NYC Graywater irrigation feasibility study

[refields]

I am conducting a feasibility study for the beneficial reuse of extracted urban groundwater for the irrigation of turf grass with some deciduous trees. The approximate coverage area to be irrigated is between 100,000 and 200,000 sf. Though the extracted groundwater is from inland Brooklyn, NY, it’s chemistry has been altered due to saltwater infiltration that has occurred as a result of over 100 years of deepwell pumping in the area. The extracted groundwater currently flows through a main line between 3,000 and 5,200 gpm and discharges into a city stormwater sewer. The following chemistry is from water samples taken from the discharge line we would be tapping for graywater irrigation purposes:

Sodium (ug/L) – 184,000

Calcium (ug/L) – 159,000

Magnesium (ug/L) – 68,200

Hardness as Calcium Carbonate (mg/L) – 676

Specific conductance (umhos/cm) – 2,200

Chloride (mg/L) – 614

TDS (mg/L) – 1,200

TSS (mg/L) – 1.3

Salinity (mg/L) – 467.9

The approximate calculated Sodium Absorption Ratio is 3.03.

Would treatment of this groundwater be necessary or recommended for grass irrigation? If so what options would be available?

In addition to water quality goals, what would be rough estimate for the anticipated system flow to irrigate such an area?

Thank you very much!

Regards,

Robert Fields

 

[bimr]

The chloride concentration is probably the limiting factor. The chloride is probably too high for the trees and grasses. You should review with the local extension agent.

http://www.ext.colostate.edu/pubs/crops/00506.html

The only option for treatment is desalination with RO treatment.

You probably would need a peak water supply of around 5,000 gallons per acre per day.

http://extension.umd.edu/publications/pdfs/fs447.pdf

 

[refields]

Thank you for the feedback. I've gathered that RO membrane systems can be very costly, would you agree? Would lime water softening might help with the Cl- levels? I would like to start pricing some of the different options.

 

[refields]

bimr, I noticed publication that you referenced had some great information for other crops, but how do they scale/equate to just plain old turfgrass? I was also wondering where you go the 5,000 gpd / ac for the turfgrass? Thanks alot.

 

[bimr]

Lime softening will have no effect on the chloride concentration. Lime softening is not an option.

 

[bimr]

How often should I water my lawn?

This question does not have a simple answer because irrigation requirements vary with grass species, with soil type, and with environmental conditions. These factors often interact in complex ways that make decision making difficult. On average, turf will usually require from 1 to 1.5 inches of water per week for normal maintenance conditions. This can be provided by rainfall or irrigation or a combination of the two.

http://www.usna.usda.gov/Gardens/faqs/turfgrassfaq2.html

Note that variations of turf grass may have vastly different watering needs. Whole books have been written on the subject.

http://www.ct.gov/dep/lib/dep/water_inland/diversions/golfcoursewaterusebmp.pdf

 

[cheute79]

As stated, the chloride level is really high. You might be able to consider salt grass or milo as a cover crop, but the Cl- is still probably way too high. Could he pH be adjusted and then aerate the water to reduce the Cl-? Also, with this water and the discussed loading, almost any cover crop will require some phosphorus addition - and phosphorus has a bad name right now, so getting a permit too ADD it could be a challenge.

 

[bimr]

That is a chloride ion (not chlorine) which is an inorganic that you are trying to aerate. If salts could be removed by aeration, you will have invented a cheap way to desalinate water.

 

[refields]

Thank you both for the responses!

bimr, the documents you have provided have proven very useful.

I would like to explore the option of ion exchange. EIther cation, anion or some combination of the two to reduce the Chloride and hardness levels. Do you have any experience with such systems? From what I have seen they would cost less than RO (in the order of $100k or less for our size application). What would the ions be replaced with after treatment and what unintended consequences, if any, could one expect from these? How about specifying a system that would tailor itself to the specific ions I want to remove. Would this be possible?

 

[bimr]

The level of salts would make ion exchange uneconomical. I would not pursue ion exchange.

 

[refields]

Bimr, I have heard from some consultants that ion exchange would be more economical than RO in this application. I would really appreciate some numbers or documentation to back up your statement. Thanks again!

 

[bimr]

You should ask your consultants where they have such systems installed.

Ion exchange was the only demineralization process available at one time. Ion exchange is now generally only used as a polishing step after RO because RO is more cost effective.

Call a supplier of ion exchange systems such as Siemens Water or Graver for information and costs, not a consultant.