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MODELING ROLE IN SETTING SITE-SPECIFIC CRITERIA & DESIGNATED USES ANDY THUMAN

BACKGROUND

MODEL DEVELOPMENT

MODEL USE IN UAA

SUMMARY

Water quality modeling under contract to Kent County Department of Public Works (KCDPW) o Joint effort between the DNREC & KCDPW

Have been working on the Murderkill River modeling since the project started in 2007 o Have also completed other TMDL modeling projects for DNREC since 2001

24 years of experience in developing water quality models for permitting & TMDL projects o 20 years as part of HydroQual, last 4 with HDR

Thank you to: o Hassan Mirsajadi (DNREC) o Hans Medlarz (KCDPW) o All researchers providing data to support the modeling (DE DF&W, UDel, Stroud Water Research Center,

DGS, UnivMD (CBA), ANS-Drexel)

HDR (HYDROQUAL) INVOLVEMENT

DNREC listed the tidal Murderkill River on the State’s 303(d) impaired waters list for nutrients & dissolved oxygen (DO) o Existing DO levels are typically below the DO standards during the summer in the tidal river

DNREC completed a nutrient & DO TMDL in 2001 and amended it in 2005

This Murderkill River study was initiated to: o Collect additional data o Complete state-of-the-art modeling o Better understand the processes

controlling water quality

BACKGROUND

Tidal Reach (Above Route 1 Bridge near Frederica to mouth at Bowers Beach)

DNREC Routine Monitoring (>15,000 observations) o 16 stations in freshwater streams & tidal river (2x/month) o Nutrients, BOD5, carbon, chl-a, DO, temperature, salinity, Secchi depth, silica, TSS, turbidity, LTBOD o F&W Fish Surveys

USGS Continuous Monitoring (>2.5 million observations) o 3 freshwater flow gages o 3 tidal salinity, temperature, conductivity, elevation, flow/velocity gages

KCDPW Monitoring o Daily effluent monitoring & 15 effluent LTBOD tests

WATER QUALITY MONITORING

Algal Production Study (UDel – Dr. Sharp) o Used to estimate algal growth rate, algal production & light limitation o Limited correlation between nutrients/DO & primary production (light limited)

Tidal Marsh Loading Study (C/N/P/DO) o Used to assign nutrient, carbon & DO loading (source/sink) in model o Fluxes are variable (tidal, seasonal, storm)

Marsh Inundation Study (LiDAR) o Marsh elevation, tidal flooding area o Used to define marsh area along length of river

Sediment Flux Study o Measured SOD & nutrient flux from sediment to water column o Calibration parameter

Sediment Core Study

RIVER STUDIES

Three major model types used:

Watershed (HSPF): calculates rainfall driven runoff & loadings from land surface (land use, soils, topography)

Hydrodynamic (ECOMSED): calculates tidal circulation (freshwater flows, salinity/temperature, tides, meteorology)

Eutrophication (RCA): calculates nutrient driven effects on phytoplankton & DO levels o Includes sediment flux sub-model o Uses tidal marsh loads from studies

WATER QUALITY MODELING

MODEL COUPLING (WATERSHED TO RECEIVING WATER)

Delaware Bay

Tidal River

Watershed

Hydrodynamic Water Quality

EUTROPHICATION MODEL

Models setup for 2-year model calibration period o 2007-2008 (variable hydrology w/ low-flow summers) o Used extensive data from monitoring programs

Model calculations compared to observed data o This is “model calibration” o Models reproduced the observed data well

After calibration, models used in “projection” mode to assess factors controlling water quality o Kent County RWTF, tidal marshes, un-impacted o These model scenarios used to help develop site-specific DO criteria along with fish surveys in river

WATER QUALITY MODEL DEVELOPMENT

TN levels decreased by 0.09-0.40 mg/L TP levels decreased by 0.07-0.35 mg/L DO levels increased by 0.17-0.70 mg/L o 0.2-0.3 mg/L increase near DO sag location

Chl-a levels decreased by 0.9-1.2 µg/L

NO KCRWTF MODEL SCENARIO (SUMMER AVERAGE MODEL RESULTS)

TN levels decreased by 0.49-1.37 mg/L TP levels decreased by 0.09-0.36 mg/L DO levels increased by 0.20-0.49 mg/L o 0.4-0.5 mg/L increase near DO sag location

Chl-a levels decreased by 7.7-14.8 µg/L

“NATURAL BACKGROUND” MODEL SCENARIO (SUMMER AVERAGE MODEL RESULTS)

TN levels increased by 0.17-0.65 mg/L TP levels decreased by 0.01-0.04 mg/L DO levels increased by 1.3-2.2 mg/L o 2.0-2.2 mg/L increase near DO sag location

Chl-a levels increased by 0.3-0.6 µg/L

NO TIDAL MARSH MODEL SCENARIO (SUMMER AVERAGE MODEL RESULTS)

Model results show minimal DO changes due to the KCRWTF load & for the “natural background” scenario o Tidal marshes are the dominant factor controlling

DO levels in the tidal river Existing DO standards remain from Oct-May 15 o 5.0 mg/L daily average & 4.0 mg/L minimum

Proposed DO criteria from May 16-Sept o Daily average DO greater than or equal to 3.0 mg/L o 1-hour minimum DO greater than or equal to 1.0 mg/L o Only applicable for tidal reach o Excludes upstream ponds/lakes & freshwater reaches

PROPOSED SITE-SPECIFIC DO CRITERIA

Dominant factor controlling DO levels are river interactions with the extensive tidal marshes o DO levels are calculated to be low even under “natural background” or non-anthropogenic conditions o This drove development of site-specific DO criteria through UAA process o DO also considered an important nutrient endpoint o Biologically diverse aquatic community exists under current DO levels

UAA developed to account for natural conditions controlling DO levels in the river o Sub-category of the DNREC fish, aquatic life & wildlife use developed o Tidal Marsh Influenced Aquatic Life o Daily average DO = 3 mg/L & daily minimum DO = 1 mg/L

Nutrient TMDL – TN = 2 mg/L & TP = 0.2 mg/L (as annual averages)

CRITERIA DEVELOPMENT SUMMARY

QUESTIONS Andy Thuman (HDR) – Water Quality Practice Lead andrew.thuman@hdrinc.com (862) 236-1709