Assessment Comments

Assessment is based on results of (1) results monthly water quality monitoring from 2010 through 2012 at the IDNR ambient station located at the County Road C43 bridge south of Garber, (2) results of monitoring at Hwy 52 from May 2011 to November 2012, (3) results of water quality monitoring conducted at Garber by USGS from 2010 to 2012, (4) results of EPA monitoring at their station BR42 from April 2010 to November 2012, (4) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2011 and 2012 near Garber, and (5) biological monitoring conducted in 2002 by the IDNR Fisheries Bureau and in 2003, 2011 and 2012 by IDNR/SHL.

Basis for Assessment

Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR Category 5a) due to levels of indicator bacteria that slightly exceeded state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR Category 3b-u) based on results of biological monitoring conducted by the IDNR Fisheries Bureau in 2002 and by IDNR/SHL in 2003.   Fish consumption uses are assessed (monitored) as "partially supported" (IR Category 5a) based on results of fish contaminant monitoring in 2011 and 2012 and issuance of a consumption advisory in 2013.   Sources of data for this assessment include (1) results monthly water quality monitoring from January 2008 through December 2010 at the IDNR ambient station (STORET station 10220001) located at the County Road C43 bridge south of Garber approximately 1 mile downstream from confluence with the Volga River, (2) results of monitoring at Hwy 52 from May 2011 to November 2012 at station TR10 at Highway 52 (STORET station 15220020), (3) results of water quality monitoring conducted at Garber by USGS from February 2010 to December 2012 (USGS station 05412500), (4) results of U.S.  EPA/IDNR fish tissue (RAFT) monitoring in 2011 and 2012 near Garber, and (5) biological sampling conducted in 2002 by the IDNR Fisheries Bureau and in 2003, 2011 and 2012 conducted by IDNR/SHL.  

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed as "partially supported" based on levels of indicator bacteria that slightly exceeded state water quality criteria.   The geometric mean of indicator bacteria (E.  coli) in the 32 monthly samples collected during the recreational seasons of 2010 through 2012 at the IDNR ambient monitoring station near Garber exceeded the Iowa water quality criterion to protect primary contact recreation uses.   Several recreation season (March-November) geometric means based on the these 32 monthly samples were above Iowa’s Class A1 water quality criterion of 126 orgs/100 ml:  the 2010 geometric mean was 309 orgs/100 ml, the 2011 geometric mean was 111 orgs/100 ml and the 2012 geometric mean as 172 orgs/100 ml.   Ten of the 32 samples (31%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  

Results of USGS bacterial monitoring at the Garber monitoring station also showed that recreation season (March-November) geometric means based on the 22 samples collected over the 2010-2012 period were above Iowa’s Class A1 water quality criterion of 126 orgs/100 ml:  the 2010 geometric mean was 246 orgs/100 ml, the 2011 geometric mean was 298 orgs/100 ml, and the 2012 geometric mean as 103 orgs/100 ml.   Nine of the 22 USGS samples (41%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  

Results of IDNR monitoring at Hwy 52 (STORET station 15220020), however, showed differing results with recreation season geometric means based on the 15 samples collected during 2011 and 2012 both meeting the Class A1 geometric mean criterion of 126 orgs/100 ml.   The 2011 geometric mean was 90 orgs/100 ml, and the 2012 geometric mean was 125 orgs/100 ml.   Four of the 15 USGS samples (27%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  

In conclusion, the results of bacterial monitoring at these three stations during the 2010-2012 period show that four of the eight recreation season geometric means exceed Iowa’s Class A1 geometric mean criterion of 126 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 is greater than 126 orgs/100 ml., the primary contact recreation uses are assessed as impaired (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, the Class A1 (primary contact recreation) uses of this segment are assessed as “partially supported”.   In addition, the percentages of samples that exceed Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml was significantly greater than 10% in all three datasets, thus also indicating impairment of the Class A1 uses.   The magnitude of impairment in this stream segment, however, is very slight:  the maximum geometric mean for the 2010-2012 period was 309 orgs/100 ml, and half the geometric means during the 2010-2012 period met the Class A1 criterion.  

Results of chemical/physical water quality monitoring by Iowa DNR, USGS, and U.S.  EPA do not suggest impairment of the Class B(WW1) aquatic life uses.   Monitoring at the IDNR, USGS, and LTRMP stations showed no violations of Class B(WW1) water quality criteria for conventional pollutants or ammonia in the approximately 50 samples analyzed at the IDNR ambient monitoring station at Garber, the 15 samples analyzed at Iowa DNR station at Hwy 52, the 32 samples analyzed at the USGS station at Garber, and in the 9 samples analyzed at the station BR42 by U.S.  EPA.   In addition, none of the 33 samples analyzed for banned pesticides (e.g., DDT, and dieldrin) by USGS violated the respective Class B(WW1) criteria.  

Results of biological monitoring conducted by the IDNR Fisheries Bureau in 2002 and by IDNR/SHL in 2003, 2011 and 2012, however, suggest that the Class B(WW1) aquatic life uses should remain assessed (evaluated) as “partially supported”.   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 2003 REMAP FIBI score was 75 (excellent).   The 2002 Fisheries FIBI was 39 (fair).   The 2011 BMIBI score was 52 (fair) and the 2012 BMIBI score was 68 (good).   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 52 and the BMIBI BIC for this ecoregion is 61.   This biological assessment is considered “evaluated” because the drainage area (1553 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 the one out of two samples failed to meet both the BMIBI and FIBI 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.   This potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation.  

Fish consumption uses are assessed (monitored) as “partially supported” (IR Category 5a) based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Garber in 2011 and 2012 and on issuance of a one meal per week consumption advisory in 2013.   This advisory was issued due to two consecutive samplings showing that levels of mercury in predator fish (smallmouth bass) exceeded the threshold for a one meal/week advisory (0.3 ppm).   The average level of mercury in the samples of smallmouth bass collected in 2011 was 0.38 ppm, and the average level in the samples of smallmouth bass collected in 2012 was 0.47 ppm.   Based on these results, a consumption advisory was issued in 2013.   The existence of, or potential for, a fish consumption advisory is the basis for assessing the degree to which Iowa’s lakes and rivers support their fish consumption uses.  Because a one meal per week fish consumption advisory was issued for this waterbody, the fish consumption uses are assessed (monitored) as “partially supported” (IR Category 5a).