Seasonal Changes in Concentrations of Dissolved Pesticides and Organic Carbon in the Sacramento–San Joaquin Delta, California, 1994–1996

By James L. Orlando and Kathryn M. Kuivila

Data Series 197, published 2006.

U.S. Department of the Interior

Dirk Kempthorne, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director
The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Acronyms

NWIS
National Water Information System

Abbreviations

Datum:
Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the insert North American Datum of 1983 (NAD 83).
Altitude
as used in this report, refers to distance above the vertical datum.
Delta
Sacramento–San Joaquin Delta
DOC
dissolved organic carbon
GC/MS
gas chromatography/mass spectrometry
in.
inch
in./day
inch per day
L
liter
µm
micrometer
mg/L
milligram per liter
mL
milliliter
mm
millimeter
ng/L
nanogram per liter
NWIS
National Water Information System
TMDL
Total Maximum Daily Load
USGS
U.S. Geological Survey
Note:
Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 × °C) + 32.
Note:
Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F – 32)/1.8.
Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C)
Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (µg/L).
NOTE TO USGS USERS:
Use of liter (L) as a special name for cubic decimeter (dm3) is restricted to the measurement of liquids and gases. No prefix other than milli should be used with liter.

Abstract

The Sacramento–San Joaquin Delta (Delta) of California is an ecologically rich and hydrologically complex region that receives runoff from nearly one-quarter of the state. Water-quality studies of surface water in the region have found dissolved pesticides in winter storm runoff at concentrations toxic to some aquatic invertebrates. However, scientists have little information on pesticide concentrations in the Delta on a seasonal timescale or the importance of pesticide contributions from within-Delta sources. Consequently, the U.S. Geological Survey conducted a study from 1994 to 1996 during which water samples were collected seasonally from 31 sites located within the Delta and on major tributaries to the Delta. Water samples were analyzed for 20 current-use pesticides and dissolved organic carbon. During the study, 11 current-use pesticides were detected; maximum concentrations ranging from 17 ng/L (for trifluralin) to 1,160 ng/L (for metolachlor). The highest concentrations of five pesticides (carbaryl, carbofuran, metolachlor, molinate, and simazine) were greater than 900 ng/L. The greatest number of pesticides was detected in the summer of 1994, whereas the least number were detected in the winter of 1994. The herbicides metolachlor and simazine were the most frequently detected pesticides and were detected in five of the six sampling seasons. The herbicides molinate and EPTC were detected only during the three summer sampling seasons. A comparison of pesticides detected during the spring and summer of 1995 showed some seasonal variability. Comparison of the three summer seasons sampled showed that a larger number of pesticides were detected, and with generally higher maximum concentrations, in 1994 than in 1995 or 1996. Dissolved organic carbon (DOC) concentrations ranged, over the course of the study, from 1.4 mg/L to 10.4 mg/L, and had a median concentration of 3.8 mg/L. On a seasonal basis, the lowest maximum DOC concentrations occurred during the summer and winter of 1994. The highest median DOC concentration on a seasonal basis occurred in the spring of 1995. This previously unreported data is being published now to provide historical information on pesticide concentrations in the Delta to water managers and the scientific community.

Introduction

The Sacramento–San Joaquin Delta (Delta) is a hydrologically complex region within the Central Valley of California comprised of interconnecting sloughs and channels and containing numerous leveed and farmed islands. The Delta is fed by two major river systems, the Sacramento and the San Joaquin as well as by a number of smaller tributaries. The Delta is a highly productive area both ecologically and economically, and is a major source of drinking water for much of California.
In total, the Delta receives runoff from a watershed of nearly 25 million acres. Over five million acres within the watershed are devoted primarily to agriculture and the production of a wide variety of crops. The region also contains numerous urban centers of varying size with a combined area of over half a million acres. During the period of this study, 1994 through 1996, an average of slightly over 55 million pounds of pesticide active ingredient were applied annually in the watershed (California Department of Pesticide Regulation, 2005).
In the Central Valley and Delta, studies have shown that the first significant rainfall (greater than 0.5 in./day) and subsequent runoff following the winter application of dormant spray pesticides is accompanied by a rise in the detected concentrations of these same pesticides in downstream surface waters (Kuivila and Foe, 1995; Kratzer, 1997, Orlando and others, 2003 and 2004). Studies have also shown these pulses of multiple pesticides to be acutely toxic to the aquatic invertebrate Ceriodaphnia dubia (Foe and Connor, 1991, Kuivila and Foe, 1995). However, scientists have little information on the seasonal variation in pesticide concentrations within the Delta or the influence of local, within-Delta, sources of pesticides.
In addition, the toxicity of pesticides to aquatic species is influenced by a variety of environmental factors in natural waters, such as dissolved organic matter (Haitzer and others, 1998). Dissolved organic matter is most commonly quantified in terms of dissolved organic carbon (DOC). The concentration and type of dissolved organic matter can influence the toxicity of a contaminant by increasing or decreasing its bioavailability to aquatic species (Kukkonen and Oikari, 1987; Benson and Long, 1991; Day, 1991; Kadlec and Benson, 1995). It is therefore valuable to measure DOC concentrations when trying to relate pesticide concentrations in natural waters to observed toxicity.
Very little historical information on pesticide concentrations in Delta waterways is available. Data from this study has not been previously published, and is being published now in an effort to augment the historical record. These data will prove useful to water managers and the scientific community in the proposed establishment of Total Maximum Daily Load (TMDL) requirements for the Delta. These data are presented at a time of increased concern over recent declines in fish populations in the region.

