Assessment Comments
Assessment remains based on results of (1) 2001 IDNR/UHL biological monitoring data collected upstream from the Milford WWTP and (2) IDNR/UHL TMDL monitoring in 2005.
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.
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 "partially supported" (IR Category 5b-t) based on results of biological monitoring conducted in 2001 for fish and aquatic macroinvertebrates. The sources of data for this assessment include results of (1) biological monitoring conducted by IDNR/UHL in September 2001 and (2) IDNR/UHL TMDL-related monitoring from July to September 2005 at two locations upstream from the Milford wastewater treatment plant and below the Lower Gar Lake outlet at TMDL Site 50 (STORET station 11300001) and downstream from the Milford wastewater treatment plant at TMDL Site 3 (STORET station 11300012).
The decision to consider this assessment as “evaluated” (lower confidence; used for Section 305(b) reporting only) versus “monitored” (higher confidence; used for Section 303(d) listing) is based on the relatively few samples collected (four at each site; total of eight samples). According to IDNR’s methodology for Section 305(b) assessments and Section 303(d) listings, at least 10 samples over a three-year period are required to develop a higher confidence (“monitored”) assessment that can support a Section 303(d) listing. Also, the difficulty of assessing headwaters using biological assessment protocols based on reference conditions in designated use (Class B(WW2) and wadeable Class B(WW1)) streams. Despite this rationale, U.S. EPA Region VII considered this assessment segment as pollutant-impaired in their May 23, 2006 transmittal of Iowa's final 2004 Section 303(d) list and thus added this segment of Milford Creek to Category 5a (=Section 303(d) list) of Iowa's 2004 Integrated Report as "monitored/partially supported." This segment was also included on Iowa’s 2006, 2008, and 2010 Section 303(d) lists and remains on Iowa’s 2012 list.
EXPLANATION: The presumptive Class A1 primary contact recreation uses remain "not assessed" due to the lack of information upon which to base an assessment. The TMDL-related monitoring conducted by IDNR/UHL in 2005 did not include analysis for indicator bacteria.
The presumptive Class B(WW1) aquatic life uses remain assessed as "partially supported" (IR Category 5b-t) based, in part, on data collected in 2001 as part of the IDNR/UHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and 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) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The FIBI score was 39 (fair); the BMIBI score was 14 (poor). The aquatic life use support was assessed (evaluated) as partially supported (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
This biological assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for headwater streams. Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. IDNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality. Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams. For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”. As noted above, however, U.S. EPA Region VII disagreed with this rationale and considered this assessment segment as pollutant-impaired in their May 23, 2006 transmittal of Iowa's final 2004 Section 303(d) list and thus added this segment of Milford Creek to Category 5a of Iowa's 2004 Integrated Report as "monitored/partially supported." This segment was also included on Iowa’s 2006 and 2008 Section 303(d) lists and remains on Iowa’s current (2012) list.
Results of IDNR/UHL chemical water quality monitoring in this stream segment show relatively good water quality, especially given the tendency for low-flow or no-flow conditions in this assessment segment. None of combined eight samples collected from July through September 2005 violated Class B(WW1) water quality criteria for pH (range of 6.8 to 8.4 units), water temperature (maximum of 25.9C), or ammonia-nitrogen (maximum value = 0.82 mg/l). Two of the four samples collected at TMDL Site 50 below the Lower Gar Lake outlet structure violated the Class B(WW1) criterion for dissolved oxygen. The samples collected on August 30 and September 14, 2005, both contained 3.6 mg/l of dissolved oxygen, thus violating the Class B(WW1) criterion of 5.0 mg/l. The segment of Milford Creek between the Lower Gar Lake outlet and the outfall of the Milford wastewater treatment plant monitored by TMDL Site 50 is prone to low-flow or no-flow conditions in summer and fall as levels of Lower Gar Lake fall below the height of the outlet weir. That levels of dissolved oxygen would occasionally fall below the Class B(WW1) criterion in this typically marginal stream habitat is not surprising. Due to the low number of chemical/physical water quality samples collected, the aquatic life uses of this segment of Milford Creek remain assessed (evaluated) as “partially supported” based on results of biological monitoring in 2001.
