-08 GRY020 StDr Dryflow 0.024 8.1 1.577 10.34 16.95 NoCal SFB 28-May-08 GRY030 RW Dryflow 2.02 8.3 1.497 12.8 20.51 NoCal SFB 28-May-08 MCC010 StDr Dryflow 0.28 8.15 1.853 9.77 16.87 NoCal SFB 28-May-08 MCC020 StDr Dryflow 0.29 8.21 1.484 9.57 14.25 NoCal SFB 28-May-08 MCC030 StDr Dryflow 0.27 8.16 1.077 8.89 17.61 NoCal SFB 28-May-08 MCC040 RW Dryflow 0.73 7.95 1.598 9.3 15.84 NoCal SFB 24-Jun-08 GRY010 StDr Dryflow fl 8.18 1.296 7.5 18.77 NoCal SFB 24-Jun-08 GRY020 StDr Dryflow 0.01 8.18 2.01 12.14 18.78 NoCal SFB 24-Jun-08 GRY030 RW Dryflow 0.90 8.58 1.092 18.29 25.91 NoCal SFB 24-Jun-08 MCC010 StDr Dryflow 0.04 8.13 1.975 9.92 17.95 NoCal SFB 24-Jun-08 MCC020 StDr Dryflow fl 8.26 1.591 9.23 15.92 NoCal SFB 24-Jun-08 MCC030 StDr Dryflow 1.23 7.85 1.147 5.83 19.08 NoCal SFB 24-Jun-08 MCC040 RW Dryflow 2.18 7.72 1.648 4.69 18.22 NoCal SFB 05-Aug-08 MCC010 StDr Dryflow 0.14 8.05 0.193 8.42 18.12 NoCal SFB 05-Aug-08 MCC020 StDr Dryflow fl 8.34 1.564 8.27 16.93 NoCal SFB 05-Aug-08 MCC030 StDr Dryflow 0.1 8.17 0.82 7.68 19.93 NoCal SFB 05-Aug-08 MCC040 RW Dryflow fl 7.66 1.644 3.71 19.63 NoCal SFB 06-Aug-08 GRY010 StDr Dryflow 0.0188 7.78 0.928 7.93 17.26 NoCal SFB 06-Aug-08 GRY020 StDr Dryflow 0.059 8.11 1.75 9.64 19.71 NoCal SFB 06-Aug-08 GRY030 RW Dryflow 5.15 8.17 0.699 7.45 20.38 NoCal SFB 01-Nov-08 GRY010 StDr Rain 7.00 7.17 0.306 8.86 16.99 NoCal SFB 01-Nov-08 GRY020 StDr Rain 0.42 7.42 0.383 9.21 17.4 
50

Table A15 continued.

Region Area 

Sample 

Date Site ID 

Water 

Body 

Sample 

Event 

Flow 

(cfs)1 pH EC (mS cm-1) DO (mg L-1) Temp (°C) 

