Assessment Comments

Assessment based on: (1) the results of IDNR/SHL ambient monthly monitoring during the 2010-2012 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and at station 10630003 near Dallas, (2) results of a fish kill investigation in August 2010, (3) IDNR/SHL biological sampling in 2012 and 2013 and (4) the results of biological monitoring conducted by the IDNR Fisheries Bureau in 1999.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream 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 the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This 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).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "not supported" based on results of a fish kill investigation in August 2010 (IR 4d) and results of biological sampling in 1999, 2012 and 2013 (IR 5b-v).   Fish consumption uses remain "not assessed" (IR 3a) 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/UHL ambient monthly monitoring during the 2010-2012 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and STORET station 10630003 near Dallas, (2) results of a fish kill investigation in August 2010, (3) IDNR/SHL biological sampling in 2012 and 2013 and (4) the results of biological monitoring conducted by the IDNR Fisheries Bureau in 1999.   Note:  IDNR routine ambient water quality monitoring was conducted at IDNR station 10630001 near Knoxville from January 2008 to March 2010 when the monitoring was moved to IDNR station 1063003 near Dallas.

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not 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 2010 through 2012 at IDNR station 10630001 and 10630003 were as follows:  the 2010 geometric mean was 489 orgs/100 ml, the 2011 geometric mean was 275 orgs/100 ml, and the 2012 geometric mean was 233 orgs/100 ml.   All three geometric means slightly 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 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.”  

This monitored aquatic life assessment was based on data collected in 2012 and 2013 as part of the IDNR/SHL large river sampling project and on data collected in 1999 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 2012 BMIBI score was 13 (poor).   The 2013 BMIBI scores were 48 and 51 (both fair).   The 1999 Fisheries FIBI score was 22 (poor).   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.    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 biological data collected at stream ecoregion reference sites from 1994-2008.   This segment failed the FIBI BIC in 1999 and passed the BMIBI BIC 1/3 times in the last two years.   This assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years in a recent five year period.  

In contrast to results of biological monitoring which suggest that aquatic life uses are "not supported", results of ambient chemical/physical water quality suggest “full support” of the aquatic life uses.   None of the 33 samples collected during the 2010-2012 assessment period at the IDNR monthly stations violated Class B(WW1) water quality criteria for dissolved oxygen, pH, temperature, ammonia-nitrogen, chloride, or sulfate.   Based, however, on results of the biological assessment (above), the aquatic life uses of this stream segment will remain assessed (monitored) as “partially supported”  (IR Category 5b-v).  

The occurrence of a fish kill at this segment in August 2010, also suggests the Class B(WW1) uses should be assessed as "partially supported."  A fish kill occurred at this site on August 23, 2010.  The kill was a result of a leak from an anhydrous ammonia tank pipe.  The cloud was sprayed down with water by the fire department.  A road culvert and a tile intake/line allowed the ammonia to reach Mill Branch Creek.  Mill Branch Creek flows into Cotton Creek, which then flows into White Breast Creek.  Dead fish were observed in all three of these streams below the tile line.  The kill affected 10.5 miles of these streams.  Approximately 2,784 fish were killed.  No information on the species of fish killed was provided.  The estimated value of these fish was $12,891.81.  IDNR sought and received restitution for this fish kill.  

According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant,” the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing.  If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody will be placed in IR Category 4d (impaired but TMDL not required).  IDNR feels that (1) TMDLs should not be required for kills caused by a one-time illegal or unauthorized release of manure or other toxic substance where enforcement actions were taken and (2) enforcement action is more appropriate, efficient, and effective for addressing a spill-related impairment than is the TMDL process.  Thus, this assessment segment was placed in Category 4d of Iowa’s 2012 Integrated Report where it remains.

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