Assessment Comments

Assessment is based on results of the following monitoring projects from 2002-04: (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 A (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E.  coli).   The Class B(WW) 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 remain 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 (monitored) 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 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 Cummings 2003, Lutz 2004, and Lutz et al.  2005), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2002-2004 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2002-2004 assessment period, and (4) results of U.S.  EPA / IDNR fish tissue (RAFT) monitoring near Booneville in 1999.  

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 A uses are "not supported" due to high levels of indicator bacteria.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 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 the 2006 Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 25 samples collected at the ISU/ACOE station during the recreational seasons of 2002, 2003 and 2004 (396 orgs/100ml) far exceeded the Iowa Class A water quality criterion of 126 orgs/100ml.   In addition, 14 of the 25 samples (56%) exceeded Iowa’s single-sample maximum value 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 (132 orgs/100ml) barely exceeded the Iowa Class A water quality criterion of 126 orgs/100ml.   In addition, 9 of the 24 samples (37.5%) exceeded Iowa’s single-sample maximum value 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 2002 through 2004 also suggest that the Class A 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 five-sample, 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:  167 violations (77%) in 2002, 109 violations (50%) in 2003, and 166 violations (76%) in 2004.   Also, a large percentage of the samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml:  69 of 167 samples (41%) in 2002, 52 of 167 samples (31%) in 2003, and 79 of 169 samples (47%) in 2004.   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 A (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(WW) water quality criteria for dissolved oxygen or pH occurred in the 36 samples collected during the 2002-2004 assessment period.   One of these samples, however, exceeded the Class B(WW) criterion for ammonia-nitrogen.   According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), uses are “fully supported” if chronic criteria for a toxic pollutant (for example, ammonia) are exceeded in up to one sample from an dataset based on monthly monitoring.   None of the eight samples analyzed for pesticides and other toxic organic compounds, and none of the approximately 30 samples analyzed for toxic metals, exceeded Class B(WW) criteria during the 2002-2004 assessment period.   This lack of violations of Class B(WW) criteria suggests that the aquatic life uses should be assessed (monitored) as “fully supported”.   During the previous (2004) assessment period, two of the 28 samples analyzed for toxic metals (7%) during the 2000-2002 monitoring period had exceeded the Class B(WW) chronic criterion for copper.   Samples collected on February 15, 2001 and June 13, 2001, both contained 40 ug/l of copper; this level is greater than the Class B(WW) chronic criterion of 35 ug/l.   These results suggested only “partial support” of the Class B(WW) uses for the 2004 reporting cycle.   Based on the more recent data from the 2002-2004 monitoring period, the assessment of the Class B(WW) uses of this river segment will be changed (upgraded) from “partially supported” to “fully supported” for the 2006 reporting/listing cycle.  

No violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen occurred in the approximately 66 samples collected at the ISU/ACOE monitoring station during the 2002-2004 assessment period.   In addition, none of the 12 samples analyzed for toxic metals exceeded their respective B(WW) 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 53% of the samples collected during the 2002-2004 assessment period (287 of 536) contained nitrate above the 10 mg/l MCL (mean = 9.7 mg/l; median = 10.5 mg/l; maximum = 18.3 mg/l).   Violations of the MCL tended to occur during the spring and early summer, although violations were also relatively frequent in late fall and winter.   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 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.   Sixty-two of the 157 weekly average nitrate levels (40%) for the period 2002-2004 exceeded the nitrate MCL (weekly mean=7.9 mg/l; weekly median=8.7 mg/l; maximum weekly average=17.1).   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 are "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:  39% of the bi-monthly samples collected during the 2002-2004 assessment period (26 of 66 samples) exceeded the nitrate MCL (mean = 8.7 mg/l; maximum = 18.2 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:  33% of the samples collected during the 2002-2004 assessment period (12 of 36 samples) exceeded the nitrate MCL (mean = 8.2 mg/l; maximum = 17.0 mg/l).   Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the lower Raccoon River during the 2002-2004 assessment period continue to suggest impairment of the drinking water uses.  

Results of monitoring during the 2002-2004 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 37 samples analyzed for the IDNR/UHL network exceeded the MCL for atrazine of 3 ppb.   (Monitoring for atrazine is not conducted as part of the ISU/ACOE monitoring network.)  According to IDNR guidelines for Section 305(b) assessments, these results suggest “full support” of the drinking water uses.  

Fish consumption uses were 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.