Background. Oso Watershed Land Uses

Transcription

1 Monitoring and Modeling of the Oso Creek and Oso Bay Watershed, Texas for a Bacteria TMDL Background Oso Creek and Oso Bay were identified as impaired segments in the 24 Texas Water Quality Inventory and 33(d) list for the parameter bacteria. Joanna Mott, Richard Hay, Zeke Campbell and Russell Carden. Texas A&M University-Corpus Christi, Texas A monitoring and modeling project was developed with funding from the Texas Commission on Environmental Quality (TCEQ) to: identify potential sources of contamination and calculate current loading, allowed load and load reductions of the fecal indicator enterococcus. Oso Watershed Land Uses Land Use Types Percent Planted/Cultivated Urban Development Grasslands Water Shrubland Wetlands Forested Upland Barren

2 Permitted Dischargers Total of 1 permitted dischargers 6 major dischargers (> 1MGD) 2 industrial 4 municipal 4 minor dischargers (< 1MGD) 1 industrial 3 municipal Permitted Discharger Permit No. Permitted Daily Avg. Flow (MGD) American Electric and Power Barney Davis Power Station City of Corpus Christi Oso WWTP City of Corpus Christi Greenwood WWTP Texas A&M University CBI La Coss Facility City of Robstown Equistar Chemical LP Corpus Christi Plant Tennessee Pipeline Construction Co. Cuddihy Airfield WWTP Corpus Christi Peoples Baptist Church Roloff WWTP Texas A&M University Agriculture Research Ext. City of Corpus Christi Storm Water NA Indicator: Enterococcus Oso Bay marine, Oso Creek part tidal, part freshwater Current EPA recommended bacterial indicator for marine (and fresh water) All water samples were analyzed for enterococci using EPA Method 16. Water Quality Standard Contact Recreation Geometric mean (GM): 35 cfu/1 ml Single sample (SS): 89 cfu/1ml (Incorrect) Proposed WQS revisions for SS criteria: 158 cfu/1 ml for moderate recreation use (i. e. away from swimming beaches) 14 cfu/1 ml for high recreation use (i.e. within 1, feet of shore in swimming beach areas) Water Quality Standard Assessment criteria Fully supporting if geometric mean < criterion and 25% of time or less, concentrations are < single sample criterion. - Not supporting if geometric mean > standard, or if concentrations are > single sample standard more than 25% of time. Review of Enterococcus Data TCEQ TRACS Data Period of Record Frequency of Data Collection Quarterly (Stations 1328 and 1344) Monthly (Oct 1999-Sep 2) 2

3 Enterococci Single Sample Exceedence of the Criterion (14 cfu/1 ml) Enterococci Geometric Mean (35 cfu/1 ml) Percent (%) cfu/1ml TCEQ Station TCEQ Station cfu/1 ml Wet Weather Enterococci Sampling 14-Mar- 15-Mar- 17-Mar- 12-Apr Study Strategy: Determine the potential sources of enterococci in the watershed by analyzing data from both targeted and ambient stations Sampling Stations Ambient 11 stations in creek/bay Historical data for 8, 3 new upstream stations Representative of watershed Targeted (after rainfall) 11 stations throughout watershed potential sources Source Assessment Sanitary Survey to assess possible sources Sample 3-5 days Potential sources Urban runoff Rural community (septic systems) Agricultural runoff Livestock Landfill runoff 3

4 Source Assessments Downstream from WWTPs Oso Bay (S1) Robstown (WWTP ditch) S7 Landfill runoff: S8 Rural communities (septic system, animals): S9 S1 Source Assessments Livestock Open storm ditch (S5) Urban runoff ditches S2, S6, S3 Agriculture S4 Oso golf course S11 Field Parameters Hydrolab H2 Multiprobe Water Quality Monitor Dissolved oxygen (DO) Conductivity Water temperature Salinity ph Days since last significant rainfall Rainfall: 24 hr, 7 day Water observations color, odor, surface Secchi disk transparency Flow Tide stage Air temperature Weather (cloudy, etc.) Wind intensity, direction Sampling Plan Salinity dry weather May 19, 25 - June 8, 26 Monthly: 11 ambient (in creek/bay) stations Weekly: Ambient stations for two months Daily for 5 days following rainfall : Ambient + targeted (22 stations) Salinity (psu) /19/5 6/19/5 7/19/5 8/19/5 9/19/5 1/19/5 11/19/5 12/19/5 1/19/6 2/19/6 3/19/6 4/19/6 5/19/

5 Exceedance dry weather SS % Exceedance Dry Weather Exceedance wet weather % Exceedance Wet Weather % (percent) CFU/1ml 158 CFU/1ml 89 CFU/1ml % (percent) CFU/1ml 158 CFU/1ml 89 CFU/1ml Station I.D Statio n I.D Exceedance: : targeted stations % (percent) % Exceedance Wet Weather S1 S2 S3 S4 S5 S6 S7 S8 S9 S1 S11 Station I.D. 14 CFU/1ml 158 CFU/1ml 89 CFU/1ml Bacteria (cfu/1ml) Bacteria concentrations Dry day sample concentrations only Geometric mean for all collected data at 1327 Geometric mean for dry day concentrations only Geometric mean rule 35 cfu/1ml 8-May-5 7-Jul-5 5-Sep-5 4-Nov-5 3-Jan-6 4-Mar All Dates Rule GM 1327-dry Station GM Dry Station GM Does not meet geometric mean rule for wet or dry conditions. Must meet dry conditions first! Results Oso Creek Oso Creek bacteria levels exceeded standards for many dry weather events as well as following rainfall events. Targeted stations sampled following rainfall provided insight into loading from a variety of sources Bacteria (cfu/1ml) Bacteria Concentrations Dry day sample concentrations only Geometric mean rule 35 cfu/1ml Geometric mean of all days Geometric mean for dry day concentrations only 8-May-5 7-Jul-5 5-Sep-5 4-Nov-5 3-Jan-6 4-Mar Rule GM Station GM dry Dry Station GM Both wet and dry conditions meet geometric mean! 5

6 Results Oso Bay With the exception of 1 station in Oso Bay (which has been identified as not representative of the bay) there were no load reductions needed to meet water quality goals Modeling A numerical bacteria loading model was developed and the required load reduction was calculated as the difference between the current loading and the allowed loading Daily Model Set-up Modeling Process Calibration period. 1/1/1999 9/31/2. Inputs. Precipitation (NEXRAD). Hourly grids combined into 1 daily grid. Runoff. Bacteria loadings for each sub-basin. basin. Initial bacteria input for each station. Land use (Event Concentrations) 12 time step intervals. Look at decay process every 2 hours. Time of flow. Nontidal stations. Calculate velocity. Tidal stations. Calculate residence times. Bacteria from upstream station depends on: Flow of water from station. Volume of water in stream. Decay Rates From station upstream Runoff Coefficient Runoff Along each subwatershed Calculate Decayed Loads Rain * Runoff Load Sum Loads EC Repeat for next subbasin Point Source Load Dry Day Loading Subbasin Locations Model Results 6

