Sand, silt and clay

Recently we have been dealing with some particularly challenging well water issues: opaque, black coloration due to casing corrosion, sudden influxes of red sediment (sand grading downward in size to silt and clay) and previously unobserved yellow and red iron staining.

In the case involving black discoloration, the prospective buyers were granted the requisite permission by the seller to evaluate the well and collect a sample for lab testing. Unfortunately the buyers opted for a water test suite that did not include turbidity (a measurement of water clarity). High turbidity, revealed by a comprehensive water test (but not observed when the buyers ran the water during a site visit), would have been a major red flag that should have triggered a more extensive well evaluation and pump test prior to purchase. The discoloration was remedied by acidizing and brushing the casing and cleaning out the well.

The water does contain elevated iron levels, which can be remedied by a water conditioner. The black water problem was probably not a newissue, butmay have been a reflection of the contrast in water-use management between a single occupant, who used the water sparingly, and a family of four. From the perspective of a real-estate deal, disclosure of the change in water color experienced when the pump rate was accelerated might have been a deal killer. But it also could have been a point of negotiation. Motivated sellers will sometimes split the remediation costs with willing buyers.

The casing corrosion problem is, fortunately, a rare occurrence; but the need for sediment filtration in private wells is common and is as highly variable as the water chemistry itself. We test water for clients who struggle with problematic sediment issues, water constituents that may be either health-risk or aesthetic contaminants, and, less commonly, bacteria. The highest priority is remediation of sediment (if present), as it affects other treatment techniques. For high turbidity and sediment issues, a good option to ascertain sediment particle size is to run the water through a series of filters of decreasing pore size. If the filter of the smallest pore size remains clean, the sediment is larger than the pore size rating of that filter. If there is an abundance of course sediment, a sand separator, which will remove sediment down to 74 microns, may be a recommended stage of pre-treatment. (One micron = 1 millionth meter.)

An efficient water conditioner can remove sediment down to 20 microns, but the presence of very fine sediment may require an additional backwashing sediment filter (removal down to 3-5 microns). If the sediment is even finer or colloidal (and it remains suspended), the options include bearing the multiple risks and expense of drilling anotherwell. Removing suspended colloidal material is usually cost-prohibitive for a private well and owners who find themselves in that position, on a property they have already purchased or on which they have even started building their home, will typically opt to build a cistern and have water hauled to the property. That is a rare occurrence, fortunately, because the high variability of delivered water presents another set of challenges.

StephenWiman has a background in earth science (M.S. and Ph.D. in geology) and is the owner of GoodWater Company and a member of the City of Santa Fe’sWater Conservation Committee. He may be reached at 505-471-9036 and skwiman@ goodwatercompany.com.