Assessment Comments
Assessment is based on: (1) water quality monitoring conducted during the 2008-2010 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 as part of the Des Moines River Water Quality Study, (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 2008-2010 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 2008-2010 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 (monitored) as "fully supporting" based on results of chemical/physical water quality monitoring in this segment. The Class C drinking water uses remain assessed (monitored) as "partially supporting" due to high levels of nitrate. Fish consumption uses are assessed as "fully supported" based on results of annual fish contaminant monitoring from 2008-2010. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted during the 2008-2010 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 Steffen 2009, Lutz 2010, and Lutz 2011), (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 2008-2010 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 2008-2010 assessment period, and (4) results of a fish kill investigation in May 2006.
Note 1: A TMDL for nitrate was prepared by IDNR and approved by EPA in September 2009. Because this TMDL covers the nitrate impairment identified for this waterbody, this impairment was moved from IR Category 5a of the 2008 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2010 cycle. This impairment remains in IR Category 4a for the current (2012) cycle.
Note 2: A TMDL for bacteria was prepared by IDNR and approved by U.S. EPA in March 2010. Because this TMDL covers all the identified impairments for the assessment segment, this segment was moved to IR Category 4a (impaired; TMDL approved) for the 2010 Integrated Reporting Cycle and remains in IR Category 4a.
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 at the Second Avenue bridge in Des Moines. 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. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10770002 upstream from Des Moines (at Sycamore Access) were as follows: the 2008 geometric mean was 16 orgs/100 ml, the 2009 geometric mean was 19 orgs/100 ml, and the 2010 geometric mean was 32 orgs/100 ml. All three geometric means meet the Class A1 criterion of 126 orgs/100 ml. Only one of the 22 samples (5%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
Similarly, the geometric means of indicator bacteria (E. coli) in the 27 samples collected during the recreational seasons of 2008 through 2010 at ISU/ACOE station 5 at Sycamore Access approximately 2 miles downstream from Saylorville Dam were as follows: the 2008 geometric mean was 19 orgs/100 ml, the 2009 geometric mean was 8 orgs/100 ml, and the 2010 geometric mean was 17 orgs/100 ml. All three geometric means are well below the Class A1 criterion of 126 orgs/100 ml. Three of the 27 samples (11%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to the IDNR assessment/listing methodology, the percentage of samples exceeding Iowa’s single-sample maximum criterion is not significantly greater than 10%; thus, this percentage does not suggest impairment of the Class A1 uses.
According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, because all recreation season geometric means from the IDNR and ISU/ACOE ambient monitoring stations are below the respective water quality criterion, the primary contact recreation uses should be assessed as "fully supported".
In contrast to the results from ISU/ACOE and IDNR/UHL monitoring at the Sycamore Access station, however, 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 2008 through 2010 suggest slightly higher levels of indicator bacteria and that the Class A1 uses should be assessed as "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 2008 through 2010. The geometric means of indicator bacteria (E. coli) in the DMWW samples collected during the recreational seasons of 2008 through 2010 near the Second Avenue Bridge were as follows: the 2008 geometric mean was 143 orgs/100 ml, the 2009 geometric mean was 77 orgs/100 ml, and the 2010 geometric mean was 88 orgs/100 ml. Only the 2008 geometric mean exceeded—and very slightly exceeded—the Class A1 criterion of 126 orgs/100 ml. One hundred fifty-two of the 509 samples (30%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Despite this impairment, levels of indicator bacteria in this segment of the Des Moines River are very low relative to levels in other Iowa rivers. Levels of indicator bacteria tend to be very low in river segments downstream from Iowa’s federal flood control reservoirs (e.g., Coralville and Red Rock reservoirs).
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 3,100 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. This is the same fish kill assessment as that developed for the 2008 assessment/listing cycle. 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 (2006-2009) 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” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Because this fish kill was the result of high water levels, and because the kill had no origin in, or relation to, pollutants of any kind, this potential impairment is not factored into the assessment of the Class B(WW1) aquatic life uses for this assessment segment.
The Class B(WW1) 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(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the approximately 66 samples collected at this station during the 2008-2010 assessment period. One of the 12 samples analyzed during this period for toxic metals contained a level of copper above the acute Class B(WW1) criterion. According to IDNR’s assessment/listing methodology, and according to U.S. EPA assessment guidance, more than one violation of a toxic contaminant in a three-year period suggests impairment of the aquatic life use. Thus, the single violation of the Class B(WW1) criterion for copper during the 2008-10 assessment period does not indicated impairment the aquatic life uses. No violations of Class B(WW1) criteria occurred in the 12 samples analyzed for other toxic metals (e.g., cadmium, chromium, mercury, nickel, and zinc. 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 33 samples collected during the 2008-2010 assessment period exceeded Class B(WW1) criteria for dissolved oxygen, pH, or ammonia-nitrogen. Neither of the two samples analyzed for toxic metals and neither of the two samples analyzed for pesticides exceeded the respective Class B(WW1) criteria.
