Memrandum T: Bassett Creek Watershed Management Cmmissin Recmmendatins: 1. Perfrm additinal mnitring f Schaper Pnd in 2018 including water quality mnitring lngitudinally thrugh the pnd, a bathymetric survey, and a carp survey. 2. Authrize expenditures f Schaper Pnd Diversin Prject CIP funds up t $21,000 fr the abve mnitring. (Current CIP funds remaining are apprximately $250,000.) 1.0 Backgrund Schaper Pnd is classified by the Minnesta Department f Natural Resurces as a public water wetland; it is lcated suth f Sweeney Lake and nrth f Highway 55 in Glden Valley. The pnd receives abut 90% f its flw frm the Sweeney Branch f Bassett Creek frm the suth (under Highway 55), and 10% f its flw frm a strm water inlet (called the Railrad inlet) in the nrthwest lbe f the pnd. The pnd utlets directly t Sweeney Lake frm the nrtheast lbe (Figure 1). In 2011, the BCWMC cmpleted the Sweeney Lake Ttal Phsphrus Ttal Maximum Daily Lad Study (TMDL). The study s implementatin prgram identified mdifying the water flw thrugh Schaper Pnd as ne f the ptins tward achieving the gal f reducing phsphrus lads t the lake. The BCWMC cmpleted a feasibility reprt fr the Schaper Pnd Imprvement Prject in February 2012. The BCWMC added the Schaper Pnd Diversin Prject t their Capital Imprvement Prgram thrugh a watershed management plan amendment in 2013 and fficially rdered the prject in September 2013. 1.1 2011 mnitring and recmmendatins In 2011, Schaper Pnd was mnitred as part f the Sweeney Lake TMDL Study. Equipment, including aut samplers, level sensrs, and area velcity meters, was installed at the utlet f Schaper Pnd, at the suthern inlet under Highway 55, and at the Railrad inlet t cllect enugh data t evaluate the phsphrus remval perfrmance f Schaper Pnd and t develp a mdel t evaluate hw remval culd be enhanced thrugh pnd mdificatins. A ttal f six cmplete (e.g., samples cllected simultaneusly at bth inlets and at the utlet) strm events were mnitred frm June 9 t August 13, 2011. Fr all events, samples were analyzed fr ttal phsphrus, ttal disslved phsphrus, ttal suspended slids, and vlatile suspended slids. Fr tw events, samples were als analyzed fr particle size. Flw was measured cntinually frm May 19 thrugh August 14, 2011. Barr Engineering C. 4300 MarketPinte Drive, Suite 200, Minneaplis, MN 55435 952.832.2600 www.barr.cm
Angel Dr Sweeney Lake Railrad Inlet Outlet!. Nrtheast Nrthwest!. Flating Water Baffle Barr Fter: ArcGIS 10.6, 2018-05-09 15:33 File: I:\Client\BassettCreek\Wrk_Orders\2018\Schaper_Pnd\Maps\Fig01 Prject Lcatin Map.mxd User: jrv S Frntage Rd Highway 55 Inlet Lilac Dr N Schaper Pnd!. 55!. Suth Center Schaper Rd!. Grab Sample Lcatins!;N Feet 150 0 150 Figure 1 MONITORING & BAFFLE LOCATIONS Schaper Pnd Effectiveness Mnitring Bassett Creek Watershed Management Cmissin 55
T: Bassett Creek Watershed Management Cmmissin Page: 3 The mnitring results prvided a gd understanding f hw Schaper Pnd functined at the time and the data were used t develp the Schaper Pnd Imprvement Prject feasibility study. The results shwed that apprximately 90% f the phsphrus lad t Schaper pnd came frm the Highway 55 inlet, but it was shrt-circuiting 65% f the pnd vlume that culd therwise be used t settle phsphrus frm this surce. Therefre, diversin f water within the pnd t the nrthwest lbe f the pnd was identified as a way t prvide mre time t settle phsphrus and imprve verall phsphrus remval perfrmance in Schaper Pnd. 1.2 Implementatin f flating barrier The BCWMC selected the Schaper Pnd Diversin Prject alternative frm the feasibility study. The City f Glden Valley cnstructed the prject, which was designed t divert water, via a flating water baffle, within the pnd t direct mre f the water flws t the nrthwest part f the pnd. Based n the 2011 mnitring data and mdeling, it was believed that the diversin wuld allw the water t remain in the pnd fr a lnger perid f time, allwing a greater amunt f sediment, phsphrus, and ther suspended slids t settle ut befre the water exits the pnd. The prject included the installatin f an apprximately 380-ft-lng flating water baffle extending ut frm the east side f the pnd and the cnstructin f tw maintenance access areas. The prject was expected t reduce the amunt f phsphrus reaching Sweeney Lake by an estimated 81-156 punds per year. The city cmpleted cnstructin f the prject in December 2015. Additinal repairs and maintenance t the flating baffle, as well as vegetatin management n the east side f the pnd ccurred in 2016. Als in 2016, the Cmmissin apprved the use f a prtin f the remaining CIP funds t study the effectiveness f the prject in 2017 by replicating the mnitring that ccurred in 2011. 