Pecks Creek IA 01-TRK-168

The presumptive Class A1 (primary contact recreation) uses are assessed as “not supported” based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 23 samples collected during the recreational seasons of 2012 through 2014 at monitoring station 11220012 (Site 326) were as follows:  the 2012 geometric mean was 500 orgs/100 ml, the 2013 geometric mean was 148 orgs/100 ml, and the 2014 geometric mean was 164 orgs/100 ml.  All three geometric means slightly exceed the Class A1 geometric mean criterion of 126 orgs/100 ml.  Ten of the 23 samples (43%) exceeded the Class A1 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). 

In contrast, the Class A2 (secondary contact recreation) uses are assessed (monitored) as "fully supported".  The geometric means during the 2012 through 2014 recreation seasons (500, 148, and 164 orgs/100 ml, respectively) are below the Class A2 geometric mean criterion of 630 E. coli orgs/100 ml, thus indicating full support of the Class A2 water contact recreation uses.  Two of the 23 samples (9%) from these stations exceeded Iowa’s Class A2 single-sample maximum criterion of 2,880 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is less than the respective criteria (630 orgs/100 ml), the Class A2 contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  In addition, the percentage of samples exceeding the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml is not significantly greater than 10%, thus indicating that these uses are not impaired. 

The assessment of the Class B(CW1) aquatic life uses remains based on data collected in 2006 and 2011 as part of the IDNR/SHL coldwater stream sampling project.  A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data.  The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach.  The biological metrics were combined to make a coldwater benthic index (CBI).  The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2006 CBI scores were 20 and 37.  The 2011 CBI scores were 44, 45, 47 and 49.  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 0/6 times in a six-year period (2006-2011). 

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 a five-year period to be considered “monitored”.  This segment had multiple samples collected in a six-year period (2006-2011).  According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).  IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  Despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s Section 303(d) list of impaired waters. 

As part of the 2002 REMAP project, stream physical habitat assessment found adverse conditions that are thought to contribute to the biological impairment.  These include, bank instability, flow impoundment, and excessive silt deposition.  Beaver activity in the vicinity of the sample site has been observed and is suspected to be a major source of habitat alteration. 

Results of chemical/physical water quality monitoring from 2012 through 2014 do not suggest impairment of the Class B(WW1) aquatic life uses.  Monitoring at station 11220012 (Site 326) showed no violations of Class B(CW1) water quality criteria for ammonia (15 samples), dissolved oxygen (22 samples), pH (22 samples), or chloride (14 samples) during the 2012-2014 monitoring period.  Two of 23 samples violated the Class B(CW1) criterion for water temperature (maximum temperature:  22.1 C).  According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as temperature suggests impairment of aquatic life uses.  Based on IDNR’s assessment methodology, however, the results from station 11220012 suggest that the frequency of temperature violations is not significantly greater than 10 percent; thus, these results do not suggest impairment of the Class B(CW1) aquatic life uses. 

However, the results of continuous dissolved oxygen (DO) and temperature monitoring at two stream locations in 2011 for the IDNR/SHL coldwater stream sampling project do suggest impairment of Class B(CW1) aquatic life uses. The lowest DO concentration recorded in 48 days of continuous monitoring was 5.5 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (5 mg/L) in 0 of 48 days. The percentage exceeding (0%) was less than (passing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level was high (>90%). In contrast, the 16-hour DO criterion (7 mg/L) was exceeded in 22 of 48 days. The percentage exceeding (46%) was greater than (failing) the 10% threshold with high statistical confidence (>90%). The maximum stream temperature recorded during the sensor deployment period was 28.3 degrees (C). The B(CW1) temperature criterion of 20 (C) was exceeded in 36 of 48 days. The percentage exceeding (75%) was greater than (failing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(CW1) aquatic life use is assessed as impaired due to DO and temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the IDNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.

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