MHvdraulics ResearcttWal}nqford

SIJ'IIGB DISPIOSAL IT LIVIBDOOL BAI

Trrelftb bed tonltorlng surecy

Ibccnher 1984 - Uarch 1985

P R K l f f B S c

Report No. SR 71January 1986

Registered Office: Hydraulics Research Limited,Wallingford, Oxfordshire OXl0 8BA.Telephone: O49l 35381. Telex: 848552

(C) Crown Copyright 1986

Publlshed by permisslon of the Controller ofI ler Majestyrs Stat ionery Off ice.

Thls report descrLbes work funded by theDepartnent of the Envl.ronment under ResearchContract PECD 7l7l lsL. I t was carr ied outunder the management of Mr M F C Thorn byMr P R Kiff of the Technical ServlcesDepartnent of Hydraul-ics Research Ltd,I,Ialllngford. The report is published onbehaLf of the Department of the Envlronment.

ABSTRACf

This report describes the twelfth survey carrLedout Ln December 1984 and March 1985 contlnuLng thelong tern monitorLng of the bed sediuents ofLiverpool Bay. The obJectlve of the progrannne Lsto determl.ne whether any changes are oceurringin the surface sedlment characterlstl.cs ae aconsequence of changes ln the rate of sewage sludged isposa l s ince L972.

comlxs

INTRODUCTION

MUD CONTENTS

ORGAI{IC MATTER

HEAVY METALS

VERTICAL DISTRIBUTIONS

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

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FIGI'BBS

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t0

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t2

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Monitor ing poslt lons

Mud content of the top 25nn of bed

Organlc matter content of mud from the top 25um of bed

Mercury concentratlon ln mud from the top 25m of bed

Zinc concentration in nud from the top 25m of bed

Lead concentratl.on in mud fron the top 25nn of bed

Nickel concentratlon ln mud from the top 25om of bed

Copper concentration in mud from the top 25m of bed

Chromium concentration ln mud from the top 25nn of bed

Total organics in nud fron the top 25nn of bed

Total mercury in mud fron the top 25nn of bed

Total zinc in nud fron the top 25nur of bed

TotaL lead in nud from the top 25nn of bed

Total nickel in nud fron the top 25m of bed

Total copper ln nud fron the top 25nn of bed

Total- chromium ln nud fron the top 25nrn of bed

Depth prof iLes of the 125nn diameter cores

Depth prof i les of the 50m dianeter cores

IITTRODUCII.OI|The DOE progranrne of monl.torlng bed sedlments inLiverpool Bay for posslble effects of sewage eludgedlsposaL wae lnLtlated ln 1973 followlng publl.ca-t lon of "Out of Sight, Out of MLnd" (Ref. l ) . ThedesirabLlity of maintaining thls check on bed con-dLtions was reaffirned in 1978 by the DOE/IWC Sub-Connit,tee on the Disposal of SLudge to Sea (Ref.3)and sLnce then, sLx bed surveys have been carrLedout (Refs 4-8) by llydrauLics Research (IfR).

The last, the subJect of thls report was started lnDecember 1984 and flnally completed ln March 1985,weather condlt ions necessttat ing a second visLt.The naJor part of the progrannme ltas undertaken onthe second trip from the Unlverslty ColLege ofNorth tlales survey vessel "Prlnce Madog". Dr SRowlatt of the IIAFF Burnham Laboratory Joined HRstaff on the sanpling survey whlch was the twelfthin the overal . l - ser ies.

Sanples were taken at sixty positl.ons lncludLngtwenty of the tlrenty-four standard sltes vLsited onall occaslons slnce 1973. The remalning four couldnot be sanpled because of deterioratlng weatherconditLons. 125rnn dlameter cores were taken at 16sites, these bel.ng up to 300um in length. 50nndiameter cores were taken ln addltion at 13 sites.These smaller diameter cores ltere up to 800mn lnlength and designed to seek the undisturbed basalstrata so that basel ine metal concentrat ions couldbe established. PrevLous endeavours to explore thedepth of netal penetratlon ltere confined to theeaatern haLf of the survey area (Ref 9). Grabsampl-es were taken at 45 sites. The overalldistrlbutlon of sampLing posltions is sholtn in Fig1 .

