Boone River IA 04-UDM-1256

The Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli).  The geometric mean level of indicator bacteria (E. coli) in the three samples collected in from May through September at the IDNR/UHL TMDL station near Woolstock (STORET station 11400001) (167 orgs/100ml) slightly exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.  Only one of the five samples (20%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).  The amount of data available for this assessment (five samples) does not meet IDNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected per site over a three-year period.  Assessments based on data that do not meet IDNR assessment/listing guidelines are considered “evaluated” (i.e., of lower confidence); these assessments are not appropriate for adding waters to Iowa’s Section 303(d) list of impaired waters.  Such assessments are, however, appropriate for addition of waters to IR subcategories 2b or 3b and to Iowa’s list of waters in need of further investigation. 

The Class B(WW1) (aquatic life) uses are assessed (monitored) as "partially supported" due to the occurrence of fish kills in 2013 and 2015.  The first kill occurred on or before October 1, 2013 near the point where the stream crosses Fisher Avenue (aka, Hamilton County road R-17).  Approximately 10 fish were killed over one mile of stream.  No estimated values of the fish killed or the cost of investigation were provided.  The cause of the kill was identified as "unknown", but a pesticide source was suspected.  The following is from the Iowa DNR fish kill report:

Unspecified number of fish killed.  Surmised that whatever killed the fish entered the stream some time around Oct 1- Oct 4.  The contaminant was toxic not only to fish but other aquatic life.  Length of kill was approx 1 mile, indicating it was not a large volume and/or dilution lowered the concentration to non-toxic levels.  Local residents interviewed did not report any activity on their part nor did they observe anything that seemed out of the ordinary.  Other fish kills with this same pattern have been caused by insecticide discharges, however there was no obvious source or evidence of this material being released.

The second kill occurred on or before August 9, 2015 near Woolstock in Wright County.  Approximately 21,700 fish were killed over 2.75 miles of stream.  The value of the fish killed was estimated at $5,570.18, and investigation costs were estimated to be $383.24.  No responsible party was identified, and the cause of the kill was reported as “unknown”. 

According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is known or suspected of being a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing.  Due to the suspicion that the 2013 kill was caused by pesticides, the aquatic life uses are assessed as “partially supported”, and the segment is added to IR Category 5b (=303(d) impaired). 

The results of IDNR/UHL TMDL-related chemical/physical water quality monitoring conducted in 2005 at station 11400001 suggested good chemical water quality in this river segment.  Results of this monitoring showed no violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen or pH) or for ammonia in the five monthly samples collected from May to September 2005.  The number of samples collected at this station (five) was relatively low and did not meet IDNR guidelines for developing a “monitored” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period).  Thus, any assessment based on these data should be considered “evaluated” (of lower confidence).  Results of limited monitoring conducted by USGS in this segment from March to October 2010 also suggested good water quality in this assessment segment with none of the five samples analyzed violating Class B(WW1) criteria for dissolved oxygen or pH. 

Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.