Indian Creek IA 03-SSK-943

The presumptive Class A1 uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at IDNR station 10500001 near Colfax were as follows: the 2012 geometric mean was 270 orgs/100 ml, the 2013 geometric mean was 378 orgs/100 ml and the 2014 geometric mean was 561 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Fifteen of the 24 samples (62%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”

Based exclusively on the results of ambient chemical/physical water quality monitoring, the Class B(WW2) aquatic life uses should be assessed (monitored) as "fully supported". Results of chemical/physical monitoring at the IDNR/SHL station show no violations of Class B(WW2) criteria for dissolved oxygen, pH, ammonia nitrogen (maximum value = 1.3 mg/l), temperature, chloride, or sulfate in the 36 samples analyzed during the 2012-2014 assessment period. 

In contrast to the assessment of aquatic life uses based on chemical/physical water quality data, the biological data collected in 2003, 2012 and 2013 indicate that the Class B(WW2) aquatic life uses be assessed as “partially supporting." A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 30 (fair). The 2012 BMIBI score was 18 (poor) and the 2013 BMIBI score was 43 (fair).  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. The segment passed the FIBI BIC 1/1 times in 2003 (using the FIBI UAV of 7 points applied to single samples) and passed the BMIBI BIC 0/2 times in the last five years.  This assessment is considered "monitored" because there were two or more samples (BMIBI) collected in multiple years from 2010-2014.