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Redwood City <br /> Water Quality Monitoring Program Plan <br /> <br /> <br />© 2014 DKF Solutions Group, LLC Page 12 of 41 <br /> <br />1. Ammonia <br /> <br />Ammonia-N, is a key indicator of the extent of the gross pollution of the receiving water from a <br />SSO. Untreated wastewater or partially-treated wastewater is generally high in ammonia-N <br />(typical 20-30 mg/L),. In comparison the natural background concentration in the surface <br />water is low, typically, less than 0.5 mg/L. Therefore, the elevated concentration of ammonia <br />of the surface water downstream or at the site of the SSO, as compared to that upstream of <br />the site is a reasonable indication of the extent of gross contamination from the SSO. <br /> <br /> <br />2. Bacteriological Indicator as specified in the local Basin Plan <br /> <br />Total coliform, fecal coliform and enterococci count are indicators of potential public health <br />impacts of an SSO on the receiving waters. If the concentrations of these groups of bacteria <br />are elevated above and beyond the natural background and/or above the RWQCB Basin Plan <br />Water Quality Standards (objective), public notification and posting may be necessary. <br /> <br />It should be noted that there may be non SSO-related causes of elevated bacteria in surface <br />water, for example, animal sources or storm drain discharge. The upstream and or other <br />samples may reflect the extent of bacterial contamination from these other sources. <br />Sometimes the extent of the SSO may be indistinguishable from the other natural sources <br />beyond the City’s control. This is particularly true when taking Source samples based on an <br />estimated downstream location of the SSO plume (reference Section 7F). <br /> <br />Generally, if the concentrations of these groups of bacteria at the downstream or at the site of <br />impact are within the range of the non-impacted site (i.e. upstream) or levels indicated in <br />historical background monitoring levels, the water quality impacts of the SSO are considered <br />insignificant. <br /> <br />The surface water quality objectives of these groups of bacteria are shown in Table 7.1 and <br />7.2, below. <br />6.2.A. - Page 178