6 Gap Analysis

The existing Russian River watershed bacterial sampling

programs tell part of the story about where and when fecal bacteria are entering the system, but there are gaps in the data and in our knowledge. As a proposed pilot study, we have developed a proposed minimum set of sites to deal with spatial and temporal gaps, which also cover several main land-cover types. Event and bi-weekly sampling at these sites during the early wet season, which is when most fecal matter and bacteria are mobilized into the system, would tell us a lot about watershed process effects on observed concentrations.

Analysis Process

We considered the following information in determining the classes and distributions of 13 proposed sites: 1) previous sampling intensity (# of sampling events), 2) previously-high E. coli concentrations, 3) previously-monitored location, and 4) representation of residential, agricultural, and wild-land sub-watershed land-covers.

1) Sampling counts among the existing tributary sample sites we analyzed closely, ranged from 1 (low intensity) to 49 (high intensity). We selected sites that had this wide range in order to cover places that were consistent wet season problems as well as places that may be problems, but sampling intensity was very low (Figure 10).

2) Previously-measured mean concentrations for the wet season varied among existing tributary sampling sites from 495 MPN/100 ml to >20,000 MPN/100 ml. We selected sites that were well above the WQO and that met other criteria.

3) We tried to select as many previously-monitored sites as possible, but in some cases had to choose new locations that appeared likely to have reasonable stream access (Figure 11).

4) We chose 1 to 3 sites per major land-cover types (Figure 11). We segregated sites by predominant adjacent and upstream/up-watershed land-cover in order to get a measure of the potential relative contributions from these different land-cover types. The land-cover categories were: [Res 1] High density/urban residential and commercial development, [Res 2] Moderate to low density residential development, [Res 3] Very low density rural-residential development; [Ag 1] Dairy/confined animals, [Ag 2] Vineyard; [Wild 1] West-side wildland of Russian River watershed, and [Wild 2] East-side wildland.

Sampling frequency

We suggest a combination of regular and event sampling at these sites to capture baseline (pre-first-flush) concentrations in early October (n=1 per site), event-related concentrations during and after the first 3 major storms (n=6), and bi-weekly sampling starting early October until the end of December (n=6). This will cover the period that has been found in our analysis to be the peak of fecal bacteria mobilization in the Russian River tributaries and in the River itself. The total number of samples would be 169 (13 sites X 13 samples/site).