7 Model Performance RMSE of log(concentration) Current data RMSE(log) Overall RMSE(log) by Station Daily Model for Current Data Stations Overall RMSE.68 log of Concentration Bay stations exhibit higher error but concentrations are low RMSE Data Variability Overall RMSE Bias in Measured and Modeled Data Measured data over current study period has 1/3 of the data collected in association with rain events. Measured data over the calibration period also had 1/3 of the data associated with rain events Only about 1/5 of the year is rainy. Modeled Load 2485a Modeled Load for non-tidal creek stations All exceed geometric mean criteria and single sample criteria Model Load w/ Dry Load in creek 1.71E E E+16 GM Concentration from Model % Exceedence from Model Modeled Load for tidal creek stations All exceed geometric mean criteria and single sample criteria Model Load w/ Dry Load in creek 2.1E E E+16 GM Concentration from Model % Exceedence from Model Modeled Load 2485 Modeled Load for bay stations. All meet geometric mean and single sample criteria Model Load w/ Dry Load in creek 9.46E E E+15 GM Concentration from Model % Exceedence from Model What is responsible for the exceedances? Dry day loading occurs every day. This keeps daily bacteria concentrations high. High daily concentrations cause the segment to violate the geometric mean criteria. Dry Day Loading Loading not associated with runoff events. Supports high bacteria concentrations without runoff input. Major factor in non-attainment for the creek section. Potential source for dry day loading: Ground water influx (septic systems). Bacteria flux from soils. Birds nesting under bridges. Wildlife or other animals in creek. Illegal discharge to stream. Leaking utilities. Natural bacterial growth. 7

8 Modeled load with no Dry Day Load - Creek Loading and concentrations for non-tidal creek section after removing dry day load contribution Model Load w/o Dry Load in creek 1.7E E E+16 GM Concentration from Model % Exceedence from Model Loading and concentrations for tidal creek section after removing dry day load contribution Model Load w/o Dry Load in creek 2.3E E E+16 GM Concentration from Model % Exceedence from Model Load Reductions Some creek segments meet Geometric Mean goals if dry day loading is eliminated! None meet Single Sample rule. Load reductions (modeled data) No Dry Day Load and reduction in runoff load of 93% (18499), 9% (185) Segment 2485a non- tidal Model Load w/nodry Load in creek 1.19E E E+15 GM Concentration from Model % Exceedence from Model Total Reduction 1.59E E E+15 Allowed Load 1.19E E E+15 No Dry Day Load and reduction in runoff load of 9% (16712), 5% (1327) - Segment 2485a tidal Model Load w/nodry Load in creek 6.64E E E+15 GM Concentration from Model % Exceedence from Model Total Reduction 1.44E E E+16 Allowed Load 6.64E E E+15 Load reductions (modeled data) No load reduction required in bay section (Segment 2485) Model Load w/ Dry Load in creek 9.46E E E+15 GM Concentration from Model % Exceedence from Model Loading on bay after upstream load reductions applied Model Load w/nodry Load in creek 6.52E E E+15 GM Concentration from Model % Exceedence from Model Load Distribution by Subbasin Annual Dry Loading WWTP Annual Loading Residential Urban Total Non- Point Source Load Upstream Load Station Crop Range Load Reductions NA NA All numbers are in 1 12 colony forming units Summary Segment 2485a (Oso Creek Tidal and non-tidal) cannot meet water quality goals without controlling Dry Day Loading and Runoff Loading. Dry day loading must be eliminated to meet geometric mean rule. Runoff loading in subbasin must be reduced by 93%. Runoff loading in subbasin 185 must be reduced by 9%. Runoff loading in subbasin must be reduced by 9%. Runoff loading in subbasin 1327 must be reduced by 5%. Most of segment 2485 (Oso Bay) meets water quality goals especially if sample collection is more representative of annual dry/wet day distribution Oso Bay TMDL report prepared by TCEQ 8

