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

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

Material Information

Title:
Optional enhanced measures for the protection of water quality in the Edwards Aquifer (revised)
Publisher:
Texas Commission on Environmental Quality
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Resource Management ( local )
Genre:
Ordinance
serial ( sobekcm )
Location:
United States

Notes

Restriction:
Open Access
Original Location:
Edwards Aquifer Authority Collection

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
K26-03185 ( USFLDC DOI )
k26.3185 ( USFLDC Handle )
11548 ( karstportal - original NodeID )

USFLDC Membership

Aggregations:
Added automatically
Karst Information Portal

Postcard Information

Format:
serial

Downloads

This item has the following downloads:


Full Text

PAGE 1

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

PAGE 2

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

PAGE 3

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

PAGE 4

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

PAGE 5

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

PAGE 6

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

PAGE 7

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

PAGE 8

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

PAGE 9

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

PAGE 10

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

PAGE 11

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

PAGE 12

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

PAGE 13

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

PAGE 14

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

PAGE 15

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

PAGE 16

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

PAGE 17

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

PAGE 18

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

PAGE 19

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 )

PAGE 20

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)

PAGE 21

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)

PAGE 22

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

PAGE 23

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

PAGE 24

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

PAGE 25

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

PAGE 26

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

PAGE 27

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

PAGE 28

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

PAGE 29

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

PAGE 30

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

PAGE 31

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

PAGE 32

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

PAGE 33

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

PAGE 34

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


printinsert_linkshareget_appmore_horiz

Download Options

close
Choose Size
Choose file type
Cite this item close

APA

Cras ut cursus ante, a fringilla nunc. Mauris lorem nunc, cursus sit amet enim ac, vehicula vestibulum mi. Mauris viverra nisl vel enim faucibus porta. Praesent sit amet ornare diam, non finibus nulla.

MLA

Cras efficitur magna et sapien varius, luctus ullamcorper dolor convallis. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce sit amet justo ut erat laoreet congue sed a ante.

CHICAGO

Phasellus ornare in augue eu imperdiet. Donec malesuada sapien ante, at vehicula orci tempor molestie. Proin vitae urna elit. Pellentesque vitae nisi et diam euismod malesuada aliquet non erat.

WIKIPEDIA

Nunc fringilla dolor ut dictum placerat. Proin ac neque rutrum, consectetur ligula id, laoreet ligula. Nulla lorem massa, consectetur vitae consequat in, lobortis at dolor. Nunc sed leo odio.