PUBLIC HEALTH ASSESSMENT
BRANDYWINE DEFENSE REUTILIZATION AND MARKETING OFFICE
ANDREWS, PRINCE GEORGE'S COUNTY, MARYLAND
- Acute Exposure:
- Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.
- Adverse Health Effect:
- A change in body function or the structures of cells that can lead to disease or health problems.
- The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.
- A group of diseases that occur when cells in the body become abnormal and grow, or multiply, out of control
- Any substance shown to cause tumors or cancer in experimental studies.
- Chronic Exposure:
- A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.
- Completed Exposure Pathway:
- See Exposure Pathway.
- Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
- CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.
- A belief or worry that chemicals in the environment might cause harm to people.
- How much or the amount of a substance present in a certain amount of soil, water, air, or food.
- See Environmental Contaminant.
- Cancer Risk Evaluation Guide, a highly conservative value that would be expected to cause no more than one excess cancer in a million persons exposed over time.
- Dermal Contact:
- A chemical getting onto your skin. (see Route of Exposure).
- The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".
- The amount of time (days, months, years) that a person is exposed to a chemical.
- Environmental Media Evaluation Guide, a media-specific comparison value that is used to select contaminants of concern. Levels below the EMEG are not expected to cause adverse noncarcinogenic health effects.
- Environmental Contaminant:
- A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in background level, or what would be expected.
- Environmental Media:
- Usually refers to the air, water, and soil in which chemicals of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.
- US Environmental Protection Agency (EPA):
- The federal agency that develops and enforces environmental laws to protect the environment and the public's health.
- The study of the different factors that determine how often, in how many people, and in which people will disease occur.
- Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)
- Exposure Pathway:
- A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.
ATSDR defines an exposure pathway as having 5 parts:
- Source of Contamination,
- Environmental Media and Transport Mechanism,
- Point of Exposure,
- Route of Exposure, and
- Receptor Population.
When all five parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these five terms is defined in this Glossary.
- How often a person is exposed to a chemical over time: for example, every day, once a week, twice a month.
- Hazardous Waste:
- Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.
- Health Effect:
- ATSDR deals only with Adverse Health Effects (see definition in this Glossary).
- Indeterminate Public Health Hazard:
- The category is used in public health assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.
- Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).
- Breathing. It is a way a chemical can enter your body (See Route of Exposure).
- Maximum Contaminant Level, the enforceable drinking water regulation that is protective of public health over a lifetime at an exposure rate of 2 liters of water per day.
- Minimal Risk Level. An estimate of daily human exposure--by a specified route and length of time--to a dose of chemical that is expected to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.
- The National Priorities List. (Part of Superfund.) A list kept by the US Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site is one that needs to be cleaned up or looked at to see if people can be exposed to chemicals from the site.
- No Apparent Public Health Hazard:
- The category is used in ATSDR's public health assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.
- No Public Health Hazard:
- The category is used in ATSDR's public health assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.
- Public Health Assessment(s):
- Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.
- A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water such as lakes, ponds and streams.
- Point of Exposure:
- The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). Examples:
an area of a playground that has contaminated dirt, a contaminated spring used for drinking water, a location where fruits or vegetables are grown in contaminated soil, or a backyard area where someone might breathe contaminated air.
- A group of people living in a certain area; or the number of people in a certain area.
- Public Health Hazard:
- The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.
- Public Health Hazard Criteria:
- PHA categories given to a site which tell whether people could be harmed by conditions present at the site. Each is defined in the Glossary. The categories are:
- Urgent Public Health Hazard
- Public Health Hazard
- Indeterminate Public Health Hazard
- No Apparent Public Health Hazard
- No Public Health Hazard
- Receptor Population:
- People who live or work in the path of one or more chemicals and who could come into contact with them (See Exposure Pathway).
- Reference Dose (RfD):
- An estimate, with safety factors (see safety factor) built in, of the daily, lifetime exposure of human populations to a possible hazard that is not expected to cause harm to the person.