9 Summary What Next? Water quality objectives for Oso Creek could be met by removing dry day loadings from all creek sub- basins and runoff loadings from 4 of the sub-basins. basins. Dry day loading in Oso Creek is a critical element in the bacteria loading of Oso Creek; however, its source(s) are unknown and will need to be identified in order to develop and implement a load reduction strategy for Oso Creek. Modeled loadings more representative of wet and dry periods than measured loadings Potential sources of dry day loading Ground water interaction with Oso Creek/Oso Bay Wildlife or other animal input Natural growth of bacteria in the creek Upper sub-basin basin source(s) of loadings Bacterial Source Tracking (Animal) Physical Source Tracking Sediment /soil studies Continued collaboration for agricultural runoff (TAES, USGS) Questions? Event Mean Concentrations Daily model with bihourly calculations required data representing actual runoff concentrations not mean concentrations over a runoff event Back calculated runoff concentrations from measured values at 1851 based on an average observed decay rate ( 2.) This estimates a runoff concentration 7 times higher that the previously applied event mean concentrations. Decay Rate Two distinct salinity zones Low salinity zone above 1327 (Staples) High salinity below Barney Davis outfall (Yorktown) Constrained by literature values for enterococci Values (calculated from observed data but constrained by literature values for enterococci ) Low salinity zone 2. (1.1 days for 9% die off) High salinity zone 4. (.57 days for 9% die off) Event Concentrations Event concentrations correspond to the actual bacteria concentration of the runoff water (first flush) EMC values were as high as 47,88 cfu/1ml EC values are now as high as 353, cfu/1ml EC values are in the range of those reported by the City of Corpus Christi in a storm water assessment program for some urban runoff (33, cfu/1ml to 445, cfu/1ml for Fecal Coliform bacteria) 9

10 Dry Day Loading Bacteria loadings were noted to occur without the driving force of precipitation Although the source is unknown, an estimate can be made of the magnitude of the loading This estimate was fitted into the model for each subbasin. Dry Day Loading was applied to the model as a constant for each subbasin with no temporal variation Dry day load ranges from 1 8 bacteria (in a segment) to 1 11 bacteria. Summary (continued) Station (in segment 2485 Oso Bay) does not meet water quality goals. Load reduction. Dry day loading must be reduced by 75% (4.7x1 12 ). Removal of runoff loading does not reduce load enough to meet geometric mean rule. Removal of load from Oso WWTP does not reduce load enough to meet geometric mean rule or the single sample rule. Station may not be representative of ambient conditions in Oso Bay. Does not respond in a similar fashion to other stations. Is not in the direct flow pattern of the Oso Bacteria (cfu/1ml) Bacteria Concentrations Dry day concentrations Geometric mean of all data for station (134) Geometric mean of dry day concentrations Geometric mean (95) rule (35 cfu/1ml) 8-May-5 7-Jul-5 5-Sep-5 4-Nov-5 3-Jan-6 4-Mar-6 Rule GM Station GM dry Dry Station GM Does not meet GM rule on dry days. Model loadings for Modeled load with dry day loadings. Model Load w/ Dry Day Load 2.64E+13 GM Concentration from Model % Exceedence from Model Modeled load with no dry day loading. Model Load w/o Dry Day Load 2.1E+13 GM Concentration from Model % Exceedence from Model Station Has been modeled as a tributary and not part of the ordered stream flow from Robstown to Corpus Christi Bay. Station responds differently than the other bay stations. Salinity similar to creek stations. Poorest model fit (compared to other stations) perhaps due to seasonality in dry day loading. Dry day loading might be attributed to shore bird population. Annual Load Reduction for 75% Load reduction of dry day loadings. 75%Reduction in Dry Day Load 2.17E+13 GM Concentration from Model % Exceedence from Model 27.5 Load Reduction 4.74E+12 Without runoff loading(1.96x1 13 bacteria). Without Runoff Load 7.E+12 GM Concentration from Model % Exceedence from Model Load Reduction 1.94E+13 Remove Annual Oso Load with WWTP no Oso WWTP Load (7x1 11 bacteria). 2.57E+13 GM Concentration from Model % Exceedence from Model Load Reduction 6.77E+11 1

11 Log Normal Distribution of Bacteria Concentrations (loading) at Station with no Loadings dry at day loading. Log(Concentration) Meets both criteria Probability Data Log Normal fit to data LogNormal fit to GM Log normal fit to SSC 25% exceedance Geometric Mean Single Sample Criteria 5% exceedance Model with Dry Load Results Enterococci numbers increase dramatically 1-2 days after rainfall Stay elevated 3-5+ days depending on rainfall Ambient stations exceeded both standards 27-1% after rainfall depending on station Targeted stations exceeded standards 39-1% after rainfall depending on station June Rain Event (26) June Rain Event (26) Ambient Stations Targeted Stations CFUs/1ml (log scale) Day 1 Day 2 Day 3 Day 4 Day 5 CFUs/1ml (log scale) S3 S7 S9 S8 S4 S1 S2 S6 S5 S11 S1 Day 1 Day 2 Day 3 Day 4 Day 5 Station I.D. Station I.D. Results Volumes Ambient freshwater stations exceeded 39-1% of the time for dry sampling dates Targeted stations sampled during dry weather exceeded standards Main channel volumes. Inputs. Upstream flow. Runoff. Additional sources (Robstown, Greenwood, Oso WWTPs, and Barney Davis power plant). 11

12 Average Monthly Flow at Barney Davis Power Plant Model Performance RMSE of log(concentration) Historic data Historic Data on Daily model with Dry loads upcreek Flow (MGD) RMSE(log) RMSE(log) Data Variability Overall Model RMSE 1.5 Jan-98 Jul-98 Jan-99 Jul-99 Jan- Jul- Jan-1 Jul-1 Jan-2 Jul-2 Jan-3 Jul-3 Jan-4 Jul Stations Overall RMSE 1.4 log of Concentration Bay station exhibit higher error but concentrations are low Log Normal Distribution of Bacteria Concentrations (loading) at Station 1327 Loadings at Red lines show a log-normal distribution of bacteria 6. concentrations that meet (just) Single Sample rule no more that 25% of values can Green lines show a log-normal distribution of 5. Data exceed 14 cfu/1ml Data Data Log Normal fit to data LogNormal fit fit to to GM data bacteria concentrations that meet (just) the LogNormal fit to GM 4. LogNormal normal fit fit to GM SSC Log normal fit to SSC 25% Log normal exceedance fit to SSC 25% exceedance Geometric Mean rule GM of ten samples must Geometric 25% exceedance Mean Geometric Mean 3. Single Geometric Sample Mean Criteria Single Sample Criteria 5% Single exceedance Sample Criteria be less than 35 cfu/1ml 5% exceedance 5% exceedance Model with Dry Load 2. Model loads for 365 days 1. Bacteria concentrations measured in this project. Log(Concentration) Probability Log-normal fit to data measured in this project Critical rule Geometric Mean Log Normal Distribution of Bacteria Concentrations (loading) at Station Log(Concentration) Meets both criteria Loadings at Probability Data Log Normal fit to data LogNormal fit to GM Log normal fit to SSC 25% exceedance Geometric Mean Single Sample Criteria 5% exceedance Model with Dry Load Log Normal Distribution of Bacteria Concentrations (loading) at Station 1327 with no dry day loading Loadings at 1327 Conclusion 7. Log(Concentration) Probability Data Log Normal fit to data LogNormal fit to GM Log normal fit to SSC 25% exceedance Geometric Mean Single Sample Criteria 5% exceedance Model with Dry Load Suggest large amount of dry daily loading Enterococci in water column or sediments Meets only Geometric Mean rule. 12

13 Outline Pathogen sources and transport Background Sampling Bacteria concentration measurements Dry day loading Ground water Fitting model to data Model performance Model results Load reductions Station Point sources Direct transport from source Wastewater Treatment Plant (WWTP) effluent Combined sewer overflows Sewer overflows Animal feeding operations Slaughterhouses Fish and Shellfish processing facilities Non-point sources Diffuse, hard to define and wide geographic area Urban Domestic pets Wildlife excrement Failing sewer lines Rural areas Leaking septic system Land application of manure Wildlife excrement Livestock Modeled load with No Dry Day Load - Bay Loading and concentrations for bay section without dry day loading Model Load w/o Dry Load in creek 9.16E E E+15 GM Concentration from Model % Exceedence from Model Stations continue to meet water quality goals 13