Sand, silt and clay

Home - Santa Fe Real Estate Guide - - OURWATERQUALITY - STEPHEN WI­MAN

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@ good­wa­ter­com­

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