- Reference Dose Media Evaluation Guide, a lifetime exposure level at which adverse, noncarcinogenic health effects would not be expected to occur.
- Route of Exposure:
- The way a chemical can get into a person's body. There are three exposure routes:
- - breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- getting something on the skin (also called dermal contact).
- Safety Factor:
- Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not expected to cause harm to people.
- Semi-volatile organic compound (SVOC):
- A class of organic (carbon-containing) chemicals similar to VOCs, but that evaporate, or volatilize, less readily.
- Source (of Contamination):
- The place where a chemical comes from, such as a landfill or a pond. Contaminant source is the first part of an Exposure Pathway.
- Special Populations:
- People who may be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older people are often considered special populations.
- Soil Screening Level, an estimate of a contaminant concentration that would not be expected to cause noncancerous health effects over a specified duration of exposure or to cause less than one excess cancer in a million (10-6) persons exposed over a 70-year life span.
- Superfund Site:
- See NPL.
- Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.
- The degree to which a substance is toxic.
- The study of the harmful effects of chemicals on humans or animals.
- Abnormal growth of tissue or cells that have formed a lump or mass.
- Urgent Public Health Hazard:
- This category is used in ATSDR's public health assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.
- Volatile Organic Compound (VOC):
- A class of organic (carbon-containing) chemicals which readily evaporate, or volatilize. VOCs are frequently used as solvents, degreasing agents, and in other industrial applications.
Overview of ATSDR's Methodology for Evaluating Potential Public Health Hazards
ATSDR evaluated exposures to groundwater, surface soil, surface water and sediment, and air atBrandywine Defense Reutilization and Marketing Office (DRMO). To do so, ATSDR evaluatedavailable data to determine whether contaminants were above ATSDR's comparison values (CVs).For those that were, ATSDR derived exposure doses and compared them against health-basedguidelines. ATSDR also reviewed relevant toxicological data to obtain information about thetoxicity of contaminants of interest.
Comparing Data to ATSDR's CVs
CVs are derived by use of conservative exposure assumptions. CVs reflect concentrations that aremuch lower than those that have been observed to cause adverse health effects. Thus, CVs areprotective of public health in essentially all exposure situations. As a result, concentrationsdetected at or below ATSDR's CVs are not considered to warrant health concern. Whileconcentrations at or below the relevant CV may reasonably be considered safe, it does notautomatically follow that any environmental concentration that exceeds a CV would be expected toproduce adverse health effects. It cannot be emphasized strongly enough that CVs are not thresholdsof toxicity. The likelihood that adverse health outcomes will actually occur depends on site-specificconditions and individual lifestyle and genetic factors that affect the route, magnitude, and durationof actual exposure, and not on environmental concentration alone.
For this public health assessment, ATSDR evaluated data that were collected from groundwater,surface water and sediment, and surface soil to determine whether people were exposed tocontaminant concentrations that exceeded ATSDR's CVs. The majority of detected contaminantsfell at or below CVs and were not evaluated further. Contaminants that were above CVs weredeemed worthy of further evaluation, prompting ATSDR to estimate exposure doses (i.e., theamount of chemical a person is exposed to over time) using site-specific exposure assumptions.
Deriving Exposure Doses
ATSDR derived exposure doses for those contaminants that were detected above ATSDR's CVs ordid not have CVs. When estimating exposure doses, health assessors evaluate contaminantconcentrations to which people may have been exposed and length of time and the frequency ofexposure. Together, these factors influence an individual's physiological response to chemicalcontaminant exposure and potential outcomes. Where possible, ATSDR used site-specificinformation about the frequency and duration of exposures. In cases where site-specific informationwas not available, ATSDR applied several conservative exposure assumptions to estimate exposuresfor off-site residents.
