Pheasant Creek IA 01-NEM-6369

Note:  A TMDL for the bacterial impairment for streams in the Duck Creek basin, including Pheasant Creek, was prepared by Iowa DNR in March 2010.  This TMDL was approved by U.S. EPA in 2011.  Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses is changed from 5a (impaired; TMDL needed) to 4a (impaired; TMDL approved). 

EXPLANATION:  Results of monitoring for indicator bacteria conducted weekly from April through October 2008 at Station PC2 suggest that the presumptive Class A1 uses of this segment of Pheasant Creek should be assessed (monitored) as "not supported."  A total of 29 samples were collected at station PC2 during this period; these data allowed calculation of twenty-five, 30-day/five-sample geometric means.  All of the 30-day geometric means exceeded Iowa’s Class A1 criterion of 126 organisms / 100 ml.  The minimum and maximum geometric means were 424 and 6,051 orgs/100 ml, with 24 of the 29 samples (83%) exceeding Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines and IDNR’s assessment/listing methodology, these results suggest non-support of the presumptive Class A1 (primary contact recreation) uses due to geometric means of E. coli that exceed Iowa’s water quality criterion of 126 E. coli organisms/100. 

Results of monthly monitoring between May and November 2013 showed continued high levels of indicator bacteria in this stream segment.  The geometric mean of E. coli in the six samples was 2,171 orgs/100 ml.  All six of the samples exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  These results suggest that this stream segment is appropriately considered impaired ("not supported") due to high levels of indicator bacteria.  

The presumptive Class B(WW1) aquatic life uses remain “not assessed” due to the lack of information upon which to base an assessment.  Levels of dissolved oxygen, however, were measured during the TMDL-related sampling in 2008 at station PC2.  Two of the 29 samples (7%) violated the Class B(WW1) criterion of 5 mg/l.  The minimum level of dissolved oxygen was 3.9 mg/l.  According to U.S. EPA guidelines for Section 305(b) reporting, if less than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).  Although these results suggest “full support” of the presumptive aquatic life uses, the lack of additional data for ammonia, toxic metals, and/or pesticides, and the lack of biological data for this segment, prevents development of a complete assessment of the aquatic life uses.  Thus, the presumptive aquatic life uses remain “not assessed”.