Results of water quality monitoring in this river segment during the 2008-10 period by the Des Moines Water Works, ISU/ACOE, and IDNR/UHL suggest “full support” of the Class C (drinking water) uses. This assessment is in contrast to assessments for previous Integrated Reporting cycles that have shown impairment of drinking water uses due to high levels of nitrate. Results of monitoring by the Des Moines Water Works in this river segment that show that none of the 739 daily samples collected during the 2008-2010 assessment period contained nitrate above the 10 mg/l MCL (mean = 5.5 mg/l; median = 5.7 mg/l; maximum = 10 mg/l). IDNR's assessment methodology states that if less than 10% of samples exceed the nitrate MCL, the Class C drinking water uses should be assessed as “fully supported”.
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 also summarizes the Des Moines River nitrate data from the DMWW as weekly averages and compares these averages to the water quality standard. Similar to the results for the individual (daily) samples, none of the 157 weekly average nitrate levels for the period 2008-2010 exceeded the nitrate MCL (weekly mean=5.5 mg/l; weekly median=5.79 mg/l; maximum weekly average=9.5 mg/l). Thus, according to IDNR's assessment guidelines, the DMWW data--whether summarized as individual samples or as weekly averages--suggest “full support” of the Class C drinking water uses.
Results of monitoring conducted at Sycamore Access as part of the ISU/ACOE network suggest a similar assessment of the Class C uses. At the ISU/ACOE station, all levels of nitrate in the 66 samples collected during the years 2008-2010 were below the nitrate MCL of 10 mg/l. At the IDNR/UHL station at Sycamore Access, all levels of nitrate in the 30 samples collected were below the nitrate MCL. According to IDNR assessment guidelines for Section 305(b) reporting, if less than 10 percent of the samples exceed the nitrate MCL, the drinking water uses should be assessed as "fully supported".
The results of limited monitoring for atrazine during the 2008-2010 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. Neither of the two samples analyzed exceeded the MCL of atrazine of 3 ppb (maximum level was 0.48 ppb). These results are consistent with those from the previous (2010) Integrated Reporting period when none of the 13 samples analyzed for the IDNR/UHL network from 2006-08 exceeded the MCL for atrazine of 3 ppb (mean value = 0.13 ppb; median = 0.08 ppb; maximum value = 0.48 ppb). According to IDNR guidelines for Section 305(b) assessments, these results suggest “full support” of the drinking water uses.
Thus, the monitoring results from the current (2008-10) assessment in this segment of the Des Moines River suggest a lowering of nitrate levels compared to those from previous assessment periods. For the 2004, 2006, 2008, and 2010 Integrated Reporting cycles (covering the monitoring years 2000-2008), from 20 to 28% of the daily samples for each three-year assessment period exceeded the nitrate MCL and from 13 to 22% of the weekly average values exceeded the nitrate MCL. The lack of violations of the MCL in either the daily samples or the weekly averages for the 2008-2010 period appears to represent an abrupt reduction in levels of nitrate in this portion of the Des Moines River and suggests that the Class C (drinking water uses) should be assessed as “fully supporting.” Due, however, to the history of high levels of nitrate in this segment of the Des Moines River, and due to the ability of the weather to influence in-stream levels of nitrate, the Class C (drinking water) uses will remain assessed as “partially supporting” for the current (2012) Integrated Reporting cycle (IR Category 4a). If, however, nitrate data for the next (2014) Integrated Reporting cycle (collected during calendar years 2010 through 2012) show “full support” of the drinking water uses, this impairment will be removed. This assessment approach is designed to help ensure that water quality improvement suggested by recent monitoring data reflects an actual change in water quality conditions and not just a temporary, weather-influenced variation in water quality.
Fish consumption (HH) uses are assessed (monitored) as “fully supported”. Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU/ACOE in 2008, 2009, and 2010 showed low levels of contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish common carp. In addition to these pesticide parameters, composite samples of whole-fish common carp were analyzed for PCBs and fillets from largemouth bass were analyzed for mercury during 2009 and 2010. Levels of PCBs in samples of whole-fish common carp were below levels of detection in both years. The results showed low levels of mercury in the samples. The mercury level in both years’ samples was 0.12 mg/kg; this level is well below Iowa’s consumption advisory threshold for a 1 meal/week advisory of 0.3 mg/kg. Based on this information, fish consumption uses are assessed (monitored) 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. The fish contaminant data generated from the 2008, 2009, and 2010 ISU/ACOE samplings (or from previous ISU/ACOE monitoring) conducted in the segment of the Des Moines River immediately downstream from Saylorville Reservoir show that levels of contaminants do not exceed any of the IDPH/IDNR consumption 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 Lutz and Steffen 2009, Lutz 2010, and Lutz 2011; the URL for the Des Moines River Water Quality Monitoring Network web site is http://home.eng.iastate.edu/~dslutz/dmrwqn/dmrwqn.html.
