SSIS Final Report

7/29/2019 SSIS Final Report

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Sep t i c Sy st em I m p ac t St u d y

G o o s e C r e e k W a te r s h e dS h e r id a n C o u n t y , W y o m in g

P r ep ar e d F o r :

T h e G o o s e C r e e k W a te rs h e dP la n n in g C o m m itte e P a rtn e r s h ipD e c e m b e r 2 0 0 6

B u i l d i n g C o m m u n i t y T h r o u gh B et t er E n g i n e er i n g

P r ep ar e d b y :


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Table of Cont ent s

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1.0 BACKGROUND ..................................................................................................... 11.1 History of the Goose Creeks Assessment and Planning Program .............. 11.2 Purpose...................................................................................................... 21.3 Proj ect Funding .......................................................................................... 21.4 Acknow ledgements .................................................................................... 3

2.0 PHASE 1 INVENTORY OF EXISTING SEPTIC SYSTEMS..................................... 42.1 Base Map.................................................................................................... 4

2.1.1 Study Area....................................................................................... 42.1.2 Cities ............................................................................................... 42.1.3 Creeks ............................................................................................. 42.1.4 Lakes ............................................................................................... 4

2.1.5 Sheridan County Roads ................................................................... 52.1.6 Nat ional Forest ................................................................................ 52.1.7 Parcel Boundary............................................................................... 52.1 .8 SAWS Boundary ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... 52.1.9 Drink ing Water ................................................................................ 52.1.10 Sewer Service Boundary................................................................... 52.1.11 Potent ial Sewer Service Boundary .................................................... 52.1.12 Sewer............................................................................................... 52.1.13 Imagery ........................................................................................... 6

2.2 Input Data .................................................................................................. 62.2.1 Water Quality Moni to ring Stat ions................................................... 62.2.2 Impaired St reams ............................................................................ 7

2.2.3 Cit y of Sheridan Wastewater Treatment Plant Outfalland Fecal Col iform Discharge Data............................................. 8

2.2.4 Sept ic Perm it s.................................................................................. 82.2 .5 SAWS Taps........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ........ 92.2.6 FEMA/ FIRM Boundary ...................................................................... 9

2.3 Data Interpretation................................................................................... 102.3.1 Sept ic Density................................................................................ 102.3.2 Developed Parcels ......................................................................... 102.3.3 Undeveloped Parcels ..................................................................... 102.3.4 Sanitary Sewer Capacity ................................................................ 11

2.4 Aqui fer Sensit ivit y Data............................................................................ 112.4.1 Depth to Init ial Groundwater......................................................... 12

2.4.2 Geohydro log ic Sett ing ................................................................... 122.4.3 Soi ls............................................................................................... 132.4.4 Aqui fer Recharge........................................................................... 132.4.5 Land Surface Slope........................................................................ 132.4.6 Vadose Zone.................................................................................. 142.4.7 Aqui fer Sensit ivit y ......................................................................... 14

2.5 Designat ion of Impact Zones ................................................................... 15


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3.0 PHASE II ASSESS OPTIONS TO MITIGATE SEPTIC RELATED IMPACTS ......... 163.1 Int roduct ion ............................................................................................. 16

3.1.1 Benefit s of Alternative Technology Evaluation .............................. 163.1.2 Juri sdict ional Oversight ................................................................. 163.1.3 Systems Considered ...................................................................... 17

3.2 Alternat ive Central Systems ..................................................................... 183.2.1 City of Sheridan Sewer System Expansion ..................................... 183.2.2 Regional Central Sewer System ..................................................... 183.2.3 Cluster Systems............................................................................. 203.2.4 Permi tt ing Considerations for Addit ional Central Systems ........... 21

3.3 Alternat ive Collect ion Systems................................................................. 22

3.3.1 Conventional Col lection Systems .................................................. 223.3.2 Sept ic Tank Effluent Collection Systems ....................................... 233.3.3 Vacuum Sewer Collect ion Systems ................................................ 24

3.4 Alternat ive Onsite Systems ...................................................................... 27Table 3.1 App licabilit y of Alternat ive Onsite Septic Systems ................... 283.4.1 Alternat ive Treatment Methods..................................................... 293.4.2 Alternat ive Septic Tank Eff luent Disposal Methods ....................... 30

3.5 Design Requirement s............................................................................... 333.6 Site Investigation ..................................................................................... 343.7 Constr uction and Post-const ruct ion Requirements.................................. 353.8 Program Management .............................................................................. 36

4.0 CONCLUSIONS AND RECOMMENDATIONS ...................................................... 384.1 Continue implementing programs out lined in the

Goose Creek Watershed Management Plan.......................................... 384.2 Sheridan County should consider updating the current septic permit ting

program .............................................................................................. 384.3 Sheridan County should consider establishing a licensing program

for sept ic system installers and pumpers............................................ 394.4 Sheridan County should select an appropr iate Management Program .... 394.5 Init iate a Regional Sewer Master Plan for the Lit tle Goose Drainage........ 394.6 The City of Sheridan should continue wastewater collection and

treatment master planning and plan implementation ......................... 40

5.0 REFERENCES ...................................................................................................... 41


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List of Figures

Figur e No.2.1 GIS Base Map Geographic Features2.2 GIS Base Map Utilit ies2.3 Water Quality Monitoring Stations and Creek Impairment2.4 Septic System, Water Tap and Floodplain Locations2.5 Septic System Density and Developed/ Undeveloped Parcels2.6 Groundwater Sensitivity Classes2.7 Sept ic Impact Zones3.1 Conventional Septic System3.2 Vacuum Sewer Valve Pit and Main3.3 Typical Vacuum Stat ion

3.4 Conventional Sept ic Tank3.5 Aerob ic Treatment Unit3.6 Septic Tank Eff luent Pumping Unit3.7 Chamber Unit Eff luent Disposal3.8 Dosed Drainf ield3.9 Mound Syst em3.10 Evapotranspiration Unit3 .11 Sand Fi lters3.12 Wetland Disposal

Attachment A CD containing GIS data f ile


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1.0 BACKGROUND

Assessment and planning act ivit ies have been actively ongo ing in t he Goose CreekWatershed since 1993. This Septi c Impact Study is one com ponent of a carefu llycrafted and well t hought-out Management Plan to address water quality concerns in the

watershed. A brief history of the water quality work in this watershed follows.

1.1 Histor y of t he Goose Creeks Assessment and Planni ng Prog ramBetween 1993 and 1997 the United States Geologic Survey (USGS) collectedwater qualit y data in the Goose Creek Watershed. This work ident if ied elevatedconcentrations of fecal colif orm bacteria in Big and Litt le Goose Creeks. Basedon the data, the Wyoming Department of Environmental Qualit y (WDEQ) placedBig Goose and Litt le Goose Creeks on Table A of the 1998 Section 303 (d) list o fimp aired waters in Wyoming.

In 1998 and 1999 , WDEQ implemented a more detailed water-quality monitoringprogram. WDEQs samp ling revealed elevated fecal coliform bacteria

concentrations on Goose Creek, Big Goose Creek and Little Goose Creekexceeding standards for the streams designated use of Recreation and HumanConsumpt ion. Elevated levels of fecal colif orm bacteria were also identi fied intributaries of the Goose Creeks, leading to the placement of Beaver Creek,Jackson Creek, Kruse Creek, Park Creek, Rapid Creek, Sackett Creek and SoldierCreek on the 303(d) list of impaired streams.

In 2000, the City and County of Sheridan and the Sheridan County ConservationDistr ict created the Goose Creek Drainage Advisory Group (GCDAG) to addressthe apparent water quality prob lem in the watershed. Procurement of a CleanWater Act Section 319 g rant ($217,500) and contr ibut ions from GCDAGmembers ($145,000) allowed a comprehensive assessment project w ith in the

watershed. The Goose Creek Watershed Assessment , undert aken by theGCDAG, was the fir st comprehensive evaluat ion of t he watershed. TheWatershed Assessment included collecting credible chemical, physical,biological, bacteriological and habitat information on Goose Creek, Big GooseCreek, Little Goose Creek and 8 tr ibutaries wit hin t he watershed. Samplingoccurred 8 times during 2001 and 2002 from 46 locations within the watershed.Samples were analyzed for 17 parameters. The final report was pub lished inJuly 2003, accompanied by a publ ic information and out reach program.

Another Section 3 19 gr ant helped fund a watershed planning process which wasini ti ated in September 2003. The Goose Creek Watershed Planning Committ eemet mont hly throug hout 200 4 to develop The Goose Creek Watershed

Management Plan, which was publi shed in December 2004 and fi led with theSheridan County Clerk s of fice in April 20 05. The planning process wascollaborative and included local landowners, watershed residents, the SheridanCounty Conservation Dist rict , the Natural Resources Conservation Service,Sheridan County of ficials, City o f Sherid an off icials, the Sheridan CountyPlanning and Zoning Commission and the Wyoming Department ofEnvironm ental Quality. An extensive public participation process, includingmass mailings and publ ic meetings, was included in the planning process.


