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Optional enhanced measures for the protection of water quality in the Edwards Aquifer (revised)

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Optional enhanced measures for the protection of water quality in the Edwards Aquifer (revised)
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Texas Commission on Environmental Quality
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Edwards Aquifer Authority Collection

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September 2007 RG-348A Optional Enhanced Measures for the Protection of Water Quality in the Edwards Aquifer (Revised) Appendix A to RG-348 Complying with the Edwards Aquifer Rules: Technical Guidance on Best Management Practices Prepared by the Chief Engineers Office, Water Programs TEXAS COMMISSION ON ENVIRONMENTAL QUALITY

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Optional Enhanced Measures for the Protection of Water Quality in the Edwards Aquifer (Revised) Appendix A to RG-348— Complying with the Edwards Aquifer Rules: Technical Guidance on Best Management Practices Prepared by Chief Engineer’s Office, Water Programs RG-348A September 2007

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T exas Commi ssi on on Env i ronment a l Q u a l i t y H S Bu dd y Ga rc ia Chai r m an L a rry R S o w a r d C o m m i ssi o ner G l e nn S h a n kl e, Ex ecut iv e Dir ect o r T e x a s Com m i ssion on Env i ronm ental Qu al ity P.O. Box 13087, MC203 Austi n, T e xa s 787 113087 The TCE Q i s an equal opport uni t y / a f f i r m a t i ve ac t i on e m pl oyer. The agenc y does not al l o w dis c r i m inat ion on t he bas is of r a c e c o lor, religion, nat ional ori g in, s e x dis abilit y age, s e x ual ori ent at i on, or vet e ran st at u s I n com p l i anc e w i t h t he A m eri c an s w i t h Di s abi l i t i es A c t t h i s doc u m ent m a y be reques t ed i n al t e rnat e f o rm a t s by c ont ac t i ng t he TCE Q at 512/ 239-0028, f a x 239-448 8, or 1-800-RE LA Y TX (TDD ), or b y wri t i ng P O B o x 13087, A u s t i n Texas 78711-3087. A u t hori z at i on f o r us e or reproduc t i on of any ori g i nal m a t e ri al c o n t ai ned i n t h i s publ i c a t i on, i e. no t obt ai ned f r o m ot her s ourc e s i s f r eel y grant ed The Com m i s s i on w oul d apprec i a t e a c k now l edgm ent

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Appendix A iii TCEQ publication RG-348A # Revised # September 2007 CONTENTS 1. Introduction................................................................................................................ ..12 2. Site Planning............................................................................................................... ..32 2.1. Sensitive Features............................................................................................................. 32 2.2. Sensitive Features Identifie d During Construction.........................................................42 2.3. Caves.......................................................................................................................... ......82 2.3.1. Gate Construction...............................................................................................102 2.4. Stream Buffers................................................................................................................1 12 3. Construction...............................................................................................................1 82 4. Permanent BMP Implementation...............................................................................192 4.1. Hazardous Material Traps (HMT)..................................................................................192 4.2. Total Suspended Solids (TSS) Removal........................................................................202 4.2.1. Step 1: Required TSS Removal..........................................................................202 4.2.2. Step 2: Select an Appropriate BMP....................................................................222 4.2.3. Step 3: Calculate TSS Load Removed by BMPs................................................222 4.2.4. Step 4: Calculate Fraction of Annual Runoff to Be Treated..............................232 4.2.5. Step 5: Calculate Capture Volume......................................................................232 5. Measures to Protect Stream Morphology...................................................................252 6. Maintenance Requirements........................................................................................282 7. References.................................................................................................................. 292 Figures Figure 2-1. Filled Solution Feature............................................................................................62 Figure 2-2. Example of Filled Void in Trench Excavation........................................................62 Figure 2-3. Utility Pipe Encased in External Steel Pipe.............................................................72 Figure 2-4. Profile View of Encased Utility Pipe.......................................................................72 Figure 2-5. Cavity Fill with Pipe to Preserve Hydrologic Connectivity....................................82 Figure 2-6. Typical Cave Gate with Secure Entrance................................................................92 Figure 2-7. Mammal Access Portals along Edge of Gate........................................................102 Figure 2-8. Example of Anchor Rebar.....................................................................................112 Figure 2-9. Example Cave Gate Access...................................................................................122 Figure 2-10. Traditional Development Adjacent to Stream Buffer............................................142 Figure 2-11. Example of Small Lot Clus ter Type Development................................................152 Figure 2-12. Example of Large Lot Low Density Development................................................162 Figure 2-13. Detail of Road Section Showing Vegetated Treatment Areas...............................172 Figure 2-14. Detail of Lot Layout with Water Quality Easements............................................172 Figure 4-1. Hazardous Material Trap inside Sand Filter..........................................................192 Figure 4-2. Typical TxDOT Automatic Siphon Detail............................................................202 Figure 4-3. Relationship between Runoff Coeffi cient and Impervious Cover.........................242

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Appendix A iv TCEQ publication RG-348A # Revised # September 2007 Tables Table 2-1. Minimum Protective Standards for Sewer and Storm Drain Trenches....................52 Table 3-1. Capture Volumes for Sediment Basins..................................................................182 Table 4-1. Impervious Cover Assumptions for Residential Tracts.........................................212 Table 4-2. Average Annual Rainfall by County.....................................................................212 Table 4-3. Approved BMPs and TSS Removal Efficiency.....................................................222 Table 4-4. Relationship between Fraction of An nual Rainfall and Rainfall Depth................242 Table 5-1. Average Annual Rainfall by County.....................................................................262

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1. Introduction One of t h e g o als of the T e xas Com m ission o n Env i r o nm e n t a l Qua lit y ( T CEQ) E d wa r d s Aqu i fer Rules is t he exi s t i ng qua li ty of g r oundwa t e r no t be d e g r aded, cons is ten t wi th th e pro t e c t i on o f publ ic h eal th and we lf are propag a t i on and p r o t ec tio n of t e r r es tr ia l an d aqu a t i c li f e th e p r ot ect ion of t h e e n v i ronm ent, the ope rat i on of exi s t i ng indu st rie s and the m a inten a nce and enhanc em ent o f longterm econom ic hea lth of th e s t at e" ( T i t l e 30 T e xas Adm i nis t ra tiv e Code 213.1(1 )). This docum ent pr esen ts o p t i ona l wate r qua li ty prot ec tion m easu r es tha t m a y be im plem ented in a r ea s sub j e c t to the T C EQ Edwa r d s Aqui fer Rule s (3 0 T A C Chapte r 213 ). T h e opt iona l wat e r qu al ity m easures and b e s t m a nagem e nt prac ti ces (BMPs ) c onta i ned in th i s docum ent hav e be en rev i e w ed by the U n it ed S t at es Fish and Wi ldl i f e Se rv ice (U SFWS), w h ic h has iss u ed a c oncu r r e nce t h at the s e v o lu nta r y enha nc ed wa ter qua li ty m easures will pr ote c t en dang ered an d can did a te spe c ies fr om i m pacts du e to w a te r qua li ty deg r adat ion. U SFWS app r ov ed the p r ede ces sor do cum e nt to th is r e v i sed a ppend ix o n Februa ry 14, 2005. T h is rev i sed an d up dated appe ndix wa s app r ov ed by correspo nde n ce from Dr. Ben j am in N. Tugg le, USFWS Reg i onal 2 Di rec t or to Go v e rnor Ri ck Per r y dated S e ptem ber 4 2007 T h is le tt er iden ti fi ed the fol l owing spe c i e s a s be ing i n clud ed und er thi s no t a k e con c ur renc e: Barton Spr i ng s sa lam a nder ( E urycea s o sor u m ) fount ain da rte r ( E the o st oma fon tic ola) Georg e town s a lam a nde r ( E uryce a nau frag ia) San Ma rco s sa lam a nder ( E uryce an nana) a n d San Ma rco s g a m busia ( G ambusia g e org e i) T h is concu r r e nce i s no t a d e leg a t i on of the USFWS s respo n si bi li ti es u nder t h e E ndang ered Spe cies A c t (ESA ) bu t r a th e r an ack now ledg em ent t h at the T C EQ E d w a rd s A q uife r P r ot ec tion Prog ram w ith the s e en han ced w a t e r q u al ity m easure s addr ess e s k now n th rea t s to th e id ent i f i e d spec ies. I f these prac ti ces c ont ain e d in thi s docum ent a r e use d they are expe ct ed to r e su lt in "no t a k e of thes e spec ie s from deg r adat ion of wat e r qua li ty by non F edera l land owner s and ot her nonFedera l m a nag e rs. 1 T h is "no tak e concu rre nce d o es n o t cov e r pro j e c ts tha t : (1 ) oc cur o u ts ide the are a reg u lat e d unde r the Edwar d s Aqu i fe r Ru le s; (2 ) resu l t in wa te r qu al ity im pact s tha t m a y affe c t Feder a l l ylist e d spe c i e s no t spe c i f ic al ly nam e d above; (3 ) r e su lt in im pact s to Feder a l l yliste d spec ies tha t ar e not wa te r qual ity re lat e d; or ( 4 ) oc cu r with in on e m ile of s p r i n g opening s that prov ide h a bi ta t fo r F e d e ra ll ylisted s p ec ies. I t is th e respo n s i bi li ty of t h e ap pl ican t to det e rm ine t h e po ten t i a l fo r im pacting endang ere d sp e cies a nd tak e app r opr ia te ac tion b a sed upo n th is in form ati on. The USFWS m a inta i n s a county b y count y li s t o f end a ng er ed spec i e s on i t s web sit e a t . T h i s li st is s u b j ec t t o chang e as n e w bio l og ica l in form atio n is g a th e r ed and shou ld N O T be us ed a s the sol e a nd fin a l sour ce f o r iden ti fy ing speci es tha t m a y be i m pact ed by a pro jec t Pl eas e con t a c t the appr opri a te USFWS f i e l d o f f i ce (s) to g e t addi ti ona l in form ati on. 1 Se c tion 9 of the E nda ng e r e d S p e c ie s A c t ( A c t ) a nd Fe de r a l r e g u la tions a d o p te d un de r s e c tion 4( d) of the A c t pr ohi bit the t a k e" of e nda ng e r e d a nd t h r e a t e n e d s p e c i e s w ithout s p e c i a l e x em ption. T a k e of lis te d s p e c i e s is de f i ne d a s ha r a s s ha rm pursue hu nt, sh oo t, w oun d k ill, tra p c a p tu re or c o lle c t or t o a tte m p t to e n g a g e in suc h c ond uc t. Ha ra ss is f u r the r de f i ne d a s a n inte ntio na l or ne g lig e n t a c t or om is s i on tha t c r e a t e s the lik e lihood of injur y to a lis te d s p e c ie s by a nnoy ing it to s u c h a n e x te nt a s to s i g n if ic a n tly dis r upt n o r m a l be ha v i or a l pa tte r n s H a r m inc l ude s s i g n if ic a n t ha bita t m odif i c a tion or de g r a d a tio n t h a t r e sults in de a t h or i n jury to liste d spe c i e s Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 1

