Assessment Comments
Assessment is based on: (1) the results of monitoring for indicator bacteria conducted at Site 9 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010 (2) results of IDNR/SHL biological sampling in 2007 and 2011, and (3) an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012.
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 presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported” (IR 2a). The Class B(CW1) coldwater aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of biological monitoring 2007 and 2011 and an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012. Fish consumption uses remain “not assessed” (IR 3a) due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment include (1) the results of monitoring for indicator bacteria conducted at Site 9 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910003) from April 2010 through October 2012, (2) results of DNR/SHL biological sampling in 2007 and 2011 and (3) an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as impaired (partially supporting) due to violations of Iowa’s water quality criteria for indicator bacteria. The presumptive Class A2 (secondary contact recreation) uses, however, remain assessed (monitored) as “fully supported". The geometric means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2010 through 2012 at UIRW Site 9 were as follows: the 2010 geometric mean was 216 orgs/100 ml, the 2011 geometric mean was 250 orgs/100 ml and the 2012 geometric mean was 131 orgs/100 ml. All three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. All three geometric means, however, are far below the Class A2 geometric mean criterion of 630 orgs/100 ml. Nine of the 20 samples (45%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; two of the 20 samples (10%) exceeded the 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, the presumptive Class A1 uses are assessed (monitored) as impaired.
IDNR’s assessment methodology also states that if significantly more than 10% of the bacterial samples in any recreation seasons exceeds Iowa’s single-sample maximum value, the respective Class A uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to this listing methodology, however, the percentage of samples that exceeded the Class A2 single-sample maximum criterion at UIRW Site 9 (10%), however is not significantly greater than 10%; thus, the Class A2 uses are assessed (monitored) as “fully supported”.
The assessment of the Class B(CW1) aquatic life uses remains based on data collected in 2007 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 2007 CBI score was 81 and the 2011 CBI score was 81. The aquatic life use support was assessed (monitored) as fully supporting (=FS), 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 2/2 times in a five-year period (2007-2011).
In addition, based on an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012, the Class B(CW1) uses are assessed as "fully supported". According to the updated summary, (Unnamed) Cold Water Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking for one species of trout and in the category of streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the resident trout species at this time for a second species of trout. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
In addition, monitoring from 2010 to 2012 at Upper Iowa River Watershed Site 9 included analysis for ammonia and temperature. None of the 20 samples analyzed contained a level of ammonia above the limit of detection (0.05 mg/l). In 2010 and 2011, water temperature was measured during 12 samplings with one of the 12 samples exceeding the Class B(CW1) criterion of 20C: August 2, 2011: 20.6C. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), "partial support" of beneficial uses is indicated if criteria are exceeded in more than 10% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen). Based on IDNR’s assessment methodology, the results from Upper Iowa River Watershed Site 10 do not suggest that the violation frequency for temperature is significantly greater than 10% and thus do not suggest impairment of Class B(CW1) uses of this assessment segment.
Fish consumption uses remain ”not assessed” due to the lack of fish contaminant monitoring in this stream segment.