The following equation was used to estimate exposure to contaminants in groundwater:
where: Conc.: Maximum concentration in parts per million (ppm) IR: Ingestion rate: adult = 2 liters per day; child = 1 liter per day EF: Exposure frequency, or number of exposure events per year of exposure: 365 days/year ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years BW: Body weight: adult = 70 kg; child = 10 kg AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)
The following equation was used to estimate recreational exposure to contaminants in surface water:
where: Conc.: Maximum concentration in ppm IR: Ingestion rate: 0.15 liters per day § EF: Exposure frequency, or number of exposure events per year of exposure: 130 days/year ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years BW: Body weight: adult = 70 kg; child = 23 kg* AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)
§ The ingestion rate is based on swimming for 3 hours per event (EPA 1997).
* ATSDR assumed that children under the age of 6 would not be expected to play in the stream.
The following equation was used to estimate exposure to contaminants in soil:
where: Conc.: Average concentration in ppm IR: Ingestion rate: adult = 100 milligrams (mg) per day; child = 200 mg per day EF: Exposure frequency, or number of exposure events per year of exposure: 130 days/year ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years BW: Body weight: adult = 70 kg; child = 23 kg* AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)
* ATSDR assumed that children under the age of 6 would probably not play in the area outside Brandywine DRMO.
Using Exposure Doses to Evaluate Potential Health Hazards
ATSDR performs weight of evidence analyses to determine whether exposures might be associated with adverse health effects (noncancer and cancer). As part of this process, ATSDR examines relevant toxicologic, medical, and epidemiologic data to determine whether estimated doses are expected to result in adverse health effects. As a first step in evaluating noncancer effects, ATSDR compares estimated exposure doses to standard health guideline values, including ATSDR's minimal risk levels (MRLs) and the US Environmental Protection Agency's (EPA's) reference doses (RfDs). The MRLs and RfDs are estimates of daily human exposure to a substance that is not expected to result in noncancer effects over a specified duration. Estimated exposure doses that are less than these values are not considered to be of health concern. To be very protective of human health, MRLs and RfDs have built in "uncertainty" or "safety" factors that make them much lower than levels at which health effects have been observed. Therefore, if an exposure dose is higher than the MRL or RfD, it does not necessarily follow that adverse health effects will occur.
If health guideline values are exceeded, ATSDR examines the effect levels seen in the literature andmore fully reviews exposure potential to help predict the likelihood of adverse health outcomes.ATSDR looks at human studies, when available, as well as experimental animal studies. Thisinformation is used to describe the disease-causing potential of a particular contaminant andcompare site-specific dose estimates with doses shown to result in illness in applicable studies(known as the margin of exposure). For cancer effects, ATSDR also reviews genotoxicity studies tofurther understand the extent to which a contaminant might be associated with cancer outcomes.This process enables ATSDR to weigh the available evidence, in light of uncertainties, and offerperspective on the plausibility of adverse health outcomes under site-specific conditions.
Evaluation of Health Hazards Associated with Brandywine DRMO
ATSDR identified several pathways that had the potential to lead to exposures to people living at orvisiting areas around Brandywine DRMO (see Table 1). For each of these potential pathways,contaminant concentrations were compared to CVs when the data were available. Many of thecontaminants were detected below their corresponding CVs. For each pathway in which chemicalswere detected above CVs or did not have CVs, exposure doses were calculated. With the exceptionof PCBs in soil, all exposure doses were less than their respective MRLs and RfDs; therefore, noneof the chemicals were detected at levels of health concern in any of the evaluated pathways.More detail about each of the exposure pathways follows.
In only once instance was exposure to contaminated groundwater occurring--trichloroethylene(TCE) was detected above its CV in one residential drinking water well in 1989. ATSDR calculatedconservative exposure doses by using the equations and assumptions described above based on themaximum concentration detected in this well (10 ppb). The resulting doses [0.0003 milligrams perkilogram per day (mg/kg/day) for adults and 0.001 mg/kg/day for children] were below EPA's RfDof 0.006 mg/kg/day. Therefore, the levels were too low to be of health concern.
