English River IA 02-IOW-671

The Class A1 (primary contact recreation) uses are assessed (monitored) as "not 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 10920001 on the English River at Riverside were as follows: the 2014 geometric mean was 911 orgs/100 ml, the 2015 geometric mean was 341 orgs/100 ml, and the 2016 geometric mean was 1174 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Fifteen of the combined 24 samples (62%) 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 Iowa 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 "not supported."

Results of biological monitoring suggest that the Class B(WW1) uses should be assessed as “partially supported.” Biological data were collected in 2001 and 2012-2014 as part of DNR/SHL stream biocriteria and large river sampling projects. 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 2001 FIBI score was 34 (fair). The 2008, 2012-2014 and 2016 BMIBI scores were 37, 40 (both fair) 62, 68, 71 (all good). The aquatic life use support was assessed 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 for this ecoregion is 51. This segment passed the FIBI BIC (using the uncertainty adjustment value (UAV) of 7 points) in 2004 and passed the BMIBI BIC 3/5 times in the last nine years. This assessment is considered evaluated because the drainage area (627 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 (using the UAV +7) and passed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn't fall in the calibrated watershed size.

In agreement with the biological assessment, the results of chemical/physical water quality monitoring at DNR station 10920001 on the English River at Riverside suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 1.9 mg/L), 35 pH samples (range = 7 to 8.2), 36 Temperature samples (maximum = 25.3°C), 36 Chloride samples (maximum = 28 mg/L), or 36 Sulfate samples (maximum = 83 mg/L) occurred during monitoring from January 2014 to December 2016. 1 of the 36 samples (3%) analyzed for Dissolved Oxygen (minimum = 2.2 mg/L) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as Dissolved Oxygen suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.