Assessment Comments
Assessment is based on (1) results of monitoring by Iowa State Univ. for the ACOE's WQ project, (2) ambient monitoring by Des Moines Water Works, (3) IDNR city monitoring, and (4) fish tissue (RAFT) monitoring.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed as "partially supported," and the Class B(WW) aquatic life uses are assessed as "not supported." The assessment for Class C (drinking water) uses remain assessed as "not supported." These assessments are also used for the adjacent upstream segment of the Raccoon River (IA 04-RAC-0010-2. Fish consumption uses remain assessed as "fully supported." 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) as part of the Des Moines River Water Quality Study (see Lutz et al. 2001 and Lutz and Esser 2002), (2) monitoring conducted on the Raccoon River by the Des Moines Water Works during the 2000-2001 biennial period, (3) results of IDNR ambient city monitoring upstream from Des Moines at Van Meter during the 2000-2001 biennial period, and (4) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring near Booneville in 1999. EXPLANATION: Results from the ISU/ACOE monitoring station located at Van Meter suggest that Class A uses are "partially supported." A total of 18 samples were analyzed for levels of indicator bacteria (fecal coliforms) during summers of 2000 and 2001. For purposes of Section 305(b) assessments, DNR 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." The geometric mean of fecal coliform bacteria in the 17 non-runoff-affected samples collected from the Van Meter station during this period (123 orgs/100 ml) is below the state WQ criterion of 200 orgs/100 ml. Four of the 17 (24%) non-runoff-affected samples, however, exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml. Although the geometric mean for the biennial period (123 orgs/100 ml) suggests full support of the primary contact recreation uses, the number of samples exceeding the U.S. EPA's single-sample maximum value indicates 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 also suggest "partial support" of the primary contact recreation uses. Seven of the 9 samples collected from the this station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these seven non-runoff-affected samples (116 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml. However, two of the 7 samples (29%) exceeded the U.S. EPA-recommended single-sample maximum value of 400 orgs/100 ml. As stated above, if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Results from the IDNR city monitoring station at Van Meter suggest that the Class B(WW) aquatic life uses are "not supported." Although none of the 14 samples collected during the 2000-2001 biennial period exceeded Class B(WW) criteria for dissolved oxygen, pH, or ammonia-nitrogen, and although none of the six samples analyzed for pesticides and other toxic organic compounds exceeded Class B(WW) criteria, two of 14 samples analyzed for toxic metals (15.8%) 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, however, more than 10% of the samples exceed state criteria for toxics (including toxic metals), the aquatic life uses are "not supported" (see pg 3-18 of U.S. EPA 1997b). Because approximately 16% of the samples from this network exceeded the Class B(WW) chronic criterion, the aquatic life uses are assessed as "not supported." No violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen occurred in the approximately 46 samples collected at this monitoring station during the 2000-2001 biennial period. One of 46 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. Five of the 10 samples analyzed for toxic metals during the 2000-01 biennial period contained levels of dissolved mercury above the Iowa WQ criterion for human health (fish) of 0.15 ug/l (none of the nine 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 recent study of mercury levels in the Des Moines River near Des Moines (see assessment for the 2000 report above), 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. Results of monitoring by the Des Moines Water Works in this river segment that show that over 28% of the samples collected during the 2000-2001 biennial period (53 of 187) contained nitrate above the 10 mg/l MCL (mean = 7.3 mg/l; median = 6.3 mg/l; maximum = 17.5 mg/l). 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). Results of monitoring conducted at Van Meter as part of the ISU/ACOE network show a lesser impact of nitrate on drinking water uses: only 13.5% of the samples collected during the 2000-2001 biennial period (6 of 44 samples) exceeded the nitrate (mean = 5.4 mg/l; median = 4.3 mg/l; maximum = 16.1 mg/l). Based on IDNR assessment guidelines for Section 305(b) reporting, if between 15 and 25 percent of the samples collected during the biennial period exceed the nitrate MCL, the drinking water uses are assessed as "partially supported." Regardless of the source of monitoring data, the levels of nitrate monitored in the Raccoon River during the 2000-2001 biennial period suggest an impairment of the drinking water uses. Results of monitoring during the 2000-2001 biennial period at Van Meter as part of the IDNR 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 14 samples analyzed for the IDNR network, and one of 16 river samples analyzed by the Des Moines Water Works, exceeded the MCL for atrazine of 3.0 ppb (IDNR network: mean atrazine = 0.7 ppb; median = 0.1 ppb; maximum = 7.2 ppb. Des Moines Water Works: mean atrazine = 1.8 ppb; median = 1.3 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. Results of U.S. EPA/DNR fish tissue (RAFT) monitoring conducted near Booneville in 1999 suggest that fish consumption uses are "fully supported" (see assessment for the 2000 report).
