Assessment Comments
Assessment is based on results of IDNR/SHL and USGS ambient water quality monitoring from 2010 through 2012 near Cedar Rapids and on IDNR/SHL biological sampling conducted in 2011.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5a) due to levels of indicator bacteria. In addition, these uses are assessed as impaired due to high levels of pH (IR 5a): this is a new impairment for this assessment segment. The Class B(WW1) aquatic life uses are also assessed (monitored) as "partially supporting" (IR 5a) due to levels of pH that violate the Class B(WW1) criteria. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment are (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR ambient city monitoring station located at County Road E36 east of Palo (STORET station 10570002); (2) the results of USGS chemical/physical water quality monitoring at the Edgewood Road (station 05464480) from March 2010 through November 2012 and (3) IDNR/SHL biological sampling conducted in 2011.
Note: A TMDL for the bacteria impairments in the two downriver assessment segments of the Cedar River was prepared and approved by EPA in February 2010. This TMDL addressed bacteria impairments in Cedar River segments IA 02-CED-0030_1 and -0030_2 but did not include this segment of the Cedar River (IA 02-CED-0030_3). The bacteria impairments in all three segments, however, are based on the same monitoring data from the same Iowa DNR ambient water quality monitoring station: Cedar River at County Road E36 east of Palo (STORET station 10570002)). As noted in comments from U.S. EPA in May 2011, however, the failure of the TMDL to include segment CED-0030_3 require that this segment remain on Iowa's Section 303(d) list.
EXPLANATION: Despite the continuance of low levels of indicator bacteria in this segment of the Cedar River, the Class A1 uses remain assessed (monitored) as "not supported" based on results of monitoring in 2008 for indicator bacteria (E. coli) at the IDNR/UHL ambient monitoring station on the Cedar River east of Palo. All geometric means for recreation seasons of 2010 through 2012 were below the Class A1 criterion of 126 orgs/100 ml at both the IDNR and USGS monitoring stations. The geometric means of indicator bacteria (E. coli) in the 24 monthly samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10570002 upstream from Cedar Rapids were as follows: the 2010 geometric mean was 122 orgs/100 ml, the 2011 geometric mean was 61 orgs/100 ml and the 2012 geometric mean was 11 orgs/100 ml. Three of the 24 samples collected (3%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.
The geometric means of indicator bacteria (E. coli) in the 12 samples collected during the recreational seasons of 2010 through 2012 at USGS station 05464480 upstream from Cedar Rapids were as follows: the 2010 geometric mean was 111 orgs/100 ml, the 2011 geometric mean was 82 orgs/100 ml, and the 2012 geometric mean was 6 orgs/100 ml. Three of the 12 samples (25%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The results at both monitoring stations--for both geometric means and for the percentage of samples that exceed Iowa’s single sample maximum criterion--suggest that the Class A1 primary contact recreation uses should be assessed as “fully supporting”. All geometric means are below the Class A1 criterion, and, according to IDNR’s assessment/listing methodology, the percentages of samples greater than the single-sample maximum criterion are not significantly greater than 10%. Because, however, IDNR’s assessment/listing methodology requires that standards be met for two consecutive assessment cycles (total of five years) before an impairment can be removed, the impairment of the Class A1 uses will remain based on the 2008 geometric mean of 202 orgs/100 ml which resulted in an impairment for the 2012 IR cycle. 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 are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses were assessed as “impaired” for the 2012 IR cycle. The 2008 recreational season geometric mean of 202 orgs/100 ml is the only E. coli geometric mean to violate the Class A1 criterion in 10 years of routine monthly ambient water quality monitoring at this station.
Regardless of the recent (2010, 2012, and 2014) bacteria impairments, levels of indicator bacteria in this segment of the Cedar River have been and continue to be very low relative to levels of bacteria in other Iowa rivers, and thus this bacterial impairment should be considered very slight in magnitude. If additional monitoring during the 2012-2014 assessment period continues to show these low levels of indicator bacteria, this impairment should be removed.
The Class B(WW1) aquatic life uses are assessed (monitored) as "partially supported" due violations of the Class B(WW1) criterion for pH. Five of the 36 samples (14%) analyzed for pH at the IDNR monitoring station upstream from Cedar Rapids from 2010-2012 violated the pH criterion, and four of 18 samples (22%) analyzed at the USGS station at Edgewood Road violated this criterion. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH and dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from the USGS station at Edgewood Road indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criteria for pH. Also, if pH samples from both the IDNR and USGS station are combined, the percentage of samples violating the Class B(WW1) criterion for pH is also significantly greater than 10%. Thus, these results suggest impairment of the Class B(WW1) aquatic life uses. Results of water quality monitoring for other parameters from 2010-2012 at the IDNR ambient station near Palo and at the USGS station at Edgewood Road, however, do not suggest impairment of the Class B(WW1) uses. Monitoring at these stations showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia-nitrogen, chloride, or sulfate in the approximately 50 samples analyzed at the two monitoring stations.
In agreement with the water quality aquatic life assessment, the evaluated aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2011 as part of the IDNR/SHL stream nutrient sampling project. A series of biological metrics that reflect 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 collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2011 BMIBI score was 45 (good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI score with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The natural substrate BMIBI BIC for this ecoregion is 70. This assessment is considered evaluated because the drainage area (6238 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. 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).
Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.
