Assessment Comments
Assessment is based on results of the following monitoring projects from 2000-02: (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
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria. The Class B(WW) aquatic life uses are assessed (monitored) as "partially supported" due to levels of copper that exceed state water quality standards. 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). These assessments are also used for the adjacent upstream segment of the Raccoon River (IA 04-RAC-0010-2). 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) as part of the Des Moines River Water Quality Study (see Lutz et al. 2001, Lutz and Esser 2002, and Lutz and Cummings 2003), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2000-2002 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at Van Meter (station 10250002) during the 2000-2002 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 "partially supported" due to high levels of indicator bacteria. At the ISU/ACOE station, a total of 26 samples were analyzed for levels of indicator bacteria (fecal coliforms) during summers of 2000, 2001, and 2002. For purposes of Section 305(b) assessments, IDNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." All 26 samples were collected at flows that were not materially affected by surface runoff. The geometric mean of fecal coliform bacteria in the 26 non-runoff-affected samples collected from the Van Meter station during this period (165 orgs/100 ml) is below the state WQ criterion of 200 orgs/100 ml. Nine of the 26 non-runoff-affected samples (35%), however, exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.
At the IDNR/UHL station, a total of 16 samples were analyzed for levels of indicator bacteria (fecal coliforms) during summers of 2000, 2001, and 2002. Thirteen of the 16 samples were collected at flows that were not materially affected by surface runoff. The geometric mean of fecal coliform bacteria in the 13 non-runoff-affected samples collected from this station during this period (80 orgs/100 ml) is well below the state WQ criterion of 200 orgs/100 ml. Three of the 13 non-runoff-affected samples (23%), however, exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.
Although the geometric means for the assessment period for both the ISU and IDNR stations suggest full support of the primary contact recreation uses, the percentages of samples exceeding the U.S. EPA's single-sample maximum value at both stations indicate only "partial support" of these uses. According to U.S. EPA guidelines for Section 305(b) reporting (see U.S. EPA 1997b, pages 3-33 to 3-35), if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
Results from the IDNR city monitoring station at Van Meter suggest that the Class B(WW) aquatic life uses are "partially supported" due to violations of state water quality criteria for copper. Although none of the 28 samples collected during the 2000-2002 assessment period exceeded Class B(WW) criteria for dissolved oxygen, pH, or ammonia-nitrogen, and although none of the ten samples analyzed for pesticides and other toxic organic compounds exceeded Class B(WW) criteria, two of the 28 samples analyzed for toxic metals (7%) 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. According to U.S. EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, more than one sample exceeds a criterion, the aquatic life uses are "partially supported." If more than 10% of the samples exceed state criteria for toxics (including toxic metals), the aquatic life uses should be assessed as "not supported" (see pg 3-18 of U.S. EPA 1997b). Because approximately 7% of the samples from this network exceeded the Class B(WW) chronic criterion, the aquatic life uses are assessed as "partially supported."
No violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen occurred in the approximately 66 samples collected at the ISU/ACOE monitoring station during the 2000-2002 assessment period. One of 66 samples from the ISU/ACOE station, however, exceeded the Class B(WW) criterion for pH. The sample collected on August 14, 2001, contained a pH level of 9.04 units, thus slightly exceeding the water quality criterion of 9.0 pH units. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentage of violations for pH at this station (2%) does not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated). In the samples analyzed for toxic metals, the only violations were for mercury. Eight of the 10 samples analyzed for toxic metals during the 2000-02 assessment period contained levels of dissolved mercury above the Iowa WQ criterion for human health (fish) of 0.15 ug/l (none of the ten samples exceeded the Class B(WW) chronic aquatic life criterion of 2.1 ug/l (maximum value of the nine samples was 0.70 ug/l)). According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), more than one violation of a water quality criterion for a toxic contaminant within a three-year period indicates that the aquatic life uses are not fully supported. Due, however, to (1) problems with analysis of mercury in water (see pages 3-58 and 3-99 to 3-100 of Iowa's 1996 Section 305(b) report), (2) the historical lack of high levels of mercury in fish tissue samples from this reach of river, and (3) a study of mercury levels in the Des Moines River near Des Moines (see assessment for the 2000 report), data for mercury in water were not used to assess support of the Class B(WW) aquatic life uses of this river reach.
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 48% of the samples collected during the 2000-2002 assessment period (187 of 393) contained nitrate above the 10 mg/l MCL (mean = 9.6 mg/l; median = 9.7 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. Forty-one of the 142 weekly average nitrate levels (29%) for the period 2000-2002 exceeded the standard (weekly mean=7.1 mg/l; weekly median=6.4 mg/l; maximum weekly average=17.3). 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" (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: 26% of the bi-monthly samples collected during the 2000-2002 assessment period (17 of 66 samples) exceeded the nitrate (mean = 7.1 mg/l; maximum = 18.2 mg/l). Similarly, results of monthly monitoring conducted upstream from Des Moines as part of the IDNR/UHL network show nonsupport of drinking water uses due to nitrate: 32% of the samples collected during the 2000-2002 assessment period (9 of 28 samples) exceeded the nitrate (mean = 7.9 mg/l; maximum = 17.0 mg/l). Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the Raccoon River during the 2000-2002 assessment period suggest an impairment of the drinking water uses.
Results of monitoring during the 2000-2002 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 29 samples analyzed for the IDNR/UHL network exceeded the MCL for atrazine of 3.0 ppb (IDNR network: mean atrazine = 0.7 ppb; median = 0.1 ppb; maximum = 7.2 ppb. Results of monitoring by the Des Moines Water Works are similar but show slightly higher values: mean atrazine = 1.5 ppb; median = 1.1 ppb; maximum = 6.7 ppb). According to IDNR guidelines for Section 305(b) assessments, these results do not suggest an impairment of drinking water uses due to atrazine but do suggest a “threat” to full support of the drinking water uses.
Fish consumption uses remain assessed as “fully supported” based on results of U.S. EPA/DNR fish tissue (RAFT) monitoring conducted near Booneville in 1999 (see assessment for the 2000 report for more information on the 1999 RAFT sampling).
