Assessment Comments

Assessment is based on results of the following monitoring projects from 2010-12: (1) ambient water quality monitoring by Iowa State Univ. for an ACOE WQ project, (2) ambient monitoring by Des Moines Water Works, (3) IDNR/UHL city monitoring, and (4) fish tissue (RAFT) monitoring in 2010.

Basis for Assessment

Note:  This assessment is also used for the adjacent upstream segment of the Raccoon River (IA 04-RAC-0010-2).  

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 4a) based on results of monitoring for indicator bacteria (E.  coli).   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of ambient chemical/physical water quality monitoring.   Although levels of nitrate appear to be trending downward, the Class C (drinking water) uses remain assessed (monitored) as "not supported" (IR 4a) due to historically high levels of nitrate that have routinely exceed state water quality standards and U.S.  EPA’s maximum contaminant level (MCL) and due to the likelihood of a return to higher nitrate levels for the next assessment/listing cycle.   Fish consumption uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of fish contaminant monitoring in 2010.   The assessments of support of the beneficial uses of this river segment are based on (1) results of monitoring conducted from 2010-2012 by Iowa State University (under contract with the U.S.   Army Corps of Engineers) (ISU/ACOE) conducted at ISU/ACOE Station 10 at Van Meter (STORET Station 17250001) as part of the Des Moines River Water Quality Study (see Lutz 2011, 2012, and 2013), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2010-2012 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2010-2012 assessment period, and (4) results of U.S.  EPA / IDNR fish tissue (RAFT) monitoring near Booneville in 2010.  

Note:  A TMDL for nitrate and pathogen indicators (E.  coli) was prepared by IDNR and approved by EPA in June 2008.   Because this TMDL covered the primary Section 303(d) impairments identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle.   This river segment remains in IR Category 4a for the current cycle.  

EXPLANATION:  Results from the Des Moines Water Works, ISU/ACOE monitoring station located at Van Meter, and the IDNR/UHL station located upstream from Des Moines all suggest that Class A1 uses should be assessed as "not supported" due to high levels of indicator bacteria.   The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10250002 upstream from Des Moines were as follows:  the 2010 geometric mean was 1,062 orgs/100 ml, the 2011 geometric mean was 102 orgs/100 ml, and the 2012 geometric mean was 107 orgs/100 ml.   Only the 2008 geometric mean exceeded the Class A1 criterion of 126 orgs/100 ml.   Ten of the 24 samples (42%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

The geometric means of indicator bacteria (E.  coli) in the 29 samples collected during the recreational seasons of 2010 through 2012 at ISU/ACOE Station 10 upstream from Des Moines at Van Meter (STORET station 17250001) were as follows:  the 2010 geometric mean was 1,413 orgs/100 ml, the 2011 geometric mean was 271 orgs/100 ml, and the 2012 geometric mean was 80 orgs/100 ml.   Both the 2010 and 2011 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Twelve of the 29 samples (41%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

Similarly, results of bacterial monitoring by the Des Moines Water Works during recreational seasons of 2010 through 2012 also suggest that the Class A1 uses should be assessed as "not supported.”  The geometric means of indicator bacteria (E.  coli) in the 510 daily samples collected during the recreational seasons of 2010 through 2012 by the Des Moines Water Works were as follows:  the 2010 geometric mean was 385 orgs/100 ml, the 2011 geometric mean was 155 orgs/100 ml, and the 2012 geometric mean was 112 orgs/100 ml.   The 2010 and 2011 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Two hundred of the 510 samples (39%) exceeded the Class A1 single-sample maximum criterion of 235 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 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 are assessed as “impaired.”  Despite the ongoing impairment of the Class A1 uses, levels of indicator bacteria during the recreation seasons of 2011 and 2012 were relatively low with recreation season geometric means in 2011 only slightly exceeding the geometric mean criterion and with no geometric means exceeding this criterion in 2012.   These results are influenced, in part, by the very dry conditions during the 2011 and 2012 recreation seasons.  

The Class B(WW1) aquatic life uses of this river segment are assessed as “fully supporting” based on results of chemical/physical water quality data.   At the IDNR/UHL city station at Van Meter, no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia, pH, temperature, chloride, or sulfate occurred in the 36 samples collected during the 2010-2012 assessment period.   This lack of violations of Class B(WW1) criteria is consistent with the history of water quality monitoring in this segment and suggests that the aquatic life uses should be assessed (monitored) as “fully supported.”  

No violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen occurred in the 66 samples collected at the ISU/ACOE monitoring station during the 2010-2012 assessment period.   In addition, none of the 12 samples analyzed for toxic metals (lead, mercury, cadmium, and copper) exceeded their respective B(WW1) criteria

The Class C (drinking water) uses remain assessed as "not supporting" due to historically high levels of nitrate in the lower Raccoon River as shown by results of monitoring conducted by the Des Moines Water Works, ISU/ACOE, and IDNR/UHL.   Similar to the previous (2008-2010) assessment period, however, levels of nitrate were relatively low during the current (2010-2012 assessment period, and according to IDNR’s assessment/listing methodology, suggest “full support” of the Class C drinking water uses.   According to the IDNR assessment/listing methodology, if less than 10% of samples exceed the nitrate MCL, the Class C uses should be assessed as “fully supported”.   Results of monitoring by the Des Moines Water Works in this river segment show that only 3% of the daily samples collected from January 2010 through December 2012 (22 of 681 samples) contained nitrate above the 10 mg/l MCL (mean = 5.1 mg/l; median = 5.7 mg/l; maximum = 11.5 mg/l).   According to IDNR's assessment guidelines, the DMWW data suggest that the Class C drinking water uses should be assessed as "fully supported".  