NoCal SFB 01-Nov-08 GRY030 RW Rain fl 7.76 0.282 5.94 17.18 NoCal SFB 01-Nov-08 MCC010 StDr Rain 3.60 7.84 0.328 9.03 18.08 NoCal SFB 01-Nov-08 MCC020 StDr Rain 4.00 7.74 0.737 8.46 12.73 NoCal SFB 01-Nov-08 MCC030 StDr Rain 39.00 7.37 0.076 9.37 17.37 NoCal SFB 01-Nov-08 MCC040 RW Rain 81.00 7.59 0.186 8.66 18.61 NoCal SFB 15-Feb-09 GRY010 StDr Rain 18.60 7.73 0.41 11.06 9.46 NoCal SFB 15-Feb-09 GRY020 StDr Rain 5.73 7.67 0.279 11.2 9.38 NoCal SFB 15-Feb-09 GRY030 RW Rain fl 7.68 0.193 10.54 9.96 NoCal SFB 15-Feb-09 MCC010 StDr Rain 6.46 8.04 0.434 11.36 11.41 NoCal SFB 15-Feb-09 MCC020 StDr Rain 2.80 8.1 0.539 10.84 10.57 NoCal SFB 15-Feb-09 MCC030 StDr Rain 7.32 7.52 0.141 10.31 12.21 NoCal SFB 15-Feb-09 MCC040 RW Rain 91.80 7.8 0.286 10.79 11.72 NoCal SFB 07-Apr-09 GRY010 StDr Rain 3.28 7.35 0.651 9.43 12.13 NoCal SFB 07-Apr-09 GRY020 StDr Rain 0.64 7.86 1.151 9.41 14.14 NoCal SFB 07-Apr-09 GRY030 RW Rain 52.50 7.55 0.399 8.41 13.39 NoCal SFB 14-Apr-09 GRY010 StDr Dryflow 0.07 8.04 2.277 9.15 12.11 NoCal SFB 14-Apr-09 GRY020 StDr Dryflow 0.07 8.06 1.44 10.38 14.33 NoCal SFB 14-Apr-09 GRY030 RW Dryflow 1.29 8.18 1.779 9.66 16.85 NoCal SFB 14-Apr-09 MCC010 StDr Dryflow 0.30 8.32 1.952 12.03 12.73 NoCal SFB 14-Apr-09 MCC020 StDr Dryflow 0.00 8.28 1.298 10.21 11.85 NoCal SFB 14-Apr-09 MCC0201 StDr Dryflow 0.16 mv mv mv mv NoCal SFB 14-Apr-09 MCC030 StDr Dryflow 0.16 7.98 1.1 9.53 15.65 NoCal SFB 14-Apr-09 MCC040 RW Dryflow 0.164 7.88 1.685 9.78 13.25 NoCal SFB 01-May-09 GRY010 StDr Rain 9.00 7.62 1.09 8.39 15.75 NoCal SFB 01-May-09 GRY020 StDr Rain 1.66 7.6 0.364 9.3 16.64 NoCal SFB 01-May-09 GRY030 RW Rain Fl 7.61 0.451 6.92 16.39 NoCal SFB 01-May-09 MCC010 StDr Rain 3.59 7.8 0.539 9 15.83 NoCal SFB 01-May-09 MCC020 StDr Rain 1.24 7.88 0.178 8.98 15.79 NoCal SFB 01-May-09 MCC030 StDr Rain 0.837 7.42 0.15 9.06 16.47 NoCal SFB 01-May-09 MCC040 RW Rain Fl 7.68 0.212 9.41 15.89 NoCal SFB 27-Aug-09 MCC010 StDr Dryflow 0.08 8.21 2.07 9.65 18.01 NoCal SFB 27-Aug-09 MCC020 StDr Dryflow fl 8.32 1.104 8.07 17.7 NoCal SFB 27-Aug-09 MCC030 StDr Dryflow 0.03 8.14 0.889 8.45 20 NoCal SFB 27-Aug-09 MCC040 RW Dryflow nf 7.52 1.668 2.28 18.74 NoCal SFB 27-Aug-09 GRY010 StDr Dryflow fl 7.34 0.8 1.33 16.77 NoCal SFB 27-Aug-09 GRY020 StDr Dryflow fl 8.22 1.825 8.58 18.5 NoCal SFB 27-Aug-09 GRY030 RW Dryflow 0.96 8.26 1.025 12.26 24.44 

2 Values for TOC and TSS are high because this sample was mostly sediment, unlike the preceding sample from the same site.
51

Table A15 continued.

Region Area 

Sample 

Date Site ID 

Water 

Body 

Sample 

Event 

Flow 

(cfs)1 pH EC (mS cm-1) DO (mg L-1) Temp (°C) 

