ADBNet

Assessment Comments

Assessment is based on results of (1) IDNR/UHL chemical/physical water quality monitoring conducted from May 2004 to November 2006 and (2) INDR bacterial monitoring from January 2006 to September 2008 at the IDNR/UHL station near county road X26 (STORET station 15030006) as part of the Yellow River Watershed Project.

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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is also now presumptively 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.   This stream segment also remains identified as an “HQR” (high quality resource) water.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria.   The Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.”  The Class B(CW1) aquatic life uses remain assessed (monitored) as "not supported" due to violations of the water quality criterion for dissolved oxygen.   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 chemical/physical water quality monitoring conducted from May 2004 to November 2006 at the IDNR/UHL station near county road X26 (STORET station 15030006) as part of the Yellow River Watershed Project and (2) results of IDNR/UHL bacterial monitoring conducted at station 150030006 from April 2006 through September 2008.

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria.   The Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.”  The geometric mean of E.   coli in the 38 samples collected at YRWP site near county road X26 (station 15030006) during the recreational seasons of 2006 through 2008 was 236 orgs/100 ml.   This geometric mean exceeds the Class A1 criterion of 126 orgs/100 ml.   Nineteen of the 38 samples (50%) exceeded Iowa’s 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 the geometric mean of E.   coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).  

The geometric mean of the 47 samples collected at this station during calendar years of 2006 through 2008 was 147 orgs/100 ml; this geometric mean is well-below the Class A2 criterion of 630 orgs/100 ml.   Only one of the 47 samples (2%) exceeded Iowa’s Class A2 single-sample maximum criterion (2,880 orgs/100 ml.).   According to U.S.   EPA guidelines for Section 305(b) reporting, if the geometric mean is less than the applicable state criterion, and if less than 10% of samples exceed the single-sample maximum criterion, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because both the Class A2 geometric mean and single-sample criteria were met, these results suggest that the Class A2 uses should be assessed as “fully supported.”  

The results of the IDNR/UHL water quality monitoring from May 2004 to November 2006 show 42 violations of the Class B(CW1) criteria for dissolved oxygen (7.0 mg/l) in the 80 samples collected for a violation frequency of 52%.   The minimum level of dissolved oxygen was 3.5 mg/l.   According to U.S.   EPA guidelines for Section 305(b) water quality assessments (U.S.   EPA 1997b, page 3-17), impairment of aquatic life uses is indicated if criteria are exceeded in more than 10% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen).   Thus, the percentage of violations of the dissolved oxygen criterion in this stream segment (52%) suggests an impairment of coldwater aquatic life uses.   Violations occurred in throughout the 2004-2006 period.   Note:  although IDNR station 15030006 was monitored for E.  coli through September 2008, monitoring for dissolved oxygen was not conducted after November 2006.

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