The top 25mn of each grab sample was removed with aflat scoop and brought back for analysis. The125mn cores were extracted on board and split Lnto0 - 25mm, 25 - L00mn and 100mm - bottom fractionsunless distinct layerlng was visibl-e when the coreswhere spi l t at the layer boundaries. In one casetthe core was too l-oosely compacted to extract wholeand a conposite sample fron the totaL was taken.The 50mn cores nere returned to the laboratoryintact, removed fron their liners by compressed airand cut lnto 5 or L0 cm sectlons. A11 sanples lteres tored a t -20"C pr lo r to ana lys is .

In the laboratory, the samples were split lnto sandand mud fractl-ons by wet sieving at 63 p n. Thesand fractlon was not graded further and only thepercentage mud by weight was recorded. The nudfraction was alr dried followed by storage ln avacuum deslccator before sub-sampllng for organiccarbon and heavy metal determinations.

Organic carbon determinationg were made by thestandard lret oxidatlon method used previously (theorganic carbon is reported as organic matter, afactor of. 2.5 belng used as in the past to convertcarbon to the equlvalent of dried organlcres idues ) .

Standard reference samples (NBS 1645) were includedwlth the samples subnitted to the commercial analy-tical laboratory for heavy metal determinations byatomic absorption spectrophotonetry as ln theprevLous two surveys. Correctlons ltere made to theresults where necessary to brlng them within the *102 error previously

""t"Ultshed for these analysEs

(Ref 7). These correct ions ensure that the resultsof the current survey are as comparabl-e as possibleto t,hose of the prevlous four surveys for which thedata ls incl-uded Ln this report .

Data from the seventh survey (1978/9) lncluded inthe last report (Ref 8) have been onit ted from thisreport part ly because of lack of space but alsobecause of the llnited coverage of the seventhsurvey (30 si te samples analysed compared with 40'50 , 63 , 54 and 60 in Surveys 8 to 12 respec t ive ly ) .The l-ast three years have reached probably theoptimum number of sanpling positions' more thandoubl ing the number or lginal ly vis i ted.Comparlsons with past results must be tempered withconsideration of the number and position of thesi tes vis i ted and the var lat ion between surveys.Each survey tends to show up speclal polnts oflnterest whlch nay be substant iated or discarded inthe light of results from the next survey and souesanpl ing posit ions are selected so as toinvestLgate further any peaks or anomalles in thecur ren t se t o f resu l ts .

}IUD COf,TEtrTSThe nud content of each of the 60 sanpllng posl-tions Ls shown tn Fig 2. Where 125nn and grabsanples have been taken at the same site, theaverage of thelr mud contents has been taken. Mudcontents of the top 25nn fron the 50mm cores havenot been lncLuded ln the averages because lt hasnot been establ lshed with this snal ler v ibro-corer,that the surface is completely undisturbed (Ref 2).The nud content fron the 5Omn core has beenlncluded for T14 however, because this was the onlysampJ-e taken at thl.s position.

The nud dlstribution is substantially the same asin the past four surveys wlth the exception of amud pocket at Gl l never before encountered. Thisalmost certainly ls another randon rogue resultderived fron the linited accuracy of positl.onf indlng between each survey.

ONGAXIC UIrlEBThe distrlbution of organlc matter in the mudfraction is shown in Ftg 3. Two sanples had toolittle mud to aLlow for organic carbon and heavymetal analyses so the organic analysis was omitted'The average concentration ls a little Lower thanlast year but sinil-er to that of L98Ll2 and 198213'The last survey (L98415) contained three sampleswith significant amounta of coal which tended toraise the average value above those of previoussurveys (mean 5 .3r , 5 , .8 r 6 .4 , 5 -4% o tgan ic mat te rf ron 198112 to 1984/5) . The peak a t M9, cLose tothe apex of the dunplng ground ls sinllar to thatot L98I l2 and the low values at T10 and T11 areslmi l-ar to those of 1980/1.

The "total" organic content (Fig 10) calculatedfrom the product of the mud and organic matterpercentage abundances ie slmllar to that of theprevlous four years and sho!f,s no evLdenie of anyincrease. I ts distr lbut ion is sinl lar to that ofthe nud (fig 2) because the variation in mudeontent is conslderably larger than the variationln organic oat€t. (Relat ive standard deviat ion2OL7" agalrnst 257"). The Mersey area agaLn shows thegreatest accumulatlon of organic matter and theonLy slgnificant dlfference ls the higher value atGl l due to the except ional ly htgh mud result f romthat s i te .

