Skunk River IA 03-SKU-889

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 18 samples collected during the recreational seasons of 2014 through 2016 At DNR ambient station 10560002, were as follows: the 2014 geometric mean was 52 orgs/100 ml, the 2015 geometric mean was 168 orgs/100 ml, and the 2016 geometric mean was 324 orgs/100 ml. Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Eight of the combined 18 samples (44%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.At USGS station 05474000 at Augusta, IA,too few bacteria samples were collected during the recreation seasons of 2014 and 2017 (total of 7 samples) to calculate meaningful geometric means. No samples were collected during the recreation season of 2014.According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary 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 "partially supported."

Additionally, no violations of Class B(WW1) acute or chronic toxics water quality criteria for 9 Dieldrin samples (maximum = <0.004 ug/L), or 9 p,p'-DDE samples (maximum = <0.0025 ug/L) occurred during monitoring from January 2014 to September 2014at USGS station 05474000.According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 1 acute violation of these Toxic parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

The results of DNR/SHL stream biological sampling in 2006, 2012, 2013 and 2015 also suggest "full support" of the Class B(WW1) aquatic life uses. This evaluated biological assessment was based on data collected in 2006, 2012, 2013 and 2015 as part of the DNR/SHL stream REMAP and stream nutrient sampling 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 2006 FIBI score was 41 (fair). The 2012 BMIBI scores were 29 (poor) and 45 (fair). The 2013 BMIBI scores were 36 and 45 (both fair). The 2015 BMIBI score was 63 (good). 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 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC is 41. This assessment is considered evaluated because the drainage areas (4342 and 4303 mi2) above the sampling sites were far 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 BIC (1/1) and the BMIBI BIC (3/5), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don't fall in the calibrated watershed size.

Results of Class HH (human health) monitoring at USGS station 05474000 at Augusta, IA also suggest “full support” of the aquatic life uses. Monitoring showedno violations of Class HH(human health) criteria for 9 Dieldrin samples (maximum = <0.004 ug/L), or 9 p,p'-DDE samples (maximum = <0.0025 ug/L) occurred during monitoring from January 2014 to September 2014. According to DNR’s assessment/listing methodology, if the mean level of a toxic metal or pesticide is greater than its respective human health criterion, impairment (“nonsupport”) of the Human Health use is indicated. Thus, these results thus suggest (“full support”) of the Class HH(human health) uses.Iowa's human health-fish (HH-fish) criterion is 0.00054 ppb (=54 parts per trillion). According to DNR’s assessment/listing methodology, if the mean level of a toxic metal or pesticide is greater than its respective human health criterion, impairment ("non-support") of the Human Health use is indicated. There were no samples with detectable levels of dieldrin, and the method detection level (0.004 ug/l) was too high (~15 times the HH criterion for dieldrin) to allow calculation of a meaningful summary statistic (e.g., mean) for dieldrin at USGS station 05474000. Regardless, the infrequent occurrence of dieldrin in water is of concern and thus suggests that the Human Health uses should remain assessed as “potentially impaired” and remain included in Category 3b of Iowa’s Integrated Report.

Fish contaminant monitoring for toxic parameters other than dieldrin (e.g., mercury, PCBs, and chlordane) suggest “full support” of fish consumption uses. This site has been sampled for whole-fish common carp since 1995 on an every-other-year basis as part of Iowa DNR trend monitoring (note: trend samples were not collected in 2012 due to low water conditions). The 2010 composite samples of whole fish samples of common carp had low levels of primary contaminants: mercury: 0.117 ppm; total PCBs: 0.162 ppm; and technical chlordane: 0.092 ppm. The 2014 whole-fish carp composite sample had 0.12 ppm of mercury; <0.24 ppm of total PCBs, and <0.05 ppm of technical chlordane. The 2016 whole-fish carp composite sample had 0.08 ppm of mercury; <0.06 ppm of total PCBs, and 0.05 ppm of technical chlordane.

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 fish contaminant data generated from the 2010, 2014 and 2016 samplings show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody. Due, however, to the low frequency with which violations of the human health (fish + water) dieldrin criterion occurs, the assessment of the HH-fish consumption uses in this river segment is considered appropriate for Iowa’s IR Category 3b (potential impairment). IR Category 3b waters will be added to Iowa’s list of waters in need of further investigation.