Impaired Waters Detail - Gunderson Valley Creek

Impaired Water - Gunderson Valley Creek (Gunderson Valley Creek)

Gunderson Valley Creek has not been assigned a designated use. Therefore, it falls into a default situation where the use may be any of the five fish and aquatic use classifications.2 It may or may not be able to support a trout fishery since the temperatures in this stream are at the maximum to support a coldwater fishery. At a minimum, it should be able to support a warmwater sport or forage fishery not dominated by tolerant eurythermal species. For purposes of this set of TMDLs, Gunderson Valley Creek is assumed to be able to support a coldwater fishery.

The coldwater IBI score for this stream, an overall indicator of fish community health, was zero and there are a number of other measures that indicate a severely degraded stream. Nutrient concentrations in this stream are very high. The mean of the total phosphorus concentrations during the 2001 growing season was 0.52 mg/l. The nutrient levels are particularly high during runoff events where total phosphorus concentrations were 4.3 mg/l on June 3, 2002 and 2.4 mg/l on June 11, 2002. A abitat survey was not conducted on Gunderson Valley Creek, but the sedimentation problem is readily apparent in the downstream portion of the stream near the confluence with Castle Rock Creek.

Dissolved oxygen levels do not meet the water quality criterion of 6 mg/l for a
coldwater stream (nor 5 mg/l for a warmwater sport or forage fishery stream). For example between June and August 2001, the minimum values occurring as part of a diel swing went down to 2.6 mg/l. Dissolved oxygen levels went below 6 mg/l on five (monthly) sampling dates in 2001 and 2002. Predawn levels were likely lower than these daytime samples. Such diel dissolved oxygen swings are indicative of nutrients supporting aquatic plant growth with in turn results in night time dissolved oxygen use.

Another concern is dissolved oxygen sue during summer storm events. The bacteria in the organic load carried in the runoff event use much of the dissolved oxygen and cause the levels to drop further. One such occurrence took place on August 5, 2002 and is described in the “Castle Rock Creek TMDL Project Final [Monitoring] Report”. This August event demonstrates the combination of dissolved oxygen being lowered by both nutrients (diel swings) and BOD (“slug load”). Manure runoff is the most likely cause of the further lowering of the dissolved oxygen. Gunderson Valley Creek also has high levels of ammonia and, based on very limited sampling, high levels of bacteria. The ammonia levels, however, do not exceed water quality criteria for either a coldwater of warmwater stream.

Based on this information, the TMDLs for Gunderson Valley Creek are developed for sediment to address the degraded habitat situation and for phosphorus to address the concerns with diurnal dissolved oxygen swings. There is no “critical” period for the sedimentation concern. The sediment is present throughout the year, although sediment loads from the watershed do come from runoff events. The “critical” period for phosphorus is summer base flow conditions. However, the phosphorus loads from runoff events - especially those in the growing season - are the source of the base flow phosphorus loads. There are no continuous discharge sources of phosphorus in the watershed.

6/28/2004

Gunderson Valley Creek sediment and TP TMDLs were approved by the USEPA August 20, 2004.

8/20/2004

Gunderson Valley Creek has not been assigned a designated use. Therefore, it falls into a default situation where the use may be any of the five fish and aquatic use classifications.2 It may or may not be able to support a trout fishery since the temperatures in this stream are at the maximum to support a coldwater fishery. At a minimum, it should be able to support a warmwater sport or forage fishery not dominated by tolerant eurythermal species. For purposes of this set of TMDLs, Gunderson Valley Creek is assumed to be able to support a coldwater fishery.

The coldwater IBI score for this stream, an overall indicator of fish community health, was zero and there are a number of other measures that indicate a severely degraded stream. Nutrient concentrations in this stream are very high. The mean of the total phosphorus concentrations during the 2001 growing season was 0.52 mg/l. The nutrient levels are particularly high during runoff events where total phosphorus concentrations were 4.3 mg/l on June 3, 2002 and 2.4 mg/l on June 11, 2002. A abitat survey was not conducted on Gunderson Valley Creek, but the sedimentation problem is readily apparent in the downstream portion of the stream near the confluence with Castle Rock Creek.

Dissolved oxygen levels do not meet the water quality criterion of 6 mg/l for a
coldwater stream (nor 5 mg/l for a warmwater sport or forage fishery stream). For example between June and August 2001, the minimum values occurring as part of a diel swing went down to 2.6 mg/l. Dissolved oxygen levels went below 6 mg/l on five (monthly) sampling dates in 2001 and 2002. Predawn levels were likely lower than these daytime samples. Such diel dissolved oxygen swings are indicative of nutrients supporting aquatic plant growth with in turn results in night time dissolved oxygen use.

Another concern is dissolved oxygen sue during summer storm events. The bacteria in the organic load carried in the runoff event use much of the dissolved oxygen and cause the levels to drop further. One such occurrence took place on August 5, 2002 and is described in the “Castle Rock Creek TMDL Project Final [Monitoring] Report”. This August event demonstrates the combination of dissolved oxygen being lowered by both nutrients (diel swings) and BOD (“slug load”). Manure runoff is the most likely cause of the further lowering of the dissolved oxygen. Gunderson Valley Creek also has high levels of ammonia and, based on very limited sampling, high levels of bacteria. The ammonia levels, however, do not exceed water quality criteria for either a coldwater of warmwater stream.

Based on this information, the TMDLs for Gunderson Valley Creek are developed for sediment to address the degraded habitat situation and for phosphorus to address the concerns with diurnal dissolved oxygen swings. There is no “critical” period for the sedimentation concern. The sediment is present throughout the year, although sediment loads from the watershed do come from runoff events. The “critical” period for phosphorus is summer base flow conditions. However, the phosphorus loads from runoff events - especially those in the growing season - are the source of the base flow phosphorus loads. There are no continuous discharge sources of phosphorus in the watershed.

5/2/2011

Gunderson Valley Creek sediment and TP TMDLs were approved by the USEPA August 20, 2004.

8/20/2004