Unnamed Tributary to Williamson Pond IA 04-LDM-1965

Assessment Comments

Assessment remains based on results of IDNR/UHL water quality monitoring conducted as part of TMDL development from March through June 2005 at station 11590001.

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(WW1) water quality criteria.   This waterbody has not been assessed for Section 305(b)/303(d) purposes prior to the current (2008) assessment/listing cycle.]

SUMMARY:  The presumptive Class A1 primary contact recreation uses remain “not assessed” due to the lack of information upon which to base an assessment.   The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supported” based on results of chemical/physical water quality monitoring during 2005.   The source of data for this assessment is the results of IDNR/UHL water quality monitoring conducted as part of TMDL development from March through June 2005 at station 11590001.  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses remain “not assessed” due to the lack of data for indicator bacteria (E.   coli) upon which to base an assessment.   The TMDL monitoring conducted at this station in 2005 did not include monitoring for indicator bacteria.  

The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of IDNR/UHL TMDL-related water quality monitoring conducted in 2005 at station 11590001.   Results of this monitoring show no violations of Class B(WW1) water quality criteria for conventional parameters dissolved oxygen or pH) or for ammonia in the five monthly samples collected from March-June 2005.   The number of samples collected at this station (five) is relatively low and does not meet IDNR guidelines for developing a “monitored” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period).   Thus, the assessment type is considered “evaluated” (lower confidence).