Assessment Comments
Assessment is based on results of monitoring of a Clean Water Act Section 319 water quality project from March 2010 through September 2011.
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, this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. Thus, for the current assessment, the available water quality monitoring data was compared to the applicable Class A1 and Class B(WW1) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supporting” based on results of limited water quality information from a two-month period in 2011. The source of data for this assessment is the results of monitoring at Site 4 near 150th Avenue (STORET ID 13790003) conducted as part of a Clean Water Act Section 319 water quality project from March 2010 through September 2011.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as “not supported due to levels of indicator bacteria (E. coli) that exceed the Class A1 geometric mean criterion. Twenty-five samples were collected at Site 4: 15 samples were collected during the 2010 recreation season, and 10 samples were collected during the 2011 season. The geometric means of indicator bacteria (E. coli) in the samples collected during the recreational seasons of 2010 and 2011 at Site 4 were 252 and 733 orgs/100 ml, respectively. Eighteen of the 26 samples analyzed (72%) during the 2010 and 2011 recreation seasons exceeded the Class A1 single-sample maximum criterion sample maximum criterion of 235 orgs/100 ml. Both the 2010 and 2011 recreation season geometric means exceed Iowa’s Class A1 geometric mean criterion of 126 E. coli orgs/100 ml, thus indicating nonsupport of the Class A1 primary contact recreation uses. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean is greater than the respective criterion (126 orgs/100 ml for Class A1, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
Results of limited chemical/physical water quality monitoring conducted from April to June 2011 suggest good water quality conditions in this assessment segment. Five samples were analyzed from April to June, 2011, for dissolved oxygen, pH, ammonia, and temperature. None of these samples violated the respective Class B(WW1) criteria. The relatively small amount of data (5 samples over a three-year period) and relatively short monitoring period (April 21 to June 22) does not meet IDNR data quantity requirements (at least 10 samples collected over a three-year period) and thus does not allow development of a higher confidence assessment of the degree to which the Class B(WW1) aquatic life uses are supported. Thus, this assessment is considered of lower confidence (i.e., “evaluated”).
