4.2.2. Data Collection & Analysis

The MWQI discrete water quality monitoring network was scaled back during the CALFED years, resulting in a network of 11 routine sampling locations by 2005 [78] that was more reflective of the IDHAMP network of the late 1980s. During this time, analysis of organic DBP precursors in channel waters shifted away from formation potential testing and the surrogate UV-254 measurement. THM formation potential testing was discontinued in 1998, reflecting a growing concern that it did not adequately represent formation in drinking water and could be misinterpreted [79]. While UV-254 data continued to be collected, their use for analysis was deemphasized because consistent spatial and temporal relationships with DOC could not be found [79] and was observed to vary from one NOM type to another. For example, agricultural drainage from peat soils (high in humic content) was found to have a UV-254:DOC ratio of 0.044–0.050 cm−1/mg/L, whereas agricultural drainage from mineralized soils (lower in humic content) was found to have a ratio of 0.035–0.370 cm−1/mg/L [21]. To place these ranges in context, the Sacramento and San Joaquin rivers are characterized by UV-254:DOC ratios of approximately 0.022 and 0.027 cm−1/mg/L, respectively. The Colorado River, outside the study area watershed, represents a source water low in humic content and has a ratio of 0.015 cm−1/mg/L. Discrete monitoring of nutrients was resumed in 2002 after being discontinued for several years. Greater emphasis was placed on data analysis, given interest in (i) potential adverse effects of nutrients on finished drinking water quality, (ii) examining their seasonal and spatial trends [20], and (iii) studying their effects on in-channel production of organic carbon [80]. Published program annual reports provide greater detail on MWQI's discrete water quality monitoring during the CALFED years [79–83].

MWQI program efforts to conduct real time monitoring and disseminate the data on the internet were initiated during the CALFED years. The first TOC analyzer was installed along the Sacramento River at Hood in 1999 in support of a pilot study of real time organic carbon monitoring [84]. TOC analyzers were later installed at Banks Pumping Plant in 2001 and along the San Joaquin River at Vernalis in 2005. The capabilities of several instruments were evaluated [85]. Anion analyzers were also installed at these locations to collect continuous data on bromide, chloride, nitrate, and sulfate [86]. These installations are believed to be the first to take continuous measurements of organic carbon, bromide, and other anions in United States waters and to publish the data immediately on the internet [87].

MWQI program staff published several peer-reviewed journal articles on laboratory methods during the CALFED years. While most of these articles related to measurement of THM precursors from organic soils [88–91], one focused on measurement of microbial contamination in natural waters [92]. The latter examined *Giardia* and *Cryptosporidium*, which are pathogens of concern in the Enhanced SWTR.
