Casey Springs IA 01-UIA-275

The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “partially supported.” The presumptive Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.” The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 11 were as follows: the 2012 geometric mean was 127orgs/100 ml, the 2013 geometric mean was 315 orgs/100 ml and the 2014 geometric mean was 506 orgs/100 ml. All three of the three geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml. All three geometric means are well below the Class A2 geometric mean criterion of 630 orgs/100 ml. Ten of the 21 samples (48%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; two of the 21 samples exceeded the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as “impaired” (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, due to geometric means greater than the Class A1 criterion, the presumptive Class A1 uses are assessed as “partially supported”. Also, according to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if significantly greater than 10% of sample exceed the single-sample maximum criterion, the contact recreation uses should be assessed as “impaired”. According to DNR’s assessment methodology, however, the percentage of samples that exceeded the Class A2 criterion of 2,880 orgs/100 ml during the 2012-2014 assessment period at Site 11 was not significantly greater than 10%. Thus, the Class A2 uses are assessed as “fully supporting. Although assessed as "impaired", this stream has exceptionally low levels of indicator bacteria relative to other Iowa streams, and thus this impairment should be considered slight.

The Class B(CW1) coldwater aquatic life uses and fish consumption uses remain assessed as “fully supporting” based on limited monitoring data at Upper Iowa River Watershed Site 11 and on a summary of trout reproduction. Monitoring from 2012 to 2014 at Upper Iowa River Watershed Site 11 included analysis for ammonia and temperature. None of the 14 samples analyzed for ammonia exceeded the respective temperature/pH-dependent Class B(CW1) criteria. None of the 14 samples exceeded the Class B(CW1) criterion for temperature. Two of the 13 samples (15%) analyzed for pH exceeded the Class B(CW1) criterion of 9.0 pH units. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if significantly greater than 10% of samples exceed criteria for conventional parameters such as pH, the assessed uses should be assessed as “impaired”. According to Iowa DNR’s assessment methodology, however, the percentage of samples that exceeded the Class B(CW1) pH criterion of 9.0 units during the 2012-2014 assessment period at Site 11 was not significantly greater than 10%. Thus, these results do not suggest impairment of the Class B(CW1) aquatic life uses.

In addition, a summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 suggests that the Class B(CW1) uses of this stream should be assessed as "fully supported". According to the updated summary, Casey Springs is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the DNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit consistent natural reproduction and maintain a wild population of brook and brown trout without any stocking (Category I stream).