Little Bear Creek IA 02-IOW-705

The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of bacteria monitoring from September 2012 through October 2014.  Five samples were collected during the recreation seasons of 2012, and 10 samples were collected at each station during both recreation seasons of 2013 and 2014 (total of 25 samples at each station during the 2012-2014 monitoring period).  The recreation season geometric means at Station LB-6 from 2012 through 2014 were 1,266 orgs/100 ml, 1,283 orgs/100 ml, and 1,429 orgs/100 ml, respectively.  The recreation season geometric means at Station LB-4 from 2012 through 2014 were 1,082 orgs/100 ml, 749 orgs/100 ml, and 1,105 orgs/100 ml, respectively.  Twenty-four of the 25 samples collected at each monitoring site (96%) exceeded the single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion, the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). 

The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting” based on data collected in 2005 and 2010 as part of the IDNR/SHL stream REMAP project.  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 2005 FIBI score was 34 (fair) and the BMIBI score was 39 (fair).  The 2010 FIBI score was 35 (fair) and the BMIBI score was 52 (fair).  The aquatic life use support was assessed 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.  This site passed the FIBI BIC 0/2 times and the BMIBI BIC 1/2 times in the last 10 years.  The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. 

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a recent five-year period.  According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).  IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s Section 303(d) list of impaired waters.

Results of chemical/physical monitoring at sites LB4 and LB6 from 2012 through 2014, however, do not suggest impairment of the Class B(WW2) uses.  No violations of Class B(WW2) criteria occurred for the following parameters monitored at Site LB4 and LB6 during the 2012-2014 period:  ammonia (20 combined samples), pH (40 combined samples), temperature (40 combined samples) and chloride (30 combined samples).  Two of 20 samples (10%) violated the Class B(WW2) criterion for dissolved oxygen at Site LB4, and one of 20 samples violated this criterion at Site LB6.  These monitoring results, however, do not suggest impairment of the Class B(WW2) aquatic life uses.  According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  According to IDNR’s assessment/listing methodology, however, the dissolved oxygen violation frequencies at sites LB4 and LB6 do not indicate that significantly greater than 10% of the samples exceed the Class B(WW2) criterion.  Thus, the results of chemical/physical water quality monitoring from 2012 to 2014 in this segment do not indicate impairment of the Class B(WW2) aquatic life uses.