Middle Fork Grand River IA 05-GRA-1378

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

The presumptive Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria at three monitoring stations that exceeded state water quality criteria: (1) Site MFGR1 (STORET station 11800001), (2) Site MFGR2 (STORET station 11800002), and (3) MFGR (REMAP #114). The geometric mean of indicator bacteria (E. coli) in the 12 samples collected during the recreational seasons of 2011 at Site MFGR1 was 1,085 orgs/100 ml. The geometric mean of indicator bacteria (E. coli) in the 12 samples collected during the recreational season of 2011 at Site MFGR2 was 956 orgs/100 ml, and the geometric mean of the 12 samples collected at MFGR (REMAP #114) was 1,435 orgs/100 ml. All 36 samples from these three station (100%) exceeded the Class A1 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”

The Class B(WW2) aquatic life uses are assessed (monitored) as “partially supporting” (IR 5b-v) based on biological data collected in 2010 and 2011 as part of the IDNR/SHL stream REMAP and SI/TMDL sampling projects. 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 benthic macroinvertebrate taxa and fish species 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 2010 FIBI score was 27 (fair) and the BMIBI score was 32 (fair). The 2011 FIBI scores were 10, 15 and 20 (all poor) and the BMIBI score was 35 (fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This segment passed the FIBI BIC 0/4 times and passed the BMIBI BIC 0/2 times in the last five years.

This aquatic life assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years during a recent five-year period.

Despite the indications of biological impairment, the results of grab samples analyzed for chemical/physical water quality parameters at the three monitoring stations in 2011 do not suggest impaired water quality conditions. There were no violations of Class B(WW2) criteria for the following parameters in the approximately 45 combined samples from these three stations in 2011: chloride (54 samples), dissolved oxygen (50 samples), ammonia (46 samples), pH (50 samples), and sulfate (54 samples). The only violations of a Class B(WW2) criterion were for water temperature, with one of 16 samples (<1%) in violation at MFGR (REMAP #114) and two of 15 samples (13%) in violation at Site MFGR2. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from Site MFGR2, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for water temperature. Thus, these results suggest that the Class B(WW2) uses should be assessed (monitored) as “fully supported.”

Contrary to the results of grab water monitoring, the results of continuous dissolved oxygen (DO) and temperature monitoring do suggest impaired water quality conditions. The lowest DO concentration recorded in 81 days of continuous monitoring was 3.8 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (4 mg/L) and the 16-hour DO criterion (5 mg/L) in 2 of 81 days each. The percentages exceeding the 24-hour and 16-hour DO criteria (2.5%) were less than (passing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level for the 24-hour analysis result was high (>90%). The maximum stream temperature recorded during the sensor deployment period was 39.8 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 52 of 81 days. The percentage exceeding (64.2%) was greater than (failing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(WW1) aquatic life use is assessed as impaired for stream temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the IDNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.