Assessment Comments
Assessment remains based on 2007 IDNR/SHL biological sampling data: FIBI = 78 (excellent); FIBI BIC = 52 and is also based on results of water quality monitoring from April to October 2011 at 135th Street (Site 5; STORET station 15960037).
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. 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.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supporting” (IR 5p) based on violations of water quality criteria. This is a new impairment for this assessment segment. The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “partially supporting” (IR 5p) due to violations of the Class B(WW1) criteria for pH in 2011; this is also a new impairment for this stream segment. Results of IDNR/SHL biological (REMAP) sampling in 2007, however, suggested “full support” of the aquatic life uses. The sources of data for this assessment include (1) results of 2007 IDNR/SHL biological sampling data and (2) results of water quality monitoring from April to October 2011 at 135th Street (Site 5; STORET station 15960037).
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 14 samples collected during the recreation season of 2011 at station 15960037 was 820 orgs/100 ml. Eleven of the 14 samples (79%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW1) aquatic life uses are assessed (monitored) as “partially supported” due to violations of Class B(WW1) criteria for pH at station 15960037. Four of the 14 samples (29%) collected from April to October 2011 exceeded the high pH criterion of 9.0 pH units with violation ranging from 9.2 to 9.7 pH units. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH or dissolved oxygen suggests impairment of aquatic life uses. Based on IDNR’s assessment methodology, these results suggest that the frequency of violations for pH is significantly greater than 10 percent; thus, these results suggest impairment of the Class B(WW12) aquatic life uses. None of the other parameters monitored (dissolved oxygen, ammonia, or temperature) violated their respective Class B(WW1) criteria the 14 samples collected during the April-October period of 2011.
In contrast, results of IDNR/SHL biological sampling suggested that the aquatic life uses should be assessed (evaluated) as “fully supporting” based on data collected in 2007 as part of the IDNR/SHL stream biological sampling program. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 FIBI score was 78 (excellent). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 52. Even though this site passed the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.