Surface Water and Sediment
Surface water and sediment were sampled from the off-site drainage ditch and on site in 1990 and1993/1994. None of the sediment samples were detected above CVs; therefore, no exposure doseswere calculated because exposure to sediment is not at a level of health concern. In surface water,two contaminants were detected above CVs (chlordane and lead) and one did not have a CV(Aroclor-1260). ATSDR calculated exposure doses for chlordane and Aroclor-1260. Lead isexamined differently and will be discussed below. The expected exposures to chlordane (0.000001mg/kg/day for adults and 0.000004 mg/kg/day for children) were well below EPA's RfD of 0.0005mg/kg/day. Aroclor-1260 does not have an MRL or RfD, however, it is similar to Aroclor-1254.Both are polychlorinated biphenyls (PCBs), so it is acceptable to compare the Aroclor-1260exposure dose to those found in the literature for Aroclor-1254. The calculated exposure doses forAroclor-1260 (0.000007 mg/kg/day for adults and 0.000023 mg/kg/day for children) were wellbelow the levels found in the literature for less serious health effects (0.005 mg/kg/day) [ATSDR1998].
When dealing with exposure to lead, ATSDR calculates what the cumulative blood lead level mightbe as a result of exposure to the level of contamination present. This is done by multiplying thedetected concentration by a slope factor of 0.26 (for water) [ATSDR 1999]. Then ATSDRcompares this expected blood lead level (0.007 micrograms per deciliter) to what the Centers forDisease Control considers to be an elevated level (10 micrograms per deciliter). In this case, thelevel of lead detected in the surface water is much too low to be of health concern.
In addition, the effluent from the groundwater pump and treat system was evaluated. One volatileorganic compound (TCE) and one semi-volatile organic compound (naphthalene) were detectedabove CVs. The calculated exposure doses (TCE = 0.000001 mg/kg/day for adults and 0.000003mg/kg/day for children; naphthalene = 0.00001 mg/kg/day for adults and 0.00004 mg/kg/day forchildren) were well below EPA's RfDs for these two contaminants (0.006 mg/kg/day for TCE and0.02 mg/kg/day for naphthalene) and are; therefore, not at levels of health concern.
Only PCB-contaminated soil outside the perimeter fence was of concern due to potential pastexposures. Since site access is restricted, exposure doses were not calculated for on-sitecontamination. Off-site surface soil was sampled by Prince George's County Health Department andMaryland Department of the Environment in 1986 and 1987. In order to estimate a probableexposure dose from occasionally playing in the area surrounding Brandywine DRMO, ATSDRcalculated an average soil concentration. However, since the highest detection (105,387 ppm) wasover one hundred times higher than the next highest concentration (855 ppm), this outlier was notused in the average soil calculation because it did not accurately represent overall off-site soilconditions. Rather, this concentration was evaluated separately as an acute exposure. The calculatedexposure doses based on a chronic exposure to the soils outside of Brandywine DRMO were0.0000565 mg/kg/day for adults and 0.000344 mg/kg/day for children which are below levelsfound in the literature for less serious health effects (0.005 mg/kg/day) and cancer effect levels (1.0mg/kg/day) [ATSDR 1998]. The calculated exposure doses expected to result from acute exposureto soil with the highest detection were 0.15 mg/kg/day for adults and 0.92 mg/kg/day for children,which are also below the health effects levels seen in the literature for acute exposure (1.0mg/kg/day).
Moreover, PCB concentrations in the soil showed a distinct pattern of decreasing concentrationsfarther away from the fence line. Soil samples taken at six feet from the fence line were below the 10ppm action level. The exposure doses that were calculated assume that children only played withinsix feet of Brandywine DRMO. It is improbable that children restricted their play to that relativelysmall area immediately outside the site, rather in all likelihood, they played throughout the entirewooded area (in areas without PCB contamination) and only occasionally encountered contaminatedsoil within six feet of the fence. In addition, the dose estimates assume that children ingested 200 mgper day of contaminated soil. According to population studies, this is the average ingestion rate forchildren ages 1 to 3. Children 6 years or older consume a much lower amount of soil (23.4 mg/day),which would result in a lower exposure dose than what was estimated (EPA 1997).
