Roberts Creek IA 01-TRK-188

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational season of 2012, 2013, and 2014 are 259, 1,682, and 234 orgs/100 ml.  All three recreation season geometric means exceed the Class A1 criterion of 126 orgs/100 ml.  Nineteen of the combined 24 samples (79%) 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 a geometric mean is greater than 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). 

The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supporting" based on data collected in 2008, 2009 and 2012 as part of IDNR/SHL stream biological sampling projects.  A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.  The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and 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) and a benthic macroinvertebrate index (BMIBI).  The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2008 FIBI scores were 43, 52 (both fair) and 64 (good) and the BMIBI scores were 61, 66, 69 (all good).  The 2009 FIBI score was 55 (good) and the BMIBI score was 67 (good).  The 2012 FIBI score was 45 (fair) and the BMIBI score was 49 (fair).  The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.  The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61.  This segment passed the FIBI BIC 3/5 times and passed the BMIBI BIC 4/5 times in the last seven years. 

This aquatic life assessment is now considered "evaluated" 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 multiple samples collected in the previous seven years (2008-2014).

Results of chemical/physical water quality monitoring conducted between April 2012 and November 2014 also suggest “full support” of the  Class B(WW2) aquatic life uses.  No violations of Class B(WW2) water quality criteria for ammonia (14 samples), dissolved oxygen (21 samples), pH (22 samples), temperature (24 samples), or chloride (15 samples) occurred during this period. 

A fish kill occurred in this stream segment on or before August 1, 2005 and was caused by a release of hog manure from an over-full storage pit.  According to the IDNR investigation, an outdoor storage pit lacked sufficient capacity to handle the amount of manure delivered to it from an indoor storage pit; thus, an overflow occurred.  Approximately 2.25 miles of Roberts Creek were affected by the resulting kill.  The kill began in an unnamed tributary to Roberts Creek (waterbody IA 01-TRK-0361-0) in Section 8 of T95N, R6W, Clayton County, and proceeded downstream through Section 9, 15, and 15 of T95N, R6W.  An estimated 8,000 fish were killed.  Based on IDNR records, the value of the fish killed was estimated at $4,893.  Other than a notation that the kill affected “mostly non-game species", no detailed information on species killed is available.  The party responsible for the kill was identified.  IDNR sought and received restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. 

According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses.  If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody should be placed in IR Category 4d (impaired but TMDL not required).  Thus, this impairment was appropriate for Category 4d of Iowa’s 2008, 2010, and 2012 Integrated Reports.  IDNR considers IR 4d fish kill waters with no subsequent kills in at least the five years subsequent to the kill as appropriate for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation).  Thus, this fish kill impairment was moved to IR Category 3b for the 2012 Integrated Report and remains in IR Category 3b.