Project Design

This project was designed to provide information on the seasonal occurrence and concentrations of current-use pesticides and DOC in surface waters within the Delta and to examine the contribution of pesticides from within-Delta sources. Water samples were collected from 31 sites located in the central Delta and from the major tributaries of the Delta (fig. 1). Samples were analyzed for dissolved pesticides, DOC, and other water-quality parameters (temperature, pH, and specific conductance). Sites were sampled quarterly, beginning in summer 1994, and continuing through summer 1995, and again in summer 1996 (table 1). Water samples were typically collected once during each seasonal period, although not every site was sampled during each period. Samples were collected without regard to the tidal cycle.
Figure 1Location of water-quality sampling sites in the Sacramento–San Joaquin Delta, California.,
(See table 1 for site information.)
Location of water-quality sampling sites in the Sacramento–San Joaquin Delta, California.,
Table 1 (View this table on a separate page.) List and location of sampling sites, sampling method, and seasonal sampling matrix for 1994–1996.
[All sites are located in California. DMS, ˝degree, minute, second˝; id, identification]
Site nameUSGS site id numberSite numberLatitude (DMS)Longitude (DMS)Sampling methodSummer 1994Fall 1994Winter 1994Spring 1995Summer 1995Summer 1996
Mokelumne River at Andrus Island near Terminous11336930138° 06′ 22″121° 34′ 16″BoatX XXXX
Beaver Slough near Thornton381215121264901238° 12′ 15″121° 26′ 49″BridgeXXXXXX
Columbia Cut near Middle River380125121303601338° 01′ 25″121° 30′ 36″Boat XXXX 
Connection Slough near Middle River380000121340801438° 00′ 00″121° 34′ 08″BoatXXXXX 
Empire Cut near Middle River375817121300001537° 58′ 17″121° 30′ 00″Boat XXXX 
False River near Oakley11313440638° 03′ 21″121° 40′ 01″BoatXXXXXX
Mokelumne River near Thornton381519121262401738° 15′ 19″121° 26′ 24″BridgeXXXXX 
Old River at Franks Tract near Bethel Island380300121344801838° 03′ 00″121° 34′ 48″Boat XXXX 
French Camp Slough at French Camp375320121160801937° 53′ 20″121° 16′ 08″BridgeXXXXXX
Grant Line Canal at Tracy Road Bridge113132001037° 49′ 15″121° 27′ 05″BridgeX XXXX
Hog Slough near Thornton3810091212736011138° 10′ 09″121° 27′ 36″Boat XXX  
Little Connection Slough near Terminous3803361213002011238° 03′ 36″121° 30′ 02″BoatXXXXX 
Middle River near Holt113126851338° 00′ 11″121° 30′ 39″BoatXXXXX 
Middle River near Middle River3757211213143011437° 57′ 21″121° 31′ 43″BridgeXXXXXX
Old River at Bacon Island113134051537° 58′ 12″121° 34′ 20″BoatXXXXXX
San Joaquin River at Bouldin Island near Terminous3805241213412011638° 05′ 24″121° 34′ 12″Boat XXXX 
Piper Slough near Bethel Island3801481213652011738° 01′ 48″121° 36′ 52″Boat XXXX 
Potato Slough near Terminous3805241213148011838° 05′ 24″121° 31′ 48″BoatX XXX 
Old River at Quimby Island near Bethel Island113114341938° 01′ 38″121° 33′ 52″Boat XXXXX
Sacramento River at Rio Vista114554202038° 09′ 44″121° 41′ 28″BridgeXXXXX 
Sacramento River at Tower Bridge at Sacramento3834301213020012138° 34′ 30″121° 30′ 24″Bridge XXXXX
San Joaquin River at Vernalis113035002237° 40′ 34″121° 15′ 59″BridgeXXXXXX
Sand Mound Slough at Bethel Island3800001213730012338° 00′ 00″121° 37′ 30″BoatXXXXX 
South Mokelumne River near Iselton3807121213336012438° 07′ 12″121° 33′ 36″Boat XXXX 
San Joaquin River near Stockton3756491212021002537° 56′ 49″121° 20′ 25″BridgeXXXXXX
Sycamore Slough near Terminous3808311212812012638° 08′ 31″121° 28′ 12″BoatX XXXX
Taylor Slough near Bethel Island3801481214004012738° 01′ 48″121° 40′ 04″Boat XXXX 
Little Potato Slough near Terminous113368002838° 06′ 52″121° 29′ 50″Boat  XXXX
Turner Cut near Holt113113002937° 59′ 33″121° 27′ 14″BoatXXXXXX
Werner Slough near Knightsen3757371213615013037° 57′ 37″121° 36′ 15″BoatXXXXXX
White Slough near Terminous3804481212808013138° 04′ 48″121° 28′ 08″Boat X XX 
Water samples were analyzed for 20 current-use pesticides by gas chromatography/mass spectrometry (GC/MS) at the U.S. Geological Survey’s (USGS) organic chemistry laboratory in Sacramento, California. The USGS’s National Research Program laboratory in Ft. Collins, Colorado, conducted the DOC analyses.

Purpose and Scope

The purpose of this report is to describe the methods and procedures used during sample collection and analysis, and presents analytical results for water samples collected during this study. Concentrations of 20 current-use pesticides analyzed in 153 water samples are presented. Dissolved organic carbon concentrations and water parameters analyzed in 132 water samples are also presented. Data contained in this report may be obtained in electronic format by contacting the USGS California Water Science Center’s public information officer in Sacramento, California.

Acknowledgments

This report was prepared in cooperation with the California Bay–Delta Authority. The authors gratefully acknowledge James DeRose, Bryan Jennings and Rob Sheipline of the USGS for assistance with sample collection and logistical support during this project. The authors also wish to acknowledge Kathryn Crepeau and Dave Baston of the USGS for their many hours of laboratory work and pesticide analyses. The U.S. Geological Survey's Toxic Substances Hydrology Program and the California Bay–Delta Authority funded this project and the publication of this report.

