Assessment Comments
Assessment is based on: (1) the results of monitoring for indicator bacteria conducted at Site 9 of the Upper Iowa River Watershed (UIRW) project from April 2004 through October 2006 (2) results of DNR/UHL biocriteria monitoring in 2004, and (3) an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006.
Basis for Assessment
[Note: Prior to the current (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 “HQ” (high quality) 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 presumptive Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.” The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as "fully supported" based on results of biological monitoring 2004 and an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006. 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 include (1) the results of monitoring for indicator bacteria conducted at Site 9 of the Upper Iowa River Watershed (UIRW) project from April 2004 through October 2006, (2) results of DNR/UHL biocriteria monitoring in 2004 and (3) an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006.
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 presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.” Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean of E. coli in the 21 samples collected at UIRW site 9 during the recreational seasons of 2004 through 2006 was 159 orgs/100 ml. This geometric mean exceeds the Class A1 criterion of 126 orgs/100 ml but is well below the Class A2 criterion of 630 orgs/100 ml. Seven of the 21 samples (33%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.; 2 of the 21 samples (10%) 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 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). Also, according to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the single-sample maximum criterion, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from UIRW site 9 suggest that the geometric mean exceeds the Class A1 criterion; thus, the Class A1 uses should be assessed as “not supported.” In terms of Class A2 criteria, however, both the geometric mean and the number of samples exceeding the Class A2 single-sample maximum criterion meet the Class A2 criteria; thus, these results suggest that the Class A2 uses should be assessed as “fully supported.” According to IDNR’s assessment/listing methodology, the results from UIRW site 9 do not indicate that significantly greater than 10% of the samples exceed the Class A2 single-sample maximum criterion.
The assessment of the Class B(CW1) aquatic life uses remains based on data collected in 2004 as part of the DNR/UHL stream biocriteria project. A series of four (4) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the biocriteria sampling data. The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa that were collected in the stream sampling reach. Sites that score 3/4 or 4/4 are Fully Supporting (FS), sites that score 1/4 or 2/4 are Partially Supporting (PS), and sites that score 0/4 are Not Supporting (NS). The 2004 coldwater biological indicator score 4/4 because it was a benthic macroinvertebrate only sample. The aquatic life use support was assessed (monitored) as Fully Supporting (=FS), based on a comparison of the coldwater biological indicator score with biological assessment criteria established for this Section 305(b) report. The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2004 and with assistance from the IDNR Fisheries Bureau.
In addition, based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006, the Class B(CW1) uses are assessed as "fully supported". According to the updated summary, (Unnamed) Cold Water Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout treams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking for one species of trout and in the category of streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the resident trout species at this time for a second species of trout. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain ”not assessed” due to the lack of fish contaminant monitoring in this stream segment.