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T h e s e o p t i ona l m easure s a r e des i g n ed to enha nce the prot ect ion of the spec ie s co v e red unde r t h is docum ent by prov idi n g for a hig h er lev e l of w a te r qu ali t y pro t ec tio n and can be used by t hos e who wish to av oid ha rm ing list e d s p ec ies fr om water qual ity im pact s. I t is the r e spons ib il ity o f the app l i can t to de te rm ine whether the op ti ona l wat e r qua li ty m easure s and b e st m a nag e m e nt prac ti ces desc ri bed in t h is d o cum e nt ar e app r opr ia te for the i r p r o j ec t. Whi l e th ese m easure s are not m a ndatory under th e Edwards Aqui fe r Prot ect io n Prog ram they m a y be subm itt ed to the T C E Q for rev i ew as pa rt of an Edw a rd s Aqu i fe r P r ot e c ti on P l an or a Contr i bu ting Z one Plan. An appl ic ant wh o cho o ses to im plem ent the m easu r es a nd bes t m a nag e m e nt pract ice s cont ain e d i n this do cum e nt w i l l st il l hav e to com p ly w ith all o t her a ppl ica b le requ irem ents fo r th e dev e l opm ent of l a nd und er the Edwards Aqu i f e r P r ot ec tio n Prog ram and rule s. T h e T C EQ cann o t g r an t v a ri ance s t o t h e m easur es a nd bes t m a nag e m e nt prac ti ces c ont ain e d i n thi s do cum e nt. I f th e a ppl ic ant w i sh es to im plem ent th ese w a te r qua li ty m easures to ful f i l l t h e "no tak e c oncu rre nce by USFWS, v a ri ance s f r om the wa ter qua li ty m easures a nd b e st m a nag e m e nt prac ti ces unde r t h e T C EQ Edw a rds A q ui fer Pro t ec ti o n Prog ram w ill not be a l l o w e d as p a r t o f th e approv ed p l an I f the app l i cant w i s h es a v a r i anc e the T C EQ cann o t is sue a p l an appr ov al let t e r w h ich ind i ca tes th e pl an is in c o m p lianc e w i th th e m easu r es con t ai ned in thi s d o cum e nt. I f the w a ter qua li ty m easure s re q u ire d to b e in com p lian ce w ith thi s docum ent c a nno t be im plem ented ful l y the ap pl ican t m a y in it iat e d i r e c t co nsu l t a t i on w ith U S F W S to de term ine i f t h ei r dev e lop m e nt w i l l r e su lt i n "no tak e the r eby en sur i ng th at th e r e qui rem e nts of th e E n d a ng ered S p ec ie s Act hav e be en m e t. T h e op ti ona l wate r qual i t y m easure s cont ain e d in th i s docum ent m a y be i m plem ented by appli cant s cond uct i ng reg u la te d act iv it ies in th e ar eas sub j e c t to t h e TC E Q E d w a rds A q u i f e r Prote c t i on Prog ram as deli neat ed in th e rule s found i n T i tle 30 T e x a s Adm i nist ra tiv e Code Chap t e r 213 Edwa r d s Aqu i fer at and on m a ps a v ai l a b l e a t . A c tiv it ie s w i thi n th e C o n t r i buti n g Z one that di stu r b les s th an f i v e ac res or ar e no t par t o f a la rg er com m on plan of d e v e lop m ent or sa le w i th the po t e nt ial to d i s t ur b cum u lat i v e ly fiv e or m o re acre s a r e no t sub j ec t t o reg u la tion u nde r Subch a pt er B of th e Edward s Aqui fe r Rules. Ther efo r e thes e ac tiv i tie s a r e no t e lig i b le to be rev i ew ed by the T C E Q T h e fo ll ow ing sec t i ons des c rib e the p r oc ess and req u i r em ents for im plem enting t h e op tion a l en hanced m easure s and bes t m a nag e m e nt prac tic es. S e c tion 2 de sc rib e s the si te p l anning pro ces s and t h e n eed fo r a G e olog i cal A sse ssm ent ea rly i n t h e pro j ec t d e v e lopm ent pha se B M Ps are de scr i bed fo r se ns it iv e fea t u r es i d en ti fie d du ring th e a s sessm ent o r a f t e r cons tr uct i on h a s b e g un. Sect ion 3 p r es ent s t h e siz i n g requi rem e nts for se dim e nt ba sin s u s ed to m a nag e co nstr uct i on ru n off and Sec tio n 4 cov e rs h a z a rdous m a teri al t r aps an d th e c a lc ula t i ons used to siz e s t orm wate r tre a tm ent sy stem s for pos t const r uc ti on run o ff m a nag e m e nt. Sectio n 5 desc rib e s t h e requ ir em ents for m a nag i ng runoff v o lu m e to help pres erv e st rea m m o rpholog y and prev ent chann e l e r os ion Fina lly Sect ion 6 p r es ent s t h e addi t i ona l m a inten a nce r e qui rem e nts t o com p ly with thes e opt ion a l m easures. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 2

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2. Site Planning I n m a ny cases i n the p a st la rg e trac ts hav e bee n subd iv ided an d road s and l o ts la id out befo re c on side ring re qui rem e nts for s t orm water t r ea tm ent. T h i s his t or ica l pr oced ure w i l l re sul t in n u m e rous dif f ic ul ti es w h en im plem enting the s e op tion a l m easu r es du e to r e qui rem e nts f o r set b ack s fr om creek s, st ream s, and sens it i v e featur es. C onse que n tly two step s shou ld proc eed a n y wor k to lay out the s ubd iv ision or oth e r dev e lopm ent. These ar e t h e g e olog ica l a sse ssm ent a nd ide n t i f i ca ti on of s t re am buffer s a s des c r i b e d be low. 2.1. Sen s iti v e F e at u r es S e nsi tiv e fe atu r e s com p ris e a larg e v a rie t y of ty pes inc l udi ng cav es, solut i on c a v itie s, so lut i o n enla rg ed fr act ure s s i nk hol es or o t he r k a rs t su rfa ce ex pres sion tha t m eet th e de fi nit i on for s e ns i tiv e f e a t ur e i n the E d ward s Aqui fer Rul e s and ide n t i f i ed us ing th e I nstr uct i on s t o Geol og ists fo r Geolog ica l Ass e ssm ents ( T CEQ0585) Sens it iv e fea t ure s m u st be id ent i f i ed be fore th e t r ac t i s subdiv i d e d and p r opos ed l o cat ions for road s de fin e d so tha t th ey m a y be av oided. A g e olog ical asse ssm ent m u st be condu cted for al l prop osed d e v e l opm ents inc l ud ing resi den t ial subd iv ision s tha t ar e bui lt on l e ss than 1 0 acr es. A g e olog ic a sse ss m e nt m u st als o be c onduc t e d fo r pro j ec ts o n the c ont rib u t i ng z one of th e aqui fe r fo r whi c h t h e ap pl i cant des i r e s cov e r a g e under thi s doc um ent. Is olated s e n s it iv e f eat u r es iden ti f i ed in t h e Geol og ical As s e s s m e nt m a y n o t be s ealed, but in s t ead m u s t be protected by n a tu ral bu ff er areas f r o m t h e poten tia l i m pacts of s t or m w a ter ru n o ff f r o m any n e w de v e lop m e n t i n t h e area. T h e con f igu r atio n o f t h e bu ff er areas are des c ribed on th e f o l lo w i n g p a g e Sealin g o f se n s iti v e f eat u r es w ill o n l y b e p e rm i tted w h ere th e y are n u m e ro u s ex tens i v e, a n d i m pos s i ble to a v oid. Seali n g of s u rf ace s e n s it iv e f eat u r es w i ll require appro v a l f r o m th e Ex ec u t i v e Director of th e T C EQ. T h e s e sen s i tiv e fea t u r es ar e ana l og ous to ic ebe r g s in th at the su rf ace exp r es sio n re pres ent s on ly a fra ct ion o f th e spa t i a l e x te nt of the fea t ur e th at exi s ts jus t bel o w the soi l p r of il e B ecaus e th es e fea t ur es can a cce pt r echa r g e ov er a subst a nt ia l ar ea pr ov iding trea tm ent of run o ff only w ithin t h e depre s s i on m a y lead to deg r ada tio n of w a te r qu al ity in the a qui fe r. Conseque nt ly the bes t pr otec ti on of thes e fe atu r es is prov id ed by a natu ral b u ffe r a r ea s i z e d based o n th e dr ain a g e area for the fea t ur e. T h e d r a i nag e are a fo r a c a v e or s i nk hol e fr equen tly wil l inc l ude a we lldefi ned bo wls haped dep r es sio n, wh i c h m a y be a f e w f e e t t o m a ny y a rds ac ros s and w h ich rep r es ent s the l o cal c o l l aps e z one ov er a subte r r a ne an cav ity The t op of th e sha r p slope b r eak p r ese n t at t h e p e rim e te r o f such a col l ap se z one shou ld cons ti tu te the edg e of th e fea ture fo r the p u rpo s es of ca lcu l at ing se tback s, s i nc e th e st eep slo p es w ith in such a bow l usu a l l y prov ide li tt le o r no w a te r q u al ity fi lt ra tio n. T h e n a t u ral buff e r aroun d a f e at u r e sh oul d ext e n d a m i ni m u m o f 150 f e e t i n al l di rect i ons. Wh ere t h e bou n d ar y of t h e drai n a g e area t o t h e f eat u r e l i e s m o re t h a n 150 f eet f r om t h e f eat u r e, t h e bu f f e r s h ould ex te n d to th e bou n d ar y of th e drain a g e area or 30 0 f eet, w h ich e v e r is le s s I n so m e cases w h er e sev e r a l po int rec h arg e f eat ure s o ccur in c l ose prox im ity set b ack prov isio ns m a y be appli e d co ll ec tiv ely or se tba c k s m a y ov erlap, p r ov ided tha t th e m i nim u m s t anda rd s e tb ack for ea ch fe atu r e is re ta ined N o storm w a ter conv ey ance sy stem s (sto rm drains, r o adsi de sw a l e s Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 3

