Assessment Comments
Assessment is based on results of the following monitoring programs from 2002-04: (1) water quality monitoring at Sycamore Access conducted by ISU as part of ACOE's WQ study (including fish contaminant monitoring, (2) ambient monitoring by Des Moines Water Works, (3) IDNR/UHL ambient city monitoring at Sycamore Access.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli) by the Des Moines Water Works. This is a new impairment for this river segment. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring. The Class C drinking water uses are assessed (monitored) as "partially supported" due to high levels of nitrate. Fish consumption uses are assessed as "fully supported" based on results of annual fish contaminant monitoring from 2002-2004. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted during the 2002-2004 assessment period approximately two miles downstream from Saylorville Dam at Sycamore Access (NW 66th Street, ISU station 5; STORET station 17770001) 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 and Cummings 2003, Lutz 2004, and Lutz et al. 2005), (2) monitoring conducted on the Des Moines River by the Des Moines Water Works for nitrate and E. coli during the 2002-2004 assessment period, and (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; station 10770002) during the 2002-2004 assessment period.
EXPLANATION: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli) by the Des Moines Water Works. Despite this impairment, results from ambient water quality monitoring conducted by ISU/ACOE and by IDNR/UHL at stations located approximately two miles downstream from Saylorville Dam continue to suggest that Class A uses are fully supported.
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 levels of indicator bacteria (E. coli) in the combined 50 samples collected during the recreational seasons of 2002 through 2004 at the ISU/ACOE station (26 samples) and the IDNR/UHL station (24 samples) (11 orgs/100ml) are far below the Iowa Class A water quality criterion of 126 orgs/100ml. Only one of the combined 50 samples exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting (pgs 3-33 to 3-35 of U.S. EPA 1997b) and according to IDNR’s assessment/listing methodology, these results strongly indicate “full support” of the Class A uses. These results are consistent with the pattern of the lowest levels of indicator bacteria in Iowa rivers occurring immediately downriver from the federal flood control reservoirs.
In sharp contrast to the results from ISU/ACOE and IDNR/UHL monitoring, results of bacterial monitoring by the Des Moines Water Works during recreational seasons of 2002 and 2003 suggest that the Class A uses are "not supported." Levels of indicator bacteria (E. coli) in the Des Moines River were monitored by DMWW on most weekdays during the recreational seasons of 2003 and 2004. 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."
Although the generally low monitoring frequency on Iowa rivers (e.g., monthly) usually does not allow strict application of the EPA guidelines to results of ambient river monitoring in Iowa, the dataset from DMWW contains sufficient data to implement these methods. Results of DMWW monitoring on the Des Moines River show that moderately large numbers of the five-sample, 30-day geometric means (with approximately 17 samples (minimum of 12 samples) collected per each 30-day period) violated Iowa’s geometric mean criterion of 126 orgs/100 ml: 18 of 211 geometric means were in violation in 2003 and 26 of 58 geometric means were in violation in 2004. Also, a moderately large percentage of the samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml: 19 of 151 samples (13%) in 2003 and 12 of 49 samples (25%) in 2004. According to U.S. EPA guidelines, the results of DMWW monitoring suggest “non-support” of the Class A (primary contact recreation) of this segment of the Des Moines River uses due to the occurrence of thirty-day geometric means that exceed Iowa’s water quality criterion of 126 E. coli organisms/100 ml.
The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported”. Results from ISU/ACOE monitoring at the Sycamore Access station show no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the approximately 66 samples collected at this station during the 2002-2004 assessment period. None of the 12 samples analyzed during this period for toxic metals contained levels above Class B(WW) criteria. Similarly, results from the IDNR city monitoring station at Sycamore Access also suggest that the Class B(WW) aquatic life uses are "fully supported." None of the 36 samples collected during the 2002-2004 assessment period exceeded Class B(WW) criteria for dissolved oxygen, pH, or ammonia-nitrogen. None of the 32 samples analyzed for toxic metals (including mercury), and none of the seven samples analyzed for pesticides and other toxic organic compounds, exceeded Class B(WW) criteria.
Results of water quality monitoring in this river segment during the 2002-04 period by the Des Moines Water Works, ISU/ACOE, and IDNR/UHL continue to suggest that the Class C (drinking water) uses should be assessed (monitored) as "partially supporting" due to high levels of nitrate. Results of monitoring by the Des Moines Water Works in this river segment that show that approximately 28% of the samples collected during the 2002-2004 assessment period (150 of 529 samples) contained nitrate above the 10 mg/l MCL (mean = 7.6 mg/l; median = 7.9 mg/l; maximum = 14.3 mg/l). Violations of the MCL tended to occur during the spring and early summer (primarily, May through July) of each year. IDNR's assessment methodology states that if significantly more than 10% of samples exceed the nitrate MCL, the Class C drinking water uses should be assessed as “impaired”. 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 Des Moines 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 DMWW 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 Des Moines River nitrate data from the DMWW as weekly averages and compared these averages to the water quality standard. Twenty-five of the 157 weekly average nitrate levels (16%) for the period 2002-2004 exceeded the nitrate MCL (weekly mean=6.5 mg/l; weekly median=6.7 mg/l; maximum weekly average=14.0). 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 impaired.
Results of monitoring conducted at Sycamore Access as part of the ISU/ACOE and IDNR/UHL networks suggest a similar assessment of the Class C uses. A combined total of 102 samples were collected during the 2002-04 period as part of these two networks (ISU/ACOE: 66 samples and IDNR/UHL: 36 samples). The mean and median nitrate concentration in these 102 samples was 6.8 and 7.0 mg/l, respectively. Of the 102 samples collected, 16 samples (16%) exceeded the nitrate MCL. According to IDNR assessment guidelines for Section 305(b) reporting, if the nitrate MCL is exceeded in more than 10 percent of the samples collected during the assessment period exceed the MCL, the drinking water uses are assessed as "partially supported". Thus, the datasets from all three agencies monitoring water quality in this segment of the Des Moines River suggest “partial support” and impairment of the Class C (drinking water) uses.
Results of monitoring during the 2002-2004 assessment period as part of the IDNR/UHL ambient city monitoring network show relatively low levels of atrazine in this segment of the Des Moines River. None of the 36 samples analyzed for the IDNR/UHL network exceeded the MCL for atrazine of 3 ppb (mean value = 0.25 ppb; median = 0.11 ppb; maximum value = 1.6 ppb). According to IDNR guidelines for Section 305(b) assessments, these results suggest “full support” of the drinking water uses.
Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU/ACOE in 2002, 2003, and 2004 showed low levels of contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish and fillets of common carp. In addition to these pesticide parameters, composite samples fillets from common carp and channel catfish from this station were analyzed in 2004 for mercury (the first analysis of fish tissue samples for mercury conducted as part of the ISU/ACOE program since 1994). Based on this information, fish consumption uses are assessed as "fully supported". 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 2002, 2003, or 2004 ISU/ACOE sampling (or from previous ISU/ACOE monitoring) conducted in the segment of the Des Moines River downstream from Saylorville Reservoir: the levels of contaminants (chlordane and mercury) do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
For more information on ISU/ACOE water quality monitoring in this river reach, see (see Lutz and Cummings 2003, Lutz 2004, and Lutz et al. 2005).