Procedures and Methods

Description of Sampling Sites

Sampling sites were selected to provide a good spatial coverage of the Delta and its major tributaries. Thirty-one sites were sampled during the study. Four of these sites (fig. 1: sites 7, 9, 21, and 22) represent flows from major tributaries to the delta: site 7 for the Cosumnes and Mokelumne Rivers, site 9 for the French Camp Slough, site 21 for the Sacramento River system, and site 22 for the San Joaquin River system (fig. 1, table 1). Most of the remaining sites were located in the central portion of the Delta. In addition to acquiring a representative sampling of Delta waters from this hydrologically complex area of interconnecting sloughs and channels, these sites were selected for their proximity to farmed Delta islands and their accessibility by boat.

Sample Collection

Water samples were collected either from bridges or by boat (table 1). All water samples were collected over a single vertical profile in the center of the channel using a USGS D77 depth-integrating sampler equipped with a 3-L Teflon bottle and nozzle. Sample water was poured directly from the 3-L Teflon collection bottle into 1-L and 250-mL baked, amber glass bottles for pesticide and DOC analysis respectively. Samples collected by boat were processed on site, whereas those collected from bridges were placed on ice and transported to the USGS’s organic chemistry laboratory for processing. DOC samples were not collected during the summer 1996 sampling event.

Sample Processing and Analysis

Pesticide Samples

Water samples collected for pesticide analysis were filtered through baked, 0.7-µm glass fiber filters within 24 hours of sampling, and a surrogate compound, terbuthylazine, was added to provide quantitative data on extraction efficiency. Samples were then extracted onto C8 solid-phase extraction cartridges. The cartridges were dried using a syringe to force air repeatedly through each cartridge, frozen, and delivered to the USGS’s organic chemistry laboratory, where they were stored frozen for up to 6 months. For analysis, the cartridges were thawed and then eluted with three 2-mL aliquots of hexane:diethyl ether (1:1). The eluate was concentrated and analyzed for 20 pesticides using a Varian gas chromatograph–mass spectrometer equipped with a Finnigan ion-trap detector. Details of the analytical method are described in Crepeau and others, 1994.
In addition to the 153 regular pesticide samples, another 53 samples were collected for quality control purposes, including 25 field equipment blanks and 28 replicate samples. Surrogate recovery in each sample was another type of quality control data evaluated during this study. None of the pesticides were detected in the field equipment blanks. For replicate samples, the relative percentage differences were less than 25 percent for all the pesticides detected. In all replicate pairs, each compound was either detected in both samples or not detected in both samples. Recovery of the surrogate, terbuthylazine, was used to assess the efficiency of each extraction. The average percentage recovery and standard deviation for terbuthylazine was calculated for each year. Sample data were excluded if the recovery of terbuthylazine was outside the control limit of the annual mean plus or minus two standard deviations.

DOC Samples and Water Parameters

Water samples collected for DOC analysis were filtered through a single 47-mm diameter, 0.45-µm pore size, silver-metal filter, within 24 hours of sample collection. Samples were processed following the procedures described in the USGS Techniques of Water-Resources Investigations handbook (Wilde and others, 1999). The samples were filtered into 250-mL baked amber glass bottles, immediately placed on ice, and shipped within 24 hours to the USGS’s National Research Program laboratory. Samples were analyzed for DOC concentration following the methods described in Aiken (1992).
Water parameters were measured on whole-water samples at the time of collection. Specific conductance and pH were measured using two handheld instruments (Cole Parmer, Model 141-61 and Orion Model 250A, respectively), following procedures outlined in the USGS’s national field manual (Wilde and Radtke, 1998). Water temperature was measured using a digital thermometer.