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etc. ) th at wou l d b r ing runo ff f r om outsi de th e e x i s t i ng d r a i n a ge a r e a s h ou l d ha ve o u t f a ll s w h ere the runo ff wou l d be di rec t e d to a sen s i tiv e fe atu r e by t h e na tur a l topog raphy T h e "n atu r a l s t a t e of a bu f f er w i l l ty pica lly be a com b ina tion of dens e na tiv e g r as ses a nd f o rb s in a m o saic o f sh rub s and t r e e s. Na tiv e v e g e tat i on, p a r t i c ula r ly l i v e oak tr ees, shou ld be pr ese r v e d w ith in t h e c a tc hm ent are a of cav es o r s i nk hole s St re am flow occu rr ing along t h e br anche s an d trunk s of l a rg e tr ees m a y e nhance inf i l t r a t i on by chan nel i ng rain fal l to the r oot z one ( T hu row e t al., 1987 ). I n troduc tion o f ornam e nta l tur f or l a nds ca ping within the ca tchm ent area is not rec om m e nded because it w i ll p r obab l y requ ire soi l am end m ents, f r equ e nt m a int e nanc e, and appl ica t i on of f e r t i liz er s, pe sti c id es, an d her b ic ide s T h e exis t i ng soil s t r u ct ure a n d v e g e tat i on a r e com p atibl e wi th p r eexist i n g recharg e con d i tio ns an d s hould requ ir e l i t t l e m a inte n a nce. I t is r ecom m ended t h at t h e buf fer s arou nd a po int r e c h arg e f eat ure o r c l us te r o f cont ig uous po in t rech arg e fe atu r es be m a inta ined in a n a tu ra l st at e to th e m a xim u m practica l ex ten t Thi s im plie s a const r uc ti onfree z one. Act i v iti es and s t r u ct ure s al low e d with in bu ffe r z ones ar e l i m ited. Res i den tia l y a rd s and hik i ng t r a ils m a y be loca ted in buf fe r z ones a s l ong as they ar e a t le ast 50 f e e t f r om the f eat ure. T h e al low a nc e of "y ards w i thin a b u f f er z one shou ld not b e tak e n to i m ply that reg u lar lan d sc aping i s app r op ri ate for buf fe rs. I n addi tio n, pes t i c id es a nd f e r t i liz er s shou ld n o t b e appl ied w ith in the bu ff er ar ea. T e m pora r y runof f pro t ec ti o n m easures shou ld be ins t al led ac cord ing to the recom m e ndations p r e sent ed in RG348 during any constru c t i on ac tiv i t i e s with in dr ain a g e area of the fea t ur e. T e m pora r y eros ion cont ro l m easures shou ld be pl ace d as n ear th e con s t r uc tio n as po ssi ble to m i nim i z e dist urba nce w ith i n the b u f f er z one s and dra i nag e area s. Wher e e x te nua ting c i r c um stanc e s exi s t and dev e lo pm ent ov er a sig n i f ic ant po int r echa r g e fe atu r e and it s cat chm e nt is prop os ed, the dev e lop e r ca n cons i d er dem onstr at ing that no fe asible a l t e r n a ti ves to con s tru c ti on over th e s e n s i t i v e f e atu r e exi s t. Feasibil ity of a l t e rna tiv es s houl d be ba sed pr im arily on te chn i ca l, e n g i nee r ing an d env i r onm ental cr ite ri a. F eas ibi l i t y should not be based pr edom inant l y on m a rk eting o r e c onom ic con s ider at ions or sp eci al or un ique cond it ion s which a r e c r ea ted a s a r e su lt o f the m e thod by which a pers on v o lunt ar ily subd iv ides o r dev e lop s land. A n ex am ple of a si tu ati on w h e r e sea l ing a s e ns it iv e fea t u r e m i g h t be w a r r a n ted is w h en th e num ber and dis t r i bu tio n of fea t ur es i s such tha t ac ces s is pr ec luded to a su bst a nt ia l por tio n of t h e tra c t tha t m i g h t othe rw is e b e dev e lop a bl e. 2.2. Sen s iti v e F e at u r es Ide n tifie d Duri ng Cons truc ti on Many sens i tiv e f eat ure s s u ch as so lut i on cav it ie s an d cav es, a r e not ide n t i f i ed during t h e G e o log i ca l Ass e ssm ent, but ar e dis c ov ered by excav at ion during the cons tru c t i on pha se o f a pro j e c t. T h is is esp e c i al ly com m on dur ing ut il ity t r en ching The f eat ure s e n coun te red at thi s ph ase of a pro j ect m u st be pr ote c t e d t o ensu re tha t wat e r qu al ity and th e s t ab il ity of the u t i l i t y insta lla ti on a r e prot ect ed. Rer out ing of the uti l i t y is alway s an opt ion and rea l ig nm ent of the l i ne should b e con side red. Featu r es d i scov er ed d u r i ng const r uc ti on o f roa d s, hous es, o r o t he r fa ci li ti es, wh ic h do not inv o lv e below g r a d e u t i l ity in st al lat i on, sha l l be f i l l ed wit h co ncre te. Grav el to f is t siz e d r o ck or sack s of g r av el m a y be pla ced in fea t u r e p r io r to p l ac em ent of the conc re te as long as a m i nim u m of eig h teen (18 ) i n che s of con c re te is us ed to c l ose the fe atur e. T a b l e 21 descr i be s the v a r i ous ty pes of fe atu r es and t h e m i nim u m trea tm ent r e q u ire d when con stru ct ing sewer s st orm dra i ns o r oth e r und erg r ound u t i l i tie s. T h e r e a r e two m a i n str a t e g i es fo r Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 4

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deal ing w ith th ese f e a t ur es depend ing on thei r ext e nt Sm all, i s ol ate d solu ti on c a v itie s m a y be com p lete ly fill ed with con c re te. An exam ple of the prope r m e thod of deal ing with th is ty pe of fea t ur e is show n in Fig u re 21. T h e featu r e i s com p let e ly fil l ed w i th conc re te and ty pical bed d ing and ba ck fil l m a ter i al is use d in the tre n ch. T a b l e 21. M i n i mu m Pro t ect iv e St an d a rd s f o r Sew e r an d St o r m Drain T r en ch es (f ro m T a bl e 51 E d w a rds A q u i f e r G u i d an ce D o c u m e n t R G 348, R e v i s e d Ju l y 2005) Case Desc rip t io n Co n cern T r eat men t No t i f i cat io n / A p pr ov a l 1 Se nsitiv e f e a t ure is le ss tha n or e qua l to six (6) i n c h e s i n a ll di rect i o n s and i s l o cat ed ab o v e t h e em be dm e n t of the pi pe A ll r o c k w ithin a n d surro un di ng the f e a ture is so un d. No t en viron m e nta l nor pipe i n te g r ity No ab at em en t req u i red No n e requ i r ed 2 Se nsitiv e f e a t ure is e ithe r la rg e r t h an si x (6 ) i n ch es i n at l east o n e dire c tion or is loc a t e d w ithi n t h e le v e l of the pipe e m be dm e n t. N o porti on of the se nsitiv e f e a t ure ma y i n t e rsect t h e p l an e o f t r en ch f l oor. A ll roc k w ithin a n d sur r o u ndi ng the f e a t ur e is s o u nd. Env i ronm e n ta l T h e se nsitiv e f e a t ure sha ll be f ille d w ith c onc re te G r a v e l to f i s t si zed ro ck o r sac k s o f grav el ma y b e p l aced i n f eat u r e p r i o r t o p l acem en t o f t h e co n cret e as l o n g as a m i n i m u m o f ei gh t een (1 8 ) i n ch es o f co n c ret e i s u s ed t o cl o s e t h e f eat u r e). Re quire s n o tif i c a tion a n d pr ior w r itten ap pr ov a l f r om the TC E Q 3 Se nsitiv e f e a t ure inte rse c t s the p l an e o f t h e t r e n ch f l o o r i s l e ss t h an f o u r ( 4 ) f eet i n an y d i rect i o n. A ll r o c k w ithin a n d s u r r ou ndi ng t h e f eat u r e i s so u n d Env i ronm e n ta l Se nsitiv e f e a t ure sha ll be f ille d w ith c onc re te G r a v e l to f ist si zed ro ck o r sacks o f gr avel ma y b e p l aced i n f eat u r e p r i o r t o pla c e m e nt of c onc r e te a t le a s t ei gh t een (1 8 ) i n ch es o f co n c ret e i s u s ed t o cl o s e t h e f eat u r e. T h e se w e r lin e o r sto r m sewer lin es sh al l b e con c ret e en cased f o r w i dth of the se nsitiv e f e a t ure plus a m i nim u m of f i v e ( 5 ) f e e t o n ei t h er en d. T h e en case m en t s h a ll pr ov ide a m i nim u m of s i x ( 6 ) inc h e s of c onc r e te on a ll s i de s of the pi pe a n d s h a ll ha v e c o m p r e s s i on s t r e ng th of a t le a s t 2,5 00 ps i ( 28da y s t r e ng th) T h e co n c rete m a y b e steel rein f o rced Re quire s n o tif i c a tion a n d pr ior w r itten ap pr ov a l f r om the TC E Q 4 Se nsitiv e f e a t ure inte rse c t s the pla n e of the tr e n c h f l oor a nd a n y o p e n i n g i n t r en ch f l oo r i s great er t h an f o u r ( 4 ) f eet i n an y d i rect i o n o r t h e t r en ch f l o o r i s un st ab l e Env i ronm e n ta l & S t ru ct u r al Req u i res an en gi n eered resol u t i o n at l east as p r o t ect i v e as Case 3 a bov e A dditi ona l pr ote c tiv e m e a s ur e s inc l udi ng r e r outi n g of line m a y be r e quir e d. Re quire s n o tif i c a tion a n d pr ior w r itten ap pr ov a l f r om the TC E Q A l l pl a n s su b m i t t e d t o t h e T C E Q regi on a l offi ce s h al l h a v e a si gn ed a n d dat e d s eal o f a T e x a s l i c e n sed P r of es s i o n al E n g i n eer. All pla n s w i ll be re v i e w ed on a cas eb y c a s e ba s i s an d addi tio n a l prote c ti v e m e a s u r es o r ad d i tio n a l i n f o r m a tio n m a y b e r e q u ir ed Other f e a t ur es di scov ered d u ring tre n ch ing opera tion s are m u ch m o re extensiv e a nd fi ll ing of the fea t ur e i s n e i t he r po ss ibl e nor d e si rab l e. I n cases wh ere the r e doe s no t appea r t o be subs tan t i a l, act iv e flow in t h e f eat ure, it m a y be possib l e to i s ol a t e t h e se ct ion in t h e v i ci ni t y of the t r en ch from the re st of th e c a v e s y stem An exam ple of t h is ty pe of in sta l lat i on i s sh own in Fig u re 22. S a nd bag s ar e in st al led to r e st ric t fi ll to t h e v i ci ni ty of the tre n ch an d con c re te is used to f i l l th e lower par t o f th e t r enc h and suppo rt the p i pe. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 5

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Figur e 2-1. Filled S o lution Fe atur e ( c our tes y K a thr y n W oodlee ) Figure 22. Exampl e of Filled Void in T r ench Exc a v a t i on ( c ourt e s y Don a ld Ba yes) I n so m e cases, i t m i g h t not be desi rab l e to pe rm anentl y encase the ut i l i t y pipe in concr e t e espe cia lly w h ere the p i pe m a y need t o be r e m o v e d for rep a ir o r r e pl acem ent. I n thos e ci rcum stanc e s an oute r ste e l enc a sem e nt pipe can be ins t al led an d t h e uti l i t y pipe ins t a lle d ins i de of i t Sec tion and pr of ile v i ew s of th is ty pe of ins t a l l a t i on a r e s hown in Fig u r e 23 and Fig u re 24. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 6

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Figur e 2-3. Utilit y P i p e E n cas ed in E x ter n al S t eel P i pe (cour tes y of Kathr y n W oodle e ) Figure 2-4. P r ofile V i ew of E n cased Utilit y P i p e (courte s y of K a thr y n W oodlee) When a larg er fe atu r e app ears be an act iv e con dui t f o r f l ow it m a y be approp r i at e to m a int a in hy drolog ic conn ect iv ity acr oss the tre n ch ex cav ati on. T h is can b e accom p li shed by instal li ng a 3 inch Sch e dul e 40 PV C pip e between the two i s ol ate d cav e sectio ns. An exam ple of thi s ty pe of ins t al la tio n i s shown in F i g u re 25. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 7

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Figure 2-5. Cav i ty Fi ll w i th P i pe to P r eserv e H y drologi c Conne ctiv ity Tem pora r y cov e ring of v o ids w h en cons tru c t i on a c t i v ities are h a l t ed c a n be a ccom p lishe d by cov e ring with fi lt er fa br ic and then p l y w ood weig hted with conc ret e block s This wil l prev en t sedim e nt from the tre n ch b e ing inadv e r t en tly in tr oduc ed in to the c a v ity 2.3. Ca v e s O p ening s of cav es are sen s it iv e fe atu r es th at shou ld hav e natu ra l bu ffe rs as d e s c rib e d a bov e. I n addi tio n, the siz e of th e o p e ning c r ea tes t h e oppo rtun i tie s for ot her po llu tan t s t o ente r the aqu i f e r. Many cav es in the Edwa rd s were h i s t or ica lly use d fo r tr ash, d e br is, and g a rbag e disp osa l T h e m a teria l f ound in cav es o f t e n in clu d es pa int, so lv ents, and o t he r tox i c/ haz a rdou s m a teria l s. Ru n off e n te ri ng the cav es can l each tox i c com pounds a nd conv ey them to the aqu i f e r. Conseque nt ly cav es t h at a r e ide n t i f i ed in the g e o l og ica l a sse ssm ent and tha t h a v e open i ng s l a r g e enoug h to ac com m odate a pe rson m u st be f i t t ed wi th a cav e g a te su ch as the one s hown in Fig u re 26. T h e g a te ha s tw o m a in p u r poses. T h e f i r s t is to redu ce acc ess t o the cav e a nd p r e v ent th e d i spo s a l of was t e s i n t h es e se nsi t i v e fea t u r es. T h e sec ond pu rp ose is to p r ev ent un tra i ne d indiv i du al s f r om acce ssi ng the c a v e w h ere t h ey m i g h t poten ti al ly beco m e trapped. The g a te shou l d als o pr ov ide a lock able a cce ss fo r qual i f i ed indiv i du al s to per f orm hy drog eolog i cal or b i ol og ical s t udi es. T h e discu s s i on o f cav e g a te s be l o w is m odif i ed from War to n (2002 ). Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 8

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Many of thes e cav es are ha bit a t for enda ng ered s p ec ie s; co nseq uen tly the g a te sh ould p r ov ide fo r fre e excha n g e of air, wa te r, org a nic deb r is, a nd sm all m a m m als that are im portan t com ponents of the cav e e c osy s tem I f cav es o r o t he r s e ns it iv e f eat ur es c ont ain Fede ra lly listed endang ere d sp e cies such as k a rs t inv e r t eb rat e s, p r o j ect p l an ner s shou ld con t ac t th e U SFWS to e n sure tha t th ei r act iv iti es w i l l no t t ak e a l i st ed sp ec ies. T h e a ppl ica n t m a y also w i sh t o con s ul t t h e T C EQ s Op tional Enhanced Mea s ures f o r the Protect ion of W a ter Q uality in the Edw a rds Aqu ifer and Related Karst Features tha t may be Habitat for Karst Dwel ling Invertebra t es: Append ix B t o RG-348. F i g u r e 26. T y p i cal Cav e G a t e w i t h S ecu re En t r an ce ( M ike W a r t o n PBS& J) I n Central T e xa s, the m o st com m on ty pe of cav e en tr a n ce o ccu rs as a sink hol e, o f ten foun d a l ong rock j o in ts. En tran ce ope ni ng s are usua lly posi tio ned on sem i f lat g r ound or a l on g hillsi d e sl opes T h e or ien t a tio n of en tra n c e open i ng s i s usu a l l y v e rti cal. Ho riz o n t al dev e lopm ent wi thi n cav e s m a y occur a t sh al low dep t h s I n this ty pe o f cav e s t r u ct ure, the k e y posi tio n of a pr ospec tiv e c a v e g a te is u s ua lly hor iz onta l with s o m e deg r ee of rec e ss in to th e en tra n ce. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 9

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T h e co ncep t of g a t e "t ran s paren c y im pli e s spe c i f ic al ly tha t the g a te is a nonsolid c o v e ring t h at w ill n o t im pede, b l ock or prev ent t h e v e rt ica l f a l l of air, w a te r, or n a tu ra l org a ni c m a teria l s f r om ente ring t h e cav e sim i l a r t o w h at occ u rs na tur a l l y Thus, the tr ansp are n t g a t e i s sem i open for thes e func ti ons. I n the cav e entra n ce eco sy stem surfa c e rela ted a nd noct u rn al inv e rteb ra te spe c i e s m a y reg u larly pass th roug h the g a te in a m a nne r not s i g n ifi can tly al te red by the pres ence of th e g a te. I n T e xas, end a ng ered inv e rte b ra te sp eci es ar e tro g l obit i c in na tur e nev e r lea v e the cav e en v i ronm ent, and n e v e r us e o r ac ces s th e g a te. They are cri t i c a lly depen d en t on the g a tes abi l i t y t o all o w unim peded washi n, or tra n spo r t of org a nic fo od sou r ce m a teri al s to en te r and re ple n is h the cav e. Up to sev e n com m on t y pes of g r ound m a m m als also fr equen t T e xa s c a v e s and hav e im port a nt na tura l rol e s in the cav e eco sy stem T h e i r poi nts o f a cce ss a nd eg re ss th roug h the cav e g a te are spe c i f ic in loca ti on Th e g a te m u st fa ci li ta te th eir eas ies t po in ts o f acc ess The acc ess por tal des i g n and s i z e ar e se t t o an e i g h tinch diam ete r or squar e ope ning as shown in Fig u re 27. Figur e 2 7 M a mma l A c c e s s P o r t a l s a l ong E dge of Ga te 2.3. 1. G a te C o n s t r u c tio n Prio r to g a te con s t r uc tio n, t h e cav es en tr ance m a y require c e r t a i n pre p ar at ions fo r acce pta n ce of the g a te. I n w e lded cons tr uct i on w h e r e g a te s ar e cu s t om built and fi tte d on s i t e com m ercia lly m a de w e lding blank e t m a ts shou ld be d r aped acr oss the en tr ance o p en ing in ba sk et posi t i on i n orde r t o p r ev ent con t am ina tion of th e c a v e by slag an d w e ld ing re sidu es. T h e g a t e i s a lev e l hor i z ontal g r id c o v e r co nst r uc t e d f r om 2inch by 2inch by 3/8inch st eel ang l e. T h e m o st im porta n t stru ctu r a l com ponen t is th e suppo rt ing substruct ure d arr a ng em ent of cr oss b eam s and d r i l l e d an chor po int s A n cho r s a r e u s ual l y 1/4inch to 1inch di am eter reb a r f r om 8 inches to 10inches in leng th (F ig ure 28). Horiz onta l beam suppor ts are bu il t by welding to g e th er two pi ece s of ang l e iron to form a boxshaped be am that i s s o l i d w e lded t o the poi nt se t ancho r s. O n ce the su bst r uc tur e is com p lete d, th e g r id pane l ar rang em ent of bar ang l es m a y beg i n. T h e bar ang l es a r e p l ace d on t h eir edg e side s, Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 10

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w ith ang l e p eak poin t ed e i t h er t o the le ft o r to the rig h t (a ll p o in ted in th e sam e di rec tion th roug h out the g a te) B y pla c ing t h e ang l e s on t h ei r edg e si de, t h e bar r i e r th ick n ess as pect of th e g a t e panel be com e s a l m o st th re e inc h es th ick ins t ead o f the 3/8inch th ick n ess of t h e a n g l e. B a r sp ac ing thro ug hout t h e g a te and acro ss the pane l a r e set to prov ide a cl ea r ope ning of 1.5 in ches i f th e cav e is not use d by bats, otherw ise the open i ng shoul d be 5.75 inch es. T h e di re cti on of ai rf lo w exchang e t o and from the cav es en tr ance m a y determ ine the l e f t or rig h t po in t i ng posi tion s of ang l e peak s. T h e a n g l e sh ape woul d be t u rn ed to su ch a pos it ion tha t c ups a nd prom otes the best a i r f low ex chang e I t s hould pr ov ide the l e v e l of air f low co nduc tiv ity tha t is a substan t ial o r prom inent cha r ac te ri st ic of the cav e. I n th is cons tru c t i on, the lo ca tion and po si ti on of th e g a te s acce ss and eg res s door is predeterm ined. T h e a cce s s door as sem b ly is: (1) ty p i ca lly 30 inch es squar e ; (2 ) tr ansp are n t in d e sig n ; (3 ) a hing ed door; an d (4) cont ain s a conce a le d l o ck m echanism and acc ess p o in t as s hown in Fig u re 29. T h e round h o le i n the g a t e is s i z e d so t h at a p e rso n can reac h t h roug h t h e g a te to a cces s t h e lock w i t h i s co nc eale d be low the g a t e T h e conce a le d l o ck box lo cat ion in thes e g a tes prev ents any dir ect at ta ck T h e lo ck box is d e s i g n ed t o house a 2inch wide l o ck with 3 / 8inch sh a c k l e. A f te r t h e acc ess doo r is in sta l l e d, the la st st ag e of th e con s t r uc tio n i s u s ua lly t h e p l acem ent o f horiz ont al st if fene rs a c ro ss ang l e expan s es. On ein ch or 2inch wide by 3/8inch thi c k flat ba r stock is use d for the s t i ffe n e rs. St if fen e r sp aci ng usual l y does not exc eed a di st an ce of f i v e feet. F o llow i ng the c o m p letio n o f al l w e l d ing th e la st stag e of g a te com p le tion is to ap ply a prot ec tiv e m e tal coat ing with a hig h qual ity rust inhi bi tiv e pai n t T h i s is ca re ful l y hand bru s hed on in ste a d of sp ray e d. Fol l owi n g g a te com p letio n, th e und er h a ng ing blank e t b a sk et is r e m o v e d and the si te shoul d be thor oug hly clea n e d of any fore ig n m a teri als. Figur e 2 8 E x a m pl e of A n c hor Re ba r 2.4. Strea m Bu ffer s Natur a l bu ffe r ar eas ad jac e nt to s t r eam s and natu ral drain a g e way s play an i m portant ro le i n m a intain ing pred ev elopm ent w a t e r q u al i t y T h e ri par i an v e g e tati on s t ab il iz es s t re am channels and Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 11