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The Watershed Management Plan ident if ies specifi c Issues and prov idesObjectives and a list of Action Items to address each Issue. This Sept ic ImpactStudy addresses, in whole or in part, three of the Action Items regarding Issue4.1.1 Rural and urban septic systems are likely contributors of bacteria to localstreams. The Action Items addressed by th is study include: 1) The Goose CreekWatershed Planning Comm itt ee will consider sponsoring a feasibilit y study to

evaluate potential sewage treatment options and/ or t he need for ex pandingcentral sewer lines to rural areas. 2) The City of Sheridan and Sheridan Countywill identify and map septic systems in or near riparian areas, and with in Citylim it s, as feasible, and 3) The Goose Creek Watershed Planning Commi tt ee wil levaluate alternative individual sanitation system technologies and systems forthe treatment of wastewater from multiple dwellings.

HKM Engineering Inc. entered into an agreement wit h the City of Sheridan andSherid an County in June 2006 t o assess the impact of sept ic systems in theGoose Creek Watershed, evaluate alternative treatment t echnolog ies anddetermine criteria for implementing various alternatives in high impact or high-risk zones. The proj ect is divided into phases. The fir st phase is the inventoryof ex isting septic systems and mapping those systems, along w ith ot herrelevant inf orm ation, on a Geographic Informati on System (GIS) map. Theoutcome of Phase I is the ident ification of zones of high risk f or im pacts togroundwater. Phase II is intended to develop opt ions to mit igate impacts fromconventional septic systems. It includes identif ying appropr iate alternativetechnologies and methods by which those technologies could be applied withinthe Sheridan County septic permitting process.

1.2 PurposeThe purpose of t his study is to develop a recommended mechanism wit h whichseptic system installat ion and replacement can be evaluated for appropr iate use

of alternative technologies in areas of h igh r isk for impacts to groundwater.This report documents the data gathered and methods used to develop arecommended evaluation criteria and septic permit ting approach.

The recommended strategy for implementing alternative septic systemtechnologies requires minor amendment to the current Sheridan County sept icsystem permit ting program. Implementation of the program should includereview and updates, if determ ined appropr iate, to t he 201 IntergovernmentalAgreement between the City and the County and t he Delegation Agreementbetween WDEQ and the County. In addi t ion, detailed evaluation criter ia anddesign guidelines should be developed, which are beyond t he scope of t hisstudy. A commitment of appropr iately trained staff to implement and

administer the program will also be necessary.

1.3 Proj ect Fund ingThis project is funded by a $ 54,000 grant secured by the City of Sheridan. Thegrant is from t he Clean Water Act Secti on 319 p rogram, administered by t heWyoming Department of Environmental Quality. A $ 36 ,000 in-kind match isalso prov ided by the City of Sheridan, Sheridan County and t he Sheridan CountyConservation Distr ict.


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1.4 AcknowledgementsThe info rmatio n gathered and mapped for this proj ect was provided frommyriad of sources including Sheridan County, the City of Sheridan, SheridanArea Water Supp ly and the University of Wyoming. Without the helpfulcooperation of staff from these agencies, this report would not be possible.

Tremendous support and guidance was provided by staff f rom the SheridanCounty Conservat ion Dist rict , and the Sheridan County and City of Sheridanengineering and planning departments.

Input from the pub lic, agency staff and policy boards was crucial for completionof th is study. The questio ns and comments provided during public meetingsheld on October 5, 2006 and December 7, 2006 helped formulate theconclusions and recommendations of this report.


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2.0 PHASE I INVENTORY OF EXISTING SEPTIC SYSTEMS

Geographic Information System (GIS) mapping was the tool selected to inventory andevaluate sept ic systems in the watershed. A GIS is a comp uter ized tool into which datais input . Using GIS, many types of data from many dif ferent sources can be stored,

analyzed and displayed on a common map allowing comparison and evaluation ofcomplex sets of data in a simple, spatial fo rmat.

A compact disk containing SHP files of all of the data described in this section isincluded wit h this report . Figures displaying selected data layers are included at theend of the report.

The follow ing sections describe the data input into the GIS map for t his project.

2.1 Base MapA base map was compiled containing general information and features withinthe watershed. The base map is a general depict ion of features of int erest in

the Sept ic Impact Study Area. The following data are included in the Base Map.

2.1.1 St udy Ar ea The study area for th is Sept ic Impact Studyencompasses the Goose Creek Watershed (excluding pub lic landsadministered by the U.S. Forest Service) and is the same as defined in theGoose Creek Watershed Management Plan. The area includes allcont ribut ing areas to Big Goose, Lit tle Goose, and Goose Creeks. BigGoose Creek flows northeast from the Big Horn Mountains and entersSheridan on the southwest end of tow n. Litt le Goose Creek flowsnort heast t o t he town of Big Horn and cont inues north, entering Sheridanon the sout h end of town. The Big and Litt le Goose Creeks jo in near thecenter of Sheridan to form Goose Creek. Goose Creek then f lows nort h

and enters the Tong ue River. The watershed boundary was downloadedfrom the Wyoming Geographic Information Science Center (WYGISC)website. The original downloadable dataset contained hydrolog ic unitwatershed boundaries for the enti re state of Wyoming. The Goose Creekwatershed boundary was extracted f rom th is larger dataset fo r use as thestudy boundary within this Septic Impact Study.2 .1 .2 Ci t ies The cit ies layer is used wit hin the Sept ic Impact Studymapping as a reference layer to describe the study boundary in t erms ofit s location wi thin Sheridan County. The dataset includes all SheridanCounty cities along with demographic inf ormation from t he 2000 U.S.Census. This data is referred to as TIGER line data and is the geographicline work created by the U.S. Census Bureau for carrying out the 1990

and 2000 Census. This data was made available for download on t heWyom ing GIS Coord inat ion St ructure (WGCS) websit e.2 .1 .3 Creeks The creek dataset includes all Sheridan County as well asthe por tion of Johnson County water features that f all within t he studyarea. Water features include canals, ditches, and streams from the 2000U.S. Census. As wit h the cities layer, th is dataset is a part of t he TIGERline data created by the U.S. Census Bureau and made available fordownload on the WGCS website.2 .1 .4 Lakes The various lakes and ponds within Sheridan County and aport ion of Johnson County are shown wi th in th is layer. Again, this TIGER


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line dataset was created by the U.S. Census Bureau and made availablefor download on t he WGCS website.2.1.5 Sher idan County Roads Road names, locations, and otheraccompanying inf ormation is presented in this dataset supplied by theSheridan County GIS department.2.1.6 Nat ional Forest This dataset illustrates the Nat ional Forest andother publ ic lands wit hin Sheridan County and the study area. TheBighorn National Forest within t he area of int erest was clipped from alarger original layer depicting all public lands within the state ofWyoming. These lands include Nat ional Forest, wilderness areas, statepark s, and others. This layer was publi shed by the Spatial Data andVisualization Center located in Laramie and was available t o downloadfrom the WGISC website.2.1.7 Parcel Boundary The parcel boundary layer contains theapprox imate parcel boundary locations within Sheridan County. A parcelis land owned by a single pr ivate owner. More than one subdivided lotmay be contained within a parcel. Addit ional inform ation is tied to th islayer in t he GIS database, includ ing ownership, parcel address, legaldescript ion, and subdivision name. This data was provided by the Countyvia the City of Sheridan GIS department and is current through April o f2006.2.1.8 SAWS Boundary This service boundary encompasses the areawith in which water service can be provided as part of the Sheridan AreaWater Supply (SAWS) regional water system. This boundary wasestablished dur ing t he planning phase of the regional water project andwas provided through the City of Sheridan GIS department.2.1.9 Dr ink ing Water The ex ist ing drinking water system pipe layoutfor t he City of Sheridan and SAWS service areas is illustrated wi th in t hisdataset. This layer was created by export ing pipe data from t he

comput erized water model of Sheridans system.2.1.10 Sewer Ser vice Boundary This boundary was established in1977 as part of the EPA 208 Wastewater Planning Study and cont inues tobe referenced as the sewer service boundary. It appears to be basedmostly on topography or areas that can be provided sewer service bygravity flow. However, in some areas this does not hold tr ue and theboundary may have been based on what was considered to bedevelopable land at t he t ime. This boundary cont inues to be studied aspart of the City of Sheridan Wastewater Collection System Assessment .2.1.11 Potential Sewer Ser vice Boundary As stated above, theex isting Sewer Service Boundary i s under review and possib le revision aspart of the City of Sheridan Wastewater Collection System Assessment .

