Drainage Ditch 61 IA 06-LSR-1953

Assessment Comments

Assessment remains based on results of IDNR/UHL water quality monitoring conducted as part of TMDL development from March through September 2005 at station 11210001.

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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 (2012) 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 remain 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 September 2005 at station 11210001.   Because these data are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (lower confidence assessment.)

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 11210001.   Results of this monitoring show no violations of Class B(WW1) water quality criteria for conventional parameters dissolved oxygen or pH in the 12 samples collected or for ammonia in the 11 samples collected from March-September 2005.   One of the 12 samples violated the Iowa criterion water temperature  the water temperature of the sample collected on August 9, 2005 was 32.7 ○C, thus exceeding the water temperature criterion of 32 ○C.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations at this station during the 2004-2006 period for temperature (8%) does not suggest a water quality impairment.   These guidelines allow up to 10% violations of conventional parameters such as dissolved oxygen, pH, and water temperature before impairment of water quality is indicated.   The violation of the criteria for water temperature is likely related to naturally-occurring conditions (bright sunshine, warm air temperatures, and a small prairie stream) and does not reflect the influence of anthropogenic pollutants.