One former Brandywine community member reported that he played (e.g., built forts) in the generalarea surrounding Brandywine DRMO from 1960 to 1972. Using the data from 1986 and 1987ATSDR calculated a conservative exposure dose for his 12 years of exposure. His average 12-yearexposure dose (0.0002 mg/kg/day) was below levels known to cause adverse health effects (0.005mg/kg/day). Moreover, the highest exposure (0.0003 mg/kg/day) having occurred at the youngestage was also well below levels seen in the literature for less serious health effects (0.005mg/kg/day).
Three cleanup actions have been accomplished to remediate the soils to concentrations below 10ppm. No exposures of health concern are expected to occur after soil was remediated. Using 10 ppmas the maximum concentration, exposure doses for adults (0.00001 mg/kg/day) incidentallyingesting 100 mg of soil 365 days a year for 30 years and children (0.00009 mg/kg/day)incidentally ingesting 200 mg of soil 365 days a year for 6 years were well below levels seen in the literature for less serious health effects (0.005 mg/kg/day).
ATSDR received the following comments during the public comment period (February 13 to March25, 2001) for the Brandywine DRMO Public Health Assessment (February 2001). For commentsthat questioned the validity of statements made in the Public Health Assessment, ATSDR verified orcorrected the statements. The list of comments does not include editorial comments concerning suchthings as word spelling or sentence syntax.
- Comment: It is unfortunate that the Public Health Assessment was completed prior to thescheduled 2001 Remedial Investigation/Feasibility Study. In many instances conclusionswere drawn using 1996 or earlier data and in some cases conclusions were drawn based onno data at all. An additional public health assessment should be performed once finalized data from the Remedial Investigation/Feasibility Study are available.
- Comment: The current pump and treat system being used at DRMO was never approved inthe 1998 Decision Document. The system that was approved by the Decision Document wasnever installed. As such, there is no Decision Document for the system that is currentlyinstalled at DRMO and the text should be changed to reflect this information.
- Comment: Statements in the Public Health Assessment imply that the groundwatertreatment system installed at DRMO can adequately capture and treat all the contaminatedgroundwater as well as protect the private drinking water wells. Currently, there are no dataavailable to indicate whether this system is capable of capturing the entire plume andprotecting the private drinking water wells. There are also no current sampling data fromeither of the private shallow drinking water wells that indicate whether these wells have been impacted by the groundwater contamination.
- Comment: On page 3, line 20, in the current version of the public health assessment, please update the sentence to reflect that the treatment system is effective.
- Comment: Public health decisions for this document regarding properties outside Air Forcecontrol, were based on data that are five years or older. Since the areal extent of the activelymoving contamination plume and its contamination concentration levels have never fullybeen characterized, the assessment was based on inadequate data. An accurate public healthassessment cannot be completed until the movement of the plume is accurately characterizedand current concentration levels of contaminants evaluated. Any analysis otherwise isspeculative at this time.
Response: ATSDR based its decisions on the best data that were available at the time. If notenough data existed upon which to make a public health decision, the pathway wasdetermined to be indeterminate (as in the case of future exposure to contaminatedgroundwater and past exposure to inhalation of smoke). If necessary and requested, ATSDRcan review any new data that are collected and analyzed (e.g., from the RemedialInvestigation/Feasibility Study). If the new data suggest that further evaluation is warranted, then ATSDR can perform the appropriate follow-up activity.
Response: ATSDR confirmed with Andrews AFB personnel for a second time that thecurrent groundwater treatment system installed at Brandywine DRMO is the one that ismentioned in the 1998 Decision Document for the Remediation of TCE-ContaminatedGroundwater at Brandywine DRMO. However, Andrews AFB personnel did note that thedocument was never formally approved by the regulators. Therefore, the text has beenmodified to reflect that the treatment system was described rather than approved.
