Assessment Comments

Assessment is based on: (1) the results of IDNR monthly ambient monitoring from January 2006 through September 2008 at the county road T75 bridge approximately 3.5 miles northwest of Cedar Falls (STORET station 10070001), (2) results of IDNR/UHL REMAP biological monitoring in 2003 and (3) 2001 IDNR Fisheries sampling.

Basis for Assessment

[Note 1:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, and due to approval of a use attainability analysis, the lower portion of this segment is also now designated for Class A1 (primary contact recreation) uses.   The entire segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

[Note 2:  Due to the completion and approval of a use attainability analysis, a portion of this assessment segment is now designated for Class A3 (children’s recreation) use; IDNR has proposed that the portions immediately upstream and downstream of this Class A3 segment be designated for Class A2 (secondary contact recreation) uses; these proposed use recommendations have not yet been approved by U.S.  EPA.   Because (1) the water quality criteria to protect Class A1 and A3 uses are identical and (2) the Class A2 recommendations have not yet been approved by EPA (i.e., these portions remain presumptively designated for Class A1 uses), the entire segment (IA 02-CED-0400_0) will be assessed as a Class A1 (primary contact recreation) segment for the current (2012) 305(b)/303(d) cycle.]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” based on results of ambient water quality monitoring, IDNR/UHL REMAP data and IDNR Fisheries data.   Fish consumption uses remained "not assessed" due to the lack of fish contaminant monitoring in this stream segment.   The sources of data for this assessment are (1) the results of IDNR monthly ambient monitoring from January 2008 through December 2010 at the county road T75 bridge approximately 3.5 miles northwest of Cedar Falls (STORET station 10070001), (2) the results of IDNR/UHL REMAP biological monitoring in 2003 and (3) 2001 IDNR Fisheries sampling.  

EXPLANATION:  The Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR ambient station 10070001 were as follows:  the 2008 geometric mean was 468 orgs/100 ml, the 2009 geometric mean was 242 orgs/100 ml and the 2010 geometric mean was 233 orgs/100 ml.   All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Thirteen of the 22 samples (59%) 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 are "not supported" (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.”  The results of bacteria monitoring from 2008 through 2010 at IDNR ambient station 10070001 show that all recreation season geometric means meet the Class A2 geometric mean criterion of 630 orgs/100 ml, and none of the 22 examples exceeds Iowa’s single-sample maximum criterion.

The Class B(WW1) aquatic life uses remain assessed as “fully supported” based on results of both chemical/physical and biological monitoring.   Results of IDNR ambient water quality monitoring station NW of Cedar Falls during the 2008-2010 assessment period showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 30 samples collected.  

The assessment of the Class B(WW1) aquatic life uses remains partially based on results of biological monitoring conducted in 2003 by IDNR/UHL as part of the REMAP project and on data collected in 2001 by the IDNR Fisheries bureau.   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 2001 IDNR Fisheries FIBI score was 61 (good).   The 2003 FIBI score was 45 (fair) and the 2003 BMIBI score was 77 (excellent).   The aquatic life use support was assessed as fully supporting (=FS), 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 1994-2004.   The non-riffle FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 1/1 times in the last eight years.  

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”.   This segment had multiple FIBI samples collected in the previous eight years (2001-2008); however, the multiple samples were not collected during a five-year period.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).    

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach.