Down­pours threat­en­ing U.S. es­tu­ary

Antelope Valley Press (Sunday) - - Second Front -

CONOWINGO, Md. (AP) — When the Conowingo Dam opened to fan­fare nearly a cen­tury ago, the mas­sive wall of con­crete and steel be­gan its job har­ness­ing wa­ter power in north­ern Mary­land. It also qui­etly pro­vided a side ben­e­fit: trap­ping sed­i­ment and silt be­fore it could flow miles down­stream and pol­lute the Chesapeake Bay, the na­tion’s largest es­tu­ary.

The old hy­dro­elec­tric dam span­ning the lower Susque­hanna River is still ably pro­duc­ing power, but its days of ef­fec­tively trap­ping sed­i­ment in a 14-mile long reser­voir be­hind its walls are over. Be­hind the 94-foot high bar­rier lies a mas­sive in­ven­tory of coal­black muck — some 200 mil­lion tons of pol­lu­tants picked up over decades from farm­lands, in­dus­trial zones and towns.

How big a threat this sed­i­ment stock­pile poses to the Chesapeake Bay or whether any­thing can even

be done about it de­pends on who you talk to. With Mary­land push­ing to curb pol­lu­tion in dam dis­charges, the is­sue has be­come a po­lit­i­cal foot­ball as Conowingo’s op­er­a­tor seeks to re­new its fed­eral license to op­er­ate the dam for 46 more years af­ter its old license ex­pired.

And as ne­go­ti­a­tions drag on, the lack of agree­ment about curb­ing runoff pol­lu­tants fol­low­ing the wettest year on record im­per­ils hard-won gains in restor­ing the Chesapeake Bay.

The iconic es­tu­ary famed for its blue crabs and oys­ters has been grad­u­ally re­bound­ing un­der a fed­eral cleanup program launched in 1983 that put an end to un­bri­dled pol­lu­tion. But the 200-mile long bay is in­creas­ingly be­ing rav­aged by runoff-trig­ger­ing down­pours, in­clud­ing record-set­ting rain­fall in 2018 and this year’s soggy spring.

In­tense cy­cles of down­pours are wash­ing pol­lu­tants into the Chesapeake from mu­nic­i­pal sewer over­flows, sub­di­vi­sions and farms where ma­nure of­ten isn’t ef­fec­tively han­dled and ni­tro­gen and phos­pho­rous-rich fer­til­iz­ers are used. Ex­perts say cli­mate change is ac­cel­er­at­ing the en­vi­ron­men­tal de­cline, po­ten­tially lead­ing to more dam­ag­ing al­gae blooms and dead zones in the Chesapeake and coastal wa­ters.

Mary­land politi­cians and wa­ter­men who make their liv­ing off the bay’s frag­ile bounty por­tray the sed­i­ment stored be­hind the Conowingo as an ex­is­ten­tial threat, as­sert­ing the mas­sive de­posit of reser­voir muck would dev­as­tate the bay if ever re­leased down­stream in a ma­jor storm. They note that sed­i­ment freely flows over the dam dur­ing down­pours, turn­ing the up­per bay’s wa­ters a murky brown.

“The sit­u­a­tion be­hind the dam is a tick­ing time bomb,” said Genevieve Cro­ker, spokes­woman for the Clean Chesapeake Coali­tion, a group­ing of ru­ral Mary­land coun­ties that have Repub­li­can Gov. Larry Ho­gan’s ear.

Qian Zhang, an as­sis­tant re­search sci­en­tist at the Univer­sity of Mary­land Cen­ter for En­vi­ron­men­tal Science, con­firms that the sed­i­ment does flow freely.

“The reser­voir is no longer ca­pa­ble of trap­ping sed­i­ment and sed­i­ment-as­so­ci­ated nu­tri­ents. It will re­lease sed­i­ment dur­ing storm events, cre­at­ing room for sed­i­ment to de­posit in sub­se­quent days. How­ever, from a long-term mass-bal­ance per­spec­tive, the reser­voir is es­sen­tially at a stage where sed­i­ments en­ter­ing the reser­voir equal sed­i­ments leav­ing,” Zhang said.

But he and nu­mer­ous other bay-area sci­en­tists say nu­tri­ent pol­lu­tion, not sed­i­ment, is the ma­jor threat, not­ing that most of the pol­lu­tants flow­ing into the Chesapeake come from up­stream, par­tic­u­larly in Penn­syl­va­nia. Most of the ni­tro­gen pol­lu­tants reach­ing the bay, for in­stance, travel there as dis­solved ni­trate and are not affected at all by the Conowingo’s sed­i­ment stor­age. They say mit­i­gat­ing the im­pacts from the huge in­fill be­hind the Mary­land dam is part of the puz­zle but hardly the key­stone piece in the restora­tion strat­egy.

“The most ef­fec­tive ap­proach has al­ways been to bet­ter man­age up­stream sources,” said Wil­liam Ball, a sci­en­tist who di­rects the Chesapeake Re­search Con­sor­tium.

Chicago-based Ex­elon Corp., the dam’s op­er­a­tor, stresses that the Conowingo it­self is not a source of pol­lu­tion and agrees the prob­lem lies up­stream. It sug­gests that more sed­i­ment could wash through the dam in com­ing years, since sus­tained down­pours lead to high river flows and re­quire more crest gate open­ings. In 2018, there were 157 days when at least one crest gate was open, com­pared to 25 days in 2017 and 17 days in 2016, ac­cord­ing to com­pany data.

“The pos­si­bil­ity that cli­mate change could re­sult in wet­ter con­di­tions in the re­gion make it all the more im­por­tant that the up­stream sources of river pol­lu­tion in the Susque­hanna be ad­dressed,” Ex­elon said in a state­ment.

Penn­syl­va­nia rou­tinely pushes back against the crit­i­cism, not­ing that it has a whop­ping 33,000 farms and more than 350 mu­nic­i­pal­i­ties in the wa­ter­shed. The state says it’s com­mit­ted to meet­ing pol­lu­tant re­duc­tion tar­gets.

As­so­ci­ated Press

Wa­ter flows through Conowingo Dam, a hy­dro­elec­tric dam span­ning the lower Susque­hanna River near Conowingo, Mary­land, on Thurs­day.

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