Assessment Comments
Assessment is based on results of (1) IDNR/UHL water quality monitoring conducted as part of TMDL development from April through September 2005 at station 11380009 and (2) Section 319 bacteria monitoring from June 2009 through November 2012.
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 (2012) 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 (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses are assessed (evaluated) as “fully supported” based on results of chemical/physical water quality monitoring during 2005. The sources of data for this assessment are (1) the results of Section 319 bacteria monitoring at station BHC-14 from June 2009 through November 2010 and (2) the results of IDNR/UHL water quality monitoring conducted as part of TMDL development from April through September 2005 at station 11380009. No additional monitoring has been conducted at this station since 2005.
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 means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2009 and 2010 at Section 319 site BHC-14 were as follows: the 2009 geometric mean was 932 orgs/100 ml and the 2010 geometric mean was 962 orgs/100 ml. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Nineteen of the 20 samples (95%) 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 remain assessed (evaluated) as “fully supported” based on results of IDNR/UHL water quality monitoring conducted at TMDL station 11380009. Results of this monitoring show no violations of Class B(WW2) water quality criteria for conventional parameters dissolved oxygen or pH) or for ammonia in the seven monthly samples collected from April-September 2005. Too few samples were collected over the 2004-2006 assessment period to allow development of a high-confidence (i.e., “monitored”) assessment.