2.0 2017 effectiveness mnitring The 2017 effectiveness mnitring was initiated a little mre than tw mnths after it was cnfirmed that the flating barrier was secured and wrking prperly. Flw mnitring began in mid-august and cntinued int the first week f Nvember. Twelve water quality samples were cllected frm the Highway 55 inlet and the Schaper Pnd utlet during cincidental events between August 25 th and Octber 25 th, while eight water quality samples were cllected frm the Railrad Inlet during cincidental events in Octber. Figure 1 shws the sampling lcatins. The 2017 and 2011 sampling lcatins, equipment and methds were identical. The water quality samples cllected fr each event were analyzed fr ttal suspended slids (TSS), vlatile suspended slids (VSS), ttal phsphrus (TP) and ttal disslved phsphrus (TDP), cnsistent with the 2011 mnitring. Similar t 2011, tw sets f samples (representing bth high and lw flw events) frm the Highway 55 inlet and Schaper Pnd utlet were analyzed fr particle size distributin t aid in determining the likelihd that the slids (and phsphrus attached t slids) in the inflw culd be settled in the pnd. 2.1 Water quality cmparisn befre/after prject implementatin Because the water quality samples were cllected ver a range f flws fr flw events f varying magnitudes, the sample results were flw-weighted (summing the prduct f average flw and P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx
T: Bassett Creek Watershed Management Cmmissin Page: 4 cnstituent cncentratin fr each sample and dividing by the ttal flw sampled) fr direct cmparisn (shwn in Table 1) between the 2011 and 2017 mnitring perids. Table 1 Cmparisn f 2011 and 2017 Water Quality Effectiveness Mnitring When cmparing the water quality in the pnd and upstream f the pnd between 2011 and 2017, the fllwing bservatins were nted: Ttal phsphrus cncentratins entering the pnd under Hwy 55 was 37% lwer in 2017 than in 2011. Ttal suspended slids cncentratins entering the pnd frm the railrad inlet were nearly twice as high in 2017 as they were in 2011. Ttal phsphrus leaving the pnd (and entering Sweeney Lake) was rughly similar between 2011 and 2017. All three mnitring lcatins had lwer disslved phsphrus cncentratins than what was bserved in 2011. Ttal suspended slids leaving the pnd were 30% higher in 2017 than in 2011. Schaper Pnd is nt remving suspended slids r ttal phsphrus as well as it did in 2011, and during mst f the mnitred events, the flw-weighted cnstituent cncentratins are higher at the pnd utlet than the cmbined inflw. There was slightly less mnitred flw during 2017 than in 2011 (i.e., the average flws were less in 2017 than in 2011). Figure 2 shws the results f particle size distributin testing n fur sets f samples, representing highand lw-flw events, cllected frm the Highway 55 inlet and Schaper Pnd utlet during 2011 and 2017. The figure allws fr cmparisns based n flw thrugh the pnd, as well as differences between the tw years f mnitring. The fllwing bservatins were nted: In 2011, the particle size distributins were similar fr the respective mnitring lcatins during lw- and high-flw events. P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx
T: Bassett Creek Watershed Management Cmmissin Page: 5 In 2017, the particle size distributins were similar fr the Highway 55 inlet during lw- and highflw events, but the pnd utlet shwed a significantly finer particle size distributin under high flw cmpared t the Highway 55 inlet. The size f particles in the water were significantly finer in 2017 than in 2011 fr all mnitring lcatins, including during lw-flw events. During 2011, the particle size distributin f the pnd inflws included significant fractins f slids that wuld mre easily settle in detentin pnds (i.e., larger-sized particles). Resuspensin f particles in the pnd may have played a rle during high-flw events in 2017, but was nt evident in 2011. As previusly discussed (and shwn in Table 1), the flw-weighted cncentratins f ttal suspended slids (TSS), vlatile suspended slids (VSS), and ttal phsphrus (TP) are higher at the pnd utlet than the cmbined inflws t Schaper Pnd. As a result, Figure 3 was develped t evaluate the sample results fr each f the 12 sampling events and cnsider whether flw r residence time (the amunt f time it takes water t travel thrugh the pnd) culd explain why Schaper Pnd is nt remving suspended slids r ttal phsphrus as well as expected r as well as it did in 2011. Figure 3 shws the relatinship between 1) the rati f the utlet sample cncentratin t the Highway 55 inlet sample cncentratin (yaxis), and 2) the Schaper utlet cmpsite sample flw. The pints shwn in Figure 3 with a rati f the utlet sample cncentratin t the Highway 55 inlet sample cncentratin greater than 1 indicate events where either TSS r TP are nt being remved by the pnd. Figure 3 shws nly ne event when the rati was greater than 1; this ccurred when the average flw was apprximately 55 cubic feet/secnd. This is the nly mnitred event that resulted in sme remval f TSS and TP. All f the ther sampling events resulted in a net exprt f phsphrus and TSS frm the pnd, with greater levels f exprt cinciding with lwer flw. Ntably, Figure 3 shws that the net exprt f TSS frm the pnd is significantly higher than TP exprt fr the crrespnding events (i.e., the rati is higher). This may be a byprduct f the higher TSS cncentratins entering the pnd frm the railrad inlet, but at a minimum, wuld appear t rule ut sediment phsphrus release as a surce f phsphrus because the disslved phsphrus levels bserved at the Schaper utlet were quite lw. P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx
Figure 2 Cmparisn f 2011 and 2017 Particle Size Distributins fr Lw and High Flw Events
T: Bassett Creek Watershed Management Cmmissin Page: 7 Figure 3 Effect f Flw n Inflw/Outflw Cncentratins during 2017 Mnitring Events As the preliminary results f the labratry sample analysis began t indicate that the TSS and TP cncentratins were higher at the Schaper Pnd utlet than the Highway 55 inlet, Barr scheduled a lngitudinal mnitring event t evaluate where the cnstituent cncentratins might becme elevated within the pnd system. Figure 1 shws the fur sampling lcatins in the pnd that were used fr the lngitudinal mnitring event and Table 2 shws the results f the analyses. The sampling ccurred n Nvember 17 th, during lw flw (less than 2 cfs). The sample results shwn in Table 2 cnfirm that phsphrus and chlrphyll becme elevated as the flw mves frm the Highway 55 inlet thrugh the pnd t the Schaper utlet. P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx
T: Bassett Creek Watershed Management Cmmissin Page: 8 Table 2 Lngitudinal Water Quality Mnitring Results Pnd Lcatin TP (µg/l) Chlrphyll-a (µg/l) Suth 28 4.3 Center -- 1 -- Nrthwest 40 -- Nrtheast 35 9.2 1 nt reprted due t disturbance f bttm sediment during sampling. 2.2 Ptential factrs limiting treatment effectiveness As a result f preliminary discussins with Glden Valley and watershed staff it was determined that there are several ptential factrs that culd have limited the 2017 treatment effectiveness f Schaper Pnd with the flating barrier in-place: Start-up cnditins the 2017 mnitring began apprximately tw mnths after the final flating barrier anchrs had been replaced. The 2017 mnitring results may have captured cnditins in which the typical flw patterns thrugh the pnd were adjusting t a new equilibrium fllwing the final implementatin f the barrier. High water the flating barrier design ensures that there will be enugh f the curtain t divert the flw in the intended directin at pnd inundatin levels that crrespnd with flws up t 25 cfs. There were five days during 2017 where the flw exceeded 25 cfs, resulting in inundatin levels that wuld have raised the curtain ff the bttm f the pnd. Figure 2 indicates that the high flw (apprximately 90 cfs) event may have resulted in resuspensin f finer particulates, which culd have ccurred when the bttm f the curtain was abve the bttm f the pnd. This wuld have temprarily allwed fr shrt-circuiting f the flw, similar t the flw pattern that wuld have existed befre the barrier was installed. Carp several bservers have nticed the presence f carp during field visits t Schaper Pnd in the past. Anecdtally, field bservatins have usually mentined the nrthwest crner f the pnd as the primary lcatin where carp were seen. It is plausible that if a significant carp ppulatin is present, and is mre ften cncentrated in the nrthwest crner f the pnd, then the flw patterns established after implementatin f the flating barrier wuld be mre likely t resuspend the slids (and assciated phsphrus) that are typically stirred up by carp. The flw patterns thrugh the pnd in 2011 had a lwer likelihd f resuspending sediment frm the nrthwest crner f the pnd. Watershed cnstructin city staff nted that Duglas Drive was under cnstructin during 2017, which may have cntributed t the elevated TSS cncentratins bserved at the railrad inlet. Because the flw frm the railrad inlet enters the pnd dwnstream frm the flating barrier, this surce f flw may nt have received the same level f treatment that wuld have ccurred in 2011. P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx
T: Bassett Creek Watershed Management Cmmissin Page: 9 Water quality changes t the Highway 55 inflw city staff nted that several upstream water quality imprvement prjects were recently implemented, which culd explain why the primary surce f inflw t Schaper Pnd is nt as treatable as it was in 2011. Changes t bathymetry during the lngitudinal water quality mnitring event, it was nted that the center f the pnd was apprximately 1 t 1.5 feet deep, which is between 0.5 and 1 ft shallwer than indicated in the previus bathymetric map. An updated bathymetric survey wuld be used t determine whether there is adequate vlume fr sediment accumulatin in the pnd and/r whether there are areas f the pnd that are subject t sediment scur r resuspensin. 3.0 Recmmendatins fr 2018 The 2017 mnitring indicated that there were unexpected factrs cntributing t the results which had nt previusly been assessed (carp) r might require updated infrmatin (such as the bathymetry). In additin, the single lngitudinal mnitring event appeared t prvide a better understanding abut where within the pnd system the treatment effectiveness is being cmprmised. Cnsequently, it is recmmended that during the remainder f 2018, the BCWMC cllectively mnitr the gaps in the available data and distinguish the surce(s) r factrs that are limiting the treatment capacity f the pnd. We recmmend perfrming lngitudinal water quality mnitring during 2018, alng with surveys f the carp and bathymetry. 3.1 Water quality mnitring Our recmmended lngitudinal water quality mnitring includes cllecting grab samples at the fur lcatins shwn in Figure 1, twice per seasn, under lw flw and strm flw cnditins. Our preliminary estimate f the lngitudinal water quality mnitring csts is $10,000, based n six sampling events. 3.2 Carp and bathymetric surveys We recmmend cnducting a single bathymetric survey this summer and cmparing the survey results t the pre-cnstructin survey frm 2011. We als recmmend cnducting a carp survey, which wuld invlve perfrming individual electrfishing surveys seasnally thrughut the pnd. The carp survey results wuld include a reprt n the ppulatin estimates f carp during 2018. A preliminary estimate f the carp survey csts is $3,000, and the bathymetric survey is estimated t cst $3,000. 3.3 Reprting n 2018 mnitring We wuld cmpile the results f the 2018 mnitring and cmpare them with past mnitring data in a technical memrandum, which wuld include cnclusins and recmmendatins fr imprving water quality treatment in Schaper Pnd/next steps. Our estimated cst t reprt n the results f the 2018 mnitring is $5,000. P:\Mpls\23 MN\27\2327051\WrkFiles\Water Quality Mnitring\2017 Schaper Pnd Mnitring\Mem\Item 5B Schaper Pnd Mnitring Mem_05102018.dcx