Rock Creek IA 01-MAQ-4

Assessment Comments

Assessment remains based on results of ambient water quality monitoring conducted in 2001 by IDNR & UHL in support of TMDL development.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.   EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses.   According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters.   Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses remain “not assessed.”  The assessment of support of the presumptive Class B(WW1) aquatic life uses developed for the previous assessment/listing cycles (“fully supported”) remains valid for the 2010 cycle; no additional data have been generated for this assessment segment.   Data used for this assessment were collected in 2001 at the TMDL monitoring station at Highway 30 (STORET station 11230009).   This monitoring was part of IDNR/UHL monitoring conducted in support of the TMDL for lower Rock Creek.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are “not assessed” due to lack of water quality data upon which to base an assessment:  the TMDL monitoring conducted in 2001 did not include analysis for indicator bacteria.   Results of monitoring at the IDNR/UHL station at Highway 30 show no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the nine samples collected from March to November 2001.   These results suggest water quality adequate to fully support the presumptive Class B(WW1) aquatic life uses of this stream segment.   Although the data from the 2001 IDNR/UHL TMDL monitoring have aged beyond five years, and thus are no longer appropriate for developing a higher-confidence (i.e., “monitored”) assessment, these data remain useful for assessing the support of the aquatic life uses designated for this stream segment.   Due to the age of these data, however, the assessment type is considered “evaluated” (i.e., of lower confidence).