Assessment Comments
Assessment is based on (1) results of monitoring in 2010 at Stations WQ-08, WQ-10, and WQ-14 of the Catfish Creek Watershed Project and (2) results of 2002 IDNR/UHL biological monitoring data: FIBI = 76 (excellent), BMIBI = 77 (excellent). FIBI BIC = 52, BMIBI BIC = 61.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, a portion of this segment is now presumptively designated for Class A1 (primary contact recreation) uses and a portion is, following U.S. EPA’s approval of a use attainability analysis (UAA), designated for Class A3 (children’s recreation) use. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1/A3 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses and the Class A3 (children’s recreation) uses are assessed (monitored) as "not supported” due to violations of the Iowa water quality criterion to protect Class A1/A3 uses. This is a new impairment for this segment. The source of data for this assessment is the results of monitoring in 2010 at Stations WQ-08, WQ-10, and WQ-14 of the Catfish Creek Watershed Project (quality assurance/project plan available upon request). The Class B(WW2) aquatic life uses remain assessed (evaluated) as "fully supported" based on results of IDNR/UHL stream REMAP biological sampling in 2002. Because these data are now older than five years, the assessment type is changed from “monitored” (higher confidence) to “evaluated” (lower confidence).
EXPLANATION: The Class A1/A3 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria at all three monitoring stations far exceeded the Class A1/A3 geometric mean criterion of 126 org/100 ml to protect primary contact recreation uses. In addition, all 33 samples collected at these stations in 2010 exceeded the single-sample maximum criterion to protect primary contact recreation.
The geometric mean of indicator bacteria (E. coli) in the 11 samples collected approximately every two weeks during the recreational season of 2010 at Site WQ-08 of the Catfish Creek Watershed Project (3,983 orgs/100 ml) far exceeded the Iowa water quality criterion to protect primary contact recreation uses (126 orgs/100 ml); all 11 samples (100%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml for primary contact uses. Similarly, at Station WQ-10, the geometric mean of E. coli in the 10 samples collected (2,860 orgs/100 ml) also far exceeded the Class A1/A3 geometric mean criterion and all 11 samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The geometric mean of the 11 samples collected at Site WQ-14 during 2010 (4,369 orgs/100 ml) also far exceeded the Class A1/A3 geometric mean criterion with, again, all 11 samples (100%) exceeding the Class A1/A3 single-sample maximum criterion. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 630 orgs/100 ml., the secondary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The assessment of the Class B(WW2) aquatic life uses remains based on data collected in 2002 as part of the IDNR/UHL 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 that were 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 2002 FIBI score was 76 (excellent) and the BMIBI score was 77 (excellent). 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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a five-year period. 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). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.