Response: Despite modeling in the 1998 Decision Document for the Remediation of TCE-Contaminated Groundwater at Brandywine DRMO that suggests that the currentgroundwater treatment system could recover a large amount of the plume, ATSDR voicedits concern on page 13 that any future public health hazards are dependent upon theeffectiveness of the system. The text was adjusted to be more specific to removing VOCsfrom groundwater in the vicinity of the site. It is ATSDR's understanding that the scheduledRemedial Investigation/Feasibility Study will determine if additional remedial actions are needed.
For a response about the status of the two wells please read the response to comment 5.
Response: Modeling in the 1998 Decision Document for the Remediation of TCE-Contaminated Groundwater at Brandywine DRMO indicated that the groundwater treatmentsystem would be effective in removing a large amount of the contamination. However, theUS Environmental Protection Agency (EPA) and Prince George's County HealthDepartment (PGCHD) disagree with the model results and the effectiveness of the treatmentsystem. Therefore, to be protective of public health, ATSDR will not assume that thetreatment system is effective until the system has been in operation long enough to generatedata that confirm that the selected remedy is adequately reducing the extent and level ofcontamination in the groundwater.
Response: The full extent of the trichloroethylene (TCE) plume was characterized in 1991(Dames & Moore 1992). The plume was defined only by its southern boundaries in 1997and 1999 (IT Corporation 1997a, 1998b). Even though the northern boundary of thegroundwater plume has not been adequately defined since 1991, ATSDR can still evaluatethe potential exposure situations. ATSDR is specifically concerned with two groundwaterwells (one on Cherry Tree Crossing Road and one on Missouri Avenue) that are currentlybeing used to supply water to residents:
- The 1991, 1997, and 1999 monitoring data indicated that the well on Cherry TreeCrossing Road was not within the boundaries of the plume. In addition, this well wassampled in 1997 by an Air Force contractor and PGCHD and no VOCs were detected(PGCHD 1998).
- The well on Missouri Avenue is located over 1,500 feet from the northwestern tip ofBrandywine DRMO. In 1991, when the northern boundary of the plume was defined, theplume extended about 600 feet from Brandywine DRMO's northwestern boundary.Currently, there is no indication that the plume has migrated as far as Missouri Avenue.
Both wells are located to the west of Brandywine DRMO, and southwest of the groundwaterplume. The overall groundwater flow pattern is to the northwest; therefore, ATSDR does notexpect the plume to migrate to where the wells are located. However, the groundwater flowpattern has been shown to vary with rainfall and there is the potential for the groundwater tomove in a southwesterly direction. Because there is the potential for the plume to migratetowards the wells and no samples have been collected from the well on Missouri Avenue,ATSDR has adjusted the hazard category for drinking water from these two groundwaterwells from "no current public health hazard" to "no apparent current public health hazard."
During the scheduled Remedial Investigation/Feasibility Study the plume's boundaries willagain be defined and samples will be collected from these two private wells. If the data fromthis investigation suggests that the groundwater wells on Cherry Tree Crossing Road andMissouri Avenue are in danger of being impacted by the plume, ATSDR will re-evaluate thepotential exposure from drinking water from these wells.
Response: ATSDR revised the text to reflect that the USGS well survey was notcomprehensive. However, ATSDR is fairly certain, based on discussions with PGCHD andexaminations of plume and parcel maps, that no other drinking water wells (other than thetwo already mentioned) exist near the plume. Please notify Andrews AFB of any other wells not already identified.
Response: ATSDR's conclusion was in reference to the community's concern aboutexposure to contamination in their shallow drinking water wells in the late 1980s. Therefore,data that is over 10 years old is appropriate for evaluating this concern. However, the secondto last sentence in this paragraph did use the present tense, therefore, it was modified to be in the past tense.