Montgomery Creek IA 03-SSK-6508
from mouth (SE1/4 NE1/4 S35 T85N R25W Boone Co.) to headwaters (NW1/4 S22 ST85N R26W Boone Co.)
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 5/7/2019 1:49:00 PM
- Updated
- 7/19/2019 11:26:36 AM
The presumptive Class A1 (primary contact recreation) uses remain assessed as “partially supporting” due to levels of indicator bacteria that exceed Iowa water quality criteria. The presumptive Class B(WW1) aquatic life uses are assessed as “fully supporting” based 2013 biological sampling data. The sources of data for this assessment are (1) the results of monitoring at Iowa DNR snapshot monitoring station SC-11 (STORET station 908020) conducted as part of Iowa DNR water quality snapshot monitoring from 2008 through 2012 and (2) an DNR/SHL biological sample collected near Gilbert in 2013.
The Class A1 (primary contact recreation) uses remain assessed as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 10 samples collected during the recreational seasons of 2008 through 2012 at station SC-11 was 465 orgs/100 ml, thus exceeding the Class A1 criterion of 126 orgs/100 ml. Seven of the 10 samples (70%) 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 DNR’s assessment/listing methodology, if a the geometric mean of at least 10 samples collected over five years of snapshot monitoring exceeds the respective water quality criterion, the contact recreation uses should be assessed as "not supported". Thus, because the geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” This evaluated biological assessment was based on data collected in 2013 as part of the DNR/SHL headwater stream sampling project. A series of biological metrics that 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 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 2013 FIBI score was 50 (fair) and the BMIBI score was 66 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The stable riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62. Even though this site passed both the FIBI BIC (with the aid of the FIBI UAV of 7 points applied to single samples) and BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small presumed BWW1 (formally general use) stream and doesn’t fall in the calibrated watershed size.