Dry Run IA 02-CED-554
mouth (S18 T89N R13W Black Hawk Co.) to confluence with unnamed tributary in S23 T89N R14W BlackHawk Co
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 8/16/2016 4:48:28 PM
- Updated
- 9/29/2016 9:12:14 AM
The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported” (IR 5a) due to levels of indicator bacteria that exceed state water quality criteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as "partially supported" (IR 5b-v) based on results of biological sampling in 2010, 2011 and 2013. This stream was added to Iowa’s 2002 Section 303(d) list of impaired waters based on results of IDNR/SHL biological (biocriteria) sampling in 1999 that showed a failure of aquatic life present in Dry Run Creek to meet regional expectations. The sources of data for this assessment include (1) the results of chemical and physical water quality monitoring conducted on Dry Run Creek from April 2013 through October 2014 at three stations sampled as part of the Dry Run Creek Watershed Project: Site 1 at Cedar Falls (STORET station 11070006), Site 4 at Cedar Falls (STORET station 11070007), and Site DRC3 at 18th Street (STORET station 15070002) and (2) the results of Section 319 bacteria monitoring at these four stations (DRC-4, DRC-1, and DRC-3) from August 2012 through October 2014. The assessment of “partial support” of the Class B(WW2) aquatic life uses remains based on results of IDNR/SHL biological sampling conducted in 2010, 2011 and 2013.
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 means of indicator bacteria (E. coli) in the approximately 24 samples collected during the recreational seasons of 2012, 2013, and 2014 at each of the three Section 319 monitoring stations in this assessment segment were as follows:
1. DRC-3, (15070002): geometric means were 317, 920, and 232 orgs/100 ml;
2. DRC-1 (11070006): geometric means were 513, 1,114, and 320 orgs/100 ml;
3. DRC-4 (11070007): geometric means were 170, 435, and 238 orgs/100 ml;
From 11 to 15% of the samples at each of the three Section 319 bacteria monitoring sites exceeded the Class A1 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 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, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
The Class B(WW2) aquatic life uses are assessed as “partially supported” based on biological data collected in 2010, 2011 and 2013 as part of the IDNR/SHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2010-2011 FIBI scores from DRC1 were 74 and 74 (both excellent); the 2010-2011 BMIBI scores at DRC1 were 47 and 49 (both fair). The 2010, 2011 and 2013 FIBI scores at DRC4 were 36, 38 and 34 (all fair); the 2010, 2011 and 2013 BMIBI scores at DRC4 were 57, 60 and 58 (all good). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The riffle site FIBI BIC is 65 and the natural substrate BMIBI BIC for this ecoregion is 70. Site DRC1 passed the FIBI BIC 2/2 times and passed the natural substrate BMIBI BIC 0/2 times. Site DRC4 passed the FIBI BIC 0/3 times and passed the natural substrate BMIBI BIC 0/3 times. Overall, this segment passed the FIBI BIC 2/5 times and passed the BMIBI BIC 0/5 times in the past five years. This assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years from 2010-2014.
Somewhat in contrast to the results of biological monitoring, results of chemical/physical monitoring conducted for the Dry Run Creek Watershed project from April 2013 through October 2014 suggested good water quality. Levels of dissolved oxygen did, however, occasionally violate Class B(WW2) criterion (5.0 mg/l). From 16 to 19 samples were collected at each of the three sample sites monitored during the 2013-2014 period (15070002, 11070006, and 11070007). None of the samples contained violations of Class B(WW2) water quality criteria for dissolved oxygen, ammonia, pH, chloride, or temperature. These results suggest “full support” of the Class B(WW2) aquatic life uses. Due, however, to results of biological monitoring from 2009-2011, the aquatic life uses of this assessment segment remain assessed as “partially supporting” (IR 5b-v).