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 2006-08, (2) IDNR/UHL ambient water quality monitoring upstream from Iowa City from 2006-08, (3) statewide assessment of freshwater mussels in 1998-99, (4) freshwater mussel surveys coordinated by the IDNR Fisheries Bureau in 2004, (5) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006 at Iowa City, (6) fish contaminant monitoring conducted in 2006 as part of the REMAP program (Site 302), (7) IDNR/UHL TMDL and REMAP biological monitoring conducted at four sites in 2005, (8) fish contaminant monitoring conducted in 2006 as part of the REMAP program, and (9) results of fish kill investigations in 2006 and 2007.
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 at Iowa City; this is a new impairment for this river segment. This impairment is covered by the TMDL for bacteria approved by EPA in 2007; thus, this impairment is place in Category 4a of Iowa's 2010 Integrated Report. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on fish kill investigations on April 13, 2006 and March 17, 2007. However, results of 2004 survey of freshwater mussels that showed significant recovery of the mussel community in this segment of the Iowa River and ongoing ambient water quality monitoring suggests "full support" of the Class B(WW1) uses. The Class C (drinking water) uses remain assessed (monitored) as "fully supported" based on results of ambient monitoring conducted by both IDNR/UHL and Corps of Engineers. Fish consumption uses remain assessed as "fully supported" based on results of annual fish contaminant monitoring conducted (1) by the University of Iowa/Corps of Engineers in 2007 and 2008, (2) as part of the 2006 U.S. EPA/IDNR fish contaminant (RAFT) monitoring program and (3) as part of the IDNR REMAP program in 2006.
The sources of data for this assessment include (1) results of water quality and fish tissue monitoring conducted from 2006-2008 near the Iowa City water treatment plant as part of the ACOE-sponsored 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 from 2006-2008, (5) results of the U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006 at Iowa City, (6) results of fish contaminant monitoring conducted in 2006 as part of the REMAP program (Site 302), (7) IDNR/UHL TMDL and REMAP biological monitoring conducted at four sites in 2005, and (8) results of fish kill investigations conducted on April 13, 2006 and March 17, 2007.
Note: A TMDL for indicator bacteria in this segment of Iowa River was prepared and approved by EPA in June 2007. The approval of this TMDL moves the bacterial impairment for this segment from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).
EXPLANATION: Results of water quality monitoring at the ACOE long-term station near the University of Iowa water treatment plant suggest that the Class A1 uses should be assessed (monitored) as "not supported." The geometric mean level of indicator bacteria (E. coli) in the 18 samples collected as part of UI/ACOE monitoring during recreational seasons of 2006 through 2008 (180 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Seven of the 18 samples (39%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b)..
The results of IDNR's ambient city monitoring for indicator bacteria upstream from Iowa City, however, suggest “full support” of primary contact recreation uses. Twenty-two samples were collected upstream from Iowa City at the IDNR/UHL station at Dubuque Street during recreational seasons of 2006 through 2008. The geometric mean of these 25 samples was only 47 E. coli orgs/100 ml; this geometric mean is well-below the Iowa criterion of 126 orgs/100 ml. Four of the 22 samples (18%) had levels of E. coli that exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, these results suggest “full support” of the Class A1 uses of this river segment.
A comparison of monitoring results from the most recent assessment periods (i.e., 2002-04, 2004-06, and 2006-08) suggests that levels of indicator bacteria in this segment of the Iowa River are relatively low. At the ACOE station near the University of Iowa water treatment plant in Iowa City (approximately 9 river miles downriver from Coralville Reservoir Dam), the geometric means of the approximately 18 samples collected in these three assessment cycles were 117, 118, and 180 orgs/100 ml, respectively. At the IDNR (Dubuque Street) station upstream from Iowa City (approximately 3 river miles downriver from the Coralville Reservoir Dam), the geometric means for these three periods were 34, 25, and 47 orgs/100 ml, respectively. The generally low levels of indicator bacteria in this assessment segment 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 (water treatment plant) monitoring station likely reflect inputs of indicator bacteria from (1) the Iowa River tributaries between these two stations (e.g., Muddy Creek and Clear Creek) and/or (2) the Iowa City/Coralville urban area. This pattern of very low levels of indicator bacteria in the Iowa River at the Dubuque Street station upstream from Iowa City and levels approaching—and sometimes exceeding—the Class A1 geometric mean water quality criterion at the ACOE station in Iowa City can be expected to continue.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on fish kill investigations on April 13, 2006 and March 17, 2007. Both kills involved only gizzard shad and were attributed to natural causes (temperature fluctuation). Waters affected by such kills are appropriate for Category 2b of Iowa's Integrated Report and will thus be added to Iowa's list of waters in need of further investigation.
