Soil and Ground Water Assessments Performed During Site Investigations Guidance Document 4-01

Transcription

1 Sil and Grund Water Assessments Perfrmed During Site Investigatins Guidance Dcument 4-01 Petrleum Remediatin Prgram This guidance dcument describes the prcedures and techniques t be used when perfrming sil and grund water assessments. Vapr intrusin assessments, which are als a necessary part f the site investigatin prcess, are discussed in Guidance Dcument 4-01a Vapr Intrusin Assessments Perfrmed During Site Investigatins. As discussed in Guidance Dcument 1-01 Petrleum Remediatin Prgram General Plicy, the tw types f site investigatins used t evaluate petrleum cntaminatin are Limited Site Investigatins (LSIs) and Remedial Investigatins (RIs). The bjective f an LSI is t quickly evaluate the level f risk assciated with a petrleum release site and identify thse lw risk sites where further investigatin r remedial actins are nt necessary. The LSI prvides a snapsht f site cnditins. Infrmatin cllected during the LSI helps determine whether mnitring wells (RI) will be necessary. An RI measures grund water cntaminant cncentratins ver time t establish plume stability relative t ptential receptrs. Permanent mnitring wells are necessary fr an RI. The Minnesta Pllutin Cntrl Agency (MPCA) encurages cmpleting the ptential water well, surface water, and vapr receptr surveys (Guidance Dcument 4-02 Ptential Receptr Surveys and Risk Evaluatin Prcedures at Petrleum Release Sites) prir t investigatin activities. Cnsider the lcatins f ptential receptrs and the pssible expsure pathways t thse receptrs when planning investigatin activities. Risks are evaluated by measuring the extent and magnitude f cntaminatin, assessing likely expsure pathways, and determining whether the cntaminatin has r will reach receptrs befre naturally attenuating. I. Sil Cntaminatin Assessment Fr bth LSIs and RIs, the sil investigatin defines site gelgy and the vertical and hrizntal extent and magnitude f sil cntaminatin. The cmpnents f a sil investigatin include the fllwing: A. Drilling Methds Preferred drilling methds include hllw-stem auger and snic drilling, r, fr LSIs where cnditins are apprpriate, push prbes. D nt use slid-stem flight augers fr sil brings unless apprved by the MPCA prject hydrlgist. Perfrm cntinuus sil sampling unless MPCA staff apprve an alternative apprach. Fr all brings, fllw the prcedures listed belw: Cmpletely clean all dwn-hle equipment and tls prir t each use t avid crss-cntaminatin. Cleaning methds include pwer spray wash, brushing with apprpriate cleaning slutin, and clean water rinse. Bre hles that are nt cmpleted as mnitring wells shuld be sealed in accrdance with the Minnesta Department f Health (MDH) well cde (Minn. R. ch. 4725). Cmplete a drilling lg fr every sil bring advanced. When mnitring wells are cmpleted in a bring, prvide well cnstructin diagrams as described in sectin II.B, belw. At a minimum, infrmatin in the lgs shuld include: 1. Depth t start and finish f each sil sample interval attempted (feet). 2. Recvery fr each sil sample interval attempted (feet). 3. Sil classificatin in accrdance with the 1952 Unified Sil Classificatin System (USCS) r with American Sciety fr Testing Materials (ASTM) methds D2487 r D Further descriptin f sil (grain size, srting, clr, gelgic rigin, etc.) 5. Depth f significant changes in material (feet). c-prp4-01 September 2008 Minnesta Pllutin Cntrl Agency 520 Lafayette Rd. N., St. Paul, MN TTY r Available in alternative frmats