This layer was provided by t he City of Sheridan as part of that ongo ingstudy . The potent ially larger Sewer Service Boundary reflects the Citysdesire to init iate inf rastructure and land use planning activit ies well intothe watershed.2 .1 .12 Sewer Sheridan s ex ist ing sewer system layout is shown w it hinthis dataset. This layer was created by export ing p ipe data from t hesewer model created by HKM as part o f t he ongo ing City of SheridanWastewater Collection System Assessment. An init ial layout of pipes wassupplied by the City of Sheridan GIS department and was used to createthe preliminary model for the draft version of t his report put out in


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January 2006 . Since then, the model has been mo dif ied and cont inues tobe updated as changes and addit ions are made to t he system.2 .1 .1 3 Im ag er y A mosaic of im agery layers were compi ledencompassing the study area. High resolut ion aerial photos exist for theCity of Sheridan and developed areas along Big Goose Creek, Lit tle GooseCreek, and Sold ier Creek. The City photog raphy was taken in April 2002

and the areas along the creeks were taken in 200 4. The remainder of t hearea was augmented using 200 2 Color Infra Red photog raphy availablefor download by quadrangle from the WGSC website.

Figures 2.1 and 2.2 represent various comb inations of informationprovided in the GIS base map.

2.2 Input DataFollowing compilation of the base map, data of specific relevance to the SepticImpact Study was input . The fol lowing sections describe the data input into theproject-specific mapping.

2.2.1 Water Qual i ty Monitor ing Stat ions Forty-six water qualitymonito ring stations were used during the 2001-2002 Goose CreekWatershed Assessment to monitor various water quality parameters onBig Goose, Litt le Goose, and Goose Creeks as well as several t ribut arystreams within the watershed. The locat ions of these stations are shownin t his layer along w ith a summary of some of the fecal coliform bacteriadata collected at each. This layer was created by comp iling select datafound within the final Goose Creek Watershed Assessment report.

Specifically, inform ation ex ists within t his layer to describe the creekmonito red and the numbers of geometr ic mean samples collected at t hat

site that exceeded the fecal colif orm standard. Fecal colif orm samplingwas conducted dur ing t he months of April , May, August, and October forboth 2001 and 2002. Five samples were collected dur ing each month fora total of 40 samp les at each site dur ing t he entire study. The fecalcoliform standard states that concentrations must not exceed ageometric mean of 200 organisms per 100 m illili ters based on aminimum of not less than f ive samples obtained during separate 24 hourperiods for any 30 day period, (Chapter 1, Wyoming Water Quality Rulesand Regulations). If t he standard was exceeded dur ing any of the eightgeometric mean sampling events, the stream segment f rom that pointupstream was considered to be impaired.

The highest occurrence of exceedance was four t imes out of t he eightgeometric mean sampling events. That occurred at only one station,Soldier Creek just upstream of the conf luence wit h Goose Creek. Threeexceedances occurred at two di ff erent sampling stations, on JacksonCreek near the community of Big Horn and on Little Goose Creek near theconf luence with Big Goose in the heart of Sheridan. All remainingstations had two or less exceedances of the fecal coliform standardduring t he eight sampling events.

The dataset used to create the Monitoring Stations layer also containsinfo rmation on the overall rank of the sites (1-46) based on the average


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fecal concentration of all 40 samples at each site. A ranking value of onedescribes the least impaired stream segment whi le a rank o f 46 describesthe worst case. The station rankings and number of exceedances areshown in Figure 2 .3.

The highest average fecal concentration occurred in Lit t le Goose Creek at

the b ridge crossing Highway 87 j ust south of Woodland Park School(LG7).

The second highest average concent ration occurred in Park Creek (BG13),which is t ribut ary to Big Goose Creek fairly high in t he watershed and inan area of very few sept ic systems. This suggests other non-pointsources of fecal colifor m bacteria are contributing to the documentedimpairment in Park Creek.

The third highest average concentration occurred at a sto rm drain out letdischarg ing into Little Goose Creek at Coffeen Avenue (LG3). This stormdrain collects runof f f rom developed areas along Coffeen Avenue, an areawhere sept ic systems are unlikely . This drain cont inuously dischargesand is therefore draining g roundwater from the area. Fecal colif orm m aybe entering t he system from leaking sanitary sewers or u nknown septicsystems in the area. Again, ot her sour ces appear to be cont ribut ing fecalcoliform impacts to the creek.

The fourt h highest average fecal concentration was in Soldier Creek (GC4)at the confluence wit h Goose Creek and the fif t h hig hest was on JacksonCreek (LG17), t ri but ary to Litt le Goose Creek near Big Horn.

2.2.2 Impaired St r eams This data layer was created based on data

obt ained from the 2001-2002 Goose Creek Watershed Assessment. Asdescribed above, if any monitoring site exceeded t he fecal coliformstandard during t he 2001-2002 monitori ng period, t he stream segmentupstream of that site is considered to be impaired. According to theWDEQ, Chapter 1, Rules and Regulat ions, fecal colif orm concentrationsshall not exceed a geometric mean of 200 organisms per 100 milliliters(based on a minim um of not less than 5 samples obtained duringseparate 24 -hour periods for any 30 day period), nor shall the geometricmean of 3 separate samp les collected wi thin a 24-hour period exceed400 organisms per 100 m illili ters. This layer shows the segments foundto be impaired due to fecal coli fo rm concentrations. The creeks layer wasused as a reference to select the impaired stream sections. These

impaired segments were then exported to a new layer entit led impairedcreeks.

Generally, impaired creek sections are located as follows: Goose Creek : From the confluence of Litt le and Big Goose,

downstream for about four miles north of Sheridan. Big Goose Creek: From Normative Services, downstream to the

confluence with Little Goose Creek. Lit tl e Goose Creek: From the br idge on Highway 87 j ust south of

the Big Horn Wye (junctio n with Highway 335), downstream to theconf luence with Big Goose Creek.


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Tributaries: All t ributaries sampled showed some level ofimpairment near t heir confluences wit h either Big Goose or LittleGoose Creeks. Sampled tri but aries included Soldier Creek (t ributaryto Goose Creek), Park Creek, Rapid Creek in the Big Goose drainageand Jackson Creek, Sackett Creek, Kruse Creek and McCorm ick Creekin the Little Goose drainage.

2.2.3 City of Sher idan Wast ewater Tr eatm ent Plant Outf all and FecalColiform Discharge Data In addition t o the 2001-2002 Goose CreekWatershed Assessment m onito ring data, fecal coliform discharge datawas also obtained f rom the City of Sheridan Wastewater Treatment Plant(WWTP). The plant out fall is located on Goose Creek approx imately 470feet nort h of Fort Road and is shown as a single point wit hin the WWTPdischarge layer. Fecal coliform geometric mean data by mont h for t hetim e period f rom January 2001 to August 20 06 is shown as a table wit hinthe map. The data shows that t he WWTP out fall has never exceeded thefecal coliform standard for the time period report ed, which includes the

t imeframe of the watershed assessment monit oring. The highestgeometric mean for this time period was 149 organisms/ 100 m loccurring in December of 2005. The average geometric mean for thislocatio n was 55 organisms/ 100 ml . The City of Sheridan WWTP dischargedoes not exceed the fecal colif orm w ater quality standard for GooseCreek.

The assessment monitoring stations, WWTP and the impaired streamsegments are shown on Figure 2.3.

2.2.4 Sept ic Perm its Data for permitted septic systems in SheridanCounty was obtained through the County GIS department. In its init ial

format, t he septic permits had been tied to a spatial location on t he mapusing a GIS technique refer red to as geocoding . This process generatedsepti c permit locations using an ex isting roads layer as a reference.Through geocoding, each septic permit address was placed as a pointsomewhere along its correspond ing road. The placement of the pointalong the road depends on the address number and point s were offsetfifty feet to the right or left of the road centerline.

The geocoding process used to generate the init ial septic permit layergave a good general representation of where sept ic systems are withinthe county. However, in order to look at development density, it wasadvantageous for each septic perm it location t o be tied t o t he correct

parcel address wit hin t he parcel boundary layer. Therefore, the t ime wastaken as part of this study to manually move each septic permi t locationfrom it s geocoded placement along the road to its correct parcel. Septicpermit s located outside of the study boundary were excluded from thisprocess.

Approxim ately 1,360 septic permits fall within t he study bound ary of t hetot al 2,356 perm itt ed septic systems within t he enti re County.


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Data Limit ations:

Many parcels have more that one septic permit tied to them. Thereason for this may be because the septi c system was initiallypermitted and was re-permitted due to repair o r replacement ofthe system. The orig inal permits were not removed from thedataset, resulting in t he duplicate permits.

Several septic perm its ex ist wit hin the City of Sheridan wheresanit ary sewer service is current ly available. Any sept ic systemswithin these areas should have been abandoned and the residenceconnected to City sewer. The sept ic dataset does not ref lectpermit ted systems that were abandoned due to connectio n to t heCity sewer however, as can be seen specif ically in the DownerNeighborhood area where sanitary sewer is now available.