Despite the occurrence of these fish kills, the remainder of the various types of water quality monitoring conducted in this river segment suggest good chemical water quality "full support" of the Class B(WW1) (aquatic life) uses. Results of ambient chemical/physical water quality monitoring at the IDNR/UHL (Dubuque Street) and UI/ACOE (UI Water Plant) stations suggest “full support" of the Class B(WW1) aquatic life uses. Monitoring at these stations showed no violations of Class B(WW1) criteria for ammonia-nitrogen, and only one violation for dissolved oxygen and pH, in the combined 97 samples collected at both stations during the 2006-2008 assessment period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10% for conventional parameters such as dissolved oxygen suggests "full support" of aquatic life uses. Thus, the percentage of violations of the dissolved oxygen criterion at the ACOE station (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(WW1) aquatic life uses. For the 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 survey had suggested a potential impairment to the aquatic life uses of this stream segment due to a significant decline in the freshwater mussel community. 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 was removed for the 2006 reporting/listing cycle.
Somewhat contradictory to the WQ sampling and mussel results, the fish and benthic macroinvertebrate results generated as part of IDNR/UHL REMAP sampling from this segment suggest (evaluated) "partial support" of aquatic life uses. However, because this segment is almost completely impounded by the lowhead dam at Burlington Street in Iowa City, and because the drainage areas above the sampling sites are much higher than the IDNR wadeable IBI calibration, the 2008 aquatic life assessment for this segment will rely on the WQ and mussel data and this biological data will be considered strictly supplemental.
Based on results of the IDNR/UHL 2005 REMAP and TMDL biological samplings, the Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting." A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2005 FIBI scores (n=7) ranged from 6 to 22 and the 2005 BMIBI scores (n=13) ranged from 16 to 46. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 0/7 times and passed the BMIBI BIC 0/13 times in 2005. This assessment is considered evaluated because the drainage area (average = 3188 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. Thus, this assessment is considered of lower confidence (evaluated) and is not appropriate for addition of a water to the state's Section 303(d) list.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in 2005; however, the samples were not collected in multiple years. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
The Class C drinking water uses are assessed (monitored) as "fully supported." Results of monitoring at the IDNR/UHL station upstream from Iowa City at Dubuque Street from 2006-08 show no violations of the atrazine MCL in the 14 samples collected and four violations of the nitrate MCL in the 33 samples collected and analyzed over the 2006-08 period. Maximum, mean, and median levels for atrazine at this station were 1.1, 0.23, and 0.14 ug/l. The maximum, mean and median levels for nitrate were 12.0, 6.3, and 6.3 mg/l; 12% of the samples exceeded the nitrate 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 less than 10% of samples violate the nitrate MCL, drinking water uses should be assessed as “fully supported”. And, based on IDNR’s assessment methodology, these results do not suggest that significantly more than 10 percent of the samples exceed the nitrate MCL and thus do not suggest an impairment of the Class C uses of this river segment.
Nine of the 65 samples (14%) collected at the ACOE station near the Iowa City water treatment plant from 2006-08 exceeded the 10 mg/l MCL for nitrate (maximum concentration = 13.6 mg/l) (atrazine is not monitored as part of the UI/ACOE program). The average nitrate level was 6.0 mg/l; the median level was 5.7 mg/l. Similar to the results for the IDNR/UHL ambient station at Dubuque Street, IDNR’s assessment methodology shows that these results do not indicate that significantly more than 10 percent of the samples exceed the nitrate MCL.
Fish consumption uses remain assessed (monitored) as "fully supporting." The results from the UI/ACOE fish contaminant monitoring in 2007 and 2008 show that levels of organochlorine contaminant are very low. Samples were collected on the Iowa River downriver from Coralville Dam in Iowa City. The duplicate composite whole-fish samples of common carp from this segment of the Iowa River had low (non-detectable) levels of chlordane measured as the sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, and oxychlordane. The UI/ACOE fish contaminant monitoring protocol does not include analysis for either mercury or PCBs.
Results from the U.S. EPA/IDNR RAFT program also suggest “full support” of the fish consumption uses in this river segment. The results from RAFT monitoring at Iowa City in 2006 show low levels of the primary contaminants (chlordane, PCBs and mercury) in the composite sample of common carp fillets: mercury: 0.195 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.021 ppm.
Similarly, results from the 2006 REMAP fish contaminant monitoring showed low levels of the primary contaminants in the composite sample of common carp fillets: mercury: 0.181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.
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 levels of contaminants in fish from this segment of the Iowa River do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