2 6. Apprximate psitin f the water table (feet); include date and time f measurement. 7. Organic vapr measurements (ppm). 8. Cmments regarding significant gelgic and hydrgelgic features, visual, r lfactry evidence f cntaminatin, etc. 9. Depth t tp and bttm f pen hle r expsed screen if cllecting water samples frm an pen bring r temprary well. 10. Date and time bring started and cmpleted. 11. Name f driller and cnsultant, as well as thers present during drilling. 12. Drilling methd. 13. Bring identificatin number. 14. Penetratin test recrds, if applicable. 15. Grund surface elevatin (feet, relative t identified datum). T establish grund surface elevatin, survey all bring lcatins. B. Drilling Lcatins Magnitude f sil cntaminatin and surce identificatin: Advance a sil bring in r immediately adjacent t any ptential cntaminatin surce areas (e.g., undergrund strage tank basins, abvegrund tank areas, prduct transfer area, lines, pump islands, remte fill pipes, knwn spill areas, and areas with visible surface staining). Hrizntal definitin: Drill a number f sil brings sufficient t define the hrizntal extent f sil cntaminatin, keeping in mind that the mst extensive sil cntaminatin may nt be near the grund surface. The number f brings will vary depending n site cnditins, extent f cntaminatin, and the lcatins f ptential receptrs. Hrizntal definitin can be cnsidered defined if there is n visual evidence f cntaminatin, there are n petrleum drs, and phtinizatin detectr (PID) readings are less than 10 ppm. Vertical definitin: Drill sil brings t 5 feet belw the water table r, if cntaminatin extends belw the water table, t 10 feet belw the deepest measurable cntaminatin, whichever is deeper. If the water table is very deep and yu have drilled 10 feet belw the deepest measurable cntaminatin in the unsaturated zne, discntinue drilling. Vertical definitin can be cnsidered defined if there is n visual evidence f cntaminatin, there are n petrleum drs, and PID readings are less than 10 ppm. If bedrck is encuntered, cntact the MPCA staff t discuss whether bedrck mnitring wells are necessary. Vertical definitin examples: If cntaminatin extends t 10 feet and the water table is at 20 feet, advance the bring t 25 feet. If cntaminatin extends t 20 feet and the water table is at 15 feet, advance the bring t 30 feet. If cntaminatin extends t 20 feet and the bring has been advanced t 30 feet withut encuntering the water table, then end the bring at 30 feet. Site stratigraphy: T evaluate site stratigraphy, cmplete at least ne sil bring t 20 feet belw the deepest site cntaminatin. If the water table is encuntered, at least ne bring a minimum f 20 feet belw the water table is necessary. If the water table is very deep and yu have drilled 20 belw the deepest sit cntaminatin in the unsaturated zne, call the MPCA staff fr apprval t discntinue drilling deeper. Lcate the sil bring near the suspected release pint but nt within a free prduct area. If there is a risk f crss-cntaminatin by piercing a cnfining unit, cmplete the bring in an uncntaminated area. If additinal site stratigraphy data are available, the MPCA staff may waive this requirement with prir apprval. Sil and Grund Water Assessments Perfrmed During Site Investigatins c-prp4-01 September 2008 Page 2 f 6

3 Site stratigraphy examples: If cntaminatin extends t 10 feet and the water table is at 20 feet, advance the bring t 40 feet. If cntaminatin extends t 25 feet and the water table is at 20 feet, advance the bring t 45 feet. If cntaminatin extends t 20 feet and the bring has been advanced t 40 feet withut encuntering the water table, then call the MPCA staff fr apprval t discntinue drilling deeper. Cntaminated surface sil: See Guidance Dcument 3-01 Excavatin f Petrleum Cntaminated Sil and Tank Remval Sampling fr requirements pertaining t cntaminated surface sil identificatin, delineatin, and excavatin. Utility backfill investigatin: In situatins where it appears likely that undergrund utilities (sanitary and strm sewer lines, water mains, etc.) intercept either the impacted sil r cntaminated grund water, advance hand-driven r hand-augured sil brings in the utility backfill t investigate the ptential fr preferential migratin f free prduct and cntaminated grund water alng these cnduits. This infrmatin is especially imprtant when sediments f lw permeability (e.g., clay) ccur near the surface. C. Sil Sampling Stratigraphy: Recrd gelgic descriptins fr all sil samples cllected and nte changing drilling cnditins that prvide relevant gelgic and stratigraphic infrmatin. Be sure t nte the presence and thickness f sand and gravel lenses within less permeable sils. Grain size sampling: Cllect sediment samples fr grain size analysis at all sites whether grund water is encuntered. Grain size analysis is required fr the purpses f verifying field classificatin f sils and estimating hydraulic cnductivity. Analyze samples using ASTM D422 Standard Test Methd f Particle-Size Analysis f Sils, ASTM Internatinal, West Cnshhcken, PA, Cllect and analyze a minimum f three (3) sil samples frm different lcatins/hrizns. In saturated cnditins, cllect the samples frm hrizns that appear t have high permeability. If a wide range f aquifer materials is present, cllect samples frm areas f apparent primary grund water flw. Recrd the depth f cllected samples n the bring lgs. Organic vapr sampling: Cllect and evaluate sil samples fr rganic vaprs at least every 5 feet in uncntaminated hrizns, at changes in material, and at least every 2.5 feet in cntaminated hrizns. Screen in accrdance with Part I f Guidance Dcument 4-04 Sil Sample Cllectin and Analysis Prcedures. Recrd the depth f cllected samples and the rganic vapr readings n the bring lgs. Labratry analysis sampling: Cllect sil samples fr analysis at the zne f maximum rganic vapr cncentratin and the water table interface r, if grund water is nt encuntered, at the terminus f the bring, unless MPCA staff apprve ther sampling guidelines. If sil cntaminatin extends belw the water table, cntinue t cllect sil samples in the saturated zne that exhibit the highest field instrument reading. If the entire bring appears uncntaminated based n field screening, cllect nly ne sil sample at the water table interface r at the terminus f the bring. Recrd the depth f cllected samples n the bring lgs. Refer t Guidance Dcument 4-04 Sil Sample Cllectin and Analysis Prcedures. Water levels: Measure water depth in all brings and cmpute grund water elevatins. Recrd the time at which water depth measurements are made. Inspect sils fr evidence f a fluctuating water table and a seasnal high water table (i.e., mttling). If sil brings in silt r clay appear unsaturated, recrd n the bring lg the amunt f time the bring was left pen fr water level measurement. Brings may be left pen up t 72 hurs t facilitate accurate water level measurements and cllectin f grund water samples. Free prduct: If free prduct is fund during bring advancement, ntify the State Duty Officer ( r ) within 24 hurs and immediately begin free prduct recvery effrts. Install permanent mnitring wells as sn as pssible t define the free prduct plume. If there are questins abut whether t cnvert a bring t a mnitring well when free prduct is discvered r appears likely t be present, cntact MPCA staff t discuss. Refer t Guidance Dcument 2-02 Free Prduct: Evaluatin and Recvery. Petrleum saturated sil: Use the petrleum sheen test described in Guidance Dcument 4-04 Sil Sample Cllectin and Analysis Prcedures t determine if sil is petrleum saturated. Sil and Grund Water Assessments Perfrmed During Site Investigatins c-prp4-01 September 2008 Page 3 f 6

