Rock Creek IA 01-MAQ-4

Assessment Comments

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

Basis for Assessment

[Note:  Prior to the current (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 (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The assessment of support of aquatic life uses developed for the 2002, 2004, and 2006 assessment/listing cycles remains valid for the 2008 cycle; no additional data have been generated for this assessment segment.   The general uses of this segment of Rock Creek remain assessed (evaluated) as "fully supported."  Data used for this assessment were generated in 2001 as part of IDNR/UHL monitoring conducted in support of the TMDL for lower Rock Creek.  

EXPLANATION:  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 general 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).