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F i g u r e 29. Examp l e Cav e G a t e A c ce ss flood pla i n are a s, reduc ing eros ion. I n addi tion th ey prov ide an are a to fi l t er ov erlan d f l ow f r om ad j a cen t dev e l opm ent. Co nseque nt ly al l s t r eam s sh ould h a v e an undi stu r bed nat i v e v e g e tation buff e r on eac h s i de a s fo l l o w s: Stre am s drai ning 640 ac res (one squ a r e m ile) or g r ea t e r s houl d hav e a m i nim u m buff e r of 300 fee t f r om the c e nt er l i ne on eac h s i de o f th e s t r e a m Streams draining less tha n 640 acres but 320 or more ac res should have a mini mum buffer of 200 feet f r om the cente rline on ea c h side of the stream. Stre am s draini ng less th an 320 acre s but 128 or m o re acre s shou ld hav e a m i n i m u m buff e r o f 100 fe et from the cent e r lin e on e ach sid e of t h e st re am Stre am s or swales dra i n i n g less than 128 acr es but 40 or m o re acres shou ld h a v e a m i nim u m buffer of 50 f eet from the c e nt er lin e on e ach side of the d r a i nag e Stre am s or sw ales dra i n i ng less th an 40 acr es but 5 or m o re acres sh ould hav e a m i ni m u m buffer of 25 f e e t f r om the c e nt er lin e on each sid e of th e dr ain a g e Site p l an s s u b m itted f o r T C E Q rev i e w m u st s h o w th e lo cat io n o f al l strea m b u f f e rs i n ad d itio n to th e pla n ele m ents requ ired b y th e Ed w a rds A q u i f e r R u les I f t h e area w i th i n t h e des i gn ate d bu ff er h a s b een altered b y clearin g c o n s tru c t i o n o r o t h e r activ itie s, th en U SFW S m u st b e co n s u l t e d Buffe r z ones sh ould g e ner a lly r e m a in f r ee o f co nst r u c ti on, d e v e lopm ent, o r o t h e r al ter a t i ons, a l thoug h sto r m water tre a tm ent sy stem s can b e con s t r uc t e d th ere if the nat u ra l d r ai n a g e to th e si te is less than 128 a c re s. The n u m b er of roadway s cros sin g throug h the buffe r z ones shoul d be m i ni m i z e d and construc ted onl y w h en necess a ry such as w h en a sig n ific ant po rt io n of the si te ca n only be rea c hed by cr oss i n g a buf fer z one. An ex am p l e o f a s i tua tion when a ro ad c r os sing wa s neces sa ry is show n in F i g u r e 211. N o te tha t ther e i s on ly a sing le cro ssi ng of eac h buff e r. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 12

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Other al te ra tion s wi th in b u ffe r z ones cou l d inc l ud e uti l i t y cro ssi ng s, but only when ne cess a ry fenc es, low im pact pa rk s, and op en sp ace. R o adw a y s and u t i l i t i es cro s s i ng s sho u ld b e app r ox i m a tely perpendi cul a r t o th e buff e r z one. Low im pact park dev e lopm ent within the buf fe r z one shoul d be lim ite d to t r ai ls, picn ic fac i l i t i e s and sim ila r con s t r uc tion th at d o no t s i g n ifica n t l y alt e r the ex is ti ng v e g e tat i on. Pa r k ing lots and road s sig n i f i c ant l y alte r ex is ting v e g e tati on and a r e no t consi d er ed low im pact. N e ith er g o lf cou r se dev e lopm ent nor was t ewa t e r eff l ue nt irr i g a tion sh al l tak e pla ce in t h e bu ff er z o n e T h e s e res t r i c tio ns a r e an i m portant rea s on why buf fe r z ones m u st be ide n t i f i ed befo re the tra c t i s subdiv i d e d. V a riou s ty pes of dev e l opm ent ar e c ons ist e nt w ith st re am buffe rs a s dem onstra t ed be low. One ty pe is a ty pic a l suburb a n si ng lef am ily de velopm ent wit h a lo t dens it y three to f o u r lot s pe r a c r e t h at ne ces si tat e s the u s e of cur b an d g u tt e r I n this sc ena r io es sen tia l l y all the im per v i ous cov e r i s con n ec ted. S t orm water runo ff d r a i ns d i rec tly to the s t r e e t wher e i t is c a ptu r ed in a n inl e t an d conv ey ed by storm sew e r in a sy stem that r e qui res larg er p i pe d i am ete r s as m o re an d m o re area con t r i bu tes. D i s c harg e is then d i r ect ed to a creek at th e low e r end o f t h e dev e lopm ent or to a co nst r uc ted tr apez oi dal c h ann e l. T h e c onv enti ona l des i g n philo sophy has been to conv ey the storm water runo ff qu ick l y and safe ly away from the sub d iv is ion Depend ing upon l o ca l r e quir e m e nts, a wa te r qu al it y pond m a y be const r uc ted j u st pr ior to di s c harg e to the cre e k Ev en i f a pond is prov ide d, li tt le or no ut il iz at ion of bu ff ers oc curs Fig u r e 2 10 prov ides an exam ple of a 14 4lot si ng lef am ily subdiv i si on bo und on one s i de by a cre e k w i t h 150 f eet of b u ff er w i dt h on each si de. I n this cas e a sedim e nta t i onfi lt rat i on p ond i s prov id ed at th e downs tr eam end. Fo r th is ex am ple, app r oxim a t e ly 39 acr es o f dev e lopm ent ar e conv ey ed to th e pon d, to ta lly by passi ng the buf fe r. Fig u re 211 is an exam ple of sm all, cl ust e r e d si ng lef am ily lots s itu at ed ar ound stre am buffer s T h is c l us te ring le av es la rg e undis t ur bed a r ea s of land as wel l as set b ack s f r om the cre e k s T h es e sm all lo ts, 60 80 f eet of fron t ag e, re qui re s t o r m sewers, bu t wi th t h e c r eek se tback s, su ff ic ien t area i s av ai lab l e fo r f r eq ue nt s t o r m sew e r d i s c harg es upg r adient f r om the cre e k buf fer W h i l e it is di ff icu lt to com p le te ly offs et the hy dro l og ic im pact of a dev e lopm ent o f th is densi t y the s e t back s and m a xim i z i ng of s h eet f l ow m i nim i z e s the im pact s. I n s tream ponds a r e prov ided in th is exam ple to supp lem e nt th e v e g e tativ e m easures fo r wa ter qua li ty and prov id e pea k flow cont ro l. Fig u re 212 is an exam ple of a la rg er, ru ra l lo t subd iv isi on ( i ndiv i du al lot s la rg er than one acr e) w ith buf fe rs m eet ing th e c r ite ri a d e sc rib e d in th is doc um ent. T h es e s i z e lot s o f fe r an opp or tuni ty to m a xim i z e sheet flow an d redu ce the are a con t r i bu t i ng to a c once n t r at ed d i sc harg e th at m u st then be r e tu rned to shee t f l ow by the m e thods discu s s e d prev ious ly T r adi tio nal l y the roadway s would hav e a road sid e di tc h on both s i des. Howev e r, i n a desig n m a xim i z i n g sheet f l ow, the h a l f of the ro adw a y drain i ng to the low sid e of th e rig h tofw a y is allow e d to co nt in ue as shee t f l ow into the l a rg e sing lef am ily lot (F ig ure 213). A l so no te that the l i m it of di stu r ba nc e is on ly a frac tion of the lot siz e (Fig ure 2 14). Great er bu ild ing setba c k s allow th e bui lde r to eas ily r oute any drai nag e around t h e house. Dra i n ag e or c onse r v a tio n e a sem e nts m u st be s hown on ap p r ov ed pla t s and d eed re st ric t ions prov ide d t o the hom e buy er lim it lands caping to nat i v e or nat i v e adapte d plan ts th at r e qui re l i t t l e or no fe rt il iz ers and are d i s ease res i s t a n t. W ith thes e sim p le de sig n fea t ur es, t h e ef fe ct iv e buf fer w i dth a l ong str eam s is in cre a sed and u n conne cte d im perv ious co v e r is m a xim i z e d. On the uphi ll s i de o f th e roadw a y the road sid e sw al e has m u ltip le po in ts of dis c harg e unde r th e ro adw a y m u ch as a storm sew e r in a m o re den s e de v e lopm ent. T h i s d r a i nag e i s th en conv ey ed in an ea s e m e nt alo n g lo t lin es an d th en r e tu rned to s h eet fl ow at the buf fer Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 13

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S T R E A M B U F F E R 14 WA TE R QU ALI T Y PON D ST O R M SEW ER IN L E T 39 AC R E DRA I NA G E AR EA F i g u r e 21 0 T r ad it io n a l Dev e lo p m en t A d j acen t t o St ream Bu f f e r ( c o u r t e s y M u rf ee En g i n eerin g )

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15 Figur e 2 1 1 E x a m pl e of S m a ll Lot Clu s te r T y p e De v e lopme n t (c our te s y M u r f e e E ngine e r i ng)

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16 Figur e 2 1 2 E x a m pl e of La r g e Lot Low De ns ity D e v e lopme n t (c our te s y M u r f e e E ngine e r ing)

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F i g u r e 21 3 Det a il o f Ro ad Se ct io n Sh o w in g Veg e t a t e d T r eat me n t A r eas Figur e 2 1 4 De ta il of Lot La y out w i th Wa te r Qua lit y E a s e m e n ts Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 17

