Department of Water Resources Home

Water Quality Evaluation Section

North Central Region Office

Water Quality Evaluation Section


3500 Industrial Blvd.
West Sacramento, CA 95691
(916) 376-9600

Mailing Address:
P.O. Box 942836
Sacramento, CA 94236-0001



Untitled Document

 Water Quality Evaluation Section

Rock Slough Monitoring Program Metadata


I. Contact Information

Program Manager: Shaun Philippart

Lead contact: Patrick Scott
Environmental Scientist
Department of Water Resources - North Central Region Office
3500 Industrial Blvd., West Sacramento 95691
Office: (916) 376-9648

DWR Bryte Chemical Laboratory
1450 Riverbank Road,
West Sacramento, CA 95605
(916) 375-6008

Sid Fong: Supervisor of Bryte Chemical Laboratory

II. Study Area and Sample Site Objectives

A. General Information

This monitoring program was initiated in August 2001 by DWR in accordance with the provisions of the SWRCB Water Right Decision (D-1641), in which SWP and CVP are responsible for maintaining the water quality objectives for municipal and industrial beneficial uses within Sacramento-San Joaquin Delta. D-1641 identified a compliance monitoring station in Rock Slough located at Contra Costa’s Water District’s Pumping Plant No. 1. This compliance station is responsible for meeting the water quality objectives set by the SWRCB that requires maximum mean daily chloride levels to be below 150 mg/L for a set number of days based on water year type (SWRCB Water Quality Control Plan 2006).

To further identify other sources and the extent of water quality degradation, specifically salt loading within Rock Slough, the Water Quality Evaluations Section of North Central Region Office was requested by the State Water Projects Analysis Office and Operations and Maintenance to establish a water quality monitoring program within Rock Slough between Old River and Contra Costa Canal. The monitoring efforts support maintaining State Water Project operational flexibility, and prepare water project managers for future SWRCB review of Delta water quality standards.

Presently the program includes 5 monitoring stations between Old River and Contra Costa Canal that continuously sample for specific conductance and water temperature. There is also a bi-weekly grab-sample taken at each monitoring station for direct laboratory analysis of chloride/bromide concentrations. Specific conductance times-series data is used as a surrogate to indirectly determine chloride concentrations on a continuous basis, through regression analysis with direct laboratory measurement results.

B. Name and Location Information for Continuous Water Quality Sampling Sites

- Rock Slough Stations Map

C.  Station Period of Record, Instrumentation, and Parameter Collection History

-Rock Slough Stations Table

D.  CDEC and Water Data Library Station Codes

-CDEC and WDL Station Codes Table

III. Sampling Frequency

A. Sonde Instrument Sampling

There are a total of 5 Rock Slough water quality monitoring stations that collect time-series data at 15 minute intervals using a YSI 6600 or 600XLM internal data logging sonde.  All stations record a single measurement for temperature (Cº) and specific conductance (µS/cm), within the 15 minute interval.

B. Field Instrument Sampling

Upon each site visitation (can vary from weekly to every 3 weeks), calibrated handheld field instruments are used to sample current water conditions and compare water quality measurements to the YSI 6600 or 600 continuous monitoring stations.  Water temperature (Cº) and specific conductance (µS/cm) measurements are field verified with an YSI 63 Handheld pH and Conductivity Instrument.

C. Discrete Sampling           

Staff collects a chloride/bromidesample in a plastic quart bottle at 1 meter depth with a Van Dorn sampling device at each site.  The chloride/bromide sample and other field measurements are sampled at a 1 meter depth since the YSI 6600 sondes are also sampling at this depth.  During each field run, DWR staff also collects a duplicate chloride/bromide sample at one of the stations to test for field and lab precision and repeatability.

IV. Field Methods

A. Field measurements

During each site visit field readings are taken using portable and handheld instruments.  These handheld instruments are calibrated to comply with manufacturers or laboratory specifications.  Field readings are taken and recorded for comparison with YSI sonde data.  Field measurements are taken at each site at a 1meter depth to duplicate depth of deployed YSI sondes. 

YSI 63 Handheld pH and Conductivity Instrument

The YSI 63 Handheld Instrument measures temperature, conductivity, pH, and salinity.  The instrument is calibrated once a month for conductivity and pH is calibrated before each field run.

YSI Professional Optical Dissolved Oxygen Meter

The YSI Professional Optical Dissolved Oxygen meter measures percent saturation and mg/L of dissolved oxygen.  The instrument is checked and calibrated before each field run.

