South Fork Iowa River IA 02-IOW-746

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli).  The following table summarized recreation season geometric means of E. coli at station BC350 over the 2010-2014 period:

All geometric means were slightly to moderately above the Class A1 criterion of 126 orgs/100 ml.  Twenty of the 39 samples (51.3%) collected over the 2010-2014 period exceeded the single-sample maximum criterion of 235 E. coli organisms/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 "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). 

The assessment of support of the Class B(WW1) uses is based, in part, on the USGS/NAWQA monitoring near New Providence (station 05451210) that showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, chloride or sulfate in the approximately 50 samples collected from March 2012 through December 2014.  No violations of the Class B(WW1) criteria for arsenic occurred in the 48 samples analyzed.  One of the 48 samples analyzed for selenium did violate the Class B(WW1) criterion.  The occurrence of one violation of the selenium criterion in this three-year period, however, does not indicate impairment of the aquatic life uses.  According to U.S. EPA guidelines and IDNR’s assessment/listing methodology, the monitoring results suggest from USGS station near New Providence do not suggest impairment  of the Class B(WW1) aquatic life uses. 

The assessment of support of the Class B(WW1) aquatic life uses is also based on monitoring at NLAE station SF450 near New Providence.  Continuous monitoring data for dissolved oxygen, pH, and water temperature for the years 2010 through 2014 are available for this station.  Eighteen of the 462 daily maximum values (3.9%) for pH exceeded the Class B(WW1) high pH criterion of 9.0; the maximum pH reported for this period was 9.2 units.  Ten of the 462 daily minimum pH values (2.2%) violated the low pH criterion of 6.5 pH units (the lowest minimum daily value was 6.2 units).  Seventeen of the 511 daily maximum values for water temperature (3.3%) exceeded Iowa’s added heat criterion of 32C (maximum value = 35.4C).  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if more than 10% of the samples for conventional parameters such as pH or temperature exceed their respective Class B(WW2) criteria, the aquatic life uses should be assessed as “impaired”.  According to Iowa’s assessment/listing methodology, however, the percentages of samples exceeding the respective Class B(WW2) criteria for pH and water temperature are not significantly greater than 10%.  Thus, the monitoring results for pH and water temperature at station SF450 do not suggest impairment. 

Of the 486 daily minimum values for dissolved oxygen generated at monitoring site SF450 over the 2010-2014 monitoring period, 64 values (31.2%) were below the 5.0 mg/l Class B(WW1) criterion (not < 5.0 mg/l at any time during a 24-hour period).  According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR’s assessment methodology, the percentage of samples that violated the 5.0 mg/l standard is significantly greater than 10%.  Thus, the Class B(WW1) aquatic life uses are assessed as “impaired” (partially supporting).  This impairment is due primarily due violations of dissolved oxygen criteria during the warm dry summer of 2012.  During the period from July 1 to September 15, 2012, the daily minimum values for dissolved oxygen in 52 of the 77 samples collected (68%) were less than the 5.0 mg/l dissolved oxygen standard.  Over 80% of the total number of violations of the dissolved oxygen criterion at this station (52 of 64) during the five year period from 2010-2014 occurred during this 78-day period during summer 2012.

The watershed of the South Fork Iowa River has a history of repeated fish kills, most often in the upper reaches of the stream.  The most recent kill documented in the lower segments of this stream occurred over 15 years ago (July 1995).  Thus, based on the (1) results of water quality monitoring and (2) the lack of recent fish kills in this assessment segment, the Class B(WW1) uses are assessed as “fully supported”. 

Fish consumption uses remain not assessed due to the lack of recent fish contaminant monitoring in this river segment.  Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the National Water Quality Assessment project.  These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions. 

Results of water quality monitoring at USGS station 05451210 during the 2008-2010 period showed that four of 36 samples (11%) contained “estimated” levels of dieldrin that violated Iowa’s HH/fish criterion of 0.00052 ppb; the remainder of the samples were below the level of detection (0.009 ug/l).  According to USGS, concentrations are reported as “estimated” because there is some uncertainty in the value.  Also, according to USGS, the results of a review these data indicate that there is no indication that these estimated sample results were the result of contamination from lab processing and analysis.  Thus, the estimated dieldrin concentrations were considered legitimate and were compared to the respective water quality criterion. 

Based on the results of USGS monitoring for dieldrin, the Human Health designated use (including the fish consumption use) was assessed (evaluated) as “partially supporting” (IR Category 3b-potentially impaired).  According to IDNR’s assessment/listing methodology, if the average level of a toxic metal or pesticide is greater than its respective human health criterion, impairment ("nonsupport") of the Human Health (HH) use is indicated.  However, the samples with detectable levels of dieldrin were too few (four) and the method detection level (0.009 ug/l) was far too high (16 times the HH criterion for dieldrin) to allow calculation of a meaningful summary statistic (i.e., mean) for dieldrin at this monitoring station.  Also, levels of dieldrin in Iowa fish have declined significantly since the early to mid-1980s when levels of 300 ppb to 500 ppb were not uncommon (see ftp://ftp.igsb.uiowa.edu/igspubs/pdf/WFS-2006-05.pdf).  Thus, the HH/fish consumption uses were assessed (evaluated) as “partially supported” (IR Category 3b) for the 2012 Integrated Reporting cycle.  IR Category 3b waters are added to Iowa’s list of waters in need of further investigation. 

Results of USGS monitoring from March 2010 to December 2012, however, showed no violations of the HH/fish criterion for dieldrin in the 24 samples analyzed.  According to the IDNR assessment/listing methodology, two consecutive IR cycles (five years) are needed with contaminant levels showing “full support” of the assessed use before an impairment or potential impairment can be removed.  Thus, if subsequent monitoring by USGS showed continued low levels of dieldrin in this assessment segment, the IR category for the HH/fish could be changed from IR 3b (potentially impaired) to IR 2a (fully supported).  Unfortunately, sampling for dieldrin was not conducted by USGS during the November 2012 to December 2014 monitoring period.  Thus, the Human Health uses will remain assessed as “partially supported” (IR 3b) due to the historic levels of dieldrin detected at this monitoring station.