Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL monthly ambient water quality monitoring conducted on Wolf Creek near LaPorte City (STORET station 10070002) during the 2008-2010 assessment period and (2) IDNR/UHL REMAP biological sampling conducted in 2004 near LaPorte City.

Basis for Assessment

[Note:  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, this segment is also now presumptively 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 presumptive 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 conducted from 2008 through 2010 and based on results of biological sampling conducted in 2004.   Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this assessment segment.   The primary sources of data for this are (1) the results of IDNR/UHL monthly ambient water quality monitoring conducted on Wolf Creek near LaPorte City (STORET station 10070002) during the 2008-2010 assessment period and (2) IDNR/UHL REMAP biological sampling conducted in 2004 near LaPorte City.   Note:  USGS conducted monitoring at station 05464220 near Dysart in October 2010.   Too few data were produced from this monitoring during the 2008-2010 assessment period (one sample) to be of use for assessment for purposes of either Section 305(b) reporting or Section 303(d) listing.

EXPLANATION:  The presumptive 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 21 samples collected during the recreational seasons of 2008 through 2010 at station 10070002 at La Porte City were as follows:  the 2008 geometric mean was 944 orgs/100 ml, the 2009 geometric mean was 301 orgs/100 ml and the 2010 geometric mean was 388 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fourteen of the 21 samples (67%) 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 remains assessed (evaluated) as “fully supporting” based on data collected in 2004 as part of the IDNR/UHL stream REMAP project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria 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 2004 FIBI score was 45 (fair) and the BMIBI score was 50 (fair).   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 non-riffle site FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.   This site met the BMIBI BIC with the aid of the BMIBI UAV of 8 points.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.  

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years in a five year period.   Despite this change in assessment methodology and type, this aquatic life assessment still suggests that this waterbody is fully supporting its' aquatic life uses.   .   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).  

Additionally, results from IDNR/UHL ambient monthly monitoring at the La Porte City station from 2008-2010 show no violations of Class B(WW1) water quality criteria in the approximately 30 samples analyzed for conventional parameters (e.g., dissolved oxygen, pH, and ammonia-nitrogen).  

Fish consumption uses are remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.   Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.   These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.