4 II. Grund Water Cntaminatin Assessment A. Limited Site Investigatins At sites where cntaminated sil is in cntact with grund water, r grund water cntaminatin appears likely, a grund water cntaminatin assessment is necessary as part f the LSI. The bjectives f the assessment are t determine whether grund water is, r likely t be, impacted with petrleum cntaminatin and whether the impacted hydrgelgic unit is cnsidered an aquifer. LSI grund water assessments accmplish the fllwing: Cllect grund water samples frm temprary mnitring wells (e.g., push prbes, hllw-stem augers, etc.) taking nte f the vertical interval sampled. Prvide well cnstructin diagrams (see belw) fr each temprary mnitring well; Cllect grund water samples frm the wrst case temprary mnitring well and a sufficient number f ther pints t dcument cntaminant cncentratins hrizntally and, if necessary, vertically; Analyze fr the apprpriate parameters (see Guidance Dcument 4-05 Grund Water Sample Cllectin and Analysis Prcedures); and Determine whether the hydrgelgic unit is an aquifer based n stratigraphy and permeability measurements (generally frm grain size distributin). The stratigraphic data gives the cntext within which the permeability estimate can be assessed. Fr the purpse f the Petrleum Remediatin Prgram, a hydrgelgic unit is an aquifer if: The hydrgelgic unit supprts a sustained yield f at least 5 gallns per minute. Because sustained yield is usually an incnvenient measurement (e.g., if n supply well is available fr testing), fr the purpse f the Petrleum Remediatin Prgram, hydrgelgic units with a transmissivity f greater than 50 ft 2 /day are cnsidered aquifers. The sediments at the site are primarily sand r gravel. The frmatin (even ne with lw permeability) prduces water t a supply well r spring. An RI is necessary if the LSI determines that: An aquifer has been (r is likely t be) cntaminated by petrleum cmpunds at cncentratins abve drinking water standards r abve 1 mg/l gasline range rganics (GRO) r diesel range rganics (DRO); Sil cntaminatin is likely t leach t grund water; Surface water has been (r is likely t be) cntaminated by petrleum cmpunds at cncentratins abve applicable surface water standards r abve 1 mg/l GRO r DRO; Free prduct is encuntered; r The plume des nt behave accrding t the cnceptual mdel (Guidance Dcument 1-01). An RI may be necessary if certain ther site-specific cnditins are present. Sil and Grund Water Assessments Perfrmed During Site Investigatins c-prp4-01 September 2008 Page 4 f 6

