Assessment Comments

Assessment is based on results of the following monitoring projects from 2008-10: (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; also, (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" based on results of monitoring for indicator bacteria (E.  coli).   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" 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 are assessed (monitored) as "not supported" due to historically high levels of nitrate that have routinely exceed state water quality standards and U.S.  EPA’s maximum contaminant level (MCL).   Fish consumption uses remain assessed (evaluated) as "fully supported" 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 2008-2010 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 and Steffen 2009, Lutz 2010, and Lutz 2011), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2008-2010 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2008-2010 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 (2012) cycle.  

EXPLANATION:  Results from both the ISU/ACOE monitoring station located at Van Meter and the IDNR/UHL station located upstream from Des Moines 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 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10250002 upstream from Des Moines were as follows:  the 2008 geometric mean was 597 orgs/100 ml, the 2009 geometric mean was 215 orgs/100 ml, and the 2010 geometric mean was 1,062 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fourteen of the 22 samples (64%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  

The geometric means of indicator bacteria (E.  coli) in the 27 samples collected during the recreational seasons of 2008 through 2010 at ISU/ACOE Station 10 upstream from Des Moines at Van Meter (STORET station 17250001) were as follows:  the 2008 geometric mean was 520 orgs/100 ml, the 2009 geometric mean was 340 orgs/100 ml and the 2010 geometric mean was 1,413 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Eighteen of the 27 samples (67%) 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 2008 through 2010 also suggest that the Class A1 uses should be assessed as "not supported.”  The geometric means of indicator bacteria (E.  coli) in the 510 samples collected during the recreational seasons of 2008 through 2010 by the Des Moines Water Works were as follows:  the 2008 geometric mean was 420 orgs/100 ml, the 2009 geometric mean was 256 orgs/100 ml and the 2010 geometric mean was 385 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Two hundred sixty-nine of the 510 samples (53%) 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.”

At the IDNR/UHL city station at Van Meter, no violations of Class B(WW1) water quality criteria for dissolved oxygen, ammonia, or pH occurred in the approximately 30 samples collected during the 2008-2010 assessment period.   Neither of the two samples analyzed for pesticides and toxic metals exceeded Class B(WW1) criteria during the 2008-2010 assessment period.   This lack of violations of Class B(WW1) criteria 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 2008-2010 assessment period.   In addition, none of the 12 samples analyzed for toxic metals 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.   During the 2008-2010 assessment period, however, levels of nitrate were relatively low 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 that show that 6% of the samples collected from January 2008 through December 2010 (44 of 737) contained nitrate above the 10 mg/l MCL (mean = 6.7 mg/l; median = 7.0 mg/l; maximum = 11.6 mg/l).   Due to over-sampling by water supply utilities during times of year when nitrate levels tend to be high, the use of a simple percentage of samples in violation of the MCL likely overestimates the percentage of time that nitrate levels actually exceed the MCL.   In addition, daily sampling likely introduces serial correlation into the resulting datasets.   Thus, to correct for these biases, IDNR staff summarized the Raccoon River nitrate data from the Des Moines Water Works as weekly averages and compared these averages to the water quality standard.   Seven of the 156 weekly average nitrate levels (4.5%) for the period 2008-2010 exceeded the nitrate MCL (weekly mean=6.7 mg/l; weekly median=7.1 mg/l; maximum weekly average=11.3 mg/l).   Thus, according to IDNR's assessment guidelines, the DMWW data--whether summarized as individual samples or as weekly averages--suggest that the Class C drinking water uses should be assessed as "fully supported" (that is, whether summarized as the raw data or as weekly averages, less than 10% of the samples exceeded the nitrate MCL).  

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:  8% of the bi-monthly samples collected during the 2008-2010 assessment period (5 of 66 samples) exceeded the nitrate MCL (mean = 7.0 mg/l; median = 7.3 mg/l; maximum = 10.9 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 30 monthly samples collected during the 2008-2010 assessment period exceeded the nitrate MCL (mean = 7.0 mg/l; median = 7.3; maximum = 10.0 mg/l).   Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the lower Raccoon River during the 2008-2010 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, and only 6% of the samples violated the MCL in the 2008-10 dataset used for the current (2012) 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, down to 6.7 mg/l in the current (2008-10) dataset.   If the DMWW daily data are summarized as weekly averages, this downward trend is also apparent, with the percentages of weekly average nitrate exceeding the MCL declining from 40% in the 2002-04 dataset to approximately 25% in the 2004-06 and 2006-08 datasets, and down to 4.5% in the current (2008-10) dataset.   Weekly average nitrate levels have generally declined over this nine-year period but less so than suggested by the raw data:  2002-04:  7.9 mg/l; 2004-06:  7.2 mg/l; 2006-08:  8.0 mg/l, and 2008-10:  6.7 mg/l.   Maximum weekly average nitrate values in these four datasets were 17.1, 16.7, 15.8, and 11.3 mg/l, respectively.

Thus, the monitoring results from the current (2008-10) 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 the history of high levels of nitrate in the lower Raccoon River, and due to the ability of the weather to influence in-stream levels of nitrate, the Class C (drinking water) uses will remain assessed as “not supporting” for the current (2012) Integrated Reporting cycle (IR Category 4a).   If, however, nitrate data for the next (2014) Integrated Reporting cycle (collected during calendar years 2010 through 2012) show “full support” of the drinking water uses, this impairment will be removed.   This assessment approach is designed to help ensure that water quality improvement suggested by recent monitoring data reflects an actual change in water quality conditions and not just a temporary, weather-influenced variation in water quality.  

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 13 samples collected over the 2006-08 period as part of IDNR/UHL monitoring exceeded the atrazine MCL of 3 ppb (average:  0.16 ppb; maximum sample value:  0.46 ppb).   Atrazine data are no longer available at the Des Moines Water Work’s web site (http://www.dmww.com/AdvancedWaterQuality.aspx), and atrazine is no longer monitored as part of the IDNR city monitoring network.   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 uses were 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.