Results of Dissolved Pesticide and DOC Analyses

This report presents dissolved pesticide and DOC concentrations and water-quality parameter values for surface-water samples collected during six seasons beginning in the summer of 1994. During the study, 153 water samples were analyzed for 20 current-use pesticides by GC/MS at the USGS’s organic chemistry laboratory. DOC concentrations were analyzed in 132 field samples at the USGS’s National Research Program laboratory. Results of these analyses are presented in the following tables: table 2, Water-quality parameters—1994 summer sampling; table 3, Pesticides—1994 summer sampling; table 4, Water-quality parameters—1994 fall sampling; table 5, Pesticides—1994 fall sampling; table 6, Water-quality parameters—1994 winter sampling; table 7, Pesticides—1994 winter sampling; table 8, Water-quality parameters—1995 spring sampling; table 9, Pesticides—1995 spring sampling; table 10, Water-quality parameters—1995 summer sampling; table 11, Pesticides—1995 summer sampling; table 12, Water-quality parameters—1996 summer sampling; and table 13, Pesticides—1996 summer sampling. Pesticides detected at concentrations below the method detection limits as reported in Crepeau and others (1994), are shown in parentheses because these values should be considered estimates. Significant figures were determined on the basis of the rounding method as described in American Society for Testing and Materials (1993).
Table 2 (View this table on a separate page.) Water-quality parameters measured during the 1994 summer sampling season.
[Sites 3, 5, 7, 8, 11, 16, 17, 19, 21, 24, 27, 28, and 31 were not sampled during the period. Sites 2, 14, and 25 were each sampled twice during the sampling period. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mg/L, milligrams per liter; mm, minutes; mm/dd/yyyy, month/day/year; na, not analyzed; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]Dissolved organic carbon (mg/L) [00681]
16/22/199418:4922.67.721721.8 
26/7/199409:3020.56.962232.5 
26/23/199415:42na7.621092.0 
46/21/199420:1922.87.773473.8 
66/23/199410:5822.17.856122.3 
96/7/199410:3018.07.071825.8 
106/7/199414:0021.57.745563.8 
126/22/199413:5122.97.62592.5 
136/21/199419:5322.87.713302.4 
146/7/199415:5021.08.00452na 
146/21/199412:54na7.194073.8 
156/22/199411:1022.87.764123.8 
186/22/199413:1722.87.771922.3 
206/8/199412:3020.77.782303.4 
226/8/199413:0025.57.96963na 
236/23/199409:1422.38.494483.5 
256/7/199416:5022.47.688208.8 
256/21/199415:4323.77.688974.4 
266/22/199416:4719.07.621762.5 
296/21/199414:1123.06.924874.1 
306/22/199409:0422.77.654474.5 
Table 3 (View this table on a separate page.) Pesticides detected during the 1994 summer sampling season.
[Sites 3, 5, 7, 8, 11, 16, 17, 19, 21, 24, 27, 28, and 31 were not sampled during the period. Sites 2, 14, and 25 were each sampled twice during the sampling period. The following pesticides were not detected in any samples: alachlor, butylate, chlorpyrifos, cyanazine, DCPA, fonofos, malathion, methidathion, napropamide, pebulate, and thiobencarb. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected; ( ), detected at a concentration less than the method detection limit]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Atrazine [39632]Carbaryl [49310]Carbofuran [49309]Diazinon [62682]EPTC [82668]Metolachlor [39415]Molinate [50375]Simazine [04035]Trifluralin [82661]
16/22/199418:49ndndndndndndndndnd
26/7/199409:30ndndndndndnd977ndnd
26/23/199415:42ndndndndndndndndnd
46/21/199420:1980ndndndnd(14)nd69nd
66/23/199410:5843ndndndndndnd67nd
96/7/199410:30nd7745nd8781,1601,090127(6)
106/7/199414:007790860ndnd51nd72nd
126/22/199413:5178ndndndnd(21)nd(60)nd
136/21/199419:5381ndndndnd(11)nd65nd
146/7/199415:50ndndndnd(22)(14)nd(55)nd
146/21/199412:5489ndndndnd(15)nd70nd
156/22/199411:1061ndndnd(69)(12)nd63nd
186/22/199413:1767ndndnd(50)(25)ndndnd
206/8/199412:30ndndndndndnd205ndnd
226/8/199413:00ndndndnd(20)(40)ndnd(17)
236/23/199409:1475ndndndndndnd(62)nd
256/7/199416:50ndndndnd(73)107262(56)nd
256/21/199415:43(23)ndndnd134124nd114nd
266/22/199416:47ndndndnd(59)(29)ndndnd
296/21/199414:11121ndndnd(125)(27)nd101nd
306/22/199409:0467ndnd(15)250(33)nd73nd
Table 4 (View this table on a separate page.) Water-quality parameters measured during the 1994 fall sampling season.
[Sites 1, 10, 18, 26, and 28 were not sampled during the period. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mg/L, milligrams per liter; mm/dd/yyyy, month/day/year; na, not analyzed; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]Dissolved organic carbon (mg/L) [00681]
29/21/199414:4022.37.652203.4
39/26/199416:2522.48.003962.2
49/26/199415:3222.07.384452.5
59/26/199413:5023.27.695235.1
69/22/199414:1220.78.139911.8
79/21/199415:2522.57.75592.3
89/28/199410:4519.57.66752.2
99/23/199414:00na6.9824710.3
119/27/199409:1520.87.281913.5
129/27/199413:1621.17.561802.1
139/26/199415:5222.57.774113.2
149/26/199413:2022.67.614346.7
159/26/199412:1921.77.118672.9
169/28/199409:5020.97.043412.3
179/22/199414:3521.17.891,1273.1
199/28/199411:1420.87.636944.0
209/21/199413:2020.57.692252.0
219/21/199408:3019.77.381741.5
229/21/199410:0022.77.348453.1
239/22/199412:1821.56.789212.0
249/27/199416:0021.07.631762.1
259/23/199413:00na6.878084.8
279/22/199413:2321.78.081,0134.8
299/26/199414:2522.57.736433.9
309/22/199416:2521.58.058823.4
319/27/199412:2421.17.551913.6
Table 5 (View this table on a separate page.) Pesticides detected during the 1994 fall sampling season.
[Sites 1, 10, 18, 26, and 28 were not sampled during the period. The following pesticides were not detected in any samples: alachlor, atrazine, butylate, carbaryl, carbofuran, chlorpyrifos, cyanazine, diazinon, EPTC, fonofos, malathion, methidathion, molinate, napropamide, pebulate, simazine, thiobencarb, and trifluralin. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected; ( ), detected at a concentration less than the method detection limit]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)DCPA [39771]Metolachlor [39415]
