Assessment Comments

Assessment is based on results of the following monitoring projects from 2006-08: (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 1999.

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.   The Class C (drinking water) uses are assessed (monitored) as "not supported" due to levels of nitrate that 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 1999.   The assessments of support of the beneficial uses of this river segment are based on (1) results of monitoring conducted from 2006-2008 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 Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2006-2008 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2006-2008 assessment period, and (4) results of U.S.  EPA / IDNR fish tissue (RAFT) monitoring near Booneville in 1999.  

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 (2010) 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 mean level of indicator bacteria (E.   coli) in the 30 samples collected at the ISU/ACOE station during the recreational seasons of 2004, 2005 and 2006 (180 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   In addition, 15 of the 30 samples (50%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   The geometric mean level of indicator bacteria (E.   coli) in the 22 samples collected at the IDNR/UHL station during this assessment period (337 orgs/100ml) also exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Ten of the 22 IDNR/UHL samples (45%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean of E.   coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

Results of bacterial monitoring by the Des Moines Water Works during recreational seasons of 2006 through 2008 also suggest that the Class A1 uses should be assessed as "not supported."  Levels of indicator bacteria (E.   coli) in the Raccoon River at the Des Moines Water Works were monitored on most weekdays during this period.   According to U.S.  EPA guidelines for determining support of primary contact recreation uses (U.S.  EPA 1997b, page 3-35), the geometric mean of E.   coli from at least five samples collected over a thirty-day period is compared to the Iowa water quality standard of 126 E.   coli organisms/100ml.   If a thirty-day geometric mean exceeds 126 orgs/100 ml, the primary contact recreation uses should be assessed as "not supported."  

To correct for serial correlation in the daily E.  coli samples collected on consecutive days, a single average E.  coli level was calculated for each week; this weekly average was used to calculate the 30-day, five sample geometric means for comparison to the 126 orgs/100 ml Class A1 criterion.   Results of DMWW monitoring on the Raccoon River show that large numbers of the 30-day, 5 sample geometric means violated Iowa’s geometric mean criterion of 126 orgs/100 ml:  25 of 32 geometric means in 2006 (78% in violation) in 2006, 33 of 33 geometric means in 2007 (100% in violation) in 2007, 31 of 31 geometric means in 2008 (100% in violation) .   Also, a large percentage of the samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml:  17 of 36 weekly averages (47%) in 2006, 26 of 37 weekly averages (70%) in 2007, and 30 of 35 weekly averages (86%) in 2008.   According to U.S.  EPA guidelines, the results of DMWW monitoring are consistent with results of IDNR/UHL as well as with ISU/ACOE monitoring and suggest “non-support” of the Class A1 (primary contact recreation) of this segment of the Raccoon River uses due to thirty-day geometric means that exceed Iowa’s water quality criterion of 126 E.   coli organisms/100 ml.  

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 34 samples collected during the 2006-2008 assessment period.   Neither of the two samples analyzed for pesticides and none of the four samples analyzed for toxic metals exceeded Class B(WW1) criteria during the 2006-2008 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 2006-2008 assessment period.   In addition, none of the 12 samples analyzed for toxic metals exceeded their respective B(WW1) criteria

The level of use support for the Class C (drinking water) uses remained assessed as "not supporting" due to 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.   Results of monitoring by the Des Moines Water Works in this river segment that show that 20% of the samples collected from January 2006 through December 2008 (268 of 853) contained nitrate above the 10 mg/l MCL (mean = 8.2 mg/l; median = 8.6 mg/l; maximum = 18.7 mg/l).   Violations of the MCL tended to occur during the spring and early summer of the 2006-2008 period.   IDNR's assessment methodology states that if more than 25% of samples exceed the nitrate MCL, nonsupport of drinking water uses is indicated.   In addition, the continued periodic use of a nitrate removal system by the Des Moines Water Works also suggests an impairment to drinking water uses due to high levels of nitrate in the Raccoon River.   According to U.S.  EPA's Section 305(b) guidelines (page 3-44 of U.S.  EPA 1997b), the use of the nitrate removal system by the DMWW constitutes "more than conventional  treatment" and thus also indicates that the designated drinking water uses are not fully supported (=impaired).    

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.   Forty of the 156 weekly average nitrate levels (25%) for the period 2006-2008 exceeded the nitrate MCL (weekly mean=8.0 mg/l; weekly median=8.3 mg/l; maximum weekly average=15.8).   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 "not supported" (that is, if the MCL is exceeded during the assessment period in more than 25% of samples, drinking water uses are “not supported”).  

Results of ambient monitoring conducted at Van Meter as part of the Iowa State University/Army Corps of Engineers network also show nonsupport of drinking water uses due to nitrate:  30% of the bi-monthly samples collected during the 2006-2008 assessment period (20 of 66 samples) exceeded the nitrate MCL (mean = 8.0 mg/l; maximum = 16.0 mg/l).   Similarly, results of IDNR/UHL ambient monthly monitoring on the Raccoon River conducted upstream from Des Moines show impairment of drinking water uses due to nitrate:  20% of the samples collected during the 2006-2008 assessment period (7 of 33 samples) exceeded the nitrate MCL (mean = 8.0 mg/l; maximum = 16.0 mg/l).   Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the lower Raccoon River during the 2006-2008 assessment period continue to suggest impairment of the drinking water uses.  

Results of monitoring during the 2004-2006 assessment period at Van Meter as part of the IDNR/UHL ambient city monitoring and by the Des Moines Water Works show relatively low levels of atrazine in this segment of the Raccoon River.   None of the 14 samples collected over the 2006-08 period as part of IDNR/UHL monitoring exceeded the atrazine MCL of 3 ppb (average:  0.15 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).   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 remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Booneville in 1999.   Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   The fish contaminant data generated from the 1999 RAFT sampling conducted in this assessment segment show that levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.