Assessment Comments
Assessment remains based on 2005 and 2010 IDNR/SHL biological sampling data (FIBI = 34, 35 (fair), BMIBI = 39, 52 (fair); FIBI BIC = 36; BMIBI BIC = 51) and is also based on results of bacteria monitoring from July 2011 to November 2012 from the Little Bear Creek Watershed Monitoring Project.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supporting” (IR 5p) due to levels of indicator bacteria that exceed state water quality standards. This is a new impairment for this assessment segment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supporting (IR 5b-t) based on biological sampling data from 2005 and 2010. The sources of data for this assessment include the results of bacteria monitoring as part of the Little Bear Creek Watershed Monitoring Project from July 2011 to November 2012 at three stations: (moving from downstream to upstream): (1) Site LB-6 at 385th Avenue (STORET ID 15790006), (2) Site LB-5 at 200th Street (STORET ID 15790005) and (3) Site LB-4 at S. Orchard Street (in Brooklyn) (STORET ID 15790004. This assessment is also based on results of IDNR/SHL biological sampling in 2005 and 2010. Note: other than monitoring for indicator bacteria, no other water quality parameters were monitored at sites LB-6, LB-5, and LB-4 during the 2011-2012 period.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of bacteria monitoring from July 2011 to November 2012. Five samples were collected during the recreation seasons of both 2011 and 2012 at each station (total of 10 samples per station). This amount of data approaches the minimum amount needed to develop an assessment of support of the Class A1 uses. The geometric mean levels of indicator bacteria (E. coli) at all three stations far exceed the Class A1 geometric mean criterion of 126 orgs/100 ml. The geometric means at Station LB-6 were 964 orgs/100 ml in 2011 and 1,598 orgs/100 ml in 2012 with all 10 samples (100%) exceeding the single-sample maximum criterion of 235 orgs/100 ml. The geometric means at Station LB-5 were 1,470 orgs/100 ml in 2011 and 1,266 orgs/100 ml in 2012 with nine of the 10 samples (90%) exceeding the single-sample maximum criterion of 235 orgs/100 ml. The geometric means at Station LB-4 were 820 orgs/100 ml in 2011 and 1,082 orgs/100 ml in 2012 with nine of the 10 samples (90%) exceeding 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 "not supported" (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 eight 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 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.
