California Department of Pesticide Regulation
Environmental Monitoring and Pest Management
1020 N Street, Room 161
Sacramento, CA 95814-5624

Updated: May 17, 1996

Study 143: Chlorpyrifos and Diazinon Monitoring in the Central Contra Costa Sanitary District Sewer System

I. Introduction

The Central Contra Costa Sanitary District (CCCSD) is a sewage collection and treatment system that serves nearly 400,000 residents in 10 cities and 2 unincorporated towns within Contra Costa county. CCCSD's treatment facility in Martinez treats approximately 38 million gallons of wastewater each day. CCCSD's influent comes from a variety of commercial and residential sources which is eventually treated and then released into adjacent Suisun Bay.

In 1986, the San Francisco Bay Regional Water Quality Control Board first made the request to the Central Contra Costa Sanitary District (CCCSD) to initiate an Effluent Toxicity Characterization Program to characterize toxicity of its treated effluent on selected aquatic test species. Results from the program revealed that 67% of the 18 test events produced acute toxicity to Ceriodaphnia dubia (AQUA-Science, 1993). The Regional Board then required that CCCSD perform Toxicity Identification Evaluation (TIE) studies to determine the specific cause(s) of the toxicity. Subsequent TIE studies revealed diazinon and chlorpyrifos, two organophosphate insecticides, as the particular contaminants causing toxicity in CCCSD's effluent (AQUA-Science, 1992).

CCCSD began monitoring studies in 1993 to identify potential sources of chlorpyrifos and diazinon (Pomroy, 1994) (AQUA-Science, 1995). These studies showed that both residential and commercial sources contributed residues of the two organophosphates to the sewer system. Residential areas sampled consisted primarily of single and multiple family dwellings. Commercial sources included pest control operators, kennels, and pet groomers. The mass contributions of each source however, have not yet been quantified nor have they been compared to the amount of each of the insecticides entering the treatment plant.

Although the concentrations of chlorpyrifos and diazinon entering the plant are found at very low levels (parts per trillion), treatment techniques currently employed by CCCSD have little effect in reducing the organophosphate levels. The option of adding treatment facilities has been considered; however, such an addition would be very costly. CCCSD has thus preferred the route of source reduction. Beginning in the Spring of 1995, CCCSD attempted to better educate the public with point-of-sale brochures, newspaper and movie theater ads, and educational workshops promoting safe pesticide usage and disposal. CCCSD has been working with members of the Pest Control Operators of California and the Contra Costa County Agricultural Commissioner to develop pollution prevention practices. The mass loading data generated from this study will be used by CCCSD to help improve the design of both residential and commercial programs to reduce the amount of organophosphates entering the sewer system.

II. Objectives

To estimate the daily mass contribution of commercial and residential sources of chlorpyrifos and diazinon in the CCCSD sewer system. To estimate the average daily mass loads of the two insecticides in CCCSD's influent during high-use months. To compare CCCSD influent mass load with those from the Union Sanitary District and the Palo Alto Regional Water Quality Control Plant.

III. Personnel

This study will be conducted by personnel from the Environmental Hazards Assessment Program in the Environmental Monitoring and Pest Management Branch of the California Department of Pesticide Regulation, and with personnel from the Source Control Section of the Central Contra Costa Sanitary District. Study personnel include:

Project Leader:Nan Singhasemanon
Field Coordinator:Craig Nordmark
Consulting Statistician:Rosie Gallavan
Laboratory Liaison:Cindy Garretson
Senior Scientist:Heinz Biermann
Agency & Public Contact:Peter Stoddard
Project Leader:Bart Brandenburg
Field Coordinators: Roberta Peterson, Beverly Baclig, Kurt Darner
Field Assistants: Dan Lescure, Warren Lai
Chemist: Tri Nguyen
Consultant: Jeff Miller (AQUA/Science)
Union Sanitary District
Agency Contact: Donna Wier
Palo Alto Regional Water Quality
Control Plant
Agency Contact: Susan Healy


IV. Study Plan and Sampling Methods

Past monitoring of CCCSD influent for chlorpyrifos and diazinon suggested that the average daily concentrations are higher in the warmer months. This could be indicative of increased uses of the insecticides in both residential and commercial sources during this period. Sampling is thus structured to cover this period and is projected to begin in June, 1996. On the following page, a sampling schedule and the proposed number of samples for the study are provided in Table 1.

