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UDC
Methodology & Data Documentation

Data Methodology & Quality Assurance

Complete documentation of sampling protocols, quality assurance procedures, parameter definitions, and data provenance. This page enables researchers to verify, cite, and reproduce analyses using UDC WRRI water quality data.

Data Dictionary
Sampling Protocols
QA/QC Procedures
Ingestion History

Data Sources & Provenance

Every reading in the database is tagged with its source for full traceability

USGSUSGS NWIS

Real-time and daily values from USGS National Water Information System. Instantaneous values via the NWIS IV Web Service.

Sites: 01651000, 01649500, 01646500
Frequency: Daily automated ingestion (06:00 UTC)
API: https://waterservices.usgs.gov
EPAEPA WQX

Historical water quality data from EPA's Water Quality Exchange portal. Provides longitudinal data back to 2020.

Sites: Anacostia watershed (HUC 02070010)
Frequency: On-demand ingestion
API: https://www.waterqualitydata.us
SEEDBaseline / Modeled

Initial dataset derived from published averages and modeled values for station commissioning. Being progressively replaced by measured data.

Sites: All 12 stations
Frequency: One-time seed data
MANUALManual Entry

Field measurements entered by WRRI researchers and trained student technicians. Includes grab samples and portable meter readings.

Sites: As collected
Frequency: Event-driven

Data Dictionary

Complete definitions for every parameter collected, including measurement methods, valid ranges, and regulatory standards

Water Temperature

field: temperature
°C

Temperature of water at sampling depth. Affects dissolved oxygen capacity, metabolic rates, and aquatic organism survival.

Method
Thermistor probe (YSI 6600)
Valid Range
-5 to 45
Detection Limit
0.01°C
EPA Standard
Varies by water body class; generally ≤32°C for warm-water aquatic life

Dissolved Oxygen

field: dissolved_oxygen
mg/L

Concentration of molecular oxygen dissolved in water. Critical for fish and macroinvertebrate survival. Levels below 5 mg/L indicate stress; below 2 mg/L is hypoxic.

Method
Optical DO sensor (luminescent)
Valid Range
0 to 20
Detection Limit
0.1 mg/L
EPA Standard
≥5.0 mg/L for aquatic life support (CWA §304(a))

pH

field: ph
Standard units

Measure of hydrogen ion concentration (acidity/alkalinity). Affects nutrient availability, metal toxicity, and biological processes.

Method
Glass electrode potentiometry
Valid Range
0 to 14
Detection Limit
0.01 SU
EPA Standard
6.5–9.0 for freshwater aquatic life (EPA Gold Book)

Turbidity

field: turbidity
NTU

Measure of water clarity caused by suspended particles. High turbidity reduces light penetration, affecting photosynthesis and can indicate erosion or pollution.

Method
Nephelometric (90° scattered light)
Valid Range
0 to 4,000
Detection Limit
0.1 NTU
EPA Standard
Narrative: shall not exceed levels detrimental to aquatic life. DC DOEE: ≤50 NTU typical reference

Specific Conductance

field: conductivity
µS/cm

Ability of water to conduct electrical current, indicating total dissolved ion concentration. Elevated values may indicate road salt, sewage, or industrial discharge.

Method
4-electrode conductivity cell, temperature-compensated to 25°C
Valid Range
0 to 10,000
Detection Limit
1 µS/cm
EPA Standard
No federal numeric standard; DC reference: 150–500 µS/cm typical freshwater

E. coli

field: ecoli_count
CFU/100mL

Fecal indicator bacteria. Indicates potential presence of pathogens from sewage or animal waste. Primary indicator for recreational water safety.

Method
Membrane filtration / Colilert Quanti-Tray (IDEXX)
Valid Range
0 to 100,000
Detection Limit
1 CFU/100mL
EPA Standard
≤410 CFU/100mL (single sample recreational contact, EPA 2012 RWQC)

Nitrate-Nitrogen

field: nitrate_n
mg/L

Inorganic nitrogen form readily used by algae and plants. Excess leads to eutrophication, algal blooms, and oxygen depletion.

Method
Ion chromatography / cadmium reduction
Valid Range
0 to 100
Detection Limit
0.01 mg/L
EPA Standard
10 mg/L (drinking water MCL, EPA 40 CFR 141)

Total Phosphorus

field: phosphorus
mg/L

Limiting nutrient for freshwater algal growth. Major contributor to eutrophication in the Anacostia. Sources include fertilizer runoff, wastewater, and erosion.

