Walnut Creek IA 02-IOW-709
from confluence with North Walnut Cr. (S7 T81N R13W Poweshiek Co.) to confluence with unnamed tributary in NW 1/4 S24 T81N R15W Poweshiek Co.
The presumptive Class A1 use remains assessed as “not supported” due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use was assessed as “not supported” based on biological sampling data. Note: A TMDL covering the bacteria impairments for all segments, with the segment code prefix "IA 02-IOW" in the Iowa River Basin, was approved by EPA in 2018. Due to the completion of the TMDL, the IR category for the presumptive Class A1 use was changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved). Because not all impairments identified for this segment are covered by the TMDL, this segment remains in Category 5 of Iowa's Integrated Report (impaired; TMDL needed).
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 BIO See Below 1231 Walnut Creek NW of Hartwick (REMAP
#418) Iowa DNR 6 WQ CY 2010-2011 13790008 Walnut Creek near
Hartwick Site WLNT-1 Iowa DNR 6 WQ CY 2010-2011 13790002 Walnut Creek at 328
AVE Site 2m Iowa DNR 6 WQ CY 2010-2011 13790004 Walnut Creek near
150 ST Site 4m Site ID Data Source ID # Samples / # Years 2010 Geometric Mean 2011 Geometric Mean Annual Geometric Mean Violation # Violations % Violations Significantly >10% Violations Assessment Type Support Level 13790008 6 25 / 2 750 1105 Yes 22 88% Yes Evaluated Not 13790002 6 25 / 2 727 977 Yes 21 84% Yes Evaluated Not 13790004 6 25 / 2 541 917 Yes 21 84% Yes Evaluated Not Site ID Date Drainage Area (mi2) Ecoregion Major Drainage BM Sample Gear BMIBI score BMIBI Class 47f BMIBI BIT BMIBI Pass/Fail 1231 8/11/22 40.7 47f MS Art Sub 39 Fair 51 Fail 1231 8/15/19 40.7 47f MS Art Sub 58 Good 51 Pass Site ID Date Drainage Area (mi2) Ecoregion Major Drainage Riffle Stream? FIBI score FIBI Class 47f FIBI BIT FIBI Pass/Fail 1231 8/11/22 40.7 47f MS NA 26 Fair 36 Fail 1231 8/15/19 40.7 47f MS NA 40 Fair 36 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic
Macroinvertebrates Evaluated Fail (1/2) Not Fish Evaluated Fail (1/2) Not Assessment was evaluated because although
the assessment used Overall Evaluated Fail Not 5bt multiple samples collected in the last five
years, it was inconclusive.
Presumptive Class A1 – Indicator Bacteria: 2010-2011
Class BWW2 - Biological Sampling:
Benthic Macroinvertebrates:
Fish:
Overall: