Onsite Sewage Facility OSSF Contamination Risk to Local Water Resources By Alvaro Garcia What is an OnSite Sewage Facility Decentralized wastewater treatment systems Efficiently treat wastewater through physical chemical and biological processes ID: 1048702
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1. A GIS-Based Model to Assess Onsite Sewage Facility (OSSF) Contamination Risk to Local Water ResourcesBy Alvaro Garcia
2. What is an On-Site Sewage Facility?Decentralized wastewater treatment systemsEfficiently treat wastewater through physical, chemical, and biological processesCost effective especially for rural areasRely on the proper design, installation, and management of the system“A Conventional Septic System”Source: EPA
3. OSSF Potential RisksPublic HealthBacterial exposure via public waterwaysDrainage ditchesResacasGroundwaterContact recreation in the Lower Laguna MadreEnvironmentNutrient dischargeEutrophicationSubwatershed Boundaries with Major Drainage Routes and Resacas (Benavides, LLM/Ship Channel Watershed Characterization, 2018)
4. OSSF Potential RisksPublic HealthBacterial exposure via public waterwaysDrainage ditchesResacasGroundwaterContact recreation in the Lower Laguna MadreEnvironmentNutrient dischargeEutrophicationLLM/Brownsville Ship Channel TCEQ Segments (Benavides, LLM/Ship Channel Watershed Characterization, 2018)
5. Research ObjectivesDevelop a GIS risk assessment model that considers relevant OSSF risk parametersDetermine the relative importance between the risk model’s parameters Evaluate the risk model’s performance using E. Coli counts.
6. Geographic Information Systems (GIS)
7. OSSF Risk Assessment Model (Oosting and Joy, 2011)EnvironmentalSoil TypeLand SlopeFloodplainGroundwater Recharge AreasOSSF System DesignLot SizeSurface Water ProximitySystem AgeWater Supply ProximityOSSF Density250 m by 250 m survey grid generated in GIS
8. OSSF DatabaseOSSF records from Cameron County Public Health department were matched with appraisal district parcel maps and 911 addressesAround 10,000 permits were automatically matchedRemaining permits are being manually matched using physical permit copiesOSSF locations of automatically matched permits.Source: Texas Water Resource Institute & Texas A&M Agrilife Extension Service
9. Environmental ParametersSoil TypeClass A and Class D = 5Class B = 3Class C = 1Land Slope< 5% = 15-10% = 210-15% = 315-20% = 4>20% = 5FloodplainWithin = 5Outside = 1Groundwater Recharge AreasWithin = 5Outside = 1
10. System Design ParametersLot Size>1 acre = 10.75 - 1 acre = 20.50 – 0.75 acres = 30.25 – 0.50 acres = 4<= 0.25 acres = 5Surface Water ProximityWithin 150 ft. = 5150 - 225 ft. = 4225 - 300 ft. = 3300 - 375 ft. = 2Beyond 375 ft. = 1
11. System Design ParametersSystem Age<10 years = 110-20 years = 220-25 years = 325-30 years = 4>30 years = 5Water Supply ProximityWithin 300 ft. = 5300 – 450 ft. = 4450 ft. – 600 ft. = 3600 ft. – 750 ft. = 2Beyond 750 ft. = 1
12. System Design ParametersTest Grid Value Risk DesignationOSSF Density0-1 = 12-4 = 25-9 = 310-16 = 417-37 = 5
13. Questions