SoCal OC 08-Apr-08 SC1 StDr Dryflow 0.02 7.53 4.289 7.72 14.46 SoCal OC 08-Apr-08 SC3 StDr Dryflow 0.05 8.2 1.527 9.58 16.43 SoCal OC 08-Apr-08 SC5 RW Dryflow 0.52 7.7 3.193 10.38 14.92 SoCal OC 08-Apr-08 WC1 StDr Dryflow 0.06 8.3 1.059 10 16.16 SoCal OC 08-Apr-08 WC2 StDr Dryflow 0.09 7.59 1.238 5.57 15.39 SoCal OC 08-Apr-08 WC3 StDr Dryflow 0.01 8.17 2.703 8.68 16.13 SoCal OC 08-Apr-08 AV01 RW Dryflow 0.12 7.94 1.28 9.09 16.54 SoCal OC 13-May-08 SC1 StDr Dryflow nf 7.57 3.095 7.07 15.75 SoCal OC 13-May-08 SC3 StDr Dryflow fl 8.53 1.793 7.6 17.6 SoCal OC 13-May-08 SC5 RW Dryflow 1.46 7.82 4.287 9.53 16.07 SoCal OC 13-May-08 WC1 StDr Dryflow 0.12 8.28 1.039 8.66 17.65 SoCal OC 13-May-08 WC2 StDr Dryflow 0.32 7.58 1.244 4.91 17.86 SoCal OC 13-May-08 WC3 StDr Dryflow fl 8.11 3.741 7.88 17.86 SoCal OC 13-May-08 AV01 RW Dryflow 3.20 7.68 1.638 5.76 17.86 SoCal OC 13-Jun-08 SC1 StDr Dryflow fl 7.4 4.107 5.81 19.29 SoCal OC 13-Jun-08 SC3 StDr Dryflow fl 8.14 2.315 8.18 22.42 SoCal OC 13-Jun-08 SC5 RW Dryflow 0.42 7.9 3.844 mv 19.85 SoCal OC 14-Jun-08 WC1 StDr Dryflow 0.10 8.13 0.907 mv 19.4 SoCal OC 14-Jun-08 WC2 StDr Dryflow 0.17 7.33 1.253 mv 17.27 SoCal OC 14-Jun-08 WC3 StDr Dryflow 0.05 8.01 1.529 8.55 19.04 SoCal OC 14-Jun-08 AV01 RW Dryflow 0.24 7.49 1.378 5.1 17.51 SoCal OC 26-Nov-08 SC1 StDr Rain fl 6.08 0.646 7.87 15.46 SoCal OC 26-Nov-08 SC3 StDr Rain fl 6.63 0.305 8.31 15.82 SoCal OC 26-Nov-08 SC5 RW Rain fl 6.47 0.594 8.84 14.72 SoCal OC 26-Nov-08 WC2 StDr Rain fl 7.43 1.072 9.34 15.58 SoCal OC 26-Nov-08 WC3 StDr Rain fl 7.63 0.569 8.18 14.43 SoCal OC 26-Nov-08 AV01 RW Rain fl 7.41 1.379 7.44 15.23 SoCal OC 05-May-09 SC1 StDr Dryflow fl 6.98 4.472 6.45 20.55 SoCal OC 05-May-09 SC3 StDr Dryflow fl 7.6 1.658 7.61 21.14 SoCal OC 05-May-09 SC5 RW Dryflow fl 7.26 3.341 7.43 18.24 SoCal OC 05-May-09 WC1 StDr Dryflow nf 6.67 1.836 5.15 20.3 SoCal OC 05-May-09 WC2 StDr Dryflow fl 6.98 1.197 4.39 18.98 SoCal OC 05-May-09 WC3 StDr Dryflow fl 7.03 2.968 5.53 18.25 SoCal OC 05-May-09 AV01 RW Dryflow fl 6.82 1.362 5.24 18.94 SoCal OC 01-Aug-09 AV01 RW Dryflow fl 7.63 0.99 6.61 22.87 SoCal OC 01-Aug-09 WC2 StDr Dryflow mv mv mv mv mv SoCal OC 01-Aug-09 WC3 StDr Dryflow mv mv mv mv mv 
52

Table A15 continued.

Region Area 

Sample 

Date Site ID 

Water 

Body 

Sample 

Event 

Flow 

(cfs)1 pH EC (mS cm-1) DO (mg L-1) Temp (°C) 

