Assessment Comments
Assessment is based on: (1) water quality monitoring conducted during the 2006-2008 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, (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 2006-2008 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 2006-2008 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 2006-2008. The assessments of support of the beneficial uses are based on results of (1) water quality monitoring conducted during the 2006-2008 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 Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009), (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 2006-2008 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 2006-2008 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 is moved from IR Category 5a of the 2008 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the current (2010) 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 is moved to IR Category 4a (impaired; TMDL approved).
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. 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 34 samples collected during the recreational seasons of 2006 through 2008 at the ISU/ACOE station (11 orgs/100 ml) and in the 22 samples collected at the IDNR/UHL station during this period (15 orgs/100ml) are far below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Only two of the combined 56 samples (4%) 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 2006 and 2008 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 2006 and 2008. 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. Given the almost daily sampling conducted by DMWW, sufficient data were available to calculate moving 30-day geometric means.
To correct for serial correlation in the daily E. coli samples collected on consecutive days, a single average E. coli level was calculated for each week; this weekly average was used to calculate the moving, 30-day, five sample geometric means for comparison to the 126 orgs/100 ml Class A1 criterion. Results of DMWW monitoring on the Des Moines River show that 16 of 32 five-sample/30-day geometric means exceeded the 126 orgs/100 ml Class A1 criterion in 2006 (50% in violation) in 2006, 18 of 32 geometric means in 2007 (56% in violation) in 2007, 20 of 31 geometric means in 2008 (65% in violation) in 2008. The number and percentage of samples exceeding Iowa’s single-sample maximum criterion of 235 orgs/100 ml were as follows: 10 of 32 weekly averages (28%) in 2006, 11 of 32 weekly averages (31%) in 2007, and 17 of 31 weekly averages (49%) in 2008. According to U.S. EPA guidelines, the results of DMWW monitoring suggest “non-support” of the Class A1 (primary contact recreation) of this segment of the Des Moines River uses due to occurrence of thirty-day geometric means that exceed Iowa’s water quality criterion of 126 E. coli organisms/100 ml.
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. 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.
Results of chemical/physical 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 66 samples collected at this station during the 2006-2008 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 34 samples collected during the 2006-2008 assessment period exceeded Class B(WW1) criteria for dissolved oxygen, pH, or ammonia-nitrogen. None of the 4 samples analyzed for toxic metals (including mercury), and neither of the two samples analyzed for pesticides exceeded Class B(WW1) criteria.
Results of water quality monitoring in this river segment during the 2006-08 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 20% of the samples collected during the 2006-2008 assessment period (135 of 670 samples) contained nitrate above the 10 mg/l MCL (mean = 7.0 mg/l; median = 7.0 mg/l; maximum = 14.2 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 “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 of the 153 weekly average nitrate levels (20%) for the period 2006-2008 exceeded the nitrate MCL (weekly mean=6.9 mg/l; weekly median=6.9 mg/l; maximum weekly average=13.8). 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 network suggest a similar assessment of the Class C uses. At the ISU/ACOE station, levels of nitrate in 13 of the 66 samples collected (20%) during the years 2006-2008 exceeded the nitrate MCL of 10 mg/l. At the IDNR/UHL station, levels of nitrate in four of 33 samples (12%) exceeded the nitrate MCL. According to IDNR assessment guidelines for Section 305(b) reporting, if the nitrate MCL is exceeded in significantly more than 10 percent of the samples collected during the assessment period exceed the MCL, the drinking water uses are assessed as "partially supported". While the percent of MCL violations in the IDNR/UHL dataset does not indicate impairment, the percentage of violations in the ISU/ACOE data set indicates that the Class C (drinking water) uses of this segment should be assessed (monitored) as “partially supported.
Results of monitoring during the 2006-2008 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 13 samples analyzed for the IDNR/UHL network 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.
Fish contaminant monitoring conducted downstream from Saylorville Reservoir by ISU/ACOE in 2006, 2007, and 2008 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 composite 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 2006-2008 sampling seasons. 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 2006, 2007, or 2008 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 (chlordane and mercury) do not exceed any of the IDPH/IDNR 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 Francois 2007, Lutz and Francois 2008, and Lutz and Steffen 2009; the URL for the Des Moines River Water Quality Monitoring Network web site is http://home.eng.iastate.edu/~dslutz/dmrwqn/dmrwqn.html.
