Assessment Comments
Assessment is based on: (1) water quality monitoring conducted during the 2010-2012 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 2010-2012 assessment period, and (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; STORET station 10770002) during the 2010-2012 assessment period.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supporting" (IR 4a) 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" (IR 4a) due to high levels of nitrate. Fish consumption uses are assessed as "fully supported" (IR 2a) based on results of annual fish contaminant monitoring from 2010-2012 by ISU/ACOE. The assessments of support of the beneficial uses are based on results of (1) water quality and fish contaminant monitoring conducted during the 2010-2012 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 2011, 2012, and 2013), (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 2010-2012 assessment period, and (3) results of IDNR/UHL ambient city monitoring upstream from Des Moines at the Sycamore Access (NW 66th Street; STORET station 10770002) during the 2010-2012 assessment period.
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 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 "partially 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 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10770002 upstream from Des Moines (at Sycamore Access) were as follows: the 2010 geometric mean was 23 orgs/100 ml, the 2011 geometric mean was 11 orgs/100 ml, and the 2012 geometric mean was 24 orgs/100 ml. All three geometric means are far below the Class A1 criterion of 126 orgs/100 ml. Only two of the 22 samples (8%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
Similarly, the geometric means of indicator bacteria (E. coli) in the 29 samples collected during the recreational seasons of 2010 through 2012 at ISU/ACOE station 5 at Sycamore Access approximately 2 miles downstream from Saylorville Dam were as follows: the 2010 geometric mean was 17 orgs/100 ml, the 2011 geometric mean was 4 orgs/100 ml, and the 2012 geometric mean was 14 orgs/100 ml. All three geometric means are far below the Class A1 criterion of 126 orgs/100 ml. Two of the 29 samples (7%) 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, and because the percentages of samples exceeding Iowa’s single-sample maximum criterion are less than 10 percent, the primary contact recreation uses should be assessed (monitored) as "fully supported".
In contrast to the results from ISU/ACOE and IDNR/UHL monitoring near Saylorville Dam 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 2010 through 2012 suggest (1) slightly higher levels of indicator bacteria and (2) that the Class A1 uses should be assessed as "partially supported.” Levels of indicator bacteria (E. coli) in the Des Moines River were monitored by DMWW on most weekdays during 2010 through 2012 with a total of 511 samples being analyzed. The geometric means of indicator bacteria (E. coli) in the DMWW samples collected during the recreational seasons of 2010 through 2012 near the Second Avenue Bridge were as follows: the 2010 geometric mean was 88 orgs/100 ml, the 2011 geometric mean was 30 orgs/100 ml, and the 2012 geometric mean was 40 orgs/100 ml. All three geometric means are below the Class A1 criterion of 126 orgs/100 ml. One hundred three of the 511 samples (20%), however, 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 all recreation season geometric means meet the respective water quality criterion, the contact recreation uses should be assessed as “fully supporting” (see pgs 3-33 to 3-35 of U.S. EPA 1997b). If, however, greater than 10% of the samples exceed the Class A1 single-sample maximum criterion of 235 orgs/100 ml, the primary contact recreation uses should be assessed as “partially supporting”. Thus, because significantly greater than 10% of the samples from the DMWW monitoring station near Second Avenue exceeded the single-sample maximum criterion, the Class A1 primary contact recreation uses should be assessed as “partially supporting”. 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 immediately downstream from all of Iowa’s federal flood control reservoirs (e.g., Saylorville, Coralville and Red Rock reservoirs).
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 2010-2012 assessment period. None of the nine samples analyzed during this period for toxic metals (e.g., cadmium, copper, mercury, and lead) exceeded the respective 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 2010-2012 assessment period exceeded Class B(WW1) criteria for dissolved oxygen, pH, or ammonia-nitrogen. Thus, the monitoring results from both the ISU/ACOE and IDNR monitoring stations suggest “full support” of the Class B(WW1) aquatic life uses.
