Assessment Comments

Assessment is based on results of (1) 2008 and 2010 IDNR/SHL biological sampling data, (2) occurrence of a fish kill in July 2002, and (3) chemical, physical, and bacterial monitoring at three stations from March 2010 to February 2011.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, and due to completion and approval of a use attainability analysis, this segment is also now designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]

SUMMARY:  The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as “not supporting” (IR 5a) due to high levels of indicator bacteria.   These are both new impairments for this assessment segment.   The Class B(CW1) aquatic life uses are assessed (monitored) as "partially supported" (IR 5b-v) based on results of biological monitoring in 2008 and 2010 conducted as part of IDNR/SHL stream sampling projects.   Occurrence of a fish kill, possibly caused by runoff by land-applied manure, indicates an additional impairment of the aquatic life uses.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this stream reach.   The sources of data for this assessment include the results of chemical, physical, and bacterial monitoring at three stations near McIntire monitored either as part of TMDL or biological monitoring from March 2010 to February 2011:  Site 75/Wap-2 (STORET station 11660002), Site Wap-1 (STORET station 11660001), and a site in the Wapsipinicon SWMA (STORET station 12660005).   Sources of data for this assessment also include results of IDNR/SHL biological monitoring in 2008, and 2010 as well as results of a fish kill investigation in July 2002.    

EXPLANATION:  
The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as "not supported" based on levels of indicator bacteria at all three monitoring stations that exceeded state water quality criteria.   In terms of the Class A1 assessment, the 2010 recreation season geometric mean of indicator bacteria (E.  coli) in the 16 samples collected during the recreational season of 2010 at site 75 (Wap-2) was 920 orgs/100 ml; the geometric mean in the 20 independent samples collected during the recreational season of 2010 at SiteWap-1 was 2,358 orgs/100 ml, and the geometric mean in the 16 samples collected during the recreational season of 2010 in the Wapsipinicon SWMA near McIntire was 1,596 orgs/100 ml.   The geometric means at all three sites far exceed the Class A1 criterion of 126 orgs/100 ml.   From 81 to 94% of the samples exceeded the Class A1 single-sample maximum criterion sample maximum criterion of 235 orgs/100 ml.   No bacterial samples were collected during the recreation season of 2011.

For the Class A2 assessment, the 2010 annual geometric mean of indicator bacteria (E.  coli) in the 18 samples collected at site 75 (Wap-2) was 636 orgs/100 ml; the geometric mean in the 22 independent samples collected during 2010 at SiteWap-1 was 1,725 orgs/100 ml, and the geometric mean in the 18 samples collected during 2010 in the Wapsipinicon SWMA near McIntire was 1,306 orgs/100 ml.   Only two samples were collected during calendar year 2011 (January and February).   These two sample geometric means were all very low (range from 32 to 46 orgs/100 ml.   The geometric means for calendar year 2010 at all three sites exceed the Class A2 criterion of 630 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 both the Class A1 and A2 uses, these uses are assessed as “impaired.”  

Results of chemical/physical monitoring in 2010 and 2011 at station 11660001 (Wap-1), 11660002 (Wap-2), and 12660005 (SWMA) suggest that the Class B(CW1) aquatic life uses should be assessed as “fully supporting”.   No violations of ammonia, pH, chloride, or sulfate occurred in the 20 samples analyzed at each station from March 2010 to February 2011.   One of the approximately 20 samples collected at each of these three station violated the Class B(CW1) criterion for dissolved oxygen of 7.0 mg/l.   Samples collected at each station on July 28, 2010 contained between 6.5 and 6.7 mg/l of dissolved oxygen, thus violating the Class B(CW1) criterion.   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as temperature, pH, and dissolved oxygen does not suggest impairment of aquatic life uses.   Thus, based on IDNR’s assessment methodology, the frequency of dissolved oxygen violations at these stations (from 4 to 5%) does not suggest impairment of the Class B(CW1) aquatic life uses.   Similarly, violations of the Class B(CW1) criterion for water temperature occurred at all three stations.   In samples taken between July 13 and August 4, 2010, water temperatures ranged from 20.5 C to 22.5 C.   Violation frequencies ranged from 10% (2 of 20 samples) at Station 11660002 to 15% (3 of 20 samples) at station 12660005.   Based on IDNR’s assessment methodology, however, these results suggest that the frequencies of violation at these stations are not significantly greater than 10 percent and thus do not suggest impairment of the Class B(CW1) aquatic life uses.  

Results of biological monitoring, however, suggest that the Class B(CW1) aquatic life uses should be assessed as “partially supporting”.   The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2008 and 2010 as part of the IDNR/SHL coldwater stream sampling project.   A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach.   The biological metrics were combined to make a coldwater benthic index (CBI).   The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2008 CBI scores were 37 and 37.   The 2010 CBI scores were 33, 37 and 43.   The aquatic life use support was assessed (monitored) as partially supporting (=PS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 0/5 times in a five-year period (2008-2012).  This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2008-2012.  

In addition, a fish kill occurred on this stream on July 29, 2002 that also indicates an impairment of the Class B(CW1) uses.   The kill followed heavy rainfall following a long period of hot, dry weather.   No specific cause was determined, but runoff from feedlots and/or land applied manure is suspected due to presence of several feedlots in the watershed of this stream.   Approximately 0.5 mile of stream was affected, and 184 fish were killed.   According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill indicates ongoing impairment of the aquatic life uses.   Any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery from the kill event.   Thus, this assessment segment will remain in Category 5b of Iowa’s Integrated Report.  

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