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3. Constructi on Erosi on and c ont rol m easu r es fo r cons tru c t i on a c t i v iti e s are d e sc rib e d in RG348. T h e s e m easur es also a pply to con s t r uc tion activ i tie s cond uct e d in c o m p liance w i th th ese e n h a nced p r ot ect io n m easures wi th the fol l owi n g additi ona l r e qui rem e nts. 1) Sedim e nt ba sin s and tr aps, which a r e requ ir ed fo r co m m on drainag e are a s s e rv i n g at lea s t 1 0 acre s w i l l be de sig n ed to captu re th e runof f from th e 2y r 24hour st orm T h e s e v o lum e s area shown in T a b l e 31. T a b l e 31. Cap t u r e Vo lu mes f o r S e d i men t Basin s County Cubic Fe e t / A c r e Bexar 8,000 Com a l 8,000 Hay s 8,000 K i n n ey 7,250 Medi na 8,000 T r av is 8,000 Uv alde 8,000 Wi ll iam s on 8,000 2) T e m pora r y sed i m e nt ba sin s and t r ap s m u st not be i n sta l l e d in th e bu ff er ar ea s of na tu ra l drai nag e s wi th a tr ibu t ary a r ea o f m o re th an 128 ac res. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 18

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4. Permanent BMP Imple m ent ation T h is s ect ion d e sc rib e s t h e conf ig urat ion an d si z i ng of perm anen t bes t m a nagem e nt prac ti ce s (BMPs ) to m eet th e re qui r e m e nts of th ese o p t i ona l m easures. Add i t i ona l in for m ation reg a rd ing desig n c r i t er ia and m a int e n a nce o f BMP s i s con t a i ned in RG348. 4 1 Ha zardous Ma te ria l Tra p s (HMT) Roadway s capa b le of conv ey ing at l eas t 25, 000 v e hi cl es a day m u st inc l ud e a haz a rdou s m a ter i a l trap (HM T ) These H M T s m u st be desig n ed to ret a in a spi ll o f 10,000 g a l l ons o f liqu i d haz a r dous m a teria l T h es e m a y be of a v a riety of des i g n s in c l ud i n g those used p r ev ious ly by the T e xa s De partm e nt of T r ansp or tat i on (T xDO T ). Fig u r e 41 de m onst r at es how an HM T can be sited wi th in the foo t pr in t o f the sto r m w a te r co nt rol ( a s a nd fi lt er in th is cas e) to ach iev e bo th ob j e c t iv es w i th out incr eas ing the la nd o r hy drauli c he ad requ ire d. N o te tha t t h e inv e rt o f the o p ening s f r om the spl i t t er b ox to t h e H M T i s set s lig ht ly low e r th an th os e into the s e dim e nta t i on ba sin. T h is a llow s any haz a rdous sp il ls as we ll as the f i r s t f l u s h of ru n o ff t o be cap tur e d by the HMT Onc e the HMT is fu ll the ba ck water lev e l r i se s and a llows the r e m a ining runof f to en te r th e sedim e nta t ion basin di rec tly Figur e 4 1 Ha za r dous M a te r i a l T r a p i n s i de Sa nd Filte r T o el im inate th e ne ed for m a nual dra i n i ng of a haz a r dous m a ter i a l tra p a f te r a ra in ev ent T x DO T dev e loped an aut o m a tic sip hon sy stem to dra i n the H M T when i t f i l l s wit h r a in water Fig u re 42 shows a ty pica l s i phon det a il from a se t of TxDOT con s tru c t i on p l an s. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 19

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2 f t 7 f t Fr am e a n d Li d 1. 0 1. 5 1. 5 1. 5 1. 5 Ho le f o r V a lv e Ac c e s s Haz a r d ous M a t e r i al V o l u m e Dome Dr ain 4 PVC Dr ai n 12 Cl ay Li ner 4 Sch 40 G a l v V a l v e Cl ose d St e e l Pipe V a l v e O pen 4 Ecce n t r i c Pl ug V a l v e Figur e 4 2 T y pic a l T x DOT A u toma tic S i phon De ta i l T h e s i phon dev i c e is d e s i g n ed to d r a i n the t r ap af te r i t be com e s fu ll f r om a r a in ev ent, bu t is in sta l l e d at an el ev atio n abo v e the ful l cap ac ity of th e trap. T h ere f o r e, as long as a haz a rd ous m a teria l sp il l does n o t o ccu r dur ing a rai n ev ent th e sy stem should c ont ain the s p i ll. T h e sip hon i s prov ided w ith by pass and shuto f f v a lv es so th at al er t onscene r e spon der s c a n s hutof f the au to m a tic siph on and the r eby m a intain s o m e conta i nm ent ev en in the ev ent of a con c urr e nt ra in/ s pi ll Other opt ions fo r sp il l con t ainm ent a r e p r es ent e d in th e m a in sec tio n of RG348. 4.2. T o t al Su sp end e d So lid s (TSS) Remo v a l 4.2. 1. S t ep 1: R e q u i red T S S R e mov a l R e du ct i o n of 80% o f t h e annual T S S l o ad i n s t or m w a t e r run o ff f r o m a s i t e i s requ i r ed f o r al l n e w dev e l o p m en t w i t h ou t re g a rd t o t h e propos ed l e v e l of i m pe rv i o u s co v e r. O n redev e l o p m en t pro j ects th at i n v o lv e m a j o r ch ang e s to e x i s ti n g i m per v ious c o v e r an d i n cl u d e m odi f i catio n of th e drain a g e s y s t e m 80% T SS rem o v a l m u s t be ach ie v e d f o r the en tire proj ect. Exam ples of r e dev e lopm en t pro j ec ts whe r e t h e en ti re s ite m u st be tre a te d inc l ud e hig h way widen ing pro j e c t s a cha n g e in l a nd use from sing le fam i l y residen t i a l to m u lti fam i l y or com m ercial, and sub s t a nt ia l exp a ns ion o f im perv ious c o v e r on a n e x is ting com m ercia l dev e l o p m ent. All t h e T SS load ca lcu l at io ns ar e ba sed on Equa tio n 4. 1 Equat i on 4. 1 L = A P Rv C 0 226 Wher e: L = annu al p o l l ut ant loa d (p ounds) A = Cont rib u t i ng drai nag e area (a cre s ) P = Av erag e annua l pr ec ipi t at ion (in c he s) Rv = Appr opr ia te r unof f co eff i c i en t C = A v erag e T SS c oncen tr ati on (m g / L) 0.226 = u n i t s co nv ersi on f a ctor Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 20

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Moni to ring da ta fr om the City of Aust in ind i ca te s tha t t h e T S S con cen tr at ion fro m dev e loped a r eas is 170 m g /L and that f r om natural a r ea s is 80 m g /L. Consequen tly the req u ire d 80% lo a d reduc ti on i s ca lcu l a t ed as : Equat i on 4. 2 L M = ( 0 8 0 226 )( A P 0 9 170 ) Wher e: L M = Requir e d T SS rem o v a l (po unds ) A = I m perv ious area (a cre s ) P = Av erag e annua l pr ec ipi t at ion (in c he s) Th is e qua tion sim p li fi es to: Equat i on 4. 3 L = 27 7 ( A P ) Wher e: L = Requi red T SS rem o v a l (pound s) A = I m perv ious area (a cre s ) P = Av erag e annua l pr ec ipi t at ion (in c he s) I m perv iousnes s is the pe rc ent, o r dec i m a l fra ct ion, o f the to ta l si te a r e a cov e red by the sum of roads pa rk ing lot s s i dewa lk s, roo f top s a nd o t he r im perm eable sur f a ces. R oof area s d i re ct ed t o rainw a te r ha rv est i ng sy stem s are exem pt from the tr eatm e nt re qui rem e nt. Wh e n calc u la t i ng the im perv ious are a of a re sid e nt ial d e v e lopm ent the a s s u m p tions show n in Ta ble 41 w ill app l y to im perv ious ar ea o n ea ch l o t to th e lo t s i z e un les s th e actu a l fut u re im perv ious co v e r is k now n to be g r eat er. Ann u al pre c ip i t a tion by county is shown in T a b l e 42. T a ble 4 1 Impe r v ious Cov e r A s s u m p tions for Re s i d e ntia l T r a c ts L o t Siz e A ssumed Imp erv ious C o v er ( f t 2 ) > 3 ac res 10,000 Between 1 and 3 ac res 7,000 Between 15,000 ft 2 and 1 a c re 5,000 Between 10,000 and 15, 00 0 ft 2 3,500 <10,000 ft 2 2,500 T a ble 4 2 A v e r a g e A nnua l Ra infa l l by County Count y Average Annua l P r eci p i t a t i on ( i n c hes ) Bexar 30 Com a l 33 Hay s 33 K i n n ey 22 Medi na 28 T r av is 32 Uv alde 25 Wi ll iam s on 32 Appendix A 21 T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7

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4.2. 2. S t ep 2: S e le ct an A p p r o p r iate B M P Selec t a B M P or s e r i es o f B M Ps tha t w i l l ach iev e at leas t an 80 % red u ct ion in T SS. T h e h i g h e r the e f f i ci ency of th e BMP, the le ss r unof f th at wi ll n e ed to be tre a te d to a c hi ev e the r e qui red re duct i on. T h e T SS r e m o v a l eff i c i ency fo r ea ch ap prov e d BMP i s shown in T a ble 4 3. T a b l e 43. A p p r o v ed BM Ps an d T SS Remo v a l Ef f i ci en c y B M P TSS Reduct i on ( % ) Reten tio n/I rrig a t i on 100 AquaLog i c C a rt ridg e F i l t e r S y stem 95 Wet B a si ns 93 Const r uc ted Wet lan d s 93 Sand Fi lt ers 89 Biore t en ti on 89 Veg e ta ted F i lte r S t r i ps 85 Ext. Det e nt ion B a si n 75 Grassy Swale s 70 Wet Vaul t See Sec t i on 3.3 o f RG348, Rev i sed J u ly 2005 4.2. 3. S t ep 3: C a lcu l at e T S S L o a d R e mov e d b y B M P s T h e fo llow i ng sec tio n de sc ribe s how to d e te rm ine th e load rem o v e d by a propos ed BMP( s). The load rem o v e d depends o n t h e am ount of T SS ent e r i ng the BMP ( s ) and i t s e f f ect iv eness The l o ad en ter i ng ea ch B M P is ca lcu l a t ed f r om the su m of the con t r i bu tio n o f the im perv ious and perv ious a r eas w i th the i r r e spec tiv e s t o r m w a ter con c e n tra t ions fo r the B M P ca tc hm ent are a Th is calc u la t i on a ssum e s t h at n o runo ff by passe s the tr ea tm ent fa ci li ty and ass i g n s the appr opr ia te runof f co ef fi cie n t a nd T SS concen tr at ions to the perv io us and im perv ious a r ea s. Equation 4.4 LR = ( B MP efficienc y ) x 0.2 26 x P x (A I x 0. 9 x 1 70 m g / L + A P x 0.03 x 80 m g /L) Wher e: LR = Load rem o v e d by B M P B M P = T SS r e m o v a l effi ci ency (exp res s ed a s a d e c i m a l f r ac t i on f r om ) AI = im perv ious tr ibu t ary a r ea to t h e B M P (a c) AP = perv iou s t r ib uta r y are a (ac ) P = av erag e annu al p r e c ip it ati on ( i nch e s, Tabl e 42) Whic h s i m p lifi e s to: Equat i on 4. 5 LR = (BMP eff i c i en cy ) x P x (AI x 34.6 + AP x 0.54 ) Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 22

