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1 _ . indicator parameters monitored can include pH, redox introducing field contaminants into a sample bottle while Potential, conductivity, dissolved oxygen(DO)and turbidity. adding the preservatives. The last three parameters are often most sensitive. Pumping rate,drawdown,and the time or volume required to obtain The preservatives should be transferred from the stabilization of parameter readings can be used as a future chemical bottle to the sample container using a disposable guide to purge the well. Measurements should be taken polyethylene pipet and the disposable pipet should be used every three to five minutes if the above suggested rates are only once and then discarded. used. Stabilization is achieved after all parameters have stabilized for three successive readings. In lieu of measuring After a sample container has been filled with ground all five parameters,a minimum subset would include pH, water,a TeflonTm (or tinylined cap is screwed on tightly to conductivity, and turbidity or DO. Three successive readings prevent the container from leaking. A sample label is filled should be within t 0.1 for pH,t 3%for conductivity,t 10 my out as specified in the FSP. The samples should be stored for redox potential, and t 10%for turbidity and DO. Stabilized inverted at 4°C. purge indicator parameter trends are generally obvious and follow either an exponential or asymptotic change to stable Specific decontamination protocols for sampling values during purging. Dissolved oxygen and turbidity usually devices are dependent to some extent on the type of device require the longest time for stabilization. The above stabiliza- used and the type of contaminants encountered. Refer to the tion guidelines are provided for rough estimates based on site QAPP and FSP for specific requirements. experience. L Blanks H. Sampling,Sample Containers,Preservation and Decontamination The following blanks should be collected: Upon parameter stabilization, sampling can be (1)field blank:one field blank should be collected from initiated. If an in-line device is used to monitor water quality each source water(distilled/deionized water)used for parameters, it should be disconnected or bypassed during sampling equipment decontamination or for assisting sample collection.Sampling flow rate may remain at estab- well development procedures. fished purge rate or may be adjusted slightly to minimize aeration, bubble formation,turbulent filling of sample bottles, (2)equipment blank:one equipment blank should be or loss of volatiles due to extended residence time in tubing. taken prior to the commencement of field work,from Typically,flow rates less than 0.5 Umin are appropriate. The each set of sampling equipment to be used for that same device should be used for sampling as was used for day. Refer to site QAPP or FSP for specific require- purging. Sampling should occur in a progression from least to ments. most contaminated well,if this is known. Generally, volatile (e.g.,solvents and fuel constituents)and gas sensitive(e.g., (3)trip blank:a trip blank is required to accompany each Fe2',CH, H2SIHS,alkalinity)parameters should be sampled volatile sample shipment. These blanks are prepared ' first. The sequence in which samples for most inorganic in the laboratory by filling a 40-mL volatile organic parameters are collected is immaterial unless filtered (dis- analysis (VOA)bottle with distilled/dellonized water. solved)samples are desired. Filtering should be done last and in-line filters should be used as discussed above. During both well purging and sampling, proper protective clothing V. Low-Permeability Formations and Fractured and equipment must be used based upon the type and level Rock of contaminants present. The overall sampling program goals or sampling The appropriate sample container will be prepared in objectives will drive how the sampling points are located, advance of actual sample collection for the analytes of installed, and choice of sampling device. Likewise,site- interest and include sample preservative where necessary. specific hydrogeologic factors will affect these decisions. Water samples should be collected directly into this container Sites with very low permeability formations or fractures ' from the pump tubing. causing discrete flow channels may require a unique monitor- ing approach. Unlike water supply wells,wells installed for Immediately after a sample bottle has been filled, it ground-water quality assessment and restoration programs must be preserved as specified in the site(QAPP). Sample are often installed in low water-yielding settings(e.g., clays, preservation requirements are based on the analyses being silts). Alternative types of sampling points and sampling performed(use site QAPP, FSR, RCRA guidance document methods are often needed in these types of environments, [U.S. EPA, 1992] or EPA SW-846[U.S.EPA, 1982]). It because low-permeability settings may require extremely low- may be advisable to add preservatives to sample bottles in a flow purging (<0.1 Umin)and may be technology-limited. controlled setting prior to entering the field in order to reduce Where devices are not readily available to pump at such low the chances of improperly preserving sample bottles or flow rates,the primary consideration is to avoid dewatering of 8 1