Assessment Comments
Assessment is based on results of (1) routine water quality & fish tissue monitoring as part of the UI/ACOE Coralville Water Quality Study from 2002-04, (2) IDNR/UHL ambient water quality monitoring upstream from Iowa City from 2002-04, (3) statewide assessment of freshwater mussels in 1998-99, and (4) freshwater mussel surveys coordinated by the IDNR Fisheries Bureau in 2004.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supported" based on results of ambient monitoring for indicator bacteria upstream from Iowa City. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of 2004 survey of freshwater mussels that showed significant recovery of the mussel community in this segment of the Iowa River. The Class C (drinking water) uses remain assessed (monitored) as "fully supported" based on results of ambient monitoring by conducted by both IDNR/UHL and University of Iowa/Corps of Engineers. Fish consumption uses remain assessed as "fully supported" based on results of annual fish contaminant monitoring conducted by the University of Iowa/Corps of Engineers in 2003 and 2004. The sources of data for this assessment include (1) results of water quality monitoring conducted near the Iowa City water treatment plant by the University of Iowa (under contract with the U.S. Army Corps of Engineers) as part of the Coralville Reservoir Water Quality Study, (2) results of a statewide assessment of freshwater mussels in 1998-1999 conducted by Iowa State University (Arbuckle at al. 2000), (3) results of mussel surveys in 2004 coordinated by the IDNR Fisheries Bureau, (4) results of monitoring from the IDNR/UHL ambient city monitoring station upstream from Iowa City at the Dubuque Street bridge, and (5) results of fish tissue monitoring in 2003 and 2004 conducted for the UI/ACOE Coralville Reservoir Water Quality Study (samples were collected on the Iowa River near the Iowa River Power Dam (Coralville) and at the Iowa City Park).
EXPLANATION: Results of water quality monitoring at both the UI/ACOE long-term station near the University of Iowa water treatment plant and the IDNR/UHL station at the Dubuque Street bridge suggest that the Class A uses should be assessed (monitored) as "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 level of indicator bacteria (E. coli) in the 18 samples collected as part of UI/ACOE monitoring during recreational seasons of 2002 through 2004 (117 orgs/100ml) is below the Iowa Class A water quality criterion of 126 orgs/100ml. Two of the 18 samples exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if levels of E. coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported.” According to IDNR’s assessment/listing methodology, however, these results do not suggest that the violation frequency of Iowa’s single-sample maximum criterion is significantly greater than 10% and thus these results do not suggest impairment of the Class A uses of this river segment.
Similarly results of IDNR's ambient city monitoring for indicator bacteria also suggest “full support” of primary contact recreation uses. Twenty-four samples were collected upstream from Iowa City at the IDNR/UHL station at Dubuque Street during recreational seasons of 2002 through 2004. The geometric mean of these 24 samples was only 34 E. coli orgs/100 ml, well-below the Iowa criterion of 126 orgs/100 ml. Three of the 24 samples had levels of E. coli that exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if levels of E. coli exceed the state’s single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported.” According to IDNR’s assessment/listing methodology, however, these results do not suggest that the violation frequency of Iowa’s single-sample maximum criterion is significantly greater than 10% and thus these results do not suggest impairment of the Class A uses of this river segment. The generally low levels of indicator bacteria at the upriver IDNR/UHL station (located approximately 3 miles downriver from Coralville Dam) are consistent with monitoring results at other stations located immediately downriver from Iowa’s federal flood control reservoirs. Typically, these stations show the lowest levels of indicator bacteria of any river monitoring stations in the state. The somewhat higher levels of bacteria at the downriver ACOE monitoring station (approximately 10 miles downriver from Coralville Dam) likely reflect inputs of indicator bacteria potentially in the Iowa River’s intervening tributaries (e.g., Muddy Creek and Clear Creek) and/or from the Iowa City/Coralville urban area.
Results of ambient chemical/physical water quality monitoring at the IDNR/UHL and UI/ACOE stations suggest “full support" of the Class B(WW) aquatic life uses. Monitoring at these stations showed no violations of Class B(WW) criteria for ammonia-nitrogen, and only one violation each for dissolved oxygen and pH, in the approximately (combined) 100 samples collected at both stations during the 2002-2004 assessment period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses. Thus, the percentages of violations of the dissolved oxygen and pH criteria at this station (approximately 1%) does not suggest an impairment of aquatic life uses in this stream segment.