HACH 2100P Portable Turbidimeter

The HACH 2100P turbidimeter measures turbidity optically using the nephelometric principle.  The portable instrument is calibrated every three months using manufactures StablCal standards to assure accuracy.

B. Sample Collection

Staff collects discrete chloride/bromide and total suspended solids at 1 meter depth with a Van Dorn at each monitoring station.  One sample field run is duplicated, on a rotating basis, for quality assurance/quality control testing at the lab

C. Sample containers and holding times

The DWR Bryte laboratory supplies all necessary sampling materials to the NCRO Water Quality Evaluation field staff. Requirements for sample containers, preservation techniques, and holding times are found in one of the following references (or later editions): Standard Methods for the Examination of Water and Waste Water, American Public Health Association, et al., 21st Edition; Handbook for Sampling and Sample Preservation of Water and Wastewater, 2005, and 1979 US EPA Manual entitled “Methods for Chemical Analysis of Water and Wastes,” EPA-600/4-79-020.

V. Laboratory Methods

All water quality analyses are conducted by staff at the DWR Bryte Laboratory. Located in West Sacramento, the lab’s primary function is to analyze drinking water, surface water, groundwater, and wastewater. Bryte lab has maintained certification by the Environmental Protection Agency and the California Department of Health Services for water analysis since 1978. It also provides quality assurance, and related technical services.

Bryte Laboratory Method Chart for Discrete Sample Analyses

VI. Data Management

A. Sonde Data

Post-deployment Quality Assurance

After the YSI 6600 sondes are removed from the field, DWR staff perform the following two procedures to check whether the sondes are still operating properly and measuring accurately:

  1. A post-deployment accuracy check on the day the sondes are removed and before the instruments are cleaned
  2. A comparison between the data measured by the handheld field instruments and the data collected by the sonde at the closest 15 minute time interval.

The accuracy of sonde probes while deployed in the field can be negatively affected by probe malfunction, drift away from initial calibration, and/or fouling caused by biological growth on the probe reading surface.  DWR staff perform the post-deployment accuracy check by the following procedure prior to cleaning the sonde probes:

  1. Placing the sonde probes in fresh calibration standards with known values
  2. Operating the sondes in the standards and recording the values the sondes are reading
  3. Rating the values collected during the accuracy check for each constituent as excellent, good, fair, or poor based on their deviation from the calibration standard according to the USGS technical report “Guidelines and Standard Procedures for Continuous Water Quality Monitors-Station Operation, Record Computation, and Data Reporting” (Wagner et al., 2006)
    The ratings obtained from the accuracy check indicate the quality, accuracy, and reliability of the data that the sonde collected while in the field. 

In addition to the post-deployment accuracy check, DWR staff compare the water temperature, specific conductance, pH, dissolved oxygen, and turbidity data measured in the field by the handheld instruments (the YSI-63, YSI Pro-ODO, and HACH 2100P) to the sonde data that is closest in time.  While taking the field measurements, DWR staff attempt to collect the field readings at the same depth that the sonde probes are measuring at (1 meter) and as close to the sonde pipe as possible.  Since the field instruments are calibrated regularly, a large difference between the sonde and field readings could indicate inaccuracy of the sonde data during the deployment period.  DWR staff consider these comparisons between the field and sonde readings and the ratings obtained from the post-deployment accuracy check while assessing data quality when entering the continuous data into the Hydstra database. 


Data Quality Assurance/Quality Control (QA/QC)

DWR staff import data files from sondes into the North Central Region Office (NCRO) Hydstra database where additional QA/QC procedures are performed.  In addition to documenting the results of quality assurance procedures discussed in the previous section, staff use the results of these procedures to flag any suspect or unreliable data.  Any obvious outliers in the continuous dataset due to fouling or other factors are flagged as unreliable.  No data that has been determined by DWR staff as suspect or unreliable were used in this chapter; only reliable data of known good quality were used.  The reliable and good quality data in Hydstra are used to populate the Water Data Library where the data for all the continuous sites are available online at

B. Field Data

Field measurements are recorded on field data sheets upon each site visitation, and if the station has a discrete grab sample component, the data is then entered into the field module of DWR Bryte Laboratory’s “Flims” database.  Laboratory analyses are performed by DWR Bryte Laboratory on the discrete grab samples and the results are entered into the “FLIMS” database at the lab. For those stations without a discrete sample component, the field data sheets are used for sonde data comparison and archived accordingly.   On a regular basis the data from “Flims” database is loaded into DWR’s Water Data Library (WDL) database for public viewing and access.  Lab results are further archived and used for data report analyses.