Clean Water Program

The purpose of in-drain sediment chemistry monitoring is to detect whether selenium levels in San Luis Drain sediments are approaching the California Department of Health Services criterion for hazardous waste. The monitoring of the selenium in sediments, coupled with flow and water quality information from the inlet (A) and outlet (B) sites, will also help to assess whether there is an influx or outflux of selenium between the sediment and the water column. Sediment samples will be analyzed for selenium and Total Organic Carbon (TOC).

The data will be used to tabulate the quantity of sediment in the various reaches of the SLD.

Distances along the SLD between structures will be measured using a cherry-picker retrofitted with an odometer that is accurate to ± 5 feet. This instrument will be calibrated daily while the surveying is being performed. The vertical measurements will be taken with a pocket tape measure along the SLD lining, and from the markings along the sediment probe to measure the depth of water above the sediment. These devices will be inspected daily.

a. Water Level Calculations

The level of the water will be determined by measuring along the lining above the water level (X). The actual water level (h) will be determined by subtracting X from the total length of lining (X1) and converting it into a vertical distance:

h = 0.55 (X1 - X)

b. Depth of Sediment

The depth of sediment (d) will be determined by subtracting the reading (y) obtained from the sediment probe to the water level (h):

d = h - y

c. Cross-Sectional Area of Sediment

An annual sediment survey of four reaches will be performed by the SLD-MWA. This will allow for the detection of movement of sediment within the SLD.

Summers Engineering, March 1987

Depth Measurement Locations

Checks 17-18, 14-15, 10-11, 1-2

The purpose of this task is to assess the transport of sediment and selenium within the SLD by conducting annual measurements of sediment quantity. Three estimates have been made of the sediment in the SLD. These surveys were performed by the USBR in January 1985, by Summers Engineering for the GWD District in March 1987 and by the SLD-MWA in August 1995. Each was performed using a slightly different method of determining sediment volume.