29/21/199419:40ndnd
39/26/199416:25ndnd
49/26/199415:32ndnd
59/26/199413:50nd(22)
69/22/199414:12ndnd
79/28/199410:45ndnd
89/21/199415:25ndnd
99/23/199414:00nd71
119/27/199419:15ndnd
129/27/199413:16ndnd
139/26/199415:52ndnd
149/26/199413:20ndnd
159/26/199412:19ndnd
169/28/199409:50ndnd
179/22/199414:35ndnd
199/28/199411:14ndnd
209/21/199413:20ndnd
219/21/199408:30ndnd
229/21/199410:00ndnd
239/22/199412:18ndnd
249/27/199416:00ndnd
259/23/199413:00nd(33)
279/22/199413:23ndnd
299/26/199414:25(20)(39)
309/22/199416:25ndnd
319/27/199412:24ndnd
Table 6 (View this table on a separate page.) Water-quality parameters measured during the 1994 winter sampling season.
[Site 31 was not sampled during the period. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mg/L, milligrams per liter; mm, minutes; mm/dd/yyyy, month/day/year; na, not analyzed; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]Dissolved organic carbon (mg/L) [00681]
111/30/199412:3110.57.702243.0
212/5/199410:159.37.212374.1
311/29/199412:3010.37.50387na
411/29/199411:269.77.635543.7
511/29/199413:2610.57.455424.2
612/1/199413:0710.68.002,8403.0
712/5/199409:509.77.251476.5
811/30/199413:3610.57.715833.5
912/5/199416:009.77.208554.8
1012/5/199414:2210.16.671,0204.1
1111/30/199409:479.97.811813.0
1211/29/199415:309.97.742594.3
1311/29/199411:559.87.583843.7
1412/5/199413:4010.27.585503.8
1511/29/199410:159.47.767213.8
1611/30/199413:1010.67.764132.9
1712/1/199414:1310.47.881,7002.5
1811/29/199416:059.87.972444.3
1911/30/199413:5610.57.825803.5
2012/5/199411:408.87.532456.7
2112/5/199408:4010.06.54160na
2212/5/199415:2010.57.369295.3
2312/1/199411:279.17.831,0653.5
2411/30/199411:3610.87.652072.8
2512/5/199413:009.77.329544.6
2611/30/199408:539.87.372453.2
2712/1/199412:209.77.871,2013.2
2811/30/199410:5510.57.642074.0
2911/29/199414:0510.17.516364.5
3011/29/199419:078.96.997375.2
Table 7 (View this table on a separate page.) Pesticides detected during the 1994 winter sampling season.
[Site 31 was not sampled during the period. The following pesticides were not detected in any samples: alachlor, atrazine, butylate, carbaryl, carbofuran, chlorpyrifos, cyanazine, DCPA, diazinon, EPTC, fonofos, malathion, methidathion, metolachlor, molinate, napropamide, pebulate, thiobencarb, and trifluralin. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Simazine [04035]
111/30/199412:31496
212/5/199410:1590
311/29/199412:30242
411/29/199411:26235
511/29/199413:26223
612/1/199413:07223
712/5/199409:50357
811/30/199413:36186
912/5/199416:00nd
1012/5/199414:22120
1111/30/199409:47227
1211/29/199415:30132
1311/29/199411:55212
1412/5/199413:40165
1511/29/199410:15191
1611/30/199413:10184
1712/1/199414:13172
1811/29/199416:05223
1911/30/199413:56207
2012/5/199411:40118
2112/5/199408:40912
2212/5/199415:20171
2312/1/199411:27207
2411/30/199411:36448
2512/5/199413:00457
2611/30/199408:53180
2712/1/199412:20169
2811/30/199410:55299
2911/29/199414:05138
3011/29/199409:07(42)
Table 8 (View this table on a separate page.) Water-quality parameters measured during the 1995 spring sampling season.
[Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mg/L, milligrams per liter; mm, minutes; mm/dd/yyyy, month/day/year; na, not analyzed; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]Dissolved organic carbon (mg/L) [00681]
13/29/199511:5510.87.401273.1
24/4/199513:0518.07.3562710.4
33/28/199515:0012.37.422885.6
43/28/199512:4212.17.383685.5
53/28/199513:1512.37.373785.7
63/29/199509:2211.77.133364.8
74/4/199512:3015.37.65901.9
83/29/199512:5212.57.353925.5
94/4/199515:4020.57.672646.3
104/5/199511:3516.57.11247na
113/29/199508:0011.76.856325.7
123/28/199516:3011.37.152564.4
133/29/199515:2712.47.27393na
144/5/199512:1517.77.732774.4
153/28/199510:5111.77.423704.7
163/29/199512:2612.07.292925.2
173/29/199509:5812.47.213715.1
183/28/199516:5611.37.351684.1
193/29/199514:3012.37.284015.6
204/5/199516:0015.27.582592.3
214/4/199510:5512.47.241351.4
224/4/199514:4815.88.143003.3
233/29/199516:5712.87.44185.5
243/29/199511:1111.37.341434.0
254/4/199516:1516.77.752553.7
263/29/199508:4911.97.662566.1
273/29/199508:3312.47.126148.1
283/29/199510:3011.67.331704.2
293/28/199513:5512.57.373235.6
303/28/199509:5011.57.344815.6
313/28/199517:5311.57.341743.9
Table 9 (View this table on a separate page.) Pesticides detected during the 1995 spring sampling season.
[The following pesticides were not detected in any samples: alachlor, atrazine, butylate, carbaryl, cyanazine, DCPA, EPTC, fonofos, malathion, methidathion, molinate, napropamide, pebulate, thiobencarb, and trifluralin. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected; ( ), detected at a concentration less than the method detection limit]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Carbofuran [49309]Chlorpyrifos [38933]Diazinon [62682]Metolachlor [39415]Simazine [04035]
13/29/199511:55ndndndnd66
24/4/199513:0595836(29)53761
33/28/199515:00ndndndnd145
43/28/199512:4237ndndnd134
53/28/199513:15ndndndnd137
63/29/199509:2279ndnd(16)137
74/4/199512:30ndndndndnd
83/29/199512:52144ndnd(14)142
94/4/199515:40ndndndnd73
104/5/199511:35ndndndndnd
113/29/199508:00ndndnd(14)73
123/28/199516:30ndndnd(11)84
133/29/199515:27130ndndnd137
144/5/199512:15ndndndndnd
153/28/199510:51ndndndnd127
163/29/199512:2664ndnd(16)125
173/29/199509:58130ndndnd138
183/28/199516:56ndndndnd84
193/29/199514:3092ndndnd122
204/5/199516:00ndndndndnd
214/4/199510:55ndndndndnd
224/4/199514:48ndndndndnd
233/29/199516:57138ndnd(18)143
243/29/199511:11ndndndnd129
254/4/199516:15ndndndnd67
263/29/199508:49ndndndnd200
273/29/199508:3366ndndnd141
283/29/199510:30ndndndnd73
293/28/199513:55ndndndnd140
303/28/199509:50114ndnd60139
313/28/199517:53ndndndnd79
Table 10 (View this table on a separate page.) Water-quality parameters measured during the 1995 summer sampling season.
[Site 11 was not sampled during the period. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mg/L, milligrams per liter; mm, minutes; mm/dd/yyyy, month/day/year; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]Dissolved organic carbon (mg/L) [00681]