Method
Ascorbic acid colorimetry (SM 4500-P E)
Valid Range
0 to 50
Detection Limit
0.005 mg/L
EPA Standard
0.1 mg/L (EPA recommended for streams; Anacostia TMDL target)

Sampling Protocols

Standard operating procedures for field data collection

Continuous Monitoring Stations

  • Multi-parameter sondes (YSI 6600 / EXO2) deployed at fixed stations
  • 15-minute recording interval for temperature, DO, pH, turbidity, conductivity
  • Sensors calibrated monthly using NIST-traceable standards
  • Anti-fouling wipers activated before each measurement cycle
  • Data transmitted via cellular telemetry to USGS NWIS database
  • Backup manual readings during maintenance windows

Grab Sampling (E. coli, Nutrients)

  • Samples collected mid-channel at 0.3m depth (wadeable) or from bridge with weighted sampler
  • Sterile 500mL Whirl-Pak bags for bacteriological samples
  • Acid-washed HDPE bottles for nutrient analysis (pre-rinsed 3×)
  • Samples stored on ice (4°C) and transported to lab within 6 hours
  • E. coli processed within 24 hours per EPA Method 1603
  • Nutrient samples filtered (0.45µm) and preserved with H₂SO₄ for nitrogen/phosphorus

Stormwater BMP Monitoring

  • Paired influent/effluent sampling at green infrastructure installations
  • Flow-weighted composite sampling during storm events (ISCO 6712)
  • Minimum 3 first-flush events captured per quarter
  • Runoff volume measured via calibrated flumes and pressure transducers
  • Pre/post performance metrics: pollutant removal efficiency (%)
  • Rainfall intensity recorded by co-located tipping bucket gauge

Field QC Requirements

  • Field duplicate collected every 10th sample (≥10% frequency)
  • Equipment blank run at start of each sampling event
  • Trip blank accompanies every cooler of samples
  • Field meter calibration documented in log book before each use
  • Chain of custody form signed at each transfer point
  • GPS coordinates recorded at each sampling location (±3m accuracy)

Quality Assurance / Quality Control

Procedures ensuring data reliability and fitness for research use

Automated Validation (Ingest Pipeline)

  • Physical range checks reject impossible values (e.g., pH > 14, negative DO)
  • USGS -999999 sentinel values filtered before storage
  • Duplicate timestamp detection per station (same source + time = skip)
  • Validation warnings logged and returned in API response
  • All rejected values recorded with reason for audit trail

Manual Review Procedures

  • Monthly data review by WRRI research staff
  • Time-series plots inspected for sensor drift or fouling artifacts
  • Cross-parameter consistency checks (e.g., high temp + low DO = expected)
  • Lab duplicate RPD must be ≤25% for acceptance
  • Flagged values annotated but retained for transparency (not deleted)

Validation Ranges (Automated Rejection Thresholds)

ParameterMinMaxUnitAction if Out-of-Range
Water Temperature-545°CValue set to NULL + warning logged
Dissolved Oxygen020mg/LValue set to NULL + warning logged
pH014Standard unitsValue set to NULL + warning logged
Turbidity04000NTUValue set to NULL + warning logged
Specific Conductance010000µS/cmValue set to NULL + warning logged
E. coli0100000CFU/100mLValue set to NULL + warning logged
Nitrate-Nitrogen0100mg/LValue set to NULL + warning logged
Total Phosphorus050mg/LValue set to NULL + warning logged

Ingestion History

Log of all data ingestion events — when data was fetched, how many records were added, and any errors encountered

How to Cite This Data

Recommended citations for academic publications and reports

Dataset Citation (APA 7th)

UDC Water Resources Research Institute. (2026). Anacostia Watershed Water Quality Monitoring Data [Dataset]. University of the District of Columbia, College of Agriculture, Urban Sustainability and Environmental Sciences (CAUSES). Retrieved from https://udc-water.vercel.app/api/export

API Endpoint for Programmatic Access

GET /api/stations — List all monitoring stations with latest readings
GET /api/stations/:id/history — Historical readings for a station
GET /api/export?format=csv&station=ANA-001 — Export data as CSV or JSON
GET /api/ingestion-log — View data ingestion history

CSV and JSON exports include machine-readable citation metadata. All exports include the source field for each reading.