Assessment Comments
Assessment remains based on: (1) bacterial monitoring conducted in 2006 approximately ½ mile downstream from Coffins Grove County Park (STORET station 15280006) and (2) bacterial monitoring conducted in 2012 in Coffins Grove Park (15280024).
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “partially supported” (IR 5p) due to levels of indicator bacteria that exceed state water quality criteria. The assessment of the Class B(WW2) aquatic life uses is changed from “fully supported” (evaluated) based on results of biological monitoring conducted in 1998 to “not assessed” (IR 3a) due to age of data. Fish consumption uses remain "not assessed" (IR 3a) for this segment. The sources of data used for this assessment are (1) bacterial monitoring conducted approximately ½ mile downstream from Coffins Grove County Park (STORET station 15280006) as part of the Lake Delhi watershed assessment from April to June, 2006 and (2) bacterial monitoring conducted at STORET station 15280024 at Coffins Grove Park in May and June 2012.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 7 samples collected at the monitoring station on Coffins Creek from April to June, 2006, was 612 orgs/100 ml. Four of the seven samples (57%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The geometric mean of E. coli in the 7 samples collected at the monitoring station in Coffins Grove Park in May and June, 2012, was 752 orgs/100 ml. All seven samples (100%) 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 the geometric mean of E. coli is greater than the state criterion of 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). Although IDNR’s listing methodology requires that a minimum of ten E. coli samples be collected over a three-year period to support a Section 303(d) listing, this segment is being added to Iowa’s 2010 Section 303(d) list based on overwhelming evidence of impairment. That is, even if three additional samples had been collected, and each of these three samples had less than 10 orgs/100 ml (the INDR detection level), the resulting geometric means of E. coli at this station (178 orgs/100 ml) would still exceed Iowa’s Class A1 criterion of 126 orgs/100 ml. Thus, the Class A1 uses of this segment are assessed (“monitored”) as “partially supported” and this impairment remains in Category 5a of IDNR’s 2012 Integrated Report (Iowa’s Section 303(d) list). Similarly, the 7 samples collected in 2012 also demonstrate overwhelming evidence of impairment: even if three additional samples had been collected, and each of these three samples had less than 10 orgs/100 ml (the INDR detection level), the resulting geometric means of E. coli at this station (201 orgs/100 ml) would still exceed Iowa’s Class A1 criterion of 126 orgs/100 ml. Thus, the Class A1 uses of this segment remain assessed (“monitored”) as “partially supported” and this impairment remains in Category 5a of IDNR’s 2014 Integrated Report (Iowa’s Section 303(d) list).
The assessment of support of the Class B(WW1) aquatic life uses is no longer based on the results of biological monitoring conducted by IDNR Fisheries in 1998. According to IDNR’s assessment/listing methodology, any non-303(d) Section 305(b) assessment based on data that have aged beyond 10 years likely does not represent current conditions and thus is not included in the current assessment cycle. Previous assessments based on these data remain in IDNR’s on-line assessment database, ADBNet.
[Note: although data for ammonia nitrogen were collected at STORET station 15280006 as part of the Lake Delhi watershed assessment project, supporting data for pH and temperature were not collected. Thus, INDR was not able to compare the sample ammonia values to the temperature/pH-dependent Class B(WW2) water quality criteria for ammonia. Similarly, data for ammonia nitrogen were collected during the seven samplings conducted in 2012, and again the supporting data for pH data were not collected. There were, however, no detectable levels of ammonia in the seven samples analyzed in 2012 (detection limit = 0.05 mg/l).]