16/2/199508:4117.07.37922.5
26/7/199515:3818.07.282055.0
36/1/199515:3420.07.161343.2
45/30/199512:5119.47.061613.8
56/1/199513:3621.06.921624.0
65/26/199511:4018.17.591583.7
76/7/199514:3017.06.75693.0
85/26/199509:1818.07.091605.1
96/8/199511:5017.07.4421510.4
106/8/199512;3015.27.541462.7
126/1/199516:1720.07.161374.8
135/30/199513:1919.76.931644.0
146/1/199512:0520.06.811496.1
155/30/199508:2918.76.691654.6
166/2/199509:5319.07.241163.8
175/26/199512:1218.57.371583.4
186/2/199509:3219.07.24932.6
195/26/199508:5618.06.721625.1
206/8/199509:3011.57.341162.7
216/5/199509:5515.06.78902.1
226/5/199511:3014.56.861364.2
235/26/199509:5818.47.31625.9
246/2/199508:1017.07.1881.4
256/8/199510:457.07.331333.4
266/2/199521:2221.08.10712.4
275/26/199510:5518.67.552544.6
286/1/199520:0019.07.28924.3
296/1/199514:1421.07.051484.2
305/30/199511:1619.67.061914.1
316/1/199519:0721.07.46882.7
Table 11 (View this table on a separate page.) Pesticides detected during the 1995 summer sampling season.
[Site 11 was not sampled during the period. The following pesticides were not detected in any samples: alachlor, atrazine, butylate, carbaryl, carbofuran, chlorpyrifos, cyanazine, DCPA, fonofos, malathion, methidathion, napropamide, pebulate, thiobencarb, and trifluralin. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected; ( ), detected at a concentration less than the method detection limit]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Diazinon [62682]EPTC [82668]Metolachlor [39415]Molinate [50375]Simazine [043035]
16/2/199508:41ndndnd148nd
26/7/199515:38ndndndndnd
36/1/199515:34ndnd(17)ndnd
45/30/199512:51ndnd(22)ndnd
56/1/199513:36nd(15)(16)ndnd
65/26/199511:40nd(43)(19)ndnd
76/7/199514:30ndndndndnd
85/26/199509:18nd(48)(15)ndnd
96/8/199511:50nd139148441116
106/8/199512:30ndnd(16)ndnd
126/1/199516:17nd(20)(14)ndnd
135/30/199513:19ndnd(19)ndnd
146/1/199512:05nd(17)(15)ndnd
155/30/199508:29nd160(17)ndnd
166/2/199509:53ndndndndnd
175/26/199512:12nd(62)(22)ndnd
186/2/199509:32ndndndndnd
195/26/199508:56nd(29)(19)ndnd
206/8/199509:30ndndnd119nd
216/5/199509:55ndndnd242nd
226/5/199511:30ndnd(11)ndnd
235/26/199509:58nd(79)(16)ndnd
246/2/199508:10ndndnd108nd
256/8/199510:45ndnd(31)ndnd
266/2/199521:22ndndndndnd
275/26/199510:55ndnd(19)ndnd
286/1/199520:00ndndnd73nd
296/1/199514:14ndnd(14)ndnd
305/30/199511:16(19)176(33)ndnd
316/1/199519:07ndndndndnd
Table 12 (View this table on a separate page.) Water-quality parameters measured during the 1996 summer sampling season.
[Sites 3, 4, 5, 7, 8, 11, 12, 13, 16, 17, 18, 20, 23, 24, 27, and 31 were not sampled during the period. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; na, not analyzed; °C; degrees Celsius; μS/cm, microsiemens per centimeter]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Temperature (°C) [00010]pH [00400]Specific conductance (μS/cm) [00094]
16/28/199611:0619.77.41118
26/28/199618:4719.77.4661
66/26/199618:5721.07.83114
97/1/199612:1524.27.68133
107/1/199614:0025.1nana
146/26/199613:3222.17.72173
156/26/199614:2621.67.46120
196/26/199612:1421.36.94160
217/1/199610:3521.17.75111  
227/1/199613:1025.07.59586
256/27/199613:4720.87.37614
266/28/199609:0419.57.1993
286/27/199617:2421.17.49140
296/27/199611:4022.17396
306/26/199615:2322.57.69132
Table 13 (View this table on a separate page.) Pesticides detected during the 1996 summer sampling season.
[Sites 3, 4, 5, 7, 8, 11, 12, 13, 16, 17, 18, 20, 23, 24, 27, and 31 were not sampled during the period. The following pesticides were not detected in any samples: alachlor, atrazine, butylate, carbofuran, cyanazine, DCPA, diazinon, fonofos, malathion, methidathion, napropamide, pebulate, and thiobencarb. Concentrations are shown in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes. hh, hours; id, identification; mm, minutes; mm/dd/yyyy, month/day/year; nd, not detected, ( ), detected at a concentration less than the method detection limit]
Site id numberDate (mm/dd/yyyy)Time (hh:mm)Carbaryl [49310]Chlorpyrifos [38933]EPTC [82668]Metolachlor [39415]Molinate [50375]Simazine [043035]Trifluralin [82661]
16/28/199611:06ndndndnd244ndnd
26/28/199618:47ndndnd72ndndnd
66/26/199618:57ndndndnd242ndnd
97/1/199612:1576.5(28)(28)141(25)(23)nd
107/1/199614:00ndnd(87)100ndndnd
146/26/199613:32ndnd(35)(23)193ndnd
156/26/199614:26ndnd(18)(11)208ndnd
196/26/199612:14ndnd(22)(12)218ndnd
217/1/199610:35ndndndnd116ndnd
227/1/199613:10ndnd(50)(44)(17)nd(11)
256/27/199613:47ndnd(62)188(14)(11)nd
266/28/199609:04ndndnd71111ndnd
286/27/199617:24ndndndnd269ndnd
296/27/199611:40ndnd(42)6765ndnd
306/26/199615:23111nd(18)(13)163ndnd
During this study, 11 current-use pesticides were detected, and maximum concentrations ranged from 17 ng/L for trifluralin to 1,160 ng/L for metolachlor. The highest concentrations of five pesticides (carbaryl, carbofuran, metolachlor, molinate, and simazine) were greater than 900 ng/L. Metolachlor and simazine were the most frequently detected pesticides (37 and 46 percent of all samples, respectively) and were observed in five out of the six sampling seasons (table 14). EPTC and molinate were detected in 20 and 15 percent of all samples, respectively, and were detected only during the three summer sampling seasons (table 14).
Table 14 (View this table on a separate page.) Seasonal detections of pesticides 1994–1996.
[Values are percent detected out of the total number of samples analyzed in a given season; number in parentheses is the maximum concentration detected for a particular compound, in nanograms per liter. Numbers in brackets are USGS National Water Information System (NWIS) parameter codes]
 Total number of samples analyzedAtrazine [39632]Carbaryl [49310]Carbofuran [49309]Chlorpyrifos [38933]DCPA [39771]Diazinon [62682]EPTC [82668]Metolachlor [39415]Molinate [50375]Simazine [043035]Trifluralin [82661]
Summer 1994 2157.1 (121)9.5 (908)9.5 (60)  4.8 (15)47.6 (878)71.4 (1,160)19.0 (1,090)66.7 (127)9.5 (17)
             
