• Surface Water Study Design
• Basic-Fixed and Intensive Site Assessment
• Bed Sediment and Tissue Occurrence Study
• Low-Intensity Phase Sampling

The approach taken by NAWQA to assess the water quality of streams is based on three interrelated components: Water Column, Bed Sediment and Tissue, and Ecological Studies. The Water Column and Bed Sediment and Tissue Studies are described here and the Ecological Studies are described under Aquatic Ecology Activities. The Water Column Studies are made up of the Basic-Fixed Site Assessment, the Intensive-Fixed Site Assessment, Synoptic Studies, and Low-Intensity Phase Sampling. The sampling strategy of these studies is based on the general concept of initial intensive sampling of few sites for all water-quality characteristics, and progressively adding more sites for more specific and less frequent sampling. For instance, fewer constituents are measured during a shorter time frame for the Synoptic Studies than for the Intensive Fixed-Site Assessment, but the spatial coverage is broader. The Bed Sediment and Tissue Study was designed to provide an initial identification of important constituents and their occurrence in the Study Unit. Concentrations and their areal distribution are assessed to identify occurrence and potential needs for more detailed study.

The primary objective of the Basic-Fixed Site Assessment was to characterize the spatial and temporal distribution of general water-quality conditions and the transport of major inorganic constituents in stream water in relation to hydrologic conditions and sources.

Data collected:
A network of 12 sites were sampled for stream flow, nutrients, major ions, organic carbon, suspended sediment, water temperature, specific conductance, pH, and dissolved oxygen during 1995 through 1998, following procedures described by Shelton (1994). Four of these Basic-Fixed Sites are also Intensive-Fixed Sites. The purpose of the Intensive-Fixed Site Assessment was to assess the seasonal and short-term temporal variability of pesticides.

The primary objective of this study is to determine which trace elements and hydrophobic organic compounds occur at elevated levels relative to background conditions or at levels potentially toxic to humans or aquatic life. The occurrence survey for contaminants in bed sediment and tissues in the Sacramento River Basin study unit focused on the perennial reach of the main stem of the Sacramento River and tributaries to this reach within the Sacramento Valley.

Bed sediment data was collected from 17 sites between October and November 1995. These samples were analyzed for polychlorinated biphenyls (PCBs), organochlorine pesticides, semivolatile organic compounds, and trace elements. Clams and fish were collected at 18 sites in October-November 1992. The tissues from these samples were analyzed for PCBs, organochlorine pesticides, and trace elements.

The Low-Intensity Phase Sampling is intended to meet the objectives of trend assessment, which are to analyze past changes in water quality and to identify, describe, and explain (as possible) current and future changes and trends in water quality.

The Sacramento River at Freeport, and Arcade Creek near Del Paso Heights sites are currently being sampled at least once a month during the low-intensity phase (2005-2008). During the time period of October 1, 2006 through September 30, 2007, only the Sacramento River site will be monitored. That site will be sampled a total of 17 times during this period and will include analyses of nutrients, pesticides, suspended sediment, pH, alkalinity, dissolved oxygen, specific conductance, chloride, and sulfate.