Assessment Comments
Assessment based on: (1) results of IDNR/SHL biological sampling in 2006 & 2007, (2) results of IDNR/SHL water quality monitoring from January 2006 to September 2008 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed project.), and (3) results of IDNR TMDL monitoring from April to October, 2011 at Site YeRi-3 (STORET station 11960006 near Castalia).
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.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “not supported” (IR 4a) due to levels of indicator bacteria that far exceed state water quality criteria. The assessment of the Class B(WW2) aquatic life uses of this stream segment remains “partially supported/monitored” based on results of biological monitoring in 2006 and 2007 (IR 5b-v) and based on violations of the Class B(WW2) criterion for pH in 2011 (IR 5a). The pH impairment is a new impairment for this assessment segment. The sources of data for this assessment include (1) results of IDNR/SHL biological monitoring in 2006 and 2007, (2) results of IDNR/UHL water quality monitoring from April to October 2011 at station 15960002 (107th Avenue crossing) as part of the Yellow River watershed project, and (3) results of IDNR monitoring from April to October 2011 at station 11960006 near Castalia.
Note: 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 (see http://www.iowadnr.gov/Environment/WaterQuality/WatershedImprovement/WatershedResearchData/WaterImprovementPlans/PublicMeetingsPlans.aspx). Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses is 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 (biological impairment of the Class B(WW2) aquatic life uses), this segment remains in Category 5 of Iowa's 2012 Integrated Report (impaired and TMDL required).
EXPLANATION: 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 14 samples collected at IDNR/UHL station 15960002 during the recreation season of 2011 was 2,386 orgs/100 ml. Similarly, the geometric mean of E. coli in the 14 samples collected at IDNR/UHL station 11960006 during the recreation season of 2011 was 1,010 orgs/100 ml. These geometric means far exceeds the Class A1 criterion of 126 orgs/100 ml. Thirteen of the 14 samples (96%) from station 1596002 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, and 12 of 14 samples (86%) exceeded this criterion at station 11960006. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’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 "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, because the geometric means for stations 15960002 and 11960006 both exceeds the Class A1 criterion, the primary contact recreation uses are assessed as “not supported.” This assessment continues a history of unusually high levels of indicator bacteria in this assessment segment.
The Class B(WW2) aquatic life uses are 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 IDNR’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.
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 five years. This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years over a five-year period (2006-2010).
