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Table of Contents
Chromium

Historic

No data are available to characterize historical conditions for this parameter in this subwatershed.

Current

As a part of their Stephens Creek Water Quality Monitoring Project, BES sampled Stephens Creek for chromium from December 1996 to June 1997. A total of 28 dissolved chromium samples and 28 total chromium samples were taken at four sites throughout the subwatershed (1D, 2D, 3D, and 4D).

Six total chromium samples each were collected from sites 1D and 2D, while 7 and 9 samples were taken from sites 3D and 4D, respectively. The total chromium concentrations observed at these locations ranged from 1.13 to 15 .8 ug/L, with an average and standard deviation of 3.75 ug/L and 3.27 ug/L, respectively.

Six dissolved chromium samples each were collected from sites 1D and 2D, while 7 and 9 samples were taken from sites 3D and 4D, respectively. Dissolved chromium was not detected in 5 of the 28 samples at a detection level of 1.0 ug/L. The dissolved chromium concentrations observed at the sampling locations ranged from <1.0 to 4.5 ug/L. Setting non-detect concentrations to the detection level, the average dissolved chromium concentration is 1.39 ug/L with a standard deviation of 0.67 ug/L, respectively. Table 17 presents a summary of data and findings.

Assessment

The total chromium concentration in one sample exceeded the 11 ug/L chronic criteria for protection of aquatic life (see Table 3). There were no exceedances of the 16 ug/L acute aquatic life criterion or the 50 ug/L water and fish ingestion criteria and drinking water MCL. The sample exceeding the chronic criterion was taken on June 9, 1997 at station 1D and had a total chromium concentration of 15.8 ug/L.

Since only one total chromium concentration exceeding criteria occurred in the 28 samples analyzed and since no recent monitoring data is available, total chromium is not a parameter of concern for this subwatershed. However, since no recent data for this parameter exists, this finding should not be considered conclusive. At a minimum, a data set that includes monthly sampling spanning a twelve month period and including two to three sampling events conducted during wet weather is needed to make a determination about whether or not this parameter is a water quality concern.
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