Cedar River IA 02-CED-456

[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.]   

The 2012-2014 monitoring period continued to show exceptionally low levels of indicator bacteria (E. coli) in this assessment segment, and thus the IR 4a impairment of the Class A1 uses is proposed for removal.  Similar to the previous monitoring periods, all geometric means for recreation seasons of 2012 through 2014 were below the Class A1 criterion of 126 orgs/100 ml at the IDNR monitoring station.  The geometric means of indicator bacteria (E. coli) in the 22 monthly samples collected during the recreational seasons of 2012 through 2014 at IDNR station 10570002 upstream from Cedar Rapids were as follows:  the 2012 geometric mean was 11 orgs/100 ml, the 2013 geometric mean was 53 orgs/100 ml and the 2014 geometric mean was 81 orgs/100 ml.  Three of the 22 samples collected (14%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  The 2008 recreational season geometric mean of 202 orgs/100 ml is the only E. coli recreation season geometric mean to violate the Class A1 criterion in 12 years of routine monthly ambient water quality monitoring at this station. 

Only seven samples were analyzed for indicator bacteria (E. coli) at USGS station 05464480 upstream from Cedar Rapids.  Four samples were collected during the 2012 recreation season (geometric mean of 6 orgs/100 ml); two samples during the 2013 season (geometric mean of 747 orgs/100 ml), and only one sample (3 orgs/100 ml) during the 2014 season.  Only one of the seven samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  According to Iowa’s assessment/listing methodology (Table 6), none of these recreation seasons has a sufficient number of data points (at least seven samples/season) for calculating a meaningful geometric mean that can be compared to Iowa’s Class A1 water quality criterion.  Thus, the USGS data are not used for this assessment. 

The results 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”.  This was the second consecutive Integrated Reporting cycle where (1) all geometric means were below the Class A1 criterion, and (2) according to IDNR’s assessment/listing methodology, the percentages of samples greater than the single-sample maximum criterion were not significantly greater than 10%.  Because, 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 be removed for the current (2016) IR cycle. 

The Class A1 (primary contact recreation) and Class B(WW1) aquatic life uses remain assessed (monitored) as "partially supported" due violations of criteria for pH during the previous (2010-2012) monitoring period when five of 36 samples (14%) analyzed for pH at IDNR monitoring station 10570002 violated the pH criterion, and four of 18 samples (22%) analyzed at USGS station 05464480 at Edgewood Road violated this criterion.  According to U.S. EPA guidelines for Section 305(b) reporting, if significantly greater than 10% of samples exceed state criteria for pH, the primary contact and aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  While the 2010-2012 results from the IDNR station did not show impairment, the violation frequency at the USGS station was significantly greater than 10%.  For the 2012-2014 monitoring period, however, levels of pH at both stations were below the impairment threshold.  Four of 33 samples (12%) from the IDNR station exceeded the pH criterion of 9.0 pH units, and two of 10 samples (20%) exceeded this criterion at the USGS station.  Neither violation frequency is significantly greater than 10%, thus suggesting “full support” of the designated uses.  Because, however, Iowa’s assessment/listing methodology requires that a standard be met for two consecutive IR cycles before an impairment can be de-listed, the pH impairment of the Class A1 and Class B(WW1) uses will remain in effect. 

Results of water quality monitoring for other parameters during the 2012-2014 monitoring period 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 43 samples analyzed at the two monitoring stations from 2012 to 2014.  In addition, levels of the pesticide carbofuran in the 26 samples analyzed at the USGS station were below the Class B(WW1) criteria.  

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, 2013 and 2014 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 2013 score was 44 (fair) and the 2014 score was 51 (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 (0/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment 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 violations of the state water quality standard (= U.S. EPA’s MCL) for nitrate.  At the Iowa DNR’s ambient monitoring station upstream from Cedar Rapids, five of the 33 monthly samples (15%) collected from 2012 through 2014 exceed the Class C criterion for nitrate.  One of ten samples (10%) violated this criterion in samples collected at the USGS station at Edgewood road.  The Cedar Rapids Water Department samples more frequently for nitrate, and 16 of the 162 samples (10%) collected at their Mohawk Park station from 2012 through 2014 exceed the Class C criterion for nitrate of 10 mg/l.  Mean and median levels of nitrate at all three monitoring stations were similar:

According to Iowa DNR’s assessment/listing methodology, none of the violation frequencies at the three monitoring stations is significantly greater than 10% which would indicate impairment of the Class C (drinking water) uses.  Thus, according to IDNR's assessment guidelines, the IDNR, USGS, and CRWD datasets for the 2012-2014 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, the tendency of nitrate levels in surface waters to fluctuate with year-to-year changes in precipitation, and nitrate violation frequencies that approach the impairment threshold, this segment will remain assessed (monitored) as “partially supported” for the 2016 Integrated Reporting cycle. 

Levels of nitrate in the Cedar River increased somewhat in the 2012-2014 monitoring period compared to previous periods.  During both the 2008-2010 and 2010-2012 IR monitoring periods, none of the samples collected at the IDNR or USGS monitoring stations contained nitrate levels above the Class C criterion of 10 mg/l.  The violation frequency in samples collected by the Cedar Rapids Water Department during the previous (2010-2012) monitoring period (3%) also suggested very low levels of nitrate in the Cedar River.  Monitoring will continue to track nitrate levels in the Cedar River during the next (2014-2016) monitoring period.  

None of the combined 37 samples from the IDNR and USGs stations that were analyzed for atrazine during the 2012-2014 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 2.6 ug/l; these results do not suggest an atrazine-related impairment of the Class C uses.  Also, none of the 41 samples analyzed for alachlor during the 2012-2014 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.