Table 1 Sampling Schedule for Study 143:
Chlorpyrifos and Diazinon Monitoring in the CCCSD Sewer System

Sample Type Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Week 11 Week 12 Total
CCCSD Influent1 2* 2 2 7 2* 2 2 7 2 2 2 7 39
Union San Influent 7 7
Palo Alto Influent 7 7
Residential (5 sites)2 1* 35 8 44
Commercial (12 sites)3 2* 6* 6 6 6 6 6 38
Field Blanks 1* 5 2* 2 2 3 1 2 2 2 22
Equipment Blanks 1* 1 1* 1 3 1 1 9
Total 7 2 3 47 11 10 11 27 12 10 11 15 166
1 = Two influent samples will be taken each week on a Sunday and on a Wednesday. During weeks 4, 8 and 12 daily samples will be taken for 7 days. All influent samples will be 24-hr. composites.

2 = The only residential sample from week 1 will be a grab for an interlaboratory split. Week 4 of residential sampling consists of simultaneous 24-hr. composites at five sites. Week 9 comprises of 3-hr. composites for a 24 hr. period at one site.

3 = Commercial samples from week 1 will be grab samples (kennel & PCO) for an interlaboratory split. The remaining commercial samples will be 24-hr. composites. Two commercial sites will be sampled per week.

* = Interlaboratory comparison samples: DPR and CCCSD for GC/MS analysis, AQUA-Science for ELISA

Influent Sampling

CCCSD Influent samples will be taken from the sewage entry point after the barscreens. A Sigma model 900 autosampler connected to the plant's influent flowmeter will be programmed to take "flow- proportioned composite samples". Thus, for a predetermined volume that enters the plant, the autosampler will collect a fixed volume in response. A 12-L compositing glass jar will be used to collect the waste water samples. When the sampling period has been completed, the composite sample will be mixed and then transferred into a 1-liter amber glass bottle with a teflon-lined cap. These bottles will be supplied and prelabeled by DPR. Any necessary preservative will be added to the sample bottle as soon as possible prior to transport to the analytical laboratory.

Semi-weekly sampling (Sundays and Wednesdays) of the CCCSD influent for a twelve-week period (in conjunction with real-time influent flow measurements) will provide an estimate for weekend and weekday inputs of diazinon and chlorpyrifos to the plant. More intensive daily sampling will occur in weeks 4, 8, and 12. In addition, simultaneous daily sampling and flow measurements of the influent at Union Sanitary District (Alameda County) and at Palo Alto Regional Water Quality Control Plant (Santa Clara County) is planned for week 8. This will make the relative comparison of mass loading among the three treatment plants possible.

Residential Sampling

Residential and commercial sampling will be done separately due to equipment and resource constraints. CCCSD and DPR crews will sample five predetermined residential sites daily for a one week period. Residential sites were selected with consideration to 1) they contained no commercial or industrial dischargers 2) they were accessible and allowed for accurate flow metering 3) they provided a representative socio-economic cross-section of the community and 4) they have been studied before in a CCCSD residential metal study (Larry Walker & Associates, 1993). Information on the selected areas are listed in Table 2.

TABLE 2: Residential Sampling Areas

Site # Location Residential Area Residences per Area Acreage per Area Density
1 2nd Ave. South Martinez/Pacheco 2,079 684 3.0
2 Turtle Rock Lane Concord 1,593 313 5.1
3 Acalanes Lafayette 829 773 1.1
4 Miner Road Orinda 858 1,285 0.7
5 Greenbrook Danville 991 345 2.9

For residential areas, samples will be taken using the ISCO 2700 or the ISCO 2900 autosamplers stocked with 24 polyethylene bottles. Since only one Montedoro-Whitney flowmeter (with a Q-Logger and Sonic Star depth/velocity probe) is available, a true flow-proportioned composite sample can not be taken simultaneously at all five residential sites and will be done manually. Flow measurements at the residential sites will be done prior to the sampling period. The daily flow regimes for each day of the week at each location will then be used to flow-proportionally composite the hourly waste water samples by determining the ratio of each hour's flow to the total daily flow. Residential flow patterns will be periodically confirmed to make certain that they have not markedly shifted during the sampling period.