EEAYY I{Bf,ALSThe heavy netal concentrations have been illustra-ted as ln prevlous reports. Flgs 4 - 9 show theconcentratlon of the metals in the mud fractl.on ofthe sedinent expressed ln mlcrograms metal per gramof nud. Flgs 11 - 16 show the "total-" metalsexpressed as the product of the netal concentra-tlon, the nud percentage, and a factor based on thenean dry bulk denslty of a nunber of cores. Thls"total" netal concentrat lon Ls expressed as ki lo-grams (nercury only) or tonnes of metal ln the top25nn per sguare kilonetre of bed. If it is assumedthat the metal content of the fine sedinent (< 63 pn) is nal.nLy derived from adsorptlon of metals fromsoLut ion, then this " total-" metal f igure representsthe input to the area fron man-nade sourcestogether wlth any natural sources that producesoluble metals.

The peak concentratlons of lead, nLckel, copper andchromlum recorded near the sludge dunplng groirnd onthe eleventh survey are not no\il apparent but a peakln the same metals has appeared at Q9, further tothe east (Ftgs 6-9). The character ist ic noted fronearlier surveys of metal peaks correspondlng withsediments having l-ess than one per cent nud isagain exernpllfled by the Q9 sampLe.

The htgh lead concentratLons found to the west ofthe dunping ground on the previous survey havedecreased sl-lghtly and the overall mean concentra-tion of lead is down to the pre 1982 figure (means349, 459, 266 yg /g fo t 1 ,982/3 , 1983/4 and 1984/5) .The reason for this r ise and faI1 is not c learother than as part of the generaL variation due toseasonal changes.

Mercury values have always been conslderably morevariable than the other metals; on the presentsurvey, RSD 2507. as against 2O-9O7". The three lowmercury concentrat ions to the south of the Merseyoutflow associated wtth low mud and low organiccontents contrast with the above average values ofmost of the other metals.

Overal l , mercury, z inc, copper and lead are lowerthan last year whereas the nickel and chromlum aresl ight ly higher in concentrat ion. Thls increase innickel and chromlun ls the fourth successiveincrease. The mean nLckel concentrat ion havingrisen fron 43 to 66 pg/g fron the 1981/2 survey

and chromiun having rLsen from 29 to 85 p g/g overthe same period. These flgures are surPrlslngtespecially as nl.ckel has been taken in the Past asof nal.nLy natural- origin and its variatlons havebeen smal l . NevertheLess, l ts dlstr lbut ion isstil-l fairly even over the area cornpared withchromium which is showing a noticeable lncreasearound the Mersey outfaLl al though the "total"

chromium is not so obvlously high. Callbratlonstandards for the two metals are sl lght ly noreerratic than for copper, zlnc and l-ead and chromiumextract ion ls subJect to above average errors (Ref5) but the correctl.ons necessary to compensate forapparent variations in the concentration of thestandard sedlments have never exceeded 207" in anyone yeai and general ly are less than 10%.

"Total" metals are also down, ltith the number ofpeak results reduced. The except lon is the peak atGll based on the high nud value prevlously noted.The buLk of the metals are found in the muddy areanort ,h of Newcone Knol l (U19, YY3, YY4) as on al lprevious surveys. Of the fLve elevated concentra-t lons of copper noted ln the last reportr only oneremains and that ls adjolning the new dredgingspoi l ground. The distr ibut ion of " total" metalsover the area is very sinil-ar, and as pointed outln prevlous reports, is pr inar i ly a funct lon of theabundance of nud in the bed sedinent.

5 VEffiTC,IL DISIAIBIITION

The two sets of cores (125m and 5onn dlaneter)were split Lnto sections and analysed Ln a sLnl.larmanner to the surface sedl.ments. The mud suspendedin the water trapped above the 125nn eore was alsoanal-ysed and the results lncorporated Lnto the toP25nn totaLs. No mud was suspended above the 50nncores because, as they were returned to the labora-tory for analysls, the nud had sett led again intothe bed surface. The results are shown in Figs 17and 18 respect ively.

ResuLts from the shorter 125nn core show littl-eevidence of any basal- strata having been reached.If mercury ls taken as the chlef pollutant metalnot present to a significant extent naturally thenthe basal uncontaminated sediments may have beenreached at. C7 below about 100m. The drop in netalcontent below 25nm at L9 is more likely to becaused by a disturbed core due to the di f f icul ty ofpenetrating the gravel bed to the south of thesLudge dunplng ground. Other than that, a certainenrl.chnent of the innediate sub--surface layer eanbe seen at aeveral s i tes but no signi f icant trendtowards metals increasing or decreasing with depthdown to the 2OO-300 nn level can be seen.