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4.2. 4. S t ep 4: C a lcu l at e F r ac tio n o f A nnu al R u n o ff to B e T r eat ed B a sed on th e lo ad r e duc ti o n cal cul a t e d abov e for eac h of the B M P s i n st al led at the si te an d th e requ ire d lo ad re duc tion, ca lcu l at e th e fr ac tion of an nu al ru nof f to b e t r ea ted u s in g Equation 4.6 T h is c a l c ul at ion a ssum e s a const a nt con cen tra t i on of TSS in t h e r unof f. L Equat i on 4. 6 F = L R Wher e: F = Fra c t i on o f th e ann u al r a inf a l l t r e a te d by the BMP L R = Load rem o v e d for e a c h BMP f r om Step 3 c a lc ula tion (pou nds ) L = Requi red lo ad r e duc tio n from Step 1 (pou nds ) 4.2. 5. S t ep 5: C a lcu l at e C a p t u r e V o lu me Th is st ep re la tes t h e st at is ti cal pr oper t ies of s t orm siz e and flow ra te in t h e reg u l a ted a r ea t o th e tot a l v o lum e of runof f. T h e s e ca lcu l at ion s depen d on whethe r the B M P is a c a pt ure and tre a t de v i ce, such as a san d f i l t e r s y stem or a flow th roug h BMP suc h as a swa l e o r wet v a ult. For f l ow th roug h ty pe dev i ces ( s wal e s and we t v a ul ts ), the siz e i s ca lcu l at ed us i n g a rainf a l l in tens ity of 1.1 inc h es /hou r. Captur e v o lum e for captu re a nd t reat dev i ces is dev e lo ped from T a b l e 4.4, whi c h re lat e s ra inf a l l d e pth to th e p e rc ent a g e of an nual ra in fal l tha t o ccu rs in storm s l e ss th a n or equa l to t h i s dept hi. e 100% of the ann u al rai n f a ll o ccu rs in s t orm s of 4 i n ches o r le ss on av erag e, while 78 % of t h e annua l runo ff oc cur s in s t o r m s of an inch or less For BMPs des i g n ed to cap ture an d tre a t th e run o ff, th e v a lue, F, calcu la ted in Step 4 is used to en te r Table 44and fin d the rai n fa ll dep t h a ssoc i a t e d with th is f r a c t i on. Once the appr opr ia te ra in fa ll de pth h a s bee n det e rm ine d from T a b l e 44, the wate r qual ity v o lum e for e ach B M P ca n be cal cul a ted fr om : Equat i on 4. 7 WQV = Rain fa ll d e pt h x R unoff Coef fi cie n t x A r ea Wher e the ra in fal l dep t h is dete rm ined from Tabl e 44, th e r unof f coe f f i ci en t co m e s from Fig u re 43 or is calcu lat e d us ing Equat i on 4.8, an d the a r ea is th e por tion o f si te co nt ri buti n g runoff to the B M P Equat i on 4. 8 Rv = 0.05 + 0.0085 (I C) Wher e: I C = Percen t im perv ious co v e r Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 23

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T a ble 4 4 Re la tions hip be tw e e n Fra c tion of A nnua l Ra infa l l a nd Ra infa ll D e pth (inc he s ) Rainfall Rainfall Rainfall Rainfall F De pth F De pth F De pth F De pth 1.0 0 4.0 0 0.8 0 1.0 8 0.6 0 0.5 8 0.4 0 0.2 9 0.9 9 3.6 6 0.7 9 1.0 4 0.5 9 0.5 6 0.3 9 0.2 8 0.9 8 3.3 3 0.7 8 1.0 0 0.5 8 0.5 4 0.3 8 0.2 7 0.9 7 3.0 0 0.7 7 0.9 7 0.5 7 0.5 2 0.3 7 0.2 5 0.9 6 2.8 0 0.7 6 0.9 4 0.5 6 0.5 0 0.3 6 0.2 4 0.9 5 2.6 0 0.7 5 0.9 2 0.5 5 0.4 9 0.3 5 0.2 3 0.9 4 2.4 0 0.7 4 0.8 9 0.5 4 0.4 7 0.3 4 0.2 3 0.9 3 2.2 0 0.7 3 0.8 6 0.5 3 0.4 6 0.3 3 0.2 2 0.9 2 2.0 0 0.7 2 0.8 3 0.5 2 0.4 5 0.3 2 0.2 1 0.9 1 1.9 1 0.7 1 0.8 0 0.5 1 0.4 4 0.3 1 0.2 0 0.9 0 1.8 2 0.7 0 0.7 8 0.5 0 0.4 2 0.3 0 0.1 9 0.8 9 1.7 3 0.6 9 0.7 5 0.4 9 0.4 1 0.2 9 0.1 8 0.8 8 1.6 4 0.6 8 0.7 3 0.4 8 0.4 0 0.2 8 0.1 8 0.8 7 1.5 5 0.6 7 0.7 1 0.4 7 0.3 8 0.2 7 0.1 7 0.8 6 1.4 6 0.6 6 0.6 9 0.4 6 0.3 7 0.2 6 0.1 6 0.8 5 1.3 7 0.6 5 0.6 7 0.4 5 0.3 6 0.2 5 0.1 5 0.8 4 1.2 8 0.6 4 0.6 6 0.4 4 0.3 4 0.8 3 1.2 0 0.6 3 0.6 4 0.4 3 0.3 3 0.8 2 1.1 6 0.6 2 0.6 2 0.4 2 0.3 2 0.8 1 1.1 2 0.6 1 0.6 0 0.4 1 0.3 1 0.8 0 1.0 8 0.6 0 0.5 8 0.4 0 0.2 9 y = 0. 0 085x + 0 05 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1 R u n o ff C o e ffi c i e n t 0 2 0 4 0 6 0 8 0 1 0 0 I m pe r v i ous C o v e r ( % ) Figur e 4 3 Re la tions hip be tw e e n Ru noff Coe ffic i e n t a nd Impe r v ious Cov e r Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 24

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5. Measures to Protect S t ream Morph o log y A s m u ch as 90 % o f the s e dim e nt an d o t he r po llu ta nts car ri ed in u r ban w a t e r w ay s are d e r i v e d from the acc el era t ed ra te o f ch anne l e r os ion cau sed b y the i n cr eas e i n r a t e an d v o lum e of s t o r m water runo ff from im perv ious cov e r as soc i a t ed wi th de v e lopm ent (Osborn e e t al., 2000). I n addi tion, c h ann e l deg r ad at ion al so elim ina t es m u ch of the r i par i an h a bi ta t requ ir ed fo r cer tai n spec ie s T o redu ce t h e r a t e of cha nnel eros ion, re st ric t i ons on the ra te o f di sch a rg e a r e ne ces sary fo r storm s l i k e ly to im pact cha nnel m o rpho log y as descr i b e d be low. Flow cont ro l is no t r e qui re d for a ll d i sc harg es t o sur f ace w a t e rs b eca use f l ow c ontro l i s not a l way s needed t o p r ot ect s t re am m o rpholog y T h e exem ptio ns li st ed b e low ar e p r o v i ded to as si st i n dete rm ining which pro j ec ts should b e sub j ec ted t o th i s requ ir em ent. Any project m a y be subj e c t to l o ca l r e qui rem e nts for f l ow cont rol to prev ent f l ood ing T h e fo ll owing pro j ec ts and d i sch a rg es are e x em pt fr om flow con t r o l r e qui rem e nts to p r ot ec t s t re am m o rpholog y 1) A n y pro j ec t ab le to d i spe r s e w ith out dis c ha rg e to s u rf ace w a ter s t h e tot a l 2y ear, 24hour runof f v o lum e for the prop osed d e v e lopm ent cond it io n on s ite. 2) A road p r o j ec t ab le to di spe r se, w itho u t d i s c ha rg e to su rfa ce wa ter s t h e t o ta l 2y ear, 24hour runof f v o lum e for the prop osed d e v e lopm ent cond it io n on s ite. 3) A pro j ect cons tr uct i ng le ss than 1 0,000 squa re fee t of t o ta l im perv ious sur f ac es. 4) A pro j ect w ith im perv ious cov e r of les s th an 15 % in a l l subwa t e r she d s on the si te. 5) A pro j ect dis c ha rg ing dire c tly to the m a in s t em of th e: a) B l anco R i v e r b) Fr i o R i v e r c) G u adalu p e R i v e r d) Medi na Riv e r e) N u eces R i v e r or f) Cany on Lak e g) Medi na Lak e 6) I n order to b e exem pted, th e dis c ha rg e m u st m eet all o f th e fo llow i ng requ ir em ents: a) T h e conv ey ance sy st em m u st ex ten d to the ord i na ry hi g h water l i ne of the rec e iv i n g wa ter, or (in ord e r to av oid co nstr uct i on ac tiv it ie s in sens i tiv e ar eas ) f l ows are prop er ly dispe r s e d be for e r each ing t h e buf fe r z one of the st rea m suffic ien t to prev en t er os ion. b) A n y erodib l e e l em ents o f t h e conv ey ance sy stem for th e pro j ec t a r ea m u st b e ad eq uate ly stab il iz ed to pr ev ent e r os io n. c) Surfa ce w a te r f r om the pro j ect are a m u st not be incr eas ed to an ex is ting w e t l and s t ream or ne ars hore ha bi tat su ff ici e nt to ca use a s i g n ifi can t ad v e rse im pact. d) T h e di scha rg e wil l no t ca us e neg a tiv e im pact s t o hab i t a t al ong the riv e rs tha t s uppo rt rar e or ca ndid a t e spe c i e s. A pro j e c t t h at do es no t m e et th e cr it er ia abov e sha ll c onst r uc t sto r m water f l ow cont rol fac i l i t i e s for any dis c ha rg e of sto r m w a te r d i re ct ly or thr oug h a co nv ey ance sy stem int o sur f a ce w a te r T h e s e fa ci li ti es ar e only re quir e d in subwa t e r sh eds on the pro j ec t si te wit h propo sed im perv ious cov e r of g r e a te r than 1 5 %. Deten tion is not re qui red i n subwa t er shed s l e ss tha n 15% im perv ious Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 25

