Assessment Comments
Assessment based on 2009 and 2012 IDNR/SHL biological sampling data: CBI = 31, 55, 52 & 27; CW BIC = 60 and is also based on IDNR monitoring at two sites from March to July, 2010, near Luxemburg.
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 “not supported” (IR Category 5p) due to high levels of indicator bacteria. This represents a new impairment for this assessment segment. The presumptive Class A2 (secondary contact recreation) uses are also assessed as “not supported” (IR Category 5p). The Class B(CW1) coldwater aquatic life uses are assessed (monitored) as "partially supported" (IR Category 5b-v) based on results of IDNR/SHL biological sampling in 2009 and 2012. Fish consumption uses remain "not assessed" (IR Category 3a) due to the lack of fish contaminant monitoring in this assessment segment. This assessment is also based on results of water quality monitoring from March to July, 2010 at STORET stations 11310005 and 11310006 near Luxemburg.
EXPLANATION: The presumptive Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the samples collected monthly during the recreational season of 2010 at stations 11310005 (16 samples) and 11310006 (nine samples)(917 and 358 orgs/100 ml, respectively) exceeded the Iowa water quality criterion to protect primary contact recreation uses (126 orgs/100 ml). Six of the nine samples (67%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml at station 11310006, and 12 of 16 samples (75%) exceeded the single sample maximum criterion at station 11310005. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The geometric mean of the 10 samples collected during calendar year 2010 at station 11310006 (461 orgs/100 ml) is 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. The geometric mean of the 17 samples collected at station 11310005 (990 orgs/100 ml),however, exceeded the Class A2 criterion. Two of the 10 samples (20%) from station 11310006 exceeded Iowa’s Class A2 single-sample maximum criterion of 2,880 orgs/100 ml, and six of 17 samples from station 11310005 exceeded this criterion. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than the respective criteria (126 orgs/100 ml for Class A1 and 630 orgs/100 ml for Class A2), the contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, both the Class A1 and Class A2 water contact recreation uses for this segment are assessed as "not supported".
The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2009 and 2012 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 2009 CBI score was 27. The 2012 CBI scores were 31, 52 and 55. The aquatic life use support was assessed (monitored) 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 0/4 times in a four-year period (2009-2012).
This aquatic life assessment is now considered "monitored" because there were multiple samples collected in multiple years in the previous five years.
Results of chemical/physical water quality monitoring from March to July 2010 at these two stations suggest "full support" of the Class B(CW1) aquatic life uses. No violations of Class B(CW1) water quality criteria for ammonia, dissolved oxygen, pH, chloride, or sulfate occurred in the approximately 25 combined samples from these two stations that were analyzed from March to July 2010. These results suggest "full support" of the Class B(CW1) aquatic life uses.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
