Assessment Comments
Assessment is based on results of (1) IDNR/SHL ambient monitoring from 2010-12 upstream from Cedar Rapids near Palo, (2) monitoring of the Cedar River for nitrate by the Cedar Rapids Water Department from 2010-13, (3) USGS ambient monitoring at Edgewood Road at Cedar Rapids from 2010-12, and (4) IDNR/SHL biological sampling conducted in 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 4a) due to levels of indicator bacteria. In addition, these uses are assessed (monitored) as "partially supporting" due to high levels of pH (IR 5a). 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. The pH impairments for the Class A1 and B(WW1) uses are new for this assessment segment. The Class C (drinking water) uses remain assessed (monitored) as "partially supported” (IR 4a) due to levels of nitrate that occasionally, but infrequently, exceed the state drinking water criterion of 10 mg/l (=U.S. EPA’s MCL for nitrate). 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 ambient monitoring of the Cedar River for nitrate by the Cedar Rapids Water Department from 2010 through August 2013, (3) results of USGS chemical/physical water quality monitoring at the Edgewood Road (station 05464480) from March 2010 through November 2012 and (4) IDNR/SHL biological sampling conducted in 2012.
Note 1: A TMDL for nitrate in this segment of the Cedar River was prepared by IDNR and approved by EPA in January 2007. Thus, the nitrate impairment in this segment is appropriate for Category 4a of Iowa’s Integrated Report.
Note 2: A TMDL for the bacteria impairment in this segment of Cedar River was prepared and approved by EPA in February 2010. Thus, the bacteria impairment in this segment is appropriate for Category 4a of Iowa’s Integrated Report.
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 "partially 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 should be assessed as "impaired" (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 3-35 of 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 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 2012 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 2012 BMIBI score was 41 (fair). 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 artificial substrate BMIBI BIC for this ecoregion is 52. This assessment is considered evaluated because the drainage area (6450 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).
Based on results of ambient monitoring conducted by USGS, IDNR/SHL, and by the Cedar Rapids Water Department, the Class C (drinking water) uses are assessed as "partially supported" due to the history of violations of the state water quality standard (= U.S. EPA’s MCL) for nitrate. Similar to results of IDNR and USGS ambient monthly monitoring on the Cedar River in this assessment segment during the previous (2008-2010) assessment listing period, no violations of the nitrate MCL occurred in the 36 monthly samples from the IDNR monitoring station (maximum=10 mg/l) or in the 15 samples from the USGS station at Edgewood Road (maximum = 7.2 mg/l). Based on IDNR's assessment/listing methodology, if less than 10% of the samples exceed the nitrate MCL, the drinking water uses should be assessed as "fully supported." Thus, according to the IDNR assessment methodology, these results do not suggest impairment of the Class C (drinking water) uses.
Similarly, monitoring of the Cedar River by the Cedar Rapids Water Department (CRWD) near their water supply intake areas from January 2010 through December 2012 also suggest that levels of nitrate in the Cedar River are typically below the MCL of 10 mg/l. The CRWD data from the Mohawk Park monitoring station show that only five of the 144 samples collected (3%) during this three-year period exceeded the 10 mg/l water quality standard. At the Mohawk Park station, the mean, median, and maximum sample values were 4.7, 5.3, and 12.1 mg/l, respectively. Four of the five violations occurred in May and June of 2011. According to IDNR's assessment guidelines, the IDNR, USGS, and CRWD datasets for the 2010-2012 period all suggest “full support” of the Class C drinking water uses. Due, however, to the history of high levels of nitrate in this assessment segment and due to the tendency of nitrate levels in surface waters to fluctuate with year-to-year changes in precipitation, this segment will remain assessed (monitored) as “partially supported” for the 2014 Integrated Reporting cycle. Although nitrate levels in this segment of the Cedar River have indicated “full support” of drinking water uses over two consecutive Integrated Reporting periods (2012 and 2014), a preliminary look at nitrate levels from January to August of 2013 suggest higher levels of nitrate in the Cedar River. Eleven of the 36 samples (31%) collected from January to August of 2013 exceeded the nitrate MCL of 10 mg/l. Although nitrate levels in all Iowa rivers increased dramatically in 2013 following two relatively dry crop years in 2011 and 2012, the higher frequency of violations of the nitrate MCL in this segment of the Cedar River suggests that keeping the nitrate impairment in-place for this river segment is appropriate. Nonetheless, nitrate levels in the Cedar River appear to be low relative to other rivers and do not appear to present a significant impact to the Class C uses of this river segment.
None of the combined 22 samples from the IDNR and USGs stations that were analyzed for atrazine during the 2010-2012 assessment period exceeded the Iowa Class C criterion for atrazine of 3 ug/l (=U.S. EPA’s MCL). The maximum level of atrazine in the combined 22 samples was 0.46 ug/l; these results do not suggest an atrazine-related impairment of the Class C uses. Also, none of the 28 samples analyzed for alachlor during the 2010-2012 period violated the Class C (drinking water) criterion (maximum = 0.1 ug/l).
Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.
