Hecker Creek IA 01-YEL-447

[Note: A TMDL for the bacterial impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and was approved by U.S. EPA in February 2013.  Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational uses is changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved).  Because not all impairments identified for this assessment segment are covered by the TMDL (biological impairment of aquatic life uses due a fish kill and due to high levels of chloride), this segment remains in Category 5 of Integrated Report (impaired and TMDL required).]

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses remain 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 49 samples collected at the monitoring station near the county road W4B crossing (station 15030010) during the recreational seasons of 2006 through 2008 was 2,335 orgs/100 ml.  This geometric mean far exceeds the Class A1 criterion of 126 orgs/100 ml.  Forty-three of the 50 samples (88%) 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 Class A1 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). 

As opposed to monitoring data from the 2004-2006 assessment period, results of IDNR/SHL ambient at this monitoring station from 2006-2008 assessment period did not indicate a water quality problem due to low levels of dissolved oxygen in Hecker Creek.  No violations of the Class B(WW1) criterion for dissolved oxygen (5.0 mg/l) occurred in the 50 samples collected between March 2006 and June 2008.  The minimum dissolved oxygen value during this period was 5.7 mg/l.  Also, none of the 31 samples analyzed for ammonia (and that had supporting data for pH and temperature) from September 2006 through June 2008 violated chronic aquatic life criteria (early life stages assumed present).  The maximum ammonia level during this period was 2.0 mg/l.  None of the 31 samples analyzed for pH at this station violated Class B(WW1) criteria (maximum:  8.8; minimum:  7.7 units).  Based on both U.S. EPA guidelines for Section 305(b) reporting and on IDNR’s assessment/listing methodology, these results suggest “full support” of aquatic life uses (see pgs 3-33 to 3-35of U.S. EPA 1997b). 

The presumptive Class B(WW1) aquatic life uses, however, are now impaired by high levels of chloride in this stream.  Chloride levels were monitored at station 15300010 from March 2006 through June 2008 as part of the Yellow River Watershed Project.  Chloride data for this stream were compared to the Class B(WW1) criteria for chloride.  Because data for neither hardness nor sulfate were collected from Hecker Creek, the default values of 200 mg/l CaCO3 hardness and 63 mg/l sulfate were used for the hardness and sulfate-dependent chloride criteria.  These default values give a Class B(WW1) chronic criterion of 389 mg/l of chloride and an acute criterion of 629 mg/l.  Of the 54 samples analyzed for chloride at this station between March 2006 and June 2008, 24 samples (44%) violated the default chronic criterion, and 16 samples (30%) violated the default acute criterion.  According to IDNR’s assessment and listing methodology, impairment of aquatic life uses is indicated if significantly more than 10% of the samples violate chronic criteria for non-priority toxics (such as chloride); also, if more than one violation of an acute criterion for a toxic parameter occurs within a three year period, the aquatic life uses are assessed as “impaired.”  Thus, these results suggested that this stream segment should be assessed as “not supported”.  Levels of chloride declined over the 2004-06 monitoring period and were much lower in 2008 than during 2005 when levels of chloride were typically greater than 1,000 mg/l.  Follow-up monitoring is needed to determine current levels of chloride in this stream segment and to determine whether the chloride impairment suggested by the 2006-08 data continues to exist.

Results of IDNR/SHL biological sampling in 2000, 2006 and 2007 suggest potential impairment of the aquatic life uses of this stream.  This monitoring was conducted in 2000, 2006 and 2007 as part of the IDNR/SHL stream biocriteria project and TMDL sampling.  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 2000 FIBI score was 16 (poor) and the 2000 BMIBI score was 53 (fair).  The 2006 FIBI score was 54 (good) and the BMIBI score was 61 (good).  The 2007 FIBI score was 30 (fair) and the BMIBI score was 70 (good).  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established 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 1/3 times and passed the BMIBI BIC 2/3 times in the last 15 years.  Even though this site failed the FIBI BIC and met the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.  Note that results of IDNR/SHL biological sampling are not typically used to develop "monitored" (i.e., high confidence) assessments because the assessment metrics are based on historical data from larger wadeable streams and rivers and are thus not strictly appropriate for assessing ecological conditions in the typically intermittent headwater streams.  For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) were not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report).  The assessment type for these assessed waters remains "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence).  Thus, the assessment segment remains in IR Category 5b-t.  

This stream was also investigated as part of a fish kill that occurred on the Yellow River on March 17, 2000.  An estimated 4,800 fish were killed; no cause or source of the kill was identified.  The following account is from the IDNR fish kill database and includes comments from the IDNR staff that investigated the kill:  "Dead fish were observed both upstream and downstream of the Smith Road bridge on the Yellow River, but only below the confluence with the unnamed tributary in section 17 [i.e., Hecker Creek].  North of Postville:  Water turbid and green, with high flow.  The kill affected a 3.1 mile segment of the Yellow River.  Dead fish were not observed in the unnamed tributary that enters into the Yellow River in Section 17."  According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill indicates impairment of the aquatic life uses.  The investigation report for this fish kill suggests that a pollutant in Hecker Creek was responsible for the kill.  According to IDNR’s assessment/listing methodology, pollutant-caused kills where the source of pollution was not identified justify addition of the affected stream segment to Iowa's Section 303(d) list of impaired waters.  Because this fish kill occurred more than five years ago, the assessment category is changed from a “monitored” (higher-confidence) assessment to an “evaluated” (lower confidence) assessments.  Regardless of this change, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill.  Thus, this assessment segment will remain in Category 5 of Iowa’s Integrated Report.