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cov e r. T h e re qui rem e nts b e low a pply to pr o j e c t s whi c h di sch a rg e i n to a wa te r body othe r t h a n those l i s t ed in I t em 5 above, ei the r d i re ct ly or i ndi rec t ly throug h a n a tu ra l o r m a nm a de conv ey ance sy stem I n order to pr ev ent l o ca liz ed ero s i on, en erg y dissi pat i on a t the poi n t o f d i sc harg e is requ ire d fo r a ll p r o j ec ts u n l e ss s i t e s pecif i c cond it ions warra n t a n exc e pt ion. T o protect s t ream m o rph o lo gy proj ects s h all li m it t h e peak rate of run o ff f o r th e 2-y ear 24h o u r s t or m t o 50% of t h e un dev e l oped rat e f o r t h at ev e n t a n d l i m i t t h e 10-y ear, 24h o u r s t o r m pea k ru n o f f rate to th at calc u lated fo r th e u n d e v elo p e d co n d itio n fo r th e sa m e s t o r m co n d itio n s Undev e loped and pro posed dev e lope d co ndi ti on r unof f v o lum e s and fl ow r a te s s h all be es tim ate d using T R 55, HEC 1, HEC HMS, or eq uiv a le nt sof t w a re. The d e sig n s t o r m for d e te rm ining both v o lum e s and flow r a t e s i s t h e SCS T y pe I I h y et og raph with the sto r m depths p r esen ted in T a b l e 51. Proj e c t s th at e x te nd a c ros s a co unty l i ne sh oul d use t h e av erag e r a in fa ll d e pths of the two count ies I n cases whe r e a l o cal jur i s d ic ti on a l so im poses de ten tio n req u i r em ent fo r the 2and 10 y ear storm ev ents (e.g C i t y of A u stin), s o f t w a re s p e c if ied a bov e is used in th e calcu la tio n, and the rai n fa ll di st ribu ti on i s c e nte r ed we ig hted (su c h a s produc ed by the al te rna ting block m e thod), param e te rs an d m e thodolo g i es spec if ied by the l o ca l autho r i t y can be used to c a lcu l a t ed runo f f v o lum e s and rat e s. An ag ency or local jur i sd ic tion a l so m a y requi re det e n tion ba sin s to be des i g n ed t o m a tch anot her retu rni nte r v a l (e.g 25y ear, 50y ear, or 100y ear) pe a k flow rate in add i tion to th e 2and 10 y ear peak fl ow r a te. I n all ca ses where t h e dis c ha rg e is t o nonexe m pt st re am s, dete nt ion b a s i ns m u st be des i g n ed to re lea s e t h e 2y ear storm at no m o re t h an 50% of the 2y ear peak flow r a t e in the undev e lope d cond i tion. I f runoff f r om the subwa t e r shed t h at wi ll be con t ro ll e d ex tend s bey ond the bou n d ary of th e s i t e and th e ru nof f f r om the o f f s it e po rt ion o f t h e w a ter s he d w i l l en te r th e de ten tio n f aci li ty then th e deten t ion fac i l ity m u st be s i z e d to con t ro l runo ff fr om the of fs ite po rt ion. When conf ig uring th e m odel for es tim ating pe ak runof f rat e s, use ei the r the curr ent l e v e l of dev e lopm ent o f t h e o f f s i t e port i on or assum e th at the ult i m a te im perv ious cov e r of the o f f s i t e p o r tion wil l be equ a l to th e im perv ious cov e r o f t h e su b w ater shed w ith in the si te b oundar i e s and use wh ich e v e r i s g r ea ter. T a ble 5-1. A v er age A nnual Rainfal l by County ( A squith and R oussel, 200 4) County 2-yr, 2 4 -hou r ra in f a ll 10-yr, 24-hou r ra in f a l l Bexar 3.5 6.0 Com a l 3.5 6.0 Hay s 3.5 6.0 K i n n ey 3.3 5.5 Medi na 3.5 6.0 T r av is 3.4 5.5 Uv alde 3.4 6.0 Wi ll iam s on 3.4 5.5 A ty pical c onf ig urat ion o f storm w a te r tr ea tm ent and deten t ion to prev en t chan n e l e r os ion woul d consi s t of two com ponen t s. T h e requ ir ed wa ter qua l ity v o lum e as cal cul a t e d a ccord ing to the m e thodolog y in Sect ion 4 is d i re ct ed to a t r e a tm ent cont rol such as a wet b a s i n or s a nd f i lte r. S a nd f i l t e r s sho u ld be con s truc ted of fl ine s o th at runo ff i n exc e ss of the w a ter q u al ity v o lum e is Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 26

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by passed to t h e de ten t ion f aci li ty for p eak runo ff con t rol. On the oth e r hand addi tion a l det e nt io n can be in cor pora t ed int o a wet bas i n wit h the a ppro p r i at e out le t conf ig ura tio n to prov ide the re quir e d pe ak shav ing Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 27

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6. Maintenanc e Requirem ent s Lack of m a in tenan c e can be on e o f the pr im ary causes of B M P fa ilu re. A l t h o u g h the cur r en t g u ideli n es in RG348 inclu d e rec o m m endation s fo r m a in tenan ce, the r e i s cur r en t l y no sy stem to docum ent when and wha t t y pe of m a intenan ce was las t per f orm e d. Conse quen tly a sy stem needs to be im plem ented t h at wo uld fa ci li ta te doc um entat i o n of m a intena nce a c t i v iti es descr i be d in th e WPAP or CZ P. T h e o w n e r o r o p e rato r o f a BMP co n s tru c ted to co m p l y w i t h th e T SS re m o v a l req u ire m e n t is o b l i g a ted to p r o v id e al l t h e m a i n t e n a n c e acti v itie s req u ired to m a i n tai n t h e fu n c tio n o f th e facilit y an d o t h e r activ ities as d e scrib e d in th e W P A P an d C Z P T h e o w n e r/o p e rato r m u s t m a i n tai n re co rd s o f all m a inten a n ce act iv i ties f o r t h e m o s t recen t 3 y ear s T h es e records m u s t be m a de a v ailabl e to t h e T C EQ u pon requ es t T o f aci l ita te i n spe c t i ons a n d repor ti ng of BMPs tha t a r e not f unc tion i ng corr ec tl y a leg i ble sig n m u st be p l ac ed at al l pond s, sa nd fi lt ers, de ten t i on b a sins, and b i or ete n t i on are a s T h e sig n s h al l be l o ca ted in pl ain v i ew o f the pub li c a nd s h al l prov i d e t h e n a m e of the owne r or op era t o r the Edwards Aqu i fe r prog ram I D for the p r o j ec t, and a t e l e phone num ber where the p a rty resp ons ibl e for the m a in tenan ce o f t h e B M P can b e con t a c te d. Equal l y im portant to t h e c o rre c t fu nct i on ing of BMPs is the p r ope r cons tru c t i on of the app r ov ed stru ctu r e. The Edw a rds A q uife r R u les requ ir e th at the ow ners o f pe rm anent B M Ps or m easur e s m u st insure tha t they are co nstr uct e d and f unc tion a s d e sig n ed. A Texas lic ense d prof ess i ona l en g i neer m u st ce rt ify in w r it ing tha t the pe rm anent B M P s o r m easur es w e re cons tr uct e d a s desig n ed. A copy of this ce rt if ica tio n m u st be k e pt b y the owner an d m a de av ailable to th e T C E Q upon r e ques t An im portan t com ponent o f wate r qu al ity pro t ec t i on o n the Edw a rd s Aqui fe r is ro utin e in spe c t i on of sewe r l i nes. T C EQ ru le s in T i tl e 30 T A C Chap te r 213 Edward s Aqui fe r re quir e owner s o f sew a g e col l ec tio n sy stem s to ensur e th at a ll exi s t i ng sew e r li nes h a v i ng a diam eter g r eater than o r equal to six inc h es, inc l ud ing priv ate se rv ice lat e ra ls m a nholes, an d con n ec tio ns, ar e t e s t ed t o dete rm ine ty pes and l o ca ti ons o f s t r u ct ura l d a m a g e and de fec t s suc h a s o ffs et s, open j o in ts, o r crack ed or cru s hed l i nes th at wou l d al low ex fi lt ra tio n to oc cur. Exi s t i ng m a nhole s and l i f t s tatio n wet well s m u st be teste d us ing m e thods for new s t ru ct ures t h at a r e app r ov ed by t h e execu tiv e di rec t or. T h e tes t i n g of all s e wag e coll ect ion sy st em s m u st be conduc ted ev ery fiv e y ears afte r be ing put into u s e to de term ine ty pes and loc a t i ons of s t ru ctu r a l dam a g e and defect s suc h as of fse t s, op en join ts, o r cr ack ed or cr ushe d line s th at w o u l d al low ex fi lt rat i on to occu r. T h e s e te st re sul t s m u s t be cer ti fi ed by a T e xas lic ensed p r of ess i on al eng i n e e r The t e st res u l t s m u st be reta ine d by the plan h o ld er for fiv e y ears a nd m a de av ailab l e to the e x ecut i v e di rec t or upon requ e s t. I n addition p r iv ate se rv ice lat e ra l conne ct ions m u st be insp ec ted af te r i n st al ling a nd pr ior to cov ering an d con n ec ting t o, a n org a niz e d sewag e co ll ect ion sy st em A T e x a s li cen sed p r of ess i ona l eng i neer T e x a s reg i st er ed sani ta ria n, o r app r op ri ate c ity ins p ec tor m u st in spec t the p r iv at e s e r v i ce la te ra l an d t h e c onne cti on to the col l ec ti on sy st em and cer ti fy tha t c ons tr uct i on c onfo r m s with the app l i cab le p r ov is i ons o f t h is g u idan ce do cum e nt, RG348 (Rev ised J u ly 2005), and loc a l plum bing codes. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 28

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7. References Asqui th, W.H., and Rou sse l, M.C., 2004, A tla s of dep t hduration fre quen c y of pre c ip ita ti on an nual m a xim a for Texas : U. S. Geolog ica l Su rv ey Scien t i f ic I n v e stig ati ons Re por t 2004 5041, 106 pp. Osborne, K G., B a r r et t, M., and M a idm e nt, D., 2 000, A water qua li ty G I S tool fo r th e Ci ty of Austi n in corp ora t i n g non p o int sou r ce s and b e s t m a nag e m e nt pra c t i ce s, Cen t er fo r Re s e a r c h i n Wa t e r Re sourc e s Onl i n e Re po r t 20 0010 < www.c r wr .ute x as .e du / r e port s > Univ ersi ty of T e x a s a t Aus t in. T h u r ow, T L., B l ack burn, W., W a rr en, S.D., and T a y l or, C.A., Jr., 1987 Ra i nf al l in te rcep ti on by m i dg rass, shor tg rass, and li v e oak m o ttes, Journ a l o f Range Managem e nt V o l. 4 0, No. 5, pp. 455460. War ton, Mik e 200 2, So l i d and I n v e rtebra te Cav e Ga te Opt i on s, in Pro cee ding s of Bat Cav e Gate Des i g n : A T e c hni cal I n ter a c tiv e For u m edited by V o rie s K T h r ogm orton, D., and Harr ing t on, A., Aus tin T e x a s, M a rc h 46, 2002. Appendix A T C EQ publicat ion R G -34 8 A # R e v i sed # S epte m ber 200 7 29