Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR/SHL ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids (station 10570001), (2) IDNR/SHL stream REMAP biological sampling in 2005, and (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 4a) due to levels of indicator bacteria that very slightly exceed state water quality criteria. Results of ambient chemical/physical water quality monitoring suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported.” However, the Class B(WW1) aquatic life uses remain assessed (evaluated) as partially supporting (IR 3b-u) based on the 2005 IDNR/SHL stream REMAP biological sampling in 2005 near Bertram. Fish consumption uses remain assessed (monitored) as “fully supported” (IR 2a) based on results of fish contaminant monitoring in 2006. The sources of data for this assessment include (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR/UHL ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids (station 10570001), (2) IDNR/SHL stream REMAP biological sampling in 2005 near Bertram, and (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006. This is the same assessment as that developed for the adjacent upstream segment of the Cedar River (IA 02-CED-0030-1).
Note: A TMDL for indicator bacteria in this segment of Cedar River was prepared and approved by EPA in February 2010. 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: The Class A1 uses are assessed as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 24 montly samples collected during the recreational seasons of 2010 through 2012 at station 10570001 downstream from Cedar Rapids were as follows: the 2008 geometric mean was 145 orgs/100 ml, the 2011 geometric mean was 79 orgs/100 ml and the 2012 geometric mean was 56 orgs/100 ml. Only the 2010 geometric mean exceed the Class A1 criterion of 126 orgs/100 ml and then only slightly. The 2011 and 2012 geometric means were well below the Class A1 criterion. Four of the 24 samples (17%) 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Despite the ongoing impairment of the Class A1 uses in this river segment, levels of indicator bacteria are very low. If levels remain similarly low over the next assessment cycle (2012-2014), the bacterial impairment of the Class A1 uses should be considered for removal.
The results of monitoring from the IDNR/sHL ambient station 10570001 at Highway 30 from 2010 through 2012 suggest "full support" of the Class B(WW1) aquatic life uses. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for ammonia-nitrogen, chloride, or sulfate in the 36 samples collected, and only one of the approximately 36 samples (3%) violated the Class B(WW1) criteria for pH and dissolved oxygen. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH and dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station 10570001 do not indicate that significantly greater than 10% of the samples exceed either the Class B(WW1) criteria for dissolved oxygen or pH. Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.
However, the results IDNR/SHL stream REMAP biological sampling in 2005 indicate that the Class B(WW1) aquatic life uses should be assessed as "partially supporting". The evaluated biological assessment was based on data collected in 2005 as part of the IDNR/SHL stream REMAP project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria 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 were 49, 46 (fair) and the BMIBI scores were 19 (poor) and 47 (fair). 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 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 0/2 times in the last eight years. This assessment is considered evaluated because the drainage area (6829 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 passed the FIBI BIC and failed to meet the BMIBI BIC, 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.
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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in 2005; however, the samples were not collected in multiple years nor in the last five 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).
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Rapids in 2006. 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 composite samples of fillets from channel catfish and freshwater drum had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0803 ppm; total PCBs: 0.091 ppm; and technical chlordane: 0.03 ppm. Levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.104 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.03 ppm. All levels of these contaminants from this monitoring are below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses in this segment of the Cedar River.