The data layer d isplays only those sept ic systems which areproperly permit ted with Sheridan County. There are undoubt edlysept ic systems in existence that were either installed prior to t heCountys permitting program (1979) or were installed without

permits.

2.2.5 SAWS Taps Data for t he number of water account s/ taps wasobtained through SAWS. These accounts represent all users served withinthe SAWS service boundary exclud ing City users. As wit h the sept icpermit s, all water t aps were ini tially geocoded by address and manuallymoved to t he correct parcel within t he parcel boundary layer.

Data Limit ations:

The SAWS tap layer contains 1,668 account s/ taps. Based on arecent repor t completed by Entech, Inc. the current number o fSAWS users is 1,449. It is believed that t he data used for t his

study and obt ained by SAWS contained some dupli cate entries ofaccounts possibly due to the comb ining of databases between theCity o f Sheridan and SAWS. SAWS also has records for t apsobtained where no service was actually installed and the cityrecords would not reflect those.

The SAWS tap inform ation was used wit hin this Sept ic Impact Studyas an aide in determining development densities and developmentpotent ial. Although the tap inform ation is not entirely accuratedue to the duplicate entries, it was suff icient to use fordevelopment as described in the data interpretation section of t hisreport.

2.2.6 FEMA/ FIRM Boundary The floodplain boundary port rayed with inthis layer was obtained from the City o f Sheridan GIS department . Thislayer contains the projected boundaries of t he 100 and 500-year floodareas as presented by FEMA through t heir FIRMs (Flood Insurance RateMaps). The data is not int ended to be used at small scales and shouldonly be used in general terms.

Figure 2 .4 shows the locations of perm itt ed septic systems, SAWS tapsand the 100-year floodp lain.


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2.3 Data Inter pretationWith project-specific data input into the GIS map, data interpretation andevaluation can be conducted. The following condit ions were determ ined usingthe input data and are considered important to understanding conditions in thewatershed t hat may affect water quality relating t o septic systems.

2.3.1 Sept ic Density In order t o bett er visualize the areas within t hestudy area where the major ity of the septic systems are located, a septicdensity layer was created using t he septi c permit layer previouslydescribed. Using GIS, the septic perm it layer was overlaid on a squaremile grid. The intersect ion too l was then used to automatically generatea new po int data layer containing one point per square mile. Each newpoint now contains data that represents the number of septic permit sfalling w ithin the square mile section. The data is displayed so thatlarger circles represent a higher density of septic systems and smallercircles represent lower densities.

Based on this dataset, areas wit h t he highest density of septic systemsare generally located along Litt le Goose Creek from just downstream ofthe Powder Horn golf course development to the areas just south of t heairport . In additio n, the comm unity of Big Horn and surrounding arearevealed similar higher densit ies. Areas along Big Goose Creek wort hnot ing include the rural subdivisions approxim ately 5 miles west of townalong Big Goose Road as well as the area to the southeast of Kendr ickGolf Cour se.

Figure 2.5 shows the septic system density w ithin the study area, as wellas the impaired segments of creeks. Within the Little Goose drainage, thehigher septic system density appears to generally correlate wit h t he creek

impairment . This correlation i s less defined in other areas of t hewatershed, again suggesting other non-point sources may becontributing to creek impairment.

2.3.2 Developed Par cels Using the septic permit, water t ap, imageryand parcel layers, a developed parcels layer was generated so that ageneral idea of development densit y may be obt ained. Since bot h watertap and septic permit infor mation were reconciled to the correct parcel asdescribed above, GIS intersect f eatures were then used to select t heparcels containing a septic permit , water tap, or both . These parcelswere then grouped into the developed parcels layer. The imagery layerswere used to check the remaining p arcels within t he study area. In some

instances, there were certain parcels that did not contain a septic permitor water tap but t he aerial photography indicated t hat the lot had beenbui lt on. These bui lt -on parcels were also added to the developed parcelsdatabase. The amount o f developed land within t he study areaencompasses approx imately 66,000 acres, or 46%of the tot al 142,000acres wit hin t he study area. There are 2,044 developed parcels of 3 ,270tot al within the study area, excluding parcels within Sheridans corporatelimits.

2.3.3 Undeveloped Par cels The undeveloped parcels layer cont ains allof t he remaining parcels wit hin the study boundary that were not


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considered developed as described above. The developed andundeveloped parcel data layers have excluded areas within the City ofSheridan corporate boundary. The amount of undeveloped land withinthe study boundary equates to approximately 76,000 acres, or 53%of theavailable parcels wit hin the study area. There are 1,226 undevelopedparcels of 3,270 t otal within the study area, exclud ing parcels wit hin

Sheridans corporate lim it s.

Figure 2.5 shows the developed and undeveloped parcels. It should benoted t hat parcels are defined by current landownership. Futuresubdivision of existing large parcels is likely, which could change densityand the mix of developed versus undeveloped parcels.

2.3.4 Sanitary Sewer Capacity This layer was developed f or t he draftCity of Sheridan Wastewater Collect ion System Assessment completed inJanuary 2006 . Modeling results from the peak hour p lus ext reme flowsplus build -out scenario are depicted in this layer. The data shows theexisting sewer system at t he time the model was completed wit h thepipes color coded by flow versus capacity. Full bui ld out to the sewerservice boundary was considered for th is analysis. This layer indicatesthat several sewer interceptors would be at capacity if build out occursduring peak condit ions. Pipe segments shown in red are those that areflow ing more that 80%ful l. The majorit y of the lines at or over capacityare located on t he western side of Sheridan.

This layer also includes a possible revised Sewer Service Boundaryanticipated to be included in the finalized Wastewater Collection SystemAssessment. This boundary extends well into t he watershed, indicatingthe Citys interest in extending it s infrastructure and land use planning

boundaries.

Data Limit ations:

This dataset is based on modeling results conducted from aprelim inary version of the sewer model of Sheridans system.Demand allocation and refinement o f t he model are currentlytaking place through the ongoing City of Sheridan WastewaterCollection System Assessment.

2.4 Aquif er Sensit ivit y DataIn 1992 a mapping project enti tled t he Wyoming Ground Water Vulnerabilit yAssessment , was undertaken by t he Wyoming Department of Environment al

Quality s Water Qualit y Division, t he University of Wyoming s Water ResourcesCenter, the Wyoming State Geolog ical Survey, the Wyoming Department o fAgr iculture, and the US Environment al Protection Agency. The projects goalwas to develop a digit al GIS-based map that could assess the states relativegroundwater sensitivity and vulnerability to contaminants that may beint roduced at some location above the uppermost aquifer.

The project was approached by fir st developing an aquif er sensitivity ratinglayer. By EPA defini t ion, aquif er sensit ivity refers to t he relat ive ease wit h whicha contaminant applied on or near the land surface can migrate to t he aquifer ofinterest, based solely on hydrogeologic factors (Wyoming Ground Water


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Vulnerability Assessment Handbook, I-25). An overlay/ index method util izingGIS technology was used to generate the aquifer sensit ivit y layer. The generalidea behind t his technique is to combine spatial data layers representing variouscharacteristi cs through the assignment of a numerical rating for each feature.The hydrogeologic factors used to develop aquifer sensitiv ity are depth togroundwater, geohydrolog ic setting, soil comp osition, recharge rate, land slope,

and vadose zone characteristi cs. Indiv idual parameter rating maps weredeveloped fo r each of the six hydrogeolog ic factors listed above. Eachindividual parameter was assigned a numerical rating ranging from one to ten,with ten representing areas where the groundwater i s more sensitive tocontaminat ion and one representing areas that are least sensit ive. Aquif ersensit ivity was then developed by overlaying each individual parameter ratingmap and summing t he rating values.

Once the aquifer sensitivity layer had been established, the mapping project wastaken a step furt her in order to define groundw ater vulnerability. Groundwatervulnerability comb ines aquifer sensitivity wit h existing land use practices andpesticide use. While aquifer sensit ivity is based exclusively on natural occurringfactors, groundwater vulnerabilit y incorporates the effects from human impactssuch as land use, management practices, and contaminant properties.

For the purposes of this Septic Impact Study, only the aquifer sensitivity dataand cont ributing layers were util ized. This info rmation is beneficial to the studyas it w ill identify areas where groundwater is more sensitive to contaminationdue to natural occurring condit ions wit hin the aquifer. The groundwatervulnerability data focuses pr imarily on pesticide use and does not apply to t hisSept ic Impact Study. However, groundwater vulnerabili ty to pesticide use is oneexample of how sensit ivity data may be combined wit h existing land usepractices.

