East Branch Iowa River IA 02-IOW-771
from confluence with Ditch No. 9 (S31 T95N R23W Hancock Co.) to confluence with unnamed tributary at Garner in SE 1/4 S25 T96N R24W Hancock Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 9/13/2016 3:03:55 PM
- Updated
- 9/13/2016 3:03:55 PM
The presumptive Class A1 (primary contact recreation) uses remain assessed (monitored) as “partially supported” (IR Category 5p) due to violations of Iowa water quality criteria for indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supporting” (IR 2a) based on results of chemical/physical monitoring from 2010-2012. The source of data for this assessment remains the results of monitoring at four sites: (1) Site 6 at 190th Street (STORET station 13410010), (2) Site 7 at Hwy 69 (STORET station 13410011), (3) near Garner (STORET station 13410001), and (4) Site 5a at 200th Street (STORET station 13410009). These stations were monitored as part of a Clean Water Act Section 319 water quality project from June 2010 through November 2012. No new data have been generated at these monitoring stations since November 2012.
[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, and due to the completion of a Use Attainability Analysis in 2007, this segment is now 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" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the approximately 20 samples collected during the recreational seasons of 2010, 2011, and 2012 at each of the four Section 319 monitoring stations in this assessment segment were as follows:
1. Site 6 (190th Street): 2010 geometric mean was 794 orgs/100 ml (10 samples);
2. Site 7 (at Hwy 69): 2010 geometric mean was 483 orgs/100 ml (9 samples);
3. Near Garner: geometric means were 534 orgs/100 ml (2010, 10 samples), 408 orgs/100 ml (2011, 12 samples), and 129 orgs/100 ml (2012, 13 samples)
4. Site 5a (at 200th Street): geometric means were 713 orgs/100 ml (2010, 8 samples), 448 orgs/100 ml (2011, 12 samples), and 117 orgs/100 ml (2012, 12 samples)
From 66 to 90% of the samples at each of the Section 319 sites exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. Geometric means at all four sites exceeded the Class A1 geometric mean criterion of 126 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 3-35of U.S. EPA 1997b).
The Class B(WW-2) aquatic life uses remain assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring from May to November 2012 at stations 13410001 and 13410009. No violations of Class B(WW2) water quality criteria for dissolved oxygen or temperature occurred in the combined 26 samples analyzed from May to November 2012. None of the combined 20 samples at these station analyzed for ammonia during the May-November 2012 period violated Class B(WW2) criteria for ammonia. One of the 13 samples (8%) collected at station 13410009 violated the Class B(WW2) criterion for pH. The sample collected on August 1, 2012, contained a pH of 9.3 units, thus violating the criterion of 9.0 units. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen or pH, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station 13410009, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW2) criterion. Thus, the results of chemical/physical water quality monitoring in 2012 in this segment suggest that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported”.