Assessment Comments
Assessment is based on results of IDNR/UHL chemical/physical/bacterial water quality monitoring conducted from (1) May 2004 to November 2006 and (2) January 2008 through September 2009 at the Hickory Creek Road crossing (STORET station 15030007) as part of the Yellow River Watershed Project. Assessment is also based on a summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.” Despite apparent improvement in water quality, the Class B(CW1) aquatic life uses remain assessed (monitored) as "partially supported" based on results of water quality monitoring from 2004-2006 that show violations of Class B(CW1) criteria for dissolved oxygen. Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment. The source of data for this assessment is (1) the results of IDNR/UHL chemical/physical/bacterial water quality monitoring conducted from (1) May 2004 to November 2006 and (2) January 2008 through September 2009 at the Hickory Creek Road crossing (STORET station 15030007) as part of the Yellow River Watershed Project.
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 due to low dissolved oxygen), 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 impaired due to violations of Iowa’s water quality criteria for indicator bacteria. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported.” The geometric means of indicator bacteria (E. coli) in the 17 samples collected during the recreational seasons of 2008 and 2009at station 15030007 were as follows: the 2008 geometric mean was 696 orgs/100 ml, and the 2009 geometric mean was 422 orgs/100 ml. Both of these geometric means exceed the Class A1 criterion of 126 orgs/100 ml. The geometric means for calendar years 2008 and 2009 were 362 and 422 orgs/100 ml, respectively. Both of these calendar year geometric means are below the Class A2 geometric mean criterion of 630 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 should be assessed as "not supported". Thus, the Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported,” while the Class A2 (secondary contact recreation) uses are assessed as “fully supported”.
Although recent data show no violations of the Class B(CW1) criteria for dissolved oxygen in the ten samples analyzed from May to September 2009, the results of IDNR/UHL water quality monitoring from May 2004 to November 2006 showed 20 violations of the Class B(CW1) criteria for dissolved oxygen (7.0 mg/l) in the 79 samples collected for a violation frequency of 25%. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), impairment of aquatic life uses is indicated if criteria are exceeded in more than 10% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen). According to the IDNR assessment and listing methodology, the percentage of violations of the dissolved oxygen criterion in this stream segment during the 2004-06 period was significantly greater than 10% and thus the Class B(CW1) uses of this segment were assessed as Section 303(d) impaired for the 2010 cycle. Based on IDNR's assessment methodology, two consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the standard are necessary to suggest de-listing of an impairment due to low dissolved oxygen. Therefore, the impairment for dissolved oxygen will remain for the 2012 assessment/listing cycle.
In contrast to the WQ data, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, suggests the Class B(CW1) uses are as "fully supported". According to the updated summary, part of this Hickory Creek segment is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.