Results of recent surveys of freshwater mussels in this river segment also suggest "full support" of the Class B(WW) aquatic life uses. For the previous (2004) reporting cycle, these aquatic life uses were assessed (monitored) as "partially supported" based on results of the 1998-99 statewide survey of freshwater mussels. Despite the indications of good water chemical/physical water quality in this segment, results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams had suggested a potential impairment to the aquatic life uses of this stream segment. More recent monitoring, however, suggests improvement in the status of the mussel community in this segment of the Iowa River, thus suggesting that the impairment based on the 1998-99 survey should be removed. The rationale for this assessment is as follows.
As part of a study to reintroduce the endangered Higgins eye mussel into the Iowa, Cedar, and Wapsipinicon rivers in eastern Iowa, a four-day mussel search was conducted in August 2004. This survey was coordinated by staff of the IDNR Fisheries Bureau from the Guttenberg and Solon fish management stations. The purpose of the survey was to search for transformed Higgins eye mussels growing in the substrate. In addition to staff from the Guttenberg and Solon stations, staff from IDNR Fisheries offices in Bellevue, Rathbun, and Manchester also assisted in the effort. Also, , volunteers, county conservation boards and three divers from the U.S. Fish and Wildlife Service assisted in the effort. The following is an excerpt from a summary of this study:
“In total, 54 river stretches were searched by diving, wading, sieving and basket trawling. Nearly 2,400 mussels were collected of 27 species from the three rivers. Particularly impressive was the apparent rebound of the mussel community in the Iowa River at Iowa City. In that reach, 24 species of mussels were collected including some of Iowa's rarer species, the yellow sandshell (Lampsilis teres) and the buckhorn (Tritogonia verrucosa). This may be the last substantial pistolgrip population left in the state of Iowa.”
The 1984 mussel survey of freshwater mussels included six sample sites in this stream segment. The species richness at these six sites was 5, 5, 13, 10, 7, and 12. In the 1998-99 survey, the corresponding species richness values were 0, 7, 1, 2, 5, and 3, respectively. A comparison of these two surveys showed an average percent change of minus 56% and thus suggested an impairment of the Class B(WW) aquatic life uses (for more information, see the assessment developed for the 2004 reporting cycle). Results of the August 2004 survey, however, suggest improved richness of mussel species that likely exceeds that found during the 1984 survey. Thus, based on this information, the mussel-related impairment of the aquatic life uses of this segment of the Iowa River is removed for the 2006 reporting/listing cycle.
The Class C drinking water uses are assessed (monitored) as "fully supported". Results of monitoring at the IDNR/UHL station upstream from Iowa City show one violation of the atrazine MCL and two violations of the nitrate MCL in the 36 samples collected and analyzed over the three-year period. Maximum, mean, and median levels for atrazine at this station were 6.3, 0.4, and 0.08 ug/l; 3% of the samples exceeded the atrazine MCL. The maximum, mean and median levels for nitrate were 12.0, 5.4, and 5.1 mg/l; 6% of the samples exceeded the MCL. Based on IDNR’s assessment and listing methodology, these violations of Iowa’s Class C criteria do not suggest impairment of drinking water uses for this river segment. According to this methodology, if average levels of atrazine are less than the MCL, drinking water uses should be assessed as “fully supported”. Similarly, if less than 10% of samples violate the nitrate MCL, drinking water uses should be assessed as “fully supported”. None of the of 65 samples collected at the UI/ACOE station near the Iowa City water treatment plant exceeded the 10 mg/l MCL for nitrate (maximum concentration = 9.7 mg/l) (atrazine is not monitored as part of the UI/ACOE program) The average nitrate level was 4.1 mg/l; the median level was 3.7 mg/l.
Fish consumption uses remain assessed as "fully supporting." The results from the UI/ACOE fish contaminant monitoring in 2003 and 2004 show that levels of organochlorine contaminant are very low. The composite whole-fish samples of common carp from this segment of the Iowa River had low levels of the technical chlordane, with neither sample containing detectable levels of chlordane (detection levels were 0.02 ppm in 2003 and 0.005 ppm in 2004). The UI/ACOE fish contaminant monitoring protocol does not include analysis for either mercury or PCBs.
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 by the UI/ACOE monitoring program for this river segment in 2003 and 2004.: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
