Assessment Comments
Assessment is based on: (1) water quality monitoring conducted during the 2004-2006 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 et al. 2005, Lutz and Francois 2006, and Lutz and Francois 2007), (2) monitoring conducted on the Des Moines River near the Second Avenue Bridge by the Des Moines Water Works for nitrate and E. coli during the 2004-2006 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; STORET station 10770002) during the 2004-2006 assessment period, and (4) results of a fish kill investigation in May of 2006.
Basis for Assessment
SUMMARY: The Class A1 (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. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on results of a fish kill investigation in May 2006. However, results of chemical/physical water quality monitoring in this segment suggest "full support" of the Class B(WW1) uses. 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 2004-2006. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted during the 2004-2006 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 et al. 2005, Lutz and Francois 2006, and Lutz and Francois 2007), (2) monitoring conducted on the Des Moines River near the Second Avenue Bridge by the Des Moines Water Works for nitrate and E. coli during the 2004-2006 assessment period, (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; STORET station 10770002) during the 2004-2006 assessment period, and (4) results of a fish kill investigation in May 2006.
EXPLANATION: The Class A1 (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 bacterial monitoring conducted by ISU/ACOE and by IDNR/UHL at the next upstream monitoring station (Sycamore Access) located approximately two miles downstream from Saylorville Dam continue to suggest that Class A1 uses of the Des Moines River upriver from Interstate 80 (i.e., segment IA 04-UDM-0010_3) 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.
As noted in the assessment for upstream segment IA 04-UDM-0010_3 (I80/I35 bridge to Saylorville Dam), the geometric mean levels of indicator bacteria (E. coli) in the 36 samples collected during the recreational seasons of 2004 through 2006 at the ISU/ACOE station (11 orgs/100 ml) and in the 24 samples collected at the IDNR/UHL station during this period (20 orgs/100ml) are far below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Only two of the combined 60 samples exceeded Iowa’s single-sample maximum criterion 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 A1 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 near Saylorville Dam, the results of bacterial monitoring by the Des Moines Water Works downriver from the I80/I35 bridge near the Second Avenue Bridge during recreational seasons of 2004 and 2006 suggest that the Class A1 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 2004 and 2006. The generally low monitoring frequency on Iowa rivers (e.g., monthly) usually does not allow strict application of the assessment EPA guidelines for assessing support of primary contact recreation uses. These guidelines specify that a geometric mean based on at least five samples collected over a 30-day period be compared to a state water quality criterion for indicator bacteria. The dataset from DMWW, however, contains sufficient data to implement these assessment 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 20 samples (minimum of 13 samples) collected per each 30-day period) violated Iowa’s geometric mean criterion of 126 orgs/100 ml: 26 of 58 geometric means were in violation in 2004 and 95 of 217 geometric means were in violation in 2006. Also, a moderately large percentage of the samples exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml: 12 of 49 samples (25%) in 2004 and 33 of 170 (19%) in 2006. According to U.S. EPA guidelines for determining support of primary contact recreation uses (U.S. EPA 1997b, page 3-35), if the geometric mean of E. coli from at least five samples collected over a thirty-day period exceeds the state water quality standard of 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 state’s single-sample maximum criterion of 235 E. coli organsims/100 ml, the primary contact recreation uses should be assessed as "partially supported."
The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported” based on results of a fish kill investigation. The kill occurred on or before May 17, 2006 and was attributed to natural causes. Approximately 3100 fish were killed when they were trapped in two areas near the dam when water levels were high. No estimate of the value of the fish was developed.
According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Results of water quality monitoring at this segment, however, suggest "full support" of the Class B(WW1) uses. Results from ISU/ACOE monitoring at the Sycamore Access station show no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the approximately 66 samples collected at this station during the 2004-2006 assessment period. None of the 12 samples analyzed during this period for toxic metals contained levels above Class B(WW1) criteria. Similarly, results from the IDNR/UHL city monitoring station at Sycamore Access also suggest that the Class B(WW1) aquatic life uses are "fully supported." None of the 36 samples collected during the 2004-2006 assessment period exceeded Class B(WW1) criteria for dissolved oxygen, pH, or ammonia-nitrogen. None of the 14 samples analyzed for toxic metals (including mercury), and none of the seven samples analyzed for pesticides exceeded Class B(WW1) criteria.
Results of water quality monitoring in this river segment during the 2004-06 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 2004-2006 assessment period (154 of 553 samples) contained nitrate above the 10 mg/l MCL (mean = 7.6 mg/l; median = 7.8 mg/l; maximum = 14.2 mg/l). These results are nearly identical to the results for the previous (2002-2004) assessment period when 150 of 529 samples (28%) exceeded the nitrate MCL and when the mean, median, and maximum values were 7.6 mg/l, 7.8 mg/l, and 14.3 mg/l, respectively. 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 “partially supported” (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. Thirty-five of the 157 weekly average nitrate levels (22%) for the period 2004-2006 exceeded the nitrate MCL (weekly mean=7.6 mg/l; weekly median=7.8 mg/l; maximum weekly average=14.2). 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 during the 2004-2006 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 = 0.20 ppb; median = 0.07 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 2004, 2005, and 2006 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 for mercury in 2004, and fillet samples from common carp and largemouth bass were analyzed for mercury in 2005 (this was the first analysis of fish tissue samples for mercury conducted as part of the ISU/ACOE program since 1994). The results showed low levels of mercury in these samples: common carp: 0.06 ppm in 2004 and 0.04 ppm in 2005; channel catfish fillets: 0.13 ppm in 2004; largemouth bass fillets: 0.11 ppm in 2005. This supplemental monitoring for mercury in fish was not conducted during the 2006 sampling season. 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 2004, 2005, or 2006 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 et al. 2005, Lutz and Francois 2006, and Lutz and Francois 2007).
