Yellow River IA 01-YEL-437

[Note 1: A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and was approved by U.S. EPA in February 2013. Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses was changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved). Because not all impairments identified for this assessment segment are covered by the TMDL (the biological and pH impairments of the Class B(WW2) aquatic life uses), this segment remains in Category 5 of Iowa's Integrated Report (impaired and TMDL required).]

[Note 2: Although a pH impairment was identified for the Class B(WW2) uses for the 2014 IR cycle, this impairment should have also been applied to the presumptive Class A1 uses. Thus, the Class A1 impairment was identified as new for the 2016 IR cycle.]

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 19 samples collected at DNR/SHL station 15960002 during the recreation season of 2014 was 1,661 orgs/100 ml. Similarly, the geometric mean of E. coli in the 20 samples collected at DNR/SHL station 11960006 during the recreation season of 2014 was 601 orgs/100 ml. These geometric means far exceed the Class A1 criterion of 126 orgs/100 ml. Seventeen of the 19 samples (89%) from station 1596002 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, and 15 of 20 samples (75%) exceeded this criterion at station 11960006. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a geometric mean of E. coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because the geometric means for stations 15960002 and 11960006 both exceed the Class A1 criterion, the primary contact recreation uses should beassessed as “impaired.” This assessment continues a history of unusually high levels of indicator bacteria in this assessment segment.

The Class B(WW2) aquatic life uses remain assessed (monitored) as “partially supported” due to violations of Class B(WW2) criteria for pH. At station 11960006, four of the 14 samples collected from April to October 2011 exceeded the high pH criterion of 9.0 pH units with violation ranging from 9.1 to 9.6 pH units. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH and dissolved oxygen suggests impairment of aquatic life uses. Based on DNR’s assessment methodology, these results suggest that the frequency of violations for pH is significantly greater than10 percent; thus, these results suggest impairment of the Class B(WW2) aquatic life uses. Only one of the 14 samples (7%) collected at station 1596002 during the April-October 2011 period violated the pH criterion. None of the other parameters monitored (dissolved oxygen, ammonia, or temperature) violated their respective Class B(WW2) criteria the 14 samples collected at both stations during the April-October period of 2011. Note: despite the continuance of bacteria monitoring at monitoring stations 15960002 and 11960006 in 2014, there are no new data for pH beyond those collected in 2011.

The results of biological monitoring in 2006 and 2007 also suggest "partial support" of the aquatic life uses in this segment. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data collected 2006. 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 2006 FIBI score was 46 (fair) and the BMIBI score was 74 (good). The 2007 FIBI scores were 48, 49 (fair) and 58 (good) and the 2007 BMIBI score was 70 (good). 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 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 1/4 times and passed the BMIBI BIC 2/2 times in the last 11 years. This aquatic life use assessment was considered "monitored" because there were two or more samples collected in multiple years over a five-year period (2006-2010). However,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). According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s 2010 Section 303(d) list of impaired waters.