Rock Creek IA 02-CED-586
from confluence with unnamed tributary (NW 1/4 SE 1/4 S17 T97N R17W Mitchell Co.) confluence with Goose Cr. in S35 T98N R18W Mitchell Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 5/13/2019 2:08:35 PM
- Updated
- 7/17/2019 9:03:06 AM
The presumptive Class A1 (primary contact recreation) remain assessed as “partially supported” due to violations of water quality criteria for indicator bacteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supported" based on results of (1) DNR/SHL biological sampling conducted in 2002, 2009 and 2013 as part of the stream biocriteria project and (2) chemical/physical water quality monitoring in 2013. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment include (1) results of DNR/SHL biological sampling conducted in 2002, 2009 and 2013 as part of the stream biocriteria project, (2) results of chemical/physical water quality monitoring conducted at STORET station 14000132 near Foothill Avenue from 2014 through 2016.
The presumptiveClass A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 16 samples collected during the recreational seasons of 2014 through 2016 at station 14000132 were as follows: the 2014 geometric mean was 271 orgs/100 ml, the 2015 geometric mean was 473 orgs/100 ml, and the 2016 geometric mean was 512 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Thirteen of the combined 16 samples (81%) 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 "partially supported." Results of chemical/physical water quality monitoring at station 14000132 suggest (evaluated) “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 3 Dissolved Oxygen samples (minimum = 8.5 mg/L), 9 pH samples (range = 7.5 to 8.2), or 9 Temperature samples (maximum = 21.9°C) occurred during monitoring from July 2015 to October 2016. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses. A fish kill occurred on in this stream segment on July 27, 2002 and was used for historic aquatic life assessments in this segment. However, based on the 2013 water quality sampling and the 2009 and 2013 biological sampling, any impairment caused by the 2002 fish kill no longer exists. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple samples collected in a recent 15 year period (2002-2016).