South Skunk River IA 03-SSK-931

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 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10850002 near Cambridge were as follows: the 2014 geometric mean was 298 orgs/100 ml, the 2015 geometric mean was 579 orgs/100 ml, and the 2016 geometric mean was 243 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Sixteen of the combined 24 samples (67%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. 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."

The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supported” based on results of biological sampling. Results of biological sampling conducted in 2012 and 2014-2016 as part of the DNR/SHL stream biocriteria project and the 2002 DNR Fisheries sampling suggest that these uses are “partially supported.” 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 2012 and 2014 BMIBI scores were 19 (poor) and 47 (fair). The 2015 and 2016 BMIBI scores were 55 (fair) and 75 (good). The 2002 Fisheries FIBI score was 48 (fair). The aquatic life use support was assessed (evaluated) as partial 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 segment passed the FIBI BIC 1/1 times in 2002 and passed the BMIBI BIC 1/4 times in the last five years. This assessment is considered evaluated because the drainage area (585 and 605 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 the FIBI BIC (1/1) and failed the BMIBI BIC (1/4), 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.

Despite the results of biological monitoring that suggest impairment of the Class B(WW2) uses, results of chemical/physical water quality monitoring at DNR station 10850002 near Cambridge suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW2) water quality criteria for 35 Ammonia samples (maximum = 1.6 mg/L), 36 Dissolved Oxygen samples (minimum = 7.4 mg/L), 35 pH samples (range = 6.9 to 8.5), 36 Temperature samples (maximum = 28.4° c), 36 Chloride samples (maximum = 130 mg/L), or 36 Sulfate samples (maximum = 140 mg/L) occurred during monitoring from January 2014 to December 2016. 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 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW2) aquatic life uses.