Assessment Comments
Assessment remains based on 2006 and 2011 IDNR/SHL biological sampling data: CBI = 20, 37, 44, 45, 47 and 49; CW BIC = 60. Assessment is also based on chemical/physical/bacterial monitoring in 2011 and 2012 at three stations: 11220012 (Site 326), 11220013 (Site PeC2), and 11220023 (Site pecr3).
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.
SUMMARY: The Class A1 (primary contact recreation) are assessed (monitored) as “partially supported” due to high levels of indicator bacteria (IR Category 5a), and the Class A2 (secondary contact recreation) are assessed (monitored) as “fully supported” (IR Category 2a). The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as “partially supporting” due to a biological impairment (IR Category 5b-t). Fish consumption uses remain “not assessed” (IR Category 2a) due to the lack of fish contaminant monitoring in this stream segment. The source of data used for this assessment are (1) biological sampling conducted on Pecks Creek in 2006 and 2011 as part of the IDNR/SHL TMDL sampling project, (2) chemical/physical/bacterial monitoring in 2011 and 2012 at three stations: 11220012 (Site 326), 11220013 (Site PeC2), and 11220023 (Site pecr3).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed as “partially supported” based on levels of indicator bacteria that exceeded state water quality criteria. While the geometric mean of indicator bacteria (E. coli) in the seven monthly samples collected during the recreational season of 2011 (110 orgs/100 ml) was below the Class A1 criterion of 126 orgs/100 ml, the geometric mean of the eight samples collected during 2012 (500 orgs/100 ml) exceeded the Class A1 criterion. Six of the combined 15 samples (40%) 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).
In contrast, the Class A2 (secondary contact recreation) uses are assessed (monitored) as "fully supported". The geometric means of the seven samples collected during calendar year 2011 at station 11220012 (108 orgs/100 ml) and of the eight samples collected during 2012 (500 orgs/100 ml) 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 15 samples (13%) 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 monitoring in 2011 and 2012 suggest “full support” of the Class B(CW1) aquatic life uses. There were no violations of ammonia criteria in the combined 44 samples collected at the three monitoring stations during 2011 and 2012. Only two of the combined 45 samples (4%) violated the Class B(CW1) criterion for dissolved oxygen of 7.0 mg/l, and only one of the combined 46 samples (2%) violated the Class B(CW1) criterion of 9.0 pH units. The percentage violation for dissolved oxygen and pH are well below the impairment threshold of greater than 10% violation. The most frequently violated criterion was for water temperature with seven of the combined 47 samples exceeding the Class B(CW1) criterion of 20C. According to the IDNR assessment methodology, however, the percentage violation is not significantly greater than 10%; thus, the these violations do not suggest impairment of the Class B(CW1) uses.
Fish consumption uses remain “not assessed” due to lack of fish contaminant monitoring in this stream segment.
