Coffins Creek IA 01-MAQ-51

The 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 seven samples collected at the monitoring station on Coffins Creek from April to June, 2006, was 612 orgs/100 ml.  Four of the seven samples (57%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  The geometric mean of E. coli in the 7 samples collected at the monitoring station in Coffins Grove Park during the 2012 recreation season was 752 orgs/100 ml and was 342 orgs/100 ml during the 2013 recreation season.  Twelve of the 14 samples (86%) collected at this station during recreation seasons of 2012 and 2013 exceeded Iowa’s 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 the geometric mean of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as impaired (see pgs 3-33 to 3-35 of U.S. EPA 1997b.  Thus, because recreation season geometric means exceeded the Class A1 criterion, the primary contact recreation uses of this segment are assessed (“monitored”) as “partially supported”    

The Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting” based on results of chemical/physical water quality monitoring in 2013 (too few samples were collected over the 2012-2014 assessment period to qualify as a higher-confidence (“monitored”) assessment).  Water quality monitoring conducted from August to November 2013 at station 15280024 showed no violations of Class B(WW1) criteria for dissolved oxygen, pH, or temperature in the seven samples collected or for ammonia in the four samples collected.  These results suggest “full support” of aquatic life uses.

In agreement with the water quality sampling, this monitored biological assessment based on data collected in 2012, 2013 and 2014 as part of the IDNR Fisheries Bureau sampling project also suggests that the Class B(WW1) aquatic life uses are "fully supporting".  A series of biological metrics that 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 collected in the stream sampling reach.  The biological metrics were combined to make a fish community index of biotic integrity (FIBI).  The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2012, 2013 and 2014 FIBI scores were 71, 72, 74, 80, 81 and 84 (all excellent).  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 biological data collected at stream ecoregion reference sites from 1994-2008.  While it is still undetermined if the Fisheries sampling sites contain stable riffle habitat, this segment passed the riffle FIBI BIC (6/6 times).  The riffle habitat FIBI BIC for this ecoregion is 65.  

This aquatic life assessment is now considered "monitored" based on a change in the 2010 IDNR assessment methodology.  IDNR now requires a segment have two or more biological samples collected from the segment in multiple years in the most recent five year period (2010-2014) to be considered “monitored”.  This segment had six samples collected in the previous five years (2010-2014).