Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient city monitoring station located downstream from Iowa City at the county road F62 bridge east of Hills, IA (station 10520003), (2) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (3) results of a fish kill investigation in March 2007, and (4) results of EPA/IDNR fish tissue (RAFT) monitoring at Iowa City in 2003.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "fully supported" based on results of ambient monitoring for indicator bacteria. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of a statewide survey of freshwater mussels in 1998-99. The fish consumption uses remain assessed as "fully supported" based on results of fish contaminant monitoring in 2003. The sources of data for this assessment are (1) the results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient city monitoring station located downstream from Iowa City at the county road F62 bridge east of Hills, IA (station 10520003), (2) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (3) results of a fish kill investigation in March 2007, and (4) results of EPA/IDNR fish tissue (RAFT) monitoring at Iowa City in 2003.
EXPLANATION: The Class A1 uses are assessed (monitored) as "fully supported" based on results of monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 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 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected during recreational seasons of 2004 through 2006 (111 orgs/100ml) is below the Iowa Class A water quality criterion of 126 orgs/100ml. Four of the 24 samples (16%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of the samples exceed the state’s single-sample maximum criterion of 235 orgs/100 ml, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, these results do not suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A uses should be assessed as “fully supported”. Although monitoring results from the 2002-04 assessment period that showed impairment (i.e., geometric mean of 117 orgs/100ml; seven of 24 samples > 235 orgs/100ml) are very similar to those from the (current) 2004-06 period (geometric mean of 117 orgs/100ml; four of 24 samples > 235 orgs/100ml),” the results from the 2004-06 period do not suggest impairment of the Class A1 uses. This difference in assessment results reflects that the bacterial impairment identified for this segment in previous assessment/listing cycles is very slight. Presuming that ambient levels of indicator bacteria remain similar to historical levels, additional changes from “full support” to “impaired” can be expected in future assessment/listing cycles.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of the statewide survey of freshwater mussels (see below). Results of monitoring from the IDNR ambient station downstream from Iowa City from 2004 through 2006, however, continue to suggest full support of the Class B(WW1) uses: none of the approximately 36 samples analyzed for dissolved oxygen, pH, or ammonia-nitrogen; none of the 14 samples analyzed for toxic metals; and none of the approximately nine samples analyzed for pesticides showed violations of the respective Class B(WW1) criteria.
Despite results of IDNR/UHL ambient water quality monitoring that suggest “full support” of aquatic life uses, results of the 1998-99 statewide survey of freshwater mussels suggest a potential impairment to these uses. [Note: because the data from Arbuckle et al. (2000) are now older than five years, the assessment category is changed from a “monitored” (i.e., a higher confidence assessment) to “evaluated” (i.e., lower confidence assessment). Despite this change in assessment category, the impairment indicated by these data remains in IR Category 5 (i.e., Section 303(d) list) until more recent data suggest a good cause for de-listing.] For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey. Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggests an impairment of the aquatic life uses. The confidence level of this assessment is relatively high; thus the assessment type is considered “monitored” in the context of Section 305(b) reporting. According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on a “monitored” assessment are candidates for Section 303(d) listing. Species richness of freshwater mussels at the 9 sample sites in this stream segment were 22, 17, 11, 10, 14, 18, 7, 16, and 6 in the 1984-85 period and were 10, 4, 3, 2, 2, 8, 6, 8, and 4, respectively, in the 1998-99 period for an average percent change of minus 59%. Despite the moderate diversity of freshwater mussels found in this river segment during the 1998-99 survey, the nearly 60% decline in species richness suggest a significant modification of this aquatic community in the short timeframe of less than 15 years. Based on these results, and based on IDNR’s assessment methodology, the “full support” of aquatic life uses suggested by results of IDNR/UHL ambient monitoring is downgraded to "partial support." Because results of chemical/physical monitoring suggest good water quality in this river segment, the impairment of aquatic life uses suggested by the apparent decline of freshwater mussels is likely related to problems with the quality of aquatic habitat as opposed to poor chemical/physical water quality. As presented by Arbuckle et al. (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high instream levels of nutrients (phosphorus and nitrogen). Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness. Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairments of these uses that may exist.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of EPA/IDNR fish tissue (RAFT) follow-up monitoring downstream Iowa City in 2001 and 2003. This river segment has a history of relatively high levels of chlordane, and RAFT follow-up monitoring has thus been conducted on an every-other-year basis since 1994 (see assessments for the 1994 through 2004 reports). The level of chlordane in the sample of channel catfish fillets collected in 2001 was 0.049 mg/kg; this level was much lower than chlordane levels in previous samples (1997: 0.17 mg/kg; 1999: 0.16 mg/kg). The level of chlordane in the sample of channel catfish fillets collected in 2003 was 0.10 mg/kg. The 2003 composite samples of fillets also had low levels of other contaminants: mercury: 0.105 ppm and total PCBs: 0.187 ppm.
The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. 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 from either the 2001 or 2003 RAFT follow-up sampling conducted in the Iowa River downstream from Iowa City: 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. RAFT follow-up monitoring in this river segment will continue to determine current levels of other contaminants (i.e., mercury and PCBs) with revised trigger levels for consumption advisories.