Conpared to the last survey, when cores were takenat a few of the same si tes, the basal strata at Ql lis substant ialLy the sane (150 v 100nn) but al lother comparl.son cores did not reach any constantlow metal concentrat ions.

The results from the longer cores suggest that thedepth of penetrat ion of anthropogenic netals islargeLy conf ined to 150nn at Ql l and SLl- , to 400mmat L10, N l l and P11, whereas the more eas tern s i tesnear the Mersey feature a greater depth of penetra-t ion, at least beyond 500mn (T14, U9, YY2, 3 and4 ) .

These varlat ions between west and east of thesurvey area are general ly consistent wlth thef indings of the only other "deep" corLng, that ofFebruary 1983 (Ref 9). However the vert ical dis-tr ibut lons and relat ive metal concentrat ionsobserved on the tno surveys at any one site havelittle in common. It ls apparent that the numberof cores is st l1l too low and the randomness of theaetal contents of indivldual strata too great forany detai led coherence in patterns to emerge.

6 coilcl.usIoNsThe twelfth survey repeated the close sanplingpattern f l rst adopted on the tenth survey.Comparison of the concentrations ln the nudfraction of the top 25nn suggest that organicmatter, lead, copper and zlnc have decreased,mercury is much the same and ntckel and chromiumhave increased. Lead concentratlona' mentioned inthe last survey as being exceptionaLly high west ofthe sludge dunping ground have come down sllghtlyas have most of the l-ead values.

When organic carbon and metal concentrations areconbined with nud abundance to yield the "total-"organic matter and "totaL" metal per unit area, theresult ls sl.niLar in nagnitude and distributlon toprevious years with the exception of the lsolatedpeak to the west produced by an exceptionally highmud concentrat l .on at Gl1.

It is recommended that on the next survey' the 2metre tlR vibro-corer should be enpl-oyed in anat,tempt to reach the basal uncontamlnated strata inthe nud area to the north of Newcombe Knoll.

7 ACKNOTII.EITGBIE{TS

Thanks are due to Mr J Blnks for executl.ng thesanpling programme and to Dr S Rowlatt of the I{AFFFlsheries Laboratory, Burnham-on-Crouch for hisassistance during the course of the f ie ldoperations. Thanks are also due to the captaln andcrew of the Unlversi ty Col lege of North Walessurvey veseel "Prince Madog".

8 BTTENMCES1. OUT OF SIGIIT, OUT OF MIND. Report of Worklng

Party on Sludge disposal ln Llverpool Bay,Vo l 1 and 2 , 1972.

2. OUT OF SIGIIT, OUT OF MIND. Report of l{orkLngParty on SJ-udge disposal in Liverpool Bay'Vol 4, L976.

3. DEPARTMENT OF THE ENVIRONMENT/NATIONAL T'IATERCOUNCIL STANDING TECIINICAL COMMITTEE. SewageSludge dlsposal ln Liverpool Bay, Researchin to e f fec ts 1975-L977. Repor t No.16 , Apr i lLg7g.

4. ITYDMULICS RESEARCIT STATION. Sludge dlsposalin LLverpooL Bay, Seventh bed monltoringsurvey, October L978 - April- 1979. ReportNo. DE 49, October L979.

5. HYDMULICS RESEARCII STATION. Sl-udge disposalln Llverpool Bay, Elghth bed nonlt,orLngsurvey, September 1980 - January 1981.Report No. DE 54, August 1981.

6. HYDMULICS RESEARCII STATION. Sludge disposalin Ll.verpool Bay, Ninth bed monitoringsurvey, November 1981 - January 1982. ReportNo. DE 58, Septenber I-982.

7. IIYDMULICS RESEARCH STATION. Sl-udge disposalin Liverpool Bay. Tenth bed monitoringaurvey, Septenber L982. Report No. DE 64,August 1983.

8. HYDMULICS RESEARCH. Sludge dlsposal lnLiverpool Bay. ELeventh bed monitoringsurvey, November 1983. Report SR9 January1 9 8 5 .

9. HYDRAULICS RESEARCIT. Vertical distributionsof heavy metals and organic carbon inLiverpool Bay (East). Report SR26 1985

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DD(B) 650449 1/86

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