Assessment Comments
Assessment is based on results of water quality monitoring, fish contaminant monitoring, and fish kill reporting conducted downstream from Red Rock Reservoir during the 2008-2010 assessment period by Iowa State University (under contract with the U.S. Army Corps of Engineers) at ISU/ACOE Station 9 at the Howell Station Landing (STORET station 17630001).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "fully supporting" based on results of routine monitoring for indicator bacteria (E. coli). The Class B(WW1) aquatic life uses remain assessed (monitored) as "not supported" due to repeated fish kills immediately downriver from Red Rock Dam. The fish consumption uses are assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2008, 2009, and 2010. The assessments of support of the beneficial uses are based on results of water quality monitoring, fish contaminant monitoring, and fish kill reporting conducted downstream from Red Rock Reservoir during the 2008-2010 assessment period by Iowa State University (under contract with the U.S. Army Corps of Engineers) at ISU/ACOE Station 9 at the Howell Station Landing (STORET station 17630001). This monitoring was conducted as part of the Des Moines River Water Quality Study (see Lutz and Steffen 2009, Lutz 2010, and Lutz 2011).
EXPLANATION: The Class A1 uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from the ISU/ACOE station 0.7 mi downstream from Red Rock Dam. The geometric means of indicator bacteria (E. coli) in the 27 samples collected during the recreational seasons of 2008 through 2010 at ISU/ACOE station 9 were as follows: the 2008 geometric mean was 4 orgs/100 ml, the 2009 geometric mean was 10 orgs/100 ml and the 2010 geometric mean was 13 orgs/100 ml. All three geometric means are far below Class A1 criterion of 126 orgs/100 ml. These geometric means are some of the lowest seen in Iowa’s ambient water quality monitoring networks and reflect the positive influence on water quality of the dam of Red Rock Reservoir just upstream from this monitoring station. None of the 27 samples 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 all recreation season geometric means meet the respective water quality criterion, the contact recreation uses are "fully supported".
Results from this ISU/ACOE monitoring station also suggest that the Class B(WW1) aquatic life uses are "fully supported"; however, the Class B(WW1) aquatic life uses remained assessed as "not supported" due to reoccurring fish kills in this river segment. No violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen, pH, ammonia-nitrogen) occurred in the 66 samples collected at this station during the 2008-2010 assessment period. A single violation of the chronic Class B(WW1) criterion for lead occurred in the 12 samples analyzed for toxic metals at this station. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), however, this one violation of a toxic contaminant does not suggest an impairment of the aquatic life uses.
The Des Moines River immediately downriver from Red Rock Dam is prone to fish kills caused by gas bubble trauma. For the period 1983 though 2008, 32 kills in the Red Rock Dam tailwater area have been attributed to gas bubble trauma (Lutz and Steffen 2009). Fish kills caused by gas bubble trauma occur due to a large imbalance between the concentrations of atmospheric gasses in the water and the levels of these gasses dissolved in the blood of the fish. The concentrations of dissolved gasses such as oxygen and nitrogen in river water tend to equal the concentrations in the blood of a fish. When the levels of atmospheric gasses dissolved in river water become very high (i.e., super-saturated)—such as can happen when water moves through or over a large dam—the levels of these gasses will also rise in the blood of fish. As long as fish can stay in deeper water, the hydrostatic (water) pressure will keep these gasses fully dissolved in the fish’s blood. If, however, the flow of water downstream from the dam is decreased suddenly, the depth of the water will also decrease. With shallower water, fish are not able to move to deeper areas to keep the hydrostatic pressure sufficiently high to keep the gasses fully dissolved in their blood. During these conditions, the gasses dissolved in the fish’s blood will gradually come out of solution as bubbles, and these bubbles will interfere with blood circulation. Symptoms of gas bubble trauma in fish include gas blisters on the skin at the margins of the scales and as pop-eye (exophthalmia) where the eyes of the fish distend from the eye sockets. In the extreme case, blood circulation is disrupted to the point that fish kills occur.
One fish kill caused by gas bubble trauma was reported for this river segment for the 2008-10 assessment period; this kill occurred in June 2008. There were no gas bubble-related fish kills reported for Station 9 during the 2009 and 2010 monitoring years. According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates that the aquatic life uses of a waterbody are only "partially supported.” Thus, due to the fish kill in 2008 period caused by gas bubble trauma, and due to the history of this type of fish kill in this river reach, the Class B(WW1) aquatic life uses remain assessed as "not supported” and will remain in IR Category 4c (i.e., impairment due to a non-pollutant stressor; TMDL not required).
Fish contaminant monitoring conducted downstream from Red Rock Reservoir by ISU/ACOE in 2008, 2009, and 2010 showed low levels of contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, trifuluralin, and chlorpyrifos) in composite samples of whole fish common carp. In addition, the 2009 and 2010 composite samples of whole-fish carp were analyzed for PCBs (Aroclors), and composite samples of fillets from a predator species (largemouth bass (Micropterus salmoides) and smallmouth bass, M. dolomieu) were analyzed for mercury. Levels of PCBs in composite whole-fish carp samples for all Aroclors analyzed (1016, 1221, 1232, 1242, 1248, 1254, and 1260) were all below levels of detection (range from 0.02 to 0.09 ppm). Average levels of mercury in the composite sample of largemouth bass fillets in 2009 was 0.12 ppm, and the average level in the composite sample of smallmouth bass fillets in 2010 was also 0.12 ppm. The levels of PCBs and mercury seen in fish tissue samples from ISU/ACOE station 9 downstream from Red Rock Dam are well below the one meal per week advisory trigger of 0.20 ppm for total PCBs (sum of Aroclors 1248, 1254, and 1260) and for mercury (0.30 ppm). Based on this information, fish consumption uses are assessed (monitored) as "fully supported".
The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2008, 2009, or 2010 ISU/ACOE samplings (or from previous ISU/ACOE monitoring) conducted in the segment of the Des Moines River immediately downstream from Red Rock Reservoir show that levels of contaminants (chlordane and mercury) do not exceed any of the IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
For more information on ISU/ACOE water quality monitoring in this river reach, see (Lutz and Steffen 2009, Lutz 2010, and Lutz 2011); the URL for the Des Moines River Water Quality Monitoring Network web site is http://home.eng.iastate.edu/~dslutz/dmrwqn/dmrwqn.html.
