Assessment Comments

Assessment is based on: (1) results of IDNR/UHL ambient monthly water quality monitoring conducted on the Upper Iowa River near Dorchester (station 10030001) from 2008-2010, (2) results of monitoring conducted by the Long-Term Resource Monitoring Program at LTRMP station UI02.9M from 2006-08, (3) results of monitoring for indicator bacteria conducted at Upper Iowa River Watershed project Site 30 near New Albin from 2008-2010, (4) results of IDNR/UHL biological monitoring in 2005 and 2008, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004, 2006, and 2010.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated for Class A1 (primary contact recreation) uses and B(WW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.   EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment remains designated for both primary contact recreation uses (still termed Class A1) and for aquatic life uses (now termed Class B(WW1).   In addition, this assessment segment also remains designated 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 “not supported” due to high levels of indicator bacteria that exceed state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported."  Fish consumption uses remain assessed (monitored) as “partially supported” based on issuance of a fish consumption advisory for this segment of the Upper Iowa River in 2008.   Sources of data for this assessment include (1) results of IDNR/UHL ambient monthly water quality monitoring conducted on the Upper Iowa River near Dorchester (station 10030001) during the period January 2008 through December 2010, (2) results of monitoring conducted by the Long-Term Resource Monitoring Program at LTRMP station UI02.9M from April 2007 through November 2008, (3) results of monitoring for indicator bacteria conducted at Upper Iowa River Watershed project Site 30 near New Albin (STORET No.   NEIARCD 190050008) from April 2008 through October 2010, (4) results of IDNR/UHL biological monitoring in 2002, and (5) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring in 2004, 2006, and 2010.    

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E coli) that exceed state water quality criteria.   Recreation season (March-November) geometric means based on the 21 samples from the IDNR ambient monitoring station near Dorchester slightly exceeded Iowa’s Class A1 water quality criterion of 126 orgs/100 ml:  the 2008 geometric mean was 334 orgs/100 ml, and the 2010 geometric mean was 263 orgs/100 ml.   The 2009 geometric mean (97 orgs/100 ml) was below the E.  coli geometric mean criterion.   Six of the 21 samples (29%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.  

Similarly, the geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at Upper Iowa River Watershed project Site 30 near New Albin also slightly exceeded the Iowa water quality criterion to protect primary contact recreation uses.   The 2008 recreation season geometric mean was 200 orgs/100 ml, the 2009 geometric mean was 188 orgs/100 ml and the 2010 geometric mean was 259 orgs/100 ml.   Levels of E.  coli in eight of the 21 samples (38%) exceeded Iowa’s 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 is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Note:  LTRMP monitoring does not include analysis for indicator bacteria.  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported."  Similar to the previous (2010) assessment cycle, none of the approximately 32 samples from the IDNR/UHL station analyzed from January 2008 through December 2010 for conventional pollutants and ammonia exceeded a state Class B(WW) criterion.   None of the 30 samples analyzed from LTRMP station UI02.9M from 2006-2008 violated Class B(WW1) criteria for ammonia, dissolved oxygen, or pH.  

Similarly, the Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting" based on data collected in 2005 and 2008 as part of the IDNR/UHL stream biocriteria and REMAP projects.   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 REMAP FIBI scores were 57 (good) and 82 (excellent).   The 2005 REMAP BMIBI scores were 87 (excellent) and 76 (excellent).   The 2008 BMIBI score was 82 (excellent).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 52 and the BMIBI BIC for this ecoregion is 61.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 3/3 times in the last six years.   This assessment is considered evaluated because the drainage areas (768 and 897 mi2) above the sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed 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.  

Fish consumption uses are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Dorchester in 2004, 2006, and 2010.   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.   The composite samples of fillets from the 2004 samples of common carp and smallmouth bass had generally low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.228 ppm; total PCBs:  0.13 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.486 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   The levels of mercury in 2004 samples of both common carp and smallmouth bass exceed the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory:  the level of mercury in the sample of common carp fillets was 0.228 ppm and in the sample of smallmouth bass fillets was 0.486 ppm.  

The composite samples of fillets from the 2006 RAFT samples of golden redhorse (Moxostoma erythrurum) and smallmouth bass had similarly high levels of mercury.   The level of mercury in the composite sample of golden redhorse fillets was 0.362 ppm, and the level of mercury in the composite sample of smallmouth bass fillets was 0.37 ppm.   According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above an advisory trigger level in fillet samples, a consumption advisory will be issued.   Because levels of mercury in both the 2004 and 2006 samples of smallmouth bass exceed the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory, a consumption advisory was issued for this segment by IDNR in March 2008.   Because level of mercury in the sample of the bottom-feeding golden redhorse was also greater than the advisory level, all species were included in the one-meal/week advisory.   The existence of a one-meal/week consumption advisory for this assessment segment suggests that the fish consumption uses are “partially supported.”  This advisory extends downriver the existing advisory issued in 2006 for the Upper Iowa River from the Lower Dam in eastern Winneshiek County upriver to County Road W20 approximately 5.5 miles upriver from Decorah.   Follow-up sampling was conducted at the Upper Iowa River near Dorchester in 2010.   The level of mercury in samples of golden redhorse fillets (0.318 ppm) and smallmouth bass fillets (0.392 ppm) were both above the advisory trigger level therefore suggesting that the fish consumption advisory should remain at this river segment.