Commercial Sampling

A total of 12 commercial sites will be selected for sampling. Seven of these sites have been sampled before in the past studies done by CCCSD. Commercial sites can generally be classified into three groups: pet groomers, kennels, and pest control operators. Commercial sites were chosen on the basis that 1) no potential sources or users of pesticides are located upstream from the site, 2) they were accessible and allowed for accurate flow measurement, 3) they represent a variety of geographic cross-sections of the CCCSD service area, 4) these locations are adequately safe for the field crew and 5) they are representative of each business type's activities.

ISCO 2900 autosamplers will also be used for the commercial sites. However, lower flows at these locations will require the use of an ISCO Flow Poke (with a model 4230 bubbler meter). Instead of manually flow compositing the samples together as is required for the residential sites, the flowmeter/autosampler combination can be programmed to take flow-proportioned composite samples. Two commercial sites will be sampled per week.

Field Quality Control

Due to the extremely low concentrations of the analytes, two types of field quality control samples will be used in this study. Field blanks will be collected (using ultra-pure water) at least once at each site to detect site specific contamination. These blanks will be subjected to the same exposure scenarios as the wastewater samples once they are removed from the autosampler. Equipment blanks or rinse blanks will be used to assess the cleanliness of the autosampler setup. These blanks will mimic a wastewater sample from when it is taken to when it is deposited into the sample container. Equipment blanks (using ultra-pure water) will be done at least once every other week to make sure that CCCSD's equipment cleaning standards and protocols are adhered to. The specific procedures for these quality control samples are described in more details in the Environmental Hazards Assessment Program's Standard Operating Procedures (SOP's).

V. Data Analysis

The mass estimate for residential sources will be determined using historical flow data (obtained with the Montedoro-Whitney flowmeter) at each sampling site and chemical results of 24-hour flow-proportioned composite samples.

The mass estimate for treatment plant influents and commercial sources will be determined using real time flow data obtained from the ISCO Flow Poke flowmeter, and chemical concentrations of 24-hour flow-proportioned composite samples.

VI. Laboratory Methods and Quality Control

The Agricultural and Priority Pollutants Laboratory (APPL) in Fresno, California will be performing the chemical analysis. An analyte stability study as well as the method development and validation will be performed according to Standard Operating Procedure QAQC001.00, prior to the study's commencement. Continuing quality control will also be conducted in accordance with this Standard Operating Procedure.

CCCSD's on-site laboratory (Martinez, California) and AQUA-Science's laboratory (Davis, California) will also be analyzing a subset of samples as a part of an interlaboratory comparison. A percentage of the environmental samples will be split three-ways for each laboratory. Both APPL and CCCSD will use the GC/MS for analysis. Aqua-Science will utilize an ELISA method for quantification.

VII. Timetable

Method Detection Limit Determination: March to May, 1996
Analyte Degradation Study: March to May, 1996
Chemical Method Validation: March to May, 1996
Residential Flow Characterization: April, 1996
Flow Meter Purchase: April, 1996
Sample Collection: June to August, 1996
Chemical Analyses: June to August, 1996
Draft Report: November, 1996

VIII. References

AQUA-Science. December, 1992. Final Report. CCCSD Phase III Toxicity Identification Evaluation Studies with Ceriodaphnia.

AQUA-Science. March, 1993. Final Report. Effluent Toxicity Characterization Program for Central Contra Costa Sanitary District. 4 Volumes.

AQUA-Science. October 18, 1995. Summary Report, Volume 1. Diazinon and Chlorpyrifos in Influent Sources from Residential and Commercial Sources.

Larry Walker & Associates. Final Report. May, 1993. Residential Metals Study. Prepared for the Central Contra Costa Sanitary District.

Pomroy, Joseph. March 25, 1994. Technical Memorandum on Pollution Prevention Effort to Identify Sources of Pesticides. Memorandum to Bart Brandenburg, Source Control Division, Central Contra Costa Sanitary District.

Standard Operating Procedure Number: QAQC001.00. Chemistry Laboratory Quality Control. California Department of Pesticide Regulation, Environmental Hazards Assessment Program, Sacramento, CA.