SoCal OC 01-Aug-09 SC1 StDr Dryflow nf mv mv mv mv SoCal OC 01-Aug-09 SC3 StDr Dryflow mv mv mv mv mv SoCal OC 01-Aug-09 SC5 RW Dryflow fl 7.33 2.494 3.67 21.19 SoCal SD 07-Apr-08 SDR101 RW Dryflow 2.2 7.7 2.565 6.79 19.1 SoCal SD 07-Apr-08 SDR102 StDr Dryflow 0.06 7.44 3.176 7.17 20.59 SoCal SD 07-Apr-08 SDR151 StDr Dryflow 0.28 7.36 2.59 4.62 21.17 SoCal SD 07-Apr-08 SDR156 StDr Dryflow 0.01 8.13 0.993 9.04 17.08 SoCal SD 07-Apr-08 SDR158 RW Dryflow nf 7.35 2.566 4.51 20.15 SoCal SD 12-May-08 SDR101 RW Dryflow 17.21 7.81 3.025 5.46 20.45 SoCal SD 12-May-08 SDR102 StDr Dryflow fl 7.41 3.462 6.85 20.73 SoCal SD 12-May-08 SDR151 StDr Dryflow 0.5806 7.31 2.587 3.62 21.45 SoCal SD 12-May-08 SDR156 StDr Dryflow fl 8.04 0.974 7.7 17.98 SoCal SD 12-May-08 SDR158 RW Dryflow fl 7.41 2.559 4.59 20.73 SoCal SD 12-May-08 SDR159C StDr Dryflow 0.43 7.36 2.595 4.6 21.36 SoCal SD 12-Jun-08 SDR151 StDr Dryflow 0.0668 7.22 2.578 3.62 21.61 SoCal SD 12-Jun-08 SDR156 StDr Dryflow fl 7.78 0.678 mv 19.55 SoCal SD 12-Jun-08 SDR158 RW Dryflow nf 7.21 2.547 5.05 21.39 SoCal SD 13-Jun-08 SDR101 RW Dryflow 1.07 7.55 3.015 2.32 22.64 SoCal SD 13-Jun-08 SDR102 StDr Dryflow fl 7.38 3.237 6.2 20.97 SoCal SD 26-Nov-08 SDR101 RW Rain 67.50 7.71 1.489 7.1 16.88 SoCal SD 26-Nov-08 SDR102 StDr Rain 1.80 7.4 1.132 8.07 17.99 SoCal SD 26-Nov-08 SDR103 StDr Rain 0.03 8.15 0.195 8.75 17.22 SoCal SD 26-Nov-08 SDR104 StDr Rain 2.00 7.62 0.148 4.37 16.59 SoCal SD 26-Nov-08 SDR151 StDr Rain nf 7.92 0.264 8.79 16.62 SoCal SD 26-Nov-08 SDR156 StDr Rain fl 7.48 0.14 8.26 17.1 SoCal SD 26-Nov-08 SDR158 RW Rain fl 7.4 0.29 8.37 16.32 SoCal SD 06-May-09 SDR101 RW Dryflow 3.22 7.6 2.947 3.68 21.88 SoCal SD 06-May-09 SDR102 StDr Dryflow 1.77 7.31 3.462 7.16 21.12 SoCal SD 06-May-09 SDR156 StDr Dryflow 0.01 8.13 0.977 8.82 18.24 SoCal SD 06-May-09 SDR158 RW Dryflow nf 7.39 1.898 2.9 21.38 SoCal SD 01-Aug-09 SDR101 RW Dryflow 1.13 7.57 4.074 0.94 23.31 SoCal SD 01-Aug-09 SDR102 StDr Dryflow 0.13 7.48 3.588 6.75 22.37 SoCal SD 01-Aug-09 SDR156 StDr Dryflow nf 8.17 0.815 7.01 22.36 SoCal SD 01-Aug-09 SDR158 RW Dryflow nf 7.32 2.637 0.88 23.22 

1fl, the water in the waterbody was flowing but flow could not be taken; nf, the water in the waterbody was not flowing. 
53

VII. APPENDIX II. QUALITY CONTROL 

1. Holding times. Holding times are the length of time from when the sample is collected to when it is 

extracted prior to analysis, and vary for the different analyte screens (Table 1). All analyses met there 

holding times, except for two synthetic auxin analyses. The holding times for two of these batches failed by 

one and two days. Due to a lab error, another batch was not extracted until 50 days after sampling. 

Conducting a lab duplicate analysis confirmed that exceeding the holding time did not affect the degradation 

of these samples. 

2. Lab Blanks. There were no detections in any of the lab blanks. 

3. Matrix and propazine surrogate spikes. With analytical batch, control water or sediment is spiked with 

known concentrations of the pesticides in that particular analytical screen. For the study there were 698 

matrix spikes; 98% of these were recovered within acceptable limits. All 194 propazine surrogates (a 

triazine surrogate) were recovered with laboratory acceptable limits, as were all of the sediment matrix 

spikes. 

4. Blind spikes, Field Blanks, and Field Duplicates. About 15% of the samples were blind spikes, field 

blanks, or field duplicates. Twenty-seven analytes in 15 blind spikes were all recovered within acceptable 

limits. However, in one analysis, fipronil was detected as a trace detection for fipronil, without fipronil 

added to the sample. 

There were no detections in any of the 37 field blanks. Of 90 field duplicate analyses (water samples), 96% 

had good reproducibility (less than 25% difference) between the original field sample and the field 

duplicate. Sediment samples had more variation, with only 80% of the samples having good reproducibility. 

The sediment matrix may be interfering with the analysis and causing some variation in the data.