Assessment Comments

Assessment is based on results of the following monitoring projects from 2004-06: (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 2004-2006 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 et al.  2005, Lutz and Francois 2006, and Lutz and Francois 2007), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2004-2006 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2004-2006 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 covers the primary Section 303(d) impairments identified for the 2006 assessment/listing cycle, this waterbody is moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 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.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 36 samples collected at the ISU/ACOE station during the recreational seasons of 2004, 2005 and 2006 (275 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   In addition, 16 of the 36 samples (44%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected at the IDNR/UHL station during this assessment period (311 orgs/100ml) also exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Thirteen of the 24 IDNR/UHL samples (42%) 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 2004 through 2006 also suggest that the Class A1 uses are "not supported."  Levels of indicator bacteria (E.  coli) in the Raccoon River at the Des Moines Water Works were monitored on 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."  In addition, the U.S.  EPA guidelines state that if more than 10% of the total samples taken during any thirty-day period has a bacterial density that exceeds the single-sample maximum criterion of 235 E.  coli organsims/100 ml, the primary contact recreation uses should be assessed as "partially supported."  Results of DMWW monitoring on the Raccoon River show that large numbers of the 30-day geometric means (with approximately 20 samples collected per each 30-day period) violated Iowa’s geometric mean criterion of 126 orgs/100 ml:  166 violations (76%) in 2004, 123 violations (56%) in 2005, and 142 violations (65%) in 2006.   Also, a large percentage of the samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml:  79 of 169 samples (47%) in 2004, 52 of 163 samples (32%) in 2005, and 60 of 170 samples (35%) in 2006.   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 36 samples collected during the 2004-2006 assessment period.   None of the ten samples analyzed for pesticides and none of the 14 samples analyzed for toxic metals exceeded Class B(WW1) criteria during the 2004-2006 assessment period.   This lack of violations of Class B(WW1) criteria suggests that the aquatic life uses should be assessed (monitored) as “fully supported.”  During the 2004 assessment period (2000-2002), two of the 28 samples analyzed for toxic metals (7%) had exceeded the Class B(WW1) chronic criterion for copper.   These results suggested only “partial support” of the Class B(WW1) uses for the 2004 reporting cycle.   No additional violations of Class B(WW1) criteria for copper have occurred in the 38 samples collected at this site and analyzed for copper from 2002 through 2006.  

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 2004-2006 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 37% of the samples collected from January 2004 through December 2006 (213 of 569) contained nitrate above the 10 mg/l MCL (mean = 8.3 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 2004-2006 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.   Thus, to correct for this bias, 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-three of the 157 weekly average nitrate levels (27%) for the period 2004-2006 exceeded the nitrate MCL (weekly mean=7.2 mg/l; weekly median=7.6 mg/l; maximum weekly average=16.7).   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:  32% of the bi-monthly samples collected during the 2004-2006 assessment period (21 of 66 samples) exceeded the nitrate MCL (mean = 7.7 mg/l; maximum = 16.6 mg/l).   Similarly, results of IDNR/UHL ambient monthly monitoring on the Raccoon River conducted upstream from Des Moines show nonsupport of drinking water uses due to nitrate:  30% of the samples collected during the 2004-2006 assessment period (13 of 43 samples) exceeded the nitrate MCL (mean = 7.6 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 2004-2006 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.   One of the 37 samples analyzed over this three-year period exceeded the atrazine MCL of 3 ppb:  the sample collected on May 12, 2005 contained 6.2 ppb of atrazine.   The average level of atrazine in the 37 samples was 0.43 ppb.   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.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 1999 RAFT sampling conducted in this assessment segment:  levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.