Results of ambient monitoring for nitrate conducted at Van Meter as part of the Iowa State University/Army Corps of Engineers network also show “full support” of drinking water uses during the 2010-2012 period:  5% of the bi-monthly samples collected during the 2010-2012 assessment period (3 of 66 samples) exceeded the nitrate MCL (mean = 5.1 mg/l; median = 5.5 mg/l; maximum = 10.4 mg/l).   Similarly, results of IDNR/UHL ambient monthly monitoring for nitrate on the Raccoon River conducted upstream from Des Moines show “full support” of drinking water uses:  none of the 36 monthly samples collected during the 2010-2012 assessment period exceeded the nitrate MCL (mean = 5.0 mg/l; median = 5.7; maximum = 9.9 mg/l).   Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the lower Raccoon River during the 2010-2012 assessment period suggest “full support” of the drinking water uses.  

In terms of the numbers and percentages of MCL violations for Integrated Reporting cycles, levels of nitrate in the lower Raccoon River appear to be trending downward.   Based on daily DMWW monitoring, the percentages of MCL violations in this dataset have declined as follows:  53% of samples violated the MCL in the 2002-04 dataset, 37% in the 2004-06 dataset, 20% in the 2006-08 dataset, 6% of samples in the 2008-10 dataset, and 3% of the sample violated the nitrate MCL in the 2010-12 dataset used for the current (2014) integrated reporting cycle.   Average levels of nitrate in these three-year assessment datasets have also declined over the last nine years from an average of 9.7 mg/l in the 2002-04 dataset to approximately 8.2 mg/l in the 2004-06 and 2006-08 datasets, 6.7 mg/l in the (2008-10) dataset, and down to 5.1 mg/l in the current (2010-12) dataset.  

Thus, the monitoring results from the current (2010-12) assessment period and the apparent downward trends in nitrate levels over the previous three Integrated Reporting cycles suggest that the Class C (drinking water) uses should be assessed as “fully supporting.”  Due, however, to (1) the history of high levels of nitrate in the lower Raccoon River, (2) the ability of the weather to influence in-stream levels of nitrate, and (3) the anticipated return of impairment levels of nitrate in the next (2016) Integrated Reporting cycle, the Class C (drinking water) uses will remain assessed as “not supporting” for the current (2014) Integrated Reporting cycle (IR Category 4a).   A preliminary analysis of 2012-2014 monitoring data from the Des Moines Water Works for nitrate in the lower Raccoon River suggests a return to impairment levels of nitrate.   Of the 530 daily measurements made by DMWW from January 1, 2012 through April 30, 2014, 94 samples (18%) violated the nitrate MCL of 10 mg/l.   The highest levels of nitrate during the period occurred from April 20 to July 15, 2013.   During this period, levels of nitrate in the 79 daily samples averaged 16.9 mg/l (SD=2.9 mg/l); the minimum nitrate level was slightly above the MCL of 10 mg/l (10.1 mg/l on May 30, 2013).   These data suggest that if the nitrate impairment for the lower Raccoon River were removed for the current (2014) IR cycle, the impairment would again be applied to this river segment for the next (2016) IR cycle.

Results of monitoring from 2006-2008 at Van Meter conducted as part of the IDNR/UHL ambient city monitoring show relatively low levels of atrazine in this segment of the Raccoon River.   None of the seven samples collected during 2012 period as part of IDNR/UHL city monitoring exceeded the atrazine MCL of 3 ppb (average:  0.14 ppb; maximum sample value:  0.2 ppb).   Atrazine data are no longer available at the Des Moines Water Work’s web site (http://www.dmww.com/AdvancedWaterQuality.aspx).   Also, monitoring at the IDNR city station and the ISU/ACOE station showed no violations of Class C criteria for the following parameters:  alachlor (13 samples), carbofuran (7 samples), chloride (48 samples), cyanazine (7 samples), and lead (10 samples).   Based on IDNR’s assessment methodology, if the average level of a pesticide is less than the respective MCL, the Class C drinking water should be assessed as “fully supported.”  Note: Monitoring for atrazine is not conducted as part of the ISU/ACOE monitoring network.)  

Fish consumption/human-health uses are assessed (monitored) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at the Raccoon River near the Booneville access in 2010.  The composite samples of fillets from common carp and flathead catfish had low levels of contaminants.  Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.105 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.  Levels of primary contaminants in the composite sample of flathead catfish fillets were as follows: mercury: 0.152 ppm.  The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.  The fish contaminant data generated from the 2010 RAFT sampling conducted at this river segment show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.   In addition, none of the 10 samples analyzed for the copper and mercury by ISU/ACOE during the 2010-2012 period exceeded the respective human-health/fish+water criteria.