Reutilización de Aguas Residuales en la Agricultura San Juan, Puerto Rico June 1, 2016 Dr. Gregory Morris PhD, PE gmorris@glmengineers.com San Juan, Puerto Rico
Coamo reservoir (fully sedimented) Santa Isabel WWTP
Process of Saline Intrusion Location of salt-fresh interface in the aquifer can be described by Ghyben-Herzberg relationship
Geology: Depth to bedrock Depth to bedrock is 1300 feet at the coastline
Maximum thickness of freshwater lens was 660 feet in 1986-1987 Max. fresh water thickness was 660 feet in 1986-87
Process of Saline Intrusion Location of salt-fresh interface in the aquifer can be described by Ghyben-Herzberg relationship
Potentiometric Levels March-April 2008
Groundwater levels Nivel Potenciometrica (pies sobre nivel del mar) 30 25 20 15 10 5 0-5 Nivel del mar Mar Reducción en Nivel Durante 9 años Pozo Alomar 1, Santa Isabel (USGS 175829066232200) Reducción en Nivel Durante 4 años -10 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 2012 2016 Fecha
Main Concepts 1. Source characteristics 2. End user characteristics 3. Delivery mechanism 4. Feasibility
Santa Isabel WWTP
Daily Discharge Santa Isabel WWTP 2.5 2.0 Excess flow on rain days Discharge (mgd) 1.5 1.0 0.5 What to do with wet weather flow? -- Hold until a dry day? -- Maintain NPDES permit and discharge? 0.0 January-16 February-16 March-16 April-16 May-16 Date
Water Quality Considerations Pathogens Total Dissolved Solids (TDS): increase TDS levels in the aquifer Nutrients: NO 3 of 7 mg/l cannot be exceeded in aquifer, and nitrates are already high BOD: Clogging of drip system & recharge sites Suspended Solids: Clogging of drip system & recharge sites
Main Concepts 1. Source characteristics 2. End user characteristics 3. Delivery mechanism 4. Feasibility
Flow Requirements for Irrigation For plantation sugarcane they could use an essentially constant year-around flow (except rain days). For vegetable and other short crops, irrigation seasons may range from 30 90 days. Strategy to maximize use of recycled water: Use recycled water first Supplement with well water as needed
Irrigation Demand is NOT Constant (monthly demand for bananas at Fortuna) Monthly Water Use (% of average) 160% 140% 120% 100% 80% 60% 40% 20% 0% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Goenaga, Ricardo, Héber Irizarry, Bruce Coleman, and Eulalio Ortiz. 1995. Drip Irrigation Recommendations for Plantain and Banana Grown on the Semiarid Southern Coast of Puerto Rico. J. Agric. Univ. P.R. 79 (1-2): 13 27.
Irrigation depth and area For year-around irrigation of banana, may need on the order of 4 of irrigation per year, with a 1.4 mgd = 131 AF/month Can sustain about 300-325 acres of banana For crops that are irrigated only 6 months per year, acreage will approximately double
Main Concepts 1. Source characteristics 2. End user characteristics 3. Delivery mechanism 4. Feasibility
Summary of Reuse Options Reuse Option % Applied to Crop Issues Direct drip irrig. 95% Pathogens, biological clogging Direct sprinkler 85% Pathogens & aerosols Indirect via canal 85% Indirect via wetland 80% Indirect via aquifer (land spreading) Indirect via aquifer (riverbed recharge) 50% Biological clogging of high-rate recharge sites 25% Ineffective when streamflow is high
Direct Reuse Options Commonly used in many areas of the world using untreated sewage Montezuma s revenge Problem of perception remains Furrow irrigation least problem but no longer commonly used in Santa Isabel area Sprinkler systems problem of aerosols Drip systems clogging from biogrowth (BOD in wastewater acts as bacterial food supply) Need some type of storage
Direct Reuse Options Drip Irrigation Treated wastewater delivered directly to irrigation pond or pumping system.
Treated wastewater delivered into storage pond. This introduces problem of algal growth in the pond due to high nutrient levels, greatly increasing solids load on filters.
Indirect Reuse Options Delivery into Juana Díaz canal Biological sealing of canal bottom, reducing recharge via canal leakage? Delivery to wetland treatment system Will reduce BOD, nutrients and other potential hazards Aquifer recharge via land spreading Reduction of soil permeability by biogrowth Aquifer recharge via discharge to river Permitting problem (zero dilution flow) Potential for biological fouling
Delivery into Juana Díaz canal
Treatment wetlands for nitrogen removal prior to land spreading in Santa Ana riverbed (Prado wetland, Riverside, California)
Soil Permeability (red is more permeable)
Aquifer Recharge Options Land Spreading Injection Well
Discharge to Río Coamo riverbed 10,000 1,000 Flow is less than 10 cfs on 57% of days. When flow exceeds 10 cfs, delivery of reused water to channel will probably not enhance recharge. DISCHARGE (cfs) 100 10 10 cfs 1 USGS gage 50106100 Río Coamo at Hwy 14 0 Jan-87 Jan-91 Jan-95 Jan-99 Jan-03 Jan-07 Jan-11 Jan-15 DATE
Main Concepts 1. Source characteristics 2. End user characteristics 3. Delivery mechanism 4. Feasibility
Options. Which is the most viable strategy? Given enough money, ANY of the options can be made to work. Cost of permitting, design and construction Operational costs (above the cost of using canal or well water) Which options might be practical? Deliver recycled water to Juana Díaz canal Deliver recycled water to irrigation pond Deliver recycled water to spreading basin
4.8 km pipeline from WWTP to existing storage pond Santa Isabel WWTP
Recharge options NOT involving wastewater Direct delivery drip irrigation Direct delivery sprinkler irrigation Indirect delivery via treatment wetland Indirect delivery via Juana Díaz canal Indirect delivery via aquifer recharge
Cost Considerations Cost of 15 pipeline and pump station for reuse will probably run on the order of $1 million for delivery to irrigation ponds Delivery to Juana Díaz canal requires more pipe and higher pressure pipeline. Operational cost will include: Pumping (30 to 60 m head, depending on discharge point) Compliance activities Must maintain normal NPDES permit
Another Option Under Consideration by DRNA Recharge of aquifer using water from Río Coamo when flows exceed 10 cfs. Divert by gravity from top of Coamo dam. Avoid water quality issues (except sediment, which is minimized by not using flood water). Avoid permitting issues. Higher quality that recycled water (TDS & NO 3 )
PE PhD gmorris@glmengineers.com Aquifer restoration options de exist: Puerto Rico faces multiple serious problems We need to be innovative and pull together We CAN solve aquifer problems and also support agriculture Thank You