The final Wyoming Ground Water Vulnerability Assessment Handbook waspubl ished in 1998 and dig ital data products were made available in 1999. Thefo llowing aquifer sensitivity data layers fo r Sheridan Count y were obtainedthrough the Wyoming Geographic Information Science Center located on theUniversity of Wyoming campus. This center is responsible for the distr ibut ionand development of a wide variety of geospatial data sets for use by variousorganizations. A descript ion o f each layer stat ing t he various sources used forit s developm ent as well as how it relates to potential contamination issummarized below.

2.4.1 Depth to In i t ia l Gr oundwater This layer describes the dept h to

first encountered groundwater generated from the State Engineers Office(SEO) well permi ts database. An interpo lation technique was used togenerate a continuous surf ace of dept h values from the mapped waterdepths of the SEO wells database. A sensit ivity rating was assigned to t hewater depths and is depicted in th is layer. Ratings range on a scale ofone to ten with t en being the most sensitive and one the least sensitive.The higher the sensit ivity rating , the closer groundwater is to t he landsurface and the quicker contaminants can reach it.

2.4.2 Geohydrologic Sett ing Geohydrologic sett ing refers to thecharacteristics of the uppermost aquifer and is based on aquifer media


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and hydraul ic conduct ivity . The Wyoming State Geolog ical Surveydeveloped th is layer using the Water Resources Research Insti tut e BasinGround Water Report Series, USGS Hydrologic Investigations Atlases, andselected USGS Water Supply Paper s. Based on these references, a rank ingsystem was developed for all geological formations in Wyoming bygeneralized hydrologic characteristics ranging from a high-yield aquifer

to an aquiclude/ aquitard with low to no yield. Geologic formations wereclassified based on The Stratigraphic Chart Showing Phanerozo icNomenclature for the State of Wyoming. Also used was the Geolog ic Mapof Wyoming . When geologic formations were combined wit h hydrolog iccharacteristi cs, the resulting geohydro logic setting sensitivity rating layerwas developed. Ratings range from one to ten with one representingunfractured massive shale wit h low hydraulic conductivity and tenrepresenting well-developed karst limestone or gravel wit h a highconductivity.

2 .4 .3 Soi l s The t hicker the soi l, the lo nger contaminants remain in thesoil and may be degraded. In add ition, the finer the soil t exture, the lesseasily contaminants can pass through open spaces to the aquifer.Organic content also plays a role in contaminant degradation due to thegreater potential for chemical reactions to degrade the contaminantsbefore reaching the aquifer. The soils layer for t his project wasdeveloped based on the following f ive soil-form ing factors: soil parentmaterial, climate, biot a, topography, and t ime. This layer was compiledbased on digi tal surficial geology, bedrock geology, and elevation. Thefollowing sources and available data were used to generate thisgeneralized soils map: publi shed soil surveys, maps, and report s of t heNatural Resource Conservation Service, the Forest Service, the Bureau ofLand Management, and numerous theses and scientific papers published

by the Wyoming Agricultural Experiment Station and the University ofWyoming . Sensit ivity ratings for soils consider the following parameterson a weighted average basis: soil t exture and rock content, depth tobedrock, depth to groundwater, and soil class mineralogy.

2.4.4 Aquifer Recharge Aquifer recharge refers to t he amount ofwater that infi lt rates the soil and percolates thro ugh the unsaturatedmaterial into the groundwater. Contaminants can move from t he groundsurface into a shallow aquifer with greater ease using recharge as aprim ary transport mechanism. Therefore, areas wit h higher amounts ofnet annual recharge are more suscept ib le to contaminat ion. Factorsaffecting recharge include precipitation , sand and rock content of the

soil, and seasonal patterns such as snowmelt runoff . This layer wasproduced using pub lished percolat ion percentages for documentedsoil/ vegetation combinations as well as soil t ype and average annualrainf all. Sensitiv ity ratings are based on a scale of one to ten with onehaving the least amount of recharge and ten having a greater amount ofrecharge.

2.4.5 Land Surf ace Slope Aquifer sensitivity is affected by landsurface slope due to t he longer surface residing times for water-bornecontaminants on a flat slope, increasing the potent ial for contamination.This dataset represents land slope calculated from the USGS 3-arc-second


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dig ital elevatio n model (DEM). GIS techniques were used to calculate thepercent change in each cell wit hin the elevation model . Sensitiv ity ratingswere assigned to t he slope map t hroug h a set of functions describinghow percent slope influences potent ial groundwater contamination.

2.4.6 Vadose Zone The vadose zone is defined as the unsatu ratedzone above the water table and below the soil hor izon. This datasetdescribes the vadose zone media in terms of how easily contaminantscan move through it. The Wyoming State Geolog ical Survey modif ied theDRASTIC model sensitivit y ratings fo r vadose zone media to includemedia typi cally found in Wyoming such as coal sequences. Sensitivit yratings range from one to ten with rank one representing a confininglayer and rank ten representing a highly fractured layer.

2.4.7 Aquifer Sensit iv i ty Aquifer sensitivity refers to the relative easewith which a contaminant applied on or near the land surface can migrateto t he aquifer of interest, based solely upon hydrogeolog ic factors. Thislayer was created using GIS map overlay techniques of the six sensit ivityrating layers described above. Each of these six sensitivity ratings wassummed wit h equal weights to develop overall aquifer sensitivit y. Highvalues indicate areas where the aquif er is m ore sensitive to contaminationwhile low values represent areas where the aquifer is least sensitive tocontamination.

Data Limit ations: The data is not int ended to replace site investigati ons. The data

should only be used for regional-scale analysis. The sensitivity rati ng values can only be used in relative terms. In

other words, the rating s only describe the regions that have a

higher po llut ion potential than others within t he same study area. The model used to assess aquifer sensitivity is referred to as the

DRASTIC model. This model defines pollut ion potent ial as the sumof seven parameter ratings (Depth to g roundw ater, recharge,aquifer med ia, soil media, topography, impact o f the vadose zone,and conductivity). Each rating parameter is mult iplied by a weightranging f rom one to five depending on t he relative importance ofeach parameter.

The procedure used for defining Sensit ivity wit hin t he WyomingGround Water Vulnerabili ty Assessment Handbook has beenmodif ied from t he original DRASTIC model in t he follow ing ways:1. The hydraulic conductivity and aquifer media layers have

been combined within t he Wyoming model to for m t hegeohydrolog ic sett ing layer. Therefore, the Wyoming m odelonly contains six model parameter layers while the DRASTICmodel contains seven.

2. The Wyoming model uses a di fferent method for assigningrating values based on the unique nature of Wyoming shydrogeologic environment.

3. Equal weights are assigned to the parameters within theWyoming model due to lack of scienti fic informationdescrib ing t he weight relationships between theseparameters.


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Figure 2.6 show the Groundwater Sensitivity Classes established by themethods described above.

2.5 Designat ion of Imp act ZonesUsing the aquifer sensitivit y classes described above, Impact Zones were

delineated within t he Septic Impact Study area. The Impact Zone designationsare intended to provide a key map which will show landowners, septic installersand the permit ting author ity in which areas alternative systems mig ht beappropriate.

For example, if a parcel proposed for development or septic replacement fallswit hin either the Critical Impact Zone, High Impact Zone or t he Medium ImpactZone, extensive site investigat ions should be required that mig ht include itemssuch as permanent groundwater moni tor ing wells or soil coring and evaluationby a trained professional. From the information gained in the site investigation,the designer can then select an appropriate sept ic techno logy. The specificalternative technologies are discussed later in th is report. If a proposed septicsystem installation or replacement f alls in t he Regular Impact Zone, the level ofsite investi gation and design and a conventional system installation should beadequate. The Impact Zones simp ly direct the determination of whether analternative system should be considered.

Designation Criteria:

The five sensitivity classes determined in the Ground Water VulnerabilityAssessment report were designated into four Impact Zones for this study.High sensitivity was designated High Impact. Medium-high sensit ivitywas designated Medium Impact. Medium, Medium-low and Lowsensitivity areas were designated Regular Impact for septic system

impacts. A Critical Impact Zone was designated for the community of Big Horn and

its surround ing area. All of this area falls within the High GroundwaterSensitivity Class and due to the unusually high density of development inthis area, it warrants a greater level of care regarding onsite wastewatermanagement.

A fif th Impact Zone of SS was designated for t hose parcels that can beconnected to an exist ing central sewer system. For the City of Sheridan,if sanitary sewer i s available with in 400 feet of a parcel boundary, it isassumed the parcel can be connected to it . For t he Powder Horn, t heenti re platted boundary was designated as the SS Impact Zone.

The Impact Zones are mapped according to parcel boundary. If a parcel

is split by a sensitivity class, the sensitivity class encompassing thegreatest area of the parcel was used to designate the Impact Zone.

Figure 2 .7 show the Impact Zone designations determined fo r th is study.


