Assessment Comments
Assessment is based on limited chemical/physical monitoring conducted in August 2006 as part of IDNR/UHL TMDL-related monitoring near Lanesboro (STORET station 11140003; TMDL site MaB2).
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(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 are assessed (evaluated) as “not supported” due to high levels of indicator bacteria. The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supported” based on results of IDNR/UHL TMDL-related chemical/physical water quality monitoring during 2006. The source of data for this assessment is the limited chemical/physical monitoring conducted in August 2006 as part of IDNR/UHL TMDL-related monitoring near Lanesboro (STORET station 11140003; TMDL site MaB2). This amount of data (two samples) does not meet IDNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected over a three-year period. Nonetheless, the limited data do suggest some directions in water quality that may be useful for interpreting results of monitoring in the downstream segment of Marrowbone Creek (IA 04-RAC-0123_0) that is Section 303(d) impaired.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (evaluated) as “not supporting” due to the high levels of indicator bacteria (E. coli) in the two available samples. The samples collected from this stream segment on August 15 and August 23, 2006, contained 250 and 2,800 orgs/100 ml, respectively. These data values are high relative to both Iowa’s geometric mean criterion (126 E. coli orgs/100 ml) and Iowa’s single sample maximum criterion of 235orgs/100 ml. While two few data are available to adequately demonstrate an impairment of the Class A1 uses, these moderately high levels do suggest at least the potential for impairment. Such assessments are appropriate for IR Categories 2b or 3b and are appropriate for addition to Iowa’s list of waters in need of further investigation.
The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “fully supported” based on results of IDNR/UHL TMDL-related water quality monitoring conducted in August 2006 at station 11140003. 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 two samples collected on August 15 and August 23, 2006. The number of samples collected at this station (two) is 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). The occurrence of much stronger levels of dissolved oxygen in this upstream (formerly, general use) segment of Marrowbone Creek (8.0 and 9.1 mg/l) is interesting given that levels of dissolved oxygen in the downstream segment on these same two dates were 0.2 and 0.0 mg/l, respectively.