Results of water quality monitoring in this river segment during the 2010-12 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 but is consistent with the previous (2012) Section 305(b) assessment. Results of monitoring by the Des Moines Water Works in this river segment that show that only four of the 732 daily samples collected during the 2010-2012 assessment period (less than 1%) contained nitrate above the 10 mg/l MCL (mean = 4.4 mg/l; median = 4.8 mg/l; maximum = 10.6 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”.
Results of ambient monitoring for nitrate conducted at Sycamore Access as part of the Iowa State University/Army Corps of Engineers network also show “full support” of drinking water uses during the 2010-2012 period: none of the 66 bi-monthly samples collected during the 2010-2012 assessment period exceeded the nitrate MCL (mean = 4.6 mg/l; median = 2.1 mg/l; maximum = 9.94 mg/l). Similarly, results of IDNR/UHL ambient monthly monitoring for nitrate on the Des Moines River conducted upstream from Des Moines show “full support” of drinking water uses: none of the 36 monthly samples collected during the 2010-2012 assessment period exceeded the nitrate MCL (mean = 4.5 mg/l; median = 4.9; maximum = 9.8 mg/l). Thus, regardless of the source of monitoring data, the levels of nitrate monitored in the Des Moines River upstream from Des Moines during the 2010-2012 assessment period suggest “full support” of the drinking water uses. Due, however, to (1) the ability of the weather to influence in-stream levels of nitrate, and (2) the anticipated return of impairment levels of nitrate in the next (2016) Integrated Reporting cycle, the Class C (drinking water) uses will remain assessed as “partially supporting” for the current (2014) Integrated Reporting cycle (IR Category 4a). A preliminary analysis of 2012-2014 monitoring data from the Des Moines Water Works for nitrate in the Des Moines River upstream from Des Moines suggests a potential return to impairment levels of nitrate. Of the 592 daily measurements made by DMWW from January 1, 2012 through April 30, 2014, 78 samples (13%) violated the nitrate MCL of 10 mg/l. The highest levels of nitrate during the period occurred from late April 30 to July 15, 2013. During this period, levels of nitrate in the 71 daily samples averaged 15.5 mg/l (SD=1.8 mg/l); the minimum nitrate level was 11.35 mg/l. These data suggest that if the nitrate impairment for this assessment segment of the Des Moines River were removed for the current (2014) IR cycle, the impairment might again be applied to this rivers segment for the next (2016) IR cycle.
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. None of the seven samples analyzed from June to December 2012 exceeded the MCL of atrazine of 3 ppb (maximum level was 0.2 ppb). These results are consistent with those from the previous Integrated Reporting periods. According to IDNR guidelines for Section 305(b) assessments, these results suggest “full support” of the drinking water uses.
Fish consumption (HH) uses are assessed (monitored) as “fully supported”. None of the nine samples analyzed for toxic metals (e.g., cadmium, copper, and mercury) contained levels that exceeded their respective Class HH (human health-fish) criteria. Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU/ACOE in 2010, 2011, and 2012 showed low levels of pesticide contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish and fillets of common carp. None of the concentrations for chlordane approached Iowa’s thresholds for issuing a one meal per week consumption advisory. In addition to these pesticide parameters, composite samples of whole-fish common carp were analyzed for PCBs in 2010 and 2012, and fillets from largemouth bass were analyzed for mercury in all three years. Levels of PCBs in samples of whole-fish common carp were below levels of detection in both 2010 and 2012. The results also showed that levels of mercury in the samples were below levels of concern. The mercury levels in fillets from predator fish in 2011 were as follows: largemouth bass: 0.26 ppm; smallmouth bass: 0.23 ppm. In 2012, the level of mercury in the fillets from a largemouth bass was 0.12 ppm. These levels are below Iowa’s consumption advisory threshold for a 1 meal/week advisory of 0.3 ppm. 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 2010, 2011, and 2012 ISU/ACOE samplings 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 2011, 2012 and 2013); the URL for the Des Moines River Water Quality Monitoring Network web site is http://home.eng.iastate.edu/~dslutz/dmrwqn/dmrwqn.html.