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3.0 PHASE II ASSESS OPTIONS TO MITIGATE SEPTIC-RELATEDIMPACTS

3.1 IntroductionA primary objective of the research and recommendations on alternative

systems under th is project is to provide technologies that may help to alleviateimpacts to t he watershed currently occurring from conventional septic tanks anddrainf ields. These alternative systems may be considered a toolbox of possiblesolutions that can be used by Sheridan County, developers, engineers andothers to provide acceptable wastewater management. Taking these steps isbeing done, in part, to fulf ill Action Items contained in t he Goose CreekWatershed Management Plan.

A pr imary purpose of enhanced policies regarding wastewater management is topreserve the environment and prot ect public health. While several technologiesare presented to provide alternatives for a particular site, there is no guaranteethat a design and application for a sewage system on every site will be

approved. The issuance of a permit t o construct treatment f acilit ies is not aguarantee that t he system will work as designed parti cularly if it i s not proper lymaintained. Design professionals need to be involved throughout planning ,design and construction of any project.

3.1.1 Benefit s of Alter native Technology EvaluationThe benefits of analyzing alternative sewage facilities include thefollowing: Comply w ith the Goose Creek Watershed Management Plan and

avoid more str ingent regulation by t he WDEQ of activit ies wit hinthis watershed.

Upgrade the level of sewage treatment t hroughout this mostpopulated area of Sheridan County.

Provide sewage treatment methods that can accommodate growt hand increased densit y of homes in t he Big and Litt le Goose valleys.

Encourage the extension of central sewage collection facilitieswhere they are determined to be feasible.

Provide alternative methods of onsite t reatment t hat are superiorto conventional systems in the parti cular circumstances of thediffering site sizes and conditions that are found throughout thisarea.

Provide alternatives for t reatment w hen considering operation,maintenance and lif e-cycle costs.

3.1.2 Jurisdict ional OversightAs alternative systems are evaluated for a particular area, the f ollowing

jur isd ict io nal and regulatory considerat ions must be made: The City of Sheridan has authority wi th in t he City and wit hin one

mile of the City, and over connections to or extension of the Cityof Sheridan sanitary sewer system.

The County reviews, approves and inspects onsite systems withinthe County that receive less than 2000 gallons per day (gpd).Detailed design crit eria and site investigation requirements areoutlined in the Countys regulations for permits to construct,


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install, or mod ify small wastewater facilit ies. These regulationscan be found on the Sheridan County web page athtt p:/ / deq.state.wy.us/ wqd/ www/ Permitting/ Pages/ SMWW/ smallwastewater.asp. The Count y regu lations includ e several opt ions foralternative systems.

The WDEQ reviews and approves onsite systems t hat receive morethan 2 000 gpd, cluster systems (central systems that do notconnect to the City sewer), and extensions of the City sewersystem. Chapter II, Part D of t he Water Qualit y Rules andRegulations specify design criteria for small wastewater systems.These rules also provide for use of several alternativetechnologies.

If a discharge is proposed from a treatm ent facility, a dischargepermit must be obtained from the WDEQ.

Developments and their associated water and sewer systems mustcomply wit h City and/ or County comprehensive plans, subdivisionrules, and appropr iate policies.

Approval is needed for subdivisions from the City PlanningCommission or County Planning and Zoning Commission, asappropriate.

Therefore, depending on the parti cular project, the City, the County o rthe WDEQ may be involved in t he review and approval of designs.

Once constructed, it is the responsibility o f the owner of the system toprovide proper operation and maintenance, keeping the system in goodwork ing order, and to comply with appropr iate state and localregulations.

Comp liance wit h local p lans and p lanning processes is an impor tantconsideratio n. While proper sewage treatm ent is a critical component tomanaging growt h in t he Goose Creek Watershed, it should not be theprim ary factor. Overall land use planning should contro l development.

3.1.3 Syst ems Consider edThe conventional onsite sewage system is a septic tank followed by adrainfield that is fed by gravity. This is the standard onsite sewer systemused in Sheridan County for homes that are not connected to a centralsystem. A conventional septic system is illustrated in Figure 3 .1.

Alternative systems that are considered i n t his report are:

City of Sheridan sewer system expansion; Regional central sewer system, including cluster systems; Alternative collection systems (for a cent ral sewer system); and Alternative onsite systems.

In addition to d iscussion on types of systems, the following relatedmatters are also discussed and recomm endations provided: Design requirements fo r proposed system; Requirements fo r t he site investigation; Construction requirements; and
http://deq.state.wy.us/wqd/www/Permitting/Pages/SMWW/smallwhttp://deq.state.wy.us/wqd/www/Permitting/Pages/SMWW/smallw


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Management and operational requirements.

3.2 Alt ernati ve Central Systems

3.2.1 Cit y of Sher idan Sewer System ExpansionThe City of Sheridan currently provides sewer to users out side of t he citylim its to a limit ed extent . The City has an extensive evaluation of it ssewer collection system underway which includes a master plan forpossible extension of t he system into unsewered areas in and around t heCity and a capital improvements plan to ident ify needed improvements toolder parts of the system. As part of th is and other on-going planningefforts, the City has tentatively established a new Sewer Service Boundarywhich is shown in the GIS mapping described in previous sections of thisreport . It is likely the Cit y will finalize this boundary to establish an areathat t he City can be expected to g row into over the coming years. TheCity p lans to eventually ex tend sanitary sewer service throughout th isarea.

The process of provid ing City sewer th roughout this area wil l t ake manyyears however, and imp rovements wil l be phased in as they aredetermined feasib le and as development occurs. In the mean time, userswill need to find alternative means to provide sewer service. Within theCity lim its, City sewer service is available immediately, however newuser(s) must provide for any needed extensions.

As the City allows extensions throughout the planning area over the nextseveral years, proposed extensions must be appr oved by the City and itmust be determined that the sewage contribut ion from these extensionswill not create capacity problems with in t he remainder of the City sewer

system. All extensions must be designed and installed accord ing to Citystandards and must be funded by those benefit ing f rom t he extensions.

Work is sti ll underway on t his master plan and f inal recommendationshave not yet been made. Ultimately, however, the most desirable opt ionfor sewer service within th is area surrounding the City is by an expansionof the Citys system.

As areas are developed prior to City service being available, thoughtshould be given to how a central collection system can eventually beinstalled to serve the development.

3.2.2 Regional Centr al Sewer Syst emAn alternative to the extension of the City sewer system beyond theplanning boundary is to create a separate central sewer system with itsown wastewater treatment plant . This is not pr oposed in the Big Gooseportion of the study area due to a much smaller population, but may befeasible in the Little Goose valley which has a much larger population andhigher density of development. Such a system would need to be ownedand operated as a public system administered by a publ ic entity such asthe County, joint powers board or an establi shed sewer distr ict.


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If a central sewer system was determined t o be f easible in t he Litt leGoose valley, it would likely commence south of the City planningboundary (south of t he Big Horn junction or Big Horn wye). It would t henextend as far south and as far out the east and west sides of the valley asis practical, based primarily on t he density of homes and number of usersgained for t he length of l ine installed. A likely service area includes the

community of Big Horn and developments such as the Powder Horn,McNally, Meadowlark Meadows, Knode Ranch and Big Horn Ranch.Currently the Powder Horn provides a central sewer system and has itsown extended aeration package treatment plant. This plant serves theapproximate 150 homes in this development, but is expandable to servea much larger number. This plant seems to provide satisfactorytreatm ent and has been complying wit h its discharge perm it. Having thissystem, the Powder Horn understands the operational requirements,responsibilities and costs associated with having a central sewer systemand package treatm ent plant . While they can cont inue as they are formany years to come, they are very interested in studying the idea of aregional or area-wide sewer system (such as the Litt le Goose valley sout hof the Citys service area), and possibly participating in such a system.

If a central sewer system is considered for this area, the collection systemis a major component in all phases of planning, design and construct ion.The three different types of collection systems as described in Section 3.3all need to be thorough ly evaluated. The costs fo r the collection systemmay exceed that for t he treatm ent plant , so careful consideration of t healternatives is required.

Advantages of a central sewer system in t he Lit tle Goose valley include: Elimination of t he many onsite systems that m ay not be working

properly and may be impacting both surface and groundwater. Itwould also greatly reduce the m aintenance requirementsassociated with onsite systems and extra costs associated withreplacement due to their limited life.

A single enti ty responsible for t he operat ion and maintenance ofthe sewer facili t ies. This typically leads to improved overallperfor mance and benefits fro m economy of scale.

While onsite systems have generally served th is area satisfactoril y,growth has been signif icant in the last 10 years and t his area willcontinue to grow. At some po int onsite systems may reach asaturation poin t. Typically areas serving more than 1,000 homescan suppor t a central sewer system, depending on t he

development density. There are over 3,200 existing parcels wit hinthe watershed outside of the City of Sheridan, so planning for anadditi onal central system is reasonable.

