Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly monitoring during the 2008-2010 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and at station 10630003 near Dallas, (2) the results of biological monitoring conducted by the IDNR Fisheries Bureau in 1999, and (3) results of a fish kill investigation in August 2010.

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" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supported" based on results of a fish kill investigation in August 2010 and results of biological monitoring in 1999.   The previous impairment due to low dissolved oxygen, however, is delisted due to the general lack of violations of this criterion over the last nine years of routine monthly ambient monitoring in this segment of White Breast Creek.   Fish consumption uses remain "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/UHL ambient monthly monitoring during the 2008-2010 assessment period at STORET station 10630001 (formerly station 100818) approximately 3 miles southwest of Knoxville and STORET station 10630003 near Dallas, (2) the results of biological monitoring conducted by the INDR Fisheries Bureau in 1999, and (3) results of a fish kill investigation in August 2010.   Note:  IDNR routine ambient water quality monitoring was conducted at IDNR station 10630001 near Knoxville from January 2008 to March 2010 when 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 23 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10630001 and 10630003 were as follows:  the 2008 geometric mean was 236 orgs/100 ml, the 2009 geometric mean was 361 orgs/100 ml and the 2010 geometric mean was 489 orgs/100 ml.   All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Seventeen of the 23 samples (74%) 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 Class B(WW1) aquatic life uses are assessed (monitored) as "partially supported" based on results of a fish kill investigation in August 2010 and data collected in 1999 as part of an IDNR Fisheries Bureau stream sampling project: Manchester research station.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 evaluated FIBI was 22 (poor).   The aquatic life use support was assessed (evaluated) as not supporting (=NS), based on a comparison of the FIBI score with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   This FIBI BIC for this ecoregion is 32 and this segment passed the FIBI BIC 0/1 times in 1999.  

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 a single sample collected in 1999.   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).   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).  

In contrast to results of biological monitoring which suggest "not supporting" of the aquatic life uses, results of ambient chemical/physical water quality suggest “full support” of the aquatic life uses.   None of the approximately 30 samples collected during the 2008-2010 assessment period at the IDNR monthly stations violated Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen.   Based, however, on results of the 1999 biological assessment, the aquatic life uses of this stream segment will remain assessed (evaluated) as “partially supported”  (IR Category 5b).   Also, the results of biological monitoring conducted in 1999 by the IDNR Fisheries Bureau suggested aquatic life conditions well-below those expected.   Follow-up monitoring should be conducted to better characterize the status of aquatic life of this stream segment.  

The previous impairment due to occasional episodes of low dissolved oxygen, however, is removed from Iowa’s Section 303(d) list due to the general lack of violations over the last 10 years.   No violations of the Class B(WW1) dissolved oxygen criterion occurred in the 30 samples collected during the current (2008-2010) assessment period.   The only violations of the Class B(WW1) criterion for dissolved oxygen documented since September 2001 was the level of 4.2 mg/l on September 6, 2005 and the level of 4.7 mg/l on August 1, 2007.   Thus, violations of the dissolved oxygen criterion have occurred very rarely over the last nine years of monthly monitoring in this segment.   The frequency of violations over this nine-year period (1.9%) is well below the frequency of dissolved oxygen violations (10%) considered by U.S.  EPA and Iowa DNR to indicate impairment of aquatic life uses.

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 2784 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 (2009-2011) 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 will be placed in Category 4d of Iowa’s 2012 Integrated Report.

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