Fall 1994 26    3.8 (20)  15.4 (71)   
             
Winter 199430         96.7 (912) 
             
Spring 199531  35.5 (958)3.2 (36) 3.2 (29) 25.8 (60) 80.6 (761) 
             
Summer 199530     3.3 (19)36.7 (176)63.3 (148)20.0 (441)3.3 (116) 
             
Summer 199615 13.3 (111) 6.7 (28)  60.0 (87)73.3 (188)86.7 (269) 13.3 (23)6.7 (11)
Seasonally, the greatest number of pesticides and the largest concentrations for 6 of the 11 pesticides were detected in the summer sampling events. In contrast, only DCPA and metolachlor were detected in the fall 1994 sampling event and only simazine was detected in the winter 1994 sampling event. It should be noted that sampling during this study was not timed to follow rainfall events, and many studies have documented elevated concentrations of multiple pesticides in surface waters following storm events (Kuivila and Foe, 1995; Orlando and others, 2003 and 2004). Greater numbers of pesticides were detected during the spring 1995, summer 1995, and summer 1996 sampling events than in the previous fall and winter samplings. Maximum concentrations were generally much higher for those pesticides that were detected in the summer of 1994 as compared with detections in the summers of 1995 and 1996 (table 14).
A comparison of pesticide detections may be made between the spring and summer 1995 seasons. During these two seasons, 30 identical sites were sampled, which provides a good basis for comparison. Five pesticides were detected in each season; three, diazinon, metolachlor, and simazine, were detected in both seasons (tables 9 and 11). The insecticides carbofuran and chlorpyrifos, which are applied to alfalfa, were detected in spring 1995, whereas EPTC and molinate, herbicides used on alfalfa and rice, respectively, were detected in summer 1995 (fig. 2). Diazinon was detected in only one sample in each season, but not at the same site, and at concentrations less than 30 ng/L. Metolachlor was detected at numerous sites, mainly in the central Delta, in both seasons, and concentrations were generally less than 35 ng/L (fig. 3). Simazine was observed at sites throughout the central Delta in spring 1995 at concentrations greater than 100 ng/L, but was present in only one sample during the summer sampling event.
Figure 2Number of sites with pesticide detections in spring and summer 1995.
Number of sites with pesticide detections in spring and summer 1995.
Figure 3AMetalachlor detections during the spring (A) and summer (B) of 1995.
Metalachlor detections during the spring (A) and summer (B) of 1995.
Figure 3BContinued.
Continued.
Comparison of the three summer sampling seasons shows that more individual pesticides were detected, and with generally higher maximum concentrations, in the summer of 1994 than in 1995 or 1996. Nine pesticides were found in samples from summer 1994, whereas five were detected in 1995 and seven in 1996. EPTC, metolachlor, molinate, and simazine were detected during each summer sampling event, though only metolachlor was detected in greater than 50 percent of the samples collected in each summer. Detection frequencies of molinate and simazine were each above 20 percent in only one of the three summers, 1996 and 1994 respectively. Detection frequencies for all pesticides were generally lowest in summer 1995 (table 14). Both metolachlor and EPTC were primarily found at sites in the central and southern Delta (figs. 4 and 5). In 1994 and 1995, molinate was detected in the north Delta and French Camp Slough, whereas in 1996 it was present throughout the central Delta (fig. 6).
Figure 4AMetolachlor detections in the summer of 1994 (A), 1995 (B), and 1996 (C).
Metolachlor detections in the summer of 1994 (A), 1995 (B), and 1996 (C).
Figure 4BContinued.
Continued.
Figure 4CContinued.
Continued.
Figure 5AEPTC detections in the summer of 1994 (A), 1995 (B), and 1996 (C).
EPTC detections in the summer of 1994 (A), 1995 (B), and 1996 (C).
Figure 5BContinued.
Continued.
Figure 5CContinued.
Continued.
Figure 6AMolinate detections in the summer of 1994 .(A), 1995 (B), and 1996 (C).
Molinate detections in the summer of 1994 .(A), 1995 (B), and 1996 (C).
Figure 6BContinued.
Continued.
Figure 6CContinued.
Continued.
Overall, DOC concentrations ranged from 1.4 mg/L to 10.4 mg/L, and had a median concentration of 3.8 mg/L. On a seasonal basis, the lowest maximum DOC concentrations occurred in summer 1994 and winter 1994. The highest median concentration on a seasonal basis occurred in spring 1995 (fig. 7). The highest DOC concentrations were detected at French Camp Slough in two of the five seasons sampled (table 15).
Figure 7Box plots of dissolved organic carbon concentration by season.
Box plots of dissolved organic carbon concentration by season.
Table 15 (View this table on a separate page.) Seasonal range, median concentration, and location of highest dissolved organic carbon concentration, 1994–1996.
[Dissolved organic carbon was not analyzed in the summer 1996 season; mg/L, milligrams per liter; na, not analyzed]
 Range of dissolved organic carbon concentrations (mg/L)Median dissolved organic carbon concentration (mg/L)Location of highest dissolved organic carbon concentrationSite number
Summer 19941.8 to 8.8 3.5Stockton25
Fall 19941.5 to 10.33.1French Camp9
Winter 19942.5 to 6.73.8Rio Vista7
Spring 19951.4 to 10.45.1Beaver Slough2
Summer 19951.4 to 10.43.9French Camp9
Summer 1996nananana