If a central sewer system is needed in the fut ure, it isadvantageous to construct t he collect ion system prior t o fu lldevelopment of the area. Costs are also saved by const ruct ing onesystem for each home, rather than an onsite system init ially andthe central system in the fut ure.


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Concerns to be more ful ly exp lored include:

Costs can be quite high for a central collection system andwastewater treatm ent plant. This will have to be studied carefullyduring preliminary engineering.

While it should be possible to obtain a discharge permit foranother treatm ent p lant, it is a significant commitm ent t o providethe level of operation and maintenance needed to comply wit h thepermit requirements over the long term.

There are considerable responsibilit ies in the ownership , operationand maint enance of a sewer system. The City has the resourcesand experience to do this. A sewer distr ict m ight need to befor med, with staff and other resources developed.

A thorough investigation is required to more fully understand thefeasibil ity of such a system and associated costs.

To be successful, this district and system would need the backingof t he residents within the area. An outreach effo rt wi ll be needed

to determine the level of support.

3.2.3 Cluster SystemsCentral sewer systems on a much smaller scale are cluster systems ordecentral ized systems. These systems serve one part iculardevelopment o r possibly adjoining developments. The system consists ofa central collection system and a single t reatment unit . The treatm entfacilities could be a mechanical extended aeration package plant, or alarger variation of the onsite systems discussed in t his report .

The primary advantages of th is type of system include: Smaller collection systems are needed, reducing costs.

Being smaller than t he central systems described above, clustersystems can be more easily planned, constructed and expanded asneeds warrant.

The primary concerns are: The system has to be ready to serve the fir st house. Some types of

treatment systems may not work well unt il several homes arecontributing f lows.

Small package treatment plants do not have a good histo ry ofprovid ing a high level of treatment because loadings tend to varyand operation is typically not at the level required t o fully managethe treatment process.

Costs for operation, m aintenance and management of the systemare often d ispropor tionately high because of t he relatively smallnumber of users. Smaller size can mean higher unit cost s due tolack of economy of scale.

It is often dif ficult to m aintain an adequately trained and cert ifiedoperator t o operate the treatment system.

The entity t hat is responsible f or t he system can be a concern.Homeowners associations or small districts of ten do not have thepersonnel, funding o r ot her resources to adequately manage asewer system over the long t erm. A larger sewer district t hat may


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manage several cluster systems would be better suited to providethe appropriate level of management and operat ion.

The feasibility of using cluster systems should be included as acomponent in any overall master planning eff ort f or providing centralsewer service within the study area.

3.2.4 Per m itt ing Considerat ions for Additi onal Cent r al Syst emsOne of the considerations as options involving add itional wastewatertreatm ent plants are evaluated, is whether these plants could obtain apermit to discharge to one of t he Goose creeks. Discharge perm itapplicatio ns and m onito ring requirement s are handled by the Cheyenneof fice of the DEQ. Leah Kraftt is the head of this program.

The City of Sheridans wastewater treatment plant has a discharge permit.Their permit establishes the lim its shown for t he following parameters.

The Citys wastewater treatment plant has a very good history ofcomplying with their discharge perm it . For examp le, BOD and TSSconsistently run under 5 mg / L, and they have not had d iff iculty meeti ngany of the ot her requi rement s. There are no current ind ications thatthese limits will become str icter in the near fut ure.

All of the Goose creeks are Class 2AB. This class of water is known tosupport game fish populations or spawning and nursery areas at leastseasonally and all their perennial tr ibutaries and adjacent wetlands andwhere a game fishery and d rink ing water use is otherwise attainable.There is no current movement to change these classifications.

There does not appear to be any increased dif ficult y in obt ainingdischarge perm its for these creeks due to t heir impairment status.Permit s require an involved appl ication and pub lic comment period .Once permit s are granted, there is on-going monito ring and report ingrequired.

It is anticipated that any addit ional requests for discharge permi ts wouldhave to meet lim its sim ilar to the Citys shown above. A properlydesigned and operated secondary treatment p lant should be able to meetthe BOD and TSS lim it s shown. Wit h the fecal coli for m lim it , disinf ectionis required. With a maxim um lim it on chlorine residual, eitherdisinfection ot her than chlor ine must be used, or de-chlorination will beneeded. The ammonia limit may be the most challenging to meet.However, this limit should not result in extraordinary technology within atreatment facility.

Param et er Average Lim it Maximum Lim it (dai ly)

BOD5 30 mg/ L (w/ 85%removal) 90 mg/ LTSS 30 mg/ L (w/ 85% removal) 90 mg/ LAmmonia 1.78 mg/ L 3.56 mg/ LpH Within range of 6-9Fecal Coliforms 200 colonies/ 100 ml 400 colonies/ 100 mlChlorine residual 0.02 mg/ L


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It appears possible to obt ain a discharge permit for another treatmentplant in the Little Goose valley south of Sheridan.

3.3 Alt ernati ve Coll ect ion Systems

3.3.1 Convent ional Coll ecti on Syst ems

A conventional sewer collection system is designed to carry raw sewagethat is discharged from all t ypes of users connecting t o the sewer system.Conventional systems that are a public sewer system or otherwiseregulated by t he Wyoming DEQ must comply w ith the requirements of: Chapter 3 Regulations for Permit to Construct, Install o r Modify

Public Water and Wastewater Facilities Chapter 5 Operator Certification Requirements Chapter 11 Design and Constr uction Standards for Sewage

Systems

Conventional collection systems m ust be designed and constructed per

Part B of Chapter 11. These requirements include: Gravity collection sewers shall be at least 8 inches in size. Lines must be laid to grade, with a minimum slope of 0.004 ft / ft . Manholes are required every 400 feet, at change of directions or

slopes. Lift stations are needed where gravity flow cannot be maintained.

These stations must include two pumps capable of handling 3-inchsolids. There are also several other requi rement s associated with araw sewage lift station.

Chapter 3 requires designs be prepared of proposed systems by alicensed professional engineer. These designs must be approved by DEQ

prio r to construction. They must also be approved by the Owner of thepub lic sewer system. Public systems may be owned by a city, county,district or j oint powers board.

Chapter 5 requires that a publ ic sewer system employ certif ied operators.Certif ication includes a specified number of contact hours with t hesystem, testing and continuing education.

Conventional gravity sewer collection systems are relatively expensivebecause of t he need to lay lines to grade and the other requirementslisted above. This result s in lines that may be relatively deep. Whileevery attempt is made to eliminate lift stations, terrain may require

pumping on a part icular project, and again these can be relativelyexpensive because of t heir depth and t he requirements of handling rawsewage.

Conventional systems typically work well wit hin a city or for a relat ivelydensely populated service area. The length of the collection systemnecessary to serve users in less densely populated areas typ ically requi resthat alternative systems be considered, due to the cost.


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Advantages of a conventional collection system include: This is a well known t echnology. Operators are very familiar wit h

these system s. It can handle raw sewage easily. Wit h the large pipe sizes and

manholes for access, maintenance is relatively straight forward. With the 8-inch minimum size, lines often have extra capacity for

growth o r above-norm al flows. Frequently ext ensions can be madeusing existing lines.

Disadvantages with a conventional collection system include: Relatively high costs per user when in a rural environment. Terrain can make it difficult to maintain gravity flow and minimum

grades.

3.3.2 Septic Ta nk Ef f l uent Collect ion Syst emsSeptic tank effluent collection systems receive septic tank effluent (alsocalled greywater). Sept ic tanks remove sol ids, therefore smaller diameter

lines can be used than are used wit h convent ional collection. Septictanks either already exist (as in t he case of an ex isting subdivision thatwas originally installed wit h sept ic tanks and drainfields), or are installedto provide the solids removal required for the user to connect to this typeof system.

There are two t ypes of septic tank eff luent collection systems: Septic tank effluent gravity systems (STEG) Septic tank effluent pumping systems (STEP)

As the above names imply, the STEG system works using g ravity fl ow andthe STEP system requires pump ing. If pum ping is requ ired, small

pumping unit s are typically installed immediately downstream of t heseptic tank, and serve only that hom e. These pumping unit s are typicallyowned and operated by the individual homeowner. Since they pumpgreywater, they do not have to handle the large solid s discussed abovefor raw sewage pum p stations. Pumps that can handle at least -inchsolids are recommended.

Sept ic tank eff luent collection systems have several advantages over aconventional collection system. These includ e: Smaller diameter lines can be used. Typically these wi ll be 4-inch,

although sizing is required based on slopes and design f lows. Variable grades can be used. This includes negative grades at

t imes. All grades and elevation of l ines must be carefully designedfrom a hydraulic standpoint.

Manholes are not normally used, however cleanouts are requiredfor maintenance. Manholes are recommended at certain key line

junct ions. Since variable grades are allowed, the lines typ ically are not as

deep as conventional lines. The shallower and smaller li nes not only save cost, but

construction t ime.


