Assessment Comments
Assessment is based on: (1) the results from the IDNR/SHL ambient monthly monitoring station downstream from Sac City in Sac County (STORET station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City from 2010-2012, (2) results of IDNR/SHL stream REMAP biological sampling in 2005, and (3) results of IDNR fish contaminant monitoring conducted in 2012 and 2014.
Basis for Assessment
[Note: This assessment is also used, in part (except for the assessment of fish consumption uses) for the adjacent upstream segment (IA 04-RAC-0040-6).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 4a) due to levels of indicator bacteria (E. coli) that slightly violate state water quality standards. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supporting" (IR 3b-u) based on results of IDNR/SHL stream REMAP biological monitoring in 2005. The fish consumption uses are assessed (monitored) as “fully supporting” (IR 2a) based on fish contaminant monitoring in 2012 and 2014. The sources of data for this assessment include (1) the results from the IDNR/SHL ambient monthly monitoring station downstream from Sac City in Sac County (STORET station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City from 2010-2012, (2) results of IDNR/SHL stream REMAP biological monitoring in 2005, and (3) results of IDNR/U.S. EPA fish contaminant monitoring conducted in 2012 and 2014.
Note: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by IDNR and approved by EPA in June 2008. Because this TMDL covers the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle. This waterbody remains in IR Category 4a for the current cycle.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E. coli) that exceed state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 25 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10810001 near (downstream from) Sac City were as follows: the 2010 geometric mean was 187 orgs/100 ml, the 2011 geometric mean was 238 orgs/100 ml, and the 2012 geometric mean was 128 orgs/100 ml. All three geometric means very slightly exceed the Class A1 criterion of 126 orgs/100 ml. Nine of the 25 samples (36%) 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 are "not supported" (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.”
The Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supporting” based on biological data collected in 2005 IDNR/SHL stream REMAP biological monitoring project. A series of biological metrics which 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 that were 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 score was 50 (fair) and 2005 BMIBI score was 48 (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 non-riffle FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This assessment is considered evaluated because the drainage area (829 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 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. Also, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). The results of this sampling thus do not meet IDNR guidelines for developing a “monitored” assessment of support of the aquatic life uses that is appropriate to support addition of this waterbody to Iowa's Section 303(d) list. The assessment type for these waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation.”
Results of IDNR/SHL ambient chemical/physical water quality monitoring at the Sac City station during the 2010-2012 assessment period, however, suggest relatively good water quality in this river segment. Results of this monitoring show no violations of Class B(WW1) (aquatic life) water quality criteria in the 36 samples analyzed for ammonia, pH, temperature, chloride, and sulfate. One of the 36 samples collected (3%) exceeded the Class A, B(WW1) criterion for pH. 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, 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 IDNR station 10810001 do not indicate that greater than 10% of the samples exceed either the Class B(WW1) criteria for pH. Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.
Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring downstream from Sac City in 2012 and 2014. Although the composite samples of fillets from channel catfish collected in 2012 had low levels of contaminant, the average level of mercury in the tissue plug samples of walleye was slightly greater than threshold for a one meal per week consumption advisory. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.147 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. The levels of contaminants in this sample are below the advisory thresholds for mercury (0.3 ppm), total PCBs (0.2 ppm) and chlordane (0.6 ppm). The average level of mercury in the tissue samples from four walleye, however, was 0.304 ppm (SD=0.45 ppm), thus slightly exceeding the one meal per week advisory threshold. 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. According to the IDNR/IDPH advisory protocol, two consecutive samplings showing that contaminant levels are above the advisory threshold level are needed to justify issuance of a consumption advisory. Additional (follow-up) monitoring of levels of mercury in smallmouth bass was conducted in August 2014 to determine whether a one-meal/week consumption advisory should be issued. The average level of mercury in the three smallmouth bass sampled was 0.16 ppm (SD= 0.105 ppm). These results suggest do not suggest the need for issuance of a one meal per week consumption advisory for predator fish in this river segment.