References

Aiken, G.R., 1992, Chloride interference in the analysis of dissolved organic carbon by the wet oxidation method: Environmental Science and Technology, v. 26, p. 2435–2439.

American Society of Testing and Materials, 1993, Annual book of ASTM standards, Committee E-11 on Quality and Statistics, ASTME29-93a—standard practice for using significant digits in test data to determine conformance with specifications: ASTM, p. 18–21.

Benson, W.H., and Long S.F., 1991, Evaluation of humic-pesticide interactions on the acute toxicity of selected organophosphate and carbamate insecticides: Ecotoxicology and Environmental Safety, v. 21, p. 301–307.

California Department of Pesticide Regulation, 2005, Pesticide use data for 1994–1996 [digital data]: Sacramento, Calif., California Department of Pesticide Regulation.

Crepeau, K.L., Domagalski, J.L., and Kuivila, K.M., 1994, Methods of analysis and quality-assurance practices of the U.S. Geological Survey Organic Laboratory, Sacramento, California—determination of pesticides in water by solid-phase extraction and capillary-column gas chromatography/mass spectrometry: U.S. Geological Survey Open-File Report 94-362, 17 p.

Day, K.E., 1991, Effects of dissolved organic carbon on accumulation and acute toxicity of fenvalerate, deltamethrin, and cyhalothrin to Daphnia magna Straus: Environmental Toxicology and Chemistry, v. 10, p. 99–101.

Foe, C.G., and Connor, Valerie, 1991, San Joaquin watershed bioassay results, 1988–1990: Sacramento, Calif., Central Valley Regional Water Quality Control Board, Staff Report, 79 p.

Haitzer, Markus; Höss, Sebastian; Traunsperger, Walter; and Steinberg, Christian; 1998, Effects of dissolved organic matter (DOM) on the bioconcentration of organic chemicals in aquatic organisms, a review: Chemosphere, v. 37, no. 7, p. 1335–1362.

Kadlec, M.C., and Benson, W.H., 1995, Relationship of aquatic natural organic material characteristics to the toxicity of selected insecticides: Ecotoxicology and Environmental Safety, v. 31, p. 84–97.

Kratzer, C.R., 1997, Transport of diazinon in the San Joaquin River Basin, California: U.S. Geological Survey Open File Report 97-411, 22 p.

Kuivila, K.M., and Foe, C.G., 1995, Concentrations, transport, and biological effects of dormant spray pesticides in the San Francisco Estuary, California: Journal of Environmental Toxicology and Chemistry, v. 14, no. 7, p. 1141–1150.

Kukkonen, Jussi; and Oikari, Aimo; 1987, Effects of aquatic humus on accumulation and acute toxicity of some organic micropollutants: Science of the Total Environment v. 62, p. 399–402.

Orlando, J.L., Jacobson, L.A., and Kuivila, K.M., 2004, Dissolved pesticide and organic carbon concentrations detected in surface waters, Northern Central Valley, California, 2001–2002: U.S. Geological Survey Open File Report 2004-1214.

Orlando, J.L., Kuivila, K.M., and Whitehead, Andrew, 2003, Dissolved pesticide concentrations detected in storm-water runoff at selected sites in the San Joaquin River Basin, California, 2000–2001: U.S. Geological Survey Open File Report 03-101.

Wilde, F.D., and Radke, eds., 1998, Field measurements: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap A6, [chapter sections variously dated].

Wilde, F.D., Radke, D.B., Gibs, J., and Iwatsubo, R.T., eds., 1999, National field manual for the collection of water quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps A2–A5, [chapter sections variously dated].