Assessment Comments
Assessment is based on results of (1) IDNR/SHL water quality monitoring from April to October 2011 at STORET station 15960042 (Site 9 at Sand Road) as part of the Yellow River watershed project, and at STORET station 11960008 (Site YeRi-5 near Castalia) and (2) results of 2007 IDNR/SHL biological sampling data: FIBI = 69 (good); FIBI BIC = 52.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 4a) due to levels of indicator bacteria that exceed state water quality criteria. The assessment of the presumptive Class B(WW1) aquatic life uses of this stream segment are assessed (monitored) as “partially supported” (IR 5p) based on violations of the Class B(WW1) criterion for pH in 2011. Both the bacteria and the pH impairments are new impairments for this assessment segment. The sources of data for this assessment include (1) results of IDNR/SHL biological sampling in 2007, (2) results of IDNR/SHL water quality monitoring from April to October 2011 at station 15960042 (Site 9 at Sand Road) as part of the Yellow River watershed project, and (3) results of IDNR monitoring from April to October 2011 at station 11960008 (Site YeRi-5 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 (aquatic life impairment due to low dissolved oxygen), this segment remains in Category 5a of Iowa's 2012 Integrated Report (impaired and TMDL required).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 13 samples collected at IDNR/UHL station 15960042 during the recreation season of 2011 was 983 orgs/100 ml. Similarly, the geometric mean of E. coli in the 13 samples collected at IDNR/UHL station 11960008 during the recreation season of 2011 was 684 orgs/100 ml. These geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Eleven of the 13 samples (85%) from station 1596042 exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml, and 12 of 13 samples (92%) exceeded this criterion at station 11960008. 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 "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, because the geometric means for stations 15960042 and 11960008 both exceed the Class A1 criterion, the primary contact recreation uses are assessed as “impaired.”
The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “partially supported” due to violations of Class B(WW1) criteria for pH. At station 11960008, four of the 13 samples (31%) collected from April to October 2011 exceeded the high pH criterion of 9.0 pH units with violation ranging up to 9.8 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. Three of the 13 samples (23%) collected at station 1596042 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 13 samples collected at both stations during the April-October period of 2011.
In contrast to the assessment of impairment suggested by the results of chemical/physical monitoring, biological data collected in 2007 as part of the IDNR/SHL stream biological sampling program suggest “full support” of the presumptive Class B(WW1) aquatic life uses. 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 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). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 FIBI score was 69 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 52. Even though this site passed the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.
