Assessment Comments
Assessment remains based on results of IDNR/SHL biological sampling in 2001 and 2010: FIBI = 44 (fair), 52, 63 (good), BMIBI = 73, 70 (good), 53 (fair) and IDNR Fisheries Bureau fish sampling in 2005: FIBI = 51 (good). Non-riffle habitat FIBI BIC = 44, natural substrate BMIBI BIC = 70 and artificial substrate BMIBI BIC = 52.) Assessment is also based on results of ambient monitoring in 2010 and 2011 at Hollenbeck Road (STORET station 15570007).
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, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
[Note: Due to the completion and approval of two use attainability analyses, portions of this assessment segment are now designated for Class A3 (children’s recreation) use while the remainder of the segment remains presumptively designated for Class A1 (primary contact recreation) use. Because (1) the water quality criteria to protect Class A1 and A3 uses are identical and (2) incorporation of the new Class A3 designations would require four splits in this assessment segment, the entire segment (IA 02-CED-0231_0) will be assessed as a Class A1 (primary contact recreation) segment.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5a) due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this assessment segment. The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supported" (IR 2a) based on (1) results of IDNR/SHL biological (biocriteria) sampling in 2001 and 2010, (2) results of one IDNR Fisheries Bureau fish sampling in 2005, and (3) results of ambient water quality montitoring from 2010 to 2011 at STORET station 15570007.
EXPLANATION: The presumptive Class A1 (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 (E. coli) in the 12 samples collected at station 15570007 during the recreational season of 2010 (903 orgs/100 ml), and the geometric mean of the 12 samples collected during the recreation season of 2011 (1,935 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. All of the combined 24 samples (100%) exceeded Iowa’s 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 is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supporting” based on biological data collected in 2001 and 2010 as part of the IDNR/SHL stream biocriteria project and on fish data collected by the IDNR Fisheries Bureau in 2005. The 2001 FIBI scores were 44 (fair) and 52 (good); the BMIBI scores were 73 (good) and 70 (good). The 2005 Fisheries Bureau FIBI score was 51 (good). The 2010 FIBI score was 63 (good) and the BMIBI score was 53 (fair). The aquatic life use support was assessed (evaluated) as fully supported (=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 non-riffle habitat FIBI BIC for this ecoregion is 44, the natural substrate BMIBI BIC (2001 BMIBI samples) for this ecoregion is 70 and the artificial substrate BMIBI BIC for this ecoregion is 52 (2010 BMIBI sample). This segment passed the FIBI BIC 4/4 times and passed the BMIBI BIC 3/3 times in the last 12 years.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 10 years (2001-2012); however, the multiple samples were not collected during a five-year period. Despite this change in assessment methodology and type, the Class B(WW2) aquatic life uses remain assessed as “fully supporting” (IR Category 2a).
The results of ambient water quality monitoring at station 15570007 in 2010 and 2011 indicate good chemical water quality in this stream segment, are consistent with the results of biological monitoring, and thus suggest “full support” of the Class B(WW2) aquatic life uses. No violations of Class B(WW2) water quality criteria for dissolved oxygen, pH or temperature occurred in the 24 samples analyzed from May 2010 to July 2011.