5 B. Remedial Investigatins Remedial Investigatins (RIs) measure grund water cntaminant cncentratins ver time t determine whether a plume is stable using mnitring wells. The fllwing text explains the placement, cmpletin, and evaluatin f data frm mnitring wells. Mnitring well placement Wrst-case mnitring wells: Place mnitring wells within r clse t any likely surce areas (e.g., undergrund strage tank basins, abvegrund strage tank areas, prduct transfer areas, buried lines, pump islands, remte fill pipes, and knwn spill areas). Install mnitring wells t define free prduct (if present). Lateral and dwngradient mnitring wells: Place mnitring wells t define plume width and length. Place mnitring wells in an arrangement that defines the dwngradient extent f the grund water cntaminant plume (any cntaminatin exceeding MDH Health Risk Limits - HRLs). Deep wells - vertical definitin f grund water cntaminatin: A deep mnitring well may be necessary if sil brings shw that petrleum cntaminatin ccurs at a depth greater than 5 feet belw the water table r an evaluatin f the hydrgelgic data indicate that dwnward cntaminant migratin is likely. In sme cases deep mnitring wells are necessary t determine if deeper aquifers are impacted r threatened by petrleum cntaminatin. If s, a netwrk f deep mnitring wells may be necessary t determine the three-dimensinal extent f the plume and calculate flw directin. Review the gelgic data frm well lgs btained during the water well receptr survey, and install deep mnitring wells if water supply aquifers are impacted r threatened. Befre installing a deep mnitring well, cntact the MPCA prject hydrgelgist. Be prepared t discuss site stratigraphy and ptential receptrs during this call. Legal access fr ff-site mnitring wells: Legal access fr ff-site mnitring well lcatins may prve difficult in sme lcatins. If legal access is nt btained after tw written attempts, cntact the MPCA prject manager fr assistance. Screen placement Install water table mnitring wells s the water table intersects the screen. Dcument and justify any exceptins in the RI reprt. Deep mnitring well screens d nt intersect the water table. Screen placement depends n the purpse f the well. If the well is installed t measure vertical gradient, the tp f the screen shuld be at least twenty feet belw the water table (but within the same aquifer). If the well is installed t mnitr water quality in a deeper aquifer, place the screen entirely within that aquifer. During mnitring well cnstructin at sites where gelgic cnditins make it difficult t determine the actual depth t water: Allw the brehle t remain pen at least 24 hurs prir t mnitring well cmpletin t allw water level stabilizatin. Cnsider using a slightly lnger well screen (15-20 feet) t cmpensate fr water table fluctuatins. Phased well installatin may be apprpriate. This allws fr determinatin f the apprximate water table depth in ne r tw wells, and then the remaining wells can be installed with prper screen placement. Sil and Grund Water Assessments Perfrmed During Site Investigatins c-prp4-01 September 2008 Page 5 f 6

6 Mnitring well cnstructin Cnstruct mnitring wells in accrdance with the MDH water well cnstructin cde. Prperly clean all mnitring well materials prir t installatin. In general, avid the use f liquid drilling fluids. Hwever, they may be apprved by the MPCA n a sitespecific basis. Prperly develp all wells t ensure adequate hydraulic cnnectin with the aquifer and t remve any drilling fluid if used. Dcument the develpment prcedures and results. Cmplete mnitring well cnstructin diagrams fr every mnitring well cnstructed. The minimum infrmatin required includes, but is nt limited t: 1. Diagram f majr well features (bre hle annulus, tp and bttm f screen, casing/riser, tp and bttm f sand pack, tp and bttm f pack seal, grut, surface seal, prtective casing, etc.) 2. Depth frm grund surface t all majr well features including tp f casing (feet). 3. Well screen slt size (inches). 4. Sand pack size (inches). 5. Inner diameters f riser casing, screen, prtective casing, and brehle (inches). 6. Well develpment infrmatin (date, start/end times, methds used, gallns pumped, turbidity, recharge, etc.) 7. Well cnstructin materials. 8. Unique well number and prject identificatin number. 9. Date well begun and cmpleted. 10. Driller and cnsultant names. 11. Elevatin f grund surface and measurement pint, i.e., tp f riser casing (feet, relative t identified datum). Sampling frequency Submit Guidance Dcument 4-06 Investigatin Reprt Frm after tw quarters f grund water sampling. Cntinue quarterly sampling frm all mnitring wells until site clsure r the MPCA prject hydrlgist apprves a new sampling schedule. Web pages and phne numbers: MPCA staff: MPCA phne: r Petrleum Remediatin Prgram Web page: MPCA Inf. Request: MPCA VIC prgram: MPCA Petrleum Brwnfields Prgram: MPCA SRS Guidance Dcuments: MDH HRLs: MDH DW Htline: Petrfund Web page: Petrfund phne: r State Duty Officer: r Sil and Grund Water Assessments Perfrmed During Site Investigatins c-prp4-01 September 2008 Page 6 f 6