South Fork Iowa River IA 02-IOW-749
from confluence with unnamed tributary in W 1/2 S19 T88N R21W Hardin Co. to confluence with unnamed tributary in E 1/2 S11 T88N R22W Hardin Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 9/9/2016 3:14:26 PM
- Updated
- 9/12/2016 11:16:46 AM
The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as "partially supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” (IR 2a) based on chemical/physical water quality monitoring conducted from 2010-2013. The sources of data for this assessment are (1) the results of monitoring from March 2010 to July 2012 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA, at station SF400 approximately 2 miles NNE of Buckeye, IA (~0.5 miles south of Hwy 20), and (2) results of USGS monitoring near Buckeye from May to August 2013 at station 05451112. This assessment is the same as that developed for the adjacent upstream segment (IA 02-IOW-0280_4).
[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.] EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli). The following table summarized recreation season geometric means of E. coli at station SF400 over the 2010-2012 period: Summary of recreation season (March 15-November 15) geometric means of indicator bacteria (E. coli) at station SF400 on South Fork Iowa River approximately 0.5 miles south of Hwy 20 in Hardin County, IA. Geometric means are number of organisms per 100 ml. Station: 2010 2011 2012 2013 2014 2015 No. samples, 2010-14 No. > 235, 2010-14 % of samples > 235 SF400 303.8 361.0 343.8 No data 23 15 65.2% Geometric means for recreation season of 2010 through 2012 slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Fifteen of the 23 samples (65.2%) collected over the 2010-2012 period exceeded the single-sample maximum criterion of 235 E. coli organisms/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level 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 3-35of U.S. EPA 1997b). Monitoring by the NLAE approximately 2 miles NNE of Buckeye (station SF400) from 2010-2014 included continuous monitoring for dissolved oxygen, pH, and water temperature. Data for daily maximum, mean, and minimum values were provided to Iowa DNR. None of the 530 daily maximum and minimum values for pH exceeded the respective Class B(WW2) pH criteria of 9.0 and 6.5 pH units. The respective maximum and minimum pH values reported for this period were 9.0 and 7 pH units. Eight of the 529 daily maximum values for water temperature (1.5%) exceeded Iowa’s added heat criterion of 32C (maximum value = 33.8C). Of the 468 daily minimum values for dissolved oxygen generated at monitoring site SF400 over the 2010-2012 monitoring period, only 1 value (0.2%) was below the 5.0 mg/l Class B(WW2) criterion (not < 5.0 mg/l during 16 hours of a 24-hour period), and no values were below Iowa’s Class B(WW2) criterion for a minimum dissolved oxygen of 4.0 mg/l at any time during a 24-hour period (minimum value = 4.95 mg/l). According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if more than 10% of the samples for conventional parameters such as temperature exceed their respective Class B(WW2) criteria, the aquatic life uses should be assessed as “impaired”. According to Iowa’s assessment/listing methodology, however, the percentage of samples exceeding the respective Class B(WW2) criteria for water temperature is not significantly greater than 10%. Thus, the monitoring results for water temperature at station SF400 do not suggest impairment of the Class B(WW2) aquatic life uses. The assessment of support of the Class B(WW2) uses is also based, in part, on results of USGS monitoring near Buckeye (station 05451112) that showed no violations of Class B(WW2) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, temperature, chloride or sulfate in the approximately 10 samples collected from May through August 2013. These monitoring results do not suggest impairment of the Class B(WW2) aquatic life uses. [Note: monitoring for dissolved oxygen and other parameters at NLAE station SF400 ended in early July 2012. July, August, and September of 2012 were very warm dry months in the South Fork Iowa River watershed and in other Iowa watersheds as well, and low levels of dissolved oxygen in summer 2012 resulted in identifications of dissolved oxygen-related impairments in other stream segments in the South Fork Iowa River watershed.]