Assessment Comments
Assessment based on (1) 2010 and 2011 IDNR/SHL biological sampling data: FIBI = 10, 15, 20 (all poor) & 27 (fair), BMIBI = 32, 35 (fair). FIBI BIC = 33; BMIBI BIC = 41 and (2) results of chemcial/physical monitoring from March to October of 2011 at three stations.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed as “not supporting” (IR 5p) due to violations of state criteria for indicator bacteria. The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supporting” (IR 5b-v) based on biological data collected in 2010 and 2011 as part of the IDNR/SHL stream REMAP and SI/TMDL sampling projects. The sources of data for this assessment are (1) results of IDNR/SHL biological sampling in 2010 and 2011 and (2) results of chemical/physical monitoring in 2011 conducted as part of TMDL-related monitoring at three station in this segment: (1) Site mfgr-1 (STORET station 11800001), (2) Site mfgr-1 (STORET station 11800002), and (3) Site 11 at Mt. Ayr (STORET station 16800002).
EXPLANATION: The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria at three monitoring stations that exceeded state water quality criteria: (1) Site mfgr-1 (STORET station 11800001), (2) Site mfgr-1 (STORET station 11800002), and (3) Site 11 at Mt. Ayr. The geometric mean of indicator bacteria (E. coli) in the 12 samples collected during the recreational seasons of 2011 at Site mfgr-1 was 1,085 orgs/100 ml. The geometric mean of indicator bacteria (E. coli) in the 12 samples collected during the recreational seasons of 2011 at Site mfgr-2 was 956 orgs/100 ml, and the geometric mean of the 12 samples collected at Site 11 at Mt. Ayr was 1,435 orgs/100 ml. All 36 samples from these three station (100%) exceeded the 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 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 Class A1 uses, these uses are assessed as “impaired.”
The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supporting” (IR 5b-v) based on biological data collected in 2010 and 2011 as part of the IDNR/SHL stream REMAP and SI/TMDL sampling projects. A series of biological metrics which reflect 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 and fish species 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 2010 FIBI score was 27 (fair) and the BMIBI score was 32 (fair). The 2011 FIBI scores were 10, 15 and 20 (all poor) and the BMIBI score was 35 (fair). The aquatic life use support was assessed as partially supporting (=PS), 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 1994-2008. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This segment passed the FIBI BIC 0/4 times and passed the BMIBI BIC 0/2 times in the last five years.
This aquatic life assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years during a recent five-year period.
Despite the indications of biological impairment, the results of chemical/physical water quality monitoring at the three monitoring stations in 2011 do not suggest impaired water quality conditions. There were no violations of Class B(WW2) criteria for the following parameters in the approximately 45 combined samples from these three stations in 2011: chloride (54 samples), dissolved oxygen (50 samples), ammonia (46 samples), pH (50 samples), and sulfate (54 samples). The only violations of a Class B(WW2) criterion were for water temperature, with one of 16 samples (<1%) in violation at Site 11 (Mt. Ayr) and two of 15 samples (13%) in violation at Site mfgr-2. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from Site mfgr-2, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for water temperature. Thus, these results suggest that the Class B(WW2) uses should be assessed (monitored) as “fully supported.”