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When a development with onsite sewage systems is beingretrof itt ed with a central collection system to eliminate drainfields,a septic tank effluent collection system is less disrupt ive than aconventional system in that the septic tank is saved (does not needto be bypassed), result ing in less excavat ion wit hin the yard. It isalso easier to adapt a variable grade design to fit a developed areathan a conventional collection system.

While more pum p stations may be needed (for t he individualusers), they are less complex than raw sewage lift stations.

Concerns regarding eff luent collection systems include: While the septic tanks remove solids, they do no t remove 100%of

the solids. Therefore there is potent ial for solids deposition andmaintenance of the variable grade line.

Septic tanks maintain anaerobic conditio ns so septic tank effluenthas an odor . Any vent ing of the sewer to the atmosphere canresult in odors. Therefore this system has to be well thought out,

so nuisance odors do not become a problem. If septi c tank eff luent f low enters a conventional collection system,

hydrogen sulfide may also be a problem. Hydrogen sulfide canresult in more corrosive condit ions than are normally found inconventional collection systems. Also, sept ic tank effluent hasanaerobic properties so the owner of any conventional sewersystem would need to approve its discharge.

Responsibilit ies and costs for the ind ividual user are greater wit hthis system than wit h a conventio nal collection system becausesept ic tanks still must be periodically pumped and maintenanceperfor med on small p ump stations if they are necessary.

Increased user responsibilities mean a more involved and on-going

publi c education process. Overall, operation and maintenance costs are generally h igher w ith

a STEG or STEP system , as opposed to a convent ional co llect ionsystem.

Septic tank effluent systems do not handle high vo lumes orunusual waste streams (such as grease or industrial or commercialwaste), as well as a convent ional collection system.

Air vents and isolation valves may be needed in t he system.

3.3.3 Vacuum Sewer Collection Syst em sWhile vacuum sewer collect ion systems are newer technology thanconventional systems, they have been used throughout the country and

in Europe for many years. They are relatively new to Wyoming, however.This newer technology should be accepted by Wyoming DEQ, providedthere is a thorough design and an appro priate entity to own and operatethe system.

As the name implies, a vacuum sewer collection system utilizes a vacuumto t ransport the sewage through t he pipes and br ing it to a point where itcan be delivered to a receiving interceptor. Vacuum technology differ sconsiderably fro m conventional technology discussed in the previoussection. Depending on the circumstances of t he area to be served,


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vacuum technology can provide some advantages. Therefore it isappropr iate to compare it to conventional technology to m ake aninformed decision.

A vacuum sewer consists of t he follow ing components: Gravity service lines. These are ident ical to a service line for a

conventional system (from the house to the yard or boulevardarea). However, it leads to a valve pit rather than to a gravity mainin the street.

Valve pit . A valve pit consists of two part s; a sump and valvehousing. The sump is located in the lower part of t he housing andsewage enters this sump from the house. The upper part of t hevalve pit includes a vacuum interface valve. This valve monito rsthe amount of sewage in the sump by a sensor p ipe. When tengallons of sewage collects, this valve opens and the differentialpressure f rom the vacuum sewer main propels the sewage into themain. Once the contents of the sump are empt ied, the interface

valve closes maint aining a vacuum on the system. Up to fourhomes can be served by one valve pit, provided they are in relativeclose prox imity to each other. There is no electricity in t he valvepit . A valve can handle a maxim um flow o f appr ox imately 30gallons per minute. A short run of smaller diameter pipe (laidrelatively flat) connects the vacuum interface valve to the vacuumsewer main in the street. Figure 3 .2 illustrates a typical valve pit.

Collection piping (vacuum sewer main). Collection piping consistsof 4 to 8 PVC pipe laid throughout the service area such that allhomes have a relatively easy connection to the collection piping.Vacuum sewer mains are airti ght w ith no m anholes. They are laidin a sawtoo th prof ile rather than to a grade as wit h a

conventional system. Between the sawt ooths, the p ipe slopes canbe minimal, at approx imately 1 foot in 500 f eet. Up to 10,000 feetof piping can connect to one vacuum station. This PVC pip ing canbe tapped for fut ure connections like a conventio nal collectionsystem. The vacuum propels the sewage through the collection ofpip ing at a velocity of about 15 feet per second. This preventssolids from settl ing out in the system. See Figure 3.2.

Vacuum station. The main component of a vacuum sewer systemis the vacuum station. The primary features of a vacuum stationare:

A co llect ion tank for the sewage brought int o t he stat ion byvacuum

The vacuum pumps which maintain a vacuum on thecollection system

The more convent ional sewage pum ps which discharge thecollected sewage to the gravity interceptor via a force main(somewhat similar to a sewage lift-station).

A basic vacuum stati on is illustrated in Figure 3.3. Up to 2000hom es can be served by a single vacuum station.

Since vacuum sewers are relatively new to this area, the owners of severalexisting vacuum sewers were cont acted. All of these owners (andoperators) were pleased with thei r system s. In many cases, they had


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installed multip le neighborhood vacuum systems because of theirexperiences wit h their init ial installation. Vacuum sewers were used inthese comm unit ies for various reasons including :

high groundwater; shallow bedrock; close prox imity to lakes; and the need to minimize trenching.

They all believed operation and maintenance was reasonable and theyhad not had significant prob lems with the valve pit s, vacuum sewers, orvacuum station. Therefore, this technology continues to be applied andshould be considered as a sewage collection alternative in t he GooseCreek Watershed.

Prim ary advantages to a vacuum sewer collection system include: Relatively ease of design for an existing neighborhood t o solve

collection problems. The shallow bury depth of t he collection sewers, thus avoiding

problems associated wit h high groundwater and soils that arediff icult to excavate. This result s in cost savings for installation.

A much reduced surface restoration effort and cost, as comparedto deeper sewers.

A shorter construction period, thus reducing disruptions to theneighborhood.

The ability to serve a large area from one vacuum station (asopposed to lif t-stations which are limi ted by the slope of thecollection sewers and the ground).

The abilit y to easily adjust t he location of the collect ion sewer i f

obstacles are encountered, as opposed to gravity l ines that m ustbe laid to a specific grade.

A resulting sewage collection system that does not leak. Manholes are not required, thus resulting in a cost savings. Easier installation around other buried util it ies. Since the vacuum ex tends from t he users valve pit th rough the

collection system, it is a cleaner system than conventional sewers. With its airtight design, odor s are not an issue. Vacuum systems are typ ically readily expandable. This may prove

valuable in the future as the initial service area may be expanded.The largest init ial investment the vacuum station, has thepotent ial to allow a considerable number of addit ional connectionsin the future.

Disadvantages of a vacuum sewer system include: A vacuum station is somewhat more complex than a conventional

lift station. A station involves both vacuum pum ps and dischargepum ps. It also is more expensive than a conventional lift station.

Vacuum technology is different t han the conventional collectionsystems with which sewage system operators are more fami liar.Training i s provided by the system manufacturer, however, and


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from d iscussions with operators, this difference is not significantonce they develop a familiarit y with the system.

Of all of the issues discussed above, a primary item to be considered isthe reduced depth requi red for t he collection sewers and thus thereduced constructio n cost. This is especially true in areas where soil type

and groundwater make installation of a conventional system d iff icult.Therefore it appears a vacuum system should result in a cost savings inmany situations.

3.4 Alt ernati ve Onsit e SystemsSeveral types of onsite, sing le-user sewage treatment and disposal systems aredescribed in this document . These systems provide the developer, homeowner,design engineer and County staff w ith alternative systems that may be used toaddress the goals of the Watershed Plan and characteristics of the particularsite.

Onsite systems should not be used when connection to a central system is anopt ion. If the new sewer service is with in 40 0 feet of a central sewer system, orfalls within the SS Zone as defined in this study, connecti on shall be made tothat system wit h the approval of the system owner. If there is a compellingreason t his connection cannot be made, the need to make this connection maybe appealed to the City Planning Commission or County Planning and ZoningCommission as appropriate.

Reasons to consider or require alternatives to the conventional septic tank andgravity fed drainfield include the need to: Address specific site condit ions

High groundwater table

Bedrock or hard soi l layers close to the ground sur face Fractured rock beneath the sit e Tight soi ls (slow percolat ion rate) Gravel ly or fr actured soi ls (high percolat ion rate) Small area avai lab le Topograph ic rest rict ions, such as slope and converging slopes

Provide improved treatment Reduce the potent ial for treated effluent leaving the propert y or reaching

ground or surface water Provide a longer life for the system Replace an existing failed conventional system.

Other considerations for alternatives at a particular site include: The level of operation and m aintenance required and the ability o f the

owner t o provide it. The prox imity of t he site to prop osed extensions of a central sewer

system. The characteristics of the wastewater.

The applicability of various alternative systems for specific sites or to addressspecific prob lems is summar

SSIS Final Report

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